A simple in vitro model of ischemia based on hippocampal slice cultures and propidium iodide fluorescence

Potential Protective Function of Aβ42 Monomer on Tauopathies

While soluble forms of amyloid-β (Aβ) and Tau work together to drive healthy neurons into a disease state, how their interaction may control the prion-like propagation and neurotoxicity of Tau is not fully understood. The cross-linking via disulfide bond formation is crucial for Tau oligomers to obtain stable conformers and spread between cells. This work thus focuses on how Aβ₄₂ regulates this critical process. By studying the interactions between Aβ₄₂ and Tau_PHF43, a construct that mimics the Tau R3 isoform, has a similar length to Aβ42, and contains one cysteine (Cys-322), we discovered that fresh Aβ₄₂ could protect Tau against the formation of disulfide cross-linked dimers. We showed that the monomeric and small Aβ oligomers (the "nonamyloidogenic Aβ") efficiently disassembled tau dimers and heparin-induced Tau oligomers to recover Tau monomers. Interestingly, Aβ serves the role of an antioxidant to prevent disulfide bond formation, as supported by the experiments of Aβ with cystine. Furthermore, using cyclosporine A (CycA), a macrocyclic β-sheet disruptor, we demonstrated that targeting amyloidogenic Aβ with CycA does not affect the Tau_PHF43 disassembly driven by Aβ₄₂. Separately, we assessed the initial toxicity of Aβ₄₂ and Tau_PHF43 in acute brain slices and found that Aβ₄₂ is more toxic than Tau_PHF43 or the two peptides combined. Our work highlights a potential protective role of Aβ₄₂ monomers in AD that was previously overlooked while focusing on the mechanism behind Aβ₄₂ aggregation leading to tau dysfunction.

Promising Strategies for the Development of Advanced In Vitro Models with High Predictive Power in Ischaemic Stroke Research

Although stroke is one of the world’s leading causes of death and disability, and more than a thousand candidate neuroprotective drugs have been proposed based on extensive in vitro and animal-based research, an effective neuroprotective/restorative therapy for ischaemic stroke patients is still missing. In particular, the high attrition rate of neuroprotective compounds in clinical studies should make us question the ability of in vitro models currently used for ischaemic stroke research to recapitulate human ischaemic responses with sufficient fidelity. The ischaemic stroke field would greatly benefit from the implementation of more complex in vitro models with improved physiological relevance, next to traditional in vitro and in vivo models in preclinical studies, to more accurately predict clinical outcomes. In this review, we discuss current in vitro models used in ischaemic stroke research and describe the main factors determining the predictive value of in vitro models for modelling human ischaemic stroke. In light of this, human-based 3D models consisting of multiple cell types, either with or without the use of microfluidics technology, may better recapitulate human ischaemic responses and possess the potential to bridge the translational gap between animal-based in vitro and in vivo models, and human patients in clinical trials.

A microfluidic bubble perfusion device for brain slice culture

Ex vivo brain slice cultures are utilized as analytical models for studying neurophysiology. Common approaches to maintaining slice cultures include roller tube and membrane interface techniques. The rise of organ-on-chip technologies has demonstrated the value of microfluidic perfusion culture systems for sampling and analysis of complex biology under well-controlled in vitro or ex vivo conditions. A number of approaches to microfluidic brain slice culture have been developed, however these typically involve complex design, fabrication, or operational parameters in order to meet the high oxygen demands of brain slices. Here, we present proof-of-principle for a novel approach to microfluidic brain slice culture. In this system, which we term a microfluidic bubble perfusion device, principles of droplet microfluidics were employed to generate droplets of perfusion media dispersed between bubbles of carbogen gas, and brain tissue slices were perfused with the resulting monodispersed droplets and bubbles. The challenge of tissue immobilization in the flow system was addressed using a two-part cytocompatible carbohydrate-based tissue adhesive. Best practices are discussed for perfusion chamber designs that maintain segmented flow throughout the course of perfusion. Control of droplet and bubble volumes was possible across the range of ca. 4-15 μL, bubble generation frequency was well controlled in the range ca. 1-7 bubbles per min, and bubble duty cycle was well controlled across the range ca. 20-80%. Murine hypothalamic tissue slices containing the suprachiasmatic nuclei were successfully maintained for durations of 8-10 hours, with tissue remaining viable for the duration of perfusion as assessed by Ca²⁺ imaging and propidium iodide (PI) staining.

Dihydrolipoic Acid-Gold Nanoclusters Regulate Microglial Polarization and Have the Potential To Alter Neurogenesis

Microglia-mediated neuroinflammation is one of the most significant features in a variety of central nervous system (CNS) disorders such as traumatic brain injury, stroke, and many neurodegenerative diseases. Microglia become polarized upon stimulation. The two extremes of the polarization are the neuron-destructive proinflammatory M1-like and the neuron-regenerative M2-like phenotypes. Thus, manipulating microglial polarization toward the M2 phenotype is a promising therapeutic approach for CNS repair and regeneration. It has been reported that nanoparticles are potential tools for regulating microglial polarization. Gold nanoclusters (AuNCs) could penetrate the blood-brain barrier and have neuroprotective effects, suggesting the possibility of utilizing AuNCs to regulate microglial polarization and improve neuronal regeneration in CNS. In the current study, AuNCs functionalized with dihydrolipoic acid (DHLA-AuNCs), an antioxidant with demonstrated neuroprotective roles, were prepared, and their effects on polarization of a microglial cell line (BV2) were examined. DHLA-AuNCs effectively suppressed proinflammatory processes in BV2 cells by inducing polarization toward the M2-like phenotype. This was associated with a decrease in reactive oxygen species and reduced NF-kB signaling and an improvement in cell survival coupled with enhanced autophagy and inhibited apoptosis. Conditioned medium from DHLA-AuNC-treated BV2 cells was able to enhance neurogenesis in both the neuronal cell line N2a and in an ex vivo brain slice stroke model. The direct treatment of brain slices with DHLA-AuNCs also ameliorated stroke-related tissue injury and reduced astrocyte activation (astrogliosis). This study suggests that by regulating neuroinflammation to improve neuronal regeneration, DHLA-AuNCs could be a potential therapeutic agent in CNS disorders.

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.

TrkB-mediated activation of the phosphatidylinositol-3-kinase/Akt cascade reduces the damage inflicted by oxygen-glucose deprivation in area CA3 of the rat hippocampus

The selective vulnerability of hippocampal area CA1 to ischemia-induced injury is a well-known phenomenon. However, the cellular mechanisms that confer resistance to area CA3 against ischemic damage remain elusive. Here, we show that oxygen-glucose deprivation-reperfusion (OGD-RP), an in vitro model that mimic the pathological conditions of the ischemic stroke, increases the phosphorylation level of tropomyosin receptor kinase B (TrkB) in area CA3. Slices preincubated with brain-derived neurotrophic factor (BDNF) or 7,8-dihydroxyflavone (7,8-DHF) exhibited reduced depression of the electrical activity triggered by OGD-RP. Consistently, blockade of TrkB suppressed the resistance of area CA3 to OGD-RP. The protective effect of TrkB activation was limited to area CA3, as OGD-RP caused permanent suppression of CA1 responses. At the cellular level, TrkB activation leads to phosphorylation of the accessory proteins SHC and Gab as well as the serine/threonine kinase Akt, members of the phosphoinositide 3-kinase/Akt (PI-3-K/Akt) pathway, a cascade involved in cell survival. Hence, acute slices pretreated with the Akt antagonist MK2206 in combination with BDNF lost the capability to resist the damage inflicted with OGD-RP. Consistently, with these results, CA3 pyramidal cells exhibited reduced propidium iodide uptake and caspase-3 activity in slices pretreated with BDNF and exposed to OGD-RP. We propose that PI-3-K/Akt downstream activation mediated by TrkB represents an endogenous mechanism responsible for the resistance of area CA3 to ischemic damage.

Reduction in N-methyl-D-aspartate Receptor-mediated Cell Death in Hippocampal Neurons by Glucose Reduction Preconditioning

BACKGROUND

Repeated episodes of reduced glucose availability can precondition the brain against damage caused by severe hypoglycemia. Because N-methyl-D-aspartate (NMDA) receptor activation may contribute to neuronal loss in the hippocampus following glucose deprivation, we tested the hypothesis that preconditioning with reduced glucose decreased NMDA receptor-mediated cell death in hippocampal neurons.

METHODS

Hippocampal slice cultures from 7-day old rats were used to study glucose reduction preconditioning and N-methyl-D-aspartate receptor (NMDAR)-mediated cell death. Preconditioning involved reductions in glucose to the following levels: 0.1 mM, 0.5, or 1.0 mM for 30 minutes, 60 minutes, or 90 minutes on 3 consecutive days. Cell death following 1-hour total glucose deprivation was measured with a vital dye technique (SYTOX fluorescence). As an index of NMDAR activity, cell death following application of 1 mM NMDA, was also measured.

RESULTS

A preconditioning protocol of 30 minutes of 0.1 mM glucose per day for 3 days reduced cell death following 1-hour total glucose by 65% to 70%, depending on cellular region. No reduction in NMDAR-mediated cell death was seen following any of the preconditioning treatments. However, when NMDAR-mediated cell death was assessed following preconditioning combined with subsequent total glucose deprivation, cell death was reduced in the cultures that had been preconditioned with 0.1 mM glucose for 30 minutes×3 days.

CONCLUSIONS

We found that that glucose reduction preconditioning protects hippocampal neurons against severe glucose deprivation-induced neuronal damage. This preconditioning was not associated with reductions in NMDAR-mediated cell death except when the preconditioning was combined with an additional exposure to a period of total glucose deprivation.

Effects of sex steroid hormones and their metabolites on neuronal injury caused by oxygen-glucose deprivation/reoxygenation in organotypic hippocampal slice cultures

In this study, protective actions of the sex steroid hormones, progesterone, testosterone, and 17β-estradiol, against oxygen-glucose deprivation (OGD)/reoxygenation-induced neuronal cell death were examined using rat organotypic hippocampal slice cultures. Progesterone, testosterone, and 17β-estradiol significantly attenuated neuronal cell death elicited by OGD/reoxygenation. While the neuroprotection conferred by progesterone was not affected by SU-10603, an inhibitor of cytochrome P45017α, finasteride, a 5α-reductase inhibitor that blocks the conversion of progesterone to allopregnanolone, partially reversed the neuroprotection induced by progesterone. The progesterone metabolite, allopregnanolone attenuated neuronal injury induced by OGD/reoxygenation. Pretreatment with letrozole, a cytochrome P450 aromatase inhibitor or 4-hydroxyphenyl-1-naphthol, a 17β-hydroxysteroid dehydrogenase 2 inhibitor showed no effect on testosterone-mediated neuroprotection, while finasteride completely abolished the protective action of testosterone. Treatment with 5α-dihydrotestosterone significantly suppressed neuronal injury. Pretreatment with mifepristone, a progesterone receptor antagonist and hydroxyflutamid, an androgen receptor antagonist significantly diminished the neuroprotective effects of progesterone and testosterone, respectively. ICI182,780, an estrogen receptor antagonist, showed no effect on neuroprotection mediated by 17β-estradiol. Pretreatment with actinomycin D or cycloheximide clearly abolished the neuroprotective effects of progesterone and testosterone, while actinomycin D and cycloheximide did not show any effect on neuroprotection mediated by 17β-estradiol. Taken together, progesterone protects neurons via progesterone receptor-dependent genomic pathway, and allopregnanolone is involved in progesterone-mediated neuroprotection. Testosterone and its metabolite 5α-dihydrotestosterone protect neurons via the genomic pathway of the androgen receptor. Metabolism of sex steroid hormones in the brain might complicate their protective actions in the brain.

A method for objectively quantifying propidium iodide exclusion in organotypic hippocampal slice cultures

BACKGROUND

Organotypic hippocampal slice cultures (OHSCs) are an attractive in vitro model to examine mechanisms of neuronal injury, because the normal hippocampal architecture, function and cellular diversity are mostly preserved. The effects of exposure to excitotoxins such as N-methyl-d-aspartate (NMDA) on cell viability can be determined by propidium iodide (PI) staining.

NEW METHOD

We describe a simple method to objectively quantify cell death in NMDA exposed slice cultures using PI that provides a standardized means of quantifying cell death in hippocampal subfields without the need to induce maximal cell death in each slice. The method employs separation of subfields using simple landmarks and densitometric quantification of PI intensity in 10 template-oriented counting fields.

RESULTS

We show that exposure to increasing concentrations of NMDA results in a dose-dependent increase in PI uptake. Additionally, our method facilitates the comparison of cell death in different hippocampal subfields, such as dentate gyrus, CA1 and CA3. Our results show marked differences of PI uptake in the hippocampal regions with the CA1 area being most sensitive to NMDA-induced injury.

COMPARISON WITH EXISTING METHOD(S)

The method provides a standardized format for quantifying PI exclusion in OHSCs that can be applied to cultures of differing shapes and sizes, permits comparisons between hippocampal subfields and does not require induction of maximal cell death.

CONCLUSION

The method of quantifying PI uptake described herein allows for an objective, quantitative and reproducible analysis and comparison of cell death in distinct regions of OHSCs.

Optimized real-time monitoring of glutathione redox status in single pyramidal neurons in organotypic hippocampal slices during oxygen-glucose deprivation and reperfusion

A redox-sensitive Grx1-roGFP2 fusion protein was introduced by transfection into single pyramidal neurons in the CA1 subfield of organotypic hippocampal slice cultures (OHSCs). We assessed changes in the GSH system in neuronal cytoplasm and mitochondria during oxygen-glucose deprivation and reperfusion (OGD/RP), an in vitro model of stroke. Pyramidal cells in a narrow range of depths below the surface of the OHSC were transfected by gene gun or single-cell electroporation with cyto- or mito-Grx1-roGFP2. To mimic the conditions of acute stroke, we developed an optimized superfusion system with the capability of rapid and reproducible exchange of the solution bathing the OHSCs. Measurements of pO2 as a function of tissue depth show that in the region containing the transfected cells, the pO2 is well-controlled. We also found that the pO2 changes on the same time scale as changes in intracranial pressure, cerebral blood flow, and pO2 during acute stroke. Determining the reduction potential, EGSH, from the ratiometric fluorescence signal requires an absolute intensity measurement during calibration of the Grx1-roGFP2. Using the signal from cotransfected tdTomato as an internal standard during calibration improves quantitative measurements of Grx1-roGFP2 redox status and allows EGSH to be determined. EGSH becomes more reducing during OGD and more oxidizing during RP in mitochondria while changes in cytoplasm are not significant compared with controls.

Organotypic Hippocampal Slices as Models for Stroke and Traumatic Brain Injury

Organotypic hippocampal slice cultures (OHSCs) have been used as a powerful ex vivo model for decades. They have been used successfully in studies of neuronal death, microglial activation, mossy fiber regeneration, neurogenesis, and drug screening. As a pre-animal experimental phase for physiologic and pathologic brain research, OHSCs offer outcomes that are relatively closer to those of whole-animal studies than outcomes obtained from cell culture in vitro. At the same time, mechanisms can be studied more precisely in OHSCs than they can be in vivo. Here, we summarize stroke and traumatic brain injury research that has been carried out in OHSCs and review classic experimental applications of OHSCs and its limitations.

The analysis of neurovascular remodeling in entorhino-hippocampal organotypic slice cultures

Ischemic brain injury is among the most common and devastating conditions compromising proper brain function and often leads to persisting functional deficits in the affected patients. Despite intensive research efforts, there is still no effective treatment option available that reduces neuronal injury and protects neurons in the ischemic areas from delayed secondary death. Research in this area typically involves the use of elaborate and problematic animal models. Entorhino-hippocampal organotypic slice cultures challenged with oxygen and glucose deprivation (OGD) are established in vitro models which mimic cerebral ischemia. The novel aspect of this study is that changes of the brain blood vessels are studied in addition to neuronal changes and the reaction of both the neuronal compartment and the vascular compartment can be compared and correlated. The methods presented in this protocol substantially broaden the potential applications of the organotypic slice culture approach. The induction of OGD or hypoxia alone can be applied by rather simple means in organotypic slice cultures and leads to reliable and reproducible damage in the neural tissue. This is in stark contrast to the complicated and problematic animal experiments inducing stroke and ischemia in vivo. By broadening the analysis to include the study of the reaction of the vasculature could provide new ways on how to preserve and restore brain functions. The slice culture approach presented here might develop into an attractive and important tool for the study of ischemic brain injury and might be useful for testing potential therapeutic measures aimed at neuroprotection.

Cell-death assessment by fluorescent and nonfluorescent cytosolic and nuclear staining techniques

Apoptosis, a genetically programmed cellular event leads to biochemical and morphological changes in cells. Alterations in DNA caused by several factors affect nucleus and ultimately the entire cell leading to compromised function of the organ and organism. DNA, a master regulator of the cellular events, is an important biomolecule with regards to cell growth, cell death, cell migration and cell differentiation. It is therefore imperative to develop the staining techniques that may lead to visualize the changes in nucleus where DNA is housed, to comprehend the cellular pathophysiology. Over the years a number of nuclear staining techniques such as propidium iodide, Hoechst-33342, 4', 6-diamidino-2-phenylindole (DAPI), Acridine orange-Ethidium bromide staining, among others have been developed to assess the changes in DNA. Some nonnuclear staining techniques such as Annexin-V staining, which although does not stain DNA, but helps to identify the events that result from DNA alteration and leads to initiation of apoptotic cell death. In this review, we have briefly discussed some of the most commonly used fluorescent and nonfluorescent staining techniques that identify apoptotic changes in cell, DNA and the nucleus. These techniques help in differentiating several cellular and nuclear phenotypes that result from DNA damage and have been identified as specific to necrosis or early and late apoptosis as well as scores of other nuclear deformities occurring inside the cells.

Limitations of Mild, Moderate, and Profound Hypothermia in Protecting Developing Hippocampal Neurons After Simulated Ischemia

Mild hypothermia (33°C-34°C) after cerebral ischemia in intact animals or ischemia-like conditions in vitro reduces neuron death. However, it is now clear that more profound hypothermia or delayed hypothermia may not provide significant protection. To further define the limitations of hypothermia after cerebral ischemia, we used hippocampal slice cultures to examine the effects of various degrees, durations, and delays of hypothermia on neuron death after an ischemia-like insult. Organotypic cultures of the hippocampus from 7- to 8 day-old rat pups were cooled to 32°C, 23°C, 17°C, or 4°C immediately or after a 2-4 hour delay from an injurious insult of oxygen and glucose deprivation (OGD). Cell death in CA1, CA3 and dentate regions of the cultures was assessed 24 hours later with SYTOX® or propidium iodide, both of which are fluorescent markers labeling damaged cells. OGD caused extensive cell death in CA1, CA3, and dentate regions of the hippocampal cultures. Hypothermia (32°C, 23°C and 17°C) for 4-6 hours immediately after OGD was protective at 24 hours, but when hypothermia was applied for longer periods or delayed after OGD, no protection or increased death was seen. Ultra-profound hypothermia (4°C) increased cell death in all cell areas of the hippocampus even when after a milder insult of only hypoxia. In an in vitro model of recovery after an ischemia-like insult, mild to profound hypothermia is protective only when applied without delay and for limited periods of time (6-8 hours). Longer durations of hypothermia, or delayed application of the hypothermia can increase neuron death. These findings may have implications for clinical uses of therapeutic hypothermia after hypoxic or ischemic insults, and suggest that further work is needed to elucidate the limitations of hypothermia as a protective treatment after ischemic stress.

Hypoxia pathways and cellular stress activate pancreatic stellate cells: development of an organotypic culture model of thick slices of normal human pancreas

Pancreatic stellate cells (PSC) are involved in fibrogenesis and oncogenesis by modulating the extracellular matrix.

Subfield-specific neurovascular remodeling in the entorhino-hippocampal-organotypic slice culture as a response to oxygen-glucose deprivation and excitotoxic cell death

Transient ischemia causes delayed neurodegeneration in selective brain areas, particularly in the CA1 field of the hippocampus. This is accompanied by neurovascular impairment. It is unknown whether neurodegeneration is the cause or consequence of vascular changes. In an entorhino-hippocampal-organotypic slice culture system with well-preserved blood vessels, we studied the interplay between neurodegeneration and neurovasculature. Short-term oxygen and glucose deprivation (OGD) resulted in upregulation of hypoxic markers and with a delay of 24 to 48 hours in selective nerve cell death in CA1. In parallel, local vessel density decreased as detected by markers of endothelial cells and of the extracellular matrix. Claudin-5, a tight junction protein and marker of the blood-brain barrier was reduced. Preventing neuronal death with tetrodotoxin or 6-cyano-7-nitroquinoxaline-2,3-dione rescued blood vessels, suggesting that vessel loss is not due to OGD per se but a consequence of neuronal death. Induction of excitotoxic neuronal death with AMPA caused widespread neurodegeneration, but vessel reduction was confined to CA1. In dentate gyrus without neuronal loss, vessel density increased. We propose that neuronal stress and death influence maintenance, loss and remodeling of the neurovasculature and that the type of vascular response is in addition determined by local factors within the hippocampus.

Anesthetic protection of neurons injured by hypothermia and rewarming: roles of intracellular Ca2+ and excitotoxicity

BACKGROUND

Mild hypothermia is neuroprotective after cerebral ischemia but surgery involving profound hypothermia (PH, temperature less than 18°C) is associated with neurologic complications. Rewarming (RW) from PH injures hippocampal neurons by glutamate excitotoxicity, N-methyl-D-aspartate receptors, and intracellular calcium. Because neurons are protected from hypoxia-ischemia by anesthetic agents that inhibit N-methyl-D-aspartic acid receptors, we tested whether anesthetics protect neurons from damage caused by PH/RW.

METHODS

Organotypic cultures of rat hippocampus were used to model PH/RW injury, with hypothermia at 4°C followed by RW to 37°C and assessment of cell death 1 or 24 h later. Cell death and intracellular Ca were assessed with fluorescent dye imaging and histology. Anesthetic agents were present in the culture media during PH and RW or only RW.

RESULTS

Injury to hippocampal CA1, CA3, and dentate neurons after PH and RW involved cell swelling, cell rupture, and adenosine triphosphate (ATP) loss; this injury was similar for 4 through 10 h of PH. Isoflurane (1% and 2%), sevoflurane (3%) and xenon (60%) reduced cell loss but propofol (3 μM) and pentobarbital (100 μM) did not. Isoflurane protection involved reduction in N-methyl-D-aspartate receptor-mediated Ca influx during RW but did not involve γ-amino butyric acid receptors or KATP channels. However, cell death increased over the next day.

CONCLUSION

Anesthetic protection of neurons rewarmed from 4°C involves suppression of N-methyl-D-aspartate receptor-mediated Ca overload in neurons undergoing ATP loss and excitotoxicity. Unlike during hypoxia/ischemia, anesthetic agents acting predominantly on γ-aminobutyric acid receptors do not protect against PH/RW. The durability of anesthetic protection against cold injury may be limited.

3-[2-(3,5-Dimethoxyphenyl)vinyl]furan protects hippocampal neurons against ischemic damage

Resveratrol, an ingredient in grapes, has been reported to exhibit anti-cancer activity, anti-inflammatory activity, and cardiovascular protection property. Interestingly, resveratrol has been recently reported to have neuroprotective effect. This study reports the neuroprotective effect of a resveratrol derivative, 3-[2-(3,5-dimethoxyphenyl)vinyl]furan (DPVF). This synthetic DPVF conferred more protection than resveratrol against neuronal cell damage induced by oxygen and glucose deprivation in a rat hippocampal slice culture. In addition, DPVF inhibited ATP depletion following oxygen and glucose deprivation in the adult hippocampal slice. Moreover, we found that DPVF is neuroprotective against ischemic damage in rats. DPVF showed potent neuroprotection on a 4-velssel-occusion model and inhibited iron-induced malondialdehyde (MDA) formation in the rat brain tissue. These results demonstrate that DPVF might be a useful agent in reducing ischemic neuronal damage.

Tributyltin induces oxidative stress and neuronal injury by inhibiting glutathione S-transferase in rat organotypic hippocampal slice cultures

Tributyltin (TBT) has been used as a heat stabilizer, agricultural pesticide and antifouling agents on ships, boats and fish-farming nets; however, the neurotoxicity of TBT has recently become a concern. TBT is suggested to stimulate the generation of reactive oxygen species (ROS) inside cells. The aim of this study was to determine the mechanism of neuronal oxidative injury induced by TBT using rat organotypic hippocampal slice cultures. The treatment of rat hippocampal slices with TBT induced ROS production, lipid peroxidation and cell death. Pretreatment with antioxidants such as superoxide dismutase, catalase or trolox, suppressed the above phenomena induced by TBT, indicating that TBT elicits oxidative stress in hippocampal slices, which causes neuronal cell death. TBT dose-dependently inhibited glutathione S-transferase (GST), but not glutathione peroxidase or glutathione reductase in the cytosol of rat hippocampus. The treatment of hippocampal slices with TBT decreased the GST activity. Pretreatment with reduced glutathione attenuated the reduction of GST activity and cell death induced by TBT, indicating that the decrease in GST activity by TBT is involved in hippocampal cell death. When hippocampal slices were treated with sulforaphane, the expression and activity of GST were increased. Notably, TBT-induced oxidative stress and cell death were significantly suppressed by pretreatment with sulforaphane. These results indicate that GST inhibition could contribute, at least in part, to the neuronal cell death induced by TBT in hippocampal slices. This study is the first report to show the link between neuronal oxidative injury and the GST inhibition elicited by TBT.

Evaluation of cell damage in organotypic hippocampal slice culture from adult mouse: a potential model system to study neuroprotection

The use of organotypic hippocampal slice culture (OHSC) has become a powerful tool for studying cell damage in different neuropathological states, since it reproduces the basic morphological and functional properties of hippocampal neuronal network. However, the conventional OHSCs are established from postnatal animals rather than adult. Here we reevaluated the features of cell death in adult OHSC in detail and found potential utility for the study of neuroprotection. Organotypic culture of hippocampal slices from adult mice under conventional conditions led to a time-dependent and reproducible cell death. Around 6days in vitro (DIV), slices lost 50% of the cells, based on LDH release assessment. The cell death was greater than 90% after DIV 15. The cell loss was linearly correlated (r=0.944, P<0.01) with the time in culture. The electrophysiological responses to the stimulus in the cultured adult slices were accordingly reduced. The cell degeneration during adult OHSC might be utilized as a tool for studying neuroprotective effects in drug development. To illustrate this potential use, adult OHSCs were challenged with brain-derived neurotrophic factor (BDNF). We found that the continuous supplementation of 300ng/ml BDNF promoted cell survival of adult OHSC. Using immunohistochemistry and Western blot analyses of neuronal markers, we also demonstrated the pro-survival effects of BDNF on neurons in the adult OHSC system. It is suggested that OHSCs from adult mice might provide an alternative model system for neuronal degeneration, suitable for studying physiological factors and pharmacological compounds contributing to neuronal survival.

Protective effect of 20-HETE inhibition in a model of oxygen-glucose deprivation in hippocampal slice cultures

Recent studies have indicated that inhibitors of the synthesis of 20-hydroxyeicosatetraenoic acid (20-HETE) may have direct neuroprotective actions since they reduce infarct volume after ischemia reperfusion in the brain without altering blood flow. To explore this possibility, the present study used organotypic hippocampal slice cultures subjected to oxygen-glucose deprivation (OGD) and reoxygenation to examine whether 20-HETE is released by organotypic hippocampal slices after OGD and whether it contributes to neuronal death through the generation of ROS and activation of caspase-3. The production of 20-HETE increased twofold after OGD and reoxygenation. Blockade of the synthesis of 20-HETE with N-hydroxy-N'-(4-butyl-2-methylphenol)formamidine (HET0016) or its actions with a 20-HETE antagonist, 20-hydroxyeicosa-6(Z),15(Z)-dienoic acid, reduced cell death, as measured by the release of lactate dehydrogenase and propidium iodide uptake. Administration of a 20-HETE mimetic, 20-hydroxyeicosa-5(Z),14(Z)-dienoic acid (5,14-20-HEDE), had the opposite effect and increased injury after OGD. The death of neurons after OGD was associated with an increase in the production of ROS and activation of caspase-3. These effects were attenuated by HET0016 and potentiated after the administration of 5,14-20-HEDE. These findings indicate that the production of 20-HETE by hippocampal slices is increased after OGD and that inhibitors of the synthesis or actions of 20-HETE protect neurons from ischemic cell death. The protective effect of 20-HETE inhibitors is associated with a decrease in superoxide production and activation of caspase-3.

Hypothermia and rewarming injury in hippocampal neurons involve intracellular Ca2+ and glutamate excitotoxicity

This study examines the causes of hypothermia and rewarming injury in CA1, CA3, and dentate neurons in rat hippocampal slice cultures. Neuronal death, assessed with propidium iodide or Sytox fluorescence, Fluoro-Jade labeling, and Cresyl Violet staining, depended on the severity and duration of hypothermia. More than 6 h at temperatures less than 12 °C followed by rewarming to 37 °C (profound hypothermia and rewarming, PH/RW) caused swelling and death in large number of neurons in CA1, CA3, and dentate. During PH, [ATP] decreased and [Ca(2+)](I) and extracellular [glutamate] increased, with neuron rupture and nuclear condensation following RW. The data support the hypothesis that neuronal death from PH/RW is excitotoxic, due to ATP loss, glutamate receptor activation and Ca(2+) influx. We found that antagonism of N-methyl-D-aspartate (NMDA) receptors, but not 2-amino-3-(5-methyl-3-oxo-1,2- oxazol-4-yl) propanoic acid or metabotropic glutamate receptors, decreased neuron death and prevented increases in [Ca(2+)](I) caused by PH/RW. Chelating extracellular Ca(2+) decreased PH/RW injury, but inhibiting L- and T-type voltage-gated Ca(2+) channels, K+ channels, Ca(2+) release from the endoplasmic reticulum, and reverse Na(+)/Ca(2+) exchange did not affect the Ca(2+) changes or cell death. We conclude that the mechanism of PH/RW neuronal injury in hippocampal slices primarily involves intracellular Ca(2+) accumulation mediated by NMDA receptors that activates necrotic, but not apoptotic processes.

Validation of organotypical hippocampal slice cultures as an ex vivo model of brain ischemia: different roles of NMDA receptors in cell death signalling after exposure to NMDA or oxygen and glucose deprivation

N-Methyl-D-aspartate receptors (NMDARs) are essential mediators of synaptic plasticity under normal physiological conditions. During brain ischemia, these receptors are excessively activated due to glutamate overflow and mediate excitotoxic cell death. Although organotypical hippocampal slice cultures are widely used to study brain ischemia in vitro by induction of oxygen and glucose deprivation (OGD), there is scant data regarding expression and functionality of NMDARs in such slice cultures. Here, we have evaluated the contribution of NMDARs in mediating excitotoxic cell death after exposure to NMDA or OGD in organotypical hippocampal slice cultures after 14 days in vitro (DIV14). We found that all NMDAR subunits were expressed at DIV14. The NMDARs were functional and contributed to cell death, as evidenced by use of the NMDAR antagonist MK-801 (dizocilpine). Excitotoxic cell death induced by NMDA could be fully antagonized by 10 μM MK-801, a dose that offered only partial protection against OGD-induced cell death. Very high concentrations of MK-801 (50-100 μM) were required to counteract cell death at long delays (48-72 h) after OGD. The relative high dose of MK-801 needed for long-term protection after OGD could not be attributed to down-regulation of NMDARs at the gene expression level. Our data indicate that NMDAR signaling is just one of several mechanisms underlying ischemic cell death and that prospective cytoprotective therapies must be directed to multiple targets.

Neuronal Ca2+-activated K+ channels limit brain infarction and promote survival

Neuronal calcium-activated potassium channels of the BK type are activated by membrane depolarization and intracellular Ca(2+) ions. It has been suggested that these channels may play a key neuroprotective role during and after brain ischemia, but this hypothesis has so far not been tested by selective BK-channel manipulations in vivo. To elucidate the in vivo contribution of neuronal BK channels in acute focal cerebral ischemia, we performed middle cerebral artery occlusion (MCAO) in mice lacking BK channels (homozygous mice lacking the BK channel alpha subunit, BK(-/-)). MCAO was performed in BK(-/-) and WT mice for 90 minutes followed by a 7-hour-reperfusion period. Coronal 1 mm thick sections were stained with 2,3,5-triphenyltetrazolium chloride to reveal the infarction area. We found that transient focal cerebral ischemia by MCAO produced larger infarct volume, more severe neurological deficits, and higher post-ischemic mortality in BK(-/-) mice compared to WT littermates. However, the regional cerebral blood flow was not significantly different between genotypes as measured by Laser Doppler (LD) flowmetry pre-ischemically, intra-ischemically, and post-ischemically, suggesting that the different impact of MCAO in BK(-/-) vs. WT was not due to vascular BK channels. Furthermore, when NMDA was injected intracerebrally in non-ischemic mice, NMDA-induced neurotoxicity was found to be larger in BK(-/-) mice compared to WT. Whole-cell patch clamp recordings from CA1 pyramidal cells in organotypic hippocampal slice cultures revealed that BK channels contribute to rapid action potential repolarization, as previously found in acute slices. When these cultures were exposed to ischemia-like conditions this induced significantly more neuronal death in BK(-/-) than in WT cultures. These results indicate that neuronal BK channels are important for protection against ischemic brain damage.

Sevoflurane postconditioning ameliorates oxygen-glucose deprivation-reperfusion injury in the rat hippocampus

INTRODUCTION

Sevoflurane is well known to exert a neuroprotective effect through anesthetic preconditioning. However, its effects on postconditioning, a neuroprotective phenomenon following an insult, have not been well studied.

AIMS

In this study, we examined the ability of sevoflurane to induce postconditioning in rat hippocampal slices, in vitro.

RESULTS

2%, 4%, and 6% sevoflurane reduced neurophysiologic and morphologic neuronal injury following oxygen-glucose deprivation (OGD) and reperfusion. The quantity of damaged neurons was significantly reduced on immunofluorescence staining; excitatory amino acids (Asp, Glu) increased and inhibitory amino acids (GABA) decreased significantly. The effect was concentration-dependent.

CONCLUSION

Postconditioning with sevoflurane reduces neuronal damage after OGD-reperfusion injury in the CA1 area of rat hippocampus, in vitro.

Analyses of neuronal damage in excitotoxically lesioned organotypic hippocampal slice cultures

Organotypic hippocampal slice cultures (OHSCs) are widely used to study the mechanisms of neurodegeneration and neuroprotection. However, there are still controversies about the most appropriate method for quantification of neuronal damage. The response to excitotoxic lesions can be determined by propidium iodide (PI) staining, which labels nuclei of degenerating cells. Semiquantitative measurements of PI staining are based on (1) recording of the propidium iodide (PI) fluorescence intensity or (2) counting of PI positive neuronal nuclei. Here, we investigated OHSCs lesioned by the application of increasing NMDA concentrations (10microM, 50microM and 500microM) at 6 days in vitro (div) for 4h or left untreated, respectively. After 9 div, PI staining was performed and the staining determined in the dentate gyrus and cornu ammonis (CA1) by measurement of PI-fluorescence intensity or by counting PI(+)-nuclei with a confocal laser scanning microscope. The fluorescence intensity of lesioned OHSCs did not show a NMDA concentration dependent difference. In contrast, confocal laser scanning microscopy revealed a significant and dose-dependent increase in the number of PI(+)-nuclei. Linear regression analysis showed a high correlation between NMDA concentration and the number of PI(+)-nuclei. A high correlation was also found between the mean number of PI(+)-nuclei determined in every third optical section and that determined in a single mid-stag optical section. The results show that proper analysis of neuronal damage requires counting of PI(+)-nuclei by confocal laser scanning microscopy.

Brain slices as models for neurodegenerative disease and screening platforms to identify novel therapeutics

Recent improvements in brain slice technology have made this biological preparation increasingly useful for examining pathophysiology of brain diseases in a tissue context. Brain slices maintain many aspects of in vivo biology, including functional local synaptic circuitry with preserved brain architecture, while allowing good experimental access and precise control of the extracellular environment, making them ideal platforms for dissection of molecular pathways underlying neuronal dysfunction. Importantly, these ex vivo systems permit direct treatment with pharmacological agents modulating these responses and thus provide surrogate therapeutic screening systems without recourse to whole animal studies. Virus or particle mediated transgenic expression can also be accomplished relatively easily to study the function of novel genes in a normal or injured brain tissue context.In this review we will discuss acute brain injury models in organotypic hippocampal and co-culture systems and the effects of pharmacological modulation on neurodegeneration. The review will also cover the evidence of developmental plasticity in these ex vivo models, demonstrating emergence of injury-stimulated neuronal progenitor cells, and neurite sprouting and axonal regeneration following pathway lesioning. Neuro-and axo-genesis are emerging as significant factors contributing to brain repair following many acute and chronic neurodegenerative disorders. Therefore brain slice models may provide a critical contextual experimental system to explore regenerative mechanisms in vitro.

Chick embryo partial ischemia model: a new approach to study ischemia ex vivo

BACKGROUND

Ischemia is a pathophysiological condition due to blockade in blood supply to a specific tissue thus damaging the physiological activity of the tissue. Different in vivo models are presently available to study ischemia in heart and other tissues. However, no ex vivo ischemia model has been available to date for routine ischemia research and for faster screening of anti-ischemia drugs. In the present study, we took the opportunity to develop an ex vivo model of partial ischemia using the vascular bed of 4(th) day incubated chick embryo.

METHODOLOGY/PRINCIPAL FINDINGS

Ischemia was created in chick embryo by ligating the right vitelline artery using sterile surgical suture. Hypoxia inducible factor- 1 alpha (HIF-1alpha), creatine phospho kinase-MB and reactive oxygen species in animal tissues and cells were measured to confirm ischemia in chick embryo. Additionally, ranolazine, N-acetyl cysteine and trimetazidine were administered as an anti-ischemic drug to validate the present model. Results from the present study depicted that blocking blood flow elevates HIF-1alpha, lipid peroxidation, peroxynitrite level in ischemic vessels while ranolazine administration partially attenuates ischemia driven HIF-1alpha expression. Endothelial cell incubated on ischemic blood vessels elucidated a higher level of HIF-1alpha expression with time while ranolazine treatment reduced HIF-1alpha in ischemic cells. Incubation of caprine heart strip on chick embryo ischemia model depicted an elevated creatine phospho kinase-MB activity under ischemic condition while histology of the treated heart sections evoked edema and disruption of myofibril structures.

CONCLUSIONS/SIGNIFICANCE

The present study concluded that chick embryo partial ischemia model can be used as a novel ex vivo model of ischemia. Therefore, the present model can be used parallel with the known in vivo ischemia models in understanding the mechanistic insight of ischemia development and in evaluating the activity of anti-ischemic drug.

Enhanced hypoxic preconditioning by isoflurane: signaling gene expression and requirement of intracellular Ca2+ and inositol triphosphate receptors

Neurons preconditioned with non-injurious hypoxia or the anesthetic isoflurane express different genes but are equally protected against severe hypoxia/ischemia. We hypothesized that neuroprotection would be augmented when preconditioning with isoflurane and hypoxic preconditioning are combined. We also tested if preconditioning requires intracellular Ca(2+) and the inositol triphosphate receptor, and if gene expression is similar in single agent and combined preconditioning. Hippocampal slice cultures prepared from 9 day old rats were preconditioned with hypoxia (95% N(2), 5% CO(2) for 15 min, HPC), 1% isoflurane for 15 min (APC) or their combination (CPC) for 15 min. A day later cultures were deprived of O(2) and glucose (OGD) to produce neuronal injury. Cell death was assessed 48 h after OGD. mRNA encoding 119 signal transduction genes was quantified with cDNA micro arrays. Intracellular Ca(2+) in CA1 region was measured with fura-2 during preconditioning. The cell-permeable Ca(2+) buffer BAPTA-AM, the IP(3) receptor antagonist Xestospongin C and RNA silencing were used to investigate preconditioning mechanisms. CPC decreased CA1, CA3 and dentate region death by 64-86% following OGD, more than HPC or APC alone (P<0.01). Gene expression following CPC was an amalgam of gene expression in HPC and APC, with simultaneous increases in growth/development and survival/apoptosis regulation genes. Intracellular Ca(2+) chelation and RNA silencing of IP(3) receptors prevented preconditioning neuroprotection and gene responses. We conclude that combined isoflurane-hypoxia preconditioning augments neuroprotection compared to single agents in immature rat hippocampal slice cultures. The mechanism involves genes for growth, development, apoptosis regulation and cell survival as well as IP(3) receptors and intracellular Ca(2+).

Regenerating cortical connections in a dish: the entorhino-hippocampal organotypic slice co-culture as tool for pharmacological screening of molecules promoting axon regeneration

We present a method for using long-term organotypic slice co-cultures of the entorhino-hippocampal formation to analyze the axon-regenerative properties of a determined compound. The culture method is based on the membrane interphase method, which is easy to perform and is generally reproducible. The degree of axonal regeneration after treatment in lesioned cultures can be seen directly using green fluorescent protein (GFP) transgenic mice or by axon tracing and histological methods. Possible changes in cell morphology after pharmacological treatment can be determined easily by focal in vitro electroporation. The well-preserved cytoarchitectonics in the co-culture facilitate the analysis of identified cells or regenerating axons. The protocol takes up to a month.

Expression of signal transduction genes differs after hypoxic or isoflurane preconditioning of rat hippocampal slice cultures

BACKGROUND

Preconditioning neurons with noninjurious hypoxia (hypoxic preconditioning, HPC) or the anesthetic isoflurane (APC) induces tolerance of severe ischemic stress. The mechanisms of both types of preconditioning in the hippocampus require moderate increases in intracellular Ca and activation of protein kinase signaling. The authors hypothesized that the expression of signal transduction genes would be similar after APC and HPC.

METHODS

Hippocampal slice cultures prepared from 9-day-old rats were preconditioned with hypoxia (5 min of 95% nitrogen/5% carbon dioxide) or 1% isoflurane in air/5% carbon dioxide for 1 h. A day later, cultures were subjected to 10 min oxygen and glucose deprivation (simulated ischemia). Intracellular Ca, measured in CA1 neurons at the completion of preconditioning, and cell death in CA1, CA3, and dentate regions was assessed 48 h after simulated ischemia. Message RNA encoding 119 signal transduction genes was quantified with rat complimentary DNA microarrays from pre-oxygen-glucose deprivation samples.

RESULTS

Both APC and HPC increased intracellular Ca approximately 50 nm and decreased CA1, CA3, and dentate neuron death by about 50% after simulated ischemia. Many signaling genes were increased after preconditioning, with hypoxia increasing more apoptosis/survival genes (8 of 10) than isoflurane (0 of 10). In contrast, isoflurane increased more cell cycle/development/growth genes than did hypoxia (8 of 14 genes, vs. 1 of 14).

CONCLUSIONS

Despite sharing similar upstream signaling and neuroprotective outcomes, the genomic response to APC and HPC is different. Increased expression of antiapoptosis genes after HPC and cell development genes after APC has implications both for neuroprotection and long-term effects of anesthetics.

Neuroprotection against neonatal hypoxia/ischemia-induced cerebral cell death by prevention of calpain-mediated mGluR1alpha truncation

Many cellular events are involved in ischemic neuronal death, and it has been difficult to identify those that play a critical role in the cascade triggered by lack of oxygen and glucose, although it has been widely recognized that overactivation of glutamate receptors represents one of the initiating factors. Different glutamate receptor antagonists, especially those for N-methyl-D-aspartate (NMDA) receptors, have achieved significant success in animal models of hypoxia/ischemia; however, these antagonists have failed in clinical trials. We previously reported that calpain-mediated truncation of metabotropic glutamate receptor 1alpha (mGluR1alpha) played a critical role in excitotoxicity, and that a TAT-mGluR1 peptide consisting of a peptide surrounding the calpain cleavage site of mGluR1alpha and the peptide transduction domain of the transactivating regulatory protein (TAT) of HIV was neuroprotective against excitotoxicity. In the present study we tested the effect of this peptide in in vitro and in vivo models of neonatal hypoxia/ischemia. TAT-mGluR1 peptide prevented oxygen/glucose deprivation- (OGD) and hypoxia/ischemia- (H/I) induced neuronal death in cultured hippocampal slices and neonatal rats, respectively. TAT-mGluR1 blocked H/I-induced mGluR1alpha degradation but had no effect on H/I-induced spectrin degradation, suggesting that neuroprotection was due to prevention of calpain-mediated mGluR1alpha truncation and not to calpain inhibition. Our results therefore suggest that mGluR1alpha truncation plays a critical role in neonatal hypoxia/ischemia and that blockade of this event may prevent the activation of many downstream cytotoxic cascades. Compared to glutamate receptor antagonists and general calpain inhibitors, TAT-mGluR1 may have limited side effects.

Inositol 1,4,5-triphosphate receptors and NAD(P)H mediate Ca2+ signaling required for hypoxic preconditioning of hippocampal neurons

Exposure of neurons to a non-lethal hypoxic stress greatly reduces cell death during subsequent severe ischemia (hypoxic preconditioning, HPC). In organotypic cultures of rat hippocampus, we demonstrate that HPC requires inositol triphosphate (IP3) receptor-dependent Ca2+ release from the endoplasmic reticulum (ER) triggered by increased cytosolic NAD(P)H. Ca2+ chelation with intracellular BAPTA, ER Ca2+ store depletion with thapsigargin, IP3 receptor block with xestospongin, and RNA interference against subtype 1 of the IP3 receptor all blunted the moderate increases in [Ca2+](i) (50-100 nM) required for tolerance induction. Increases in [Ca2+](i) during HPC and neuroprotection following HPC were not prevented with NMDA receptor block or by removing Ca2+ from the bathing medium. Increased NAD(P)H fluorescence in CA1 neurons during hypoxia and demonstration that NADH manipulation increases [Ca2+](i) in an IP3R-dependent manner revealed a primary role of cellular redox state in liberation of Ca2+ from the ER. Blockade of IP3Rs and intracellular Ca2+ chelation prevented phosphorylation of known HPC signaling targets, including MAPK p42/44 (ERK), protein kinase B (Akt) and CREB. We conclude that the endoplasmic reticulum, acting via redox/NADH-dependent intracellular Ca2+ store release, is an important mediator of the neuroprotective response to hypoxic stress.

A method for identifying viable and damaged neurons in adult mouse brain slices

The cell survival assay is a commonly used technique for studying cellular mechanisms and degree of neuroprotection following cerebral ischemia. The in vitro preparations for studying ischemia are often hypoxic models induced by oxygen and glucose deprivation (OGD). In vitro studies have been carried out using embryonic/neonatal neuronal cell cultures to estimate the ratio of viable to damaged neurons and the degree of neuroprotection following OGD. Brain slices are more physiologically relevant preparations compared to cell cultures. However, no simple assay is currently available to identify both damaged and viable cells in the same brain slice. In addition, since stroke-related ischemic neuronal injury occurs primarily in adults, adult brain slices exposed to OGD may be beneficial for studying cerebral ischemia. Here, we describe a reliable double-labelling procedure using propidium iodide (PI) and anti-neuronal nuclei (NeuN) antibody to detect both damaged and viable neurons in the same adult mouse brain slice subjected to OGD. In addition to the cerebral ischemia, this method may prove useful in other neuronal stress models.

Successful inhibition of excitotoxic neuronal damage and microglial activation after delayed application of interleukin-1 receptor antagonist

Interleukin (IL)-1 is an important mediator of neuronal demise and glial activation after acute central nervous system lesions and is antagonized by IL-1 receptor antagonist (IL-1RA). Here we determined the time window in which IL-1RA elicits neuroprotective effects in rat organotypic hippocampal slice cultures (OHSC). OHSC were lesioned with N-methyl-D-aspartate (NMDA) and treated with IL-1RA (100 ng/ml) at different time points postinjury or were left untreated. Damaged neurons, microglial cells, and astrocytes were labelled with NeuN, propidium iodide, isolectin B(4), or glial fibrillary acidic protein (GFAP), respectively, and were analyzed by confocal laser scanning microscopy. In lesioned OHSC, the most dramatic increase in microglial cell number occurred between 8 and 16 hr postinjury, and the maximal neuronal demise was found between 16 and 24 hr postinjury. The cellular source of IL-1beta was investigated by immunohistochemistry, and IL-1beta immunoreactivity was found in few microglial cells at 4 hr postinjury and in numerous microglial cells and astrocytes at 16 hr postinjury. In both glial populations, IL-1beta immunoreactivity peaked at 24 hr postinjury. IL-1RA treatment potently suppressed neuronal damage by 55% when initiated within the first 16 hr postinjury (P < 0.05), and IL-1RA treatment initiated at 24 hr postinjury resulted in weaker but still significant neuroprotection. IL-1RA treatment also reduced the number of microglial cells significantly when initiated within 36 hr postinjury (P < 0.05). In conclusion, IL-1RA exhibits significant neuroprotective effects in this in vitro model of excitotoxic injury even after delayed application.

Investigating the mechanisms underlying neuronal death in ischemia using in vitro oxygen-glucose deprivation: potential involvement of protein SUMOylation

It is well established that brain ischemia can cause neuronal death via different signaling cascades. The relative importance and interrelationships between these pathways, however, remain poorly understood. Here is presented an overview of studies using oxygen-glucose deprivation of organotypic hippocampal slice cultures to investigate the molecular mechanisms involved in ischemia. The culturing techniques, setup of the oxygen-glucose deprivation model, and analytical tools are reviewed. The authors focus on SUMOylation, a posttranslational protein modification that has recently been implicated in ischemia from whole animal studies as an example of how these powerful tools can be applied and could be of interest to investigate the molecular pathways underlying ischemic cell death.

EUK-207, a superoxide dismutase/catalase mimetic, is neuroprotective against oxygen/glucose deprivation-induced neuronal death in cultured hippocampal slices

EUK-207 is a synthetic superoxide dismutase/catalase mimetic that has been shown to reverse age-related learning deficits and brain oxidative stress in mice. In the present experiments, we tested the effects of EUK-207 on oxygen/glucose deprivation (OGD)-induced cell death in cultured hippocampal slices and on several mechanisms that have been postulated to participate in this process. Cultured hippocampal slices were subjected to 1 h OGD followed by 3 or 24 h recovery in regular medium with glucose and oxygen. Lactate dehydrogenase (LDH) release in culture medium and propidium iodide (PI) uptake in slices were used to evaluate cell viability. When EUK-207 was applied either 1 or 2 h before OGD, OGD-induced LDH release was significantly reduced. When EUK-207 was applied 1 h before OGD and during 24 h recovery, PI uptake was also reduced. OGD-induced accumulation of reactive oxygen species (ROS) was evaluated with the fluorescent probe DCF. DCF fluorescence in slices increased steadily during OGD treatment, rapidly disappeared following return to regular medium before slowly increasing again during the 24 h recovery period. When measured 3 h after OGD, increased ROS levels were significantly reduced by EUK-207. OGD also increased lipid peroxidation levels and this effect was also reduced by EUK-207 6 h following OGD. Cytosolic cytochrome c and nuclear apoptosis-inducing factor (AIF) were increased 3 h after OGD, and the translocation of AIF from mitochondria to nucleus was partly blocked by treatment with EUK-207. In conclusion, EUK-207 provides neuroprotection against OGD-induced cell death in cultured hippocampal slices. As EUK-207 prevents free radical formation and lipid peroxidation, the neuroprotection is related to elimination of free radical generation and lipid peroxidation, as well as to decreased activation of pro-apoptotic factors. Our data support the further clinical evaluation of this class of molecules for the prevention of ischemic cell damage.

Reduced early hypoxic/ischemic brain damage is associated with increased GLT-1 levels in mice expressing mutant (P301L) human tau

Mutations in tau proteins are associated with a group of neurodegenerative diseases, termed tauopathies. To investigate whether over-expressing human tau with P301L mutation also affects stroke-induced brain damage, we performed hypoxia/ischemia (H/I) in young adult P301L tau transgenic mice. Surprisingly, brain infarct volume was significantly smaller in transgenic mice compared to wild-type mice 24 h after H/I induction. TUNEL staining also revealed less brain apoptosis in transgenic mice following H/I. H/I resulted in a significant increase in tau fragments generated by caspase activation and a marked decrease in tau phosphorylation at residue T231 in cortex of wild-type but not transgenic mice. Activation of calpain and caspase-3 following H/I was also reduced in transgenic compared to wild-type mice, as reflected by lower levels of the specific spectrin breakdown products generated by calpain or caspase-3. Finally, basal levels of the glial glutamate transporter, GLT-1, were higher in brains of transgenic as compared to wild-type mice. These results support the idea that enhanced levels of GLT-1 in transgenic mice are responsible for reducing H/I-induced brain damage by decreasing extracellular glutamate accumulation and subsequent calpain and caspase activation.

Mechanisms of neuronal death in disease: defining the models and the players

Dysregulation of life and death at the cellular level leads to a variety of diseases. In the nervous system, aberrant neuronal death is an outstanding feature of neurodegenerative diseases. Since the discovery of the caspase family of proteases, much effort has been made to determine how caspases function in disease, including neurodegenerative diseases. Although many papers have been published examining caspases in neuronal death and disease, the pathways have not been fully clarified. In the present review, we examine the potential players in the death pathways, the current tools for examining these players and the models for studying neurological disease. Alzheimer's disease, the most common neurodegenerative disorder, and cerebral ischaemia, the most common cause of neurological death, are used to illustrate our current understanding of death signalling in neurodegenerative diseases. A better understanding of the neuronal death pathways would provide targets for the development of therapeutic interventions for these diseases.