Astrogliosis in CNS pathologies: is there a role for microglia?

Neuroprotective Effect of Chitosan Oligosaccharide on Hypoxic-Ischemic Brain Damage in Neonatal Rats

Neonatal hypoxic-ischemic brain damage (HIBD) is one of the leading causes of neonatal mortality and permanent neurological disability worldwide and the effective treatment strategies are not yet available. It has been demonstrated that Chitosan oligosaccharide (COS) exerts protective effect in vitro ischemic brain injury. However, no information is available on possible effects of COS on neonatal HIBD. To investigate the hypothesis of the potential neuroprotective effect of COS on the brain injury due to HIBD, 7-day-old Sprague-Dawley rats were treated with left carotid artery ligation followed by exposure to 8% oxygen (balanced with nitrogen) for 2.5 h at 37 °C. After COS treatment, the cerebral damage was measured by behavior tasks, 2,3,5-triphenyltetrazolium chloride(TTC), Hematoxyline-Eosin(HE), Nissl and Fluoro-Jade B(FJB)staining. In addition, the oxidative stress were assayed with ipsilateral hemisphere homogenates. Immunofluorescence staining were used to examine the activation of the astrocyte and microglia. Expression of inflammatory-related proteins were analyzed by western-blot analysis. In this study we found that administration of COS ameliorated early neurological reflex behavior, significantly reduce brain infarct volume and attenuated neuronal cell injury and degeneration. Furthermore, COS markedly decreased the level of MDA, lactic acid and increased SOD, GSH-Px and T-AOC. COS attenuated hypoxic-ischemic induced up-regulation of expressions of interleukin-1β (IL-1β), tumor necrosis factor alpha (TNF-α), meanwhile it dramatically increased the interleukin-10 (IL-10). These results suggest that COS exerts neuroprotection on hypoxic-ischemic brain damage in neonatal rats, it implies COS might be a potential therapeutic for the treatment of HIBD.

IL-2/Anti-IL-2 Complex Attenuates Inflammation and BBB Disruption in Mice Subjected to Traumatic Brain Injury

Traumatic brain injury (TBI) induces the excessive inflammation and disruption of blood–brain barrier, both of which are partially mediated by the activation of microglia and release of inflammatory cytokines. Previous reports showed that administration of regulatory T cells (Tregs) could suppress inflammation and promote neurological function recovery, and that the IL-2/anti-IL-2 complex (IL-2C) could increase the number of Tregs. Thus, we hypothesized that IL-2C-mediated expansion of Tregs would be beneficial in mice subjected to TBI. In this study, mice received an intraperitoneal injection of IL-2C for three consecutive days. We observed that IL-2C dose-dependently increased Tregs without affecting the populations of CD4, CD8, or natural killer cells. IL-2C could improve the neurological recovery and reduce brain edema, tissue loss, neutrophils infiltration, and tight junction proteins degradation. Furthermore, this complex could also reduce the expression of CD16/32, IL-1β, or TNF-α, and elevate the expression of CD206, arginase 1, or TGF-β. These results suggest that IL-2C could be a potential therapeutic method to alleviate excessive inflammation and maintain blood vessel stability after TBI.

Metyrapone prevents brain damage induced by status epilepticus in the rat lithium-pilocarpine model

The status epilepticus (SE) induced by lithium-pilocarpine is a well characterized rodent model of the human temporal lobe epilepsy (TLE) which is accompanied by severe brain damage. Stress and glucocorticoids markedly contribute to exacerbate neuronal damage induced by seizures but the underlying mechanisms are poorly understood. Herein we sought to investigate whether a single administration of metyrapone (150 mg/kg, i.p.), an 11β-hydroxylase inhibitor, enzyme involved in the peripheral and central synthesis of corticosteroids, had neuroprotective properties in this model. Two experiments were carried out. In exp. 1, metyrapone was administered 3 h before pilocarpine injection whereas in exp. 2, metyrapone administration took place at the onset of the SE. In both experiments, 3 days after the insult, brain metabolism was assessed by in vivo 2-deoxy-2-[¹⁸F]fluoro-d-glucose ([¹⁸F]FDG) positron emission tomography (PET). Brains were processed for analyses of markers of hippocampal integrity (Nissl staining), neurodegeneration (Fluoro-Jade C), astrogliosis (glial fibrillary acidic protein (GFAP) immunohistochemistry) and, for a marker of activated microglia by in vitro autoradiography with the TSPO (18 kDa translocator protein) radioligand [¹⁸F]GE180. The SE resulted in a consistent hypometabolism in hippocampus, cortex and striatum and neuronal damage, hippocampal neurodegeneration, neuronal death and gliosis. Interestingly, metyrapone had neuroprotective effects when administered before, but not after the insult. In summary, we conclude that metyrapone administration prior but not after the SE protected from brain damage induced by SE in the lithium-pilocarpine model. Therefore, it seems that the effect of metyrapone is preventive in nature and likely related to its antiseizure properties.

Microglia amplify inflammatory activation of astrocytes in manganese neurotoxicity

BACKGROUND

As the primary immune response cell in the central nervous system, microglia constantly monitor the microenvironment and respond rapidly to stress, infection, and injury, making them important modulators of neuroinflammatory responses. In diseases such as Parkinson's disease, Alzheimer's disease, multiple sclerosis, and human immunodeficiency virus-induced dementia, activation of microglia precedes astrogliosis and overt neuronal loss. Although microgliosis is implicated in manganese (Mn) neurotoxicity, the role of microglia and glial crosstalk in Mn-induced neurodegeneration is poorly understood.

METHODS

Experiments utilized immunopurified murine microglia and astrocytes using column-free magnetic separation. The effect of Mn on microglia was investigated using gene expression analysis, Mn uptake measurements, protein production, and changes in morphology. Additionally, gene expression analysis was used to determine the effect Mn-treated microglia had on inflammatory responses in Mn-exposed astrocytes.

RESULTS

Immunofluorescence and flow cytometric analysis of immunopurified microglia and astrocytes indicated cultures were 97 and 90% pure, respectively. Mn treatment in microglia resulted in a dose-dependent increase in pro-inflammatory gene expression, transition to a mixed M1/M2 phenotype, and a de-ramified morphology. Conditioned media from Mn-exposed microglia (MCM) dramatically enhanced expression of mRNA for Tnf, Il-1β, Il-6, Ccl2, and Ccl5 in astrocytes, as did exposure to Mn in the presence of co-cultured microglia. MCM had increased levels of cytokines and chemokines including IL-6, TNF, CCL2, and CCL5. Pharmacological inhibition of NF-κB in microglia using Bay 11-7082 completely blocked microglial-induced astrocyte activation, whereas siRNA knockdown of Tnf in primary microglia only partially inhibited neuroinflammatory responses in astrocytes.

CONCLUSIONS

These results provide evidence that NF-κB signaling in microglia plays an essential role in inflammatory responses in Mn toxicity by regulating cytokines and chemokines that amplify the activation of astrocytes.

Prolonged Dysfunction of Astrocytes and Activation of Microglia Accelerate Degeneration of Dopaminergic Neurons in the Rat Substantia Nigra and Block Compensation of Early Motor Dysfunction Induced by 6-OHDA

Progressive degeneration of dopaminergic neurons in the substantia nigra (SN) is the underlying cause of Parkinson’s disease (PD). The disease in early stages is difficult to diagnose, because behavioral deficits are masked by compensatory processes. Astrocytic and microglial pathology precedes motor symptoms. Besides supportive functions of astrocytes in the brain, their role in PD is unrecognized. Prolonged dysfunction of astrocytes could increase the vulnerability of dopaminergic neurons and advance their degeneration during aging. The aim of our studies was to find out whether prolonged dysfunction of astrocytes in the SN is deleterious for neuronal functioning and if it influences their survival after toxic insult or changes the compensatory potential of the remaining neurons. In Wistar rat model, we induced activation, prolonged dysfunction, and death of astrocytes by chronic infusion of fluorocitrate (FC) into the SN, without causing dopaminergic neuron degeneration. Strongly enhanced dopamine turnover in the SN after 7 days of FC infusion was induced probably by microglia activated in response to astrocyte stress. The FC effect was reversible, and astrocyte pool was replenished 3 weeks after the end of infusion. Importantly, the prolonged astrocyte dysfunction and microglia activation accelerated degeneration of dopaminergic neurons induced by 6-hydroxydopamine and blocked the behavioral compensation normally observed after moderate neurodegeneration. Impaired astrocyte functioning, activation of microglia, diminishing compensatory capability of the dopaminergic system, and increasing neuronal vulnerability to external insults could be the underlying causes of PD. This animal model of prolonged astrocyte dysfunction can be useful for in vivo studies of glia–microglia–neuron interaction.

A tailored mouse model of CLN2 disease: A nonsense mutant for testing personalized therapies

The Neuronal Ceroid Lipofuscinoses (NCLs), also known as Batten disease, result from mutations in over a dozen genes. Although, adults are susceptible, the NCLs are frequently classified as pediatric neurodegenerative diseases due to their greater pediatric prevalence. Initial clinical presentation usually consists of either seizures or retinopathy but develops to encompass both in conjunction with declining motor and cognitive function. The NCLs result in premature death due to the absence of curative therapies. Nevertheless, preclinical and clinical trials exist for various therapies. However, the genotypes of NCL animal models determine which therapeutic approaches can be assessed. Mutations of the CLN2 gene encoding a soluble lysosomal enzyme, tripeptidyl peptidase 1 (TPP1), cause late infantile NCL/CLN2 disease. The genotype of the original mouse model of CLN2 disease, Cln2^-/-, excludes mutation guided therapies like antisense oligonucleotides and nonsense suppression. Therefore, the purpose of this study was to develop a model of CLN2 disease that allows for the assessment of all therapeutic approaches. Nonsense mutations in CLN2 disease are frequent, the most common being CLN2^R208X. Thus, we created a mouse model that carries a mutation equivalent to the human p.R208X mutation. Molecular assessment of Cln2^R207X/R207X tissues determined significant reduction in Cln2 transcript abundance and TPP1 enzyme activity. This reduction leads to the development of neurological impairment (e.g. tremors) and neuropathology (e.g. astrocytosis). Collectively, these assessments indicate that the Cln2^R207X/R207X mouse is a valid CLN2 disease model which can be used for the preclinical evaluation of all therapeutic approaches including mutation guided therapies.

Poly(ADP-ribose) polymerase-1 regulates microglia mediated decrease of endothelial tight junction integrity

Alzheimer's disease pathology includes, beside neuronal damage, reactive gliosis and reduced blood-brain barrier (BBB) integrity. Microglia are intimately associated with the BBB and upon AD pathology, pro-inflammatory responses of microglia could contribute to BBB damage. To study whether microglia can directly affect BBB integrity, the effects of amyloid beta (Aβ) -stimulated primary murine microglia on co-cultured mouse brain endothelial cells (bEnd3) and murine astrocyte cultures were assessed. We also assessed whether microglial phenotype modulation via poly(ADP-ribose) polymerase-1 (PARP-1) inhibition/ablation can reverse microglial impact on these BBB forming cells. Unstimulated microglia promoted expression of tight junction proteins (TJPs), zonula ocluden-1 (ZO-1) and occludin in co-cultured endothelia cells, whereas Aβ-stimulated microglia reduced endothelial expression of ZO-1 and occludin. Astrocytes co-cultured with microglia showed elevated glial fibrillary acidic protein (GFAP) expression, which was further increased if microglia had been stimulated with Aβ. Aβ induced microglial release of nitric oxide (NO) and tumour necrosis factor alpha (TNFα), which resulted in reduced endothelial expression of TJPs and increased paracellular permeability. Microglial PARP-1 inhibition attenuated these Aβ-induced events. These findings demonstrate that PARP-1 mediated microglial responses (NO and TNFα) can directly reduce BBB integrity by promoting TJP degradation, increasing endothelial cell permeability and inducing astrogliosis. PARP-1 as a modulator of microglial phenotype can prevent microglial BBB damaging events, and thus is a potential therapeutic target.

Exposure to gestational diabetes mellitus induces neuroinflammation, derangement of hippocampal neurons, and cognitive changes in rat offspring

Background

Birth cohort studies link gestational diabetes mellitus (GDM) with impaired cognitive performance in the offspring. However, the mechanisms involved are unknown. We tested the hypothesis that obesity-associated GDM induces chronic neuroinflammation and disturbs the development of neuronal circuitry resulting in impaired cognitive abilities in the offspring.

Methods

In rats, GDM was induced by feeding dams a diet high in sucrose and fatty acids. Brains of neonatal (E20) and young adult (15-week-old) offspring of GDM and lean dams were analyzed by immunohistochemistry, cytokine assay, and western blotting. Young adult offspring of GDM and lean dams went also through cognitive assessment. Cultured microglial responses to elevated glucose and/or fatty acids levels were analyzed.

Results

In rats, impaired recognition memory was observed in the offspring of GDM dams. GDM exposure combined with a postnatal high-fat and sucrose diet resulted in atypical inattentive behavior in the offspring. These cognitive changes correlated with reduced density and derangement of Cornu Ammonis 1 pyramidal neuronal layer, decreased hippocampal synaptic integrity, increased neuroinflammatory status, and reduced expression of CX3CR1, the microglial fractalkine receptor regulating microglial pro-inflammatory responses and synaptic pruning. Primary microglial cultures that were exposed to high concentrations of glucose and/or palmitate were transformed into an activated, amoeboid morphology with increased nitric oxide and superoxide production, and altered their cytokine release profile.

Conclusions

These findings demonstrate that GDM stimulates microglial activation and chronic inflammatory responses in the brain of the offspring that persist into young adulthood. Reactive gliosis correlates positively with hippocampal synaptic decline and cognitive impairments. The elevated pro-inflammatory cytokine expression at the critical period of hippocampal synaptic maturation suggests that neuroinflammation might drive the synaptic and cognitive decline in the offspring of GDM dams. The importance of microglia in this process is supported by the reduced Cx3CR1 expression as an indication of the loss of microglial control of inflammatory responses and phagocytosis and synaptic pruning in GDM offspring.

The Role of HIV Infection in Neurologic Injury

The central nervous system (CNS) is a very challenging HIV-1 sanctuary, in which HIV-1 replication is established early on during acute infection and can persist despite potent antiretroviral treatments. HIV-1 infected macrophages play a pivotal role acting as vehicles for HIV-1 to spread into the brain, and can be the major contributor of an early compartmentalization. HIV-1 infection in CNS may lead to a broad spectrum of neurological syndromes, such as dementia, mild neurocognitive disorders, and asymptomatic impairment. These clinical manifestations are caused by the release of neurotoxins from infected cells (mainly macrophages), and also by several HIV-1 proteins, able to activate cell-signaling involved in the control of cellular survival and apoptosis. This review is aimed at highlighting the virological aspects associated with the onset of neurocognitive disorders and at addressing the novel therapeutic approaches to stop HIV-1 replication in this critical sanctuary.

Specific suppression of microgliosis cannot circumvent the severe neuropathology in peroxisomal β-oxidation-deficient mice

An important hallmark of various neurodegenerative disorders is the proliferation and activation of microglial cells, the resident immune cells of the central nervous system (CNS). Mice that lack multifunctional protein-2 (MFP2), the key enzyme in peroxisomal β-oxidation, develop excessive microgliosis that positively correlates with behavioral deficits whereas no neuronal loss occurs. However, the precise contribution of neuroinflammation to the fatal neuropathology of MFP2 deficiency remains largely unknown. Here, we first attempted to suppress the inflammatory response by administering various anti-inflammatory drugs but they failed to reduce microgliosis. Subsequently, Mfp2^-/- mice were treated with the selective colony-stimulating factor 1 receptor (CSF1R) inhibitor PLX5622 as microglial proliferation and survival is dependent on CSF1R signaling. This resulted in the elimination of >95% of microglia from control mice but only 70% of the expanded microglial population from Mfp2^-/- mice. Despite microglial diminution in Mfp2^-/- brain, inflammatory markers remained unaltered and residual microglia persisted in a reactive state. CSF1R inhibition did not prevent neuronal dysfunction, cognitive decline and clinical deterioration of Mfp2^-/- mice. Collectively, the unaltered inflammatory profile despite suppressed microgliosis concurrent with persevering clinical decline strengthens our hypothesis that neuroinflammation importantly contributes to the Mfp2^-/- phenotype.

Immune involvement in the pathogenesis of schizophrenia: a meta-analysis on postmortem brain studies

Although the precise pathogenesis of schizophrenia is unknown, genetic, biomarker and imaging studies suggest involvement of the immune system. In this study, we performed a systematic review and meta-analysis of studies investigating factors related to the immune system in postmortem brains of schizophrenia patients and healthy controls. Forty-one studies were included, reporting on 783 patients and 762 controls. We divided these studies into those investigating histological alterations of cellular composition and those assessing molecular parameters; meta-analyses were performed on both categories. Our pooled estimate on cellular level showed a significant increase in the density of microglia (P=0.0028) in the brains of schizophrenia patients compared with controls, albeit with substantial heterogeneity between studies. Meta-regression on brain regions demonstrated this increase was most consistently observed in the temporal cortex. Densities of macroglia (astrocytes and oligodendrocytes) did not differ significantly between schizophrenia patients and healthy controls. The results of postmortem histology are paralleled on the molecular level, where we observed an overall increase in expression of proinflammatory genes on transcript and protein level (P=0.0052) in patients, while anti-inflammatory gene expression levels were not different between schizophrenia and controls. The results of this meta-analysis strengthen the hypothesis that components of the immune system are involved in the pathogenesis of schizophrenia.

Polarization of microglia and its role in bacterial sepsis

Microglial polarization in response to brain inflammatory conditions is a crescent field in neuroscience. However, the effect of systemic inflammation, and specifically sepsis, is a relatively unexplored field that has great interest and relevance. Sepsis has been associated with both early and late harmful events of the central nervous system, suggesting that there is a close link between sepsis and neuroinflammation. During sepsis evolution it is supposed that microglial could exert both neurotoxic and repairing effects depending on the specific microglial phenotype assumed. In this context, here it was reviewed the role of microglial polarization during sepsis-associated brain dysfunction.

Astrocyte-derived tissue Transglutaminase affects fibronectin deposition, but not aggregation, during cuprizone-induced demyelination

Astrogliosis as seen in Multiple Sclerosis (MS) develops into astroglial scarring, which is beneficial because it seals off the site of central nervous system (CNS) damage. However, astroglial scarring also forms an obstacle that inhibits axon outgrowth and (re)myelination in brain lesions. This is possibly an important cause for incomplete remyelination in the CNS of early stage MS patients and for failure in remyelination when the disease progresses. In this study we address whether under demyelinating conditions in vivo, tissue Transglutaminase (TG2), a Ca2+ -dependent enzyme that catalyses posttranslational modification of proteins, contributes to extracellular matrix (ECM) deposition and/or aggregation. We used the cuprizone model for de- and remyelination. TG2 immunoreactivity and enzymatic activity time-dependently appeared in astrocytes and ECM, respectively, in the corpus callosum of cuprizone-treated mice. Enhanced presence of soluble monomeric and multimeric fibronectin was detected during demyelination, and fibronectin immunoreactivity was slightly decreased in cuprizone-treated TG2-/- mice. In vitro TG2 overexpression in astrocytes coincided with more, while knock-down of TG2 with less fibronectin production. TG2 contributes, at least partly, to fibronectin production, and may play a role in fibronectin deposition during cuprizone-induced demyelination. Our observations are of interest in understanding the functional implications of TG2 during astrogliosis.

Chronic caffeine exposure attenuates blast-induced memory deficit in mice

OBJECTIVE

To investigate the effects of three different ways of chronic caffeine administration on blast- induced memory dysfunction and to explore the underlying mechanisms.

METHODS

Adult male C57BL/6 mice were used and randomly divided into five groups: control: without blast exposure, con-water: administrated with water continuously before and after blast-induced traumatic brain injury (bTBI), con-caffeine: administrated with caffeine continuously for 1 month before and after bTBI, pre-caffeine: chronically administrated with caffeine for 1 month before bTBI and withdrawal after bTBI, post-caffeine: chronically administrated with caffeine after bTBI. After being subjected to moderate intensity of blast injury, mice were recorded for learning and memory performance using Morris water maze (MWM) paradigms at 1, 4, and 8 weeks post-blast injury. Neurological deficit scoring, glutamate concentration, proinflammatory cytokines production, and neuropathological changes at 24 h, 1, 4, and 8 weeks post-bTBI were examined to evaluate the brain injury in early and prolonged stages. Adenosine A1 receptor expression was detected using qPCR.

RESULTS

All of the three ways of chronic caffeine exposure ameliorated blast-induced memory deficit, which is correlated with the neuroprotective effects against excitotoxicity, inflammation, astrogliosis and neuronal loss at different stages of injury. Continuous caffeine treatment played positive roles in both early and prolonged stages of bTBI; pre-bTBI and post-bTBI treatment of caffeine tended to exert neuroprotective effects at early and prolonged stages of bTBI respectively. Up-regulation of adenosine A1 receptor expression might contribute to the favorable effects of chronic caffeine consumption.

CONCLUSION

Since caffeinated beverages are widely consumed in both civilian and military personnel and are convenient to get, the results may provide a promising prophylactic strategy for blast-induced neurotrauma and the consequent cognitive impairment.

Differential hypothalamic leptin sensitivity in obese rat offspring exposed to maternal and postnatal intake of chocolate and soft drink

Background/objective:

Intake of high-energy foods and maternal nutrient overload increases the risk of metabolic diseases in the progeny such as obesity and diabetes. We hypothesized that maternal and postnatal intake of chocolate and soft drink will affect leptin sensitivity and hypothalamic astrocyte morphology in adult rat offspring.

Methods:

Pregnant Sprague-Dawley rats were fed ad libitum chow diet only (C) or with chocolate and high sucrose soft drink supplement (S). At birth, litter size was adjusted into 10 male offspring per mother. After weaning, offspring from both dietary groups were assigned to either S or C diet, giving four groups until the end of the experiment at 26 weeks of age.

Results:

As expected, adult offspring fed the S diet post weaning became obese (body weight: P<0.01, %body fat per kg: P<0.001) and this was due to the reduced energy expenditure (P<0.05) and hypothalamic astrogliosis (P<0.001) irrespective of maternal diet. Interesting, offspring born to S-diet-fed mothers and fed the S diet throughout postnatal life became obese despite lower energy intake than controls (P<0.05). These SS offspring showed increased feed efficiency (P<0.001) and reduced fasting pSTAT3 activity (P<0.05) in arcuate nucleus (ARC) compared with other groups. The findings indicated that the combination of the maternal and postnatal S-diet exposure induced persistent changes in leptin signalling, hence affecting energy balance. Thus, appetite regulation was more sensitive to the effect of leptin than energy expenditure, suggesting differential programming of leptin sensitivity in ARC in SS offspring. Effects of the maternal S diet were normalized when offspring were fed a chow diet after weaning.

Conclusions:

Maternal intake of chocolate and soft drink had long-term consequences for the metabolic phenotype in the offspring if they continued on the S diet in postnatal life. These offspring displayed obesity despite lowered energy intake associated with alterations in hypothalamic leptin signalling.

FcRγ-dependent immune activation initiates astrogliosis during the asymptomatic phase of Sandhoff disease model mice

Sandhoff disease (SD) is caused by the loss of β-hexosaminidase (Hex) enzymatic activity in lysosomes resulting from Hexb mutations. In SD patients, the Hex substrate GM2 ganglioside accumulates abnormally in neuronal cells, resulting in neuronal loss, microglial activation, and astrogliosis. Hexb^−/− mice, which manifest a phenotype similar to SD, serve as animal models for examining the pathophysiology of SD. Hexb^−/− mice reach ~8 weeks without obvious neurological defects; however, trembling begins at 12 weeks and is accompanied by startle reactions and increased limb tone. These symptoms gradually become severe by 16–18 weeks. Immune reactions caused by autoantibodies have been recently associated with the pathology of SD. The inhibition of immune activation may represent a novel therapeutic target for SD. Herein, SD mice (Hexb^−/−) were crossed to mice lacking an activating immune receptor (FcRγ^−/−) to elucidate the potential relationship between immune responses activated through SD autoantibodies and astrogliosis. Microglial activation and astrogliosis were observed in cortices of Hexb^−/− mice during the asymptomatic phase, and were inhibited in Hexb^−/−FcRγ^−/− mice. Moreover, early astrogliosis and impaired motor coordination in Hexb^−/− mice could be ameliorated by immunosuppressants, such as FTY720. Our findings demonstrate the importance of early treatment and the therapeutic effectiveness of immunosuppression in SD.

Hyperbaric Oxygen Effects on Depression-Like Behavior and Neuroinflammation in Traumatic Brain Injury Rats

OBJECTIVE

The aim of this study was to determine whether hyperbaric oxygen (HBO) therapy causes attenuation of traumatic brain injury (TBI)-induced depression-like behavior and its associated anti-neuroinflammatory effects after fluid percussion injury.

METHODS

Anesthetized male Sprague-Dawley rats were divided into 3 groups: sham operation plus normobaric air (NBA) (21% oxygen at 1 absolute atmosphere [ATA]), TBI plus NBA, and TBI plus HBO (100% oxygen at 2.0 ATA). HBO was applied immediately for 60 min/d after TBI for 3 days. Depression-like behavior was tested by a forced swimming test, motor function was tested by an inclined plane test, and infarction volume was tested by triphenyltetrazolium chloride (TTC) staining on days 4, 8, and 15. Neuronal apoptosis (terminal deoxynucleotidyl transferase dUTP nick-end labeling assay), microglial (marker OX42) activation, and tumor necrosis factor (TNF)-α expression in microglia in the hippocampus CA3 were measured by immunofluorescence methods.

RESULTS

Compared with the TBI controls, without significant changes in TTC staining or in the motor function test, TBI-induced depression-like behavior was significantly attenuated by HBO therapy by day 15 after TBI. Simultaneously, TBI-induced neuronal apoptosis, microglial (marker OX42) activation, and TNF-α expression in the microglia in the hippocampus CA3 were significantly reduced by HBO.

CONCLUSIONS

Our results suggest that HBO treatment may ameliorate TBI-induced depression-like behavior in rats by attenuating neuroinflammation, representing one possible mechanism by which depression-like behavior recovery might occur. We also recommend HBO as a potential treatment for TBI-induced depression-like behavior if early intervention is possible.

Immune and Neuroendocrine Mechanisms of Stress Vulnerability and Resilience

Diagnostic criteria for mood disorders including major depressive disorder (MDD) largely ignore biological factors in favor of behavioral symptoms. Compounding this paucity of psychiatric biomarkers is a need for therapeutics to adequately treat the 30-50% of MDD patients who are unresponsive to traditional antidepressant medications. Interestingly, MDD is highly prevalent in patients suffering from chronic inflammatory conditions, and MDD patients exhibit higher levels of circulating pro-inflammatory cytokines. Together, these clinical findings suggest a role for the immune system in vulnerability to stress-related psychiatric illness. A growing body of literature also implicates the immune system in stress resilience and coping. In this review, we discuss the mechanisms by which peripheral and central immune cells act on the brain to affect stress-related neurobiological and neuroendocrine responses. We specifically focus on the roles of pro-inflammatory cytokine signaling, peripheral monocyte infiltration, microglial activation, and hypothalamic-pituitary-adrenal axis hyperactivity in stress vulnerability. We also highlight recent evidence suggesting that adaptive immune responses and treatment with immune modulators (exogenous glucocorticoids, humanized antibodies against cytokines) may decrease depressive symptoms and thus represent an attractive alternative to the current antidepressant treatments.

Natural Compounds as a Therapeutic Intervention following Traumatic Brain Injury: The Role of Phytochemicals

There has been a tremendous focus on the discovery and development of neuroprotective agents that might have clinical relevance following traumatic brain injury (TBI). This type of brain injury is very complex and is divided into two major components. The first component, a primary injury, occurs at the time of impact and is the result of the mechanical insult itself. This primary injury is thought to be irreversible and resistant to most treatments. A second component or secondary brain injury, is defined as cellular damage that is not immediately obvious after trauma, but that develops after a delay of minutes, hours, or even days. This injury appears to be amenable to treatment. Because of the complexity of the secondary injury, any type of therapeutic intervention needs to be multi-faceted and have the ability to simultaneously modulate different cellular changes. Because of diverse pharmaceutical interactions, combinations of different drugs do not work well in concert and result in adverse physiological conditions. Research has begun to investigate the possibility of using natural compounds as a therapeutic intervention following TBI. These compounds normally have very low toxicity and have reduced interactions with other pharmaceuticals. In addition, many natural compounds have the potential to target numerous different components of the secondary injury. Here, we review 33 different plant-derived natural compounds, phytochemicals, which have been investigated in experimental animal models of TBI. Some of these phytochemicals appear to have potential as possible therapeutic interventions to offset key components of the secondary injury cascade. However, not all studies have used the same scientific rigor, and one should be cautious in the interpretation of studies using naturally occurring phytochemical in TBI research.

Smooth muscle-generated methylglyoxal impairs endothelial cell-mediated vasodilatation of cerebral microvessels in type 1 diabetic rats

BACKGROUND AND PURPOSE

Endothelial cell-mediated vasodilatation of cerebral arterioles is impaired in individuals with Type 1 diabetes (T1D). This defect compromises haemodynamics and can lead to hypoxia, microbleeds, inflammation and exaggerated ischaemia-reperfusion injuries. The molecular causes for dysregulation of cerebral microvascular endothelial cells (cECs) in T1D remains poorly defined. This study tests the hypothesis that cECs dysregulation in T1D is triggered by increased generation of the mitochondrial toxin, methylglyoxal, by smooth muscle cells in cerebral arterioles (cSMCs).

EXPERIMENTAL APPROACH

Endothelial cell-mediated vasodilatation, vascular transcytosis inflammation, hypoxia and ischaemia-reperfusion injury were assessed in brains of male Sprague-Dawley rats with streptozotocin-induced diabetes and compared with those in diabetic rats with increased expression of methylglyoxal-degrading enzyme glyoxalase-I (Glo-I) in cSMCs.

KEY RESULTS

After 7-8 weeks of T1D, endothelial cell-mediated vasodilatation of cerebral arterioles was impaired. Microvascular leakage, gliosis, macrophage/neutrophil infiltration, NF-κB activity and TNF-α levels were increased, and density of perfused microvessels was reduced. Transient occlusion of a mid-cerebral artery exacerbated ischaemia-reperfusion injury. In cSMCs, Glo-I protein was decreased, and the methylglyoxal-synthesizing enzyme, vascular adhesion protein 1 (VAP-1) and methylglyoxal were increased. Restoring Glo-I protein in cSMCs of diabetic rats to control levels via gene transfer, blunted VAP-1 and methylglyoxal increases, cECs dysfunction, microvascular leakage, inflammation, ischaemia-reperfusion injury and increased microvessel perfusion.

CONCLUSIONS AND IMPLICATIONS

Methylglyoxal generated by cSMCs induced cECs dysfunction, inflammation, hypoxia and exaggerated ischaemia-reperfusion injury in diabetic rats. Lowering methylglyoxal produced by cSMCs may be a viable therapeutic strategy to preserve cECs function and blunt deleterious downstream consequences in T1D.

Early electroacupuncture treatment ameliorates neuroinflammation in rats with traumatic brain injury

Background

Neuroinflammation is the leading cause of neurological sequelae after traumatic brain injury (TBI). The aim of the present study was to investigate whether the neuroprotective effects of electroacupuncture (EA) are mediated by anti-neuroinflammatory effects in a rat model of TBI.

Methods

Male Sprague-Dawley rats were randomly divided into three groups: sham-operated, TBI control, and EA-treated. The animals in the sham-operated group underwent a sham operation, those in the TBI control group were subjected to TBI, but not EA, and those in the EA group were treated with EA for 60 min immediately after TBI, daily for 3 consecutive days. EA was applied at the acupuncture points GV20, GV26, LI4, and KI1, using a dense-dispersed wave, at frequencies of 0.2 and 1 Hz, and an amplitude of 1 mA. Cell infarction volume (TTC stain), neuronal apoptosis (markers: TUNEL and Caspase-3), activation of microglia (marker: Iba1) and astrocytes (marker: GFAP), and tumor necrosis factor (TNF)-α expression in the microglia and astrocytes were evaluated by immunofluorescence. Functional outcomes were assessed using the inclined plane test. All tests were performed 72 h after TBI.

Results

We found that TBI-induced loss of grasp strength, infarction volume, neuronal apoptosis, microglial and astrocyte activation, and TNF-α expression in activated microglia and astrocytes were significantly attenuated by EA treatment.

Conclusions

Treatment of TBI in the acute stage with EA for 60 min daily for 3 days could ameliorate neuroinflammation. This may thus represent a mechanism by which functional recovery can occur after TBI.

MPP+-Lesioned Mice: an Experimental Model of Motor, Emotional, Memory/Learning, and Striatal Neurochemical Dysfunctions

The neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) induces motor and nonmotor dysfunctions resembling Parkinson's disease (PD); however, studies investigating the effects of 1-methyl-4-phenylpyridinium (MPP⁺), an active oxidative product of MPTP, are scarce. This study investigated the behavioral and striatal neurochemical changes (related to oxidative damage, glial markers, and neurotrophic factors) 24 h after intracerebroventricular administration of MPP⁺ (1.8-18 μg/mouse) in C57BL6 mice. MPP⁺ administration at high dose (18 μg/mouse) altered motor parameters, since it increased the latency to leave the first quadrant and reduced crossing, rearing, and grooming responses in the open-field test and decreased rotarod latency time. MPP⁺ administration at low dose (1.8 μg/mouse) caused specific nonmotor dysfunctions as it produced a depressive-like effect in the forced swim test and tail suspension test, loss of motivational and self-care behavior in the splash test, anxiety-like effect in the elevated plus maze test, and short-term memory deficit in the step-down inhibitory avoidance task, without altering ambulation. MPP⁺ at doses of 1.8-18 μg/mouse increased tyrosine hydroxylase (TH) immunocontent and at 18 μg/mouse increased α-synuclein and decreased parkin immunocontent. The astrocytic calcium-binding protein S100B and glial fibrillary acidic protein (GFAP)/S100B ratio was decreased following MPP⁺ administration (18 μg/mouse). At this highest dose, MPP⁺ increased the ionized calcium-binding adapter molecule 1 (Iba-1) immunocontent, suggesting microglial activation. Also, MPP⁺ at a dose of 18 μg/mouse increased thiobarbituric acid reactive substances (TBARS) and glutathione (GSH) levels and increased glutathione peroxidase (GPx) and hemeoxygenase-1 (HO-1) immunocontent, suggesting a significant role for oxidative stress in the MPP⁺-induced striatal damage. MPP⁺ (18 μg/mouse) also increased striatal fibroblast growth factor 2 (FGF-2) and brain-derived neurotrophic factor (BDNF) levels. Moreover, MPP⁺ decreased tropomyosin receptor kinase B (TrkB) immunocontent. Finally, MPP⁺ (1.8-18 μg/mouse) increased serum corticosterone levels and did not alter acetylcholinesterase (AChE) activity in the striatum but increased it in cerebral cortex and hippocampus. Collectively, these results indicate that MPP⁺ administration at low doses may be used as a model of emotional and memory/learning behavioral deficit related to PD and that MPP⁺ administration at high dose could be useful for analysis of striatal dysfunctions associated with motor deficits in PD.

Hypothalamic TLR2 triggers sickness behavior via a microglia-neuronal axis

Various pathophysiologic mechanisms leading to sickness behaviors have been proposed. For example, an inflammatory process in the hypothalamus has been implicated, but the signaling modalities that involve inflammatory mechanisms and neuronal circuit functions are ill-defined. Here, we show that toll-like receptor 2 (TLR2) activation by intracerebroventricular injection of its ligand, Pam3CSK4, triggered hypothalamic inflammation and activation of arcuate nucleus microglia, resulting in altered input organization and increased activity of proopiomelanocortin (POMC) neurons. These animals developed sickness behavior symptoms, including anorexia, hypoactivity, and hyperthermia. Antagonists of nuclear factor kappa B (NF-κB), cyclooxygenase pathway and melanocortin receptors 3/4 reversed the anorexia and body weight loss induced by TLR2 activation. These results unmask an important role of TLR2 in the development of sickness behaviors via stimulation of hypothalamic microglia to promote POMC neuronal activation in association with hypothalamic inflammation.

Histological study on the protective role of vitamin B complex on the cerebellum of diabetic rat

BACKGROUND

Disorder in cerebellar structure was reported in diabetes mellitus. B vitamins are involved in many significant metabolic processes within the brain.

AIM OF THE WORK

To detect the protective role of vitamin B complex on the histological structure of the cerebellum of experimentally induced diabetic rat.

MATERIAL & METHODS

Eighteen adult male Wistar rats were divided into two groups. Group I: normal vehicle control (n=6). Group II: streptozotocin-induced diabetic rats (n=12), which was equally divided into two subgroups; IIA (diabetic vehicle control), IIB (diabetic vitamin B complex-treated): streptozotocin-induced diabetic rats treated with vitamin B complex (1mg/kg/day) for 6 weeks. Specimens from the cerebellum were processed for light and electron microscopy.

RESULTS

In vitamin B complex treated group, the histological changes in Purkinje cells, astrocytes and oligodendrocytes were improved compared with the diabetic non-treated group. The white matter revealed intact myelinated axons. Inducible nitric oxide synthase (iNOS) and caspase-3 expression reduced. Glial fibrillary acidic protein (GFAP) expression revealed less activated astroglia. The number of Purkinje cells/mm(2) significantly increased. While, the number of GFAP positive astrocytes/mm(2) significantly decreased. In addition, the blood glucose level was reduced.

CONCLUSION

Vitamin B complex protected the cerebellum from the histological changes which occurred in STZ- induced diabetic rats.

Astrocytic GAP43 Induced by the TLR4/NF-κB/STAT3 Axis Attenuates Astrogliosis-Mediated Microglial Activation and Neurotoxicity

Growth-associated protein 43 (GAP43), a protein kinase C (PKC)-activated phosphoprotein, is often implicated in axonal plasticity and regeneration. In this study, we found that GAP43 can be induced by the endotoxin lipopolysaccharide (LPS) in rat brain astrocytes both in vivo and in vitro. The LPS-induced astrocytic GAP43 expression was mediated by Toll-like receptor 4 and nuclear factor-κB (NF-κB)- and interleukin-6/signal transducer and activator of transcription 3 (STAT3)-dependent transcriptional activation. The overexpression of the PKC phosphorylation-mimicking GAP43(S41D) (constitutive active GAP43) in astrocytes mimicked LPS-induced process arborization and elongation, while application of a NF-κB inhibitory peptide TAT-NBD or GAP43(S41A) (dominant-negative GAP43) or knockdown of GAP43 all inhibited astrogliosis responses. Moreover, GAP43 knockdown aggravated astrogliosis-induced microglial activation and expression of proinflammatory cytokines. We also show that astrogliosis-conditioned medium from GAP43 knock-down astrocytes inhibited GAP43 phosphorylation and axonal growth, and increased neuronal damage in cultured rat cortical neurons. These proneurotoxic effects of astrocytic GAP43 knockdown were accompanied by attenuated glutamate uptake and expression of the glutamate transporter excitatory amino acid transporter 2 (EAAT2) in LPS-treated astrocytes. The regulation of EAAT2 expression involves actin polymerization-dependent activation of the transcriptional coactivator megakaryoblastic leukemia 1 (MKL1), which targets the serum response elements in the promoter of rat Slc1a2 gene encoding EAAT2. In sum, the present study suggests that astrocytic GAP43 mediates glial plasticity during astrogliosis, and provides beneficial effects for neuronal plasticity and survival and attenuation of microglial activation.

SIGNIFICANCE STATEMENT

Astrogliosis is a complex state in which injury-stimulated astrocytes exert both protective and harmful effects on neuronal survival and plasticity. In this study, we demonstrated for the first time that growth-associated protein 43 (GAP43), a well known growth cone protein that promotes axonal regeneration, can be induced in rat brain astrocytes by the proinflammatory endotoxin lipopolysaccharide via both nuclear factor-κB and signal transducer and activator of transcription 3-mediated transcriptional activation. Importantly, LPS-induced GAP43 mediates plastic changes of astrocytes while attenuating astrogliosis-induced microglial activation and neurotoxicity. Hence, astrocytic GAP43 upregulation may serve to indicate beneficial astrogliosis after CNS injury.

Pneumococcal meningitis is promoted by single cocci expressing pilus adhesin RrgA

Streptococcus pneumoniae (pneumococcus) is the primary cause of bacterial meningitis. Pneumococcal bacteria penetrates the blood-brain barrier (BBB), but the bacterial factors that enable this process are not known. Here, we determined that expression of pneumococcal pilus-1, which includes the pilus adhesin RrgA, promotes bacterial penetration through the BBB in a mouse model. S. pneumoniae that colonized the respiratory epithelium and grew in the bloodstream were chains of variable lengths; however, the pneumococci that entered the brain were division-competent, spherical, single cocci that expressed adhesive RrgA-containing pili. The cell division protein DivIVA, which is required for an ovoid shape, was localized at the poles and septum of pneumococcal chains of ovoid, nonseparated bacteria, but was absent in spherical, single cocci. In the bloodstream, a small percentage of pneumococci appeared as piliated, RrgA-expressing, DivIVA-negative single cocci, suggesting that only a minority of S. pneumoniae are poised to cross the BBB. Together, our data indicate that small bacterial cell size, which is signified by the absence of DivIVA, and the presence of an adhesive RrgA-containing pilus-1 mediate pneumococcal passage from the bloodstream through the BBB into the brain to cause lethal meningitis.

A research update on the potential roles of aquaporin 4 in neuroinflammation

The presence of aquaporins (AQPs) in the brain has led to intense research on the underlying roles of this family of proteins under both normal and pathological conditions. Aquaporin 4 (AQP4) is the major water-channel membrane protein expressed in the central nervous system (CNS), primarily in astrocytes. Emerging evidence suggests that AQP4 could play an important role in water and ion homeostasis in the brain, and it has been studied in various brain pathological conditions. However, far less is known about the potential for AQP4 to influence neuroinflammation and, furthermore, its potential role in neurodegenerative disorders such as Alzheimer's disease (AD). It has been suggested that the pathogenesis of many clinical diseases, such as neuromyelitis optica (NMO), multiple sclerosis (MS) and brain injuries, is related to the regulation of AQP4 expression. Investigating the effects of AQP4 on microglia and astrocytes could be important to understand its role in the pathogenesis of neuroinflammation. Although the exact roles of non-steroidal anti-inflammatory drugs (NSAIDs) in protection against the detrimental effects of neuroinflammation remain unclear, research into the possible neuroprotective effects of AQP4 against neuroinflammation regulation seems to be important for future investigations.

Abnormalities in Diffusional Kurtosis Metrics Related to Head Impact Exposure in a Season of High School Varsity Football

The purpose of this study was to determine whether the effects of cumulative head impacts during a season of high school football produce changes in diffusional kurtosis imaging (DKI) metrics in the absence of clinically diagnosed concussion. Subjects were recruited from a high school football team and were outfitted with the Head Impact Telemetry System (HITS) during all practices and games. Biomechanical head impact exposure metrics were calculated, including: total impacts, summed acceleration, and Risk Weighted Cumulative Exposure (RWE). Twenty-four players completed pre- and post-season magnetic resonance imaging, including DKI; players who experienced clinical concussion were excluded. Fourteen subjects completed pre- and post-season Immediate Post-Concussion Assessment and Cognitive Testing (ImPACT). DKI-derived metrics included mean kurtosis (MK), axial kurtosis (K axial), and radial kurtosis (K radial), and white matter modeling (WMM) parameters included axonal water fraction, tortuosity of the extra-axonal space, extra-axonal diffusivity (D_e axial and radial), and intra-axonal diffusivity (D_a). These metrics were used to determine the total number of abnormal voxels, defined as 2 standard deviations above or below the group mean. Linear regression analysis revealed a statistically significant relationship between RWE combined probability (RWE_CP) and MK. Secondary analysis of other DKI-derived and WMM metrics demonstrated statistically significant linear relationships with RWE_CP after covariate adjustment. These results were compared with the results of DTI-derived metrics from the same imaging sessions in this exact same cohort. Several of the DKI-derived scalars (D_a, MK, K axial, and K radial) explained more variance, compared with RWE_CP, suggesting that DKI may be more sensitive to subconcussive head impacts. No significant relationships between DKI-derived metrics and ImPACT measures were found. It is important to note that the pathological implications of these metrics are not well understood. In summary, we demonstrate a single season of high school football can produce DKI measurable changes in the absence of clinically diagnosed concussion.

Ornithine and Homocitrulline Impair Mitochondrial Function, Decrease Antioxidant Defenses and Induce Cell Death in Menadione-Stressed Rat Cortical Astrocytes: Potential Mechanisms of Neurological Dysfunction in HHH Syndrome

Hyperornithinemia-hyperammonemia-homocitrullinuria (HHH) syndrome is caused by deficiency of ornithine translocase leading to predominant tissue accumulation and high urinary excretion of ornithine (Orn), homocitrulline (Hcit) and ammonia. Although affected patients commonly present neurological dysfunction manifested by cognitive deficit, spastic paraplegia, pyramidal and extrapyramidal signs, stroke-like episodes, hypotonia and ataxia, its pathogenesis is still poorly known. Although astrocytes are necessary for neuronal protection. Therefore, in the present study we investigated the effects of Orn and Hcit on cell viability (propidium iodide incorporation), mitochondrial function (thiazolyl blue tetrazolium bromide-MTT-reduction and mitochondrial membrane potential-ΔΨm), antioxidant defenses (GSH) and pro-inflammatory response (NFkB, IL-1β, IL-6 and TNF-α) in unstimulated and menadione-stressed cortical astrocytes that were previously shown to be susceptible to damage by neurotoxins. We first observed that Orn decreased MTT reduction, whereas both amino acids decreased GSH levels, without altering cell viability and the pro-inflammatory factors in unstimulated astrocytes. Furthermore, Orn and Hcit decreased cell viability and ΔΨm in menadione-treated astrocytes. The present data indicate that the major compounds accumulating in HHH syndrome impair mitochondrial function and reduce cell viability and the antioxidant defenses in cultured astrocytes especially when stressed by menadione. It is presumed that these mechanisms may be involved in the neuropathology of this disease.

Endogenous IL-6 of mesenchymal stem cell improves behavioral outcome of hypoxic-ischemic brain damage neonatal rats by supressing apoptosis in astrocyte

Mesenchymal stem cell (MSC) transplantation reduces the neurological impairment caused by hypoxic-ischemic brain damage (HIBD) via immunomodulation. In the current study, we found that MSC transplantation improved learning and memory function and enhanced long-term potentiation in neonatal rats subjected to HIBD and the amount of IL-6 released from MSCs was far greater than that of other cytokines. However, the neuroprotective effect of MSCs infected with siIL-6-transduced recombinant lentivirus (siIL-6 MSCs) was significantly weakened in the behavioural tests and electrophysiological analysis. Meanwhile, the hippocampal IL-6 levels were decreased following siIL-6 MSC transplantation. In vitro, the levels of IL-6 release and the levels of IL-6R and STAT3 expression were increased in both primary neurons and astrocytes subjected to oxygen and glucose deprivation (OGD) following MSCs co-culture. The anti-apoptotic protein Bcl-2 was upregulated and the pro-apoptotic protein Bax was downregulated in OGD-injured astrocytes co-cultured with MSCs. However, the siIL-6 MSCs suppressed ratio of Bcl-2/Bax in the injured astrocytes and induced apoptosis number of the injured astrocytes. Taken together, these data suggest that the neuroprotective effect of MSC transplantation in neonatal HIBD rats is partly mediated by IL-6 to enhance anti-apoptosis of injured astrocytes via the IL-6/STAT3 signaling pathway.

Recombinant adeno-associated viral (rAAV) vectors mediate efficient gene transduction in cultured neonatal and adult microglia

Microglia are a specialized population of myeloid cells that mediate CNS innate immune responses. Efforts to identify the cellular and molecular mechanisms that regulate microglia behaviors have been hampered by the lack of effective tools for manipulating gene expression. Cultured microglia are refractory to most chemical and electrical transfection methods, yielding little or no gene delivery and causing toxicity and/or inflammatory activation. Recombinant adeno-associated viral (rAAVs) vectors are non-enveloped, single-stranded DNA vectors commonly used to transduce many primary cell types and tissues. In this study, we evaluated the feasibility and efficiency of utilizing rAAV serotype 2 (rAAV2) to modulate gene expression in cultured microglia. rAAV2 yields high transduction and causes minimal toxicity or inflammatory response in both neonatal and adult microglia. To demonstrate that rAAV transduction can induce functional protein expression, we used rAAV2 expressing Cre recombinase to successfully excise a LoxP-flanked miR155 gene in cultured microglia. We further evaluated rAAV serotypes 5, 6, 8, and 9, and observed that all efficiently transduced cultured microglia to varying degrees of success and caused little or no alteration in inflammatory gene expression. These results provide strong encouragement for the application of rAAV-mediated gene expression in microglia for mechanistic and therapeutic purposes. Neonatal microglia are functionally distinct from adult microglia, although the majority of in vitro studies utilize rodent neonatal microglia cultures because of difficulties of culturing adult cells. In addition, cultured microglia are refractory to most methods for modifying gene expression. Here, we developed a novel protocol for culturing adult microglia and evaluated the feasibility and efficiency of utilizing Recombinant Adeno-Associated Virus (rAAV) to modulate gene expression in cultured microglia.

Mechanisms of long-term cognitive dysfunction of sepsis: from blood-borne leukocytes to glial cells

Several mechanisms are associated with brain dysfunction during sepsis; one of the most important are activation of microglia and astrocytes. Activation of glial cells induces changes in permeability of the blood-brain barrier, secretion of inflammatory cytokines, and these alterations could induce neuronal dysfunction. Furthermore, blood-borne leukocytes can also reach the brain and participate in inflammatory response. Mechanisms involved in sepsis-associated brain dysfunction were revised here, focusing in neuroinflammation and involvement of blood-borne leukocytes and glial cells in this process.

Purines in neurite growth and astroglia activation

The mammalian nervous system is a complex, functional network of neurons, consisting of local and long-range connections. Neuronal growth is highly coordinated by a variety of extracellular and intracellular signaling molecules. Purines turned out to be an essential component of these processes. Here, we review the current knowledge about the involvement of purinergic signaling in the regulation of neuronal development. We particularly focus on its role in neuritogenesis: the formation and extension of neurites. In the course of maturation mammals generally lose their ability to regenerate the central nervous system (CNS) e.g. after traumatic brain injury; although, spontaneous regeneration still occurs in the peripheral nervous system (PNS). Thus, it is crucial to translate the knowledge about CNS development and PNS regeneration into novel approaches to enable neurons of the mature CNS to regenerate. In this context we give a general overview of growth-inhibitory and growth-stimulatory factors and mechanisms involved in neurite growth. With regard to neuronal growth, astrocytes are an important cell population. They provide structural and metabolic support to neurons and actively participate in brain signaling. Astrocytes respond to injury with beneficial or detrimental reactions with regard to axonal growth. In this review we present the current knowledge of purines in these glial functions. Moreover, we discuss organotypic brain slice co-cultures as a model which retains neuron-glia interactions, and further presents at once a model for CNS development and regeneration. In summary, the purinergic system is a pivotal factor in neuronal development and in the response to injury. This article is part of the Special Issue entitled 'Purines in Neurodegeneration and Neuroregeneration'.

The role of the surface on microglia function: implications for central nervous system tissue engineering

In tissue engineering, it is well accepted that a scaffold surface has a decisive impact on cell behaviour. Here we focused on microglia-the resident immune cells of the central nervous system (CNS)-and on their response to poly(trimethylene carbonate-co-ε-caprolactone) (P(TMC-CL)) fibrous and flat surfaces obtained by electrospinning and solvent cast, respectively. This study aims to provide cues for the design of instructive surfaces that can contribute to the challenging process of CNS regeneration. Cell morphology was evidently affected by the substrate, mirroring the surface main features. Cells cultured on flat substrates presented a round shape, while cells with elongated processes were observed on the electrospun fibres. A higher concentration of the pro-inflammatory cytokine tumour necrosis factor-α was detected in culture media from microglia on fibres. Still, astrogliosis is not exacerbated when astrocytes are cultured in the presence of microglia-conditioned media obtained from cultures in contact with either substrate. Furthermore, a significant percentage of microglia was found to participate in the process of myelin phagocytosis, with the formation of multinucleated giant cells being observed only on films. Altogether, the results presented suggest that microglia in contact with the tested substrates may contribute to the regeneration process, putting forward P(TMC-CL) substrates as supporting matrices for nerve regeneration.

Neuroprotective effects of nitidine against traumatic CNS injury via inhibiting microglia activation

Glial cell response to injury has been well documented in the pathogenesis after traumatic brain injury (TBI) and spinal cord injury (SCI). Although microglia, the resident macrophages in the central nervous system (CNS), are responsible for clearing debris and toxic substances, excessive activation of these cells will lead to exacerbated secondary damage by releasing a variety of inflammatory and cytotoxic mediators and ultimately influence the subsequent repair after CNS injury. In fact, inhibition of microgliosis represents a therapeutic strategy for CNS trauma. We here showed that nitidine, a benzophenanthridine alkaloid, restricted reactive microgliosis and promoted CNS repair after traumatic injury. Nitidine was shown to prevent cultured microglia from LPS-induced reactive activation by regulation of ERK and NF-κB signaling pathway. Furthermore, the nitidine-mediated inhibition of microgliosis was also shown in injured brain and spinal cord, which significantly increased neuronal survival and decreased neural tissue damage after injury. Importantly, behavioral analysis revealed that nitidine-treated mice with SCI had improved functional recovery as assessed by Basso Mouse Scale and swimming test. Together, these findings indicated that nitidine increased CNS tissue sparing and improved functional recovery by attenuating reactive microgliosis, suggestive of the potential therapeutic benefit for CNS injury.

Lipoic acid and pentoxifylline mitigate nandrolone decanoate-induced neurobehavioral perturbations in rats via re-balance of brain neurotransmitters, up-regulation of Nrf2/HO-1 pathway, and down-regulation of TNFR1 expression

Behavioral perturbations associated with nandrolone decanoate abuse by athletes and adolescents may be attributed to oxidative stress and inflammation. However, the underlying mechanisms are not yet fully explored. On the other hand, the natural antioxidant lipoic acid can pass the blood brain barrier and enhance Nrf2/HO-1 (nuclear factor erythroid-2 related factor 2/heme oxygenase-1) pathway. In addition, the phosphodiesterase-IV inhibitor xanthine derivative pentoxifylline has a remarkable inhibitory effect on tumor necrosis factor-alpha (TNF-α). Therefore, this study aimed at investigation of the possible protective effects of lipoic acid and/or pentoxifylline against nandrolone-induced neurobehavioral alterations in rats. Accordingly, male albino rats were randomly distributed into seven groups and treated with either vehicle, nandrolone (15mg/kg, every third day, s.c.), lipoic acid (100mg/kg/day, p.o.), pentoxifylline (200mg/kg/day, i.p.), or nandrolone with lipoic acid and/or pentoxifylline. Rats were challenged in the open field, rewarded T-maze, Morris water maze, and resident-intruder aggression behavioral tests. The present findings showed that nandrolone induced hyperlocomotion, anxiety, memory impairment, and aggression in rats. These behavioral abnormalities were accompanied by several biochemical changes, including altered levels of brain monoamines, GABA, and acetylcholine, enhanced levels of malondialdehyde and TNF-α, elevated activity of acetylcholinesterase, and up-regulated expression of TNF-α receptor-1 (TNFR1). In addition, inhibited catalase activity, down-regulated Nrf2/HO-1 pathway, and suppressed acetylcholine receptor expression were observed. Lipoic acid and pentoxifylline combination significantly mitigated all the previously mentioned deleterious effects mainly via up-regulation of Nrf2/HO-1 pathway, inhibition of TNF-α and down-regulation of TNFR1 expression. In conclusion, the biochemical and histopathological findings of this study revealed the protective mechanisms of lipoic acid and pentoxifylline against nandrolone-induced behavioral changes and neurotoxicity in rats.

Induction of a Proinflammatory Response in Cortical Astrocytes by the Major Metabolites Accumulating in HMG-CoA Lyase Deficiency: the Role of ERK Signaling Pathway in Cytokine Release

3-Hydroxy-3-methylglutaric aciduria (HMGA) is an inherited metabolic disorder caused by 3-hydroxy-3-methylglutaryl-CoA lyase deficiency. It is biochemically characterized by predominant tissue accumulation and high urinary excretion of 3-hydroxy-3-methylglutarate (HMG) and 3-methylglutarate (MGA). Affected patients commonly present acute symptoms during metabolic decompensation, including vomiting, seizures, and lethargy/coma accompanied by metabolic acidosis and hypoketotic hypoglycemia. Although neurological manifestations are common, the pathogenesis of brain injury in this disease is poorly known. Astrocytes are important for neuronal protection and are susceptible to damage by neurotoxins. In the present study, we investigated the effects of HMG and MGA on important parameters of redox homeostasis and cytokine production in cortical cultured astrocytes. The role of the metabolites on astrocyte mitochondrial function (thiazolyl blue tetrazolium bromide (MTT) reduction) and viability (propidium iodide incorporation) was also studied. Both organic acids decreased astrocytic mitochondrial function and the concentrations of reduced glutathione without altering cell viability. In contrast, they increased reactive species formation (2'-7'-dichlorofluorescein diacetate (DCFHDA) oxidation), as well as IL-1β, IL-6, and TNF α release through the ERK signaling pathway. Taken together, the data indicate that the principal compounds accumulating in HMGA induce a proinflammatory response in cultured astrocytes that may possibly be involved in the neuropathology of this disease.

Mass Spectrometry in Pharmacokinetic Studies of a Synthetic Compound for Spinal Cord Injury Treatment

The studies of drugs that could constitute a palliative to spinal cord injury (SCI) are a continuous and increasing demand in biomedicine field from developed societies. Recently we described the chemical synthesis and antiglioma activity of synthetic glycosides. A synthetic sulfated glycolipid (here IG20) has shown chemical stability, solubility in polar solvents, and high inhibitory capacity over glioma growth. We have used mass spectrometry (MS) to monitor IG20 (m/z = 550.3) in cells and tissues of the central nervous system (CNS) that are involved in SCI recovery. IG20 was detected by MS in serum and homogenates from CNS tissue of rats, though in the latter a previous deproteinization step was required. The pharmacokinetic parameters of serum clearance at 24 h and half-life at 4 h were determined for synthetic glycoside in the adult rat using MS. A local administration of the drug near of spinal lesion site is proposed.

Emerging pharmacotherapy for treatment of traumatic brain injury: targeting hypopituitarism and inflammation

INTRODUCTION

Traumatic brain injury (TBI) is a common cause of morbidity and mortality in the developed world. In particular, TBI is an important cause of death and disability in young adults with consequences ranging from physical disabilities to long-term cognitive, behavioural, psychological and social defects.

AREAS COVERED

There is a large body of evidence that suggest that TBI conditions may adversely affect pituitary function in both the acute and chronic phases of recovery. Prevalence of hypopituitarism, from total to isolated pituitary deficiency, ranges from 5 to 90%. The time interval between TBI and pituitary function evaluation is one of the major factors responsible for variations in the prevalence of hypopituitarism reported. Diagnosis of hypopituitarism and accurate treatment of pituitary disorders offers the opportunity to improve mortality and outcome in TBI conditions.

EXPERT OPINION

The aim of this paper is to review the history and pathophysiology of TBI and to summarize the best evidence of TBI as a cause of pituitary deficiency. Moreover, in this article we will describe the multiple changes which occur within the hypothalamic-pituitary-thyroid axis in critical illness, giving rise to 'sick euthyroid syndrome', focus our attention on thyroid hormones circulating levels from the initial insult to critical illness.

Histological and immunohistochemical study of the effect of gold nanoparticles on the brain of adult male albino rat

Gold nanoparticles (GNPs) have numerous medical applications as in biological imaging, cancer treatment and in implants (pacemakers and stents). Many conflicting results about GNPs safety and its accumulation in liver, kidney and brain were recorded. This work was carried out to study the histological effect of long period exposure to gold nanoparticle on the brain of adult male albino rat. Twenty adult male albino rats were divided into two equal groups: The first one served as a control group and the second one received 400 μg/kg/day GNPs by gastric tube once daily for eight weeks. Brain specimens were collected at the end of the experiment for histological and immunohistochemical studies using caspase-3 and glial fibrillary acidic protein (GFAP). GNPs treated group revealed wide spread histological alterations and deposition of gold nanoparticle aggregates in the neurons of cerebral cortex and hippocampus and also in the epithelium of choroid plexus with hyalinization of the wall of some blood vessels and disruption of the capillaries. All these changes were associated with localized positive caspase 3 reaction. Various degrees of astrogliosis were evidenced by astrocytic proliferation and increase size of their cell body with increase number and length of their processes. It could be concluded that repeated exposure of adult male albino rats to gold nanoparticles induced its deposition in the brain in association with histological alterations and various degrees of astrogliosis.

Cyclohexane produces behavioral deficits associated with astrogliosis and microglial reactivity in the adult hippocampus mouse brain

Cyclohexane is a volatile substance that has been utilized as a safe substitute of several organic solvents in diverse industrial processes, such as adhesives, paints, paint thinners, fingernail polish, lacquers, and rubber industry. A number of these commercial products are ordinarily used as inhaled drugs. However, it is not well known whether cyclohexane has noxious effects in the central nervous system. The aim of this study was to analyze the effects of cyclohexane inhalation on motor behavior, spatial memory, and reactive gliosis in the hippocampus of adult mice. We used a model that mimics recreational drug use in male Balb/C mice (P60), divided into two groups: controls and the cyclohexane group (exposed to 9,000 ppm of cyclohexane for 30 days). Both groups were then evaluated with a functional observational battery (FOB) and the Morris water maze (MWM). Furthermore, the relative expression of AP endonuclease 1 (APE1), and the number of astrocytes (GFAP+ cells) and microglia (Iba1+ cells) were quantified in the hippocampal CA1 and CA3 areas. Our findings indicated that cyclohexane produced severe functional deficits during a recreational exposure as assessed by the FOB. The MWM did not show statistically significant changes in the acquisition and retention of spatial memory. Remarkably, a significant increase in the number of astrocytes and microglia cells, as well as in the cytoplasmic processes of these cells were observed in the hippocampal CA1 and CA3 areas of cyclohexane-exposed mice. This cellular response was associated with an increase in the expression of APE1 in the same brain regions. In summary, cyclohexane exposure produces functional deficits that are associated with an important increase in the APE1 expression as well as the number of astrocytes and microglia cells and their cytoplasmic complexity in the CA1 and CA3 regions of the adult hippocampus.

Hyperbaric oxygen effects on neuronal apoptosis associations in a traumatic brain injury rat model

BACKGROUND

The neuroprotective mechanisms of hyperbaric oxygen (HBO) therapy on traumatic brain injury (TBI) remain unclear, especially neuronal apoptosis associations such as the expression of tumor necrosis factor alpha (TNF-α), transforming growth-interacting factor (TGIF), and TGF-β1 after TBI. The aim of this study was to investigate the neuroprotective effects of HBO therapy in a rat model of TBI.

MATERIALS AND METHODS

The experimental rats were randomly divided into three groups as follows: TBI + normobaric air (21% O₂ at one absolute atmosphere), TBI + HBO, and sham-operated normobaric air. The TBI + HBO rats received 100% O₂ at 2.0 absolute atmosphere for 1 h immediately after TBI. Local and systemic TNF-α expression, neuropathology, levels of the neuronal apoptosis-associated proteins TGIF and TGF-β1, and functional outcome were evaluated 72 h after the onset of TBI.

RESULTS

Compared to the TBI control groups, the running speed of rats on the TreadScan after TBI was significantly attenuated by HBO therapy. The TBI-induced local and systemic TNF-α expression, neuronal damage score, and neuronal apoptosis were also significantly reduced by HBO therapy. Moreover, HBO treatment attenuated the expression of TGIF but increased TGF-β1 expression in neurons.

CONCLUSIONS

We concluded that treatment of TBI with HBO during the acute phase of injury can decrease local and systemic proinflammatory cytokine TNF-α production, resulting in neuroprotective effects. We also suggest that decreased levels of TGIF and increased levels of TGF-β in the injured cortex leading to decreased neuronal apoptosis is one mechanism by which functional recovery may occur.

A novel pathogenic mechanism for cerebellar lesions produced by Solanum bonariense in cattle

Intoxication with Solanum bonariense in cattle causes cerebellar cortical degeneration with perikaryal vacuolation, axonal swelling, and death primarily of Purkinje cells, with accumulation of electron-dense residual storage bodies in membrane-bound vesicles. The pathogenesis of this disease is not fully understood. Previously, we proposed that inhibition of protein synthesis in Purkinje cells among other altered metabolic pathways could lead to cytoskeletal alterations, subsequently altering cell-specific axonal transport. In the present study, immunohistochemical and histochemical methods were used to identify neuronal cytoskeletal alterations and axonal loss, demyelination, and astrogliosis in the cerebellum of intoxicated bovines. Samples of cerebellum from 3 natural and 4 experimental cases and 2 control bovines were studied. Immunoreactivity against neurofilament (NF)-200KDa confirmed marked loss of Purkinje neurons, and phospho-NF protein, β-tubulin, and affinity reaction against phalloidin revealed an altered perikaryal distribution of neuronal cytoskeletal proteins in the remaining Purkinje cells in intoxicated cattle. Reactive astrogliosis in every layer of the cerebellar cortex was also observed with anti-glial fibrillary acidic protein immunohistochemistry. In affected cattle, demyelination and axonal loss in the cerebellar white matter, as well as basket cell loss were demonstrated with Klüver-Barrera and Bielschowsky stains, respectively. Based on these results, we propose that neuronal cytoskeletal alterations with subsequent interference of the axonal transport in Purkinje cells may play a relevant role in the pathogenesis of this neurodegenerative disorder, and also that demyelination and axonal loss in the cerebellar white matter, as well as astrogliosis in the gray matter, likely occur secondarily to Purkinje cell degeneration and death.

The degeneration of dopaminergic synapses in Parkinson's disease: A selective animal model

Available evidence increasingly suggests that the degeneration of dopamine neurons in Parkinson's disease starts in the striatal axons and synaptic terminals. A selective procedure is described here to study the mechanisms involved in the striatal denervation of dopaminergic terminals. This procedure can also be used to analyze mechanisms involved in the dopaminergic re-innervation of the striatum, and the role of astrocytes and microglia in both processes. Adult Sprague-Dawley rats were injected in the lateral ventricles with increasing doses of 6-hydroxydopamine (12-50 μg), which generated a dose-dependent loss of dopaminergic synapses and axons in the striatum, followed by an axonal sprouting (weeks later) and by a progressive recovery of striatal dopaminergic synapses (months later). Both the degeneration and regeneration of the dopaminergic terminals were accompanied by astrogliosis. Because the experimental manipulations did not induce unspecific damage in the striatal tissue, this method could be particularly suitable to study the basic mechanisms involved in the distal degeneration and regeneration of dopaminergic nigrostriatal neurons, and the possible role of astrocytes and microglia in the dynamics of both processes.

Microglial Heparan Sulfate Proteoglycans Facilitate the Cluster-of-Differentiation 14 (CD14)/Toll-like Receptor 4 (TLR4)-Dependent Inflammatory Response

Microglia rapidly mount an inflammatory response to pathogens in the central nervous system (CNS). Heparan sulfate proteoglycans (HSPGs) have been attributed various roles in inflammation. To elucidate the relevance of microglial HSPGs in a pro-inflammatory response we isolated microglia from mice overexpressing heparanase (Hpa-tg), the HS-degrading endoglucuronidase, and challenged them with lipopolysaccharide (LPS), a bacterial endotoxin. Prior to LPS-stimulation, the LPS-receptor cluster-of-differentiation 14 (CD14) and Toll-like receptor 4 (TLR4; essential for the LPS response) were similarly expressed in Ctrl and Hpa-tg microglia. However, compared with Ctrl microglia, Hpa-tg cells released significantly less tumor necrosis factor-α (TNFα), essentially failed to up-regulate interleukin-1β (IL1β) and did not initiate synthesis of proCD14. Isolated primary astroyctes expressed TLR4, but notably lacked CD14 and in contrast to microglia, LPS challenge induced a similar TNFα response in Ctrl and Hpa-tg astrocytes, while neither released IL1β. The astrocyte TNFα-induction was thus attributed to CD14-independent TLR4 activation and was unaffected by the cells HS status. Equally, the suppressed LPS-response in Hpa-tg microglia indicated a loss of CD14-dependent TLR4 activation, suggesting that microglial HSPGs facilitate this process. Indeed, confocal microscopy confirmed interactions between microglial HS and CD14 in LPS-stimulated microglia and a potential HS-binding motif in CD14 was identified. We conclude that microglial HSPGs facilitate CD14-dependent TLR4 activation and that heparanase can modulate this mechanism.

Astrocyte heterogeneity in the brain: from development to disease

In the last decades, astrocytes have risen from passive supporters of neuronal activity to central players in brain function and cognition. Likewise, the heterogeneity of astrocytes starts to become recognized in contrast to the homogeneous population previously predicted. In this review, we focused on astrocyte heterogeneity in terms of their morphological, protein expression and functional aspects, and debate in a historical perspective the diversity encountered in glial progenitors and how they may reflect mature astrocyte heterogeneity. We discussed data that show that different progenitors may have unsuspected roles in developmental processes. We have approached the functions of astrocyte subpopulations on the onset of psychiatric and neurological diseases.

Recent advances in methamphetamine neurotoxicity mechanisms and its molecular pathophysiology

Methamphetamine (METH) is a sympathomimetic amine that belongs to phenethylamine and amphetamine class of psychoactive drugs, which are widely abused for their stimulant, euphoric, empathogenic, and hallucinogenic properties. Many of these effects result from acute increases in dopamine and serotonin neurotransmission. Subsequent to these acute effects, METH produces persistent damage to dopamine and serotonin release in nerve terminals, gliosis, and apoptosis. This review summarized the numerous interdependent mechanisms including excessive dopamine, ubiquitin-proteasome system dysfunction, protein nitration, endoplasmic reticulum stress, p53 expression, inflammatory molecular, D₃ receptor, microtubule deacetylation, and HIV-1 Tat protein that have been demonstrated to contribute to this damage. In addition, the feasible therapeutic strategies according to recent studies were also summarized ranging from drug and protein to gene level.