THE LOCALIZATION OF EXTERNAL OR FUNCTIONAL ACETYLCHOLINESTERASE AT THE SYNAPSES OF AUTONOMIC GANGLIA

¹ Department of Physiology and Pharmacology, Graduate School of Medicine, University of Pennsylvania, Philadelphia 4, Pennsylvania

The location of the external, or functional, AChE of autonomic ganglia of the cat was determined by comparing histochemically the sites of AChE-inhibition by ambenonium in normal and preganglionically denervated ganglia. In the stellate and superior cervical ganglia, essentially all the functional AChE was found to be presynaptic; this was noted with synapses involving ganglion cells which give rise to either adrenergic or cholinergic postganglionic fibers. The ciliary ganglion presented a different pattern: here, functional AChE was observed both pre- and postsynaptically. Findings with the sphenopalatine ganglion were similar to those with the ciliary, but less conclusive.

From the present results, and observations cited from the literature, it is proposed that the primary physiological role of the functional AChE of autonomic ganglia, and possibly of other cholinergic neurons as well, is the prevention of postsynaptic activation by ACh liberated by the preganglionic fibers during the resting stage. Possible secondary functions might include prevention of accumulation and spread of ACh during the course of repeated preganglionic volleys, and protection of the presynaptic terminals against initiation of antidromic firing by ACh.

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