Neural circuitry among connecting the hippocampus, prefrontal cortex and basolateral amygdala in a mouse depression model: Associations correlations between BDNF levels and BOLD – fMRI signals

From Perspective of Hippocampal Plasticity: Function of Antidepressant Chinese Medicine Xiaoyaosan

The hippocampus is one of the most commonly studied brain regions in the context of depression. The volume of the hippocampus is significantly reduced in patients with depression, which severely disrupts hippocampal neuroplasticity. However, antidepressant therapies that target hippocampal neuroplasticity have not been identified as yet. Chinese medicine (CM) can slow the progression of depression, potentially by modulating hippocampal neuroplasticity. Xiaoyaosan (XYS) is a CM formula that has been clinically used for the treatment of depression. It is known to protect Gan (Liver) and Pi (Spleen) function, and may exert its antidepressant effects by regulating hippocampal neuroplasticity. In this review, we have summarized the association between depression and aberrant hippocampal neuroplasticity. Furthermore, we have discussed the researches published in the last 30 years on the effects of XYS on hippocampal neuroplasticity in order to elucidate the possible mechanisms underlying its therapeutic action against depression. The results of this review can aid future research on XYS for the treatment of depression.

How BDNF affects working memory in acute sleep deprivation: The mediating role of spontaneous brain activity

The brain-derived neurotrophic factor (BDNF) mediates the plasticity associated with memory processing, and compensatorily increases after acute sleep deprivation (SD). However, whether the altered spontaneous brain activity mediates the association between BDNF and working memory in SD remains unknown. Here, we aimed to probe the mediating role of the spontaneous brain activity between plasma BDNF and WM function in SD. A total of 30 healthy subjects with regular sleep were enrolled in this study. Resting-sate functional magnetic resonance imaging (fMRI) scans and the peripheral blood were collected before and after 24 h SD. All participants also received n-back task assessing working memory (WM) performance. The amplitude of low-frequency fluctuation (ALFF) and fractional ALFF (fALFF) were calculated to reflect the intensity of regional spontaneous brain activity. Plasma BDNF was measured by sandwich ELISA. Our results revealed a significant decline in WM and increase in plasma BDNF level after SD, and negative association between the changed WM performance and plasma BDNF level. Specially, the ALFF of the left inferior parietal cortex and right inferior frontal cortex, and fALFF of the left anterior cingulate and medial prefrontal cortex and left posterior opercular cortex regulated the association between the BDNF and one-back reaction time respectively. Our results suggest that the association between BDNF and working memory may be mediated through regional spontaneous brain activity involving in the cerebral cortex, which may provide new sight into the interaction between neurotrophic factors and cognition, and potential targets for noninvasive brain stimulation on WM decline after acute SD.

Role of Brain-Derived Neurotrophic Factor in Anxiety or Depression After Percutaneous Coronary Intervention

Anxiety or depression after percutaneous coronary intervention (PCI) is one of the key clinical problems in cardiology that need to be solved urgently. Brain-derived neurotrophic factor (BDNF) may be a potential biomarker for the pathogenesis and treatment of anxiety or depression after PCI. This article reviews the correlation between BDNF and cardiovascular system and nervous system from the aspects of synthesis, release and action site of BDNF, and focuses on the latest research progress of the mechanism of BDNF in anxiety or depression after PCI. It includes the specific mechanisms by which BDNF regulates the levels of inflammatory factors, reduces oxidative stress damage, and mediates multiple signaling pathways. In addition, this review summarizes the therapeutic potential of BDNF as a potential biomarker for anxiety or depression after PCI.

Effects of Chaihu Shugan San on Brain Functional Network Connectivity in the Hippocampus of a Perimenopausal Depression Rat Model

In this study, we used Chaihu Shugan San (CSS), a traditional Chinese herbal formula, as a probe to investigate the involvement of brain functional network connectivity and hippocampus energy metabolism in perimenopausal depression. A network pharmacology approach was performed to discover the underlying mechanisms of CSS in improving perimenopausal depression, which were verified in perimenopausal depression rat models. Network pharmacology analysis indicated that complex mechanisms of energy metabolism, neurotransmitter metabolism, inflammation, and hormone metabolic processes were closely associated with the anti-depressive effects of CSS. Thus, the serum concentrations of estradiol (E2), glutamate (Glu), and 5-hydroxytryptamine (5-HT) were detected by ELISA. The brain functional network connectivity between the hippocampus and adjacent brain regions was evaluated using resting-state functional magnetic resonance imaging (fMRI). A targeted metabolomic analysis of the hippocampal tricarboxylic acid cycle was also performed to measure the changes in hippocampal energy metabolism using liquid chromatography-tandem mass spectrometry (LC-MS/MS). CSS treatment significantly improved the behavioral performance, decreased the serum Glu levels, and increased the serum 5-HT levels of PMS + CUMS rats. The brain functional connectivity between the hippocampus and other brain regions was significantly changed by PMS + CUMS processes but improved by CSS treatment. Moreover, among the metabolites in the hippocampal tricarboxylic acid cycle, the concentrations of citrate and the upregulation of isocitrate and downregulation of guanosine triphosphate (GTP) in PMS + CUMS rats could be significantly improved by CSS treatment. A brain functional network connectivity mechanism may be involved in perimenopausal depression, wherein the hippocampal tricarboxylic acid cycle plays a vital role.

The Effects of Chronic Unpredictable Mild Stress and Semi-Pure Diets on the Brain, Gut and Adrenal Medulla in C57BL6 Mice

Chronic stress is known to perturb serotonergic regulation in the brain, leading to mood, learning and memory impairments and increasing the risk of developing mood disorders. The influence of the gut microbiota on serotonergic regulation in the brain has received increased attention recently, justifying the investigation of the role of diet on the gut and the brain in mood disorders. Here, using a 4-week chronic unpredictable mild stress (CUMS) model in mice, we aimed to investigate the effects of a high-fat high-glycaemic index (HFD) and high-fibre fruit & vegetable "superfood" (SUP) modifications of a semi-pure AIN93M diet on behaviour, serotonin synthesis and metabolism pathway regulation in the brain and the gut, as well as the gut microbiota and the peripheral adrenal medullary system. CUMS induced anxiety-like behaviour, dysregulated the tryptophan and serotonin metabolic pathways in the hippocampus, prefrontal cortex, and colon, and altered the composition of the gut microbiota. CUMS reduced the catecholamine synthetic capacity of the adrenal glands. Differential effects were found in these parameters in the HFD and SUP diet. Thus, dietary modifications may profoundly affect the multiple dynamic systems involved in mood disorders.

Anxiety and depression: A top-down, bottom-up model of circuit function

A functional interplay of bottom-up and top-down processing allows an individual to appropriately respond to the dynamic environment around them. These processing modalities can be represented as attractor states using a dynamical systems model of the brain. The transition probability to move from one attractor state to another is dependent on the stability, depth, neuromodulatory tone, and tonic changes in plasticity. However, how does the relationship between these states change in disease states, such as anxiety or depression? We describe bottom-up and top-down processing from Marr's computational-algorithmic-implementation perspective to understand depressive and anxious disease states. We illustrate examples of bottom-up processing as basolateral amygdala signaling and projections and top-down processing as medial prefrontal cortex internal signaling and projections. Understanding these internal processing dynamics can help us better model the multifaceted elements of anxiety and depression.

MicroRNA-124-3p alleviates cerebral ischaemia-induced neuroaxonal damage by enhancing Nrep expression

OBJECTIVE

Ischaemic stroke has a high death rate and frequently results in long-term and severe brain damage in survivors. miRNA-124-3p (miR-124-3p) treatment has been suggested to reduce ischaemia and play a vital function in avoiding neuron death. An investigation of the role of miR-124-3p, in the ischaemia damage repair or protection in the middle cerebral artery occlusion (MCAO) model and oxygen-glucose deprivation/reperfusion (OGD/R) model, was the purpose of this research.

METHODS

The expression of miRNA and mRNA in the MCAO model was predicted using bioinformatics analysis. The OGD/R neuronal model was developed. We examined the influence of a number of compounds on the OGD/R model in vitro using gain- and loss-of-function approaches.

RESULTS

For starters, miR-124-3p and Nrep level in the MCAO model were found to be lower in the model predicted by bioinformatics than in the sham-operated group. And then in the OGD/R model, miR-124-3p treatment reduced OGD/R neuronal damage, increased neuronal survival, and reduced apoptosis in cell lines. Moreover, we further looked at the impact of miR-124-3p on downstream Rnf38 and Nrep using the OGD/R model. Western blot analysis and dual-luciferase reporter assays indicated that miR-124-3p binds and inhibits Rnf38. Finally, although Nrep expression was reduced in the OGD/R model neuronal model, it was shown that miR-124-3p administration reduced apoptosis and increased neuronal activity, particularly with regard to axon regeneration-related proteins.

CONCLUSION

Our studies have shown that miR-124-3p may reduce neuronal injury by preventing Rnf38-mediated effects on the Nrep axis.

Potential Therapeutic Effects of NAMPT-Mediated NAD Biosynthesis in Depression In Vivo

This study aimed to investigate the potential therapeutic effects of nicotinamide phosphoribosyltransferase (NAMPT)-mediated adenine dinucleotide (NAD) biosynthesis in depression models in vivo. Nampt^flox/flox mice were used to evaluate the role of NAMPT in depression. NAMPT and NAD levels in the prefrontal cortex (PFC) were measured, and depression-associated behavior, cognitive function, and social interaction were evaluated. The expression levels of BDNF, pCREB, CREB, monoamine neurotransmitters, and corticosterone (CORT) were also detected in the PFC. The contents of NAMPT and NAD decreased in the PFC in Nampt^flox/flox mice. Nampt^flox/flox mice showed depression-like behaviors, cognitive function deterioration, decreased social ability, and decreased dominance. Meanwhile, there were decreased expression levels of the pCREB/CREB ratio, but not BDNF, in the PFC. Levels of DA, 5-HT, and NE were decreased, and CORT was activated in the PFC of Nampt^flox/flox mice. Additionally, the role of NAMPT-NAD was examined in rats treated with nicotinamide riboside (NR) after being exposed to chronic unexpected mild stress (CUMS). NR reversed the decreased NAMPT expression in the PFC and HIP, and the NAD content in the PFC, but not HIP in rats with CUMS-induced depression. NR also improved depressive- and anxiolytic-like behaviors, locomotor activity, and cognitive function. BDNF expression and the pCREB/CREB ratio were significantly increased in both the PFC and HIP after NR treatment. The activation of CORT and decreased content of DA were reversed after NR treatment in the PFC. There was no difference in the 5-HT content among groups in both the PFC and HIP. Taken together, NAD synthesis induced by NAMPT could be associated with depression-like behaviors in mice, and the elevated NAD level by NR improved depression in rats.

Differential Regulation of the BDNF Gene in Cortical and Hippocampal Neurons

Brain-derived neurotrophic factor (BDNF) is a widely expressed neurotrophin that supports the survival, differentiation, and signaling of various neuronal populations. Although it has been well described that expression of BDNF is strongly regulated by neuronal activity, little is known whether regulation of BDNF expression is similar in different brain regions. Here, we focused on this fundamental question using neuronal populations obtained from rat cerebral cortices and hippocampi of both sexes. First, we thoroughly characterized the role of the best-described regulators of BDNF gene - cAMP response element binding protein (CREB) family transcription factors, and show that activity-dependent BDNF expression depends more on CREB and the coactivators CREB binding protein (CBP) and CREB-regulated transcriptional coactivator 1 (CRTC1) in cortical than in hippocampal neurons. Our data also reveal an important role of CREB in the early induction of BDNF mRNA expression after neuronal activity and only modest contribution after prolonged neuronal activity. We further corroborated our findings at BDNF protein level. To determine the transcription factors regulating BDNF expression in these rat brain regions in addition to CREB family, we used in vitro DNA pulldown assay coupled with mass spectrometry, chromatin immunoprecipitation (ChIP), and bioinformatics, and propose a number of neurodevelopmentally important transcription factors, such as FOXP1, SATB2, RAI1, BCL11A, and TCF4 as brain region-specific regulators of BDNF expression. Together, our data reveal complicated brain region-specific fine-tuning of BDNF expression.SIGNIFICANCE STATEMENT To date, majority of the research has focused on the regulation of brain-derived neurotrophic factor (BDNF) in the brain but much less is known whether the regulation of BDNF expression is universal in different brain regions and neuronal populations. Here, we report that the best described regulators of BDNF gene from the cAMP-response element binding protein (CREB) transcription factor family have a more profound role in the activity-dependent regulation of BDNF in cortex than in hippocampus. Our results indicate a brain region-specific fine tuning of BDNF expression. Moreover, we have used unbiased determination of novel regulators of the BDNF gene and report a number of neurodevelopmentally important transcription factors as novel potential regulators of the BDNF expression.

Dose-dependent effects of esketamine on brain activity in awake mice: A BOLD phMRI study

Pharmacological magnetic resonance imaging (phMRI) is a noninvasive method used to evaluate neural circuitry involved in the behavioral effects of drugs like ketamine, independent of their specific biochemical mechanism. The study was designed to evaluate the immediate effect of esketamine, the S-isomer of (±) ketamine on brain activity in awake mice using blood oxygenation level dependent (BOLD) imaging. It was hypothesized the prefrontal cortex, hippocampus, and brain areas associated with reward and motivation would show a dose-dependent increase in brain activity. Mice were given vehicle, 1.0, 3.3, or 10 mg/kg esketamine I.P. and imaged for 10 min post-treatment. Data for each treatment were registered to a 3D MRI mouse brain atlas providing site-specific information on 134 different brain areas. There was a global change in brain activity for both positive and negative BOLD signal affecting over 50 brain areas. Many areas showed a dose-dependent decrease in positive BOLD signal, for example, cortex, hippocampus, and thalamus. The most common profile when comparing the three doses was a U-shape with the 3.3 dose having the lowest change in signal. At 1.0 mg/kg there was a significant increase in positive BOLD in forebrain areas and hippocampus. The anticipated dose-dependent increase in BOLD was not realized; instead, the lowest dose of 1.0 mg/kg had the greatest effect on brain activity. The prefrontal cortex and hippocampus were significantly activated corroborating previous imaging studies in humans and animals. The unexpected sensitivity to the 1.0 mg/kg dose of esketamine could be explained by imaging in fully awake mice without the confound of anesthesia and/or its greater affinity for the N-methyl-d-aspartate receptor (NMDAR) receptor than (±) ketamine.

Neuroimmune crosstalk through brain-derived neurotrophic factor and its precursor pro-BDNF: New insights into mood disorders

Mood disorders are the most common mental disorders, affecting approximately 350 million people globally. Recent studies have shown that neuroimmune interaction regulates mood disorders. Brain-derived neurotrophic factor (BDNF) and its precursor pro-BDNF, are involved in the neuroimmune crosstalk during the development of mood disorders. BDNF is implicated in the pathophysiology of psychiatric and neurological disorders especially in antidepressant pharmacotherapy. In this review, we describe the functions of BDNF/pro-BDNF signaling in the central nervous system in the context of mood disorders. In addition, we summarize the developments for BDNF and pro-BDNF functions in mood disorders. This review aims to provide new insights into the impact of neuroimmune interaction on mood disorders and reveal a new basis for further development of diagnostic targets and mood disorders.

How Microbes Affect Depression: Underlying Mechanisms via the Gut-Brain Axis and the Modulating Role of Probiotics

Accumulating evidence suggests that the gut microbiome influences the brain functions and psychological state of its host via the gut-brain axis, and gut dysbiosis has been linked to several mental illnesses, including major depressive disorder (MDD). Animal experiments have shown that a depletion of the gut microbiota leads to behavioral changes, and is associated with pathological changes, including abnormal stress response and impaired adult neurogenesis. Short-chain fatty acids such as butyrate are known to contribute to the up-regulation of brain-derived neurotrophic factor (BDNF), and gut dysbiosis causes decreased levels of BDNF, which could affect neuronal development and synaptic plasticity. Increased gut permeability causes an influx of gut microbial components such as lipopolysaccharides, and the resultant systemic inflammation may lead to neuroinflammation in the central nervous system. In light of the fact that gut microbial factors contribute to the initiation and exacerbation of depressive symptoms, this review summarizes the current understanding of the molecular mechanisms involved in MDD onset, and discusses the therapeutic potential of probiotics, including butyrate-producing bacteria, which can mediate the microbiota-gut-brain axis.

Sex Differences in Affective Dysfunction and Alterations in Parvalbumin in Rodent Models of Early Life Adversity

The early life environment markedly influences brain and behavioral development, with adverse experiences associated with increased risk of anxiety and depressive phenotypes, particularly in females. Indeed, early life adversity (ELA) in humans (i.e., caregiver deprivation, maltreatment) and rodents (i.e., maternal separation, resource scarcity) is associated with sex-specific emergence of anxious and depressive behaviors. Although these disorders show clear sex differences in humans, little attention has been paid toward evaluating sex as a biological variable in models of affective dysfunction; however, recent rodent work suggests sex-specific effects. Two widely used rodent models of ELA approximate caregiver deprivation (i.e., maternal separation) and resource scarcity (i.e., limited bedding). While these approaches model aspects of ELA experienced in humans, they span different portions of the pre-weaning developmental period and may therefore differentially contribute to underlying mechanistic risk. This is borne out in the literature, where evidence suggests differences in trajectories of behavior depending on the type of ELA and/or sex; however, the neural underpinning of these differences is not well understood. Because anxiety and depression are thought to involve dysregulation in the balance of excitatory and inhibitory signaling in ELA-vulnerable brain regions (e.g., prefrontal cortex, amygdala, hippocampus), outcomes are likely driven by alterations in local and/or circuit-specific inhibitory activity. The most abundant GABAergic subtypes in the brain, accounting for approximately 40% of inhibitory neurons, contain the calcium-binding protein Parvalbumin (PV). As PV-expressing neurons have perisomatic and proximal dendritic targets on pyramidal neurons, they are well-positioned to regulate excitatory/inhibitory balance. Recent evidence suggests that PV outcomes following ELA are sex, age, and region-specific and may be influenced by the type and timing of ELA. Here, we suggest the possibility of a combined role of PV and sex hormones driving differences in behavioral outcomes associated with affective dysfunction following ELA. This review evaluates the literature across models of ELA to characterize neural (PV) and behavioral (anxiety- and depressive-like) outcomes as a function of sex and age. Additionally, we detail a putative mechanistic role of PV on ELA-related outcomes and discuss evidence suggesting hormone influences on PV expression/function which may help to explain sex differences in ELA outcomes.

MiR-139-5p has an antidepressant-like effect by targeting phosphodiesterase 4D to activate the cAMP/PKA/CREB signaling pathway

Background

Phosphodiesterase 4D (PDE4D) inhibitor is commonly used to treat depression, but side effects seriously decrease its efficacy. PDE4D was a downstream target mRNA of miR-139-5p. Therefore, we examined the effects of hippocampal miR-139-5p gain- and loss-of-function on depression-like behaviors, the expression level of PDE4D, and hippocampus neurogenesis.

Methods

Bioinformatic analyses were carried out to to screen differential genes. Quantitative real-time polymerase chain reaction (qRT-PCR) and luciferase reporter assay were used to confirm the relationship between miR-139-5p and PDE4D. MiR-139-5p mimics, miR-139-5p inhibitor, or miR-NC were used to explore the function of miR-139-5p in HT-22 cells. We further explored the role of miR-139-5p in vivo using AAV-injection. Elisa, western blotting, and fluorescence in situ hybridization (FISH) were used to detect the expression of miR-139-5p and PDE4D in CRC tissues.

Results

Here, we showed that PDE4D messenger RNA (mRNA) was a direct target of microRNA (miR)-139-5p, which was downregulated in a chronic ultra-mild stress (CUMS)-induced depression mouse model. Moreover, in experiments in vitro, miR-139-5p mimic repressed PDE4D expression in HT-22 cells, but promoted phosphorylated cyclic-AMP response element-binding protein (p-CREB) and brain-derived neurotrophic factor (BDNF) expression. Interestingly, adeno-associated virus (AAV)-miR-139-5p downregulated susceptibility to stress-induced depression-like behaviors in mice. AAV-miR-139-5p suppressed PDE4D in mouse hippocampal cells, increasing expression level of cyclic adenosine monophosphate (cAMP), p-CREB, and BDNF, and stimulating mouse hippocampal neurogenesis.

Conclusions

Our findings suggested that miR-139-5p acted like an antidepressant by targeting PDE4D, thereby regulating the cAMP/protein kinase A (PKA)/CREB/BDNF pathway to improve depression.

Xiaoyaosan Exerts Antidepressant Effect by Downregulating RAGE Expression in Cingulate Gyrus of Depressive-Like Mice

Xiaoyaosan (XYS), as a classic Chinese medicine compound, has been proven to have antidepressant effect in many studies, but its mechanism has not been clarified. In our previous studies, we found that chronic stress can induce depressive-like behavior and lead to emotion-related cingulate gyrus (Cg) dysfunction, as well as the decrease of neurotrophic factors and the increase of inflammatory-related proteins. Therefore, we speculated that XYS may play an antidepressant role by regulating the inflammation-related receptor of advanced glycation protein end product (RAGE) to affect the functional connectivity (FC) signal of the Cg and improve the depressive-like behavior. In order to verify this hypothesis, we analyzed the FC and RAGE expression in the Cg of depressive-like mice induced by chronic unpredictable mild stress (CUMS) and verified it with RAGE knockout mice. At the same time, we detected the effect of XYS on the depressive-like behavior, expression of RAGE, and the FC of the Cg of mice. The results showed that the FC of the Cg of depressive-like mice induced by CUMS was weakened, and the expression of RAGE was upregulated. The antidepressant effect of XYS is similar to that of fluoxetine hydrochloride, which can significantly reduce the depressive-like behavior of mice and inhibit the expression of the RAGE protein and mRNA in the Cg, and increase the FC of the Cg in mice. In conclusion, XYS may play an antidepressant role by downregulating the expression of RAGE in the Cg of depressive-like mice induced by CUMS, thereby affecting the functional signal and improving the depressive-like behavior.

Brain-derived neurotrophic factor upregulates synaptic GluA1 in the amygdala to promote depression in response to psychological stress

Psychological stress impairs neuronal structure and function and leads to emotional disorders, but the underlying mechanisms have not yet been fully elucidated. The amygdala is closely correlated with emotional regulation. In the present study, we analyzed whether the amygdala plasticity is regulated by psychological stress and explored their regulatory mechanism. We established a mouse psychological stress model using an improved communication box, wherein mice were exposed to chronic fear and avoided physical stress interference. After the 14-day psychological stress paradigm, mice exhibited significantly increased depressive behaviors (decreased sucrose consumption in the sucrose preference test and longer immobility time in the forced swimming test). HPLC, ELISA, and molecular and morphological evidences showed that psychological stress increased the content of glutamate and the expression of glutamatergic neurons, upregulated the content of the stress hormone corticosterone, and activated the CREB/BDNF pathway in the amygdala. Furthermore, psychological stress induced an increased density of dendritic spines and LTD impairment in the amygdala. Importantly, virus-mediated silencing of BDNF in the basolateral amygdala (BLA) nuclei reversed the depression-like behaviors and the increase of synaptic GluA1 and its phosphorylation at Ser831 and Ser845 sites in psychologically stressed mice. This process was likely achieved through mTOR signaling activation. Finally, we treated primary amygdala neurons with corticosterone to mimic psychological stress; corticosterone-induced upregulation of GluA1 was prevented by BDNF and mTOR antagonists. Thus, activation of the CREB/BDNF pathway in the amygdala following psychological stress upregulates synaptic GluA1 via mTOR signaling, which dysregulates synaptic plasticity of the amygdala, eventually promoting depression.

Proteomic and metabolomic characterization of amygdala in chronic social defeat stress rats

BACKGROUND

Depression is a leading cause of disability worldwide. There is increasing evidence showing that depression is associated with the pathophysiology in amygdala; however, the underlying mechanism remains poorly understood.

METHOD

We established a rat model of chronic social defeat stress (CSDS) and conducted a series of behavior tests to observe behavioral changes. Then liquid chromatography mass spectrometry (LC-MS)-based metabolomics and isobaric tags for relative and absolute quantitation (iTRAQ)-based proteomics were employed to detect metabolomes and proteomes in the amygdala, respectively. Ingenuity pathway analysis (IPA) and other bioinformatic analyses were used to analyze differentially expressed metabolites and proteins.

RESULTS

The significantly lower sucrose preference index in the sucrose preference test and longer immobile time in the forced swim test were observed in the CSDS rats compared with control rats. In the multi-omics analysis, thirty-seven significantly differentially expressed metabolites and 123 significant proteins were identified. Integrated analysis of differentially expressed metabolites and proteins by IPA revealed molecular changes mainly associated with synaptic plasticity, phospholipase c signaling, and glutamine degradation I. We compared the metabolites in the amygdala with those in the hippocampus and prefrontal cortex from our previous studies and found two common metabolites: arachidonic acid and N-acetyl-l-aspartic acid among these three brain regions.

CONCLUSION

Our study revealed the presence of depressive-like behaviors and molecular changes of amygdala in the CSDS rat model, which may provide further insights into the pathogenesis of depression, and help to identify potential targets for antidepressants.

[Energy metabolism disorder and functional magnetic resonance imaging of the medial prefrontal cortex in mice with chronic unpredictable mild stress]

OBJECTIVE

To analyze spontaneous activities and energy metabolism in the medial prefrontal cortex (mPFC) of mice with chronic unpredictable mild stress (CUMS) and explore the correlation of these changes with the mTORC1 signaling pathway.

OBJECTIVE

Normal C57Bl/6 mice were randomly divided into control group (n=16) and depression model group (n= 16), and the mice in the latter group were subjected to 8 weeks of modeling with CUMS. Behavioral tests including open field test, sucrose consumption test, tail suspension test and forced swimming test were performed, and the changes in prefrontal gray matter volume and the amplitude of low frequency fluctuation (ALFF) in the mice were detected with functional magnetic resonance imaging. The CUMS mice were then randomized into two groups for treatment with ketamine (n=8) or saline (n=8). The mPFC tissues of the mice were collected for detecting the phosphorylation levels of mTORC1-related proteins with Western blotting and ATP level and NADP ⁺/NADPH ratio with ELISA in the 3 groups.

OBJECTIVE

Compared with the control mice, CUMS mice exhibited a distinct depressive phenotype with significantly decreased sucrose preference (P < 0.05) and shortened total distances (P < 0.01) and central exercise distances (P < 0.05) in the open field test without obvious changes of immobile time in tail suspension test and forced swimming test (P>0.05). Prefrontal gray matter volume and mALFF increased (P < 0.01), and the phosphorylation level of mTORC1- related proteins, ATP level and NADP ⁺/NADPH ratio all decreased significantly (P < 0.05) in CUMS mice. After ketamine treatment, the phosphorylation level of mTORC1-related proteins and ATP level increased significantly in CUMS mice (P < 0.05), but the increase of NADP ⁺/NADPH ratio was not statistically significant.

OBJECTIVE

The mPFC of CUMS mice shows increased spontaneous activities but lowered productivity efficiency, indicating the presence of energy metabolism disorder in the mPFC, which is related with reduced mTORC1 phosphorylation and can be alleviated by activating the mTORC1 pathway with ketamine.

Beneficial Effect of Alkaloids From Sophora alopecuroides L. on CUMS-Induced Depression Model Mice via Modulating Gut Microbiota

It was recently shown that the gut microbiota of both depression patients and depression model animals is significantly altered, suggesting that gut microbes are closely related to depression. Here, we investigated the effects of Sophora alopecuroides L.-derived alkaloids on the gut microbiota of mice with depression-like behaviors. We first established a mouse model of depression via chronic unpredictable mild stress (CUMS) and detected changes in depression-like behaviors and depression-related indicators. Simultaneously, 16S rRNA sequencing was performed to investigate gut microbiota changes. Sophora alopecuroides L.-derived alkaloids improved depression-like behaviors and depression-related indicators in mice. The alkaloids decreased the gut microbiota diversity of CUMS mice and depleted intestinal differentially abundant "harmful" microbiota genera. Spearman analysis showed that there is a certain correlation between the differential microbiota (Lactobacillus, Helicobacter, Oscillospira, Odoribacter, Mucispirillum, Ruminococcus), depression-like behaviors, and depression-related indicators. Combined with the predictive analysis of gut microbiota function, these results indicate that alkaloids improve depression in mice through modulating gut microbiota.

The path from trigeminal asymmetry to cognitive impairment: a behavioral and molecular study

Trigeminal input exerts acute and chronic effects on the brain, modulating cognitive functions. Here, new data from humans and animals suggest that these effects are caused by trigeminal influences on the Locus Coeruleus (LC). In humans subjects clenching with masseter asymmetric activity, occlusal correction improved cognition, alongside with reductions in pupil size and anisocoria, proxies of LC activity and asymmetry, respectively. Notably, reductions in pupil size at rest on the hypertonic side predicted cognitive improvements. In adult rats, a distal unilateral section of the trigeminal mandibular branch reduced, on the contralateral side, the expression of c-Fos (brainstem) and BDNF (brainstem, hippocampus, frontal cortex). This counterintuitive finding can be explained by the following model: teeth contact perception loss on the lesioned side results in an increased occlusal effort, which enhances afferent inputs from muscle spindles and posterior periodontal receptors, spared by the distal lesion. Such effort leads to a reduced engagement of the intact side, with a corresponding reduction in the afferent inputs to the LC and in c-Fos and BDNF gene expression. In conclusion, acute effects of malocclusion on performance seem mediated by the LC, which could also contribute to the chronic trophic dysfunction induced by loss of trigeminal input.

Brain areas associated with resilience to depression in high-risk young women

Previous structural brain-imaging studies in first-degree relatives of depressed patients showed alterations that are generally accepted as vulnerability markers for depression. However, only half of the relatives had depression at follow-up, while the other half did not. The aim of this study was to identify the brain areas associated with resilience to depression in high-risk subjects with familial depression. We recruited 59 young women with a history of depressed mothers. Twenty-nine of them (high-risk group [HRG]) had no depression history, while 30 (depressive group) had at least 1 depressive episode in adolescence. The brain structures of the groups were compared through voxel-based morphometry and analysis of cortical thickness. Individual amygdala nuclei and hippocampal subfield volumes were measured. The analysis showed larger amygdala volume, thicker subcallosal cortex and bilateral insula in the women in the HRG compared with those in the depressive group. In addition, we detected more gray matter in the left temporal pole in the HRG. The larger gray matter volume and increased cortical thickness in the key hub regions of the salience network (amygdala and insula) and structurally connected regions in the limbic network (subcallosal area and temporal pole) might prevent women in the HRG from converting to depression.

Meranzin hydrate elicits antidepressant effects and restores reward circuitry

The burden of depression is enormous, and numerous studies have found that major depressive disorder (MDD) induces cardiovascular disorders (CVD) and functional dyspepsia (FD). Excitingly, meranzin hydrate (MH), an absorbed bioactive compound of Aurantii Fructus Immaturus, reverses psychosocial stress-induced mood disorders, gastrointestinal dysfunction and cardiac disease. Pharmacological methods have repeatedly failed in antidepressant development over the past few decades, but repairing aberrant neural circuits might be a reasonable strategy. This article aimed to explore antidepressant-like effects and potential mechanisms of MH in a rat model of unpredictable chronic mild stress (UCMS). Utilizing blood oxygen level-dependent (BOLD) functional magnetic resonance imaging (fMRI), we sought to find reliable neurocircuits or a dominant brain region revealing the multiple effects of MH. The results show that compared with UCMS rats, MH (10 mg/kg/day for 1 week i.g.)-treated rats exhibited decreased depression-like behaviour; increased expression of brain-derived neurotrophic factor (BDNF) in the hippocampal dentate gyrus; and normalized levels of adrenocorticotropic hormone (ACTH), corticosterone (CORT), and acylated ghrelin (AG). Additionally, the UCMS-induced rise in BOLD activation in the reward system was attenuated after MH treatment. A literature search shown that nucleus accumbens (NAc) and hypothalamus of the reward system might reveal multiple effects of MH on MDD-FD-CVD comorbidity. Further research will focus on the role of these two brain regions in treating depression associated with comorbidities.

17β-Estradiol augments the neuroprotective effect of agomelatine in depressive- and anxiety-like behaviors in ovariectomized rats

RATIONALE AND OBJECTIVE

Estradiol decline has been associated with depression and anxiety in post-menopausal women. Agomelatine (Ago) is an agonist of the melatonergic MT1/MT2 receptors and an antagonist of the serotonergic 5-HT2c receptors. The present study aimed to evaluate the effects of combining Ago with 17β-estradiol (E2) on ovariectomy (OVX)-induced depressive- and anxiety-like behaviors in young adult female rats.

METHODS

OVX rats were treated with Ago (40 mg/kg/day, p.o.) for 10 days starting 1 week after surgery alone or combined with two doses of E2 (40 μg/kg/day, s.c.) given before behavioral testing.

RESULTS

Co-administration of E2 enhanced the anti-depressant and anxiolytics effects of Ago as evidenced by decreased immobility time in the forced swimming test, as well as increased time spent in the open arms and number of entries to open arms in the elevated plus-maze. In parallel, Ago increased hippocampal norepinephrine, dopamine, melatonin, and brain-derived neurotrophic factor (BDNF). Meanwhile, Ago-treated rats exhibited reduced hippocampal nuclear factor kappa beta (NF-kB) P65 expression and pro-inflammatory cytokine level. Ago upregulated estrogen receptor (ER α and β) mRNA expression in the hippocampus of OVX rats and elevated serum estradiol levels. Co-administration of E2 with Ago synergistically decreased NF-kB P65 expression and pro-inflammatory cytokines, and increased BDNF levels.

CONCLUSION

E2 augmented the neuroprotective effect of Ago in OVX rats via its anti-inflammatory and neurotrophic effects. The combined treatment of E2 and Ago should be further investigated as a treatment of choice for depression, anxiety, and sleep disturbances associated with menopause.

MRS Shows Regionally Increased Glutamate Levels among Patients with Exhaustion Syndrome Due to Occupational Stress

Despite the rapid increase of reports of exhaustion syndrome (ES) due to daily occupational stress, the mechanisms underlying ES are unknown. We used voxel-based 1H-MR spectroscopy to examine the potential role of glutamate in this condition. The levels of glutamate were found to be elevated among ES patients (n = 30, 16 females) compared with controls (n = 31, 15 females). Notably, this increase was detected only in the anterior cingulate and mesial prefrontal cortex (ACC/mPFC), and the glutamate levels were linearly correlated with the degree of perceived stress. Furthermore, there was a sex by group interaction, as the glutamate elevation was present only in female patients. Female but not male ES patients also showed an increase in N-acetyl aspartate (NAA) levels in the amygdala. No group differences were detected in glutamine concentration (also measured). These data show the key role of glutamate in stress-related neuronal signaling and the specific roles of the amygdala and ACC/mPFC. The data extend previous reports about the neurochemical basis of stress and identify a potential neural marker and mediator of ES due to occupational stress. The observation of specific sex differences provides a tentative explanation to the well-known female predominance in stress-related psychopathology.

Brain-derived neurotrophic factor association with amygdala response in major depressive disorder

BACKGROUND

Brain-derived neurotrophic factor (BDNF) has an essential role in synaptic plasticity and neurogenesis. BDNF mediates amygdala-dependent learning for both aversive and appetitive emotional memories. The expression of BDNF in limbic regions is posited to contribute the development of depression, and amygdala responsivity is a potential marker of depressive state.

METHODS

The present study examined the relationship between platelet BDNF levels and amygdala volume and function in major depressive disorder (MDD). Participants were 23 MDD (mean age 38.9 years) and 23 healthy controls (mean age 38.8 years). All participants were recruited from the community. MDD participants were in a current depressive episode of moderate severity and medication-free. Amygdala responses were acquired during a functional MRI task of implicit emotional processing with sad facial expressions.

RESULTS

Significant correlation was observed between platelet BDNF levels and left amygdala responses, but no significant correlations were found with right amygdala responses or with amygdala volumes.

LIMITATIONS

Interactions with neuroprotective as well as neurotoxic metabolites in the kyneurenine pathway were not examined.

CONCLUSIONS

Relationship between BDNF levels and amygdala responsivity to emotionally salient stimuli in MDD could reflect the importance of BDNF in amygdala-dependent learning with clinical implications for potential pathways for treatment.

The cellular and molecular basis of major depressive disorder: towards a unified model for understanding clinical depression

Major depressive disorder (MDD) is considered a serious public health issue that adversely impacts an individual's quality of life and contributes significantly to the global burden of disease. The clinical heterogeneity that exists among patients limits the ability of MDD to be accurately diagnosed and currently, a symptom-based approach is utilized in many cases. Due to the complex nature of this disorder, and lack of precise knowledge regarding the pathophysiology, effective management is challenging. The aetiology and pathophysiology of MDD remain largely unknown given the complex genetic and environmental interactions that are involved. Nonetheless, the aetiology and pathophysiology of MDD have been the subject of extensive research, and there is a vast body of literature that exists. Here we overview the key hypotheses that have been proposed for the neurobiology of MDD and highlight the need for a unified model, as many of these pathways are integrated. Key pathways discussed include neurotransmission, neuroinflammation, clock gene machinery pathways, oxidative stress, role of neurotrophins, stress response pathways, the endocannabinoid and endovanilloid systems, and the endogenous opioid system. We also describe the current management of MDD, and emerging novel therapies, with particular focus on patients with treatment-resistant depression (TRD).

A study of limbic brain derived neurotrophic factor gene expression in male Sprague-Dawley rats trained on a learned helplessness task

BACKGROUND

Brain derived neurotrophic factor (BDNF) has been linked to the etiology and pathology of Major Depressive Disorder (MDD). Here, the relationship between learned helplessness (LH), a cognitive/motivational state relevant to MDD, and BDNF mRNA in various limbic regions, was investigated.

METHODS

In Sprague-Dawley male rats, LH was induced by escape training, using a triadic design of stressor controllability involving exposure to no shocks (NS), escapable shocks (ES) or yoked inescapable shocks (IES). LH was subsequently assessed in an active avoidance task, and levels of BDNF mRNA in limbic brain regions were compared across the triad following testing.

RESULTS

Although the IES group displayed greater LH, BDNF mRNA levels were lower in the hippocampus and higher in the nucleus accumbens of both IES and ES groups. In contrast, BDNF mRNA in the basolateral amygdala was elevated only in rats exposed to IES.

CONCLUSION

These results suggest that the inability to control an aversive stimulus can lead to a LH behavioural phenotype that is associated with region-specific alterations of BDNF gene expression in limbic nuclei.

Deletion of Dtnbp1 in mice impairs threat memory consolidation and is associated with enhanced inhibitory drive in the amygdala

Schizophrenia is a severe and highly heritable disorder. Dystrobrevin-binding protein 1 (DTNBP1), also known as dysbindin-1, has been implicated in the pathophysiology of schizophrenia. Specifically, dysbindin-1 mRNA and protein expression are decreased in the brains of subjects with this disorder. Mice lacking dysbinidn-1 also display behavioral phenotypes similar to those observed in schizophrenic patients. However, it remains unknown whether deletion of dysbindin-1 impacts functions of the amygdala, a brain region that is critical for emotional processing, which is disrupted in patients with schizophrenia. Here, we show that dysbindin-1 is expressed in both excitatory and inhibitory neurons of the basolateral amygdala (BLA). Deletion of dysbindin-1 in male mice (Dys-/-) impaired cued and context-dependent threat memory, without changes in measures of anxiety. The behavioral deficits observed in Dys-/- mice were associated with perturbations in the BLA, including the enhancement of GABAergic inhibition of pyramidal neurons, increased numbers of parvalbumin interneurons, and morphological abnormalities of dendritic spines on pyramidal neurons. Our findings highlight an important role for dysbindin-1 in the regulation of amygdalar function and indicate that enhanced inhibition of BLA pyramidal neuron activity may contribute to the weakened threat memory expression observed in Dys-/- mice.

Early Stage Alterations in White Matter and Decreased Functional Interhemispheric Hippocampal Connectivity in the 3xTg Mouse Model of Alzheimer's Disease

Alzheimer’s disease (AD) is characterized in the late stages by amyloid-β (Aβ) plaques and neurofibrillary tangles. Nevertheless, recent evidence has indicated that early changes in cerebral connectivity could compromise cognitive functions even before the appearance of the classical neuropathological features. Diffusion tensor imaging (DTI), resting-state functional magnetic resonance imaging (rs-fMRI) and volumetry were performed in the triple transgenic mouse model of AD (3xTg-AD) at 2 months of age, prior to the development of intraneuronal plaque accumulation. We found the 3xTg-AD had significant fractional anisotropy (FA) increase and radial diffusivity (RD) decrease in the cortex compared with wild-type controls, while axial diffusivity (AD) and mean diffusivity (MD) were similar. Interhemispheric hippocampal connectivity was decreased in the 3xTg-AD while connectivity in the caudate putamen (CPu) was similar to controls. Most surprising, ventricular volume in the 3xTg-AD was four times larger than controls. The results obtained in this study characterize the early stage changes in interhemispheric hippocampal connectivity in the 3xTg-AD mouse that could represent a translational biomarker to human models in preclinical stages of the AD.

Modified Xiaoyaosan (MXYS) Exerts Anti-depressive Effects by Rectifying the Brain Blood Oxygen Level-Dependent fMRI Signals and Improving Hippocampal Neurogenesis in Mice

As the traditional Chinese herbal formula, Xiaoyaosan and its modified formula have been described in many previous studies with definite anti-depressive effects, but its underlying mechanism remains mystery. Previous work in our lab has demonstrated that depression induced by chronic stress could generate brain blood oxygen level-dependent (BOLD) functional magnetic resonance imaging (fMRI) signals disorder, accompanied by the impairment of hippocampal neuronal plasticity, decrease of brain-derived neurotrophic factor, and reduction of the number and complexity of adult neurons in the dentate gyrus. We hypothesized that herbal formula based on Xiaoyaosan could exert anti-depressive effects through restoring these neurobiological dysfunctions and rectifying BOLD-fMRI signals. To test this hypothesis, we examined the effect of modified Xiaoyaosan (MXYS) on depressive-like behaviors, as well as hippocampal neurogenesis and BOLD signals in a mice model of chronic unpredictable mild stress (CUMS)-induced depression. MXYS exerted anti-depressant effects on CUMS-induced depression that were similar to the effects of classical antidepressants drug (fluoxetine hydrochloride), with a significant alleviation of depressive-like behaviors, an improvement of hippocampal neurogenesis, and a reversal of activation of BOLD in the limbic system, particularly in the hippocampus. These results suggested that MXYS attenuated CUMS-induced depressive behaviors by rectifying the BOLD signals in the mice hippocampus. These novel results demonstrated that MXYS had anti-depressive effects accompanied by improving BOLD signals and hippocampal neurogenesis, which suggested that BOLD-fMRI signals in brain regions could be a key component for the evaluation of novel antidepressant drugs.