Effort-related functions of nucleus accumbens dopamine and associated forebrain circuits

A Behavioural and neurobiological assessment of effort-based decision-making in cannabis use disorder: An initial/preliminary investigation

Low motivation for noncannabis rewards is a common clinical feature of cannabis use disorder (CUD), yet its underlying neurobiological mechanisms remain largely unknown. This study applied a sequential effort-based decision-making task during functional magnetic resonance imaging to quantify motivation and test for potential neurofunctional differences during prospective effort/reward encoding (Cue1), integration of effort and reward cues (Cue2), and choice behaviour in individuals with CUD (n = 21) and healthy controls (HCs) (n = 20). Behavioural in-scanner results demonstrated that participants in both groups made significantly fewer high-effort choices as effort levels increased on the task, yet they selected significantly more high-reward choices as reward magnitude increased. At the neural level, the CUD group showed decreased ventromedial prefrontal cortex activity, as well as reduced activity in the culmen, posterior cingulate, and superior temporal gyrus during the encoding of prospective effort and reward cues (Cue1) respectively, compared with controls. Conversely, the CUD group showed increased parietal lobule, superior temporal gyrus, fusiform gyrus, middle occipital gyrus, cingulate gyrus, and claustrum activity during the integration phase of the task (Cue2) relative to controls. Exploratory correlations revealed that bilateral ventral striatum activity during prospective effort cues was associated with the proportion of accepted high-effort and high-reward trials, predominantly driven by the CUD group. Altogether, these findings indicate fronto-striatal but also posterior cortical processing alterations during prospective signaling and during effort-reward information integration. By temporally disconnecting effort expenditure from reward magnitude, the current findings shed light on how these constructs independently and simultaneously influence dysregulated effortful goal-directed choice behaviour in CUD.

Delivering a new generation of translational animal models for depression research

Early animal models of depression focused on developing methods that could predict treatment efficacy and were validated based on pharmacological responses to known antidepressants. As our understanding of major depressive disorder (MDD) and the pharmacology of antidepressants progressed, so did the need for better animal models. This need was met with the development of new disease models, such as the chronic mild stress model, and behavioural readouts such as the sucrose preference test, which more closely aligned with risk factors and symptoms seen in patients. These approaches have supported huge advances in the understanding of how stress affects the brain and impacts on reward-related behaviours. However, there remain significant challenges when trying to model complex psychiatric symptoms and disorders in non-human animals. In this perspective article, a brief history of animal models of depression and associated readouts is discussed with specific reference to the important contributions from Paul Willner. The main discussion then focuses on translational validity and approaches that may support delivering this objective. This is illustrated with the example of the affective bias test and reward learning assays, which have been developed to recapitulate in animals the neuropsychological impairments observed in MDD and modulation by antidepressants.

An ace in the hole? Opportunities and limits of using mice to understand schizophrenia neurobiology

In applying model organisms to study the neurobiology of mental disorders, rodents offer unique potential for probing, with high spatiotemporal resolution, the neural and molecular mechanisms underlying behavior in a mammalian system. Furthermore, investigators can wield exceptional power to manipulate genes, molecules, and circuits in mice to pin down causal relationships. While these advantages have allowed us to understand much more deeply than ever before the brain mechanisms regulating complex behaviors, the impact of rodent models on developing therapeutic strategies for psychiatric disorders has remained thus far limited. Herein, we will discuss the opportunities and limits of using mouse models in the context of schizophrenia, a complex psychiatric disorder with strong genetic basis that poses various unmet clinical needs calling out for basic science research. We review approaches for employing behavioral, genetic, and circuit-based methods in rodents to inform schizophrenia symptomatology, pathophysiology, and, ultimately, treatment.

Effort-related motivational effects of methylphenidate: Reversal of the low-effort bias induced by tetrabenazine and enhancement of progressive ratio responding in male and female rats

Dopamine (DA) regulates behavioral activation and effort-related aspects of motivation. Blockade of DA storage by tetrabenazine (TBZ) induces depressive symptoms in humans, including fatigue and apathy. TBZ shifts choice behavior in rodents from high-effort to low-effort options, which can be used to model motivational symptoms observed in psychiatric disorders. The catecholamine transport inhibitor methylphenidate (MPH) reverses the effort-related effects of TBZ in male rats, but this effect needs to be investigated in females. The current study examined the effects of MPH on effort-based choice in male and female rats. Animals were tested on the fixed ratio 5 (FR5)/chow feeding choice task. Because of sex differences in the effects of TBZ, 1.0 mg/kg was used in males, while 2.0 mg/kg was used in females. In both sexes, TBZ shifted choice from lever pressing to chow intake. Co-administration of MPH reversed the effort-related effects of TBZ in males at all doses tested (0.5-4.0 mg/kg IP), whereas only 1.0 and 2.0 mg/kg MPH reversed the effects of TBZ in females. Rats also were tested on a progressive ratio (PROG) schedule and a PROG/chow feeding choice task to assess the effects of MPH administered alone (0.5-4.0 mg/kg IP). MPH increased high-effort PROG responding on both tasks in males, whereas females showed no significant increase in lever pressing across the dose range tested. Investigating sex differences in the pharmacology and neurochemistry of effort-based choice enhances our understanding of sex as a factor in motivational dysfunctions, and may foster the development of treatments for effort-related psychiatric symptoms.

The nucleus accumbens-prefrontal connectivity as a predictor of chronic low back pain

ABSTRACT

The nucleus accumbens (NAc) and its prefrontal connections are implicated in the aetiology of chronic low back pain (CLBP). Animal and human studies suggest that the NAc and its connections play a critical role in the transition from acute to CLBP. However, whole-brain connectivity in individuals with longstanding CLBP has not been systematically investigated. Using a functional connectomics approach, we examined whether the 2 NAc subregions-shell and core-exhibit different whole-brain connectivity between CLBP patients and healthy controls (HCs; total N = 197). The identified connections were correlated with CLBP intensity (multiple comparisons corrected), and their reproducibility was validated in 2 independent cohorts. These clinically relevant and reproducible connections were further leveraged to classify CLBP using machine learning. Compared with HC (n = 41), individuals with CLBP (n = 39) exhibited hyperconnectivity between the NAc shell and core and the prefrontal cortex (PFC). Although several NAc-PFC connections were linked to higher CLBP intensity, only the connections between the left NAc shell and core to the right dorsolateral PFC were reproduced in validation cohorts (total CLBP n = 53; HC n = 64). Nucleus accumbens-right dorsolateral PFC connections achieved 84% classification accuracy using logistic regression. The machine learning analyses demonstrate how knowledge-based feature selection can reliably detect CLBP. Overall, we report that NAc-PFC connectivity consistently distinguishes people with CLBP from HC and suggest an abnormal interaction between the NAc and brain regions involved in motivation, decision-making, and pain regulation.

Reward Processing in Mood Disorders and Schizophrenia: A Neurodevelopmental Framework

Major depressive disorder (MDD), bipolar disorder, and schizophrenia involve disruptions in processing rewarding stimuli. In this review, we propose that distinct mechanistic pathways underlie these disruptions in mood disorders versus schizophrenia, and we highlight the importance of understanding these differences for developing personalized treatments. We summarize evidence suggesting that reward processing abnormalities in mood disorders are driven by dysregulated motivational systems; MDD is characterized by blunted responses to reward cues, and bipolar disorder is characterized by heightened responses. In contrast, we argue that reward processing disruptions in schizophrenia do not reflect abnormalities in motivation or hedonic experience; rather, they reflect impairments in the cognitive representation of past and future rewards as well as misdirected attention to irrelevant stimuli. To integrate these findings, we present a neurodevelopmental framework for the onset of mood and psychotic disorders and explore how disruptions in normative brain development contribute to their pathophysiology, timing, and onset. Additionally, we move beyond viewing these conditions as homogeneous disorders and discuss how reward processing profiles may align with specific symptom dimensions.

Shielding working memory from distraction is more effortful than flexible updating

Exerting cognitive control is known to carry a subjective effort cost and people are generally biased to avoid it. Recent theorizing suggests that the cost of cognitive effort serves as a motivational signal to bias people away from excessive focusing and towards more cognitive flexibility. We asked whether the effort cost of stable distractor resistance is higher than that of non-selective flexible updating of working memory representations. We tested this prediction by using (1) a delayed response paradigm in which we manipulate demands for distractor resistance and flexible updating, as well as (2) a subsequent cognitive effort discounting paradigm that allows us to quantify subjective effort costs. We demonstrate, in two different samples (28 and 62 participants) that participants discount tasks both high in distractor resistance and flexible updating when comparing with taking a break. As predicted, when directly contrasting distractor resistance and non-selective flexible updating the subjective cost of performing a task requiring distractor resistance is higher than that requiring flexible updating.

Noradrenergic modulation of stress induced catecholamine release: Opposing influence of FG7142 and yohimbine

Life stress modulates decision making, particularly in the face of risk, in some cases prompting vulnerable populations to make suboptimal, life-altering choices. In the brain, stress is known to alter the extracellular release of catecholamines in structures such as basolateral amygdala (BLA) and nucleus accumbens (NAc), but the relationship between catecholamines and decision-making behavior under stress has not been systemically explored. We developed an operant touchscreen decision-making task for rats comprising elements of loss aversion and risk seeking behavior. Rats were first injected systemically with an adrenergic α2A-receptor agonist (guanfacine) and antagonist (yohimbine), as well as a partial inverse GABAA agonist, FG 7142, known to induce anxiety and stress related physiological responses in a variety of species, including humans. We then used fiber photometry to monitor NE in the basolateral amygdala (BLA), and DA activity in the nucleus accumbens (NAc) while animals engaged in decision-making and following systemic injections of FG 7142 and yohimbine. We found that neither yohimbine nor guanfacine had any impact on decision making strategy but altered motivational state with yohimbine making the animal almost insensitive to the reward outcome. The pharmacological induction of stress with FG 7142 biased the rats' decisions towards safety, but this bias shifted towards risk when co-treated with yohimbine. In the BLA and NAc, FG 7142 altered catecholamine release with systemic yohimbine producing opposing effects on NE and DA release. These findings highlight the catecholamine basis of loss aversion and neuromodulation of critical brain structures during stress through α2A adrenoreceptors.

Restorative properties of chronic lurasidone treatment on emotional dysfunction in rats exposed to chronic unavoidable stress: A role for medial prefrontal cortex - nucleus accumbens network

Anhedonia, a transdiagnostic symptom prevalent in depressive and psychotic disorders, poses a significant challenge for pharmacological intervention due to its association with impaired motivation. Understanding how psychotropic drugs can modulate this pathological domain and elucidating the molecular mechanisms underlying such effects are crucial endeavors in psychiatric research. In this study, we aimed to investigate the pro-motivational properties of lurasidone in a rat (Sprague Dawley males) model of anhedonia and to unravel the interplay between lurasidone and the brain regions critical for reward processing. Exposure to unpredictable chronic stress (UCS) led to a marked reduction in motivation, a deficit that was restored by lurasidone treatment at 3 mg/kg, but not at 10 mg/kg. Interestingly, the stress-induced decrease in reactivity to negative stimuli was reversed by both doses of lurasidone. At the molecular level, stressed animals exhibited reduced expression of neuroplastic markers, that was increased following lurasidone administration. Furthermore, UCS exposure impaired the activation of the medial prefrontal cortex (mPFC) and nucleus accumbens (NAc) in response to hedonic stimuli, an effect amended by lurasidone treatment. Additionally, lurasidone restored the impaired phosphorylation of DARPP-32, a key regulator of dopamine signaling, in mPFC and NAc of UCS rats exposed to a hedonic stimulus. These findings underscore the potential of lurasidone in improving various psychopathological domains, like impaired motivation and emotional reactivity, core elements contributing to the disability associated with mental disorders. These effects highlight the therapeutic potential of lurasidone in addressing the intricate behavioral and neurochemical alterations associated with anhedonia and related mood disorders.

Cross-species dissection of the modular role of the ventral tegmental area in depressive disorders

Depressive disorders, including major depressive disorder (MDD), represent one of the most prevalent set of disorders worldwide. MDD is characterized by a range of cognitive, behavioral, and neurobiological changes that contribute to the vast array of symptom profiles that make this disorder particularly difficult to treat. A multitude of established evidence suggests a role for the dopamine system, stemming in part from the ventral tegmental area (VTA), in mediating symptoms and behavioral changes that underlie depression. Developments in cutting-edge technologies in pre-clinical models of depressive phenotypes, such as retrograde tracing, electrophysiological recordings, immunohistochemistry, and molecular profiling, have allowed a deeper characterization of singular VTA neuron molecular, physiological, and projection properties. These developments have highlighted that the VTA is not a homogenous cell population but instead comprises vast cellular diversity that underscores its modular role across various functions related to reward processing, aversion, salience processing, learning and motivation. In this review, we begin by introducing the various cell types and brain regions that comprise the VTA circuitry. Then, we introduce the role of the VTA in reward processing as it compares to aversion processing. Next, we characterize distinct neural pathways within the VTA circuitry to understand the effects of chronic social and non-social stress and tie together how these neurobiological changes manifest into specific behavioral phenotypes. Finally, we relate these preclinical findings to clinical findings to parse the heterogeneity of depressive phenotypes and explain the efficacy of recent novel pharmacological interventions that may target the VTA in MDD.

Gut Microbial Control of Neurotransmitters and Their Relation to Neurological Disorders: A Comprehensive Review

The study explores the vital role of gut microbiota in regulating neurotransmitters and its subsequent effects on brain function and mental health. It aims to unravel the mechanisms by which microbial metabolites influence neurotransmitter synthesis and signaling. The ultimate goal is to identify potential therapeutic strategies targeting gut microbiota for the management and treatment of neurological disorders, such as depression, autism spectrum disorder (ASD), anxiety, and Parkinson's disease. The review synthesizes current research on the gut-brain axis, focusing on the influence of gut microbial metabolites on key neurotransmitters, including dopamine, serotonin, and gamma-aminobutyric acid (GABA). It incorporates a multidisciplinary approach, linking microbiology, neurobiology, and clinical research. Each section presents an in-depth review of scientific studies, clinical trials, and emerging therapeutic strategies. The findings highlight the intricate interplay between gut microbiota and the central nervous system. Gut microbes significantly impact the synthesis and signaling of crucial neurotransmitters, which play a pivotal role in neurological health. Evidence supports the hypothesis that modulating gut microbiota can alter neurotransmitter output and alleviate symptoms associated with neurological disorders. Notable therapeutic potentials include microbiota-targeted interventions for managing depression, ASD, anxiety, and Parkinson's disease. This comprehensive analysis underscores the critical connection between gut microbiota and neurological health. By bridging gaps between microbiology, neurobiology, and clinical practice, the study opens avenues for innovative therapeutic approaches. It provides a valuable resource for researchers, clinicians, and students, emphasizing the need for continued investigation into gut microbiota's role in neurological disorders and its therapeutic potential.

Decision cost hypersensitivity underlies Huntington's disease apathy

The neuropsychiatric syndrome of apathy is now recognized to be a common and disabling condition in Huntington's disease. However, the mechanisms underlying it are poorly understood. One way to investigate apathy is to use a theoretical framework of normal motivated behaviour, to determine where breakdown has occurred in people with this behavioural disruption. A fundamental computation underlying motivated, goal-directed behaviour across species is weighing up the costs and rewards associated with actions. Here, we asked whether people with apathy are more sensitive to costs of actions (physical effort and time delay), less sensitive to rewarding outcomes, or both. Based on the unique anatomical substrates associated with Huntington's disease pathology, we hypothesized that a general hypersensitivity to costs would underpin Huntington's disease apathy. Genetically confirmed carriers of the expanded Huntingtin gene (premanifest to mild motor manifest disease, n = 53) were compared to healthy controls (n = 38). Participants performed a physical effort-based decision-making task (Apple Gathering Task) and a delay discounting task (Money Choice Questionnaire). Choice data was analysed using linear regression and drift diffusion models that also accounted for the time taken to make decisions. Apathetic people with Huntington's disease accepted fewer offers overall on the Apple Gathering Task, specifically driven by increased sensitivity to physical effort costs, and not explained by motor severity, mood, cognition or medication. Drift diffusion modelling provided further evidence of effort hypersensitivity, with apathy associated with a faster drift rate towards rejecting offers as a function of varying effort. Increased delay sensitivity was also associated with apathy, both when analysing raw choice and drift rate, where there was moderate evidence of Huntington's disease apathy drifting faster towards the immediately available (low-cost) option. Furthermore, the effort and delay sensitivity parameters from these tasks were positively correlated. The results demonstrate a clear mechanism for apathy in Huntington's disease, cost hypersensitivity, which manifests in both the effort and time costs associated with actions towards rewarding goals. This suggests that Huntington's disease pathology may cause a domain-general disruption of cost processing, which is distinct from apathy occurrence in other brain disorders and may require different therapeutic approaches.

Devaluing memories of reward: a case for dopamine

Midbrain dopamine cells encode differences in predictive and expected value to support learning through reward prediction error. Recent findings have questioned whether reward prediction error can fully account for dopamine function and suggest a more complex role for dopamine in encoding detailed features of the reward environment. In this series of studies, we describe a novel role for dopamine in devaluing sensory features of reward. Mesencephalic dopamine cells activated during a mediated devaluation phase were later chemogenetically reactivated. This retrieval of the devalued reward memory elicited a reduction in the hedonic evaluation of sucrose reward. Through optogenetic and chemogenetic manipulations, we confirm dopamine cells are both sufficient and necessary for mediated devaluation, and retrieval of these memories reflected dopamine release in the nucleus accumbens. Consistent with our computational modeling data, our findings indicate a critical role for dopamine in encoding predictive representations of the sensory features of reinforcement. Overall, we elucidate a novel role for dopamine function in mediated devaluation and illuminate a more elaborate framework through which dopamine encodes reinforcement signals.

Unconscious will as a neurobehavioral mechanism against adversity

Incentive salience theory both explains the directional component of motivation (in terms of cue attraction or "wanting") and its energetic component, as a function of the strength of cue attraction. This theory characterizes cue- and reward-triggered approach behavior. But it does not tell us how behavior can show enhanced vigor under reward uncertainty, when cues are inconsistent or resources hidden. Reinforcement theory is also ineffective in explaining enhanced vigor in case reward expectation is low or nil. This paper provides a neurobehavioral interpretation of effort in situations of adversity (which always include some uncertainty about outcomes) that is complementary to the attribution of incentive salience to environmental cues. It is argued that manageable environmental challenges activate an unconscious process of self-determination to achieve "wanted" actions. This unconscious process is referred to as incentive effort, which involves the hypothalamo-pituitary-adrenal (HPA) axis, noradrenaline, as well as striatal dopamine. Concretely, HPA-induced dopamine release would have the function to make effort-or effortful actions-"wanted" in a challenging context, in which the environmental cues are poorly predictive of reward-i.e., unattractive. Stress would only emerge in the presence of unmanageable challenges. It is hypothesized that incentive effort is the core psychological basis of will-and is, for this reason, termed "willing."

Improving brain health via the central executive network

Cognitive and physical stress have significant effects on brain health, particularly through their influence on the central executive network (CEN). The CEN, which includes regions such as the dorsolateral prefrontal cortex, anterior cingulate cortex and inferior parietal lobe, is central to managing the demands of cognitively challenging motor tasks. Acute stress can temporarily reduce connectivity within the CEN, leading to impaired cognitive function and emotional states. However a rebound in these states often follows, driven by motivational signals through the mesocortical and mesolimbic pathways, which help sustain inhibitory control and task execution. Chronic exposure to physical and cognitive challenges leads to long-term improvements in CEN functionality. These changes are supported by neurochemical, structural and systemic adaptations, including mechanisms of tissue crosstalk. Myokines, adipokines, anti-inflammatory cytokines and gut-derived metabolites contribute to a biochemical environment that enhances neuroplasticity, reduces neuroinflammation and supports neurotransmitters such as serotonin and dopamine. These processes strengthen CEN connectivity, improve self-regulation and enable individuals to adopt and sustain health-optimizing behaviours. Long-term physical activity not only enhances inhibitory control but also reduces the risk of age-related cognitive decline and neurodegenerative diseases. This review highlights the role of progressive physical stress through exercise as a practical approach to strengthening the CEN and promoting brain health, offering a strategy to improve cognitive resilience and emotional well-being across the lifespan.

Neurobiological foundations and clinical relevance of effort-based decision-making

Applying effort-based decision-making tasks provides insights into specific variables influencing choice behaviors. The current review summarizes the structural and functional neuroanatomy of effort-based decision-making. Across 39 examined studies, the review highlights the ventromedial prefrontal cortex in forming reward-based predictions, the ventral striatum encoding expected subjective values driven by reward size, the dorsal anterior cingulate cortex for monitoring choices to maximize rewards, and specific motor areas preparing for effort expenditure. Neuromodulation techniques, along with shifting environmental and internal states, are promising novel treatment interventions for altering neural alterations underlying decision-making. Our review further articulates the translational promise of this construct into the development, maintenance and treatment of psychiatric conditions, particularly those characterized by reward-, effort- and valuation-related deficits.

The Development of Cannabinoids as Therapeutic Agents in the United States

Cannabis is one of the oldest and widely used substances in the world. Cannabinoids within the cannabis plant, known as phytocannabinoids, mediate cannabis' effects through interactions with the body's endogenous cannabinoid system. This endogenous system, the endocannabinoid system, has important roles in physical and mental health. These roles point to the potential to develop cannabinoids as therapeutic agents while underscoring the risks related to interfering with the endogenous system during nonmedical use. This scoping narrative review synthesizes the current evidence for both the therapeutic and adverse effects of the major (i.e., Δ9-tetrahydrocannabinol and cannabidiol) and lesser studied minor phytocannabinoids, from nonclinical to clinical research. We pay particular attention to the areas where evidence is well established, including analgesic effects after acute exposures and neurocognitive risks after acute and chronic use. In addition, drug development considerations for cannabinoids as therapeutic agents within the United States are reviewed. The proposed clinical study design considerations encourage methodological standards for greater scientific rigor and reproducibility to ultimately extend our knowledge of the risks and benefits of cannabinoids for patients and providers. SIGNIFICANCE STATEMENT: This work provides a review of prior research related to phytocannabinoids, including therapeutic potential and known risks in the context of drug development within the United States. We also provide study design considerations for future cannabinoid drug development.

From movement to motivation: a proposed framework to understand the antidepressant effect of exercise

Depression is the leading cause of disability worldwide, exerting a profound negative impact on quality of life in those who experience it. Depression is associated with disruptions to several closely related neural and cognitive processes, including dopamine transmission, fronto-striatal brain activity and connectivity, reward processing and motivation. Physical activity, especially aerobic exercise, reduces depressive symptoms, but the mechanisms driving its antidepressant effects are poorly understood. Here we propose a novel hypothesis for understanding the antidepressant effects of exercise, centred on motivation, across different levels of explanation. There is robust evidence that aerobic exercise decreases systemic inflammation. Inflammation is known to reduce dopamine transmission, which in turn is strongly implicated in effort-based decision making for reward. Drawing on a broad range of research in humans and animals, we propose that by reducing inflammation and boosting dopamine transmission, with consequent effects on effort-based decision making for reward, exercise initially specifically improves 'interest-activity' symptoms of depression-namely anhedonia, fatigue and subjective cognitive impairment - by increasing propensity to exert effort. Extending this framework to the topic of cognitive control, we explain how cognitive impairment in depression may also be conceptualised through an effort-based decision-making framework, which may help to explain the impact of exercise on cognitive impairment. Understanding the mechanisms underlying the antidepressant effects of exercise could inform the development of novel intervention strategies, in particular personalised interventions and boost social prescribing.

Motivational Modulation Enhances Movement Performance in Parkinson's Disease: A Systematic Review

Background

The assessment of motivation and its modulation during treatment are essential aspects of physical therapy practice. However, the modulation of motivation has been sparsely investigated in persons with Parkinson's disease (PD) and at present no studies have synthesized its effects on movement performance.

Objectives

4The purpose of this study was to systematically examine the efficacy of motivational modulation on movement performance in PD and to provide recommendations for its role in physical therapy practice.

Methods

Systematic identification of published literature was performed adhering to PRISMA guidelines, from January 2005 to March 2023. Keywords were used in the following electronic databases: PubMed, Academic Search Complete, the Cochrane Database, Google Scholar, and the Physiotherapy Evidence Database (PEDro). A level of evidence rating was completed according to the scale provided by the American Academy of Cerebral Palsy and Development Medicine. Quality assessments were performed using the Modified Downs and Black checklist.

Results

Eight studies were included in this review, all achieving level III evidence. The methodological quality of studies was varied, with most studies attaining a fair rating. Persons with PD performed upper extremity movement tasks with greater intensity when incentivized with larger rewards compared to smaller incentives. Dopamine replacement medication, Deep Brain Stimulation, and a history of depression, had mediating effects on the response to motivational modulation.

Conclusions

Our findings suggest that it is plausible to improve adherence to exercise when physical therapists modulate motivation through computerized game achievements, gamification of tasks, or other forms of reward and non-rewarding stimuli.

Noradrenergic modulation of stress induced catecholamine release: Opposing influence of FG7142 and yohimbine

Background

Life stress modulates decision making, particularly in the face of risk, in some cases prompting vulnerable populations to make suboptimal, life-altering choices. In the brain, stress is known to alter the extracellular release of catecholamines in structures such as basolateral amygdala (BLA) and nucleus accumbens (NAc), but the relationship between catecholamines and decision-making behavior under stress has not been systemically explored.

Methods

We developed an operant touchscreen decision-making task for rats comprising elements of loss aversion and risk seeking behavior. Rats were first injected systemically with an adrenergicα 2 A -receptor agonist (guanfacine) and antagonist (yohimbine), as well as a partial inverse GABAA agonist, FG 7142, known to induce anxiety and stress related physiological responses in a variety of species, including humans. We then used fiber photometry to monitor NE in the basolateral amygdala (BLA), and DA activity in the nucleus accumbens (NAc) while animals engaged in decision-making and following systemic injections of FG 7142 and yohimbine.

Results

Neither yohimbine nor guanfacine had any impact on decision making strategy but altered motivational state with yohimbine making the animal almost insensitive to the reward outcome. The pharmacological induction of stress with FG 7142 biased the rats' decisions towards safety, but this bias shifted toward risk when co-treated with yohimbine. In the BLA and NAc, the FG 7142 altered catecholamine release, with systemic yohimbine producing opposing effects on NE and DA release.

Conclusions

Stress induced changes in catecholamine release in the BLA and NAc can directly influence loss sensitivity, decisions and motivation, which can be modulated by theα 2 A adrenoreceptor antagonist, yohimbine.

Dopamine, activation of ingestion and evaluation of response efficacy: a focus on the within-session time-course of licking burst number

RATIONALE

Evidence on the effect of dopamine D1-like and D2-like receptor antagonists on licking microstructure and the forced swimming response led us to suggest that (i) dopamine on D1-like receptors plays a role in activating reward-directed responses and (ii) the level of response activation is reboosted based on a process of evaluation of response efficacy requiring dopamine on D2-like receptors. A main piece of evidence in support of this hypothesis is the observation that the dopamine D2-like receptor antagonist raclopride induces a within-session decrement of burst number occurring after the contact with the reward. The few published studies with a detailed analysis of the time-course of this measure were conducted in our laboratory.

OBJECTIVES

The aim of this review is to recapitulate and discuss the evidence in support of the analysis of the within-session burst number as a behavioural substrate for the study of the mechanisms governing ingestion, behavioural activation and the related evaluation processes, and its relevance in the analysis of drug effects on ingestion.

CONCLUSIONS

The evidence gathered so far suggests that the analysis of the within-session time-course of burst number provides an important behavioural substrate for the study of the mechanisms governing ingestion, behavioural activation and the related evaluation processes, and might provide decisive evidence in the analysis of the effects of drugs on ingestion. However, further evidence from independent sources is necessary to validate the use and the proposed interpretation of this measure.

Social isolation postweaning alters reward-related dopamine dynamics in a region-specific manner in adolescent male rats

Early development is characterized by dynamic transitions in brain maturation, which may be impacted by environmental factors. Here, we sought to determine the effects of social isolation from postweaning and during adolescence on reward behavior and dopaminergic signaling in male rats. Subjects were socially isolated or group housed at postnatal day 21. Three weeks later, extracellular dopamine concentrations were examined in the medial prefrontal cortex (mPFC) and nucleus accumbens shell (NAc) during a feeding bout. Surprisingly, opposing effects were found in which increased mPFC dopamine concentrations were observed in group housed, but not isolated, rats. In stark contrast, increased dopamine levels were found in the NAc of isolated, but not group housed, rats. Moreover, the absence of an effect in the mPFC of the isolated rats could not be reversed by subsequent group housing, demonstrating the remarkable long-term effects on dopamine signaling dynamics. When provided a highly palatable food, the isolated subjects exhibited a dramatic increase in mPFC dopamine levels when the chocolate was novel, but no effects following chronic chocolate consumption. In contrast, the group housed subjects showed significantly increased dopamine levels only with chronic chocolate consumption. The dopamine changes were correlated with differences in behavioral measures. Importantly, the deficit in reward-related behavior during isolation could be reversed by microinjection of either dopamine or cocaine into the mPFC. Together, these data provide evidence that social isolation from postweaning and during adolescence alters reward-induced dopamine levels in a brain region-specific manner, which has important functional implications for reward-related behavior.

Using caffeine as a chemical means to induce flow states

Flow is an intrinsically rewarding state characterised by positive affect and total task absorption. Because cognitive and physical performance are optimal in flow, chemical means to facilitate this state are appealing. Caffeine, a non-selective adenosine receptor antagonist, has been emphasized as a potential flow-inducer. Thus, we review the psychological and biological effects of caffeine that, conceptually, enhance flow. Caffeine may facilitate flow through various effects, including: i) upregulation of dopamine D1/D2 receptor affinity in reward-associated brain areas, leading to greater energetic arousal and 'wanting'; ii) protection of dopaminergic neurons; iii) increases in norepinephrine release and alertness, which offset sleep-deprivation and hypoarousal; iv) heightening of parasympathetic high frequency heart rate variability, resulting in improved cortical stress appraisal, v) modification of striatal endocannabinoid-CB1 receptor-signalling, leading to enhanced stress tolerance; and vi) changes in brain network activity in favour of executive function and flow. We also discuss the application of caffeine to treat attention deficit hyperactivity disorder and caveats. We hope to inspire studies assessing the use of caffeine to induce flow.

Decoding Post-Viral Fatigue: The Basal Ganglia's Complex Role in Long-COVID

Long-COVID afflicts millions with relentless fatigue, disrupting daily life. The objective of this narrative review is to synthesize current evidence on the role of the basal ganglia in long-COVID fatigue, discuss potential mechanisms, and highlight promising therapeutic interventions. A comprehensive literature search was conducted using PubMed, Scopus, and Web of Science databases. Mounting evidence from PET, MRI, and functional connectivity data reveals basal ganglia disturbances in long-COVID exhaustion, including inflammation, metabolic disruption, volume changes, and network alterations focused on striatal dopamine circuitry regulating motivation. Theories suggest inflammation-induced signaling disturbances could impede effort/reward valuation, disrupt cortical-subcortical motivational pathways, or diminish excitatory input to arousal centers, attenuating drive initiation. Recent therapeutic pilots targeting basal ganglia abnormalities show provisional efficacy. However, heterogeneous outcomes, inconsistent metrics, and perceived versus objective fatigue discrepancies temper insights. Despite the growing research, gaps remain in understanding the precise pathways linking basal ganglia dysfunction to fatigue and validating treatment efficacy. Further research is needed to advance understanding of the basal ganglia's contribution to long-COVID neurological sequelae and offer hope for improving function across the expanding affected population.

Orexins/Hypocretins: Gatekeepers of Social Interaction and Motivation

Ever since the discovery of the brain's orexin/hypocretin system, most research was directed toward unveiling its contribution to the normal functioning of individuals. The investigation of reward-seeking behaviors then gained a lot of attention once the distribution of orexinergic neurons was revealed. Here, we discuss findings on the involvement of orexins in social interaction, a natural reward type. While some studies have succeeded in defining the relationship between orexin and social interaction, the controversy regarding its nature (direct or inverse relation) raises questions about what aspects have been overlooked until now. Upon examining the literature, we identified a research gap concerning conditions influencing the impact of orexins on social behavior expression. In this review, we introduce a number of factors (e.g., stress, orexin's source) that must be considered while studying the role of orexins in social interaction. Furthermore, we refer to published research to investigate the stage at which orexins affect social interaction and we highlight the nucleus accumbens (NAc) shell's role in social interaction and other rewarding behaviors. Finally, the underlying orexin molecular pathway influencing social motivation in particular illnesses is proposed. We conclude that orexin's impact on social interaction is multifactorial and depends on specific conditions available at a time.

Motivational Vigor in Parkinson's Disease Requires the Short and Long Duration Response to Levodopa

BACKGROUND

Impaired movement vigor (bradykinesia) is a cardinal feature of Parkinson's disease (PD) and hypothesized to result from abnormal motivational processes-impaired motivation-vigor coupling. Dopamine replacement therapy (DRT) improves bradykinesia, but the response to DRT is multifaceted, comprising a short-duration response (SDR) and a long-duration response (LDR) only manifesting with chronic treatment. Prior experiments assessing motivation-vigor coupling in PD used chronically treated subjects, obscuring the roles of the SDR and LDR.

METHODS

To disambiguate the SDR and LDR, 11 de novo PD subjects (6 male [M]:5 female [F]; mean age, 67) were studied before treatment, after an acute levodopa (l-dopa) dose, and in both the practical "off" (LDR) and "on" (LDR + SDR) states after chronic stable treatment. At each visit, subjects were characterized with a standard battery including the Movement Disorder Society-Sponsored Revision of the Unified Parkinson's Disease Rating Scale (MDS-UPDRS) and an incentivized joystick task to assess motor performance in response to varying rewards.

RESULTS

l-Dopa induced a robust SDR and LDR, with further improvement in the combined SDR + LDR state. At baseline, after acute treatment (SDR), and after LDR induction, subjects did not exhibit the normal increase in movement speed with increasing reward. Only in the combined SDR + LDR state was there restoration of motivation-vigor coupling.

CONCLUSIONS

Although consistent with prior results in chronically treated PD subjects, the significant improvement in motor performance observed with the SDR and LDR suggests that bradykinesia is not solely secondary to deficient modulation of motivational processes. © 2023 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Reviewing the neurobiology of electroconvulsive therapy on a micro- meso- and macro-level

BACKGROUND

Electroconvulsive therapy (ECT) remains the one of the most effective of biological antidepressant interventions. However, the exact neurobiological mechanisms underlying the efficacy of ECT remain unclear. A gap in the literature is the lack of multimodal research that attempts to integrate findings at different biological levels of analysis METHODS: We searched the PubMed database for relevant studies. We review biological studies of ECT in depression on a micro- (molecular), meso- (structural) and macro- (network) level.

RESULTS

ECT impacts both peripheral and central inflammatory processes, triggers neuroplastic mechanisms and modulates large scale neural network connectivity.

CONCLUSIONS

Integrating this vast body of existing evidence, we are tempted to speculate that ECT may have neuroplastic effects resulting in the modulation of connectivity between and among specific large-scale networks that are altered in depression. These effects could be mediated by the immunomodulatory properties of the treatment. A better understanding of the complex interactions between the micro-, meso- and macro- level might further specify the mechanisms of action of ECT.

High intensity interval training exercise increases dopamine D2 levels and modulates brain dopamine signaling

Background

Previous research has outlined the health benefits of exercise including its therapeutic potential for substance use disorders (SUD). These data have already been utilized and it is now common to find exercise as part of SUD treatment and relapse prevention programs. However, we need to better understand different exercise regimens and determine which would be the most beneficial for SUDs. Recently, high intensity interval training (HIIT) has gained attention in comparison with aerobic and resistance exercise. Little is known regarding the neurobiological mechanisms of HIIT, including its effects on dopamine signaling and receptor levels in the brain. The present study examined the effects of chronic HIIT exercise on dopamine signaling as measured by dopamine type 1-like receptor (D1R)-like, dopamine type 2-like receptor (D2R)-like, and tyrosine hydroxylase (TH) quantification in the brains of male and female rats as measured by [3H] SCH 23390 and [3H] spiperone autoradiography, and TH-immunoreactive optical density values.

Methods

Rats were separated in two groups: sedentary and HIIT exercise. Exercise was on a treadmill for 30 min daily (10 3 min cycles) for six weeks with progressive speed increased up to 0.8 mph (21.5 m/min).

Results

Results showed for D2R-like binding, a significant effect across the ventral caudate putamen (V CPU) between sexes, such that mean D2R-like binding was 14% greater for males than females. In the nucleus accumbens shell (Nac Shell), the HIIT Exercise rats showed 16% greater D2R-like binding as compared to the sedentary rats. No significant effects of HIIT exercise were found across groups for brain D1R-like binding levels or TH expression.

Conclusion

These results suggest that HIIT exercise can modulate dopamine signaling by way of increased D2R. These findings support the premise that HIIT exercise plays an important role in dopamine signaling and, may provide a potential mechanism for how HIIT exercise can impact the brain and behavior.

Activation of Kv7 channels normalizes hyperactivity of the VTA-NAcLat circuit and attenuates methamphetamine-induced conditioned place preference and sensitization in mice

The brain circuit projecting from the ventral tegmental area (VTA) to the nucleus accumbens lateral shell (NAcLat) has a key role in methamphetamine (MA) addiction. As different dopamine (DA) neuron subpopulations in the VTA participate in different neuronal circuits, it is a challenge to isolate these DA neuron subtypes. Using retrograde tracing and Patch-seq, we isolated DA neurons in the VTA-NAcLat circuit in MA-treated mice and performed gene expression profiling. Among the differentially expressed genes, KCNQ genes were dramatically downregulated. KCNQ genes encode Kv7 channel proteins, which modulate neuronal excitability. Injection of both the Kv7.2/3 agonist ICA069673 and the Kv7.4 agonist fasudil into the VTA attenuated MA-induced conditioned place preference and locomotor sensitization and decreased neuronal excitability. Increasing Kv7.2/3 activity decreased neural oscillations, synaptic plasticity and DA release in the VTA-NacLat circuit in MA-treated mice. Furthermore, overexpression of only Kv7.3 channels in the VTA-NacLat circuit was sufficient to attenuate MA-induced reward behavior and decrease VTA neuron excitability. Activation of Kv7 channels in the VTA may become a novel treatment strategy for MA abuse.

Delayed estrogen actions diminish food consumption without changing food approach, motor activity, or hypothalamic activation elicited by corticostriatal µ-opioid signaling

Mu-opioid receptor (μ-OR) signaling in forebrain sites including nucleus accumbens (Acb) and ventromedial prefrontal cortex (vmPFC) modulates reward-driven feeding and may play a role in the pathophysiology of disordered eating. In preclinical models, intra-Acb or intra-vmPFC μ-OR stimulation causes overeating and vigorous responding for food rewards. These effects have been studied mainly in male animals, despite demonstrated sex differences and estrogen modulation of central reward systems. Hence, the present study investigated sex differences and estrogen modulation of intra-Acb and intra-vmPFC μ-OR-driven feeding behaviors. First, the dose-related effects of intra-Acb and intra-vmPFC infusions of the μ-OR-selective agonist, DAMGO, were compared among intact female, ovariectomized (OVX) female, and intact male rats. The DAMGO feeding dose-effect function was flattened in intact females relative to the robust, dose-dependent effects observed in OVX females and intact males. Thus, in intact females, intra-Acb DAMGO failed to elevate food intake relative to vehicle, while intra-vmPFC DAMGO elevated food intake, but to a smaller degree compared to males and OVX females. Next, to explore the possible role of estrogen in mediating the diminished DAMGO response observed in intact females, OVX rats were given intra-Acb or intra-vmPFC infusions of DAMGO either immediately after a subcutaneous injection of 17-beta-estradiol 3-benzoate (EB; 5 μg/0.1 mL) or 24 h after EB injection. Intra-Acb DAMGO effects were not changed at the immediate post-EB time point. At the delayed post-EB timepoint, significant lordosis was noted and the duration of intra-Acb DAMGO-driven feeding bouts was significantly reduced, with no change in the number of bouts initiated, locomotor hyperactivity, or Fos immunoreactivity in hypothalamic feeding and arousal systems. Similarly, EB failed to alter the motor-activational effects of intra-vmPFC DAMGO while reducing feeding. These findings indicate that delayed, presumably genomically mediated estrogen actions modulate the μ-OR-generated motivational state by reducing consummatory activity while sparing goal-approach and general arousal/activity. The results additionally suggest that EB regulation of consummatory activity occurs outside of forebrain-μ-OR control of hypothalamic systems.

A Multi-task Platform for Profiling Cognitive and Motivational Constructs in Humans and Nonhuman Primates

Background

Understanding the neurobiological substrates of psychiatric disorders requires comprehensive evaluations of cognitive and motivational functions in preclinical research settings. The translational validity of such evaluations will be supported by (1) tasks with high construct validity that are engaging and easy to teach to human and nonhuman participants, (2) software that enables efficient switching between multiple tasks in single sessions, (3) software that supports tasks across a broad range of physical experimental setups, and (4) by platform architectures that are easily extendable and customizable to encourage future optimization and development.

New Method

We describe the Multi-task Universal Suite for Experiments ( M-USE ), a software platform designed to meet these requirements. It leverages the Unity video game engine and C# programming language to (1) support immersive and engaging tasks for humans and nonhuman primates, (2) allow experimenters or participants to switch between multiple tasks within-session, (3) generate builds that function across computers, tablets, and websites, and (4) is freely available online with documentation and tutorials for users and developers. M-USE includes a task library with seven pre-existing tasks assessing cognitive and motivational constructs of perception, attention, working memory, cognitive flexibility, motivational and affective self-control, relational long-term memory, and visuo-spatial problem solving.

Results

M-USE was used to test NHPs on up to six tasks per session, all available as part of the Task Library, and to extract performance metrics for all major cognitive and motivational constructs spanning the Research Domain Criteria (RDoC) of the National Institutes of Mental Health.

Comparison with Existing Methods

Other experiment design and control systems exist, but do not provide the full range of features available in M-USE, including a pre-existing task library for cross-species assessments; the ability to switch seamlessly between tasks in individual sessions; cross-platform build capabilities; license-free availability; and its leveraging of video-engine capabilities used to gamify tasks.

Conclusions

The new multi-task platform facilitates cross-species translational research for understanding the neurobiological substrates of higher cognitive and motivational functions.

Sex and age differences in mice models of effort-based decision-making and anergia in depression: the role of dopamine, and cerebral-dopamine-neurotrophic-factor

Mesolimbic dopamine (DA) regulates vigor in motivated behavior. While previous results have mainly been performed in male rodents, the present studies compared CD1 male and female mice in effort-based decision-making tests of motivation. These tests offered choices between several reinforcers that require different levels of effort (progressive ratio/choice task and 3-choice-T-maze task). Sweet reinforcers were used in both tasks. In the operant tasks, females worked harder as the task required more effort to access a 10% sucrose solution. Although males and females did not differ in preference for 10% vs 3% solutions under free concurrent presentation, females consumed more of the 10% solution when tested alone. The operant task requires a long period of training and changes in the DA system due to age can be mediating long-term changes in effort. Thus, age and sex factors were evaluated in the T-maze task, which requires only a short training period. Both sexes and ages were equally active when habituated to the running wheel (RW), but females consumed more sweet pellets than males, especially at an older age. Both sexes had a strong preference for the RW compared to more sedentary reinforcers in the 3-choice-T-maze test, but older animals spent less time running and ate more than the young ones. The DA-depleting agent tetrabenazine reduced time running in older mice but not in adolescents. Cerebral-dopamine-neurotrophic-factor was reduced in older mice of both sexes compared to adolescent mice. These results emphasize the importance of taking into account differences in sex and age when evaluating willingness to exert effort for specific reinforcers.

Not all bad decisions are alike: approach and avoidant bad decisions are associated with distinct network organization

Introduction

Decisions under ambiguity occurs daily for everyone. Subsequently, we all deliberate upon options to initiate an action most appropriate for current goal demands. Researchers has attempted to identify factors which contribute to risk taking, alongside the neurocircuitry underpinning it. Empirically, uncertain decision making is frequently assessed using the Iowa Gambling Task (IGT). Research have reliably identified varying regions implicating two broader circuits known as the reward and salience networks. However, considerable work has focused on contrasting "good" versus "bad" decisions.

Methods

The present investigation attempted a unique approach to analyzing the modified IGT acquired during fMRI (n = 24) and focused on active and passive bad decisions to identify potential internetwork connectivity, dissociable connectivity patterns between approach and avoidant bad decisions, and their relationship with personality traits, which can be linked with behavioral approach styles.

Results

Network cluster analyses revealed general internetwork connectivity when passing (avoiding) good decks; however, the OFC was functionally disconnected from the rest of the selected brain regions when playing (approaching) bad decks. Decreased reward responsiveness was linked to increased functional connectivity between the lateral OFC and aSMG, while drive was associated with increased functional connectivity between dACC and aINS.

Discussion

We report evidence that approach and avoidant bad decisions are associated with distinct neural communication patterns. Avoidant decisions were marked by substantial network integration and coherence, contrasted with the general scarcity of internetwork communication observed for approach decisions. Furthermore, the present investigation observed preliminary evidence of personality traits linked with neural communication between salience and reward evaluative networks.

Effort-related effects of chronic administration of the DA D2 receptor antagonist haloperidol via subcutaneous programmable minipumps: Reversal by co-administration of the adenosine A2A antagonist istradefylline

RATIONALE

Long-acting antipsychotics such as haloperidol decanoate are becoming more commonly used. Long-acting depot formulations have several advantages, but secondary negative effects of prolonged delivery, including motivational dysfunctions, could have debilitating effects. Assessing the behavioral changes that emerge during chronic antipsychotic administration in rats could provide insight regarding the development of motivational dysfunctions and drug tolerance.

OBJECTIVES

Acute administration of dopamine D2 antagonists such as haloperidol induce motivational deficits in rats, as marked by a shift towards a low-effort bias during effort-based choice tasks. In the present studies, programmable subcutaneous infusion pumps provided continuous and controlled drug delivery of haloperidol. Animals were assessed using a fixed ratio (FR) 5 lever pressing schedule and the FR5/chow feeding test of effort-based choice. The adenosine A2A antagonist istradefylline was studied for its ability to reverse the effects of chronic haloperidol.

RESULTS

Continuous chronic infusions of haloperidol produced significant reductions in FR5 performance and a shift from lever pressing to chow intake in rats tested on FR5/chow feeding choice, with no evidence of tolerance over the 4-week infusion period. Behavior returned to baseline during the vehicle-infusion washout period. Istradefylline significantly reversed the effects of haloperidol, increasing lever pressing and decreasing chow intake in haloperidol-treated rats.

CONCLUSIONS

These studies provide an important behavioral characterization of the effects of chronically infused haloperidol, and demonstrate that A2A antagonism reverses the effects of chronic haloperidol. This research could contribute to the understanding and treatment of motivational dysfunctions seen in schizophrenia, Parkinson's disease, and other disorders involving dopamine.

A functional account of stimulation-based aerobic glycolysis and its role in interpreting BOLD signal intensity increases in neuroimaging experiments

In aerobic glycolysis, oxygen is abundant, and yet cells metabolize glucose without using it, decreasing their ATP per glucose yield by 15-fold. During task-based stimulation, aerobic glycolysis occurs in localized brain regions, presenting a puzzle: why produce ATP inefficiently when, all else being equal, evolution should favor the efficient use of metabolic resources? The answer is that all else is not equal. We propose that a tradeoff exists between efficient ATP production and the efficiency with which ATP is spent to transmit information. Aerobic glycolysis, despite yielding little ATP per glucose, may support neuronal signaling in thin (< 0.5 µm), information-efficient axons. We call this the efficiency tradeoff hypothesis. This tradeoff has potential implications for interpretations of task-related BOLD "activation" observed in fMRI. We hypothesize that BOLD "activation" may index local increases in aerobic glycolysis, which support signaling in thin axons carrying "bottom-up" information, or "prediction error"-i.e., the BIAPEM (BOLD increases approximate prediction error metabolism) hypothesis. Finally, we explore implications of our hypotheses for human brain evolution, social behavior, and mental disorders.

Deficits in consummatory reward relate to severity of cocaine use

BACKGROUND AND AIMS

Identifying modifiable neuropsychological factors associated with more severe CUD could improve CUD treatment. Impairments in processing of non-drug rewards may be one such factor. This study assessed the relationship between reward functioning and cocaine use severity using multi-modal measures of three distinct reward functions: consummatory reward (pleasure or "liking"); motivational reward ("wanting") and reward learning.

METHODS

Fifty-three adults with at least moderate CUD completed self-report and behavioral measures of consummatory reward, motivational reward and reward learning, and a composite cocaine use severity measure including quantity, frequency and life impacts of cocaine use. We conducted parallel Frequentist and Bayesian multiple regressions with measures of reward functioning as predictors of cocaine use severity.

RESULTS

Less self-reported ability to experience pleasure, a hypothesized measure of consummatory reward, significantly predicted greater severity after adjustment for covariates and multiple hypothesis testing, β = 0.39, t(38) = 2.86, p = 0.007. Bayesian analyses confirmed a highly likely association between severity and ability to experience pleasure, and provided moderate evidence for associations with willingness to exert effort and reward learning.

CONCLUSIONS

Our results suggest that less experience of subjective pleasure is related to greater cocaine use severity. This cross-sectional study cannot establish whether differences in consummatory reward are pre-existing, a result of CUD, or both. However, these results suggest interventions focused on increasing subjective pleasure, such as mindful "savoring", should be investigated for CUD.

Strain-specific changes in nucleus accumbens transcriptome and motivation for palatable food reward in mice exposed to maternal separation

Introduction

In humans, adversity in childhood exerts enduring effects on brain and increases the vulnerability to psychiatric diseases. It also leads to a higher risk of eating disorders and obesity. Maternal separation (MS) in mice has been used as a proxy of stress during infancy. We hypothesized that MS in mice affects motivation to obtain palatable food in adulthood and changes gene expression in reward system.

Methods

Male and female pups from C57Bl/6J and C3H/HeN mice strains were subjected to a daily MS protocol from postnatal day (PND) 2 to PND14. At adulthood, their motivation for palatable food reward was assessed in operant cages.

Results

Compared to control mice, male and female C3H/HeN mice exposed to MS increased their instrumental response for palatable food, especially when the effort required to obtain the reward was high. Importantly, this effect is shown in animals fed ad libitum. Transcriptional analysis revealed 375 genes differentially expressed in the nucleus accumbens of male MS C3H/HeN mice compared to the control group, some of these being associated with the regulation of the reward system (e.g., Gnas, Pnoc). Interestingly, C57Bl/6J mice exposed to MS did not show alterations in their motivation to obtain a palatable reward, nor significant changes in gene expression in the nucleus accumbens.

Conclusion

MS produces long-lasting changes in motivation for palatable food in C3H/HeN mice, but has no impact in C57Bl/6J mice. These behavioral alterations are accompanied by drastic changes in gene expression in the nucleus accumbens, a key structure in the regulation of motivational processes.

A preclinical secondary pharmacology resource illuminates target-adverse drug reaction associations of marketed drugs

In vitro secondary pharmacology assays are an important tool for predicting clinical adverse drug reactions (ADRs) of investigational drugs. We created the Secondary Pharmacology Database (SPD) by testing 1958 drugs using 200 assays to validate target-ADR associations. Compared to public and subscription resources, 95% of all and 36% of active (AC50 < 1 µM) results are unique to SPD, with bias towards higher activity in public resources. Annotating drugs with free maximal plasma concentrations, we find 684 physiologically relevant unpublished off-target activities. Furthermore, 64% of putative ADRs linked to target activity in key literature reviews are not statistically significant in SPD. Systematic analysis of all target-ADR pairs identifies several putative associations supported by publications. Finally, candidate mechanisms for known ADRs are proposed based on SPD off-target activities. Here we present a freely-available resource for benchmarking ADR predictions, explaining phenotypic activity and investigating clinical properties of marketed drugs.

Effort-Cost Decision-making Among Individuals With Schizophrenia: A Systematic Review and Meta-analysis

Importance

Motivational impairments in schizophrenia are by definition associated with poor outcome. It is postulated that the reduction of goal-directed behavior arises from abnormal trade-offs between rewards and efforts.

Objective

To examine whether schizophrenia is associated with impairments in effort-cost decision-making.

Data Sources

For this systematic review and meta-analysis, the PubMed, ScienceDirect, PsycINFO, Embase, and ClinicalTrials.gov databases were searched from inception to July 2022 for studies that investigated effort-cost decision-making in schizophrenia. Search terms included effort, cost, and schizophrenia.

Study Selection

Consensual criteria for inclusion were peer-reviewed studies published in English that used a computerized effort-cost decision-making behavioral paradigm and compared individuals with schizophrenia with control individuals.

Data Extraction and Synthesis

The Preferred Reporting Items for Systematic Reviews and Meta-analyses reporting guideline was used for abstracting data. Data were extracted independently by 2 authors and then pooled using random-effects sizes and bayesian approaches.

Main Outcomes and Measures

The main outcomes were performance on effort-cost decision-making tasks requiring an effort-reward trade-off, measured by Hedges g effect size. Effects of moderators were tested with meta-regressions and subgroup analyses.

Results

Twenty studies involving 1503 participants were included: 837 individuals with schizophrenia (541 [64.6%] male; mean [SD] age, 35.89 [6.70] years) and 666 control individuals without schizophrenia (360 [54.1%] male; mean [SD] age, 34.16 [5.92] years). Participants with schizophrenia had significantly reduced willingness to expend effort for rewards compared with controls (k = 20; effect size, 0.43; 95% CI, 0.30-0.56; P < .001; I2 = 33.1%; Q test P = .08). The magnitude of the deficit was significantly greater for high-reward trials. The severity of negative symptoms was negatively associated with effort-cost decision-making (k = 8; effect size, -0.33; 95% CI, -0.50 to -0.15; P < .001), while participants with a high number of negative symptoms had a significantly larger impairment in effort-cost decision-making (k = 5; effect size, 0.47; 95% CI, 0.10-0.84; P = .01).

Conclusions and Relevance

In this systematic review and meta-analysis, schizophrenia was associated with deficits in effort allocation as indexed by effort-cost decision-making tasks. Understanding the cognitive and neurobiological mechanisms driving effort allocation impairments may assist in developing novel interventions.

The persistence of stress-induced physical inactivity in rats: an investigation of central monoamine neurotransmitters and skeletal muscle oxidative stress

Introduction

Sedentary lifestyles have reached epidemic proportions world-wide. A growing body of literature suggests that exposures to adverse experiences (e.g., psychological traumas) are a significant risk factor for the development of physically inactive lifestyles. However, the biological mechanisms linking prior stress exposure and persistent deficits in physical activity engagement remains poorly understood.

Methods

The purpose of this study was twofold. First, to identify acute stress intensity thresholds that elicit long-term wheel running deficits in rats. To that end, young adult male rats were exposed to a single episode of 0, 50, or 100 uncontrollable tail shocks and then given free access to running wheels for 9 weeks. Second, to identify stress-induced changes to central monoamine neurotransmitters and peripheral muscle physiology that may be maladaptive to exercise output. For this study, rats were either exposed to a single episode of uncontrollable tail shocks (stress) or left undisturbed in home cages (unstressed). Eight days later, monoamine-related neurochemicals were quantified by ultra-high performance liquid chromatography (UHPLC) across brain reward, motor, and emotion structures immediately following a bout of graded treadmill exercise controlled for duration and intensity. Additionally, protein markers of oxidative stress, inflammation, and metabolic activity were assessed in the gastrocnemius muscle by Western blot.

Results

For experiment 1, stress exposure caused a shock number-dependent two to fourfold decrease in wheel running distance across the entire duration of the study. For experiment 2, stress exposure curbed an exercise-induced increase of dopamine (DA) turnover measures in the prefrontal cortex and hippocampus, and augmented serotonin (5HT) turnover in the hypothalamus and remaining cortical area. However, stress exposure also caused several monoaminergic changes independent of exercise that could underlie impaired motivation for physical activity, including a mild dopamine deficiency in the striatal area. Finally, stress potently increased HSP70 and lowered SOD2 protein concentrations in the gastrocnemius muscle, which may indicate prolonged oxidative stress.

Discussion

These data support some of the possible central and peripheral mechanisms by which exposure to adverse experiences may chronically impair physical activity engagement.

The differential neural substrates for reward choice under gain-loss contexts and risk in alcohol use disorder: Evidence from a voxel-based meta-analysis

BACKGROUND

Making a risky decision is a complex process that involves the evaluation of both the values of the options and the associated risk level; this process is distinct from reward processing in gain versus loss contexts. Although disrupted reward processing in mesolimbic dopamine circuitry is suggested to underlie pathological incentive processing in patients with alcohol use disorder (AUD), the differential neural processes subserving these motivational tendencies for risk situations or gain/loss choices in decision-making have not been identified.

METHODS

To examine the common or distinct neural mechanisms in the evaluation of risk versus outcomes for AUD, we conducted two separate coordinate-based meta-analyses of functional neuroimaging studies by using Seed-Based d Mapping software to evaluate 13 studies investigating gain and loss processing and 10 studies investigating risky decision-making.

RESULTS

During gain and loss processing, relative to healthy controls, AUD patients showed reduced activation in the mesocortical-limbic circuit, including the orbital prefrontal cortex (OFC), dorsal striatum, insula, hippocampus, cerebellum, cuneus cortex and superior temporal gyrus, but hyperactivation in the inferior temporal gyrus and paracentral lobule (extending to the middle cingulate cortex (MCC) and precuneus). During decision-making under risk, AUD patients exhibited hypoactivity of the prefrontal and cingulate cortices, including the posterior cingulate cortex (extending to the MCC), middle frontal gyrus, medial prefrontal cortex, dorsolateral prefrontal cortex, OFC and anterior cingulate cortex.

CONCLUSIONS

Our results extend existing neurological evidence by showing that a reduced response in the mesocortical-limbic circuit is found in gain versus loss processing, with decreased responsivity in cortical regions in risk decision-making. Our results implicate dissociable neural circuit responses for gain-loss processing and risk decision-making, which contribute to a better understanding of the pathophysiological mechanism underlying nondrug incentive and risk processing in individuals with AUD.

The association of CNR1 genetic variants with resting-state functional connectivity in youth bipolar disorder

Cannabinoid 1 receptors coded by the CNR1 gene are implicated in mood disorders and addiction. Given the prevalence and negative correlates of cannabis use in bipolar disorder (BD), we examined CNR1 polymorphism rs1324072 in relation to resting-state functional connectivity (rsFC) in youth BD. Participants included 124 youth, ages 13-20 years: 17 BD G-carriers, 48 BD non-carriers, 16 healthy controls (HC) G-carriers, and 43 HC non-carriers. rsFC was obtained using 3T-MRI. General linear models examined main effects of diagnosis, gene, and diagnosis-by-gene interaction, controlling for age, sex, and race. Regions-of-interests in seed-to-voxel analyses included: bilateral amygdala, hippocampus, nucleus accumbens (NAc), and orbitofrontal cortex (OFC). Main effects of diagnosis were observed for rsFC between the right amygdala seed and right occipital pole, and between the left NAc seed and left superior parietal lobe. Interaction analyses identified 6 significant clusters. G-allele was associated with negative connectivity in BD and positive connectivity in HC for: left amygdala seed with right intracalcarine cortex; right NAc seed with left inferior frontal gyrus; and right hippocampal seed with bilateral cuneal cortex (all p<0.001). G-allele was associated with positive connectivity in BD and negative connectivity in HC for: right hippocampal seed with left central opercular cortex (p = 0.001), and left NAc seed with left middle temporal cortex (p = 0.002). In conclusion, CNR1 rs1324072 was differentially associated with rsFC in youth with BD in regions relevant to reward and emotion. Future studies powered to integrate CNR1 alongside cannabis use are warranted to examine the inter-relationship between rs1324072 G-allele, cannabis use, and BD.

Learning critically drives parkinsonian motor deficits through imbalanced striatal pathway recruitment

Dopamine (DA) loss in Parkinson's disease (PD) causes debilitating motor deficits. However, dopamine is also widely linked to reward prediction and learning, and the contribution of dopamine-dependent learning to movements that are impaired in PD-which often do not lead to explicit rewards-is unclear. Here, we used two distinct motor tasks to dissociate dopamine's acute motoric effects vs. its long-lasting, learning-mediated effects. In dopamine-depleted mice, motor task performance gradually worsened with task exposure. Task experience was critical, as mice that remained in the home cage during the same period were relatively unimpaired when subsequently probed on the task. Repeated dopamine replacement treatments acutely rescued deficits and gradually induced long-term rescue that persisted despite treatment withdrawal. Surprisingly, both long-term rescue and parkinsonian performance decline were task specific, implicating dopamine-dependent learning. D1R activation potently induced acute rescue that gradually consolidated into long-term rescue. Conversely, reduced D2R activation potently induced parkinsonian decline. In dopamine-depleted mice, either D1R activation or D2R activation prevented parkinsonian decline, and both restored balanced activation of direct vs. indirect striatal pathways. These findings suggest that reinforcement and maintenance of movements-even movements not leading to explicit rewards-are fundamental functions of dopamine and provide potential mechanisms for the hitherto unexplained "long-duration response" by dopaminergic therapies in PD.

Repeated dosing with cocaine produces strain-dependent effects on responding for conditioned reinforcement in Collaborative Cross mice

RATIONALE

Cocaine use disorder (CUD) is a highly heritable form of substance use disorder, with genetic variation accounting for a substantial proportion of the risk for transitioning from recreational use to a clinically impairing addiction. With repeated exposures to cocaine, psychomotor and incentive sensitization are observed in rodents. These phenomena are thought to model behavioral changes elicited by the drug that contribute to the progression into addiction, but little is known about how genetic variation may moderate these consequences.

OBJECTIVES

Here, we describe the use of two Collaborative Cross (CC) recombinant inbred mouse strains that either exhibit high (CC018/UncJ) or no (CC027/GeniUncJ) psychomotor sensitization in response to cocaine to measure phenotypes related to incentive sensitization after repeated cocaine exposures; given the relationship of incentive motivation to nucleus accumbens core (NAc) dopamine release and reuptake, we also assessed these neurochemical mechanisms.

METHODS

Adult male and female CC018/UncJ and CC027/GeniUncJ mice underwent Pavlovian conditioning to associate a visual cue with presentation of a palatable food reward, then received five, every-other-day injections of cocaine or vehicle. Following Pavlovian re-training, they underwent testing acquisition of a new operant response for the visual cue, now serving as a conditioned reinforcer. Subsequently, electrically evoked dopamine release was assessed using fast-scan cyclic voltammetry from acute brain slices containing the NAc.

RESULTS

While both strains acquired the Pavlovian association, only CC018/UncJ mice showed conditioned reinforcement and incentive sensitization in response to cocaine, while CC027/GeniUncJ mice did not. Voltammetry data revealed that CC018/UncJ, compared to CC027/GeniUnc, mice exhibited higher baseline dopamine release and uptake. Moreover, chronic cocaine exposure blunted tonic and phasic dopamine release in CC018/UncJ, but not CC027/GeniUncJ, mice.

CONCLUSIONS

Genetic background is a moderator of cocaine-induced neuroadaptations in mesolimbic dopamine signaling, which may contribute to both psychomotor and incentive sensitization and indicate a shared biological mechanism of variation.

Perimenopausal Effects of Estradiol on Anhedonia and Psychosis Study (PEEPs): study protocol for a neural and molecular mechanistic clinical trial

BACKGROUND

The perimenopausal transition is accompanied by psychiatric symptoms in over 10% of women. Symptoms commonly include depressed mood and anhedonia and less commonly include psychosis. Psychiatric symptoms have been linked to the depletion and/or variability of circulating estradiol, and estradiol treatment reduces perimenopausal anhedonia and psychosis in some women. Estrogen fluctuations may disrupt function in the mesolimbic reward system in some women, leading to psychiatric symptoms like anhedonia or psychosis. The Perimenopausal Effects of Estradiol on Anhedonia and Psychosis Study (PEEPs) is a mechanistic clinical trial that aims to (1) identify relationships between perimenopausal-onset anhedonia and psychosis and neuromolecular markers of mesolimbic reward responses and (2) determine the extent to which estradiol treatment-induced changes in mesolimbic reward responses are associated with alleviation of perimenopausal onset anhedonia or psychosis.

METHODS

This study will recruit 100 unmedicated women ages 44-55 in the late-stage perimenopausal transition, sampling across the range of mild-to-high anhedonia and absent-to-moderate psychosis symptoms. Patients will be randomized to receive either estradiol or placebo treatment for 3 weeks. Clinical outcome measures will include symptoms of anhedonia (measured with Snaith-Hamilton Pleasure Scale; SHAPS) and psychosis (measured with Brief Psychiatric Rating Scale; BPRS psychosis subscale) as well as neural markers of mesolimbic reward system functioning, including reward-related fMRI activation and PET-derived measure of striatal dopamine binding. Pre-treatment associations between (1) SHAPS/BPRS scores and (2) reward-related striatal dopamine binding/BOLD activation will be examined. Furthermore, longitudinal mixed models will be used to estimate (1) symptom and neuromolecular trajectories as a function of estradiol vs. placebo treatment and (2) how changes in reward-related striatal dopamine binding and BOLD activation predict variability in symptom trajectories in response to estradiol treatment.

DISCUSSION

This clinical trial will be the first to characterize neural and molecular mechanisms by which estradiol treatment ameliorates anhedonia and psychosis symptoms during the perimenopausal transition, thus laying the groundwork for future biomarker research to predict susceptibility and prognosis and develop targeted treatments for perimenopausal psychiatric symptoms. Furthermore, in alignment with the National Institute for Mental Health Research Domain Criteria initiative, this trial will improve our understanding of a range of disorders characterized by anhedonia, psychosis, and reward system dysfunction.

TRIAL REGISTRATION

ClinicalTrials.gov NCT05282277.

Matcha Tea Powder's Antidepressant-like Effect through the Activation of the Dopaminergic System in Mice Is Dependent on Social Isolation Stress

Matcha tea powder is believed to have various physiological benefits; however, its detailed mechanism of action has been poorly understood. Here, we investigated whether the mental state of mice, due to social isolation stress, affects the antidepressant-like effect of Matcha tea powder by using the tail suspension test. Oral administration of Matcha tea powder reduced the duration of immobility in the stress-susceptible C57BL/6J strain, but not in BALB/c strain. In C57BL/6J mice, SCH23390, a dopamine D1 receptor blocker, prevented Matcha tea powder from exerting its antidepressant-like effect. Matcha tea powder also increased the number of c-Fos-positive cells in the prefrontal cortex (PFC) region and the nucleus accumbens (NAc) region in C57BL/6J mice, but not in BALB/c mice. In contrast, Matcha tea powder did not change the number of c-Fos-positive cells in the ventral tegmental area (VTA) region. Notably, C57BL/6J mice with a shorter immobility time had a higher number of c-Fos-positive cells in the PFC, NAc, and VTA regions. However, no such correlation was observed in the stress-tolerant BALB/c mice. These results suggest that Matcha tea powder exerts an antidepressant-like effect through the activation of the dopaminergic system including the PFC-NAc-VTA circuit and that mental states are important factors affecting the physiological benefits of Matcha tea powder.

Potential therapeutic mechanism of deep brain stimulation of the nucleus accumbens in obsessive-compulsive disorder

Deep brain stimulation (DBS) of the nucleus accumbens (NAc) (NAc-DBS) is an effective solution to refractory obsessive-compulsive disorder (OCD). However, evidence for the neurobiological mechanisms of OCD and the effect of NAc-DBS is still lacking. One hypothesis is that the electrophysiological activities in the NAc are modulated by DBS, and another hypothesis is that the activities of neurotransmitters in the NAc are influenced by DBS. To investigate these potential alterations, rats with quinpirole (QNP)- induced OCD were treated with DBS of the core part of NAc. Then, extracellular spikes (SPK) and local field potentials (LFP) in the NAc were recorded, and the levels of relevant neurotransmitters and related proteins were measured. Analysis of SPK revealed that the firing rate was decreased and the firing pattern was changed after NAc-DBS, and analysis of LFP showed that overall power spectral density (PSD) levels were reduced after NAc-DBS. Additionally, we found that the relative powers of the theta band, alpha band and beta band were increased in OCD status, while the relative powers of the delta band and gamma band were decreased. This pathological pattern of power distribution was reformed by NAc-DBS. Furthermore, we found that the local levels of monoamines [dopamine (DA) and serotonin (5-HT)] and amino acids [glutamate (Glu) and gamma-aminobutyric acid (GABA)] in the NAc were increased in OCD status, and that the expression of the two types of DA receptors in the NAc exhibited an opposite change. These abnormalities could be reversed by NAc-DBS. These findings provide a more comprehensive understanding about the function of the NAc in the pathophysiology of OCD and provide more detailed evidence for the potential effect of NAc-DBS.

Accumbal adenosine A2A receptor inactivation biases for large and costly rewards in the effort- but not delay-based decision making

The cost-benefit decision-making (CBDM) is critical to normal human activity and a diminished willingness to expend effort to obtain rewards is a prevalent/noted characteristic of neuropsychiatric disorders such as schizophrenia, Parkinson's disease. Numerous studies have identified nucleus accumbens (NAc) as an important locus for CBDM control but their neuromodulatory and behavioral mechanisms remain largely under-explored. Adenosine A_2A receptors (A_2ARs), which are highly concentrated in the striatopallidal neurons, can integrate glutamate and dopamine signals for controlling effort-related choice behaviors. While the involvement of A_2ARs in effort-based decision making is well documented, the role of other decision variables (reward discrimination) in effort-based decision making and the role of A_2AR in delay-based decision making are less clear. In this study, we have developed a well-controlled CBDM behavioral paradigm to manipulate effort/cost and reward independently or in combination, allowing a dissection of four behavioral elements: effort-based CBDM (E-CBDM), delay-based CBDM (D-CBDM), reward discrimination (RD), effort discrimination (ED), and determined the effect of genetic knockdown (KD) of NAc A_2AR on the four behavioral elements. We found that A_2AR KD in NAc increased the choice for larger, more costly reward in the E-CBDM, but not D-CBDM. Furthermore, this high-effort/high-reward bias was attributable to the increased willingness to engage in effort but not the effect of discrimination of reward magnitude. Our findings substantiate an important role of the NAc A_2AR in control of E-CBDM and support that pharmacologically targeting NAc A_2ARs would be a useful strategy for treating the aberrant effort-based decision making in neuropsychiatric disorders.

Physical Effort Exertion for Peer Feedback Reveals Evolving Social Motivations From Adolescence to Young Adulthood

Peer relationships and social belonging are particularly important during adolescence. Using a willingness-to-work paradigm to quantify incentive motivation, we examined whether evaluative information holds unique value for adolescents. Participants (N = 102; 12-23 years old) rated peers, predicted how peers rated them, and exerted physical effort to view each peer's rating. We measured grip force, speed, and opt-out behavior to examine the motivational value of peer feedback, relative to money in a control condition, and to assess how peer desirability and participants' expectations modulated motivated effort across age. Overall, when compared with adolescents, adults were relatively less motivated for feedback than money. Whereas adults exerted less force and speed for feedback when expecting rejection, adolescents exerted greater force and speed when expecting to be more strongly liked or disliked. These findings suggest that the transition into adulthood is accompanied by a self-protective focus, whereas adolescents are motivated to consume highly informative feedback, even if negative.

Critical review of RDoC approaches to the study of motivation with animal models: effort valuation/willingness to work

The NIMH research domain criteria (RDoC) approach was instigated to refocus mental health research on the neural circuits that mediate psychological functions, with the idea that this would foster an understanding of the neural basis of specific psychiatric dysfunctions (i.e. 'symptoms and circuits') and ultimately facilitate treatment. As a general idea, this attempt to go beyond traditional diagnostic categories and focus on neural circuit dysfunctions related to specific symptoms spanning multiple disorders has many advantages. For example, motivational dysfunctions are present in multiple disorders, including depression, schizophrenia, Parkinson's disease, and other conditions. A critical aspect of motivation is effort valuation/willingness to work, and several clinical studies have identified alterations in effort-based decision making in various patient groups. In parallel, formal animal models focusing on the exertion of effort and effort-based decision making have been developed. This paper reviews the literature on models of effort-based motivational function in the context of a discussion of the RDoC approach, with an emphasis on the dissociable nature of distinct aspects of motivation. For example, conditions associated with depression and schizophrenia blunt the selection of high-effort activities as measured by several tasks in animal models (e.g. lever pressing, barrier climbing, wheel running). Nevertheless, these manipulations also leave fundamental aspects of hedonic reactivity, food motivation, and reinforcement intact. This pattern of effects demonstrates that the general emphasis of the RDoC on the specificity of the neural circuits mediating behavioral pathologies, and the dissociative nature of these dysfunctions, is a valid concept. Nevertheless, the specific placement of effort-related processes as simply a 'sub-construct' of 'reward processing' is empirically and conceptually problematic. Thus, while the RDoC is an excellent general framework for new ways to approach research and therapeutics, it still needs further refinement.