VENTRAL TEGMENTAL MICROINJECTION OF DELTA(9)-TETRAHYDROCANNABINOL ENHANCES VENTRAL TEGMENTAL SOMATODENDRITIC DOPAMINE LEVELS BUT NOT FOREBRAIN DOPAMINE LEVELS - EVIDENCE FOR LOCAL NEURAL ACTION BY MARIJUANAS PSYCHOACTIVE INGREDIENT

Basal extracellular levels of dopamine (DA) and its metabolites in both ventral tegmental area (VTA) and nucleus accumbens (Acb) were simultaneously monitored by in vivo brain microdialysis in laboratory rats. Microinjection of 12 mug or 24 mug DELTA9-tetrahydrocannabinol (DELTA9-THC). the psychoactive ingredient in marijuana and hashish, into the VTA produced a dose-dependent increase in somatodendritic DA levels in VTA but failed to produce any simultaneous change in extracellular DA in Acb. Direct DELTA9-THC perfusion (5 X 10(-5) and 2 x 10(-4) M) into Acb via the microdialysis probes caused a significant increase in extracellular DA levels in Acb. These findings suggest that (1) DELTA9-THC has a facilitating effect on somatodendritic DA efflux, and (2) the elevation of Acb DA levels seen in our previous studies with systemic administration of DELTA9-THC may result from local actions of DELTA9-THC at or near the DA terminal projections in Acb.