Distribution of FMRFamide-like immunoreactivity in the brain and suboesophageal ganglion of the sphinx mothManduca sexta and colocalization with SCPB-, BPP-, and GABA-like immunoreactivity

Summary Using an antiserum against the tetrapeptide FMRFamide, we have studied the distribution of FMRFamide-like substances in the brain and suboesophageal ganglion of the sphinx mothManduca sexta. More than 2000 neurons per hemisphere exhibit FMRFamide-like immunoreactivity. Most of these cells reside within the optic lobe. Particular types of FMRFamide-immunoreactive neurons can be identified. Among these are neurosecretory cells, putatively centrifugal neurons of the optic lobe, local interneurons of the antennal lobe, mushroom-body Kenyon cells, and small-field neurons of the central complex. In the suboesophageal ganglion, groups of ventral midline neurons exhibit FMRFamide-like immunoreactivity. Some of these cells have axons in the maxillary nerves and apparently give rise to FMRFamide-immunoreactive terminals in the sheath of the suboesophageal ganglion and the maxillary nerves. In local interneurons of the antennal lobe and a particular group of protocerebral neurons, FMRFamide-like immunoreactivity is colocalized with GABA-like immunoreactivity. This suggests that FMRFamide-like peptides may be cotransmitters of these putatively GABAergic interneurons. All FMRFamide-immunoreactive neurons are, furthermore, immunoreactive with an antiserum against bovine pancreatic polypeptide, and the vast majority is also immunoreactive with an antibody against the molluscan small cardioactive peptide SCP_B. Therefore, it is possible that more than one peptide is localized within many FMRFamide-immunoreactive neurons. The results suggest that FMRFamide-related peptides are widespread within the nervous system ofM. sexta and might function as neurohormones and neurotransmitters in a variety of neuronal cell types.Abbreviations AL antennal lobe - BPPLI bovine pancreatic polypeptide-like immunoreactivity - FLI FMRFamide-like immunoreactivity - GLI GABA-like immunoreactivity - NSC neurosecretory cell - SCP _B LI small cardioactive peptide_B-like immunoreactivity - SLI serotonin-like immunoreactivity - SOG suboesophageal ganglion     

Allatotropin-like peptide in Heliothis virescens: tissue localization and quantification

The mating-induced increase in juvenile hormone (JH) biosynthesis in Heliothis virescens females may be stimulated by production and/or release of stimulatory neuropeptides such as allatotropins (AT). Although there is evidence that H. virescens allatotropin may be structurally related to Manduca sexta allatotropin (Manse-AT), little is known of its occurrence and distribution in H. virescens. An enzyme-linked immunosorbent assay (ELISA) using a monoclonal antibody against Manse-AT was used to quantify concentrations of Manse-AT immunoreactivity in tissue extracts of H. virescens. In mated females, the highest concentrations of Manse-AT-like material occurred in the brain. The ventral nervous system and the accessory glands also contained considerable amounts of Manse-AT-like material, whereas concentrations were very low in ovaries, fat body, and flight muscle. The Manse-AT antibody was used for whole-mount immunocytochemistry to localize Manse-AT-immunoreactivity in the central nervous system. Several groups of Manse-AT-immunoreactive cells were discovered in the brain, subesophageal ganglion, and thoracic and abdominal ganglia of H. virescens females and males. Strong immunoreactivity was detected in axons going through the corpora cardiaca and branching out over the surface of the corpora allata. The presence of Manse-AT-like material in various locations in the central nervous system suggests that these peptides may have other as yet unknown functions. At the posterior margin of the terminal ganglion of males, a group of large immunoreactive cells was observed that was not present in females. Other than that, there were no obvious differences between virgin and mated females or males. The lack of differences in AT distribution in mated and virgin females suggests that mating-induced differences in female JH biosynthesis rates may be caused by changes in cellular response to AT at the level of the CA, rather than by changes in the amounts of AT acting on the CA.     

Identification of an urotensin I-like peptide in the pituitary of the lungfish Protopterus annectens: immunocytochemical localization and biochemical characterization

In the present study we have investigated the localization and biochemical characteristics of urotensin I (UI)-like and urotensin II (UII)-like immunoreactive peptides in the central nervous system (CNS) and pituitary of the lungfish, Protopterus annectens, by using antisera raised against UI from the white sucker Catostomus commersoni and against UII from the goby Gillichythys mirabilis. UI-like immunoreactive material was found within the melanotrope cells of the intermediate lobe of the pituitary. By contrast, no UI-immunoreactive structures were found in the brain. No UII-like peptides structurally similar to goby UII were found in the brain and pituitary of P. annectens. The UI-immunoreactive material localized in the pituitary was characterized by combining reversed-phase high-performance liquid chromatography (HPLC) analysis and radioimmunological detection. The UI-like immunoreactivity contained in a pituitary extract eluted as a single peak with a retention time intermediate between those of sucker UI and rat corticotropin-releasing factor (CRF). Control tests on adjacent sections of pituitary showed that the UI antiserum cross-reacted with the frog skin peptide sauvagine, but lungfish UI did not co-elute with synthetic sauvagine on HPLC. On the contrary, no cross-reaction was observed between the UI antiserum and CRF or alpha-melanocyte-stimulating hormone (alpha-MSH). The occurrence of an UI-like peptide in the intermediate lobe of the pituitary of P. annectens suggests that, in lungfish, this peptide may act as a classic pituitary hormone or may be involved in the control of melanotrope cell secretion.     

Distribution and characterization of Corazonin in the central nervous system of Triatoma infestans (Insecta: Heteroptera)

The distribution of corazonin in the central nervous system of the heteropteran insect Triatoma infestans was studied by immunohistochemistry. The presence of corazonin isoforms was investigated using MALDI-TOF mass spectrometry in samples containing the brain, the subesophageal ganglion, the corpora cardiaca-corpus allatum complex and the anterior part of the aorta. Several groups of immunopositive perikarya were detected in the brain, the subesophageal ganglion and the thoracic ganglia. Regarding the brain, three clusters were observed in the protocerebrum. One of these clusters was formed by somata located near the entrance of the ocellar nerves whose fibers supplied the aorta and the corpora cardiaca. The remaining groups of the protocerebrum were located in the lateral soma cortex and at the boundary of the protocerebrum with the optic lobe. The optic lobe housed immunoreactive somata in the medial soma layer of the lobula and at the level of the first optic chiasma. The neuropils of the deutocerebrum and the tritocerebrum were immunostained, but no immunoreactive perikarya were detected. In the subesophageal ganglion, immunostained somata were found in the soma layers of the mandibular and labial neuromeres, whereas in the mesothoracic ganglionic mass, they were observed in the mesothoracic, metathoracic and abdominal neuromeres. Immunostained neurites were also found in the esophageal wall. The distribution pattern of corazonin like immunoreactivity in the central nervous system of this species suggests that corazonin may act as a neurohormone. Mass spectrometric analysis revealed that [Arg⁷]-corazonin was the only isoform of the neuropeptide present in T. infestans tissue samples.     

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.     

Distribution of PACAP-like immunoreactivity in the nervous system of oligochaeta

The marked similarity between the primary structures of human, other vertebrate, and the invertebrate tunicate PACAP suggests that PACAP is one of the most highly conserved peptides during the phylogeny of the metazoans. We investigated the distribution of PACAP-like immunoreactivity in the nervous system of three oligochaete (Annelida) worms with immunocytochemistry. The distribution pattern of immunoreactivity was similar in all three species (Lumbricus terrestris, Eisenia fetida, and Lumbricus polyphemus). The cerebral ganglion contains numerous immunoreactive cells and fibers. A few cells and fibers were found in the medial and lateral parts of the subesophageal and ventral cord ganglia. In the peripheral nervous system, immunoreactivity was found in the enteric nervous system, in epidermal sensory cells, and in the clitellum.     

Pigment-dispersing hormone-like immunoreactive neurons in the central nervous system of the gastropods, Helix pomatia and Lymnaea stagnalis

By using an antiserum raised against a crustacean #-pigment-dispersing hormone (PDH), the distribution and chemical neuroanatomy of PDH-like immunoreactive neurons was investigated in the central nervous system of the gastropod snails, Helix pomatia and Lymnaea stagnalis. The number of immunoreactive cells in the Helix central nervous system was found to be large (700-900), whereas in Lymnaea, only a limited number (50-60) of neurons showed immunoreactivity. The immunostained neurons in Helix were characterized by rich arborizations in all central ganglia and revealed massive innervation of all peripheral nerves and the neural (connective tissue) sheath around the ganglia and peripheral nerve trunks. A small number of Helix nerve cell bodies in the viscero-parietal ganglion complex were also found to be innervated by PDH-like immunoreactive processes. Hence, a complex central and peripheral regulatory role, including neurohormonal actions, is suggested for a PDH-like substance in Helix, whereas the sites of action may be more limited in Lymnaea.     

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

Summary The distribution of a neuropeptide, previously shown to have the same or a very similar amino acid composition as vertebrate pancreatic polypeptide (PP), has been studied in the nervous system and gut of the blowfly, Calliphora vomitoria. Neurones immunoreactive to a bovine PP antiserum occur in the thoracic and abdominal ganglionic components of the central nervous system, in addition to the brain and suboesophageal ganglion. Pancreatic polypeptide appears to be relayed from its cells of origin to a neurohaemal organ in the dorsal sheath of the thoracic ganglion. PP immunoreactivity is also found in cells of the hypocerebral ganglion of the stomatogastric nervous system and in associated nerve fibres. The mid-gut contains PP-positive material in flask-shaped cells of its epithelial lining.     

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.     

Identification by radioimmunoassay and HPLC of morphine modulatory peptide-immunoreactivity in rat spinal cord and brain

Two so-called morphine modulatory peptides, an octapeptide and an octadecapeptide, have recently been isolated from bovine spinal cord. We have raised antibodies to the octapeptide (Phe-Leu-Phe-Gln-Pro-Gln-Arg-Phe-NH₂: FF-8), which in radioimmunoassay react with peptides terminating in Arg-Phe-NH₂. This dipeptide is common to both the morphine modulatory peptides and the molluscan neuropeptide FMRF amide. The distribution and molecular forms of immunoreactive peptides were examined in the rat central nervous system and gastrointestinal tract. Highest concentrations of FF-8-like immunoreactivity were found in the dorsal spinal cord, brain stem and hypothalamus. The immunoreactive material in central nervous system extracts was resolved by reversed phase HPLC into three peaks of activity, the two largest peaks eluted in similar positions to the standard octapeptide and octadecapeptide. It appears that previously observed FMRF amide-like immunoreactivity in the rat central nervous system corresponds to peptides immunochemically and chromatographically similar to the two bovine spinal cord peptides.     

The first nonsulfated sulfakinin activity reported suggests nsDSK acts in gut biology

Invertebrate sulfakinins are structurally and functionally homologous to vertebrate cholecystokinin (CCK) and gastrin. To date, sulfakinins are reported to require a sulfated tyrosine for activity; sulfated and nonsulfated CCK and gastrin are active. This is the first nonsulfated sulfakinin activity reported. Nonsulfated Drosophila melanogaster sulfakinins or drosulfakinins (nsDSK I; PheAspAspTyrGlyHisMetArgPheNH2) and (nsDSK II; GlyGlyAspAspGlnPheAspAspTyrGlyHisMetArgPheNH2) decreased the frequency of contractions of adult D. melanogaster foregut (crop) in vivo. The EC50's for nsDSK I and nsDSK II were approximately 2 x 10(-9)M and approximately 3 x 10(-8)M, respectively. Nonsulfated DSK peptides also decreased the frequency of larval anterior midgut contractions. Sulfated DSK peptides decreased both adult and larval gut contractions. Whether sulfation is required for sulfakinin activity may depend on where the peptide is applied, what tissue is analyzed, or what preparation is used. D. melanogaster contains two sulfakinin receptors, DSK-R1 and DSK-R2; vertebrates contain two CCK receptors, CCK-1 and CCK-2. A sulfated DSK I analog, [Leu7] sDSK I, binds to expressed DSK-R1; the corresponding nonsulfated analog does not bind to DSK-R1. No DSK-R2 binding data are reported. Sulfated and nonsulfated CCK peptides preferentially bind to CCK-1 or CCK-2, respectively. Sulfated and nonsulfated sulfakinins may bind to DSK-R1 or DSK-R2, respectively. Sulfakinin activities, spatial and temporal distribution, and homology to CCK and gastrin suggest sulfated and nonsulfated DSK peptides act in diverse roles in the neural and gastrointestinal systems including gut emptying and satiety.     

Localization of atrial natriuretic factor (ANF)-related peptides in the central nervous system of the elasmobranch fish Scyliorhinus canicula

We have investigated the localization of atrial natriuretic factor (ANF)-like immunoreactivity in the central nervous system of the cartilaginous fish, Scyliorhinus canicula, using the indirect immunofluorescence technique. Immunoreactive perikarya and fibers were observed in two regions of the telencephalon, the area superficialis basalis and the area periventricularis ventrolateralis. In the diencephalon, the hypothalamus exhibited a moderate number of ANF-containing neurons and fibers located in the preoptic and periventricular nuclei and in the nucleus lateralis tuberis. The most important group of ANF-immunoreactive cells was observed in the nucleus tuberculi posterioris of the diencephalon. In contrast, the mesencephalon showed only a few ANF-positive nerve processes located in the tegmentum mesencephali. Numerous fine fibers and nerve terminals were found in the dorsal area of the neurointermediate lobe of the pituitary. These results provide the first evidence for the presence of ANF-related peptides in the brain of a cartilaginous fish. The widespread distribution of ANF-positive cells and fibers in the brain and pituitary suggests that this peptide may act both as a neurotransmitter and (or) a neurohormone in fish.     

Distribution and functional significance of Met-enkephalin-Arg6-Phe7- and Met-enkephalin-Arg6-Gly7-Leu8-like peptides in the blowfly Calliphora vomitoria

Summary Neuronal pathways immunoreactive to antisera against the extended-enkephalins, Met-enkephalin-Arg⁶-Phe⁷ (Met-7) and Met-enkephalin-Arg⁶-Gly⁷-Leu⁸ (Met-8), have been identified in the brain of the blowfly Calliphora vomitoria. Co-localisation with other enkephalins in certain neurons suggests that a precursor similar to preproenkephalin A exists in insects and that differential enzymatic processing occurs as in vertebrates. Co-localisations of the extended-enkephalin-like peptides with other vertebrate-type peptides, including cholecystokinin and pancreatic polypeptide, also occur. The enkephalinergic pathways are specific, comprising a few groups of highly characteristic neurons and areas of neuropil. Of special interest is the finding that parts of the antennal chemosensory and the optic lobe visual systems contain Met-8 immunoreactive neurons. Within the median neurosecretory cell groups, some of the giant neurons show immunoreactivity to Met-8 and others to both Met-8 and Met-7. Fibres from these cells project to the corpus cardiacum and also to the suboesophageal ganglion, where arborisations occur in the tritocerebral neuropil. Co-localisation studies of these cells have shown that at certain terminals, one particular type of peptide is the dominant neuroregulator, whilst at other terminals, within the same cell, a different co-synthesised peptide predominates. Several groups of lateral neurosecretory cells show clearly defined enkephalinergic pathways, most of which have connections with the central body. The complex patterns of immunoreactivity seen in terminals in the different parts of the central body, suggest an important role for the enkephalin-like peptides in the integration of multimodal sensory inputs. The physiological functions of the extended-enkephalin-like peptides in the brain of Calliphora is still unknown, but the anatomical evidence suggests they may have a role similar to that in mammals, where they are thought to control aspects of feeding behaviour.     

Myosin II distribution in neurons is consistent with a role in growth cone motility but not synaptic vesicle mobilization.

We have generated a polyclonal antibody against myosin II from a neuronally derived cell line in order to assess potential roles for myosin II in growth cone movement and synaptic transmission. The distribution of neuronal myosin II, in isolated cells as well as in tissues of the adult rat brain and spinal cord, was examined at the light microscopic and ultrastructural levels. In isolated neuroblastoma cells and dorsal root ganglion neurons, myosin II was found at the leading edge of growth cones, within neuritic processes and cell soma, and adjacent to the plasma membrane. The subcellular distribution of myosin II overlapped significantly with that of both actin and single-headed myosin I. These results implicate both myosin I and myosin II as molecular motors required for neurite elongation and growth cone motility. An exclusive postsynaptic distribution of myosin II in neurons of the mature central nervous system suggests that myosin II cannot play a role in the mobilization of synaptic vesicles, but could participate in synaptic plasticity.     

Presence of sauvagine-like epitopes in the interrenal gland of the bullfrog Rana catesbeiana

Immunocytochemistry was used to investigate the presence of corticotropin-releasing factor-like peptides in the interrenal (adrenal) glands of the bullfrog Rana catesbeiana by using specific antisera raised against synthetic nonconjugated rat/human corticotropin-releasing factor, urotensin I, and sauvagine. From these three antisera, covering a broad range of corticotropin-releasing factor-like immunoreactivities, only the sauvagine antiserum gave positive immunoreactivity. Sauvagine immunoreactivity was found in cortical cells grouped into cords in the renal zone of the interrenal gland. The central and subcapsular cords were less stained. Tyrosine hydroxylase-positive chromaffin cells were not sauvagine-immunoreactive. The immunoreactivity was abolished, in all cases, by previous immunoabsorption of the sauvagine antiserum with synthetic sauvagine (0.1 7M), but it was not eliminated by sucker (Catostomus commersoni) urotensin I, sole (Hippoglossoides elassodon) urotensin I, sucker corticotropin-releasing factor, rat/human corticotropin-releasing factor, or ovine corticotropin-releasing factor (0.1-10 7M). In a sauvagine radioimmunoassay, interrenal extracts displaced ¹²⁵I-sauvagine from antiserum only partially, and not in parallel with the sauvagine standard curve. The results suggest that the sauvagine immunoreactivity in the R. catesbeiana interrenal gland may represent a novel sauvagine-like peptide.     

The different effects of structurally related sulfakinins on Drosophila melanogaster odor preference and locomotion suggest involvement of distinct mechanisms

Sulfakinins are myoactive peptides and antifeedant factors. Naturally occurring drosulfakinin I (DSK I; FDDYGHMRFNH₂) and drosulfakinin II (DSK II; GGDDQFDDYGHMRFNH₂) contain sulfated or nonsulfated tyrosine. We discovered sDSK II and nsDSK II influenced Drosophila melanogaster larval odor preference. However, sDSK I, nsDSK I, MRFNH₂, and saline did not influence odor preference. We discovered sDSK I and nsDSK I influenced larval locomotion. However, sDSK II, nsDSK II, MRFNH₂, and saline did not influence locomotion. Our novel data suggest distinct mechanisms underlie the effects of DSK I and DSK II peptides on odor preference and locomotion, parameters important to many facets of animal survival.     

Isolation and Immunocytochemical Characterization of Three Tachykinin-Related Peptides from the Mosquito,Culex salinarius

Three myotropic peptides belonging to the Arg-amide insect tachykinin family were isolated from whole-body extracts of the mosquito, Culex salinarius. The peptides, APSGFMGMR-NH₂, APYGFTGMR-NH₂ and APSGFFGMR-NH₂ (designated culetachykinin I, II, and III) were isolated and purified on the basis of their ability to stimulate muscle contractions of isolated Leucophaea maderae hindgut. Biologically inactive methionine sulfoxides of two of the three peptides were isolated using an ELISA system based upon antiserum raised against APYGFTGMR-NH₂ and identified with mass spectrometry. Immunocytochemistry localized these peptides in cells in the brain, antennae, subesophageal, thoracic and abdominal ganglion, proventriculus and midgut. Nerve tracts containing these peptides were found in the median nerve of the brain, central body, nervi corpus cardiaci, cervical nerve, antennal lobe and on the surface of the midgut.     

Quantitative distribution of galanin-like immunoreactivity in the rat central nervous system

Using an antiserum directed against synthetic galanin (GAL) a sensitive radioimmunoassay was developed. The antiserum interaction with GAL was characterized by displacement curve characteristics and high performance liquid chromatography. Besides the main GAL-immunoreactive peak several small peaks with GAL-like immunoreactivity were observed. No cross-reactivity of the GAL-antiserum with several other peptides was observed. GAL-like immunoreactivity was measured in 37 microdissected areas of the rat central nervous system. High concentrations (greater than 2000 fmol/mg protein) were observed in the amygdaloid nuclei, the septum, globus pallidus, bed nuclei of the stria terminalis, all hypothalamic nuclei, the superior colliculus, locus coeruleus, the nucleus of the solitary tract and the neurointermediate lobe of the pituitary. Moderate concentrations (1000-2000 fmol/mg protein) were observed in the hippocampus, the nucleus accumbens and nucleus of the diagonal tract, the caudate-putamen, the central gray, the nucleus, tract and substantia gelatinosa of the spinal trigeminal nerve. The results generally correlate with those previously published by immunocytochemistry. The widespread distribution of GAL-like immunoreactivity in the rat central nervous system suggests an involvement of GAL in a variety of brain functions.     

Localization of a SALMFamide Neuropeptide in the Larval Nervous System of the Sand Dollar Dendraster excentricus

Using immunocytochemical methods we describe the localization of serotonin and the SALMFamide peptide, S1 (GFNSALMFamide), during embryonic and larval development of the echinoid Dendraster excentricus. Anti-SI immunoreactivity first appears in the apical ganglion in late gastrulae at the same time as anti-serotonin immunoreactivity. Initially, anti-S1 immunoreactivity is restricted to fibres of the neuropile, but in later feeding stages, cell bodies are also immunoreactive. Anti-S1 immunoreactivity appears as 2–4 cells in the oral ganglion of early prism stage larvae, whereas anti-serotonin immunoreactivity does not occur in the oral ganglion until the 8-arm stage. Anti-S1 immunoreactivity also occurs in diffuse fibres in the oesophagus and in a single fibre encircling the pyloric sphincter of the gut. A reticular network associated with the apical surface of the epithelial cells of the vestibule of the adult rudiment was anti-S1 immunoreactive. In double-labelling experiments, anti-serotonin and anti-S1 immunoreactivity co-localize in the neuropile of the apical ganglion. The distribution of S1, in association with putative sensory cells in the apical and oral ganglia and with muscles of the oesophagus and gut, suggests S1 may have diverse functions in the larval nervous system. The distribution of anti-S1 immunoreactivity in echinoid embryos and larvae supports the proposal that SALMFamide-like peptides are widely shared in echinoderms and potentially have a fundamental role in neural function.