Comparative autoradiographic and metabolic study of ? 8- and ? 9-Tetrahydrocannabinol in the brain of the marmoset Callithrix jacchus

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Abstract
The label distribution in the brain of the marmoset Callithrix jacchus following intravenous application of radioactively labeled Δ 8-tetrahydrocannabinol (Δ 8-THC) and Δ 9-THC is investigated by autoradiographic technique. Accumulations of label are observed in nuclei concerned with motor function, in the optic and acoustic pathways, and a few other structures. Of the two hydroxylated isomeres which were shown to be equally psychoactive the brain concentration of 11-OH-Δ 9-THC was found to be about 3 times higher as compared with 11-OH-Δ 8-THC, which may explain whyΔ 9-THC is more potent than Δ 8-THC. More than 90% of the radioactivity found in the brain can be attributed to the THCs and their 11-hydroxylated isomeres. Polar metabolites are almost completely absent from the brain.