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

Characterization of viscerofugal neurons in human colon by retrograde tracing and multi-layer immunohistochemistry

Background and Aims

Viscerofugal neurons (VFNs) have cell bodies in the myenteric plexus and axons that project to sympathetic prevertebral ganglia. In animals they activate sympathetic motility reflexes and may modulate glucose metabolism and feeding. We used rapid retrograde tracing from colonic nerves to identify VFNs in human colon for the first time, using ex vivo preparations with multi-layer immunohistochemistry.

Methods

Colonic nerves were identified in isolated preparations of human colon and set up for axonal tracing with biotinamide. After fixation, labeled VFN cell bodies were subjected to multiplexed immunohistochemistry for 12 established nerve cell body markers.

Results

Biotinamide tracing filled 903 viscerofugal nerve cell bodies (n = 23), most of which (85%) had axons projecting orally before entering colonic nerves. Morphologically, 97% of VFNs were uni-axonal. Of 215 VFNs studied in detail, 89% expressed ChAT, 13% NOS, 13% calbindin, 9% enkephalin, 7% substance P and 0 of 123 VFNs expressed CART. Few VFNs contained calretinin, VIP, 5HT, CGRP, or NPY. VFNs were often surrounded by dense baskets of axonal varicosities, probably reflecting patterns of connectivity; VAChT+ (cholinergic), SP+ and ENK+ varicosities were most abundant around them. Human VFNs were diverse; showing 27 combinations of immunohistochemical markers, 4 morphological types and a wide range of cell body sizes. However, 69% showed chemical coding, axonal projections, soma-dendritic morphology and connectivity similar to enteric excitatory motor neurons.

Conclusion

Viscerofugal neurons are present in human colon and show very diverse combinations of features. High proportions express ChAT, consistent with cholinergic synaptic outputs onto postganglionic sympathetic neurons in prevertebral ganglia.

Localization and neurochemical characteristics of the extrinsic sympathetic neurons projecting to the pylorus in the domestic pig

The pylorus, an important part of the digestive tract controlling the flow of chyme between the stomach and the duodenum, is widely innervated by intrinsic and extrinsic nerves. To determine the locations of postganglionic sympathetic perikarya that innervate the pylorus of the domestic pig, a retrograde tracing method with application of Fast Blue tracer was used. All positive neuronal cell bodies (ca. 1750) were found in the celiac-cranial mesenteric ganglion complex (CSMG), however, the coeliac poles of this complex provided the major input to the pylorus. Afterwards, the immunohistochemical staining procedure was applied to determine biologically active substances expressed in the FB-labeled perikarya. Approximately 77% of the FB-positive cell bodies contained tyrosine hydroxylase (TH), 87% dopamine β-hydroxylase (DβH), 40% neuropeptide Y (NPY), 12% somatostatin (SOM) and 7% galanin (GAL). The presence of all these substances in the ganglion tissue was confirmed by RT-PCR technique. Double immunocytochemistry revealed that all of the TH-positive perikarya contained DβH, about 40% NPY, 12% SOM and 8% GAL. Additionally, all above-cited immunohistochemical markers as well as VIP, PACAP, ChAT, LEU, MET, SP and nNOS were observed within nerve fibers associated with the FB-positive perikarya. Immunocytochemical labeling of the pyloric wall tissue disclosed that TH+, DβH+ and NPY+ nerve fibers innervated ganglia of the myenteric and submucosal plexuses, blood vessels, both muscular layers and the muscularis mucosae; nerve fibers immunoreactive to GAL mostly innervated both muscular layers, while SOM+ nerve fibers were observed within the myenteric plexus. Presented study revealed sources of origin and immunohistochemical characteristics of the sympathetic postganglionic perikarya innervating the porcine pylorus.

Sympathetic innervation of the ileocecal junction in horses

The distribution and chemical phenotypes of sympathetic and dorsal root ganglion (DRG) neurons innervating the equine ileocecal junction (ICJ) were studied by combining retrograde tracing and immunohistochemistry. Immunoreactivity (IR) for tyrosine hydroxylase (TH), dopamine beta-hydroxylase (DBH), neuronal nitric oxide synthase (nNOS), calcitonin gene-related peptide (CGRP), substance P (SP), and neuropeptide Y (NPY) was investigated. Sympathetic neurons projecting to the ICJ were distributed within the celiac (CG), cranial mesenteric (CranMG), and caudal mesenteric (CaudMG) ganglia, as well as in the last ganglia of the thoracic sympathetic chain and in the splanchnic ganglia. In the CG and CranMG 91 +/- 8% and 93 +/- 12% of the neurons innervating the ICJ expressed TH- and DBH-IR, respectively. In the CaudMG 90 +/- 15% and 94 +/- 5% of ICJ innervating neurons were TH- and DBH-IR, respectively. Sympathetic (TH-IR) fibers innervated the myenteric and submucosal ganglia, ileal blood vessels, and the muscle layers. They were more concentrated at the ICJ level and were also seen encircling myenteric plexus (MP) and submucosal plexus (SMP) descending neurons that were retrogradely labeled from the ICJ. Among the few retrogradely labeled DRG neurons, nNOS-, CGRP-, and SP-IR nerve cells were observed. Dense networks of CGRP-, nNOS-, and SP-IR varicosities were seen around retrogradely labeled prevertebral ganglia neurons. The CGRP-IR fibers are probably the endings of neurons projecting from the intestine to the prevertebral ganglia. These findings indicate that this crucial region of the intestinal tract is strongly influenced by the sympathetic system and that sensory information of visceral origin influences the sympathetic control of the ICJ.

The neurochemistry and innervation patterns of extrinsic sensory and sympathetic nerves in the myenteric plexus of the C57Bl6 mouse jejunum

In vitro anterograde tracing of axons in mesenteric nerve trunks using biotinamide in combination with immunohistochemical labelling was used to characterize the extrinsic nerve projections in the myenteric plexus of the mouse jejunum. Anterogradely-labelled spinal sensory fibres innervating the enteric nervous system were identified by their immunoreactivity for calcitonin gene-related peptide (CGRP), while sympathetic noradrenergic fibres were detected with tyrosine hydroxylase (TH), using confocal microscopy. The presence of these markers has been previously described in the spinal sensory and sympathetic fibres. Labelled extrinsic nerve fibres in the myenteric plexus were identified apposing enteric neurons that were immunoreactive for either calretinin (CalR), calbindin (CalB) or nitric oxide synthase (NOS). Of the total anterogradely labelled axons in the myenteric plexus, 20% were CGRP-immunoreactive. Labelled CGRP-immunoreactive varicosities were closely apposed to CalR-immunoreactive myenteric cells, many of which were Dogiel type I (40%; interneurons) or type II (20%; intrinsic sensory) neurons. Labelled CGRP-immunoreactive varicosities were also observed in close appositions to CalB-immunoreactive myenteric cell bodies, of which a small subset had type II morphology (18%; intrinsic sensory neurons). A further 43% of all biotinamide-filled fibres were immunoreactive for TH and these fibres were apposed to CalR-immunoreactive cell bodies (small-sized; excitatory motor neurons) and NOS-immunoreactive cell bodies (either type I or small neurons; inhibitory motor neurons and interneurons) in the myenteric plexus. The results provide a neurochemical and neuroanatomical basis for connections between dorsal root afferent neurons and myenteric neurons and suggest an anatomical substrate for the well-known modulation of enteric circuits from sympathetic nerves. No anterogradely-labelled fibres were stained for NOS-immunoreactivity, despite more than 60% of dorsal root ganglion (DRG) neurons retrogradely labelled from the jejunum showing NOS-immunoreactivity. This was due to a substantial, time-dependent, and apparently selective, loss of NOS from extrinsic axons under in vitro conditions. Lastly, a small population of non-immunoreactive biotinamide-filled fibres (<1%) gave rise to dense terminal structures around individual myenteric cell bodies lacking CalR, CalB or NOS. These specialized endings may represent vagal fibres or a subset of spinal sensory neurons that do not contain CGRP.

The distribution and chemical coding of intramural neurons supplying the porcine stomach - the study on normal pigs and on animals suffering from swine dysentery

The present study was designed to investigate the expression of biologically active substances by intramural neurons supplying the stomach in normal (control) pigs and in pigs suffering from dysentery. Eight juvenile female pigs were used. Both dysenteric (n = 4; inoculated with Brachyspira hyodysenteriae) and control (n = 4) animals were deeply anaesthetized, transcardially perfused with buffered paraformalehyde, and tissue samples comprising all layers of the wall of the ventricular fundus were collected. The cryostat sections were processed for double-labelling immunofluorescence to study the distribution of the intramural nerve structures (visualized with antibodies against protein gene-product 9.5) and their chemical coding using antibodies against vesicular acetylcholine (ACh) transporter (VAChT), nitric oxide synthase (NOS), galanin (GAL), vasoactive intestinal polypeptide (VIP), somatostatin (SOM), Leu(5)-enkephalin (LENK), substance P (SP) and calcitonin gene-related peptide (CGRP). In both inner and outer submucosal plexuses of the control pigs, the majority of neurons were SP (55% and 58%, respectively)- or VAChT (54%)-positive. Many neurons stained also for CGRP (43 and 45%) or GAL (20% and 18%) and solitary perikarya were NOS-, SOM- or VIP-positive. The myenteric plexus neurons stained for NOS (20%), VAChT (15%), GAL (10%), VIP (7%), SP (6%) or CGRP (solitary neurons), but they were SOM-negative. No intramural neurons immunoreactive to LENK were found. The most remarkable difference in the chemical coding of enteric neurons between the control and dysenteric pigs was a very increased number of GAL- and VAChT-positive nerve cells (up to 61% and 85%, respectively) in submucosal plexuses of the infected animals. The present results suggest that GAL and ACh have a specific role in local neural circuits of the inflamed porcine stomach in the course of swine dysentery.

Circumferential, not longitudinal, colonic stretch increases synaptic input to mouse prevertebral ganglion neurons

The relationship between longitudinal and circular muscle tension in the mouse colon and mechanosensory excitatory synaptic input to neurons in the superior mesenteric ganglion (SMG) was investigated in vitro. Electrical activity was recorded intracellularly from SMG neurons, and muscle tension was simultaneously monitored in the longitudinal, circumferential, or both axes. Colonic intraluminal pressure and volume changes were also monitored simultaneously with muscle tension changes. The results showed that the frequency of fast excitatory postsynaptic potentials (fEPSPs) in SMG neurons increased when colonic muscle tension decreased, when the colon relaxed and refilled with fluid after contraction, and during receptive relaxation preceding spontaneous colonic contractions. In contrast, fEPSP frequency decreased when colonic muscle tension increased during spontaneous colonic contraction and emptying. Manual stretch of the colon wall to 10-15% beyond resting length in the circumferential axis of flat sheet preparations increased fEPSP frequency in SMG neurons, but stretch in the longitudinal axis to 15% beyond resting length in the same preparations did not. There was no increase in synaptic input when tubular colon segments were stretched in their long axes up to 20% beyond their resting length. The circumferential stretch-sensitive increase in the frequency of synaptic input to SMG neurons persisted when the colonic muscles were relaxed pharmacologically by nifedipine (2 microM) or nicardipine (3 microM). These results suggest that colonic mechanosensory afferent nerves projecting to the SMG function as length or stretch detectors in parallel to the circular muscle layer.

Relationship between colonic motility and cholinergic mechanosensory afferent synaptic input to mouse superior mesenteric ganglion

Abstract Abdominal prevertebral ganglion neurones receive excitatory synaptic input from intestinofugal neurones. To better understand the physiological significance of this input, we examined the relationship between synaptic input to mouse superior mesenteric ganglion (SMG) neurones and intracolonic pressure and volume changes that accompany spontaneous colonic contractions in vitro. Electrical activity was recorded intracellularly from SMG neurones in ganglia attached to a segment of distal colon. The majority of neurones examined received ongoing fast excitatory potentials (F-EPSPs). F-EPSP frequency increased when the colon was distended with fluid and during spontaneous increases in colonic volume that accompanied colonic relaxation. In contrast, F-EPSP frequency in SMG neurones decreased when the colon emptied, and remained at a reduced frequency until the colon refilled and volume increased. Nicotinic blockade of the colon abolished spontaneous colonic contractions and reduced or abolished synaptic input to SMG neurones, suggesting that most of the synaptic input arose from second or higher order neurones. Retrograde labelling identified cell bodies of intestinofugal neurones in myenteric ganglia. Most had short, club-like dendritic processes and appeared uni-axonal. These results show that mechanosensory intestinofugal afferent nerves monitor intracolonic volume changes.

Neuronal organization and cell interactions of the cat stellate ganglion

The functional structure of the cat stellate ganglion (SG) and, in particular, its extra- and intraganglionic connections and neuronal organization, were investigated using histochemical, immunohistochemical, morphological and histological methods. Retrograde axonal transport of horseradish peroxidase was used to determine most of the extraganglionic interactions. Of the targets tested, the most extensive efferent connections of the SG were with the stemocleidomastoid muscle, trachea, esophagus and heart. Neurons of the SG also send a small number of postganglionic efferents to the thyroid and stomach. Furthermore, ganglion cells send axons to the spinal ganglia. Several afferent connections of the SG were determined. Sympathetic preganglionic neurons of segments C8-T10 of the spinal cord, sensory neurons of C8-T9 spinal ganglia, intramural ganglia of the thoracic viscera and the reticular formation of the medulla oblongata send their axons to the SG. Intraganglionic interactions of intemeurons with principal ganglionic cells were assumed to occur, based on the presence of interneurons immunoreactive to GABA and substance P. GABA- and substance P-immunoreactive fibers located around a small number of postganglionic neurons were also identified. Morphological study revealed asymmetry between the left and right ganglia: the right ganglion is larger than the left and contains more cells. This asymmetry was also reflected in basic structural parameters of neurons, such as average neuronal area and average diameter of cell somata. The present data has been used to develop a scheme for the basic inter- and intraneuronal connections of the cat SG. This ganglion is a true nervous center, with postganglionic neurons, some of which might be performing sensory functions, and interneurons. The ganglion is connected not only with the spinal cord and spinal ganglia, but also with neurons of the intramural ganglia and, by direct links, with efferent neurons of the medulla oblongata. Thus, the SG may play an essential role in viscera-visceral reflexes.

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.

Peptidergic nerve fibres in the human liver

The autonomic nervous system plays a significant role in liver physiology and pathology. The aim of the present study was to investigate peptidergic nerve fibres in the liver of patients with malignant gastrointestinal tumors that are not metastasizing in this organ. Using light and electron microscopic immunohistochemistry, somatostatin (SOM)-, neuropeptide Y (NPY)-, substance P (SP)- and calcitonin gene-related peptide (CGRP)-immunoreactive (IR) nerve fibres (NF) were detected in the portal tract and perisinusoidally. Histologically, the liver showed dilated sinusoids, filled with lymphoid cells, and scarcely marked perisinusoidal fibrosis. Neuropeptide-IR NF were found in close contact with hepatic sinusoids. Numerous IR varicosities were detected in the sinusoidal wall. We discuss the origin and role of these NF in the liver. Probable quantitative changes in peptidergic NF ensue the inflammatory reaction in sinusoids in malignant gastrointestinal tumors. This could also reflect the increased exposure of the liver to toxic substances in the portal blood flow.

Immunocytochemical localization of the neurons in the superior mesenteric ganglion innervating the small intestine of the cat

Retrograde tracing was used to determine the localization of neuronal perikarya and fibres in the feline superior mesenteric ganglion (SMG), projecting to the small intestine. In the distal part of the ileum, a retrograde neuronal tracer Fast Blue (FB) was injected and after approximately thirty five to forty days the animals were killed by perfusion. The SMG were removed and the neuropeptide contents of the neurons, projecting to the distal ileum, were determined by means of immunofluorescence with antisera to neuropeptide Y (NPY), calcitonin gene-related peptide (CGRP), substance P (SP), somatostatin (SOM), and vasoactive intestinal polypeptide (VIP). Neurons innervating the small intestine were located in the upper part of the SMG and all of them were NPY-immunopositive. The group of CGRP-immunoreactive (IR) cells was less numerous (73.33%). Probably the FB-labeled fibres, containing the same neuropeptides, arise from these perikarya. SP- or VIP-immunopositive neuronal processes were found to surround immunonegative ganglionic cells but their origin is not in the ganglion. Only single FB-marked cells were VIP-immunopositive. SP- and SOM-immunoreactive amounted respectively to 2.28% and 3.01% of all the neuronal population, but only a few of these cells were FB-labelled.

Regulation of ion transport in the porcine intestinal tract by enteric neurotransmitters and hormones

In the present paper, the mechanisms underlying the neural and hormonal regulation of mucosal ion transport in the pig intestinal tract are reviewed. The active transport of NaCl by isolated sheets of porcine intestinal mucosa is modulated by cholinergic and non-cholinergic neurons of undetermined neurochemical identity that lie in the submucosa. The application of electrical field stimulation to mucosa-submucosa preparations from porcine jejunum, ileum, or colon produces rapid elevations in short-circuit current which are inhibited by tetrodotoxin or omega-conotoxin GVIA, blockers of neuronal Na+ and Ca2+ channels, respectively. In porcine ileum, these elevations in current are mimicked in large part by cholinergic agonists and have been attributed to anion secretion. The majority of classical neurotransmitters and gut peptides that have been examined to date increase active transepithelial anion secretion through interactions with G protein-coupled receptors associated with submucosal neurons or situated on the basolateral membranes of epithelial cells. A small number of neuropeptides interact with neuronal receptors to augment NaCl absorption or decrease anion secretion. Noradrenergic control of intestinal transport differs in the porcine small and large intestines, and displays considerable inter-species variability in its cellular underpinnings. Transport regulation by bombesin-like peptides may be mediated by receptors distributed in both the apical and basolateral membrane domains of epithelial cells in porcine colon. The transport process affected by these peptides may be linked to epithelial growth and differentiation. The pig intestinal tract appears to be a useful biological model for resolving the cellular mechanisms by which gut neurotransmitters and hormones act in regulating transepithelial ion fluxes. Its general relevance to human intestinal function is discussed.

Structural organization and neuropeptide distribution in the mammalian enteric nervous system, with special attention to those components involved in mucosal reflexes

Gastrointestinal events such as peristalsis and secretion/absorption processes are influenced by the enteric nervous system, which is capable of acting largely independently from other parts of the nervous system. Several approaches have been used to further our understanding of the underlying mechanisms of specific enteric microcircuits. Apart from pharmacological and physiological studies, the deciphering of the chemical coding of distinct morphological and functional enteric neuron classes, together with a detailed analysis of their projections by the application of immunocytochemistry, of tracing, and of denervation techniques, have substantially contributed to our knowledge. In view of existing interspecies and regional differences, it is of major importance to expand our knowledge of the enteric nervous system in mammals other than the guinea-pig, the most commonly used experimental animal in this research area. This will increase our chances of finding a valid model, from which well-founded extrapolations can be made regarding the precise function of distinct enteric neuron types regulating motility and ion transport in the human gastrointestinal tract.

Signal transduction pathways for serotonin as an intestinal secretagogue

This review presents a signal transduction pathways for serotonin (5-hydroxytryptamine, 5-HT) as an intestinal secretagogue and some recently published related findings. 5-HT is a secretagogue in the small and large intestine of all studied species including pig and man. 5-HT mediates intestinal secretion through activation of at least the epithelial 5-HT2, and neuronal 5-HT3, and 5-HT4 receptors in the submucosal plexus, including a reflex arc. 5-HT activates both a cholinergic and a non-cholinergic pathway in its secretory response. Intracellular mediators include at least eicosanoids (prostaglandin E2), calcium, phosphoinositols (1,4,5-inositol trisphosphate) and maybe nitric oxide and cyclic nucleotides. Pig small intestine appears to be an appropriate model for the human small intestine with respect to the signal transduction pathways for 5-HT as an intestinal secretagogue. Species and segmental differences in the signal transduction pathways for 5-HT as an intestinal secretagogues are discussed together with related news on 5-HT receptors, 5-HT antagonists in clinical use, the enteric nervous system, and intracellular mediators.

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.

5-Hydroxytryptamine-immunoreactive nerve fibers in the rat and porcine prevertebral sympathetic ganglia: effect of precursor loading and relation to catecholaminergic neurons

Localization of 5-hydroxytryptamine immunoreactivity was studied in the rat coeliac-superior mesenteric ganglion complex and in the porcine superior and inferior mesenteric ganglia by the indirect immunofluorescence technique. In normal rats, only 5-hydroxytryptamine immunoreactive SIF cells were seen in the coeliac-superior mesenteric ganglion complex. In the rats, pretreated with a 5-hydroxytryptamine precursor, L-tryptophan, and with a monoamine oxidase inhibitor, nialamide, a large number of 5-hydroxytryptamine-immunoreactive nerve fiber terminals were detected. In normal porcine superior and inferior mesenteric ganglia, intense 5-hydroxytryptamine immunoreactivity was found in numerous nerve fibers which were located around tyrosine hydroxylase-immunoreactive principal neurons. The origin and function of these fibers are discussed.

Distribution and morphological characterization of viscerofugal projections from the large intestine to the inferior mesenteric and pelvic ganglia of the male rat

Viscerofugal neurons are enteric neurons in the myenteric plexus of the stomach and intestine that project to the prevertebral ganglia as the afferent limb of intestino-intestinal reflexes. This study characterizes viscerofugal projections to the inferior mesenteric ganglion and investigates the possibility of similar projections to the major pelvic ganglia in the male rat. The colon and rectum were examined for retrogradely labelled neurons following the injection of retrograde tracer into the inferior mesenteric or major pelvic ganglia, or following the application of tracer to the caudal end of the cut intermesenteric nerves, or either end of the cut hypogastric nerves. All labelled viscerofugal neurons were found in the myenteric plexus and were often grouped near the mesenteric attachment. The number of viscerofugal neurons projecting to the inferior mesenteric ganglion via the lumbar colonic nerves increases along the length of the large intestine with the maximum number of viscerofugal neurons found in the rectum. Some viscerofugal neurons from the distal colon and rectum reach the inferior mesenteric ganglion via the hypogastric nerves. A similar number and distribution of viscerofugal neurons project via the inferior mesenteric ganglion into the intermesenteric nerves as terminate in the inferior mesenteric ganglion. Very few viscerofugal neurons project to the neurons of the major pelvic ganglia via the rectal nerves, and no viscerofugal neurons project caudally in the hypogastric nerves to these ganglia. The majority of labelled neurons resembled Dogiel type I morphology. Thus the inferior mesenteric ganglion receives a substantial innervation from viscerofugal neurons of the large intestine, with the greatest supply from the distal colon and rectum.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

Three-dimensional reconstructions of autonomic projections to the gastrointestinal tract

Three-dimensional reconstruction protocols in confocal microscopy are typically considered in terms of rendering separate stacks of optical sections. Single stacks, however, include volumes that are often too small to permit descriptions of entire neurons, complete axonal arbors, or complex neural networks. Furthermore, traditional tissue preparation protocols generally yield specimens too limited to permit reconstructions of complex neural systems. For 3-D analyses of extensive networks such as the autonomic nervous system projections within the viscera, it is critical to incorporate appropriate tissue techniques, including suitable tracer protocols, into the reconstruction strategy. This report summarizes complementary technologies, including whole mount procedures, tracer techniques for identifying single fibers in situ, and methods of examining stacks of optical images, which make it practical to describe the complete terminal field of an individual axon in the gastrointestinal tract. Such methods establish that vagal motor axons travel long distances within their target organs, collateralize frequently, and ramify extensively. Vagal afferents have extensive, complex, and, in some cases, polytopic arbors within target tissues.

Nitric oxide synthase-containing neurons in the pig large intestine: topography, morphology, and viscerofugal projections

The distribution of neurons that are capable of synthesizing nitric oxide (NO) has been demonstrated in the porcine large intestine by means of NO synthase (NOS) immunocytochemistry and nicotinamide adenine dinucleotide phosphate diaphorase (NADPHd) histochemistry. An overall colocalization of NOS immunoreactivity and NADPHd staining was observed. Nitrergic neurons were abundant in the myenteric and outer submucous plexus of the caecum, colon, and rectum. Only a few nitrergic perikarya were seen in the inner submucous plexus of the colon and caecum, whereas a substantially larger number was observed in the rectum. Nitrergic nerve fibers were present in the three ganglionic nerve plexuses. Contrary to the outer longitudinal muscle layer and the mucosal region, the circular muscle layer received a dense nitrergic innervation. The nitrergic nerve cells were variable in size and shape, and several displayed vasoactive intestinal polypeptide (VIP) immunoreactivity (IR). Retrograde tracing studies revealed the existence of nitrergic neurons that project to the caudal (inferior) mesenteric ganglion. They were observed in the myenteric and outer submucous plexus of the transverse and descending colon and the rectum. These observations strongly suggest that several subpopulations of NO-synthesizing neurons, namely, motor neurons and interneurons, should be distinguished in the porcine large intestine, thereby emphasizing the importance of NO as a biologically active mediator.

Structural organization and neuropeptide distributions in the equine enteric nervous system: an immunohistochemical study using whole-mount preparations from the small intestine

The architecture and neurochemistry of the enteric nervous system was studied by use of whole-mount preparations obtained by microdissection of the horse jejunum. A myenteric plexus and two plexuses within the submucosa were identified. The external submucosal plexus lying in the outermost region of the submucosa had both neural and vascular connections with the inner submucosal plexus situated closer to the mucosa. Counts of neurones stained for NADH-diaphorase demonstrated the wide variation in size, shape and neurone content of individual ganglia in both the external and internal submucosal plexuses. The average number of cells/ganglion was similar in each plexus (about 25 cells). Immunoreactivities for galanin, vasoactive intestinal peptide and neuropeptide Y were observed in nerve cell bodies and fibres of each of the plexuses. Immunoreactivity for substance P was extensive and strong in nerve fibres of all plexuses but was weaker in cell bodies of the submucosal neurones and absent in the cell bodies of the myenteric plexus. Comparative quantitative analysis of immunoreactive cell populations with total cell numbers (enzyme staining) was indicative of neuropeptide colocalization in the external submucosal plexus.

Topographical distribution and immunocytochemical features of colonic neurons that project to the cranial mesenteric ganglion in the pig

Using the retrograde neuronal tracers Fast blue and Fluorogold, the topographical distribution and morphological features of porcine colonic neurons projecting to the cranial (superior) mesenteric ganglion have been investigated. Two to four weeks after injection of the tracer into the cranial mesenteric ganglion of immature pigs, labelled neurons were found throughout the colon. In the myenteric and outer submucous plexuses, they were present in ganglia situated to the side of the mesenteric attachment. The highest density of labelled neurons was observed at the end of the ascending colon, which in the pig represents 78-80% of the total colon length. The viscerofugal neurons had a multidendritic appearance and part of them were immunoreactive for calcitonin gene-related peptide or serotonin. This study has revealed similarities but also significant differences in the colono-sympathico-colonic pathways between the pig and small laboratory animals such as the guinea-pig.

Distribution and morphological features of nitrergic neurons in the porcine large intestine

The distribution of nitric oxide synthase (NOS), an enzyme involved in the synthesis of the presumed non-adrenergic noncholinergic inhibitory neurotransmitter nitric oxide (NO), was demonstrated in the enteric nervous system of the porcine caecum, colon and rectum. Techniques used were NOS-immunocytochemistry and nicotinamide adenine dinucleotide phosphate diaphorase (NADPHd)-histochemistry. Throughout the entire large intestine, NOS-immunoreactive (IR) and NADPHd-positive neurons were abundant in the myenteric and outer submucous plexus. In the inner submucous plexus, only a small number of positive neurons were found in the caecum and colon, while a moderate number was observed in the rectum. The nitrergic neurons in the porcine enteric nerve plexuses were of a range of sizes and shapes, with a small proportion showing immunostaining for vasoactive intestinal polypeptide. Varicose and non-varicose NOS-IR and NADPHd-positive nerve fibres were present in the ganglia and connecting strands of all three plexuses. Nerve fibres were also numerous in the circular muscle layer, scarce in the longitudinal muscle coat and negligible in the mucosal region. The abundance of NOS/NADPHd in the intrinsic innervation of the caecum, colon and rectum of the pig implicates NO as an important neuronal messenger in these regions of the gastrointestinal tract.