HAIR CELL REGENERATION AND RECOVERY OF FUNCTION IN THE AVIAN AUDITORY-SYSTEM

Chickens were exposed to an intense pure tone that destroyed the hair cells and tectorial membrane in a crescent shaped patch along the abne ural edge of the basilar papilla. During the following weeks, when the hair cells and tectorial membrane were regenerating, psychophysical a nd electrophysiological measures were obtained to assess the time cour se and degree of recovery. Immediately after the exposure, the behavio ral thresholds were elevated 30-40 dB and auditory temporal integratio n was greatly reduced; however, both measures fully recovered by 28 da ys post-exposure. In addition, tone-on-tone masking patterns recovered to normal. immediately after the exposure, the thresholds of single c ochlear ganglion neurons were elevated more than 30 dB, tuning curves were broader than normal, two-tone rate suppression (TTRS) boundary sl opes were shallower than normal and spontaneous activity was reduced. Threshold and spontaneous discharge rate fully recovered after the exp osure. Tuning and TTRS also recovered significantly in most neurons; h owever, some units with characteristic frequencies (CFs) near the expo sure frequency showed abnormal tuning and TTRS suppression. The regene ration of the hair cells and lower honeycomb layer of the tectorial me mbrane is associated with considerable recovery of function; however, the incomplete recovery of tuning and TTRS in some neurons may be link ed to the incomplete regeneration of the tectorial membrane.