Comparable roles for serotonin in rats and humans for computations underlying flexible decision-making.

Serotonin is critical for adapting behavior flexibly to meet changing environmental demands. Cognitive flexibility is important for successful attainment of goals, as well as for social interactions, and is frequently impaired in neuropsychiatric disorders, including obsessive-compulsive disorder. However, a unifying mechanistic framework accounting for the role of serotonin in behavioral flexibility has remained elusive. Here, we demonstrate common effects of manipulating serotonin function across two species (rats and humans) on latent processes supporting choice behavior during probabilistic reversal learning, using computational modelling. The findings support a role of serotonin in behavioral flexibility and plasticity, indicated, respectively, by increases or decreases in choice repetition ('stickiness') or reinforcement learning rates following manipulations intended to increase or decrease serotonin function. More specifically, the rate at which expected value increased following reward and decreased following punishment (reward and punishment 'learning rates') was greatest after sub-chronic administration of the selective serotonin reuptake inhibitor (SSRI) citalopram (5 mg/kg for 7 days followed by 10 mg/kg twice a day for 5 days) in rats. Conversely, humans given a single dose of an SSRI (20 mg escitalopram), which can decrease post-synaptic serotonin signalling, and rats that received the neurotoxin 5,7-dihydroxytryptamine (5,7-DHT), which destroys forebrain serotonergic neurons, exhibited decreased reward learning rates. A basic perseverative tendency ('stickiness'), or choice repetition irrespective of the outcome produced, was likewise increased in rats after the 12-day SSRI regimen and decreased after single dose SSRI in humans and 5,7-DHT in rats. These common effects of serotonergic manipulations on rats and humans-identified via computational modelling-suggest an evolutionarily conserved role for serotonin in plasticity and behavioral flexibility and have clinical relevance transdiagnostically for neuropsychiatric disorders.

Signaling-specific inhibition of the CB1 receptor for cannabis use disorder: phase 1 and phase 2a randomized trials.

Cannabis use disorder (CUD) is widespread, and there is no pharmacotherapy to facilitate its treatment. AEF0117, the first of a new pharmacological class, is a signaling-specific inhibitor of the cannabinoid receptor 1 (CB1-SSi). AEF0117 selectively inhibits a subset of intracellular effects resulting from Δ9-tetrahydrocannabinol (THC) binding without modifying behavior per se. In mice and non-human primates, AEF0117 decreased cannabinoid self-administration and THC-related behavioral impairment without producing significant adverse effects. In single-ascending-dose (0.2 mg, 0.6 mg, 2 mg and 6 mg; n = 40) and multiple-ascending-dose (0.6 mg, 2 mg and 6 mg; n = 24) phase 1 trials, healthy volunteers were randomized to ascending-dose cohorts (n = 8 per cohort; 6:2 AEF0117 to placebo randomization). In both studies, AEF0117 was safe and well tolerated (primary outcome measurements). In a double-blind, placebo-controlled, crossover phase 2a trial, volunteers with CUD were randomized to two ascending-dose cohorts (0.06 mg, n = 14; 1 mg, n = 15). AEF0117 significantly reduced cannabis' positive subjective effects (primary outcome measurement, assessed by visual analog scales) by 19% (0.06 mg) and 38% (1 mg) compared to placebo (P < 0.04). AEF0117 (1 mg) also reduced cannabis self-administration (P < 0.05). In volunteers with CUD, AEF0117 was well tolerated and did not precipitate cannabis withdrawal. These data suggest that AEF0117 is a safe and potentially efficacious treatment for CUD.ClinicalTrials.gov identifiers: NCT03325595 , NCT03443895 and NCT03717272 .

Cingulate-motor circuits update rule representations for sequential choice decisions.

Anterior cingulate cortex mediates the flexible updating of an animal's choice responses upon rule changes in the environment. However, how anterior cingulate cortex entrains motor cortex to reorganize rule representations and generate required motor outputs remains unclear. Here, we demonstrate that chemogenetic silencing of the terminal projections of cingulate cortical neurons in secondary motor cortex in the rat disrupts choice performance in trials immediately following rule switches, suggesting that these inputs are necessary to update rule representations for choice decisions stored in the motor cortex. Indeed, the silencing of cingulate cortex decreases rule selectivity of secondary motor cortical neurons. Furthermore, optogenetic silencing of cingulate cortical neurons that is temporally targeted to error trials immediately after rule switches exacerbates errors in the following trials. These results suggest that cingulate cortex monitors behavioral errors and updates rule representations in motor cortex, revealing a critical role for cingulate-motor circuits in adaptive choice behaviors.

Differential attentional control mechanisms by two distinct noradrenergic coeruleo-frontal cortical pathways.

The attentional control of behavior is a higher-order cognitive function that operates through attention and response inhibition. The locus coeruleus (LC), the main source of norepinephrine in the brain, is considered to be involved in attentional control by modulating the neuronal activity of the prefrontal cortex (PFC). However, evidence for the causal role of LC activity in attentional control remains elusive. Here, by using behavioral and optogenetic techniques, we investigate the effect of LC neuron activation or inhibition in operant tests measuring attention and response inhibition (i.e., a measure of impulsive behavior). We show that LC neuron stimulation increases goal-directed attention and decreases impulsivity, while its suppression exacerbates distractibility and increases impulsive responding. Remarkably, we found that attention and response inhibition are under the control of two divergent projections emanating from the LC: one to the dorso-medial PFC and the other to the ventro-lateral orbitofrontal cortex, respectively. These findings are especially relevant for those pathological conditions characterized by attention deficits and elevated impulsivity.

A biopsychosocial model of violence when sleepwalking: review and reconceptualisation.

SUMMARY: Violence towards others during sleepwalking is relatively uncommon, but can result in serious injury or even death. Much of the research in this field has focused on the forensic consequences of violence during sleepwalking without sufficient attention to an understanding of the risk factors for violence during sleepwalking and the development of prevention and interventions based on these risk factors. This paper reviews the characteristics of impulsive violence in general and reconceptualises violence during sleepwalking as an extension of this prior vulnerability. We propose a biopsychosocial model of the risk for violence during sleepwalking that is supported through a review of empirical literature both within sleepwalking and violent behaviour more generally. Biological, psychological and social risk factors are hypothesised to mediate the relationship between sleepwalking and violence. Implications for prevention and treatment of this potentially fatal problem are discussed. DECLARATION OF INTEREST: None. COPYRIGHT AND USAGE: © The Royal College of Psychiatrists 2017. This is an open access article distributed under the terms of the Creative Commons Non-Commercial, No Derivatives (CC BY-NC-ND) license.

Inhibition and impulsivity: behavioral and neural basis of response control.

In many circumstances alternative courses of action and thoughts have to be inhibited to allow the emergence of goal-directed behavior. However, this has not been the accepted view in the past and only recently has inhibition earned its own place in the neurosciences as a fundamental cognitive function. In this review we first introduce the concept of inhibition from early psychological speculations based on philosophical theories of the human mind. The broad construct of inhibition is then reduced to its most readily observable component which necessarily is its behavioral manifestation. The study of 'response inhibition' has the advantage of dealing with a relatively simple and straightforward process, the overriding of a planned or already initiated action. Deficient inhibitory processes profoundly affect everyday life, causing impulsive conduct which is generally detrimental for the individual. Impulsivity has been consistently linked to several types of addiction, attention deficit/hyperactivity disorder, mania and other psychiatric conditions. Our discussion of the behavioral assessment of impulsivity will focus on objective laboratory tasks of response inhibition that have been implemented in parallel for humans and other species with relatively few qualitative differences. The translational potential of these measures has greatly improved our knowledge of the neurobiological basis of behavioral inhibition and impulsivity. We will then review the current models of behavioral inhibition along with their expression via underlying brain regions, including those involved in the activation of the brain's emergency 'brake' operation, those engaged in more controlled and sustained inhibitory processes and other ancillary executive functions.

Measuring the construct of executive control in schizophrenia: defining and validating translational animal paradigms for discovery research.

Executive control is an aspect of cognitive function known to be impaired in schizophrenia. Previous meetings of the Cognitive Neuroscience Treatment Research to Improve Cognition in Schizophrenia (CNTRICS) group have more precisely defined executive control in terms of two constructs: "rule generation and selection", and "dynamic adjustments of control". Next, human cognitive tasks that may effectively measure performance with regard to these constructs were identified to be developed into practical and reliable measures for use in treatment development. The aim of this round of CNTRICS meetings was to define animal paradigms that have sufficient promise to warrant further investigation for their utility in measuring these constructs. Accordingly, "reversal learning" and the "attentional set-shifting task" were nominated to assess the construct of rule generation and selection, and the "stop signal task" for the construct of dynamic adjustments of control. These tasks are described in more detail here, with a particular focus on their utility for drug discovery efforts. Presently, each assay has strengths and weaknesses with regard to this point and increased emphasis on improving practical aspects of testing, understanding predictive validity, and defining biomarkers of performance represent important objectives in attaining confidence in translational validity here.

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.

Serotonin modulates sensitivity to reward and negative feedback in a probabilistic reversal learning task in rats.

Depressed patients show cognitive deficits that may depend on an abnormal reaction to positive and negative feedback. The precise neurochemical mechanisms responsible for such cognitive abnormalities have not yet been clearly characterized, although serotoninergic dysfunction is frequently associated with depression. In three experiments described here, we investigated the effects of different manipulations of central serotonin (5-hydroxytryptamine, 5-HT) levels in rats performing a probabilistic reversal learning task that measures response to feedback. Increasing or decreasing 5-HT tone differentially affected behavioral indices of cognitive flexibility (reversals completed), reward sensitivity (win-stay), and reaction to negative feedback (lose-shift). A single low dose of the selective serotonin reuptake inhibitor citalopram (1 mg/kg) resulted in fewer reversals completed and increased lose-shift behavior. By contrast, a single higher dose of citalopram (10 mg/kg) exerted the opposite effect on both measures. Repeated (5 mg/kg, daily, 7 days) and subchronic (10 mg/kg, b.i.d., 5 days) administration of citalopram increased the number of reversals completed by the animals and increased the frequency of win-stay behavior, whereas global 5-HT depletion had the opposite effect on both indices. These results show that boosting 5-HT neurotransmission decreases negative feedback sensitivity and increases reward (positive feedback) sensitivity, whereas reducing it has the opposite effect. However, these effects depend on the nature of the manipulation used: acute manipulations of the 5-HT system modulate negative feedback sensitivity, whereas long-lasting treatments specifically affect reward sensitivity. These results parallel some of the findings in humans on effects of 5-HT manipulations and are relevant to hypotheses of altered response to feedback in depression.

Dissociable effects of noradrenaline, dopamine, and serotonin uptake blockade on stop task performance in rats.

RATIONALE: The stop-signal paradigm measures the ability to stop a motor response after its execution has been initiated. Impairments in inhibiting inappropriate behavior and prolonged stop-signal reaction times (SSRTs) are characteristic of several psychiatric disorders, most notably attention deficit/hyperactivity disorder. While there is relative consensus regarding the anatomical substrates of behavioral inhibition, the neurochemical imbalance responsible for the deficits in stopping displayed by impulsive individuals is still a matter of debate. OBJECTIVE: The aim of this study was to investigate the effects of manipulating brain monoamine levels on stop task parameters. METHODS: Lister-hooded rats were trained on the rodent version of the stop-signal task and administered different monoamine transporter inhibitors: citalopram, which selectively blocks the serotonin transporter; atomoxetine, which selectively blocks the noradrenaline transporter; and GBR-12909, which selectively blocks the dopamine transporter (DAT), and the alpha-2 adrenergic agonist guanfacine. RESULTS: Atomoxetine speeded SSRT and increased accuracy for go-trials. Citalopram slowed go reaction time and decreased go accuracy at the highest dose (1 mg/kg). GBR-12909 speeded go reaction time and impaired both go and stop accuracy. Guanfacine negatively modulated all principal stop and go measures at the highest dose used (0.3 mg/kg). CONCLUSIONS: The results suggest that atomoxetine exerts its beneficial effects on SSRT via its action on noradrenaline re-uptake, as the specific DAT blocker GBR-12909 and serotonin reuptake blockade had only minor effects on SSRT. The speeding of the go reaction time by dopamine reuptake blockade is consistent with the hypothesis that the hypothetical stop and go processes are modulated by distinct monoaminergic systems.

The neuropsychopharmacology of action inhibition: cross-species translation of the stop-signal and go/no-go tasks.

BACKGROUND AND RATIONALE: The term 'action inhibition' encapsulates the ability to prevent any form of planned physical response. Growing evidence suggests that different 'stages' or even subtypes of action inhibition activate subtly different neuropharmacological and neuroanatomical processes. OBJECTIVES: In this review, we present evidence from two commonly used and apparently similar behavioural tests, the stop-signal task and the go/no-go task, to determine if these have similar neuroanatomical and neurochemical modulation. RESULTS: Whilst performance of the stop-signal and go/no-go tasks is modulated across only subtly different anatomical networks, serotonin (5-HT) is strongly implicated in inhibitory control on the go/no-go but not the stop-signal task, whereas the stop-signal reaction time appears more sensitive to the action of noradrenaline. CONCLUSIONS: There is clear neuropharmacological and neuroanatomical evidence that stop-signal and go/no-go tasks represent different forms of action inhibition. This evidence translates with remarkable consistency across species. We discuss the possible implications of this evidence with respect to the development of novel therapeutic treatments for disorders in which inhibitory deficits are prominent and debilitating.

Opposite environmental regulation of heroin and amphetamine self-administration in the rat.

RATIONALE: The circumstances of drug taking are thought to play a role in drug abuse but the evidence of it is anecdotal. Previous studies have shown that the intravenous self-administration of cocaine is facilitated in rats non-residing in the test chambers relative to rats that live in the test chambers at all times. We investigated here whether environmental context could exert its modulatory influence on heroin and amphetamine self-administration as well. MATERIALS AND METHODS: Independent groups of rats were given the possibility to self-administer different doses of heroin or amphetamine (12.5, 25.0, or 50.0 microg/kg). Some animals were housed in the self-administration chambers (resident groups) whereas other rats were transported to the self-administration chambers only for the test sessions (non-resident groups). RESULTS: Amphetamine-reinforcing effects were more pronounced in non-resident rats than in resident rats, as previously reported for cocaine. Quite unexpectedly, the opposite was found for heroin. Because of this surprising dissociation, some of the rats trained to self-administer amphetamine were later given the opportunity to self-administer heroin. Also in this case, resident rats took more heroin than non-resident rats. CONCLUSIONS: These findings suggest an unforeseen dissociation between opioid and psychostimulant reward and demonstrate that even in the laboratory rat some contexts are associated with the propensity to self-administer more opioid than psychostimulant drugs and vice versa, thus indicating that drug taking is influenced not only by economical or cultural factors but also can be modulated at a much more basic level by the setting in which drugs are experienced.

The application of the 5-choice serial reaction time task for the assessment of visual attentional processes and impulse control in rats.

One popular way of measuring visual attentional processes in the rat is using 5-choice serial reaction time task (5-CSRTT). This paradigm requires subjects to detect brief flashes of light presented in a pseudorandom order in one of five spatial locations over a large number of trials. For this task, the animals are trained for approximately 30-40 daily sessions during which they gradually learn to respond in the appropriate aperture within a certain amount of time. If they fail to respond, respond in the wrong hole or at an inappropriate time, a short period of darkness (time-out) is presented as punishment and no reward is delivered. The 5-CSRTT provides the possibility to test the effects of various neural, pharmacological and behavioral manipulations on discrete and somewhat independent measures of behavioral control, including accuracy of discrimination, impulsivity, perseverative responses and response latencies.

Similar effects of the selective noradrenaline reuptake inhibitor atomoxetine on three distinct forms of impulsivity in the rat.

Atomoxetine is a noradrenaline-specific reuptake inhibitor used clinically for the treatment of childhood and adult attention deficit hyperactivity disorder (ADHD). Studies in human volunteers and patient groups have shown that atomoxetine improves stop-signal reaction time (SSRT) performance, an effect consistent with a reduction in motor impulsivity. However, ADHD is a heterogeneous disorder and it is of interest to determine whether atomoxetine is similarly effective against other forms of impulsivity, as well as the attentional impairment present in certain subtypes of ADHD. The present study examined the effects of atomoxetine on impulsivity using an analogous SSRT task in rats and two additional tests of impulsivity; delay discounting of reward and the five-choice serial reaction time task (5CSRTT), the latter providing an added assessment of sustained visual attention. Atomoxetine produced a significant dose-dependent speeding of SSRT. In addition, atomoxetine produced a selective, dose-dependent decrease in premature responding on the 5CSRTT. Finally, on the delay-discounting task, atomoxetine significantly decreased impulsivity by increasing preference for the large-value reward across increasing delay. These findings conclusively demonstrate that atomoxetine decreases several distinct forms of impulsivity in rats. The apparent contrast of these effects with stimulant drugs such as amphetamine and methylphenidate, which generally act to increase impulsivity on the 5CSRTT, may provide new insights into the mechanisms of action of stimulant and nonstimulant drugs in ADHD.