Feeding induced by cannabinoids is mediated independently of the melanocortin system

Background: Cannabinoids, the active components of marijuana, stimulate appetite, and cannabinoid receptor-1 (CB1-R) antagonists suppress appetite and promote weight loss. Little is known about how CB1-R antagonists affect the central neurocicuitry, specifically the melanocortin system that regulates energy balance. Methodology/Principal Finding: Here, we show that peripherally administered CB1-R antagonist (AM251) or agonist equally suppressed or stimulated feeding respectively in A^y, which lack a functional melanocortin system, and wildtype mice, demonstrating that cannabinoid effects on feeding do no require melanocortin circuitry. CB1-R antagonist or agonist administered into the ventral tegmental area (VTA) equally suppressed or stimulated feeding respectively, in both genotypes. In addition, peripheral and central cannabinoid administration similarly induced c-Fos activation in brain sites suggesting mediation via motivational dopaminergic circuitry. Amperometry-detected increases in evoked dopamine (DA) release by the CB1-R antagonist in nucleus accumbens slices indicates that AM251 modulates DA release from VTA terminals. Conclusions/Significance: Our results demonstrate that the effects of cannabinoids on energy balance are independent of hypothalamic melanocortin circuitry and is primarily driven by the reward system.