The Impact of Selective Dopamine D2, D3 and D4 Ligands on the Rat Gambling Task

Cholinergic regulation of decision making under risk of punishment

The ability to choose between options that differ in their risks and rewards depends on brain regions within the mesocorticolimbic circuit and regulation of their activity by neurotransmitter systems. Dopamine neurotransmission in particular plays a critical role in modulating such risk-taking behavior; however, the contribution of other major modulatory neurotransmitters, such as acetylcholine, is not as well-defined, especially for decision making in which the risk associated with more rewarding outcomes involves adverse consequences. Consequently, the goal of the current experiments was to examine how cholinergic signaling influences decision making involving risk of explicit punishment. Male and female rats were trained in a decision-making task in which they chose between a small safe food reward and a larger food reward accompanied by a risk of footshock punishment. After training in this task, the effects of nicotinic and muscarinic agonists and antagonists on risk-taking performance were evaluated. Neither nicotine, a nicotinic receptor agonist, nor mecamylamine, a nicotinic receptor antagonist, affected preference for the risky lever, although mecamylamine did alter latencies to press the risky lever and the percentage of omissions. The muscarinic receptor agonist oxotremorine decreased preference for the large, risky lever; similar effects on behavior were observed with the administration of the muscarinic receptor antagonist scopolamine. Control experiments were therefore conducted in which these same muscarinic receptor ligands were administered prior to testing in a reward discrimination task. These experiments revealed that the effects of oxotremorine and scopolamine on risk taking may be due to altered motivational processes rather than to changes in sensitivity to risk of punishment. Importantly, there were no sex differences in the effects of cholinergic manipulations on preference for the large, risky lever. Collectively, these findings suggest that in both males and females, cholinergic signaling via muscarinic receptors is involved in decision making involving risk of explicit punishment, with a specific role in modulating sensitivity to differences in reward magnitude. Future studies will expand upon this work by exploring whether targeting cholinergic receptors has therapeutic potential for psychiatric conditions in which risk taking is pathologically altered.

Involvement of dopamine D3 receptor in impulsive choice decision-making in male rats

Impulsive decision-making has been linked to impulse control disorders and substance use disorders. However, the neural mechanisms underlying impulsive choice are not fully understood. While previous PET imaging and autoradiography studies have shown involvement of dopamine and D2/3 receptors in impulsive behavior, the roles of distinct D1, D2, and D3 receptors in impulsive decision-making remain unclear. In this study, we used a food reward delay-discounting task (DDT) to identify low- and high-impulsive rats, in which low-impulsive rats exhibited preference for large delayed reward over small immediate rewards, while high-impulsive rats showed the opposite preference. We then examined D1, D2, and D3 receptor gene expression using RNAscope in situ hybridization assays. We found that high-impulsive male rats exhibited lower levels of D2 and D3, and particularly D3, receptor expression in the nucleus accumbens (NAc), with no significant changes in the insular, prelimbic, and infralimbic cortices. Based on these findings, we further explored the role of the D3 receptor in impulsive decision-making. Systemic administration of a selective D3 receptor agonist (FOB02-04) significantly reduced impulsive choices in high-impulsive rats but had no effects in low-impulsive rats. Conversely, a selective D3 receptor antagonist (VK4-116) produced increased both impulsive and omission choices in both groups of rats. These findings suggest that impulsive decision-making is associated with a reduction in D3 receptor expression in the NAc. Selective D3 receptor agonists, but not antagonists, may hold therapeutic potentials for mitigating impulsivity in high-impulsive subjects.

The neuropharmacological profile of interval responding during operant tasks

Responses occurring during intervals of operant tasks have been subdivided as interim, facultative, and terminal, depending on the time between response onset and reward. Although interval responses, also known as adjunctive responses, have been described in pigeons, rats, mice, monkeys, and humans, most experiments have been conducted in rats. We review the neurochemical basis of interval responses and examine the hypothesis that these responses modulate operant performance. Preliminary experiments indicate the involvement of biogenic amines, acetylcholine, and GABA during interval responding associated with operant tasks. In particular, catecholaminergic deafferentation of the basal ganglia modulated interval responses as did the peripheral injection of catecholamine reuptake blockers. Under the influence of amphetamine, interval responding may either increase or decrease, so that a wide range of responses must be selected to gauge drug effects. In non-drugged pigeons and rats, the expression of interval responses facilitates operant training.

Circuit and cell-specific contributions to decision making involving risk of explicit punishment in male and female rats

Decision making is a complex cognitive process that recruits a distributed network of brain regions, including the basolateral amygdala (BLA) and nucleus accumbens shell (NAcSh). Recent work suggests that communication between these structures, as well as activity of cells expressing dopamine D2 receptors (D2R) in the NAcSh, are necessary for some forms of decision making; however, the contributions of this circuit and cell population during decision making under risk of punishment are unknown. The current experiments addressed this question using circuit- and cell type-specific optogenetic approaches in rats during a decision-making task involving risk of punishment. In Experiment 1, Long-Evans rats received intra-BLA injections of halorhodopsin or mCherry (control) and in Experiment 2, D2-Cre transgenic rats received intra-NAcSh injections of Cre-dependent halorhodopsin or mCherry. Optic fibers were implanted in the NAcSh in both experiments. Following training in the decision-making task, BLA→NAcSh or D2R-expressing neurons were optogenetically inhibited during different phases of the decision process. Inhibition of the BLA→NAcSh during deliberation (the time between trial initiation and choice) increased choice of the large, risky reward (increased risk taking). Similarly, inhibition during delivery of the large, punished reward increased risk taking, but only in males. Inhibition of D2R-expressing neurons in the NAcSh during deliberation increased risk taking. In contrast, inhibition of these neurons during delivery of the small, safe reward decreased risk taking. These findings extend our knowledge of the neural dynamics of risk taking, revealing sex-dependent circuit recruitment and dissociable activity of selective cell populations during decision making.

Sex-specific decision-making impairments and striatal dopaminergic changes after binge drinking history in rats

Binge drinking (BD) is a harmful behavior for health and is a predictive factor for the development of alcohol addiction. Weak decision-making (DM) capacities could play a role in the vulnerability to BD which in turn would lead to DM impairments, thus perpetuating BD. Longitudinal preclinical studies are however lacking and necessary to understand this complex relationship. Both DM and BD are influenced by sex and involve dopamine release in the core of the nucleus accumbens, a central mechanism regulated by dopamine D2/3 autoreceptors. In this context, we used an operant self-administration procedure of BD in male and female rats, and longitudinally assessed DM capacity, memory and anxiety-like behavior. To better understand the mechanisms potentially involved in the relationship between DM and BD, ex vivo dopamine transmission was assessed short term after the end of the binge exposure in the core of the nucleus accumbens (NAc) using the fast-scan cyclic voltammetry (FSCV) technique and the D2/3 agonist quinpirole. We found important basal sex differences in DM, with female rats showing better performances at baseline. Choice processes were impaired exclusively in males after BD history, associated with a decrease in impulse control in both sexes, while memory and anxiety-like behavior were not affected. Our neurobiological results demonstrate that BD did not affect basal dopamine signaling in the NAc core, regardless of the sex, but reveal changes in the sensitivity to the inhibitory effects of quinpirole in females. DM impairments were neither associated with changes in basal dopamine signaling nor pre-synaptic D2 activity. Overall, our findings show that BD affects both DM processes and dopamine transmission in the core of the NAc in a sex-related manner, further suggesting that these effects may play a role in the vicious cycle leading to BD perpetuation and the early onset of AUD. Our results may inform novel strategies for therapeutic and prevention interventions.

Concurrent measures of impulsive action and choice are partially related and differentially modulated by dopamine D1- and D2-like receptors in a rat model of impulsivity

Impulsivity is a multidimensional construct, but the relationships between its constructs and their respective underlying dopaminergic underpinnings in the general population remain unclear. A cohort of Roman high- (RHA) and low- (RLA) avoidance rats were tested for impulsive action and risky decision-making in the rat gambling task, and then for delay discounting in the delay-discounting task to concurrently measure the relationships among the three constructs of impulsivity using a within-subject design. Then, we evaluated the effects of dopaminergic drugs on the three constructs of impulsivity, considering innate differences in impulsive behaviors at baseline. Risky decision-making and delay-discounting were positively correlated, indicating that both constructs of impulsive choice are related. Impulsive action positively correlated with risky decision-making but not with delay discounting, suggesting partial overlap between impulsive action and impulsive choice. RHAs showed a more impulsive phenotype in the three constructs of impulsivity compared to RLAs, demonstrating the comorbid nature of impulsivity in a population of rats. Amphetamine increased impulsive action and had no effect on risky decision-making regardless of baseline levels of impulsivity, but it decreased delay discounting only in high impulsive RHAs. In contrast, while D₁R and D₃R agonism as well as D_2/3R partial agonism decreased impulsive action regardless of baseline levels of impulsivity, D_2/3R agonism decreased impulsive action exclusively in high impulsive RHAs. Irrespective of baseline levels of impulsivity, risky decision-making was increased by D₁R and D_2/3R agonism but not by D₃R agonism or D_2/3R partial agonism. Finally, while D₁R and D₃R agonism, D_2/3R partial agonism and D₂R blockade increased delay discounting irrespective of baseline levels of impulsivity, D_2/3R agonism decreased it in low impulsive RLAs only. These findings indicate that the acute effects of dopamine drugs were partially overlapping across dimensions of impulsivity, and that only D_2/3R agonism showed baseline-dependent effects on impulsive action and impulsive choice.

Monoaminergic modulation of decision-making under risk of punishment in a rat model

The ability to decide advantageously among options that vary in both their risks and rewards is critical for survival and well-being. Previous work shows that some forms of risky decision-making are robustly modulated by monoamine signaling, but it is less clear how monoamine signaling modulates decision-making under risk of explicit punishment. The goal of these experiments was to determine how this form of decision-making is modulated by dopamine, serotonin, and norepinephrine signaling, using a task in which rats choose between a small, 'safe' food reward and a large food reward associated with variable risks of punishment. Preference for the large, risky reward (risk-taking) was reduced by administration of a D2/3 dopamine receptor agonist (bromocriptine) and a selective D2 agonist (sumanirole). The selective D3 agonist PD128907 appeared to attenuate reward discrimination abilities but did not affect risk-taking per se. In contrast, drugs targeting serotonergic and noradrenergic signaling had few if any effects on choice behavior. These data suggest that in contrast to other forms of risky decision-making, decision-making under risk of punishment is selectively modulated by dopamine signaling, predominantly through D2 receptors.

Examining the neurochemical underpinnings of animal models of risky choice: Methodological and analytic considerations

Because risky choice is associated with several psychiatric conditions, recent research has focused on examining the underlying neurochemical processes that control risk-based decision-making. Not surprisingly, several tasks have been developed to study the neural mechanisms involved in risky choice. The current review will briefly discuss the major tasks used to measure risky choice and will summarize the contribution of several major neurotransmitter systems to this behavior. To date, the most common measures of risky choice are the probability discounting task, the risky decision task, and the rat gambling task. Across these three tasks, the contribution of the dopaminergic system has been most studied, although the effects of serotonergic, adrenergic, cholinergic, and glutamatergic ligands will be discussed. Drug effects across these tasks have been inconsistent, which makes determining the precise role of neurotransmitter systems in risky choice somewhat difficult. Furthermore, procedural differences can modulate drug effects in these procedures, and the way data are analyzed can alter the interpretations one makes concerning pharmacological manipulations. By taking these methodological/analytic considerations into account, we may better elucidate the neurochemistry of risky decision-making. (PsycINFO Database Record (c) 2019 APA, all rights reserved).

Review: brain neurobiology of gambling disorder based on rodent models

Different literature reviews of gambling disorder (GD) neurobiology have been focused on human studies, others have focused on rodents, and others combined human and rodent studies. The main question of this review was: which are the main neurotransmitters systems and brain structures relevant for GD based on recent rodent studies? This work aims to review the experimental findings regarding the rodent´s neurobiology of GD. A search in the Pub Med database was set (October 2012-October 2017) and 162 references were obtained. After screening, 121 references were excluded, and only 41 references remained from the initial output. More, other 25 references were added to complement (introduction section, neuroanatomical descriptions) the principal part of the work. At the end, a total of 66 references remained for the review. The main conclusions are: 1) according to studies that used noninvasive methods for drug administration, some of the neurotransmitters and receptors involved in behaviors related to GD are: muscarinic, N-methyl-D-aspartate (NMDA), cannabinoid receptor 1 (CB₁), cannabinoid receptor 2 (CB₂), dopamine 2 receptor (D₂), dopamine 3 receptor (D₃), and dopamine 4 receptor (D₄); 2) moreover, there are other neurotransmitters and receptors involved in GD based on studies that use invasive methods of drug administration (eg, brain microinjection); example of these are: serotonin 1A receptor (5-HT_1A), noradrenaline receptors, gamma-aminobutyric acid receptor A (GABA_A), and gamma-aminobutyric acid receptor B (GABA_B); 3) different brain structures are relevant to behaviors linked to GD, like: amygdala (including basolateral amygdala (BLA)), anterior cingulate cortex (ACC), hippocampus, infralimbic area, insular cortex (anterior and rostral agranular), nucleus accumbens (NAc), olfactory tubercle (island of Calleja), orbitofrontal cortex (OFC), medial prefrontal cortex (mPFC), prefrontal cortex (PFC) - subcortical network, striatum (ventral) and the subthalamic nucleus (STN); and 4) the search for GD treatments should consider this diversity of receptor/neurotransmitter systems and brain areas.

Examination of the effects of cannabinoid ligands on decision making in a rat gambling task

Although exposure to delta-9-tetrahydrocannabinol (THC) is perceived to be relatively harmless, mounting evidence has begun to show that it is associated with a variety of cognitive deficits, including poor decision making. THC-induced impairments in decision making are thought to be the result of cannabinoid CB1 receptor activation, and although clinical literature suggests that chronic activation via THC contributes to perturbations in decision making, acute CB1 receptor modulation has yielded mixed results. Using an animal model to examine how CB1-specific ligands impact choice biases would provide significant insight as to how recruitment of the endocannabinoid system may influence decision making. Here, we used the rat gambling task (rGT), a validated analogue of the human Iowa Gambling Task, to assess baseline decision making preferences in male Wistar rats. After acquisition rGT performance was measured. Animals were challenged with the CB1 receptor antagonist rimonabant, the partial agonist THC, and the synthetic agonist WIN55,212-2. Animals were also treated acutely with the fatty acid amide hydrolase (FAAH) inhibitor URB597 to selectively upregulate the endocannabinoid anandamide. Blockade of the CB1 receptor produced a trend improvement in decision making in animals who preferred the advantageous task options, yet left choice unaffected in risk-prone rats. Neither CB1 receptor agonist had strong effects on decision making, but a high dose THC decreased premature responses, whereas WIN55,212-2 did the opposite. URB597 did not affect task performance. These results indicate that although chronic CB1 receptor activation may be associated with impaired decision making, acute modulation has modest effects on choice and instead may play a substantive role in regulating impulsive responding.

Dopamine and Stress System Modulation of Sex Differences in Decision Making

Maladaptive decision making is associated with several neuropsychiatric disorders, including problem gambling and suicidal behavior. The prevalence of these disorders is higher in men vs women, suggesting gender-dependent regulation of their pathophysiology underpinnings. We assessed sex differences in decision making using the rat version of the Iowa gambling task. Female rats identified the most optimal choice from session 1, whereas male rats from session 5. Male, but not female rats, progressively improved their advantageous option responding and surpassed females. Estrus cycle phase did not affect decision making. To test whether pharmacological manipulations targeting the dopaminergic and stress systems affect decision making in a sex-dependent manner, male and female rats received injections of a dopamine D₂ receptor (D₂R) antagonist (eticlopride), D₂R agonist (quinpirole), corticotropin-releasing factor 1 (CRF₁) antagonist (antalarmin), and α₂-adrenergic receptor antagonist (yohimbine; used as a pharmacological stressor). Alterations in mRNA levels of D₂R and CRF₁ were also assessed. Eticlopride decreased advantageous responding in male, but not female rats, whereas quinpirole decreased advantageous responding specifically in females. Yohimbine dose-dependently decreased advantageous responding in female rats, whereas decreased advantageous responding was only observed at higher doses in males. Antalarmin increased optimal choice responding only in female rats. Higher Drd2 and Crhr1 expression in the amygdala were observed in female vs male rats. Higher amygdalar Crhr1 expression was negatively correlated with advantageous responding specifically in females. This study demonstrates the relevance of dopaminergic- and stress-dependent sex differences to maladaptive decision making.

Effects of disulfiram on choice behavior in a rodent gambling task: association with catecholamine levels

RATIONALE

Gambling disorder is a growing societal concern, as recognized by its recent classification as an addictive disorder in the DSM-5. Case reports have shown that disulfiram reduces gambling-related behavior in humans.

OBJECTIVES

The purpose of the present study was to determine whether disulfiram affects performance on a rat gambling task, a rodent version of the Iowa gambling task in humans, and whether any changes were associated with alterations in dopamine and/or norepinephrine levels.

METHODS

Rats were administered disulfiram prior to testing on the rat gambling task or prior to analysis of dopamine or norepinephrine levels in brain homogenates. Rats in the behavioral task were divided into two subgroups (optimal vs suboptimal) based on their baseline levels of performance in the rat gambling task. Rats in the optimal group chose the advantageous strategy more, and rats in the suboptimal group (a parallel to problem gambling) chose the disadvantageous strategy more. Rats were not divided into optimal or suboptimal groups prior to neurochemical analysis.

RESULTS

Disulfiram administered 2 h, but not 30 min, before the task dose-dependently improved choice behavior in the rats with an initial disadvantageous "gambling-like" strategy, while having no effect on the rats employing an advantageous strategy. The behavioral effects of disulfiram were associated with increased striatal dopamine and decreased striatal norepinephrine.

CONCLUSIONS

These findings suggest that combined actions on dopamine and norepinephrine may be a useful treatment for gambling disorders.

Sex differences in animal models of decision making

The ability to weigh the costs and benefits of various options to make an adaptive decision is critical to an organism's survival and wellbeing. Many psychiatric diseases are characterized by maladaptive decision making, indicating a need for better understanding of the mechanisms underlying this process and the ways in which it is altered under pathological conditions. Great strides have been made in uncovering these mechanisms, but the majority of what is known comes from studies conducted solely in male subjects. In recent years, decision-making research has begun to include female subjects to determine whether sex differences exist and to identify the mechanisms that contribute to such differences. This Mini-Review begins by describing studies that have examined sex differences in animal (largely rodent) models of decision making. Possible explanations, both theoretical and biological, for such differences in decision making are then considered. The Mini-Review concludes with a discussion of the implications of sex differences in decision making for understanding psychiatric conditions. © 2016 Wiley Periodicals, Inc.

The effects of buspirone on occupancy of dopamine receptors and the rat gambling task

BACKGROUND

The dopamine D3 receptor (DRD₃) has been proposed as a target for drug development for the treatment of addictive disorders. Recently, the anxiolytic buspirone has been shown to have affinity for DRD₃ and DRD₄, and interest in repurposing it for addictive disorders has grown.

METHODS

Binding of [³H]-(+)-PHNO in the rat cerebellum and striatum was used to measure occupancy by buspirone of DRD₃ or DRD₂, respectively. Effects of buspirone in the rat gambling task (rGT) and the five-choice serial reaction time task (5-CSRTT) were examined.

RESULTS

Buspirone occupied both the DRD₂ and DRD₃ at high doses and the DRD₃, but not the DRD₂, in the narrow dose range of 3 mg/kg. At 10 mg/kg, a disruption of performance on rGT was observed. All measures of performance on the rGT, except for perseverations, were affected at 3 mg/kg. On the 5-CSRTT, omissions were increased. Impairments in the rGT were not mimicked by the effects induced by satiation. Further, buspirone did not impair food-maintained responding under a progressive ratio schedule of reinforcement at any dose, suggesting that the effects of buspirone on the rGT cannot be explained by non-selective actions.

CONCLUSIONS

Although buspirone had effects on the rGT at the dose that selectively occupied the DRD₃, the effects found do not parallel those found in previous studies of the effects of selective DRD₃ antagonists on the rGT. Thus, buspirone may impair performance on the rGT through actions at multiple receptor sites.

Cannabis use by women during pregnancy does not influence infant DNA methylation of the dopamine receptor DRD4

Background: Maternal cannabis use in pregnancy is linked with long-term adverse behavioral outcomes in offspring. Epigenetic processes established in utero that affect dopaminergic (reward) signaling may mediate risks. Associations between cannabis use and offspring DNA methylation have not been investigated; however, maternal tobacco smoking in pregnancy is associated with distinct patterns of DNA methylation at birth and beyond. Objectives: To determine whether maternal cannabis use is associated with methylation of the dopamine receptor gene DRD4 promoter in infants. Methods: Mothers in the Triple B study provided detailed information on drug use in each trimester of pregnancy. Buccal swabs were collected from neonates at 8 weeks (n = 804, 51.7% male, and 48.3% female). DRD4 promoter DNA methylation was measured using SEQUENOM MassARRAY. Results: Fifty-seven of the women in the study reported drug use during pregnancy, of whom 44 used cannabis. Of 19 cytosine-phosphate-guanine dinucleotides (CpG) units tested in DRD4, gestational cannabis use was associated with offspring methylation at 1 CpG unit in multivariate models (β + 1.48, CI: 0.02 to 2.93, and p = 0.047). At another site there was weak evidence that both cannabis and other drug use were independently associated with increased methylation, while the association with tobacco was in the reverse direction (cannabis use β + 0.67, CI: −0.12 to 1.46, and p = 0.09; other drug use β + 1.11, CI: 0.17 to 2.05, and p = 0.02; tobacco use β −0.41, CI: −0.85 to 0.03, and p = 0.07). None of the associations would remain significant after correction for multiple testing. Conclusion: There is no strong evidence that maternal cannabis use in pregnancy is associated with offspring DRD4 methylation.

Effects of various cannabinoid ligands on choice behaviour in a rat model of gambling

It is estimated that 0.6-1% of the population in the USA and Canada fulfil the Diagnostic and Statistical Manual of Mental Disorders, 5th ed. (DSM-5) criteria for gambling disorders (GD). To date, there are no approved pharmacological treatments for GD. The rat gambling task (rGT) is a recently developed rodent analogue of the Iowa gambling task in which rats are trained to associate four response holes with different magnitudes and probabilities of food pellet rewards and punishing time-out periods. Similar to healthy human volunteers, most rats adopt the optimal strategies (optimal group). However, a subset of animals show preference for the disadvantageous options (suboptimal group), mimicking the choice pattern of patients with GD. Here, we explored for the first time the effects of various cannabinoid ligands (WIN 55,212-2, AM 4113, AM 630 and URB 597) on the rGT. Administration of the cannabinoid agonist CB1/CB2 WIN 55,212-2 improved choice strategy and increased choice latency in the suboptimal group, but only increased perseverative behaviour, when punished, in the optimal group. Blockade of CB1 or CB2 receptors or inhibition of fatty-acid amide hydrolase did not affect rGT performance. These results suggest that stimulation of cannabinoid receptors could affect gambling choice behaviours differentially in some subgroups of subjects.

Perinatal maternal alcohol consumption and methylation of the dopamine receptor DRD4 in the offspring: the Triple B study

Maternal alcohol use during the perinatal period is a major public health issue, the higher ends of which are associated with foetal alcohol spectrum disorder and a range of adverse health outcomes in the progeny. The underlying molecular mechanisms remain largely unknown but may include the epigenetic disruption of gene activity during development. Alcohol directly activates the neurotransmitter dopamine, which plays an essential role in neurodevelopment. To investigate whether antenatal and early postnatal alcohol consumption were associated with differential dopamine receptor DRD4 promoter methylation in infants (n = 844). Data were drawn from the large population based Triple B pregnancy cohort study, with detailed information on maternal alcohol consumption in each trimester of pregnancy and early postpartum. DNA was extracted from infant buccal swabs collected at 8-weeks. DRD4 promoter DNA methylation was analysed by Sequenom MassARRAY. No strong evidence was found for an association between alcohol consumption during pregnancy and infant DRD4 methylation at 8-weeks postpartum. However, maternal alcohol consumption assessed contemporaneously at 8-weeks postpartum was associated with increased methylation at 13 of 19 CpG units examined (largest Δ + 3.20%, 95%Confidence Interval:1.66,4.75%, P = 0.0001 at CpG.6). This association was strongest in women who breastfeed, suggesting the possibility of a direct effect of alcohol exposure via breast milk. The findings of this study could influence public health guidelines around alcohol consumption for breastfeeding mothers; however, further research is required to confirm these novel findings.

Elucidating the role of D4 receptors in mediating attributions of salience to incentive stimuli on Pavlovian conditioned approach and conditioned reinforcement paradigms

The power of drug-associated cues to instigate drug 'wanting' and consequently promote drug seeking is a corner stone of contemporary theories of addiction. Gambling disorder has recently been added to the pantheon of addictive disorders due to the phenomenological similarities between the diseases. However, the neurobiological mechanism that may mediate increased sensitivity towards conditioned stimuli in addictive disorders is unclear. We have previously demonstrated using a rodent analogue of a simple slot machine that the dopamine D4 receptor is critically engaged in controlling animals' attribution of salience to stimuli associated with reward in this paradigm, and consequently may represent a target for the treatment of gambling disorder. Here, we investigated the role of acute administration of a D4 receptor agonist on animals' responsivity to conditioned stimuli on both a Pavlovian conditioned approach (autoshaping) and a conditioned reinforcement paradigm. Following training on one of the two tasks, separate cohorts of rats (male and female) were administered a dose of PD168077 shown to be maximally effective at precipitating errors in reward expectancy on the rat slot machine task (10mg/kg). However, augmenting the activity of the D4 receptors in this manner did not alter behaviour on either task. These data therefore provide novel evidence that the D4 receptor does not alter incentive motivation in response to cues on simple behavioural tasks.

Cocaine choice procedures in animals, humans, and treatment-seekers: Can we bridge the divide?

Individuals with cocaine use disorder chronically self-administer cocaine to the detriment of other rewarding activities, a phenomenon best modeled in laboratory drug-choice procedures. These procedures can evaluate the reinforcing effects of drugs versus comparably valuable alternatives under multiple behavioral arrangements and schedules of reinforcement. However, assessing drug-choice in treatment-seeking or abstaining humans poses unique challenges: for ethical reasons, these populations typically cannot receive active drugs during research studies. Researchers have thus needed to rely on alternative approaches that approximate drug-choice behavior or assess more general forms of decision-making, but whether these alternatives have relevance to real-world drug-taking that can inform clinical trials is not well-understood. In this mini-review, we (A) summarize several important modulatory variables that influence cocaine choice in nonhuman animals and non-treatment seeking humans; (B) discuss some of the ethical considerations that could arise if treatment-seekers are enrolled in drug-choice studies; (C) consider the efficacy of alternative procedures, including non-drug-related decision-making and 'simulated' drug-choice (a choice is made, but no drug is administered) to approximate drug choice; and (D) suggest opportunities for new translational work to bridge the current divide between preclinical and clinical research.

Skewed by Cues? The Motivational Role of Audiovisual Stimuli in Modelling Substance Use and Gambling Disorders

The similarity between gambling disorder (GD) and drug addiction has recently been recognized at the diagnostic level. Understanding the core cognitive processes involved in these addiction disorders, and in turn their neurobiological mechanisms, remains a research priority due to the enormous benefits such knowledge would have in enabling effective treatment design. Animal models can be highly informative in this regard. Although numerous rodent behavioural paradigms that capture different facets of gambling-like behaviour have recently been developed, the motivational power of cues in biasing individuals towards risky choice has so far received little attention despite the central role played by drug-paired cues in successful laboratory models of chemical dependency. Here, we review some of the comparatively simple paradigms in which reward-paired cues are known to modulate behaviour in rodents, such as sign-tracking, Pavlovian-to-instrumental transfer and conditioned reinforcement. Such processes are thought to play an important role in mediating responding for drug reward, and the need for future studies to address whether similar processes contribute to cue-driven risky choice is highlighted.