Conductive hearing loss affects the growth of the cochlear nuclei over an extended period of time

During normal growth in CBA/J mice, the volume of dorsal and ventral cochlear nuclei change very little between 1 and 3 days of age; then more than double between 6 and 12 days of age. After 12 days, the rate of growth declines, but growth continues through at least 90 days. The globular cells of the ventral cochlear nucleus also double their soma areas between 6 and 12 days, but then grow no more. The number of ventral cochlear nucleus neurons containing Nissl substance doubles between 6 and 12 days of age and then remains stable. This increase in neuronal numbers is probably caused by differentiation of neuroblasts into neurons, not by mitoses. Conductive losses from 4 to 45 days, and from 24 to 45 days, both result in reduced volume of the ventral cochlear nucleus, but have no effect on the volume of the dorsal cochlear nucleus. Globular cell area is affected by a conductive loss from 4 to 45 days of age, but not by a conductive loss from 24 to 45 days. Therefore, conductive losses affect neuropil growth beyond the time when soma size is no longer affected by these losses.