title: Orexin/hypocretin role in reward: implications for opioid and other addictions.
abstract: Addiction is a devastating disorder that affects 15.3 million people worldwide. While prevalent, few effective treatments exist. Orexin receptors have been proposed as a potential target for anti-craving medications. Orexins, also known as hypocretins, are neuropeptides produced in neurons of the lateral and dorsomedial hypothalamus and perifornical area, which project widely throughout the brain. The absence of orexins in rodents and humans leads to narcolepsy. However, orexins also have an established role in reward seeking. This review will discuss some of the original studies describing the roles of the orexins in reward seeking as well as specific works that were presented at the 2013 International Narcotics Research Conference. Orexin signalling can promote drug-induced plasticity of glutamatergic synapses onto dopamine neurons of the ventral tegmental area (VTA), a brain region implicated in motivated behaviour. Additional evidence suggests that orexin signalling can also promote drug seeking by initiating an endocannabinoid-mediated synaptic depression of GABAergic inputs to the VTA, and thereby disinhibiting dopaminergic neurons. Orexin neurons co-express the inhibitory opioid peptide dynorphin. It has been proposed that orexin in the VTA may not mediate reward per se, but rather occludes the 'anti-reward' effects of dynorphin. Finally, orexin signalling in the prefrontal cortex and the central amygdala is implicated in reinstatement of reward seeking. This review will highlight recent work describing the role of orexin signalling in cellular processes underlying addiction-related behaviours and propose novel hypotheses for the mechanisms by which orexin signalling may impart drug seeking.
  
  
  BACKGROUND
  This article is part of a themed section on Opioids: New Pathways to Functional Selectivity. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2015.172.issue-2.
authors.affiliation: Department of Physiology and Pharmacology, The University of Calgary, Calgary, AB, Canada; Department of Anesthesiology, Pharmacology and Therapeutics, The University of British Columbia, Vancouver, BC, Canada.
authors.forename: Corey
authors.initials: C
authors.lastname: Baimel
authors.forename: Selena E
authors.initials: SE
authors.lastname: Bartlett
authors.forename: Lih-Chu
authors.initials: LC
authors.lastname: Chiou
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Lawrence
authors.forename: John W
authors.initials: JW
authors.lastname: Muschamp
authors.forename: Omkar
authors.initials: O
authors.lastname: Patkar
authors.forename: Li-Wei
authors.initials: LW
authors.lastname: Tung
authors.forename: Stephanie L
authors.initials: SL
authors.lastname: Borgland
mesh_terms: D000818:Animals; D004399:Dynorphins / Q000378:metabolism; D000431:Ethanol / Q000008:administration & dosage; D006801:Humans; D007031:Hypothalamus / Q000378:metabolism; D047908:Intracellular Signaling Peptides and Proteins / Q000378:metabolism*; D009479:Neuropeptides / Q000378:metabolism*; D064446:Orexin Receptors / Q000378:metabolism; D000068797:Orexins; D012201:Reward; D019966:Substance-Related Disorders / Q000378:metabolism*; D017557:Ventral Tegmental Area / Q000378:metabolism
chemical_list: D047908:Intracellular Signaling Peptides and Proteins; D009479:Neuropeptides; D064446:Orexin Receptors; D000068797:Orexins; D000431:Ethanol; D004399:Dynorphins
keywords: VTA; addiction; dopamine; dynorphin; hypocretin; morphine; orexin