Evidence of individual differences in motives for nicotine seeking in classical nicotine self-administration and associated outcomes of varenicline administration

Background Smokers vary in their motives for tobacco seeking, suggesting that they could benefit from personalized treatments. However, these variations have received little attention in animal models for the study of tobacco dependence. In the most classically used model, ie. intravenous self-administration of nicotine in the rat, seeking behaviour is reinforced by the combination of intravenous nicotine with a discrete stimulus (eg. discrete cue light). In both human and animals, two types of psychopharmacological interactions between nicotine and environmental stimuli have been evidenced. Whether these two types of interactions contribute equally to nicotine seeking in all individuals is unknown. Methods We combined behavioural pharmacology and clustering analysis. In an outbred male rat population, we tested whether nicotine and the discrete nicotine-associated cue light contributed equally to self-administration in all individuals. Two clusters of rats were identified, in which we further studied the nature of the psychopharmacological interaction between nicotine and the cue, as well as the response to the cessation aid varenicline when nicotine was withdrawn. Results Notably, withdrawing nicotine produced drastic opposed effects on seeking behavior in the two identified clusters of rats; a 50% increase vs a 18% decrease, respectively. The first cluster of rats sought for the primary reinforcing effects of nicotine and the discrete cue light that has gained nicotine-like secondary reinforcing properties. The second cluster sought nicotine for its ability to enhance the primary reinforcing effects of the discrete cue light. Critically, the approved cessation aid Varenicline counteracted the absence of nicotine in both, but eventually decreasing seeking in the former but increasing it in the latter. Conclusions Classical rodent models for the study of the reinforcing and addictive effects of nicotine hide individual variations in the psychopharmacological motives supporting seeking behavior. These variations may be a decisive asset for improving their predictive validity in the perspective of precision medicine for smoking cessation.

A natural antisense to brain-derived neurotrophic factor impairs extinction of drug seeking

ABSTRACTBACKGROUNDBrain derived neurotrophic factor (BDNF) is critical for the extinction of drug-seeking. Expression of the Bdnf gene is highly regulated via interactions with non-coding RNA, which themselves are altered following drug exposure. Here we investigate whether a novel long non-coding RNA antisense to Bdnf prevents extinction of drug-seeking. METHODS: Strand-specific RNA sequencing identified a novel long non-coding RNA antisense to exon IV of the Bdnf gene in the ventromedial prefrontal cortex of 8 adult male rats. We then assessed asBdnf-IV expression using strand-specific reverse transcription and quantitative polymerase chain reaction following acquisition, extinction or abstinence from intravenous nicotine self-administration (N = 116). A functional role of the asBdnf-IV in extinction of nicotine-seeking was established by infusing gapmer oligonucleotides into the infralimbic cortex prior to extinction and testing for the effect of these infusions on reinstatement and reacquisition of nicotine-seeking (N = 36).RESULTSRNA sequencing identified the presence of a novel long non-coding RNA antisense to exon IV of the Bdnf gene (asBdnf-IV). Expression of asBdnf-IV was elevated following intravenous nicotine self-administration but not experimenter-administered nicotine. Elevated asBdnf-IV persisted across abstinence and to a greater extent following extinction training, suggesting an interaction between abstinence and extinction learning. In support of this, knockdown of the asBdnf-IV across extinction, but not abstinence, significantly attenuated nicotine-primed reinstatement of nicotine-seeking.CONCLUSIONSasBdnf-IV accumulates in the infralimbic cortex across self-administration training, interferes with the inhibitory learning that underpins extinction of drug-seeking, and predisposes animals to drug relapse.

Acute effects of inhaled menthol on the rewarding effects of intravenous nicotine in smokers

Objective: This double-blind, placebo controlled study examined whether menthol inhaled from an electronic cigarette (e-cigarette) would change subjective and withdrawal alleviating effects of intravenous nicotine in young adult smokers. Methods: A total of 32 menthol-preferring smokers and 25 non-menthol-preferring smokers participated in the study that consisted of a random sequence of three different inhaled menthol conditions (0.0%, 0.5%, and 3.2%) across three test sessions (a single menthol condition per session). In each test session (performed at least 24 hours apart), a random order of saline, and two different nicotine infusions of 0.25 mg and 0.5 mg/70 kg of bodyweight were administered, one hour apart, concurrent with menthol inhalation. Results: While menthol did not alter the positive subjective effects of nicotine, menthol significantly enhanced aversive effects of nicotine in non-menthol-preferring smokers and reduced smoking urges in menthol-preferring smokers. In addition, menthol-preferring smokers reported blunted positive subjective responses to nicotine and less severe nicotine withdrawal after overnight nicotine deprivation. Finally, compared to non-menthol-preferring smokers, menthol-preferring smokers had a significantly lower baseline nicotine metabolite ratio indicating slower nicotine metabolism within our sample of menthol-preferring smokers. Conclusions: Our findings did not support an enhancement of nicotine’s positive subjective effects from inhaled menthol. However, as compared to non-menthol-preferring smokers, menthol-preferring smokers had blunted positive subjective responses to nicotine and reduced overnight withdrawal severity that may be partly due to inhibition of nicotine metabolism from chronic exposure to inhaled menthol. Collectively, these results reveal a more complex and nuanced role of inhaled menthol in smokers than previously recognized.