A new model of ischemic preconditioning using young adult hippocampal slice cultures

A Novel Ex Vivo Model to Study Therapeutic Treatments for Myelin Repair following Ischemic Damage

Stroke is a major reason for persistent disability due to insufficient treatment strategies beyond reperfusion, leading to oligodendrocyte death and axon demyelination, persistent inflammation and astrogliosis in peri-infarct areas. After injury, oligodendroglial precursor cells (OPCs) have been shown to compensate for myelin loss and prevent axonal loss through the replacement of lost oligodendrocytes, an inefficient process leaving axons chronically demyelinated. Phenotypic screening approaches in demyelinating paradigms revealed substances that promote myelin repair. We established an ex vivo adult organotypic coronal slice culture (OCSC) system to study repair after stroke in a resource-efficient way. Post-photothrombotic OCSCs can be manipulated for 8 d by exposure to pharmacologically active substances testing remyelination activity. OCSCs were isolated from a NG2-CreERT2-td-Tomato knock-in transgenic mouse line to analyze oligodendroglial fate/differentiation and kinetics. Parbendazole boosted differentiation of NG2⁺ cells and stabilized oligodendroglial fate reflected by altered expression of associated markers PDGFR-α, CC1, BCAS1 and Sox10 and GFAP. In vitro scratch assay and chemical ischemia confirmed the observed effects upon parbendazole treatment. Adult OCSCs represent a fast, reproducible, and quantifiable model to study OPC differentiation competence after stroke. Pharmacological stimulation by means of parbendazole promoted OPC differentiation.

Optimized Model of Cerebral Ischemia In situ for the Long-Lasting Assessment of Hippocampal Cell Death

Among all the brain, the hippocampus is the most susceptible region to ischemic lesion, with the highest vulnerability of CA1 pyramidal neurons to ischemic damage. This damage may cause either prompt neuronal death (within hours) or with a delayed appearance (over days), providing a window for applying potential therapies to reduce or prevent ischemic impairments. However, the time course when ischemic damage turns to neuronal death strictly depends on experimental modeling of cerebral ischemia and, up to now, studies were predominantly focused on a short time-window—from hours to up to a few days post-lesion. Using different schemes of oxygen-glucose deprivation (OGD), the conditions taking place upon cerebral ischemia, we optimized a model of mimicking ischemic conditions in organotypical hippocampal slices for the long-lasting assessment of CA1 neuronal death (at least 3 weeks). By combining morphology and electrophysiology, we show that prolonged (30-min duration) OGD results in a massive neuronal death and overwhelmed astrogliosis within a week post-OGD whereas OGD of a shorter duration (10-min) triggered programmed CA1 neuronal death with a significant delay—within 2 weeks—accompanied with drastically impaired CA1 neuron functions. Our results provide a rationale toward optimized modeling of cerebral ischemia for reliable examination of potential treatments for brain neuroprotection, neuro-regeneration, or testing neuroprotective compounds in situ.

The neuroprotective effect of magnesium sulfate in preterm fetal mice

OBJECTIVE

To investigate the use of magnesium sulfate (MgSO4) as a neuroprotective agent in a mouse model of inflammation-associated and noninflammation-associated preterm birth.

METHODS

On embryonic day 15 of gestation, lipopolysaccharide (LPS) and mifepristone (RU486) were used, respectively, to create mouse models of inflammation and noninflammation-associated preterm birth. After intraperitoneal injection of LPS, RU486, or normal saline solution (NS), dams were randomized to intraperitoneal MgSO4 or NS injection. From the 6 treatment groups (NS+NS, LPS+NS, NS+MgSO4, LPS+MgSO4, RU486+NS and RU486+MgSO4), fetal brains were collected for Western blot analysis and neuronal cultures. Protein expression of S100B was assessed, and immunohistochemistry was performed to detect NeuN. The numbers of NeuN-labeled cells were counted using confocal laser scanning microscopy.

RESULTS

The expression of S100B significantly differed among the groups and was decreased in the LPS+MgSO4 group compared to the LPS+NS group. The expression of S100B did not differ between the RU486+NS and RU486+MgSO4 groups. NeuN-labeled cells were increased in the LPS+MgSO4 group compared with the LPS+NS group. NeuN-labeled cells were decreased in the RU486+MgSO4 group compared with the RU486+NS group.

CONCLUSIONS

We observed that prenatal treatment with MgSO4 was associated with decreased expression of S100B and increased numbers of NeuN-labeled cells in an inflammation-associated preterm mouse model but not in a noninflammation-associated preterm mouse model. Our results suggest that prenatal treatment of MgSO4 reduces inflammation-associated brain injury in fetal mice.

Sirtuin regulation in aging and injury

Sirtuins or Sir2 family of proteins are a class of NAD(+) dependent protein deacetylases which are evolutionarily conserved from bacteria to humans. Some sirtuins also exhibit mono-ADP ribosyl transferase, demalonylation and desuccinylation activities. Originally identified in the yeast, these proteins regulate key cellular processes like cell cycle, apoptosis, metabolic regulation and inflammation. Humans encode seven sirtuin isoforms SIRT1-SIRT7 with varying intracellular distribution. Apart from their classic role as histone deacetylases regulating transcription, a number of cytoplasmic and mitochondrial targets of sirtuins have also been identified. Sirtuins have been implicated in longevity and accumulating evidence indicate their role in a spectrum of diseases like cancer, diabetes, obesity and neurodegenerative diseases. A number of studies have reported profound changes in SIRT1 expression and activity linked to mitochondrial functional alterations following hypoxic-ischemic conditions and following reoxygenation injury. The SIRT1 mediated deacetylation of targets such as PGC-1α, FOXO3, p53 and NF-κb has profound effect on mitochondrial function, apoptosis and inflammation. These biological processes and functions are critical in life-span determination and outcome following injury. Aging is reported to be characterized by declining SIRT1 activity, and its increased expression or activation demonstrated prolonged life-span in lower forms of animals. A pseudohypoxic state due to declining NAD(+) has also been implicated in aging. In this review we provide an overview of studies on the role of sirtuins in aging and injury.

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.

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.

Ethanol transiently suppresses choline-acetyltransferase in basal nucleus of Meynert slices

The cholinergic system plays a major role in learning and cognition and cholinergic neurons appear to be particularly vulnerable to ethanol (EtOH) exposure. There are conflicting results if EtOH directly damages cholinergic neurons. Thus, the aims of the present study were (1) to investigate the effect of different EtOH concentrations on cholinergic neurons in organotypic brain slices of the nucleus basalis of Meynert (nbM) and (2) to study if the most potent cholinotrophic substance nerve growth factor (NGF) or inhibitors of mitogen activated kinase (MAPK) p38- and nitric-oxide synthase (NOS)-pathways may counteract any EtOH effect. Two-week old organotypic rat brain slices of the nbM were exposed to 1–100 mM EtOH for 7 days with or without drugs and the number of choline-acetyltransferase (ChAT)-positive neurons was counted. Our data show that EtOH significantly reduced the number of ChAT-positive neurons with the most potent effect at a concentration of 50 mM EtOH (54 ± 5 neurons per slice, p < 0.001), compared to control slices (120 ± 13 neurons per slice). Inhibition of MAPK p38 (SB 203580, 10 μM) and NOS (L-thiocitrulline, 10 μM) counteracted the EtOH-induced decline of cholinergic neurons and NGF protected cholinergic neurons against the EtOH-induced effect. Withdrawal of EtOH resulted in a reversal of cholinergic neurons to nearly controls. In conclusion, EtOH caused a transient decline of cholinergic neurons, possibly involving MAPK p38- and NOS-pathways suggesting that EtOH does not induce direct cell death, but causes a transient downregulation of the cholinergic key enzyme, possibly reflecting a form of EtOH-associated plasticity.

A new pH-sensitive rectifying potassium channel in mitochondria from the embryonic rat hippocampus

Patch-clamp single-channel studies on mitochondria isolated from embryonic rat hippocampus revealed the presence of two different potassium ion channels: a large-conductance (288±4pS) calcium-activated potassium channel and second potassium channel with outwardly rectifying activity under symmetric conditions (150/150mM KCl). At positive voltages, this channel displayed a conductance of 67.84pS and a strong voltage dependence at holding potentials from -80mV to +80mV. The open probability was higher at positive than at negative voltages. Patch-clamp studies at the mitoplast-attached mode showed that the channel was not sensitive to activators and inhibitors of mitochondrial potassium channels but was regulated by pH. Moreover, we demonstrated that the channel activity was not affected by the application of lidocaine, an inhibitor of two-pore domain potassium channels, or by tertiapin, an inhibitor of inwardly rectifying potassium channels. In summary, based on the single-channel recordings, we characterised for the first time mitochondrial pH-sensitive ion channel that is selective for cations, permeable to potassium ions, displays voltage sensitivity and does not correspond to any previously described potassium ion channels in the inner mitochondrial membrane. This article is part of a Special Issue entitled: 17th European Bioenergetics Conference (EBEC 2012).

Primary culture of cellular subtypes from postnatal mouse for in vitro studies of oxygen glucose deprivation

One of the most widely utilized in vitro models of ischemia or oxygen glucose deprivation (OGD) is the hippocampal organotypical culture (HOTC). The HOTC is used not only for the study of the mechanisms of cell death, but also has been the cornerstone of synaptic physiology. Although the intact nature of the HOTC is one of its primary advantages, some studies require a dissociated preparation in order to distinguish cell type specific responses. Typically, primary dissociated neuronal cultures are prepared from embryonic tissue. Since the HOTC is prepared from postnatal pups, we wanted to establish a primary culture of hippocampus from postnatal pups to parallel our studies in the HOTC preparation. Mixed cultures were prepared by enzymatic dissociation of hippocampus from 7-day-old mouse pups. These cultures responded to OGD with a time course of delayed cell death that was similar to that reported in HOTC. Dual label immunocytochemical staining revealed that neurons, but not astrocytes, were dying from apoptosis following OGD. To examine this vulnerability further, we also prepared neuronal enriched cultures by treating mixed cultures with cytosine-β-d-arabinofuranoside (CBA). These neuronal cultures appear to be even more sensitive to OGD. In addition, we have established primary astrocyte-enriched cultures from the same age pups to examine the vulnerability of astrocytes to OGD. These three culture preparations are useful for comparison of the responses of the two major cell types in the same culture, and the enriched cultures will allow biochemical, electrophysiological and molecular studies of homogenous cell populations.

Adult rat hippocampal slices as in vitro models for neurodegeneration: Studies on cell viability and apoptotic processes

Adult hippocampal slice cultures were used in the modeling of apoptotic aspects of neurodegeneration. Slice viability was determined by the use of trypan blue (TB) staining, and apoptosis was assessed by caspase-3 immunohistochemistry. A large number of pyramidal cells showed signs of degeneration 30 min after sectioning (58.4% of the total number of pyramidal cells), as they exhibited TB uptake, and about 71.6% of these neurons became stained by the third day in culture, when patches in the stratum oriens also demonstrated distinct TB staining. By the sixth day of culturing, almost all cells in the pyramidal cell layer became TB positive (88.4%). The caspase-3 immunoreactivity displayed a different pattern, as the most intense immunoreactivity, detected mainly in the pyramidal cells, peaked 6 h after culturing, and then decreased steadily. The present data show that in adult hippocampal slices a large number of pyramidal cells initiate apoptotic processes as a result of irreparable damage sustained during slice preparation and culture maintenance, and support the notion that apoptosis is an integral part of the neurodegenerative processes not only in vivo but also in vitro. Elucidation of mechanisms for the apoptotic processes in adult hippocampal slice cultures could lead to the development of new therapeutic strategies; moreover, the utilization of adult hippocampal slice cultures could be a viable alternative technique to in vivo experiments in studying the mechanisms responsible for neurodegeneration.

Preconditioning-induced ischemic tolerance: a window into endogenous gearing for cerebroprotection

Ischemic tolerance defines transient resistance to lethal ischemia gained by a prior sublethal noxious stimulus (i.e., preconditioning). This adaptive response is thought to be an evolutionarily conserved defense mechanism, observed in a wide variety of species. Preconditioning confers ischemic tolerance if not in all, in most organ systems, including the heart, kidney, liver, and small intestine. Since the first landmark experimental demonstration of ischemic tolerance in the gerbil brain in early 1990's, basic scientific knowledge on the mechanisms of cerebral ischemic tolerance increased substantially. Various noxious stimuli can precondition the brain, presumably through a common mechanism, genomic reprogramming. Ischemic tolerance occurs in two temporally distinct windows. Early tolerance can be achieved within minutes, but wanes also rapidly, within hours. Delayed tolerance develops in hours and lasts for days. The main mechanism involved in early tolerance is adaptation of membrane receptors, whereas gene activation with subsequent de novo protein synthesis dominates delayed tolerance. Ischemic preconditioning is associated with robust cerebroprotection in animals. In humans, transient ischemic attacks may be the clinical correlate of preconditioning leading to ischemic tolerance. Mimicking the mechanisms of this unique endogenous protection process is therefore a potential strategy for stroke prevention. Perhaps new remedies for stroke are very close, right in our cells.

Low-dose cardiotonic steroids increase sodium-potassium ATPase activity that protects hippocampal slice cultures from experimental ischemia

The sodium-potassium ATPase (Na/K ATPase) is a major ionic transporter in the brain and is responsible for the maintenance of the Na(+) and K(+) gradients across the cell membrane. Cardiotonic steroids such as ouabain, digoxin and marinobufagenin are well-characterized inhibitors of the Na/K ATPase. Recently, cardiotonic steroids have been shown to have additional effects at concentrations below their IC(50) for pumping. The cardiotonic steroids ouabain, digoxin, and marinobufagenin all show an inverted U-shaped dose-response curve with inhibition of pumping at concentrations near their IC(50), while increasing Na/K ATPase activity at doses below their IC(50). This stimulatory effect of cardiotonic steroids was observed in vitro in hippocampal slice cultures as well as in the hippocampus in vivo. Increased Na/K ATPase activity has been shown to protect slice culture neurons from hypoxia-hypoglycemia. Ouabain protected slice culture neurons from experimental ischemia at concentrations that increased Na/K ATPase. This protective effect was observed when ouabain was dosed 30min before, or 2h following experimental ischemia. Ouabain no longer protected against experimental ischemia if the increase of Na/K ATPase was blocked. These data suggest that the protective effect of ouabain was due to increased Na/K ATPase activity. The demonstration of a neuroprotective effect of cardiotonic steroids could potentially assist in the treatment of stroke since digoxin, one of the cardiotonic steroids examined in this study, has approval by the Food and Drug Administration and can be safely administered at the concentrations that increase Na/K ATPase activity.

Genomic analysis of ischemic preconditioning in adult rat hippocampal slice cultures

Understanding endogenous mechanisms of neuroprotection may have important clinical applications. It is well established that brain tissue becomes more resistant to ischemic injury following a sublethal ischemic insult. This process, called ischemic preconditioning (IPC), can be induced in adult rat hippocampal slice cultures by a brief oxygen-glucose deprivation (OGD) [Hassen, G.W., Tian, D., Ding, D., Bergold, P.J., 2004. A new model of ischemic preconditioning using young adult hippocampal slice cultures. Brain Res. Brain Res. Protoc. 13, 135-143]. We have analyzed the changes in gene expression brought about by IPC in this model in order to understand the mechanisms involved. Total RNA was isolated at different time points following a brief OGD (3, 6 and 12 h) and used to probe genome-wide expression microarrays. Genes were identified that were significantly up- or down-regulated relative to controls. We placed genes that were differentially expressed into statistically significant groups based on Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways and gene ontology (GO) terms. Genes involved in signal transduction, transcription, and oxidative phosphorylation are differentially expressed at each time point. The analysis demonstrates that alterations in signaling pathways (TGF-beta, Wnt, MAPK, ErbB, Toll-like receptor, JAK-STAT, VEGF) consistently accompany IPC. RT-PCR was used to confirm that members of these signaling pathways are regulated as predicted by the microarray analysis. We verified that protein translation following OGD is necessary for IPC. We also found that blocking the NMDA receptor during OGD does not significantly inhibit IPC in this model or produce large changes in gene expression. Our data thus suggests that changes in signaling pathways and their down-stream targets play an important role in triggering endogenous neuroprotection.

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.

Cellular and molecular neurobiology of brain preconditioning

The tolerant brain which is a consequence of adaptation to repeated nonlethal insults is accompanied by the upregulation of protective mechanisms and the downregulation of prodegenerative pathways. During the past 20 years, evidence has accumulated to suggest that protective mechanisms include increased production of chaperones, trophic factors, and other antiapoptotic proteins. In contrast, preconditioning can cause substantial dampening of the organism's metabolic state and decreased expression of proapoptotic proteins. Recent microarray analyses have also helped to document a role of several molecular pathways in the induction of the brain refractory state. The present review highlights some of these findings and suggests that a better understanding of these mechanisms will inform treatment of a number of neuropsychiatric disorders.

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.

Protein kinase M zeta regulation of Na/K ATPase: a persistent neuroprotective mechanism of ischemic preconditioning in hippocampal slice cultures

In ischemic preconditioning, a sublethal ischemic insult protects neurons from subsequent ischemia. In organotypic hippocampal slice cultures a sublethal 5-minute hypoxia-hypoglycemia treatment prevented neuronal loss after a 10-minute experimental ischemic (EI) treatment of hypoxia-hypoglycemia. Whereas preconditioning protected against EI given 24 h later, it did not protect when EI was given 2 h later, suggesting a slow development of neuroprotection. This model identified two regulators of ischemic preconditioning: the atypical protein kinase M zeta (PKMzeta), and the Na/K ATPase. Two hours following preconditioning, when there was no neuroprotection, Na/K ATPase activity was unchanged. In contrast, Na/K ATPase activity significantly increased 24 h after the preconditioning treatment. Elevated Na/K ATPase activity was accompanied by increased surface expression of the alpha1 and alpha2 isoforms of the Na/K ATPase. Similarly, active PKMzeta levels were increased at 24 h, but not 2 h, after preconditioning. PKMzeta overexpression by sindbis virus vectors also increased Na/K ATPase activity. To examine PKMzeta regulation of Na/K ATPase, occlusion experiments were performed using marinobufagenin to inhibit alpha1, dihydroouabain to inhibit alpha2/3 and a zeta-pseudosubstrate peptide to inhibit PKMzeta. These experiments showed that PKMzeta regulated both the activity and surface expression of the alpha1 isoform of the Na/K ATPase. Marinobufagenin, dihydroouabain, and zeta-pseudosubstrate peptide were used to determine if PKMzeta or the alpha1 and alpha2 Na/K ATPase isoforms protected neurons. All three compounds blocked neuroprotection following ischemic preconditioning. PKMzeta levels were elevated 3 days after ischemic preconditioning. These data indicate key roles of PKMzeta and Na/K ATPase in ischemic preconditioning.

Contribution of endogenous glycine and d-serine to excitotoxic and ischemic cell death in rat cerebrocortical slice cultures

N-methyl-D-aspartate (NMDA) receptors, whose activation requires glycine site stimulation, play crucial roles in various physiological and pathological conditions in the brain. We investigated the regulatory roles of potential endogenous glycine site agonists, glycine and d-serine, in excitotoxic and ischemic cell death in the cerebral cortex. Cytotoxicity of NMDA on rat cerebrocortical slice cultures was potentiated by addition of glycine or d-serine. In contrast, cell death induced by oxygen/glucose deprivation (OGD) was not affected by exogenous glycine or d-serine, although blockade of NMDA receptors by MK-801 abolished cell death. In addition, higher concentrations of 2,7-dichlorokynurenic acid (DCKA), a competitive glycine site antagonist, were required to suppress OGD-induced cell death than those to suppress NMDA cytotoxicity. We also found that OGD triggered a robust increase in extracellular glycine. A glycine transporter blocker ALX 5407 increased the extracellular level of glycine, and the protective effect of DCKA against NMDA cytotoxicity was diminished in the presence of ALX 5407. Sensitivity of NMDA cytotoxicity to DCKA was also diminished by l-serine that increased the extracellular level of d-serine. These results indicate that both glycine and d-serine can act as endogenous ligands for NMDA receptor glycine site in the cerebral cortex, and that endogenous glycine may saturate the glycine site under ischemic conditions. The present findings are important for the interpretation of the mechanisms of NMDA and OGD cytotoxicity.

Effects of acetylpuerarin on hippocampal neurons and intracellular free calcium subjected to oxygen–glucose deprivation/reperfusion in primary culture

OBJECTIVES

This study was undertaken to find out the effects of acetylpuerarin on hippocampal neurons and intracellular free calcium in primary culture subjected to oxygen-glucose deprivation/reperfusion.

METHODS

According to different reperfusion time (1 h, 6 h, 12 h, 24 h), three concentrations (1.6 micromol l(-1), 0.4 micromol l(-1), 0.1 micromol l(-1)) of acetylpuerarin, and MK-801 (10 micromol l(-1)), a positive control drug, neurons were randomly divided into 21 groups. Each group was observed by inverted phase contrast microscope; neuron viability was measured by the reduction of 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT); intracellular Ca(2+) was observed by Fura-2/AM ester through fluorospectrophotometer.

RESULTS

The injured neurons were protected and degeneration and necrosis were alleviated in treatment groups of acetylpuerarin and MK-801. Acetylpuerarin increased the neuron viability at high, middle and low concentrations. Fluorescence detection results showed that the calcium concentration in the group treated with acetylpuerarin and MK-801 was lowered in each reperfusion time.

CONCLUSION

Our results demonstrated that acetylpuerarin could protect the hippocampal neurons from ischemia-reperfusion injury in rats by alleviating the morphological damage, increasing neuron viability and decreasing calcium concentration in neuron.

Elevated lactate suppresses neuronal firing in vivo and inhibits glucose metabolism in hippocampal slice cultures

Glucose is well accepted as the major fuel for neuronal activity, while it remains controversial whether lactate also supports neural activity. In hippocampal slice cultures, synaptic transmission supported by glucose was reversibly suppressed by lactate. To test whether lactate had a similar inhibitory effect in vivo, lactate was perfused into the hippocampi of unanesthetized rats while recording the firing of nearby pyramidal cells. Lactate perfusion suppressed pyramidal cell firing by 87.5+/-8.3% (n=6). Firing suppression was slow in onset and fully reversible and was associated with increased lactate concentration at the site of the recording electrode. In vivo suppression of neural activity by lactate occurred in the presence of glucose; therefore we tested whether suppression of neural firing was due to lactate interference with glucose metabolism. Competition between glucose and lactate was measured in hippocampal slice cultures. Lactate had no effect on glucose uptake. Lactate suppressed glucose oxidation when applied at an elevated, pathological concentration (10 mM), but not at its physiological concentration (1 mM). Pyruvate (10 mM) also inhibited glucose oxidation but was significantly less effective than lactate. The greater suppressive effect of lactate as compared to pyruvate suggests that alteration of the NAD(+)/NADH ratio underlies the suppression of glucose oxidation by lactate. ATP in slice culture was unchanged in glucose (1 mM), but significantly reduced in lactate (1 mM). ATP in slice culture was significantly increased by combination of glucose (1 mM) and lactate (1 mM). These data suggest that alteration of redox ratio underlies the suppression of neural discharge and glucose metabolism by lactate.

Enhanced neuronal damage after ischemic insults in mice lacking Kir6.2-containing ATP-sensitive K+ channels

Adenosine triphosphate (ATP)-sensitive potassium (KATP) channels, incorporating Kir6.x and sulfonylurea receptor subunits, are weak inward rectifiers that are thought to play a role in neuronal protection from ischemic insults. However, the involvement of Kir6.2-containing KATP channel in hippocampus and neocortex has not been tested directly. To delineate the physiological roles of Kir6.2 channels in the CNS, we used knockout (KO) mice that do not express Kir6.2. Immunocytochemical staining demonstrated that Kir6.2 protein was expressed robustly in hippocampal neurons of the wild-type (WT) mice and absent in the KO. To examine neuronal sensitivity to metabolic stress in vitro, and to ischemia in vivo, we 1) exposed hippocampal slices to transient oxygen and glucose deprivation (OGD) and 2) produced focal cerebral ischemia by middle cerebral artery occlusion (MCAO). Both slice and whole animal studies showed that neurons from the KO mice were severely damaged after anoxia or ischemia, whereas few injured neurons were observed in the WT, suggesting that Kir6.2 channels are necessary to protect neurons from ischemic insults. Membrane potential recordings from the WT CA1 pyramidal neurons showed a biphasic response to OGD; a brief hyperpolarization was followed by a small depolarization during OGD, with complete recovery within 30 min after returning to normoxic conditions. By contrast, CA1 pyramidal neurons from the KO mice were irreversibly depolarized by OGD exposure, without any preceding hyperpolarization. These data suggest that expression of Kir6.2 channels prevents prolonged depolarization of neurons resulting from acute hypoxic or ischemic insults, and thus protects these central neurons from the injury.

Hypoxia/hypoglycemia preconditioning prevents the loss of functional electrical activity in organotypic slice cultures

In cerebral ischemic preconditioning (IPC), a first sublethal ischemia increases the resistance of neurons to a subsequent severe ischemia. Despite numerous studies, the mechanisms are not yet fully understood. Our goal is to develop an in vitro model of IPC on hippocampal organotypic slice cultures. Instead of anoxia, we chose to apply varying degrees of hypoxia that allows us various levels of insult graded from mild to severe. Cultures are exposed to combined oxygen and glucose deprivation (OGD) of varying intensities, ranging from mild to severe, assessing both the electrical activity and cell death. IPC was accomplished by exposure to the mildest ischemia condition (10% of O2 for 15 min) 24 h before the severe deprivation (5% of O2 for 30 min). Interestingly, IPC not only prevented delayed ischemic cell death 6 days after insult but also the transient loss of evoked potential response. The major interest and advantage of this system over both the acute slice preparation and primary cell cultures is the ability to simultaneously measure the delayed neuronal damage and neuronal function.

Pre- or Postinsult Administration of Lidocaine or Thiopental Attenuates Cell Death in Rat Hippocampal Slice Cultures Caused by Oxygen-Glucose Deprivation

Lidocaine and thiopental improve recovery when administrated during hypoxia and ischemia; however, the effect of pre- or postinsult treatment alone is unknown. We applied either lidocaine or thiopental to hippocampal slice cultures from 20-day-old rats either before or after 10 min of oxygen-glucose deprivation (OGD). Propidium iodide (PI) fluorescence was used as an indicator of neuronal death for 7 days after OGD. OGD-induced neuronal death, in both the Cornus Ammonis 1 (CA1) and the dentate gyrus regions, peaked the first day after ischemia. Preinsult administration of either lidocaine (10, 100 microM) or thiopental (250, 600 microM) significantly reduced the damage measured on the first and second days after OGD; these drugs also significantly decreased the summed daily post-OGD PI fluorescence in both regions. Postinsult administration of lidocaine (10, 100 microM) or thiopental (250, 600 microM) significantly decreased the PI fluorescence on the first day after OGD; postinsult administration of these drugs also attenuated the summed daily post-OGD PI. These data indicate that the administration of lidocaine or thiopental either before or directly after OGD reduced neuronal damage in this in vitro model of cerebral ischemia. Postischemic administration is frequently the first opportunity for treatment.

IMPLICATIONS

Lidocaine or thiopental applied either 10 min before or 10 min directly after oxygen-glucose deprivation reduced neuronal cell death in rat hippocampal slice cultures. Postinsult administration is often the first opportunity for treatment after stroke; lidocaine and thiopental reduced damage caused by oxygen-glucose deprivation, an in vitro model of stroke.

Oxidation of 14C-labeled substrates by hippocampal slice cultures

In vitro studies of glucose and lactate utilization have been performed in acute hippocampal slices or dissociated neurons and glia. While some studies concluded that lactate and glucose are equivalent substrates to support evoked synaptic activity, others showed decreased synaptic activity in the presence of lactate as compared to glucose. We found diminished neural activity in the presence of lactate in hippocampal slice cultures. We developed a method to examine the oxidation rates of 14C-labeled substrates by hippocampal slice cultures. The rate of 14CO2 production from either 14C-glucose or 14C-lactate remained unchanged for 6 h suggesting that slice cultures are metabolically stable. While the glucose oxidation rate saturated between 2.8 and 10 mM, lactate oxidation rate had not saturated at 10 mM. These data suggest that organotypic slice cultures provide a method to examine elements of cerebral metabolism in vitro.