Depolarization or glutamate receptor activation blocks apoptotic cell death of cultured cerebellar granule neurons.

Cerebellar granule neurons can be readily maintained in culture if depolarized with high concentrations of K+ or subtoxic concentrations of various excitatory amino acids. We now report that these depolarizing stimuli promote cerebellar granule neuron survival by blocking their programmed death via apoptosis. Cerebellar granule neurons maintained in depolarizing conditions and then changed to non-depolarizing conditions, exhibit the morphological and biochemical features of apoptosis, including cytoplasmic blebbing, condensation and aggregation of nuclear chromatin and internucleosomal DNA fragmentation. Inhibitors of RNA or protein synthesis greatly attenuate cell death induced by non-depolarizing culture conditions. In contrast, cerebellar granule neurons, when exposed to fresh serum-containing medium or to high concentrations of glutamate, exhibit a delayed-type of neurotoxicity which is non-apoptotic in nature. Given the actions of excitatory amino acid receptor agonists in preventing apoptosis of cultured cerebellar granule neurons, we hypothesize that the functional innervation of postmigratory granule neurons during cerebellar development may prevent further elimination of these neurons by blocking their programmed death.