Ontogeny of the VIP system in the gastro-intestinal tract of the Axolotl,<Emphasis Type="Italic"> Ambystoma mexicanum</Emphasis>: successive appearance of co-existing PACAP and NOS

Evidence for the presence and potential co-existence of vasoactive intestinal polypeptide (VIP), pituitary adenylate cyclase-activating polypeptide (PACAP) and nitric oxide synthase (NOS) in gastro-intestinal endocrine cells and/or nerve fibers is conflicting and very few results exist on development. This immunofluorescence study aims to clarify the appearance and localization of VIP, PACAP and NOS in the gastro-intestinal tract of the Axolotl, Ambystoma mexicanum, during ontogeny. VIP-immunoreactivity appeared in nerve fibers as early as on day 3 after hatching likely indicating a particular role, such as a trophic action, of VIP in very early development. PACAP-immunoreactivity was observed 3 days later within the VIP-immunoreactive (-IR) fibers. From this time on, VIP- and PACAP-immunoreactivity exhibited complete co-existence. VIP/PACAP-IR fibers were found throughout the gastro-intestinal tract. They were most prominent in the myenteric plexus and the muscle layers and less frequent in the submucosa. NOS-immunoreactivity appeared as late as at the 1st (64 days) juvenile stage in a subpopulation of the VIP/PACAP-IR fibers that contacted submucosal arteries. We found only very few VIP/PACAP-IR perikarya, indicating that part of the VIP/PACAP-IR fibers is of extrinsic origin. On day 12 and in the 1st and 2nd (104 days) juvenile stage, infrequent PACAP-IR entero-endocrine cells were noted, while neither VIP- nor NOS-immunoreactivity occurred in endocrine cells at any stage of development. The complete coexistence of neuronal PACAP- and VIP-immunoreactivities and their very early appearance in ontogeny may suggest important and coordinated roles of both peptides in the control of Axolotl gastro-intestinal activity, while the VIP/ PACAP/NOS-IR fibers may be involved in the regulation of submucosal blood flow.     

Light and electron microscopic studies of pituitary adenylate cyclase-activating peptide (PACAP) – immunoreactive neurons in the enteric nervous system of rat small and large intestine

 Pituitary adenylate cyclase-activating peptide (PACAP)-immunoreactive (IR) neurons in the myenteric and submucosal plexus of the rat small and large intestine were examined by immunostaining with purified polyclonal antiserum against PACAP (1–15), using both light and electron microscopy. Many PACAP-IR neuronal cell bodies and fibers were found in the myenteric and submucosal plexus. Many of the PACAP-IR fibers originated from the cell bodies of the myenteric and submucosal ganglia. The ganglia were also innervated by PACAP-IR fibers. PACAP-IR fibers penetrated both the circular and longitudinal muscle layers, confirming the previous observations indicating that PACAP neurons act as motor neurons. Ultrastructural study demonstrated that PACAP-IR nerve terminals formed synaptic contacts with PACAP-IR nerve cell bodies or dendritic processes. This observation suggests that PACAP-IR neurons innervate other PACAP-IR neurons, and that PACAP neurons work as interneurons in the enteric nervous system. PACAP-IR nerve cells received not only PACAP-positive nerve terminal input also PACAP-negative nerve terminal input. It also suggests that PACAP neurons are regulated not only by PACAP-IR enteric neurons, but also by neurons originating elsewhere. Our observations support the view that PACAP-IR neurons are involved in the control of gut motility. Accepted: 20 April 1998     

Target-specific projections of intrinsic ganglionic neurons with different chemical codes in the canine larynx.

The distribution and origin of peptide-containing intrinsic nerve fibers within the larynx were examined by immunohistochemistry and denervation experiments in the dog. In the normal larynx, a dense network of vasoactive intestinal polypeptide (VIP)-immunoreactive (IR) fibers was seen around the acini of submucosal glands. VIP-, substance P (SP)-, or calcitonin gene-related peptide (CGRP)-IR fibers were seen in the walls of submucosal arteries, and VIP-, neuropeptide Y (NPY)-, or enkephalin (ENK)-IR fibers were seen around the arteries in the muscle tissue. Most of these peptide-IR fibers remained after bilateral denervation of the superior and inferior laryngeal nerves. Several small intrinsic ganglia were found along the peripheral branches of the laryngeal nerves. About 97% of the ganglionic neurons were VIP-IR; of these, 44% were immunoreactive to VIP alone, 22% to VIP and NPY, 13% to VIP and SP, 7% to VIP and ENK, and 14% to VIP, NPY and SP. These results reveal that the exocrine glands and blood vessels are innervated by the intrinsic ganglionic neurons and that subpopulations of ganglionic neurons with different chemical codes innervate specific target organs in the canine larynx.     

猪食管神经支配的神经化学研究——一氧化氮类及肽类成分在平滑肌中的分布(英文)

采用免疫荧光组织化学技术及迷走神经切断术,探讨猪食管一氧化氮类及肽类神经支配的神经化学特性。在光学显微镜下可观察到肌间神经丛及粘膜下神经丛中有部分神经元呈nNOS、VIP、GAL、NPY、PACAP、L-ENK、SP、5-HT及CB免疫阳性,但未见CGRP及SOM阳性神经元。nNOS及CB免疫阳性产物主要分布于不同的神经元胞体内。将PGP9.5作为神经元胞体的标记物,并采用免疫荧光免疫组织化学双重染色方法,分别观察了PGP9.5与nNOS、VIP、SP的双标情况。结果如下:(1)nNOS免疫阳性神经元约占PGP9.5标记神经元总数的63%,而VIP免疫阳性神经元约占36%,SP免疫阳性神经元约占28%;(2)神经节内神经元的平均数量呈现吻尾方向的递增趋势,且食管腹段神经丛内神经节数量明显高于食管其他部位;(3)食管肌层内VIP/GAL/NPY免疫阳性纤维分布最广,其中部分阳性纤维同时呈nNOS或PACAP免疫阳性;SP和/或L-ENK免疫阳性纤维在粘膜肌层的分布明显多于平滑肌层。CGRP阳性纤维非常少见,这一点不同于对其他动物的观察结果;(4)经一侧迷走神经切断后,肌间神经丛内PACAP及5-HT免疫阳性纤维明显减少,提示这些纤维可能来源于迷走神经;而平滑肌中VIP/GAL/NPY和/或nNOS免疫阳性纤维数量未发现明显变化,可能为内源性来源。     

Glomerular handling of immune complex in the acute phase of active in situ immune complex glomerulonephritis employing cationized ferritin in rats

The distribution and co-localization of nitric oxide synthase (NOS) and vasoactive intestinal polypeptide (VIP) were examined by means of immunohistochemistry and NADPH diaphorase (NADPH-d) histochemistry in the gut of patients with Hirschsprung's disease. In the normoganglionic segment, many nitrergic nerve cells were localized in Auerbach's plexus and nerve fibres were observed preferentially in the circular muscle. The submucosal nitrergic nerve cells were mainly situated in Schabadasch's plexus with occasional cells demonstrable in Meissner's plexus. NOS and VIP were co-localized in most ganglion cells of Auerbach's plexus. In the oligoganglionic segment, a marked reduction of NOS- and VIP- positive nerve cells and fibres was noticed in both the myenteric and submucosal plexuses, and nitrergic fibres had disappeared in the inner layer of the circular muscle. In the aganglionic segment, NOS and VIP were revealed only in extrinsic nerve fasciculi and rami and co-localized in a few fibres. From these observations, the inner layer of the circular muscle of the oligoganglionic segment and the whole of the muscularis propria of the aganglionic segment were considered to be totally lacking in nitrergic innervation. Nitrergic nerves of the human colon comprise both intrinsic and extrinsic elements and the majority of intrinsic nitrergic nerve cells contain VIP. Very low numbers of extrinsic nitrergic fibres contain VIP.     

Co-localization of vasoactive intestinal peptide- and substance P-containing nerves in cat bronchi

The occurrence of vasoactive intestinal peptide (VIP) and substance P in nerve fibers within the lung is well established, and both VIP- and substance P-containing nerve fibers are known to supply pulmonary vascular and bronchial smooth muscle and submucosal glands. In the present study, we have investigated the co-localization of these two peptides in cat lung. The co-localization procedure follows a standard immunocytochemical protocol except that the primary and labeled secondary antisera each contain a combination of two antisera allowing the simultaneous detection of two antigens in a single tissue section. Using fluorescence microscopy, VIP- and substance P-containing nerve fibers were co-localized in bronchial smooth muscle, in the walls of pulmonary and bronchial arteries, and around submucosal glands. VIP and substance P were also co-localized in nerve cell bodies that comprised the intrinsic airway ganglia. Substance P-containing nerve fibers were observed within the bronchial epithelium, but VIP was not present at this location. The co-localization of VIP and substance P in the same nerve fibers suggests that airway and pulmonary vascular function may be partially regulated by the simultaneous or sequential release of VIP and substance P from the same nerve fibers. The results also suggest that, in addition to extrinsic nerve fibers that contain substance P, the airways of cats are supplied by substance P-containing nerve fibers that originate from intrinsic nerve cell bodies.     

Pituitary adenylatecyclase-activating polypeptide-immunoreactive nerve fibers in the rat epiglottis and pharynx

The distribution of pituitary adenylatecyclase-activating polypeptide-immunoreactive (PACAP-IR) nerve fibers was studied in the rat epiglottis and pharynx. PACAP-IR nerve fibers were located beneath the mucous epithelium, and occasionally penetrated the epithelium. These nerve fibers were abundant on the laryngeal side of the epiglottis and in the dorsal and lateral border region between naso-oral and laryngeal parts of the pharynx. PACAP-IR nerve fibers were also detected in taste buds within the epiglottis and pharynx. In addition, many PACAP-IR nerve fibers were found around acinar cells and blood vessels. The double immunofluorescence method demonstrated that distribution of PACAP-IR nerve fibers was similar to that in CGRP-IR nerve fibers in the epithelium and taste bud. However, distributions of PACAP-IR and CGRP-IR nerve fibers innervating mucous glands and blood vessels were different. The retrograde tracing method also demonstrated that PACAP and CGRP were co-expressed by vagal and glossopharyngeal sensory neurons innervating the pharynx. These findings suggest that PACAP-IR nerve fibers in the epithelium and taste bud of the epiglottis and pharynx which originate from the vagal and glossopharyngeal sensory ganglia include nociceptors and chemoreceptors. The origin of PACAP-IR nerve fibers which innervate mucous glands and blood vessels may be the autonomic ganglion.     

Innervation pattern of polycystic ovaries in the women

The aim of the present study was to determine the changes in both the distribution pattern and density of nerve fibers containing dopamine β-hydroxylase (DβH), vesicular acetylcholine transporter (VAChT), neuronal nitric oxide synthase (nNOS), substance P (SP), calcitonin gene related peptide (CGRP), neuropeptide Y (NPY), vasoactive intestinal peptide (VIP), somatostatin (SOM), galanin (GAL) and pituitary adenylate cyclase-activating polypeptide (PACAP) in the human polycystic ovaries. In the polycystic ovaries, when compared to the immunoreactions pattern observed in the control gonads, following changes were revealed: (1) an increase in the number of DβH-, VAChT-, VIP- or GAL-immunoreactive (IR) nerve fibers within the stroma as well as in the number of DβH-IR fibers near primordial follicles and medullar veins and venules; (2) a reduction in the number of nerve fibers containing nNOS, CGRP, SOM, PACAP within the stroma and in the numbers of CGRP-IR fibers around arteries; (3) an appearance of SP- and GAL-IR fibers around medullar and cortical arteries, arterioles, veins and venules, with except of GAL-IR fibers supplying medullar veins; and (4) the lack of nNOS-IR nerve fibers near primordial follicles and VIP-IR nerves around medullar arteries and arterioles. In conclusion, our results suggest that the changes in the innervation pattern of the polycystic ovaries in human may play an important role in the pathogenesis and/or course of this disorder.     

An immunohistochemical analysis of the ontogeny,distribution and coexistence of 12 regulatory peptides and serotonin in endocrine cells and nerve fibers of the digestive tract of the turbot,Scophthalmus maximus (Teleostei)

The ontogeny of endocrine cells and nerve fibers containing immunoreactivities for 12 regulatory peptides and serotonin was studied in the digestive tract of a flatfish, the turbot (Scophthalmus maximus), using antisera specific for mammalian and teleostean hormones. Transient insulin-immunoreactive (-IR) endocrine cells were detected from day 5 to day 10 in stomach and intestine I. Somatostatin (SOM)-IR cells appeared at day 8 in the stomach anlage and intestine I. In contrast to the islet cells, they reacted with antisera against mammalian (m) SOM-14 and salmon (s) SOM-25. Infrequent nerve fibers reacting only with anti-mSOM-14 appeared around day 24. Thus, different forms of SOM seem to be present in the gastro-entero-pancreatic system and the enteric nervous system. Neuropeptide Y (NPY)-, salmon pancreatic polypeptide (sPP)- and mPP-immunoreactivities coexisted thoughout development. In entero-endocrine cells, NPY/PP-immunoreactivity was first observed at day 8 and around day 24 in enteric nerve fibers. Glucagon (GLUC)-IR entero-endocrine cells appeared at day 5. No coexistence of NPY/PP- and GLUC-immunoreactivities was observed. The first insulin-like growth factor I (IGF-I)-IR cells were identified around day 8. They seemed to contain none of the other peptides. Their number and distribution exhibited great interindividual differences. Vasoactive intestinal polypeptide (VIP)-IR entero-endocrine cells appeared as late as around day 24. The first VIP-IR nerve fibers, however, were identified at day 5. Infrequent neurotensin (NT)-IR cells appeared along the intestine around day 10 and NT-IR nerve fibers at day 17. The first serotonin (SER)-IR cells were observed in the stomach anlage around day 10 and SER-IR nerve fibers at day 15 thoughout the gastro-intestinal tract. Gastrin (GAS)/cholecystokinin (CCK)-IR cells appeared around day 11 in stomach and intestine I. The first substance P (SP)-IR enteric nerve fibers were detected around day 8 and SP-IR endocrine cells at day 11. Pancreastatin (PST)-IR cells were identified in the stomach anlage and intestine I around day 8 and contained NT-, GAS/CCK- and SER-immunoreactivities in coexistence. Thus, several developmental phases can be distinguished: (1) at the onset of exogenous feeding only transient INS-IR cells and VIP-IR nerve fibers are present; (2) a differentiated entero-endocrine system establishes during the early phase of exogenous feeding; (3) before the final differentiation of stomach and gut GAS/CCK-IR cells appear; (4) after metamorphosis most of the different types of regulatory peptide-containing nerve fibers develop, probably setting up the fine regulation of gastro-intestinal blood flow and motility.     

Pituitary adenylate cyclase activating peptide: a novel vasoactive intestinal peptide-like neuropeptide in the gut.

Pituitary adenylate cyclase activating peptide (PACAP) is a vasoactive intestinal peptide (VIP)-like hypothalamic peptide occurring in two forms, PACAP-27 and the C-terminally extended PACAP-38. The predicted rat and human PACAP sequence is identical to the isolated ovine one. In the present study, the occurrence and distribution of PACAP-like peptides were examined in the gut of several species by immunocytochemistry and immunochemistry using an antibody raised against PACAP-27. PACAP-like immunoreactivity was observed in nerve fibers in the gut wall of all species examined (chicken, mouse, rat, hamster, guinea-pig, ferret, cat, pig, sheep and man). In the chicken and human gut, immunoreactive fibers were numerous in all layers. In the other species examined the fibers were predominantly found in the myenteric ganglia and smooth muscle. Delicate PACAP-immunoreactive fibers were seen in the gastric mucosa of mouse, rat, hamster and man but not in the other species examined. The chicken proventriculus harbored numerous PACAP-immunoreactive endocrine cells which were identical with the serotonin-containing cells storing gastrin-releasing peptide. PACAP-immunoreactive nerve cell bodies were numerous in the submucous ganglia and moderate in number in the myenteric ganglia of the human gut. They were few in the intramural ganglia of the other species examined. Extrinsic denervation (performed on segments of rat and guinea-pig small intestine) did not visibly affect the PACAP innervation, indicating an intramural origin of most PACAP-immunoreactive fibers. Double immunostaining for VIP and PACAP revealed co-existence of the two peptides in nerve cell bodies and nerve fibers of the human and chicken gut and in fibers in the gastric mucosa of mouse and rat. In all other species examined and in all other locations in the gut PACAP-immunoreactive nerve cell bodies and nerve fibers were distinct from those storing VIP; many of them contained gastrin-releasing peptide instead. Immunochemistry revealed PACAP-like peptides in gut extracts of all species studied; upon high performance liquid chromatography the immunoreactive material co-eluted with synthetic PACAP-27. The distribution of PACAP-immunoreactive nerve cell bodies and nerve fibers in the gut wall suggests their involvement in the regulation of both motor and secretory activities.     

An immunohistochemical analysis of the ontogeny, distribution and coexistence of 12 regulatory peptides and serotonin in endocrine cells and nerve fibers of the digestive tract of the turbot, Scophthalmus maximus (Teleostei)

 The ontogeny of endocrine cells and nerve fibers containing immunoreactivities for 12 regulatory peptides and serotonin was studied in the digestive tract of a flatfish, the turbot (Scophthalmus maximus), using antisera specific for mammalian and teleostean hormones. Transient insulin-immunoreactive (-IR) endocrine cells were detected from day 5 to day 10 in stomach and intestine I. Somatostatin (SOM)-IR cells appeared at day 8 in the stomach anlage and intestine I. In contrast to the islet cells, they reacted with antisera against mammalian (m) SOM-14 and salmon (s) SOM-25. Infrequent nerve fibers reacting only with anti-mSOM-14 appeared around day 24. Thus, different forms of SOM seem to be present in the gastro-entero-pancreatic system and the enteric nervous system. Neuropeptide Y (NPY)-, salmon pancreatic polypeptide (sPP)- and mPP-immunoreactivities coexisted thoughout development. In entero-endocrine cells, NPY/PP-immunoreactivity was first observed at day 8 and around day 24 in enteric nerve fibers. Glucagon (GLUC)-IR entero-endocrine cells appeared at day 5. No coexistence of NPY/PP- and GLUC-immunoreactivities was observed. The first insulin-like growth factor I (IGF-I)-IR cells were identified around day 8. They seemed to contain none of the other peptides. Their number and distribution exhibited great interindividual differences. Vasoactive intestinal polypeptide (VIP)-IR entero-endocrine cells appeared as late as around day 24. The first VIP-IR nerve fibers, however, were identified at day 5. Infrequent neurotensin (NT)-IR cells appeared along the intestine around day 10 and NT-IR nerve fibers at day 17. The first serotonin (SER)-IR cells were observed in the stomach anlage around day 10 and SER-IR nerve fibers at day 15 thoughout the gastro-intestinal tract. Gastrin (GAS)/cholecystokinin (CCK)-IR cells appeared around day 11 in stomach and intestine I. The first substance P (SP)-IR enteric nerve fibers were detected around day 8 and SP-IR endocrine cells at day 11. Pancreastatin (PST)-IR cells were identified in the stomach anlage and intestine I around day 8 and contained NT-, GAS/CCK- and SER-immunoreactivities in coexistence. Thus, several developmental phases can be distinguished: (1) at the onset of exogenous feeding only transient INS-IR cells and VIP-IR nerve fibers are present; (2) a differentiated entero-endocrine system establishes during the early phase of exogenous feeding; (3) before the final differentiation of stomach and gut GAS/CCK-IR cells appear; (4) after metamorphosis most of the different types of regulatory peptide-containing nerve fibers develop, probably setting up the fine regulation of gastro-intestinal blood flow and motility. Accepted: 24 June 1996     

Coexistence of vasoactive intestinal polypeptide- and substance P-like immunoreactivities in the tongue of the guinea pig

Vasoactive intestinal polypeptide (VIP)- and substance P (SP)-like immunoreactivities were examined in the tongue of the guinea pig by using the double immunofluorescence method. Coexistence of VIP- and SP-like immunoreactivities was suggested in many nerve fibers innervating the lingual salivary glands, as well as in a few intralingual ganglionic cells.     

Innervation of the fibro-elastic type of the penis: an immunohistochemical study in the male pig

The occurrence and colocalization of several biologically active neuropeptides, catecholamine-, acetylcholine- or nitric oxide-synthesizing enzymes-tyrosine hydroxylase (TH), dopamine-beta-hydroxylase (D beta H), choline acetyl-transferase (ChAT) and nitric oxide synthase (NOS I), respectively, as well as the vesicular acetylcholine transporter (VAChT) were investigated in the penile glans (GP), corpus and crura (CP), as well as in the retractor penis muscle (RPM) of juvenile and adult boars. Immunohistochemistry revealed that nerves immunoreactive (IR) to TH, D beta H, vasoactive intestinal polypeptide (VIP) and somatostatin (SOM) were the most numerous, followed (in decreasing order of density) by nerves IR to NOS, neuropeptide Y (NPY), substance P (SP), calcitonin gene-related peptide (CGRP), galanin (GAL), Leu5-enkephalin (LENK) and ChAT/VAChT. The CP contained the largest number of nerve fibres followed by the RPM, GP and corpus. Enzyme/peptide-containing nerves were associated with both the vascular and non-vascular penile structures. However, differences existed for their density and intrapenile distribution. Nerve terminals IR for different combinations of VIP, GAL or SOM were more frequent than those IR for NOS or CGRP in the non-vascular penile structures while the vasculature and the RPM received a prominent TH/D beta H-, VIP-, SOM- or NOS-IR nerve input. The present data indicate that the porcine penis receives nerve fibres that exhibit diverse chemical codes and that differences in the chemical coding of the nerve fibres may depend on their penile target-structure.     

Distribution and origin of nerve fibers in the rat temporomandibular joint capsule

 The distribution and origin of nerve fibers containing neuropeptides and NOS projecting to the temporomandibular joint capsule (TMJ) of the rat were studied by retrograde tracing in combination with immunocytochemistry. Numerous nerve fibers were seen in the TMJ as revealed by the neuronal marker protein gene product 9.5. Nerve fibers containing neuropeptide Y (NPY), vasoactive intestinal peptide (VIP), pituitary adenylate cyclase activating peptide (PACAP), substance P (SP), calcitonin gene-related peptide (CGRP), and nitric oxide synthase (NOS) were seen in the synovial membrane, the joint capsule and entering the articular disc. Injection of the retrograde tracer True Blue (TB) into the TMJ resulted in the appearance of numerous labeled nerve cell bodies in the trigeminal and superior cervical ganglia, and moderate numbers in the nodose, the otic, the sphenopalatine, the stellate and the dorsal root ganglia at levels C2–C5. Most of the TB-labeled cell bodies in the superior cervical and stellate ganglia contained NPY. In the trigeminal ganglion, numerous TB labeled cell bodies contained CGRP and a minor population stored SP, a few cell bodies were seen to store NOS or PACAP. In the sphenopalatine and otic ganglia, TB labeled cell bodies contained NOS or VIP. In the nodose ganglion, labeled cell bodies contained CGRP; other labeled cell bodies harbored NOS. In the cervical dorsal root ganglia, the majority of the labeled cell bodies stored CGRP and smaller populations stored SP and PACAP. Thus, the innervation of the TMJ is complex and many different ganglia are involved. Accepted: 13 October 1997     

Investigation of the interaction of VIP binding sites with VIP and PACAP in human brain.

We have compared the binding of [125I]vasoactive intestinal polypeptide (VIP) to human brain membranes with that of [125I]PACAP27. [125I]VIP was displaced by PACAP27, VIP and two synthetic peptides, peptide-1 (N-terminal PACAP27/C-terminal VIP) and peptide-2 (N-terminal VIP/C-terminal PACAP27), but the IC50 of PACAP27 and peptide-1 were 10-20 times lower than those of VIP and peptide-2. [125I]PACAP27 was readily displaced by PACAP27 and peptide-1, with an IC50 of less than 1 nM, but poorly by VIP and peptide-2. Chemical cross-linking revealed that both labels were bound to polypeptides of Mr 66,000 and Mr 50,000. The results indicate that in human brain membranes both binding sites have a higher affinity to the N-terminal sequence of PACAP27, and VIP binding sites prefer PACAP27 to VIP itself.     

Pituitary adenylate cyclase activating peptide (PACAP) in the enteropancreatic innervation

Pancreatic ganglia are innervated by neurons in the gut and are formed by precursor cells that migrate into the pancreas from the bowel. The innervation of the pancreas, therefore, may be considered an extension of the enteric nervous system. Pituitary adenylate cyclase-activating polypeptide (PACAP) is present in a subset of enteric neurons. We investigated the presence of PACAP in the enteropancreatic innervation in guinea pigs, and the response of pancreatic neurons to PACAP-related peptides. PACAP immunoreactivity was found in nerve fibers in both enteric and pancreatic ganglia and in nerve bundles that travelled between the duodenum and pancreas. PACAP-immunoreactive nerve fibers were densely distributed in the pancreatic ganglia, where they surrounded a subset of cholinergic cell bodies. Pancreatic ganglia did not contain PACAP-immunoreactive cell bodies; however, neuronal perikarya with PACAP immunoreactivity were found in the myenteric plexus of the duodenum. These cells co-stored vasoactive intestinal peptide (VIP). PACAP depolarized pancreatic neurons. Pancreatic neurons were also depolarized by VIP; however, PACAP was more efficacious at depolarizing pancreatic cells than VIP. These findings are consistent with the view that the PACAP effects were mediated through PACAP-selective (PAC1) receptors. PACAP-responsive neurons displayed PAC1 receptor immunoreactivity, which was also found in islet cells and enteric neurons. These results provide support for the hypothesis that PACAP modulates reflex activity between the gut and pancreas. The excitatory effect of PACAP would be expected to potentiate pancreatic secretion.