The Effect of Physostigmine on the Latency of the Cochlear Potentials

Abstract

One of the main pieces of evidence favouring the participation of acetylcholine in the generation of nerve impulses in the cochlea is the reported prolongation of the latency of the cochlear potentials following injections of physostigmine. Direct measurements of the latencies of the cochlear microphonic (CM) and the nerve action potential (AP) in guinea-pigs, using a new on-line technique, are described in this paper. Our investigation confirmed that the latency of the CM remains stable while that of the AP varies inversely with temperature. Intra-venous injections of physostigmine did not change the latency of either CM or AP as anticipated. Some very small irregular changes were noted accompanying violent systemic reactions to the drug. It is concluded that systemic injections of physostigmine do not prolong the latency of either CM or AP and we surmise that previous reports of this effect were due to undetected temperature changes.