Fig. 3. Isoflurane blocks the induction of long-term potentiation (LTP). Two independent synaptic responses were evoked: LTP without isoflurane (input 1, open circles) and LTP in isoflurane (input 2, filled circles). A tetanus (100 Hz, 1 s) was delivered to input 1 (arrowhead). This induced stable LTP of field excitatory postsynaptic potentials (fEPSPs) in input 1 but not in input 2. Fifty minutes after induction of LTP in input 1, isoflurane was applied for 90 min. After establishment of steady state with respect to drug effect for 20 min, a tetanus (100 Hz, 1 s; indicated by the arrowhead) delivered to input 2 failed to induce LTP. Each data point was obtained from the average of two consecutive fEPSPs and normalized to the 20-min period before delivering the tetanus.