Suppression of male copulatory behavior by delta 9-THC is not dependent on changes in plasma testosterone or...

Castrated B6D2 F1 male mice were tested for their sexual responses after being administered 0.5 mg/kg delta 9-tetrahydrocannabinol (THC) 50 mg/kg THC or oil. The animals that received 50 mg/kg, but not 0.5 mg/kg THC, showed deficits in copulatory behavior. Another group of B6D2 F1 castrates were given testosterone propionate (TP) replacement therapy plus 50 mg/kg THC or oil. Similarly, those mice which received 50 mg/kg THC showed behavioral deficits. Lastly, a group of intact B6D2 F1 males were treated with 0.5 mg/kg THC, 50 mg/kg THC or oil, were bled and decapitated, and their brains removed 10 min or 4 hr after treatment. Plasma testosterone (T) and hypothalamic dopamine (DA) levels were unaltered 4 hr after treatment with 50 mg/kg THC, but the concentration of serotonin (5-HT) in their hypothalami was elevated. This effect of THC on hypothalamic 5-HT concentration was not apparent in a larger group of randomly bred animals that were tested. These data strongly suggest that THC's behavioral effects are not mediated by variations in T levels, or by changes in hypothalamic 5-HT or DA concentrations.