Building the antennal lobe: engrailed expression reveals a contribution from protocerebral neuroblasts in the grasshopper Schistocerca gregaria

The expression pattern of the engrailed protein was studied in neuroblasts which delaminate at the border of the protocerebrum and antennal lobe of the deutocerebrum in the early embryonic brain of the grasshopper. The antennal lobe is a complex structure comprising both glomerular and non-glomerular components, a cellular organization which distinguishes it from the striate-like neuropil comprising the remainder of the deutocerebrum. Early in embryogenesis engrailed expression in the protocerebrum is restricted to a compact block of neuroblasts located at its interface with the antennal lobe. Subsequently engrailed expression in these cells disappears in a stepwise manner from anterior to posterior so that by 37% of embryogenesis only a single row of three engrailed positive neuroblasts and their progeny remains. Contemporaneously engrailed expression reappears in a group of more anterior progeny deriving from neuroblasts which are no longer immunoreactive. The three remaining engrailed positive neuroblasts then become separated from their non-immunoreactive neighbours by an invagination of the perineurium called the lateral cleft and come to lie completely within the developing antennal lobe. These cells then direct columns of immunoreactive progeny centrifugally towards the centre of the lobe. Such a protocerebral contribution to the antennal lobe suggests that the evolution and ontogeny of this brain region need to be reconsidered.     

The developmental expression of serotonin-immunoreactivity in the brain of the pupal honeybee

The biogenic amine serotonin is a neurotransmitter and modulator in both vertebrates and invertebrates. In the CNS of insects, serotonin is expressed by identifiable subsets of neurons. In this paper, we characterize the onset of expression in the brain and suboesophageal ganglion of the honeybee during pupal development. Several identified serotonin-immunoreactive neurons are present in the three neuromeres of the suboesophageal ganglion the dorsal protocerebrum, and the deutocerebrum at pupal ecdysis. Further immunoreactive neurons are incorporated into the developing pupal brain in two characteristic developmental phases. During the first phase, 5 days after pupal ecdysis, serotonin immunoreactivity is formed in the protocerebral central body, the lamina and lobula, and the deutocerebral antennal lobe. During the second phase, 2 days later, immunoreactivity appears in neurons of the protocerebral noduli of the central complex, the medulla, and the pedunculi and lobes of the mushroom bodies. Three novel serotonin-immunoreactive neurons that innervate the central complex and the mushroom bodies can be individually identified.     

Embryonic expression of engrailed in sea urchins

Neural patterning genes that are expressed along the anterior-posterior axis of deuterostomes are expressed late in larval development in echinoderms and are thought to function in establishing the highly-derived, adult body plan. We have used genomic resources to clone an engrailed gene (SpEn) from Strongylocentrotus purpuratus, and with this we have developed an antibody specific for SpEn. SpEn is expressed late in embryogenesis in the developing larval nervous system. At the prism stage, a small number of neuroblasts in the oral ectoderm on the edge of the larval mouth begin expressing SpEn. The cells are in bilaterally symmetric positions. The expression of SpEn precedes the expression of the neural markers, synaptotagmin and serotonin in the SpEn immunoreactive cells. The SpEn cells are located on the margin of the domain of cells expressing SpNK2.1, but they do not have nuclear SpNK2.1. Expression of engrailed in a pair of bilateral neural structures in early development appears to be a shared feature of bilaterians.     

Development of neural lineages derived from the sine oculis positive eye field of Drosophila

The Anlage of the Drosophila visual system, called eye field, comprises a domain in the dorso-medial neurectoderm of the embryonic head and is defined by the expression of the early eye gene sine oculis (so). Beside the eye and optic lobe, the eye field gives rise to several neuroblasts that contribute their lineages to the central brain. Since so expression is only very short lived, the later development of these neuroblasts has so far been elusive. Using the P-element replacement technique [Genetics, 151 (1999) 1093] we generated a so-Gal4 line driving the reporter gene LacZ that perdures in the eye field derived cells throughout embryogenesis and into the larval period. This allowed us to reconstruct the morphogenetic movements of the eye field derived lineages, as well as the projection pattern of their neurons. The eye field produces a dorsal (Pc1/2) and a ventral (Pp3) group of three to four neuroblasts each. In addition, the target neurons of the larval eye, the optic lobe pioneers (OLPs) are derived from the eye field. The embryonically born (primary) neurons of the Pp3 lineages spread out at the inner surface of the optic lobe. Together with the OLPs, their axons project to the dorsal neuropile of the protocerebrum. Pp3 neuroblasts reassume expression of so-Gal4 in the larval period and produce secondary neurons whose axonal projection coincides with the pattern formed by the primary Pp3 neurons. Several other small clusters of neurons that originate from outside the eye field, but have axonal connections to the dorsal protocerebrum, also express so and are labeled by so-Gal4 driven LacZ. We discuss the dynamic pattern of the so-positive lineages as a tool to reconstruct the morphogenesis of the larval brain.     

Immunocytochemical identification of neuroactive substances in the antennal lobe of the male silkworm moth Bombyx mori

As a first step towards understanding the functional role of neuroactive substances in the first olfactory center of the male silkworm moth Bombyx mori, we carried out an immunocytochemical identification of antennal lobe neurons. Antibodies against gamma-aminobutyric acid (GABA), FMRFamide, serotonin, tyramine and histamine were applied to detect their existence in the antennal lobe. In the present immunocytochemical study, we clarified four antenno-cerebral tracts from their origin and projection pathways to the protocerebrum, and revealed the following immunoreactive cellular organization in the antennal lobe. 1) Local interneurons with cell bodies in the lateral cell cluster showed GABA, FMRFamide and tyramine immunoreactivity. 2) Projection neurons passing through the middle antenno-cerebral tract with cell bodies in the lateral cell cluster showed GABA and FMRFamide immunoreactivity. Projection neurons passing through the outer antenno-cerebral tract with cell bodies in the lateral cell cluster showed FMRFamide immunoreactivity. 3) Centrifugal neurons passing through the inner antenno-cerebral tract b with cell bodies located outside the antennal lobe showed serotonin and tyramine immunoreactivity. Our results revealed basic distribution patterns of neuroactive substances in the antennal lobe and indicated that each projection pathway from the antennal lobe to the protocerebrum contains specific combination of neuroactive substances.     

Neuroblast lineage-specific origin of the neurons of the Drosophila larval olfactory system

The complete neuronal repertoire of the central brain of Drosophila originates from only approximately 100 pairs of neural stem cells, or neuroblasts. Each neuroblast produces a highly stereotyped lineage of neurons which innervate specific compartments of the brain. Neuroblasts undergo two rounds of mitotic activity: embryonic divisions produce lineages of primary neurons that build the larval nervous system; after a brief quiescence, the neuroblasts go through a second round of divisions in larval stage to produce secondary neurons which are integrated into the adult nervous system. Here we investigate the lineages that are associated with the larval antennal lobe, one of the most widely studied neuronal systems in fly. We find that the same five neuroblasts responsible for the adult antennal lobe also produce the antennal lobe of the larval brain. However, there are notable differences in the composition of larval (primary) lineages and their adult (secondary) counterparts. Significantly, in the adult, two lineages (lNB/BAlc and adNB/BAmv3) produce uniglomerular projection neurons connecting the antennal lobe with the mushroom body and lateral horn; another lineage, vNB/BAla1, generates multiglomerular neurons reaching the lateral horn directly. lNB/BAlc, as well as a fourth lineage, vlNB/BAla2, generate a diversity of local interneurons. We describe a fifth, previously unknown lineage, BAlp4, which connects the posterior part of the antennal lobe and the neighboring tritocerebrum (gustatory center) with a higher brain center located adjacent to the mushroom body. In the larva, only one of these lineages, adNB/BAmv3, generates all uniglomerular projection neurons. Also as in the adult, lNB/BAlc and vlNB/BAla2 produce local interneurons which, in terms of diversity in architecture and transmitter expression, resemble their adult counterparts. In addition, lineages lNB/BAlc and vNB/BAla1, as well as the newly described BAlp4, form numerous types of projection neurons which along the same major axon pathways (antennal tracts) used by the antennal projection neurons, but which form connections that include regions outside the “classical” olfactory circuit triad antennal lobe-mushroom body-lateral horn. Our work will benefit functional studies of the larval olfactory circuit, and shed light on the relationship between larval and adult neurons.     

Distribution of tachykinin-related neuropeptide in the developing central nervous system of the moth Spodoptera litura

Neuropeptides with similarities to vertebrate tachykinins, designated tachykinin-related peptides (TRPs), have been identified in several insect species. In this investigation we have utilized an antiserum raised to one of the locust TRPs, locustatachykinin-I (LomTK-I), to determine the distribution pattern of LomTK-like immunoreactive (LTKLI) neurons in the developing nervous system of the moth Spodoptera litura. A number of LTKLI neurons could be followed from the larval to the adult nervous system: a set of median neurosecretory cells (MNCs) in the brain, a pair of brain descending neurons and a few sets on neurons in the ventral nerve cord. The distribution of LTKLI neurons in the adult brain is very similar to that seen in other insect species with prominent arborizations in the central body, antennal lobes, mushroom body calyces, optic lobe neuropils and other distinct neuropil areas in the protocerebrum and tritocerebrum. A new finding is the presence of LTKLI neurosecretory cells with axon terminals in the anterior aorta and corpora cardiaca, suggesting for the first time a neurohormonal role of tachykinin-related peptide(s) in insects. During postembryonic development the number of LTKLI neurons in the ventral nerve cord decreases somewhat, whereas the number increases in the brain. Thus the functional roles of TRPs may change to some extent during development.     

Early steps in building the insect brain: neuroblast formation and segmental patterning in the developing brain of different insect species

In insects, morphological, molecular and genetic studies have provided a detailed insight into the ontogenetic processes that shape the ventral nerve cord. On the other hand, owing to its complexity and less obvious segmental composition, the knowledge about the development of the brain is still fragmentary. A promising approach towards gaining insight into fundamental processes underlying brain development is the comparison of embryonic brain development among different insect species. However, so far such comparative analyses are scarce. In this review, we summarize and compare data on the early steps in brain formation in different hemi- and holometabolous insects. We show that basic aspects of the spatial and temporal development of the embryonic brain neuroblast pattern are conserved among insects. Furthermore, we compare the number and proliferation patterns of neuroblasts related to major neuropil structures such as mushroom bodies, central complex, and antennal lobe. Finally, comparing the expression patterns of engrailed in different species, and considering new data from Drosophila melanogaster, we discuss the segmental organization of the insect brain.     

Timelines in the insect brain: fates of identified neural stem cells generating the central complex in the grasshopper Schistocerca gregaria

This study employs labels for cell proliferation and cell death, as well as classical histology to examine the fates of all eight neural stem cells (neuroblasts) whose progeny generate the central complex of the grasshopper brain during embryogenesis. These neuroblasts delaminate from the neuroectoderm between 25 and 30 % of embryogenesis and form a linear array running from ventral (neuroblasts Z, Y, X, and W) to dorsal (neuroblasts 1-2, 1-3, 1-4, and 1-5) along the medial border of each protocerebral hemisphere. Their stereotypic location within the array, characteristic size, and nuclear morphologies, identify these neuroblasts up to about 70 % of embryogenesis after which cell shrinkage and shape changes render progressively more cells histologically unrecognizable. Molecular labels show all neuroblasts in the array are proliferative up to 70 % of embryogenesis, but subsequently first the more ventral cells (72–75 %), and then the dorsal ones (77–80 %), cease proliferation. By contrast, neuroblasts elsewhere in the brain and optic lobe remain proliferative. Apoptosis markers label the more ventral neuroblasts first (70–72 %), then the dorsal cells (77 %), and the absence of any labeling thereafter confirms that central complex neuroblasts have exited the cell cycle via programmed cell death. Our data reveal appearance, proliferation, and cell death proceeding as successive waves from ventral to dorsal along the array of neuroblasts. The resulting timelines offer a temporal blueprint for building the neuroarchitecture of the various modules of the central complex.     

Anatomy of antenno-cerebral pathways in the brain of the sphinx moth Manduca sexta

Summary In the moth Manduca sexta, the number and morphology of neuronal connections between the antennal lobes and the protocerebrum were examined. Cobalt injections revealed eight morphological types of neurons with somata adjacent to the AL neuropil that project in the inner, middle, and outer antenno-cerebral tracts to the protocerebrum. Neurons innervating the macroglomerular complex and many neurons with fibers in the inner antennocerebral tract have uniglomerular antennal-lobe arborizations. Most neurons in the middle and outer antenno-cerebral tracts, on the other hand, seem to innervate more than one glomerulus. Protocerebral areas receiving direct input from the antennal lobe include the calyces of the mushroom bodies, and circumscribed areas termed olfactory foci in the lateral horn of the protocerebrum and several other regions, especially areas in close proximity to the mushroom bodies. Fibers in the inner antenno-cerebral tract that innervate the male-specific macroglomerular complex have arborizations in the protocerebrum that are distinct from the projections of sexually non-specific neurons. Protocerebral neurons projecting into the antennal lobe are much less numerous than antennal-lobe output cells. Most of these protocerebral fibers enter the antennal lobe in small fiber tracts that are different from those described above. In the protocerebrum, these centrifugal cells arborize in olfactory foci and also in the inferior median protocerebrum and the lateral accessory lobes. The morphological diversity of connections between the antennal lobes and the protocerebrum, described here for the first time on a single-cell level, suggests a much greater physiological complexity of the olfactory system than has been assumed so far.     

Characterization of the dCaMKII-GAL4 driver line whose expression is controlled by the <Emphasis Type="Italic">Drosophila</Emphasis> Ca<Superscript>2+</Superscript>/calmodulin-dependent protein kinase II promoter

Transgenic flies that can drive GAL4 expression under the control of the 7 kb 5'-region of the Drosophila Ca(2+)/calmodulin-dependent protein kinase II (dCaMKII) gene (dCaMKII-GAL4) were established. Characteristic features of this dCaMKII-GAL4 driven reporter expression were compatible with the endogenous dCaMKII expression pattern: The dCaMKII-GAL4 driven reporter gene was expressed preferentially in the central nervous system of the embryo and larvae. Reporter expression was also observed in the brain, thoracic ganglion, and gut of the adult. The whole-brain distribution and projections of dCaMKII-GAL4-expressing cells in the adults were visualized three-dimensionally by using UAS-linked reporter genes. Prominent signals of nuclear-localized beta-Gal reporter gene expression were found in extensive brain regions, especially in the Kenyon cells of the mushroom body (MB), cells in the pars intercerebralis, and subesophageal ganglion (SOG). tau reporter gene expression highlighting neurite projections was detected in the MB lobes, median bundle, antennal lobe glomeruli, and fibers of clusters in the SOG, ventrolateral protocerebrum and superior lateral protocerebrum. These observations agree with those of a previous study mapping the dCaMKII-dependent memory circuits in courtship conditioning. Interestingly, green fluorescent protein reporter gene expression in adult MB lobes was predominantly observed in the alpha and beta lobes with a core-deficient pattern, but not in the alpha' and beta' lobes, similar to Fasciclin II immunoreactivity.     

A neuroanatomical study on the organization of the central antennal pathways in insects

1. Single unimodal (olfactory) or multimodal (olfactory and mechanosensory) neurons in the antennal lobe of the deutocerebrum of the American cockroach were characterized functionally by microelectrode recording, and their morphological types and positions in the brain were established by dye injection. Thus individual, physiologically identified neurons of known shape could be mapped in reference to the areas of soma groups, glomeruli, tracts and their projection regions in the brain. 2. All of these neurons send processes to deutocerebral glomeruli, i.e., the regions in which the axons of antennal sensory cells terminate. Output neurons have axons that leave the deutocerebrum whereas local interneurons are anaxonic. 3. An output neuron innervates only one glomerulus, sending its axon into the calyces of the corpora pedunculata (CP) in the protocerebrum, where by multiple branching they reach many CP neurons. The same axons send collaterals into the lateral lobe of the protocerebrum. Because of this arrangement, each deutocerebral glomerulus is represented individually and separately in the two projection regions. The fine structure of the endings of the deutocerebral axons in the protocerebrum is described. In the CP calyces they form microglomeruli with typical divergent connectivity. 4. A local interneuron innervates many glomeruli without sending processes to other parts of the brain. 5. Unimodal olfactory and multimodal neurons can be either output neurons or local interneurons; multimodal information is sent to the protocerebrum directly, in parallel with the unimodal information. 6. At least one glomerulus--the macroglomerulus of the male deutocerebrum--is specialized so as to provide an exclusive topographic representation of certain olfactory stimuli not represented elsewhere (female sexual pheromone).     

Physiology and morphology of olfactory neurons associating with the protocerebral lobe of the honeybee brain

Physiology and morphology of olfactory neurons associated with the protocerebral lobe around the alpha-lobe of the mushroom body were studied in the brain of the honeybee Apis mellifera using intracellular recording and staining techniques. The responses of neurons to behaviorally relevant odorants (a blend, and components of the Nasonov pheromone, and some other non-pheromonal odors) were recorded. Different response patterns were observed within different neurons, and often within the same neuron, in response to different stimuli. All the neurons stained had innervations in the protocerebral lobe. The cell profiles varied from cells connecting the antennal lobe with both the protocerebral and lateral protocerebral lobes (projection neurons), cells linking the pedunculus of the mushroom body with both the protocerebral and lateral protocerebral lobes (PE1 neurons), cells linking the alpha-lobe and protocerebral lobe with the calyces of the mushroom body (feedback neurons), and cells linking the alpha-lobe and protocerebral lobe with the antennal lobe (recurrent neurons), to cells connecting the protocerebral lobe with the contralateral protocerebrum (bilateral neurons). These findings suggest that the protocerebral lobe acts as an olfactory center associating with other centers, and provides multi-layered recurrent networks within the protocerebrum and between the deutocerebrum and the protocerebrum in honeybee olfactory pathways.     

An ontogenetic analysis of locustatachykinin-like expression in the central complex of the grasshopper Schistocerca gregaria

We have investigated the ontogenetic basis of locustatachykinin-like expression in a group of cells located in the pars intercerebralis of the grasshopper midbrain. These cells project fibers to the protocerebral bridge and the central body via a characteristic set of fiber bundles called the w, x, y, z tracts. Lineage analyses associate the immunoreactive cells with one of four neuroblasts (termed W, X, Y, Z) in each protocerebral hemisphere of the early embryo. Locustatachykinin is a ubiquitous myotropic peptide among the insects and its expression in the pars intercerebralis begins at approximately 60-65% of embryogenesis. This coincides with the appearance of the columnar neuroarchitecture characteristic of the central body. The number of immunoreactive cells in a given lineage is initially small, increases significantly in later embryogenesis, and attains the adult situation (about 7% of a lineage) in the first larval instar after hatching. Although each neuroblast generates progeny displaying a spectrum of cell body sizes, there is a clear morphological gradient, which reflects birth order within the lineage. Locustatachykinin expressing cells are located stereotypically at or near the tip of their lineage, which an age profile reveals places them amongst the first born progeny of their respective neuroblasts. Although these neuroblasts begin to generate progeny at approximately 25-27% of embryogenesis, their daughter cells remain quiescent with respect to locustatachykinin expression for over 30% of embryogenesis.     

Morphogenesis and cellular proliferation pattern in the developing antennal lobe of Drosophila melanogaster

The adult antennal lobe of Drosophila melanogaster emerges from a precursor, the larval antennal lobe. Pulse and pulse-chase labelling of dividing cells in larvae and pupae with bromodeoxyuridine confirmed previous data that some of the interneurons of the adult antennal lobe derive from a lateral neuroblast which starts to divide early in the first larval instar. However, the majority of these interneurons originate from neuroblasts that initiate mitosis at later stages, with a peak of about 10–12 pairs of dividing neuroblasts in the late third larval instar. No clustering of adult antennal lobe neurons according to their birthdates was observed. In contrast to neurons, terminal divisions of glia in the antennal lobe reach their maximum only 12 h after puparium formation.     

Serotonin-immunoreactive neurons in the antennal sensory system of the brain in the carpenter ant, Camponotus japonicus

Social Hymenoptera such as ants or honeybees are known for their extensive behavioral repertories and plasticity. Neurons containing biogenic amines appear to play a major role in controlling behavioral plasticity in these insects. Here we describe the morphology of prominent serotonin-immunoreactive neurons of the antennal sensory system in the brain of an ant, Camponotus japonicus. Immunoreactive fibers were distributed throughout the brain and the subesophageal ganglion (SOG). The complete profile of a calycal input neuron was identified. The soma and dendritic elements are contralaterally located in the lateral protocerebrum. The neuron supplies varicose axon terminals in the lip regions of the calyces of the mushroom body, axon collaterals in the basal ring but not in the collar region, and other axon terminals ipsilaterally in the lateral protocerebrum. A giant neuron innervating the antennal lobe has varicose axon terminals in most of 300 glomeruli in the ventral region of the antennal lobe (AL) and a thick neurite that spans the entire SOG and continues towards the thoracic ganglia. However, neither a soma nor a dendritic element of this neuron was found in the brain or the SOG. A deutocerebral projection neuron has a soma in the lateral cell-body group of the AL, neuronal branches at most of the 12 glomeruli in the dorsocentral region of the ipsilateral AL, and varicose terminal arborizations in both hemispheres of the protocerebrum. Based on the present results, tentative subdivisions in neuropils related to the antennal sensory system of the ant brain are discussed.     

Proliferative cell types in embryonic lineages of the central complex of the grasshopper Schistocerca gregaria

The central complex of the grasshopper Schistocerca gregaria develops to completion during embryogenesis. A major cellular contribution to the central complex is from the w, x, y, z lineages of the pars intercerebralis, each of which comprises over 100 cells, making them by far the largest in the embryonic protocerebrum. Our focus has been to find a cellular mechanism that allows such a large number of cell progeny to be generated within a restricted period of time. Immunohistochemical visualization of the chromosomes of mitotically active cells has revealed an almost identical linear array of proliferative cells present simultaneously in each w, x, y, z lineage at 50% of embryogenesis. This array is maintained relatively unchanged until almost 70% of embryogenesis, after which mitotic activity declines and then ceases. The array is absent from smaller lineages of the protocerebrum not associated with the central complex. The proliferative cells are located apically to the zone of ganglion mother cells and amongst the progeny of the neuroblast. Comparisons of cell morphology, immunoreactivity (horseradish peroxidase, repo, Prospero), location in lineages and spindle orientation have allowed us to distinguish the proliferative cells in an array from neuroblasts, ganglion mother cells, neuronal progeny and glia. Our data are consistent with the proliferative cells being secondary (amplifying) progenitors and originating from a specific subtype of ganglion mother cell. We propose a model of the way that neuroblasts, ganglion mother cells and secondary progenitors together produce the large cell numbers found in central complex lineages.     

Organization of local interneurons in optic glomeruli of the dipterous visual system and comparisons with the antennal lobes

The lateral protocerebrum of the fly's brain is composed of a system of optic glomeruli, the organization of which compares to that of antennal lobe glomeruli. Each optic glomerulus receives converging axon terminals from a unique ensemble of optic lobe output neurons. Glomeruli are interconnected by systems of spiking and nonspiking local interneurons that are morphologically similar to diffuse and polarized local interneurons in the antennal lobes. GABA-like immunoreactive processes richly supply optic glomeruli, which are also invaded by processes originating from the midbrain and subesophageal ganglia. These arrangements support the suggestion that circuits amongst optic glomeruli refine and elaborate visual information carried by optic lobe outputs, relaying data to long-axoned neurons that extend to other parts of the central nervous system including thoracic ganglia. The representation in optic glomeruli of other modalities suggests that gating of visual information by other sensory inputs, a phenomenon documented from the recordings of descending neurons, could occur before the descending neuron dendrites. The present results demonstrate that future studies must consider the roles of other senses in visual processing.     

Sensory processing of ambient CO<Subscript>2</Subscript> information in the brain of the moth<Emphasis Type="Italic"> Manduca sexta</Emphasis>

Insects use information about CO₂ to perform vital tasks such as locating food sources. In certain moths, CO₂ is involved in oviposition behavior. The labial palps of adult moths that feed as adults have a pit organ containing sensory receptor cells that project into the antennal lobes, the sites of primary processing of olfactory information in the brain. In the moth Manduca sexta and certain other species of Lepidoptera, these receptor cells in the labial-palp pit organ have been shown to be tuned to CO₂, and their axons project to a single, identified glomerulus in the antennal lobe, the labial-palp pit organ glomerulus. At present, however, nothing is known about the function of this glomerulus or how CO₂ information is processed centrally. We used intracellular recording and staining to reveal projection (output) neurons in the antennal lobes that respond to CO₂ and innervate the labial-palp pit organ glomerulus. Our results demonstrate that this glomerulus is the site of first-order processing of sensory information about ambient CO₂. We found three functional types of CO₂-responsive neurons (with their cell bodies in the antennal lobe or the protocerebrum) that provide output from the antennal lobe to higher centers in the brain. Some physiological characteristics of those neurons are described.Abbreviations AL Antennal lobe - AN Antennal nerve - CMB Calyces of the mushroom body - IPSP Inhibitory postsynaptic potential - LC-I Dorsal cluster of the lateral group of AL neuronal somata - LH Lateral horn of the protocerebrum - LPN Labial-palp nerve - LPO Labial-palp pit organ - LPOG LPO glomerulus - PC Protocerebrum - PI AL neuron that projects to the PC through the inner antenno-cerebral tract - PN Projection neuron