Stimulation-dependent development of neuronal cytoplasm in mouse cochlear nucleus

The extent of neuronal development in the mouse ventral cochlear nucleus was examined in normal and developmentally auditory deprived mice. Mice were unilaterally deprived on postnatal day three by external auditory meatus removal and sacrificed with controls on day 45, which is after the developmental period. Light microscopic morphometry of neuronal nucleus and cytoplasm areas demonstrated that the normal spherical and globular cells were larger in their low frequency regions than in their high frequency regions. This size difference occurred mainly in the cytoplasm. Developmental deprivation reduced neuronal cytoplasm areas similarly in the high and low frequency regions of both neuronal types, but had no effect on the size of the neuronal nucleus. It was interpreted that cytoplasmic metabolic events are dependent on developmental levels of stimulation and high and low frequency regions normally are differentially stimulated. Furthermore, these stimulation-dependent cytoplasmic events are impaired by developmental hypostimulation, which retards neuronal metabolism and growth. No changes were observed in the cochlear nucleus contralateral to the deprived side, suggesting that compensatory changes, such as hypertrophy, did not occur.