Effects of chronic nicotine, nicotine withdrawal and subsequent nicotine challenges on behavioural inhibition in rats

Effect of chronic vapor nicotine exposure on affective and cognitive behavior in male mice

Nicotine use is a leading cause of preventable deaths worldwide, and most of those who attempt to quit will relapse. While electronic cigarettes and other electronic nicotine delivery systems (ENDS) were presented as a safer alternative to traditional cigarettes and promoted as devices to help traditional tobacco smokers reduce or quit smoking, they have instead contributed to increasing nicotine use among youths. Despite this, ENDS also represent a useful tool to create novel preclinical animal models of nicotine exposure that more accurately represent human nicotine use. In this study, we validated a chronic, intermittent, ENDS-based passive vapor exposure model in mice, and then measured changes in multiple behaviors related to nicotine abstinence. First, we performed a behavioral dose curve to investigate the effects of different nicotine inter-vape intervals on various measures including body weight, locomotor activity, and pain hypersensitivity. Next, we performed a pharmacokinetic study to measure plasma levels of nicotine and cotinine following chronic exposure for each inter-vape interval. Finally, we utilized a behavior test battery at a single dosing regimen that produces blood levels equivalent to human smokers in order to characterize the effects of chronic nicotine, vehicle, or passive airflow and identified nicotine-induced impairments in cognitive behavior.

Effect of chronic vapor nicotine exposure on affective and cognitive behavior in male mice

Nicotine use is a leading cause of preventable deaths worldwide, and most of those who attempt to quit will relapse. While electronic cigarettes and other electronic nicotine delivery systems (ENDS) were presented as a safer alternative to traditional cigarettes and promoted as devices to help traditional tobacco smokers reduce or quit smoking, they have instead contributed to increasing nicotine use among youths. Despite this, ENDS also represent a useful tool to create novel preclinical animal models of nicotine exposure that more accurately represent human nicotine use. In this study, we validated a chronic, intermittent, ENDS-based passive vapor exposure model in mice, and then measured changes in multiple behaviors related to nicotine abstinence. First, we performed a behavioral dose curve to investigate the effects of different nicotine inter-vape intervals on various measures including body weight, locomotor activity, and pain hypersensitivity. Next, we performed a pharmacokinetic study to measure plasma levels of nicotine and cotinine following chronic exposure for each inter-vape interval. Finally, we utilized a behavior test battery at a single dosing regimen that produces blood levels equivalent to human smokers in order to characterize the effects of chronic nicotine, vehicle, or passive airflow and identified nicotine-induced impairments in cognitive behavior.

Differences in attentional bias to smoking-related, affective, and sensation-seeking cues between smokers and non-smokers: an eye-tracking study

RATIONALE

One of the behavioural features of tobacco use disorder is the presence of attentional bias (AB) to smoking-related stimuli. However, much of the research investigating these associations have been limited to the use of reaction-based indices.

OBJECTIVES

We aimed to investigate differences in AB to smoking, affective, and sensation-seeking cues in smokers and non-smokers using novel, free-viewing, eye-tracking technology. Secondary aims included investigating impulsivity-by-group interaction effects on AB to sensation-seeking cues.

METHODS

Participants were either otherwise-healthy smokers of at least 8 cigarettes per day or otherwise-healthy non-smokers (< 100 cigarettes in their lifetime and no smoking in the past year). AB was measured using a free-viewing, eye-tracking system. Participants were presented a series of slides divided into 3 themes: smoking, affective, and sensation-seeking. Each slide contained 4 images (1 theme-related, 1 neutral, 2 competitive). Primary outcome measure was the difference in the proportion of time spent viewing the theme-related cue to neutral cue. Impulsivity was measured using a monetary delayed discounting task.

RESULTS

The sample consisted of 50 smokers (41 ± 12 years old) and 50 age- and sex-matched non-smokers (40 ± 14 years old). Smokers spent over 2 times longer looking at smoking-related images than non-smokers (F = 25.50, p < 0.001). As well, greater impulsivity was significantly associated with increased AB to sensation-seeking cues (R² = 0.059, F = 2.98, p = 0.04) in smokers but not non-smokers. No differences were found on AB to affective cues.

CONCLUSION

The eye-tracking procedure is a sensitive tool for assessing AB in smokers compared to non-smokers to both smoking and sensation-seeking cues.

Prolonged Peripheral Immunosuppressive Responses as Consequences of Random Amphetamine Treatment, Amphetamine Withdrawal and Subsequent Amphetamine Challenges in Rats

Drug-induced immunosuppression may underline increased hypothalamic-pituitary-adrenal axis response to stress observed following chronic psychostimulant treatment. However, the consequences of random amphetamine (AMPH) treatment, withdrawal and AMPH challenge after withdrawal on the peripheral immunity and systemic corticosterone response are unknown. In this study, the total blood and spleen leukocyte, lymphocyte, T, B, NK, TCD4+/TCD8+ cell numbers and ratio, pro-inflammatory interferon gamma (IFN-γ), and anti-inflammatory interleukin-4 (IL-4) production, and plasma corticosterone concentration in Wistar rats were investigated after: chronic, random AMPH/SAL treatment alone (20 injections in 60 days, 1 mg/kg b.w., i.p.), AMPH/SAL withdrawal (for 20 consecutive days after random AMPH/SAL exposure) or AMPH/SAL challenge after withdrawal (single injection after the AMPH/SAL withdrawal phase). The results showed blood and spleen leukopenia, lymphopenia, lower blood production of IFN-ɤ, and increased plasma corticosterone concentration after the AMPH treatment, which were more pronounced in the AMPH after withdrawal group. In contrast, an increased number of blood NK cells and production of IL-4 after chronic, random AMPH treatment alone, were found. Blood AMPH-induced leukopenia and lymphopenia were due to decreased total number of T, B lymphocytes and, at least in part, of granulocytes and monocytes. Moreover, decreases in the number of blood TCD4+ and TCD8+ lymphocytes both in the AMPH chronic alone and withdrawal phases, were found.The major findings of this study are that AMPH treatment after the long-term withdrawal from previous random AMPH exposure, accelerates the drug-induced immunosuppressive and systemic corticosterone responses, suggesting prolonged immunosuppressive effects and an increase in incidence of infectious diseases. Prolonged peripheral immunosuppressive responses as consequences of random amphetamine…The results indicate that the chronic and random AMPH exposure alone and the acute (single injection) challenge of the drug after the withdrawal phase induced long-term immunosuppressive effects, which were similar to those occurring during the stress response, and sensitized the peripheral immunosuppressive and corticosterone responses of the rat to the disinhibitory effects of this stressor.

Effects of substance misuse on reward-processing in patients with attention-deficit/hyperactivity disorder

Attention-Deficit/Hyperactivity Disorder (ADHD) and Substance Use Disorder (SUD) often co-occur and are associated with treatment resistance. Both disorders are characterized by similar reward-processing deficits with decreased striatal responses to reward anticipation, though literature is inconsistent. It is unclear whether substance misuse exaggerates reward-processing deficits observed in ADHD. The aim of this study was to examine substance misuse effects on reward-processing in ADHD. Functional MRI data in a Monetary Incentive Delay (MID) task from a multi-site study were compared across ADHD groups with and without substance misuse (ADHD + SM and ADHD-only, respectively) and healthy controls (n = 40/group, 74 males and 46 females, aged 13.7-25.9 years). Substance misuse was defined as misuse of alcohol, nicotine, or drugs. Groups were matched with presence/absence of parental SUD to avoid interference with SUD trait effects. Compared to ADHD-only and controls, ADHD + SM showed hyperactivation in putamen during reward anticipation. Compared to controls, the ADHD groups showed hypoactivation in motor/sensory cortices and hyperactivation in frontal pole and OFC during reward outcome. ADHD + SM also showed hyperactivation in frontal pole during neutral outcome. Moreover, ADHD + SM patients showed higher callous-unemotional (CU) traits that were positively correlated with putamen responses to reward anticipation. Our results show distinct condition-independent neural activation profile for ADHD + SM compared to ADHD-only and controls. Effects of comorbid substance misuse and variability of its prevalence across ADHD studies might have contributed to inconsistencies in ADHD literature. Contrasted with findings for reward-processing in SUD literature, results potentially suggest distinct underlying mechanisms for SUD subgroups with different characteristics, like antisocial/psychopathic traits.

Disentangling the effects of cannabis and cigarette smoking on impulsivity

BACKGROUND

Cannabis smoking and cigarette smoking often co-occur, yet limited research has investigated the potentially different role impulsivity may play when these behaviours occur in isolation, compared with in combination.

AIMS

This study examined trait and behavioural impulsivity as a function of both cigarette and cannabis smoking.

METHODS

Trait impulsivity (BIS-11) was compared between 44 non-smokers, 76 cigarette only, 47 cannabis only and 58 cannabis plus cigarette smokers. The effects of cigarette and cannabis smoking on behavioural impulsivity (stop-signal and information sampling tasks) were then assessed in 87 of these participants during a laboratory session.

RESULTS

Trait impulsivity was significantly higher in cigarette smokers than non-smokers, irrespective of cannabis use, except for motor impulsivity, where cigarette smoking was only associated with elevated trait impulsivity in non-smokers of cannabis. Dimensions of trait impulsivity were significantly positively related to cigarette smoking frequency and nicotine dependence, but not to cannabis smoking frequency or dependence. Smoking cigarettes or cannabis was associated with significantly impaired reflection impulsivity relative to not smoking either substance. However, no additional increases in reflection impulsivity were observed in those who smoked both cigarettes and cannabis. No group differences in response inhibition were detected.

CONCLUSIONS

Heightened trait impulsivity appears to be uniquely related to cigarette smoking, whilst the smoking of cigarettes or cannabis is associated with impairments in reflection impulsivity. Improved outcomes for treating cannabis dependence may result from encouraging concomitant cigarette smokers to cease using both drugs simultaneously in order to reduce heightened impulsivity and risk of relapse.

Cognitive rigidity and BDNF-mediated frontostriatal glutamate neuroadaptations during spontaneous nicotine withdrawal

Cognitive flexibility is the ability to switch strategic responses adaptively in changing environments. Cognitive rigidity imposed by neural circuit adaptations during nicotine abstinence may foster maladaptive nicotine taking in addicts. We systematically examined the effects of spontaneous withdrawal in mice exposed to either nicotine (6.3 or 18 mg/kg/day) or saline for 14 days on cognitive flexibility using an operant strategy set-shifting task. Because frontostriatal circuits are critical for cognitive flexibility and brain-derived neurotrophic factor (BDNF) modulates glutamate plasticity in these circuits, we also explored the effects of nicotine withdrawal on these neurochemical substrates. Mice undergoing nicotine withdrawal required more trials to attain strategy-switching criterion. Error analysis show that animals withdrawn from both nicotine doses committed higher perseverative errors, which correlated with measures of anxiety. However, animals treated with the higher nicotine dose also displayed more strategy maintenance errors that remained independent of negative affect. BDNF mRNA expression increased in the medial prefrontal cortex (mPFC) following nicotine withdrawal. Surprisingly, BDNF protein declined in mPFC but was elevated in dorsal striatum (DS). DS BDNF protein positively correlated with perseverative and maintenance errors, suggesting mPFC-DS overflow of BDNF during withdrawal. BDNF-evoked glutamate release and synapsin phosphorylation was attenuated within DS synapses, but enhanced in the nucleus accumbens, suggesting a dichotomous role of BDNF signaling in striatal regions. Taken together, these data suggest that spontaneous nicotine withdrawal impairs distinct components of cognitive set-shifting and these deficits may be linked to BDNF-mediated alterations in glutamate signaling dynamics in discrete frontostriatal circuits.

Adolescent and adult nicotine exposure differentially impacts oral nicotine and oral saccharin self-administration in mice

Smokers that begin during adolescence are more likely to develop nicotine dependence than those who begin as adults. However, the factors that contribute to this remain largely unknown. Here we utilized a novel operant oral nicotine self-administration procedure in mice to assess the consequences of adolescent nicotine exposure on nicotine and saccharin (non-drug) reinforcement in adults. Animals were given non-contingent exposure to either saline or nicotine using the osmotic minipumps during both adolescence and adulthood for 2 weeks. Reinforcing efficacy for oral nicotine and saccharin was assessed using the progressive ratio schedule 2-weeks following the washout period in adults. Non-contingent nicotine exposure in adolescence drastically increased operant responding for oral nicotine but reduced responding for oral saccharin in the group re-exposed to nicotine in adulthood. Interestingly, adolescent nicotine-exposed mice that received saline exposure as adults exhibited higher preference for oral saccharin. However, breakpoints for oral nicotine in these mice remained comparable to control animals. Surprisingly, both adolescent and adult nicotine exposure increased inactive lever responding during self-administration presumably reflecting impulsive responding. Our data suggest that adolescent nicotine exposure produces an increase in reinforcement sensitivity in adulthood as reflected by increased saccharin self-administration but this sensitivity becomes biased towards nicotine self-administration when re-exposed to nicotine in adulthood. Moreover, nicotine/saccharin reinforcement could be impacted by changes in cognitive control, such as increased impulsivity. These distinct behavioral mechanisms may act in concert to facilitate maladaptive nicotine taking in smokers that initiate nicotine use during adolescence.

Performance monitoring in nicotine dependence: Considering integration of recent reinforcement history

INTRODUCTION

Impaired monitoring of errors and conflict (performance monitoring; PM) is well documented in substance dependence (SD) including nicotine dependence and may contribute to continued drug use. Contemporary models of PM and complementary behavioural evidence suggest that PM works by integrating recent reinforcement history rather than evaluating individual behaviours. Despite this, studies of PM in SD have typically used indices derived from reaction to task error or conflict on individual trials. Consequently impaired integration of reinforcement history during action selection tasks requiring behavioural control in SD populations has been underexplored.

METHODS

A reinforcement learning task assessed the ability of abstinent, satiated, former and never smokers (N=60) to integrate recent reinforcement history alongside a more typical behavioural index of PM reflecting the degree of reaction time slowing following an error (post-punishment slowing; PPS).

RESULTS

On both indices there was a consistent pattern in PM data: Former smokers had the greatest and satiated smokers the poorest PM. Specifically satiated smokers had poorer reinforcement integration than former (p=0.005) and never smokers (p=0.041) and had less post-punishment slowing than former (p<0.001), never (p=0.003) and abstinent smokers (p=0.026).

CONCLUSIONS

These are the first data examining the effects of smoking status on PM that use an integration of reinforcement history metric. The concordance of the reinforcement integration and PPS data suggest that this could be a promising method to interrogate PM in future studies. PM is influenced by smoking status. As PM is associated with adapting behaviour, poor PM in satiated smokers may contribute towards continued smoking despite negative consequences. Former smokers show elevated PM suggesting this may be a good relapse prevention target for individuals struggling to remain abstinent however prospective and intervention studies are needed. A better understanding of PM deficits in terms of reinforcement integration failure may stimulate development of novel treatment approaches.

Contributions of β2 subunit-containing nAChRs to chronic nicotine-induced alterations in cognitive flexibility in mice

RATIONALE

Deficits in executive functions underlie compulsive drug use, and understanding how nicotine influences these cognitive processes may provide important information on neurobiological substrates of nicotine addiction. Accumulating evidence suggests that β2 subunit-containing nicotinic receptors (nAChRs) are involved in the reinforcing process of nicotine addiction. Whether these nAChRs also contributes to the detrimental effects of chronic nicotine on flexible decision-making is not known.

OBJECTIVES

In the present study, the effects of chronic nicotine were assessed in mice with partial or complete deletion of the β2 subunit-containing nAChR gene (β2+/- or β2-/-) performing an operant cognitive flexibility task.

RESULTS

Visual discrimination learning was not affected in saline-treated β2 nAChR mutants as compared to the wild-type (β2+/+) mice; yet, chronic nicotine facilitated acquisition of visual discrimination in all genotypes. The acquisition of new egocentric response strategy set-shifting remained similar in all genotypes, and there was no effect of treatment. Chronic nicotine treatment impaired reversal learning in β2+/+ mice by increasing response perseveration to the previously rewarded stimulus. Moreover, the acquisition of inverted stimulus-reward contingencies did not differ between β2+/+ and β2-/- mice exposed to chronic nicotine. Interestingly, nicotine-induced reversal learning deficits were not observed in β2+/- mice.

CONCLUSIONS

Collectively, these findings suggest that β2 subunit-containing nAChRs are not critical for visual discrimination learning and extra dimensional rule shift. However, sustained activation of these nAChRs with nicotine may interfere with inhibitory control processes influencing affective shifts in stimulus-reward contingencies.

Smoking abstinence and neurocognition: implications for cessation and relapse

In this chapter, we review the last decade of research on the effects of smoking abstinence on various forms of neurocognition, including executive function (working memory, sustained attention, response inhibition), reward processing, and cue-reactivity. In our review we identify smoking abstinence-induced deficits in executive function mediated by effects on frontal circuitry, which in turn is known to be affected by modulation of cholinergic, dopaminergic, and other neurotransmitter systems. We also review evidence that smoking abstinence blunts reactivity to non-drug reinforcers-a finding that is consistent with results in the animal literature. Finally, our review of cue-reactivity indicates that smoking abstinence does not appear to amplify cue-provoked craving, although it may increase attentional bias to smoking-related cues. Inconsistencies across findings and potential contributing factors are discussed. In addition, we review the literature on the effects of nicotine and non-nicotine factors in neurocognition. Finally, we provide a multi-factor model and an agenda for future research on the effects of smoking abstinence on neurocognition. The model includes four distinct yet interacting factors, including: Negative Reinforcement, Drug-Reward Bias, Goal and Skill Interference, and Non-Cognitive Factors. Additional research is needed to further evaluate the scope and time-course of abstinence-induced changes in neurocognition, the mechanisms that underlie these changes and the specific role of these processes in drug reinforcement, lapse, and relapse.

Nicotine exposure and transgenerational impact: a prospective study on small regulatory microRNAs

Early developmental stages are highly sensitive to stress and it has been reported that pre-conditioning with tobacco smoking during adolescence predisposes those youngsters to become smokers as adults. However, the molecular mechanisms of nicotine-induced transgenerational consequences are unknown. In this study, we genome-widely investigated the impact of nicotine exposure on small regulatory microRNAs (miRNAs) and its implication on health disorders at a transgenerational aspect. Our results demonstrate that nicotine exposure, even at the low dose, affected the global expression profiles of miRNAs not only in the treated worms (F0 parent generation) but also in two subsequent generations (F1 and F2, children and grandchildren). Some miRNAs were commonly affected by nicotine across two or more generations while others were specific to one. The general miRNA patterns followed a “two-hit” model as a function of nicotine exposure and abstinence. Target prediction and pathway enrichment analyses showed daf-4, daf-1, fos-1, cmk-1, and unc-30 to be potential effectors of nicotine addiction. These genes are involved in physiological states and phenotypes that paralleled previously published nicotine induced behavior. Our study offered new insights and further awareness on the transgenerational effects of nicotine exposed during the vulnerable post-embryonic stages, and identified new biomarkers for nicotine addiction.

Trait differences in response to chronic nicotine and nicotine withdrawal in rats

INTRODUCTION

Understanding an individual's vulnerability to drug addiction has important implications for the development of effective personal treatment plans. Although theories acknowledge impulsive behaviour as a key component of drug addiction, little is known about the influence of trait impulsivity on an individual's susceptibility to the effects of psychostimulants on impulsivity at critical phases of the addiction cycle.

METHODS

This study investigated the short and longer-term effects of chronic nicotine administration on impulsive choice in rats selected for high (HI) and low impulsivity (LI) on a delay discounting task. Rats prepared with subcutaneously osmotic mini-pumps received either nicotine (3.16 mg/kg/day [freebase]) or saline for 7 days. Performance was assessed during chronic treatment, early and late withdrawal, and in response to acute nicotine challenges following prolonged abstinence.

RESULTS

Chronic nicotine increased impulsive choice in LI but not HI animals. Spontaneous withdrawal was associated with a nicotine abstinence syndrome, the early stages of which were characterised by opposing effects on impulsive choice in HI and LI animals. A transient decrease in impulsivity was observed in HI animals whilst the LI group remained more impulsive for up to 1 week following drug termination. Following normalisation of behaviour, acute nicotine challenges (0.125, 0.25, 0.5 mg/kg, SC) markedly increased impulsive choice regardless of trait impulsivity and drug history.

CONCLUSION

The results indicate that only LI individuals are vulnerable to chronic drug- and withdrawal-induced impairments in self-control which may increase the likelihood of the transition to, and maintenance of, nicotine dependence.

Cognitive function during nicotine withdrawal: Implications for nicotine dependence treatment

Nicotine withdrawal is associated with deficits in neurocognitive function including sustained attention, working memory, and response inhibition. Several convergent lines of evidence suggest that these deficits may represent a core dependence phenotype and a target for treatment development efforts. A better understanding of the mechanisms underlying withdrawal-related cognitive deficits may lead to improve nicotine dependence treatment. We begin with an overview of the neurocognitive effects of withdrawal in rodent and human models, followed by discussion of the neurobehavioral mechanisms that are thought to underlie these effects. We then review individual differences in withdrawal-related neurocognitive effects including genetics, gender, and psychiatric comorbidity. We conclude with a discussion of the implications of this research for developing improved therapies, both pharmacotherapy and behavioral treatments, that target cognitive symptoms of nicotine withdrawal. This article is part of a Special Issue entitled 'NIDA 40th Anniversary Issue'.