Acute stress rapidly and persistently enhances memory formation in the male rat

Previous studies, as well as the present one, report that acute exposure to intermittent tailshocks enhances classical eyeblink conditioning in male r ats when trained 24 h after stressor cessation. In Experiment 1, it was det ermined that the facilitating effect of stress on conditioning could also b e obtained in response to a stresser of acute inescapable swim stress but n ot inescapable noise or the unconditioned stimulus of periorbital eyelid st imulation. These selective responses arose despite comparable enhancements of the stress-related hormone corticosterone in response to tailshocks, per iorbital eyelid stimulation, noise stress, and supraelevation in response t o swim stress. Although corticosterone is necessary for the enhanced learni ng in response to stress (Beylin & Shors, 1999), these results suggest that it is not sufficient. In addition, the results suggest that the enhancemen t is not dependent on common characteristics between the stresser and the c onditioning stimuli (stimulus generalization). In Experiment 2, it was dete rmined that the facilitating effect of the stresser on conditioning occurs within 30 min of stresser cessation. Thus, the mechanism responsible for fa cilitating memory formation is rapidly induced as well as persistently expr essed. In Experiment 3, it was determined that exposure to the stresser doe s not enhance performance of the conditioned response after the response ha s been acquired. Thus, exposure to the stresser enhances the formation of n ew associations rather than affecting retention or performance of the motor response. These studies extend the circumstances under which stress is kno wn to enhance associative learning and implicate neural mechanisms of memor y enhancement that are rapidly induced and persistently expressed. (C) 2001 Academic Press.