The distribution of pancreatic polypeptide in the nervous system and gut of the blowfly, Calliphora vomitoria (Diptera)

A comparative review of short and long neuropeptide F signaling in invertebrates: Any similarities to vertebrate neuropeptide Y signaling?

Neuropeptides referred to as neuropeptide F (NPF) and short neuropeptide F (sNPF) have been identified in numerous invertebrate species. Sequence information has expanded tremendously due to recent genome sequencing and EST projects. Analysis of sequences of the peptides and prepropeptides strongly suggest that NPFs and sNPFs are not closely related. However, the NPFs are likely to be ancestrally related to the vertebrate family of neuropeptide Y (NPY) peptides. Peptide diversification may have been accomplished by different mechanisms in NPFs and sNPFs; in the former by gene duplications followed by diversification and in the sNPFs by internal duplications resulting in paracopies of peptides. We discuss the distribution and functions of NPFs and their receptors in several model invertebrates. Signaling with sNPF, however, has been investigated mainly in insects, especially in Drosophila. Both in invertebrates and in mammals NPF/NPY play roles in feeding, metabolism, reproduction and stress responses. Several other NPF functions have been studied in Drosophila that may be shared with mammals. In Drosophila sNPFs are widely distributed in numerous neurons of the CNS and some gut endocrines and their functions may be truly pleiotropic. Peptide distribution and experiments suggest roles of sNPF in feeding and growth, stress responses, modulation of locomotion and olfactory inputs, hormone release, as well as learning and memory. Available data indicate that NPF and sNPF signaling systems are distinct and not likely to play redundant roles.

Neuropeptides in the nervous system of Drosophila and other insects: multiple roles as neuromodulators and neurohormones

Neuropeptides in insects act as neuromodulators in the central and peripheral nervous system and as regulatory hormones released into the circulation. The functional roles of insect neuropeptides encompass regulation of homeostasis, organization of behaviors, initiation and coordination of developmental processes and modulation of neuronal and muscular activity. With the completion of the sequencing of the Drosophila genome we have obtained a fairly good estimate of the total number of genes encoding neuropeptide precursors and thus the total number of neuropeptides in an insect. At present there are 23 identified genes that encode predicted neuropeptides and an additional seven encoding insulin-like peptides in Drosophila. Since the number of G-protein-coupled neuropeptide receptors in Drosophila is estimated to be around 40, the total number of neuropeptide genes in this insect will probably not exceed three dozen. The neuropeptides can be grouped into families, and it is suggested here that related peptides encoded on a Drosophila gene constitute a family and that peptides from related genes (orthologs) in other species belong to the same family. Some peptides are encoded as multiple related isoforms on a precursor and it is possible that many of these isoforms are functionally redundant. The distribution and possible functions of members of the 23 neuropeptide families and the insulin-like peptides are discussed. It is clear that each of the distinct neuropeptides are present in specific small sets of neurons and/or neurosecretory cells and in some cases in cells of the intestine or certain peripheral sites. The distribution patterns vary extensively between types of neuropeptides. Another feature emerging for many insect neuropeptides is that they appear to be multifunctional. One and the same peptide may act both in the CNS and as a circulating hormone and play different functional roles at different central and peripheral targets. A neuropeptide can, for instance, act as a coreleased signal that modulates the action of a classical transmitter and the peptide action depends on the cotransmitter and the specific circuit where it is released. Some peptides, however, may work as molecular switches and trigger specific global responses at a given time. Drosophila, in spite of its small size, is now emerging as a very favorable organism for the studies of neuropeptide function due to the arsenal of molecular genetics methods available.

The distribution and myotropic activity of locustatachykinin-like peptides in locust midgut

The midgut of the African migratory locust, Locusta migratoria, was found to contain endocrine-like cells that stained positively for locustatachykinin I (Lom TK I)-like immunoreactivity. These cells were distributed in an unequal manner throughout the midgut of the locust, with a greater density of Lom TK I-like immunoreactive endocrine-like cells occurring in the posterior region of the midgut. These singly occurring cells appear elongate with an apical extension projecting toward the midgut lumen and a smaller projection extending towards the midgut basal lamina. No immunoreactive neuronal processes were detected along the midgut wall. Radioimmunoassays revealed that the female midgut contained two to three times more Lom TK I-like material than the male midgut, and radioimmunoassay coupled to high-performance liquid chromatography analysis revealed that at least five locustatachykinin isoforms appear to be present in the midgut. This distribution of Lom TK I-like material suggests possible functional differences in the various regions of the midgut. The role that these cells may play in locust midgut secretory activity and motility remains unknown. However, the addition of synthetic Lom TK I through IV to a ring type midgut muscle preparation stimulated contraction of midgut circular muscles, suggesting a possible physiological role for these peptides. Dose-response curves constructed for Lom TK I-IV revealed that the peptide-induced contractions increased in a dose-dependent manner.

Immunohistological localization of regulatory peptides in the midgut of the female mosquito Aedes aegypti

The midgut of the female mosquito Aedes aegypti was studied immunohistologically with antisera to various regulatory peptides. Endocrine cells immunoreactive with antisera to perisulfakinin, RFamide, bovine pancreatic polypeptide, urotensin 1, locustatachykinin 2 and allatostatins A1 and B2 were found in the midgut. Perisulfakinin, RFamide and bovine pancreatic polypeptide all react with the same, about 500 endocrine cells, which were evenly distributed throughout the posterior midgut, with the exception of its most frontal and caudal regions. In addition, these antisera recognized three to five neurons in each ingluvial ganglion and their axons, which ran longitudinally over the anterior midgut, as well as axons innervating the pyloric sphincter. The latter axons appear to be derived from neurons located in the abdominal ganglia. Antisera to two different allatostatins recognized about 70 endocrine cells in the most caudal area of the posterior midgut and axons in the anterior midgut whose cell bodies were probably located in either the brain or the frontal ganglion. Antiserum to locustatachykinin 2 recognized endocrine cells present in the anterior midgut and the most frontal part of the posterior midgut, as well as about 50 cells in the most caudal region of the posterior midgut. Urotensin 1 immunoreactivity was found in endocrine cells in the same region as the perisulfakinin-immunoreactive cells, but no urotensin-immunoreactive axons were found in the midgut. Double labeling experiments showed that the urotensin and perisulfakinin immunoreactivities were located in different cells. Such experiments also showed that the locustatachykinin and allatostatin immunoreactivities in the most caudal area of the posterior midgut were present in different cells. No immunoreactivity was found in the mosquito midgut when using antisera to corazonin, allatropin or leucokinin IV. Since these peptides have either been isolated from, or can reasonably be expected to be present in mosquitoes, it was concluded that these peptides are not present in the mosquito midgut.

Distribution and functional significance of Leu-callatostatins in the blowfly Calliphora vomitoria

The Leu-callatostatins are a series of four neuropeptides isolated from nervous tissues of the blowfly Calliphora vomitoria that show C-terminal sequence homology to the allatostatins of cockroaches. The allatostatins have an important role in the reproductive processes of insects as inhibitors of the synthesis and release of juvenile hormone from the corpus allatum. In this study, the distribution of the Leu-callatostatin-immunoreactive neurones and endocrine cells has been mapped in C. vomitoria and, in contrast to the cockroach allatostatins, it has been shown that there is no cytological basis to suggest that the dipteran peptides act as regulators of juvenile hormone. Although occurring in various neurones in the brain and thoracico-abdominal ganglion, there is no evidence of Leu-callatostatin-immunoreactive pathways linking the brain to the corpus allatum, or of immunoreactive terminals in this gland. Three different types of functions for the Leu-callatostatins are suggested by the occurrence of immunoreactive material in cells and by the pathways that have been identified. (1) A role in neurotransmission or neuromodulation appears evident from immunoreactive neurones in the medulla of the optic lobes, and from immunoreactive material in the central body and in descending interneurones in the suboesophageal ganglion that project to the neuropile of the thoracico-abdominal ganglion. (2) Leu-callatostatin neurones directly innervate muscles of the hindgut and the heart. Immunoreactive fibres from neurones of the abdominal ganglion pass by way of the median abdominal nerve to ramify extensively over several areas of the hindgut. Physiological experiments with synthetic peptides show that the Leu-callatostatins are potent inhibitors of peristaltic movements of the ileum. Leu-callatostatin 3 is active at 10(-16) to 10(-13) M. This form of regulatory control over gut motility appears to be highly specific since the patterns of contraction in other regions are unaffected by these peptides. (3) Evidence that the Leu-callatostatins act as neurohormones comes from the presence of varicosities in axons passing through the corpus cardiacum (but not the corpus allatum) and also from material in extraganglionic neurosecretory cells in the thorax. Fibres from these peripheral neurones are especially prominent over the large nerve bundles supplying the legs. There are also a considerable number of Leu-callatostatin-immunoreactive endocrine cells in a specific region of the midgut. The conclusion from this study is that although conservation of the structure of the allatostatin-type of peptides is evident through a long period of evolution it cannot be assumed that all of their functions have also been conserved.(ABSTRACT TRUNCATED AT 400 WORDS)

Localisation of sulfakinin neuronal pathways in the blowfly Calliphora vomitoria

The distribution of neurones immunoreactive to antisera raised against the undecapeptide C-terminal fragment of drosulfakinin II (DrmSKII), Asp-Gln-Phe-Asp-Asp-Tyr(SO3H)-Gly-His-Met-Arg-Phe-NH2, has been studied in the blowfly Calliphora vomitoria. Antisera were preabsorbed with combinations of the parent antigen, the tetrapeptide Phe-Met-Arg-Phe-NH2 and cholecystokinin, the vertebrate sulfated octapeptide (CCK-8), Asp-Tyr(SO3H)-Met-Gly-Trp-Met-Asp-Phe-NH2, in order to ensure specificity for the sulfakinin peptides of C. vomitoria (the nonapeptide callisulfakinin I is identical to drosulfakinin I and callisulfakinin II differs from DrmSK II only by the presence of -Glu3-Glu4- in place of -Asp3-Asp4-). Only four pairs of sulfakinin-immunoreactive neurons have been visualised in the entire nervous system. These occur in the brain: two pairs of cells situated medially in the caudo-dorsal region close to the roots of the ocellar nerve and two other pairs at the same level but positioned more laterally. Despite the small number of sulfakinin-immunoreactive cells, there are extensive projections to many areas of neuropile in the brain and the thoracic ganglion. The pathway of the medial sulfakinin cells extends into each of the three thoracic ganglia and a metameric arrangement of sulfakinin neuronal projections is also seen in the abdominal ganglia. Neither the dorsal neural sheath of the thoracic ganglion, nor the abdominal nerves contain sulfakinin-immunoreactive material. These observations suggest that the sulfakinins of the blowfly function as neurotransmitters or neuromodulators. They do not appear to have a direct role in gut physiology, as has been shown by in vitro bioassays for the sulfakinins of orthopterans and blattodeans. In addition to the neurones that display specific sulfakinin immunoreactivity, other cells within the brain and thoracic ganglion are immunoreactive to cholecystokinin/gastrin antisera. There are, therefore, at least two types of dipteran neuropeptides with amino acid sequences that are similar to the vertebrate molecules cholecystokinin and gastrin.

Distribution of FMRFamide-related peptides in the blood-feeding bug, Rhodnius prolixus

Immunohistochemistry was used to study the distribution of FMRFamide-like material in the central and peripheral nervous systems and visceral tissues of 5th instar Rhodnius prolixus. Over 200 immunoreactive cell bodies and their processes as well as extensive neuropile regions were distributed throughout the nervous system. Immunoreactive processes were seen over the cephalic aorta, corpus cardiacum/corpus allatum complex, and in neurohaemal sites on the abdominal nerves. In visceral tissues, immunoreactive processes were seen innervating the salivary glands, the foregut, and the hindgut. Immunoreactive cells were also found in the anterior midgut (i.e., the crop and the anterior intestine). A radioimmunoassay specific for "RFamide" carboxy-terminal peptides was used to quantify the amount and the distribution of FMRFamide-like material. Reversed-phase high performance liquid chromatography of nervous tissue extracts revealed several peaks of immunoreactive material. The results suggest the existence of a number of FMRFamide-related peptides in Rhodnius which may have roles in both central and peripheral transmission, may be released as neurohormones and may have endocrine functions in the gut.

The complete primary structure of pancreatic polypeptide from the European common frog, Rana temporaria

Using an antiserum directed against the highly-conserved C-terminal hexapeptide amide of mammalian pancreatic polypeptide (PP), numerous immunoreactive endocrine cells were identified within the pancreas of the European common frog, R. temporaria. An acidified ethanolic extract of pancreatic tissue (0.859 g, n = 35) contained 26.2 nmol equivalents/g of tissue. Gel permeation chromatography of the extract resolved a single peak of immunoreactivity co-eluting with synthetic bovine PP standard. Reverse phase HPLC of this material resolved a single peak of immunoreactivity which was purified to homogeneity following chromatography on a semipreparative C-18 column and an analytical C-8 column. Plasma desorption mass spectrometry (PDMS) of the purified peptide resolved a single component with a molecular mass of 4240.9 Da. Direct gas phase sequencing established the sequence of the first 26 residues. Following incubation of the peptide with endopeptidase Asp-N and direct application of the digest to the sequencer, the entire primary structure of the peptide was established as: APSEPHHPGDQATQDQLAQYYSDLYQYITFVTRPRF. The derived molecular mass of this peptide, incorporating a C-terminal amide, was 4240.6 Da which is entirely consistent with that obtained by PDMS.

The serotoninergic, cholinergic and peptidergic components of the nervous system in the monogenean parasite, Diclidophora merlangi: a cytochemical study

Confocal scanning laser microscopy has been employed with immunocytochemical techniques to map the distribution of serotoninergic and peptidergic components in the nervous system of the monogenean gill-parasite, Diclidophora merlangi; results are compared with the distribution of cholinergic components, following histochemical staining for cholinesterase activity. While all three neurochemical elements are present in the central and peripheral nervous systems, the cholinergic and peptidergic systems dominate the CNS, whereas the PNS has a majority of serotoninergic nerve fibres. The cholinergic and peptidergic neuronal pathways overlap extensively in staining patterns, suggesting possible co-localization of acetylcholine and neuropeptides. Within the peptidergic nervous system, immunoreactivity to the pancreatic polypeptide family of peptides and FMRFamide were the most prevalent. Gastrin/cholecystokinin (CCK)-, neuropeptide Y-, substance P-, neurokinin A- and eledoisin-like immunoreactivities have been demonstrated for the first time in a monogenean parasite. The gastrin/CCK- and tachykinin-like immunoreactivities had an apparently restricted distribution in the worm.

Peptidergic nerve elements in three developmental stages of the tetraphyllidean tapeworm Trilocularia acanthiaevulgaris. An immunocytochemical study

The localization and distribution of seven neuropeptides in the nervous system of the plerocercoid, adult and free proglottis stages of the tetraphyllidean tapeworm Trilocularia acanthiaevulgaris have been determined by an indirect immunofluorescence technique. Six of the peptides are vertebrate-derived, namely, pancreatic polypeptide (PP), peptide tyrosine tyrosine (PYY), vasoactive intestinal polypeptide (VIP), peptide histidine isoleucine (PHI), substance P (SP) and somatostatin (SRIF); the seventh is the invertebrate neuropeptide, FMR Famide. This is the first demonstration of VIP and SP immunoreactivity in a cestode parasite, and for SRIF this is its first description in any parasitic platyhelminth. Cell bodies and nerve fibres immunoreactive to PP, PYY, VIP, SP and FMRFamide are present throughout the CNS; the distributions of PHI and SRIF were more restricted. In the PNS, nerve fibres immunoreactive to PP occur in the bothridia, whilst in the free proglottis nerve fibres immunoreactive to PYY and VIP innervate the gonads; VIP-immunoreactive nerve elements also supply the reproductive ducts. Extra-neuronal sitings of peptide immunoreactivities were evident for PHI, in association with the excretory system, and for SRIF, in presumed tegumental cell bodies in the free proglottis. The results are discussed in relation to the possible roles of the peptides in the neurophysiology and developmental biology of the worm.

Localization, quantification, and characterization of pancreatic polypeptide immunoreactivity in the parasitic flatworm Diclidophora merlangi and its fish host (Merlangius merlangus)

Pancreatic polypeptide (PP) immunoreactivity (IR) has been identified, quantified, and subsequently chemically characterised in the parasitic platyhelminth, Diclidophora merlangi, and its specific teleostean host the whiting, Merlangius merlangus. Immunocytochemistry demonstrated PP-IR throughout the central and peripheral nervous systems of the parasite and in open-type endocrine cells of the gastric mucosa of its host. Radioimmunoassay detected PP-IR in alcoholic extracts of whole parasites (39.2 ng/g) and in extracts of gastrointestinal tract (2.1 ng/g), brain (4.6 ng/g), and pancreas (12 ng/g) of the host. Chromatographic analysis of parasite extracts revealed a single immunoreactive species of PP in both high-performance gel permeation and reverse-phase systems. The molecular size of this peptide was similar to bovine PP standard. In contrast, whiting tissues contained two immunoreactive species of PP in both gel permeation and reverse-phase systems. The major species was similar in size to bovine PP standard and the minor species was smaller, with a molecular size comparable to bovine neurotensin. Reverse-phase HPLC revealed that parasite and host peptides were not identical.

Development of the enteric nervous system in the moth. I. Diversity of cell types and the embryonic expression of FMRFamide-related neuropeptides

The enteric nervous system (ENS) of the larval moth Manduca sexta consists of two small ganglia and several nerve networks that lie superficially along the alimentary tract. Within this system are approximately 600 neurons that exhibit a spectrum of biochemical and morphological characteristics and that express these features in a definable sequence during development. The accessibility of both the neural and nonneural components of the moth ENS throughout embryogenesis makes it a potentially useful model in which to examine the developmental regulation of transmitter phenotype. In this paper, we have focused on the differentiation of the enteric plexus (EP) cells, a heterogeneous population of enteric neurons that are distributed across the foregut-midgut boundary. Unlike many neurons of the CNS in insects, the cells of the enteric plexus are not uniquely identifiable. While the total number of EP cells is constant, their locations vary significantly from animal to animal. However, several distinct classes of neurons can be identified within this population on the basis of morphology and transmitter phenotype, including one class that contains substances related to the molluscan peptide Phe-Met-Arg-Phe-amide (FMRFamide). Expression of this FMRFamide-like material within the enteric plexus is position-specific, occurring only in neurons on the midgut and not in those on the foregut. FMRFamide-like immunoreactivity first appears in approximately one-third of these cells at 65% of development; this pattern is retained without apparent modification throughout subsequent embryonic and postembryonic development. In the following paper, we describe the sequence of stereotyped cell migration that precedes the expression of this peptidergic phenotype and that underlies the formation of the enteric plexus during embryogenesis.

Immunohistological demonstration of a substance related to neuropeptide Y and FMRFamide in the cephalic and thoracic nervous systems of the locust Locusta migratoria

A neuropeptide related to the mammalian neuropeptide Y (NPY) is present in various neurosecretory cells (NSC) of the cephalic and thoracic nervous systems of the insect Locusta migratoria. Immunoreactive perikarya are detected in the protocerebrum, tritocerebrum, optic lobes and the suboesophageal and thoracic ganglia. They give rise to many immunoreactive processes that ramify extensively throughout the neuropiles. In the brain, prominent axon bundles tightly surround the tractus I to the corpora cardiaca. This fiber pattern suggests that the NPY-like substance may have a neuromodulator and/or neurotransmitter function. This substance may also have a neurohormonal role, since some immunoreactive tracts penetrate into neurohaemal organs via the nervi corporis cardiaci II and the thoracic median nerves. NCS containing NPY-like neuropeptide also display an FMRFamide-like immunoreactivity (except for the abdominal part of the metathoracic ganglion). NPY or FMRFamide antisera are not inactivated after preabsorption with FMRFamide or NPY, respectively. It might therefore be inferred that in locust NSC these two antisera recognize two distinct antigenic sites belonging either to a large polypeptide, or to two distinct neuropeptides.

NPY-like peptides occur in the nervous system and midgut of the migratory locust, Locusta migratoria and in the brain of the grey fleshfly, Sarcophaga bullata

The distribution of the NPY-like substances in the nervous system and the midgut of the migratory locust, Locusta migratoria and in the brain of the grey fleshfly, Sarcophaga bullata was determined by immunocytochemistry using an antiserum directed against synthetic porcine NPY. The peroxidase-antiperoxidase procedure revealed that NPY immunoreactive cell bodies and nerve fibers were observed in the brain, optic lobes, corpora cardiaca, suboesophageal ganglion and ventral nerve cord of the locust and in the brain, optic lobes and suboesophageal ganglion of the fleshfly. In the locust midgut, numerous endocrine cells and nerve fibers penetrating the outer musculature contained NPY-like immunoreactivity. The concentrations of NPY immunoreactive material in acetic acid extracts of locust brain, optic lobes, thoracic ganglia, ovaries and midguts was measured using a specific radioimmunoassay technique. The dilution curves of the crude tissue extracts were parallel to the standard curve. The highest amount of NPY-like immunoreactivity was found in the locust ovary and midgut. Reverse-phase high-performance liquid chromatography (RP-HPLC) and radioimmunoassay were used to characterize the NPY-like substances in the locust brain and midgut. HPLC-analysis revealed that NPY-immunoreactivity in the locust brain eluted as three separate peaks. The major peak corresponded to a peptide less hydrophobic than synthetic porcine NPY. RP-HPLC analysis of midgut extracts revealed the presence of an additional NPY-immunoreactive peak which had a retention time similar to the porcine NPY standard. The present data show the existence of a widespread network of NPY immunoreactive neurons in the nervous system of the locust and the fleshfly. Characterization of the immunoreactive substances indicates that peptides similar but not identical to porcine NPY are present in the central nervous system and midgut of insects.

Mapping of enkephalin-related peptides in the nervous system of the blowfly, Calliphora vomitoria, and their co-localization with cholecystokinin (CCK)- and pancreatic polypeptide (PP)-like peptides

The distribution of enkephalin-like immunoreactive material has been studied in the CNS of C. vomitoria. The presence of both Met- and Leu-enkephalin-related peptides is suggested by differential immunostaining with a variety of antisera. Comparisons made between certain of the enkephalin-immunoreactive perikarya, nerve fibres and terminals with cells in corresponding positions as evidenced in previously published neuroanatomical studies of the dipteran brain have suggested specific enkephalinergic pathways. As examples, one Met-enkephalin-immunoreactive neuron appears to link the lobula with the dorsal protocerebrum, and a group of Leu-enkephalin cells in the pars intercerebralis appear to have arborisations in both the central body (fan-shaped body) and the tritocerebral neuropil around the oesophageal foramen. Neuronal pathways of this type indicate that the enkephalin-like peptides of the fly brain are functioning as neurotransmitters and/or neuromodulators. In the thoracic ganglia, symmetrically arranged cells, immunoreactive to both Met- and Leu-enkephalin antisera, are positioned ventrally in pairs on either side of the mid-line in a sagittal plane. Very little immunoreactive material is observed in the neuropil, however, and the source of the accumulation of Leu-enkephalin-immunoreactivity in the dorsal neural sheath is not certain. It is suggested that this material, in contrast to that present in areas of the brain, acts as a neurohormone and that it may have a physiological role following its release into the haemolymph. The enkephalin-like immunoreactive material of certain neurons identified within the brain and thoracic ganglion shows a complex pattern of co-existence with pancreatic polypeptide- and gastrin/cholecystokinin-like peptides.

Distal retinal pigment of the fiddler crab, Uca pugilator: release of the dark-adapting hormone by methionine enkephalin and FMRFamide

The neuropeptides methionine enkephalin and FMRFamide, when injected into intact fiddler crabs, Uca pugilator, produce dark adaptation of the distal retinal pigment. Furthermore, both neuropeptides stimulate release of distal retinal pigment dark-adapting hormone activity from the isolated eyestalk neuroendocrine complex. It is hypothesized that both neuropeptides, when injected into intact fiddler crabs, act only indirectly on the distal retinal pigment, by stimulating release of this dark-adapting hormone.

FMRFamide- and pancreatic polypeptide-like immunoreactivity of endocrine cells in the midgut of a mosquito

Immunocytochemical surveys of midguts from female mosquitoes, Aedes aegypti, reveal that half of the estimated 500 endocrine cells in a midgut contain a substance recognized by antisera to bovine pancreatic polypeptide and a molluscan peptide, FMRFamide (phenylalanine-methionine-arginine-phenylalanine-amide). With light microscopy the cells resemble an endocrine type because of their basal position in the epithelium, conical shape, and, in some instances, apical extensions to the lumen. At the ultrastructural level, the immunoreactive substance is contained specifically within the secretory granules of such cells. Immunoreactive cells are distributed exclusively in the midgut region where blood is stored, and ingestion of vertebrate blood reduces the number of such cells and the intensity of reaction in others. These two facts suggest that a blood meal stimulates release of the immunoreactive substance from the cells. Since the immunocytochemical localization is supplemented by a demonstrated secretory response, the cells are considered to be peptidergic endocrine cells.

Neurons reactive to antibodies against serotonin in the stomatogastric nervous system and in the alimentary canal of locust and crickets (Orthoptera, Insecta)

Immunoreactive neurons in the stomatogastric nervous system and in the alimentary tract of the locust Schistocerca gregaria and the crickets Gryllus bimaculatus and Acheta domesticus have been examined using antibodies against serotonin (5-hydroxytryptamine; 5-HT). For comparative anatomical analysis cobalt chloride infusion was applied. The innervation of the visceral muscles was studied electron microscopically. In all three species the majority of the 5-HT-immunoreactive cell bodies of the stomatogastric nervous system occur in the frontal ganglion in which 30-40% of the total number of cell bodies react with anti-5-HT. In the occipital ganglion only two to four cell bodies (1-2%) are 5-HT-immunoreactive. Single immunoreactive cell bodies were observed in the ventricular ganglia in only a few preparations. The 5-HT-immunoreactive neurons in the frontal ganglion are pseudounipolar or multipolar. The main process of the 5-HT-immunoreactive neurons of the frontal ganglion descend along the entire stomatogastric nervous system. Some arborizations of these processes ascend into the brain and others supply the neuropil of all stomatogastric ganglia. Side branches leave the stomatogastric nervous system and form a plexus along the surface of the entire intestinal tract from where 5-HT-immunoreactive fibers supply: all muscle layers of the muscularis; the external dilator muscles of the foregut and probably some somatic muscles, neurohaemal organs and Malpighian tubules (excretory system). Serotonin-immunoreactive fibers further proceed into salivary gland and the retrocerebral complex (corpora cardiaca and corpora allata). The retrocerebral glandular complex and the hindgut receive additional immunoreactive neurons from the central nervous system. Electron microscopic analysis of nerves innervating the muscle layers of the alimentary tract revealed one type of 5-HT-immunoreactive and one or two types of non-5-HT-immunoreactive fibers. All fiber types contact the sarcolemma of muscle fibers without any obvious synaptic membrane specializations. The 5-HT-immunoreactive fibers are in some regions in close contact with the haemolymph. These regions can be regarded as sites of neurohormonal release. The distribution of serotonin-immunoreactive neurons suggests that 5-HT acts as a neurotransmitter and/or modulator on intestinal muscles and some somatic muscles and glandular cells, and as a neurohormone released from neurohaemal sites into the body fluid.

Distinct localization of FMRFamide- and bovine pancreatic polypeptide-like material in the brain, retrocerebral complex and suboesophageal ganglion of the cockroach Periplaneta americana L

One bovine pancreatic polypeptide (BPP) antiserum and two FMRFamide antisera were applied in the peroxidase-antiperoxidase (PAP) immunohistochemical technique on a complete series of sections of brains, suboesophageal ganglia (SOG), corpora cardiaca (CC) and corpora allata of Periplaneta americana L. Double immunohistochemical staining demonstrated that the same perikarya and processes were stained by both the BPP and FMRFamide antisera. This was caused by cross-reaction of the BPP and FMRFamide antisera with common antigenic determinants as was shown by a number of solid-phase absorptions. Application of a third FMRFamide antiserum, which was especially selected for its inability to react with bovine and avian pancreatic polypeptide, showed that more than half of the structures that were stained with the 'unspecific' BPP and FMRFamide antisera, contained material which was genuinely FMRFamide-like. This peptide material was located in cerebral neuronal structures, in the SOG, in the storage site of the CC and in numerous nerve fibres throughout the neuropile regions, which suggested a neurotransmitter/modulator as well as a neurohormonal role. The FMRFamide-like peptide was also found to be present in the same brain sites as an adipokinetic hormone-like peptide, but double labelling revealed that these two substances were never located in the same perikarya or fibres.

Serotonergic terminals in the neural sheath of the blowfly nervous system: electron microscopical immunocytochemistry and 5,7-dihydroxytryptamine labelling

With serotonin immunocytochemistry we have demonstrated an extensive plexus of immunoreactive varicose fibres in the neural sheath of the nervous system of the blowfly, Calliphora. These fibres are located in the neural sheath of the following regions: the maxillary-labial and labrofrontal nerves of the cerebral ganglia, the cervical connective, the dorsal surface of the thoracicoabdominal ganglia, two pairs of prothoracic nerves and the median abdominal nerve. We identified the serotonin-immunoreactive neural processes in the electron microscope by means of the peroxidase-antiperoxidase method. Immunoreactivity was seen in large granular vesicles (ca 100 nm), on membranes of smaller (ca 60 nm) and larger (ca 100 nm) agranular vesicles, along the inner surface of the axolemma, along neurotubules and outer membranes of mitochondria. By conventional electron microscopy we found numerous varicose neural processes in the neural sheath of some of the above regions. These varicosities are of at least two types. One type corresponds to the serotonin-immunoreactive profiles. A second type contains large granular vesicles (ca 200 nm) of variable electron density. 5,7-Dihydroxytryptamine injected into the head capsule labelled varicosities in the neural sheath, corresponding to the ones identified with serotonin immunocytochemistry. The electron-dense labelling was seen in flattened vesicles within these varicosities. We propose that the serotonin-immunoreactive fibers in the neural sheath constitute neurohemal regions for the release of serotonin into the circulation. The finding of another morphological type of varicose fibers in the neural sheath suggests the presence of further putative neurohormones in these regions.

The distribution of bovine pancreatic polypeptide/FMRFamide-like immunoreactivity in the ventral nervous system of the locust

The distribution of bovine pancreatic polypeptide (BPP) FMRFamide-like immunoreactivity is described in the ganglia of the ventral nerve cord and in the peripheral median nervous system of the locust, Schistocerca gregaria. Immunoreactive cell bodies occur in three regions of the thoracic ganglia: 1) two pairs of cells lie in the anterior of the ganglion ventral to the root of nerve 1 and the anterior ventral association centre; 2) a group of cells lies in the ventral midline at the level at which nerves 3 and 4 leave the ganglion; 3) and two bilaterally symmetrical, posterior lateral groups lie between nerves 5 and 6 at the edge of the ganglion. Immunoreactive cell bodies in the suboesophageal and abdominal ganglia are confined to the midline and are distributed along the anterior-posterior axis both dorsally and ventrally. The processes of the posterior lateral groups have been traced into the neurohaemal organs of the median nerve and beyond. In the periphery such processes innervate the salivary glands and various muscles. The nature of the endogenous antigen contained in the immunoreactive cells has been investigated with the use of antisera against other peptides of the pancreatic polypeptide family, namely avian pancreatic polypeptide, neuropeptide Y, and peptide YY. In addition, BPP antisera not specific for the C terminal hexapeptide have been tested. Liquid preabsorption experiments with BPP and FMRFamide (the molluscan cardioacceleratory peptide) suggest that the endogenous peptide antigen contained in the stained neurones may belong to the pancreatic polypeptide family or to the FMRFamide family.

Mapping and ultrastructure of serotonin-immunoreactive neurons in the optic lobes of three insect species

With antibodies to serotonin (5-HT) we have mapped immunoreactive neurons in the optic lobes of three species, the blowfly Calliphora, the desert ant Cataglyphis, and the worker bee Apis. The main emphasis in this investigation is on a system of 5-HT-positive neurons connecting the most peripheral neuropil of the optic lobes, the lamina, to more central neuropil regions. To aid in electron microscopical identification of these neurons we used immunocytochemistry at the EM-level and Golgi-EM for Calliphora and horseradish peroxidase (HRP) labelling for the other two insects. The immunoreactive terminals in Calliphora and the HRP-labelled ones in the other insects contain large (c. 100 nm) granular vesicles and smaller (c.60 nm) clear vesicles. In Cataglyphis and Apis the profiles with granular vesicles are presynaptic to second order neurons of the lamina, whereas in Calliphora no synaptic contacts were found. In this animal the 5-HT-positive terminals are situated distal to the synaptic layer of the lamina, in a region of retinal photoreceptor axons and perikarya of the lamina monopolar neurons. In Catagylphis and Apis the interactions of the 5-HT-neurons with the laminar neurons might occur through chemical synapses, whereas in Calliphora neuroactive substance could be released non-synaptically from varicosities distal to the synaptic layer. The possible involvement of 5-HT in control of neuronal activity in the optic lobes is discussed.

Neuropeptide immunocytochemistry in protostomian invertebrates, with special reference to insects and molluscs

In some molluscs (Aplysia and Fusitriton) and insects (silkworm and cricket), occurrence and distribution of neuropeptides in the nervous system and gut were studied with following results: in these invertebrates and also in planaria, PP-like immunoreactivity is extensively distributed in neurons and (in insects) in gut endocrine paraneurons. These cells are negative for NPY, the mammalian neuropeptide related to PP in molecular structure. PHI-like immunoreactivity is widely distributed in the neurons of those invertebrates; it occurs also in gut endocrine paraneurons in insects. The PHI-immunopositive cells are immunonegative for VIP and the coexistence of both peptides due to the common precursor in mammals cannot be recognized in these invertebrates. Immunoreactivity for urotensin I, the neuropeptide derived from teleostean urophysial neurons, is widely distributed in the neurons of the invertebrates. In insects (cricket) it occurs in gut endocrine cells.

Immunohistochemical identification of growth hormone-releasing factor-like material in the nervous system of an insect, Aeshna cyanea (Odonata)

Cells immunoreactive to antibodies raised against human pancreatic growth hormone releasing factor 1-44-NH2 (hp GRF) were detected in the brain and the suboesophageal ganglion of an insect. The presence of immunoreactive deposits within the insect neurohaemal organ, the corpora cardiaca and within the nervi corporis cardiaci which, at least, transfers part of the neurosecretory products of the brain to the corpora cardiaca, may indicate the participation of GRF-like substance in some neurohormonal function (s) in addition to having probably a neurotransmitter role within the nervous system.

Immunocytochemical mapping of gastrin/CCK-like peptides in the neuroendocrine system of the blowfly Calliphora vomitoria (Diptera)

The distribution of gastrin/CCK-like immunoreactive material has been studied in the retrocerebral complex of Calliphora. The material reacts with antisera specific for the common COOH terminus of gastrin and CCK but not with N-terminal antisera. The three thoracic ganglia and the fused abdominal ganglia each contain a specific number of symmetrically arranged immunoreactive cells both dorsally and ventrally in pairs on either side of the midline in a sagittal plane. The neuropil of these ganglia also contains a considerable amount of immunoreactive fibres and droplets. Reconstructed axonal pathways suggest that some of the nerve fibres have their origins within the brain and/or the suboesophageal ganglion. Immunoreactive material may also be seen apparently leaving the thoracic ganglion posteriorly via the abdominal nerves, and there is strong evidence of a neurohaemal organ within the dorsal sheath in the region of the metathoracic and abdominal ganglia. There appears to be a direct correlation between the content of peptidergic material of cells and fibres and the age and diet of the flies. The corpus cardiacum contains COOH-terminal specific gastrin/CCK-like material within the intrinsic cells and in the neuropil. It is present also in the cardiac-recurrent nerve entering the corpus cardiacum anteriorly and in the nerves leaving the gland dorsoposteriorly, the aortic or cardiac nerves. It is not observed, however, in the nerves leaving the corpus cardiacum ventroposteriorly, the so-called oesophageal, gastric or crop-duct nerves. The corpus allatum and the hypocerebral ganglion do not contain immunoreactive material of this type. Gastrin/CCK-like and secretin-like immunoreactive materials appear to co-exist in the cells of the corpus cardiacum and co-existence of gastrin/CCK-like and pancreatic polypeptide-like substances occurs within certain cells of the thoracic ganglion.

Immunocytochemical localization of neurons in the nervous system of the Colorado potato beetle with antisera against FMRFamide and bovine pancreatic polypeptide

Particular neurons in the nervous system of the Colorado potato beetle, Leptinotarsa decemlineata, are recognized by antisera against bovine pancreatic polypeptide and FMRFamide. Both antisera react with the same neurons. Solid phase absorptions showed that antiserum against bovine pancreatic polypeptide cross-reacts with FMRFamide, whereas antiserum against FMRFamide cross-reacts with bovine pancreatic polypeptide. Some of the immunoreactive neurons have axons branching extensively within the neuropile, which suggests that the peptide is used as transmitter. In the corpus cardiacum, a neurohaemal organ in insects, numerous immunoreactive axon terminals are present. Here, the peptide material is presumably released as a hormone.

Cobalt-immunocytochemical identification of peptidergic neurons in Calliphora innervating central and peripheral targets

Certain neurons of the blowfly, Calliphora erythrocephala, show immunoreactivity to anti-gastrin/cholecystokinin (CCK) COOH terminal specific antisera. However, as is common to immunocytochemical staining, much of the structure of the immunoreactive neurons escapes detection. We describe here whole-neuron identification by backfilling with Co2+ and subsequent silver reduction, combined with immunocytochemistry of the filled cells. Cobalt-silver filled neurons can be examined directly by fluorescence microscopy for the presence of a secondary, rhodamine-conjugated antibody linked to the primary one. Two peptide-containing pathways have been resolved, one leading out of the brain to the corpus cardiacum, the other innervating certain higher brain centres, such as the central body. Both arise from neurosecretory cells of the mid-brain. Immunoreactive peptidergic neurons leading, respectively, to the corpus cardiacum and to the central body have been matched to single nerve cells visualized by Golgi impregnation, cobalt backfilling or focal injection of cobalt into the brain.

Immunocytochemical identification of alpha-endorphin-like material in neurones of the brain and corpus cardiacum of the blowfly, Calliphora vomitoria (Diptera)

A group of the 24-26 paraldehyde fuchsin-positive median neurosecretory cells (MNC) in the pars intercerebralis of the brain of the blowfly, Calliphora vomitoria, has shown immunoreactivity towards three different antibodies to alpha-endorphin, a peptide that corresponds to the amino acid sequence present between residues 61 and 76 of the precursor molecule, beta-lipotropin (beta-LPH). The immunoreactive material could be followed in axons within the median bundle, the tract through which neurosecretory material from the MNC is passed down to the corpus cardiacum (CC). The alpha-endorphin-immunoreactive material was observed leaving the CC in the cardiac-recurrent nerve, dorsal to the proventriculus, in the direction of the abdomen. The cells that contain the alpha-endorphin-like material are different from those of the MNC that contain insulin-, pancreatic polypeptide-, and gastrin/CCK-like peptides. This finding demonstrates the considerable complexity and peptidergic nature of the MNC and constitutes further evidence that morphinomimetic-like peptides are present in the nervous system of invertebrates.