CANNABINOIDS EXCITE DOPAMINE NEURONS IN THE VENTRAL TEGMENTUM AND SUBSTANTIA-NIGRA

EXTRACELLULAR recordings were used to determine the effects of cannabi noids on the activity of dopamine neurons within the ventral tegmental area (VTA) and substantia nigra pars compacta (SNC), Systemic adminis tration of the natural psychoactive cannabinoid Delta 9-tetrahydrocann abinol (Delta 9-THC) and the cannabimimetic aminoalkylindole WIN 55,21 2-2 produced dose-dependent increases in firing rate and burst firing in both neuronal populations. These effects appear to be specific as t he non-psychoactive cannabidiol and the inactive enantiomer WIN 55,212 -3 failed to alter either parameter of neuronal excitability. Furtherm ore, dopamine neurons in the VTA were more sensitive than those in the SNC to the stimulatory actions of Delta 9-THC. These results may prov ide a mechanism by which psychoactive cannabinoids increase extracellu lar dopamine levels in mesolimbic and striatal tissues, and thereby co ntribute to the reinforcing effects of marijuana.