NeuroanatomyMuscarinic M2 acetylcholine receptor distribution in the guinea-pig gastrointestinal tract
Section snippets
Experimental procedures
Adult male Hartley guinea-pigs aged 4–6 weeks and weighing 250–400 g (Japan SLC, Hamamatsu, Shizuoka, Japan) were used in this study. All animal experiments were carried out in accordance with the National Institutes of Health Guide for the Care and Use of Laboratory Animals and the Guidelines for Animal Experiments, University of Fukui Faculty of Medical Sciences. All efforts were made to minimize the number of animals used and their suffering. All guinea-pigs were anesthetized with an i.p.
Results
M2 receptor-like immunoreactivity (M2R-LI) was observed associated with smooth muscle cells in the gastrointestinal tract (Fig. 1, Table 1). The external muscle layers, except the esophagus, were immunoreactive for M2 receptor. The intensity of immunoreactivity was higher in the stomach, small intestine, cecum, distal colon and rectum than in the proximal colon. Distinct immunoreaction was also observed in the muscularis mucosae in the pylorus, colon and rectum.
Discussion
In this study, we obtained evidence that muscarinic M2 acetylcholine receptor-like immunoreactivity (M2R-LI) is distributed in the smooth muscle cells and interstitial cells of Cajal in the musculature of the guinea-pig gastrointestinal tract. These findings are the first evidence of M2 receptor distribution on a morphological level.
Presence of M2 receptor in the smooth muscle tissue is known by immunoprecipitation studies, ligand binding studies and PCR studies (Dorje et al 1991, Eglen et al
Conclusion
In summary, we examined the immunohistochemical distribution of the muscarinic M2 acetylcholine receptor, which is the major muscarinic receptor subtype expressed by smooth muscle tissues in the guinea-pig gastrointestinal tract. M2R-LI was mainly observed as associated with smooth muscle cells in the gastrointestinal tract. M2R-LI in smooth muscle cells was distributed throughout the cell membrane associated with caveolae. Interstitial cells of Cajal in the small intestine DMP and in the
Acknowledgment
We thank Prof. N. W. Bunnett (University of California, San Francisco) for the gift of the anti-neurokinin 1 receptor (#94168). This work was supported by Grant-in-Aid for Scientific Research from Japan Society for Promotion of Science.
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