Experimental modification of cerebellar development in tissue culture: x-irradiation induces granular degeneration and unattached purkinje cell dendritic spines.

Cerebellum explants from 15--16 day fetal mice were irradiated with 500--1000 rad X-ray and were grown in tissue culture for 12--18 days. At the dose of 500 rad, a reduction of granule cell population was observed in the explant. At the dose of 1000 rad, granule cells were mostly destroyed leaving Purkinje cells disarrayed and clustered. Electron microscopy of the explants revealed the presence of unattached dendritic spines of Purkinje cell. It was noted that although numerous free spines could be seen in X-irradiated cultures, the postsynaptic specialization of these spines occurred only in ones embedded in astrocytic cytoplasm. The results indicate that (a) the formation of dendritic spines is a property of the Purkinje cell which probably is preprogrammed and (b) the postsynaptic differentiation of the unattached spines is directly related to their contacts with astrocytes.