Behavioral activity and active avoidance learning and retention in rats neonatally exposed to painful stimuli.

Twice daily for the first 15 days after birth, rats from the same litters were either placed for 5 sec on a hot plate (55 degrees C) (treated group), or on a plate maintained at body temperature (38 degrees C) (manipulated group). Controls were left undisturbed. When 90 days old, they were studied for pain threshold, open-field behavior, and two-way active avoidance learning and retention. Weight gain, pain threshold, open-field behavior, and active avoidance retention were not significantly different in the three groups. On the other hand, the rate of two-way active avoidance learning was significantly greater in treated rats. These results suggest that repeated neonatal exposure to painful stimuli, in rats raised under otherwise normal conditions, improves later active avoidance performance. The most likely mechanisms are discussed.