Altered tone-induced Fos expression in the mouse inferior colliculus after early exposure to intense noise

Mice become highly susceptible to audiogenic seizures (AGS) after being exposed to intense, high-frequency noise during a critical period of early life (priming). To determine the critical site for AGS priming in the auditory brainstem, animals in the experimental group were primed at 21 days, and the tone-induced Fos immunoreactivity was examined 1, 7, and 14 days after priming as an index of excitability of neurons. Enhanced Fos immunoreactivity was observed in the inferior colliculus (IC) of the primed mice 7 and 14 days after priming as compared to that of non-primed mice and attenuated Fos expression was observed 1 day after priming. No significant elevation of Fos expression was observed in the cochlear nucleus and the deep layer of the superior colliculus of either type of mice. These results strongly suggest that the IC is the target site of AGS priming.