Short-latency excitation of brain stem neurones in the rat by acetylcholine.

A fast excitatory response to acetylcholine (ACh) which has not previously been reported, has been found in the rat brain stem. Micro-iontophoretic applications of ACh to single brain stem neurones in unanaesthetized rats excited 81% and inhibited 3% of neurones studied. Two types of excitatory response were distinguished by their time course. Type I ACh excitation of neurones was of long latency resembling that previously reported in various parts of the brain. Type II excitation was of short latency, similar to that of micro-iontophoretically applied glutamate ions and to ACh excitation of Renshaw cells.