METABOLIC-ACTIVITY OF THE CENTRAL AUDITORY STRUCTURES FOLLOWING PROLONGED DEAFFERENTATION

The goal of this work was to evaluate, using autoradiographic techniqu es, the effects of variable periods of deafness on resting and evoked metabolic activity in central auditory structures elicited by direct e lectrical cochlear nucleus (CN) stimulation, Thirty-five pigmented gui nea pigs, divided into five groups, underwent acute implantation of bi polar electrodes in the CN. One group was not deafened and served as h earing controls. The other four groups were deafened using an establis hed protocol of sequential kanamycin/ethacrynic acid treatment and wer e tested at 4 weeks, 9 weeks, 16 weeks, and 15 months after deafening. Threshold currents for eliciting evoked middle latency responses (EML Rs) with direct CN stimulation were not significantly different betwee n hearing and deafened groups. Autoradiographic data showed progressiv e reduction of the evoked metabolic response with incremental periods of deafferentation. Nevertheless, central auditory structures remained responsive to direct electrical stimulation of the CN. These data ind icate that direct CN stimulation remains capable of activating the aud itory tract despite prolonged periods of deafness.