RETENTION OF CONDITIONED AUTONOMIC AND BEHAVIORAL-RESPONSES IN PREWEANLING RATS - FORGETTING AND REINSTATEMENT

Preweanling rats, 16 days of age, responded to an olfactory conditione d stimulus (CS) paired with a shock unconditioned stimulus (US) with i ncreases in heart rate and behavioral activation. In two experiments t his finding was replicated and, in addition, it was found that the for m of these conditioned responses (CRs) changed after a retention inter val. When tested 24 h after CS-US pairings, the subjects displayed a d ecrease in heart rate accompanied by CS-elicited freezing. Giving two unsignaled shocks prior to the delayed test effectively reinstated the tachycardia and behavioral arousal CRs. The results are discussed in terms of contextual influences on the form of the CR and how changes i n the magnitude of context fear may alter responding to an olfactory C S.