The presence of vasoactive intestinal polypeptide-like immunoreactive structures projecting from the myenteric ganglion of the stomach to the celiac ganglion revealed by a double-labelling technique

Enteric Control of the Sympathetic Nervous System

The autonomic nervous system that regulates the gut is divided into sympathetic (SNS), parasympathetic (PNS), and enteric nervous systems (ENS). They inhibit, permit, and coordinate gastrointestinal motility, respectively. A fourth pathway, "extrinsic sensory neurons," connect gut to the central nervous system, mediating sensation. The ENS resides within the gut wall and its activities are critical for life; ENS failure to populate the gut in development is lethal without intervention."Viscerofugal neurons" are a distinctive class of enteric neurons, being the only type that escapes the gut wall. They form a unique circuit: their axons project out of the gut wall and activate sympathetic neurons, which then project back to the gut, and inhibit gut movements.For 80 years viscerofugal/sympathetic circuits were thought to have a restricted role, mediating simple sensory-motor reflexes. New data shows viscerofugal and sympathetic neurons behaving unexpectedly, compelling a re-evaluation of these circuits: both viscerofugal and sympathetic neurons transmit higher order, synchronized firing patterns that originate within the ENS. This identifies them as driving long-range motility control between different gut regions.There is need for gut motor control over distances beyond the range of ENS circuits, yet no mechanism has been identified to date. The entero-sympathetic circuits are ideally suited to meet this need. Here we provide an overview of the structure and functions of these peripheral sympathetic circuits, including new data showing the firing patterns generated by enteric networks can transmit through sympathetic neurons.

Immunohistochemical analysis of the mouse celiac ganglion: An integrative relay station of the peripheral nervous system

Celiac ganglia are important sites of signal integration and transduction. Their complex neurochemical anatomy has been studied extensively in guinea pigs but not in mice. The goal of this study was to provide detailed neurochemical characterization of mouse celiac ganglia and noradrenergic nerves in two target tissues, spleen and stomach. A vast majority of mouse celiac neurons express a noradrenergic phenotype, which includes tyrosine hydroxylase (TH), vesicular monoamine transporter 2, and the norepinephrine transporter. Over 80% of these neuron also express neuropeptide Y (NPY), and this coexpression is maintained by dissociated neurons in culture. Likewise, TH and NPY were colocalized in noradrenergic nerves throughout the spleen and in stomach blood vessels. Somatostatin was not detected in principal neurons but did occur in small, TH-negative cells presumed to be interneurons and in a few varicose nerve fibers. Cholinergic nerves provided the most abundant input to the ganglia, and small percentages of these also contained nitric oxide synthase or vasoactive intestinal polypeptide. A low-to-moderate density of nerves also stained separately for the latter markers. Additionally, nerve bundles and varicose nerve fibers containing the sensory neuropeptides, calcitonin gene-related polypeptide, and substance P, occurred at variable density throughout the ganglia. Collectively, these findings demonstrate that principal neurons of mouse celiac ganglia have less neurochemical diversity than reported for guinea pig and other species but receive input from nerves expressing an array of neurochemical markers. This profile suggests celiac neurons integrate input from many sources to influence target tissues by releasing primarily norepinephrine and NPY.

Outer submucous plexus: an intrinsic nerve network involved in both secretory and motility processes in the intestine of large mammals and humans

The architecture of the enteric nerve networks in the gastrointestinal tract appears to be more complex in large mammals, including humans, than in small laboratory animals. At least two distinct ganglionic nerve plexuses could be identified in the submucous layer in the digestive tract of large mammals. While functionally and morphologically similar neuron populations are found in the intestinal wall of both small and large mammals, significant differences in their topographical organization and neurochemical features may be present. This short review clearly illustrates that the close and exclusive association, which has been assumed so far between the efferent pathways of the submucous plexus and regulation of intestinal secretion/absorption on the one hand and between the myenteric plexus and regulation of intestinal motility on the other hand, cannot be interpreted that strictly. An attempt has been made to give a briefoverview of the current status of the identification of distinct functional enteric neuronal classes in the gastrointestinal tract of large mammals using the pig and human intestine as references, and to compare these data with the more extensive information gathered from the guinea-pig intestine.

Identification of intestinofugal neurons projecting to the coeliac and superior mesenteric ganglia in the rat

Intestinofugal neurons are parts of the afferent limbs of inhibitory intestino-intestinal reflexes. These neurons have been mapped in guinea-pigs, where they have a gradient of increasing frequency of occurrence from oral to anal, but not in other species. In the present work in the rat, a species that is more amenable to physiological study than the guinea-pig, we have used retrograde tracing to map the distribution of the cell bodies of intestinofugal neurons projecting to the coeliac-superior mesenteric ganglion complex. Labelled nerve cells were found in the myenteric, but not the submucosal plexus. They were mono-axonal neurons, most with Dogiel type I morphology, and were immunoreactive for choline acetyltransferase, implying that they are cholinergic, which is consistent with functional studies. The cells increased in number per unit area from the stomach, through the small intestine, to the caecum. The results are consistent with physiological studies that reveal distal to proximal inhibitory reflexes that are more potent from distal compared to proximal sites.

Chemical coding of neurons that project from different regions of intestine to the coeliac ganglion of the guinea pig

The chemical codings of neurons that project from the small intestine, caecum, proximal colon, distal colon and rectum to the coeliac ganglion of the guinea pig were investigated. The coeliac ganglion was injected with the retrogradely transported dye Fast Blue, and each of the regions was examined 6 days later in wholemounts that had been prepared for immunohistochemical localisation of pairs of antigens. In both the small and large intestines, all intestinofugal neurons were immunoreactive (IR) for choline acetyltransferase (ChAT). In each region of the large intestine, the largest population, representing 50-60% of retrogradely labelled neurons in each region, was immunoreactive for ChAT, bombesin (BN), calbindin (Calb) and nitric oxide synthase (NOS). Most intestinofugal neurons in the small intestine contain bombesin and VIP-IR along with ChAT-IR but none contain either Calb or NOS. Thus, nerve endings of enteric origin in the coeliac ganglion that contain NOS-IR or Calb-IR come from the large intestine and those with bombesin-IR but not NOS-IR are from the small intestine. The gastric wall was injected with Fast Blue in order to label noradrenergic (NA) neurons in the coeliac ganglion and to determine, by localisation of NOS and bombesin-IR, whether they receive inputs from the small and large intestine. Some NA neurons received inputs from the large intestine (and perhaps also from the small intestine) and some received inputs exclusively from the small intestine. Most NA neurons that received intestinofugal inputs had the chemical code NA/-; some were immunoreactive for somatostatin (NA/SOM neurons), but those with IR for neuropeptide Y (NA/NPY) rarely received intestinofugal inputs.

The origin and distribution of neurons with projections passing through the inferior mesenteric ganglion of the guinea-pig

Retrograde tracing with the fluorescent dye, Fast Blue, was used to examine the origin and distribution of neurons whose axons project through the inferior mesenteric ganglion (IMG) of the guinea-pig. These studies were performed by applying the tracer to (a) the rostral cut-end of the hypogastric nerves and (b) the caudal cut-end of the inter-mesenteric nerve (IMN). After application of tracer to the hypogastric nerves retrogradely labelled cell profiles were observed in the IMG and the superior mesenteric ganglion (SMG). The number of labelled cell profiles in the SMG was consistently about 15% of the number in the IMG. In only one of seven animals tested were labelled cells seen in the wall of the colon. Application of tracer to the IMN labelled cells in the IMG and in the wall of the colon. The distribution of the labelled enteric neurons was skewed towards the anal end of the colon. These results confirm that postganglionic sympathetic neurons in the SMG project axons through the guinea-pig IMG and describe the colonic distribution of enteric neurons that project through the IMG and into the IMN.

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.

Neuronal projections to the guinea pig stellate ganglion investigated by retrograde tracing

Previous electrophysiological studies have revealed a peripheral sensory input to the stellate ganglion which does not originate from the dorsal root ganglia. The present retrograde tracing study aimed at evaluating whether the parent cell bodies are located in the periphery, i.e. in mediastinal ganglia. Following injection of Fast blue or wheat germ agglutinin-horseradish peroxidase into the right stellate ganglion of the guinea pig, retrogradely labelled cell bodies were observed in the intermediolateral and intercalated nuclei of the spinal cord as well as in dorsal root ganglia at segmental levels C8 to T6. In another case, the stellate ganglion was resected and replaced by a sponge soaked with 10 microliters of Fast blue. Labelling of preganglionic and sensory neurons parallelled that obtained by tracer injections. In neither case, however, were retrogradely labelled neurons found within or around the thoracic viscera (thymus, trachea, bronchi, esophagus, heart, great vessels of upper mediastinum) when these were cut serially en bloc. Controls performed by injection of Fast blue into the inferior mesenteric ganglion and investigation of the distal colon showed that our experimental protocol was able to visualize a peripheral projection towards a sympathetic ganglion--in this case from myenteric ganglia to the inferior mesenteric ganglion. We conclude that, in contrast to the circuitry connecting prevertebral sympathetic ganglia with the gut, the neuronal cell bodies providing peripheral sensory input from thoracic viscera to the right stellate ganglion most likely are not located within the mediastinal ganglia. Instead, they may reside within the stellate ganglion itself.

Inhibition of peripheral fast synaptic inputs to celiac ganglion neurons by splanchnic preganglionic fibers in the cat

Fast nicotinic transmission was studied in vitro in isolated cat celiac ganglion neurons using intracellular recording techniques. Fast synaptic activation was evoked by stimulation (0.1 Hz) of the anterior peripheral rami. A long-lasting inhibition of this response was triggered by repetitive splanchnic stimulation (30-50 Hz) for 10 s. Evidence is given that this inhibition occurs at presynaptic level. Our results indicate that central inputs modulate transmission of fast synaptic peripheral inputs to prevertebral ganglionic neurons. This would be another integrative mechanism in the prevertebral ganglia.

Neuronal specificity and plasticity in the autonomic nervous system

The autonomic nervous system is divided into the sympathetic, parasympathetic and enteric subdivisions. The present review is focussed upon the highly specialized reflex organization and neurochemistry of sympathetic parasympathetic neurons. The currently available informations allow to conclude that autonomic control of each peripheral target tissue is specifically regulated under normal conditions but nevertheless able to respond to altered conditions by changes in neural activity and mediator expression.

Calbindin-immunoreactive nerve terminals in the guinea pig coeliac ganglion originate from colonic nerve cells

Previous work has shown that calbindin-immunoreactive (calbindin-IR) nerve terminals are numerous in guinea pig prevertebral ganglia. A high proportion of those colonic nerve cells that project to the inferior mesenteric ganglia are calbindin-IR, but none of the neurons that project from the small intestine to the coeliac ganglion are immunoreactive for calbindin. The present work was designed to determine the source of the calbindin-IR fibres and the pathways by which they reach the coeliac ganglion. Sections through the major nerve trunks that connect with the coeliac ganglion revealed numerous calbindin-IR fibres in the inferior coeliac nerves and in the intermesenteric nerves, while there were very few fibres in the splanchnic or superior coeliac nerves. When all peripheral nerve connections to a lobe of the coeliac ganglion were cut, all calbindin-IR terminals degenerated. Cutting the ileo-caeco-colic nerves caused a substantial reduction in the density of nerve fibres in the coeliac ganglion, whereas no significant reduction could be detected when the intermesenteric nerves were cut. However, lesion of both the ileo-caeco-colic and intermesenteric nerves caused all the calbindin-IR nerve fibres in the coeliac ganglion to degenerate. It is concluded that most or all of the calbindin-reactive nerve terminals in the coeliac ganglion originate from the large intestine and that most reach the ganglion via the ileo-caeco-colic nerves. Thus many colonic intestinofugal neurons, supplying both the coeliac and inferior mesenteric ganglia, are immunoreactive for calbindin, whereas small intestinal intestinofugal neurons are not immunoreactive for this protein.

Evaluation of the activity of chemically identified enteric neurons through the histochemical demonstration of cytochrome oxidase

The measurement of the density of the reaction product produced by the histochemical demonstration of cytochrome oxidase activity provides a method for the visual identification of physiologically active enteric neurons. The current study utilized the cytochrome oxidase technique in order to evaluate the metabolic history of neurons in different regions of the bowel and in chemically identified types of neuron. In addition, the effect of drugs or neurotoxins commonly used in the immunocytochemical identification of enteric neuronal phenotypes was also analyzed. Cytochrome oxidase activity was visualized with a blue-black reaction product resulting from the cobalt-intensified oxidation of 3,3'-diaminobenzidine. Peptides or 5-hydroxytryptamine (5-HT) were localized with biotinylated secondary antibodies and alkaline phosphatase-labeled avidin. Bound avidin or endogenous alkaline phosphatase was visualized with a red reaction product in the presence or absence, respectively, of levamisole. Use of measured without interference from a simultaneously demonstrated histo- or immunochemical marker. A multi-peptidergic class of cholinergic submucosal secretomotor neuron containing neuropeptide Y (NPY) and calcitonin gene related peptide (CGRP) immunoreactivities was found to be less metabolically active than the average of all submucosal neurons. In contrast, a non-cholinergic submucosal secretomotor neuron containing dynorphin (which is also known to contain vasoactive intestinal peptide) immunoreactivity was more metabolically active than submucosal neurons that do not contain this peptide. On average, submucosal neurons were more metabolically active than those of the myenteric plexus, and levels of metabolic activity in the myenteric plexus were found to be higher in the duodenum and the cecum than in the jejunum-ileum or colon. Myenteric neurons characterized by CGRP or NPY immunoreactivities or by endogenous alkaline phosphatase activity, were all less metabolically active than the average of all neurons in myenteric ganglia. Colchicine, which stimulates intestinal motility, was observed to increase cytochrome oxidase activity in enteric neurons, suggesting that an effect on the enteric nervous system contributes to its action on the bowel. The neurotoxins, 6-hydroxydopamine and 5,7-dihydroxytryptamine (5,7-DHT) were each found to stimulate neuronal metabolic activity. 5,7-DHT appeared to activate excitatory subtypes of 5-HT receptor since its effects were blocked or mimicked by compounds that act as antagonists or agonists, respectively, at these receptors.(ABSTRACT TRUNCATED AT 400 WORDS)

Distribution of enteric nerve cells that project from the small intestine to the coeliac ganglion in the guinea-pig

The retrograde tracing agent, Fast blue, was injected into the coeliac ganglia of guinea-pigs and 4-7 days later, nerve cell bodies containing this dye were examined in the small intestine. The cell bodies were found in the ganglia of the myenteric plexus but not in submucous ganglia. The labeled cell bodies were large, on average 42 by 19 microns when viewed in whole mounts, with 4-9 fine processes. The cells increased in frequency anally along the small intestine; the number of neurons per unit length of gut in the distal ileum was more than double that near the duodeno-jejunal flexure. At all points along the intestine the nerve cells were more numerous near the mesenteric attachment than opposite this attachment. About half of the neurons showed immunoreactivity for VIP. It is deduced that the neurons that project from the intestine to the coeliac ganglion are likely to be second-order neurons in the afferent limbs of intestino-visceral reflex pathways.

Distribution of peptidergic terminals of enteric origin in the rat celiac ganglion

We examined the distribution of enterofugal nerve terminals of bombesin-, cholecystokinin- and vasoactive intestinal polypeptide-like immunoreactivity in the rat celiac-superior mesenteric ganglion complex. The majority of these nerve terminals were concentrated in the mesenteric side of the ganglion. The present findings suggest that some functional specialization occurs in the celiac ganglion of the rat.

An electron microscopic study on VIP-, BOM- and CCK-like immunoreactive terminals in the celiac-superior mesenteric ganglion complex of the guinea pig

The distribution and fine structure were studied of the following 3 peptide-containing fibers of enteric origin, vasoactive intestinal polypeptide (VIP), bombesin (BOM) and cholecystokinin (CCK)-like immunoreactive peptide in the celiac-superior mesenteric ganglion complex (CMG) of the guinea pig. These peptides, especially VIP, were distributed more densely on the mesenteric side than on the celiac side of the CMG, and their distribution shared a similar mosaic pattern. Immunoelectron microscopic analysis revealed that the fibers formed synaptic contacts with the proximal dendrites of the principal ganglion cells, however, the profiles of these synaptic junctions differed between fibers. Those containing VIP or CCK formed symmetrical synapses, while those containing BOM formed assymetrical ones. This suggests that there are some functional differences between these enterofugal fibers in the CMG.

Projections of bombesin-like immunoreactive fibers from the rat stomach to the celiac ganglion revealed by a double-labeling technique

Gastrofugal bombesin (BOM)-like immunoreactive (BOMI) structures in the rat were studied by immunocytochemistry combined with retrograde labeling. Transection of the mesenteric nerve peripheral to the celiac ganglion resulted in the complete disappearance of BOMI nerve terminals, whereas transection of the splanchnic nerves did not alter the immunoreactivity. Injection of biotinylated wheat germ agglutinin into the celiac ganglion labeled several neurons in the myenteric ganglion of the stomach. Simultaneous staining with antiserum against BOM showed that some of them are BOMI-positive. These findings demonstrate that BOMI neurons in the myenteric ganglion of the rat stomach project to the celiac ganglion.