INPUTS TO A PHYSIOLOGICALLY CHARACTERIZED REGION OF THE INFERIOR COLLICULUS OF THE YOUNG-ADULT CBA MOUSE

Presbycusis is a sensory perceptual disorder involving loss of high-pi tch hearing and reduced ability to process biologically relevant acous tic signals in noisy environments. The present investigation is part o f an ongoing series of studies aimed at discerning the neural bases of presbycusis. The purpose of the present experimen: was to delineate t he inputs to a functionally characterized region of the dorsomedial in ferior colliculus (IC, auditory midbrain) in young, adult CBA mice. Fo cal, iontophoretic injections of horseradish peroxidase were made ill the 18-24 kHz region of dorsomedial IC of the CBA strain following phy siological mapping experiments. Serial sections were reacted with diam inobenzidine or tetramethylbenzidine, counterstained and examined for retrogradely labeled cell bodies. Input projections were observed cont ralaterally: from: all three divisions of cochlear nucleus, intermedia te and dorsal nuclei of the lateral lemniscus (LL); and the central nu cleus, external nucleus and dorsal cortex of the IC. Input projections were observed ipsilaterally from: the medial and lateral superior oli vary nuclei; the superior paraolivary nucleus; the dorsolateral and an terolateral periolivary nuclei; the dorsal and ventral divisions of th e ventral nucleus of LL; the dorsal and intermediate nuclei of LL; the central nucleus, external nucleus and dorsal cortex of the IC outside the injection site; and small projections from central gray and the m edial geniculate body. These findings in young, adult mice with normal hearing call now serve as a baseline for similar experiments being co nducted in mice of older ages and with varying degrees of hearing loss to discover neural changes that may cause age-related hearing disorde rs. (C) 1998 Elsevier Science B.V.