Early bilateral deafening prevents calretinin up-regulation in the dorsal cortex of the inferior colliculus of aged CBA/CaJ mice.

This study was conducted to test the hypothesis that age-related calretinin (CR) up-regulation seen in the dorsal cortex of the inferior colliculus (ICdc) of old hearing CBA mice is dependent upon neural activity within the auditory pathway. We tested this hypothesis by bilaterally deafening young CBA/CaJ mice with kanamycin, and then aging them until 24 months. This manipulation mimics the lack of sound-evoked auditory activity experienced by old C57BL/6J mice, who are deaf and do not show CR up-regulation with age. Cell counts revealed that the density of CR+ cells in the ICdc of old hearing CBA mice was statistically different from old deafened CBA mice raised under identical conditions. Old hearing CBAs possessed an average of 27.54 more CR+ cells/100 microm2 than old deafened CBAs. When old deafened CBAs were compared to young hearing CBAs, young hearing C57s, and old deaf C57s, there was no significant difference in mean CR+ cell density in ICdc. Thus, only the old normal hearing CBAs showed an increase in CR+ cells with age, supporting the hypothesis that CR up-regulation depends upon sound-evoked activity. Moreover, these results demonstrate that up-regulation of CR expression was not simply due to a mouse strain difference.