Projections and chemical coding of neurons with immunoreactivity for nitric oxide synthase in the guinea-pig small intestine

Localization of choline acetyltransferase and NADPH diaphorase activities in the submucous ganglia of the guinea-pig colon

A combined immunohistochemical and histochemical demonstration of choline acetyltransferase (ChAT) and nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-d) was carried out, respectively, to determine the localization of the neurotransmitters, acetylcholine and nitric oxide (NO) in the submucous neurons of guinea-pig colon. Almost half of the submucous neurons in the guinea-pig colon exhibited ChAT-immunoreactivity. Some of the ChAT-immunoreactive neurons were also stained for NADPH-d, although most of them showed only weak to moderate diaphorase activity. Many of the submucous neurons displayed exclusively either ChAT or NADPH-d activity. A close spatial relationship was observed between the cholinergic and nitrergic submucous neurons. Thus, in light microscopy, some ChAT-immunoreactive fibres were closely associated with the NADPH-d-positive nerve cell bodies. Ultrastructural study extended the fact that many of the ChAT-immunoreactive terminals made synaptic contacts with the soma of the NADPH-d-positive submucous neurons. A remarkable feature was the demonstration of ChAT and NADPH-d in some of the neurons and their presynaptic axon terminals, suggesting the co-localization of acetylcholine and NO as neurotransmitters in the submucous neurons and their presynaptic axon terminals. It is suggested that the submucous neurons with their specific neurochemical codings would subserve different functions.

Nitrergic innervation and relaxant response of rectal circular smooth muscle

PURPOSE

This study was designed to investigate whether nitric oxide mediates inhibitory innervation in human rectal circular smooth muscle.

METHODS

Tissue was obtained from the midrectum of patients undergoing anterior resection for carcinoma. Adjacent strips of circular muscle were dissected and mounted in superfusion organ baths for isometric tension recording and initially loaded with 1 g of weight. Strips were continuously bathed with standard Krebs solution (37 degrees C, bubbled with 97 percent O2/3 percent CO2) containing 3 X X 10(-6) M guanethidine and 3 X 10(-6) M atropine sulfate to block adrenergic and muscarinic cholinergic neurotransmission. After equilibration, strips had no intrinsic tone, and reproducible and stable tension was, therefore, induced by the addition of 3 X 10 M histamine for five-minute "test" periods, during which electrical field stimulation (EFS) and additional drugs were applied.

RESULTS

EFS elicited frequency-dependent, neurogenic (tetrodotoxin-sensitive) relaxations of precontracted strips. Addition of N-w-nitro-L-arginine, a powerful competitive inhibitor of nitric oxide synthase, reduced the relaxant response to EFS in a dose-dependent fashion, and effect reversed by addition of s X 10(-4) M L-arginine but not by D-arginine. Addition of exogenous nitric oxide (sodium nitroprusside) mimicked the relaxant response induced by EFT.

CONCLUSIONS

Human rectal circular smooth muscle receives an intrinsic inhibitory innervation mediated by nitric oxide. The presennce of a residual response following blockade of the enzyme nitric oxide synthase suggests the involvement of additional neurotransmitters.

Co-localization of NADPH diaphorase reactivity and vasoactive intestinal polypeptide in human colon

Nitric oxide-containing nervous structures were localized in the human colon using NADPH diaphorase activity and nitric oxide synthase immunoreactivity. We found some, solitary NADPH diaphorase-reactive and nitric oxide synthase-immunoreactive neurons in the submucous plexus, while the myenteric plexus contained several neurons, often arranged in clusters, and nerve fibers showing these markers. The circular muscle layer contained a dense plexus of NADPH diaphorase-reactive nerves, which was greater than that in the longitudinal muscle layer. We report on co-localization of NADPH diaphorase activity and VIP immunoreactivity in several neurons of the myenteric ganglia. Such co-localization has not been reported previously for human colon. Localization of nitric oxide synthase and VIP in the myenteric plexus and in the nerves of circular muscle layer raises the possibility that nitric oxide contributes to the regulation of motility in the human colon.

Nitric oxide synthase and chemical coding in cat sympathetic postganglionic neurons

Nitric oxide synthase-like immunoreactivity was found in a subpopulation of sympathetic postganglionic neurons in the cat stellate and lower lumbar ganglia. In the ganglia of other segments such cells were rare. Double staining for tyrosine hydroxylase-like immunoreactivity and nitric oxide synthase-like immunoreactivity or the reduced nicotinamide adenine dinucleotide phosphate diaphorase reaction indicated that nitric oxide synthase-like immunoreactivity and reduced nicotinamide adenine dinucleotide phosphate diaphorase reactivity was always co-localized and was confined to tyrosine hydroxylase-negative (presumably cholinergic) ganglion cells, and was present in most of them. The occurrence of nitric oxide synthase in two subpopulations of cholinergic postganglionic neurons was investigated in triple staining experiments. Presumptive sudomotor neurons have been previously defined as scattered cells containing calcitonin gene-related peptide-like immunoreactivity, usually accompanied by vasoactive intestinal peptide-like immunoreactivity: 99% of these contained nitric oxide synthase. Presumptive muscle vasodilator neurons have been previously identified as clumped cells with strong vasoactive intestinal peptide-like immunoreactivity but no calcitonin gene-related peptide-like immunoreactivity: 70% of these contained nitric oxide synthase. Sweat glands were found in the paw pad skin surrounded by varicose fibres showing calcitonin gene-related peptide-like immunoreactivity and vasoactive intestinal peptide-like immunoreactivity, confirming previous work. Such fibres also stained for nitric oxide synthase-like immunoreactivity and reduced nicotinamide adenine dinucleotide phosphate diaphorase reactivity, although their staining was relatively weaker than in the corresponding cell bodies. Varicose fibres with the same chemical coding were also found around all large and most medium and small arteries in the paw skin as well as around arteriovenous anastomoses. Fibres with the muscle vasodilator coding (vasoactive intestinal peptide-like immunoreactivity without calcitonin gene-related peptide-like immunoreactivity) were not seen in paw skin. These results suggest that nitric oxide may act as a co-transmitter (with acetylcholine, substance P, vasoactive intestinal peptide and calcitonin gene-related peptide) in sudomotor neurons and (with acetylcholine and vasoactive intestinal peptide) in vasodilator neurons. Collateral branches of sudomotor neurons may innervate skin vessels, and release vasodilator transmitters including nitric oxide to cause the vasodilatation which provides the fluid supply for sweat formation. Alternatively, separate vasodilator neurons to skin may share the same chemical code as sudomotor neurons.

Nitrergic inhibitory innervation of porcine rectal circular smooth muscle

This study was performed to determine whether nitric oxide contributes to inhibitory non-adrenergic non-cholinergic (NANC) neurotransmission in the circular smooth muscle layer of pig rectum. Smooth muscle strips were mounted for isometric tension recording in superfusion organ baths. In the presence of atropine sulphate and guanethidine, transmural electrical field stimulation (EFS) produced frequency-dependent relaxation of precontracted muscle strips. N omega-nitro-L-arginine (L-NOArg), a powerful competitive antagonist of nitric oxide synthase, reduced the relaxant response in dose-dependent fashion; this response was maximally reduced by mean(s.e.m.) 86.5(2.6) per cent (P = 0.0003) at a concentration of 3 x 10(-5) mol/l L-NOArg. The response was restored by the addition of L-arginine. Sodium nitroprusside, an exogenous donor of nitric oxide, mimicked the relaxant response. Responses to EFS were abolished by tetrodotoxin. These results suggest that inhibitory NANC neurotransmission in this tissue is mediated, at least in part, by nitric oxide. The failure of L-NOArg to completely abolish the relaxant response suggests that additional neurotransmitters may be involved.

Do vasoactive intestinal peptide (VIP)- and nitric oxide synthase-immunoreactive terminals synapse exclusively with VIP cell bodies in the submucous plexus of the guinea-pig ileum?

In the submucous plexus of the guinea-pig ileum, previous light-microscopic studies have revealed that vasoactive intestinal peptide (VIP)-immunoreactive and nitric oxide synthase (NOS)-immunoreactive terminals are found predominantly in association with VIP-immunoreactive nerve cell bodies. In this study, double-label immunohistochemistry at the light-microscopic level demonstrated co-localization of NOS-immunoreactivity and VIP-immunoreactivity in axon terminals in submucous ganglia. About 90% of nerve fibres with NOS-immunoreactivity or VIP-immunoreactivity were immunoreactive for both antigens; only about 10% of labelled varicosities contained only NOS-immunoreactivity or VIP-immunoreactivity. The VIP/NOS varicosities were more often seen in the central parts of the ganglia, close to the VIP-immunoreactive cell bodies. Ultrastructural immunocytochemistry with antibodies to VIP was used to determine if NOS/VIP terminals synapse exclusively with VIP-immunoreactive nerve cell bodies. We examined the targets of VIP-immunoreactive boutons in two submucous ganglia from different animals. Serial ultrathin sections were taken through the ganglia after they had been processed for VIP immunocytochemistry. For each cell body, the number of VIP inputs (synapses and close contacts) was determined. The number of VIP-immunoreactive synapses received by the cell bodies of submucous neurons varied from 0-4 and the number of VIP-immunoreactive close contacts varied from 3-10. There was no significant difference between VIP-immunoreactive nerve cell bodies and non-VIP nerve cell bodies in the number of VIP-immunoreactive synapses and close contacts they received. Thus, the implication from light microscopy that NOS/VIP terminals end predominantly on VIP nerve cells was not vindicated by electron microscopy.

Distribution and colocalization of NADPH-diaphorase activity, nitric oxide synthase immunoreactivity, and VIP immunoreactivity in the newly hatched chicken gut

BACKGROUND

The distribution and colocalization of nitric oxide synthase and NADPH-diaphorase have been investigated quite extensively in the mammalian gut; however, no such study has been undertaken in the avian gut. In the present report, we have therefore studied the distribution and coexpression of nitric oxide synthase (NOS), NADPH-diaphorase, and vasoactive intestinal polypeptide (VIP) in enteric neurons of the newly hatched chicken gut.

METHODS

Immunohistochemical methods were used to detect NOS immunoreactivity (NOS-IR) and VIP immunoreactivity (VIP-IR). NADPH-diaphorase activity was detected using a histochemical technique.

RESULTS

Neurons expressing NADPH-diaphorase activity, NOS-IR, and VIP-IR were detected in both the myenteric and submucous plexus of all regions of the gastrointestinal tract examined. All NADPH-diaphorase positive neurons were also NOS-IR and all NOS-IR neurons were NADPH-diaphorase positive, in both plexuses, indicating that NADPH-diaphorase can be used as a marker for NOS containing neurons in the chicken gut. The majority of VIP-IR neurons also expressed NADPH-diaphorase activity. Only few neurons that expressed NADPH-diaphorase activity did not express VIP-IR. The proportion of VIP immunopositive neurons that were NADPH-diaphorase negative increased anally and these neurons were more prominent in the submucous than the myenteric plexus ganglia. NADPH-diaphorase positive, NOS-IR, and VIP-IR nerve fibres were detected in the circular muscle, but very few, if any, were present in the longitudinal muscle. VIP-IR, but not NOS-IR or NADPH-diaphorase activity, was detected in mucosal fibres, in contrast to the situation in the mammalian gut.

CONCLUSIONS

These results indicate that in birds, as in mammals, nitric oxide may play a role in the neural control of the gut musculature, but that it is unlikely to be involved in the nervous control of mucosal activity.

Origins of nerve fibers containing nitric oxide synthase in the rat celiac-superior mesenteric ganglion

The origin of nitric oxide synthase-containing nerve fibers in rat celiac-superior mesenteric ganglion was examined using retrograde tracing techniques combined with the immunofluorescence method. Fluoro-Gold was injected into the celiac-superior mesenteric ganglion. Neuronal cell bodies retrogradely labeled with Fluoro-Gold in the thoracic spinal cord, the dorsal root ganglia at the thoracic level, the nodose ganglion, and the intestine from the duodenum to the proximal colon were examined for nitric oxide synthase immunoreactivity. About 60% of sympathetic preganglionic neurons in the intermediolateral nucleus projecting to the celiac-superior mesenteric ganglion were immunoreactive for nitric oxide synthase, as were approximately 27% of nodose ganglion neurons and about 65% of dorsal root ganglion neurons projecting to the celiac-superior mesenteric ganglion. Neurons projecting to the celiac-superior mesenteric ganglion were found in the myenteric plexus of the small and large intestine. In the proximal colon, about 23% of such neurons were immunoreactive for nitric oxide synthase. However, in the small intestine, no immunoreactivity was found in these neurons.

Alpha-NADPH appears to be primarily oxidized by the NADPH-diaphorase activity of nitric oxide synthase (NOS)

Biochemical studies have shown that the NADPH-diaphorase (NADPH-d) activity of nitric oxide synthase (NOS) represents only a part of the total cellular diaphorase pool. Histochemically, NADPH-d activity can be demonstrated in cells expressing no constitutive NOS. Therefore, attempts aimed to improve the specificity of the NADPH-d reaction are currently being undertaken. In this study, the effect of replacing the natural and common diaphorase substrate beta-NADPH with the artificial stereoisomer alpha-NADPH on the extent of NADPH-d staining was examined. When beta-NADPH served as the substrate, discrete populations of central and peripheral neurons as well as numerous non-neural cells in many organs of common laboratory rodents (mouse, rat, gerbil, hamster, guinea pig) and marmosets were found to generate formazan. Substitution of alpha-NADPH for beta-NADPH resulted in reduced staining intensity of nerve cells and muscle fibers. Furthermore, alpha-NADPH-d staining of macula densa cells, enterocytes and granulocytes varied according to the species examined. No reaction was observed in most other cells which stained positively for beta-NADPH-d activity. Examination of adjacent sections, incubated for the demonstration of NOS-immunoreactivity, revealed that alpha-NADPH-d activity and NOS immunostaining are strictly colocalized in neurons, striated muscle fibers and, species-dependently, in macula densa cells. It can thus be concluded that, with the exception of gut granulocytes, alpha-NADPH is primarily metabolized by the reductase activity of NOS.

Nitric oxide in the peripheral nervous system

Nitric oxide (NO) is a neurotransmitter and neuromodulator in the central nervous system, but this small labile substance also seems to serve as a peripheral neurotransmitter. Abundant evidence is now available that NO, synthesized from L-arginine by NO synthase (NOS), is a nonadrenergic noncholinergic relaxant transmitter of gastrointestinal smooth muscle. Electrically induced nonadrenergic noncholinergic relaxations are antagonized by NOS inhibitors in vitro and in vivo. In a bioassay superfusion system, the release of a substance with the pharmacological characteristics of NO from a gastrointestinal smooth muscle preparation was detected; also, indirect measurements (e.g. of the NO metabolite nitrite or of the co-product of its synthesis L-citrulline) suggest NO release. Immunohistochemistry with antibodies raised against the neuronal NOS showed immunoreactivity in cell bodies of neurones in the myenteric plexus and in nerve fibres in the muscular layer. These data suggest that nerve endings, innervating smooth muscle, are able to release NO that will penetrate the cells to induce relaxation (i.e. nitrergic neurotransmission). It is unlikely that NO as such is stored and it is generally accepted that it is synthesized on demand when the nerve endings are excited, although the possibility of the release of a NO-containing molecule protecting it from degradation in the junction has been proposed. Other sources than neurones (interstitial cells, smooth muscle cells) for the NO involved in nonadrenergic noncholinergic inhibitory transmission have also been proposed. Using NADPH diaphorase as a marker for neuronal NOS, deficiency of the nitrergic innervation has been shown in isolated tissue from patients with infantile hypertrophic pyloric stenosis, achalasia and Hirschsprung's disease, suggesting that a lack of NO release might be involved in these disorders. Evidence in favour of nitrergic neurotransmission to smooth muscle has also been obtained in the respiratory and lower urinary tract, the corpora cavernosa and some blood vessels.

Ultrastructural examination of the targets of serotonin-immunoreactive descending interneurons in the guinea pig small intestine

Serotonin neurons are descending interneurons in the myenteric plexus of the guinea pig small intestine. Preembedding single- and double-label immunocytochemistries at the ultrastructural level were used to identify the targets of these serotonin interneurons. Serial ultrathin sections were taken through a myenteric ganglion that had been processed for serotonin immunocytochemistry. The ganglion contained the cell bodies of 69 neurons, including 2 serotonin neurons and 6 neurons with the ultrastructural features of Dogiel type II cells. For each cell body in the ganglion, the number of serotonin inputs (synapses and close contacts) was determined. About 59% of the cell bodies did not receive any serotonin inputs. The most abundant serotonin terminals were related to two targets: other serotonin descending interneurons and a population of neurons with Dogiel type I morphology, but whose neurochemistry and function is unknown. The serotonin inputs to the serotonin cell bodies were located predominantly on the lamellar dendrites. Each of the Dogiel type II neurons received 3 or fewer serotonin inputs, and none of the serotonin inputs to Dogiel type II neurons formed a synapse. Overall, about 40% of the serotonin inputs formed synapses. The serotonin inputs to neurons that received many serotonin inputs were more likely to show synaptic specializations than serotonin inputs to neurons that received few serotonin inputs. Inhibitory motor neurons contain nitric oxide synthase (NOS). At the light microscope level, serotonin nerve fibers do not form dense pericellular baskets around NOS cell bodies. To determine whether there are serotonin inputs to NOS neurons, serial ultrathin sections were taken through a myenteric ganglion that had been processed for preembedding double-label immunocytochemistry, in which the NOS neurons were labeled with peroxidase-diaminobenzidine and the serotonin neurons with silver-intensified 1 nm gold. Only 1 out of 9 NOS cells examined in serial section received more than 5 serotonin inputs. The results suggest that, in the guinea pig small intestine, the serotonin descending interneurons are not an essential element of the descending inhibitory reflex.

Colocalization of neuropeptides and NADPH-diaphorase in the intra-adrenal neuronal cell bodies and fibres of the rat

Colocalization of vasoactive intestinal peptide, neuropeptide Y, calcitonin gene-related peptide, substance P, and tyrosine hydroxylase, respectively, with NADPH-diaphorase staining in rat adrenal gland was investigated using the double labelling technique. All vasoactive intestinal peptide- and some neuropeptide Y-immunoreactive intrinsic neuronal cell bodies seen in the gland were double stained with NADPH-diaphorase. Double labelling also occurred in some nerve fibres immunoreactive to vasoactive intestinal peptide and neuropeptide Y in the medulla and cortex. No colocalization of calcitonin gene-related peptide, substance P or tyrosine hydroxylase immunoreactivity with NADPH-diaphorase staining was observed. However, nerve fibres with varicosities immunoreactive for all the neuropeptides examined were closely associated with some of the NADPH-diaphorase-stained neuronal cell bodies. Thus, in rat adrenal gland, nitric oxide is synthesized in all ganglion cells containing vasoactive intestinal peptide and in some containing neuropeptide Y, but not in those containing calcitonin gene-related peptide, substance P or tyrosine hydroxylase.

Vagal control of nitric oxide and vasoactive intestinal polypeptide release in the regulation of gastric relaxation in rat

1. Gastric motility and neurotransmitter release in response to vagal stimulation were studied using a vascularly isolated perfused rat stomach. Gastric motor responses were recorded by a strain gauge force transducer implanted on the proximal stomach. 2. Electrical stimulation of vagal trunk (0.5-20 Hz) produced a triphasic response which was composed of a rapid transient relaxation (first phase) followed by a phasic contraction (second phase) and a delayed prolonged relaxation (third phase). Maximum responses of the first, second and third phase were observed at 2.5, 5 and 10 Hz, respectively. Intra-arterial infusion of tetrodotoxin (0.1 microM) or hexamethonium (100 microM) completely abolished the triphasic response. 3. The nitric oxide (NO) biosynthesis inhibitor NG-nitro-L-arginine (L-NNA; 100 microM) significantly antagonized the rapid relaxation but had no effect on the delayed relaxation, while vasoactive intestinal polypeptide (VIP) antagonist (1 microM) significantly reduced the delayed relaxation without affecting the rapid relaxation. 4. In response to vagal stimulation, NO production ([3H]citrulline formation in gastric tissue preloaded with [3H]arginine) was maximum at 2.5 Hz, whereas VIP release into the venous effluent was largest at 10 Hz. Hexamethonium abolished vagal-stimulated NO production and VIP release. L-NNA had no effect on VIP release in response to vagal stimulation. 5. The nicotinic receptor agonist 1,1-dimethyl-4-phenylpiperizinium (DMPP; 100 microM) also caused a triphasic response similar to that observed with vagal stimulation and produced a significant increase in VIP and NO formation. DMPP-evoked VIP release was not affected by L-NNA. Similarly, DMPP-evoked NO production was not antagonized by VIP antagonist. 6. These results suggest that vagus nerve stimulation evokes NO and VIP release via nicotinic synapses which cause different modes of relaxation of the stomach. There is no interaction between NO and VIP release in response to vagal stimulation.

NADPH-diaphorase-positive nerve fibers in smooth muscle layers of opossum esophagus: gradients in density

Nitric-oxide-releasing nerves regulate esophageal smooth muscle function. The density of such nerve fibers may differ in the different functional parts of the esophagus. We used both inspection and gray-scale analysis of digitized images to seek differences in density of such nerve fibers, stained for reduced nicotinamide adenine dinucleotide phosphate diaphorase (NADPH-diaphorase), between esophageal body and esophago-gastric sphincter and between smooth muscle layers in the opossum esophagus. Sections of Swiss roll preparations of the entire organ were stained for NADPH-diaphorase and for immunoreactivity to vasoactive intestinal polypeptide (VIP), calcitonin gene-related peptide (CGRP), galanin (GAL), substance P (SP) and constitutive nitric oxide synthase (cNOS). In the circular muscle layer, NADPH-diaphorase-positive fibers were most abundant at the cephalic end of the esophageal body with a significant decline toward and through the esophago-gastric sphincter. In the longitudinal muscle layer and the longitudinally-oriented muscularis mucosae, NADPH-diaphorase-positive nerve fibers were most abundant at the esophago-gastric sphincter with a significant decline toward and through the striated-smooth muscle junction. cNOS immunoreactivity co-localized with NADPH-diaphorase activity. Fibers stained for CGRP immunoreactivity were distributed like the NADPH-diaphorase-positive fibers. Fibers stained for immunoreactivity to the other peptides (VIP, GAL, SP) showed no clear differences in distribution along the esophagus in any of the muscle layers.

Characterisation of neurons with nitric oxide synthase immunoreactivity that project to prevertebral ganglia

Retrograde dye tracing was combined with immunohistochemistry to determine the distributions of nitric oxide synthase (NOS) immunoreactive nerve cells that project to prevertebral ganglia from the gastrointestinal tract and spinal cord of the guinea pig. An antiserum was raised against the neuronal form of NOS by selecting an amino-acid sequence specific to this form as immunogen. The antiserum recognised a single band at 150 kDa on Western blots of rat brain extract. Enteric nerve cells that were labelled by Fast Blue injected into the coeliac ganglion were not NOS immunoreactive in the small intestine, whereas 40-70% were reactive in the large intestine. Retrograde dye injected into the inferior mesenteric ganglion labels cells in the colon and rectum; 60-70% were immunoreactive for NOS. The NOS-immunoreactive nerve fibres arising in the intestine appear to end selectively around somatostatin-immunoreactive nerve cells in the coeliac and inferior mesenteric ganglia. Preganglionic nerve cell bodies in the intermediolateral column and dorsal commissural nucleus from T12 to L2 were labelled from the inferior mesenteric ganglion. Nearly 70% of neurons at each level were NOS immunoreactive. Thus, two sources of NOS terminals in prevertebral ganglia have been identified, intestinofugal neurons of the large, but not the small intestine, and sympathetic preganglionic neurons.

Localization of NADPH-diaphorase activity in the submucous plexus of the guinea-pig intestine: light and electron microscopic studies

The localization of reduced nicotinamide adenine dinucleotide phosphate diaphorase in the submucous plexus of duodenum, jejunum, ileum, proximal colon, distal colon and rectum in the guinea-pig was examined histochemically by light and electron microscopy. The majority of reactive submucous neurons displayed features common to either Dogiel type I or type II neurons; some were closely adherent to the outer walls of lymphatic vessels. The use of 2-(2'-benzothiazolyl)-5-styryl-3-(4'-phthalhydrazidyl) tetrazolium chloride (BSPT) at the ultrastructural level showed that nicotinamide adenine dinucleotide phosphate diaphorase is a membrane-associated protein widely distributed in the cells, including the rough endoplasmic reticulum, Golgi apparatus and synaptic vesicles in the axon terminals associated with submucous neurons. On the basis of their diaphorase reactivity or the lack of it, the submucous neuronal somata and their associated terminals were observed to form several different kinds of synaptic configurations. The present quantitative analysis showed that the frequency of reactive submucous neurons in the large intestine was significantly higher than in the small intestine. Based on the ultrastructural localization of the diaphorase reaction product in positive cells, it is speculated that nitric oxide might be synthesized within the neurons. The demonstration of different synaptic configurations in the submucous ganglia suggests that the functional interaction between submucous neurons is extremely complex. Finally, the higher frequency of diaphorase reactive submucous neurons in the large intestine than in the small intestine indicates that submucous neurons in these two gut regions may not play equivalent roles.

Colocalization of NADPH-diaphorase staining and VIP immunoreactivity in neurons in opossum internal anal sphincter

Nitric oxide and vasoactive intestinal polypeptide (VIP) are important inhibitory neurotransmitters mediating relaxation of the internal anal sphincter. The location and coexistence of these two neurotransmitters in the internal anal sphincter has not been examined. We performed a double-labeling study to examine the coexistence of nitric oxide synthase and VIP in the opossum internal anal sphincter using the NADPH-diaphorase technique which is a histochemical stain for nitric oxide synthase. In perfusion-fixed, frozen-sectioned tissue, VIP-immunoreactive neurons were labeled using immunofluorescence histochemistry. After photographing the VIP-immunoreactive neurons, nitric oxide synthase was labeled using the NADPH-diaphorase technique. Ganglia containing neuronal cell bodies were present in the myenteric plexus for the entire extent of the internal anal sphincter. VIP-immunoreactive and NADPH-diaphorase-positive neurons were present in ganglia in the myenteric as well as the submucosal plexuses. Most of the VIP-immunoreactive neurons were also NADPH-diaphorase positive. VIP and nitric oxide synthase are present and frequently coexist in neurons in the internal anal sphincter of the opossum. These neurons may be an important source of inhibitory innervation mediating the rectoanal reflex-induced relaxation of the sphincter. The demonstration of the coexistence of these two neurotransmitters will be of fundamental importance in unraveling their relationship and interaction in the internal anal sphincter as well as other systems.

Neurochemical coding of enteric neurons in the guinea pig stomach

The aim of this study was to investigate the neurochemical coding of myenteric neurons in the guinea pig gastric corpus by using immunohistochemical methods. Antibodies and antisera against calbindin (CALB), calretinin (CALRET), choline acetyltransferase (ChAT), calcitonin gene-related peptide (CGRP), dopamine beta-hydroxylase (DBH), beta-endorphin (ENK), neuropeptide Y (NPY), neuron-specific enolase (NSE), nitric oxide synthase (NOS), protein gene product 9.5 (PGP), parvalbumin (PARV), serotonin (5-HT), somatostatin (SOM), substance P (SP), tyrosine hydroxylase (TH), and vasoactive intestinal peptide (VIP) were used. Double- and triple-labeling studies revealed colocalization of certain transmitters and enabled the identification of distinct subpopulations of gastric enteric neurons. NPY/VIP/NOS/ENK were present in 28% of all neurons, whereas 11% had NPY/VIP/DBH/ChAT; NOS-only neurons made up 2% of the population. The combination SP/ChAT/ENK occurred in 21% of the population, whereas SP/ChAT/ENK/CALRET and SP/CHAT/SOM/ +/- CALRET was identified in 5% and 6% of all cells, respectively. 5-HT-containing neurons comprised 2% of all cells and could be further classified by the presence of additional antigens as 5-HT/SP/(ChAT) or 5-HT/VIP/(ChAT). Approximately 21% of all neurons contained only ChAT with no additional antigen present and are referred to as ChAT/-. Gastric myenteric ganglion cells were not immunoreactive for CALB, PARV, CGRP, or TH. The results of this study indicate that gastric myenteric neurons can be characterized on the basis of different chemical coding. Neurochemical coding of corpus myenteric neurons revealed some similarities and significant differences in comparison with other regions of the gut. These differences might reflect adaptation of enteric nerves according to regional specialization and the distinct functions of the proximal stomach as a gastric reservoir.

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.

Coexistence of nitric oxide synthase, tyrosine hydroxylase and vasoactive intestinal polypeptide in human penile tissue--a triple histochemical and immunohistochemical study

Recently, nitric oxide (NO) has been believed to act as a neuronal messenger to mediate penile erection. In the present study using human penile tissue, we investigated the coexistence of neuronal NO synthase (NOS), tyrosine hydroxylase (TH) and vasoactive intestinal polypeptide (VIP) by a triple staining method using NADPH diaphorase (ND) staining, a specific histochemical marker of neuronal NOS, and immunohistochemical staining for TH and VIP. Numerous ND-positive nerve fibers and TH-containing fibers were seen in axon bundles, but their distributions were different. Only a few axons in the bundles showed VIP immunoreactivity. Abundant fine varicose nerve terminals innervating cavernous smooth muscles and deep and helicine arteries were observed. The proportion of fibers showing TH-immunoreactivity in ND-positive terminals in the cavernous space was about 25%, and that of VIP was about 40%. Vasoactive intestinal polypeptide may act as a coworker in these fibers both in cavernous trabeculae and around arteries, as about 40% of NOS-containing fibers also showed VIP immunoreactivity. The physiological significance of the colocalization of TH and NOS is unclear, and further studies are required to know the physiological significance of the colocalization of NOS and other neurotransmitters in penile tissue.

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.

Nitric oxide nerves in the uterus are parasympathetic, sensory, and contain neuropeptides

Nitric oxide (NO) is synthesized in neurons and is a potent relaxor of vascular and nonvascular smooth muscle. The uterus contains abundant NO-synthesizing nerves which could be autonomic and/or sensory. This study was undertaken to determine: 1) the source(s) of NO-synthesizing nerves in the rat uterus and 2) what other neuropeptides or transmitter markers might coexist with NO in these nerves. Retrograde axonal tracing, utilizing Fluorogold injected into the uterine cervix, was employed for identifying sources of uterine-projecting neurons. NO-synthesizing nerves were visualized by staining for nicotinamide adenine dinucleotide phosphate (reduced)-diaphorase (NADPH-d) and immunostaining with an antibody against neuronal/type I NO synthase (NOS). NADPH-d-positive perikarya and terminal fibers were NOS-immunoreactive (-I). Some NOS-I/NADPH-d-positive nerves in the uterus are parasympathetic and originate from neurons in the pelvic paracervical ganglia (PG) and some are sensory and originate from neurons in thoracic, lumbar, and sacral dorsal root ganglia. No evidence for NOS-I/NADPH-d-positive sympathetic nerves in the uterus was obtained. Furthermore, double immunostaining revealed that in parasympathetic neurons, NOS-I/NADPH-d-reactivity coexists with vasoactive intestinal polypeptide, neuropeptide Y, and acetylcholinesterase and in sensory nerves, NOS-I/NADPH-d-reactivity coexists with calcitonin gene-related peptide and substance P. In addition, tyrosine hydroxylase(TH)-I neurons of the PG do not contain NOS-I/NADPH-d-reactivity, but some TH-I neurons are apposed by NOS-I varicosities. These results suggest NO-synthesizing nerves in the uterus are autonomic and sensory, and could play significant roles, possibly in conjunction with other putative transmitter agents, in the control of uterine myometrium and vasculature.

Immunohistochemical identification of neurons in ganglia of the guinea pig sphincter of Oddi

The sphincter of Oddi is a smooth muscle sphincter that regulates the flow of bile into the duodenum. To identify potential chemical coding in sphincter of Oddi neurons, immunohistochemistry and histochemistry were employed to assay for putative neurotransmitters and related synthetic enzymes in wholemount preparations, with and without colchicine treatment. Immunoreactivities for enkephalin-endorphin (ENK-END), substance P (SP), nitric oxide synthase, vasoactive intestinal peptide (VIP), neuropeptide Y (NPY), and calcitonin gene-related peptide (CGRP) were demonstrated within the ganglionated plexus. Roughly half of the neurons in the sphincter of Oddi expressed immunoreactivity for both SP and ENK-END, but not for nitric oxide synthase. About 25% of the neurons expressed nitric oxide synthase immunoreactivity as well as NADPH-diaphorase activity. This contingent of neurons was made up of two subgroups: one that expressed immunoreactivity for VIP, the other for NPY. Neurons that expressed CGRP immunoreactivity were sparse in sphincter of Oddi ganglia; however, many axons immunoreactive for both CGRP and SP were present in the ganglionated plexus. The CGRP/SP fibers are probably visceral afferents that may influence ganglionic output through axon reflex circuits. These results, along with studies of the actions of these neuroactive compounds on sphincter tone, support the view that ganglia of the sphincter of Oddi are largely comprised of excitatory (SP/ENK-END-immunoreactive) and inhibitory (nitric oxide synthase/VIP- or NPY-immunoreactive) neurons, and that sphincter of Oddi tone is controlled by the regulation of the outputs of these two groups of cells.

Appearance of neuropeptides and NADPH-diaphorase during development of the enteropancreatic innervation

Pancreatic ganglia are formed by neural crest-derived precursors, are innervated by enteric neurons, and contain neuropeptides. In addition, the enzyme NADPH-diaphorase is located in a subset of enteric and pancreatic neurons. The expression of neural markers (GAP-43 and NC-1), neurotransmitter-related markers (including neuropeptide Y (NPY), vasoactive intestinal peptide (VIP), gastrin-releasing peptide (GRP), galanin (GAL), dopamine beta hydroxylase (DBH), substance P (SP), calcitonin gene-related peptide (CGRP)), and NADPH-diaphorase was studied in the fetal and neonatal rat gut and pancreas (E12-P28) in situ and in vitro. NC-1, GAP-43 and DBH-immunoreactive cells were found in the primordial stomach on day E12, and in the pancreas on day E13, along with NPY in endocrine cells. Pancreatic NPY-immunoreactive neurons were detected by day E18. CGRP was seen in the foregut at day E12 but not in the pancreas until day E14. Other neuropeptides (SP, GAL, GRP and VIP) all appeared in the foregut earlier than in the pancreas. NADPH-diaphorase activity was first found in situ in foregut neurons on day E13, and in the pancreas on day E14, but seen in explants a day earlier. These observations show that development of neurons occurs earlier in the gut than in the pancreas, and that NADPH-diaphorase activity appears earlier than the immunoreactivities of the neuropeptides.

Pharmacological evidence that nitric oxide may be a retrograde messenger in the enteric nervous system

1. The effects of inhibition of nitric oxide synthase on neuro-neuronal and neuromuscular transmission during motility reflexes in the small intestine of the guinea-pig were examined. 2. Isolated segments of intestine were secured in a three chambered organ bath so that different parts of the reflex pathways could be independently exposed to drug-containing solutions. Reflexes were evoked by distension or compression of the mucosa in two adjacent chambers and reflex responses were recorded from the circular muscle with intracellular microelectrodes in the third chamber. Thus, the actions of drugs at connections between sensory neurones and interneurones, between interneurones and other interneurones and at motor neurones could be distinguished. 3. NG-monomethyl-L-arginine (L-NMMA; 100 microM), an inhibitor of nitric oxide synthase, did not affect the ascending excitatory reflex when added to either the central stimulation chamber or the recording chamber. 4. In contrast, L-NMMA (100 microM) enhanced the descending inhibitory reflex when added to the chamber in which stimuli were applied. This effect was prevented by prior exposure to L-arginine (100 microM), which had no effect by itself. Conduction of reflexes between the stimulus chamber and the recording chamber was unaffected by the presence of L-NMMA in an intervening chamber. 5. L-NMMA (100 microM) added to the recording chamber depressed the descending inhibitory reflex, an effect that was prevented by previous exposure to L-arginine. 6. The nitric oxide donor, sodium nitroprusside (100 microM), added to the stimulus chamber, depressed both ascending excitatory and descending inhibitory reflexes. When added to the middle chamber,sodium nitroprusside had no effect on conduction of reflexes through this chamber.7. It is deduced that nitric oxide, released from the cell bodies of descending interneurones, suppresses transmission from synaptic connections made with them by enteric sensory neurones.

Regulation of the descending relaxation phase of intestinal peristalsis by PACAP

The presence of pituitary adenylate cyclase-activating peptide (PACAP), a homologue of vasoactive intestinal peptide (VIP), in enteric neurons suggests that it may involved in the regulation of the descending relaxation phase of the peristaltic reflex. The role of PACAP was evaluated by measurement of PACAP release and by immuno-neutralization with specific monoclonal antibodies to PACAP-27 and PACAP-38, and an antibody to VIP. Electrical field stimulation at 4 Hz caused a 12-fold increase in PACAP release that was inhibited by 53 +/- 6% (P < 0.01) by the nitric oxide synthase inhibitor, NG-nitro-L-arginine (L-NNA). Orad stretch of colonic segments elicited descending relaxation and PACAP release in proportion to the degree of stretch. PACAP release induced by 10-g stretch was inhibited by 67 +/- 10% (P < 0.01) by L-NNA. Previous studies (Am. J. Physiol., 264 (1993) G334-G340) showed that orad stretch elicits also VIP release and nitric oxide (NO) production and that VIP release is inhibited (59%) by L-NNA. Preincubation of the segments with PACAP-27 plus PACAP-38 antibodies (50 micrograms/ml each), or with VIP antibody (1:60) inhibited descending relaxation at all degrees of stretch (inhibition with PACAP antibodies: 90 +/- 8% with 2-g and 22 +/- 5% with 10-g stretch). Preincubation with both PACAP and VIP antibodies virtually abolished descending relaxation. A similar pattern was observed with the antagonists, PACAP6-38 and VIP10-28, alone and in combination.(ABSTRACT TRUNCATED AT 250 WORDS)

Distribution pattern, neurochemical features and projections of nitrergic neurons in the pig small intestine

The presence and topographical distribution of nitrergic neurons in the enteric nervous system (ENS) of the pig small intestine have been investigated by means of nitric oxide synthase (NOS) immunocytochemistry and nicotinamide dinucleotide phosphate diaphorase (NADPHd) histochemistry. Both techniques yielded similar results, thus confirming that within the pig ENS the neuronal isoform of NOS corresponds to NADPHd. Intrinsic nitrergic neurons were not confined to the myenteric plexus; considerable numbers were also present in the outer submucous plexus. In the inner submucous plexus, NOS immunoreactivity or NADPHd staining was restricted to a few nerve fibres and nerve cell bodies. The nitrergic neurons displayed a wide variety in size and shape, but could all be characterized as being multidendritic uniaxonal. Nerve lesion experiments showed that the majority of the myenteric nitrergic neurons project in an anal direction. Evidence is at hand to show that a substantial proportion of these neurons contribute to the dense nitrergic innervation of the tertiary plexus and the circular smooth muscle layer. Some of the nitrergic neurons of the outer submucous plexus were equally found to send their axons towards the circular muscle layer. In some of the nitrergic enteric neurons, VIP, neuropeptide Y, galanin or protein 10 occurred colocalized, but not calbindin or serotonin. The present findings provide morphological evidence for the presence of NOS in a proportion of the enteric neurons in the small intestine of a large omnivorous mammal, i.e. the pig. The topographical features of the staining patterns of NOS and NADPHd are in accord with the results of neuropharmacological studies and argue for the existence of distinct nitrergic subpopulations acting either as interneurons or as motor neurons.

Characterization of alkaline phosphatase-reactive neurons in the guinea-pig small intestine

Endogenous alkaline phosphatase activity has been localized histochemically on the surface of enteric neurons of the guinea-pig small intestine by both light and electron microscopy. The enzyme activity was associated with some myenteric neurons that had Dogiel type I morphology, and the histochemical reaction products typically formed a honeycomb-like structure on labelled cell bodies. No Dogiel type II neurons in the myenteric plexus or submucous neurons showed alkaline phosphatase reactivity. Nerve fibres reactive for alkaline phosphatase were present in the myenteric plexus and ran in bundles in the circular muscle and deep muscular plexus. In addition, reactive varicose axons supplied the submucous plexus and non-ganglionated plexus of the mucosa. The results of interruption of the enteric neuronal pathways demonstrated that alkaline phosphatase-reactive myenteric neurons project anally to other myenteric ganglia, to the circular muscle and to the submucous plexus. Sequential enzyme histochemistry showed that virtually all alkaline phosphatase-reactive neurons also contained nitric oxide synthase, revealed by NADPH-diaphorase reactivity. It was estimated that 14-18% of all myenteric neurons showed alkaline phosphatase reactivity. About one-third of nitric oxide synthase-containing myenteric neurons, however, did not contain alkaline phosphatase activity. At the ultrastructural level, alkaline phosphatase activity was associated specifically with the plasma membranes of nerve cell bodies, axons and dendrites of some myenteric neurons. Reactive nerve fibres made close appositions with non-reactive submucous neurons and, within myenteric ganglia, predominantly with other alkaline phosphatase-reactive neurons. In addition to its presence in neurons, alkaline phosphatase reactivity was also present in some endothelial cells in blood vessels in the submucosa and in capillary pericytes. It is concluded, on the basis of the projections and neurochemistry, that in the guinea-pig small intestine alkaline phosphatase activity is associated with nitric oxide synthase-containing neurons which include inhibitory motor neurons to the circular muscle, and anally-directed interneurons to other myenteric and submucous neurons.

Colocalization of NADPH-diaphorase with neuropeptides in the intrapancreatic neurons of the chicken

Colocalization of nitric oxide with neuropeptides was investigated in the chicken pancreas by use of double staining combined with the indirect immunofluorescence technique and histochemistry for NADPH-diaphorase, a specific marker for neural nitric oxide synthase. NADPH-diaphorase positive ganglia were easily detected in the interlobular connective tissue. Many NADPH-diaphorase positive ganglion cells also showed immunoreactivity for VIP (80.9%) or galanin (76.2%). Some ganglion cells showed enzyme activity only (about 20%). Very few neurons were NADPH-diaphorase negative, but immunopositive for VIP (2.0%) or galanin (3.7%). The present study provides evidence that nitric oxide colocates with VIP and galanin in the chicken pancreas.

Relationship between nitric oxide and vasoactive intestinal polypeptide in enteric inhibitory neurotransmission

Although considerable evidence suggests that NO serves as a neurotransmitter in gastrointestinal muscles, it is unlikely to be the only substance involved in enteric inhibitory neurotransmission. Vasoactive intestinal polypeptide (VIP) is known to be expressed by inhibitory motor neurons in the gut, and it appears to be co-localized with nitric oxide synthase (NOS) in a subpopulation of enteric neurons. These data suggest that NO and VIP may be parallel neurotransmitters. Others have suggested that VIP is the primary inhibitory transmitter, and it stimulates production of NO in smooth muscle cells. In this "serial cascade" model NO is a paracrine substance. We performed experiments on circular muscles and cells from the canine proximal colon to further test the idea that NO and VIP are parallel neurotransmitters and to determine the validity of the serial cascade model in these muscles. We found that NO-independent inhibitory effects were unmasked when excitatory and NO-dependent inhibitory responses were blocked. NO-independent inhibitory effects were reduced by alpha-chymotrypsin and blocked by tetrodotoxin. NOS- and VIP-like immunoreactivities were co-localized in enteric neurons and varicose fibers in the circular muscle layer. Similar to several other reports we found no evidence for a constitutive NOS in smooth muscle cells. Several aspects of the serial cascade model were not supported by our results: (i) the electrical and mechanical effects of VIP did not depend upon NO synthesis; (ii) VIP-induced changes in [Ca2+]i did not depend upon NO synthesis; and (iii) VIP did not cause the release of NO from canine colonic muscles. These results are consistent with the hypothesis that NO and VIP are co-transmitters, released in parallel from enteric inhibitory nerves.

NOS-containing neurons in the rat gut and coeliac ganglia

Nitric oxide (NO) is considered an important inhibitory neurotransmitter in the gut. Nitric oxide synthase (NOS)-containing neurons were visualized by immunocytochemistry using antibodies against neuronal NOS in the oesophagus, the gastrointestinal tract and the coeliac ganglion of rat. NOS-containing nerve cell bodies were numerous in the myenteric but fewer in the submucous ganglia all along the gut. Synthesis of NOS in enteric nerve cell bodies was confirmed by in situ hybridization, demonstrating the presence of NOS mRNA. Varicose nerve fibers formed extensive networks in the circular smooth muscle and the myenteric ganglia. The pyloric sphincter contained abundant NOS-containing nerve fibers. NOS-containing nerve terminals were frequently found around the Brunner glands in the duodenum; scattered nerve terminals occurred in the gastric and colonic mucosa and around blood vessels in the submucosa all along the gut. The neuronal cell bodies in the coeliac ganglion were non-immunoreactive but frequently surrounded by baskets of NOS-immunoreactive nerve fibers. Double staining for NOS and neuropeptides in oesophagus, stomach and small and large intestine revealed that a small subpopulation of the NOS-containing nerve cell bodies stored in addition vasoactive intestinal peptide (VIP), and in oesophagus, stomach and small intestine also neuropeptide Y (NPY). However, NOS-containing nerve terminals, particularly those in the circular muscle of the gut, frequently contained VIP throughout the gut; in the oesophagus, stomach and the small intestine they contained also NPY.(ABSTRACT TRUNCATED AT 250 WORDS)

Distribution, origin and projections of nitric oxide synthase-containing neurons in gut and pancreas

Nitric oxide has been put forward as an important inhibitory neurotransmitter in the gut. Nitric oxide synthase-containing neurons were visualized by immunocytochemistry using antibodies against neuronal nitric oxide synthase or by beta-nicotinamide adenine dinucleotide phosphate diaphorase staining in whole mounts and cryostat sections from the gastrointestinal tract and pancreas of several mammals (mouse, rat, hamster, guinea-pig, cat and man). Nitric oxide synthase-containing neuronal cell bodies were numerous in the myenteric but fewer in the submucous ganglia all along the gut of all species. Varicose nerve terminals formed extensive networks in the circular smooth muscle and the myenteric ganglia. Nitric oxide synthase-containing nerve terminals were frequently found around the Brunner glands in the duodenum; scattered nerve terminals were also found in the gastric and colonic mucosa and around blood vessels in the submucosa all along the gut. In the rat small and large intestine nitric oxide synthase-containing submucous neurons terminated within the mucosa/submucosa and nitric oxide synthase-containing myenteric neurons issued short descending projections, approximately 3 mm, to the smooth muscle and other myenteric ganglia. In the pancreas of all species nitric oxide synthase-containing nerve cell bodies were regularly seen in intrapancreatic ganglia. Positive nerve fibers were mainly found within nerve trunks in interlobular spaces and as delicate fibers within the islets. Double staining for nitric oxide synthase and neuropeptides in intestine and pancreas of rat, guinea-pig and man revealed that only occasionally the nitric oxide synthase-containing nerve cell bodies stored in addition vasoactive intestinal peptide and neuropeptide Y, or enkephalin. However, nitric oxide synthase-containing nerve terminals, particularly those in the circular muscle of the gut, frequently contained vasoactive intestinal peptide/neuropeptide Y (rat and man) or vasoactive intestinal peptide/enkephalin (guinea-pig). In intrapancreatic ganglia few nitric oxide synthase-containing nerve cell bodies were also vasoactive intestinal peptide-immunoreactive. Coexistence of nitric oxide synthase and vasoactive intestinal peptide in nerve terminals could here be detected around blood vessels and interlobular ducts. The distribution of nitric oxide synthase indicates a major role of nitric oxide in the regulation of gut motility; a role in the regulation of blood flow and secretion in both gut and pancreas is also likely.

Nitric oxide-like activity in guinea pig colon as determined by effector responses, bioassay and chemiluminescence analysis

The role of nerve-induced release of nitric oxide (NO) as a modulator of neuroeffector transmission was studied in the longitudinal muscle of the guinea pig colon. The biological activity of a vascular relaxing factor released by nerve stimulation was examined in a bioassay cascade system. Furthermore, biochemical measurements of nerve-induced release of the NO metabolite nitrite (NO2-) were made with a chemiluminescence technique. Transmural nerve stimulation elicited contractile responses that were partly blocked by atropine and further inhibited after additional application of the tachykinin receptor antagonist CP-96, 345. The NO-synthase inhibitor N omega-nitro-L-arginine (NOARG) enhanced the nerve-induced contractions and concomitantly increased the basal degree of contraction ('tone'). The relaxations obtained by nerve stimulation after treatment with atropine and histamine were inhibited by NOARG. Electrical stimulation of the guinea pig colon released a non-adrenergic non-cholinergic (NANC) vascular relaxing factor into the tissue superfusate. The half-life of this factor down the cascade was the same as that observed with exogenous application of NO NOARG and tetrodotoxin (TTX) inhibited the release of the relaxing factor. During transmural nerve stimulation there was a significant increase in NO/NO2- release. This increase was inhibited by TTX and N omega-nitro-L-arginine methyl ester (L-NAME). In conclusion, pharmacological analysis as well as bioassay and biochemical measurements suggest that NO is released during nerve stimulation in the guinea pig colon, where it mediates smooth muscle relaxation.

Co-localization of nitric oxide synthase and vasoactive intestinal peptide immunoreactivity in neurons of the major pelvic ganglion projecting to the rat rectum and penis

Nitric oxide synthase (NOS)- and vasoactive intestinal peptide (VIP)-immunoreactive neurons projecting to the upper rectum or penis were examined using retrograde tracing combined with immunohistochemistry in the major pelvic ganglion of male rats. Five days after injection of Fluoro-Gold (FG) into the upper rectum or penis, the major pelvic ganglion was treated with colchicine. FG injected into the upper rectum labelled many ganglion neurons in the major pelvic ganglion. Immunohistochemistry showed that 37% of FG-labelled neurons were immunoreactive for NOS and 33% for VIP. After injection of FG into the penis, 41% of FG-labelled neurons were immunoreactive for NOS and 25% for VIP. Serial cryostat sections stained for NOS and VIP, respectively, showed the co-localization of NOS and VIP in the ganglion cells projecting to the rectum and penis. In the major pelvic ganglion of the colchicine-treated animals, about 17% of the ganglion cells were immunoreactive for NOS and 32% were immunoreactive for VIP. These neurons were small in diameter (less than 30 microns). A histogram showing cell sizes in cross-sectional areas of NOS-immunoreactive neurons coincided with that of VIP-immunoreactive neurons. Most of the NOS- and VIP-immunoreactive neurons were less than 600 microns. These results indicate that small neurons containing both NOS and VIP in the major pelvic ganglion project to the rectum and penis. In the penile erectile tissues and enteric ganglia, NO and VIP may be released from the same axons and may act concomitantly on the target tissue.

Tachykinin NK3 receptor mediates NANC hyperpolarization and relaxation via nitric oxide release in the circular muscle of the guinea-pig colon

In the presence of atropine (1 microM), guanethidine (3 microM) and of the tachykinin NK1 (SR 140,333 0.1 microM) and NK2 (GR 94,800 3 microM) receptor antagonists, the application of the tachykinin NK3 receptor selective agonist senktide, or that of neurokinin B, produced concentration-dependent sustained nonadrenergic noncholinergic (NANC) relaxation of mucosa-free circular muscle strips from the guinea-pig proximal colon. The maximal relaxant responses to senktide and neurokinin B were similar, approaching about 70% of the relaxation to 1 microM isoprenaline. Senktide (EC50 0.16 nM) was about 64-fold more potent than neurokinin B (EC50 10.3 nM). When tested in the presence of peptidase inhibitors (thiorphan 1 microM, captopril 1 microM and amastatin 10 microM), neurokinin B (EC50 0.24 nM) was equipotent to senktide (EC50 0.19 nM). At 1 nM, substance P and neurokinin A were ineffective in producing a NANC relaxation of the colon. At 1 microM substance P, neurokinin A and neurokinin B produced a NANC relaxation, which averaged 23, 40 and 79% of the maximal response to isoprenaline, respectively. In the presence of peptidase inhibitors, 1 nM substance P and neurokinin A produced threshold relaxant responses and, at 1 microM, the three natural tachykinins were equieffective (66 +/- 8, 72 +/- 5 and 75 +/- 5% of the relaxation to isoprenaline for substance P, neurokinin A and neurokinin B, respectively). The relaxant response to 1 nM senktide (producing about 70-80% of its maximal effect) was totally abolished by 1 microM tetrodotoxin and largely (> 90%) inhibited by 100 microM L-nitroarginine (L-NOARG). The inhibition by L-NOARG was partially reversed by L-arginine (3 mM) but not D-arginine. Apamin (1 microM) produced a slight (about 20%) inhibition of the response to senktide. The peptide blocker of N-type calcium channels, omega-conotoxin (0.1 microM) was ineffective. In sucrose gap electrophysiological experiments, superfusion with senktide (0.1 microM for 10 s) produced a slowly developing and prolonged hyperpolarization of the membrane and relaxation. Both effects were inhibited by L-NOARG while apamin had no effect. These findings indicate that a neuronal NK3 receptor mediates NANC hyperpolarization and relaxation of the circular muscle of the guinea-pig proximal colon, principally through the release of NO. NO generation/release in response to NK3 receptor stimulation does not require calcium influx through N-type calcium channels.

Colocalization of nitric oxide synthase with vasoactive intestinal peptide, neuropeptide Y, and tyrosine hydroxylase in nerves supplying the human ureter

The distribution and patterns of colocalization of nitric oxide synthase (NOS), vasoactive intestinal peptide (VIP), neuropeptide Y (NPY) and the catecholamine-synthesizing enzyme tyrosine hydroxylase (TH) were examined in nerve fibers supplying the human lower ureter using double label immunofluorescence. Many nerve fibers immunoreactive for NOS were observed within the ureter. Positive varicose fibers were seen running longitudinally within the smooth muscle bundles, particularly those of the inner layers of the ureter. Immunoreactive axons were also prominent within the subepithelium, and as plexi surrounding many blood vessels. The colocalization studies indicated that NOS was never present in presumptive sympathetic nerve fibers expressing TH. All fibers containing VIP, however, were also immunoreactive for NOS. In addition, a minor population of NOS fibers did not contain VIP. Neuropeptide Y coexisted with NOS in a significant number of nerve terminals, although fibers expressing only NPY were equally common. Several immunochemically distinct nerve populations can therefore be distinguished in the human ureter: (1) nerves containing NOS either with or without VIP; (2) NOS-immunoreactive fibers with NPY; and (3) those fibers expressing TH or NPY which do not contain NOS. The results indicate that some non-noradrenergic peptide-containing nerves in the human ureter have the capacity to synthesize nitric oxide (NO), and that NO may be involved in the regulation of ureteric motility.

Evidence for coexistence of ATP and nitric oxide in non-adrenergic, non-cholinergic (NANC) inhibitory neurones in the rat ileum, colon and anococcygeus muscle

The possible coexistence of the two non-adrenergic, non-cholinergic (NANC) inhibitory neurotransmitters, adenosine 5'-triphosphate and nitric oxide in the myenteric plexus was investigated using whole-mount preparations of rat ileum, proximal colon and anococcygeus muscle. The presence of adenosine 5'-triphosphate in neurones was examined using the quinacrine fluorescence technique. After localizing and taking photographs of quinacrine-fluorescent neurones and nerve fibres, the same tissues were then fixed and processed for NADPH-diaphorase activity, a marker for nitric oxide-containing neurones. We have demonstrated for the first time that almost all quinacrine-fluorescent myenteric neurones in the proximal colon are also NADPH-diaphorase reactive, while only a subpopulation of quinacrine-fluorescent neurones in ileum and anococcygeus muscle were also NADPH-diaphorase reactive.

Immunohistochemical demonstration of nitric oxide synthase in the peripheral autonomic nervous system

In the present immunohistochemical study the distribution of nitric oxide synthase (NOS) was studied in various autonomic ganglia and in related peripheral tissues of the rat. For comparison some other neuronal markers including acetylcholinesterase and tyrosine hydroxylase as well as several neuropeptides were analysed on adjacent or the same sections. The distribution of NOS-like immunoreactivity (LI) and of these other markers has been semiquantitatively summarized. In some parasympathetic ganglia such as the sphenopalatine and submandibular ganglia NOS-LI was present in most ganglion cells, at least partly coexisting with peptide histidine isoleucine (PHI), vasoactive intestinal polypeptide (VIP) and neuropeptide tyrosine (NPY). In the pelvic ganglia a comparatively smaller proportion of neurons was NOS-positive and they often contained VIP-LI and less frequently NPY-LI. In the tissues innervated by these ganglia, such as nasal mucosa and salivary glands, NOS-positive fibers were observed around blood vessels and within the glandular parenchyma, although generally less abundant than VIP/PHI nerves, while in the uterus, vas deferens and penis a more close correlation was seen. NOS-positive fibers were also widely distributed in other tissues. In the sympathetic ganglia NOS-LI was mainly present in dense fiber networks, which disappeared after transection of the sympathetic trunc central to the ganglion. Since many cell bodies in the sympathetic lateral column of the spinal cord also were NOS-positive, it is likely that the majority of preganglionic fibers innervating sympathetic ganglia are NOS-positive. VIP-positive cells in stellate ganglia did not contain NOS-LI. The present results suggest that NO may be a messenger molecule both in parasympathetic postganglionic neurons and in preganglionic sympathetic neurons.

Colocalization of neuropeptides with calbindin D28k and NADPH diaphorase in the enteric nerve plexuses of normal human ileum

BACKGROUND/AIMS

The chemical coding of enteric neurons differs significantly among species. In the present study, the innervation of normal human ileum was characterized with respect to its chemical coding.

METHODS

The submucosa was subdivided into zones 1-3 based on its thickness and distribution of ganglia. The neuropeptides, calbindin D28k, and protein gene product 9.5 were identified by immunocytochemistry. Nitric oxide production was identified by nicotinamide adenine dinucleotide phosphate (NADPH) diaphorase histochemistry.

RESULTS

Protein gene product 9.5 staining indicated that cell bodies of the submucosa could be subdivided into zones 1-3. Two major groups of submucosal cell bodies contained either substance P/somatostatin/calcitonin gene-related peptide or vasoactive intestinal peptide/neuropeptide Y/calbindin D28k. Gastrin-releasing peptide-containing cell bodies also colocalized with a subgroup of somatostatin cell bodies. No galanin, met-enkephalin, or NADPH diaphorase-positive cell bodies were present. In the myenteric plexus, the two major groups of cell bodies contained either calbindin or NADPH diaphorase. A proportion of the latter group costained with vasoactive intestinal peptide and met-enkephalin. Cell bodies containing substance P, somatostatin, and calcitonin gene-related peptide were present, forming three different subgroups.

CONCLUSIONS

Of the species investigated to date, the chemical coding of human ileal cell bodies most closely resembles that of the rat.

Localization of age-related changes in NADPH-diaphorase activity in pancreatic neurons

The distribution of NADPH-diaphorase activity in the pancreatic neurons of neonatal, adult and aging rats was investigated using histochemistry. In the neonates, only 40% of the neuronal population showed NADPH-diaphorase labelling, and there was variation in the intensity of labelling ranging from light to heavy staining. In the young and mature adults, 95% of the neurons were labelled for NADPH-diaphorase activity, with most of the neurons being heavily labelled for the enzyme in the older animals. Immediately after birth, the pancreatic neurons found were small clusters of smaller sized cells compared with those observed in the mature adults. Their number reached the adult level by the third month after birth; this was maintained throughout the mature adult phase and subsequently decreased in the aging rats.

Electrophysiological evidence for different release mechanism of ATP and NO as inhibitory NANC transmitters in guinea-pig colon

1. The effect of the P2-purinoceptor antagonist, suramin, the specific N-type voltage-dependent calcium channel blocker, omega-conotoxin GVIA (omega-CgTx) and the delta-opioid receptor agonist [D-Pen2,D-Pen5] enkephalin (DPDPE) on the apamin-sensitive and apamin-resistant inhibitory junction potentials (i.j.ps) produced by electrical field stimulation (EFS) were investigated by means of a sucrose-gap technique in the circular muscle of the guinea-pig colon. 2. After incubation of muscle strips in either atropine (1 microM), guanethidine (3 microM) and NG-nitro-L-arginine (L-NOARG, 30 microM) or atropine, guanethidine and apamin (0.3 microM), the addition of the NK1 receptor antagonist, SR 140,333 (1 microM) abolished the non-adrenergic, non-cholinergic (NANC) excitatory junction potential (e.j.p.) and unmasked a pure apamin-sensitive i.j.p. (in the presence of L-NOARG) or a pure apamin-resistant i.j.p. (in the presence of apamin). Both types of i.j.p. were abolished by tetrodotoxin. 3. Suramin (30-300 microM) concentration-dependently inhibited the apamin-sensitive i.j.p., while the apamin-resistant i.j.p. was not significantly affected by suramin (up to 300 microM). L-NOARG (30 microM) markedly reduced the apamin-resistant i.j.p. 4. The delta-opioid receptor agonist, DPDPE (0.03-3 microM) concentration-dependently reduced the apamin-sensitive i.j.p., while leaving the apamin-resistant i.j.p. unaffected. Naloxone (1 microM) prevented the i.j.p. inhibition evoked by DPDPE (0.3 microM). 5. omega-CgTx (0.3 microM) markedly reduced the apamin-sensitive but not the apamin-resistant i.j.p. The application of DPDPE (3 MicroM), after development of a steady state inhibitory effect by omega-CgTx, evoked further inhibition of the apamin-sensitive ij.p., similar to the effect produced by DPDPE alone. The L-type calcium channel blocker, nifedipine (1 MicroM) did not significantly affect either the apamin-sensitive or the apamin-resistant ij.ps.6. These findings support the purinergic origin of the fast, apamin-sensitive ij.p. produced by EFS in the circular muscle of the guinea-pig colon and strongly suggest that the apamin-sensitive and the apamin-resistant components of the evoked ij.p. utilize different mechanisms for the secretion of theNANC transmitters, ATP and NO, respectively.

Quantitative study of the NADPH-diaphorase-positive myenteric neurons of the rat ileum

The subpopulation of myenteric neurons able to synthesize nitric oxide was studied quantitatively in the adult rat, using the NADPH-diaphorase histochemical method on whole-mount preparations of distended distal ileum. The spatial density of NADPH-diaphorase-positive myenteric neurons was 2388 +/- 193/cm2 (S.D.; five rats), comprising about 27% of the nerve cell bodies per ganglion. Most neurons were intensely stained and displayed predominantly a Dogiel type I morphology; about 8% of the labelled nerve cells were ovoid neurons, exhibiting a pale cytoplasmic reaction product. The mean somatic size of all NADPH-diaphorase-positive myenteric neurons was 446 +/- 40 microns2, with a mean nuclear size of 96 +/- 18 microns2 (mean values +/- S.D.; five rats). Such values fell exactly within the range of neuronal sizes of the total myenteric population, marked by means of NADH-diaphorase histochemistry. Therefore, the morphometric analysis did not identify any peculiar cell size feature, characterizing this specific nerve cell subpopulation. Thus, the present study provides quantitative data on the size, density and proportion of those myenteric neurons that may synthesize nitric oxide in the distal ileum of the rat.

Nitric oxide synthase in the enteric nervous system of the guinea-pig: a quantitative description

The distribution and abundance of nitric oxide synthase (NOS)-containing neurons and their terminals in the gastrointestinal tract of the guinea-pig were examined in detail using NADPH diaphorase histochemistry and NOS immunohistochemistry. NOS-containing cell bodies were found in the myenteric plexus throughout the gastrointestinal tract and in the submucous plexus of the stomach, colon and rectum. NOS-containing neurons comprised between 12% (in the duodenum) and 54% (in the esophagus) of total myenteric neurons. In the ileum, NOS neurons represented 19% of total myenteric neurons. Most of the NOS neurons throughout the gastrointestinal tract possessed lamellar dendrites and a single axon. NOS-containing terminals were abundant in the circular muscle, including that of the sphincters, but were rare in the longitudinal muscle, except for the taeniae of the caecum. The muscularis mucosae of the esophagus, stomach, colon and rectum received a medium to dense innervation by NOS terminals. Within myenteric ganglia, NOS-containing terminals were extremely sparse in the esophagus, stomach and duodenum, common in the ileum and distal colon and extremely dense in the proximal colon and rectum. The submucous plexus in the ileum and large intestine contained a sparse plexus of NOS-containing terminals. NOS terminals were not observed in the mucosa of any region. We conclude that throughout the gastrointestinal tract of the guinea-pig, NOS neurons are inhibitory motor neurons to the circular muscle; in the ileum and large intestine, NOS neurons may also function as interneurons.

The role of enteric inhibitory motoneurons in peristalsis in the isolated guinea-pig small intestine

1. Peristalsis is a co-ordinated motor behaviour in which an anally propagated contraction of the circular muscle propels intraluminal contents. The role of excitatory motoneurons in peristalsis is well established; however the role of enteric inhibitory motoneurons is unknown. 2. A combination of a nitric oxide synthase inhibitor and apamin, which blocks relaxation of the circular muscle of guinea-pig small intestine mediated by enteric inhibitory motoneurons, was used to investigate the role of inhibitory motoneurons in peristalsis in isolated segments of guinea-pig small intestine. 3. N omega-nitro-L-arginine methyl ester (L-NAME, 400 microM) and N omega-nitro-L-arginine (L-NOArg, 100 microM) significantly reduced the threshold volume required to trigger emptying of the intestine. This effect was reversed by L-arginine (4 mM) and L-arginine alone increased the threshold volume for initiation of peristalsis. Sodium nitroprusside (0.1-10 microM), which generates nitric oxide, also increased the threshold volume. L-NAME, L-NOArg, L-arginine and sodium nitroprusside did not alter the maximal intraluminal pressure generated during emptying. Contraction of the longitudinal muscle during the initial phase of fluid infusion was significantly increased by L-NAME and L-NOArg and reduced by sodium nitroprusside (1 nM to 10 microM). 4. Apamin (0.5 microM) did not significantly alter the threshold volume necessary to initiate peristalsis or contraction of the longitudinal muscle. However, the maximal pressure generated when the intestine was emptying was significantly increased. Furthermore, short segments of circular muscle contracted apparently randomly, before peristaltic emptying was triggered. 5. A combination of L-NAME and apamin completely disrupted peristalsis. Contractions of the circular muscle did not always start at the oral end. Stationary contractions as well as contractions propagating orally and anally were observed. 6. It is concluded that enteric inhibitory motoneurons are crucial for peristalsis to occur. They are important in setting the threshold at which peristaltic emptying is triggered, via nitric oxide. They are essential for the propagation of the circular muscle contraction, via an apamin-sensitive mechanism of transmission. Contraction of the longitudinal muscle during peristalsis is partly inhibited by a nitric oxide-mediated mechanism.