Cytosine arabinoside effects in mouse cerebellar cultures in the presence of astrocytes.
Organotypic cerebellar cultures derived from neonatal mice were exposed to recent preparations of cytosine arabinoside that destroyed oligodendrocytes and drastically reduced granule cells, but did not reduce the astrocyte population. The cultures were analysed by light and electron microscopy, and by extracellular electrophysiological recording. Purkinje cells survived in greater numbers than in untreated explants and sprouted excess recurrent axon collaterals that formed heterotypical synapses with Purkinje cell dendritic spines. These changes were similar to those found in earlier studies with a cytosine arabinoside preparation that did reduce the astrocyte population, in addition to destroying oligodendrocytes and granule cells. Results with recent cytosine arabinoside preparations that differed from those obtained previously included astrocytic ensheathment of Purkinje cells and apposition of many unattached dendritic spines, encasement of heterotypical synapses by astroglial processes, a loss of Purkinje cell somatic spines, and a lack of somatic hyperinnervation of Purkinje cells by sprouted recurrent axon collateral terminals. All of these differences were attributed to the presence of adequate numbers of competent astrocytes. Heterotypical synapses formed by sprouted recurrent axon collateral terminals and Purkinje cell dendritic spines were functional, as indicated by cortical inhibition in response to antidromic Purkinje cell activation in the absence of somatic hyperinnervation. These results give further definition to the role of astrocytes in cerebellar development and plasticity.