A neurochemical characterisation of the golden hamster myenteric plexus

The neurochemical composition of nerve fibres and cell bodies in the myenteric plexus of the proventriculus, stomach and small and large intestines of the golden hamster was investigated by using immunohistochemical and histochemical techniques. In addition, the procedures for localising nitric-oxide-utilising neurones by histochemical (NADPH-diaphorase) and immunohistochemical (nitric oxide synthase) methods were compared. The co-localisation of vasoactive intestinal polypeptide and nitric oxide synthase in the myenteric plexus of all regions of the gut was also assessed. The results demonstrated the presence of nerve fibres and nerve cell bodies immunoreactive to protein gene product, vasoactive intestinal polypeptide, substance P, calcitonin gene-related peptide, tyrosine hydroxylase, 5-hydroxytryptamine and nitric oxide synthase in all regions of the gastrointestinal tract examined. The pattern of distribution of immunoreactive nerve fibres and nerve cell bodies containing the above markers was found to vary in different regions of the gut. Myenteric neurones and nerve fibres containing immunoreactivity to nitric oxide synthase and NADPH-diaphorase reactivity, however, were shown to have an identical distribution throughout the gut. In contrast to some studies on the guinea-pig and rat, the co-existence of vasoactive intestinal polypeptide and nitric oxide synthase was seen in only a small population of myenteric neurones.     

Distinct distribution of CGRP-, enkephalin-, galanin-, neuromedin U-, neuropeptide Y-, somatostatin-, substance P-, VIP- and serotonin-containing neurons in the two submucosal ganglionic neural networks of the porcine small intestine

Summary In addition to differences between the two submucosal ganglionic neural networks, i.e., the plexus submucosus externus (Schabadasch) and the plexus submucosus internus (Meissner), with respect to the occurrence and distribution of serotonin as neurotransmitter, immunocytochemistry also revealed a distinct distribution for various neuropeptides in these two plexuses. Immunoreactivity for galanin, vasoactive intestinal polypeptide, calcitonin gene-related peptide, substance P, neuromedin U, enkephalin, somatostatin and neuropeptide Y was found in varicose and non-varicose nerve fibres of both submucosal ganglionic plexuses, albeit with a distinct distributional pattern. The difference in neurotransmitter and/or neuromodulator content between both neural networks became even more obvious when attention was focussed on the immunoreactivity of the nerve cell bodies for these substances. Indeed, neuropeptide Y, enkephalin-and somatostatin-immunoreactive neuronal perikarya as well as serotonergic neuronal cell bodies appear solely in the plexus submucosus externus. Neuromedin U-immunoreactive perikarya, mostly coexisting with substance P, are observed in large numbers in the plexus submucosus internus, whilst they are rare in the plexus submucosus externus. Double-labelling immunostaining for substance P with CGRP and galanin revealed a different coexistence pattern for the two submucosal ganglionic plexuses. The differing chemical content of the neuronal populations supports the hypothesis that the existence of the two submucosal ganglionic plexuses, present in most large mammals including man, not only reflects a morphological difference but also points to differentiated functions.     

Projections of neurons with neuromedin U-like immunoreactivity in the small intestine of the guinea-pig

Summary Neuromedin U immunoreactivity was located histochemically in the guinea-pig small intestine. Projections of immunoreactive neurons were determined by analysing patterns of degeneration following nerve lesions. The co-localization of neuromedin U immunoreactivity with immunoreactivity for substance P, neuropeptide Y, vasoactive intestinal peptide and calbindin was also investigated. Neuromedin U immunoreactivity was found in nerve cells in the myenteric and submucous plexuses and in nerve fibres in these ganglionated plexuses, around submucous arterioles and in the mucosa. Reactive fibres did not supply the muscle layers. Most reactive nerve cells in the myenteric ganglia had Dogiel type-II morphology and in many there was co-localization of calbindin, although some Dogiel type-II neuromedin U neurons were calbindin negative. Lesion studies suggest that these myenteric neurons project circumferentially to local myenteric ganglia. Projections from myenteric neurons also run anally in the myenteric plexus, while other projections extend to submucous ganglia, and still further projections run from the intestine to provide terminals in the coeliac ganglia. In the submucous ganglia neuromedin U was co-localized in three populations of nerve cells: (i) those with vasoactive intestinal peptide immunoreactivity, (ii) neurons containing neuropeptide Y, and (iii) neurons containing substance P. Each of these populations sends nerve fibres to the mucosa. Neuromedin U immunoreactivity is thus located in a variety of neurons serving different functions in the intestine and therefore probably does not have a single role in intestinal physiology.     

Evidence that myenteric neurons of the gastric corpus project to both the mucosa and the external muscle: myectomy operations on the canine stomach

Summary The distribution of nerve cell bodies and fibres in the canine stomach was investigated using antibodies to the general neuronal marker, neuron-specific enolase. Prominent ganglia containing many reactive nerve cells were found in the myenteric plexus of the gastric corpus and antrum. Nerve cells were absent from the submucosa of the corpus and were extremely rare in the antrum. Renoval of areas of longitudinal muscle and myenteric plexus from the corpus (myectomy), with 7 days allowed for axon degeneration, resulted in the loss of fibres reactive for galanin, gastrin-releasing peptide, substance P and vasoactive intestinal peptide from both the circular muscle and mucosa in the area covered by the lesion. Combined vagotomy and sympathetic denervation did not significantly affect these fibres, but did cause fibres reactive for calcitonin gene-related peptide to degenerate. It is concluded that the myenteric plexus of the gastric corpus, like the myenteric plexus of the small intestine and colon, is the source of nerve fibres innervating the circular muscle, but, in contrast to other regions of the gastrointestinal tract, myenteric ganglia, not submucous ganglia, are the major, or sole, source of the intrinsic innervation of the mucosa.     

Projections of neurochemically specified neurons in the porcine colon

The intramural projections of nerve cells containing serotonin (5-HT), calcitonin gene-related peptide (CGRP), vasoactive intestinal peptide (VIP) and nitric oxide synthase or reduced nicotinamide adenine dinucleotide phosphate diaphorase (NOS/NADPHd) were studied in the ascending colon of 5- to 6-week-old pigs by means of immunocytochemistry and histochemistry in combination with myectomy experiments. In control tissue of untreated animals, positive nerve cells and fibres were common in the myenteric and outer submucous plexus and, except for 5-HT-positive perikarya, immunoreactive cell bodies and fibres were also observed in the inner submucous plexus. VIP- and NOS/NADPHd-positive nerve fibres occurred in the ciruclar muscle layer while VIP was also abundant in nerve fibres of the mucosal layer. 5-HT- and CGRP-positive nerve fibres were virtually absent from the aganglionic nerve networks. In the submucosal layer, numerous paravascular CGRP-immunoreactive (IR) nerve fibres were encountered. Myectomy studies revealed that 5-HT-, CGRP-, VIP- and NOS/NADPHd-positive myenteric neurons all displayed anal projections within the myenteric plexus. In addition, some of the serotonergic myenteric neurons projected anally to the outer submucous plexus, whereas a great number of the VIP-ergic and nitrergic myenteric neurons send their axons towards the circular muscle layer. The possible function of these nerve cells in descending nerve pathways in the porcine colon is discussed in relation to the distribution pattern of their perikarya and processes and some of their morphological characteristics.     

Neuromedin U-immunoreactivity in the nervous system of the small intestine of the pig and its coexistence with substance P and CGRP

Summary In the small intestine of the pig, neuromedin U (NMU)-immunoreactivity was mainly confined to the nerve plexus of the inner submucosal and mucosal regions. After colchicine treatment, a high number of immunoreactive nerve cell bodies was observed in the plexus submucosus internus (Meissner), whereas only a low number was found in the plexus submucosus externus (Schabadasch). The plexus myentericus as well as the aganglionic nerve meshworks in the circular and longitudinal smooth muscle layers almost completely lacked NMU-immunoreactivity. Double-labeling experiments demonstrated the occurrence of distinct NMU-containing neuron populations in the plexus submucosus internus: (1) relatively large type-II neurons revealing immunoreactivity for NMU and calcitonin gene-related peptide (CGRP) and/or substance P (SP); (2) a group of small NMU- and SP-immunoreactive neurons; (3) a relatively low number of small neurons displaying immunoreactivity for NMU but not for SP. Based on its distributional pattern, it is concluded that NMU plays an important role in the regulation and control of mucosal functions.     

Calcitonin gene-related peptide immunoreactivity in the biliary pathway and liver of the guinea-pig: distribution and colocalization with substance P

Summary Calcitonin gene-related peptide immunoreactivity was localized immunohistochemically in nerve fibers innervating the biliary pathway and liver of the guinea-pig. Immunoreactive fibers are present in all layers of the gallbladder and biliary tract and are particularly numerous around blood vessels. In the liver, immunoreactive processes are usually restricted to the interlobular space and porta hepatis, and only a few, very thin, beaded processes were observed in the hepatic parenchyma. A rich innervation is also associated with the vena portae. Positive ganglion cell bodies were not visualized within the ganglionated plexus of the biliary system, whereas they were found in the myenteric and submucosal plexus in the cranial portion of the duodenum corresponding to the sphincter of Oddi. The vast majority, if not all, of calcitonin gene-related peptide-immunoreactive fibers contain substance P immunoreactivity; however, there are some substance P-containing fibers lacking calcitonin gene-related peptide immunoreactivity. The lack of co-occurrence of calcitonin gene-related peptide and substance P immunoreactivities in intrinsic ganglion cells suggests that these two peptides are coexpressed in the extrinsic component of the innervation of the hepatobiliary system.     

Neuropeptides in the intestine of two teleost species (Oreochromis mossambicus,Carassius auratus): Localization and electrophysiological effects on the epithelium

Summary The presence of bioactive peptides in the gut and their possible electrophysiological effects on the intestinal epithelium were studied in two teleost species, the tilapia (Oreochromis mossambicus) and the goldfish (Carassius auratus). Vasoactive intestinal polypeptide-like immunoreactive nerve fibres were found beneath the intestinal epithelium of both species. Galanin-, metenkephalin-and calcitonin gene-related peptide-like immunoreactive nerve fibres were found exclusively in the mucosa of the tilapia. Both species had vasoactive intestinal polypeptide-, enkephalin- or neuropeptide Y-like immunoreactive endocrine cells; calcitonin gene-related peptide-like immunoreactive endocrine cells were additionally found in the tilapia. Somatostatin- and dopamine--hydroxylase-like immunoreactivities were not observed. Nerve cell bodies in the myenteric plexus of both species showed immunoreactivity for calcitonin gene-related peptide-, vasoactive intestinal polypeptide-, and galanin-like peptide. Enkephalin-like immunoreactive nerve cell bodies were present in the tilapia only. None of the peptides had a pronounced electrogenic effect. However, calcitonin gene-related peptide added to stripped intestinal epithelium of the tilapia, reduced the ion selectivity, and addition of galanin increased the ion selectivity. In goldfish intestine, both galanin and calcitonin gene-related peptide were without effect. Enkephalin counteracted the serotonin-induced reduction of the ion selectivity of the goldfish intestinal epithelium, but had no effect on the tilapia epithelium. In both species, vasoactive intestinal polypeptide reduced the ion selectivity of the intestinal epithelium, and neuropeptide Y induced an increase of the ion selectivity. Somatostatin showed no effect on the epithelial ion selectivity of either species. Tetrodotoxin did not inhibit the effects of the peptides studied. The changes in ion selectivity suggest that the enterocytes may be under the regulatory control of these peptides.     

The nervous system of the chicken proventriculus: an immunocytochemical and ultrastructural study

The proventriculus constitutes the glandular region of the chicken stomach. This organ is innervated by two parasympathetic networks, the myenteric and submucous plexus, and here we present a systematic study of this system by immunohistochemistry and electron microscopy. All the neurons and fibres were positive for the neural markers, protein gene product 9.5 and the amidating enzymes. Immunoreactivities for the constitutive neuronal isoform of the enzyme nitric oxide synthase and the vasoactive intestinal peptide were present in neuronal bodies suggesting an intrinsic origin for the similarly immunoreactive fibres found in the proventriculus. On the other hand, immunoreactivity to gastric inhibitory peptide was only found in varicose fibres making contact with the blood vessels and the glandular epithelium, but never in the neuronal somas, suggesting that this substance may be provided by an extrinsic nervous system whose neuronal bodies are located elsewhere. Electron microscopy revealed frequent neuromuscular and neuroepithelial connections in the muscle layers, the wall of the blood vessels and the epithelium. In addition, synapsis-like structures were identified in the proximity of cells belonging to the diffuse endocrine system, providing a new example of neuroendocrine contacts. No positivity was found for antibodies against other neural substances including somatostatin, peptide histidine–isoleucine, peptide tyrosine–tyrosine, neuropeptide tyrosine, bombesin, met-enkephalin, serotonin, substance P, galanin, calcitonin gene-related peptide and S-100 protein.     

Plasticity in expression of calcitonin gene-related peptide and substance P immunoreactivity in ganglia and fibres following guanethidine and/or capsaicin denervation

Summary This study was designed to investigate the effects of multiple denervation procedures on calcitonin gene-related peptide- and substance P-immunoreactive neurons in sympathetic and sensory cranial ganglia and in selected targets. Sympathectomy by long-term guanethidine treatment induced a pronounced increase in calcitonin gene-related peptide-immunoreactive and substance P-immunoreactive nerve fibres in all the tissues investigated, in contrast to a significant reduction of immunoreactive cell bodies. Neonatal capasaicin treatment abolished substance P immunoreactivity in many targets and caused a dramatic reduction of substance P-immunoreactive sensory nerve cell bodies; calcitonin gene-related peptide-immunoreactive nerve density was decreased, but the number of immunoreactive nerve cell bodies was unchanged. Guanethidine treatment of capsaicin-injected rats reversed the loss of calcitonin gene-related peptide-immunoreactive nerves, but not that of substance P-immunoreactive neurons. In the iris, capsaicin treatment had little effect on calcitonin gene-related peptide- and substance P-immunoreactive nerves, suggesting that in rats the majority of these fibres originate from capsaicin-insensitive neurons. The results suggest that the denervation procedures used in this study alter the synthesis and transport of neuropeptides in sensory neurons in conjunction with changes in the number of nerve fibres.     

An immunohistochemical study of the innervation of the large intestine of the toad (Bufo marinus)

The distribution of intrinsic enteric neurons and extrinsic autonomic and sensory neurons in the large intestine of the toad, Bufo marinus, was examined using immunohistochemistry and glyoxylic acid-induced fluoresecence. Three populations of extrinsic nerves were found: unipolar neurons with morphology and location typical of parasympathetic postganglionic neurons containing immunoreactivity to galanin, somatostatin and 5-hydroxytryptamine were present in longitudinally running nerve trunks in the posterior large intestine and projected to the muscle layers and myenteric plexus throughout the large intestine. Sympathetic adrenergic fibres supplied a dense innervation to the circular muscle layer, myenteric plexus and blood vessels. Axons containing colocalized calcitonin gene-related peptide immunoractivity and substance P immunoreactivity distributed to all layers of the large intestine and are thought to be axons of primary afferent neurons. Five populations of enteric neurons were found. These contained immunoreactivity to vasoactive intestinal peptide, which distributed to all layers of the large intestine; galanin/vasoactive intestinal peptide, which projected to the submucosa and mucosa; calcitonin gene-related peptide/vasoactive intestinal peptide, which supplied the circular muscle, submucosa and mucosa; galanin, which projected to the submucosa and mucosa; and enkephalin, which supplied the circular muscle layer.     

VIP-, Bombesin- and Neurotensin-Like Immunoreactivity in Neurons of the Gut of the Holostean Fish,Lepisosteus platyrhincus

VIP-like immunoreactivity was found in nerve fibres in all layers of the gut wall in both stomach and intestine, and was abundant in the myenteric and submucous plexuses. A few fibres were associated with blood vessels. Nerve cells showing VIP-like immunoreactivity were found in the myenteric plexus. Neurotensin-like immunoreactivity was found in nerve cells and numerous nerve fibres in the myenteric plexus of both stomach and intestine and in nerve fibres of the circular muscle layer, while bombesin-like immunoreactivity was confined to a low number of nerve fibres in the myenteric plexus of the stomach. The results indicate that a VIP-like, a neurotensin-like and a bombesin-like peptide are present in neurons of the gut of Lepisosteus.     

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.     

Rapid anterograde and retrograde tracing from mesenteric nerve trunks to the guinea-pig small intestine in vitro

A novel technique for rapid anterograde labelling of cut axons in vitro was used to visualise the peripheral branches of mesenteric nerve trunks supplying the guinea-pig small intestine. Biotinamide, dissolved in an artificial intracellular solution, was applied to the cut ends of the mesenteric nerves and the tissue was maintained in organ culture overnight. Labelled nerve fibres were visualised by fluorescein isothiocyanate (FITC)-conjugated streptavidin. Intense staining of nerve fibres and terminal varicosities in the ganglia and internodal strands of the myenteric plexus was achieved up to 15 mm from the application site. Filled fibres formed baskets around some myenteric nerve cell bodies, suggesting target-specific neurotransmission. When combined with multiple-labelling immunohistochemistry for tyrosine hydroxylase (TH), calcitonin gene-related protein (CGRP) or choline acetyltransferase (ChAT), most anterogradely labelled nerve fibres, and many pericellular baskets, were found to be TH immunoreactive, indicating their postganglionic sympathetic origin. Double-labelling immunohistochemistry revealed that the postganglionic sympathetic pericellular baskets preferentially surrounded 5-hydroxytryptamine (5-HT)-handling myenteric neurons. Some biotinamide-filled fibres were CGRP immunoreactive, and are likely to originate from spinal sensory neurons. We describe for the first time many pericellular baskets labelled from the mesenteric nerves which were ChAT immunoreactive. Retrogradely filled intestinofugal nerve cell bodies were also observed, all of which had a single axon arising from a small nerve cell body with short filamentous or lamellar dendrites. Many of these cells were ChAT immunoreactive. This in vitro technique is effective in identifying the fine arrangement of nerve terminals arising from nerve trunks in the periphery.     

The distribution and colocalization of neuropeptides in perivascular nerves innervating the large arteries and veins of the snake,Elaphe obsoleta

Summary Single- and dual-labelling immunohistochemistry were used to determine the distribution and coexistence of neuropeptides in perivascular nerves of the large arteries and veins of the snake, Elaphe obsoleta, using antibodies for vasoactive intestinal polypeptide, substance P, calcitonin gene-related peptide, neuropeptide Y, galanin, somatostatin, and leu-enkephalin. Blood vessels were sampled from four regions along the body of the snake: region 1, arteries and veins anterior to the heart; region 2, central vasculature 5 cm anterior and 10 cm posterior to the heart; region 3, arteries and veins in a 30-cm region posterior to the liver; and region 4, dorsal aorta and renal arteries, renal and intestinal veins, 5–30 cm cephalad of the vent. A moderate to dense distribution of vasoactive intestinal polypeptide-like immunoreactive fibres was found in most arteries and veins of regions 1–3, but fibres were absent from the vessels of region 4. The majority of vasoactive intestinal polypeptide-like immunoreactive fibres contained colocalized substance P-like immunoreactivity, and these fibres were unaffected by either capsaicin or 6-hydroxydopamine (6-OHDA) pretreatment. In the anterior section of the snake, the vagal trunks contained many cell bodies with colocalized vasoactive intestinal polypeptide and substance P-like immunoreactivity. It is suggested that the vasoactive intestinal polypeptide/substance P-like immunoreactive cell bodies and fibres are parasympathetic postganglionic nerves. Neuropeptide Y-like immunoreactive fibres were observed in all arteries and veins, being most dense in regions 3 and 4. The majority of these fibres also contained colocalized galanin-like immunoreactivity, and were absent in tissues from 6-OHDA pretreated snakes, suggesting that neuropeptide Y and galanin are colocalized in adrenergic nerves. A small number of neuropeptide Y-like immunoreactive fibres contained vasoactive intestinal polypeptide but not galanin, and were unaffected by 6-OHDA treatment. All calcitonin gene-related peptide-like immunoreactive fibres contained colocalized substance P-like immunoreactivity, and these fibres were observed in all vessels, being particularly dense in the carotid artery and jugular veins. All calcitonin gene-related peptide/substance P-like immunoreactive fibres appeared damaged after capsaicin treatment suggesting they represent fibres from afferent sensory neurons. A sparse plexus of somatostatin-like immunoreactive fibres was observed in the vessels only from region 4. No enkephalin-like immunoreactive fibres were found in any blood vessels from any region. This study provides morphological evidence to suggest that there is considerable functional specialization within the components of the rat snake peripheral autonomic system controlling the circulation, in particular the regulation of venous capacitance.     

Calcitonin gene-related peptide-like immunoreactivity in nerve fibers in the human skin. Relation to fibers containing substance P-, somatostatin- and vasocactive intestinalpolypeptide-like immunoreactivity

Calcitonin gene-related peptide-like immunoreactivity was demonstrated in in sensory nerve fibers in the epidermis and dermis as free nerve endings and around blood vessels and hair follicles of the human finger pad and arm skin. The vast majority of the calcitonin gene-related immunoreactive fibers was shown to display also substance P-like immunoreactivity and a few fibers in the dermis were somatostatin positive. No fibers displaying both substance P and somatostatin-like immunoreactivity were found but a few substance P immunoreactive fibers in the dermis-epidermis region were found to contain also vasointestinal polypeptide-like immunoreactivity. In the sweat glands, abundant calcitonin gene-related peptide positive, but substance P negative, fibers were observed with a similar distribution pattern as the vasoactive intestinal polypeptide immunoreactive fibers and these fibers were suggested to be of sympathetic origin.     

The distribution of substance P-, CGRP-, galanin-and ANP-like immunoreactive nerves in human sweat glands

Summary The distribution in immunoreactivities towards atrial natriuretic peptide, calcitonin gene-related peptide, galanin and substance P were demonstrated in human skin at the light and electron microscopic levels. Nerves immunoreactive to the first three of these peptides were found around eccrine sweat glands, whereas only a few positively-labelled nerve fibres could be seen around apocrine glands. At the ultrastructural level, immunoreactivity to the neuropeptides was localized in the large dense-cored vesicles of the nerve terminals. No immunoreactivity to substance P could be detected around sweat glands. In addition to these findings, the four types of immunoreactivity were seen in the thick preterminal nerve bundles.     

Colocalization of NADPH-diaphorase activity and certain neuropeptides in the esophagus of opossum (Didelphis virginiana)

Nitric oxide and various neuropeptides in the myenteric plexus regulate esophageal motility. We sought colocalization of nitric oxide synthase and neuropeptides in frozen sections of mid-portion of smoothmuscled opossum esophagus using NADPH-diaphorase activity to mark the synthase and immunoreactivity to detect peptides. The peptides, all with demonstrated physiological activity in this organ, were calcitonin generelated peptide, galanin, neuropeptide Y, substance P, and vasoactive intestinal polypeptide. The ExtrAvidin Peroxidase immunostain for each peptide was carried up to the final peroxidase reaction with 3-amino-9-ethylcarbazole. The NADPH-diaphorase reaction was applied with short incubation to provide light staining just before the peroxidase reaction was performed. We examined sections for the proportions of singly and dually labeled nerve cells in the myenteric plexus. NADPH-diaphorase activity was highly colocalized with calcitonin gene-related peptide (59%), galanin (54%), and vasoactive intestinal polypeptide (53%). It showed little colocalization with neuropeptide Y (10%) and substance P (8%). The proportions of all nerve cells containing each of the substances were: NADPH-diaphorase-33%, calcitonin gene-related peptide-30%, galanin-55%, neuropeptide Y-16%, substance P-35%, and vasoactive intestinal polypeptide-58%. We conclude that the nerves responsible for peristalsis in the esophagus may act by releasing nitric oxide along with other inhibitory substances, calcitonin gene-related peptide, galanin, and vasoactive intestinal polypeptide, but not excitatory substances, neuropeptide Y and substance P.     

The proliferation marker pKi-67 becomes masked to MIB-1 staining after expression of its tandem repeats

The P2X(2) subtype of purine receptor was localised by immunohistochemistry to nerve cells of the myenteric ganglia of the stomach, small and large intestines of the guinea-pig, and nerve cells of submucosal ganglia in the intestine. Nerve cells with strong and with weak immunoreactivity could be distinguished. Immunoreactivity in both strongly and weakly immunoreactive neurons was absorbed with P2X(2) receptor peptide. In the myenteric plexus, strong immunoreactivity was in nitric oxide synthase (NOS)- and in calbindin-immunoreactive neurons. In all regions, over 90% of NOS-immunoreactive neurons were strongly P2X(2) receptor immunoreactive. The intensity of reaction varied in calbindin neurons; in the ileum, 90% were immunoreactive for the receptor, about one-third having a strong reaction. In the submucosal ganglia, all vasoactive intestinal peptide-immunoreactive neurons were P2X(2) receptor immunoreactive, but there was no receptor immunoreactivity of calretinin or neuropeptide Y neurons. Varicose nerve fibres with P2X(2) receptor immunoreactivity were found in the gastric myenteric ganglia. These fibres disappeared after vagus nerve section. It is concluded that the P2X(2) receptor is expressed by specific subtypes of enteric neurons, including inhibitory motor neurons, non-cholinergic secretomotor neurons and intrinsic primary afferent neurons, and that the receptor also occurs on the endings of vagal afferent fibres in the stomach.