Isolation-stress-induced facilitation of passive avoidance memory in the day-old chick.

This study showed that facilitation of recall of a weak version of the 1-trial passive avoidance learning task could be achieved by behavioral "stressing" of day-old chicks after training. Recall, usually retained for less than 9 hr, was extended by socially isolating the chicks for 1 hr immediately after training. There was a brief 3-fold increase in plasma corticosterone levels 10 min after isolation. Facilitated recall was not evident when chicks were isolated 2 hr after training, and it was blocked by intracerebral administration of 2-ng RU 38486, a specific glucocorticoid receptor antagonist, per chick. Male chicks responded more to isolation than did female chicks, presumably a consequence of the additional stress of the injection procedure.