MORPHOLOGY OF THE INFERIOR COLLICULUS IN C57BL 6J AND CBA/J MICE ACROSS THE LIFE-SPAN/

Basic anatomical features were evaluated in the inferior colliculus (I C) of C57BL/6J and CBA/J mice across the adult life span (1.5 to 30 mo nths of age). C57BL/6J mice exhibit progressive age-related cochlear p athology and become severely hearing-impaired during the second year o f life; CBA/J mice exhibit little hearing loss as they age. Age had li ttle effect on the size of the IC, the size of IC neurons, or the pack ing density of IC neurons and there was no evidence of age-related neu ron loss. However, old CBA/J mice developed numerous spongiform lesion s throughout the brainstem. The absence of morphological changes in th e IC of hearing-impaired C57BL/6J mice supports the hypothesis that fe atures such as the size of neurons, survival of neurons, and volume of the neuropil are not affected by chronic sensorineural pathology in c entral auditory nuclei (e.g., as the IC) that do not receive direct in put from primary afferent fibers. The data from both strains taken tog ether indicate that certain basic anatomical properties of the mouse I C persist in the face of aging.