Neural Control of the Internal Anal Sphincter Motility.

Abstract

Control mechanism of smooth muscle movement of the internal anal sphincter (IAS) by enteric and extrinsic neuvous systems in the dog was investigated. Responses of IAS muscle strips to electrical field stimulation (EFS) and neurotransmitter agents were recorded in vitro. The contraction response to norepinephrine or to EFS was inhibited by phentolamine. The relaxation induced by EFS was not affected by phentolamine, propranolol or atropine. The mechanical activity of smooth muscle in colon and anorectum during spontaneous defecation was recorded using strain gauge force transducers. The colon and anorectum showed the characteristic motility pattern during defecation: 1) The giant migrating contraction of the colon propagated to the rectum, 2) The relaxation of the rectum prior to the contraction, and 3) The IAS muscles continued to relax while the giant contractions of the colon were migrating to the rectum. Sacral nerves were stimulated electrically and the responses of smooth muscles in the rectum and IAS were recorded. The sacral nerve stimulation induced a relaxation followed by contraction of smooth muscle in the rectum and the relaxation in IAS. The mechanical responses of smooth muscle in the IAS were modulated by α-adrenergic excitatory and non-adrenergic, non-cholinergic inhibitory nerves. During defecation, the relaxation of IAS smooth muscle was associated with a characteristic motility pattern of the colon and anorectum. The enteric nervous systems may be organizing the motility of these muscles by way of the motor neurones under the control the extrinsic nervous systems.

Modular and functionally-different descending recto-anal motor pathways in a rat model

“…This finding is in agreement with data showing the relaxation as response of internal anal sphincter [25][26][27]. EFS elicited a contraction in the isolated anal canal.…”

“…It is now accepted that recto-anal evacuation activity is a complex biological process involving the voluntary control of excretion as well as the autonomic innervation of the rectum and internal and external anal sphincters. The autonomic reflex pathways underlying the motility are known to be located in the gut wall and isolated preparations of the mammalian large intestine display motor activity [1][2][3][4].…”

Molecular, functional, and pharmacological targets for the development of gut promotility drugs

“…The GMCs fit the criteria of the classic peristaltic reflex (5,22,23). The descending inhibition triggered by GMCs in respective organs also relaxes the lower esophageal sphincter (LES), ileocecal junction, and internal anal sphincter to let the luminal contents pass through without resistance (4,40). The spontaneously occurring RPCs in the sigmoid colon/ rectum and ileum do not produce descending inhibition to relax the internal anal and ileocecal sphincters, respectively.…”

Causes and Prevention of Functional Disturbances Following Low Anterior Resection for Rectal Cancer

“…Blocking the sympathicus with high spinal anesthesia led to a significant reduction in resting anal pressure compared with a parasympathetic blockade using low spinal anesthesia (31). The activity of the internal sphincter is controlled predominantly by the alpha adrenergic mechanism, as has been shown in in vitro studies using preparations from different species and from humans (34,104), as well as in in vivo studies (4). The pelvic floor and the external and internal sphincters (164)) are controlled by special motor neurons, the Onuf nucleus, which lies between the spinal cord segments S2 and S3, medial to the ganglion cells in the anterior horn.…”