Neuroendocrine system of the digestive tract in Rhamdia quelen juvenile: an immunohistochemical study

In this work, an immunohistochemical study was performed to determine the distribution and relative frequencies of some neuromodulators of the digestive tract of silver catfish (Rhamdia quelen). The digestive tract of silver catfish was divided into six portions; the oesophagus, stomach, intestine (ascendant, descendant and convoluted segments), and rectum. Immunohistochemical method using a pool of specific antisera against-gastrin, -cholecystokinin-8, -leu-enkephalin, -neuropeptide Y, -calcitonin gene-related peptide (CGRP), and -vasoactive intestinal peptide (VIP) was employed. Immunoreactivity to all antisera was identified in neuroendocrine cells (NECs) localized in the gut epithelium, although no reaction was observed in the oesophagus or stomach. The morphology of NECs immunopositive to each antibody was similar. They were slender in shape, with basally located nucleus, and their main axis perpendicular to the basement membrane. The number of NECs immunoreactive to all antisera was higher in the ascendant and descendant intestine, exhibiting a decreasing trend toward distal segments of the gut. In addition, immunoreactivity to CGRP and VIP was observed in the myenteric plexus and nerve fibers distributed in the mucosal, submucosal and muscular layers. The higher number of immunopositive NECs in the ascendant and descendant intestine may indicate the primary role of these segments in the control of food intake by means of orexigenic and anorexigenic peripheral signals.     

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.     

Immunocytochemical demonstration of vertebrate neuropeptides in the earthworm Lumbricus terrestris (Annelida,Oligochaeta)

Summary The localisation and distribution of 10 vertebrate-derived neuropeptides in the earthworm, Lumbricus terrestris, have been determined by an indirect immunofluorescence technique. The peptides are pancreatic polypeptide (PP), peptide tyrosine tyrosine (PYY), neuropeptide Y (NPY), glucagon (C-terminal), vasoactive intestinal polypeptide (VIP), peptide histidine isoleucine (PHI), gastrinreleasing peptide (GRP), calcitonin gene-related peptide (CGRP), neurotensin (NT), and met-enkephalin. For 6 of the peptides — PYY, NPY, PHI, glucagon, GRP and CGRP — this is the first demonstration of their presence in any annelid, and NT has not previously been described in an oligochaete. Cell bodies and nerve fibres immunoreactive to the 10 peptides occur throughout the CNS. In the PNS, epidermal sensory cells displayed immunoreactivities to PP and PYY, and PP-, PYY-, NPY-, PHI- and GRP-like immunoreactivities occurred in nerve fibres supplying the main body muscles. Nerve fibres immunoreactive to PP and PYY are also associated with the innervation of the gut (pharynx, oesophageal glands, and mid and posterior regions of the intestine). No endocrine cells immunoreactive for any of the antisera tested could be identified in the gut epithelium, suggesting that dual location of peptides in the brain and gut epithelium is a phenomenon that occurred at a later stage in evolution. No immunoreactive elements were detected in any of the organs and ducts of the reproductive and excretory systems.     

Calcitonin gene-related peptide neurons innervating the canine digestive system.

The pattern of nerve cells and fibers containing calcitonin gene-related peptide immunoreactivity (CGRP-IR) was investigated in the canine digestive tract by means of immunohistochemistry. CGRP-IR nerve fibers innervate all the layers of the gut, including the vasculature, with different densities depending on the region. CGRP-IR processes are sparse in the esophagus and stomach, where they are mostly confined to the enteric plexuses and vasculature. CGRP-IR fibers are quite abundant in the small and large intestine, where they form dense arborizations in the mucosa, and are numerous in the muscularis mucosae, deep muscular plexus and circular muscle. The myenteric and submucous plexuses of the intestine contain dense networks of CGRP-IR fibers and numerous CGRP-IR ganglion cells. On the other hand, in the enteric ganglia of the esophagus and stomach, in the intrapancreatic ganglia and in the ganglionated plexus of the gallbladder, CGRP-IR is restricted to non-varicose processes. A moderate density of CGRP-IR fibers supplies the endocrine and exocrine pancreas, and the fibromuscular layer and lamina propria of the gallbladder. The density of CGRP innervation in different regions can be summarized as follows: intestine > pancreas and gallbladder > or = antrum > cardia > gastric corpus and distal esophagus. CGRP- and tachykinin (TK)-IRs are colocalized in a substantial population of fibers, particularly those distributed to the mucosa, muscularis mucosae and vasculature, whereas there was no evidence of colocalization in intrinsic ganglion cells. The present results suggest that (1) the CGRP innervation of the dog digestive system includes an intrinsic and an extrinsic component, and (2) CGRP- and TK-IRs are co-expressed in extrinsic nerve fibers. These findings extend previous observations in rats and guinea pigs and provide insights into the sites of action of CGRP in the digestive system of the dog, which has served as a model for CGRP functional studies.     

Morphology of the digestive system in carnivorous freshwater dourado Salminus brasiliensis

The digestive system of teleost shows remarkable functional and morphological diversity. In this study, the digestive tract and accessory organs of dourado Salminus brasiliensis are characterized using anatomical, histological, histochemical and immunohistochemical analyses. The existence of taste buds bordered by microridges in the oesophagus of dourado was recorded for the first time, thus showing that the species drives food intake by either swallowing or rejecting the food item. The Y-shaped stomach of dourado consisted of cardiac, cecal and pyloric regions with tubular gastric glands registered solely in the cardiac and cecal segments. The intestine is a short N-shaped tube with two loops, an intestinal coefficient of 0.73. The structure of pyloric caeca is similar to that of the intestine wall, comprising tunica mucosa, tela submucosa, tunica muscularis and tunica serosa layers. Histochemical analyses revealed an increased incidence of goblet cells from the midgut to the hindgut segment. A well-developed enteric plexus of scattered nerve cell and fibres are found along the digestive tract, and the calcitonin gene-related peptide (CGRP) immunoreactive neurons and fibres were identified in the myenteric plexus from the oesophagus to the hindgut. The exocrine pancreas appears diffuse in the mesentery around the stomach, intestine and also reaches the liver, and the endocrine pancreas is organized as a few islets of Langerhans. The liver comprises three distinct, asymmetric lobes, and the portal triad arrangement was registered in this tissue.     

Calcitonin gene-related peptide regulates amino acid absorption across rat jejunum

The calcitonin gene related peptide (CGRP) is widely distributed in the enteric nervous system and gut afferents. Its role in normal digestion and absorption is not characterised. This study is conducted to elucidate whether CGRP regulates amino acid absorption in the small intestine. In in vivo experiments using the single-pass perfusion technique, intravenous infusion of CGRP (250–750 pmol/kg-min) reduced alanine absorption by 35–40%. The effects were completely blocked by the antagonist hCGRP (8–37). Moreover, intravenous infusion of CGRP antagonist blocked the inhibitory effect of intraluminal capsaicin perfusion on alanine absorption. Similarly, intracerebral injection of CGRP decreased alanine absorption, an effect which was reduced by vagotomy. In vitro experiments using isolated jejunal strips showed that CGRP reduced alanine absorption in a dose-dependent manner. At 6 pM, CGRP decreased alanine absorption by 33%. Similarly, CGRP reduced the absorption of proline and taurine by 20 and 11.5%, respectively. Kinetic studies revealed that CGRP reduces alanine influx into intestinal epithelial cells by inhibiting the affinity of the carriers. It is demonstrated that CGRP is involved in the regulation of jejunal amino acid absorption through intrinsic (enteric) and extrinsic (central) neural mechanisms.     

The small intestine plays an important role in upregulating CGRP during sepsis

Although studies have indicated that calcitonin gene-related peptide (CGRP), a potent vasodilatory peptide, is upregulated after endotoxic shock, it remains controversial whether this peptide increases during sepsis and, if so, whether the gut is a significant source of CGRP under such conditions. To study this, polymicrobial sepsis was induced by cecal ligation and puncture (CLP) followed by fluid resuscitation. Plasma levels of CGRP were measured at 2, 5, and 10 h after CLP (i.e., early, hyperdynamic sepsis) and at 20 h after CLP (late, hypodynamic sepsis). The results indicate that plasma CGRP did not increase at 2--5 h but increased by 177% at 10 h after CLP (P < 0.05). At 20 h after the onset of sepsis, however, the elevated plasma CGRP returned to the sham level. To determine the source of the increased plasma CGRP, the liver, spleen, small intestine, lungs, and heart were harvested, and tissue CGRP was assayed at 10 h after CLP in additional animals. Only the small intestine showed a significant increase in tissue levels of CGRP (by 129%, P < 0.05). Determination of portal vs. systemic levels of CGRP indicates that portal CGRP was 65.7 +/- 22.7% higher than the systemic level at 10 h after CLP, whereas portal CGRP in sham-operated rats was only 4.9 +/- 2.1% higher. Immunohistochemistry examination revealed that CGRP-positive stainings increased in the intestinal tissue but not in the liver at 10 h after the onset of sepsis. The distribution of CGRP stainings was associated with intestinal nerve fibers. These results, taken together, demonstrate that upregulation of CGRP occurs transiently during the progression of sepsis (at the late phase of the hyperdynamic sepsis), and the gut appears to be a major source of such an increase in circulating levels of this peptide.     

Neurohormonal peptides, serotonin, and nitric oxide synthase in the enteric nervous system and endocrine cells of the gastrointestinal tract of neotenic and thyroid hormone-treated axolotls (Ambystoma mexicanum)

Immunoreactivity against vasoactive intestinal polypeptide (VIP), neurotensin (NT), substance P (SP), calcitonin gene-related peptide (CGRP), gastrin/cholecystokinin (GAS/CCK), somatostatin (SOM), serotonin (SER), and nitric oxide synthase (NOS) was investigated in the gastrointestinal tract of the urodele Ambystoma mexicanum, the axolotl, by the use of immunohistochemical techniques. The study also compares the distribution patterns and frequencies of the neurohormones, and NOS in neotenic and thyroxine-treated (metamorphosed) individuals. GAS/CCK, SP, NT, SOM, and SER immunoreactivities occurred in endocrine mucosal cells and VIP, SP, CGRP, NTSER, SER, and NOS immunoreactivities in the enteric nervous system. The GAS/CCK-immunoreactive (-IR) cells were restricted to the upper small intestine. NT-IR and SP-IR endocrine cells were found in the entire gastrointestinal tract and were most prominent in the distal large intestine. The density of the SOM-IR cells decreased from the stomach toward the large intestine. SER-IR endocrine cells were found throughout the gastrointestinal tract, with particularly high densities in the stomach and distal large intestine. The VIP-IR enteric nerve fibers were the most prominent ones, present in all layers of the entire gastrointestinal tract, and supplied the smooth muscle and the vasculature. The SER-IR fibers exhibited similar distribution patterns but were less numerous. Very few NT-IR but many SP-IR fibers were found in the muscle and submucosal layers. The NT-IR fibers mainly supplied blood vessels, while the SP-IR fibers were also in contact with the smooth muscle. In the muscle and submucosal layers, CGRP-IR fibers were associated to the vasculature; CGRP immunoreactivity occurred also in a minority of SP-IR fibers. NOS-IR nerve fibers were in contact with submucosal arteries but were the least frequent . After metamorphosis provoked by exogenous thyroxine, the number of SOM-IR endocrine cells in the stomach mucosa was increased as well as the density of VIP-IR, SER-IR, and SP-IR nerve fibers in the gastrointestinal tract. It is proposed that the observed increases may reflect refinements of the neurohormonal system after metamorphosis.     

Comparative neurochemical features of the innervation patterns of the gut of the basal actinopterygian,Lepisosteus oculatus,and the euteleost,Clarias batrachus

The structure and physiology of enteric system are very similar in all classes of vertebrates, although they have been investigated only occasionally in non‐mammalian vertebrates. Very little is known about the distribution of the neurotransmitters in the gut of actinopterygian fishes. Anatomical and physiological studies of enteric nervous systems in the spotted gar (Lepisosteus oculatus) and airbreathing catfish (Clarias batrachus), a non‐teleost and teleost actinopterygian, respectively, have not been undertaken. This study provides the first comprehensive characterization of the range of neurochemical coding in the enteric nervous system of these two species, including the chemical diversity of the mucosal endocrine cells in the pyloric stomach of Clarias. Autonomic innervation of the secretory glands is also described and reported herein for the first time for fishes. We also report splanchnic (spinal) innervation of the stomach, submucosal ganglia (that also colocalize with nNOS) and caudal intestine of Clarias. In both fish species, numerous 5HT, ChAT, nNOS and TH‐positive nerve fibres have been observed. These discoveries demonstrate that much more physiological and pharmacological data are needed before a comprehensive model of enteric nervous system control in vertebrates can be developed.     

Somatostatin, substance P and calcitonin gene-related peptide-positive intramural nerve structures of the human large intestine affected by carcinoma

The aim of this study was to investigate the arrangement and chemical coding of enteric nerve structures in the human large intestine affected by cancer. Tissue samples comprising all layers of the intestinal wall were collected during surgery form both morphologically unchanged and pathologically altered segments of the intestine (n=15), and fixed by immersion in buffered paraformaldehyde solution. The cryostat sections were processed for double-labelling immunofluorescence to study the distribution of the intramural nerve structures (visualized with antibodies against protein gene-product 9.5) and their chemical coding using antibodies against somatostatin (SOM), substance P (SP) and calcitonin gene-related peptide (CGRP). The microscopic observations revealed distinct morphological differences in the enteric nerve system structure between the region adjacent to the cancer invaded area and the intact part of the intestine. In general, infiltration of the cancer tissue resulted in the gradual (depending on the grade of invasion) first decomposition and reduction to final partial or complete destruction and absence of the neuronal elements. A comparative analysis of immunohistochemically labeled sections (from the unchanged and pathologically altered areas) revealed a statistically significant decrease in the number of CGRP-positive neurons and nerve fibres in both submucous and myenteric plexuses in the transitional zone between morphologically unchanged and cancer-invaded areas. In this zone, a decrease was also observed in the density of SP-positive nerve fibres in all intramural plexuses. Conversely, the investigations demonstrated statistically insignificant differences in number of SP- and SOM-positive neurons and a similar density of SOM-positive nerve fibres in the plexuses of the intact and pathologically changed areas. The differentiation between the potential adaptive changes in ENS or destruction of its elements by cancer invasion should be a subject of further investigations.     

Osteotropic effects by the neuropeptides calcitonin gene-related peptide, substance P and vasoactive intestinal peptide

Immunohistochemical phenotypic characterization of skeletal nerve fibers has demonstrated the expression of a restricted number of neuropeptides, including calcitonin gene-related peptide (CGRP), substance P (SP) and vasoactive intestinal peptide (VIP). According to the neuro-osteological hypothesis, such neuropeptides can be released and exert paracrine biological effects on bone cells present close to the nerve endings expressing these signaling molecules. The existence of such interplay is most convincingly shown by the hypothalamic control of bone formation, in the case of leptin stimulation of hypothalamic nuclei mediated by the sympathetic nervous system and inhibitory beta-adrenergic receptors on osteoblasts. In addition to these receptors, osteoblasts and osteoclasts express functional receptors for CGRP, SP and VIP, which can regulate both bone formation and bone resorption. The evidence for these observations is summarized in the present paper.     

Distribution of immunoreactive neuropeptides in the pancreas of the bullfrog,Rana catesbeiana,demonstrated by immunofluorescence

Indirect double immunofluorescence labelling for eight neuropeptides in the pancreas of the bullfrog, Rana catesbeiana, demonstrated the occurrence, distribution, and coexistence of certain neuropeptides in the exocrine and endocrine pancreas. Immunoreactivity of substance P (SP), calcitonin gene-related peptide (CGRP), vasoactive intestinal polypeptide (VIP), neuropeptide Y (NPY), FMRFamide (FMRF), and galanin (GAL) was localized in nerve fibers distributed between the acini and around the duct system and vasculature of the exocrine pancreas. In these regions, CGRP-immunoreactive fibers were more numerous than those containing the other five peptides. Almost all SP fibers showed coexistence of SP with CGRP, and about one third of fibers also showed coexistence of SP with VIP, NPY, FMRF, and GAL. In the endocrine pancreas, SP, CGRP, VIP, and GAL were recognized in the nerve fibers around and within the islets of Langerhans, and VIP and GAL fibers were more numerous than SP and CGRP fibers. All CGRP fibers, and about half of the VIP and GAL fibers were immunoreactive for SP. NPY- and FMRF-immunoreactive cells were found at the periphery of the islets. These findings suggest that the exocrine and endocrine pancreatic functions of the bullfrog are under the control of peptidergic innervation.     

Changes in urine levels of substance P,vasoactive intestinal peptide and calcitonin-gene-related peptide in patients with urinary tract infections

Urinary tract infections (UTI) are important health problems and predisposing causes of UTI are not entirely known. Neuro-immune interactions play an important role in human health and disease. Capsaicin-sensitive sensory nerves which in nerve bladder extensively regulate immune system through neuropeptides such as substance P (SP), calcitonin-gene related peptide (CGRP) and vasoactive intestinal peptide (VIP). In addition these neuropeptides also have anti-bacterial effects. To determine how the levels of these peptides changes during UTI, 67 patients (50–90 years-old) diagnosed with UTI in Akdeniz University Faculty of Medicine Hospital were compared with 37 healthy people 50 years or older as the control group. Additionally, 7 patients with UTI symptoms (dysuria, urgency) but with sterile pyuria were also included in the study. Urine samples from 15 patients, whose symptoms regressed with control urine cultures being sterile, were taken after completion of the treatments. Urine neuropeptide levels were determined by ELISA. CGRP levels are significantly higher in patients with UTI, but did not associate with pyuria whereas SP and VIP levels were significantly lower in patients with sterile pyuria, indicating sensory nerve deficiency. Since CGRP exerts immunosuppressive effects, increased levels of the peptide may predispose to UTI. Furthermore, the connection between the observed sensory nerve deficiency and sterile pyuria warrants further studies.     

Peptidergic innervation of the human clitoris.

In the present study, the distributions of neuropeptides in the normal human clitoris and in a clitoris from an adrenogenital syndrome (AGS) was demonstrated by immunohistochemistry (IHC). Immunohistochemical screening detected a complex network of nerve fibers containing vasoactive intestinal polypeptide (VIP), peptide histidine methionine (PHM), neuropeptide tyrosine (neuropeptide Y), C-flanking peptide of neuropeptide Y (CPON), calcitonin gene-related peptide (CGRP) and substance P immunoreactivities. Special attention was given to the VIP-related peptide helospectin, that has been detected in neuronal elements in the clitoris. No visible differences between the localization and distribution of peptidergic nerve fibers of normal and hypertrophic clitoris from AGS have been observed. Co-localization studies showed the co-existence of VIP, PHM and partly helospectin and neuropeptide Y with CPON within nerve fibers in the cavernous tissue and substance P and CGRP co-expression in nerve fibers especially underneath and within the glans clitoris.     

VIP and PHI coexist with an NPY-like peptide in intramural neurones of the small intestine

Vasoactive intestinal peptide (VIP), peptide histidine isoleucine (PHI) and neuropeptide Y (NPY) are neuropeptides present in all layers of the small intestine. NPY-immunoreactive fibres in the gut seem to derive from two sources. One population is of extramural (sympathetic) origin and contains noradrenaline, another is of intramural origin and does not contain noradrenaline. In the present study of mouse, rat and pig, immunocytochemistry showed immunoreactive PHI to coexist completely with immunoreactive VIP. This was predictable, since VIP and PHI derive from the same precursor. In addition, however, VIP and PHI were found to coexist with immunoreactive NPY in non-adrenergic (but not in adrenergic) nerve fibres and nerve cell bodies. This coexistence was unexpected, since the VIP precursor does not contain NPY-like sequences.     

Calcitonin gene-related peptide-like immunoreactivity in the human small intestine.

Calcitonin-gene-related-peptide (CGRP)-like immunoreactivity was localized in nerve fibres, neuronal somata and in mucosal endocrine cells of the human small intestine. Immunoreactive enteric neurons were more numerous in the submucous plexuses than in the myenteric plexus. Morphologically, they predominantly had the appearance of type II neurons. The majority of the CGRP-like immunoreactive nerve fibres ran within the ganglionic nerve plexuses. Only a small proportion could be observed in the lamina propria, the lamina muscularis mucosae, or the circular and longitudinal outer smooth muscle layer. These findings suggest that within the wall of the human small intestine neuronal CGRP of either extrinsic or intrinsic origin exerts its effect chiefly on other enteric neurons, and might be indirectly involved in the regulatory functions of the human small intestine.     

Neuropeptides in guinea pig trachea: Distribution and evidence for the release of CGRP into tracheal lumen

The airways of the guinea pig are richly innervated by peptide-containing nerve fibers. Among the most abundant neuropeptides are calcitonin gene-related peptide (CGRP) and substance P (SP), which are stored in nerve fibers located predominantly within and beneath the epithelium, and vasoactive intestinal peptide (VIP), which is located in fibers running mainly among smooth muscle bundles and seromucous glands. Sensory denervation (capsaicin treatment) of adult guinea pigs caused an almost total disappearance of CGRP- and SP-containing nerve fibers, while the density of VIP-containing nerve fibers located in smooth muscle seemed to increase. In the isolated trachea, perfused luminally, CGRP was found to appear in the intraluminal fluid after exposure to capsaicin but not after electrical vagal stimulation. CGRP concentrations in the tracheal wall did not change significantly. Luminally applied CGRP did not affect smooth muscle tension, measured as intraluminal volume changes.     

Secretoneurin: A new peptide in the human enteric nervous system

Secretoneurin is a functional neuropeptide derived from secretogranin II (chromogranin C). This proprotein is processed to varying degrees in neuroendocrine tissues. In the present study we established by gel filtration high performance liquid chromatography that in human intestinal wall and mucosa an antiserum against secretoneurin detects as the major immunoreactive moiety the free peptide secretoneurin. In the mucosa some larger immunoreactive peptides were also present, however, a significant amount of the intact proprotein secretogranin II could not be detected. By immunohistochemistry we studied the distribution of secretoneurin within the gut. Antibodies to protein gene product 9.5 and chromogranin A were used to identify all neurons and endocrine cells, respectively, whilst those to the peptides substance P. CGRP and somatostatin were used for the further characterization of individual secretoneurin-positive structures. Secretoneurin immunoreactivity was found in nerve fibres in all layers of the gut wall. In both myenteric and submucous plexuses, nerve fibres and the majority of ganglion cells were secretoneurin-immunoreactive. In the mucosa, some secretoneurin-positive nerve processes ran parallel to the basal membrane of epithelial cells, occasionally invading the epithelial layer. Secretoneurin immunoreactivity was found in endocrine cells, mostly D cells, in the following regions in descending order of density: stomach/duodenum; rectum; colon; ileum. Thus, secretoneurin is a new major peptide within the human enteric neuroendocrine system. Its presence in abundant myenteric ganglion cells may imply a role in the modulation of gastrointestinal motility. The chemotactic properties of secretoneurin and its possible localization in sensory fibres suggest that this peptide may be involved in the genesis of intestinal inflammation.     

Innervation of the gastrointestinal canal of the toad Bufo marinus by neurons containing 5-hydroxytryptamine-like immunoreactivity

Summary The gut of the toad, Bufo marinus, was examined for evidence of enteric neurons containing 5-hydroxytryptamine-like immunoreactivity. Such neurons were absent from the stomach. They were present in the small intestine, with processes confined to the myenteric plexus. Immunoreactive nerve cell bodies lay on branches of the pelvic nerves supplying the large intestine; fibres were found in the submucosa of the posterior large intestine and in the muscularis externa of the anterior large intestine. It is concluded, on morphological grounds, that the neurons in the small intestine are interneurons, whereas those in the large intestine are postganglionic parasympathetic motoneurons.