Effects of cholinergic blockers on auditory brain-stem evoked potentials in rats

The pharmacology of auditory brain-stem evoked potentials (ABEP) pathways i s poorly understood. There are anecdotal reports on the involvement of vari ous neurotransmitters but they were not investigated systematically. The ai m of this study was to investigate the effects on ABEP of muscarinic and ni cotinic blockers, administered into the cerebral ventricles. Atropine sulfa te, d-Tubocurarine and saline were injected stereotactically into the later al cerebral ventricle of anesthetized male rats. Auditory clicks were given at a rate of 20 s(-1). ABEP recording was performed before and 30 min afte r injection. Pre- and post-injection peak latencies and peak-to-peak amplit udes of positive waves were compared for each animal. Atropine reduced the amplitudes of waves P1, P3 and P4 and increased mildly the brain stem trans mission time. d-Tubocurarine reduced the amplitudes of P1 and P4 with no si gnificant effect on the peak latencies. Saline injection had no effect on a ny of the parameters. These results show that both cholinergic systems are involved in ABEP generation or transmission. Mechanism of action could be e ither direct inhibition of afferent pathways or indirect effect, via modula ting efferent pathways. (C) 1999 Elsevier Science B.V. All rights reserved.