BetaIII tubulin-expressing neurons reveal enhanced neurogenesis in hippocampal and cortical structures after a contusion trauma in rats

Influential factors on stem cell therapy success in canine model of spinal cord Injury: A systematic review and meta-analysis

Spinal cord injury (SCI) is a serious medical condition. The search for an effective cure remains a persistent challenge. Current treatments, unfortunately, are unable to sufficiently improve neurological function, often leading to lifelong disability. This systematic review and meta-analysis evaluated the effectiveness of stem cell therapy for SCI using canine models. It also explored the optimal protocol for implementing stem cell therapy. A comprehensive search of studies was conducted from 2000 to October 2022. This study focused on five outcomes: motor function score, histopathology, IHC, western blot, and SEP. The results demonstrated a significant improvement in locomotion post-SCI in dogs treated with stem cell therapy. The therapy also led to an average increase of 3.15 points in the Olby score of the treated dogs compared to the control group. These findings highlights stem cell therapy's potential as a promising SCI treatment. The meta-analysis suggests that using bone marrow stem cells, undergoing neural differentiation in vitro, applying a surgical implantation or intrathecal route of administration, associating matrigel in combination with stem cells, and a waiting period of two weeks before starting treatment can enhance SCI treatment effectiveness.

Migratory Response of Cells in Neurogenic Niches to Neuronal Death: The Onset of Harmonic Repair?

Harmonic mechanisms orchestrate neurogenesis in the healthy brain within specific neurogenic niches, which generate neurons from neural stem cells as a homeostatic mechanism. These newly generated neurons integrate into existing neuronal circuits to participate in different brain tasks. Despite the mechanisms that protect the mammalian brain, this organ is susceptible to many different types of damage that result in the loss of neuronal tissue and therefore in alterations in the functionality of the affected regions. Nevertheless, the mammalian brain has developed mechanisms to respond to these injuries, potentiating its capacity to generate new neurons from neural stem cells and altering the homeostatic processes that occur in neurogenic niches. These alterations may lead to the generation of new neurons within the damaged brain regions. Notwithstanding, the activation of these repair mechanisms, regeneration of neuronal tissue within brain injuries does not naturally occur. In this review, we discuss how the different neurogenic niches respond to different types of brain injuries, focusing on the capacity of the progenitors generated in these niches to migrate to the injured regions and activate repair mechanisms. We conclude that the search for pharmacological drugs that stimulate the migration of newly generated neurons to brain injuries may result in the development of therapies to repair the damaged brain tissue.

The Dialogue Between Neuroinflammation and Adult Neurogenesis: Mechanisms Involved and Alterations in Neurological Diseases

Adult neurogenesis occurs mainly in the subgranular zone of the hippocampal dentate gyrus and the subventricular zone of the lateral ventricles. Evidence supports the critical role of adult neurogenesis in various conditions, including cognitive dysfunction, Alzheimer's disease (AD), and Parkinson's disease (PD). Several factors can alter adult neurogenesis, including genetic, epigenetic, age, physical activity, diet, sleep status, sex hormones, and central nervous system (CNS) disorders, exerting either pro-neurogenic or anti-neurogenic effects. Compelling evidence suggests that any insult or injury to the CNS, such as traumatic brain injury (TBI), infectious diseases, or neurodegenerative disorders, can provoke an inflammatory response in the CNS. This inflammation could either promote or inhibit neurogenesis, depending on various factors, such as chronicity and severity of the inflammation and underlying neurological disorders. Notably, neuroinflammation, driven by different immune components such as activated glia, cytokines, chemokines, and reactive oxygen species, can regulate every step of adult neurogenesis, including cell proliferation, differentiation, migration, survival of newborn neurons, maturation, synaptogenesis, and neuritogenesis. Therefore, this review aims to present recent findings regarding the effects of various components of the immune system on adult neurogenesis and to provide a better understanding of the role of neuroinflammation and neurogenesis in the context of neurological disorders, including AD, PD, ischemic stroke (IS), seizure/epilepsy, TBI, sleep deprivation, cognitive impairment, and anxiety- and depressive-like behaviors. For each disorder, some of the most recent therapeutic candidates, such as curcumin, ginseng, astragaloside, boswellic acids, andrographolide, caffeine, royal jelly, estrogen, metformin, and minocycline, have been discussed based on the available preclinical and clinical evidence.

Human Multipotent Mesenchymal Stromal Cell–Derived Extracellular Vesicles Enhance Neuroregeneration in a Rat Model of Sciatic Nerve Crush Injury

Peripheral nerve injury remains a serious problem for medicine, with no effective method of treatment at the moment. The most prominent example of this problem is neonatal brachial plexus palsy, which results from the stretching of the brachial plexus nerves in the birth or perinatal period. Multipotent mesenchymal cells (MSCs) and the extracellular vesicles (EVs) they produce are known to have a marked neuroprotective effect in central nervous system injuries. We suggested that the use of MSCs-derived EVs may be an effective approach to the regeneration of peripheral nerves after injury. Sciatic nerve injury was modeled in rats via crushing, and then a gel containing MSCs–EVs was applied to the injured area. After 15 and 30 days, a histological, physiological, and functional assessment of nerve, dorsal root ganglia (DRG), and innervated muscles’ recovery was performed. Transplantation of EVs to the area of sciatic nerve injury significantly reduced muscle atrophy as compared to the control group. Functional recovery of the innervated muscles, as measured by the extensor postural thrust test, was revealed 30 days after the surgery. We associate the obtained results with EVs-induced neuroprotective mechanisms, which were expressed in a decrease in apoptotic neuronal death and an increase in regeneration-associated proteins NF-200 and GAP-43, as well as in DRG and damaged nerve. We suggest that the therapeutic scheme we used is efficient for the treatment of acute peripheral nervous system injuries and can be transferred to the clinics. However, additional studies are required for a more detailed analysis of neuroprotection mechanisms.

Design, Synthesis, and Biological Evaluation of Novel Tetramethylpyrazine- nitrone Derivatives as Antioxidants

Background:

Thrombolysis and endovascular thrombectomy are the two main therapeutic strategies for ischemic stroke in clinic. However, reperfusion injury causes oxidative stress leading to overproduction of reactive oxygen species, mitochondrial dysfunction and subsequent cell death.

Methods:

We designed and synthesized two tetramethylpyrazine-nitrone derivatives (T-003 and T- 005) and investigated their abilities for scavenging free radicals and protective effects as well as neurite outgrowth promotion in vitro.

Results:

Both of them showed potent radical-scavenging activity and neuroprotective effects against iodoacetic acid-induced cell injury. Furthermore, T-003 and T-005 significantly promoted neurite outgrowth in PC12 cells.

Conclusion:

Our results suggest that compound T-003 and T-005 could be potent antioxidants for the treatment of neurological disease, particularly ischemic stroke.

Maturation of Neural Cells Leads to Enhanced Axon-Extracellular Matrix Adhesion and Altered Injury Response

Although it is known that stronger cell-extracellular matrix interactions will be developed as neurons mature, how such change influences their response against traumatic injury remains largely unknown. In this report, by transecting axons with a sharp atomic force microscope tip, we showed that the injury-induced retracting motion of axon can be temporarily arrested by tight NCAM (neural cell adhesion molecule) mediated adhesion patches, leading to a retraction curve decorated with sudden bursts. Interestingly, although the size of adhesion clusters (~0.5–1 μm) was found to be more or less the same in mature and immature neurons (after 7- and 3-days of culturing, respectively), the areal density of such clusters is three times higher in mature axons resulting in a much reduced retraction in response to injury. A physical model was also adopted to explain the observed retraction trajectories which suggested that apparent adhesion energy between axon and the substrate increases from ~0.12 to 0.39 mJ/m² as neural cell matures, in good agreement with our experiments.

Pharmacological blockers of CCR5 and CXCR4 improve recovery after traumatic brain injury

CCR5 and CXCR4 are structurally related chemokine receptors that belong to the superfamily of G-protein coupled receptors through which the HIV virus enters and infects cells. Both receptors are also related to HIV-associated neurocognitive disorders that include difficulties in concentration and memory, impaired executive functions, psychomotor slowing, depression and irritability, which are also hallmarks of the long-term sequelae of TBI. Moreover, A growing body of evidence attributes negative influences to CCR5 activation on cognition, particularly after stroke and traumatic brain injury (TBI). Here we investigated the effect of their blockage on motor and cognitive functions, on brain tissue loss and preservation and on some of the biochemical pathways involved. We examined the effect of maraviroc, a CCR5 antagonist used in HIV patients as a viral entry inhibitor, and of plerixafor (AMD3100), a CXCR4 antagonist used in cancer patients as an immune-modulator, on mice subjected to closed head injury (CHI). Mice were treated with maraviroc or plerixafor after CHI for the following 4 or 5 days, respectively. Neurobehavior was assessed according to the Neurological Severity Score; cognitive tests were performed by using the Y-maze, Barnes maze and the novel object recognition test; anxiety was evaluated with the open field test. The mice were sacrificed and brain tissues were collected for Western blot, pathological and immunohistochemical analyses. Both drugs enhanced tissue preservation in the cortex, hippocampus, periventricular areas, corpus callosum and striatum, and reduced astrogliosis)GFAP expression). They also increased the levels of synaptic cognition-related signaling molecules such as phosphorylated NR1 and CREB, and the synaptic plasticity protein PSD95. Both treatments also enhanced the expression of CCR5 and CXCR4 on different brain cell types. In summary, the beneficial effects of blocking CCR5 and CXCR4 after CHI suggest that the drugs used in this study, both FDA approved and in clinical use, should be considered for translational research in TBI patients.

Neurogenesis after traumatic brain injury - The complex role of HMGB1 and neuroinflammation

INTRODUCTION

Traumatic brain injury (TBI) is amongst the leading causes of morbidity and mortality worldwide. Despite evidence of neurogenesis post-TBI, survival and integration of newborn neurons remains impaired. High Mobility Group Box protein 1 (HMGB1) is an 'alarmin' released hyper-acutely following TBI and implicated in hosting the neuro-inflammatory response to injury. It is also instrumental in mediating neurogenesis under physiological conditions. Given its dual role in mediating neuro-inflammation and neurogenesis, it serves as a promising putative target for therapeutic modulation. In this review, we discuss neurogenesis post-TBI, neuro-pharmacological aspects of HMGB1, and its potential as a therapeutic target.

METHODS

PubMed database was searched with varying combinations of the following search terms: HMGB1, isoforms, neurogenesis, traumatic brain injury, Toll-like receptor (TLR), receptor for advanced glycation end-products (RAGE).

RESULTS

Several in vitro and in vivo studies demonstrate evidence of neurogenesis post-injury. The HMGB1-RAGE axis mediates neurogenesis throughout development, whilst interaction with TLR-4 promotes the innate immune response. Studies in the context of injury demonstrate that these receptor effects are not mutually exclusive. Despite recognition of different HMGB1 isoforms based on redox/acetylation status, effects on neurogenesis post-injury remain unexplored. Recent animal in vivo studies examining HMGB1 antagonism post-TBI demonstrate predominantly positive results, but specific effects on neurogenesis and longer-term outcomes remain unclear.

CONCLUSION

HMGB1 is a promising therapeutic target but its effects on neurogenesis post-TBI remains unclear. Given the failure of several pharmacological strategies to improve outcomes following TBI, accurate delineation of HMGB1 signalling pathways and effects on post-injury neurogenesis are vital.

Glycyrrhizin Blocks the Detrimental Effects of HMGB1 on Cortical Neurogenesis After Traumatic Neuronal Injury

Despite medical advances, neurological recovery after severe traumatic brain injury (TBI) remains poor. Elevated levels of high mobility group box protein-1 (HMGB1) are associated with poor outcomes; likely via interaction with receptors for advanced-glycation-end-products (RAGE). We examined the hypothesis that HMGB1 post-TBI is anti-neurogenic and whether this is pharmacologically reversible. Post-natal rat cortical mixed neuro-glial cell cultures were subjected to needle-scratch injury and examined for HMGB1-activation/neuroinflammation. HMGB1-related genes/networks were examined using genome-wide RNA-seq studies in cortical perilesional tissue samples from adult mice. Post-natal rat cortical neural stem/progenitor cell cultures were generated to quantify effects of injury-condition medium (ICM) on neurogenesis with/without RAGE antagonist glycyrrhizin. Needle-injury upregulated TNF-α/NOS-2 mRNA-expressions at 6 h, increased proportions of activated microglia, and caused neuronal loss at 24 h. Transcriptome analysis revealed activation of HMGB1 pathway genes/canonical pathways in vivo at 24 h. A 50% increase in HMGB1 protein expression, and nuclear-to-cytoplasmic translocation of HMGB1 in neurons and microglia at 24 h post-injury was demonstrated in vitro. ICM reduced total numbers/proportions of neuronal cells, but reversed by 0.5 μM glycyrrhizin. HMGB1 is activated following in vivo post mechanical injury, and glycyrrhizin alleviates detrimental effects of ICM on cortical neurogenesis. Our findings highlight glycyrrhizin as a potential therapeutic agent post-TBI.

Formyl Peptide Receptor 1 Signaling in Acute Inflammation and Neural Differentiation Induced by Traumatic Brain Injury

Traumatic brain injury (TBI) is a shocking disease frequently followed by behavioral disabilities, including risk of cerebral atrophy and dementia. N-formylpeptide receptor 1 (FPR1) is expressed in cells and neurons in the central nervous system. It is involved in inflammatory processes and during the differentiation process in the neural stem cells. We investigate the effect of the absence of Fpr1 gene expression in mice subjected to TBI from the early stage of acute inflammation to neurogenesis and systematic behavioral testing four weeks after injury. C57BL/6 animals and Fpr1 KO mice were subjected to TBI and sacrificed 24 h or four weeks after injury. Twenty-four hours after injury, TBI Fpr1 KO mice showed reduced histological impairment, tissue damage and acute inflammation (MAPK activation, NF-κB signaling induction, NRLP3 inflammasome pathway activation and oxidative stress increase). Conversely, four weeks after TBI, the Fpr1 KO mice showed reduced survival of the proliferated cells in the Dentate Gyrus compared to the WT group. Behavioral analysis confirmed this trend. Moreover, TBI Fpr1 KO animals displayed reduced neural differentiation (evaluated by beta-III tubulin expression) and upregulation of astrocyte differentiation (evaluated by GFAP expression). Collectively, our study reports that, immediately after TBI, Fpr1 increased acute inflammation, while after four weeks, Fpr1 promoted neurogenesis.

A novel mouse model of mild traumatic brain injury using laser-induced shock waves

Blast-induced mild traumatic brain injury (mild bTBI) has been a frequent battlefield injury in soldiers during the conflicts in Iraq and Afghanistan. Understanding the pathophysiology and determining effective treatments for mild bTBI has become an international problem in the field of neurotrauma research. Contributing to this problem is a lack of an experimental model that accurately mimics the characteristics of mild bTBI. To date, the "mild'' versions of common experimental models of TBI have simply been less severe degrees of traumatic injury; these animals do not necessarily exhibit the clinical characteristics of mild bTBI seen in humans. Therefore, our first objective was to develop a highly controlled mouse model of bTBI using laser-induced shockwaves (LISWs). We established the parameters necessary to cause a reproducible injury of very mild severity, the most important feature seen in clinical practice. We defined very mild bTBI as having no traumatic change on the head visible to the naked eye after the insult was applied using very mild shockwaves to the heads of mice. Our very mild bTBI mouse model exhibited neurobehavioral changes in the chronic phase, such as cognitive impairment and depression-like behavior. We also observed an increase in 5-bromo-2'-deoxyuridine-positive, proliferating cells in the dentate gyrus during the acute phase and a subsequent decrease during the chronic phase. This model appears to be an accurate representation of the damage occurring in actual mild bTBI patients. We also found that an increase in cell proliferation in the dentate gyrus during the acute phase is the most prominent feature after a TBI.

Histone Deacetylase 4 Downregulation Elicits Post-Traumatic Psychiatric Disorders through Impairment of Neurogenesis

An enduring deficit in neurogenesis largely contributes to the development of severe post-traumatic psychiatric disorders such as anxiety, depression, and memory impairment following traumatic brain injury (TBI); however, the mechanism remains obscure. Here we have shown that an imbalance in the generation of γ-aminobutyric acid (GABA)ergic and glutamatergic neurons due to aberrant induction of vesicular glutamate transporter 1 (vGlut1)-positive glutamatergic cells is responsible for impaired neuronal differentiation in the hippocampus following TBI. To elucidate the molecular mechanism, we found that TBI activates a transcription factor, Pax3, by increasing its acetylation status, and subsequently induces Ngn2 transcription. This event, in turn, augments the vGlut1-expressing glutamatergic neurons and accumulation of excess glutamate in the hippocampus that can affect neuronal differentiation. In our study the acetylation of Pax3 was increased due to loss of its interaction with a deacetylase, histone deacetylase 4 (HDAC4), which was downregulated after TBI. TBI-induced activation of GSK3β was responsible for the degradation of HDAC4. We also showed that overexpression of HDAC4 before TBI reduces Pax3 acetylation by restoring an interaction between HDAC4 and Pax3 in the hippocampus. This event prevents the aberrant induction of vGlut1-positive glutamatergic neurons by decreasing the Ngn2 level and subsequently reinforces the balance between GABAergic and glutamatergic neurons following TBI. Further, we found that overexpression of HDAC4 in the hippocampus improves anxiety, depressive-like behavior, and memory functions following TBI.

Musashi 1-positive cells derived from mouse embryonic stem cells treated with LY294002 are prone to differentiate into intestinal epithelial-like tissues

The majority of Musashi 1 (Msi1)‑positive cells derived from mouse embryonic stem cells (mESCs) are prone to differentiate into neural epithelial‑like cells, and only a small proportion of Msi1‑positive cells differentiate into intestinal epithelial‑like cells. Whether inhibiting the phosphatidylinositol 3‑kinase (PI3K) signaling of mESCs can promote the differentiation of Msi1‑positive cells into intestinal epithelial‑like cells remains to be fully elucidated. In the present study, to inhibit PI3K signaling, mESCs were treated with LY294002. A pMsi1‑green fluorescence protein reporter plasmid was used to sort the Msi1‑positive cells from mESCs treated and untreated with LY294002 (5 µmol/l). The Msi1‑positive cells were hypodermically engrafted into the backs of non‑obese diabetic/severe combined immunodeficient mice. The presence of neural and intestinal epithelial‑like cells in the grafts was detected by reverse transcription‑quantitative polymerase chain reaction analysis and immunohistochemistry. Compared with the Msi1‑positive cells derived from mESCs without LY294002 treatment, Msi1‑positive cells derived from mESCs treated with LY294002 expressed higher levels of leucine‑rich repeat‑containing G‑protein coupled receptor, a marker of intestinal epithelial stem cells, and lower levels of Nestin, a marker of neural epithelial stem cells. The grafts from Msi1‑positive cells treated with LY294002 contained more intestinal epithelial‑like tissues and fewer neural epithelial‑like tissues, compared with those from untreated Msi1‑positive cells. LY294002 had the ability to promote the differentiation of mESCs into intestinal epithelial‑like tissues. The Msi1‑positive cells selected from the cell population derived from mESCs treated with LY294002 exhibited more characteristics of intestinal epithelial stem cells than those from the untreated group.

Functional Neurochemistry of the Ventral and Dorsal Hippocampus: Stress, Depression, Dementia and Remote Hippocampal Damage

The hippocampus is not a homogeneous brain area, and the complex organization of this structure underlies its relevance and functional pleiotropism. The new data related to the involvement of the ventral hippocampus in the cognitive function, behavior, stress response and its association with brain pathology, in particular, depression, are analyzed with a focus on neuroplasticity, specializations of the intrinsic neuronal network, corticosteroid signaling through mineralocorticoid and glucocorticoid receptors and neuroinflammation in the hippocampus. The data on the septo-temporal hippicampal gradient are analyzed with particular emphasis on the ventral hippocampus, a region where most important alteration underlying depressive disorders occur. According to the recent data, the existing simple paradigm "learning (dorsal hippocampus) versus emotions (ventral hippocampus)" should be substantially revised and specified. A new hypothesis is suggested on the principal involvement of stress response mechanisms (including interaction of released glucocorticoids with hippocampal receptors and subsequent inflammatory events) in the remote hippocampal damage underlying delayed dementia and depression induced by focal brain damage (e.g. post-stroke and post-traumatic). The translational validity of this hypothesis comprising new approaches in preventing post-stroke and post-trauma depression and dementia can be confirmed in experimental and clinical studies.

Traumatic Brain Injury and Stem Cell: Pathophysiology and Update on Recent Treatment Modalities

Traumatic brain injury (TBI) is a complex condition that presents with a wide spectrum of clinical symptoms caused by an initial insult to the brain through an external mechanical force to the skull. In the United States alone, TBI accounts for more than 50,000 deaths per year and is one of the leading causes of mortality among young adults in the developed world. Pathophysiology of TBI is complex and consists of acute and delayed injury. In the acute phase, brain tissue destroyed upon impact includes neurons, glia, and endothelial cells, the latter of which makes up the blood-brain barrier. In the delayed phase, “toxins” released from damaged cells set off cascades in neighboring cells eventually leading to exacerbation of primary injury. As researches further explore pathophysiology and molecular mechanisms underlying this debilitating condition, numerous potential therapeutic strategies, especially those involving stem cells, are emerging to improve recovery and possibly reverse damage. In addition to elucidating the most recent advances in the understanding of TBI pathophysiology, this review explores two primary pathways currently under investigation and are thought to yield the most viable therapeutic approach for treatment of TBI: manipulation of endogenous neural cell response and administration of exogenous stem cell therapy.

Traumatic Brain Injury Stimulates Neural Stem Cell Proliferation via Mammalian Target of Rapamycin Signaling Pathway Activation

Neural stem cells in the adult brain possess the ability to remain quiescent until needed in tissue homeostasis or repair. It was previously shown that traumatic brain injury (TBI) stimulated neural stem cell (NSC) proliferation in the adult hippocampus, indicating an innate repair mechanism, but it is unknown how TBI promotes NSC proliferation. In the present study, we observed dramatic activation of mammalian target of rapamycin complex 1 (mTORC1) in the hippocampus of mice with TBI from controlled cortical impact (CCI). The peak of mTORC1 activation in the hippocampal subgranular zone, where NSCs reside, is 24-48 h after trauma, correlating with the peak of TBI-enhanced NSC proliferation. By use of a Nestin-GFP transgenic mouse, in which GFP is ectopically expressed in the NSCs, we found that TBI activated mTORC1 in NSCs. With 5-bromo-2'-deoxyuridine labeling, we observed that TBI increased mTORC1 activation in proliferating NSCs. Furthermore, administration of rapamycin abolished TBI-promoted NSC proliferation. Taken together, these data indicate that mTORC1 activation is required for NSC proliferation postinjury, and thus might serve as a therapeutic target for interventions to augment neurogenesis for brain repair after TBI.

Post-Injury Treatment of 7,8-Dihydroxyflavone Promotes Neurogenesis in the Hippocampus of the Adult Mouse

Traumatic brain injury (TBI) at the moderate level of impact induces massive cell death and results in extensive dendrite degeneration in the brain, leading to persistent cognitive, sensory, and motor dysfunction. Our previous reports have shown that adult-born immature granular neurons in the dentate gyrus are the most vulnerable cell type in the hippocampus after receiving a moderate TBI with a controlled cortical impact (CCI) device. There is no effective approach to prevent immature neuron death or degeneration following TBI. Our recent study found that pretreatment of 7,8-dihydroxyflavone (DHF), a small molecule imitating brain-derived neurotrophic factor, protected immature neurons in the hippocampus from death following TBI. In the present study, we systemically treated moderate CCI-TBI mice or sham surgery mice with DHF once a day for 2 weeks via intraperitoneal injection, and then assessed the immature neurons in the hippocampus the 2nd day after the last DHF injection. We found that post-injury treatment of DHF for 2 weeks not only increased the number of adult-born immature neurons in the hippocampus, but also promoted their dendrite arborization in the injured brain following TBI. Thus, DHF may be a promising compound that can promote neurogenesis and enhance immature neuron development following TBI.

Traumatic Brain Injury Causes Aberrant Migration of Adult-Born Neurons in the Hippocampus

Traumatic brain injury (TBI) promotes neural stem/progenitor cell (NSC) proliferation in an attempt to initiate innate repair mechanisms. However, all immature neurons in the CNS are required to migrate from their birthplace to their final destination to develop into functional neurons. Here we assessed the destination of adult-born neurons following TBI. We found that a large percentage of immature neurons migrated past their normal stopping site at the inner granular cell layer (GCL), and became misplaced in the outer GCL of the hippocampal dentate gyrus. The aberrant migration of adult-born neurons in the hippocampus occurred 48 hours after TBI, and lasted for 8 weeks, resulting in a great number of newly generated neurons misplaced in the outer GCL in the hippocampus. Those misplaced neurons were able to become mature and differentiate into granular neurons, but located ectopically in the outer GCL with reduced dendritic complexity after TBI. The adult-born neurons at the misplaced position may make wrong connections with inappropriate nearby targets in the pre-existing neural network. These results suggest that although stimulation of endogenous NSCs following TBI might offer new avenues for cell-based therapy, additional intervention is required to further enhance successful neurogenesis for repairing the damaged brain.

Traumatic Brain Injury Severity Affects Neurogenesis in Adult Mouse Hippocampus

Traumatic brain injury (TBI) has been proven to enhance neural stem cell (NSC) proliferation in the hippocampal dentate gyrus. However, various groups have reported contradictory results on whether TBI increases neurogenesis, partially due to a wide range in the severities of injuries seen with different TBI models. To address whether the severity of TBI affects neurogenesis in the injured brain, we assessed neurogenesis in mouse brains receiving different severities of controlled cortical impact (CCI) with the same injury device. The mice were subjected to mild, moderate, or severe TBI by a CCI device. The effects of TBI severity on neurogenesis were evaluated at three stages: NSC proliferation, immature neurons, and newly-generated mature neurons. The results showed that mild TBI did not affect neurogenesis at any of the three stages. Moderate TBI promoted NSC proliferation without increasing neurogenesis. Severe TBI increased neurogenesis at all three stages. Our data suggest that the severity of injury affects adult neurogenesis in the hippocampus, and thus it may partially explain the inconsistent results of different groups regarding neurogenesis following TBI. Further understanding the mechanism of TBI-induced neurogenesis may provide a potential approach for using endogenous NSCs to protect against neuronal loss after trauma.

Activation of Type 4 Metabotropic Glutamate Receptor Attenuates Oxidative Stress-Induced Death of Neural Stem Cells with Inhibition of JNK and p38 MAPK Signaling

Promoting both endogenous and exogenous neural stem cells' (NSCs) survival in the hostile host environments is essential to cell replacement therapy for central nervous system (CNS) disorders. Type 4 metabotropic glutamate receptor (mGluR4), one of the members of mGluRs, has been shown to protect neurons from acute and chronic excitotoxic insults in various brain damages. The present study investigated the preventive effects of mGluR4 on NSC injury induced by oxidative stress. Under challenge with H2O2, loss of cell viability was observed in cultured rat NSCs, and treatment with selective mGluR4 agonist VU0155041 conferred protective effects against the loss of cellular viability in a concentration-dependent manner, as shown by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay. Pretreatment of VU0155041 (30 μM) also inhibited the excessive NSC death induced by H2O2, and group III mGluRs antagonist (RS)-a-methylserine-O-phosphate (MSOP) or gene-targeted knockdown abolished the protective action of mGluR4, indicated by propidium iodide-Hoechst and terminal deoxynucleotidyl transferase-mediated UTP nick end labeling (TUNEL) staining. Western blot assay demonstrated that mGluR4 activation reversed the decreased procaspase-8/9/3and the destructed Bcl-2/Bax expressing balance, and likewise, MSOP and mGluR4 knockdown abrogated the action of mGluR4 activity. Furthermore, inhibition of JNK and p38 mitogen-activated protein kinases (MAPKs) were observed after mGluR4 activation, and as paralleling control, JNK-specific inhibitor SP600125 and p38-specific inhibitor SB203580 significantly rescued the H2O2-mediated NSC apoptosis and cleavage of procaspase-3. We suggest that activation of mGluR4 prevents oxidative stress-induced NSC death and apoptotic-associated protein activities with involvement of inhibiting the JNK and p38 pathways in cell culture. Our findings may help to develop strategies for enhancing the resided and transplanted NSC survival after oxidative stress insult of CNS.

Temporal patterns of cortical proliferation of glial cell populations after traumatic brain injury in mice

TBI (traumatic brain injury) triggers an inflammatory cascade, gliosis and cell proliferation following cell death in the pericontusional area and surrounding the site of injury. In order to better understand the proliferative response following CCI (controlled cortical impact) injury, we systematically analyzed the phenotype of dividing cells at several time points post-lesion. C57BL/6 mice were subjected to mild to moderate CCI over the left sensory motor cortex. At different time points following injury, mice were injected with BrdU (bromodeoxyuridine) four times at 3-h intervals and then killed. The greatest number of proliferating cells in the pericontusional region was detected at 3 dpi (days post-injury). At 1 dpi, NG2⁺ cells were the most proliferative population, and at 3 and 7 dpi the Iba-1⁺ microglial cells were proliferating more. A smaller, but significant number of GFAP⁺ (glial fibrillary acidic protein) astrocytes proliferated at all three time points. Interestingly, at 3 dpi we found a small number of proliferating neuroblasts [DCX⁺ (doublecortin)] in the injured cortex. To determine the cell fate of proliferative cells, mice were injected four times with BrdU at 3 dpi and killed at 28 dpi. Approximately 70% of proliferative cells observed at 28 dpi were GFAP⁺ astrocytes. In conclusion, our data suggest that the specific glial cell types respond differentially to injury, suggesting that each cell type responds to a specific pattern of growth factor stimulation at each time point after injury.

Maturation-dependent response of neurogenesis after traumatic brain injury in children

OBJECT

Traumatic brain injury (TBI) is the leading cause of acquired disability in children, yet innate repair mechanisms are incompletely understood. Given data from animal studies documenting neurogenesis in response to trauma and other insults, the authors investigated whether similar responses could be found in children of different ages after TBI.

METHODS

Immunohistochemistry was used to label doublecortin (DCX), a protein expressed by immature migrating neuroblasts (newborn neurons), in specimens from patients ranging in age from 3 weeks to 10 years who had died either after TBI or from other causes. Doublecortin-positive (DCX+) cells were examined in the subventricular zone (SVZ) and periventricular white matter (PWM) and were quantified within the granule cell layer (GCL) and subgranular zone (SGZ) of the dentate gyrus to determine if age and/or injury affect the number of DCX+ cells in these regions.

RESULTS

The DCX+ cells decreased in the SVZ as patient age increased and were found in abundance around a focal subacute infarct in a 1-month-old non-TBI patient, but were scarce in all other patients regardless of age or history of trauma. The DCX+ cells in the PWM and dentate gyrus demonstrated a migratory morphology and did not co-localize with markers for astrocytes, microglia, or macrophages. In addition, there were significantly more DCX+ cells in the GCL and SGZ of the dentate gyrus in children younger than 1 year old than in older children. The density of immature migrating neuroblasts in infants (under 1 year of age) was significantly greater than in young children (2-6 years of age, p = 0.006) and older children (7-10 years of age, p = 0.007).

CONCLUSIONS

The main variable influencing the number of migrating neuroblasts observed in the SVZ, PWM, and hippocampus was patient age. Trauma had no discernible effect on the number of migrating neuroblasts in this cohort of patients in whom death typically occurred within hours to days after TBI.

Neurogenesis in adult human brain after traumatic brain injury

While much work has been conducted regarding the neurogenesis response to traumatic brain injury (TBI) in rodents, it remains largely unknown whether neurogenesis in adult human brain also responds to TBI in a similar manner. Here, we performed immunocytochemistry on 11 brain specimens from patients with traumatic brain injury, who underwent surgical intervention. We found that expression of neural stem/progenitor cell (NSC) protein markers, including DCX, TUC4, PSA-NCAM, SOX2 and NeuroD, was increased in the perilesional cortex of human brain after TBI compared to that of normal brain. Confocal images showed that these NSC proteins were expressed in one single cell. We also found that proliferative markers were expressed in NSC protein-positive cells after TBI, and the number of proliferative NSCs was significantly increased after TBI. Our data suggest that TBI may also induce neurogenesis in human brain.

Intraperitoneal treatment with S100B enhances hippocampal neurogenesis in juvenile mice and after experimental brain injury

BACKGROUND

Neurogenesis is documented in adult mammals including humans, is promoted by neurotrophic factors, and constitutes an innate repair mechanism following brain injury. The glial neurotrophic protein S100B is released following various types of brain injuries, enhances hippocampal neurogenesis and improves cognitive function following brain injury in rats when applied intrathecally. The present study was designed to elucidate whether the beneficial effect of S100B on injury-induced neurogenesis can be confirmed in mice when applied intraperitoneally (i.p.), and whether this effect is dose-dependent.

METHODS

Male juvenile mice were subjected to a unilateral parietal cryolesion or sham injury, and treated with S100B at 20nM, 200nM or vehicle i.p. once daily. Hippocampal progenitor cell proliferation was quantified following labelling with bromo-deoxyuridine (BrdU, 50 mg/KG i.p.) in the germinative area of the dentate gyrus, the subgranular zone (SGZ), on day 4 as well as on cell survival and migration to the granular cell layer (GCL) on day 28. Progenitor cell differentiation was assessed following colabelling with the glial marker GFAP and the neuronal marker NeuN.

RESULTS

S100B enhanced significantly the early progenitor cell proliferation in the SGZ as well as cell survival and migration to the GCL, and promoted neuronal differentiation. While these effects were predominately dose-dependent, 200nM S100B failed to enhance the proliferation in the SGZ on day 4 post-injury.

CONCLUSION

We conclude that S100B participates in hippocampal neurogenesis after injury at lower nanomolar concentrations. Therefore S100B may serve as a potential adjunct treatment to promote neuroregeneration following brain damage.

Moderate traumatic brain injury promotes neural precursor proliferation without increasing neurogenesis in the adult hippocampus

Traumatic brain injury (TBI) promotes neural stem/progenitor cell (NSC) proliferation in the adult hippocampus; however, it remains inconclusive whether proliferation of these cells results in newly generated mature neurons, leading to increased neurogenesis. When we traced the fates of proliferating cells labeled with bromodeoxyuridine (5-bromo-2-deoxyuridine, BrdU) we found that the number of BrdU-positive cells increased in the hippocampus of TBI mice compared to the sham control. However, double immunostaining to distinguish their cell types showed that most of these cells were glia, and that only a small subpopulation is newborn granular neurons. There was no significant difference with respect to neurogenesis in the adult hippocampus between the injured and the control mice. These results indicate that TBI promotes cell proliferation including astrocyte activation and NSC proliferation. Nevertheless, the majority of the BrdU-positive cells are glia. The neurogenesis is not increased by TBI. These data suggest that TBI activates through promotion of NSC proliferation an innate repair and/or plasticity mechanism in the brain. However, additional intervention is required to increase neurogenesis for successfully repairing the damaged brain following TBI.

Posttraumatic hypothermia increases doublecortin expressing neurons in the dentate gyrus after traumatic brain injury in the rat

Previous studies have demonstrated that moderate hypothermia reduces histopathological damage and improves behavioral outcome after experimental traumatic brain injury (TBI). Further investigations have clarified the mechanisms underlying the beneficial effects of hypothermia by showing that cooling reduces multiple cell injury cascades. The purpose of this study was to determine whether hypothermia could also enhance endogenous reparative processes following TBI such as neurogenesis and the replacement of lost neurons. Male Sprague-Dawley rats underwent moderate fluid-percussion brain injury and then were randomized into normothermia (37°C) or hypothermia (33°C) treatment. Animals received injections of 5-bromo-2'-deoxyuridine (BrdU) to detect mitotic cells after brain injury. After 3 or 7 days, animals were perfusion-fixed and processed for immunocytochemistry and confocal analysis. Sections were stained for markers selective for cell proliferation (BrdU), neuroblasts and immature neurons (doublecortin), and mature neurons (NeuN) and then analyzed using non-biased stereology to quantify neurogenesis in the dentate gyrus (DG). At 7 days after TBI, both normothermic and hypothermic TBI animals demonstrated a significant increase in the number of BrdU-immunoreactive cells in the DG as compared to sham-operated controls. At 7 days post-injury, hypothermia animals had a greater number of BrdU (ipsilateral cortex) and doublecortin (ipsilateral and contralateral cortex) immunoreactive cells in the DG as compared to normothermia animals. Because adult neurogenesis following injury may be associated with enhanced functional recovery, these data demonstrate that therapeutic hypothermia sustains the increase in neurogenesis induced by TBI and this may be one of the mechanisms by which hypothermia promotes reparative strategies in the injured nervous system.

Post-traumatic seizure susceptibility is attenuated by hypothermia therapy

Traumatic brain injury (TBI) is a major risk factor for the subsequent development of epilepsy. Currently, chronic seizures after brain injury are often poorly controlled by available antiepileptic drugs. Hypothermia treatment, a modest reduction in brain temperature, reduces inflammation, activates pro-survival signaling pathways, and improves cognitive outcome after TBI. Given the well-known effect of therapeutic hypothermia to ameliorate pathological changes in the brain after TBI, we hypothesized that hypothermia therapy may attenuate the development of post-traumatic epilepsy and some of the pathomechanisms that underlie seizure formation. To test this hypothesis, adult male Sprague Dawley rats received moderate parasagittal fluid-percussion brain injury, and were then maintained at normothermic or moderate hypothermic temperatures for 4 h. At 12 weeks after recovery, seizure susceptibility was assessed by challenging the animals with pentylenetetrazole, a GABA(A) receptor antagonist. Pentylenetetrazole elicited a significant increase in seizure frequency in TBI normothermic animals as compared with sham surgery animals and this was significantly reduced in TBI hypothermic animals. Early hypothermia treatment did not rescue chronic dentate hilar neuronal loss nor did it improve loss of doublecortin-labeled cells in the dentate gyrus post-seizures. However, mossy fiber sprouting was significantly attenuated by hypothermia therapy. These findings demonstrate that reductions in seizure susceptibility after TBI are improved with post-traumatic hypothermia and provide a new therapeutic avenue for the treatment of post-traumatic epilepsy.

Axonal shearing in mature cortical neurons induces attempted regeneration and the reestablishment of neurite polarity

While functional recovery after injury is limited, it has become evident that the mature central nervous system does retain some ability to regenerate. This study investigated the intrinsic capacity of relatively mature cortical neurons (21 days in vitro) to respond to axonal loss. Neurons, growing as clusters on poly-L-lysine, were completely sheared of axons through chemical and mechanical disruption and transferred to either an intact astrocyte monolayer or a substrate of poly-L-lysine. Injured neurons exhibited a regenerative sprouting response that was independent of neuronal cell division or neural progenitors, as demonstrated by negative bromodeoxyuridine (BrdU) and the neuronal precursor intermediate filament nestin, labeling. At 24 h after injury, neurons had extended appropriately polarized neurites, demonstrated by compartmentalized microtubule-associated proteins MAP2 and tau immunolabeling. Newly sprouting axons were tipped by growth cones; however, growth cones on the tips of sprouting axons (mean area, 26.32 +/- 2.20 microm) were significantly (p<0.05) smaller than their developmental counterparts (mean area, 48.64 +/- 5.9 microm), independent of substrate. Furthermore, live imaging indicated that regenerating neurons exhibited distinct axonal dynamics, with a significant (p<0.05) reduction (70%) in pausing, considered vital for interstitial branching and pathfinding, relative to developmental growth cones. This study indicates that mature cultured cortical pyramidal and interneurons have the intrinsic potential to survive, extend processes, and reestablish neurite polarity following significant physical damage. These results may aid in defining the cellular basis of neuronal structural plasticity and defining the role of astrocyte reactivity in the response to trauma.

Direct Rho-associated kinase inhibition [correction of inhibiton] induces cofilin dephosphorylation and neurite outgrowth in PC-12 cells

Axons fail to regenerate in the adult central nervous system (CNS) following injury. Developing strategies to promote axonal regeneration is therapeutically attractive for various CNS pathologies such as traumatic brain injury, stroke and Alzheimer’s disease. Because the RhoA pathway is involved in neurite outgrowth, Rho-associated kinases (ROCKs), downstream effectors of GTP-bound Rho, are potentially important targets for axonal repair strategies in CNS injuries. We investigated the effects and downstream mechanisms of ROCK inhibition in promoting neurite outgrowth in a PC-12 cell model. Robust neurite outgrowth (NOG) was induced by ROCK inhibitors Y-27632 and H-1152 in a time-and dose-dependent manner. Dramatic cytoskeletal reorganization was noticed upon ROCK inhibition. NOG initiated within 5 to 30 minutes followed by neurite extension between 6 and 10 hours. Neurite processes were then sustained for over 24 hours. Rapid cofilin dephosphorylation was observed within 5 minutes of Y-27632 and H-1152 treatment. Re-phosphorylation was observed by 6 hours after Y-27632 treatment, while H-1152 treatment produced sustained cofilin dephosphorylation for over 24 hours. The results suggest that ROCK-mediated dephosphorylation of cofilin plays a role in the initiation of NOG in PC-12 cells.

Glutathione peroxidase overexpression does not rescue impaired neurogenesis in the injured immature brain

Traumatic brain injury (TBI) is a leading cause of disability among young children and is associated with long-term cognitive deficits. These clinical findings have prompted an investigation of the hippocampus in an experimental model of trauma to the developing brain at postnatal day (p21). Previous studies using this model have revealed a progressive loss of neurons in the hippocampus as brain-injured animals mature to young adulthood. Here we determined whether this hippocampal vulnerability is likewise reflected in altered neurogenesis and whether the antioxidant glutathione peroxidase (GPx) modulates neurogenesis during maturation of the injured immature brain. Male transgenic mice that overexpress GPx and wild-type littermates were subjected to controlled cortical impact or sham surgery on p21. At 2 weeks postinjury, the numbers of proliferating cells and immature neurons within the subgranular zone were measured by using Ki-67 and doublecortin, respectively. Bromodeoxyuridine (BrdU) was used to label dividing cells beginning 2 weeks postinjury. Survival (BrdU(+)) and neuronal differentiation (BrdU(+)/NeuN(+)) were then measured 4 weeks later via confocal microscopy. Two-way ANOVA revealed no significant interaction between genotype and injury. Subsequent analysis of the individual effects of injury and genotype, however, showed a significant reduction in subgranular zone proliferation (Ki-67) at 2 weeks postinjury (P = 0.0003) and precursor cell survival (BrdU(+)) at 6 weeks postinjury (P = 0.016) and a trend toward reduced neuronal differentiation (BrdU(+)/NeuN(+)) at 6 weeks postinjury (P = 0.087). Overall, these data demonstrate that traumatic injury to the injured immature brain impairs neurogenesis during maturation and suggest that GPx cannot rescue this reduced neurogenesis.

Direct isolation of neural stem cells in the adult hippocampus after traumatic brain injury

Recently, we have manipulated endogenous neural stem/progenitor cells (NSCs) in situ in the adult mouse to undergo neurogenesis and anatomic circuit re-formation de novo in the neocortex, where it does not normally occur, by using a highly targeted brain injury model. However, how the NSCs respond to injury in the adult mouse brain is poorly understood. While studying the molecular mechanisms that regulate NSC fates after brain injury, it is important to develop a strategy to identify NSCs in niches and isolate them directly from fresh tissue after brain injury. Here we report that we directly isolated NSCs from adult brains after traumatic brain injury by genetically labeling NSCs with EGFP combined with fluorescence-activated cell sorting (FACS) technique without an intervening cell culture and with high concentrations of growth factors. The isolated EGFP-positive cells can self-renew and have the potential to differentiate into both neurons and glia in vitro, confirming that the FACS-sorted EGFP-positive cells are NSCs. This unique approach provides a useful tool to isolate large amounts of endogenous NSCs in situ for identifying the critical molecules that regulate fate decision and neurogenesis in the adult brain after injury.

A population of serum deprivation-induced bone marrow stem cells (SD-BMSC) expresses marker typical for embryonic and neural stem cells

The bone marrow represents an easy accessible source of adult stem cells suitable for various cell based therapies. Several studies in recent years suggested the existence of pluripotent stem cells within bone marrow stem cells (BMSC) expressing marker proteins of both embryonic and tissue committed stem cells. These subpopulations were referred to as MAPC, MIAMI and VSEL-cells. Here we describe SD-BMSC (serumdeprivation-induced BMSC) which are induced as a distinct subpopulation after complete serumdeprivation. SD-BMSC are generated from small-sized nestin-positive BMSC (S-BMSC) organized as round-shaped cells in the top layer of BMSC-cultures. The generation of SD-BMSC is caused by a selective proliferation of S-BMSC and accompanied by changes in both morphology and gene expression. SD-BMSC up-regulate not only markers typical for neural stem cells like nestin and GFAP, but also proteins characteristic for embryonic cells like Oct4 and SOX2. We hypothesize, that SD-BMSC like MAPC, MIAMI and VSEL-cells represent derivatives from a single pluripotent stem cell fraction within BMSC exhibiting characteristics of embryonic and tissue committed stem cells. The complete removal of serum might offer a simple way to specifically enrich this fraction of pluripotent embryonic like stem cells in BMSC cultures.

Water soluble single-walled carbon nanotubes inhibit stimulated endocytosis in neurons

We report the use of chemically functionalized water soluble single-walled carbon nanotube (SWNT) graft copolymers to inhibit endocytosis. The graft copolymers were prepared by the functionalization of SWNTs with polyethylene glycol. When added to the culturing medium, these functionalized water soluble SWNTs were able to increase the length of various neuronal processes, neurites, as previously reported. Here we have determined that SWNTs are able to block stimulated membrane endocytosis in neurons, which could then explain the previously noted extended neurite length.

A quantitative proteomic analysis of mitochondrial participation in p19 cell neuronal differentiation

A quantitative proteomic analysis of changes in protein expression accompanying the differentiation of P19 mouse embryonal carcinoma cells into neuron-like cells using isobaric tag technology coupled with LC-MS/MS revealed protein changes reflecting withdrawal from the cell cycle accompanied by a dynamic reorganization of the cytoskeleton and an up-regulation of mitochondrial biogenesis. Further study of quantitative changes in abundance of individual proteins in a purified mitochondrial fraction showed that most mitochondrial proteins increased significantly in abundance. A set of chaperone proteins did not participate in this increase, suggesting that neuron-like cells are relatively deficient in mitochondrial chaperones. We developed a procedure to account for differences in recovery of mitochondrial proteins during purification of organelles from distinct cell or tissue sources. Proteomic data supported by RT-PCR analysis suggests that enhanced mitochondrial biogenesis during neuronal differentiation may reflect a large increase in expression of PGC-1alpha combined with down-regulation of its negative regulator, p160 Mybbp1a.

Survival, migration and neuronal differentiation of human fetal striatal and cortical neural stem cells grafted in stroke-damaged rat striatum

Stroke is a neurodegenerative disorder and the leading cause of disability in adult humans. Treatments to support efficient recovery in stroke patients are lacking. Several studies have demonstrated the ability of grafted neural stem cells (NSCs) to partly improve impaired neurological functions in stroke-subjected animals. Recently, we reported that NSCs from human fetal striatum and cortex exhibit region-specific differentiation in vitro, but survive, migrate and form neurons to a similar extent after intrastriatal transplantation in newborn rats. Here, we have transplanted the same cells into the stroke-damaged striatum of adult rats. The two types of NSCs exhibited a similar robust survival (30%) at 1 month after transplantation, and migrated throughout the damaged striatum. Striatal NSCs migrated farther and occupied a larger volume of striatum. In the transplantation core, cells were undifferentiated and expressed nestin and, to a lesser extent, also GFAP, betaIII-tubulin, DCX and calretinin, markers of immature neural lineage. Immunocytochemistry using markers of proliferation (p-H3 and Ki67) revealed a very low content of proliferating cells (<1%) in the grafts. Human cells outside the transplantation core differentiated, exhibited mature neuronal morphology and expressed mature neuronal markers such as HuD, calbindin and parvalbumin. Interestingly, striatal NSCs generated a greater number of parvalbumin+ and calbindin+ neurons. Virtually none of the grafted cells differentiated into astrocytes or oligodendrocytes. Based on these data, human fetal striatum- and cortex-derived NSCs could be considered potentially safe and viable for transplantation, with strong neurogenic potential, for further exploration in animal models of stroke.

Alterations in hippocampal neurogenesis following traumatic brain injury in mice

Clinical and experimental data show that traumatic brain injury (TBI)-induced cognitive changes are often manifest as deficits in hippocampal-dependent functions of spatial information processing. The underlying mechanisms for these effects have remained elusive, although recent studies have suggested that the changes in neuronal precursor cells in the dentate subgranular zone (SGZ) of the hippocampus might be involved. Here, we assessed the effects of unilateral controlled cortical impact on neurogenic cell populations in the SGZ in 2-month-old male C57BL6 mice by quantifying numbers of dying cells (TUNEL), proliferating cells (Ki-67) and immature neurons (Doublecortin, Dcx) up to 14 days after TBI. Dying cells were seen 6 h after injury, peaked at 24 h and returned to control levels at 14 days. Proliferating cells were decreased on the ipsilateral and contralateral sides at all the time points studied except 48 h after injury when a transient increase was seen. Simultaneously, immature neurons were reduced up to 84% relative to controls on the ipsilateral side. In the first week post-TBI, reduced numbers of Dcx-positive cells were also seen in the contralateral side; a return to control levels occurred at 14 days. To determine if these changes translated into longer-term effects, BrdU was administered 1 week post-injury and 3 weeks later the phenotypes of the newly born cells were assessed. TBI induced decreases in the numbers of BrdU-positive cells and new neurons (BrdU/NeuN) on the ipsilateral side without apparent changes on the contralateral side, whereas astrocytes (BrdU/GFAP) were increased on the ipsilateral side and activated microglia (BrdU/CD68) were increased on both ipsi- and contralateral sides. No differences were noted in oligodendrocytes (BrdU/NG2). Taken together, these data demonstrate that TBI alters both neurogenesis and gliogenesis. Such alterations may play a contributory role in TBI-induced cognitive impairment.

Animal models of post-traumatic epilepsy

Epilepsy is a major unfavorable long-term consequence of traumatic brain injury (TBI). Moreover, TBI is one of the most important predisposing factors for the development of epilepsy, particularly in young adults. Understanding the molecular and cellular cascades that lead to the development of post-traumatic epilepsy (PTE) is key for preventing its development or modifying the disease process in such a way that epilepsy, if it develops, is milder and easier-to-treat. Tissue from TBI patients undergoing epileptogenesis is not available for such studies, which underscores the importance of developing clinically relevant animal models of PTE. The goal of this review is to (1) provide a description of PTE in humans, which is critical for the development of clinically relevant models of PTE, (2) review the characteristics of currently available PTE models, and (3) provide suggestions for the development of future models of PTE based on our current understanding of the mechanisms of TBI and epilepsy. The development of clinically relevant models of PTE is critical to advance our understanding of the mechanisms of post-traumatic epileptogenesis and epilepsy, as well as for producing breakthroughs in the development and testing of novel antiepileptogenic treatments.

Proteome analysis of up-regulated proteins in the rat spinal cord induced by transection injury

The inability of the CNS to regenerate in adult mammals propels us to reveal associated proteins involved in the injured CNS. In this paper, either thoracic laminectomy (as sham control) or thoracic spinal cord transection was performed on male adult rats. Five days after surgery, the whole spinal cord tissue was dissected and fractionated into water-soluble (dissolved in Tris buffer) and water-insoluble (dissolved in a solution containing chaotropes and surfactants) portions for 2-DE. Protein identification was performed by MS and further confirmed by Western blot. As a result, over 30 protein spots in the injured spinal cord were shown to be up-regulated no less than 1.5-fold. These identified proteins possibly play various roles during the injury and repair process and may be functionally categorized as several different groups, such as stress-responsive and metabolic changes, lipid and protein degeneration, neural survival and regeneration. In particular, over-expression of 11-zinc finger protein and glypican may be responsible for the inhibition of axonal growth and regeneration. Moreover, three unknown proteins with novel sequences were found to be up-regulated by spinal cord injury. Further characterization of these molecules may help us come closer to understanding the mechanisms that underlie the inability of the adult CNS to regenerate.

Enhanced hippocampal neurogenesis by intraventricular S100B infusion is associated with improved cognitive recovery after traumatic brain injury

Evidence of injury-induced neurogenesis in the adult hippocampus suggests that an endogenous repair mechanism exists for cognitive dysfunction following traumatic brain injury (TBI). One factor that may be associated with this restoration is S100B, a neurotrophic/mitogenic protein produced by astrocytes, which has been shown to improve memory function. Therefore, we examined whether an intraventricular S100B infusion enhances neurogenesis within the hippocampus following experimental TBI and whether the biological response can be associated with a measurable cognitive improvement. Following lateral fluid percussion or sham injury in male rats (n = 60), we infused S100B (50 ng/h) or vehicle into the lateral ventricle for 7 days using an osmotic micro-pump. Cell proliferation was assessed by injecting the mitotic marker bromodeoxyuridine (BrdU) on day 2 postinjury. Quantification of BrdU-immunoreactive cells in the dentate gyrus revealed an S100B-enhanced proliferation as assessed on day 5 post-injury (p < 0.05), persisting up to 5 weeks (p < 0.05). Using cell-specific markers, we determined the relative numbers of these progenitor cells that became neurons or glia and found that S100B profoundly increased hippocampal neurogenesis 5 weeks after TBI (p < 0.05). Furthermore, spatial learning ability, as assessed by the Morris water maze on day 30-34 post-injury, revealed an improved cognitive performance after S100B infusion (p < 0.05). Collectively, our findings indicate that an intraventricular S100B infusion induces neurogenesis within the hippocampus, which can be associated with an enhanced cognitive function following experimental TBI. These observations provide compelling evidence for the therapeutic potential of S100B in improving functional recovery following TBI.

Neurogenèse dans les pathologies du système nerveux

Neural stem cells (NSCs) are the self-renewing, multipotent cells that generate neurons, astrocytes, and oligodendrocytes in the nervous system. Contrary to the long-held dogma, neurogenesis occurs in discrete areas of the adult brain, the hippocampus and the subventricular zone, and NSCs reside in the adult central nervous system. Recent studies have shown that neurogenesis is increased in the diseased brains, after strokes and traumatic brain injuries, and that new neuronal cells are generated at the sites of injury, where they replace some of the degenerated nerve cells. Thus, the central nervous system has the capacity to regenerate after injury. The contribution and function of the increased neurogenesis in the pathologies of the nervous system remain to be understood. The increased hippocampal neurogenesis may play a role in neuroadaptation, such as in memory troubles and depression, associated with these pathologies. The increased neurogenesis at the sites of injury may represent an attempt by the central nervous system to regenerate itself after injury. Newly generated neuronal cells at the sites of injury originate from the subventricular zone. Hence, strategies that would promote neurogenesis in the subventricular zone may promote neuronal repair after injury of the nervous system. In this manuscript, we will review the studies on neurogenesis in the pathologies of the nervous system.

Light and electron microscopic assessment of progressive atrophy following moderate traumatic brain injury in the rat

The presence of progressive white matter atrophy following traumatic brain injury (TBI) has been reported in humans as well as in animal models. However, a quantitative analysis of progressive alterations in myelinated axons and other cellular responses to trauma has not been conducted. This study examined quantitative differences in myelinated axons from several white and gray matter structures between non-traumatized and traumatized areas at several time points up to 1 year. We hypothesize that axonal numbers decrease over time within the structures analyzed, based on our previous work demonstrating shrinkage of tissue in these vulnerable areas. Intubated, anesthetized male Sprague-Dawley rats were subjected to moderate (1.8-2.2 atm) parasagittal fluid-percussion brain injury, and perfused at various intervals after surgery. Sections from the fimbria, external capsule, thalamus and cerebral cortex from the ipsilateral hemisphere of traumatized and sham-operated animals were prepared and. estimated total numbers of myelinated axons were determined by systematic random sampling. Electron micrographs were obtained for ultrastructural analysis. A significant (P<0.05) reduction in the number of myelinated axons in the traumatized hemisphere compared to control in all structures was observed. In addition, thalamic and cortical axonal counts decreased significantly (P<0.05) over time. Swollen axons and macrophage/microglia infiltration were present as late as 6 months post-TBI in various structures. This study is the first to describe quantitatively chronic axonal changes in vulnerable brains regions after injury. Based on these data, a time-dependent decrease in the number of myelinated axons is seen to occur in vulnerable gray matter regions including the cerebral cortex and thalamus along with distinct morphological changes within white matter tracts after TBI. Although this progressive axonal response to TBI may include Wallerian degeneration, other potential mechanisms underlying this progressive pathological response within the white matter are discussed.

Increased neurogenesis and the ectopic granule cells after intrahippocampal BDNF infusion in adult rats

There is evidence that BDNF influences the birth of granule cells in the dentate gyrus, which is one of the few areas of the brain that demonstrates neurogenesis throughout life. However, studies to date have not examined this issue directly. To do so, we compared the effects of BDNF, phosphate-buffered saline (PBS), or bovine serum albumin (BSA) on neurogenesis after infusion into the hippocampus of the normal adult rat, using osmotic pumps that were implanted unilaterally in the dorsal hilus. BDNF, PBS, and BSA were infused for 2 weeks. The mitotic marker bromodeoxyuridine (BrdU) was administered twice daily during the 2-week infusion period. At least 1 month after infusion ended, brains were processed immunocytochemically using antibodies to BrdU, a neuronal nuclear protein (NeuN), or calbindin D28K (CaBP), which labels mature granule cells. Stereology was used to quantify BrdU-labeled cells in the dorsal hippocampus that were double-labeled with NeuN or CaBP. There was a statistically significant increase in BrdU(+)/NeuN(+) double-labeled cells in the granule cell layer after BDNF infusion relative to controls. The values for BrdU(+)/NeuN(+) cells were similar to BrdU(+)/CaBP(+) cells, indicating that most new neurons were likely to be granule cells. In addition, BrdU(+)/NeuN(+)-labeled cells developed in the hilar region after BDNF infusion, which have previously only been identified after severe continuous seizures (status epilepticus) and associated pathological changes. Remarkably, neurogenesis was also increased contralaterally, but BDNF did not appear to spread to the opposite hemisphere. Thus, infusion of BDNF to a local area can have widespread effects on hippocampal neurogenesis. The results demonstrate that BDNF administration to the dentate gyrus leads to increased neurogenesis of granule cells. They also show that ectopic granule cells develop after BDNF infusion, which suggests that ectopic migration is not necessarily confined to pathological conditions. These results are discussed in light of the evidence that BDNF increases neuronal activity in hippocampus. Thus, the mechanisms underlying neurogenesis following BDNF infusion could be due to altered activity as well as direct effects of BDNF itself, and this is relevant to studies of other growth factors because many of them have effects on neuronal excitability that are often not considered.

Microglia-derived tumor necrosis factor-α exaggerates death of newborn hippocampal progenitor cells in vitro

Production of new hippocampal neurons continues in adult mammals and different brain insults can significantly increase this process. However, many hippocampal progenitor cells (HPC) die shortly after birth. Here we investigated the possibility that increased release of cytokines by activated microglia contributes to the death of HPC. We showed that addition of tumor necrosis factor-alpha (TNFalpha) to the medium of a cultured HPC line (HiB5) shortly after the cells stopped division causes significant apoptotic cell death. Conditioned medium from an activated microglial cell line (BV-2) had a similar effect, though conditioned medium from nonactivated microglia increased the survival of HPC. Reverse transcription-PCR indicated that HPC and microglial cells express both TNF receptors, TNF-R1 and TNF-R2. Coculturing of HPC with activated microglial cells aggravated death of hippocampal progenitors and also caused death of microglial cells themselves. Our data indicate that activated microglia-released TNFalpha might be an important contributor in inflammation-induced exaggeration of death of newly formed HPC in the adult brain after an insult.

NG2-positive cells in the mouse white and grey matter display distinct physiological properties

Cells that express the NG2 proteoglycan are the largest proliferative progenitor population in the postnatal central nervous system (CNS). Although this entire population has long been considered to be oligodendrocyte progenitors, numerous NG2(+) cells are present in the cerebral cortex, where relatively little myelination occurs, and also persist long after myelination is complete in the CNS. Several studies have alluded to the presence of distinct NG2(+) cell subtypes based on marker expression, but no experimentally derived hypotheses about the physiological role of these subtypes has been proposed. In the current study, whole-cell patch-clamp data from acutely isolated slices demonstrate that subcortical white matter and cortical NG2(+) cells display distinct membrane properties in addition to possessing differing K(+)- and Na(+)-channel expression profiles. A striking observation is that a subpopulation of cortical, but not white matter NG2(+) cells, elicit depolarization-induced spikes that are akin to immature action potentials. Our data demonstrate that a population of cortical NG2(+) cells display physiological properties that differ from their white matter counterparts.

Preferential vulnerability of astroglia and glial precursors to combined opioid and HIV-1 Tat exposure in vitro

Human immunodeficiency virus (HIV)-1 infection can cause characteristic neural defects such as progressive motor dysfunction, striatal pathology and gliosis. Recent evidence suggests that HIV-induced pathogenesis is exacerbated by heroin abuse and that the synergistic neurotoxicity is a direct effect of heroin on the CNS, an alarming observation considering the high incidence of HIV infection with injection drug abuse. Although HIV infection results in neurodegeneration, neurons themselves are not directly infected. Instead, HIV affects microglia and astroglia, which subsequently contributes to the neurodegenerative changes. Opioid receptors are widely expressed by macroglia and macroglial precursors, and the activation of mu-opioid receptors can modulate programmed cell death, as well as the response of neural cells to cytotoxic insults. For this reason, we questioned whether opioid drugs might modify the vulnerability of macroglia and macroglial precursors to HIV-1 Tat protein. To address this problem, the effects of morphine and/or HIV Tat(1-72) on the viability of macroglia and macroglial precursors were assessed in mixed-glial cultures derived from mouse striatum. Our findings indicate that sustained exposure to morphine and Tat(1-72) viral protein induces the preferential death of glial precursors and some astrocytes. Moreover, the increased cell death is mediated by mu-opioid receptors and accompanied by the activation of caspase-3. Our results imply that opiates can enhance the cytotoxicity of HIV-1 Tat through direct actions on glial precursors and/or astroglia, suggesting novel cellular targets for HIV-opiate interactions.