GABA levels in the dorsal anterior cingulate cortex associated with difficulty ignoring smoking-related cues in tobacco-dependent volunteers

Changes in aspartate metabolism in the medial-prefrontal cortex of nicotine addicts based on J-edited magnetic resonance spectroscopy

This study aims to explore the changes of the aspartate (Asp) level in the medial-prefrontal cortex (mPFC) of subjects with nicotine addiction (nicotine addicts [NAs]) using the J-edited 1 H MR spectroscopy (MRS), which may provide a positive imaging evidence for intervention of NA. From March to August 2022, 45 males aged 40-60 years old were recruited from Henan Province, including 21 in NA and 24 in nonsmoker groups. All subjects underwent routine magnetic resonance imaging (MRI) and J-edited MRS scans on a 3.0 T MRI scanner. The Asp level in mPFC was quantified with reference to the total creatine (Asp/Cr) and water (Aspwater-corr , with correction of the brain tissue composition) signals, respectively. Two-tailed independent samples t-test was used to analyze the differences in levels of Asp and other coquantified metabolites (including total N-acetylaspartate [tNAA], total cholinine [tCho], total creatine [tCr], and myo-Inositol [mI]) between the two groups. Finally, the correlations of the Asp level with clinical characteristic assessment scales were performed using the Spearman criteria. Compared with the control group (n = 22), NAs (n = 18) had higher levels of Asp (Asp/Cr: p = .005; Aspwater-corr : p = .004) in the mPFC, and the level of Asp was positively correlated with the daily smoking amount (Asp/Cr: p < .001; Aspwater-corr : p = .004). No significant correlation was found between the level of Asp and the years of nicotine use, Fagerstrom Nicotine Dependence (FTND), Russell Reason for Smoking Questionnaire (RRSQ), or Barratt Impulsivity Scale (BIS-11) score. The elevated Asp level was observed in mPFC of NAs in contrast to nonsmokers, and the Asp level was positively correlated with the amount of daily smoking, which suggests that nicotine addiction may result in elevated Asp metabolism in the human brain.

A review of functional brain differences predicting relapse in substance use disorder: Actionable targets for new methods of noninvasive brain stimulation

Neuroimaging studies have identified a variety of brain regions whose activity predicts substance use (i.e., relapse) in patients with substance use disorder (SUD), suggesting that malfunctioning brain networks may exacerbate relapse. However, this knowledge has not yet led to a marked improvement in treatment outcomes. Noninvasive brain stimulation (NIBS) has shown some potential for treating SUDs, and a new generation of NIBS technologies offers the possibility of selectively altering activity in both superficial and deep brain structures implicated in SUDs. The goal of the current review was to identify deeper brain structures involved in relapse to SUD and give an account of innovative methods of NIBS that might be used to target them. Included studies measured fMRI in currently abstinent SUD patients and tracked treatment outcomes, and fMRI results were organized with the framework of the Addictions Neuroclinical Assessment (ANA). Four brain structures were consistently implicated: the anterior and posterior cingulate cortices, ventral striatum and insula. These four deeper brain structures may be appropriate future targets for the treatment of SUD using these innovative NIBS technologies.

Quantifying GABA in Addiction: A Review of Proton Magnetic Resonance Spectroscopy Studies

Gamma-aminobutyric acid (GABA) signaling plays a crucial role in drug reward and the development of addiction. Historically, GABA neurochemistry in humans has been difficult to study due to methodological limitations. In recent years, proton magnetic resonance spectroscopy (1H-MRS, MRS) has emerged as a non-invasive imaging technique that can detect and quantify human brain metabolites in vivo. Novel sequencing and spectral editing methods have since been developed to allow for quantification of GABA. This review outlines the clinical research utilization of 1H-MRS in understanding GABA neurochemistry in addiction and summarizes current literature that reports GABA measurements by MRS in addiction. Research on alcohol, nicotine, cocaine, and cannabis addiction all suggest medications that modulate GABA signaling may be effective in reducing withdrawal, craving, and other addictive behaviors. Thus, we discuss how improvements in current MRS techniques and design can optimize GABA quantification in future studies and explore how monitoring changes to brain GABA could help identify risk factors, improve treatment efficacy, further characterize the nature of addiction, and provide crucial insights for future pharmacological development.

A role of anterior cingulate cortex in the emergence of worker-parasite relationship

We studied the brain mechanisms underlying action selection in a social dilemma setting in which individuals' effortful gains are unfairly distributed among group members. A stable "worker-parasite" relationship developed when three individually operant-conditioned rats were placed together in a Skinner box equipped with response lever and food dispenser on opposite sides. Specifically, one rat, the "worker," engaged in lever-pressing while the other two "parasitic" rats profited from the worker's effort by crowding the feeder in anticipation of food. Anatomically, c-Fos expression in the anterior cingulate cortex (ACC) was significantly higher in worker rats than in parasite rats. Functionally, ACC inactivation suppressed the worker's lever-press behavior drastically under social, but only mildly under individual, settings. Transcriptionally, GABA_A receptor- and potassium channel-related messenger RNA expressions were reliably lower in the worker's, relative to parasite's, ACC. These findings indicate the requirement of ACC activation for the expression of exploitable, effortful behavior, which could be mediated by molecular pathways involving GABA_A receptor/potassium channel proteins.

Independent and Combined Effects of Nicotine or Chronic Tobacco Smoking and HIV on the Brain: A Review of Preclinical and Clinical Studies

Tobacco smoking is highly prevalent among HIV-infected individuals. Chronic smokers with HIV showed greater cognitive deficits and impulsivity, and had more psychopathological symptoms and greater neuroinflammation than HIV non-smokers or smokers without HIV infection. However, preclinical studies that evaluated the combined effects of HIV-infection and tobacco smoking are scare. The preclinical models typically used cell cultures or animal models that involved specific HIV viral proteins or the administration of nicotine to rodents. These preclinical models consistently demonstrated that nicotine had neuroprotective and anti-inflammatory effects, leading to cognitive enhancement. Although the major addictive ingredient in tobacco smoking is nicotine, chronic smoking does not lead to improved cognitive function in humans. Therefore, preclinical studies designed to unravel the interactive effects of chronic tobacco smoking and HIV infection are needed. In this review, we summarized the preclinical studies that demonstrated the neuroprotective effects of nicotine, the neurotoxic effects of the HIV viral proteins, and the scant literature on nicotine or tobacco smoke in HIV transgenic rat models. We also reviewed the clinical studies that evaluated the neurotoxic effects of tobacco smoking, HIV infection and their combined effects on the brain, including studies that evaluated the cognitive and behavioral assessments, as well as neuroimaging measures. Lastly, we compared the different approaches between preclinical and clinical studies, identified some gaps and proposed some future directions. Graphical abstract Independent and combined effects of HIV and tobacco/nicotine. Left top and bottom panels: Both clinical studies of HIV infected persons and preclinical studies using viral proteins in vitro or in vivo in animal models showed that HIV infection could lead to neurotoxicity and neuroinflammation. Right top and bottom panels: While clinical studies of tobacco smoking consistently showed deleterious effects of smoking, clinical and preclinical studies that used nicotine show mild cognitive enhancement, neuroprotective and possibly anti-inflammatory effects. In the developing brain, however, nicotine is neurotoxic. Middle overlapping panels: Clinical studies of persons with HIV who were smokers typically showed additive deleterious effects of HIV and tobacco smoking. However, in the preclinical studies, when nicotine was administered to the HIV-1 Tg rats, the neurotoxic effects of HIV were attenuated, but tobacco smoke worsened the inflammatory cascade.

Salience network coupling is linked to both tobacco smoking and symptoms of attention deficit hyperactivity disorder (ADHD)

INTRODUCTION

Attention deficit hyperactivity disorder (ADHD) symptoms, even those below diagnostic threshold, enhance the likelihood of nicotine dependence, suggesting a neurobiological link between disorders. Of particular interest is the salience network (SN), which mediates attention to salient internal/external stimuli to guide behavior and is anchored by the dorsal anterior cingulate cortex (dACC) and bilateral anterior insula (AI). Disrupted interactions between the SN and the default mode (DMN) and central executive networks (CEN) have been noted in both ADHD and nicotine dependence. Further, enhanced intra-SN coupling between the dACC-AI influences aspects of nicotine dependence such as reactivity to smoking cues.

METHODS

To identify links between SN functional connectivity and ADHD symptoms in nicotine dependence, we compared 21 nicotine dependent individuals with 17 non-smokers on ADHD symptoms as measured by the ADHD self-report scale (ASRS) and resting state intra and inter-SN functional connectivity.

RESULTS

Relative to healthy controls, nicotine dependent individuals had significantly higher ASRS scores and greater dACC-AI coupling. No group differences were noted on inter-SN network coupling. A significant association was found between ASRS and dACC-AI coupling both in the entire cohort and specifically when evaluating nicotine dependent individuals alone.

CONCLUSIONS

The greater ASRS scores in nicotine dependent individuals is in line with existent literature and the stronger dACC-AI coupling in smokers further supports the role of this network in nicotine dependence. The significant association between dACC-AI coupling and ASRS suggests that intra-SN coupling strength may impact neurocognitive functioning associated with both ADHD symptoms and nicotine dependence.

Evidence for GABA-A receptor dysregulation in gambling disorder: correlation with impulsivity

As a behavioural addiction, gambling disorder (GD) provides an opportunity to characterize addictive processes without the potentially confounding effects of chronic excessive drug and alcohol exposure. Impulsivity is an established precursor to such addictive behaviours, and GD is associated with greater impulsivity. There is also evidence of GABAergic dysregulation in substance addiction and in impulsivity. This study therefore investigated GABA_A receptor availability in 15 individuals with GD and 19 healthy volunteers (HV) using [¹¹C]Ro15‐4513, a relatively selective α5 benzodiazepine receptor PET tracer and its relationship with impulsivity. We found significantly higher [¹¹C]Ro15‐4513 total distribution volume (V_T) in the right hippocampus in the GD group compared with HV. We found higher levels of the ‘Negative Urgency’ construct of impulsivity in GD, and these were positively associated with higher [¹¹C]Ro15‐4513 V_T in the amygdala in the GD group; no such significant correlations were evident in the HV group. These results contrast with reduced binding of GABAergic PET ligands described previously in alcohol and opiate addiction and add to growing evidence for distinctions in the neuropharmacology between substance and behavioural addictions. These results provide the first characterization of GABA_A receptors in GD with [¹¹C]Ro15‐4513 PET and show greater α5 receptor availability and positive correlations with trait impulsivity. This GABAergic dysregulation is potential target for treatment.

Revisiting the role of the insula and smoking cue-reactivity in relapse: A replication and extension of neuroimaging findings

INTRODUCTION

The ability to direct smoking cessation treatment based on neuroscientific findings holds incredible promise. However, there is a strong need for consistency across studies to confirm neurobiological targets. While our prior work implicated enhanced insula reactivity to smoking cues in tobacco smoking relapse vulnerability, this finding has not been confirmed.

METHOD

Using functional magnetic resonance imaging (fMRI), we evaluated the pre-cessation brain reactivity to smoking vs. neutral cues in nicotine dependent smokers who were and were not able to maintain subsequent abstinence.

RESULTS

Of the 23 (7 women) individuals assessed, 13 relapsed and there were no demographic differences between those who did and did not relapse. However, smokers who relapsed showed enhanced reactivity to smoking cues in the right insula and dorsal striatum, showing significant overlap between our current and prior work despite methodological differences, including the fact that our previous work only included women.

CONCLUSION

The current work supports our prior results and builds on the concept that the insula and dorsal striatum work in concert to maintain nicotine dependence. Specifically, dorsal striatal-mediated habitual responding may be triggered both by the external drug-associated cues, and the insula-mediated internal states that provide additional context motivating drug use. This replicated finding also mirrors preclinical work that finds the same individualized distinction, as only some rodents attribute incentive salience to drug cues and are more likely to reinstate drug seeking after extinction. To effectively treat addiction, these individual characteristics and their underlying neurobiological foundations must be considered.

Postnatal Cardiovascular Consequences in the Offspring of Pregnant Rats Exposed to Smoking and Smoking Cessation Pharmacotherapies

Approximately 20% of pregnant women smoke despite intentions to quit. Smoking cessation drugs, such as nicotine replacement therapy (NRT) and bupropion, are recommended treatments. Adverse cardiovascular outcomes in offspring have raised concerns about NRT's safety during pregnancy. However, the effect of bupropion is unknown. Using a rat model, we determined whether NRT and bupropion interventions during pregnancy are safer than continued smoking on offspring's cardiovascular function. Male offspring of controls and dams exposed to cigarette smoke (1.6 packs/day, inhalation), nicotine (2 mg/kg/d subcutaneously), and bupropion (13 mg/kg twice daily orally) were assessed for fetoplacental weight, cardiac function, blood pressure, and vascular reactivity. Fetoplacental weights were decreased and spontaneous beating and intracellular calcium in neonatal cardiomyocytes were increased in smoking, nicotine, and bupropion offspring; however, these effects were more accentuated in smoking followed by nicotine and bupropion offspring. Increased heart rate and decreased cardiac output, stroke volume, and left ventricular percent posterior wall thickening were observed in smoking, nicotine, and bupropion offspring. The left ventricular mass was reduced in smoking and nicotine but not in bupropion offspring. Blood pressure was higher with decreased endothelium-dependent relaxation and exaggerated vascular contraction to angiotensin II in smoking and nicotine offspring, with more pronounced dysfunctions in smoking than nicotine offspring. Maternal bupropion did not impact offspring's blood pressure, endothelium-dependent relaxation, and vascular contraction. In conclusion, maternal nicotine intervention adversely affects offspring's cardiovascular outcomes, albeit less severely than continued smoking. However, bupropion causes cardiac derangement in offspring but does not adversely affect blood pressure and vascular function.

Dorsal anterior cingulate glutamate is associated with engagement of the default mode network during exposure to smoking cues

BACKGROUND

When exposed to smoking cues, nicotine dependent individuals activate brain regions overlapping with the default mode network (DMN), a network of regions involved in internally-focused cognition. The salience network (SN), which includes the dorsal anterior cingulate cortex (dACC), is thought to interact with the DMN and aids in directing attention toward salient internal or external stimuli. One possibility is that neurochemical variation in SN regions such as the dACC impact DMN reactivity to personally relevant stimuli such as smoking cues. This is consistent with emerging evidence suggesting an association between midline cortical glutamate (Glu) and activity in brain regions overlapping with the DMN.

METHODS

In 18 nicotine-dependent individuals, we assessed the relationship between DMN activation to smoking relative to neutral cues using functional magnetic resonance imaging and dACC Glu as measured by magnetic resonance spectroscopy. This association also was tested in a replication sample of 14 nicotine-dependent participants.

RESULTS

Not only was the DMN significantly less suppressed during smoking cue exposure, but also there was a positive association between DMN reactivity to smoking relative to neutral cues and dACC Glu (r=0.56, p<0.02). This finding was confirmed in the independent replication cohort (r=0.64, p<0.02).

CONCLUSIONS

The current findings confirm that the DMN is less suppressed when smokers view smoking relative to neutral cues, suggesting that smoking cues engage self-relevant processing. Furthermore, these results indicate that dACC Glu is associated with enhanced DMN engagement when nicotine-dependent individuals are exposed to self-relevant smoking cues.

Gendering Genetics: Biological Contingencies in the Protective Effects of Social Integration for Men and Women

Evidence that social and biological processes are intertwined in producing health and human behavior is rapidly accumulating. Using a feminist approach, this research explores how gender moderates the interaction between biological processes and men's and women's behavioral and emotional responses to similar social environments. Using data from the Collaborative Study on the Genetics of Alcoholism, the influence of gender, social integration, and genetic risk on nicotine and alcohol dependence is examined. Three-way interaction models reveal gender-specific moderation of interactions between genetic risk score and social integration. Namely, being currently married and reporting positive social psychological integration are predictive of reduced risk of nicotine dependence among men with genetic susceptibility to strong nicotine cravings in the presence of social cues like stress. In contrast, the protective effects of marital status and social integration are substantially attenuated and absent, respectively, among women with high-risk genotypes. This pattern reflects the dualism (i.e., simultaneous costs and benefits) inherent in social integration for women, which may disproportionately affect those with a genetic sensitivity to stress. These findings contest the notion of genotype as static biological hardwiring that is independent from social and cultural systems of gender difference.

Insula reactivity to negative stimuli is associated with daily cigarette use: A preliminary investigation using the Human Connectome Database

BACKGROUND

Individuals who smoke more cigarettes per day are at greater risk for developing smoking-related illness and have more difficulty quitting. Withdrawal-related negative mood is one factor thought to motivate drug use. However, heavy smokers are generally more sensitive to negative affect, not just negative emotion stemming from withdrawal. One possibility is that individual differences in how the brain processes negative stimuli may impact smoking use. Given the wealth of data implicating the insula in nicotine dependence and affective processing we hypothesize that the number of cigarettes an individual smokes per day will relate to insula reactivity to negative stimuli.

METHODS

A functional magnetic resonance imaging (fMRI) emotional processing task collected by the Human Connectome Project was assessed in 21 daily tobacco smokers who reported smoking between 5 and 20 cigarettes per day. The number of cigarettes smoked per day was correlated with right and left anterior insula reactivity to faces expressing a negative emotion relative to a control. This anterior insula region of interest has been associated with treatment outcome and smoking cue-reactivity in our prior work.

RESULTS

Those who smoked more daily cigarettes showed greater right insula reactivity to negative stimuli (r=0.564, p=0.008). Left insula reactivity was not associated with cigarettes smoked per day.

CONCLUSION

Smokers who use more cigarettes per day have greater insula reactivity to negative stimuli, furthering the field's understanding of the insula's involvement in nicotine use. This preliminary work also suggests a mechanism contributing to higher rates of daily smoking.

Noninvasive brain stimulation to suppress craving in substance use disorders: Review of human evidence and methodological considerations for future work

Substance use disorders (SUDs) can be viewed as a pathology of neuroadaptation. The pharmacological overstimulation of neural mechanisms of reward, motivated learning and memory leads to drug-seeking behavior. A critical characteristic of SUDs is the appearance of craving, the motivated desire and urge to use, which is a main focus of current pharmacological and behavioral therapies. Recent proof-of-concept studies have tested the effects of noninvasive brain stimulation on craving. Although its mechanisms of action are not fully understood, this approach shows interesting potential in tuning down craving and possibly consumption of diverse substances. This article reviews available results on the use of repetitive transcranial magnetic stimulation (rTMS) and transcranial electrical stimulation (tES) in SUDs, specifically tobacco, alcohol and psychostimulant use disorders. We discuss several important factors that need to be addressed in future works to improve clinical assessment and effects of noninvasive brain stimulation in SUDs. Factors discussed include brain stimulation devices and parameters, study designs, brain states and subjects' characteristics.

Advances in nicotine research in Addiction Biology

The aim of Addiction Biology is to advance our understanding of the action of drugs of abuse and addictive processes via the publication of high-impact clinical and pre-clinical findings resulting from behavioral, molecular, genetic, biochemical, neurobiological and pharmacological research. As of 2013, Addiction Biology is ranked number 1 in the category of Substance Abuse journals (SCI). Occasionally, Addiction Biology likes to highlight via review important findings focused on a particular topic and recently published in the journal. The current review summarizes a number of key publications from Addiction Biology that have contributed to the current knowledge of nicotine research, comprising a wide spectrum of approaches, both clinical and pre-clinical, at the cellular, molecular, systems and behavioral levels. A number of findings from human studies have identified, using imaging techniques, alterations in common brain circuits, as well as morphological and network activity changes, associated with tobacco use. Furthermore, both clinical and pre-clinical studies have characterized a number of mechanistic targets critical to understanding the effects of nicotine and tobacco addiction. Together, these findings will undoubtedly drive future studies examining the dramatic impact of tobacco use and the development of treatments to counter nicotine dependence.

Insula-Dorsal Anterior Cingulate Cortex Coupling is Associated with Enhanced Brain Reactivity to Smoking Cues

The insula plays a critical role in maintaining nicotine dependence and reactivity to smoking cues. More broadly, the insula and the dorsal anterior cingulate cortex (dACC) are key nodes of the salience network (SN), which integrates internal and extrapersonal information to guide behavior. Thus, insula-dACC interactions may be integral in processing salient information such as smoking cues that facilitate continued nicotine use. We evaluated functional magnetic resonance imaging (fMRI) data from nicotine-dependent participants during rest, and again when they viewed smoking-related images. Greater insula-dACC coupling at rest was significantly correlated with enhanced smoking cue-reactivity in brain areas associated with attention and motor preparation, including the visual cortex, right ventral lateral prefrontal cortex, and the dorsal striatum. In an independent cohort, we found that insula-dACC connectivity was stable over 1-h delay and was not influenced by changes in subjective craving or expired carbon monoxide, suggesting that connectivity strength between these regions may be a trait associated with heightened cue-reactivity. Finally, we also showed that insula reactivity to smoking cues correlates with a rise in cue-reactivity throughout the entire SN, indicating that the insula's role in smoking cue-reactivity is not functionally independent, and may actually represent the engagement of the entire SN. Collectively, these data provide a more network-level understanding of the insula's role in nicotine dependence and shows a relationship between inherent brain organization and smoking cue-reactivity.

Bridging the gap between the neurocognitive lab and the addiction clinic

In the past decennium there has been an enormous increase in new insights in cognitive mechanisms of addiction and their neural substrates. These candidate neurocognitive mechanisms, particularly those associated with "drive" and "control" aspects of addiction, are clearly involved in substance use problems but do not yet provide a full explanation. The neurocognitive mechanisms addressed in the present perspective are attentional bias, reward processing (both drive aspects) and error-processing and cognitive control (both control aspects). The time has come to transfer these recent insights more consistently to clinical practice by studying their relevance for diagnosis and treatment in patient samples. The present perspective echoes the development of recent initiatives such as the RDoC system to integrate developments in neuroscience into clinical practice. The aim of this article is to open new vistas for addiction diagnosis and treatment and to discuss why and how these neurocognitive aspects of addictive behavior can be used in clinical practice. In addition, present problematic issues and a future research agenda are provided.

New perspectives on using brain imaging to study CNS stimulants

While the recent application of brain imaging to study CNS stimulants has offered new insights into the fundamental factors that contribute to their use and abuse, many gaps remain. Brain circuits that mediate pleasure, dependence, craving and relapse are anatomically, neurophysiologically and neurochemically distinct from one another, which has guided the search for correlates of stimulant-seeking and taking behavior. However, unlike other drugs of abuse, metrics for tolerance and physical dependence on stimulants are not obvious. The dopamine theory of stimulant abuse does not sufficiently explain this disorder as serotonergic, GABAergic and glutamagergic circuits are clearly involved in stimulant pharmacology and so tracking the source of the "addictive" processes must adopt a more multimodal, multidisciplinary approach. To this end, both anatomical and functional magnetic resonance imaging (MRI), MR spectroscopy (MRS) and positron emission tomography (PET) are complementary and have equally contributed to our understanding of how stimulants affect the brain and behavior. New vistas in this area include nanotechnology approaches to deliver small molecules to receptors and use MRI to resolve receptor dynamics. Anatomical and blood flow imaging has yielded data showing that cognitive enhancers might be useful adjuncts in treating CNS stimulant dependence, while MRS has opened opportunities to examine the brain's readiness to accept treatment as GABA tone normalizes after detoxification. A desired outcome of the above approaches is being able to offer evidence-based rationales for treatment approaches that can be implemented in a more broad geographic area, where access to brain imaging facilities may be limited. This article is part of the Special Issue entitled 'CNS Stimulants'.

Neural correlates of attentional bias in addiction

A small but growing neuroimaging literature has begun to examine the neural mechanisms underlying the difficulty that substance-use dependent (SUD) groups have with ignoring salient, drug-related stimuli. Drug-related attentional bias appears to implicate the countermanding forces of cognitive control and reward salience. Basic cognitive neuroscience research suggests that ignoring emotionally evocative stimuli in our environment requires both up-regulation of control networks and down-regulation of processing in emotion and reward regions. Research to date suggests that attentional biases for drug-related stimuli emerge from a failure to sufficiently increase control of attention over salient, but task-irrelevant stimuli. While SUD samples have typically shown increased activity in the cognitive control regions (ie, lateral prefrontal and dorsal anterior cingulate), during attentional bias such increases appear to have been insufficient for the concomitant increases in processing by the emotion/reward regions (ie, amygdala, insula, and striatum). Given the potential contribution of attentional biases to perpetuating drug use and the development of interventions (both pharmaceutical and cognitive-behavioral) to treat biases, understanding the neural basis of successfully reducing bias remains an important, but as yet unanswered, question for our field.

Dissociable contributions of anterior cingulate cortex and basolateral amygdala on a rodent cost/benefit decision-making task of cognitive effort

Personal success often requires the choice to expend greater effort for larger rewards, and deficits in such effortful decision making accompany a number of illnesses including depression, schizophrenia, and attention-deficit/hyperactivity disorder. Animal models have implicated brain regions such as the basolateral amygdala (BLA) and anterior cingulate cortex (ACC) in physical effort-based choice, but disentangling the unique contributions of these two regions has proven difficult, and effort demands in industrialized society are predominantly cognitive in nature. Here we utilize the rodent cognitive effort task (rCET), a modification of the five-choice serial reaction-time task, wherein animals can choose to expend greater visuospatial attention to obtain larger sucrose rewards. Temporary inactivation (via baclofen-muscimol) of BLA and ACC showed dissociable effects: BLA inactivation caused hard-working rats to 'slack off' and 'slacker' rats to work harder, whereas ACC inactivation caused all animals to reduce willingness to expend mental effort. Furthermore, BLA inactivation increased the time needed to make choices, whereas ACC inactivation increased motor impulsivity. These data illuminate unique contributions of BLA and ACC to effort-based decision making, and imply overlapping yet distinct circuitry for cognitive vs physical effort. Our understanding of effortful decision making may therefore require expanding our models beyond purely physical costs.

Involvement of glutamatergic and GABAergic systems in nicotine dependence: Implications for novel pharmacotherapies for smoking cessation

Tobacco smoking continues to be a major global health hazard despite significant public awareness of its harmful consequences. Although several treatment options are currently available for smoking cessation, these medications are effective in only a small subset of smokers, and relapse rates continue to be high. Therefore, a better understanding of the neurobiological mechanisms that mediate tobacco dependence is essential for the development of effective smoking cessation medications. Nicotine is the primary psychoactive component of tobacco that drives the harmful tobacco smoking habit. Nicotine binds to nicotinic acetylcholine receptors (nAChRs) in the brain, resulting in the release of a wide range of neurotransmitters, including glutamate and γ-aminobutyric acid (GABA). This review article focuses on the role of the excitatory glutamate system and inhibitory GABA system in nicotine dependence. Accumulating evidence suggests that blockade of glutamatergic transmission or facilitation of GABAergic transmission attenuates the positive reinforcing and incentive motivational aspects of nicotine, inhibits the reward-enhancing and conditioned rewarding effects of nicotine, and blocks nicotine-seeking behavior. Chronic nicotine exposure produced long-term neuroadaptations that contribute to nicotine withdrawal, but the role of GABA and glutamate transmission in nicotine withdrawal is less understood. Overall, the findings presented in this review provide strong converging evidence for the potential effectiveness of glutamatergic and GABAergic medications in nicotine dependence. This article is part of a Special Issue entitled 'NIDA 40th Anniversary Issue'.