Meta-analysis of the acute effects of nicotine and smoking on human performance

Varenicline potentiates alcohol-induced negative subjective responses and offsets impaired eye movements

BACKGROUND

Varenicline (VAR) is a partial nicotinic receptor agonist that is an effective smoking cessation medication. Preliminary evidence indicates that it may also reduce alcohol consumption, but the underlying mechanism is not clear. For example, VAR may reduce alcohol consumption by attenuating its subjectively rewarding properties or by enhancing its aversive effects. In this study, we examined the effects of an acute dose of VAR upon subjective, physiological, and objective responses to low and moderate doses of alcohol in healthy social drinkers.

METHODS

Healthy men and women (N = 15) participated in 6 randomized sessions; 3 sessions each with 2 mg VAR and placebo (PL) followed 3 hours later by a beverage containing PL, low-dose alcohol (0.4 g/kg), or high-dose alcohol (0.8 g/kg). Subjective mood and drug effects (i.e., stimulation, drug liking), physiological measures (heart rate, blood pressure), and eye tracking tasks were administered at various intervals before and after drug and alcohol administration.

RESULTS

VAR acutely increased blood pressure, heart rate, ratings of dysphoria and nausea, and also improved eye tracking performance. After alcohol drinking (vs. PL), VAR increased dysphoria and tended to reduce alcohol liking ratings. It also attenuated alcohol-induced eye-tracking impairments. These effects were independent of the drug's effects on nausea before drinking.

CONCLUSIONS

Our data support the theory that VAR may reduce drinking by potentiating aversive effects of alcohol. VAR also offsets alcohol-induced eye movement impairment. The evidence suggests that VAR may decrease alcohol consumption by producing effects, which oppose the rewarding efficacy of alcohol.

Effects of varenicline and bupropion on cognitive processes among nicotine-deprived smokers

Nicotine deprivation is associated with craving, negative affect, and difficulty concentrating, which may contribute to subsequent relapse. Bupropion and varenicline are both effective treatments for smoking cessation, and evidence from clinical trials suggests that these treatments increase abstinence rates. However, the mechanism by which these medications reduce relapse remains unclear. Recent research has focused on cognitive processes, such as attention and working memory, which may predict relapse. In addition, there may also be sex differences in cognitive-related deficits during nicotine deprivation. The current sample consisted of 58 (22 females) daily smokers (at least 10 cigarettes per day) randomized to receive bupropion (300 mg/day), varenicline (2 mg/day), or placebo. After a 1-week run-up phase, participants completed a 9.5-hr laboratory session after overnight abstinence (CO verified). Participants completed measures of attention (Conners' Continuous Performance Task [CPT]), working memory (digits backward), and delay discounting. Measures of craving, withdrawal, and mood were also collected. Between-subjects ANCOVA models revealed that varenicline speeded reaction time, but reduced accuracy on the CPT compared with placebo. Sex moderated the effect of bupropion compared with placebo on working memory and delay discounting. Bupropion enhanced working memory for females but not males, and this pattern was reversed for delay discounting. The current data highlight the complex processes associated with nicotine deprivation and the need for future research to examine whether cognitive-related deficits are related to relapse. Identifying these mechanisms may help in the development of new pharmacological treatments.

Resting state functional connectivity in addiction: Lessons learned and a road ahead

Despite intensive scientific investigation and public health imperatives, drug addiction treatment outcomes have not significantly improved in more than 50 years. Non-invasive brain imaging has, over the past several decades, contributed important new insights into the neuroplastic adaptations that result from chronic drug intake, but additional experimental approaches and neurobiological hypotheses are needed to better capture the totality of the motivational, affective, cognitive, genetic and pharmacological complexities of the disease. Recent advances in assessing network dynamics through resting-state functional connectivity (rsFC) may allow for such systems-level assessments. In this review, we first summarize the nascent addiction-related rsFC literature and suggest that in using this tool, circuit connectivity may inform specific neurobiological substrates underlying psychological dysfunctions associated with reward, affective and cognitive processing often observed in drug addicts. Using nicotine addiction as an exemplar, we subsequently provide a heuristic framework to guide future research by linking recent findings from intrinsic network connectivity studies with those interrogating nicotine's neuropharmacological actions. Emerging evidence supports a critical role for the insula in nicotine addiction. Likewise, the anterior insula, potentially together with the anterior cingulate cortex, appears to pivotally influence the dynamics between large-scale brain networks subserving internal (default-mode network) and external (executive control network) information processing. We suggest that a better understanding of how the insula modulates the interaction between these networks is critical for elucidating both the cognitive impairments often associated with withdrawal and the performance-enhancing effects of nicotine administration. Such an understanding may be usefully applied in the design and development of novel smoking cessation treatments.

Nicotinic receptors in the dorsal and ventral hippocampus differentially modulate contextual fear conditioning

Nicotine administration alters various forms of hippocampus-dependent learning and memory. Increasing work has found that the dorsal and ventral hippocampus differentially contribute to multiple behaviors. Thus, the present study examined whether the effects of nicotine in the dorsal and ventral hippocampus have distinct influences on contextual fear learning in male C57BL/6J mice. Direct infusion of nicotine into the dorsal hippocampus resulted in an enhancement of contextual fear learning, whereas nicotine infused into the ventral hippocampus resulted in deficits. Nicotine infusions into the ventral hippocampus did not alter hippocampus-independent cued fear conditioning or time spent in the open arm of the elevated plus maze, a measure of anxiety, suggesting that the effects are due to alterations in contextual learning and not other general processes. Finally, results from using direct infusions of MLA, a low-affinity α7 nicotinic acetylcholine receptor (nAChR) antagonist, in conjunction with systemic nicotine, provide evidence that α7-nAChRs in the ventral hippocampus mediate the detrimental effect of ventral hippocampal nicotine on contextual fear learning. These results suggest that with systemic nicotine administration, competition exists between the dorsal and ventral hippocampus for behavioral control over contextual learning.

Acute and residual interactive effects of repeated administrations of oral methamphetamine and alcohol in humans

Although methamphetamine and alcohol are commonly used together in a binge-like pattern, there is a dearth of empirical data investigating the repeated effects of this drug combination. The current study examined acute and residual mood, performance, and physiological effects of methamphetamine alone, alcohol alone, and the combination. Nine adult male volunteers completed this 20-day within-participant, residential laboratory study. During four 5-day blocks of sessions, participants were administered oral methamphetamine (0, 10 mg) combined with alcohol (0, 0.375, 0.75 g/kg) three times (day 2: AM, day 2: PM, and day 3: PM). Breath alcohol concentrations, cardiovascular, subjective, and cognitive/psychomotor performance effects were assessed before drug administration and repeatedly thereafter. Subjective and objective sleep measures were also assessed; residual effects were assessed on days 3-5 of each block. Following the first drug administration, the methamphetamine-alcohol combination produced greater elevations of heart rate and ratings of "good drug effect" compared to either drug alone. Methamphetamine attenuated alcohol-related performance decrements and feelings of intoxication, whereas alcohol attenuated methamphetamine-related sleep disruptions. By the third administration, many of these effects were significantly diminished, suggesting that participants developed tolerance. Few residual effects were observed. These data show that methamphetamine combined with alcohol produced a profile of effects that was different from the effects of either drug alone. The largely positive effects of the drug combination (i.e., greater euphoria, and fewer performance and sleep disruptions) might explain why these drugs are often used in combination.

Reward expectations lead to smoking uptake among depressed adolescents

AIMS

While the comorbidity between adolescent depression and smoking has been well documented, less is known about why smoking is disproportionately higher among depressed adolescents. Emerging research suggests that reward-related mechanisms may be important to consider. This study sought to determine whether adolescents with higher depression symptoms have greater smoking reward expectations, which in turn, influence smoking progression.

PARTICIPANTS

The sample was composed of 1393 adolescents participating in a longitudinal survey study of adolescent health behaviors.

DESIGN AND MEASUREMENTS

In this prospective cohort study, variables were measured via self-report every six months from age 14 to age 17 resulting in six waves of data. Findings Parallel processes latent growth curve modeling indicated that higher depression symptoms across mid to late adolescence predicted a 17% increase in smoking reward expectations (β=3.50, z=2.85, p=0.004), which in turn predicted a 23% increase in the odds of smoking progression (β=0.206, z=3.29, p=0.001). The indirect effect was significant with delta method (β(indirect)=0.72, z=3.09, p=0.002; 95% CI=0.26, 1.18) and bootstrap (β(indirect)=0.72, z=2.10, p=0.03; 95% CI=0.05, 1.39) standard errors.

CONCLUSIONS

The study provides novel evidence that expectations of smoking reward facilitate smoking uptake among depressed adolescents. Smoking reward expectations may identify depressed adolescents at risk of smoking. Addressing alternative ways to meet the reward expectations rather than smoking may be an important component to consider in the preventing smoking and promoting smoking cessation among adolescents with elevated depression symptoms.

Contrasting behavioral effects of acute nicotine and chronic smoking in detoxified alcoholics

BACKGROUND

Current literature suggests that acute nicotine administration provides a compensatory mechanism by which alcoholics might alleviate attentional deficits. In contrast, chronic smoking is increasingly recognized as negatively affecting neurobehavioral integrity. These opposing effects have not been simultaneously examined. Thus, we sought to a) extend previous work by exploring the effects of acute nicotine effects on vigilance components of attention and replicate previous findings suggesting that treatment-seeking alcoholics experience benefit to a greater extent than do other groups; and b) to examine the impact of chronic smoking on these tasks and across subgroups.

METHODS

Substance abusing participants (N=86) were recruited and subgrouped on the basis of dependency criteria as either alcoholics, alcoholics with co-morbid stimulant dependence, or stimulant dependent individuals. Groups of cigarette-smoking (N=17) and non-smoking (N=22) community controls were recruited as comparison groups. Smoking subjects were assigned a placebo, low, or high dose nicotine patch in a double-blind placebo controlled fashion. Non-smoking controls were administered either a placebo or low dose. Testing occurred after dose stabilization.

RESULTS

General linear models indicated greater sensitivity to acute nicotine administration among alcoholics than other groups when controlling for the effect of intensity of smoking history, as reflected by pack-years. Pack-years correlated negatively with performance measures in alcoholics but not stimulant abusing subgroups or smoking controls. Finally, regression analyses demonstrated that pack-years predicted poorer performance only for the alcoholic subgroup.

CONCLUSIONS

These results support previous work finding a compensatory effect of acute nicotine administration on attentional performance in alcoholics and reinforce the consideration of recent nicotine use as a confound in neurocognitive studies of alcoholics. Of particular interest is the finding that smoking history as reflected in pack-years predicted poorer performance, but only among alcoholics. Further systematic study of these opposing effects among alcoholics and other groups using a broader array of tasks is needed.

Spatial and sustained attention in relation to smoking status: behavioural performance and brain activation patterns

Nicotine enhances attentional functions. Since chronic nicotine exposure through smoking induces neuroadaptive changes in the brain at a structural and molecular level, the present functional MRI (fMRI) study aimed at investigating the neural mechanisms underlying visuospatial and sustained attention in smokers and non-smokers. Visuospatial attention was assessed with a location-cueing paradigm, while sustained attention was measured by changes in response speed over time. During invalid trials, neural activity within the basal forebrain was selectively enhanced in smokers and higher basal forebrain activity was associated with increased parietal cortex activation. Moreover, higher levels of expired carbon monoxide in smokers before scanning were associated with higher parietal cortex activation and faster responses to invalidly cued targets. Smokers showed a slowing of responses and additionally recruited an area within the right supramarginal gyrus with increasing time on task. Activity decreases over time were observed in visual areas in smokers. The data provide evidence for altered attentional functions in smokers as compared with non-smokers, which were partly modulated by residual nicotine levels and were observed at a behavioural level for sustained and at a neural level for spatial and sustained attention.

Association of BDNF and COMT genotypes with cognitive processing of anti-smoking PSAs

Anti-smoking public service announcements (PSAs) often use persuasive arguments to attempt to influence attitudes about smoking. The persuasiveness of a PSA has previously been associated with factors that influence the cognitive processing of its message. Genetic factors that influence cognitive processing might thus affect individuals' responses to the persuasive arguments presented in PSAs. In the present study, we examined polymorphisms in the genes encoding brain-derived neurotrophic factor (BDNF Val66Met) and catechol-O-methyltransferase (COMT Val158Met), which affect cognitive processing in the prefrontal cortex, to identify genetic factors associated with self-reported outcomes of message processing, perceived effectiveness and quitting intentions among smokers viewing PSAs. A total of 120 smokers viewed sets of four PSAs that varied with respect to features of argument strength (AS) and message sensation value. We observed significant associations of BDNF genotype with central processing, narrative processing, perceived effectiveness of the anti-smoking PSAs and participant quitting intentions; the BDNF Met allele was associated with lower scores on all these measures. Central processing acted as a mediator of the association of genotype with quitting intentions and perceived effectiveness. There was a significant interaction of COMT genotype by AS in the model of narrative processing, such that individuals homozygous for the COMT Val allele reported higher narrative processing in the high-AS condition but not in the low-AS condition. To our knowledge, this is the first study to identify genetic factors associated with cognitive processing of anti-smoking PSAs.

Smoking and Neuroimaging: A Review

Cigarette smoking is a significant public health concern, often resulting in nicotine dependence, a chronic-relapsing psychiatric diagnosis that is responsible for up to 10% of the global cardiovascular disease burden. Due to its significantly deleterious effects on health, much research has been dedicated to elucidating the underlying neurobiology of smoking. This brief article is intended to provide a digestible synopsis of the considerable research being conducted on the underlying neural bases of cigarette smoking and nicotine dependence, especially for cardiologists who are often at the front lines of treating nicotine dependence. To this end, we first review some of the most common neuroimaging methodologies used in the study of smoking, as well as the most recent findings from this exciting area of research. Then, we focus on several fundamental topics including the acute pharmacological effects, acute neurocognitive effects, and the long-term neurobiological effects associated with smoking. We finally review recent findings regarding the neuropsychological processes associated with smoking cessation, including cue-induced craving and regulation of craving. Research in this field beginning to uncover how some of these neuropsychological processes are similar across clinical disorders which cardiologists also encounter frequently, such as craving for food resulting in overeating. We conclude with recommendations for future neuroimaging work on these topics.

The effects of acute, chronic, and withdrawal from chronic nicotine on novel and spatial object recognition in male C57BL/6J mice

RATIONALE

Spatial and novel object recognition learning is different from learning that uses aversive or appetitive stimuli to shape acquisition because no overt contingencies are needed. While this type of learning occurs on a daily basis, little is known about how nicotine administration affects it.

OBJECTIVES

To determine the effects of acute, chronic, and withdrawal from chronic nicotine on two related but distinct incidental learning tasks, novel and spatial object recognition.

METHODS

In C57BL/6J mice, the effects of acute (0.045-0.18 mg/kg), chronic (6.3 mg/kg/day), and withdrawal from chronic nicotine on novel and spatial object recognition were examined.

RESULTS

With a 48-h delay between training and testing, acute nicotine enhanced spatial (difference score, saline = 3.34 s, nicotine = 7.71 s, p = 0.029) but resulted in a deficit in novel object recognition (difference score, saline = 8.76 s, nicotine = 4.48 s, p = 0.033). Chronic nicotine resulted in a strong trend towards a deficit in spatial object recognition (difference score, saline = 4.01 s, nicotine = 1.81 s, p = 0.059) but had no effect on novel object recognition, and withdrawal from chronic nicotine disrupted spatial object recognition (difference score, saline = 3.00 s, nicotine = 0.17 s, p = 0.004) but had no effect on novel object recognition.

CONCLUSIONS

The effects of nicotine on spatial object recognition shift from enhancement to deficit as administration changes from acute to chronic and withdrawal. These effects were specific for spatial object recognition, which may be due to differing underlying neural substrates involved in these tasks. Understanding how nicotine alters learning has implications for understanding diseases associated with altered cholinergic function.

Selective nicotinic receptor antagonists: effects on attention and nicotine-induced attentional enhancement

RATIONALE

The question of the subtype(s) of the nicotinic acetylcholine receptor (nAChR) mediating the attention-enhancing effects of nicotine is still unsettled. While early studies pointed towards subtypes other than the homomeric α7 nAChR, pro-cognitive effects of α7 nAChR agonists have since been demonstrated.

OBJECTIVES

This study tested whether the performance-enhancing effects of nicotine in a rodent model of attention could be reversed by the α4β2, α4β4, α3β2, and α2β2 nAChR antagonist dihydro-β-erythroidine (DHβE), or the α7 antagonist methyllycaconitine (MLA).

METHODS

In repeated tests, 12 rats trained to perform the 5-choice serial reaction time task were systemically injected with nicotine or vehicle in the presence of increasing doses of DHβE or MLA.

RESULTS

DHβE did not antagonize the attention-enhancing effects of nicotine reflected by measures of accuracy and omission errors, suggesting that its previously reported antagonism of nicotine effects on latency and anticipatory responses specifically reflected the stimulant effects of nicotine. MLA dose-dependently reversed the reduction in omission errors by nicotine. In the absence of nicotine, low doses of MLA (0.4 and 1.3 mg/kg) not previously tested on attention improved response accuracy, resulting in an inverted U-shape dose-response function.

CONCLUSIONS

nAChR subtypes involved in the performance-enhancing effects of nicotine appear to vary depending on the function assessed. Our findings suggest a greater involvement of α7 nAChRs in the effects of nicotine on attention than first suggested by preclinical studies, with different optimal receptor tones for aspects of stimulus detection and response readiness to task stimuli.

Cigarette smoking status in pathological gamblers: association with impulsivity and cognitive flexibility

BACKGROUND

While the majority of pathological gamblers are current cigarette smokers (CS), some have quit smoking (former smokers, FS) while others never smoked (never smokers, NS). The reasons for elevated smoking rates in pathological gambling are not known, but gamblers may use nicotine as a putative cognitive enhancer. This study evaluated impulsivity and cognitive flexibility in a sample of pathological gamblers with differing smoking status.

METHODS

Fifty-five subjects with pathological gambling (CS, n=34; FS, n=10; NS, n=11) underwent cognitive assessments using the Stop-Signal (SST) and Intradimensional/Extra-dimensional (ID/ED) set-shift tasks.

RESULTS

CS reported less severe gambling problems than either FS or NS on the Yale Brown Obsessive Compulsive Scale modified for Pathological Gambling, and CS was associated with significantly fewer directional errors on the SST task, compared to NS. In addition, in CS, higher daily cigarette consumption was associated with fewer total errors on the ID/ED task.

CONCLUSIONS

The potential role of nicotine as a cognitive enhancer was supported by objective tests of impulsivity and cognitive flexibility. Human laboratory studies using nicotine challenges in pathological gambling will shed further light on this relationship.

Nicotine restores morphine-induced memory deficit through the D1 and D2 dopamine receptor mechanisms in the nucleus accumbens

Involvement of the dopamine D1 and D2 receptors in the nucleus accumbens (NAc) with interaction between morphine and nicotine on inhibitory avoidance (IA) memory was investigated. A step-through type of inhibitory avoidance tasks was used to assess memory in male Wistar rats. The results showed that subcutaneous (s.c.) administration of morphine (7.5 mg/kg) after training decreased retrieval of IA memory in the animals when tested 24 h later. Pre-test administration of the same dose of morphine significantly reversed the deficiency in retrieval. The results also showed that pre-test administration of nicotine (0.2 and 0.4 mg/kg, s.c.) by itself mimicked the effect of pre-test morphine, and lower doses of nicotine (0.1 and 0.2 mg/kg) also improved the effect of a low dose of morphine (2.5 mg/kg) on retrieval of IA memory. Pre-test intra-NAc administration of the dopamine D1 receptor antagonist, SCH 23390 (0.001 and 0.01 µg/rat), and the dopamine D2 receptor antagonist, sulpiride (0.5 and 1 µg/rat) caused no significant effects on IA memory by themselves, but both prevented reinstatement of the retrieval of IA memory by the effective dose of nicotine (0.4 mg/kg). It can be concluded that the dopaminergic mechanism(s) in the NAc is a crosslink for the effect of morphine and nicotine on reinstatement of retrieval of IA memory impaired by post-training administration of morphine.

Acute nicotine enhances strategy-based semantic processing in Parkinson's disease

Nicotinic mechanisms may play a role in the cognitive deficits of Parkinson's disease (PD). Recently, on a cognitively demanding strategy-based priming task, nicotine selectively affected controlled semantic processing in young adult non-smokers as reported by Holmes et al. (International Journal of Neuropsychopharmacology 11, 389-399, 2008). Such controlled semantic processing is compromised in PD. This study investigated the effects of acute transdermal nicotine on controlled semantic processing in non-smokers with PD (n = 10) and non-smoking matched controls (n = 16) using a strategy-based semantic priming paradigm. Transdermal nicotine patches (7 mg/24 h) were administered in a double-blind, placebo-controlled, crossover design. Participants were instructed to expect target words from specified semantic categories based on the primes, while unexpected targets were also presented. Priming conditions included those concurring with trained expectations (expected-related and expected-unrelated), those which did not (unexpected-related and unexpected-unrelated), and neutral-baseline conditions. Controls evidenced significant expectancy effects (i.e. reaction-time differences for expected vs. unexpected conditions) under both drug states. An expectancy effect was not evident for PD under placebo due to a lack of reaction-time slowing for unexpected conditions. However, under nicotine an expectancy effect was present for PD at a level comparable to controls. Overall the findings indicate that nicotine can improve impaired controlled semantic processing in PD possibly via enhanced expectancy or inhibitory mechanisms.

Predictors of smoking severity in patients with schizophrenia and alcohol use disorders

The goal of the present study was to identify predictors of smoking severity in patients with schizophrenia and co-occurring alcohol use disorders (AUD). Our hypothesis was that negative symptoms of schizophrenia, severity of depression, male gender, drinking severity, and recreational drug use were associated with increased smoking. Clinical data, including demographic variables, alcohol and substance use severity, psychiatric medications, severity of depression, positive and negative symptoms of schizophrenia were analyzed in a cohort of 90 patients with schizophrenia or schizoaffective disorder and AUD. Eighty-eight percent of participants were smokers, they smoked an average of 15 cigarettes/day. Zero-inflated negative binomial (ZINB) regression analyses demonstrated that alcohol use severity, gender, and severity of negative symptoms were not predictive of the number of cigarettes smoked. Smoking severity was positively related to Caucasian race, psychosis severity (Positive and Negative Syndrome Scale [PANSS] general score), and medications (conventional antipsychotics). Subjects who used recreational drugs smoked less. In summary, severe, treatment resistant schizophrenia, and conventional antipsychotic treatment is associated with heavy smoking in patients with schizophrenia and AUD regardless of gender or alcohol use.

Nicotine effects on immediate and delayed verbal memory after substance use detoxification

Decrements in verbal memory are commonly reported by detoxified treatment-seeking individuals. Although acute nicotine has been shown to improve attentional performance, its effects on verbal memory in substance abusers have not been addressed. Treatment-seeking alcohol-dependent (ALCs, n = 29; 14 male), illicit-stimulant-dependent (predominantly cocaine; STIMs, n = 25; 15 male), and alcohol- and illicit-stimulant-dependent (ALC/STIMs, n = 50; 35 male) participants with comorbid nicotine dependence were studied. Subjects had been abstinent from their drugs of choice for 41 (±18) days and were in short-term abstinence from tobacco (∼8-10 hours). Subjects received double-blind administration of either transdermal nicotine (high dose: 21/14 mg for men and women, respectively, or low dose: 7 mg) or placebo. The Logical Memory (LM) subtest from the Wechsler Memory Scale-Revised (WMS-R) was used to assess immediate and delayed verbal memory recall. Results indicated that STIMs receiving the high dose of nicotine recalled more words at immediate recall than STIMs who received placebo. Trend level differences were also noted at delayed recall between STIM nicotine and placebo doses. Nicotine failed to impact either recall in alcoholic subgroups. Although not the primary focus, results also revealed differences in the forgetting rates between the groups with the ALC/STIMs demonstrating the steepest forgetting slope. In summary, this study suggests that nicotine effects may be differentially experienced by substance-using subgroups; that nicotine may have a direct effect on memory; and that in considering neurocognitive processes (e.g., encoding vs. retrieval), underlying endpoint indicators (e.g., correct recall) may be critical in predicting outcomes.

Functional brain imaging of nicotinic effects on higher cognitive processes

Significant advances in human functional brain imaging offer new opportunities for direct observation of the effects of nicotine, novel nicotinic agonists and nicotinic antagonists on human cognitive and behavioral performance. Careful research over the last decade has enabled investigators to explore the role of nicotinic systems on the functional neuroanatomy and neural circuitry of cognitive tasks in domains such as selective attention, working memory, episodic memory, cognitive control, and emotional processing. In addition, recent progress in understanding functional connectivity between brain regions utilized during cognitive and emotional processes offers new opportunities for examining drug effects on network-related activity. This review will critically summarize available nicotinic functional brain imaging studies focusing on the specific cognitive domains of attention, memory, behavioral control, and emotional processing. Generally speaking, nicotine appears to increase task-related activity in non-smokers and deprived smokers, but not active smokers. By contrast, nicotine or nicotinic stimulation decreases the activity of structures associated with the default mode network. These particular patterns of activation and/or deactivation may be useful for early drug development and may be an efficient and cost-effective method of screening potential nicotinic agents. Further studies will have to be done to clarify whether such activity changes correlate with cognitive or affective outcomes that are clinically relevant. The use of functional brain imaging will be a key tool for probing pathologic changes related to brain illness and for nicotinic drug development.

Effects of nicotine on attention and inhibitory control in healthy nonsmokers

Nicotine improves cognitive functioning in smokers and psychiatric populations, but its cognitive-enhancing effects in healthy nonsmokers are less well understood. Nicotine appears to enhance certain forms of cognition in nonsmokers, but its specificity to subtypes of cognition is not known. This study sought to replicate and extend previous findings on the effects of nicotine on cognitive performance in healthy nonsmokers. Healthy young adults (N = 40, 50% women) participated in a placebo-controlled, double-blind, repeated measures experiment examining the effects of 7 mg transdermal nicotine or placebo. Participants completed tests of attention (Attention Network Test), behavioral inhibition (stop signal task, Stroop test), reward responsiveness (signal detection task), and risk-taking behavior (Balloon Analogue Risk Task). Physiological (heart rate, blood pressure) and subjective (Profile of Mood States, Drug Effects Questionnaire) measures were also obtained. Nicotine significantly improved performance only on the Stroop test, but it impaired performance on one aspect of the Attention Network Test, the orienting effect. Nicotine produced its expected effects on physiologic and subjective measures within the intended time course. The findings of this study contribute to a growing literature indicating that nicotine differentially affects specific subtypes of cognitive performance in healthy nonsmokers.

Smoking withdrawal symptoms are more severe among smokers with ADHD and independent of ADHD symptom change: results from a 12-day contingency-managed abstinence trial

INTRODUCTION

Smokers with attention deficit hyperactivity disorder (ADHD) have greater difficulty quitting than those without ADHD, but preliminary data (McClernon, Kollins, Lutz, Fitzgerald, Murray, Redman, et al., 2008) suggest equivalent severity of withdrawal symptoms following brief abstinence. The objective of this study was to characterize the differential effects of intermediate term smoking abstinence on self-reported withdrawal and ADHD symptoms in adult smokers with and without ADHD.

METHODS

Forty adult (50% female), nontreatment seeking moderate-to-heavy smokers with and without ADHD were enrolled in a 12-day quit study in which monetary incentives were provided for maintaining biologically verified abstinence. Self-reported withdrawal, mood, and ADHD symptoms were measured pre- and post-quitting.

RESULTS

ADHD and controls did not vary on smoking or demographic variables. Significant Group × Session interactions were observed across a broad range of withdrawal symptoms and were generally characterized by greater withdrawal severity among ADHD smokers, particularly during the first 5 days of abstinence. In addition, Group × Sex × Session interactions were observed for craving, somatic symptoms, negative affect, and habit withdrawal; these interactions were driven by greater withdrawal severity among females with ADHD. Group × Session interactions were not observed for ADHD symptom scales.

CONCLUSIONS

The results of this study suggest that smokers with ADHD, and ADHD females in particular, experience greater withdrawal severity during early abstinence-independent of effects on ADHD symptoms. Whereas additional research is needed to pinpoint mechanisms, our findings suggest that smoking cessation interventions targeted at smokers with ADHD should address their more severe withdrawal symptoms following quitting.

Cognitive enhancers for the treatment of ADHD

Attention-deficit hyperactivity disorder (ADHD) is associated with multiple cognition-related phenotypic features in both children and adults. This review aims to clarify the role of cognition in ADHD and how prevailing treatments, which are often highly effective at reducing the clinical symptoms of the disorder, fare in modulating ADHD-related cognitive processes. First, we consider how the broad construct of cognition can be conceptualized in the context of ADHD. Second, we review the available evidence for how a range of both pharmacological and non-pharmacological interventions have fared with respect to enhancing cognition in individuals affected by this pervasive disorder. Findings from the literature suggest that the effects across a broad range of pharmacological and non-pharmacological interventions on the characteristic symptoms of ADHD can be distinguished from their effects on cognitive impairments. As such the direct clinical relevance of cognition enhancing effects of different interventions is somewhat limited. Recommendations for future research are discussed, including the identification of cognition-related endophenotypes, the refinement of the ADHD clinical phenotype, and studying the difference between acute and chronic treatment regimens.

Cognitive enhancers in the treatment of substance use disorders: clinical evidence

Attenuation of drug reward has been the major focus of medication development in the addiction area to date. With the growth of research in the area of cognitive neuroscience, the importance of executive function and inhibitory cognitive control in addictive disorders is becoming increasingly apparent. An emerging strategy in the pharmacotherapy of addictions and other psychiatric disorders involves the use of medications that improve cognitive function. In particular, agents that facilitate inhibitory and attentional control, improve abstraction, planning and mental flexibility could be beneficial in the treatment of substance use disorders. Because there are multiple neurotransmitter systems involved in the regulation of cognitive function, agents from a number of drug classes have been tested. In particular, agents acting through the cholinergic, adrenergic and glutamatergic systems have shown potential for improving cognitive function in a number of psychiatric and neurologic disorders, but most of these agents have not been tested in the treatment of individuals with substance use disorders. This manuscript provides a review of clinical data supporting the use of the major classes of cognitive enhancing agents in substance use disorders. Agents that have shown promise in cognitive enhancement in other disorders, and have a theoretical or mechanistic rationale for application to substance use disorders are also highlighted.

Acute effects of nicotine administration during prospective memory, an event related fMRI study

We previously demonstrated that stimulating neuronal nicotinic acetylcholine receptors modulates prospective memory (PM), the ability to remember and implement a prior intention. Here we used fMRI to explore the neuronal correlates of acute nicotinic (1mg) modulation during PM, employing a double blind, valence-matched placebo-controlled design, and a solely event-related analysis. Eight healthy adults completed on two occasions (1 week washout) a simple attentional task containing infrequent PM trials. PM activated bilateral parietal, prefrontal (BA10) and anterior cingulate, and deactivated genual cingulate and medial prefrontal regions. Further, acute nicotine administration decreased activity within a largely overlapping right parietal region. This data validates a purely event-related approach to exploring PM, and suggests procholinergic modulation of PM by parietal rather than BA10/frontal regions.

The influence of nicotine dose and nicotine dose expectancy on the cognitive and subjective effects of cigarette smoking

This study investigated the independent and interactive effects of nicotine dose and nicotine dose expectancy on smoking outcomes using a 2 (given nicotine vs. placebo) × 2 (told nicotine vs. placebo) Balanced Placebo Design (BPD). Smokers (N = 148) completed the Rapid Visual Information Processing Task (RVIP) and measures of smoking urge, mood, and cigarette ratings (e.g., satisfying) after smoking a nicotine or placebo cigarette crossed with instructions that the cigarette contained either nicotine or no nicotine. Nicotine cigarettes (0.6 mg nicotine) produced better sustained attention performance than placebos as indicated by RVIP reaction time, hits, and sensitivity (A'). Nicotine cigarettes also produced better mood and greater rewarding subjective effects of the cigarettes on 11 of 11 dimensions compared to placebos. Nicotine instructions resulted in fewer RVIP false alarms, better mood, and greater rewarding subjective effects of the cigarettes on 9 of 11 dimensions compared to placebo instructions. Nicotine dose by nicotine dose expectancy interactions were also observed for urge and tension-anxiety, such that the dose expectancy manipulation produced differential effects only among those who smoked placebo cigarettes. In contrast a significant interaction for self-reported vigor-activity demonstrated that the dose expectancy manipulation produced effects only among those who smoked nicotine cigarettes. This study provides additional evidence that nicotine improves cognitive performance, and provides initial evidence that denicotinized cigarettes smoked under the guise that they contain nicotine influence cognitive performance, albeit with less robust effects than nicotine. These data may inform the development of expectancy-based interventions for tobacco dependence.

Zebrafish for the study of the biological effects of nicotine

INTRODUCTION

Zebrafish are emerging as a powerful animal model for studying the molecular and physiological effects of nicotine exposure. The zebrafish have many advantageous physical characteristics, including small size, high fecundity rates, and externally developing transparent embryos. When combined with a battery of molecular-genetic tools and behavioral assays, these attributes enable studies to be conducted that are not practical using traditional animal models.

METHODS

We reviewed the literature on the application of the zebrafish model as a preclinical model to study the biological effects of nicotine exposure.

RESULTS

The identified studies used zebrafish to examine the effects of nicotine exposure on early development, addiction, anxiety, and learning. The methods used included green fluorescent protein-labeled proteins to track in vivo nicotine-altered neuron development, nicotine-conditioned place preference, and locomotive sensitization linked with high-throughput molecular and genetic screens and behavioral models of learning and stress response to nicotine. Data are presented on the complete homology of all known human neural nicotinic acetylcholine receptors in zebrafish and on the biological similarity of human and zebrafish dopaminergic signaling.

CONCLUSIONS

Tobacco dependence remains a major health problem worldwide. Further understanding of the molecular effects of nicotine exposure and genetic contributions to dependence may lead to improvement in patient treatment strategies. While there are limitations to the use of zebrafish as a preclinical model, it should provide a valuable tool to complement existing model systems. The reviewed studies demonstrate the enormous opportunity zebrafish have to advance the science of nicotine and tobacco research.

The cholinergic hypothesis of cognitive aging revisited again: cholinergic functional compensation

It is now possible to reevaluate the cholinergic hypothesis of age-related cognitive dysfunction based on a synthesis of new evidence from cholinergic stimulation studies and cognitive models. We propose that a change of functional circuitry that can be observed through a combination of pharmacologic challenge and functional neuroimaging is associated with age-related changes in cholinergic system functioning. Psychopharmacological manipulations using cholinergic agonists and antagonists have been consistent in replicating patterns of aging seen in functional imaging studies. In addition, studies of anticholinesterase drugs in patients with Alzheimer's disease and mild cognitive impairment show support for the proposal that cholinergic compensation causes alterations in task-related brain activity. Thus, the cholinergic hypothesis of age-related cognitive dysfunction deserves further consideration as new methodologies for evaluating its validity are increasingly being used. Future directions for testing hypotheses generated from this model are presented.

Nicotine ameliorates impairment of working memory in methamphetamine-treated rats

Nicotine is hypothesized to have therapeutic effects on attentional and cognitive abnormalities in psychosis. In this study, we investigated the effect of nicotine on impaired spatial working memory in repeated methamphetamine (METH)-treated rats. Rats were administered METH (4 mg/kg, s.c.) once a day for 7 days, and their working memory was assessed with a delayed spatial win-shift task in a radial arm maze. The task consisted of two phases, a training phase and a test phase, separated by a delay. Control animals showed impaired performance in the test phase when the delay time was increased to 120 min or longer, while METH-treated rats showed impaired performance with a shorter delay time of 90 min. Memory impairment in METH-treated rats persisted for at least 14 days after drug withdrawal. METH-induced impairment of working memory was reversed by nicotine (0.3mg/kg, p.o., for 7 days), but the effect was diminished 7 days after the withdrawal. In control rats, nicotine decreased the number of working memory errors in the test with delay time of 120 min when administered before the training phase. Neither post-training nor pre-test administration of nicotine had any effect on working memory. These findings suggest that nicotine may have some protective effect against the impairment of working memory.

Chronic smoking, but not acute nicotine administration, modulates neural correlates of working memory

RATIONALE

Beyond the amelioration of deprivation-induced impairments, and in contrast to effects on attentional processes, the cognitive-enhancing properties of nicotine on working memory (WM) operations remain unclear.

OBJECTIVES

In an effort to elucidate potential enhancing effects, we explored the impact of transdermal nicotine on neural functioning in minimally deprived smokers and, in addition, assessed differences between smokers and non-smokers using a mixed block/event-related fMRI design that attempted to isolate specific central executive operations (attentional switch events) within general WM function (task blocks).

METHODS

In task blocks, participants performed a continuous counting paradigm that required the simultaneous maintenance of, and frequent switching of attentional focus between, two running tallies in WM on some trials. Cigarette smokers (n = 30) were scanned twice, once each with a nicotine and placebo patch, while non-smokers (n = 27) were scanned twice with no patch.

RESULTS

Across both groups, task blocks were associated with bilateral activation, notably in medial and lateral prefrontal cortex (PFC), anterior insula, and parietal regions, whereas individual attentional switch trials were associated with activation in a similar, but predominantly left-lateralized network. Within the smoker group, although nicotine increased heart rate, altered performance and mood, and reduced tobacco cravings, no acute drug (state-like) effect on brain activity was detected for either the task or switch effects. However, relative to non-smokers, smokers showed greater tonic activation in medial superior frontal cortex, right anterior insula, and bilateral anterior PFC throughout task blocks (trait-like effect).

CONCLUSIONS

These data suggest smokers require recruitment of additional WM and supervisory control operations during task performance.

Prompt but inefficient: nicotine differentially modulates discrete components of attention

RATIONALE

Nicotine has been shown to improve both memory and attention when assessed through speeded motor responses. Since very few studies have assessed effects of nicotine on visual attention using measures that are uncontaminated by motoric effects, nicotine's attentional effects may, at least partially, be due to speeding of motor function.

OBJECTIVES

Using an unspeeded, accuracy-based test, the CombiTVA paradigm, we examined whether nicotine enhances attention when it is measured independently of motor processing.

METHODS

We modelled data with a computational theory of visual attention (TVA; Bundesen 1990) so as to derive independent estimates of several distinct components of attention from performance of the single task: threshold of visual perception, perceptual processing speed, visual short-term memory storage capacity and top-down controlled selectivity. Acute effects of nicotine (2 mg gum) on performance were assessed in 24 healthy young non-smokers in a placebo-controlled counterbalanced, crossover design. Chronic effects of nicotine were investigated in 24 age- and education-matched minimally deprived smokers.

RESULTS

Both an acute dose of nicotine in non-smokers and chronic nicotine use in temporarily abstaining smokers improved perceptual thresholds but slowed subsequent perceptual speed. Moreover, both acute and chronic nicotine use reduced attentional selectivity though visual short-term memory capacity was unimpaired.

CONCLUSIONS

Nicotine differentially affected discrete components of visual attention, with acute and chronic doses revealing identical patterns of performance. We challenge prior reports of nicotine-induced speeding of information processing by showing, for the first time, that nicotine slows down perceptual processing speed when assessed using accuracy-based measures of cognitive performance.

Herbal extracts and phytochemicals: plant secondary metabolites and the enhancement of human brain function

Humans consume a wide range of foods, drugs, and dietary supplements that are derived from plants and which modify the functioning of the central nervous sytem (CNS). The psychoactive properties of these substances are attributable to the presence of plant secondary metabolites, chemicals that are not required for the immediate survival of the plant but which are synthesized to increase the fitness of the plant to survive by allowing it to interact with its environment, including pathogens and herbivorous and symbiotic insects. In many cases, the effects of these phytochemicals on the human CNS might be linked either to their ecological roles in the life of the plant or to molecular and biochemical similarities in the biology of plants and higher animals. This review assesses the current evidence for the efficacy of a range of readily available plant-based extracts and chemicals that may improve brain function and which have attracted sufficient research in this regard to reach a conclusion as to their potential effectiveness as nootropics. Many of these candidate phytochemicals/extracts can be grouped by the chemical nature of their potentially active secondary metabolite constituents into alkaloids (caffeine, nicotine), terpenes (ginkgo, ginseng, valerian, Melissa officinalis, sage), and phenolic compounds (curcumin, resveratrol, epigallocatechin-3-gallate, Hypericum perforatum, soy isoflavones). They are discussed in terms of how an increased understanding of the relationship between their ecological roles and CNS effects might further the field of natural, phytochemical drug discovery.

Acetylcholine and attention

Historically, ACh has been implicated in learning and short-term memory functions. However, more recent studies have provided support for a role of cortical ACh in attentional effort, orienting and the detection of behavioral significant stimuli. The current review article summarizes studies in animals and humans which have investigated the role of ACh in attention and cognition. An attempt has been made to differentiate between brain regions involved in attentional processes versus those important for other cognitive functions. To this purpose, various experimental methods and interventions were used. Animal behavioral studies have injected the selective immunotoxin IgG-saporin to induce specific cholinergic lesions, employed electrochemical techniques such as microdialysis, or have administered cholinergic compounds into discrete parts of the brain. Human studies that give some indication on the link between central cholinergic signaling and cognition are obviously confined to less invasive, imaging methods such as fMRI. The brain areas that are deemed most important for intact attentional processing in both animals and humans appear to be the (pre)frontal, parietal and somatosensory (especially visual) regions, where ACh plays a vital role in the top-down control of attentional orienting and stimulus discrimination. In contrast, cholinergic signaling in the septohippocampal system is suggested to be involved in memory processes. Thus, it appears that the role of ACh in cognition is different per brain region and between nicotinic versus muscarinic receptor subtypes.

Chronic cigarette smoking: implications for neurocognition and brain neurobiology

Compared to the substantial volume of research on the general health consequences associated with chronic smoking, little research has been specifically devoted to the investigation of its effects on human neurobiology and neurocognition. This review summarizes the peer-reviewed literature on the neurocognitive and neurobiological implications of chronic cigarette smoking in cohorts that were not seeking treatment for substance use or psychiatric disorders. Studies that specifically assessed the neurocognitive or neurobiological (with emphasis on computed tomography and magnetic resonance-based neuroimaging studies) consequences of chronic smoking are highlighted. Chronic cigarette smoking appears to be associated with deficiencies in executive functions, cognitive flexibility, general intellectual abilities, learning and/or memory processing speed, and working memory. Chronic smoking is related to global brain atrophy and to structural and biochemical abnormalities in anterior frontal regions, subcortical nuclei and commissural white matter. Chronic smoking may also be associated with an increased risk for various forms of neurodegenerative diseases. The existing literature is limited by inconsistent accounting for potentially confounding biomedical and psychiatric conditions, focus on cross-sectional studies with middle aged and older adults and the absence of studies concurrently assessing neurocognitive, neurobiological and genetic factors in the same cohort. Consequently, the mechanisms promoting the neurocognitive and neurobiological abnormalities reported in chronic smokers are unclear. Longitudinal studies are needed to determine if the smoking-related neurobiological and neurocognitive abnormalities increase over time and/or show recovery with sustained smoking cessation.

The role of nicotinic acetylcholine receptors in the medial prefrontal cortex and hippocampus in trace fear conditioning

Acute nicotine enhances multiple types of learning including trace fear conditioning but the underlying neural substrates of these effects are not well understood. Trace fear conditioning critically involves the medial prefrontal cortex and hippocampus, which both express nicotinic acetylcholine receptors (nAChRs). Therefore, nicotine could act in either or both areas to enhance trace fear conditioning. To identify the underlying neural areas and nAChR subtypes, we examined the effects of infusion of nicotine, or nicotinic antagonists dihydro-beta-erythroidine (DHβE: high-affinity nAChRs) or methyllycaconitine (MLA: low-affinity nAChRs) into the dorsal hippocampus, ventral hippocampus, and medial prefrontal cortex (mPFC) on trace and contextual fear conditioning. We found that the effects of nicotine on trace and contextual fear conditioning vary by brain region and nAChR subtype. The dorsal hippocampus was involved in the effects of nicotine on both trace and contextual fear conditioning but each task was sensitive to different doses of nicotine. Additionally, dorsal hippocampal infusion of the antagonist DHβE produced deficits in trace but not contextual fear conditioning. Nicotine infusion into the ventral hippocampus produced deficits in both trace and contextual fear conditioning. In the mPFC, nicotine enhanced trace but not contextual fear conditioning. Interestingly, infusion of the antagonists MLA or DHβE in the mPFC also enhanced trace fear conditioning. These findings suggest that nicotine acts on different substrates to enhance trace versus contextual fear conditioning, and that nicotine-induced desensitization of nAChRs in the mPFC may contribute to the effects of nicotine on trace fear conditioning.