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

The pharmacology of auditory brain-stem evoked potentials (ABEP) pathways is poorly understood. There are anecdotal reports on the involvement of various neurotransmitters but they were not investigated systematically. The aim of this study was to investigate the effects on ABEP of muscarinic and nicotinic blockers, administered into the cerebral ventricles. Atropine sulfate, d-Tubocurarine and saline were injected stereotactically into the lateral 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 after injection. Pre- and post-injection peak latencies and peak-to-peak amplitudes of positive waves were compared for each animal. Atropine reduced the amplitudes of waves P1, P3 and P4 and increased mildly the brain stem transmission time. d-Tubocurarine reduced the amplitudes of P1 and P4 with no significant effect on the peak latencies. Saline injection had no effect on any of the parameters. These results show that both cholinergic systems are involved in ABEP generation or transmission. Mechanism of action could be either direct inhibition of afferent pathways or indirect effect, via modulating efferent pathways.