Inner ear lesion alters acoustically induced c-Fos expression in the rat auditory rhomboencephalic brainstem.

The pattern of c-Fos expression was mapped in the adult rat's brain following unilateral cochlear lesions. In normal and cochlear lesioned rats, c-Fos expression was induced with sound stimuli. Acoustic stimulation consisted of pulses of four tones. An additional control group consisted of non-stimulated rats. In the cochlear nuclei (CN), c-Fos activation was scarce in isolated rats and increased strongly following sound stimulation. Following unilateral cochlear lesion, acoustically driven expression was decreased in all CN in both the lesioned and the untreated sides. The ventromedial periolivary nucleus and the rostral periolivary nucleus showed c-Fos activation in isolated conditions and were strongly activated following sound stimulation. The rest of the superior olivary complex showed no c-Fos activation in isolated rats and a weak activation following sound stimulation. Following unilateral cochlear lesions, acoustically driven expression was decreased in some, but not all superior olivary nuclei in both the lesioned and the untreated sides. In the lateral lemniscus complex, c-Fos activation was scarce in isolated rats and increased strongly after stimulation. Following unilateral cochlear lesion, acoustically driven expression decreased bilaterally in all nuclei. We have found that unilateral inner ear lesions lead to bilateral impairment of the capability of acoustic pathway neurons, to being c-Fos-activated following sound stimulation.