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)

Early life stress induced sex-specific changes in behavior is paralleled by altered locus coeruleus physiology in BALB/cJ mice

Adverse childhood experiences have been associated with many neurodevelopmental and affective disorders including attention deficit hyperactivity disorder and generalized anxiety disorder, with more exposures increasing negative risk. Sex and genetic background are biological variables involved in adverse psychiatric outcomes due to early life trauma. Females in general have an increased prevalence of stress-related psychopathologies beginning after adolescence, indicative of adolescence being a female-specific sensitive period. To understand the underlying neuronal mechanisms potentially responsible for this relationship between genetic background, sex, stress/trauma, and cognitive/affective behaviors, we assessed behavioral and neuronal changes in a novel animal model of early life stress exposure. Male and female BALB/cJ mice that express elevated basal anxiety-like behaviors and differences in monoamine signaling-associated genes, were exposed to an early life variable stress protocol that combined deprivation in early life with unpredictability in adolescence. Stress exposure produced hyperlocomotion and attention deficits (5-choice serial reaction time task) in male and female mice along with female-specific increased anxiety-like behavior. These behavioral changes were paralleled by reduced excitability of locus coeruleus (LC) neurons, due to resting membrane potential hyperpolarization in males and a female-specific increase in action potential delay time. These data describe a novel interaction between sex, genetic background, and early life stress that results in behavioral changes in clinically relevant domains and potential underlying mechanistic lasting changes in physiological properties of neurons in the LC.

Single administration of a psychedelic [(R)-DOI] influences coping strategies to an escapable social stress

Psychedelic compounds have potentially rapid, long-lasting anxiolytic, antidepressive and anti-inflammatory effects. We investigated whether the psychedelic compound (R)-2,5-dimethoxy-4-iodoamphetamine [(R)-DOI], a selective 5-HT2A receptor partial agonist, decreases stress-related behavior in male mice exposed to repeated social aggression. Additionally, we explored the likelihood that these behavioral changes are related to anti-inflammatory properties of [(R)-DOI]. Animals were subjected to the Stress Alternatives Model (SAM), an escapable social stress paradigm in which animals develop reactive coping strategies - remaining in the SAM arena (Stay) with a social aggressor, or dynamically initiated stress coping strategies that involve utilizing the escape holes (Escape) to avoid aggression. Mice expressing these behavioral phenotypes display behaviors like those in other social aggression models that separate animals into stress-vulnerable (as for Stay) or stress-resilient (as for Escape) groups, which have been shown to have distinct inflammatory responses to social stress. These results show that Stay animals have heightened cytokine gene expression, and both Stay and Escape mice exhibit plasma and neural concentrations of the inflammatory cytokine tumor necrosis factor-α (TNFα) compared to unstressed control mice. Additionally, these results suggest that a single administration of (R)-DOI to Stay animals in low doses, can increase stress coping strategies such as increasing attention to the escape route, promoting escape behavior, and reducing freezing during socially aggressive interaction in the SAM. Lower single doses of (R)-DOI, in addition to shifting behavior to suggest anxiolytic effects, also concomitantly reduce plasma and limbic brain levels of the inflammatory cytokine TNFα.

Pramipexole restores behavioral inhibition in highly impulsive rats through a paradoxical modulation of frontostriatal networks

Impulse control disorders (ICDs), a wide spectrum of maladaptive behaviors which includes pathological gambling, hypersexuality and compulsive buying, have been recently suggested to be triggered or aggravated by treatments with dopamine D2/3 receptor agonists, such as pramipexole (PPX). Despite evidence showing that impulsivity is associated with functional alterations in corticostriatal networks, the neural basis of the exacerbation of impulsivity by PPX has not been elucidated. Here we used a hotspot analysis to assess the functional recruitment of several corticostriatal structures by PPX in male rats identified as highly (HI), moderately impulsive (MI) or with low levels of impulsivity (LI) in the 5-choice serial reaction time task (5-CSRTT). PPX dramatically reduced impulsivity in HI rats. Assessment of the expression pattern of the two immediate early genes C-fos and Zif268 by in situ hybridization subsequently revealed that PPX resulted in a decrease in Zif268 mRNA levels in different striatal regions of both LI and HI rats accompanied by a high impulsivity specific reduction of Zif268 mRNA levels in prelimbic and cingulate cortices. PPX also decreased C-fos mRNA levels in all striatal regions of LI rats, but only in the dorsolateral striatum and nucleus accumbens core (NAc Core) of HI rats. Structural equation modeling further suggested that the anti-impulsive effect of PPX was mainly attributable to the specific downregulation of Zif268 mRNA in the NAc Core. Altogether, our results show that PPX restores impulse control in highly impulsive rats by modulation of limbic frontostriatal circuits.

Effects of psilocybin, the 5-HT2A receptor agonist TCB-2, and the 5-HT2A receptor antagonist M100907 on visual attention in male mice in the continuous performance test

RATIONALE

Neuropsychiatric disorders such as depression are characterized in part by attention deficits. Attention is modulated by the serotonin (5-HT) neurotransmitter system. The 5-HT2A agonist and hallucinogen psilocybin (PSI) is a promising treatment for disorders characterized by attention changes. However, few studies have investigated PSI's direct effect on attention.

OBJECTIVE

Using the rodent continuous performance task (CPT), we assessed PSI's effect on attention. We also evaluated the impact of 5-HT2A receptor agonist TCB-2 and antagonist M100907 for comparative purposes.

METHODS

In the CPT, mice learned to distinguish visual targets from non-targets for milkshake reward. Performance was then tested following injections of PSI (0.3, 1, and 3 mg/kg), TCB-2 (0.3, 1, and 3 mg/kg), or M100907 (0.1, 0.3, and 1 mg/kg). Subsequently, drug effects were then evaluated using a more difficult CPT with variable stimulus durations. Mice were then tested on the CPT following repeated PSI injections. Drug effects on locomotor activity were also measured.

RESULTS

In the CPT, all three drugs reduced hit and false alarm rate and induced conservative responding. PSI also reduced target discrimination. These effects were seen primarily at doses that also significantly reduced locomotor activity. No drug effects were seen on the more difficult CPT or following repeated PSI injections.

CONCLUSIONS

Psilocybin, TCB-2, and M100907 impaired performance of the CPT. However, this may be in part due to drug-induced locomotor changes. The results provide little support for the idea that psilocybin alters visual attention, or that 5-HT2A receptors modulate this process.

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.

Contrasting effects of DOI and lisuride on impulsive decision-making in delay discounting task

RATIONALE

The 5-HT2A receptor is the major target of classic hallucinogens. Both DOI (2,5-dimethoxy-4-iodoamphetamine) and lisuride act at 5-HT2A receptors, and lisuride shares comparable affinity with DOI and acts as a partial agonist at 5-HT2A receptors. However, not like DOI, lisuride lacks hallucinogenic properties. Impulsive decision-making refers to the preference for an immediate small reinforcer (SR) over a delayed large reinforcer (LR).

OBJECTIVES

The current study aims to compare the effects of DOI and lisuride on impulsive decision-making and further to investigate the possible receptor mechanisms responsible for the actions of the two drugs.

METHODS

Impulsive decision-making was evaluated in male Sprague-Dawley rats by the percentage of choice for the LR in delay discounting task (DDT). Delay to the LR changed in an ascending order (0, 4, 8, 16, and 32 s) across one session.

RESULTS

DOI (0.5 and 1.0 mg/kg) increased impulsive decision-making, and the effects of DOI (1.0 mg/kg) were blocked by the 5-HT2A receptor antagonist ketanserin (1.0 mg/kg) rather than the 5-HT2C receptor antagonist SB-242084 (1.0 mg/kg). Contrarily, lisuride (0.1, 0.3, and 0.5 mg/kg) decreased impulsive decision-making. The effects of lisuride (0.3 mg/kg) were not antagonized by ketanserin (1.0 mg/kg), selective 5-HT1A antagonist WAY-100635 (1.0 mg/kg), or selective dopamine D4 receptor antagonist L-745870 (1.0 mg/kg) but were attenuated by the selective dopamine D2/D3 receptor antagonist tiapride (40 mg/kg).

CONCLUSIONS

DOI and lisuride have contrasting effects on impulsive decision-making via distinct receptors. DOI-induced increase of impulsivity is mediated by the 5-HT2A receptor, while lisuride-induced inhibition of impulsivity is regulated by the dopamine D2/D3 receptor.

Animal Behavior in Psychedelic Research

Psychedelic-assisted psychotherapy holds great promise in the treatment of mental health disorders. Research into 5-hydroxytryptamine 2A receptor (5-HT_2AR) agonist psychedelic compounds has increased dramatically over the past two decades. In humans, these compounds produce drastic effects on consciousness, and their therapeutic potential relates to changes in the processing of emotional, social, and self-referential information. The use of animal behavior to study psychedelics is under debate, and this review provides a critical perspective on the translational value of animal behavior studies in psychedelic research. Acute activation of 5-HT_2ARs produces head twitches and unique discriminative cues, disrupts sensorimotor gating, and stimulates motor activity while inhibiting exploration in rodents. The acute treatment with psychedelics shows discrepant results in conventional rodent tests of depression-like behaviors but generally induces anxiolytic-like effects and inhibits repetitive behavior in rodents. Psychedelics impair waiting impulsivity but show discrepant effects in other tests of cognitive function. Tests of social interaction also show conflicting results. Effects on measures of time perception depend on the experimental schedule. Lasting or delayed effects of psychedelics in rodent tests related to different behavioral domains appear to be rather sensitive to changes in experimental protocols. Studying the effects of psychedelics on animal behaviors of relevance to effects on psychiatric symptoms in humans, assessing lasting effects, publishing negative findings, and relating behaviors in rodents and humans to other more translatable readouts, such as neuroplastic changes, will improve the translational value of animal behavioral studies in psychedelic research. SIGNIFICANCE STATEMENT: Psychedelics like LSD and psilocybin have received immense interest as potential new treatments of psychiatric disorders. Psychedelics change high-order consciousness in humans, and there is debate about the use of animal behavior studies to investigate these compounds. This review provides an overview of the behavioral effects of 5-HT_2AR agonist psychedelics in laboratory animals and discusses the translatability of the effects in animals to effects in humans. Possible ways to improve the utility of animal behavior in psychedelic research are discussed.

Modafinil rescues repeated morphine-induced synaptic and behavioural impairments via activation of D1R-ERK-CREB pathway in medial prefrontal cortex

Long-term opioid abuse causes a variety of long-lasting cognitive impairments such as attention, impulsivity and working memory. These cognitive impairments undermine behavioural treatment for drug abuse and lead to poor treatment retention and outcomes. Modafinil is a wake-promoting drug that shows potential in improving attention and memory in humans and animals. However, modafinil's effect on opioid-induced cognitive impairments remains unclear, and the underlying mechanism is poorly understood. This study showed that repeated morphine administration significantly impairs attention, increases impulsivity and reduces motivation to natural rewards in mice. Systemic modafinil treatment at low dose efficiently ameliorates morphine-induced attention dysfunction and improves motivation and working memory in mice. High dose of modafinil has adverse effects on impulsive action and attention. Local infusion of D1R antagonist SCH-23390 reverses the morphine-induced synaptic abnormalities and activation of the D1R-ERK-CREB pathway in medial prefrontal cortex (mPFC). This study demonstrated a protective effect of modafinil in mPFC neurons and offered a therapeutic potential for cognitive deficits in opioid abuse.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSION

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

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.

Amphetamine improves mouse and human attention in the 5-choice continuous performance test

Non-medical use of prescription stimulants amongst college students is common, with claims of cognitive and academic benefits. The mechanism, magnitude, and pervasiveness of the cognitive enhancing effects of stimulants in healthy adults remain poorly understood however. The present study determined the effects of dextroamphetamine (D-amp) on the 5-choice continuous performance test (5C-CPT) of attention in healthy young adult humans and mice. A mixed gender sample received placebo (n = 29), 10 (n = 17) or 20 mg D-amp (n = 25) in a double-blind fashion before 5C-CPT testing. In addition, male C57BL/6J mice were trained on a touchscreen adaptation of the 5C-CPT and tested after receiving saline or D-amp (0.1, 0.3, 1.0 mg/kg; n = 8/dose). In humans, D-amp significantly improved 5C-CPT performance. Both doses improved signal detection driven by increased hit rate (reduced omissions). Both doses also improved response accuracy and reduced hit reaction time (HRT) variability. In mice, similar effects (improved signal detection, hit rate, and response accuracy) were observed at the moderate dose (0.3 mg/kg). In contrast to human participants however, no effect on HRT variability was detected in mice, with no effect on HRT in either species. Human 5C-CPT performance was consistent with prior studies and consistent with alternative CPT paradigms. The performance of C57BL/6J mice on the touchscreen 5C-CPT mirrored performance of this strain on 5-hole operant chambers. Importantly, comparable facilitation of attention with D-amp was observed in both species. The 5C-CPT provides a cross-species paradigm by which the cognitive enhancing properties of stimulants and the neural underpinnings of attention can be assessed.