Abstract
Δ1-Tetrahydrocannabinol (Δ1-THC) and 7-hydroxy-Δ1-THC were injected into the cerebral ventricles of mice by an improved technique, and the potencies of the drugs were measured by the mouse catalepsy test. Both drugs were found to have the same activity when administered by this route as after intravenous injection. Autoradiographic experiments with tritium-labelled compounds showed that at the time of the peak behavioural effect almost all the injected dose of 3H-Δ1-THC (1.6 mg kg−1) or 3H-7-hydroxy-Δ1-THC (0.6 mg kg−1) remained in the intraventricular space and had not penetrated the brain tissue. Δ1-THC was found to remain in the ventricles after the behavioural effect had disappeared; 3% of the injected dose was still present 2 days after injection of 3H-Δ1-THC (1.6 mg kg−1).