Pharmacological evidence for a protective role of the endogenous opioid system on electroshock-induced seizures in the mouse.

Acute administration of morphine produced a protective effect on electroshock (ECS)-induced seizures in mice, while naloxone and naltrexone decreased ECS seizure threshold. Chronic morphine administration in mice resulted in a decrease of ECS-induced seizure threshold evident within 24 h following the end of drug treatment. This effect disappeared 5 days after the end of chronic morphine treatment. Moreover, tolerance to the anticonvulsant effect of morphine was evident in mice chronically treated with morphine and subjected to ECS 30 min after the last injection of the drug, as well as in mice subjected to ECS 24 h after the end of chronic treatment.