TRIMETHYLTIN DISRUPTS N-1 SENSITIVITY, BUT HAS LIMITED EFFECTS ON THESUMMATING POTENTIAL AND COCHLEAR MICROPHONIC

Trimethyltin (TMT), a model neurotoxicant, has previously been demonst rated to disrupt auditory thresholds in laboratory subjects. In this e xperiment we characterized the potency of this ototoxicant by means of a dose response study and then evaluated the functional effects of TM T administration when tone-bursts were presented at supra-threshold le vels. Guinea pigs were anaesthetized and prepared for electrophysiolog ical measurement of the compound action potential (CAP) and cochlear m icrophonic (CM). Subsequently averaged wave forms generated by tone-bu rsts of 0-80 dB SPL were evaluated in order to calculate both a N-1 an d a summating potential (SP) input-output function. We show that TMT a t doses as low as 0.2 mg/kg produce elevations in N-1, but not in the CM isopotential curve. Using exposures to 0.5 mg/kg TMT we show a prof ound reduction in the slope of the N, input-output curve, but no shift in the SP. The results are consistent with the hypothesis that TMT di srupts function at the synapse between the inner hair cell and the Typ e 1 spiral ganglion cell.