Effect of capsaicin on learning, retention and extinction of spatial and active avoidance tasks in adult rats...

The relationship between learning capability and neurological damage following neonatal treatment with capsaicin (50 mg/kg) was studied in adult Wistar rats of either sex using different experimental procedures. First of all, the reaction to a stress-inducing situation was evaluated by analysing the behavior of capsaicin and vehicle-treated rats in an open field situation. No differences were observed between these two groups. Moreover, the parameters considered were similar to those of untreated, age-matched animals. Rats treated with capsaicin showed a marked learning impairment of an appetitive task in a complex maze. On the contrary, no alterations were observed in both retention and extinction of this conditioned behavior. In spatial discrimination investigated using a different maze (8-arm radial maze) but with the same reinforcement (food), no difference was found between capsaicin-and vehicle-treated rats. In both groups a trial number-related increase of the responding efficiency and a decrease in the mean running time were observed. Neonatally treated rats behaved also similarly in aversive conditioning. However, their learning performances were much better than those of untreated rats. These results confirm that neonatal exposure to painful stimuli later improves active avoidance performance. Capsaicin treatment did not have any effect on the latency of nociceptive response in the hot-plate test.