AJP - Gastrointestinal and Liver Physiology, Vol 253, Issue 3 345-G350, Copyright © 1987 by American Physiological Society
Influence of sacral nerves on the internal anal sphincter of the opossum
S. Rattan and R. Shah
The purpose of the present studies is to 1) compare the effects of
stimulation of different sacral nerves (S1-S5) on internal anal sphincter
(IAS) pressures and 2) examine the nature of synaptic transmission in the
sacral inhibitory pathway to the IAS. Pressures from the IAS of
alpha-chloralose-anesthetized opossums were recorded using a low-compliance
continuously perfused catheter assembly. Electrical stimulation of the
third and fourth sacral nerves (S3 and S4) caused frequency-dependent IAS
relaxation, whereas stimulation of other sacral nerves was without
significant effect on the IAS. Relaxation of the IAS in response to S4
stimulation was not significantly modified by atropine, pirenzepine
dihydrochloride, hexamethonium chloride, or adrenergic antagonists.
However, a combination of either atropine and hexamethonium or pirenzepine
and hexamethonium caused a significant antagonism of sacral
nerve-stimulated relaxation without modifying the inhibitory responses of
local transmural nerve stimulation and isoproterenol. From these studies we
conclude that 1) in the opossum the sacral nerves primarily exert
inhibitory influences on the IAS and 2) the sacral inhibitory pathway
involves the release of acetylcholine from preganglionic fibers, which in
turn causes the activation of both muscarinic (M1) and nicotinic receptors
on postganglionic, noncholinergic, nonadrenergic inhibitory neurons.
