Δ9-tetrahydrocannabinol: Central distribution after intravenous administration in the awake rat

Tritiated Δ⁹-tetrahydrocannabinol, in doses of 36 or 72 μCi (1.9 or 3.8 μg) per kg, was injected into the jugular vein of unanaesthetized male Sprague-Dawley rats (weight range 225-275 g) via a chronically-implanted polyethylene catheter. The rats were decapitated after different survival times ranging from 3 to 60 min. The whole brains were removed and sliced transversely in 1 mm thicknesses. While visualized under a zoom stereomicroscope, specific brain structures were dissected bilaterally from each slice using microdissection needles. Each structure was then reconstituted in toto from its parts from the different slices. After weighing, the counts per minute per unit wet weight were determined for each reconstituted structure in a liquid scintillation counter. A regional variation in the counts was found and this variation differed with the survival time, although the counts for all structures were low at 60 min. The most pronounced counts were from the amygdala, the striatum, the periaqueductal grey and the cerebellum; the lowest counts were from the hypothalamus and the mesencephalic reticular formation.