Thick nerve bundles, called shunt fascicles, running in the cranio-caudad axis, have recently been described in the myenteric plexus of the distal colon of a variety of mammals. These appear to connect the myenteric plexus of the anorectal region to that of more proximal parts of the colon. From their position, they appear to be a means to coordinate anorectal function with the operation of more proximal levels of the colon. Also, the myenteric plexis of the distal rectum has been found to display an irregularity and sparsity that distinguish that region from the rest of the colon. Both of these new findings, the rectal plexus and the shunt fascicles of the distal colon have been found in several carnivores, in marsupials and in one primate (the Cynomolgus monkey). This proposal outlines projects designed to discover if these anatomic features characterize other primates including man. Also, it is proposed to examine this region of the colon in specimens removed from patients for treatment of anorectal or dyschetic constipation. These studies will make use of silver-impregnation methods in whole-mounts and planar sections, and more conventional nerve staining methods. Also, the connections of the shunt fascicles to other elements of the myenteric plexus, and to the extrinsic innervation of the colon will be determined in the cat by the use of horseradish peroxidase tracing and nerve degeneration techniques. Also, the physiology of the shunt fascicles will be examined in vitro by (1) the study of colo-colonic and colo-sphincteric reflexes in vivo and in vitro with recording of electrical activity in the shunt fascicles, (2) the analysis of the compound action potentials evoked in shunt fascicles in an Eccles chamber, and (3) the examination of the effect of electrical stimulation of shunt fascicles upon the contractions and electromyogram of the proximal colon. In these analyses, nerve section, section of shunt fascicles, nerve stimulation and autonomic antagonist drugs will be used to explain mechanisms of effects seen. The experiments will be relevant to our understanding of the character of the nerves that define the function of the distal colonic segment and may expand our understanding of the pathogenesis of anorectal or dyschetic constipation.
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