Contrasting roles for dopamine D1 and D2 receptor subtypes in the dorsomedial striatum but not the nucleus accumbens core during behavioral inhibition in the stop-signal task in rats

Noradrenergic versus dopaminergic modulation of impulsivity, attention and monitoring behaviour in rats performing the stop-signal task: possible relevance to ADHD

RATIONALE

Deficient response inhibition is a prominent feature of many pathological conditions characterised by impulsive and compulsive behaviour. Clinically effective doses of catecholamine reuptake inhibitors are able to improve such inhibitory deficits as measured by the stop-signal task (SST) in humans and other animals. However, the precise therapeutic mode of action of these compounds in terms of their relative effects on dopamine (DA) and noradrenaline (NA) systems in prefrontal cortical and striatal regions mediating attention and cognitive control remains unclear.

OBJECTIVES

We sought to fractionate the effects of global catecholaminergic manipulations on SST performance by using receptor-specific compounds for NA or DA. The results are described in terms of the effects of modulating specific receptor subtypes on various behavioural measures such as response inhibition, perseveration, sustained attention, error monitoring and motivation.

RESULTS

Blockade of α2-adrenoceptors improved sustained attention and response inhibition, whereas α1 and β1/2 adrenergic receptor antagonists disrupted go performance and sustained attention, respectively. No relevant effects were obtained after targeting DA D1, D2 or D4 receptors, while both a D3 receptor agonist and antagonist improved post-error slowing and compulsive nose-poke behaviour, though generally impairing other task measures.

CONCLUSIONS

Our results suggest that the use of specific pharmacological agents targeting α2 and β noradrenergic receptors may improve existing treatments for attentional deficits and impulsivity, whereas DA D3 receptors may modulate error monitoring and perseverative behaviour.

Deep brain stimulation of the subthalamic nucleus, but not dopaminergic medication, improves proactive inhibitory control of movement initiation in Parkinson's disease

Slowness in movement initiation is a cardinal feature of Parkinson's disease (PD) that is still poorly understood and unsuccessfully alleviated by standard therapies. Here, we raise this major clinical issue within the framework of a novel theoretical model that allows a better understanding of the basic mechanisms involved in movement initiation. This model assumes that movement triggering is inhibited by default to prevent automatic responses to unpredictable events. We investigated to which extent the top-down control necessary to release this locking state before initiating actions is impaired in PD and restored by standard therapies. We used a cue-target reaction time task to test both the ability to initiate fast responses to targets and the ability to refrain from reacting to cues. Fourteen patients with dopaminergic (DA) medication and 11 with subthalamic nucleus (STN) stimulation were tested on and off treatment, and compared with 14 healthy controls. We found evidence that patients withdrawn from treatment have trouble voluntarily releasing proactive inhibitory control; while DA medication broadly reduces movement initiation latency, it does not reinstate a normal pattern of movement initiation; and stimulation of the STN specifically re-establishes the efficiency of the top-down control of proactive inhibition. These results suggest that movement initiation disorders that resist DA medication are due to executive, not motor, dysfunctions. This conclusion is discussed with regard to the role the STN may play as an interface between non-DA executive and DA motor systems in cortico-basal ganglia loops.

Dopamine D₂ receptor modulation of human response inhibition and error awareness

Response inhibition, comprising action cancellation and action restraint, and error awareness are executive functions of considerable clinical relevance to neuropsychiatric disorders. Nevertheless, our understanding of their underlying catecholamine mechanisms, particularly regarding dopamine, is limited. Here, we used the dopamine D2 agonist cabergoline to study its ability to improve inhibitory control and modulate awareness of performance errors. A randomized, double-blind, placebo-controlled, crossover design with a single dose of cabergoline (1.25 mg) and placebo (dextrose) was employed in 25 healthy participants. They each performed the stop-signal task, a well-validated measure of action cancellation, and the Error Awareness Task, a go/no-go measure of action restraint and error awareness, under each drug condition. Cabergoline was able to selectively reduce stop-signal RT, compared with placebo, indicative of enhanced action cancellation (p < .05). This enhancement occurred without concomitant changes in overall response speed or RT variability and was not seen for errors of commission on the Error Awareness Task. Awareness of performance errors on the go/no-go task was, however, significantly improved by cabergoline compared with placebo (p < .05). Our results contribute to growing evidence for the dopaminergic control of distinct aspects of human executive ability, namely, action cancellation and error awareness. The findings may aid the development of new, or the repurposing of existing, pharmacotherapy that targets the cognitive dysfunction of psychiatric and neurological disorders. They also provide further evidence that specific cognitive paradigms have correspondingly specific neurochemical bases.

Response inhibition signals and miscoding of direction in dorsomedial striatum

The ability to inhibit action is critical for everyday behavior and is affected by a variety of disorders. Behavioral control and response inhibition is thought to depend on a neural circuit that includes the dorsal striatum, yet the neural signals that lead to response inhibition and its failure are unclear. To address this issue, we recorded from neurons in rat dorsomedial striatum (mDS) in a novel task in which rats responded to a spatial cue that signaled that reward would be delivered either to the left or to the right. On 80% of trials rats were instructed to respond in the direction cued by the light (GO). On 20% of trials a second light illuminated instructing the rat to refrain from making the cued movement and move in the opposite direction (STOP). Many neurons in mDS encoded direction, firing more or less strongly for GO movements made ipsilateral or contralateral to the recording electrode. Neurons that fired more strongly for contralateral GO responses were more active when rats were faster, showed reduced activity on STOP trials, and miscoded direction on errors, suggesting that when these neurons were overly active, response inhibition failed. Neurons that decreased firing for contralateral movement were excited during trials in which the rat was required to stop the ipsilateral movement. For these neurons activity was reduced when errors were made and was negatively correlated with movement time suggesting that when these neurons were less active on STOP trials, response inhibition failed. Finally, the activity of a significant number of neurons represented a global inhibitory signal, firing more strongly during response inhibition regardless of response direction. Breakdown by cell type suggests that putative medium spiny neurons (MSNs) tended to fire more strongly under STOP trials, whereas putative interneurons exhibited both activity patterns.

Striatal dopamine D₂/D₃ receptors mediate response inhibition and related activity in frontostriatal neural circuitry in humans

Impulsive behavior is thought to reflect a traitlike characteristic that can have broad consequences for an individual's success and well-being, but its neurobiological basis remains elusive. Although striatal dopamine D₂-like receptors have been linked with impulsive behavior and behavioral inhibition in rodents, a role for D₂-like receptor function in frontostriatal circuits mediating inhibitory control in humans has not been shown. We investigated this role in a study of healthy research participants who underwent positron emission tomography with the D₂/D₃ dopamine receptor ligand [¹⁸F]fallypride and BOLD fMRI while they performed the Stop-signal Task, a test of response inhibition. Striatal dopamine D₂/D₃ receptor availability was negatively correlated with speed of response inhibition (stop-signal reaction time) and positively correlated with inhibition-related fMRI activation in frontostriatal neural circuitry. Correlations involving D₂/D₃ receptor availability were strongest in the dorsal regions (caudate and putamen) of the striatum, consistent with findings of animal studies relating dopamine receptors and response inhibition. The results suggest that striatal D₂-like receptor function in humans plays a major role in the neural circuitry that mediates behavioral control, an ability that is essential for adaptive responding and is compromised in a variety of common neuropsychiatric disorders.

Dopamine agonists and the suppression of impulsive motor actions in Parkinson disease

The suppression of spontaneous motor impulses is an essential facet of cognitive control that is linked to frontal-BG circuitry. BG dysfunction caused by Parkinson disease (PD) disrupts the proficiency of action suppression, but how pharmacotherapy for PD impacts impulsive motor control is poorly understood. Dopamine agonists improve motor symptoms of PD but can also provoke impulsive-compulsive behaviors (ICB). We investigated whether dopamine agonist medication has a beneficial or detrimental effect on impulsive action control in 38 PD patients, half of whom had current ICB. Participants performed the Simon conflict task, which measures susceptibility to acting on spontaneous action impulses as well as the proficiency of suppressing these impulses. Compared with an off-agonist state, patients on their agonists were no more susceptible to reacting impulsively but were less proficient at suppressing the interference from the activation of impulsive actions. Importantly, agonist effects depended on baseline performance in the off-agonist state; more proficient suppressors off agonist experienced a reduction in suppression on agonist, whereas less-proficient suppressors off agonist showed improved suppression on agonist. Patients with active ICB were actually less susceptible to making fast, impulsive response errors than patients without ICB, suggesting that behavioral problems in this subset of patients may be less related to impulsivity in motor control. Our findings provide further evidence that dopamine agonist medication impacts specific cognitive control processes and that the direction of its effects depends on individual differences in performance off medication.

Dopamine receptors D1 and D2 are related to observed maternal behavior

The dopamine pathway and especially the dopamine receptors 1 and 2 (DRD1 and DRD2) are implicated in the regulation of mothering in rats. Evidence for this in humans is lacking. Here, we show that genetic variation in both DRD1 and DRD2 genes in a sample of 187 Caucasian mothers predicts variation in distinct maternal behaviors during a 30-min mother-infant interaction at 6 months postpartum. Two DRD1 single-nucleotide polymorphisms (SNPs rs265981 and rs686) significantly associated with maternal orienting away from the infant (P = 0.002 and P = 0.003, respectively), as did DRD1 haplotypes (P = 0.03). Two DRD2 SNPs (rs1799732 and rs6277) significantly associated with maternal infant-directed vocalizing (P = 0.001 and P = 0.04, respectively), as did DRD2 haplotypes (P = 0.01). We present evidence for heterosis in DRD1 where heterozygote mothers orient away from their infants significantly less than either homozygote group. Our findings provide important evidence that genetic variation in receptors critical for mothering in non-human species also affect human maternal behaviors. The findings also highlight the importance of exploring multiple dimensions of the complex human mothering phenotype.

Chronic corticosterone exposure during adolescence reduces impulsive action but increases impulsive choice and sensitivity to yohimbine in male Sprague-Dawley rats

Chronic stress during adolescence is associated with an increased risk for alcoholism and addictive disorders. Addiction is also associated with increased impulsivity, and stress during adolescence could alter cortical circuits responsible for response inhibition. Therefore, the present study determined the effect of chronic exposure to the stress hormone corticosterone (CORT) during adolescence on tests of impulsivity in adulthood and examined possible biochemical mechanisms. Male Sprague-Dawley rats were exposed to CORT by their drinking water during adolescence (post-natal day 30-50). The rats were then tested in adulthood to assess behavior on the 5-choice serial reaction time task (5CSRTT), stop-signal reaction time task (SSRTT), and the delay-discounting task, which differentially assess attention, impulsive action, and impulsive choice. Yohimbine-induced impulsivity on the 5CSRTT and biochemical analysis of the lateral orbital frontal cortex (lOFC) was also assessed owing to the ability of yohimbine to activate the hypothalamic-pituitary-adrenal axis and influence impulsivity. Adolescent CORT-treated rats were found to behave largely like controls on the 5CSRTT, but did show reduced premature responses when the intertrial interval was increased. Nevertheless, the CORT-treated rats tended to have more yohimbine-induced impulsive responses at low doses on this task, which was not found to be due to increased pCREB in the lOFC, but could be related to a higher expression/activity of the AMPA receptor subunit GluR1. Adolescent CORT-treated rats performed more accurately on the SSRTT, but showed greater impulsivity on the delay-discounting task, as indicated by steeper discounting functions. Therefore, adolescent CORT exposure reduced impulsive action but increased impulsive choice, indicating that chronic stress hormone exposure in adolescence can have long-term consequences on behavior.

Protective effect of extract of Acanthopanax senticosus Harms on dopaminergic neurons in Parkinson's disease mice

To study the neuroprotective effect of extract of Acanthopanax senticosus Harms against MPTP-induced mice model of Parkinson's disease and its mechanism. The Parkinson's disease mice model was induced by 1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine Hydrochloride (MPTP-HCl, 30mg/kg daily for 5 days). High dose group and low dose group were medicated with extract of Acanthopanax senticosus Harms for 20 days, dose amounted to 182mg/kg and 45.5mg/kg daily respectively. The behavioral testing of mice was assessed using pole-climbing test. The levels of Dopamine (DA) and Homovanillic acid (HVA) in striatum were determined by Ultra-performance liquid chromatography combined with time-of-flight mass spectrometry (UPLC-ToF-MS). The levels of dopamine receptor 1 and 2 in striatum were assayed simultaneously with the help of immunohistochemical method. The level of Caspase-3 protein in substantia nigra was analyzed by Western Blot. From Day 5 during the administration of extract of Acanthopanax senticosus Harms, pole-climbing time in low and high dose group were significantly less than model group (p<0.05). Compared with model group, the DA level of striatum in low dose group was significantly higher (p<0.01), the number of dopamine receptor 1 and dopamine receptor 2-positive cells in low and high dose group were significantly less (p<0.05), the Caspase-3 protein level of substantia nigra in low and high dose group were significantly less (p<0.05). The neuroprotective effect of extract of Acanthopanax senticosus Harms may be able to protect C57BL/6 mice against MPTP-induced dopaminergic neuronal damage.

Dopamine, serotonin and impulsivity

Impulsive people have a strong urge to act without thinking. It is sometimes regarded as a positive trait but rash impulsiveness is also widely present in clinical disorders such as attention deficit hyperactivity disorder (ADHD), drug dependence, mania, and antisocial behaviour. Contemporary research has begun to make major inroads into unravelling the brain mechanisms underlying impulsive behaviour with a prominent focus on the limbic cortico-striatal systems. With this progress has come the understanding that impulsivity is a multi-faceted behavioural trait involving neurally and psychologically diverse elements. We discuss the significance of this heterogeneity for clinical disorders expressing impulsive behaviour and the pivotal contribution made by the brain dopamine and serotonin systems in the aetiology and treatment of behavioural syndromes expressing impulsive symptoms.

When too much is not enough: obsessive-compulsive disorder as a pathology of stopping, rather than starting

Background

In obsessive-compulsive disorder (OCD), individuals feel compelled to repeatedly perform security-related behaviors, even though these behaviours seem excessive and unwarranted to them. The present research investigated two alternative ways of explaining such behavior: (1) a dysfunction of activation—a starting problem—in which the level of excitation in response to stimuli suggesting potential danger is abnormally strong; versus (2) a dysfunction of termination—a stopping problem—in which the satiety-like process for shutting down security-related thoughts and actions is abnormally weak.

Method

In two experiments, 70 patients with OCD (57 with washing compulsions, 13 with checking compulsions) and 72 controls were exposed to contamination cues—immersing a hand in wet diapers —and later allowed to wash their hands, first limited to 30 s and then for as long as desired. The intensity of activation of security motivation was measured objectively by change in respiratory sinus arrythmia. Subjective ratings (e.g., contamination) and behavioral measures (e.g., duration of hand washing) were also collected.

Results

Compared to controls, OCD patients with washing compulsions did not differ significantly in their levels of initial activation to the threat of contamination; however, they were significantly less able to reduce this activation by engaging in the corrective behavior of hand-washing. Further, the deactivating effect of hand-washing in OCD patients with checking compulsions was similar to that for controls, indicating that the dysfunction of termination in OCD is specific to the patient's symptom profile.

Conclusions

These results are the first to show that OCD is characterized by a reduced ability of security-related behavior to terminate motivation evoked by potential danger, rather than a heightened initial sensitivity to potential threat. They lend support to the security-motivation theory of OCD (Szechtman & Woody, 2004) and have important implications both for research into the biological mechanisms underlying OCD and for the development of new treatment approaches.

Quetiapine improves response inhibition in alcohol dependent patients: a placebo-controlled pilot study

RATIONALE

Quetiapine has been shown to be a promising medication for the treatment of alcoholism. As an atypical antipsychotic medication with antagonist activity at D1 and D2, 5-HT(1A) and 5-HT(2A), H(1) and α1 and α2 receptors, quetiapine has been found to decrease impulsivity in other psychiatric disorders but its effects on impulsivity have not been studied in alcohol dependent patients.

OBJECTIVE

This study seeks to test the effects of quetiapine on a specific dimension of impulsivity, namely response inhibition. This pilot study seeks to further elucidate the mechanisms of action of quetiapine for alcohol use disorders.

METHOD

A total of 20 non-treatment seeking alcohol dependent individuals were randomized to one of the following conditions in a double-blind, placebo-controlled design: (1) quetiapine (400 mg/day); or (2) matched placebo. Participants completed two counterbalanced intravenous placebo-alcohol administration sessions as well as behavioral measure of response inhibition (i.e. stop signal task) pre and post placebo-alcohol administration sessions.

RESULTS

Analyses revealed a significant effect of quetiapine in improving response inhibition as measured by the stop signal task. These results provide preliminary evidence suggesting that quetiapine improves response inhibition in alcohol dependent patients, as compared to placebo.

CONCLUSION

This pilot study contributes a novel putative mechanism of action of quetiapine in alcoholism, namely an improvement in response inhibition.

Prefrontal and monoaminergic contributions to stop-signal task performance in rats

Defining the neural and neurochemical substrates of response inhibition is of crucial importance for the study and treatment of pathologies characterized by impulsivity such as attention-deficit/hyperactivity disorder and addiction. The stop-signal task (SST) is one of the most popular paradigms used to study the speed and efficacy of inhibitory processes in humans and other animals. Here we investigated the effect of temporarily inactivating different prefrontal subregions in the rat by means of muscimol microinfusions on SST performance. We found that dorsomedial prefrontal cortical areas are important for inhibiting an already initiated response. We also investigated the possible neural substrates of the selective noradrenaline reuptake inhibitor atomoxetine via its local microinfusion into different subregions of the rat prefrontal cortex. Our results show that both orbitofrontal and dorsal prelimbic cortices mediate the beneficial effects of atomoxetine on SST performance. To assess the neurochemical specificity of these effects, we infused the α2-adrenergic agonist guanfacine and the D(1)/D(2) antagonist α-flupenthixol in dorsal prelimbic cortex to interfere with noradrenergic and dopaminergic neurotransmission, respectively. Guanfacine, which modulates noradrenergic neurotransmission, selectively impaired stopping, whereas blocking dopaminergic receptors by α-flupenthixol infusion prolonged go reaction time only, confirming the important role of noradrenergic neurotransmission in response inhibition. These results show that, similar to humans, distinct networks play important roles during SST performance in the rat and that they are differentially modulated by noradrenergic and dopaminergic neurotransmission. This study advances our understanding of the neuroanatomical and neurochemical determinants of impulsivity, which are relevant for a range of psychiatric disorders.

Abnormal structure of frontostriatal brain systems is associated with aspects of impulsivity and compulsivity in cocaine dependence

A growing body of preclinical evidence indicates that addiction to cocaine is associated with neuroadaptive changes in frontostriatal brain systems. Human studies in cocaine-dependent individuals have shown alterations in brain structure, but it is less clear how these changes may be related to the clinical phenotype of cocaine dependence characterized by impulsive behaviours and compulsive drug-taking. Here we compared self-report, behavioural and structural magnetic resonance imaging data on a relatively large sample of cocaine-dependent individuals (n = 60) with data on healthy volunteers (n = 60); and we investigated the relationships between grey matter volume variation, duration of cocaine use, and measures of impulsivity and compulsivity in the cocaine-dependent group. Cocaine dependence was associated with an extensive system of abnormally decreased grey matter volume in orbitofrontal, cingulate, insular, temporoparietal and cerebellar cortex, and with a more localized increase in grey matter volume in the basal ganglia. Greater duration of cocaine dependence was correlated with greater grey matter volume reduction in orbitofrontal, cingulate and insular cortex. Greater impairment of attentional control was associated with reduced volume in insular cortex and increased volume of caudate nucleus. Greater compulsivity of drug use was associated with reduced volume in orbitofrontal cortex. Cocaine-dependent individuals had abnormal structure of corticostriatal systems, and variability in the extent of anatomical changes in orbitofrontal, insular and striatal structures was related to individual differences in duration of dependence, inattention and compulsivity of cocaine consumption.