Naloxone enhances epileptogenic and behavioral effects of pentazocine in rats

Eight groups of six rats were either injected with saline, pentazocine, naloxone, or a combination of pentazocine and naloxone. Studied were the effects on EEG and behavior. It was found that pentazocine induced epileptic seizures in a dose-dependent fashion. In addition, similar behavioral changes were present after all three doses of pentazocine. High doses of naloxone did not cause epilepsy and affected behavior only slightly. Seizures induced by pentazocine were not antagonized by the opiate antagonist naloxone, but were facilitated after the combination of a noneffective dose of pentazocine and a noneffective dose of naloxone. In addition, exploratory behavior was facilitated by the combination of pentazocine and naloxone. It seems that both an opiate and a nonopiate system are involved in this type of epilepsy and in this type of behavior.