Effects of Electric Stimulation of the Crossed Olivocochlear Bundle on the Ultrasonic Evoked Cochlear Nerve Action Potential

Abstract

The effects of the electric stimulation of crossed olivocochlear bundle (COCB) on the ultrasonic (98.8kHz) evoked cochlear nerve action potential (UAP) were investigated and the results were compared with its effects on the AP evoked by 12kHz tone bursts (burst AP) in 5 guinea pigs.
As COCB stimulation, the rectangular pulse trains were repeatedly applied to the animals before each tone stimulus at the floor of the fourth ventricle with an isolated bipolar electrode was delivered. The responses were obtained from the round window and analysed after averaging.
With COCB stimulation, the burst AP amplitude showed a significant decrease, and its latency was slightly elongated, especially in the responses near threshold. On the other hand, no effect of COCB stimulation was detected in the amplitude and the latency of UAP. According to the results of our previous experiments, the receptors of ultrasonic sound were thought to have rather wide distribution in the basal turn of cochlea, which should have the greatest efferent projection density and consequently should effectively be suppressed by COCB stimulation.
The result of this study will become one of the circumstantial evidences in favor of the hypothesis that the transduction of ultrasonic sound is performed by IHC of the basal turn of cochlea without any modulation or enhancement by normal OHC function.