Addiction and arousal: The hypocretin connection

The hypocretins, also known as orexins, are two neuropeptides now commonly described as critical components to maintain and regulate the stability of arousal. Several lines of evidence have raised the hypothesis that hypocretin-producing neurons are part of the circuitries that mediate the hypothalamic response to acute stress. Intracerebral administration of hypocretin leads to a dose-related reinstatement of drug and food seeking behaviors. Furthermore, stress-induced reinstatement can be blocked with hypocretin receptor I antagonism. These results, together with recent data showing that hypocretin is critically involved in cocaine sensitization through the recruitment of NMDA receptors in the ventral tegmental area, strongly suggest that activation of hypocretin neurons play a critical role in the development of the addiction process. The activity of hypocretin neurons may affect addictive behavior by contributing to brain sensitization or by modulating the brain reward system. Hypocretinergic cells, in coordination with brain stress systems may lead to a vulnerable state that facilitates the resumption of drug seeking behavior. Hence, the hypocretinergic system is a new drug target that may be used to prevent relapse of drug seeking. (C) 2007 Elsevier Inc. All rights reserved.