Behavioral disinhibition requires dopamine receptor activation

Noradrenergic modulation of stress induced catecholamine release: Opposing influence of FG7142 and yohimbine

Background

Life stress modulates decision making, particularly in the face of risk, in some cases prompting vulnerable populations to make suboptimal, life-altering choices. In the brain, stress is known to alter the extracellular release of catecholamines in structures such as basolateral amygdala (BLA) and nucleus accumbens (NAc), but the relationship between catecholamines and decision-making behavior under stress has not been systemically explored.

Methods

We developed an operant touchscreen decision-making task for rats comprising elements of loss aversion and risk seeking behavior. Rats were first injected systemically with an adrenergicα 2 A -receptor agonist (guanfacine) and antagonist (yohimbine), as well as a partial inverse GABAA agonist, FG 7142, known to induce anxiety and stress related physiological responses in a variety of species, including humans. We then used fiber photometry to monitor NE in the basolateral amygdala (BLA), and DA activity in the nucleus accumbens (NAc) while animals engaged in decision-making and following systemic injections of FG 7142 and yohimbine.

Results

Neither yohimbine nor guanfacine had any impact on decision making strategy but altered motivational state with yohimbine making the animal almost insensitive to the reward outcome. The pharmacological induction of stress with FG 7142 biased the rats' decisions towards safety, but this bias shifted toward risk when co-treated with yohimbine. In the BLA and NAc, the FG 7142 altered catecholamine release, with systemic yohimbine producing opposing effects on NE and DA release.

Conclusions

Stress induced changes in catecholamine release in the BLA and NAc can directly influence loss sensitivity, decisions and motivation, which can be modulated by theα 2 A adrenoreceptor antagonist, yohimbine.

Amylin Modulates a Ventral Tegmental Area-to-Medial Prefrontal Cortex Circuit to Suppress Food Intake and Impulsive Food-Directed Behavior

BACKGROUND

A better understanding of the neural mechanisms regulating impaired satiety to palatable foods is essential to treat hyperphagia linked with obesity. The satiation hormone amylin signals centrally at multiple nuclei including the ventral tegmental area (VTA). VTA-to-medial prefrontal cortex (mPFC) projections encode food reward information to influence behaviors including impulsivity. We hypothesized that modulation of VTA-to-mPFC neurons underlies amylin-mediated decreases in palatable food-motivated behaviors.

METHODS

We used a variety of pharmacological, behavioral, genetic, and viral approaches (n = 4-16/experiment) to investigate the anatomical and functional circuitry of amylin-controlled VTA-to-mPFC signaling in rats.

RESULTS

To first establish that VTA amylin receptor (calcitonin receptor) activation can modulate mPFC activity, we showed that intra-VTA amylin decreased food-evoked mPFC cFos. VTA amylin delivery also attenuated food-directed impulsive behavior, implicating VTA amylin signaling as a regulator of mPFC functions. Palatable food activates VTA dopamine and mPFC neurons. Accordingly, dopamine receptor agonism in the mPFC blocked the hypophagic effect of intra-VTA amylin, and VTA amylin injection reduced food-evoked phasic dopamine levels in the mPFC, supporting the idea that VTA calcitonin receptor activation decreases dopamine release in the mPFC. Surprisingly, calcitonin receptor expression was not found on VTA-to-mPFC projecting neurons but was instead found on GABAergic (gamma-aminobutyric acidergic) interneurons in the VTA that provide monosynaptic inputs to this pathway. Blocking intra-VTA GABA signaling, through GABA receptor antagonists and DREADD (designer receptor exclusively activated by designer drugs)-mediated GABAergic neuronal silencing, attenuated intra-VTA amylin-induced hypophagia.

CONCLUSIONS

These results indicate that VTA amylin signaling stimulates GABA-mediated inhibition of dopaminergic projections to the mPFC to mitigate impulsive consumption of palatable foods.

Development of a novel rodent rapid serial visual presentation task reveals dissociable effects of stimulant versus nonstimulant treatments on attentional processes

The rapid serial visual presentation (RSVP) task and continuous performance tasks (CPT) are used to assess attentional impairments in patients with psychiatric and neurological conditions. This study developed a novel touchscreen task for rats based on the structure of a human RSVP task and used pharmacological manipulations to investigate their effects on different performance measures. Normal animals were trained to respond to a target image and withhold responding to distractor images presented within a continuous sequence. In a second version of the task, a false-alarm image was included, so performance could be assessed relative to two types of nontarget distractors. The effects of acute administration of stimulant and nonstimulant treatments for ADHD (amphetamine and atomoxetine) were tested in both tasks. Methylphenidate, ketamine, and nicotine were tested in the first task only. Amphetamine made animals more impulsive and decreased overall accuracy but increased accuracy when the target was presented early in the image sequence. Atomoxetine improved accuracy overall with a specific reduction in false-alarm responses and a shift in the attentional curve reflecting improved accuracy for targets later in the image sequence. However, atomoxetine also slowed responding and increased omissions. Ketamine, nicotine, and methylphenidate had no specific effects at the doses tested. These results suggest that stimulant versus nonstimulant treatments have different effects on attention and impulsive behaviour in this rat version of an RSVP task. These results also suggest that RSVP-like tasks have the potential to be used to study attention in rodents.

Sex, but not juvenile stress, affects reversal learning and DRL performance following cocaine administration

INTRODUCTION

Early adversity, impulsivity and sex all contribute to the risk of developing substance use disorder. Using rats, we examined how juvenile stress interacts with sex and cocaine to affect performance on a serial reversal task and a differential reinforcement of low rates 10 s (DRL10) task. The expression of dopamine-related proteins in several brain areas was also assessed.

METHODS

From postnatal days (PND) 25-29, rats were exposed to a variable stress protocol. In adulthood, rats were trained on the reversal task and the effects of cocaine (0, 10, or 20 mg/kg, IP) on performance were assessed. Next, rats were trained on the DRL10 task and the effects of cocaine on performance were assessed. Finally, brains were extracted, and Western blot analyses conducted.

RESULTS

Juvenile stress did not affect behavior. Sex did not affect baseline performance in either task. In the reversal task, cocaine decreased % high probability responses and the number of rewards earned in both sexes. Cocaine had sex-dependent effects on omissions, low probability responses and response latencies. In the DRL10 task, cocaine decreased the peak latency to respond and the number of rewards earned in both sexes. Cocaine had sex-dependent effects on peak rate of responding, response efficiency, burst responses and long responses. Female rats exhibited increased expression of DRD1 receptors in the striatum.

DISCUSSION

These data contribute to the growing literature demonstrating sex differences in the behavioral effects of cocaine and suggest that DRD1 receptors could contribute to the observed behavioral sex differences.

Nicotinic Acetylcholine Receptor Dysfunction in Addiction and in Some Neurodegenerative and Neuropsychiatric Diseases

The cholinergic system plays an essential role in brain development, physiology, and pathophysiology. Herein, we review how specific alterations in this system, through genetic mutations or abnormal receptor function, can lead to aberrant neural circuitry that triggers disease. The review focuses on the nicotinic acetylcholine receptor (nAChR) and its role in addiction and in neurodegenerative and neuropsychiatric diseases and epilepsy. Cholinergic dysfunction is associated with inflammatory processes mainly through the involvement of α7 nAChRs expressed in brain and in peripheral immune cells. Evidence suggests that these neuroinflammatory processes trigger and aggravate pathological states. We discuss the preclinical evidence demonstrating the therapeutic potential of nAChR ligands in Alzheimer disease, Parkinson disease, schizophrenia spectrum disorders, and in autosomal dominant sleep-related hypermotor epilepsy. PubMed and Google Scholar bibliographic databases were searched with the keywords indicated below.

Assessing attention and impulsivity in the variable stimulus duration and variable intertrial interval rodent continuous performance test schedules using dopamine receptor antagonists in female C57BL/6JRj mice

RATIONALE

Dopaminergic dysfunction is implicated in disorders of impulsivity and inattention. The rodent continuous performance test (rCPT) has been used to quantify changes in attention and impulsivity.

OBJECTIVE

To examine the roles of dopamine receptors in attention and impulsivity behaviours measured in the rCPT variable stimulus duration (vSD) and the variable intertrial interval schedules (vITI) using DA receptor antagonists.

METHODS

Two cohorts of 35 and 36 female C57BL/6JRj mice were examined separately in the rCPT, vSD, and vITI schedules, respectively. Both cohorts received antagonists of the following receptors: D1/5 (SCH23390, SCH: 0.01, 0.02, 0.04 mg/kg) and D2/3 (raclopride, RAC 0.03, 0.10, 0.30 mg/kg) in consecutive balanced Latin square designs with flanking reference measurements. The antagonists were subsequently examined for effects on locomotor activity.

RESULTS

SCH showed similar effects in both schedules, and the effects were reference-dependent in the vITI schedule. SCH reduced responding, but improved response accuracy, impulsivity, discriminability, and locomotor activity. RAC showed mixed effects on responsivity, but improved accuracy and discriminability. The discriminability improvement was driven by an increase in hit rate in the vITI schedule and a reduction in false alarm rate in the vSD schedule. RAC also decreased locomotor activity.

CONCLUSION

Both D1/5 and D2/3 receptor antagonism reduced responding, but the outcome on discriminability differed, stemming from individual effects on hit and false alarm rate, and the weight of omissions within the calculation. The effects of SCH and RAC suggest that endogenous DA increases responding and impulsivity, but reduces accuracy and shows mixed effects on discriminability.

Increased meso-striatal connectivity mediates trait impulsivity in FTO variant carriers

Objective

While variations in the first intron of the fat mass and obesity-associated gene (FTO, rs9939609 T/A variant) have long been identified as a major contributor to polygenic obesity, the mechanisms underlying weight gain in risk allele carriers still remain elusive. On a behavioral level, FTO variants have been robustly linked to trait impulsivity. The regulation of dopaminergic signaling in the meso-striatal neurocircuitry by these FTO variants might represent one mechanism for this behavioral alteration. Notably, recent evidence indicates that variants of FTO also modulate several genes involved in cell proliferation and neuronal development. Hence, FTO polymorphisms might establish a predisposition to heightened trait impulsivity during neurodevelopment by altering structural meso-striatal connectivity. We here explored whether the greater impulsivity of FTO variant carriers was mediated by structural differences in the connectivity between the dopaminergic midbrain and the ventral striatum.

Methods

Eighty-seven healthy normal-weight volunteers participated in the study; 42 FTO risk allele carriers (rs9939609 T/A variant, FTO ⁺ group: AT, AA) and 39 non-carriers (FTO ^- group: TT) were matched for age, sex and body mass index (BMI). Trait impulsivity was assessed via the Barratt Impulsiveness Scale (BIS-11) and structural connectivity between the ventral tegmental area/substantia nigra (VTA/SN) and the nucleus accumbens (NAc) was measured via diffusion weighted MRI and probabilistic tractography.

Results

We found that FTO risk allele carriers compared to non-carriers, demonstrated greater motor impulsivity (p = 0.04) and increased structural connectivity between VTA/SN and the NAc (p< 0.05). Increased connectivity partially mediated the effect of FTO genetic status on motor impulsivity.

Conclusion

We report altered structural connectivity as one mechanism by which FTO variants contribute to increased impulsivity, indicating that FTO variants may exert their effect on obesity-promoting behavioral traits at least partially through neuroplastic alterations in humans.

Inhibition of ventral tegmental area projections to the nucleus accumbens shell increases premature responding in the five-choice serial reaction time task in rats

Exaggerated impulsivity and attentional impairments are hallmarks of certain disorders of behavioural control such as attention-deficit/hyperactivity disorder (ADHD), schizophrenia and addiction. Pharmacological studies have implicated elevated dopamine (DA) levels in the nucleus accumbens shell (NAcbS) in impulsive actions. The NAcbS receives its DA input from the ventral tegmental area (VTA), and we have previously shown that optogenetic activation of VTA-NAcbS projections impaired impulse control and attention in the five-choice serial reaction time task (5-CSRTT) in rats. To better understand the role of VTA-NAcbS projections in impulsivity and attention, the present study sought to inhibit this projection using optogenetics. We demonstrate that inhibiting VTA-NAcbS efferents during the last seconds of the inter-trial interval (i.e. immediately before presentation of the instructive cue) induces exaggerated impulsive action, in the absence of changes in attentional or motivational parameters in the 5-CSRTT. Together with our earlier observations, this suggests that impulse control in the 5-CSRTT is tightly controlled by VTA-NAcbS activity, with deviations in both directions resulting in increased impulsivity.

Effects of 5-HT2C receptor stimulation in male mice on behaviour and Fos expression: feeding, reward and impulsivity

Serotonin modulates many motivated behaviours via multiple receptor subtypes. Agonists at 5-HT_2C receptors have potential for treating behavioural problems associated with obesity and drug use. In this work we examined the impact of the 5-HT_2C receptor agonist lorcaserin on several motivated behaviours related to feeding, reward and waiting impulsivity, and on neuronal activation in key brain areas mediating those behaviours. In male C57BL/6J mice effects of lorcaserin (0.2, 1 and 5mg/kg) were examined on feeding, and on operant responding for a palatable reward. Feeding was reduced only at 5mg/kg, whereas operant responding was reduced at 1mg/kg. At a much lower dose range lorcaserin 0.05-0.2mg/kg also reduced impulsive behaviour measured as premature responding in the 5-choice serial reaction time (5-CSRT) test, without affecting attention or ability to perform the task. Lorcaserin induced Fos expression in brain regions related to feeding (paraventricular nucleus and arcuate nucleus), reward (ventral tegmental area), and impulsivity (medial prefrontal cortex, VTA) although these effects did not show the same differential sensitivity to lorcaserin as the behavioural measures. These results indicate a broad profile of action of 5-HT_2C receptor stimulation on brain circuitry and on motivated behaviours, but with clear evidence of differential sensitivity across behavioural domains. This is exemplified by that fact that impulsive behaviour was reduced at a much lower dose range than was feeding behaviour. Along with previous work, and some clinical observations, this work supports the idea that 5-HT_2C agonists may be useful for behavioural problems associated with impulsivity.

Blockade of the orexin 1-receptors and 'cocaine- and amphetamine-regulated transcript' in the nucleus accumbens shell alters impulse control in rats

Impulsivity is a multifaceted construct and alterations in impulsiveness are often associated with psychiatric diseases, including drug addiction and binge eating disorder. Impulse control involves several brain regions. The present study assessed the role of the orexigenic, appetite stimulating neuropeptide orexin (OX) and the anorexigenic, appetite reducing neuropeptide cocaine- and amphetamine-regulated transcript (CART) within the nucleus accumbens shell (NAcSh) in impulse control in rats. The animals were ranked for their trait impulsivity based on a screening in the 5-choice serial reaction time task (5-CSRTT). The rats' performances were analysed after bilateral infusions of the OX 1-receptor antagonist SB-334867 (SB) and CART-antibodies (CART-ABs) into the NAcSh. After SB infusions, there was no change in premature responses observed on average. Further analysis revealed a negative linear correlation between the effect of intra-NAcSh SB infusions on premature responses and trait impulsivity. The effect of SB ranged from an increase, no change to a decrease in premature responses in the individual animals with increasing trait impulsivity. Infusions of CART-ABs led to consistently enhanced impulse control with fewer irrelevant actions, independent of trait impulsivity. These data suggest that both OX, especially OX A, and CART in the NAcSh, can be considered endogenous regulators of impulsive action, dependent on underlying impulsivity in the case of OX and independent from trait impulsivity in the case of CART.

D2/3 Agonist during Learning Potentiates Cued Risky Choice

Impulse control and/or gambling disorders can be triggered by dopamine agonist therapies used to treat Parkinson's disease, but the cognitive and neurobiological mechanisms underlying these adverse effects are unknown. Recent data show that adding win-paired sound and light cues to the rat gambling task (rGT) potentiates risky decision-making and impulsivity via the dopamine system, and that changing dopaminergic tone has a greater influence on behavior while subjects are learning task contingencies. Dopamine agonist therapy may therefore be potentiating risk-taking by amplifying the behavioral impact of gambling-related cues on novel behavior. Here, we show that ropinirole treatment in male rats transiently increased motor impulsivity but robustly and progressively increased choice of the high-risk/high-reward options when administered during acquisition of the cued but not uncued rGT. Early in training, ropinirole increased win-stay behavior after large unlikely wins on the cued rGT, indicative of enhanced model-free learning, which mediated the drug's effect on later risk preference. Ex vivo cFos imaging showed that both chronic ropinirole and the addition of win-paired cues suppressed the activity of dopaminergic midbrain neurons. The ratio of midbrain:prefrontal cFos+ neurons was lower in animals with suboptimal choice patterns and tended to predict risk preference across all rats. Network analyses further suggested that ropinirole induced decoupling of the dopaminergic cells of the VTA and nucleus accumbens but only when win-paired cues were present. Frontostriatal activity uninformed by the endogenous dopaminergic teaching signal therefore appeared to perpetuate risky choice, and ropinirole exaggerated this disconnect in synergy with reward-paired cues.SIGNIFICANCE STATEMENT D2/3 receptor agonists, used to treat Parkinson's disease, can cause gambling disorder through an unknown mechanism. Ropinirole increased risky decision-making in rats, but only when wins were paired with casino-inspired sounds and lights. This was mediated by increased win-stay behavior after large unlikely wins early in learning, indicating enhanced model-free learning. cFos imaging showed that ropinirole suppressed activity of midbrain dopamine neurons, an effect that was mimicked by the addition of win-paired cues. The degree of risky choice rats exhibited was uniquely predicted by the ratio of midbrain dopamine:PFC activity. Depriving the PFC of the endogenous dopaminergic teaching signal may therefore drive risky decision-making on-task, and ropinirole acts synergistically with win-paired cues to amplify this.

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.

Theory of visual attention (TVA) applied to rats performing the 5-choice serial reaction time task: differential effects of dopaminergic and noradrenergic manipulations

RATIONALE

Attention is compromised in many psychiatric disorders, including attention-deficit/hyperactivity disorder (ADHD). While dopamine and noradrenaline systems have been implicated in ADHD, their exact role in attentional processing is yet unknown.

OBJECTIVES

We applied the theory of visual attention (TVA) model, adapted from human research, to the rat 5-choice serial reaction time task (5CSRTT) to investigate catecholaminergic modulation of visual attentional processing in healthy subjects of high- and low-attention phenotypes.

METHODS

Rats trained on the standard 5CSRTT and tested with variable stimulus durations were treated systemically with noradrenergic and/or dopaminergic agents (atomoxetine, methylphenidate, amphetamine, phenylephrine and atipamezole). TVA modelling was applied to estimate visual processing speed for correct and incorrect visual perceptual categorisations, independent of motor reaction times, as measures of attentional capacity.

RESULTS

Atomoxetine and phenylephrine decreased response frequencies, including premature responses, increased omissions and slowed responding. In contrast, methylphenidate, amphetamine and atipamezole sped up responding and increased premature responses. Visual processing speed was also affected differentially. Atomoxetine and phenylephrine slowed, whereas methylphenidate and atipamezole sped up, visual processing, both for correct and incorrect categorisations. Amphetamine selectively improved visual processing for correct, though not incorrect, responses in high-attention rats only, possibly reflecting improved attention.

CONCLUSIONS

These data indicate that the application of TVA to the 5CSRTT provides an enhanced sensitivity to capturing attentional effects. Unexpectedly, we found overall slowing effects, including impaired visual processing, following drugs either increasing extracellular noradrenaline (atomoxetine) or activating the α1-adrenoceptor (phenylephrine), while also ameliorating premature responses (impulsivity). In contrast, amphetamine had potential pro-attentional effects by enhancing visual processing, probably due to central dopamine upregulation.

Monoamine Oxidase B (MAO-B): A Target for Rational Drug Development in Schizophrenia Using PET Imaging as an Example

Monoamine oxidase B (MAO-B) is an important high-density enzyme involved in the generation of oxidative stress and central in the catabolism of dopamine, particularly in brain subcortical regions with putative implications in the pathophysiology of schizophrenia. In this chapter, we review postmortem studies, preclinical models, and peripheral and genetic studies implicating MAO-B in psychosis. A literature search in PubMed was conducted and 64 studies were found to be eligible for systematic review. We found that MAO-B could be identified as a potential target in schizophrenia. Evidence comes mostly from studies of peripheral markers, showing reduced platelet MAO-B activity in schizophrenia, together with preclinical results from MAO-B knock-out mice resulting in a hyperdopaminergic state and behavioral disinhibition. However, whether brain MAO-B is altered in vivo in patients with schizophrenia remains unknown. We therefore review methodological studies involving MAO-B positron emission tomography (PET) radioligands used to quantify MAO-B in vivo in the human brain. Given the limitations of currently available treatments for schizophrenia, elucidating whether MAO-B could be used as a target for risk stratification or clinical staging in schizophrenia could allow for a rational search for newer antipsychotics and the development of new treatments.

Nucleus accumbens D1-receptors regulate and focus transitions to reward-seeking action

It is well established that dopamine transmission is integral in mediating the influence of reward expectations on reward-seeking actions. However, the precise causal role of dopamine transmission in moment-to-moment reward-motivated behavioral control remains contentious, particularly in contexts where it is necessary to refrain from responding to achieve a beneficial outcome. To examine this, we manipulated dopamine transmission pharmacologically as rats performed a Go/No-Go task that required them to either make or withhold action to gain either a small or large reward. D1R Stimulation potentiated cue-driven action initiation, including fast impulsive actions on No-Go trials. By contrast, D1R blockade primarily disrupted the successful completion of Go trial sequences. Surprisingly, while after global D1R blockade this was characterized by a general retardation of reward-seeking actions, nucleus accumbens core (NAcC) D1R blockade had no effect on the speed of action initiation or impulsive actions. Instead, fine-grained analyses showed that this manipulation decreased the precision of animals' goal-directed actions, even though they usually still followed the appropriate response sequence. Strikingly, such "unfocused" responding could also be observed off-drug, particularly when only a small reward was on offer. These findings suggest that the balance of activity at NAcC D1Rs plays a key role in enabling the rapid activation of a focused, reward-seeking state to enable animals to efficiently and accurately achieve their goal.

The effects of early life stress on impulsivity

Elevated impulsivity is a symptom shared by various psychiatric disorders such as substance use disorder, bipolar disorder, and attention-deficit/hyperactivity disorder. However, impulsivity is not a unitary construct and impulsive behaviors fall into two subcategories: impulsive action and impulsive choice. Impulsive choice refers to the tendency to prefer immediate, small rewards over delayed, large rewards, whereas impulsive action involves difficulty inhibiting rash, premature, or mistimed behaviors. These behaviors are mediated by the mesocorticolimbic dopamine (DA) system, which consists of projections from the ventral tegmental area to the nucleus accumbens and prefrontal cortex. Early life stress (ELS) alters both impulsive choice and impulsive action in rodents. ELS also changes DA receptor expression, transmission, and activity within the mesocorticolimbic system. This review integrates the dopamine, impulsivity, and ELS literature to provide evidence that ELS alters impulsivity via inducing changes in the mesocorticolimbic DA system. Understanding how ELS affects brain circuits associated with impulsivity can help advance treatments aimed towards reducing impulsivity symptoms in a variety of psychiatric disorders.

Nicotine Differentially Modulates Emotional-Locomotor Interactions for Adult or Adolescent Rats

Previous research has shown that exposure to nicotine and other drugs of abuse stimulate dopaminergic neurons in the mesolimbic circuit. Sustained activation of this circuit by prolonged exposure to drugs promotes locomotor sensitization. However, there are inconsistent reports about nicotine-induced locomotor sensitization when assessed among different developmental stages. We evaluated exploratory behavior on specific areas of the open field as an indicator of behavioral disinhibition and general locomotor activity as an indicator of nicotine-induced locomotor sensitization, to further explore the mechanisms underlying behavioral adaptations to nicotine exposure in animals from different developmental stages. We found that while adolescent and adult rats are equally responsive to nicotine-induced locomotor sensitization, nicotine disrupts inhibition of risk-related behavior only in adolescent rats. Together, our results suggest that chronic daily exposure to nicotine promotes potentiation of its stimulant effects on locomotor activity. In adolescents, this effect is accompanied by a decreased capacity to inhibit risk-related behaviors under the acute effect of the drug.   How to cite this article: Novoa, C., Solano, J. L., Ballesteros-Acosta, H., Lamprea, R. M., & Ortega, L. A. (2021). Nicotine Differentially Modulates Emotional-Locomotor Interactions for Adult or Adolescent Rats. Revista Colombiana de Psicología, 31(1), 13-22. https://doi.org/10.15446/rcp.v31n1.89822

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.

Performance on a modified signal detection task of attention is impaired in male and female rats following developmental exposure to the synthetic progestin, 17α-hydroxyprogesterone caproate

Based on evidence that the developing mesocortical dopamine pathway is sensitive to progestins, in the present study we tested the hypothesis that attention, a fundamental component of successful cognitive behavior, is disrupted by developmental exposure to the synthetic progestin, 17-α-hydroxyprogesterone caproate (17-OHPC). To assess attentional impairments, a modified signal detection task was utilized with three stimulus modalities: compound (light and tone), light alone, and tone alone, for four stimulus durations (2, 0.5, 0.25, 0.125 s). Adult rats were trained to push one lever if they detected the stimulus, and another lever if the stimulus was not presented. 17-OHPC animals were able to attend to the task, as evidenced by similar correct responses as controls. However, as the task became increasingly difficult at shorter durations, 17-OHPC animals made significantly more omissions compared to controls, suggesting that 17-OHPC treatment may disrupt attentional processes and/or delay response time. These findings add to the current body of literature demonstrating that exposure to 17-OHPC during development produces deficits in cognitive behavior in adulthood. These results may inform potential risks associated with 17-OHPC treatment in pregnant women with a history of preterm delivery who are commonly recipients of such treatment.

Juvenile stress increases cocaine-induced impulsivity in female rats

In humans, adverse childhood experiences are associated with an increased risk of developing a neuropsychiatric disorder. Changes in social behavior and cognitive function are hallmarks of numerous neuropsychiatric disorders. Here we examined the effects of exposure to variable stress during the juvenile period on social behavior, reward, and cognitive function (as measured in the 5-choice serial reaction time task (5CSRTT)) in rats. From postnatal days (PND) 25-29 male and female rats were exposed to a variable stress protocol. In adulthood, social interactions and sucrose preference were assessed prior to training on the 5CSRTT. Once successfully trained, rats were challenged with different task versions, and then the effects of cocaine (0, 10, or 20 mg/kg, IP) on performance were assessed. A follow-up experiment examined the ability of the D2 receptor antagonist eticlopride (0.0, 0.025, 0.05 mg/kg, IP) to block the effects of cocaine on 5CSRTT performance in female rats. Male rats exposed to juvenile stress tended to engage in less social behavior and had an increased correct response latency in the 5CSRTT following cocaine administration. Female rats exposed to juvenile stress exhibited a trend towards increased social behavior and demonstrated increased cocaine-induced impulsivity. The increase in impulsivity was not blocked by co-administration of eticlopride. Juvenile stress had minimal effects on adult behavior in male rats, but increased cocaine-induced impulsivity in female rats. Such an effect could contribute to the enhanced escalation of drug-use observed in females that experience juvenile stress. This possibility awaits further testing.

Where Dopaminergic and Cholinergic Systems Interact: A Gateway for Tuning Neurodegenerative Disorders

Historically, many investigations into neurodegenerative diseases have focused on alterations in specific neuronal populations such as, for example, the loss of midbrain dopaminergic neurons in Parkinson's disease (PD) and loss of cholinergic transmission in Alzheimer's disease (AD). However, it has become increasingly clear that mammalian brain activities, from executive and motor functioning to memory and emotional responses, are strictly regulated by the integrity of multiple interdependent neuronal circuits. Among subcortical structures, the dopaminergic nigrostriatal and mesolimbic pathways as well as cholinergic innervation from basal forebrain and brainstem, play pivotal roles in orchestrating cognitive and non-cognitive symptoms in PD and AD. Understanding the functional interactions of these circuits and the consequent neurological changes that occur during degeneration provides new opportunities to understand the fundamental inter-workings of the human brain as well as develop new potential treatments for patients with dysfunctional neuronal circuits. Here, excerpted from a session of the European Behavioral Pharmacology Society meeting (Braga, Portugal, August 2019), we provide an update on our recent work in behavioral and cellular neuroscience that primarily focuses on interactions between cholinergic and dopaminergic systems in PD models, as well as stress in AD. These brief discussions include descriptions of (1) striatal cholinergic interneurons (CINs) and PD, (2) dopaminergic and cholinergic modulation of impulse control, and (3) the use of an implantable cell-based system for drug delivery directly the into brain and (4) the mechanisms through which day life stress, a risk factor for AD, damage protein and RNA homeostasis leading to AD neuronal malfunction.

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.

Cannabinoid Modulation of Dopamine Release During Motivation, Periodic Reinforcement, Exploratory Behavior, Habit Formation, and Attention

Motivational and attentional processes energize action sequences to facilitate evolutionary competition and promote behavioral fitness. Decades of neuropharmacology, electrophysiology and electrochemistry research indicate that the mesocorticolimbic DA pathway modulates both motivation and attention. More recently, it was realized that mesocorticolimbic DA function is tightly regulated by the brain's endocannabinoid system and greatly influenced by exogenous cannabinoids-which have been harnessed by humanity for medicinal, ritualistic, and recreational uses for 12,000 years. Exogenous cannabinoids, like the primary psychoactive component of cannabis, delta-9-tetrahydrocannabinol, produce their effects by acting at binding sites for naturally occurring endocannabinoids. The brain's endocannabinoid system consists of two G-protein coupled receptors, endogenous lipid ligands for these receptor targets, and several synthetic and metabolic enzymes involved in their production and degradation. Emerging evidence indicates that the endocannabinoid 2-arachidonoylglycerol is necessary to observe concurrent increases in DA release and motivated behavior. And the historical pharmacology literature indicates a role for cannabinoid signaling in both motivational and attentional processes. While both types of behaviors have been scrutinized under manipulation by either DA or cannabinoid agents, there is considerably less insight into prospective interactions between these two important signaling systems. This review attempts to summate the relevance of cannabinoid modulation of DA release during operant tasks designed to investigate either motivational or attentional control of behavior. We first describe how cannabinoids influence DA release and goal-directed action under a variety of reinforcement contingencies. Then we consider the role that endocannabinoids might play in switching an animal's motivation from a goal-directed action to the search for an alternative outcome, in addition to the formation of long-term habits. Finally, dissociable features of attentional behavior using both the 5-choice serial reaction time task and the attentional set-shifting task are discussed along with their distinct influences by DA and cannabinoids. We end with discussing potential targets for further research regarding DA-cannabinoid interactions within key substrates involved in motivation and attention.

Lateral habenula cannabinoid CB1 receptor involvement in drug-associated impulsive behavior

Animal and human studies show that cannabis or its derivatives can increase relapse to cocaine seeking following withdrawal. Moreover, cannabis use in humans is associated with impulse control deficits and animal studies implicate endogenous cannabinoids (eCB) in several impulsivity constructs. However, the brain areas where cannabinoids might control impulsivity or cocaine seeking are largely unknown. Here, we assess Lateral Habenula (LHb) involvement on performance in the 5-choice serial reaction time task (5CSRTT) in rats and investigate whether LHb cannabinoid CB1 receptors (CB1R) are involved in these effects. Systemic cocaine increased premature responding, a measure of impulsivity, at a dose (5 mg/kg) that did not alter other measures of task performance. Intra-LHb infusion of the CB1R antagonist AM251 blocked this effect. Systemic injection of the psychoactive constituent of cannabis, Δ⁹-tetrahydrocannabinol (Δ⁹-THC, 1 mg/kg), also increased 5CSRTT premature responding at a dose that did not otherwise disrupt task performance. This was blocked by intra-LHb infusion of AM251 in a subgroup of rats showing the largest increases in Δ⁹-THC-evoked premature responses. Systemic Δ⁹-THC also prompted impulsive cocaine seeking in a Go/NoGo cocaine self-administration task and this was blocked by intra-LHb AM251. These data show that LHb CB1Rs are involved in deficits in impulse control initiated by cocaine and Δ⁹-THC, as assessed by the 5CSRTT, and play a role in impulsive cocaine seeking during cocaine self-administration. This suggests that the LHb eCB system contributes to the control of impulsive behavior, and thus represents a potential target for therapeutic treatment of substance use disorders (SUDs) in humans.

Temporally Specific Roles of Ventral Tegmental Area Projections to the Nucleus Accumbens and Prefrontal Cortex in Attention and Impulse Control

Deficits in impulse control and attention are prominent in the symptomatology of mental disorders such as attention deficit hyperactivity disorder (ADHD), substance addiction, schizophrenia, and bipolar disorder, yet the underlying mechanisms are incompletely understood. Frontostriatal structures, such as the nucleus accumbens (NAcb), the medial prefrontal cortex (mPFC), and their dopaminergic innervation from the ventral tegmental area (VTA) have been implicated in impulse control and attention. What remains unclear is how the temporal pattern of activity of these VTA projections contributes to these processes. Here, we optogenetically stimulated VTA dopamine (DA) cells, as well as VTA projections to the NAcb core (NAcbC), NAcb shell (NAcbS), and the mPFC in male rats performing the 5-choice serial reaction time task (5-CSRTT). Our data show that stimulation of VTA DA neurons, and VTA projections to the NAcbC and the mPFC immediately before presentation of the stimulus cue, impaired attention but spared impulse control. Importantly, in addition to reducing attention, activation of VTA-NAcbS also increased impulsivity when tested under a longer intertrial interval (ITI), to provoke impulsive behavior. Optogenetic stimulation at the beginning of the ITI only partially replicated these effects. In sum, our data show how attention and impulsivity are modulated by neuronal activity in distinct ascending output pathways from the VTA in a temporally specific manner. These findings increase our understanding of the intricate mechanisms by which mesocorticolimbic circuits contribute to cognition.SIGNIFICANCE STATEMENT Deficits in impulse control and attention are prominent in the symptomatology of several mental disorders, yet the brain mechanisms involved are incompletely understood. Since frontostriatal circuits have been implicated in impulse control and attention, we here examined the role of ascending projections from the midbrain ventral tegmental area (VTA) to the nucleus accumbens (NAcb) and prefrontal cortex (PFC). Using optogenetics to individually stimulate these projections with time-locked precision, we distinguished the role that each of these projections plays, in both impulse control and attention. As such, our study enhances our understanding of the neuronal circuitry that drives impulsive and attentive behavior.

Toxoplasma gondii, Suicidal Behavior, and Intermediate Phenotypes for Suicidal Behavior

Within the general literature on infections and suicidal behavior, studies on Toxoplasma gondii (T. gondii) occupy a central position. This is related to the parasite's neurotropism, high prevalence of chronic infection, as well as specific and non-specific behavioral alterations in rodents that lead to increased risk taking, which are recapitulated in humans by T. gondii's associations with suicidal behavior, as well as trait impulsivity and aggression, mental illness and traffic accidents. This paper is a detailed review of the associations between T. gondii serology and suicidal behavior, a field of study that started 15 years ago with our publication of associations between T. gondii IgG serology and suicidal behavior in persons with mood disorders. This "legacy" article presents, chronologically, our primary studies in individuals with mood disorders and schizophrenia in Germany, recent attempters in Sweden, and in a large cohort of mothers in Denmark. Then, it reviews findings from all three meta-analyses published to date, confirming our reported associations and overall consistent in effect size [ranging between 39 and 57% elevation of odds of suicide attempt in T. gondii immunoglobulin (IgG) positives]. Finally, the article introduces certain links between T. gondii and biomarkers previously associated with suicidal behavior (kynurenines, phenylalanine/tyrosine), intermediate phenotypes of suicidal behavior (impulsivity, aggression) and state-dependent suicide risk factors (hopelessness/dysphoria, sleep impairment). In sum, an abundance of evidence supports a positive link between suicide attempts (but not suicidal ideation) and T. gondii IgG (but not IgM) seropositivity and serointensity. Trait impulsivity and aggression, endophenotypes of suicidal behavior have also been positively associated with T. gondii seropositivity in both the psychiatrically healthy as well as in patients with Intermittent Explosive Disorder. Yet, causality has not been demonstrated. Thus, randomized interventional studies are necessary to advance causal inferences and, if causality is confirmed, to provide hope that an etiological treatment for a distinct subgroup of individuals at an increased risk for suicide could emerge.

Injury during adolescence leads to sex-specific executive function deficits in adulthood in a pre-clinical model of mild traumatic brain injury

Adolescents are more likely than adults to develop chronic symptoms, such as impulsivity and difficulty concentrating, following a mild traumatic brain injury (mTBI) which may relate to disruption of pre-frontal cortex (PFC development). During adolescence the PFC is undergoing extensive remodelling, driving maturation of executive functions incorporating attention, motivation and impulse control. In part maturation of the PFC is driven by outgrowth of dopaminergic neurons to the PFC under the guidance of specific axonal targeting cues, including netrin-1. How a mTBI in adolescence may alter the expression of these axonal targeting cues, and the influence on PFC development is not yet known. As such the effects of mTBI in mid-adolescence on executive functioning in adulthood (12 weeks) were examined via the 5-choice serial reaction task in both male and female Sprague Dawley rats. Animals at p35 (n = 12-16 per group) were injured via weight drop (100 g from 0.75 m) and injury confirmed by a significant increase in righting reflex. Interestingly, while a mid-adolescence mTBI in females led to significantly higher omissions and decreased accuracy when task difficulty was high (stimulus duration 1 s), males had significantly increased premature response rate when the intertrial interval was varied. Examination of levels of TH, as a reflection of dopaminergic innervation, found no difference in either gender post-TBI in the PFC, but a significant increase in the limbic system (nucleus accumbens) in males, but not females, chronically post-TBI, suggesting an imbalance between the regions. The increase in TH was accompanied by a chronic reduction in netrin-1 within the nucleus accumbens in males only. Taken together, these results indicate that mTBI in adolescence leads to sex specific effects in different domains of PFC function in adulthood, which may relate to subtle alterations in the developmental trajectory of the mesocortical limbic pathway in males only.

Relationship between elevated impulsivity and cognitive declines in elderly community-dwelling individuals

Impulse control disorders are recognized as one of the behavioral and psychological symptoms of dementia (BPSD). Majority of studies on the treatment of BPSD related to impulsivity have rather focused on the aggression and agitation. In particular, it has not been investigated how cognitive declines are associated with impulsivity in community-dwelling elderly people. Here, we have measured the cognitive and memory functions and impulsivity of 212 elderly community-dwelling people using a psychometric test battery and analyzed the correlation between their level of impulsivity and cognitive functions by multiple regression analysis. We found an elevation of impulsivity, which was evaluated by the Barratt Impulsiveness Scale-11, closely related to decline of cognitive functions, which were evaluated by the Montreal Cognitive Assessment and the Mini-Mental State Examination, and Logical Memory function, which were evaluated by the Wechsler Memory Scale-Delayed Recall. Then we have divided them into groups based on the severity of cognitive decline and conducted an analysis of each group, the result of which showed that as this tendency was particularly noticeable in the suspected dementia group. Therefore, we have concluded that heightened impulsivity is negatively associated with cognitive and memory functions in community-dwelling elderly people.

Dopamine D2/3 Receptor Availabilities and Evoked Dopamine Release in Striatum Differentially Predict Impulsivity and Novelty Preference in Roman High- and Low-Avoidance Rats

BACKGROUND

Impulsivity and novelty preference are both associated with an increased propensity to develop addiction-like behaviors, but their relationship and respective underlying dopamine (DA) underpinnings are not fully elucidated.

METHODS

We evaluated a large cohort (n = 49) of Roman high- and low-avoidance rats using single photon emission computed tomography to concurrently measure in vivo striatal D2/3 receptor (D2/3R) availability and amphetamine (AMPH)-induced DA release in relation to impulsivity and novelty preference using a within-subject design. To further examine the DA-dependent processes related to these traits, midbrain D2/3-autoreceptor levels were measured using ex vivo autoradiography in the same animals.

RESULTS

We replicated a robust inverse relationship between impulsivity, as measured with the 5-choice serial reaction time task, and D2/3R availability in ventral striatum and extended this relationship to D2/3R levels measured in dorsal striatum. Novelty preference was positively related to impulsivity and showed inverse associations with D2/3R availability in dorsal striatum and ventral striatum. A high magnitude of AMPH-induced DA release in striatum predicted both impulsivity and novelty preference, perhaps owing to the diminished midbrain D2/3-autoreceptor availability measured in high-impulsive/novelty-preferring Roman high-avoidance animals that may amplify AMPH effect on DA transmission. Mediation analyses revealed that while D2/3R availability and AMPH-induced DA release in striatum are both significant predictors of impulsivity, the effect of striatal D2/3R availability on novelty preference is fully mediated by evoked striatal DA release.

CONCLUSIONS

Impulsivity and novelty preference are related but mediated by overlapping, yet dissociable, DA-dependent mechanisms in striatum that may interact to promote the emergence of an addiction-prone phenotype.

Effects of Diazepam on Reaction Times to Stop and Go

Introduction: The ability to stop the execution of a movement in response to an external cue requires intact executive function. The effect of psychotropic drugs on movement inhibition is largely unknown. Movement stopping can be estimated by the Stop Signal Reaction Time (SSRT). In a recent publication, we validated an improved measure of SSRT (optimum combination SSRT, ocSSRT). Here we explored how diazepam, which enhances transmission at GABA_A receptors, affects ocSSRT.

Methods: Nine healthy individuals were randomized to receive placebo, 5 mg or 10 mg doses of diazepam. Each participant received both the dosage of drug and placebo orally on separate days with adequate washout. The ocSSRT and simple reaction time (RT) were estimated through a stop-signal task delivered via a battery-operated box incorporating green (Go) and red (Stop) light-emitting diodes. The task was performed just before and 1 h after dosing.

Result: The mean change in ocSSRT after 10 mg diazepam was significantly higher (+27 ms) than for placebo (−1 ms; p = 0.012). By contrast, the mean change in simple response time remained comparable in all three dosing groups (p = 0.419).

Conclusion: Our results confirm that a single therapeutic adult dose of diazepam can alter motor inhibition in drug naïve healthy individuals. The selective effect of diazepam on ocSSRT but not simple RT suggests that GABAergic neurons may play a critical role in movement-stopping.

Chemogenetic Suppression of the Subthalamic Nucleus Induces Attentional Deficits and Impulsive Action in a Five-Choice Serial Reaction Time Task in Mice

The subthalamic nucleus (STN), a key component of the basal ganglia circuitry, receives inputs from broad cerebral cortical areas and relays cortical activity to subcortical structures. Recent human and animal studies have suggested that executive function, which is assumed to consist of a set of different cognitive processes for controlling behavior, depends on precise information processing between the cerebral cortex and subcortical structures, leading to the idea that the STN contains neurons that transmit the information required for cognitive processing through their activity, and is involved in such cognitive control directly and dynamically. On the other hand, the STN activity also affects intracellular signal transduction and gene expression profiles influencing plasticity in other basal ganglia components. The STN may also indirectly contribute to information processing for cognitive control in other brain areas by regulating slower signaling mechanisms. However, the precise correspondence and causal relationship between the STN activity and cognitive processes are not fully understood. To address how the STN activity is involved in cognitive processes for controlling behavior, we applied Designer Receptors Exclusively Activated by Designer Drugs (DREADD)-based chemogenetic manipulation of neural activity to behavioral analysis using a touchscreen operant platform. We subjected mice selectively expressing DREADD receptors in the STN neurons to a five-choice serial reaction time task, which has been developed to quantitatively measure executive function. Chemogenetic suppression of the STN activity reversibly impaired attention, especially required under highly demanding conditions, and increased impulsivity but not compulsivity. These findings, taken together with the results of previous lesion studies, suggest that the STN activity, directly and indirectly, participates in cognitive processing for controlling behavior, and dynamically regulates specific types of subprocesses in cognitive control probably through fast synaptic transmission.

The role of impulsivity as predisposing behavioural trait in different aspects of alcohol self-administration in rats

BACKGROUND

Therapeutic interventions to promote abstinence and prevent relapse in alcohol use disorder (AUD) are limitedly available. Therefore, targeting risk factors in the onset and maintenance of AUD could pose an interesting alternative treatment strategy. In this regard, over the last decade trait impulsivity has received considerable attention as such a risk factor predisposing substance dependence both in clinical populations and preclinical rodent studies. This study investigated whether different forms of impulsivity (action versus choice) predict distinct stages of instrumental alcohol self-administration, extinction and cue-induced relapse.

METHODS

Two cohorts of n = 48 rats each were trained in an operant tasks for either impulsive action or impulsive choice. Subsequently, high and low impulsive rats were then tested in an alcohol self-administration and relapse model and following this retested in the impulsivity tasks to evaluate possible changes in impulsivity levels.

RESULTS

The current data show that neither impulsive action, nor impulsive choice predict the extent to which rats consume alcohol and the extent to which rats are motivated to self-administer alcohol. Moreover, extinction of responding for alcohol and cue-induced relapse was not predicted by impulsivity. Interestingly, rats and most prominently low impulsive rats became more impulsive after the alcohol self-administration procedure. Although due to employed experimental design it is not clear whether this resulted from alcohol consumption or alcohol abstinence.

CONCLUSION

Together, these findings lend further support for the notion of a unidirectional relationship between self-administration of the depressant drug alcohol and impulsivity.

Childhood Maltreatment and Impulsivity: A Meta-Analysis and Recommendations for Future Study

Both childhood maltreatment and impulsivity have been implicated in a broad array of negative public health outcomes and have been much studied in relation to each other. Characterizing this relationship, and the processes underlying it, are important for informing intervention efforts targeting this association and its psychopathological sequelae. The current review presented a systematic meta-analysis of the empirical literature on childhood maltreatment and impulsivity. In all, 55 eligible studies were identified and included in this review. General support was found for a positive association between childhood maltreatment, including its specific subtypes, and general trait impulsivity, with pooled effect sizes ranging from small in the case of childhood sexual abuse (OR = 1.59 [95% CI = 1.38-1.84]) to medium-to-large in the case of childhood emotional abuse (OR = 3.10 [95% CI = 2.27-4.23]). Support for a relationship between childhood maltreatment and laboratory-based measures of impulsive behavior was generally lacking. The current findings must be interpreted with a degree of caution, given several methodological limitations characterizing much of the empirical literature. Recommendations for addressing these limitations and directions for future research are provided.

Characterization of Amphetamine, Methylphenidate, Nicotine, and Atomoxetine on Measures of Attention, Impulsive Action, and Motivation in the Rat: Implications for Translational Research

Amphetamine (AMP), methylphenidate (MPH), and atomoxetine (ATX) are approved treatments for ADHD, and together with nicotine (NIC), represent pharmacological agents widely studied on cognitive domains including attention and impulsive action in humans. These agents thus represent opportunities for clinical observation to be reinvestigated in the preclinical setting, i.e., reverse translation. The present study investigated each drug in male, Long Evans rats trained to perform either (1) the five-choice serial reaction time task (5-CSRTT), (2) Go/NoGo task, or (3) a progressive ratio (PR) task, for the purpose of studying each drug on attention, impulsive action and motivation. Specific challenges were adopted in the 5-CSRTT designed to tax attention and impulsivity, i.e., high frequency of stimulus presentation (sITI), variable reduction in stimulus duration (sSD), and extended delay to stimulus presentation (10-s ITI). Initially, performance of a large (> 80) cohort of rats in each task variant was conducted to examine performance stability over repeated challenge sessions, and to identify subgroups of "high" and "low" attentive rats (sITI and sSD schedules), and "high" and "low" impulsives (10-s ITI). Using an adaptive sequential study design, the effects of AMP, MPH, ATX, and NIC were examined and contrasting profiles noted across the tests. Both AMP (0.03-0.3 mg/kg) and MPH (1-6 mg/kg) improved attentional performance in the sITI but not sSD or 10-s ITI condition, NIC (0.05-0.2 mg/kg) improved accuracy across all conditions. ATX (0.1-1 mg/kg) detrimentally affected performance in the sITI and sSD condition, notably in "high" performers. In tests of impulsive action, ATX reduced premature responses notably in the 10-s ITI condition, and also reduced false alarms in Go/NoGo. Both AMP and NIC increased premature responses in all task variants, although AMP reduced false alarms highlighting differences between these two measures of impulsive action. The effect of MPH was mixed and appeared baseline dependent. ATX reduced break point for food reinforcement suggesting a detrimental effect on motivation for primary reward. Taken together these studies highlight differences between AMP, MPH, and ATX which may translate to their clinical profiles. NIC had the most reliable effect on attentional accuracy, whereas ATX was reliably effective against all tests of impulsive action.

ADHD medication and the inverted U-shaped curve: A pharmacological study in female mice performing the rodent Continuous Performance Test (rCPT)

BACKGROUND

The rodent Continuous Performance Test (rCPT) is an analogue of human CPTs where mice have to discriminate between target and non-target stimuli. The rCPT offers a readout of attentional performance and impulsive behaviour. This study aimed to determine if female C57BL/6 J mice could be trained in the rCPT since previously published rCPT studies have only used male mice and to study whether the effects of methylphenidate (MPH), atomoxetine (ATX), and dexamphetamine (AMPH) on attention and impulsivity depend on baseline (reference) levels of performance.

METHODS

48 female mice underwent rCPT training. Effects of MPH (1, 2, and 3 mg/kg), ATX (1, 3, and 5 mg/kg) and AMPH (0.3, 0.6, and 1 mg/kg) were assessed in a variable stimulus duration probe. Drugs were administered intraperitoneally and sequentially tested following a Latin-square design. Data were analysed using a repeated measurements mixed effect model and reference-dependent effects were studied.

RESULTS

ATX and AMPH improved performance as seen by increases in discriminability. These improvements were a result of a decreased false-alarm rate. AMPH showed a reference-dependent effect, improving the task performance of low-performing mice and decreasing the performance of high-performing mice. MPH also showed this reference-dependent effects, albeit to a lesser extent. ATX and AMPH decreased premature responses and increased response criterion, but no reference-dependent effects were observed for these parameters.

CONCLUSION

This study presents a novel method to analyse baseline-dependent effects. It shows that the rCPT can be successfully used in pharmacological studies in female mice and demonstrates that the effect of ADHD medication is in line with the inverted U-shape theory of performance-arousal relationship.

Age-dependent effects of repeated methamphetamine exposure on locomotor activity and attentional function in rats

Many adolescents use amphetamines which are the second most common abused illegal drugs. Methamphetamine (Meth), as a potent amphetamine affects attentional functions. However, the most significant factor for susceptibility to Meth is the age of exposure, most studies have examined the effects of Meth after early adolescence stage. The present experiment was aimed to investigate some possible short- and long-term effects of Meth at two distinct points of adolescence stage (early versus late) on 1) locomotor activity in adolescent rats and 2) attentional functions in their adulthood. Rats received Meth (5 mg/kg, i.p., for consecutive 10 days) during early adolescence (postnatal days (PND) 30-39) or late adolescence (PND 50-59). Locomotor activity was assessed after the first and tenth injections. Then, in adulthood, rats were trained and tested on the Five-choice serial reaction time task (5-CSRTT) to display possible attentional impairments. The first Meth administration in early exposed adolescent (EEA) group produced the highest level of activity, compared with the first exposure in late exposed adolescent (LEA) group and tenth administrations in both groups. In adulthood, LEA group significantly delayed learning the 5-CSRTT and exhibited attentional impairments, as demonstrated by significant reduced response accuracy and increased omission errors under pharmacological challenge, compared with control group. The susceptibility to Meth depends on the age of exposure and Meth administration during late adolescence stage may cause prolonged attentional deficits in adulthood.

Clarifying the Role of Negative Emotions in the Origin and Control of Impulsive Actions

This critical review elaborates on the origin of impulsive actions and how these can be controlled. We focus in particular on the role of negative events. First, we outline how impulsive actions often originate from negative events that are (emotionally) appraised. A discrepancy between this current state and a desired goal state leads to action tendencies. The urgency of the resulting action depends on the importance of the goal and the size of the discrepancy. Second, we discuss how such impulsive actions can be regulated or controlled e.g. by biasing competition between different options, or by completely suppressing all motor output. Importantly, such control mechanisms might also depend on emotional factors. To reconcile these findings, we present a coherent theoretical framework, taking into account various cognitive, affective, and motivational mechanisms as well as contextual factors that play a crucial role in the origin and control of impulsive actions.

The Neuropharmacology of Impulsive Behaviour, an Update

Neuropharmacological interventions in preclinical translational models of impulsivity have tremendously contributed to a better understanding of the neurochemistry and neural basis of impulsive behaviour. In this regard, much progress has been made over the last years, also due to the introduction of novel techniques in behavioural neuroscience such as optogenetics and chemogenetics. In this chapter, we will provide an update of how the behavioural pharmacology field has progressed and built upon existing data since an earlier review we wrote in 2008. To this aim, we will first give a brief background on preclinical translational models of impulsivity. Next, recent interesting evidence of monoaminergic modulation of impulsivity will be highlighted with a focus on the neurotransmitters dopamine and noradrenaline. Finally, we will close the chapter by discussing some novel directions and drug leads in the neuropharmacological modulation of impulsivity.

Dopaminergic contributions to behavioral control under threat of punishment in rats

RATIONALE

Excessive intake of rewards, such as food and drugs, often has explicit negative consequences, including the development of obesity and addiction, respectively. Thus, choosing not to pursue reward is the result of a cost/benefit decision, proper execution of which requires inhibition of behavior. An extensive body of preclinical and clinical evidence implicates dopamine in certain forms of inhibition of behavior, but it is not fully known how it contributes to behavioral inhibition under threat of explicit punishment.

OBJECTIVES

To assess the involvement of midbrain dopamine neurons and their corticostriatal output regions, the ventral striatum and prefrontal cortex, in control over behavior under threat of explicit (foot shock) punishment in rats.

METHODS

We used a recently developed behavioral inhibition task, which assesses the ability of rats to exert behavioral restraint at the mere sight of food reward, under threat of foot shock punishment. Using in vivo fiber photometry, chemogenetics, c-Fos immunohistochemistry, and behavioral pharmacology, we investigated how dopamine neurons in the ventral tegmental area, as well as its output areas, the ventral striatum and prefrontal cortex, contribute to behavior in this task.

RESULTS

Using this multidisciplinary approach, we found little evidence for a direct involvement of ascending midbrain dopamine neurons in inhibitory control over behavior under threat of punishment. For example, photometry recordings suggested that VTA DA neurons do not directly govern control over behavior in the task, as no differences were observed in neuronal population activity during successful versus unsuccessful behavioral control. In addition, chemogenetic and pharmacological manipulations of the mesocorticolimbic DA system had little or no effect on the animals' ability to exert inhibitory control over behavior. Rather, the dopamine system appeared to have a role in the motivational components of reward pursuit.

CONCLUSIONS

Together, our data provide insight into the mesocorticolimbic mechanisms behind motivated behaviors by showing a modulatory role of dopamine in the expression of cost/benefit decisions. In contrast to our expectations, dopamine did not appear to directly mediate the type of behavioral control that is tested in our task.

Differential contributions of striatal dopamine D1 and D2 receptors to component processes of value-based decision making

Dopamine has been implicated in value-based learning and decision making by signaling reward prediction errors and facilitating cognitive flexibility, incentive motivation, and voluntary movement. Dopamine receptors can roughly be divided into the D1 and D2 subtypes, and it has been hypothesized that these two types of receptors have an opposite function in facilitating reward-related and aversion-related behaviors, respectively. Here, we tested the contribution of striatal dopamine D1 and D2 receptors to processes underlying value-based learning and decision making in rats, employing a probabilistic reversal learning paradigm. Using computational trial-by-trial analysis of task behavior after systemic or intracranial treatment with dopamine D1 and D2 receptor agonists and antagonists, we show that negative feedback learning can be modulated through D2 receptor signaling and positive feedback learning through D1 receptor signaling in the ventral striatum. Furthermore, stimulation of D2 receptors in the ventral or dorsolateral (but not dorsomedial) striatum promoted explorative choice behavior, suggesting an additional function of dopamine in these areas in value-based decision making. Finally, treatment with most dopaminergic drugs affected response latencies and number of trials completed, which was also seen after infusion of D2, but not D1 receptor-acting drugs into the striatum. Together, our data support the idea that dopamine D1 and D2 receptors have complementary functions in learning on the basis of emotionally valenced feedback, and provide evidence that dopamine facilitates value-based and motivated behaviors through distinct striatal regions.

Examination of the effects of SCH23390 and raclopride infused in the dorsal striatum on amphetamine-induced timing impulsivity measured on a differential reinforcement of low-rate responding (DRL) task in rats

Although the striatal dopamine (DA) is reportedly involved in impulsive action, little is known about the DA subtype receptors of dorsal striatum (dSTR) in the impulsive control involved in differential reinforcement of low-rate-responding (DRL) behavior. We examined the receptor-specific dopaminergic modulation of d-amphetamine (AMP)-altered DRL 10 s (DRL-10 s) performance by locally infusing SCH23390 (SCH) and raclopride (RAC), DA D1 and D2 receptor antagonists, respectively, into the rat's dSTR. Systemic injection of AMP significantly affected DRL-10 s behavior by increasing total, non-reinforced, and bust responses, as well as by decreasing reinforced responses, which correspondingly caused a leftward shift of the inter-response-time distribution curve as confirmed by a profound decrease in peak time (i.e., <10 s). Neither SCH nor RAC into dSTR pharmacologically reversed the timing impulsivity produced by AMP as measured by non-reinforced responses and peak time. However, the increase in total responses and the decrease in reinforced responses by AMP were reversed by intra-dSTR SCH or RAC. These results suggest that the D1 and D2 receptors of the dSTR may be involved in behavioral components apart from the timing impulsivity produced by AMP on a DRL task, which components are distinctly different from those in other terminal areas of midbrain DA systems.

Blonanserin suppresses impulsive action in rats

High impulsivity will increase the risk of criminal behavior, drug abuse, and suicide. We chose two drugs by following a strategy recently we proposed for identifying potential anti-impulsivity drugs, and examined the effects on impulsive action in rats by using a 3-choice serial reaction time task. We showed that the administration of blonanserin, an atypical antipsychotic, reduced impulsive actions in a U-shaped manner. 1-(2-Pyriidinyl)-piperazine, an active metabolite of buspirone or tandospirone, also slightly reduced impulsive actions, though it impaired motor functions. These results affirm the validity of our strategy, but require its refinement for developing anti-impulsivity drugs.

Optogenetic and chemogenetic approaches to manipulate attention, impulsivity and behavioural flexibility in rodents

Studies manipulating neural activity acutely with optogenetic or chemogenetic intervention in behaving rodents have increased considerably in recent years. More often, these circuit-level neural manipulations are tested within an existing framework of behavioural testing that strives to model complex executive functions or symptomologies relevant to multidimensional psychiatric disorders in humans, such as attentional control deficits, impulsivity or behavioural (in)flexibility. This methods perspective argues in favour of carefully implementing these acute circuit-based approaches to better understand and model cognitive symptomologies or their similar isomorphic animal behaviours, which often arise and persist in overlapping brain circuitries. First, we offer some practical considerations for combining long-term, behavioural paradigms with optogenetic or chemogenetic interventions. Next, we examine how cell-type or projection-specific manipulations to the ascending neuromodulatory systems, local brain region or descending cortical glutamatergic projections influence aspects of cognitive control. For this, we primarily focus on the influence exerted on attentional and motor impulsivity performance in the (3-choice or) 5-choice serial reaction time task, and impulsive, risky or inflexible choice biases during alternative preference, reward discounting or reversal learning tasks.

Effects of amphetamine, methylphenidate, atomoxetine, and morphine in rats responding under an adjusting stop signal reaction time task

RATIONALE

Stop signal reaction time procedures are used to investigate behavioral and neurobiological processes that contribute to behavioral inhibition and to evaluate potential therapeutics for disorders characterized by disinhibition and impulsivity. The current study examined effects of amphetamine, methylphenidate, atomoxetine, and morphine in rats responding under an adjusting stop signal reaction time task that measures behavioral inhibition, as well as motor impulsivity.

METHODS

Rats (n = 8) completed a two-response sequence to earn food. During most trials, responses following presentation of a visual stimulus (go signal) delivered food. Occasionally, a tone (stop signal) was presented signifying that food would be presented only if the second response was withheld. Responding after the stop signal measured inhibition and responding prior to the start of the trial (premature) measured motor impulsivity. Delay to presentation of the stop signal was adjusted for individual subjects based on performance.

RESULTS

Amphetamine and methylphenidate increased responding after presentation of the stop signal and markedly increased premature responding. Atomoxetine modestly improved accuracy on stop trials and decreased premature responding. Morphine did not alter stop trial accuracy or premature responding up to doses that decreased the number of trials initiated.

CONCLUSIONS

These data demonstrate the sensitivity of an adjusting stop signal reaction time task to a range of drug effects and shows that some drugs that enhance dopaminergic transmission, such as amphetamine, can differentially alter various types of impulsive behavior.

Preclinical evidence for combining the 5-HT2C receptor agonist lorcaserin and varenicline as a treatment for nicotine dependence

Varenicline, a nicotinic acetylcholine receptor partial agonist, is used to treat nicotine dependence. Lorcaserin, a 5-HT_2C receptor agonist has been approved in some countries to treat obesity. Based on preclinical and preliminary clinical evidence, lorcaserin may have potential to treat nicotine dependence. These experiments examined in rats the effects of combining varenicline (0.5 or 1 mg/kg) and lorcaserin (0.3, 0.6 and 1 mg/kg) on nicotine self-administration, reinstatement of nicotine seeking, responding for food and impulsive action. Both drugs alone reduced nicotine self-administration. Combining varenicline and 0.6 mg/kg lorcaserin reduced responding to a greater extent than either drug alone. In a relapse model, extinguished nicotine seeking was reinstated by a priming injection of nicotine and nicotine-associated cues. Reinstatement was reduced by varenicline (1 mg/kg) and by lorcaserin (0.3 mg/kg). Combining lorcaserin (0.3 mg/kg) with varenicline (0.5 or 1 mg/kg) reduced reinstatement to a greater degree than either drug alone. Both drugs had minimal effects on responding for food, alone or in combination. In the five-choice serial reaction time test, varenicline (0.5 or 1 mg/kg) increased impulsivity, measured as increased premature responding. This effect was reduced by lorcaserin (0.3 mg/kg). Plasma levels of varenicline or lorcaserin were not altered by co-administration of the other drug. Varenicline and lorcaserin have additive effects on nicotine self-administration, and on nicotine seeking. Lorcaserin prevents impulsivity induced by varenicline. This pattern of effects suggests that co-administration of varenicline and lorcaserin has potential as a treatment for nicotine dependence that may exceed the value of either drug alone.

Adolescent morphine exposure induces immediate and long-term increases in impulsive behavior

RATIONALE

Adolescence in humans represents a unique and critical developmental time point associated with increased risk-taking behavior. Converging clinical and epidemiological studies report a peak of drug use during adolescence, leading to the hypothesis that the developing adolescents brain is at risk to lose control over drug intake. Both adolescence and drug abuse are associated with significant cognitive and psychological changes such as lack of impulse control. A simple definition for impulsive behavior is the tendency to act prematurely without foresight. Increase in impulsivity is evident in acute morphine consumption, but to date, little is known with respect to subchronic morphine administration in impulsive behavior, particularly comparing time-dependent effects in adults, young adults, and adolescents.

METHODS

To evaluate this, adult, young adult, and adolescent rats were treated with a subchronic regimen of morphine or saline during 5 days (s.c.). Thereafter, we examined impulsive behavioral effects of morphine administration, 24 h and 25 days after administration in rats, while responding under a five-choice serial reaction time task (5-CSRTT).

RESULTS

Subchronic morphine administration increased premature responding 24 h after the last injection of morphine in adult, young adult, and adolescent rats without increasing motor activity but a significant change in motivation in adult and young adult rats only. After 25 days of abstinence, premature responses were significantly increased in comparison with baseline in adolescent rats but not in adults and young adults.

CONCLUSION

The main conclusion of this study is that morphine exposure in adolescents has a long-term profound effect on motor impulsive behavior later in adulthood. An implication of our findings might be that we should be especially careful about consuming and prescribing opioid drugs in adolescents.

Moderation of the relationship between Toxoplasma gondii seropositivity and trait impulsivity in younger men by the phenylalanine-tyrosine ratio

Previously, we reported that Toxoplasma gondii (T. gondii)-seropositivity is associated with higher impulsive sensation seeking in younger men. As dopaminergic and serotonergic signaling regulate impulsivity, and as T. gondii directly and indirectly affects dopaminergic signaling and induces activation of the kynurenine pathway leading to the diversion of tryptophan from serotonin production, we investigated if dopamine and serotonin precursors or the tryptophan metabolite kynurenine interact with the T. gondii-impulsivity association. In 950 psychiatrically healthy participants, trait impulsivity scores were related to T. gondii IgG seropositivity. Interactions were also identified between categorized levels of phenylalanine (Phe), tyrosine (Tyr), Phe:Tyr ratio, kynurenine (Kyn), tryptophan (Trp) and Kyn:Trp ratio, and age and gender. Only younger T. gondii-positive men with a high Phe:Tyr ratio, were found to have significantly higher impulsivity scores. There were no significant associations in other demographic groups, including women and older men. No significant effects or interactions were identified for Phe, Tyr, Kyn, Trp, or Kyn:Trp ratio. Phe:Tyr ratio, therefore, may play a moderating role in the association between T. gondii seropositivity and impulsivity in younger men. These results could potentially lead to individualized approaches to reduce impulsivity, based on combined demographic, biochemical and serological factors.

Continuous performance test impairment in a 22q11.2 microdeletion mouse model: improvement by amphetamine

The 22q11.2 deletion syndrome (22q11.2DS) confers high risk of neurodevelopmental disorders such as schizophrenia and attention-deficit hyperactivity disorder. These disorders are associated with attentional impairment, the remediation of which is important for successful therapeutic intervention. We assessed a 22q11.2DS mouse model (Df(h22q11)/+) on a touchscreen rodent continuous performance test (rCPT) of attention and executive function that is analogous to human CPT procedures. Relative to wild-type littermates, Df(h22q11)/+ male mice showed impaired attentional performance as shown by decreased correct response ratio (hit rate) and a reduced ability to discriminate target stimuli from non-target stimuli (discrimination sensitivity, or d'). The Df(h22q11)/+ model exhibited decreased prefrontal cortical-hippocampal oscillatory synchrony within multiple frequency ranges during quiet wakefulness, which may represent a biomarker of cognitive dysfunction. The stimulant amphetamine (0-1.0 mg/kg, i.p.) dose-dependently improved d' in Df(h22q11)/+ mice whereas the highest dose of modafinil (40 mg/kg, i.p.) exacerbated their d' impairment. This is the first report to directly implicate attentional impairment in a 22q11.2DS mouse model, mirroring a key endophenotype of the human disorder. The capacity of the rCPT to detect performance impairments in the 22q11.2DS mouse model, and improvement following psychostimulant-treatment, highlights the utility and translational potential of the Df(h22q11)/+ model and this automated behavioral procedure.