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

Pituitary Adenylate Cyclase-Activating Polypeptide (PACAP) in Physiological and Pathological Processes within the Gastrointestinal Tract: A Review

Pituitary adenylate cyclase-activating polypeptide (PACAP) is a neuropeptide widely distributed in the central nervous system (CNS) and many peripheral organs, such as the digestive tract, endocrine, reproductive and respiratory systems, where it plays different regulatory functions and exerts a cytoprotective effect. The multifarious physiological effects of PACAP are mediated through binding to different G protein-coupled receptors, including PAC1 (PAC1-R), VPAC1 (VPAC1-R) and VPAC2 (VPAC2-R) receptors. In the gastrointestinal (GI) tract, PACAP plays an important regulatory function. PACAP stimulates the secretion of digestive juices and hormone release, regulates smooth muscle contraction, local blood flow, cell migration and proliferation. Additionally, there are many reports confirming the involvement of PACAP in pathological processes within the GI tract, including inflammatory states, neuronal injury, diabetes, intoxication and neoplastic processes. The purpose of this review is to summarize the distribution and pleiotropic action of PACAP in the control of GI tract function and its cytoprotective effect in the course of GI tract disorders.

Diabetes Affects the Pituitary Adenylate Cyclase-Activating Polypeptide (PACAP)-Like Immunoreactive Enteric Neurons in the Porcine Digestive Tract

Diabetic gastroenteropathy is a common complication, which develops in patients with long-term diabetes. The pituitary adenylate cyclase-activating polypeptide (PACAP) is a neuropeptide known for its cytoprotective properties and plays an important role in neuronal development, neuromodulation and neuroprotection. The present study was designed to elucidate, for the first time, the impact of prolonged hyperglycaemia conditions on a population of PACAP-like immunoreactive neurons in selected parts of the porcine gastrointestinal tract. The experiment was conducted on 10 juvenile female pigs assigned to two experimental groups: The DM group (pigs with streptozocin-induced diabetes) and the C group (control pigs). Diabetes conditions were induced by a single intravenous injection of streptozocin. Six weeks after the induction of diabetes, all animals were euthanised and further collected, and fixed fragments of the stomach, duodenum, jejunum, ileum and descending colon were processed using the routine double-labelling immunofluorescence technique. Streptozotocin-induced hyperglycaemia caused a significant increase in the population of PACAP-containing enteric neurons in the porcine stomach, small intestines and descending colon. The recorded changes may result from the direct toxic effect of hyperglycaemia on the ENS neurons, oxidative stress or inflammatory conditions accompanying hyperglycaemia and suggest that PACAP is involved in regulatory processes of the GIT function in the course of diabetes.

The zebrafish mutant lessen: an experimental model for congenital enteric neuropathies

BACKGROUND

Congenital enteric neuropathies of the distal intestine (CEN) are characterized by the partial or complete absence of enteric neurons. Over the last decade, zebrafish has emerged as a leading model organism in experimental research. Our aim was to demonstrate that the mutant zebrafish, lessen, expressing CEN characteristics, is an equally valuable animal model alongside mammalian models for CEN, by studying its enteric phenotype.

METHODS

The effect of the lessen mutation on the development of the enteric nervous system (ENS), interstitial cells of Cajal (ICC), and intestinal motility in each intestinal region of mutant and wild-type (wt) zebrafish embryos at 3-6 dpf, was analyzed by immunofluorescent detection of neurochemical markers and motility assays.

KEY RESULTS

Development of intestinal motility in the mutant was delayed and the majority of the observed contractions were disturbed. A significant disturbance in ENS development resulted in a distal intestine that was almost free of neuronal elements, in reduced neuronal density in the proximal and mid-intestine, and in a defect in the expression of neurochemical markers. Furthermore, markedly disturbed development of ICC gave rise to a less dense network of ICC.

CONCLUSIONS & INFERENCES

The observed alterations in intestinal motility, intrinsic innervation and ICC network of the mutant in comparison with the wt zebrafish, are similar to those seen in the oligo- and aganglionic regions of the intestine of CEN patients. It is concluded that the zebrafish mutant lessen is an appropriate animal model to investigate CEN.

Expression of neuropeptides and anoctamin 1 in the embryonic and adult zebrafish intestine, revealing neuronal subpopulations and ICC-like cells

This immunohistochemical study in zebrafish aims to extend the neurochemical characterization of enteric neuronal subpopulations and to validate a marker for identification of interstitial cells of Cajal (ICC). The expression of neuropeptides and anoctamin 1 (Ano1), a selective ICC marker in mammals, was analyzed in both embryonic and adult intestine. Neuropeptides were present from 3 days postfertilization (dpf). At 3 dpf, galanin-positive nerve fibers were found in the proximal intestine, while calcitonin gene-related peptide (CGRP)- and substance P-expressing fibers appeared in the distal intestine. At 5 dpf, immunoreactive fibers were present along the entire intestinal length, indicating a well-developed peptidergic innervation at the onset of feeding. In the adult intestine, vasoactive intestinal peptide (VIP), pituitary adenylate cyclase-activating peptide (PACAP), galanin, CGRP and substance P were detected in nerve fibers. Colchicine pretreatment enhanced only VIP and PACAP immunoreactivity. VIP and PACAP were coexpressed in enteric neurons. Colocalization stainings revealed three neuronal subpopulations expressing VIP and PACAP: a nitrergic noncholinergic subpopulation, a serotonergic subpopulation and a subpopulation expressing no other markers. Ano1-immunostaining revealed a 3-dimensional network in the adult intestine containing multipolar cells at the myenteric plexus and bipolar cells interspersed between circular smooth muscle cells. Ano1 immunoreactivity first appeared at 3 dpf, indicative of the onset of proliferation of ICC-like cells. It is shown that the Ano1 antiserum is a selective marker of ICC-like cells in the zebrafish intestine. Finally, it is hypothesized that ICC-like cells mediate the spontaneous regular activity of the embryonic intestine.

Prolonged elevation of galanin and tachykinin expression in mucosal and myenteric enteric nerves in trinitrobenzene sulphonic acid colitis

Diverticulitis causes recurrent abdominal pain associated with increased mucosal expression of mucosal galanin and substance P (SP). We studied changes in mucosal and myenteric plexus neuropeptides in adult rats using a model of colonic inflammation, trinitrobenzenesulphonic acid colitis. We assessed the effects on the pan-neuronal markers protein gene product 9.5 (PGP9.5) and neurofilament protein, as well as specific neuropeptides at 1, 2, 3, 4, 6, 8, 10 and 14 weeks. Following the acute injury there was macroscopic resolution of inflammation but minor microscopic abnormalities persisted. Percent area stained of mucosal PGP9.5 fell initially but average levels on days 21 and 28 levels were significantly elevated (P < 0.001), returning to normal by day 42. Percent area staining of PGP9.5 in the muscle rose immediately and remained significantly elevated at 70 days (P < 0.001). SP, neuropeptide K and galanin followed a similar overall pattern. SP to PGP9.5 ratio was significantly increased in the muscle both acutely (days 1-28) and in the long term (days 70 and 98), whereas the galanin to PGP9.5 ratio was significantly increased in the mucosa throughout the study. Low-grade chronic inflammation after an acute initial insult causes a persistent increase in the expression of galanin in the mucosa and SP in muscle layer.

Distribution of PACAP-38 in the central nervous system of various species determined by a novel radioimmunoassay

Pituitary adenylate cyclase activating polypeptide (PACAP) occurs in two molecular forms: PACAP-38 and PACAP-27. Soon after the isolation and chemical characterization of PACAP, the first radioimmunoassay (RIA) methods have been developed, but it is a still rarely used laboratory technique in the field of PACAP research. The aim of the present study was to develop a novel, highly specific PACAP-38 assay to investigate the quantitative distribution of PACAP-38 in the central nervous system of various vertebrate species under the same technical and experimental conditions. Different areas of the brain and the spinal cord were removed from rats, chickens and fishes and the tissue samples were processed for PACAP-38 RIA. Our results indicate that the antiserum used in the RIA is C-terminal specific, without affinity for other members of the vasoactive intestinal polypeptide (VIP)/secretin/glucagon peptide family. The average ID50 value was 48.6+/-3.4 fmol/ml determined in 10 consecutive assays. Detection limit for PACAP-38 proved to be 2 fmol/ml. PACAP-38 immunoreactivity was present in the examined brain areas of each species studied, with highest concentration in the rat diencephalons. High levels of PACAP-38 were also detected in the rat telencephalon, followed by spinal cord and brainstem. The central nervous system of the fish also contained considerable concentrations of PACAP-38, whereas lowest concentrations were measured in the central nervous system of the chicken.

Expression of pituitary adenylate cyclase-activating polypeptide and PACAP type 1 receptor in the rat gastric and colonic myenteric neurons

Pituitary adenylate cyclase-activating polypeptide (PACAP) is known to regulate gastric acid secretion and intestinal motility. In the present study, the pattern of distribution of PACAP and PACAP type 1 receptor (PAC1) immunoreactivities were examined in the rat stomach and distal colon using a specific polyclonal antibody raised against rat/human PAC1. Western blot of the membrane preparations of NIH/3T3 cells transfected with the human PAC1 obtained by using rabbit polyclonal anti-PAC1 antibody showed a protein band with a molecular mass of approximately 50 kDa. NIH/3T3 cells transfected with the human PAC1 and incubated with the anti-PAC1 antibody displayed surface cell-type immunoreactivity, which was internalized following ligand exposure. In gastric or colonic longitudinal muscle/myenteric plexus (LMMP) whole mount preparations as well as cryostat sections, PACAP immunoreactivity was observed in cell bodies within the myenteric ganglia and nerve fibers in the muscle layers and mucosa. PAC1 immunoreactivity was confined mainly on the surface of the nerve cells. PACAP and PAC1 immunoreactivities showed a similar pattern of distribution in gastric and colonic tissues. Adjacent sections or LMMP whole mount preparations labeled with protein gene product 9.5 (PGP 9.5) revealed the neuronal identity of myenteric cells bearing PAC1. The neuronal localization of PACAP and PAC1 receptors supports their role in the neural regulation of gastric acid secretion and gastrointestinal motor function.

In vitro evaluation of VIP/PACAP receptors in healthy and diseased human tissues. Clinical implications

The evaluation of peptide receptors in man is relevant to identifying the physiological target tissues of a given peptide and to selecting diseases with a sufficient receptor overexpression for diagnostic or therapeutic intervention. VIP/PACAP receptors have been evaluated in normal and diseased human non-neuronal tissues by using in vitro receptor autoradiography with 125I-VIP or 125I-PACAP in tissue sections. As assessed by subtype-selective VIP analogs, VIP receptors of the VPAC1 subtype are found in a wide variety of tissues including liver, breast, kidney, prostate, ureter, bladder, pancreatic ducts, gastrointestinal mucosa, lung, thyroid, adipose, and lymphoid tissues. VPAC2 receptors are predominantly found in vessels and smooth muscles, whereas PAC1 receptors are present in the adrenal medulla. VIP/PACAP receptors are expressed in the majority of the most frequently occurring human tumors, including breast, prostate, pancreas, lung, colon, stomach, liver, and bladder carcinomas, as well as lymphomas and meningiomas, predominantly as VPAC1 receptors, as do their tissues of origin. Although leiomyomas predominantly express VPAC2 receptors, glial tumors, pituitary adenomas, neuroblastomas, paragangliomas, pheochromocytomas, and endometrial carcinomas preferentially express PAC1 receptors. The very wide distribution of VIP/PACAP receptors in the normal human body is indicative of the key role of these peptides in human physiology and pathophysiology. Moreover, the receptor expression in tumors is the molecular basis for clinical applications of VIP/PACAP such as in vivo scintigraphy and radiotherapy of tumors as well as VIP/PACAP analog treatment for tumor growth inhibition.

Presence of pituitary adenylate cyclase-activating polypeptide (PACAP) and its relaxant activity in the rectum of a teleost, the stargazer, Uranoscopus japonicus

Pituitary adenylate cyclase-activating polypeptide (PACAP) is a neuropeptide and a member of the secretin/glucagon superfamily of peptides that include vasoactive intestinal polypeptide. PACAP is not only present in the central nervous system but also in peripheral organs, such as the gastrointestinal tract, gonads and adrenal glands, and plays various roles in mammals. Recently, we isolated and characterized PACAP, which is very similar to PACAP of mammalian origin, from the brain of a teleost, the stargazer, Uranoscopus japonicus. In the present study, the expression of PACAP mRNA was detected in the stargazer rectum using the reverse transcriptase/polymerase chain reaction (RT-PCR) method. The distribution of PACAP-like immunoreactivity in the rectum was also examined immunohistochemically, using an antiserum raised against PACAP 27, and PACAP-like immunoreactive neuronal cell bodies and fibers were found in the myenteric plexuses and the smooth muscle layers of the rectum. The present study also investigated the relaxant activity of synthesized homologous PACAP on rectal contraction. Stargazer PACAP, like that of mammalian origin, inhibited contractions stimulated by acetylcholine or potassium chloride. PACAP-induced inhibition was not affected by preincubation with atropine, propranolol, or phentolamine. These results suggest that PACAP may act directly as an inhibitory neuropeptide in the stargazer rectum.

Role of PACAP1 receptor in regulation of ECL cells and gastric acid secretion by pituitary adenylate cyclase activating peptide

We previously reported that PAC1 is expressed on ECL cells resulting in stimulation of [Ca2+]i, histamine and acid secretion. The study reported here characterized the signaling by PAC1 on ECL cells; determined the effects of PACAP on the gastric acid secretion in vivo, and determined the effects of chronic administration of PACAP-27 on ECL cell proliferation. PACAP-27 dose dependently stimulated ECL cell Ca2+ and AC with detectable stimulation at 1 nM and maximal stimulation at 100 nM (six-fold). In rats PACAP-27 administration (10 pmol/kg/h) increased the rate of gastric acid secretion when an antisomatostatin antibody was co-administered. Chronic administration of PACAP (10 pmol/h for seven days) via osmotic pump resulted in a more than twofold increase in BrdU incorporation into ECL cells. PACAP acting at the PAC1 results in dual signaling responses to both [Ca2+]i. AC in ECL cells stimulates gastric acid secretion via the actions of histamine acting at the parietal cell and in whole animals leads to proliferation of ECL cells when administered chronically.

Biological relevance of pituitary adenylate cyclase-activating polypeptide (PACAP) in the gastrointestinal tract

Since its initial discovery in 1989, pituitary adenylate cyclase activating peptide (PACAP) has been noted to distribute widely in the brain, the respiratory and the gastrointestinal system. It occurs in two bioactive molecules, PACAP-27 and the C-terminally extended PACAP-38, which evoke activity by binding to three distinct types of high-affinity, G-protein coupled membrane receptors. It is present throughout the entirety of the gut but is rare in certain areas such as the intestinal mucosa and islets of Langerhans. PACAP-induced biological effects are protean and include alterations of motility in the bowel and the gallbladder, stimulation of gastric acid and intestinal secretion, hormone/enzyme release from the exocrine and endocrine pancreas, and the induction as well as inhibition of proliferation in neuroendocrine cells and tumors. Its hepatic activity has to date not been elucidated in detail. One of the interesting features of PACAP is the species and organ dependent variation of its biological effects. Of particular note is its superior potency when compared with other neuropeptides identified in the gut, and the involvement of a number of different second messenger systems upon PACAP receptor activation.

Pituitary adenylate cyclase-activating polypeptide and islet amyloid polypeptide in primary sensory neurons: functional implications from plasticity in expression on nerve injury and inflammation

Primary sensory neurons serve a dual role as afferent neurons, conveying sensory information from the periphery to the central nervous system, and as efferent effectors mediating, e.g., neurogenic inflammation. Neuropeptides are crucial for both these mechanisms in primary sensory neurons. In afferent functions, they act as messengers and modulators in addition to a principal transmitter; by release from peripheral terminals, they induce an efferent response, "neurogenic inflammation," which comprises vasodilatation, plasma extravasation, and recruitment of immune cells. In this article, we introduce two novel members of the sensory neuropeptide family: pituitary adenylate cyclase-activating polypeptide (PACAP) and islet amyloid polypeptide (IAPP). Whereas PACAP, a vasoactive intestinal polypeptide-resembling peptide, predominantly occurs in neuronal elements, IAPP, which is structurally related to calcitonin gene-related peptide, is most widely known as a pancreatic beta-cell peptide; as such, it has been recognized as a constituent of amyloid deposits in type 2 diabetes. In primary sensory neurons, under normal conditions, both peptides are predominantly expressed in small-sized nerve cell bodies, suggesting a role in nociception. On axotomy, the expression of PACAP is rapidly induced, whereas that of IAPP is reduced. Such a regulation of PACAP suggests that it serves a protective role during nerve injury, but that of IAPP may indicate that it is an excitatory messenger under normal conditions. In contrast, in localized adjuvant-induced inflammation, expression of both peptides is rapidly induced. For IAPP, studies in IAPP-deficient mice support the notion that IAPP is a pronociceptive peptide, because these mutant mice display a reduced nociceptive response when challenged with formalin.

The pituitary adenylate cyclase activating polypeptide type 1 receptor (PAC1-R) is expressed on gastric ECL cells: evidence by immunocytochemistry and RT-PCR

The current study was undertaken to determine the presence and distribution of PAC1-Rs within the gastric mucosa. Polyclonal antibodies to the carboxyl terminus of the rat PAC1-R were generated and shown to be specific against the PAC1-R expressed in NIH 3T3 cells. Western blot analysis using isolated (approximately 85% pure) ECL cell membranes identified a 48 kD protein consistent with the calculated molecular mass of the cloned PAC1-R. RT/PCR performed using specific primers for the PAC1-R confirmed the presence of splice variants of the rat PAC1-R, but not VPAC1-R or VPAC2-R. These data provide the first direct evidence for the existence of functional PACAP Type I receptors on ECL cells of the gastric mucosa and suggest a potential role for PACAP in the stimulation of gastric acid secretion and in the regulation of the growth of ECL cells.

Sites of actions of contractile and relaxant effects of pituitary adenylate cyclase activating peptide (PACAP) in the internal anal sphincter smooth muscle

In summary, PACAP exerts a biphasic effect (an initial contraction followed by a relaxation) in the IAS. The initial contractile effect with higher concentrations of PACAP was found to be mediated by the activation of PACAP receptor at the substance P-containing nerve terminals. The PACAP receptor(s) responsible for the inhibitory action of the neuropeptide is(are) hypothesized to be present in the IAS smooth muscle cells and on the myenteric nerve terminals. The exact nature and the role of PACAP and the PACAP receptors in the inhibitory neurotransmission, the relationship of PACAP receptors with substance P-containing neurons and IAS smooth muscle cells, and interactions with the NOS pathway and VIP remain to be determined.

Perspectives on pituitary adenylate cyclase activating polypeptide (PACAP) in the neuroendocrine, endocrine, and nervous systems

PACAP is a pleiotropic neuropeptide that belongs to the secretin/glucagon/VIP family. PACAP functions as a hypothalamic hormone, neurotransmitter, neuromodulator, vasodilator, and neurotrophic factor. Its structure has been remarkably conserved during evolution. The PACAP receptor is G protein-coupled with seven transmembrane domains and also belongs to the VIP receptor family. PACAP, but not VIP, binds to PAC1-R, whereas PACAP and VIP bind to VPAC1-R and VPAC2-R with a similar affinity. Despite the sizable homology of the structures of PACAP and VIP and their receptors, the distribution of these peptides and receptors is quite different. At least eight subtypes of PACAP specific, or PAC1-R, result from alternate splicing. Each subtype is coupled with specific signaling pathways, and its expression is tissue or cell specific. Although PACAP fulfills most requirements for a physiological hypothalamic hypophysiotropic hormone, it does not consistently stimulate secretion of the adenohypophysial hormones, except for stimulation of IL-6 release from the FS cells of the pituitary. The major regulatory role of PACAP in pituitary cells appears to be the regulation of gene expression of pituitary hormones and/or regulatory proteins that control growth and differentiation of the pituitary glandular cells. These effects appear to be exhibited directly and indirectly through a paracrine or autocrine action. Although PACAP stimulates the release of AVP, the physiological role of neurohypophysial PACAP remains unknown. One important action of PACAP in the endocrine system is its role as a potent secretagogue for adrenaline from the adrenal medulla through activation of TH. PACAP also stimulates the release of insulin and increases [Ca2+]i from pancreatic beta-cells at an extremely small concentration. The stage-specific expression of PACAP in testicular germ cells during spermatogenesis suggests its regulatory role in the maturation of germ cells. In the ovary, PACAP is transiently expressed in the granulosa cells of the preovulatory follicles and appears to be involved in the LH-induced cellular events in the ovary, including prevention of follicular apoptosis. In the central nervous system, PACAP acts as a neurotransmitter or neuromodulator, which has been supported by IHC and electrophysiological methods. More important, PACAP is a neurotrophic factor that may play an important role during the development of the brain. In the adult brain, PACAP appears to function as a neuroprotective factor that attenuates the neuronal damage resulting from various insults.

Involvement of pituitary adenylate cyclase-activating peptide in opossum internal anal sphincter relaxation

Despite its widespread distribution and significance in the gut, the role of pituitary adenylate cyclase-activating peptide (PACAP) in internal anal sphincter (IAS) relaxation has not been examined. This study examined the role of PACAP in nonadrenergic noncholinergic (NANC) nerve-mediated relaxation of IAS smooth muscle. Circular smooth muscle strips from the opossum IAS were prepared for measurement of isometric tension. The influence of PACAP and vasoactive intestinal peptide (VIP) antagonists and tachyphylaxis on the neurally mediated IAS relaxation was examined either separately or in combination. The release of these neuropeptides in response to NANC nerve stimulation before and after the nitric oxide (NO) synthase inhibitor Nomega-nitro-L-arginine and NO was also investigated. Both PACAP and VIP antagonists caused significant attenuation of IAS relaxation by NANC nerve stimulation. The combination of the antagonists, however, did not have an additive effect on IAS relaxation. VIP tachyphylaxis caused significant suppression of IAS relaxation by NANC nerve stimulation. PACAP and VIP were found to be released by NANC nerve stimulation and exogenous NO. The data suggest the involvement of PACAP in IAS relaxation primarily by the activation of PACAP1/VIP receptor and lack of its independent role in the relaxation. Furthermore, NO may regulate the presynaptic release of PACAP and VIP.

Nitric oxide synthase in neurons of the human gall-bladder and its colocalization with neuropeptides

The distributions of nerve cells and fibres that are immunoreactive for nitric oxide synthase (NOS) have been investigated in the human gall-bladder. In addition, the colocalization of NOS immunoreactivity (IR) with neuropeptide Y (NPY), pituitary adenylyl cyclase activating peptide (PACAP), somatostatin (SOM), substance P (SP), tyrosine hydroxylase (TH) and vasoactive intestinal peptide (VIP)-IR was determined. Nitric oxide synthase-IR nerve cell bodies comprised 13 and 30% of nerve cells in ganglia of the fibromuscular and subepithelial layers, respectively. To determine these percentages, neuron-specific enolase-IR was used as a marker for all nerve cells. Although SOM- and VIP-IR nerve cell bodies were found in both ganglia, they rarely contained NOS-IR. In the fibromuscular layer, NOS-IR nerve fibres were abundant and most PACAP-, SOM- and VIP-IR fibres and many NPY-IR fibres were also NOS positive. No colocalization was observed between NOS- and SP- or TH-IR. In the mucosal layer, moderate numbers of NOS-IR fibres were found and the degree of colocalization of NOS-IR with each of NPY-, PACAP-, SOM-, SP- and VIP-IR were as follows: PACAP and NPY > VIP > SOM and SP. Nitric oxide synthase and TH were not colocalized in mucosal fibres. These results suggest that nerve fibres in the fibromuscular layer in the human gall-bladder with the chemical coding NOS/NPY/PACAP/SOM/VIP are axons of inhibitory motor neurons. Nitric oxide synthase-IR fibres in the mucosal layer that contained NPY, PACAP, SOM, SP and VIP with various degrees of colocalization probably contribute to the control of epithelial secretion or absorption.

Effects of PACAP-38 on the SA nodal pacemaker activity in autonomically decentralized hearts of anesthetized dogs

Pituitary adenylate cyclase-activating polypeptide (PACAP) receptors exist, but the physiologic role of PACAP is unclear in the heart in situ. We investigated effects of PACAP-38 on sinus rate and on the negative chronotropic response to acetylcholine (ACh) or stimulation of the intracardiac parasympathetic nerve fibers to the sinoatrial nodal region in the automatically decentralized heart of the open chest, anesthetized dog. PACAP-38 (0.1-1 nmol) injected directly into the sinus node artery caused transient positive followed by negative chronotropic responses. Both pretreatment with atropine and tetrodotoxin inhibited the negative chronotropic responses to PACAP-38. However, hexamethonium did not block the negative responses to PACAP-38. After treatment with PACAP-38 (0.1-1 nmol), ACh induced atrial fibrillation significantly (p < 0.01). On the other hand, the negative chronotropic responses to intracardiac parasympathetic stimulation were not changed. These results suggest that (a) PACAP-38 induces negative chronotropic responses and liberates ACh from intracardiac postganglionic parasympathetic nerves, and that (b) PACAP-38 reduces ACh-induced atrial fibrillation threshold in the dog heart in situ.

Distribution of two VIP-related peptides, helospectin and pituitary adenylate cyclase activating peptide (PACAP), in the human upper respiratory system

Helospectin (HS) and pituitary adenylate cyclase activating peptide (PACAP) are newly discovered peptides isolated from the salivary gland venom of the lizard Heloderma horridum and the ovine hypothalamus, respectively. They show chemical similarities to vasoactive intestinal polypeptide (VIP), appear to have similar functions and are present in gut, brain, lung, male and female genitourinary tract. In the present study, the distribution of the helospectin and PACAP-27 in the human upper respiratory system was investigated using indirect immunofluorescence and electron-microscopical ABC-pre-embedding methods. Immunohistochemistry revealed helospectin-like (HS-LI) and PACAP-like (PACAP-LI) immunoreactivity in nerve fibers in human nasal, the larynx (vocal cord, ventricular fold, epiglottis), the tongue and the soft palate mucosa. Helospectin-LI and PACAP-LI containing nerve fibers were mainly found in close association to blood vessels and glandular structures. Colocalization studies carried out by application of double immunofluorescence showed that HS and/(or) PACAP-LI coexist with VIP in apparently the same nerve fibers in the upper respiratory system, although single nerve fibers seem to exclusively express helospectin. The localization patterns of helospectin and PACAP-LI in the human upper respiratory system suggests their possible involvement in the regulation of secretory activities and local blood flow.

Cloning and characterization of the signal transduction of four splice variants of the human pituitary adenylate cyclase activating polypeptide receptor. Evidence for dual coupling to adenylate cyclase and phospholipase C

Alternative splicing of two exons of the rat pituitary adenylate cyclase activating polypeptide (PACAP) receptor gene generates four major splice variants that are differentially expressed in specific tissues and variably coupled to intracellular second messengers. To evaluate the potential implications of these findings in human physiology, the human PACAP receptor gene was cloned. Alternative splicing about two exons of the gene allowed for four major splice variants that were subsequently identified on cDNA cloning. Each of the four splice variant cDNAs (null, SV-1, SV-2, and SV-3) was stably expressed in NIH/3T3 cells at similar receptor densities. For each splice variant, PACAP (both PACAP-38 and PACAP-27) had similar affinity and potency for stimulating either adenylate cyclase or phospholipase C. However, each receptor splice variant differed in their ligand-stimulated maximal response (efficacy) for total inositol phosphate accumulation with the SV-2 showing the greatest efficacy, followed by the null, SV-1, and SV-3 splice variants. Therefore, unlike the rat, PACAP binds and stimulates signal transduction with nearly equal affinity and potency for each of the receptor splice variants although with varying efficacy for the stimulation of phospholipase C. These results suggest a novel and potentially important mechanism for a single hormone to not only couple to dual signal transduction cascades but also elicit tissue-specific differential activation of phospholipase C in humans.

Hirschprung's disease

Current evidence on the pathogenesis of Hirschprung's disease, then, favours the 'abnormal microenvironment' hypothesis wherein the developing and migrating normal neural crest cells confront a segmentally abnormal and hostile microenvironment in the colon. This hypothesis would account both for the congenital absence of ganglion cells in the wall of colon and also for the range of enteric neuronal abnormalities encountered including neuronal dysplasia, hypoganglionosis, and zonal aganglionosis. The abnormal constitution of the mesenchymal and basement membrane extracellular matrix in the affected segment of colon is presumably genetically determined and further understanding of the pathogenesis of this disorder will emerge as molecular geneticists characterise the specific genes and gene products associated with Hirschprung's disease. Advances in this field should permit gene probes to be developed to facilitate prenatal and postnatal diagnosis.

Pituitary adenylate cyclase activating polypeptide is expressed in autonomic neurons

Pituitary adenylate cyclase activating polypeptide (PACAP) is a novel vasoactive intestinal peptide (VIP)-like peptide, which is present in neuronal elements of several peripheral organs, and thus a putative neurotransmitter/modulator. In the present study, the expression of PACAP in two parasympathetic ganglia (otic, sphenopalatine) and one mixed parasympathetic/sensory ganglion (jugular-nodose) in rat was characterized by use of in situ hybridization and immunocytochemistry and compared to that of VIP and calcitonin gene-related peptide (CGRP). PACAP and VIP were expressed in virtually all nerve cell bodies in the otic and sphenopalatine ganglia; PACAP and VIP were also expressed in subpopulations of nerve cell bodies in the jugular-nodose ganglion. CGRP was expressed in numerous nerve cell bodies in the jugular-nodose ganglion and in a few, scattered, nerve cell bodies in the sphenopalatine ganglion. In the otic and sphenopalatine ganglia, PACAP- and VIP-like immunoreactivities were frequently co-localized; in the jugular-nodose ganglion, PACAP-like immunoreactivity was frequently co-localized with CGRP-like immunoreactivity in presumably sensory neurons and to a lesser extent with VIP in parasympathetic neurons. Thus, PACAP is synthesized and stored in autonomic parasympathetic neurons as well as in vagal sensory neurons, which provides an anatomical basis for the diverse effects of PACAP previously described.

Distribution of pituitary adenylyl cyclase activating peptide (PACAP) immunoreactivity in neurons of the guinea-pig digestive tract and their projections in the ileum and colon

Pituitary adenylyl cyclase activating peptide (PACAP) is a novel hypothalamic peptide that is widely distributed in neurons, including those of the gastrointestinal tract. In this study, a polyclonal antiserum directed against PACAP-27 was used to investigate the localisation of PACAP throughout the gut and to determine the projections of PACAP-immunoreactive (IR) neurons in the guinea-pig small and large intestines. PACAP-IR fibres were seen in the myenteric and submucous plexuses, in the longitudinal and circular muscle layers and around blood vessels of the submucosa throughout the gut. In both the small and large intestine, PACAP-IR cell bodies, most with Dogiel type-I morphology, were seen in the myenteric ganglia following colchicine treatment. Lesion studies (myotomy and myectomy operations) revealed that PACAP-IR interneurons projected anally in the ileum and colon. Myectomy operations resulted in a loss of PACAP-IR fibres in the circular muscle under the operation, whereas PACAP-IR fibres remained in the submucosa and around blood vessels. Following extrinsic denervation of the ileum, the number of PACAP-IR fibres in the submucosal ganglia and around blood vessels decreased. This suggests that a portion of PACAP-IR fibres supplying the submucosal ganglia and blood vessels have an extrinsic source. To investigate this, immunohistochemical studies were performed on sympathetic and dorsal root ganglia. Numerous reactive cells were seen in the dorsal root ganglia, but none was seen in sympathetic pre- or paravertebral ganglia.

Plurichemical transmission and chemical coding of neurons in the digestive tract

The enteric nervous system contains neurons with well-defined functions. However, when neurons of the same function are examined in different regions or species, they are found to show subtle differences in their pharmacologies of transmission and different chemical coding. Individual enteric neurons use more than one transmitter, i.e., transmission is plurichemical. For example, enteric inhibitory neurons have three or more primary transmitters, including nitric oxide, vasoactive intestinal peptide, and possibly adenosine triphosphate and pituitary adenylyl cyclase activating peptide. Primary transmitters are highly conserved, although their relative roles vary considerably between gut regions. Multiple substances, including transmitters and their synthesizing enzymes and nontransmitters (such as neurofilament proteins), provide neurons with a chemical coding through which their functions and projections can be identified. Although equivalent neurons in different regions have the same primary transmitters, other chemical markers differ substantially. Caution must be taken in extrapolating pharmacological and neurochemical observations between species or even between regions in the one species. On the other hand, careful interregion and interspecies comparisons lead to an understanding of the features of enteric neurons that are highly conserved and can be used in valid extrapolation.

Pituitary adenylate cyclase activating polypeptide expression in sensory neurons

Pituitary adenylate cyclase activating polypeptide (PACAP) is a novel vasoactive intestinal peptide (VIP)-like peptide isolated from ovine hypothalami. The presence of PACAP-like immunoreactivity was recently demonstrated in nerve cell bodies of sensory ganglia in the rat. Since PACAP belongs to a large family of chemically related neuropeptides, we have, in the present study, tried to establish the synthesis of PACAP in neurons of sensory ganglia, using in situ hybridization with a 35S-labelled oligonucleotide probe complementary to PACAP mRNA. The expression of PACAP was compared to that of calcitonin gene-related peptide (CGRP) using a radiolabelled CGRP oligonucleotide probe. The PACAP probe labelled small to medium-sized neurons in the trigeminal ganglion and dorsal root ganglia at different levels, indicating the presence of PACAP mRNA. The CGRP probe labelled nerve cell bodies of varying size, outnumbering those labelled by the PACAP probe. In dorsal root ganglia, cells expressing PACAP constituted c. 10% and those expressing CGRP 46% of the total number of nerve cell bodies. Expression of PACAP was seen in a small subpopulation of cells expressing CGRP. We conclude that PACAP is synthesized in a subpopulation of neurons of sensory ganglia in the rat. Therefore, the recently described effects of PACAP--cutaneous vasodilation, potentiation of oedema formation and depression of nociceptive spinal reflexes--may be physiological and related to neurogenic inflammation and modulation of pain transmission.

Pituitary adenylate cyclase-activating polypeptide (PACAP)-like immunoreactive neuronal elements in rat hypothalamus and median eminence with special reference to morphological background of its effect on anterior pituitary--light and electron microscopic immunocytochemistry

Pituitary adenylate cyclase-activating polypeptide-like immunoreactive (PACAP-LI) neuronal elements in the rat hypothalamus including the median eminence (ME) were investigated by light and electron microscopic immunocytochemistry. PACAP-LI neuronal perikarya with well-developed cell organelles and dense granules were distributed mainly in the magnocellualr portion of the paraventricular nucleus and throughout the entire supraoptic nucleus. In the ME, numerous PACAP-LI neuronal processes were found in the internal layer (IL), and immunoreactive terminals containing dense granules, vesicles and mitochondria were detected around portal capillaries which penetrated into the IL from the external layer. Thereafter, PACAP is released into the portal capillaries in the IL, transported to the anterior pituitary and plays a role in the stimulation of adenylate cyclase of anterior pituitary cells.

Chromogranin A and B in neuronal elements in Hirschsprung's disease: an immunocytochemical and radioimmunoassay study

Chromogranin A and B (CAB) occur in several peptide hormone-producing cells and in neurons of the brain. The aim of the present study was to investigate the possible neuronal localization of these chromogranins in the ganglionic and aganglionic bowel in Hirschsprung's disease by immunocytochemistry and radioimmunoassay, using antibodies recognizing either chromogranin A or both chromogranin A and B. Further, the coexistence of chromogranins and other neuronal constituents was studied. CAB were found in nerve fibers and occasionally in nerve cell bodies of submucous and myenteric ganglia in the ganglionic bowel, indicating that at least a population of chromogranin-immunoreactive nerve fibers is intrinsic in origin. CAB-immunoreactive fibers were numerous in the muscle layers of the aganglionic segment. These fibers contained tyrosine hydroxylase (TH), which indicates that they are adrenergic, in both ganglionic and aganglionic bowel. In the muscle layers of aganglionic (but not ganglionic) bowel, chromogranin A coexisted with galanin, neuropeptide Y (NPY), and vasoactive intestinal peptide (VIP). The concentration of CAB in smooth muscle specimens was higher in the aganglionic bowel than in the ganglionic bowel. Thus, chromogranins are present in the human enteric gut hyperinnervating the aganglionic bowel of Hirschsprung's disease.

Immunocytochemical evidence for chromogranin A and B in neuronal elements in human gut

Chromogranins are a family of acidic proteins known to occur in the secretory granules of endocrine cells and neurons in mammals. The aim of the present study was to investigate the possible neuronal localisation of chromogranins in human intestine and their relationship with other neuronal constituents using one antibody recognizing both chromogranin A and B (CAB) and others recognizing only chromogranin A. Immunoreactive CAB was found to occur in mucosal endocrine cells and in neuronal elements of all layers throughout human gut. A few to large number of CAB-immunoreactive nerve fibers were seen in smooth muscles as well as in submucous and myenteric ganglia and they were regularly found around blood vessels. Occasional CAB immunoreactive nerve cell bodies could be demonstrated in both submucous and myenteric ganglia indicating a local origin of some of the immunoreactive fibers. Most of these neurons seemed to lack acetylcholine esterase, and could be classified as non-cholinergic. CAB coexisted with the catecholamine-synthesizing enzyme tyrosine hydroxylase indicating the presence of chromogranins in noradrenergic nerve fibers. The presence of CAB-immunoreactive nerve cell bodies indicates that some CAB-containing fibers are intrinsic in origin. The distribution of chromogranin A and B immunoreactive nerve fibers in all layers of the gut wall suggests multiple targets for neuronal CAB, and/or their processing products.

Pituitary adenylate cyclase activating peptide is a sensory neuropeptide: immunocytochemical and immunochemical evidence

Pituitary adenylate cyclase activating peptide (PACAP) is a vasoactive intestinal peptide-like hypothalamic peptide occurring as two variants, PACAP-27 and the C-terminally extended PACAP-38. Immunoreactive PACAP has also been demonstrated in the enteric nervous system and in the innervation of the respiratory tract. We have examined the possibility that PACAP occurs in the sensory nervous system of the rat. Immunocytochemistry revealed PACAP in numerous nerve fibres in the superficial layer of the dorsal horns of the spinal cord, in nerve cell bodies (most of them of small size) of the spinal ganglia and trigeminal ganglia and in nerve fibres running close to and within the surface epithelium in the skin of the nose, the tongue, the larynx-trachea, and the urinary bladder as well as around the ducts of the submandibular gland. In all locations, PACAP co-existed with calcitonin gene-related peptide and substance P, the PACAP-immunoreactive fibres and cell bodies constituting a subpopulation of those storing substance P and/or calcitonin gene-related peptide. Additional PACAP-immunoreactive fibres not associated with epithelia seemed to lack calcitonin gene-related peptide and substance P. Capsaicin treatment reduced the density of PACAP- and calcitonin gene-related peptide/substance P-immunoreactive fibres in the tissues examined. On the whole, the immunocytochemical results agreed with those obtained by radioimmunoassay for PACAP and CGRP. The data favour a role for PACAP in primary sensory neurons.

Type I receptors for PACAP (a neuropeptide even more important than VIP?)

Among vertebrates, there is an extreme conservation in amino acid sequence for the neuropeptide PACAP-38 and its C-terminal shortened derivative PACAP-27. The PACAP gene is assigned to chromosome 18 in man and its organization has been characterized. PACAP-38 and its minor derivative PACAP-27 are widely distributed in the central nervous system. PACAP-38 is particularly abundant in hypothalamus. The mapping of the afferentation and efferentation of PACAP systems are progressively delineated, including a search for the colocalization with other neurotransmitters. In several peripheral organs positive neuronal perikarya and fibers are also seen. PACAP acts through two types of receptors: (1) the highly selective type I that displays a 500 to 2000 selectivity for PACAP-38 and PACAP-27 as compared to VIP; (2) type II is the so-called VIP receptor showing similar high affinity for PACAP-38, PACAP-27 and VIP. It is less selective, therefore, than previously thought. This is why this second receptor, qualifying as an unspecific VIP-PACAP receptor, is hardly considered here. Type I receptors can stimulate two enzymes: the adenylate cyclase and phospholipase C (whose activation leads to the inositol phosphate-cytosolic Ca2+ cascade). This dual coupling may have several distal consequences including on gene expression, cell growth and differentiation. Although a relatively comprehensive spectrum of pharmacological activities has already been established we still need to limit the physiological roles of PACAP as neurotransmitter and/or neuromodulator. Concerning the hypothalamo-pituitary axis, PACAP reduces food intake in mice and raises plasma arginine vasopressin in rat, probably through PACAP-ir neurons in paraventricular and supraoptic nuclei projecting to the neurohypophysis. PACAP originating in the hypothalamus may also be transported to the anterior pituitary through portal vessels. Data on the antehypophysis suggest a role on i.a. reproduction and growth. PACAP stimulates adenylate cyclase and increases [Ca2+] in gonadotropes, somatotropes, and folliculo-stellate cells. It elevates the secretion of alpha-MSH from melanotropes, and that of interleukin-6 from pituitary folliculo-stellate cells. PACAP potentiates the effects of LHRH on LH and FSH secretion. More clearly perhaps, PACAP increases the synthesis of LH, GH, PRL and ACTH after 1-2 days. In human pathology, PACAP-27 and PACAP-38 stimulate adenylate cyclase activity in membranes from 'null'-, gonadotropin-, GH-, and ACTH-producing pituitary adenomas but are inactive in prolactinomas.(ABSTRACT TRUNCATED AT 400 WORDS)