The mechanism of cerebral hypoxic-ischemic damage

Effects of riboflavin in the treatment of brain damage caused by oxygen deprivation: an integrative systematic review

Brain oxygen deprivation causes morphological damage involved in the formation of serious pathological conditions such as stroke and cerebral palsy. Therapeutic methods for post-hypoxia/anoxia injuries are limited and still have deficiencies in terms of safety and efficacy. Recently, clinical studies of stroke have reported the use of drugs containing riboflavin for post-injury clinical rehabilitation, however, the effects of vitamin B2 on exposure to cerebral oxygen deprivation are not completely elucidated. This review aimed to investigate the potential antioxidant, anti-inflammatory and neuroprotective effects of riboflavin in cerebral hypoxia/anoxia. After a systematic search, 21 articles were selected, 8 preclinical and 12 clinical studies, and 1 translational study. Most preclinical studies used B2 alone in models of hypoxia in rodents, with doses of 1-20 mg/kg (in vivo) and 0.5-5 µM (in vitro). Together, these works suggested greater regulation of lipid peroxidation and apoptosis and an increase in neurotrophins, locomotion, and cognition after treatment. In contrast, several human studies have administered riboflavin (5 mg) in combination with other Krebs cycle metabolites, except one study, which used only B2 (20 mg). A reduction in lactic acidosis and recovery of sensorimotor functions was observed in children after treatment with B2, while adults and the elderly showed a reduction in infarct volume and cognitive rehabilitation. Based on findings from preclinical and clinical studies, we conclude that the use of riboflavin alone or in combination acts beneficially in correcting the underlying brain damage caused by hypoxia/anoxia and its inflammatory, oxidative, and behavioral impairments.

Traumatic brain injury screening and neuropsychological functioning in women who experience intimate partner violence

Objective: The potential for traumatic brain injury (TBI) to occur as the result of intimate partner violence (IPV) has received increased interest in recent years. This study sought to investigate the possible occurrence of TBI in a group of women who survived IPV and to measure the specific profile of cognitive deficits using standardized neuropsychological measures. Method: A comprehensive questionnaire about abuse history; neuropsychological measures of attention, memory and executive functioning; and measures of depression, anxiety and post-traumatic stress disorder were given to women who were IPV survivors, women who were sexual assault (SA) survivors, and a comparison group of women who did not experience IPV or SA. Results: Overall, rates of potential TBI, as measured by the HELPS brain injury screening tool, were high and consistent with previous studies. Consistent with potential TBI, lower scores were demonstrated on measures of memory and executive functioning compared to survivors of SA or those not exposed to violence. Importantly, significant differences on measures of memory and executive functioning remained, after controlling for measures of emotion. Of note, cognitive changes were highest among women who experienced non-fatal strangulation (NFS) compared to IPV survivors who did not. Conclusions: Rates of TBI may be high in women who survive IPV, especially those who survive strangulation. Better screening measures and appropriate interventions are needed as well as larger studies that look at social factors associated with IPV.

Calcium channels and their blockers in intraocular pressure and glaucoma

Several factors besides high intraocular pressure assumed to be associated with the development and progression of glaucoma, and calcium channel blockers (CCBs) have been an anticipated option for glaucoma treatment by improving ocular perfusion and/or exerting neuroprotective effects on retinal ganglion cells with safety established in wide and long-term usage. Decrease in IOP has been reported after topical application of CCBs, however, the effect is much smaller and almost negligible after systemic application. Various CCBs have been reported to increase posterior ocular blood flow in vivo and to exert direct neuroprotection in neurons in vitro. Distribution of the drug at a pharmacologically active concentration in the posterior ocular tissues across the blood-brain barrier or blood-retina barrier, especially in the optic nerve head and retina where the ganglion cells mainly suffer from glaucomatous damage, is essential for clinical treatment of glaucoma. Improved visual functions such as sensitivity in the visual field test have been reported after administration of CCBs, but evidences from the randomized studies have been limited and effects of CCBs on blood flow and direct neuroprotection are hardly distinguished from each other.

Protective effects of minocycline against short-term ischemia-reperfusion injury in rat brain

The aim of this study was to assess the effects of minocycline on cerebral ischemia-reperfusion (I/R) injury in rats. The study was carried out on 24 male Wistar albino rats, weighing 200-250 g, which were divided into three groups: (i) control (n = 8), (ii) I/R (n = 8) and (iii) I/R + minocycline (n = 8). Minocycline was administrated at a dose of 90 mg/kg p.o. to the I/R group 48, 24 and 1 h before ischemia. Following bilateral exposure of the common carotid arteries by anterior cervical dissection and separation of the vagus nerve, I/R injury was performed by occlusion. Following reperfusion, malondialdehyde (MDA), superoxide dismutase, glutathione peroxidase and catalase levels in the blood and brain tissue, and creatine kinase (CK), CK-BB, lactate dehydrogenase (LDH), neuron-specific enolase (NSE) and protein S100β levels in the blood were measured and the histopathological changes were monitored. Regarding histopathological evaluation, symptoms of degeneration were significantly improved in the I/R + minocycline group compared to the I/R-only group. Statistical analysis of the biochemical parameters revealed significant differences in MDA (p < 0.001), nitric oxide (p < 0.05), CK (p < 0.05) and CK-MB (p < 0.05) levels between the I/R + minocycline group and the I/R group. According to the literature, the effect of minocycline is firstly assessed by LDH, CK-MB, NSE and S-100β analysis in addition to antioxidant status and histopathological analysis.

Preemptive regulation of intracellular pH in hippocampal neurons by a dual mechanism of depolarization-induced alkalinization

Numerous studies have documented the mechanisms that regulate intracellular pH (pH(i)) in hippocampal neurons in response to an acid load. Here, we studied the response of pH(i) to depolarization in cultured hippocampal neurons. Elevation of external K+ (6-30 mm) elicited an acid transient followed by a large net alkaline shift. Similar responses were observed in acutely dissociated hippocampal neurons. In Ca2+ -free media, the acid response was curtailed and the alkaline shift enhanced. DIDS blocked the alkaline response and revealed a prolonged underlying acidification that was highly dependent on Ca2+ entry. Similar alkaline responses could be elicited by AMPA, indicating that this rise in pH(i) was a depolarization-induced alkalinization (DIA). The DIA was found to consist of Cl- -dependent and Cl- -independent components, each accounting for approximately one-half of the peak amplitude. The Cl- -independent component was postulated to arise from operation of the electrogenic Na+ -HCO3- cotransporter NBCe1. Quantitative PCR and single-cell multiplex reverse transcription-PCR demonstrated message for NBCe1 in our hippocampal neurons. In neurons cultured from Slc4a4 knock-out (KO) mice, the DIA was reduced by approximately one-half compared with wild type, suggesting that NBCe1 was responsible for the Cl- -independent DIA. In Slc4a4 KO neurons, the remaining DIA was virtually abolished in Cl- -free media. These data demonstrate that DIA of hippocampal neurons occurs via NBCe1, and a parallel DIDS-sensitive, Cl- -dependent mechanism. Our results indicate that, by activating net acid extrusion in response to depolarization, hippocampal neurons can preempt a large, prolonged, Ca2+ -dependent acidosis.

Cognitive correlates with functional outcomes after anoxic brain injury: a case-controlled comparison with traumatic brain injury

OBJECTIVES

To assess the effectiveness of inpatient rehabilitation in adults who have sustained an anoxic brain injury (AnBI). Secondly, to identify areas of cognition that predict functional outcomes at discharge.

DESIGN

Retrospective, matched case-controlled study.

METHODS

Ten patients with moderate-to-severe AnBI and 10 patients with traumatic brain injury (TBI), treated in an inpatient neurorehabilitation programme, were matched on age, acute care length of stay and admission Functional Independence Measure (FIM). Functional outcome was assessed using the FIM and Disability Rating Scale (DRS).

RESULTS

Patients with AnBI performed worse on all measures of functional outcome relative to patients with TBI. Patients with AnBI achieved significantly lower FIM motor and cognitive gain compared with patients with TBI (11.5, SD 13.6 vs. 31.0, SD 19.7 and 2.4, SD 3.9 vs. 7.5, SD 4.2, respectively (p < 0.02)). DRS data showed similar trends of functional improvement between the groups. Several neuropsychometric tests correlated with functional outcome (p < 0.01).

CONCLUSIONS

Patients with AnBI had worse functional outcomes following rehabilitation than patients with TBI, confirming the results of previous reports. Poor cognitive function predicted poor functional outcomes on the FIM and somewhat on the DRS. Research is needed to assess why these differences occur and to improve or develop new effective rehabilitation treatments for AnBI.

Possible role of vitamin E, coenzyme Q10 and rutin in protection against cerebral ischemia/reperfusion injury in irradiated rats

PURPOSE

To investigate the possible role of vitamin E, coenzyme Q10 and rutin in ameliorating the biochemical changes in brain and serum induced by cerebral ischemia/reperfusion (I/R) in whole body γ-irradiated rats.

MATERIALS AND METHODS

Cerebral ischemia was induced in male Wistar rats (either irradiated or non-irradiated) followed by reperfusion.

RESULTS

I/R increased brain content of malondialdehyde (MDA) and depleted its glutathione (GSH) content with a compensatory elevation in cytosolic activities of glutathione peroxidase (GPx) and glutathione reductase (GR) enzymes. It also raised brain cytosolic lactate dehydrogenase (LDH) activity and calcium (Ca(2+)) level. Furthermore, I/R provoked an inflammatory response reflected by an increment in serum levels of the proinflammatory cytokines tumour necrosis factor-α (TNF-α) and interlukin-1β (IL-1β). Moreover, induction of I/R in irradiated rats resulted in a further increase in brain oxidative stress and cytosolic LDH activity, disturbed brain Ca(2+) homeostasis and exaggerated the inflammatory reaction. During irradiation, administration of each of vitamin E, coenzyme Q10 (CoQ10) and rutin to irradiated rats before induction of I/R, alleviated the brain oxidative stress. Moreover, these antioxidants caused attenuation of the rise of the cytosolic activities of GPx and GR. A lowering effect of the cytosolic LDH activity and Ca(2+) level were caused by treatment with antioxidants. Each of vitamin E and rutin revealed an anti-inflammatory action of these antioxidants, while CoQ10 had no effect on serum levels of TNF-α and IL-1β.

CONCLUSION

These findings indicate that supplementation with either vitamin E, CoQ10 or rutin ameliorated most of the biochemical changes induced by I/R in irradiated rat brain and serum.

Effect of Huwentoxin-I on the Fas and TNF apoptosis pathway in the hippocampus of rat with global cerebral ischemia

Neuronal injury is the most important reason for various brain injuries. Cytosolic Ca(2+) overloading has been proposed as one of the main cellular processes leading to neuronal death during cerebral ischemia. It is well accepted that Ca(2+) channel blockers can protect cerebral neurons from ischemic injury. In the present studies, we investigated the molecular mechanism for the neuro-protective effect of Huwentoxin-I (HWTX-I), a spider toxin selectively blocking N-type voltage-dependent Ca((2+)) channel, on rat models with global cerebral ischemia-reperfusion injury. Our studies demonstrated that HWTX-I could maintain the morphological stability of pyramidal cells in this model. Furthermore, HWTX-I could decrease the concentration of malon-dialdehyde, but increase the activity of superoxide dismutase and glutathione peroxidase. It also reduced the expression level of related factors of Fas and tumor necrosis factor death receptor apoptosis pathways in the hippocampus. In summary, HWTX-I has an obvious neuroprotective effect, which may act through its inhibition on a certain apoptosis pathway.

Effect of hypothermia on postmortem alterations in MAP2 immunostaining in the human hippocampus

Ischemic neuronal injury induce degradation of microtubule-associated protein 2 (MAP2). In addition to ischemia, postmortem brains show alterations in MAP2 immunoreactivity in the hippocampus, suggesting that the factors inducing cytoskeletal disruption in postmortem brain are similar to those in ischemic brains. Hypothermia reduces the severity of ischemic injury including disruption of MAP2 in the hippocampus. However, whether hypothermia reduces postmortem changes of MAP2 was not clear. In this study, we evaluated the effect of hypothermia on postmortem degradation of MAP2 in the human hippocampus at various postmortem intervals using immunohistochemistry. In postmortem brains without hypothermia (the normothermic group), the locus of MAP2 immunoreactivity moved from the dendrites to the cell bodies prior to becoming undetectable with increasing postmortem interval, particularly in the CA1-subiculum region. On the other hand, the change in MAP2 immunoreactivity was remarkably attenuated in brains of death from cold (the hypothermic group). The present study demonstrated that MAP2 disruption is remarkable in the CA1-subiculum region of autopsied brains and that hypothermia reduces the postmortem change of MAP2, as observed in ischemic brain. Therefore, immunostaining of MAP2 in the hippocampus could be used to diagnose hypothermia.

Effect of hypothermia on postmortem alterations in MAP2 immunostaining in the human hippocampus

Ischemic neuronal injury induce degradation of microtubule-associated protein 2 (MAP2). In addition to ischemia, postmortem brains show alterations in MAP2 immunoreactivity in the hippocampus, suggesting that the factors inducing cytoskeletal disruption in postmortem brain are similar to those in ischemic brains. Hypothermia reduces the severity of ischemic injury including disruption of MAP2 in the hippocampus. However, whether hypothermia reduces postmortem changes of MAP2 was not clear. In this study, we evaluated the effect of hypothermia on postmortem degradation of MAP2 in the human hippocampus at various postmortem intervals using immunohistochemistry. In postmortem brains without hypothermia (the normothermic group), the locus of MAP2 immunoreactivity moved from the dendrites to the cell bodies prior to becoming undetectable with increasing postmortem interval, particularly in the CA1-subiculum region. On the other hand, the change in MAP2 immunoreactivity was remarkably attenuated in brains of death from cold (the hypothermic group). The present study demonstrated that MAP2 disruption is remarkable in the CA1-subiculum region of autopsied brains and that hypothermia reduces the postmortem change of MAP2, as observed in ischemic brain. Therefore, immunostaining of MAP2 in the hippocampus could be used to diagnose hypothermia.

Anoxic Versus Traumatic Brain Injury: Amount of Tissue Loss, Not Etiology, Alters Cognitive and Emotional Function

Research in neuropsychology suggests that the etiology of a neurologic injury determines the neuropathological and neuropsychological changes. This study compared neuropsychological outcome in subjects who had traumatic brain injury (TBI) with subjects who had anoxic brain injury (ABI), who were matched for age, gender, and ventricle-to-brain ratio. There were no group differences for morphologic or neuropsychological measures. Both groups exhibited impaired memory, attention, and executive function, as well as slowed mental processing speed. Intelligence correlated with whole brain volume, and measures of memory correlated with hippocampal atrophy. There was no unique contribution of hippocampal atrophy on neuropsychological outcome between the groups. In the absence of localized lesions, the amount of neural tissue loss, rather than etiology, may be the critical factor in neuropsychological outcome.

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.

In, out, shake it all about: elevation of [Ca2+]i during acute cerebral ischaemia

Because of the extensive second messenger role played by calcium, free intracellular calcium levels are strictly regulated. Under normal physiological conditions, this is achieved through a combination of restricted calcium entry, efficient efflux and restricted intracellular mobility. Overall, the process of regulating free calcium is dependent on ATP derived from oxidative metabolism. Under conditions of cerebral ischaemia, ATP levels fall rapidly and calcium homeostasis becomes significantly disturbed resulting in the initiation of calcium-dependent neurodegenerative processes. In this review, the mechanisms underlying physiological calcium homeostasis and the links between calcium disregulation and neurodegeneration will be discussed.

A newborn piglet study of moderate hypoxic-ischemic brain injury by 1H-MRS and MRI

Cerebral hypoxia-ischemia (HI) is an important cause of perinatal brain damage in the term newborn. The areas most affected are the parasagittal regions of the cerebral cortex and, in severe situations, the basal ganglia. The aim of this study was to show that the newborn piglet model can be used to produce neuropathology resulting from moderate HI insult and to monitor damage for 7 days. Two acute cerebral HI were induced in newborn Large White piglets by reducing the inspired oxygen fraction to 4% and occluding the carotid arteries. Newborn piglets were resuscitated, extubated and monitored for 7 days. (31)P magnetic resonance spectroscopy (MRS) offers the ability to monitor the severity of the HI insults. Lactate (Lac) was detected in the HI group at 2 h, 3 days and 5 days after insult by (1)H MRS. Lac/n-acetylaspartate and Lac/choline and Lac/creatine ratios increased significantly (p < 0.01) in the HI group 2 h after HI insults and remained high over 7 days. For the HI group, mean T(2) values increased significantly in the parietal white matter (subcortical) for 5 days after HI insult [117.5 (+/-7.4) to 158.5 (+/-19.2) at T+3 days, 167.7 (+/-15.4) at T+5 days and 160.9 (+/-10.1) at T+7 days (p < 0.01)]. This newborn piglet model of moderate HI brain injury with reproducible cerebral damage could be use as reference for the study of neuroprotective strategy for a period of 7 days.

Short-term, delayed, and working memory are impaired during hypoglycemia in individuals with type 1 diabetes

OBJECTIVE

To examine the effects of acute insulin-induced hypoglycemia on short-term, delayed, and working memory in individuals with type 1 diabetes.

RESEARCH DESIGN AND METHODS

A hyperinsulinemic glucose clamp was used to maintain arterialized blood glucose level at either 4.5 mmol/l (euglycemia) or 2.5 mmol/l (hypoglycemia) on two separate occasions in 16 adults with type 1 diabetes. The participants completed tests of immediate and delayed verbal memory, immediate and delayed visual memory, and working memory during each experimental condition. Two other mental tests, the Trail Making B Test and the Digit Symbol Test, were also administered.

RESULTS

Performance in tests of immediate verbal and immediate visual memory was significantly impaired during hypoglycemia. The effect of hypoglycemia on working memory and delayed memory was more profound. Performance in the nonmemory tests, the Trail Making B Test, and the Digit Symbol Test also deteriorated during hypoglycemia.

CONCLUSIONS

All of the memory systems examined in the present study were affected significantly by acute hypoglycemia, particularly working memory and delayed memory. Mild (self-treated) hypoglycemia is common in individuals with insulin-treated diabetes; therefore, these observed effects of hypoglycemia on memory are of potential clinical importance because they could interfere with many everyday activities.

Programmed cell death induced by glutathione depletion in PC 12 cells is blocked by inhibitors of 12 lipoxygenase, but does not appear to be mediated through the formation of 12 HETE derivatives

Lipoxygenase metabolites have been postulated to be involved in the degenerative events provoked by oxidative stress in neuronal and nonneuronal targets, but their roles remain controversial. In the present work, we investigated the putative role of 12 lipoxygenase metabolites in the programmed cell death induced by glutathione depletion in PC 12 cells. Determinations of 12 lipoxygenase expression and activity reveal the presence of the enzyme in PC 12 cells, but the formation of arachidonate metabolites appears rather low and is not influenced by glutathione depletion. In addition, although the death induced by buthionine sulfoximine (BSO) treatment is abolished by known inhibitors of lipoxygenase enzymes, dexamethasone, a potent steroidal inhibitor of both cyclooxygenase and lipoxygenase pathways, fails to protect the cells from BSO-induced degeneration. Finally, incubation of the cells for 24 h in the presence of exogenous 12 HETE did not induce any significant decrease in cell viability. Our results indicate that 12 lipoxygenase is unlikely to play a major role in the process of cell degeneration provoked by glutathione depletion.

Upregulation of phospholipase D in astrocytes in response to transient forebrain ischemia

Previous in vitro studies using cell cultures or brain slices have demonstrated that phospholipase D (PLD) in the nervous system is involved in the signaling mechanism in response to a variety of agonists. However, little is known about the pathophysiological role of PLD-mediated signaling in the adult brain. We examined the changes in the expression of a PLD isozyme, PLD1, in the adult rat hippocampus, using immunological approaches and an assay for PLD activity after transient forebrain ischemia (four-vessel occlusion model) that results in the selective delayed death of CA1 pyramidal cells and induces reactive astrocytes in the CA1 subfield. In the control hippocampus, PLD1 the level of immunoreactivity was very low. After ischemia, in parallel with the results of Western blot analysis and the PLD activity assay, immunohistochemical analysis of PLD1 demonstrated that the immunoreactive proteins peaked at 7-14 days and were most prominent in the CA1 and the dentate hilar region. The temporal and spatial patterns of immunoreactivity of both PLD1 and glial fibrillary acidic protein (GFAP) were very similar, indicating that reactive astrocytes express PLD1, confirmed by double staining for PLD1 and GFAP. These results demonstrate that reactive astrocytes upregulate PLD in vivo after injury in the adult rat hippocampus.

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.

Expression of nerve growth factor in astrocytes of the hippocampal CA1 area following transient forebrain ischemia

We have examined by immunoassay and immunohistochemistry, the expression of nerve growth factor in the rat hippocampus, one to 28 days after transient forebrain ischemia. In the CA1 area, the overall level of nerve growth factor expression remained constant over the first three days of reperfusion while it increased by about 45% of control levels after longer postischemic periods. In contrast, a slight decrease in nerve growth factor levels, which was most prominent at three days postlesion, was observed in the other hippocampal regions. Immunohistochemical analysis of the distribution of nerve growth factor showed that its expression was up-regulated in astrocytes but not in microglia of the postischemic CA1 region and that the intensity and temporal profile of the changes in nerve growth factor immunostaining in these cells, was consistent with that observed in the immunoassay. Interestingly, the regulation of the nerve growth factor expression in reactive astrocytes of the postischemic CA1 area closely parallels that of kainate receptor subunits GluR5-7, raising the possibility of a cause-effect relationship. These results indicate that after ischemia nerve growth factor expression is up-regulated in reactive astrocytes suggesting that these cells may contribute to rescuing damaged neurons by means of increasing nerve growth factor production.

Electrophysiological changes of CA3 neurons and dentate granule cells following transient forebrain ischemia

The electrophysiological responses of CA3 pyramidal neurons and dentate granule (DG) cells in rat hippocampus were studied after transient forebrain ischemia using intracellular recording and staining techniques in vivo. Approximately 5 min of ischemic depolarization was induced using 4-vessel occlusion method. The spike threshold and rheobase of CA3 neurons remained unchanged up to 12 h following reperfusion. No significant change in spike threshold was observed in DG cells but the rheobase transiently increased 6-9 h after ischemia. The input resistance and time constant of CA3 neurons increased 0-3 h after ischemia and returned to control ranges at later time periods. The spontaneous firing rate in CA3 neurons transiently decreased shortly following reperfusion, while that of DG cells progressively decreased after ischemia. In CA3 neurons, the amplitude and slope of excitatory postsynaptic potentials (EPSPs) transiently decreased 0-3 h after reperfusion, and the stimulus intensity threshold for EPSPs transiently increased at the same time. No significant changes in amplitude and slope of EPSPs were observed in DG cells, but the stimulus intensity threshold for EPSPs slightly increased shortly after reperfusion. The present study demonstrates that the excitability of CA3 pyramidal neurons and DG cells after 5 min ischemic depolarization is about the same as control levels, whereas the synaptic transmission to these cells was transiently suppressed after the ischemic insult. These results suggest that synaptic transmission is more sensitive to ischemia than membrane properties, and the depression of synaptic transmission may be a protective mechanism against ischemic insults.

Long-term neuroprotection by benzodiazepine full versus partial agonists after transient cerebral ischemia in the gerbil [corrected]

The ability of diazepam, a benzodiazepine full agonist, and imidazenil, a benzodiazepine partial agonist, to protect hippocampal area CA1 neurons from death for at least 35 days after cerebral ischemia was investigated. Diazepam (10 mg/kg) administered to gerbils 30 and 90 minutes after forebrain ischemia produced significant protection of hippocampal area CA1 pyramidal neurons 7 days later. In gerbils surviving for 35 days, diazepam produced the same degree of neuroprotection (70% +/- 30%) in the hippocampus compared with 7 days after ischemia. The therapeutic window for diazepam was short; there was no significant neuroprotection when the administration of diazepam was delayed to 4 hours after ischemia. The neuroprotective dose of diazepam also produced hypothermia (approximately 32 degrees C) for several hours after injection. To assess the role of hypothermia in neuroprotection by diazepam, hypothermia depth and duration was simulated using a cold-water spray in separate gerbils. Seven days after ischemia, neuroprotection by hypothermia was similar to that produced by diazepam. However, 35 days after ischemia, there was no significant protection by hypothermia, suggesting that hypothermia does not play a significant role in long-term diazepam neuroprotection. Imidazenil (3 mg/kg), which produced only minimal hypothermia, protected area CA1 of hippocampus to the same degree as that by diazepam 7 days after ischemia. At 35 days after ischemia, significant protection remained, but it was considerably reduced compared with 7 days. Like diazepam, the therapeutic window for imidazenil was short. Imidazenil neuroprotection was lost when the drug was administered as early as 2 hours after ischemia. The ability of ischemia to produce deficits in working memory and of benzodiazepines to prevent the deficits also was investigated. Gerbils trained on an eight-arm radial maze before ischemia demonstrated a significant increase in the number of working errors 1 month after ischemia. The ischemia-induced deficits in working memory were completely prevented by diazepam but not by imidazenil. There was a significant, but weak, negative correlation between the degree of CA1 pyramidal cell survival and the number of working errors in both the diazepam and imidazenil groups. Thus, if given early enough during reperfusion, both benzodiazepine full and partial agonists are neuroprotective for at least 35 days, but the lack of sedating side effects of imidazenil must be weighed against its reduced efficacy.

Calcium influx from the extracellular space promotes NADH hyperoxidation and electrical dysfunction after anoxia in hippocampal slices

A characteristic event during reperfusion after cerebral ischemia in vivo, and reoxygenation after anoxia in vitro, is hyperoxidation of the electron carriers of the mitochondrial respiratory chain. Current studies have tested the hypothesis that there is a relation among calcium molecules derived from extracellular sources, mitochondrial hyperoxidation, and electrical recovery after anoxia in hippocampal slices. Rat hippocampal slices were superfused with artificial cerebrospinal fluids (ACSF) containing calcium chloride (CaCl2) in concentrations of: 0.5, 1, 2, and 4 mmol/L. Slices were made anoxic and then allowed to recover for 60 minutes. Reduction-oxidation shifts of NADH were measured by rapid-scanning spectrofluorometry. Synaptic activity was indicated by population spike amplitudes in the CA1 pyramidal cell subfield of the hippocampus in response to stimulation of the Schaffer collaterals. Low calcium ACSF concentrations ameliorated NADH hyperoxidation and improved synaptic transmission recovery after anoxia. High calcium ACSF concentrations had opposite effects. These data suggest a link between mitochondrial hyperoxidation and electrical recovery after postanoxia reoxygenation and support the hypothesis that cytosolic calcium overload promotes mitochondrial hyperoxidation and limits electrical recovery.

SNX-111, a novel, presynaptic N-type calcium channel antagonist, is neuroprotective against focal cerebral ischemia in rabbits

Cytosolic Ca2+ overload has been proposed as a main cause of neuronal injury during cerebral ischemia. SNX-111, a synthetic product of the naturally occurring omega-conotoxin MVIIA, is a novel, presynaptic N-type Ca2+ channel antagonist and has been reported to be neuroprotective against cerebral ischemia. We studied the neuroprotective effects of SNX-111 in a rabbit model of focal cerebral ischemia. New Zealand white male rabbits (2.5-3.5 kg) were given 1 mg/kg/h i.v. SNX-111 (n=8) or normal saline (n=8) 10 min after onset of a 2-h period of transient focal cerebral ischemia induced by occlusion of the left middle cerebral, anterior cerebral and internal carotid arteries followed by 4 h reperfusion. SNX-111 significantly attenuated overall cortical ischemic neuronal damage by 44% (saline, 38.7+/-3.0%; SNX-111, 21.5+/-6.0%, P<0.05) and regions of hyperintensity on T2-weighted MRI by 30% (saline, 70.6+/-4.0%; SNX-111, 49.3+/-11.0%, P<0.05). No significant difference in (regional cerebral blood flow) rCBF or MAP (mean arterial blood pressure) was found between SNX-111- and saline-treated rabbits suggesting that neuroprotection is due to a cellular effect. We conclude that SNX-111 reduces ischemic injury in this model. Its use as a clinical neuroprotective agent for cerebrovascular surgery or stroke should be investigated further.

Free radical-induced elevation of ornithine decarboxylase activity in developing rat brain slices

OBJECTIVE

In developing brain, we have previously shown both in vivo [L.D. Longo, S. Packianathan, J.A. McQueary, R.B. Stagg, C.V. Byus and C.D. Cain, Acute hypoxia increases ornithine decarboxylase activity and polyamine concentrations in fetal rat brain, Proc. Natl. Acad. Sci. USA, Vol. 90 (1993) 692-696] and in vitro [S. Packianathan, C.D. Cain, B.H. Liwnicz and L.D. Longo, Ornithine decarboxylase activity in vitro in response to acute hypoxia: a novel use of newborn rat brain slices, Brain Res., Vol. 688 (1995) 61-71] that acute hypoxia is associated with a significant increase in ornithine decarboxylase (ODC) activity and polyamine concentrations. We tested the hypothesis that oxygen free radicals induce an increase in ODC activity similar to that of hypoxia and that both this and the hypoxia-induced response are inhibited by free radical scavengers.

MATERIALS AND METHODS

Slices of cerebrum, 300-500 microm thick, were made from P3 newborn Sprague-Dawley rat pups and equilibrated for 1 h in artificial cerebrospinal fluid continuously bubbled with 95% O2/5% CO2. Free radical-induced ODC activity response was measured beginning after a 1-h recovery period. Experiments were performed on slices treated with 5 X 10(-7) M xanthine (X) + 10 mU/ml xanthine oxidase (XO), with or without the free radical scavengers superoxide dismutase (SOD; 100 U/ml), catalase (CAT; 700 U/ml) or glutathione peroxidase (GPX; 3 U/ml). We also quantified slice malonaldehyde concentrations in response to hypoxia (21% O2/5% CO2/74% N2).

RESULTS

Under control conditions, ODC activity was stable during the 2-h post-recovery period. In response to X/XO treatment, ODC activity increased 2.3-fold at 1.5 h post-recovery. In examining ODC activity as a function of xanthine dose, we noted that ODC activity increased in response to 2.5 X 10(-7) M xanthine; however, it decreased in response to 7.5 X 10(-7) M or higher concentrations. Free radical-induced ODC activity was significantly decreased by addition of the free radical scavengers, SOD, CAT or GPX. In addition, the hypoxic-induced increases in ODC activity and malonaldehyde concentration was also eliminated by the addition of SOD with CAT.

CONCLUSIONS

(1) Oxygen free radicals, particularly hydroxyl radical (OH.), appear to trigger an induction of ODC activity in newborn rat cerebrum slices. (2) Oxygen free radicals also appear to mediate the hypoxic-induced increase in ODC activity. (3) Any consequent increase in polyamine synthesis may have profound effects on neurogenesis and neurodifferentiation in the developing brain.

Postischemic, systemic administration of polyamine-modified superoxide dismutase reduces hippocampal CA1 neurodegeneration in rat global cerebral ischemia

Antioxidant enzymes such as superoxide dismutase (SOD) have shown neuroprotective effects in animal models of cerebral ischemia, but only at very high doses. Modifications to increase the plasma half-life or blood-brain barrier (BBB) permeability of SOD have resulted in limited neuroprotective effects. No one has demonstrated neuroprotection with postischemic administration. The specific aim of the present study was to administer systemically a polyamine-modified SOD, having increased BBB permeability and preserved enzymatic activity, following global cerebral ischemia in rats and analyze the effects on the selective vulnerability of CA1 hippocampal neurons. Following 12 min of four-vessel occlusion, global cerebral ischemia, male Wistar rats were dosed (i.v.) with either saline, native SOD (5000 U/kg), polyamine-modified SOD (5000 U/kg), or enzymatically inactive, polyamine-modified SOD (2.1 mg/kg) twice daily for 3 days. Neuroprotective effects on hippocampal CA1 neurons were assessed using standard histological methods. Saline-treated animals had very few remaining CA1 neurons (1.44 +/- 0.60 neurons/reticle; x +/- S.E.M.) compared to sham rats (58.57 +/- 0.69). Native (10.38 +/- 2.96) or inactive, polyamine-modified SOD (7.32 +/- 2.68) did not show significant neuroprotective effects. Polyamine-modified SOD, however, resulted in the survival of significantly more CA1 neurons (24.61 +/- 5.90; P < 0.01). Postischemic, systemic administration of polyamine-modified SOD, having increased BBB permeability and preserved enzymatic activity, significantly reduced hippocampal CA1 neuron loss following global cerebral ischemia. Similar modification of other antioxidant enzymes and neurotrophic factors with polyamines may provide a useful technique for the systemic delivery of therapeutic proteins across the BBB for the treatment of stroke and other neurodegenerative disorders.

Expression of ionotropic glutamate receptor subunits in glial cells of the hippocampal CA1 area following transient forebrain ischemia

We examined by immunohistochemistry the expression of ionotropic glutamate receptor subunits (GluRs) in glial cells of the rat dorsal hippocampus 3 to 28 days after transient forebrain ischemia. In general, the expression of GluRs at all time points studied underwent a drastic reduction that was primarily restricted to the CA1 region. In addition to the disappearance of GluRs as a result of neuronal cell death, we observed their expression in reactive glial cells. The time course of expression and the subunits involved were different for astrocytes and microglia. Reactive astrocytes exhibited kainate, GluR5-7, and N-methyl-D-aspartate (NMDA), NR2A/B, receptor subunits, both of which were maximally expressed approximately 4 weeks after ischemia. In contrast, reactive microglia expressed GluR4 and NR1 subunits, alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA), and NMDA receptor subtypes, respectively, with maximal expression observed between 3 and 7 days after ischemia. These results demonstrate that specific types of GluRs are expressed in reactive glial cells after ischemia and that, overall, their expression levels peak around or after the periods of maximal astrogliosis and microgliosis. Thus, modulation of GluR expression may be one of the molecular components accompanying the gliotic process.

Hippocampal damage and cytoskeletal disruption resulting from impaired energy metabolism. Implications for Alzheimer disease

To determine if impaired energy metabolism might contribute to some aspects of Alzheimer disease (AD), including the vulnerability of the CA1 region of the hippocampal formation and the altered cytoskeleton evident in neurofibrillary tangles, we examined the effects of metabolic poisons on neuronal damage and cytoskeletal disruption in the hippocampal formation. Intrahippocampal injection of 3-nitropropionic acid (3-NP) and malonic acid resulted in neuronal death, particularly in CA1. Cytoskeletal disruption included loss of dendritic MAP2, but sparing of axonal gamma. MK-801 (a noncompetitive NMDA receptor antagonist) did not atentuate the lesions produced by intrahippocampal injection of malonate. MK-801, however, was effective against intrastriatal malonate. Acute systemic 3-NP resulted in neuronal damage and cytoskeletal disruption in the CA1 region of the hippocampal formation, including an extensive loss of MAP2 immuno-reactivity, but sparing of gamma. The neuronal loss in CA1 was delayed as compared to striatum. Chronic intraventricular infusion of 3-NP produced a different pattern of neuronal damage. Loss of gamma-1 immuno-reactivity was observed in CA3 and CA1 s. orients, whereas MAP2 immunostaining was preserved. These results demonstrate that chronic and acute administration of metabolic inhibitors produce distinct patterns of neuronal damage and cytoskeletal disruption. The results further suggest a differential involvement of the NMDA receptor in malonate-induced neuronal damage in striatum as compared to the hippocampus. The pattern of neuronal damage and cytoskeletal disruption observed following acute metabolic impairment resembled some aspects of neurofibrillary pathology in AD, but did not result in gamma hyperphosphorylation.

The effects of ifenprodil and eliprodil on voltage-dependent Ca2+ channels and in gerbil global cerebral ischaemia

Ifenprodil and eliprodil are both non-competitive NMDA receptor antagonists which have been shown to inhibit neuronal Ca2+ channel currents. We have examined the effects of these agents on two defined subtypes of voltage-dependent Ca2+ channels and in the gerbil model of global cerebral ischaemia. Recombinantly expressed human alpha 1B-1 alpha 2b beta 1-3 Ca2+ subunits in HEK293 cells, which results in an omega-conotoxin-sensitive neuronal N-type voltage-dependent Ca2+ channel and omega-Aga IVA sensitive Ca2+ channels (P-type) in acutely isolated cerebellar Purkinje neurones were reversibly inhibited by ifenprodil and eliprodil. Human N-type Ca2+ channel currents were inhibited by ifenprodil and eliprodil with IC50 values of 50 microM and 10 microM respectively whereas P-type Ca2+ channel currents were inhibited reversibly by ifenprodil and eliprodil with approximate IC50 values of 60 microM and 9 microM respectively. Maximum current block observed for both channel subtypes was approximately 80% for both ifenprodil and eliprodil. For neuroprotection studies, animals were subjected to 5 min bilateral carotid artery occlusion with or without administration of either ifenprodil or eliprodil (5, 10 or 20 mg/kg i.p.) immediately after surgery followed by two further doses (2.5, 5 or 10 mg/kg, respectively) at 3 and 6 h post-occlusion. Both compounds provided significant protective effects against ischaemia-induced neurodegeneration in the CA1 region of the hippocampus. These results indicate that both ifenprodil and eliprodil protect against ischaemia-induced neurodegeneration when administered post-occlusion and that they also block N and P-type voltage-dependent Ca2+ channels.

Ischemia and lesion induced imbalances in cortical function

Cortical structures are often critically affected by ischemic and traumatic lesions which may cause transient or permanent functional disturbances. These disorders consist of changes in the membrane properties of single cells and alterations in synaptic network interactions within and between cortical areas including large-scale reorganizations in the representation of the peripheral input. Prominent functional modifications consisting of massive membrane depolarizations, suppression of intracortical inhibitory synaptic mechanisms and enhancement of excitatory synaptic transmission can be observed within a few minutes following the onset of cortical hypoxia or ischemia and probably represent the trigger signals for the induction of neuronal hyperexcitability, irreversible cellular dysfunction and cell death. Pharmacological manipulation of these early events may therefore be the most effective approach to control ischemia and lesion induced disturbances and to attenuate long-term neurological deficits. The complexity of secondary structural and functional alterations in cortical and subcortical structures demands an early and powerful intervention before neuronal damage expands to intact regions. The unsatisfactory clinical experience with calcium and N-methyl-D-aspartate antagonists suggests that this result might be achieved with compounds that show a broad spectrum of actions at different ligand-activated receptors, voltage-dependent channels and that also act at the vascular system. Whether the same therapy strategies developed for the treatment of ischemic injury in the adult brain may be applied for the immature cortex is questionable, since young cortical networks with a high degree of synaptic plasticity reveal a different response pattern to hypoxic and ischemic insults. Age-dependent molecular biological, morphological and physiological parameters contribute to an enhanced susceptibility of the immature brain to these noxae during early ontogenesis and have to be investigated in more detail for the development of adequate clinical therapy.

The novel sigma ligand JO 1994 protects against ischaemia-induced behavioural changes, cell death and receptor dysfunction in the gerbil

To assess the effects of the novel sigma ligand JO 1994 on behavioural, histological and autoradiographical changes following global ischaemia, the Mongolian gerbil was used. Three experiments were carried out and in each case ischaemia was induced by bilateral carotid occlusion (BCO) for 5 min. In the first experiment we examined the effects of JO 1994 administered at doses of 0.25, 0.5 and 1 mg/kg i.p. 1 h before 5 min BCO on histological parameters 96 h after surgery. In the second experiment the effects of JO 1994 administered at doses of 2.5, 5, 10 and 20 mg/kg i.p. 1 h before 5 min BCO on locomotor activity 24, 48 and 72 h after surgery and on histological parameters 96 h after surgery was examined. In the third experiment the effects of JO 1994 (2.5 and 5 mg/kg i.p.), BMY 14802 (1 and 10 mg/kg i.p.) and MK-801 (2.5 mg/kg i.p.) administered 30 min, 6, 24, 48, 72, 96 and 120 h post-surgery on the densities of M1 and M2 muscarinic receptors in 35 brain regions, 7 days after surgery was examined. Results indicated that 5 min bilateral carotid occluded animals were hyperactive 24, 48 and 72 h after surgery. JO 1994 attenuated this hyperactivity. Extensive neuronal death was observed in the CA1 layer of the hippocampus in 5 min BCO animals 96 h after surgery. The low doses of JO 1994 (0.25, 0.5 and 1 mg/kg) had no effect on the ischaemia-induced cell death. However JO 1994 (2.5, 5, 10 and 20 mg/kg i.p.) protected against the neuronal death of cells in the CA1 layer (P < 0.01-0.03). There was a large loss of M1 and M2 receptors in the CA1 regions of the hippocampus. MK-801, BMY 14802 and JO 1994 provided significant (P < 0.01) protection against this ischaemia-induced receptor loss.

The sigma receptor ligand JO 1784 (igmesine hydrochloride) is neuroprotective in the gerbil model of global cerebral ischaemia

To assess the effects of the novel sigma receptor ligand JO 1784 ((+)-N-cyclopropyl-methyl-N-methyl-1,4-diphenyl-1-yl-but-3-en-1-ylami ne, hydrochloride or igmesine hydrochloride) on behavioural and histological changes following cerebral ischaemia, the gerbil model of cerebral ischaemia was used. Two experiments were carried out. In the first animals were either sham operated, subjected to 5 min of bilateral carotid occlusion or administered JO 1784 (25, 50, 75 or 100 mg/kg p.o.) 1, 24 and 48 h after 5 min bilateral carotid occlusion and histological evaluation carried out 96 h after surgery. In the second experiment the effects of JO 1784 administered at a dose of 100 mg/kg i.p. 30 min, 6, 24 and 48 h post-surgery on home cage activity and nitric oxide (NO) synthase activity in the cortex, hippocampus, cerebellum and brain stem 4 days after surgery was examined. Extensive neuronal death was observed in the CA1 region of 5 min occluded animals. JO 1784 (50, 75 and 100 mg/kg) provided significant protection against this ischaemia-induced cell death (P < 0.03-0.005). In the second experiment a large increase in home cage activity was observed for 5 min occluded animals for 12 h after surgery (P = 0.0018-0.02). A large increase in NO synthase activity was observed in all brain regions for 5 min occluded animals. Post-administration of JO 1784 attenuated the ischaemia-induced hyperactivity and increased NO synthase activities.(ABSTRACT TRUNCATED AT 250 WORDS)

Severe anoxia with and without concomitant brain atrophy and neuropsychological impairments

Significant anoxia may cause a variety of neuropathologic changes as well as cognitive deficits. We have recently seen 3 patients who have suffered severe anoxic episodes all with initial Glasgow Coma Scores (GCS) of 3 with sustained coma for 10-14 d. All 3 patients had extended hospitalizations and rehabilitation therapy. A neuropsychological test battery was administered and volumetric analyses of MRI scans were carried out in each case at least 6 mo postinjury. Two of the patients display distinct residual cognitive and neuropathologic changes while 1 patient made a remarkable recovery without evidence of significant morphological abnormality. These three cases demonstrate, that even with similar admission GCS, the outcome is variable and the degree of neuropsychological impairment appears to match the degree of morphologic abnormalities demonstrated by quantitative MR image analysis. An important finding of this study is that even though subjects with an anoxic insult exhibit severe cognitive and memory impairments along with concomitant morphologic changes, their attention/concentration abilities appear to be preserved. MR morphometry provides an excellent means by which neural structural changes can be quantified and compared to neuropsychological and behavioral outcomes.

Ornithine decarboxylase activity in vitro in response to acute hypoxia: a novel use of newborn rat brain slices

In fetal as well as newborn rats, acute hypoxic exposure results in significantly elevated brain ornithine decarboxylase (ODC) activity, polyamine concentrations, and ODC mRNA. The interpretations of these in vivo hypoxic-induced changes, however, are complicated by maternal confounding effects. To test the hypothesis that acute hypoxia will also increase ODC activity in vitro, we developed a brain slice preparation which eliminates such maternal effects. Sections of whole cerebrum, approximately 300-500 microns thick, were made from 3- to 4-day old Sprague-Dawley rat pups. The slices were equilibrated for 1 h in artificial cerebrospinal fluid (ACSF) continuously bubbled with 95% O2/5% CO2, prior to induction of hypoxia. We induced hypoxia by changing the oxygen concentration to 40%, 30%, 21%, 15%, 10%, or 0% O2, all with 5% CO2 and balance N2. In the normoxic control brain slices, low but stable basal ODC activity persisted for up to 5 h post-sacrifice. Slices in ACSF treated with bovine serum albumin (BSA), or both BSA and fetal bovine serum (FBS), however, showed stable ODC activity values 2- to 3-fold higher than slices in ACSF alone, for up to 5 h. In response to acute hypoxia (i.e., 15, 21, and 30% O2), ODC activity was elevated 1.5- to 2-fold above control values between 1 and 2 h after initiation of hypoxia. Qualitative light and electron microscopic examination of the neonatal brain slices following 2 h hypoxic exposure suggested that the great majority of cells did not show severe hypoxic damage or necrosis. It was concluded that: (1) in neonatal rat brain slices in vitro, stable ODC activity values approximating the whole brain ODC activity seen at sacrifice, can be maintained for several hours; (2) the in vivo hypoxic-induced increase in ODC activity can be approximated in vitro; (3) the neonatal rat brain slice preparation may be an alternative to other methods for studying hypoxic-induced ODC enzyme kinetics, or other brain enzymes, without maternal confounding effects; and (4) ODC activity may be an indicator of active metabolism within the newborn brain slice both in normoxia and hypoxia.

Hypoxia, excitotoxicity, and neuroprotection in the hippocampal slice preparation

The excitotoxic hypothesis postulates a central role for the excitatory amino acids (EAAs) and their receptors in the neuronal damage that ensues cerebral ischemia-hypoxia and numerous other brain disorders. A major premise of the excitotoxic hypothesis is that neuronal protection can be achieved via blockade of EAA receptors with specific antagonists. This paper describes the use of the rat hippocampal slice preparation in the evaluation of various EAAs and their analogues for their potency as excitotoxins (agonists) and antagonists of the NMDA and the kainate/AMPA glutamate receptor subtypes. The hypersensitivity of hypoxic hippocampal slices to the presence of excitotoxins provided us with an inexpensive, sensitive tool to distinguish between structurally similar compounds. Moreover, these studies indicate that hypoxic neuronal damage cannot solely result from an excitotoxic mechanism; the involvement of voltage-dependent calcium channels in such damage is likely, as is evident from experiments performed in calcium-depleted medium and with the non-competitive NMDA antagonist MK-801. At sub-toxic doses, quinolinate, a tryptophan metabolite implicated in Huntington's disease, appears to be a strong potentiator of the toxicity of all excitotoxins tested.

Ischaemia-induced long-term hyperexcitability in rat neocortex

The long-term structural and functional consequences of transient forebrain ischaemia were studied with morphological, immunohistochemical and in vitro electrophysiological techniques in the primary somatosensory cortex of Wistar rats. After survival times of 10-17 months postischaemia, neocortical slices obtained from ischaemic animals were characterized by a pronounced neuronal hyperexcitability in comparison with untreated age-matched controls. Extra- and intracellular recordings in supragranular layers revealed all-or-none long-latency recurrent responses to orthodromic synaptic stimulation of the afferent pathway. These responses were characterized by durations up to 1.7 s, by multiple components and by repetitive synaptic burst discharges. The reversible blockade of this late activity by DL-amino-phosphonovaleric acid (APV) suggested that this activity was mediated by N-methyl-D-aspartate (NMDA) receptors. The peak conductance of inhibitory postsynaptic potentials was significantly smaller in neurons recorded in neocortical slices obtained from ischaemic animals than those from the controls. However, the average number of parvalbumin (PV)-labelled neurons per mm3, indicative of a subpopulation of GABAergic interneurons, and the average number and length of dendritic processes arising from PV-containing cells was not significantly different between ischaemic and control cortex. The prominent dysfunction of the inhibitory system in ischaemic animals occurred without obvious structural alterations in PV-labelled cells, indicating that this subpopulation of GABAergic interneurons is not principally affected by ischaemia. Our data suggest a long-term down-regulation of inhibitory function and a concurrent NMDA receptor-mediated hyperexcitability in ischaemic neocortex. These alterations may result from structural and/or functional properties of inhibitory non-PV-positive neurons or permanent functional modifications on the subcellular molecular level, i.e. alterations in the phosphorylation status of GABA and/or NMDA receptors. The net result of these long-term changes is an imbalance between the excitatory and inhibitory systems in the ischaemic cortex with the subsequent expression and manifestation of intracortical hyperexcitability.

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

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

Cognitive deficits induced by global cerebral ischaemia: relationship to brain damage and reversal by transplants

The CA1 and hilar fields of the hippocampus are highly vulnerable to lack of oxygen after interruption of blood flow to the brain. Severe anterograde memory loss, seen in a significant proportion of heart attack survivors, has been attributed to selective bilateral ischaemic damage to the hippocampus. Animal models of global ischaemia, induced by extracranial occlusion of the major ascending arteries, enable assessment of the neuropathological and functional consequences of transient interruption of cerebral blood flow, and can inform strategies to reduce or alleviate ischaemic brain damage. This review focuses firstly on the nature of cognitive deficits induced by global ischaemia, how far they are consistent with lesion-based accounts of hippocampal function, and the extent to which these deficits can be correlated with CA1 cell loss. The second focus of the review is to examine the limited evidence for graft-induced recovery of cognitive function in animals subjected to global ischaemia. Recent findings that grafted foetal cells from discrete hippocampal fields follow appropriate laminar routes to form functional connections with host neurons, and that growth factors protect cells from ischaemic damage, have suggested that CA1 or trophic grafts placed in the region of ischaemic CA1 cell loss might restore or protect this vulnerable sector, and reduce cognitive deficits.

Dextromethorphan attenuates hypoxia-induced neuronal dysfunction in rat neocortical slices

We investigated the effects of the antitussive dextromethorphan (DM; 100 microM) on the extracellular DC potential, extracellular calcium concentration ([Ca2+]o) and on stimulus-evoked field potential (FP) responses in rat neocortical slices during hypoxia. DM significantly reduced the amplitude of the anoxic depolarization (AD) and the associated [Ca2+]o decrease by 47.6% and 48.5%, respectively, but did not change the onset latency and the duration of the AD. DM did not affect the preservation or recovery of excitatory synaptic transmission and significantly suppressed paired-pulse inhibition in the postanoxic recovery phase. These results indicate that DM exerts its potential neuroprotective action by reducing the hypoxia-induced depolarization and Ca2+ influx.

NG-Nitro-L-arginine protects against ischaemia-induced increases in nitric oxide and hippocampal neuro-degeneration in the gerbil

To assess the effects of the nitric oxide synthase inhibitor NG-Nitro-L-arginine on behavioural, biochemical and histological changes following global ischaemia, the Mongolian gerbil was used. Ischaemia was induced by bilateral carotid occlusion for 5 min. NG-Nitro-L-arginine was administered i.p. at either 1 or 10 mg/kg 30 min, 6, 24, and 48 h after surgery. 5 min bilateral carotid occluded animals were hyperactive 24, 48 and 72 h after surgery. NG-Nitro-L-arginine caused some attenuation in this hyperactivity. The activity of nitric oxide synthase was increased in the cerebellum, brain stem, striatum, cerebral cortex and hippocampus of 5 min bilateral carotid occluded animals. NG-Nitro-L-arginine reversed the increase in nitric oxide synthase activity in all brain regions. Extensive neuronal death was observed in the CA1 layer of the hippocampus in 5 min bilateral carotid occluded animals 96 h after surgery. NG-Nitro-L-arginine significantly protected against the neuronal death of cells in the CA1 layer.

Postischemic diazepam is neuroprotective in the gerbil hippocampus

In this study, we address the hypothesis that enhancement of gamma-aminobutyric acid (GABA) neurotransmission following an ischemic episode is neuroprotective in the hippocampus. Mongolian gerbils were subjected to transient forebrain ischemia for 5 min by occlusion of the carotid arteries and then administered diazepam (10 mg/kg i.p.) 30 min or 30 and 90 min following ischemia. Diazepam produced a significant decrease in both rectal and brain temperature (4-6 degrees C) in the sham and ischemic gerbils. 1 day following the onset of reperfusion, diazepam substantially reduced the hyperactivity normally induced by the ischemic episode. 7 days later, neuronal viability in the hippocampus was assessed. The single dose of diazepam completely protected the CA1 pyramidal cells of the hippocampus in 62% of the gerbils and the double dose of diazepam completely protected CA1 pyramidal neurons in 67% of the gerbils. There was a significant correlation between the degree of pyramidal cell degeneration in the CA1 area of the hippocampus measured 7 days following ischemia and the degree of hyperactivity measured 1 day following ischemia. Diazepam also prevented the loss of [35S]t-butylbicyclophosphorothionate ([35S]TBPS) binding to GABA-gated chloride channels in the dendritic fields of the CA1 area of the hippocampus. Our findings support the hypothesis that enhancement of GABA neurotransmission following an ischemic event may offset neuronal excitability and prevent neuronal death in specific brain regions. We conclude that GABA-enhancing drugs, such as diazepam, are attractive candidates as neuroprotective agents following ischemic insults.

Effects of ischaemia on neurotransmitter release from the isolated retina

The effects of "ischaemia" (glucose-free Krebs-bicarbonate medium gassed with N2/CO2) on the release of glutamate and other major neurotransmitters in the retina were examined using the isolated rat and rabbit retina. Amino acid transmitters, acetylcholine, and dopamine were measured by HPLC. The release of glutamate, aspartate, GABA, and glycine from ischaemic retinas was more than doubled after 30 min, and after 90 min of ischaemia the release of amino acids was approximately 15-20-fold that of control values. Ischaemia also produced large increases in the release of dopamine from both the rat and especially the rabbit retina. In contrast, the release of acetylcholine from the rat retina was significantly decreased by ischaemia, although the release of choline was increased. Because the ischaemia-induced release of glutamate, aspartate, and GABA from the rat retina was completely Ca independent, and exposure of the retina to high K (50 mM) did not stimulate amino acid release, it is concluded that the mechanisms underlying the ischaemia-induced release do not involve an initial release of K or an influx of calcium.

Bidirectional modulation of GABA-gated chloride channels by divalent cations: inhibition by Ca2+ and enhancement by Mg2+

The effects of the divalent cations Ca2+, Sr2+, Ba2+, Mg2+, Mn2+, and Cd2+ were studied on gamma-aminobutyric acidA (GABAA) responses in rat cerebral cortical synaptoneurosomes. The divalent cations produced bidirectional modulation of muscimol-induced 36Cl- uptake consistent with their ability to permeate and block Ca2+ channels. The order of potency for inhibition of muscimol responses was Ca2+ > Sr2+ > Ba2+, similar to the order for permeation of Ca2+ channels in neurons. The order of potency for enhancement of muscimol responses was Cd2+ > Mn2+ > Mg2+, similar to the order for blockade of Ca2+ channels in neurons. Neither Ca2+ nor Mg2+ caused accumulation of GABA in the extravesicular space due to increased GABA release or decreased reuptake of GABA by the synaptoneurosomes. The inhibition of muscimol responses by Ca2+ was most likely via an intracellular site of action because additional inhibition could be obtained in the presence of the Ca2+ ionophore, A23187. This confirms electrophysiologic findings in cultured neurons from several species. In contrast, the effects of Cd2+, Mn2+, and Mg2+ may be mediated via blockade of Ca2+ channels or by intracellular sites, although the results of these studies do not distinguish between the two loci. The effects of Zn2+ were also studied, because this divalent cation is reported to have widely divergent effects on GABAA responses. In contrast to other studies, we demonstrate that Zn2+ inhibits GABAA responses in an adult neuronal preparation. Zn2+ produced a concentration-dependent inhibition (limited to 40%) of muscimol responses with an EC50 of 60 microM. The inhibition of muscimol-induced 36Cl- uptake by Zn2+ was noncompetitive.(ABSTRACT TRUNCATED AT 250 WORDS)

Rapid decline of GABAA receptor subunit mRNA expression in hippocampus following transient cerebral ischemia in the gerbil

Inhibitory neurotransmission may play an important role in neuronal degeneration following transient cerebral ischemia. We studied the effect of transient forebrain ischemia on the GABAA receptor system in the gerbil hippocampus. Gerbils were subjected to 5 minutes of bilateral carotid occlusion and were sacrificed at various times over 4 days following reperfusion. There was a substantial loss of pyramidal cells in the CA1 area of the hippocampus 4 days following ischemia. No cell loss was detected in CA3 pyramidal cells of the hippocampus, granule cell layer of the dentate gyrus, and ventroposterior medial and ventroposterior lateral nuclei of the thalamus at any time following ischemia. Examination of brain slices by in situ hybridization histochemistry revealed that a change in expression of the GABAA receptor alpha 1 and beta 2 subunit mRNAs occurred in two phases following onset of reperfusion. The early phase (rapid) occurred within the first 4 hours following reperfusion. The expression of mRNAs significantly decreased (up to 25%) within 1 hour after occlusion in CA1 and CA3 pyramidal cell layers of the hippocampus and in the granule cell layer of the dentate gyrus. The expression of the mRNAs in these regions continued to decrease for 4 hours (up to 43%). In the second phase, which began between 4 and 12 hours following reperfusion, mRNA expression started to return to control levels in CA3 hippocampus and in the dentate. However, expression of both mRNAs continued to decline slowly in the CA1 pyramidal cell layer (up to 85%) over the next 3 days, concomitantly with degeneration of the CA1 pyramidal cells. Expression of mRNAs in the ventroposterior medial or ventroposterior lateral nuclei of the thalamus was similar to control values. To determine if a change in GABAA receptor distribution paralleled changes in receptor subunit mRNA expression, we also measured the binding of [35S]t-butylbicyclophosphorothionate to GABAA receptor chloride channels. The t-butylbicyclophosphorothionate [35S] binding decreased between 1 and 4 days after reperfusion in the dendritic fields of CA1 pyramidal cells (strata oriens, radiatum, and lacunosum-moleculare) but not in the pyramidal cell body layer. These results indicate that expression of GABAA receptor subunit mRNAs decrease well before CA1 pyramidal cell degeneration and loss of GABAA receptors. At present, it is not clear if an early loss of mRNA expression after an ischemic insult leads to a functional defect in GABAA receptors. If so, a loss of GABA neurotransmission may contribute to the development of neuronal degeneration following cerebral ischemia.(ABSTRACT TRUNCATED AT 400 WORDS)

Evolving concepts about the role of acidosis in ischemic neuropathology

Cerebral ischemia is one of the most common neurological insults. Many pathological events are undoubtedly triggered by ischemia, but only recently has it become accepted that ischemic cell injury arises from a complex interaction between multiple biochemical cascades. Tissue acidosis is a well established feature of ischemic brain tissue, but its role in ischemic neuropathology is still not fully understood. Within the last few years, new evidence has challenged the historically negative view of acidosis and suggests that it may play more of a beneficial role than previously thought. This review reintroduces the concept of acidosis to ischemic brain injury and presents some new perspectives on its neuroprotective potential.