Acute neuronal injury after hypoxia is influenced by the reoxygenation mode in juvenile hippocampal slice cultures

Neurocognitive Outcome After Treatment With(out) ECMO for Neonatal Critical Respiratory or Cardiac Failure

Over the years, it has become clear that children growing up after neonatal critical illness are at high risk of long-term neurocognitive deficits that impact their school performance and daily life activities. Although the pathophysiological mechanisms remain largely unknown, emerging evidence seems to suggest that long-term neuropsychological deficits following neonatal critical illness are not associated with the type of treatment, such as extracorporeal membrane oxygenation (ECMO), but rather with underlying disease processes. In this review, neurocognitive outcome and brain pathology following neonatal critical respiratory and cardiac illness, either treated with or without ECMO, are described and compared in order to gain insight into potential underlying pathophysiological mechanisms. Putting these findings together, it becomes apparent that both children with complex congenital heart disease and children who survived severe respiratory failure are at risk of neurocognitive deficits later in life. Neurorehabilitation strategies, such as Cogmed working-memory training, are discussed. While prevention of neurocognitive deficits altogether should be strived for in the future, this is not realistic at this moment. It is therefore of great importance that children growing up after neonatal critical illness receive long-term care that includes psychoeducation and personalized practical tools that can be used to improve their daily life activities.

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.

Time dependent impact of perinatal hypoxia on growth hormone, insulin-like growth factor 1 and insulin-like growth factor binding protein-3

Hypoxic-ischemia (HI) is a widely used animal model to mimic the preterm or perinatal sublethal hypoxia, including hypoxic-ischemic encephalopathy. It causes diffuse neurodegeneration in the brain and results in mental retardation, hyperactivity, cerebral palsy, epilepsy and neuroendocrine disturbances. Herein, we examined acute and subacute correlations between neuronal degeneration and serum growth factor changes, including growth hormone (GH), insulin-like growth factor 1 (IGF-1) and insulin-like growth factor binding protein-3 (IGFBP-3) after hypoxic-ischemia (HI) in neonatal rats. In the acute phase of hypoxia, brain volume was increased significantly as compared with control animals, which was associated with reduced GH and IGF-1 secretions. Reduced neuronal survival and increased DNA fragmentation were also noticed in these animals. However, in the subacute phase of hypoxia, neuronal survival and brain volume were significantly decreased, accompanied by increased apoptotic cell death in the hippocampus and cortex. Serum GH, IGF-1, and IGFBP-3 levels were significantly reduced in the subacute phase of HI. Significant retardation in the brain and body development were noted in the subacute phase of hypoxia. Here, we provide evidence that serum levels of growth-hormone and factors were decreased in the acute and subacute phase of hypoxia, which was associated with increased DNA fragmentation and decreased neuronal survival.

Extrasynaptic glutamate release through cystine/glutamate antiporter contributes to ischemic damage

During brain ischemia, an excessive release of glutamate triggers neuronal death through the overactivation of NMDA receptors (NMDARs); however, the underlying pathways that alter glutamate homeostasis and whether synaptic or extrasynaptic sites are responsible for excess glutamate remain controversial. Here, we monitored ischemia-gated currents in pyramidal cortical neurons in brain slices from rodents in response to oxygen and glucose deprivation (OGD) as a real-time glutamate sensor to identify the source of glutamate release and determined the extent of neuronal damage. Blockade of excitatory amino acid transporters or vesicular glutamate release did not inhibit ischemia-gated currents or neuronal damage after OGD. In contrast, pharmacological inhibition of the cystine/glutamate antiporter dramatically attenuated ischemia-gated currents and cell death after OGD. Compared with control animals, mice lacking a functional cystine/glutamate antiporter exhibited reduced anoxic depolarization and neuronal death in response to OGD. Furthermore, glutamate released by the cystine/glutamate antiporter activated extrasynaptic, but not synaptic, NMDARs, and blockade of extrasynaptic NMDARs reduced ischemia-gated currents and cell damage after OGD. Finally, PET imaging showed increased cystine/glutamate antiporter function in ischemic rats. Altogether, these data suggest that cystine/glutamate antiporter function is increased in ischemia, contributing to elevated extracellular glutamate concentration, overactivation of extrasynaptic NMDARs, and ischemic neuronal death.

Hyperbaric hyperoxia and normobaric reoxygenation increase excitability and activate oxygen-induced potentiation in CA1 hippocampal neurons

Breathing hyperbaric oxygen (HBO) is common practice in hyperbaric and diving medicine. The benefits of breathing HBO, however, are limited by the risk of central nervous system O2 toxicity, which presents as seizures. We tested the hypothesis that excitability increases in CA1 neurons of the rat hippocampal slice (400 microm) over a continuum of hyperoxia that spans normobaric and hyperbaric pressures. Amplitude changes of the orthodromic population spike were used to assess neuronal O2 sensitivity before, during, and following exposure to 0, 0.6, 0.95 (control), 2.84, and 4.54 atmospheres absolute (ATA) O2. Polarographic O2 electrodes were used to measure tissue slice PO2 (PtO2). In 0.95 ATA O2, core PtO2 at 200 microm deep was 115±16 Torr (mean±SE). Increasing O2 to 2.84 and 4.54 ATA increased core PtO2 to 1,222±77 and 2,037±157 Torr, respectively. HBO increased the orthodromic population spike amplitude and usually induced hyperexcitability (i.e., secondary population spikes) and, in addition, a long-lasting potentiation of the orthodromic population spike that we have termed "oxygen-induced potentiation" (OxIP). Exposure to 0.60 ATA O2 and hypoxia (0.00 ATA) decreased core PtO2 to 84±6 and 20±4 Torr, respectively, and abolished the orthodromic response. Reoxygenation from 0.0 or 0.6 ATA O2, however, usually produced a response similar to that of HBO: hyperexcitability and activation of OxIP. We conclude that CA1 neurons exhibit increased excitability and neural plasticity over a broad range of PtO2, which can be activated by a single, hyperoxic stimulus. We postulate that transient acute hyperoxia stimulus, whether caused by breathing HBO or reoxygenation following hypoxia (e.g., disordered breathing), is a powerful stimulant for orthodromic activity and neural plasticity in the CA1 hippocampus.

High brain tissue oxygen tension during ventilation with 100% oxygen after fetal asphyxia in newborn sheep

The optimal inhaled oxygen fraction for newborn resuscitation is still not settled. We hypothesized that short-lasting oxygen ventilation after intrauterine asphyxia would not cause arterial or cerebral hyperoxia, and therefore be innocuous. The umbilical cord of fetal sheep was clamped and 10 min later, after delivery, ventilation with air (n = 7) or with 100% oxygen for 3 (n = 6) or 30 min (n = 5), followed by air, was started. Among the 11 lambs given 100% oxygen, oxygen tension (PO2) was 10.7 (1.8-56) kPa [median (range)] in arterial samples taken after 2.5 min of ventilation. In those ventilated with 100% oxygen for 30 min, brain tissue PO2 (PbtO2) increased from less than 0.1 kPa in each lamb to individual maxima of 56 (30-61) kPa, whereas in those given oxygen for just 3 min, PbtO2 peaked at 4.2 (2.9-46) kPa. The maximal PbtO2 in air-ventilated lambs was 2.9 (0.8-5.4) kPa. Heart rate and blood pressure increased equally fast in the three groups. Thus, prolonged ventilation with 100% oxygen caused an increase in PbtO2 of a magnitude previously only reported under hyperbaric conditions. Reducing the time of 100% oxygen ventilation to 3 min did not consistently avert systemic hyperoxia.

Phosphorus magnetic resonance spectroscopy 2 h after perinatal cerebral hypoxia-ischemia prognosticates outcome in the newborn piglet

Phosphorus magnetic resonance spectroscopy ((31)P MRS) often reveals apparently normal brain metabolism in the first hours after intrapartum hypoxia-ischemia (HI) at a time when conventional clinical assessment of injury severity is problematic. We aimed to elucidate very-early, injury-severity biomarkers. Twenty-seven newborn piglets underwent cerebral HI: (31)P-MRS measures approximately 2 h after HI were compared between injury groups defined by secondary-energy-failure severity as quantified by the minimum nucleotide triphosphate (NTP) observed after 6 h. For severe and moderate injury versus baseline, [Pi]/[total exchangeable high-energy phosphate pool (EPP)] was increased (p < 0.001 and < 0.02, respectively), and [NTP]/[EPP] decreased (p < 0.03 and < 0.006, respectively): severe-injury [Pi]/[EPP] was also increased versus mild injury (p < 0.04). Mild-injury [phosphocreatine]/[EPP] was increased (p < 0.004). Severe-injury intracellular pH was alkaline versus baseline (p < 0.002). For severe and moderate injury [total Mg]/[ATP] (p < 0.0002 and < 0.02, respectively) and [free Mg] (p < 0.0001 and < 0.02, respectively) were increased versus baseline. [Pi]/[EPP], [phosphocreatine]/[Pi] and [NTP]/[EPP] correlated linearly with injury severity (p < 0.005, < 0.005 and < 0.02, respectively). Increased [Pi]/[EPP], intracellular pH and intracellular Mg approximately 2 h after intrapartum HI may prognosticate severe injury, whereas increased [phosphocreatine]/[EPP] may suggest mild damage. In vivo(31)P MRS may have potential to provide very-early prognosis in neonatal encephalopathy.

Bench to bedside strategies for optimizing neuroprotection following perinatal hypoxia-ischaemia in high and low resource settings

BACKGROUND

Therapeutic hypothermia gathers impetus in the developed world as a safe and effective therapy for term asphyxial encephalopathy. Although many questions still remain about the optimal application of hypothermic neuroprotection it is difficult to ignore the developing world where the prevalence of asphyxial encephalopathy is much higher. Experimental studies to optimize high tech cooling need to run in parallel with trials to determine the possible benefits of therapeutic hypothermia in low resource settings.

METHODS

We used a validated newborn piglet model of transient HI to determine (i) whether optimal neuroprotection occurs at different temperatures in the cortical and deep grey matter; (ii) the effect of body size on regional brain temperature under normothermia and hypothermia; (iii) the effect of insult severity on the therapeutic window duration; (iv) whether cooling using a water bottle is feasible. In this model hypoxia-ischaemia is induced by reversible occlusion of the common carotid arteries by remotely controlled vascular occluders and simultaneous reduction in the inspired oxygen fraction to 0.12. Intensive care can be administered to the piglet maintaining metabolic and physiological homeostasis throughout the experiment, and cerebral energy metabolism is monitored continuously providing quantitative measures of the HI insult, latent phase and secondary energy failure using phosphorus-31 ((31)P) magnetic resonance spectroscopy (MRS).

RESULTS

(i) The optimal temperature for cooling was lower in the cortex than deep grey matter. (ii) Cerebral temperatures were body-weight dependent: a smaller body weight led to a lower brain temperature especially with selective head cooling. (iii) Latent-phase duration is inversely related to insult severity. (iv) Low tech, simple cooling methods using a water bottle can induce and maintain moderate hypothermia.

CONCLUSIONS

Small shifts in brain temperature critically influence the survival of neuronal cells and body size critically influences brain-temperature gradients - smaller subjects have a larger surface area to brain volume and hence more heat is lost. The clinical implication is that smaller infants may require higher cap or body temperatures to avoid detrimental effects of over-zealous cooling. Latent-phase brevity may explain less effective neuroprotection following severe HI in some clinical studies. "Tailored" treatments which take into account individual and regional characteristics may increase the effectiveness of therapeutic hypothermia in the developed world. Low tech cooling methods using water bottles may be feasible although adequate staffing and monitoring would be required.

Superoxide (·O2−) Production in CA1 Neurons of Rat Hippocampal Slices Exposed to Graded Levels of Oxygen

Neuronal signaling, plasticity, and pathologies in CA1 hippocampal neurons are all intimately related to the redox environment and, thus tissue oxygenation. This study tests the hypothesis that hyperoxic superfusate (95% O2) causes a time-dependent increase in superoxide anion (·O2−) production in CA1 neurons in slices, which will decrease as oxygen concentration is decreased. Hippocampal slices (400 μm) from weaned rats were incubated with the fluorescent probe dihydroethidium (DHE), which detects intracellular ·O2− production. Slices were loaded for 30 min using 10 μM DHE and maintained using one-sided superfusion or continuously loaded using 2.5 μM DHE and maintained using two-sided superfusion (36°C). Continuous loading of DHE and two-sided superfusion gave the highest temporal resolution measurements of ·O2− production, which was estimated by the increase in fluorescence intensity units (FIUs) per minute (FIU/min ± SE) over 4 h. Superoxide production (2.5 μM DHE, 2-sided superfusion) was greatest in 95% O2 (6.6 ± 0.4 FIU/min) and decreased significantly during co-exposure with antioxidants (100 μM melatonin, 25 μM MnTMPyP) and lower levels of O2 (60, 40, and 20% O2 at 5.3 ± 0.3, 3.3 ± 0.1, and 1.6 ± 0.2 FIU/min, respectively). CA1 cell death after 4 h (ethidium homodimer-1 staining) was greatest in 95% O2 and lowest in 40 and 20% O2. CA1 neurons generated evoked action potentials in 20% O2 for >4 h, indicating viability at lower levels of oxygenation. We conclude that ·O2− production and cell death in CA1 neurons increases in response to increasing oxygen concentration product (= PO2 × time). Additionally, lower levels of oxygen (20–40%) and antioxidants should be considered to minimize superoxide-induced oxidative stress in brain slices.

Organotypic slice culture of the hypothalamic paraventricular nucleus of rat

Organotypic slice cultures have been developed as an alternative to acute brain slices because the neuronal viability and synaptic connectivity in these cultures can be preserved well for a prolonged period of time. This study evaluated a stationary organotypic slice culture developed for the hypothalamic paraventricular nucleus (PVN) of rat. The results showed that the slice cultures maintain the typical shape of the nucleus, the immunocytochemical signals for oxytocin, vasopressin, and corticotropin-releasing hormone, and the electrophysiological properties of PVN neurons for up to 3 weeks in vitro. The PVN neurons in the culture expressed the green fluorescent protein gene that had been delivered by the adenoviral vectors. The results indicate that the cultured slices preserve the properties of the PVN neurons, and can be used in longterm studies on these neurons in vitro.

Cerebral inflammatory response after fetal asphyxia and hyperoxic resuscitation in newborn sheep

Resuscitation with pure oxygen at birth after fetal asphyxia may aggravate brain damage by inducing pro-inflammation. The toll-like receptors (TLRs) may serve a pro-inflammatory role in hyperoxemia during ischemia-reperfusion. Sixteen near-term fetal sheep (132-136 d) were subjected to 10 min of cord occlusion, delivery and mechanical ventilation with 100% O2 (n = 8), or 21% O2 (n = 8) for 30 min followed by normoxemia for 90 min. Eight sheep fetuses were delivered immediately with inspired O2 targeted at normoxemia for 120 min (controls). Levels and distributions of mRNAs for IL-1beta, TNF-alpha, IL-12p40, IL-18, IL-6, IL-10, IFN-gamma, TLR-2, -3 and -4 in cerebral tissue at 2 h after birth were evaluated with real-time polymerase chain reaction (PCR) and in situ hybridization. Expressions of IL-1beta, IL-12p40, TLR-2, and TLR-4 were increased in cortex/subcortex after resuscitation with 100% O2 compared with 21% O2 (all p < 0.05) and to controls (all p < 0.05). Increased cellular expression of IL-1beta was localized to sub-meningeal cortical layers and to sub-cortical white matter. Hyperoxic resuscitation at birth following fetal asphyxia induces a cerebral pro-inflammatory response with an up-regulation of TLR-2 and -4. These may be early events leading to increased tissue damage after exposure to hyperoxemia at birth.

"Therapeutic time window" duration decreases with increasing severity of cerebral hypoxia-ischaemia under normothermia and delayed hypothermia in newborn piglets

OBJECTIVE

For optimal neuroprotection following transient perinatal hypoxia-ischaemia (HI), therapy should start before overt secondary energy failure and its irreversible neurotoxic cascade. Hypothermia is a promising neuroprotective intervention that also prolongs the therapeutic time window ("latent-phase"; the period between re-establishment of apparently normal cerebral metabolism after HI, and the start of secondary energy failure). The influences of HI severity on latent-phase duration and regional neuroprotection are unclear. Under normothermia and delayed whole-body cooling to 35 and 33 degrees C we aimed to assess relationships between HI severity and: (i) latent-phase duration; (ii) secondary-energy-failure severity; and (iii) neuronal injury 48 h following HI.

METHODS

Newborn piglets were randomized to: (i) HI-normothermia (n=12), (ii) HI-35 degrees C (n=7), and (iii) HI-33 degrees C (n=10). HI-35 degrees C and HI-33 degrees C piglets were cooled between 2 and 26 h after HI. Insult and secondary-energy-failure severity and latent-phase duration were evaluated using phosphorus magnetic resonance spectroscopy and compared with neuronal death in cortical-grey and deep-grey matter.

RESULTS

More severe HI was associated with shorter latent-phase (p=0.002), worse secondary energy failure (p=0.023) and more cortical-grey-matter neuronal death (p=0.016).

CONCLUSIONS

Latent-phase duration is inversely related to insult severity; latent-phase brevity may explain the apparently less effective neuroprotection following severe cerebral HI.

Neuroprotective potential of ceftriaxone in in vitro models of stroke

Astrocytic glutamate transporters are considered an important target for neuroprotective therapies as the function of these transporters is abnormal in stroke and other neurological disorders associated with excitotoxicity. Recently, Rothstein et al., [Rothstein JD, Patel S, Regan MR, Haenggeli C, Huang YH, Bergles DE, Jin L, Dykes Hoberg M, Vidensky S, Chung DS, Toan SV, Bruijn LI, Su ZZ, Gupta P, Fisher PB (2005) Beta-lactam antibiotics offer neuroprotection by increasing glutamate transporter expression. Nature 433:73-77] reported that beta-lactam antibiotics (including ceftriaxone, which easily crosses the blood-brain barrier) increase glutamate transporter 1 (GLT-1) expression and reduce cell death resulting from oxygen-glucose deprivation (OGD) in dissociated embryonic cortical cultures. To determine whether a similar neuroprotective mechanism operates in more mature neurons, which show a different pattern of response to ischemia than primary cultures, we exposed acute hippocampal slices obtained from rats treated with ceftriaxone for 5 days (200 mg/kg; i.p.) to OGD. Whole-cell patch clamp recording of glutamate-induced N-methyl-d-aspartate (NMDA) currents from CA1 pyramidal neurons showed a larger potentiation of these currents after application of 15 microM dl-threo-beta-benzyloxyaspartic acid (TBOA; a potent blocker of glutamate transporters) in ceftriaxone-injected animals than in untreated animals, indicating increased glutamate transporter activity. Western blot analysis did not reveal GLT-1 upregulation in the hippocampus. Delay to OGD-induced hypoxic spreading depression (HSD) recorded in slices obtained from ceftriaxone-treated rats was longer (6.3+/-0.2 vs. 5.2+/-0.2 min; P<0.001) than that in the control group, demonstrating a neuroprotective action of the antibiotic in this model. The effect of ceftriaxone was also tested in organotypic hippocampal slices obtained from P7-9 rats (>14 days in vitro). OGD or glutamate (3.5-5.0 mM) damaged CA1 pyramidal neurons as assessed by propidium iodide (PI) fluorescence. Similar damage was observed after pre-treatment with ceftriaxone (10-200 microM; 5 days) and ceftriaxone exposure did not result in GLT-1 upregulation as assayed by Western blot. Treatment of slice cultures with dibutyryl cAMP (100-250 microM; 5 days) increased GLT-1 expression but did not reduce cell damage induced by OGD or glutamate. Thus we confirm the neuroprotective effect of antibiotic exposure on OGD-induced injury, but suggest that this action is related to independent modulation of transporter activity rather than to the level of GLT-1 protein expression. In addition, our results indicate that the protective effects of beta-lactam antibiotics are highly dependent on the experimental model.

Changes of neuronal activity in areas CA1 and CA3 during anoxia and normoxic or hyperoxic reoxygenation in juvenile rat organotypic hippocampal slice cultures

In neonates, asphyxia is usually followed by hyperoxic treatment. In order to study whether hyperoxic reoxygenation might cause additional impairment of neuronal function, we subjected organotypic hippocampal slice cultures of juvenile rats (7 DIV, P6-8) to 30 min anoxia followed by 60 min hyperoxic or normoxic reoxygenation (95% or 19% O2, respectively). Spontaneous and evoked field potentials as well as [Ca2+]o were recorded in the pyramidal layer of area CA1 or area CA3. In area CA1, 30 min of anoxia led to decline of evoked field potential amplitudes by on average 67% and to profound changes in field potential characteristics and Ca2+ homeostasis which were not related to outcome after reoxygenation. Hyperoxic reoxygenation resulted first in a fast recovery of the field potential amplitude to 82% of the control value and then, in 75% of slice cultures, in a large negative field potential shift accompanied by a prolonged decrease of [Ca2+]o and loss of excitability outlasting the experiment. Recovery of field potential amplitude under normoxic conditions stayed poor, with a first increase to 51% and a second decrease to 22%. In contrast, field potential amplitude in area CA3 recovered to 80% of the initial amplitude, irrespective of the reoxygenation mode. The selective loss of function during hyperoxic reoxygenation in area CA1 might be a first sign of neuronal injury that we observed 1 h after end of hyperoxic reoxygenation in a previous study. Whether the poor outcome after normoxic reoxygenation would favour long-term recovery remains to be determined.

Morphological and functional changes in rat hippocampal slice cultures after short-term oxygen-glucose deprivation

To study effects of short-term cerebral ischemia, hippocampal slice cultures were subjected to oxygen and glucose deprivation (OGD) followed by a period of normoxic reoxygenation. Propidium iodide staining, and MTT/formazan-assay were used to evaluate cell viability and metabolic activity. CA1 pyramidal cells were analyzed at the light- and electron microscopic levels. Cell damage was found to be insignificant during the first hour after 10 min OGD but profound following 4 h, showing delayed neuronal cell damage caused by short-term OGD. Our model can be used to characterize the mechanisms of cell damage caused by mild cerebral ischemia. These data might apply to further development of neuroprotective tools for the treatment of brain diseases.

Extracellular superoxide concentration increases following cerebral hypoxia but does not affect cerebral blood flow

Abnormalities of cerebral blood flow during and following hypoxia and ischemia contribute to the progression of tissue injury. Oxidative stress during and following hypoxia is known to markedly increase superoxide anion concentration. There is conflicting evidence that the concentration of superoxide anion regulates cerebral blood flow through its effect on vascular tone, although difficulties in measurement of superoxide anion complicate these studies. In order to test the hypothesis that changes in cerebral blood flow during and following hypoxia are due to changes in extracellular superoxide anion levels, we examined tissue oxygen levels by fiberoptic oximetry and superoxide anion levels using a previously validated cytochrome c coated electrode on the cortical surface and correlated these measurements to cerebral blood flow measured by laser Doppler in rats subjected to 20 min of hypoxia followed by hyperoxic reoxygenation recovery. The results showed a burst of superoxide anion with the onset of reoxygenation that temporally correlated with a transient peak in tissue oxygen tension lasting 10 min. and was eliminated by pretreatment with Cu-Zn superoxide dismutase conjugated to polyethylene glycol. Cerebral blood flow did not differ during hypoxia or recovery in the polyethylene glycol conjugated superoxide dismutase and control treatment groups. This study demonstrated no effect of increased superoxide anion concentration on cerebral blood flow during hyperoxic recovery following hypoxia.

Free radical-mediated cell damage after experimental status epilepticus in hippocampal slice cultures

Generation of free radicals may have a key role in the nerve cell damage induced by prolonged or frequently recurring convulsions (status epilepticus). Mitochondrial function may also be altered due to production of free radicals during seizures. We therefore studied changes in field potentials (fp) together with measurements of extracellular, intracellular, and intramitochondrial calcium concentration ([Ca(2+)]e, [Ca(2+)]i, and [Ca(2+)]m, respectively), mitochondrial membrane potential (deltapsi), NAD(P)H auto-fluorescence, and dihydroethidium (HEt) fluorescence in hippocampal slice cultures by means of simultaneous electrophysiological and microfluorimetric measurements. As reported previously, each seizure-like event (SLE) resulted in mitochondrial depolarization associated with a delayed rise in oxidation of HEt to ethidum, presumably indicating ROS production. We show here that repeated SLEs led to a decline in intracellular and intramitochondrial Ca(2+) signals despite unaltered Ca(2+) influx. Also, mitochondrial depolarization and the NAD(P)H signal became smaller during recurring SLEs. By contrast, the ethidium fluorescence rises remained constant or even increased from SLE to SLE. After about 15 SLEs, activity changed to continuous afterdischarges with steady depolarization of mitochondrial membranes. Staining with a cell death marker, propidium iodide, indicated widespread cell damage after 2 h of recurring SLEs. The free radical scavenger, alpha-tocopherol, protected the slice cultures against this damage and also reduced the ongoing impairment of NAD(P)H production. These findings suggest involvement of reactive oxygen species (ROS) of mitochondrial origin in the epileptic cell damage and that free radical scavenging may prevent status epilepticus-induced cell loss.