Journal
BIOLOGICAL PSYCHIATRY
Volume 75, Issue 6, Pages 499-507Publisher
ELSEVIER SCIENCE INC
DOI: 10.1016/j.biopsych.2013.06.012
Keywords
Cannabinoid; dopamine; hypocretin; knockout; reward; WIN55,212-2
Categories
Funding
- Instituto de Salud Carlos III [PI07/0559, PI10/00316, RD06/001/001]
- Spanish Ministry of Science and Technology [SAF2007-64062, SAF2011-29864]
- Catalan Government [SGR2009-00731]
- Institucio Catalana de Recerca i Estudis Avancats (ICREA Academia program)
- Spanish Ministry of Education
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Background: Cannabis is the most widely used illicit drug in the world. Although there is a high prevalence of users who seek treatment for cannabis dependence, no accepted pharmacologic treatment is available to facilitate and maintain abstinence. The hypocretin/orexin system plays a critical role in drug addiction, but the potential participation of this system in the addictive properties of cannabinoids is unknown. Methods: We investigated the effects of hypocretins in the intravenous self-administration of the synthetic cannabinoid agonist WIN55,212-2 using hypocretin receptor-1 (Hcrtr-1) and hypocretin receptor-2 antagonists and Hcrtr-1 knockout mice. Additional groups of mice were trained to obtain water to rule out operant responding impairments. Activation of hypocretin neurons was analyzed by using double-label immunofluorescence of FosB/Delta FosB with hypocretin-1. Microdialysis studies were performed to evaluate dopamine extracellular levels in the nucleus accumbens after acute Delta(9)-tetrahydrocannabinol administration. Results: Systemic administration of the Hcrtr-1 antagonist SB334867 reduced intravenous self-administration of WIN55,212-2, as well as the maximum effort to obtain a WIN55,212-2 infusion, as revealed under a progressive ratio schedule. This role of Hcrtr-1 in the reinforcing and motivational properties of WIN55,212-2 was confirmed in Hcrtr-1 knockout mice. Contingent, but not noncontingent, WIN55,212-2 self-administration increased the percentage of hypocretin cells expressing FosB/.FosB in the lateral hypothalamus. The enhancement in dopamine extracellular levels in the nucleus accumbens induced by.9-tetrahydrocannabinol was blocked in mice lacking the Hcrtr-1. Conclusions: These findings demonstrate that Hcrtr-1 modulates the reinforcing properties of cannabinoids, which could have a clear therapeutic interest.
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