Three-dimensional organization and topographical features of the myenteric plexus (Auerbach) in the porcine small intestine: scanning electron microscopy after enzymatic digestion and HCl-hydrolysis

The present scanning electron microscopical (SEM) study was initiated to visualize the surface topography of Auerbach's plexus in the ileum of the pig. After enzymatic digestion of the connective-tissue components of the tunica muscularis and the tunica serosa followed by glutaraldehyde fixation, HCl-hydrolysis and stripping off either the longitudinal or circular smooth muscle layer, the three-dimensional architecture and topographical features of the myenteric plexus can clearly be observed. In this way, ganglia, primary, secondary and tertiary strands, and single nerve fibres can be demonstrated. Individual nerve cells, which are incompletely covered by glial cells and by remnants of the basal lamina, can be recognized in the centre and periphery of the ganglia and adjacent to primary and secondary nerve strands.     

Oral inoculation with herpes simplex virus type 1 infects enteric neuron and mucosal nerve fibers within the gastrointestinal tract in mice.

Herpes simplex virus type 1 (HSV-1) is commonly encountered first during childhood as an oral infection. After this initial infection resolves, the virus remains in a latent form within innervating sensory ganglia for the life of the host. We have previously shown, using a murine model, that HSV-1 placed within the lumen of the esophagus gains access to nerves within the gut wall and establishes a latent infection in sensory ganglia (nodose ganglia) of the tenth cranial nerve (R. M. Gesser, T. Valyi-Nagy, S. M. Altschuler, and N. W. Fraser, J. Gen. Virol. 75:2379-2386, 1994). Peripheral processes of neurons in these ganglia travel through the vagus nerve and function as primary sensory receptors in most of the gastrointestinal tract, relaying information from the gut wall and mucosal surface to secondary neurons within the brain stem. In the work described here, we further examined the spread of HSV-1 through the enteric nervous system after oral inoculation. By immunohistochemistry, HSV-1 was found to infect myenteric ganglia in Auerbach's plexus between the inner and outer muscle layers of the gut wall, submucosal ganglia (Meisner's plexus), and periglandular ganglion plexuses surrounding submucosal glands. Virus-infected nerve fibers were also seen projecting through the mucosal layer to interact directly with surface epithelial cells. These intramucosal nerve fibers may be a conduit by which intraluminal virus is able to gain access to the enteric nervous system from the gastrointestinal lumen.     

Adrenergic innervation of the oesophagus in the cat (Fellis domestica) and rhesus monkey (Macacus rhesus)

Summary The distribution of monoamines in the pharynx and oesophagus of the rhesus monkey (Macacus rhesus) and the cat (Felis domestica) was investigated by means of fluorescence microscopical and chemical methods. Fluorimetric determinations reveal the presence of varying amounts of noradrenaline in the pharynx and oesophagus of the rhesus monkey. The lowest amount (0.05 (g/g) was found in the lower part of the oesophagus, the so-called sphincter-segment. The middle and upper part of the oesophagus contain medium amounts of noradrenaline (0.06–0.09 g) whereas the highest concentration was detected in the pharynx (0.14 (g/g). Neither dopamine nor adrenaline occurred in the tissue pieces analyzed. Fluorescence microscopically noradrenaline was found to be located in varicose intramural nerve fibre plexus which innervate mucous glands and blood vessels in the pharynx of both species. In the rhesus monkey, the lamina muscularis mucosae of all parts of the oesophagus is supplied by a well developed noradrenergic ground-plexus. Preterminal and terminal varicose nerve fibres are distributed in myenteric and submucous ganglia of the oesophagus; the number of such ganglia decreases towards the lower segment. The density of the adrenergic innervation is higher in myenteric when compared to submucous ganglia. The arrangement of the intraganglionic terminals suggests that both axosomatic and axodendritic contacts occur in Auerbach's ganglia whereas axodendritic contacts seem to predominate in Meissner's ganglia. Myenteric ganglia situated close to the submucosa as well as true submucous ganglia may be occasionally seen to be traversed by faintly fluorescent non-varicosed fibres which do not establish any synaptic contacts. The fluorescence intensity of intraganglionic varicosities varies considerably; accordingly the transmitter content of individual varicosities seems to be very variable. The adrenergic innervation of the lamina muscularis is restricted to single contorted fibres being sparsely distributed throughout the longitudinal smooth muscle layer. The circularly arranged smooth musculature of the sphincter-segment lacks an adrenergic nerve supply. The vagus nerve carries sympathetic adrenergic fibres to the lower oesophagus and the cardia. Species differences between the innervation pattern in rhesus monkeys and cats are outlined: No adrenergically innervated ganglia occur in the submucosa of the cat. However, part of the myenteric ganglia in cats exhibit an adrenergic innervation pattern similar to that seen in submucous ganglia of the rhesus monkey. They might therefore be regarded as morphologically equivalent to the plexus submucosus which is, however, present in the whole gut. The density of the noradrenergic ground-plexus in the muscularis mucosae of the cat's oesophagus is less than that of the corresponding plexus in rhesus monkeys.The influence of noradrenaline upon the smooth musculature and the neurons from myenteric as well as submucous ganglia is discussed. From the point of view of the adrenergic innervation there is no structure corresponding to the sphincterlike lower oesophageal segment.Supported by the Deutsche Forschungsgemeinschaft and the Joachim-Jungius-Gesellschaft zur Förderung der Wissenschaften, Hamburg.     

Fine structure of neurons synthesizing vasoactive intestinal peptide in the human colon from patients with Hirschsprung's disease

Summary The fine structure of neuronal perikarya and processes containing VIP-like immunoreactive material in the colon of patients with Hirschsprung's disease was investigated by immunoelectron microscopy. No VIP-like immunoreactive terminals were found in Auerbach's plexus of the ganglionic segment. However, VIP-like immunoreactive preterminal axons were frequently found to make synaptic contact with both immunoreactive and non-immunoreactive elements within Meissner's plexus. Therefore, the function of the VIP neurons in Auerbach's plexus seems to differ from that in Meissner's plexus. In the oligoganglionic segment, there were a few VIP-like immunoreactive processes, but no VIP-like immunoreactive synaptic formations. VIP-like immunoreactive processes were rarely encountered in the aganglionic segment. In both the oligo-and aganglionic segments, bowel relaxation is considered to be disturbed due to the lack of synaptic contacts of VIP-like immunoreactive neurons with other neuronal components.This work was supported in part by a grant (no. 57370002) from the Ministry of Education, Science and Culture, Japan     

Histo- and immunocytochemical characterization of the neurons of the mucosal plexus in the rat colon.

The mucosal plexus of the rat colon descendens is constituted of a network of nerves that, in contrast to most other segments of the digestive tract, contains also ganglia. The ganglia, consisting of neurons and glial cells, are located in the basal part of the lamina propria at distances between 100 and 1,200 microns. They are not vascularized. The neurons in these ganglia were characterized by means of: (1) the histochemical demonstration of acetylcholinesterase (AChE) activity, (2) the immunocytochemical identification of neurofilament proteins (NFP; 200 kD) and (3) their ultrastructure. The glial cells, which were AChE negative, could be distinguished from the neurons by differences in size and chromatin pattern. All neurons of the mucosal plexus reveal AChE activity in the perikaryon, but only parts of the axons are AChE positive. NFP-like immunoreactivity was detected in the perikarya but only in a minor part of the axons. These findings confirm previous light-microscopical observations and add new evidence for the existence of neurons (ganglia) in the mucosal plexus of the rat colon.     

Occurrence,distribution and neurochemical features of small intestinal neurons projecting to the cranial mesenteric ganglion in the pig

The small intestine of the pig has been investigated for its topographical distribution of enteric neurons projecting to the cranial mesenteric ganglion, by using Fast Blue or Fluorogold as a retrogradely transported neuronal tracer. Contrary to the situation in small laboratory animals such as rat and guinea-pig, the intestinofugally projecting neurons in the porcine small intestine were not restricted to the myenteric plexus, but were observed in greater numbers in ganglia of the outer submucous plexus. The inner submucous plexus was devoid of labelled neurons. Retrogradely labelled neurons were mostly found, either singly or in small aggregates, in ganglia located within a narrow border on either side of the mesenteric attachment. For both nerve networks, their number increased from duodenum to ileum. All the retrogradely labelled neurons exhibited a multidendritic uniaxonal appearance. Some of them displayed type-III morphology and stained for serotonin. This study indicates that, in the pig, not only the myenteric plexus but also one submucous nerve network is involved in the afferent component of intestino-sympathico-intestinal reflex pathways. The finding that some of the morphologically defined type-III neurons participate in these reflexes is in accord with the earlier proposal that type-III neurons are supposed to fulfill an interneuronal role, whether intra- or extramurally.     

Calbindin immunoreactivity of enteric neurons in the guinea-pig ileum

Previous studies have identified Dogiel type II neurons with cell bodies in the myenteric plexus of guinea-pig ileum to be intrinsic primary afferent neurons. These neurons also have distinctive electrophysiological characteristics (they are AH neurons) and 82-84% are immunoreactive for calbindin. They are the only calbindin-immunoreactive neurons in the plexus. Neurons with analogous shape and electrophysiology are found in submucosal ganglia, but, with antibodies used in previous studies, they lack calbindin immunoreactivity. An antiserum that is more effective in revealing calbindin in the guinea-pig enteric nervous system has been reported recently. In the present work, we found that this antiserum reveals the same population that was previously identified in myenteric ganglia, and does not reveal any further population of myenteric nerve cells. In submucosal ganglia, 9-10% of nerve cells were calbindin immunoreactive with this antiserum. The submucosal neurons with calbindin immunoreactivity were also immunoreactive for choline acetyltransferase, but not for neuropeptide Y (NPY) or vasoactive intestinal peptide (VIP). Small calbindin-immunoreactive neurons (average profile 130 microm2) were calretinin immunoreactive, whereas the large calbindin-immunoreactive neurons (average profile 330 microm2) had tachykinin (substance P) immunoreactivity. Calbindin immunoreactivity was seen in about 50% of the calretinin neurons and 40% of the tachykinin-immunoreactive submucosal neurons. It is concluded that, in the guinea-pig ileum, only one class of myenteric neuron, the AH/Dogiel type II neuron, is calbindin immunoreactive, but, in the submucosal ganglia, calbindin immunoreactivity occurs in cholinergic, calretinin-immunoreactive, secretomotor/vasodilator neurons and AH/Dogiel type II neurons.     

Fluorescence microscopic study of the architecture and structure of an adrenergic network in the plexus myentericus (Auerbach), plexus submucosus externus (Schabadasch) and plexus submucosus internus (Meissner) of the porcine small intestine

The distribution of adrenergic fibres in the ganglionated plexuses of the porcine small intestine has been made on air-dried stretch preparations using the glyoxylic acid fluorescence method. Adrenergic fluorescent fibres occur in the ganglia and internodal strands of the three fundamental ganglionated plexuses: the myenteric plexus (Auerbach) and the two superimposed meshworks of the plexus submucosus , i.e. the plexus submucosus externus ( Schabadasch ) and the plexus submucosus internus (Meissner). The plexus Auerbach consists of densely glyoxylic acid induced fluorescent (GIF) elongated ganglia with in general a longitudinal axis running parallel to the circular muscle layer and large dense interconnecting fibre tracts with primary, secondary and tertiary subdivisions. In the ganglia, the fibres are varicose, forming large fluorescent 'baskets' which might be related to the occurrence of well defined enteric neurones. The plexus Schabadasch can be distinguished from the plexus Meissner by its size, strongly fluorescent ganglia and broad densely fluorescent internodal strands. The pattern of fluorescing ring-like formations at the margin and out of the nodes, clearly present in the Auerbach and Schabadasch plexuses, completely lack in the plexus Meissner, the latter being narrow-meshed with smaller fluorescent 'baskets', indicating that the corresponding neurones are smaller in size. In the ganglionic nodes of all three plexuses the axons display comparatively more varicosities than in the fibre tracts. Each of the three main ganglionated enteric plexuses are quite different with regard to the pattern of the adrenergic network both in the ganglia and in the strands.     

Fine structure of neurons synthesizing vasoactive intestinal peptide in the human colon from patients with Hirschsprung's disease

The fine structure of neuronal perikarya and processes containing VIP-like immunoreactive material in the colon of patients with Hirschsprung's disease was investigated by immunoelectron microscopy. No VIP-like immunoreactive terminals were found in Auerbach's plexus of the ganglionic segment. However, VIP-like immunoreactive preterminal axons were frequently found to make synaptic contact with both immunoreactive and non-immunoreactive elements within Meissner's plexus. Therefore, the function of the VIP neurons in Auerbach's plexus seems to differ from that in Meissner's plexus. In the oligoganglionic segment, there were a few VIP-like immunoreactive processes, but no VIP-like immunoreactive synaptic formations. VIP-like immunoreactive processes were rarely encountered in the aganglionic segment. In both the oligo- and aganglionic segments, bowel relaxation is considered to be disturbed due to the lack of synaptic contacts of VIP-like immunoreactive neurons with other neuronal components.     

GABA, Glutamic Acid Decarboxylase, and GABA Transaminase Levels in the Myenteric Plexus in the Intestine of Humans and Other Mammals

Abstract: Regional distribution of endogenous γ- aminobutyric acid (GABA), its synthesizing enzyme, glutamic acid decarboxylase (GAD), and metabolic enzyme, GABA transaminase (GABA-T), were determined in the intestinal tract of guinea pigs and cats and the findings compared with the number of ganglion cells in Auerbach's plexus. There were positive correlations among the GABA contents and the numbers of neural cells of the plexus. The precise localization of GABA and GAD in individual layers (mucosa, circular and longitudinal muscles, and Auerbach's plexus) in the human and cat colon was also determined. The endogenous GABA contents and GAD activity were the highest in Auerbach's plexus in tissues of both species. These results indicate that GABA is synthesized and localized in Auerbach's plexus and probably plays a significant role in the enteric nervous system.     

Origins of the insect enteric nervous system: differentiation of the enteric ganglia from a neurogenic epithelium.

The enteric nervous system (ENS) of the moth Manduca sexta is organized into two distinct cellular domains: an anterior domain that includes several small ganglia on the surface of the foregut, and a more posterior domain consisting of a branching nerve plexus (the enteric plexus) that spans the foregut-midgut boundary. Previously, we showed that the neurons of the posterior domain, the enteric plexus, are generated from a large placode that invaginates from the caudal lip of the foregut; subsequently, the cells become distributed throughout the enteric plexus by a sequence of active migration. We now demonstrate that the neurons of the anterior domain, the cells of the enteric ganglia, arise via a distinct developmental sequence. Shortly after the foregut has begun to form, three neurogenic zones differentiate within the foregut epithelium and give rise to chains of cells that emerge onto the foregut surface. The three zones are not sites of active mitosis, as indicated by the absence of labelling with a thymidine analogue and by clonal analyses using intracellularly injected dyes. Rather, the zones serve as loci through which epithelial cells are recruited into a sequence of delamination and neuronal differentiation. As they emerge from the epithelium, the cells briefly become mitotically active, each cell dividing once or twice. In this manner, they resemble the midline precursor class of neural progenitors in the insect central nervous system more than neuroblast stem cells. The progeny of these zone-derived precursors then gradually coalesce into the ganglia and nerves of the anterior ENS. Although this reorganization results in some variability in the precise configuration of neurons within the ganglia, the overall morphology of the ganglia is highly stereotyped, consisting of cortical layers of cells that surround a ventral neuropil. In addition, a number of the neurons within the frontal and hypocerebral ganglia express identifiable phenotypes in a manner that is similar to many cells of the insect central nervous system. These observations indicate that the differentiation of the enteric ganglia in Manduca involves an unusual combination of features seen during the formation of other regions of the nervous system and, as such, constitutes a distinct program of neurogenesis.     

先天性巨结肠病结肠壁内P物质能神经的免疫电镜观察

本研究应用电镜免疫细胞化学方法,对小儿先天性巨结肠病结肠壁内含Ｐ物质（ＳＰ）神经进行了观察。结果发现：狭窄段与结肠扩张段相比较,狭窄段含ＳＰ神经元缺失,神经终末减少,含无颗粒囊泡的神经终末增多,而含小颗粒囊泡的神经终末相对较少。本研究在超微结构水平为先天性巨结肠病结肠壁内肽能神经成份的改变及其与临床症状的可能关系提供了形态学证据。     

Properties of descending dorsal unpaired median (DUM) neurons of the locust suboesophageal ganglion

A group of six dorsal unpaired median (DUM) neurons of the suboesophageal ganglion (SOG) of locusts was studied with neuroanatomical and electrophysiological techniques. The neurons are located posteriorly in the SOG and have axons that descend into the ganglia of the ventral nerve cord, some as far as the terminal abdominal ganglion. Within thoracic ganglia the neurons have profuse dendritic ramifications in many neuropiles, including ventral sensory neuropiles. Based on their projection patterns three different morphological types of neurons can be distinguished. These neurons receive excitatory inputs through sensory pathways that ascend from the thoracic ganglia and are activated by limb movements. They may be involved in the modulation of synaptic transmission in thoracic ganglia.     

Extra-organic sources of innervation of the sigmoid]

By means of horseradish peroxidase administration into the wall of the sigmoid colon central part, localization, relative amount, body forms and size of the neurons, dealing with innervation of the given part of the colon have been determined. Labelled neurons are present in the colon wall, in ganglia of the caudal mesenteric artery nervous plexus, in the caudal and cranial mesenteric ganglia in the celiac plexus ganglia, in nodes and internodal branches of the lumbar part of the sympathetic trunk (the left one predominantly) and in the spinal ganglia from TXIII up to LVII. In the grey substance of the spinal cord labelled neurons are not revealed. The main part of the postganglionar sympathetic neurons, projecting their axons to the sigmoid colon, are situated in the caudal mesenteric ganglion. In the spinal ganglia the most part of the labelled neurons are to the left at the level of LII-LVI, to the right--at the level of LII-LV. The optimal time for revealing the greatest number of the labelled neurons are the 1st-3d days after administration of the enzyme. Capture of the lable takes place later in the neurons of those ganglia, which are situated more further from the place of peroxidase administration.     

Cholinergic innervation of the human stomach.

A histochemical method for the acetylcholinesterase activity was used to establish the parasympathetic components of the gastric coats in man. The four gastric layers contain a rich cholinergic innervation. In the mucosa the positive nerve fibers are located around the gastric glands and between the muscles of the muscularis mucosae. In the submucosa rich interconnected nerve fibers, rare large nerve trunks, and scarce ganglia cells show a strong cholinergic reaction. The muscular layer contains the highest density of cholinergic nerve fibers, isolated or in large bundles. Auerbach's plexus has a strong acetylcholinesterase activity in the nerve cell bodies. The subserous layer is very rich in cholinergic nerve fibers, rarely isolated, but interconnected. The vessels of each gastric layer exhibit a rich cholinergic innervation in the adventitia and the outside part of media.     

Distribution and projections of neurons with immunoreactivity for both gastrin-releasing peptide and bombesin in the guinea-pig small intestine

Summary Bombesin-like and gastrin-releasing peptide (GRP)-like immunoreactivities were localized in nerves of the guinea-pig small intestine and celiac ganglion with the use of antibodies raised against the synthetic peptides. The anti-bombesin serum (preincubated to avoid cross reactivity with substance P) and the anti-GRP serum revealed the same population of neurons. Preincubation of the antibombesin serum with bombesin abolished the immunoreactivity in nerves while absorption of the anti-GRP serum with either bombesin or the 14–27 C-terminal of GRP only reduced the immunoreactivity. The immunoreactivity was abolished by incubation with GRP 1–27.Immunoreactive nerves were found in the myenteric plexus, circular muscle, submucous plexus and in the celiac ganglion. Faintly reactive nerve cell bodies were found in the myenteric ganglia (3.2% of all neurons) but not in submucous ganglia. After all ascending and descending pathways in the myenteric plexus had been cut, reactive terminals disappeared in the myenteric plexus, circular muscle (including the deep muscular plexus) and the submucous plexus on the anal side. After the mesenteric nerves were cut no changes were observed in the intestinal wall but the reactive fibres in celiac ganglia disappeared. It is deduced that GRP/bombesin-immunoreactive nerve cell bodies in myenteric ganglia project from the myenteric plexus to other myenteric ganglia situated further anally (average length 12 mm), anally to the circular muscle (average length 9 mm), anally to submucous ganglia (average length 13 mm) and external to the intestine to the celiac ganglia.It is concluded that the GRP/bombesin-reactive neurons in the intestinal wall represent a distinct population of enteric neurons likely to be involved in controlling motility and in the coordination of other intestinal functions.     

Development of the enteric nervous system in the moth. I. Diversity of cell types and the embryonic expression of FMRFamide-related neuropeptides

The enteric nervous system (ENS) of the larval moth Manduca sexta consists of two small ganglia and several nerve networks that lie superficially along the alimentary tract. Within this system are approximately 600 neurons that exhibit a spectrum of biochemical and morphological characteristics and that express these features in a definable sequence during development. The accessibility of both the neural and nonneural components of the moth ENS throughout embryogenesis makes it a potentially useful model in which to examine the developmental regulation of transmitter phenotype. In this paper, we have focused on the differentiation of the enteric plexus (EP) cells, a heterogeneous population of enteric neurons that are distributed across the foregut-midgut boundary. Unlike many neurons of the CNS in insects, the cells of the enteric plexus are not uniquely identifiable. While the total number of EP cells is constant, their locations vary significantly from animal to animal. However, several distinct classes of neurons can be identified within this population on the basis of morphology and transmitter phenotype, including one class that contains substances related to the molluscan peptide Phe-Met-Arg-Phe-amide (FMRFamide). Expression of this FMRFamide-like material within the enteric plexus is position-specific, occurring only in neurons on the midgut and not in those on the foregut. FMRFamide-like immunoreactivity first appears in approximately one-third of these cells at 65% of development; this pattern is retained without apparent modification throughout subsequent embryonic and postembryonic development. In the following paper, we describe the sequence of stereotyped cell migration that precedes the expression of this peptidergic phenotype and that underlies the formation of the enteric plexus during embryogenesis.     

Connections between neurons of sympathetic ganglia and the myenteric nerve plexus of the mammalian colon

By means of retrograde transport of the fluorescent marker primulin the initial part of the sympathetic innervation of the myenteric nervous plexus of the descending colon has been characterized in cats and guinea pigs. When primulin is injected into the myenteric nervous plexus, marked neurons are revealed in the caudal mesenteric ganglion, in the celiac plexus ganglia, in the sympathetic trunk ganglia. The marked nervous populations of the extramural sympathetic ganglia differ in their form, size, number of neurons and their distribution.     

Vanilloid receptor (VR1) expression in vagal afferent neurons innervating the gastrointestinal tract

The vanilloid receptor VR1 is a nonselective cation channel activated by capsaicin as well as increases in temperature and acidity, and can be viewed as molecular integrator of chemical and physical stimuli that elicit pain. The distribution of VR1 receptors in peripheral and central processes of rat primary vagal afferent neurons innervating the gastrointestinal tract was investigated by immunohistochemistry. Forty-two percent of neurons in the nodose ganglia retrogradely labeled from the stomach wall expressed low to moderate VR1 immunoreactivity (VR1-IR). VR1-IR was considerably lower in the nodose ganglia as compared to the jugular and dorsal root ganglia. In the vagus nerve, strongly VR1-IR fibers ran in separate fascicles that supplied mainly cervical and thoracic targets, leaving only weakly VR1-IR fibers in the subdiaphragmatic portion. Vagal afferent intraganglionic laminar endings (IGLEs) in the gastric and duodenal myenteric plexus did not express VR1-IR. Similarly, VR1-IR was contained in fibers running in perfect register with vagal afferents, but was not colocalized with horseradish peroxidase in the same varicosities of intramuscular arrays (IMAs) and vagal afferent fibers in the duodenal submucosa anterogradely labeled from the nodose ganglia. Only in the gastric mucosa did we find evidence for colocalization of VR1-IR in vagal afferent terminals. In contrast, many nerve fibers coursing through the myenteric and submucosal plexuses contained detectable VR1-IR, the majority of which colocalized calcitonin gene-related peptide immunoreactivity. In the dorsal medulla there was a dense plexus of VR1-IR varicose fibers in the commissural, dorsomedial and gelatinosus subnuclei of the medial NTS and the lateral aspects of the area postrema, which was substantially reduced, but not eliminated on the ipsilateral side after supranodose vagotomy. It is concluded that about half of the vagal afferents innervating the gastrointestinal tract express low levels of VR1-IR, but that presence in most of the peripheral terminal structures is below the immunohistochemical detection threshold.     

Cholinergic, nitrergic and peptidergic (Substance P- and CGRP-utilizing) innervation of the horse intestine. A histochemical and immunohistochemical study

The small and large intestine of adult horses were histochemically and immunohistochemically investigated in order to evidence components of the intramural nervous system. The general structural organization of the intramural nervous system was examined by using Nissl-thionin staining as well as the anti-neurofilament 200 (NF200) immunoreaction, which demonstrated the presence of neurons in the submucous as well as myenteric plexuses. The additional presence of subserosal ganglia was shown in the large intestine. Acetylcholinesterase (AChEase) activity was observed in both the submucous and myenteric plexuses. Localization of acetylcholine-utilizing neurons was also evidenced by immunohistochemical reactions for choline acetyltransferase (ChAT) and vesicular acetylcholine transporter (VAChT). With both histochemistry and immunohistochemistry possible cholinergic nerve fibres were detected in the inner musculature. The two possible cholinergic co-mediators Calcitonin Gene-Related Peptide (CGRP) and Substance P (SP) have been investigated by an immunohistochemical approach. CGRP immunoreactivity was detected in roundish nerve cell bodies as well as in nerve fibres of the submucous plexus, whereas SP immunoreactivity was evidenced in nerve fibres of the tunica mucosa, in nerve cell bodies and fibres of the submucous plexus and in nerve fibres of the myenteric plexus. NADPH-diaphorase reactivity, which is linked to the synthesis and release of nitric oxide, was detected in nerve cell bodies and nerve fibres of both the submucous and myenteric plexuses as well as in a subserosal localization of the large intestine. The nitrergic components were confirmed by the anti-NOS (nitric oxide synthase) immunoreaction. Results are compared with those of other mammals and related to the complex intestinal horse physiology and pathophysiology.