Figure 5.

Differential regulation of synaptic plasticity after recovery from MK-801 and AP-5 block. A, After full recovery of sEPSCs from AP-5 block, standard LTP-producing stimulus (2 Hz, 200 pulses during a 2.5 min depolarization to 0 mV) can induce LTP of AMPAR-mediated EPSCs. Left of the vertical dashed line, NMDAR-mediated sEPSCs at different time points before and after recovery from AP-5. Full recovery of both sEPSC amplitude and frequency were observed. Right of the dashed line, Evoked EPSC (0.125 Hz) before and after a brief LTP-producing stimulation. B, Conversion of synaptic plasticity direction from LTP to LTD after partial recovery from MK-801 block. After partial recovery of EPSC amplitude and full recovery of EPSC frequency from MK-801 (10 μm) block, the same LTP-producing stimulus protocol (2 Hz, 200 pulses during a 2.5 min depolarization to 0 mV) induced LTD instead of LTP of AMPAR-mediated EPSCs. To confirm that the LTD is not attributable to deterioration of the cell recorded, AP-5 was applied at the end of recording and LTD was abolished, which demonstrated that the observed LTD was dependent on NMDAR activity. C and D are statistical plots showing the whole recording process delineated in A and B, respectively. n = 7 for C and D. Representative traces from indicated times are presented above the graphs. E, In the control condition with only paired-pulse stimulation, neither change of sEPSC nor conversion from LTP to LTD was observed. Representative traces from indicated times are presented above the graphs.