AJP - Gastrointestinal and Liver Physiology, Vol 265, Issue 4 628-G637, Copyright © 1993 by American Physiological Society
Role of the enteric nervous system in the control of migrating spike complexes in the feline small intestine
W. C. De Vos
Department of Physiology and Biophysics, University of Illinois, Urbana 61801.
The effects of agonists and antagonists of nicotinic, muscarinic (M1 and
M2), and adrenergic receptors on migrating spike complexes (MSC) in ileum
of fasting cats are reported. Hexamethonium decreased MSC frequency and
blocked propagation. Atropine at low concentrations increased MSC frequency
and increased velocity of propagation; atropine at high concentration
blocked propagation. Pirenzepine (Pz; M1 antagonist) increased MSC
frequency and propagation velocity. McNeil A-343 (M1 agonist), by a
Pz-sensitive phentolamine-insensitive mechanism, and
4-diethylamine-methylpiperidine (4-DAMP; M2 antagonist) blocked propagation
of an ongoing MSC but had no significant effect on frequency or velocity.
Bethanechol (M2-receptor agonist) increased phasic spiking by a
4-DAMP-sensitive mechanism and blocked MSC propagation by a Pz-sensitive
mechanism. Phenylephrine (alpha 1-adrenoceptor agonist) or oxymetazoline
(alpha 2-adrenoceptor agonist) blocked MSC propagation but had no effect on
MSC frequency or velocity. Phentolamine (nonselective alpha 1-adrenoceptor
antagonist), prazosin (alpha 1-adrenoceptor antagonist), or yohimbine
(alpha 2-adrenoceptor antagonist) alone had no effect on MSC activity. The
conclusion is that the enteric nervous system controls and regulates the
MSC by the following proposed mechanisms. 1) M1-muscarinic receptors,
located either on postganglionic inhibitory neurons or presynaptically at a
nicotinic synapse and/or neuromuscular junction, are involved in the tonic
inhibitory control of MSC initiation and propagation. 2) Nicotinic and M2
muscarinic receptors, located on excitatory postganglionic motoneurons and
smooth muscle cells, respectively, are important in the initiation and/or
propagation of MSC. 3) alpha 1-Adrenoceptors on the smooth muscle cells and
alpha 2-adrenoceptors located presynaptically at the nicotinic ganglionic
synapses are not tonically active but inhibit MSC activity (4). Smooth
muscle beta-adrenoceptors do not play a significant role in neural control
of MSC activity.
