Substance P-like immunoreactive neurons in the nervous system of Drosophila

Neuromodulation of Innate Behaviors in Drosophila

Animals are born with a rich repertoire of robust behaviors that are critical for their survival. However, innate behaviors are also highly adaptable to an animal's internal state and external environment. Neuromodulators, including biogenic amines, neuropeptides, and hormones, are released to signal changes in animals' circumstances and serve to reconfigure neural circuits. This circuit flexibility allows animals to modify their behavioral responses according to environmental cues, metabolic demands, and physiological states. Aided by powerful genetic tools, researchers have made remarkable progress in Drosophila melanogaster to address how a myriad of contextual information influences the input-output relationship of hardwired circuits that support a complex behavioral repertoire. Here we highlight recent advances in understanding neuromodulation of Drosophila innate behaviors, with a special focus on feeding, courtship, aggression, and postmating behaviors.

Role of a tachykinin-related peptide and its receptor in modulating the olfactory sensitivity in the oriental fruit fly, Bactrocera dorsalis (Hendel)

Insect tachykinin-related peptide (TRP), an ortholog of tachykinin in vertebrates, has been linked with regulation of diverse physiological processes, such as olfactory perception, locomotion, aggression, lipid metabolism and myotropic activity. In this study, we investigated the function of TRP (BdTRP) and its receptor (BdTRPR) in an important agricultural pest, the oriental fruit fly Bactrocera dorsalis. BdTRPR is a typical G-protein coupled-receptor (GPCR), and it could be activated by the putative BdTRP mature peptides with the effective concentrations (EC₅₀) at the nanomolar range when expressed in Chinese hamster ovary cells. Consistent with its role as a neuromodulator, expression of BdTRP was detected in the central nervous system (CNS) of B. dorsalis, specifically in the local interneurons with cell bodies lateral to the antennal lobe. BdTRPR was found in the CNS, midgut and hindgut, but interestingly also in the antennae. To investigate the role of BdTRP and BdTRPR in olfaction behavior, adult flies were subjected to RNA interference, which led to a reduction in the antennal electrophysiological response and sensitivity to ethyl acetate in the Y-tube assay. Taken together, we demonstrate the impact of TRP/TRPR signaling on the modulation of the olfactory sensitivity in B. dorsalis. The result improve our understanding of olfactory processing in this agriculturally important pest insect.

Tachykinin-related peptides and their receptors in invertebrates: a current view

Members of the tachykinin peptide family have been well conserved during evolution and are mainly expressed in the central nervous system and in the intestine of both vertebrates and invertebrates. In these animals, they act as multifunctional messengers that exert their biological effects by specifically interacting with a subfamily of structurally related G protein-coupled receptors. Despite the identification of multiple tachykinin-related peptides (TKRPs) in species belonging to the insects, crustaceans, mollusks and echiuroid worms, only five invertebrate receptors harboring profound sequence similarities to mammalian receptors for tachykinins have been functionally characterized to date. Three of these have been cloned from dipteran insect species, i.e. NKD (neurokinin receptor from Drosophila), DTKR (Drosophila tachykinin receptor) and STKR (tachykinin-related peptide receptor from the stable fly, Stomoxys calcitrans). In addition, two receptors from non-insect species, present in echiuroid worms and mollusks, respectively have been identified as well. In this brief review, we will survey some recent findings and insights into the signaling properties of invertebrate tachykinin-related peptides via their respective receptors. In this context, we will also point out the necessity to take into account differences in signaling mechanisms induced by distinct TKRP isoforms in insects.

Charting the Drosophila neuropile: a strategy for the standardised characterisation of genetically amenable neurites

Insect neurons are individually identifiable and have been used successfully to study principles of the formation and function of neuronal circuits. In the fruitfly Drosophila, studies on identifiable neurons can be combined with efficient genetic approaches. However, to capitalise on this potential for studies of circuit formation in the CNS of Drosophila embryos or larvae, we need to identify pre- and postsynaptic elements of such circuits and describe the neuropilar territories they occupy. Here, we present a strategy for neurite mapping, using a set of evenly distributed landmarks labelled by commercially available anti-Fasciclin2 antibodies which remain comparatively constant between specimens and over developmental time. By applying this procedure to neurites labelled by three Gal4 lines, we show that neuritic territories are established in the embryo and maintained throughout larval life, although the complexity of neuritic arborisations increases during this period. Using additional immunostainings or dye fills, we can assign Gal4-targeted neurites to individual neurons and characterise them further as a reference for future experiments on circuit formation. Using the Fasciclin2-based mapping procedure as a standard (e.g., in a common database) would facilitate studies on the functional architecture of the neuropile and the identification of candiate circuit elements.

Tachykinin-like peptides and their receptors. A review

Tachykinin-like peptides have been identified in many vertebrate and invertebrate species. On the basis of the data reviewed in this paper, these peptides can be classified into two distinct subfamilies, which are recognized by their respective sequence characteristics. All known vertebrate tachykinins and a few invertebrate ones share a common C-terminal sequence motif, -FXGLMa. The insect tachykinins, which have a common -GFX1GX2Ra C-terminus, display about 30% of sequence homology with the first group. Tachykinins are multifunctional brain/gut peptides. In mammals and insects, various isoforms play an important neuromodulatory role in the central nervous system. They are involved in the processing of sensory information and in the control of motor activities. In addition, members of both subfamilies elicit stimulatory responses on a variety of visceral muscles. The receptors for mammalian and insect tachykinins show a high degree of sequence conservation and their functional characteristics are very similar. In both mammals and insects, angiotensin-converting enzyme (ACE) plays a prominent role in tachykinin peptide metabolism.

Tachykinin-related peptides in invertebrates: a review

Peptides with sequence similarities to members of the tachykinin family have been identified in a number of invertebrates belonging to the mollusca, echiuridea, insecta and crustacea. These peptides have been designated tachykinin-related peptides (TRPs) and are characterized by the preserved C-terminal pentapeptide FX1GX2Ramide (X1 and X2 are variable residues). All invertebrate TRPs are myostimulatory on insect hindgut muscle, but also have a variety of additional actions: they can induce contractions in cockroach foregut and oviduct and in moth heart muscle, trigger a motor rhythm in the crab stomatogastric ganglion, depolarize or hyperpolarize identified interneurons of locust and the snail Helix and induce release of adipokinetic hormone from the locust corpora cardiaca. Two putative TRP receptors have been cloned from Drosophila; both are G-protein coupled and expressed in the nervous system. The invertebrate TRPs are distributed in interneurons of the CNS of Limulus, crustaceans and insects. In the latter two groups TRPs are also present in the stomatogastric nervous system and in insects endocrine cells of the midgut display TRP-immunoreactivity. In arthropods the distribution of TRPs in neuronal processes of the brain displays similar patterns. Also in coelenterates, flatworms and molluscs TRPs have been demonstrated in neurons. The activity of different TRPs has been explored in several assays and it appears that an amidated C-terminal hexapeptide (or longer) is required for bioactivity. In many invertebrate assays the first generation substance P antagonist spantide I is a potent antagonist of invertebrate TRPs and substance P. Locustatachykinins stimulate adenylate cyclase in locust interneurons and glandular cells of the corpora cardiaca, but in other tissues the putative second messenger systems have not yet been identified. The heterologously expressed Drosophila TRP receptors coupled to the phospholipase C pathway and could induce elevations of inositol triphosphate. The structures, distributions and actions of TRPs in various invertebrates are compared and it is concluded that the TRPs are multifunctional peptides with targets both in the central and peripheral nervous system and other tissues, similar to vertebrate tachykinins. Invertebrate TRPs may also be involved in developmental processes.

Insect neurotransmission: neurotransmitters and their receptors

The roles of acetylcholine, dopamine, octopamine, tyramine, 5-hydroxytryptamine, histamine, glutamate, 4-aminobutanoic acid (gamma-aminobutyric acid) and a range of peptides as insect neurotransmitters are evaluated in terms of the criteria used to identify transmitters. Of the biogenic amines considered, there is good evidence that acetylcholine, dopamine, octopamine, 5-hydroxytryptamine, and histamine should be considered to be neurotransmitters, but the case for tyramine is less convincing at the moment. The evidence supporting neurotransmitter roles for glutamate and gamma-aminobutyric acid at specific insect synapses is overwhelming, but much work remains to be undertaken before the full significance of these molecules in the insect nervous system is appreciated. Attempts to characterise biogenic amine and amino acid receptors using pharmacological and molecular biological techniques have revealed considerable differences between mammalian and insect receptors. The number of insect neuropeptides isolated and identified has increased spectacularly in recent years, but genuine physiological or biochemical functions can be assigned to very few of these molecules. Of these, only proctolin fulfills the criteria expected of a neurotransmitter, and the recent discovery of proctolin receptor antagonists should enable the biology of this pentapeptide to be explored fully.

Immunocytochemical localization of Diploptera punctata allatostatin-like peptide in Drosophila melanogaster

Allatostatins isolated from the cockroach Diploptera punctata are a family of neuropeptides that inhibit juvenile hormone synthesis in cockroaches and related insects but not in flies. In cockroaches, these widely distributed peptides have been shown to have other functions. This report provides evidence for the presence of allatostatin-like peptides in Drosophila melanogaster by demonstration of allatostatic activity of extracts of central nervous system from larvae and adults on corpora allata of Diploptera and by immunocytochemical localization of peptides in Drosophila with monoclonal antibody against Diploptera allatostatin I. Extract of adult central nervous system showed four times more allatostatic activity than that of the larva or twice the activity per unit volume of central nervous system. This is reflected in an increase in number and arborization of immunoreactive neurons in the adult. The immunoreactive neurons in the central nervous system appear to be interneurons, with the exception of motoneurons in the last abdominal neuromere that project to muscles of the hindgut, a pair of peripheral cells in each of two thoracic segments in the larva and on nerves to wings and halteres in the adult, and endocrine cells of the midgut epithelium. Nerves to the corpus allatum were not immunoreactive. The presence of Diploptera allatostatin-like peptides in interneurons and motoneurons, in the neurohemal networks, and in endocrine cells of the midgut and their absence in nerves to the corpus allatum in Drosophila suggests that these peptides may function as neuromodulators, myomodulators, and neurohormones and not as regulators of the corpus allatum.

Chemical analysis of neurotransmitter candidates in clonal cell lines from Drosophila central nervous system, II: Neuropeptides and amino acids

In a previous study, we have found acetylcholine and/or L-DOPA in 10 colonial clones from one cell line of Drosophila larval central nervous system (CNS). In this study, to characterize clonal neuronal phenotypes further, we have examined three neuropeptides and 19 amino acids using HPLC system. Substance P and proctolin were found in seven and eight out of ten clones, respectively. On the other hand, somatostatin was expressed in all ten clones. GABA and taurine were not detected in any clones. Glutamate, which is an excitatory transmitter in Drosophila, was found in all the clones, although its content was different seven times among them. Glycine, which is not known as a transmitter in Drosophila, was found to be unevenly expressed among them. Therefore, the conspicuous expression of peptides or amino acids in some clones suggests that the substances have a special role in Drosophila CNS.

A neuropeptide gene defined by the Drosophila memory mutant amnesiac

Mutations in genes required for associative learning and memory in Drosophila exist, but isolation of the genes has been difficult because most are defined by a single, chemically induced allele. Here, a simplified genetic screen was used to identify candidate genes involved in learning and memory. Second site suppressors of the dunce (dnc) female sterility phenotype were isolated with the use of transposon mutagenesis. One suppressor mutation that was recovered mapped in the amnesiac (amn) gene. Cloning of the locus revealed that amn encodes a previously uncharacterized neuropeptide gene. Thus, with the cloning of amn, specific neuropeptides are implicated in the memory process.

Tachykinin-related neuropeptides in the central nervous system of the snail Helix pomatia: an immunocytochemical study

The distribution of neurons reacting with an antibody raised against an insect neuropeptide, locustatachykinin I, was investigated in the CNS of the snail Helix pomatia. The localization of the neurons was compared with that of the substance P-like immunoreactive (SPLI) neurons in the different ganglia. Altogether, there are approximately 800-1000 locustatachykinin-like immunoreactive (LomTKLI) neurons in the Helix CNS, occurring with an overwhelming dominancy (83.5%) in the cerebral ganglia. Within the cerebral ganglia, the majority of LomTKLI neurons were localized in the procerebrum. The number of SPLI neurons was high; approximately 2000 SPLI nerve cells were found in the Helix CNS. The majority (44.5%) of SPLI neurons was also found in the cerebral ganglia and they were also concentrated in the procerebrum. The neuropils of all ganglia were densely innervated by both LomTKLI and SPLI fibers except the medullary mass of the procerebrum where only SPLI elements form an extremely dense innervation. In addition to the neutrophil processes, LomTKLI neurons sent axon processes to the peripheral nerves. SPLI fibers also formed a dense network of varicose fibers in the connective tissue sheath around the ganglia where they innervated the blood vessel walls too. Immunolabeling on alternating cryostat sections revealed that LomTKLI and SPLI neurons are localized near each other in most cases; co-localization of the two immunoreactive materials could be seen in a very small number of neurons of the pedal and pleural ganglia. The present results show that the Helix CNS possesses distinct neuronal populations using different tachykinin-related peptides. It is suggested that the differential distribution of these neuropeptides also implies a diversity in their central and peripheral functions.

Locustatachykinin immunoreactivity in the blowfly central nervous system and intestine

An antiserum raised against locustatachykinin I, one of four myotropic peptides that have been isolated from the locust brain and corpora cardiaca, was characterized by enzyme-linked immunosorbent assay (ELISA) and used for immunocytochemical detection of neurons and endocrine cells in the nervous system and intestine of the blowfly Calliphora vomitoria. The ELISA characterization indicated that the antiserum recognizes the common C-terminus sequence of the locustatachykinins I-III. Hence, the cross reaction with locustatachykinin IV is less, and in competitive ELISAs no cross reaction was detected with a series of vertebrate tachykinins tested. It was also shown that the antiserum recognized material in extracts of blowfly heads, as measured in ELISA. In high-performance liquid chromatography the extracted locustatachykinin-like immunoreactive (LomTK-LI) material eluted in two different ranges. A fairly large number of LomTK-LI neurons was detected in the blowfly brain and thoracicoabdominal ganglion. A total of about 160 LomTK-LI neurons was seen in the proto-, deuto-, and tritocerebrum and subesophageal ganglion. Immunoreactive processes from these neurons could be traced in many neuropil regions of the brain: superior and dorsomedian protocerebrum, optic tubercle, fan-shaped body and ventral bodies of the central complex, all the glomeruli of the antennal lobes, and tritocerebral and subesophageal neuropil. No immunoreactivity was seen in the mushroom bodies or the optic lobes. In the fused thoracicoabdominal ganglion, 46 LomTK-LI neurons could be resolved. The less evolved larval nervous system was also investigated to obtain additional information on the morphology and projections of immunoreactive neurons. In neither the larval nor the adult nervous systems could we identify any efferent or afferent immunoreactive axons or neurosecretory cells. The widespread distribution of LomTK-LI material in interneurons suggests an important role of the native peptide(s) as a neurotransmitter or neuromodulator within the central nervous system. Additionally a regulatory function in the intestine is indicated by the presence of immunoreactivity in endocrine cells of the midgut.

Neurotensin-like immunoreactivity in locust supraesophageal ganglion and optic lobes

A substance immunoreactive to antibodies directed against bovine neurotensin (NT) was localized in neurons in the supraesophageal ganglion (SEG) and optic lobes of larval and adult Locusta migratoria L. Two large somata were located in the caudal cortex, ventral to the calyces and symmetrical to the median of the SEG. Four smaller somata also in the caudal cortex were located as two symmetrical pairs at the level of the central body. These somata formed a diffuse network of varicose fibers from the superior lateral to the ventro-lateral protocerebrum between the pedunculi and frontal cortical region. Some fibers crossed the median to the contralateral sides of the SEG. Another pair of immunoreactive somata whose terminating processes remained unclear was found at the level of the antennal lobes. Intrinsic networks of fibers were labeled in the accessory medulla and in layer 4/5 of the medulla. These fibers originated from 8-10 small somata near the dorso-frontal rim of the medulla. All larval stages contained these NT-like immunoreactive structures. Results from isoelectric focusing and press-blot analysis of SEG homogenates, synthetic neurotensin and neurotensin fragments indicate that this substance is similar to bovine neurotensin(1-13).

Sialokinin I and II: vasodilatory tachykinins from the yellow fever mosquito Aedes aegypti

The saliva of the mosquito Aedes aegypti has previously been reported to contain a 1400-Da peptide with pharmacological properties typical of a tachykinin. In the present study this vasodilator has been purified to homogeneity and found to consist of two peptides: sialokinin I, with the sequence Asn-Thr-Gly-Asp-Lys-Phe-Tyr-Gly-Leu-Met-NH2, and sialokinin II, identical to sialokinin I except for an Asp in position 1. These peptides are present in amounts of 0.62 and 0.16 pmol (711 and 178 ng), respectively, per salivary gland pair. When assayed on the guinea pig ileum, both peptides are as active as the mammalian tachykinin substance P, with K0.5 values of 5.07, 6.58, and 4.94 nM for sialokinin I, sialokinin II, and substance P, respectively.

The myotropic peptides of Locusta migratoria: structures, distribution, functions and receptors

The search for myotropic peptide molecules in the brain, corpora cardiaca, corpora allata suboesophageal ganglion complex of Locusta migratoria using a heterologous bioassay (the isolated hindgut of the cockroach, Leucophaea maderae) has been very rewarding. It has lead to the discovery of 21 novel biologically active neuropeptides. Six of the identified Locusta peptides show sequence homologies to vertebrate neuropeptides, such as gastrin/cholecystokinin and tachykinins. Some peptides, especially the ones belonging to the FXPRL amide family display pleiotropic effects. Many more myotropic peptides remain to be isolated and sequenced. Locusta migratoria has G-protein coupled receptors, which show homology to known mammalian receptors for amine and peptide neurotransmitters and/or hormones. Myotropic peptides are a diverse and widely distributed group of regulatory molecules in the animal kingdom. They are found in neuroendocrine systems of all animal groups investigated and can be recognized as important neurotransmitters and neuromodulators in the animal nervous system. Insects seem to make use of a large variety of peptides as neurotransmitters/neuromodulators in the central nervous system, in addition to the aminergic neurotransmitters. Furthermore quite a few of the myotropic peptides seem to have a function in peripheral neuromuscular synapses. The era in which insects were considered to be "lower animals" with a simple neuroendocrine system is definitely over. Neural tissues of insects contain a large number of biologically active peptides and these peptides may provide the specificity and complexity of intercellular communications in the nervous system.

Insulin-like receptor and insulin-like peptide are localized at neuromuscular junctions in Drosophila

Insulin and insulin-like growth factor (IGF) receptors are members of the tyrosine kinase family of receptors, and are thought to play an important role in the development and differentiation of neurons. Here we report the presence of an insulin-like peptide and an insulin receptor (dInsR) at the body wall neuromuscular junction of developing Drosophila larvae. dInsR-like immunoreactivity was found in all body wall muscles at the motor nerve branching regions, where it surrounded synaptic boutons. The identity of this immunoreactivity as a dInsR was confirmed by two additional schemes, in vivo binding of labeled insulin and immunolocalization of phosphotyrosine. Both methods produced staining patterns markedly similar to dInsR-like immunoreactivity. The presence of a dInsR in whole larvae was also shown by receptor binding assays. This receptor was more specific for insulin (> 25-fold) than for IGF II, and did not appear to bind IGF I. Among the 30 muscle fibers per hemisegment, insulin-like immunoreactivity was found only on one fiber, and was localized to a subset of morphologically distinct synaptic boutons. Staining in the CNS was limited to several cell bodies in the brain lobes and in a segmental pattern throughout most of the abdominal ganglia, as well as in varicosities along the neuropil areas of the ventral ganglion and brain lobes. Insulin-like peptide and dInsR were first detected by early larval development, well after neuromuscular transmission begins. The developmental significance of an insulin-like peptide and its receptor at the neuromuscular junction is discussed.

Insect myotropic peptides: differential distribution of locustatachykinin- and leucokinin-like immunoreactive neurons in the locust brain

Locustatachykinin I is one of four closely related myotropic neuropeptides isolated from brain and corpora-cardiaca complexes of the locust Locusta migratoria. Antiserum was raised against locustatachykinin I for use in immunocytochemistry. It was found that the antiserum recognizes also locustatachykinin II and hence probably also the other two locustatachykinins due to their similarities in primary structure. Locustatachykinin-like immunoreactive (LomTK-LI) neurons were mapped in the brain of the locust, L. migratoria. A total of approximately 800 LomTK-LI neurons were found with cell bodies distributed in the proto-, deuto- and tritocerebrum, in the optic lobes and in the frontal ganglion. Processes of these neurons innervate most of the synaptic neuropils of the brain and optic lobes, as well as the frontal ganglion and hypocerebral ganglion. The widespread distribution of LomTK-LI neurons in the locust brain indicates an important role of the locustatachykinins in signal transfer or regulation thereof. As a comparison neurons were mapped with an antiserum against the cockroach myotropic peptide leucokinin I. This antiserum, which probably recognizes the native peptide locustakinin, labels a population of about 140 neurons distinct from the LomTK-LI neurons (no colocalized immunoreactivity). These neurons have cell bodies that are distributed in the proto- and tritocerebrum and in the optic lobe. The processes of the leucokinin-like immunoreactive (LK-LI) neurons do not invade as large areas in neuropil as the LomTK-LI neurons do and some neuropils, e.g. the mushroom bodies, totally lack innervation by LK-LI fibers. In some regions, however, the processes of the LomTK-LI and LK-LI neurons are superimposed: most notably in the central body and optic lobes. A functional relation between the two types of neuropeptide in the locust brain can, however, not be inferred from the present findings.

Tachykinin- and leucokinin-related peptides in the nervous system of the blowfly: immunocytochemical and chromatographical diversity

We are interested in the presence and function in insects of neuropeptides related to the vertebrate tachykinins. Hence, we have used antisera raised against the tachykinins substance P and kassinin, and against the insect neuropeptide leucokinin I, for localization studies and immunochemical analysis of related peptides in the nervous system of the blowfly Phormia terraenovae. In radioimmunoassays (with antisera against kassinin and leucokinin I) used in combination with reverse-phase HPLC, it was shown that the antisera recognize immunoreactive material with distinctly hydrophobic properties and each antiserum appear to detect several forms of immunochemically related peptides. With immunocytochemistry it was shown that the kassinin and leucokinin antisera each reacted with material in a distinct set of neurons. The leucokinin-immunoreactive material is present both in interneurons and in neurosecretory cells, suggesting roles of native leucokinin-like peptides as neuromodulators in the nervous system and as neurohormones acting on peripheral targets. The kassinin immunoreactivity was seen in interneurons, but could not be conclusively localized in neurosecretory cells, possibly indicating a role only within the nervous system.

Monoclonal antibodies which stain small subsets of neurons in the Drosophila central nervous system

Monoclonal antibodies (MAbs) specific to small subsets of neurons in the central nervous system (CNS) of Drosophila melanogaster were described. MAbs 43A8, 45C6 and 65C11, which were obtained in fusion experiments using the third instar larval or prepupal CNS as an immunogen, stained a small number of neurons in the postembryonic CNS. Functional implications of the observed immunoreactivities during neural development in the Drosophila CNS are discussed.

Neurons in the cockroach nervous system reacting with antisera to the neuropeptide leucokinin I

Antisera were raised against the myotropic neuropeptide leucokinin I, originally isolated from head extracts of the cockroach Leucophaea maderae. Processes of leucokinin I immunoreactive (LKIR) neurons were distributed throughout the nervous system, but immunoreactive cell bodies were not found in all neuromeres. In the brain, about 160 LKIR cell bodies were distributed in the protocerebrum and optic lobes (no LKIR cell bodies were found in the deuto- and tritocerebrum). In the ventral ganglia, LKIR cell bodies were seen distributed as follows: eight (weakly immunoreactive) in the subesophageal ganglion; about six larger and bilateral clusters of 5 smaller in each of the three thoracic ganglia, and in each of the abdominal ganglia, two pairs of strongly immunoreactive cell bodies were resolved. Many of the LKIR neurons could be described in detail. In the optic lobes, immunoreactive neurons innervate the medulla and accessory medulla. In the brain, three pairs of bilateral LKIR neurons supply branches to distinct sets of nonglomerular neuropil, and two pairs of descending neurons connect the posterior protocerebrum to the antennal lobes and all the ventral ganglia. Other brain neurons innervate the central body, tritocerebrum, and nonglomerular neuropil in protocerebrum. LKIR neurons of the median and lateral neurosecretory cell groups send axons to the corpora cardiaca, frontal ganglion, and tritocerebrum. In the muscle layer of the foregut (crop), bi- and multipolar LKIR neurons with axons running to the retrocerebral complex were resolved. The LKIR neurons in the abdominal ganglia form efferent axons supplying the lateral cardiac nerves, spiracles, and the segmental perivisceral organs. The distribution of immunoreactivity indicates roles for leucokinins as neuromodulators or neurotransmitters in central interneurons arborizing in different portions of the brain, visual system, and ventral ganglia. Also, a function in circuits regulating feeding can be presumed. Furthermore, a role in regulation of heart and possibly respiration can be suggested, and probably leucokinins are released from corpora cardiaca as neurohormones. Leucokinins were isolated by their myotropic action on the Leucophaea hindgut, but no innervation of this portion of the gut could be demonstrated. The distribution of leucokinin immunoreactivity was compared to immunolabeling with antisera against vertebrate tachykinins and lysine vasopressin.

The VD1/RPD2 neuronal system in the central nervous system of the pond snail Lymnaea stagnalis studied by in situ hybridization and immunocytochemistry

VD1 and RPD2 are two giant neuropeptidergic neurons in the central nervous system (CNS) of the pond snail Lymnaea stagnalis. We wished to determine whether other central neurons in the CNS of L. stagnalis express the VD1/RPD2 gene. To this end, in situ hybridization with the cDNA probe of the VD1/RPD2 gene and immunocytochemistry with antisera specific to VD1 and RPD2 (the alpha 1-antiserum, Mab4H5 and ALMA 6) and to R15 (the alpha 1 and 16-mer antisera) were performed on alternate tissue sections. A VD1/RPD2 neuronal system comprising three classes of neurons (A1-A3) was found. All neurons of the system express the gene. Division into classes is based on immunocytochemical characteristics. Class A1 neurons (VD1 and RPD2) immunoreact with the alpha 1-antiserum, Mab4H5 and ALMA 6. Class A2 neurons (1-5 small and 1-5 medium sized neurons in the visceral and right parietal ganglion, and two clusters of small neurons and 5 medium-sized neurons in the cerebral ganglia) immunoreact with the alpha 1-antiserum and Mab4H5, but not with ALMA 6. Class A3 neurons (3-4 medium-sized neurons and a cluster of 4-5 small neurons located in the pedal ganglion) immunoreact with the alpha 1-antiserum only. All neurons of the system are immunonegative to the R15 antisera. The observations suggest that the neurons of the VD1/RPD2 system produce different sets of neuropeptides. A group of approximately 15 neurons (class B), scattered in the ganglia, immunostained with one or more of the antisera, but did not react with the cDNA probe in in situ hybridization.

Insect tachykinin-like peptide: distribution of leucokinin immunoreactive neurons in the cockroach and blowfly brains

Antisera were raised against leucokinin I, a cockroach myotropic neuropeptide with some resemblance to vertebrate tachykinins. These antisera were used for immunocytochemical mapping of neurons and neurosecretory cells in the brains of a cockroach and a blowfly species. The leucokinin immunoreactive cells are distinct from neurons that can be labeled with antisera against vertebrate type tachykinins. It is suggested that leucokinin-like peptides may have roles as neurohormones and neuromodulators in the insect nervous system.

Metamorphosis of the central nervous system of Drosophila

The study of the metamorphosis of the central nervous system of Drosophila focused on the ventral CNS. Many larval neurons are conserved through metamorphosis but they show pronounced remodeling of both central and peripheral processes. In general, transmitter expression appears to be conserved through metamorphosis but there are some examples of possible changes. Large numbers of new, adult-specific neurons are added to this basic complement of persisting larval cells. These cells are produced during larval life by embryonic neuroblasts that had persisted into the larval stage. These new neurons arrest their development soon after their birth but then mature into functional neurons during metamorphosis. Programmed cell death is also important for sculpting the adult CNS. One round of cell death occurs shortly after pupariation and a second one after the emergence of the adult fly.

Histaminelike immunoreactive neurons innervating putative neurohaemal areas and central neuropil in the thoraco-abdominal ganglia of the flies Drosophila and Calliphora

The fused thoraco-abdominal ganglia of the flies Calliphora vomitoria and Drosophila melanogaster were investigated immunocytochemically with antisera against histamine. In both insect species, 18 histaminelike immunoreactive (HA-IR) neurons were resolved in these ganglia. Six of these neurons have cell bodies in the thoracic neuromeres and 12 in the fused abdominal neuromeres. All cell bodies are situated ventrally. In Calliphora all cell bodies are arranged in a segmental pattern. In Drosophila only the thoracic cell bodies have a segmental arrangement, whereas the abdominal ones are clustered anteriorly close to the last thoracic neuromere. In both species the six thoracic neurons supply processes to the synaptic neuropil in the thoracic neuromeres and to the dorsal neural sheath. The processes in the neural sheath run anteriorly in the lateral portions of the ganglion into the cervical connective. In a few regions laterally arborizing terminals are found in putative neurohaemal areas. These areas were investigated by electron microscopic immunocytochemistry in Calliphora. The HA-IR terminals (containing small granular vesicles) were found outside the "blood-brain barrier" below the acellular basal lamina of the neural sheath. Release of histamine into the circulation is therefore theoretically possible. The central processes of the six thoracic HA-IR neurons may interact synaptically with large numbers of other neurons in the neuropil, and the peripheral varicose fibers from the same HA-IR neurons possibly are neurohaemal release sites. The abdominal HA-IR neurons, in contrast, form extensive arborizations within the synaptic neuropil only. Both thoracic and abdominal neurons have ipsilateral and contralateral branches as well as processes that invade more than one neuromere. A single HA-IR neuron thus invades large volumes of synaptic neuropil. Histamine may be used by neurons of the ventral ganglia both as neurotransmitter (or neuromodulator) and as a circulating neurohormone released from the neural sheath.