Neuroprotection by both NMDA and non-NMDA receptor antagonists in in vitro ischemia

Neuroprotection against supra-lethal 'stroke in a dish' insults by an anti-excitotoxic receptor antagonist cocktail

The goal of this study was to identify cocktails of drugs able to protect cultured rodent cortical neurons against increasing durations of oxygen-glucose deprivation (OGD). As expected, a cocktail composed of an NMDA and AMPA receptor antagonists and a voltage gated Ca²⁺ channel blocker (MK-801, CNQX and nifedipine, respectively) provided complete neuroprotection against mild OGD. Increasingly longer durations of OGD necessitated increasing the doses of MK-801 and CNQX, until these cocktails ultimately failed to provide neuroprotection against supra-lethal OGD, even at maximal drug concentrations. Surprisingly, supplementation of any of these cocktails with blockers of TRPM7 channels for increasing OGD durations was not neuroprotective, unless these blockers possessed the ability to inhibit NMDA receptors. Supplementation of the maximally effective cocktail with other NMDA receptor antagonists augmented neuroprotection, suggesting insufficient NMDAR blockade by MK-801. Substitution of MK-801 in cocktails with high concentrations of a glycine site NMDA receptor antagonist caused the greatest improvements in neuroprotection, with the more potent SM-31900 superior to L689,560. Substitution of CQNX in cocktails with AMPA receptor antagonists at high concentrations also improved neuroprotection, particularly with the combination of SYM 2206 and NBQX. The most neuroprotective cocktail was thus composed of SM-31900, SYM2206, NBQX, nifedipine and the antioxidant trolox. Thus, the cumulative properties of antagonist potency and concentration in a cocktail dictate neuroprotective efficacy. The central target of supra-lethal OGD is excitotoxicity, which must be blocked to the greatest extent possible to minimize ion influx.

Inhibition of ionotropic GluR signaling preserves oligodendrocyte lineage and myelination in an ex vivo rat model of white matter ischemic injury

Preterm infants have a high risk of neonatal white matter injury (WMI). WMI leads to reduced myelination, inflammation, and clinical neurodevelopmental deficits for which there are no effective treatments. Ionotropic glutamate receptor (iGluR) induced excitotoxicity contributes to oligodendrocyte (OL) lineage cell loss and demyelination in brain models of neonatal and adult WMI. Here, we hypothesized that simulated ischemia (oxygen‑glucose deprivation) damages white matter via activation of iGluR signaling, and that iGluR inhibition shortly after WMI could mitigate OL loss, enhance myelination, and suppress inflammation in an ex vivo cerebellar slice model of developing WMI. Inhibition of iGluR signaling by a combined block of AMPA and NMDA receptors, shortly after simulated ischemia, restored myelination, reduced apoptotic OLs, and enhanced OL precursor cell proliferation and maturation as well as upregulated expression of transcription factors regulating OL development and remyelination. Our findings demonstrate that iGluR inhibition post‑injury alleviates OL lineage cell loss and inflammation and promotes myelination upon developing WMI. The findings may help to develop therapeutic interventions for the WMI treatment.

A Rationale for Hypoxic and Chemical Conditioning in Huntington's Disease

Neurodegenerative diseases are characterized by adverse cellular environments and pathological alterations causing neurodegeneration in distinct brain regions. This development is triggered or facilitated by conditions such as hypoxia, ischemia or inflammation and is associated with disruptions of fundamental cellular functions, including metabolic and ion homeostasis. Targeting intracellular downstream consequences to specifically reverse these pathological changes proved difficult to translate to clinical settings. Here, we discuss the potential of more holistic approaches with the purpose to re-establish a healthy cellular environment and to promote cellular resilience. We review the involvement of important molecular pathways (e.g., the sphingosine, δ-opioid receptor or N-Methyl-D-aspartate (NMDA) receptor pathways) in neuroprotective hypoxic conditioning effects and how these pathways can be targeted for chemical conditioning. Despite the present scarcity of knowledge on the efficacy of such approaches in neurodegeneration, the specific characteristics of Huntington’s disease may make it particularly amenable for such conditioning techniques. Not only do classical features of neurodegenerative diseases like mitochondrial dysfunction, oxidative stress and inflammation support this assumption, but also specific Huntington’s disease characteristics: a relatively young age of neurodegeneration, molecular overlap of related pathologies with hypoxic adaptations and sensitivity to brain hypoxia. The aim of this review is to discuss several molecular pathways in relation to hypoxic adaptations that have potential as drug targets in neurodegenerative diseases. We will extract the relevance for Huntington’s disease from this knowledge base.

The NMDA Receptor Antibody Paradox: A Possible Approach to Developing Immunotherapies Targeting the NMDA Receptor

N-methyl-D-aspartate receptors (NMDAR) play a key role in brain development and function, including contributing to the pathogenesis of many neurological disorders. Immunization against the GluN1 subunit of the NMDAR and the production of GluN1 antibodies is associated with neuroprotective and seizure-protective effects in rodent models of stroke and epilepsy, respectively. Whilst these data suggest the potential for the development of GluN1 antibody therapy, paradoxically GluN1 autoantibodies in humans are associated with the pathogenesis of the autoimmune disease anti-NMDA receptor encephalitis. This review discusses possible reasons for the differential effects of GluN1 antibodies on NMDAR physiology that could contribute to these phenotypes.

Long-term, Repeated Dose In Vitro Neurotoxicity of the Glutamate Receptor Antagonist L-AP3, Demonstrated in Rat Hippocampal Slice Cultures by Using Continuous Propidium Iodide Incubation

Most in vitro models are only used to assess short-term effects of test compounds. However, as demonstrated here, hippocampal slice cultures can be used for long-term studies. The test compound used was the metabotropic glutamate receptor antagonist, L(+)-2-amino-3-phosphonopropionic acid (L-AP3), which is known to be toxic in vivo after subchronic, but not acute, administration. Degenerative effects were monitored by measuring the cellular uptake of propidium iodide (PI; continuously present in the medium) and lactate dehydrogenase (LDH) leakage, and by using a panel of histological stains. Hippocampal slices, derived from 2-3 day old rats and grown for 3 weeks, were subsequently exposed for the next 3 weeks to 0, 10 or 100microM L-AP3, with PI (2microM) in the culture medium. Exposure to 100microM L-AP3 induced severe toxicity after 4-6 days, shown by massive PI uptake, LDH leakage, changes in MAP2 and GFAP immunostaining, and in Nissl and Timm staining. In contrast, 10microM L-AP3 did not induce detectable neuronal degeneration. Treatment with the NMDA receptor antagonist, MK-801, or the AMPA/KA receptor antagonist NBQX, together with 100microM L-AP3, reduced neurodegeneration down to close to control values. It is concluded that continuous incubation of hippocampal slice cultures with PI is technically feasible for use in studies of inducible neuronal degeneration over time.

The Role of Connexin-43 in the Inflammatory Process: A New Potential Therapy to Influence Keratitis

The studies outlined in this review highlight the relationship between inflammatory signaling molecules and connexin-43 (Cx43). Gap junction (GJ) channels and hemichannels (HCs) participate in the metabolic activity between intra- and extracellular space. Some ions and small molecules are exchanged from cell to cell or cell to extracellular space to affect the process of inflammation via GJ. We analyzed the effects of signaling molecules, such as innate immunity messengers, transcription factors, LPS, cytokine, inflammatory chemokines, and MMPs, on Cx43 expression during the inflammatory process. At the same time, we found that these signaling molecules play a critical role in the pathogenesis of keratitis. Thus, we assessed the function of Cx43 during inflammatory corneal disease. Corneal healing plays an essential role in the late stage of keratitis. We found that Cx43 is involved in wound healing. Studies have shown that the decrease of Cx43 can decrease the time of healing. We also report several Cx43 mimic peptides which can inhibit the activity of Cx43 Hc to mediate the releasing of adenosine triphosphate (ATP), which may in turn influence the inflammatory process.

From Cultured Rodent Neurons to Human Brain Tissue: Model Systems for Pharmacological and Translational Neuroscience

To investigate the enormous complexity of the functional and pathological brain there are a number of possible experimental model systems to choose from. Depending on the research question choosing the appropriate model may not be a trivial task, and given the dynamic and intricate nature of an intact living brain several models might be needed to properly address certain questions. In this review, we aim to provide an overview of neural cell and tissue culture, reflecting on historic methodological milestones and providing a brief overview of the state-of-the-art. We additionally present an example of an effective model system pipeline, composed of dissociated mouse cultures, organotypics, acute mouse brain slices, and acute human brain slices, in that order. The sequential use of these four model systems allows a balance and progression from experimental control to human applicability, and provides a meta-model that can help validate basic research findings in a translational setting. We then conclude with a few remarks regarding the necessity of an integrated approach when performing translational and neuropharmacological studies.

Differences in Reperfusion-Induced Mitochondrial Oxidative Stress and Cell Death Between Hippocampal CA1 and CA3 Subfields Are Due to the Mitochondrial Thioredoxin System

AIMS

The susceptibility of CA1 over CA3 to damage from cerebral ischemia may be related to the differences in reactive oxygen species (ROS) production/removal between the two hippocampal subfields. We aimed to measure CA1/CA3 differences in net ROS production in real time in the first 30 min of reperfusion in pyramidal cells. We aimed to determine the underlying cause of the differential vulnerability of CA1 and CA3.

RESULTS

Real-time determinations of mitochondrial H₂O₂ and, independently, glutathione (GSH) redox status from roGFP-based probes in individual pyramidal cells in organotypic hippocampal cultures during oxygen-glucose deprivation (OGD)-reperfusion (RP) demonstrate a significantly more oxidizing environment during RP in CA1 than CA3 mitochondria. Protein levels (immunohistochemistry and Western blots), roGFP2-based probe measurements during controlled mitochondrial production of ROS, and thioredoxin reductase (TrxR) inhibition by auranofin are consistent with a more effective mitochondrial thioredoxin (Trx) system in CA3. Inhibition of TrxR eliminates the differences in redox status and cell death between the regions. Overexpression of cytosolic Trx1 does not influence mitochondrial H₂O₂ production.

INNOVATION

Real-time changes of mitochondrial H₂O₂ and GSH in tissue cultures during early RP, and also during controlled production of superoxide and peroxide, reveal significant differences between CA1 and CA3. The mitochondrial Trx system is responsible for the observed differences during RP as well as for delayed cell death 18 h afterward.

CONCLUSION

Greater mitochondrial Trx efficacy in CA3 pyramidal cells results in less vulnerability to ischemia/reperfusion because of the less oxidizing environment in CA3 mitochondria during RP. Antioxid. Redox Signal. 27, 534-549.

The Role of Connexins in Wound Healing and Repair: Novel Therapeutic Approaches

Gap junctions are intercellular proteins responsible for mediating both electrical and biochemical coupling through the exchange of ions, second messengers and small metabolites. They consist of two connexons, with (one) connexon supplied by each cell. A connexon is a hexamer of connexins and currently more than 20 connexin isoforms have been described in the literature thus far. Connexins have a short half-life, and therefore gap junction remodeling constantly occurs with a high turnover rate. Post-translational modification, such as phosphorylation, can modify their channel activities. In this article, the roles of connexins in wound healing and repair are reviewed. Novel strategies for modulating the function or expression of connexins, such as the use of antisense technology, synthetic mimetic peptides and bioactive materials for the treatment of skin wounds, diabetic and pressure ulcers as well as cornea wounds, are considered.

The action of mimetic peptides on connexins protects fibroblasts from the negative effects of ischemia reperfusion

Connexins have been proposed as a target for therapeutic treatment of a variety of conditions. The main approaches have been by antisense or small peptides specific against connexins. Some of these peptides enhance communication while others interfere with connexin binding partners or bind to the intracellular and extracellular loops of connexins. Here, we explored the mechanism of action of a connexin mimetic peptide by evaluating its effect on gap junction channels, connexin protein levels and hemichannel activity in fibroblast cells under normal conditions and following ischemia reperfusion injury which elevates Cx43 levels, increases hemichannel activity and causes cell death. Our results showed that the effects of the mimetic peptide were concentration-dependent. High concentrations (100-300 μM) significantly reduced Cx43 protein levels and GJIC within 2 h, while these effects did not appear until 6 h when using lower concentrations (10-30 μM). Cell death can be reduced when hemichannel opening and GJIC were minimised.

Summary: Connexin mimetic peptides can reduce the levels of connexin proteins in cells and can prevent the spread of cell death that occurs following ischemia reperfusion injury, which has therapeutic potential.

Stressed neurons protect themselves by a tissue-type plasminogen activator-mediated EGFR-dependent mechanism

In the central nervous system, tissue-type plasminogen activator (tPA) has been associated with both pro-death and prosurvival actions on neurons. In most cases, this has been related to exogenous tPA. In the present study, we addressed the influence of endogenous tPA. We first observed an increased transcription of tPA following either in vivo global brain ischemia in rats or in vitro oxygen glucose deprivation (OGD) on mice and rats hippocampal slices. Hippocampal slices from tPA-deficient mice were more sensitive to OGD than wild-type slices. Pharmacological approaches targeting the known receptors of tPA revealed that only the inhibition of phosphorylation of epidermal growth factor receptors (EGFRs) prevented the neuroprotective effect of endogenous tPA. This study shows that ischemic hippocampal neurons overproduce endogenous tPA as an intend to protect themselves from ischemic death, by a mechanism involving an activation of EGFRs. Thus, strategies contributing to promote either endogenous production of tPA or its associated EGFR-linked signaling pathway may have beneficial effects following brain injuries such as stroke.

An Immunological Approach to Increase the Brain's Resilience to Insults

We have previously demonstrated the therapeutic potential of inducing a humoral response with autoantibodies to the N-methyl D-aspartate (NMDA) receptor using a genetic approach. In this study, we generated three recombinant proteins to different functional domains of the NMDA receptor, which is implicated in mediating brain tolerance, specifically NR1[21-375], NR1[313-619], NR1[654-800], and an intracellular scaffolding protein, Homer1a, with a similar anatomical expression pattern. All peptides showed similar antigenicity and antibody titers following systemic vaccination, and all animals thrived. Two months following vaccination, rats were administered the potent neurotoxin, kainic acid. NR1[21-375] animals showed an antiepileptic phenotype but no neuroprotection. Remarkably, despite ineffective antiepileptic activity, 6 of 7 seizing NR1[654-800] rats showed absolutely no injury with only minimal changes in the remaining animal, whereas the majority of persistently seizing rats in the other groups showed moderate to severe hippocampal injury. CREB, BDNF, and HSP70, proteins associated with preconditioning, were selectively upregulated in the hippocampus of NR1[654-800] animals, consistent with the observed neuroprotective phenotype. These results identify NR1 epitopes important in conferring anticonvulsive and neuroprotective effects and support the concept of an immunological strategy to induce a chronic state of tolerance in the brain.

N-acetyl-serotonin offers neuroprotection through inhibiting mitochondrial death pathways and autophagic activation in experimental models of ischemic injury

N-acetylserotonin (NAS) is an immediate precursor of melatonin, which we have reported is neuroprotective against ischemic injury. Here we test whether NAS is a potential neuroprotective agent in experimental models of ischemic injury. We demonstrate that NAS inhibits cell death induced by oxygen-glucose deprivation or H2O2 in primary cerebrocortical neurons and primary hippocampal neurons in vitro, and organotypic hippocampal slice cultures ex vivo and reduces hypoxia/ischemia injury in the middle cerebral artery occlusion mouse model of cerebral ischemia in vivo. We find that NAS is neuroprotective by inhibiting the mitochondrial cell death pathway and the autophagic cell death pathway. The neuroprotective effects of NAS may result from the influence of mitochondrial permeability transition pore opening, mitochondrial fragmentation, and inhibition of the subsequent release of apoptogenic factors cytochrome c, Smac, and apoptosis-inducing factor from mitochondria to cytoplasm, and activation of caspase-3, -9, as well as the suppression of the activation of autophagy under stress conditions by increasing LC3-II and Beclin-1 levels and decreasing p62 level. However, NAS, unlike melatonin, does not provide neuroprotection through the activation of melatonin receptor 1A. We demonstrate that NAS reaches the brain subsequent to intraperitoneal injection using liquid chromatography/mass spectrometry analysis. Given that it occurs naturally and has low toxicity, NAS, like melatonin, has potential as a novel therapy for ischemic injury.

N-acetyl-serotonin offers neuroprotection through inhibiting mitochondrial death pathways and autophagic activation in experimental models of ischemic injury

N-acetylserotonin (NAS) is an immediate precursor of melatonin, which we have reported is neuroprotective against ischemic injury. Here we test whether NAS is a potential neuroprotective agent in experimental models of ischemic injury. We demonstrate that NAS inhibits cell death induced by oxygen-glucose deprivation or H2O2 in primary cerebrocortical neurons and primary hippocampal neurons in vitro, and organotypic hippocampal slice cultures ex vivo and reduces hypoxia/ischemia injury in the middle cerebral artery occlusion mouse model of cerebral ischemia in vivo. We find that NAS is neuroprotective by inhibiting the mitochondrial cell death pathway and the autophagic cell death pathway. The neuroprotective effects of NAS may result from the influence of mitochondrial permeability transition pore opening, mitochondrial fragmentation, and inhibition of the subsequent release of apoptogenic factors cytochrome c, Smac, and apoptosis-inducing factor from mitochondria to cytoplasm, and activation of caspase-3, -9, as well as the suppression of the activation of autophagy under stress conditions by increasing LC3-II and Beclin-1 levels and decreasing p62 level. However, NAS, unlike melatonin, does not provide neuroprotection through the activation of melatonin receptor 1A. We demonstrate that NAS reaches the brain subsequent to intraperitoneal injection using liquid chromatography/mass spectrometry analysis. Given that it occurs naturally and has low toxicity, NAS, like melatonin, has potential as a novel therapy for ischemic injury.

Hyperglycemia in stroke and possible treatments

Hyperglycemia affects approximately one-third of acute ischemic stroke patients and is associated with poor clinical outcomes. In experimental and clinical stroke studies, hyperglycemia has been shown to be detrimental to the penumbral tissue for several reasons. First, hyperglycemia exacerbates both calcium imbalance and the accumulation of reactive oxygen species (ROS) in neurons, leading to increased apoptosis. Second, hyperglycemia fuels anaerobic energy production, causing lactic acidosis, which further stresses neurons in the penumbral regions. Third, hyperglycemia decreases blood perfusion after ischemic stroke by lowering the availability of nitric oxide (NO), which is a crucial mediator of vasodilation. Lastly, hyperglycemia intensifies the inflammatory response after stroke, causing edema, and hemorrhage through disruption of the blood brain barrier and degradation of white matter, which leads to a worsening of functional outcomes. Many neuroprotective treatments addressing hyperglycemia in stroke have been implemented in the past decade. Early clinical use of insulin provided mixed results due to insufficiently controlled glucose levels and heterogeneity of patient population. Recently, however, the latest Stroke Hyperglycemia Insulin Network Effort trial has addressed the shortcomings of insulin therapy. While glucagon-like protein-1 administration, hyperbaric oxygen preconditioning, and ethanol therapy appear promising, these treatments remain in their infancy and more research is needed to better understand the mechanisms underlying hyperglycemia-induced injuries. Elucidation of these mechanistic pathways could lead to the development of rational treatments that reduce hyperglycemia-associated injuries and improve functional outcomes for ischemic stroke patients.

Organotypic brain slice cultures of adult transgenic P301S mice--a model for tauopathy studies

BACKGROUND

Organotypic brain slice cultures represent an excellent compromise between single cell cultures and complete animal studies, in this way replacing and reducing the number of animal experiments. Organotypic brain slices are widely applied to model neuronal development and regeneration as well as neuronal pathology concerning stroke, epilepsy and Alzheimer's disease (AD). AD is characterized by two protein alterations, namely tau hyperphosphorylation and excessive amyloid β deposition, both causing microglia and astrocyte activation. Deposits of hyperphosphorylated tau, called neurofibrillary tangles (NFTs), surrounded by activated glia are modeled in transgenic mice, e.g. the tauopathy model P301S.

METHODOLOGY/PRINCIPAL FINDINGS

In this study we explore the benefits and limitations of organotypic brain slice cultures made of mature adult transgenic mice as a potential model system for the multifactorial phenotype of AD. First, neonatal (P1) and adult organotypic brain slice cultures from 7- to 10-month-old transgenic P301S mice have been compared with regard to vitality, which was monitored with the lactate dehydrogenase (LDH)- and the MTT (3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assays over 15 days. Neonatal slices displayed a constant high vitality level, while the vitality of adult slice cultures decreased significantly upon cultivation. Various preparation and cultivation conditions were tested to augment the vitality of adult slices and improvements were achieved with a reduced slice thickness, a mild hypothermic cultivation temperature and a cultivation CO(2) concentration of 5%. Furthermore, we present a substantial immunohistochemical characterization analyzing the morphology of neurons, astrocytes and microglia in comparison to neonatal tissue.

CONCLUSION/SIGNIFICANCE

Until now only adolescent animals with a maximum age of two months have been used to prepare organotypic brain slices. The current study provides evidence that adult organotypic brain slice cultures from 7- to 10-month-old mice independently of the transgenic modification undergo slow programmed cell death, caused by a dysfunction of the neuronal repair systems.

Rat hippocampal slice culture models for the evaluation of neuroprotective agents

Organotypic slices cultured for weeks in vitro represent an extremely valuable strategy for the investigation of the long-term properties of neuronal circuits under physiological and pathological conditions. Here, we describe how to prepare rat organotypic hippocampal slice cultures and how to expose them for appropriate periods of time to excitotoxic agents or to oxygen and glucose deprivation conditions, in order to mimic the pattern of pyramidal cell damage which is observed in vivo and in other in vitro models. This preparation is very useful not only to study synaptic plasticity or the pathways and mechanisms of neurodegeneration but also to evaluate the effects of neuroprotective agents.

Interleukin-1beta does not affect the energy metabolism of rat organotypic hippocampal-slice cultures

The aim of this study was to examine the effect of the archetypal pro-inflammatory cytokine, interleukin-1beta (IL-1β), on high-energy phosphate levels within an ex vivo rat organotypic hippocampal-slice culture (OHSC) preparation using phosphorus ((31)P) magnetic resonance spectroscopy (MRS). Intrastriatal microinjection of IL-1β induces a chronic reduction in the apparent diffusion coefficient (ADC) of tissue water, which may be indicative of metabolic failure as established by in vivo models of acute cerebral ischaemia. The OHSC preparation enables examination of the effects of IL-1β on brain parenchyma per se, independent of the potentially confounding effects encountered in vivo such as perfusion changes, blood-brain barrier (BBB) breakdown and leukocyte recruitment. (31)P MRS is a technique that can detect multiple high-energy phosphate metabolites within a sample non-invasively. Here, for the first time, we characterise the energy metabolism of OHSCs using (31)P MRS and demonstrate that IL-1β does not compromise high-energy phosphate metabolism. Thus, the chronic reduction in ADC observed in vivo is unlikely to be a consequence of metabolic failure.

S100b counteracts neurodegeneration of rat cholinergic neurons in brain slices after oxygen-glucose deprivation

Alzheimer's disease is a severe chronic neurodegenerative disorder characterized by beta-amyloid plaques, tau pathology, cerebrovascular damage, inflammation, reactive gliosis, and cell death of cholinergic neurons. The aim of the present study is to test whether the glia-derived molecule S100b can counteract neurodegeneration of cholinergic neurons after oxygen-glucose deprivation (OGD) in organotypic brain slices of basal nucleus of Meynert. Our data showed that 3 days of OGD induced a marked decrease of cholinergic neurons (60% of control), which could be counteracted by 50 μg/mL recombinant S100b. The effect was dose and time dependent. Application of nerve growth factor or fibroblast growth factor-2 was less protective. C-fos-like immunoreactivity was enhanced 3 hours after OGD indicating metabolic stress. We conclude that S100b is a potent neuroprotective factor for cholinergic neurons during ischemic events.

Hypoxia in high glucose followed by reoxygenation in normal glucose reduces the viability of cortical astrocytes through increased permeability of connexin 43 hemichannels

Brain ischemia causes more extensive injury in hyperglycemic than normoglycemic subjects, and the increased damage is to astroglia as well as neurons. In the present work, we found that in cortical astrocytes from rat or mouse, reoxygenation after hypoxia in a medium mimicking interstitial fluid during ischemia increases hemichannel activity and decreases cell-cell communication via gap junctions as indicated by dye uptake and dye coupling, respectively. These effects were potentiated by high glucose during the hypoxia in a concentration-dependent manner (and by zero glucose) and were not observed in connexin 43(-/-) astrocytes. The responses were transient and persistent after short and long periods of hypoxia, respectively. The persistent responses were associated with a progressive reduction in cell viability that was prevented by La(3+) or peptides that block connexin 43 (Cx43) hemichannels or by inhibition of p38 MAP kinase prior to hypoxia-reoxygenation but not by treatments that block pannexin hemichannels. Block of Cx43 hemichannels did not affect the reduction in gap junction mediated dye coupling observed during reoxygenation. Cx43 hemichannels may be a novel therapeutic target to reduce cell death following stroke, particularly in hyperglycemic conditions.

Argon: neuroprotection in in vitro models of cerebral ischemia and traumatic brain injury

INTRODUCTION

Recently, it has been shown in several experimental settings that the noble gases xenon and helium have neuroprotective properties. In this study we tested the hypothesis that the noble gas argon has a neuroprotective potential as well. Since traumatic brain injury and stroke are widespread and generate an enormous economic and social burden, we investigated the possible neuroprotective effect in in vitro models of traumatic brain injury and cerebral ischemia.

METHODS

Organotypic hippocampal slice cultures from mice pups were subjected to either oxygen-glucose deprivation or to a focal mechanical trauma and subsequently treated with three different concentrations (25, 50 and 74%) of argon immediately after trauma or with a two-or-three-hour delay. After 72 hours of incubation tissue injury assessment was performed using propidium iodide, a staining agent that becomes fluorescent when it diffuses into damaged cells via disintegrated cell membranes.

RESULTS

We could show argon's neuroprotective effects at different concentrations when applied directly after oxygen-glucose deprivation or trauma. Even three hours after application, argon was still neuroprotective.

CONCLUSIONS

Argon showed a neuroprotective effect in both in vitro models of oxygen-glucose deprivation and traumatic brain injury. Our promising results justify further in vivo animal research.

Differential NMDA receptor-dependent calcium loading and mitochondrial dysfunction in CA1 vs. CA3 hippocampal neurons

Hippocampal CA1 pyramidal neurons are selectively vulnerable to ischemia, while adjacent CA3 neurons are relatively resistant. Although glutamate receptor-mediated mitochondrial Ca(2+) overload and dysfunction is a major component of ischemia-induced neuronal death, no direct relationship between selective neuronal vulnerability and mitochondrial dysfunction has been demonstrated in intact brain preparations. Here, we show that in organotypic slice cultures NMDA induces much larger Ca(2+) elevations in vulnerable CA1 neurons than in resistant CA3. Consequently, CA1 mitochondria exhibit stronger calcium accumulation, more extensive swelling and damage, stronger depolarization of their membrane potential, and a significant increase in ROS generation. NMDA-induced Ca(2+) and ROS elevations were abolished in Ca(2+)-free medium or by NMDAR antagonists, but not by zinc chelation. We conclude that Ca(2)(+) overload-dependent mitochondrial dysfunction is a determining factor in the selective vulnerability of CA1 neurons.

A secretory phospholipase A2-mediated neuroprotection and anti-apoptosis

BACKGROUND

Phospholipase A2 liberates free fatty acids and lysophospholipids upon hydrolysis of phospholipids and these products are often associated with detrimental effects such as inflammation and cerebral ischemia. The neuroprotective effect of neutral phospholipase from snake venom has been investigated.

RESULTS

A neutral anticoagulant secretory phospholipase A2 (nPLA) from the venom of Naja sputatrix (Malayan spitting cobra) has been found to reduce infarct volume in rats subjected to focal transient cerebral ischemia and to alleviate the neuronal damage in organotypic hippocampal slices subjected to oxygen-glucose deprivation (OGD). Real-time PCR based gene expression analysis showed that anti-apoptotic and pro-survival genes have been up-regulated in both in vivo and in vitro models. Staurosporine or OGD mediated apoptotic cell death in astrocytoma cells has also been found to be reduced by nPLA with a corresponding reduction in caspase 3 activity.

CONCLUSION

We have found that a secretory phospholipase (nPLA) purified from snake venom could reduce infarct volume in rodent stroke model. nPLA, has also been found to reduce neuronal cell death, apoptosis and promote cell survival in vitro ischemic conditions. In all conditions, the protective effects could be seen at sub-lethal concentrations of the protein.

EFFECTS OF ISCHEMIA-REPERFUSION ON NMDA RECEPTOR SUBUNITS 2A AND 2B LEVEL IN RAT HIPPOCAMPUS

The authors investigated the effects of ischemia and reperfusion on the N-methyl-D-aspartate receptor (NMDAR) subunits 2A and 2B concentration in rat hippocampus. At the protein level, significant increase in the amounts of NMDAR 2A and NMIDAR 2B in the rat hippocampus was observed at 1 h after reperfusion compared with control group. These results suggested that the alteration in hippocampal NMDAR2 subunit concentrations after ischemia-reperfusion might be invovlved in cognitive dysfunction and excitotoxicity.

Involvement of nitric oxide in 3-nitropropionic acid-induced depression of spinal reflexes in neonatal rat spinal cord in vitro

The objective of the present investigation is to study the involvement of nitric oxide (NO) in 3-nitropropionic acid (3-NPA)-induced depression of spinal reflexes. Experiments were conducted on preparations of hemisected spinal cord isolated from 4 to 8 day old rats. Stimulation of a dorsal root evoked reflex potentials (monosynaptic, MSR; polysynaptic, PSR) in the corresponding segmental ventral root. Superfusion of 3-NPA (3.4 mM) depressed the spinal reflexes in a time-dependent manner and the reflexes were abolished after 35 min. The time required to produce 50% depression of the reflexes (T-50) was 17.8+/-5.3 min for MSR and 17.5+/-2.1 min for PSR. L-NAME (Nomega-nitro-L-arginine methyl ester; 100 microM), a nitric oxide synthase inhibitor, antagonized the 3-NPA (3.4 mM)-induced depression of reflexes and increased the T-50 values (34 and 30 min for MSR and PSR, respectively) significantly (P<0.05). In addition, hemoglobin (Hb, 100 microM), a NO scavenger, blocked the 3-NPA-induced depression of reflexes significantly (P<0.05). T-50 values in Hb pretreated cords were 57 and 45 min for MSR and PSR, respectively which were greater than the cords pretreated with L-NAME. The nitrite (NO(2)(-)) content of the 3-NPA exposed cords was 84 microM/g of tissue which was significantly greater than the control (13 microM/g; P<0.05). Pretreatment of cords with L-NAME or Hb antagonized the 3-NPA-induced increase in NO(2)(-). The results indicate that NO produced by 3-NPA is involved in the 3-NPA-induced depression of spinal reflexes.

Berberine exerts neuroprotective actions against in vitro ischemia-induced neuronal cell damage in organotypic hippocampal slice cultures: involvement of B-cell lymphoma 2 phosphorylation suppression

In this study we elucidated the effects of berberine, a major alkaloid component contained in medicinal herbs, such as Phellodendri Cortex and Coptidis Rhizoma, on ischemic neuronal damage in mouse organotypic hippocampal slice cultures (OHSCs) caused by oxygen and glucose deprivation (OGD) and N-methyl-D-aspartate (NMDA) -type glutamate receptor stimulation. Hippocampal slices obtained from 7-d-old ICR mice were cultured for 10 d before the experiments. Ischemia-related damage was induced by OGD (5, 15, 45 min) or NMDA (10 microM) treatment, and was evaluated by measuring propidium iodide (PI) uptake. Levels of apoptotic marker proteins, B-cell lymphoma 2 (Bcl-2) and phosphorylated-Bcl-2 (p-Bcl-2), in the OHSCs were measured as indices of biochemical neuronal cell damage by Western blotting. Berberine (5, 25 microM) or the NMDA antagonist MK-801 (25 microM) was added to the medium 30 min before OGD or NMDA treatment. OGD time-dependently increased PI uptake of the OHSCs. Both berberine (5, 25 microM) and MK-801 (25 microM) significantly inhibited PI uptake at 24 h after 45-min OGD treatment and PI uptake in OHSCs exposed to NMDA for 24 h. OGD treatment also significantly increased the level of p-Bcl-2 but not that of Bcl-2 or glyceraldehyde-3-phosphate dehydrogenase (GAPDH) in OHSCs. Berberine (5-25 microM) significantly suppressed the OGD-induced increase of p-Bcl-2 level in OHSCs when tissue was exposed to the alkaloid prior to OGD or simultaneously with OGD. These findings suggest that berberine has protective effects against ischemic damage in mouse OHSCs and that the effects are at least partly mediated by suppression of Bcl-2 phosphorylation.

3-Nitropropionic acid depresses spinal reflexes involving GABAergic and glycinergic transmission in neonatal rat spinal cord in vitro

AIMS

3-Nitropropionic acid (3-NPA) is a naturally occurring fungal toxin that leads to ATP-depletion by inhibiting mitochondrial succinate dehydrogenase and produces chemical anoxia. The present study was conducted to identify the involvement of inhibitory system in 3-NPA-induced depression of spinal reflexes.

METHODS

The monosynaptic (MSR) and polysynaptic reflex (PSR) potentials were recorded at ventral root by stimulating the corresponding dorsal root in hemisected (sagitally) spinal cord from 4-8 day old rats. Effect of 3-NPA in the absence and presence of antagonists was evaluated on the reflexes.

KEY FINDINGS

Superfusion of 3-NPA (3.4 mM) depressed the reflexes in a time-dependent manner abolishing them by 35 min. The T-50 values were around 18 and 16 min for MSR and PSR, respectively. An NMDA receptor antagonist, DL-2-amino-5-phosphonovaleric acid (10 microM) failed to block the 3-NPA (3.4 mM)-induced depression of reflexes. Superfusion of bicuculline (GABAA receptor antagonist; 1 microM), or strychnine (glycineA receptor antagonist; 1 microM) antagonized the 3-NPA-induced depression of reflexes significantly. The T-50 values were 26 and 30 min in bicuculline and strychnine pretreated groups, respectively and were significantly greater than 3-NPA only group.

SIGNIFICANCE

The results indicate that 3-NPA-induced depression of spinal reflexes is partially mediated by GABAergic and glycinergic inhibitory transmission.

Neuroprotective effects of the AMPA antagonist PNQX in oxygen-glucose deprivation in mouse hippocampal slice cultures and global cerebral ischemia in gerbils

PNQX (9-methyl-amino-6-nitro-hexahydro-benzo(F)quinoxalinedione) is a selective AMPA antagonist with demonstrated neuroprotective effects in focal ischemia in rats. Here we report corresponding effects in mouse hippocampal slice cultures subjected to oxygen and glucose deprivation (OGD) and in transient global cerebral ischemia in gerbils. For in vitro studies, hippocampal slice cultures derived from 7-day-old mice and grown for 14 days, were submersed in oxygen-glucose deprived medium for 30 min and exposed to PNQX for 24 h, starting together with OGD, immediately after OGD, or 2 h after OGD. For comparison, other cultures were exposed to the NMDA antagonist MK-801 using the same protocol. Both PNQX and MK-801 displayed significant neuroprotective effects in all hippocampal subfields when present during and after OGD. When added just after OGD, only PNQX retained some neuroprotective effect. When added 2 h after OGD neither PNQX nor MK-801 had an effect. Transient global cerebral ischemia was induced in Mongolian gerbils by occlusion of both common carotid arteries for 4.5 min, with PNQX (10 mg/kg) being injected i.p. 30, 60 and 90 min after the insult. Subsequent analysis of brain sections stained for the neurodegeneration marker Fluoro-Jade B and immunostained for the astroglial marker glial fibrillary acidic protein revealed a significant PNQX-induced decrease in neuronal cell death and astroglial activation. We conclude that, PNQX provided neuroprotection against both global cerebral ischemia in gerbils in vivo and oxygen-glucose deprivation in mouse hippocampal slice cultures.

Toxicity of corticosteroids and catecholamines for mice neuronal cell cultures: Role of preservatives

OBJECTIVE

To confirm previous reports on dexamethasone and sulfite neurotoxicity, and to investigate methylprednisolone, dopamine, and dobutamine neurotoxicity.

METHODS

Pure dexamethasone, injectable dexamethasone containing sodium metabisulfite (Soludecadron), pure methylprednisolone, injectable methylprednisolone (Solu-Medrol), pure dopamine, injectable dopamine containing potassium metabisulfite (Revivan), pure dobutamine, injectable dobutamine containing sodium metabisulfite (Dobutrex), and sodium metabisulfite were added to the medium of mixed glial-neuronal cell cultures at concentrations of 0.1, 1, 10, and 100 microM. Cell damage induced by glucocorticoids was assessed by measuring the release of lactate dehydrogenase (LDH) from the injured cells into the extracellular fluid during the 24 hours of exposure to drugs. Cell damage induced by catecholamines was assessed using the fluorescent dye propidium iodide (PI) method 24 hours after exposure to the drugs.

RESULTS

Methylprednisolone and Solu-Medrol did not affect neuronal death, which was increased by dexamethasone and Soludecadron at 100 microM and sodium metabisulfite at 10 and 100 microM. Neuronal death was significantly increased by dopamine, Revivan, dobutamine, Dobutrex, and sulfites at 10 and 100 microM concentrations.

CONCLUSIONS

In vitro dexamethasone, Soludecadron, and sulfites increase neuronal cell death, while methylprednisolone and Solu-Medrol are not neurotoxic; dopamine and dobutamine were found neurotoxic independently from sulfite toxicity.

Cannabinoid modulation of neuronal function after oxygen/glucose deprivation in area CA1 of the rat hippocampus

Endocannabinoids released during cerebral ischemia have been implicated as neuroprotective agents. We assessed the role of cannabinoid receptors in modulating the response of neurons to oxygen/glucose deprivation (OGD), a model for in vitro ischemia, in rat hippocampal slices using extracellular recording techniques. Under control conditions, 15 min OGD resulted in only 50% recovery of CA1 field excitatory postsynaptic potentials (fEPSPs) 60 min post-insult. This post-OGD depression of function was primarily NMDA receptor-dependent as the NMDA receptor antagonist MK-801 (50 microM) promoted recovery of synaptic transmission to 76% of the baseline. Treatment with the CB1 receptor antagonist AM251 (1 microM), which prevented the depression of excitatory synaptic transmission caused by WIN55,212-2 (1 microM), also markedly enhanced recovery of function (71% of control). The enhanced recovery after OGD in the presence of AM251 was independent of both GABA(A) receptors and NMDA receptors since co-application of AM251 with either bicuculline (10 microM) or MK-801 (50 microM) did not alter recovery, or further improved recovery, respectively. These results suggest endocannabinoids released during OGD may modulate synaptic transmission and post-OGD neuronal outcome via activation of an AM251-sensitive cannabinoid receptor.

Down-regulation of GRK2 after oxygen and glucose deprivation in rat hippocampal slices: role of the PI3-kinase pathway

G protein-coupled receptor kinase 2 (GRK2) modulates G protein-coupled receptor desensitization and signaling. We previously described down-regulation of GRK2 expression in vivo in rat neonatal brain following hypoxia-ischemia. In this study, we investigated the molecular mechanisms involved in GRK2 down-regulation, using organotypic cultures of neonatal rat hippocampal slices exposed to oxygen and glucose deprivation (OGD). We observed a 40% decrease in GRK2 expression 4 h post-OGD. No changes in GRK2 protein occurred after exposure of hippocampal slices to glucose deprivation only. No significant alterations in GRK2 mRNA expression were detected, suggesting a post-transcriptional effect of OGD on GRK2 expression. Blockade of the proteasome pathway by MG132 prevented OGD-induced decrease of GRK2. It has been shown that extracellular signal-regulated kinase-dependent phosphorylation of GRK2 at Ser670 triggers its turnover via the proteasome pathway. However, despite a significant increase of pSer670-GRK2 after OGD, inhibition of the extracellular signal-regulated kinase pathway by PD98059 did neither prevent the hypoxia-ischemia-induced increase in pSer670-GRK2 nor the down-regulation of GRK2 protein. Interestingly, inhibition of phosphoinositide-3-kinase with wortmannin inhibits both OGD-induced phosphorylation of GRK2 on Ser670 and the GRK2 decrease. In conclusion, OGD-induced phosphoinositide-3-kinase-dependent phosphorylation of GRK2 on Ser670 is a novel mechanism leading to down-regulation of GRK2 protein via a proteasome-dependent pathway.

Protective effect of (4-methoxybenzylidene)-(3-methoxynophenyl)amine against neuronal cell death induced by oxygen and glucose deprivation in rat organotypic hippocampal slice culture

Resveratrol (trans-3,4',5-trihydroxystilbene) is a natural phytoalexin found in grape skin, and has been suggested to be an antioxidant agent, an anticancer agent and a cardioprotective agent. In particular, recent experimental evidence has demonstrated that resveratrol exhibits neuroprotective effects in various assay systems. During the study on the resveratrol derivatives, we found that (4-methoxybenzylidene)-(3-methoxyphenyl)amine (MBMPA), which has blocked free phenolic groups, strongly protects neuronal cells against ischemic damage on a higher activity than resveratrol. The MBMPA potently reduced the level of neuronal cell death in an oxygen and glucose deprivation-exposed rat organotypic hippocampal slice culture. In addition, ATP depletion following the onset of oxygen and glucose deprivation in an adult hippocampal slice was blocked by the MBMPA treatment. These results suggest that MBMPA has a neuroprotective effect on an in vitro ischemia model, and may be useful for treating stroke.

Quantitative structure−activity relationship (QSAR) for neuroprotective activity of terpenoids

Neuroprotective activity of thirteen terpenoids on human neuroblastoma SH-SY5Y was evaluated in vitro by using a simulated ischemia model. The protective effects on ischemic damage ranged from 3.0% to 56.5%, and trans-4,11,11-trimethyl-8-methylenebicyclo[7,2,0]undec-4-ene (trans-caryophyllene) showed the highest neuroprotective activity. A quantitative structure-activity relationship (QSAR) model was developed for eleven terpenoids with significant neuroprotective activity using TSAR software. The QSAR study produced two equations with significant predictive values (r(2) and p value) and indicated that the activity was mainly governed by lipophilicity, shape index, and electrostatic property. This QSAR approach can contribute to a better understanding of structural properties of the terpenoids responsible for neuroprotection, and can be useful in predicting the neuroprotective activity of other terpenoids.

Inducible cAMP early repressor (ICER)-evoked delayed neuronal death in the organotypic hippocampal culture

Programmed cell death involving gene regulation and de novo protein synthesis is a major component of both normal development and a number of disease conditions. Hence, knowledge of its mechanisms, especially transcription factors, that regulate expression of the genes involved in neurodegenerative disorders is of great importance. cAMP-responsive element-binding protein (CREB) has repeatedly been implicated in the neuronal survival. In the present study we showed that inducible cAMP early repressor (ICER), an endogenous CREB antagonist, is expressed during both excitotoxic and spontaneous neuronal cell death in organotypic hippocampal slice cultures in vitro. Furthermore, overexpression of ICER via an adenoviral vector evoked neuronal cell loss in such cultures. The time course of ICER-dependent cell death was hippocampal subdivision specific, with dentate gyrus neurons dying mostly 3-7 days after the adenovector infection, followed by CA3, where neuronal death peaked after 7 days, and then CA1, where most neuronal death occurred after 7-14 days. These results underscore the usefulness of the organotypic cultures for studies of neurodegeneration and point to neuronal loss having a multifaceted nature in a complex cellular environment.

3-Nitropropionic acid toxicity in hippocampus: protection through N-methyl-D-aspartate receptor antagonism

The over-activation of glutamate receptors can lead to excitotoxic cell death and is believed to be involved in the progression of neurodegenerative events in the vulnerable hippocampus. Here, we used an in vitro slice model to study toxicity produced in the hippocampus by the mitochondrial toxin 3-nitropropionic acid (3-NP). The organotypic slice cultures exhibit native cellular organization as well as dense arborization of neuronal processes and synaptic contacts. The hippocampal slices were exposed to 3-NP for 2-20 days, causing calpain-mediated breakdown of the spectrin cytoskeleton, a loss of pre- and postsynaptic markers, and neuronal atrophy. The N-methyl-D-aspartate (NMDA) receptor antagonist memantine reduced both the cytoskeletal damage and synaptic decline in a dose-dependent manner. 3-NP-induced cytotoxicity, as determined by the release of lactate dehydrogenase, was also reduced by memantine with EC50 values from 1.7 to 2.3 microM. Propidium iodide fluorescence and phase contrast microscopy confirmed memantine neuroprotection against the chronic toxin exposure. In addition, the protected tissue exhibited normal neuronal morphology in the major hippocampal subfields. These results indicate that antagonists of NMDA-type glutamate receptors are protective during the toxic outcome associated with mitochondrial dysfunction. They also provide further evidence of memantine's therapeutic potential against neurodegenerative diseases.

Oxidative modification of M-type K(+) channels as a mechanism of cytoprotective neuronal silencing

Voltage-gated K(+) channels of the Kv7 family underlie the neuronal M current that regulates action potential firing. Suppression of M current increases excitability and its enhancement can silence neurons. We here show that three of five Kv7 channels undergo strong enhancement of their activity by oxidative modification induced by physiological concentrations of hydrogen peroxide. A triple cysteine pocket in the channel S2-S3 linker is critical for this effect. Oxidation-induced enhancement of M current produced a hyperpolarization and a dramatic reduction of action potential firing frequency in rat sympathetic neurons. As hydrogen peroxide is robustly produced during hypoxia-induced oxidative stress, we used an oxygen/glucose deprivation neurodegeneration model that showed neuronal death to be severely accelerated by M current blockade. Such blockade had no effect on survival of normoxic neurons. This work describes a novel pathway of M-channel regulation and suggests a role for M channels in protective neuronal silencing during oxidative stress.

Quercetin inhibition of ROS-dependent and -independent apoptosis in rat glioma C6 cells

In the present study, we investigated the protective mechanism of quercetin (QUE) and its glycosides, rutin (RUT) and quercitrin (QUI), on reactive oxygen species (ROS)-dependent (H(2)O(2)) and -independent (chemical anoxia) cell death in rat glioma C6 cells. Induction of HO-1 protein expression was detected in QUE- but not RUT- or QUI-treated C6 cells, and this was prevented by cycloheximide and actinomycin D. Incubation of C6 cells with QUE, but not RUT or QUI, protected C6 cells from H(2)O(2)- and chemical anoxia-induced cytotoxicity according to the MTT and LDH release assays. Apoptotic characteristics including chromatin condensation, DNA ladders, and hypodiploid cells appeared in H(2)O(2)-and chemical anoxia-treated C6 cells, and those events were significantly suppressed by adding QUE (but not RUT or QUI). Increases in caspase 3, 8, and 9 enzyme activities with decreases in pro-PARP and pro-caspase 3 protein levels and an increase in cleaved D4-GDI protein were identified in H(2)O(2)-and chemical anoxia-treated C6 cells, and these were blocked by the addition of QUE, but not by RUT or QUI. Intracellular peroxide levels increased with H(2)O(2) and decreased with chemical anoxia, and the addition of QUE reduced the intracellular peroxide levels induced by H(2)O(2). Results of an anti-DPPH radical assay showed that QUE, RUT, and QUI dose-dependently inhibited the production of DPPH radicals in vitro; however, QUE (but not RUT or QUI) prevention of DNA damage induced by OH radicals was identified with a plasmid digestion assay. Increases in phosphorylated ERK and p53 protein expressions were detected in H(2)O(2)- but not chemical anoxia-treated C6 cells, and the addition of QUE significantly blocked H(2)O(2)-induced phosphorylated ERK and p53 protein expressions. Adding the HO-1 inhibitors, SnPP, CoPP, and ZnPP, reversed the protective effect of QUE against H(2)O(2)- and chemical anoxia-induced cell death according to the MTT assay and morphological observations. Additionally, QUE exhibited inhibitory effects on LPS/TPA-induced transformation in accordance with a decrease in MMP-9 enzyme activity and iNOS protein expression in C6 cells. Taken together, the results of this study suggest that QUE exhibits an inhibitory effect on both ROS-dependent and -independent cell death, and induction of HO-1 protein expression is involved.

Inhibitory effect of Total Flavone of Abelmoschus manihot L. Medic on NMDA receptor-mediated current in cultured rat hippocampal neurons

The modulatory effect of Total Flavone of Abelmoschus manihot L. Medic (TFA) on NMDA-activated current (I(NMDA)) was investigated in cultured rat hippocampal neurons using the whole-cell patch-clamp technique. TFA rapidly and reversibly inhibited the I(NMDA) in a concentration-dependent manner. Furthermore, TFA non-competitively inhibited the I(NMDA) by enhancement of the NMDA receptor desensitization. In addition, intracellular application of TFA did not alter the TFA inhibition of I(NMDA). These results suggest that the inhibition of the NMDA receptor response by TFA could be one of the mechanisms for TFA-mediated neuroprotective actions.

Glutamate receptor changes associated with transient anoxia/hypoglycaemia in hippocampal slice cultures

Transient anoxia/hypoglycaemia in organotypic hippocampal slice cultures, a model of transient brain ischaemia, ultimately results in delayed cell death. Although the mechanisms underlying this delayed death remain unknown, an increase in excitatory drive has been postulated. We report here that transient anoxia/hypoglycaemia in rat hippocampal slice cultures resulted in a 70-80% enhancement of evoked, alpha-amino-3-hydroxy-5-methyl-4-isoxazolpropionic acid (AMPA) receptor-mediated, excitatory responses lasting over 60 min. This effect was prevented by blockade of N-methyl-d-aspartate (NMDA) receptors, did not involve changes of paired-pulse facilitation ratio, but was associated with a 50% increase in amplitude, but not frequency, of spontaneous miniature excitatory postsynaptic currents (mEPSCs). Consistent with this, paired recordings revealed the appearance of AMPA receptor-mediated EPSCs at previously silent synapses and occlusion by prior induction of long-term potentiation (LTP). Transient anoxia/hypoglycaemia further resulted in a 63% potentiation of evoked NMDA receptor-dependent synaptic responses, accounting for the 20% increase in ratio of AMPA to NMDA responses. No change in rectification properties of AMPA receptor-mediated currents could be detected within the first hour following anoxia/hypoglycaemia-induced potentiation. Western blot analyses of slice cultures exposed to either control conditions or a short anoxia/hypoglycaemia revealed a marked, 50-70% increase of GluR1, GluR2/3 and NR1 subunits 1 h, but not 15 min, after the anoxic/hypoglycaemic episode. This increase was blocked by an inhibitor of protein synthesis. Together these results indicate that a transient anoxia/hypoglycaemia is associated with a marked enhancement of excitatory transmission sharing similarities with the mechanisms underlying LTP, and is correlated with an increased synthesis of excitatory receptor subunits.

Organotypic cultures as tools for functional screening in the CNS

A major challenge for the pharmaceutical industry is the development of relevant model systems in which knowledge gained from high-throughput, genomic and proteomic approaches can be integrated to study function. Animal models are still the main choice for such studies but over the past few years powerful new in vitro systems have begun to emerge as useful tools to study function. Organotypic cultures made from slices of explanted tissue represent a complex multi-cellular in vitro environment with the potential to assess biological function and are uniquely placed to act as an important link between high-throughput approaches and animal models.

Ionotropic glutamate receptors and glutamate transporters are involved in necrotic neuronal cell death induced by oxygen-glucose deprivation of hippocampal slice cultures

Organotypic hippocampal slice cultures represent a feasible model for studies of cerebral ischemia and the role of ionotropic glutamate receptors in oxygen-glucose deprivation-induced neurodegeneration. New results and a review of existing data are presented in the first part of this paper. The role of glutamate transporters, with special reference to recent results on inhibition of glutamate transporters under normal and energy-failure (ischemia-like) conditions is reviewed in the last part of the paper. The experimental work is based on hippocampal slice cultures derived from 7 day old rats and grown for about 3 weeks. In such cultures we investigated the subfield neuronal susceptibility to oxygen-glucose deprivation, the type of induced cell death and the involvement of ionotropic glutamate receptors. Hippocampal slice cultures were also used in our studies on glutamate transporters reviewed in the last part of this paper. Neurodegeneration was monitored and/or shown by cellular uptake of propidium iodide, loss of immunocytochemical staining for microtubule-associated protein 2 and staining with Fluoro-Jade B. To distinguish between necrotic vs. apoptotic neuronal cell death we used immunocytochemical staining for active caspase-3 (apoptosis indicator) and Hoechst 33342 staining of nuclear chromatin. Our experimental studies on oxygen-glucose deprivation confirmed that CA1 pyramidal cells were the most susceptible to this ischemia-like condition. Judged by propidium iodide uptake, a selective CA1 lesion, with only minor affection on CA3, occurred in cultures exposed to oxygen-glucose deprivation for 30 min. Nuclear chromatin staining by Hoechst 33342 and staining for active caspase-3 showed that oxygen-glucose deprivation induced necrotic cell death only. Addition of 10 microM of the N-methyl-D-aspartate glutamate receptor antagonist MK-801, and 20 microM of the non-N-methyl-D-aspartate glutamate receptor antagonist 2,3-dihyroxy-6-nitro-7-sulfamoyl-benzo(F)quinoxaline to the culture medium confirmed that both N-methyl-D-aspartate and non-N-methyl-D-aspartate ionotropic glutamate receptors were involved in the oxygen-glucose deprivation-induced cell death. Glutamate is normally quickly removed, from the extracellular space by sodium-dependent glutamate transporters. Effects of blocking the transporters by addition of the DL-threo-beta-benzyloxyaspartate are reviewed in the last part of the paper. Under normal conditions addition of DL-threo-beta-benzyloxyaspartate in concentrations of 25 microM or more to otherwise untreated hippocampal slice cultures induced neuronal cell death, which was prevented by addition of 2,3-dihyroxy-6-nitro-7-sulfamoyl-benzo(F)quinoxaline and MK-801. In energy failure situations, like cerebral ischemia and oxygen-glucose deprivation, the transporters are believed to reverse and release glutamate to the extracellular space. Blockade of the transporters by a subtoxic (10 microM) dose of DL-threo-beta-benzyloxyaspartate during oxygen-glucose deprivation (but not during the next 48 h after oxygen-glucose deprivation) significantly reduced the oxygen-glucose deprivation-induced propidium iodide uptake, suggesting a neuroprotective inhibition of reverse transporter activity by DL-threo-beta-benzyloxyaspartate during oxygen-glucose deprivation under these conditions. Adding to this, other results from our laboratory have demonstrated that pre-treatment of the slice cultures with glial cell-line derived neurotrophic factor upregulates glutamate transporters. As a logical, but in some glial cell-line derived neurotrophic factor therapy-related conditions clearly unwanted consequence the susceptibility for oxygen-glucose deprivation-induced glutamate receptor-mediated cell death is increased after glial cell-line derived neurotrophic factor treatment. In summary, we conclude that both ionotropic glutamate receptors and glutamate transporters are involved in oxygen-glucose deprivation-induced necrotic cell death in hippocampal slice cultures, which have proven to be a feasible tool in experimental studies on this topic.

Repetitive Spreading Depression-Like Events Result in Cell Damage in Juvenile Hippocampal Slice Cultures Maintained in Normoxia

Prolonged seizures, e.g., induced by fever, experienced early in life are considered a precipitating injury for the subsequent development of temporal lobe epilepsy. During in vitro epileptiform activity, spreading depressions (SDs) have often been observed. However, their contribution to changes in the properties of juvenile neuronal tissue is unknown. We therefore used the juvenile hippocampal slice culture preparation (JHSC) maintained in normoxia (20% O(2)-5% CO(2)-75% N(2)) to assess the effect of repetitive SD-like events (SDLEs) on fast field potentials and cell damage. Repetitive SDLEs in the CA1 region could be induced in about two-thirds of the investigated JHSCs (n = 61) by repetitive electrical stimulation with 2-200 pulses. SDLEs were characterized by a transient large negative field potential shift accompanied by intracellular depolarization, ionic redistribution, slow propagation (assessed by intrinsic optical signals) and glutamate receptor antagonist sensitivity. The term "SDLE" was used because evoked fast field potentials were only incompletely suppressed and superimposed discharges occurred. With 20 +/- 1 repetitive SDLEs (interval of 10-15 min, n = 7 JHSCs), the events got longer, their amplitude of the first peak declined, while threshold for induction became reduced. Evoked fast field potentials deteriorated and cell damage (assessed by propidium iodide fluorescence) occurred, predominantly in regions CA1 and CA3. As revealed by measurements of tissue partial oxygen pressure during SDLEs repetitive transient anoxia accompanying SDLE might be critical for the observed cell damage. These results, limited so far to the slice culture preparation, suggest SDs to be harmful events in juvenile neuronal tissue in contrast to what is known about their effect on adult neuronal tissue.