A Motivational and Neuropeptidergic Hub: Anatomical and Functional Diversity within the Nucleus Accumbens Shell

Effects of 3,4-methylenedioxymethamphetamine on neural activity in the nucleus accumbens of male mice engaged in social behavior

3,4-methylenedioxymethamphetamine (MDMA), a commonly abused recreational drug, induces prosocial effects such as increased sociability and empathy. The nucleus accumbens (NAc) has been suggested to play a crucial role in these MDMA-mediated prosocial effects. However, the relationship between social behavior and NAc neural activity, and the effects of MDMA on this relationship, remain unknown. In this study, we measured NAc neural activity using fiber photometry and classified the behaviors of mice at times of transient increases in NAc neural activity during the social approach test (SAT). We found that NAc neural activity transiently increased at the onset of turning toward and sniffing novel mice during the SAT, although the frequency of turning was relatively low. We then examined the effects of MDMA on behavior and NAc neural activity and found that MDMA decreased the duration of sniffing per bout but did not alter NAc neural activity at the onset of turning toward or sniffing novel mice. These results suggest that MDMA does not affect the transient increase in NAc neural activity at the onset of social behaviors.

Role of the ventral tegmental area in general anesthesia

The ventral tegmental area (VTA), located in the midbrain, plays a pivotal role in the regulation of many important behaviors, such as reward, addiction, aversion, memory, learning, and sleep-wakefulness cycles. The majority of VTA neurons are dopaminergic neurons, although there is a significant proportion of GABAergic neurons and few glutamatergic neurons. These neuronal types project to different brain regions, thus mediating various biological functions. Therefore, the diverse roles of the VTA might depend on its heterogeneous neuronal types and projecting circuits. General anesthesia and sleep-wakefulness cycles share the feature of reversible loss of consciousness, and several common neural mechanisms underlie these two conditions. In addition to the well-known regulatory role of VTA in sleep-wakefulness, emerging evidence has demonstrated that VTA activity is also associated with promoting emergence from general anesthesia. Herein, we reviewed the literature and summarized the evidence regarding the modulation of the VTA by general anesthesia in rodents, which will improve the understanding of the modulatory mechanism of the VTA in general anesthesia.

Enhanced motivated behavior mediated by pharmacological targeting of the FGF14/Nav1.6 complex in nucleus accumbens neurons

Protein/protein interactions (PPI) play crucial roles in neuronal functions. Yet, their potential as drug targets for brain disorders remains underexplored. The fibroblast growth factor 14 (FGF14)/voltage-gated Na+ channel 1.6 (Nav1.6) complex regulates excitability of medium spiny neurons (MSN) of the nucleus accumbens (NAc), a central hub of reward circuitry that controls motivated behaviors. Here, we identified compound 1028 (IUPAC: ethyl 3-(2-(3-(hydroxymethyl)-1H-indol-1-yl)acetamido)benzoate), a brain-permeable small molecule that targets FGF14R117, a critical residue located within a druggable pocket at the FGF14/Nav1.6 PPI interface. We found that 1028 modulates FGF14/Nav1.6 complex assembly and depolarizes the voltage-dependence of Nav1.6 channel inactivation with nanomolar potency by modulating the intramolecular interaction between the III-IV linker and C-terminal domain of the Nav1.6 channel. Consistent with the compound's effects on Nav1.6 channel inactivation, 1028 enhances MSN excitability ex vivo and accumbal neuron firing rate in vivo in murine models. Systemic administration of 1028 maintains behavioral motivation preferentially during motivationally deficient conditions in murine models. These behavioral effects were abrogated by in vivo gene silencing of Fgf14 in the NAc and were accompanied by a selective reduction in accumbal dopamine levels during reward consumption in murine models. These findings underscore the potential to selectively regulate complex behaviors associated with neuropsychiatric disorders through targeting of PPIs in neurons.

Disrupting heroin-associated memory reconsolidation through actin polymerization inhibition in the nucleus accumbens core

BACKGROUND

Understanding drug addiction as a disorder of maladaptive learning, where drug-associated or environmental cues trigger drug cravings and seeking, is crucial for developing effective treatments. Actin polymerization, a biochemical process, plays a crucial role in drug-related memory formation, particularly evident in conditioned place preference paradigms involving drugs like morphine and methamphetamine. However, the role of actin polymerization in the reconsolidation of heroin-associated memories remains understudied.

METHODS

This study employed a rodent model of self-administered heroin to investigate the involvement of actin polymerization in the reconsolidation of heroin-associated memories. Rats underwent ten days of intravenous heroin self-administration paired with conditioned cues. Subsequently, a 10-day extinction phase aimed to reduce heroin-seeking behaviors. Following this, rats participated in a 15-minute retrieval trial with or without cues. Immediately post-retrieval, rats received bilateral injections of the actin polymerization inhibitor Latrunculin A (Lat A) into the nucleus accumbens core (NACc), a critical brain region for memory reconsolidation.

RESULTS

Immediate administration of Lat A into the NACc post-retrieval significantly reduced cue-induced and heroin-primed reinstatement of heroin-seeking behavior for at least 28 days. However, administering Lat A 6-hour post-retrieval or without a retrieval trial, as well as administering Jasplakionlide prior to memory reactivation did not affect heroin-seeking behaviors.

CONCLUSIONS

Inhibiting actin polymerization during the reconsolidation window disrupts heroin-associated memory reconsolidation, leading to decreased heroin-seeking behavior and prevention of relapse. These effects are contingent upon the presence of a retrieval trial and exhibit temporal specificity, shedding light on addiction mechanisms and potential therapeutic interventions.

Dissociable control of motivation and reinforcement by distinct ventral striatal dopamine receptors

Dopamine (DA) release in striatal circuits, including the nucleus accumbens medial shell (mNAcSh), tracks separable features of reward like motivation and reinforcement. However, the cellular and circuit mechanisms by which DA receptors transform DA release into distinct constructs of reward remain unclear. Here we show that DA D3 receptor (D3R) signaling in the mNAcSh drives motivated behavior in mice by regulating local microcircuits. Furthermore, D3Rs coexpress with DA D1 receptors, which regulate reinforcement, but not motivation. Paralleling dissociable roles in reward function, we report nonoverlapping physiological actions of D3R and DA D1 receptor signaling in mNAcSh neurons. Our results establish a fundamental framework wherein DA signaling within the same nucleus accumbens cell type is physiologically compartmentalized via actions on distinct DA receptors. This structural and functional organization provides neurons in a limbic circuit with the unique ability to orchestrate dissociable aspects of reward-related behaviors relevant to the etiology of neuropsychiatric disorders.

Dopaminergic circuits controlling threat and safety learning

The ability to learn from experience that certain cues and situations are associated with threats or safety is crucial for survival and adaptive behavior. Understanding the neural substrates of threat and safety learning has high clinical significance because deficits in these forms of learning characterize anxiety disorders. Traditionally, dopamine neurons were thought to uniformly support reward learning by signaling reward prediction errors. However, the dopamine system is functionally more diverse than was initially appreciated and is also critical for processing threat and safety. In this review, I highlight recent studies demonstrating that dopamine neurons generate prediction errors for threat and safety, and describe how dopamine projections to the amygdala, medial prefrontal cortex (mPFC), and striatum regulate associative threat and safety learning.

Developmental and Adult Striatal Patterning of Nociceptin Ligand Marks Striosomal Population With Direct Dopamine Projections

Circuit influences on the midbrain dopamine system are crucial to adaptive behavior and cognition. Recent developments in the study of neuropeptide systems have enabled high-resolution investigations of the intersection of neuromodulatory signals with basal ganglia circuitry, identifying the nociceptin/orphanin FQ (N/OFQ) endogenous opioid peptide system as a prospective regulator of striatal dopamine signaling. Using a prepronociceptin-Cre reporter mouse line, we characterized highly selective striosomal patterning of Pnoc mRNA expression in mouse dorsal striatum, reflecting the early developmental expression of Pnoc. In the ventral striatum, Pnoc expression in the nucleus accumbens core was grouped in clusters akin to the distribution found in striosomes. We found that PnoctdTomato reporter cells largely comprise a population of dopamine receptor D1 (Drd1) expressing medium spiny projection neurons localized in dorsal striosomes, known to be unique among striatal projection neurons for their direct innervation of midbrain dopamine neurons. These findings provide a new understanding of the intersection of the N/OFQ system among basal ganglia circuits with particular implications for developmental regulation or wiring of striato-nigral circuits.

Nucleus accumbens shell electrical lesion attenuates seizures and gliosis in chronic temporal lobe epilepsy rats

OBJECTIVE

Temporal lobe epilepsy (TLE) is the most prevalent form of epilepsy. Prior research has indicated the involvement of the nucleus accumbens shell (NAcSh) in the process of epileptogenesis, thereby implying its potential as a therapeutic target for TLE. In the present study, we investigated the antiepileptic effect of the NAcSh electrical lesion.

METHODS

Chronic TLE was induced by stereotactic injection of kainic acid (KA) into the hippocampus 3 weeks after KA administration, and NAcSh electrical lesions were performed. Seizures in rats were monitored by video electroencephalogram (EEG) 1 week following the NAcSh electrical lesion. Besides, the spatial memory function assessment in rats was conducted using the Morris water maze (MWM) test in the final week of the experiment. Later, hippocampal glial cell activation and neuron loss in rats were evaluated through immunohistochemistry.

RESULTS

TLE rats subjected to NAcSh electrical lesion exhibited a significant reduction in the frequency of seizures compared to untreated TLE rats. Furthermore, NAcSh electrical lesion led to less activation of hippocampal glial cells and fewer neuronal loss in TLE rats. It is worth noting that the NAcSh electrical lesion did not cause additional memory impairment.

SIGNIFICANCE

In the present study, the NAcSh electrical lesion exhibited a definitive therapeutic effect on the chronic TLE rat model, potentially due to decreased hippocampal TLE-induced activation of glial cells and neuron loss. In conclusion, our results indicated that the NAcSh is a promising therapeutic target for TLE and possesses high potential for clinical application.

An amygdalar oscillator coordinates cellular and behavioral rhythms

Circadian rhythms are generated by the master pacemaker suprachiasmatic nucleus (SCN) in concert with local clocks throughout the body. Although many brain regions exhibit cycling clock gene expression, the identity of a discrete extra-SCN brain oscillator that produces rhythmic behavior has remained elusive. Here, we show that an extra-SCN oscillator in the lateral amygdala (LA) is defined by expression of the clock-output molecule mWAKE/ANKFN1. mWAKE is enriched in the anterior/dorsal LA (adLA), and, strikingly, selective disruption of clock function or excitatory signaling in adLAmWAKE neurons abolishes Period2 (PER2) rhythms throughout the LA. mWAKE levels rise at night and promote rhythmic excitability of adLAmWAKE neurons by upregulating Ca2+-activated K+ channel activity specifically at night. adLAmWAKE neurons coordinate rhythmic sensory perception and anxiety in a clock-dependent and WAKE-dependent manner. Together, these data reveal the cellular identity of an extra-SCN brain oscillator and suggest a multi-level hierarchical system organizing molecular and behavioral rhythms.

Activation of the nucleus accumbens promotes place preference and counteracts stress-induced hyperthermia

Positive affect promotes mental health and physical well-being, which may involve modifications in the autonomic nervous system activity. Here, we examine, using chemogenetic techniques, the effects of nucleus accumbens (NAc) activation on affect and body temperature regulation as a proxy of autonomic function. A conditioned place preference test revealed that nucleus accumbens activation induced positive affect. Chemogenetic and natural activations inhibited intruder stress-induced hyperthermia and prostaglandin E2-induced fever. Chemogenetic inhibition did not show a negative affect but canceled the positive affect induced by the natural stimulus of chocolate or sucrose. Counting of c-Fos expression confirmed chemogenetic and sucrose-induced activation of the NAc. Our findings indicate that nucleus accumbens activation modifies a component of autonomic nervous activity and that this mechanism may underscore the link between positive affect and physical well-being. Applying our observations to humans may reduce fever side reactions of vaccines by employing preventive treatments that induce positive affect.

Microglia Sing the Prelude of Neuroinflammation-Associated Depression

Major depressive disorder (MDD) is a psychiatric condition characterized by sadness and anhedonia and is closely linked to chronic low-grade neuroinflammation, which is primarily induced by microglia. Nonetheless, the mechanisms by which microglia elicit depressive symptoms remain uncertain. This review focuses on the mechanism linking microglia and depression encompassing the breakdown of the blood-brain barrier, the hypothalamic-pituitary-adrenal axis, the gut-brain axis, the vagus and sympathetic nervous systems, and the susceptibility influenced by epigenetic modifications on microglia. These pathways may lead to the alterations of microglia in cytokine levels, as well as increased oxidative stress. Simultaneously, many antidepressant treatments can alter the immune phenotype of microglia, while anti-inflammatory treatments can also have antidepressant effects. This framework linking microglia, neuroinflammation, and depression could serve as a reference for targeting microglia to treat depression.

Melanin concentrating hormone projections to the nucleus accumbens enhance the reward value of food consumption and do not induce feeding or REM sleep

Regulation of food intake and energy balance is critical to survival. Hunger develops as a response to energy deficit and drives food-seeking and consumption. However, motivations to eat are varied in nature, and promoted by factors other than energy deficit. When dysregulated, non-homeostatic drives to consume can contribute to disorders of food intake, adding to the increasing prevalence of restrictive eating disorders and obesity. Melanin-concentrating hormone (MCH) neurons have been implicated in the regulation of feeding behavior, in addition to a number of other fundamental behaviors including sleep, anxiety, and maternal behavior. Several studies suggest that MCH peptide increases food consumption, while studies of MCH neurons show effects only on cued feeding, and others show no effect of MCH neuron manipulation on feeding. MCH neurons have widespread projections to diverse downstream brain regions yet few studies have investigated the function of specific projections or differentiated the behaviors they regulate. Here we use optogenetics, in combination with different behavioral paradigms, to elucidate the role of MCH projections to the nucleus accumbens (NAc) in sleep and feeding behavior. We show that MCH neurons projecting to the NAc do not induce changes in baseline feeding or REM sleep, but do enhance the preference for a food paired with optogenetic stimulation. Furthermore, this effect is diminished in female mice relative to males, in line with previous results suggesting sex differences in the functional role of MCH neurons. These results suggest that MCH projections to the NAc can enhance the rewarding value of consumed food.

The Impacts of Adolescent Cannabinoid Exposure on Striatal Anxiety- and Depressive-Like Pathophysiology Are Prevented by the Antioxidant N-Acetylcysteine

Background

Exposure to Δ9-tetrahydrocannabinol (THC) is an established risk factor for later-life neuropsychiatric vulnerability, including mood- and anxiety-related symptoms. The psychotropic effects of THC on affect and anxiogenic behavioral phenomena are known to target the striatal network, particularly the nucleus accumbens, a neural region linked to mood and anxiety disorder pathophysiology. THC may increase neuroinflammatory responses via the redox system and dysregulate inhibitory and excitatory neural balance in various brain circuits, including the striatum. Thus, interventions that can induce antioxidant effects may counteract the neurodevelopmental impacts of THC exposure.

Methods

In the current study, we used an established preclinical adolescent rat model to examine the impacts of adolescent THC exposure on various behavioral, molecular, and neuronal biomarkers associated with increased mood and anxiety disorder vulnerability. Moreover, we investigated the protective properties of the antioxidant N-acetylcysteine against THC-related pathology.

Results

We demonstrated that adolescent THC exposure induced long-lasting anxiety- and depressive-like phenotypes concomitant with differential neuronal and molecular abnormalities in the two subregions of the nucleus accumbens, the shell and the core. In addition, we report for the first time that N-acetylcysteine can prevent THC-induced accumbal pathophysiology and associated behavioral abnormalities.

Conclusions

The preventive effects of this antioxidant intervention highlight the critical role of redox mechanisms underlying cannabinoid-induced neurodevelopmental pathology and identify a potential intervention strategy for the prevention and/or reversal of these pathophysiological sequelae.

Nucleus Accumbens Corticotropin-Releasing Hormone Neurons Projecting to the Bed Nucleus of the Stria Terminalis Promote Wakefulness and Positive Affective State

The nucleus accumbens (NAc) plays an important role in various emotional and motivational behaviors that rely on heightened wakefulness. However, the neural mechanisms underlying the relationship between arousal and emotion regulation in NAc remain unclear. Here, we investigated the roles of a specific subset of inhibitory corticotropin-releasing hormone neurons in the NAc (NAcCRH) in regulating arousal and emotional behaviors in mice. We found an increased activity of NAcCRH neurons during wakefulness and rewarding stimulation. Activation of NAcCRH neurons converts NREM or REM sleep to wakefulness, while inhibition of these neurons attenuates wakefulness. Remarkably, activation of NAcCRH neurons induces a place preference response (PPR) and decreased basal anxiety level, whereas their inactivation induces a place aversion response and anxious state. NAcCRH neurons are identified as the major NAc projection neurons to the bed nucleus of the stria terminalis (BNST). Furthermore, activation of the NAcCRH-BNST pathway similarly induced wakefulness and positive emotional behaviors. Taken together, we identified a basal forebrain CRH pathway that promotes the arousal associated with positive affective states.

Functional Connectivity Differences in the Resting-state of the Amygdala in Alcohol-dependent Patients with Depression

RATIONALE AND OBJECTIVES

The mechanism of comorbidity between alcohol dependence and depressive disorders are not well understood. This study investigated differences in the brain function of alcohol-dependent patients with and without depression by performing functional connectivity analysis using resting-state functional magnetic resonance imaging.

MATERIALS AND METHODS

A total of 29 alcohol-dependent patients with depression, 31 alcohol-dependent patients without depression and 31 healthy control subjects were included in this study. The resting-state functional connectivity between the amygdala and the whole brain was compared among the three groups. Additionally, we examined the correlation between functional connectivity values in significantly different brain regions and levels of alcohol dependence and depression.

RESULTS

The resting-state functional connectivity between the left amygdala and the right caudate nucleus was decreased in alcohol-dependent patients. Additionally, the resting-state functional connectivity of the right amygdala with the right caudate nucleus, right transverse temporal gyrus, right temporal pole: superior temporal gyrus were also decreased. In alcohol-dependent patients with depression, not only was functional connectivity between the above brain regions significantly decreased, but so was functional connectivity between the right amygdala and the left middle temporal gyrus. Also, there was no significant correlation between the resting-state functional connectivity values in statistically significant brain regions and the levels of alcohol dependence and depression.

CONCLUSION

The impairment of the functional connectivity of the amygdala with caudate nucleus and partial temporal lobe may be involved in the neural mechanism of alcohol dependence comorbidity depressive disorders.

The Perineuronal Net Protein Brevican Acts in Nucleus Accumbens Parvalbumin-Expressing Interneurons of Adult Mice to Regulate Excitatory Synaptic Inputs and Motivated Behaviors

BACKGROUND

Experience-dependent functional adaptation of nucleus accumbens (NAc) circuitry underlies the development and expression of reward-motivated behaviors. Parvalbumin-expressing GABAergic (gamma-aminobutyric acidergic) interneurons (PVINs) within the NAc are required for this process. Perineuronal nets (PNNs) are extracellular matrix structures enriched around PVINs that arise during development and have been proposed to mediate brain circuit stability. However, their function in the adult NAc is largely unknown. Here, we studied the developmental emergence and adult regulation of PNNs in the NAc of male and female mice and examined the cellular and behavioral consequences of reducing the PNN component brevican in NAc PVINs.

METHODS

We characterized the expression of PNN components in mouse NAc using immunofluorescence and RNA in situ hybridization. We lowered brevican in NAc PVINs of adult mice using an intersectional viral and genetic method and quantified the effects on synaptic inputs to NAc PVINs and reward-motivated learning.

RESULTS

PNNs around NAc PVINs were developmentally regulated and appeared during adolescence. In the adult NAc, PVIN PNNs were also dynamically regulated by cocaine. Transcription of the gene that encodes brevican was regulated in a cell type- and isoform-specific manner in the NAc, with the membrane-tethered form of brevican being highly enriched in PVINs. Lowering brevican in NAc PVINs of adult mice decreased their excitatory inputs and enhanced both short-term novel object recognition and cocaine-induced conditioned place preference.

CONCLUSIONS

Regulation of brevican in NAc PVINs of adult mice modulates their excitatory synaptic drive and sets experience thresholds for the development of motivated behaviors driven by rewarding stimuli.

Mu opioid receptor expression by nucleus accumbens inhibitory interneurons promotes affiliative social behavior

Mu opioid receptors in the nucleus accumbens regulate motivated behavior, including pursuit of natural rewards like social interaction as well as exogenous opioids. We used a suite of genetic and viral strategies to conditionally delete mu opioid receptor expression from all major neuron types in the nucleus accumbens. We pinpoint inhibitory interneurons as an essential site of mu opioid receptor expression for typical social behavior, independent from exogenous opioid sensitivity.

Microdosing of a kappa opioid receptor agonist within proximal nucleus accumbens shell microstructures revealing opposing behavioral outcomes

Targeted intracranial delivery of molecularly-specific therapies within intricate brain structures poses a formidable challenge due to the heterogeneity of neuronal phenotypes and functions. Here we report the use of an implantable, miniaturized neural drug delivery system permitting dynamic adjustment of pharmacotherapies. Specifically, we exploit the spatial accuracy afforded by this method for targeting modulation of neuronal microstructures. Kappa opioid receptors (KOR) within the dorsal medial nucleus accumbens shell (NASh) are selectively activated through micro infusions of the KOR agonist, U-50488. Remarkably, we demonstrate that micro infusions of U-50488 into the dorsal NASh induces reward-like conditioned place preferences, whereas a mere 1 mm shift ventrally results in conditioned place aversions. The striking precision afforded by this method may prove useful in other neurotherapeutic interventions.

The mediation role of gray matter volume in the relationship between childhood maltreatment and psychological resilience in adolescents with first-episode major depressive disorder

Previous studies have revealed morphologic alterations in patients with major depressive disorder (MDD) with experiences of childhood trauma. However, the underlying neural mechanisms remain largely unknown. This study aims to explore the brain structural changes and their possible mediation role in the relationship between childhood maltreatment and psychological resilience in drug-naïve adolescents with first-episode MDD. A total of 57 adolescents with first-episode MDD and 36 healthy controls (HCs) completed the T1-weighted magnetic resonance imaging scan. The adverse childhood experiences and current psychological resilience were assessed using the Childhood Trauma Questionnaire-Short Form and the Connor Davidson Resilience Scale, respectively. The voxel-based morphometry approach was applied to examine changes in the gray matter volume (GMV). Compared with the HCs, adolescents with MDD had significantly reduced GMV volumes in the left fusiform gyrus, right orbitofrontal gyrus, right superior temporal gyrus, right calcarine cortex, right middle frontal gyrus, left angular gyrus, right precuneus, right posterior cingulate gyrus, and right posterior central gyrus, as well as significantly increased GMV volumes in the left lenticular putamen and right lenticular pallidum. The GMV of the right calcarine cortex was found to be negatively correlated with the severity of emotional abuse and positively correlated with the level of psychological resilience. Moreover, the GMV of the right calcarine cortex might partially mediate the relationship between childhood maltreatment and psychological resilience. The present study provided further evidence for structural impairments in adolescents with MDD. Our findings also confirmed the important role of depression-related GMV changes in childhood growth experiences and psychological resilience characteristics during adolescent brain maturation.

Role of the Nucleus Accumbens in Signaled Avoidance Actions

Animals, humans included, navigate their environments guided by sensory cues, responding adaptively to potential dangers and rewards. Avoidance behaviors serve as adaptive strategies in the face of signaled threats, but the neural mechanisms orchestrating these behaviors remain elusive. Current circuit models of avoidance behaviors indicate that the nucleus accumbens (NAc) in the ventral striatum plays a key role in signaled avoidance behaviors, but the nature of this engagement is unclear. Evolving perspectives propose the NAc as a pivotal hub for action selection, integrating cognitive and affective information to heighten the efficiency of both appetitive and aversive motivated behaviors. To unravel the engagement of the NAc during active and passive avoidance, we used calcium imaging fiber photometry to examine NAc GABAergic neuron activity in ad libitum moving mice performing avoidance behaviors. We then probed the functional significance of NAc neurons using optogenetics and genetically targeted or electrolytic lesions. We found that NAc neurons code contraversive orienting movements and avoidance actions. However, direct optogenetic inhibition or lesions of NAc neurons did not impair active or passive avoidance behaviors, challenging the notion of their purported pivotal role in adaptive avoidance. The findings emphasize that while the NAc encodes avoidance movements, it is not required for avoidance behaviors, highlighting the distinction between behavior encoding or representation and mediation or generation.

Highly sensitive in vivo detection of dynamic changes in enkephalins following acute stress

Enkephalins are opioid peptides that modulate analgesia, reward, and stress. In vivo detection of enkephalins remains difficult due to transient and low endogenous concentrations and inherent sequence similarity. To begin to address this we previously developed a system combining in vivo optogenetics with microdialysis and a highly sensitive mass spectrometry-based assay to measure opioid peptide release in freely moving rodents (Al-Hasani, 2018, eLife). Here we show improved detection resolution and stabilization of enkephalin detection, which allowed us to investigate enkephalin release during acute stress. We present an analytical method for real-time, simultaneous detection of Met- and Leu-Enkephalin (Met-Enk & Leu-Enk) in the mouse Nucleus Accumbens shell (NAcSh) after acute stress. We confirm that acute stress activates enkephalinergic neurons in the NAcSh using fiber photometry and that this leads to the release of Met- and Leu-Enk. We also demonstrate the dynamics of Met- and Leu-Enk release as well as how they correlate to one another in the ventral NAc shell, which was previously difficult due to the use of approaches that relied on mRNA transcript levels rather than post-translational products. This approach increases spatiotemporal resolution, optimizes the detection of Met-Enkephalin through methionine oxidation, and provides novel insight into the relationship between Met- and Leu-Enkephalin following stress.

Mono-methylation of lysine 27 at histone 3 confers lifelong susceptibility to stress

Histone post-translational modifications are critical for mediating persistent alterations in gene expression. By combining unbiased proteomics profiling and genome-wide approaches, we uncovered a role for mono-methylation of lysine 27 at histone H3 (H3K27me1) in the enduring effects of stress. Specifically, mice susceptible to early life stress (ELS) or chronic social defeat stress (CSDS) displayed increased H3K27me1 enrichment in the nucleus accumbens (NAc), a key brain-reward region. Stress-induced H3K27me1 accumulation occurred at genes that control neuronal excitability and was mediated by the VEFS domain of SUZ12, a core subunit of the polycomb repressive complex-2, which controls H3K27 methylation patterns. Viral VEFS expression changed the transcriptional profile of the NAc, led to social, emotional, and cognitive abnormalities, and altered excitability and synaptic transmission of NAc D1-medium spiny neurons. Together, we describe a novel function of H3K27me1 in the brain and demonstrate its role as a "chromatin scar" that mediates lifelong stress susceptibility.

Comparison of dopamine release and uptake parameters across sex, species and striatal subregions

For over four decades, fast-scan cyclic voltammetry (FSCV) has been used to selectively measure neurotransmitters such as dopamine (DA) with high spatial and temporal resolution, providing detailed information about the regulation of DA in the extracellular space. FSCV is an optimal method for determining concentrations of stimulus-evoked DA in brain tissue. When modelling diseases involving disturbances in DA transmission, preclinical rodent models are especially useful because of the availability of specialized tools and techniques that serve as a foundation for translational research. There is known heterogeneity in DA dynamics between and within DA-innervated brain structures and between males and females. However, systematic evaluations of sex- and species-differences across multiple areas are lacking. Therefore, using FSCV, we captured a broad range of DA dynamics across five sub-regions of the dorsal and ventral striatum of males and females of both rats and mice that reflect the functional heterogeneity of DA kinetics and dynamics within these structures. While numerous differences were found, in particular, we documented a strong, consistent pattern of increased DA transporter activity in females in all of the regions surveyed. The data herein are intended to be used as a resource for further investigation of DA terminal function.

The effects of different types of social interactions on the electrophysiology of neurons in the nucleus accumbens in rodents

BORLAND, J.M., The effects of different types of social interactions on the electrophysiology of neurons in the nucleus accumbens in rodents, NEUROSCI BIOBEH REV 21(1) XXX-XXX, 2024.-Sociality shapes an organisms' life. The nucleus accumbens is a critical brain region for mental health. In the following review, the effects of different types of social interactions on the physiology of neurons in the nucleus accumbens is synthesized. More specifically, the effects of sex behavior, aggression, social defeat, pair-bonding, play behavior, affiliative interactions, parental behaviors, the isolation from social interactions and maternal separation on measures of excitatory synaptic transmission, intracellular signaling and factors of transcription and translation in neurons in the nucleus accumbens in rodent models are reviewed. Similarities and differences in effects depending on the type of social interaction is then discussed. This review improves the understanding of the molecular and synaptic mechanisms of sociality.

Kappa-opioid receptor stimulation in the nucleus accumbens shell and ethanol drinking: Differential effects by rostro-caudal location and level of drinking

Although the kappa-opioid receptor (KOR) and its endogenous ligand, dynorphin, are believed to be involved in ethanol drinking, evidence on the direction of their effects has been mixed. The nucleus accumbens (NAc) shell densely expresses KORs, but previous studies have not found KOR activation to influence ethanol drinking. Using microinjections into the NAc shell of male and female Long-Evans rats that drank under the intermittent-access procedure, we found that the KOR agonist, U50,488, had no effect on ethanol drinking when injected into the middle NAc shell, but that it promoted intake in males and high-drinking females in the caudal NAc shell and high-drinking females in the rostral shell, and decreased intake in males and low-drinking females in the rostral shell. Conversely, injection of the KOR antagonist, nor-binaltorphimine, stimulated ethanol drinking in low-drinking females when injected into the rostral NAc shell and decreased drinking in high-drinking females when injected into the caudal NAc shell. These effects of KOR activity were substance-specific, as U50,488 did not affect sucrose intake. Using quantitative real-time PCR, we found that baseline gene expression of the KOR was higher in the rostral compared to caudal NAc shell, but that this was upregulated in the rostral shell with a history of ethanol drinking. Our findings have important clinical implications, demonstrating that KOR stimulation in the NAc shell can affect ethanol drinking, but that this depends on NAc subregion, subject sex, and ethanol intake level, and suggesting that this may be due to differences in KOR expression.

Distinct cholinergic circuits underlie discrete effects of reward on attention

Attention and reward are functions that are critical for the control of behavior, and massive multi-region neural systems have evolved to support the discrete computations associated with each. Previous research has also identified that attention and reward interact, though our understanding of the neural mechanisms that mediate this interplay is incomplete. Here, we review the basic neuroanatomy of attention, reward, and cholinergic systems. We then examine specific contexts in which attention and reward computations interact. Building on this work, we propose two discrete neural circuits whereby acetylcholine, released from cell groups located in different parts of the brain, mediates the impact of stimulus-reward associations as well as motivation on attentional control. We conclude by examining these circuits as a potential shared loci of dysfunction across diseases states associated with deficits in attention and reward.

Corticotropin-Releasing Factor Release From a Unique Subpopulation of Accumbal Neurons Constrains Action-Outcome Acquisition in Reward Learning

BACKGROUND

The nucleus accumbens (NAc) mediates reward learning and motivation. Despite an abundance of neuropeptides, peptidergic neurotransmission from the NAc has not been integrated into current models of reward learning. The existence of a sparse population of neurons containing corticotropin-releasing factor (CRF) has been previously documented. Here, we provide a comprehensive analysis of their identity and functional role in shaping reward learning.

METHODS

Our multidisciplinary approach included fluorescent in situ hybridization (n = ≥3 mice), tract tracing (n = 5 mice), ex vivo electrophysiology (n = ≥30 cells), in vivo calcium imaging with fiber photometry (n = ≥4 mice), and use of viral strategies in transgenic lines to selectively delete CRF peptide from NAc neurons (n = ≥4 mice). Behaviors used were instrumental learning, sucrose preference, and spontaneous exploration in an open field.

RESULTS

We showed that the vast majority of NAc CRF-containing neurons are spiny projection neurons (SPNs) comprising dopamine D1-, D2-, or D1/D2-containing SPNs that primarily project and connect to the ventral pallidum and to a lesser extent the ventral midbrain. As a population, they display mature and immature SPN firing properties. We demonstrated that NAc CRF-containing neurons track reward outcomes during operant reward learning and that CRF release from these neurons acts to constrain initial acquisition of action-outcome learning and at the same time facilitates flexibility in the face of changing contingencies.

CONCLUSIONS

CRF release from this sparse population of SPNs is critical for reward learning under normal conditions.

The nucleus accumbens in reward and aversion processing: insights and implications

The nucleus accumbens (NAc), a central component of the brain's reward circuitry, has been implicated in a wide range of behaviors and emotional states. Emerging evidence, primarily drawing from recent rodent studies, suggests that the function of the NAc in reward and aversion processing is multifaceted. Prolonged stress or drug use induces maladaptive neuronal function in the NAc circuitry, which results in pathological conditions. This review aims to provide comprehensive and up-to-date insights on the role of the NAc in motivated behavior regulation and highlights areas that demand further in-depth analysis. It synthesizes the latest findings on how distinct NAc neuronal populations and pathways contribute to the processing of opposite valences. The review examines how a range of neuromodulators, especially monoamines, influence the NAc's control over various motivational states. Furthermore, it delves into the complex underlying mechanisms of psychiatric disorders such as addiction and depression and evaluates prospective interventions to restore NAc functionality.

Dynorphin modulates motivation through a pallido-amygdala cholinergic circuit

The endogenous opioid peptide dynorphin and its receptor κ-opioid receptor (KOR) have been implicated in divergent behaviors, but the underlying mechanisms remain elusive. Here we show that dynorphin released from nucleus accumbens dynorphinergic neurons exerts powerful modulation over a ventral pallidum (VP) disinhibitory circuit, thereby controlling cholinergic transmission to the amygdala and motivational drive in mice. On one hand, dynorphin acts postsynaptically via KORs on local GABAergic neurons in the VP to promote disinhibition of cholinergic neurons, which release acetylcholine into the amygdala to invigorate reward-seeking behaviors. On the other hand, dynorphin also acts presynaptically via KORs on dynorphinergic terminals to limit its own release. Such autoinhibition keeps cholinergic neurons from prolonged activation and release of acetylcholine, and prevents perseverant reward seeking. Our study reveals how dynorphin exquisitely modulate motivation through cholinergic system, and provides an explanation for why these neuromodulators are involved in motivational disorders, including depression and addiction.

The nucleus accumbens shell: a neural hub at the interface of homeostatic and hedonic feeding

Feeding behavior is a complex physiological process regulated by the interplay between homeostatic and hedonic feeding circuits. Among the neural structures involved, the nucleus accumbens (NAc) has emerged as a pivotal region at the interface of these two circuits. The NAc comprises distinct subregions and in this review, we focus mainly on the NAc shell (NAcSh). Homeostatic feeding circuits, primarily found in the hypothalamus, ensure the organism's balance in energy and nutrient requirements. These circuits monitor peripheral signals, such as insulin, leptin, and ghrelin, and modulate satiety and hunger states. The NAcSh receives input from these homeostatic circuits, integrating information regarding the organism's metabolic needs. Conversely, so-called hedonic feeding circuits involve all other non-hunger and -satiety processes, i.e., the sensory information, associative learning, reward, motivation and pleasure associated with food consumption. The NAcSh is interconnected with hedonics-related structures like the ventral tegmental area and prefrontal cortex and plays a key role in encoding hedonic information related to palatable food seeking or consumption. In sum, the NAcSh acts as a crucial hub in feeding behavior, integrating signals from both homeostatic and hedonic circuits, to facilitate behavioral output via its downstream projections. Moreover, the NAcSh's involvement extends beyond simple integration, as it directly impacts actions related to food consumption. In this review, we first focus on delineating the inputs targeting the NAcSh; we then present NAcSh output projections to downstream structures. Finally we discuss how the NAcSh regulates feeding behavior and can be seen as a neural hub integrating homeostatic and hedonic feeding signals, via a functionally diverse set of projection neuron subpopulations.

CRF release from a unique subpopulation of accumbal neurons constrains action-outcome acquisition in reward learning

Background

The nucleus accumbens (NAc) mediates reward learning and motivation. Despite an abundance of neuropeptides, peptidergic neurotransmission from the NAc has not been integrated into current models of reward learning. The existence of a sparse population of neurons containing corticotropin releasing factor (CRF) has been previously documented. Here we provide a comprehensive analysis of their identity and functional role in shaping reward learning.

Methods

To do this, we took a multidisciplinary approach that included florescent in situ hybridization (N mice ≥ 3), tract tracing (N mice = 5), ex vivo electrophysiology (N cells ≥ 30), in vivo calcium imaging with fiber photometry (N mice ≥ 4) and use of viral strategies in transgenic lines to selectively delete CRF peptide from NAc neurons (N mice ≥ 4). Behaviors used were instrumental learning, sucrose preference and spontaneous exploration in an open field.

Results

Here we show that the vast majority of NAc CRF-containing (NAc CRF ) neurons are spiny projection neurons (SPNs) comprised of dopamine D1-, D2- or D1/D2-containing SPNs that primarily project and connect to the ventral pallidum and to a lesser extent the ventral midbrain. As a population, they display mature and immature SPN firing properties. We demonstrate that NAc CRF neurons track reward outcomes during operant reward learning and that CRF release from these neurons acts to constrain initial acquisition of action-outcome learning, and at the same time facilitates flexibility in the face of changing contingencies.

Conclusion

We conclude that CRF release from this sparse population of SPNs is critical for reward learning under normal conditions.

CRF regulates pain sensation by enhancement of corticoaccumbal excitatory synaptic transmission

Both peripheral and central corticotropin-releasing factor (CRF) systems have been implicated in regulating pain sensation. However, compared with the peripheral, the mechanisms underlying central CRF system in pain modulation have not yet been elucidated, especially at the neural circuit level. The corticoaccumbal circuit, a structure rich in CRF receptors and CRF-positive neurons, plays an important role in behavioral responses to stressors including nociceptive stimuli. The present study was designed to investigate whether and how CRF signaling in this circuit regulated pain sensation under physiological and pathological pain conditions. Our studies employed the viral tracing and circuit-, and cell-specific electrophysiological methods to label the CRF-containing circuit from the medial prefrontal cortex to the nucleus accumbens shell (mPFCCRF-NAcS) and record its neuronal propriety. Combining optogenetic and chemogenetic manipulation, neuropharmacological methods, and behavioral tests, we were able to precisely manipulate this circuit and depict its role in regulation of pain sensation. The current study found that the CRF signaling in the NAc shell (NAcS), but not NAc core, was necessary and sufficient for the regulation of pain sensation under physiological and pathological pain conditions. This process was involved in the CRF-mediated enhancement of excitatory synaptic transmission in the NAcS. Furthermore, we demonstrated that the mPFCCRF neurons monosynaptically connected with the NAcS neurons. Chronic pain increased the protein level of CRF in NAcS, and then maintained the persistent NAcS neuronal hyperactivity through enhancement of this monosynaptic excitatory connection, and thus sustained chronic pain behavior. These findings reveal a novel cell- and circuit-based mechanistic link between chronic pain and the mPFCCRF → NAcS circuit and provide a potential new therapeutic target for chronic pain.

Activity of the Sodium Leak Channel Maintains the Excitability of Paraventricular Thalamus Glutamatergic Neurons to Resist Anesthetic Effects of Sevoflurane in Mice

BACKGROUND

Stimulation of the paraventricular thalamus has been found to enhance anesthesia recovery; however, the underlying molecular mechanism by which general anesthetics modulate paraventricular thalamus is unclear. This study aimed to test the hypothesis that the sodium leak channel (NALCN) maintains neuronal activity in the paraventricular thalamus to resist anesthetic effects of sevoflurane in mice.

METHODS

Chemogenetic and optogenetic manipulations, in vivo multiple-channel recordings, and electroencephalogram recordings were used to investigate the role of paraventricular thalamus neuronal activity in sevoflurane anesthesia. Virus-mediated knockdown and/or overexpression was applied to determine how NALCN influenced excitability of paraventricular thalamus glutamatergic neurons under sevoflurane. Viral tracers and local field potentials were used to explore the downstream pathway.

RESULTS

Single neuronal spikes in the paraventricular thalamus were suppressed by sevoflurane anesthesia and recovered during emergence. Optogenetic activation of paraventricular thalamus glutamatergic neurons shortened the emergence period from sevoflurane anesthesia, while chemogenetic inhibition had the opposite effect. Knockdown of the NALCN in the paraventricular thalamus delayed the emergence from sevoflurane anesthesia (recovery time: from 24 ± 14 to 64 ± 19 s, P < 0.001; concentration for recovery of the righting reflex: from 1.13% ± 0.10% to 0.97% ± 0.13%, P < 0.01). As expected, the overexpression of the NALCN in the paraventricular thalamus produced the opposite effects. At the circuit level, knockdown of the NALCN in the paraventricular thalamus decreased the neuronal activity of the nucleus accumbens, as indicated by the local field potential and decreased single neuronal spikes in the nucleus accumbens. Additionally, the effects of NALCN knockdown in the paraventricular thalamus on sevoflurane actions were reversed by optical stimulation of the nucleus accumbens.

CONCLUSIONS

Activity of the NALCN maintains the excitability of paraventricular thalamus glutamatergic neurons to resist the anesthetic effects of sevoflurane in mice.

EDITOR’S PERSPECTIVE

Rethinking dopamine-guided action sequence learning

As opposed to those requiring a single action for reward acquisition, tasks necessitating action sequences demand that animals learn action elements and their sequential order and sustain the behaviour until the sequence is completed. With repeated learning, animals not only exhibit precise execution of these sequences but also demonstrate enhanced smoothness and efficiency. Previous research has demonstrated that midbrain dopamine and its major projection target, the striatum, play crucial roles in these processes. Recent studies have shown that dopamine from the substantia nigra pars compacta (SNc) and the ventral tegmental area (VTA) serve distinct functions in action sequence learning. The distinct contributions of dopamine also depend on the striatal subregions, namely the ventral, dorsomedial and dorsolateral striatum. Here, we have reviewed recent findings on the role of striatal dopamine in action sequence learning, with a focus on recent rodent studies.

Prefrontal cortical dynorphin peptidergic transmission constrains threat-driven behavioral and network states

Prefrontal cortical (PFC) circuits provide top-down control of threat reactivity. This includes ventromedial PFC (vmPFC) circuitry, which plays a role in suppressing fear-related behavioral states. Dynorphin (Dyn) has been implicated in mediating negative affect and maladaptive behaviors induced by severe threats and is expressed in limbic circuits, including the vmPFC. However, there is a critical knowledge gap in our understanding of how vmPFC Dyn-expressing neurons and Dyn transmission detect threats and regulate expression of defensive behaviors. Here, we demonstrate that Dyn cells are broadly activated by threats and release Dyn locally in the vmPFC to limit passive defensive behaviors. We further demonstrate that vmPFC Dyn-mediated signaling promotes a switch of vmPFC networks to a fear-related state. In conclusion, we reveal a previously unknown role of vmPFC Dyn neurons and Dyn neuropeptidergic transmission in suppressing defensive behaviors in response to threats via state-driven changes in vmPFC networks.

Compartmental neuronal degeneration in the ventral striatum induced by status epilepticus in young rats' brain in comparison with adults

According to experimental and clinical studies, status epilepticus (SE) causes neurodegenerative morphological changes not only in the hippocampus and other limbic structures, it also affects the thalamus and the neocortex. In addition, several studies reported atrophy, metabolic changes, and neuronal degeneration in the dorsal striatum. The literature lacks studies investigating potential neuronal damage in the ventral component of the striatopallidal complex (ventral striatum [VS] and ventral pallidum) in SE experimentations. To better understand the development of neuronal damage in the striatopallidal complex associated with SE, the detected neuronal degeneration in the compartments of the VS, namely, the nucleus accumbens (NAc) and the olfactory tubercle (OT), was analyzed. The experiments were performed on Wistar rats at age of 25-day-old pups and 3-month-old adult animals. Lithium-pilocarpine model of SE was used. Lithium chloride (3 mmol/kg, ip) was injected 24 h before administering pilocarpine (40 mg/kg, ip). This presented study demonstrates the variability of post SE neuronal damage in 25-day-old pups in comparison with 3-month-old adult rats. The NAc exhibited small to moderate number of Fluoro-Jade B (FJB)-positive neurons detected 4 and 8 h post SE intervals. The number of degenerated neurons in the shell subdivision of the NAc significantly increased at survival interval of 12 h after the SE. FJB-positive neurons were evidently more prominent occupying the whole anteroposterior and mediolateral extent of the nucleus at longer survival intervals of 24 and 48 h after the SE. This was also the case in the bordering vicinity between the shell and the core compartments but with clusters of degenerating cells. The severity of damage of the shell subdivision of the NAc reached its peak at an interval of 24 h post SE. Isolated FJB-positive neurons were detected in the ventral peripheral part of the core compartment. Degenerated neurons persisted in the shell subdivision of the NAc 1 week after SE. However, the quantity of cell damage had significantly reduced in comparison with the aforementioned shorter intervals. The third layer of the OT exhibited more degenerated neurons than the second layer. The FJB-positive cells in the young animals were higher than in the adult animals. The morphology of those cells was identical in the two age groups except in the OT.

Low and high-order topological disruption of functional networks in multiple system atrophy with freezing of gait: A resting-state study

OBJECTIVE

Freezing of gait (FOG), a specific survival-threatening gait impairment, needs to be urgently explored in patients with multiple system atrophy (MSA), which is characterized by rapid progression and death within 10 years of symptom onset. The objective of this study was to explore the topological organisation of both low- and high-order functional networks in patients with MAS and FOG.

METHOD

Low-order functional connectivity (LOFC) and high-order functional connectivity FC (HOFC) networks were calculated and further analysed using the graph theory approach in 24 patients with MSA without FOG, 20 patients with FOG, and 25 healthy controls. The relationship between brain activity and the severity of freezing symptoms was investigated in patients with FOG.

RESULTS

Regarding global topological properties, patients with FOG exhibited alterations in the whole-brain network, dorsal attention network (DAN), frontoparietal network (FPN), and default network (DMN), compared with patients without FOG. At the node level, patients with FOG showed decreased nodal centralities in sensorimotor network (SMN), DAN, ventral attention network (VAN), FPN, limbic regions, hippocampal network and basal ganglia network (BG), and increased nodal centralities in the FPN, DMN, visual network (VIN) and, cerebellar network. The nodal centralities of the right inferior frontal sulcus, left lateral amygdala and left nucleus accumbens (NAC) were negatively correlated with the FOG severity.

CONCLUSION

This study identified a disrupted topology of functional interactions at both low and high levels with extensive alterations in topological properties in MSA patients with FOG, especially those associated with damage to the FPN. These findings offer new insights into the dysfunctional mechanisms of complex networks and suggest potential neuroimaging biomarkers for FOG in patients with MSA.

Chst9 marks a spatially and transcriptionally unique population of Oprm1-expressing neurons in the nucleus accumbens

Opioids produce addictive, analgesic, and euphoric effects via actions at mu opioid receptors (μORs). The μOR is encoded by the Oprm1 gene and is expressed in multiple brain regions that regulate reward and motivation, such as the nucleus accumbens (NAc). Oprm1 expression in NAc medium spiny neurons (MSNs) mediates opioid place preference, seeking, and consumption. However, recent single nucleus RNA sequencing (snRNA-seq) studies have revealed that multiple subpopulations of NAc neurons express Oprm1 mRNA, making it unclear which populations mediate diverse behaviors resulting from μOR activation. Using published snRNA-seq datasets from the rat NAc, we identified a novel population of MSNs that express the highest levels of Oprm1 of any NAc cell type. Here, we show that this population is selectively marked by expression of Chst9, a gene encoding a carbohydrate sulfotransferase. Notably, Chst9+ neurons exhibited more abundant expression of Oprm1 as compared to other cell types, and formed discrete cellular clusters along the medial and ventral borders of the NAc shell subregion. Moreover, CHST9 mRNA was also found to mark specific MSN populations in published human and primate snRNA-seq studies, indicating that this unique population may be conserved across species. Together, these results identify a spatially and transcriptionally distinct NAc neuron population characterized by the expression of Chst9. The abundant expression of Oprm1 in this population and the conservation of these cells across species suggests that they may play a key functional role in opioid response and identify this subpopulation as a target for further investigation.

Exploring the therapeutic potential of cannabidiol for sleep deprivation-induced hyperalgesia

Hyperalgesia resulting from sleep deprivation (SD) poses a significant a global public health challenge with limited treatment options. The nucleus accumbens (NAc) plays a crucial role in the modulation of pain and sleep, with its activity regulated by two distinct types of medium spiny neurons (MSNs) expressing dopamine 1 or dopamine 2 (D1-or D2) receptors (referred to as D1-MSNs and D2-MSNs, respectively). However, the specific involvement of the NAc in SD-induced hyperalgesia remains uncertain. Cannabidiol (CBD), a nonpsychoactive phytocannabinoid, has demonstrated analgesic effects in clinical and preclinical studies. Nevertheless, its potency in addressing this particular issue remains to be determined. Here, we report that SD induced a pronounced pronociceptive effect attributed to the heightened intrinsic excitability of D2-MSNs within the NAc in Male C57BL/6N mice. CBD (30 mg/kg, i.p.) exhibited an anti-hyperalgesic effect. CBD significantly improved the thresholds for thermal and mechanical pain and increased wakefulness by reducing delta power. Additionally, CBD inhibited the intrinsic excitability of D2-MSNs both in vitro and in vivo. Bilateral microinjection of the selective D2 receptor antagonist raclopride into the NAc partially reversed the antinociceptive effect of CBD. Thus, these findings strongly suggested that SD activates NAc D2-MSNs, contributing heightened to pain sensitivity. CBD exhibits antinociceptive effects by activating D2R, thereby inhibiting the excitability of D2-MSNs and promoting wakefulness under SD conditions.

Developmental and adult striatal patterning of nociceptin ligand marks striosomal population with direct dopamine projections

Circuit influences on the midbrain dopamine system are crucial to adaptive behavior and cognition. Recent developments in the study of neuropeptide systems have enabled high-resolution investigations of the intersection of neuromodulatory signals with basal ganglia circuitry, identifying the nociceptin/orphanin FQ (N/OFQ) endogenous opioid peptide system as a prospective regulator of striatal dopamine signaling. Using a prepronociceptin-Cre reporter mouse line, we characterized highly selective striosomal patterning of Pnoc mRNA expression in mouse dorsal striatum, reflecting early developmental expression of Pnoc . In the ventral striatum, Pnoc expression was was clustered across the nucleus accumbens core and medial shell, including in adult striatum. We found that Pnoc tdTomato reporter cells largely comprise a population of dopamine receptor D1 ( Drd1 ) expressing medium spiny projection neurons localized in dorsal striosomes, known to be unique among striatal projections neurons for their direct innervation of midbrain dopamine neurons. These findings provide new understanding of the intersection of the N/OFQ system among basal ganglia circuits with particular implications for developmental regulation or wiring of striatal-nigral circuits.

Parvalbumin neurons in the nucleus accumbens shell modulate seizure in temporal lobe epilepsy

A growing number of clinical and animal studies suggest that the nucleus accumbens (NAc), especially the shell, is involved in the pathogenesis of temporal lobe epilepsy (TLE). However, the role of parvalbumin (PV) GABAergic neurons in the NAc shell involved in TLE is still unclear. In this study, we induced a spontaneous TLE model by intrahippocampal administration of kainic acid (KA), which generally induce acute seizures in first 2 h (acute phase) and then lead to spontaneous recurrent seizures after two months (chronic phase). We found that chemogenetic activation of NAc shell PV neurons could alleviate TLE seizures by reducing the number and period of focal seizures (FSs) and secondary generalized seizures (sGSs), while selective inhibition of PV exacerbated seizure activity. Ruby-virus mapping results identified that the hippocampus (ventral and dorsal) is one of the projection targets of NAc shell PV neurons. Chemogenetic activation of the NAc-Hip PV projection fibers can mitigate seizures while inhibition has no effect on seizure ictogenesis. In summary, our findings reveal that PV neurons in the NAc shell could modulate the seizures in TLE via a long-range NAc-Hip circuit. All of these results enriched the investigation between NAc and epilepsy, offering new targets for future epileptogenesis research and precision therapy.

Intrauterine exposure to chorioamnionitis and neuroanatomical alterations at term-equivalent age in preterm infants

PURPOSE

Infants born to mothers with chorioamnionitis (CAM) are at increased risk of developing adverse neurodevelopmental disorders in later life. However, clinical magnetic resonance imaging (MRI) studies examining brain injuries and neuroanatomical alterations attributed to CAM have yielded inconsistent results. We aimed to determine whether exposure to histological CAM in utero leads to brain injuries and alterations in the neuroanatomy of preterm infants using 3.0- Tesla MRI at term-equivalent age.

METHODS

A total of 58 preterm infants born before 34 weeks of gestation at Nagoya University Hospital between 2010 and 2018 were eligible for this study (CAM group, n = 21; non-CAM group, n = 37). Brain injuries and abnormalities were assessed using the Kidokoro Global Brain Abnormality Scoring system. Gray matter, white matter, and subcortical gray matter (thalamus, caudate nucleus, putamen, pallidum, hippocampus, amygdala, and nucleus accumbens) volumes were evaluated using segmentation tools (SPM12 and Infant FreeSurfer).

RESULTS

The Kidokoro scores for each category and severity in the CAM group were comparable to those observed in the non-CAM group. White matter volume was significantly smaller in the CAM group after adjusting for covariates (postmenstrual age at MRI, infant sex, and gestational age) (p = 0.007), whereas gray matter volume was not significantly different. Multiple linear regression analyses revealed significantly smaller volumes in the bilateral pallidums (right, p = 0.045; left, p = 0.038) and nucleus accumbens (right, p = 0.030; left, p = 0.004) after adjusting for covariates.

CONCLUSIONS

Preterm infants born to mothers with histological CAM showed smaller volumes in white matter, pallidum, and nucleus accumbens at term-equivalent age.

Manifestations, social impact, and decay of conceptual beliefs: A cultural perspective

INTRODUCTION

Believing comprises multifaceted processes that integrate information from the outside world through meaning-making processes with personal relevance.

METHODS

Qualitative Review of the current literature in social cognitive neuroscience.

RESULTS

Although believing develops rapidly outside an individual's conscious awareness, it results in the formation of beliefs that are stored in memory and play an important role in determining an individual's behavior. Primal beliefs reflect an individual's experience of objects and events, whereas conceptual beliefs are based on narratives that are held in social groups. Conceptual beliefs can be about autobiographical, political, religious, and other aspects of life and may be encouraged by participation in group rituals. We hypothesize that assertions of future gains and rewards that transcend but are inherent in these codices provide incentives to follow the norms and rules of social groups.

CONCLUSION

The power of conceptual beliefs to provide cultural orientation is likely to fade when circumstances and evidence make it clear that what was asserted no longer applies.

Foxp2 Is Required for Nucleus Accumbens-mediated Multifaceted Limbic Function

The forkhead box protein P2 (Foxp2), initially identified for its role in speech and language development, plays an important role in neural development. Previous studies investigated the function of the Foxp2 gene by deleting or mutating Foxp2 from developmental stages. Little is known about its physiological function in adult brains. Although Foxp2 has been well studied in the dorsal striatum, its function in the nucleus accumbens (NAc) of the ventral striatum remains elusive. Here, we examine the physiological function of Foxp2 in NAc of mouse brains. We conditionally knocked out Foxp2 by microinjections of AAV-EGFP-Cre viruses into the medial shell of NAc of Foxp2 floxed (cKO) mice. Immunostaining showed increased c-Fos positive cells in cKO NAc at basal levels, suggesting an abnormality in Foxp2-deficient NAc cells. Unbiased behavioral profiling of Foxp2 cKO mice showed abnormalities in limbic-associated function. Foxp2 cKO mice exhibited abnormal social novelty without preference for interaction with strangers and familiar mice. In appetitive reward learning, Foxp2 cKO mice failed to learn the time expectancy of food delivery. In fear learning, Foxp2 cKO mice exhibited abnormal increases in freezing levels in response to tone paired with foot shock during fear conditioning. The extinction of the fear response was also altered in Foxp2 cKO mice. In contrast, conditional knockout of Foxp2 in NAc did not affect locomotion, motor coordination, thermal pain sensation, anxiety- and depression-like behaviors. Collectively, our study suggests that Foxp2 has a multifaceted physiological role in NAc in the regulation of limbic function in the adult brain.

The resting-state brain activity signatures for addictive disorders

BACKGROUND

Addiction is a chronic and relapsing brain disorder. Despite numerous neuroimaging and neurophysiological studies on individuals with substance use disorder (SUD) or behavioral addiction (BEA), currently a clear neural activity signature for the addicted brain is lacking.

METHODS

We first performed systemic coordinate-based meta-analysis and partial least-squares regression to identify shared or distinct brain regions across multiple addictive disorders, with abnormal resting-state activity in SUD and BEA based on 46 studies (55 contrasts), including regional homogeneity (ReHo) and low-frequency fluctuation amplitude (ALFF) or fractional ALFF. We then combined Neurosynth, postmortem gene expression, and receptor/transporter distribution data to uncover the potential molecular mechanisms underlying these neural activity signatures.

FINDINGS

The overall comparison between addiction cohorts and healthy subjects indicated significantly increased ReHo and ALFF in the right striatum (putamen) and bilateral supplementary motor area, as well as decreased ReHo and ALFF in the bilateral anterior cingulate cortex and ventral medial prefrontal cortex, in the addiction group. On the other hand, neural activity in cingulate cortex, ventral medial prefrontal cortex, and orbitofrontal cortex differed between SUD and BEA subjects. Using molecular analyses, the altered resting activity recapitulated the spatial distribution of dopaminergic, GABAergic, and acetylcholine system in SUD, while this also includes the serotonergic system in BEA.

CONCLUSIONS

These results indicate both common and distinctive neural substrates underlying SUD and BEA, which validates and supports targeted neuromodulation against addiction.

FUNDING

This work was supported by the National Natural Science Foundation of China and Intramural Research Program of the National Institute on Drug Abuse, National Institutes of Health.

A nociceptive amygdala-striatal pathway for chronic pain aversion

The basolateral amygdala (BLA) is essential for assigning positive or negative valence to sensory stimuli. Noxious stimuli that cause pain are encoded by an ensemble of nociceptive BLA projection neurons (BLAnoci ensemble). However, the role of the BLAnoci ensemble in mediating behavior changes and the molecular signatures and downstream targets distinguishing this ensemble remain poorly understood. Here, we show that the same BLAnoci ensemble neurons are required for both acute and chronic neuropathic pain behavior. Using single nucleus RNA-sequencing, we characterized the effect of acute and chronic pain on the BLA and identified enrichment for genes with known functions in axonal and synaptic organization and pain perception. We thus examined the brain-wide targets of the BLAnoci ensemble and uncovered a previously undescribed nociceptive hotspot of the nucleus accumbens shell (NAcSh) that mirrors the stability and specificity of the BLAnoci ensemble and is recruited in chronic pain. Notably, BLAnoci ensemble axons transmit acute and neuropathic nociceptive information to the NAcSh, highlighting this nociceptive amygdala-striatal circuit as a unique pathway for affective-motivational responses across pain states.

State and rate-of-change encoding in parallel mesoaccumbal dopamine pathways

The nervous system uses fast- and slow-adapting sensory detectors in parallel to enable neuronal representations of external states and their temporal dynamics. It is unknown whether this dichotomy also applies to internal representations that have no direct correlation in the physical world. Here we find that two distinct dopamine (DA) neuron subtypes encode either a state or its rate-of-change. In mice performing a reward-seeking task, we found that the animal's behavioral state and rate-of-change were encoded by the sustained activity of DA neurons in medial ventral tegmental area (VTA) DA neurons and transient activity in lateral VTA DA neurons, respectively. The neural activity patterns of VTA DA cell bodies matched DA release patterns within anatomically defined mesoaccumbal pathways. Based on these results, we propose a model in which the DA system uses two parallel lines for proportional-differential encoding of a state variable and its temporal dynamics.

Dorsal hippocampus to nucleus accumbens projections drive reinforcement via activation of accumbal dynorphin neurons

The hippocampus is pivotal in integrating emotional processing, learning, memory, and reward-related behaviors. The dorsal hippocampus (dHPC) is particularly crucial for episodic, spatial, and associative memory, and has been shown to be necessary for context- and cue-associated reward behaviors. The nucleus accumbens (NAc), a central structure in the mesolimbic reward pathway, integrates the salience of aversive and rewarding stimuli. Despite extensive research on dHPC→NAc direct projections, their sufficiency in driving reinforcement and reward-related behavior remains to be determined. Our study establishes that activating excitatory neurons in the dHPC is sufficient to induce reinforcing behaviors through its direct projections to the dorso-medial subregion of the NAc shell (dmNAcSh). Notably, dynorphin-containing neurons specifically contribute to dHPC-driven reinforcing behavior, even though both dmNAcSh dynorphin- and enkephalin-containing neurons are activated with dHPC stimulation. Our findings unveil a pathway governing reinforcement, advancing our understanding of the hippocampal circuity's role in reward-seeking behaviors.

Effects of Maternal Separation on Effort-based Responding for Sucrose Are Associated with c-Fos Expression in the Nucleus Accumbens Core

In both people and animals, exposure to adverse experiences early in life can alter neurodevelopment and lead to long-term behavioral effects, including effects on reward processing. In the current study, we use a well-validated rodent model of maternal neglect, maternal separation (MS), to investigate the impact of early life adversity on reward learning and motivation and identify associated modifications in cellular activation in reward-relevant areas. Litters of Long-Evans rats were separated from the dam for either 15 min (brief) or 180 min (prolonged)/day from postnatal day (PND)2 to PND14. As adults, offspring were trained to lever press for a sucrose pellet using fixed ratio (FR) schedules and motivation was tested using a progressive ratio (PR) schedule over 10 daily sessions to assess sustained effects on effort-based responding. Immunohistochemical staining for c-Fos was conducted in a subset of animals that underwent an additional PR session. While there were no effects on reward learning, both MS180 males and females demonstrated increased effort-based responding on the first day of PR testing, while only MS180 males demonstrated a sustained increase in effort across all 10 days. MS180-induced changes in c-Fos expression in the dorsal and ventral striatum were observed, with subregion-specific effects along the rostrocaudal axis. Moreover, regression analyses suggest that motivated responding for a sucrose food reward in MS180-exposed, but not MS15-exposed animals, was associated with increased c-Fos expression in the rostral nucleus accumbens core. These findings implicate specific striatal regions in sex-specific modulation of sustained effort-based reward behavior following early life adversity.