Indirect and Direct Cannabinoid Agonists Differentially Affect Mesolimbic Dopamine Release and Related Behaviors

Abstract

The cannabinoid system is being researched as a potential pharmaceutical target for a multitude of disorders. The present study examined the effect of indirect and direct cannabinoid agonists on mesolimbic dopamine release and related behaviors in C57BL/6J (B6) mice. The indirect cannabinoid agonist N-arachidonoyl serotonin (AA-5-HT) indirectly agonizes the cannabinoid system by preventing the metabolism of endocannabinoids through fatty acid amide hydrolase (FAAH) inhibition while also inhibiting transient receptor potential vanilloid type 1 (TRPV1) channels. Effects of AA-5-HT were compared with the direct cannabinoid receptor type 1 (CB1R) agonist arachidonoyl-2-chloroethylamide (ACEA). In Experiment 1, mice were pretreated with 7 daily injections of AA-5-HT, ACEA, or vehicle prior to assessments of locomotor activity using open field (OF) testing and phasic dopamine release using in vivo fixed potential amperometry. Chronic exposure to AA-5-HT did not alter locomotor activity or mesolimbic dopamine functioning. Chronic exposure to ACEA did not alter locomotor activity but did decrease phasic dopamine release while increasing the dopaminergic response to cocaine. In Experiment 2, mice underwent AA-5-HT, ACEA, or vehicle conditioned place preference (CPP) then saccharin preference testing, a measure commonly associated with anhedonia. Mice did not develop a CPP or aversion for AA-5-HT or ACEA, and repeated exposure to AA-5-HT or ACEA did not alter saccharin preference. Altogether, the findings suggest that neither of these drugs induce behaviors that are classically associated with abuse liability in mice; however, direct CB1R agonism may play more of a role in mediating mesolimbic dopamine functioning than indirect cannabinoid agonism.