Differentiation of the giant and fusiform cells in the dorsal cochlear nucleus of the hamster.
Two categories of large neurons--fusiform cells and giant cells--can be distinguished in the dorsal cochlear nucleus of the hamster. In the adult, these neurons are located in separate laminae in the nucleus and have distinct dendritic morphology. However, the two cell types are not distinguishable in the newborn hamster. At birth the large cells in the dorsal cochlear nucleus are clustered into one group and are alike morphologically. On postnatal day 5, laminae are still not apparent, but the neurons have begun to acquire their adult shapes. By day 15 laminae have formed, and the cells appear mature with the one exception that the apical dendrites of the fusiform cells have not acquired the spines which will cover their surface in the adult. The appearance of laminae coincides with the growth of axons and dendrites into a interstitial zone between the layers of cell bodies. Dendritic growth occurs during the time of axonal ingrowth and establishment of contacts between the axons and dendrites. The growth of the apical dendrites of fusiform cells, which are not contacted by these fibers, lags behind. These results demonstrate that afferent ingrowth and the differentiation of dendrites in the dorsal cochlear nucleus are temporally related. The synchronous development may serve to ensure a specific synaptic arrangement between the axons and their target dendrites.
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