Retention of conditioned autonomic and behavioral responses in preweanling rats: Forgetting and reinstatement

Abstract

Preweanling rats, 16 days of age, responded to an olfactory conditioned stimulus (CS) paired with a shock unconditioned stimulus (US) with increases in heart rate and behavioral activation. In two experiment this finding was replicated and, it was found that the form of these conditioned responses (CRs) changed after a retention interval. When tested 24 h after CS-US pairings, the subjects displayed a decrease 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 in the magnitude of context fear may alter responding to an olfactory CS.