Effects of cholinergic agents on single‐unit responses in the rat inferior colliculus

Abstract

Cholinergic agents were injected iontophoretically during unit recordings from the inferior colliculi of rats anesthetized with urethane. Prior to drug administration, neurons typically showed little spontaneous activity and possessed nonmonotonic rate‐versus‐intensity functions for pure‐tone stimuli. This was especially true near CF. Maximum driven rate was usually greater for tones below CF than for tones at or above CF. Application of the cholinergic agonist carbamylcholine usually produced dose‐dependent decreases in driven rates to CF tones but did not alter response threshold. When injected alone, cholinergic antagonists usually produced dose‐dependent increases in driven activity and, at higher doses, generation of “bursty” spontaneous activity. Interactions between agonists and antagonists were common. More units were sensitive to atrophine, a muscarinic antagonist, than to curare, a nicotinic antagonist. Some neurons were sensitive only to curate, and a few neurons were sensitive to both curate and atropine. The data suggest that acetylcholine is not the afferent neurotransmitter in the rat inferior colliculus, but that it mediates a tonically active inhibition which has both muscarinic and nicotinic properties. [Work supported by NINCDS grant NS‐14880 and NSF grant BNS‐8006643.]