Interstitial cells of Cajal are innervated by nitrergic nerves and express nitric oxide-sensitive guanylate cyclase in the guinea-pig gastrointestinal tract

Nitric oxide (NO) is a major signaling molecule in the gastrointestinal tract, and released NO inhibits muscular contraction. The actions of NO are mediated by stimulation of soluble guanylate cyclase (sGC, NO-sensitive GC) and a subsequent increase in cGMP concentration. To elucidate NO targets in the gastrointestinal musculature, we investigated the immunohistochemical localization of the beta1 and alpha1 subunits of sGC and the distribution of neuronal NO synthase (nNOS) -containing nerves in the guinea-pig gastrointestinal tract. Distinct immunoreactivity for sGCbeta1 and sGCalpha1 was observed in the interstitial cells of Cajal (ICC), fibroblast-like cells (FLC) and enteric neurons in the musculature. Double immunohistochemistry using anti-c-Kit antibody and anti-sGCbeta1 antibody revealed sGCbeta1 immunoreactivity in almost all intramuscular ICC throughout the entire gastrointestinal tract. Immunoelectron microscopy revealed that sGCbeta1-immunopositive cells possessed some of the criteria for intramuscular ICC: presence of caveolae; frequently associated with nerve bundles; and close contact with smooth muscle cells. sGCbeta1-immunopositive ICC were closely apposed to nNOS-containing nerve fibers in the muscle layers. Immunohistochemical and immunoelectron microscopical observations revealed that FLC in the musculature also showed sGCbeta1 immunoreactivity. FLC were often associated with nNOS-immunopositive nerve fibers. In the myenteric layer, almost all myenteric ganglia contained nNOS-immunopositive nerve cells and were surrounded by myenteric ICC and FLC. Myenteric ICC in the large intestine and FLC in the entire gastrointestinal tract showed sGCbeta1 immunoreactivity in the myenteric layer. Smooth muscle cells in the stomach and colon showed weak sGCbeta1 immunoreactivity, and those in the muscularis mucosae and vasculature also showed evident immunoreactivity. These data suggest that ICC are primary targets for NO released from nNOS-containing enteric neurons, and that some NO signals are received by FLC and smooth muscle cells in the gastrointestinal tract.     

Interstitial cells of Cajal: primary targets of enteric motor innervation

For many years morphologists have noted the close relationship between interstitial cells of Cajal (ICC) and nerve fibers within the tunica muscularis of gastrointestinal (GI) organs. These observations led to speculations about a role for ICC in mediating neural inputs to the GI tract. Immunohistochemical and functional studies demonstrated the presence of receptors for the neurotransmitters utilized by enteric motor neurons, and changes in second messengers in ICC after field stimulation of intrinsic enteric neurons showed that ICC were functionally innervated in GI muscles. Recent double labeling experiments have shown that both excitatory and inhibitory enteric motor neurons are closely associated with ICC in the deep muscular plexus (IC-DMP) of the small intestine and intramuscular ICC (IC-IM) of the proximal and distal GI tract. Enteric motor neurons form synaptic-like structures with IC-IM and IC-DMP. Far fewer close contacts are found between enteric motor neurons and smooth muscle cells. Experiments on W/W(V) mutants that lack IC-IM in the stomach, lower esophageal sphincter, and pylorus have shown that these ICC are critical components of the neuromuscular junction. Cholinergic excitatory and nitrergic inhibitory neurotransmission are severely decreased in tissues lacking IC-IM, yet there is no loss of cholinergic or nitrergic neurons in W/W(V) mutants. These data suggest that either the post-junctional mechanisms responsible for receiving and transducing neurotransmitter signals are specifically expressed by ICC, or that the large extracellular spaces typically between nerve terminals and smooth muscle cells may not allow effective concentrations of neurotransmitters to reach receptors expressed by smooth muscle cells. These findings indicate an important role for certain classes of ICC in enteric neurotransmission and predict that loss of ICC in human motor disturbances may significantly compromise neural regulation of GI motility.     

Involvement of intramuscular interstitial cells of Cajal in neuroeffector transmission in the gastrointestinal tract

Specialized cells known as interstitial cells of Cajal (ICC) are distributed in specific locations within the tunica muscularis of the gastrointestinal (GI) tract. ICC serve as electrical pacemakers, provide pathways for the active propagation of slow waves, are mediators of enteric motor neurotransmission and play a role in afferent neural signalling. Morphological studies have provided evidence that motor neurotransmission in the GI tract does not occur through poorly defined structures between nerves and smooth muscle, but rather via specialized synapses that exist between enteric nerve terminals and intramuscular ICC or ICC-IM. ICC-IM are coupled to smooth muscle cells via gap junctions and post-junctional responses elicited in ICC-IM are conducted to neighbouring smooth muscle cells. Electrophysiological studies from the stomachs and sphincters of wild-type and mutant animals that lack ICC-IM have provided functional evidence for the importance of ICC in cholinergic excitatory and nitrergic inhibitory motor neurotransmission. Intraperitoneal injection of animals with Kit neutralizing antibody or organ culture of gastrointestinal tissues in the presence of neutralizing antibody, which blocks the development and maintenance of ICC, has provided further evidence for the role of ICC in enteric motor transmission. ICC-IM also generate an ongoing discharge of unitary potentials in the gastric fundus and antrum that contributes to the overall excitability of the stomach.     

Interstitial cells: involvement in rhythmicity and neural control of gut smooth muscle

Many smooth muscles display spontaneous electrical and mechanical activity, which persists in the absence of any stimulation. In the past this has been attributed largely to the properties of the smooth muscle cells. Now it appears that in several organs, particularly in the gastrointestinal tract, activity in smooth muscles arises from a separate group of cells, known as interstitial cells of Cajal (ICC), which are distributed amongst the smooth muscle cells. Thus in the gastrointestinal tract, a network of interstitial cells, usually located near the myenteric plexus, generates pacemaker potentials that are conducted passively into the adjacent muscle layers where they produce rhythmical membrane potential changes. The mechanical activity of most smooth muscle cells, can be altered by autonomic, or enteric, nerves innervating them. Previously it was thought that neuroeffector transmission occurred simply because neurally released transmitters acted on smooth muscle cells. However, in several, but not all, regions of the gastrointestinal tract, it appears that nerve terminals, rather than communicating directly with smooth muscle cells, preferentially form synapses with ICC and these relay information to neighbouring smooth muscle cells. Thus a set of ICC, which are distributed amongst the smooth muscle cells of the gut, are the targets of transmitters released by intrinsic enteric excitatory and inhibitory nerve terminals: in some regions of the gastrointestinal tract, the same set of ICC also augment the waves of depolarisation generated by pacemaker ICC. Similarly in the urethra, ICC, distributed amongst the smooth muscle cells, generate rhythmic activity and also appear to be the targets of autonomic nerve terminals.     

Interstitial cells of cajal are involved in neurotransmission in the gastrointestinal tract

Interstitial cells of Cajal (ICC) are important cells which coordinate gastrointestinal motility. ICC express Kit receptor tyrosine kinase, and Kit immunohistochemistry reveals ICC morphology and distribution in the gastrointestinal musculature. ICC show a highly branched morphology and form unique networks. Myenteric ICC (ICC-MY) are located at the layer of the myenteric plexus and serve as electrical pacemakers. Intramuscular ICC (ICC-IM) and ICC in the deep muscular plexus (ICC-DMP) are distributed within the muscular layers, and are densely innervated by excitatory and inhibitory enteric motor neurons and in close contact with nerve terminals. Recent studies combined with morphological and functional techniques directly revealed that ICC-IM and ICC-DMP are mediators of enteric motor neuro-transmission. These types of ICC express several receptors for neurotransmitters such as acetylcholine and substance P and show responses to excitatory nerve stimulations. ICC also express receptive mechanisms for nitric oxide, which is an inhibitory neurotransmitter in the gastrointestinal tract. They can respond to nitrergic nerve stimulation by cyclic GMP production. Kit mutant mice lack ICC-IM and show attenuated postsynaptic responses after intrinsic nerve stimulation. These findings indicate the importance for ICC in neurotransmission in the gastrointestinal tract.     

长爪沙鼠胃肠道Cajal间质细胞的形态学

目的 探讨长爪沙鼠胃肠道Cajal间质细胞（ICCs）的形态和分布规律。 方法 采用10只成年长爪沙鼠,体重50~70g,取胃、小肠、结肠制作冷冻切片,结合全层铺片的c-Kit免疫荧光染色。结果 ICCs呈网络状分布于整个胃肠道,不同部位ICCs的分布及形态有所不同。在胃底部,仅见肌内ICCs(ICC-IM）,而在胃体和胃窦部除ICC-IM外,可见肌间ICCs(ICC-MY)分布在肌间神经丛周围;其细胞密度胃底ICC-IM最多,由胃底至胃窦逐渐减少,而ICC-MY由胃体至胃窦逐渐增多。在小肠可见ICC-IM, ICC-MY和深肌层ICCs(ICC-DMP)3个亚群,结肠管壁内也分布有ICC-IM、ICC-MY和黏膜下ICCs(ICC-SM)3个亚群。结论 沙鼠可用于有关ICCs正常形态、结构及功能的研究。     

Muscarinic M(2) acetylcholine receptor distribution in the guinea-pig gastrointestinal tract

In the enteric nervous system, acetylcholine is the most common neurotransmitter to induce gastrointestinal smooth muscle contractions. Cholinergic signaling is mediated by muscarinic acetylcholine receptors on the surface of smooth muscle cells. Five different muscarinic receptor subtypes (M(1)-M(5)) have been identified and characterized, all of which belong to the superfamily of the G-protein-coupled receptor. The muscarinic M(2) acetylcholine receptor is the major muscarinic receptor subtype expressed by smooth muscle tissues in the gastrointestinal tract, where it is coexpressed with a smaller population of M(3) receptor. In this study, we examined the immunohistochemical distribution of the M(2) receptor using a specific antibody in the guinea-pig gastrointestinal tract. M(2) receptor-like immunoreactivity was mainly observed as associated with smooth muscle cells in the gastrointestinal tract. M(2) receptor-like immunoreactivity in smooth muscle cells was distributed throughout the cell membrane associated with caveolae. In the proximal colon, M(2) receptor-like immunoreactivity in the smooth muscle cells was weak. In the small intestine, interstitial cells of Cajal that possessed neurokinin 1 receptor-like immunoreactivity had intense M(2) receptor-like immunoreactivity. In the proximal colon, intramuscular and myenteric interstitial cells of Cajal exhibited M(2) receptor-like immunoreactivity. These findings indicate that, in the gastrointestinal musculature, M(2) receptors are distributed both in the smooth muscle cells and interstitial cells of Cajal, suggesting that the M(2) receptor elicits smooth muscle cell contraction and the interstitial cells of Cajal are the sites of innervation by enteric cholinergic neurons.     

In vitro functional gut-like organ formation from mouse embryonic stem cells.

BACKGROUND AND AIMS: Embryonic stem (ES) cells have a pluripotent ability to differentiate into a variety of cell lineages in vitro. We have recently found that ES cells can give rise to a functional gut-like unit, which forms a three-dimensional dome-like structure with lumen and exhibits mechanical activity, such as spontaneous contraction and peristalsis. The aim of the present study was to investigate the electrophysiological and morphological properties of ES cell-derived contracting clusters. METHODS: Electrical activity was examined by an extracellular recording. Morphology and cellular components were investigated by immunohistochemistry and electron microscopy. RESULTS: Clusters with rhythmic contractions displayed electrical slow waves at a regular rhythm, and clusters with highly coordinated peristalsis showed regular slow waves and spontaneous spike action potentials. Immunoreactivity for c-Kit, a marker of interstitial cells of Cajal (ICC), was observed in dense network structures. Neuronal marker PGP9.5 immunoreactivity was observed only in clusters with peristalsis. The topographical structure of the wall was organized by an inner epithelial layer and outer smooth muscle layer. The smooth muscle layer was provided with an ICC network and innervated with enteric neurons. CONCLUSIONS: ES cells can differentiate into a functional gut-like organ in vitro that exhibits physiological and morphological properties characteristic of the gastrointestinal (GI) tract. This ES cell-derived gut provides a powerful tool for studying GI motility and gut development in vitro, and has potential for elucidating and treating a variety of motility disorders.     

Structure and organization of interstitial cells of Cajal in the gastrointestinal tract

The morphological features of interstitial cells of Cajal (ICC) in the gastrointestinal (GI) tract are described based on observations of laboratory animals including mice, rats and guinea-pigs, using immunohistochemical staining for Kit and electron microscopy. ICC show a specific distribution, arrangement and cell shape depending on their location within various regions and tissue layers of the GI tract. Hence they are classified into several subtypes. The stomach shows distinct regional variations in the distribution of subtypes of ICC from the cardia to pylorus, whereas the small intestine and colon both seem to retain nearly the same distribution pattern of subtypes of ICC throughout each organ. All subtypes of ICC share common ultrastructural features, such as the presence of numerous mitochondria, abundant intermediate filaments, and formation of gap junctions with the same type of cells and with smooth muscle cells. In addition, depending on their species and anatomical location, some subtypes of ICC show some features typical of smooth muscle cells including a basal lamina, caveolae, subsurface cisterns and dense bodies. ICC are somewhat heterogeneous morphologically. A question is raised on a special relationship between their ultrastructural features and dependency on Kit/stem cell factor system. As the neuromediator function of ICC, reciprocal distribution of ICC and gap junctions in the muscle coat is demonstrated by the comparison of Kit immunoreactive cells and gap junction protein connexin 43 in both small intestine and colon.     

Kit mutants and gastrointestinal physiology

There has been considerable speculation about the function of interstitial cells of Cajal (ICC) since their discovery more than 100 years ago. It has been difficult to study these cells under native conditions, but great insights about the function of ICC have come from studies of genetic models with loss-of function mutations in the Kit signalling pathway. First it was discovered that signalling via Kit (a receptor tyrosine kinase) was vital for the development and maintenance of the ICC phenotype in gastrointestinal (GI) muscles. In compound heterozygotes ( W/W^V and Sl/Sl^d animals), where there are partial loss-of-function mutations in Kit receptors or Kit ligand (stem cell factor), ICC failed to develop in various regions of the GI tract, but no major changes in the smooth muscle layers or enteric nervous system occurred in the absence of these cells. Animals with these mutations provided an unprecedented opportunity to understand the role of ICC in GI motor function, and it is now clear from these studies that ICC serve as: (i) pacemaker cells, generating the spontaneous electrical rhythms of the gut known as slow waves; (ii) a propagation pathway for slow waves so that large areas of the musculature can be entrained to a dominant pacemaker frequency; (iii) mediators of excitatory cholinergic and inhibitory nitrergic neural inputs from the enteric nervous system, and (iv) stretch receptors that modulate membrane potential and electrical slow wave frequency. This review describes the use of genetic models to understand the important physiological role of ICC in the GI tract.     

Interstitial cells of Cajal – their role in pacing and signal transmission in the digestive system

Interstitial cells of Cajal (ICC) are located in most parts of the digestive system. Although they were discovered over 100 years ago, their function began to be unravelled only recently. Morphological observations have led to a number of hypotheses on the possible physiological roles of ICC: (1) these cells may be the source of slow electrical waves recorded in gastrointestinal (GI) muscles; (2) they participate in the conduction of electrical currents, and (3) mediate neural signals between enteric nerves and muscles. These hypotheses were supported by experiments in which the ICC‐containing layer was removed surgically, or when ICC were ablated chemically, and as a consequence the slow waves were absent. Electrophysiological experiments on isolated cells confirmed that ICC can generate rhythmic electrical activity and can also respond to messenger molecules known to be released from enteric nerves. In mice mutants deficient in ICC, or in mice treated with antibody against the protein c‐Kit, slow wave activity was impaired. These results support the role of ICC as pacemaker cells. Physiological studies have shown that ICC in certain GI regions are important for signal transmission between nerves and smooth muscle. There is evidence that pathological changes in ICC may be associated with GI motility disorders. The full interpretation of the role of ICC in disease conditions will require much further study on the physiology and pharmacology of these cells.     

消化道蠕动的起搏器与Cajal间质细胞

消化道蠕动是消化道平滑肌群的节律性收缩活动。越来越多的研究证据表明,这种活动是由一类叫做(pacem aker)起搏器的特殊细胞引起的。这些细胞可能就是分布在消化道平滑肌层间的(interstitialcells of Cajal)ICC。它们因分布的部位不同而形态各异。但它们都含有丰富的线粒体,呈c-K it免疫染色阳性,并伸出很多突起形成网络。他们相互之间及与周围的平滑肌细胞之间以缝隙结合相连接。这篇综述主要介绍此类细胞的形态结构及分布特点。     

Kit signaling is essential for development and maintenance of interstitial cells of Cajal and electrical rhythmicity in the embryonic gastrointestinal tract.

Interstitial cells of Cajal (ICC) are specialized cells in smooth muscle organs that generate and propagate pacemaker activity, receive inputs from motor neurons, and serve as mechanosensors. In the gastrointestinal tract, development and maintenance of the ICC phenotype have been linked to intracellular signaling via Kit, but its role in development of ICC during embryogenesis is controversial. Here we have studied the development of functional ICC-MY during the late gestational period in mice. Blocking Kit with a neutralizing antibody before and after development of spontaneous electrical activity (E17 to P0) caused loss of ICC-MY networks and pacemaker activity. ICC-MY and pacemaker activity developed normally in W/+ and W(V)/+ heterozygotes, but failed to develop between E17 to P0 in W/W(V) embryos with compromised Kit function. Muscles treated with Kit neutralizing antibody or the tyrosine kinase inhibitor, imatinib mesylate (STI571), from E17-P0 for 3 days caused loss of functionally developed ICC-MY networks, but ICC-MY and pacemaker activity recovered within 9 days after discontinuing treatment with neutralizing antibody or imatinib mesylate. These data suggest that Kit signaling is an important factor in lineage decision and in the development of functional ICC in late gestation. ICC-MY demonstrate significant plasticity in gastrointestinal tissues. Manipulation of the ICC phenotype might provide useful therapies in gastrointestinal disease where the Kit-positive cell population is either lost or amplified.     

Cellular mechanisms of myogenic activity in gastric smooth muscle

In many regions of the intestine, a thin layer of interstitial cells of Cajal (ICC) lie in the myenteric region, between the circular and longitudinal muscle layers. ICC are connected by gap junctions to surrounding ICC and also with circular and longitudinal smooth muscle cells, forming a large electrical syncytium. Damage of the ICC causes a disorder in the patterns of rhythmic activity. Isolated ICC produce a rhythmic oscillation of the membrane potential. All these observations have led to the suggestion that ICC may be the pacemaker cell responsible for intestinal activity. Gastric smooth muscles generate slow oscillatory membrane potential changes (slow waves) and spike potentials. The activity is considered to be linked to the metabolism in the cell. Three types of cells located in the gastric wall (circular and longitudinal smooth muscle cells and ICC) produce synchronized electrical responses with different shapes. The electrical responses appear to originate in ICC and then spread to the smooth muscle layers, indicating that ICC may also be the pacemaker cells responsible for gastric activity. However, isolated circular smooth muscle tissues spontaneously generate regenerative potentials, suggesting that there are at least two sites for the initiation of spontaneous activity in the stomach. Regenerative potentials persist in the presence of Ca-antagonists and are inhibited by agents which disrupt intracellular Ca(2+) homeostasis. Depolarization of the membrane elicits regenerative potentials after a long delay and the potentials have long refractory periods. This suggests that an unidentified 2nd messenger may be formed during the delay between membrane depolarization and the initiation of a regenerative potential. In gastric muscles of mutant mice which do not express inositol trisphosphate (InsP(3)) receptors, spike potentials but not slow waves are generated, suggesting the possible involvement of InsP(3) in the initiation of spontaneous activity.     

Differential expression of ionic conductances in interstitial cells of Cajal in the murine gastric antrum

Two distinct populations of interstitial cells of Cajal (ICC) exist within the tunica muscularis of the gastric antrum, and these cells serve different physiological functions. One population of ICC generates and actively propagates electrical slow waves, and the other population of ICC is innervated by excitatory and inhibitory motor neurons and mediates enteric motor neurotransmission. In spite of the key role of ICC in gastric excitability, little is known about the ionic conductances that underlie the functional diversity of these cells. In the present study we isolated ICC from the murine gastric antrum and investigated the Ca²⁺-dependent ionic conductances expressed by these cells using the patch clamp technique. Conductances in ICC were compared with those expressed in smooth muscle cells. The cells studied were identified by RT-PCR using cell-specific primers that included Myh11 (smooth muscle cells), Kit (ICC) and Uchl1 (enteric neurons) following electrophysiolgical recordings. Distinct ionic conductances were observed in Kit-positive cells. One group of ICC expressed a basal non-selective cation conductance (NSCC) that was inhibited by an increase in [Ca²⁺]_i in a calmodulin (CaM)-dependent manner. A second population of ICC generated spontaneous transient inward currents (STICs) and expressed a basal noisy NSCC that was facilitated by an increase in [Ca²⁺]_i in a CaM-dependent manner. The [Ca²⁺]_i-facilitated NSCC in ICC was blocked by the Cl⁻ channel antagonists 4,4'-diisothiocyanatostilbene-2,2'-disulphonic acid (DIDS), anthracene-9-carboxylate (9-AC) and niflumic acid. These data suggest that distinct NSCC are expressed in subpopulations of ICC and these conductances may underlie the functional differences of these cells within the gastric antrum.     

Distribution and ultrastructure of interstitial cells of Cajal in the gastric antrum of wild-type and Ws/Ws rats

Interstitial cells of Cajal (ICC) in the stomach of wild-type and Ws/Ws mutant rats that are deficient in c-kit were studied by immunohistochemistry and electron microscopy to elucidate their regional specialization in the gastric antrum. Immunohistochemistry for Kit protein demonstrated that in wild-type rats ICC were located at the submucosal border of the circular muscle layer (ICC-SM) in a limited extension of the antrum from the pyloric sphincter towards the corpus, as well as within both the circular (ICC-CM) and longitudinal (ICC-LM) muscle layers and in the myenteric plexus region (ICC-AP). In c-kit mutant Ws/Ws rats while ICC-CM and ICC-LM were not observed, but unexpectedly, a few ICC-SM and ICC-AP were found. By electron microscopy, ICC-SM and ICC-AP were characterized by abundant mitochondria, many caveolae, a distinct basal lamina and formed gap junctions with other ICC or with smooth muscle cells and make close contacts with nerves. Thus, ICC-SM and ICC-AP of the rat antrum were classified as Type 3 ICC, the type most similar to smooth muscle cells. The functional significance of ICC-SM and their survival in the c-kit mutant animals is discussed in reference to the role of the c-kit/stem cell factor system for their cellular maturation.     

Distribution of interstitial cells of Cajal and gap junction protein,Cx 43 in the stomach of wild-type and W/Wv mutant mice

The distribution of different subtypes of interstitial cells of Cajal (ICC) in the tunica muscularis of the stomach of wild-type and W/W (v) mice was studied by immunohistochemical staining for Kit. Special attention was also given to the distribution of the gap junction protein connexin 43 (Cx 43) immunoreactivity. Kit-immunoreactive cells of the circular and longitudinal muscle layers (ICC-CM and ICC-LM) were densely distributed throughout the cardia, fundus, the squamous epithelial portion of the corpus and the pylorus, but they were decreased in number within the glandular epithelial portion of the corpus. Kit-immunoreactive cells of the myenteric region (ICC-AP) emerged slightly proximal to the squamous-glandular epithelial transition and increased in number towards the pylorus. Kit-positive cells were also observed at the submucosal border of the circular muscle layer (ICC-SM). ICC-CM and ICC-LM were not observed in the stomachs of W/W (v) mice, but a few ICC-AP were observed in the pylorus. Cx 43 immunoreactive deposits were only sparsely distributed in the circular muscle layers of the cardia, fundus and the squamous epithelial portion of corpus. However, the Cx 43 immunoreactive deposits were densely distributed in the glandular epithelial portion of the corpus that contained fewer ICC-CM. Cx 43 immunoreactive deposits were rare in the circular muscle layer of the pylorus. No Cx 43 immunoreactivity was detected in the longitudinal muscle layer throughout the whole stomach. The distribution of Cx 43 immunoreactivity in the W/W (v) mouse stomach was almost the same as in wild-type mice. The functional significance of each type of ICC at each region is discussed in reference to regional differences in the distribution of both ICC and Cx 43, and differences between wild-type and W/W (v) mice.     

Nitric oxide synthase immunoactivity and NADPH diaphorase enzyme activity in neurons of the gastrointestinal tract of the toad, Bufo marinus.

The presence of nitric oxide synthase (NOS) was demonstrated immunohistochemically, and NADPH diaphorase was demonstrated by enzyme histochemistry in neurons throughout the gastrointestinal tract of the anuran amphibian, Bufo marinus. Successive staining showed that NOS immunoreactivity and NADPH diaphorase activity occurred in precisely the same subgroup of enteric neurons. Subsequent detailed studies of the distribution of these neurons were made using NADPH diaphorase histochemistry. Numerous reactive nerve cell bodies and fibres were found in the myenteric plexus from the esophagus to the cloaca. A dense innervation of the longitudinal and circular muscle layers occurred throughout the gastrointestinal tract. The lamina muscularis mucosae was only prominent in the stomach, where it was sparsely innervated. Reactive nerve cell bodies were common in the submucosa of the large intestine, less common in the small intestine and extremely rare in the stomach and esophagus. Reactive fibres contributed to subepithelial plexuses in the esophagus, colon, rectum and cloaca. It is concluded that NOS/NADPH diaphorase is conserved amongst vertebrate classes and that NO is a likely neurotransmitter in the toad gastrointestinal tract.     

Interstitial cells of Cajal in the deep muscular plexus mediate enteric motor neurotransmission in the mouse small intestine

Interstitial cells of Cajal (ICC) provide important regulatory functions in the motor activity of the gastrointestinal tract. In the small intestine, ICC in the myenteric region (ICC-MY), between the circular and longitudinal muscle layers, generate and propagate electrical slow waves. Another population of ICC lies in the plane of the deep muscular plexus (ICC-DMP), and these cells are closely associated with varicose nerve terminals of enteric motor neurons. Here we tested the hypothesis that ICC-DMP mediate excitatory and inhibitory neural inputs in the small bowel. ICC-DMP develop largely after birth. ICC-DMP, with receptor tyrosine kinase Kit-like immunoreactivity, appear first in the jejunum and then in the ileum. We performed electrophysiological experiments on mice immediately after birth (P0) or at 10 days post partum (P10) to determine whether neural responses follow development of ICC-DMP. At P0, slow-wave activity was present in the jejunum, but neural responses were poorly developed. By P10, after ICC-DMP developed, both cholinergic excitatory and nitrergic inhibitory neural responses were intact. Muscles of P0 mice were also put into organotypic cultures and treated with a neutralizing Kit antibody. Neural responses developed in culture within 3–6 days in control muscles, but blocking Kit caused loss of ICC and loss of cholinergic and nitrergic neural responses. Non-cholinergic excitatory responses remained after loss of ICC-DMP. Our observations are consistent with the idea that cholinergic and nitrergic motor neural inputs are mediated, to a large extent, via ICC-DMP. Thus, ICC-DMP appear to serve a function in the small intestine that is similar to the role of the intramuscular ICC in the stomach.     

Gastrointestinal pacemaker cell tumor (GIPACT): gastrointestinal stromal tumors show phenotypic characteristics of the interstitial cells of Cajal.

The interstitial cells of Cajal (ICC) form a complex cell network within the gastrointestinal tract wall where they function as a pacemaker system. Expression of the kit proto-oncogene is essential for the development of this system. The aim of our study was to examine the hypothesis that gastrointestinal stromal tumors differentiate toward cells with an ICC phenotype. Ultrastructurally, 58 stromal tumors were characterized and found to share many features with ICC. Seventy-eight stromal tumors were immunophenotyped, particularly with regard to the kit receptor. All 78 tumors revealed strong, homogeneous immunoreactivity for the kit receptor as did ICC of adjacent and control gastrointestinal walls. Focal hyperplasia and hypertrophy of kit receptor positive cells were also observed in the gastrointestinal wall adjacent to the tumors. CD34 immunoreactivity observed in interstitial cells surrounding Auerbach's ganglia suggests that a subpopulation of ICC is CD34 positive and may explain why 56 of 78 stromal tumors were CD34 positive. Thirty control tumors, including gastrointestinal leiomyomas and leiomyosarcomas, were all negative for the kit receptor. We conclude that gastrointestinal stromal tumors show striking morphological and immunophenotypic similarities with ICC and that they may originate from stem cells that differentiate toward a pacemaker cell phenotype. We propose that the noncommittal name "gastrointestinal stromal tumor" be replaced by gastrointestinal pacemaker cell tumor.