VTA GABA Neurons at the Interface of Stress and Reward

Role of Lactobacillus plantarum-Derived Extracellular Vesicles in Regulating Alcohol Consumption

Alcohol Use Disorder (AUD), characterized by repeated alcohol consumption and withdrawal symptoms, poses a significant public health issue. Alcohol-induced impairment of the intestinal barrier results in alterations in intestinal permeability and the composition of the intestinal microbiota. Such alterations lead to a reduced relative abundance of intestinal lactic acid bacteria. However, the role of gut microbiota in alcohol consumption is not yet fully understood. In this study, we explore the mechanism by which gut microbiota regulates alcohol consumption, specifically using extracellular vesicles derived from Lactobacillus plantarum (L-EVs). L-EVs were administered to Sprague-Dawley rats either through intraperitoneal injection or microinjection into the ventral tegmental area (VTA), resulting in a significant reduction in alcohol consumption 72 hours after withdrawal. The observed reduction was akin to the effect of an intra-VTA microinjection of Brain-Derived Neurotrophic Factor (BDNF). Intriguingly, the microinjection of K252a (a Trk B antagonist) into the VTA blocked the reducing effect of L-EVs on alcohol consumption. The intraperitoneal injection of L-EVs restored the diminished BDNF expression in the VTA of alcohol-dependent rats. Furthermore, L-EVs rescued the low BDNF expression in alcohol-incubated PC12 cells. In conclusion, our study demonstrates that L-EVs attenuated alcohol consumption by enhancing BDNF expression in alcohol-dependent rats, thus suggesting the significant therapeutic potential of L-EVs in preventing excessive alcohol consumption.

Nitrous oxide exerts rewarding effect via regulating D1 receptor and BDNF pathway in ventral tegmental area-nucleus accumbens dopamine circuit

Recreational use of nitrous oxide (N2O) has risen dramatically over the past decades. This study aimed to examine its rewarding effect and the underlying mechanisms. The exposure of mice to a subanesthetic concentration (20%) of N2O for 30 min for 4 consecutive days paired with N2O in the morning and paired with the air in the afternoon produced apparent rewarding behavior in the conditioned place preference (CPP) paradigm. This was abrogated by microinjection into the nucleus accumbens (NAc) of the dopamine (DA) D1 receptor antagonist SCH23390, but not the D2 antagonist haloperidol. N2O robustly enhanced DAergic neuronal activity of the ventral tegmental area (VTA) and the concentration of DA in the NAc. The repeated N2O exposure also upregulated the expression of brain-derived neurotrophic factor (BDNF) in the VTA and its multiple downstream mediators in the NAc. Conversely, VTA focal knockdown of BDNF and the inhibition of the downstream mediators suppressed the N2O-induced rewarding effect and the DAergic neuronal activity of the VTA. Further, the combined intervention of BDNF knockdown and D1 antagonist significantly inhibited the N2O-induced rewarding effect in mice, which was greater than that of BDNF knockdown alone, but was not significantly different from that of D1 antagonist alone. These results indicate that the rewarding properties of N2O at subanesthetic concentration are associated with its upregulation of the VTA-NAc DA reward pathway probably via mediation of D1 receptor and BDNF/TrkB signaling. Among them, the modulation of BDNF may be the upstream of D1 receptor involved in N2O rewarding effect.

Ventral tegmental area interneurons revisited: GABA and glutamate projection neurons make local synapses

The ventral tegmental area (VTA) contains projection neurons that release the neurotransmitters dopamine, GABA, and/or glutamate from distal synapses. VTA also contains GABA neurons that synapse locally on to dopamine neurons, synapses widely credited to a population of so-called VTA interneurons. Interneurons in cortex, striatum, and elsewhere have well-defined morphological features, physiological properties, and molecular markers, but such features have not been clearly described in VTA. Indeed, there is scant evidence that local and distal synapses originate from separate populations of VTA GABA neurons. In this study we tested whether several markers expressed in non-dopamine VTA neurons are selective markers of interneurons, defined as neurons that synapse locally but not distally. Challenging previous assumptions, we found that VTA neurons genetically defined by expression of parvalbumin, somatostatin, neurotensin, or mu-opioid receptor project to known VTA targets including nucleus accumbens, ventral pallidum, lateral habenula, and prefrontal cortex. Moreover, we provide evidence that VTA GABA and glutamate projection neurons make functional inhibitory or excitatory synapses locally within VTA. These findings suggest that local collaterals of VTA projection neurons could mediate functions prior attributed to VTA interneurons. This study underscores the need for a refined understanding of VTA connectivity to explain how heterogeneous VTA circuits mediate diverse functions related to reward, motivation, or addiction.

Significance statement

GABA neurons in VTA are key regulators of VTA dopamine neurons and considered central to the mechanisms by which opioids and other drugs of abuse can induce addiction. Conventionally, these VTA GABA neurons are considered interneurons, but GABA projection neurons are also abundant in VTA, and it is unclear if these represent separate populations. We found that several markers enriched in non-dopamine neurons of VTA, including Mu-opioid receptor, are also expressed in projection neurons, and thus are not selective interneuron markers. Moreover, we found that VTA GABA and glutamate projection neurons collateralize within VTA where they make local synapses. These data challenge the notion of a VTA interneuron that synapses only within VTA and suggest that inhibitory projection neurons can serve functions previously attributed to VTA interneurons.

Chronic ethanol exposure in mice evokes pre- and postsynaptic deficits in GABAergic transmission in ventral tegmental area GABA neurons

BACKGROUND AND PURPOSE

GABAergic neurons in mouse ventral tegmental area (VTA) exhibit elevated activity during withdrawal following chronic ethanol exposure. While increased glutamatergic input and decreased GABAA receptor sensitivity have been implicated, the impact of inhibitory signaling in VTA GABA neurons has not been fully addressed.

EXPERIMENTAL APPROACH

We used electrophysiological and ultrastructural approaches to assess the impact of chronic intermittent ethanol vapour exposure in mice on GABAergic transmission in VTA GABA neurons during withdrawal. We used CRISPR/Cas9 ablation to mimic a somatodendritic adaptation involving the GABAB receptor (GABABR) in ethanol-naïve mice to investigate its impact on anxiety-related behaviour.

KEY RESULTS

The frequency of spontaneous inhibitory postsynaptic currents was reduced in VTA GABA neurons following chronic ethanol treatment and this was reversed by GABABR inhibition, suggesting chronic ethanol strengthens the GABABR-dependent suppression of GABAergic input to VTA GABA neurons. Similarly, paired-pulse depression of GABAA receptor-dependent responses evoked by optogenetic stimulation of nucleus accumbens inputs from ethanol-treated mice was reversed by GABABR inhibition. Somatodendritic currents evoked in VTA GABA neurons by GABABR activation were reduced following ethanol exposure, attributable to the suppression of GIRK (Kir3) channel activity. Mimicking this adaptation enhanced anxiety-related behaviour in ethanol-naïve mice.

CONCLUSIONS AND IMPLICATIONS

Chronic ethanol weakens the GABAergic regulation of VTA GABA neurons in mice via pre- and postsynaptic mechanisms, likely contributing to their elevated activity during withdrawal and expression of anxiety-related behaviour. As anxiety can promote relapse during abstinence, interventions targeting VTA GABA neuron excitability could represent new therapeutic strategies for treatment of alcohol use disorder.

GABAergic neurons from the ventral tegmental area represent and regulate force vectors

The ventral tegmental area (VTA), a midbrain region associated with motivated behaviors, consists predominantly of dopaminergic (DA) neurons and GABAergic (GABA) neurons. Previous work has suggested that VTA GABA neurons provide a reward prediction, which is used in computing a reward prediction error. In this study, using in vivo electrophysiology and continuous quantification of force exertion in head-fixed mice, we discovered distinct populations of VTA GABA neurons that exhibited precise force tuning independently of learning, reward prediction, and outcome valence. Their activity usually preceded force exertion, and selective optogenetic manipulations of these neurons systematically modulated force exertion without influencing reward prediction. Together, these findings show that VTA GABA neurons continuously regulate force vectors during motivated behavior.

Ventral tegmental area GABA neurons integrate positive and negative valence

Ventral tegmental area (VTA) dopamine (DA) neurons are classically linked to Pavlovian reward learning and reinforcement. Intermingled VTA GABA neurons are positioned to regulate dopaminergic and striatal systems, but we lack critical insight into how this population contributes to conditioned motivation in different learning contexts. Recording DA and GABA neurons across multiple conditioning paradigms, we found that GABA neurons not only actively encode appetitive and aversive cues and outcomes separately, but uniquely integrate salient events of both valences to guide reward seeking.

The therapeutic potential of low-intensity focused ultrasound for treating substance use disorder

Substance use disorder (SUD) is a persistent public health issue that necessitates the exploration of novel therapeutic interventions. Low-intensity focused ultrasound (LIFU) is a promising modality for precise and invasive modulation of brain activity, capable of redefining the landscape of SUD treatment. The review overviews effective LIFU neuromodulatory parameters and molecular mechanisms, focusing on the modulation of reward pathways in key brain regions in animal and human models. Integration of LIFU with established therapeutics holds promise for augmenting treatment outcomes in SUD. The current research examines LIFU's efficacy in reducing cravings and withdrawal symptoms. LIFU shows promise for reducing cravings, modulating reward circuitry, and addressing interoceptive dysregulation and emotional distress. Selecting optimal parameters, encompassing frequency, burst patterns, and intensity, is pivotal for balancing therapeutic efficacy and safety. However, inconsistencies in empirical findings warrant further research on optimal treatment parameters, physiological action mechanisms, and long-term effects. Collaborative interdisciplinary investigations are imperative to fully realize LIFU's potential in revolutionizing SUD treatment paradigms and enhancing patient outcomes.

The Involvement of the Ventral Tegmental Area in the Electroacupuncture Alleviation of Anxiety-Like Behaviors Induced by Chronic Restraint Stress in Mice

Emotional stress is a significant environmental risk factor for various mental health disabilities, such as anxiety. Electroacupuncture (EA) has been demonstrated to have pronounced anxiolytic effects. However, the neural mechanisms underlying these effects and their contribution to behavioral deficits remain poorly understood. Here, we addressed these issues using a classical mouse anxiety model induced by chronic restraint stress (CRS).Anxiety-like behaviors were evaluated with the open field test and elevated plus maze. Neuronal activation in various brain regions was marked using c-Fos, followed by calculations of interregional correlation to characterize a network that became functionally active following EA at the HT7 acupoint (EA-HT7). We selected the hub regions and further investigated their functions and connections in regulating anxiety-like behaviors by using a combination of chemogenetic manipulations and behavioral testing. CRS exposure induced anxiety-like behaviors. Interestingly, EA-HT7 mitigated these behavioral abnormalities. The c-Fos expression in 30 brain areas revealed a vital brain network for acupuncture responsiveness in naïve mice. Neural activity in the NAcSh (nucleus accumbens shell), BNST (bed nucleus of the stria terminalis), VMH (Ventromedial Hypothalamus), ARC (arcuate nucleus), dDG (dorsal dentate gyrus), and VTA (ventral tegmental area) was significantly altered following acupuncture. Notably, both c-Fos immunostaining and brain functional connectivity analysis revealed the significant activation of VTA following EA-HT7. Interestingly, blocking the VTA eliminated the anxiolytic effects of EA-HT7, whereas chemogenetic activation of the VTA replicated the therapeutic effects of EA-HT7. EA-HT7 has demonstrated benefits in treating anxiety and enhances brain functional connectivity. The VTA is functionally associated with the anxiolytic effects of EA-HT7.

Empathic pain: Exploring the multidimensional impacts of biological and social aspects in pain

Empathic pain refers to an individual's perception, judgment, and emotional response to others' pain. This complex social cognitive ability is crucial for healthy interactions in human society. In recent years, with the development of multidisciplinary research in neuroscience, psychology and sociology, empathic pain has become a focal point of widespread attention in these fields. However, the neural mechanism underlying empathic pain remain a controversial and unresolved area. This review aims to comprehensively summarize the history, influencing factors, neural mechanisms and pharmacological interventions of empathic pain. We hope to provide a comprehensive scientific perspective on how humans perceive and respond to others' pain experiences and to provide guidance for future research directions and clinical applications. This article is part of the Special Issue on "Empathic Pain".

Reward and punishment contingency shifting reveals distinct roles for VTA dopamine and GABA neurons in behavioral flexibility

In dynamic environments where stimuli predicting rewarding or aversive outcomes unexpectedly change, it is critical to flexibly update behavior while preserving recollection of previous associations. Dopamine and GABA neurons in the ventral tegmental area (VTA) are implicated in reward and punishment learning, yet little is known about how each population adapts when the predicted outcome valence changes. We measured VTA dopamine and GABA population activity while male and female rats learned to associate three discrete auditory cues to three distinct outcomes: reward, punishment, or no outcome within the same session. After learning, the reward and punishment cue-outcome contingencies were reversed, and subsequently re-reversed. As expected, the dopamine population rapidly adapted to learning and contingency reversals by increasing the response to appetitive stimuli and decreasing the response to aversive stimuli. In contrast, the GABA population increased activity to all sensory events regardless of valence, including the neutral cue. Reversing learned contingencies selectively influenced GABA responses to the reward-predictive cue, prolonging increased activity within and across sessions. The observed valence-specific dissociations in the directionality and temporal progression of VTA dopamine and GABA calcium activity indicates that these populations are independently recruited and serve distinct roles during appetitive and aversive associative learning and contingency reversal.

Shank3 deficiency alters midbrain GABAergic neuron morphology, GABAergic markers and synaptic activity in primary striatal neurons

Abnormalities in gamma-aminobutyric acid (GABA)ergic neurotransmission play a role in the pathogenesis of autism, although the mechanisms responsible for alterations in specific brain regions remain unclear. Deficits in social motivation and interactions are core symptoms of autism, likely due to defects in dopaminergic neural pathways. Therefore, investigating the morphology and functional roles of GABAergic neurons within dopaminergic projection areas could elucidate the underlying etiology of autism. The aim of this study was to (1) compare the morphology and arborization of glutamate decarboxylase (GAD)-positive neurons from the midbrain tegmentum; (2) evaluate synaptic activity in primary neurons from the striatum; and (3) assess GABAergic postsynaptic puncta in the ventral striatum of wild-type (WT) and Shank3-deficient mice. We found a significant decrease in the number of short neurites in GAD positive primary neurons from the midbrain tegmentum in Shank3-deficient mice. The application of a specific blocker of GABAA receptors (GABAAR) revealed significantly increased frequency of spontaneous postsynaptic currents (sPSCs) in Shank3-deficient striatal neurons compared to their WT counterparts. The mean absolute amplitude of the events was significantly higher in striatal neurons from Shank3-deficient compared to WT mice. We also observed a significant reduction in gephyrin/GABAAR γ2 colocalization in the striatum of adult male Shank3-deficient mice. The gene expression of collybistin was significantly lower in the nucleus accumbens while gephyrin and GABAAR γ2 were lower in the ventral tegmental area (VTA) in male Shank3-deficient compared to WT mice. In conclusion, Shank3 deficiency leads to alterations in GABAergic neurons and impaired GABAergic function in dopaminergic brain areas. These changes may underlie autistic symptoms, and potential interventions modulating GABAergic activity in dopaminergic pathways may represent new treatment modality.

Stress and substance use disorders: risk, relapse, and treatment outcomes

Stress has long been associated with substance misuse and substance use disorders (SUDs). The past two decades have seen a surge in research aimed at understanding the underlying mechanisms driving this association. This Review introduces a multilevel "adaptive stress response" framework, encompassing a stress baseline, acute reaction, and recovery with return-to-homeostasis phase that occurs at varying response times and across domains of analysis. It also discusses evidence showing the disruption of this adaptive stress response in the context of chronic and repeated stressors, trauma, adverse social and drug-related environments, as well as with acute and chronic drug misuse and with drug withdrawal and abstinence sequelae. Subjective, cognitive, peripheral, and neurobiological disruptions in the adaptive stress response phases and their link to inflexible, maladaptive coping; increased craving; relapse risk; and maintenance of drug intake are also presented. Finally, the prevention and treatment implications of targeting this "stress pathophysiology of addiction" are discussed, along with specific aspects that may be targeted in intervention development to rescue stress-related alterations in drug motivation and to improve SUD treatment outcomes.

GABA system in the prefrontal cortex involved in psychostimulant addiction

Drug addiction is a chronic and relapse brain disorder. Psychostimulants such as cocaine and amphetamine are highly addictive drugs. Abuse drugs target various brain areas in the nervous system. Recent studies have shown that the prefrontal cortex (PFC) plays a key role in regulating addictive behaviors. The PFC is made up of excitatory glutamatergic cells and gamma-aminobutyric acid (GABAergic) interneurons. Recently, studies showed that GABA level was related with psychostimulant addiction. In this review, we will introduce the role and mechanism of GABA and γ-aminobutyric acid receptors (GABARs) of the PFC in regulating drug addiction, especially in psychostimulant addiction.

Linking Mitochondrial Dysfunction, Neurotransmitter, and Neural Network Abnormalities and Mania: Elucidating Neurobiological Mechanisms of the Therapeutic Effect of the Ketogenic Diet in Bipolar Disorder

There is growing interest in the ketogenic diet as a treatment for bipolar disorder (BD), and there are promising anecdotal and small case study reports of efficacy. However, the neurobiological mechanisms by which diet-induced ketosis might ameliorate BD symptoms remain to be determined, particularly in manic and hypomanic states-defining features of BD. Identifying these mechanisms will provide new markers to guide personalized interventions and provide targets for novel treatment developments for individuals with BD. In this critical review, we describe recent findings highlighting 2 types of neurobiological abnormalities in BD: 1) mitochondrial dysfunction and 2) neurotransmitter and neural network functional abnormalities. We link these abnormalities to mania/hypomania and depression in BD and then describe the biological underpinnings by which the ketogenic diet may have a beneficial effect in individuals with BD. We end the review by describing approaches that can be employed in future studies to elucidate the neurobiology that underlies the therapeutic effect of the ketogenic diet in BD. Doing this may provide marker predictors to identify individuals who will respond well to the ketogenic diet, as well as offer neural targets for novel treatment developments for BD.

Dopamine Dysregulation in Reward and Autism Spectrum Disorder

Autism spectrum disorder (ASD) is primarily characterized by core deficits in social skills, communication, and cognition and by repetitive stereotyped behaviors. These manifestations are variable between individuals, and ASD pathogenesis is complex, with over a thousand implicated genes, many epigenetic factors, and multiple environmental influences. The mesolimbic dopamine (DA) mediated brain reward system is held to play a key role, but the rapidly expanding literature reveals intricate, nuanced signaling involving a wide array of mesolimbic loci, neurotransmitters and receptor subtypes, and neuronal variants. How altered DA signaling may constitute a downstream convergence of the manifold causal origins of ASD is not well understood. A clear working framework of ASD pathogenesis may help delineate common stages and potential diagnostic and interventional opportunities. Hence, we summarize the known natural history of ASD in the context of emerging data and perspectives to update ASD reward signaling. Then, against this backdrop, we proffer a provisional framework that organizes ASD pathogenesis into successive levels, including (1) genetic and epigenetic changes, (2) disrupted mesolimbic reward signaling pathways, (3) dysregulated neurotransmitter/DA signaling, and finally, (4) altered neurocognitive and social behavior and possible antagonist/agonist based ASD interventions. This subdivision of ASD into a logical progression of potentially addressable parts may help facilitate the rational formulation of diagnostics and targeted treatments.

Stress-induced anxiety-related behavior in mice is driven by enhanced excitability of ventral tegmental area GABA neurons

Introduction

Stress and trauma are significant risk factors for many neuropsychiatric disorders and diseases, including anxiety disorders. Stress-induced anxiety symptoms have been attributed to enhanced excitability in circuits controlling fear, anxiety, and aversion. A growing body of evidence has implicated GABAergic neurons of the ventral tegmental area (VTA) in aversion processing and affective behavior.

Methods

We used an unpredictable footshock (uFS) model, together with electrophysiological and behavioral approaches, to investigate the role of VTA GABA neurons in anxiety-related behavior in mice.

Results

One day after a single uFS session, C57BL/6J mice exhibited elevated anxiety-related behavior and VTA GABA neuron excitability. The enhanced excitability of VTA GABA neurons was correlated with increased glutamatergic input and a reduction in postsynaptic signaling mediated via GABAA and GABAB receptors. Chemogenetic activation of VTA GABA neurons was sufficient to increase anxiety-related behavior in stress-naïve mice. In addition, chemogenetic inhibition of VTA GABA neurons suppressed anxiety-related behavior in mice exposed to uFS.

Discussion

These data show that VTA GABA neurons are an early substrate for stress-induced anxiety-related behavior in mice and suggest that approaches mitigating enhanced excitability of VTA GABA neurons may hold promise for the treatment of anxiety provoked by stress and trauma.

VTA μ-opioidergic neurons facilitate low sociability in protracted opioid withdrawal

Opioids initiate dynamic maladaptation in brain reward and affect circuits that occur throughout chronic exposure and withdrawal that persist beyond cessation. Protracted withdrawal is characterized by negative affective behaviors such as heightened anxiety, irritability, dysphoria, and anhedonia, which pose a significant risk factor for relapse. While the ventral tegmental area (VTA) and mu-opioid receptors (MORs) are critical for opioid reinforcement, the specific contributions of VTAMOR neurons in mediating protracted withdrawal-induced negative affect is not fully understood. In our study, we elucidate the role of VTAMOR neurons in mediating negative affect and altered brain-wide neuronal activities following opioid exposure and withdrawal in male and female mice. Utilizing a chronic oral morphine administration model, we observe increased social deficit, anxiety-related, and despair-like behaviors during protracted withdrawal. VTAMOR neurons show heightened neuronal FOS activation at the onset of withdrawal and connect to an array of brain regions that mediate reward and affective processes. Viral re-expression of MORs selectively within the VTA of MOR knockout mice demonstrates that the disrupted social interaction observed during protracted withdrawal is facilitated by this neural population, without affecting other protracted withdrawal behaviors. Lastly, VTAMORs contribute to heightened neuronal FOS activation in the anterior cingulate cortex (ACC) in response to an acute morphine challenge, suggesting their unique role in modulating ACC-specific neuronal activity. These findings identify VTAMOR neurons as critical modulators of low sociability during protracted withdrawal and highlight their potential as a mechanistic target to alleviate negative affective behaviors associated with opioid withdrawal.

Ventral tegmental area glutamate neurons mediate nonassociative consequences of stress

Exposure to trauma is a risk factor for the development of a number of mood disorders, and may enhance vulnerability to future adverse life events. Recent data demonstrate that ventral tegmental area (VTA) neurons expressing the vesicular glutamate transporter 2 (VGluT2) signal and causally contribute to behaviors that involve aversive or threatening stimuli. However, it is unknown whether VTA VGluT2 neurons regulate transsituational outcomes of stress and whether these neurons are sensitive to stressor controllability. This work adapted an operant mouse paradigm to examine the impact of stressor controllability on VTA VGluT2 neuron function as well as the role of VTA VGluT2 neurons in mediating transsituational stressor outcomes. Uncontrollable (inescapable) stress, but not physically identical controllable (escapable) stress, produced social avoidance and exaggerated fear in male mice. Uncontrollable stress in females led to exploratory avoidance of a novel brightly lit environment. Both controllable and uncontrollable stressors increased VTA VGluT2 neuronal activity, and chemogenetic silencing of VTA VGluT2 neurons prevented the behavioral sequelae of uncontrollable stress in male and female mice. Further, we show that stress activates multiple genetically-distinct subtypes of VTA VGluT2 neurons, especially those that are VGluT2+VGaT+, as well as lateral habenula neurons receiving synaptic input from VTA VGluT2 neurons. Our results provide causal evidence that mice can be used for identifying stressor controllability circuitry and that VTA VGluT2 neurons contribute to transsituational stressor outcomes, such as social avoidance, exaggerated fear, or anxiety-like behavior that are observed within trauma-related disorders.

Amylin Modulates a Ventral Tegmental Area-to-Medial Prefrontal Cortex Circuit to Suppress Food Intake and Impulsive Food-Directed Behavior

BACKGROUND

A better understanding of the neural mechanisms regulating impaired satiety to palatable foods is essential to treat hyperphagia linked with obesity. The satiation hormone amylin signals centrally at multiple nuclei including the ventral tegmental area (VTA). VTA-to-medial prefrontal cortex (mPFC) projections encode food reward information to influence behaviors including impulsivity. We hypothesized that modulation of VTA-to-mPFC neurons underlies amylin-mediated decreases in palatable food-motivated behaviors.

METHODS

We used a variety of pharmacological, behavioral, genetic, and viral approaches (n = 4-16/experiment) to investigate the anatomical and functional circuitry of amylin-controlled VTA-to-mPFC signaling in rats.

RESULTS

To first establish that VTA amylin receptor (calcitonin receptor) activation can modulate mPFC activity, we showed that intra-VTA amylin decreased food-evoked mPFC cFos. VTA amylin delivery also attenuated food-directed impulsive behavior, implicating VTA amylin signaling as a regulator of mPFC functions. Palatable food activates VTA dopamine and mPFC neurons. Accordingly, dopamine receptor agonism in the mPFC blocked the hypophagic effect of intra-VTA amylin, and VTA amylin injection reduced food-evoked phasic dopamine levels in the mPFC, supporting the idea that VTA calcitonin receptor activation decreases dopamine release in the mPFC. Surprisingly, calcitonin receptor expression was not found on VTA-to-mPFC projecting neurons but was instead found on GABAergic (gamma-aminobutyric acidergic) interneurons in the VTA that provide monosynaptic inputs to this pathway. Blocking intra-VTA GABA signaling, through GABA receptor antagonists and DREADD (designer receptor exclusively activated by designer drugs)-mediated GABAergic neuronal silencing, attenuated intra-VTA amylin-induced hypophagia.

CONCLUSIONS

These results indicate that VTA amylin signaling stimulates GABA-mediated inhibition of dopaminergic projections to the mPFC to mitigate impulsive consumption of palatable foods.

Chromatin accessibility during human first-trimester neurodevelopment

The human brain develops through a tightly organized cascade of patterning events, induced by transcription factor expression and changes in chromatin accessibility. Although gene expression across the developing brain has been described at single-cell resolution1, similar atlases of chromatin accessibility have been primarily focused on the forebrain2-4. Here we describe chromatin accessibility and paired gene expression across the entire developing human brain during the first trimester (6-13 weeks after conception). We defined 135 clusters and used multiomic measurements to link candidate cis-regulatory elements to gene expression. The number of accessible regions increased both with age and along neuronal differentiation. Using a convolutional neural network, we identified putative functional transcription factor-binding sites in enhancers characterizing neuronal subtypes. We applied this model to cis-regulatory elements linked to ESRRB to elucidate its activation mechanism in the Purkinje cell lineage. Finally, by linking disease-associated single nucleotide polymorphisms to cis-regulatory elements, we validated putative pathogenic mechanisms in several diseases and identified midbrain-derived GABAergic neurons as being the most vulnerable to major depressive disorder-related mutations. Our findings provide a more detailed view of key gene regulatory mechanisms underlying the emergence of brain cell types during the first trimester and a comprehensive reference for future studies related to human neurodevelopment.

Exploring the potential relationship between short sleep risks and cognitive function from the perspective of inflammatory biomarkers and cellular pathways: Insights from population-based and mice studies

AIMS

The molecular mechanism of short-sleep conditions on cognition remains largely unknown. This research aimed to investigate associations between short sleep, inflammatory biomarkers and cognitive function in the US population (NHANES data 2011-2014) and explore cellular mechanisms in mice.

METHODS

Systemic immune-inflammation index (SII) was calculated using blood-cell based biomarkers. Further, we employed integrated bioinformatics and single-cell transcriptomics (GSE137665) to examine how short sleep exposure influenced the molecular pathways associated with inflammation in the brain. To explore the signaling pathways and biological processes of sleep deprivation, we carried out enrichment analyses utilizing the GO and KEGG databases.

RESULTS

Population results showed that, compared with normal sleep group, severe short sleep was associated with lower cognitive ability in all the four tests. Moreover, a higher SII level was correlated with lower scores of cognitive tests. In mice study, elevated activation of the inflammatory pathway was observed in cell subgroups of neurons within the sleep deprivation and recovery sleep cohorts. Additionally, heightened expression of oxidative stress and integrated stress response pathways was noted in GABAergic neurons during sleep deprivation.

CONCLUSION

This study contributed to the understanding of the influence of short sleep on cognitive function and its cellular mechanisms.

The avBNSTGABA-VTA and avBNSTGABA-DRN pathways are respectively involved in the regulation of anxiety-like behaviors in parkinsonian rats

The anteroventral bed nucleus of stria terminalis (avBNST) is a key brain region which involves negative emotional states, such as anxiety. The most neurons in the avBNST are GABAergic, and it sends GABAergic projections to the ventral tegmental area (VTA) and the dorsal raphe nucleus (DRN), respectively. The VTA and DRN contain dopaminergic and serotonergic cell groups in the midbrain which regulate anxiety-like behaviors. However, it is unclear the role of GABAergic projections from the avBNST to the VTA and the DRN in the regulation of anxiety-like behaviors, particularly in Parkinson's disease (PD)-related anxiety. In the present study, unilateral 6-hydroxydopamine (6-OHDA) lesions of the substantia nigra pars compacta in rats induced anxiety-like behaviors, and decreased level of dopamine (DA) in the basolateral amygdala (BLA). Chemogenetic activation of avBNSTGABA-VTA or avBNSTGABA-DRN pathway induced anxiety-like behaviors and decreased DA or 5-HT release in the BLA in sham and 6-OHDA rats, while inhibition of avBNSTGABA-VTA or avBNSTGABA-DRN pathway produced anxiolytic-like effects and increased level of DA or 5-HT in the BLA. These findings suggest that avBNST inhibitory projections directly regulate dopaminergic neurons in the VTA and serotonergic neurons in the DRN, and the avBNSTGABA-VTA and avBNSTGABA-DRN pathways respectively exert impacts on PD-related anxiety-like behaviors.

Transcriptional signatures of fentanyl use in the mouse ventral tegmental area

Synthetic opioids such as fentanyl contribute to the vast majority of opioid-related overdose deaths, but fentanyl use remains broadly understudied. Like other substances with misuse potential, opioids cause lasting molecular adaptations to brain reward circuits, including neurons in the ventral tegmental area (VTA). The VTA contains numerous cell types that play diverse roles in opioid use and relapse; however, it is unknown how fentanyl experience alters the transcriptional landscape in specific subtypes. Here, we performed single nuclei RNA sequencing to study transcriptional programs in fentanyl-experienced mice. Male and female C57/BL6 mice self-administered intravenous fentanyl (1.5 μg/kg/infusion) or saline for 10 days. After 24 h abstinence, VTA nuclei were isolated and prepared for sequencing on the 10× platform. We identified different patterns of gene expression across cell types. In dopamine neurons, we found enrichment of genes involved in growth hormone signalling. In dopamine-glutamate-GABA combinatorial neurons, and some GABA neurons, we found enrichment of genes involved in Pi3k-Akt signalling. In glutamate neurons, we found enrichment of genes involved in cholinergic signalling. We identified transcriptional regulators for the differentially expressed genes in each neuron cluster, including downregulated transcriptional repressor Bcl6, and upregulated transcription factor Tcf4. We also compared the fentanyl-induced gene expression changes identified in mouse VTA with a published rat dataset in bulk VTA, and found overlap in genes related to GABAergic signalling and extracellular matrix interaction. Together, we provide a comprehensive picture of how fentanyl self-administration alters the transcriptional landscape of the mouse VTA that serves as the foundation for future mechanistic studies.

Recent advances in neural mechanism of general anesthesia induced unconsciousness: insights from optogenetics and chemogenetics

For over 170 years, general anesthesia has played a crucial role in clinical practice, yet a comprehensive understanding of the neural mechanisms underlying the induction of unconsciousness by general anesthetics remains elusive. Ongoing research into these mechanisms primarily centers around the brain nuclei and neural circuits associated with sleep-wake. In this context, two sophisticated methodologies, optogenetics and chemogenetics, have emerged as vital tools for recording and modulating the activity of specific neuronal populations or circuits within distinct brain regions. Recent advancements have successfully employed these techniques to investigate the impact of general anesthesia on various brain nuclei and neural pathways. This paper provides an in-depth examination of the use of optogenetic and chemogenetic methodologies in studying the effects of general anesthesia on specific brain nuclei and pathways. Additionally, it discusses in depth the advantages and limitations of these two methodologies, as well as the issues that must be considered for scientific research applications. By shedding light on these facets, this paper serves as a valuable reference for furthering the accurate exploration of the neural mechanisms underlying general anesthesia. It aids researchers and clinicians in effectively evaluating the applicability of these techniques in advancing scientific research and clinical practice.

Integrative Pharmacology in the Treatment of Substance Use Disorders

The detrimental physical, mental, and socioeconomic effects of substance use disorders (SUDs) have been apparent to the medical community for decades. However, it has become increasingly urgent in recent years to develop novel pharmacotherapies to treat SUDs. Currently, practitioners typically rely on monotherapy. Monotherapy has been shown to be superior to no treatment at all for most substance classes. However, many randomized controlled trials (RCTs) have revealed that monotherapy leads to poorer outcomes when compared with combination treatment in all specialties of medicine. The results of RCTs suggest that monotherapy frequently fails since multiple dysregulated pathways, enzymes, neurotransmitters, and receptors are involved in the pathophysiology of SUDs. As such, research is urgently needed to determine how various neurobiological mechanisms can be targeted by novel combination treatments to create increasingly specific yet exceedingly comprehensive approaches to SUD treatment. This article aims to review the neurobiology that integrates many pathophysiologic mechanisms and discuss integrative pharmacology developments that may ultimately improve clinical outcomes for patients with SUDs. Many neurobiological mechanisms are known to be involved in SUDs including dopaminergic, nicotinic, N-methyl-D-aspartate (NMDA), and kynurenic acid (KYNA) mechanisms. Emerging evidence indicates that KYNA, a tryptophan metabolite, modulates all these major pathophysiologic mechanisms. Therefore, achieving KYNA homeostasis by harmonizing integrative pathophysiology and pharmacology could prove to be a better therapeutic approach for SUDs. We propose KYNA-NMDA-α7nAChRcentric pathophysiology, the "conductor of the orchestra," as a novel approach to treat many SUDs concurrently. KYNA-NMDA-α7nAChR pathophysiology may be the "command center" of neuropsychiatry. To date, extant RCTs have shown equivocal findings across comparison conditions, possibly because investigators targeted single pathophysiologic mechanisms, hit wrong targets in underlying pathophysiologic mechanisms, and tested inadequate monotherapy treatment. We provide examples of potential combination treatments that simultaneously target multiple pathophysiologic mechanisms in addition to KYNA. Kynurenine pathway metabolism demonstrates the greatest potential as a target for neuropsychiatric diseases. The investigational medications with the most evidence include memantine, galantamine, and N-acetylcysteine. Future RCTs are warranted with novel combination treatments for SUDs. Multicenter RCTs with integrative pharmacology offer a promising, potentially fruitful avenue to develop novel therapeutics for the treatment of SUDs.

The neurobiological effects of senescence on dopaminergic system: A comprehensive review

Over time, the body undergoes a natural, multifactorial, and ongoing process named senescence, which induces changes at the molecular, cellular, and micro-anatomical levels in many body systems. The brain, being a highly complex organ, is particularly affected by this process, potentially impairing its numerous functions. The brain relies on chemical messengers known as neurotransmitters to function properly, with dopamine being one of the most crucial. This catecholamine is responsible for a broad range of critical roles in the central nervous system, including movement, learning, cognition, motivation, emotion, reward, hormonal release, memory consolidation, visual performance, sexual drive, modulation of circadian rhythms, and brain development. In the present review, we thoroughly examine the impact of senescence on the dopaminergic system, with a primary focus on the classic delimitations of the dopaminergic nuclei from A8 to A17. We provide in-depth information about their anatomy and function, particularly addressing how senescence affects each of these nuclei.

VTA Excitatory Neurons Control Reward-driven Behavior by Modulating Infralimbic Cortical Firing

The functional dichotomy of anatomical regions of the medial prefrontal cortex (mPFC) has been tested with greater certainty in punishment-driven tasks, and less so in reward-oriented paradigms. In the infralimbic cortex (IL), known for behavioral suppression (STOP), tasks linked with reward or punishment are encoded through firing rate decrease or increase, respectively. Although the ventral tegmental area (VTA) is the brain region governing reward/aversion learning, the link between its excitatory neuron population and IL encoding of reward-linked behavioral expression is unclear. Here, we present evidence that IL ensembles use a population-based mechanism involving broad inhibition of principal cells at intervals when reward is presented or expected. The IL encoding mechanism was consistent across multiple sessions with randomized rewarded target sites. Most IL neurons exhibit FR (Firing Rate) suppression during reward acquisition intervals (T1), and subsequent exploration of previously rewarded targets when the reward is omitted (T2). Furthermore, FR suppression in putative IL ensembles persisted for intervals that followed reward-linked target events. Pairing VTA glutamate inhibition with reward acquisition events reduced the weight of reward-target association expressed as a lower affinity for previously rewarded targets. For these intervals, fewer IL neurons per mouse trial showed FR decrease and were accompanied by an increase in the percentage of units with no change in FR. Together, we conclude that VTA glutamate neurons are likely involved in establishing IL inhibition states that encode reward acquisition, and subsequent reward-target association.

Optical Intracranial Self-Stimulation (oICSS): A New Behavioral Model for Studying Drug Reward and Aversion in Rodents

Brain-stimulation reward, also known as intracranial self-stimulation (ICSS), is a commonly used procedure for studying brain reward function and drug reward. In electrical ICSS (eICSS), an electrode is surgically implanted into the medial forebrain bundle (MFB) in the lateral hypothalamus or the ventral tegmental area (VTA) in the midbrain. Operant lever responding leads to the delivery of electrical pulse stimulation. The alteration in the stimulation frequency-lever response curve is used to evaluate the impact of pharmacological agents on brain reward function. If a test drug induces a leftward or upward shift in the eICSS response curve, it implies a reward-enhancing or abuse-like effect. Conversely, if a drug causes a rightward or downward shift in the functional response curve, it suggests a reward-attenuating or aversive effect. A significant drawback of eICSS is the lack of cellular selectivity in understanding the neural substrates underlying this behavior. Excitingly, recent advancements in optical ICSS (oICSS) have facilitated the development of at least three cell type-specific oICSS models-dopamine-, glutamate-, and GABA-dependent oICSS. In these new models, a comparable stimulation frequency-lever response curve has been established and employed to study the substrate-specific mechanisms underlying brain reward function and a drug's rewarding versus aversive effects. In this review article, we summarize recent progress in this exciting research area. The findings in oICSS have not only increased our understanding of the neural mechanisms underlying drug reward and addiction but have also introduced a novel behavioral model in preclinical medication development for treating substance use disorders.

Transcriptional Dysregulation of Cholesterol Synthesis Underlies Hyposensitivity to GABA in the Ventral Tegmental Area During Acute Alcohol Withdrawal

BACKGROUND

The ventral tegmental area (VTA) is a dopaminergic brain area that is critical in the development and maintenance of addiction. During withdrawal from chronic ethanol exposure, the response of VTA neurons to GABA (gamma-aminobutyric acid) is reduced through an epigenetically regulated mechanism. In the current study, a whole-genome transcriptomic approach was used to investigate the underlying molecular mechanism of GABA hyposensitivity in the VTA during withdrawal after chronic ethanol exposure.

METHODS

We performed RNA sequencing of the VTA of Sprague Dawley male rats withdrawn for 24 hours from a chronic ethanol diet as well as sequencing of the VTA of control rats fed the Lieber-DeCarli diet. RNA sequencing data were analyzed using weighted gene coexpression network analysis to identify modules that contained coexpressed genes. Validation was performed with quantitative polymerase chain reaction, gas chromatography-mass spectrometry, and electrophysiological assays.

RESULTS

Pathway and network analysis of weighted gene coexpression network analysis module 1 revealed a significant downregulation of genes associated with the cholesterol synthesis pathway. Consistent with this association, VTA cholesterol levels were significantly decreased during withdrawal. Chromatin immunoprecipitation indicated a decrease in levels of acetylated H3K27 at the transcriptional control regions of these genes. Electrophysiological studies in VTA slices demonstrated that GABA hyposensitivity during withdrawal was normalized by addition of exogenous cholesterol. In addition, inhibition of cholesterol synthesis produced GABA hyposensitivity, which was reversed by adding exogenous cholesterol to VTA slices.

CONCLUSIONS

These results suggest that decreased expression of cholesterol synthesis genes may regulate GABA hyposensitivity of VTA neurons during alcohol withdrawal. Increasing cholesterol levels in the brain may be a novel avenue for therapeutic intervention to reverse detrimental effects of chronic alcohol exposure.

Central role of the habenulo-interpeduncular system in the neurodevelopmental basis of susceptibility and resilience to anxiety in mice

Having experienced stress during sensitive periods of brain development strongly influences how individuals cope with later stress. Some are prone to develop anxiety or depression, while others appear resilient. The as-yet-unknown mechanisms underlying these differences may lie in how genes and environmental stress interact to shape the circuits that control emotions. Here, we investigated the role of the habenulo-interpeduncular system (HIPS), a critical node in reward circuits, in early stress-induced anxiety in mice. We found that habenular and IPN components characterized by the expression of Otx2 are synaptically connected and particularly sensitive to chronic stress (CS) during the peripubertal period. Stress-induced peripubertal activation of this HIPS subcircuit elicits both HIPS hypersensitivity to later stress and susceptibility to develop anxiety. We also show that HIPS silencing through conditional Otx2 knockout counteracts these effects of stress. Together, these results demonstrate that a genetic factor, Otx2, and stress interact during the peripubertal period to shape the stress sensitivity of the HIPS, which is shown to be a key modulator of susceptibility or resilience to develop anxiety.

Input-output relation of midbrain connectomics in a rodent model of depression

BACKGROUND

The symptoms associated with depression are believed to arise from disruptions in information processing across brain networks. The ventral tegmental area (VTA) influences reward-based behavior, motivation, addiction, and psychiatric disorders, including depression. Deep brain stimulation (DBS) of the medial forebrain bundle (MFB), is an emerging therapy for treatment-resistant depression. Understanding the depression associated anatomical networks crucial for comprehending its antidepressant effects.

METHODS

Flinders Sensitive Line (FSL), a rodent model of depression and Sprague-Dawley rats (n = 10 each) were used in this study. We used monosynaptic tracing to map inputs of VTA efferent neurons: VTA-to-NAc nucleus accumbens (NAc) (both core and shell) and VTA-to-prefrontal cortex (PFC). Quantitative analysis explored afferent diversity and strengths.

RESULTS

VTA efferent neurons receive a variety of afferents with varying input weights and predominant neuromodulatory representation. Notably, NAc-core projecting VTA neurons showed stronger afferents from dorsal raphe, while NAc shell-projecting VTA neurons displayed lower input strengths from cortex, thalamus, zona incerta and pretectal area in FSL rats. NAc shell-projecting VTA neurons showed the most difference in connectivity across the experimental groups.

LIMITATIONS

Lack of functional properties of the anatomical connections is the major limitation of this study. Incomplete labeling and the cytotoxicity of the rabies virus should be made aware of.

CONCLUSIONS

These findings provide the first characterization of inputs to different VTA ascending projection neurons, shedding light on critical differences in the connectome of the midbrain-forebrain system. Moreover, these differences support potential network effects of these circuits in the context of MFB DBS neuromodulation for depression.

The role of the GABAergic cells of the median raphe region in reinforcement-based learning

Learning and memory are important in everyday life as well as in pathological conditions. The median raphe region (MRR) contributes to memory formation; however, its precise role and the neurotransmitters involved have yet to be elucidated. To address this issue, we stimulated the MRR neurons of mice by chemogenetic technique and studied them in the operant conditioning and active avoidance tests. The virus carrier infected a variety of neuron types including both GABAergic and glutamatergic ones. Behavior was not influenced by stimulation. We hypothesize that the lack of effect was due to opposing effects exerted via GABAergic and glutamatergic neurons. Therefore, next we used VGAT-Cre mice that allowed the specific manipulation of MRR-GABAergic neurons. The stimulation did not affect behavior in the learning phase of the operant conditioning task, but increased reward preference and total responses when operant contingencies were reversed. The enhanced responsiveness might be a proclivity to impulsive behavior. Stimulation facilitated learning in the active avoidance test but did not affect reversal learning in this paradigm. Our findings suggest that MRR-GABAergic neurons are involved in both learning and reversal learning, but the type of learning that is affected depends on the task.

Endogenous Opioids in the Homeostatic Regulation of Hunger, Satiety, and Hedonic Eating: Neurobiological Foundations

This chapter (part one of a trilogy) summarizes the neurobiological foundations of endogenous opioids in the regulation of energy balance and eating behavior, dysregulation of which translates to maladaptive dietary responses in individuals with obesity and eating disorders, including anorexia, bulimia, and binge eating disorder. Knowledge of these neurobiological foundations is vital to researchers' and clinicians' understanding of pathophysiology as well as the science-based development of multidisciplinary diagnoses and treatments for obesity and eating disorders. We highlight mechanisms of endogenous opioids in both homeostatic and hedonic feeding behavior, review research on the dysregulation of food reward that plays a role in a wide array of obesity and disordered eating, and the clinical implications of neurobiological responses to food for current science-based treatments for obesity and eating disorders.

Transcriptional signatures of fentanyl use in the mouse ventral tegmental area

Synthetic opioids such as fentanyl contribute to the vast majority of opioid-related overdose deaths, but fentanyl use remains broadly understudied. Like other substances with misuse potential, opioids cause lasting molecular adaptations to brain reward circuits, including neurons in the ventral tegmental area (VTA). The VTA contains numerous cell types that play diverse roles in opioid use and relapse, however it is unknown how fentanyl experience alters the transcriptional landscape in specific subtypes. Here, we performed single nuclei RNA sequencing to study transcriptional programs in fentanyl experienced mice. Male and female C57/BL6 mice self-administered intravenous fentanyl (1.5 µg/kg/infusion) or saline for 10 days. After 24 hr abstinence, VTA nuclei were isolated and prepared for sequencing on the 10X platform. We identified different patterns of gene expression across cell types. In dopamine neurons, we found enrichment of genes involved in growth hormone signaling. In dopamine-glutamate-GABA combinatorial neurons, and some GABA neurons, we found enrichment of genes involved in Pi3k-Akt signaling. In glutamate neurons, we found enrichment of genes involved in cholinergic signaling. We identified transcriptional regulators for the differentially expressed genes in each neuron cluster, including downregulation of transcriptional repressor Bcl6, and upregulation of Wnt signaling partner Tcf4. We also compared the fentanyl-induced gene expression changes identified in mouse VTA with a published rat dataset in bulk VTA, and found overlap in genes related to GABAergic signaling and extracellular matrix interaction. Together, we provide a comprehensive picture of how fentanyl self-administration alters the transcriptional landscape of the mouse VTA, that serves for the foundation for future mechanistic studies.

Altered neural activity in the mesoaccumbens pathway underlies impaired social reward processing in Shank3-deficient rats

Social behaviors are crucial for human connection and belonging, often impacted in conditions like Autism Spectrum Disorder (ASD). The mesoaccumbens pathway (VTA and NAc) plays a pivotal role in social behavior and is implicated in ASD. However, the impact of ASD-related mutations on social reward processing remains insufficiently explored. This study focuses on the Shank3 mutation, associated with a rare genetic condition and linked to ASD, examining its influence on the mesoaccumbens pathway during behavior, using the Shank3-deficient rat model. Our findings indicate that Shank3-deficient rats exhibit atypical social interactions and have difficulty adjusting behavior based on reward values, associated with modified neuronal activity of VTA dopaminergic and GABAergic neurons and reduced dopamine release in the NAc. Moreover, we demonstrate that manipulating VTA neuronal activity can normalize this behavior, providing insights into the effects of Shank3 mutations on social reward and behavior, and identify a potential neural pathway for intervention.

Brain-wide correspondence of neuronal epigenomics and distant projections

Single-cell analyses parse the brain's billions of neurons into thousands of 'cell-type' clusters residing in different brain structures1. Many cell types mediate their functions through targeted long-distance projections allowing interactions between specific cell types. Here we used epi-retro-seq2 to link single-cell epigenomes and cell types to long-distance projections for 33,034 neurons dissected from 32 different regions projecting to 24 different targets (225 source-to-target combinations) across the whole mouse brain. We highlight uses of these data for interrogating principles relating projection types to transcriptomics and epigenomics, and for addressing hypotheses about cell types and connections related to genetics. We provide an overall synthesis with 926 statistical comparisons of discriminability of neurons projecting to each target for every source. We integrate this dataset into the larger BRAIN Initiative Cell Census Network atlas, composed of millions of neurons, to link projection cell types to consensus clusters. Integration with spatial transcriptomics further assigns projection-enriched clusters to smaller source regions than the original dissections. We exemplify this by presenting in-depth analyses of projection neurons from the hypothalamus, thalamus, hindbrain, amygdala and midbrain to provide insights into properties of those cell types, including differentially expressed genes, their associated cis-regulatory elements and transcription-factor-binding motifs, and neurotransmitter use.

In Context: A Developmental Model of Reward Processing, With Implications for Autism and Sensitive Periods

OBJECTIVE

Differences in reward processing have been associated with numerous psychiatric disorders, including autism and attention-deficit/hyperactivity disorder (ADHD). Many attempts to understand reward processing characterize differences in clinical populations after disorder onset; however, divergence may begin much earlier. In fact, the typical developmental progression of reward processing in infancy and early childhood is poorly understood. We re-conceptualize classic infant developmental constructs such as preferential looking into a Six-Component Developmental Model of Reward Processing: an infant- and young child-focused framework to guide research and assessment of reward processing across development.

METHOD

The extant developmental literature including recent textbooks, systematic reviews, and meta-analyses was reviewed to build a conceptual framework. We describe experimental paradigms to assess each developmental component of reward processing longitudinally from infancy. A timeline of each component's emergence was estimated.

RESULTS

Six components of reward processing were identified-association, discrimination, preference/valuation, effort, anticipation, and response. Selected evidence suggests emergence between birth and 6 months. Application of this model to autism led to a reinterpretation of existing disparate results, and illuminated a path to study the developmental processes underlying a popular hypothesis of autism, the motivation hypothesis. Current evidence further suggests that a sensitive period may exist for the emergence of reward processing.

CONCLUSION

The proposed framework offers a useful reconceptualization of the extant literature. Future longitudinal work using the suggested experimental paradigms with high-risk populations could elucidate the developmental trajectory of the components and timing of potential sensitive period(s) for each component.

Negative Emotions Recruit the Parabrachial Nucleus Efferent to the VTA to Disengage Instrumental Food Seeking

The parabrachial nucleus (PBN) interfaces between taste and feeding systems and is also an important hub for relaying distress information and threats. Despite that the PBN sends projections to the ventral tegmental area (VTA), a heterogeneous brain region that regulates motivational behaviors, the function of the PBN-to-VTA connection remains elusive. Here, by using male mice in several behavioral paradigms, we discover that VTA-projecting PBN neurons are significantly engaged in contextual fear, restraint or mild stress but not palatable feeding, visceral malaise, or thermal pain. These results suggest that the PBN-to-VTA input may relay negative emotions under threat. Consistent with this notion, optogenetic activation of PBN-to-VTA glutamatergic input results in aversion, which is sufficient to override palatable feeding. Moreover, in a palatable food-reinforced operant task, we demonstrate that transient optogenetic activation of PBN-to-VTA input during food reward retrieval disengages instrumental food-seeking behaviors but spares learned action-outcome association. By using an activity-dependent targeting approach, we show that VTA DA neurons are disengaged by the PBN afferent activation, implicating that VTA non-DA neurons may mediate PBN afferent regulation. We further show that optogenetic activation of VTA neurons functionally recruited by the PBN input results in aversion, dampens palatable feeding, and disengages palatable food self-administration behavior. Finally, we demonstrate that transient activation of VTA glutamatergic, but not GABAergic, neurons recapitulates the negative regulation of the PBN input on food self-administration behavior. Together, we reveal that the PBN-to-VTA input conveys negative affect, likely through VTA glutamatergic neurons, to disengage instrumental food-seeking behaviors.SIGNIFICANCE STATEMENT The PBN receives multiple inputs and thus is well positioned to route information of various modalities to engage different downstream circuits to attend or respond accordingly. We demonstrate that the PBN-to-VTA input conveys negative affect and then triggers adaptive prioritized responses to address pertinent needs by withholding ongoing behaviors, such as palatable food seeking or intake shown in the present study. It has evolutionary significance because preparing to cope with stressful situations or threats takes priority over food seeking to promote survival. Knowing how appropriate adaptive responses are generated will provide new insights into circuitry mechanisms of various coping behaviors to changing environmental stimuli.

Acute stress selectively blunts reward anticipation but not consumption: An ERP study

Stress-induced dysfunction of reward processing is documented to be a critical factor associated with mental illness. Although many studies have attempted to clarify the relationship between stress and reward, few studies have investigated the effect of acute stress on the temporal dynamics of reward processing. The present study applied event-related potentials (ERP) to examine how acute stress differently influences reward anticipation and consumption. In this study, seventy-eight undergraduates completed a two-door reward task following a Trier Social Stress Task (TSST) or a placebo task. The TSST group showed higher cortisol levels, perceived stress, anxiety, and negative affect than the control group. For the control group, a higher magnitude of reward elicited a reduced cue-N2 but increased stimulus-preceding negativity (SPN), suggesting that controls were sensitive to reward magnitude. In contrast, these effects were absent in the stress group, suggesting that acute stress reduces sensitivity to reward magnitude during the anticipatory phase. However, the reward positivity (RewP) and P3 of both groups showed similar patterns, which suggests that acute stress has no impact on reward responsiveness during the consummatory phase. These findings suggest that acute stress selectively blunts sensitivity to reward magnitude during the anticipatory rather than the consummatory phase.

Lateral preoptic area glutamate neurons relay nociceptive information to the ventral tegmental area

The ventral tegmental area (VTA) has been proposed to play a role in pain, but the brain structures modulating VTA activity in response to nociceptive stimuli remain unclear. Here, we demonstrate that the lateral preoptic area (LPO) glutamate neurons relay nociceptive information to the VTA. These LPO glutamatergic neurons synapsing on VTA neurons respond to nociceptive stimulation and conditioned stimuli predicting nociceptive stimulation and also mediate aversion. In contrast, LPO GABA neurons synapsing in the VTA mediate reward. By ultrastructural quantitative synaptic analysis, ex vivo electrophysiology, and functional neuroanatomy we identify a complex circuitry between LPO glutamatergic and GABAergic neurons and VTA dopaminergic, GABAergic, and glutamatergic neurons. We conclude that LPO glutamatergic neurons play a causal role in the processing of nociceptive stimuli and in relaying information about nociceptive stimuli. The pathway from LPO glutamatergic neurons to the VTA represents an unpredicted interface between peripheral nociceptive information and the limbic system.

Hedonic eating, obesity, and addiction result from increased neuropeptide Y in the nucleus accumbens during human brain evolution

The nucleus accumbens (NAc) is central to motivation and action, exhibiting one of the highest densities of neuropeptide Y (NPY) in the brain. Within the NAc, NPY plays a role in reward and is involved in emotional behavior and in increasing alcohol and drug addiction and fat intake. Here, we examined NPY innervation and neurons of the NAc in humans and other anthropoid primates in order to determine whether there are differences among these various species that would correspond to behavioral or life history variables. We quantified NPY-immunoreactive axons and neurons in the NAc of 13 primate species, including humans, great apes, and monkeys. Our data show that the human brain is unique among primates in having denser NPY innervation within the NAc, as measured by axon length density to neuron density, even after accounting for brain size. Combined with our previous finding of increased dopaminergic innervation in the same region, our results suggest that the neurochemical profile of the human NAc appears to have rendered our species uniquely susceptible to neurophysiological conditions such as addiction. The increase in NPY specific to the NAc may represent an adaptation that favors fat intake and contributes to an increased vulnerability to eating disorders, obesity, as well as alcohol and drug dependence. Along with our findings for dopamine, these deeply rooted structural attributes of the human brain are likely to have emerged early in the human clade, laying the groundwork for later brain expansion and the development of cognitive and behavioral specializations.

Effects and safety of vagus nerve stimulation on upper limb function in patients with stroke: a systematic review and meta-analysis

Vagus nerve stimulation (VNS) is used to deliver electric current to stimulate the vagus nerve. The aim of this study is to carry out a systematic review and meta-analysis to determine its effects on motor function in patients with stroke. PubMED, Embase, Web of Science (WoS), and Scopus were searched. Data on time since stroke, and mean scores and standard deviation on outcomes such as level of impairment and motor function were extracted. The results showed that invasive (MD 2.66, 95% CI 1.19-4.13, P = 0.0004) and non-invasive (MD 24.16, 95% CI 23.56-24.75, P = 0.00001) VNS are superior at improving level of motor impairment than the control post intervention and at follow-up respectively. Similarly, VNS improved motor function post intervention (MD 0.28, 95% CI 0.15-0.41, P < 0.0001); and there was no significant difference in adverse events between invasive VNS and control (OR 2.15, 95% CI 0.97-4.74, P = 0.06), and between non-invasive VNS and control (OR 4.54, 95% CI 0.48-42.97, P = 0.19). VNS can be used to improve motor function in patients with stroke.

Pharmacological activation of the amygdala, but not single prolonged footshock-induced acute stress, interferes with cue-induced motivation toward food rewards in rats

In the face of threats, animals adapt their behaviors to cope with the situation. Under such circumstances, irrelevant behaviors are usually suppressed. In this study, we examined whether food-seeking motivation would decrease under activation of the amygdala, an important nucleus in the regulation of stress response in the central nervous system, or after a physical acute stress session. In Experiment 1, we pharmacologically activated the basolateral nucleus (BLA) or the central nucleus of the amygdala (CeA) before a cue-induced reinstatement test in rats. Our results showed that activation of the BLA or the CeA abolished cue-induced motivation toward food rewards, while locomotor activity and free food intake were not affected. In Experiments 2 and 3, we further assessed anxiety and despair levels, as well as cue-induced reinstatement, after a single prolonged footshock-induced acute stress in rats. Behaviorally, acute stress did not affect anxiety level, despair level, or cue-induced motivation toward food rewards. Physiologically, there was no difference in cellular activities of the amygdala immediately after acute stress. To conclude, our results suggested that pharmacological activation of the amygdala decreased cue-induced motivation toward food reward. However, physiological acute stress did not immediately interfere with the negative emotions, motivation, or amygdala activities of the animals.

Stress to inflammation and anhedonia: Mechanistic insights from preclinical and clinical models

Anhedonia, as evidenced by impaired pleasurable response to reward, reduced reward motivation, and/or deficits in reward-related learning, is a common feature of depression. Such deficits in reward processing are also an important clinical target as a risk factor for depression onset. Unfortunately, reward-related deficits remain difficult to treat. To address this gap and inform the development of effective prevention and treatment strategies, it is critical to understand the mechanisms that drive impairments in reward function. Stress-induced inflammation is a plausible mechanism of reward deficits. The purpose of this paper is to review evidence for two components of this psychobiological pathway: 1) the effects of stress on reward function; and 2) the effects of inflammation on reward function. Within these two areas, we draw upon preclinical and clinical models, distinguish between acute and chronic effects of stress and inflammation, and address specific domains of reward dysregulation. By addressing these contextual factors, the review reveals a nuanced literature which might be targeted for additional scientific inquiry to inform the development of precise interventions.

Novel Compounds in the Treatment of Schizophrenia-A Selective Review

Schizophrenia is a chronic neuropsychiatric syndrome that significantly impacts daily function and quality of life. All of the available guidelines suggest a combined treatment approach with pharmacologic agents and psychological interventions. However, one in three patients is a non-responder, the effect on negative and cognitive symptoms is limited, and many drug-related adverse effects complicate clinical management. As a result, discovering novel drugs for schizophrenia presents a significant challenge for psychopharmacology. This selective review of the literature aims to outline the current knowledge on the aetiopathogenesis of schizophrenia and to present the recently approved and newly discovered pharmacological substances in treating schizophrenia. We discuss ten novel drugs, three of which have been approved by the FDA (Olanzapine/Samidorphan, Lumateperone, and Pimavanserin). The rest are under clinical trial investigation (Brilaroxazine, Xanomeline/Trospium, Emraclidine, Ulotaront, Sodium Benzoate, Luvadaxistat, and Iclepertin). However, additional basic and clinical research is required not only to improve our understanding of the neurobiology and the potential novel targets in the treatment of schizophrenia, but also to establish more effective therapeutical interventions for the syndrome, including the attenuation of negative and cognitive symptoms and avoiding dopamine blockade-related adverse effects.

Sex-specific adaptations to VTA circuits following subchronic stress

Dysregulation of the mesolimbic reward circuitry is implicated in the pathophysiology of stress-related illnesses such as depression and anxiety. These disorders are more frequently diagnosed in females, and sex differences in the response to stress are likely to be one factor that leads to enhanced vulnerability of females. In this study, we use subchronic variable stress (SCVS), a model in which females are uniquely vulnerable to behavioral disturbances, to investigate sexually divergent mechanisms of regulation of the ventral tegmental area by stress. Using slice electrophysiology, we find that female, but not male mice have a reduction in the ex vivo firing rate of VTA dopaminergic neurons following SCVS. Surprisingly, both male and female animals show an increase in inhibitory tone onto VTA dopaminergic neurons and an increase in the firing rate of VTA GABAergic neurons. In males, however, this is accompanied by a robust increase in excitatory synaptic tone onto VTA dopamine neurons. This supports a model by which SCVS recruits VTA GABA neurons to inhibit dopaminergic neurons in both male and female mice, but males are protected from diminished functioning of the dopaminergic system by a compensatory upregulation of excitatory synapses.

Ethanol blocks a novel form of iLTD, but not iLTP of inhibitory inputs to VTA GABA neurons

The ventral tegmental area (VTA) is an essential component of the mesocorticolimbic dopamine (DA) circuit that processes reward and motivated behaviors. The VTA contains DA neurons essential in this process, as well as GABAergic inhibitory cells that regulate DA cell activity. In response to drug exposure, synaptic connections of the VTA circuit can be rewired via synaptic plasticity-a phenomenon thought to be responsible for the pathology of drug dependence. While synaptic plasticity to VTA DA neurons as well as prefrontal cortex to nucleus accumbens GABA neurons are well studied, VTA GABA cell plasticity, specifically inhibitory inputs to VTA GABA neurons, is less understood. Therefore, we investigated the plasticity of these inhibitory inputs. Using whole cell electrophysiology in GAD67-GFP mice to identify GABA cells, we observed that these VTA GABA cells experience either inhibitory GABAergic long-term potentiation (iLTP) or inhibitory long-term depression (iLTD) in response to a 5 Hz stimulus. Paired pulse ratios, coefficient of variance, and failure rates suggest a presynaptic mechanism for both plasticity types, where iLTP is NMDA receptor-dependent and iLTD is GABAB receptor-dependent-this being the first report of iLTD onto VTA GABA cells. As illicit drug exposure can alter VTA plasticity, we employed chronic intermittent exposure (CIE) to ethanol (EtOH) vapor in male and female mice to examine its potential impact on VTA GABA input plasticity. Chronic EtOH vapor exposure produced measurable behavioral changes illustrating dependence and concomitantly prevented previously observed iLTD, which continued in air-exposed controls, illustrating the impact of EtOH on VTA neurocircuitry and suggesting physiologic mechanisms at play in alcohol use disorder and withdrawal states. Taken together, these novel findings of unique GABAergic synapses exhibiting either iLTP or iLTD within the mesolimbic circuit, and EtOH blockade specifically of iLTD, characterize inhibitory VTA plasticity as a malleable, experience-dependent system modified by EtOH.

Exercise therapy for chronic pain: How does exercise change the limbic brain function?

We are exposed to various external and internal threats which might hurt us. The role of taking flexible and appropriate actions against threats is played by "the limbic system" and at the heart of it there is the ventral tegmental area and nucleus accumbens (brain reward system). Pain-related fear causes excessive excitation of amygdala, which in turn causes the suppression of medial prefrontal cortex, leading to chronification of pain. Since the limbic system of chronic pain patients is functionally impaired, they are maladaptive to their situations, unable to take goal-directed behavior and are easily caught by fear-avoidance thinking. We describe the neural mechanisms how exercise activates the brain reward system and enables chronic pain patients to take goal-directed behavior and overcome fear-avoidance thinking. A key to getting out from chronic pain state is to take advantage of the behavioral switching function of the basal nucleus of amygdala. We show that exercise activates positive neurons in this nucleus which project to the nucleus accumbens and promote reward behavior. We also describe fear conditioning and extinction are affected by exercise. In chronic pain patients, the fear response to pain is enhanced and the extinction of fear memories is impaired, so it is difficult to get out of "fear-avoidance thinking". Prolonged avoidance of movement and physical inactivity exacerbate pain and have detrimental effects on the musculoskeletal and cardiovascular systems. Based on the recent findings on multiple bran networks, we propose a well-balanced exercise prescription considering the adherence and pacing of exercise practice. We conclude that therapies targeting the mesocortico-limbic system, such as exercise therapy and cognitive behavioral therapy, may become promising tools in the fight against chronic pain.

Somatostatin-Expressing Neurons in the Ventral Tegmental Area Innervate Specific Forebrain Regions and Are Involved in Stress Response

Expanding knowledge about the cellular composition of subcortical brain regions demonstrates large heterogeneity and differences from the cortical architecture. Previously we described three subtypes of somatostatin-expressing (Sst) neurons in the mouse ventral tegmental area (VTA) and showed their local inhibitory action on the neighboring dopaminergic neurons (Nagaeva et al., 2020). Here, we report that Sst+ neurons especially from the anterolateral part of the mouse VTA also project far outside the VTA and innervate forebrain regions that are mainly involved in the regulation of emotional behavior, including the ventral pallidum, lateral hypothalamus, the medial part of the central amygdala, anterolateral division of the bed nucleus of stria terminalis, and paraventricular thalamic nucleus. Deletion of these VTASst neurons in mice affected several behaviors, such as home cage activity, sensitization of locomotor activity to morphine, fear conditioning responses, and reactions to the inescapable stress of forced swimming, often in a sex-dependent manner. Together, these data demonstrate that VTASst neurons have selective projection targets distinct from the main targets of VTA dopamine neurons. VTASst neurons are involved in the regulation of behaviors primarily associated with the stress response, making them a relevant addition to the efferent VTA pathways and stress-related neuronal network.