Pituitary adenylate cyclase-activating polypeptide in intrinsic and extrinsic nerves of the rat pancreas

Pituitary adenylate cyclase-activating polypeptide (PACAP) is the latest member of the vasoactive intestinal polypeptide (VIP) family of neuropeptides present in nerve fibres in many peripheral organs. Using double immunohistochemistry, with VIP as a marker for intrinsic innervation and calcitonin-gene related peptide (CGRP) as a marker for mainly extrinsic innervation, the distribution and localization of PACAP were studied in the rat pancreas. PACAP was demonstrated in nerve fibres in all compartments of the pancreas and in a subpopulation of intrapancreatic VIP-containing ganglion cells. PACAP and VIP were co-stored in intra- and interlobular nerve fibres innervating acini, blood vessels, and in nerve fibres within the islets of Langerhans. No PACAP immunoreactivity was observed in the islet cells. Another population of PACAP-immunoreactive nerve fibres co-localized with CGRP innervated ducts, blood vessels and acini. PACAP/CGRP-positive nerve fibres were also demonstrated within the islets. Neonatal capsaicin reduced the PACAP-38 concentration by approximately 50%, and accordingly a marked reduction in PACAP/CGRP-immunoreactive nerve fibres in the exocrine and endocrine pancreas was observed. Bilateral subdiaphragmatic vagotomy caused a slight but significant decrease in the PACAP-38 concentration compared with controls. In conclusion, PACAP-immunoreactive nerve fibres in the rat pancreas seem to have dual origin: extrinsic, most probably sensory fibres co-storing CGRP; and intrinsic, constituting a subpopulation of VIP-containing nerve cell bodies and fibres innervating acinar cells and islet cells. Our data provide a morphological basis for the reported effects of PACAP in the pancreas and suggest that PACAP-containing nerves in the rat pancreas may have both efferent and sensory functions.     

Nitric oxide synthase-containing, peptide-containing, and acetylcholinesterase-positive nerves in the cat lower oesophagus

Summary The innervation of the cat lower oesophagus, including the lower oesophageal sphincter, was studied by enzyme histochemistry, immunohistochemistry, and confocal microscopy. In the lower oesophageal sphincter, and at a level 2 cm above it, no apparent differences were seen in the nerve distribution pattern. Among the nerve populations studied, acetylcholinesterase (AChE)-positive nerves were the most abundant in both these regions. The density of AChE-positive nerves was particularly marked in the circular muscle layer. A rich supply of nitric oxide synthase (NOS)-containing nerves was identified by using an antiserum against neuronal NOS, or by enzyme histochemical staining for NADPH diaphorase activity. Vasoactive intestinal peptide (VIP)-immunoreactive nerves had a similar distribution pattern as NOS-immunoreactive nerves, and nerves displaying immunoreactivity for NOS and VIP often showed profiles coinciding with AChE-positive nerves. As judged by confocal microscopy, immunoreactivities for helospectin, pituitary adenylate cyclase-activating peptide (PACAP) and VIP, to a large extent were found in the same nerves. At a level 7 cm above the lower oesophageal sphincter, the total nerve supply was less than in the sphincter itself and 2 cm above it. Immunoreactivity towards VIP, PACAP and helospectin was also found to co-exist with NOS and neuropeptide Y within the same nerve structures. It is concluded that there is an intricate innervation pattern in the feline lower oesophagus reflecting the complexity in the regulation of its motility.     

Distribution of PACAP (pituitary adenylate cyclase-activating polypeptide)-like and helospectin-like peptides in the teleost gut

Pituitary adenylate cyclase-activating polypeptide (PACAP) and helospectin are two vasoactive intestinal polypeptide (VIP)-related neuropeptides that have recently been demonstrated in the mammalian gut; the aim of this study was to reveal their occurrence and localisation in the gastrointestinal tract, swimbladder, urinary bladder and the vagal innervation of the gut of teleosts, using immunohistochemical methods on whole-mounts and sections of these tissues from the Atlantic cod, Gadus morhua and the rainbow trout, Oncorhynchus mykiss. Both PACAP-like and helospectin-like peptides were present in the gut wall of the two species. Immunoreactive nerve fibres were found in all layers but were most frequent in the myenteric plexus and along the circular muscle fibres. Immunoreactivity was also demonstrated in nerves innervating the swimbladder wall, the urinary bladder and blood vessels to the gut. Immunoreactive nerve cell bodies were found in the myenteric plexus of the gut and in the muscularis mucosae of the swimbladder. In the vagus nerve, non-immunoreactive nerve cells were surrounded by PACAP-immunoreactive fibres. Double staining revealed the coexistence of PACAP-like and helospectin-like peptides with VIP in all visualized nerve fibres and in some endocrine cells. It is concluded that PACAP-like and helospectin-like peptides coexist with VIP in nerves innervating the gut of two teleost species. The distribution suggests that both PACAP and helospectin, like VIP, are involved in the control of gut motility and secretion.     

Innervation of the rat pineal gland by pituitary adenylate cyclase-activating polypeptide (PACAP)-immunoreactive nerve fibres

Pituitary adenylate cyclase-activating polypeptide (PACAP)-immunoreactive nerve fibres were demonstrated in the rat pineal gland. These fibres entered the pineal gland through the conarian nerve at the distal tip of the gland. A high density of the fibres was observed in the capsule of the gland, from where the immunoreactive elements penetrated into the pineal perivascular spaces and parenchyma. The majority of PACAP-immunoreactive nerve fibres also contained calcitonin gene-related peptide (CGRP). Some PACAP-immunoreactive nerve fibres contained neuropeptide Y (NPY), but only occasionally was PACAP colocalized with vasoactive intestinal peptide (VIP). After removal of both superior cervical ganglia, a high number of PACAP-containing nerve fibres were still present in the gland. In the nervous system PACAP is present in two isoforms, PACAP-38 and PACAP-27. The concentration of PACAP-38 in the superficial pineal gland was determined by radioimmunoassay to be 20.4 pmol/g tissue at midday and 18.9 pmol/g tissue at midnight. The concentration of PACAP-27 was only about 3% of the concentration of PACAP-38. In summary, this study is the first demonstration of a PACAP-containing innervation of the rat pineal gland. The PACAP concentration in the pineal gland does not exhibit a day-night difference. The colocalization of PACAP with calcitonin gene-related peptide in the pincalopetal nerve fibres indicates that the majority of PACAP-immunoreactive nerve fibres might originate from the trigeminal ganglion.     

Neurotrophin receptors and enteric neuronal development during metamorphosis in the amphibian<Emphasis Type="Italic"> Xenopus laevis</Emphasis>

During metamorphosis, the frog intestine goes through a dramatic shortening with extensive apoptosis and regeneration in the epithelial layer and connective tissue. Our aim was to study changes in the enteric nervous system represented by one inhibitory (vasoactive intestinal polypeptide; VIP) and one excitatory (substance P, neurokinin A; SP/NKA) nerve population and concomitant changes in neurotrophin receptor occurrence during this development in the gut of Xenopus laevis adults and tadpoles at different stages of metamorphosis (NF stages 57–66). Sections were incubated with antibodies against the neurotrophin Trk receptors and p75^NTR, and the neurotransmitters VIP and SP/NKA. Trk-immunoreactive nerves increased dramatically but transiently in number during early metamorphic climax. Nerves immunoreactive for p75^NTR were present throughout the gut, decreased in number in the middle intestine during climax, and increased in the large intestine during late metamorphosis. The percentage of VIP-immunoreactive nerves did not change during metamorphosis. SP/NKA-immunoreactive nerves were first apparent at NF stages 61–62 in the middle intestine and increased in the stomach and large intestine during metamorphosis. Endocrine cells expressing SP/NKA increased in number in stomach, proximal, and middle intestine during metamorphic climax. Thus, neurotrophin receptors are expressed transiently in neurons of the enteric nervous system during metamorphosis in Xenopus laevis and SP/NKA innervation is more abundant in the intestine of the postmetamorphic frog than in the tadpole.This study was supported by grants from the Swedish Research Council to S. Holmgren     

Ontogeny of excitatory and inhibitory control of gastrointestinal motility in the African clawed frog, Xenopus laevis

The transparent body wall of Xenopus laevis larvae during the first developmental stages allows in vivo studies of gastrointestinal tract activity. The purpose of this study was to chart the ontogeny of gut motility in Xenopus larvae and to identify the most important control systems during the first developmental stages. Coordinated descending contraction waves first occurred in the gut at Nieuwkoop and Faber stage 43 [0.8 +/- 0.1 contractions/min (cpm)] and increased to 4.9 +/- 0.1 cpm at stage 47. The cholinergic receptor agonist carbachol (5-10 microM) increased contraction frequency already at stage 43, as did neurokinin A (NKA, 0.3-1 microM). The muscarinic antagonist atropine (100 microM) first affected contraction frequency at stage 45, which coincides with the onset of feeding. The tachykinin antagonist MEN-10,376 (6 microM) blocked NKA-induced contractions but not spontaneous motility. Both sodium nitroprusside [nitric oxide (NO) donor, 1-10 microM] and vasoactive intestinal peptide (VIP, 0.1-1 microM) inhibited contractions from the earliest stage onward. Blocking NO synthesis using NG-nitro-L-arginine methyl ester (100 microM) had no effect per se, but antagonized VIP evoked inhibition at stage 47. We conclude that gastrointestinal motility is well developed in the Xenopus laevis larvae before the onset of feeding. Functional muscarinic and tachykinin receptors are present already at the onset of motility, whereas a cholinergic tone develops around the onset of feeding. No endogenous tachykinin tone was found. Functional VIP receptors mediate inhibition at the onset of motility. NO seems to mediate the VIP effect at later stages.     

PACAP 1-38 as neurotransmitter in the porcine antrum

The concentration of PACAP 1-38 in porcine antrum amounted to 15.4+/-7.9 and 20.3+/-8 pmol/g tissue in the mucosal and muscular layers. PACAP immunoreactive (IR) fibres innervated the muscular (co-localised with VIP) and submucosal/mucosal layers (some co-storing VIP and CGRP) including myenteric and submucosal plexus and blood vessels. Only myenteric nerve cell bodies contained PACAP-IR (co-storing VIP). In isolated perfused antrum, vagus nerve stimulation (8 Hz) and capsaicin (10(-5) M) increased PACAP 1-38 release. PACAP 1-38 (10(-9) M) increased substance P (SP), gastrin releasing peptide (GRP) and VIP release. PACAP 1-38 (10(-8) M) inhibited gastrin secretion and stimulated somatostatin secretion and motility dose-dependently. PACAP-induced motility was strongly inhibited by the antagonist PACAP 6-38 but also by atropine and substance P-antagonists (CP99994/SR48968) but PACAP 6-38 had no effect on vagus-induced secretion or motility. Conclusion: PACAP 1-38 may be involved in antral motility and secretion by interacting with cholinergic, SP-ergic, GRP-ergic and/or VIP-ergic neurones, and may also be involved in afferent reflex pathways.     

Coexistence of NADPH-diaphorase and vasoactive intestinal polypeptide in the enteric nervous system of the Atlantic cod (Gadus morhua) and the spiny dogfish (Squalus acanthias)

The distribution of NADPH (nicotinamide adenine dinucleotide phosphate)-diaphorase in nerve cells in the gastrointestinal tract has been investigated and compared in three fish species representing different evolutionary branches. In mammals, NADPH-diphorase is identical to nitric oxide synthase (NOS) and can, in the presence of NADPH, reduce the dye nitroblue tetrazolium, resulting in a blue product. Using this method, we have found numerous NADPH-diaphorase-containing nerve cells in the myenteric plexus of the Atlantic cod (Gadus morhua) and the spiny dogfish (Squalus acanthias) but none in the hagfish (Myxine glutinosa). In the cod, nerve fibres were sparsely stained, whereas in the dogfish, they formed a dense pattern of fibre bundles. Double-staining for NADPH-diaphorase and the neuropolypeptides VIP (vasoactive intestinal polypeptide) and PACAP (pituitary adenylate cyclase activating peptide) revealed three separate populations designated VIP/NADPH, VIP/- and NADPH/-. The majority but not all of the NADPH-diaphorase-positive cells also showed VIP or PACAP immunoreactivity and vice versa. The presence of NADPH-diaphorase in neurons and the distribution of these neurons in the gastrointestinal tract of the two species indicate a physiological role for nitric oxide in the control of gut motility.     

Nitric oxide synthase in the gastrointestinal tract of the estuarine crocodile, Crocodylus porosus

The aim of this study was to investigate the distribution of nitric oxide synthase (NOS)-containing nerve cells in the gastrointestinal tract of a reptile and to compare it with the pattern in other vertebrate classes. In the estuarine crocodile, Crocodylus porosus, NOS-positive nerve cell bodies and fibres were found in all regions of the gut examined. Most myenteric microganglia contained one or several NOS-immunoreactive neurons together with unlabelled neurons. The majority of the neurons were multipolar, ranging from 10 to 25 microns in diameter. Both the circular and the longitudinal muscle layers were innervated by NOS-immunoreactive nerve fibres, which mostly ran parallel to the muscle fibres. In addition, small blood vessels in the submucosa and on the serosal surface of the gut were innervated by NOS-immunoreactive fibres. Double labelling with antisera to NOS and vasoactive intestinal peptide (VIP) revealed three neuronal subpopulations. A small proportion of the NOS-immunoreactive cells also contained immunoreactivity to VIP while a majority of the VIP-immunoreactive cells were NOS immunoreactive. There were more nerve fibres showing VIP immunoreactivity than fibres with NOS immunoreactivity, although most of the latter also contained immunoreactivity to VIP. VIP-immunoreactive fibres often surrounded the NOS-immunoreactive nerve cells. These results suggest that neuronally released nitric oxide is likely to be involved in the control of gastrointestinal motility in the crocodile as in most other vertebrate species.     

Pituitary adenylate cyclase activating peptide (PACAP) immunoreactivity in the ureter of the duck

The presence, distribution and colocalisation of pituitary adenylate cyclase activating peptide (PACAP) immunoreactivity have been studied in the duck ureter by using Western blot analysis, radioimmunoassays (RIA) and immunohistochemistry. The presence of both PACAP-38 and PACAP-27 was demonstrated, PACAP-38 being the predominant form. PACAP-immunoreactive fibres and neurons were found in all the ureteral layers. Double immunostaining showed that PACAP was almost completely colocalised with vasoactive intestinal peptide (VIP). Moreover, PACAP was found in substance P (SP)-containing ureteral nerve fibres and in SP-containing dorsal root ganglion neurons. RIA performed on denervated ureters demonstrated that almost half of the ureteral PACAP was extrinsic in origin. These findings suggest that, in birds, PACAP has a role in diverse nerve-mediated ureteral functions.     

Pituitary adenylate cyclase activating polypeptide (PACAP) in the rat mammary gland

Pituitary adenylate cyclase activating polypeptide (PACAP), a member of the vasoactive intestinal polypeptide (VIP) family of peptides, is present in the brain and in neuronal elements of a number of peripheral organs. Since no information on PACAP in the mammary gland exists, we have investigated, by radioimmunoassay and immunohistochemistry, the occurrence and distribution of PACAP immunoreactivity in the mammary gland of lactating and non-lactating rats. A specific monoclonal mouse anti-PACAP antibody'has been used to show that the peptide is located in nerve fibres associated with bundles of circular and longitudinal smooth muscle surrounding the lactiferous duct of the nipple. PACAP-immunoreactive nerve fibres and nerve bundles are present in the subepidermal connective tissue of the nipple and in the mammary parenchyma, some of the fibres being in close contact with blood vessels. Occasionally, a few delicate varicose fibres are associated with secretory alveoli and lactiferous ducts. The majority of PACAP-positive nerve fibres are, however, located in the glabrous skin of the nipple and the hairy skin adjacent to the nipple forming a subepithelial plexus from which delicate varicose nerve fibres enter the overlying epithelium. Double immunostaining for PACAP and a marker for sensory neurons, calcitonin gene-related peptide, has disclosed that the two peptides are almost completely co-localized. A minor population of the PACAP-immunoreactive nerve fibres shows co-existence with VIP. Although no obvious changes at the immunohistochemical level could be observed during pregnancy or lactation, elevated concentrations of immunoreactive PACAP-38 in mammary extracts have been found during lactation. Our data suggest that PACAP is involved in the nervous control of mammary gland function, probably in the transmission of suckling stimuli.     

Origin and development of VIP and substance P containing neurons in the embryonic avian gut

The development of substance P (SP) and VIP containing structures of the quail and chick guts was studied by immunocytochemistry. The appearance of VIP and substance P nerves follows a rostrocaudal pattern from day 9 in the quail and day 10 in the chick embryo. Immunoreactive fibres are first visible in the oesophagus and at 12 days they extend over the whole length of the intestine. VIP and substance P ganglionic cells are first localized in the foregut (day 9 for VIP containing neurons and day 13 for SP ones) and observed in the mid- and hind-gut just before hatching. Transplantation on the chorioallantoic membrane (CAM) of fragments of various parts of the digestive tract were carried out to see whether in such circumstances the pattern of VIP and SP containing nerves was comparable to normal. The explants contained numerous SP and VIP immunofluorescent nerve fibres. In addition, cell bodies with VIP and SP immunoreactivity appeared brightly fluorescent in the enteric ganglia of the graft showing that these peptidergic nerve cells belong to the intrinsic innervation of the gut.     

Origin and development of VIP and substance P containing neurons in the embryonic avian gut

Summary The development of substance P (SP) and VIP containing structures of the quail and chick guts was studied by immunocytochemistry. The appearance of VIP and substance P nerves follows a rostrocaudal pattern from day 9 in the quail and day 10 in the chick embryo. Immunoreactive fibres are first visible in the oesophagus and at 12 days they extend over the whole length of the intestine. VIP and substance P ganglionic cells are first localized in the foregut (day 9 for VIP containing neurons and day 13 for SP ones) and observed in the mid- and hind-gut just before hatching. Transplantation on the chorioallantoic membrane (CAM) of fragments of various parts of the digestive tract were carried out to see whether in such circumstances the pattern of VIP and SP containing nerves was comparable to normal. The explants contained numerous SP and VIP immunofluorescent nerve fibres. In addition, cell bodies with VIP and SP immunoreactivity appeared brightly fluorescent in the enteric ganglia of the graft showing that these peptidergic nerve cells belong to the intrinsic innervation of the gut.     

Myenteric plexus of obese diabetic mice (an animal model of human type 2 diabetes)

The myenteric plexus of the gastrointestinal tract was investigated in the obese diabetic mouse, an animal model of human type 2 diabetes. Sections were immunostained by the avidin-biotin complex method, using a general nerve marker, protein gene product 9.5 (PGP 9.5), as well as antibodies to several important neurotransmitters. Computerized image analysis was used for quantification. When diabetic mice were compared with controls, no difference was found in the density of PGP 9.5-immunoreactive (IR) nerve fibres in antrum, duodenum or colon. In antrum and duodenum, diabetic mice showed a decreased number of vasoactive intestinal peptide (VIP)-IR neurons in myenteric ganglia as well a decreased relative volume density in myenteric plexus (though not significantly in antrum, p=0.073). No difference was found regarding VIP-IR nerves in colon. The volume density of nitric oxide synthase (NOS)-IR nerve fibres was decreased in antrum and duodenum of diabetic mice, whereas no difference was found in colon. The density of galanin-IR nerve fibres was decreased in duodenum. Whereas neuropeptide Y (NPY)- and vesicular acetylcholine transporter (VAChT)-IR nerve fibres was increased in density in colon of diabetic mice, no difference was found in antrum and duodenum. Regarding substance P, there was no difference between diabetic and control mice in antrum, duodenum or colon. The present study shows that gut innervation is affected in this animal model of human type 2 diabetes. It is possible that the present findings may have some relevance for the gastrointestinal dysfunctions seen in patients with type 2 diabetes.     

Immunoreactivity for high-affinity choline transporter colocalises with VAChT in human enteric nervous system

Cholinergic nerves are identified by labelling molecules in the ACh synthesis, release and destruction pathway. Recently, antibodies against another molecule in this pathway have been developed. Choline reuptake at the synapse occurs via the high-affinity choline transporter (CHT1). CHT1 immunoreactivity is present in cholinergic nerve fibres containing vesicular acetylcholine transporter (VAChT) in the human and rat central nervous system and rat enteric nervous system. We have examined whether CHT1 immunoreactivity is present in nerve fibres in human intestine and whether it is colocalised with markers of cholinergic, tachykinergic or nitrergic circuitry. Human ileum and colon were fixed, sectioned and processed for fluorescence immunohistochemistry with antibodies against CHT1, class III beta-tubulin (TUJ1), synaptophysin, common choline acetyl-transferase (cChAT), VAChT, nitric oxide synthase (NOS), substance P (SP) and vasoactive intestinal peptide (VIP). CHT1 immunoreactivity was present in many nerve fibres in the circular and longitudinal muscle, myenteric and submucosal ganglia, submucosa and mucosa in human colon and ileum and colocalised with immunoreactivity for TUJ1 and synaptophysin confirming its presence in nerve fibres. In nerve fibres in myenteric ganglia and muscle, CHT1 immunoreactivity colocalised with immunoreactivity for VAChT and cChAT. Some colocalisation occurred with SP immunoreactivity, but little with immunoreactivity for VIP or NOS. In the mucosa, CHT1 immunoreactivity colocalised with that for VIP and SP in nerve fibres and was also present in vascular nerve fibres in the submucosa and on epithelial cells on the luminal border of crypts. The colocalisation of CHT1 immunoreactivity with VAChT immunoreactivity in cholinergic enteric nerves in the human bowel thus suggests that CHT1 represents another marker of cholinergic nerves.     

Effects of digestive status on the reptilian gut

Reptiles, including the Burmese python, Python molurus bivittatus, that feed at infrequent intervals show a prominent increase in gastrointestinal mass, metabolism and brush border transport rates after feeding. Current knowledge and theories around these phenomena, as well as studies on the innervation of the reptilian gut, are summarised in this review. Little is known about the putative changes in the nervous and humoral control systems of the gut, and it is not known whether feeding affects innervation and motility of the stomach and intestine. Using immunohistochemistry, we have investigated possible up/down regulation of several neurotransmitters in specimens that had been fasted for a minimum of 3 weeks and specimens that had ingested a large meal 2 days before the experiments were conducted. There were no major changes in the innervation by nerves containing calcitonin gene-related peptide (CGRP), galanin, nitric oxide synthase (NOS), pituitary adenylate cyclase-activating polypeptide (PACAP), somatostatin (SOM), substance P/neurokinin A (SP/NKA), or vasoactive intestinal polypeptide (VIP)-like immunoreactivity. Nor did we find any differences in the effect of substance P (stomach and intestine), galanin (intestine), or bradykinin (intestine) on motility in strip preparations from the gut wall. A significant increase in dry weight of the intestine was obtained 48 h after feeding. We conclude that although there are considerable changes in gut thickness and absorptive properties after feeding, the smooth muscle and its control appear little affected.     

Development of VIP in the peripheral nervous system of avian embryo

The distribution of the VIP containing structures was studied in the gut and in the paravertebral sympathetic ganglia of the quail and chick embryos by immunocytochemistry. In the gut, development of peptidergic nerves followed a craniocaudal gradient. Immunoreactive fibres were first visible in the oesophagus at day 9 in the quail and day 10 in the chick, at 12 days they extended over the whole length of the gut. Cell bodies were localized at day 9 in the foregut and observed in the mid- and hind-gut just before hatching. Transplantations on the chorioallantoic membrane of fragments of various parts of the digestive tract clearly demonstrated that VIP nerve cell bodies belonged to the intrinsic innervation of the gut. Besides the gut, sympathetic paravertebral ganglia contained cells with VIP immunoreactivity detected at day 9 and 10 in quail and chick respectively. In order to find out whether VIP containing neurons differentiated normally in chick embryos in which quail neural crest cells had been implanted at an early stage of development we looked for the appearance of peptidergic neurones in the following situations: when the quail neural primordium had been grafted orthotopically and isochronically into chick host (1) at the adrenomedullary (somites 18-24) and (2) at the vagal (somites 1-7) levels of the neural axis. In all conditions VIP immunoreactivity was observed in quail cells located either in the sympathetic paravertebral ganglia of the trunk at the level of the graft or in the enteric ganglia according to the graft was made at the adrenomedullary and vagal levels respectively.(ABSTRACT TRUNCATED AT 250 WORDS)     

Functional characterization of a receptor for vasoactive-intestinal-peptide-related peptides in cultured dermal melanophores from Xenopus laevis

A receptor for vasoactive-intestinal-peptide (VIP)-related peptides was functionally characterized in a cell line derived from Xenopus melanophores using a recently described microtiter-plate-based bioassay. Activation of the melanophore VIP receptor by VIP or the peptides pituitary-adenylate-cyclase-activating polypeptide (PACAP 38), PACAP 27, and helodermin stimulated intracellular 3'-5' cyclic adenosine monophosphate (cAMP) accumulation and pigment dispersion in the cells. Helodermin, with an EC50 (concentration of peptide inducing half-maximal melanosome dispersion) of 46.5 pM, was the most potent activator of pigment dispersion, followed by PACAP 38 > VIP > PACAP 27. A similar order of potencies was observed for the peptides to induce cAMP accumulation. The responses to VIP agonists were selectively inhibited by the VIP antagonists PACAP-(6-27) and (N-Ac-Tyr(1)-D-Phe2)-growth-hormone-releasing factor[GRF](1-29)-NH2. Taken together, the results suggest that the melanophores express a VIP receptor that shares certain characteristics of, but also differs significantly from, other previously identified VIP receptors.     

A novel neuropeptide,pituitary adenylate cyclase-activating polypeptide (PACAP), in human intestine: evidence for reduced content in Hirschsprung's disease

Summary A novel neuropeptide, pituitary adenylate cyclase-activating polypeptide (PACAP), exhibits sequence homology with vasoactive intestinal polypeptide (VIP) and occurs in the mammalian brain, lung and gut. The distribution of PACAP in ganglionic and aganglionic portions of the large intestine of patients with Hirschsprung's disease was examined by immunohistochemistry and radioimmunoassay. PACAP-immunoreactive nerve fibers were distributed in all layers of the ganglionic and aganglionic segments of the intestine, although they were less numerous in the latter, and PACAP-immunoreactive nerve cell bodies were seen in the ganglionic portion of the intestine. The concentration of immunoreactive PACAP was lower in the aganglionic than in the ganglionic segment of the intestinal wall. PACAP and VIP were found to coexist in both ganglionic and aganglionic segments of the intestine. Apparently, PACAP participates in the regulation of gut motility. The scarcer PACAP innervation of the aganglionic segment may contribute to the defect in intestinal relaxation seen in patients with Hirschsprung's disease.