VIP-, Bombesin- and Neurotensin-Like Immunoreactivity in Neurons of the Gut of the Holostean Fish,Lepisosteus platyrhincus

VIP-like immunoreactivity was found in nerve fibres in all layers of the gut wall in both stomach and intestine, and was abundant in the myenteric and submucous plexuses. A few fibres were associated with blood vessels. Nerve cells showing VIP-like immunoreactivity were found in the myenteric plexus. Neurotensin-like immunoreactivity was found in nerve cells and numerous nerve fibres in the myenteric plexus of both stomach and intestine and in nerve fibres of the circular muscle layer, while bombesin-like immunoreactivity was confined to a low number of nerve fibres in the myenteric plexus of the stomach. The results indicate that a VIP-like, a neurotensin-like and a bombesin-like peptide are present in neurons of the gut of Lepisosteus.     

Evidence for 5-hydroxytryptamine in neurones in the gut of the toad,Bufo marinus

Summary The stomach, small intestine and large intestine of the toad, Bufo marinus, were processed for formaldehyde-induced fluorescence histochemistry. After extrinsic denervation or pretreatment with 6-hydroxydopamine to remove catecholamine fluorescence, yellow fluorescence typical of 5-hydroxytryptamine was observed in neurones in the small intestine only. The cell bodies and their processes were confined to the myenteric plexus. Additional pretreatment with 5-hydroxytryptamine enhanced the fluorescence of neurones in the small intestine and revealed yellowfluorescent nerve fibres, but not cell bodies, in the longitudinal and circular muscle layers and myenteric plexus of the large intestine. No fluorescent neurones were observed in the stomach. Following reserpine treatment, which removed native yellow fluorescence in the small intestine, exposure to 5-hydroxytryptophan produced yellow fluorescence in axons in both small and large intestine; exposure to tryptophan never restored fluorescence. The neurotoxin, 5,7-dihydroxytryptamine had no effect on the distribution of yellow-fluorescent neurones in the small and large intestine. No 5-HT-containing mast cells were present in either the small or large intestine. Thin layer chromatography with three different mobile phases showed a 5-hydroxytryptamine-like compound in extracts of mucosa-free small and large intestine but not of stomach.     

NO-Ergic Innervation of the Intestine of the Snow Sculpin Myoxocephalus brandti

Distribution, localization, and morphological peculiarities of NO-ergic nerve cells in the intestine of the snow sculpin Myoxocephalus brandti (Cottidae family) were studied using histochemical staining for NADPH-diaphorase ( NADPH-d). These cells were shown to be present in the pyloric appendages, middle and posterior parts of the intestine and in its rectal part. The NO-ergic cells are the most numerous in the myenteric plexus and circular muscle layer of all studied parts of the intestine. Single NO-ergic nerve cells are revealed in the submucosal plexus of pyloric appendages, middle and posterior parts of the intestine. No NO-ergic neural cells were found in subserosal and subepithelial plexuses, longitudinal layer of smooth muscle in all studied parts, and in the submucosal plexus of the rectal part of the intestine.     

Three-dimensional structures of c-Kit-positive cellular networks in the guinea pig small intestine and colon

Cryosections and whole-mount preparations of the guinea pig small intestine and colon were single or double immunolabeled using the anti-c-Kit and protein gene product 9.5 antibodies. Immunolabeled specimens were observed under a confocal laser scanning microscope. The main findings of the present study are: (1) the distribution and profiles of three-dimensional structures of c-Kit-positive cellular networks in the small intestine and colon, and (2) the anatomical relations of c-Kit-positive cells to the enteric nerves in the layers. In the small intestine, c-Kit-positive cellular networks were observed at levels of the deep muscular plexus and myenteric plexus. The c-Kit-positive cellular networks ran along or overlay the nerve fibers at the deep muscular plexus, while they showed the reticular structures intermingled with the nerve elements at the myenteric plexus. In the colon, c-Kit-positive cellular networks were observed at levels of the submuscular plexus and myenteric plexus, and were further identified within the circular and longitudinal muscle layers as well as in the subserosal layer. In the circular muscle layer, c-Kit-positive cells surrounded the associated nerve fibers and extended several long processes toward the adjacent c-Kit-positive cells. The c-Kit-positive cellular networks within the longitudinal muscle layer as well as in the subserosal layer were not associated with the nerve fibers. In the layers of the intestinal wall with c-Kit-positive cells, the cellular networks of the interstitial cells were identified in ultrastructure. The characteristic profiles of c-Kit-positive cellular networks provide a morphological basis upon which to investigate the mechanisms regulating intestinal movement. Received: 14 July 1998 / Accepted: 2 September 1998     

Structure of the tertiary component of the myenteric plexus in the guinea-pig small intestine

The tertiary component of the myenteric plexus consists of interlacing fine nerve fibre bundles that run between its principal ganglia and connecting nerve strands. It was revealed by zinc iodide-osmium impregnation and substance P immunohistochemistry at the light-microscope level. The plexus was situated against the inner face of the longitudinal muscle and was present along the length of the small intestine at a density that did not vary markedly from proximal to distal. Nerve bundles did not appear to be present in the longitudinal muscle as judged by light microscopy, although numberous fibre bundles were encountered within the circular muscle layer. At the ultrastructural level, nerve fibre bundles of the tertiary plexus were found in grooves formed by the innermost layer of longitudinal smooth muscle cells. In the distal parts of the small intestine, some of these nerve fibre bundles occasionally penetrated the longitudinal muscle coat. Vesiculated profiles in nerve fibre bundles of the tertiary plexus contained variable proportions of small clear and large granular vesicles; they often approached to within 50–200 nm of the longitudinal smooth muscle cells. Fibroblast-like cells lay between strands of the tertiary plexus and the circular muscle but were never intercalated between nerve fibre varicosities and the longitudinal muscle. These anatomical relationships are consistent with the tertiary plexus being the major site of neurotransmission to the longitudinal muscle of the guinea-pig small intestine.     

Calcitonin gene-related peptide neurons innervating the canine digestive system.

The pattern of nerve cells and fibers containing calcitonin gene-related peptide immunoreactivity (CGRP-IR) was investigated in the canine digestive tract by means of immunohistochemistry. CGRP-IR nerve fibers innervate all the layers of the gut, including the vasculature, with different densities depending on the region. CGRP-IR processes are sparse in the esophagus and stomach, where they are mostly confined to the enteric plexuses and vasculature. CGRP-IR fibers are quite abundant in the small and large intestine, where they form dense arborizations in the mucosa, and are numerous in the muscularis mucosae, deep muscular plexus and circular muscle. The myenteric and submucous plexuses of the intestine contain dense networks of CGRP-IR fibers and numerous CGRP-IR ganglion cells. On the other hand, in the enteric ganglia of the esophagus and stomach, in the intrapancreatic ganglia and in the ganglionated plexus of the gallbladder, CGRP-IR is restricted to non-varicose processes. A moderate density of CGRP-IR fibers supplies the endocrine and exocrine pancreas, and the fibromuscular layer and lamina propria of the gallbladder. The density of CGRP innervation in different regions can be summarized as follows: intestine > pancreas and gallbladder > or = antrum > cardia > gastric corpus and distal esophagus. CGRP- and tachykinin (TK)-IRs are colocalized in a substantial population of fibers, particularly those distributed to the mucosa, muscularis mucosae and vasculature, whereas there was no evidence of colocalization in intrinsic ganglion cells. The present results suggest that (1) the CGRP innervation of the dog digestive system includes an intrinsic and an extrinsic component, and (2) CGRP- and TK-IRs are co-expressed in extrinsic nerve fibers. These findings extend previous observations in rats and guinea pigs and provide insights into the sites of action of CGRP in the digestive system of the dog, which has served as a model for CGRP functional studies.     

c-kit immunoreactive interstitial cells of Cajal in the human small and large intestine

 c-kit immunohistochemistry was performed on unfixed frozen sections of human small (duodenum, jejunum, and ileum) and large intestine (ascending, transverse, descending, and sigmoid colon). The c-kit immunoreactive cells in the muscularis externa of the intestinal wall were identified as interstitial cells of Cajal (ICC) and mast cells. ICC were identified by their morphology, localization, and organization based on previous light and electron microscopic studies. In the small intestine, ICC were located primarily in relation to the myenteric plexus of Auerbach, but also in septa between circular muscle lamellae. In the large intestine, ICC were seen in relation to Auerbach’s plexus, but also and in great numbers in the circular muscle layer and in teniae of the longitudinal muscle layer. The morphology of the ICC was similar in the small and large intestine, but the pattern of distribution was obviously different. c-kit immunoreactive mast cells were found predominantly in the inner part of the circular muscle layer. The anti-c-kit method is found to be an easy and reliable method to study at least most of the interstitial cells of Cajal and thereby contribute to further normal and pathological studies. Accepted: 31 July 1997     

人胎大肠氮能神经元发育的研究

By using histochemical methed of NADPH-diaphorse, the development of the nitrergic neurons in the large intestine of human fetus were studied. The results showed: At the fifth month of gestation, weak positive reaction of nitric oxide synthase (NOS) appeared in part of the round cells of intermuscular ganglia. The round cells differentiated into the nitrergic nerve cells. At the sixth month, the bodies of nitrergic neurons were obviously enlarged, the processes of which were lengthened. The nitrergic nerve fibers were seen in the muscle layer, the submucosa and the base of the intestinal gland. The growth and development of nitrergic neurons reached its peak at the seventh month. The number of intermuscular ganglionic cells was increased. The density of nitrergic nerve fibers was increased in the inner circular muscle layer, and have bead-like structures. At the eighth to tenth month, the staining intensity of nitrergic neurons was increased. The myenteric plexus was densely distributed with nitrergic nerve cell bodies, whereas the submucosa and the inner circular muscle layers contained only a few neurons. The nitrergic nerve fibers were observed in all layer of large intestine, the density of the distribution of nitrergic nerve fibers was by far the highest in the inner circular muscle layer, less in the submucosa and outer longitudinal muscle layer, and only a few were found in the mucous layer. To our knowledge, it is the first time that the development of nitrergic neurons in the large intestine of human fetus was demonstrated.     

人胎大肠氮能神经元发育的研究

用NADPH-d组织化学法对人胎大肠氮能神经元的发育进行了观察.结果表明第5个月胎龄时,肌间神经节处圆形细胞中部分细胞出现一氧化氮合酶(NOS)阳性反应,并分化成氮能神经细胞.第6个月胎龄时,氮能神经元胞体增大,突起伸长,在肌层、粘膜下层和肠腺基部出现氮能神经纤维分布.第7个月胎龄时,氮能神经元生长发育达到高峰,肌间神经节细胞数目增多,环肌层神经纤维分布密度增加,膨体结构明显.第8-10个月胎龄时,氮能神经元染色强度加深,其胞体分布以肌间神经节最多,粘膜下层和内环肌层较少.氮能神经纤维的分布密度以内环肌层最高,粘膜下层和外纵肌层次之,粘膜层较低.本研究揭示了大肠氮能神经元发育的变化规律.     

Structure of the Digestive Tube in the Holothurian Eupentacta fraudatrix (Holothuroidea: Dendrochirota)

In the holothurian Eupentacta fraudatrix,the gut wall exhibits trilaminar organization. It consists of an inner digestive epithelium, a middle layer of connective tissue, and an outer mesothelium (coelomic epithelium). The pharynx, esophagus, and stomach are lined with a cuticular epithelium composed of T-shaped cells. The lining epithelium of the intestine and cloaca lacks a cuticle and consists of columnar vesicular enterocytes. Mucocytes are also encountered in the digestive epithelium. The connective tissue layer is composed of a ground substance, which houses collagen fibers, amoebocytes, morula cells, and fibroblasts. The gut mesothelium is a pseudostratified epithelium, which is dominated by peritoneal and myoepithelial cells and also includes the perikarya and processes of the neurons of the hyponeural plexus and vacuolated cells.     

Immunohistochemistry and nerve lesion experiments on the methionine-enkephalin immunopositive neurons in the small intestine of the bullfrog (Rana catesbeiana)

Summary Nerve elements in the small intestine of the bullfrog. Rana catesbeiana, were studied by immunohistochemistry with anti-methionine enkephalin antisera and by nerve lesion experiments, using laser irradiation. Methionine-enkephalin immunopositive nerve fibers occur in the myenteric plexus, circular muscle layer, submucosa, and mucosa. Immunopositive nerve cell bodies in the myenteric plexus have dendrite-like and a long axon-like processes. In the froglet (3 months after metamorphosis), these axon-like processes lead posteriorly in the nerve strand of the myenteric plexus. Some bifurcate, one branch continuing posteriorly, the other doubling back to lead anteriorly; both form terminal varicose fibers in the circular muscle layer. Nerve lesion experiments, in the adult bullfrog, resulted in accumulations of methionine-enkephalin immunoreactivity at the oral and hinder edges of the laser-irradiated necrotic area; there were sprouting and nonsprouting immunopositive stumps. It is suggested that bidirectional flow of methionine-enkephalin in the myenteric plexus is mediated via the anterior and posterior branches of the axon-like process. The difference in sprouting behavior of immunopositive nerve fiber stumps, after nerve lesion, is discussed with reference to regional differences of the axon-like process.     

Neuropeptides in the gastrointestinal canal of Necturus maculosus

Summary The presence and distribution of regulatory peptides in nerves and endocrine cells of the stomach, intestine and rectum of a urodele amphibian, the mudpuppy, Necturus maculosus, was studied immunohistochemically in sections or whole-mount preparations of the gut wall. The effect of the occurring peptides on gut motility was studied in isolated strip preparations of circular and longitudinal smooth muscle from different parts of the gut.Bombesin-, neurotensin-, substance P- and VIP-like immunoreactivity was present in abundant nerve fibres in the myenteric plexus of both stomach, intestine and rectum. Single fibres or bundles were present in the circular muscle layer and in a well-developed deep muscular plexus in the intestine and rectum. Immunoreactive nerve cells were found in the myenteric plexus of the stomach, intestine (neurotensin only) and rectum. Gastrin/CCK-like immunoreactivity was observed only in a few fibres in stomach and rectum.Endocrine cells containing bombesin-, met-enkephalin-, gastrin/CCK-, neurotensin-, somatostatin- or substance P- like immunoreactivity were present in the mucosa.The effect of bombesin was an inhibition of the rhythmic activity in circular muscle preparations and in longitudinal muscle from the rectum, while longitudinal muscle from the stomach usually responded with a weak increase in tonus. Neurotensin, like bombesin, was inhibitory on the spontaneous rhythmic activity of circular muscle throughout the gut, while the effect on longitudinal muscle was an increase in tonus. Met-enkephalin and substance P increased the tonus of all types of preparations, and often, in addition, initiated a rhythmic activity superimposed on this maintained tonus. VIP had a general inhibitory effect on the preparations, decreasing tonus and/or abolishing rhythmic activity.It is concluded that bombesin-, neurotensin-, substance P- and VIP-like peptides are present in nerves throughout the urodele gut and may have physiological functions in regulating the motility of the gut. The gastrin/CCK-like peptide present in nerves of the stomach and rectum may affect the function of these parts of the gut. The regulatory peptides present in endocrine cells may, perhaps with the exception of the somatostatin-like peptide, affect the motility humorally.     

Immunohistochemical study of 5-HT-containing neurons in the teleost intestine: relationship to the presence of enterochromaffin cells

Summary The formaldehyde-induced fluorescence technique had shown 5-hydroxytryptamine-containing enteric neurons in the intestine of the teleost Platycephalus bassensis, but did not reveal such neurons in the intestine of Tetractenos glaber or Anguilla australis. Re-examination of these animals with 5-hydroxytryptamine immunohistochemistry showed immunoreactive enteric neurons in the intestine of all three teleost species. The 5-hydroxytryptamine-containing enteric neurons showed essentially the same morphology in all species examined: the somata were situated in the myenteric plexus, extending down into the circular muscle layer, but none were found in the submucosa; processes were found in the myenteric plexus, the circular muscle layer and the lamina propria. It was concluded that the neurons may innervate the muscle layers or the mucosal epithelium, but were unlikely to be interneurons. In a range of teleosts, enterochromaffin cells were found in the intestine of only those species in which the formaldehyde technique did not visualize neuronal 5-hydroxytryptamine. Available evidence suggests that, in vertebrates, 5-HT-containing enterochromaffin cells are lacking only where there is an innervation of the gut mucosa by nerve fibres containing high concentrations of 5-HT.     

Ultrastructure of the Alimentary Canal in Five-Month-Old Pentactulae of the Holothurian Eupentacta fraudatrix

Five-month-old pentactulae (juveniles) of the holothurian Eupentacta fraudatrixpossess a well-developed alimentary canal comprising an esophagus, a stomach, an intestine, and a rectum. The intestine in turn consists of five parts. The esophagus, stomach, and rectum are lined with a cuticular epithelium. The intestinal lining lacks a cuticle and is composed of mainly polyfunctional vesicular enterocytes. Granular enterocytes are less abundant; their cytoplasm contains electron-dense granules, which are probably zymogenic. The gut connective tissue consists of electron-lucent ground substance with collagen fibers and embedded coelomocytes. The gut mesothelium is composed of myoepithelial and peritoneal cells and contains the neurons of the hyponeural nerve plexus.     

Immunohistochemical identification of serotonin and noradrenalin containing structures within the nerve plexuses of rat ileum

The distribution of 5-hydroxytryptamine (= serotonin = 5-HT) and noradrenalin (NA) in the enteric plexuses of the rat ileum was studied using immunocytochemical techniques. 5-HT-like immunoreactive fibers were observed only in the myenteric plexus, surrounding the ganglionic cells, which are all unreactive. NA-like immunoreactive fibers were present in all layers of the ileum: in the myenteric plexus, they were localized in the nodes, forming a network all round the neuronal perikarya; in the Meissner plexus, positive axons were arranged in a delicate network; submucosal blood vessels were often provided by NA-immunopositive nerve plexus. In the inner circular muscle layer the immunoreactive NA-positive fibers run within nerve bundles mainly parallel with the smooth muscle cells. The 5-HT immunoreactive material was depleted by treatment with reserpine; depletion of NA by 6-hydroxy-dopamine was also observed; on the contrary, no depletion of 5-HT by 5,7-dihydroxytryptamine was obtained. To confirm the validity of these results, specific antibodies to tyrosine hydroxylase (TH) and aromatic 1-aminoacid-decarboxylase (AADC), two enzymes involved in the synthesis of catecholamines, were used. In conclusion these experiments indicate that 5-HT is present, probably as a transmitter, in certain fibres of the rat myenteric plexus, distributed in a way similar to that of NA-containing fibers. However, at variance with NA fibers, 5-HT fibers are not present in other regions of the intestine wall.     

Distribution of NADPH Diaphorase-Positive Neurons in the Enteric Nervous System of the Rabbit Intestine

Nitric oxide (NO) has been proposed as an inhibitory transmitter in gastrointestinal muscle relaxation. We analyzed the distribution of nitric-oxide producing neurons in the rabbit intestine through nicotinamide-adenine-dinucleotide-phosphate-diaphorase histochemistry. By this reliable and convenient method, we visualized neuronal nitric-oxide-synthase, the enzyme responsible for nitric oxide generation, in the rabbit intestine. In the ileum and rectum, nitric-oxide-synthase-related diaphorase activity was present in the myenteric plexus ganglion cells, and in the nerve fibers in the internodal strand, secondary, and tertiary plexuses. These fibers were particularly abundant in the deep circular rather than in the outer longitudinal muscle layer. In the inner submucosal plexus, we found scarce labeled neurons. Labeled neural somata showed a range of sizes and shapes suggesting different functional roles. The present basic information is required to use the rabbit as an experimental animal in neurochemical NO enteric research.     

Ultrastructure of the Blood System in the Phoronid Phoronopsis harmeri Pixell, 1912: 1. Capillaries

Four types of blood capillaries of the phoronid Phoronopsis harmeri are described. These are capillaries of the tentacles, of the body, of the stomach plexus, and of the vasoperitoneal tissue. The wall of capillary consists of cells of the coelomic lining, a layer of extracellular matrix, and separate endothelial cells. Myoepithelial coelomic cells of tentacle capillaries contain cross-striated fibers. In capillaries of the body and the stomach plexus, the myofilaments are smooth. In the cells of the wall of vasoperitoneal tissue capillaries, myofilaments are lacking. The cells of the vessel wall of the tentacles, the body, and the vasoperitoneal tissue bear a single cilium. The cells of capillaries of the stomach plexus lack a cilium. The ultrastructure of erythrocytes and amebocytes is described. In the cytoplasm of erythrocytes, there is a basal body. It is assumed that erythrocytes originated from the ciliary cells of the wall of the blood vessels.     

Pivotal role of the interstitial cells of Cajal in the nitric oxide signaling pathway of rat small intestine. Morphological evidence

The nitric oxide (NO) signaling pathway is a major nonadrenergic-noncholinergic transmitter mechanism in the enteric nervous system. Our aim was to localize the enzymes in question, i.e., neuronal nitric oxide synthase (nNOS), soluble guanylate cyclase (sGC), and cGMP-dependent kinase type I (cGK-I) in rat small intestine by indirect immunofluorescence. nNOS staining was found in neurons of the myenteric plexus and in varicose nerve fibers mainly in the circular muscle layer. The cells positive for neurokinin-1 (NK-1) receptor and c-kit (interstitial cells of Cajal, ICC) in the deep muscular plexus (DMP) did not show nNOS reactivity, but nNOS-positive nerve fibers were directly adjacent to them. sGC was found in flattened cells surrounding myenteric ganglia (periganglionic cells, PGC), in ICC of the DMP, faintly in smooth muscle cells (SMC), and in cells perivascularly scattered throughout the circular muscle layer. cGK-I immunoreactivity was found abundantly in PGC (which presumably are ICC), in ICC of DMP, in SMC of the innermost circular and longitudinal muscle layers, but less intensively in the outer circular layer. Weak cGK-I staining occurred in nerve cells within the myenteric and submucosal plexus. Conclusively the key enzymes of the NO signaling pathway are differentially distributed: Occurrence of nNOS exclusively in neurons and the presence of sGC and cGK-I predominantly in ICC suggest a sequence of neuronal NO release, activation of ICC, and consecutive smooth muscle relaxation. ICC of the DMP seem to be the primary targets for neurally released NO.     

Nitric oxide synthase immunoreactivity in the enteric nervous system of the developing human digestive tract

We have investigated indirectly the presence of nitric oxide in the enteric nervous system of the digestive tract of human fetuses and newborns by nitric oxide synthase (NOS) immunocytochemistry and nicotinamide adenine dinucleotide phosphate diaphorase (NADPHd) histochemistry. In the stomach, NOS immunoactivity was confined to the myenteric plexus and nerve fibres in the outer smooth musculature; few immunoreactive nerve cell bodies were found in ganglia of the outer submucous plexus. In the pyloric region, a few nitrergic perikarya were seen in the inner submucous plexus and some immunoreactive fibres were found in the muscularis mucosae. In the small intestine, nitrergic neurons clustered just underneath or above the topographical plane formed by the primary nerve strands of the myenteric plexus up to the 26th week of gestation, after which stage, they occurred throughout the ganglia. Many of their processes contributed to the dense fine-meshed tertiary nerve network of the myenteric plexus and the circular smooth muscle layer. NOS-immunoreactive fibres directed to the circular smooth muscle layer originated from a few NOS-containing perikarya located in the outer submucous plexus. In the colon, caecum and rectum, labelled nerve cells and fibres were numerous in the myenteric plexus; they were also found in the outer submucous plexus. The circular muscle layer had a much denser NOS-immunoreactive innervation than the longitudinally oriented taenia. The marked morphological differences observed between nitrergic neurons within the developing human gastrointestinal tract, together with the typical innervation pattern in the ganglionic and aganglionic nerve networks, support the existenc of distinct subpopulations of NOS-containing enterice neurons acting as interneurons or (inhibitory) motor neurons.     

VIP-, substance P-, gastrin/CCK-, bombesin-, somatostatin- and glucagon-like immunoreactivities in the gut of the rainbow trout,Salmo gairdneri

Summary The presence of peptides in the gastrointestinal tract of the rainbow trout, Salmo gairdneri, was investigated immunocytochemically. VIP-like immunoreactivity was demonstrated in nerves in all layers of the stomach and the intestine, whereas substance P-like immunoreactivity was localized to endocrine cells, predominantly in the mucosa of the stomach, and to nerves mainly concentrated in the myenteric plexus throughout the gut. Endocrine cells reactive to gastrin/CCK antiserum were demonstrated in the intestinal mucosa, while no immunoreactivity was found in the stomach. Bombesin-immunoreactive and somatostatin-immunoreactive cells were localized in the stomach mucosa, and cells reactive to glucagon antiserum in the intestinal mucosa. Radioimmunoassay of stomach mucosa and muscle confirmed the presence of VIP-like and substance P-like immunoreactivity in these tissues, while gastrin/CCK-like immunoreactivity was low and bombesin-like immuno-reactivity was insignificant. In conclusion, molecules resembling the mammalian brain-gut peptides may be involved in the neuronal and hormonal control of gut function in fish.