Mydriasis induced by tetrahydrocannabinol (THC) in rats

Male albino rats, injected intravenously or intracerebroventricularly with delta 1-tetrahydrocannabinol (THC), develop mudriasis. The median effective dose of the intravenous administration group was 5 mg/kg THC, whereas that for the intracerebroventricular route was 150 microgram/kg THC. Sympathectomy significantly decreased the THC-induced mydriasis. The mydriatic effect was not influenced by naloxone. We conclude that THC produces mydriasis through a central action, the efferent pathway of which is the sympathetic system.