Fos-like immunoreactivity in auditory and nonauditory brain structures of hamsters previously exposed to intense sound.

Fos-like immunoreactivity (FLI) was evaluated in auditory and nonauditory brain structures in hamsters that had been exposed previously to intense sound and tested behaviorally for tinnitus. The immunocytochemical results demonstrated a significant increase in exposed animals of FLI in auditory brain structures such as the lateral lemniscus, central nucleus of inferior colliculus, and auditory cortex, as well as in some nonauditory brain structures such as the locus coeruleus, lateral parabrachial nucleus, certain subregions of the hypothalamus, and amygdala. The behavioral scores suggest that animals that had been exposed to intense sound developed tinnitus. This is consistent with the hypothesis that FLI induced by intense sound exposure might represent a neural correlate of tinnitus or of plasticity associated with tinnitus. The possibility and the mechanisms underlying the increased FLI are discussed.