Nicotine treatment regulates neuropeptide S system expression in the rat brain Ricardo Lage a,1 , C. Ruth Gonza ´lez a,1 , Carlos Die ´guez a,b , Miguel Lo ´pez a,b, * a Department of Physiology, School of Medicine, University of Santiago de Compostela, Santiago de Compostela, Spain b CIBER of Obesity and Nutrition, Instituto Salud Carlos III, Santiago de Compostela, Spain Received 24 October 2006; accepted 6 June 2007 Available online 23 June 2007 Abstract Nicotine has marked effects on sleep, arousal and body weight. However, the neuronal mechanisms underlying these actions are not fully understood. Neuropeptide S (NPS) is a recently discovered neuropeptide regulating sleep, anxiety and feeding. Here, we examined the effect of acute and chronic nicotine treatment on the expression of NPS and its receptor (NPS-R) in the hypothalamus and brainstem of rats by using real- time PCR. Our results showed that chronic nicotine treatment induced significant changes in NPS and NPS-R expression whereas acute treatment exclusively induces a marked increase in the mRNA levels of NPS-R in the brainstem. Interestingly, we detected no changes in the expression levels of other set of genes present both in hypothalamus and brainstem. Overall, these data suggest that NPS system is specifically regulated by nicotine in the rat hypothalamus and brainstem. # 2007 Elsevier Inc. All rights reserved. Keywords: Body weight; Brainstem; Nicotine; Hypothalamus; Neuropeptide S; Sleep–wake cycle 1. Introduction Nicotine is considered the most addictive element of tobacco. Nicotine induces arousal and wakefulness but at the same time produces ansiolytic-like effect (Nesbitt, 1973). Acute nicotine administration decreases rapid eyes movement (REM) sleep, slow-wave sleep (SWS) and increases wakefulness time in humans and rodents (Gillin et al., 1994; Salin-Pascual et al., 1999). Even so, the role of nicotine and nicotine receptors in the sleep–wake cycle is complex because most of the neurotransmitter systems modified by nicotine are also implicated in sleep–wake regulation (i.e. acetylcholine, serotonin, dopamine, and norepinephrine). Different variables such as dosage, animal model, and time of administration, as well as the way in which nicotine is administered changes the manner in which sleep is modified (Salin-Pascual, 2006). In addition to its controversial effects on sleep and anxiety, nicotine has also marked effects on body weight. Nicotine markedly decreases body weight in humans and rodents (Klesges et al., 1989; Miyata et al., 1999). Conversely, nicotine withdrawal results in profound hyperphagia and body weight gain (Filozof et al., 2004). It has been proposed that classic brain neurotransmitters, such as dopamine and serotonin (5-HT) (Miyata et al., 1999; Meguid et al., 2000), as well as hypothalamic neuropeptide systems, such as agouti-related protein (AgRP) (Fornari et al., 2007), neuropeptide Y (NPY) (Frankish et al., 1995; Li et al., 2000; Fornari et al., 2007) and POMC (Huang and Winzer- Serhan, 2007) neurons in the arcuate nucleus of the hypothalamus (ARC), cocaine and amphetamine-regulated transcript (CART) neurons in the paraventricular (PVN) en dorsomedial hypothalamic nuclei (DMN) (Kramer et al., 2007) and orexin neurons in the lateral hypothalamic area (LHA) (Kane et al., 2000, 2001), may be involved in the actions of nicotine on body weight. However, the reported evidence is mainly associative and the molecular mechanisms NeuroToxicology 28 (2007) 1129–1135 * Corresponding author at: Department of Physiology, School of Medicine, University of Santiago de Compostela, S. Francisco s/n, 15705 Santiago de Compostela (A Corun ˜a), Spain. Tel.: +34 981582658; fax: +34 981574145. E-mail address: miguellp@usc.es (M. Lo ´pez). 1 These authors have contributed equally to this work. 0161-813X/$ – see front matter # 2007 Elsevier Inc. All rights reserved. doi:10.1016/j.neuro.2007.06.003