Emerging evidence suggests that the hypocretinergic system is involved in addictive behavior. In this study, we investigated the role of these hypothalamic neuropeptides in anxiety-like responses of nicotine and stress-induced reinstatement of nicotine-seeking behavior. Acute nicotine (0.8 mg/kg, s.c.) induced anxiogenic-like effects in the elevated plus-maze and activated the paraventricular nucleus of the/nhypothalamus (PVN) as revealed by c-Fos expression. Pretreatment with the hypocretin receptor 1 (Hcrtr-1) antagonist SB334867 or/npreprohypocretin gene deletion blocked both nicotine effects. In the PVN, SB334867 also prevented the activation of corticotrophin/nreleasing factor (CRF) and arginine-vasopressin (AVP) neurons, which expressed Hcrtr-1. In addition, an increase of the percentage of c-Fos-positive hypocretin cells in the perifornical and dorsomedial hypothalamic (PFA/DMH) areas was found after nicotine (0.8 mg/kg,/ns.c.) administration. Intracerebroventricular infusion of hypocretin-1 (Hcrt-1) (0.75 nmol/1 l) or footshock stress reinstated a previously/nextinguished nicotine-seeking behavior. The effects of Hcrt-1 were blocked by SB334867, but not by the CRF1 receptor antagonist/nantalarmin. Moreover, SB334867 did not block CRF-dependent footshock-induced reinstatement of nicotine-seeking while antalarmin was effective in preventing this nicotine motivational response. Therefore, the Hcrt system interacts with CRF and AVP neurons in the PVN and modulates the anxiogenic-like effects of nicotine whereas Hcrt and CRF play a different role in the reinstatement of nicotineseeking./nIndeed, Hcrt-1 reinstates nicotine-seeking through a mechanism independent of CRF activation whereas CRF mediates the reinstatement induced by stress.

This work was supported by the Instituto de Salud Carlos III Grants PI070559 (FIS) and RD06/001/001 (RTA-RETICS), by the Spanish Ministry of Science and Technology (Consolider-C, SAF2007-64062), by the European Commission (IP LSHM-CT-2004-05166, GENADDICT; and STREP LHSM-CT-2007-037669, PHECOMP), by the Catalan Institution for Research and Advanced Studies (ICREA Academia program), and by Generalitat de Catalunya (2009SGR00731). L.d.L. is supported by grants from the National Institute on Drug Abuse, National Alliance for Research on Schizophrenia and Depression, and Defense Advanced Research Projects Agency.E.M.-G.was supported by a postdoctoral fellowship from the Spanish Instituto de Salud Carlos III. A.P.-Z. is a recipient of a predoctoral fellowship from the Spanish Ministry of Education. We thank R. Cabrera, M. Linares, T. Hansson, and C. Fernández-Avilés for invaluable technical assistance, and T. Sakurai and M. Yanagisawa for generously providing preprohypocretin knock-out mice