Measuring impulsivity in mice: the five-choice serial reaction time task

BK channel dysfunction disrupts attention-controlled behaviors and altered perseverative responses in murine instrumental learning

This study examined the effect of knockout of KCNMA1 gene, coding for the BK channel, on cognitive and attentional functions in mice, with an aim to better understand its implications for human neurodevelopmental disorders. The study used the 3-choice serial reaction time task (3-CSRTT) to assess the learning performance, attentional abilities, and repetitive behaviors in mice lacking the KCNMA1 gene (KCNMA1-/-) compared to wild-type (WT) controls. Results showed no significant differences in learning accuracy between the two groups. However, KCNMA1-/- mice were more prone to omitting responses to stimuli. In addition, when the timing of cue presentation was randomized, the KCNMA1-/- showed premature responses. Notably, these mice also demonstrated a marked reduction in perseverative responses, which include repeated nose-poke behaviors following decisions. These findings highlight the involvement of the KCNMA1 gene in managing attention, impulsivity, and potentially moderating repetitive actions.

Inhibitory control in teleost fish: a methodological and conceptual review

Inhibitory control (IC) plays a central role in behaviour control allowing an individual to resist external lures and internal predispositions. While IC has been consistently investigated in humans, other mammals, and birds, research has only recently begun to explore IC in other vertebrates. This review examines current literature on teleost fish, focusing on both methodological and conceptual aspects. I describe the main paradigms adopted to study IC in fish, identifying well-established tasks that fit various research applications and highlighting their advantages and limitations. In the conceptual analysis, I identify two well-developed lines of research with fish examining IC. The first line focuses on a comparative approach aimed to describe IC at the level of species and to understand the evolution of interspecific differences in relation to ecological specialisation, brain size, and factors affecting cognitive performance. Findings suggest several similarities between fish and previously studied vertebrates. The second line of research focuses on intraspecific variability of IC. Available results indicate substantial variation in fish IC related to sex, personality, genetic, age, and phenotypic plasticity, aligning with what is observed with other vertebrates. Overall, this review suggests that although data on teleosts are still scarce compared to mammals, the contribution of this group to IC research is already substantial and can further increase in various disciplines including comparative psychology, cognitive ecology, and neurosciences, and even in applied fields such as psychiatry research.

Repeated Cocaine Intake Differentially Impacts Striatal D2/3 Receptor Availability, Psychostimulant-Induced Dopamine Release, and Trait Behavioral Markers of Drug Abuse

Current research indicates that altered dopamine (DA) transmission in the striatum contributes to impulsivity and novelty-seeking, and it may mediate a link concerning a higher susceptibility to drug abuse. Whether increased susceptibility to drug abuse results from a hyperdopaminergic or hypodopaminergic state is still debated. Here, we simultaneously tracked changes in DA D2/3 receptor (D2/3R) availability and amphetamine-(AMPH)-induced DA release in relation to impulsivity and novelty-seeking prior to, and following, cocaine self-administration (SA) in Roman high- (RHA) and low- (RLA) avoidance rats. We found that high-impulsive/high novelty-seeking RHA rats exhibited lower D2/3R availabilities and higher AMPH-induced DA release in the striatum that predicted higher levels of cocaine intake compared with RLAs. Cocaine SA did not alter striatal D2/3R availability or impulsivity in RHA or RLA rats. Critically, cocaine exposure led to a baseline-dependent blunting of stimulated DA release in high-impulsive/high novelty-seeking RHA rats only, and to a baseline-dependent increase in novelty-seeking in low-impulsive/low novelty-seeking RLA rats only. Altogether, we propose that susceptibility to drug abuse results from an innate hyper-responsive DA system, promoting impulsive action and novelty-seeking, and producing stronger initial drug-reinforcing effects that contribute to the initiation and perpetuation of drug use. However, with repeated cocaine use, a tolerance to drug-induced striatal DA elevations develops, leading to a compensatory increase in drug consumption to overcome the reduced reward effects.

Assessing the nature of premature responses in the rodent continuous performance test variable intertrial interval schedule using atomoxetine and amphetamine

BACKGROUND

Rodent operant tests that include premature responses (PR) as a measure of impulsivity commonly use variable intertrial interval (vITI) schedules. The rodent continuous performance test (rCPT) is suitable for a vITI schedule.

NEW METHOD

We optimised the analysis for a rCPT vITI schedule with intertrial intervals (ITIs) of 3, 6, and 12 s. Examining the nature of first (FiT) and following touches (FoT) to the blank screen led to a separate quantification of these two behaviours into the first touches level (%FiT) and the following-to-first touches ratio (FoT/FiT).

RESULTS

FiTs occurred more frequently in the 12 s ITIs than at shorter ITIs. Within 12 s ITIs, %FiT was only moderately higher during the last half than the first half, suggesting that long ITIs have a minimal effect on impulsivity, but allow a longer time for its detection. %FiT and the FoT/FiT ratio were uncorrelated. %FiT was negatively correlated with response criterion (C) and uncorrelated with discriminability. Conversely, FoT/FiT ratio was negatively correlated with discriminability, without correlation to C. Atomoxetine decreased %FiT but did not affect FoT/FiT ratio. Amphetamine increased %FiT and decreased the FoT/FiT ratio.

COMPARISON WITH EXISTING METHOD(S)

The results suggest that %FiT is analogous to %PR in related tasks and is a more suitable measure of waiting impulsivity in the rCPT. FoT/FiT ratio is unrelated to %FiT.

CONCLUSIONS

Long ITIs increase the detectability of, but has minimal effect on, waiting impulsivity. %FiT is analogous to %PR in related tasks, while the FoT/FiT ratio is a separate behaviour requiring further characterization.

Cell-type-specific population dynamics of diverse reward computations

Computational analysis of cellular activity has developed largely independently of modern transcriptomic cell typology, but integrating these approaches may be essential for full insight into cellular-level mechanisms underlying brain function and dysfunction. Applying this approach to the habenula (a structure with diverse, intermingled molecular, anatomical, and computational features), we identified encoding of reward-predictive cues and reward outcomes in distinct genetically defined neural populations, including TH+ cells and Tac1+ cells. Data from genetically targeted recordings were used to train an optimized nonlinear dynamical systems model and revealed activity dynamics consistent with a line attractor. High-density, cell-type-specific electrophysiological recordings and optogenetic perturbation provided supporting evidence for this model. Reverse-engineering predicted how Tac1+ cells might integrate reward history, which was complemented by in vivo experimentation. This integrated approach describes a process by which data-driven computational models of population activity can generate and frame actionable hypotheses for cell-type-specific investigation in biological systems.

Dissociation of impulsive traits by subthalamic metabotropic glutamate receptor 4

Behavioral strategies require gating of premature responses to optimize outcomes. Several brain areas control impulsive actions, but the neuronal basis of natural variation in impulsivity between individuals remains largely unknown. Here, by combining a Go/No-Go behavioral assay with resting-state (rs) functional MRI in mice, we identified the subthalamic nucleus (STN), a known gate for motor control in the basal ganglia, as a major hotspot for trait impulsivity. In vivo recorded STN neural activity encoded impulsive action as a separable state from basic motor control, characterized by decoupled STN/substantia nigra pars reticulata (SNr) mesoscale networks. Optogenetic modulation of STN activity bidirectionally controlled impulsive behavior. Pharmacological and genetic manipulations showed that these impulsive actions are modulated by metabotropic glutamate receptor 4 (mGlu4) function in STN and its coupling to SNr in a behavioral trait-dependent manner, and independently of general motor function. In conclusion, STN circuitry multiplexes motor control and trait impulsivity, which are molecularly dissociated by mGlu4. This provides a potential mechanism for the genetic modulation of impulsive behavior, a clinically relevant predictor for developing psychiatric disorders associated with impulsivity.

Lytic Cell Death in Specific Microglial Subsets Is Required for Preventing Atypical Behavior in Mice

Microglial cells are known to contribute to brain development and behaviors, but the mechanisms behind such functions are not fully understood. Here, we show that mice deficient in inflammasome regulators, including caspase-1 (Casp1), NLR family pyrin domain containing 3 (Nlrp3), IL-1 receptor (Il-1r), and gasdermin D (Gsdmd), exhibit behavior abnormalities characterized by hyperactivity and low anxiety levels. Furthermore, we found that expression of Casp1 in CX3CR1⁺ myeloid cells, which includes microglia, is required for preventing these abnormal behaviors. Through tissue clearing and 3D imaging, we discovered that small numbers of Cx3cr1-GFP⁺ fetal microglial cells formed clusters and underwent lytic cell death in the primitive thalamus and striatum between embryonic day (E)12.5 and E14.5. This lytic cell death was diminished in Casp1-deficient mice. Further analysis of the microglial clusters showed the presence of Pax6⁺ neural progenitor cells (NPCs); thus, we hypothesized that microglial lytic cell death is important for proper neuronal development. Indeed, increased numbers of neurons were observed in the thalamic subset in adult Casp1^−/− brains. Finally, injection of drug inhibitors of NLRP3 and CASP1 into wild-type (WT) pregnant mice from E12.5 to E14.5, the period when lytic cell death was detected, was sufficient to induce atypical behaviors in offspring. Taken together, our data suggests that the inflammasome cascade in microglia is important for regulating neuronal development and normal behaviors, and that genetic or pharmacological inhibition of this pathway can induce atypical behaviors in mice.

Brain-Derived neurotrophic factor Val66Met induces female-specific changes in impulsive behaviour and alcohol self-administration in mice

Substance use disorders are a debilitating neuropsychiatric condition, however it remains unclear why some individuals are at greater risk of substance use disorders than others and what genetic factors determine such individual differences. Impulsivity appears a promising candidate endophenotype to bridge the gap between genetic risk and addiction. Brain-derived neurotrophic factor (BDNF), and in particular the BDNF^Val66Met polymorphism, has been suggested to be involved in both impulsivity and substance use disorders, however results so far have been inconsistent. To investigate the role of BDNF, and more specifically the BDNF^Val66Met polymorphism, in both impulsivity and operant alcohol self-administration using the same animal model. Separate cohorts of humanized Val66Met transgenic mice were assessed for either trait impulsivity in the 5-choice serial reaction time (5-CSRT) touchscreen task, or propensity towards obtaining ethanol in an operant paradigm. It was found that female hBDNF^Val/Val mice exhibited both greater impulsivity compared to hBDNF^Met/Met mice of the same sex as shown by a higher number of premature responses at one of three increased inter-trial intervals tested in the 5-CSRT task, and a greater propensity toward stable ethanol self-administration relative to male mice of the same genotype in the operant paradigm. By contrast, male mice showed no difference between genotypes in impulsivity or stable ethanol self-administration. The hBDNF^Met/Met genotype appears to sex-specifically alter aspects of both impulsive behaviour and addiction propensity. These results suggest that impulse behaviour may be a possible predictor of addiction risk.

Sex differences in impulsivity in adult rats are mediated by organizational actions of neonatal gonadal hormones and not by hormones acting at puberty or in adulthood

Males as compared to females display increased impulsivity and inefficient inhibitory control and are more frequently diagnosed with disorders characterized by impulsivity. We previously demonstrated male rats make more impulsive action responses (i.e. premature responding) than females on the 5-choice serial reaction time task (5-CSRTT). Furthermore, pre-pubertal male rats make more impulsive choice responses (i.e. choosing an immediate small reward over a delayed larger reward) than females on a delayed-based reward T-maze task. The goal of the current work was to determine if gonadal hormones impact sex differences in impulsivity in adult rats. In an initial experiment, male and female rats underwent sham surgeries or were gonadectomized either pre-pubertally or during adulthood and tested on the 5-CSRTT in adulthood. Males displayed more impulsive action responses than females regardless of hormone status. In a second experiment, females received testosterone or vehicle injections on postnatal days 1 and 2. Males received vehicle injections. All rats were gonadectomized prior to puberty and tested on the 5-CSRTT in adulthood. Females treated neonatally with testosterone and control males made more impulsive action responses than control females. In another set of experiments, manipulation of gonadal hormones led to no differences in performance on the delayed-based reward T-maze task in males and females. Results indicate that no sex difference is apparent in impulsive choice on a delayed-base reward task in adult rats. They also reveal that adult sex differences on a task of impulsive action is mediated by organizational effects of gonadal hormones acting during the neonatal period and not impacted by hormones acting during puberty or adulthood.

Revealing a compulsive phenotype in cholinergic M4-/- mice depends on the inter-trial interval initiation settings in a five choice serial reaction time task

BACKGROUND

Muscarinic acetylcholine receptor 4 (M₄) modulates dopaminergic neurotransmission and is a target for novel treatments of schizophrenia, cognitive deficits, and addiction. Impulsive and compulsive behaviors are key traits of addiction, yet the importance of M₄ receptor signaling to these traits is poorly understood. We investigated impulsive action and compulsivity by measuring premature and perseverative responses in the five choice serial reaction time task (5CSRTT). Furthermore, we hypothesized that inter-trial interval (ITI) initiation settings affected training durations and test performances in these experiments.

METHODS

M₄^-/- and wildtype mice were trained and tested on two versions of the 5CSRTT with different ITI initiation settings. One setting, the head-in condition, allowed the ITI to start while the mouse's head remained in the reward receptacle (magazine). The other setting, the head-out condition, required the mouse to remove its head from the magazine to initiate the ITI.

RESULTS AND DISCUSSION

We did not observe differences in premature or perseverative responses in M₄^-/- mice in either condition, but found evidence of reward-related compulsive behavior in M₄^-/- mice. In the head-in condition, M₄^-/- mice were slower to acquire the 5CSRTT, had more omissions, and had longer correct response latencies than wildtype mice. In the head-out condition, genotypes did not differ in training, but M₄^-/- mice showed small decreases in accuracy. Our findings demonstrate that ITI initiation settings contribute to different training durations and tested behaviors in M₄^-/- mice, suggesting ITI initiation settings are an important consideration for the general use of the 5CSRTT.

Understanding Addiction Using Animal Models

Drug addiction is a neuropsychiatric disorder with grave personal consequences that has an extraordinary global economic impact. Despite decades of research, the options available to treat addiction are often ineffective because our rudimentary understanding of drug-induced pathology in brain circuits and synaptic physiology inhibits the rational design of successful therapies. This understanding will arise first from animal models of addiction where experimentation at the level of circuits and molecular biology is possible. We will review the most common preclinical models of addictive behavior and discuss the advantages and disadvantages of each. This includes non-contingent models in which animals are passively exposed to rewarding substances, as well as widely used contingent models such as drug self-administration and relapse. For the latter, we elaborate on the different ways of mimicking craving and relapse, which include using acute stress, drug administration or exposure to cues and contexts previously paired with drug self-administration. We further describe paradigms where drug-taking is challenged by alternative rewards, such as appetitive foods or social interaction. In an attempt to better model the individual vulnerability to drug abuse that characterizes human addiction, the field has also established preclinical paradigms in which drug-induced behaviors are ranked by various criteria of drug use in the presence of negative consequences. Separation of more vulnerable animals according to these criteria, along with other innate predispositions including goal- or sign-tracking, sensation-seeking behavior or impulsivity, has established individual genetic susceptibilities to developing drug addiction and relapse vulnerability. We further examine current models of behavioral addictions such as gambling, a disorder included in the DSM-5, and exercise, mentioned in the DSM-5 but not included yet due to insufficient peer-reviewed evidence. Finally, after reviewing the face validity of the aforementioned models, we consider the most common standardized tests used by pharmaceutical companies to assess the addictive potential of a drug during clinical trials.

Response-inhibition capacity in spontaneously hypertensive and Wistar rats: acquisition of fixed minimum interval performance and responsiveness to D-amphetamine

Reduced response-inhibition capacity is a defining feature of attention-deficit hyperactivity disorder. The fixed minimum interval (FMI) schedule has been systematically validated to assess such capacity in rats. On each FMI trial, the first lever press initiates an inter-response time (IRT); a potentially consummatory response terminates the IRT; only IRTs longer than a target interval result in access to food. Despite task validity, steady-state FMI performance in the most common animal model of attention-deficit hyperactivity disorder, the spontaneously hypertensive rat (SHR), is similar to normotensive control performance, even though SHR performs at lower levels, especially during acquisition, in similar response-withholding tasks. To determine whether such limitations of the model are specific to stable-state performance, this experiment compared FMI 6-s performance in SHR and Wistar rats during acquisition and in steady state, and assessed the effect of acute D-amphetamine (AMP) administration (0.1, 0.5, and 1.0 mg/kg) on steady-state performance. Median latencies to first lever press were consistently shorter in SHR than in Wistar rats; IRTs were shorter for SHR than for Wistar rats during acquisition, but substantially less so during asymptotic performance. AMP dose-dependently reduced latencies, shortened IRTs, and, at the highest dose, increased the proportion of IRTs under schedule control. These results suggest that, relative to Wistar rats, SHR have a reduced capacity to learn to withhold a reinforced response; once the FMI is acquired, high doses of D-AMP disrupt withholding performance in both strains, but they also enhance the responsiveness of both strains to reinforcement contingencies.

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.

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.

Dopamine D2 receptor-mediated circuit from the central amygdala to the bed nucleus of the stria terminalis regulates impulsive behavior

Impulsivity is closely associated with addictive disorders, and changes in the brain dopamine system have been proposed to affect impulse control in reward-related behaviors. However, the central neural pathways through which the dopamine system controls impulsive behavior are still unclear. We found that the absence of the D2 dopamine receptor (D2R) increased impulsive behavior in mice, whereas restoration of D2R expression specifically in the central amygdala (CeA) of D2R knockout mice (Drd2 ^-/- ) normalized their enhanced impulsivity. Inhibitory synaptic output from D2R-expressing neurons in the CeA underlies modulation of impulsive behavior because optogenetic activation of D2R-positive inhibitory neurons that project from the CeA to the bed nucleus of the stria terminalis (BNST) attenuate such behavior. Our identification of the key contribution of D2R-expressing neurons in the CeA → BNST circuit to the control of impulsive behavior reveals a pathway that could serve as a target for approaches to the management of neuropsychiatric disorders associated with impulsivity.

Dopamine D2 Receptors in Dopaminergic Neurons Modulate Performance in a Reversal Learning Task in Mice

Neuroimaging studies in animal models and human subjects have each revealed that relatively low striatal dopamine D2-like receptor binding potential is associated with poor impulse control and with vulnerability for addiction-related behaviors. These studies cannot, however, disambiguate the roles for various pools of D2 receptors found in the striatum (e.g., those expressed on medium spiny striato-pallidal neurons vs on dopamine-releasing nerve terminals) in these behavioral outcomes. To clarify the role of the latter pool, namely, D2 autoreceptors, we studied mice carrying a conditional DRD2 gene, with or without Cre-recombinase expressed under the transcriptional control of the dopamine transporter gene locus (autoDrd2-KO, n = 19 and controls, n = 21). These mice were tested for locomotor response to cocaine, and spatial reversal learning was assessed in operant conditioning chambers. As predicted, compared to control mice, autoDrd2-KO animals demonstrated heightened sensitivity to the locomotor stimulating effect of cocaine (10 mg/kg, i.p.), confirming previous research using a similar genetic model. In the spatial reversal learning task, autoDrd2-KO mice were slower to reach a learning criterion and had difficulty sustaining a prolonged nose poke response, measurements conceptually related to impaired response inhibition. Rate of learning of the initial discrimination and latencies to collect rewards, to initiate trials and to produce a response were unaffected by genetic deletion of D2 autoreceptors, discarding possible motor and motivational factors. Together, these findings confirm the role of D2 autoreceptors in reversal learning and suggest a broader involvement in behavioral inhibition mechanisms.

Influence of intertrial interval on basal and drug-induced impulsive action in the 5-choice serial reaction time task: Effects of d-amphetamine and (±)-2,5-dimethoxy-4-iodoamphetamine (DOI)

Impulsivity is a characteristic of a number of neuropsychiatric disorders such as attention-deficit/hyperactivity disorder. The 5-choice serial reaction time task (5-CSRTT) is a rodent paradigm extensively used to assess attention and impulsivity. Notably, 5-CSRTT studies do not typically account for the reduction in premature responding, the measure of impulsive action, occurring upon repeated exposure to test sessions with long or variable intertrial intervals (ITIs). This present 5-CSRTT study investigated the use of variable ITIs (5, 10 or 15s) across 15 test days (4 training days followed by 1 drug test day per week for three weeks) as previous experience had shown that 4 training days would be sufficient to induce consistent premature response levels in male C57BL/6J mice. Once a steady state was achieved, the effects of dextroamphetamine (AMPH) and (±)-2,5-dimethoxy-4-iodoamphetamine (DOI) were then assessed using a Latin-square design to determine whether pharmacological-induced impulsive actions depended on ITI length. Mice habituated to the variable ITI schedule after only 3days and showed consistently lower premature response levels until the end of the study. AMPH (p<0.05) and DOI (p<0.05) increased the percentage of premature responses at 15s ITI trials, while only DOI (p<0.05) increased impulsive action at 10s ITI trials. Additionally, DOI increased omission rates (p<0.001), mean correct latency (p<0.01), reward collection latency (p<0.001), and reduced the total attempted trials (p<0.001). In summary, we demonstrated that mice habituate to the variable ITI schedule, suggesting that using the variable ITI schedule during training allowed premature response rates to stabilize before commencing pharmacological testing. Moreover, in these habituated mice AMPH and DOI significantly enhanced impulsive action at the long ITI trials only. We propose that experimental design considerations can improve the sensitivity of the 5-CSRTT to detect pharmacologicallyinduced impulsive action.

Rodent Test of Attention and Impulsivity: The 5-Choice Serial Reaction Time Task

The 5-choice serial reaction time task (5-CSRTT) is employed extensively to measure attention in rodents. The assay involves animals trained to respond to a brief, unpredictable visual stimulus presented in one of five locations. The effects of experimental manipulations on response speed and choice accuracy are measured, and each related to attentional performance. The 5-CSRTT is also used to measure motor impulsivity. Adapted from a human task, the 5-CSRTT can be employed with rodents or primates, highlighting its translational value. Another strength of this procedure is its adaptability to task modification. An example is the 5-choice continuous performance task, which has both target and non-target trial types. Overall, the 5-CSRTT has proven to be valuable for drug discovery efforts aimed at identifying new agents for the treatment of central nervous system disorders and for further understanding the neurobiological processes of attention and impulsivity. Its flexibility offers considerable scope to the experimenter, and in this respect the task continues to evolve. © 2017 by John Wiley & Sons, Inc.

Considerations on nonclinical approaches to modeling risk factors of suicidal ideation and behavior

Given the serious nature of suicidal ideation and behavior (SIB) and the possibility of treatment-emergent SIB, pharmaceutical companies are now applying more proactive approaches in clinical trials and are considering the value of nonclinical models to predict SIB. The current review summarizes nonclinical approaches to modeling three common risk factors associated with SIB: aggression, impulsivity, and anhedonia. For each risk factor, a general description, advantages and disadvantages, species considerations, nonclinical to clinical translation, and pharmacological validation with respect to treatments associated with SIB are summarized. From this review, several gaps were identified that need to be addressed before use of these nonclinical models can be considered a viable option to predict the relative risk for SIB. Other future directions that may compliment these nonclinical approaches, including the use of selectively-bred or genetically-modified rodent models, transgenic models, gene expression profiling, and biomarker analysis, are discussed. This article was developed with the support of the DruSafe Leadership Group of the International Consortium for Innovation and Quality in Pharmaceutical Development (IQ, www.iqconsortium.org).

Chemogenetic Modulation of G Protein-Coupled Receptor Signalling in Visual Attention Research

Attention is a fundamental cognitive process involved in nearly all aspects of life. Abnormal attentional control is a symptom of many neurological disorders, most notably recognized in ADHD (attention deficit hyperactivity disorder). Although attentional performance and its malfunction has been a major area of investigation, it has proven difficult to accurately associate specific neuronal projections, cell types, neurotransmitter systems and receptors with distinct phenotypes owing to its complexity. In this MiniReview, we present a recently invented technology known as Designer Receptors Exclusively Activated by Designer Drugs (DREADDs). The DREADD technology is an emerging and transformative method that allows selective manipulation of G protein-coupled receptor (GPCR) signalling, and its broad-ranging usefulness in attention research is now beginning to emerge. We first describe the different DREADDs available and explain how unprecedented specificity of neuronal signalling can be achieved using DREADDs. We next discuss various studies performed in animal models of visual attention, where different brain regions and neuronal populations have been probed by DREADDs. We highlight the interplay between the dopamine (DA) and noradrenaline (NA) catecholamine systems in visual attention and explain why DREADD technology can untangle and help us better understand such complex systems in normal and malfunctioning conditions.

Theory of Visual Attention (TVA) applied to mice in the 5-choice serial reaction time task

RATIONALE

The 5-choice serial reaction time task (5-CSRTT) is widely used to measure rodent attentional functions. In humans, many attention studies in healthy and clinical populations have used testing based on Bundesen's Theory of Visual Attention (TVA) to estimate visual processing speeds and other parameters of attentional capacity.

OBJECTIVES

We aimed to bridge these research fields by modifying the 5-CSRTT's design and by mathematically modelling data to derive attentional parameters analogous to human TVA-based measures.

METHODS

C57BL/6 mice were tested in two 1-h sessions on consecutive days with a version of the 5-CSRTT where stimulus duration (SD) probe length was varied based on information from previous TVA studies. Thereafter, a scopolamine hydrobromide (HBr; 0.125 or 0.25 mg/kg) pharmacological challenge was undertaken, using a Latin square design. Mean score values were modelled using a new three-parameter version of TVA to obtain estimates of visual processing speeds, visual thresholds and motor response baselines in each mouse.

RESULTS

The parameter estimates for each animal were reliable across sessions, showing that the data were stable enough to support analysis on an individual level. Scopolamine HBr dose-dependently reduced 5-CSRTT attentional performance while also increasing reward collection latency at the highest dose. Upon TVA modelling, scopolamine HBr significantly reduced visual processing speed at both doses, while having less pronounced effects on visual thresholds and motor response baselines.

CONCLUSIONS

This study shows for the first time how 5-CSRTT performance in mice can be mathematically modelled to yield estimates of attentional capacity that are directly comparable to estimates from human studies.

A one-week 5-choice serial reaction time task to measure impulsivity and attention in adult and adolescent mice

Many psychiatric disorders emerge during adolescence. The study of executive functions in animal models of these disorders critically requires short-duration tasks measuring these functions before the animal ages. Here, a novel 5-choice serial reaction time task (5-CSRTT) protocol is presented, to measure attention and impulsivity within one week, without scheduled food deprivation and with little animal handling. Mice were allowed 24-h/day task access from their home-cage, during which they could self-pace task progression and earn unlimited food rewards depending on task performance. Manipulation of task parameters in this self-paced 5-CSRTT protocol (SP-5C) affected attentional performance and impulsivity to a similar extent as previously observed in the 5-CSRTT. Task activity followed intrinsic circadian rhythm, distinctive for the SP-5C protocol, with task performance stable over the day. The sensitivity of the SP-5C protocol to detect strain differences between C57BL/6J, DBA/2 J, BXD16 and BXD62 mice was demonstrated as well as its suitability for testing adolescent mice. Acute administration of the muscarinic acetylcholine receptor antagonist scopolamine impaired attentional performance, providing initial pharmacological validation of the task. The SP-5C substantially shortens the assessment of impulsivity and attention, increases test efficiency and enables the assessment of adolescent mouse models of psychiatric disorders.

Effects of amphetamine and methylphenidate on attentional performance and impulsivity in the mouse 5-Choice Serial Reaction Time Task

BACKGROUND

Few studies have investigated the effects of conventional attention deficit-hyperactivity disorder (ADHD) medication in the mouse 5-choice serial reaction time task (5-CSRTT), and rat studies have yielded inconsistent results.

OBJECTIVE

We aimed to examine the effects of acute methylphenidate (MPH) and amphetamine (AMPH) treatment in the mouse 5-CSRTT.

METHODS

Trained male C57Bl/6J mice were tested in a variable stimulus duration schedule. Effects of AMPH (0.25, 0.5, and 1 mg/kg) and MPH (0.5, 1.0, and 2.0 mg/kg) on discriminative accuracy, omissions, and premature responses were assessed. Saline treatment data determined high- and low-attentive (LA), and high- and low-impulsive (LI) subgroups according to the upper and lower 30th percentiles, respectively.

RESULTS

In the LA subgroup accuracy was improved by 0.5 mg/kg AMPH and 2 mg/kg MPH, while no effect was found in the high-attentive (HA) subgroup. Premature responses were increased by 1 mg/kg AMPH and 0.5 mg/kg MPH for all animals, and by 1 mg/kg AMPH for the LI subgroup.

CONCLUSIONS

The use of variable stimulus duration, along with the division into high- and LA, and high-and LI subgroups, may improve the sensitivity of the 5-CSRTT when investigating drug effects on attention and impulsivity.

Mice haploinsufficient for Map2k7, a gene involved in neurodevelopment and risk for schizophrenia, show impaired attention, a vigilance decrement deficit and unstable cognitive processing in an attentional task: impact of minocycline

RATIONALE

Members of the c-Jun N-terminal kinase (JNK) family of mitogen-activated protein (MAP) kinases, and the upstream kinase MKK7, have all been strongly linked with synaptic plasticity and with the development of the neocortex. However, the impact of disruption of this pathway on cognitive function is unclear.

OBJECTIVE

In the current study, we test the hypothesis that reduced MKK7 expression is sufficient to cause cognitive impairment.

METHODS

Attentional function in mice haploinsufficient for Map2k7 (Map2k7 ^+/- mice) was investigated using the five-choice serial reaction time task (5-CSRTT).

RESULTS

Once stable performance had been achieved, Map2k7 ^+/- mice showed a distinctive attentional deficit, in the form of an increased number of missed responses, accompanied by a more pronounced decrement in performance over time and elevated intra-individual reaction time variability. When performance was reassessed after administration of minocycline-a tetracycline antibiotic currently showing promise for the improvement of attentional deficits in patients with schizophrenia-signs of improvement in attentional performance were detected.

CONCLUSIONS

Overall, Map2k7 haploinsufficiency causes a distinctive pattern of cognitive impairment strongly suggestive of an inability to sustain attention, in accordance with those seen in psychiatric patients carrying out similar tasks. This may be important for understanding the mechanisms of cognitive dysfunction in clinical populations and highlights the possibility of treating some of these deficits with minocycline.

Improvements and important considerations for the 5-choice serial reaction time task-An effective measurement of visual attention in rats

BACKGROUND

The 5-choice serial reaction time task (5-CSRTT) is an automated operant conditioning task that measures rodent attention. The task allows the measurement of several parameters such as response accuracy, speed of processing, motivation, and impulsivity. The task has been widely used to investigate attentional processes in rodents for attention deficit and hyperactivity disorder and has expanded to other illnesses such as Alzheimer's disease, depression, and schizophrenia.

NEW METHOD

The 5-CSRTT is accompanied with two significant caveats: a time intensive training period and largely varied individual rat capability to learn and perform the task. Here we provide a regimented acquisition protocol to enhance training for the 5-CSRTT and discuss important considerations for researchers using the 5-CSRTT.

RESULTS

We offer guidelines to ensure that inferences on performance in the 5-CSRTT are in fact a result of experimental manipulation rather than training differences, or individual animal capability. According to our findings only rats that have been trained successfully within a limited time frame should be used for the remainder of the study.

COMPARISON WITH EXISTING METHOD(S)

Currently the 5-CSRTT employs a training period of variable duration and procedure, and its inferences on attention must overcome heterogeneous innate animal differences.

CONCLUSIONS

The 5-CSRTT offers valuable and valid insights on various rodent attentional processes and their translation to the underpinnings of illnesses such as schizophrenia. The recommendations made here provide important criteria to ensure inferences made from this task are in fact relevant to the attentional processes being measured.

Apolipoprotein E (APOE) genotype and the pesticide chlorpyrifos modulate attention, motivation and impulsivity in female mice in the 5-choice serial reaction time task

Organophosphate pesticides - and chlorpyrifos (CPF) in particular - contribute to a wide range of neurobehavioural disorders. Most experimental research focuses on learning and memory processes, while other behaviours remain understudied. The isoforms of the human apolipoprotein E (apoE) confer different cognitive skills on their carriers, but data on this topic are still limited. The current study was performed to assess whether the APOE genotypic variability differently modulates the effects of CPF on attentional performance, inhibitory control and motivation. Human apoE targeted replacement adult female mice (apoE2, apoE3 and apoE4) were trained to stably perform the 5-choice serial reaction time task (5-CSRTT). Animals were then subjected to daily dietary CPF (3.75 mg/kg body weight) for 4 weeks. After CPF exposure, we established a 4-week CPF-free period to assess recovery. All individuals acquired the task, apoE2 mice showed enhanced learning, while apoE4 mice displayed increased premature and perseverative responding. This genotype-dependent lack of inhibitory control was reversed by CPF. Overall, the pesticide induced protracted impairments in sustained attention and motivation, and it reduced anticipatory responding. ApoE3 mice exhibited delayed attentional disruptions throughout the wash-out period. Taken together, these findings provide notable evidence on the emergence of CPF-related attentional and motivational deficits.

Mouse and Human Genetic Analyses Associate Kalirin with Ventral Striatal Activation during Impulsivity and with Alcohol Misuse

Impulsivity is associated with a spectrum of psychiatric disorders including drug addiction. To investigate genetic associations with impulsivity and initiation of drug taking, we took a two-step approach. First, we identified genes whose expression level in prefrontal cortex, striatum and accumbens were associated with impulsive behavior in the 5-choice serial reaction time task across 10 BXD recombinant inbred (BXD RI) mouse strains and their progenitor C57BL/6J and DBA2/J strains. Behavioral data were correlated with regional gene expression using GeneNetwork (www.genenetwork.org), to identify 44 genes whose probability of association with impulsivity exceeded a false discovery rate of < 0.05. We then interrogated the IMAGEN database of 1423 adolescents for potential associations of SNPs in human homologs of those genes identified in the mouse study, with brain activation during impulsive performance in the Monetary Incentive Delay task, and with novelty seeking scores from the Temperament and Character Inventory, as well as alcohol experience. There was a significant overall association between the human homologs of impulsivity-related genes and percentage of premature responses in the MID task and with fMRI BOLD-response in ventral striatum (VS) during reward anticipation. In contrast, no significant association was found between the polygenic scores and anterior cingulate cortex activation. Univariate association analyses revealed that the G allele (major) of the intronic SNP rs6438839 in the KALRN gene was significantly associated with increased VS activation. Additionally, the A-allele (minor) of KALRN intronic SNP rs4634050, belonging to the same haplotype block, was associated with increased frequency of binge drinking.

Cognitive Dysfunction in Major Depressive Disorder. A Translational Review in Animal Models of the Disease

Major Depressive Disorder (MDD) is the most common psychiatric disease, affecting millions of people worldwide. In addition to the well-defined depressive symptoms, patients suffering from MDD consistently complain about cognitive disturbances, significantly exacerbating the burden of this illness. Among cognitive symptoms, impairments in attention, working memory, learning and memory or executive functions are often reported. However, available data about the heterogeneity of MDD patients and magnitude of cognitive symptoms through the different phases of MDD remain difficult to summarize. Thus, the first part of this review briefly overviewed clinical studies, focusing on the cognitive dysfunctions depending on the MDD type. As animal models are essential translational tools for underpinning the mechanisms of cognitive deficits in MDD, the second part of this review synthetized preclinical studies observing cognitive deficits in different rodent models of anxiety/depression. For each cognitive domain, we determined whether deficits could be shared across models. Particularly, we established whether specific stress-related procedures or unspecific criteria (such as species, sex or age) could segregate common cognitive alteration across models. Finally, the role of adult hippocampal neurogenesis in rodents in cognitive dysfunctions during MDD state was also discussed.

Measuring Attention in Rodents: Comparison of a Modified Signal Detection Task and the 5-Choice Serial Reaction Time Task

Neuropsychiatric research has utilized cognitive testing in rodents to improve our understanding of cognitive deficits and for preclinical drug development. However, more sophisticated cognitive tasks have not been as widely exploited due to low throughput and the extensive training time required. We developed a modified signal detection task (SDT) based on the growing body of literature aimed at improving cognitive testing in rodents. This study directly compares performance on the modified SDT with a traditional test for measuring attention, the 5-choice serial reaction time task (5CSRTT). Adult male Sprague-Dawley rats were trained on either the 5CSRTT or the SDT. Briefly, the 5CSRTT required rodents to pay attention to a spatial array of five apertures and respond with a nose poke when an aperture was illuminated. The SDT required the rat to attend to a light panel and respond either left or right to indicate the presence of a signal. In addition, modifications were made to the reward delivery, timing, control of body positioning, and the self-initiation of trials. It was found that less training time was required for the SDT, with both sessions to criteria and daily session duration significantly reduced. Rats performed with a high level of accuracy (>87%) on both tasks, however omissions were far more frequent on the 5CSRTT. The signal duration was reduced on both tasks as a manipulation of task difficulty relevant to attention and a similar pattern of decreasing accuracy was observed on both tasks. These results demonstrate some of the advantages of the SDT over the traditional 5CSRTT as being higher throughput with reduced training time, fewer omission responses and their body position was controlled at stimulus onset. In addition, rats performing the SDT had comparable high levels of accuracy. These results highlight the differences and similarities between the 5CSRTT and a modified SDT as tools for assessing attention in preclinical animal models.

Attentional performance, impulsivity, and related neurotransmitter systems in apoE2, apoE3, and apoE4 female transgenic mice

RATIONALE

The apolipoprotein E (apoE) genotype influences cognitive performance in humans depending on age and sex. While the detrimental role of the apoE4 isoform on spatial learning and memory has been well-established in humans and rodents, less is known on its impact on the executive functions.

OBJECTIVES

We aimed to evaluate the effect of apoE isoforms (apoE2, apoE3, apoE4) on visuospatial attention and inhibitory control performance in female transgenic mice, and to determine the neurochemical and neuropharmacological basis of this potential relationship.

METHODS

Female mice carrying apoE2, apoE3, and apoE4 were trained in the five-choice serial reaction time task (5-CSRTT). Upon a stable performance, we manipulated the inter-trial interval and the stimulus duration to elicit impulsive responding and engage attention respectively. We further performed a pharmacological challenge by administering cholinergic and GABAergic agents. Finally, we analyzed the levels of brain amino acids and monoamines by using reversed phase high-performance liquid chromatography (HPLC).

RESULTS

ApoE4 mice showed a deficient inhibitory control as revealed by increased perseveration and premature responding. When attention was challenged, apoE4 mice also showed a higher drop in accuracy. The adverse effect of scopolamine on the task was attenuated in apoE4 mice compared to apoE2 and apoE3. Furthermore, apoE4 mice showed less dopamine in the frontal cortex than apoE2 mice.

CONCLUSIONS

We confirmed that the apoE genotype influences attention and inhibitory control in female transgenic mice. The influence of apoE isoforms in the brain neuromodulatory system may explain the cognitive and behavioral differences attributable to the genotype.

Repeated ethanol exposure during early and late adolescence: double dissociation of effects on waiting and choice impulsivity

BACKGROUND

A strong association exists between impulsivity and binge drinking, and between adolescent alcohol exposure and alcohol abuse in humans. To understand the extent to which early-life alcohol exposure contributes to increased impulsivity, we developed an animal model of binge drinking using 2 strains of mice, C57BL/6J (B6) and DBA2/J (D2), that differ in both motor impulsivity and alcohol drinking.

METHODS

Mice were treated with 2 g/kg ethanol (EtOH) during their early (intermittent ethanol exposure [IEE]_Early; postnatal day [PND]30 to 45) or late (IEE_Late; PND45 to 60) adolescence or with saline (control group [CON]) throughout the adolescence period. To determine the consequences IEE on waiting impulsivity and attentional function, the number of premature responses and omissions, respectively, were evaluated in adulthood using the 5-choice serial reaction time task (5-CSRTT). To examine the effects of IEE on choice impulsivity, risky decision making was assessed in adulthood using a mouse version of the Iowa Gambling Task (mIGT). Additionally, the acute effects of EtOH in adulthood on waiting impulsivity and choice preference were investigated.

RESULTS

We provide experimental evidence that IEE during late, but not early, adolescence disrupts waiting impulsivity and attentional abilities in the 5-CSRTT. In contrast, IEE during early, but not late, adolescence altered risky decision making in the mIGT. D2 mice consistently showed lower premature responding than B6 mice in both the mIGT and the 5-CSRTT, but greater risky decision making on the mIGT. IEE and CON mice showed similar responsiveness to the acute EtOH effects on premature responding, but increased risky choices only in B6_IEE_Early mice.

CONCLUSIONS

Our observations suggest a direct effect of IEE during adolescence on waiting and choice impulsivity and attention later in life.

Alleviating waiting impulsivity and perseverative responding by μ-opioid receptor antagonism in two inbred mouse strains

RATIONALE

Recent evidence has implicated the opioid system in exaggerated ethanol consumption and impulsivity deficits. The opioid receptor antagonist naltrexone (NTX) has proven efficient in reducing alcohol consumption; however, its role on impulsive behaviour is not fully characterised.

OBJECTIVE

The aim of this study was to investigate the effects of NTX on two measures of impulsive behaviour in two inbred mouse strains that differ in ethanol preference and impulsive phenotype.

METHODS

Two separate groups of C57BL/6J (B6, n = 24) and DBA2/J (D2, n = 24) male mice were exposed to intermittent ethanol (IEE; 2 g/kg) during early (PND 30-45, IEE_Early) or late (PND 45-60, IEE_Late) adolescence or the respective saline control. The ability of NTX (10 mg/kg) alone, or co-administered with ethanol (0.5 g/kg), to diminish waiting impulsivity in the five-choice serial reaction time task (5-CSRTT), or improve decision-making in a mouse version of the Iowa Gambling Task (mIGT), was examined in adulthood.

RESULTS

In the 5-CSRTT, NTX diminished impulsivity in both strains of mice, irrespective of previous ethanol experience. In the mIGT, NTX failed to alter risky decision-making but decreased perseverative responding.

CONCLUSIONS

Blocking the actions of endogenous opioids may attenuate waiting impulsivity, in addition to alleviating perseverative responding. In a broader context, μ-opiate antagonism may be of potential interest for impulse-control disorders.

Attention

The ability to focus one's attention on important environmental stimuli while ignoring irrelevant stimuli is fundamental to human cognition and intellectual function. Attention is inextricably linked to perception, learning and memory, and executive function; however, it is often impaired in a variety of neuropsychiatric disorders, including Alzheimer's disease, schizophrenia, depression, and attention deficit hyperactivity disorder (ADHD). Accordingly, attention is considered as an important therapeutic target in these disorders. The purpose of this chapter is to provide an overview of the most common behavioral paradigms of attention that have been used in animals (particularly rodents) and to review the literature where these tasks have been employed to elucidate neurobiological substrates of attention as well as to evaluate novel pharmacological agents for their potential as treatments for disorders of attention. These paradigms include two tasks of sustained attention that were developed as rodent analogues of the human Continuous Performance Task (CPT), the Five-Choice Serial Reaction Time Task (5-CSRTT) and the more recently introduced Five-Choice Continuous Performance Task (5C-CPT), and the Signal Detection Task (SDT) which was designed to emphasize temporal components of attention.

Investigating glutamatergic mechanism in attention and impulse control using rats in a modified 5-choice serial reaction time task

The 5-choice serial reaction time task (5CSRTT) has been widely used to study attention and impulse control in rodents. In order to mimic cognitive impairments in psychiatry, one approach has been to use acute administration of NMDA antagonists. This disruption in glutamatergic transmission leads to impairments in accuracy, omissions, and premature responses although findings have been inconsistent. In this study, we further investigated glutamatergic mechanisms using a novel version of the 5CSRTT, which we have previously shown to be more sensitive to cognitive enhancers. We first investigated the effects of systemic treatment with NMDA antagonists. We also carried out a preliminary investigation using targeted medial prefrontal cortex infusions of a NMDA antagonist (MK801), mGluR2/3 antagonist (LY341495), and mGluR7 negative allosteric modulator (MMPIP). Acute systemic administration of the different NMDA antagonists had no specific effects on accuracy. At higher doses PCP, ketamine, and memantine, increased omissions and affected other measures suggesting a general disruption in task performance. Only MK801 increased premature responses, and reduced omissions at lower doses suggesting stimulant like effects. None of the NMDA antagonists affected accuracy or any other measures when tested using a short stimulus challenge. Infusions of MK801 had no effect on accuracy but increased premature responses following infralimbic, but not prelimbic infusion. LY341495 had no effects in either brain region but a decrease in accuracy was observed following prelimbic infusion of MMPIP. Contrary to our hypothesis, disruptions to glutamate transmission using NMDA antagonists did not induce any clear deficits in accuracy in this modified version of the 5CSRTT. We also found that the profile of effects for MK801 differed from those observed with PCP, ketamine, and memantine. The effects of MK801 in the infralimbic cortex add to the literature indicating this brain region and glutamate play an important role in impulse control.

Exaggerated waiting impulsivity associated with human binge drinking, and high alcohol consumption in mice

There are well-established links between impulsivity and alcohol use in humans and animal models; however, whether exaggerated impulsivity is a premorbid risk factor or a consequence of alcohol intake remains unclear. In a first approach, human young (18-25 years) social binge and non-binge drinkers were tested for motor impulsivity and attentional abilities in a human version of the Five-Choice Serial Reaction Time Task (Sx-5CSRTT), modeled on the rodent 5CSRTT. Participants completed four variants of the Sx-5CSRT, in addition to being screened for impulsive traits (BIS-11 questionnaire) and impulsive behavior (by means of the Delay Discounting Questionnaire, Two-Choice Impulsivity Paradigm (TCIP), Stop Signal Reaction Time, and Time Estimation Task). Using a second approach, we compared one of these impulsivity measures, 5CSRTT performance, in two inbred strains of mice known to differ in alcohol intake. Compared with non-bingers (NBD; n=22), binge drinkers (BD, n=22) showed robust impairments in attention and premature responding when evaluated under increased attentional load, in addition to presenting deficits in decision making using the TCIP. The best predictors for high binge drinking score were premature responding in the Sx-5CSRTT, trait impulsivity in the BIS-11, and decision making in the TCIP. Alcohol-naïve C57BL/6J (B6) mice (alcohol preferring) were more impulsive in the 5CSRTT than DBA2/J (D2) mice (alcohol averse); the degree of impulsivity correlated with subsequent alcohol consumption. Homologous measures in animal and human studies indicate increased premature responding in young social BD and in the ethanol-preferring B6 strain of mice.

New Insights into the Mechanisms of Action of Cotinine and its Distinctive Effects from Nicotine

Tobacco consumption is far higher among a number of psychiatric and neurological diseases, supporting the notion that some component(s) of tobacco may underlie the oft-reported reduction in associated symptoms during tobacco use. Popular dogma holds that this component is nicotine. However, increasing evidence support theories that cotinine, the main metabolite of nicotine, may underlie at least some of nicotine's actions in the nervous system, apart from its adverse cardiovascular and habit forming effects. Though similarities exist, disparate and even antagonizing actions between cotinine and nicotine have been described both in terms of behavior and physiology, underscoring the need to further characterize this potentially therapeutic compound. Cotinine has been shown to be psychoactive in humans and animals, facilitating memory, cognition, executive function, and emotional responding. Furthermore, recent research shows that cotinine acts as an antidepressant and reduces cognitive-impairment associated with disease and stress-induced dysfunction. Despite these promising findings, continued focus on this potentially safe alternative to tobacco and nicotine use is lacking. Here, we review the effects of cotinine, including comparisons with nicotine, and discuss potential mechanisms of cotinine-specific actions in the central nervous system which are, to date, still being elucidated.

Alpha-synuclein deletion decreases motor impulsivity but does not affect risky decision making in a mouse Gambling Task

RATIONALE

There is evidence to support the role of alpha-synuclein in motor impulsivity, but the extrapolation of this finding to other types of impulsivity remains to be elucidated.

OBJECTIVE

This study aims to investigate the role of alpha-synuclein in choice impulsivity/risky decision-making by means of a mouse version of the Iowa Gambling Task (mIGT).

METHODS

Two strains of mice that differ in the expression of the alpha-synuclein gene, the C57BL/6JOlaHsd (HA) and C57BL/6J (CR), were tested in the mIGT. HA mice differ from their CR ancestors in possessing a chromosomal deletion resulting in the loss of two genes: snca, encoding alpha-synuclein and mmrn1, encoding multimerin-1. Mice were trained in the mIGT until a stable pattern of responding was achieved and then the acute effects of ethanol and cocaine in choice preference were investigated.

RESULTS

No differences between the strains were evident in risky decision-making in any of the experiments, but HA mice showed consistently reduced levels of premature responding in comparison with CR mice, confirming the reduced motor impulsivity found in a previous study. Ethanol did not modify the percentage of advantageous choices in either strain, while cocaine increased the risky choice behaviour by increasing the percentage of disadvantageous choices in both strains.

CONCLUSIONS

We provide further evidence for the involvement of alpha-synuclein in motor impulsivity and suggest that alpha-synuclein does not play a role in risky decision-making as evaluated in the mIGT.

The influence of test experience and NK1 receptor antagonists on the performance of NK1R-/- and wild type mice in the 5-Choice Serial Reaction-Time Task

Genetically-altered mice, lacking functional NK1 receptors (NK1R-/-), express abnormal behaviours that are prominent in Attention Deficit Hyperactivity Disorder: namely, inattentiveness and impulsivity (indicated by their greater % omissions and premature responses in the 5-Choice Serial Reaction-Time Task (5-CSRTT) and locomotor hyperactivity. We investigated how behaviour in the 5-CSRTT is affected by repeated testing and whether the abnormalities expressed by NK1R-/- mice are mimicked by treating wild type mice with a NK1R antagonist (L 733060 or RP 67580; 5 or 10 mg/kg). Repeated testing with a variable (VITI) or fixed, prolonged (LITI) intertrial interval reduced % omissions. Premature responses also declined, but only in NK1R-/- mice, in the VITI test. By contrast, perseveration increased in both genotypes. RP 67580 (10 mg/kg) increased the % omissions in both genotypes in the VITI, an action which cannot be attributed to NK1R antagonism. Neither drug affected perseveration. However, for premature responses, the response profile suggested that the low and high doses of RP 67580 (VITI) and L 733060 (LITI) had opposing effects on this behaviour. We infer that the effect of NK1R antagonists in the 5-CSRTT is confounded by animals' test experience and non-specific drug effects at sites other than NK1R, possibly L-type Ca²⁺(v) channels.

Prenatal exposure to psychostimulants increases impulsivity, compulsivity, and motivation for rewards in adult mice

Given the widespread use and misuse of methamphetamine (METH) and methylphenidate (MPD), especially in relation to women of childbearing age, it is important to consider the long-lasting effects of these drugs on the brain of the developing fetus. Male and female C57Bl/6J mice were prenatally exposed to METH (5mg/kg), MPD (10mg/kg), or saline. Following a 3-month washout, behavioral analysis using the 5-Choice Serial Reaction Time Task (5CSRTT) was performed on adult mice. After reaching training criteria, performance on a pseudo-random intertrial interval test session revealed decrements in 5CSRTT behavior. Prenatally-treated METH and MPD mice demonstrated significant increases in impulsivity, compulsivity, and motivation for reward compared to their saline controls. There were sex by drug interactions indicating a possible sexually dimorphic response to these prenatal drug exposures. Of particular clinical interest, we find that mice prenatally exposed to METH or MPD express characteristics of both inhibitory control decrements and heightened motivation for rewards, which represent core symptoms of addiction and other impulse control disorders.

The BTBR mouse model of autism spectrum disorders has learning and attentional impairments and alterations in acetylcholine and kynurenic acid in prefrontal cortex

Autism is a complex spectrum of disorders characterized by core behavioral deficits in social interaction, communication, repetitive stereotyped behaviors and restricted interests. Autism frequently presents with additional cognitive symptoms, including attentional deficits and intellectual disability. Preclinical models are important tools for studying the behavioral domains and biological underpinnings of autism, and potential treatment targets. The inbred BTBR T+tf/J (BTBR) mouse strain has been used as an animal model of core behavioral deficits in autism. BTBR mice exhibit repetitive behaviors and deficits in sociability and communication, but other aspects of their cognitive phenotype, including attentional performance, are not well characterized. We examined the attentional abilities of BTBR mice in the 5-choice serial reaction time task (5-CSRTT) using an automated touchscreen testing apparatus. The 5-CSRTT is an analogue of the human continuous performance task of attention, and so both the task and apparatus have translational relevance to human touchscreen cognitive testing. We also measured basal extracellular levels of a panel of neurotransmitters within the medial prefrontal cortex, a brain region critically important for performing the 5-CSRTT. We found that BTBR mice have increased impulsivity, defined as an inability to withhold responding, and decreased motivation, as compared to C57Bl/6J mice. Both of these features characterize attentional deficit disorders in humans. BTBR mice also display decreased accuracy in detecting short stimuli, lower basal levels of extracellular acetylcholine and higher levels of kynurenic acid within the prefrontal cortex. Intact cholinergic transmission in prefrontal cortex is required for accurate performance of the 5-CSRTT, consequently this cholinergic deficit may underlie less accurate performance in BTBR mice. Based on our findings that BTBR mice have attentional impairments and alterations in a key neural substrate of attention, we propose that they may be valuable for studying mechanisms for treatment of cognitive dysfunction in individuals with attention deficits and autism.

Cognitive dysfunction and depression in Parkinson's disease: what can be learned from rodent models?

Parkinson's disease (PD) has for decades been considered a pure motor disorder and its cardinal motor symptoms have been attributed to the loss of dopaminergic (DAergic) neurons in the substantia nigra pars compacta and to nigral Lewy body pathology. However, there has more recently been a shift in the conceptualization of the disease, and its pathological features have now been recognized as involving several other areas of the brain and indeed even outside the central nervous system. There are a corresponding variety of intrinsic non-motor symptoms such as autonomic dysfunction, cognitive impairment, sleep disturbances and neuropsychiatric problems, which cannot be explained exclusively by nigral pathology. In this review, we will focus on cognitive impairment and affective symptoms in PD, and we will consider whether, and how, these deficits can best be modelled in rodent models of the disorder. As only a few of the non-motor symptoms respond to standard DA replacement therapies, the quest for a broader therapeutic approach remains a major research effort, and success in this area in particular will be strongly dependent on appropriate rodent models. In addition, better understanding of the different models, as well as the advantages and disadvantages of the available behavioural tasks, will result in better tools for evaluating new treatment strategies for PD patients suffering from these neuropsychological symptoms.

Antagonism of L-type Ca(v) channels with nifedipine differentially affects performance of wildtype and NK1R-/- mice in the 5-Choice Serial Reaction-Time Task

Mice with functional ablation of the substance P-preferring receptor gene ('Nk1r' in mice ('NK1R-/-'), 'TACR1' in humans) display deficits in cognitive performance that resemble those seen in patients with Attention Deficit Hyperactivity Disorder (ADHD): namely, inattentiveness, impulsivity and perseveration. A recent report suggested that the L-type Ca(v) channel blocker, nifedipine, can ameliorate behavioral abnormalities of this type in humans. In light of evidence that NK1R antagonists modulate the opening of these L-type channels, we investigated whether nifedipine modifies %premature responses (impulsivity), perseveration or %omissions (inattentiveness) in the 5-Choice Serial Reaction-Time Task (5-CSRTT) and whether the response differs in NK1R-/- and wildtype mice. %Premature responses and perseveration were reduced in both genotypes, although wildtype mice were more sensitive to the effects of nifedipine than NK1R-/- mice. By contrast, nifedipine greatly increased %omissions but, again, was more potent in wildtypes. %Accuracy and locomotor activity were unaffected in either genotype. We infer that behavior of mice in the 5-CSRTT depends on the regulation of striato-cortical networks by L-type Ca(v) channels and NK1R. We further suggest that disruption of NK1R signaling in patients with ADHD, especially those with polymorphisms of the TACR1 gene, could lead to compensatory changes in the activity of L-type channels that underlie or exacerbate their problems. This article is part of a Special Issue entitled 'Cognitive Enhancers'.

Deletion of alpha-synuclein decreases impulsivity in mice

The presynaptic protein alpha-synuclein, associated with Parkinson's Disease (PD), plays a role in dopaminergic neurotransmission and is implicated in impulse control disorders (ICDs) such as drug addiction. In this study we investigated a potential causal relationship between alpha-synuclein and impulsivity, by evaluating differences in motor impulsivity in the 5-choice serial reaction time task (5-CSRTT) in strains of mice that differ in the expression of the alpha-synuclein gene. C57BL/6JOlaHsd mice differ from their C57BL/6J ancestors in possessing a chromosomal deletion resulting in the loss of two genes, snca, encoding alpha-synuclein, and mmrn1, encoding multimerin-1. C57BL/6J mice displayed higher impulsivity (more premature responding) than C57BL/6JOlaHsd mice when the pre-stimulus waiting interval was increased in the 5-CSRTT. In order to ensure that the reduced impulsivity was indeed related to snca, and not adjacent gene deletion, wild type (WT) and mice with targeted deletion of alpha-synuclein (KO) were tested in the 5-CSRTT. Similarly, WT mice were more impulsive than mice with targeted deletion of alpha-synuclein. Interrogation of our ongoing analysis of impulsivity in BXD recombinant inbred mouse lines revealed an association of impulsive responding with levels of alpha-synuclein expression in hippocampus. Expression of beta- and gamma-synuclein, members of the synuclein family that may substitute for alpha-synuclein following its deletion, revealed no differential compensations among the mouse strains. These findings suggest that alpha-synuclein may contribute to impulsivity and potentially, to ICDs which arise in some PD patients treated with dopaminergic medication.