The role of dopamine in human addiction: From reward to motivated attention

Genetic polymorphisms and their association with neurobiological and psychological factors in anorexia nervosa: a systematic review

Background and aims

Anorexia nervosa (AN) is a complex neuropsychiatric disorder. This systematic review synthesizes evidence from diverse studies to assess and investigate the association between gene polymorphisms and psychological and neurobiological factors in patients with AN.

Methods

A systematic search across PubMed, PsycINFO, Scopus, and Web of Science databases, along with manual searching, was conducted. The review protocol was approved by PROSPERO (CRD42023452548). Out of 1,250 articles, 11 met the inclusion criteria. The quality of eligible articles was assessed using the Newcastle-Ottawa Scale (NOS) tool. The systematic review followed the PRISMA guidelines.

Results

The serotoninergic system, particularly the 5-HTTLPR polymorphism, is consistently linked to altered connectivity in the ventral attention network, impaired inhibitory control, and increased susceptibility to AN. The 5-HTTLPR polymorphism affects reward processing, motivation, reasoning, working memory, inhibition, and outcome prediction in patients with AN. The dopaminergic system, involving genes like COMT, DRD2, DRD3, and DAT1, regulates reward, motivation, and decision-making. Genetic variations in these dopaminergic genes are associated with psychological manifestations and clinical severity in patients with AN. Across populations, the Val66Met polymorphism in the BDNF gene influences personality traits, eating behaviors, and emotional responses. Genes like OXTR, TFAP2B, and KCTD15 are linked to social cognition, emotional processing, body image concerns, and personality dimensions in patients with AN.

Conclusion

There was an association linking multiple genes to the susceptibly and/or severity of AN. This genetic factor contributes to the complexity of AN and leads to higher diversity of its clinical presentation. Therefore, conducting more extensive research to elucidate the underlying mechanisms of anorexia nervosa pathology is imperative for advancing our understanding and potentially developing targeted therapeutic interventions for the disorder.Systematic review registration: [https://clinicaltrials.gov/], identifier [CRD42023452548].

Dead rats, dopamine, performance metrics, and peacock tails: Proxy failure is an inherent risk in goal-oriented systems

When a measure becomes a target, it ceases to be a good measure. For example, when standardized test scores in education become targets, teachers may start "teaching to the test," leading to breakdown of the relationship between the measure - test performance - and the underlying goal - quality education. Similar phenomena have been named and described across a broad range of contexts, such as economics, academia, machine learning, and ecology. Yet it remains unclear whether these phenomena bear only superficial similarities, or if they derive from some fundamental unifying mechanism. Here, we propose such a unifying mechanism, which we label proxy failure. We first review illustrative examples and their labels, such as the "cobra effect," "Goodhart's law," and "Campbell's law." Second, we identify central prerequisites and constraints of proxy failure, noting that it is often only a partial failure or divergence. We argue that whenever incentivization or selection is based on an imperfect proxy measure of the underlying goal, a pressure arises that tends to make the proxy a worse approximation of the goal. Third, we develop this perspective for three concrete contexts, namely neuroscience, economics, and ecology, highlighting similarities and differences. Fourth, we outline consequences of proxy failure, suggesting it is key to understanding the structure and evolution of goal-oriented systems. Our account draws on a broad range of disciplines, but we can only scratch the surface within each. We thus hope the present account elicits a collaborative enterprise, entailing both critical discussion as well as extensions in contexts we have missed.

Crosstalk between the endocannabinoid and mid-brain dopaminergic systems: Implication in dopamine dysregulation

Endocannabinoids (eCBs) and the expanded endocannabinoid system (ECS)-"endocannabinoidome", consists of the endogenous ligands, eCBs, their canonical and non-canonical receptor subtypes, and their synthesizing and metabolizing enzymes. This system modulates a wide range of body functions and acts as a retrograde signaling system within the central nervous system (CNS) by inhibition of classical transmitters, and plays a vital modulatory function on dopamine, a major neurotransmitter in the CNS. Dopamine is involved in different behavioral processes and contributes to different brain disorders-including Parkinson's disease, schizophrenia, and drug addiction. After synthesis in the neuronal cytosol, dopamine is packaged into synaptic vesicles until released by extracellular signals. Calcium dependent neuronal activation results in the vesicular release of dopamine and interacts with different neurotransmitter systems. The ECS, among others, is involved in the regulation of dopamine release and the interaction occurs either through direct or indirect mechanisms. The cross-talk between the ECS and the dopaminergic system has important influence in various dopamine-related neurobiological and pathologic conditions and investigating this interaction might help identify therapeutic targets and options in disorders of the CNS associated with dopamine dysregulation.

Machine learning with neuroimaging biomarkers: Application in the diagnosis and prediction of drug addiction

Drug abuse is a serious problem worldwide. Owing to intermittent intake of certain substances and the early inconspicuous clinical symptoms, this brings huge challenges for timely diagnosing addiction status and preventing substance use disorders (SUDs). As a non-invasive technique, neuroimaging can capture neurobiological signatures of abnormality in multiple brain regions caused by drug consumption in each clinical stage, like parenchymal morphology alteration as well as aberrant functional activity and connectivity of cerebral areas, making it realizable to diagnosis, prediction and even preemptive therapy of addiction. Machine learning (ML) algorithms primarily used for classification have been extensively applied in analysing medical imaging datasets. Significant neurobiological characteristics employed and revealed by classifiers were used to diagnose addictive states and predict initiation and vulnerability to drug usage, treatment abstinence, relapse and resilience of addicts and the risk of SUD. In this review, we summarize application of ML methods in neuroimaging focusing on addicts' diagnosis of clinical status and risk prediction and elucidate the discriminative neurobiological features from brain electrophysiological, morphological and functional perspectives that contribute most to the classifier, finally highlighting the auxiliary role of ML in addiction treatment.

Rewarding and Reinforcing Effects of 25H-NBOMe in Rodents

The drug 25H-NBOMe is a new psychoactive substance (NPS). The use of these substances is likely to pose a threat to public health because they elicit effects similar to those of known psychoactive substances with similar chemical structures. However, data regarding the abuse potential of 25H-NBOMe are lacking. Here, we evaluated the abuse liability of 25H-NBOMe in rodents. The rewarding and reinforcing effects were evaluated through conditioned place preference (CPP) and self-administration (SA) tests after administration of 25H-NBOMe. To investigate the effects of 25H-NBOMe on the central nervous system, we determined the changes in dopamine levels by in vivo microdialysis. In the locomotor activity test, 25H-NBOme significantly increased locomotor activity in mice. In the place conditioning test, the 25H-NBOMe (0.1 and 0.5 mg/kg) groups showed a significantly increase in CPP in mice. In the SA test, the 25H-NBOMe (0.01 mg/kg) administered group showed a significant increased number of infusions and active lever presses. In microdialysis, the 25H-NBOMe (10 mg/kg) administered group was significantly increased in rats.

Electrochemical dopamine sensor based on bi-metallic Co/Zn porphyrin metal-organic framework

Integrating other metal ions into mono-metallic metal-organic framework (MOF) to form bi-metallic MOF is an effective strategy to enhance the performance of MOFs from the internal structure. In this study, two-dimensional (2D) cobalt/zinc-porphyrin (Co/Zn-TCPP) MOF nanomaterials with different Co/Zn molar ratios were synthesised using a simple surfactant-assisted method, and novel dopamine (DA) sensing methods were constructed based on these materials. The characterisation results showed that all MOF with different Co/Zn molar ratios presented a nanofilm, and the Co and Zn elements were uniformly distributed. All sensors based on Co_xZn_100-x-TCPP had a certain catalytic performance to DA. Among them, the sensor based on CO₂₅Zn₇₅-TCPP showed the strongest signal response, indicating that the catalytic performance of MOF on DA can be adjusted by changing the Co/Zn molar ratio. The doping of metal ions improves the chemical environment of the pores, and increases the types and spatial arrangement of the active sites of the MOF, which is beneficial to the electron transfer and exchange with DA; Co²⁺ and Zn²⁺ active centres have a synergistic promotion effect, so the catalytic activity of MOF is significantly improved. The linear range at the potential of 0.1 V based on Co₂₅Zn₇₅-TCPP for DA was 5 nM-177.8 μM, with a detection limit of 1.67 nM (S/N = 3). The sensor exhibited a good selectivity for detecting DA. This research is expected to provide new ideas and references for constructing high-performance sensing interfaces and platforms.

Granulocyte colony-stimulating factor (G-CSF) enhances cocaine effects in the nucleus accumbens via a dopamine release-based mechanism

Cocaine use disorder is associated with alterations in immune function including altered expression of multiple peripheral cytokines in humans-several of which correlate with drug use. Individuals suffering from cocaine use disorder show altered immune system responses to drug-associated cues, highlighting the interaction between the brain and immune system as a critical factor in the development and expression of cocaine use disorder. We have previously demonstrated in animal models that cocaine use upregulates the expression of granulocyte colony-stimulating factor (G-CSF)-a pleiotropic cytokine-in the serum and the nucleus accumbens (NAc). G-CSF signaling has been causally linked to behavioral responses to cocaine across multiple behavioral domains. The goal of this study was to define whether increases in G-CSF alter the pharmacodynamic effects of cocaine on the dopamine system and whether this occurs via direct mechanisms within local NAc microcircuits. We find that systemic G-CSF injection increases cocaine effects on dopamine terminals. The enhanced dopamine levels in the presence of cocaine occur through a release-based mechanism, rather than through effects on the dopamine transporter-as uptake rates were unchanged following G-CSF treatment. Critically, this effect could be recapitulated by acute bath application of G-CSF to dopamine terminals, an effect that was occluded by prior G-CSF treatment, suggesting a similar mechanistic basis for direct and systemic exposures. This work highlights the critical interaction between the immune system and psychostimulant effects that can alter drug responses and may play a role in vulnerability to cocaine use disorder.

Sign and goal tracker rats process differently the incentive salience of a conditioned stimulus

Sign and goal tracker animals show different behavioral patterns in response to conditioned stimuli, which may be driven by different neural circuits involved in processing stimuli. Here, we explored whether sign and goal-tracker profiles implicated different brain regions and responses to incentive salience of stimuli. We performed three experiments using male Wistar rats. Experiment 1 showed that lesioning the medial prefrontal cortex increased the prevalence of the goal-tracker phenotype. Experiment 2 assessed the developmental trajectory of the salience incentive attribution to a conditioned stimulus, showing that increased incentive salience of stimuli increased the prevalence of the sign-tracker phenotype in mature, but not preadolescent rats. In experiment 3, the functional impact of the medial prefrontal cortex circuits was analyzed with a latent inhibition procedure. Sign tracker rats showed a reduced latent inhibition to stimuli previously exposed when compared to goal tracker or intermediate rats. The overall results of this study highlight a key role of the medial prefrontal cortex for sign tracking behavior. The expression of sign and goal tracker phenotypes changed after lesion to the medial prefrontal cortex (experiment 1), differed across development (experiment 2), and showed differences in the attentional processes to previously exposed stimuli, as preexposure to CS was ineffective in sign tracker animals (experiment 3). These data indicate that the responses to the incentive salience of stimuli in sign tracker and goal tracker profiles are likely driven by different neural circuitry, with a different role of prefrontal cortical function.

The Acute Effects of a Dopamine D3 Receptor Preferring Agonist on Motivation for Cigarettes in Dependent and Occasional Cigarette Smokers

Background

Dopaminergic functioning is thought to play critical roles in both motivation and addiction. There is preliminary evidence that dopamine agonists reduce the motivation for cigarettes in smokers. However, the effects of pramipexole, a dopamine D3 receptor preferring agonist, have not been investigated.

The aim of this study was to examine the effects of an acute dose of pramipexole on the motivation to earn cigarettes and nondrug rewards.

Methods

Twenty dependent and 20 occasional smokers received 0.5 mg pramipexole using a double-blind, placebo-controlled crossover design. Motivation for cigarettes and consummatory nondrug rewards was measured using the DReaM-Choice task, in which participants earned, and later “consumed,” cigarettes, music, and chocolate. Demand for cigarettes was measured using the Cigarette Purchase Task (CPT). Self-reported craving, withdrawal, and drug effects were also recorded.

Results

Dependent smokers chose (p < .001) and button-pressed for (p < .001) cigarettes more, and chose chocolate less (p < .001), than occasional smokers. Pramipexole did not affect the number of choices for or amount of button-pressing for any reward including cigarettes, which was supported by a Bayesian analysis. The dependent smokers had greater demand for cigarettes than occasional smokers across all CPT outcomes (ps < .021), apart from elasticity. Pramipexole did not affect demand for cigarettes, and this was supported by Bayesian analyses. Pramipexole produced greater subjective “feel drug” and “dislike drug” effects than placebo.

Conclusions

Dependent and occasional cigarette smokers differed in their motivation for cigarettes but not for the nondrug rewards. Pramipexole did not acutely alter motivation for cigarettes. These findings question the role of dopamine D3 receptors in cigarette-seeking behavior in dependent and occasional smokers.

Implications

This study adds to the growing literature about cigarette versus nondrug reward processing in nicotine dependence and the role of dopamine in cigarette-seeking behavior. Our results suggest nicotine dependence is associated with a hypersensitivity to cigarette rewards but not a hyposensitivity to nondrug rewards. Furthermore, our results question the importance of dopamine D3 receptors in motivational processing of cigarettes in occasional and dependent smokers.

A systematic review: Candidate gene and environment interaction on alcohol use and misuse among adolescents and young adults

BACKGROUND AND OBJECTIVES

Youth drinking is a pervasive public health concern with serious negative developmental implications. Candidate gene and environment interaction studies (cGxE) show that environmental effects on drinking behaviors may differ by individuals' genotypes. Yet little is known about whether genetic and environmental effects on drinking behaviors are developmentally specific.

METHODS

This systematic review evaluated 42 cGxE studies of drinking in adolescence and young adulthood.

RESULTS

Although there are mixed findings, studies of cGxE effects involving DRD4, 5-HTTLPR, DRD2, and OPRM1 genotypes showed relatively consistent patterns. The effects of under-controlled environments (eg, low levels of parental monitoring) on early and middle adolescent drinking appeared to differ across DRD2 or OPRM1 genotypes. Effects of alcohol-facilitating environments (eg, heavy drinking peers) on late adolescent and young adult drinking appeared to differ across DRD4 or OPRM1 genotypes. Interactions between 5-HTTLPR genotype with stressful environments (eg, negative life events) were found throughout adolescence and young adulthood, although there were some inconsistencies regarding the risk-conferring allele. There was limited evidence for other cGxE effects due to the small number of studies.

CONCLUSIONS AND SCIENTIFIC SIGNIFICANCE

This review suggests that GxE findings may advance our knowledge regarding which developmentally specific conditions result in the expression of candidate genes that influence youth alcohol use and misuse. However, since a significant number of studies had small sample sizes and most studies had small effect sizes, findings need replication across independent studies with large samples. (Am J Addict 2018;XX:1-19).

Early Socioemotional Intervention Mediates Long-Term Effects of Atypical Rearing on Structural Covariation in Gray Matter in Adult Chimpanzees

Atypical rearing has deleterious effects on chimpanzee behavior during development, some of which can be ameliorated with a responsive care intervention (RCI). Here, we obtained in vivo magnetic resonance images of adult brains of 27 chimpanzees given institutional care, with and without RCI, and compared them with those of 16 chimpanzees mother-reared from birth. We found significant long-term rearing effects on structural covariation and gray matter volume, specifically in the basal forebrain (i.e., caudate, putamen, nucleus accumbens, rectus gyrus, and orbital prefrontal cortex), indicating that RCI prevented brain changes due to atypical rearing. A significant correlation between covariation in these brain areas and caregiver nurturing, experienced in the first month of life, suggests a possible developmental mechanism for the effect of early experience on brain networks. We identified an early intervention that prevents changes in the basal forebrain that otherwise emerge as a consequence of institutionalized rearing without species-typical socioemotional experiences.

Dopamine transporter mutant animals: a translational perspective

The dopamine transporter (DAT) plays an important homeostatic role in the control of both the extracellular and intraneuronal concentrations of dopamine, thereby providing effective control over activity of dopaminergic transmission. Since brain dopamine is known to be involved in numerous neuropsychiatric disorders, investigations using mice with genetically altered DAT function and thus intensity of dopamine-mediated signaling have provided numerous insights into the pathology of these disorders and novel pathological mechanisms that could be targeted to provide new therapeutic approaches for these disorders. In this brief overview, we discuss recent investigations involving animals with genetically altered DAT function, particularly focusing on translational studies providing new insights into pathology and pharmacology of dopamine-related disorders. Perspective applications of these and newly developed models of DAT dysfunction are also discussed.

Chemogenetic Activation of Midbrain Dopamine Neurons Affects Attention, but not Impulsivity, in the Five-Choice Serial Reaction Time Task in Rats

Attentional impairments and exaggerated impulsivity are key features of psychiatric disorders, such as attention-deficit/hyperactivity disorder, schizophrenia, and addiction. These deficits in attentional performance and impulsive behaviors have been associated with aberrant dopamine (DA) signaling, but it remains unknown whether these deficits result from enhanced DA neuronal activity in the midbrain. Here, we took a novel approach by testing the impact of chemogenetically activating DA neurons in the ventral tegmental area (VTA) or substantia nigra pars compacta (SNc) on attention and impulsivity in the five-choice serial reaction time task (5-CSRTT) in rats. We found that activation of DA neurons in both the VTA and SNc impaired attention by increasing trial omissions. In addition, SNc DA neuron activation decreased attentional accuracy. Surprisingly, enhanced DA neuron activity did not affect impulsive action in this task. These results show that enhanced midbrain DA neuronal activity induces deficits in attentional performance, but not impulsivity. Furthermore, DA neurons in the VTA and SNc have different roles in regulating attention. These findings contribute to our understanding of the neural substrates underlying attention deficits and impulsivity, and provide valuable insights to improve treatment of these symptoms.

Brain reactivity to alcohol and cannabis marketing during sobriety and intoxication

Drugs of abuse stimulate striatal dopamine release and activate reward pathways. This study examined the impact of alcohol and cannabis marketing on the reward circuit in alcohol and cannabis users while sober and intoxicated. It was predicted that alcohol and cannabis marketing would increase striatal activation when sober and that reward sensitivity would be less during alcohol and cannabis intoxication. Heavy alcohol (n = 20) and regular cannabis users (n = 21) participated in a mixed factorial study involving administration of alcohol and placebo in the alcohol group and cannabis and placebo in the cannabis group. Non-drug users (n = 20) served as between group reference. Brain activation after exposure to alcohol and cannabis marketing movies was measured using functional magnetic resonance imaging and compared between groups while sober and compared with placebo while intoxicated. Implicit alcohol and cannabis cognitions were assessed by means of a single-category implicit association test. Alcohol and cannabis marketing significantly increased striatal BOLD activation across all groups while sober. Striatal activation however decreased during intoxication with alcohol and cannabis. Implicit associations with cannabis marketing cues were significantly more positive in alcohol and cannabis users as compared with non-drug using controls. Public advertising of alcohol or cannabis use elicits striatal activation in the brain's reward circuit. Reduction of marketing would reduce brain exposure to reward cues that motivate substance use. Conversely, elevated dopamine levels protect against the reinforcing potential of marketing.

Pre-ejection period reactivity to reward is associated with anhedonic symptoms of depression among adolescents

Pre-ejection period (PEP) reactivity to reward has been posited as a specific index of behavioral approach and incentive motivation, suggesting it might be uniquely associated with the affective and motivational deficits of anhedonia. This study evaluated PEP reactivity to a reward task as a predictor of depressive symptoms among adolescents, examining global depressive symptoms as well as specific anhedonic and nonanhedonic symptoms clusters. Participants included 76 adolescents, ages 11-15 years (52% female). This study found marginal support for an association between PEP reactivity to reward and concurrent anhedonia symptoms, but no association with nonanhedonic or the global scale. Findings are discussed in terms of potential associations between peripheral psychophysiological measures and dopaminergic functioning and also the utility of this measure for future research on anhedonia.

Differential motivational profiles following adolescent sucrose access in male and female rats

Adolescents are the highest consumers of sugar sweetened drinks. Excessive consumption of such drinks is a likely contributor to the development of obesity and may be associated with enduring changes in the systems involved in reward and motivation. We examined the impact of daily sucrose consumption in young male and female rats (N=12 per group) across the adolescent period on the motivation to perform instrumental responses to gain food rewards as adults. Rats were or were not exposed to a sucrose solution for 2 h each day for 28 days across adolescence [postnatal days (P) 28-56]. They were then trained as adults (P70 onward) to lever press for a palatable 15% cherry flavored sucrose reward and tested on a progressive ratio (PR) schedule to assess motivation to respond for reinforcement. Female rats exposed to sucrose had higher breakpoints on the PR schedule than controls, whereas male rats exposed to sucrose had lower breakpoints than controls. These results show that consumption of sucrose during adolescence produced sex-specific behavioral changes in responding for sucrose as adults.

Electrophysiology for addiction medicine: From methodology to conceptualization of reward deficits

In the past decade, electroencephalographic research on addiction has employed passive viewing, oddball, inhibition, prediction, gambling, and reversal learning tasks to study how substance users neurally prioritize drug-related rewards at the expense of nondrug rewards. On the whole, findings across substances (alcohol, cannabis, cocaine, nicotine, opiates, gambling, and gaming) demonstrate impairments in the differentiation of monetary incentives and the inhibition of prepotent responses. Furthermore, exaggerated resources devoted to drug cues and attenuated processing of other types of pleasant emotional stimuli predict greater probability of future drug use. However, drug use recency, frequency, sensitivity, and insight all appear to be moderators of these effects. We argue that more longitudinal studies are warranted to determine the time course of reward processing as a function of development and chronicity.

Pathological Buying Online as a Specific Form of Internet Addiction: A Model-Based Experimental Investigation

The study aimed to investigate different factors of vulnerability for pathological buying in the online context and to determine whether online pathological buying has parallels to a specific Internet addiction. According to a model of specific Internet addiction by Brand and colleagues, potential vulnerability factors may consist of a predisposing excitability from shopping and as mediating variable, specific Internet use expectancies. Additionally, in line with models on addiction behavior, cue-induced craving should also constitute an important factor for online pathological buying. The theoretical model was tested in this study by investigating 240 female participants with a cue-reactivity paradigm, which was composed of online shopping pictures, to assess excitability from shopping. Craving (before and after the cue-reactivity paradigm) and online shopping expectancies were measured. The tendency for pathological buying and online pathological buying were screened with the Compulsive Buying Scale (CBS) and the Short Internet Addiction Test modified for shopping (s-IATshopping). The results demonstrated that the relationship between individual's excitability from shopping and online pathological buying tendency was partially mediated by specific Internet use expectancies for online shopping (model's R² = .742, p < .001). Furthermore, craving and online pathological buying tendencies were correlated (r = .556, p < .001), and an increase in craving after the cue presentation was observed solely in individuals scoring high for online pathological buying (t(28) = 2.98, p < .01, d = 0.44). Both screening instruments were correlated (r = .517, p < .001), and diagnostic concordances as well as divergences were indicated by applying the proposed cut-off criteria. In line with the model for specific Internet addiction, the study identified potential vulnerability factors for online pathological buying and suggests potential parallels. The presence of craving in individuals with a propensity for online pathological buying emphasizes that this behavior merits potential consideration within the non-substance/behavioral addictions.

Modulating dopamine release by optogenetics in transgenic mice reveals terminal dopaminergic dynamics

Dopamine (DA) release and uptake dynamics in the nucleus accumbens (NAc) have important implications for neurological diseases and mammalian animal behaviors. We demonstrate here the use of cell-type-specific optogenetic targeting in conjunction with fast-scan cyclic voltammetry applied to brain slices prepared from specifically tailored transgenic mice, which conditionally express channelrhodopsin-2 (ChR2) through dopamine transporter (DAT)-Cre. Terminal dopaminergic dynamics and the direct manipulation of induced DA release level by controlling light intensity, pulse width, and the shape of stimulation waveforms were studied. Effective cell terminal-targeting optogenetic induction of DA release at physiological levels in NAc is demonstrated and discussed. It was found that delivering more light energy by increasing stimulation intensity and length is not the only way to control DA release; the temporal shape of the stimulus waveform at light onset is also critically related to induced DA concentrations. In addition, DA uptake dynamics as well as the recovery of the presynaptic releasable DA pool are studied and modeled. More broadly, our experimental findings provide important further evidence for effectively applying optogenetics to induce neurotransmitter release in the behaviorally relevant region of the brain in a highly cell-type selective context.

Brain regions affected by impaired control modulate responses to alcohol and smoking cues

OBJECTIVE

Despite the commonly observed comorbidity of alcohol and tobacco use disorders and years of research, the mechanism underlying concurrent use of alcohol and tobacco is not yet clear. In this study, we used functional magnetic resonance imaging (fMRI) to investigate the relationship between brain responses to alcohol and smoking cues in 45 subjects with episodic drinking and regular smoking.

METHOD

fMRI data were collected from two studies performing an alcohol-craving task and a smoking-craving task. First, we identified brain voxels significantly activated for both substance cues and then associated the activation of these voxels with various alcohol- and nicotine-dependence measures. Significant clusters (cluster-wise p < .05) correlated with behavioral assessments were extracted, and clusters identified from both cues were compared.

RESULTS

The association tests with various dependence scores showed that the loss of behavioral control subcategory in the Alcohol Dependence Scale was significantly correlated with brain activation of the posterior cingulate cortex (PCC) and right posterior insula regardless of cue types.

CONCLUSIONS

Our findings suggest that the PCC and right posterior insula, each playing a role in the salience network, are affected significantly by impaired control for alcohol and in turn influence brain responses to not only alcohol but also smoking cues, providing insight to neuronal mechanisms for concurrent use or comorbidity of alcohol and nicotine dependence.

Altering attentional control settings causes persistent biases of visual attention

Attentional control settings have an important role in guiding visual behaviour. Previous work within cognitive psychology has found that the deployment of general attentional control settings can be modulated by training. However, research has not yet established whether long-term modifications of one particular type of attentional control setting can be induced. To address this, we investigated persistent alterations to feature search mode, also known as an attentional bias, towards an arbitrary stimulus in healthy participants. Subjects were biased towards the colour green by an information sheet. Attentional bias was assessed using a change detection task. After an interval of either 1 or 2 weeks, participants were then retested on the same change detection task, tested on a different change detection task where colour was irrelevant, or were biased towards an alternative colour. One experiment included trials in which the distractor stimuli (but never the target stimuli) were green. The key finding was that green stimuli in the second task attracted attention, despite this impairing task performance. Furthermore, inducing a second attentional bias did not override the initial bias toward green objects. The attentional bias also persisted for at least two weeks. It is argued that this persistent attentional bias is mediated by a chronic change to participants' attentional control settings, which is aided by long-term representations involving contextual cueing. We speculate that similar changes to attentional control settings and continuous cueing may relate to attentional biases observed in psychopathologies. Targeting these biases may be a productive approach to treatment.

Reward and Cognition: Integrating Reinforcement Sensitivity Theory and Social Cognitive Theory to Predict Drinking Behavior

BACKGROUND

Both Reinforcement Sensitivity Theory and Social Cognitive Theory have been applied to understanding drinking behavior. We propose that theoretical relationships between these models support an integrated approach to understanding alcohol use and misuse.

OBJECTIVES

We aimed to test an integrated model in which the relationships between reward sensitivity and drinking behavior (alcohol consumption, alcohol-related problems, and symptoms of dependence) were mediated by alcohol expectancies and drinking refusal self-efficacy.

METHODS

Online questionnaires assessing the constructs of interest were completed by 443 Australian adults (M age = 26.40, sd = 1.83) in 2013 and 2014.

RESULTS

Path analysis revealed both direct and indirect effects and implicated two pathways to drinking behavior with differential outcomes. Drinking refusal self-efficacy both in social situations and for emotional relief was related to alcohol consumption. Sensitivity to reward was associated with alcohol-related problems, but operated through expectations of increased confidence and personal belief in the ability to limit drinking in social situations. Conversely, sensitivity to punishment operated through negative expectancies and drinking refusal self-efficacy for emotional relief to predict symptoms of dependence.

CONCLUSIONS

Two pathways relating reward sensitivity, alcohol expectancies, and drinking refusal self-efficacy may underlie social and dependent drinking, which has implications for development of intervention to limit harmful drinking.

Factors associated with depression and suicide attempts in patients undergoing rehabilitation for substance abuse

BACKGROUND

Comorbidity of major depression with substance abuse increases the risk of committing suicide. The objective of this work was to determine the psychological and socio-demographic factors associated with depression and suicide attempts in patients rehabilitating for drug consumption.

METHOD

57 Patients attending a center for drug abuse treatment answered the following instruments: the Mini-international neuropsychiatric interview, a questionnaire of general information and background data on consumption of substances, depression and suicide attempts, and the Spanish adaptation of the Holmes and Rahe scale for the assessment of life events. Chi-square and logistic regression tests were used to establish associations between variables.

RESULTS

68.4% of the Patients had current major depression, of these, 75.4% experienced it before the onset of substance abuse. Patients attempting suicide before drug use corresponded to 26%, whilst 28.1% attempted suicide within the last year. Current depression-related variables were receiving a diagnosis of depression prior to the consumption of drugs and the first used drugs, which were alcohol or marijuana. The adverse life event "Familial drug abuse history", was also significantly related to depression (p=0.02). Variables associated with current suicide attempts were: receiving a diagnosis of depression prior to the consumption of drugs (p=0.02), and suicide attempts previous to drug use (p<0.003).

LIMITATION

A limitation of this study was the small size of the sample.

CONCLUSION

Patients with depression who attempted suicide prior to the use of drugs also experienced these conditions during the rehabilitation process. Substance use in the family was a risk factor for both, underscoring the need of actions aimed at preventing addictions in the household environment.

Brain dopaminergic system changes in drug addiction: a review of positron emission tomography findings

Dopamine (DA) is considered crucial for the rewarding effects of drugs of abuse, but its role in addiction remains unclear. Positron emission tomography (PET) is the first technology used for in vivo measurement of components of the dopaminergic system in the human brain. In this article, we review the major findings from PET imaging studies on the involvement of DA in drug addiction, including presynaptic DA synthesis, vesicular monoamine transporter 2, the DA transporter, and postsynaptic DA receptors. These results have corroborated the role of DA in addiction and increased the understanding of its underlying mechanisms.

L-Stepholidine, a naturally occurring dopamine D1 receptor agonist and D2 receptor antagonist, attenuates heroin self-administration and cue-induced reinstatement in rats

Opiate addiction is a chronic, relapsing brain disease characterized by persistent and uncontrolled drug-seeking behavior despite negative effects. L-Stepholidine (L-SPD) is an alkaloid extract of the Chinese herb Stephania intermedia with dopamine D1 receptor partial agonistic and D2 receptor antagonistic dual actions. The unique pharmacological profile of L-SPD suggests that L-SPD may be effective for the treatment of opiate addiction. The aim of this study was to characterize the effects of L-SPD on heroin self-administration on a fixed-ratio 1 schedule and cue-induced reinstatement under an extinction/reinstatement protocol. The effect of L-SPD on the locomotor activity of heroin-free rats was also tested. We found that 2.5, 5, and 10 mg/kg of L-SPD attenuated heroin self-administration and cue-induced reinstatement without affecting locomotor activity. These results showed that L-SPD, which has dual actions on dopamine D1 and D2 receptors, attenuates heroin self-administration and cue-induced reinstatement.

Heterogeneity of dopamine neuron activity across traits and states

Midbrain dopamine neurons fire irregularly, with interspersed clusters of high-frequency spikes, commonly called 'bursts'. In this review we examine such heterogeneity in activity, and provide insight into how it can participate in psychiatric conditions such as drug addiction. We first describe several techniques used to evaluate dopamine neuron activity, and comment on the different measures that each provides. We next describe the activity of dopamine neurons in 'basal' conditions. Specifically, we discuss how the use of anesthesia and reduced preparations may alter aspects of dopamine cell activity, and how there is heterogeneity across species and regions. We also describe how dopamine cell firing changes throughout the peri-adolescent period and how dopamine neuron activity differs across the population. In the final section, we discuss how dopamine neuron activity changes in response to life events. First, we focus attention on drugs of abuse. Drugs themselves change firing activity through a variety of mechanisms, with effects on firing while drug is present differing from those seen after drug discontinuation. We then review how stimuli that are rewarding, aversive, or salient can evoke changes in firing rate and discharge pattern of dopamine neurons, and provide behavioral relevance of dopamine signaling. Finally, we discuss how stress can modulate dopamine neuron firing and how this may contribute to the role that stressful experiences play in psychiatric disorders such as addiction and depression.

A triadic neurocognitive approach to addiction for clinical interventions

According to the triadic neurocognitive model of addiction to drugs (e.g., cocaine) and non-drugs (e.g., gambling), weakened "willpower" associated with these behaviors is the product of an abnormal functioning in one or more of three key neural and cognitive systems: (1) an amygdala-striatum dependent system mediating automatic, habitual, and salient behaviors; (2) a prefrontal cortex dependent system important for self-regulation and forecasting the future consequences of a behavior; and (3) an insula dependent system for the reception of interoceptive signals and their translation into feeling states (such as urge and craving), which in turn plays a strong influential role in decision-making and impulse control processes related to uncertainty, risk, and reward. The described three-systems account for poor decision-making (i.e., prioritizing short-term consequences of a decisional option) and stimulus-driven actions, thus leading to a more elevated risk for relapse. Finally, this article elaborates on the need for "personalized" clinical model-based interventions targeting interactions between implicit processes, interoceptive signaling, and supervisory function aimed at helping individuals become less governed by immediate situations and automatic pre-potent responses, and more influenced by systems involved in the pursuit of future valued goals.

Individual variation in resisting temptation: implications for addiction

When exposed to the sights, sounds, smells and/or places that have been associated with rewards, such as food or drugs, some individuals have difficulty resisting the temptation to seek out and consume them. Others have less difficulty restraining themselves. Thus, Pavlovian reward cues may motivate maladaptive patterns of behavior to a greater extent in some individuals than in others. We are just beginning to understand the factors underlying individual differences in the extent to which reward cues acquire powerful motivational properties, and therefore, the ability to act as incentive stimuli. Here we review converging evidence from studies in both human and non-human animals suggesting that a subset of individuals are more "cue reactive", in that certain reward cues are more likely to attract these individuals to them and motivate actions to get them. We suggest that those individuals for whom Pavlovian reward cues become especially powerful incentives may be more vulnerable to impulse control disorders, such as binge eating and addiction.

The role of dopamine in inhibitory control in smokers and non-smokers: a pharmacological fMRI study

Contemporary theoretical models of substance dependence posit that deficits in inhibitory control play an important role in substance dependence. The neural network underlying inhibitory control and its association with substance dependence have been widely investigated. However, the pharmacology of inhibitory control is still insufficiently clear. The aims of the current study were twofold. First, we investigated the role of dopamine in inhibitory control and associated brain activation. Second, the proposed link between dopamine and impaired inhibitory control in nicotine dependence was investigated by comparing smokers and non-smoking controls. Haloperidol (2 mg), a dopamine D2/D3 receptor antagonist, and placebo were administered to 25 smokers and 25 non-smoking controls in a double-blind randomized cross-over design while performing a Go/NoGo task during fMRI scanning. Haloperidol reduced NoGo accuracy and associated brain activation in the ACC, right SFG and left IFG, showing that optimal dopamine levels are crucial to effectively implement inhibitory control. In addition, smokers showed behavioral deficits on the Go/NoGo task as well as hypoactivity in the left IFG, right MFG and ACC after placebo, supporting the hypothesis of a hypoactive prefrontal system in smokers. Haloperidol had a stronger impact on prefrontal brain activation in non-smoking controls compared to smokers, which is in line with the inverted 'U' curve theory of dopamine and cognitive control. The current findings suggest that altered baseline dopamine levels in addicted individuals may contribute to the often observed reduction in inhibitory control in these populations.

Acamprosate in alcohol dependence: implications of a unique mechanism of action

Acamprosate, in combination with psychosocial therapy, has been shown to be clinically effective in maintaining abstinence in alcohol dependence. Current research suggests that its mechanism of action involves functional antagonism of the ionotropic glutamate N-methyl-d-aspartate (NMDA) receptor. However, direct interactions between acamprosate and the NMDA receptor are weak, and recent findings suggest that acamprosate may modulate NMDA receptors via regulatory polyamine sites, or that it may act directly on metabotropic glutamate receptors. All of these mechanisms are novel for the treatment of alcohol dependence and have far-reaching implications for understanding relapse, as well as for the discovery of drugs with greater efficacy. Understanding the mechanism of action of acamprosate may be an important stimulus for change in the perception and treatment of alcohol dependence.

Phentermine, sibutramine and affective disorders

A safe and effective way to control weight in patients with affective disorders is needed, and phentermine is a possible candidate. We performed a PubMed search of articles pertaining to phentermine, sibutramine, and affective disorders. We compared the studies of phentermine with those of sibutramine. The search yielded a small number of reports. Reports concerning phentermine and affective disorders reported that i) its potency in the central nervous system may be comparatively low, and ii) it may induce depression in some patients. We were unable to find more studies on the subject; thus, it is unclear presently whether phentermine use is safe in affective disorder patients. Reports regarding the association of sibutramine and affective disorders were slightly more abundant. A recent study that suggested that sibutramine may have deleterious effects in patients with a psychiatric history may provide a clue for future phentermine research. Three explanations are possible concerning the association between phentermine and affective disorders: i) phentermine, like sibutramine, may have a depression-inducing effect that affects a specific subgroup of patients, ii) phentermine may have a dose-dependent depression-inducing effect, or iii) phentermine may simply not be associated with depression. Large-scale studies with affective disorder patients focusing on these questions are needed to clarify this matter before investigation of its efficacy may be carried out and it can be used in patients with affective disorders.

Dissociated grey matter changes with prolonged addiction and extended abstinence in cocaine users

Extensive evidence indicates that current and recently abstinent cocaine abusers compared to drug-naïve controls have decreased grey matter in regions such as the anterior cingulate, lateral prefrontal and insular cortex. Relatively little is known, however, about the persistence of these deficits in long-term abstinence despite the implications this has for recovery and relapse. Optimized voxel based morphometry was used to assess how local grey matter volume varies with years of drug use and length of abstinence in a cross-sectional study of cocaine users with various durations of abstinence (1–102 weeks) and years of use (0.3–24 years). Lower grey matter volume associated with years of use was observed for several regions including anterior cingulate, inferior frontal gyrus and insular cortex. Conversely, higher grey matter volumes associated with abstinence duration were seen in non-overlapping regions that included the anterior and posterior cingulate, insular, right ventral and left dorsal prefrontal cortex. Grey matter volumes in cocaine dependent individuals crossed those of drug-naïve controls after 35 weeks of abstinence, with greater than normal volumes in users with longer abstinence. The brains of abstinent users are characterized by regional grey matter volumes, which on average, exceed drug-naïve volumes in those users who have maintained abstinence for more than 35 weeks. The asymmetry between the regions showing alterations with extended years of use and prolonged abstinence suggest that recovery involves distinct neurobiological processes rather than being a reversal of disease-related changes. Specifically, the results suggest that regions critical to behavioral control may be important to prolonged, successful, abstinence.

A neurocognitive approach to understanding the neurobiology of addiction

Recent concepts of addiction to drugs (e.g. cocaine) and non-drugs (e.g. gambling) have proposed that these behaviors are the product of an imbalance between three separate, but interacting, neural systems: an impulsive, largely amygdala-striatum dependent, neural system that promotes automatic, habitual and salient behaviors; a reflective, mainly prefrontal cortex dependent, neural system for decision-making, forecasting the future consequences of a behavior, and inhibitory control; and the insula that integrates interoception states into conscious feelings and into decision-making processes that are involved in uncertain risk and reward. These systems account for poor decision-making (i.e. prioritizing short-term consequences of a decisional option) leading to more elevated addiction risk and relapse. This article provides neural evidence for this three-systems neural model of addiction.

Addiction

Drug and alcohol addiction is a debilitating disorder characterized by persistent drug-seeking behaviors despite negative physiological, medical, or social consequences. Neurobiological models of addiction propose that the reinforcing effects of addictive drugs are associated with altered neurotransmission within the reward 'mesocorticolimbic' circuitry in the brain. Immense efforts are therefore designed to target the mesocorticolimbic circuitry in attenuating drug dependence and addiction-related behaviors. Yet, to date, most addiction treatments have demonstrated only limited success in reducing addiction-related behaviors. Accumulating and compelling evidence suggests that novel nonsurgical brain stimulation techniques, such as transcranial magnetic stimulation and transcranial direct current stimulation, could serve as promising tools for indexing altered neurotransmission associated with repetitive drug use, and moreover, may hold therapeutic potential for the treatment of drug dependence and addiction-related behaviors. This chapter reviews and discusses the current and potential applications of such techniques in the study and treatment of addiction; we focus on a number of common drugs of abuse, including nicotine, alcohol, cocaine, cannabis, and ecstasy.

The phosphodiesterase-4 (PDE4) inhibitor rolipram decreases ethanol seeking and consumption in alcohol-preferring Fawn-Hooded rats

BACKGROUND

Alcohol dependence is a complex psychiatric disorder demanding development of novel pharmacotherapies. Because the cyclic adenosine monophosphate (cAMP) signaling cascade has been implicated in mediating behavioral responses to alcohol, key components in this cascade may serve as potential treatment targets. Phosphodiesterase-4 (PDE4), an enzyme that specifically catalyzes the hydrolysis of cAMP, represents a key point in regulating intracellular cAMP levels. Thus, it was of interest to determine whether PDE4 was involved in the regulation of alcohol use and abuse.

METHODS

Male Fawn-Hooded (FH/Wjd) rats were tested for 5% (v/v) ethanol (EtOH) and 10% (w/v) sucrose operant oral self-administration following treatment with the selective PDE4 inhibitor rolipram (0.0125, 0.025, or 0.05 mg/kg, subcutaneous [s.c.]); rolipram at higher doses (0.05, 0.1, and 0.2 mg/kg, s.c.) was tested to determine its impact on the intake of EtOH, sucrose, or water using the 2-bottle choice drinking paradigm. Subsequent open-field testing was performed to evaluate the influence of higher doses of rolipram on locomotor activity.

RESULTS

Acute administration of rolipram dose-dependently reduced operant self-administration of 5% EtOH, but had no effect on 10% sucrose responding. Time-course assessment revealed significant decreases in EtOH consumption after rolipram (0.1, 0.2 mg/kg) treatment in continuous- and intermittent access to EtOH at 5% or 10%, respectively. Moreover, chronic rolipram treatment time-dependently decreased 5% EtOH consumption and preference during treatment days and after the termination of rolipram administration. Rolipram at the highest doses (0.1 and 0.2 mg/kg) did decrease locomotor activity, but the effect lasted only 10 and 20 minutes, respectively, which did not likely alter long-term EtOH drinking.

CONCLUSIONS

These results suggest that PDE4 plays a role in alcohol seeking and consumption behavior. Drugs interfering with PDE4 may be a potential pharmacotherapy for alcohol dependence.

Modularity of mind and the role of incentive motivation in representing novelty

Animal and human brains contain a myriad of mental representations that have to be successfully tracked within fractions of a second in a large number of situations. This retrieval process is hard to explain without postulating the massive modularity of cognition. Assuming that the mind is massively modular, it is then necessary to understand how cognitive modules can efficiently represent dynamic environments-in which some modules may have to deal with change-induced novelty and uncertainty. Novelty of a stimulus is a problem for a module when unknown, significant stimuli do not satisfy the module's processing criteria-or domain specificity-and cannot therefore be included in its database. It is suggested that the brain mechanisms of incentive motivation, recruited when faced with novelty and uncertainty, induce transient variations in the domain specificity of cognitive modules in order to allow them to process information they were not prepared to learn. It is hypothesised that the behavioural transitions leading from exploratory activity to habit formation are correlated with (and possibly caused by) the organism's ability to counter novelty-induced uncertainty.

Positron emission tomography molecular imaging of dopaminergic system in drug addiction

Dopamine (DA) is involved in drug reinforcement, but its role in drug addiction remains unclear. Positron emission tomography (PET) is the first technology used for the direct measurement of components of the dopaminergic system in the living human brain. In this article, we reviewed the major findings of PET imaging studies on the involvement of DA in drug addiction, especially in heroin addiction. Furthermore, we summarized PET radiotracers that have been used to study the role of DA in drug addiction. To investigate presynaptic function in drug addiction, PET tracers have been developed to measure DA synthesis and transport. For the investigation of postsynaptic function, several radioligands targeting dopamine one (D1) receptor and dopamine two (D2) receptor are extensively used in PET imaging studies. Moreover, we also summarized the PET imaging findings of heroin addiction studies, including heroin-induced DA increases and the reinforcement, role of DA in the long-term effects of heroin abuse, DA and vulnerability to heroin abuse and the treatment implications. PET imaging studies have corroborated the role of DA in drug addiction and increase our understanding the mechanism of drug addiction.

The neurobiology of cognitive control in successful cocaine abstinence

INTRODUCTION

Extensive evidence demonstrates that current cocaine abusers show hypoactivity in anterior cingulate and dorsolateral prefrontal cortex and respond poorly relative to drug-naïve controls on tests of executive function. Relatively little is known about the cognitive sequelae of long-term abstinence in cocaine addicts.

METHODS

Here, we use a GO-NOGO task in which successful performance necessitated withholding a prepotent response to assay cognitive control in short- and long-term abstinent cocaine users (1-5 weeks and 40-102 weeks, respectively).

RESULTS

We report significantly greater activity in prefrontal, cingulate, cerebellar and inferior frontal gyrii in abstinent cocaine users for both successful response inhibitions and errors of commission. Moreover, this relative hyperactivity was present in both abstinent groups, which, in the presence of comparable behavioral performance, suggests a functional compensation.

CONCLUSIONS

Differences between the short- and long-abstinence groups in the patterns of functional recruitment suggest different cognitive control demands at different stages in abstinence. Short-term abstinence showed increased inhibition-related dorsolateral and inferior frontal activity indicative of the need for increased inhibitory control while long-term abstinence showed increased error-related ACC activity indicative of heightened behavioral monitoring. The results suggest that the integrity of prefrontal systems that underlie cognitive control functions may be an important characteristic of successful long-term abstinence.

Glücksspiel im Gehirn: Neurobiologische Grundlagen pathologischen Glücksspielens

Hintergrund: Pathologisches Glücksspielen (PG) wird in den internationalen Klassifikationssystemen bislang als Impulskontrollstörung klassifiziert. Erst in jüngster Zeit wird aufgrund der Ähnlichkeiten in Phänomenologie, Ätiologie, Verlauf sowie genetischen und neurobiologischen Faktoren mit der Substanzabhängigkeit eine Einordnung des PGs als Verhaltenssucht diskutiert. Insbesondere neurobiologische und neuropsychologische Befunde haben zu dieser veränderten Sichtweise beigetragen. Methode: Im vorliegenden Beitrag werden Befunde zu neurobiologischen Grundlagen PGs vorgestellt. Der Schwerpunkt liegt auf neurokognitiven Prozessen wie Belohnungs- und Bestrafungsverarbeitung, Cue-Reaktivität, Impulsivität und Entscheidungsfindung. Die Befunde werden im Hinblick auf Ähnlichkeiten und Unterschiede PGs zur Substanzabhängigkeit diskutiert. Ergebnisse: Ähnlich wie bei der Substanzabhängigkeit zeigt sich auch bei pathologischen Spielern Veränderungen mesolimbischer-präfrontaler Netzwerke, die sich in einer verminderten Belohnungs- und Bestrafungssensitivität, Impulshemmung und einer erhöhten Cue-Reaktivität auf glücksspielassoziierte Reize äußern können. Jedoch sind die Befunde teilweise nicht eindeutig und eine Vielzahl der Studien unterliegt methodischen Einschränkungen. Schlussfolgerungen: Bisherige Befunde stützen die Einordnung pathologischen Spielverhaltens als Verhaltenssucht.

Punishing an error improves learning: the influence of punishment magnitude on error-related neural activity and subsequent learning

Punishing an error to shape subsequent performance is a major tenet of individual and societal level behavioral interventions. Recent work examining error-related neural activity has identified that the magnitude of activity in the posterior medial frontal cortex (pMFC) is predictive of learning from an error, whereby greater activity in this region predicts adaptive changes in future cognitive performance. It remains unclear how punishment influences error-related neural mechanisms to effect behavior change, particularly in key regions such as pMFC, which previous work has demonstrated to be insensitive to punishment. Using an associative learning task that provided monetary reward and punishment for recall performance, we observed that when recall errors were categorized by subsequent performance--whether the failure to accurately recall a number-location association was corrected at the next presentation of the same trial--the magnitude of error-related pMFC activity predicted future correction. However, the pMFC region was insensitive to the magnitude of punishment an error received and it was the left insula cortex that predicted learning from the most aversive outcomes. These findings add further evidence to the hypothesis that error-related pMFC activity may reflect more than a prediction error in representing the value of an outcome. The novel role identified here for the insular cortex in learning from punishment appears particularly compelling for our understanding of psychiatric and neurologic conditions that feature both insular cortex dysfunction and a diminished capacity for learning from negative feedback or punishment.

Food-related Stroop interference in obese and normal-weight individuals: behavioral and electrophysiological indices

The primary objective of the present study was to investigate differences in the attentional processing of food-related words in a Stroop task, as assessed by means of behavioral (reaction times) and electrophysiological (P200 and P300 amplitudes) indices, between obese and normal-weight individuals. Results revealed a P200 bias to food-related words in obese participants, which was not seen in normal-weight participants. This indicates that, in an early, automatic stage of information processing, obese participants already tend to engage more attention towards food-related stimuli than to neutral stimuli. With respect to reaction times and P300 scores, as alleged indices of more conscious maintained attention, a general food-related bias was observed, with no between-group differences. Further, in the obese group, significant positive correlations were observed between the food-related reaction time bias, food craving, and external eating, whereas in the normal-weight group, food craving scores correlated positively with P200/P300 amplitude biases. It can be concluded that obese individuals display an enhanced automatic, preconscious attentional processing of food-related stimuli, and this can be regarded as an initial expression of a greater responsiveness to food cues. In the current food-abundant environment, such a heightened food cue-responsiveness might contribute substantially to the tendency to overeat.

Altered neurocircuitry in the dopamine transporter knockout mouse brain

The plasma membrane transporters for the monoamine neurotransmitters dopamine, serotonin, and norepinephrine modulate the dynamics of these monoamine neurotransmitters. Thus, activity of these transporters has significant consequences for monoamine activity throughout the brain and for a number of neurological and psychiatric disorders. Gene knockout (KO) mice that reduce or eliminate expression of each of these monoamine transporters have provided a wealth of new information about the function of these proteins at molecular, physiological and behavioral levels. In the present work we use the unique properties of magnetic resonance imaging (MRI) to probe the effects of altered dopaminergic dynamics on meso-scale neuronal circuitry and overall brain morphology, since changes at these levels of organization might help to account for some of the extensive pharmacological and behavioral differences observed in dopamine transporter (DAT) KO mice. Despite the smaller size of these animals, voxel-wise statistical comparison of high resolution structural MR images indicated little morphological change as a consequence of DAT KO. Likewise, proton magnetic resonance spectra recorded in the striatum indicated no significant changes in detectable metabolite concentrations between DAT KO and wild-type (WT) mice. In contrast, alterations in the circuitry from the prefrontal cortex to the mesocortical limbic system, an important brain component intimately tied to function of mesolimbic/mesocortical dopamine reward pathways, were revealed by manganese-enhanced MRI (MEMRI). Analysis of co-registered MEMRI images taken over the 26 hours after introduction of Mn²⁺ into the prefrontal cortex indicated that DAT KO mice have a truncated Mn²⁺ distribution within this circuitry with little accumulation beyond the thalamus or contralateral to the injection site. By contrast, WT littermates exhibit Mn²⁺ transport into more posterior midbrain nuclei and contralateral mesolimbic structures at 26 hr post-injection. Thus, DAT KO mice appear, at this level of anatomic resolution, to have preserved cortico-striatal-thalamic connectivity but diminished robustness of reward-modulating circuitry distal to the thalamus. This is in contradistinction to the state of this circuitry in serotonin transporter KO mice where we observed more robust connectivity in more posterior brain regions using methods identical to those employed here.

The M5 muscarinic receptor as possible target for treatment of drug abuse

Two reports published in the latter 1980s are generally given credit for being the first to announce the discovery of a new subtype of muscarinic acetylcholine receptor (mAChR), designated m5 or M5, and now officially M(5) (1). Both identifications were assigned using molecular biology techniques. Then - as now - no selective high-affinity ligands or toxins were available. In situ hybridization and reverse-transcriptase PCR have found M(5) AChR expression in brain to be distinct from that of the four other G protein-coupled mAChR subtypes and primarily localized to the substantia nigra, ventral tegmental area, hippocampus (CA1 and CA2 subfields), cerebral cortex (outermost layer) and striatum (caudate putamen). M(5) AChR brain region localization and involvement in the regulation of striatal dopamine release and in rewarding brain stimulation suggests a possible role for M(5) AChR as a target for novel therapy to treat excess hedonic drive, including drug abuse.