Consolidated memories may result into a labile one after retrieval. It was proposed that this memory plasticity can allow incorporate new environmental information to the original trace. One of the aims of the present research was to assess whether a stressful stimulus prior to reactivation would influence such trace. Adult male Wistar rats were subjected to a contextual fear conditioning paradigm using a single footshock (weak training session). One day after training, rats were subjected to a stressful situation (restraint for 30 min.). Half of the rats were re-exposed to the original context of conditioning (test 1) for 3 minutes one day after the stress. There was an increase of freezing only in those animals re-exposed to the associated context, which persisted in test 2 performed ten days after stress exposure. Midazolam Intra-Basolateral amygdala (BLA) previous to stress prevented such increase. Similarly, NMDA antagonist intra-BLA prior to reactivation attenuated stress-induced increase of freezing. The intra-BLA infusion of an inhibitor of protein degradation (B-lac) did not prevent the enhancement of fear memory in stressed animals. Although there is a clear interaction between stress and fear memory that leads to an improved fear memory, such increase seems not to be dependent on protein degradation in BLA.
