FMRFamide-immunoreactive Neurons Research Articles

The Stomatogastric and Enteric Nervous System of the Pulmonate Snail Megalobulimus abbreviatus: A Neurochemical Analysis.

Chemical coding of stomatogastric nervous system (STNS) and enteric nervous system (ENS) of midgut and hindgut in the snail Megalobulimus abbreviatus was investigated using histochemistry, histofluorescence, and immunohistochemistry. The gastrointestinal plexuses, constituted by intrinsic neurons and fibers originating from the subesophageal ganglia and/or STNS, showed intense acetylcholinesterase (AChE) and nicotinamide adenine dinucleotide diaphorase (NADPHd) activity. The enteric neurons and fibers with AChE activity are scattered in the submucosa and between both muscular layers of gastrointestinal tract, whereas NADPHd neurons and fibers are more abundant between muscular layers than in the submucosa. Catecholaminergic nerve fibers and varicosities are found mainly within the submucosa across the mid- and hindgut. Serotoninand FMRFamide-immunoreactive neurons and fibers originating from the STNS are distributed in the submucosa of the intestine and rectum. FMRFamide-immunoreactive neurons and fibers are present in the mucosa, submucosa, and muscular layers of mid- and hindgut. The neuron-like intraepithelial cells exhibited AChE activity, a few NADPHd activity, and immunoreactivity for serotonin and FMRFamide. Intense glial fibrillary acidic protein (GFAP) immunoreaction is found throughout the intestine plexuses and in the STNS ganglia. The GFAP immunoreaction in intramural plexuses suggests the presence of glial cells as an important component of ENS in this pulmonate snail.

Muscle and nerve net organization in stalked jellyfish (Medusozoa: Staurozoa).

Staurozoan cnidarians display an unusual combination of polyp and medusa characteristics and their morphology may be informative about the evolutionary origin of medusae. We studied neuromuscular morphology of two staurozoans, Haliclystus 'sanjuanensis' and Manania handi, using whole mount immunohistochemistry with antibodies against FMRFamide and α-tubulin to label neurons and phalloidin to label muscles. All muscles appeared to lack striations. Longitudinal interradial muscles are probable homologues of stalk muscles in scyphopolyps, but in adult staurozoans they are elaborated to inwardly flex marginal lobes of the calyx during prey capture; these muscles are pennate in M. handi. Manubrial perradial muscles, like the manubrium itself, are an innovation shared with pelagic medusae and manubrial interradial muscles are shared with scyphozoan ephyra. Marginal muscles of M. handi displayed occasional synchronous contraction reminiscent of a medusa swim pulse, but contractions were not repetitive. The nerve net in both species showed regional variation in density and orientation of neurons. Some areas labeled predominantly by α-tubulin antibodies (exumbrellar epidermis), other areas labeled exclusively by FMRFamide antibodies (dense plexus of neurites surrounding the base of secondary tentacles, neuronal concentration at the base of transformed primary tentacles; gastrodermal nerve net), but most areas showed a mix of neurons labeled by these two antibodies and frequent co-labeling of neurons. Transformed primary tentacles had a concentration of FMRFamide-immunoreactive neurons at their base that was associated with a pigment spot in M. handi; this is consistent with their homology with rhopalia of medusae, which are also derived from primary tentacles. The muscular system of these staurozoans embodies characteristics of both scyphopolyps and pelagic medusae. However, their nerve net is more polyp-like, although marginal concentrations of the net associated with primary and secondary tentacles may facilitate the richer behavioral repertoire of staurozoans relative to polyps of other medusozoans. J. Morphol. 278:29-49, 2017. ©© 2016 Wiley Periodicals,Inc.

Early development, pattern, and reorganization of the planula nervous system in Aurelia (Cnidaria, Scyphozoa)

We examined the development of the nervous system in Aurelia (Cnidaria, Scyphozoa) from the early planula to the polyp stage using confocal and transmission electron microscopy. Fluorescently labeled anti-FMRFamide, antitaurine, and antityrosinated tubulin antibodies were used to visualize the nervous system. The first detectable FMRFamide-like immunoreactivity occurs in a narrow circumferential belt toward the anterior/aboral end of the ectoderm in the early planula. As the planula matures, the FMRFamide-immunoreactive cells send horizontal processes (i.e., neurites) basally along the longitudinal axis. Neurites extend both anteriorly/aborally and posteriorly/orally, but the preference is for anterior neurite extension, and neurites converge to form a plexus at the aboral/anterior end at the base of the ectoderm. In the mature planula, a subset of cells in the apical organ at the anterior/aboral pole begins to show FMRFamide-like and taurine-like immunoreactivity, suggesting a sensory function of the apical organ. During metamorphosis, FMRFamide-like immunoreactivity diminishes in the ectoderm but begins to occur in the degenerating primary endoderm, indicating that degenerating FMRFamide-immunoreactive neurons are taken up by the primary endoderm. FMRFamide-like expression reappears in the ectoderm of the oral disc and the tentacle anlagen of the growing polyp, indicating metamorphosis-associated restructuring of the nervous system. These observations are discussed in the context of metazoan nervous system evolution.

Evidence for a Common Pattern of Peptidergic Innervation of Cnidocytes

Tentacles from representatives of all four classes of the phylum Cnidaria were examined using antibodies against the neuropeptides FMRFamide and RFamide to reveal the organization of neurons and nerve nets associated with cnidocytes. The tentacles of all species examined contained FMRFamide- or RFamide-immunoreactive neurons, in varying densities. In representatives from the Scyphozoa, Hydrozoa, and Cubozoa, the FMRFamide-immunoreactive neurons formed plexuses at the base of the cnidocyte assemblages; in anthozoans, the absence of discrete assemblies of cnidocytes precluded visual co-localization of cnidocytes and immunoreactive neurons. In all four classes, immunoreactive sensory cells connected these peptidergic nerve nets to the surface of the tentacle. These findings suggest that members of all four cnidarian classes share a common organizational pattern, and it is proposed that this peptidergic innervation may be involved in the chemosensory regulation of cnidocyte discharge.

Structure of the nervous system in the tornaria larva of Balanoglossus proterogonius (Hemichordata: Enteropneusta) and its phylogenetic implications

The tornaria larva of hemichordates occupies a central position in phylogenetic discussions on the relationships between Echinodermata, Hemichordata, and Chordata. Dipleurula-type larvae (tornaria and echinoderm larvae) are considered to be primary in the life cycle and thus provide a model for the ancestral animal common to all three taxa (the theory of W. Garstang). If the similarities between tornaria and the larvae in Echinodermata result from homology, their nervous systems should be basically similar as well. The present study utilizes anti-serotonin and FMRFamide antisera together with laser scanning microscopy, and transmission electron microscopy, to describe in detail the nervous system of the tornaria of Balanoglossus proterogonius. Serotonin immunoreactive neurons were found in the apical and esophageal ganglia, and in the stomach epithelium. FMRFamide immunoreactive neurons, probably sensory in nature, were detected in the apical ganglion and in the equatorial region of the stomach epithelium. At the ultrastructural level, the apical organ consists of a columnar epithelium of monociliated cells and includes a pair of symmetrical eyespots. The apical ganglion is located at its base and has a well-developed neuropil. Different types of neurons are described in the apical organ, esophagus, and stomach. Comparison with larvae in Echinodermata shows several significant differences in the way the larval nervous system is organized. This calls into question the homology between tornariae and echinoderm larvae. The possibility of convergence between the two larval types is discussed.

Neuromusculature of the ovijector of ascaris suum (Ascaroidea, nematoda): an ultrastructural and immunocytochemical study.

This study used electron microscopy and confocal scanning laser microscopy interfaced with cytochemistry to study neuromuscular interrelationships in the ovijector of Ascaris suum. An extensive nerve plexus with both FaRPergic and non-FaRPergic components extends over the outer surface of the ovijector. The non-FaRPergic component is derived from nerve branches of the ventral nerve cord, whereas the FaRPergic component emanates from two large FMRFamide-immunoreactive neurons. In the vagina vera, most myofibrils are circular in orientation and a number of them divide and run for short distances in longitudinal and diagonal directions, their myofilaments are also orientated in a variety of directions. Parallel nerve fibres run in tracts along the length of the vagina vera with branches that penetrate the muscle layers. The vagina uteri possesses a thicker hypodermis than that of the vagina vera. It appears rich in secretory and phagocytic vesicles and the luminal side is invested with an electron-dense substance. The musculature of the vagina uteri is less well developed than that of the vagina vera, being restricted to circular myofibrils, with an apparent diagonal arrangement of myofilaments. Also, the innervation is less extensive in the vagina uteri with many fibres returning to the vagina vera to rejoin the nerve net and others continuing into the uteri.

Effects of naloxone on c-jun/AP-1 in met-enkephalin- and FMRFamide-immunoreactive neurons of a gastropod snail

1. Opioid- and FMRFamide (FMRFa)-ergic systems are believed to play antagonistic behavioral roles in both higher and lower animals. In our previous experiments on a snail, behavioral choice has been demonstrated to be dependent on a balance between FMRFa and enkephalins [7]. Here, we examined if the disturbance of the balance causes changes in the activity of both systems. Opiate receptor blocker naloxone was applied and its effect on c-jun expression of met-enkephalin (MEnk)- and FMRFa-ergic neurons was examined immunocytochemically in terrestrial gastropod snail Cepaea nemoralis. 2. In control, untreated snails, central neurons with c-jun/AP-1-like-immunoreactivity were found to occur. These included MEnk-, FMRFa- and 5HT-immunoreactive (-ir) neurons, as was revealed by double-labelling. 3. After treatment with naloxone for 4 h, the following changes were observed: (i) increase in the number of MEnk-ir neurons; increase in the number of neurons showing c-jun/AP-1 and MEnk double-labeling; (ii) disappearance of c-jun/AP-1-immunoreactivity from some FMRFa-ir neurons. 4. It is suggested that immediate early genes are involved in the mechanisms responsible for the reciprocal regulation of the opioid and antiopioid neuropeptide systems.

Distribution of FMRFamide-like immunoreactivity in the nervous system of Lumbricus terrestris.

The distribution of FMRFamide-like immunoreactive cell bodies and fibers in the nervous system of the earthworm Lumbricus terrestris has been studied by means of immunocytochemistry. The cerebral ganglion contains 150-170 immunoreactive nerve cells that are organized into six major groups in the rostral and five major groups in the caudal part of the ganglion; 160-180 immunoreactive nerve cells are present in the subesophageal ganglion, and 80-90 in the ventral cord ganglia. Immunoreactive neurons of the subesophageal and the ventral cord ganglia show similar distributions, in that FMRFamide-like immunoreactive cells form a ventromedial and a lateral cell group. Neuropil in all parts of the central nervous system shows intensively stained varicose and non-varicose fibers. Each segmental nerve contains FMRFamide-like immunoreactive fibers that can partly be traced to the two muscle layers of the body wall, and a fine immunoreactive network lies among the muscle fibers. A similar network is found in the wall of the alimentary canal. Immunopositive perikarya and fibers have been detected in the prostomial nerves, in the stomatogastric system. Some epithelial cells of the body wall are also immunopositive. The morphological characteristics and localization of FMRFamide immunoreactive neurons suggest that they may be involved in: (1) central integratory processes; (2) neuromuscular regulation in both the body wall and enteric system; (3) sensory processes.

Migration of GnRH-immunoreactive neurons from the olfactory placode to the brain: a study using avian embryonic chimeras

Previous studies suggest that gonadotropin-releasing hormone (GnRH) neurons appear in the olfactory placode and subsequently migrate into the brain during embryonic development. The aim of the present study was to obtain direct evidence for migration of GnRH neurons from the olfactory placode into the brain. Olfactory placodes from quail embryos were transplanted isotopically and isochronically, to replace the unilaterally ablated olfactory placodes of chick embryos. The chimeric embryos were allowed to develop for several days until they reached the embryonic stages when GnRH neurons are seen in the brain in normal embryos. Quail olfactory epithelia were formed in the host chick embryos. Quail olfactory nerves were also formed and reached the olfactory bulb or primordial olfactory bulb. GnRH-immunoreactive cells of quail origin revealed by a triple staining method were observed in the quail olfactory epithelium, quail olfactory nerve, chick olfactory bulb, and chick septo-preoptic area. These results indicate that GnRH neurons originate in the olfactory placode and migrate into the telencephalon including the septo-preoptic area. A migratory route of GnRH neurons was well documented by the use of a quail neuron-specific antibody, QN. The migratory route in the brain is discussed with special reference to the terminal nerve. A GnRH-immunoreactive neuronal group of chick origin appeared in the diencephalon of chimeric embryos. These diencephalic neurons may be of non-placodal origin. FMRFamide-immunoreactive neurons of quail origin were also found in the quail olfactory nerve and the host olfactory bulb, suggesting that FMRFamide neurons also originate in the olfactory placode and migrate into the brain.

Distribution of FMRFamide-like immunoreactivity in the brain of the lungfish Protopterus annectens

The distribution of FMRFamide-like immunoreactive peptides was studied in the brain of the African lungfish, Protopterus annectens, using the indirect immunofluorescence technique. The main populations of FMRFamide-positive cell bodies were detected in the forebrain and in the mesencephalic tegmentum. In the telencephalon, only a small number of FMRFamide-immunoreactive neurons was localized at the level of the subpallium, in the nucleus septi medialis. The diencephalon contained two prominent groups of FMRFamide-positive cell bodies located in the preoptic and periventricular preoptic nuclei. The thalamus exhibited only scattered FMRFamide-immunoreactive perikarya in its ventral part. In the mesencephalon, a group of positive cell bodies was identified in the caudal region of the tegmentum. A strong immunoreaction was also detected in the nervus terminalis. In the pituitary, most of the cells of the intermediate lobe were brightly stained. FMRFamide-like immunoreactive fibers and nerve terminals were widely distributed in the brain. In the telecephalon, numerous fibers were observed in several regions of the pallium and subpallium. A dense plexus of fibers was found in the hypothalamus and the thalamus. Immunoreactive fibers were seen coursing along the ventral wall of the infundibular cavity and terminating in the pars nervosa of the pituitary. The tectum and the ventral mesencephalon were also densely innervated. In contrast, the caudal brainstem only showed scarce immunoreactive processes. Coexistence of FMRFamide- and neuropeptide Y-like immunoreactivity was observed in the preoptic nucleus and in the nervus terminalis. The widespread distribution of FMRFamide-immunoreactive neurons in the brain and pituitary of P. annectens suggests that the peptide may exert both neuromodulator and neuroendocrine functions. The similarity between the distribution patterns of FMRFamide and neuropeptide Y in the brain of lungfish and amphibians supports the concept of a close phylogenetic link between these two groups.

Distribution of FMRFamide-like immunoreactivity in the brain of the lizard Podarcis sicula

The distribution of FMRFamide-like immunoreactive peptides was investigated in the brain of the lizard, Podarcis sicula, using the indirect immunofluorescence technique. The main populations of FMRFamide-immunoreactive cell bodies were located in the forebrain. In the telencephalon, FMRFamide-containing neurons were found both in the pallium and subpallium, namely in the medial cortex, the anterior olfactory nucleus, the nucleus accumbens, the septal nuclei, the nucleus of the medial forebrain bundle, and the nucleus of the diagonal band of Broca. In the diencephalon, a dense accumulation of FMRFamide-immunoreactive neurons was observed in the area preoptica lateralis, the nucleus suprachiasmaticus, the nucleus periventricularis hypothalami, the area lateralis hypothalami, and the dorsal region of the nucleus geniculatus lateralis. In the midbrain, sparse immunoreactive perikarya were found in the tegmentum of the mesencephalon. FMRFamide-immunoreactive fibers were visualized in all regions containing positive cell bodies. In particular, dense bundles of immunoreactive processes were seen in the area preoptica lateralis, in the hypothalamus, and in the median eminence. The tectum and the basal mesencephalon were also densely innervated. Conversely, the caudal brain stem only exhibited scarce immunoreactive processes. The distribution pattern of FMRFamide-immunoreactive neurons in the brain of Podarcis sicula exhibits a number of similarities with that reported in mammals, but significantly differs from that reported in amphibians and fish, suggesting that the neuromodulatory functions of FMRFamide may have diverged during the emergence of terrestrial life.

A simple method for immunofluorescent double staining with primary antisera from the same species.

We have developed a new double immunofluorescence technique by which two neuroactive substances in the same tissue section can be labeled with primary antisera raised in the same species. The optic lobes of the locust Schistocerca gregaria were used as a model system to develop the staining procedure. FMRFamide-immunoreactive neurons were detected by rabbit antisera against FMRFamide and FITC-conjugated secondary antibodies. Antibodies against the second peptide, pigment-dispersing hormone (PDH), also raised in rabbit, were biotinylated and detected via streptavidin-Texas Red. Crossreactivity of the PDH immunoglobulins with the FITC-conjugated secondary antiserum was prevented by pre-incubation with rabbit gamma globulins. The two peptide immunoreactivities could be conveniently observed on the same section with the different fluorescent markers. This double labeling technique with modified antibodies is easily performed and highly useful for co-localization studies with antisera raised in the same species.

Structure and development of the larval central complex in a holometabolous insect, the beetle Tenebrio molitor

The neuroarchitecture of the central complex, a prominent neuropil in the midbrain of the holometabolan, Tenebrio molitor, is described throughout larval development. The analysis is based on classical silver impregnations and on fate-mapping of identified neurons using antisera against serotonin and FMRF-amide. In T. molitor, the central body is present in the first larval instar, and is formed by side branches of contralaterally projecting neurons. Glial cells surround eight neuropil compartments in the first larval instar. These subdivisions in the organization of the fan-shaped body are maintained throughout development. Intrinsic interneurons are found from the 5th larval instar onwards. In the last larval stage, the central complex consists of the fan-shaped body, the protocerebral bridge, and the anlage of the ellipsoid body. The cellular architecture of the fan-shaped body of the last larval instar resembles the basic structural characteristics of the adult. Serotonin-immunoreactive neurons and FMRF-amide immunoreactive neurons in the midbrain of the first larval instar show the basic structural features of the respective imaginal cells. The structural organizations of larval and adult midbrain are compared.

Immunocytochemical localization of FMRFamide in the central nervous system and the kidney of Helisoma duryi (Mollusca): Its possible antidiuretic role

The distribution of FMRFamide-immunoreactive neurons in the central nervous system of the freshwater pulmonate, Helisoma duryi is described. All parts of the central nervous system except the two pleural and the right parietal ganglia, contain immunoreactive neurons. By immunogold techniques, only one kind of neurosecretory FMRFamide-immunoreactive cell (previously identified as the type-3 cell) was localized in the visceral and left parietal ganglia. This cell type has been previously implicated in an antidiuretic role. FMRFamide-immunoreactive material is found in the whole mount of the kidney as well as in kidney sections. Electron microscopic examination shows that the axons innervating either the smooth muscles of the kidney or the kidney itself contain neurosecretory granules morphologically similar to type-3 cells of the visceral and left parietal ganglia. When incubated in saline containing nanogram quantities of FMRFamide, the wet weight of the kidney increased. It is suggested that FMRFamide-like substance may function as an antidiuretic factor and that the kidney is a target organ of this peptide for osmoregulation.

In situ hybridization analysis of the FMRFamide neuropeptide gene in Drosophila. II. Constancy in the cellular pattern of expression during metamorphosis.

We have studied changes in the pattern of specific neuropeptide gene expression during the metamorphosis of the Drosophila nervous system. Prior to metamorphosis, the Drosophila FMRFamide gene is expressed exclusively within the central nervous system in a stereotyped pattern that comprises roughly 60 neurons (Schneider et al., '91). Using in situ hybridization, we found that the FMRFamide gene was continuously expressed throughout all stages examined: at each of 15 stages of adult development and through at least the first 10 days of adult life. There were no differences between the results observed with 2 exon-specific hybridization probes, thus indicating little if any alternative splicing during postembryonic development. Despite many changes in the positions of individual hybridization signals due to the large-scale reorganization of the nervous system, the continuous pattern of gene expression through adult development permitted many adult signals to be identified as larval signals. We concluded that the adult pattern of FMRFamide gene expression was largely derived from persistent larval neurons. Adult-specific hybridization signals in the brain and ventral ganglion were also detected and these corresponded to many of the approximately 40 adult-specific FMRFamide-immunoreactive neurons. One specific larval signal was lost during adult development and the intensities of other signals fluctuated in reproducible manners. These stereotyped differences in hybridization signal intensity resemble similar observations made in larval stages (Schneider et al., '91) and support the hypothesis that the steady-state levels of FMRFamide transcripts are differentially regulated among the diverse neurons that express the gene.

In situ hybridization analysis of the FMRFamide neuropeptide gene in Drosophila. I. Restricted expression in embryonic and larval stages.

We have used in situ hybridization techniques to describe the cellular distribution of transcripts from a Drosophila gene that encodes multiple FMRFamide-related neuropeptides. The Drosophila FMRFamide gene consists of two exons and is expressed predominantly as a approximately 1.7 kb RNA throughout postembryonic stages (Nambu et al., '88; Schneider and Taghert, '88, '90). We used exon-specific oligonucleotide probes to assay transcription in both embryonic and larval stages and found a pattern of hybridization signals that was restricted to the central nervous system and, within that tissue, was cell-specific. The pattern included 36 distinct signals distributed throughout both the brain and segmental nerve cord (ventral ganglion). These observations suggest that the cell-specific pattern of FMRFamide-like neuropeptide expression in the Drosophila CNS (White et al., '86; Taghert and Schneider, '90) is due to the restricted expression of specific gene transcripts. The results also indicate that, with few exceptions, all previously identified FMRFamide-immunoreactive neurons in Drosophila larvae express FMRFamide gene transcripts. The 36 hybridization regions of the CNS could be divided into three categories, based on their signal intensities (strong, moderate, and weak). The differences in intensity were reproducible and suggest that steady-state levels of specific neuropeptide RNA differ among individual neurons. The two exon-specific probes produced patterns that were indistinguishable both in pattern and in intensity. This result supports the previous conclusion that the one detectable FMRFamide transcript contains both exons (Schneider and Taghert, '90). A single identifiable signal was detected during embryogenesis (beginning at stage 16), but the mature complement of signals was not fully established until the final larval stages.

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

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 moth Manduca 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 SCPB. 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 of M. sexta and might function as neurohormones and neurotransmitters in a variety of neuronal cell types.

FMRF-amide-like immunoreactive efferent fibers and FMRF-amide suppression of pacemaker neurons in eyes of Bulla.

The eyes of certain marine gastropods including Aplysia and Bulla, contain circadian pacemakers, which produce a circadian rhythm of autogenous compound action potential (CAP) activity. The CAPs are generated by the synchronous spike discharge of a distinctive population of retinal pacemaker neurons whose axons convey the CAP activity to the CNS. When CAP activity is recorded from a preparation with eyes attached to the CNS, the CAP activity is modulated by efferent activity. In this study we have identified FMRF-amide-like immunoreactive efferent axons in the optic nerves of Bulla. These axons arborize in the basal retinal neuropil adjacent to the pacemaker neurons and are in a position to make synaptic contacts with their dendrites. Similar immunoreactive fibers are not observed in Aplysia eyes. Exogenous FMRF-amide at micromolar concentrations suppresses ongoing CAP activity in isolated eyes but does not suppress the ERG or phase shift the circadian rhythm of CAP activity. Intracellular recordings from the retinal pacemaker neurons reveal that FMRF-amide hyperpolarizes the membrane potential, suppresses spike discharge, and decreases the input resistance, suggesting that a K conductance is increased. Electrical stimulation of the region of the cerebral ganglion that contains FMRF-amide immunoreactive neurons suppresses ongoing CAP activity. All these results are consistent with the idea that the FMRF-amide immunoreactive central neurons and their axons provide a pathway for efferent modulation of the CAP rhythm generated by the retinal pacemaker neurons.

FMRFamide immunoreactive neurons in the central nervous system of the snail, Achatin a fulica

1. 1. FMRFamide immunoreactive neurons were detected in the central nervous system of the snail, Achatina fulica. 2. 2. FMRFamide immunoreactive neurons were found in all the ganglia comprising the central nervous system. In particular, the immunoreactivity was recognized in both the ordinary and giant neurons of the visceral and right parietal ganglia. 3. 3. In the cerebral and pleural ganglia, FMRFamide immunoreactive neurons were found only in the ordinary neurons. The immunoreactivity was shown to have a tendency to form a group in the cerebral and pedal ganglia.

FMRFamide immunoreactivity in the nervous system of the medusa Polyorchis penicillatus.

Three different antisera to the molluscan neuropeptide Phe-Met-Arg-Phe-amide (FMRFamide) and two different antisera to the fragment RFamide were used to stain sections or whole mounts of the hydrozoan medusa Polyorchis penicillatus. All antisera stained the same neuronal structures. Strong immunoreactivity was found in neurons of the ectodermal nerve nets of the manubrium and tentacles, in neurons of the sensory epithelium, and in neurons at the periphery of the sphincter muscle. Strong immunoreactivity was also present in processes and perikarya of the whole outer nerve ring, in the ocellar nerves, and in nerve cells lying at the periphery of the ocellus. The inner nerve ring contained a moderate number of immunoreactive processes and perikarya, which were distinct from the swimming motor neurons. In contrast to the situation in the hydrozoan polyp Hydra attenuata, no immunoreactivity was found with several antisera to oxytocin/vasopressin and bombesin/gastrin-releasing peptide. The morphology and location of most FMRFamide-immunoreactive neurons in Polyorchis coincides with two identified neuronal systems, which have been recently discovered from neurophysiological studies.