ASA 124th Meeting New Orleans 1992 October

4aPP11. Functional and structural changes in nucleus magnocellularis (NM) of the neonatal chick exposed to intense sound.

James C. Saunders

Yale E. Cohen

Ken Kazahaya

Dept. of Otorhinolaryngol.: Head and Neck Surgery, Univ. of Pennsylvania, Philadelphia, PA 19104

Young chicks were exposed to a 0.9-kHz tone for 48 h at 120 dB SPL. Experimental groups were formed at 0 and 12 days post exposure along with age-matched control groups. Single-cell responses in the NM, cochlear pathology along the basilar papilla, and brainstem neuroanatomy in NM, were evaluated in each animal. At 0 days of recovery, single-cell tuning properties, spontaneous activity, rate-intensity functions, phase locking, BF sensitivity, etc., were all severely altered by the exposure. The tonotopic organization of the NM was unaffected. The cochlea exhibited significant damage to the short hair cells and the tectorial membrane. Further, a significant reduction in the surface area of NM cells was noted. All physiologic dimensions recovered completely within 12 days, and the short hair cells were nearly completely replaced. However, in spite of a normal compliment of physiologic behaviors at the cellular level, there remained a substantial disruption to the tectorial membrane. Moreover, the surface area of the NM cells remained significantly reduced. The relation between abnormal cochlear and neural structures, with normal physiologic function in the peripheral auditory system, is discussed. [Work supported by the NIDCD and the Pennsylvania Lions Hearing Research Foundation.]