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Cisplatin-induced Increases in Spontaneous Neural Activity in the Dorsal Cochlear Nucleus and Associated Outer Hair Cell Loss

Tinnitus is one of the consequences of cisplatin chemotherapy, but its underlying mechanisms are not well understood. Since it has been shown that cisplatin causes outer hair cell loss, it is possible that loss of these cells might induce tinnitus by increasing spontaneous activity in the central auditory system. To test this possibility, the present study examined the effects of cisplatin treatment on cochlear hair cells and on spontaneous neural activity in the dorsal cochlear nucleus of hamsters. Recordings, carried out approximately 1 month after cisplatin treatment, demonstrated significant increases in spontaneous activity across broad regions of the dorsal cochlear nucleus relative to levels in saline-treated controls. Histological results showed that cisplatin-treated animals also displayed dramatic loss of outer hair cells over most of the basal turn of the cochlea. Inner hair cells remained intact, although some evidence of damage to their stereocilia was evident. These findings indicate that cisplatin treatment causes abnormalities in spontaneous activity in the dorsal cochlear nucleus that are associated with widespread damage to outer hair cells. However, since some damage to inner hair cells was also observed, the role of inner hair cell injury in contributing to higher spontaneous activity cannot be ruled out.