A Selective Increase in Phosporylation of Protein F1, a Protein Kinase C Substrate, Directly Related to Three Day Growth of Long Term Synaptic Enhancement

Increased in vitro phosphorylation of the 47 kdalton, 4.5 pI protein F1 was observed in dorsal hippocampal tissue from animals exhibiting long term enhancement (LTE) three days after high frequency stimulation of the perforant pathway, as compared to tissue from low frequency stimulated controls or from unoperated animals. The increase in protein F1 phosphorylation was related to LTE rather than simple activation of perforant path-dentate gyrus synapses. This is the first report of a change in brain protein phosphorylation accompanying synaptic enhancement lasting days. The extent of growth of LTE over the three days following stimulation was directly related (r = +0.66, P less than 0.05) to protein F1 phosphorylation. Among the phosphoproteins studied this relationship between LTE and phosphorylation was selective for protein F1. This suggests that protein F1 may regulate growth of synaptic plasticity for at least a three day period. The mechanism for the LTE-related increase in protein F1 phosphorylation has not been established. However, recent evidence from this laboratory indicates: that protein F1 is phosphorylated by the calcium/phospholipid-dependent protein kinase C; and that kinase C is activated 1 h after LTE. Therefore, the increase in protein F1 phosphorylation following LTE may result from long term activation of protein C kinase.