Electrical stimulation of cochlear efferents at the round window reduces auditory desensitization in guinea pigs. I. Dependence on electrical stimulation parameters

Abstract

Electrical stimulation at the round window with pulsed short trains has been shown to elicit classical efferent effects on N 1 amplitudes at the cochlea. This report demonstrates that round window stimulation as a continuous burst can reduce temporary threshold shifts (TTS) caused by a simultaneous monaural loud sound exposure. This result is similar to recent reports that stimulation of the crossed olivocochlear bundle (COCB) at the floor of the fourth ventricle can reduce TTS. Like COCB stimulation at the brainstem, the effect of round window stimulation could be abolished by strychnine, with a time course paralleling the blocking action of strychnine on the traditional COCB effects of pulsed short trains on N 1 amplitudes. This report also established parameters for optimal effects of the round window stimulus and found them to be similar to the optimal parameters for the effects of brainstem stimulation on TTS. Tonic effects on TTS were also observed, with reductions in TTS being obtained as much as 7 min after a 1 min-long round window stimulus. Such tonic effects did not appear to be due to persistent effects at the cochlea but were suggested to be due to a long term resetting of some central site activated by antidromic stimulation from the round window.