EFFECT OF CAPSAICIN ON LEARNING, RETENTION AND EXTINCTION OF SPATIAL AND ACTIVE-AVOIDANCE TASKS IN ADULT-RATS NEONATALLY TREATED

The relationship between learning capability and neurological damage f ollowing neonatal treatment with capsaicin (50 mg/kg) was studied in a dult Wistar rats of either sex using different experimental procedures . First of all, the reaction to a stress-inducing situation was evalua ted by analysing the behavior of capsaicin and vehicle-treated rats in an open field situation. No differences were observed between these t wo groups. Moreover, the parameters considered were similar to those o f untreated, age-matched animals. Rats treated with capsaicin showed a marked learning impairment of an appetitive task in a complex maze. O n the contrary, no alterations were observed in both retention and ext inction of this conditioned behavior. In spatial discrimination invest igated using a different maze (8-arm radial maze) but with the same re inforcement (food), no difference was found between capsaicin-and vehi cle-treated rats. In both groups a trial number-related increase of th e responding efficiency and a decrease in the mean running time were o bserved. Neonatally treated rats behaved also similarly in aversive co nditioning. 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. Capsa icin treatment did not have any effect on the latency of nociceptive r esponse in the hot-plate test.