This is a proposal to study the role of the adenylate cyclase-cAMP system in signal transduction in enteric neurons. The project is based on the following interpretations of results obtained by electrical recording of electrical and synaptic behavior of the neurons: (1) Slow synaptic excitation (slow EPSP) is a long-lasting increase in excitability that has important function in neural control of the intestine. (2) Biogenic amines, brain-gut peptides and acetylcholine mimic slow EPSPs in subpopulations of neurons. (3) Activation of adenylate cyclase by forskolin mimics slow EPSP. (4) Elevation of cAMP by intraneuronal injection, application of permeable analogs of cAMP or treatment with phosphodiesterase inhibitors also mimic slow EPSPs. (5) Second messenger function of cAMP is involved in the transduction process for slow EPSPs. (6) Application of adenosine simulates slow synaptic inhibition and blocks the action of forskolin (7) The inhibitory action of adenosine reflects purinergic suppression of enzymatic activity of adenylate cyclase. (8) Adenosine blocks the slow EPSP-like actions of histamine, CCK, VIP and bombesin, but not substance P, serotonin or calcitonin gene-related peptide. (9) All of the slow EPSP mimetics, except substance P, CGRP and serotonin, act by stimulation of adenylate cyclase and adenosine blocks these effects by preventing activation of the enzyme. This project is designed to test these electrophysiological interpretations by direct measurement of changes in cAMP levels in response to the same perturbations that were applied in the electrophysiological studies. cAMP determinations will be made in a newly-developed preparation consisting of dissociated ganglia from the myenteric plexus of guinea-pig small intestine.
