LTP induced by theta frequency stimulation is not accessible to synaptic capture. (A) Diagram illustrating the placement of stimulating (S1, S2) and recording electrodes (R) for synaptic capture experiments. (B) Four trains of 100 Hz tetanus delivered to the S1 pathway induced L-LTP (top). A single train of 100-Hz tetanus applied 60 min after in S2 pathway induced an enduring LTP (bottom). (C) Theta frequency stimulation (5 Hz, 30 sec) delivered to S1 induced LTP in this pathway (top). A single train of 100-Hz stimulation applied 60 min after in S2 failed to induce enduring LTP (bottom). (D) A single train of tetanus (1 × 100Hz) (S2) applied 15 min after 5-Hz LTP in S1 induces a transient LTP (bottom). Insets in B, C, and D are the sample traces before and 90 min after the LTP-inducing protocol. Calibration: 3 mV, 5 msec.