Neuropeptides in the intestine of two teleost species (Oreochromis mossambicus, Carassius auratus): Localization and electrophysiological effects on the epithelium

Autonomic control of gut motility: a comparative view

Gut motility is regulated to optimize food transport and processing. The autonomic innervation of the gut generally includes extrinsic cranial and spinal autonomic nerves. It also comprises the nerves contained entirely within the gut wall, i.e. the enteric nervous system. The extrinsic and enteric nervous control follows a similar pattern throughout the vertebrate groups. However, differences are common and may occur between groups and families as well as between closely related species. In this review, we give an overview of the distribution and effects of common neurotransmitters in the vertebrate gut. While the focus is on birds, reptiles, amphibians and fish, mammalian data are included to form the background for comparisons. While some transmitters, like acetylcholine and nitric oxide, show similar distribution patterns and effects in most species investigated, the role of others is more varying. The significance for these differences is not yet fully understood, emphasizing the need for continued comparative studies of autonomic control.

Histopathology and ultrastructure of Platichthys flesus naturally infected with Anisakis simplex s.l. larvae (Nematoda: Anisakidae)

The histopathology, ultrastructure, and immunohistochemistry of the alimentary canal of flounder Platichthys flesus (L.), naturally infected with the nematode Anisakis simplex s.l. (Rudolphi 1809) from the River Forth (Scotland), were investigated and described. Eight of the 16 flounders were infected with A. simplex s.l. larvae (L3); parasites were encapsulated by serosa on the external surface of the host's digestive tract (intensity of infection 1-8 parasites per host), although nematode larvae were found encysted under the peritoneal visceral serosa of the host spleen and liver and, occasionally, in the liver parenchyma (intensity of infection 3-10 parasites per host). In all sites, different structural elements were recognized within the capsule surrounding larvae. Among the epithelial cells of the intestine of 5 flounders with larvae encysted on external surface of the gut, the presence of several rodlet cells (RCs) was observed. Furthermore, often the occurrence of macrophage aggregates (MAs) was noticed in infected liver and spleen, mainly around the parasite larvae. Eight neuropeptide antisera were tested with immunohistochemistry methods on gut sections of 4 P. flesus infected with extraintestinal nematodes. Sections from the gut of 5 uninfected flounder were used for comparative purposes. In the tunica mucosa of parasitized P. flesus, several endocrine epithelial cells were immunoreactive to anti-CCK-39 (cholecystokinin 39) and -NPY (neuropeptide Y) sera; furthermore, in the myenteric plexus, a high number of neurons were immunoreactive to antibombesin, -galanin, and several to -NPY and -PHI (peptide histidine isoleucine) sera.

Structure and autonomic innervation of the swim bladder in the zebrafish (Danio rerio)

Many teleosts actively regulate buoyancy by using a gas-filled swim bladder, which is thought to be under autonomic control. Here we investigated the swim bladder in the zebrafish to determine possible mechanisms of gas-content regulation. Fluorescently labelled phalloidin revealed myocytes that appeared to form a possible sphincter at the junction of the pneumatic duct and esophagus. Myocytes also formed thick bands along the ventral surface of the anterior chamber and bilaterally along the posterior chamber. Thinner layers of myocytes were located elsewhere. Staining of peroxidase within erythrocytes revealed a putative rete and smaller blood vessels in muscle bands and elsewhere. The antibodies zn-12, a general neuronal marker, and SV2, a synaptic vesicle marker labelling presynaptic terminals, revealed widespread innervation of the swim bladder system. Widespread innervation of the swim bladder was also indicated by acetylcholinesterase histochemistry, but choline acetyltransferase-immunoreactive (-IR) somata and fibers were limited to the junction of the pneumatic duct and esophagus. In contrast, varicose tyrosine hydroxylase-IR fibers innervated muscles and blood vessels throughout the system. Neuropeptide Y-IR somata were located near the junction of the duct and esophagus and varicose fibers innervated muscles and vasculature of the posterior chamber and duct. Vasoactive intestinal polypeptide immunoreactivity was abundant throughout the anterior chamber but sparsely distributed elsewhere. Serotonin-IR fibers and varicosities were located only along blood vessels near the junction of the pneumatic duct and posterior chamber. Our results suggest that the zebrafish swim bladder is a complex and richly innervated organ and that buoyancy-regulating effectors may be controlled by multiple populations of autonomic neurons.

An immunohistochemical study on the neuroendocrine system in the alimentary canal of the brown trout, Salmo trutta, L., 1758

Several neurohormonal peptides of the gastrointestinal system of fish have been revealed by immunohistochemical methods. Among salmonids, the rainbow trout, Oncorhynchus mykiss (Walbaum) is the most studied species, whereas the informations about other species of the taxonomic group are lacking. The regional distribution and relative densities of cells belonging to the neuroendocrine system have been in this paper demonstrated in the gut of the brown trout, Salmo trutta Linnaeus. In the gastric mucosa, endocrine cells were detected, which were immunoreactive to bombesin-, gastrin-, and secretin-antisera. Endocrine cells containing gastrin-, bombesin-, cholecystokinin-8-, glucagon-, and leptin-like immunoreactivities were present in the pyloric caeca and intestine. The pancreatic endocrine islets contained glucagon-, and, possibly, secretin-like-immunoreactive endocrine cells, as well as a contingent of galanin-like-immunoreactive nerve fibres. The exocrine pancreatic parenchyma showed bombesin-like-immunoreactive nerve fibres. Within the tested regulatory peptides, bombesin and leptin were observed in both endocrine cells and nerve cell bodies and fibres. Leptin was in addition detected in epithelial cells of the gastric glands. In the brown trout we have never observed any immunoreactivity to the VIP antiserum (either in the stomach or in the intestine). Some special structural patterns (in particular those ones related to galanin- and leptin-immunohistochemical data) have thus been detected for the first time in the brown trout, and provide further data for a better knowledge of gut morpho-functional aspects in this economically important fish.

The presence of a galanin-like peptide in the gut neuroendocrine system of Lampetra fluviatilis and Acipenser transmontanus: an immunohistochemical study

Galanin is a brain-gut neuropeptide present in the central and peripheral nervous systems of vertebrates. In the present survey, the galaninergic and the diffuse endocrine systems of the alimentary canal of the river lamprey, Lampetra fluviatilis, and the white sturgeon, Acipenser transmontanus, were studied by immunohistochemistry. The results show the presence of galanin-like immunoreactive endocrine cells in the gut of L. fluviatilis. In addition, a galanin-like immunoreactivity was detected in enteric intramural neurons of both species. It is conceivable that the galaninergic system plays in both species a role in the regulation of the gut muscle contractility and in the modulation of mucosal secretive/absorptive processes. In A. transmontanus, the presence of galanin-like immunoreactive nerve fibres associated with components of the gut associated-lymphoid tissue is possibly correlated with a control of the defensive events at this site. The presence of a galanin-like immunoreactivity in the neuroendocrine system of these two ancient fishes confirms the hypothesis on the early occurrence of this regulative molecule in the gastro-enteric system of vertebrates.

Effect of calcitonin gene related peptide on the adenylate cyclase activity in abalone gill membranes

The aim of the present study was to investigate and to compare the effect of calciotropic hormones, human calcitonin gene related peptide (CGRP) I and II, salmon calcitonin (CT) and human amylin on the adenylate cyclase activity in abalone gill membranes. In addition to human CGRPI, human CGRPII and salmon CT stimulated the adenylate cyclase activity. No effect was observed with amylin. The higher effect was observed with human CGRPI and II that induced a 160-170% increase of the enzyme activity. Fifty percent of the maximal activity was observed with 3 and 8 nM of CGRP I and II, respectively. Salmon CT induced a lower effect: the maximal activity was obtained with a hormone concentration of 266 nM and represented a 130% stimulation of the basal activity. In the presence of CGRP 8-37, a competitive antagonist of CGRP action, the stimulation observed with CGRPI was abolished and returned to the basal level. This study points out that, in invertebrates, CGRP receptors present in gill membranes are linked to an adenylate cyclase system similar to that described in vertebrates. In addition, these data are in favour of a role for CGRP in branchial function both in non-mammalian vertebrates and invertebrates

Co-localization of Trk neurotrophin receptors and regulatory peptides in the endocrine cells of the teleostean stomach

Recently it has been observed that a subpopulation of gut endocrine cells in vertebrates express Trk-like proteins, suggesting that neurotrophins could regulate the synthesis and storage of amines and peptides of these cells. Nevertheless, the peptides and amines present in the endocrine cells that express Trks have not been characterized. In this study we used immunohistochemistry to investigate the occurrence of Trk-like proteins (TrkA-like, TrkB-like and TrkC-like) and the possible co-localization of these with peptides and/or biogenic amines in the endocrine cells of the stomach of three teleost (bass, gilt-head and scorpionfish). No TrkA-like immunoreactivity (IR) was detected in the stomach of these species, whereas TrkB-like IR and TrkC-like IR were observed in numerous cells of the gastric epithelium. TrkB-like immunoreactive cells were present in all three species examined, and were particularly abundant in the blind sac. Conversely, TrkC-like immunoreactive cells were found only in the bass stomach, apparently co-localized with TrkB-like IR. TrkB-like IR was found co-localized with somatostatin IR in scorpionfish, and with somatostatin and CGRP IR in gilt-head and bass. Gastric endocrine cells expressing 5-HT, glucagon, insulin, met-, leu-enkephalin, substance P, PYY, VIP, CCK, NPY, bombesin and motilin were unreactive for Trk-like proteins. The present results provide direct evidence for the occurrence of Trk-like neurotrophin receptor proteins in a subpopulation of the teleostean gastric endocrine cells and suggest that neurotrophins could regulate, as in neurons, the expression of some neuropeptides such as somatostatin and CGRP.

Contrasting cardiovascular effects following central and peripheral injections of trout galanin in trout

Little is known about the role of galanin (Gal) in fish. In the present study, cardiovascular effects of central and peripheral administrations of a synthetic replicate of trout Gal (tGal) were investigated in the unanesthetized trout. Intracerebroventricular injection of 0.1, 0.5, 1.0, and 3.0 nmol/kg body mass of the peptide demonstrated that the two highest doses tested produced a significant (P < 0.001) and equivalent increase in mean dorsal aortic blood pressure (PDA) without changing heart rate (HR). At a dose of 1.0 nmol/kg, the systemic vascular resistance (Rs) increased, but no change was detected in cardiac output compared with that produced by intracerebroventricular injection of vehicle only. In contrast, intra-arterial injections of 0.1, 0.5, and 1.0 nmol/kg body mass of tGal produced a dose-dependent decrease in PDA with a threshold dose for significant effects observed at a dose of 0.5 nmol/kg. None of the doses tested changed HR. At a dose of 1 nmol/kg, a significant decrease in Rs (P < 0.001) was the factor responsible for the fall in PDA. Intra-arterial injection of porcine Gal (1 nmol/kg) produced a change in PDA similar to that of the same dose of tGal, but HR increased slightly. Pretreatments of trout with the cyclooxygenase inhibitors indomethacin and meclofenamate did not inhibit the vasodepressor effects of tGal. However, after intra-arterial injection of NG-nitro-L-arginine methyl ester, an inhibitor of nitric oxide synthase, the hypotensive action of Gal was reduced threefold, suggesting the possible involvement of the nitric oxide system in mediating the vasodilatory effect of Gal. In conclusion, our results have shown that tGal may have contrasting cardiovascular regulatory functions in trout depending on whether its site of action is the brain or the peripheral circulation.

Ontogeny of serotonin-immunoreactive cells in the gut epithelium of the cloudy dogfish, Scyliorhinus torazame, with reference to coexistence of serotonin and neuropeptide Y

The ontogeny of serotonin (5-HT)-immunoreactive (IR) cells in the gut epithelium of an oviparous elasmobranch, Scyliorhinus torazame, was examined immunohistochemically. 5-HT-IR cells first appeared in the proximal part of the vitellointestinal duct (VID) and in the anterior part of the midgut of the embryo (30 mm in total length). At the 40-mm stage, the cells slightly increased in number and spread to the posterior part of the midgut, but no labeled cells were found in the foregut or hindgut. By the late embryonic (74- and 80-mm) stages, 5-HT-IR cells were markedly increased in number in the spiral intestine and stomach, whereas they were few in the VID and rectum. During these stages, the density of the cells in the inner yolk sac, the derivative of the VID, tended to be increased. This tendency seemed to be consistent in the posthatching juveniles at the 95-mm stage. In juveniles, 125 mm in length and 1.7 months after hatching, the cells further increased in number in the spiral intestine, reaching their adult value. Double immunostaining by the use of anti-5-HT and -neuropeptide Y (NPY) antisera demonstrated that some of the 5-HT-IR cells were also positive for NPY.

Ontogenetic development of neuropeptide Y-like-immunoreactive cells in the gastroenteropancreatic endocrine system of the dogfish

This immunocytochemical study was carried out to elucidate the ontogenetic development of neuropeptide Y-like-immunoreactive cells in the gastroenteropancreatic endocrine system of the cloudy dogfish, Scyliorhinus torazame. Immunostained cells first appeared in the pancreas of the embryo at the 15-mm stage, and were also detected in the vitello-intestinal duct of the yolk stalk at the 20-mm stage. These cells were polymorphic, with occasional processes that were sometimes directed toward the vascular wall or into the cavity of the vitello-intestinal duct. At the 34-mm stage, immunostained cells could also be found in the proximal part of the spiral intestine and, by the 74-mm stage, immunopositive cells were present in the gastric mucosa. In the gut and pancreas, the cells gradually increased in number with development, whereas in the vitello-intestinal duct and internal yolk sac, they decreased and seemed to disappear following hatching. Thus, in juveniles, the distribution of the neuropeptide Y-like-immunoreactive cells in the gastroenteropancreatic endocrine system had attained that of adults. Electron-microscopic immunocytochemistry demonstrated that, in the labeled cells of the vitellointestinal duct, the neuropeptide Y-like antigen was located in cytoplasmic granules, as in the cells of the gut and pancreas.

The galanin-induced feeding stimulation is mediated via alpha 2-adrenergic receptors in goldfish

In the present study we examined the effects of intracerebroventricular (ICV) or intraperitoneal (IP) galanin administration on food intake in satiated goldfish, at different time intervals after injections, 0-2, 2-8 and 0-8 h. We found that food intake was increased by ICV administered galanin (1 and 3.33 micrograms) at 2 and 8 h postinjection, while no modifications on feeding were observed after intraperitoneal injection in any of the studied time intervals. The galanin receptor antagonist, galantide, blocked the galanin-induced feeding increase. Pretreatment with yohimbine (alpha 2-adrenergic receptor antagonist), but not with prazosin (alpha 1-adrenergic receptor antagonist) antagonized the stimulatory effect of galanin on ingestive behavior. These results suggest that galanin is involved in the central regulation of feeding in goldfish, being the food intake stimulatory effect mediated by the alpha 2-adrenergic system.

Endogenous opiates: 1993

This paper is the sixteenth installment of our annual review of research concerning the opiate system. It is restricted to papers published during 1993 that concern the behavioral effects of the endogenous opiate peptides, and does not include papers dealing only with their analgesic properties. The specific topics this year include stress; tolerance and dependence; eating; drinking; gastrointestinal, renal, and hepatic function; mental illness and mood; learning, memory, and reward; cardiovascular responses; respiration and thermoregulation; seizures and other neurological disorders; electrical-related activity; general activity and locomotion; development; immunological responses; and other behaviors.