The persistent PTD is unaffected by the block of receptors reported to be required for postsynaptic LTD induction and involved in presynaptic modulation.

<p><b><b><i>A,</i></b></b> The SSE is significantly decreased in 1 mM MCPG. The plot shows the average (n = 7) fEPSP/FV normalized to its averaged baseline value 2 min prior the 10-pulse burst. Asterisks are for p<0.02. <b><i>B,</i></b> Same plot on a longer time scale, showing that MCPG does not affect the persistent PTD, in contrast to its effect of the SSE. <b><i>C,</i></b> Summary bar chart showing the persistent PTD amplitude, 4–6 min following a 10-pulse 200 Hz burst. Blocker concentrations were (µM): MCPG (1000); L-NNA (100); D-AP5 (50); SYM2081 (10); MSOP (200); CGP55845 (5); DPCPX (5); K252a (2). In all conditions, the persistent PTD is significant (p<0.01) and not different from control (p>0.35).