The early decay of long-term potentiation in the hippocampal CA1 region in vitro is reduced by activators of protein kinase C.

The effect of the exogenous protein kinase C (PKC) activator phorbol-12,13-diacetate (PDAc) on the early (0-10 min) time course of long-term potentiation (LTP) has been studied in the CA1 region of the guinea pig hippocampal slice. As shown previously, following a brief tetanus LTP develops almost linearly towards a peak value within 20-25 s, and decays thereafter rapidly to about a third of the peak value within 10 min after tetanization before a more stable level is reached. In the presence of 1.0 microM PDAc the growth phase of LTP is prolonged to 40-50 s, and the subsequent early decay is reduced. This reduction of the early decay resembles that previously found when increasing the number of afferent impulses of the LTP-generating tetanus. Examination of the early time course in solutions with different calcium-magnesium concentration ratios suggests that the observed effect of PDAc is not directly mediated via a change in presynaptic release probability, another effect observed after phorbol ester application. The results show that PKC activity is involved in the early stage of LTP development and support the idea that the early phase of LTP represents the same modification process as that underlying the more sustained phase of LTP.