Glucose deprivation neuronal injury in cortical culture

Strategies for the development of in vitro models of spinal cord ischemia-reperfusion injury: Oxygen-glucose deprivation and reoxygenation

BACKGROUND

In vitro models tailored for spinal cord ischemia-reperfusion injury are pivotal for investigation of the mechanisms underlying spinal cord injuries. We conducted a two-phased study to identify the optimal conditions for establishing an in vitro model of spinal cord ischemia-reperfusion injury using primary rat spinal motor neurons.

NEW METHOD

In the first phase, cell cultures were subjected to oxygen deprivation (OD) only, glucose deprivation (GD) only, or simultaneous deprivation of oxygen and glucose [oxygen-glucose deprivation (OGD)] for different durations (1, 2, and 6 h). In the second phase, different durations of re-oxygenation (1, 12, and 24 h) were applied after 1 h of OGD to determine the optimal duration simulating reperfusion injury.

RESULTS AND COMPARISON WITH EXISTING METHOD(S)

GD for 6 h significantly reduced cell viability (91 % of control, P<0.001) and increase cytotoxicity (111 % of control, P<0.001). OGD for 1 h and 2 h, resulted in a significant decrease in cell viability (80 % of control P<0.001, respectively), and increase in cytotoxicity (130 % of control, P<0.001, respectively). Re-oxygenation for 1, 12, and 24 h worsened ischemic injury following 1 h of OGD (all P<0.05).

CONCLUSIONS

Our results may provide a valuable guide to devise in vitro models of spinal cord ischemia-reperfusion injury using primary spinal motor neurons.

Neuronal let-7b-5p acts through the Hippo-YAP pathway in neonatal encephalopathy

Despite increasing knowledge on microRNAs, their role in the pathogenesis of neonatal encephalopathy remains to be elucidated. Herein, we identify let-7b-5p as a significant microRNA in neonates with moderate to severe encephalopathy from dried blood spots using next generation sequencing. Validation studies using Reverse Transcription and quantitative Polymerase Chain Reaction on 45 neonates showed that let-7b-5p expression was increased on day 1 in neonates with moderate to severe encephalopathy with unfavourable outcome when compared to those with mild encephalopathy. Mechanistic studies performed on glucose deprived cell cultures and the cerebral cortex of two animal models of perinatal brain injury, namely hypoxic-ischaemic and intrauterine inflammation models confirm that let-7b-5p is associated with the apoptotic Hippo pathway. Significant reduction in neuronal let-7b-5p expression corresponded with activated Hippo pathway, with increased neuronal/nuclear ratio of Yes Associated Protein (YAP) and increased neuronal cleaved caspase-3 expression in both animal models. Similar results were noted for let-7b-5p and YAP expression in glucose-deprived cell cultures. Reduced nuclear YAP with decreased intracellular let-7b-5p correlated with neuronal apoptosis in conditions of metabolic stress. This finding of the Hippo-YAP association with let-7b needs validation in larger cohorts to further our knowledge on let-7b-5p as a biomarker for neonatal encephalopathy.

Using next generation sequencing of dried blood spots and subsequent validation, Ponnusamy et al identify let-7b-5p as an elevated microRNA in neonates with moderate to severe encephalopathy. Using cell culture and murine models of perinatal brain injury they demonstrate that the effects of let-7b-5p are elicited via the Hippo-YAP pathway, which should be validated in large neonate cohorts to expand our understanding of let-7b-5p as a biomarker for neonatal encephalopathy.

Excitotoxicity: Still Hammering the Ischemic Brain in 2020

Interest in excitotoxicity expanded following its implication in the pathogenesis of ischemic brain injury in the 1980s, but waned subsequent to the failure of N-methyl-D-aspartate (NMDA) antagonists in high profile clinical stroke trials. Nonetheless there has been steady progress in elucidating underlying mechanisms. This review will outline the historical path to current understandings of excitotoxicity in the ischemic brain, and suggest that this knowledge should be leveraged now to develop neuroprotective treatments for stroke.

Xenon-helium gas mixture at equimolar concentration of 37.5% protects against oxygen and glucose deprivation-induced injury and inhibits tissue plasminogen activator

Xenon (Xe) is considered to be the golden standard neuroprotective gas. However, Xe has a higher molecular weight and lower thermal conductivity and specific heat than those of nitrogen, the main diluent of oxygen in air. These physical characteristics could impair or at least reduce the intrinsic neuroprotective action of Xe by increasing the patient's respiratory workload and body temperature. In contrast, helium (He) is a cost-efficient gas with a lower molecular weight and higher thermal conductivity and specific heat than those of nitrogen, but is far less potent than Xe. In this study, we hypothesized that mixing Xe and He could allow obtaining a neuroprotective gas mixture with advantageously reduced molecular weight and increased thermal conductivity. We found that Xe and He at the equimolar concentration of 37.5% reduced oxygen-glucose deprivation-induced increase in lactate dehydrogenase in brain slices, an ex vivo model of acute ischemic stroke. These results together with the effects of Xe-He on the thrombolytic efficiency of tissue plasminogen activator are discussed.

Complex mechanisms linking neurocognitive dysfunction to insulin resistance and other metabolic dysfunction

Scientific evidence has established several links between metabolic and neurocognitive dysfunction, and epidemiologic evidence has revealed an increased risk of Alzheimer’s disease and vascular dementia in patients with diabetes. In July 2015, the National Institute of Diabetes, Digestive, and Kidney Diseases gathered experts from multiple clinical and scientific disciplines, in a workshop entitled “The Intersection of Metabolic and Neurocognitive Dysfunction”, to clarify the state-of-the-science on the mechanisms linking metabolic dysfunction, and insulin resistance and diabetes in particular, to neurocognitive impairment and dementia. This perspective is intended to serve as a summary of the opinions expressed at this meeting, which focused on identifying gaps and opportunities to advance research in this emerging area with important public health relevance.

A Cytotoxic, Co-operative Interaction Between Energy Deprivation and Glutamate Release From System xc- Mediates Aglycemic Neuronal Cell Death

The astrocyte cystine/glutamate antiporter (system xc(-)) contributes substantially to the excitotoxic neuronal cell death facilitated by glucose deprivation. The purpose of this study was to determine the mechanism by which this occurred. Using pure astrocyte cultures, as well as, mixed cortical cell cultures containing both neurons and astrocytes, we found that neither an enhancement in system xc(-) expression nor activity underlies the excitotoxic effects of aglycemia. In addition, using three separate bioassays, we demonstrate no change in the ability of glucose-deprived astrocytes--either cultured alone or with neurons--to remove glutamate from the extracellular space. Instead, we demonstrate that glucose-deprived cultures are 2 to 3 times more sensitive to the killing effects of glutamate or N-methyl-D-aspartate when compared with their glucose-containing controls. Hence, our results are consistent with the weak excitotoxic hypothesis such that a bioenergetic deficiency, which is measureable in our mixed but not astrocyte cultures, allows normally innocuous concentrations of glutamate to become excitotoxic. Adding to the burgeoning literature detailing the contribution of astrocytes to neuronal injury, we conclude that under our experimental paradigm, a cytotoxic, co-operative interaction between energy deprivation and glutamate release from astrocyte system xc(-) mediates aglycemic neuronal cell death.

Non-cell autonomous influence of the astrocyte system xc- on hypoglycaemic neuronal cell death

Despite longstanding evidence that hypoglycaemic neuronal injury is mediated by glutamate excitotoxicity, the cellular and molecular mechanisms involved remain incompletely defined. Here, we demonstrate that the excitotoxic neuronal death that follows GD (glucose deprivation) is initiated by glutamate extruded from astrocytes via system xc---an amino acid transporter that imports L-cystine and exports L-glutamate. Specifically, we find that depriving mixed cortical cell cultures of glucose for up to 8 h injures neurons, but not astrocytes. Neuronal death is prevented by ionotropic glutamate receptor antagonism and is partially sensitive to tetanus toxin. Removal of amino acids during the deprivation period prevents--whereas addition of L-cystine restores--GD-induced neuronal death, implicating the cystine/glutamate antiporter, system xc-. Indeed, drugs known to inhibit system xc- ameliorate GD-induced neuronal death. Further, a dramatic reduction in neuronal death is observed in chimaeric cultures consisting of neurons derived from WT (wild-type) mice plated on top of astrocytes derived from sut mice, which harbour a naturally occurring null mutation in the gene (Slc7a11) that encodes the substrate-specific light chain of system xc- (xCT). Finally, enhancement of astrocytic system xc- expression and function via IL-1β (interleukin-1β) exposure potentiates hypoglycaemic neuronal death, the process of which is prevented by removal of l-cystine and/or addition of system xc- inhibitors. Thus, under the conditions of GD, our studies demonstrate that astrocytes, via system xc-, have a direct, non-cell autonomous effect on cortical neuron survival.

Neuroprotective effects of xenon: a therapeutic window of opportunity in rats subjected to transient cerebral ischemia

Brain insults are a major cause of acute mortality and chronic morbidity. Given the largely ineffective current therapeutic strategies, the development of new and efficient therapeutic interventions is clearly needed. A series of previous investigations has shown that the noble and anesthetic gas xenon, which has low-affinity antagonistic properties at the N-methyl-D-aspartate (NMDA) receptor, also exhibits potentially neuroprotective properties with no proven adverse side effects. Surprisingly and in contrast with most drugs that are being developed as therapeutic agents, the dose-response neuroprotective effect of xenon has been poorly studied, although this effect could be of major critical importance for its clinical development as a neuroprotectant. Here we show, using ex vivo and in vivo models of excitotoxic insults and transient brain ischemia, that xenon, administered at subanesthetic doses, offers global neuroprotection from reduction of neurotransmitter release induced by ischemia, a critical event known to be involved in excitotoxicity, to reduction of subsequent cell injury and neuronal death. Maximal neuroprotection was obtained with xenon at 50 vol%, a concentration at which xenon further exhibited significant neuroprotective effects in vivo even when administered up to 4 h after intrastriatal NMDA injection and up to at least 2 h after induction of transient brain ischemia.

Cellular mechanisms of brain hypoglycemia

Data on intracellular processes induced by a low glucose level in nerve tissue are presented. The involvement of glutamate and adenosine receptors, mitochondria, reactive oxygen species (ROS), and calcium ions in the development of hypoglycemia-induced damage of neurons is considered. Hypoglycemia-induced calcium overload of neuronal mitochondria is suggested to be responsible for the increased ROS production by mitochondria.

Neuroprotective activity of honokiol and magnolol in cerebellar granule cell damage

The aim of the present study was to investigate the neuroprotective effects of honokiol and magnolol, two major bioactive constituents of the bark of Magnolia officinalis, against neuron toxicity induced by glucose deprivation, excitatory amino acids and hydrogen peroxide (H(2)O(2)) in cultured rat cerebellar granule cells. Cell membrane damage was measured with a lactate dehydrogenase (LDH) release assay and 3-(4,5-dimethyl-2 thiazoyl)-2,5-diphenyl-tetrazolium bromide (MTT) assay was used to assess mitochondrial activity, reflecting cell survival. Results showed that honokiol and magnolol alone did not affect mitochondrial function and cell damage, but significantly reversed glucose deprivation-induced mitochondrial dysfunction and cell damage. The glutamate receptor blocker MK-801 and antioxidant vitamin E also provided protection against this damage. Furthermore, honokiol was more potent than magnolol in protecting against glutamate-, N-methyl-D-aspartate (NMDA)- and H(2)O(2)-induced mitochondrial dysfunction. These results demonstrated that the neuroprotective effects of honokiol and magnolol may be related to their anti-oxidative actions and antagonism of excitotoxicity induced by excitatory amino acids, suggesting that both compounds may be potential therapeutic agents for neurodegenerative diseases.

Functional in vitro characterization of CR 3394: a novel voltage dependent N-methyl-D-aspartate (NMDA) receptor antagonist

Using the patch-clamp technique, we studied the effect of two novel adamantane derivatives, N-[2-(3,5-dimethyl-1-adamantyl)ethyl] guanidine (CR 3391) and N-[2-(3,5-dimethyl-1-adamantyl) ethyl]acetamidine (CR 3394), on NMDA receptors expressed in cortical neuron cultures. Our data show that CR 3391 and CR 3394 reduce NMDA-evoked currents (IC50 = 1.7 +/- 0.6 microM and 6.7 +/- 1.5 microM, respectively). This antagonism is non-competitive and is completely reversible. The effect of CR 3394, like that of memantine, was strongly voltage dependent. HEK293 cells expressing NR1a/NR2B recombinant NMDA receptors and immature neurons (DIV 8-9) were more sensitive to CR 3394 antagonism than NR1a/NR2A expressing cells and DIV 15 neurons. CR 3394 also reduced the duration and amplitude of miniature excitatory post-synaptic currents mediated exclusively by NMDA receptors (NMDA-mEPSCs). Both memantine and CR 3394 inhibited NMDA-evoked [3H]norepinephrine release from rat hippocampal slices in a concentration-dependent manner with similar potency. CR 3394, but not memantine, increased cathecholamine resting release at low micromolar concentrations. Moreover, in an in vitro model of neurotoxicity, CR 3394 strongly reduced glutamate- and NMDA-induced neuronal death. Taken together, our data highlight pharmacological features of CR 3394 in vitro that prompt us to further evaluate it as a candidate for the treatment of neurodegenerative disorders.

Susceptibility of hippocampus and cerebral cortex to oxidative damage in streptozotocin treated mice: prevention by extracts of Withania somnifera and Aloe vera

Diabetes mellitus is reported to impair the memory function in experimental animals. Since the mammalian hippocampus and cerebral cortex play a pivotal role in a diverse set of cognitive functions, such as novelty detection and memory, we examined the vulnerability of cortex and hippocampus regions of the brain to oxidative damage in streptozotocin (STZ) diabetic mice. We next examined the attenuating effect of extracts of Withania somnifera and Aloe vera on prevention of hippocampal and cortical cell degenerations. Doses of both plant extracts given to experimental animals were based on the evaluation of their total antioxidant activity and also their potency to reduce Fe(3+). We assayed lipid peroxidation (LPO) and protein carbonyl (PC) in both regions of the brain and observed the changes in memory and motor behavioral functions in diabetic and control mice. The results showed a significant (P < 0.05) increase in LPO and PC in hippocampus and cortical regions of STZ diabetic mice. We also found a significant impairment in both motor and memory behavioral functions in diabetic mice. However, when diabetic mice were supplemented with the extracts of Withania somnifera and Aloe vera, the oxidative damage in both brain regions was reduced as marked by a significant (p < 0.05) declines in both LPO and PC. The combination of extracts of Withania somnifera and Aloe vera was more effective in reducing oxidative damage in brain regions than the supplementation of single plant extract. The combination also lowered the blood glucose level in comparison to STZ diabetic mice. Memory impairment and motor dysfunction were also improved by the plant extracts supplementation. We conclude that impairments in the hippocampus and cortex in STZ diabetic mice are associated with an increased free radical mediated oxidative damage and that the supplementation of plant extracts showed preventive effects in attenuating oxidative damage in both brain regions possibly via antioxidative mechanisms.

Lactate and glucose as energy substrates during, and after, oxygen deprivation in rat hippocampal acute and cultured slices

The effects of raised brain lactate levels on neuronal survival following hypoxia or ischemia is still a source of controversy among basic and clinical scientists. We have sought to address this controversy by studying the effects of glucose and lactate on neuronal survival in acute and cultured hippocampal slices. Following a 1-h hypoxic episode, neuronal survival in cultured hippocampal slices was significantly higher if glucose was present in the medium compared with lactate. However, when the energy substrate during the hypoxic period was glucose and then switched to lactate during the normoxic recovery period, the level of cell damage in the CA1 region of organotypic cultures was significantly improved from 64.3 +/- 2.1 to 74.6 +/- 2.1% compared with cultures receiving glucose during and after hypoxia. Extracellular field potentials recorded from the CA1 region of acute slices were abolished during oxygen deprivation for 20 min, but recovered almost fully to baseline levels with either glucose (82.6 +/- 10.0%) or lactate present in the reperfusion medium (108.1 +/- 8.3%). These results suggest that lactate alone cannot support neuronal survival during oxygen deprivation, but a combination of glucose followed by lactate provides for better neuroprotection than either substrate alone.

Differences in ionotropic glutamate receptor subunit expression are not responsible for strain-dependent susceptibility to excitotoxin-induced injury

Systemic administration of kainic acid in C57BL/6 and FVB/N mice induces a comparable level of seizure induction yet results in differential susceptibility to seizure-induced cell death. While kainate administration causes severe hippocampal damage in mice of the FVB/N strain, C57BL/6 mice display no demonstrable cell loss or damage. At present, while the cellular mechanisms underlying strain-dependent differences in susceptibility remain unclear, some of this variation is assumed to have a genetic basis. As glutamate receptors are thought to participate in seizure induction and the subsequent neuronal degeneration that ensues, previous studies have proposed that variation in the precise subunit composition of glutamate receptors may result in differential susceptibility to excitotoxic cell death. Thus, we chose to examine the relationship between the cellular distribution and expression of glutamate receptor subunit proteins and cell loss within the hippocampus in mouse strains resistant and susceptible to kainate-induced excitotoxicity. Using semi-quantitative Western blot techniques and immunohistochemistry with the use of antibodies that recognize subunits of the KA (GluR5,6,7), AMPA (GluR1, GluR2, and GluR4), and NMDA (NMDAR1 and NMDAR2A/2B) receptors, we found no significant strain-dependent differences in the expression or distribution of these glutamate receptor subunits in the intact hippocampus. Following kainate administration, expression changes in ionotropic glutamate receptor subunits paralleled the development of susceptibility to cell death in the FVB/N strain only. Strain differences in hippocampal vulnerability to kainate-induced status epilepticus are not due to glutamate receptor protein expression.

Suppression of BDNF-induced expression of neuropeptide Y (NPY) in cortical cultures by oxygen-glucose deprivation: a model system to study ischemic mechanisms in the perinatal brain

The aim of this study was to establish a culture system that can serve as a model to study hypoxic-ischemic mechanisms regulating the functional expression of NPY neurons in the perinatal brain. Using an aggregate culture system derived from the rat fetal cortex, we defined the effects of oxygen and glucose deprivation on NPY expression, using BDNF-induced production of NPY as a functional criterion. NPY neurons exhibited a differential susceptibility to oxygen and glucose deprivation. Although the neurons could withstand oxygen deprivation for 16 hr, they were dramatically damaged by 8 hr of glucose deprivation and by 1-4 hr of deprivation of both oxygen and glucose (N+Glu-). One-hour exposure to N+Glu- led to a transient inhibition ( approximately 50%) of NPY production manifesting within 24 hr and recovering by 5 days thereafter, a 2-hr exposure to N+Glu- led to a sustained inhibition (50-75%) manifesting 1-5 days thereafter, and a 4-hr exposure to N+Glu- led to a total irreversible suppression of BDNF-induced production of NPY manifesting within 24 hr and lasting 8 days after re-supply of oxygen and glucose. Moreover, 1-hr exposure to N+Glu- led to a substantial and 4-hr exposure led to a total disappearance of immunostaining for MAP-2 and NPY but not for GFAP; indicating that neurons are the primary cell-type damaged by oxygen-glucose deprivation. Analysis of cell viability (LDH, MTT) indicated that progressive changes in cell integrity take place during the 4-hr exposure to N+Glu- followed by massive cell death 24 hr thereafter. Thus, we defined a culture system that can serve as a model to study mechanisms by which ischemic insult leads to suppression and eventually death of NPY neurons. Importantly, changes in NPY neurons can be integrated into the overall scheme of ischemic injury in the perinatal brain.

Traumatic brain injury: developmental differences in glutamate receptor response and the impact on treatment

Perinatal brain injury following trauma, hypoxia, and/or ischemia represents a substantial cause of pediatric disabilities including mental retardation. Such injuries lead to neuronal cell death through either necrosis or apoptosis. Numerous in vivo and in vitro studies implicate ionotropic (iGluRs) and metabotropic (mGluRs) glutamate receptors in the modulation of such cell death. Expression of glutamate receptors changes as a function of developmental age, with substantial implications for understanding mechanisms of post-injury cell death and its potential treatment. Recent findings suggest that the developing brain is more susceptible to apoptosis after injury and that such caspase mediated cell death may be exacerbated by treatment with N-methyl-D-aspartate receptor antagonists. Moreover, group I metabotropic glutamate receptors appear to have opposite effects on necrotic and apoptotic cell death. Understanding the relative roles of glutamate receptors in post-traumatic or post-ischemic cell death as a function of developmental age may lead to novel targeted approaches to the treatment of pediatric brain injury.

Modification of glutamate binding sites in newborn brain during hypoglycemia

We have shown that acute insulin-induced hypoglycemia leads to specific changes in the cerebral NMDA receptor-associated ion channel in the newborn piglet. The present study tests the hypothesis that exposure to acute hypoglycemia in the newborn will alter the glutamate binding site of both NMDA and kainate receptors. Studies were performed in 3-6 days-old piglets randomized to control (n=6) or hypoglycemic (n=6) groups. Hypoglycemia was maintained for 120 min using insulin infusion. Saturation binding assays were performed in cerebral cell membranes using (3)H-glutamate or (3)H-kainate to determine the characteristics of the glutamate binding sites of the NMDA and kainate receptors, respectively. The concentration of glucose in cerebral cortex was 10-fold less in hypoglycemic piglets than in controls (P<0.05). Brain ATP was not significantly decreased during hypoglycemia, but phosphocreatine decreased from control of 6.6 +/- 1.3 micromoles/g brain to 3.2 +/- 1.9 micromoles/g brain in hypoglycemic piglets. The B(max) for NMDA-displaceable (3)H-glutamate binding was 992 +/- 64 fmol/mg protein in hypoglycemic animals, significantly higher than the control value of 746 +/- 42 fmol/mg protein. However, the dissociation constant for glutamate was unchanged during hypoglycemia. The (3)H-kainate binding studies demonstrated no change in B(max) of high-affinity kainate receptors during hypoglycemia. In contrast, the affinity of the kainate receptor glutamate binding site significantly increased compared to control. Thus, acute hypoglycemia in the newborn piglet had specific effects on the glutamate binding sites of the NMDA and kainate receptors that could be due to alterations in cell membrane lipids or modification of receptor proteins.

Glutamate regulates the viability of retinal cells in culture

In this study, we show that glutamate regulates the viability of cultured retinal cells upon transient glucose deprivation. At low concentrations (10-100 microM) glutamate decreased MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] reduction to about 50% of control and decreased intracellular ATP levels (about 4-fold) after transient glucose removal. Under these conditions, the decrease in MTT reduction was associated with the activation of NMDA (N-methyl-D-aspartate) receptors. Upon exposure to high (10 mM) glutamate and transient glucose deprivation, the intracellular levels of glutamate increased. High glutamate significantly counteracted the decrease in MTT reduction and ATP production observed in the presence of low glutamate concentrations. AOAA (aminooxyacetic acid), a non-specific inhibitor of mitochondrial transaminases, enhanced the intracellular glutamate levels, but did not largely affect glutamate-mediated changes in MTT reduction or ATP production. Furthermore, the intracellular levels of pyruvate were not significantly altered, suggesting that changes in ATP production were not due to an increase in glycolysis. Thus, the recovery from glucose deprivation seems to be facilitated in retinal neuronal cells that had been exposed to high glutamate, in comparison with low glutamate, suggesting a role for high glutamate and glucose in maintaining retinal cell function following conditions of glucose scarcity.

Hypoglycemia enhances ionotropic but reduces metabotropic glutamate responses in substantia nigra dopaminergic neurons

It is widely accepted that energy deprivation causes a neuronal death that is mainly determined by an increase in the extracellular level of glutamate. Consequently an excessive membrane depolarization and a rise in the intracellular concentration of sodium and calcium are produced. In spite of this scenario, the function of excitatory and inhibitory amino acids during an episode of energy failure has not been studied yet at a cellular level. In a model of cerebral hypoglycemia in the rat substantia nigra pars compacta, we measured neuronal responses to excitatory amino acid agonists. Under single-electrode voltage-clamp mode at -60 mV, the application of the ionotropic glutamate receptor agonists N-methyl-D-aspartate, alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid, kainate, and the metabotropic group I agonist (S)-3,5-dihydroxyphenilglycine (DHPG) produced reversible inward currents in the dopaminergic cells. In addition, an outward current was caused by the superfusion of the metabotropic GABA(B) agonist baclofen. Glucose deprivation enhanced the inward responses caused by each ionotropic glutamate agonist. In contrast, hypoglycemia depressed the DHPG-induced inward current and the baclofen-induced outward current. These effects of hypoglycemia were reversible. To test whether a failure of the Na(+)/K(+) ATPase pump could account for the modification of the agonist-induced currents during hypoglycemia, we treated the midbrain slices with strophanthidin (1-3 microM). Strophanthidin enhanced the inward currents caused by glutamate agonists. However, it did not modify the GABA(B)-induced outward current. Our data suggest that glucose deprivation enhances the inward current caused by the stimulation of ionotropic glutamate receptors while it dampens the responses caused by the activation of metabotropic receptors. Thus a substantial component of the augmented neuronal response to glutamate, during energy deprivation, is very likely due to the failure of Na(+) and Ca(2+) extrusion and might ultimately favor excitotoxic processes in the dopaminergic cells.

Stretch injury causes calpain and caspase-3 activation and necrotic and apoptotic cell death in septo-hippocampal cell cultures

Traumatic brain injury (TBI) results in numerous central and systemic responses that complicate interpretation of the effects of the primary mechanical trauma. For this reason, several in vitro models of mechanical cell injury have recently been developed that allow more precise control over intra- and extracellular environments than is possible in vivo. Although we recently reported that calpain and caspase-3 proteases are activated after TBI in rats, the role of calpain and/or caspase-3 has not been examined in any in vitro model of mechanical cell injury. In this investigation, varying magnitudes of rapid mechanical cell stretch were used to examine processing of the cytoskeletal protein alpha-spectrin (280 kDa) to a signature 145-kDa fragment by calpain and to the apoptotic-linked 120-kDa fragment by caspase-3 in septo-hippocampal cell cultures. Additionally, effects of stretch injury on cell viability and morphology were assayed. One hour after injury, maximal release of cytosolic lactate dehydrogenase and nuclear propidium iodide uptake were associated with peak accumulations of the calpain-specific 145-kDa fragment to alpha-spectrin at each injury level. The acute period of calpain activation (1-6 h) was associated with subpopulations of nuclear morphological alterations that appeared necrotic (hyperchromatism) or apoptotic (condensed, shrunken nuclei). In contrast, caspase-3 processing of alpha-spectrin to the apoptotic-linked 120-kDa fragment was only detected 24 h after moderate, but not mild or severe injury. The period of caspase-3 activation was predominantly associated with nuclear shrinkage, fragmentation, and apoptotic body formation characteristic of apoptosis. Results of this study indicate that rapid mechanical stretch injury to septo-hippocampal cell cultures replicates several important biochemical and morphological alterations commonly observed in vivo brain injury, although important differences were also noted.

Intracellular survival pathways against glutamate receptor agonist excitotoxicity in cultured neurons. Intracellular calcium responses

Cultured rat cerebellar granule cells are resistant to the excitotoxic effects of N-methyl-D-aspartate (NMDA) and non-NMDA receptor agonists under three conditions: 1) prior to day seven in vitro when cultured in depolarizing concentrations of potassium [25 mM]; 2) at any time in vitro when cultured in non-depolarizing concentrations of potassium 5 mM[; and 3) when neurons, cultured in depolarizing concentrations of potassium 25 mM[ for eight days in vitro, are pretreated with a subtoxic concentration of NMDA. The focus of this paper is to determine: a) whether the resistance to excitotoxicity by NMDA and non-NMDA receptor agonists is due to a decreased intracellular calcium Ca++[i response to glutamate receptor agonists in cultured rat cerebellar granule cells; or b) whether Ca++[i levels induced by the agonists are similar to those observed under excitotoxic conditions. Granule cells, matured in non-depolarizing growth medium, treated with glutamate resulted in an increase in Ca++[i followed by a plateau that remained above baseline in virtually all neurons that responded to glutamate. The response was rapid in onset (< 10 sec) and the pattern of response heterogeneous in that cells responsive to glutamate increased their Ca++[i to different extents; some cells did not respond to glutamate. Kainate also produced significant elevations in Ca++[i. The Ca++[i response to glutamate in neurons matured in depolarizing (25 mM K+) growth medium for three days was rapid, transient and heterogeneous, which reached a plateau that was elevated above baseline levels; removing the glutamate markedly reduced the Ca++[i concentration. Activation of the alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)/kainate receptors by kainic acid produced similar changes in Ca++[i responses. At a time when cultured cerebellar granule cells become susceptible to the excitotoxic effects of glutamate acting at NMDA receptors (day in vitro (DIV) 8) in depolarizing growth medium, glutamate elicited Ca++[i responses similar to those observed at a culture time when the neurons are not susceptible to the excitotoxic effects of glutamate (DIV 3). Pretreatment of the cultured neurons with a subtoxic concentration of NMDA, which protects all neurons against the excitotoxic effects of glutamate, did not alter the maximal Ca++[i elicited by an excitotoxic concentration of glutamate.

Neuroprotective effect of high glucose against NMDA, free radical, and oxygen-glucose deprivation through enhanced mitochondrial potentials

Cultured cortical neurons maintained in 25 mM glucose underwent a widespread neuronal death after exposure to NMDA, AMPA, and kainate. Among these, NMDA toxicity was substantially reduced in neurons maintained in 100 mM glucose. NMDA-induced increase in [Ca(2+)](i) and reactive oxygen species was attenuated in neurons maintained in high glucose that revealed increased mitochondrial membrane and redox potentials as determined using rhodamine 123 and 3-(4, 5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide. p-trifluoromethoxy-phenylhydrazone, KCN, and rotenone, the selective inhibitors of mitochondrial potential, abrogated neuroprotective effect of high glucose against NMDA. The neuroprotective action of high glucose was extended against oxygen or combined oxygen-glucose deprivation. The present study provides evidence that prolonged exposure of cortical cells to high glucose attenuates NMDA- and free radical-mediated neuronal death via enhanced mitochondrial function.

Hypoxia-inducible factor-1alpha mediates hypoxia-induced delayed neuronal death that involves p53

Hypoxia-induced delayed neuronal death is known to require de novo gene expression; however, the molecular mediators that are involved remain undefined. The transcription factor hypoxia-inducible factor-1alpha (HIF-1alpha), in addition to promoting the expression of adaptive genes under conditions of hypoxia, has been implicated as being a necessary component in p53-mediated cell death in tumors. Using herpes amplicon-mediated gene transfer in cortical neuronal cultures, we demonstrate that delivery of a dominant-negative form of HIF-1alpha (HIFdn), capable of disrupting hypoxia-dependent transcription, reduces delayed neuronal death that follows hypoxic stress. In contrast, hypoxia-resistant p53-null primary cultures are not protected by HIFdn expression. These data indicate that, in hypoxic neurons, HIF-1alpha and p53 conspire to promote a pathological sequence resulting in cell death.

Neuroprotection of cultured foetal rat hippocampal cells against glucose deprivation: are GABAergic neurons less vulnerable or more sensitive to TCP protection?

In the rat brain, hippocampal neurons are particularly sensitive to secondary excitotoxic injury induced by ischaemia or hypoglycaemia. To determine some distinctive features of vulnerability among neuronal phenotypes in the hippocampus following a metabolic insult, we used an in vitro model of mild glucose deprivation. Primary cultures from the rat hippocampus (21 days in vitro) were deprived of glucose for 4 h and then were returned to the standard medium for 24 or 48 h. Survival of the GABAergic neuronal population was evaluated both by measuring [3H]GABA uptake and by counting GAD65-immunostained cells. This was compared with the survival of the total neuronal population evaluated by counting the neurofilament-200-immunostained cells. Glucose deprivation for 4 h followed by a recovery period of 48 h induced a decrease of 59% and 40% in the number of GAD65- and neurofilament-200-immunostained cells, respectively. Thus, GABAergic neurons were slightly more vulnerable to glucose deprivation than the other neurons in the hippocampal cell cultures. When the excitotoxic component of cellular death was blocked in the presence of TCP, an NMDA-antagonist, the survival of GABAergic neurons was almost complete after 48 h of recovery. In contrast, measurements of the release of lactate dehydrogenase in the medium indicated that TCP largely protected hippocampal cells after 24 h but was ineffective after 48 h. This observation was confirmed by immunostaining data which showed that after 48 h TCP did not significantly increase the survival of neurofilament-200-immunostained cells. These results indicate that after glucose deprivation and a recovery period of 48 h, GABAergic neurons in hippocampal cell cultures are not more resistant than other neurons but they are more sensitive to TCP protection.

A submersion method to induce hypoxic damage in organotypic hippocampal cultures

Organotypic brain slices cultured on semi-porous membranes is an increasingly popular in vitro preparation for studying mechanisms of ischemic brain damage. To model in vivo hypoxia, cultured brain slices are exposed to anaerobic atmosphere by placing them into a special incubator. This requirement limits the use of in vitro ischemic models to highly specialized laboratories. Here, we describe a simple method that reproduces hypoxic injury, where cultured hippocampal slices are submerged into glucose-free deoxygenated medium for 1 h. The extent and distribution of hippocampal neuronal loss obtained with this treatment resembled that caused by hypoxia in living tissue in situ, i.e. CA1 pyramidal cell layer was most vulnerable and dentate granular cell layer was least susceptible to hypoxia as measured with fluorescence of the viability marker propidium iodide (PI). Electrophysiologic functional impairment determined by field recordings of CA1 pyramidal neurones temporally coincided with the extent of neuronal death. In addition, known neuroprotective treatments, such as hypothermia and phenytoin application ameliorated neuronal damage in a pattern similar to previously published reports. Therefore, the present in vitro model of ischemia is simple, reliable and of low cost. It is well suited for short and long-term studies of the mechanisms of hypoxic brain damage.

Effect of glucose deprivation and acute glutamate exposure in cultured retinal cells

The relationship between bioenergetics and the glutamate system was analyzed in a neuronal model of retinal cells in culture, submitted to glucose deprivation and exposed to glutamate for 2 h, and compared with exposure to glutamate in the presence of glucose. Under glucose deprivation, a reduction (about 1.1-fold) in the energy charge of the cells occurred, probably as a result of a decrement (by about 75%) in the cellular redox efficacy, as determined by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) test. In the absence of glucose, exposure of retinal cells to 10 microM glutamate potentiated the reduction in the energy charge (by about 1.2-fold) and induced a significant increase in the uptake of 45Ca2+ by the cells (1.3-fold), although no significant changes were observed in the presence of glucose. Under glucose deprivation, 100 microM glutamate caused an irreversible cell membrane damage, as shown by the significant increase in lactate dehydrogenase (LDH) leakage (about 1.8-fold). A significant increase in membrane depolarization, measured by the reduction of [3H]tetraphenylphosphonium+ ([3H]TPP+) uptake, was also observed after glutamate exposure in the absence of glucose. In the presence of glucose, high glutamate concentrations (10 mM) induced a major increase in Ca2+ entry into the cells and membrane depolarization, without affecting the energy charge or cell survival. In contrast, in the absence of glucose, 10 mM glutamate did not alter Ca2+ accumulation by the cells and a smaller decrease in membrane potential occurred, as compared to 100 microM glutamate exposure. Data shown in this study suggest that during a prolonged (2 h) and acute exposure to high glutamate (10 mM), under glucose deprivation conditions, the neuronal systems have "adaptive" mechanisms that allow the survival of cells. These findings may have implications in neuronal degeneration occurring during brain ischemia.

Heme oxygenase-mediated resistance to oxygen toxicity in hamster fibroblasts

The role of heme oxygenase (HO)-1 was evaluated in the oxygen-resistant hamster fibroblast cell line, O2R95, which moderately overexpress HO when compared with the parental cell line, HA-1. To suppress HO-1 expression, O2R95 were transfected with HO-1 antisense oligonucleotide or treated with tin-mesoporphyrin (SnMP). To increase HO-1 expression, cells were transfected with HO-1 cDNA in a pRC/cytomegalovirus (CMV) vector. All cells were challenged with a 48-h exposure to 95% O2 (hyperoxia). When HO activity was suppressed, O2R95 cells had significantly decreased cell viability, increased susceptibility to lipid peroxidation, and increased protein oxidation in hyperoxia. In contrast, further overexpression of HO-1 did not improve resistance to oxygen toxicity. Antisense-transfected cells and SnMP-treated cells with lowered HO activity showed increased levels of cellular heme compared with controls. In the HO-1 cDNA-transfected O2R95 cells, cellular heme was lowered compared with controls; however, cellular redox active iron levels were increased. We conclude that HO mediates cytoprotection to oxygen toxicity within a narrow range of expression. We speculate that this protective effect may be mediated in part through increased metabolism of the pro-oxidant heme but that higher levels of HO activity obviate protection by increased redox active iron release.

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

We have investigated the relative contributions of oxygen and glucose deprivation to ischaemic neurodegeneration in organotypic hippocampal slice cultures. Cultures prepared from 10-day-old rats were maintained in vitro for 14 days and then deprived of either oxygen (hypoxia), glucose (hypoglycaemia), or both oxygen and glucose (ischaemia). Hypoxia alone induced degeneration selectively in CA1 pyramidal cells and this was greatly potentiated if glucose was removed from the medium. We have also characterised the effects of both pre- and post-treatment using glutamate receptor antagonists and the sodium channel blocker tetrodotoxin (TTX). Neuronal death following either hypoxia or ischaemia was prevented by pre-incubation with CNQX, MK-801 or tetrodotoxin. MK-801 or CNQX also prevented death induced by either hypoxia or ischaemia if added immediately post-insult, however, post-insult addition of TTX prevented hypoxic but not ischaemic damage. Organotypic hippocampal slice cultures are sensitive to both NMDA and non-NMDA glutamate receptor blockade and thus represent a useful in vitro system for the study of ischaemic neurodegeneration paralleling results reported using in vivo models of ischaemia.

Effects of alpha-phenyl-tert-butyl nitrone on neuronal survival and motor function following intrastriatal injections of quinolinate or 3-nitropropionic acid

We have investigated the neuroprotective effects of the the spin-trapping agent alpha-phenyl-tert-butyl nitrone on striatal lesions produced by local injections of the excitotoxin quinolinate or the mitochondrial toxin 3-nitropropionic acid. We have assessed both the behavioural and morphological consequences of the lesion. Thus, we tested paw-reaching ability and amphetamine- and apomorphine-induced rotational behaviour in lesioned rats with or without alpha-phenyl-tert-butyl nitrone treatment, and also explored the relationship between the outcome of the behavioural studies and the extent of the lesion. In the morphological analysis, we chose immunocytochemistry for dopamine- and cyclic AMP-regulated phosphoprotein with a molecular weight of 32,000 as a specific marker for striatal neurons. The paw-reaching ability of rats with the quinolinate and 3-nitropropionic acid lesions was significantly impaired compared to normal control animals. Treatment with alpha-phenyl-tert-butyl nitrone significantly ameliorated the paw-reaching deficits produced by the quinolinate lesion, whereas the 3-nitropropionic acid-induced deficits were unaffected by alpha-phenyl-tert-butyl nitrone. Both quinolinate and 3-nitropropionic acid lesions resulted in a rotation asymmetry towards the lesioned side in response to both amphetamine and apomorphine. In the quinolinate lesion model, the alpha-phenyl-tert-butyl nitrone treatment resulted in a less marked motor asymmetry in response to both drugs. By contrast, alpha-phenyl-tert-butyl nitrone did not significantly reduce the drug-induced rotation asymmetry in rats with a 3-nitropropionic acid lesion. Morphological analyses disclosed that alpha-phenyl-tert-butyl nitrone significantly increased the size of the spared striatum in the quinolinate lesions, but only caused a non-significant trend towards an attenuation of the 3-nitropropionic acid lesions. The behavioural deficits were inversely correlated to the size of the spared residual striatum. The intrastriatal injection of 3-nitropropionic acid, unlike the injection of quinolinate, caused degeneration of the nigrostriatal dopamine system as well as of transverse fibre bundles of the internal capsule in the striatum, in addition to the striatal lesion. The behavioural studies revealed that the combination of multiple lesions seen in 3-nitropropionic acid-lesioned rats significantly exacerbated paw-reaching deficits and amphetamine-induced rotation asymmetry. In conclusion, alpha-phenyl-tert-butyl nitrone attenuated behavioural and morphological consequences of striatal lesions induced by local injections of quinolinate, but not of 3-nitropropionic acid. Deficits in behavioural tests of striatal function reflected well the extent of striatal lesion. The intrastriatal injection of 3-nitropropionic acid led to degeneration of both intrinsic striatal neurons and the nigrostriatal dopaminergic system, suggesting that this lesion may provide an animal model of a form of multiple system atrophy rather than Huntington's disease.

CGS 19755 (Selfotel): A Novel Neuroprotective Agent Against CNS Injury

The hypothesis that excitoxicity is a mechanism of damage following different types of cerebral injury including global and focal ischemia (34), and head and spinal cord trauma (6,7,9,25) has been supported by numerous findings. During ischemia for example, glutamate neurotoxicity is mediated in part through N-methyl-D-aspartate (NMDA) receptors, since selective antagonists to this receptor protect against hypoxic-ischemic injury (10,35,41). In the last few years, different NMDA antagonists have been developed and tested; they can be divided into competitive and noncompetitive antagonists. Noncompetitive NMDA antagonists are extremely lipophilic and reach high levels in the brain after systemic administration. Various studies have demonstrated that these agents provide neuroprotection against hypoxic-ischemic injury (for review see ref. 29). Many competitive NMDA antagonists are hydrophilic and require direct cerebral administration to obtain high brain levels. Newer competitive NMDA blockers, such as cis-4-phosphonomethyl-2-piperidine carboxylic acid (CGS 19755, selfotel), provide neuroprotection against global ischemia, focal ischemia, and trauma when given systemically (2,3,32,33). Selfotel is currently being studied in multicenter safety and efficacy trials for stroke (17) and head trauma (6).

Antioxidant treatment protects striatal neurons against excitotoxic insults

It has been suggested that oxidative stress plays an important role in mediating excitotoxic neuronal death. We have therefore investigated the protective effects of antioxidants against excitotoxic injury in the rat on striatal neurons both in vitro and in vivo. In the first part of the study, we determined whether two different types of antioxidants, the spin trapping agent, alpha-phenyl-tert-butyl nitrone and an inhibitor of lipid peroxidation, U-83836E, could protect cultured striatal neurons against either hypoglycemic injury or N-methyl-D-aspartate-induced excitotoxicity. Dopamine- and cyclic AMP-regulated phosphoprotein, which is enriched in medium-sized spiny neurons, was chosen as a marker for striatal neurons. alpha-Phenyl-t-butyl nitrone and U-83836E both significantly reduced cell death induced by these insults as indicated by an increased number of surviving dopamine- and cyclic AMP-regulated phospho-protein-positive neurons. The two antioxidants also promoted the survival of cultured striatal neurons grown at low cell density under serum-free culture conditions. In an in vivo experiment systemically administered alpha-phenyl-t-butyl nitrone exerted neuroprotective effects in the rat striatum following injection of the excitotoxin quinolinic acid. Apomorphine-induced rotation tests revealed that alpha-phenyl-t-butyl nitrone-treated animals were significantly less asymmetric in their motor behavior than control rats. Treatment with alpha-phenyl-t-butyl nitrone significantly reduced the size of the quinolinic acid-induced striatal lesions, as assessed by the degree of sparing of dopamine- and cyclic AMP-regulated phospho-protein-positive and nicotinamide adenine dinucleotide phosphate-diaphorase-positive neurons, and of microtubule-associated protein-2-immunorective areas. Furthermore, lesion-induced morphological changes in the substantia nigra pars reticulate, i.e. loss of dopamine- and cyclic AMP-regulated phosphoprotein-positive afferent fibers and atrophic changes due to transsynaptic degeneration, were also less extensive in the alpha-phenyl-t-butyl nitrone-treated animals. The results support the hypothesis that oxygen-free radicals contribute to excitotoxic neuronal injury. The in vivo cytoprotective effects of alpha-phenyl-t-butyl nitrone against striatal excitotoxic lesions suggest that antioxidants could be used as potential neuroprotective agents in Huntington's disease, which has been suggested to involve excitotoxicity.

The effects of insulin-like growth factor analogues on survival of cultured cerebral cortex and cerebellar granule neurones

Insulin and insulin-like growth factors (IGF-I, IGF-II) are closely related polypeptides which are found in the CNS and which promote neuronal survival and neurite outgrowth. They are each associated with specific cell surface receptors and several soluble binding proteins (IGFBPs) which are involved in regulating function and availability. Two analogues of IGF-I were produced by site directed mutagenesis: (Gln3, Ala4, Tyr15, (Leu16)IGF-1 (QAYL-IGF) and a B-chain mutant in which the first 16 amino acids of IGF-1 were replaced by the first 17 amino acids of insulin. These analogues have significantly reduced binding affinity for IGFBPs. Using glucose deprivation as a damaging stimulus and assaying lactate dehydrogenase released from cultures as a marker for cell death, we have investigated the effect of IGF analogues on cell death of cerebrocortical and cerebellar granule cell cultures. In the presence of IGF-I, QAYL-IGF or B-chain mutant, the amount of LDH released from cortical and cerebellar granule cell cultures was significantly reduced compared to control (no glucose), indicating that these molecules promote survival. Both QAYL and B-chain mutants, which have reduced affinity for IGFBPs, are as effective as IGF-I in promoting cell survival in conditions of glucose deprivation and their reduced affinity for IGFBPs has no apparent deleterious effect on their neuroprotective function. We also show that the neuroprotective effect of the IGF analogues is due to a direct effect on the neurones in these cultures and is independent of the presence of glia.

Hypoglycaemic brain damage: effect of a dihydropyridine calcium channel antagonist in rats

Hypoglycaemic brain damage consists of selective necrosis of cerebral neurons related to the extracellular release of excitatory amino acids. Neuronal excitatory amino acid receptors are activated and calcium channels are opened. The present investigation was designed to test the effectiveness of dihydropyridine blockade of voltage-sensitive calcium channels in hypoglycaemic brain damage. Sixty-four rats were given either high-dose nimodipine, consisting of an initial bolus of 300 micrograms/kg nimodipine administered at the stage of EEG slowing (blood glucose levels of 1.0-1.5 mmol/l), followed by continuous intravenous nimodipine infusion at 1.5 micrograms.kg-1.min-1, low-dose nimodipine, consisting of an initial bolus of 30 micrograms/kg at the time of EEG slowing, followed by 0.15 microgram.kg-1.min-1, an equal volume of vehicle solution, or 154 mmol/l NaCl. Animals receiving either low- or high-dose nimodipine had higher mortality, and increased brain damage compared with controls. Examination of the perfusion-fixed brains 1 week after recovery with glucose revealed that quantitated neuronal necrosis was worsened by nimodipine in the hippocampus, caudate nucleus and cerebral cortex. The present results in profound hypoglycaemia (accompanied by a flat EEG) contrast with the beneficial effect of nimodipine in brain ischaemia.

Trophic and protective actions of brain-derived neurotrophic factor on striatal DARPP-32-containing neurons in vitro

We have examined the effects of either brain-derived neurotrophic factor (BDNF), the BB-isoform of platelet-derived growth factor (PDGF-BB), or a combination of these growth factors on the survival and the morphological development of embryonic striatal neurons grown under serum-free culture conditions. Striatal neurons were identified using immunocytochemistry for "dopamine- and adenosine 3':5'-monophosphate-regulated phosphoprotein with a molecular weight of 32 kilodalton" (DARPP-32). BDNF and PDGF-BB promoted the survival of DARPP-32-positive neurons, with the magnitude of their effects being comparable. A combination of these growth factors exerted no significant additive effects on cell survival. BDNF stimulated morphological differentiation of DARPP-32-containing neurons by increasing the length of neurites, the number of branching points on the neurites, and the soma area. By contrast, PDGF-BB increased the neurite length and the cell body area, but not the number of branching points. BDNF also protected striatal neurons from excitotoxicity induced by N-methyl-D-aspartate, whereas PDGF-BB had no effect under the same treatment conditions as those for BDNF. Thus, BDNF is trophic for striatal DARPP-32-containing neurons in vitro by enhancing the survival, morphological differentiation and resistance to excitotoxicity, and its mechanisms of action are probably different from those of PDGF-BB.

Correlation of CGS 19755 neuroprotection against in vitro excitotoxicity and focal cerebral ischemia

The in vivo neuroprotective effect and brain levels of cis-4-phosphonomethyl-2-piperidine carboxylic acid (CGS 19755), a competitive N-methyl-D-aspartate (NMDA) antagonist, were compared with its in vitro neuroprotective effects. The dose-response for in vitro neuroprotection against both NMDA toxicity and combined oxygen-glucose deprivation (OGD) was determined in murine neocortical cultures. Primary cultures of neocortical cells from feta mice were injured by exposure to 500 microM NMDA for 10 min or to OGD for 45 min. The effect of CGS 19755 in both injury paradigms was assessed morphologically and quantitated by determination of lactate dehydrogenase release. Near complete neuroprotection was found at high doses of CGS 19755. The ED50 for protection against NMDA toxicity was 25.4 micro M, and against OGD the ED50 was 15.2 microM. For the in vivo paradigm rabbits underwent 2 h of left internal carotid, anterior cerebral, and middle cerebral artery occlusion followed by 4 h reperfusion; ischemic injury was assessed by magnetic resonance imaging and histopathology. The rabbits were treated with 40 mg/kg i.v. CGS 19755 or saline 10 min after arterial occlusion. CSF and brain levels of CGS 19755 were 12 microM and 5 microM, respectively, at 1 h, 6 microM and 5 microM at 2 h, and 13 microM and 7 microM at 4 h. These levels were neuroprotective in this model, reducing cortical ischemic edema by 48% and ischemic neuronal damage by 76%. These results suggest that a single i.v. dose penetrates the blood-brain barrier, attaining sustained neuroprotective levels that are in the range for in vitro neuroprotection.

The inhibitory mGluR agonist, S-4-carboxy-3-hydroxy-phenylglycine selectively attenuates NMDA neurotoxicity and oxygen-glucose deprivation-induced neuronal death

We examined the effect of two novel phenylglycine derivative drugs on excitotoxicity in murine cortical cell cultures: S-4-carboxy-3-hydroxy-phenylglycine (4C3HPG), a selective agonist of mGluRs 2/3 and an antagonist at mGluRs 1/5, and S-3 hydroxy-phenylglycine (3HPG), an agonist of mGluRs 1/5. 4C3HPG attenuated slowly-triggered NMDA-induced excitotoxic neuronal death, as well as the death induced by combined oxygen-glucose deprivation, but did not affect slowly-triggered excitotoxicity induced by AMPA or kainate. As expected, 4C3HPG also reduced NMDA-induced increases in cAMP in near-pure neuronal cultures, and the protective effect of 4C3HPG on NMDA toxicity could be reversed by adding 8-(4-chlorophenylthio)-adenosine 3':5'-cyclic-monophosphate (CPT cAMP) to the exposure medium. In contrast, 3HPG did not did not have any protective effects in these paradigms; in fact, slowly-triggered NMDA-induced excitotoxicity and the neuronal cell death induced by oxygen-glucose deprivation were potentiated. These results are consistent with the idea that the "inhibitory" mGluRs 2/3 exert a negative modulatory action on NMDA receptor-mediated excitotoxicity via reduction in neuronal cAMP levels.

Protection from neuronal damage induced by combined oxygen and glucose deprivation in organotypic hippocampal cultures by glutamate receptor antagonists

Organotypic hippocampal cultures were exposed to defined periods (30 and 60 min) of combined oxygen and glucose deprivation, mimicking transient ischemic conditions. The involvement of different glutamate receptors in individual hippocampal subfields (CA1, CA3 and dentate gyrus) was studied using antagonists of NMDA (dizocilpine) and AMPA/kainate receptors (CNQX and GYKI 52466). Staining with the fluorescent dye propidium iodide (PI) allowed detection of damaged cells. For quantitative determination of neuronal damage, fluorescence intensity was measured after a 22 h recovery period and was related to maximal fluorescence intensity measured after fixation and PI restaining of the cultures at the end of the experiment. Dizocilpine (10 microM), CNQX (100 microM) and GYKI 52466 (100 microM) provided complete protection in CA1, CA3 and dentate gyrus following the moderate ischemic insult, when the antagonists were present permanently. This indicates that none of the ionotropic glutamate receptor subtypes dominated toxicity in the most sensitive subpopulation of neurons. When applied only during the recovery period protection with dizocilpine (10 microM) or CNQX (100 microM) was drastically reduced by about 60% in the most sensitive area (CA1), but only slightly by 15% in CA3. Therefore the onset of irreversible damage seems to occur earlier in CA1 than in CA3. Blockade of AMPA/kainate receptors by GYKI 52466 (100 microM) offered no neuroprotection if the compound was applied only during the recovery period.(ABSTRACT TRUNCATED AT 250 WORDS)

Protection against CNS ischemia by temporary interruption of function-related processes of neurons

Previous studies have shown that most of the energy consumption of CNS tissue is used for processes that subserve signaling functions of the cells. Since these function-related processes are probably not essential to cell viability, blocking them reversibly with a combination of pharmacologic agents should protect cells from a reduction in energy metabolism. Preliminary experiments to test this hypothesis were performed on isolated rabbit retinas. They were maintained in a newly devised chamber that permitted continuous monitoring of electrophysiological function for > or = 8 h. Ischemia was simulated by a 6-fold reduction in both O2 and glucose. This caused a rapid (t1/2 75 s) and complete loss of the light-evoked response in the optic nerve. Untreated retinas showed full recovery after 1/2 h of deprivation, but only 50% recovery after 1 h and little or no recovery after 2 or 3 h. Retinas exposed during 3 h of deprivation to a combination of six agents that abolished electrophysiologic function and reduced glucose utilization [tetrodotoxin (TTX), 2-amino-4-phosphonobutyric acid (APB), 2-amino-5-phosphonovaleric acid (APV), amiloride, Mg2+, and Li+] showed full recovery. We conclude that reducing energy requirements by blocking functional processes can prevent ischemic damage.

Quantitative measurement of neuronal degeneration in organotypic hippocampal cultures after combined oxygen/glucose deprivation

Organotypic hippocampal cultures were used to study cell degeneration during the recovery period after defined periods (30 and 60 min) of combined oxygen/glucose deprivation mimicking transient ischemic conditions. Staining with the fluorescent dye propidium iodide allowed detection of damaged cells. Fluorescence intensity was measured by an image analysis system and used to quantify cell damage at different time points during the recovery period (up to 22 h). At 30 min of oxygen/glucose deprivation cells in the CA1 area were relatively more sensitive compared to CA3 and dentate gyrus cells, with respect to the time course of degeneration and the percentage of affected cells. Expanding the oxygen/glucose deprivation period from 30 to 60 min drastically increased the percentage of cells dying in all hippocampal areas. Still, however, cells in CA1 degenerated faster compared to those in the CA3 area and dentate gyrus. A histological analysis of toluidine blue as well as MAP2-immunostained sections revealed that almost all neurons degenerated in all hippocampal areas following the 60-min deprivation period, whereas GFAP-stained astrocytes appeared to be unaffected. Therefore, neuronal degeneration could be quantified by taking the fluorescence intensity values 22 h after 60 min of oxygen/glucose deprivation as 100% neuronal damage. The possibility to quantify neuronal damage in organotypic cultures offers a useful tool for detailed studies on mechanisms of neuronal cell death in a cell culture system which is closer to in situ conditions than monolayer cell cultures.

The effect of acute hypoglycemia on the cerebral NMDA receptor in newborn piglets

The effects of acute insulin-induced hypoglycemia on the cerebral NMDA receptor in the newborn were examined by determining [3H]MK-801 binding as an index of NMDA receptor function in 6 control and 7 hypoglycemic piglets. In hypoglycemic animals, the glucose clamp technique with constant insulin infusion was used to maintain a blood glucose concentration of 1.2 mmol/l for 120 min before obtaining cerebral cortex for further analysis; controls received a saline infusion. Concentrations of glucose, lactate, ATP, and PCr were measured in cortex, and Na+,K(+)-ATPase activity was determined in a brain cell membrane preparation. [3H]MK-801 binding was evaluated by: (1) saturation binding assays over the range of 0.5-50 nM [3H]MK-801 in the presence of 100 microM glutamate and glycine; and (2) binding assays at 10 nM [3H]MK-801 in the presence of glutamate and/or glycine at 0, 10, or 100 microM. Blood and brain glucose concentrations were significantly lower in hypoglycemic animals than controls. There was no change in brain ATP with hypoglycemia, but PCr was decreased 80% compared to control (P < 0.05). Na+,K(+)-ATPase activity was 13% lower in hypoglycemic animals (P < 0.05). Based on saturation binding data, hypoglycemia had no effect on the number of functional receptors (Bmax), but the apparent affinity was significantly increased, as indicated by a decrease in the Kd (dissociation constant) from the control value of 8.1 +/- 1.6 nM to 5.5 +/- 2.1 nM (P < 0.05). Augmentation of [3H]MK-801 binding by glutamate and glycine alone or in combination was also significantly greater in the hypoglycemic animals.(ABSTRACT TRUNCATED AT 250 WORDS)

A simple method for evaluation of superoxide radical production in neural cells under various culture conditions: application to hypoxia

To evaluate the potential deleterious influence of oxygen-derived free radicals following hypoxia in a model of primary culture of neurons obtained from the fetal rat brain, superoxide radicals were measured as a function of time in the extracellular medium. Neuronal cells were grown for 8 days in the presence or absence of serum, then incubated in a buffered Krebs-Ringer solution containing 60 microM acetyl-cytochrome c. The rate of superoxide radical formation was quantified spectrophotometrically by measuring the specific reduction of acetyl-cytochrome c. Under normoxic conditions (95% air-5% CO2), basal production of superoxide that increased with time was recorded. It was significantly more pronounced in cells grown in serum-free medium. Under both culture conditions, acute hypoxia (95% N2-5% CO2) for 6 h increased superoxide radical amounts in the extracellular medium, and they were still enhanced 3 h after reoxygenation. The addition of superoxide dismutase to the incubating medium abolished the detection of superoxide radicals. The present study describes a new reliable method for superoxide radical measurement in cells in vitro and demonstrates hypoxia/reoxygenation-induced overproduction of superoxide in cultured neurons that may account for cell injury.

Picolinic acid protects against quinolinic acid-induced depletion of NADPH diaphorase containing neurons in the rat striatum

Previous studies in our laboratory have demonstrated that focal injections of picolinic acid (PIC) protect the cholinergic neurons of the nucleus basalis magnocellularis (nbm) against quinolinic acid (QUIN)-induced neurotoxicity. The present study was designed to examine the effects of chronic infusions of QUIN and PIC on nicotinamide adenine dinucleotide (NADPH) diaphorase containing neurons of the rat striatum. Using osmotic minipumps, QUIN (6 nmol/h) and PIC (18 nmol/h) were infused alone or in combination to examine the neurotoxic effects of QUIN and the potential anti-neurotoxic action of PIC. Exposure to QUIN for 7 days severely depleted NADPH diaphorase-positive neurons. When co-infused with this neurotoxic dose of QUIN, PIC attenuated the depletion of NADPH diaphorase neurons induced by QUIN. The infusion of PIC alone did not affect the number of these neurons. These results indicate that PIC itself is not neurotoxic and effectively prevents chronic QUIN-induced neurotoxicity in the rat striatum. Since PIC and QUIN are derived from the same metabolic pathway, a balance between endogenous compounds that produce neurotoxicity and those antagonizing these effects may be important in normal neuronal function.

Adenosinergic modulation of CA1 neuronal tolerance to glucose deprivation in organotypic hippocampal cultures

Glucose deprivation produced neuronal degeneration of CA1 pyramidal neurons in hippocampal slice cultures. The effects of the adenosine agonist cyclohexyladenosine (CHA) and antagonist cyclopentylxanthine (CPX) on CA1 neuronal loss following hypoglycemia was examined using propidium iodide fluorescence as an indicator of cell death. The intensity of propidium iodide fluorescence in hippocampal area CA1 was quantified using Optimas image analysis software. Following 2 or 3 h of glucose deprivation, CPX significantly enhanced injury in the CA1 region while CHA provided significant protection. These results suggest that adenosine plays an important role in endogenous neuronal protection during hypoglycemic injury, and also supports a role for the use of adenosine agonists as neuroprotective agents.

Ethanol and glucose-deprivation neurotoxicity in cortical cell cultures

The toxic effects of ethanol on rat cortical cell cultures were compared with neuronal damage induced by glucose deprivation. Exposure to decreased glucose concentrations produced dose-dependent neuronal injury, as indicated by the release of lactate dehydrogenase (LDH) into the culture medium. Complete glucose deprivation resulted in mean LDH release that was more than 60% greater than that from sister cultures incubated in the presence of 5.5 mmol/L glucose. Exposure to ethanol (25, 50, or 100 mmol/L) similarly resulted in dose-related LDH release. The degree of injury resulting from complete glucose deprivation or 100 mmol/L ethanol approximated that produced by exposure to 100 mmol/L glutamic acid. Ethanol did not significantly alter LDH release from cultures consisting of only astrocytes. Both effects were inhibited by the N-methyl-D-aspartate (NMDA) receptor antagonist, D,L-2-amino-5-phosphonovaleric acid (APV). Glutamate levels were increased in the culture medium to 191% +/- 8% of the control value after glucose deprivation (P < .001) and to 186% +/- 16% after exposure to 100 mmol/L ethanol (P < .01). 3H-glutamate uptake by cultured astrocytes was reduced by glucose deprivation and by ethanol. This range of ethanol concentrations has previously been shown to inhibit hexose uptake by cultured astrocytes. The present results suggest that decreased glucose uptake by astrocytes in the presence of ethanol impairs their uptake of glutamate, which contributes to excitotoxic neuronal injury.