Developmental changes in glutamate receptor-activated translocation of protein kinase C in cerebellar granule neurons

Developmental changes in glutamate receptor agonist-produced enhancement of 4-beta-[H-3]phorbol-12,13-dibutyrate binding ([H-3]-PDBu binding), indicative of an intracellular translocation of protein kinase C (PKC), were investigated in cerebellar granule cells. Our observations demonstrate that the magnitude of glutamate-, NMDA-, and kainate-produced enhancement of PKC translocation was dramatically decreased between 2 and 12 DIV, whereas there was only a minor reduction in the corresponding response caused by the non-NMDA receptor agonist, AMPA. The maximally enhanced stimulation of PKC translocation caused by glutamate and NMDA was significantly reduced already at 4 DIV, whereas a significant reduction of the kainate-induced enhancement of [H-3]PDBu binding was not observed until 8 DIV. Glutamate- and NMDA-induced responses were effectively blocked by the specific NMDA receptor antagonists MK-801 (1 mu M) and APV (100 mu M) as well as by the addition of Mg2+ into assay media. In contrast, the non-NMDA receptor antagonist, CNQX (10 mu M), effectively blocked the kainate-induced enhancement of [H-3]PDBu binding, but had no effect on the NMDA- and glutamate-induced stimulation of PKC translocation. The metabotropic glutamate receptor agonist, ACPD (up to 250 mu M), had no effect on the translocation of PKC. Taken together, our data support the working hypothesis that the rapidly occurring changes in the glutamate receptor agonist-produced translocation of PKC are most likely due to a differential maturation of glutamate ionotropic receptor subtypes and/or to development-dependent alterations in mechanisms responsible for the coupling between the glutamate receptor subtypes and the activation of PKC translocation in cerebellar granule neurons.