A, LTP was induced by 60 BSs repetitively applied at 1 Hz, but not when the bath solution contained the NOS inhibitor l-NAME (100 μm). Left panel, changes in PF-EPSC amplitude before and after BS (arrow). The amplitude was normalized by the mean value observed for 10 min before BS. Middle panel, sample traces immediately before (1) and 30 min after BS (2). Right panel, average PF-EPSC amplitude during the 21–30 min period after BS. Mean ± s.e.m. (n = 5). B, absence of change in PPR after BS-induced LTP. Left panel, the PPR values 10 min before (○) and 30 min after (•) BS. Ten paired-pulse stimuli were repeatedly applied at 0.2 Hz at each interpulse interval (50, 100 or 200 ms). Mean ± s.e.m. (n = 5). Right panel, typical traces of PF-EPSC evoked by paired-pulse stimulus (100 ms interpulse interval) 10 min before and 30 min after BS. Each trace represents an average of 5–10 sweeps. C, no effect of ODQ on the BS-induced LTP. Left panel, changes in the amplitude of PF-EPSC before and after BS (arrow). The amplitude was normalized by the mean value observed for 10 min before BS. Middle panel, sample traces immediately before (1) and 30 min after (2) BS. Each trace represents average of 5–10 sweeps. Right panel, averaged amplitude of PF-EPSC during the 21–30 min period after BS.Mean ± s.e.m. (n = 5). D, synaptic specificity of LTP induced by 1 Hz BS. Two separate beams of PFs were stimulated using two electrodes (S1 and S2) placed 23–43 μm apart. LTP was observed at S1-stimulated synapses, in which 60 BSs were applied at 1 Hz (arrow), but was absent in S2-stimulated synapses, in which BS was not applied. Mean ± s.e.m. (n = 4). E, the distance between the two electrodes (S1 and S2) was varied, and the extent of LTP at the S2-stimulated synapses was normalized by that at S1 (left panel). The extent of overlap between S1-stimulated and S2-stimulated synapses was estimated by cross facilitation (right panel). The data point at zero distance is the paired-pulse ratio at S1. (Mean ± s.e.m., n = 10). BS was applied only to S1 as in D. Statistical differences were evaluated by student's t-test.