Leslie P Tolbert

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• Oland, L. A., Oland, L. A., Tolbert, L. P., Tolbert, L. P., Liu, K. E., Liu, K. E., Tran, C. T., Tran, C. T., Fetter, R. D., Fetter, R. D., Cardona, A., Cardona, A., MacNamee, S. E., & MacNamee, S. E. (2016). Astrocytic glutamate transport regulates a Drosophila CNS synapse that lacks astrocyte ensheathment. Journal of Comparative Neurology.
• Gibson, N. J., Tolbert, L. P., & Oland, L. A. (2012). Activation of glial FGFRs is essential in glial migration, proliferation, and survival and in glia-neuron signaling during olfactory system development. PLoS ONE, 7(4).
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  PMID: 22493675;PMCID: PMC3320908;Abstract: Development of the adult olfactory system of the moth Manduca sexta depends on reciprocal interactions between olfactory receptor neuron (ORN) axons growing in from the periphery and centrally-derived glial cells. Early-arriving ORN axons induce a subset of glial cells to proliferate and migrate to form an axon-sorting zone, in which later-arriving ORN axons will change their axonal neighbors and change their direction of outgrowth in order to travel with like axons to their target areas in the olfactory (antennal) lobe. These newly fasciculated axon bundles will terminate in protoglomeruli, the formation of which induces other glial cells to migrate to surround them. Glial cells do not migrate unless ORN axons are present, axons fail to fasciculate and target correctly without sufficient glial cells, and protoglomeruli are not maintained without a glial surround. We have shown previously that Epidermal Growth Factor receptors and the IgCAMs Neuroglian and Fasciclin II play a role in the ORN responses to glial cells. In the present work, we present evidence for the importance of glial Fibroblast Growth Factor receptors in glial migration, proliferation, and survival in this developing pathway. We also report changes in growth patterns of ORN axons and of the dendrites of olfactory (antennal lobe) neurons following blockade of glial FGFR activation that suggest that glial FGFR activation is important in reciprocal communication between neurons and glial cells. © 2012 Gibson et al.
• Oland, L. A., & Tolbert, L. P. (2011). Roles of glial cells in neural circuit formation: Insights from research in insects. Glia, 59(9), 1273-1295.
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  PMID: 21732424;Abstract: Investigators over the years have noted many striking similarities in the structural organization and function of neural circuits in higher invertebrates and vertebrates. In more recent years, the discovery of similarities in the cellular and molecular mechanisms that guide development of these circuits has driven a revolution in our understanding of neural development. Cellular mechanisms discovered to underlie axon pathfinding in grasshoppers have guided productive studies in mammals. Genes discovered to play key roles in the patterning of the fruitfly's central nervous system have subsequently been found to play key roles in mice. The diversity of invertebrate species offers to investigators numerous opportunities to conduct experiments that are harder or impossible to do in vertebrate species, but that are likely to shed light on mechanisms at play in developing vertebrate nervous systems. These experiments elucidate the broad suite of cellular and molecular interactions that have the potential to influence neural circuit formation across species. Here we focus on what is known about roles for glial cells in some of the important steps in neural circuit formation in experimentally advantageous insect species. These steps include axon pathfinding and matching to targets, dendritic patterning, and the sculpting of synaptic neuropils. A consistent theme is that glial cells interact with neurons in two-way, reciprocal interactions. We emphasize the impact of studies performed in insects and explore how insect nervous systems might best be exploited next as scientists seek to understand in yet deeper detail the full repertory of functions of glia in development. © 2010 Wiley-Liss, Inc.
• Koussa, M. A., Tolbert, L. P., & Oland, L. A. (2010). Development of a glial network in the olfactory nerve: Role of calcium and neuronal activity. Neuron Glia Biology, 6(4), 245-261.
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  PMID: 21933469;Abstract: In adult olfactory nerves of mammals and moths, a network of glial cells ensheathes small bundles of olfactory receptor axons. In the developing antennal nerve (AN) of the moth Manduca sexta, the axons of olfactory receptor neurons (ORNs) migrate from the olfactory sensory epithelium toward the antennal lobe. Here we explore developmental interactions between ORN axons and AN glial cells. During early stages in AN glial-cell migration, glial cells are highly dye coupled, dividing glia are readily found in the nerve and AN glial cells label strongly for glutamine synthetase. By the end of this period, dye-coupling is rare, glial proliferation has ceased, glutamine synthetase labeling is absent, and glial processes have begun to extend to enwrap bundles of axons, a process that continues throughout the remainder of metamorphic development. Whole-cell and perforated-patch recordings in vivo from AN glia at different stages of network formation revealed two potassium currents and an R-like calcium current. Chronic in vivo exposure to the R-type channel blocker SNX-482 halted or greatly reduced AN glial migration. Chronically blocking spontaneous Na-dependent activity by injection of tetrodotoxin reduced the glial calcium current implicating an activity-dependent interaction between ORNs and glial cells in the development of glial calcium currents. © 2011 Cambridge University Press.
• Oland, L. A., Gibson, N. J., & Tolbert, L. P. (2010). Localization of a GABA transporter to glial cells in the developing and adult olfactory pathway of the moth Manduca sexta. Journal of Comparative Neurology, 518(6), 815-838.
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  PMID: 20058309;PMCID: PMC2920212;Abstract: Glial cells have several critical roles in the developing and adult olfactory (antennal) lobe of the moth Manduca sexta. Early in development, glial cells occupy discrete regions of the developing olfactory pathway and processes of γ-aminobutyric acid (GABA)ergic neurons extend into some of these regions. Because GABA is known to have developmental effects in a variety of systems, we explored the possibility that the glial cells express a GABA transporter that could regulate GABA levels to which olfactory neurons and glial cells are exposed. By using an antibody raised against a characterized high-affinity M. sexta GABA transporter with high sequence homology to known mammalian GABA transporters (Mbungu et al. [1995] Arch. Biochem. Biophys. 318:489-497; Umesh and Gill [2002] J. Comp. Neurol. 448:388-398), we found that the GABA transporter is localized to subsets of centrally derived glial cells during metamorphic adult development. The transporter persists into adulthood in a subset of the neuropil-associated glial cells, but its distribution pattern as determined by light-and electron-microscopic-level immunocytochemistry indicates that it could not serve to regulate GABA concentration in the synaptic cleft. Instead, its role is more likely to regulate extracellular GABA levels within the glomerular neuropil. Expression in the sorting zone glial cells disappears after the period of olfactory receptor axon ingrowth, but may be important during ingrowth if GABA regulates axon growth. Glial cells take up GABA, and that uptake can be blocked by L-2,4-diaminobutyric acid (DABA). This is the first molecular evidence that the central glial cell population in this pathway is heterogeneous. © 2009 Wiley-Liss, Inc.
• Gibson, N. J., Tolbert, L. P., & Oland, L. A. (2009). Roles of specific membrane lipid domains in EGF receptor activation and cell adhesion molecule stabilization in a developing old factory system. PLoS ONE, 4(9).
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  PMID: 19787046;PMCID: PMC2746287;Abstract: Background: Reciprocal interactions between glial cells and olfactory receptor neurons (ORNs) cause ORN axons entering the brain to sort, to fasciculate into bundles destined for specific glomeruli, and to form stable protoglomeruli in the developing olfactory system of an experimentally advantageous animal species, the moth Manduca sexta. Epidermal growth factor receptors (EGFRs) and the cell adhesion molecules (IgCAMs) neuroglian and fasciclin II are known to be important players in these processes. Methodology/Principal Findings: We report in situ and cell-culture studies that suggest a role for glycosphingolipid-rich membrane subdomains in neuron-glia interactions. Disruption of these subdomains by the use of methyl-β-cyclodextrin results in loss of EGFR activation, depletion of fasciclin II in ORN axons, and loss of neuroglian stabilization in the membrane. At the cellular level, disruption leads to aberrant ORN axon trajectories, small antennal lobes, abnormal arrays of olfactory glomerul, and loss of normal glial cell migration. Conclusions/Significance: We propose that glycosphingolipid-rich membrane subdomains (possible membrane rafts or platforms) are essential for IgCAM-mediated EGFR activation and for anchoring of neuroglian to the cytoskeleton, both required for normal extension and sorting of ORN axons. © 2009 Gibson et al.
• Oland, L. A., Biebelhausen, J. P., & Tolbert, L. P. (2008). Glial investment of the adult and developing antennal lobe of Drosophila. Journal of Comparative Neurology, 509(5), 526-550.
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  PMID: 18537134;PMCID: PMC2767108;Abstract: In recent years the Drosophila olfactory system, with its unparalleled opportunities for genetic dissection of development and functional organization, has been used to study the development of central olfactory neurons and the molecular basis of olfactory coding. The results of these studies have been interpreted in the absence of a detailed understanding of the steps in maturation of glial cells in the antennal lobe. Here we present a high-resolution study of the glia associated with olfactory glomeruli in adult and developing antennal lobes. The study provides a basis for comparison of findings in Drosophila with those in the moth Manduca sexta that indicate a critical role for glia in antennal lobe development. Using flies expressing GFP under a Nervanal driver to visualize glia for confocal microscopy, and probing at higher resolution with the electron microscope, we find that glial development in Drosophila differs markedly from that in moths: glial cell bodies remain in a rind around the glomerular neuropil; glial processes ensheathe axon bundles in the nerve layer but likely contribute little to axonal sorting; their processes insinuate between glomeruli only very late and then form only a sparse, open network around each glomerulus; and glial processes invade the synaptic neuropil. Taking our results in the context of previous studies, we conclude that glial cells in the developing Drosophila antennal lobe are unlikely to play a strong role in either axonal sorting or glomerulus stabilization and that in the adult, glial processes do not electrically isolate glomeruli from their neighbors. © 2008 Wiley-Liss, Inc.
• Gibson, N. J., & Tolbert, L. P. (2006). Activation of epidermal growth factor receptor mediates receptor axon sorting and extension in the developing olfactory system of the moth Manduca sexta. Journal of Comparative Neurology, 495(5), 554-572.
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  PMID: 16498681;PMCID: PMC2709604;Abstract: During development of the adult olfactory system of the moth Manduca sexta, olfactory receptor neurons extend axons from the olfactory epithelium in the antenna into the brain. As they arrive at the brain, interactions with centrally derived glial cells cause axons to sort and fasciculate with other axons destined to innervate the same glomeruli. Here we report studies indicating that activation of the epidermal growth factor receptor (EGFR) is involved in axon ingrowth and targeting. Blocking the EGFR kinase domain pharmacologically leads to stalling of many axons in the sorting zone and nerve layer as well as abnormal axonal fasciculation in the sorting zone. We also find that neuroglian, an IgCAM known to activate the EGFR through homophilic interactions in other systems, is transiently present on olfactory receptor neuron axons and on glia during the critical stages of the sorting process. The neuroglian is resistant to extraction with Triton X-100 in the sorting zone and nerve layer, possibly indicating its stabilization by homophilic binding in these regions. Our results suggest a mechanism whereby neuroglian molecules on axons and possibly sorting zone glia bind homophilically, leading to activation of EGFRs, with subsequent effects on axon sorting, pathfinding, and extension, and glomerulus development. © 2006 Wiley-Liss, Inc.
• Lipscomb, B. W., & Tolbert, L. P. (2006). Temporally staggered glomerulus development in the Moth Manduca sexta. Chemical Senses, 31(3), 237-247.
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  PMID: 16407570;Abstract: Glomeruli, neuropilar structures composed of olfactory receptor neuron (ORN) axon terminals and central neuron dendrites, are a common feature of olfactory systems. Typically, ORN axons segregate into glomeruli based on odor specificity, making glomeruli the basic unit for initial processing of odorant information. Developmentally, glomeruli arise from protoglomeruli, loose clusters of ORN axons that gradually synapse onto dendrites. Previous work in the moth Manduca sexta demonstrated that protoglomeruli develop in a wave across the antennal lobe (AL) during stage 5 of the 18 stages of metamorphic adult development. However, ORN axons from the distal segments of the antenna arrive at the AL for several more days. We report that protoglomeruli present at stage 5 account for only approximately two or three of adult glomeruli with the number of structures increasing over subsequent stages. How do these later arriving axons incorporate into glomeruli? Examining the dendritic projections of a unique serotonin-containing neuron into glomeruli at later stages revealed glomeruli with immature dendritic arbors intermingled among more mature glomeruli. Labeling ORN axons that originate in proximal segments of the antenna suggested that early-arriving axons target a limited number of glomeruli. We conclude that AL glomeruli form over an extended time period, possibly as a result of ORNs expressing new odorant receptors arriving from distal antennal segments. © 2006 Oxford University Press.
• Oland, L. A., Gibson, N. J., & Tolbert, L. P. (2005). NO-mediated signaling from olfactory receptor axons to peripheral ensheathing glia in the moth olfactory pathway. Chemical Senses, 30, 265-278.
• Tolbert, L. P., & Westbrook, G. (2004). Special annual meeting issue. Journal of Neuroscience, 24(42), ii.
• Tolbert, L. P., Oland, L. A., Tucker, E. S., Gibson, N. J., Higgins, M. R., & Lipscomb, B. W. (2004). Bidirectional influences between neurons and glial cells in the developing olfactory system. Progress in Neurobiology, 73(2), 73-105.
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  PMID: 15201035;Abstract: Olfactory systems serve as excellent model systems for the study of numerous widespread aspects of neural development and also for the elucidation of features peculiar to the formation of neural circuits specialized to process odor inputs. Accumulated research reveals a fine balance between developmental autonomy of olfactory structures and intercellular interactions essential for their normal development. Recent findings have uncovered evidence for more autonomy than previously realized, but simultaneously have begun to reveal the complex cellular and molecular underpinnings of key interactions among neurons and glial cells at several important steps in olfactory development. Striking similarities in the functional organization of olfactory systems across vertebrate and invertebrate species allow the advantages of different species to be used to address common issues. Our own work in the moth Manduca sexta has demonstrated reciprocal neuron-glia interactions that have key importance in two aspects of development, the sorting of olfactory receptor axons into fascicles targeted for specific glomeruli and the creation of glomeruli. Studies in vertebrate species suggest that similar neuron-glia interactions may underlie olfactory development, although here the roles have not been tested so directly. Similar cellular interactions also are likely to play roles in development of some other systems in which axons of intermixed neurons must sort according to target specificity and systems in which reiterated modules of synaptic neuropil develop. © 2004 Elsevier Ltd. All rights reserved.
• Tucker, E. S., Oland, L. A., & Tolbert, L. P. (2004). In vitro analyses of interactions between olfactory receptor growth cones and glial cells that mediate axon sorting and glomerulus formation. Journal of Comparative Neurology, 472, 478-95.
• Oland, L. A., & Tolbert, L. P. (2003). Key Interactions Between Neurons and Glial Cells During Neural Development in Insects. Annual Review of Entomology, 48, 89-110.
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  PMID: 12194908;Abstract: Nervous system function is entirely dependent on the intricate and precise pattern of connections made by individual neurons. Much of the insightful research into mechanisms underlying the development of this pattern of connections has been done in insect nervous systems. Studies of developmental mechanisms have revealed critical interactions between neurons and glia, the non-neuronal cells of the nervous system. Glial cells provide trophic support for neurons, act as struts for migrating neurons and growing axons, form boundaries that restrict neuritic growth, and have reciprocal interactions with neurons that govern specification of cell fate and axonal pathfinding. The molecular mechanisms underlying these interactions are beginning to be understood. Because many of the cellular and molecular mechanisms underlying neural development appear to be common across disparate insect species, and even between insects and vertebrates, studies in developing insect nervous systems are elucidating mechanisms likely to be of broad significance.
• Tolbert, L. P., Oland, L. A., Christensen, T. C., & Goriely, A. R. (2003). Neuronal and glial morphology in olfactory systems: Significance for information-processing and underlying developmental mechanisms. Brain and Mind, 4(1), 27-49.
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  Abstract: The shapes of neurons and glial cells dictate many important aspects of their functions. In olfactory systems, certain architectural features are characteristics of these two cell types across a wide variety of species. The accumulated evidence suggests that these common features may play fundamental roles in olfactory information processing. For instance, the primary olfactory neuropil in most vertebrate and invertebrate olfactory systems is organized into discrete modules called glomeruli. Inside each glomerulus, sensory axons and CNS neurons branch and synapse in patterns that are repeated across species. In many species, moreover, the glomeruli are enveloped by a thin and ordered layer of glial processes. The glomerular arrangement reflects the processing of odor information in modules that encode the discrete molecular attributes of odorant stimuli being processed. Recent studies of the mechanisms that guide the development of olfactory neurons and glial cells have revealed complex reciprocal interactions between these two cell types, which may be necessary for the establishment of modular compartments. Collectively, the findings reviewed here suggest that specialized cellular architecture plays key functional roles in the detection, analysis, and discrimination of odors at early steps in olfactory processing.
• Tucker, E. S., & Tolbert, L. P. (2003). Reciprocal interactions between olfactory receptor axons and olfactory nerve glia cultured from the developing moth Manduca sexta. Developmental Biology, 260(1), 9-30.
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  PMID: 12885552;Abstract: In olfactory systems, neuron-glia interactions have been implicated in the growth and guidance of olfactory receptor axons. In the moth Manduca sexta, developing olfactory receptor axons encounter several types of glia as they grow into the brain. Antennal nerve glia are born in the periphery and enwrap bundles of olfactory receptor axons in the antennal nerve. Although their peripheral origin and relationship with axon bundles suggest that they share features with mammalian olfactory ensheathing cells, the developmental roles of antennal nerve glia remain elusive. When cocultured with antennal nerve glial cells, olfactory receptor growth cones readily advance along glial processes without displaying prolonged changes in morphology. In turn, olfactory receptor axons induce antennal nerve glial cells to form multicellular arrays through proliferation and process extension. In contrast to antennal nerve glia, centrally derived glial cells from the axon sorting zone and antennal lobe never form arrays in vitro, and growth-cone glial-cell encounters with these cells halt axon elongation and cause permanent elaborations in growth cone morphology. We propose that antennal nerve glia play roles similar to olfactory ensheathing cells in supporting axon elongation, yet differ in their capacity to influence axon guidance, sorting, and targeting, roles that could be played by central olfactory glia in Manduca. © 2003 Elsevier Science (USA). All rights reserved.
• Goriely, A. R., Secomb, T. W., & Tolbert, L. P. (2002). Effect of the glial envelope on extracellular K ⁺ diffusion in olfactory glomeruli. Journal of Neurophysiology, 87(4), 1712-1722.
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  PMID: 11929893;Abstract: In many species, including vertebrates and invertebrates, first-order olfactory neuropils are organized into spherical glomeruli, partially enveloped by glial borders. The effect of this characteristic organization on olfactory information processing is poorly understood. The extracellular concentration of potassium ions ([K +]) must rise around olfactory receptor axons in specific glomeruli following odor-induced activation. To explore the time course and magnitude of K + accumulation and possible effects of such accumulation on neural activity within and among glomeruli, we developed a theoretical model to simulate the diffusion of K + in extracellular spaces of the glomeruli of the moth Manduca sexta. K + released by activated axons was assumed to diffuse through the extracellular spaces in glomeruli and the glial borders that surround them. The time-dependent diffusion equations were solved in spherical coordinates using a finite-difference method. The results indicate that the glial envelope forms a significant barrier to the spread of K + between neighboring glomeruli, thus reducing the likelihood of cross-talk between glomeruli, and may cause elevation of extracellular [K +] to levels that influence neural activity within the activated glomerulus for many seconds. Such effects could enhance olfactory discrimination and sensitivity, respectively.
• Higgins, M. R., Gibson, N. J., Eckholdt, P. A., Nighorn, A., Copenhaver, P. F., Nardi, J., & Tolbert, L. P. (2002). Different isoforms of fasciclin II are expressed by a subset of developing olfactory receptor neurons and by olfactory-nerve glial cells during formation of glomeruli in the moth Manduca sexta. Developmental Biology, 244(1), 134-154.
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  PMID: 11900464;Abstract: During development of the primary olfactory projection, olfactory receptor axons must sort by odor specificity and seek particular sites in the brain in which to create odor-specific glomeruli. In the moth Manduca sexta, we showed previously that fasciclin II, a cell adhesion molecule in the immunoglobulin superfamily, is expressed by the axons of a subset of olfactory receptor neurons during development and that, in a specialized glia-rich "sorting zone," these axons segregate from nonfasciclin II-expressing axons before entering the neuropil of the glomerular layer. The segregation into fasciclin II-positive fascicles is dependent on the presence of the glial cells in the sorting zone. Here, we explore the expression patterns for different isoforms of Manduca fasciclin II in the developing olfactory system. We find that olfactory receptor axons express transmembrane fasciclin II during the period of axonal ingrowth and glomerulus development. Fascicles of TM-fasciclin II+ axons target certain glomeruli and avoid others, such as the sexually dimorphic glomeruli. These results suggest that TM-fasciclin II may play a role in the sorting and guidance of the axons. GPI-linked forms of fasciclin II are expressed weakly by glial cells associated with the receptor axons before they reach the sorting zone, but not by sorting-zone glia. GPI-fasciclin II may, therefore, be involved in axon-glia interactions related to stabilization of axons in the nerve, but probably not related to sorting. © 2002 Elsevier Science (USA).
• Lohr, C., Tucker, E. S., Oland, L. A., & Tolbert, L. P. (2002). Development of depolarization-induced calcium transients in insect glial cells is dependent on the presence of afferent axons. Journal of Neurobiology, 52, 85-98.
• Dubuque, S. H., Schachtner, J., Nighorn, A. J., Menon, K. P., Zinn, K., & Tolbert, L. P. (2001). Immunolocalization of synaptotagmin for the study of synapses in the developing antennal lobe of Manduca sexta. Journal of Comparative Neurology, 441(4), 277-287.
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  PMID: 11745650;Abstract: In the mature olfactory systems of most organisms that possess a sense of smell, synapses between olfactory receptor neurons and central neurons occur in specialized neuropil structures called glomeruli. The development of olfactory glomeruli has been studied particularly heavily in the antennal lobe of the moth Manduca sexta. In the current study, we address the development of synapses within the antennal lobe of M. sexta by reporting on the localization of synaptotagmin, a ubiquitous synaptic vesicle protein, throughout development. A cDNA clone coding for M. sexta synaptotagmin was characterized and found to encode a protein that shares 67% amino acid identity with Drosophila synaptotagmin and 56% amino acid identity with human synaptotagmin I. Conservation was especially high in the C2 domains near the C-terminus and very low near the N-terminus. A polyclonal antiserum (MSYT) was raised against the unique N-terminus of M. sexta synaptotagmin, and a monoclonal antibody (DSYT) was raised against the highly conserved C-terminus of D. melanogaster synaptotagmin. In Western blot analyses, both antibodies labeled a 60 kD protein, which very likely corresponds to synaptotagmin. On sections, both antibodies labeled known synaptic neuropils in M. sexta and yielded similar labeling patterns in the developing antennal lobe. In addition, DSYT detected synaptotagmin-like protein in three other insect species examined. Analysis of synaptotagmin labeling at the light microscopic level during development of the antennal lobe of M. sexta confirmed and extended previous electron microscopic studies. Additional synapses in the coarse neuropil and a refinement of synaptic densities in the glomeruli during the last one-third of metamorphic development were revealed. © 2001 Wiley-Liss, Inc.
• Gibson, N. J., Roessler, W. R., Nighorn, A. J., Oland, L. A., Hildebrand, J. G., & Tolbert, L. P. (2001). Neuron-glia communication via nitric oxide is essential in establishing antennal-lobe structure in Manduca sexta. Developmental Biology, 240, 326-39.
• Lohr, C., Oland, L. A., & Tolbert, L. P. (2001). Olfactory receptor axons influence the development of glial potassium currents in the antennal lobe of the moth Manduca sexta. Glia, 36, 309-320.
• Wegerhoff, R., Rössler, W., Higgins, M., Oland, L. A., & Tolbert, L. P. (2001). Fenvalerate treatment affects development of olfactory glomeruli in Manduca sexta. Journal of Comparative Neurology, 430(4), 533-541.
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  PMID: 11169485;Abstract: Low doses of fenvalerate, a widely used type-II pyrethroid insecticide, have been shown previously to produce abnormal olfactory centers in the brain and abnormal olfactory-mediated behavior in beetles (Wegerhoff et al. [1998] Neuroreport 9:3241-3245). Here, we use the experimental advantages of the moth Manduca sexta to explore the cellular changes that lead to these abnormalities. Our results indicate that treatment with fenvalerate may affect multiple aspects of the development of the primary olfactory centers, the antennal lobes, in Manduca, including ingrowth of olfactory receptor axons, axon fasciculation, and targeting within the antennal lobe, and intercellular signaling between the receptor axons and the glial cells that ordinarily surround and stabilize the developing olfactory glomeruli. © 2001 Wiley-Liss, Inc.
• Burd, G. D., & Tolbert, L. P. (2000). Development of the Olfactory System. In "Neurobiology of Taste and Smell" (eds. T Finger, W Silver,D Restreppo), 233-255.
• Roessler, W., Tolbert, L. P., & Hildebrand, J. G. (2000). Importance of timing of olfactory receptor-axon outgrowth for glomerulus development in Manduca sexta. Journal of Comparative Neurology, 425, 233-243.
• Roessler, W. R., Oland, L. A., Higgins, M. R., Hildebrand, J. G., & Tolbert, L. P. (1999). Development of a glia-rich axon-sorting zone in the olfactory pathway of the moth Manduca sexta. Journal of Neuroscience, 19, 9865-77.
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  PMID: 10559396
• Roessler, W., Randolph, P. W., Tolbert, L. P., & Hildebrand, J. G. (1999). Axons of olfactory receptor cells of trans-sexually grafted antennae induce development of sexually dimorphic glomeruli in Manduca sexta. Journal of Neurobiology, 38, 521-541.
• Edwards, J. S., & Tolbert, L. P. (1998). Insect Neuroglia. in "Microscopic Anatomy of the Invertebrates" (ed. M Locke), 11B, 449-466.
• Oland, L. A., & Tolbert, L. P. (1998). Glomerulus development in the absence of a set of mitral-like neurons in the insect olfactory lobe. Journal of Neurobiology, 36(1), 41-52.
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  PMID: 9658337;Abstract: Mitral cells are the first neurons in the mammalian olfactory bulb to synapse with olfactory receptor axons during glomerulus development, and in an invertebrate, the moth Manduca sexta, mitral-like neurons overlap very early with olfactory receptor axons as they begin to form protoglomeruli. The possibility for early interaction between receptor neurons and mitral-like neurons led us to ask whether such an interaction plays an essential role in glomerulus development. In the current study in the moth, we surgically removed a major class of these mitral-like neurons before glomeruli began to form and asked: (a) Is the formation of the array of olfactory glomeruli triggered by an interaction of the first-arriving receptor axons with the dendrites of mitral-like neurons? (b) At the level of individual glomeruli, must the mitral-like dendrites be in place either to maintain receptor axons in a glomerular arrangement, or to guide later-growing dendrites of other types into the developing glomeruli? Our results indicate that even without the participation of this group of mitral-like neurons, the array of sexually isomorphic ordinary glomeruli forms and the basic substructure of individual glomeruli develops apparently normally. We conclude that the mitral-like neurons in Manduca are not essential for the formation of ordinary olfactory glomeruli during development.
• Oland, L. A., Pott, W. M., Higgins, M. R., & Tolbert, L. P. (1998). Targeted ingrowth and axon-glial cell relationships of olfactory receptor axons in the primary olfactory pathway of an insect. Journal of Comparative Neurology, 398, 119-138.
• Roessler, W., Tolbert, L. P., & Hildebrand, J. G. (1998). Early formation of sexually dimorphic glomeruli in the developing olfactory lobe of the brain of the moth Manduca sexta. Journal of Comparative Neurology, 396, 415-428.
• Sun, X., Tolbert, L. P., Hildebrand, J. G., & Meinertzhagen, I. A. (1998). A rapid method for combined laser scanning confocal microscopic and electron microscopic visualization of biocytin- or neurobiotin-labeled neurons. Journal of Histochemistry and Cytochemistry, 46, 263-273.
• Tolbert, L. P. (1998). Olfactory development in invertebrates: On the scent of central developmental issues. Annals of the New York Academy of Sciences, 855, 95-103.
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  PMID: 10049235;Abstract: Invertebrate olfactory systems offer many advantages for cellular and molecular studies of development and for functional studies of developmental plasticity. For example, nematodes have chemical senses that can be studied using genetic approaches. Arthropods, which include insects and crustacea, have the advantages that certain neurons can be reliably identified from one individual to another, and that olfactory receptor neurons are located on peripheral appendages and thus can be manipulated independently of their brain targets, even very early in development. Among the insects, olfactory learning can be displayed and used as a basis for studying olfactory plasticity in bees; genes are especially tractable in flies; individual growth cones can be visualized in the grasshopper embryo; and receptor neurons and glomeruli of known olfactory specificity and behavioral significance can be followed during early development in moths. In addition, many insect nervous systems are amenable to organ culture and dissociated-cell culture, opening the door to experimental studies of cellular interactions that can not be performed in situ. Recent research in the moth Manduca sexta attempts to identify the nature of the interactions between olfactory sensory axons, olfactory neurons of the brain, and glial cells in the creation of the array of glomeruli that underlie olfaction in the adult. Results indicate that timing of the ingrowth of olfactory receptor axons is critical for normal glomerulus development, that a subset of axons expresses a fasciclin II-like molecule that may play a role in guidance of their growth, and that glial cells must surround developing glomeruli in order to stabilize the 'protoglomerular' template made by receptor axon terminals. Moreover, glial cells are dye-coupled to each other early in glomerulus development and gradually become uncoupled. Electrical activity in neurons is not necessary for glomerulus formation; and some intercellular interactions, perhaps involving soluble factors, appear to involve tyrosine phosphorylation. In sum, a detailed picture is emerging of the cellular interactions that lead to the formation of glomeruli.
• Sun, X., Tolbert, L. P., & Hildebrand, J. G. (1997). Synaptic organization of the uniglomerular projection neurons of the antennal lobe of the moth Manduca sexta: a laser scanning confocal and electron microscopic study. Journal of Comparative Neurology, 379, 2-20.
• Baumann, P. M., Oland, L. A., & Tolbert, L. P. (1996). Glial cells stabilize axonal protoglomeruli in the developing olfactory lobe of the moth Manduca sexta. Journal of Comparative Neurology, 373(1), 118-128.
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  PMID: 8876467;Abstract: Odor information is processed in spherical structures called glomeruli, which in all animals with differentiated olfactory systems are sites of densely spaced synaptic contacts between olfactory sensory axons and target central nervous system (CNS) neurons. Glomerulus development in the antennal (olfactory) lobe of the moth brain, which is initiated by the arrival of antennal receptor axons, requires interaction among three elements: glial cells, receptor axons, and their targets, the antennal-lobe neurons. Receptor axons form an array of protoglomeruli that become surrounded by glia and serve as a template for mature glomeruli. Previous experiments showed that when the number of glial cells is sharply reduced during development either by irradiation or by an anti-mitotic agent, receptor axons form protoglomeruli, but in the mature lobes, glomeruli are absent and central neurons lack the characteristic glomerular tufting of their arbors. The current investigation was conducted to determine which cellular events in the process of glomerulus formation are disrupted by severe reduction in glial- cell number. The branching patterns of receptor axons and antennal-lobe neurons were examined in animals that had been irradiated to produce glia- deficient antennal lobes at stages during which glomeruli normally would develop. We found that the receptor axons did form protoglomeruli, but that the protoglomeruli quickly disintegrated in glia-deficient antennal lobes; the receptor axons branched diffusely, except where several neighboring glia survived irradiation and together formed a wall of processes that appeared to block the passage of neuronal processes. Multi-glomerular antennal-lobe neurons never developed tufted arbors even at early stages. These results suggest that maintenance of protoglomeruli depends on the border of glia that forms around each protoglomerulus and that the subsequent tufting of antennal-lobe neurons depends on maintenance of the protoglomerular template during the period of dendritic growth.
• Oland, L. A., & Tolbert, L. P. (1996). Multiple factors shape development of olfactory glomeruli: Insights from an insect model system. Journal of Neurobiology, 30(1), 92-109.
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  PMID: 8727986;Abstract: The antennal system of the moth Manduca sexta is a useful model for studies of the development of olfactory glomeruli, the complex synaptic structures that typically underlie the initial processing of olfactory input in vertebrates and invertebrates. In this review, we summarize cellular events in the construction of glomeruli in Manduca and highlight experiments that reveal factors that influence glomerulus development. By methodically manipulating each of various cell types, both neuronal and glial, that contribute to glomerular architecture, we have found that: olfactory receptor axons lay a template for developing glomeruli, stabilization of the template by glial cells is necessary to permit subsequent steps in development of the glomeruli, and the hormone that regulates adult development causes production of adequate numbers of glial cells. Neither electrical activity nor the presence of a serotonin-containing neuron that persists throughout development is required for a glomerular pattern to develop; these factors might, however, influence the synaptic organization of individual glomeruli.
• Oland, L. A., Pott, W. M., Bukhman, G., Sun, X. J., & Tolbert, L. P. (1996). Activity blockade does not prevent the construction of olfactory glomeruli in the moth Manduca sexta. International Journal of Developmental Neuroscience, 14(7-8), 983-996.
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  PMID: 9010740;Abstract: During metamorphic development, the arrival at the olfactory (antennal) lobe of olfactory receptor axons initiates the process of glomerulus formation. The glomeruli are discrete spheroidal regions of neuropil that are the sites of synaptic interactions among receptor neurons and their target antennal-lobe neurons. The process of glomerulus formation begins as groups of receptor axons form protoglomeruli. These dense clusters of terminal branches mostly are discrete entities from the time they can be recognized, although a few branches from neighboring protoglomeruli overlap laterally. A previous study by Schweitzer et al. has shown that odor-induced activity in the receptor neurons can be detected first in recordings from the axons in the antennal nerve only in the last Few days of metamorphic development and thus could not influence the process of glomerulus formation. In this study, we have tested directly the possibility that an earlier presence of spontaneous activity in either the receptor axons or the antennal-lobe neurons could affect the process. Tetrodotoxin, a Na+-channel blocker, was injected into the hemolymph prior to the onset of glomerulus formation to block any spontaneous Na+-dependent activity. Subsequent intracellular recordings from antennal-lobe neurons revealed no spike activity. Comparison with vehicle-injected control animals at stages during and after glomerulus formation revealed no differences in the localization of receptor-axon terminal branches in the glomeruli, in the border of glial cells that forms around each glomerulus, or in the morphology of the tufted glomerular arbors of one of the antennal-lobe neurons. We conclude that: (1) the process of glomerulus formation is largely independent of activity; and (2) glomeruli as modular units of the CNS more closely resemble cortical barrels than cortical columns, both in their ontogeny and in the lack of an obvious effect of activity on the morphology of the neurons arborizing within them.
• Tolbert, L. P., Sun, X., & Hildebrand, J. G. (1996). Combining laser scanning confocal microscopy and electron microscopy in studies of the insect nervous system. Journal of Neuroscience Methods, 69, 25-32.
• Kirschenbaum, S. R., Higgins, M. R., Tveten, M., & Tolbert, L. P. (1995). 20-Hydroxyecdysone stimulates proliferation of glial cells in the developing brain of the moth Manduca sexta. Journal of Neurobiology, 28(2), 234-247.
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  PMID: 8537827;Abstract: The steroid hormone 20-hydroxyecdysone (20-HE) controls diverse aspects of neuronal differentiation during metamorphosis in the hawkmoth Manduca sexta. In the present study we have examined the effect of 20-HE on glial cells of the brain during the metamorphic period. The antennal (olfactory) lobe of Manduca provides an ideal system in which to study effects of hormones on glial cells, since three known classes of glial cells participate in its development, and at least one type is critically important for establishment of normal neuronal morphology. These glial cells, associated with the neuropil, form boundaries for developing olfactory glomeruli as a result of proliferation and migration. We determined whether glial cells proliferate in response to 20-HE by injecting a pulse of 20-HE into the hemolymph at different stages of development and monitoring proliferation of all three types of glial cells. Hormone injections at the beginning and end of metamorphic development, when hormone titers are normally low, did not stimulate proliferation of neuropil-associated glial cells. Injections during the period when hormone titers are normally rising produced significant increases in their proliferation. Injections when hormone titers are normally high were ineffective at enhancing their proliferation. One other class of glial cells, the perineurial cells, also proliferate in response to 20-HE. Thus, glial proliferation in the brain is under the control of steroid hormones during metamorphic development.
• Oland, L. A., Kirschenbaum, S. R., Pott, W. M., Mercer, A. R., & Tolbert, L. P. (1995). Development of an identified serotonergic neuron in the antennal lobe of the moth and effects of reduction in serotonin during construction of olfactory glomeruli. Journal of Neurobiology, 28(2), 248-267.
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  PMID: 8537828;Abstract: Each olfactory (antennal) lobe of the moth Manduca sexta contains a single serotonin (5-HT) immunoreactive neuron whose processes form tufted arbors in the olfactory glomeruli. To extend our present understanding of the intercellular interactions involved in glomerulus development to the level of an individual, identified antennal lobe neuron, we first studied the morphological development of the 5-HT neuron in the presence and absence of receptor axons. Development of the neuron's glomerular tufts depends, as it does in the case of other multiglomerular neurons, on the presence of receptor axons. Processes of the 5-HT neuron are excluded from the region in which the initial steps of glomerulus construction occur and thus cannot provide a physical scaffolding on which the array of glomeruli is organized. Because the neuron's processes are present in the antennal lobe neuropil throughout postembryonic development, 5-HT could provide signals that influence the pattern of development in the lobe. By surgically producing 5- HT-depleted antennal lobes, we also tested the importance of 5-HT in the construction of olfactory glomeruli. Even in the apparent absence of 5-HT, the glomerular array initiated by the receptor axons was histologically normal, glial cells migrated to form glomerular borders, and receptor axons formed terminal branches in their normal region within each glomerulus. In some cases, 5-HT-immunoreactive processes from abnormal sources entered the lobe and formed the tufted intraglomerular branches typical of most antennal lobe neurons, suggesting that local cues strongly influence the branching patterns of developing antennal lobe neurons.
• Oland, L. A., Krull, C. E., & Tolbert, L. P. (1995). Glial cells play a key role in the construction of insect olfactory glomeruli. in "Neuron-Glia Interrelations During Phylogeny: II. Plasticity and Regeneration" (eds. A Vernadakis and B Roots).
• Sun, X., Tolbert, L. P., & Hildebrand, J. G. (1995). Using laser scanning confocal microscopy as a guide for electron microscopic study of labeled neurons. Journal of Histochemistry and Cytochemistry, 43, 329-335.
• Willis, M. A., Butler, M. A., & Tolbert, L. P. (1995). Normal glomerular organization of the antennal lobes is not necessary for odor-modulated flight in female moths. Journal of Comparative Physiology A, 176(2), 205-216.
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  PMID: 7884684;Abstract: A prominent hypothesis for the function of the glomerular structures in the primary olfactory neuropil of many groups of vertebrate and invertebrate animals is that they enable the processing and coding of information about the chemical compounds that compose complex odors. Previous studies have indicated that various degrees of glomerulus formation in the antennal lobes of the brain of the moth Manduca sexta can be effected by reducing the number of olfactory sensory axons that grow from the antenna into the antennal lobe during metamorphosis. To test the hypothesis that the presence of glomerular structure is necessary to process and identify odors, we substantially reduced, by surgery, the number of antennal segments in developing moths and upon metamorphosis we observed and quantified behavioral responses known to be elicited by odors. Intact and lesioned adult female moths were challenged to fly upwind to the source of an attractive host-plant odor in a wind tunnel. Some of the moths that had developed with reduced olfactory input flew upwind to the odor source. The flight behavior of these individuals was similar to the odor-mediated flight typically observed in moths that had developed normally. Histological analysis of the moths' antennal lobes revealed that the lobes of more than half of the respondents that had been lesioned during development lacked normal glomerular organization. The neuropil of these abnormally developed antennal lobes was mostly aglomerular, but with a few isolated, clearly abnormal glomerulus-like structures. This suggests either that even a few abnormal glomeruli are sufficient to mediate this specific behavior or that "canonical" glomerular organization per se is not necessary for this odor-mediated behavior. © 1995 Springer-Verlag.
• Alonso-Pimentel, H., Tolbert, L. P., & Heed, W. B. (1994). Ultrastructural examination of the insemination reaction in Drosophila. Cell & Tissue Research, 275(3), 467-479.
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  PMID: 8137397;Abstract: The insemination reaction is a swelling of the female vagina caused by the male ejaculate. This postmating phenomenon is common among species in the genus Drosophila. It could act as a plug securing male paternity. It is not clear, however, what benefits it provides to the female. The structure formed in the female vagina is expelled in some species and disappears gradually in others suggesting different phenomena. Based on ultrastructural examination of the vaginal contents of five Drosophila species (D. mettleri, D. nigrospiracula, D. melanogaster, D. mojavensis, and D. hexastigma), we propose three terms to describe these vaginal structures: the sperm sac, the mating plug, and the true insemination reaction. Each term describes a distinct structure associated with a specific female postmating behavior. This study questions the concept of the insemination reaction as a single phenomenon and discusses its possible functions from an evolutionary perspective. © 1996 Springer-Verlag.
• Krull, C. E., Morton, D. B., Faissner, A., Schachner, M., & Tolbert, L. P. (1994). Spatiotemporal pattern of expression of tenascin-like molecules in a developing insect olfactory system. Journal of Neurobiology, 25(5), 515-534.
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  PMID: 7520933;Abstract: During the development of the olfactory (antennal) lobe of the moth Manduca sexta, olfactory sensory axons induce glomerular branching patterns in their target neurons. Glial cells, by surrounding the developing glomerular template, are thought to mediate the developmental influence of olfactory axons on these branching patterns. Previous studies have demonstrated that, in the absence of glia, neurons in the antennal lobe branch in an aglomerular fashion, even in the presence of competent antennal axons (Oland and Tolbert, 1988, J. Comp. Neurol. 278:377-387; Oland et al., 1988, J. Neurosci. 8:353-367). We have begun to explore the molecular basis by which glial cells could influence patterns of neurite branching. For this work, we have utilized immunocytochemical techniques and a partial biochemical analysis to demonstrate that molecules antigenically similar and comparable in size to mammalian tenascin are localized on the neuropil- associated glial cells that form borders around glomeruli in the developing antennal lobe. These tenascin-like molecules associated with neuropilar glia are present at critical stages of glomerulus development; tenascin-like immunoreactivity declines after glomeruli form and become stabilized. Neither the arrival nor the absence of antennal axons in the lobe induces changes in either the molecular forms or the amounts of tenascin-like molecules. The spatiotemporal pattern of expression of tenascin-like molecules suggests that they are in a position to participate in the formation of a glomerular neuropil and could form a molecular barrier that constrains neurite outgrowth strictly to glomeruli.
• Krull, C. E., Oland, L. A., Faissner, A., Schachner, M., & Tolbert, L. P. (1994). In vitro analyses of neurite outgrowth indicate a potential role for tenascin-like molecules in the development of insect olfactory glomeruli. Journal of Neurobiology, 25(8), 989-1004.
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  PMID: 7525872;Abstract: Tenascin-like material is associated with glial cells that form borders around developing glomerular units in the olfactory (antennal) lobe of the moth Manduca sexta and is present at critical stages of glomerulus formation (Krull et al., 1994, J. Neurobiol. 25:515-534). Tenascin-like immunoreactivity declines in the mature lobe, coincident with a wave of synapse formation within the glomeruli and glomerulus stabilization. Tenascin-like molecules associated with neuropilar glia are in the correct position to influence the branching patterns of growing neurites by constraining them to glomeruli. In this study, we examine the growth of cultured moth antennal-lobe neurons in response to mouse CNS tenascin. Uniform tenascin provides a poor substrate for cell-body attachment and neurite outgrowth. Neuronal cell bodies provided with a striped substratum consisting of tenascin and concanavalin-A (con-A)/laminin attach preferentially to con-A/laminin lanes. Most neurons restrict their branching to con-A/laminin lanes both at early and later times in culture but others send processes across multiple tenascin and con-/laminin lanes in an apparently indiscriminate manner. Tenascin can inhibit the neuritic outgrowth of most antennal-lobe neurons, and this raises the possibility that the tenascin-like molecules associated with neuropilar glia in vivo act to constrain growing neurites to glomeruli. Thus, glial cells, acting in concert with olfactory axons, might act to promote glomerular patterns of branching by antennal-lobe neurons.
• Malun, D., Oland, L. A., & Tolbert, L. P. (1994). Uniglomerular projection neurons participate in early development of olfactory glomeruli in the moth Manduca sexta. Journal of Comparative Neurology, 350(1), 1-22.
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  PMID: 7860794;Abstract: Glomerular organization of the antennal (olfactory) lobe is initiated by the arrival of sensory axons from the antenna. Bundles of axon terminals coalesce into spheroidal knots of neuropil called protoglomeruli. Previous studies have suggested that the protoglomeruli form a template for the mature glomerular array, but an early role for projection neurons in establishing the template has not been excluded. We examined with the confocal laser scanning microscope the morphological development of the uniglomerular projection neurons during the stages in which glomeruli are constructed. Groups of projection neurons were stained with the lipophilic dye DiI to assess the development of the population as a whole; individual neurons were filled intracellularly with Lucifer Yellow to examine in detail the development of shape. In some preparations, sensory axons and glial cells also were labeled by using different fluorescent dyes to reveal possible interactions between projection neuron dendrites and sensory axons or glial cells. Protoglomeruli form in a wave beginning at the entry point of the antennal nerve and proceeding across the lobe to the opposite pole. A second wave follows in which projection neurons become tufted and innervate the newly formed glomeruli, sometimes extending into the glial border surrounding the protoglomeruli. In animals deprived of sensory axons, some projection neurons still form tufted dendritic trees and, in one region of the neuropil, a glomerulus-like structure. The early presence of projection neuron processes in the protoglomeruli and the formation of at least one glomerulus- like structure in unafferented lobes suggest that uniglomerular projection neurons play an active role in the construction of olfactory glomeruli.
• Boeckh, J., & Tolbert, L. P. (1993). Synaptic organization and development of the antennal lobe in insects. Microscopy Research and Technique, 24(3), 260-280.
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  PMID: 8431606;Abstract: Many insects possess a highly developed sense of smell. This paper summarizes the cellular and synaptic organization of the antennal (olfactory) lobe of the insect brain and then reviews morphological and fine-structural aspects of the development of the lobe. Visualization of synapses between classes of neurons identified by physiological, morphological, or transmitter-cytochemical properties has provided insights into arrangements of contacts and their possible roles in information processing. Studies of development have revealed the requirement for afferent axons from the antenna for the formation of olfactory glomeruli, where virtually all of the synapses in the lobe occur, and have suggested the possibility that glial cells play a role in the instructive influence of the axons on their target neurons in the lobe. The findings reviewed in this paper are primarily from one representative hemimetabolous insect, the American cockroach, and one representative holometabolous insect, a hawkmoth, and comparisons are made with vertebrate systems when appropriate.
• Sun, X., Tolbert, L. P., & Hildebrand, J. G. (1993). Ramification pattern and ultrastructural characteristics of the serotonin immunoreactive neuron in the antennal lobe of the moth Manduca sexta: a laser-scanning confocal and electron microscopic study. Journal of Comparative Neurology, 338, 5-16.
• Tolbert, L. P. (1993). Foreword. Microscopy Research and Technique, 24(2), 105-.
• Oland, L. A., Orr, G., & Tolbert, L. P. (1990). Construction of a protoglomerular template by olfactory axons initiates the formation of olfactory glomeruli in the insect brain. Journal of Neuroscience, 10(7), 2096-2112.
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  PMID: 2376770;Abstract: Olfactory glomeruli in insects share many features of organization with their vertebrate counterparts, and yet offer distinct advantages for study of neuronal development. Previous studies have revealed that the olfactory lobes of the brain of the moth Manduca sexta arise postembryonically and that glomeruli in the lobe are induced by olfactory afferent axons (Hildebrand et al., 1979; Oland and Tolbert, 1987). In the present study, we have used the Golgi method, intracellular labeling of neurons with Lucifer yellow, and electron microscopy to follow neuronal development in the antennal lobe through the period when glomeruli develop. Our results, taken together with other results from our laboratory, suggest that olfactory sensory axons have the intrinsic ability to form protoglomeruli, and that an interaction between these axons and glial cells (but not the majority of the neurons of the antennal lobe) causes the glial cells to surround the protoglomeruli. Ingrowth of the neurites of most antennal-lobe neurons into the protoglomeruli occurs after a small delay and appears to be constrained to glomerular units by the presence of the glial boundaries. Synapses, initially not detected in the protoglomeruli, begin to appear as soon as the neuntes of antennal-lobe neurons appear in the glomeruli. Thus, antennal axons, instead of immediately seeking out postsynaptic targets, first form the template for organization of future glomeruli. The neuntes of most of the neurons of the antennal lobe grow outward to meet the olfactory sensory axons, and in doing so, join with these axons to form glomeruli. Preliminary results concerning the development of a second class of neuron in the lobe, the projection neurons, indicate that at least some of these neurons may arborize in the region of the protoglomeruli very early and therefore participate with the afferent axons in laying the foundation for glomeruli.
• Tolbert, L. P., & Oland, L. A. (1990). Glial cells form boundaries for developing insect olfactory glomeruli. Experimental Neurology, 109, 19-28.
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  invited review
• Tolbert, L. P., & Sirianni, P. A. (1990). Requirement for olfactory axons in the induction and stabilization of olfactory glomeruli in an insect. Journal of Comparative Neurology, 298(1), 69-82.
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  PMID: 2212098;Abstract: The role of antennal sensory axons in the induction and stabilization of olfactory glomeruli has been explored in the moth Manduca sexta. First, we asked the question: how many axons are necessary to induce glomerulus formation within the first-order olfactory neuropil of the brain? Axons from as few as 10 of the normal 70-80 repeating antennal segments were sufficient to induce glomeruli. However, there was a dose dependence in the number of glomeruli that developed in partially innervated lobes. When only 11 segments of the antenna were allowed to provide innervation to the lobe, only 37 of the normal 59 ± 2 glomeruli developed; over 20 segments were necessary to induce the normal number of glomeruli. In a second set of experiments, we asked: for how long must antennal axons be present to stabilize newly formed glomeruli? We found that antennal axons must be intact for at least 2 to 4 stages (roughly equivalent to 2 to 4 days) for glomeruli to be stable even if the axons are subsequently severed. This finding, taken in the light of other recent findings in our laboratory, suggests that the formation of synapses may be crucial element in the stabilization of glomerular structure. All together, the results of the present study indicate that induction and stabilization of glomeruli are separable events with different underlying cellular bases.
• Oland, L. A., & Tolbert, L. P. (1989). Patterns of glial proliferation during formation of olfactory glomeruli in an insect.. Glia, 2(1), 10-24.
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  PMID: 2523336;Abstract: Partitioning of the first-order olfactory neuropil into glomeruli in the developing brain of the moth Manduca sexta occurs only in the presence of olfactory sensory axons and appears to be mediated by changes in glial cells (Oland et al.: J. Neurosci., 8:353-367, 1988). The arrival of sensory axons in the brain triggers changes in glial shape and position that lead to the formation of a glial scaffolding for the developing glomeruli. The presence of mitotic figures in glial cells at stages before glomeruli emerge (Oland and Tolbert: J. Comp. Neurol., 255:196-207, 1987) suggested that glial proliferation might also contribute to the formation of the glomerular envelopes. To determine whether glial proliferation is induced by olfactory axons, we have used 3H-thymidine to label dividing cells before, during, and after the formation of glomeruli and have compared the patterns of proliferation in normal and chronically unafferented olfactory neuropils. We found significant differences in mitotic indices only after glomerular walls had been established, indicating that the sensory axons induce the formation of glomerular envelopes primarily via the changes in glial morphology and distribution, not by stimulating glial proliferation.
• Tolbert, L. P. (1989). Afferent axons from the antenna influence the number and placement of intrinsic synapses in the antennal lobes of Manduca sexta. Synapse, 3(1), 83-95.
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  PMID: 2919370;Abstract: The present study compares the placement and frequency of occurrence of synapses in normally developing antennal lobes of the brain of the moth Manduca sexta and in lobes developing in the absence of afferent axons from the antenna. The antennal lobes develop during the metamorphosis from larva to moth, and require antennal afferent input to develop their characteristic knots of synaptic neuropil, the glomeruli, that are arrayed around a central core of coarse neuropil. Synapses begin to form throughout the neuropil of the antennal lobe before ingrowth of antennal axons into the lobe. During normal development, almost all synapses (those among intrinsic neurons as well as those made by antennal afferent axons) become segregated into glomeruli as the glomeruli are established. Thus, in normal mature lobes, the radial segregation between synaptic (glomerular) and nonsynaptic (central) regions is virtually complete. In lobes that have never been allowed to receive antennal axons, an outer ring of 'protoglomerular' neuropil develops in place of the glomeruli. A similar segregation of synaptic and nonsynaptic regions occurs, with two major differences: the frequency of synapses that develops in the outer ring of fine-textured neuropil is almost 50% higher than in normal glomeruli, and the small number of synapses that occur in the coarse central neuropil now occur on aberrant fine processes in that neuropil. Apparently, in the absence of their normal massive input from the antenna, elements intrinsic to the antennal lobe are induced to form extra synapses with each other, and to send aberrant fine branches to synapse in a region of neuropil normally containing predominantly large-caliber neurite trunks and few synapses.
• Tolbert, L. P. (1989). Intercellular interactions in the construction of olfactory glomeruli in an insect. in "ISOT X: Proceedings of the Tenth International Conference on Olfaction and Taste" (ed. K Doving), 236-245.
• Tolbert, L. P., & Oland, L. A. (1989). A role for glia in the development of organized neuropilar structures. Trends in Neurosciences, 12(2), 70-75.
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  PMID: 2469214;Abstract: Intercellular interactions are critical in the development of the nervous system. In the olfactory system of a moth, sensory axons induce the formation of large synaptic glomeruli, each surrounded by a glial envelope, in the antennal lobe of the brain. During development, the sensory axons cause changes in glial shape and disposition one day before glomeruli are recognized. Early removal of glial cells prevents the development of glomeruli despite the presence of afferent axons. Thus, the glial cells appear to play a role as intermediaries in the induction of glomeruli by afferent axons. Recent findings in the mammalian somatosensory cortex suggest a similar role for glia there. © 1989.
• Oland, L. A., & Tolbert, L. P. (1988). Effects of hydroxyurea parallel the effects of radiation in developing olfactory glomeruli in insects. Journal of Comparative Neurology, 278(3), 377-378.
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  PMID: 3216049;Abstract: Previous observations (Oland and Tolbert: J. Comp. Neurol. 255:196-207, '87, Soc. Neurosci. Abstr. 13:1144, '87; Oland et al.: J. Neurosci. 8:353-367, '88) have provided evidence that the afferent-axon-induced development of synaptic glomeruli in the antennal lobe of the moth Manduca sexta depends upon an interaction between ingrowing sensory axons and the glial cells of the antennal lobe. In order to differentiate between the roles of glial cells and of afferent axons on the partitioning of the lobe into glomeruli, we have used the antimitotic agent hydroxyurea to produce lobes deficient in glial cells by retaining sensory input. The resulting lobes were analyzed in the light and electron microscopes, and the integrity of their antennal input was evaluated by examining the gross and microscopic structure of the antennae, the number of antennal afferent axons, and electroantennogram responses to odors. Our results with hydroxyurea show that in treated animals with adequate antennal input the degree to which the antennal-lobe neuropil becomes glomerular varies with the number of glial cells remaining in the lobe; when less than approximately one quarter of the normal glial complement is present, glomeruli do not develop at all. These experiments complement and extend previous experiments in which the number of glial cells was reduced with radiation (Oland et al.: J. Neurosci. 8:353-367, '88). The fact that the present results mimic the previous results with radiation strongly suggest that glial cells do mediate the afferent-axon-induced formation of olfactory glomeruli in the moth.
• Oland, L. A., Tolbert, L. P., & Mossman, K. L. (1988). Radiation-induced reduction of the glial population during development disrupts the formation of olfactory glomeruli in a insect. Journal of Neuroscience, 8(1), 353-367.
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  PMID: 3339417;Abstract: Interactions between neurons and between neurons and glial cells have been shown by a number of investigators to be critical for normal development of the nervous system. In the olfactory of Manduca sexta, sensory axons have been shown to induce the formation of synaptic glomeruli in the antennal lobe of the brain (Hildebrand et al., 1979). Oland and Tolbert (1987) found that the growth of sensory axons into the developing antennal lobe causes changes in glial shape and disposition that presage the establishment of glomeruli, each surrounded by a glial envelope. Several lines of evidence lead us to hypothesize that the glial cells of the lobe may be acting as intermediaries in developmental interactions between sensory axons and neurons of the antennal lobe. In the present study, we have tested this hypothesis by using gamma-radiation to reduce the number of glial cells at a time when neurons of the antennal system are postmitotic but glomeruli have not yet developed. When glial numbers are severely reduced, the neuropil of the resulting lobe lacks glomeruli. Despite the presence of afferent axons, the irradiated lobe has many of the features of a lobe that developed in the absence of afferent axons. Our findings indicate that the glial cells must play a necessary role in the inductive influence of the afferent axons.
• Tolbert, L. P. (1988). Review of "Synapse". Quarterly Review of Biology, 63, 243.
• Oland, L. A., & Tolbert, L. P. (1987). Glial patterns during early development of antennal lobes of Manduca sexta: A comparison between normal lobes and lobes deprived of antennal axons.. Journal of Comparative Neurology, 255, 196-207.
• Arbas, E. A., & Tolbert, L. P. (1986). Presynaptic terminals persist following degeneration of 'flight' muscle during development of a flightless grasshopper. Journal of Neurobiology, 17(6), 627-636.
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  PMID: 3794689;
• Tolbert, L. P., & Calabrese, R. L. (1985). Anatomical analysis of contacts between identified neurons that control heartbeat in the leech Hirudo medicinalis. Cell and Tissue Research, 242(2), 257-267.
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  Abstract: The rhythmic constriction of the heart tubes in the leech Hirudo medicinalis is controlled by an identified set of motor neurons (HE cells) and interneurons (HN cells) (reviewed by Calabrese and Peterson 1983). Electrophysiological recordings have indicated particular synaptic relationships among HE and HN cells. In the present study, the synaptic framework mediating the interactions among HE cells and HN cells was examined anatomically. Using light and electron microscopy of physiologically identified, HRP-injected cells, we have examined the zones of interaction and types of contacts between specific cells. HE cells, which have very fine, threadlike processes, interact with their contralateral homologues throughout most of the middle third of the ganglionic neuropil. When HE-cell neuntes come together, the apposed plasma membranes are rigidly parallel, separated by an intercellular gap of 6 nm, for up to 6 μm. These specializations must form the structural basis for the strong electrical coupling observed (Peterson 1983) between HE-cell pairs. HE cells also emit from the main neurite a series of extremely fine processes that extend dorsally. These appear in the light microscope to contact processes of the ipsilateral HN cell of the same ganglion, and are also in a position to make contact with the axons of more anterior HN cells. The intraganglionic processes of HN cells, which are studded with large varicosities, ramify in part of the region of neuropil occupied by HE-cell processes, as well as more posteriorly. Contacts between HE and HN cells, which are known to be mostly inhibitory synaptic contacts, are seen in the electron microscope to be formed between medium-diameter HN processes, which are filled with clear round synaptic vesicles, and multiple fine tendrils of the HE cell that surround the HN process. Certain HN cells form reciprocal inhibitory synapses with their contralateral homologues. These contacts occur near the midline, sometimes in the major mass of neuropil and sometimes embedded in the extracellular material that ensheathes the neuropil. The contacts are between medium-and small-diameter profiles that are both filled with synaptic vesicles. Our findings indicate that various classes of physiological interactions among HE and HN cells are mediated by anatomically distinct types of contacts and, at least in some cases, are segregated from each other on the neuritic trees of the cells. © 1985 Springer-Verlag.
• Tolbert, L. P., Matsumoto, S. G., & Hildebrand, J. G. (1983). The development of synapses in the antennal lobes of the moth Manduca sexta. Journal of Neuroscience, 3, 1158-1175.
• Hildebrand, J. G., Matsumoto, S. G., Tolbert, L. P., & Schneiderman, A. S. (1982). Postembryonic development of the antennal lobes in the moth Manduca sexta. Neuroscience Research Program Bulletin, 20, 891-900.
• Tolbert, L. P., & Morest, D. K. (1982). The neuronal architecture of the anteroventral cochlear nucleus of the cat in the region of the cochlear nerve root: Electron microscopy. Neuroscience, 7(12), 3053-3067.
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  PMID: 7162626;Abstract: We have studied the posterior division of the anteroventral cochlear nucleus, where the cochlear nerve root enters the brain, in the cat. In Nissl preparations, this region contains two types of neuronal cell bodies: globular and multipolar. The two types can be identified in the electron-microscope by comparing Nissl substance and rough endoplasmic reticulum. Globular cell bodies receive many synaptic terminals, which cover 85% of the surface. In contrast, multipolar cell bodies are almost entirely wrapped by thin glial sheets-synaptic terminals contact less than 15% of the surface and tend to cluster at the bases of dendrites. Synaptic terminals are of three kinds, types 1, 2, and 3, which contain large round, small round-to-oval, and small flattened synaptic vesicles, respectively. Terminals of all three kinds synapse on both types of cell bodies. However, only globular cell bodies receive the largest type 1 terminals, which correspond to end-bulbs, seen in Golgi impregnations to arise from cochlear nerve axons. Cochlear ablation leads to degeneration of type 1, but not type 2 or 3 terminals. We conclude that neurons with globular cell bodies receive heavy somatic input from the cochlear nerve, as well as from other sources. Neurons with multipolar cell bodies receive very little input to their perikarya-giving their dendrites a more important role in determining their response properties. We suggest a morphological basis for correlating individual kinds of neurons with certain electrophysiological response types. © 1982.
• Tolbert, L. P., & Morest, D. K. (1982). The neuronal architecture of the anteroventral cochlear nucleus of the cat in the region of the cochlear nerve root: Golgi and Nissl methods. Neuroscience, 7(12), 3013-3025,3027-3030.
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  PMID: 6186942;Abstract: This report characterizes the cells and fibers in one part of the cochlear nucleus, the posterior division of the anteroventral cochlear nucleus. This includes the region where the cochlear nerve root enters the brain and begins to form endings. Nissl stains reveal the somata of globular cells with dispersed Nissl substance and those of multipolar cells with coarse, clumped Nissl bodies. Both parts of the posterior division contain cells with each Nissl pattern, but in different relative numbers and locations. Golgi impregnations demonstrate two types of neurons: bushy cells, with short bush-like dendrites, and stellate and elongate cells, with long tapered dendrites. Several varieties of bushy cells, differing in the morphology of the cell body and in the size and extent of the dendritic field, can be distinguished. Comparison of the distributions of these cell types, as well as cellular morphology, suggest that the globular cells recognized in Nissl stains correspond to bushy neurons, while the multipolar cells correspond to stellate and elongate neurons. Golgi impregnations reveal large end-bulbs and smaller boutons from cochlear nerve fibers, as well as boutons from other, unidentified sources, ending in this region. The particular arrangements of the dendritic fields of the different cell types and the axonal endings associated with them indicate that these neurons must have different physiological properties, since they define different domains with respect to the cochlear and non-cochlear inputs. © 1982.
• Tolbert, L. P., Morest, D. K., & Yurgelun-Todd, D. (1982). The neuronal architecture of the anteroventral cochlear nucleus of the cat in the region of the cochlear nerve root: Horseradish peroxidase labelling of identified cell types. Neuroscience, 7(12), 3031-3052.
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  PMID: 6298659;Abstract: Golgi impregnations of the posterior part of the cat's anteroventral cochlear nucleus have revealed two types of neurons, bushy cells with short bush-like dendrites and stellate cells with long, tapered processes; Nissl stains have revealed globular and multipolar cell bodies with dispersed and clumped ribosomal patterns, respectively. In the present study, we injected horseradish peroxidase into the trapezoid body. Ipsilaterally, retrograde, diffuse labelling of neurons, presumably through damaged fibers, yielded Golgi-like profiles of numerous bushy cells with typical dendrites and with thick axons projecting toward the trapezoid body. Stellate cells were almost never labelled in this way. Anterograde diffuse labelling of thick axons demonstrated calyx endings in the contralateral medial nucleus of the trapezoid body. In the electron-microscope, the perikarya of diffusely-filled bushy neurons were found to have the dispersed ribosomal pattern and the kinds of synaptic endings typical of globular cells, including large profiles of end-bulbs from cochlear nerve axons. After injections restricted to the medial trapezoid nucleus, granularly-labelled cells in the cochlear nucleus were almost completely confined to the contralateral side; Nissl counterstaining showed them to be globular cells in the posterior part of the anteroventral cochlear nucleus. After larger injections, involving surrounding regions of the superior olivary complex, granular labelling occurred throughout the ventral cochlear nucleus on both sides. There is also evidence that stellate cells in Golgi impregnations correspond to multipolar cell bodies in Nissl stains. We conclude that bushy cells typically correspond to globular cells, which receive end-bulbs from the cochlea and send thick axons to the contralateral medial trapezoid nucleus, where they form calyces on principal cells. Principal cells, in turn, are known to project to the lateral superior olive and to one of the nuclei of origin of the crossed olivo-cochlear bundle, which feeds back to the cochlea. In this circuit, correlations between synaptic patterns and particular physiological signal transfer characteristics can be suggested. These could be related to binaural intensity interactions in the lateral superior olive and to a regulatory loop involving the olivo-cochlear bundles. © 1982.
• Tolbert, L. P., & Hildebrand, J. G. (1981). Organization and synaptic ultrastructure of glomeruli in the antennal lobes of the moth Manduca sexta: a study using thin sections and freeze-fracture. Proceedings of the Royal Society of London B, 213, 279-301.
• Hildebrand, J. G., Matsumoto, S. G., Camazine, S. M., Tolbert, L. P., Blank, S., Ferguson, H., & Ecker, V. (1979). Organization and physiology of antennal centers in the brain of the moth Manduca sexta. In "Insect Neurobiology and Pesticide Action", 375-382.
• Hildebrand, J. G., Roessler, W., & Tolbert, L. P. (1979). Postembryonic development of the olfactory system in the moth Manduca sexta: primary-afferent control of glomerular development. Seminars in Cell and Developmental BIology, 8, 163-170.

Presentations

• Tolbert, L. P., & Tolbert, L. P. (2017, February). Good Taste - The Neuroscience of Taste and Smell. Yale Club meeting.
• Tolbert, L. P. (2014, Spring). Research and Design: Daring to Fail. Keynote speech for Northern Arizona University annual Undergraduate Research Symposium. Flagstaff, AZ: Northern Arizona University.
• Tolbert, L. P. (2014, fall). Big Data and the Brain. presentation to the Harvard Club of Southern Arizona. Tucson, AZ.
• Tolbert, L. P. (2014, spring). Federally Funded Research: Expect the Unexpected. symposium on Golden Goose Award, AAAS Annual Meeting. Chicago, IL.
• Tolbert, L. P. (2013, fall). Olfaction: An Acquired Taste. public talk in Science Café series of the UA School of Mind, Brain, and Behavior. Tucson, AZ.
• Tolbert, L. P. (2012, fall). Maintaining a Positive Research Enterprise to Address the Grand Global Challenges – A Land-Grant University Perspective. Council of Scientific Society Presidents biannual meeting on science and science policy. Washington, DC.
• Tolbert, L. P. (2012, fall). Research seminar for Rutgers University Women in Neuroscience program. Rutgers University Women in Neuroscience program. Piscataway, NJ.
• Tolbert, L. P. (2012, fall). The Role of Research Universities in Securing America’s Future Prosperity: Challenges and Expectations. Invited testimony for Subcommittee on Research and Science Education of the Committee on Science and Technology of the U.S. House of RepresentativesAssociation of American Universities and Association of Public and Land-grant Universities.
• Tolbert, L. P. (2012, spring). Bidirectional interactions between neurons and glial cells during development of an olfactory system. Neuroscience Day of the Ohio Miami Valley Chapter of the Society for Neuroscience. Oxford, OH: Miami University.
• Tolbert, L. P. (2010, Spring). The Plastic Brain. Public lecture for UA College of Science lecture series on "Mind and Brain".
• Tolbert, L. P. (2010, winter). The State of Research Infrastructure at U.S. Universities. Invited testimony for Subcommittee on Research and Science Education of the Committee on Science and Technology of the U.S. House of Representatives.
• Tolbert, L. P. (2008, Srping). The Apprenticeship Model: Learning for the 21st Century. Toyota Technological Institutes President's Forum on "The Role of Universities in the 21st Century". Nagoya, Japan: Toyota Technological Institute.

Poster Presentations

• Hernandez, E., Macnamee, S. E., Kaplan, L. R., Charlton, J. A., Farhadi, D. S., Lance, K. L., Tolbert, L. P., & Oland, L. A. (2016, Nov). Drosophila astrocytes span functional neural domains. Society for Neuroscience.
• Hernandez, E., Lance, K. N., Charlton, J. A., MacNamee, S. E., Oland, L. A., Tolbert, L. P., Hernandez, E., Lance, K. N., Charlton, J. A., MacNamee, S. E., Oland, L. A., Tolbert, L. P., Hernandez, E., Lance, K. N., Charlton, J. A., MacNamee, S. E., Oland, L. A., & Tolbert, L. P. (2015, Fall). Morphological analysis of astrocyte-like glial cells in the Drosophila ventral nerve cord. Society for Neuroscience annual meeting. Chicago, IL: Society for Neuroscience.
• MacNamee, S. E., Liu, K., Gerhard, S., Fetter, R., Tolbert, L. P., Cardona, A., & Oland, L. A. (2015, Fall). Drosophila Astrocytes transport glutamate at identified non-tri-partite synapses. Society for Neuroscience annual meeting. Chicago, IL: Society for Neuroscience.
• Oland, L. A., Tolbert, L. P., & MacNamee, S. E. (2015, Fall). Astrocytic glutamate transport via dEEAT1 regulates a pre-motor synapse. Cold Spring Harbor Drosophila Neurobiology meeting. Cold Spring Harbor, NY: Cold Spring Harbor.
• Oland, L. A., Tolbert, L. P., Charlton, J. A., Lance, K. N., Tran, C. T., Oland, L. A., Tolbert, L. P., Charlton, J. A., Lance, K. N., & Tran, C. T. (2015, Fall). Modulation of neural activity affects astrocyte morphology in Drosophila melanogaster. Society for Neuroscience annual meeting. Chicago, IL: Societyfor Neuroscience.
• Bender, C., Bender, C., Watkins, J. C., Watkins, J. C., Tolbert, L. P., & Tolbert, L. P. (2012, October). Assessing Undergraduate Research and BioMath Efforts at the University of Arizona. Howard Hughes Medical Institute Program Directors' Meeting. Chevy Chase, Maryland: Howard Hughes Medical Institute.