Vasoactive intestinal polypeptide (VIP)-like immunoreactivity in anuran intestine

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.

Comparative distribution of VIP in the central nervous system of various species measured by a new radioimmunoassay

Vasoactive intestinal polypeptide (VIP) occurs in high concentrations throughout the gut and the nervous system. The presence of VIP has been shown in a number of species, mainly by immunohistochemistry. The aim of the present study was to develop a new, highly specific VIP radioimmunoassay to investigate the distribution of VIP in the central nervous system of various vertebrate and invertebrate species. Different areas of the brain and spinal cord were removed from rats, chickens, turtles, frogs and fishes. The cerebral ganglia and the ventral ganglionic chain were investigated in the earthworm. The tissue samples were processed for VIP radioimmunoassay. Our results show that the antiserum used in the radioimmunoassay turned to be C-terminal specific, without significant affinity to other members of the VIP peptide family. Detection limit of the assay was 0.1 fmol/ml. Highest concentrations were found in the turtle diencephalon, followed by other brain areas in the turtle and rat. All other brain areas in the examined species contained significant levels of VIP. Immunoreactivity was also shown in the cerebral and ventral ganglia of the earthworm. In summary, our results show comparative quantitative distribution in representative species of the phylogenetic line, using the same experimental conditions.

Distribution of vasoactive intestinal peptide-like immunoreactivity in the brain and pituitary of the frog (Rana esculenta) during development

The localization of vasoactive intestinal peptide (VIP)-like immunoreactive (ir) elements was investigated in the brain of the anuran amphibian, Rana esculenta, during development. Using an antiserum raised against the porcine VIP, ir cell bodies and fibers were observed in the forebrain of tadpoles a few days after hatching. During early premetamorphosis, ir perikarya were distributed in the ventral infundibular nucleus of the hypothalamus and in the posterocentral nucleus of the thalamus. Labeled fibers were detected in the olfactory bulbs and in the hypothalamus. In these larvae, furthermore, several VIP-ir cells were found in the pars distalis of the pituitary and there were ir fibers in the pars nervosa. In tadpoles at stages VIII-IX, a new group of VIP-labeled neurons was observed in the dorsal part of the infundibular nucleus. In other brain regions, the distribution of the immunoreactivity was similar to that described in the earliest stages, i.e., IV-VII. During mid-premetamorphosis, stages X-XII of development, an additional set of ir perikarya appeared in the ventrolateral area of the thalamus. During late premetamorphosis, stages XIII-XVIII, the organization of VIP-like immunoreactivity was more complex and its distribution more widespread. Two new groups of ir cell bodies appeared, one in the preoptic nucleus and another in the anteroventral area of the thalamus, and for the first time, VIP immunoreactivity was observed in the median eminence. This distribution pattern persisted through to the prometamorphic, four-limb stage. Strikingly, no VIP-ir elements were observed anywhere in the mid- and hindbrain. The present results indicate that a VIP-like ir peptide may be involved in the processing of olfactory information or may act as a neurohormone, hypophysiotropic factor, and neuromodulator in the brain of R. esculenta during development.

Relationships between nitric oxide synthase, vasoactive intestinal peptide and substance P immunoreactivities in neurons of the amphibian intestine

Nitric oxide synthase (NOS)-containing neurons (localized using NADPH diaphorase histochemistry or NOS immunoreactivity) and vasoactive intestinal peptide-immunoreactive (VIP-IR) neurons were found in the myenteric plexus of the gastrointestinal tract of the amphibian, Bufo marinus. Only limited co-localization of the two substances was observed in nerve cell bodies, about 11% of the NOS-containing neurons were also labelled by VIP-IR and about 37% of VIP-IR nerve cell bodies contained NOS. The relationship between VIP, NOS and SP-IR in nerve fibres in the circular muscle was examined. There was partial co-localization of VIP and NOS, but no co-localization of NOS or VIP with substance P. Of fibres that were immunoreactive for VIP or NOS, fewer than 10% contained VIP alone.

Immunocytochemical and ultrastructural characterization of endocrine cells and nerves in the intestine of Rana temporaria

Endocrine cells have been identified in the intestine of the frog Rana temporaria after application of the Grimelius and Masson-Fontana techniques. These endocrine cells were examined using immunocytochemical techniques on paraffin and semithin sections for light microscopy. After testing 19 antisera, 12 immunoreactivities were identified. Numerous serotonin-, somatostatin- and GLP-1-immunoreactive cells; a moderate number of PYY-, glucagon-, VIP-, gastrin/CCK-immunoreactive cells and few human PP-, bombesin-, substance P- and neurotensin-immunoreactive cells were found. VIP- and met-enkephalin were identified in nerve fibers of the muscular layer. Using semithin-thin sections five types of endocrine cells (serotonin-, somatostatin-, gastrin/CCK-, glucagon- and bombesin-immunoreactive cells) have been characterized according to their immunocytochemical reaction and the ultrastructure of the secretory granules.

Movements of the large intestine in the anuran larvae, Xenopus laevis

1. The contractile behavior of the large intestine of Xenopus laevis tadpoles was studied. 2. The large intestine is divided into a colon and rectum, and shows three types of movements: rhythmic ascending (antiperistaltic) waves of contraction originating at the anal end of the large bowel, rhythmic longitudinal contractions in the rectum and colon, and irregular contractions. The first two patterns occur in the large bowel in situ and thus appear mature. The last one occurred only in older preparations, and thus appeared pathological. 3. Antiperistaltic waves of contractions and longitudinal contractions are generated independent of each other, suggesting that circular muscles and longitudinal muscles contract separately. 4. Acetylcholine, adrenaline and noradrenaline augment motility. 5. The premetamorphic motility of the large bowel is similar to that seen in adult frogs. Comparable motility was not observed elsewhere in the larval alimentary tract. The large intestine appears to be the first portion of the anuran alimentary tract to acquire the adult physiological and morphological profile.

The autonomic innervation of Rana ridibunda intestine

1. The innervation of Rana ridibunda intestine has been studied by the following methods: (a) demonstration of cholinesterase activity; (b) FIF method for catecholamines; (c) immunohistochemistry for VIP, SP and SOM, and (d) conventional electron microscopy. 2. The intrinsic intestinal innervation is represented by cholinergic-, VIPergic-, SP- and SOM-like plexuses. The intestinal adrenergic component is of extrinsic origin. 3. The intestinal peptidergic innervation is the most developed, the large intestine being the portion where the studied peptidergic plexuses are more widely distributed. 4. Against a poorly developed cholinergic/adrenergic innervation, it seems that there is a predominant peptidergic innervation in the amphibians intestine wall. 5. Taking into account that amphibians sacral parasympathetic as well as sympathetic innervation development are limited, it could be considered that in vertebrates the intestinal peptidergic innervation is phylogenetically earlier and hence better developed.

Isolation and partial sequence of elasmobranch VIP

We have used a combination of gel filtration, ion exchange chromatography and reversed-phase HPLC to isolate and characterize a VIP-related peptide from the gut of the elasmobranch Scyliorhinus canicula. The N-terminal decapeptide of the Scyliorhinus material was identical with that of porcine VIP. However, Scyliorhinus VIP did not cross react with antisera specific for the C-terminus of porcine VIP. Like porcine VIP, Scyliorhinus VIP was a potent stimulant of exocrine pancreatic secretion in the turkey, but the response to Scyliorhinus VIP had a shorter duration. VIP from a second elasmobranch, Squalus acanthius was partially purified, and had biological and immunochemical properties similar to those of Scyliorhinus VIP. The results indicate that elasmobranch VIP is identical to porcine VIP at its N-terminus, but differs at the C-terminus. These structural differences may influence the rate of metabolism of the peptide.

The enteric nervous system of Rana ridibunda stomach

The innervation of Rana ridibunda stomach has been studied by the following methods: demonstration of cholinesterase activity; FIF method for catecholamines; immunohistochemistry for VIP; SP and SOM and conventional electron microscopy. The cholinergic innervation is important in the stomach wall where in addition to the intrinsic plexuses there is an extrinsic contribution coming with the vagus nerve. The density of the fibres decreases towards the pyloric sphincter. The adrenergic innervation seems to be almost entirely of extrinsic origin. Fine networks have been localized at the myenteric and submucosal plexuses. The fibres density increases at the pylorus. At the myenteric plexus, apart from the cholinergic neurons, we have found VIP and SOM like cells. The VIP like plexus is very well developed. A SOM like plexus is also present but with scarce fibres in comparison with the VIPergic one. The submucosal plexus is exclusively made by nervous fibres of the types described for the myenteric one. We have got positive immunoreactivity for SP only on the fibres. They are scarce in the stomach wall, only at the pyloric region their density increases. We describe the ultrastructural morphological characteristics of the enteric neurons as well as the fine inter-relationships between the nervous elements and the functional components of the stomach wall.

Purification and characterisation of VIP from two species of dogfish

Acid extracts of intestine from the dogfish Scyliorhinus canicula and Squalus acanthius were purified by gel filtration, ion exchange chromatography, and reversed-phase HPLC. In radioimmunoassays, VIP-like material from both species of dogfish cross reacted with N-terminal, but not C-terminal antisera. Like porcine VIP, both Scyliorhinus and Squalus VIP were stimulants of exocrine pancreatic secretion in the turkey. The time course of the responses to dogfish VIP were, however, different from that seen with porcine VIP. The present study has developed methods for the isolation of VIP-like peptides from elasmobranchs and has demonstrated that elasmobranch VIP differs from Porcine VIP in the C-terminal region, and that these differences may affect biological activity.

An immunocytochemical study of endocrine pancreas of snakes

The pancreas from eleven species of snakes representing both advanced and primitive families has been investigated for the presence of eleven regulatory peptides reported to occur in the mammalian endocrine pancreas. Of the eleven peptides studied, insulin, pancreatic glucagon and somatostatin were present in endocrine cells within the islets of all the species investigated. The neuropeptide, vasoactive intestinal polypeptide, was located within nerve terminals innervating the islets in the Boidinae, Colubrinae, Elaphidae and Crotalidae but absent from the Natricinae investigated. No immunoreactivity was demonstrable with the antisera to substance P, met-enkephalin, C-terminal gastrin, bombesin, glicentin and gastric inhibitory polypeptide. Pancreatic polypeptide-like immunoreactivity was demonstrable only in the boid snakes and exclusively stained by a C-terminal specific antiserum.

The endocrine pancreas of Alligator mississippiensis. An immunocytochemical investigation

Immunocytochemical methods for light and electron microscopy were used to demonstrate the regulatory peptides present in the endocrine pancreas of the alligator, Alligator mississippienses. The peptides studied included insulin, glucagon (pancreatic and enteric), somatostatin, pancreatic polypeptide (avian, bovine and human), vasoactive intestinal polypeptide, substance P, metenkephalin, beta-endorphin, C-terminal gastrin/CCK and gastric inhibitory polypeptide. Endocrine cells were detected using antisera to insulin, pancreatic glucagon, somatostatin and avian pancreatic polypeptide, whereas peptidergic nerves were stained with antisera to vasoactive intestinal polypeptide. All other antisera were unreactive in the alligator pancreas. The peptide-containing structures were identified ultrastructurally by both the semithin/thin and immuno-gold methods. The results showed that five of the regulatory peptides commonly detected in the mammalian pancreas were immunologically recognisable in the alligator. In addition, the ultrastructural appearance of the peptide-containing cells was clearly distinct from that reported in mammals.