Chronic unpredictable stress induces depression-related behaviors by suppressing AgRP neuron activity

VGluT2 neuron subtypes in the paraventricular thalamic nucleus regulate depression in paraquat-induced Parkinson's disease

Parkinson's disease (PD) is a prevalent neurodegenerative disease and approximately one third of patients with PD are estimated to experience depression. Paraquat (PQ) is the most widely used herbicide worldwide and PQ exposure is reported to induce PD with depression. However, the specific brain region and neural networks underlying the etiology of depression in PD, especially in the PQ-induced model, have not yet been elucidated. Here, we report that the VGluT2-positive glutamatergic neurons in the paraventricular thalamic nucleus (PVT) promote depression in the PQ-induced PD mouse model. Our results show that PVTVGluT2 neurons are activated by PQ and their activation increases the susceptibility to depression in PD mice. Conversely, inhibition of PVTVGluT2 neurons reversed the depressive-behavioral changes induced by PQ. Similar to the effects of intervention the soma of PVTVGluT2 neurons, stimulation of their projections into the central amygdaloid nucleus (CeA) also strongly influenced depression in PD mice. PQ induced malfunctioning of the glutamate system and changes in the dendritic and synaptic morphology in the CeA through its role on PVTVGluT2 neuronal activation. In summary, our results demonstrate that PVTVGluT2 neurons are key neuronal subtypes for depression in PQ-induced PD and promote depression processes through the PVTVGluT2-CeA pathway.

Unraveling the potential of Morinda officinalis oligosaccharides as an adjuvant of escitalopram in depression treatment and exploring the underlying mechanisms

ETHNOPHAMACOLOGICAL RELEVANCE

Morinda officinalis oligosaccharides (MOs) is a mixture of oligosaccharides extracted from the roots of Morinda officinalis (MO). It is approved by Chinese Food and Drug Administration (CFDA) for depression treatment. MOs could improve the antidepressant efficacy of escitalopram in clinic.

AIM OF THE STUDY

We aim to explore the antidepressant activity and potential mechanism of the combination usage of MOs and escitalopram on animal model of depression.

MATERIALS AND METHODS

Depressive animal model was induced by chronic mild stress (CMS). Behavioral tests were conducted to evaluate the antidepressant efficacy of MOs and escitalopram. Serum neurotransmitter levels were detected by High-performance liquid chromatography (HPLC). Quantitative real-time PCR and Western blotting were applied to assay the hippocampus neurotrophic factors' mRNA and protein levels. Peripheral cytokines levels were measured through Enzyme-Linked Immunosorbent Assay (ELISA). Micorglia polization phenotype was assayed by immunofluorescence and flow cytometry.

RESULTS

MOs and escitalopram obviously attenuated depression-like behaviors of CMS mice. Importantly, MOs plus escitalopram exhibited better antidepressant activity on CMS mice than monotherapy. At the same time, MOs combined escitalopram treatment significantly increased hippocampus neurotransmitters and neurotrophic factor levels, stimulated hippocampus neurogenesis and relieved central nervous system (CNS) microglia over-activation of CMS mice. The combination therapy had greater effect on neuroprotection and inflammation attenuation of CMS mice than monotherapy.

CONCLUSION

Our results indicates MOs combined escitalopram might produce antidepressant activity through protecting neuron activity, relieving inflammation and modulating microglia polarization process.

Repeated stress triggers seeking of a starvation-like state in anxiety-prone female mice

Elevated anxiety often precedes anorexia nervosa and persists after weight restoration. Patients with anorexia nervosa often describe self-starvation as pleasant, potentially because food restriction can be anxiolytic. Here, we tested whether repeated stress can cause animals to prefer a starvation-like state. We developed a virtual reality place preference paradigm in which head-fixed mice can voluntarily seek a starvation-like state induced by optogenetic stimulation of hypothalamic agouti-related peptide (AgRP) neurons. Prior to stress exposure, males but not females showed a mild aversion to AgRP stimulation. Strikingly, following multiple days of stress, a subset of females developed a strong preference for AgRP stimulation that was predicted by high baseline anxiety. Such stress-induced changes in preference were reflected in changes in facial expressions during AgRP stimulation. Our study suggests that stress may cause females predisposed to anxiety to seek a starvation state and provides a powerful experimental framework for investigating the underlying neural mechanisms.

Selective disruption of mTORC1 and mTORC2 in VTA astrocytes induces depression and anxiety-like behaviors in mice

Dysfunction of the mechanistic target of rapamycin (mTOR) signaling pathway is implicated in neuropsychiatric disorders including depression and anxiety. Most studies have been focusing on neurons, and the function of mTOR signaling pathway in astrocytes is less investigated. mTOR forms two distinct complexes, mTORC1 and mTORC2, with key scaffolding protein Raptor and Rictor, respectively. The ventral tegmental area (VTA), a vital component of the brain reward system, is enrolled in regulating both depression and anxiety. In the present study, we aimed to examine the regulation effect of VTA astrocytic mTOR signaling pathway on depression and anxiety. We specifically deleted Raptor or Rictor in VTA astrocytes in mice and performed a series of behavioral tests for depression and anxiety. Deletion of Raptor and Rictor both decreased the immobility time in the tail suspension test and the latency to eat in the novelty suppressed feeding test, and increased the horizontal activity and the movement time in locomotor activity. Deletion of Rictor decreased the number of total arm entries in the elevated plus-maze test and the vertical activity in locomotor activity. These data suggest that VTA astrocytic mTORC1 plays a role in regulating depression-related behaviors and mTORC2 is involved in both depression and anxiety-related behaviors. Our results indicate that VTA astrocytic mTOR signaling pathway might be new targets for the treatment of psychiatric disorders.

Prolonged stress response induced by chronic stress and corticosterone exposure causes adult neurogenesis inhibition and astrocyte loss in mouse hippocampus

Chronic stress is a pervasive and complex issue that contributes significantly to various mental and physical health disorders. Using the previously established chronic unpredictable stress (CUS) model, which simulates human stress situations, it has been shown that chronic stress induces major depressive disorder (MDD) and memory deficiency. However, this established model is associated with several drawbacks, such as limited research reproducibility and the inability to sustain stress response. To resolve these issues, we developed a new CUS model (CUS+C) that included exogenous corticosterone exposure to induce continuous stress response. Thereafter, we evaluated the effect of this new model on brain health. Thus, we observed that the use of the CUS+C model decreased body and brain weight gain and induced an uncontrolled coat state as well as depressive-like behavior in adult mice. It also impaired learning memory function and cognitive abilities, reduced adult hippocampal neurogenesis as well as the number of hippocampal astrocytes, and downregulated glial fibrillary acidic protein expression in the brains of adult mice. These findings can promote the utilization and validity of the animal stress model and provide new information for the treatment of chronic stress-induced depressive and memory disorders.

Stress integration by an ascending adrenergic-melanocortin circuit

Stress is thought to be an important contributing factor for eating disorders; however, neural substrates underlying the complex relationship between stress and appetite are not fully understood. Using in vivo recordings from awake behaving mice, we show that various acute stressors activate catecholaminergic nucleus tractus solitarius (NTSTH) projections in the paraventricular hypothalamus (PVH). Remarkably, the resulting adrenergic tone inhibits MC4R-expressing neurons (PVHMC4R), which are known for their role in feeding suppression. We found that PVHMC4R silencing encodes negative valence in sated mice and is required for avoidance induced by visceral malaise. Collectively, these findings establish PVHMC4R neurons as an effector of stress-activated brainstem adrenergic input in addition to the well-established hypothalamic-pituitary-adrenal axis. Convergent modulation of stress and feeding by PVHMC4R neurons implicates NTSTH → PVHMC4R input in stress-associated appetite disorders.

The anterior cingulate cortex controls the hyperactivity in subthalamic neurons in male mice with comorbid chronic pain and depression

Neurons in the subthalamic nucleus (STN) become hyperactive following nerve injury and promote pain-related responses in mice. Considering that the anterior cingulate cortex (ACC) is involved in pain and emotion processing and projects to the STN, we hypothesize that ACC neurons may contribute to hyperactivity in STN neurons in chronic pain. In the present study, we showed that ACC neurons enhanced activity in response to noxious stimuli and to alterations in emotional states and became hyperactive in chronic pain state established by spared nerve injury of the sciatic nerve (SNI) in mice. In naïve mice, STN neurons were activated by noxious stimuli, but not by alterations in emotional states. Pain responses in STN neurons were attenuated in both naïve and SNI mice when ACC neurons were inhibited. Furthermore, optogenetic activation of the ACC-STN pathway induced bilateral hyperalgesia and depression-like behaviors in naive mice; conversely, inhibition of this pathway is sufficient to attenuate hyperalgesia and depression-like behaviors in SNI mice and naïve mice subjected to stimulation of STN neurons. Finally, mitigation of pain-like and depression-like behaviors in SNI mice by inhibition of the ACC-STN projection was eliminated by activation of STN neurons. Our results demonstrate that hyperactivity in the ACC-STN pathway may be an important pathophysiology in comorbid chronic pain and depression. Thus, the ACC-STN pathway may be an intervention target for the treatment of the comorbid chronic pain and depression.

Effects of unpredictable chronic mild stress on the cellular redox state and mitochondrial energy homeostasis in rat adipose tissue: A comprehensive metabolic study

Unpredictable chronic mild stress (UCMS) leads to variable metabolic effects. Oxidative stress (OS) of adipose tissue (AT) and mitochondrial energy homeostasis is little investigated. This work studied the effects of UCMS on OS and the antioxidant/redox status in AT and mitochondrial energy homeostasis in rats. Twenty-four male Wistar rats (180-220 g) were divided into two equal groups; the normal control (NC) group and the UCMS group which were exposed to various stresses for 28 days. An indirect calorimetry machine was used to measure volumes of respiratory gases (VO2 & VCO2 ), total energy expenditure (TEE), and food intake (FI). The AT depots were collected, weighed, and used for measuring activities and gene expression of key antioxidant enzymes (GPx1, SOD, CAT, GR, GCL, and GS), OS marker levels including superoxide anion (SA), peroxynitrite radical (PON), nitric oxide (NO), hydrogen peroxide (H2 O2 ), lipid peroxides (LPO), t-protein carbonyl content (PCC), and reduced/oxidized glutathione levels (GSH, GSSG). Additionally, AT mitochondrial fractions were used to determine the activities of the tricarboxylic acid cycle (TCA) cycle enzymes (CS, α-KGDH, ICDH, SDH, MDH), respiratory chain complexes I-III, II-III, IV, the nicotinamide coenzymes NAD+ , NADH, and ATP/ADP levels. Compared with the NC group, the UCMS group showed very significantly increased OS marker levels, lowered antioxidant enzyme activities and gene expression, as well as lowered TCA cycle and respiratory chain activity and NAD+ , NADH, and ATP levels (p < .001 for all comparisons). Besides, the UCMS group had lowered TEE and insignificant FI and weight gain. In conclusion, AT of the UCMS-subjected rats showed a state of disturbed redox balance linked to disrupted energy homeostasis producing augmentation of AT.

Novel antidepressant mechanism of hypericin: Role of connexin 43-based gap junctions

Hypericin is widely utilized for its precise antidepressant properties, but its exact antidepressant mechanism remains unclear. Gap junctions, which were predominantly expressed in astrocytes in the central nervous system, are concerned with the pathogenesis of depression. However, the role of hypericin in gap junctional dysfunction in depression has rarely been investigated. Here, we found that gap junctions were ultra-structurally broadened in the chronic unpredictable stress (CUS) rat model of depression, while hypericin repaired the dysfunction of gap junctions. Suppression of gap junctions by bilateral injection of carbenoxolone (CBX) in the prefrontal cortex of rats significantly inhibited the restoration of gap junctional dysfunction in depression by hypericin. Meanwhile, hypericin failed to show antidepressant benefits. Furthermore, in corticosterone (CORT)-stimulated primary astrocytes derived from neonatal rats, hypericin dramatically reversed the phosphorylation of connexin 43 (Cx43), normalizing the expression of Cx43 and thereby ameliorating gap junctional dysfunction. Comparatively, CBX inhibited the remission of hypericin on gap junctional intercellular communication function. Gap junctional function might be a novel therapeutic target for hypericin in the treatment of depression and provide potential novel insights into the antidepressant mechanism of other herbal ingredients.

Acute inhibition of hunger-sensing AgRP neurons promotes context-specific learning in mice

OBJECTIVE

An environmental context, which reliably predicts food availability, can increase the appetitive food drive within the same environment context. However, hunger is required for the development of such a context-induced feeding (CIF) response, suggesting the neural circuits sensitive to hunger link an internal energy state with a particular environment context. Since Agouti related peptide (AgRP) neurons are activated by energy deficit, we hypothesised that AgRP neurons are both necessary and sufficient to drive CIF.

METHODS

To examine the role of AgRP neurons in the CIF process, we used fibre photometry with GCaMP7f, chemogenetic activation of AgRP neurons, as well as optogenetic control of AgRP neurons to facilitate acute temporal control not permitted with chemogenetics.

RESULTS

A CIF response at test was only observed when mice were fasted during context training and AgRP population activity at test showed an attenuated inhibitory response to food, suggesting increased food-seeking and/or decreased satiety signalling drives the increased feeding response at test. Intriguingly, chemogenetic activation of AgRP neurons during context training did not increase CIF, suggesting precise temporal firing properties may be required. Indeed, termination of AgRP neuronal photostimulation during context training (ON-OFF in context), in the presence or absence of food, increased CIF. Moreover, photoinhibition of AgRP neurons during context training in fasted mice was sufficient to drive a subsequent CIF in the absence of food.

CONCLUSIONS

Our results suggest that AgRP neurons regulate the acquisition of CIF when the acute inhibition of AgRP activity is temporally matched to context exposure. These results establish acute AgRP inhibition as a salient neural event underscoring the effect of hunger on associative learning.

The Impact of Chronic Stress on Behavior and Body Mass in New Animal Models

(1) Background: Exposure to different sources of stress can have a significant effect on both psychological and physical processes. (2) Methods: The study took place over a period of 34 days and included a total of 40 animals. Regarding the exposure to chronic stressors, we opted for physiological, non-invasive stressors, e.g., running, swimming, and changes in the intensity of light. An unforeseen stress batch was also created that alternated all these stress factors. The animals were divided into five experimental groups, each consisting of eight individuals. In the context of conducting the open field test for behavioral assessment before and after stress exposure, we aimed to investigate the impact of stress exposure on the affective traits of the animals. We also monitored body mass every two days. (3) Results: The control group exhibited an average increase in weight of approximately 30%. The groups exposed to stress factors showed slower growth rates, the lowest being the running group, recording a rate of 20.55%, and the unpredictable stress group at 24.02%. The anxious behavior intensified in the group with unforeseen stress, in the one with light variations, and in the running group. (4) Conclusions: Our research validates the animal model of intermittent light exposure during the dark phase as a novel method of inducing stress. The modification of some anxiety parameters was observed; they vary according to the type of stress. Body mass was found to increase in all groups, especially in the sedentary groups, likely due to the absence of cognitive, spatial, and social stimuli except for cohabitation.

A dual-pathway architecture enables chronic stress to promote habit formation

Chronic stress can change how we learn and, thus, how we make decisions by promoting the formation of inflexible, potentially maladaptive, habits. Here we investigated the neuronal circuit mechanisms that enable this. Using a multifaceted approach in male and female mice, we reveal a dual pathway, amygdala-striatal, neuronal circuit architecture by which a recent history of chronic stress shapes learning to disrupt flexible goal-directed behavior in favor of inflexible habits. Chronic stress inhibits activity of basolateral amygdala projections to the dorsomedial striatum to impede the action-outcome learning that supports flexible, goal-directed decisions. Stress also increases activity in direct central amygdala projections to the dorsomedial striatum to promote the formation of rigid, inflexible habits. Thus, stress exerts opposing effects on two amygdala-striatal pathways to promote premature habit formation. These data provide neuronal circuit insights into how chronic stress shapes learning and decision making, and help understand how stress can lead to the disrupted decision making and pathological habits that characterize substance use disorders and other psychiatric conditions.

Repressed Blautia-acetate immunological axis underlies breast cancer progression promoted by chronic stress

Chronic stress is a known risk factor for breast cancer, yet the underlying mechanisms are unclear. This study explores the potential involvement of microbial and metabolic signals in chronic stress-promoted breast cancer progression, revealing that reduced abundances of Blautia and its metabolite acetate may contribute to this process. Treatment with Blautia and acetate increases antitumor responses of CD8+ T cells and reverses stress-promoted breast cancer progression in female mice. Patients with depression exhibit lower abundances of Blautia and acetate, and breast cancer female patients with depression display lower abundances of acetate, decreased numbers of tumor-infiltrating CD8+ T cells, and an increased risk of metastasis. These results suggest that Blautia-derived acetate plays a crucial role in modulating the immune response to breast cancer, and its reduction may contribute to chronic stress-promoted cancer progression. Our findings advance the understanding of microbial and metabolic signals implicated in cancer in patients with depression and may provide therapeutic options for female patients with breast cancer and depression.

Male mice engaging differently in emotional eating present distinct plasmatic and neurological profiles

Objective: Stressed individuals tend to turn to calorie-rich food, also known as 'comfort food' for the temporary relief it provides. The emotional eating drive is highly variable among subjects. Using a rodent model, we explored the plasmatic and neurobiological differences between 'high and low emotional eaters' (HEE and LEE).Methods: 40 male mice were exposed for 5 weeks to a protocol of unpredictable chronic mild stress. Every 3 or 4 days, they were submitted to a 1-h restraint stress, immediately followed by a 3-h period during which a choice between chow and chocolate sweet cereals was proposed. The dietary intake was measured by weighing. Plasmatic and neurobiological characteristics were compared in mice displaying high vs low intakes.Results: Out of 40 mice, 8 were considered as HEE because of their high post-stress eating score, and 8 as LEE because of their consistent low intake. LEE displayed higher plasma corticosterone and lower levels of NPY than HEE, but acylated and total ghrelin were similar in both groups. In the brain, the abundance of NPY neurons in the arcuate nucleus of the hypothalamus was similar in both groups, but was higher in the ventral hippocampus and the basal lateral amygdala of LEE. The lateral hypothalamus LEE had also more orexin (OX) positive neurons. Both NPY and OX are orexigenic peptides and mood regulators.Discussion: Emotional eating difference was reflected in plasma and brain structures implicated in emotion and eating regulation. These results concur with the psychological side of food consumption.

Establishment of insomnia model of chronic unpredictable stress in rats

It is well known that stressful situation is one of the important factors causing insomnia, however, the underlying mechanism is still elusive. Therefore, the establishment of a suitable animal model of stress insomnia will be of great help to solve this problem. In this study, by combining with chronic unpredictable stress (multitude of stressors) and sleep deprivation, we attempted to establish a rat model of stress insomnia. It was observed that rats with stress insomnia showed significant weight loss, and less sleep quality in pentobarbital sodium induced sleep test and electroencephalogram detection. Moreover, rats with stress insomnia showed greater depression and anxiety detected by forced swimming, sucrose preference test and open field. Since oxidative stress has been reported to be involved in insomnia, we further evaluated the production of oxidative stress and found that the levels of lipid peroxidation product malondialdehyde (MDA) in liver, serum total bilirubin and urine biopyrrin were all significantly increased in rats with stress insomnia. In addition, we also found that the memory of these rats with stress insomnia was also obviously reduced in water maze. Taken together, these results demonstrate that the emotional behaviors, memory, oxidative and metabolism of the rats were all significantly changed after modeling, indicating a rat model of stress insomnia was successful establishment, and this animal model will provide basis to further explore the underlying mechanism of chronic stress in insomnia.

Chronic unpredictable stress induces depression/anxiety-related behaviors and alterations of hippocampal monoamine receptor mRNA expression in female mice at different ages

Depression and anxiety are the most common mental health disorders. Though they affect people at any age and occur more often in females, the pathophysiological changes under these conditions are less investigated. In the present study, we examined the effects of age and stress on depression- and anxiety-related behaviors in female mice. Saccharin preference and the open field test were carried out before and after chronic unpredictable stress in 4-, 14- and 25-month-old female mice. After behavioral tests, mRNA levels of monoamine receptors in the hippocampus were measured by real-time RT-PCR. Chronic unpredictable stress decreased saccharin preference in 4-, 14- and 25-month-old mice and the time spent in the center in the open field test in 25-month-old mice. For monoamine receptors, analysis of variance revealed significant effects of age on mRNA levels of Htr1a, Htr2a, Htr6, Adra1a, Adrb2, and Adrb3, significant effects of stress on mRNA levels of Htr4, Adra2c, Adrb1, and Adrb2, and interactions of age × stress on mRNA levels of Htr1a, Htr5b, Adra1d, Adra2a, Adra2c, and Adrb1. Chronic unpredictable stress decreased mRNA levels of Htr4, Htr5b, Adra2c, and Adrb1 in 4-month-old female mice. Correlations were observed between saccharin preference and mRNA levels of Htr4, Htr5b, Htr6, Adra1d, Adra2a, and Adra2c in 4-month-old mice and between the time spent in the center in the open field test and mRNA levels of Htr1b in 4-month-old mice, Htr3a, Htr7, and Adrb2 in 14-month-old mice, and Drd2 in 4- and 14-month-old mice. Our findings support that stress induces depression- and anxiety-related behaviors and the expression of hippocampal monoamine receptors in an age-dependent manner in female mice.

Intestinal activating transcription factor 4 regulates stress-related behavioral alterations via paraventricular thalamus in male mice

Chronic stress induces depression- and anxiety-related behaviors, which are common mental disorders accompanied not only by dysfunction of the brain but also of the intestine. Activating transcription factor 4 (ATF4) is a stress-induced gene, and we previously show that it is important for gut functions; however, the contribution of the intestinal ATF4 to stress-related behaviors is not known. Here, we show that chronic stress inhibits the expression of ATF4 in gut epithelial cells. ATF4 overexpression in the colon relieves stress-related behavioral alterations in male mice, as measured by open-field test, elevated plus-maze test, and tail suspension test, whereas intestine-specific ATF4 knockout induces stress-related behavioral alterations in male mice. Furthermore, glutamatergic neurons are inhibited in the paraventricular thalamus (PVT) of two strains of intestinal ATF4-deficient mice, and selective activation of these neurons alleviates stress-related behavioral alterations in intestinal ATF4-deficient mice. The highly expressed gut-secreted peptide trefoil factor 3 (TFF3) is chosen from RNA-Seq data from ATF4 deletion mice and demonstrated decreased in gut epithelial cells, which is directly regulated by ATF4. Injection of TFF3 reverses stress-related behaviors in ATF4 knockout mice, and the beneficial effects of TFF3 are blocked by inhibiting PVT glutamatergic neurons using DREADDs. In summary, this study demonstrates the function of ATF4 in the gut-brain regulation of stress-related behavioral alterations, via TFF3 modulating PVT neural activity. This research provides evidence of gut signals regulating stress-related behavioral alterations and identifies possible drug targets for the treatment of stress-related behavioral disorders.

Medial prefrontal cortex input to basolateral amygdala controls acute stress-induced short-term anxiety-like behavior in mice

Anxiety is a normal and transitory emotional state that allows the organisms to cope well with the real or perceived threats, while excessive or prolonged anxiety is a key characteristic of anxiety disorders. We have recently revealed that prolonged anxiety induced by chronic stress is associated with the circuit-varying dysfunction of basolateral amygdala projection neurons (BLA PNs). However, it is not yet known whether similar mechanisms also emerge for acute stress-induced, short-lasting increase of anxiety. Here, using a mouse model of acute restraint stress (ARS), we found that ARS mice showed increased anxiety-like behavior at 2 h but not 24 h after stress, and this effect was accompanied by a transient increase of the activity of BLA PNs. Specifically, ex vivo patch-clamp recordings revealed that the increased BLA neuronal activity did not differ among the distinct BLA neuronal populations, regardless of their projection targets being the dorsomedial prefrontal cortex (dmPFC) or elsewhere. We further demonstrated that such effects were mainly mediated by the enhanced presynaptic glutamate release in dmPFC-to-BLA synapses but not lateral amygdala-to-BLA ones. Furthermore, while optogenetically weakening the presynaptic glutamate release in dmPFC-to-BLA synapses ameliorated ARS-induced anxiety-like behavior, strengthening the release increased in unstressed mice. Together, these findings suggest that acute stress causes short-lasting increase in anxiety-like behavior by facilitating synaptic transmission from the prefrontal cortex to the amygdala in a circuit-independent fashion.

Increased intrinsic and synaptic excitability of hypothalamic POMC neurons underlies chronic stress-induced behavioral deficits

Chronic stress exposure induces maladaptive behavioral responses and increases susceptibility to neuropsychiatric conditions. However, specific neuronal populations and circuits that are highly sensitive to stress and trigger maladaptive behavioral responses remain to be identified. Here we investigate the patterns of spontaneous activity of proopiomelanocortin (POMC) neurons in the arcuate nucleus (ARC) of the hypothalamus following exposure to chronic unpredictable stress (CUS) for 10 days, a stress paradigm used to induce behavioral deficits such as anhedonia and behavioral despair [1, 2]. CUS exposure increased spontaneous firing of POMC neurons in both male and female mice, attributable to reduced GABA-mediated synaptic inhibition and increased intrinsic neuronal excitability. While acute activation of POMC neurons failed to induce behavioral changes in non-stressed mice of both sexes, subacute (3 days) and chronic (10 days) repeated activation of POMC neurons was sufficient to induce anhedonia and behavioral despair in males but not females under non-stress conditions. Acute activation of POMC neurons promoted susceptibility to subthreshold unpredictable stress in both male and female mice. Conversely, acute inhibition of POMC neurons was sufficient to reverse CUS-induced anhedonia and behavioral despair in both sexes. Collectively, these results indicate that chronic stress induces both synaptic and intrinsic plasticity of POMC neurons, leading to neuronal hyperactivity. Our findings suggest that POMC neuron dysfunction drives chronic stress-related behavioral deficits.

Inhibition of c-Jun in AgRP neurons increases stress-induced anxiety and colitis susceptibility

Psychiatric disorders, such as anxiety, are associated with inflammatory bowel disease (IBD), however, the neural mechanisms regulating this comorbidity are unknown. Here, we show that hypothalamic agouti-related protein (AgRP) neuronal activity is suppressed under chronic restraint stress (CRS), a condition known to increase anxiety and colitis susceptibility. Consistently, chemogenic activation or inhibition of AgRP neurons reverses or mimics CRS-induced increase of anxiety-like behaviors and colitis susceptibility, respectively. Furthermore, CRS inhibits AgRP neuronal activity by suppressing the expression of c-Jun. Moreover, overexpression of c-Jun in these neurons protects against the CRS-induced effects, and knockdown of c-Jun in AgRP neurons (c-Jun^∆AgRP) promotes anxiety and colitis susceptibility. Finally, the levels of secreted protein thrombospondin 1 (THBS1) are negatively associated with increased anxiety and colitis, and supplementing recombinant THBS1 rescues colitis susceptibility in c-Jun^∆AgRP mice. Taken together, these results reveal critical roles of hypothalamic AgRP neuron-derived c-Jun in orchestrating stress-induced anxiety and colitis susceptibility.

Knowledge domains and emerging trends of microglia research from 2002 to 2021: A bibliometric analysis and visualization study

Background

Microglia have been identified for a century. In this period, their ontogeny and functions have come to light thanks to the tireless efforts of scientists. However, numerous documents are being produced, making it challenging for scholars, especially those new to the field, to understand them thoroughly. Therefore, having a reliable method for quickly grasping a field is crucial.

Methods

We searched and downloaded articles from the Web of Science Core Collection with "microglia" or "microglial" in the title from 2002 to 2021. Eventually, 12,813 articles were located and, using CiteSpace and VOSviewer, the fundamental data, knowledge domains, hot spots, and emerging trends, as well as the influential literature in the field of microglia research, were analyzed.

Results

Following 2011, microglia publications grew significantly. The two prominent journals are Glia and J Neuroinflamm. The United States and Germany dominated the microglia study. The primary research institutions are Harvard Univ and Univ Freiburg, and the leading authors are Prinz Marco and Kettenmann Helmut. The knowledge domains of microglia include eight directions, namely neuroinflammation, lipopolysaccharide, aging, neuropathic pain, macrophages, Alzheimer's disease, retina, and apoptosis. Microglial phenotype is the focus of research; while RNA-seq, exosome, and glycolysis are emerging topics, a microglial-specific marker is still a hard stone. We also identified 19 influential articles that contributed to the study of microglial origin (Mildner A 2007; Ginhoux F 2010), identity (Butovsky O 2014), homeostasis (Cardona AE 2006; Elmore MRP 2014); microglial function such as surveillance (Nimmerjahn A 2005), movement (Davalos D 2005; Haynes SE 2006), phagocytosis (Simard AR 2006), and synapse pruning (Wake H 2009; Paolicelli RC 2011; Schafer DP 2012; Parkhurst CN 2013); and microglial state/phenotype associated with disease (Keren-Shaul H 2017), as well as 5 review articles represented by Kettenmann H 2011.

Conclusion

Using bibliometrics, we have investigated the fundamental data, knowledge structure, and dynamic evolution of microglia research over the previous 20 years. We hope this study can provide some inspiration and a reference for researchers studying microglia in neuroscience.

Dietary intervention in depression - a review

Depression is a mental illness that affects the normal lives of over 300 million people. Unfortunately, about 30% to 40% of patients do not adequately respond to pharmacotherapy and other therapies. This review focuses on exploring the relationship between dietary nutrition and depression, aiming to find safer and efficient ingredients to alleviate depression. Diet can affect depression in numerous ways. These pathways include the regulation of tryptophan metabolism, inflammation, hypothalamic-pituitary-adrenal (HPA) axis, microbe-gut-brain axis, brain-derived neurotrophic factor (BDNF) and epigenetics. Furthermore, probiotics, micronutrients, and other active substances exhibit significant antidepressant effects by regulating the above pathways. These provide insights for developing antidepressant foods.

TET3 epigenetically controls feeding and stress response behaviors via AGRP neurons

The TET family of dioxygenases promote DNA demethylation by oxidizing 5-methylcytosine to 5-hydroxymethylcytosine (5hmC). Hypothalamic agouti-related peptide-expressing (AGRP-expressing) neurons play an essential role in driving feeding, while also modulating nonfeeding behaviors. Besides AGRP, these neurons produce neuropeptide Y (NPY) and the neurotransmitter GABA, which act in concert to stimulate food intake and decrease energy expenditure. Notably, AGRP, NPY, and GABA can also elicit anxiolytic effects. Here, we report that in adult mouse AGRP neurons, CRISPR-mediated genetic ablation of Tet3, not previously known to be involved in central control of appetite and metabolism, induced hyperphagia, obesity, and diabetes, in addition to a reduction of stress-like behaviors. TET3 deficiency activated AGRP neurons, simultaneously upregulated the expression of Agrp, Npy, and the vesicular GABA transporter Slc32a1, and impeded leptin signaling. In particular, we uncovered a dynamic association of TET3 with the Agrp promoter in response to leptin signaling, which induced 5hmC modification that was associated with a chromatin-modifying complex leading to transcription inhibition, and this regulation occurred in both the mouse models and human cells. Our results unmasked TET3 as a critical central regulator of appetite and energy metabolism and revealed its unexpected dual role in the control of feeding and other complex behaviors through AGRP neurons.

High-Fat Diet and Short-Term Unpredictable Stress Increase Long-Chain Ceramides Without Enhancing Behavioral Despair

Clinical and preclinical studies suggest that increases in long-chain ceramides in blood may contribute to the development of depressive-like behavior. However, which factors contribute to these increases and whether the increases are sufficient to induce depressive-like behaviors is unclear. To begin to address this issue, we examined the effects of high fat diet (HFD) and short-term unpredictable (STU) stress on long-chain ceramides in the serum of male and female rats. We found that brief exposure to HFD or unpredictable stress was sufficient to induce selective increases in the serum concentrations of long-chain ceramides, associated with depression in people. Furthermore, combined exposure to HFD and unpredictable stress caused a synergistic increase in C16:0, C16:1, and C18:0 ceramides in both sexes and C18:1 and C24:1 in males. However, the increased peripheral long-chain ceramides were not associated with increases in depressive-like behaviors suggesting that increases in serum long-chain ceramides may not be associated with the development of depressive-like behaviors in rodents.

The co-chaperone FKBP51 modulates HPA axis activity and age-related maladaptation of the stress system in pituitary proopiomelanocortin cells

Glucocorticoid (GC)-mediated negative feedback of the hypothalamic-pituitary-adrenal (HPA) axis, the body's physiological stress response system, is tightly regulated and essential for appropriate termination of this hormonal cascade. Disturbed regulation and maladaptive response of this axis are fundamental components of multiple stress-induced psychiatric and metabolic diseases and aging. The co-chaperone FK506 binding protein 51 (FKBP51) is a negative regulator of the GC receptor (GR), is highly stress responsive, and its polymorphisms have been repeatedly associated with stress-related disorders and dysfunctions in humans and rodents. Proopiomelanocortin (Pomc)-expressing corticotropes in the anterior pituitary gland are one of the key cell populations of this closed-loop GC-dependent negative feedback regulation of the HPA axis in the periphery. However, the cell type-specific role of FKBP51 in anterior pituitary corticotrope POMC cells and its impact on age-related HPA axis disturbances are yet to be elucidated. Here, using a combination of endogenous knockout and viral rescue, we show that male mice lacking FKBP51 in Pomc-expressing cells exhibit enhanced GR-mediated negative feedback and are protected from age-related disruption of their diurnal corticosterone (CORT) rhythm. Our study highlights the complexity of tissue- and cell type-specific, but also cross-tissue effects of FKBP51 in the rodent stress response at different ages and extends our understanding of potential targets for pharmacological intervention in stress- and age-related disorders.

Chemogenetics as a neuromodulatory approach to treating neuropsychiatric diseases and disorders

Chemogenetics enables precise, non-invasive, and reversible modulation of neural activity via the activation of engineered receptors that are pharmacologically selective to endogenous or exogenous ligands. With recent advances in therapeutic gene delivery, chemogenetics is poised to support novel interventions against neuropsychiatric diseases and disorders. To evaluate its translational potential, we performed a scoping review of applications of chemogenetics that led to the reversal of molecular and behavioral deficits in studies relevant to neuropsychiatric diseases and disorders. In this review, we present these findings and discuss the potential and challenges for using chemogenetics as a precision medicine-based neuromodulation strategy.

Interferon-γ enhances neocortical synaptic inhibition by promoting membrane association and phosphorylation of GABAA receptors in a protein kinase C-dependent manner

Interferon-γ (IFN-γ), an important mediator of the antiviral immune response, can also act as a neuromodulator. CNS IFN-γ levels rise acutely in response to infection and therapeutically applied IFN-γ provokes CNS related side effects. Moreover, IFN-γ plays a key role in neurophysiological processes and a variety of chronic neurological and neuropsychiatric conditions. To close the gap between basic research, behavioral implications and clinical applicability, knowledge of the mechanism behind IFN-γ related changes in brain function is crucial. Here, we studied the underlying mechanism of acutely augmented neocortical inhibition by IFN-γ (1.000 IU ml^-1) in layer 5 pyramidal neurons of male Wistar rats. We demonstrate postsynaptic mediation of IFN-γ augmented inhibition by pressure application of GABA and analysis of paired pulse ratios. IFN-γ increases membrane presence of GABA_AR γ₂, as quantified by cell surface biotinylation and functional synaptic GABA_AR number, as determined by peak-scaled non-stationary noise analysis. The increase in functional receptor number was comparable to the increase in underlying miniature inhibitory postsynaptic current (mIPSC) amplitudes. Blockage of putative intracellular mediators, namely phosphoinositide 3-kinase and protein kinase C (PKC) by Wortmannin and Calphostin C, respectively, revealed PKC-dependency of the pro-inhibitory IFN-γ effect. This was corroborated by increased serine phosphorylation of P-serine PKC motifs on GABA_AR γ₂ upon IFN-γ application. GABA_AR single channel conductance, intracellular chloride levels and GABA_AR driving force are unlikely to contribute to the effect, as shown by single channel recordings and chloride imaging. The effect of IFN-γ on mIPSC amplitudes was similar in female and male rats, suggesting a gender-independent mechanism of action. Collectively, these results indicate a novel mechanism for the regulation of inhibition by IFN-γ, which could impact on neocortical function and therewith behavior.

Microglia Loss and Astrocyte Activation Cause Dynamic Changes in Hippocampal [18F]DPA-714 Uptake in Mouse Models of Depression

Major depression is a serious and chronic mental illness. However, its etiology is poorly understood. Although glial cells have been increasingly implicated in the pathogenesis of depression, the specific role of microglia and astrocytes in stress-induced depression remains unclear. Translocator protein (TSPO) has long been considered a marker of neuroinflammation and microglial activation. However, this protein is also present on astrocytes. Thus, it is necessary to explore the relationships between TSPO, microglia, and astrocytes in the context of depression. In this study, C57BL/6J male mice were subjected to chronic unpredictable stress (CUS) for 5 weeks. Subsequently, sucrose preference and tail suspension tests (TSTs) were performed to assess anhedonia and despair in these mice. [18F]DPA-714 positron emission tomography (PET) was adopted to dynamically assess the changes in glial cells before and 2, 4, or 5 weeks after CUS exposure. The numbers of TSPO+ cells, ionized calcium-binding adaptor molecule (Iba)-1+ microglial cells, TSPO+/Iba-1+ cells, glial fibrillary acidic protein (GFAP)+ astrocytes, TSPO+/GFAP+ cells, and TUNEL-stained microglia were quantified using immunofluorescence staining. Real-time PCR was used to evaluate interleukin (IL)-1β, IL-4, and IL-18 expression in the hippocampus. We observed that hippocampal [18F]DPA-714 uptake significantly increased after 2 weeks of CUS. However, the signal significantly decreased after 5 weeks of CUS. CUS significantly reduced the number of Iba-1+, TSPO+, and TSPO+/Iba-1+ cells in the hippocampus, especially in the CA1 and dentate gyrus (DG) subregions. However, this intervention increased the number of GFAP+ astrocytes in the CA2/CA3 subregions of the hippocampus. In addition, microglial apoptosis in the early stage of CUS appeared to be involved in microglia loss. Further, the expression of pro-inflammatory cytokines (IL-1β and IL-18) was significantly decreased after CUS. In contrast, the expression of the anti-inflammatory cytokine IL-4 was significantly increased after 2 weeks of CUS. These results suggested that the CUS-induced dynamic changes in hippocampal [18F]DPA-714 uptake and several cytokines may be due to combined microglial and astrocyte action. These findings provide a theoretical reference for the future clinical applications of TSPO PET.

Improving health in the military and beyond using salutogenic design

Purpose

Service members of the US Department of Defense (DoD) have alarmingly high rates of depression, anxiety, probable stress disorders and suicidality, all of which are negative health conditions exacerbated by various external stressors. High-stress work conditions – to include shift work, hazardous territories, high-stakes mission sets and generally disconnected sites – require a work environment that facilitates, rather than inhibits, stress reduction and mental well-being. This paper aims to present “salutogenic design” as an innovative approach: Salutogenic design offers demonstrated architectural solutions that improve health and well-being.

Design/methodology/approach

This paper describes salutogenic design strategies beginning with the need for such an approach, the call to action to implement strategic and tactical solutions and the challenges and financial impacts of such a broad and innovative strategy to improve workplace health, well-being and performance in the DoD and beyond. Examples of these strategies, via biophilic design solutions, are presented in the central Table 1 as an easy-to-reference tool and supported by the voluminous literature as referenced, in part, through this research paper.

Findings

Salutogenic design strategies offer innovative, financially viable solutions to help mitigate stress and improve workforce well-being while maintaining the highest level of building security requirements in access-controlled spaces and disconnected sites, such as military installations and government compounds.

Research limitations/implications

Issues of mental and physical health are complex and multi-faceted, and they require complex and multi-faceted solutions. Salutogenic design is presented as one facet of that solution: a tangible solution to an often-intangible issue. Further, as a novel approach to address a critical DoD issue, Table 1 bridges the common gap between high-concept design theory and practical construction-application solutions, with positive value to the health, performance, quality-of-life and well-being of service members.

Originality/value

To the best of the author’s knowledge, this paper is the first to approach the DoD’s imperative to reduce service members’ mental stress with “salutogenic design.”

Leptin enhances social motivation and reverses chronic unpredictable stress-induced social anhedonia during adolescence

Social anhedonia, a loss of interest and pleasure in social interactions, is a common symptom of major depression as well as other psychiatric disorders. Depression can occur at any age, but typically emerges in adolescence or early adulthood, which represents a sensitive period for social interaction that is vulnerable to stress. In this study, we evaluated social interaction reward using a conditioned place preference (CPP) paradigm in adolescent male and female mice. Adolescent mice of both sexes exhibited a preference for the social interaction-associated context. Chronic unpredictable stress (CUS) impaired the development of CPP for social interaction, mimicking social anhedonia in depressed adolescents. Conversely, administration of leptin, an adipocyte-derived hormone, enhanced social interaction-induced CPP in non-stressed control mice and reversed social anhedonia in CUS mice. By dissecting the motivational processes of social CPP into social approach and isolation avoidance components, we demonstrated that leptin treatment increased isolation aversion without overt social reward effect. Further mechanistic exploration revealed that leptin stimulated oxytocin gene transcription in the paraventricular nucleus of the hypothalamus, while oxytocin receptor blockade abolished the leptin-induced enhancement of socially-induced CPP. These results establish that chronic unpredictable stress can be used to study social anhedonia in adolescent mice and provide evidence that leptin modulates social motivation possibly via increasing oxytocin synthesis and oxytocin receptor activation.

Chronic Restraint Stress Decreases the Excitability of Hypothalamic POMC Neuron and Increases Food Intake

Stress activates the hypothalamic-pituitary-adrenal system, and induces the release of glucocorticoids, stress hormones, into circulation. Many studies have shown that stress affects feeding behavior, however, the underlying circuitry and molecular mechanisms are not fully understood. The balance between orexigenic (simulating appetite) and anorexigenic (loss of appetite) signals reciprocally modulate feeding behavior. It is suggested that proopiomelanocortin (POMC) and neuropeptide Y (NPY) neurons in the arcuate nucleus (ARC) of the hypothalamus are the first-order neurons that respond to the circulating signals of hunger and satiety. Here, we examined a chronic restraint stress model and observed an increase in food intake, which was not correlated with anhedonia. We investigated whether stress affects the properties of POMC and NPY neurons and found that chronic restraint stress reduced the excitatory inputs onto POMC neurons and increased the action potential threshold. Therefore, our study suggests that chronic stress modulates the intrinsic excitability and excitatory inputs in POMC neurons, leading to changes in feeding behavior.

Anxiety and ultrastructural consequences of chronic mild stress in rats

Detrimental consequences following exposure to severe stress, either acute or chronic are well recognized. Chronic mild stress (CMS) is also a leading cause of emotional distress and neuropsychiatric conditions such as anxiety disorders. However, the neurobiological substrates of the latter, particularly at the ultrastructural levels have not been adequately investigated. In this study, adult male Wistar rats were subjected to 4 h daily mild restraint for 20 days and their behavior in open field and elevated plus maze (EPM) were evaluated 24 h after the last restraint. Anxiety-like behavior was evident in CMS exposed rats by increases in rearing and grooming in the open field and the avoidance of open arms in the EPM. Concomitant ultrastructural alterations such as chromatolysis, agglutination of synaptic vesicles or mitochondrial damage were also observed in the central nucleus of amygdala (CNA), an area intimately involved in emotional and fear response, in CMS exposed rats. These results while confirming detrimental consequences of CMS, also suggest that ultrastructural alterations in CNA may be a basis for CMS-induced anxiety.

Early life stress induces age-dependent epigenetic changes in p11 gene expression in male mice

Early life stress (ELS) causes long-lasting changes in gene expression through epigenetic mechanisms. However, little is known about the effects of ELS in adulthood, specifically across different age groups. In this study, the epigenetic modifications of p11 expression in adult mice subjected to ELS were investigated in different stages of adulthood. Pups experienced maternal separation (MS) for 3 h daily from postnatal day 1 to 21. At young and middle adulthood, behavioral test, hippocampal p11 expression levels, and levels of histone acetylation and methylation and DNA methylation at the hippocampal p11 promoter were measured. Middle-aged, but not young adult, MS mice exhibited increased immobility time in the forced swimming test. Concurrent with reduced hippocampal p11 levels, mice in both age groups showed a decrease in histone acetylation (AcH3) and permissive histone methylation (H3K4me3) at the p11 promoter, as well as an increase in repressive histone methylation (H3K27me3). Moreover, our results showed that the expression, AcH3 and H3Kme3 levels of p11 gene in response to MS were reduced with age. DNA methylation analysis of the p11 promoter revealed increased CpG methylation in middle-aged MS mice only. The results highlight the age-dependent deleterious effects of ELS on the epigenetic modifications of p11 transcription.

Chronic Isolation Stress Affects Central Neuroendocrine Signaling Leading to a Metabolically Active Microenvironment in a Mouse Model of Breast Cancer

Social isolation is a powerful stressor capable of affecting brain plasticity and function. In the case of breast cancer, previous data indicate that stressful experiences may contribute to a worse prognosis, activating neuroendocrine and metabolism pathways, although the mechanisms underlying these effects are still poorly understood. In this study, we tested the hypothesis that chronic isolation stress (IS) may boost hypothalamic–pituitary–adrenal (HPA) axis activity, leading to changes in the hypothalamic expression of genes modulating both mood and metabolism in an animal model of breast cancer. This centrally activated signaling cascade would, in turn, affect the mammary gland microenvironment specifically targeting fat metabolism, leading to accelerated tumor onset. MMTVNeuTg female mice (a model of breast cancer developing mammary hyperplasia at 5 months of age) were either group-housed (GH) or subjected to IS from weaning until 5 months of age. At this time, half of these subjects underwent acute restraint stress to assess corticosterone (CORT) levels, while the remaining subjects were characterized for their emotional profile in the forced swimming and saccharin preference tests. At the end of the procedures, all the mice were sacrificed to assess hypothalamic expression levels of Brain-derived neurotrophic factor (Bdnf), Neuropeptide Y (NpY), Agouti-Related Peptide (AgRP), and Serum/Glucocorticoid-Regulated Protein Kinase 1 (SgK1). Leptin and adiponectin expression levels, as well as the presence of brown adipose tissue (BAT), were assessed in mammary fat pads. The IS mice showed higher CORT levels following acute stress and decreased expression of NpY, AgRP, and SgK1, associated with greater behavioral despair in the forced swimming test. Furthermore, they were characterized by increased consumption of saccharin in a preference test, suggesting an enhanced hedonic profile. The IS mice also showed an earlier onset of breast lumps (assessed by palpation) accompanied by elevated levels of adipokines (leptin and adiponectin) and BAT in the mammary fat pads. Overall, these data point to IS as a pervasive stressor that is able to specifically target neuronal circuits, mastered by the hypothalamus, modulating mood, stress reactivity and energy homeostasis. The activation of such IS-driven machinery may hold main implications for the onset and maintenance of pro-tumorigenic environments.

Cellular senescence as a driver of cognitive decline triggered by chronic unpredictable stress

When an individual is under stress, the undesired effect on the brain often exceeds expectations. Additionally, when stress persists for a long time, it can trigger serious health problems, particularly depression. Recent studies have revealed that depressed patients have a higher rate of brain aging than healthy subjects and that depression increases dementia risk later in life. However, it remains unknown which factors are involved in brain aging triggered by chronic stress. The most critical change during brain aging is the decline in cognitive function. In addition, cellular senescence is a stable state of cell cycle arrest that occurs because of damage and/or stress and is considered a sign of aging. We used the chronic unpredictable stress (CUS) model to mimic stressful life situations and found that, compared with nonstressed control mice, CUS-treated C57BL/6 mice exhibited depression-like behaviors and cognitive decline. Additionally, the protein expression of the senescence marker p16^INK4a was increased in the hippocampus, and senescence-associated β-galactosidase (SA-β-gal)-positive cells were found in the hippocampal dentate gyrus (DG) in CUS-treated mice. Furthermore, the levels of SA-β-gal or p16^INK4a were strongly correlated with the severity of memory impairment in CUS-treated mice, whereas clearing senescent cells using the pharmacological senolytic cocktail dasatinib plus quercetin (D + Q) alleviated CUS-induced cognitive deficits, suggesting that targeting senescent cells may be a promising candidate approach to study chronic stress-induced cognitive decline. Our findings open new avenues for stress-related research and provide new insight into the association of chronic stress-induced cellular senescence with cognitive deficits.

A Novel Role for Hypothalamic AgRP Neurons in Mediating Depressive Behavior

A recent paper by Fang et al. examined the role of Agouti-Related Peptide (AgRP)-expressing neurons in the arcuate nucleus of the hypothalamus in mediating depressive-like behavior in mice. Chronic, but not acute stress, led to changes in neuronal excitability in AgRP neurons concomitant with the display of depressive-like behaviors, which were bidirectionally modulated using AgRP-selective chemogenetic manipulations. Together, these findings broaden our understanding of the diverse roles AgRP neurons play in driving motivational states, aside from their influence on hunger and feeding behaviors.