Impaired morphological development of the dorsal cochlear nucleus in hamsters treated postnatally with α -difluoromethylornithine

Abstract

The dorsal cochlear nucleus is a highly organized nucleus in the auditory system in which the ramifications of depletion of specific cell types during development can be studied. Granule cells, small interneurons that are located in all layers of the DCN in the adult hamster, proliferate postnatally and are, therefore, potentially vulnerable to anti-mitotic agents that are administered after birth. The present experiments describe the effects of α-difluoromethylornithine, a drug that inhibits proliferation of cerebellar granule cells, on the granule cells in the dorsal cochlear nucleus. As in the cerebellum, the density of granule cells in the dorsal cochlear nucleus is reduced after α-difluoromethylornithine treatment. In hamsters treated with α-difluoromethylornithine (200 or 500 mg/kg subcutaneously (s.c.), twice daily on postnatal days 4–14), the numerical density of granule cells was reduced in the superficial dorsal cochlear nucleus at 15 days; by 40 days this effect was also apparent in the deep layer, suggesting that cells located superficially that would have migrated into the deep dorsal cochlear nucleus had either failed to develop or did not arrive at their final location. This evidence suggests that the cells normally migrate down from the superficial proliferative zone into the deeper layers. In the drug-treated animals, a layer of mixed granule cells and fusiform cells was thinner than in controls probably due to the reduction in interspersed granule cells since the number of fusiform cells was unaffected. There was also a dose-dependent effect on cell growth; fusiform cells were affected at both doses, while giant cells were only affected at the highest dose. Granule cells form a major input to the fusiform cells and their depletion may account for some of the effects on fusiform cell growth. There could also be additional direct actions of α-difluoromethylornithine on this population.