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 bot h ventral tegmental area (VTA) and nucleus accumbens (Acb) were simult aneously 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) int o Acb via the microdialysis probes caused a significant increase in ex tracellular DA levels in Acb. These findings suggest that (1) DELTA9-T HC 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.