BDNF overexpression in mouse hippocampal astrocytes promotes local neurogenesis and elicits anxiolytic-like activities

An astroglial basis of major depressive disorder: Molecular, Cellular, and Circuit Features

Major depressive disorder (MDD) is a common psychiatric disorder and has been a leading cause of disability worldwide. Astrocytes play a role in the maintenance of the function of the central nervous system (CNS), both physiologically and pathologically. Accumulated evidence indicates that the astrocyte is an important contributor to the pathophysiology of MDD including blood-brain barrier (BBB) integrity, gap junctions, gliotransmission, glutamate homeostasis, and energy metabolism. Here, we comprehensively summarize an astroglial basis for MDD based on molecular, cellular, and circuit properties, suggesting that astrocytes appear to be highly sensitive to stress and are likely to be uniquely positioned to integrate peripheral and central stress responses.

The multifaceted effects of fluoxetine treatment on cognitive functions

Fluoxetine, the prototypical selective serotonin reuptake inhibitor (SSRI), is widely used to treat major depressive disorder (MDD) and a variety of other central nervous system conditions, primarily due to its established clinical safety profile. Although its efficacy in treating depression is well-recognized, the impact of fluoxetine on cognitive functions remains inconsistent and elusive. In this review, we first examine the well-substantiated biological mechanisms underlying fluoxetine's antidepressant effects, which include serotonin reuptake inhibition and activation of TrkB receptors-key to brain-derived neurotrophic factor (BDNF) signaling. Subsequently, we delve into the cognitive side effects observed in both preclinical and clinical studies, affecting domains such as memory, attention, and executive functions. While certain studies indicate cognitive improvements in patients with underlying disorders, there is also evidence of negative effects, influenced by variables like gender, duration of treatment, age, disease pathology, and the specifics of cognitive testing. Significantly, the negative cognitive outcomes reported in preclinical research often involve healthy, non-diseased animals. This review underscores the necessity for heightened caution in fluoxetine prescription and further investigation into its potentially detrimental cognitive effects, even when used prophylactically.

The effect of SSRIs on unconditioned anxiety: a systematic review and meta-analysis of animal studies

RATIONALE

Selective serotonin reuptake inhibitors (SSRIs) are the first choice of treatment for anxiety-like disorders. However, which aspects of anxiety are affected by SSRIs is not yet fully understood.

OBJECTIVE

We aimed to systematically review the effect of six clinically effective SSRIs on four aspects of unconditioned anxiety: approach-avoidance behaviour (elevated plus maze), repetitive behaviour (marble burying), distress behaviour (ultrasonic vocalization), and activation of the autonomous nervous system (stress-induced hyperthermia).

METHODS

We identified publications by searching Medline and Embase databases and assessed the risk of bias. A random effects meta-analysis was performed and moderator effects were analysed with Bayesian penalized meta-regression.

RESULTS

Our search yielded 105 elevated plus maze, 63 marble burying, 11 ultrasonic vocalization, and 7 stress-induced hyperthermia articles. Meta-analysis suggested that SSRIs reduce anxiety-like behaviour in the elevated plus maze, marble burying and ultrasonic vocalization test and that effects are moderated by pre-existing stress conditions (elevated plus maze) and dose dependency (marble burying) but not by duration of treatment or type of SSRI. The reporting quality was low, publication bias was likely, and heterogeneity was high.

CONCLUSION

SSRIs seem to reduce a broad range of unconditioned anxiety-associated behaviours. These results should be interpreted with caution due to a high risk of bias, likely occurrence of publication bias, substantial heterogeneity and limited moderator data availability. Our review demonstrates the importance of including bias assessments when interpreting meta-analysis results. We further recommend improving the reporting quality, the conduct of animal research, and the publication of all results regardless of significance.

Chronic chemogenetic activation of hippocampal progenitors enhances adult neurogenesis and modulates anxiety-like behavior and fear extinction learning

Adult hippocampal neurogenesis is a lifelong process that involves the integration of newborn neurons into the hippocampal network, and plays a role in cognitive function and the modulation of mood-related behavior. Here, we sought to address the impact of chemogenetic activation of adult hippocampal progenitors on distinct stages of progenitor development, including quiescent stem cell activation, progenitor turnover, differentiation and morphological maturation. We find that hM3Dq-DREADD-mediated activation of nestin-positive adult hippocampal progenitors recruits quiescent stem cells, enhances progenitor proliferation, increases doublecortin-positive newborn neuron number, accompanied by an acceleration of differentiation and morphological maturation, associated with increased dendritic complexity. Behavioral analysis indicated anxiolytic behavioral responses in transgenic mice subjected to chemogenetic activation of adult hippocampal progenitors at timepoints when newborn neurons are predicted to integrate into the mature hippocampal network. Furthermore, we noted an enhanced fear memory extinction on a contextual fear memory learning task in transgenic mice subjected to chemogenetic activation of adult hippocampal progenitors. Our findings indicate that hM3Dq-DREAD-mediated chemogenetic activation of adult hippocampal progenitors impacts distinct aspects of hippocampal neurogenesis, associated with the regulation of anxiety-like behavior and fear memory extinction.

Role of Glial Cells in Neuronal Function, Mood Disorders, and Drug Addiction

Mood disorders and substance use disorder (SUD) are of immense medical and social concern. Although significant progress on neuronal involvement in mood and reward circuitries has been achieved, it is only relatively recently that the role of glia in these disorders has attracted attention. Detailed understanding of the glial functions in these devastating diseases could offer novel interventions. Here, following a brief review of circuitries involved in mood regulation and reward perception, the specific contributions of neurotrophic factors, neuroinflammation, and gut microbiota to these diseases are highlighted. In this context, the role of specific glial cells (e.g., microglia, astroglia, oligodendrocytes, and synantocytes) on phenotypic manifestation of mood disorders or SUD are emphasized. In addition, use of this knowledge in the potential development of novel therapeutics is touched upon.

Brain-derived neurotrophic factor from microglia regulates neuronal development in the medial prefrontal cortex and its associated social behavior

Microglia and brain-derived neurotrophic factor (BDNF) are essential for the neuroplasticity that characterizes critical developmental periods. The experience-dependent development of social behaviors-associated with the medial prefrontal cortex (mPFC)-has a critical period during the juvenile period in mice. However, whether microglia and BDNF affect social development remains unclear. Herein, we aimed to elucidate the effects of microglia-derived BDNF on social behaviors and mPFC development. Mice that underwent social isolation during p21-p35 had increased Bdnf in the microglia accompanied by reduced adulthood sociability. Additionally, transgenic mice overexpressing microglial Bdnf-regulated using doxycycline at different time points-underwent behavioral, electrophysiological, and gene expression analyses. In these mice, long-term overexpression of microglial BDNF impaired sociability and excessive mPFC inhibitory neuronal circuit activity. However, administering doxycycline to normalize BDNF from p21 normalized sociability and electrophysiological function in the mPFC, whereas normalizing BDNF from later ages (p45-p50) did not normalize electrophysiological abnormalities in the mPFC, despite the improved sociability. To evaluate the possible role of BDNF in human sociability, we analyzed the relationship between adverse childhood experiences and BDNF expression in human macrophages, a possible proxy for microglia. Results show that adverse childhood experiences positively correlated with BDNF expression in M2 but not M1 macrophages. In summary, our study demonstrated the influence of microglial BDNF on the development of experience-dependent social behaviors in mice, emphasizing its specific impact on the maturation of mPFC function, particularly during the juvenile period. Furthermore, our results propose a translational implication by suggesting a potential link between BDNF secretion from macrophages and childhood experiences in humans.

Intermittent theta burst stimulation combined with cognitive training improves cognitive dysfunction and physical dysfunction in patients with post-stroke cognitive impairment

OBJECTIVE

Post-stroke cognitive impairment (PSCI) is a common complication of stroke. Intermittent theta burst stimulation (iTBS) can inducing motor learning. We observed the effects of combination of iTBS with cognitive training on physical/cognitive dysfunctions in PSCI patients.

METHODS

PSCI patients treated with basic treatment & cognitive training (Control group)/iTBS & cognitive training (iTBS group) were enrolled, with Mini-mental State Examination (MMSE)/Montreal Cognitive Assessment (MoCA)/Frontal Assessment Battery (FAB)/barthel index (BI)/Upper Limb Fugl-Meyer Assessment (U-FMA)/Action Research Arm Test (ARAT) scores compared. Gait spatiotemporal parameters/dynamic parameters were analyzed by 3D gait analysis. Correlations between MMSE/MoCA scores and gait parameters in PSCI patients after iTBS & cognitive training were analyzed by Spearman analysis.

RESULTS

Increased MMSE/MoCA/FAB/BI/U-FMA/ARAT scores, step speed, step frequency, stride length, step width, step length on the affected side, percentage of swing phase on the affected side, hip joint flexion angle on the affected side, knee joint flexion angle on the affected side, and ankle plantar flexion angle on the affected side and reduced gait period on the affected side and percentage of stance phase on the affected side were found in patients of both groups after treatment, with the effects in the iTBS group more profound.

CONCLUSION

iTBS & cognitive training obviously improved the cognitive function scores/upper limb function scores/gait parameters in PSCI patients versus cognitive training treatment. After combination therapy, the MMSE/MoCA scores of PSCI patients were significantly correlated with gait parameters. This provided more data support for iTBS & cognitive training application in the rehabilitation treatment of PSCI patients.

Effect of 2-Week Naringin Supplementation on Neurogenesis and BDNF Levels in Ischemia-Reperfusion Model of Rats

BACKGROUND

Ischemic stroke is the leading cause of mortality and disability worldwide with more than half of survivors living with serious neurological sequelae; thus, it has recently attracted a lot of attention in the field of medical study.

PURPOSE

The aim of this study was to determine the effect of naringin supplementation on neurogenesis and brain-derived neurotrophic factor (BDNF) levels in the brain in experimental brain ischemia-reperfusion.

STUDY DESIGN

The research was carried out on 40 male Wistar-type rats (10-12 weeks old) obtained from the Experimental Animals Research and Application Center of Selçuk University. Experimental groups were as follows: (1) Control group, (2) Sham group, (3) Brain ischemia-reperfusion group, (4) Brain ischemia-reperfusion + vehicle group (administered for 14 days), and (5) Brain ischemia-reperfusion + Naringin group (100 mg/kg/day administered for 14 days).

METHODS

In the ischemia-reperfusion groups, global ischemia was performed in the brain by ligation of the right and left carotid arteries for 30 min. Naringin was administered to experimental animals by intragastric route for 14 days following reperfusion. The training phase of the rotarod test was started 4 days before ischemia-reperfusion, and the test phase together with neurological scoring was performed the day before and 1, 7, and 14 days after the operation. At the end of the experiment, animals were sacrificed, and then hippocampus and frontal cortex tissues were taken from the brain. Double cortin marker (DCX), neuronal nuclear antigen marker (NeuN), and BDNF were evaluated in hippocampus and frontal cortex tissues by Real-Time qPCR analysis and immunohistochemistry methods.

RESULTS

While ischemia-reperfusion increased the neurological score values, DCX, NeuN, and BDNF levels decreased significantly after ischemia in the hippocampus and frontal cortex tissues. However, naringin supplementation restored the deterioration to a certain extent.

CONCLUSION

The results of the study show that 2 weeks of naringin supplementation may have protective effects on impaired neurogenesis and BDNF levels after brain ischemia and reperfusion in rats.

Association between CNS-active drugs and risk of Alzheimer's and age-related neurodegenerative diseases

Objective

As neuropsychiatric conditions can increase the risk of age-related neurodegenerative diseases (NDDs), the impact of CNS-active drugs on the risk of developing Alzheimer's Disease (AD), non-AD dementia, Multiple Sclerosis (MS), Parkinson's Disease (PD) and Amyotrophic Lateral Sclerosis (ALS) was investigated.

Research design and methods

A retrospective cohort analysis of a medical claims dataset over a 10 year span was conducted in patients aged 60 years or older. Participants were propensity score matched for comorbidity severity and demographic parameters. Relative risk (RR) ratios and 95% confidence intervals (CI) were determined for age-related NDDs. Cumulative hazard ratios and treatment duration were determined to assess the association between CNS-active drugs and NDDs at different ages and treatment duration intervals.

Results

In 309,128 patients who met inclusion criteria, exposure to CNS-active drugs was associated with a decreased risk of AD (0.86% vs 1.73%, RR: 0.50; 95% CI: 0.47-0.53; p <.0001) and all NDDs (3.13% vs 5.76%, RR: 0.54; 95% CI: 0.53-0.56; p <.0001). Analysis of impact of drug class on risk of AD indicated that antidepressant, sedative, anticonvulsant, and stimulant medications were associated with significantly reduced risk of AD whereas atypical antipsychotics were associated with increased AD risk. The greatest risk reduction for AD and NDDs occurred in patients aged 70 years or older with a protective effect only in patients with long-term therapy (>3 years). Furthermore, responders to these therapeutics were characterized by diagnosed obesity and higher prescriptions of anti-inflammatory drugs and menopausal hormonal therapy, compared to patients with a diagnosis of AD (non-responders). Addition of a second CNS-active drug was associated with greater reduction in AD risk compared to monotherapy, with the combination of a Z-drug and an SNRI associated with greatest AD risk reduction.

Conclusion

Collectively, these findings indicate that CNS-active drugs were associated with reduced risk of developing AD and other age-related NDDs. The exception was atypical antipsychotics, which increased risk. Potential use of combination therapy with atypical antipsychotics could mitigate the risk conferred by these drugs. Evidence from these analyses advance precision prevention strategies to reduce the risk of age-related NDDs in persons with neuropsychiatric disorders.

Major depressive disorder: hypothesis, mechanism, prevention and treatment

Worldwide, the incidence of major depressive disorder (MDD) is increasing annually, resulting in greater economic and social burdens. Moreover, the pathological mechanisms of MDD and the mechanisms underlying the effects of pharmacological treatments for MDD are complex and unclear, and additional diagnostic and therapeutic strategies for MDD still are needed. The currently widely accepted theories of MDD pathogenesis include the neurotransmitter and receptor hypothesis, hypothalamic-pituitary-adrenal (HPA) axis hypothesis, cytokine hypothesis, neuroplasticity hypothesis and systemic influence hypothesis, but these hypothesis cannot completely explain the pathological mechanism of MDD. Even it is still hard to adopt only one hypothesis to completely reveal the pathogenesis of MDD, thus in recent years, great progress has been made in elucidating the roles of multiple organ interactions in the pathogenesis MDD and identifying novel therapeutic approaches and multitarget modulatory strategies, further revealing the disease features of MDD. Furthermore, some newly discovered potential pharmacological targets and newly studied antidepressants have attracted widespread attention, some reagents have even been approved for clinical treatment and some novel therapeutic methods such as phototherapy and acupuncture have been discovered to have effective improvement for the depressive symptoms. In this work, we comprehensively summarize the latest research on the pathogenesis and diagnosis of MDD, preventive approaches and therapeutic medicines, as well as the related clinical trials.

Neurotrophins and neural stem cells in posttraumatic brain injury repair

Traumatic brain injury (TBI) is the main cause of disability, mental health disorder, and even death, with its incidence and social costs rising steadily. Although different treatment strategies have been developed and tested to mitigate neurological decline, a definitive cure for these conditions remains elusive. Studies have revealed that various neurotrophins represented by the brain-derived neurotrophic factor are the key regulators of neuroinflammation, apoptosis, blood-brain barrier permeability, neurite regeneration, and memory function. These factors are instrumental in alleviating neuroinflammation and promoting neuroregeneration. In addition, neural stem cells (NSC) contribute to nerve repair through inherent neuroprotective and immunomodulatory properties, the release of neurotrophins, the activation of endogenous NSCs, and intercellular signaling. Notably, innovative research proposals are emerging to combine BDNF and NSCs, enabling them to synergistically complement and promote each other in facilitating injury repair and improving neuron differentiation after TBI. In this review, we summarize the mechanism of neurotrophins in promoting neurogenesis and restoring neural function after TBI, comprehensively explore the potential therapeutic effects of various neurotrophins in basic research on TBI, and investigate their interaction with NSCs. This endeavor aims to provide a valuable insight into the clinical treatment and transformation of neurotrophins in TBI, thereby promoting the progress of TBI therapeutics.

Identification of the antidepressant effect of electroconvulsive stimulation-related genes in hippocampal astrocyte

Major depressive disorder (MDD) remains a significant global health concern, with limited and slow efficacy of existing antidepressants. Electroconvulsive therapy (ECT) has superior and immediate efficacy for MDD, but its action mechanism remains elusive. Therefore, the elucidation of the action mechanism of ECT is expected to lead to the development of novel antidepressants with superior and immediate efficacy. Recent studies suggest a potential role of hippocampal astrocyte in MDD and ECT. Hence, we investigated antidepressant effect of electroconvulsive stimulation (ECS), an animal model of ECT, -related genes in hippocampal astrocyte with a mouse model of MDD, in which corticosterone (CORT)-induced depression-like behaviors were recovered by ECS. In this model, both of CORT-induced depression-like behaviors and the reduction of hippocampal astrocyte were recovered by ECS. Following it, astrocytes were isolated from the hippocampus of this model and RNA-seq was performed with these isolated astrocytes. Interestingly, gene expression patterns altered by CORT were reversed by ECS. Additionally, cell proliferation-related signaling pathways were inhibited by CORT and recovered by ECS. Finally, serum and glucocorticoid kinase-1 (SGK1), a multi-functional protein kinase, was identified as a candidate gene reciprocally regulated by CORT and ECS in hippocampal astrocyte. Our findings suggest a potential role of SGK1 in the antidepressant effect of ECS via the regulation of the proliferation of astrocyte and provide new insights into the involvement of hippocampal astrocyte in MDD and ECT. Targeting SGK1 may offer a novel approach to the development of new antidepressants which can replicate superior and immediate efficacy of ECT.

The Beneficial Role of Apigenin against Cognitive and Neurobehavioural Dysfunction: A Systematic Review of Preclinical Investigations

Apigenin is a flavone widely present in different fruits and vegetables and has been suggested to possess neuroprotective effects against some neurological disorders. In this study, we systematically reviewed preclinical studies that investigated the effects of apigenin on learning and memory, locomotion activity, anxiety-like behaviour, depressive-like behaviour and sensorimotor and motor coordination in rats and mice with impaired memory and behaviour. We searched SCOPUS, Web of Science, PubMed and Google Scholar for relevant articles. A total of 34 studies were included in this review. The included studies revealed that apigenin enhanced learning and memory and locomotion activity, exhibited anxiolytic effects, attenuated depressive-like behaviour and improved sensorimotor and motor coordination in animals with cognitive impairment and neurobehavioural deficit. Some of the molecular and biochemical mechanisms of apigenin include activation of the ERK/CREB/BDNF signalling pathway; modulation of neurotransmitter levels and monoaminergic, cholinergic, dopaminergic and serotonergic systems; inhibition of pro-inflammatory cytokine production; and attenuation of oxidative neuronal damage. These results revealed the necessity for further research using established doses and short or long durations to ascertain effective and safe doses of apigenin. These results also point to the need for a clinical experiment to ascertain the therapeutic effect of apigenin.

Upregulation of proBDNF/p75NTR signaling in immune cells and its correlation with inflammatory markers in patients with major depression

ProBDNF is the precursor protein of brain-derived neurotrophic factor (BDNF) expressed in the central nervous system and peripheral tissues. Previous studies showed that the blood levels of both proBDNF and p75 neurotrophic receptors (p75NTR) in major depressive disorder (MDD) were increased, but which blood cell types express proBDNF and its receptors is not known. Furthermore, the relationship between proBDNF/p75NTR and inflammatory cytokines in peripheral blood of MDD is unclear. Peripheral blood mononuclear cells (PBMCs) and serum were obtained from depressive patients (n = 32) and normal donors (n = 20). We examined the expression of proBDNF and inflammatory markers and their correlative relationship in patients with major depression. Using flow cytometry analysis, we examined which blood cells express proBDNF and its receptors. Finally, the role of proBDNF/p75NTR signal in inflammatory immune activity of PBMCs was verified in vitro experiments. Inflammatory cytokines in PBMC from MDD patients were increased and correlated with the major depression scores. The levels of IL-1β and IL-10 were also positively correlated with the major depression scores, while the levels of TNF-α and IL-6 were negatively correlated with the major depression scores. Intriguingly, the levels of sortilin were positively correlated with IL-1β. Q-PCR and Western blots showed proBDNF, p75NTR, and sortilin levels were significantly increased in PBMCs from MDD patients compared with that from the normal donors. Flow cytometry studies showed that proBDNF and p75NTR were present mainly in CD4+ and CD8+ T cells. The number of proBDNF and p75NTR positive CD4+ and CD8+ T cells from MDD patients was increased and subsequently reversed after therapeutic management. Exogenous proBDNF protein or p75ECD-Fc treatment of cultured PBMC affected the release of inflammatory cytokines in vitro. ProBDNF promoted the expression of inflammatory cytokines, while p75ECD-Fc inhibited the expression of inflammatory cytokines. Given there was an inflammatory response of lymphocytes to proBDNF, it is suggested that proBDNF/p75NTR signaling may upstream inflammatory cytokines in MDD. Our data suggest that proBDNF/p75NTR signaling may not only serve as biomarkers but also may be a potential therapeutic target for MDD.

The impact of flavonoids and BDNF on neurogenic process in various physiological/pathological conditions including ischemic insults: a narrative review

OBJECTIVE

Ischemic stroke is the leading cause of mortality and disability worldwide with more than half of survivors living with serious neurological sequelae thus, it has recently attracted considerable attention in the field of medical research. Neurogenesis is the process of formation of new neurons in the brain, including the human brain, from neural stem/progenitor cells [NS/PCs] which reside in neurogenic niches that contain the necessary substances for NS/PC proliferation, differentiation, migration, and maturation into functioning neurons which can integrate into a pre-existing neural network.Neurogenesis can be modulated by many exogenous and endogenous factors, pathological conditions. Both brain-derived neurotrophic factor, and flavonoids can modulate the neurogenic process in physiological conditions and after various pathological conditions including ischemic insults.

AIMS

This review aims to discuss neurogenesis after ischemic insults and to determine the role of flavonoids and BDNF on neurogenesis under physiological and pathological conditions with a concentration on ischemic insults to the brain in particular.

METHOD

Relevant articles assessing the impact of flavonoids and BDNF on neurogenic processes in various physiological/pathological conditions including ischemic insults within the timeline of 1965 until 2023 were searched using the PubMed database.

CONCLUSIONS

The selected studies have shown that ischemic insults to the brain induce NS/PC proliferation, differentiation, migration, and maturation into functioning neurons integrating into a pre-existing neural network. Flavonoids and BDNF can modulate neurogenesis in the brain in various physiological/pathological conditions including ischemic insults. In conclusion, flavonoids and BDNF may be involved in post-ischemic brain repair processes through enhancing endogenous neurogenesis.

Astroglial Connexin 43-Mediated Gap Junctions and Hemichannels: Potential Antidepressant Mechanisms and the Link to Neuroinflammation

Major depression disorder (MDD) is a neuropsychiatric disorder associated with a high suicide rate and a higher disability rate than any other disease. Evidence suggests that the pathological mechanism of MDD is related to astrocyte dysfunction. Depression is mainly associated with the expression of connexin 43 (Cx43) and the function of Cx43-mediated gap junctions and hemichannels in astrocytes. Moreover, neuroinflammation has been a hotspot in research on the pathology of depression, and Cx43-mediated functions are thought to be involved in neuroinflammation-related depression. However, the specific mechanism of Cx43-mediated functions in neuroinflammation-related depression pathology remains unclear. Therefore, this review summarizes and discusses Cx43 expression, the role of gap junction intercellular communication, and its relationship with neuroinflammation in depression. This review also focuses on the effects of antidepressant drugs (e.g., monoamine antidepressants, psychotropic drugs, and N-methyl-D-aspartate receptor antagonists) on Cx43-mediated function and provides evidence for Cx43 as a novel target for the treatment of MDD. The pathogenesis of MDD is related to astrocyte dysfunction, with reduced Cx43 expression, GJ dysfunction, decreased GJIC and reduced BDNF expression in the depressed brain. The effect of Cx43 on neuroinflammation-related depression involving inflammatory cytokines, glutamate excitotoxicity, and HPA axis dysregulation. Antidepressant drugs targeting Cx43 can effectively relieve depressive symptoms.

Molecular mechanisms underlying physical exercise-induced brain BDNF overproduction

Accumulating evidence supports that physical exercise (EX) is the most effective non-pharmacological strategy to improve brain health. EX prevents cognitive decline associated with age and decreases the risk of developing neurodegenerative diseases and psychiatric disorders. These positive effects of EX can be attributed to an increase in neurogenesis and neuroplastic processes, leading to learning and memory improvement. At the molecular level, there is a solid consensus to involve the neurotrophin brain-derived neurotrophic factor (BDNF) as the crucial molecule for positive EX effects on the brain. However, even though EX incontestably leads to beneficial processes through BDNF expression, cellular sources and molecular mechanisms underlying EX-induced cerebral BDNF overproduction are still being elucidated. In this context, the present review offers a summary of the different molecular mechanisms involved in brain's response to EX, with a specific focus on BDNF. It aims to provide a cohesive overview of the three main mechanisms leading to EX-induced brain BDNF production: the neuronal-dependent overexpression, the elevation of cerebral blood flow (hemodynamic hypothesis), and the exerkine signaling emanating from peripheral tissues (humoral response). By shedding light on these intricate pathways, this review seeks to contribute to the ongoing elucidation of the relationship between EX and cerebral BDNF expression, offering valuable insights into the potential therapeutic implications for brain health enhancement.

A new perspective on hippocampal synaptic plasticity and post-stroke depression

Post-stroke depression, a common complication after stroke, severely affects the recovery and quality of life of patients with stroke. Owing to its complex mechanisms, post-stroke depression treatment remains highly challenging. Hippocampal synaptic plasticity is one of the key factors leading to post-stroke depression; however, the precise molecular mechanisms remain unclear. Numerous studies have found that neurotrophic factors, protein kinases and neurotransmitters influence depressive behaviour by modulating hippocampal synaptic plasticity. This review further elaborates on the role of hippocampal synaptic plasticity in post-stroke depression by summarizing recent research and analysing possible molecular mechanisms. Evidence for the correlation between hippocampal mechanisms and post-stroke depression helps to better understand the pathological process of post-stroke depression and improve its treatment.

Serum BDNF levels and state anxiety are associated with somatic symptoms in patients with panic disorder

Background

We aimed to explore the predictive role of serum BDNF and anxiety-related variables in changes in somatic symptoms post-escitalopram treatment in panic disorder (PD) patients.

Methods

Ninety PD patients and 99 healthy controls (HCs) were enrolled. PD patients received an 8-week escitalopram treatment. All patients were administered the Panic Disorder Severity Scale-Chinese Version (PDSS-CV) and State-Trait Anxiety Inventory (STAI) to assess panic and anxiety-related symptoms, respectively. Patient Health Questionnaire 15-item scale (PHQ-15) was performed to measure somatic symptoms, and the blood sample was collected to detect serum BDNF levels in all participants. We performed partial correlation analysis and multiple linear regression to explore correlates of PHQ-15 and predictors of PHQ-15 changes post-escitalopram treatment after controlling for age, gender, education levels (set as a dummy variable), the current duration, comorbid AP, and/or GAD.

Results

Compared to HCs, PD patients had lower serum BDNF levels and higher PHQ-15 scores that could be improved post-escitalopram treatment. Lower baseline STAI state (b = -0.07, p = 0.004), and PDSS-CV scores (b = -0.25, p = 0.007), but higher baseline serum BDNF levels (b = 0.35, p = 0.007) contributed to the prediction of PHQ-15 changes post-escitalopram treatment.

Conclusion

State anxiety, serum BDNF levels, and panic severity could predict changes in somatic symptoms post-escitalopram treatment, our results highlighted that serum BDNF could serve as a biological indicator for improving somatic symptoms in PD patients.

Peripheral Regulation of Central Brain-Derived Neurotrophic Factor Expression through the Vagus Nerve

The brain-derived neurotrophic factor (BDNF) is an extensively studied neurotrophin es sential for both developing the brain and maintaining adult brain function. In the adult hippocampus, BDNF is critical for maintaining adult neurogenesis. Adult hippocampal neurogenesis is involved not only in memory formation and learning ability, but also mood regulation and stress responses. Accordingly, decreased levels of BDNF, accompanied by low levels of adult neurogenesis, occurs in brains of older adults with impaired cognitive function and in those of patients with major depression disorder. Therefore, elucidating the mechanisms that maintain hippocampal BDNF levels is biologically and clinically important. It has been revealed that signalling from peripheral tissues contribute to the regulation of BDNF expression in the brain across the blood-brain barrier. Moreover, recent studies indicated evidence that neuronal pathways can also be a mechanism by which peripheral tissues signal to the brain for the regulation of BDNF expression. In this review, we give an overview of the current status in the regulation of central BDNF expression by peripheral signalling, with a special interest in the regulation of hippocampal BDNF levels by signals via the vagus nerve. Finally, we discuss the relationship between signalling from peripheral tissues and age-associated control of central BDNF expression.

Adult hippocampal neurogenesis in Alzheimer's disease: A roadmap to clinical relevance

Adult hippocampal neurogenesis (AHN) drops sharply during early stages of Alzheimer's disease (AD), via unknown mechanisms, and correlates with cognitive status in AD patients. Understanding AHN regulation in AD could provide a framework for innovative pharmacological interventions. We here combine molecular, behavioral, and clinical data and critically discuss the multicellular complexity of the AHN niche in relation to AD pathophysiology. We further present a roadmap toward a better understanding of the role of AHN in AD by probing the promises and caveats of the latest technological advancements in the field and addressing the conceptual and methodological challenges ahead.

Adiponectin Promotes Neurogenesis After Transient Cerebral Ischemia Through STAT3 Mediated BDNF Upregulation in Astrocytes

Newborn neurons from the subventricular zone (SVZ) are essential to functional recovery following ischemic stroke. However, the number of newly generated neurons after stroke is far from enough to support a potent recovery. Adiponectin could increase neurogenesis in the dentate gyrus of hippocampus in neurodegenerative diseases. However, the effect of adiponectin on the neurogenesis from SVZ and the functional recovery after ischemic stroke was unknown, and the underlying mechanism was not specified either. The middle cerebral artery occlusion model of mice was adopted and adiponectin was administrated once a day from day 3 to 7 of reperfusion. The levels of BDNF and p-STAT3 were detected by western blotting on day 7 of reperfusion. The virus-encoded BDNF shRNA with GFAP promoter and a STAT3 inhibitor Stattic were used, respectively. Neurogenesis was evidenced by the expression of doublecortin and 5-bromo-2'-deoxyuridine (BrdU) labelling and brain atrophy was revealed by Nissl staining on day 28 of reperfusion. Neurological functional recovery was assessed by the adhesive removal test and the forepaw grip strength. We found that adiponectin increased both the doublecortin-positive cells and NeuN/BrdU double-positive cells around the injured area on day 28 of reperfusion, along with the improved long-term neurological recovery. Mechanistically, adiponectin increased the protein levels of p-STAT3 and BDNF in astrocytes on day 7 of reperfusion, while silencing BDNF diminished the adiponectin-induced neurogenesis and functional recovery. Moreover, inhibition of STAT3 not only prevented the increase of BDNF but also the improved neurogenesis and functional recovery after stroke. In conclusion, adiponectin enhances neurogenesis and functional recovery after ischemic stroke via STAT3/BDNF pathway in astrocytes.

Protective Effects of Early Caffeine Administration in Hyperoxia-Induced Neurotoxicity in the Juvenile Rat

High-risk preterm infants are affected by a higher incidence of cognitive developmental deficits due to the unavoidable risk factor of oxygen toxicity. Caffeine is known to have a protective effect in preventing bronchopulmonary dysplasia associated with improved neurologic outcomes, although very early initiation of therapy is controversial. In this study, we used newborn rats in an oxygen injury model to test the hypothesis that near-birth caffeine administration modulates neuronal maturation and differentiation in the hippocampus of the developing brain. For this purpose, newborn Wistar rats were exposed to 21% or 80% oxygen on the day of birth for 3 or 5 days and treated with vehicle or caffeine (10 mg/kg/48 h). Postnatal exposure to 80% oxygen resulted in a drastic reduction of associated neuronal mediators for radial glia, mitotic/postmitotic neurons, and impaired cell-cycle regulation, predominantly persistent even after recovery to room air until postnatal day 15. Systemic caffeine administration significantly counteracted the effects of oxygen insult on neuronal maturation in the hippocampus. Interestingly, under normoxia, caffeine inhibited the transcription of neuronal mediators of maturing and mature neurons. The early administration of caffeine modulated hyperoxia-induced decreased neurogenesis in the hippocampus and showed neuroprotective properties in the neonatal rat oxygen toxicity model.

Pharmacological and Physiological Correlates of the Bidirectional Fear Phenotype of the Carioca Rats and Other Bidirectionally Selected Lines

The Carioca rat lines originated from the selective bidirectional breeding of mates displaying extreme defense responses to contextual conditioned fear. After three generations, two distinct populations could be distinguished: the Carioca High- and Low-conditioned Freezing rats, CHF, and CLF, respectively. Later studies identified strong anxiety-like behaviors in the CHF line, while indications of impulsivity and hyperactivity were prominent in the CLF animals. The present review details the physiological and pharmacological-related findings obtained from these lines. The results discussed here point towards a dysfunctional fear circuitry in CHF rats, including alterations in key brain structures and the serotoninergic system. Moreover, data from these animals highlight important alterations in the stress-processing machinery and its associated systems, such as energy metabolism and antioxidative defense. Finally, evidence of an alteration in the dopaminergic pathway in CLF rats is also debated. Thus, accumulating data gathered over the years, place the Carioca lines as significant animal models for the study of psychiatric disorders, especially fear-related ones like anxiety.

Astrocytes Mediate Cholinergic Regulation of Adult Hippocampal Neurogenesis and Memory Through M1 Muscarinic Receptor

BACKGROUND

In the neurogenic niches of the adult hippocampus, new functional neurons are continuously generated throughout life, and generation of these neurons has been implicated in learning and memory. Astrocytes, as components of the neurogenic niches, are critical in the regulation of adult hippocampal neurogenesis (AHN). However, little is known about how astrocytes receive and respond to extrinsic cues to regulate AHN.

METHODS

By using a transgenic strategy to conditionally delete astrocytic CRHM1 in mice and AAV (adeno-associated virus)-mediated overexpression of astrocytic CHRM1 specifically in the hippocampal dentate gyrus, we systematically investigated the role of astrocytic CHRM1 in the regulation of AHN and the underlying mechanisms using the combined approaches of immunohistochemistry, retrovirus labeling, electrophysiology, primary astrocyte cultures, immunoblotting, and behavioral assays.

RESULTS

We report that genetic ablation of CHRM1 in astrocytes led to defects in neural stem cell survival, neuronal differentiation, and maturation and integration of newborn neurons in the dentate gyrus. Astrocytic CHRM1-mediated modulation of AHN was mediated by BDNF (brain-derived neurotrophic factor) signaling. Furthermore, CHRM1 ablation in astrocytes impaired contextual fear memory. These impairments in both AHN and memory were rescued by overexpression of astrocytic CHRM1 in the dentate gyrus.

CONCLUSIONS

Our findings reveal a critical role for astrocytes in mediating cholinergic regulation of AHN and memory through CHRM1.

Antidepressant Active Components of Bupleurum chinense DC-Paeonia lactiflora Pall Herb Pair: Pharmacological Mechanisms

Depression is a serious psychological disorder with a rapidly increasing incidence in recent years. Clinically, selective serotonin reuptake inhibitors are the main therapy. These drugs, have serious adverse reactions, however. Traditional Chinese medicine has the characteristics of multiple components, targets, and pathways, which has huge potential advantages for the treatment of depression. The antidepressant potential of the herbal combination of Bupleurum chinense DC (Chaihu) and Paeonia lactiflora Pall (Baishao) has been extensively studied previously. In this review, we summarized the antidepressant active components and mechanism of Chaihu-Baishao herb pair. We found that it works mainly through relieving oxidative stress, regulating HPA axis, and protecting neurons. Nevertheless, current research of this combined preparation still faces many challenges. On one hand, most of the current studies only stay at the level of animal models, lacking of sufficient clinical double-blind controlled trials for further verification. In addition, studies on the synergistic effect between different targets and signaling pathways are scarce. On the other hand, this preparation has numerous defects such as poor stability, low solubility, and difficulty in crossing the blood-brain barrier.

Role of neuroinflammation mediated potential alterations in adult neurogenesis as a factor for neuropsychiatric symptoms in Post-Acute COVID-19 syndrome-A narrative review

Persistence of symptoms beyond the initial 3 to 4 weeks after infection is defined as post-acute COVID-19 syndrome (PACS). A wide range of neuropsychiatric symptoms like anxiety, depression, post-traumatic stress disorder, sleep disorders and cognitive disturbances have been observed in PACS. The review was conducted based on PRISMA-S guidelines for literature search strategy for systematic reviews. A cytokine storm in COVID-19 may cause a breach in the blood brain barrier leading to cytokine and SARS-CoV-2 entry into the brain. This triggers an immune response in the brain by activating microglia, astrocytes, and other immune cells leading to neuroinflammation. Various inflammatory biomarkers like inflammatory cytokines, chemokines, acute phase proteins and adhesion molecules have been implicated in psychiatric disorders and play a major role in the precipitation of neuropsychiatric symptoms. Impaired adult neurogenesis has been linked with a variety of disorders like depression, anxiety, cognitive decline, and dementia. Persistence of neuroinflammation was observed in COVID-19 survivors 3 months after recovery. Chronic neuroinflammation alters adult neurogenesis with pro-inflammatory cytokines supressing anti-inflammatory cytokines and chemokines favouring adult neurogenesis. Based on the prevalence of neuropsychiatric symptoms/disorders in PACS, there is more possibility for a potential impairment in adult neurogenesis in COVID-19 survivors. This narrative review aims to discuss the various neuroinflammatory processes during PACS and its effect on adult neurogenesis.

The neuroprotective effects of glucagon-like peptide 1 in Alzheimer’s and Parkinson’s disease: An in-depth review

Currently, there is no disease-modifying treatment available for Alzheimer’s and Parkinson’s disease (AD and PD) and that includes the highly controversial approval of the Aβ-targeting antibody aducanumab for the treatment of AD. Hence, there is still an unmet need for a neuroprotective drug treatment in both AD and PD. Type 2 diabetes is a risk factor for both AD and PD. Glucagon-like peptide 1 (GLP-1) is a peptide hormone and growth factor that has shown neuroprotective effects in preclinical studies, and the success of GLP-1 mimetics in phase II clinical trials in AD and PD has raised new hope. GLP-1 mimetics are currently on the market as treatments for type 2 diabetes. GLP-1 analogs are safe, well tolerated, resistant to desensitization and well characterized in the clinic. Herein, we review the existing evidence and illustrate the neuroprotective pathways that are induced following GLP-1R activation in neurons, microglia and astrocytes. The latter include synaptic protection, improvements in cognition, learning and motor function, amyloid pathology-ameliorating properties (Aβ, Tau, and α-synuclein), the suppression of Ca2+ deregulation and ER stress, potent anti-inflammatory effects, the blockage of oxidative stress, mitochondrial dysfunction and apoptosis pathways, enhancements in the neuronal insulin sensitivity and energy metabolism, functional improvements in autophagy and mitophagy, elevated BDNF and glial cell line-derived neurotrophic factor (GDNF) synthesis as well as neurogenesis. The many beneficial features of GLP-1R and GLP-1/GIPR dual agonists encourage the development of novel drug treatments for AD and PD.

An Ultra-Low Dose of ∆9-Tetrahydrocannabinol Alleviates Alzheimer's Disease-Related Cognitive Impairments and Modulates TrkB Receptor Expression in a 5XFAD Mouse Model

Alzheimer’s disease (AD) is the most common form of dementia, but there is still no available treatment. Δ9-tetrahydrocannabinol (THC) is emerging as a promising therapeutic agent. Using THC in conventional high doses may have deleterious effects. Therefore, we propose to use an ultra-low dose of THC (ULD-THC). We previously published that a single injection of ULD-THC ameliorated cognitive functioning in several models of brain injuries as well as in naturally aging mice. Here, 5xFAD AD model mice received a single treatment of ULD-THC (0.002 mg/kg) after disease onset and were examined in two separate experiments for cognitive functions, neurotropic, and inflammatory factors in the hippocampus. We show that a single injection of ULD-THC alleviated cognitive impairments in 6- and 12-month-old 5xFAD mice. On the biochemical level, our results indicate an imbalance between the truncated TrkB receptor isoform and the full receptor, with AD mice showing a greater tendency to express the truncated receptor, and ULD-THC improved this imbalance. We also investigated the expression of three AD-related inflammatory markers and found an ameliorating effect of ULD-THC. The current research demonstrates for the first time the beneficial effects of a single ultra-low dose of THC in a mouse model of AD after disease onset.

Astrocytes: the neglected stars in the central nervous system and drug addiction

With the advent of improved tools to examine the astrocytes, which have been believed to play a supportive role in the central nervous system (CNS) for years, their participation in the operation of the CNS and drug addiction was unveiled. Assisting the formation and function of the CNS, astrocytes are involved in physiological and pathological brain activities. Drug addiction is a pervasive psychiatric disorder, characterized by compulsive drug-taking behavior and high rate of relapse, impacting individual health and society stability and safety. When exposed to drugs of abuse, astrocytes go through a series of alterations, contributing to the development of addiction. Here we review how astrocytes contribute to the CNS and drug addiction. We hope that understanding the interaction between addictive drugs and astrocytes may help discover new mechanisms underlying the addiction and produce novel therapeutic treatments.

The intersection of astrocytes and the endocannabinoid system in the lateral habenula: on the fast-track to novel rapid-acting antidepressants

Despite attaining significant advances toward better management of depressive disorders, we are still facing several setbacks. Developing rapid-acting antidepressants with sustained effects is an aspiration that requires thinking anew to explore possible novel targets. Recently, the lateral habenula (LHb), the brain's "anti-reward system", has been shown to go awry in depression in terms of various molecular and electrophysiological signatures. Some of the presumed contributors to such observed aberrations are astrocytes. These star-shaped cells of the brain can alter the firing pattern of the LHb, which keeps the activity of the midbrain's aminergic centers under tight control. Astrocytes are also integral parts of the tripartite synapses, and can therefore modulate synaptic plasticity and leave long-lasting changes in the brain. On the other hand, it was discovered that astrocytes express cannabinoid type 1 receptors (CB₁R), which can also take part in long-term plasticity. Herein, we recount how the LHb of a depressed brain deviates from the "normal" one from a molecular perspective. We then try to touch upon the alterations of the endocannabinoid system in the LHb, and cast the idea that modulation of astroglial CB₁R may help regulate habenular neuronal activity and synaptogenesis, thereby acting as a new pharmacological tool for regulation of mood and amelioration of depressive symptoms.

The Role of Brain-Derived Neurotrophic Factor Signaling in Central Nervous System Disease Pathogenesis

Recent studies have found abnormal levels of brain-derived neurotrophic factor (BDNF) in a variety of central nervous system (CNS) diseases (e.g., stroke, depression, anxiety, Alzheimer’s disease, and Parkinson’s disease). This suggests that BDNF may be involved in the pathogenesis of these diseases. Moreover, regulating BDNF signaling may represent a potential treatment for such diseases. With reference to recent research papers in related fields, this article reviews the production and regulation of BDNF in CNS and the role of BDNF signaling disorders in these diseases. A brief introduction of the clinical application status of BDNF is also provided.

Kynurenine monooxygenase inhibition and associated reduced quinolinic acid reverses depression-like behaviour by upregulating Nrf2/ARE pathway in mouse model of depression: In-vivo and In-silico studies

Kynurenine pathway, a neuroimmunological pathway plays a substantial role in depression. Consistently, increased levels of neurotoxic metabolite of kynurenine pathway; quinolinic acid (QA) found in the suicidal patients and remitted major depressive patients. QA, an endogenous modulator of N-methyl-d-aspartate receptor is produced by microglial cells, may serve as a potential candidate for a link between antioxidant defence system and immune changes in depression. Further, nuclear factor (erythroid-derived 2) like 2 (Nrf2), an endogenous antioxidant transcription factor plays a significant role in maintaining antioxidant homeostasis during basal and stress conditions. The present study was designed to explore the effects of KMO-inhibition (Kynurenine monooxygenase) and association of reduced QA on Keap1/Nrf2/ARE pathway activity in olfactory bulbectomized mice (OBX-mice). KMO catalysis the neurotoxic branch of kynurenine pathway directing the synthesis of QA. KMO inhibitionshowed significant reversal of depressive-like behaviour, restored Keap-1 and Nrf2 mRNA expression, and associated antioxidant levels in cortex and hippocampus of OBX-mice. KMO inhibition also increased PI3K/AKT mRNA expression in OBX-mice. KMO inhibition and associated reduced QA significantly decreased inflammatory markers, kynurenine and increased the 5-HT, 5-HIAA and tryptophan levels in OBX-mice. Furthermore, molecular docking studies has shown good binding affinity of QA towards ubiquitin proteasome complex and PI3K protein involved in Keap-1 dependent and independent proteasome degradation of Nrf2 respectively supporting our in-vivo findings. Hence, QA might act as pro-oxidant through downregulating Nrf2/ARE pathway along with modulating other pathways and KMO inhibition could be a potential therapeutic target for depression treatment.

Blood levels of brain-derived neurotrophic factor (BDNF) in people with multiple sclerosis (MS): A systematic review and meta-analysis

BACKGROUND

Multiple sclerosis is an autoimmune demyelinating disease marked by the involvement of multiple pathophysiological pathways, including BDNF. BDNF (brain-derived neurotrophic factor) is one of the main neurotrophic factors in the adult brain. The amount of BDNF in the blood can be utilized as a surrogate for the central expression of this marker. Given contradicting reports, we set out to answer the question, "How do blood levels of BDNF differ in people with multiple sclerosis (PwMS) compared to controls?"

METHODS

We performed a thorough search in MEDLINE, EMBASE, Web of Science, and the Cochrane Library databases, resulting in 13 eligible investigations. Eleven studies compared BDNF in serum of PwMS versus healthy controls (HC), and two studies provided BDNF levels in the plasma of PwMs. R version 4.0.4 was used for meta-analysis and visualizations. Mean difference (MD) was used for the measurement of effect size.

RESULTS

The final analysis included thirteen studies with 689 patients with MS and 583 controls. The preliminary results indicated that MS patients had statistically significant lower levels of BDNF than controls: SMD -5.1992 (95% CI [-8.4488; -1.9496], p-value < 0.0001. Additionally, subgroup analysis revealed a statistically significant difference in serum and plasma levels (p-value=0.01). Performing univariate meta-regression, disease duration and the proportion of males had, respectively, a significant negative and positive correlation with BDNF levels.

CONCLUSION

Circulating levels of BDNF are decreased in MS. Future studies should investigate the role of BDNF as a biomarker of disease severity and/or progression for a personalized approach to MS.

Imbalance in Sirt1 Alternative Splicing in Response to Chronic Stress during the Adolescence Period in Female Mice

Stressful unpredictable life events have been implicated in numerous diseases. It is now becoming clear that some life periods are more vulnerable than others. As adolescence is a sensitive period in brain development, the long-term effects of stress during this period could be significant. We investigated the long-term effects of exposure to unpredictable chronic mild stress in adolescent mice on alternative splicing of Sirtuin 1. One-month-old mice were exposed to 4 weeks of UCMS and examined for anxiety and cognition at the age of 2, 4 and 6 months. We found a rise in anxious behavior immediately after the exposure to stress. Notably, there was a long-term impairment of performance in cognitive tasks and an imbalance in Sirtuin 1 and TrkB receptor alternative splicing in the stress-exposed mice compared with controls. To conclude, our results show that exposure to unpredictable chronic mild stress during adolescence affects cognition in adulthood. Understanding pathways affiliated with stress may help minimize the long-term emotional effects of an unpredictable, stressful event.

Clathrin-nanoparticles deliver BDNF to hippocampus and enhance neurogenesis, synaptogenesis and cognition in HIV/neuroAIDS mouse model

Brain derived neurotrophic factor (BDNF) promotes the growth, differentiation, maintenance and survival of neurons. These attributes make BDNF a potentially powerful therapeutic agent. However, its charge, instability in blood, and poor blood brain barrier (BBB) penetrability have impeded its development. Here, we show that engineered clathrin triskelia (CT) conjugated to BDNF (BDNF-CT) and delivered intranasally increased hippocampal BDNF concentrations 400-fold above that achieved previously with intranasal BDNF alone. We also show that BDNF-CT targeted Tropomyosin receptor kinase B (TrkB) and increased TrkB expression and downstream signaling in iTat mouse brains. Mice were induced to conditionally express neurotoxic HIV Transactivator-of-Transcription (Tat) protein that decreases BDNF. Down-regulation of BDNF is correlated with increased severity of HIV/neuroAIDS. BDNF-CT enhanced neurorestorative effects in the hippocampus including newborn cell proliferation and survival, granule cell neurogenesis, synaptogenesis and increased dendritic integrity. BDNF-CT exerted cognitive-enhancing effects by reducing Tat-induced learning and memory deficits. These results show that CT bionanoparticles efficiently deliver BDNF to the brain, making them potentially powerful tools in regenerative medicine.

Astroglia Abnormalities in Post-stroke Mood Disorders

Stroke is the leading cause of human death and disability. After a stroke, many patients may have some physical disability, including difficulties in moving, speaking, and seeing, but patients may also exhibit changes in mood manifested by depression, anxiety, and cognitive changes which we call post-stroke mood disorders (PSMDs). Astrocytes are the most diverse and numerous glial cell type in the central nervous system (CNS). They provide structural, nutritional, and metabolic support to neurons and regulate synaptic activity under normal conditions. Astrocytes are also critically involved in focal ischemic stroke (FIS). They undergo many changes after FIS. These changes may affect acute neuronal death and brain damage as well as brain recovery and PSMD in the chronic phase after FIS. Studies using postmortem brain specimens and animal models of FIS suggest that astrocytes/reactive astrocytes are involved in PSMD. This chapter provides an overview of recent advances in the molecular base of astrocyte in PSMD. As astrocytes exhibit high plasticity after FIS, we suggest that targeting local astrocytes may be a promising strategy for PSMD therapy.

Neuroplastic Effect of Exercise Through Astrocytes Activation and Cellular Crosstalk

Physical exercise is an effective therapy for neurorehabilitation. Exercise has been shown to induce remodeling and proliferation of astrocyte. Astrocytes potentially affect the recruitment and function of neurons; they could intensify responses of neurons and bring more neurons for the process of neuroplasticity. Interactions between astrocytes, microglia and neurons modulate neuroplasticity and, subsequently, neural circuit function. These cellular interactions promote the number and function of synapses, neurogenesis, and cerebrovascular remodeling. However, the roles and crosstalk of astrocytes with neurons and microglia and any subsequent neuroplastic effects have not been studied extensively in exercise-induced settings. This article discusses the impact of physical exercise on astrocyte proliferation and highlights the interplay between astrocytes, microglia and neurons. The crosstalk between these cells may enhance neuroplasticity, leading to the neuroplastic effects of exercise.

N-3 polyunsaturated fatty acids promote astrocyte differentiation and neurotrophin production independent of cAMP in patient-derived neural stem cells

Evidence from epidemiological and laboratory studies, as well as randomized placebo-controlled trials, suggests supplementation with n-3 polyunsaturated fatty acids (PUFAs) may be efficacious for treatment of major depressive disorder (MDD). The mechanisms underlying n-3 PUFAs potential therapeutic properties remain unknown. There are suggestions in the literature that glial hypofunction is associated with depressive symptoms and that antidepressants may normalize glial function. In this study, induced pluripotent stem cells (iPSC)-derived neuronal stem cell lines were generated from individuals with MDD. Astrocytes differentiated from patient-derived neuronal stem cells (iNSCs) were verified by GFAP. Cells were treated with eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA) or stearic acid (SA). During astrocyte differentiation, we found that n-3 PUFAs increased GFAP expression and GFAP positive cell formation. BDNF and GDNF production were increased in the astrocytes derived from patients subsequent to n-3 PUFA treatment. Stearic Acid (SA) treatment did not have this effect. CREB activity (phosphorylated CREB) was also increased by DHA and EPA but not by SA. Furthermore, when these astrocytes were treated with n-3 PUFAs, the cAMP antagonist, RP-cAMPs did not block n-3 PUFA CREB activation. However, the CREB specific inhibitor (666-15) diminished BDNF and GDNF production induced by n-3 PUFA, suggesting CREB dependence. Together, these results suggested that n-3 PUFAs facilitate astrocyte differentiation, and may mimic effects of some antidepressants by increasing production of neurotrophic factors. The CREB-dependence and cAMP independence of this process suggests a manner in which n-3 PUFA could augment antidepressant effects. These data also suggest a role for astrocytes in both MDD and antidepressant action.

Zeb2/Axin2-Enriched BMSC-Derived Exosomes Promote Post-Stroke Functional Recovery by Enhancing Neurogenesis and Neural Plasticity

Exosomes harvested from bone marrow-derived mesenchymal stromal cells (BMSCs) have shown treatment potential in many diseases. In vitro, Zeb2/Axin2 stimulated endogenous neurogenesis, which induced functional recovery after stroke. Here, we investigated whether the Zeb2/Axin2-enriched exosomes harvested from BMSCs transfected with a Zeb2/Axin2 overexpression plasmid would enhance neurological recovery. Compared with the control, both exosome treatments significantly improved functional recovery, and Zeb2/Axin2-enriched exosomes had significantly more improved effects on neurological function, neurogenesis, and neurite remodeling/neuronal dendrite plasticity than the control BMSC exosome treatment in a middle cerebral artery occlusion MCAO rat model. After stimulation with Zeb2/Axin2-enriched BMSC exosomes, the spatial memory and nerve function of MCAO rats showed marked recovery. The number of neurons was increased in the subventricular zone (SVZ), hippocampus, and cortex area, while the expression of nerve growth factors (NGF, BDNF, etc.) was upregulated. In the ischemic boundary zone, Zeb2/Axin2-enriched exosomes promoted synaptic remodeling by increasing the number of synapses and reversed the axonal loss of phosphorylated neurofilament (SMI-31) and synaptophysin (SYN) caused by ischemic injury, thus alleviating axonal demise and promoting synaptic proliferation. In vitro, Zeb2/Axin2-enriched exosomes significantly increased neurite branching and elongation of cultured cortical embryonic rat neurons under oxygen- and glucose-deprived (OGD) conditions. Moreover, Ex-Zeb2/Axin2-enriched exosomes downregulated the protein level of SOX10, endothelin-3/EDNRB, and Wnt/β-catenin expression. In conclusion, exosomes harvested from Ex-Zeb2/Axin2 BMSC could improve post-stroke neuroplasticity and functional recovery in MCAO rats by promoting proliferation and differentiation of neural stem cells. The mechanism may be related to the SOX10, Wnt/β-catenin, and endothelin-3/EDNRB pathways.

A Runner's High for New Neurons? Potential Role for Endorphins in Exercise Effects on Adult Neurogenesis

Physical exercise has wide-ranging benefits to cognitive functioning and mental state, effects very closely resembling enhancements to hippocampal functioning. Hippocampal neurogenesis has been implicated in many of these mental benefits of exercise. However, precise mechanisms behind these effects are not well known. Released peripherally during exercise, beta-endorphins are an intriguing candidate for moderating increases in neurogenesis and the related behavioral benefits of exercise. Although historically ignored due to their peripheral release and status as a peptide hormone, this review highlights reasons for further exploring beta-endorphin as a key mediator of hippocampal neurogenesis. This includes possible routes for beta-endorphin signaling into the hippocampus during exercise, direct effects of beta-endorphin on cell proliferation and neurogenesis, and behavioral effects of manipulating endogenous opioid signaling. Together, beta-endorphin appears to be a promising mechanism for understanding the specific ways that exercise promotes adult neurogenesis specifically and brain health broadly.

Baicalin Attenuates Oxygen-Glucose Deprivation/Reoxygenation-Induced Injury by Modulating the BDNF-TrkB/PI3K/Akt and MAPK/Erk1/2 Signaling Axes in Neuron-Astrocyte Cocultures

Background: Baicalin (BCL), a candidate drug for ischemic stroke, has been indicated to protect neurons by promoting brain-derived neurotrophic factor (BDNF). However, the cellular source of BDNF release promoted by baicalin and its detailed protective mechanism after ischemia/reperfusion remains to be studied. The aim of this study was to investigate the neuroprotective mechanisms of baicalin against oxygen-glucose deprivation/reoxygenation (OGD/R) in a neuron-astrocyte coculture system and to explore whether the BDNF-TrkB pathway is involved. Methods and Results: A neuron-astrocyte coculture system was established to elucidate the role of astrocytes in neurons under OGD/R conditions. The results demonstrated that astrocytes became reactive astrocytes and released more BDNF in the coculture system to attenuate neuronal apoptosis and injury after OGD/R. BCL maintained the characteristics of reactive astrocytes and obviously increased the expression of cyclic AMP response element-binding protein (CREB) and the levels of BDNF in the coculture system after OGD/R. To further verify whether BDNF binding to its receptor tyrosine kinase receptor B (TrkB) was required for the neuroprotective effect of baicalin, we examined the effect of ANA-12, an antagonist of TrkB, on NA system injury, including oxidative stress, inflammation, and apoptosis induced by OGD/R. The results showed that treatment of NA systems with ANA-12 significantly attenuated the neuroprotection of BCL. The phosphatidylinositol 3-kinase (PI3K)/protein kinase B (Akt) and mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinase (ERK) pathways are two important downstream cascades of signaling pathways activated by BDNF binding to TrkB. We investigated the expressions of TrkB, PI3K, Akt, MAPK, and ERK. The results demonstrated that baicalin significantly increased the expressions of TrkB, PI3K/AKT, and MAPK/ERK. Conclusion: The neuroprotective effects of baicalin against oxidative stress, inflammation, and apoptosis were improved by astrocytes, mainly mediated by increasing the release of BDNF and its associated receptor TrkB and downstream signaling regulators PI3K/Akt and MAPK/ERK1/2.

The efficacy of systemic administration of lipopolysaccharide in modelling pre-motor Parkinson's disease in C57BL/6 mice

Parkinson's disease (PD) is the second most common neurodegenerative disease, characterised by the loss of dopaminergic neurons in the substantia nigra. Mounting evidence indicates a crucial role of inflammation and concomitant oxidative stress in the disease progression. Therefore, the aim of this study was to investigate the ability of systemically administered lipopolysaccharide (LPS) to induce motor and non-motor symptoms of PD, inflammation, oxidative stress and major neuropathological hallmarks of the disease in regions postulated to be affected, including the olfactory bulb, hippocampus, midbrain and cerebellum. Twenty-one male C57BL/6 mice, approximately 20 weeks old, received a dose of 0.3 mg/kg/day of LPS systemically on 4 consecutive days and behavioural testing was conducted on days 14-18 post-treatment, followed by tissue collection. Systemically administered LPS increased latency time in the buried food seeking test (indicative of olfactory impairment), and decreased time spent in central zone of the open field (anxiety-like behaviour). However, there was no change in latency time in the rotarod test or the expression of tyrosine hydroxylase (TH) in the midbrain. Systemically administered LPS induced increased glial markers GFAP and Iba-1 and oxidative stress marker 3-nitrotyrosine (3-NT) in the olfactory bulb, hippocampus, midbrain and cerebellum, and there were region specific changes in the expression of NFκB, IL-1β, α-synuclein, TH and BDNF proteins. The model could be useful to further elucidate early non-motor aspects of PD and the possible mechanisms contributing to the non-motor deficits.

5-HT4 Receptors Are Not Involved in the Effects of Fluoxetine in the Corticosterone Model of Depression

Clinical and preclinical studies report the implication of 5-hydroxytryptamine 4 receptors (5-HT₄Rs) in depression and anxiety. Here, we tested whether the absence of 5-HT4Rs influences the response to the antidepressant fluoxetine in mice subjected to chronic corticosterone administration, an animal model of depression and anxiety. Therefore, the effects of chronic administration of fluoxetine in corticosterone-treated wild-type (WT) and 5-HT₄R knockout (KO) mice were evaluated in the open-field and novelty suppressed feeding tests. As 5-HT_1A receptor (5-HT_1AR) and brain-derived neurotrophic factor (BDNF) are critically involved in depression and anxiety, we further evaluated 5-HT_1A receptor functionality by [³⁵S]GTPγS autoradiography and BDNF mRNA expression by in situ hybridization techniques. We found that 5-HT₄R KO and WT mice displayed anxiety- and depressive-like behavior following chronic administration of corticosterone, as evidenced in the open-field and novelty suppressed feeding tests. In the open-field, a decreased central activity was observed in naïve and corticosterone-treated mice of both genotypes following chronic fluoxetine administration. In the novelty suppressed feeding test, a predictive paradigm of antidepressant activity, chronic treatment with fluoxetine reverted the latency to eat in both genotypes. The antidepressant also potentiated the corticosterone-induced desensitization of the 5-HT_1AR in the dorsal raphe nucleus. Further, chronic fluoxetine increased BDNF mRNA expression in the dentate gyrus of the hippocampus in corticosterone-treated mice of both genotypes. Therefore, our findings indicate that the behavioral effects of fluoxetine in the corticosterone model of depression and anxiety appear not to be dependent on 5-HT₄Rs.

Immunoregulation and antidepressant effect of ketamine

Major depressive disorder (MDD) is a common mental health disorder that brings severe disease burden worldwide. Traditional antidepressants are mainly targeted at monoamine neurotransmitters, with low remission rates and high recurrence rates. Ketamine is a noncompetitive glutamate N-methyl-d-aspartate receptor (NMDAR) antagonist, and its rapid and powerful antidepressant effects have come to light. Its antidepressant mechanism is still unclarified. Research found that ketamine had not only antagonistic effect on NMDAR but also strong immunomodulatory effect, both of which were closely related to the pathophysiology of MDD. Although there are many related studies, they are relatively heterogeneous. Therefore, this review mainly describes the immune mechanisms involved in MDD and how ketamine plays an antidepressant role by regulating peripheral and central immune system, including peripheral inflammatory cytokines, central microglia, and astrocytes. This review summarizes the related research, finds out the deficiencies of current research, and provides ideas for future research and the development of novel antidepressants.

Astroglial Connexins in Neurological and Neuropsychological Disorders and Radiation Exposure

Radiotherapy is a common treatment for brain and spinal cord tumors and also a risk factor for neuropathological changes in the brain leading to different neurological and neuropsychological disorders. Astroglial connexins are involved in brain inflammation, development of Alzheimer's Disease (AD), depressive, epilepsy, and amyotrophic lateral sclerosis, and are affected by radiation exposure. Therefore, it is speculated that radiation-induced changes of astroglial connexins may be related to the brain neuropathology and development of neurological and neuropsychological disorders. In this paper, we review the functional expression and regulation of astroglial connexins expressed between astrocytes and different types of brain cells (including oligodendrocytes, microglia, neurons and endothelial cells). The roles of these connexins in the development of AD, depressive, epilepsy, amyotrophic lateral sclerosis and brain inflammation have also been summarized. The radiation-induced astroglial connexins changes and development of different neurological and neuropsychological disorders are then discussed. Based on currently available data, we propose that radiation-induced astroglial connexins changes may be involved in the genesis of different neurological and neuropsychological disorders which depends on the age, brain regions, and radiation doses/dose rates. The abnormal astroglial connexins may be novel therapeutic targets for the prevention of radiation-induced cognitive impairment, neurological and neuropsychological disorders.

Kv1.1 channels regulate early postnatal neurogenesis in mouse hippocampus via the TrkB signaling pathway

In the postnatal brain, neurogenesis occurs only within a few regions, such as the hippocampal sub-granular zone (SGZ). Postnatal neurogenesis is tightly regulated by factors that balance stem cell renewal with differentiation, and it gives rise to neurons that participate in learning and memory formation. The Kv1.1 channel, a voltage-gated potassium channel, was previously shown to suppress postnatal neurogenesis in the SGZ in a cell-autonomous manner. In this study, we have clarified the physiological and molecular mechanisms underlying Kv1.1-dependent postnatal neurogenesis. First, we discovered that the membrane potential of neural progenitor cells is highly dynamic during development. We further established a multinomial logistic regression model for cell-type classification based on the biophysical characteristics and corresponding cell markers. We found that the loss of Kv1.1 channel activity causes significant depolarization of type 2b neural progenitor cells. This depolarization is associated with increased tropomyosin receptor kinase B (TrkB) signaling and proliferation of neural progenitor cells; suppressing TrkB signaling reduces the extent of postnatal neurogenesis. Thus, our study defines the role of the Kv1.1 potassium channel in regulating the proliferation of postnatal neural progenitor cells in mouse hippocampus.

BDNF Overexpression in the Ventral Hippocampus Promotes Antidepressant- and Anxiolytic-Like Activity in Serotonin Transporter Knockout Rats

BDNF plays a pivotal role in neuroplasticity events, vulnerability and resilience to stress-related disorders, being decreased in depressive patients and increased after antidepressant treatment. BDNF was found to be reduced in patients carrying the human polymorphism in the serotonin transporter promoter region (5-HTTLPR). The serotonin knockout rat (SERT^-/-) is one of the animal models used to investigate the underlying molecular mechanisms of depression in humans. They present decreased BDNF levels, and anxiety- and depression-like behavior. To investigate whether upregulating BDNF would ameliorate the phenotype of SERT^-/- rats, we overexpressed BDNF locally into the ventral hippocampus and submitted the animals to behavioral testing. The results showed that BDNF overexpression in the vHIP of SERT^-/- rats promoted higher sucrose preference and sucrose intake; on the first day of the sucrose consumption test it decreased immobility time in the forced swim test and increased the time spent in the center of a novel environment. Furthermore, BDNF overexpression altered social behavior in SERT^-/- rats, which presented increased passive contact with test partner and decreased solitary behavior. Finally, it promoted decrease in plasma corticosterone levels 60 min after restraint stress. In conclusion, modulation of BDNF IV levels in the vHIP of SERT^-/- rats led to a positive behavioral outcome placing BDNF upregulation in the vHIP as a potential target to new therapeutic approaches to improve depressive symptoms.

Selective Ablation of BDNF from Microglia Reveals Novel Roles in Self-Renewal and Hippocampal Neurogenesis

Microglia, the resident immune cells of the CNS, have emerged as key regulators of neural precursor cell activity in the adult brain. However, the microglia-derived factors that mediate these effects remain largely unknown. In the present study, we investigated a role for microglial brain-derived neurotrophic factor (BDNF), a neurotrophic factor with well known effects on neuronal survival and plasticity. Surprisingly, we found that selective genetic ablation of BDNF from microglia increased the production of newborn neurons under both physiological and inflammatory conditions (e.g., LPS-induced infection and traumatic brain injury). Genetic ablation of BDNF from microglia otherwise also interfered with self-renewal/proliferation, reducing their overall density. In conclusion, we identify microglial BDNF as an important factor regulating microglia population dynamics and states, which in turn influences neurogenesis under both homeostatic and pathologic conditions.SIGNIFICANCE STATEMENT (1) Microglial BDNF contributes to self-renewal and density of microglia in the brain. (2) Selective ablation of BDNF in microglia stimulates neural precursor proliferation. (3) Loss of microglial BDNF augments working memory following traumatic brain injury. (4) Benefits of repopulating microglia on brain injury are not mediated via microglial BDNF.