Intracellular transduction mechanisms for the slow synaptic events

Electrical activities of the postganglionic neurons in the superior cervical ganglia of rabbits are modulated in various ways following activation of the subtypes of muscarinic acetylcholine receptors. (i) M1 receptors mediate a slow depolarization consisting of at least three types of ionic conductance changes, and one of these is possibly mediated by cyclic GMP. (ii) M2 receptors mediate a slow hyperpolarization that seems to be generated by inositol triphosphate derived from phosphatidylinositol breakdown. (iii) M2 receptors also cause, through an activation of C kinase, a suppression of Ca entry during action potentials that results in a characteristic change in the action potentials and thereby modulates excitability of superior cervical ganglion neurons. Each subtype of muscarinic receptors thus regulates different pathways of intracellular transduction and modulates the electrical signaling of sympathetic neurons.