Glial changes following an excitotoxic lesion in the CNS--II. Astrocytes

Cell-type specific circadian transcription factor BMAL1 roles in excitotoxic hippocampal lesions to enhance neurogenesis

Circadian clocks, generating daily rhythms in biological processes, maintain homeostasis in physiology, so clock alterations are considered detrimental. Studies in brain pathology support this by reporting abnormal circadian phenotypes in patients, but restoring the abnormalities by light therapy shows no dramatic effects. Recent studies on glial clocks report the complex effects of altered clocks by showing their beneficial effects on brain repairs. However, how neuronal clocks respond to brain pathology is elusive. This study shows that neuronal BMAL1, a core of circadian clocks, reduces its expression levels in neurodegenerative excitotoxicity. In the dentate gyrus of excitotoxic hippocampal lesions, reduced BMAL1 in granule cells precedes apoptosis. This subsequently reduces BMAL1 levels in neighbor neural stem cells and progenitors in the subgranular zone, enhancing proliferation. This shows the various BMAL1 roles depending on cell types, and its alterations can benefit brain repair. Thus, cell-type-specific BMAL1 targeting is necessary to treat brain pathology.

The effects of Src tyrosine kinase inhibitor, saracatinib, on the markers of epileptogenesis in a mixed-sex cohort of adult rats in the kainic acid model of epilepsy

Neurodegeneration and neuroinflammation are key processes of epileptogenesis in temporal lobe epilepsy (TLE). A considerable number (∼30%) of patients with epilepsy are resistant to currently available antiseizure drugs and thus there is a need to develop adjunct therapies to modify disease progression. A vast majority of interventional strategies to treat TLE have utilized males which limits the translational nature of the studies. In this study, we investigated the effects of repeated low-dose kainic acid (KA) injection on the initial status epilepticus (SE) and the effects of Src kinase inhibitor, saracatinib (SAR/AZD0530; 20 mg/kg, oral, daily for 7 days), in a mixed-sex cohort of adult Sprague Dawley rats during early epileptogenesis. There were no sex differences in response to KA-induced SE, and neither did the stage of estrus influence SE severity. KA-induced SE caused significant astrogliosis and microgliosis across the hippocampus, piriform cortex, and amygdala. SAR treatment resulted in a significant reduction of microgliosis across brain regions. Microglial morphometrics such as branch length and the endpoints strongly correlated with CD68 expression in the vehicle-treated group but not in the SAR-treated group, indicating mitigation by SAR. KA-induced SE caused significant neuronal loss, including parvalbumin-positive inhibitory neurons, in both vehicle (VEH) and SAR-treated groups. SAR treatment significantly mitigated FJB-positive neuronal counts as compared to the VEH group. There was an increase in C3-positive reactive astrocytes in the VEH-treated group, and SAR treatment significantly reduced the increase in the piriform cortex. C3-positive astrogliosis significantly correlated with CD68 expression in the amygdala (AMY) of VEH-treated rats, and SAR treatment mitigated this relationship. There was a significant increase of pSrc(Y419)-positive microglia in both KA-treated groups with a statistically insignificant reduction by SAR. KA-induced SE caused the development of classical glial scars in the piriform cortex (PIR) in both KA-treated groups, while SAR treatment led to a 42.17% reduction in the size of glial scars. We did not observe sex differences in any of the parameters in this study. SAR, at the dose tested in the rat kainate model for a week in this study mitigated some of the markers of epileptogenesis in both sexes.

Characterization of Cortical Glial Scars in the Diisopropylfluorophosphate (DFP) Rat Model of Epilepsy

Glial scars have been observed following stab lesions in the spinal cord and brain but not observed and characterized in chemoconvulsant-induced epilepsy models. Epilepsy is a disorder characterized by spontaneous recurrent seizures and can be modeled in rodents. Diisopropylfluorophosphate (DFP) exposure, like other real-world organophosphate nerve agents (OPNAs) used in chemical warfare scenarios, can lead to the development of status epilepticus (SE). We have previously demonstrated that DFP-induced SE promotes epileptogenesis which is characterized by the development of spontaneous recurrent seizures (SRS), gliosis, and neurodegeneration. In this study, we report classical glial scars developed in the piriform cortex, but not in the hippocampus, by 8 days post-exposure. We challenged both male and female rats with 4–5 mg/kg DFP (s.c.) followed immediately by 2 mg/kg atropine sulfate (i.m.) and 25 mg/kg pralidoxime (i.m.) and one hour later by midazolam (i.m). Glial scars were present in the piriform cortex/amygdala region in 73% of the DFP treated animals. No scars were found in controls. Scars were characterized by a massive clustering of reactive microglia surrounded by hypertrophic reactive astrocytes. The core of the scars was filled with a significant increase of IBA1 and CD68 positive cells and a significant reduction in NeuN positive cells compared to the periphery of the scars. There was a significantly higher density of reactive GFAP, complement 3 (C3), and inducible nitric oxide synthase (iNOS) positive cells at the periphery of the scar compared to similar areas in controls. We found a significant increase in chondroitin sulfate proteoglycans (CS-56) in the periphery of the scars compared to a similar region in control brains. However, there was no change in TGF-β1 or TGF-β2 positive cells in or around the scars in DFP-exposed animals compared to controls. In contrast to stab-induced scars, we did not find fibroblasts (Thy1.1) in the scar core or periphery. There were sex differences with respect to the density of iNOS, CD68, NeuN, GFAP, C3 and CS-56 positive cells. This is the first report of cortical glial scars in rodents with systemic chemoconvulsant-induced SE. Further investigation could help to elucidate the mechanisms of scar development and mitigation strategies.

Neurotensin receptor 2 is induced in astrocytes and brain endothelial cells in relation to neuroinflammation following pilocarpine-induced seizures in rats

Neurotensin (NT) acts as a primary neurotransmitter and neuromodulator in the CNS and has been involved in a number of CNS pathologies including epilepsy. NT mediates its central and peripheral effects by interacting with the NTSR1, NTSR2, and Sort1/NTSR3 receptor subtypes. To date, little is known about the precise expression of the NT receptors in brain neural cells and their regulation in pathology. In the present work, we studied the cellular distribution of the NTSR2 protein in the rat hippocampus and questioned whether its expression was modulated in conditions of neuroinflammation using a model of temporal lobe epilepsy induced by pilocarpine. This model is characterized by a rapid and intense inflammatory reaction with reactive gliosis in the hippocampus. We show that NTSR2 protein is expressed in hippocampal astrocytes and its expression increases together with astrocyte reactivity following induction of status epilepticus. NTSR2 immunoreactivity is also increased in astrocytes proximal to blood vessels and their end-feet, and in endothelial cells. Proinflammatory factors such as IL1β and LPS induced NTSR2 mRNA and protein in cultured astroglial cells. Antagonizing NTSR2 with SR142948A decreased NTSR2 expression as well as astroglial reactivity. Together, our results suggest that NTSR2 is implicated in astroglial and gliovascular inflammation and that targeting the NTSR2 receptor may open new avenues in the regulation of neuroinflammation in CNS diseases.

TSPO imaging in animal models of brain diseases

Over the last 30 years, the 18-kDa TSPO protein has been considered as the PET imaging biomarker of reference to measure increased neuroinflammation. Generally assumed to image activated microglia, TSPO has also been detected in endothelial cells and activated astrocytes. Here, we provide an exhaustive overview of the recent literature on the TSPO-PET imaging (i) in the search and development of new TSPO tracers and (ii) in the understanding of acute and chronic neuroinflammation in animal models of neurological disorders. Generally, studies testing new TSPO radiotracers against the prototypic [¹¹C]-R-PK11195 or more recent competitors use models of acute focal neuroinflammation (e.g. stroke or lipopolysaccharide injection). These studies have led to the development of over 60 new tracers during the last 15 years. These studies highlighted that interpretation of TSPO-PET is easier in acute models of focal lesions, whereas in chronic models with lower or diffuse microglial activation, such as models of Alzheimer's disease or Parkinson's disease, TSPO quantification for detection of neuroinflammation is more challenging, mirroring what is observed in clinic. Moreover, technical limitations of preclinical scanners provide a drawback when studying modest neuroinflammation in small brains (e.g. in mice). Overall, this review underlines the value of TSPO imaging to study the time course or response to treatment of neuroinflammation in acute or chronic models of diseases. As such, TSPO remains the gold standard biomarker reference for neuroinflammation, waiting for new radioligands for other, more specific targets for neuroinflammatory processes and/or immune cells to emerge.

Reactivity of microglia and astrocytes after an excitotoxic injury induced by kainic acid in the rat spinal cord

After injury of the nervous system glial cells react according to the stimuli by modifying their morphology and function. Glia activation was reported in different kainic acid (KA)-induced neurodegeneration models. Here, we describe glial morphometric changes occurring in an excitotoxic KA-induced cervical spinal cord injury model. Concomitant degenerative and apoptotic processes are also reported. Male rats injected at the spinal cord C5 segment either with KA or saline were euthanized at post-injection (PI) days 1, 2, 3 or 7. Anti-IBA-1 and anti-GFAP antibodies were used to identify microglia and activated astrocytes, respectively, and to morphometrically characterized them. Fluoro-Jade B staining and TUNEL reaction were used to determine neuronal and glial degeneration and apoptosis. KA-injected group showed a significant increase in microglia number at the ipsilateral side by PI day 3. Different microglia reactive phenotypes were observed. Reactive microglia was still present by PI day 7. Astrocytes in KA-injected group showed a biphasic increase in number at PI days 1 and 3. Degenerative and apoptotic events were only observed in KA-injected animals, increasing mainly by PI day 1. Understanding the compromise of glia in different neurodegenerative processes may help to define possible common or specific therapeutic approaches directed towards neurorestorative strategies.

Longitudinal positron emission tomography imaging of glial cell activation in a mouse model of mesial temporal lobe epilepsy: Toward identification of optimal treatment windows

OBJECTIVE

Mesiotemporal lobe epilepsy is the most common type of drug-resistant partial epilepsy, with a specific history that often begins with status epilepticus due to various neurological insults followed by a silent period. During this period, before the first seizure occurs, a specific lesion develops, described as unilateral hippocampal sclerosis (HS). It is still challenging to determine which drugs, administered at which time point, will be most effective during the formation of this epileptic process. Neuroinflammation plays an important role in pathophysiological mechanisms in epilepsy, and therefore brain inflammation biomarkers such as translocator protein 18 kDa (TSPO) can be potent epilepsy biomarkers. TSPO is associated with reactive astrocytes and microglia. A unilateral intrahippocampal kainate injection mouse model can reproduce the defining features of human temporal lobe epilepsy with unilateral HS and the pattern of chronic pharmacoresistant temporal seizures. We hypothesized that longitudinal imaging using TSPO positron emission tomography (PET) with ¹⁸ F-DPA-714 could identify optimal treatment windows in a mouse model during the formation of HS.

METHODS

The model was induced into the right dorsal hippocampus of male C57/Bl6 mice. Micro-PET/computed tomographic scanning was performed before model induction and along the development of the HS at 7 days, 14 days, 1 month, and 6 months. In vitro autoradiography and immunohistofluorescence were performed on additional mice at each time point.

RESULTS

TSPO PET uptake reached peak at 7 days and mostly related to microglial activation, whereas after 14 days, reactive astrocytes were shown to be the main cells expressing TSPO, reflected by a continuing increased PET uptake.

SIGNIFICANCE

TSPO-targeted PET is a highly potent longitudinal biomarker of epilepsy and could be of interest to determine the therapeutic windows in epilepsy and to monitor response to treatment.

Redirection of neuroblast migration from the rostral migratory stream into a lesion in the prefrontal cortex of adult rats

Clinical treatment of structural brain damage today is largely limited to symptomatic approaches and the avoidance of secondary injury. However, neuronal precursor cells are constantly produced within specified regions of the mammalian brain throughout life. Here we evaluate the potential of the known chemoattractive properties of the glycoprotein laminin on neuroblasts to relocate the cells into damaged brain areas. Injection of a thin laminin tract, leading from the rostral migratory stream to an excitotoxic lesion within the medial prefrontal cortex of rats, enabled neuroblasts to migrate away from their physiological route towards the olfactory bulb into the lesion site. Once they reached the damaged tissue, they migrated further in a non-uniform orientation within the lesion. Furthermore, our data indicate that the process of diverted migration is still active 6 weeks after the treatment and that at least some of the neuroblasts are capable of maturing into adult neurons.

Spinal cord regeneration

Three theories of regeneration dominate neuroscience today, all purporting to explain why the adult central nervous system (CNS) cannot regenerate. One theory proposes that Nogo, a molecule expressed by myelin, prevents axonal growth. The second theory emphasizes the role of glial scars. The third theory proposes that chondroitin sulfate proteoglycans (CSPGs) prevent axon growth. Blockade of Nogo, CSPG, and their receptors indeed can stop axon growth in vitro and improve functional recovery in animal spinal cord injury (SCI) models. These therapies also increase sprouting of surviving axons and plasticity. However, many investigators have reported regenerating spinal tracts without eliminating Nogo, glial scar, or CSPG. For example, many motor and sensory axons grow spontaneously in contused spinal cords, crossing gliotic tissue and white matter surrounding the injury site. Sensory axons grow long distances in injured dorsal columns after peripheral nerve lesions. Cell transplants and treatments that increase cAMP and neurotrophins stimulate motor and sensory axons to cross glial scars and to grow long distances in white matter. Genetic studies deleting all members of the Nogo family and even the Nogo receptor do not always improve regeneration in mice. A recent study reported that suppressing the phosphatase and tensin homolog (PTEN) gene promotes prolific corticospinal tract regeneration. These findings cannot be explained by the current theories proposing that Nogo and glial scars prevent regeneration. Spinal axons clearly can and will grow through glial scars and Nogo-expressing tissue under some circumstances. The observation that deleting PTEN allows corticospinal tract regeneration indicates that the PTEN/AKT/mTOR pathway regulates axonal growth. Finally, many other factors stimulate spinal axonal growth, including conditioning lesions, cAMP, glycogen synthetase kinase inhibition, and neurotrophins. To explain these disparate regenerative phenomena, I propose that the spinal cord has evolved regenerative mechanisms that are normally suppressed by multiple extrinsic and intrinsic factors but can be activated by injury, mediated by the PTEN/AKT/mTOR, cAMP, and GSK3b pathways, to stimulate neural growth and proliferation.

[18F]DPA-714 PET imaging of translocator protein TSPO (18 kDa) in the normal and excitotoxically-lesioned nonhuman primate brain

PURPOSE

We aimed to characterize pharmacologically the TSPO- radioligand [(18)F]DPA-714 in the brain of healthy cynomolgus monkeys and evaluate the cellular origin of its binding in a model of neurodegeneration induced by intrastriatal injection of quinolinic acid (QA).

METHODS

[(18)F]DPA-714 PET images were acquired before and at 2, 7, 14, 21, 49, 70, 91 days after putaminal lesioning. Blocking and displacement studies were carried out (PK11195). Different modelling approaches estimated rate constants and V T (total distribution volume) which was used to measure longitudinal changes in the lesioned putamen. Sections for immunohistochemical labelling were prepared at the same time-points to evaluate correlations between in vivo [(18)F]DPA-714 binding and microglial/astrocytic activation.

RESULTS

[(18)F]DPA-714 showed a widespread distribution with a higher signal in the thalamus and occipital cortex and lower binding in the cerebellum. TSPO was expressed throughout the whole brain and about 73 % of [(18)F]DPA-714 binding was specific for TSPO in vivo. The one-tissue compartment model (1-TCM) provided good and reproducible estimates of V T and rate constants, and V T values from the 1-TCM and the Logan approach were highly correlated (r (2) = 0.85). QA lesioning induced an increase in V T, which was +17 %, +54 %, +157 % and +39 % higher than baseline on days 7, 14, 21 and 91 after QA injection, respectively. Immunohistochemistry revealed an early microglial and a delayed astrocytic activation after QA injection. [(18)F]DPA-714 binding matched TSPO immunopositive areas and showed a stronger colocalization with CD68 microglia than with GFAP-activated astrocytes.

CONCLUSION

[(18)F]DPA-714 binds to TSPO with high specificity in the primate brain under normal conditions and in the QA model. This tracer provides a sensitive tool for assessing neuroinflammation in the human brain.

β1-Integrin and integrin linked kinase regulate astrocytic differentiation of neural stem cells

Astrogliosis with glial scar formation after damage to the nervous system is a major impediment to axonal regeneration and functional recovery. The present study examined the role of β1-integrin signaling in regulating astrocytic differentiation of neural stem cells. In the adult spinal cord β1-integrin is expressed predominantly in the ependymal region where ependymal stem cells (ESCs) reside. β1-integrin signaling suppressed astrocytic differentiation of both cultured ESCs and subventricular zone (SVZ) progenitor cells. Conditional knockout of β1-integrin enhanced astrogliogenesis both by cultured ESCs and by SVZ progenitor cells. Previous studies have shown that injection into the injured spinal cord of a self-assembling peptide amphiphile that displays an IKVAV epitope (IKVAV-PA) limits glial scar formation and enhances functional recovery. Here we find that injection of IKVAV-PA induced high levels of β1-integrin in ESCs in vivo, and that conditional knockout of β1-integrin abolished the astroglial suppressive effects of IKVAV-PA in vitro. Injection into an injured spinal cord of PAs expressing two other epitopes known to interact with β1-integrin, a Tenascin C epitope and the fibronectin epitope RGD, improved functional recovery comparable to the effects of IKVAV-PA. Finally we found that the effects of β1-integrin signaling on astrogliosis are mediated by integrin linked kinase (ILK). These observations demonstrate an important role for β1-integrin/ILK signaling in regulating astrogliosis from ESCs and suggest ILK as a potential target for limiting glial scar formation after nervous system injury.

Transplantation of induced pluripotent stem cells improves functional recovery in Huntington's disease rat model

The purpose of this study was to determine the functional recovery of the transplanted induced pluripotent stem cells in a rat model of Huntington's disease with use of 18F-FDG microPET/CT imaging.

METHODS

In a quinolinic acid-induced rat model of striatal degeneration, induced pluripotent stem cells were transplanted into the ipsilateral lateral ventricle ten days after the quinolinic acid injection. The response to the treatment was evaluated by serial 18F-FDG PET/CT scans and Morris water maze test. Histological analyses and Western blotting were performed six weeks after stem cell transplantation.

RESULTS

After induced pluripotent stem cells transplantation, higher 18F-FDG accumulation in the injured striatum was observed during the 4 to 6-weeks period compared with the quinolinic acid-injected group, suggesting the metabolic recovery of injured striatum. The induced pluripotent stem cells transplantation improved learning and memory function (and striatal atrophy) of the rat in six week in the comparison with the quinolinic acid-treated controls. In addition, immunohistochemical analysis demonstrated that transplanted stem cells survived and migrated into the lesioned area in striatum, and most of the stem cells expressed protein markers of neurons and glial cells.

CONCLUSION

Our findings show that induced pluripotent stem cells can survive, differentiate to functional neurons and improve partial striatal function and metabolism after implantation in a rat Huntington's disease model.

Visualization and genetic modification of resident brain microglia using lentiviral vectors regulated by microRNA-9

Functional studies of resident microglia require molecular tools for their genetic manipulation. Here we show that microRNA-9-regulated lentiviral vectors can be used for the targeted genetic modification of resident microglia in the rodent brain. Using transgenic reporter mice, we demonstrate that murine microglia lack microRNA-9 activity, whereas most other cells in the brain express microRNA-9. Injection of microRNA-9-regulated vectors into the adult rat brain induces transgene expression specifically in cells with morphological features typical of ramified microglia. The majority of transgene-expressing cells colabels with the microglia marker Iba1. We use this approach to visualize and isolate activated resident microglia without affecting circulating and infiltrating monocytes or macrophages in an excitotoxic lesion model in rat striatum. The microRNA-9-regulated vectors described here are a straightforward and powerful tool that facilitates functional studies of resident microglia.

Innate immunity in the Grid2Lc/+ mouse model of cerebellar neurodegeneration: glial CD95/CD95L plays a non-apoptotic role in persistent neuron loss-associated inflammatory reactions in the cerebellum

Background

There is growing evidence that the death receptor CD95 has a wider role in non-apoptotic functions. In the brain, it may contribute to neural death and to the associated inflammatory reaction via a non-apoptotic pathway. Brain injury triggers an inflammatory reaction in which the CD95/CD95L system acts principally through peripheral cells recruited to the lesion. In cases of inflammation within the brain, with no blood–brain barrier leakage, the role of the CD95/CD95L system is thus unclear. We investigated the possible role of CD95 and CD95L in such conditions, by studying the relationships between glial cell activation, neuron death and CD95/CD95L expression in the cerebellum of the Lurcher (Grid2^Lc/+) mutant mouse, a model of cerebellar neurodegeneration.

Methods

Glial cells in slices of wild-type and Lurcher mouse cerebella were observed by light microscopy at various ages overlapping periods of neuron loss and of pre- and post-neurodegeneration. Subcellular organization was studied by electron microscopy. We assessed CD95 levels by western blotting, RT-PCR and glial cell cultures. The levels of CD95L and IL-6 were studied by ELISA and a biological assay, respectively.

Results

In the Grid2^Lc/+cerebellum, neuron loss triggers a typical, but abnormally persistent, inflammatory reaction. We identified two phases of astrogliosis: an early burst of large glial cell activation, peaking at postnatal days 25 to 26, coinciding with peak cerebellar neuron loss, followed by a long period of slow decline indicating that the strength of the glial reaction is modulated by neuron mortality rates. Comparisons of time-courses of glial cell activation, cytokine production and neuron loss revealed that the number of surviving neurons decreased as CD95 increased. Thus, CD95 cannot be directly involved in neuron death, and its role must be limited to a contribution to the inflammatory reaction. The upregulation of CD95 likely on astrocytes coincides with increases in the levels of IL-6, a cytokine produced principally by astrocytes, and soluble CD95L.

Conclusions

These results suggest that CD95 and soluble CD95L contribute, via non-apoptotic signaling, to the inflammatory reaction initiated early in neuron death within the Grid2^Lc/+ cerebellum.

Human mesenchymal stem cells prolong survival and ameliorate motor deficit through trophic support in Huntington's disease mouse models

We investigated the therapeutic potential of human bone marrow-derived mesenchymal stem cells (hBM-MSCs) in Huntington's disease (HD) mouse models. Ten weeks after intrastriatal injection of quinolinic acid (QA), mice that received hBM-MSC transplantation showed a significant reduction in motor function impairment and increased survival rate. Transplanted hBM-MSCs were capable of survival, and inducing neural proliferation and differentiation in the QA-lesioned striatum. In addition, the transplanted hBM-MSCs induced microglia, neuroblasts and bone marrow-derived cells to migrate into the QA-lesioned region. Similar results were obtained in R6/2-J2, a genetically-modified animal model of HD, except for the improvement of motor function. After hBM-MSC transplantation, the transplanted hBM-MSCs may integrate with the host cells and increase the levels of laminin, Von Willebrand Factor (VWF), stromal cell-derived factor-1 (SDF-1), and the SDF-1 receptor Cxcr4. The p-Erk1/2 expression was increased while Bax and caspase-3 levels were decreased after hBM-MSC transplantation suggesting that the reduced level of apoptosis after hBM-MSC transplantation was of benefit to the QA-lesioned mice. Our data suggest that hBM-MSCs have neural differentiation improvement potential, neurotrophic support capability and an anti-apoptotic effect, and may be a feasible candidate for HD therapy.

Bioengineered scaffolds for spinal cord repair

Spinal cord injury can lead to devastating and permanent loss of neurological function, affecting all levels below the site of trauma. Unfortunately, the injured adult mammalian spinal cord displays little regenerative capacity and little functional recovery in large part due to a tissue environment that is nonpermissive for regenerative axon growth. Artificial tissue repair scaffolds may provide a physical guide to allow regenerative axon growth that bridges the lesion cavity and restores functional neural connectivity. By integrating different strategies, including the use of various biomaterials and microstructures as well as incorporation of bioactive molecules and living cells, combined or synergistic effects for spinal cord repair through regenerative axon growth may be achieved. This article briefly reviews the development of bioengineered scaffolds for spinal cord repair, focusing on spinal cord injury and the subsequent cellular response, scaffold materials, fabrication techniques, and current therapeutic strategies. Key issues and challenges are also identified and discussed along with recommendations for future research.

Chronic spinal injury repair by olfactory bulb ensheathing glia and feasibility for autologous therapy

Olfactory bulb ensheathing glia (OB-OEG) promote repair of spinal cord injury (SCI) in rats after transplantation at acute or subacute (up to 45 days) stages. The most relevant clinical scenario in humans, however, is chronic SCI, in which no more major cellular or molecular changes occur at the injury site; this occurs after the third month in rodents. Whether adult OB-OEG grafts promote repair of severe chronic SCI has not been previously addressed. Rats with complete SCI that were transplanted with OB-OEG 4 months after injury exhibited progressive improvement in motor function and axonal regeneration from different brainstem nuclei across and beyond the SCI site. A positive correlation between motor outcome and axonal regeneration suggested a role for brainstem neurons in the recovery. Functional and histological outcomes did not differ after transplantation at subacute or chronic stages. Thus, autologous transplantation is a feasible approach as there is a time frame for patient stabilization and OEG preparation; moreover, the healing effects of OB-OEG on established injuries may offer new therapeutic opportunities for chronic SCI patients.

NEOSTRIATAL CYTOSKELETON CHANGES FOLLOWING PERINATAL ASPHYXIA: EFFECT OF HYPOTHERMIA TREATMENT

Long-term changes of different types of neurofilaments (NF) and glial fibrillar acid protein (GFAP) were studied in neostriatal rat subjected to perinatal asphyxia (PA) under normothermic and hypothermic (15 degrees C) conditions, using immunohistochemistry for light and electron microscopy. Neostriatal neurons of 6-month-old rats that were subjected to 19 and 20 min of PA, showed an increase of NF 200 kDa immunostaining mainly in the axon fascicles in comparison with the control and hypothermia groups. In contrast, no alterations were seen with NF68 and NF160 neurofilament antibodies. Furthermore, the same PA groups showed astroglial cells with enhanced GFAP immunoreactivity, evidencing a typical astroglial reaction with a clear hypertrophy of these cells. A quantitative image analysis confirmed these observations. Hypothermic treated animals did show neither astroglial nor neuronal cytoskeletal changes in comparison to the control group. These findings showed that PA produces chronic cytoskeletal alterations in the neostriatum cells that can be prevented by hypothermia.

Neurons control the expression of connexin 30 and connexin 43 in mouse cortical astrocytes

A characteristic feature of astrocytes is their high level of intercellular communication mediated by gap junctions. The two main connexins, Cx30 and Cx43, that form these junctions in astrocytes of adult brain display different developmental and regional expression, with a delayed onset of appearance for Cx30. In primary cultures of astrocytes from newborn cerebral cortex, while Cx43 is abundantly expressed, Cx30 is not detectable. In the present report, Western blot and confocal immunofluorescence analysis performed in astrocyte/neuron cocultures demonstrate that neurons upregulate the expression of Cx43 and induce that of Cx30 in subsets of astrocytes preferentially located in close proximity to neuronal soma. In Cx43 lacking astrocytes cocultured with neurons, the induction of Cx30 allows the restoration of dye coupling within islets of Cx30-positive astrocytes, indicating that intercellular channels formed by Cx30 are functional. The upregulating effect of neurons on the expression of connexins in cortical astrocytes is independent of their electrical activity and requires tight interactions between both cell types. This effect is reversed after neuronal death induced by neurotoxic treatments. Furthermore, excitotoxic treatments triggering neuronal death in vivo lead to a downregulation of both connexins in reactive astrocytes located within the area depleted in neurons. Altogether these observations indicate that the expression of the two main astrocyte connexins is tightly regulated by neurons.

The promotive effects of thymosin beta4 on neuronal survival and neurite outgrowth by upregulating L1 expression

Thymosin beta(4) (Tbeta4) is a major actin-sequestering peptide widely distributed in mammalian tissues including the nervous system. The presence of this peptide in the nervous system likely plays a role in synaptogensis, axon growth, cell migration, and plastic changes in dendritic spine. However, the effects of Tbeta4 on the survival of neurons and axonal outgrowth have still not been fully understood. So far it is not clear if the effects of Tbeta4 are associated with L1 functions. In the present study, we hypothesized that Tbeta4-induced up-regulation of L1 synthesis could be involved in the survival and axon outgrowth of cultured spinal cord neurons. To test this hypothesis, primarily cultured neurons were prepared from the mouse spinal cord and treated with various concentrations of Tbeta4 ranging from 0.1 to 10 microg/ml. The analysis of L1 mRNA expression and protein synthesis in neurons was then carried out using RT-PCR and western blot assays, respectively. After the addition of Tbeta4 to cultures, cells were then treated with antibodies against distinct domains of L1-Fc. Subsequently, beta-tubulin III and L1 double-labeled indirect immunofluorescence was carried out. Meanwhile, L1 immunofluorescent reactivity was analyzed and compared in cells treated with Tbeta4. Furthermore, the number of beta-tubulin III-positive cells and neurite lengths were measured. We found that Tbeta4 enhanced L1 expression in a dose-dependent manner, and the highest L1 mRNA and protein synthesis in cells increased by more than 2.1- and 2.3-fold in the presence of Tbeta4 at identical concentrations, respectively. Moreover, it also dose dependently enhanced neurite outgrowth and neuronal survival. Compared to conditions without Tbeta4, the length of neurite and neuronal survival increased markedly in presence of 0.5, 1, and 5 microg/ml Tbeta4, respectively, whereas the effects of Tbeta4 were significantly attenuated or inhibited in the process of L1-Fc antibodies treatment. These above results indicate that the promotive effect of Tbeta4 on the survival and neurite outgrowth of cultured spinal cord neurons might be mediated, at least in part via a stimulation of the production of L1 in the neurons.

Rat focal cerebral ischemia induced astrocyte proliferation and delayed neuronal death are attenuated by cyclin-dependent kinase inhibition

Astroglial proliferation and delayed neuronal death are two common pathological processes in the ischemic brain. However, it is not clear if astrogliosis causes delayed neuronal death. In this study, we addressed this potential linkage by examining the relationship between attenuated astrocyte proliferation, induced by cyclin-dependent kinase (CDK) inhibition, and delayed neuronal death in rat ischemic hippocampus. Our results show that following middle cerebral artery occlusion (MCAO), astrocyte hypertrophy and proliferation were closely associated with delayed neuronal death. Importantly, administration of olomoucine, a selective CDK inhibitor, not only suppressed astroglial proliferation and glial scar formation, but also decreased neuronal cell death in the ischemic boundary zone and hippocampal CA1 region at days 1 and 30 after MCAO. These results indicate that reactive astrogliosis and delayed neuronal death, at least in rat hippocampus, are sequential pathological events following MCAO. Therefore, suppressing astroglial cell cycle progression in acute focal cerebral ischemia may be beneficial to neuronal survival. Our study also implies that cell cycle regulation should be considered as a promising future therapeutic intervention in treating those neurological diseases characterized by an excessive astrocyte proliferation.

Time of transplantation and cell preparation determine neural stem cell survival in a mouse model of Huntington’s disease

Cell replacement therapies for neurodegenerative diseases, using multipotent neural stem cells (NSCs), require above all, a good survival of the graft. In this study, we unilaterally injected quinolinic acid (QA) into the striatum of adult mice and transplanted syngeneic NSCs of enhanced green fluorescent protein-transgenic mice into the lesioned striatum. The injection of QA leads to an excitotoxic lesion with selective cell death of the medium sized spiny neurons, the same cells that are affected in Huntington's disease. In order to investigate the best timing of transplantation for the survival of donor cells, we transplanted the stem cells at 2, 7 and 14 days after injury. In addition, the influence of graft preparation prior to transplantation, i.e., intact neurospheres versus dissociated cell suspension on graft survival was investigated. By far the best survival was found with the combination of early transplantation (i.e., 2 days after QA-lesion) with the use of neurospheres instead of dissociated cell suspension. This might be due to the different states of host's astrocytic and microglia activation which we found to be moderate at 2, but pronounced at 7 and 14 days after QA-lesion. We also investigated brain derived neurotrophic factor (BDNF)-expression in the striatum after QA-lesion and found no significant change in BDNF protein-level. We conclude that already the method of graft preparation of NSCs for transplantation, as well as the timing of the transplantation procedure strongly affects the survival of the donor cells when grafted into the QA-lesioned striatum of adult mice.

Long-term gliosis around chronically implanted platinum electrodes in the Rhesus macaque motor cortex

Chronically implanted microelectrodes have been an important tool used by neuroscientists for many years and are critical for the development of neural prostheses designed to restore function after traumatic central nervous system (CNS) injury. It is well established that a variety of mammals, including non-human primates (NHP), tolerate noble metal electrodes in the cortex for extended periods of time, but little is known about the long-term effects of electrode implantation at the cellular level. While data from rodents have clearly shown gliosis around such implants, there have been difficulties in demonstrating these reactions in NHP. Glial reactions are to be expected in NHP, since any trauma to the mammalian CNS is believed to result in the formation of a glial scar consisting of reactive astrocytes and microglia around the injury site. Because a glial scar can potentially affect the quality of recordings or stimulations from implanted electrodes, it is important to determine the extent of gliosis around implants in NHP. We studied the response of cortical glial cells to chronic electrode implantation in the motor cortices of Rhesus macaques (Macaca mulatta) after 3 months and 3 years duration. Antibodies specific for astrocytes and microglia were used to detect the presence of glial reactions around electrode implant sites. Reactive glia were found within the cortical neuropil surrounding the chronically implanted noble metal electrodes. Reactive gliosis persisted over the time periods studied and demonstrates the importance of developing strategies to minimize this event, even around noble metal implants.

Progressive Reparative Gliosis in Aged Hosts and Interferences with Neural Grafts in an Animal Model of Huntington's Disease

1. Neural transplantation in Huntington's diseased patients is currently the only approach in the treatment of this neurodegenerative disorder. The clinical trial, unfortunately, includes only a small number of patients until now, since many important questions have not been answered yet. One of them is only mild to moderate improvement of the state in most of grafted patients. 2. We examined the morphological correlates in the response to intrastriatal grafting of fragments of foetal rat ventral mesencephalic tissue 1 month after transplantation in male Wistar rats within varying durations (from 2 to 38 weeks) of experimentally induced neurodegenerative process of the striatum (used as a model of Huntington's disease). Our goal was to determine the impact of advanced striatal damage and gliosis on the graft viability and host-graft integration. 3. The findings can be summarized as follows: The progressive reactive gliosis, which is not able to compensate continual reduction of the grey matter leading to an extensive atrophy of the striatum in a long-term lesions, results in formation of the compact glial network. This tissue cannot be considered the suitable terrain for successful graft development and formation of host-graft interconnections. 4. The progression of irreversible morphological changes in long-lasting neurodegenerative process within the striatum can be supposed one of the important factors, which may decrease our prospect of distinct improvement after neural grafting in patients in advanced stage of Huntington's disease, who still remain the leading group in clinical trials.

Neuroprotective agents: is effective on toxicity in glial cells?

1. Glial cells are the most abundant cell population in the central nervous system. The aim of this study was to examine the effects of melatonin, 7-nitroindazole, and riluzole on glutamate toxicity in primary glial cell culture. 2. Glutamate toxicity was induced by addition of 100 microM glutamate to the cultures, and then 100 microM melatonin, 500 microM 7-nitroindazole, and 10 (M riluzole were administered in different groups. Lactate Dehydrogenase activity and nitrite levels were determined at the 1st, 6th, and 24th h. 3. Melatonin, 7-nitroindazole, and riluzole decrease Lactate Dehydrogenase activity at the 1st, 6th, and 24th h (at all hours, p<0.05). Nitrite levels were decreased by melatonin and riluzole at the 1st, 6th, and 24th h. 4. In this study, we observed that melatonin, 7-nitroindazole, and riluzole are effective as protective agents on glutamate toxicity in mixed glial cells.

Effects of ischemia and anoxia on cell activation and cell cycle of cultured astrocytes in vitro

To examine the effects of ischemia and anoxia on cell activation and cell cycle of astrocytes in vitro, the cell cycles and the proliferation of astrocytes in different time points after ischemia and anoxia were studied by flow cytometry and BrdU labeling and the expression of GFAP and cyclin D1 was detected by the fluorescence immunochemistry. After ischemia and anoxia in vitro, the astrocytes in S phase were significantly increased as compared with those in the normal group and the proliferating ability of the astrocytes was highest 6 h after the treatment as revealed by BrdU pulse labeling, but the astrocytes in S phase and proliferating ability were decreased after 6 h. At the early stages of ischemia and anoxia, the positive staining intensity of GFAP was increased, peaked at 6th h, while 12 h after the ischemia and anoxia, the positive staining intensity of GFAP became weak, and the expression of cyclin D1 was gradually increased after the ischemic and anoxic damage. It is concluded that astrocytes are activated to proliferate and enter new cycle events by ischemia and anoxia, and cyclin D1 is implicated in the proliferation and repair of astrocytes. The cell cycle events are closely associated with the proliferation and activation of astrocytes.

Coding for the initiation of pseudopregnancy by temporally patterned activation of amygdalar NMDA receptors

Female rats modulate the number and interval between the intromissions the female receives during mating. This patterned vaginocervical stimulation (VCS) is critical for triggering long-term changes in prolactin (PRL) secretion necessary for pregnancy or pseudopregnancy (P/PSP). Previous work has shown that NMDA receptor activation in the posterodorsal medial amygdala (MEApd) is required at the time of mating for VCS to induce the twice-daily PRL surges characteristic of P/PSP. The current studies examined whether patterned activation of glutamate receptors within the MEApd induces P/PSP. In anesthetized, cycling females, three 0.27 microg NMDA infusions given at 30 min intervals into the MEApd initiated P/PSP, whereas a single NMDA infusion of the same total dose (0.8 microg) had no effect. In conscious, freely behaving females, three infusions of an excitatory amino acid (EAA) mixture applied at the same interval were more effective in initiating P/PSP and nocturnal PRL surges than were single infusions at the same or higher concentrations. Infusion intervals of 5 and 60 min as well as continuous 1 h infusion did not induce P/PSP. Finally, a synergistic effect was observed between EAA and mating stimulation, because a subthreshold EAA infusion combined with subthreshold numbers of intromissions induced P/PSP. These results demonstrate that repeated, properly spaced, temporally discreet periods of glutamate receptor activation within the MEApd, which mimic mating stimulation, encode for P/PSP. Such findings suggest that single intromissions normally release individually subthreshold quanta of glutamate within the MEApd that summate to induce P/PSP.

Grafts of brain-derived neurotrophic factor and neurotrophin 3-transduced primate Schwann cells lead to functional recovery of the demyelinated mouse spinal cord

Experimental studies provided overwhelming proof that transplants of myelin-forming cells achieve efficient remyelination in the CNS. Among cellular candidates, Schwann cells can be used for autologous transplantation to ensure robust remyelination of lesions and to deliver therapeutic factors in the CNS. In the present study, macaque Schwann cells expressing green fluorescent protein (GFP) were infected with human immunodeficiency virus-derived vectors overexpressing brain-derived neurotrophic factor (BDNF) or Neurotrophin 3 (NT-3), two neurotrophins that also modulate glial cell biology. The ability of transgenic Schwann cells to secrete growth factors was assessed by ELISA and showed 35- and 62-fold increases in BDNF and NT-3, respectively, in transduced macaque Schwann cell supernatants. Conditioned media of BDNF- and NT-3-transduced Schwann cells reduced Schwann cell proliferation and favored their differentiation in vitro. Transgenic cells were grafted in demyelinated spinal cords of adult nude mice. Two behavioral assays showed that NT-3- and BDNF-transduced Schwann cells promoted faster and stronger functional recovery than GFP-transduced Schwann cells. Morphological analysis indicated that functional recovery correlated with enhanced proliferation and differentiation of resident oligodendrocyte progenitors and enhanced oligodendrocyte and Schwann cell differentiation. Moreover, NT-3-transduced Schwann cells provided neuroprotection and reduced astrogliosis. These results underline the potential therapeutic benefit of combining neuroprotection and activation of myelin-forming cells to restore altered functions in demyelinating diseases of the CNS.

Similar calcification process in acute and chronic human brain pathologies

Cellular microcalcification observed in a diversity of human pathologies, such as vascular dementia, Alzheimer's disease, Parkinson's disease, astrogliomas, and posttraumatic epilepsy, also develops in rodent experimental models of central nervous system (CNS) neurodegeneration. Central to the neurodegenerative process is the inability of neurons to regulate intracellular calcium levels properly, and this is extensible to fine regulation of the CNS. This study provides evidence of a common pattern of brain calcification taking place in several human pathologies, and in the rat with glutamate-derived CNS lesions, regarding the chemical composition, physical characteristics, and histological environment of the precipitates. Furthermore, a common physical mechanism of deposit formation through nucleation, lineal growth, and aggregation is presented, under the modulation of protein deposition and elemental composition factors. Insofar as calcium precipitation reduces activity signals at no energy expense, the presence in human and rodent cerebral brain lesions of a common pattern of calcification may reflect an imbalance between cellular signals of activity and energy availability for its execution. If this is true, this new step of calcium homeostasis can be viewed as a general cellular adaptative mechanism to reduce further brain damage.

Glial overexpression of heme oxygenase-1: a histochemical marker for early stages of striatal damage

The level of heme oxygenase-1 (HO-1) in the normal striatum is below the limit of immunodetection. However, HO-1 is overexpressed in both neural and non-neural cells in response to a wide range of lesions. We induced different types of lesions affecting the striatal cells or the main striatal afferent systems in rats to investigate if overexpression of HO-1 could be a useful histochemical marker of striatal damage. Thirty-six hours after intrastriatal or intraventricular injection of excitotoxins that affect striatal neurons (ibotenic acid) or of neurotoxins that affect striatal dopaminergic (6-hydroxydopamine) or serotonergic (5,7-dihydroxytriptamine) afferent terminals, or after surgical lesioning of cortico-striatal projections, there was intense induction of striatal HO-1 immunoreactivity (HO-1-ir). Double immunolabeling revealed that the HO-1-ir was located in glial cells. After intrastriatal injection of ibotenic acid, a central zone of neuronal degeneration contained numerous round and pseudopodic HO-1-ir cells, and was surrounded by a ring of HO-1-ir cells, most of which were immunoreactive for astroglial markers. Intraventricular injection of neurotoxins induced astroglial HO-1-ir cells which were more evenly distributed throughout the lesioned or denervated areas. HO-1-ir microglial cells were also observed in areas subjected to mechanical damage. The HO-1-ir was markedly lower or absent 1 week after lesion, and even more so 3 weeks after, although some HO-1-ir cells were still observed after intrastriatal injection of ibotenic acid or surgical corticostriatal deafferentation. The results indicate that determination of glial HO-1-ir is a useful histochemical marker for early stages of striatal damage.

Soman poisoning increases neural progenitor proliferation and induces long-term glial activation in mouse brain

To date, only short-term glial reaction has been extensively studied following soman or other warfare neurotoxicant poisoning. In a context of cell therapy by neural progenitor engraftment to repair brain damage, the long-term effect of soman on glial reaction and neural progenitor division was analyzed in the present study. The effect of soman poisoning was estimated in mouse brains at various times ranging from 1 to 90 days post-poisoning. Using immunochemistry and dye staining techniques (hemalun-eosin staining), the number of degenerating neurons, the number of dividing neural progenitors, and microglial, astroglial or oligodendroglial cell activation were studied. Soman poisoning led to rapid and massive (post-soman day 1) death of mature neurons as assessed by hemalun-eosin staining. Following this acute poisoning phase, a weak toxicity effect on mature neurons was still observed for a period of 1 month after poisoning. A massive short-termed microgliosis peaked on day 3 post-poisoning. Delayed astrogliosis was observed from 3 to 90 days after soman poisoning, contributing to glial scar formation. On the other hand, oligodendroglial cells or their precursors were practically unaffected by soman poisoning. Interestingly, neural progenitors located in the subgranular zone of the dentate gyrus (SGZ) or in the subventricular zone (SVZ) of the brain survived soman poisoning. Furthermore, soman poisoning significantly increased neural progenitor proliferation in both SGZ and SVZ brain areas on post-soman day 3 or day 8, respectively. This increased proliferation rate was detected up to 1 month after poisoning.

Changes in sleep-wakefulness in the medial preoptic area lesioned rats: role of thermal preference

Changes in sleep-wakefulness (S-W) were studied in adult male Wistar rats, along with body temperature (T(b)), locomotor activity (LMA) and thermal preference, after the lesion of the medial preoptic area (mPOA) with N-methyl-D-aspartic acid (NMDA). The sleep was decreased after the lesion of the mPOA, but there was recovery when the rats were given freedom to stay in an ambient temperature (T(amb)) which they preferred. When given a choice between three T(amb) (24, 27 and 30 degrees C), the rats preferred 27 degrees C before the mPOA lesion, and 24 degrees C during the initial days after the lesion. There was a shift in the thermal preference to 30 degrees C, on the fourth week after the lesion, which coincided with the considerable recovery of sleep. The preference for higher T(amb) probably helped to improve sleep, as T(amb) of 30 degrees C is known to promote sleep. When the lesioned rats were not given the freedom to select the T(amb), there was no recovery in sleep. The mPOA seems to be essential for increasing the durations of slow wave sleep (SWS) episodes, especially the light SWS (S1), as they remained shorter than the pre-lesion value, even when the rats were given freedom to stay in a preferred T(amb). The homeostatic recovery of sleep, especially the night time sleep, resulted in the disruption of circadian sleep rhythm. But, the LMA, T(b) and thermal preference maintained their diurnal variation. T(b) and LMA were elevated after the mPOA lesion and they remained so till the end of the study.

Astrocytosis, microglia activation, oligodendrocyte degeneration, and pyknosis following acute spinal cord injury

Glial activation and degeneration are important outcomes in the pathophysiology of acute brain and spinal cord injury (SCI). Our main goal was to investigate the pattern of glial activation and degeneration during secondary degeneration in both gray matter (GM) and white matter (WM) following SCI. Adult rats were deeply anesthetized and injected with 20 nmol of N-methyl-D-aspartate (NMDA) into the ventral horn of rat spinal cord (SC) on T7. Animals were perfused after survival times of 1, 3, and 7 days. Ten-micrometer sections were submitted to immunocytochemistry for activated macrophages/microglia, astrocytes, oligodendrocytes, and myelin. Astrocyte activation was more intense in the vacuolated white matter than in gray matter and was first noticed in this former region. Microglial activation was more intense in the gray matter and was clear by 24 h following NMDA injection. Both astrocytosis and microglial activation were more intense in the later survival times. Conspicuous WM vacuolation was present mainly at the 3-day survival time and decreased by 7 days after the primary damage. Quantitative analysis revealed an increase in the number of pyknotic bodies mainly at the 7-day survival time in both ventral and lateral white matter. These pyknotic bodies were frequently found inside white matter vacuoles like for degenerating oligodendrocytes. These results suggest a differential pattern of astrocytosis and microglia activation for white and gray matter following SCI. This phenomenon can be related to the different pathological outcomes for this two SC regions following acute injury.

Inhibition of aconitase in astrocytes increases the sensitivity to chemical convulsants

Although there is evidence that astrocytes support neuronal function, the contribution of astrocytes to seizure onset and termination is not known. To determine whether there are changes in seizure susceptibility or neuronal damage when the ability of astrocytes to generate ATP is reduced, 0.5 nmol of fluorocitrate (FC) was injected into the right ventricle. Injection of FC alone did not produce electrographic or behavioral seizures and did not stress or injure neurons or astrocytes, as measured with silver stain and immunohistochemistry for HSP32 or HSP72. However, in animals pretreated with FC, administration of kainic acid, at a dose that does not initiate seizures in control animals (7 mg/kg), caused wet dog shakes and neuronal damage in the hilus. Wet dog shakes did not cause any neuronal damage in control animals. If the dose of FC was increased to 0.75 nmol, then subsequent administration of the same dose of kainic acid (7 mg/kg) caused stage 3-5 seizures. Injection of FC also reduced the dose of pilocarpine needed to produce seizures. Given simultaneously with FC, isocitrate, which bypasses the biochemical inhibition of aconitase, blocked the effects of FC in both kainic acid and pilocarpine treated animals. The data demonstrate that inhibition of aconitase in astrocytes lowers the doses of both kainic acid and pilocarpine that will cause behavioral seizures and may increase neuronal vulnerability to seizures.

Systemic administration of N-acetylcysteine protects dopaminergic neurons against 6-hydroxydopamine-induced degeneration

The results of several in vitro studies have shown that cysteine prodrugs, particularly N-acetylcysteine, are effective antioxidants that increase the survival of dopaminergic neurons. N-acetylcysteine can be systemically administered to deliver cysteine to the brain and is of potential use for providing neuroprotection in the treatment of Parkinson's disease. However, it has also been reported that an excess of cysteine may induce neurotoxicity. In the present study, we injected adult rats intrastriatally with 2.5 microl of 6-hydroxydopamine (7.5 microg) and N-acetylcysteine (240 mM) or cysteine (240 mM) or intraventricularly with 6-hydroxydopamine (200 microg) and subcutaneously with N-acetylcysteine (10 and 100 mg/kg). We studied the effects of these compounds on both the nigrostriatal dopaminergic terminals and the surrounding striatal tissue. The tissue was stained with fluoro-jade (a marker of neuronal degeneration) and processed by immunohistochemistry to detect tyrosine hydroxylase, neuronal and glial markers, and the stress protein heme-oxygenase-1. After intrastriatal injection, both cysteine and N-acetylcysteine had clear neuroprotective effects on the striatal dopaminergic terminals, but also led to neuronal degeneration (as revealed by fluoro-jade staining) and astroglial and microglial activation, as well as intense induction of heme-oxygenase-1 in astrocytes and microglial cells. Subcutaneous administration of N-acetylcysteine also induced significant reduction of the dopaminergic lesion (about 30% reduction). However, we did not observe appreciable N-acetylcysteine-induced fluoro-jade labeling in striatal neurons or any of the above-mentioned changes in striatal glial cells. The results suggest that low doses of cysteine prodrugs may be useful neuroprotectors in the treatment of Parkinson's disease.

Ectopic parvalbumin expression in mouse forebrain neurons increases excitotoxic injury provoked by ibotenic acid injection into the striatum

A neuroprotective role for Ca(2+)-binding proteins in neurodegenerative conditions ranging from ischemia to Alzheimer's disease has been suggested in several studies. A key phenomenon in neurodegeneration is the Ca(2+)-mediated excitotoxicity brought about by the neurotransmitter glutamate. To evaluate the relative ability to resist excitotoxicity of neurons containing the slow-onset Ca(2+)-binding protein parvalbumin (PV), we injected the glutamate agonist ibotenic acid (IBO) into the striatum of adult mice ectopically expressing PV in neurons. Striatal ibotenic acid injection results in local nerve cell loss and reactive astrogliosis. Light microscopic evaluation, carried out after a delay of 2 and 4 weeks, reveals an enlarged and accelerated neurodegenerative process in mice ectopically expressing neuronal PV. Thus, PV is not neuroprotective, it rather enhances nerve cell death. This result implicates that the increase in cytosolic Ca(2+)-buffering capacity in the transgenic mice impairs other systems involved in Ca2+ sequestration. In addition, ultrastructural morphometric analysis shows that in neurons the mitochondrial volume is reduced in mice ectopically expressing neuronal PV. This is paralleled by a reduction in the amount of the mitochondrial marker enzyme cytochrome c oxidase subunit I (COXI). We conclude that alterations in the Ca(2+) homeostasis present in mice ectopically expressing neuronal PV are more deleterious under excitotoxic stress and largely outweigh the potential benefits of an increased Ca(2+)-buffering capacity resulting from PV.

Novel peripheral benzodiazepine receptor ligand [11C]DAA1106 for PET: An imaging tool for glial cells in the brain

Peripheral benzodiazepine receptor (PBR) is expressed in most organs and its expression is reported to be increased in activated microglia in the brain. [(11)C]PK11195 has been widely used for the in vivo imaging of PBRs, but its signal in the brain was not high enough for stable quantitative analysis. We synthesized a novel positron emission tomography (PET) ligand, [(11)C]DAA1106, for PBR and investigated its in vivo properties in rat and monkey brain. High uptake of [(11)C]DAA1106 was observed in the olfactory bulb and choroid plexus area, followed by the pons/medulla and cerebellum by in vivo autoradiography of rat brain, correlating with the binding in vitro. [(11)C]DAA1106 binding was increased in the dorsal hippocampus with neural destruction, suggesting glial reaction. [(11)C]DAA1106 binding was both inhibited and displaced by 1.0 mg/kg of DAA1106 and 5 mg/kg of PK11195 by 80% and 70%, respectively. Specific binding was estimated as 80% of total binding. [(11)C]DAA1106 binding was four times higher compared to the binding of [(11)C]PK11195 in the monkey occipital cortex. These results indicated that [(11)C]DAA1106 might be a good ligand for in vivo imaging of PBR.

Long-term pregabalin treatment protects basal cortices and delays the occurrence of spontaneous seizures in the lithium-pilocarpine model in the rat

PURPOSE

To determine whether a pharmacologic treatment could delay or prevent the epileptogenesis induced by status epilepticus (SE) through the protection of some brain areas, we studied the effects of the long-term exposure to pregabalin (PGB) on neuronal damage and epileptogenesis induced by lithium-pilocarpine SE.

METHODS

SE was induced in adult and 21-day-old (P21) rats. At 20 min after pilocarpine, rats received 50 mg/kg PGB (pilo-preg) or saline (pilo-saline). PGB treatment was given daily at the dose of 50 mg/kg for 7 days after SE and at 10 mg/kg from day 8 until killing. Neuronal damage was assessed in hippocampus and piriform and entorhinal cortices in brain sections stained with thionine and obtained from adult and P21 animals killed 6 days after SE. The number of glial fibrillary acidic protein (GFAP)-reactive astrocytes was tested by immunohistochemistry in sections adjacent to those used for cell counting. The latency to spontaneous seizures was controlled by visual observation and EEG recording.

RESULTS

PGB induced neuroprotection in layer II of piriform cortex and layers III-IV of ventral entorhinal cortex of adult rats, whereas no hippocampal region was protected. In P21 rats, damage was limited to the hilus and similar in pilo-preg and pilo-saline animals. The number of GFAP-positive astrocytes was higher in pilocarpine- than in saline-treated rats. It was decreased in pilo-preg compared with pilo-saline rats in layer II of the piriform cortex. Adult pilo-preg rats became epileptic after a longer latency (39 days) than did pilo-saline rats (22 days).

CONCLUSIONS

These data underline the antiepileptogenic consequences of long-term PGB treatment, possibly mediated by the protection of piriform and entorhinal cortices in the lithium-pilocarpine model of epilepsy.

Thrombin induces in vivo degeneration of nigral dopaminergic neurones along with the activation of microglia

Seven days after the injection of different concentrations of thrombin into the nigrostriatal pathway, a strong macrophage/microglial reaction was observed in the substantia nigra (SN), indicated by immunostaining, using OX-42 and OX-6 antibodies, and by the induction of iNOS, IL-1alpha, Il-1beta and TNF-alpha. Moreover, selective damage to dopaminergic neurones was produced after thrombin injection, evidenced by loss of tyrosine hydroxylase immunostaining and tyrosine hydroxylase mRNA-expressing cell bodies, and the unaltered transcription of glutamic acid decarboxylase mRNA in the SN and striatum. These thrombin effects could be produced by its ability to induce the activation of microglia described in in vitro studies, and are in agreement with the effects described for other proinflammatory compounds. Thrombin effects are produced by its biological activity since they almost disappeared when thrombin was heat-inactivated or injected along with its inhibitor alpha-NAPAP. Thrombin is a multi-functional serine protease rapidly produced from prothrombin at the sites of tissue injury, and also upon breakdown of the blood-brain barrier, which strongly suggests it could easily enter into the CNS. These results could have special importance in some degenerative processes of the nigrostriatal dopaminergic system.

Excitotoxic lesioning of the rat basal forebrain with S-AMPA: consequent mineralization and associated glial response

Regional depositions of calcium within the basal ganglia, cortex, cerebellum, and white matter and at perivascular sites have been observed in several pathological conditions. These generally indicate signs of ongoing apoptosis or necrotic processes, whereby the activation of glutamate receptors causes a rise in intracellular calcium levels leading to mineralization of neurons, and ultimately to cell death. The selective degeneration of cholinergic neurons in the basal forebrain is a major neuropathological component of Alzheimer's disease, and may result in abnormal deposition of calcium. In experimental models, selective lesions of the basal forebrain can be induced by intraparenchymal infusions of excito- or immunotoxins targeting cholinergic neurons. Excitotoxic lesions are often accompanied by calcium deposition within affected areas. In a previous study we also noted the presence of unusual deposition in areas close to the site of injections following unilateral S-AMPA-induced lesions of the basal forebrain (T. Perry, H. Hodges, and J. A. Gray, 2001, Brain Res. Bull. 54, 29-48). In this paper, we have characterized these deposits histologically and evaluated the microglial (CD11b) and astrocytic (GFAP) responses at 8 and 16 weeks following lesioning of the nucleus basalis magnocellularis with S-AMPA. The resulting deposits were heterogeneous in morphology and composed primarily of calcium. Small granular deposits were detected around blood vessels, whereas larger calcospherites were situated within the parenchyma. These deposits were more widely dispersed at 16 weeks postlesioning, affected neighboring nuclei, and displayed a progressive increase in size and frequency of occurrence. However, calcification within these regions was differentially associated with microglial and astrocytic reactivity at the two time points. Both microglial and astrocytic responses were pronounced at 8 weeks, whereas at 16 weeks, astrocytic reactivity prevailed and the microglial response was markedly attenuated. Importantly, the pattern of reactivity for microglia detected at 8 weeks was specifically localized to vulnerable nucleated areas prior to their substantial accumulation of calcium deposits, which was clearly evident by 16 weeks. We suggest that the initial microglial response could be used as a selective predictor of tissue necrosis and subsequent calcification, and that astrocytes, which form a glial scar in the affected tissues, may contribute toward the buildup of calcium deposits. The functional relevance of these findings is discussed.

Lesion of substantia nigra pars compacta by the GluR5 agonist ATPA

Dopamine (DA) released by substantia nigra pars compacta (SNc) neurons is a key regulator of motor activity. A deficiency in the striatum DA content due to SNc degeneration is a characteristic of Parkinson's disease. The involvement of excitotoxic mechanisms in this pathology has been suggested. The kainate receptor subunit GluR5 has been identified in a few basal ganglia but it is strongly expressed in SNc. Here we examine whether (RS)-2-amino-3-(3-hydroxy-5-tbutylisoxazol-4-yl) propanoic acid (ATPA), a selective agonist of GluR5, induces damage in dopaminergic (DAergic) neurons. ATPA (13 nmol) was administered to rat SNc. Immediately after recovery from surgery, the rats displayed ipsilateral turning. This behavior disappeared in subsequent days. The administration of the D1/D2 agonist, apomorphine (1 mg/kg, s.c.) 1 and 2 weeks after ATPA-infusion also induced ipsilateral turning. Histological studies-performed 21 days after ATPA-infusion-showed a lesion of the lateral and central part of the SNc, where a significant loss (36%) of DAergic cells was detected by tyrosine hydroxylase immunohistochemistry. The lesion was restricted to the SNc, since no damage or glial reaction was observed in the substantia nigra pars reticulata as assessed by Nissl staining, tomato lectin staining for microglial cells and GFAP immunohistochemistry for astrocytes.

IN CONCLUSION

(1). ATPA-infusion induces neuronal damage in the SNc in the rat and (2). the behavioral effects of unilateral infusion of ATPA are consistent with DAergic alterations in basal ganglia.

Connexin-30 mRNA is up-regulated in astrocytes and expressed in apoptotic neuronal cells of rat brain following kainate-induced seizures

Glial connexins (Cxs) make an extensively interconnected functional syncytium created by a network of gap junctions between astrocytes and oligodendrocytes. Among Cxs expressed in the brain, Cx30 is expressed in grey matter astrocytes, as shown at the protein level by immunoistochemistry. In the present study we aimed to perform a detailed study of the regional distribution of Cx30 mRNA in the adult and postnatal developing rat brain, analyzing its expression by in situ hybridization, and determining its cell type localization by double labeling. Recently, it has been suggested that neuronal activity may control the level of intercellular communication between astrocytes through gap junctions channels. Thus, a second aim of the present study was to investigate the short-term effects of kainate-induced seizures on Cx30 expression. The results showed that, in basal condition, Cx30 was expressed only in grey matter astrocytes with distinct regional patterns in developing and adult brain. Kainate treatment induced strong and region-specific changes of astroglial Cx30 mRNA levels and expression of Cx30 mRNA in neuronal cells undergoing cell death, suggesting a direct or indirect involvement of this connexin in the neuronal apoptotic process.