Parallel role for the dopamine D1 receptor in gambling and amphetamine reinforcement in healthy volunteers

Lack of effect of methamphetamine on reward-related brain activity in healthy adults

INTRODUCTION

Stimulant drugs are thought to alter processing of rewarding stimuli. However, the mechanisms by which they do this are not fully understood.

METHOD

In this study we used EEG to assess effects of single doses of methamphetamine (MA) on neural responses during anticipation and receipt of reward in healthy volunteers. Healthy young men and women (N = 28) completed three sessions in which they received placebo, a low MA dose (10 mg) or a higher MA dose (20 mg) under double blind conditions. Subjective and cardiovascular measures were obtained, and EEG was used to assess brain activity during an electrophysiological version of the Monetary Incentive Delay (eMID) task.

RESULTS

EEG measures showed expected patterns during anticipation and receipt of reward, and MA produced its expected effects on mood and cardiovascular function. However, MA did not affect EEG responses during either anticipation or receipt of rewards.

CONCLUSIONS

These findings suggest that the effects of MA on EEG signals of reward processing are subtle, and not related to the drug's effects on subjective feelings of well-being. The findings contribute to our understanding of the neural effects of MA during behaviors related to reward.

Priming effects of a slot machine game and amphetamine on probabilistic risk-taking in people with gambling disorder and healthy controls

INTRODUCTION

The Game of Dice Task (GDT) captures probabilistic risk-taking, which is an important feature of addictions and integral to gambling disorder (GD). No research appears to have assessed effects of gambling-specific priming manipulations or the pharmacological basis of such effects on the GDT.

AIMS

To investigate effects of slot machine gambling (Slots) and d-amphetamine (AMPH; 20 mg) on risk-taking in people with GD and healthy controls (HCs) (n = 30/group). The role of dopamine (DA) was assessed by pre-treating participants with the D2 receptor (D2R)-preferring antagonist, haloperidol (HAL; 3-mg) or mixed D1R-D2R antagonist, fluphenazine (FLU; 3-mg).

HYPOTHESES

Slots and AMPH will each increase risk-taking based on fewer (less probable) possible outcomes selected (POS) and poorer net monetary outcomes (NMO; gains minus losses) on the GDT, with stronger effects in Group GD. If DA mediates these effects, outcomes will vary with pre-treatment.

METHOD

Participants attended a pre-experimental baseline session and 4 test sessions. Antagonist Group (HAL, FLU) was manipulated between-participants. Pre-treatment (antagonist, placebo) was manipulated within-participants and counterbalanced over sessions for Slots and AMPH test phases. Moderator/mediator effects of trait and neuropsychological factors and GD severity (South Oaks Gambling Screen; SOGS) were explored via covariance.

RESULTS

AMPH led to an escalation in risky POS over trial blocks in both groups, regardless of pre-treatment. Cognitive inflexibility (high perseveration-proneness) moderated this effect in Group HC. In Group GD, SOGS selectively predicted riskier POS on AMPH sessions. Group GD achieved poorer NMO vs. Group HC on the pre-experimental baseline and Placebo-Slots sessions. Group HC selectively displayed poorer NMO on the Antagonist-Slots session.

CONCLUSIONS

The GDT can detect behavioral and pharmacological priming effects. Cognitive inflexibility and symptom severity moderate AMPH-induced risk-taking in HC and GD participants, respectively. Sensitization-related "wanting" of risk may contribute to the latter effect in people with GD.

Tactile Stimulation in Adult Rats Modulates Dopaminergic Molecular Parameters in the Nucleus accumbens Preventing Amphetamine Relapse

Amphetamine (AMPH) is a psychostimulant drug frequently related to addiction, which is characterized by functional and molecular changes in the brain reward system, favoring relapse development, and pharmacotherapies have shown low effectiveness. Considering the beneficial influences of tactile stimulation (TS) in different diseases that affect the central nervous system (CNS), here we evaluated if TS applied in adult rats could prevent or minimize the AMPH-relapse behavior also accessing molecular neuroadaptations in the nucleus accumbens (NAc). Following AMPH conditioning in the conditioned place preference (CPP) paradigm, male rats were submitted to TS (15-min session, 3 times a day, for 8 days) during the drug abstinence period, which were re-exposed to the drug in the CPP paradigm for additional 3 days for relapse observation and molecular assessment. Our findings showed that besides AMPH relapse, TS prevented the dopamine transporter (DAT), dopamine 1 receptor (D1R), tyrosine hydroxylase (TH), mu opioid receptor (MOR) increase, and AMPH-induced delta FosB (ΔFosB). Based on these outcomes, we propose TS as a useful tool to treat psychostimulant addiction, which is subsequent to clinical studies; it could be included in detoxification programs together with pharmacotherapies and psychological treatments already conventionally established.

Aerobic exercise improves memory and prevents cognitive deficits of relevance to schizophrenia in an animal model

INTRODUCTION AND OBJECTIVES

Cognitive impairment associated with schizophrenia (CIAS) greatly reduces patients' functionality, and remains an unmet clinical need. The sub-chronic phencyclidine (scPCP) rat model is commonly employed in studying CIAS. We have previously shown that voluntary exercise reverses impairments in novel object recognition (NOR) induced by scPCP. However, there has not been a longitudinal study investigating the potential protective effects of exercise in a model of CIAS. This study aimed to investigate the pro-cognitive and protective effects of exercise on CIAS using the translational NOR and attentional set-shifting tasks (ASST).

METHODS

Female Lister Hooded rats were either exercised (wheel running for one hour per day, five days per week, for six weeks; n=20) or not (n=20) and then tested in a natural-forgetting NOR test. Rats in each group were then administered either PCP (2 mg/kg intraperitoneally (i.p.)) or saline solution (1 mL/kg i.p.) for seven days, followed by seven days washout. Three NOR tests were conducted immediately and two and nine weeks after washout, and a natural-forgetting NOR test was carried out again eight weeks post washout. Rats were trained and tested in ASST from week 6 to week 10 post washout.

RESULTS

Non-exercised rats displayed a deficit in both of the natural-forgetting NOR tests, whereas exercised rats did not. The scPCP exercise group did not show the expected deficit in NOR at any time point, and had a significantly ameliorated deficit in the ASST compared to the scPCP control group.

CONCLUSION

Voluntary exercise has long-lasting pro-cognitive and protective effects in two cognitive domains. Exercise improves cognition and could provide protection against CIAS.

Dopamine and Gambling Disorder: Prospects for Personalized Treatment

Purpose of Review

To address variation in the severity of gambling disorder, this review evaluates the contribution of mesocorticolimbic dopamine neurons to potential behavioral endophenotypes, the influence of individual differences in the dopamine system on gambling and related behaviors, and the possible role for dopaminergic medications in the treatment of gambling disorder.

Recent Findings

Newer work has suggested that dopaminergic dysfunction can lead to increased reward anticipation and a greater sensitivity to uncertainty, which in turn may drive addictive gambling behaviors. In addition, increased impulsivity, a well-recognized risk factor for gambling disorder, has been linked to dopaminergic dysfunction. More recently, emerging evidence has suggested that dopaminergic medications can influence the discounting of delayed rewards.

Summary

Dopaminergic drugs that increase the salience of long-term over short-term goals may ameliorate symptoms of impulsive individuals with gambling disorder. More broadly, improved understanding of intermediate behavioral and other phenotypes with a defined neurobiological substrate may allow for personalized treatment of gambling disorder and other psychiatric conditions.

Impulsivity moderates the effects of dopamine D2 and mixed D1-D2 antagonists in individuals with gambling disorder

BACKGROUND

The functional role of dopamine D1 and D2 receptors in gambling disorder (GD) remains unclear.

AIMS

This study aimed to investigate the role of D1 activation and the moderating effects of impulsivity, a trait linked with weaker D2-mediated inhibition of dopamine release, in GD subjects.

METHODS

Thirty (nine female) non-comorbid GD subjects with low (LI), moderate (MI), or high impulsivity (HI) received the preferential D2 antagonist haloperidol (HAL; 3 mg) or the mixed D1-D2 antagonist fluphenazine (FLU; 3 mg), on separate sessions before a 15-minute slot machine game or amphetamine (AMPH; 20 mg), in a placebo-controlled, double-blind, counterbalanced design.

RESULTS

On their own, HAL and FLU led to linear increases and decreases, respectively, in desire to gamble across increasing levels of impulsivity. The slot machine and AMPH each evoked an inverted-U pattern of desire to gamble across increasing impulsivity. HAL reversed this effect of the game, whereas FLU did not alter post-game desire. HAL and FLU decreased and increased psychostimulant-like effects of the game, respectively, in LI and MI subjects, but consistently reduced these effects in HI subjects. HAL also altered the salience of negative affective words on a reading task, such that greater salience of negative words coincided with lower post-game desire to gamble.

CONCLUSIONS

D1 receptors appear to gauge the incentive value of gambling in GD subjects. D1 activation has negative reinforcing effects in HI gamblers and positive reinforcing effects in LI gamblers. Medications that activate D1 could curtail chasing in HI gamblers. D1 blockade could benefit HI gamblers whose main concern is craving.

Acute effects of lisdexamfetamine and D-amphetamine on social cognition and cognitive performance in a placebo-controlled study in healthy subjects

RATIONALE

Amphetamines are used as medications but are also misused as cognitive enhancers by healthy subjects and may have additional effects on social cognition.

METHODS

We investigated the acute effects of single, high, equimolar doses of D-amphetamine (40 mg) and lisdexamfetamine (100 mg) on social cognition and cognitive performance using a randomized, placebo-controlled, double-blind, cross-over design in 24 healthy volunteers. Effects on social cognition were assessed using the Facial Emotion Recognition Task (FERT), Multifaceted Empathy Test (MET), and Sexual Arousal Task (SAT). Cognitive performance was measured using the Digit Symbol Substitution Test (DSST), Digit Span (DS), Stop-Signal Task (SST), and Mackworth Clock Test (MCT).

RESULTS

D-Amphetamine and lisdexamfetamine had small effects on measures of social cognition. There were no effects on emotion recognition on the FERT. D-Amphetamine increased direct empathy on the MET, but only for positive stimuli. Both amphetamines increased ratings of pleasantness and attractiveness on the SAT in response to sexual but also to neutral stimuli. D-Amphetamine and lisdexamfetamine increased cognitive performance (go-accuracy and vigilance on the SST and MCT, respectively). Lisdexamfetamine increased processing speed on the DSST. Neither drug had an effect on the DS.

CONCLUSION

Single, high, equimolar doses of D-amphetamine and lisdexamfetamine enhanced certain aspects of cognitive performance in healthy non-sleep-deprived subjects. Both amphetamines also slightly altered aspects of social cognition. Whether these small effects also influence social interaction behavior in amphetamine users remains to be investigated.

TRIAL REGISTRATION

The study was registered at ClinicalTrials.gov (NCT02668926).

Improving Abnormality Detection on Chest Radiography Using Game-Like Reinforcement Mechanics

RATIONALE AND OBJECTIVES

Despite their increasing prevalence, online textbooks, question banks, and digital references focus primarily on explicit knowledge. Implicit skills such as abnormality detection require repeated practice on clinical service and have few digital substitutes. Using mechanics traditionally deployed in video games such as clearly defined goals, rapid-fire levels, and narrow time constraints may be an effective way to teach implicit skills.

MATERIALS AND METHODS

We created a freely available, online module to evaluate the ability of individuals to differentiate between normal and abnormal chest radiographs by implementing mechanics, including instantaneous feedback, rapid-fire cases, and 15-second timers. Volunteer subjects completed the modules and were separated based on formal experience with chest radiography. Performance between training and testing sets were measured for each group, and a survey was administered after each session.

RESULTS

The module contained 74 cases and took approximately 20 minutes to complete. Thirty-two cases were normal radiographs and 56 cases were abnormal. Of the 60 volunteers recruited, 25 were "never trained" and 35 were "previously trained." "Never trained" users scored 21.9 out of 37 during training and 24.0 out of 37 during testing (59.1% vs 64.9%, P value <.001). "Previously trained" users scored 28.0 out of 37 during training and 28.3 out of 37 during testing phases (75.6% vs 76.4%, P value = .56). Survey results showed that 87% of all subjects agreed the module is an efficient way of learning, and 83% agreed the rapid-fire module is valuable for medical students.

CONCLUSIONS

A gamified online module may improve the abnormality detection rates of novice interpreters of chest radiography, although experienced interpreters are less likely to derive similar benefits. Users reviewed the educational module favorably.