Research report Opposite effects of sleep rebound on orexin OX 1 and OX 2 receptor expression in rat brain Va ˆnia D’Almeida a,b , De ´bora C. Hipo ´ lide a , Roger Raymond c , Karen B.L. Barlow c , Jun-Han Parkes c , Mario Pedrazzoli a , Sergio Tufik a , Jose ´ N. Nobrega c, T a Department of Psychobiology, Universidade Federal de Sa ˜o Paulo, Sa ˜o Paulo, Brazil b Department of Pediatrics, Universidade Federal de Sa ˜o Paulo, Sa ˜o Paulo, Brazil c NeuroImaging Research Section, Centre for Addiction and Mental Health, 250 College St, Toronto, ON, Canada M5T 1R8 Accepted 3 February 2005 Available online 11 March 2005 Abstract Orexins (hypocretins) have been implicated in the regulation of the normal sleep–wake cycle, in sensorimotor programming, and in other homeostatic and neuroregulatory processes. The present study examined the effects of sleep deprivation (SD) and sleep recovery on the expression of orexin 1 receptors (OX 1 R) and orexin 2 receptors (OX 2 R) throughout the brain. Rats were sacrificed either immediately after 96 h of sleep deprivation (SD group) or after SD followed by 24 h of sleep recovery (Rebound group). Prepro-orexin mRNA showed a non- significant increase in the SD group relative to controls, but a pronounced and significant increase in the Rebound group (+88%, P b 0.007). Similarly, sleep deprivation produced no effect on OX 1 R or OX 2 R mRNA levels. However, in the Rebound group, OX 1 R mRNA levels increased significantly, compared to either control or SD groups, in 37 of 92 brain regions analyzed, with particularly strong effects in the amygdala and hypothalamus. Changes in OX 2 R mRNA levels were also seen only in the sleep Rebound group, but they were fewer in number (10 out of 86 regions), were in the direction of decreased rather than increased expression, and were predominantly confined to cerebral cortical areas. These observations indicate that some factor associated with sleep recovery, possibly the compensatory increase in REM sleep, has strong effects on the orexin system at the mRNA level. They further indicate that OX 1 and OX 2 receptors are affected in opposite way and that the former are more vulnerable to these effects than the latter. D 2005 Elsevier B.V. All rights reserved. Theme: Neurotransmitters, modulators, transporters, and receptors Topic: Peptides: anatomy and physiology Keywords: Sleep deprivation; Hypocretin; In situ hybridization; Gene expression; Hypersomnia; REM sleep 1. Introduction Orexin A and B, also referred to as hypocretin 1 and 2, are hypothalamic neuropeptides derived by a proteolytic process from the same 130-amino acid precursor prepro- orexin [22]. Orexins A and B were first identified by de Lecea et al. [4] in mRNAs from rat hypothalamus and were initially associated with feeding behavior [4,22], although subsequent evidence has been inconsistent in this respect [25,34]. The prepro-orexin gene is expressed in a very restricted, largely perifornical area of the hypothal- amus [15,18]. Two G protein-coupled receptors for orexins have been identified, the orexin receptor type 1 (OX 1 R) and orexin receptor type 2 (OX 2 R) [22]. Orexin A binds equally to both receptor subtypes, while orexin B has a preferential affinity for OX 2 R [9,22]. The large number of projections of orexin-producing cells throughout the central nervous system [18] and the widespread distribu- tion of the two receptors in the brain [8,13,32] suggest that these neuropeptides may have broad physiological functions. 0169-328X/$ - see front matter D 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.molbrainres.2005.02.002 T Corresponding author. Fax: +1 417 979 4739. E-mail address: jose _ nobrega@camh.net (J.N. Nobrega). Molecular Brain Research 136 (2005) 148 – 157 www.elsevier.com/locate/molbrainres