Effects of ketamine on memory and nociception in rats.

BACKGROUND Ketamine is intravenous anaesthetic with NMDA-glutamate receptors mechanism of action. MATERIAL AND METHODS Male Wistar rats were treated with saline (group A) or 10, 15 or 20 mg/kg of ketamine (groups B, C and D, respectively). For active avoidance test an automatic reflex conditioner was used. The observed variables were number of avoidances, escapes and intertrial crossings. Step-through and step-down passive avoidance tests were done with learning and memory retention test. Criteria for step-through test were latency of reactions of 180 sec in the light chamber. Criteria for step-down test were latency of reaction of 60 sec on the platform. The hot-plate test evaluates the reaction time of the rats dropped on a heated surface. The analgesy-meter test exerts a force increased at constant rate. RESULTS In active avoidance test the controls increased the number of avoidances during learning and memory tests. Ketamine in all doses used increased the number of avoidances during learning and in memory test. Controls did not change the number of escapes, but the ketamine treated animals decreased it. The number of intertrial crossings was not changed by controls or ketamine-treated rats during learning and memory tests. In passive avoidance tests the controls and ketamine-treated rats increased the latency time during learning and memory retention tests. In hot-plate analgesic test and in analgesy-meter test the controls and ketamine-treated rats did not change the latency of reaction. CONCLUSION The results suggest that ketamine improves learning and memory processes and has no analgesic effect in the doses applied.