Intracellular analysis of potentiation of CA1 hippocampal synaptic transmission by phorbol ester application.

(1) The effect of active and inactive phorbol esters on synaptic transmission and on membrane properties of CA1 pyramidal cells in hippocampus have been analyzed by intracellular recording. (2) 4 beta-phorbol-12,13 dibutyrate (beta PDBu), but not the alpha-isomer, increased the firing probability, reduced the spike latency and enhanced the EPSP amplitude in response to synaptic activation. The effect was similar to the changes seen in long term potentiation. After alpha PDBu addition it was possible to elicit further enhancement by tetanization, but not after beta PDBu administration. (3) A slowly developing hyperpolarization was seen after active phorbol ester application without apparent changes in the soma input resistance. (4) Active phorbol esters reduced the slow afterhyperpolarization (AHP) in these cells without affecting the intermediate AHP.