An immunohistochemical study of serotonin-containing nerves in the colon of rats

The localization of the serotonin-like immunoreactive nerves of the rat colon was investigated by means of immunohistochemistry, utilizing an antibody against serotonin. In non-treated colons, serotonin-positive neuropils were consistently detected around the myenteric plexus. In pargyline-treated colons, serotonin-like fibres were demonstrated in association with either the small intramural blood vessels of the submucosa or the extramural nerve bundles. Treatment with 5-hydroxytryptophan (5-HTP) permitted the visualization of additional serotonin-immunoreactive fibres around the large extramural blood vessels. Immunoreactive nerve cell bodies were demonstrated in the myenteric plexus of colons treated with 5-HTP or colchicine. From these observations, it is suggested that the serotoninergic nerves of the rat colon comprise both intrinsic and extrinsic elements.     

An immunohistochemical study of serotonin-containing nerves in the colon of rats

Summary The localization of the serotonin-like immunoreactive nerves of the rat colon was investigated by means of immunohistochemistry, utilizing an antibody against serotonin. In non-treated colons, serotonin-positive neuropils were consistently detected around the myenteric plexus. In pargyline-treated colons, serotonin-like fibres were demonstrated in association with either the small intramural blood vessels of the submucosa or the extramural nerve bundles. Treatment with 5-hydroxytryptophan (5-HTP) permitted the visualization of additional serotonin-immunoreactive fibres around the large extramural blood vessels. Immunoreactive nerve cell bodies were demonstrated in the myenteric plexus of colons treated with 5-HTP or colchicine. From these observations, it is suggested that the serotoninergic nerves of the rat colon comprise both intrinsic and extrinsic elements.     

Somatostatin in human enteric nerves

Summary Somatostatin-immunoreactive nerves and endocrine cells were localized by use of immunohistochemistry in human stomach, small and large intestine. The nature of the immunoreactivity in acid extracts of separated layers of intestine was determined with separation by high pressure liquid chromatography followed by detection with radioimmunoassay; authentic somatostatin-14 was found in the external musculature, which contains nerves, and in the submucosa and mucosa, which contain both nerve fibres and endocrine cells.The distribution of somatostatin nerves in the gastric antrum, duodenum, jejunum, ileum, ascending and sigmoid colon, and rectum is described. In the intestine many positive perikarya and fine varicose fibres were seen. Mucosal fibres formed a sub-epithelial plexus and a looser network in the lamina propria; this nerve supply was less dense in the large intestine. Submucous ganglia contained positive perikarya and terminals; many terminals formed pericellular baskets, mainly around non-reactive cells. A small number of nerve fibres were associated with submucosal blood vessels. The innervation of the circular and longitudinal muscle was sparse. Positive nerve terminals were seen in the myenteric plexus, although fewer than in the submucous ganglia; positive perikarya were scarce in myenteric ganglia. Somatostatin-immunoreactive nerves were found in the muscle layers and myenteric plexus of the gastric antrum, but were not detected in the antral mucosa and all layers of the gastric body.The distribution of human enteric somatostatin nerves is compared to that in small laboratory animals, and possible roles for these nerves are discussed.     

Neuroplasticity in the smooth muscle of the myenterically and extrinsically denervated rat jejunum

The objective of this study was to examine the effects of two different denervation procedures on the distribution of nerve fibers and neurotransmitter levels in the rat jejunum. Extrinsic nerves were eliminated by crushing the mesenteric pedicle to a segment of jejunum. The myenteric plexus and extrinsic nerves were eliminated by serosal application of the cationic surfactant benzyldimethyltetradecylammonium chloride (BAC). The effects of these two denervation procedures were evaluated at 15 and 45 days. The level of norepinephrine in whole segments of jejunum was initially reduced by more than 76% after both denervation procedures, but by 45 days the level of norepinephrine was the same as in control tissue. Tyrosine hydroxylase (nor-adrenergic nerve marker) immunostaining was absent at 15 days, but returned by 45 days. However, the pattern of noradrenergic innervating axons was altered in the segment deprived of myenteric neurons. Immunohistochemical studies showed protein gene product 9.5 (PGP 9.5)-immunoreactive fibers in whole-mount preparations of the circular smooth muscle in the absence of the myenteric plexus and extrinsic nerves. At 45 days, the number of nerve fibers in the circular smooth muscle increased. Vasoactive intestinal polypeptide (VIP)-immunoreactive fibers, a subset of the PGP 9.5 nerve fibers, were present in the circular smooth muscle at both time points examined. Choline acetyltransferase (CAT) activity and VIP and leucine enkephalin levels were measured in separated smooth muscle and submucosa-musosal layers of the denervated jejunum. VIP and leucine-enkephalin levels were no different from control in tissue that was extrinsically denervated alone. However, the levels of these peptides were elevated two-fold in the smooth muscle 15 and 45 days after myenteric and extrinsic denervation. In the submucosa-mucosa, VIP and leucine enkephalin levels also were elevated two-fold at 15 days, but comparable to control at 45 days. CAT activity was equal to control in the smooth muscle but elevated two-fold in the submucosa-mucosa at both times. These results provide evidence for innervation of the circular smooth muscle by the submucosal plexus. Moreover, these nerve fibers originating from the submucosal plexus proliferate in the absence of the myenteric plexus. Furthermore, the myenteric neurons appear to be essential for normal innervation of the smooth muscle by the sympathetic nerve fibers. It is speculated that the sprouting of the submucosal plexus induced by myenteric plexus ablation is mediated by increased production of trophic factors in the hyperplastic smooth muscle.     

Innervation of interstitial cells of Cajal by vasoactive intestinal polypeptide containing nerves in canine colon.

The hypothesis was tested, through structural and functional studies, that interstitial cells of Cajal receive and can respond to direct innervation from nerves containing the vasoactive intestinal polypeptide neuromediator. The submucosal network of interstitial cells of Cajal has been postulated to provide pacemaking activity for the circular muscle and to be involved in neurotransmission from nonadrenergic, noncholinergic nerves for which vasoactive intestinal polypeptide is a putative mediator. The distribution of vasoactive intestinal polypeptide and substance P immunoreactive material in nerve profiles of the enteric nervous system of the canine colon was examined. In addition, electrophysiological studies were done on the interstitial cells bordering the submucosal side of the circular muscle layer after they were electrically isolated using heptanol. The vasoactive intestinal polypeptide immunoreactivity, located exclusively in nerve large granular vesicles, was found throughout the enteric nervous system (myenteric plexus, submucous plexus, and circular muscle--submucosa interface). The highest proportion (38% compared with 22-24%) of profiles of large granular vesicles with vasoactive intestinal polypeptide immunoreactivity was found in nerve profiles of the circular muscle--submucosa interface. In contrast, substance P immunoreactivity was found in nerve profiles of myenteric plexus (33% of large granular vesicles were positive) but not associated with submucosal interstitial cell nerve network. The vasoactive intestinal polypeptide hyperpolarized interstitial cells by 9 mV when electrically isolated by 1 mM heptanol and markedly reduced (about 50%) their input membrane resistance. We conclude that the distribution of vasoactive intestinal polypeptide immunoreactivity and its action are consistent with a postulated role of the interstitial cells as a major site of neurally mediated inhibition of colonic pacemaker activity.     

Three-dimensional structures of c-Kit-positive cellular networks in the guinea pig small intestine and colon

Cryosections and whole-mount preparations of the guinea pig small intestine and colon were single or double immunolabeled using the anti-c-Kit and protein gene product 9.5 antibodies. Immunolabeled specimens were observed under a confocal laser scanning microscope. The main findings of the present study are: (1) the distribution and profiles of three-dimensional structures of c-Kit-positive cellular networks in the small intestine and colon, and (2) the anatomical relations of c-Kit-positive cells to the enteric nerves in the layers. In the small intestine, c-Kit-positive cellular networks were observed at levels of the deep muscular plexus and myenteric plexus. The c-Kit-positive cellular networks ran along or overlay the nerve fibers at the deep muscular plexus, while they showed the reticular structures intermingled with the nerve elements at the myenteric plexus. In the colon, c-Kit-positive cellular networks were observed at levels of the submuscular plexus and myenteric plexus, and were further identified within the circular and longitudinal muscle layers as well as in the subserosal layer. In the circular muscle layer, c-Kit-positive cells surrounded the associated nerve fibers and extended several long processes toward the adjacent c-Kit-positive cells. The c-Kit-positive cellular networks within the longitudinal muscle layer as well as in the subserosal layer were not associated with the nerve fibers. In the layers of the intestinal wall with c-Kit-positive cells, the cellular networks of the interstitial cells were identified in ultrastructure. The characteristic profiles of c-Kit-positive cellular networks provide a morphological basis upon which to investigate the mechanisms regulating intestinal movement. Received: 14 July 1998 / Accepted: 2 September 1998     

Composition of the medial and posterior articular nerves of the mouse knee joint

The number and the distribution of fiber size in the medial (MAN) and posterior (PAN) articular nerves of the mouse knee joint were studied by electron microscopy. The MAN contained 75 +/- 28 nerve fibers consisting of 63 +/- 24 unmyelinated and 12 +/- 6 myelinated fibers. The PAN was composed of 195 +/- 50 nerve fibers, namely 129 +/- 28 unmyelinated and 66 +/- 24 myelinated fibers. A skewed unimodal distribution of the unmyelinated nerve fiber diameters was seen in both nerves ranging from 0.1 to 1.2 microm with a maximum between 0.3 and 0.6 microm. The myelinated nerve fibers in the MAN ranged from 1 to 8 microm with a peak between 2 and 5 microm. In the PAN, their diameters ranged from 1 to 12 microm with a clearly visible peak at 4-5 microm and a plateau at 8-9 microm that may represent a second maximum. These data show that the knee joint innervation of the mouse is comparable to those of the cat and rat concerning the types of nerve fibers and the composition of the two nerves. However, in relation to the much smaller area of tissue to be innervated the total number of primary afferents is considerable smaller in the mouse.     

Spatial relationship between telocytes,interstitial cells of Cajal and the enteric nervous system in the human ileum and colon

Telocytes (TCs) are recently described interstitial cells, present in almost all human organs. Among many other functions, TCs regulate gastrointestinal motility together with the interstitial cells of Cajal (ICCs). TCs and ICCs have close localization in the human myenteric plexus; however, the exact spatial relationship cannot be clearly examined by previously applied double immunofluorescence/confocal microscopy. Data on TCs and submucosal ganglia and their relationship to intestinal nerves are scarce. The aim of the study was to analyse the spatial relationship among these components in the normal human ileum and colon with double CD34/CD117 and CD34/S100 immunohistochemistry and high-resolution light microscopy. TCs were found to almost completely encompass both myenteric and submucosal ganglia in ileum and colon. An incomplete monolayer of ICCs was localized between the TCs and the longitudinal muscle cells in ileum, whereas only scattered ICCs were present on both surfaces of the colonic myenteric ganglia. TC-telopodes were observed within colonic myenteric ganglia. TCs, but no ICCs, were present within and around the interganglionic nerve fascicles, submucosal nerves and mesenterial nerves, but were only observed along small nerves intramuscularly. These anatomic differences probably reflect the various roles of TCs and ICCs in the bowel function.     

EFFECT OF EXTRINSIC DENERVATION ON ENDOGENOUS NORADRENALINE AND [3H]NORADRENALINE UPTAKE IN THE GUINEA-PIG COLON

—The concentration of noradrenaline was studied in the proximal colon of the guinea-pig, where intrinsic adrenergic neurons are present in the myenteric plexus. The noradrenaline content is higher than in the myenteric plexus of other parts of the alimentary tract. After extrinsic denervation of the colon, about 25% of the original content of noradrenaline remains in the myenteric plexus, and this is considered to be the amount due to the intrinsic adrenergic neurons; also a substantial noradrenaline uptake activity is still detectable. On the other hand, in the part of the wall formed by circular muscle-submucous plexus-submucosa-mucosa, which has control values close to those of the ileum, extrinsic denervation causes a nearly complete depletion of noradrenaline. This is considered as evidence that the intrinsic neurons do not project to the circular musculature, or the submucosa or mucosa.     

The chorda tympani and glossopharyngeal nerves in the adult hamster

The numbers and diameters of axons in the intact chorda tympani(CT) and lingual branch of the glossopharyngeal nerve (GN) arequantified with the use of electron microscopic photomontages.The cross-sectional diameters of the CT and GN average 68 and86 microns, respectively. The intact CT contains {small tilde}1050 fibers, 63% are unmyelinated and 37% are myelinated. TheGN contains {small tilde} 1600 fibers, 79% are unmyelinatedand 21% are myelinated. Both nerves are made up of relativelysmall unmyelinated and myelinated fibers, although the GN showsa broader distribution of diameters for its myelinated fibersdue to the presence of general somatosensory fibers. Followingde-efferentation, there is a 48% reduction in the number ofunmyelinated fibers in the CT. Fifty-two per cent of the unmyelinatedfibers are sensory. The number of myelinated fibers is not significantlyreduced and nearly all of the myelinated fibers are sensory.Sixty-seven per cent of the fibers within the CT are sensory.The de-efferented CT contains an equal number of unmyelinatedand myelinated axons and a total of {small tilde} 700 fibers.Comparable data in the rat indicate that its intact and de-efferentedCT are organized differently in regards to the numbers of sensoryand motor, and myelinated versus unmyelinated fibers. The findingsof the present study, together with the available data fromother species, suggest that anatomical differences in the make-upof the major gustatory nerves do not contribute in any obviousway to the known differences in the response properties betweenthe rat and hamster CT, and that the number of myelinated fibersin the visceral motor component of the CT varies considerablyacross species.     

Potentiation by cocaine of relaxations of the guinea-pig colon caused by noradrenaline and by stimulation of adrenergic nerves.

The distal colon of the guinea-pig is relaxed by noradrenaline, by isoprenaline and by the stimulation of fibres running with the colonic nerves or intramurally. The relaxations in response to stimulation of the colonic nerves have a guanethidine-sensitive (adrenergic) and a guanethidine-insensitive (non-adrenergic) component. Cocaine causes a three-fold sensitization of the muscle to noradrenaline but no sensitization to isoprenaline. Cocaine increases the duration, but does not affect the amplitude, of the relaxation observed when adrenergic nerves are stimulated, and affects neither duration nor amplitude of the non-adrenergic response. The adrenergic nerve terminals lie in Auerbach's plexus, not in the longitudinal muscle. It is concluded that the sensitization to noradrenaline and the increases in durations of responses to adrenergic nerve stimulation are due to inhibition of catecholamine uptake into adrenergic nerves by cocaine. It appears that, even where the neuromuscular separation is large as it is in the colon, the concentration of exogenous noradrenaline at the receptors can be decreased by neuronal uptake, and the uptake mechanism can modify responses to nerve stimulation in vitro.     

The origin and distribution of adrenergic nerve fibres in the guinea-pig colon

Summary A detailed study of the origin and distribution of sympathetic fibres in the distal colon of the guinea-pig has been made using the fluorescent histochemical method for localizing catecholamines. The extrinsic adrenergic fibres of the colonie sympathetic nerves follow the inferior mesenteric artery and its branches to the colon. Some of the extrinsic adrenergic fibres are associated with the parasympathetic fibres of the pelvic nerves near the colon. Complete adrenergic denervation follows the removal of the inferior mesenteric ganglion or the destruction of the nerves running with the inferior mesenteric artery.No fluorescent fibres, other than those associated with blood vessels, were observed in air-dried stretch preparations of the isolated longitudinal muscle. However, a substantial number of varicose, terminal fibres, not associated with blood vessels, were observed in the circular muscle. Some varicose fibres, apart from those associated with ganglion cells, were observed in the myenteric plexus. These fibres were seen in the bundles of nerves running between the nodes of the plexus and also as single fibres which branched from the plexus to end in areas free of ganglion cells.Three plexuses of adrenergic nerve fibres have been distinguished in the submucosa: a dense plexus of terminal fibres innervating both the veins and arteries; a plexus consisting of innervated nodes of ganglion cells, connected by bundles of fluorescent and non-fluorescent nerves; and a plexus of varicose and non-varicose fibres, which is not associated with ganglion cells. Some groups of ganglion cells in the submucosa were without adrenergic innervation.A plexus of varicose fibres forms a meshwork in the lamina propria of the mucosa. The muscularis mucosae is sparsely innervated. Most of the blood vessels in the mucosa are not associated with adrenergic fibres.     

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.     

Ultrastructure of interstitial cells of Cajal in myenteric plexus of human colon

The role of the interstitial cells of Cajal (ICC) associated with the myenteric plexus (ICC-MP) as regulators of the motility of the colonic external muscle remains unclear. Ultrastructural studies of myenteric interstitial cells are lacking in human colon. We therefore characterized the distinctive ultrastructure of these cells in the myenteric region of the colon by transmission electron microscopy of the region between the main muscle layers in all parts of the colon in unaffected areas of resected specimens from nine adult human patients. ICC-MP were similar in various colonic regions and had myoid features such as scattered caveolae, prominent intermediate filaments, and cytoplasmic dense bodies. We found characteristic dense membrane-associated bands with a patchy basal lamina, invaginating cellular protrusions (peg and socket junctions) between ICC and between ICC and muscle cells, and close contacts (<100 nm) between ICC and nerves. No gap junctions were observed. Fibroblast-like cells (FLC) were abundant showing well-developed secretory organelles, including coated vesicles, but lacked prominent intermediate filaments and caveolae. FLC had a patchy basal lamina, and peg and socket junctions were observed between them. Macrophage-like cells frequently occurred in close apposition with FLC and, more seldomly, with ICC-MP. The ultrastructure of ICC and FLC in the myenteric region of the human colon thus differs characteristically, but significant overlaps in the ultrastructure between ICC and FLC might complicate any interpretation in pathological ultrastructural studies of the human colonic muscle layer. An erratum to this article can be found at     

Composition of the medial and posterior articular nerves of the mouse knee joint

The number and the distribution of fiber size in the medial (MAN) and posterior (PAN) articular nerves of the mouse knee joint were studied by electron microscopy. The MAN contained 75 &#45 28 nerve fibers consisting of 63 &#45 24 unmyelinated and 12 &#45 6 myelinated fibers. The PAN was composed of 195 &#45 50 nerve fibers, namely 129 &#45 28 unmyelinated and 66 &#45 24 myelinated fibers. A skewed unimodal distribution of the unmyelinated nerve fiber diameters was seen in both nerves ranging from 0.1 to 1.2 &#119 m with a maximum between 0.3 and 0.6 &#119 m. The myelinated nerve fibers in the MAN ranged from 1 to 8 &#119 m with a peak between 2 and 5 &#119 m. In the PAN, their diameters ranged from 1 to 12 &#119 m with a clearly visible peak at 4-5 &#119 m and a plateau at 8-9 &#119 m that may represent a second maximum. These data show that the knee joint innervation of the mouse is comparable to those of the cat and rat concerning the types of nerve fibers and the composition of the two nerves. However, in relation to the much smaller area of tissue to be innervated the total number of primary afferents is considerable smaller in the mouse.     

Extrinsic control of the release of galanin and VIP from intrinsic nerves of isolated, perfused, porcine ileum.

By immunohistochemistry galanin-like immunoreactivity and vasoactive intestinal polypeptide (VIP)-like immunoreactivity were found in nerve cell bodies mostly in the submucous plexus and in nerve fibres in the mucosa, submucosa and muscularis including the myenteric plexus of the porcine ileum and were found to co-exist in most of these structures. Using isolated, perfused porcine ileum we studied the release of galanin and VIP in response to electrical stimulation of the mixed periarterial nerves or to intraarterial infusions of different neuroactive agents. Nerve stimulation (4-10 Hz) inhibited the basal release of galanin and VIP from the ileum (to 69 +/- 6 and 62 +/- 6% of basal release). After infusion of the alpha-adrenergic blocker, phentolamine, (10(-6) M) electrical stimulation increased the release of both galanin and VIP (to 140 +/- 12 and 133 +/- 13% of basal output). This increase was abolished by atropine (10(-6) M) and by hexamethonium (3.10(-5) M). Infusion of norepinephrine (10(-6) M) inhibited, whereas acetylcholine (10(-6) M) stimulated the release of both peptides. The effect of the latter was abolished by atropine. The inhibitory effect of nerve stimulation was not influenced by atropine. Our results suggest that the galanin- and VIP-producing intrinsic neurons receive inhibitory signals by noradrenergic nerve fibers and stimulatory signals mediated by cholinergic nerves, possibly via a cholinergic interneuron.     

Vasoactive intestinal polypeptide and nitric oxide synthase distribution in the enteric plexuses of the human colon: an histochemical study and quantitative analysis

Vasoactive intestinal polypeptide (VIP) and nitric oxide synthase (NOS) positive innervation patterns were immunohistochemically and statistically evaluated in the human colon. Specimens from the right colon (cecum, ascending and right transverse colon) and left colon (left transverse and descending colon) were obtained surgically, fixed either in paraformaldehyde or in Carnoy's or in Bouin's, and paraffin embedded. Sections were stained with hematoxylin-eosin, toluidine blue, cresyl violet, neuron-specific enolase, anti-VIP, and anti-NOS. The same results were obtained regardless of the fixative used. Enolase-positive, VIP-positive, and NOS-positive cells were occasionally found within the circular muscle and interpreted as neurons. VIP-positive nerve fibers were evenly distributed within the circular muscle while NOS-positive ones were lacking in its inner portion. The left colon was richer in neurons than the right colon, at both plexuses. VIP- and NOS-positive neuron densities were higher at the left than at the right colon, whereas at all colonic levels VIP-positive neuron percentages at both plexuses and NOS-positive ones at the myenteric plexus were simular. At the submucous plexus the NOS-positive neuron percentage was lower than that of the VIP-positive one. In conclusion: (a) the right colon contains a lower number of neurons and of VIP- and NOS-positive ones than the left colon, and (b) VIP- and NOS-positive fibers are differently distributed in the inner and outer portions of the circular muscle.     

Possible involvement of muscularis resident macrophages in impairment of interstitial cells of Cajal and myenteric nerve systems in rat models of TNBS-induced colitis

Resident macrophages are distributed in the network of interstitial cells of Cajal (ICC) and the myenteric nerve within the myenteric plexus. We evaluated changes in chemoattractant protein mRNA expression in macrophages and neutrophils, the ICC, nerve and macrophages in the myenteric plexus of model rats with TNBS-induced colitis. Chemoattractant proteins, MCP-1, GRO, MIP-2 and CINC-2α were upregulated in the colonic muscle layer after inflammation. Leukocyte infiltration and MPO activity were increased in the muscle layer. Electron microscopy indicated an irregular contour of the myenteric ganglia into which numerous macrophages had penetrated. Macrophages were also distributed near the ICC in the inflamed myenteric plexus. Immunohistochemistry showed that the ICC network and myenteric nerve system had disappeared from the inflamed region, whereas the number of resident macrophages was increased. TTX-insensitive, possibly ICC-mediated, rhythmic contractions of circular smooth muscle strips and enteric neuron-mediated TTX-sensitive peristalsis in the whole proximal colon tissue were significantly inhibited in the inflamed colon, indicating that the ICC-myenteric nerve system was dysfunctional in the inflamed muscle layer. Their accumulation around the myenteric nerve plexus and the ICC network suggests that macrophages play an important role in inducing intestinal dysmotility in gut inflammation.     

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.