Contributions of the paraventricular thalamic nucleus in the regulation of stress, motivation, and mood

Sustained antidepressant effects of ketamine metabolite involve GABAergic inhibition-mediated molecular dynamics in aPVT glutamatergic neurons

Despite the rapid and sustained antidepressant effects of ketamine and its metabolites, their underlying cellular and molecular mechanisms are not fully understood. Here, we demonstrate that the sustained antidepressant-like behavioral effects of (2S,6S)-hydroxynorketamine (HNK) in repeatedly stressed animal models involve neurobiological changes in the anterior paraventricular nucleus of the thalamus (aPVT). Mechanistically, (2S,6S)-HNK induces mRNA expression of extrasynaptic GABAA receptors and subsequently enhances GABAA-receptor-mediated tonic currents, leading to the nuclear export of histone demethylase KDM6 and its replacement by histone methyltransferase EZH2. This process increases H3K27me3 levels, which in turn suppresses the transcription of genes associated with G-protein-coupled receptor signaling. Thus, our findings shed light on the comprehensive cellular and molecular mechanisms in aPVT underlying the sustained antidepressant behavioral effects of ketamine metabolites. This study may support the development of potentially effective next-generation pharmacotherapies to promote sustained remission of stress-related psychiatric disorders.

Novel rat model of gaming disorder: assessment of social reward and sex differences in behavior and c-Fos brain activity

RATIONALE

In 2018, the International Classification of Diseases (ICD-11) classified Gaming Disorder (GD) as a mental disorder. GD mainly occurs among adolescents, who, after developing addiction, show psychopathological traits, such as social anxiety, depression, social isolation, and attention deficit. However, the different studies conducted in humans so far show several limitations, such as the lack of demographic heterogeneity and equal representation of age, differences in the type of game and in the follow-up period. Furthermore, at present, no animal models specific to GD are available.

OBJECTIVES

To address the lack of an experimental model for GD, in the present work, we proposed a new GD rat model to investigate some peculiar tracts of the disorder.

METHODS

Two-month-old Wistar Kyoto rats, both males and females, were subject to a five-week training with a new innovative touch-screen platform. After five weeks of training, rats were assessed for: (a) their attachment to the play under several conditions, (b) their hyperactivity during gaming, and (c) the maintenance of these conditions after a period of game pause and reward interruption. After sacrifice, using immunohistochemistry techniques, the immunoreactivity of c-Fos (a marker of neuronal activity) was analyzed to study different neural areas.

RESULTS

After the training, the rats subjected to GD protocol developed GD-related traits (e.g., hyperactivity, loss control), and the behavioral phenotype was maintained consistently over time. These aspects were completely absent in the control groups. Lastly, the analysis of c-Fos immunoreactivity in prelimbic cortex (PrL), orbitofrontal cortex (OFC), nucleus Accumbens, amygdala and bed nucleus of stria terminalis (BNST) highlighted significant alterations in the GD groups compared to controls, suggesting modifications in neural activity related to the development of the GD phenotype.

CONCLUSIONS

The proposal of a new GD rat model could represent an innovative tool to investigate, in both sexes, the behavioral and neurobiological features of this disorder, the possible role of external factors in the predisposition and susceptibility and the development of new pharmacological therapies.

Presentation and Management of Acute Mania in Fanconi-Bickel Syndrome, A Metabolic Genetic Disorder

Fanconi-Bickel syndrome (FBS) is a rare metabolic disorder caused by decreased glucose transporter 2 (GLUT2) function due to several known mutations in the SLC2A2 gene. As of 2020, 144 cases of FBS have been described in the literature. Metabolic and somatic sequelae include dysglycemia and accumulation of glycogen in the kidney and liver. However, there are no descriptions in the literature of possible neuropsychiatric manifestations of FBS. This case report is to our knowledge the first in this regard, describing a patient with FBS who was admitted to our psychiatric inpatient unit while experiencing acute mania. We conceptualize the case as a novel psychiatric presentation of acute mania in FBS, which may inform our understanding of bipolar disorder pathophysiology because of the hypothesized functional changes in neural pathways involving the paraventricular thalamus induced by decreased GLUT2 activity in FBS.

Brain volumes, behavioral inhibition, and anxiety disorders in children: results from the adolescent brain cognitive development study

BACKGROUND

Magnetic resonance imaging (MRI) studies have identified brain changes associated with anxiety disorders (ADs), but the results remain mixed, particularly at a younger age. One key predictor of ADs is behavioral inhibition (BI), a childhood tendency for high avoidance of novel stimuli. This study aimed to evaluate the relationships between candidate brain regions, BI, and ADs among children using baseline data from the Adolescent Brain Cognitive Development (ABCD) study.

METHODS

We analyzed global and regional brain volumes of 9,353 children (9-10 years old) in relation to BI and current ADs, using linear mixed models accounting for family clustering and important demographic and socioeconomic covariates. We further investigated whether and how past anxiety was related to brain volumes.

RESULTS

Among included participants, 249 (2.66%) had a current AD. Larger total white matter (Beta = -0.152; 95% CI [-0.281, -0.023]), thalamus (Beta = -0.168; 95% CI [-0.291, -0.044]), and smaller hippocampus volumes (Beta = 0.094; 95% CI [-0.008, 0.196]) were associated with lower BI scores. Amygdala volume was not related to BI. Larger total cortical (OR = 0.751; 95% CI [0.580;0.970]), amygdala (OR = 0.798; 95%CI [0.666;0.956]), and precentral gyrus (OR = 0.802; 95% CI [0.661;0.973]) volumes were associated with lower odds of currently having ADs. Children with past ADs had smaller total white matter and amygdala volumes.

CONCLUSIONS

The results show associations between brain volumes and both BI and ADs at an early age. Importantly, results suggest that ADs and BI have different neurobiological correlates and that earlier occurrences of ADs may influence brain structures related to BI and ADs, motivating research that can better delineate the similarities and divergence in the neurobiological underpinnings and building blocks of BI and ADs across their development in early life.

Discrete prefrontal neuronal circuits determine repeated stress-induced behavioral phenotypes in male mice

Chronic stress is a major risk factor for psychiatric disorders, including depression. Although depression is a highly heterogeneous syndrome, it remains unclear how chronic stress drives individual differences in behavioral responses. In this study, we developed a subtyping-based approach wherein stressed male mice were divided into four subtypes based on their behavioral patterns of social interaction deficits and anhedonia, the core symptoms of psychiatric disorders. We identified three prefrontal cortical neuronal projections that regulate repeated stress-induced behavioral phenotypes. Among them, the medial prefrontal cortex (mPFC)→anterior paraventricular thalamus (aPVT) pathway determines the specific behavioral subtype that exhibits both social deficits and anhedonia. Additionally, we identified the circuit-level molecular mechanism underlying this subtype: KDM5C-mediated epigenetic repression of Shisa2 transcription in aPVT projectors in the mPFC led to social deficits and anhedonia. Thus, we provide a set of biological aspects at the cellular, molecular, and epigenetic levels that determine distinctive stress-induced behavioral phenotypes.

Ghrelin and depressive symptoms in patients with first-episode drug-naïve major depressive disorder: The mediating role of hypothalamic-pituitary-adrenal axis

BACKGROUND

Major depressive disorder (MDD) is one of the global burdens of disease, and its pathogenesis remains unclear. An increasing amount of research indicates that ghrelin regulates mood in patients with MDD. Still, current results are inconsistent, and the mechanisms underlying how ghrelin modulates depressive symptoms are inconclusive, especially in first-episode drug-naïve MDD patients. Therefore, this study aims to investigate the relationship and potential mechanism between ghrelin and first-episode drug-naïve MDD.

METHODS

Ninety first-episode drug-naïve MDD patients and 65 healthy controls (HCs) were included. Hamilton Depression Scale (HAMD-17) as a measure of depressive symptoms. Plasma levels of ghrelin and hypothalamic-pituitary-adrenal axis (HPA-axis) hormones were measured in all participants.

RESULTS

Compared to HCs, the ghrelin levels were higher in the MDD (p < .001) and still showed significance after covarying for sex, age, and Body Mass Index (BMI). Ghrelin was positively related to corticotropin-releasing-hormone (CRH) levels (r = .867, p < .001), adrenocorticotropic hormone (ACTH) levels (r = .830, p < .001), and cortisol levels (r = .902, p < .001) in partial correlation analysis. In addition, there was a positive correlation between HAMD total score and ghrelin levels (r = .240, p = .026). Other than that, the HAMD total score also had a positive correlation with the CRH (r = .333, p = .002) and cortisol (r = .307, p = .004) levels. Further mediation analysis demonstrated that the relationship between ghrelin and HAMD total score was mediated by CRH (ab-path; β = .4457, 95% CI = 0.0780-1.0253, c-path; β = .2447, p = .0260, c'-path; β = -.2009, p = .3427).

CONCLUSIONS

These findings revealed that plasma ghrelin provides a pivotal link to depressive symptoms in first-episode drug-naive MDD patients. CRH mediated the relationship between ghrelin and HAMD total score. It might provide new insights into understanding the pathogenesis of MDD, contributing to intervention and treatment from this approach.

The central renin-angiotensin system: A genetic pathway, functional decoding, and selective target engagement characterization in humans

Accumulating evidence suggests that the brain renin angiotensin system (RAS) plays a pivotal role in the regulation of cognition and behavior as well as in the neuropathology of neurological and mental disorders. The angiotensin II type 1 receptor (AT1R) mediates most functional and neuropathology-relevant actions associated with the central RAS. However, an overarching comprehension to guide translation and utilize the therapeutic potential of the central RAS in humans is currently lacking. We conducted a comprehensive characterization of the RAS using an innovative combination of transcriptomic gene expression mapping, image-based behavioral decoding, and pre-registered randomized controlled discovery-replication pharmacological resting-state functional magnetic resonance imaging (fMRI) trials (N = 132) with a selective AT1R antagonist. The AT1R exhibited a particular dense expression in a subcortical network encompassing the thalamus, striatum, and amygdalo-hippocampal formation. Behavioral decoding of the AT1R gene expression brain map showed an association with memory, stress, reward, and motivational processes. Transient pharmacological blockade of the AT1R further decreased neural activity in subcortical systems characterized by a high AT1R expression, while increasing functional connectivity in the cortico-basal ganglia-thalamo-cortical circuitry. Effects of AT1R blockade on the network level were specifically associated with the transcriptomic signatures of the dopaminergic, opioid, acetylcholine, and corticotropin-releasing hormone signaling systems. The robustness of the results was supported in an independent pharmacological fMRI trial. These findings present a biologically informed comprehensive characterization of the central AT1R pathways and their functional relevance on the neural and behavioral level in humans.

Neuronal activity in the anterior paraventricular nucleus of thalamus positively correlated with sweetener consumption in mice

Although the brain can discriminate between various sweet substances, the underlying neural mechanisms of this complex behavior remain elusive. This study examines the role of the anterior paraventricular nucleus of the thalamus (aPVT) in governing sweet preference in mice. We fed the mice six different diets with equal sweetness for six weeks: control diet (CD), high sucrose diet (HSD), high stevioside diet (HSSD), high xylitol diet (HXD), high glycyrrhizin diet (HGD), and high mogroside diet (HMD). The mice exhibited a marked preference specifically for the HSD and HSSD. Following consumption of these diets, c-Fos expression levels in the aPVT were significantly higher in these two groups compared to the others. Utilizing fiber photometry calcium imaging, we observed rapid activation of aPVT neurons in response to sucrose and stevioside intake, but not to xylitol or water. Our findings suggest that aPVT activity aligns with sweet preference in mice, and notably, stevioside is the sole plant-based sweetener that elicits an aPVT response comparable to that of sucrose.

Differential recruitment of brain circuits during fear extinction in non-stressed compared to stress resilient animals

Dysfunctional fear responses in post-traumatic stress disorder (PTSD) may be partly explained by an inability to effectively extinguish fear responses elicited by trauma-related cues. However, only a subset of individuals exposed to traumatic stress develop PTSD. Therefore, studying fear extinction deficits in animal models of individual differences could help identify neural substrates underlying vulnerability or resilience to the effects of stress. We used a rat model of social defeat in which rats segregate into passively and actively coping rats. In previous work, we showed that passively coping rats exhibit disruptions in social interaction whereas actively coping rats do not display behaviors differently from controls, indicating their resilience. Here, adult male rats exposed to 7 days of social defeat were tested for fear extinction, retention of extinction, and persistence of retention using contextual fear and ethologically-relevant fear tests. Passively coping rats exhibited elevated freezing in response to the previously extinguished context. Analyses of cFos expressing cells across select brain regions showed high correlations within dorsal hippocampal subregions, while passively coping rats had high correlations between the dorsal hippocampus CA1 and the central and basolateral subregions of the amygdala. Importantly, although control and actively coping rats showed similar levels of behavioral extinction, there was little similarity between activated structures, suggesting stress resilience in response to chronic social defeat involves an adaptive differential recruitment of brain circuits to successfully extinguish fear memories.

Direct paraventricular thalamus-basolateral amygdala circuit modulates neuropathic pain and emotional anxiety

The comorbidity of chronic pain and mental dysfunctions such as anxiety disorders has long been recognized, but the underlying mechanisms remained poorly understood. Here, using a mouse model of neuropathic pain, we demonstrated that the thalamic paraventricular nucleus (PVT) played a critical role in chronic pain-induced anxiety-like behavioral abnormalities. Fiber photometry and electrophysiology demonstrated that chronic pain increased the activities in PVT glutamatergic neurons. Chemogenetic manipulation revealed that suppression of PVT glutamatergic neurons relieved pain-like behavior and anxiety-like behaviors. Conversely, selective activation of PVT glutamatergic neurons showed algesic and anxiogenic effects. Furthermore, the elevated excitability of PVT glutamatergic neurons resulted in increased excitatory inputs to the basolateral complex (BLA) neurons. Optogenetic manipulation of the PVT-BLA pathway bilaterally modulates both the pain-like behavior and anxiety-like phenotypes. These findings shed light on how the PVT-BLA pathway contributed to the processing of pain-like behavior and maladaptive anxiety, and targeting this pathway might be a straightforward therapeutic strategy to both alleviate nociceptive hypersensitivity and rescue anxiety behaviors in chronic pain conditions.

Static electric field exposure decreases white blood cell count in peripheral blood through activating hypothalamic-pituitary-adrenal axis

With the development of ultra-high-voltage (UHV) direct-current (DC) transmission, the health risk from the static electric field (SEF) generated by UHV DC transmission lines has drawn public attention. To investigate the effect of SEF exposure on white blood cell (WBC) count, mice were exposed to 56.3 kV/m SEF. Results revealed that total WBC count and lymphocyte count significantly decreased and serum levels of corticotropin-releasing hormone, adrenocorticotropic hormone and corticosterone (CORT) significantly increased after the exposure of 7d and 14d. All indices above recovered after the exposure of 21d. Analysis showed that the exposure of 7d and 14d could activate hypothalamic-pituitary-adrenal (HPA) axis. The increased CORT could bind to the glucocorticoid receptor (GR) in lymphocytes, and then promote the migration and apoptosis of lymphocytes. After the exposure of 21d, the magnitude of HPA axis activation declined through CORT-mediated negative feedback and the regulation of stress-related neural circuitry, so WBC count recovered.

Genetic Tagging Uncovers a Robust, Selective Activation of the Thalamic Paraventricular Nucleus by Adverse Experiences Early in Life

Background

Early-life adversity (ELA) is associated with increased risk for mood disorders, including depression and substance use disorders. These disorders are characterized by impaired reward-related behaviors, suggesting compromised operations of reward-related brain circuits. However, the brain regions engaged by ELA that mediate these enduring consequences of ELA remain largely unknown. In an animal model of ELA, we identified aberrant reward-seeking behaviors, a discovery that provides a framework for assessing the underlying circuits.

Methods

Employing TRAP2 (targeted recombination in active populations) male and female mice, in which neurons activated within a defined time frame are permanently tagged, we compared ELA- and control-reared mice, assessing the quantity and distribution of ELA-related neuronal activation. After validating the TRAP2 results using native c-Fos labeling, we defined the molecular identity of this population of activated neurons.

Results

We uniquely demonstrated that the TRAP2 system is feasible and efficacious in neonatal mice. Surprisingly, the paraventricular nucleus of the thalamus was robustly and almost exclusively activated by ELA and was the only region distinguishing ELA from typical rearing. Remarkably, a large proportion of ELA-activated paraventricular nucleus of the thalamus neurons expressed CRF1, the receptor for the stress-related peptide, corticotropin-releasing hormone, but these neurons did not express corticotropin-releasing hormone itself.

Conclusions

The paraventricular nucleus of the thalamus, an important component of reward circuits that is known to encode remote, emotionally salient experiences to influence future motivated behaviors, encodes adverse experiences as remote as those occurring during the early postnatal period and is thus poised to contribute to the enduring deficits in reward-related behaviors consequent to ELA.

fMRI reveals overlapping and non-overlapping neural bases of domain-general and emotional conflict control

The present study uses functional magnetic resonance image (fMRI) to examine the overlapping and specific neural correlates of contextualized emotional conflict control and domain-general conflict control. During a performance on emotional and domain-general conflict tasks, conjunction analyses showed that neural areas distributed in the frontoparietal network were engaged in both processes, supporting the notion that similar neural mechanisms are implemented in these two types of control. Importantly, disjunction analyses revealed a broader neural recruitment of emotional conflict control compared to domain-general conflict control as shown by the possible lateralization of the lateral prefrontal cortex (lPFC), such that emotional conflict control significantly involved the left lPFC while domain-general conflict control seemly involved the right lPFC. Results of generalized psychophysiological interaction (gPPI) analyses further demonstrated that emotional conflict control, compared to domain-general conflict control, elicited broader synergistic activities in individuals' brain networks. Together, these findings offer novel and compelling neural evidence that furthers our understanding of the complex relationship between domain-general and emotional conflict control.

Lipocalin 2 in the Paraventricular Thalamic Nucleus Contributes to DSS-Induced Depressive-Like Behaviors

The incidence rate of anxiety and depression is significantly higher in patients with inflammatory bowel diseases (IBD) than in the general population. The mechanisms underlying dextran sulfate sodium (DSS)-induced depressive-like behaviors are still unclear. We clarified that IBD mice induced by repeated administration of DSS presented depressive-like behaviors. The paraventricular thalamic nucleus (PVT) was regarded as the activated brain region by the number of c-fos-labeled neurons. RNA-sequencing analysis showed that lipocalin 2 (Lcn2) was upregulated in the PVT of mice with DSS-induced depressive behaviors. Upregulating Lcn2 from neuronal activity induced dendritic spine loss and the secreted protein induced chemokine expression and subsequently contributed to microglial activation leading to blood-brain barrier permeability. Moreover, Lcn2 silencing in the PVT alleviated the DSS-induced depressive-like behaviors. The present study demonstrated that elevated Lcn2 in the PVT is a critical factor for DSS-induced depressive behaviors.

Paraventricular Thalamus Dynamically Modulates Aversive Memory via Tuning Prefrontal Inhibitory Circuitry

The impact of stress on the formation and expression of memory is well studied, especially on the contributions of stress hormones. But how stress affects brain circuitry dynamically to modulate memory is far less understood. Here, we used male C57BL6/J mice in an auditory fear conditioning as a model system to examine this question and focused on the impact of stress on dorsomedial prefrontal cortex (dmPFC) neurons which play an important role in probabilistic fear memory. We found that paraventricular thalamus (PVT) neurons are robustly activated by acute restraining stress. Elevated PVT activity during probabilistic fear memory expression increases spiking in the dmPFC somatostatin neurons which in turn suppresses spiking of dmPFC parvalbumin (PV) neurons, and reverts the usual low fear responses associated with probabilistic fear memory to high fear. This dynamic and reversible modulation allows the original memory to be preserved and modulated during memory expression. In contrast, elevated PVT activity during fear conditioning impairs synaptic modifications in the dmPFC PV-neurons and abolishes the formation of probabilistic fear memory. Thus, PVT functions as a stress sensor to modulate the formation and expression of aversive memory by tuning inhibitory functions in the prefrontal circuitry.SIGNIFICANCE STATEMENT The impact of stress on cognitive functions, such as memory and executive functions, are well documented especially on the impact by stress hormone. However, the contributions of brain circuitry are far less understood. Here, we show that a circuitry-based mechanism can dynamically modulate memory formation and expression, namely, higher stress-induced activity in paraventricular thalamus (PVT) impairs the formation and expression of probabilistic fear memory by elevating the activity of somatostatin-neurons to suppress spiking in dorsomedial prefrontal parvalbumin (PV) neurons. This stress impact on memory via dynamic tuning of prefrontal inhibition preserves the formed memory but enables a dynamic expression of memory. These findings have implications for better stress coping strategies as well as treatment options including better drug targets/mechanisms.

Distribution of estrogen receptors alpha and beta in the brain of male rats with same-sex preference

Two distinct estrogen receptors (ERs) exist, ERα and ERβ. Both receptors participate in the sexual differentiation of the rat brain and likely participate in the regulation of adult sexual orientation (i.e. partner preference). This last idea was investigated herein by examining males treated with the aromatase inhibitor, letrozole, administered prenatally (0.56 μg/kg G10-22). This treatment usually provokes same-sex preference in 1-2 males per litter. Vehicle-treated males (with female preference) and females in spontaneous proestrus (with male preference) were included as controls. ERα and ERβ expression was analyzed by immunohistochemistry in brain areas known to control masculine sexual behavior and partner preference, like the medial preoptic area (MPOA), bed nucleus of the stria terminalis (BNST), medial amygdala (MeA) and ventromedial hypothalamic nucleus (VMH), as well as other brain regions suspected to participate in these processes. In addition, serum levels of estradiol were determined in all male groups. Letrozole-treated male rats that preferred sexually experienced males (LPM) showed over-expressed ERα in the hippocampal cornu Ammonis (CA 1, 3, 4) and dentate gyrus. The LPM group showed up-regulated ERβ expression in the CA2 and reticular thalamic nucleus. The levels of estradiol did not differ between the groups. The higher expression of ERs in these males was different than their expression in females, with male sex-preference. This suggests that males with same-sex preference showed a unique brain, this sui generis steroid receptor expression probably participates in the biological underpinnings of sexual preference.

Neural and Molecular Investigation into the Paraventricular Thalamic-Nucleus Accumbens Circuit for Pain Sensation and Non-opioid Analgesia

The paucity of medications with novel mechanisms for pain treatment combined with the severe adverse effects of opioid analgesics has led to an imperative pursuit of non-opioid analgesia and a better understanding of pain mechanisms. Here, we identify the putative glutamatergic inputs from the paraventricular thalamic nucleus to the nucleus accumbens (PVT^Glut→NAc) as a novel neural circuit for pain sensation and non-opioid analgesia. Our in vivo fiber photometry and in vitro electrophysiology experiments found that PVT^Glut→NAc neuronal activity increased in response to acute thermal/mechanical stimuli and persistent inflammatory pain. Direct optogenetic activation of these neurons in the PVT or their terminals in the NAc induced pain-like behaviors. Conversely, inhibition of PVT^Glut→NAc neurons or their NAc terminals exhibited a potent analgesic effect in both naïve and pathological pain mice, which could not be prevented by pretreatment of naloxone, an opioid receptor antagonist. Anterograde trans-synaptic optogenetic experiments consistently demonstrated that the PVT^Glut→NAc circuit bi-directionally modulates pain behaviors. Furthermore, circuit-specific molecular profiling and pharmacological studies revealed dopamine receptor 3 as a candidate target for pain modulation and non-opioid analgesic development. Taken together, these findings provide a previously unknown neural circuit for pain sensation and non-opioid analgesia and a valuable molecular target for developing future safer medication.

Abnormal brain network community structure related to psychological stress in schizophrenia

Recent functional imaging studies in schizophrenia consistently report a disruption of brain connectivity. However, most of these studies analyze the brain connectivity during resting state. Since psychological stress is a major factor for the emergence of psychotic symptoms, we sought to characterize the brain connectivity reconfiguration induced by stress in schizophrenia. We tested the hypothesis that an alteration of the brain's integration-segregation dynamic could be the result of patients with schizophrenia facing psychological stress. To this end, we studied the modular organization and the reconfiguration of networks induced by a stress paradigm in forty subjects (twenty patients and twenty controls), thus analyzing the dynamics of the brain in terms of integration and segregation processes by using 3T-fMRI. Patients with schizophrenia did not show statistically significant differences during the control task compared with controls, but they showed an abnormal community structure during stress condition and an under-connected reconfiguration network with a reduction of hub nodes, suggesting a deficit of integration dynamic with a greater compromise of the right hemisphere. These results provide evidence that schizophrenia has a normal response to undemanding stimuli but shows a disruption of brain functional connectivity between key regions involved in stress response, potentially leading to altered functional brain dynamics by reducing integration capacity and showing deficits recruiting right hemisphere regions. This could in turn underlie the hyper-sensitivity to stress characteristic of schizophrenia.

A paraventricular thalamus to central amygdala neural circuit modulates acute stress-induced heightened wakefulness

Heightened wakefulness in response to stressors is essential for survival but can also lead to sleep disorders like insomnia. The paraventricular thalamus (PVT) is both a critical thalamic area for wakefulness and a stress-sensitive brain region. However, whether the PVT and its neural circuitries are involved in controlling wakefulness in stress conditions remains unknown. Here, we find that PVT neurons projecting to the central amygdala (CeA) are activated by different stressors. These neurons are wakefulness-active and increase their activities upon sleep to wakefulness transitions. Optogenetic activation of the PVT-CeA circuit evokes transitions from sleep to wakefulness, whereas selectively silencing the activity of this circuit decreases time spent in wakefulness. Specifically, chemogenetic inhibition of CeA-projecting PVT neurons not only alleviates stress responses but also attenuates the acute stress-induced increase of wakefulness. Thus, our results demonstrate that the PVT-CeA circuit controls physiological wakefulness and modulates acute stress-induced heightened wakefulness.

Raphe serotonin projections dynamically regulate feeding behavior through targeting inhibitory circuits from rostral zona incerta to paraventricular thalamus

OBJECTIVE

Rostral zona incerta (ZIR) evokes feeding by sending GABA transmission to paraventricular thalamus (PVT). Although central serotonin (5-HT) signaling is known to play critical roles in the regulation of food intake and eating disorders, it remains unknown whether raphe 5-HT neurons functionally innervate ZIR-PVT neural pathway for feeding control. Here, we sought to reveal how raphe 5-HT signaling regulates both ZIR and PVT for feeding control.

METHODS

We used retrograde neural tracers to map 5-HT projections in Sert-Cre mice and slice electrophysiology to examine the mechanism by which 5-HT modulates ZIR GABA neurons. We also used optogenetics to test the effects of raphe-ZIR and raphe-PVT 5-HT projections on feeding motivation and food intake in mice regularly fed, 24 h fasted, and with intermittent high-fat high-sugar (HFHS) diet. In addition, we applied RNAscope in situ hybridization to identify 5-HT receptor subtype mRNA in ZIR.

RESULTS

We show raphe 5-HT neurons sent projections to both ZIR and PVT with partial collateral axons. Photostimulation of 5-HT projections inhibited ZIR but excited PVT neurons to decrease motivated food consumption. However, both acute food deprivation and intermittent HFHS diet downregulated 5-HT inhibition on ZIR GABA neurons, abolishing the inhibitory regulation of raphe-ZIR 5-HT projections on feeding motivation and food intake. Furthermore, we found high-level 5-HT1a and 5-HT2c as well as low-level 5-HT7 mRNA expression in ZIR. Intermittent HFHS diet increased 5-HT7 but not 5-HT1a or 5-HT2c mRNA levels in the ZIR.

CONCLUSIONS

Our results reveal that raphe-ZIR 5-HT projections dynamically regulate ZIR GABA neurons for feeding control, supporting that a dynamic fluctuation of ZIR 5-HT inhibition authorizes daily food intake but a sustained change of ZIR 5-HT signaling leads to overeating induced by HFHS diet.

Sex differences in electrophysiological properties and voltage-gated ion channel expression in the paraventricular thalamic nucleus following repeated stress

Background

Habituation to repeated stress refers to a progressive reduction in the stress response following multiple exposures to the same, predictable stressor. We previously demonstrated that the posterior division of the paraventricular thalamic nucleus (pPVT) nucleus regulates habituation to 5 days of repeated restraint stress in male rats. Compared to males, female rats display impaired habituation to 5 days of restraint. To better understand how activity of pPVT neurons is differentially impacted in stressed males and females, we examined the electrophysiological properties of pPVT neurons under baseline conditions or following restraint.

Methods

Adult male and female rats were exposed to no stress (handling only), a single period of 30 min restraint or 5 daily exposures to 30 min restraint. 24 h later, pPVT tissue was prepared for recordings.

Results

We report here that spontaneous excitatory post-synaptic current (sEPSC) amplitude was increased in males, but not females, following restraint. Furthermore, resting membrane potential of pPVT neurons was more depolarized in males. This may be partially due to reduced potassium leakage in restrained males as input resistance was increased in male, but not female, rats 24 h following 1 or 5 days of 30-min restraint. Reduced potassium efflux during action potential firing also occurred in males following a single restraint as action potential half-width was increased following a single restraint. Restraint had limited effects on electrophysiological properties in females, although the mRNA for 10 voltage-gated ion channel subunits was altered in the pPVT of female rats.

Conclusions

The results suggest that restraint-induced changes in pPVT activation promote habituation in males. These findings are the first to describe a sexual dimorphism in stress-induced electrophysiological properties and voltage-gated ion channel expression in the pPVT. These results may explain, at least in part, why habituation to 5 days of restraint is disrupted in female rats.

Male, but not female, pPVT neurons display increases in EPSC amplitude and decay time 24 h following one and five restraints.

Input resistance is increased 24 h following one and five restraints in male, but not female, pPVT neurons.

Afterhyperpolarization potential is greater in pPVT neurons of females compared to males, regardless of restraint.

Restraint alters the expression of 10 voltage-gated ion channel transcripts in the pPVT of females, but only 3 in males.

Structural and functional organization of the midline and intralaminar nuclei of the thalamus

The midline and intralaminar nuclei of the thalamus form a major part of the "limbic thalamus;" that is, thalamic structures anatomically and functionally linked with the limbic forebrain. The midline nuclei consist of the paraventricular (PV) and paratenial nuclei, dorsally and the rhomboid and nucleus reuniens (RE), ventrally. The rostral intralaminar nuclei (ILt) consist of the central medial (CM), paracentral (PC) and central lateral (CL) nuclei. We presently concentrate on RE, PV, CM and CL nuclei of the thalamus. The nucleus reuniens receives a diverse array of input from limbic-related sites, and predominantly projects to the hippocampus and to "limbic" cortices. The RE participates in various cognitive functions including spatial working memory, executive functions (attention, behavioral flexibility) and affect/fear behavior. The PV receives significant limbic-related afferents, particularly the hypothalamus, and mainly distributes to "affective" structures of the forebrain including the bed nucleus of stria terminalis, nucleus accumbens and the amygdala. Accordingly, PV serves a critical role in "motivated behaviors" such as arousal, feeding/consummatory behavior and drug addiction. The rostral ILt receives both limbic and sensorimotor-related input and distributes widely over limbic and motor regions of the frontal cortex-and throughout the dorsal striatum. The intralaminar thalamus is critical for maintaining consciousness and directly participates in various sensorimotor functions (visuospatial or reaction time tasks) and cognitive tasks involving striatal-cortical interactions. As discussed herein, while each of the midline and intralaminar nuclei are anatomically and functionally distinct, they collectively serve a vital role in several affective, cognitive and executive behaviors - as major components of a brainstem-diencephalic-thalamocortical circuitry.

The influence of the subcortex and brain stem on overeating: How advances in functional neuroimaging can be applied to expand neurobiological models to beyond the cortex

Functional neuroimaging has become a widely used tool in obesity and eating disorder research to explore the alterations in neurobiology that underlie overeating and binge eating behaviors. Current and traditional neurobiological models underscore the importance of impairments in brain systems supporting reward, cognitive control, attention, and emotion regulation as primary drivers for overeating. Due to the technical limitations of standard field strength functional magnetic resonance imaging (fMRI) scanners, human neuroimaging research to date has focused largely on cortical and basal ganglia effects on appetitive behaviors. The present review draws on animal and human research to highlight how neural signaling encoding energy regulation, reward-learning, and habit formation converge on hypothalamic, brainstem, thalamic, and striatal regions to contribute to overeating in humans. We also consider the role of regions such as the mediodorsal thalamus, ventral striatum, lateral hypothalamus and locus coeruleus in supporting habit formation, inhibitory control of food craving, and attentional biases. Through these discussions, we present proposals on how the neurobiology underlying these processes could be examined using functional neuroimaging and highlight how ultra-high field 7-Tesla (7 T) fMRI may be leveraged to elucidate the potential functional alterations in subcortical networks. Focus is given to how interactions of these regions with peripheral endocannabinoids and neuropeptides, such as orexin, could be explored. Technical and methodological aspects regarding the use of ultra-high field 7 T fMRI to study eating behaviors are also reviewed.

Maternal Methamphetamine Exposure Influences Behavioral Sensitization and Nucleus Accumbens DNA Methylation in Subsequent Generation

The deleterious effects of methamphetamine (METH) exposure extend beyond abusers, and may potentially impact the vulnerability of their offspring in developing addictive behaviors. Epigenetic signatures have been implicated in addiction, yet the characteristics to identify prenatal METH abuse to offspring addiction risk remains elusive. Here, we used escalating doses of METH-exposed mouse model in F0 female mice before and during pregnancy to simulate the human pattern of drug abuse and generated METH-induced behavioral sensitization to investigate the addictive behavior in offspring mice. We then utilized whole genome-bisulfite sequencing (WGBS) to investigate the methylation signature of nucleus accumbens (NAc) in male METH-sensitized mice. Interestingly, male but not female offspring exhibited an enhanced response to METH-induced behavioral sensitization. Additionally, the METH-exposed group of male mice underwent a more comprehensive wave of epigenome remodeling over all genomic elements compared with unexposed groups due to drug exposure history. 104,219 DMCs (METH-SAL vs. SAL-SAL) induced by prenatal METH-exposure were positively correlated with that of postnatal METH-exposure (38,570, SAL-METH vs. SAL-SAL). Moreover, 4,983 DMCs induced by pre- and postnatal METH exposure (METH-METH vs. SAL-METH) were negatively correlated with that of postnatal METH exposure, and 371 commonly changed DMCs between the two comparison groups also showed a significantly negative correlation and 86 annotated genes functionally enriched in the pathways of neurodevelopment and addiction. Key annotated genes included Kirrel3, Lrpprc, and Peg3, implicated in neurodevelopmental processes, were down-regulated in METH-METH group mice compared with the SAL-METH group. Taken together, we render novel insights into the epigenetic correlation of drug exposure and provide evidence for epigenetic characteristics that link maternal METH exposure to the intensity of the same drug-induced behavioral sensitization in adult offspring.

The Effects of Prenatal Exposure to Neighborhood Crime on Neonatal Functional Connectivity

BACKGROUND

Maternal exposure to adversity during pregnancy has been found to affect infant brain development; however, the specific effect of prenatal crime exposure on neonatal brain connectivity remains unclear. Based on existing research, we hypothesized that living in a high-crime neighborhood during pregnancy would affect neonatal frontolimbic connectivity over and above other individual- and neighborhood-level adversity and that these associations would be mediated by maternal psychosocial stress.

METHODS

Participants included 399 pregnant women, recruited as part of the eLABE (Early Life Adversity, Biological Embedding, and Risk for Developmental Precursors of Mental Disorders) study. In the neonatal period, 319 healthy, nonsedated infants were scanned using resting-state functional magnetic resonance imaging (repetition time = 800 ms; echo time = 37 ms; voxel size = 2.0 × 2.0 × 2.0 mm3; multiband = 8) on a Prisma 3T scanner and had at least 10 minutes of high-quality data. Crime data at the block group level were obtained from Applied Geographic Solution. Linear regressions and mediation models tested associations between crime, frontolimbic connectivity, and psychosocial stress.

RESULTS

Living in a neighborhood with high property crime during pregnancy was related to weaker neonatal functional connectivity between the thalamus-anterior default mode network (aDMN) (β = -0.15, 95% CI = -0.25 to -0.04, p = .008). Similarly, high neighborhood violent crime was related to weaker functional connectivity between the thalamus-aDMN (β = -0.16, 95% CI = -0.29 to -0.04, p = .01) and amygdala-hippocampus (β = -0.16, 95% CI = -0.29 to -0.03, p = .02), controlling for other types of adversity. Psychosocial stress partially mediated relationships between the thalamus-aDMN and both violent and property crime.

CONCLUSIONS

These findings suggest that prenatal exposure to crime is associated with weaker neonatal limbic and frontal functional brain connections, providing another reason for targeted public policy interventions to reduce crime.

Convergence of monosynaptic inputs from neurons in the brainstem and forebrain on parabrachial neurons that project to the paraventricular nucleus of the thalamus

The paraventricular nucleus of the thalamus (PVT) projects to areas of the forebrain involved in regulating behavior. Homeostatic challenges and salient cues activate the PVT and evidence shows that the PVT regulates appetitive and aversive responses. The brainstem is a source of afferents to the PVT and the present study was done to determine if the lateral parabrachial nucleus (LPB) is a relay for inputs to the PVT. Retrograde tracing experiments with cholera toxin B (CTB) demonstrate that the LPB contains more PVT projecting neurons than other regions of the brainstem including the catecholamine cell groups. The hypothesis that the LPB is a relay for signals to the PVT was assessed using an intersectional monosynaptic rabies tracing approach. Sources of inputs to LPB included the reticular formation; periaqueductal gray (PAG); nucleus cuneiformis; and superior and inferior colliculi. Distinctive clusters of input cells to LPB-PVT projecting neurons were also found in the dorsolateral bed nucleus of the stria terminalis (BSTDL) and the lateral central nucleus of the amygdala (CeL). Anterograde viral tracing demonstrates that LPB-PVT neurons densely innervate all regions of the PVT in addition to providing collateral innervation to the preoptic area, lateral hypothalamus, zona incerta and PAG but not the BSTDL and CeL. The paper discusses the anatomical evidence that suggests that the PVT is part of a network of interconnected neurons involved in arousal, homeostasis, and the regulation of behavioral states with forebrain regions potentially providing descending modulation or gating of signals relayed from the LPB to the PVT.

Arc-Mediated Plasticity in the Paraventricular Thalamic Nucleus Promotes Habituation to Stress

BACKGROUND

Habituation is defined as a progressive decline in response to repeated exposure to a familiar and predictable stimulus and is highly conserved across species. Disrupted habituation is a signature of posttraumatic stress disorder. In rodents, habituation is observed in neural, neuroendocrine, and behavioral responses to repeated exposure to predictable and moderately intense stress or restraint. We previously demonstrated that lesioning the posterior paraventricular thalamic nucleus (pPVT) impairs habituation. However, the underlying molecular mechanisms and specific neural connections among the pPVT and other brain regions that underlie habituation are unknown.

METHODS

Behavioral and neuroendocrine habituation was assessed in adult male Sprague Dawley rats using the repeated restraint paradigm. Pan-neuronal and Cre-dependent DREADDs (designer receptors exclusively activated by designer drugs) were used to chemogenetically inhibit the pPVT and the subpopulation of pPVT neurons that project to the medial prefrontal cortex (mPFC), respectively. Activity-regulated cytoskeleton-associated protein (Arc) expression was knocked down in the pPVT using small interfering RNA. Structural plasticity of pPVT neurons was assessed using Golgi staining. Local field potential recordings were used to assess coherent neural activity between the pPVT and mPFC. The attentional set shifting task was used to assess mPFC-dependent behavior.

RESULTS

Here, we show that Arc promotes habituation by increasing stress-induced spinogenesis in the pPVT, increasing coherent neural activity with the mPFC, and improving mPFC-mediated cognitive flexibility.

CONCLUSIONS

Our results demonstrate that Arc induction in the pPVT regulates habituation and mPFC function. Therapies that improve synaptic plasticity during posttraumatic stress disorder therapy may enhance habituation and the efficacy of posttraumatic stress disorder treatment.

Hindbrain catecholaminergic inputs to the paraventricular thalamus scale feeding and metabolic efficiency in stress-related contexts

The regulation of food intake and energy balance relies on the dynamic integration of exteroceptive and interoceptive signals monitoring nutritional, metabolic, cognitive, and emotional states. The paraventricular thalamus (PVT) is a central hub that, by integrating sensory, metabolic, and emotional states, may contribute to the regulation of feeding and homeostatic/allostatic processes. However, the underlying PVT circuits still remain elusive. Here, we aimed at unravelling the role of catecholaminergic (CA) inputs to the PVT in scaling feeding and metabolic efficiency. First, using region-specific retrograde disruption of CA projections, we show that PVT CA inputs mainly arise from the hindbrain, notably the locus coeruleus (LC) and the nucleus tractus solitarius. Second, taking advantage of integrative calorimetric measurements of metabolic efficiency, we reveal that CA inputs to the PVT scale adaptive feeding and metabolic responses in environmental, behavioural, physiological, and metabolic stress-like contexts. Third, we show that hindbrain^TH →PVT inputs contribute to modulating the activity of PVT as well as lateral and dorsomedial hypothalamic neurons. In conclusion, the present study, by assessing the key role of CA inputs to the PVT in scaling homeostatic/allostatic regulations of feeding patterns, reveals the integrative and converging hindbrain^TH →PVT paths that contribute to whole-body metabolic adaptations in stress-like contexts. KEY POINTS: The paraventricular thalamus (PVT) is known to receive projections from the hindbrain. Here, we confirm and further extend current knowledge on the existence of hindbrain^TH →PVT catecholaminergic inputs, notably from the locus coeruleus and the nucleus tractus solitarius, with the nucleus tractus solitarius representing the main source. Disruption of hindbrain^TH →PVT inputs contributes to the modulation of PVT neuron activity. Hindbrain^TH →PVT inputs scale feeding strategies in environmental, behavioural, physiological, and metabolic stress-like contexts. Hindbrain^TH →PVT inputs participate in regulating metabolic efficiency and nutrient partitioning in stress-like contexts. Hindbrain^TH →PVT inputs, directly and/or indirectly, contribute to modulating the downstream activity of lateral and dorsomedial hypothalamic neurons.

Eating driven by the gustatory insula: contrasting regulation by infralimbic vs. prelimbic cortices

Subregions within insular cortex and medial prefrontal cortex (mPFC) have been implicated in eating disorders; however, the way these brain regions interact to produce dysfunctional eating is poorly understood. The present study explored how two mPFC subregions, the infralimbic (IL) and prelimbic (PRL) cortices, regulate sucrose hyperphagia elicited specifically by a neurochemical manipulation of the agranular/dysgranular region of gustatory insula (AI/DI). Using intra-AI/DI infusion of the mu-opioid receptor (µ-OR) agonist, DAMGO (1 µg), sucrose hyperphagia was generated in ad-libitum-maintained rats, while in the same rat, either the IL or prelimbic (PRL) subregion of mPFC was inactivated bilaterally with muscimol (30 ng). Intra-IL muscimol markedly potentiated AI/DI DAMGO-induced sucrose hyperphagia by increasing eating bout duration and food consumption per bout. In contrast, PRL attenuated intra-AI/DI DAMGO-driven sucrose intake and feeding duration and eliminated the small DAMGO-induced increase in feeding bout initiation. Intra-IL or -PRL muscimol alone (i.e., without intra-AI/DI DAMGO) did not alter feeding behavior, but slightly reduced exploratory-like rearing in both mPFC subregions. These results reveal anatomical heterogeneity in mPFC regulation of the intense feeding-motivational state engendered by µ-OR signaling in the gustatory insula: IL significantly curtails consummatory activity, while PRL modestly contributes to feeding initiation. Results are discussed with regard to potential circuit-based mechanisms that may underlie the observed results.

Oxytocin Receptor-Expressing Neurons in the Paraventricular Thalamus Regulate Feeding Motivation through Excitatory Projections to the Nucleus Accumbens Core

Oxytocin receptors (OTR) have been found in the paraventricular thalamus (PVT) for the regulation of feeding and maternal behaviors. However, the functional projections of OTR-expressing PVT neurons remain largely unknown. Here, we used chemogenetic and optogenetic tools to test the role of OTR-expressing PVT neurons and their projections in the regulation of food intake in both male and female OTR-Cre mice. We found chemogenetic activation of OTR-expressing PVT neurons promoted food seeking under trials with a progressive ratio schedule of reinforcement. Using Feeding Experimentation Devices for real-time meal measurements, we found chemogenetic activation of OTR-expressing PVT neurons increased meal frequency but not cumulative food intake because of a compensatory decrease in meal sizes. In combination with anterograde neural tracing and slice patch-clamp recordings, we found optogenetic stimulation of PVT OTR terminals excited neurons in the posterior basolateral amygdala (pBLA) and nucleus accumbens core (NAcC) as well as local PVT neurons through monosynaptic glutamatergic transmissions. Photostimulation of OTR-expressing PVT-NAcC projections promoted food-seeking, whereas selective activation of PVT-pBLA projections produced little effect on feeding. In contrast to selective activation of OTR terminals, photostimulation of a broader population of glutamatergic PVT terminals exerted direct excitation followed by indirect lateral inhibition on neurons in both NAcC and anterior basolateral amygdala. Together, these results suggest that OTR-expressing PVT neurons are a distinct population of PVT glutamate neurons that regulate feeding motivation through projections to NAcC.SIGNIFICANCE STATEMENT The paraventricular thalamus plays an important role in the regulation of feeding motivation. However, because of the diversity of paraventricular thalamic neurons, the specific neuron types promoting food motivation remain elusive. In this study, we provide evidence that oxytocin receptor-expressing neurons are a specific group of glutamate neurons that primarily project to the nucleus accumbens core and posterior amygdala. We found that activation of these neurons promotes the motivation for food reward and increases meal frequency through projections to the nucleus accumbens core but not the posterior amygdala. As a result, we postulate that oxytocin receptor-expressing neurons in the paraventricular thalamus and their projections to the nucleus accumbens core mainly regulate feeding motivation but not food consumption.

PBN-PVT projections modulate negative affective states in mice

Long-lasting negative affections dampen enthusiasm for life, and dealing with negative affective states is essential for individual survival. The parabrachial nucleus (PBN) and thalamic paraventricular nucleus (PVT) are critical for modulating affective states in mice. However, the functional roles of PBN-PVT projections in modulating affective states remain elusive. Here, we show that PBN neurons send dense projection fibers to the PVT and form direct excitatory synapses with PVT neurons. Activation of the PBN-PVT pathway induces robust behaviors associated with negative affective states without affecting nociceptive behaviors. Inhibition of the PBN-PVT pathway reduces aversion-like and fear-like behaviors. Furthermore, the PVT neurons innervated by the PBN are activated by aversive stimulation, and activation of PBN-PVT projections enhances the neuronal activity of PVT neurons in response to the aversive stimulus. Consistently, activation of PVT neurons that received PBN-PVT projections induces anxiety-like behaviors. Thus, our study indicates that PBN-PVT projections modulate negative affective states in mice.

Ghrelin mediated regulation of neurosynaptic transmitters in depressive disorders

Ghrelin is a peptide released by the endocrine cells of the stomach and the neurons in the arcuate nucleus of the hypothalamus. It modulates both peripheral and central functions. Although ghrelin has emerged as a potent stimulator of growth hormone release and as an orexigenic neuropeptide, the wealth of literature suggests its involvement in the pathophysiology of affective disorders including depression. Ghrelin exhibits a dual role through the advancement and reduction of depressive behavior with nervousness in the experimental animals. It modulates depression-related signals by forming neuronal networks with various neuropeptides and classical neurotransmitter systems. The present review emphasizes the integration and signaling of ghrelin with other neuromodulatory systems concerning depressive disorders. The role of ghrelin in the regulation of neurosynaptic transmission and depressive illnesses implies that the ghrelin system modulation can yield promising antidepressive therapies.

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Ghrelin is the orexigenic type of neuropeptide.

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It binds with the growth hormone secretagogue receptor (GHSR).

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GHSR is ubiquitously present in the various brain regions.

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Ghrelin is involved in the regulation of depression-related behavior.

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The review focuses on the neurotransmission and signaling of ghrelin in neuropsychiatric and depressive disorders.

Reviewing the role of the orexinergic system and stressors in modulating mood and reward-related behaviors

In this review study, we aimed to introduce the orexinergic system as an important signaling pathway involved in a variety of cognitive functions such as memory, motivation, and reward-related behaviors. This study focused on the role of orexinergic system in modulating reward-related behavior, with or without the presence of stressors. Cross-talk between the reward system and orexinergic signaling was also investigated, especially orexinergic signaling in the ventral tegmental area (VTA), the nucleus accumbens (NAc), and the hippocampus. Furthermore, we discussed the role of the orexinergic system in modulating mood states and mental illnesses such as depression, anxiety, panic, and posttraumatic stress disorder (PTSD). Here, we narrowed down our focus on the orexinergic signaling in three brain regions: the VTA, NAc, and the hippocampus (CA1 region and dentate gyrus) for their prominent role in reward-related behaviors and memory. It was concluded that the orexinergic system is critically involved in reward-related behavior and significantly alters stress responses and stress-related psychiatric and mood disorders.

Bipolar Disorder: From Pathophysiology to Treatment

Bipolar disorder is a mental disorder that involves a manic or hypomanic state and a depressive state, and was once called manic-depressive disorder and was considered one of the two major mental disorders along with schizophrenia. Major depressive disorder, on the other hand, is a disorder in which only depressive states occur, and the two are sometimes referred to together as "mood disorders. This review will introduce the pathophysiology, diagnosis, epidemiology, and treatment of bipolar disorder, focusing on the current situation in Japan.

MeCP2 haplodeficiency and early-life stress interaction on anxiety-like behavior in adolescent female mice

BACKGROUND

Early-life stress can leave persistent epigenetic marks that may modulate vulnerability to psychiatric conditions later in life, including anxiety, depression and stress-related disorders. These are complex disorders with both environmental and genetic influences contributing to their etiology. Methyl-CpG Binding Protein 2 (MeCP2) has been attributed a key role in the control of neuronal activity-dependent gene expression and is a master regulator of experience-dependent epigenetic programming. Moreover, mutations in the MECP2 gene are the primary cause of Rett syndrome and, to a lesser extent, of a range of other major neurodevelopmental disorders. Here, we aim to study the interaction of MeCP2 with early-life stress in variables known to be affected by this environmental manipulation, namely anxiety-like behavior and activity of the underlying neural circuits.

METHODS

Using Mecp2 heterozygous and wild-type female mice we investigated the effects of the interaction of Mecp2 haplodeficiency with maternal separation later in life, by assessing anxiety-related behaviors and measuring concomitant c-FOS expression in stress- and anxiety-related brain regions of adolescent females. Moreover, arginine vasopressin and corticotropin-releasing hormone neurons of the paraventricular hypothalamic nucleus were analyzed for neuronal activation.

RESULTS

In wild-type mice, maternal separation caused a reduction in anxiety-like behavior and in the activation of the hypothalamic paraventricular nucleus, specifically in corticotropin-releasing hormone-positive cells, after the elevated plus maze. This effect of maternal separation was not observed in Mecp2 heterozygous females that per se show decreased anxiety-like behavior and concomitant decreased paraventricular nuclei activation.

CONCLUSIONS

Our data supports that MeCP2 is an essential component of HPA axis reprogramming and underlies the differential response to anxiogenic situations later in life.

Aversive stimuli bias corticothalamic responses to motivationally significant cues

Making predictions about future rewards or punishments is fundamental to adaptive behavior. These processes are influenced by prior experience. For example, prior exposure to aversive stimuli or stressors changes behavioral responses to negative- and positive-value predictive cues. Here, we demonstrate a role for medial prefrontal cortex (mPFC) neurons projecting to the paraventricular nucleus of the thalamus (PVT; mPFC→PVT) in this process. We found that a history of aversive stimuli negatively biased behavioral responses to motivationally relevant cues in mice and that this negative bias was associated with hyperactivity in mPFC→PVT neurons during exposure to those cues. Furthermore, artificially mimicking this hyperactive response with selective optogenetic excitation of the same pathway recapitulated the negative behavioral bias induced by aversive stimuli, whereas optogenetic inactivation of mPFC→PVT neurons prevented the development of the negative bias. Together, our results highlight how information flow within the mPFC→PVT circuit is critical for making predictions about motivationally-relevant outcomes as a function of prior experience.

Hypoactive Thalamic Crh+ Cells in a Female Mouse Model of Alcohol Drinking After Social Trauma

BACKGROUND

Comorbid stress-induced mood and alcohol use disorders are increasingly prevalent among female patients. Stress exposure can disrupt salience processing and goal-directed decision making, contributing to persistent maladaptive behavioral patterns; these and other stress-sensitive cognitive and behavioral processes rely on dynamic and coordinated signaling by midline and intralaminar thalamic nuclei. Considering the role of social trauma in the trajectory of these debilitating psychopathologies, identifying vulnerable thalamic cells may provide guidance for targeting persistent stress-induced symptoms.

METHODS

A novel behavioral protocol traced the progression from social trauma to the development of social defensiveness and chronically escalated alcohol consumption in female mice. Recent cell activation-measured as cFos-was quantified in thalamic cells after safe social interactions, revealing stress-sensitive corticotropin-releasing hormone-expressing (Crh+) anterior central medial thalamic (aCMT) cells. These cells were optogenetically stimulated during stress-induced social defensiveness and abstinence-escalated binge drinking.

RESULTS

Crh+ aCMT neurons exhibited substantial activation after social interactions in stress-naïve but not in stressed female mice. Photoactivating Crh+ aCMT cells dampened stress-induced social deficits, whereas inhibiting these cells increased social defensiveness in stress-naïve mice. Optogenetically activating Crh+ aCMT cells diminished abstinence-escalated binge alcohol drinking in female mice, regardless of stress history.

CONCLUSIONS

This work uncovers a role for Crh+ aCMT neurons in maladaptive stress-induced social interactions and in binge drinking after forced abstinence in female mice. This molecularly defined thalamic cell population may serve as a critical stress-sensitive hub for social deficits caused by exposure to social trauma and for patterns of excessive alcohol drinking in female populations.

Circadian rhythms and pain

The goal of this review is to provide a perspective on the nature and importance of the relationship between the circadian and pain systems. We provide: 1) An overview of the circadian and pain systems, 2) a review of direct and correlative evidence that demonstrates diurnal and circadian rhythms within the pain system; 3) a perspective highlighting the need to consider the role of a proposed feedback loop of circadian rhythm disruption and maladaptive pain; 4) a perspective on the nature of the relationship between circadian rhythms and pain. In summary, we propose that there is no single locus responsible for producing the circadian rhythms of the pain system. Instead, circadian rhythms of pain are a complex result of the distributed rhythms present throughout the pain system, especially those of the descending pain modulatory system, and the rhythms of the systems with which it interacts, including the opioid, endocrine, and immune systems.

Vision for action: thalamic and cortical inputs to the macaque superior parietal lobule

The dorsal visual stream, the cortical circuit that in the primate brain is mainly dedicated to the visual control of actions, is split into two routes, a lateral and a medial one, both involved in coding different aspects of sensorimotor control of actions. The lateral route, named "lateral grasping network", is mainly involved in the control of the distal part of prehension, namely grasping and manipulation. The medial route, named "reach-to-grasp network", is involved in the control of the full deployment of prehension act, from the direction of arm movement to the shaping of the hand according to the object to be grasped. In macaque monkeys, the reach-to-grasp network (the target of this review) includes areas of the superior parietal lobule (SPL) that hosts visual and somatosensory neurons well suited to control goal-directed limb movements toward stationary as well as moving objects. After a brief summary of the neuronal functional properties of these areas, we will analyze their cortical and thalamic inputs thanks to retrograde neuronal tracers separately injected into the SPL areas V6, V6A, PEc, and PE. These areas receive visual and somatosensory information distributed in a caudorostral, visuosomatic trend, and some of them are directly connected with the dorsal premotor cortex. This review is particularly focused on the origin and type of visual information reaching the SPL, and on the functional role this information can play in guiding limb interaction with objects in structured and dynamic environments.

Extinction blunts paraventricular thalamic contributions to heroin relapse

Here, we use optogenetics and chemogenetics to investigate the contribution of the paraventricular thalamus (PVT) to nucleus accumbens (NAc) pathway in aversion and heroin relapse in two different heroin self-administration models in rats. In one model, rats undergo forced abstinence in the home cage prior to relapse testing, and in the other, they undergo extinction training, a procedure that is likened to cognitive behavioral therapy. We find that the PVT→NAc pathway is both sufficient and necessary to drive aversion and heroin seeking after abstinence, but not extinction. The ability of extinction to reduce this pathway's contribution to heroin relapse is accompanied by a loss of synaptic plasticity in PVT inputs onto a specific subset of NAc neurons. Thus, extinction may exert therapeutic reductions in opioid seeking by altering synaptic plasticity within the PVT→NAc pathway, resulting in reduced aversion during opioid withdrawal as well as reduced relapse propensity.

Blockade of corticotropin-releasing factor receptor 1 in the central amygdala prevents cocaine-seeking behaviour induced by orexin-A administered to the posterior paraventricular nucleus of the thalamus in male rats

BACKGROUND

Orexin-A (OrxA) administration in the posterior paraventricular nucleus of the thalamus (pPVT) reinstates extinguished cocaine-seeking behaviour following extended access to the drug (a model of dependence). The pPVT receives and integrates information associated with emotionally salient events and sends excitatory inputs to brain regions involved in the expression of emotional states, such as those driving cocaine-seeking behaviour (i.e., the nucleus accumbens, the central nucleus of the amygdala [CeA], the basolateral amygdala, the bed nucleus of the stria terminalis [BNST] and the prefrontal cortex).

METHODS

We monitored the activation pattern of these regions (measured by Fos) during cocaine-seeking induced by OrxA administered to the pPVT. The BNST and CeA emerged as being selectively activated. To test whether the functionality of these regions was pivotal during OrxA-induced cocaine-seeking behaviour, we transiently inactivated these regions concomitantly with OrxA administration to the pPVT. We then tested the participation of corticotropin-releasing factor receptors (CRF1) in the CeA during OrxA-induced cocaine-seeking using the CRF1 antagonist CP154526.

RESULTS

We observed selective activation of the CeA and BNST during cocaine-seeking induced by OrxA administered to the pPVT, but only transient inactivation of the CeA prevented cocaine-seeking behaviour. Administration of CP154526 to the CeA prevented OrxAinduced cocaine-seeking behaviour.

LIMITATIONS

The use of only male rats could have been a limitation. Other limitations could have been the use of an indirect approach to test the hypothesis that administration of OrxA to the pPVT drives cocaine-seeking via CRF1 signalling in the CeA, and a lack of analysis of the participation of CeA subregions.

CONCLUSION

Cocaine-seeking behaviour induced by OrxA administered to the pPVT is driven by activation of the CeA via CRF1 signalling.

Thalamo-Nucleus Accumbens Projections in Motivated Behaviors and Addiction

The ventral striatum, also called nucleus accumbens (NAc), has long been known to integrate information from cortical, thalamic, midbrain and limbic nuclei to mediate goal-directed behaviors. Until recently thalamic afferents have been overlooked when studying the functions and connectivity of the NAc. However, findings from recent studies have shed light on the importance and roles of precise Thalamus to NAc connections in motivated behaviors and in addiction. In this review, we summarize studies using techniques such as chemo- and optogenetics, electrophysiology and in vivo calcium imaging to elucidate the complex functioning of the thalamo-NAc afferents, with a particular highlight on the projections from the Paraventricular Thalamus (PVT) to the NAc. We will focus on the recent advances in the understanding of the roles of these neuronal connections in motivated behaviors, with a special emphasis on their implications in addiction, from cue-reward association to the mechanisms driving relapse.

The Paraventricular Thalamus as a Critical Node of Motivated Behavior via the Hypothalamic-Thalamic-Striatal Circuit

In this review, we highlight evidence that supports a role for the paraventricular nucleus of the thalamus (PVT) in motivated behavior. We include a neuroanatomical and neurochemical overview, outlining what is known of the cellular makeup of the region and its most prominent afferent and efferent connections. We discuss how these connections and distinctions across the anterior-posterior axis correspond to the perceived function of the PVT. We then focus on the hypothalamic-thalamic-striatal circuit and the neuroanatomical and functional placement of the PVT within this circuit. In this regard, the PVT is ideally positioned to integrate information regarding internal states and the external environment and translate it into motivated actions. Based on data that has emerged in recent years, including that from our laboratory, we posit that orexinergic (OX) innervation from the lateral hypothalamus (LH) to the PVT encodes the incentive motivational value of reward cues and thereby alters the signaling of the glutamatergic neurons projecting from the PVT to the shell of the nucleus accumbens (NAcSh). The PVT-NAcSh pathway then modulates dopamine activity and resultant cue-motivated behaviors. As we and others apply novel tools and approaches to studying the PVT we will continue to refine the anatomical, cellular, and functional definitions currently ascribed to this nucleus and further elucidate its role in motivated behaviors.

From Brain Organoids to Networking Assembloids: Implications for Neuroendocrinology and Stress Medicine

Brain organoids are three-dimensional cultures that contain multiple types of cells and cytoarchitectures, and resemble fetal human brain structurally and functionally. These organoids are being used increasingly to model brain development and disorders, however, they only partially recapitulate such processes, because of several limitations, including inability to mimic the distinct cortical layers, lack of functional neuronal circuitry as well as non-neural cells and gyrification, and increased cellular stress. Efforts to create improved brain organoid culture systems have led to region-specific organoids, vascularized organoids, glia-containing organoids, assembloids, sliced organoids and polarized organoids. Assembloids are fused region-specific organoids, which attempt to recapitulate inter-regional and inter-cellular interactions as well as neural circuitry development by combining multiple brain regions and/or cell lineages. As a result, assembloids can be used to model subtle functional aberrations that reflect complex neurodevelopmental, neuropsychiatric and neurodegenerative disorders. Mammalian organisms possess a highly complex neuroendocrine system, the stress system, whose main task is the preservation of systemic homeostasis, when the latter is threatened by adverse forces, the stressors. The main central parts of the stress system are the paraventricular nucleus of the hypothalamus and the locus caeruleus/norepinephrine-autonomic nervous system nuclei in the brainstem; these centers innervate each other and interact reciprocally as well as with various other CNS structures. Chronic dysregulation of the stress system has been implicated in major pathologies, the so-called chronic non-communicable diseases, including neuropsychiatric, neurodegenerative, cardiometabolic and autoimmune disorders, which lead to significant population morbidity and mortality. We speculate that brain organoids and/or assembloids could be used to model the development, regulation and dysregulation of the stress system and to better understand stress-related disorders. Novel brain organoid technologies, combined with high-throughput single-cell omics and gene editing, could, thus, have major implications for precision medicine.

Extensive divergence of projections to the forebrain from neurons in the paraventricular nucleus of the thalamus

Neurons in the paraventricular nucleus of the thalamus (PVT) respond to emotionally salient events and project densely to subcortical regions known to mediate adaptive behavioral responses. The areas of the forebrain most densely innervated by the PVT include striatal-like subcortical regions that consist of the shell of the nucleus accumbens (NAcSh), the dorsolateral region of the bed nucleus of the stria terminalis (BSTDL) and the lateral-capsular division of the central nucleus of the amygdala (CeL). A recent tracing experiment demonstrated that the PVT is composed of two intermixed populations of neurons that primarily project to either the dorsomedial (dmNAcSh) or ventromedial region of the NAcSh (vmNAcSh) with many of the vmNAcSh projecting neurons providing collateral innervation of the BSTDL and CeL. The present study used triple injections of the retrograde tracer cholera toxin B to provide a detailed map of the location of PVT neurons that provide collaterals to the vmNAcSh, BSTDL and CeL. These neurons were intermixed throughout the PVT and did not form uniquely localized subpopulations. An intersectional viral anterograde tracing approach was used to demonstrate that regardless of its presumed target of innervation (dmNAcSh, vmNAcSh, BSTDL, or CeL), most neurons in the PVT provide collateral innervation to a common set of forebrain regions. The paper shows that PVT-dmNAcSh projecting neurons provide the most divergent projection system and that these neurons express the immediate early gene product cFos following an aversive incident. We propose that the PVT may regulate a broad range of responses to physiological and psychological challenges by simultaneously influencing functionally diverse regions of the forebrain that include the cortex, striatal-like regions in the basal forebrain and a number of hypothalamic nuclei.

Distinct Transcriptomic Cell Types and Neural Circuits of the Subiculum and Prosubiculum along the Dorsal-Ventral Axis

Subicular regions play important roles in spatial processing and many cognitive functions, and these are mainly attributed to the subiculum (Sub) rather than the prosubiculum (PS). Using single-cell RNA sequencing, we identify 27 transcriptomic cell types residing in sub-domains of the Sub and PS. Based on in situ expression of reliable transcriptomic markers, the precise boundaries of the Sub and PS are consistently defined along the dorsoventral axis. Using these borders to evaluate Cre-line specificity and tracer injections, we find bona fide Sub projections topographically to structures important for spatial processing and navigation. In contrast, the PS sends its outputs to widespread brain regions crucial for motivation, emotion, reward, stress, anxiety, and fear. The Sub and PS, respectively, dominate dorsal and ventral subicular regions and receive different afferents. These results reveal two molecularly and anatomically distinct circuits centered in the Sub and PS, respectively, providing a consistent explanation for historical data and a clearer foundation for future studies.