Evidence for an Interaction between CB1 Cannabinoid and Melanocortin MCR-4 Receptors in Regulating Food Intake

Melanocortin receptor 4 (MCR4) and CB1 cannabinoid receptors independently modulate food intake. Although an interaction between the cannabinoid and melanocortin systems has been found in recovery from hemorrhagic shock, the interaction between these systems in modulating food intake has not yet been examined. The present study had two primary purposes: 1) to examine whether the cannabinoid and melanocortin systems act independently or synergistically in suppressing food intake; and 2) to determine the relative position of the CB1 receptors in the chain of control of food intake in relation to the melanocortin system. Rats were habituated to the test environment and injection procedure and then received intracerebroventicular injections of various combinations of the MCR4 receptor antagonist JKC-363, the CB1 receptor agonist Δ9-tetrahydrocannabinol, the MCR4 receptor agonist α-MSH, or the cannabinoid CB1 receptor antagonist SR 141716. Food intake and locomotor activity were then recorded for 120 min. When administrated alone, SR 141716 and α-MSH dose-dependently attenuated baseline feeding, whereas sub-anorectic doses of SR 141716 and α-MSH synergistically attenuated baseline feeding when combined. Δ9-Tetrahydrocannabinol-induced feeding was not blocked by α-MSH, whereas SR 141716 dose-dependently attenuated JKC-363-induced feeding. Locomotor activity was not significantly affected by any drug treatment, suggesting that the observed effects on feeding were not due to a nonspecific reduction in motivated behavior. These findings revealed a synergistic interaction between the cannabinoid and melanocortin systems in feeding behavior. These results further suggested that CB1 receptors are located downstream from melanocortin receptors and CB1 receptor signaling is necessary to prevent the melanocortin system from altering food intake.