The 5-choice serial reaction time task: behavioural pharmacology and functional neurochemistry

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.

Profile of cortical N-methyl-D-aspartate receptor subunit expression associates with inherent motor impulsivity in rats

Impulsivity is a multifaceted behavioral manifestation with implications in several neuropsychiatric disorders. Glutamate neurotransmission through the N-methyl-D-aspartate receptors (NMDARs) in the medial prefrontal cortex (mPFC), an important brain region in decision-making and goal-directed behaviors, plays a key role in motor impulsivity. We discovered that inherent motor impulsivity predicted responsiveness to D-cycloserine (DCS), a partial NMDAR agonist, which prompted the hypothesis that inherent motor impulsivity is associated with the pattern of expression of cortical NMDAR subunits (GluN1, GluN2A, GluN2B), specifically the protein levels and synaptosomal trafficking of the NMDAR subunits. Outbred male Sprague-Dawley rats were identified as high (HI) or low (LI) impulsive using the one-choice serial reaction time task. Following phenotypic identification, mPFC synaptosomal protein was extracted from HI and LI rats to assess the expression pattern of the NMDAR subunits. Synaptosomal trafficking and stabilization for the GluN2 subunits were investigated by co-immunoprecipitation for postsynaptic density 95 (PSD95) and synapse associated protein 102 (SAP102). HI rats had lower mPFC GluN1 and GluN2A, but higher GluN2B and pGluN2B synaptosomal protein expression versus LI rats. Further, higher GluN2B:PSD95 and GluN2B:SAP102 protein:protein interactions were detected in HI versus LI rats. Thus, the mPFC NMDAR subunit expression pattern and/or synaptosomal trafficking associates with high inherent motor impulsivity. Increased understanding of the complex regulation of NMDAR balance within the mPFC as it relates to inherent motor impulsivity may lead to a better understanding of risk factors for impulse-control disorders.

Atomoxetine improves memory and other components of executive function in young-adult rats and aged rhesus monkeys

Atomoxetine is a norepinephrine reuptake inhibitor and FDA-approved treatment for attention deficit/hyperactivity disorder (ADHD) in children, adolescents, and adults. While there is some evidence that atomoxetine may improve additional domains of cognition beyond attention in both young adults and aged individuals, this subject has not been extensively investigated. Here, we evaluated atomoxetine (in low mg/kg doses) in a variable stimulus duration (vSD) and a variable intertrial interval (vITI) version of the five choice-serial reaction time task (5C-SRTT), and an eight-arm radial arm maze (RAM) procedure in young-adult rats. The compound was further evaluated (in μg/kg-low mg/kg doses) along with nicotine (as a reference compound) and the Alzheimer's disease treatment donepezil in a distractor version of a delayed match to sample task (DMTS-D) in aged monkeys (mean age = 21.8 years). Atomoxetine (depending on the dose) improved accuracy (sustained attention) as well as behaviors related to impulsivity, compulsivity and cognitive inflexibility in both the vSD and vITI tasks and it improved spatial reference memory in the RAM. In the DMTS-D task, both nicotine and atomoxetine, but not donepezil attenuated the effects of the distractor on accuracy at short delays (non-spatial working/short term memory). However, combining sub-effective doses of atomoxetine and donepezil did enhance DMTS-D accuracy indicating the potential of using atomoxetine as an adjunctive treatment with donepezil. Collectively, these animal studies support the further evaluation of atomoxetine as a repurposed drug for younger adults as well older individuals who suffer from deficits in attention, memory and other components of executive function.

Incisional Nociceptive Input Impairs Attention-related Behavior and Is Associated with Reduced Neuronal Activity in the Prefrontal Cortex in Rats

WHAT WE ALREADY KNOW ABOUT THIS TOPIC

WHAT THIS ARTICLE TELLS US THAT IS NEW: BACKGROUND:: Cognitive capacity may be reduced from inflammation, surgery, anesthesia, and pain. In this study, we hypothesized that incision-induced nociceptive input impairs attentional performance and alters neuronal activity in the prefrontal cortex.

METHODS

Attentional performance was measured in rats by using the titration variant of the 5-choice serial reaction time to determine the effect of surgical incision and anesthesia in a visual attention task. Neuronal activity (single spike and local field potentials) was measured in the medial prefrontal cortex in animals during the task.

RESULTS

Incision significantly impaired attention postoperatively (area under curve of median cue duration-time 97.2 ± 56.8 [n = 9] vs. anesthesia control 25.5 ± 14.5 s-days [n = 9], P = 0.002; effect size, η = 0.456). Morphine (1 mg/kg) reduced impairment after incision (area under curve of median cue duration-time 31.6 ± 36.7 [n = 11] vs. saline 110 ± 64.7 s-days [n = 10], P < 0.001; η = 0.378). Incision also decreased cell activity (n = 24; 1.48 ± 0.58 vs. control, 2.93 ± 2.02 bursts/min; P = 0.002; η = 0.098) and local field potentials (n = 28; η = 0.111) in the medial prefrontal cortex.

CONCLUSIONS

These results show that acute postoperative nociceptive input from incision reduces attention-related task performance and decreases neuronal activity in the medial prefrontal cortex. Decreased neuronal activity suggests nociceptive input is more than just a distraction because neuronal activity increases during audiovisual distraction with similar behavioral impairment. This suggests that nociceptive input and the medial prefrontal cortex may contribute to attentional impairment and mild cognitive dysfunction postoperatively. In this regard, pain may affect postoperative recovery and return to normal activities through attentional impairment by contributing to lapses in concentration for routine and complex tasks.

Pharmacokinetic and pharmacodynamic analysis of d-amphetamine in an attention task in rodents

Amphetamine is a common therapeutic agent for alleviating the core symptoms associated with attention-deficit hyperactivity disorder (ADHD) in children and adults. The current study used a translational model of attention, the five-choice serial reaction time (5-CSRT) procedure with rats, to examine the time-course effects of d-amphetamine. Effects of different dosages of d-amphetamine were related to drug-plasma concentrations, fashioned after comprehensive pharmacokinetic/pharmacodynamic assessments that have been employed in clinical investigations. We sought to determine whether acute drug-plasma concentrations that enhance performance in the 5-CSRT procedure are similar to those found to be therapeutic in patients diagnosed with ADHD. Results from the pharmacokinetic/pharmacodynamic assessment indicate that d-amphetamine plasma concentrations associated with improved performance on the 5-CSRT procedure overlap with those that have been reported to be therapeutic in clinical trials. The current findings suggest that the 5-CSRT procedure may be a useful preclinical model for predicting the utility of novel ADHD therapeutics and their effective concentrations.

Inhibitory Control Deficits Associated with Upregulation of CB1R in the HIV-1 Tat Transgenic Mouse Model of Hand

In the era of combined antiretroviral therapy, HIV-1 infected individuals are living longer lives; however, longevity is met with an increasing number of HIV-1 associated neurocognitive disorders (HAND) diagnoses. The transactivator of transcription (Tat) is known to mediate the neurotoxic effects in HAND by acting directly on neurons and also indirectly via its actions on glia. The Go/No-Go (GNG) task was used to examine HAND in the Tat transgenic mouse model. The GNG task involves subjects discriminating between two stimuli sets in order to determine whether or not to inhibit a previously trained response. Data reveal inhibitory control deficits in female Tat(+) mice (p = .048) and an upregulation of cannabinoid type 1 receptors (CB₁R) in the infralimbic (IL) cortex in the same female Tat(+) group (p < .05). A significant negative correlation was noted between inhibitory control and IL CB₁R expression (r = −.543, p = .045), with CB₁R expression predicting 30% of the variance of inhibitory control (R² = .295, p = .045). Furthermore, there was a significant increase in spontaneous excitatory postsynaptic current (sEPSC) frequencies in Tat(+) compared to Tat(−) mice (p = .008, across sexes). The increase in sEPSC frequency was significantly attenuated by bath application of PF3845, a fatty acid amide hydrolase (FAAH) enzyme inhibitor (p < .001). Overall, the GNG task is a viable measure to assess inhibitory control deficits in Tat transgenic mice and results suggest a potential therapeutic treatment for the observed deficits with drugs which modulate endocannabinoid enzyme activity.

Graphical Abstract

Acute Administration of URB597 Fatty Acid Amide Hydrolase Inhibitor Prevents Attentional Impairments by Distractors in Adolescent Mice

The maturation of attentional control during adolescence might influence later functional outcome or predisposition to psychiatric disorders. During adolescence, the cannabinoid system is particularly sensitive to pharmacological challenges, with potential impact on cognitive functions. Here, we used a recently validated five-choice serial reaction time task protocol to test adolescent C57BL/6J mice. We showed that the pharmacological inhibition (by URB597) of the fatty acid amide hydrolase (FAAH), the major enzyme implicated in anandamide degradation, prevented cognitive disruptions induced by distracting cues in adolescent mice. In particular, these protective effects were indicated by increased accuracy and correct responses and decreased premature responses selectively in the distractor trials. Notably, at the relatively low dose used, we detected no effects in other cognitive, motor, or incentive measures nor long-lasting or rebound effects of FAAH inhibition in cognitive functions. Overall, these data provide initial evidence of selective procognitive effects of FAAH inhibition in measures of attentional control in adolescent mice.

The Arctic/Swedish APP mutation alters the impact of chronic stress on cognition in mice

Chronic stress is a major risk factor for developing Alzheimer's disease (AD) and promotes the processing of amyloid precursor protein (APP) to β-amyloid (Aβ). However, the precise relationship of stress and disease-typical cognitive decline is presently not well understood. The aim of this study was to investigate how early life stress may affect cognition in adult mice with and without soluble Aβ pathology typical for the early stages of the disease. We focussed on sustained attention and response control, aspects of cognition mediated by the prefrontal cortex that are consistently impaired both in early AD and after chronic stress exposure. Young wild-type mice as well as transgenic arcAβ mice overexpressing the hAPParc/swe transgene were exposed to a chronic unpredictable stress paradigm (age 3-8 weeks). At 15 weeks, these mice were tested on the 5-choice serial reaction time task, a test of sustained attention and executive control. We found that, expectedly, chronic stress increased impulsive choices and impaired sustained attention in wild-type mice. However, the same treatment reduced impulsivity and did not interfere with sustained attention in arcAβ mice. These findings suggest an unexpected interaction between chronic stress and Aβ whereby Aβ-pathology caused by the hAPParc/swe mutation prevented and/or reversed stress-induced cognitive changes through mechanisms that deserve further investigation. They also indicate that Aβ, in modest amounts, may have a beneficial role for cognitive stability, for example by protecting neural networks from the impact of further physiological or behavioural stress.

Evaluation of attention in APP/PS1 mice shows impulsive and compulsive behaviours

While Alzheimer's disease (AD) is traditionally associated with deficits in episodic memory, early changes in other cognitive domains, such as attention, have been gaining interest. In line with clinical observations, some animal models of AD have been shown to develop attentional deficits, but this is not consistent across all models. The APPswe/PS1ΔE9 (APP/PS1) mouse is one of the most commonly used AD models and attention has not yet been scrutinised in this model. We set out to assess attention using the 5-choice serial reaction time task (5CSRTT) early in the progression of cognitive symptoms in APP/PS1 mice, using clinically translatable touchscreen chambers. APP/PS1 mice showed no attentional changes across 5CSRTT training or any probes from 9 to 11 months of age. Interestingly, APP/PS1 mice showed increased impulsive and compulsive responding when task difficulty was high. This suggests that while the APP/PS1 mouse model may not be a good model of attentional changes in AD, it may be useful to study the early changes in impulsive and compulsive behaviour that have been identified in patient studies. As these changes have not previously been reported without attentional deficits in the clinic, the APP/PS1 mouse model may provide a unique opportunity to study these specific behavioural changes seen in AD, including their mechanistic underpinnings and therapeutic implications.

Cognitive Effects of MDMA in Laboratory Animals: A Systematic Review Focusing on Dose

±3,4-Methylenedioxymethamphetamine (MDMA) is a synthetic, psychoactive drug that is primarily used recreationally but also may have some therapeutic value. At low doses, MDMA produces feelings of relaxation, empathy, emotional closeness, and euphoria. Higher doses can produce unpleasant psychostimulant- and hallucinogen-like adverse effects and therefore are usually not taken intentionally. There is considerable evidence that MDMA produces neurotoxicity and cognitive deficits at high doses; however, these findings may not generalize to typical recreational or therapeutic use of low-dose MDMA. Here, we systematically review 25 years of research on the cognitive effects of MDMA in animals, with a critical focus on dose. We found no evidence that doses of less than 3 mg/kg MDMA-the dose range that users typically take-produce cognitive deficits in animals. Doses of 3 mg/kg or greater, which were administered most often and frequently ranged from 5 to 20 times greater than an average dose, also did not produce cognitive deficits in a slight majority of experiments. Overall, the preclinical evidence of MDMA-induced cognitive deficits is weak and, if anything, may be the result of unrealistically high dosing. While factors associated with recreational use such as polydrug use, adulterants, hyperthermia, and hyponatremia can increase the potential for neurotoxicity, the short-term, infrequent, therapeutic use of ultra low-dose MDMA is unlikely to pose significant cognitive risks. Future studies must examine any adverse cognitive effects of MDMA using clinically relevant doses to reliably assess its potential as a psychotherapeutic.

The myeloarchitecture of impulsivity: premature responding in youth is associated with decreased myelination of ventral putamen

Impulsivity has been suggested as a neurocognitive endophenotype conferring risk across a number of neuropsychiatric conditions, including substance and behavioural addictions, eating disorders, and attention deficit/hyperactivity disorder. We used a paradigm with interspecies translation validity (the four-choice serial reaction time task, 4CSRTT) to assess 'waiting' impulsivity in a youth sample (N = 99, aged 16-26 years). We collected magnetization prepared two rapid acquisition gradient echo (MP2RAGE) scans, which enabled us to measure R1, the longitudinal relaxation rate, a parameter closely related to tissue myelin content, as well as quantify grey matter volume. We also assessed inhibitory control (commission errors) on a Go/NoGo task and measured decisional impulsivity (delay discounting) using the Monetary Choice Questionnaire (MCQ). We found R1 of the bilateral ventral putamen was negatively correlated with premature responding, the index of waiting impulsivity on the 4CSRTT. Heightened impulsivity in youth was significantly and specifically associated with lower levels of myelination in the ventral putamen. Impulsivity was not associated with grey matter volume. The association with myelination was specific to waiting impulsivity: R1 was not associated with decisional impulsivity on the MCQ or inhibitory control on the Go/NoGo task. We report that heightened waiting impulsivity, measured as premature responding on the 4CSRTT, is specifically associated with lower levels of ventral putaminal myelination, measured using R1. This may represent a neural signature of vulnerability to diseases associated with excessive impulsivity and demonstrates the added explanatory power of quantifying the mesoscopic organization of the human brain, over and above macroscopic volumetric measurements.

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.

Effect of ADHD medication in male C57BL/6J mice performing the rodent Continuous Performance Test

RATIONALE

The rodent Continuous Performance Test (rCPT) is a novel rodent paradigm to assess attention and impulsivity that resembles the human CPT. This task measures the rodents' ability to discriminate between target and non-target stimuli. The effect of attention-deficit/hyperactivity disorder (ADHD) medication on rCPT performance in mice remains to be fully characterized.

OBJECTIVE

To investigate the predictive validity of the mouse rCPT by studying the effects of ADHD medication methylphenidate, atomoxetine, amphetamine, guanfacine, and modafinil in four behavioral subgroups based on performance and impulsivity levels.

METHODS

Two cohorts of male C57BL/6J mice were used, and the effect of treatment was tested in a variable stimulus duration probe. Performance and impulsive subgroups were made based on discriminability and percentage premature responses, respectively.

RESULTS

Methylphenidate, atomoxetine, and amphetamine improved performance in the low-performing animals, with no effect in the high-performers. These improvements were a result of increased hit rate and/or decreased false-alarm rate. Furthermore, these drugs decreased percentage premature responses in the high-impulsive group. Methylphenidate, guanfacine, and modafinil increased premature responses in the low-impulsive group. Modafinil impaired performance in the high-performers by increasing false-alarm rate.

CONCLUSION

The effect of ADHD treatment was dependent on baseline, as seen by increases in performance for the low-performers and decreases in impulsivity for the high-impulsive animals. These results agree with clinical data and may support the inverted U-shaped arousal-performance theory. The rCPT combined with behavioral separation into subgroups has high predictive validity, and our study is a step forward towards establishing the clinical translatability of the rCPT.

Effects of haloperidol on cognitive function and behavioural flexibility in the IntelliCage social home cage environment

This study examined the effects of chronic administration of haloperidol in female C57BL/6 mice. As patients with schizophrenia often show perseverant behaviours and lack of behavioural flexibility, it is important to know whether the effect of haloperidol makes these traits worse. This study, therefore, was designed to evaluate the effects of haloperidol on the learning performance of mice using an automated home cage environment, the IntelliCage. Behavioural shuttling in the IntelliCage enabled us to assess learning in tasks including place discrimination learning and reversal place learning. In reversal place learning, spatial patterns of rewarded and non-rewarded places that mice had learned to discriminate were reversed, and the adaptability of mice to change the previously acquired place learning was measured. Haloperidol (1 mg/kg/day) reduced locomotor activity and water intake. Haloperidol impaired the cognitive flexibility of mice during reversal place learning rewarded by access to water but enhanced the rapid acquisition of behavioural flexibility when airpuff punishment was applied.

Impaired social discrimination behavior despite normal social approach by kallikrein-related peptidase 8 knockout mouse

For social mammals, recognition of conspecifics and discrimination of each other (social memory) is crucial to living in a stable colony. Here, we investigated whether kallikrein-related peptidase 8 (KLK8)-neuregulin 1 (NRG1)-ErbB signaling is crucial for social discrimination behavior using the social discrimination three chamber behavioral test. Klk8 knockout mice (NRG1-deactivated mice) exhibited normal social approach but impaired social discrimination. Intraventricular injection of recombinant NRG1_177-246 into Klk8 knockout mice reversed this impaired social discrimination. This study reveals that KLK8 is a key regulator of NRG1-ErbB signaling, which contributes to social discrimination behavior.

Naloxone reversed cognitive impairments induced by repeated morphine under heavy perceptual load in the 5-choice serial reaction time task

Repeated opioids abuse may produce long-lasting and complicated cognitive deficits in individuals. Naloxone is a typical mu-opioid receptor antagonist widely used in clinical treatment for opioid overdose and opioid abuse. However, it remains unclear whether naloxone affects morphine-induced cognitive deficits. Using the 5-choice serial reaction time task (5-CSRTT), the present study investigated cognitive profiles including attention, impulsivity, compulsivity, and processing speed in repeated morphine-treated mice. Repeated morphine administration (10 mg/kg, i.p.) induced complex cognitive changes including decreased attention and increased impulsivity, compulsivity, processing speed. Systemic naloxone administration (5 mg/kg, i.p.) reversed these cognitive changes under the heavy perceptual load in 5-CSRTT. Using the novel object recognition (NOR), Y-maze and open-field test (OFT), the present study investigated the memory ability and locomotor activity. Naloxone reversed the effect of morphine on recognition memory and locomotion but had no effect on working memory. In addition, repeated morphine administration decreased the expression of postsynaptic density protein 95 (PSD95) and cAMP response element binding protein (CREB) phosphorylation in the prefrontal cortex (PFC) and hippocampus (HIP), and these effects were significantly reversed by naloxone in PFC. Our study suggests that repeated exposure to morphine affects multiple cognitive aspects and impairs synaptic functions. Systemic naloxone treatment reverses the mu-opioids-induced cognitive changes, especially under the heavy perceptual load, possibly by restoring the synaptic dysfunctions.

Effects of early postnatal MK-801 treatment on behavioral properties in rats: Differences according to treatment schedule

It has been proposed that animals administered early postnatal NMDA (N-methyl-d-aspartate) glutamate receptor antagonists represent a model of schizophrenia; however, drug treatment schedules remain quite different among these animal studies. In this study, we compared the behavioral effects of long-term (14-day) and short-term (5-day) early postnatal treatment of the NMDA receptor antagonist MK-801 (dizocilpine; 5-methyl-10,11-dihydro-5H-dibenzo[a,d]-cyclohepten-5,10-imine). In addition, different drug treatment periods were applied to the short-term treatment study in order to determine the critical developmental period of drug effects. For experiment 1, rats were treated with MK-801 (0.2 or 0.4 mg/kg, twice daily) during postnatal days (PNDs) 7-20. For experiment 2, MK-801 (0.2 mg/kg, twice daily) was administered during the periods of PNDs 7-11, 12-16, and 17-21. In adulthood, several behavioral tests, including prepulse inhibition, open-field, and spontaneous alternation tests, were performed in experiments 1 and 2. The delayed nonmatching-to-position task was also conducted in experiment 2 on separate rats treated for 5 days in the same manner. Our results indicated that the 14-day MK-801 treatment inhibited the prepulse inhibition and decreased immobility in the forced-swim test, whereas the 5-day MK-801 treatment induced only slight behavioral effects. Collectively, our findings suggest that long-term early postnatal treatment with an NMDA receptor antagonist may be detrimental to some behavioral functions, such as sensorimotor gating and stress coping; however, treatment for longer periods is needed to elicit detrimental effects.

General Anesthesia Does Not Have Persistent Effects on Attention in Rodents

Background: Studies in animals have shown that general anesthesia can cause persistent spatial memory impairment, but the influence of anesthetics on other cognitive functions is unclear. This study tested whether exposure to general anesthesia without surgery caused a persistent deficit in attention in rodents.

Methods: To evaluate whether anesthesia has persistent effects on attention, rats were randomized to three groups. Group A was exposed for 2 h to isoflurane anesthesia, and tested the following seven days for attentional deficits. Group B was used as a control and received room air before attentional testing. Since there is some evidence that a subanesthetic dose of ketamine can improve cognition and reduce disorders of attention after surgery, rats in group C were exposed to isoflurane anesthesia in combination with a ketamine injection before cognitive assessment. Attention was measured in rats using the 5-Choice Serial Reaction Time Task, for which animals were trained to respond with a nose poke on a touchscreen to a brief, unpredictable visual stimulus in one of five possible grid locations to receive a food reward. Attention was analyzed as % accuracy, % omission, and premature responses.

Results: Evaluating acute attention by comparing baseline values with data from the day after intervention did not reveal any differences in attentional measurements. No significant differences were seen in % accuracy, % omission, and premature responses for the three groups tested for 7 consecutive days.

Conclusion: These data in healthy rodents suggest that general anesthesia without surgery has no persistent effect on attention and the addition of ketamine does not alter the outcome.

Modulating Dopamine Signaling and Behavior with Chemogenetics: Concepts, Progress, and Challenges

For more than 60 years, dopamine (DA) has been known as a critical modulatory neurotransmitter regulating locomotion, reward-based motivation, and endocrine functions. Disturbances in DA signaling have been linked to an array of different neurologic and psychiatric disorders, including Parkinson's disease, schizophrenia, and addiction, but the underlying pathologic mechanisms have never been fully elucidated. One major obstacle limiting interpretation of standard pharmacological and transgenic interventions is the complexity of the DA system, which only appears to widen as research progresses. Nonetheless, development of new genetic tools, such as chemogenetics, has led to an entirely new era for functional studies of neuronal signaling. By exploiting receptors that are engineered to respond selectively to an otherwise inert ligand, so-called Designer Receptors Exclusively Activated by Designer Drugs (DREADDs), chemogenetics enables pharmacological remote control of neuronal activity. Here we review the recent, extensive application of this technique to the DA field and how its use has advanced the study of the DA system and contributed to our general understanding of DA signaling and related behaviors. Moreover, we discuss the challenges and pitfalls associated with the chemogenetic technology, such as the metabolism of the DREADD ligand clozapine N-oxide (CNO) to the D2 receptor antagonist clozapine. We conclude that despite the recent concerns regarding CNO, the chemogenetic toolbox provides an exceptional approach to study neuronal function. The huge potential should promote continued investigations and additional refinements to further expound key mechanisms of DA signaling and circuitries in normal as well as maladaptive behaviors.

Anterior Cingulate Cortex Input to the Claustrum Is Required for Top-Down Action Control

Cognitive abilities, such as volitional attention, operate under top-down, executive frontal cortical control of hierarchically lower structures. The circuit mechanisms underlying this process are unresolved. The claustrum possesses interconnectivity with many cortical areas and, thus, is hypothesized to orchestrate the cortical mantle for top-down control. Whether the claustrum receives top-down input and how this input may be processed by the claustrum have yet to be formally tested, however. We reveal that a rich anterior cingulate cortex (ACC) input to the claustrum encodes a preparatory top-down information signal on a five-choice response assay that is necessary for optimal task performance. We further show that ACC input monosynaptically targets claustrum inhibitory interneurons and spiny glutamatergic projection neurons, the latter of which amplify ACC input in a manner that is powerfully constrained by claustrum inhibitory microcircuitry. These results demonstrate ACC input to the claustrum is critical for top-down control guiding action.

Corticolimbic Mechanisms of Behavioral Inhibition under Threat of Punishment

Being able to limit the pursuit of reward to prevent negative consequences is an important expression of behavioral inhibition. Everyday examples of an inability to exert such control over behavior are the overconsumption of food and drugs of abuse, which are important factors in the development of obesity and addiction, respectively. Here, we use a behavioral task that assesses the ability of male rats to exert behavioral restraint at the mere sight of palatable food during the presentation of an audiovisual threat cue to investigate the corticolimbic underpinnings of behavioral inhibition. We demonstrate a prominent role for the medial prefrontal cortex in the exertion of control over behavior under threat of punishment. Moreover, task engagement relies on function of the ventral striatum, whereas the basolateral amygdala mediates processing of the threat cue. Together, these data show that inhibition of reward pursuit requires the coordinated action of a network of corticolimbic structures.SIGNIFICANCE STATEMENT There is a need for translational models that allow to dissect mechanisms underlying the processes involved in controlling behavior. In this study, we present a novel behavioral task that assesses the ability of rats to exert behavioral restraint over the consumption of a visually present sucrose pellet during the presentation of an audiovisual threat cue. This task requires relatively little behavioral training and it discerns distinct behavioral impairments, including a failure to retrieve stimulus value, a reduced task engagement, and compromised inhibition of behavior. Using pharmacological inactivations of different regions of the corticolimbic system of the rat, we demonstrate dissociable roles for the prefrontal cortex, amygdala, and striatum in inhibition of reward pursuit under threat of punishment.

TouchScreen-based phenotyping: altered stimulus/reward association and lower perseveration to gain a reward in mu opioid receptor knockout mice

While the contribution of Mu Opioid Receptors (MORs) to hedonic aspects of reward processing is well-established, the notion that these receptors may also regulate motivation to gain a reward, and possibly other related cognitive dimensions, has been less investigated. The prefrontal cortex (PFC) is a critical site for these processes. Our previous functional magnetic resonance imaging study found alterations of functional connectivity (FC) in reward/aversion networks in MOR knockout mice. Here we pursued voxelwise seed-based FC analyses using the same dataset with a focus on the PFC. We observed significant reduction of PFC FC in mutant mice, predominantly with the nucleus accumbens, supporting the notion of altered reward-driven top-down controls. We tested motivation for palatable food in a classical operant self-administration paradigm, and found delayed performance for mutant mice. We then evaluated motivational and cognitive abilities of MOR knockout mice in TouchScreen-based behavioral tests. Learning was delayed and stimulus/reward association was impaired, suggesting lower hedonic reward value and reduced motivation. Perseverative responses were decreased, while discriminatory behavior and attention were unchanged, indicative of increased inhibitory controls with otherwise intact cognitive performance. Together, our data suggest that MORs contribute to enhance reward-seeking and facilitate perseverative behaviors. The possibility that MOR blockade could reduce maladaptive compulsivity deserves further investigation in addiction and self-control disorder research.

Prior Exposure to Salient Win-Paired Cues in a Rat Gambling Task Increases Sensitivity to Cocaine Self-Administration and Suppresses Dopamine Efflux in Nucleus Accumbens: Support for the Reward Deficiency Hypothesis of Addiction

Rats trained to perform a version of the rat gambling task (rGT) in which salient audiovisual cues accompany reward delivery, similar to commercial gambling products, show greater preference for risky options. Given previous demonstrations that probabilistic reinforcement schedules can enhance psychostimulant-induced increases in accumbal DA and locomotor activity, we theorized that performing this cued task could perpetuate a proaddiction phenotype. Significantly more rats developed a preference for the risky options in the cued versus uncued rGT at baseline, and this bias was further exacerbated by cocaine self-administration, whereas the choice pattern of optimal decision-makers was unaffected. The addition of reward-paired cues therefore increased the proportion of rats exhibiting a maladaptive cognitive response to cocaine self-administration. Risky choice was not associated with responding for conditioned reinforcement or a marker of goal/sign-tracking, suggesting that reward-concurrent cues precipitate maladaptive choice via a unique mechanism unrelated to simple approach toward, or responding for, conditioned stimuli. Although "protected" from any resulting decision-making impairment, optimal decision-makers trained on the cued rGT nevertheless self-administered more cocaine than those trained on the uncued task. Collectively, these data suggest that repeated engagement with heavily cued probabilistic reward schedules can drive addiction vulnerability through multiple behavioral mechanisms. Rats trained on the cued rGT also exhibited blunted locomotor sensitization and lower basal accumbal DA levels, yet greater cocaine-induced increases in accumbal DA efflux. Gambling in the presence of salient cues may therefore result in an adaptive downregulation of the mesolimbic DA system, rendering individuals more sensitive to the deleterious effects of taking cocaine.SIGNIFICANCE STATEMENT Impaired cost/benefit decision making, exemplified by preference for the risky, disadvantageous options on the Iowa Gambling Task, is associated with greater risk of relapse and treatment failure in substance use disorder. Understanding factors that enhance preference for risk may help elucidate the neurobiological mechanisms underlying maladaptive decision making in addiction, thereby improving treatment outcomes. Problem gambling is also highly comorbid with substance use disorder, and many commercial gambling products incorporate salient win-paired cues. Here we show that adding reward-concurrent cues to a rat analog of the IGT precipitates a hypodopaminergic state, characterized by blunted accumbal DA efflux and attenuated locomotor sensitization, which may contribute to the enhanced responsivity to uncertain rewards or the reinforcing effects of cocaine we observed.

Differential effects of chemogenetic inhibition of dopamine and norepinephrine neurons in the mouse 5-choice serial reaction time task

Attention-deficit/hyperactivity disorder (ADHD) is a psychiatric disorder characterized by inattention, aberrant impulsivity, and hyperactivity. Although the underlying pathophysiology of ADHD remains unclear, dopamine and norepinephrine signaling originating from the ventral tegmental area (VTA) and locus coeruleus (LC) is thought to be critically involved. In this study, we employ Designer Receptor Exclusively Activated by Designer Drugs (DREADDs) together with the mouse 5-Choice Serial Reaction Time Task (5-CSRTT) to investigate the necessary roles of these catecholamines in ADHD-related behaviors, including attention, impulsivity, and motivation. By selective inhibition of tyrosine hydroxylase (TH)-positive VTA dopamine neurons expressing the Gi-coupled DREADD (hM4Di), we observed a marked impairment of effort-based motivation and subsequently speed and overall vigor of responding. At the highest clozapine N-oxide (CNO) dose tested (i.e. 2 mg/kg) to activate hM4Di, we detected a reduction in locomotor activity. DREADD-mediated inhibition of LC norepinephrine neurons reduced attentional performance in a variable stimulus duration test designed to increase task difficulty, specifically by increasing trials omissions, reducing mean score, and visual processing speed. These findings show that VTA dopamine and LC norepinephrine neurons differentially affect attention, impulsive and motivational control. In addition, this study highlights how molecular genetic probing of selective catecholamine circuits can provide valuable insights into the mechanisms underlying ADHD-relevant behaviors.

Controllability affects endocrine response of adolescent male rats to stress as well as impulsivity and behavioral flexibility during adulthood

Exposure to stress during adolescence exerts a long-term impact on behavior and might contribute to the development of several neuropsychiatric disorders. In adults, control over stress has been found to protect from the negative consequences of stress, but the influence of controllability at early ages has not been extensively studied. Here, we evaluated in a rodent model the effects of repeated exposure in adolescent male rats to controllable versus uncontrollable foot-shock stress (CST or UST, respectively). Rats were assigned to three groups: non-stress (stress-naïve), CST (exposed to 8 sessions of a two-way shuttle active avoidance task over a period of 22 days) and UST (receiving the same amount of shocks as CST, regardless of their actual behavior). During adulthood, different cohorts were tested in several tasks evaluating inhibitory control and cognitive flexibility: 5-choice serial reaction time, delay-discounting, gambling test and probabilistic reversal learning. Results showed that the hypothalamic-pituitary-adrenal response to the first shock session was similar in CST and UST animals, but the response to the 8^th session was lower in CST animals. In adulthood, the UST animals presented impaired motor (but not cognitive) impulsivity and more perseverative behavior. The behavioral effects of UST were associated with increased number of D2 dopamine receptors in dorsomedial striatum, but not in other striatal regions. In summary, UST exposure during adolescence induced long-term impairments in impulsivity and compulsivity, whereas CST had only minor effects. These data support a critical role of stress uncontrollability on the long-lasting consequences of stress, as a risk factor for mental illnesses.

Executive Function in Fragile X Syndrome: A Systematic Review

Executive function (EF) supports goal-directed behavior and includes key aspects such as working memory, inhibitory control, cognitive flexibility, attention, processing speed, and planning. Fragile X syndrome (FXS) is the leading inherited monogenic cause of intellectual disability and is phenotypically characterized by EF deficits beyond what is expected given general cognitive impairments. Yet, a systematic review of behavioral studies using performance-based measures is needed to provide a summary of EF deficits across domains in males and females with FXS, discuss clinical and biological correlates of these EF deficits, identify critical limitations in available research, and offer suggestions for future studies in this area. Ultimately, this review aims to advance our understanding of the underlying pathophysiological mechanisms contributing to EF in FXS and to inform the development of outcome measures of EF and identification of new treatment targets in FXS.

An automated home-cage-based 5-choice serial reaction time task for rapid assessment of attention and impulsivity in rats

RATIONALE

The 5-choice serial reaction time task (5-CSRTT) is a widely used operant task for measuring attention and motor impulsivity in rodents. Training animals in this task requires an extensive period of daily operant sessions. Recently, a self-paced, automated version of this task has been developed for mice, which substantially reduces training time. Whether a similar approach is effective for rats is currently unknown.

OBJECTIVE

Here, we tested whether attention and impulsivity can be assessed in rats with a self-paced version of the 5-CSRTT.

METHODS

Operant boxes were connected to home-cages with tunnels. Two groups of rats self-paced their training by means of an automated script. The first group of animals was allowed unlimited access (UA) to start trials in the task; for the second group, trial availability was restricted to the first 2.5 h of the dark cycle (TR). Task parameter manipulations, such as variable inter-trial intervals and stimulus durations as well as pharmacological challenges with scopolamine, were tested to validate the task.

RESULTS

Self-paced training took less than 1 week. Animals in the UA group showed higher levels of omissions compared with the TR group. In both protocols, variable inter-trial intervals increased impulsivity, and variable stimulus durations decreased attentional performance. Scopolamine affected cognitive performance in the TR group only.

CONCLUSIONS

Home-cage-based training of the 5-CSRTT in rats, especially the TR protocol, presents a valid and fast alternative for measuring attention and impulsivity.

Animal models of cognitive aging and circuit-specific vulnerability

Medial temporal lobe and prefrontal cortical structures are particularly vulnerable to dysfunction in advanced age and neurodegenerative diseases. This review focuses on cognitive aging studies in animals to illustrate the important aspects of the animal model paradigm for investigation of age-related memory and executive function loss. Particular attention is paid to the discussion of the face, construct, and predictive validity of animal models for determining the possible mechanisms of regional vulnerability in aging and for identifying novel therapeutic strategies. Aging is associated with a host of regionally specific neurobiologic alterations. Thus, targeted interventions that restore normal activity in one brain region may exacerbate aberrant activity in another, hindering the restoration of function at the behavioral level. As such, interventions that target the optimization of "cognitive networks" rather than discrete brain regions may be more effective for improving functional outcomes in the elderly.

Adverse neuropsychiatric development following perinatal brain injury: from a preclinical perspective

Perinatal brain injury is a leading cause of death and disability in young children. Recent advances in obstetrics, reproductive medicine and neonatal intensive care have resulted in significantly higher survival rates of preterm or sick born neonates, at the price of increased prevalence of neurological, behavioural and psychiatric problems in later life. Therefore, the current focus of experimental research shifts from immediate injury processes to the consequences for brain function in later life. The aetiology of perinatal brain injury is multi-factorial involving maternal and also labour-associated factors, including not only placental insufficiency and hypoxia-ischaemia but also exposure to high oxygen concentrations, maternal infection yielding excess inflammation, genetic factors and stress as important players, all of them associated with adverse long-term neurological outcome. Several animal models addressing these noxious stimuli have been established in the past to unravel the underlying molecular and cellular mechanisms of altered brain development. In spite of substantial efforts to investigate short-term consequences, preclinical evaluation of the long-term sequelae for the development of cognitive and neuropsychiatric disorders have rarely been addressed. This review will summarise and discuss not only current evidence but also requirements for experimental research providing a causal link between insults to the developing brain and long-lasting neurodevelopmental disorders.

Modelling Differential Vulnerability to Substance Use Disorder in Rodents: Neurobiological Mechanisms

Despite the prevalence of drug use within society, only a subset of individuals actively taking addictive drugs lose control over their intake and develop compulsive drug-seeking and intake that typifies substance use disorder (SUD). Although research in this field continues to be an important and dynamic discipline, the specific neuroadaptations that drive compulsive behaviour in humans addicted to drugs and the neurobiological mechanisms that underlie an individual's innate susceptibility to SUD remain surprisingly poorly understood. Nonetheless, it is clear from research within the clinical domain that some behavioural traits are recurrently co-expressed in individuals with SUD, thereby inviting the hypothesis that certain behavioural endophenotypes may be predictive, or at least act in some way, to modify an individual's probability for developing this disorder. The analysis of such endophenotypes and their catalytic relationship to the expression of addiction-related behaviours has been greatly augmented by experimental approaches in rodents that attempt to capture diagnostically relevant aspects of this progressive brain disorder. This work has evolved from an early focus on aberrant drug reinforcement mechanisms to a now much richer account of the putatively impaired cognitive control processes that ultimately determine individual trajectories to compulsive drug-related behaviours. In this chapter we discuss the utility of experimental approaches in rodents designed to elucidate the neurobiological and genetic underpinnings of so-called risk traits and how these innate vulnerabilities collectively contribute to the pathogenesis of SUD.

Brain and Cognition for Addiction Medicine: From Prevention to Recovery Neural Substrates for Treatment of Psychostimulant-Induced Cognitive Deficits

Addiction to psychostimulants like cocaine, methamphetamine, and nicotine poses a continuing medical and social challenge both in the United States and all over the world. Despite a desire to quit drug use, return to drug use after a period of abstinence is a common problem among individuals dependent on psychostimulants. Recovery for psychostimulant drug-dependent individuals is particularly challenging because psychostimulant drugs induce significant changes in brain regions associated with cognitive functions leading to cognitive deficits. These cognitive deficits include impairments in learning/memory, poor decision making, and impaired control of behavioral output. Importantly, these drug-induced cognitive deficits often impact adherence to addiction treatment programs and predispose abstinent addicts to drug use relapse. Additionally, these cognitive deficits impact effective social and professional rehabilitation of abstinent addicts. The goal of this paper is to review neural substrates based on animal studies that could be pharmacologically targeted to reverse psychostimulant-induced cognitive deficits such as impulsivity and impairment in learning and memory. Further, the review will discuss neural substrates that could be used to facilitate extinction learning and thus reduce emotional and behavioral responses to drug-associated cues. Moreover, the review will discuss some non-pharmacological approaches that could be used either alone or in combination with pharmacological compounds to treat the above-mentioned cognitive deficits. Psychostimulant addiction treatment, which includes treatment for cognitive deficits, will help promote abstinence and allow for better rehabilitation and integration of abstinent individuals into society.

Dysregulation of the Lateral Habenula in Major Depressive Disorder

Clinical and preclinical evidence implicates hyperexcitability of the lateral habenula (LHb) in the development of psychiatric disorders including major depressive disorder (MDD). This discrete epithalamic nucleus acts as a relay hub linking forebrain limbic structures with midbrain aminergic centers. Central to reward processing, learning and goal directed behavior, the LHb has emerged as a critical regulator of the behaviors that are impaired in depression. Stress-induced activation of the LHb produces depressive- and anxiety-like behaviors, anhedonia and aversion in preclinical studies. Moreover, deep brain stimulation of the LHb in humans has been shown to alleviate chronic unremitting depression in treatment resistant depression. The diverse neurochemical processes arising in the LHb that underscore the emergence and treatment of MDD are considered in this review, including recent optogenetic studies that probe the anatomical connections of the LHb.

Indices of comparative cognition: assessing animal models of human brain function

Understanding the cognitive capacities of animals is important, because (a) several animal models of human neurodegenerative disease are considered poor representatives of the human equivalent and (b) cognitive capacities may provide insight into alternative animal models. We used a three-stage process of cognitive and neuroanatomical comparison (using sheep as an example) to assess the appropriateness of a species to model human brain function. First, a cognitive task was defined via a reinforcement-learning algorithm where values/constants in the algorithm were taken as indirect measures of neurophysiological attributes. Second, cognitive data (values/constants) were generated for the example species (sheep) and compared to other species. Third, cognitive data were compared with neuroanatomical metrics for each species (endocranial volume, gyrification index, encephalisation quotient, and number of cortical neurons). Four breeds of sheep (n = 15/sheep) were tested using the two-choice discrimination-reversal task. The 'reversal index' was used as a measure of constants within the learning algorithm. Reversal index data ranked sheep as third in a table of species that included primates, dogs, and pigs. Across all species, number of cortical neurons correlated strongest against the reversal index (r2 = 0.66, p = 0.0075) followed by encephalization quotient (r2 = 0.42, p = 0.03), endocranial volume (r2 = 0.30, p = 0.08), and gyrification index (r2 = 0.16, p = 0.23). Sheep have a high predicted level of cognitive capacity and are thus a valid alternative model for neurodegenerative research. Using learning algorithms within cognitive tasks increases the resolution of methods of comparative cognition and can help to identify the most relevant species to model human brain function and dysfunction.

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.

Vigilance demand and the effects of stimulant drugs in a five-choice reaction-time procedure in mice

Stimulant drugs used for treating attention-deficit hyperactivity disorder (ADHD) increase signal-detection accuracy in five-choice serial reaction-time procedures. These increases may result from drug-induced increases in control exerted by the stimuli that prompt responses, which was assessed in the present study. Mice were trained with food reinforcement to nose poke into one of five holes after its illumination (signal), and effects of methylphenidate, d-amphetamine, and pentobarbital were assessed. Subsequently, the time from trial onset to signal was changed from fixed to variable for one group of subjects. A 'warning' stimulus (change in ambient lighting) preceding the signal was added for a second group. Effects of the drugs were reassessed. Dose-related increases in accuracy of signal detection (nose pokes in hole where a signal was displayed) were obtained with methylphenidate and d-amphetamine, but not with pentobarbital. When the presignal time was variable, increases in signal detection were not obtained with either stimulant. When a warning stimulus preceded the signal, the increases in accuracy were similar to those obtained without the warning stimulus. Hence, a procedure that increased vigilance demand (using a variable prestimulus period) eliminated the effects of drugs useful in treating ADHD, whereas a procedure that decreased vigilance demand (adding the warning light) had no appreciable effects on the response to stimulant drugs. Taken together, the present results suggest that the five-choice serial reaction-time has predictive validity for selecting drugs effective for treating ADHD, although effects can depend critically on the stimulus conditions used and the vigilance required by the procedure.

Cisplatin treatment induces attention deficits and impairs synaptic integrity in the prefrontal cortex in mice

Patients treated for cancer frequently experience chemobrain, characterized by impaired memory and reduced attention. These deficits often persist after treatment, and no preventive or curative interventions exist. In mice, we assessed the effect of cisplatin chemotherapy on attention using the 5-choice serial reaction time task and on synaptic integrity. We also assessed the capacity of mesenchymal stem cells to normalize the characteristics of chemobrain. Mice were trained in the 5-choice serial reaction time task. After reaching advancement criteria at a 4-second stimulus time, they were treated with cisplatin followed by nasal administration of mesenchymal stem cells. Cisplatin reduced the percentage of correct responses due to an increase in omissions, indicating attention deficits. Mesenchymal stem cell treatment reversed these cisplatin-induced deficits in attention. Cisplatin also induced abnormalities in markers of synaptic integrity in the prefrontal cortex. Specifically, cisplatin decreased expression of the global presynaptic marker synaptophysin and the glutamatergic presynaptic marker vGlut2. Expression of the presynaptic GABAergic marker vGAT increased. Nasal mesenchymal stem cell administration normalized these markers of synaptic integrity. In conclusion, cisplatin induces long-lasting attention deficits that are associated with decreased synaptic integrity in the prefrontal cortex. Nasal administration of mesenchymal stem cells reversed these behavioural and structural deficits.

Pramipexole-induced impulsivity in mildparkinsonian rats: a model of impulse control disorders in Parkinson's disease

Treatment with dopaminergic agonists such as pramipexole (PPX) contributes to the development of impulse control disorders (ICDs) in patients with Parkinson's disease (PD). As such, animal models of abnormal impulse control in PD are needed to better study the pathophysiology of these behaviors. Thus, we investigated impulsivity and related behaviors using the 5-choice serial reaction time task, as well as FosB/ΔFosB expression, in rats with mild parkinsonism induced by viral-mediated substantia nigra overexpression of human A53T mutated α-synuclein, and following chronic PPX treatment (0.25 mg/kg/d) for 4 weeks. The bilateral loss of striatal dopamine transporters (64%) increased the premature response rate of these rats, indicating enhanced waiting impulsivity. This behavior persisted in the OFF state after the second week of PPX treatment and it was further exacerbated in the ON state throughout the treatment period. The enhanced rate of premature responses following dopaminergic denervation was positively correlated with the premature response rate following PPX treatment (both in the ON and OFF states). Moreover, the striatal dopaminergic deficit was negatively correlated with the premature response rate at all times (pretreatment, ON and OFF states) and it was positively correlated with the striatal FosB/ΔFosB expression. By contrast, PPX treatment was not associated with changes in compulsivity (perseverative responses rate). This model recapitulates some features of PD with ICD, namely the dopaminergic deficit of early PD and the impulsivity traits provoked by dopaminergic loss in association with PPX treatment, making this model a useful tool to study the pathophysiology of ICDs.

Investigating the Neurological Correlates of Workplace Deviance Using a Rodent Model of Extinction

Employee deviance and time theft is an expensive and pervasive workplace problem. Research indicates that a primary reason employees engage in deviant behaviour is the perception of injustice often associated with psychological contract breach (i.e., broken promises). This study used a rodent model to mimic said experience of broken promises and then examined the subsequent neurophysiological changes that lead to the display of deviant behaviours. Specifically, we generated a psychological contract using a 3 choice serial reaction task, then broke the promise, and finally examined deviant behaviours and neurological correlates. After the broken promise, rats had elevated levels of corticosterone and testosterone, engaged in riskier behaviour, and were more aggressive. The most prominent changes in gene expression were associated with serotonin and stress, and were found in the nucleus accumbens. This study highlights the value of pre-clinical models in the investigation of the theoretical tenants of industrial and organizational psychology.

A new human delayed-matching-to-place test in a virtual environment reverse-translated from the rodent watermaze paradigm: Characterization of performance measures and sex differences

Watermaze tests of place learning and memory in rodents and corresponding reverse-translated human paradigms in real or virtual environments are key tools to study hippocampal function. In common variants, the animal or human participant has to find a hidden goal that remains in the same place over many trials, allowing for incremental learning of the place with reference to distal cues surrounding the circular, featureless maze. Although the hippocampus is involved in incremental place learning, rodent studies have shown that the delayed-matching-to-place (DMP) watermaze test is a more sensitive assay of hippocampal function. On the DMP test, the goal location changes every four trials, requiring the rapid updating of place memory. Here, we developed a virtual DMP test reverse-translated from the rat watermaze DMP paradigm. In two replications, participants showed 1-trial place learning, evidenced by marked latency and path length savings between Trials 1 and 2 to the same goal location, and by search preference for the vicinity of the goal when Trial 2 was run as probe trial (during which the goal was removed). The performance was remarkably similar to rats' performance on the watermaze DMP test. In both replications, male participants showed greater savings and search preferences compared to female participants. Male participants also showed better mental rotation performance, although mental rotation scores did not consistently correlate with DMP performance measures, pointing to distinct neurocognitive mechanisms. The remarkable similarity between rodent and human DMP performance suggests similar underlying neuro-psychological mechanisms, including hippocampus dependence. The new virtual DMP test may, therefore, provide a sensitive tool to probe human hippocampal function.

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.

Kappa opioid receptors mediate yohimbine-induced increases in impulsivity in the 5-choice serial reaction time task

Dynorphin (DYN), and its receptor, the kappa opioid receptor (KOR) are involved in drug seeking and relapse but the mechanisms are poorly understood. One hypothesis is that DYN/KOR activation promotes drug seeking through increased impulsivity, because many stimuli that induce DYN release increase impulsivity. Here, we systematically compare the effects of drugs that activate DYN/KOR on performance on the 5-choice serial reaction time task (5-CSRTT), a test of sustained attention and impulsivity. In Experiment 1, we determined the effects of U50,488 (0, 2.5, 5 mg/kg), yohimbine (0, 1.25, 2.5 mg/kg), and nicotine (0, 0.15, 0.3 mg/kg) on 5-CSRTT performance. In Experiment 2, we determined the effects of alcohol (0, 0.5, 1.0, 1.5 g/kg) on 5-CSRTT performance before and after voluntary, intermittent alcohol exposure. In Experiment 3, we determined the potential role of KOR in the pro-impulsive effects of yohimbine (1.25 mg/kg) and nicotine (0.3 mg/kg) by the prior administration of the KOR antagonist nor-BNI (10 mg/kg). Premature responding, the primary measure of impulsivity, was reduced by U50,488 and alcohol, but these drugs had a general suppressive effect. Yohimbine and nicotine increased premature responding. Yohimbine-, but not nicotine-induced increases in premature responding were blocked by nor-BNI, suggesting that impulsivity induced by yohimbine is KOR dependent. This may suggests a potential role for KOR-mediated increases in impulsivity in yohimbine-induced reinstatement.