Systemic morphine injection can also induce endogenous updating. Graphs show percent of freezing time, expressed as mean ± SEM. The open field graph shows crossing number. The experimental design is shown in the top of each panel. (A) Morphine injection after memory reactivation impairs memory retrieval during test 1. This phenomenon is reverted with the injection of the same doses of morphine before test 2 (n = 10 per group). (B) Omitting the reactivation session, morphine impairs memory retrieval during test 2 (vehicle n = 7, morphine n = 8). (C) Nimodipine injection before memory reactivation prevents the impairment of morphine on memory reconsolidation and the state-dependent phenomenon (VVVV, n = 10, NMVV n = 8, VMVV n = 9, NMVM n = 9, VMVM n = 9). (D) Systemic morphine injection has no effects in motor performance (n = 7 per group). (V) Vehicle, (N) nimodipine, (M) morphine. Groups marked with the same letter (e.g., “a”) are statistically equal to each other and different from those marked with different letters (e.g., “a” groups differ from “b” groups), with significance level of P < 0.05.
