Extract of the full text
of this article appear below.
Has the presence of distinct types of muscarine receptors in the LES been detected in man as in animals ?
J.R. Crist (Boston)
There is good evidence to suggest that intramural cholinergic neurons present in the LES cause contraction of the LES through activation of muscarine receptors on circular smooth muscle celles (figure /) [2, 5]. This is evidenced by a number of findings including: 1) muscarine agents cause contraction of the LES in man and various other species, 2) binding studies in the cat LES demonstrate muscarinic cholinergic receptors and, 3) intramural cholinergic neurons have been identified in the opossum LES using acetylcholinesterase and choline acetyltransferase histochemical techniques [4]. These cholinergic neurons exert their influence on LES tone by releasing the neurotransmitter acetylcholine which stimulate muscarinic receptors on the LES circular smooth muscle cells. There is continued controversy as to what role continuous release of acetylcholine from these intramural nerves might play in resting LES tone in man. In most studies, the muscarinic antagonist atropine causes a small decrease in resting LES tone.
Figure 1. Cholinergic motorneuron innervating circular smooth muscle of the LES. Acetylcholine is released at the neuromuscular junction resulting in activatin of muscarinic receptors and contraction of the smooth muscle.
There is also good evidence to suggest that muscarinic receptors are present on the soma or dendrites of noncholinergic inhibitory neurons in the LES (figure 2) [2, 5]. Activation of these muscarinic receptors cause release of an unknown inhibitory neurotransmitter at the neuromuscular junction resulting in relaxation of the LES [ 1 ]. Since the relaxation produced by activation of muscarinic receptors on inhibitory neurons is nerve-mediated, it is blocked by the nerve blocker tetrodotoxin in addition to the muscarinic antagonist atropine.
...
only available for members ()
|
