Postsynaptic modulation of excitatory process in sympathetic ganglia by cyclic AMP.

THE principal neurones of the vertebrate sympathetic ganglia usually respond to suitable preganglionic stimuli with three types of temporally distinguishable postsynaptic potential (PSPs) in the following sequence: an initial excitatory one (fast EPSP), a slow inhibitory one (slow IPSP) and a slow excitatory one (slow EPSP)1,2. These three responses can also be distinguished pharmacologically: the fast EPSP is mediated by a nicotinic acetylcholine receptor, and the slow EPSP by a muscarinic acetylcholine receptor. The synaptic pathway of the slow IPSP includes intervening adrenergic cells (called “SIF” cells3) which release a catecholamine transmitter (identified as dopamine in the case of rabbbit4,5), in response to the muscarinic action of acetylcholine, and in turn hyperpolarise the ganglion cells.