Quantitative aspects of reactive gliosis: a review

P2Y2 receptor-Gq/11 signaling at lipid rafts is required for UTP-induced cell migration in NG 108-15 cells

Lipid rafts, formed by sphingolipids and cholesterol within the membrane bilayer, are believed to have a critical role in signal transduction. P2Y(2) receptors are known to couple with G(q) family G proteins, causing the activation of phospholipase C (PLC) and an increase in intracellular Ca(2+) ([Ca(2+)](i)) levels. In the present study, we investigated the involvement of lipid rafts in P2Y(2) receptor-mediated signaling and cell migration in NG 108-15 cells. When NG 108-15 cell lysates were fractionated by sucrose density gradient centrifugation, Galpha(q/11) and a part of P2Y(2) receptors were distributed in a fraction where the lipid raft markers, cholesterol, flotillin-1, and ganglioside GM1 were abundant. Methyl-beta-cyclodextrin (CD) disrupted not only lipid raft markers but also Galpha(q/11) and P2Y(2) receptors in this fraction. In the presence of CD, P2Y(2) receptor-mediated phosphoinositide hydrolysis and [Ca(2+)](i) elevation were inhibited. It is noteworthy that UTP-induced cell migration was inhibited by CD or the G(q/11)-selective inhibitor YM254890 [(1R)-1-{(3S,6S,9S,12S,18R,21S,22R)-21-acetamido-18-benzyl-3-[(1R)-1-methoxyethyl]-4,9,10,12,16, 22-hexamethyl-15-methylene-2,5,8,11,14,17,-20-heptaoxo-1,19-dioxa-4,7,10,13,16-pentaazacyclodocosan-6-yl}-2-methylpropyl rel-(2S,3R)-2-acetamido-3-hydroxy-4-methylpentanoate]. Moreover CD and YM254890 completely inhibited Rho-A activation. Downstream of Rho-A signaling, stress fiber formation and phosphorylation of cofilin were also inhibited by CD or YM254890. However, UTP-induced phosphorylation of cofilin was not affected by the expression of p115-regulator of G protein signaling, which inhibits the G(12/13) signaling pathway. This implies that UTP-induced Rho-A activation was relatively regulated by the G(q/11) signaling pathway. These results suggest that lipid rafts are critical for P2Y(2) receptor-mediated G(q/11)-PLC-Ca(2+) signaling and this cascade is important for cell migration in NG 108-15 cells.

Beta-catenin signaling increases in proliferating NG2+ progenitors and astrocytes during post-traumatic gliogenesis in the adult brain

Wnt/beta-catenin signaling can influence the proliferation and differentiation of progenitor populations in the hippocampus and subventricular zone, known germinal centers in the adult mouse brain. It is not known whether beta-catenin signaling occurs in quiescent glial progenitors in cortex or spinal cord, nor is it known whether beta-catenin is involved in the activation of glial progenitor populations after injury. Using a beta-catenin reporter mouse (BATGAL mouse), we show that beta-catenin signaling occurs in NG2 chondroitin sulfate proteoglycan+ (NG2) progenitors in the cortex, in subcallosal zone (SCZ) progenitors, and in subependymal cells surrounding the central canal. Interestingly, cells with beta-catenin signaling increased in the cortex and SCZ following traumatic brain injury (TBI) but did not following spinal cord injury. Initially after TBI, beta-catenin signaling was predominantly increased in a subset of NG2+ progenitors in the cortex. One week following injury, the majority of beta-catenin signaling appeared in reactive astrocytes but not oligodendrocytes. Bromodeoxyuridine (BrdU) paradigms and Ki-67 staining showed that the increase in beta-catenin signaling occurred in newly born cells and was sustained after cell division. Dividing cells with beta-catenin signaling were initially NG2+; however, by four days after a single injection of BrdU, they were predominantly astrocytes. Infusing animals with the mitotic inhibitor cytosine arabinoside prevented the increase of beta-catenin signaling in the cortex, confirming that the majority of beta-catenin signaling after TBI occurs in newly born cells. These data argue for manipulating the Wnt/beta-catenin pathway after TBI as a way to modify post-traumatic gliogenesis.

GFAP expression in the rat brain following sub-chronic exposure to a 900 MHz electromagnetic field signal

PURPOSE

The rapid development and expansion of mobile communications contributes to the general debate on the effects of electromagnetic fields emitted by mobile phones on the nervous system. This study aims at measuring the glial fibrillary acidic protein (GFAP) expression in 48 rat brains to evaluate reactive astrocytosis, three and 10 days after long-term head-only sub-chronic exposure to a 900 MHz electromagnetic field (EMF) signal, in male rats.

METHODS

Sprague-Dawley rats were exposed for 45 min/day at a brain-averaged specific absorption rate (SAR) = 1.5 W/kg or 15 min/day at a SAR = 6 W/kg for five days per week during an eight-week period. GFAP expression was measured by the immunocytochemistry method in the following rat brain areas: Prefrontal cortex, cerebellar cortex, dentate gyrus of the hippocampus, lateral globus pallidus of the striatum, and the caudate putamen.

RESULTS

Compared to the sham-treated rats, those exposed to the sub-chronic GSM (Global System for mobile communications) signal at 1.5 or 6 W/kg showed an increase in GFAP levels in the different brain areas, three and ten days after treatment.

CONCLUSION

Our results show that sub-chronic exposures to a 900 MHz EMF signal for two months could adversely affect rat brain (sign of a potential gliosis).

P2Y2 nucleotide receptor-mediated responses in brain cells

Acute inflammation is important for tissue repair; however, chronic inflammation contributes to neurodegeneration in Alzheimer's disease (AD) and occurs when glial cells undergo prolonged activation. In the brain, stress or damage causes the release of nucleotides and activation of the G(q) protein-coupled P2Y(2) nucleotide receptor subtype (P2Y(2)R) leading to pro-inflammatory responses that can protect neurons from injury, including the stimulation and recruitment of glial cells. P2Y(2)R activation induces the phosphorylation of the epidermal growth factor receptor (EGFR), a response dependent upon the presence of a SH3 binding domain in the intracellular C terminus of the P2Y(2)R that promotes Src binding and transactivation of EGFR, a pathway that regulates the proliferation of cortical astrocytes. Other studies indicate that P2Y(2)R activation increases astrocyte migration. P2Y(2)R activation by UTP increases the expression in astrocytes of alpha(V)beta(3/5) integrins that bind directly to the P2Y(2)R via an Arg-Gly-Asp (RGD) motif in the first extracellular loop of the P2Y(2)R, an interaction required for G(o) and G(12) protein-dependent astrocyte migration. In rat primary cortical neurons (rPCNs) P2Y(2)R expression is increased by stimulation with interleukin-1beta (IL-1beta), a pro-inflammatory cytokine whose levels are elevated in AD, in part due to nucleotide-stimulated release from glial cells. Other results indicate that oligomeric beta-amyloid peptide (Abeta(1-42)), a contributor to AD, increases nucleotide release from astrocytes, which would serve to activate upregulated P2Y(2)Rs in neurons. Data with rPCNs suggest that P2Y(2)R upregulation by IL-1beta and subsequent activation by UTP are neuroprotective, since this increases the non-amyloidogenic cleavage of amyloid precursor protein. Furthermore, activation of IL-1beta-upregulated P2Y(2)Rs in rPCNs increases the phosphorylation of cofilin, a cytoskeletal protein that stabilizes neurite outgrowths. Thus, activation of pro-inflammatory P2Y(2)Rs in glial cells can promote neuroprotective responses, suggesting that P2Y(2)Rs represent a novel pharmacological target in neurodegenerative and other pro-inflammatory diseases.

EphA4 deficient mice maintain astroglial-fibrotic scar formation after spinal cord injury

One important aspect of recovery and repair after spinal cord injury (SCI) lies in the complex cellular interactions at the injury site that leads to the formation of a lesion scar. EphA4, a promiscuous member of the EphA family of repulsive axon guidance receptors, is expressed by multiple cell types in the injured spinal cord, including astrocytes and neurons. We hypothesized that EphA4 contributes to aspects of cell-cell interactions at the injury site after SCI, thus modulating the formation of the astroglial-fibrotic scar. To test this hypothesis, we studied tissue responses to a thoracic dorsal hemisection SCI in an EphA4 mutant mouse line. We found that EphA4 expression, as assessed by beta-galactosidase reporter gene activity, is associated primarily with astrocytes in the spinal cord, neurons in the cerebral cortex and, to a lesser extent, spinal neurons, before and after SCI. However, we did not observe any overt reduction of glial fibrillary acidic protein (GFAP) expression in the injured area of EphA4 mutants in comparison with controls following SCI. Furthermore, there was no evident disruption of the fibrotic scar, and the boundary between reactive astrocytes and meningeal fibroblasts appeared unaltered in the mutants, as were lesion size, neuronal survival and inflammation marker expression. Thus, genetic deletion of EphA4 does not significantly alter the astroglial response or the formation of the astroglial-fibrotic scar following a dorsal hemisection SCI in mice. In contrast to what has been proposed, these data do not support a major role for EphA4 in reactive astrogliosis following SCI.

Chronic ethanol-induced glial fibrillary acidic protein (GFAP) immunoreactivity: an immunocytochemical observation in various regions of adult rat brain

In the present study, the effects of chronic ethanol (ETOH) treatment on the glial fibrillary acidic protein (GFAP) immunoreactivity was investigated in adult rat brains. ETOH were administered as increasing concentrations of 2.4%-7.2% (v/v) gradually for 21 days. Immunocytochemistry revealed that chronic-ETOH treatment increased synthesis of GFAP. The increase in the diameter and the number of GFAP (+) cells were statistically significant compared with the control group (p <. 05). An increase of GFAP immunoreactivity was evident in various white matter and gray matter structures. We concluded that functional astrocytic cells responded to chronic ETOH exposure by increasing the synthesis of GFAP.

Astrocytes: biology and pathology

Astrocytes are specialized glial cells that outnumber neurons by over fivefold. They contiguously tile the entire central nervous system (CNS) and exert many essential complex functions in the healthy CNS. Astrocytes respond to all forms of CNS insults through a process referred to as reactive astrogliosis, which has become a pathological hallmark of CNS structural lesions. Substantial progress has been made recently in determining functions and mechanisms of reactive astrogliosis and in identifying roles of astrocytes in CNS disorders and pathologies. A vast molecular arsenal at the disposal of reactive astrocytes is being defined. Transgenic mouse models are dissecting specific aspects of reactive astrocytosis and glial scar formation in vivo. Astrocyte involvement in specific clinicopathological entities is being defined. It is now clear that reactive astrogliosis is not a simple all-or-none phenomenon but is a finely gradated continuum of changes that occur in context-dependent manners regulated by specific signaling events. These changes range from reversible alterations in gene expression and cell hypertrophy with preservation of cellular domains and tissue structure, to long-lasting scar formation with rearrangement of tissue structure. Increasing evidence points towards the potential of reactive astrogliosis to play either primary or contributing roles in CNS disorders via loss of normal astrocyte functions or gain of abnormal effects. This article reviews (1) astrocyte functions in healthy CNS, (2) mechanisms and functions of reactive astrogliosis and glial scar formation, and (3) ways in which reactive astrocytes may cause or contribute to specific CNS disorders and lesions.

Acute glial activation by stab injuries does not lead to overt damage or motor neuron degeneration in the G93A mutant SOD1 rat model of amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease where motor neurons within the brain and spinal cord are lost, leading to paralysis and death. Recently, a correlation between head trauma and the incidence of ALS has been reported. Furthermore, new invasive neurosurgical studies are being planned which involve inserting needles directly to the spinal cord. We therefore tested whether acute trauma to the spinal cord via a knife wound injury would lead to accelerated disease progression in rodent models of ALS (SOD1(G93A) rats). A longitudinal stab injury using a small knife was performed within the lumbar spinal cord region of presymptomatic SOD1(G93A) rats. Host glial activation was detected in the lumbar area surrounding a micro-knife lesion at 2 weeks after surgery in both wild type and SOD1(G93A) animals. However, there was no sign of motor neuron loss in the injured spinal cord of any animal and normal motor function was maintained in the ipsilateral limb. These results indicate that motor neurons in presymptomatic G93A animals are not affected by an invasive puncture wound injury involving reactive astrocytes. Furthermore, acute trauma alone does not accelerate disease onset or progression in this ALS model which is important for future strategies of gene and cell therapies directly targeting the spinal cord of ALS patients.

Effects of dietary restriction on mortality and age-related phenotypes in the short-lived fish Nothobranchius furzeri

The short-lived annual fish Nothobranchius furzeri shows extremely short captive life span and accelerated expression of age markers, making it an interesting model system to investigate the effects of experimental manipulations on longevity and age-related pathologies. Here, we tested the effects of dietary restriction (DR) on mortality and age-related markers in N. furzeri. DR was induced by every other day feeding and the treatment was performed both in an inbred laboratory line and a longer-lived wild-derived line. In the inbred laboratory line, DR reduced age-related risk and prolonged maximum life span. In the wild-derived line, DR induced early mortality, did not reduce general age-related risk and caused a small but significant extension of maximum life span. Analysis of age-dependent mortality revealed that DR reduced demographic rate of aging, but increased baseline mortality in the wild-derived strain. In both inbred- and wild-derived lines, DR prevented the expression of the age markers lipofuscin in the liver and Fluoro-Jade B (neurodegeneration) in the brain. DR also improved performance in a learning test based on conditioning (active avoidance in a shuttle box). Finally, DR induced a paradoxical up-regulation of glial fibrillary acidic protein in the brain.

Consumption of green tea alters glial fibriliary acidic protein immunoreactivity in the spinal cord astrocytes of STZ-diabetic rats

We examined the effect of green tea consumption on glial fibriliary acidic protein (GFAP) expression in spinal cord of streptozotocin (STZ) treated rats. Three groups (n = 10) were used in this study: (i) controls; (ii) STZ-induced diabetic rats given tap water; and (iii) an STZ-induced diabetic group given green tea. Immunohistochemistry showed a significant (P < 0.001) decrease in the number of GFAP immunoreactive astrocytes in spinal cord sections of diabetic rats compared to non-diabetic controls. Diabetic rats treated with green tea showed a significant (P < 0.01) increase in the number GFAP-immunoreactive astrocytes in all the spinal cord gray areas as compared to water-drinking diabetic rats. Immunoblotting confirmed that the diabetic spinal cord tissue expressed 71.0 +/- 7.0% less GFAP compared to non-diabetic controls and that the GFAP content in diabetic rats increased up to 86.34 +/- 18.74% compared to non-diabetic controls after 12 weeks of green tea consumption. In conclusion, consumption of green tea may represent an achievable adjunct therapy for improving changes seen in diabetic spinal cord.

Local exposure of 849 MHz and 1763 MHz radiofrequency radiation to mouse heads does not induce cell death or cell proliferation in brain

Even though there is no direct evidence to prove the cellular and molecular changes induced by radiofrequency (RF) radiation itself, we cannot completely exclude the possibility of any biological effect of mobile phone frequency radiation. We established a carousel-type exposure chamber for 849 MHz or 1763 MHz of mobile phone RF radiation to expose RF to the heads of C57BL mice. In this chamber, animals were irradiated intermittently at 7.8 W/kg for a maximum of 12 months. During this period, the body weights of 3 groups-sham, 849 MHz RF, and 1763 MHz RF-did not show any differences between groups. The brain tissues were obtained from 3 groups at 6 months and 12 months to examine the differences in histology and cell proliferation between control and RF exposure groups, but we could not find any change upon RF radiation. Likewise, we could not find changes in the expression and distribution of NeuN and GFAP in hippocampus and cerebellum, or in cell death by TUNEL assay in RF exposure groups. From these data, we conclude that the chronic exposure to 849 MHz and 1763 MHz RF radiation at a 7.8 W/kg specific absorption rate (SAR) could not induce cellular alterations such as proliferation, death, and reactive gliosis.

Acute methamphetamine intoxication: brain hyperthermia, blood-brain barrier, brain edema, and morphological cell abnormalities

Methamphetamine (METH) is a powerful and often abused stimulant with potent addictive and neurotoxic properties. While it is generally assumed that multiple chemical substances released in the brain following METH-induced metabolic activation (or oxidative stress) are primary factors underlying damage of neural cells, in this work we present data suggesting a role of brain hyperthermia and associated leakage of the blood-brain barrier (BBB) in acute METH-induced toxicity. First, we show that METH induces a dose-dependent brain and body hyperthermia, which is strongly potentiated by associated physiological activation and in warm environments that prevent proper heat dissipation to the external environment. Second, we demonstrate that acute METH intoxication induces robust, widespread but structure-specific leakage of the BBB, acute glial activation, and increased water content (edema), which are related to drug-induced brain hyperthermia. Third, we document widespread morphological abnormalities of brain cells, including neurons, glia, epithelial, and endothelial cells developing rapidly during acute METH intoxication. These structural abnormalities are tightly related to the extent of brain hyperthermia, leakage of the BBB, and brain edema. While it is unclear whether these rapidly developed morphological abnormalities are reversible, this study demonstrates that METH induces multiple functional and structural perturbations in the brain, determining its acute toxicity and possibly contributing to neurotoxicity.

Diffusion in brain extracellular space

Diffusion in the extracellular space (ECS) of the brain is constrained by the volume fraction and the tortuosity and a modified diffusion equation represents the transport behavior of many molecules in the brain. Deviations from the equation reveal loss of molecules across the blood-brain barrier, through cellular uptake, binding, or other mechanisms. Early diffusion measurements used radiolabeled sucrose and other tracers. Presently, the real-time iontophoresis (RTI) method is employed for small ions and the integrative optical imaging (IOI) method for fluorescent macromolecules, including dextrans or proteins. Theoretical models and simulations of the ECS have explored the influence of ECS geometry, effects of dead-space microdomains, extracellular matrix, and interaction of macromolecules with ECS channels. Extensive experimental studies with the RTI method employing the cation tetramethylammonium (TMA) in normal brain tissue show that the volume fraction of the ECS typically is approximately 20% and the tortuosity is approximately 1.6 (i.e., free diffusion coefficient of TMA is reduced by 2.6), although there are regional variations. These parameters change during development and aging. Diffusion properties have been characterized in several interventions, including brain stimulation, osmotic challenge, and knockout of extracellular matrix components. Measurements have also been made during ischemia, in models of Alzheimer's and Parkinson's diseases, and in human gliomas. Overall, these studies improve our conception of ECS structure and the roles of glia and extracellular matrix in modulating the ECS microenvironment. Knowledge of ECS diffusion properties is valuable in contexts ranging from understanding extrasynaptic volume transmission to the development of paradigms for drug delivery to the brain.

Astrocytes in multiple sclerosis: a product of their environment

It has long been thought that astrocytes, like other glial cells, simply provide a support mechanism for neuronal function in the healthy and inflamed central nervous system (CNS). However, recent evidence suggests that astrocytes play an active and dual role in CNS inflammatory diseases such as multiple sclerosis (MS). Astrocytes not only have the ability to enhance immune responses and inhibit myelin repair, but they can also be protective and limit CNS inflammation while supporting oligodendrocyte and axonal regeneration. The particular impact of these cells on the pathogenesis and repair of an inflammatory demyelinating process is dependent upon a number of factors, including the stage of the disease, the type and microenvironment of the lesion, and the interactions with other cell types and factors that influence their activation. In this review, we summarize recent data supporting the idea that astrocytes play a complex role in the regulation of CNS autoimmunity.

Rapid morphological brain abnormalities during acute methamphetamine intoxication in the rat: an experimental study using light and electron microscopy

This study describes morphological abnormalities of brain cells during acute methamphetamine (METH) intoxication in the rat and demonstrates the role of hyperthermia, disruption of the blood-brain barrier (BBB) and edema in their development. Rats with chronically implanted brain, muscle and skin temperature probes and an intravenous (i.v.) catheter were exposed to METH (9 mg/kg) at standard (23 degrees C) and warm (29 degrees C) ambient temperatures, allowing for the observation of hyperthermia ranging from mild to pathological (38-42 degrees C). When brain temperature peaked or reached a level suggestive of possible lethality (>41.5 degrees C), rats were injected with Evans blue (EB), rapidly anesthetized, perfused, and their brains were taken for further analyses. Four brain areas (cortex, hippocampus, thalamus and hypothalamus) were analyzed for EB extravasation, water and electrolyte (Na(+), K(+), Cl(-)) contents, immunostained for albumin and glial fibrillary acidic protein (GFAP), and examined for neuronal, glial and axonal alterations using standard light and electron microscopy. These examinations revealed profound abnormalities in neuronal, glial, and endothelial cells, which were stronger with METH administered at 29 degrees C than 23 degrees C and tightly correlated with brain and body hyperthermia. These changes had some structural specificity, but in each structure they tightly correlated with increases in EB levels, the numbers of albumin-positive cells, and water and ion contents, suggesting leakage of the BBB, acutely developing brain edema, and serious shifts in brain ion homeostasis as leading factors underlying brain abnormalities. While most of these acute structural and functional abnormalities appear to be reversible, they could trigger subsequent cellular alterations in the brain and accelerate neurodegeneration-the most dangerous complication of chronic amphetamine-like drug abuse.

STAT3 is a critical regulator of astrogliosis and scar formation after spinal cord injury

Signaling mechanisms that regulate astrocyte reactivity and scar formation after spinal cord injury (SCI) are not well defined. We used the Cre recombinase (Cre)-loxP system under regulation of the mouse glial fibrillary acidic protein (GFAP) promoter to conditionally delete the cytokine and growth factor signal transducer, signal transducer and activator of transcription 3 (STAT3), from astrocytes. After SCI in GFAP-Cre reporter mice, >99% of spinal cord cells that exhibited Cre activity as detected by reporter protein expression were GFAP-expressing astrocytes. Conditional deletion (or knock-out) of STAT3 (STAT3-CKO) from astrocytes in GFAP-Cre-loxP mice was confirmed in vivo and in vitro. In uninjured adult STAT3-CKO mice, astrocytes appeared morphologically similar to those in STAT3+/+ mice except for a partially reduced expression of GFAP. In STAT3+/+ mice, phosphorylated STAT3 (pSTAT3) was not detectable in astrocytes in uninjured spinal cord, and pSTAT3 was markedly upregulated after SCI in astrocytes and other cell types near the injury. Mice with STAT3-CKO from astrocytes exhibited attenuated upregulation of GFAP, failure of astrocyte hypertrophy, and pronounced disruption of astroglial scar formation after SCI. These changes were associated with increased spread of inflammation, increased lesion volume and partially attenuated motor recovery over the first 28 d after SCI. These findings indicate that STAT3 signaling is a critical regulator of certain aspects of reactive astrogliosis and provide additional evidence that scar-forming astrocytes restrict the spread of inflammatory cells after SCI.

Astrocytic and microglial response and histopathological changes in the brain of horses with experimental chronic Trypanosoma evansi infection

This study aimed to characterize astrocytic and microglial response in the central nervous system (CNS) of equines experimentally infected with T. evansi. The experimental group comprised males and females with various degrees of crossbreeding, ages between four and seven years. The animals were inoculated intravenously with 10(6) trypomastigotes of T. evansi originally isolated from a naturally infected dog. All equines inoculated with T. evansi were observed until they presented symptoms of CNS disturbance, characterized by motor incoordination of the pelvic limbs, which occurred 67 days after inoculation (DAI) and 124 DAI. The animals in the control group did not present any clinical symptom and were observed up to the 125th DAI. For this purpose the HE histochemical stain and the avidin biotin peroxidase method was used. Lesions in the CNS of experimentally infected horses were those of a wide spread non suppurative meningoencephalomyelitis.The severity of lesions varied in different parts of the nervous system, reflecting an irregular distribution of inflammatory vascular changes. The infiltration of mononuclear cells was associated with anisomorphic gliosis and reactive microglia was identified. The intensity of the astrocytic response in the CNS of the equines infected by T. evansi characterizes the importance of the performance of these cells in this trypanosomiasis. The characteristic gliosis observed in the animals in this experiment suggests the ability of these cells as mediators of immune response. The parasite, T. evansi, was not identified in the nervous tissues.

TNF-alpha receptor 1 deficiency enhances kainic acid-induced hippocampal injury in mice

The exact role of TNF-alpha in excitotoxic neurodegeneration of the brain is unclear. To address this issue, the kainic acid (KA)-induced hippocampal injury model, a well-characterized model of human neurodegenerative diseases, was used in TNF-alpha receptor 1 (TNFR1)-knockout (TNFR1-/-) mice in the present study. After nasal application of a single dose of 40 mg of KA per kilogram body weight, TNFR1-/- mice showed significantly more severe seizures than the wild-type mice. In addition, obvious neurodegeneration, enhanced microglia activation, and astrogliosis in the hippocampus, as well as increased locomotor activity, were found in TNFR1-/- mice compared with the wild-type controls 8 days after KA delivery. Moreover, CC chemokine receptor 3 expression on activated microglia was increased 3 days after KA treatment in TNFR1-/- mice, as measured by flow cytometry. These data suggest that TNF-alpha may play a protective role through TNFR1 signaling.

Alteration of glial fibrillary acidic proteins immunoreactivity in astrocytes of the spinal cord diabetic rats

Diabetes affects retinal and nervous glial cells, especially the astrocytes. A key indicator of this response is the alteration in the level of intermediate filament glial fibrillary acidic protein (GFAP) and number of GFAP-immunoreactive astrocytes. To date, no study has investigated the effect of diabetes on the distribution of GFAP-immunoreactive astrocytes in the spinal cord. Therefore, the present study investigated the effect of diabetes on the number of GFAP-immunoreactive astrocytes in the gray matter of the spinal cord of streptozotocin-induced diabetic Wistar rats. Animals were divided into six groups (n = 7); 6 weeks and 12 weeks diabetic duration groups and their respective age-matched normal control and sham control groups. Our results demonstrated a significant (P < 0.001) decrease in the number of GFAP-immunoreactive astrocytes in different areas of the spinal cord sections of the 6 weeks and 12 weeks long diabetic rats when compared with the spinal cord of normal and sham control groups of comparable age. The mean percentage in total number of GFAP-immunoreactive astrocytes in the whole gray matter areas of the spinal cord of the 6 and 12 weeks diabetic groups were approximately 28% and 41% less than control groups. Furthermore, the 12 weeks diabetic group showed a significant (P < 0.001) reduction in the number of GFAP-immunoreactive astrocytes when compared with the 6 weeks diabetic animals. These results suggest that the induction of diabetes is associated with a reduction in GFAP-positive astrocytes in the spinal cord, which may affect the functional support and role of astrocytic cells in the nervous tissue. This in turn may contribute to the pathological changes associated with diabetic state in the central nervous system.

Deterioration on magnetic resonance imaging despite good clinical recovery after viral encephalitis

We present a 2-year-old patient who showed progressive widespread white-matter abnormalities on magnetic resonance imaging 1 month after viral encephalitis, despite her good clinical recovery. These lesions on magnetic resonance imaging had not responded to therapies commonly used to treat secondary immune-mediated demyelinating lesions, as observed in acute disseminated encephalomyelitis. Acute viral encephalitis caused cortical blindness, but no other clinical signs developed during her clinical course. The progressive white-matter lesion in our case was different from the exacerbation of viral encephalitis or secondary immune-mediated encephalitis. A year later, magnetic resonance imaging-demonstrated brain atrophy with cystic changes in the bilateral occipital area, with remarkably reduced white-matter lesions. We hypothesize that the progressive white-matter changes resulted from the process of atrophy, degeneration, and cystic formation after viral encephalitis, rather than from the immune-mediated demyelinating process.

Translocator protein 18 kDa (TSPO): molecular sensor of brain injury and repair

For over 15 years, the peripheral benzodiazepine receptor (PBR), recently named translocator protein 18 kDa (TSPO) has been studied as a biomarker of reactive gliosis and inflammation associated with a variety of neuropathological conditions. Early studies documented that in the brain parenchyma, TSPO is exclusively localized in glial cells. Under normal physiological conditions, TSPO levels are low in the brain neuropil but they markedly increase at sites of brain injury and inflammation making it uniquely suited for assessing active gliosis. This research has generated significant efforts from multiple research groups throughout the world to apply TSPO as a marker of "active" brain pathology using in vivo imaging modalities such as Positron Emission Tomography (PET) in experimental animals and humans. Further, in the last few years, there has been an increased interest in understanding the molecular and cellular function(s) of TSPO in glial cells. The latest evidence suggests that TSPO may not only serve as a biomarker of active brain disease but also the use of TSPO-specific ligands may have therapeutic implications in brain injury and repair. This review presents an overview of the history and function of TSPO focusing on studies related to its use as a sensor of active brain disease in experimental animals and in human studies.

Inflammatory responses in the rat brain in response to different methods of intra-cerebral administration

Direct intra-cerebral administration of substances into the brain parenchyma is a common technique used by researchers in neuroscience. However, inflammatory responses to the needle may confound the results obtained following injection of these substances. In this paper we show that the use of a glass micro-needle for intra-cerebral injection reduces mechanical injury, blood-brain barrier breakdown and neutrophil recruitment in response to the injection of vehicle or interleukin-1, compared to using a 26-gauge Hamilton syringe. Therefore, the use of a glass micro-needle to inject substances intra-cerebrally appears to cause minimal injection artefact and should be the method of choice.

Extrasynaptic transmission and the diffusion parameters of the extracellular space

Extrasynaptic volume transmission, mediated by the diffusion of neuroactive substances in the extracellular space (ECS), plays an important role in short- and long-distance communication between nerve cells. The ability of a substance to reach extrasynaptic high-affinity receptors via diffusion depends on the ECS diffusion parameters, ECS volume fraction alpha (alpha=ECS volume/total tissue volume) and tortuosity lambda (lambda2=free/apparent diffusion coefficient), which reflects the presence of diffusion barriers represented by, e.g., fine astrocytic processes or extracellular matrix molecules. These barriers channel the migration of molecules in the ECS, so that diffusion may be facilitated in a certain direction, i.e. anisotropic. The diffusion parameters alpha and lambda differ in various brain regions, and diffusion in the CNS is therefore inhomogeneous. Changes in diffusion parameters have been found in many physiological and pathological states, such as development and aging, neuronal activity, lactation, ischemia, brain injury, degenerative diseases, tumor growth and others, in which cell swelling, glial remodeling and extracellular matrix changes are key factors influencing diffusion. Changes in ECS volume, tortuosity and anisotropy significantly affect the accumulation and diffusion of neuroactive substances and thus extrasynaptic transmission, neuron-glia communication, mediator "spillover" and synaptic crosstalk as well as, cell migration. The various changes occurring during pathological states can be important for diagnosis, drug delivery and treatment.

Brain edema and breakdown of the blood-brain barrier during methamphetamine intoxication: critical role of brain hyperthermia

To clarify the role of brain temperature in permeability of the blood-brain barrier (BBB), rats were injected with methamphetamine (METH 9 mg/kg) at normal (23 degrees C) and warm (29 degrees C) environmental conditions and internal temperatures were monitored both centrally (nucleus accumbens, NAcc) and peripherally (skin and nonlocomotor muscle). Once NAcc temperatures peaked or reached 41.5 degrees C (a level suggesting possible lethality), animals were administered Evans blue dye (protein tracer that does not normally cross the BBB), rapidly anaesthetized, perfused and had their brains removed. All METH-treated animals showed brain and body hyperthermia associated with relative skin hypothermia, suggesting metabolic activation coupled with peripheral vasoconstriction. While METH-induced NAcc temperature elevation varied from 37.60 to 42.46 degrees C (or 1.2-5.1 degrees C above baseline), it was stronger at 29 degrees C (+4.13 degrees C) than 23 degrees C (+2.31 degrees C). Relative to control, METH-treated animals had significantly higher brain levels of water, Na(+), K(+) and Cl(-), suggesting brain edema, and intense immunostaining for albumin, indicating breakdown of the BBB. METH-treated animals also showed strong immunoreactivity for glial fibrillary acidic protein (GFAP), possibly suggesting acute abnormality or damage of astrocytes. METH-induced changes in brain water, albumin and GFAP correlated linearly with NAcc temperature (r = 0.93, 0.98 and 0.98, respectively), suggesting a key role of brain hyperthermia in BBB permeability, development of brain edema and subsequent functional and structural neural abnormalities. Therefore, along with a direct destructive action on neural cells and functions, brain hyperthermia, via breakdown of the BBB, may be crucial for both decompensation of brain functions and cell injury following acute METH intoxication, possibly contributing to neurodegeneration resulting from chronic drug use.

Chronic erythropoietin-mediated effects on the expression of astrocyte markers in a rat model of contusive spinal cord injury

Using a standardized rat model of contusive spinal cord injury (SCI; [Gorio A, Gokmen N, Erbayraktar S, Yilmaz O, Madaschi L, Cichetti C, Di Giulio AM, Vardar E, Cerami A, Brines M (2002) Recombinant human erythropoietin counteracts secondary injury and markedly enhances neurological recovery from experimental spinal cord trauma. Proc Natl Acad Sci U S A 99:9450-9455]), we previously showed that the administration of recombinant human erythropoietin (rhEPO) improves both tissue sparing and locomotory outcome. In the present study, to better understand rhEPO-mediated effects on chronic astrocyte response to SCI in rat, we have used immunocytochemical methods combined with confocal and electron microscopy to investigate, 1 month after injury, the effects of a single rhEPO administration on the expression of a) aquaporin 4 (AQP4), the main astrocytic water channel implicated in edema development and resolution, and two molecules (dystrophin and syntrophin) involved in its membrane anchoring; b) glial fibrillary acidic protein (GFAP) and vimentin as markers of astrogliosis; c) chondroitin sulfate proteoglycans of the extracellular matrix which are upregulated after SCI and can inhibit axonal regeneration and influence neuronal and glial properties. Our results show that rhEPO administration after SCI modifies astrocytic response to injury by increasing AQP4 immunoreactivity in the spinal cord, but not in the brain, without apparent modifications of dystrophin and syntrophin distribution. Attenuation of astrogliosis, demonstrated by the semiquantitative analysis of GFAP labeling, was associated with a reduction of phosphacan/RPTP zeta/beta, whereas the levels of lecticans remained unchanged. Finally, the relative volume of a microvessel fraction was significantly increased, indicating a pro-angiogenetic or a vasodilatory effect of rhEPO. These changes were consistently associated with remarkable reduction of lesion size and with improvement in tissue preservation and locomotor recovery, confirming previous observations and underscoring the potentiality of rhEPO for the therapeutic management of SCI.

Immunohistochemical evaluation of the effect of lead exposure on subcommissural organ innervation and secretion in Shaw's Jird (Meriones shawi)

The secretory activity of subcommissural organ cells is controlled by various extrinsic and intrinsic factors. Lead has been recognised as a neurotoxic heavy metal, since it induces morphological and functional abnormalities in the brain. In this work, we examined the effect of lead exposure on the subcommissural organ (SCO), a brain gland known by its secretion of Reissner's fiber (RF) in cerebro-spinal fluid. Glycoprotein secretion and serotonin (5HT) innervation of the SCO was examined after acute and chronic lead exposures in the sub-desert rodent Meriones shawi. Lead exposures were achieved by, respectively, intra-peritoneal injection of 25 mg/kg body weight of lead acetate for 3 days and 0.5% of lead acetate in the drinking water over 4 months until adult age. 5HT and RF immunolabeling in the SCO revealed several serotoninergic fibers reaching the SCO and abundant secretory material. An increase in both 5HT innervation and secretory material of the SCO was recorded after both acute and chronic lead exposure. These results show that lead exposure affects the serotonergic innervation of the SCO. Moreover, the enhancement of SCO secretion suggests a role of this gland in neuroprotection and lead detoxification of the brain in Meriones shawi.

Increased beta(2)-adrenergic receptor activity by thyroid hormone possibly leads to differentiation and maturation of astrocytes in culture

(1) Our earlier studies indicate a downsteam regulatory role of the beta-adrenergic receptor (beta-AR) system in thyroid hormone induced differentiation and maturation of astrocytes. In the present study we have investigated the contributions of the subtypes of beta-AR in the above phenomenon. (2) Primary astrocyte cultures were grown under thyroid hormone deficient as well as under euthyroid conditions. [(125)I]Pindolol ([(125)I]PIN) binding studies showed a gradual increase in the specific binding to beta(2)-AR when observed at 5, 10, 15, and 20 days under both cultural conditions. Thyroid hormone caused an increase in binding of [(125)I]PIN to beta(2)-AR compared to thyroid hormone deficient controls at all ages of astrocyte culture. (3) Saturation studies using [(125)I]PIN in astrocyte membranes prepared from 20-day-old cultures showed a significant increase in the affinity of the receptors (K (D)) in the thyroid hormone treated cells without any change in receptor number (B (max)). (4) beta(2)-AR mRNA levels were measured by real-time PCR during ontogenic development as well as during exposure of 10-day-old hypothyroid cultures to normal levels of thyroid hormone for 2, 6, 12, and 24 h. None of the conditions caused any significant change in the beta(2)-adrenergic receptor mRNA levels when compared with corresponding hypothyroid controls. (5) Over expression of beta(2)-AR cDNA in hypothyroid astrocytes caused morphological transformation in spite of the absence of thyroid hormone in the medium. (6) Taken together, results suggest thyroid hormone causes a selective increase in [(125)I]PIN binding to beta(2)-AR due to increase in receptor affinity, which may lead to maturation of astrocytes.

The cyclic GMP-protein kinase G pathway regulates cytoskeleton dynamics and motility in astrocytes

We have previously demonstrated that inflammatory compounds that increase nitric oxide (NO) synthase expression have a biphasic effect on the level of the NO messenger cGMP in astrocytes. In this work, we demonstrate that NO-dependent cGMP formation is involved in the morphological change induced by lipopolysaccharide (LPS) in cultured rat cerebellar astroglia. In agreement with this, dibutyryl-cGMP, a permeable cGMP analogue, and atrial natriuretic peptide, a ligand for particulate guanylyl cyclase, are both able to induce process elongation and branching in astrocytes resulting from a rapid, reversible and concentration-dependent redistribution of glial fibrillary acidic protein (GFAP) and actin filaments without significant change in protein levels. These effects are also observed in astrocytes co-cultured with neurons. The cytoskeleton rearrangement induced by cGMP is prevented by the specific protein kinase G inhibitor Rp-8Br-PET-cGMPS and involves downstream inhibition of RhoA GTPase since is not observed in cells transfected with constitutively active RhoA. Furthermore, dibutyryl-cGMP prevents RhoA-membrane association, a step necessary for its interaction with effectors. Stimulation of the cGMP-protein kinase G pathway also leads to increased astrocyte migration in an in vitro scratch-wound assay resulting in accelerated wound closure, as seen in reactive gliosis following brain injury. These results indicate that cGMP-mediated pathways may regulate physio-pathologically relevant responses in astroglial cells.

Reactive changes of retinal astrocytes and Müller glial cells in kainate-induced neuroexcitotoxicity

The aim of this study was to investigate reactive changes of astrocytes and Müller glial cells in rats subjected to kainate treatment, which leads to neuronal degeneration in the ganglion cell layer and the inner border of the inner nuclear layer as confirmed by labelling with Fluoro-Jade B, a marker for degenerating neurons and fibres. Both the astrocytes and the Müller glial cells reacted vigorously to kainate injection as shown by their up-regulated expression of nestin, glial fibrillary acidic protein and glutamine synthetase. A major finding was the induced expression of nestin together with glial fibrillary acidic protein beginning at 1 day post-injection of kainate. The marked nestin expression appeared to be most intense at 1 day and was sustained till 2 weeks as compared with the untreated/normal retina. Western blotting analysis confirmed a marked increase in expression of nestin, glial fibrillary acidic protein and glutamine synthetase as compared with untreated/normal retina. Double labelling study revealed that astrocytes and Müller glial cells expressed the radial glia marker nestin, and incorporated bromodeoxyuridine to re-enter into their cell cycle. The induced expression of these proteins in astrocytes and Müller glial cells indicated an induction of gliotic responses and de-differentiation that may be associated with regenerative efforts after kainate-induced injury. Indeed, with the acquisition of an immature molecular profile as manifested by the induced expression of brain lipid-binding protein and doublecortin in astrocytes and Müller glial cells, the potential of these cells to de-differentiate in retinal neurodegeneration is greatly amplified.

Extracellular signal-regulated kinase involvement in human astrocyte migration

Glial scar formation occurs after virtually any injury to the brain. The migration of astrocytes into regions of brain injury underlies the formation of the glial scar. The exact role of the glial scar has yet to be elucidated, although it is likely to impair brain recovery. Understanding astrocyte migration is fundamental to understanding the formation of the glial scar. We have used human astrocytes (NT2A cells), derived from human NT2/D1 precursor cells to study astrocyte migration using an in vitro scratch wound model. Time-lapse microscopy and bromodeoxyuridine labeling revealed that the astrocytes migrated rather than proliferated across the scratch. Time course immunocytochemical studies showed that scratching human astrocytes induced the activation (phosphorylation) of ERK 1/2 at 10 min after scratch. The MEK 1/2 inhibitor U0126 inhibited both the ERK 1/2 phosphorylation and the migration of the astrocytes across the wound after scratch. Thus, the migration of human astrocytes after injury is partly initiated by activation of the MEK-ERK signalling pathway.

Effect of an acute 900MHz GSM exposure on glia in the rat brain: a time-dependent study

Because of the increasing use of mobile phones, the possible risks of radio frequency electromagnetic fields adverse effects on the human brain has to be evaluated. In this work we measured GFAP expression, to evaluate glial evolution 2, 3, 6 and 10 days after a single GSM exposure (15min, brain averaged SAR=6W/kg, 900MHz signal) in the rat brain. A statistically significant increase of GFAP stained surface area was observed 2 days after exposure in the frontal cortex and the caudate putamen. A smaller statistically significant increase was noted 3 days after exposure in the same areas and in the cerebellum cortex. Our results confirm the Mausset-Bonnefont et al. study [Mausset-Bonnefont, A.L., Hirbec, H., Bonnefont, X., Privat, A., Vignon, J., de Seze, R., 2004. Acute exposure to GSM 900MHz electromagnetic fields induces glial reactivity and biochemical modifications in the rat brain. Neurobiol. Dis. 17, 445-454], showing the existence of glial reactivity after a 15min GSM acute exposure at a brain averaged SAR of 6W/kg. We conclude to a temporary effect, probably due to a hypertrophy of glial cells, with a temporal and a spatial modulation of the effect. Whether this effect could be harmful remains to be studied.

Neuroprotection conferred by astrocytes is insufficient to protect animals from succumbing to Japanese encephalitis

Astrocytes play a key role in regulating aspects of inflammation and in the homeostatic maintenance of the central nervous system (CNS). However, the role of astrocytes in viral encephalitis mediated inflammation is not well documented. As Japanese encephalitis virus (JEV) infection is localized to neurons and considering the importance of astrocytes in supporting neuronal survival and function, we have exploited an experimental model of Japanese encephalitis (JE) to better understand the role of astrocytes in JE. Suckling mice pups were inoculated with the virus and 2 and 4 days later we analyzed a panel of molecules characteristic of reactive astrogliosis. We show that JEV infection increases the expression of astrocyte-specific glial fibrillary acidic protein (GFAP), the glutamate aspartate transporter (GLAST), glutamate transporter-1 (GLT-1) and ceruloplasmin (CP). The transcript levels of growth factors produced predominantly by activated astrocytes such as nerve growth factor (NGF) and ciliary neurotrophin factor (CNTF) were elevated following JEV infection. The transcript level of brain-derived neurotrophic factor (BDNF) was also elevated following JEV infection. Both NGF and CNTF were capable of preventing ROS mediated neuronal death following in vitro JEV infection to a certain extent. Taken altogether, these data indicate that increased astrogliosis following JEV infection is accompanied by the enhanced ability of astrocytes to detoxify glutamate, inactivate free radical and produce neurotrophic factors that are involved in neuronal protection. However, this elevated physiological state of astrocyte is insufficient in conferring neuroprotection, as infected animals eventually succumb to infection. The response of astrocytes to JE can be amplified to modulate the adaptive response of brain to induce neuroprotection.

The emergence of proteinase-activated receptor-2 as a novel target for the treatment of inflammation-related CNS disorders

The signalling molecules that are involved in inflammatory pathways are now thought to play a part in many disorders of the central nervous system (CNS). In common with peripheral chronic inflammatory diseases such a rheumatoid arthritis and ulcerative colitis, evidence now exists for the involvement of inflammatory cytokines, for example tumour necrosis factor (TNF) and interleukins (IL), in neurological disorders. A common factor observed with the up-regulation of these cytokines in peripheral inflammatory diseases, is the increased expression of the proteinase-activated receptor (PAR) subtype PAR-2. Indeed, recent evidence suggests that targeting PAR-2 helps reduce joint swelling observed in animal models of arthritis. So could targeting this receptor prove to be useful in treating those CNS disorders where inflammatory processes are thought to play an intrinsic role? The aim of this review is to summarize the emerging data regarding the role of PAR-2 in neuroinflammation and ischaemic injury and discuss its potential as an exciting new target for the prevention and/or treatment of CNS disorders.

Health effects of subchronic exposure to diesel-water-methanol emulsion emission

The U.S. Environmental Protection Agency's National Ambient Air Quality Standards for ozone and particulate matter (PM) require urban non-attainment areas to implement pollution-reduction strategies for anthropogenic source emissions. The type of fuel shown to decrease combustion emissions components versus traditional diesel fuel, is the diesel emulsion. The Lubrizol Corporation, in conjunction with Lovelace Respiratory Research Institute and several subcontracting laboratories, recently conducted a health assessment of the combustion emissions of PuriNOx diesel fuel emulsion (diesel-water-methanol) in rodents. Combustion emissions from either of two, 2002 model Cummins 5.9L ISB engines, were diluted with charcoal-filtered air to exposure concentrations of 125, 250 and 500 microg total PM/m3. The engines were operated on a continuous, repeating, heavy-duty certification cycle (U.S. Code of Federal Regulations, Title 40, Chapter I) using Rotella-T 15W-40 engine oil. Nitrogen oxide (NO) and PM were reduced when engines were operated on PuriNOx versus California Air Resources Board diesel fuel under these conditions. Male and female F344 rats were housed in Hazleton H2000 exposure chambers and exposed to exhaust atmospheres 6 h/day, five days/week for the first 11 weeks and seven days/week thereafter. Exposures ranged from 61 to 73 days depending on the treatment group. Indicators of general toxicity (body weight, organ weight, clinical pathology and histopathology), neurotoxicity (glial fibrillary acidic protein assay), genotoxicity (Ames assay, micronucleus, sister chromatid exchange), and reproduction and development were measured. Overall, effects observed were mild. Emulsion combustion emissions were not associated with neurotoxicity, reproductive/developmental toxicity, or in vivo genotoxicity. Small decreases in serum cholesterol in the 500-microg/m3 exposure group were observed. PM accumulation within alveolar macrophages was evident in all exposure groups. The latter findings are consistent with normal physiological responses to particle inhalation. Other statistically significant effects were present in some measured parameters of other exposed groups, but were not clearly attributed to emissions exposure. Positive mutagenic responses in several strains of Salmonella typhimurium were observed subsequent to treatment with emulsion emissions subfractions. Based on the cholesterol results, it can be concluded that the 250-microg/m3 exposure level was the no observed effect level. In general, biological findings in exposed rats and bacteria were consistent with exposure to petroleum diesel exhaust in the F344 rat and Ames assays.

Recapitulation of cell signaling events associated with astrogliosis using the brain slice preparation

Astroglial activation constitutes a dominant response to all types of injuries of the CNS. Despite the ubiquitous nature of this cellular reaction to neural injury, a little is known concerning the signaling mechanisms that initiate it. Recently, we demonstrated that astrocytic hypertrophy and enhanced expression of glial fibrillary acidic protein resulting from toxicant-induced neurodegeneration are linked to activation of the janus kinase (JAK)-signal transducer and activator of transcription-3 (STAT3) pathway. These observations implicate ligands at the gp130 receptor as potential upstream effectors of astrogliosis. Here we used the brain slice preparation to examine potential activators of the JAK-STAT3 pathway. Following incubation of freshly cut striatal slices in phosphate-free oxygenated buffer for up to 75 min, we found that slicing the striatum itself was a sufficient stimulus to initiate a rapid activation of the JAK-STAT3 pathway as assessed with immunoblots of pSTAT3((tyr705)) using phospho-state specific antibodies. The mRNA for the gp130 cytokines, leukemia inhibitory factor, interleukin-6 and oncostatin M or the beta-chemokine, monocyte chemoattractive protein (CCl2) also were up-regulated in the slice. Moreover, we could enhance the activation of STAT3((tyr705)) by adding exogenous cytokines to the slice and we could inhibit phosphorylation of STAT3((tyr705)) by addition of tyrosine kinase inhibitors (Lav A and AG490) or neutralizing antibodies directed against leukemia inhibitory factor or oncostatin M. These data suggest that STAT3 activation is an early event in slice-induced glial activation and establishes the brain slice preparation method as a reliable model to examine the signaling mechanisms that underlie glial activation.

Differentiated astrocytes acquire sensitivity to hydrogen sulfide that is diminished by the transformation into reactive astrocytes

Hydrogen sulfide (H2S) enhances the induction of hippocampal long-term potentiation (LTP) and induces calcium waves in astrocytes. Based on these observations, H2S has been proposed to be a synaptic modulator in the brain. Here we show that differentiated astrocytes acquire sensitivity to H2S that is diminished by their transformation into reactive astrocytes. Although sodium hydrosulfide hydrate (NaHS), a donor of H2S, did not increase the intracellular concentration of Ca2+ in progenitors, exposure of progenitors to leukemia inhibitory factor (LIF), which induces differentiation into glial fibrillary acidic protein (GFAP)-positive astrocytes, greatly increased the sensitivity to NaHS. In contrast, epidermal growth factor (EGF), transforming growth factor-alpha (TGF-alpha), dibutyryl cyclic AMP (db cAMP) and interleukin-1beta (IL-1beta) induced the conversion to reactive astrocytes with diminished sensitivity to NaHS. This suppressive effect of EGF on the sensitivity to NaHS was inhibited by cycloheximide, indicating that de novo protein synthesis was required for the suppression of H2S sensitivity.

Implantable microscale neural interfaces

Implantable neural microsystems provide an interface to the nervous system, giving cellular resolution to physiological processes unattainable today with non-invasive methods. Such implantable microelectrode arrays are being developed to simultaneously sample signals at many points in the tissue, providing insight into processes such as movement control, memory formation, and perception. These electrode arrays have been microfabricated on a variety of substrates, including silicon, using both surface and bulk micromachining techniques, and more recently, polymers. Current approaches to achieving a stable long-term tissue interface focus on engineering the surface properties of the implant, including coatings that discourage protein adsorption or release bioactive molecules. The implementation of a wireless interface requires consideration of the necessary data flow, amplification, signal processing, and packaging. In future, the realization of a fully implantable neural microsystem will contribute to both diagnostic and therapeutic applications, such as a neuroprosthetic interface to restore motor functions in paralyzed patients.

Insulin-like growth factor binding proteins: regulation in chronic active plaques in multiple sclerosis and functional analysis of glial cells

Studies in experimental allergic encephalomyelitis, an animal model of multiple sclerosis (MS), suggest that astrocyte-secreted insulin-like growth factor binding protein-2 (IGFBP-2) helps target IGF-1 to IGF-1 receptor-expressing oligodendrocytes and promote remyelination. We examined the presence of IGFBPs 1-6 in astrocytes in normal post-mortem human brain tissue and lesions of MS by means of immunohistochemistry. Under normal conditions all six IGFBPs were detected. Compared to controls, hypertrophic astrocytes at the borders of chronic active MS lesions displayed increased immunoreactivity for IGFBP-2 and IGFBP-4. In vitro studies were performed to analyse the effects of IGFBPs on cellular proliferation of neonatal rat glial cells. Treatment of astrocytes with IGF-1 and -2 enhanced proliferation whereas IGFBP-2 and -4 inhibited cellular growth. Interestingly, combined treatment with IGFBP-2 and IGF-1 potentiated effects on cellular proliferation whereas combined treatment with IGFBP-2 and IGF-2 inhibited growth. Unlike IGFBP-2, IGFBP-4 inhibited proliferation in combined treatment with IGF-1. In contrast, combined treatment with IGFBP-2 and IGF-1 resulted in decreased cell survival of oligodendrocyte precursor cells. Our results suggest that the up-regulation of IGFBP-2 in reactive astrocytes in MS lesions may primarily serve to enhance the IGF-1-mediated mitogenic stimulus for astrocytes rather than supporting oligodendrocyte survival.

Characterization of R-ras3/m-ras null mice reveals a potential role in trophic factor signaling

R-Ras3/M-Ras is a member of the RAS superfamily of small-molecular-weight GTP-binding proteins. Previous studies have demonstrated high levels of expression in several regions of the central nervous system, and a constitutively active form of M-Ras promotes cytoskeletal reorganization, cellular transformation, survival, and differentiation. However, the physiological functions of M-Ras during embryogenesis and postnatal development have not been elucidated. By using a specific M-Ras antibody, we demonstrated a high level of M-Ras expression in astrocytes, in addition to neurons. Endogenous M-Ras was activated by several trophic factors in astrocytes, including epidermal growth factor (EGF), basic fibroblast growth factor, and hepatocyte growth factor. Interestingly, M-Ras activation by EGF was more sustained compared to prototypic Ras. A mouse strain deficient in M-Ras was generated to investigate its role in development. M-Ras null mice appeared phenotypically normal, and there was a lack of detectable morphological and neurological defects. In addition, primary astrocytes derived from Mras(-/-) mice did not appear to display substantial alterations in the activation of both the mitogen-activated protein kinase and phosphatidylinositol 3-kinase pathways in response to trophic factors.

Inflammation-Like Glial Response in Lead-Exposed Immature Rat Brain

Numerous studies on lead (Pb) neurotoxicity have indicated this metal to be a dangerous toxin, particularly during developmental stages of higher organisms. Astrocytes are responsible for sequestration of this metal in brain tissue. Activation of astroglia may often lead to loss of the buffering function and contribute to pathological processes. This phenomenon is accompanied by death of neuronal cells and may be connected with inflammatory events arising from the production of a wide range of cytokines and chemokines. The effects of prolonged exposure to Pb upon glial activation are examined in immature rats to investigate this potential proinflammatory effect. When analyzed at the protein level, glial activation is observed after Pb exposure, as reflected by the increased level of glial fibrillary acidic protein and S-100beta proteins in all parts of the brain examined. These changes are associated with elevation of proinflammatory cytokines. Production of interleukin (IL)-1beta and tumor necrosis factor-alpha is observed in hippocampus, and production of IL-6 is seen in forebrain. The expression of fractalkine is observed in both hippocampus and forebrain but inconsiderably in the cerebellum. In parallel with cytokine expression, signs of synaptic damage in hippocampus are seen after Pb exposure, as indicated by decreased levels of the axonal markers synapsin I and synaptophysin. Obtained results indicate chronic glial activation with coexisting inflammatory and neurodegenerative features as a new mechanism of Pb neurotoxicity in immature rat brain.

Intraspinal grafting procedures: spinal cord effects induced in the adult rat: a clinical, histopathological, and immunohistochemical study

OBJECTIVE

Intraspinal grafting procedures using peripheral nerve grafts (PNG) or collagen guidance channels (CGC) have been recently used to treat brachial plexus injuries in humans and spinal cord injuries in animals. This study examined the effects of these procedures in the adult rat.

METHODS

In adult rats, we performed an avulsion of left C5, C6, and C7 nerve roots, followed by a myelotomy of the left ventrolateral aspect of the spinal cord between C5 and C6. The rats were subsequently assigned to one of three groups: group A (n = 10), no additional procedure; group B (n = 10), implantation of a PNG following myelotomy; group C (n = 10), implantation of a CGC. Clinical evaluation was postoperatively assessed. Rats were euthanized at day 6 or 21. Spinal cord lesions induced by surgery were assessed by measuring depth and rostrocaudal extent. Reactive astrogliosis, as a reaction to neuroglial damage, was assessed by revealing the glial fibrillary acidic protein with immunochemistry method.

RESULTS

No animal showed persistent neurological deficit at day 21. The depth and rostrocaudal extent of tissue damage was comparable in all groups at days 6 and 21. At day 6, the astrocytic reaction observed at the myelotomy/implantation site was statistically stronger in group C (CGC). At day 21, the astrocytic reaction became identical in all groups.

CONCLUSION

This study shows that grafting a PNG or a CGC into the spinal cord does not create significant additional iatrogenic effects and can be used in repair strategies to treat nerve root avulsions or spinal cord injuries.