The myent ric plexus of the ileum has an independent neuronal circuitry for the integration of the input and the generation of the output, controlling the peristaltic movement; local blood flow, exocrine and electrolyte secretions, and absorption of the small intestine. The integrative circuitry is more compat.ble to that of the CNS than the peripheral nerves in its morphological and neuromodulai ry aspects. The cholinergic system is the major motor output of the myenteric plexus, and its activi y is modulated by various neurotransmitters and modulators whose presences In the plexus have b en identified. Investigations of modes of these modulations could lend some clues to the understanding of the much more complex CNS. Advantages of the myenteric plexus in the study of the euromodulat.ion are the simpler architecture and the effector system, smooth muscle, which is coupled to the plexus.
In this stud, modulations by adenosine and muscarinic agonists are presented as examples of aspects of the odulations. Both modulations are via specific subsets of the receptors. Adenosine was shown to exe t an inhibitory control over the plexus, inhibiting the release of ACh, via Al subtype of the purmeg c receptors. This receptor characterization was done on the synaptosomal preparation from the plea is, by obtaining the order of potencies in -inhibiting the ACh release among several agonists;
CHA? () PIA>NECA>ANCA> > (+) PIA,
which is com6atible to the Al subtype. In addition, it appeared that there was a continuous tonic regulation of the cholinergic activity by the endogenous adenosine. The feedback inhibition of the cholinergic ac ivity via a muscarinic receptor has been described pretty clearly. Another subset of the muscarini receptor in the plexus was characterized in this presentation, which was involved in a excitatory anode and appeared to be a separate subtype of the muscarinic receptor from that of the feedback inhibition.
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