Opposite actions of forskolin at pre- and postsynaptic sites in rat sympathetic ganglia.

In isolated rat superior cervical ganglia, forskolin, a powerful activator of adenylate cyclase, augmented the amplitude of fast excitatory postsynaptic potentials. Quantal analysis showed that forskolin acts presynaptically to facilitate the release of the transmitter. The time course of the presynaptic action of forskolin paralleled that of the increase in cyclic AMP level in the ganglia. In addition, forskolin exerted a postsynaptic action on the nicotinic acetylcholine receptor so that the acetylcholine-induced depolarization was depressed. The action of forskolin on the nicotinic acetylcholine receptor seems to be unrelated to the cyclic AMP system.