Calcium fluxes, calcium antagonists, and calcium-related pathology in brain ischemia, hypoglycemia, and spreading depression: a unifying hypothesis

Perinatal brain injury

Perinatal brain damage in the mature fetus is usually brought about by severe intrauterine asphyxia following an acute reduction of the uterine or umbilical circulation. The areas most heavily affected are the parasagittal region of the cerebral cortex and the basal ganglia. The fetus reacts to a severe lack of oxygen with activation of the sympathetic-adrenergic nervous system and a redistribution of cardiac output in favor of the central organs (brain, heart and adrenals). If the asphyxic insult persists, the fetus is unable to maintain circulatory centralization, and the cardiac output and extent of cerebral perfusion fall. Owing to the acute reduction in oxygen supply, oxidative phosphorylation in the brain comes to a standstill. The Na+/K+ pump at the cell membrane has no more energy to maintain the ionic gradients. In the absence of a membrane potential, large amounts of calcium ions flow through the voltage-dependent ion channels, down an extreme extra-/intracellular concentration gradient, into the cell. Current research suggests that the excessive increase in levels of intracellular calcium, so-called calcium overload, leads to cell damage through the activation of proteases, lipases and endonucleases. During ischemia, besides the influx of calcium ions into the cells via voltage-dependent calcium channels, more calcium enters the cells through glutamate-regulated ion channels. Glutamate, an excitatory neurotransmitter, is released from presynaptic vesicles during ischemia following anoxic cell depolarization. The acute lack of cellular energy arising during ischemia induces almost complete inhibition of cerebral protein biosynthesis. Once the ischemic period is over, protein biosynthesis returns to preischemic levels in non-vulnerable regions of the brain, while in more vulnerable areas it remains inhibited. The inhibition of protein synthesis, therefore, appears to be an early indicator of subsequent neuronal cell death. A second wave of neuronal cell damage occurs during the reperfusion phase. This cell damage is thought to be caused by the postischemic release of oxygen radicals, synthesis of nitric oxide (NO), inflammatory reactions and an imbalance between the excitatory and inhibitory neurotransmitter systems. Part of the secondary neuronal cell damage may be caused by induction of a kind of cellular suicide programme known as apoptosis. Interestingly, there is increasing evidence from recent clinical studies that perinatal brain damage is closely associated with ascending intrauterine infection before or during birth. However, a major part of this damage is likely to be of hypoxic-ischemic nature due to LPS-induced effects on fetal cerebral circulation. Knowledge of these pathophysiological mechanisms has enabled scientists to develop new therapeutic strategies with successful results in animal experiments. The potential of such therapies is discussed here, particularly the promising effects of intravenous administration of magnesium or postischemic induction of cerebral hypothermia.

Real-time, two-dimensional visualization of ischaemia-induced glutamate release from hippocampal slices

The involvement of excitatory amino acid (EAA) toxicity in ischaemia-induced neuronal cell death has long been suggested. However, in the hippocampus, the brain site most vulnerable to ischaemia, the detailed spatial and temporal patterns of EAA release are not yet known. To address this issue, we have developed a novel strategy for the continuous, real-time, two-dimensional monitoring of EAA release from brain slices. As EAA detector, we used a cell line transformed with the N-methyl-D-aspartate (NMDA) receptor, which is exclusively activated by EAAs, leading to an increase in the intracellular Ca(2+) level. Combined with a calcium imaging technique, the use of this cell line allowed the temporal and regional analysis of EAA release from a brain slice placed directly on top of the clonal cells in a culture dish. Using this strategy, we demonstrated ischaemia-induced EAA release in rat hippocampal slices. Increased EAA release was seen initially in the CA1 region, about 3 min after the beginning of ischaemia, then in the CA3 region and dentate gyrus, and, finally, throughout the hippocampal slice. Regional differences in extracellular EAA levels were also seen, with more EAA being released from the CA1 region than from the middle dentate gyrus. The present results are especially interesting as neurons in the CA1 region are more vulnerable to ischaemia than those in the CA3 region and dentate gyrus.

Calcium antagonists for ischemic stroke: a systematic review

BACKGROUND AND PURPOSE

Stroke is a common disease, and many trials with calcium antagonists as possible neuroprotective agents have been conducted. The aim of this review is to determine whether calcium antagonists reduce the risk of death or dependency after acute ischemic stroke.

METHODS

Acute stroke trials were identified with help of the Cochrane Collaboration Stroke Group and personal contacts. All randomized trials (published and unpublished) investigating a calcium antagonist (acting on voltage-sensitive calcium channels) were included. Poor outcome, defined as death or dependency in activities of daily living, was used as main outcome. Analyses were, if possible, "intention-to-treat"; pooled relative risks with 95% CIs were calculated.

RESULTS

Forty-seven trials were identified, of which 29 were included (7665 patients). No effect of calcium antagonists on poor outcome at the end of follow-up (relative risk, 1.04; 95% CI, 0.98 to 1.09) or on death at end of follow-up (relative risk, 1.07; 95% CI, 0.98 to 1.17) was found. Sensitivity analyses on route of administration and time interval between stroke and start of treatment showed no effect on outcome. In subgroups of unpublished and methodologically sound trials, a statistically significant negative effect for calcium antagonists was found. This contrasts with results of published trials and trials of moderate or poor methodological quality.

CONCLUSIONS

The presented evidence rules out a clinically important effect of calcium antagonists after ischemic stroke. The large amount of data leads to narrow CIs with no significant heterogeneity, and the overall results are therefore likely to be statistically robust.

Vatanidipine hydrochloride: a new long-lasting antihypertensive agent

Vatanidipine is a novel dihydropyridine (DHP)-type calcium channel blocker with slow-onset pharmacological actions, which are probably due to both its slow uptake into vascular tissues and resistance in its approach to the calcium channel binding site. Vatanidipine once incorporated into vascular tissues is not easily released, even by repeated washing, thus resulting in a long-lasting action of the agent. A slow-onset and long-lasting hypotensive action was observed in various experimental hypertensive models. Clinical trials using human subjects with essential hypertension indicated that vatanidipine exerts an antihypertensive effect with a slow onset and long duration. In spite of its potent hypotensive effect, the incidence of adverse effects by vatanidipine administration has been reported to be lower than that in cases of nitrendipine. In addition to its vasodilatory effects, vatanidipine efficiently suppressed noradrenaline release from sympathetic nerve endings, thus suggesting this agent exhibits a beneficial effect in the treatment of hypertensive patients, in which the reflex activation of peripheral sympathetic nerves is unfavourable to antihypertensive therapy. In a double-blind study, vatanidipine did not show reflex tachycardia, despite producing a potent and long-lasting hypotensive effect, in contrast to the administration of nitrendipine. In an animal study, vatanidipine exhibited a protective effect against cerebrovascular lesions, through a mechanism independent of its hypotensive effect. In addition, a renoprotective effect was also observed in experimental hypertensive models. In cholesterol-fed rabbits, vatanidipine exerted an anti-atherosclerotic action, which is probably attributable to the inhibitory action of the agent on low-density lipoprotein oxidation. In essential hypertensive patients, the plasma levels of cholesterol and triglyceride decreased after vatanidipine treatment, thus suggesting that this agent may have a therapeutic potential in preventing such vascular diseases as atherosclerosis. Taken together, vatanidipine appears to be a novel and useful antihypertensive agent, which can both prevent target-organ damage and reduce cardiovascular morbidity and mortality.

Acute protective effect of nimodipine and dimethyl sulfoxide against hypoxic and ischemic damage in brain slices

Nimodipine and dimethyl sulfoxide (DMSO) were tested (alone and in combination) regarding their ability to increase hypoxic tolerance of brain slices under 'hypoxic' (deprivation of oxygen) or 'ischemic' (hypoxia+withdrawal of glucose) conditions. Direct current (DC) and evoked potentials were recorded in the CA1 region of hippocampal slices of adult guinea pigs. After induction of hypoxia or ischemia, the latency of anoxic terminal negativity (ATN) of the DC potential was determined during superfusion with artificial cerebrospinal fluid alone (aCSF), and during superfusion with aCSF containing DMSO [0.1% (14.1 mmol/l) and 0.4% (56.3 mmol/l)] with the addition of nimodipine (40 micromol/l). Latencies of ATN with first hypoxia were 6.7+/-3.7 min in the control group, 9. 3+/-4.2 min in the 0.4% DMSO group and 12.3+/-5.5 min (P=0.007) in the nimodipine/0.4% DMSO group. Latencies of ATN with first ischemia were 2.9+/-2 min in the control group, 4.1+/-1.6 min in the 0.1% DMSO group, 7.1+/-3.9 min in the 0.4% DMSO group (P=0.006), 5.3+/-1. 5 min in the nimodipine/0.1% DMSO group and 7.6+/-3 min (P<0.001) in the nimodipine/0.4% DMSO group. DMSO (0.4%), either alone or in combination with nimodipine, increase the latency of the ATN after acute onset of hypoxia and ischemia.

The AMPAR subunit GluR2: still front and center-stage

Abnormal influx of Ca(2+) through AMPA-type glutamate receptors (AMPARs) is thought to contribute to the neuronal death associated with a number of brain disorders. AMPARs exist as both Ca(2+)-impermeable and Ca(2+)-permeable channels. AMPARs are encoded by four genes designated GluR1 (GluR-A) through GluR4 (GluR-D). The presence of the GluR2 subunit renders heteromeric AMPA receptor assemblies Ca(2+)-impermeable. Molecular diversity of AMPARs under physiological and pathological conditions is generated by differential spatio-temporal patterns of GluR expression, by alternative RNA splicing and editing and by targeting and trafficking of receptor subunits at dendritic spines. The GluR2 gene is under transcriptional control by the RE1 element specific transcription factor, a gene silencing factor which renders it neuron-specific. GluR2 transcripts are edited by ADAR2 (double-stranded RNA-specific editase 1). AMPAR targeting and trafficking to spines are regulated by synaptic activity and are critical to synaptic plasticity. Recent studies involving animal models of transient forebrain ischemia and epilepsy show that GluR2 mRNA and GluR2 subunit expression are downregulated in vulnerable neurons prior to cell death. Ca(2+) imaging and electrical recording from individual pyramidal neurons in hippocampal slices reveal changes in AMPAR functional properties after ischemia. In slices from post-ischemia animals, CA1 neurons with robust action potentials exhibit greatly enhanced AMPA-elicited rises in intracellular Ca(2+). Excitatory postsynaptic currents in post-ischemic CA1 exhibit an enhanced Ca(2+)-dependent component that appears to be mediated by Ca(2+)-permeable AMPARs. These studies provide evidence for Ca(2+) influx through AMPARs in neurons destined to die. To examine whether acute GluR2 downregulation, even in the absence of a neurological insult, can induce neuronal death, we performed knockdown experiments in rats and gerbils with antisense oligonucleotides targeted to GluR2 mRNA. GluR2 antisense oligonucleotide induced neuronal cell death of pyramidal neurons and enhanced pathogenicity of brief ischemic episodes. These observations provide evidence for Ca(2+) influx through AMPARs in neurons destined to die and implicate Ca(2+)-permeable AMPARs in the pathogenesis of ischemia-induced neuronal death.

Postischemic changes in the immunophilin FKBP12 in the rat brain

An immunosuppressant tacrolimus (FK506) protects against neuronal damage following cerebral ischemia. On the other hand, the major physiological role of the immunophilin FK506-binding protein-12 (FKBP12) is a modulation of intracellular calcium flux. Since an increase in intracellular calcium concentration is a major mediator of ischemic neuronal death, we investigated the changes in FKBP12 following cerebral ischemia in the rat. We induced focal cerebral ischemia by intraluminal occlusion of the middle cerebral artery for 1 h, and global cerebral ischemia for 10 min by bilateral carotid artery occlusion combined with hypotension. The animals were killed at 4 h to 7 days after reperfusion. Immunohistochemistry was performed on paraffin sections using a monoclonal antibody raised against recombinant FKBP12. Immunoreactivity to FKBP12 in control brains was most pronounced in the CA1 subfield of the hippocampus and the striatum, the localization being primarily neuronal. Following focal ischemia, FKBP12 immunoreactivity decreased rapidly in the ischemic core by 4 h, but increased in surviving neurons in penumbra areas (4 h-7 days). Within an area of infarction, invading leukocytes and macrophages exhibited immunoreactivity to FKBP12 (3-7 days). Following global ischemia, FKBP12 immunoreactivity in CA1 neurons decreased after 1 day, and then it was lost between 2 and 7 days, although many CA1 neurons showed a transient increase in FKBP12 at 2 days. No FKBP12 immunoreactivity was observed in reactive glial cells. Thus, FKBP12 declined in dying neurons, whereas FKBP12 was upregulated in less severely injured neurons. The findings suggest that (1) FKBP12 plays an important role in the process of neuronal survival and death following cerebral ischemia, and (2) FKBP12 is involved in inflammatory reactions that occur within an area of infarction.

Physiological blocking of the mechanisms of cold death: theoretical and experimental considerations

The cold inhibited functions of skin thermoreceptors, of the thermoregulation centre, and the respiration centre during deep hypothermia can be restored without rewarming the body. The methods used were developed to test the hypothesis that during deep hypothermia calcium ion concentration [Ca(2+)](i) in the cytoplasm increases. This causes a perturbation of cell metabolism, the impairment of cell membrane function that cause the inhibition of cell functioning, resulting in cell death. Such an increase in [Ca(2+)](i) most likely would result from an energy deficit in a deeply cooled cell, which would compromise the processes that maintain the [Ca(2+)](i) at about 10(-7) M. These processes require large amounts of energy since they occur against a large concentration gradient. With the use of EDTA the extracellular concentration of Ca(2+) has been lowered by 15-27%, so reducing the concentration gradient for Ca(2+) between the cell and the medium and in consequence facilitated the process the extrusion of cell Ca(2+).During a period of cooling, sufficient to impair normal functioning, the experimental lowering of blood Ca(2+) allowed the restoration of normal function without the need to rewarm. In such cases the animals survived after cooling the body to temperatures at which they would normally have succumbed. The data presented support the stated hypothesis that the impairment of cellular function in mammals by low temperatures is the result of an uncorrected rise in [Ca(2+)](i).

Enhancement of whole cell calcium currents following transient MCAO

Cerebral infarctions have been shown to cause widespread changes of neuronal excitability in non-infarcted tissue. Calcium currents are major determinants of neuronal behavior, and pathological modulation of Ca(2+)-channels is known to lead to altered excitability states in a variety of paradigms. In the present study we addressed the question to what extent whole cell calcium currents are altered after middle cerebral artery occlusion (MCAO) in both the ipsi- and contralateral sensory cortex. Transient middle cerebral artery occlusion was induced for 1 h in rats using the intraluminal thread model. After 7 or 28 days survival, whole cell patch clamp studies were carried out on freshly isolated neurons of the ipsi- and contralateral sensory cortex, and high voltage activated (HVA) calcium currents were examined. In lesioned animals, we found a significant increase of calcium current amplitude and maximal conductance in the sensory cortex contralateral to the infarcts. This was paralleled by a prominent positive shift of the potential of half-maximal activation (V(h,a)) in these cells. Changes were long-lasting and at least stable for the following 28 days. These alterations were present in animals with lesions of moderate size, but not in those with massive infarction, and only in the cortex contralateral to the lesion. Following cortical infarctions, changes of calcium current properties are selectively observed in neurons contralateral to the lesion. At the behavioral level, compensatory mechanisms involving the unaffected hemisphere may induce this alteration of calcium current properties.

Cations of cisternal cerebrospinal fluid in humans and the effect of different doses of nimodipine on CSF calcium after stroke

Cisternal samples of cerebrospinal fluid (CSF) were analyzed for protein, albumin, sodium (Na), potassium (K), and calcium (Ca) content in 21 control subjects and 64 patients who had experienced acute stroke. A second cisternal CSF sample was taken in 37 of the stroke patients after 2-3 weeks treatment with the calcium antagonist nimodipine. Increased permeability of the blood-brain barrier was reflected by the significantly higher CSF/serum ratio of albumin in stroke patients than in control subjects (0.0046 vs. 0.0028,p = 0.0012). Serum and CSF concentrations of Na, K, and Ca did not differ between control subjects and stroke patients. In control subjects and in stroke patients, concentration of calcium in cisternal CSF ([Ca]) was smaller than values reported by others in lumbar samples. In stroke patients, the pH of CSF was lower than that of simultaneously taken blood (7.38 vs. 7.44, p < 0.001). No differences between stroke patients and control subjects were found for the cisternal CSF/serum ratios of Na (1.0 and 0.99), K (0.61 and 0.63), and Ca (0.25 and 0.24). When patients and controls were pooled together, CSF total [Ca] correlated weakly with serum total [Ca] (Spearman r = 0.28, p = 0.014) and with serum ionized [Ca] (Spearman r = 0.27, p = 0.016). After 2-3 weeks of nimodipine treatment, CSF [Ca] was significantly lower in the subgroup treated with 60 mg nimodipine four times daily (240 mg/d) than with 30 mg four times daily. A nimodipine dosage of 30 mg four times daily (120 mg/d) did not affect CSF [Ca]. A 240 mg daily dosage, but not a 120 mg daily dosage, of nimodipine may affect the Ca transport system in humans at the choroid plexus.

Levels of neurotransmitter amino acids in the cerebrospinal fluid of patients with acute ischemic insult

The dynamics of excitatory (glutamate, aspartate) and inhibitory (GABA, glycine) neurotransmitter amino acid contents in the cerebrospinal fluid were studied in 110 patients with hemispheric ischemic insult. These studies revealed significant increases in the levels of glutamate and aspartate in the first six hours of illness, and the level and duration of these changes correlated with the severity of the insult. Peak GABA and glycine levels were seen at the end of the first day after strokes, reflecting the delayed activation of the mechanisms of protective inhibition. The insufficiency of GABAergic mediation in strokes located in the hemispheres to a significant extent mirrored the severity of clinical features and the potential of restorative processes. Early significant biochemical criteria were identified for objective assessment of the severity of brain ischemia, and these had prognostic value for the course and outcome of strokes. The most unfavorable prognostic signs were the presence of low (or undetectable) GABA levels in the first days after insult and progressive increases in aspartate levels to the third day on the background of sharp reductions in glutamate levels (after initial elevation on the first day).

Neuronal cell death and reactive oxygen species

1. We have investigated the role of reactive oxygen species (ROS) in cell death induced by ischemia or application of the excitatory amino acid agonist, N-methyl-D-aspartate (NMDA) or kainate (KA), in acutely isolated rat cerebellar granule cell neurons, studied by flow cytometry. Various fluorescent dyes were used to monitor intracellular calcium concentration, ROS concentration, membrane potential, and viability in acutely dissociated neurons subjected to ischemia and reoxygenation alone, NMDA or kainate alone, and ischemia and reoxygenation plus NMDA or kainate. 2. With ischemia followed by reoxygenation, ROS concentrations rose slightly and there was only a modest increase in cell death after 60 min. 3. When NMDA or kainate alone was applied to the cells there was a large increase in ROS and in intracellular calcium concentration but only a small loss of cellular viability. However, when NMDA or kainate was applied during the reoxygenation period there was a large loss of viability, accompanied by membrane depolarization, but the elevations of ROS and intracellular calcium concentration were not greater than seen with the excitatory amino acids alone. 4. These observations indicate that other factors beyond ROS and intracellular calcium concentration contribute to cell death in cerebellar granule cell neurons.

Blocking the glycine-binding site of NMDA receptors prevents the progression of ischemic pathology induced by bilateral carotid artery occlusion in spontaneously hypertensive rats

This study was designed to investigate the participation of N-methyl-D-aspartate (NMDA) receptors in the progression of the pathology induced by bilateral carotid artery occlusion (BCAo) in spontaneously hypertensive rats (SHRs). We examined the effects of the selective NMDA receptor glycine-binding site antagonist SM-18400 on the mortality rate, deterioration of neurological signs, and formation of brain edema in the SHR-BCAo model. SM-18400 (15 or 30 mg/kg) was administered via the tail vein immediately and 2 h after BCAo. Neurological signs were monitored continuously for 8 h after BCAo, and the mortality rates were followed for 5 days. All SM-18400-treated animals were still alive 5 h after BCAo, whereas 38% of the animals died in the vehicle-treated group. The mortality rates of the SM-18400-treated groups were still lower than those of the vehicle-treated group 5 days after BCAo. In addition, SM-18400 markedly prevented the deterioration of neurological signs. The water content of the telencephalon and diencephalon/mesencephalon in the vehicle-treated group, measured 3 h after BCAo, was significantly higher than in the sham-operated group. SM-18400 significantly inhibited the increase in water content in both regions in a dose-dependent manner. These findings suggest that NMDA receptors participate in the increase in the mortality rate, deterioration of neurological signs, and formation of brain edema following ischemic brain damage in the SHR-BCAo model, and that SM-18400 can prevent ischemic insults.

Mitochondrial and intrinsic optical signals imaged during hypoxia and spreading depression in rat hippocampal slices

During hypoxia in the CA1 region of the rat hippocampus, spreading-depression-like depolarization (hypoxic spreading depression or HSD) is accompanied by both a negative shift of the extracellular DC potential (DeltaV(o)), and a sharp decrease in light transmittance (intrinsic optical signal or IOS). To investigate alterations in mitochondrial function during HSD and normoxic spreading depression (SD), we simultaneously imaged mitochondrial depolarization, using rhodamine-123 (R123) fluorescence, and IOS while monitoring extracellular voltage. Three major phases of the R123 signal were observed during hypoxia: a gradual, diffuse fluorescence increase, a sharp increase in fluorescence coincident with the HSD-related DeltaV(o), primarily in the CA1 region, and a plateau-like phase if reoxygenation is delayed after HSD onset, persisting until reoxygenation occurs. Two phases occurred following re-oxygenation: an abrupt and then slow decrease in fluorescence to near baseline and a slow secondary increase to slightly above baseline and a late recovery. Parallel phases of the IOS response during hypoxia were also observed though delayed compared with the R123 responses: an initial increase, a large decrease coincident with the HSD-related DeltaV(o), and a trough following HSD. After reoxygenation, there occurred a delayed increase in transmittance and then a slow decrease, returning to near baseline. When Ca(2+) was removed from the external medium, resulting in complete synaptic blockade, the mitochondrial response to hypoxia did not significantly differ from control (normal Ca(2+)) conditions. In slices maintained in low-chloride (2.4 mM) medium, a dramatic reversal in the direction of the IOS signal associated with HSD occurred, and the R123 signal during HSD was severely attenuated. Normoxic SD induced by micro-injection of KCl was also associated with a decrease in light transmittance and a sharp increase in R123 fluorescence but both responses were less pronounced than during HSD. Our results show two mitochondrial responses to hypoxia: an initial depolarization that appears to be caused by depressed electron transport due to lack of oxygen and a later, sudden, sharp depolarization linked to HSD. The depression of the second, sharp depolarization and the inversion of the IOS in low-chloride media suggest a role of Cl(-)-dependent mitochondrial swelling. Lack of effect of Ca(2+)-free medium on the R123 and IOS responses suggests that the protection against hypoxic damage by low Ca(2+) is not due to the prevention of mitochondrial depolarization.

Effects of arachidonic acid on unitary calcium currents in rat sympathetic neurons

We have characterized the actions of arachidonic acid (AA) on whole cell and unitary calcium (Ca2+) currents in rat neonatal superior cervical ganglion (SCG) neurons using barium (Ba2+) as the charge carrier. Whole cell currents were elicited by stepping the membrane potential from -90 mV to +10 mV. Arachidonic acid (5 microM) was introduced into the bath in the continued presence of 1 microM (+)-202-791, an L-type Ca2+ channel agonist. Under these conditions, the peak current, comprised mainly of N-type current, and a slow, (+)-202-791-induced component of the tail current were inhibited by 67 +/- 6 and 60 +/- 10 %, respectively, indicating that AA inhibits both N- and L-type currents. At a test potential of +30 mV, AA (5 microM) decreased unitary L- and N-type Ca2+ channel open probability (Po) in cell-attached patches that contained a single channel. For both channels, the underlying causes of the decrease in Po were similar. Arachidonic acid caused an increase in the percentage of null sweeps and in the number of null sweeps that clustered together. In sweeps with activity, the average number of openings per sweep decreased, while first latency and mean closed time increased. Arachidonic acid had no significant effect on unitary current amplitude or mean open time. Our findings are the first description of the inhibition of unitary L- and N-type Ca2+ channel activity by AA and are consistent with both channels spending more time in their null mode and with increased dwell time in one or more closed states.

Inhibition of neuronal Ca(2+) influx by gabapentin and subsequent reduction of neurotransmitter release from rat neocortical slices

Cytosolic calcium ion concentrations ([Ca(2+)](i)) were measured in rat neocortical synaptosomes using fura-2, and depolarization of synaptosomal membranes was induced by K(+) (30 mM). The release of the endogenous excitatory amino acids glutamate and aspartate was evoked by K(+) (50 mM) and determined by HPLC. The release of [(3)H]-noradrenaline from rat neocortical synaptosomes or slices was evoked by K(+) (15 and 25 mM) and measured by liquid scintillation counting. Gabapentin produced a concentration-dependent inhibition of the K(+)-induced [Ca(2+)](i) increase in synaptosomes (IC(50)=14 microM; maximal inhibition by 36%). The inhibitory effect of gabapentin was abolished in the presence of the P/Q-type Ca(2+) channel blocker omega-agatoxin IVA, but not by the N-type Ca(2+) channel antagonist omega-conotoxin GVIA. Gabapentin (100 microM) decreased the K(+)-evoked release of endogenous aspartate and glutamate in neocortical slices by 16 and 18%, respectively. Gabapentin reduced the K(+)-evoked [(3)H]-noradrenaline release in neocortical slices (IC(50)=48 microM; maximal inhibition of 46%) but not from synaptosomes. In the presence of the AMPA receptor antagonists 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) and 2, 3-dioxo-6-nitro-1,2,3,4-tetrahydro[f]quinoxaline-7-sulphonamide (NBQX), gabapentin did not reduce [(3)H]-noradrenaline release. Gabapentin did, however, cause inhibition in the presence of the NMDA receptor antagonist DL-(E)-2-amino-4-methyl-5-phosphono-3-pentanoic acid (CGP 37849). Gabapentin is concluded to reduce the depolarization-induced [Ca(2+)](i) increase in excitatory amino acid nerve terminals by inhibiting P/Q-type Ca(2+) channels; this decreased Ca(2+) influx subsequently attenuates K(+)-evoked excitatory amino acid release. The latter effect leads to a reduced activation of AMPA receptors which contribute to K(+)-evoked noradrenaline release from noradrenergic varicosities, resulting in an indirect inhibition of noradrenaline release.

Phospholipases A2 in ischemic and toxic brain injury

Phospholipases A2 (PLA2s) regulate hydrolysis of fatty acids, including arachidonic acid, from the sn-2 position of phospholipid membranes. PLA2 activity has been implicated in neurotoxicity and neurodegenerative processes secondary to ischemia and reperfusion and other oxidative stresses. The PLA2s constitute a superfamily whose members have diverse functions and patterns of expression. A large number of PLA2s have been identified within the central nervous systems of rodents and humans. We postulated that group IV large molecular weight, cytosolic phospholipase A2 (cPLA2) has a unique role in neurotoxicity associated with ischemic or toxin stress. We created mice deficient in cPLA2 and tested this hypothesis in two injury models, ischemia/reperfusion and MPTP neurotoxicity. In each model cPLA2 deficient mice are protected against neuronal injury when compared to their wild type littermate controls. These experiments support the hypothesis that cPLA2 is an important mediator of ischemic and oxidative injuries in the brain.

Electrical responses in hippocampal slices after prolonged global ischemia: effects of neuroprotectors

A simple and reproducible animal model of global ischemia, induced by decapitation in 30-day-old Wistar rats, has been developed. It allows to perform electrophysiological analysis of the postischemic reperfusion period in the brain slices. Periods of ischemia up to 40 min increase population spikes measured in the CA1 area of the hippocampus during 2-5 h of reperfusion. Thus after 30-min decapitation-induced ischemia (at t(ischem)=25 degrees C), the mean amplitude of the recorded maximum orthodromic population spikes was 159% of the control obtained in the non-ischemic animals. Longer ischemic episodes result in the depression of the population spikes. After 2 h of ischemia, the amplitude of population spikes was about 89% of control. After 3 h of decapitation ischemia, the neurons could not be reactivated. The duration of ischemic episode needed for the irreversible depression of the electrical activity of the brain neurons drastically depends on the temperature at which the ischemic brain is maintained. Thus, only 2 h were needed at 30 degrees C as compared to nearly 3 h at 25 degrees C. We have found that intraperitoneal injection of neuroprotectors which precedes decapitation enables reactivation of the post-ischemic neurons even after very long periods of global ischemia. Thus, MK-801, a non-competitive NMDA receptors antagonist, or NBQX, a blocker of AMPA receptors, administrated 15 min before the long-term (90 min) decapitation ischemia (30 degrees C), induced dose-dependent recovery of population spike with ED(50) values 0.2 mg/kg and 3 mg/kg respectively. Our results demonstrate that, in spite of the high vulnerability of hippocampal neurons to hypoxia and ischemia, their electrical activity can be restored after prolonged (more then 1 h) decapitation ischemia. Administration of NMDA or AMPA antagonists enhances recovery.

Stanniocalcin: A molecular guard of neurons during cerebral ischemia

Stanniocalcin (STC) is a glycoprotein hormone originally found in bony fish, in which it regulates calcium/phosphate homeostasis and protects against hypercalcemia. The recently characterized human STC shows about 70% homology with fish STC. We previously reported a constitutive expression of STC in terminally differentiated neurons. Here, we show that exposure of human neural-crest-derived cell line Paju to hypercalcemic culture medium induced expression of STC. Treatment of Paju cells with recombinant human STC increased their uptake of inorganic phosphate. Paju cells expressing STC by cDNA transfection displayed increased resistance to ischemic challenge and to elevated intracellular free calcium induced by treatment with thapsigargin. An up-regulated and redistributed expression of STC was observed in neurons surrounding the core of acute infarcts in human and rat brains. Given that mobilization and influx of calcium is considered a main neurotoxic mechanism following ischemia, our results suggest that the altered expression of STC contributes to the protection of cerebral neurons against hypoxic/ischemic damage. Manipulation of the STC expression may therefore offer a therapeutic approach to limit the injury after ischemic brain insults.

Stanniocalcin: A molecular guard of neurons during cerebral ischemia

Stanniocalcin (STC) is a glycoprotein hormone originally found in bony fish, in which it regulates calcium/phosphate homeostasis and protects against hypercalcemia. The recently characterized human STC shows about 70% homology with fish STC. We previously reported a constitutive expression of STC in terminally differentiated neurons. Here, we show that exposure of human neural-crest-derived cell line Paju to hypercalcemic culture medium induced expression of STC. Treatment of Paju cells with recombinant human STC increased their uptake of inorganic phosphate. Paju cells expressing STC by cDNA transfection displayed increased resistance to ischemic challenge and to elevated intracellular free calcium induced by treatment with thapsigargin. An up-regulated and redistributed expression of STC was observed in neurons surrounding the core of acute infarcts in human and rat brains. Given that mobilization and influx of calcium is considered a main neurotoxic mechanism following ischemia, our results suggest that the altered expression of STC contributes to the protection of cerebral neurons against hypoxic/ischemic damage. Manipulation of the STC expression may therefore offer a therapeutic approach to limit the injury after ischemic brain insults.

The protective action of tetrodotoxin and (+/-)-kavain on anaerobic glycolysis, ATP content and intracellular Na+ and Ca2+ of anoxic brain vesicles

Because recent reports point to Na+ channel blockers as protective agents directed against anoxia-induced neuronal damage including protection of anaerobic glycolysis, the influences of tetrodotoxin (TTX) and (+/-)-kavain on anoxic rat brain vesicles were investigated with respect to lactate synthesis, vesicular ATP content and cytosolic free Na+ and Ca2+ ([Na+]i, [Ca2+]i), both of the latter determined fluorometrically employing SBFI and FURA-2, respectively. After anoxia, basal lactate production was increased from 2.9 to 9.8 nmol lactate/min/mg protein. Although lactate synthesis seemed to be stable for at least 45 min of anoxia, as deduced from the linearity of lactate production, the ATP content declined continuously with a half life (tau 1/2) of 14.5 min, indicating that anaerobic glycolysis was insufficient to cover the energy demand of anoxic vesicles. Correspondingly, [Na+]i and [Ca2+]i increased persistently after anoxia by 22.1 mmol/l Na+ and 274.9 nmol/l Ca2+, determined 6.3 min after onset. An additional stimulation of vesicles with veratridine accelerated the drop of ATP (tau 1/2 = 5.1 min) and provoked a massive Na+ overload, which levelled off to 119 mmol/l Na+ within a few minutes. Concomitantly, [Ca2+]i increased linearly with a rate of 355 nmol Ca2+/l/min. Despite the massive perturbation of ion homeostasis, lactate production was unaffected during the first 8 min of veratridine stimulation. However, complete inhibition of lactate synthesis took place 30 min after veratridine was added. The Na+ channel blockers TTX and (+/-)-kavain, if applied before anoxia, preserved vesicular ATP content, diminished anoxia-induced increases in [Na+]i and [Ca2+]i and prevented both the veratridine-induced increases of [Na+]i and [Ca2+]i and the inhibition of lactate production. The data indicate a considerable Na+ influx via voltage-dependent Na+ channels during anoxia, which speeds up the decline in ATP and provokes an increase in [Ca2+]i. A massive Na+ and Ca2+ overload induced by veratridine failed to influence lactate synthesis directly, but initiated its inhibition.

Hearing loss and glutamate efflux in the perilymph following transient hindbrain ischemia in gerbils

The mechanism underlying ischemia-induced hearing loss was studied in gerbils with transient hindbrain ischemia. Occlusion of the vertebral arteries caused an increase in the concentration of glutamate in the perilymph and elevated the compound action potential (CAP) threshold to 24.6 dB at 5 minutes. the CAP threshold subsequently recovered on reperfusion, gradually reaching 8.3 dB 120 minutes after reperfusion. Under electron microscopy, afferent dendrites of the cochlear nerve in contact with inner hair cells exhibited abnormal swelling 5 minutes after ischemia/reperfusion. These morphological changes were not observed in cochleas treated with an alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA)/kainate-type glutamate receptor antagonist, 6-7-dinitroquinoxaline-2,3-dione (DNQX), before hindbrain ischemia; an N-methyl-D-aspartate (NMDA)-type receptor antagonist, D-2-amino-5-phosphonopentanoate (D-AP5), was ineffective. Moreover, the histopathological alterations noted 5 minutes after reperfusion were spontaneously ameliorated 120 minutes after ischemia/reperfusion. These findings suggest that the ischemia-induced increase in extracellular glutamate concentration with subsequent activation of AMPA/kainate receptors is responsible for neurite degeneration and hearing loss in the early stages following transient hindbrain ischemia.

Distribution of glutamate and preproenkephalin messenger RNAs following transient focal cerebral ischemia

Middle cerebral artery occlusion may result in increased activation of N-methyl-D-aspartate- or alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA)-type receptors by glutamate and lead to neuronal cell death. To characterize molecular events that precede cell death following transient focal ischemia, in situ hybridization histochemistry was used to measure levels of glutamate receptor subunit 1 (GluR1), GluR2, GluR3, N-methyl-D-aspartate receptor subunit 1 (NR1) and preproenkephalin messenger RNAs in adult rats at various recirculation times (1.5, 3 and 24 h) following a 90-min period of middle cerebral artery occlusion. At 1.5 and 3 h recirculation, autoradiography showed pronounced but differential decreases in AMPA, NR1 and preproenkephalin messenger RNA expression throughout the infarcted ipsilateral striatum. Non-uniform patterns of in situ hybridization grains emerged such that many striatal neurons were depleted of AMPA and preproenkephalin messenger RNAs, while others retained control levels. In cortical regions destined to undergo infarction, GluR2 and NR1 messenger RNAs were preferentially reduced relative to the contralateral side (to 75+/-8.5% and 66+/-4.5%, respectively); GluR1, GluR3 and preproenkephalin messenger RNAs were unaltered. At 24 h recirculation, depletion of striatal and cortical messenger RNAs became less selective. GluR3 and preproenkephalin messenger RNAs were up-regulated in ipsilateral spared regions of the striatum, and GluR1 and GluR2 messenger RNAs increased bilaterally in the cingulate cortex and in selective nuclei of the amygdala. Histological cell death or neurodegeneration was not detected in areas of reduced glutamate and preproenkephalin messenger RNA expression in either the ipsilateral striatum or cortex before 24 h. These findings suggest that complex and long-lasting decreases in messenger RNA expression occur prior to significant cell loss in regions destined to undergo infarction. Increased formation of Ca2+-permeable AMPA receptor assemblies may occur in "unspared" and "spared" regions via different mechanisms and contribute to alterations in post-ischemic synaptic activity. The possibility arises that there may be altered relationships between glutamatergic and enkephalin synapses, since the dorsolateral striatum, where preproenkephalin messenger RNA expression is acutely reduced, receives innervation by the affected ipsilateral cortical region.

Apoptosis and necrosis in cerebrovascular disease

Neuronal death following ischemic insults has been thought to reflect necrosis. However, recent evidence from several labs suggests that programmed cell death, leading to apoptosis, might additionally contribute to this death. We have used both in vitro and in vivo models to study the role of apoptosis in ischemic cell death. Some features of apoptosis (TUNEL staining, internucleosomal DNA fragmentation, sensitivity to cycloheximide) were observed following transient focal ischemia in rats. Brief transient focal ischemia was followed by delayed infarction more than 3 days later; this delayed infarction was sensitive to cycloheximide. A cycloheximide-sensitive component of neuronal cell death was also observed in cultured murine neocortical neurons deprived of oxygen-glucose in the presence of glutamate receptor antagonists. This presumed ischemic apoptosis was attenuated by caspase inhibitors, or by homozygous deletion of the bax gene. Neurons may undergo both apoptosis and necrosis after ischemic insults, and thus it may be therapeutically desirable to block both processes.

Neuroprotection and the ischemic cascade

Brain ischemia is a process of delayed neuronal cell death, not an instantaneous event. The concept of neuroprotection is based on this principle. Diminished cerebral blood flow initiates a series of events (the "ischemic cascade") that lead to cell destruction. This ischemic cascade is akin to a spreading epidemic starting from a hypothesized core of ischemia and radiating outward. If intervention occurs early, the process may be halted. Interventions have been directed toward salvaging the ischemic penumbra. Hypothermia decreases the size of the ischemic insult in both anecdotal clinical and laboratory reports. In addition, a wide variety of agents have been shown to reduce infarct volume in animal models. Pharmacologic interventions that involve thrombolysis, calcium channel blockade, and cell membrane receptor antagonism have been studied and have been found to be beneficial in animal cortical stroke models. Human trials of neuroprotective therapies have been disappointing. Other than thrombolytics, no agents have shown an unequivocal benefit. The future of neuroprotection will require a logical extension of what has been learned in the laboratory and previous human trials. A sensible approach to the use of multiple-agent cocktails used in combination with thrombolytics is likely to offer the highest chance for benefit.

Free radicals are involved in the damage to protein synthesis after anoxia/aglycemia and NMDA exposure

Neuronal protein synthesis is inhibited in CA1 pyramidal neurons for many hours after ischemia, hypoxia or hypoglycemia. This inhibition precedes cell death, is a hallmark characteristic of necrotic damage and may play a key role in the death of vulnerable neurons after these insults. The sequence of events leading to this inhibition remains to be fully elucidated. The protein synthesis failure after 7.5 min anoxia/aglycemia in the rat hippocampal slice can be prevented by blocking N-methyl-D-aspartate receptors in a reduced calcium environment during the insult. In this study, we demonstrate that N-methyl-D-aspartate exposure directly causes a dose-dependent, receptor-mediated and prolonged protein synthesis inhibition in CA1 pyramidal neurons. The free radical scavenger Vitamin E significantly attenuates this damage due to low concentrations of N-methyl-D-aspartate (10 microM). Free radical generation by xanthine/xanthine oxidase (XOD) can directly damage protein synthesis in neurons of the slice. Vitamin E, ascorbic acid and N-acetylcysteine can each prevent the damage due to anoxia/aglycemia and to higher concentrations of N-methyl-D-aspartate (50 microM), provided calcium levels are reduced concomitantly. These findings indicate that both free radicals and calcium play a role in the sequence of events leading to protein synthesis failure after energetic stress like anoxia/aglycemia. They further suggest that the mechanism by which N-methyl-D-aspartate receptor activation damages protein synthesis involves free radical generation.

Increase in receptor binding affinity for nimodipine in the rat brain with permanent occlusion of bilateral carotid arteries

The permanent occlusion of bilateral common carotid arteries (2VO) in rats has been shown to cause progressive and long-lasting cognitive deficits which may be due to impairment of memory retention and/or memory recall process. To clarify the function of voltage dependent calcium channels and the receptor binding of nimodipine by chronic cerebral ischemia, we examined specific (+)-[3H]PN 200-110 binding and the effect of oral administration of nimodipine in brain regions and hearts of rats, at 2 weeks to 4 months after permanent 2VO. There was no significant difference in either dissociation constant (Kd) or maximal number of binding sites (Bmax) for (+)-[3H]PN 200-110 in the cerebral cortex, hippocampus, corpus striatum and thalamus between 2VO and sham rats. In addition, in vitro inhibitory effect of nimodipine on cerebral cortical (+)-[3H]PN 200-110 binding in 2VO rats was similar to that in sham rats. Compared to control rats, oral administration of nimodipine to both 2VO and sham rats at 2 months after permanent 2VO brought about a significant increase in Kd values of specific (+)-[3H]PN 200-110 binding in the cerebral cortex, hippocampus, thalamus and myocardium, and the increase in Kd values was much larger in brain regions of 2VO rats than sham rats. However, the increase in Kd values in the myocardium did not differ between 2VO and sham rats. This observation suggests an increased in vivo binding affinity for nimodipine in chronic ischemic brain. In conclusion, the present study has shown that oral administration of nimodipine may cause a greater occupation in vivo of 1,4-dihydropyridine (DHP) calcium channel antagonist receptors in brains of permanent 2VO rats than in sham rats. Thus, nimodipine may be pharmacologically effective in preventing brain dysfunction due to cerebral ischemia in vivo.

Involvement of extracellular signal-regulated protein kinase in gliosis induced during recovery from metabolic inhibition

Brain reperfusion may be of particular importance in the etiology of periventricular leukomalacia, of which the common findings are gliosis and ventricular dilatation. To investigate the mechanism of this pathogenesis, we used a metabolic inhibition (MI) model using cyanide plus deoxyglucose treatment of cultured glia isolated from fetal rat brain and examined the activity of extracellular signal-regulated protein kinase (ERK) during MI and also during the recovery from MI of 30 min. ERK activation was stimulated during MI and the recovery from MI. The time course and extent of activation of ERK during MI and the recovery from MI, however, were distinctly different. Activation of ERK was stimulated within 5 min of MI and declined thereafter. Activation of ERK was sustained during the recovery phase from MI and the extent of the activation was much greater than that during MI. Pretreatment with EGTA to eliminate extracellular Ca(2+), or with APV, an NMDA receptor antagonist, to inhibit Ca(2+) influx through the NMDA receptor, attenuated the activation of ERK. Moreover, pretreatment with PMA to downregulate PKC abolished the activation of ERK. PD98059, an inhibitor of ERK kinase, attenuated the cell proliferation induced by MI followed by recovery from MI. These results suggest that ERK is involved in gliosis during the recovery phase from MI and may play a role in the etiology of periventricular leukomalacia.

Ameliorative effects of tamolarizine on place learning impairment induced by transient forebrain ischemia in rats

In the present study we investigated the effect of (+/-)-1-(3, 4-dimethoxyphenyl)-2-(4-diphenylmethylpiperazinyl) ethanol dihydrochloride (tamolarizine), a calcium entry blocker, on place learning impairment in rats with damage selective to the hippocampal CA1 subfield induced by transient forebrain ischemia. Tamolarizine was administered (40 mg/kg) immediately after 15-min brain ischemia. Place learning was tested in a task in which the rat was required to alternatively visit two places located diametrically opposite each other in an open field. The ischemia+saline group showed severe learning impairment in this task; their performance level was significantly inferior to that of the sham-operated group through the test period (30 days). Although the ischemia+tamolarizine group showed slight impairment of place learning during the course of this test, they later reached almost the same performance level as the sham-operated group. Selective neuronal loss in the CA1 subfield was much less in the ischemia+tamolarizine group than in the ischemia+saline group. These results indicate that tamolarizine treatment protects the hippocampus from ischemic brain damage and ameliorates place learning impairment.

Periinfarct and remote excitability changes after transient middle cerebral artery occlusion

Transient middle cerebral artery (MCA) occlusion results in substantially smaller cortical infarcts than permanent MCA occlusion if reperfusion is initiated within the first few hours. Only little information is available on the long-term functional outcome of the cortical regions "salvaged" by early reperfusion. To address this issue we examined basic electrophysiologic parameters in vitro using standard extracellular recording techniques at 7 and 28 days after transient MCA occlusion (1- and 2-hour ischemia) in rats. Both neocortical areas ipsi- and contralateral to MCA occlusion were systematically mapped to delineate the extent of periinfarct and remote alterations. In the periinfarct region we found a significant reduction of field potential amplitudes up to 3 mm when measuring from the infarct border at 7 days and up to 7 mm at 28 days. Paired-pulse inhibition, an indicator of GABAergic transmission, was only moderately impaired in this region at 7 days and not significantly different from control at 28 days. Remote effects were observed both ipsi- and contralaterally. Ipsilaterally they were restricted to a region close to the midline (presumably motor cortex) and were most likely attributable to the degeneration of corticostriatal connections. The extent of the contralateral excitability changes was clearly related to the size of the neocortical infarcts with large infarcts resulting in the widespread reduction of field potential amplitudes and an impairment of paired-pulse inhibition. The results show that there is a relatively large periinfarct region with decreased overall excitability after transient MCA occlusion which is likely to have a profound effect on perilesional processes involved in functional recovery. Remote excitability changes may contribute to the functional deficit and are probably related to deafferentation.

Hypoglycemic brain injury: potentiation from respiratory depression and injury aggravation from hyperglycemic treatment overshoots

Hypoglycemia can cause brain dysfunction, brain injury, and death. The present study seeks to broaden current information regarding mechanisms of hypoglycemic brain injury by investigating a novel etiology. The cat's high resistance to brain injury from hypoglycemia suggested that additional influences such as respiratory depression might play a facilitating role. Three groups of cats were exposed to fasting and insulin-induced hypoglycemia (HG; n = 6), euglycemic respiratory depression (RD; n = 5), and combined hypoglycemic respiratory depression (HG/RD; n = 10). The HG animals were maintained at <1.5 mmol (mean 1 mmol) serum glucose concentration for 2 to 6.6 hours. The respiratory depression was associated with PaO2 and PaCO2 values of approximately 50 mm Hg for 1 hour and of approximately 35 and approximately 75 mm Hg, respectively, for the second hour. Magnetic resonance diffusion-weighted imaging estimated brain energy state before, during, and after hypoglycemia. The hypoglycemic respiratory depression exposures were terminated either to euglycemia (n = 4) or to hyperglycemia (n = 6). Brain injury was assessed after 5 to 7 days of survival. Cats exposed to hypoglycemia alone maintained unchanged diffusion coefficients; that is, they lacked evidence of brain energy failure and all six remained brain-intact. Only 1 of 5 euglycemic RD but 10 of 10 HG/RD cats developed brain damage (HG and RD vs. HG/RD, P < 0.01). This difference in brain injury rates suggests injury potentiation by hypoglycemia and respiratory depression acting together. Three injury patterns emerged, including activation of microglia, selective neuronal necrosis, and laminar cortical necrosis. Widespread activation of microglia suggesting damage to neuronal cell processes affected all damaged brains. Selective neuronal necrosis affecting the cerebral cortex, hippocampus, and basal ganglia was observed in all but one case. Instances of laminar cortical necrosis were limited to cats exposed to hypoglycemic respiratory depression treated with hyperglycemia. Thus, treatment with hyperglycemia compared with euglycemia after hypoglycemic respiratory depression exposures significantly increased the brain injury scores (24 +/- 6 vs. 13 +/- 2 points; P < 0.05). This new experimental hypoglycemia model's contribution lies in recognizing additional factors that critically define the occurrence of hypoglycemic brain injury.

The novel compound LOE 908 attenuates acute neuromotor dysfunction but not cognitive impairment or cortical tissue loss following traumatic brain injury in rats

Experimental traumatic brain injury (TBI) initiates massive disturbances in Ca2+ concentrations in the brain that may contribute to neuronal damage. Intracellular Ca2+ may be elevated via influx through voltage-operated cation channels, ligand-gated ionotropic channels, and store-operated cation channels (SOCs). In the present study, we evaluated the neurobehavioral and histological effects of acute posttraumatic administration of (R,S)-(3,4-dihydro-6,7-dimethoxy-isoquinoline-1-yl)-2-phenyl-N,N-di[2-(2 ,3,4-trimethoxyphenyl)ethyl]-acetamide (LOE 908), a broad spectrum inhibitor of voltage-operated cation channels and SOCs. Male Sprague-Dawley rats (n = 53) were trained in the Morris water maze, anesthetized (60 mg/kg pentobarbital, i.p.), and subjected to lateral fluid percussion brain injury (2.5-2.7 atm; n = 38) or surgery without injury (n = 15). At 15 min postinjury, animals were randomized to receive intravenous administration of either a high dose of LOE 908 (4 mg/kg bolus followed by 160 mg/kg over 24 h; n = 13), a low dose of LOE 908 (2 mg/kg bolus followed by 80 mg/kg over 24 h; n = 12), or vehicle (n = 13). Uninjured controls received the high dose of LOE 908 (n = 8) or vehicle (n = 7). Treatment with either dose of LOE 908 significantly improved neuromotor function at 48 h postinjury when compared to vehicle treatment. Although a significant deficit in visuospatial memory was observed in brain-injured animals at this timepoint when compared to uninjured animals, neither dose of LOE 908 attenuated injury-induced cognitive dysfunction. Histological evaluation revealed that neither dose of LOE 908 affected cortical lesion size at 48 h postinjury. These data suggest that broad spectrum cation channel blockers may be beneficial in the treatment of neurological motor dysfunction when administered in the acute posttraumatic period.

Calcium antagonists for acute ischemic stroke

BACKGROUND

The sudden loss of blood supply in ischemic stroke is associated with increased levels of calcium ions within neurones. Inhibiting this increase could protect neurones and is thought to reduce neurological impairment, disability and handicap after stroke.

OBJECTIVES

The aim of this review is to determine whether calcium antagonists reduce the risk of death or dependency after acute ischemic stroke. The influence of different drugs, dosages, routes of administration, time intervals after stroke and trial design on the risk of poor outcome was investigated.

SEARCH STRATEGY

Relevant trials were identified in the Specialised Register of Controlled Trials (last searched: March 1999).

SELECTION CRITERIA

All truly randomised trials comparing a calcium antagonist with control in patients with acute ischaemic stroke were included.

DATA COLLECTION AND ANALYSIS

Two authors assessed all trials and extracted the data. Poor outcome, defined as death or dependency in activities of daily living, was used as the main outcome. Analyses were, if possible, "intention-to-treat".

MAIN RESULTS

46 trials were identified of which 28 were included (7521 patients). No effect of calcium antagonists on poor outcome at the end of follow-up (OR 1.07, 95% CI 0.97/1.18), or on death at end of follow-up (OR 1.10, 95% CI 0.98/1.24) was found. Intravenous administration (i.v.) of calcium antagonists was associated with an increase in the number of patients with poor outcome compared to oral administration (indirect comparisons). Comparisons of different doses of nimodipine suggested that the highest doses were associated with poorer outcome. Administration within 12 hours of onset was associated with an increase in the proportion of patients with poor outcome, but this effect was largely due to the poor results associated with i.v. administration. A subgroup analysis on nimodipine (oral, 120 mg/day) started within 12 hours of stroke onset, did not show a beneficial effect.

REVIEWER'S CONCLUSIONS

No evidence is available to justify the use of calcium antagonists in patients with acute ischaemic stroke.

CPP antagonizes hypoxia-induced changes in dopamine metabolism in the striatum of newborn rat

Treatment with 3-(2-carboxypiperazin-4-yl)-propyl-1-phosphonic acid (CPP), a potent and competitive N-methyl-D-aspartate antagonist, is able to reduce the hypoxia-induced increase in striatal dopamine level by 26% even after the hypoxic insult has occurred. The hypoxia-induced decrease of the striatal 3,4-dihydroxyphenylacetic acid level can also be reversed by CPP. This study demonstrates that CPP can antagonize the hypoxia-induced changes in the dopamine metabolism in the striatum of the newborn rat.

Ca2+ store-dependent potentiation of Ca2+-activated non-selective cation channels in rat hippocampal neurones in vitro

1. Potentiation of calcium-activated non-selective cation (CAN) channels was studied in rat hippocampal neurones. CAN channels were activated by IP3-dependent Ca2+ release following metabotropic glutamate receptor (mGluR) stimulation either by Schaffer collateral input to CA1 neurones in brain slices in which ionotropic glutamate and GABAA receptors, K+ channels, and the Na+-Ca2+ exchanger were blocked or by application of the mGluR antagonist ACPD in cultured hippocampal neurones. 2. The CAN channel-dependent depolarization (DeltaVCAN) was potentiated when [Ca2+]i was increased in neurones impaled with Ca2+-containing microelectrodes. 3. Fura-2 measurements revealed a biphasic increase in [Ca2+]i when 200 microM ACPD was bath applied to cultured hippocampal neurones. This increase was greatly attenuated in the presence of Cd2+. 4. Thapsigargin (1 microM) caused marked potentiation of DeltaVCAN in CA1 neurones in the slices and of the CAN current (ICAN) measured in whole cell-clamped cultured hippocampal neurones. 5. Ryanodine (20 microM) also led to a potentiation of DeltaVCAN while neurones pretreated with 100 microM dantrolene failed to show potentiation of DeltaVCAN when impaled with Ca2+-containing microelectrodes. 6. The mitochondrial oxidative phosphorylation uncoupler carbonyl cyanide m-chlorophenyl hydrazone (2 microM) also caused a potentiation of DeltaVCAN. 7. CAN channels are subject to considerable potentiation following an increase in [Ca2+]i due to Ca2+ release from IP3-sensitive, Ca2+-sensitive, or mitochondrial Ca2+ stores. This ICAN potentiation may play a crucial role in the 'amplification' phase of excitotoxicity.

Effects of stobadine, melatonin, and other antioxidants on hypoxia/reoxygenation-induced synaptic transmission failure in rat hippocampal slices

In vitro reversible ischemia was simulated with rat hippocampal slices in order to test the neuroprotective activity of selected antioxidants with emphasis on the pyridoindole stobadine. Slices were exposed to hypoxia (HYP) combined with lowered D-glucose concentration to induce synaptic transmission (ST) failure, which turned out to be irreversible in approximately 80%-100% of slices during reoxygenation (ROX). The amplitude of population spikes (PoS) evoked trans-synaptically by electrical stimulation of Schäffer collaterals and recorded in CA1 neurons was the parameter of ST. Pretreatment of slices with stobadine dissolved in slice superfusion media (1 to 100 microM) improved ST recovery after 20-min tissue ROX. Stobadine decreased the number of irreversibly damaged slices and increased the average amplitude of PoS during tissue ROX. The concentration-response relationship of protective activity was bell-shaped, with maximum at 3-30 microM. Moreover, the half-time of PoS decay (t1/2) during HYP was significantly delayed in stobadine treated groups (10 to 100 microM). The neurohormone melatonin (30 to 100 microM) and 21-aminosteroid U-74389G (10 microM) revealed similar protective activity on ST recovery and on t1/2 during HYP. Trolox (200 microM) improved the PoS recovery, yet it had no effect on t1/2. The iron chelator deferoxamine (250 and 500 microM) had no protective effects at all. alpha-Tocopherol administered to animals orally (200 mg/kg for 10 days) only marginally improved the PoS recovery. Comparing the protective effect of compounds tested on PoS recovery, we assume the following rank order of potency: U-74389G > stobadine > melatonin >> trolox. Our findings suggest that stobadine as well as trolox, U-74389G and melatonin, antioxidants with remarkably different chemical structures, exerted neuroprotective activity, probably determined by antioxidative properties of these compounds. Moreover, stobadine, U-74389G, and melatonin were able to delay the early ST decay during HYP, which might indicate improved energetic state of neurons in the treated tissue. The study supports the notion about the neuroprotective activity of certain antioxidants.

Release of cytochrome c from mitochondria to cytosol in gerbil hippocampal CA1 neurons after transient forebrain ischemia

We examined cytosolic cytochrome c in gerbil hippocampal CA1 and CA3 regions after induction of 5-min ischemia by immunoblotting. In the CA1 region, cytochrome c was detected in the cytosolic fraction from 1 to 6 h after ischemia by Western blotting, while it was not detected in the CA3 region. Following intraventricular administration of cyclosporin A (CsA), detectable cytosolic cytochrome c was dramatically decreased, and about 80% of CA1 neurons survived after ischemia. The present studies demonstrate that cytochrome c is translocated from mitochondria to the cytosol in the early stage of delayed neuronal cell death, and suggest the involvement of the mitochondrial permeability transition.

55Cobalt (Co) as a PET-tracer in stroke, compared with blood flow, oxygen metabolism, blood volume and gadolinium-MRI

Several studies have shown the feasibility of divalent cobalt (Co)-isotopes (55Co and 57Co) in imaging of neuronal damage in stroke, multiple sclerosis, cerebral tumors and traumatic brain injury. Little is known how regional Co uptake relates to other pathophysiological changes after stroke. Therefore, we compared 55Co-PET with functional parameters such as regional cerebral blood flow (rCBF) using C(15)O(2), regional oxygen metabolism (rCMRO(2)) using 15O(2), regional cerebral blood volume (rCBV) and post-gadolinium (Gd) T(1)w-MRI to assess the permeability of the blood-brain-barrier (BBB). Sixteen patients (10 female; six male) aged 43 to 84 (mean 69) years with first ever stroke, as shown by CT or MRI, were examined with 55Co-PET and C(15)O(2)-, 15O(2)- and C(15)O-PET in one single session, in a period varying from 0 to 30 days after stroke-onset. Regions of infarction on C(15)O(2)- and 15O(2)-PET (defined by rCMRO(2)<65% or rCBF<45% of the contralateral value) were subsequently superimposed on the 55Co-PET scan. Clinical status was established using the Orgogozo stroke scale, which was assessed both at day 1 and at discharge (at least 6 weeks after day 1). Accumulation of 55Co was seen in eight out of 16 patients, occurring in areas showing a diminished oxygen metabolism, was only partially related to blood flow, and was located mainly outside the extent of the infarction or luxury perfusion as seen on post-Gd T(1)w-MRI. Statistical analysis showed a negative correlation between the Orgogozo score at discharge and the uptake of radioactive cobalt.

Neurotrauma care in the new millennium

The next millennium will see an explosion of neuromonitoring technology that will provide a more detailed understanding of brain-injured patients. This understanding will allow an individualized and intelligent application of the wide range of therapies that will become available. The measure of success for all of these endeavors will be individual patients and physicians' ability to return them to their normal lives.

A global hypoxia preconditioning model: neuroprotection against seizure-induced specific gravity changes (edema) and brain damage in rats

Hypoxia preconditioning states that a sublethal hypoxia episode will afford neuroprotection against a second challenge in the near future. We describe and discuss a procedure for the development of global hypoxia preconditioning in adult male Wistar rats, using a mildly hypoxic (9% O(2), 91% N(2)) atmospheric exposure of 8 h. The persistence of neuroprotection was analyzed using a kainic acid (KA) model of brain injury. Rats were challenged with KA (14 mg/kg, i.p.) on 1-14 days post-hypoxia. The effects of hypoxia preconditioning on seizure score, weight loss, brain edema and histopathology were assessed. Brain edema, predominantly of vasogenic origin, was measured 24 h after KA administration using a reproducible and quantitative method based on the specific gravities of tissue samples. A density gradient column (1.0250-1.0650 g/cm(3)) comprised of kerosene and bromobenzene was used to assess the presence of edema in regions involved in seizure initiation and propagation that are normally extensively damaged (i.e., piriform cortex and hippocampus). Specific gravities of tissues were calculated through extrapolation with known NaCl standards. We found that hypoxia preconditioning prevented the formation of edema in these brain regions when KA challenge was given 1, 3, and 7, but not 14 days post-hypoxia exposure. Furthermore, neuroprotection was observed in animals that had robust seizures. The described procedure may be used to examine the neuroprotective mechanisms induced by global hypoxia preconditioning against many subsequent challenges reflecting a variety of experimental models of brain injury, and will provide a better understanding of the brain response to hypoxia and stress.

Hypoglycemia in children with type 1 diabetes mellitus. Risk factors, cognitive function, and management

This article examines the relationship between hypoglycemia and brain function in children with type 1 diabetes. Hypoglycemic episodes occurring in the first 5 years of life may permanently disrupt cognitive function in a subset of children with diabetes, and a single acute episode of hypoglycemia may produce a transient reduction in mental efficiency, alter the electroencephalogram, and increase regional cerebral blood flow. Because iatrogenic development of hypoglycemic unawareness and autonomic failure are the most likely mediators of moderately severe hypoglycemia, medical management efforts should be directed at the prevention of frequently recurring, mild hypoglycemia.

Glutamate receptor requirement for neuronal death from anoxia-reoxygenation: an in Vitro model for assessment of the neuroprotective effects of estrogens

1. Previous studies demonstrated that estrogens, specifically 17 beta-estradiol, the potent, naturally occurring estrogen, are neuroprotective in a variety of models including glutamate toxicity. The aim of the present study is twofold: (1) to assess the requirement for glutamate receptors in neuronal cell death associated with anoxia-reoxygenation in three cell types, SK-N-SH and HT-22 neuronal cell lines and primary rat cortical neuronal cultures, and (2) to evaluate the neuroprotective activity of both 17 beta-estradiol and its weaker isomer, 17 alpha-estradiol, in both anoxia-reoxygenation and glutamate toxicity. 2. SK-N-SH and HT-22 cell lines, both of which lack NMDA receptors as assessed by MK-801 binding assays, were resistant to both anoxia-reoxygenation and glutamate-induced cell death. In contrast, primary rat cortical neurons, which exhibit both NMDA and AMPA receptors, were sensitive to brief periods of exposure to anoxia-reoxygenation or glutamate. As such, there appears to be an obligatory requirement for NMDA and/or AMPA receptors in neuronal cell death resulting from brief periods of anoxia followed by reoxygenation. 3. Using primary rat cortical neuronal cultures, we evaluated the neuroprotective activity of 17 beta-estradiol (1.3 or 133 nM) and 17 alpha-estradiol (133 nM) in both anoxia-reoxygenation and excitotoxicity models of cell death. We found that the 133 nM but not the 1.3 nM dose of the potent estrogen, 17 beta-estradiol, protected 58.0, 57.5, and 85.3% of the primary rat cortical neurons from anoxia-reoxygenation, glutamate, or AMPA toxicity, respectively, and the 133 nM dose of the weak estrogen, 17 alpha-estradiol, protected 74.6, 81.7, and 85.8% of cells from anoxia-reoxygenation, glutamate, or AMPA toxicity, respectively. These data demonstrate that pretreatment with estrogens can attenuate glutamate excitotoxicity and that this protection is independent of the ability of the steroid to bind the estrogen receptor.

Unilateral GluR2(B) hippocampal knockdown: a novel partial seizure model in the developing rat

Kainic acid (KA) induces status epilepticus in both adult and young rats but with different consequences on pathology and gene expression. In adults, GluR2(B) AMPA subunit expression is markedly reduced in CA3 neurons before neurodegeneration. In pups, the GluR2(B) subunit is sustained, possibly contributing to neuronal survival. Mechanisms underlying the reduced vulnerability of developing neurons to seizures was investigated by examining the effects of unilateral microinfusions of GluR2(B) antisense oligodeoxynucleotides (AS-ODNs) into the hippocampus of young rats in the presence or absence of a subconvulsive dose of KA. GluR2(B) AS-ODN infusions resulted in spontaneous seizure-like behavior, high stimulus intensity population spikes in the absence of long-term potentiation, and neurodegeneration of CA3 neurons lateral to the infusion site. Electroencephalography revealed paroxysmal activity and high-frequency high-amplitude discharges associated with vigorous and continuous scratching, wild running, or bilateral jerking movements. Pups lacking phenotypic behavior exhibited high-rhythmic oscillations and status epilepticus by the dose of KA used. Radiolabeled AS-ODNs accumulated throughout the ipsilateral dorsal hippocampus. GluR2(B) but not GluR1(A) receptor protein was markedly reduced after GluR2(B) knockdown. In contrast, GluR1(A) knockdown reduced GluR1(A) but not GluR2(B) protein without change in behavior or morphology. Therefore, unilateral downregulation of hippocampal GluR2(B) but not GluR1(A) protein reduces the seizure threshold and survival of CA3 neurons in the immature hippocampus, possibly providing a novel partial seizure model in the developing rat.

Neuronal damage in gerbils caused by intermittent forebrain ischemia

OBJECT

The purpose of this study was to investigate the possibility of preventing cumulative neuronal damage after repetitive severe ischemia.

METHODS

The authors monitored ischemic depolarization in the gerbil hippocampus, which has recently been shown to be a good experimental model of the effects of brief ischemia on the brain, and evaluated neuronal damage in the CA1 subregion 7 days after the ischemic insult. In a single-ischemia paradigm, the results indicate that induction of ischemia-induced neuronal damage depended on the duration of ischemic depolarization. Neuronal damage can be detected in the CA1 subregion after a period of depolarization lasting 210 seconds. Using a double-ischemia paradigm in which the animals were subjected to two periods of ischemia, there was apparently no accumulation of neuronal damage from the first ischemic episode to the second, provided the duration of the first period of ischemic depolarization did not exceed 90 seconds. Neuronal damage accumulated when the duration of the first ischemia episode exceeded 90 seconds, regardless of the duration of the reperfusion interval between the two ischemic insults. Finally, when the ischemic insult was spread over four separate episodes, each lasting 90 seconds (with a reperfusion interval of 5 minutes), neuronal damage was not found when the total depolarization period was less than 420 seconds.

CONCLUSIONS

The authors conclude that cumulative neuronal damage may be avoided by adopting an intermittent ischemia approach. The implications of these results for human surgery requiring temporary occlusion of the cerebral arteries are discussed.

Ischemic brain edema

Brain edema is a life-threatening complication of cerebral infarction. The molecular cascade initiated by cerebral ischemia includes the loss of membrane ionic pumps and cell swelling. Secondary formation of free radicals and proteases disrupts brain-cell membranes, causing irreversible damage. New diagnostic methods based on magnetic resonance imaging have markedly improved diagnostic accuracy. Cytotoxic and vasogenic edema is maximal by 24 to 72 hours after the ischemic event. Thrombolytics reperfuse tissue and improve outcome; when treatment is delayed, they can increase edema and blood-brain barrier opening. Although osmotherapy reduces brain water, and is used to treat ischemic edema, its efficacy remains to be proven. As the molecular events become clearer, novel treatments that block different stages of the injury cascade will be available for clinical testing.

Serial study of apparent diffusion coefficient and anisotropy in patients with acute stroke

BACKGROUND AND PURPOSE

We sought to characterize the evolution of apparent diffusion coefficient (ADC) and apparent diffusion anisotropy (ADA) in acute stroke and to evaluate their roles in predicting stroke evolution and outcome.

METHODS

We studied 26 stroke patients acutely (<24 hours), subacutely (3 to 5 days), and at outcome (3 months). Ratios of the ADC and ADA within a region of infarction and the normal contralateral region were evaluated and compared with the Canadian Neurological Scale, Barthel Index, and Rankin Scale.

RESULTS

Heterogeneity in ADC and ADA evolution was observed not only between patients but also within individual lesions. Three patterns of ADA evolution were observed: (1) elevated ADA acutely and subacutely; (2) elevated ADA acutely and reduced ADA subacutely; and (3) reduced ADA acutely and subacutely. At outcome, reduced ADA with elevated ADC was observed generally. We identified 3 phases of diffusion abnormalities: (1) reduced ADC and elevated ADA; (2) reduced ADC and reduced ADA; and (3) elevated ADC and reduced ADA. The ADA ratios within 12 hours correlated with the acute Canadian Neurological Scale (r=0.46, P=0.06), subacute Canadian Neurological Scale (r=0.55, P=0.02), outcome Barthel Index (r=0.62, P=0.01), and Rankin Scale (r=-0.77, P<0.0005) scores.

CONCLUSIONS

Combined ADC and ADA provide differential patterns of stroke evolution. Early ADA changes reflect cellular alterations in acute ischemia and may provide a potential marker to predict stroke outcome.