Intracellular perfusion of the PKA inhibitor PKI(6–22) amide (2 mm) decreased the early LTP induced by pairing. A, In the first input, pairing procedure induced large LTP. Two minutes after pairing, PKI was perfused inside the cell. A pairing procedure applied to the second input in the presence of PKI produced significantly smaller LTP (n = 8; p < 0.001).B, In similar experiments, AC3 control peptide (2 mm) was perfused into the cell after the first pairing. A pairing procedure applied to the second input (in the presence of AC3) produced LTP of the same size as a first pairing (n= 6; p > 0.35). C, Replot of LTP induced by second pairing procedure shows significant inhibition of LTP by PKI as compared to control peptide (p < 0.01). Insets represent averaged EPSC (n = 40) from individual experiments 5 min before and 30 min after the pairing.