Proconvulsant effect of morphine on seizures induced by pentylenetetrazol in the rat

The chemoconvulsant pentylenetetrazol (PTZ) was administered by a variety of routes to rats pretreated with morphine (10-50 mg/kg s.c.). In a naloxone-reversible, dose-dependent manner, morphine decreased the threshold for seizures induced by the slow intravenous infusion of PTZ. In addition, morphine increased the severity of seizures induced by the intravenous, intraperitoneal, and subcutaneous routes of administration of PTZ. Morphine also caused an increased incidence of multiple seizures following subcutaneous administration of PTZ. These results demonstrate that morphine has a proconvulsant effect on PTZ-induced seizures in the rat.