Nicotine Regulates Cocaine- Amphetamine-Regulated Transcript (Cart) in the Mesocorticolimbic System EGEMEN KAYA, 1,2 OGUZ GOZEN, 1,2 MUZEYYEN UGUR, 1 ERSIN O. KOYLU, 1,2 LUTFIYE KANIT, 1,2 AND BURCU BALKAN 1,2 * 1 Department of Physiology, School of Medicine, Ege University, Izmir, Turkey 2 Center for Brain Research, Ege University, Izmir, Turkey KEY WORDS rat; reward; brain ABSTRACT Cocaine-and-Amphetamine Regulated Transcript (CART) mRNA and peptides are intensely expressed in the brain regions comprising mesocorticolimbic system. Studies suggest that CART peptides may have a role in the regulation of reward circuitry. The present study aimed to examine the effect of nicotine on CART expression in the mesocorticolimbic system. Three different doses of nicotine (0.2, 0.4, 0.6 mg/kg free base) were injected subcutaneously for 5 days, and on day 6, rats were decapitated following a challenge dose. CART mRNA and peptide levels in medial pre- frontal cortex (mPFC), nucleus accumbens (NAc), dorsal striatum (DST), amygdala (AMG), lateral hypothalamic area (LHA), and ventral tegmental area (VTA) were measured by quantitative real-time PCR (qPCR) and Western Blot analysis, respec- tively. In the mPFC, 0.4 and 0.6 mg/kg nicotine, decreased CART peptide levels whereas there was no effect on CART mRNA levels. In the VTA, a down-regulation of CART peptide expression was observed with 0.2 and 0.6 mg/kg nicotine. Conversely, 0.4 and 0.6 mg/kg nicotine increased CART mRNA levels in the AMG without affecting the CART peptide expression. Nicotine did not regulate CART mRNA or CART peptide expression in the NAc, DST, and LHA. We conclude that nicotine regulates CART expression in the mesocorticolimbic system and this regulation may play an important role in nicotine reward. Synapse 70:283–292, 2016. V C 2016 Wiley Periodicals, Inc. INTRODUCTION The mesocorticolimbic dopamine system is regarded as the major neurochemical pathway which regulates reward (Ikemoto and Bonci, 2014). It plays a critical role in the reinforcing properties of natural rewards and drugs of abuse (Fulton, 2010; Pierce and Kumaresan, 2006). Cholinergic neurotransmission through nicotinic receptors is an important regulator of dopamine signaling in this system (Livingstone and Wonnacott, 2009). Nicotinic receptors are abun- dant in the prefrontal cortex (PFC) (Livingstone and Wonnacott, 2009), striatum (Hill et al., 1993), amyg- dala (AMG) (Hill et al., 1993; S egu ela et al., 1993), ventral tegmental area (VTA) (Klink et al., 2001), and hypothalamus (Clarke et al., 1985; Hill et al., 1993; S egu ela et al., 1993). Acute activation of nico- tinic receptors by systemic nicotine administration increases the firing rate and bursting pattern of dopamine neurons in the VTA (Grenhoff et al., 1986), enhances dopamine release in the nucleus accumbens (NAc) (Nisell et al., 1994), dorsal striatum (DST) (Janhunen and Ahtee, 2004), PFC (Rossi et al., 2005), and lateral hypothalamic area (LHA) (Zhang et al., 2001), and causes hyperlocomotion (Benwell and Bal- four, 1992). Nicotine is also reported to increase dopa- mine release from rat amygdala slices (Palotai et al., 2013). Furthermore, following repeated daily nicotine injections, sensitization of the locomotor activity and dopamine overflow in the NAc (Benwell and Balfour, 1992; Cadoni and Di Chiara, 2000; Le Foll et al., 2003), DST (Marshall et al., 1997) and PFC (Nisell et al., 1996) are observed. This sensitized response is implicated in the transition to dependence (Robinson and Berridge, 2000). Cocaine-and-Amphetamine Regulated Transcript (CART) plays an important role in the regulation of Contract grant sponsor: Ege University Research; Contract grant number: 2013-TIP-052. *Correspondence to: Burcu Balkan, Department of Physiology, School of Medicine, Ege University, Izmir 35100, Turkey. E-mail: burcubalkan69@gmail. com or burcu.balkan@ege.edu.tr Received 10 December 2015; Revised 3 March 2016; Accepted 10 March 2016 DOI: 10.1002/syn.21903 Published online 30 March 2016 in Wiley Online Library (wileyonlineli- brary.com). Ó 2016 WILEY PERIODICALS, INC. SYNAPSE 70:283–292 (2016)