Takeda G Protein-Coupled Receptor 5 Modulates Depression-like Behaviors via Hippocampal CA3 Pyramidal Neurons Afferent to Dorsolateral Septum

The Impact of Depression on Detrimental Changes in Bone Microstructure in Female Mice

Background

Several clinical studies have examined the connection between depression and bone loss, but the cause-and-effect relationship between the two conditions, especially in animal models, is not well-studied.

Methods

A total of 32 female mice were, randomly divided into control group (CON, n=19) and depression group (DEP, n=13). The mice in the DEP group were subjected to 21 consecutive days of restraint stress, following depressive-like behaviors were assessment. The femurs were collected using Micro-Computed Tomography (μCT) and histochemical staining. In parallel, levels of serotonin-related proteins in the brain were measured using Western blot analysis, and sex hormone profiles were determined through liquid chromatography-mass spectrometry/mass spectrometry (LC-MS/MS).

Results

The mice in the DEP group exhibited clear signs of depressive-like behaviors and an increase in serotonin transporter levels (t=-2.435, P< 0.05). In comparison to the CON mice, the DEP mice showed a decrease in bone mineral density (t =3.741, P< 0.05), bone surface area density (t =8.009, P<0.01), percent bone volume (t =4.293, P< 0.05), trabecular number (t =5.844, P<0.01), and connected density (t =11.000, P< 0.05). Additionally, there was an increase in trabecular separation (t =-7.436, P<0.01) in DEP mice. Furthermore, the DEP mice displayed a significant reduction in serum estrogen levels (t =4.340, P< 0.05) and changes in its metabolite (t =-3.325, P< 0.05), while the levels of androgens remained unchanged.

Conclusion

The restraint stress not only led to the development of depressive-like behaviors but also disrupted the estrogen metabolism pathway, resulting in damage to bone mass and microstructure in female mice. These findings suggest that stress-induced depression may pose a risk for bone loss in female mice by altering estrogen metabolism pathways.

TGR5 deficiency in excitatory neurons ameliorates Alzheimer's pathology by regulating APP processing

Bile acids (BAs) metabolism has a significant impact on the pathogenesis of Alzheimer's disease (AD). We found that deoxycholic acid (DCA) increased in brains of AD mice at an early stage. The enhanced production of DCA induces the up-regulation of the bile acid receptor Takeda G protein-coupled receptor (TGR5), which is also specifically increased in neurons of AD mouse brains at an early stage. The accumulation of exogenous DCA impairs cognitive function in wild-type mice, but not in TGR5 knockout mice. This suggests that TGR5 is the primary receptor mediating these effects of DCA. Furthermore, excitatory neuron-specific knockout of TGR5 ameliorates Aβ pathology and cognition impairments in AD mice. The underlying mechanism linking TGR5 and AD pathology relies on the downstream effectors of TGR5 and the APP production, which is succinctly concluded as a "p-STAT3-APH1-γ-secretase" signaling pathway. Our studies identified the critical role of TGR5 in the pathological development of AD.

TGR5-mediated lateral hypothalamus-dCA3-dorsolateral septum circuit regulates depressive-like behavior in male mice

Although bile acids play a notable role in depression, the pathological significance of the bile acid TGR5 membrane-type receptor in this disorder remains elusive. Using depression models of chronic social defeat stress and chronic restraint stress in male mice, we found that TGR5 in the lateral hypothalamic area (LHA) predominantly decreased in GABAergic neurons, the excitability of which increased in depressive-like mice. Upregulation of TGR5 or inhibition of GABAergic excitability in LHA markedly alleviated depressive-like behavior, whereas down-regulation of TGR5 or enhancement of GABAergic excitability facilitated stress-induced depressive-like behavior. TGR5 also bidirectionally regulated excitability of LHA GABAergic neurons via extracellular regulated protein kinases-dependent Kv4.2 channels. Notably, LHA GABAergic neurons specifically innervated dorsal CA3 (dCA3) CaMKIIα neurons for mediation of depressive-like behavior. LHA GABAergic TGR5 exerted antidepressant-like effects by disinhibiting dCA3 CaMKIIα neurons projecting to the dorsolateral septum (DLS). These findings advance our understanding of TGR5 and the LHAGABA→dCA3CaMKIIα→DLSGABA circuit for the development of potential therapeutic strategies in depression.

The oxytocin receptor is essential for the protective effect of pair housing on post-stroke depression in mice

The beneficial effect of social interaction in mitigating the incidence of post-stroke depression (PSD) and ameliorating depressive symptoms has been consistently demonstrated through preclinical and clinical studies. However, the underlying relationship with oxytocin requires further investigation. In light of this, the present study aimed to explore the protective effect of pair housing on the development of PSD and the potential relationship with oxytocin receptors. The PSD model was induced by middle cerebral artery occlusion (MCAO) for 50 min, followed by 4-week isolated housing and restrained stress. Subsequently, each mouse in the pair-housing group (PH) was pair-housed with an isosexual healthy partner. Another group was continuously administrated fluoxetine (10 mg/Kg, i.p, once a day) for 3 weeks. To elucidate the potential role of oxytocin, we subjected pair-housed PSD mice to treatment with an oxytocin receptor (OXTR) antagonist (L368,889) (5 mg/Kg, i.p, once a day) for 3 weeks. At 31 to 32 days after MCAO, anxiety- and depressive-like behaviors were assessed using sucrose consumption, forced swim test, and tail-suspension test. The results showed that pair housing significantly improved post-stroke depression to an extent comparable to that of fluoxetine treatment. Furthermore, pair housing significantly decreased corticosterone in serum, increasing OXT mRNA expression in the hypothalamus. Treatment with L368,889 essentially reversed the effect of pair housing, with no discernible sex differences apart from changes in body weight. Pair housing increased hippocampal serotonin (5-HT), but treatment with L368,889 had no significant impact. Additionally, pair housing effectively reduced the number of reactive astrocytes and increased Nissl's body in the cortex and hippocampal CA3 regions. Correspondingly, treatment with L368,889 significantly reversed the changes in the Nissl's body and reactive astrocytes. Moreover, pair housing downregulated mRNA levels of TNF-α, IL-1β, and IL-6 in the cortex caused by PSD, which was also reversed by treatment with L368,889. In conclusion, pair housing protects against the development of PSD depending on OXT and OXTR in the brain, with no significant divergence based on sex. These findings provide valuable insights into the potential of social interaction and oxytocin as therapeutic targets for PSD. Further research into the underlying mechanisms of these effects may contribute to the development of novel treatments for PSD.

The antidepressant effects of protein arginine methyltransferase 2 involve neuroinflammation

Protein arginine methyltransferase (PRMT) 2 catalyzes the methylation of arginine residues in histones. Depression is associated with histone methylation; however, more comprehensive research is needed on how PRMT2 regulates depression. The present study aimed to investigate the effects and possible mechanism(s) of PRMT2 overexpression on depression-like behavior induced by chronic unpredictable mild stress (CUMS) in rats, and whether lentivirus-mediated PRMT2 overexpression in the hippocampus suppresses depression-like behavior. Furthermore, the PRMT2 inhibitor MS023 was administered to the animals to investigate whether the antidepressant effect of PRMT2 overexpression could be reversed. Behavioral experiments were performed to detect depression-like behavior in rats. Western blotting was used to determine protein expression levels of PRMT2, histone H3R8 asymmetric dimethylation (H3R8me2a), inducible nitric oxide synthase (iNOS), and arginase 1 (Arg1) in rat hippocampal tissues. Hippocampal microglia and PRMT2 were stained using immunofluorescence techniques. Enzyme-linked immunosorbent assay was used to determine the levels of various inflammatory factors in rat hippocampal tissue. Results of analysis revealed that PRMT2 overexpression in the hippocampus exerted an antidepressant effect. PRMT2 overexpression in the hippocampus reduced the proportion of activated microglia in the hippocampus, upregulated Arg1 and H3R8me2a expression, and downregulated iNOS expression. PRMT2 overexpression in the hippocampus inhibited the release of pro-inflammatory factors and promoted the release of anti-inflammatory factors. In summary, PRMT2 overexpression in the hippocampus promoted the conversion of microglia from the M1 to M2 type, resulting in an antidepressant effect. These results suggest that PRMT2 may be a potential therapeutic target to prevent and treat depression.

Increased intestinal bile acid absorption contributes to age-related cognitive impairment

Cognitive impairment in the elderly is associated with alterations in bile acid (BA) metabolism. In this study, we observe elevated levels of serum conjugated primary bile acids (CPBAs) and ammonia in elderly individuals, mild cognitive impairment, Alzheimer's disease, and aging rodents, with a more pronounced change in females. These changes are correlated with increased expression of the ileal apical sodium-bile acid transporter (ASBT), hippocampal synapse loss, and elevated brain CPBA and ammonia levels in rodents. In vitro experiments confirm that a CPBA, taurocholic acid, and ammonia induced synaptic loss. Manipulating intestinal BA transport using ASBT activators or inhibitors demonstrates the impact on brain CPBA and ammonia levels as well as cognitive decline in rodents. Additionally, administration of an intestinal BA sequestrant, cholestyramine, alleviates cognitive impairment, normalizing CPBAs and ammonia in aging mice. These findings highlight the potential of targeting intestinal BA absorption as a therapeutic strategy for age-related cognitive impairment.

Optogenetic behavioral studies in depression research: A systematic review

Optogenetics has made substantial contributions to our understanding of the mechanistic underpinnings of depression. This systematic review employs quantitative analysis to investigate the impact of optogenetic stimulation in mice and rats on behavioral alterations in social interaction, sucrose consumption, and mobility. The review analyses optogenetic behavioral studies using standardized behavioral tests to detect behavioral changes induced via optogenetic stimulation in stressed or stress-naive mice and rats. Behavioral changes were evaluated as either positive, negative, or not effective. The analysis comprises the outcomes of 248 behavioral tests of 168 studies described in 37 articles, including negative and null results. Test outcomes were compared for each behavior, depending on the animal cohort, applied type of stimulation and the stimulated neuronal circuit and cell type. The presented synthesis contributes toward a comprehensive picture of optogenetic behavioral research in the context of depression.

Gut bacteria-driven homovanillic acid alleviates depression by modulating synaptic integrity

The gut-brain axis is implicated in depression development, yet its underlying mechanism remains unclear. We observed depleted gut bacterial species, including Bifidobacterium longum and Roseburia intestinalis, and the neurotransmitter homovanillic acid (HVA) in individuals with depression and mouse depression models. Although R. intestinalis does not directly produce HVA, it enhances B. longum abundance, leading to HVA generation. This highlights a synergistic interaction among gut microbiota in regulating intestinal neurotransmitter production. Administering HVA, B. longum, or R. intestinalis to mouse models with chronic unpredictable mild stress (CUMS) and corticosterone (CORT)-induced depression significantly improved depressive symptoms. Mechanistically, HVA inhibited synaptic autophagic death by preventing excessive degradation of microtubule-associated protein 1 light chain 3 (LC3) and SQSTM1/p62 proteins, protecting hippocampal neurons' presynaptic membrane. These findings underscore the role of the gut microbial metabolism in modulating synaptic integrity and provide insights into potential novel treatment strategies for depression.

Bile acid signaling in the regulation of whole body metabolic and immunological homeostasis

Bile acids (BAs) play a crucial role in nutrient absorption and act as key regulators of lipid and glucose metabolism and immune homeostasis. Through the enterohepatic circulation, BAs are synthesized, metabolized, and reabsorbed, with a portion entering the vascular circulation and distributing systemically. This allows BAs to interact with receptors in all major organs, leading to organ-organ interactions that regulate both local and global metabolic processes, as well as the immune system. This review focuses on the whole-body effects of BA-mediated metabolic and immunological regulation, including in the brain, heart, liver, intestine, eyes, skin, adipose tissue, and muscle. Targeting BA synthesis and receptor signaling is a promising strategy for the development of novel therapies for various diseases throughout the body.

Locus Coeruleus-Dorsolateral Septum Projections Modulate Depression-Like Behaviors via BDNF But Not Norepinephrine

Locus coeruleus (LC) dysfunction is involved in the pathophysiology of depression; however, the neural circuits and specific molecular mechanisms responsible for this dysfunction remain unclear. Here, it is shown that activation of tyrosine hydroxylase (TH) neurons in the LC alleviates depression-like behaviors in susceptible mice. The dorsolateral septum (dLS) is the most physiologically relevant output from the LC under stress. Stimulation of the LCTH -dLSSST innervation with optogenetic and chemogenetic tools bidirectionally can regulate depression-like behaviors in both male and female mice. Mechanistically, it is found that brain-derived neurotrophic factor (BDNF), but not norepinephrine, is required for the circuit to produce antidepressant-like effects. Genetic overexpression of BDNF in the circuit or supplementation with BDNF protein in the dLS is sufficient to produce antidepressant-like effects. Furthermore, viral knockdown of BDNF in this circuit abolishes the antidepressant-like effect of ketamine, but not fluoxetine. Collectively, these findings underscore the notable antidepressant-like role of the LCTH -dLSSST pathway in depression via BDNF-TrkB signaling.

TGR5 deficiency-induced anxiety and depression-like behaviors: The role of gut microbiota dysbiosis

BACKGROUND AND PURPOSE

Anxiety and depression have been associated with imbalances in the gut microbiota and bile acid metabolism. Takeda G protein-coupled receptor 5 (TGR5), a bile acid receptor involved in metabolism, is influenced by the gut microbiota. This study aimed to investigate the relationship between anxiety, depression, and microbiota using TGR5 knockout mice.

METHODS

We employed the following methods: (1) Assessment of behavioral changes, (2) Measurement of 5-HT levels and protein expression, (3) Analysis of stool samples, (4) Utilization of gene sequencing and statistical analysis to identify microbial signatures, (5) Examination of correlations between microbial signatures and 5-HT levels, and (6) Fecal microbiota transplantation experiments of TGR5-/- mice.

RESULTS

The deletion of TGR5 was found to result in increased anxiety- and depression-like behaviors in mice. TGR5 knockout mice exhibited significant reductions in 5-hydroxytryptamine (5-HT) levels in both serum and hippocampus, accompanied by a decrease in the expression of 5-HT1A receptor in the hippocampus. Moreover, TGR5 deficiency was associated with a decrease in the species richness of the gut microbiota. Specifically, the gut microbiota compositions of TGR5 knockout mice displayed distinct differences compared to their littermates, characterized by higher abundances of Anaeroplasma, Prevotella, Staphylococcus, Jeotgalicoccus, and Helicobacter, and a lower abundance of Bifidobacterium. Notably, a strong association between Jeotgalicoccus as well as Staphylococcus and serum 5-HT levels was observed in co-occurrence network. Furthermore, mice that received fecal microbiota transplants from TGR5-/- mice displayed anxiety and depression -like behaviors, accompanied by alterations in 5-HT levels in the hippocampus and serum.

LIMITATIONS

Study limitations for gut bacteria were analyzed at the genus level only.

CONCLUSION

TGR5 deletion in mice induces anxiety and depression-like behaviors, linked to reduced 5-HT levels in serum and the hippocampus. Gut microbiota changes play a direct role in these behaviors and serotonin alterations. This implicates TGR5 and gut bacteria in mood regulation, with potential therapeutic implications.

The role of CD38 in inflammation-induced depression-like behavior and the antidepressant effect of (R)-ketamine

CD38 is involved in immune responses, cell proliferation, and has been identified in the brain, where it is implicated in inflammation processes and psychiatric disorders. We hypothesized that dysfunctional CD38 activity in the brain may contribute to the pathogenesis of depression. To investigate the underlying mechanisms, we used a lipopolysaccharide (LPS)-induced depression-like model and conducted behavioral tests, molecular and morphological methods, along with optogenetic techniques. We microinjected adeno-associated virus into the hippocampal CA3 region with stereotaxic instrumentation. Our results showed a marked increase in CD38 expression in both the hippocampus and cortex of LPS-treated mice. Additionally, pharmacological inhibition and genetic knockout of CD38 effectively alleviated neuroinflammation, microglia activation, synaptic defects, and Sirt1/STAT3 signaling, subsequently improving depression-like behaviors. Moreover, optogenetic activation of glutamatergic neurons of hippocampal CA3 reduced the susceptibility of mice to depression-like behaviors, accompanied by reduced CD38 expression. We also found that (R)-ketamine, which displayed antidepressant effects, was linked to its anti-inflammatory properties by suppressing increased CD38 expression and reversing synaptic defects. In conclusion, hippocampal CD38 is closely linked to depression-like behaviors in an inflammation model, highlighting its potential as a therapeutic target for antidepressant development.

miR-204-5p Plays a Critical Role in the Pathogenesis of Depression and Anti-depression Action of Venlafaxine in the Hippocampus of Mice

BACKGROUND

Venlafaxine has been demonstrated to treat diseases such as social anxiety disorder and depression. Most of antidepressants including venlafaxine have a certain effect, but significant side effects. Therefore, it is necessary for us to research the development of novel antidepressants for effective treatment in practice. MicroRNA-204 (miR-204) is highly expressed in brain tissue, and plays a critical role in the synaptic plasticity of hippocampal neurons in rats. However, the underlying molecular mechanism of miR-204 remains unclear to date, this study aims to offer unique insights into depression and provide a theoretical basis for clinical physicians.

METHODS

A chronic social defeat stress (CSDS) was initially adopted for establishing a mice model of depression in this research and depression-like behaviors were evaluated by a series of behavioral experiments including the sucrose preference test (SPT), the tail suspension test (TST), the forced swim test (FST) and the social interaction test (SIT). Quantitative real-time reverse transcription PCR (qRT-PCR) was also conducted to test the expression levels of miR-204 and BDNF in the hippocampus of mice. Finally, gene interference of miR-204-5p was further adopted to test whether miR-204-5p played an effective role in the antidepressant effects of venlafaxine in mice.

RESULTS

Our data implicated that CSDS significantly increased the miR-204-5p but not miR-204-3p levels in the hippocampus of mice. The treatment of venlafaxine obviously relieved depression- like behaviors of CSDS-induced mice. The usage of venlafaxine abolished the increasing effects on the expression of miR-204-5p but up-regulated the BDNF expression level in CSDS-exposured mice. More importantly, we found that genetic overexpression of miR-204-5p decreased the reverse effects of venlafaxine on depressive-like behaviors and genetic knockdown of hippocampal miR-204-5p relieved the depressive-like behaviors and neurogenesis in CSDS-induced mice.

CONCLUSION

miR-204-5p played an effective role in the antidepressant effects of venlafaxine in CSDS-induced mice.

The efficacy and safety of some new GABAkines for treatment of depression: A systematic review and meta-analysis from randomized controlled trials

Positive allosteric modulators of γ-aminobutyric acid-A (GABAA) receptors, or GABAkines, play important roles in the treatment of depression, epilepsy, insomnia, and other disorders. Recently, some new GABAkines (zuranolone and brexanolone) have been administrated to patients with major depressive disorder (MDD) or postpartum depression (PPD) in randomized controlled trials (RCTs). This study aims to systematically review and examine the efficacy and safety of zuranolone or brexanolone for treatment of depression. A systematic literature retrieval was conducted through August 20, 2023. RCTs evaluating the efficacy and safety of zuranolone or brexanolone for treatment of depression were included. Eight studies (nine reports) were identified in the study. The percentages of patients with PPD achieving Hamilton Depression Rating Scale (HAM-D) response and remission were significantly higher after brexanolone or zuranolone administration compared with placebo at different points. The percentages of patients with MDD achieving HAM-D response and remission were significantly increased during the zuranolone treatment period compared with placebo. In addition, zuranolone caused more adverse events in patients with MDD compared with placebo. Our findings support the effects of brexanolone on improving the core symptoms of depression in patients with PPD, and the potential of zuranolone in treating patients with MDD or PPD.

Involvement of brain cell phenotypes in stress-vulnerability and resilience

Stress-related disorders' prevalence is epidemically increasing in modern society, leading to a severe impact on individuals' well-being and a great economic burden on public resources. Based on this, it is critical to understand the mechanisms by which stress induces these disorders. The study of stress made great progress in the past decades, from deeper into the hypothalamic-pituitary-adrenal axis to the understanding of the involvement of a single cell subtype on stress outcomes. In fact, many studies have used state-of-the-art tools such as chemogenetic, optogenetic, genetic manipulation, electrophysiology, pharmacology, and immunohistochemistry to investigate the role of specific cell subtypes in the stress response. In this review, we aim to gather studies addressing the involvement of specific brain cell subtypes in stress-related responses, exploring possible mechanisms associated with stress vulnerability versus resilience in preclinical models. We particularly focus on the involvement of the astrocytes, microglia, medium spiny neurons, parvalbumin neurons, pyramidal neurons, serotonergic neurons, and interneurons of different brain areas in stress-induced outcomes, resilience, and vulnerability to stress. We believe that this review can shed light on how diverse molecular mechanisms, involving specific receptors, neurotrophic factors, epigenetic enzymes, and miRNAs, among others, within these brain cell subtypes, are associated with the expression of a stress-susceptible or resilient phenotype, advancing the understanding/knowledge on the specific machinery implicate in those events.

AI Machine Learning Technique Characterizes Potential Markers of Depression in Two Animal Models of Depression

(1) Background: there is an urgent clinical need for rapid and effective antidepressants. (2) Methods: We employed proteomics to profile proteins in two animal models (n = 48) of Chronic Unpredictable Stress and Chronic Social Defeat Stress. Additionally, partial least squares projection to latent structure discriminant analysis and machine learning were used to distinguish the models and the healthy control, extract and select protein features and build biomarker panels for the identification of different mouse models of depression. (3) Results: The two depression models were significantly different from the healthy control, and there were common changes in proteins in the depression-related brain regions of the two models; i.e., SRCN1 was down-regulated in the dorsal raphe nucleus in both models of depression. Additionally, SYIM was up-regulated in the medial prefrontal cortex in the two depression models. Bioinformatics analysis suggested that perturbed proteins are involved in energy metabolism, nerve projection, etc. Further examination confirmed that the trends of feature proteins were consistent with mRNA expression levels. (4) Conclusions: To the best of our knowledge, this is the first study to probe new targets of depression in multiple brain regions of two typical models of depression, which could be targets worthy of study.

Lateral septum adenosine A2A receptors control stress-induced depressive-like behaviors via signaling to the hypothalamus and habenula

Major depressive disorder ranks as a major burden of disease worldwide, yet the current antidepressant medications are limited by frequent non-responsiveness and significant side effects. The lateral septum (LS) is thought to control of depression, however, the cellular and circuit substrates are largely unknown. Here, we identified a subpopulation of LS GABAergic adenosine A2A receptors (A2AR)-positive neurons mediating depressive symptoms via direct projects to the lateral habenula (LHb) and the dorsomedial hypothalamus (DMH). Activation of A2AR in the LS augmented the spiking frequency of A2AR-positive neurons leading to a decreased activation of surrounding neurons and the bi-directional manipulation of LS-A2AR activity demonstrated that LS-A2ARs are necessary and sufficient to trigger depressive phenotypes. Thus, the optogenetic modulation (stimulation or inhibition) of LS-A2AR-positive neuronal activity or LS-A2AR-positive neurons projection terminals to the LHb or DMH, phenocopied depressive behaviors. Moreover, A2AR are upregulated in the LS in two male mouse models of repeated stress-induced depression. This identification that aberrantly increased A2AR signaling in the LS is a critical upstream regulator of repeated stress-induced depressive-like behaviors provides a neurophysiological and circuit-based justification of the antidepressant potential of A2AR antagonists, prompting their clinical translation.

Bile Acids Induce Neurite Outgrowth in Nsc-34 Cells via TGR5 and a Distinct Transcriptional Profile

Increasing evidence supports a neuroprotective role for bile acids in major neurodegenerative disorders. We studied major human bile acids as signaling molecules for their two cellular receptors, farnesoid X receptor (FXR or NR1H4) and G protein-coupled bile acid receptor 1 (GPBAR1 or TGR5), as potential neurotrophic agents. Using quantitative image analysis, we found that 20 μM deoxycholic acid (DCA) could induce neurite outgrowth in NSC-34 cells that was comparable to the neurotrophic effects of the culture control 1 μM retinoic acid (RA), with lesser effects observed for chenodexoycholic acid (CDCA) at 20 μM, and similar though less robust neurite outgrowth in SH-SY5Y cells. Using chemical agonists and antagonists of FXR, LXR, and TGR5, we found that TGR5 agonism was comparable to DCA stimulation and stronger than RA, and that neither FXR nor liver X receptor (LXR) inhibition could block bile acid-induced neurite growth. RNA sequencing identified a core set of genes whose expression was regulated by DCA, CDCA, and RA. Our data suggest that bile acid signaling through TGR5 may be a targetable pathway to stimulate neurite outgrowth.

GABAergic neurons in the dorsomedial hypothalamus regulate states of consciousness in sevoflurane anesthesia

The neural inhibitory gamma-aminobutyric acid (GABA) system in the regulation of anesthetic consciousness is heterogeneous, and the medial hypothalamus (MH), consisting of ventromedial hypothalamus (VMH) and dorsomedial hypothalamus (DMH), plays an important role in sleep and circadian rhythm. However, the role of MH GABAergic neurons (MH^GABA) in anesthesia remains unclear. In this study, we used righting reflex, electroencephalogram (EEG), and arousal behavioral score to evaluate the sevoflurane anesthesia. Activation of MH^GABA or DMH^GABA neurons prolonged the anesthesia induction time, shortened the anesthesia emergence time, and induced EEG arousal and body movement during anesthesia; meanwhile, VMH^GABA neurons activated only induced EEG changes during 1.5% sevoflurane anesthesia. Furthermore, inhibition of DMH^GABA neurons significantly deepened sevoflurane anesthesia. Therefore, DMH^GABA neurons exert a strong emergence-promoting effect on induction, maintenance, and arousal during sevoflurane general anesthesia, which helps to reveal the mechanism of anesthesia.

Depressive patient-derived GABA interneurons reveal abnormal neural activity associated with HTR2C

Major depressive disorder with suicide behavior (sMDD) is a server mood disorder, bringing tremendous burden to family and society. Although reduced gamma amino butyric acid (GABA) level has been observed in postmortem tissues of sMDD patients, the molecular mechanism by which GABA levels are altered remains elusive. In this study, we generated induced pluripotent stem cells (iPSC) from five sMDD patients and differentiated the iPSCs to GABAergic interneurons (GINs) and ventral forebrain organoids. sMDD GINs exhibited altered neuronal morphology and increased neural firing, as well as weakened calcium signaling propagation, compared with controls. Transcriptomic sequencing revealed that a decreased expression of serotoninergic receptor 2C (5-HT2C) may cause the defected neuronal activity in sMDD. Furthermore, targeting 5-HT2C receptor, using a small molecule agonist or genetic approach, restored neuronal activity deficits in sMDD GINs. Our findings provide a human cellular model for studying the molecular mechanisms and drug discoveries for sMDD.

Linking Nonalcoholic Fatty Liver Disease and Brain Disease: Focusing on Bile Acid Signaling

A metabolic illness known as non-alcoholic fatty liver disease (NAFLD), affects more than one-quarter of the world's population. Bile acids (BAs), as detergents involved in lipid digestion, show an abnormal metabolism in patients with NAFLD. However, BAs can affect other organs as well, such as the brain, where it has a neuroprotective effect. According to a series of studies, brain disorders may be extrahepatic manifestations of NAFLD, such as depression, changes to the cerebrovascular system, and worsening cognitive ability. Consequently, we propose that NAFLD affects the development of brain disease, through the bile acid signaling pathway. Through direct or indirect channels, BAs can send messages to the brain. Some BAs may operate directly on the central Farnesoid X receptor (FXR) and the G protein bile acid-activated receptor 1 (GPBAR1) by overcoming the blood-brain barrier (BBB). Furthermore, glucagon-like peptide-1 (GLP-1) and the fibroblast growth factor (FGF) 19 are released from the intestine FXR and GPBAR1 receptors, upon activation, both of which send signals to the brain. Inflammatory, systemic metabolic disorders in the liver and brain are regulated by the bile acid-activated receptors FXR and GPBAR1, which are potential therapeutic targets. From a bile acid viewpoint, we examine the bile acid signaling changes in NAFLD and brain disease. We also recommend the development of dual GPBAR1/FXR ligands to reduce side effects and manage NAFLD and brain disease efficiently.

Activation of Somatostatin-Expressing Neurons in the Lateral Septum Improves Stress-Induced Depressive-like Behaviors in Mice

Depression is a debilitating mood disorder with highly heterogeneous pathogenesis. The limbic system is well-linked to depression. As an important node in the limbic system, the lateral septum (LS) can modulate multiple affective and motivational behaviors. However, the role of LS in depression remains unclear. By using c-Fos expression mapping, we first screened and showed activation of the LS in various depression-related behavioral tests, including the forced swim test (FST), tail suspension test (TST), and sucrose preference test. In the LS, more than 10% of the activated neurons were somatostatin-expressing (SST) neurons. We next developed a microendoscopic calcium imaging method in freely moving mice and revealed that LS^SST neural activity increased during mobility in the TST but not open field test. We hypothesize that LS^SST neuronal activity is linked to stress and depression. In two mouse models of depression, repeated lipopolysaccharide (LPS) injection and chronic restraint stress (CRS), we showed that LS neuronal activation was suppressed. To examine whether the re-activation of LS^SST neurons can be therapeutically beneficial, we optogenetically activated LS^SST neurons and produced antidepressant-like effects in LPS-injected mice by increasing TST motility. Moreover, chemogenetic activation of LS^SST neurons increased FST struggling in the CRS-exposed mice. Together, these results provide the first evidence of a role for LS^SST neurons in regulating depressive-like behaviors in mice and identify them as a potential therapeutic target for neuromodulation-based intervention in depression.

Social defeat drives hyperexcitation of the piriform cortex to induce learning and memory impairment but not mood-related disorders in mice

Clinical studies have shown that social defeat is an important cause of mood-related disorders, accompanied by learning and memory impairment in humans. The mechanism of mood-related disorders has been widely studied. However, the specific neural network involved in learning and memory impairment caused by social defeat remains unclear. In this study, behavioral test results showed that the mice induced both learning and memory impairments and mood-related disorders after exposure to chronic social defeat stress (CSDS). c-Fos immunofluorescence and fiber photometry recording confirmed that CaMKIIα expressing neurons of the piriform cortex (PC) were selectively activated by exposure to CSDS. Next, chemogenetics and optogenetics were performed to activate PC CaMKIIα expressing neurons, which showed learning and memory impairment but not mood-related disorders. Furthermore, chemogenetic inhibition of PC CaMKIIα expressing neurons significantly alleviated learning and memory impairment induced by exposure to CSDS but did not relieve mood-related disorders. Therefore, our data suggest that the overactivation of PC CaMKIIα expressing neurons mediates CSDS-induced learning and memory impairment, but not mood-related disorders, and provides a potential therapeutic target for learning and memory impairment induced by social defeat.

Dynamic influences on the neural encoding of social valence

Social signals can serve as potent emotional triggers with powerful impacts on processes from cognition to valence processing. How are social signals dynamically and flexibly associated with positive or negative valence? How do our past social experiences and present social standing shape our motivation to seek or avoid social contact? We discuss a model in which social attributes, social history, social memory, social rank and social isolation can flexibly influence valence assignment to social stimuli, termed here as 'social valence'. We emphasize how the brain encodes each of these four factors and highlight the neural circuits and mechanisms that play a part in the perception of social attributes, social memory and social rank, as well as how these factors affect valence systems associated with social stimuli. We highlight the impact of social isolation, dissecting the neural and behavioural mechanisms that mediate the effects of acute versus prolonged periods of social isolation. Importantly, we discuss conceptual models that may account for the potential shift in valence of social stimuli from positive to negative as the period of isolation extends in time. Collectively, this Review identifies factors that control the formation and attribution of social valence - integrating diverse areas of research and emphasizing their unique contributions to the categorization of social stimuli as positive or negative.

Activation of liver X receptors protects oligodendrocytes in CA3 of stress-induced mice

Depression is a complex disorder that is associated with various structural abnormalities. Oligodendrocyte (OL) dysfunction is associated with the pathogenesis of depression and the promotion of hippocampal oligodendrocyte maturation and myelination could be a novel therapeutic strategy for ameliorating depressive behaviors. Recent studies have shown that activation of liver X receptors (LXRs) by GW3965 improves depressive phenotypes, but the effects of GW3965 on OL function and myelination in the hippocampus of depression remain relatively unclear. To address this issue, we investigated the effects of GW3965 on mature OL in the hippocampus and on the myelin sheaths of mice subjected to chronic unpredictable stress (CUS). Behavioral tests were performed to assess depressive behaviors. Then, the number of mature OLs (CC1⁺) in each hippocampal subregion was precisely quantified with immunohistochemical and stereological methods, and the density of newborn mature OLs (BrdU⁺/Olig2⁺/CC1⁺ cells) in each hippocampal subregion was quantified with immunofluorescence. In addition, myelin basic protein (MBP) staining intensity in the cornu ammonis 3 (CA3) region was assessed by using immunofluorescence. We found that both the number of CC1⁺ OLs and the density of BrdU⁺/Olig2⁺/CC1⁺ cells were obviously decreased in each hippocampal subregion of mice subjected to CUS, and 4 weeks of GW3965 treatment reversed these effects only in the CA3 region. Furthermore, the decreased MBP expression in the CA3 region of mice subjected to CUS was ameliorated by GW3965 treatment. Collectively, these results suggested that improvement of OL maturation and enhancement of myelination may be structural mechanisms underlying the antidepressant effects of LXR agonists.

Reduced astrocytic mGluR5 in the hippocampus is associated with stress-induced depressive-like behaviors in mice

Major depressive disorder (MDD) is one of the most common and disabling mental disorders that characterized by profound disturbances in emotional regulation, motivation, cognition, and the physiology of affected individuals. Although MDD was initially thought to be primarily triggered through neuronal dysfunction, the pathological alterations in astrocytic function have been previously reported in MDD. We report that chronic restraint stress (CRS) induces astrocyte activation and decreases expression of astrocytic mGluR5 in the hippocampal CA1 of susceptible mice exhibited depressive-like behaviors. Reducing expression of astrocytic mGluR5 in dorsal CA1 simulates CRS-induced depressive-like behaviors and impairs excitatory synaptic function in mice, while overexpression of astrocytic mGluR5 in dorsal CA1 rescues CRS-induced depressive-like traits and excitatory synaptic dysfunction. Thus, we provide direct evidence for an important role of astrocytic mGluR5 in producing the behavioral phenotypes of MDD, supporting astrocytic mGluR5 may serve as an effective therapeutic target for MDD.

Antidepressant Active Ingredients From Chinese Traditional Herb Panax Notoginseng: A Pharmacological Mechanism Review

Depression is one of the most common mental illnesses in the world and is highly disabling, lethal, and seriously endangers social stability. The side effects of clinical drugs used to treat depression are obvious, and the onset time is longer. Therefore, there is a great demand for antidepressant drugs with better curative effects, fewer side effects, and shorter onset time. Panax notoginseng, a Chinese herbal medication, has been used to treat depression for thousands of years and shown to have a therapeutic effect on depression. This review surveyed PubMed’s most recent 20 years of research on Panax notoginseng’s use for treating depression. We mainly highlight animal model research and outlined the pathways influenced by medicines. We provide a narrative review of recent empirical evidence of the anti-depressive effects of Panax Notoginseng and novel ideas for developing innovative clinical antidepressants with fewer side effects.

Adaptation of prelimbic cortex mediated by IL-6/STAT3/Acp5 pathway contributes to the comorbidity of neuropathic pain and depression in rats

Background

The adaption of brain region is fundamental to the development and maintenance of nervous system disorders. The prelimbic cortex (PrL) participates in the affective components of the pain sensation. However, whether and how the adaptation of PrL contributes to the comorbidity of neuropathic pain and depression are unknown.

Methods

Using resting-state functional magnetic resonance imaging (rs-fMRI), genetic knockdown or overexpression, we systematically investigated the activity of PrL region in the pathogenesis of neuropathic pain/depression comorbid using the combined approaches of immunohistochemistry, electrophysiology, and behavior.

Results

The activity of PrL and the excitability of pyramidal neurons were decreased, and the osteoclastic tartrate-resistant acid phosphatase 5 (Acp5) expression in PrL neurons was upregulated following the acquisition of spared nerve injury (SNI)-induced comorbidity. Genetic knockdown of Acp5 in pyramidal neurons, but not parvalbumin (PV) neurons or somatostatin (SST) neurons, attenuated the decrease of spike number, depression-like behavior and mechanical allodynia in comorbidity rats. Overexpression of Acp5 in PrL pyramidal neurons decreased the spike number and induced the comorbid-like behavior in naïve rats. Moreover, the expression of interleukin-6 (IL-6), phosphorylated STAT3 (p-STAT3) and acetylated histone H3 (Ac-H3) were significantly increased following the acquisition of comorbidity in rats. Increased binding of STAT3 to the Acp5 gene promoter and the interaction between STAT3 and p300 enhanced acetylation of histone H3 and facilitated the transcription of Acp5 in PrL in the modeled rodents. Inhibition of IL-6/STAT3 pathway prevented the Acp5 upregulation and attenuated the comorbid-like behaviors in rats.

Conclusions

These data suggest that the adaptation of PrL mediated by IL-6/STAT3/Acp5 pathway contributed to the comorbidity of neuropathic pain/depression induced by SNI.

Activation of TGR5 Ameliorates Streptozotocin-Induced Cognitive Impairment by Modulating Apoptosis, Neurogenesis, and Neuronal Firing

Takeda G protein-coupled receptor 5 (TGR5) is the first known G protein-coupled receptor specific for bile acids and is recognized as a new and critical target for type 2 diabetes and metabolic syndrome. It is expressed in many brain regions associated with memory such as the hippocampus and frontal cortex. Here, we hypothesize that activation of TGR5 may ameliorate streptozotocin- (STZ-) induced cognitive impairment. The mouse model of cognitive impairment was established by a single intracerebroventricular (ICV) injection of STZ (3.0 mg/kg), and we found that TGR5 activation by its agonist INT-777 (1.5 or 3.0 μg/mouse, ICV injection) ameliorated spatial memory impairment in the Morris water maze and Y-maze tests. Importantly, INT-777 reversed STZ-induced downregulation of TGR5 and glucose usage deficits. Our results further showed that INT-777 suppressed neuronal apoptosis and improved neurogenesis which were involved in tau phosphorylation and CREB-BDNF signaling. Moreover, INT-777 increased action potential firing of excitatory pyramidal neurons in the hippocampal CA3 and medial prefrontal cortex of ICV-STZ groups. Taken together, these findings reveal that activation of TGR5 has a neuroprotective effect against STZ-induced cognitive impairment by modulating apoptosis, neurogenesis, and neuronal firing in the brain and TGR5 might be a novel and potential target for Alzheimer's disease.

Gut Microbiota-Mediated Elevated Production of Secondary Bile Acids in Chronic Unpredictable Mild Stress

A growing body of evidence suggests that gut microbiota could participate in the progression of depression via the microbiota–gut–brain axis. However, the detailed microbial metabolic profile changes in the progression of depression is still not fully elucidated. In this study, a liquid chromatography coupled to mass spectrometry-based untargeted serum high-throughput metabolomics method was first performed to screen for potential biomarkers in a depressive-like state in a chronic unpredictable mild stress (CUMS)-induced mouse model. Our results identified that the bile acid and energy metabolism pathways were significantly affected in CUMS progression. The detailed bile acid profiles were subsequently quantified in the serum, liver, and feces. The results showed that CUMS significantly promoted the deconjugation of conjugated bile acid and secondary bile acid biosynthesis. Furthermore, 16S rRNA gene sequencing revealed that the increased secondary bile acid levels in the feces positively correlated with Ruminococcaceae_UCG-010, Ruminococcus, and Clostridia_UCG-014 abundance. Taken together, our study suggested that changes in family Ruminococcaceae abundance following chronic stress increased biosynthesis of deoxycholic acid (DCA), a unconjugated secondary bile acid in the intestine. Aberrant activation of secondary bile acid biosynthesis pathway thereby increased the hydrophobicity of the bile acid pool, which might, in turn, promoted metabolic disturbances and disease progression in CUMS mice.

A circuit from dorsal hippocampal CA3 to parvafox nucleus mediates chronic social defeat stress-induced deficits in preference for social novelty

The preference for social novelty is crucial to the social life of humans and rodents. However, the neural mechanisms underlying social novelty preference are poorly understood. Here, we found that chronic social defeat stress (CSDS) reduced the preference for social novelty in mice by impairing the response of CaMKIIα⁺ neurons in the CA3 region of dorsal hippocampus (dCA3) during approach to an unfamiliar mouse. The deficits of social novelty preference in CSDS-treated mice were reversed by activating the output from dCA3 to the GABAergic neurons in the lateral septum (LS). The activation of GABAergic projection from LS recruited a circuit that inhibited the Foxb1⁺ neurons in the parvafox nucleus (PFN), which drove social avoidance by projecting to the lateral periaqueductal gray (lPAG). These results suggest that a previously unidentified circuit of dCA3^CaMKIIα+→LS^GABA+→PFN^Foxb1+→lPAG mediates the deficits of social novelty preference induced by CSDS.

Hippocampal CysLT1R overexpression or activation accelerates memory deficits, synaptic dysfunction, and amyloidogenesis in young APP/PS1 transgenic mice

Background

Our previous studies demonstrated that cysteinyl leukotrienes receptor 1 (CysLT₁R) knockout, pharmacological blockade, or hippocampus knockdown produced beneficial effects against Alzheimer’s disease (AD); however, whether CysLT₁R upregulation has deleterious effects on AD remains elusive.

Methods

In this study, we investigated the changes in behaviors, hippocampal amyloidogenesis, and synapse plasticity after CysLT₁R overexpression by microinfusion of the lentiviral vector, containing its coding sequence of mouse (LV-CysLT₁R), into the bilateral dentate gyri (DG) of the hippocampus or CysLT₁R activation by repeated systemic administration of its agonist YM-17690 (0.1 mg/kg, once a day, i.p., for 28 d).

Results

The behavior data showed that overexpression of CysLT₁R in hippocampal DG or administration of YM-17690 deteriorated behavioral performance in Morris water maze (MWM), Y-maze tests, and novel object recognition (NOR) in young APP/PS1 mice. The further studies showed that these treatments significantly destroyed synaptic function, as evidenced by impaired hippocampal long-term potentiation (LTP), decreased spine density, low number of synapses, and decreased postsynaptic protein (PSD95), and promoted the generation of amyloid β (Aβ) through increased expression of BACE1 and PS1 in the hippocampus of young APP/PS1 mice.

Conclusions

Together, our results indicate that CysLT₁R upregulation accelerates memory impairment in young APP/PS1 mice, which is associated with promoting synaptic dysfunction and amyloidogenesis in the hippocampus.