FMRFamide-like Immunoreactive Neurons Research Articles

Distribution of FMRFamide-related peptides and co-localization with glutamate in Cupiennius salei, an invertebrate model system.

FMRFamide-related proteins have been described in both vertebrate and invertebrate nervous systems and have been suggested to play important roles in a variety of physiological processes. One proposed function is the modulation of signal transduction in mechanosensory neurons and their associated behavioral pathways in the Central American wandering spider Cupiennius salei; however, little is known about the distribution and abundance of FMRFamide-related proteins (FaRPs) within this invertebrate system. We employ immunohistochemistry, Hoechst nuclear stain and confocal microscopy of serial sections to detect, characterize and quantify FMRFamide-like immunoreactive neurons throughout all ganglia of the spider brain and along leg muscle. Within the different ganglia, between 3.4 and 12.6% of neurons showed immunolabeling. Among the immunoreactive cells, weakly and strongly labeled neurons could be distinguished. Between 71.4 and 81.7% of labeled neurons showed weak labeling, with 18.3 to 28.6% displaying strong labeling intensity. Among the weakly labeled neurons were characteristic motor neurons that have previously been shown to express ɣ-aminobutyric acid or glutamate. Ultrastructural investigations of neuromuscular junctions revealed mixed presynaptic vesicle populations including large electron-dense vesicles characteristic of neuropeptides. Double labeling for glutamate and FaRPs indicated that a subpopulation of neurons may co-express both neuroactive compounds. Our findings suggest that FaRPs are expressed throughout all ganglia and that different neurons have different expression levels. We conclude that FaRPs are likely utilized as neuromodulators in roughly 8% of neurons in the spider nervous system and that the main transmitter in a subpopulation of these neurons is likely glutamate.

Regional and segmental differences in the embryonic expression of a putative leech Hox gene, Lox2, by central neurons immunoreactive to FMRFamide-like neuropeptides

We performed immunofluorescence experiments using a rat polyclonal antibody on formaldehyde-fixed whole-mount embryos to characterize the expression of a putative leech Hox gene, Lox2, during embryonic development. The main goal was to determine whether the differentiation of subsets of FMRFamide-like immunoreactive (FLI) neurons coincide with the expression domain of Lox2. The earliest expression of Lox2 was detected in relatively large, prominent nuclei in the posterior region at embryonic day 4, a very early stage. Lox2 expression was also detected in subsets of central neurons (neurons located in the CNS) located in midbody ganglia 6 (M6)-M21. In addition, Lox2 was expressed by a number of segment-specific and segmentally repeated central FLI neurons. Lox2-positive FLI neurons of interest included some of those previously identified: the rostral most ventral (RMV) neurons, the circular ventral (CV) neurons, and cell 261. The paired RMVs, which are located in all midbody ganglia, expressed Lox2 only in M7-M19. The CV neurons, specialized motor neurons that innervate the circular ventral muscles of the body wall, expressed Lox2 in M7-M19. The putative cell 261 expressed Lox2 in M7-M12, where Lox1 is also expressed. FMRFamide staining in putative segmental homologs of cell 261 was not detected in other segmental ganglia. Our results suggest a role for Lox2 in very early embryonic development (before the formation of the CNS), and in the differentiation of segmentally repeated and region-specific FLI neurons.

Analysis of neurotransmitter distribution in brain development of benthic and pelagic octopod cephalopods

The database on neurotransmitter distribution during central nervous system development of cephalopod mollusks is still scarce. We describe the ontogeny of serotonergic (5-HT-ir) and FMRFamide-like immunoreactive (Fa-lir) neurons in the central nervous system of the benthic Octopus vulgaris and Fa-lir distribution in the pelagic Argonauta hians. Comparing our data to previous studies, we aim at revealing shared immunochemical domains among coleoid cephalopods, i.e., all cephalopods except nautiluses. During development of O. vulgaris, 5-HT-ir and Fa-lir elements occur relatively late, namely during stage XII, when the brain neuropils are already highly differentiated. In stage XII-XX individuals, Fa-lir cell somata are located in the middle and posterior subesophageal mass and in the optic, posterior basal, and superior buccal lobes. 5-HT is predominately expressed in cell somata of the superior buccal, anterior basal, and optic lobes, as well as in the subesophageal mass. The overall population of Fa-lir neurons is larger than the one expressing 5-HT. Fa-lir elements are distributed throughout homologous brain areas of A. hians and O. vulgaris. We identified neuronal subsets with similar cell number and immunochemical phenotype in coleoids. These are located in corresponding brain regions of developmental stages and adults of O. vulgaris, A. hians, and the decapod squid Idiosepius notoides. O. vulgaris and I. notoides exhibit numerous 5-HT-ir cell somata in the superior buccal lobes but none or very few in the inferior buccal lobes. The latter have previously been homologized to the gastropod buccal ganglia, which also lack 5-HT-ir cell somata in euthyneuran gastropods. Among coleoids, 5-HT-ir neuronal subsets, which are located ventrally to the lateral anterior basal lobes and in the anterior middle subesophageal mass, are candidates for homologous subsets. Contrary to I. notoides, octopods exhibit Fa-lir cell somata ventrally to the brachial lobes and 5-HT-ir cell somata close to the stellate ganglia.

FMRFamide-like immunoreactivity in the central nervous system of the cephalopod mollusc,Idiosepius notoides

For more than a century, cephalopod molluscs have been the subject of extensive studies with respect to their complex neuroanatomy and behavior. In comparison to gastropod molluscs surprisingly little work has been carried out on the characterization of neurons in the central nervous system (CNS) of cephalopods with respect to their neurotransmitter phenotypes. This study presents preliminary results on the distribution of FMRFamide-like immunoreactive neurons within the CNS of the pygmy squid Idiosepius notoides. Its gross neuroanatomy resembles that of other cephalopods. FMRFamide-like immunoreactivity was observed in most of the brain lobes. High abundance of FMRFamidergic perikarya was found in the dorsal basal, the central palliovisceral, and the olfactory lobes, whereas none were observed in the middle suboesophageal mass. Single individual perikarya are located within the optic lobes and the vertical lobes. Although certain immunohistochemical traits are shared with other cephalopods, such as a wall-like arrangement of FMRFamide-like immunoreactive cell somata within the dorsal basal lobe, others have so far only been found in Idiosepius. However, future investigations on other species are necessary in order to broaden our knowledge on a common recruitment of certain neurotransmitters in distinct brain lobes of the highly advanced brain of cephalopods.

Comparative immunocytochemical study of FMRFamide neuronal system in the brain of Danio rerio and Acipenser ruthenus during development

The distribution of FMRFamide-like immunoreactive (ir) neurons and fibers was investigated in the central nervous system of developing zebrafish and juvenile sturgeon (sterlet). Adult zebrafish was also studied. In zebrafish embryos FMRFamide-ir elements first appeared 30 h post-fertilization (PF). Ir somata were located in the olfactory placode and in the ventral diencephalon. FMRFamide-ir fibers originating from diencephalic neurons were found in the ventral telencephalon and in ventral portions of the brainstem. At 48 h PF, the ir perikarya in the olfactory placode displayed increased immunoreactivity and stained fibers emerged from the somata. At 60 h PF, bilaterally, clusters of FMRFamide-ir neurons were found along the rostro-caudal axis of the brain, from the olfactory placode to rostral regions of the ventro-lateral telencephalon. At 60 h PF, numerous ir fibers appeared in the dorsal telencephalon, optic lobes, optic nerves, and retina. Except for ir fibers in the hypophysis at the age of 72 h PF, and a few ir cells in the nucleus olfacto-retinalis (NOR) at the age of 2 months PF, no major re-organization was noted in subsequent ontogenetic stages. The number of stained NOR neurons increased markedly in sexually mature zebrafish. In adult zebrafish, other ir neurons were located in the dorsal zones of the periventricular hypothalamus and in components of the nervus terminalis. We are inclined to believe that neurons expressing FMRFamide originate in the olfactory placode and in the ventricular ependyma in the hypothalamus. On the same grounds, a dual origin of FMRFamide-ir neurons is inferred in the sturgeon, an ancestral bony fish: prior to the observation of ir cells in the nasal area and in the telencephalon stained neurons were noted in circumventricular hypothalamic regions.

Co-localization of serotonin and FMRFamide-like immunoreactivities in the central nervous system of the earthworm, Eisenia Jetida

In the present study co-localization of serotonin and FMRFamide-like immunoreactivities was studied in the central nervous system of the earthworm, Eisenia fetida. Alternate serial sections were stained with antisera raised against serotonin and FMRFamide, using the peroxidase-antiperoxidase method. The immunostained consecutive sections were compared by light-microscopy and on reconstructed images using NIH Image and Neurolucida programs. Although there was a large number of serotonin and FMRFamide-like immunoreactive neurons in the central nervous system of Eisenia, co-localization of immunostaining was relatively rare. In the cerebral ganglion no cells were found that stained for both antisera. In the subesophageal and ventral cord ganglia the neurons reacting for both antisera represented approximately 17-23% and 10-14% of the serotonin- and 7-11% and 9-17% of the FMRF-amide-like immunoreactive cells, respectively. It is suggested, that FMRFamide-related peptides act as neuromodulators and may also influence the activity of serotonergic neurons.

DEVELOPMENT OF NEURONS EXHIBITING FMRFAMIDE-RELATED IMMUNOREACTIVITY IN THE CENTRAL NERVOUS SYSTEM OF LARVAE OF THE SPIDER CRAB HYAS ARANEUS L. (DECAPODA: MAJIDAE)

ABSTRACT The ontogeny of neuropeptide-expressing neurons during larval development of the crustacean central nervous system is as yet poorly understood. Recently, homologues of the molluscan neuropeptide FMRFamide have been isolated from the central nervous system of adult crustaceans. In order to identify sets of neurons which might express FMRFamide-related neuropeptides and to follow their development, whole mount preparations of the brain and ventral nerve cord of laboratory-reared spider crab larvae (Hyas araneus) were labeled with an antibody against the tetrapeptide FMRFamide. The distribution and morphology of FMRFamide-like immunoreactive neurons, their primary neurites, and neuropils were mapped throughout development of the stages zoea I and zoea 2. Ontogenetic alterations in the staining pattern were recorded and the results compared to the distribution of FMRFamide-like immunoreactivity in other crustaceans.

Peripheral connections of FMRFamide-like immunoreactive neurons in the snail, helix pomatia: an immunogold electron microscopic study.

Using a postembedding immunogold electron microscopic method, the ultrastructure and synaptic connections of FMRFamide-like immunoreactive varicosities were investigated in different peripheral organs of the snail Helix pomatia, including the heart (auricle), intestine, hepatopancreas, upper tentacle and salivary gland. The FMRFamide-like immunoreactive varicosities contained granules and vesicles as described in a previous study of the CNS of this species, and additionally, based on their granule content, two novel types of varicosities were found in the auricle. A selective accumulation of gold particles over the granules could be demonstrated. The FMRFamide-like immunoreactive varicosities formed unspecialized contacts with postsynaptic target cells in all peripheral organs investigated, with the exception of the tentacle retractor muscle. Both the neuro-muscular and the neuro-glandular contacts were characterized by either unspecialized close apposition of the 'pre- and postsynaptic' membranes or the immunoreactive elements faced the target cell(s) across a relatively wide extracellular space. In the tentacle retractor muscle some of the neuromuscular contacts showed appositions of electron dense material along the presynaptic membrane, clustering of agranular synaptic vesicles and intersynaptic cleft material. The present observations support previous electrophysiological findings and suggest a versatile modulatory role of FMRFamide and related substances in the Helix PNS.

Localization of FMRFamide- and ACEP-1-like immunoreactivities in the nervous system and heart of a pulmonate mollusc, Achatina fulica.

Immunohistochemical localization of two neuropeptides possibly involved in the regulation of cardiac activity in a pulmonate mollusc, Achatina fulica Férussac, was studied. On the ventral surface of the right cerebral ganglion, more than 50 neurons with diameters of 30-50 microns showed immunoreactivity to the antiserum of the neuropeptide FMRFamide. Many were also immunoreactive to an antiserum raised against Achatina cardio-excitatory peptide-1 (ACEP-1). Although FMRFamide-like immunoreactive neurons occurred in all components of the subesophageal ganglia, identifiable ACEP-1-like immunoreactive neurons were located only in the visceral ganglion and the right parietal ganglion. In the heart, FMRFamide- and ACEP-1-like immunoreactive fibers were restricted to the atrium and the aortic end of the ventricle, consistent with morphological observations of cardiac innervation. The present results suggest that FMRFamide- and ACEP-1-like peptides are involved in regulating the heart beat of this snail.

FMRFamide-like immunoreactive neurons in the brain of the beetle, Tenebrio molitor L. (coleoptera : tenebrionidae): constancies and variations in development from the embryo to the adult

FMRFamide-like immunoreactive neurons in the brain of Tenebrio molitor (Coleoptera : Tenebrionidae) have been demonstrated and mapped throughout the late embryonic and postembryonic development. Twenty-six bilaterally symmetrical clusters of immunopositive brain neurons were identified as persisting from the embryo to the adult, maintaining their essential topological characteristics. It was demonstrated that neuropil regions and even basic structural features of identified neurons are laid down architectonically during embryonic development and persist throughout postembryonic development of Tenebrio. Such persistence was found in midbrain interneurons and in interneurons associated with the antennal sensory neuropils. In case of identified descending interneurons and in neurons associated with the optic foci, structural variations of their respective arborization patterns were described and followed in detail throughout embryonic and postembryonic development.

Serotonin-and FMRFamide-immunoreactive nerve elements in the chiton Lepidopleurus asellus (Mollusca, Polyplacophora)

The distribution of serotonin-like and FMRFamide-like immunoreactive (5HT-ir and FMRFa-ir, respectively) neurons in the nervous system of the chiton Lepidopleurus asellus (Mollusca, Polyplacophora) was studied using an immunocytochemical technique. The neurons were distributed in characteristic patterns in the central nervous system, the 5HT-ir neurons predominating in the ventral (pedal) cords and FMRFa-ir neurons in the lateral cords. In the body wall including the foot, a tight network of 5HT-ir and FMRFa-ir nerve fibers is found, the former being mostly attributed to the musculature whereas the latter seems to be associated with the blood sinuses. Intraepithelial neurons of both types are abundant in the fore-and hindgut. The presence and general distribution in the central and peripheral nervous system of the 5HT-ir and FMRFa-ir elements seems thus to be similar in simple and advanced molluscs. The relationship between these neurons and their targets in the body also appears to be well conserved in molluscs.

An immunogold electron microscopic analysis of FMRFamide-like immunoreactive neurons in the CNS ofHelix pomatia: ultrastructure and synaptic connections

The ultrastructure and synaptic connections of FMRFamide-like immunoreactive neurons were investigated in the CNS of the snail Helix pomatia, following the application of a post-embedding immunogold method. For comparison, first, we analyzed the ultrastructure and granule content of the identified FMRFamide-containing C3 neuron in the cerebral ganglion. Three types of unidentified immunoreactive neuronal perikarya, and five types of varicosities could be distinguished on the basis of granule content. The different granule types revealed a highly selective accumulation of gold particles. One granule type contained by one FMRFamide-like immunoreactive neuron type (N1) and by one varicosity type (T2) showed similar ultrastructure to that of the granules seen in the C3 cell. In the neuropil, the majority of FMRFamide-like immunoreactive varicosities (four of the five varicosity types) established specialized synaptic contacts with unidentified postsynaptic profiles. In the connective tissue sheath around the ganglia, three types of FMRFamide-like immunoreactive varicosities were found to establish unspecialized contacts with smooth muscle fibres or to be free in the mass of collagen fibres. On the basis of these observations, we suggest (1) an extensive diversity of the localization of FMRFamide (and related substances) at the ultrastructural level; (2) the involvement of FMRFamide-like immunoreactive varicosities in synaptic, modulatory and neurohormonal regulatory processes in the Helix nervous system.

Distribution of modulatory inputs to the stomatogastric ganglion of the crab, Cancer borealis.

The pyloric and gastric mill neural networks in the crustacean stomatogastric ganglion receive modulatory inputs from more anteriorly located ganglia via the stomatogastric nerve. In this study we employed biocytin backfilling and immunostaining, as well as electron microscopy, to determine the origin of these inputs in the crab, Cancer borealis. Fiber counts from electron micrographs of sections through the stomatogastric nerve showed that this nerve contains 55-60 medium to large diameter fibers (1-13 microns). These fibers were individually wrapped by several layers of membrane, presumably glial in origin. There was also a single cluster of jointly wrapped, small diameter (< 1 micron) fibers that may originate from peripheral sensory somata. Biocytin backfills revealed that approximately two thirds of the individually wrapped fibers in this nerve originate from somata in the other three ganglia of the stomatogastric nervous system, including the paired commissural ganglia and the single oesophageal ganglion. There were approximately 20 biocytin-labeled somata in each commissural ganglion and 3 somata in the oesophageal ganglion. An additional ten somata were localized to the stomatogastric ganglion itself. This accounts for nearly all of the medium to large diameter fibers in the stomatogastric nerve. We used double-labeling with backfills and immunocytochemistry to determine that there are two proctolin-immunoreactive neurons and four FMRFamide-like immunoreactive neurons among the biocytin-labeled neurons in each commissural ganglion. Both peptides modulate neural network activity in the stomatogastric ganglion.(ABSTRACT TRUNCATED AT 250 WORDS)

Action and immunoreactivity of neuropeptides in the buccal neuromuscular system of a prosobranch mollusc, Rapana thomasiana

In a prosobranch mollusc, Rapana thomasiana, the catch-relaxing peptide H-Ala-Met-Pro-Met-Leu-Arg-Leu-NH2 (CARP) was found to depress the contraction of the radula protractor and retractor elicited by electrical stimulations. The action of CARP was in contrast to that of other neuropeptides, H-Phe-Met-Arg-Phe-NH2 (FMRFamide) and H-Phe-Leu-Arg-Phe-NH2 (FLRFamide), which enhanced the contraction of the radula protractor and retractor, respectively. By immunohistochemical examinations, FMRFamide-like immunoreactive neurons were found on the rostral side of the right buccal ganglion and the caudal side of the left ganglion, where some CARP-like immunoreactive neurons were also distributed, indicating a possible coexistence of FMRFamide and CARP. FMRFamide- and CARP-like immunoreactivities were also detected in the neuropile of buccal ganglia, radula nerves arising from the ganglia, and nerve fibers in the radula muscles. The present results suggest that FMRFamide- and CARP-like peptides are involved in the regulation of the contraction of the radula muscles.

Distribution of FMRFamide-like immunoreactive neurons in the central nervous system of the snail Helix pomatia

The distribution of FMRFamide-like immunoreactive (FLI) neurons and their morphological characteristics have been investigated in the central nervous system of the snail, Helix pomatia L. Approximately phageal ganglion complex. More than 50% of the FLI neurons were located in the cerebral ganglia. The FLI neurons could be divided into four groups according to size: (i) giant neurons (over 100 μm); (ii) large neurons (80–100 μm); (iii) medium-sized neurons (40–70 μm); (iv) small neurons (12–30 μm). They were distributed i) in groups or clusters, typical of small neurons and ii) in solitary form or in groups comprising 2–3 cells, typical of large and giant neurons. Giant and large neurons revealed only limited arborizations in the neuropil, but rich branching towards and in the peripheral nerves. Some of the small neurons had extensive arborizations of varicose fibers in the neuropil. They may therefore play some role in integratory processes. Varicose FLI fibers were visualized in the cell body layer of the different ganglia, and in the neural sheath of both the ganglia and the peripheral nerves. We propose a multifunctional involvement of FLI neurons and FMRFamide-like neuropeptides in the Helix nervous system: (i) a synaptic or modulatory role in axo-axonic interactions in the neuropil; (ii) a direct influence on neuronal cell bodies in the cortical layer, (iii) innervation of different peripheral organs; and (iv) remote neurohormonal control of peripheral events through the neural sheath.

Catecholamine-containing, serotonin-like, and FMRFamide-like immunoreactive neurons and processes in the nervous system of the early actinotroch larva of Phoronis vancouverensis (Phoronida): distribution and development

The distribution and development of neurons and nerve processes containing the putative neurotransmitters catecholamines (CA), serotonin-like immunoreactivity (5-HT-ir), and FMRFamide-like immunoreactivity (FMRFamide-ir) have been investigated by means of glyoxylic acid induced fluorescence in CA and antibodies against 5-HT and FMRFamide in the 0- to 6-tentacle actinotroch larvae of Phoronis vancouverensis Pixell, 1912. CA and 5-HT-ir were observed in the apical ganglion at all stages (beginning at the early 0-tentacle stage); FMRFamide-ir appeared first at the late 0-tentacle stage. The CA-containing cells are located in a ring at the periphery of the apical ganglion, whereas the 5-HT-immunoreactive cells form a U-shaped area in the centre of the epistome. In late 0-tentacle stages, CA, 5-HT-ir, and FMRFamide-ir are found in processes along the future ciliary band of the tentacles and the margin of the epistome. At the 2-tentacle stage, processes are observed in the apical ganglion extending from the neuropil towards the tentacles and the margin of the epistome. At the 4- to 6-tentacle stage, processes loosely concentrated in large bundles are found along the epistome margin projecting on the ventral side of the mesosome towards the tentacles (CA, 5-HT-ir, and FMRFamide-ir), extending from the apical ganglion towards the tentacles (5-HT-ir and FMRFamide-ir), along the ciliary band of the tentacles (CA, 5-HT-ir, and FMRFamide-ir), and along the posterior ciliary band (CA, 5-HT-ir, and FMRFamide-ir).

Distribution of catecholamine-containing, serotonin-like and neuropeptide FMRFamide-like immunoreactive neurons and processes in the nervous system of the actinotroch larva ofPhoronis muelleri (Phoronida)

Glyoxylic-acid-induced fluorescence of catecholamines and antibodies against serotonin and FMRFamide were used to study the distribution of putative neurotransmitters in the actinotroch larva ofPhoronis muelleri Selys-Longchamps, 1903. Catecholamines occur in the neuropile of the apical ganglion, in the longitudinal median epistome nerves, in the epistome marginal nerves, and in the nerve along the bases of the tentacles. The tentacles have laterofrontal and latero-abfrontal bundles of processes that form two minor nerves along the lateral ciliary band of the tentacles, and a medio-frontal bundle of processes. Monopolar cells are located on the ventro-lateral part of the mesosome. Processes are located along the posterior ciliary band and as a reticulum in the epidermis. Serotonin-like immunoreactive cells and processes are located in the apical ganglion, in the longitudinal median epistome nerves, and as a dorsal and ventral pair of bundles along the tentacle bases. Processes from the latter extend into the tentacles as the medioabfrontal processes. The latero-abfrontal processes form a minor nerve along the ciliary band. The dorsal bundles forms the major nerve ring along the tentacles and processes extend from it to the metasome. Processes are located along the posterior ciliary band. FMRFamide-like immunoreactive cells and processes are found in the apical ganglion, in the longitudinal median epistome nerves and as a pair of lateral epistome processes projecting towards the ring of tentacles. In the tentacles, a pair of latero-frontal processes are found; these form a minor nerve along the ciliary band. A band of cells can be seen along the tentacle ring.

Distribution of FMRFamide-like immunoreactivity in the brain and neurohypophysis of the lamprey, Lampetra japonica.

Distribution of molluscan cardio-excitatory tetrapeptide Phe-Met-Arg-Phe-NH2 (FMRFamide) was determined by means of immunohistochemistry in the brain and neurohypophysis of the lamprey, Lampetra japonica. Many FMRFamide-like immunoreactive neurons were found in the periventricular nuclear region and in a region near the mammillary recess. Neurons situated in the former region were larger. The immunoreactive cell groups were shown to be located at sites differing from those of the AF-positive cell groups. The fibers of immunoreactive neurons extended in all directions within the brain and towards the spinal cord, some reaching the third ventricle and capillaries. Thus, FMRFamide-like immunoreactive peptides appear to function as neurotransmitters or neuromodulators and possibly also as neurohormones. FMRFamide-like immunoreactive material was rarely observed in the posterior neurohypophysis (neural lobe), but was noted to be present to a limited extent in the caudal part of the anterior neurohypophysis (median eminence). It would thus follow that FMRFamide-like immunoreactive neurons may not necessarily be related to the hypothalamo-neural lobe system, but may possibly be associated with the hypothalamo-adenohypophysial system. The pineal body showed no FMRFamide-like immunoreactivity.

FMRFamide-like immunoreactive neurons of the nervus terminalis of teleosts innervate both retina and pineal organ

The tetrapeptide FMRFamide (Phe-Met-Arg-Phe-NH 2) was first isolated from molluscan ganglia. Subsequently, it has become clear that vertebrate brains also contain endogenous FMRFamide-like substances. In teleosts, the neurons of the nervus terminalis contain an FMRFamide-like substance, and provide a direct innervation to the retina ( Proc. Natl. Acad. Sci. U.S.A., 81 [1984] 940–944). Here we report the presence of FMRFamide-immunoreactive axonal bundles in the pineal organ of Coho salmon and three-spined sticklebacks. The largest numbers of axons were observed proximal to the brain, in the pineal stalk, while the distal part of the pineal organ contained only few axons. No FMRFamide-like-immunoreactive (IR) cell bodies were observed in the pineal organ. In adult fish it was not possible to determine the origin of these axons, due to the large numbers of FMRFamide-like IR axons in the teleost brain. However, by following the development of FMRFamide-like IR neurons in the embryonic and larval stickleback brain, it was possible to conclude that, at least in newly hatched fish, FMRFamide-like IR axons that originate in the nucleus nervus terminalis reach the pineal organ. Thus, it seems there is a direct connection between a specialized part of the chemosensory system and both the retina and the pineal organ in teleost fish.

Distribution of FMRFamide-like immunoreactivity in the nervous system of the slug Limax maximus.

The distribution of FMRFamide-like immunoreactive neurons in the nervous system of the slug Limax maximus was studied using immunohistochemical methods. Approximately one thousand FMRFamide-like immunoreactive cell bodies were found in the central nervous system. Ranging between 15 micron and 200 micron in diameter, they were found in all 11 ganglia of the central nervous system. FMRFamide-like immunoreactive cell bodies were also found at peripheral locations on buccal nerve roots. FMRFamide-like immunoreactive nerve fibres were present in peripheral nerve roots and were distributed extensively throughout the neuropil and cell body regions of the central ganglia. They were also present in the connective tissue of the perineurium, forming an extensive network of varicose fibres. The large number, extensive distribution and great range in size of FMRFamide-like immunoreactive cell bodies and the wide distribution of immunoreactive fibres suggest that FMRFamide-like peptides might serve several different functions in the nervous system of the slug.