Ischemia-induced neurogenesis of neocortical layer 1 progenitor cells

Improving Outcomes After Post-Cardiac Arrest Brain Injury: A Scientific Statement From the International Liaison Committee on Resuscitation

This scientific statement presents a conceptual framework for the pathophysiology of post-cardiac arrest brain injury, explores reasons for previous failure to translate preclinical data to clinical practice, and outlines potential paths forward. Post-cardiac arrest brain injury is characterized by 4 distinct but overlapping phases: ischemic depolarization, reperfusion repolarization, dysregulation, and recovery and repair. Previous research has been challenging because of the limitations of laboratory models; heterogeneity in the patient populations enrolled; overoptimistic estimation of treatment effects leading to suboptimal sample sizes; timing and route of intervention delivery; limited or absent evidence that the intervention has engaged the mechanistic target; and heterogeneity in postresuscitation care, prognostication, and withdrawal of life-sustaining treatments. Future trials must tailor their interventions to the subset of patients most likely to benefit and deliver this intervention at the appropriate time, through the appropriate route, and at the appropriate dose. The complexity of post-cardiac arrest brain injury suggests that monotherapies are unlikely to be as successful as multimodal neuroprotective therapies. Biomarkers should be developed to identify patients with the targeted mechanism of injury, to quantify its severity, and to measure the response to therapy. Studies need to be adequately powered to detect effect sizes that are realistic and meaningful to patients, their families, and clinicians. Study designs should be optimized to accelerate the evaluation of the most promising interventions. Multidisciplinary and international collaboration will be essential to realize the goal of developing effective therapies for post-cardiac arrest brain injury.

Bioactivities of morroniside: A comprehensive review of pharmacological properties and molecular mechanisms

Morroniside (MOR) is an iridoid glycoside and the main active principle of the medicinal plant, Cornus officinalis Sieb. This phytochemical is associated with numerous health benefits due to its antioxidant properties. The primary objective of the present study was to assess the pharmacological effects and underlying mechanisms of MOR, utilizing published data obtained from literature databases. Data collection involved accessing various sources, including PubMed/Medline, Scopus, Science Direct, Google Scholar, Web of Science, and SpringerLink. Our findings demonstrate that MOR can be utilized for the treatment of several diseases and disorders, as numerous studies have revealed its significant therapeutic activities. These activities encompass anti-inflammatory, antidiabetic, lipid-lowering capability, anticancer, trichogenic, hepatoprotective, gastroprotective, osteoprotective, renoprotective, and cardioprotective effects. MOR has also shown promising benefits against various neurological ailments, including Alzheimer's disease, Parkinson's disease, spinal cord injury, cerebral ischemia, and neuropathic pain. Considering these therapeutic features, MOR holds promise as a lead compound for the treatment of various ailments and disorders. However, further comprehensive preclinical and clinical trials are required to establish MOR as an effective and reliable therapeutic agent.

Directed differentiation of functional corticospinal-like neurons from endogenous SOX6+/NG2+ cortical progenitors

Corticospinal neurons (CSN) centrally degenerate in amyotrophic lateral sclerosis (ALS), along with spinal motor neurons, and loss of voluntary motor function in spinal cord injury (SCI) results from damage to CSN axons. For functional regeneration of specifically affected neuronal circuitry in vivo , or for optimally informative disease modeling and/or therapeutic screening in vitro , it is important to reproduce the type or subtype of neurons involved. No such appropriate in vitro models exist with which to investigate CSN selective vulnerability and degeneration in ALS, or to investigate routes to regeneration of CSN circuitry for ALS or SCI, critically limiting the relevance of much research. Here, we identify that the HMG-domain transcription factor Sox6 is expressed by a subset of NG2+ endogenous cortical progenitors in postnatal and adult cortex, and that Sox6 suppresses a latent neurogenic program by repressing inappropriate proneural Neurog2 expression by progenitors. We FACS-purify these genetically accessible progenitors from postnatal mouse cortex and establish a pure culture system to investigate their potential for directed differentiation into CSN. We then employ a multi-component construct with complementary and differentiation-sharpening transcriptional controls (activating Neurog2, Fezf2 , while antagonizing Olig2 with VP16:Olig2 ). We generate corticospinal-like neurons from SOX6+/NG2+ cortical progenitors, and find that these neurons differentiate with remarkable fidelity compared with corticospinal neurons in vivo . They possess appropriate morphological, molecular, transcriptomic, and electrophysiological characteristics, without characteristics of the alternate intracortical or other neuronal subtypes. We identify that these critical specifics of differentiation are not reproduced by commonly employed Neurog2 -driven differentiation. Neurons induced by Neurog2 instead exhibit aberrant multi-axon morphology and express molecular hallmarks of alternate cortical projection subtypes, often in mixed form. Together, this developmentally-based directed differentiation from genetically accessible cortical progenitors sets a precedent and foundation for in vitro mechanistic and therapeutic disease modeling, and toward regenerative neuronal repopulation and circuit repair.

Thyroid hormone action in adult neurogliogenic niches: the known and unknown

Over the last decades, thyroid hormones (THs) signaling has been established as a key signaling cue for the proper maintenance of brain functions in adult mammals, including humans. One of the most fascinating roles of THs in the mature mammalian brain is their ability to regulate adult neurogliogenic processes. In this respect, THs control the generation of new neuronal and glial progenitors from neural stem cells (NSCs) as well as their final differentiation and maturation programs. In this review, we summarize current knowledge on the cellular organization of adult rodent neurogliogenic niches encompassing well-established niches in the subventricular zone (SVZ) lining the lateral ventricles, the hippocampal subgranular zone (SGZ), and the hypothalamus, but also less characterized niches in the striatum and the cerebral cortex. We then discuss critical questions regarding how THs availability is regulated in the respective niches in rodents and larger mammals as well as how modulating THs availability in those niches interferes with lineage decision and progression at the molecular, cellular, and functional levels. Based on those alterations, we explore the novel therapeutic avenues aiming at harnessing THs regulatory influences on neurogliogenic output to stimulate repair processes by influencing the generation of either new neurons (i.e. Alzheimer's, Parkinson's diseases), oligodendrocytes (multiple sclerosis) or both (stroke). Finally, we point out future challenges, which will shape research in this exciting field in the upcoming years.

Stroke and Neurogenesis: Bridging Clinical Observations to New Mechanistic Insights from Animal Models

Stroke was the 2nd leading cause of death and a major cause of morbidity. Unfortunately, there are limited means to promote neurological recovery post-stroke, but research has unearthed potential targets for therapies to encourage post-stroke neurogenesis and neuroplasticity. The occurrence of neurogenesis in adult mammalian brains, including humans, was not widely accepted until the 1990s. Now, adult neurogenesis has been extensively studied in human and mouse neurogenic brain niches, of which the subventricular zone of the lateral ventricles and subgranular zone of the dentate gyrus are best studied. Numerous other niches are under investigation for neurogenic potential. This review offers a basic overview to stroke in the clinical setting, a focused summary of recent and foundational research literature on cortical neurogenesis and post-stroke brain plasticity, and insights regarding how the meninges and choroid plexus have emerged as key players in neurogenesis and neuroplasticity in the context of focal cerebral ischemia disrupting the anterior circulation. The choroid plexus and meninges are vital as they are integral sites for neuroimmune interactions, glymphatic perfusion, and niche signaling pertinent to neural stem cells and neurogenesis. Modulating neuroimmune interactions with a focus on astrocyte activity, potentially through manipulation of the choroid plexus and meningeal niches, may reduce the exacerbation of stroke by inflammatory mediators and create an environment conducive to neurorecovery. Furthermore, addressing impaired glymphatic perfusion after ischemic stroke likely supports a neurogenic environment by clearing out inflammatory mediators, neurotoxic metabolites, and other accumulated waste. The meninges and choroid plexus also contribute more directly to promoting neurogenesis: the meninges are thought to harbor neural stem cells and are a niche amenable to neural stem/progenitor cell migration. Additionally, the choroid plexus has secretory functions that directly influences stem cells through signaling mechanisms and growth factor actions. More research to better understand the functions of the meninges and choroid plexus may lead to novel approaches for stimulating neuronal recovery after ischemic stroke.

Targeting Neurogenesis in Seeking Novel Treatments for Ischemic Stroke

The interruption of cerebral blood flow leads to ischemic cell death and results in ischemic stroke. Although ischemic stroke is one of the most important causes of long-term disability and mortality, limited treatments are available for functional recovery. Therefore, extensive research has been conducted to identify novel treatments. Neurogenesis is regarded as a fundamental mechanism of neural plasticity. Therefore, therapeutic strategies targeting neurogenesis are thought to be promising. Basic research has found that therapeutic intervention including cell therapy, rehabilitation, and pharmacotherapy increased neurogenesis and was accompanied by functional recovery after ischemic stroke. In this review, we consolidated the current knowledge of the relationship between neurogenesis and treatment for ischemic stroke. It revealed that many treatments for ischemic stroke, including clinical and preclinical ones, have enhanced brain repair and functional recovery post-stroke along with neurogenesis. However, the intricate mechanisms of neurogenesis and its impact on stroke recovery remain areas of extensive research, with numerous factors and pathways involved. Understanding neurogenesis will lead to more effective stroke treatments, benefiting not only stroke patients but also those with other neurological disorders. Further research is essential to bridge the gap between preclinical discoveries and clinical implementation.

Structural plasticity in the entorhinal and perirhinal cortices following hippocampal lesions in rhesus monkeys

Immature neurons expressing the Bcl2 protein are present in various regions of the mammalian brain, including the amygdala and the entorhinal and perirhinal cortices. Their functional role is unknown but we have previously shown that neonatal and adult hippocampal lesions increase their differentiation in the monkey amygdala. Here, we assessed whether hippocampal lesions similarly affect immature neurons in the entorhinal and perirhinal cortices. Since Bcl2-positive cells were found mainly in areas Eo, Er, and Elr of the entorhinal cortex and in layer II of the perirhinal cortex, we also used Nissl-stained sections to determine the number and soma size of immature and mature neurons in layer III of area Er and layer II of area 36 of the perirhinal cortex. We found different structural changes in these regions following hippocampal lesions, which were influenced by the time of the lesion. In neonate-lesioned monkeys, the number of immature neurons in the entorhinal and perirhinal cortices was generally higher than in controls. The number of mature neurons was also higher in layer III of area Er of neonate-lesioned monkeys but no differences were found in layer II of area 36. In adult-lesioned monkeys, the number of immature neurons in the entorhinal cortex was lower than in controls but did not differ from controls in the perirhinal cortex. The number of mature neurons in layer III of area Er did not differ from controls, but the number of small, mature neurons in layer II of area 36 was lower than in controls. In sum, hippocampal lesions impacted populations of mature and immature neurons in discrete regions and layers of the entorhinal and perirhinal cortices, which are interconnected with the amygdala and provide major cortical inputs to the hippocampus. These structural changes may contribute to some functional recovery following hippocampal injury in an age-dependent manner.

Transient neurogenesis in ischemic cortex from Sox2+ astrocytes

The adult cortex has long been regarded as non-neurogenic. Whether injury can induce neurogenesis in the adult cortex is still controversial. Here, we report that focal ischemia stimulates a transient wave of local neurogenesis. Using 5'-bromo-2'-deoxyuridine labeling, we demonstrated a rapid generation of doublecortin-positive neuroblasts that died quickly in mouse cerebral cortex following ischemia. Nestin-Cre^ER-based cell ablation and fate mapping showed a small contribution of neuroblasts by subventricular zone neural stem cells. Using a mini-photothrombotic ischemia mouse model and retrovirus expressing green fluorescent protein labeling, we observed maturation of locally generated new neurons. Furthermore, fate tracing analyses using PDGFRα-, GFAP-, and Sox2-Cre^ER mice showed a transient wave of neuroblast generation in mild ischemic cortex and identified that Sox2-positive astrocytes were the major neurogenic cells in adult cortex. In addition, a similar upregulation of Sox2 and appearance of neuroblasts were observed in the focal ischemic cortex of Macaca mulatta. Our findings demonstrated a transient neurogenic response of Sox2-positive astrocytes in ischemic cortex, which suggests the possibility of inducing neuronal regeneration by amplifying this intrinsic response in the future.

Expression and distribution of generated neurons and endogenous precursors in rat cerebral cortical venous ischemia

Neurogenesis in the subventricular zone (SVZ), subgranular zone (SGZ), and cerebral cortex is now a familiar event to confirm by cerebral arterial ischemia in rat models. However, it remains unclear whether cerebral venous ischemia (CVI) alone causes neurogenesis, and where that neurogenesis occurs. After creating CVI rat models via a two-vein occlusion (2-VO) method, neurogenesis was immunohistochemically evaluated by double-labeling 5-bromo-2'-deoxyuridine (BrdU)-positive cells with neuronal nuclei (NeuN) or doublecortin (DCX) antibody. Fifty Wistar rats were divided into two major groups (BrdU-NeuN and BrdU-DCX) and then separated into two subgroups (2-VO or sham). The total number of double-positive cells expressed inside a predefined region of interest (ROI) covering the ischemic area was compared between the two subgroups. Then, we divided the ROI into six sections to evaluate and compare the distribution of double-positive cells generated in each section between the two subgroups. The 2-VO subgroup presented more double-positive cells than the sham group in both BrdU-NeuN and BrdU-DCX groups, while the BrdU-DCX+2-VO group showed a characteristic distribution of double-positive cells in ROI 2 and ROI 3, suggesting areas of the ischemic core and penumbra, with a significant difference compared to the BrdU-DCX+sham group. This study demonstrates that CVI has the potential to induce endogenous neurogenesis, with significant numbers of both newly generated neurons and precursors observed in the ischemic area. The distribution of these cells suggests that the cortex could be the main origin of neurogenesis after cortical CVI.

Sphingosine-1-phosphate receptor modulation improves neurogenesis and functional recovery after stroke

Cerebral ischemia activates neural progenitors that participate in brain remodeling following acute injury. Sphingosine-1-phosphate receptor (S1PR) signaling governs cell proliferation and mobilization, yet its potential impact on neural progenitors and stroke recovery remains poorly understood. The goal of this study was to investigate the impact of S1PR modulation on post-stroke neurogenesis and functional recovery, using a S1PR modulator BAF312. Mice were subjected to 60 min middle cerebral artery occlusion (MCAO) and received BAF312 starting from day 3 after MCAO until the end of experiment. BAF312 facilitated motor function recovery in MCAO mice until day 14 after surgery. Flow cytometry analysis revealed that BAF312 treatment led to an increase of type A cells in subventricular zone (SVZ), but not other progenitor cell subsets in MCAO mice. We found an increase of BrdU incorporation in SVZ DCX⁺ cells from MCAO mice receiving BAF312 and augmented proliferation of DCX⁺ cells in cultured neurospheres isolated from SVZ tissues. Notably, a S1PR1 antagonist W146 abolished BAF312-induced increase of SVZ type A cells from MCAO mice and proliferation of DCX⁺ cells in cultured neurospheres. Additionally, the benefit of BAF312 to improve neurogenesis and stroke recovery remains in Rag2^-/- mice lacking of T and B cells. Our results demonstrate that S1PR modulation improves neurogenesis and functional recovery following brain ischemia.

Quantitative proteomic landscapes of primary and recurrent glioblastoma reveal a protumorigeneic role for FBXO2-dependent glioma-microenvironment interactions

BACKGROUND

Recent efforts have described the evolution of glioblastoma from initial diagnosis to post-treatment recurrence on a genomic and transcriptomic level. However, the evolution of the proteomic landscape is largely unknown.

METHODS

Sequential window acquisition of all theoretical fragment ion spectra mass spectrometry (SWATH-MS) was used to characterize the quantitative proteomes of two independent cohorts of paired newly diagnosed and recurrent glioblastomas. Recurrence-associated proteins were validated using immunohistochemistry and further studied in human glioma cell lines, orthotopic xenograft models, and human organotypic brain slice cultures. External spatial transcriptomic, single-cell, and bulk RNA sequencing data were analyzed to gain mechanistic insights.

RESULTS

Although overall proteomic changes were heterogeneous across patients, we identified BCAS1, INF2, and FBXO2 as consistently upregulated proteins at recurrence and validated these using immunohistochemistry. Knockout of FBXO2 in human glioma cells conferred a strong survival benefit in orthotopic xenograft mouse models and reduced invasive growth in organotypic brain slice cultures. In glioblastoma patient samples, FBXO2 expression was enriched in the tumor infiltration zone and FBXO2-positive cancer cells were associated with synaptic signaling processes.

CONCLUSIONS

These findings demonstrate a potential role of FBXO2-dependent glioma-microenvironment interactions to promote tumor growth. Furthermore, the published datasets provide a valuable resource for further studies.

Change of hypothalamic adult neurogenesis in mice by chronic treatment of fluoxetine

OBJECTIVE

More than half of patients with depression display eating disorders, such as bulimia nervosa and anorexia nervosa. Feeding centers are located in the hypothalamus, and hypothalamic adult neurogenesis has an important role in feeding and energy balance. Antidepressants, which can regulate adult neurogenesis in the hippocampus, olfactory bulb, and neocortex, are used for eating disorders, but it is unclear whether antidepressants change hypothalamic adult neurogenesis. In this study, we used immunohistological analysis to assess effects of the antidepressant fluoxetine (FLX) on hypothalamic adult neurogenesis of adult mice.

RESULTS

Expressions of the proliferating cell marker, Ki67, and the neural stem cell marker, nestin, were significantly decreased in the hypothalamus by FLX. As regard to postmitotic cells, the number of the neural marker, NeuN, positive cells was significantly upregulated by FLX, but that of the astrocytic marker, S100B, positive cells was significantly reduced by FLX. The number of the oligodendrocyte marker, Olig2, positive cells was not changed by FLX. Interestingly, FLX treatment did not affect the total number of newly generated cells in the hypothalamus, comparing that in controls. These results suggest that FLX treatment influence hypothalamic adult neurogenesis and shift the balance between the numbers of neurons and astrocytes under studied conditions.

The SDF1-CXCR4 Axis Is Involved in the Hyperbaric Oxygen Therapy-Mediated Neuronal Cells Migration in Transient Brain Ischemic Rats

Neurogenesis is a physiological response after cerebral ischemic injury to possibly repair the damaged neural network. Therefore, promoting neurogenesis is very important for functional recovery after cerebral ischemic injury. Our previous research indicated that hyperbaric oxygen therapy (HBOT) exerted neuroprotective effects, such as reducing cerebral infarction volume. The purposes of this study were to further explore the effects of HBOT on the neurogenesis and the expressions of cell migration factors, including the stromal cell-derived factor 1 (SDF1) and its target receptor, the CXC chemokine receptor 4 (CXCR4). Thirty-two Sprague–Dawley rats were divided into the control or HBO group after receiving transient middle cerebral artery occlusion (MCAO). HBOT began to intervene 24 h after MCAO under the pressure of 3 atmospheres for one hour per day for 21 days. Rats in the control group were placed in the same acrylic box without HBOT during the experiment. After the final intervention, half of the rats in each group were cardio-perfused with ice-cold saline followed by 4% paraformaldehyde under anesthesia. The brains were removed, dehydrated and cut into serial 20μm coronal sections for immunofluorescence staining to detect the markers of newborn cell (BrdU⁺), mature neuron cell (NeuN⁺), SDF1, and CXCR4. The affected motor cortex of the other half rats in each group was separated under anesthesia and used to detect the expressions of brain-derived neurotrophic factor (BDNF), SDF1, and CXCR4. Motor function was tested by a ladder-climbing test before and after the experiment. HBOT significantly enhanced neurogenesis in the penumbra area and promoted the expressions of SDF1 and CXCR4. The numbers of BrdU⁺/SDF1⁺, BrdU⁺/CXCR4⁺, and BrdU⁺/NeuN⁺ cells and BDNF concentrations in the penumbra were all significantly increased in the HBO group when compared with the control group. The motor functions were improved in both groups, but there was a significant difference between groups in the post-test. Our results indicated that HBOT for 21 days enhanced neurogenesis and promoted cell migration toward the penumbra area in transient brain ischemic rats. HBOT also increased BDNF expression, which might further promote the reconstructions of the impaired neural networks and restore motor function.

A Non-Invasive Determination of Ketosis-Induced Elimination of Chronic Daytime Somnolence in a Patient with Late-Stage Dementia (Assessed with Type 3 Diabetes): A Potential Role of Neurogenesis

Background

The study involved a female patient diagnosed with late-stage dementia, with chronic daytime somnolence (CDS) as a prominent symptom.

Objective

To explore whether her dementia resulted from Type 3 diabetes, and whether it could be reversed through ketosis therapy.

Methods

A ketogenic diet (KD) generating low-dose 100 μM Blood Ketone Levels (BKL) enhanced by a brief Ketone Mono Ester (KME) regimen with high-dose 2-4 mM BKLs was used.

Results

Three sets of data describe relief (assessed by % days awake) from CDS: 1) incremental, slow, time-dependent KD plus KME-induced sigmoid curve responses which resulted in partial wakefulness (0-40% in 255 days) and complete wakefulness (40-85% in 50 days); 2) both levels of wakefulness were shown to be permanent; 3) initial permanent relief from CDS with low-dose ketosis from 6.7% to 40% took 87 days. Subsequent low-dose recovery from illness-induced CDS (6.9% to 40%) took 10 days. We deduce that the first restoration involved permanent repair, and the second energized the repaired circuits.

Conclusion

The results suggest a role for ketosis in the elimination of CDS with the permanent functional restoration of the awake neural circuits of the Sleep-Wake cycle. We discuss whether available evidence supports ketosis-induced bioenergetics alone or whether other mechanisms of functional renewal were the basis for the elimination of CDS. Given evidence for permanent repair, two direct links between ketosis and neurogenesis in the adult mammalian brain are discussed: Ketosis-induced 1) brain-derived neurotrophic factor, resulting in neural progenitor/stem cell proliferation, and 2) mitochondrial bioenergetics-induced stem cell biogenesis.

Modulation of gene expression on a transcriptome-wide level following human neural stem cell transplantation in aged mouse stroke brains

INTRODUCTION

Neural stem cell (NSC) transplantation offers great potential for treating ischemic stroke. Clinically, ischemia followed by reperfusion results in robust cerebrovascular injury that upregulates proinflammatory factors, disrupts neurovascular units, and causes brain cell death. NSCs possess multiple actions that can be exploited for reducing the severity of neurovascular injury. Our previous studies in young adult mice showed that human NSC transplantation during the subacute stage diminishes stroke pathophysiology and improves behavioral outcome.

METHODS

We employed a well-established and commonly used stroke model, middle cerebral artery occlusion with subsequent reperfusion (MCAO/R). Here, we assessed the outcomes of hNSC transplantation 48 h post-MCAO (24 h post-transplant) in aged mouse brains in response to stroke because aging is a crucial risk factor for cerebral ischemia. Next, we tested whether administration of the integrin α5β1 inhibitor, ATN-161, prior to hNSC transplantation further affects stoke outcome as compared with NSCs alone. RNA sequencing (RNA-seq) was used to assess the impact of hNSC transplantation on differentially expressed genes (DEGs) on a transcriptome-wide level.

RESULTS

Here, we report that hNSC-engrafted brains with or without ATN-161 showed significantly reduced infarct size, and attenuated the induction of proinflammatory factors and matrix metalloproteases. RNA-seq analysis revealed DEGs and molecular pathways by which hNSCs induce a beneficial post-stroke outcome in aged stroke brains. 811 genes were differentially expressed (651 downregulated and 160 upregulated) in hNSC-engrafted stroke brains. Functional pathway analysis identified enriched and depleted pathways in hNSC-engrafted aged mouse stroke brains. Depletion of pathways following hNSC-engraftment included signaling involving neuroinflammation, acute phase response, leukocyte extravasation, and phagosome formation. On the other hand, enrichment of pathways in hNSC-engrafted brains was associated with PPAR signaling, LXR/RXR activation, and inhibition of matrix metalloproteases. Hierarchical cluster analysis of DEGs in hNSC-engrafted brains indicate decreased expression of genes encoding TNF receptors, proinflammatory factors, apoptosis factors, adhesion and leukocyte extravasation, and Toll-like receptors.

CONCLUSIONS

Our study is the first to show global transcripts differentially expressed following hNSC transplantation in the subacute phase of stroke in aged mice. The outcome of our transcriptome study would be useful to develop new therapies ameliorating early-stage stroke injury.

Oxytocin and Related Peptide Hormones: Candidate Anti-Inflammatory Therapy in Early Stages of Sepsis

Sepsis is a potentially life-threatening systemic inflammatory syndrome characterized by dysregulated host immunological responses to infection. Uncontrolled immune cell activation and exponential elevation in circulating cytokines can lead to sepsis, septic shock, multiple organ dysfunction syndrome, and death. Sepsis is associated with high re-hospitalization and recovery may be incomplete, with long term sequelae including post-sepsis syndrome. Consequently, sepsis continues to be a leading cause of morbidity and mortality across the world. In our recent review of human chorionic gonadotropin (hCG), we noted that its major properties including promotion of fertility, parturition, and lactation were described over a century ago. By contrast, the anti-inflammatory properties of this hormone have been recognized only more recently. Vasopressin, a hormone best known for its anti-diuretic effect, also has anti-inflammatory actions. Surprisingly, vasopressin's close cousin, oxytocin, has broader and more potent anti-inflammatory effects than vasopressin and a larger number of pre-clinical studies supporting its potential role in limiting sepsis-associated organ damage. This review explores possible links between oxytocin and related octapeptide hormones and sepsis-related modulation of pro-inflammatory and anti-inflammatory activities.

Overexpression of EphB4 promotes neurogenesis, but inhibits neuroinflammation in mice with acute ischemic stroke

Ischemic stroke is one of the most common diseases that has a high rate of mortality, and has become a burden to the healthcare system. Previous research has shown that EPH receptor B4 (EphB4) promotes neural stem cell proliferation and differentiation in vitro. However, little is known regarding its role in the neurogenesis of ischemic stroke in vivo. Thus, the present study aimed to verify whether EphB4 was a key regulator of neurogenesis in ischemic stroke in vivo. Cerebral ischemia was induced in C57BL/6J mice via middle cerebral artery occlusion (MCAO), followed by reperfusion. Immunofluorescence staining was performed to evaluate the effect of EphB4 on the neurogenesis in cerebral cortex. The levels of inflammatory cytokines were determined using an ELISA kit. The expression levels of ABL proto-oncogene 1, non-receptor tyrosine kinase (ABL1)/Cyclin D1 signaling pathway-related proteins were detected via western blotting. The current findings indicated that EphB4 expression was significantly increased in the cerebral cortex of MCAO model mice in comparison with sham-operated mice. Moreover, EphB4 appeared to be expressed in neural stem cells (Nestin⁺), and persisted as these cells became neuronal progenitors (Sox2⁺), neuroblasts [doublecortin (DCX)⁺], and eventually mature neurons [neuronal nuclei (NeuN)⁺]. Overexpression of EphB4 elevated the number of proliferating (bromodeoxyuridine⁺, Ki67⁺) and differentiated cells (Nestin⁺, Sox2⁺, DCX⁺ and NeuN⁺), indicating the promoting effect of EphB4 on the neurogenesis of ischemic stroke. Furthermore, EphB4 overexpression alleviated the inflammation injury in MCAO model mice. The expression levels of proteins-related to the ABL1/Cyclin D1 signaling pathway were significantly increased by the overexpression of EphB4, which suggested that restoration of EphB4 promoted the activation of the ABL1/Cyclin D1 signaling pathway. In conclusion, this study contributes to the current understanding of the mechanisms of EphB4 in exerting neurorestorative effects and may recommend a potential new strategy for ischemic stroke treatment.

Combination of Drugs and Cell Transplantation: More Beneficial Stem Cell-Based Regenerative Therapies Targeting Neurological Disorders

Cell transplantation therapy using pluripotent/multipotent stem cells has gained attention as a novel therapeutic strategy for treating neurodegenerative diseases, including Parkinson’s disease, Alzheimer’s disease, Huntington’s disease, ischemic stroke, and spinal cord injury. To fully realize the potential of cell transplantation therapy, new therapeutic options that increase cell engraftments must be developed, either through modifications to the grafted cells themselves or through changes in the microenvironment surrounding the grafted region. Together these developments could potentially restore lost neuronal function by better supporting grafted cells. In addition, drug administration can improve the outcome of cell transplantation therapy through better accessibility and delivery to the target region following cell transplantation. Here we introduce examples of drug repurposing approaches for more successful transplantation therapies based on preclinical experiments with clinically approved drugs. Drug repurposing is an advantageous drug development strategy because drugs that have already been clinically approved can be repurposed to treat other diseases faster and at lower cost. Therefore, drug repurposing is a reasonable approach to enhance the outcomes of cell transplantation therapies for neurological diseases. Ideal repurposing candidates would result in more efficient cell transplantation therapies and provide a new and beneficial therapeutic combination.

Characterization and Stage-Dependent Lineage Analysis of Intermediate Progenitors of Cortical GABAergic Interneurons

Intermediate progenitors of both excitatory and inhibitory neurons, which can replenish neurons in the adult brain, were recently identified. However, the generation of intermediate progenitors of GABAergic inhibitory neurons (IPGNs) has not been studied in detail. Here, we characterized the spatiotemporal distribution of IPGNs in mouse cerebral cortex. IPGNs generated neurons during both embryonic and postnatal stages, but the embryonic IPGNs were more proliferative. Our lineage tracing analyses showed that the embryonically proliferating IPGNs tended to localize to the superficial layers rather than the deep cortical layers at 3 weeks after birth. We also found that embryonic IPGNs derived from the medial and caudal ganglionic eminence (CGE) but more than half of the embryonic IPGNs were derived from the CGE and broadly distributed in the cerebral cortex. Taken together, our data indicate that the broadly located IPGNs during embryonic and postnatal stages exhibit a different proliferative property and layer distribution.

The effects of maternal SSRI exposure on the serotonin system, prefrontal protein expression and behavioral development in male and female offspring rats

Fluoxetine (FLX), a commonly used selective serotonin reuptake inhibitor, is often used to treat depression during pregnancy. However, prenatal exposure to FLX has been associated with a series of neuropsychiatric illnesses. The use of a rodent model can provide a clear indication as to whether prenatal exposure to SSRIs, independent of maternal psychiatric disorders or genetic syndromes, can cause long-term behavioral abnormalities in offspring. Thus, the present study aimed to explore whether prenatal FLX exposure causes long-term neurobehavioral effects, and identify the underlying mechanism between FLX and abnormal behaviors. In our study, 12/mg/kg/day of FLX or equal normal saline (NS) was administered to pregnant Sprague-Dawley (SD) rats (FLX = 30, NS = 27) on gestation day 11 till birth. We assessed the physical development and behavior of offspring, and in vivo magnetic resonance spectroscopy (MRS) was conducted to quantify biochemical alterations in the prefrontal cortex (PFC). Ex vivo measurements of brain serotonin level and a proteomic analysis were also undertaken. Our results showed that the offspring (male offspring in particular) of fluoxetine exposed mothers showed delayed physical development, increased anxiety-like behavior, and impaired social interaction. Moreover, down-regulation of 5-HT and SERT expression were identified in the PFC. We also found that prenatal FLX exposure significantly decreased NAA/tCr with 1H-MRS in the PFC of offspring. Finally, a proteomic study revealed sex-dependent differential protein expression. These findings may have translational importance suggesting that using SSRI medication alone in pregnant mothers may result in developmental delay in their offspring. Our results also help guide the choice of outcome measures in identifying of molecular and developmental mechanisms.

Conversion of Reactive Astrocytes to Induced Neurons Enhances Neuronal Repair and Functional Recovery After Ischemic Stroke

The master neuronal transcription factor NeuroD1 can directly reprogram astrocytes into induced neurons (iNeurons) after stroke. Using viral vectors to drive ectopic ND1 expression in gliotic astrocytes after brain injury presents an autologous form of cell therapy for neurodegenerative disease. Cultured astrocytes transfected with ND1 exhibited reduced proliferation and adopted neuronal morphology within 2-3 weeks later, expressed neuronal/synaptic markers, and extended processes. Whole-cell recordings detected the firing of evoked action potentials in converted iNeurons. Focal ischemic stroke was induced in adult GFAP-Cre-Rosa-YFP mice that then received ND1 lentivirus injections into the peri-infarct region 7 days after stroke. Reprogrammed cells did not express stemness genes, while 2-6 weeks later converted cells were co-labeled with YFP (constitutively activated in astrocytes), mCherry (ND1 infection marker), and NeuN (mature neuronal marker). Approximately 66% of infected cells became NeuN-positive neurons. The majority (~80%) of converted cells expressed the vascular glutamate transporter (vGLUT) of glutamatergic neurons. ND1 treatment reduced astrogliosis, and some iNeurons located/survived inside of the savaged ischemic core. Western blotting detected higher levels of BDNF, FGF, and PSD-95 in ND1-treated mice. MultiElectrode Array (MEA) recordings in brain slices revealed that the ND1-induced reprogramming restored interrupted cortical circuits and synaptic plasticity. Furthermore, ND1 treatment significantly improved locomotor, sensorimotor, and psychological functions. Thus, conversion of endogenous astrocytes to neurons represents a plausible, on-site regenerative therapy for stroke.

Microglial activation and adult neurogenesis after brain stroke

The discovery that new neurons are produced in some regions of the adult mammalian brain is a paradigm-shift in neuroscience research. These new-born cells are produced from neuroprogenitors mainly in the subventricular zone at the margin of the lateral ventricle, subgranular zone in the hippocampal dentate gyrus and in the striatum, a component of the basal ganglia, even in humans. In the human hippocampus, neuroblasts are produced even in elderlies. The regulation of adult neurogenesis is a complex phenomenon involving a multitude of molecules, neurotransmitters and soluble factors released by different sources including glial cells. Microglia, the resident macrophages of the central nervous system, are considered to play an important role on the regulation of adult neurogenesis both in physiological and pathological conditions. Following stroke and other acute neural disorders, there is an increase in the numbers of neuroblast production in the neurogenic niches. Microglial activation is believed to display both beneficial and detrimental role on adult neurogenesis after stroke, depending on the activation level and brain location. In this article, we review the scientific evidence addressing the role of microglial activation on adult neurogenesis after ischemia. A comprehensive understanding of the microglial role after stroke and other neural disorders it is an important step for development of future therapies based on manipulation of adult neurogenesis.

An Overview of Adult Neurogenesis

Neurogenesis is maintained in the mammalian brain throughout adulthood in two main regions: the subventricular zone (SVZ) of the lateral ventricles and the subgranular zone (SGZ) of the hippocampal dentate gyrus. Adult neurogenesis is a process composed of multiple steps by which neurons are generated from dividing adult neural stem cells and migrate to be integrated into existing neuronal circuits. Alterations in any of these steps impair neurogenesis and may compromise brain function, leading to cognitive impairment and neurodegenerative diseases. Therefore, understanding the cellular and molecular mechanisms that modulate adult neurogenesis is the centre of attention of regenerative research. In this chapter, we review the main properties of the adult neurogenic niches.

Woo E, Patten A, Yau SY, Gil-Mohapel J. Beyond the Hippocampus and the SVZ: Adult Neurogenesis Throughout the Brain

Convincing evidence has repeatedly shown that new neurons are produced in the mammalian brain into adulthood. Adult neurogenesis has been best described in the hippocampus and the subventricular zone (SVZ), in which a series of distinct stages of neuronal development has been well characterized. However, more recently, new neurons have also been found in other brain regions of the adult mammalian brain, including the hypothalamus, striatum, substantia nigra, cortex, and amygdala. While some studies have suggested that these new neurons originate from endogenous stem cell pools located within these brain regions, others have shown the migration of neurons from the SVZ to these regions. Notably, it has been shown that the generation of new neurons in these brain regions is impacted by neurologic processes such as stroke/ischemia and neurodegenerative disorders. Furthermore, numerous factors such as neurotrophic support, pharmacologic interventions, environmental exposures, and stem cell therapy can modulate this endogenous process. While the presence and significance of adult neurogenesis in the human brain (and particularly outside of the classical neurogenic regions) is still an area of debate, this intrinsic neurogenic potential and its possible regulation through therapeutic measures present an exciting alternative for the treatment of several neurologic conditions. This review summarizes evidence in support of the classic and novel neurogenic zones present within the mammalian brain and discusses the functional significance of these new neurons as well as the factors that regulate their production. Finally, it also discusses the potential clinical applications of promoting neurogenesis outside of the classical neurogenic niches, particularly in the hypothalamus, cortex, striatum, substantia nigra, and amygdala.

Oxytocin Receptor Signaling in Vascular Function and Stroke

The oxytocin receptor (OXTR) is a G protein-coupled receptor with a diverse repertoire of intracellular signaling pathways, which are activated in response to binding oxytocin (OXT) and a similar nonapeptide, vasopressin. This review summarizes the cell and molecular biology of the OXTR and its downstream signaling cascades, particularly focusing on the vasoactive functions of OXTR signaling in humans and animal models, as well as the clinical applications of OXTR targeting cerebrovascular accidents.

Human neural stem cells improve early stage stroke outcome in delayed tissue plasminogen activator-treated aged stroke brains

INTRODUCTION

Clinically, significant stroke injury results from ischemia-reperfusion (IR), which induces a deleterious biphasic opening of the blood-brain barrier (BBB). Tissue plasminogen activator (tPA) remains the sole pharmacological agent to treat ischemic stroke. However, major limitations of tPA treatment include a narrow effective therapeutic window of 4.5 h in most patients after initial stroke onset and off-target non-thrombolytic effects (e.g., the risk of increased IR injury). We hypothesized that ameliorating BBB damage with exogenous human neural stem cells (hNSCs) would improve stroke outcome to a greater extent than treatment with delayed tPA alone in aged stroke mice.

METHODS

We employed middle cerebral artery occlusion to produce focal ischemia with subsequent reperfusion (MCAO/R) in aged mice and administered tPA at a delayed time point (6 h post-stroke) via tail vein. We transplanted hNSCs intracranially in the subacute phase of stroke (24 h post-stroke). We assessed the outcomes of hNSC transplantation on pathophysiological markers of stroke 48 h post-stroke (24 h post-transplant).

RESULTS

Delayed tPA treatment resulted in more extensive BBB damage and inflammation relative to MCAO controls. Notably, transplantation of hNSCs ameliorated delayed tPA-induced escalated stroke damage; decreased expression of proinflammatory factors (tumor necrosis factor-alpha (TNF-α) and interleukin (IL)-6), decreased the level of matrix metalloprotease-9 (MMP-9), increased the level of brain-derived neurotrophic factor (BDNF), and reduced BBB damage.

CONCLUSIONS

Aged stroke mice that received delayed tPA treatment in combination with hNSC transplantation exhibited reduced stroke pathophysiology in comparison to non-transplanted stroke mice with delayed tPA. This suggests that hNSC transplantation may synergize with already existing stroke therapies to benefit a larger stroke patient population.

Adult Neurogenesis Following Ischemic Stroke and Implications for Cell-Based Therapeutic Approaches

Ischemic stroke is one of the most intractable diseases of the central nervous system and is also a major cause of mortality and disability in adult humans. Unfortunately, current therapies target vessel recanalization, which has a narrow treatment window, and the potential adverse effects lead to a low rate of clinical employment; in addition, neuroprotective strategies are not effective for stroke treatment. It is necessary to discover new approaches to develop neuroprotective, neuroregenerative treatment strategies for stroke. At present, accumulating evidence suggests that adult neurogenesis is a novel topic with extensive research on its potential to be harnessed for therapy in various neurologic disorders, and the neurogenesis capacity in the subventricular zone was shown to be increased in response to brain ischemic stroke. In this review, we describe the cellular and molecular mechanisms underlying potential adult neurogenesis and review current preclinical and clinical cell-based therapies for enhancing neural regeneration after adult ischemic stroke. Although stroke-induced neurogenesis in humans does not seem to translate to neurofunctional recovery, we also summarize factors of potential treatment strategies with transplanted cells, including transplantation time, cell dosage, and administration route, to achieve optimum and effective cell-based therapy, thereby harnessing this neuroregenerative response to improve neurofunctional recovery after ischemic stroke.

Different exercises can modulate the differentiation/maturation of neural stem/progenitor cells after photochemically induced focal cerebral infarction

INTRODUCTION

Exercise therapies during rehabilitation significantly promote recovery from various deficits after cerebral infarction, which is mediated by neuronal plasticity with distinct inputs. Although adult neurogenesis can also be modulated by neuronal activity before synaptogenesis, how distinct exercises contribute to the neurological reorganization of the injured cerebral cortex remains unclear. In the present study, we aimed to elucidate the effects of different exercise therapies on motor recovery and neuronal reorganization after photochemically induced focal cerebral infarction.

METHODS

Here, we examined the effects of three different exercises-(a) forced lower-intensity and (b) higher-intensity treadmill exercises, and (c) voluntary exercise with wheel running-on motor recovery and adult neurogenesis in a rat model of focal cerebral infarction. Photochemically induced thrombosis (PIT) was used to generate focal infarction in rats that was mostly confined to their motor cortices.

RESULTS

Beam walking tests showed that recovery after PIT-induced cortical infarction differed in acute and chronic stages and was influenced by the type of exercise. Furthermore, forced low-intensity training had more positive effects on functional recovery than other exercises or control. To evaluate the production of newly generated cells including de novo neurogenesis, we performed lineage analysis with BrdU labeling and immunofluorescence experiments. Lower-intensity treadmill exercise increased the number of BrdU/NeuN colabeled cells, but not total BrdU-retaining or BrdU/Sox2-colabeled cells, in the peri-infarct region of the ipsilateral cortex. In contrast, high-intensity treadmill or voluntary exercises had the opposite effects.

CONCLUSIONS

These results suggest that neuronal maturation can be differently modulated by distinct exercises and that low-intensity treadmill exercise could result in more potent generation of mature neurons. This also suggests the possibility that the generation of neural stem/progenitor cells and differentiation might be modulated by rehabilitation-mediated neural plasticity.

Dopamine as a growth differentiation factor in the mammalian brain

The catecholamine, dopamine, plays an important role in the central nervous system of mammals, including executive functions, motor control, motivation, arousal, reinforcement, and reward. Dysfunctions of the dopaminergic system lead to diseases of the brains, such as Parkinson's disease, Tourette's syndrome, and schizophrenia. In addition to its fundamental role as a neurotransmitter, there is evidence for a role as a growth differentiation factor during development. Recent studies suggest that dopamine regulates the development of γ-aminobutyric acidergic interneurons of the cerebral cortex. Moreover, in adult brains, dopamine increases the production of new neurons in the hippocampus, suggesting the promoting effect of dopamine on proliferation and differentiation of neural stem cells and progenitor cells in the adult brains. In this mini-review, I center my attention on dopaminergic functions in the cortical interneurons during development and further discuss cell therapy against neurodegenerative diseases.

Static Magnetic Field Exposure In Vivo Enhances the Generation of New Doublecortin-expressing Cells in the Sub-ventricular Zone and Neocortex of Adult Rats

Static magnetic field (SMF) is gaining interest as a potential technique for modulating CNS neuronal activity. Previous studies have shown a pro-neurogenic effect of short periods of extremely low frequency pulsatile magnetic fields (PMF) in vivo and pro-survival effect of low intensity SMF in cultured neurons in vitro, but little is known about the in vivo effects of low to moderate intensity SMF on brain functions. We investigated the effect of continuously-applied SMF on subventricular zone (SVZ) neurogenesis and immature doublecortin (DCX)-expressing cells in the neocortex of young adult rats and in primary cultures of cortical neurons in vitro. A small (3 mm diameter) magnetic disc was implanted on the skull of rats at bregma, producing an average field strength of 4.3 mT at SVZ and 12.9 mT at inner neocortex. Levels of proliferation of SVZ stem cells were determined by 5-ethynyl-2'-deoxyuridine (EdU) labelling, and early neuronal phenotype development was determined by expression of doublecortin (DCX). To determine the effect of SMF on neurogenesis in vitro, permanent magnets were placed beneath the culture dishes. We found that low intensity SMF exposure enhances cell proliferation in SVZ and new DCX-expressing cells in neocortical regions of young adult rats. In primary cortical neuronal cultures, SMF exposure increased the expression of newly generated cells co-labelled with EdU and DCX or the mature neuronal marker NeuN, while activating a set of pro neuronal bHLH genes. SMF exposure has potential for treatment of neurodegenerative disease and conditions such as CNS trauma and affective disorders in which increased neurogenesis is desirable.

Role of FOXC1 in regulating APSCs self-renewal via STI-1/PrPC signaling

Forkhead box protein C1 (FOXC1) is known to regulate developmental processes in the skull and brain. Methods: The unique multipotent arachnoid-pia stem cells (APSCs) isolated from human and mouse arachnoid-pia membranes of meninges were grown as 3D spheres and displayed a capacity for self-renewal. Additionally, APSCs also expressed the surface antigens as mesenchymal stem cells. By applying the FOXC1 knockout mice and mouse brain explants, signaling cascade of FOXC1-STI-1-PrP^C was investigated to demonstrate the molecular regulatory pathway for APSCs self-renewal. Moreover, APSCs implantation in stroke model was also verified whether neurogenic property of APSCs could repair the ischemic insult of the stroke brain. Results: Activated FOXC1 regulated the proliferation of APSCs in a cell cycle-dependent manner, whereas FOXC1-mediated APSCs self-renewal was abolished in FOXC1 knockout mice (FOXC1^-/- mice). Moreover, upregulation of STI-1 regulated by FOXC1 enhanced cell survival and self-renewal of APSCs through autocrine signaling of cellular prion protein (PrP^C). Mouse brain explants STI-1 rescues the cortical phenotype in vitro and induces neurogenesis in the FOXC1 ^-/- mouse brain. Furthermore, administration of APSCs in ischemic brain restored the neuroglial microenvironment and improved neurological dysfunction. Conclusion: We identified a novel role for FOXC1 in the direct regulation of the STI-1-PrP^C signaling pathway to promote cell proliferation and self-renewal of APSCs.

Fluoxetine-induced dematuration of hippocampal neurons and adult cortical neurogenesis in the common marmoset

The selective serotonin reuptake inhibitor fluoxetine (FLX) is widely used to treat depression and anxiety disorders. Chronic FLX treatment reportedly induces cellular responses in the brain, including increased adult hippocampal and cortical neurogenesis and reversal of neuron maturation in the hippocampus, amygdala, and cortex. However, because most previous studies have used rodent models, it remains unclear whether these FLX-induced changes occur in the primate brain. To evaluate the effects of FLX in the primate brain, we used immunohistological methods to assess neurogenesis and the expression of neuronal maturity markers following chronic FLX treatment (3 mg/kg/day for 4 weeks) in adult marmosets (n = 3 per group). We found increased expression of doublecortin and calretinin, markers of immature neurons, in the hippocampal dentate gyrus of FLX-treated marmosets. Further, FLX treatment reduced parvalbumin expression and the number of neurons with perineuronal nets, which indicate mature fast-spiking interneurons, in the hippocampus, but not in the amygdala or cerebral cortex. We also found that FLX treatment increased the generation of cortical interneurons; however, significant up-regulation of adult hippocampal neurogenesis was not observed in FLX-treated marmosets. These results suggest that dematuration of hippocampal neurons and increased cortical neurogenesis may play roles in FLX-induced effects and/or side effects. Our results are consistent with those of previous studies showing hippocampal dematuration and increased cortical neurogenesis in FLX-treated rodents. In contrast, FLX did not affect hippocampal neurogenesis or dematuration of interneurons in the amygdala and cerebral cortex.

New Neurons in the Post-ischemic and Injured Brain: Migrating or Resident?

The endogenous potential of adult neurogenesis is of particular interest for the development of new strategies for recovery after stroke and traumatic brain injury. These pathological conditions affect endogenous neurogenesis in two aspects. On the one hand, injury usually initiates the migration of neuronal precursors (NPCs) to the lesion area from the already existing, in physiological conditions, neurogenic niche - the ventricular-subventricular zone (V-SVZ) near the lateral ventricles. On the other hand, recent studies have convincingly demonstrated the local generation of new neurons near lesion areas in different brain locations. The striatum, cortex, and hippocampal CA1 region are considered to be locations of such new neurogenic zones in the damaged brain. This review focuses on the relative contribution of two types of NPCs of different origin, resident population in new neurogenic zones and cells migrating from the lateral ventricles, to post-stroke or post-traumatic enhancement of neurogenesis. The migratory pathways of NPCs have also been considered. In addition, the review highlights the advantages and limitations of different methodological approaches to the definition of NPC location and tracking of new neurons. In general, we suggest that despite the considerable number of studies, we still lack a comprehensive understanding of neurogenesis in the damaged brain. We believe that the advancement of methods for in vivo visualization and longitudinal observation of neurogenesis in the brain could fundamentally change the current situation in this field.

Region-specific and activity-dependent regulation of SVZ neurogenesis and recovery after stroke

Recovery after stroke involves remodeling in brain tissue adjacent to the stroke site. In this remodeling, neurogenesis after stroke involves the formation of new neurons. The role of neurogenesis in stroke recovery and the role of brain and behavioral activity in this process remain undefined. Using orthogonal transgenic mouse tracing and rabies virus approaches, we demonstrate that brain regions unexpectedly compete for new neurons after stroke and that the behavioral or cellular activity establishes this competition. These new neurons synaptically integrate into cortex, and this integration is necessary for poststroke recovery.

Stroke is the leading cause of adult disability. Neurogenesis after stroke is associated with repair; however, the mechanisms regulating poststroke neurogenesis and its functional effect remain unclear. Here, we investigate multiple mechanistic routes of induced neurogenesis in the poststroke brain, using both a forelimb overuse manipulation that models a clinical neurorehabilitation paradigm, as well as local manipulation of cellular activity in the peri-infarct cortex. Increased activity in the forelimb peri-infarct cortex via either modulation drives increased subventricular zone (SVZ) progenitor proliferation, migration, and neuronal maturation in peri-infarct cortex. This effect is sensitive to competition from neighboring brain regions. By using orthogonal tract tracing and rabies virus approaches in transgenic SVZ-lineage-tracing mice, SVZ-derived neurons synaptically integrate into the peri-infarct cortex; these effects are enhanced with forelimb overuse. Synaptic transmission from these newborn SVZ-derived neurons is critical for spontaneous recovery after stroke, as tetanus neurotoxin silencing specifically of the SVZ-derived neurons disrupts the formation of these synaptic connections and hinders functional recovery after stroke. SVZ-derived neurogenesis after stroke is activity-dependent, region-specific, and sensitive to modulation, and the synaptic connections formed by these newborn cells are functionally critical for poststroke recovery.

Dopamine stimulates differentiation and migration of cortical interneurons

Cortical GABAergic interneurons originate and migrate tangentially from the medial ganglionic eminence (MGE), but its mechanism remains unknown. In this study, we show that dopamine (DA) stimulates the differentiation and migration of cortical interneurons derived from MGE cells. Using immunohistochemistry for the DA marker, tyrosine hydroxylase (TH), TH positive axons enter the MGE by E12.5. In E11.5 MGE primary cultures, DA enhances the expression of cortical interneuron marker proteins, such as GAD67 and neuropilin1, via D1 receptor, and also up-regulates D2 receptor. In E14.5 organotypic slice cultures, the migration of MGE cells is occurred in a D2 receptor-dependent manner, whose stimulation increased the synthesis of neurotrophins, in E11.5 MGE primary cultures. Furthermore, TH neurons-depletion by 6-hydroxydopamine treatments led to a significant reduction of cortical calbindin positive cells in the cerebral cortex, compared with the controls. Therefore, these results suggest that DA can stimulate the differentiation and migration of cortical interneurons.

Histamine H1 Receptors in Neural Stem Cells Are Required for the Promotion of Neurogenesis Conferred by H3 Receptor Antagonism following Traumatic Brain Injury

The neurological recovery following traumatic brain injury (TBI) is limited, largely due to a deficiency in neurogenesis. The present study explores the effects of histamine H3 receptor (H3R) antagonism on TBI and mechanisms related to neurogenesis. H3R antagonism or H3R gene knockout alleviated neurological injury in the late phase of TBI, and also promoted neuroblast differentiation to enhance neurogenesis through activation of the histaminergic system. Histamine H1 receptor, but not H2 receptor, in neural stem cells is shown to be essential for this promotion by using Hrh1^fl/fl;Nestin^CreERT2 and Hrh2^fl/fl;Nestin^CreERT2 mice. Moreover, increase in mature and functional neurons at the penumbra area conferred by H3R antagonism was abrogated in Hrh1^fl/fl;Nestin^CreERT2 mice. Taken together, H3R antagonism provides neuroprotection against TBI in the late phase through the promotion of neurogenesis, and the H1 receptor in neural stem cells is required for this action. H3R may serve as a new target for clinical treatment of TBI.

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Histamine H3R antagonism provides neuroprotection against traumatic brain injury

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H3R antagonism promotes neuroblast differentiation to enhance neurogenesis

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H1R in NSCs is required for the promotion of neurogenesis

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H3R antagonism increases mature and functional neurons mediated by H1R in NSCs

Expression of DCX and Transcription Factor Profiling in Photothrombosis-Induced Focal Ischemia in Mice

Adult neurogenesis is present in the dentate gyrus and the subventricular zone in mammalian brain under physiological conditions. Recently, adult neurogenesis has also been reported in other brain regions after brain injury. In this study, we established a focal striatal ischemic model in adult mice via photothrombosis (PT) and investigated how focal ischemia elicits neurogenesis in the striatum. We found that astrocytes and microglia increased in early post-ischemic stage, followed by a 1-week late-onset of doublecortin (DCX) expression in the striatum. The number of DCX-positive neurons reached the peak level at day 7, but they were still observed at day 28 post-ischemia. Moreover, Rbp-J (a key effector of Notch signaling) deletion in astrocytes has been reported to promote the neuron regeneration after brain ischemia, and we provided the change of gene expression profile in the striatum of astrocyte-specific Rbp-J knockout (KO) mice glial fibrillary acidic protein (GFAP-Cre^ER:Rbp-J^fl/fl), which may help to clarify detailed potential mechanisms for the post-ischemic neurogenesis in the striatum.

Adaptive neurogenesis in the cerebral cortex and contralateral subventricular zone induced by unilateral cortical devascularization: Possible modulation by dopamine neurotransmission

Understanding endogenous neurogenesis and neuronal replacement to mature circuits is a topic of discussion as a therapeutic alternative under acute and chronic neurodegenerative disorders. Adaptive neurogenic response may result as a result of ischemia which could support long-term recovery of behavioral functions. Endogenous sources of neural progenitors may be stimulated by changes in blood flow or neuromodulation. Using a mouse model of unilateral cortical devascularization, we have observed reactive neurogenesis in the perilesional cortex and subventricular zone neurogenic niche. C57BL/6L 4 weeks old male mice were craneotomized at 1 mm caudal from frontal suture and 1 mm lateral from midline to generate a window of 3 mm side. Brain injury was produced by removal of the meninges and superficial vasculature of dorsal parietal cortex. BrdU agent (50 mg/kg, ip) was injected to lesioned and sham animals, during days 0 and 1 after surgery. Sagittal sections were analyzed at 1, 4, 7, and 10 days post-injury. A time-dependent increase in BrdU⁺ cells in the perilesional parietal cortex was accompanied by augmented BrdU⁺ cells in the sub ventricular and rostral migratory stream of ipsilateral and contralateral hemispheres. Neural progenitors and neuroblasts proliferated in the lesioned and non-lesioned subventricular zone and rostral migratory stream on day 4 after injury. Augmented contralateral neurogenesis was associated with an increase in vesicular monoamine transporter 2 protein in the striosomal sub ventricular neurogenic niche of non-lesioned hemisphere.

Inflammation and neural repair after ischemic brain injury

Stroke causes neuronal cell death and destruction of neuronal circuits in the brain and spinal cord. Injury to the brain tissue induces sterile inflammation triggered by the extracellular release of endogenous molecules, but cerebral inflammation after stroke is gradually resolved within several days. In this pro-resolving process, inflammatory cells adopt a pro-resolving or repairing phenotype in the injured brain, activating endogenous repairing programs. Although the mechanisms involved in the transition from inflammation to neural repair after stroke remain largely unknown to date, some of the mechanisms for inflammation and neural repair have been clarified in detail. This review focuses on the molecular or cellular mechanisms involved in sterile inflammation and neural repair after stroke. This accumulation of evidence may be helpful for speculating about the endogenous repairing mechanisms in the brain and identifying therapeutic targets for improving the functional prognoses of stroke patients.

Hyaluronic acid is present on specific perineuronal nets in the mouse cerebral cortex

In the central nervous system (CNS), extracellular matrix (ECM) molecules comprise more than 20% of the volume and are involved in neuronal plasticity, synaptic transmission, and differentiation. Perineuronal nets (PNNs) are ECM molecules that highly accumulate around the soma of neurons. The components of the ECM in the CNS include proteins, proteoglycans, and glycosaminoglycans. Although hyaluronic acid (HA) is considered a constituent element of PNNs, the distribution of HA in the cortex has not been clarified. To elucidate the cortical region-specific distribution of HA, we quantitatively analyzed HA binding protein (HABP)-positive PNNs in the mature mouse cerebral cortex. Our findings revealed that HABP-positive PNNs are present throughout the mouse cortex. The distribution of many HABP-positive PNNs differed from that of Wisteria floribunda agglutinin-positive PNNs. Furthermore, we observed granular-like HABP-positive PNNs in layer 1 of the cortex. These findings indicate that PNNs in the mouse cortex show region-dependent differences in composition. HABP-positive PNNs in layer 1 of the cortex may have different functions such as neuronal differentiation, proliferation, and migration unlike what has been reported for PNNs so far.

Physical enrichment enhances memory function by regulating stress hormone and brain acetylcholinesterase activity in rats exposed to restraint stress

To study the effects of stress on mental health activity is of great importance in neuropsychological studies as it may affect the lifelong performance related to brain and overall health and wellbeing of an individual. It is observed very often that exposure to stress during early life can alter the brain function which may reflect as cognitive disability. Impairment of memory is associated with increased oxidative stress which is due to enhanced production of free radicals that may lead to lipid peroxidation and disintegration of cell structure and functions. Exposure to enriched environment has shown to enhance spatial learning and memory, although the underlying mechanism covering the regulation of antioxidant capacity is limited. Here we investigated short and long term memory using Morris water maze before and after giving restraint stress procedure in rats exposed to social and physically enriched environment. Levels of malondialdehyde (MDA), activity of superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), and acetylcholinesterase (AChE) in brain tissue were estimated. Plasma corticosterone was also determined after decapitation. Results demonstrated that rats pre-exposed to physical along with social enrichment showed improved short and long term memory as compared to control group. However, restraint stress exerted differential effects in socially and physically enriched groups. Reduced lipid peroxidation and decreased activity of SOD, GPx and AChE were observed in physically enriched rats subjected to stress as compared to stressed rats kept in social environment. Levels of corticosterone were also found to be significantly reduced in rats kept in physically enriched environment. This study shows the beneficial effects of environmental enrichment on learning and spatial memory by reducing oxidative stress via reducing lipid peroxidation and regulation of antioxidant enzymes in rats.

Stromal cells/telocytes and endothelial progenitors in the perivascular niches of the trigeminal ganglion

Stromal cells/telocytes (SCs/TCs) were recently described in the human adult trigeminal ganglion (TG). As some markers are equally expressed in SCs/TCs and endothelial cells, we hypothesized that a subset of the TG SCs/TCs is in fact represented by endothelial progenitor cells of a myelomonocytic origin. This study aimed to evaluate whether the interstitial cells of the human adult TG correlate with the myelomonocytic lineage. We used primary antibodies for c-erbB2/HER-2, CD31, nestin, CD10, CD117/c-kit, von Willebrand factor (vWF), CD34, Stro-1, CD146, α-smooth muscle actin (α-SMA), CD68, VEGFR-2 and cytokeratin 7 (CK7). The TG pial mesothelium and subpial vascular microstroma expressed c-erbB2/HER-2, CK7 and VEGFR-2. SCs/TCs neighbouring the neuronoglial units (NGUs) also expressed HER-2, which suggests a pial origin. These cells were also positive for CD10, CD31, CD34, CD68 and nestin. Endothelial cells expressed CD10, CD31, CD34, CD146, nestin and vWF. We also found vasculogenic networks with spindle-shaped and stellate endothelial progenitors expressing CD10, CD31, CD34, CD68, CD146 and VEGFR-2. Isolated mesenchymal stromal cells expressed Stro-1, CD146, CK7, c-kit and nestin. Pericytes expressed α-SMA and CD146. Using transmission electron microscopy (TEM), we found endothelial-specific Weibel-Palade bodies in spindle-shaped stromal progenitors. Our study supports the hypothesis that an intrinsic vasculogenic niche potentially involved in microvascular maintenance and repair might be present in the human adult trigeminal ganglion and that it might be supplied by either the pial mesothelium or the bone marrow niche.

Loss of GABAB -mediated interhemispheric synaptic inhibition in stroke periphery

KEY POINTS

Recovery from the potentially devastating consequences of stroke depends largely upon plastic changes occurring in the lesion periphery and its inputs. In a focal model of stroke in mouse somatosensory cortex, we found that the recovery of sensory responsiveness occurs at the level of synaptic inputs, without gross changes of the intrinsic electrical excitability of neurons, and also that recovered responses had longer than normal latencies. Under normal conditions, one somatosensory cortex inhibits the responsiveness of the other located in the opposite hemisphere (interhemispheric inhibition) via activation of GABA_B receptors. In stroke-recovered animals, the powerful interhemispheric inhibition normally present in controls is lost in the lesion periphery. By contrast, contralateral hemisphere activation selective contributes to the recovery of sensory responsiveness after stroke.

ABSTRACT

Recovery after stroke is mediated by plastic changes largely occurring in the lesion periphery. However, little is known about the microcircuit changes underlying recovery, the extent to which perilesional plasticity occurs at synaptic input vs. spike output level, and the connectivity behind such synaptic plasticity. We combined intrinsic imaging with extracellular and intracellular recordings and pharmacological inactivation in a focal stroke in mouse somatosensory cortex (S1). In vivo whole-cell recordings in hindlimb S1 (hS1) showed synaptic responses also to forelimb stimulation in controls, and such responses were abolished by stroke in the neighbouring forelimb area (fS1), suggesting that, under normal conditions, they originate via horizontal connections from the neighbouring fS1. Synaptic and spike responses to forelimb stimulation in hS1 recovered to quasi-normal levels 2 weeks after stroke, without changes in intrinsic excitability and hindlimb-evoked spike responses. Recovered synaptic responses had longer latencies, suggesting a long-range origin of the recovery, prompting us to investigate the role of callosal inputs in the recovery process. Contralesional S1 silencing unmasked significantly larger responses to both limbs in controls, a phenomenon that was not observed when GABA_B receptors were antagonized in the recorded area. Conversely, such GABA_B -mediated interhemispheric inhibition was not detectable after stroke: callosal input silencing failed to change hindlimb responses, whereas it robustly reduced recovered forelimb responses. Thus, recovery of subthreshold responsiveness in the stroke periphery is accompanied by a loss of interhemispheric inhibition and this is a result of pathway-specific facilitatory action on the affected sensory response from the contralateral cortex.

Sevoflurane preconditioning induced endogenous neurogenesis against ischemic brain injury by promoting microglial activation

Brain ischemia causes irreversible damage to functional neurons in cases of infarct. Promoting endogenous neurogenesis to replace necrotic neurons is a promising therapeutic strategy for ischemia patients. The neuroprotective role of sevoflurane preconditioning implies that it might also enhance endogenous neurogenesis and functional restoration in the infarct region. By using a transient middle cerebral artery occlusion (tMCAO) model, we discovered that endogenous neurogenesis was enhanced by sevoflurane preconditioning. This enhancement process is characterized by the promotion of neuroblast proliferation within the subventricular zone (SVZ), migration and differentiation into neurons, and the presence of astrocytes and oligodendrocytes at the site of infarct. The newborn neurons in the sevoflurane preconditioning group showed miniature excitatory postsynaptic currents (mEPSCs), increased synaptophysin and PSD95 staining density, indicating normal neuronal function. Furthermore, long-term behavioral improvement was observed in the sevoflurane preconditioning group consistent with endogenous neurogenesis. Further histological analyses showed that sevoflurane preconditioning accelerated microglial activation, including migration, phagocytosis and secretion of brain-derived neurotrophic factor (BDNF). Intraperitoneal injection of minocycline, a microglial inhibitor, suppressed microglial activation and reversed neurogenesis. Our data showed that sevoflurane preconditioning promoted microglial activities, created a favorable microenvironment for endogenous neurogenesis and accelerated functional reconstruction in the infarct region.

[Apoptosis as a systemic adaptive mechanism in ischemic stroke]

This paper presents a literature review considering the role and mechanism of apoptosis in the pathogenesis of ischemic stroke (IS). The authors introduce a new concept: the functional request of the patient as a set of external (the nature and intensity of rehabilitation measures, characteristics of everyday life, diet, etc.) and internal (genetic factors, internal picture of the disease, availability of rental and other psychological facilities and etc.) attributes. This concept allows a new angle in understanding the pathogenesis of IS and creates fundamental and clinical potential for more successful approaches to therapy and rehabilitation after IS.

Use of 2,3,5-triphenyltetrazolium chloride-stained brain tissues for immunofluorescence analyses after focal cerebral ischemia in rats

The middle cerebral artery occlusion (MCAO) model in rodents has been widely used as model for studying brain ischemic stroke. TTC (2,3,5-triphenyltetrazolium chloride) staining in fresh tissues is used to evaluate the size of the infarct in MCAO model, and TTC-stained brain tissues are considered to be possible to bring a damage to the anatomical structure of neuronal cells and unsuitable for immunofluorescence analyses of cytology, and discarded after evaluation of infarct volume. Another group of models with in vivo fixation was required to the pathological or histological analyses of the infarct brains, which lead to double the numbers of animals in researches. However, some evidences indicate that if we properly optimized staining protocol, TTC-stained brain tissues might be suitable for cytological analyses. In this work, we have optimized the immunofluorescent staining methods of TTC-stained brain slices, and found that TTC-stained brain tissues are suitable for quantitative and qualitative analyses of microglia, astrocytes and neuroblasts, the morphology of theses cell were nearly identical to the in-vivo fixed models. Our optimized-protocol provide two advantages over traditional methods one of them is providing the precise the infarct region, which reduces the differences within groups, the other one is decreasing the total number of animals in research dramatically.

Neuronal replacement therapy: previous achievements and challenges ahead

Lifelong neurogenesis and incorporation of newborn neurons into mature neuronal circuits operates in specialized niches of the mammalian brain and serves as role model for neuronal replacement strategies. However, to which extent can the remaining brain parenchyma, which never incorporates new neurons during the adulthood, be as plastic and readily accommodate neurons in networks that suffered neuronal loss due to injury or neurological disease? Which microenvironment is permissive for neuronal replacement and synaptic integration and which cells perform best? Can lost function be restored and how adequate is the participation in the pre-existing circuitry? Could aberrant connections cause malfunction especially in networks dominated by excitatory neurons, such as the cerebral cortex? These questions show how important connectivity and circuitry aspects are for regenerative medicine, which is the focus of this review. We will discuss the impressive advances in neuronal replacement strategies and success from exogenous as well as endogenous cell sources. Both have seen key novel technologies, like the groundbreaking discovery of induced pluripotent stem cells and direct neuronal reprogramming, offering alternatives to the transplantation of fetal neurons, and both herald great expectations. For these to become reality, neuronal circuitry analysis is key now. As our understanding of neuronal circuits increases, neuronal replacement therapy should fulfill those prerequisites in network structure and function, in brain-wide input and output. Now is the time to incorporate neural circuitry research into regenerative medicine if we ever want to truly repair brain injury.

Hippocampal GABAergic Inhibitory Interneurons

In the hippocampus GABAergic local circuit inhibitory interneurons represent only ~10-15% of the total neuronal population; however, their remarkable anatomical and physiological diversity allows them to regulate virtually all aspects of cellular and circuit function. Here we provide an overview of the current state of the field of interneuron research, focusing largely on the hippocampus. We discuss recent advances related to the various cell types, including their development and maturation, expression of subtype-specific voltage- and ligand-gated channels, and their roles in network oscillations. We also discuss recent technological advances and approaches that have permitted high-resolution, subtype-specific examination of their roles in numerous neural circuit disorders and the emerging therapeutic strategies to ameliorate such pathophysiological conditions. The ultimate goal of this review is not only to provide a touchstone for the current state of the field, but to help pave the way for future research by highlighting where gaps in our knowledge exist and how a complete appreciation of their roles will aid in future therapeutic strategies.

Population dynamics of neural progenitor cells during aging in the cerebral cortex

Recent studies indicate that adult neurogenesis occurs in the cerebral cortex of rodents. Neural progenitor cells (NPCs) have been found in the adult cerebral cortex. These cells are expected to be regulated by various stimuli, including environmental enrichment, exercise, learning, and stress. However, it is unclear what stimuli can regulate cortical NPCs. In this study, we examined whether aging has an impact on population dynamics of NPCs in the murine cerebral cortex, using immunohistological staining for NPCs. The density of NPCs was kept from 5- to 12-month-old, dramatically decreased at 17-month-old, and thereafter maintained the same level until 24-month-old. Comparing the densities of NPCs in the cortical areas, such as the cingulate, primary motor, primary somatosensory, and insular cortices, we found that the degrees of decreased densities of NPCs in the cingulate and insular cortices were significantly smaller than those in the primary motor and somatosensory cortices. NPCs in aged cortex produced new neurons by ischemia. These results indicate that in aged mice, NPCs exist and produce new neurons in the cerebral cortex. Additionally, the extent of reduction of the density of NPCs in the cortices with higher cognitive functions may be less than that in the primary motor and somatosensory cortices.