Relapse-like behavior and nAChR sensitization following intermittent access nicotine self-administration

Many tobacco smokers consume nicotine intermittently, but the underlying mechanisms and neurobiological changes associated with intermittent nicotine intake are unclear. Understanding intermittent nicotine intake is a high priority, as it could promote therapeutic strategies to attenuate tobacco consumption. We examined nicotine intake behavior and neurobiological changes in male rats that were trained to self-administer nicotine during brief (5 min) trials interspersed with longer (15 min) drug-free periods. Rats readily adapted to intermittent access (IntA) SA following acquisition on a continuous access (ContA) schedule. Probabilistic analysis of IntA nicotine SA suggested reduced nicotine loading behavior compared to ContA, and nicotine pharmacokinetic modeling revealed that rats taking nicotine intermittently may have increased intake to maintain blood levels of nicotine that are comparable to ContA SA. After IntA nicotine SA, rats exhibited an increase in unreinforced responses for nicotine-associated cues (incubation of craving) and specific alterations in the striatal proteome after 7 days without nicotine. IntA nicotine SA also induced nAChR functional upregulation in the interpeduncular nucleus (IPN), and it enhanced nicotine binding in the brain as determined via [11C]nicotine positron emission tomography. Reducing the saliency of the cue conditions during the 5 min access periods attenuated nicotine intake, but incubation of craving was preserved. Together, these results indicate that IntA conditions promote nicotine SA and nicotine seeking after a nicotine-free period.

Cannabidiol effects on cocaine-seeking behaviour and incubation of craving in mice

ABSTRACTBackground and PurposeTo remain abstinent represents one of the major challenges for the treatment of cocaine use disorder. Cocaine seeking elicited by drug-associated cues progressively intensifies during abstinence in a process termed incubation of craving, representing an aggravating factor for relapse. Cannabidiol is a phytocannabinoid that exerts protecting effects upon cocaine-seeking behaviour, although its effects on cocaine-craving incubation have never been elucidated.Experimental ApproachWe developed a mouse model of behavioural economic analysis of demand curves and incubation of cue-induced cocaine craving. Changes in the protein expression of AMPAR subunits and ERK1/2 phosphorylation were analysed. We also assessed the effects of cannabidiol (20 mg·kg-1) administered either during acquisition of cocaine self-administration or abstinence.Key ResultsMice efficiently performed the demand task and incubation of cocaine craving. Besides, changes in GluA1 and GluA2 protein levels were found along the abstinence in prelimbic cortex, ventral striatum and amygdala, as well as a decrease in ERK1/2 phosphorylation in ventral striatum. Cannabidiol reduced ongoing cocaine intake when administered during the acquisition phase of the self-administration, but failed to alter the subsequent demand task performance and incubation of cocaine craving. No effects were found when cannabidiol was administered during the abstinence period.Conclusion and ImplicationsWe provide here a novel model of behavioural economic analysis of demand curves and cue-induced incubation of cocaine-seeking behaviour for mice. Moreover, we show that cannabidiol exerts differential effects on the current model depending on the self-administration phase in which it was administered.What is already knownBehavioural economics and incubation of cocaine craving are well-stablished paradigms to evaluate cocaine seeking in rats.CBD reduces cocaine-seeking and cocaine-taking behaviours.What this study addsA mouse model of behavioural economic analysis of demand curves and incubation of cue-induced cocaine craving.CBD reduces cocaine self-administration and has no effect over demand task and cocaine-craving incubation.Clinical significanceA new behavioural model for studying cocaine addiction in mice.CBD exerts differential effects depending on when it was administered in the addictive process.Tables of Links

Abstinence-dependent dissociable central amygdala microcircuits control drug craving

We recently reported that social choice-induced voluntary abstinence prevents incubation of methamphetamine craving in rats. This inhibitory effect was associated with activation of protein kinase-Cδ (PKCδ)-expressing neurons in central amygdala lateral division (CeL). In contrast, incubation of craving after forced abstinence was associated with activation of CeL-expressing somatostatin (SOM) neurons. Here we determined the causal role of CeL PKCδ and SOM in incubation using short-hairpin RNAs against PKCδ or SOM that we developed and validated. We injected two groups with shPKCδ or shCtrlPKCδinto CeL and trained them to lever press for social interaction (6 d) and then for methamphetamine infusions (12 d). We injected two other groups with shSOM or shCtrlSOMinto CeL and trained them to lever press for methamphetamine infusions (12 d). We then assessed relapse to methamphetamine seeking after 1 and 15 abstinence days. Between tests, the rats underwent either social choice-induced abstinence (shPKCδ groups) or homecage forced abstinence (shSOM groups). After test day 15, we assessed PKCδ and SOM, Fos, and double-labeled expression in CeL and central amygdala medial division (CeM). shPKCδ CeL injections decreased Fos in CeL PKCδ-expressing neurons, increased Fos in CeM output neurons, and reversed the inhibitory effect of social choice-induced abstinence on incubated drug seeking on day 15. In contrast, shSOM CeL injections decreased Fos in CeL SOM-expressing neurons, decreased Fos in CeM output neurons, and decreased incubated drug seeking after 15 forced abstinence days. Our results identify dissociable central amygdala mechanisms of abstinence-dependent expression or inhibition of incubation of craving.