Temporal differences in the phosphorylation state of pre- and postsynaptic protein kinase C substrates B-50/GAP-43 and neurogranin during long term potentiation

The phosphorylation state of two identified neural-specific protein kinase C substrates (the presynaptic protein B-50 and the postsynaptic protein neurogranin) was monitored after the induction of long term potentiation in the CA1 field of rat hippocampus slices by quantitative immunoprecipitation following ³²P(i) labeling in the recording chamber. B-50 phosphorylation was increased from 10 to 60 min, but no longer at 90 min after long term potentiation had been induced, neurogranin phosphorylation only at 60 min. Increased phosphorylation was not found when long term potentiation was blocked with the N-methyl-D-aspartate receptor antagonist D-2-amino-5- phosphonovalerate, when only low frequency stimulation was applied or tetanic stimulation failed to induce long term potentiation. Our data show that both B-50 and neurogranin phosphorylation are increased following the induction of long term potentiation, thus providing strong evidence for pro- and postsynaptic protein kinase C activation during narrow, partially overlapping, time windows after the induction of long term potentiation.