Hypocretin regulates brain reward function and cocaine consumption in rats. The hypocretinergic (Hcrt) system is implicated in energy homeostasis, feeding and sleep regulation. Hypocretinergic cell bodies are located in the lateral hypothalamus (LH) and project throughout the brain. The aim of the present studies was to investigate the role of the Hcrt system in regulating brain reward function and the reinforcing properties of cocaine in rats. Intracranial self-stimulation (ICSS) thresholds provide an accurate measure of brain reward function in rats. Here (...) we show that a single injection of Hcrt-1 (5 µg icv) induced persistent, long-lasting elevations in ICSS thresholds in drug-naïve rats. Indeed, Hrct-1 elevated ICSS thresholds for 36 h, with peak elevations between 6 and 12 hours after injection. Hrct-1-induced threshold elevations were attenuated by an antibody known to neutralize the binding of hcrt-1 to its receptors. Taken together, these observations suggest that Hrct-1 negatively regulates brain reward function in rats. Because Hrct-1 negatively regulates brain reward function, we hypothesized that it may attenuate the increased brain reward function usually observed after cocaine consumption, and thereby alter cocaine self-administration behavior. A daily injection of Hrct-1 (1 µg icv), for 4 consecutive days, slightly increased cocaine self-administration (0.25 mg/infusion) in rats. Overall, these data demonstrate that Hrct-1 negatively regulates brain reward function, and as such may indirectly alter cocaine self-administration. Given the well-established role of hypocretin neurons in regulating feeding behavior and sleep, we hypothesize that hypocretinergic regulation of brain reward function may provide a mechanism by which appropriate and competing behaviors (e.g. sleep or feeding) may be engaged to maintain energy homeostasis. (shrink)