Figure 4.

Chronic blockade of NMDA receptors in the mPFC during the first week of the postlearning period prevents retention of remotely acquired memory. A, Experimental design. The rats received chronic infusion of d-APV (n = 7) or aCSF (n = 6) during the initial week of the postlearning period. Their memory retention was measured 6 weeks after conditioning when memory depends critically on the mPFC. B, Mean percentage of adaptive CRs during the last 3 d of the initial conditioning and reconditioning. Negative values on the abscissa represent the last 3 d of the initial conditioning (the session in which the rat reached the criterion is denoted −1) and positive values represent the reconditioning. During reconditioning, the APV group (filled circles) showed a significantly lower adaptive CR percentage in the first session, although it could relearn the adaptive CR up to the level of the aCSF group (empty circles) with subsequent retraining. C, Mean percentage of adaptive CRs during session 1 divided into 10 blocks. The daily 100 trials were divided into 10 blocks. The APV group (filled circles) consistently exhibited a lower adaptive CR percentage than the aCSF group (empty circles) during session 1. D, Averaged EMG amplitude of the aCSF group (thin line) and the APV group (thick line) in session 1. The solid line under each trace indicates the timing of the 350 ms CS and the 100 ms US. The vertical scale indicates the average EMG amplitude before the CS presentation. The temporal pattern of CRs in the APV group exhibited no notable change that could explain the impairment observed in this group.