LFS-elicited LTD was occluded by conditioned morphine withdrawal. A, LFS-LTD can be induced in naive rats (*) and blocked by Tat-GluR23Y (♢) but not Tat-GluR23S (▵). B, LFS-LTD also can be induced in saline pairing control (B, □) and unconditioned morphine withdrawal (B, ●) rats. C, D, LFS-LTD is blocked in conditioned morphine withdrawal rats (C) and is rescued by Tat-GluR23Y 24 h before conditioned morphine withdrawal (D, ▴) but not Tat-GluR23S (D, ▴). Insets are the representative examples of each group.