THE POSTNATAL-GROWTH OF COCHLEAR NUCLEUS SUBDIVISIONS AND NEURONAL SOMATA OF THE ANTEROVENTRAL COCHLEAR NUCLEUS IN THE MONGOLIAN GERBIL (MERIONES-UNGUICULATUS)

We have analysed the postnatal volume increase of the cochlear nucleus subdivisions from birth to senescence in the Mongolian gerbil. All su bdivisions showed the most prominent growth in the 2nd week of life be fore the onset of hearing on day 12. After the onset of hearing, the d orsal and the posteroventral portion of the cochlear nucleus showed on ly a moderate degree of further growth. The antero-ventral cochlear nu cleus, however, almost doubled in volume after the onset of hearing, r eaching a maximum in 4-month-old animals. In ageing gerbils, we observ ed a small but systematic reduction of the cochlear nucleus volume. To further assess which elements contribute to the growth of the antero- ventral cochlear nucleus after the onset of hearing, we analysed the s omal size of the neurones. Before the onset of hearing, somal and volu me growth were highly correlated. However, somata had reached an adult size by the onset of hearing. We conclude that the growth of the ante ro-ventral cochlear nucleus after the onset of hearing is due to chang es in the neuropil.