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 (I Cdc) of old hearing CBA mice is dependent upon neural activity within the a uditory pathway. We tested this hypothesis by bilaterally deafening young C BA/CaJ mice with kanamycin, and then aging them until 24 months. This manip ulation mimics the lack of sound-evoked auditory activity experienced by ol d C57BL/6J mice, who are deaf and do not show CR upregulation with age. Cel l counts revealed that the density of CR+ cells in the lCdc of old hearing CBA mice was statistically different from old deafened CBA mice raised unde r identical conditions. Old hearing CBAs possessed an average of 27.54 more CR+ cells/100 mum(2) than old deafened CBAs. When old deafened CBAs were c ompared 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, Supp orting the hypothesis that CR up-regulation depends upon sound-evoked activ ity. Moreover, these results demonstrate that up-regulation of CR expressio n was not simply due to a mouse strain difference. (C) 2001 Published by El sevier Science B.V.