Chronic atomoxetine treatment during adolescence does not influence decision-making on a rodent gambling task, but does modulate amphetamine's effect on impulsive action in adulthood

Methamphetamine increases risky choice in rats, but only when magnitude and probability of reinforcement are manipulated within a session

Risky choice is associated with maladaptive behaviors, particularly substance use disorders. Current animal models of risky choice are often confounded by other constructs like behavioral flexibility and suboptimal choice. The purpose of the current experiment was to determine if the psychostimulant methamphetamine, a drug whose popularity has increased in recent years, increases risky choice in an equivalent expected value (EEV) task. In the EEV task, rats are given a choice between two reinforcer alternatives that differ in magnitude and probability of delivery, but have equivalent expected value. Forty-eight Sprague Dawley rats were tested in three versions of the EEV task. In the first version of the EEV task, both reinforcer magnitude and probability were adjusted across blocks of trials for both alternatives. In the second and the third versions of the EEV task, reinforcer magnitude was held constant across each block of trials (either 1 vs. 2 pellets or 4 vs. 5 pellets). We found that male rats preferred the "riskier" option, except when reinforcer magnitudes were held constant at 4 and 5 pellets across each block of trials. Methamphetamine (0.5 mg/kg) increased preference for the risky option in both males and females, but only when both reinforcer magnitude and probability were manipulated across blocks of trials for each alternative. The current results demonstrate that both magnitude of reinforcement and probability of reinforcement interact to influence risky choice. Overall, this study provides additional support for using reinforcers with expected value to measure risky choice.

Noradrenergic regulation of cue-guided decision making and impulsivity is doubly dissociable across frontal brain regions

RATIONALE

Win-paired stimuli can promote risk taking in experimental gambling paradigms in both rats and humans. We previously demonstrated that atomoxetine, a noradrenaline reuptake inhibitor, and guanfacine, a selective α2A adrenergic receptor agonist, reduced risk taking on the cued rat gambling task (crGT), a rodent assay of risky choice in which wins are accompanied by salient cues. Both compounds also decreased impulsive premature responding.

OBJECTIVE

The key neural loci mediating these effects were unknown. The lateral orbitofrontal cortex (lOFC) and the medial prefrontal cortex (mPFC), which are highly implicated in risk assessment, action selection, and impulse control, receive dense noradrenergic innervation. We therefore infused atomoxetine and guanfacine directly into either the lOFC or prelimbic (PrL) mPFC prior to task performance.

RESULTS

When infused into the lOFC, atomoxetine improved decision making score and adaptive lose-shift behaviour in males, but not in females, without altering motor impulsivity. Conversely, intra-PrL atomoxetine improved impulse control in risk preferring animals of both sexes, but did not alter decision making. Guanfacine administered into the PrL, but not lOFC, also altered motor impulsivity in all subjects, though in the opposite direction to atomoxetine.

CONCLUSIONS

These data highlight a double dissociation between the behavioural effects of noradrenergic signaling across frontal regions with respect to risky choice and impulsive action. Given that the influence of noradrenergic manipulations on motor impulsivity could depend on baseline risk preference, these data also suggest that the noradrenaline system may function differently in subjects that are susceptible to the risk-promoting lure of win-associated cues.

Type of medication therapy for ADHD and stimulant misuse during adolescence: a cross-sectional multi-cohort national study

Background

Attention-deficit/hyperactivity disorder (ADHD) is associated with higher substance use rates. Stimulant and non-stimulant pharmacotherapy improve adolescent ADHD, but their associations with prescription stimulant misuse (PSM), cocaine, and methamphetamine use are unclear. Using 2005-2020 US Monitoring the Future data, we investigated relationships between ADHD pharmacotherapy history and PSM, cocaine, or methamphetamine use.

Methods

Secondary students (13-19 years) provided data on pharmacotherapy history (N = 199,560; 86.3% of total sample) between January 1, 2005 and May 31, 2020 in a cross-sectional multi-cohort study; weights assured a nationally representative sample. Participants were grouped by ADHD pharmacotherapy history: none (88.7%; principally non-ADHD controls); stimulant-only (5.8%); non-stimulant-only (3.3%); both stimulant and non-stimulant (2.1%). Outcomes were past-year PSM, cocaine, and methamphetamine use. Logistic regressions examined relationships between pharmacotherapy history and outcomes, controlling for sociodemographics, recent substance use, and stimulant treatment cessation.

Findings

Past-year outcome rates were lowest in adolescents with no pharmacotherapy history: 4.7% for PSM [8310/174,561], 1.6% for cocaine [2858/174,688], and 0.7% for methamphetamine [1036/148,378]. A history of both stimulant and non-stimulant treatment was associated with the highest rates: 22.3% for PSM [940/4098], 10.4% for cocaine [450/4110], and 7.8% for methamphetamine [275/3427]. Adolescents who received monotherapy (stimulant- or non-stimulant-only) had intermediate rates, with no differences between monotherapy groups.

Interpretation

While elevated PSM and illicit stimulant use rates are likely influenced by ADHD, our findings suggested adolescents with a history of both stimulant and non-stimulant pharmacotherapy are at highest risk for these stimulant outcomes. Adolescents receiving ADHD pharmacotherapy should be monitored for PSM and illicit stimulant use.

Funding

National Institute on Drug Abuse/National Institutes of Health (USA) and Food and Drug Administration (USA).

The Effects of Drug Treatments for ADHD in Measures of Cognitive Performance

Based on core symptoms of inattention and deficient impulse control, and the identification of effective pharmacotherapies such as amphetamine (AMP; Adderall^®), methylphenidate (MPH; Ritalin^®), and atomoxetine (ATX; Strattera^®), ADHD is a clinical condition which provides opportunity for translational research. Neuropsychological tests such as the 5-Choice and Continuous Performance Tasks, which measure aspects of attention and impulse control in animals and humans, provide scope for both forward (animal to human) and reverse (human to animal) translation. Rodent studies support pro-attentive effects of AMP and MPH and effectiveness in controlling some forms of impulsive behavior. In contrast, any pro-attentive effects of ATX appear to be less consistent, the most reliable effects of ATX are recorded in tests of impulsivity. These differences may account for AMP and MPH being recognized as first-line treatments for ADHD with a higher efficacy relative to ATX. DSM-5 classifies three "presentations" of ADHD: predominantly inattentive type (ADHD-I), predominantly hyperactive/impulsive type (ADHD-HI), or combined (ADHD-C). Presently, it is unclear whether AMP, MPH, or ATX has differential levels of efficacy across these presentation types. Nonetheless, these studies encourage confidence for the forward translation of NCEs in efforts to identify newer pharmacotherapies for ADHD.

Noradrenergic contributions to cue-driven risk-taking and impulsivity

RATIONALE

The flashing lights and sounds of modern casinos are alluring and may contribute to the addictive nature of gambling. Such cues can have a profound impact on the noradrenaline (NA) system, which could therefore be a viable therapeutic target for gambling disorder (GD). While there is substantial evidence to support the involvement of NA in the impulsive symptoms of GD, its function in mediating the "pro-addictive" impact of cues is less understood.

OBJECTIVE

We wished to investigate the role of NA in our rodent assay of decision making and impulsivity, the cued rat gambling task (crGT). Given that sex differences are prominent in addiction disorders, and increasingly reported in the monoaminergic regulation of behaviour, we also prioritised evaluating noradrenergic drugs in both sexes.

METHODS

Female and male rats were trained to stability on the crGT and then given intraperitoneal injections of the noradrenaline reuptake inhibitor atomoxetine, the α_2A receptor agonist guanfacine, the beta receptor antagonist propranolol, and the α₂ receptor antagonist yohimbine.

RESULTS

Atomoxetine dose-dependently improved decision-making score. Guanfacine selectively enhanced decision making in risk-preferring males and optimal performing females. Propranolol and yohimbine did not influence decision making. Atomoxetine and guanfacine reduced premature responses, while yohimbine bi-phasically affected this index of motor impulsivity.

CONCLUSIONS

These results support the hypothesis that NA is an important neuromodulator of the cue-induced deficits in decision making observed in laboratory-based gambling paradigms, and suggest that NAergic drugs like atomoxetine and guanfacine may be useful in treating GD.

Contrasting effects of d-amphetamine and atomoxetine on measures of impulsive action and choice

Amphetamine (AMP) and atomoxetine (ATX) represent two of the most widely studied drug treatments used in the investigation of impulsive behaviour. While both drugs have relatively well defined effects in tests designed to investigate impulsive action (e.g. 5-choice task; 5-CSRTT), the effects of both drugs in tests of impulsive choice (e.g. delay discounting) are less consistent. In the present study both AMP and ATX were tested in a rodent gambling task (rGT) and delay discounting in rats separately trained to either an ascending or descending delay schedule. Effects of both drugs were compared to measures of impulsive action (premature (PREM) responses) and perseverative (PSV) responses measured in the 5-choice and rGT tasks. Consistent with previous studies, AMP (0.1-1 mg/kg) increased both PREM and PSV responses, and ATX (0.5-2 mg/kg) reduced both measures in the 5-choice and rGT tasks. At equivalent doses ATX had no reliable effect on choice behaviour in either the rGT or delay discounting suggesting a null effect of this drug on impulsive choice and risky decision making. The effects of AMP were more complex, with a subtle shift in preference to a low risk (P1) choice in the rGT, and an effect on discounting that was unrelated to reinforcer value, but instead dependent on delay sequence and baseline choice preference. One aspect to these outcomes is to highlight the importance of multiple methodological factors when assessing drug effects on complex behaviours such as impulsive choice, and question what are the most appropriate test conditions under which to examine these drugs on discounting.

Exposure to uncertainty mediates the effects of traumatic brain injury on probabilistic decision-making in rats

Primary Objective: Traumatic brain injury (TBI) is associated with numerous psychiatric comorbidities, and subclinical psychiatric symptoms. While many symptoms have been replicated in animal models of brain injury, a vast majority of studies utilize naïve rats as subjects, which fail to mimic the complex learning history of human patients.Methods and Procedures: In the current study, we evaluated the effects of a brain injury in animals with early exposure to uncertainty on post-injury decision-making in a probabilistic task, the rodent gambling task (RGT).Main Outcomes and Results: Exposure to uncertainty resulted in a heterogeneous sample relative to prior publications, and brain-injured rats showed no deficits in choice behavior compared to shams which contrasts with large, pervasive deficits in previously published work. However, TBI increased impulsivity and caused transient changes in behavioral variables indicative of initial motivational deficits (pellets earned, omitted responses). Notably, effects of amphetamine were similar on this heterogeneous sample of rats relative to a number of other published reports, suggesting consistent effects of gross monoaminergic manipulations on choice behavior, independent of experience.Conclusions: Going forward, translational studies need to consider the heterogeneity that exists at the clinical level and account for these problems when modeling diseases in animals.

Relative insensitivity to time-out punishments induced by win-paired cues in a rat gambling task

RATIONALE

Pairing rewarding outcomes with audiovisual cues in simulated gambling games increases risky choice in both humans and rats. However, the cognitive mechanism through which this sensory enhancement biases decision-making is unknown.

OBJECTIVES

To assess the computational mechanisms that promote risky choice during gambling, we applied a series of reinforcement learning models to a large dataset of choices acquired from rats as they each performed one of two variants of a rat gambling task (rGT), in which rewards on "win" trials were delivered either with or without salient audiovisual cues.

METHODS

We used a sampling technique based on Markov chain Monte Carlo to obtain posterior estimates of model parameters for a series of RL models of increasing complexity, in order to assess the relative contribution of learning about positive and negative outcomes to the latent valuation of each choice option on the cued and uncued rGT.

RESULTS

Rats which develop a preference for the risky options on the rGT substantially down-weight the equivalent cost of the time-out punishments during these tasks. For each model tested, the reduction in learning from the negative time-outs correlated with the degree of risk preference in individual rats. We found no apparent relationship between risk preference and the parameters that govern learning from the positive rewards.

CONCLUSIONS

The emergence of risk-preferring choice on the rGT derives from a relative insensitivity to the cost of the time-out punishments, as opposed to a relative hypersensitivity to rewards. This hyposensitivity to punishment is more likely to be induced in individual rats by the addition of salient audiovisual cues to rewards delivered on win trials.

Long-term deficits in risky decision-making after traumatic brain injury on a rat analog of the Iowa gambling task

Traumatic brain injury (TBI) affects 2.8 million people annually in the United States, with significant populations suffering from ongoing cognitive dysfunction. Impairments in decision-making can have major implications for patients and their caregivers, often enduring for years to decades, yet are rarely explored in experimental TBI. In the current study, the Rodent Gambling Task (RGT), an Iowa Gambling Task analog, was used to assess risk-based decision-making and motor impulsivity after TBI. During testing, rats chose between options associated with different probabilities of reinforcement (sucrose) or punishment (timeout). To determine effects of TBI on learned behaviors versus the learning process, rats were trained either before, or after, a bilateral frontal controlled cortical impact TBI, and then assessed for 12 weeks. To evaluate the degree to which monoamine systems, such as dopamine, were affected by TBI, rats were given an amphetamine challenge, and behavior recorded. Injury immediately and chronically decreased optimal decision-making, and biased rats towards both riskier, and safer (but suboptimal) choices, regardless of prior learning history. TBI also increased motor impulsivity across time, reflecting ongoing neural changes. Despite these similarities in trained and acquisition rats, those that learned the task after injury demonstrated reduced effects of amphetamine on optimal decision-making, suggesting a lesser role of monoamines in post-injury learning. Amphetamine also dose-dependently reduced motor impulsivity in injured rats. This study opens up the investigation of psychiatric-like dysfunction in animal models of TBI and tasks such as the RGT will be useful in identifying therapeutics for the chronic post-injury period.

MAM-E17 rat model impairments on a novel continuous performance task: effects of potential cognitive enhancing drugs

RATIONALE

Impairments in attention and inhibitory control are endophenotypic markers of neuropsychiatric disorders such as schizophrenia and represent key targets for therapeutic management. Robust preclinical models and assays sensitive to clinically relevant treatments are crucial for improving cognitive enhancement strategies.

OBJECTIVES

We assessed a rodent model with neural and behavioral features relevant to schizophrenia (gestational day 17 methylazoxymethanol acetate treatment (MAM-E17)) on a novel test of attention and executive function, and examined the impact of putative nootropic drugs.

METHODS

MAM-E17 and sham control rats were trained on a novel touchscreen-based rodent continuous performance test (rCPT) designed to closely mimic the human CPT paradigm. Performance following acute, systemic treatment with an array of pharmacological compounds was investigated.

RESULTS

Two cohorts of MAM-E17 rats were impaired on rCPT performance including deficits in sensitivity (d') and increased false alarm rates (FARs). Sulpiride (0-30 mg/kg) dose-dependently reduced elevated FAR in MAM-E17 rats whereas low-dose modafinil (8 mg/kg) only improved d' in sham controls. ABT-594 (5.9-19.4 μg/kg) and modafinil (64 mg/kg) showed expected stimulant-like effects, while LSN2463359 (5 mg/kg), RO493858 (10 mg/kg), atomoxetine (0.3-1 mg/kg), and sulpiride (30 mg/kg) showed expected suppressant effects on performance across all animals. Donepezil (0.1-1 mg/kg) showed near-significant enhancements in d', and EVP-6124 (0.3-3 mg/kg) exerted no effects in the rCPT paradigm.

CONCLUSION

The MAM-E17 model exhibits robust and replicable impairments in rCPT performance that resemble attention and inhibitory control deficits seen in schizophrenia. Pharmacological profiles were highly consistent with known drug effects on cognition in preclinical and clinical studies. The rCPT is a sensitive and reliable tool with high translational potential for understanding the etiology and treatment of disorders affecting attention and executive dysfunction.

Gambling disorder: an integrative review of animal and human studies

Gambling disorder (GD), previously called pathological gambling and classified as an impulse control disorder in DSM-III and DSM-IV, has recently been reclassified as an addictive disorder in the DSM-5. It is widely recognized as an important public health problem associated with substantial personal and social costs, high rates of psychiatric comorbidity, poor physical health, and elevated suicide rates. A number of risk factors have been identified, including some genetic polymorphisms. Animal models have been developed in order to study the underlying neural basis of GD. Here, we discuss recent advances in our understanding of the risk factors, disease course, and pathophysiology. A focus on a phenotype-based dissection of the disorder is included in which known neural correlates from animal and human studies are reviewed. Finally, current treatment approaches are discussed, as well as future directions for GD research.

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.

Developmental DSP4 effects on cortical Arc expression

Activity Regulated Cytoskeleton Associated Protein (Arc) is an immediate early gene that is critical to brain plasticity. In this study, norepinephrine's regulation of Arc expression was examined during different stages of postnatal development. Rats were injected with N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine hydrochloride (DSP-4), a selective noradrenergic neurotoxin, during preadolescence (PND 0 or 13), adolescence (PND 23 or 48) or adulthood (PND 60). After each DSP4 treatment, brains were harvested later in development and Arc mRNA levels analyzed with in situ hybridization. Rats lesioned with DSP4 during preadolescence showed no differences in Arc level compared to saline treated controls. In contrast, adolescence was a time of changing Arc mRNA response to DSP4. Rats lesioned during early adolescence showed Arc expression increases, while rats lesioned during late adolescence showed dramatic Arc expression decreases. Decreases in Arc level caused by late adolescent DSP4 were similar to those found in lesioned adults. These findings highlight a qualitatively different regulation of Arc expression by norepinephrine according to developmental stage, and indicate that mature regulation is not intact until late adolescence. These data point to important developmental differences in norepinephrine's regulation of brain plasticity. These differences may underlie contrasting psychotropic responses in children and adolescents compared to adults.