In vitro alteration of the subcellular distribution of ³H reserpine in the rat forebrain by Δ⁹ tetrahydrocannabinol

Δ⁹ Tetrahydrocannabinol (Δ⁹ THC) has been reported to attenuate both reserpine induced serotonin depletion and reserpine induced hypothermia. The authors have observed that Δ⁹ THC preincubation led to a dose responsive increase in the amount of ³H reserpine bound to a crude mitochondrial fraction of rat forebrain. The experiments reported here further characterize this phenomenon. Preincubation with Δ⁹ THC produced a shift in the localization of ³H reserpine from the incubation medium and the microsomal supernatant (decrease of 66%) to the crude mitochondrial (CM) pellet (increase of 15.4%). The CM pellet was subfractionated both by differential centrifugation after osmotic shock and by layering on a five step discontinuous sucrose gradient and centrifuging at 80,000 x g. Osmotic shock with 0.032 M sucrose and centrifugation revealed that the Δ⁹ THC induced increase in ³H reserpine was contained in both the synaptic vesicle fraction (24.7%) and the fraction containing myelin, ruptured synaptosomes and mitochondria (324%). Separating the CM fraction into five component parts showed that Δ⁹ THC increased the ³H reserpine bound by about 275% in the three fractions containing myelin, membrane fragments or mitochondria. Even more dramatic increases (> 1000%) were observed in the two fractions containing cholinergic and non cholinergic nerve endings. In addition, the authors have determined that many other drugs which are believed to have membrane mediated mechanisms have no effect on the amount of ³H reserpine bound to the crude mitochondrial fraction. Although other possibilities exist, these data support the hypothesis that Δ⁹ THC retards the action of reserpine by altering the normal distribution of reserpine in various membrane components of the rat brain.