Figure 3.

LTP is induced by cortical tetanic stimulation coupled with postsynaptic depolarization. Results illustrated in A and B are from two separated experiments. (A) Demonstration of striatal LTP. In this experiment, the tetanus was delivered during membrane depolarization induced by an injection of dc current (+0.8 nA) leading the membrane potential from −72 to −37 mV (tetanus parameters: train of 2.5 sec at 100 Hz repeated four times at 10-sec interval). (A1–2) Superimposed EPSPs (n = 3) recorded 1 min before (A1) and 24 min after (A2) conditioning. (A3) Superimposition of averaged EPSPs (n = 10) showing that the kinetic of synaptic responses was unchanged after potentiation. (A4) The constancy of the mean voltage response to −0.4 nA indicates the input resistance stability of the cell. (B) Time course of striatal LTP. The conditioning protocol consisted in a preliminary depolarization induced by an injection of dc current (+1 nA) followed by tetanic stimulation (train of 1 sec at 100 Hz repeated four times at 10-sec interval). (Inset, Left) Superimposed averaged EPSPs for the periods indicated in the plot below (a, control; b, from +65′ to +68′ after tetanus) showing that synaptic potentiation was still present more than 1 hr after conditioning (P < 0.0005). (Inset, Right) The intrinsic membrane excitability tested by depolarizing current (+0.8 nA) was not modified, as indicated by the superimposed traces obtained just before tetanization and at the end of the recording session.