Although norepinephrine (NE) does not typically modulate cocaine self-administration under traditional schedules of reinforcement it is required for different inducers of the reinstatement of cocaine-seeking behavior via activation of multiple adrenergic receptor subtypes. saline. Yohimbine (2.5?mg/kg) was purchased from Sigma and dissolved in distilled water. Food Training All rats were trained to lever-press for food on a fixed-ratio 1 (FR1) schedule in standard rat operant chambers (Med Associates St Albans VT) before exposure to drug to facilitate acquisition of drug self-administration as described (Schroeder tests when comparing more than two groups using Prism 6.0 for Macintosh. RESULTS Nepicastat Dose-Dependently Attenuates Novelty-Induced Locomotor Activity We showed before that nepicastat at a dose (50?mg/kg) that reduces brain NE levels by ～40% prevents drug-primed reinstatement of cocaine seeking but not food-primed reinstatement of food seeking (Schroeder tests showed a significant difference between vehicle and the high dose of nepicastat during the first 10?min of the test (tests showed that cues significantly reinstated active lever responding compared with extinction levels in both the vehicle and nepicastat groups but that nepicastat significantly reduced active lever pressing during reinstatement compared with vehicle. No differences in inactive lever pressing were found. Figure 3 Nepicastat attenuates cue-induced reinstatement of Baricitinib (LY3009104) cocaine seeking. Once maintenance and extinction criteria for operant self-administration were met rats (tests showed that footshock significantly reinstated active lever responding compared with extinction levels in the vehicle but not in the nepicastat group and that nepicastat significantly reduced active lever pressing during reinstatement compared with vehicle. No differences in inactive lever pressing were found although there was a trend for increased responding during reinstatement that was reduced by nepicastat. Figure 4 Nepicastat blocks footshock-induced reinstatement. Once maintenance and extinction criteria for operant self-administration were met rats (tests showed that yohimbine Rabbit Polyclonal to TRXR2. significantly reinstated active lever responding compared with extinction levels in the vehicle but not in the nepicastat group and that nepicastat significantly reduced active lever pressing during reinstatement compared with vehicle. There was also a trend for increased inactive lever Baricitinib (LY3009104) responding during reinstatement and a significant difference in inactive lever presses between the vehicle and the nepicastat groups. Figure 5 Nepicastat blocks yohimbine-induced reinstatement. Once maintenance and extinction criteria for operant self-administration were met rats (antagonists to impair cue-induced reinstatement (Smith and Aston-Jones 2011 we hypothesized that nepicastat would block all forms of reinstatement. As predicted nepicastat either eliminated (footshock Baricitinib (LY3009104) yohimbine) or attenuated (cue) the ability of these distinct triggers to precipitate cocaine-seeking behavior. This is in line with the clinical finding that clonidine which activates α2-adrenergic autoreceptors and decreases NE release reduces cue- and stress-induced craving in human addicts (Jobes et al 2011 The mechanism by which nepicastat blocks yohimbine-induced reinstatement is unclear. Yohimbine was originally believed to precipitate reinstatement by blocking α2-adrenergic autoreceptors and increasing NE release but recent studies indicate that yohimbine-induced reinstatement appears to be independent of NE and the related stress hormone CRF in rats (Brown et al Baricitinib (LY3009104) 2009 The only partial reduction of cue-induced reinstatement could be the result of incomplete DBH inhibition as Baricitinib (LY3009104) the dose of nepicastat we used decreases brain NE levels by ～40% (Schroeder et al 2010 and testing a higher dose would be confounded by non-specific effects on motor activity (see Figure 1). However because even relatively high doses of α1AR+βAR antagonists that likely occlude nearly all noradrenergic transmission also only partially impair cue-induced reinstatement we favor the idea that this form of reinstatement does not depend completely on NE signaling. It is Baricitinib (LY3009104) well established that cue-induced reinstatement involves several other neurotransmitter systems and circuits that may not be engaged by NE in this paradigm (James et al 2011 Mahler et al 2012 See.