Tissue culture studies of neural plasticity.

Exposure of cerebellar cultures derived from neonatal mice to cytosine arabinoside for the first 5 days in vitro results in destruction of cerebellar granule cells and inhibition of glial maturation. Such cultures undergo reorganizational changes, primary features of which are a sprouting of Purkinje cell recurrent axon collaterals and the formation of recurrent axon collateral-Purkinje cell dendritic spine synapses. Such heterotypical synapses are inhibitory, in contrast to the excitatory parallel fiber-Purkinje cell dendritic spine synapses normally present. If locus coeruleus neurons are included with the cerebellar cultures, the catecholaminergic axons also sprout, and tissue levels of catecholamines are increased. Purkinje cell survival is enhanced in Ara C-treated cultures, as the target field for Purkinje cell axonal projections is expanded. Oligodendrocyte inhibition results in failure of myelination, and astrocyte inhibition, when it occurs, is associated with a failure of Purkinje cell ensheathment and a hypennnervation of Purkinje cell somata by sprouted recurrent axon collateral terminals. Transplantation of such cultures with granule cells and glia reverses many of these changes. Parallel fiber-Purkinje cell dendritic spine synapses are formed, and most heterotypical synapses disappear. The Purkinje cell population is reduced to normal, and most of the sprouted recurrent axon collaterals are eliminated. However, sprouted catecholaminergic axons are not significantly reduced. Transplanted cultures become myelinated and Purkinje cells acquire astrocytic sheaths, with an associated reduction of axosomatic synapses. Transplantation with glia alone does not reduce the sprouted recurrent axon collaterals, but does result in astrocytic ensheathment of Purkinje cells and an associated decrease of axosomatic synapses. These tissue culture models illustrate some of the plastic changes that the nervous system may undergo following injury and transplantation.