Furthermore, cocaine or HF pellet self-administration resulted in an enhanced sensitivity to low concentrations of oxA/hcrt-1 suggesting that self-administration of these highly salient reinforcers resulted in an alteration of ox/hcrt-1R coupling, or an enhancement in the signal transduction pathway in presynaptic afferents to the VTA
Furthermore, cocaine or HF pellet self-administration resulted in an enhanced sensitivity to low concentrations of oxA/hcrt-1 suggesting that self-administration of these highly salient reinforcers resulted in an alteration of ox/hcrt-1R coupling, or an enhancement in the signal transduction pathway in presynaptic afferents to the VTA. Orexin/hypocretin neurons are activated by corticotropin releasing factor (CRF) and other Rabbit Polyclonal to CSFR (phospho-Tyr699) stressful stimuli (Winsky-Sommerer et al., 2004; Boutrel and de Lecea, 2008). salient reinforcers and may represent a unique opportunity to design novel therapies that selectively reduce excessive drive to consume positive reinforcers of high salience. Introduction The ventral tegmental area (VTA) is an important brain structure for relaying salient information (Berridge, 2007), and neural plasticity of dopamine neurons in this region plays an important role in early behavioral responses following initial drug exposures (Ungless et al., 2001; Borgland et al., 2004). It has been hypothesized that strengthened excitatory synapses onto dopamine neurons leads to burst-like firing, and consequently, enhanced dopamine release in VTA target regions involved in the attachment of salience to events associated with exposure to commonly addictive drugs (Jones and Bonci, 2005). The orexins, also known as hypocretins, are neuropeptides produced in the lateral hypothalamic area that contribute to homeostatic processes such as arousal and feeding (de Lecea et al., 1998; Sakurai et al., 1998). They are comprised of two distinct peptides; orexin A/hypocretin-1 (oxA/hcrt-1) and orexin B/hypocretin-2. Orexin/hypocretin neurons project locally within the hypothalamus and widely throughout the brain, including a substantial projection to catecholaminergic regions such as the VTA and locus ceruleus (Peyron et al., 1998). Although orexin/hypocretin neurons form only 5% of synapses in the VTA, the presence of intra-VTA orexin-containing dense core vesicles (Balcita-Pedicino and Sesack, 2007) indicates that these peptides are likely released extrasynaptically into the VTA to mediate its functional effects, including increasing firing rate (Korotkova et al., 2003; Muschamps et al., 2007), strengthening AZ505 ditrifluoroacetate glutamatergic synapses (Borgland et al., 2006) and enhancing dopamine release in VTA target regions (Narita et al., 2006; Vittoz and Berridge, 2006; Vittoz et al., 2008). Activation of orexin/hypocretin neurons contributes to homeostatic processes such as arousal and feeding (de Lecea et al., 1998; Sakurai et al., 1998). Selective activation of orexin/hypocretin neurons in mice using optogenetic technology promoted the transition from sleep to wakefulness (Adamantidis et al., 2007). Furthermore, orexin/hypocretin neuronal firing, identified by antidromic stimulation from the VTA, is usually linked to movement and EEG arousal during says that have strong emotional components, such as exploratory behavior and approaching food, suggesting a potential role for these neurons in arousal for goal-directed behaviors (Mileykovskiy et al., 2005). Accordingly, intracerebroventricular (i.c.v.) injections of oxA/hcrt-1 increases home cage food intake (Sakurai et al., 1998), and activation of orexin/hypocretin-1 receptors (ox/hcrt-1R) has been shown to play a role in palatable, high-fat food intake, as the ox/hcrt-1R antagonist, SB334867 reduced home cage feeding (Clegg et al., 2002; Zheng et al., 2007) and operant self-administration of high-fat-containing food (Nair et al., 2008). Recent AZ505 ditrifluoroacetate evidence links the orexin system with reward AZ505 ditrifluoroacetate and reinforcement (Aston-Jones et al., 2009). For example, orexin/hypocretin neurons are activated when rats prefer contexts associated with addictive drugs or food (Harris et al., 2005). Further, reinstatement to cocaine (Harris et al., 2005; Boutrel et al., 2006; Smith et al., 2009) or ethanol (Lawrence et al., 2006), and the development of behavioral sensitization to cocaine (Borgland et al., 2006), is usually blocked by the ox/hcrt-1R antagonist, SB334867. We previously reported that oxA/hcrt-1 AZ505 ditrifluoroacetate enhanced excitatory synaptic transmission in the VTA and also enabled plasticity associated with cocaine (Borgland et al., 2006), suggesting an underlying mechanism for the proposed reinforcing effects of oxA/hcrt-1. Because orexin/hypocretins are known to mediate both arousal and reward, we wanted to determine whether these peptides can drive motivated behavior. We hypothesized that by blocking ox/hcrt-1R signaling, we could reduce the effort rats are willing to exert for drug and palatable food reinforcers. Materials and Methods Individually housed male Sprague Dawley rats (350C400 g; Charles River Laboratories and the University of British Columbia) were used in all experiments. Animals were maintained on a 12 h light/dark cycle (lights on 7 A.M.C7 P.M.) with food and water available unless stated below. Both behavioral experiments and decapitations for slice electrophysiology occurred at ZT = 8 1 h (3 P.M.). All animal procedures were approved by the Institutional Animal Care and Use Committee of the Ernest Gallo Clinic and Research Center and the Animal Care Centre at the University of British Columbia. Surgery. Animals were implanted with a chronically indwelling intravenous catheter and trained.