Limbic and cortical information processing in the nucleus accumbens

Rasd2 regulates depression-like behaviors via DRD2 neurons in the prelimbic cortex afferent to nucleus accumbens core circuit

Depressive symptoms, such as anhedonia, decreased social interaction, and lack of motivation, implicate brain reward systems in the pathophysiology of depression. Exposure to chronic stress impairs the function of brain reward circuits and is well-known to be involved in the etiology of depression. A transcriptomic analysis found that stress alters the expression of Rasd2 in mice prefrontal cortex (PFC). Similarly, in our previous study, acute fasting decreased Rasd2 expression in mice PFC, and RASD2 modulated dopamine D2 receptor (DRD2)-mediated antidepressant-like effects in ovariectomized mice. This research suggests the role of RASD2 in stress-induced depression and its underlying neural mechanisms that require further investigation. Here, we show that 5-day unpredictable mild stress (5-d UMS) exposure reduces RASD2 expression in both the nucleus accumbens (NAc) and medial prefrontal cortex (mPFC) of mice, while overexpression (but not knock-down) of Rasd2 in the NAc core (NAcc) alleviates 5-d UMS-induced depression-like behaviors and activates the DRD2-cAMP-PKA-DARPP-32 signaling pathway. Further studies investigated neuronal projections between the mPFC (Cg1, PrL, and IL) and NAcc, labeled by the retrograde tracer Fluorogold. Depression-like behaviors induced by 5-d UMS were only related to inhibition of the PrL-NAcc circuit. DREADD (Designer receptors exclusively activated by designer drug) analysis found that the activation of PrL-NAcc glutaminergic projection alleviated depression-like behaviors and increased DRD2- and RASD2-positive neurons in the NAcc. Using Drd2-cre transgenic mice, we constructed mice with Rasd2 overexpression in DRD2PrL-NAcc neurons, finding that Rasd2 overexpression ameliorated 5-d UMS-induced depression-like behaviors. These findings demonstrate a critical role for RASD2 modulation of DRD2PrL-NAcc neurons in 5-d UMS-induced depression-like behaviors. In addition, the study identifies a new potential strategy for precision medical treatment of depression.

Linking haploinsufficiency of the autism- and schizophrenia-associated gene Cyfip1 with striatal-limbic-cortical network dysfunction and cognitive inflexibility

Impaired behavioural flexibility is a core feature of neuropsychiatric disorders and is associated with underlying dysfunction of fronto-striatal circuitry. Reduced dosage of Cyfip1 is a risk factor for neuropsychiatric disorder, as evidenced by its involvement in the 15q11.2 (BP1-BP2) copy number variant: deletion carriers are haploinsufficient for CYFIP1 and exhibit a two- to four-fold increased risk of schizophrenia, autism and/or intellectual disability. Here, we model the contributions of Cyfip1 to behavioural flexibility and related fronto-striatal neural network function using a recently developed haploinsufficient, heterozygous knockout rat line. Using multi-site local field potential (LFP) recordings during resting state, we show that Cyfip1 heterozygous rats (Cyfip1+/-) harbor disrupted network activity spanning medial prefrontal cortex, hippocampal CA1 and ventral striatum. In particular, Cyfip1+/- rats showed reduced influence of nucleus accumbens and increased dominance of prefrontal and hippocampal inputs, compared to wildtype controls. Adult Cyfip1+/- rats were able to learn a single cue-response association, yet unable to learn a conditional discrimination task that engages fronto-striatal interactions during flexible pairing of different levers and cue combinations. Together, these results implicate Cyfip1 in development or maintenance of cortico-limbic-striatal network integrity, further supporting the hypothesis that alterations in this circuitry contribute to behavioural inflexibility observed in neuropsychiatric diseases including schizophrenia and autism.

Mechanisms of neuromodulatory volume transmission

A wealth of neuromodulatory transmitters regulate synaptic circuits in the brain. Their mode of signaling, often called volume transmission, differs from classical synaptic transmission in important ways. In synaptic transmission, vesicles rapidly fuse in response to action potentials and release their transmitter content. The transmitters are then sensed by nearby receptors on select target cells with minimal delay. Signal transmission is restricted to synaptic contacts and typically occurs within ~1 ms. Volume transmission doesn't rely on synaptic contact sites and is the main mode of monoamines and neuropeptides, important neuromodulators in the brain. It is less precise than synaptic transmission, and the underlying molecular mechanisms and spatiotemporal scales are often not well understood. Here, we review literature on mechanisms of volume transmission and raise scientific questions that should be addressed in the years ahead. We define five domains by which volume transmission systems can differ from synaptic transmission and from one another. These domains are (1) innervation patterns and firing properties, (2) transmitter synthesis and loading into different types of vesicles, (3) architecture and distribution of release sites, (4) transmitter diffusion, degradation, and reuptake, and (5) receptor types and their positioning on target cells. We discuss these five domains for dopamine, a well-studied monoamine, and then compare the literature on dopamine with that on norepinephrine and serotonin. We include assessments of neuropeptide signaling and of central acetylcholine transmission. Through this review, we provide a molecular and cellular framework for volume transmission. This mechanistic knowledge is essential to define how neuromodulatory systems control behavior in health and disease and to understand how they are modulated by medical treatments and by drugs of abuse.

Morphogenetic theory of mental and cognitive disorders: the role of neurotrophic and guidance molecules

Mental illness and cognitive disorders represent a serious problem for the modern society. Many studies indicate that mental disorders are polygenic and that impaired brain development may lay the ground for their manifestation. Neural tissue development is a complex and multistage process that involves a large number of distant and contact molecules. In this review, we have considered the key steps of brain morphogenesis, and the major molecule families involved in these process. The review provides many indications of the important contribution of the brain development process and correct functioning of certain genes to human mental health. To our knowledge, this comprehensive review is one of the first in this field. We suppose that this review may be useful to novice researchers and clinicians wishing to navigate the field.

Mutation of novel ethanol-responsive lncRNA Gm41261 impacts ethanol-related behavioral responses in mice

Chronic alcohol exposure results in widespread dysregulation of gene expression that contributes to the pathogenesis of Alcohol Use Disorder (AUD). Long noncoding RNAs are key regulators of the transcriptome that we hypothesize coordinate alcohol-induced transcriptome dysregulation and contribute to AUD. Based on RNA-Sequencing data of human prefrontal cortex, basolateral amygdala and nucleus accumbens of AUD versus non-AUD brain, the human LINC01265 and its predicted murine homolog Gm41261 (i.e., TX2) were selected for functional interrogation. We tested the hypothesis that TX2 contributes to ethanol drinking and behavioral responses to ethanol. CRISPR/Cas9 mutagenesis was used to create a TX2 mutant mouse line in which 306 base-pairs were deleted from the locus. RNA analysis revealed that an abnormal TX2 transcript was produced at an unchanged level in mutant animals. Behaviorally, mutant mice had reduced ethanol, gaboxadol and zolpidem-induced loss of the righting response and reduced tolerance to ethanol in both sexes. In addition, a male-specific reduction in two-bottle choice every-other-day ethanol drinking was observed. Male TX2 mutants exhibited evidence of enhanced GABA release and altered GABAA receptor subunit composition in neurons of the nucleus accumbens shell. In C57BL6/J mice, TX2 within the cortex was cytoplasmic and largely present in Rbfox3+ neurons and IBA1+ microglia, but not in Olig2+ oligodendrocytes or in the majority of GFAP+ astrocytes. These data support the hypothesis that TX2 mutagenesis and dysregulation impacts ethanol drinking behavior and ethanol-induced behavioral responses in mice, likely through alterations in the GABAergic system.

DRD3 Predicts Cognitive Impairment and Anxiety in Parkinson's Disease: Susceptibility and Protective Effects

Background

A possible genetic contribution of dopamine D3 receptor (DRD3) to cognitive impairment in Parkinson's disease (PD) has yet to be investigated.

Objective

To explore the effects of rs6280 (Ser9Gly) genotype on PD patients' cognitive performance and to clarify possible interactions with psychopathology.

Methods

Two hundred and fifty-three consecutive PD patients underwent neurological and neuropsychological evaluations, which included: Unified Parkinson's Disease Rating Scale (UPDRS), Hoehn & Yahr scale (H&Y), Dementia Rating Scale-2 (DRS-2), and Hospital Anxiety and Depression Scale (HADS). rs6280 polymorphism was genotyped for all PD patients and for 270 ethnically matched healthy volunteers (HC). Non-parametric group comparisons and logistic regressions were used for data analyses.

Results

rs6280 genotype did not differ between PD and HC groups. PD patients with rs6280 CC genotype had more impaired cognitive performance (i.e., <1st percentile of demographically adjusted norms) on DRS-2 subscales Initiation/Perseveration and Construction than those with TT genotype. These associations remained statistically significant when other covariates (e.g., demographic features, disease duration, severity of motor symptoms in OFF and ON states, anti-parkinsonian medication, and psychopathology symptoms) were taken into consideration. PD patients with rs6280 TC had less anxiety (i.e., HADS Anxiety≥11) than those with TT (p = 0.012). This association was also independent of other covariates.

Conclusions

Study findings suggest that rs6280 CC genotype predisposes to executive dysfunction and visuoconstructional deficits, whereas the heterozygous genotype protects from anxiety in PD. These effects do not appear to be dependent of one another. rs6280 is not a genotypic susceptibility factor for PD.

Application of the wholebrain calculation interactive framework to map whole-brain neural connectivity networks

The aim of this work was to develop a simple and feasible method of mapping the neural network topology of the mouse brain. Wild-type C57BL/6 J mice (n = 10) aged 8-10 weeks were injected with the cholera toxin subunit B (CTB) tracer in the anterior (NAcCA) and posterior (NAcCP) parts of the nucleus accumbens (NAc) core and in the medial (NAcSM) and lateral (NAcSL) parts of the NAc shell. The labeled neurons were reconstructed using the WholeBrain Calculation Interactive Framework. The NAcCA receives neuronal projections from the olfactory areas (OLF) and isocortex; the thalamus and isocortex project more fibers to the NAcSL, and the hypothalamus send more fiber projections to the NAcSM. Cell resolution can be automatically annotated, analyzed, and visualized using the WholeBrain Calculation Interactive Framework, making large-scale mapping of mouse brains at cellular and subcellular resolutions easier and more accurate.

Enhanced decision-making in nicotine dependent individuals who abstain: A computational analysis using Hierarchical Drift Diffusion Modeling

BACKGROUND

Variability in decision-making capacity and reward responsiveness may underlie differences in the ability to abstain from smoking. Computational modeling of choice behavior, as with the Hierarchical Drift Diffusion Model (HDDM), can help dissociate reward responsiveness from underlying components of decision-making. Here we used the HDDM to identify which decision-making or reward-related parameters, extracted from data acquired in a reward processing task, contributed to the ability of people who smoke that are not seeking treatment to abstain from cigarettes during a laboratory task.

METHODS

80 adults who smoke cigarettes completed the Probabilistic Reward Task (PRT) - a signal detection task with a differential reinforcement schedule - following smoking as usual, and the Relapse Analogue Task (RAT) - a task in which participants could earn money for delaying smoking up to 50min - after a period of overnight abstinence. Two cohorts were defined by the RAT; those who waited either 0-min (n=36) or the full 50-min (n=44) before smoking.

RESULTS

PRT signal detection metrics indicated all subjects learned the task contingencies, with no differences in response bias or discriminability between the two groups. However, HDDM analyses indicated faster drift rates in 50-min vs. 0-min waiters.

CONCLUSIONS

Relative to those who did not abstain, computational modeling indicated that people who abstained from smoking for 50min showed faster evidence accumulation during reward-based decision-making. These results highlight the importance of decision-making mechanisms to smoking abstinence, and suggest that focusing on the evidence accumulation process may yield new targets for treatment.

Reactivation of Early-Life Stress-Sensitive Neuronal Ensembles Contributes to Lifelong Stress Hypersensitivity

Early-life stress (ELS) is one of the strongest lifetime risk factors for depression, anxiety, suicide, and other psychiatric disorders, particularly after facing additional stressful events later in life. Human and animal studies demonstrate that ELS sensitizes individuals to subsequent stress. However, the neurobiological basis of such stress sensitization remains largely unexplored. We hypothesized that ELS-induced stress sensitization would be detectable at the level of neuronal ensembles, such that cells activated by ELS would be more reactive to adult stress. To test this, we leveraged transgenic mice to genetically tag, track, and manipulate experience-activated neurons. We found that in both male and female mice, ELS-activated neurons within the nucleus accumbens (NAc), and to a lesser extent the medial prefrontal cortex, were preferentially reactivated by adult stress. To test whether reactivation of ELS-activated ensembles in the NAc contributes to stress hypersensitivity, we expressed hM4Dis receptor in control or ELS-activated neurons of pups and chemogenetically inhibited their activity during experience of adult stress. Inhibition of ELS-activated NAc neurons, but not control-tagged neurons, ameliorated social avoidance behavior following chronic social defeat stress in males. These data provide evidence that ELS-induced stress hypersensitivity is encoded at the level of corticolimbic neuronal ensembles.SIGNIFICANCE STATEMENT Early-life stress enhances sensitivity to stress later in life, yet the mechanisms of such stress sensitization are largely unknown. Here, we show that neuronal ensembles in corticolimbic brain regions remain hypersensitive to stress across the life span, and quieting these ensembles during experience of adult stress rescues stress hypersensitivity.

Dopaminoceptive D1 and D2 neurons in ventral hippocampus arbitrate approach and avoidance in anxiety

The hippocampus 1-7, as well as dopamine circuits 8-11, coordinate decision-making in anxiety-eliciting situations. Yet, little is known about how dopamine modulates hippocampal representations of emotionally-salient stimuli to inform appropriate resolution of approach versus avoidance conflicts. We here study dopaminoceptive neurons in mouse ventral hippocampus (vHipp), molecularly distinguished by their expression of dopamine D1 or D2 receptors. We show that these neurons are transcriptionally distinct and topographically organized across vHipp subfields and cell types. In the ventral subiculum where they are enriched, both D1 and D2 neurons are recruited during anxiogenic exploration, yet with distinct profiles related to investigation and behavioral selection. In turn, they mediate opposite approach/avoidance responses, and are differentially modulated by dopaminergic transmission in that region. Together, these results suggest that vHipp dopamine dynamics gate exploratory behaviors under contextual uncertainty, implicating dopaminoception in the complex computation engaged in vHipp to govern emotional states.

Attention allocation to negatively-valenced stimuli in PTSD is associated with reward-related neural pathways

BACKGROUND

In a recent eye-tracking study we found a differential dwell time pattern for negatively-valenced and neutral faces among patients with posttraumatic stress disorder (PTSD), trauma-exposed healthy control (TEHCs), and healthy control (HC) participants. Here, we explored whether these group differences relate to resting-state functional connectivity (rsFC) patterns of brain areas previously linked to both attention processes and PTSD. These encompass the amygdala, dorsal anterior cingulate cortex (dACC), dorsolateral prefrontal cortex (dlPFC), ventrolateral prefrontal cortex (vlPFC), and nucleus accumbens (NAcc).

METHODS

Ten minutes magnetic resonance imaging rsFC scans were recorded in 17 PTSD patients, 21 TEHCs, and 16 HCs. Participants then completed a free-viewing eye-tracking task assessing attention allocation outside the scanner. Dwell time on negatively-valenced stimuli (DT%) were assessed relative to functional connectivity in the aforementioned seed regions of interest (amygdala, dACC, dlPFC, vlPFC, and NAcc) to whole-brain voxel-wise rsFC.

RESULTS

As previously reported, group differences occurred in attention allocation to negative-valence stimuli, with longer dwell time on negatively valence stimuli in the PTSD and TEHC groups than the HC group. Higher DT% correlated with weaker NAcc-orbitofrontal cortex (OFC) connectivity in patients with PTSD. Conversely, a positive association emerged in the HC group between DT% and NAcc-OFC connectivity.

CONCLUSIONS

While exploratory in nature, present findings may suggest that reward-related brain areas are involved in disengaging attention from negative-valenced stimuli, and possibly in regulating ensuing negative emotions.

Anatomical and Functional Connectivity of Critical Deep Brain Structures and Their Potential Clinical Application in Brain Stimulation

Subcortical structures, such as the hippocampus, amygdala, and nucleus accumbens (NAcc), play crucial roles in human cognitive, memory, and emotional processing, chronic pain pathophysiology, and are implicated in various psychiatric and neurological diseases. Interventions modulating the activities of these deep brain structures hold promise for improving clinical outcomes. Recently, non-invasive brain stimulation (NIBS) has been applied to modulate brain activity and has demonstrated its potential for treating psychiatric and neurological disorders. However, modulating the above deep brain structures using NIBS may be challenging due to the nature of these stimulations. This study attempts to identify brain surface regions as source targets for NIBS to reach these deep brain structures by integrating functional magnetic resonance imaging (fMRI) and diffusion tensor imaging (DTI). We used resting-state functional connectivity (rsFC) and probabilistic tractography (PTG) analysis to identify brain surface stimulation targets that are functionally and structurally connected to the hippocampus, amygdala, and NAcc in 119 healthy participants. Our results showed that the medial prefrontal cortex (mPFC) is functionally and anatomically connected to all three subcortical regions, while the precuneus is connected to the hippocampus and amygdala. The mPFC and precuneus, two key hubs of the default mode network (DMN), as well as other cortical areas distributed at the prefrontal cortex and the parietal, temporal, and occipital lobes, were identified as potential locations for NIBS to modulate the function of these deep structures. The findings may provide new insights into the NIBS target selections for treating psychiatric and neurological disorders and chronic pain.

Ketamine rescues anhedonia by cell-type and input specific adaptations in the Nucleus Accumbens

Ketamine's role in providing a rapid and sustained antidepressant response, particularly for patients unresponsive to conventional treatments, is increasingly recognized. A core symptom of depression, anhedonia, or the loss of enjoyment or interest in previously pleasurable activities, is known to be significantly alleviated by ketamine. While several hypotheses have been proposed regarding the mechanisms by which ketamine alleviates anhedonia, the specific circuits and synaptic changes responsible for its sustained therapeutic effects are not yet understood. Here, we show that the nucleus accumbens (NAc), a major hub of the reward circuitry, is essential for ketamine's effect in rescuing anhedonia in mice subjected to chronic stress, a critical risk factor in the genesis of depression in humans. Specifically, a single exposure to ketamine rescues stress-induced decreased strength of excitatory synapses on NAc D1 dopamine receptor-expressing medium spiny neurons (D1-MSNs). By using a novel cell-specific pharmacology method, we demonstrate that this cell-type specific neuroadaptation is necessary for the sustained therapeutic effects of ketamine. To test for causal sufficiency, we artificially mimicked ketamine-induced increase in excitatory strength on D1-MSNs and found that this recapitulates the behavioral amelioration induced by ketamine. Finally, to determine the presynaptic origin of the relevant glutamatergic inputs for ketamine-elicited synaptic and behavioral effects, we used a combination of opto- and chemogenetics. We found that ketamine rescues stress-induced reduction in excitatory strength at medial prefrontal cortex and ventral hippocampus inputs to NAc D1-MSNs. Chemogenetically preventing ketamine-evoked plasticity at those unique inputs to the NAc reveals a ketamine-operated input-specific control of hedonic behavior. These results establish that ketamine rescues stress-induced anhedonia via cell-type-specific adaptations as well as information integration in the NAc via discrete excitatory synapses.

Brain developmental trajectories associated with childhood stuttering persistence and recovery

Stuttering is a neurodevelopmental disorder affecting 5-8 % of preschool-age children, continuing into adulthood in 1 % of the population. The neural mechanisms underlying persistence and recovery from stuttering remain unclear and little information exists on neurodevelopmental anomalies in children who stutter (CWS) during preschool age, when stuttering symptoms typically first emerge. Here we present findings from the largest longitudinal study of childhood stuttering to date, comparing children with persistent stuttering (pCWS) and those who later recovered from stuttering (rCWS) with age-matched fluent peers, to examine the developmental trajectories of both gray matter volume (GMV) and white matter volume (WMV) using voxel-based morphometry. A total of 470 MRI scans were analyzed from 95 CWS (72 pCWS and 23 rCWS) and 95 fluent peers between 3 and 12 years of age. We examined overall group and group by age interactions in GMV and WMV in preschool age (3-5 years old) and school age (6-12 years old) CWS and controls, controlling for sex, IQ, intracranial volume, and socioeconomic status. The results provide broad support for a possible basal ganglia-thalamocortical (BGTC) network deficit starting in the earliest phases of the disorder and point to normalization or compensation of earlier occurring structural changes associated with stuttering recovery.

Ambient fine particulate exposure and subcortical gray matter microarchitecture in 9- and 10-year-old children across the United States

Neuroimaging studies showing the adverse effects of air pollution on neurodevelopment have largely focused on smaller samples from limited geographical locations and have implemented univariant approaches to assess exposure and brain macrostructure. Herein, we implement restriction spectrum imaging and a multivariate approach to examine how one year of annual exposure to daily fine particulate matter (PM_2.5), daily nitrogen dioxide (NO₂), and 8-h maximum ozone (O₃) at ages 9-10 years relates to subcortical gray matter microarchitecture in a geographically diverse subsample of children from the Adolescent Brain Cognitive Development (ABCD) Study^℠. Adjusting for confounders, we identified a latent variable representing 66% of the variance between one year of air pollution and subcortical gray matter microarchitecture. PM_2.5 was related to greater isotropic intracellular diffusion in the thalamus, brainstem, and accumbens, which related to cognition and internalizing symptoms. These findings may be indicative of previously identified air pollution-related risk for neuroinflammation and early neurodegenerative pathologies.

Synapse-Specific Modulation of Synaptic Responses by Brain States in Hippocampal Pathways

Synaptic changes play a major role in memory processes. Modulation of synaptic responses by brain states remains, however, poorly understood in hippocampal networks, even in basal conditions. We recorded evoked synaptic responses at five hippocampal pathways in freely moving male rats. We showed that, at the perforant path to dentate gyrus (PP-DG) synapse, responses increase during wakefulness compared with sleep. At the Schaffer collaterals to CA1 (SC-CA1) synapse, responses increase during non-REM sleep (NREM) compared with the other states. During REM sleep (REM), responses decreased at the PP-DG and SC-CA1 synapses compared with NREM, while they increased at the fornix to nucleus accumbens synapse (Fx-NAc) during REM compared with the other states. In contrast, responses at the fornix to medial PFC synapse (Fx-PFC) and at the fornix to amygdala synapse (Fx-Amy) were weakly modulated by vigilance states. Extended sleep periods led to synaptic changes at PP-DG and Fx-Amy synapses but not at the other synapses. Synaptic responses were also linked to local oscillations and were highly correlated between Fx-PFC and Fx-NAc but not between Fx-Amy and these synapses. These results reveal synapse-specific modulations that may contribute to memory consolidation during the sleep-wake cycle.SIGNIFICANCE STATEMENT Surprisingly, the cortical network dynamics remains poorly known at the synaptic level. We tested the hypothesis that brain states would modulate synaptic changes in the same way at different cortical connections. To tackle this issue, we implemented an approach to explore the synaptic behavior of five connections upstream and downstream the rat hippocampus. Our study reveals that synaptic responses are modulated in a highly synapse-specific manner by wakefulness and sleep states as well as by local oscillations at these connections. Moreover, we found rapid synaptic changes during wake and sleep transitions as well as synaptic down and upregulations after extended periods of sleep. These synaptic changes are likely related to the mechanisms of sleep-dependent memory consolidation.

Nucleus accumbens: a systematic review of neural circuitry and clinical studies in healthy and pathological states

OBJECTIVE

The nucleus accumbens (NAcc) of the ventral striatum is critically involved in goal- and reward-based behavior. Structural and functional abnormalities of the NAcc or its associated neural systems are involved in neurological and psychiatric disorders. Studies of neural circuitry have shed light on the subtleties of the structural and functional derangements of the NAcc across various diseases. In this systematic review, the authors sought to identify human studies involving the NAcc and provide a synthesis of the literature on the known circuity of the NAcc in healthy and diseased states, as well as the clinical outcomes following neuromodulation.

METHODS

A systematic review was conducted using the PubMed, Embase, and Scopus databases. Neuroimaging studies that reported on neural circuitry related to the human NAcc with sample sizes greater than 5 patients were included. Demographic data, aim, design and duration, participants, and clinical and neurocircuitry details and outcomes of the studies were extracted.

RESULTS

Of 3591 resultant articles, 123 were included. The NAcc and its corticolimbic connections to other brain regions, such as the prefrontal cortex, are largely involved in reward and pain processes, with distinct functional circuitry between the shell and core in healthy patients. There is heterogeneity between clinical studies with regard to the NAcc indirect targeting coordinates, methods for postoperative confirmation, and blinded trial design. Neuromodulation studies provided promising clinical results in the context of addiction and substance misuse, obsessive-compulsive disorder, and mood disorders. The most common complications were impaired memory or concentration, and a notable serious complication was hypomania.

CONCLUSIONS

The functional diversity of the NAcc highlights the importance of studying the NAcc in healthy and pathological states. The results of this review suggest that NAcc neuromodulation has been attempted in the management of diverse psychiatric indications. There is promising, emerging evidence that the NAcc may be an effective target for specific reward- or pain-based pathologies with a reasonable risk profile.

A quadruple dissociation of reward-related behaviour in mice across excitatory inputs to the nucleus accumbens shell

The nucleus accumbens shell (NAcSh) is critically important for reward valuations, yet it remains unclear how valuation information is integrated in this region to drive behaviour during reinforcement learning. Using an optogenetic spatial self-stimulation task in mice, here we show that contingent activation of different excitatory inputs to the NAcSh change expression of different reward-related behaviours. Our data indicate that medial prefrontal inputs support place preference via repeated actions, ventral hippocampal inputs consistently promote place preferences, basolateral amygdala inputs produce modest place preferences but as a byproduct of increased sensitivity to time investments, and paraventricular inputs reduce place preferences yet do not produce full avoidance behaviour. These findings suggest that each excitatory input provides distinct information to the NAcSh, and we propose that this reflects the reinforcement of different credit assignment functions. Our finding of a quadruple dissociation of NAcSh input-specific behaviours provides insights into how types of information carried by distinct inputs to the NAcSh could be integrated to help drive reinforcement learning and situationally appropriate behavioural responses.

Probing the antidepressant potential of psilocybin: integrating insight from human research and animal models towards an understanding of neural circuit mechanisms

Interest in the therapeutic potential of serotonergic psychedelic compounds including psilocybin has surged in recent years. While human clinical research suggests psilocybin holds promise as a rapid and long-lasting antidepressant, little is known about how its acute mechanisms of action mediate enduring alterations in cognition and behavior. Human neuroimaging studies point to both acute and sustained modulation of functional connectivity in key cortically dependent brain networks. Emerging evidence in preclinical models highlights the importance of psilocybin-induced neuroplasticity and alterations in the prefrontal cortex (PFC). Overviewing research in both humans and preclinical models suggests avenues to increase crosstalk between fields. We review how acute modulation of PFC circuits may contribute to long-term structural and functional alterations to mediate antidepressant effects. We highlight the potential for preclinical circuit and behavioral neuroscience approaches to provide basic mechanistic insight into how psilocybin modulates cognitive and affective neural circuits to support further development of psilocybin as a promising new treatment for depression.

Acute Stress Induces Different Changes on the Expression of BDNF and trkB in the Mesocorticolimbic System of Two Lines of Rats Differing in Their Response to Stressors

The present work was undertaken to investigate the effects of acute forced swimming (FS) on the levels of brain-derived neurotrophic factor (BDNF) and tyrosine kinase receptor B (trkB) proteins in: the ventral tegmental area (VTA); the nucleus accumbens (Acb) shell and core compartments; and the anterior cingulate (ACg), prelimbic (PL) and infralimbic (IL) territories of the prefrontal cortex of genetic models of vulnerability (RLA, Roman low-avoidance rats) and resistance (RHA, Roman high-avoidance rats) to stress-induced depression. We report for the first time that FS induced very rapid and distinct changes in the levels of BDNF and trkB proteins in different areas of the mesocorticolimbic system of RHA and RLA rats. Thus, (1) in the VTA and Acb core, FS elicited a significant increase of both BDNF- and trkB-LI in RHA but not RLA rats, whereas in the Acb shell no significant changes in BDNF- and trkB-LI across the line and treatment were observed; (2) in RLA rats, the basal levels of BDNF-LI in the IL/PL cortex and of trkB-LI in the ACg cortex were markedly lower than those of RHA rats; moreover, BDNF- and trkB-LI in the IL/PL and ACg cortex were increased by FS in RLA rats but decreased in their RHA counterparts. These results provide compelling evidence that the genetic background influences the effects of stress on BDNF/trkB signaling and support the view that the same stressor may impact differently on the expression of BDNF in discrete brain areas.

Differential transcriptome profile underlying risky choice in a rat gambling task

BACKGROUND AND AIMS

Proper measurement of expected risk is important for making rational decisions, and maladaptive decision making may underlie various psychiatric disorders. However, differentially expressed genetic profiling involved in this process is still largely unknown. A rodent version of the gambling task (rGT) has been developed to measure decision-making by adopting the same principle of Iowa Gambling Task in humans. In the present study, we examined using next-generation sequencing (NGS) technique whether there are differences in gene expression profiles in the medial prefrontal cortex (mPFC) and the nucleus accumbens (NAc) when rats make different choices toward risk in rGT.

METHODS

Rats were trained in a touch screen chamber to learn the relationships between 4 different light signals on the window of the screen and accompanied reward outcomes or punishments set up with different magnitudes and probabilities. Once they showed a stabilized pattern of preference upon free choice, rats were classified into risk-averse or risk-seeking groups. After performing the rGT, rats were decapitated, the mPFC and the NAc was dissected out, and NGS was performed with the total RNA extracted.

RESULTS

We found that 477 and 36 genes were differentially expressed (approximately 75 and 83% out of them were downregulated) in the mPFC and the NAc, respectively, in risk-seeking compared to risk-averse rats. Among those, we suggested a few top ranked genes that may contribute to promoting risky choices.

DISCUSSION AND CONCLUSIONS

Our findings provide insights into transcriptional components underlying risky choices in rats.

Sound evoked fos-like immunoreactivity in the big brown bat

Most bat species have highly developed audio-vocal systems, which allow them to adjust the features of echolocation calls that are optimized for different sonar tasks, such as detecting, localizing, discriminating and tracking targets. Furthermore, bats can also produce a wide array of social calls to communicate with conspecifics. The acoustic properties of some social calls differ only subtly from echolocation calls, yet bats have the ability to distinguish them and reliably produce appropriate behavioral responses. Little is known about the underlying neural processes that enable the correct classification of bat social communication sounds. One approach to this question is to identify the brain regions that are involved in the processing of sounds that carry behavioral relevance. Here, we present preliminary data on neuronal activation, as measured by c-fos expression, in big brown bats (Eptesicus fuscus) exposed to either social calls, echolocation calls or kept in silence. We focused our investigation on five relevant brain areas; three within the canonical auditory pathway (auditory cortex, inferior colliculus and medial geniculate body) and two that are involved in the processing of emotive stimulus content (amygdala and nucleus accumbens). In this manuscript we report c-fos staining of the areas of interest after exposure to conspecific calls. We discuss future work designed to overcome experimental limitations and explore whether c-fos staining reveals anatomical segregation of neurons activated by echolocation and social call categories.

Larger striatal volume is associated with increased adult psychopathy

Prior studies have inconsistently reported increased volumes of the striatum in adults with psychopathy. A meta-analysis presented here indicates an overall effect size of d = 0.44. Nevertheless, variability in findings exist, and questions remain on confounding clinical conditions and generalizability to females. This study tests the hypothesis that striatal volumes are increased in adults with psychopathic traits, and that this relationship is mediated by stimulation-seeking and impulsivity. Striatal volume was assessed using magnetic resonance imaging in 108 adult community-dwelling males alongside psychopathy using the Psychopathy Checklist - Revised. Subsidiary, exploratory analyses were conducted on a small sample of females. Correlational analyses showed that increased striatal volumes were associated with more psychopathic traits (p = .001). Effects were observed for all striatal regions, controlling for age, substance dependence and abuse, antisocial personality disorder, attention deficit hyperactivity disorder, social adversity, and total brain volume. An analysis of 18 psychopathic individuals showed that striatal volumes were increased 9.4% compared with 18 matched controls (p = .01). Psychopathy in females was also significantly associated with increased striatal volume (p = .02). Stimulation-seeking and impulsivity partly mediated the striatal-psychopathy relationship, accounting for 49.4% of this association. Findings from these two samples replicate and build on initial studies indicating striatal enlargement in adults with psychopathy, yielding an updated effect size of d = 0.48. Results are consistent with the notion that striatal abnormalities in individuals with psychopathy partly reflect increased sensation-seeking and impulsivity, and support the hypothesis of abnormal reward processing in psychopathy.

Nicotine and opioid co-dependence: Findings from bench research to clinical trials

Concomitant use of tobacco and opioids represents a growing public health concern. In fact, the mortality rate due to smoking-related illness approaches 50% among SUD patients. Cumulative evidence demonstrates that the vulnerability to drugs of abuse is influenced by behavioral, environmental, and genetic factors. This review explores the contribution of genetics and neural mechanisms influencing nicotine and opioid reward, respiration, and antinociception, emphasizing the interaction of cholinergic and opioid receptor systems. Despite the substantial evidence demonstrating nicotine-opioid interactions within the brain and on behavior, the currently available pharmacotherapies targeting these systems have shown limited efficacy for smoking cessation on opioid-maintained smokers. Thus, further studies designed to identify novel targets modulating both nicotinic and opioid receptor systems may lead to more efficacious approaches for co-morbid nicotine dependence and opioid use disorder.

Comparing behavior following binge ethanol in adolescent and adult DBA/2 J mice

The adolescent brain undergoes maturation in areas critically involved in reward, addiction, and memory. Adolescents consume alcohol more than any other drug, typically in a binge-like manner. While adults also binge on alcohol, the adolescent brain is more susceptible to ethanol-related damages due to its ongoing development, which may result in persistent behavioral and physical changes, including differences in myelination in the frontal cortex. Sex also impacts ethanol metabolism and addiction progression, suggesting females are more sensitive than males. This study addressed memory, sociability, ethanol sensitivity, and myelin gene expression changes due to binge ethanol, sex, and age. DBA/2 J males and females were exposed to intermittent binge ethanol (4 g/kg, i.g.) from postnatal day (PND) 29-42 or as adults from PND 64-77. Age groups were tested for behaviors at the early phase (24 h - 7 days) and late phase (starting 3 weeks) after the last dose. Adult prefrontal cortex was collected at both phases. Adolescent ethanol impaired late phase memory while adult ethanol showed no impairment. Meanwhile, adolescent males showed early phase tolerance to ethanol-induced locomotor activation, while adult females showed tolerance at both phases. Adult-treated mice displayed reductions in social interaction. Adult ethanol decreased Mal expression, a gene involved in myelin integrity, at the early phase. No differences in myelin gene expression were observed at the late phase. Thus, adolescent binge ethanol more severely impacts memory and myelin gene expression compared to adult exposure, while adult mice display ethanol-induced reductions in social interaction and tolerance to ethanol's locomotor activation.

Decrease of glycogen synthase kinase 3β phosphorylation in the rat nucleus accumbens shell is necessary for amphetamineinduced conditioned locomotor activity

Phosphorylation levels of glycogen synthase kinase 3β (GSK3β) negatively correlated with psychomotor stimulant-induced locomotor activity. Locomotor sensitization induced by psychomotor stimulants was previously shown to selectively accompany the decrease of GSK3β phosphorylation in the nucleus accumbens (NAcc) core, suggesting that intact GSK3β activity in this region is necessary for psychomotor stimulants to produce locomotor sensitization. Similarly, GSK3β in the NAcc was also implicated in mediating the conditioned effects formed by the associations of psychomotor stimulants. However, it remains undetermined whether GSK3β plays a differential role in the two sub-regions (core and shell) of the NAcc in the expression of drug-conditioned behaviors. In the present study, we found that GSK3β phosphorylation was significantly lower in the NAcc shell obtained from rats expressing amphetamine (AMPH)-induced conditioned locomotor activity. Further, we demonstrated that these effects were normalized by treatment with lithium chloride, a GSK3β inhibitor. These results suggest that the behavior produced by AMPH itself and a conditioned behavior formed by associations with AMPH are differentially mediated by the two sub-regions of the NAcc.

Impact of Early Life Stress on Reward Circuit Function and Regulation

Early life stress - including experience of child maltreatment, neglect, separation from or loss of a parent, and other forms of adversity - increases lifetime risk of mood, anxiety, and substance use disorders. A major component of this risk may be early life stress-induced alterations in motivation and reward processing, mediated by changes in the nucleus accumbens (NAc) and ventral tegmental area (VTA). Here, we review evidence of the impact of early life stress on reward circuit structure and function from human and animal models, with a focus on the NAc. We then connect these results to emerging theoretical models about the indirect and direct impacts of early life stress on reward circuit development. Through this review and synthesis, we aim to highlight open research questions and suggest avenues of future study in service of basic science, as well as applied insights. Understanding how early life stress alters reward circuit development, function, and motivated behaviors is a critical first step toward developing the ability to predict, prevent, and treat stress-related psychopathology spanning mood, anxiety, and substance use disorders.

dCA1-NAc shell glutamatergic projection mediates context-induced memory recall of morphine

Opioid relapse is generally caused by the recurrence of context-induced memory reinstatement of reward. However, the internal mechanisms that facilitate and modify these processes remain unknown. One of the key regions of the reward is the nucleus accumbens (NAc) which receives glutamatergic projections from the dorsal hippocampus CA1 (dCA1). It is not yet known whether the dCA1 projection to the NAc shell regulates the context-induced memory recall of morphine. Here, we used a common model of addiction-related behavior conditioned place preference paradigm, combined with immunofluorescence, chemogenetics, optogenetics, and electrophysiology techniques to characterize the projection of the dCA1 to the NAc shell, in context-induced relapse memory to morphine. We found that glutamatergic neurons of the dCA1 and gamma aminobutyric acidergic (GABA) neurons of the NAc shell are the key brain areas and neurons involved in the context-induced reinstatement of morphine memory. The dCA1-NAc shell glutamatergic input pathway and the excitatory synaptic transmission of the dCA1-NAc shell were enhanced via the α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR) when mice were re-exposed to environmental cues previously associated with drug intake. Furthermore, chemogenetic and optogenetic inactivation of the dCA1-NAc shell pathway decreased the recurrence of long- and short-term morphine-paired context memory in mice. These results provided evidence that the dCA1-NAc shell glutamatergic projections mediated the context-induced memory recall of morphine.

Brain Atrophy Mediates the Relationship between Misfolded Proteins Deposition and Cognitive Impairment in Parkinson's Disease

Parkinson’s disease is associated with cognitive decline, misfolded protein deposition and brain atrophy. We herein hypothesized that structural abnormalities may be mediators between plasma misfolded proteins and cognitive functions. Neuropsychological assessments including five domains (attention, executive, speech and language, memory and visuospatial functions), ultra-sensitive immunomagnetic reduction-based immunoassay (IMR) measured misfolded protein levels (phosphorylated-Tau, Amyloidβ-42 and 40, α-synuclein and neurofilament light chain) and auto-segmented brain volumetry using FreeSurfur were performed for 54 Parkinson’s disease (PD) patients and 37 normal participants. Our results revealed that PD patients have higher plasma misfolded protein levels. Phosphorylated-Tau (p-Tau) and Amyloidβ-42 (Aβ-42) were correlated with atrophy of bilateral cerebellum, right caudate nucleus, and right accumbens area (RAA). In mediation analysis, RAA atrophy completely mediated the relationship between p-Tau and digit symbol coding (DSC). RAA and bilateral cerebellar cortex atrophy partially mediated the Aβ-42 and executive function (DSC and abstract thinking) relationship. Our study concluded that, in PD, p-Tau deposition adversely impacts DSC by causing RAA atrophy. Aβ-42 deposition adversely impacts executive functions by causing RAA and bilateral cerebellum atrophy.

Medial Prefrontal Cortex Has a Causal Role in Selectively Enhanced Consolidation of Emotional Memories after a 24-Hour Delay: A TBS Study

Previous research points to an association between retrieval-related activity in the medial prefrontal cortex (mPFC) and preservation of emotional information compared with co-occurring neutral information following sleep. Although the role of the mPFC in emotional memory likely begins at encoding, little research has examined how mPFC activity during encoding interacts with consolidation processes to enhance emotional memory. This issue was addressed in the present study using transcranial magnetic stimulation in conjunction with an emotional memory paradigm. Healthy young adults encoded negative and neutral scenes while undergoing concurrent TMS with a modified short intermittent theta burst stimulation (sTBS) protocol. Participants received stimulation to either the mPFC or an active control site (motor cortex) during the encoding phase. Recognition memory for scene components (objects and backgrounds) was assessed after a short delay (30 min) and a long delay [24 h (including a night of sleep)] to obtain measures of specific and gist-based memory processes. The results demonstrated that, relative to control stimulation, sTBS to the mPFC enhanced memory for negative objects on the long delay test (collapsed across specific and gist-based memory measures). mPFC stimulation had no discernable effect on memory for objects on the short delay test nor on the background images at either test. These results suggest that mPFC activity occurring during encoding interacts with consolidation processes to preferentially preserve negatively salient information.SIGNIFICANCE STATEMENT Understanding how emotional information is remembered over time is critical to understanding memory in the real world. The present study used noninvasive brain stimulation [repetitive transcranial magnetic stimulation (rTMS)] to investigate the interplay between mPFC activity that occurs during memory encoding and its subsequent interactions with consolidation processes. rTMS delivered to the mPFC during encoding enhanced memory for negatively valenced pictures on a test following a 24 h delay, with no such effect on a test occurring shortly after the encoding phase. These results are consistent with the hypothesis that emotional aspects of memories are differentially subjected to consolidation processes, and that the mPFC might contribute to this "tag-and-capture" mechanism during the initial formation of such memories.

Translational Research in Nicotine Addiction

While commendable strides have been made in reducing smoking initiation and improving smoking cessation rates, current available smoking cessation treatment options are still only mildly efficacious and show substantial interindividual variability in their therapeutic responses. Therefore, the primary goal of preclinical research has been to further the understanding of the neural substrates and genetic influences involved in nicotine's effects and reassess potential drug targets. Pronounced advances have been made by investing in new translational approaches and placing more emphasis on bridging the gap between human and rodent models of dependence. Functional neuroimaging studies have identified key brain structures involved with nicotine-dependence phenotypes such as craving, impulsivity, withdrawal symptoms, and smoking cessation outcomes. Following up with these findings, rodent-modeling techniques have made it possible to dissect the neural circuits involved in these motivated behaviors and ascertain mechanisms underlying nicotine's interactive effects on brain structure and function. Likewise, translational studies investigating single-nucleotide polymorphisms (SNPs) within the cholinergic, dopaminergic, and opioid systems have found high levels of involvement of these neurotransmitter systems in regulating the reinforcing aspects of nicotine in both humans and mouse models. These findings and coordinated efforts between human and rodent studies pave the way for future work determining gene by drug interactions and tailoring treatment options to each individual smoker.

Spatial and temporal scales of dopamine transmission

Dopamine is a prototypical neuromodulator that controls circuit function through G protein-coupled receptor signalling. Neuromodulators are volume transmitters, with release followed by diffusion for widespread receptor activation on many target cells. Yet, we are only beginning to understand the specific organization of dopamine transmission in space and time. Although some roles of dopamine are mediated by slow and diffuse signalling, recent studies suggest that certain dopamine functions necessitate spatiotemporal precision. Here, we review the literature describing dopamine signalling in the striatum, including its release mechanisms and receptor organization. We then propose the domain-overlap model, in which release and receptors are arranged relative to one another in micrometre-scale structures. This architecture is different from both point-to-point synaptic transmission and the widespread organization that is often proposed for neuromodulation. It enables the activation of receptor subsets that are within micrometre-scale domains of release sites during baseline activity and broader receptor activation with domain overlap when firing is synchronized across dopamine neuron populations. This signalling structure, together with the properties of dopamine release, may explain how switches in firing modes support broad and dynamic roles for dopamine and may lead to distinct pathway modulation.

Decreased Functional Connectivity in the Reward Network and Its Relationship With Negative Emotional Experience After Total Sleep Deprivation

Sleep deprivation (SD) induces a negative emotional experience due to a prolonged time spent awake. However, few studies have focused on the mechanism underlying communication within brain networks or alterations during this emotional deterioration. We propose that negative reward judgment is important in poor emotional processing after SD, which will be reflected in functional connectivity in the reward network. We sought to analyze alterations in functional connectivity within the reward network and cerebral cortex. Furthermore, we analyzed changes in functional connectivity correlation with negative emotional experience after SD. Twenty-six healthy volunteers participated in this study. Two resting-state fMRI scans were obtained from the participants, once during resting wakefulness, and once after 36 h of total SD. The bilateral nucleus accumbens (NAc) was selected as a seed region for region of interest (ROI)-to-ROI functional connectivity analysis. Correlation analyses between functional connectivity alterations within the reward network and negative emotional experience were also performed. We found that SD decreased functional connectivity between the left NAc and anterior cingulate cortex (ACC) compared with resting wakefulness. There was a decreased functional connectivity with the ACC and right inferior frontal gyrus (IFG) after SD in the right NAc. Furthermore, decreased functional connectivity between the right NAc and right IFG, and NAc and ACC was negatively correlated with emotional experience scores. Sleep deprivation decreased functional connectivity within the reward network. This may be associated with the enhanced negative emotional experience that was found after total sleep deprivation.

Deep Brain Stimulation of the Subgenual Cingulate Cortex for the Treatment of Chronic Low Back Pain

OBJECTIVES

Despite converging basic scientific and clinical evidence of the link between chronic pain and depression, existing therapies do not often take advantage of this overlap. Here, we provide a critical review of the literature that highlights the intersection in brain networks between chronic low back pain (CLBP) and depression and discuss findings from previous deep brain stimulation (DBS) studies for pain. Based on a multidimensional model of pain processing and the connectivity of the subgenual cingulate cortex (SCC) with areas that are implicated in both CLBP and depression, we propose a novel approach to the treatment of CLBP using DBS of the SCC.

MATERIALS AND METHODS

A narrative review with literature assessment.

RESULTS

CLBP is associated with a shift away from somatosensory representation toward brain regions that mediate emotional processes. There is a high degree of overlap between these regions and those involved in depression, including the anterior cingulate cortex, medial prefrontal cortex, nucleus accumbens, and amygdala. Whereas targets sites from previous DBS trials for pain were not anatomically positioned to engage these areas and their associated networks, the SCC is structurally connected to all of these regions and as well as others involved in mediating sensory, cognitive, and affective processing in CLBP.

CONCLUSIONS

CLBP and depression share a common underlying brain network interconnected by the SCC. Current data and novel technology provide an optimal opportunity to develop clinically effective trials of SCC DBS for CLBP.

Modulation of stimulated dopamine release in rat nucleus accumbens shell by GABA in vitro: Effect of sub-chronic phencyclidine pretreatment

Dopamine signaling in nucleus accumbens (NAc) is modulated by γ-aminobutyric acid (GABA), acting through GABA-A and GABA-B receptors: dysregulation of GABAergic control of dopamine function may be important in behavioral deficits in schizophrenia. We investigated the effect of GABA-A (muscimol) and GABA-B (baclofen) receptor agonists on electrically stimulated dopamine release. Furthermore, we explored whether drug-induced changes were disrupted by pretreatment with phencyclidine, which provides a well-validated model of schizophrenia. Using brain slices from female rats, fast-scan cyclic voltammetry was used to measure electrically stimulated dopamine release in NAc shell. Both muscimol and baclofen caused concentration-dependent attenuation of evoked dopamine release: neither effect was changed by dihydro-β-erythroidine, a nicotinic acetylcholine receptor antagonist, or the α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)-type glutamate receptor antagonist, 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), precluding indirect mechanisms using these transmitter systems in the GABAergic actions. In slices taken from rats pretreated with phencyclidine, the attenuation of evoked dopamine release by baclofen was abolished, but the attenuation by muscimol was unaffected. Since phencyclidine pretreatment was followed by drug-free washout period of at least a week, the drug was not present during recording. Therefore, disruption of GABA-B modulation of dopamine is due to long-term functional changes resulting from the treatment, rather than transient changes due to the drug's presence at test. This enduring dysregulation of GABA-B modulation of accumbal dopamine release provides a plausible mechanism through which GABA dysfunction influences accumbal dopamine leading to behavioral changes seen in schizophrenia and may provide a route for novel therapeutic strategies to treat the condition.

BEHAVIORAL AND NEUROBIOLOGICAL MECHANISMS OF PAVLOVIAN AND INSTRUMENTAL EXTINCTION LEARNING

This article reviews the behavioral neuroscience of extinction, the phenomenon in which a behavior that has been acquired through Pavlovian or instrumental (operant) learning decreases in strength when the outcome that reinforced it is removed. Behavioral research indicates that neither Pavlovian nor operant extinction depends substantially on erasure of the original learning but instead depends on new inhibitory learning that is primarily expressed in the context in which it is learned, as exemplified by the renewal effect. Although the nature of the inhibition may differ in Pavlovian and operant extinction, in either case the decline in responding may depend on both generalization decrement and the correction of prediction error. At the neural level, Pavlovian extinction requires a tripartite neural circuit involving the amygdala, prefrontal cortex, and hippocampus. Synaptic plasticity in the amygdala is essential for extinction learning, and prefrontal cortical inhibition of amygdala neurons encoding fear memories is involved in extinction retrieval. Hippocampal-prefrontal circuits mediate fear relapse phenomena, including renewal. Instrumental extinction involves distinct ensembles in corticostriatal, striatopallidal, and striatohypothalamic circuits as well as their thalamic returns for inhibitory (extinction) and excitatory (renewal and other relapse phenomena) control over operant responding. The field has made significant progress in recent decades, although a fully integrated biobehavioral understanding still awaits.

Synergistic Effect of Several Neurotransmitters in PFC-NAc-VTA Neural Circuit for the Anti-Depression Effect of Shuganheweitang in a Chronic Unpredictable Mild Stress Model

Depression, a major worldwide mental disorder, leads to massive disability and can result in death. The PFC-NAc-VTA neuro circuit is related to emotional, neurovegetative, and cognitive functions, which emerge as a circuit-level framework for understanding reward deficits in depression. Neurotransmitters, which are widely distributed in different brain regions, are important detected targets for the evaluation of depression. Shuganheweitang (SGHWT) is a popular prescription in clinical therapy for depression. In order to investigate its possible pharmacodynamics and anti-depressive mechanism, the complex plant material was separated into different fractions. These in low and high doses, along with low and high doses of SGHWT were tested in animal behavior tests. The low and high doses of SGHWT were more effective than the various fractions, which indicate the importance of synergistic function in traditional Chinese medicine. Furthermore, amino acid (GABA, Glu) and monoamine neurotransmitters (DA, 5-HT, NA, 5-HIAA) in the PFC-NAc-VTA neuro circuit were investigated by UPLC-MS/MS. The level trend of DA and 5-HT were consistent in the PFC-NAc-VTA neuro circuit, whereas 5-HIAA was decreased in the PFC, Glu was decreased in the PFC and VTA, and NA and GABA were decreased in the NAc. The results indicate that the pathogenesis of depression is associated with dysfunction of the PFC-NAc-VTA neural circuit, mainly through the neural projection effects of neurotransmitters associated with various brain regions in the neural circuit. PCA and OPLS-DA score plots demonstrated the similarities of individuals within each group and the differences among the groups. In this study, SGHWT could regulate the concentration level of different neurotransmitters in the PFC-NAc-VTA neuro circuit to improve the depression, which benefitted from the recognition of the brain reward circuitry in mood disorders.

Animal models for the study of depressive disorder

Depressive disorder is one of the most widespread forms of psychiatric pathology, worldwide. According to a report by the World Health Organization, the number of people with depression, globally, is increasing dramatically with each year. Previous studies have demonstrated that various factors, including genetics and environmental stress, contribute to the risk of depression. As such, it is crucial to develop a detailed understanding of the pathogenesis of depressive disorder and animal studies are essential for identifying the mechanisms and genetic disorders underlying depression. Recently, many researchers have reported on the pathology of depression via various models of depressive disorder. Given that different animal models of depression show differences in terms of patterns of depressive behavior and pathology, the comparison between depressive animal models is necessary for progress in the field of the depression study. However, the various animal models of depression have not been fully compared or evaluated until now. In this paper, we reviewed the pathophysiology of the depressive disorder and its current animal models with the analysis of their transcriptomic profiles. We provide insights for selecting different animal models for the study of depression.

Hoarding and Animal Hoarding: Psychodynamic and Transitional Aspects

Hoarding is a disorder that has only recently begun to be understood by researchers and clinicians. This disorder has been examined from a biopsychosocial perspective and has features that overlap with obsessive-compulsive disorder as well as some unique characteristics. Hoarding disorder is widespread and maybe related to the evolution of collecting and storing resources among humans and other animals. While there have been a number of non-analytic theories related to hoarding and its treatment, psychoanalytic thinkers have rarely described the disorder or explored its underlying psychodynamics. Beginning with Freud, it is possible to understand hoarding in relationship to the vicissitudes of the anal stage of development. However, loss of a loved object, especially loss of the mother, can play an important role in the development of hoarding behavior in adults. The hoarding of inanimate items, examined from a developmental object-relations perspective, appears to involve transitional phenomena. Animal hoarding also involves transitional phenomena, but animals, which can serve as animated transitional objects, also have a repetition compulsion function. These psychodynamic characteristics are relevant for establishing a working transference with the analyst or therapist, in order to promote positive therapeutic outcomes.

Anhedonia correlates with functional connectivity of the nucleus accumbens subregions in patients with major depressive disorder

BACKGROUND

The nucleus accumbens (NAc) is an important region in reward circuit that has been linked with anhedonia, which is a characteristic symptom of major depressive disorder (MDD). However, the relationship between the functional connectivity of the NAc subregions and anhedonia in MDD patients remains unclear.

METHODS

We acquired resting-state functional magnetic resonance imaging (fMRI) scans from fifty-one subjects (23 MDD patients and 28 healthy controls). We assessed subjects' trait anhedonia with the Temporal Experience of Pleasure Scale (TEPS). Seed-based resting-state functional connectivity (rsFC) was conducted for each of the NAc subregions (bilateral core-like and shell-like subdivisions) separately to identify regions whose rsFCs with the NAc subregions were altered in the MDD patients and regions whose rsFCs with the NAc subregions showed different correlates with anhedonia between the MDD patients and the healthy controls.

RESULTS

Compared with the health controls, the MDD patients showed decreased rsFCs of the right NAc core-like subdivision with the left mid-anterior orbital prefrontal cortex and the right inferior parietal lobe as well as decreased rsFC of the left NAc core-like subdivision with the right middle frontal gyrus. Moreover, the severity of anhedonia by the group interaction was significant for the rsFC of the right NAc shell-like subdivision with the subgenual/pregenual anterior cingulate cortex and the rsFC of the right NAc core-like subdivision with the precuneus.

CONCLUSIONS

We found that the neural correlates of anhedonia indicated by the rsFCs of the NAc subregions were modulated by depression. The modulation effect was regionally-dependent. These findings enrich our understanding of the neural basis of anhedonia in MDD.

Motivational competition and the paraventricular thalamus

Although significant progress has been made in understanding the behavioral and brain mechanisms for motivational systems, much less is known about competition between motivational states or motivational conflict (e.g., approach - avoidance conflict). Despite being produced under diverse conditions, behavior during motivational competition has two signatures: bistability and metastability. These signatures reveal the operation of positive feedback mechanisms in behavioral selection. Different neuronal architectures can instantiate this selection to achieve bistability and metastability in behavior, but each relies on circuit-level inhibition to achieve rapid and stable selection between competing tendencies. Paraventricular thalamus (PVT) is identified as critical to this circuit level inhibition, resolving motivational competition via its extensive projections to local inhibitory networks in the ventral striatum and extended amygdala, enabling adaptive responding under motivational conflict.

Age-dependent effects of protein restriction on dopamine release

Despite the essential role of protein intake for health and development, very little is known about the impact of protein restriction on neurobiological functions, especially at different stages of the lifespan. The dopamine system is a central actor in the integration of food-related processes and is influenced by physiological state and food-related signals. Moreover, it is highly sensitive to dietary effects during early life periods such as adolescence due to its late maturation. In the present study, we investigated the impact of protein restriction either during adolescence or adulthood on the function of the mesolimbic (nucleus accumbens) and nigrostriatal (dorsal striatum) dopamine pathways using fast-scan cyclic voltammetry in rat brain slices. In the nucleus accumbens, protein restriction in adults increased dopamine release in response to low and high frequency trains of stimulation (1-20 Hz). By contrast, protein restriction during adolescence decreased nucleus accumbens dopamine release. In the dorsal striatum, protein restriction at adulthood has no impact on dopamine release but the same diet during adolescence induced a frequency-dependent increase in stimulated dopamine release. Taken together, our results highlight the sensitivity of the different dopamine pathways to the effect of protein restriction, as well as their vulnerability to deleterious diet effects at different life stages.

Immunohistochemical detection of GluA1 subunit of AMPA receptor in the rat nucleus accumbens following cocaine exposure

α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) receptors are differentially regulated in the nucleus accumbens (NAcc) of the brain after cocaine exposure. However, these results are supported only by biochemical and electrophysiological methods, but have not been validated with immunohistochemistry. To overcome the restriction of antigen loss on the postsynaptic target molecules that occurs during perfusion-fixation, we adopted an immersion-fixation method that enabled us to immunohistochemically quantify the expression levels of the AMPA receptor GluA1 subunit in the NAcc. Interestingly, compared to saline exposure, cocaine significantly increased the immunofluorescence intensity of GluA1 in two sub-regions, the core and the shell, of the NAcc on withdrawal day 21 following cocaine exposure, which led to locomotor sensitization. Increases in GluA1 intensity were observed in both the extra-post synaptic density (PSD) and PSD areas in the two sub-regions of the NAcc. These results clearly indicate that AMPA receptor plasticity, as exemplified by GluA1, in the NAcc can be visually detected by immunohistochemistry and confocal imaging. These results expand our understanding of the molecular changes occurring in neuronal synapses by adding a new form of analysis to conventional biochemical and electrophysiological methods.

The Projection From Ventral CA1, Not Prefrontal Cortex, to Nucleus Accumbens Core Mediates Recent Memory Retrieval of Cocaine-Conditioned Place Preference

Drug-paired cues inducing memory retrieval by expressing drug-seeking behaviors present a major challenge to drug abstinence. How neural circuits coordinate for drug memory retrieval remains unclear. Here, we report that exposure of the training chamber where cocaine-conditioned place preference (CPP) was performed increased neuronal activity in the core of nucleus accumbens (AcbC), ventral CA1 (vCA1), and medial prefrontal cortex (mPFC), as shown by elevated pERK and c-Fos levels. Chemogenetic inhibition of neuronal activity in the vCA1 and AcbC, but not mPFC, reduced the time spent in the cocaine-paired compartment, suggesting that the vCA1 and AcbC are required for the retrieval of cocaine-CPP memory and are key nodes recruited for cocaine memory storage. Furthermore, chemogenetic inhibition of the AcbC-projecting vCA1 neurons, but not the AcbC-projecting mPFC neurons, decreased the expression of cocaine-CPP. Optogenetic inhibition of the vCA1–AcbC projection, but not the mPFC–AcbC projection, also reduced the preference for the cocaine-paired compartment. Taken together, the cue-induced natural recall of cocaine memory depends on vCA1–AcbC circuits. The connectivity from the vCA1 to the AcbC may store the information of the cue–cocaine reward association critically required for memory retrieval. These data thus provide insights into the neural circuit basis of retrieval of drug-related memory.

Brain activity and transcriptional profiling in mice under chronic jet lag

Shift work is known to be associated with an increased risk of neurological and psychiatric diseases, but how it contributes to the development of these diseases remains unclear. Chronic jet lag (CJL) induced by shifting light-dark cycles repeatedly is a commonly used protocol to mimic the environmental light/dark changes encountered by shift workers. Here we subjected wildtype mice to CJL and performed positron emission tomography imaging of glucose metabolism to monitor brain activities. We also conducted RNA sequencing using prefrontal cortex and nucleus accumbens tissues from these animals, which are brain regions strongly implicated in the pathology of various neurological and psychiatric conditions. Our results reveal the alterations of brain activities and systematic reprogramming of gene expression in brain tissues under CJL, building hypothesis for how CJL increases the susceptibility to neurological and psychiatric diseases.

The Projection Targets of Medium Spiny Neurons Govern Cocaine-Evoked Synaptic Plasticity in the Nucleus Accumbens

We examine synaptic connectivity and cocaine-evoked plasticity at specific networks within the nucleus accumbens (NAc). We identify distinct subpopulations of D1+ medium spiny neurons (MSNs) that project to either the ventral pallidum (D1+^VP) or the ventral tegmental area (D1+^VTA). We show that inputs from the ventral hippocampus (vHPC), but not the basolateral amygdala (BLA), are initially biased onto D1+^VTA MSNs. However, repeated cocaine exposure eliminates the bias of vHPC inputs onto D1+^VTA MSNs, while strengthening BLA inputs onto D1+^VP MSNs. Our results reveal that connectivity and plasticity depend on the specific inputs and outputs of D1+ MSNs and highlight the complexity of cocaine-evoked circuit level adaptations in the NAc.

Baimel et al. examine how cocaine exposure alters specific circuits in the nucleus accumbens medial shell. They find that D1-expressing (D1+) medium spiny neurons projecting to ventral tegmental area and ventral pallidum are distinct populations. These two cell types differ in both their baseline synaptic connectivity and cocaine-evoked synaptic plasticity.

Acute and Post-Traumatic Stress Disorders: A biased nervous system

Acute stress disorder and post-traumatic stress disorder are generally triggered by an exceptionally intense threat. The consequences of this traumatogenic situation are explored here in chronological order, from exposure to the threat to development of symptoms. Such a situation may disrupt the equilibrium between two fundamental brain circuits, referred to as the "defensive" and "cognitive". The defensive circuit triggers the stress response as well as the formation of implicit memory. The cognitive circuit triggers the voluntary response and the formation of explicit autobiographical memory. During a traumatogenic situation, the defensive circuit could be over-activated while cognitive circuit is under-activated. In the most severe cases, overactivation of the defensive circuit may cause its brutal deactivation, resulting in dissociation. Here, we address the underlying neurobiological mechanisms at every scale: from neurons to behaviors, providing a detailed explanatory model of trauma.

The ventral striatum dissociates information expectation, reward anticipation, and reward receipt

Do dopaminergic reward structures represent the expected utility of information similarly to a reward? Optimal experimental design models from Bayesian decision theory and statistics have proposed a theoretical framework for quantifying the expected value of information that might result from a query. In particular, this formulation quantifies the value of information before the answer to that query is known, in situations where payoffs are unknown and the goal is purely epistemic: That is, to increase knowledge about the state of the world. Whether and how such a theoretical quantity is represented in the brain is unknown. Here we use an event-related functional MRI (fMRI) task design to disentangle information expectation, information revelation and categorization outcome anticipation, and response-contingent reward processing in a visual probabilistic categorization task. We identify a neural signature corresponding to the expectation of information, involving the left lateral ventral striatum. Moreover, we show a temporal dissociation in the activation of different reward-related regions, including the nucleus accumbens, medial prefrontal cortex, and orbitofrontal cortex, during information expectation versus reward-related processing.

A Critical Role of Basolateral Amygdala-to-Nucleus Accumbens Projection in Sleep Regulation of Reward Seeking

BACKGROUND

Sleep impacts reward-motivated behaviors partly by retuning the brain reward circuits. The nucleus accumbens (NAc) is a reward processing hub sensitive to acute sleep deprivation. Glutamatergic transmission carrying reward-associated signals converges in the NAc and regulates various aspects of reward-motivated behaviors. The basolateral amygdala projection (BLAp) innervates broad regions of the NAc and critically regulates reward seeking.

METHODS

Using slice electrophysiology, we measured how acute sleep deprivation alters transmission at BLAp-NAc synapses in male C57BL/6 mice. Moreover, using SSFO (stabilized step function opsin) and DREADDs (designer receptors exclusively activated by designer drugs) (Gi) to amplify and reduce transmission, respectively, we tested behavioral consequences following bidirectional manipulations of BLAp-NAc transmission.

RESULTS

Acute sleep deprivation increased sucrose self-administration in mice and altered the BLAp-NAc transmission in a topographically specific manner. It selectively reduced glutamate release at the rostral BLAp (rBLAp) onto ventral and lateral NAc (vlNAc) synapses, but spared caudal BLAp onto medial NAc synapses. Furthermore, experimentally facilitating glutamate release at rBLAp-vlNAc synapses suppressed sucrose reward seeking. Conversely, mimicking sleep deprivation-induced reduction of rBLAp-vlNAc transmission increased sucrose reward seeking. Finally, facilitating rBLAp-vlNAc transmission per se did not promote either approach motivation or aversion.

CONCLUSIONS

Sleep acts on rBLAp-vINAc transmission gain control to regulate established reward seeking but does not convey approach motivation or aversion on its own.