title: Blockade of orexin-1 receptors in the ventral tegmental area could attenuate the lateral hypothalamic stimulation-induced potentiation of rewarding properties of morphine.
abstract: The orexins (hypocretins) are lateral hypothalamic (LH) neuropeptides that have been implicated in a variety of behaviors ranging from feeding to sleep and arousal. Evidence from animal models suggests a role for orexins in reward processing and drug addiction. In the present study, we investigated the direct effect of an orexin antagonist in the ventral tegmental area (VTA) on acquisition and expression of morphine conditioned place preference (CPP) induced by concurrent stimulation of the LH. Eighty-one adult male Wistar rats weighing 220-280 g were unilaterally implanted by two separate cannulae into the LH and VTA. The CPP paradigm was done; conditioning score and locomotor activity were recorded by Ethovision software. The animals received SB334867 as a selective orexin-1 receptor antagonist (0.1, 1 and 10 nmol/0.3 μl DMSO) in the VTA, just 5 min prior to intra-LH administration of ineffective dose of carbachol as a cholinergic agonist (62.5 nmol/0.5 μl saline) that stimulates orexin neurons in the LH and ineffective dose of morphine (1 mg/kg, subcutaneously) concurrently during conditioning phase (acquisition experiments) or post-conditioning phase (expression experiments). Data showed that the blockade of orexin-1 receptors in the VTA could inhibit the acquisition (development) but not expression of LH stimulation-induced morphine CPP in the rats. Our findings suggest that the orexinergic projections from the LH to the VTA are involved in the development of the LH stimulation-induced potentiation of morphine rewarding properties and orexin-1 receptors in the VTA have a substantial role in this phenomenon.
authors.affiliation: Neuroscience Research Center, Shahid Beheshti University of Medical Sciences, P.O. Box 19615-1178, Tehran, Iran.
authors.forename: Leila
authors.initials: L
authors.lastname: Zarepour
authors.affiliation: Physiology-Pharmacology Research Center, Rafsanjan University of Medical Sciences, Rafsanjan, Iran.
authors.forename: Zahra
authors.initials: Z
authors.lastname: Fatahi
authors.affiliation: Neurophysiology Research Center, Hamadan University of Medical Sciences, Hamadan, Iran. Electronic address: asarihi@yahoo.com.
authors.forename: Abdolrahman
authors.initials: A
authors.lastname: Sarihi
authors.affiliation: Neuroscience Research Center, Shahid Beheshti University of Medical Sciences, P.O. Box 19615-1178, Tehran, Iran. Electronic address: haghparast@yahoo.com.
authors.forename: Abbas
authors.initials: A
authors.lastname: Haghparast
mesh_terms: D000818:Animals; D001583:Benzoxazoles / Q000494:pharmacology; D002217:Carbachol / Q000494:pharmacology; D018679:Cholinergic Agonists / Q000494:pharmacology*; D003213:Conditioning, Psychological / Q000187:drug effects; D007026:Hypothalamic Area, Lateral / Q000187:drug effects*; D008297:Male; D009020:Morphine / Q000494:pharmacology*; D009043:Motor Activity / Q000187:drug effects; D009287:Naphthyridines; D009294:Narcotics / Q000494:pharmacology*; D000068796:Orexin Receptor Antagonists; D051381:Rats; D017208:Rats, Wistar; D012201:Reward; D014508:Urea / Q000031:analogs & derivatives / Q000494:pharmacology; D017557:Ventral Tegmental Area / Q000187:drug effects*
chemical_list: C420062:1-(2-methylbenzoxazol-6-yl)-3-(1,5)naphthyridin-4-yl urea; D001583:Benzoxazoles; D018679:Cholinergic Agonists; D009287:Naphthyridines; D009294:Narcotics; D000068796:Orexin Receptor Antagonists; D009020:Morphine; D014508:Urea; D002217:Carbachol
keywords: Conditioned place preference; Lateral hypothalamus; Morphine; Orexin; Reward; Ventral tegmental area