Classification of ischemic-induced damage to Na+, K+-ATPase in gerbil forebrain. Modification by therapeutic agents

Effects of the hyperbaric oxygen treatment on the Na+,K+ -ATPase and superoxide dismutase activities in the optic nerves of global cerebral ischemia-exposed rats

The effects of hyperbaric oxygen (HBO) treatment on the Na+,K+ -ATPase and superoxide dismutase (SOD) activities were examined in the optic nerves of the rats exposed to global cerebral ischemia. Animals were exposed to global cerebral ischemia of 20-min duration and were either sacrificed or exposed to the first HBO treatment immediately, 0.5, 1, 2, 6, 24, 48, 72 or 168 h after ischemic procedure (for Na+,K+ -ATPase activities measurement) or 2, 24, 48 or 168 h after ischemia (for SOD activities measurement). HBO procedure was repeated for 7 consecutive days. It was found that global cerebral ischemia induced a statistically significant decrease in the Na+,K+ -ATPase activity of the optic nerves, starting from 0.5 to 168 h of reperfusion. Maximal enzymatic inhibition was registered 24 h after the ischemic damage. The decline in the Na+,K+ -ATPase activity was prevented in the animals exposed to HBO treatment within the first 6 h of reperfusion. The results of the presented experiments demonstrated also a statistically significant increase in the SOD activity after 24, 48 and 168 h of reperfusion in the optic nerves of non-HBO-treated ischemic animals as well as in the ischemic animals treated with HBO. Our results indicate that global cerebral ischemia induced a significant alterations in the Na+,K+ -ATPase and SOD activities in the optic nerves during different periods of reperfusion. HBO treatment, started within the first 6 h of reperfusion, prevented ischemia-induced changes in the Na+,K+ -ATPase activity, while the level of the SOD activity in the ischemic animals was not changed after HBO administration.

Hyperbaric oxygen treatment: the influence on the hippocampal superoxide dismutase and Na+,K+-ATPase activities in global cerebral ischemia-exposed rats

The influence of hyperbaric oxygen (HBO) treatment on the activities of superoxide dismutase (SOD) and Na(+),K(+)-ATPase was determined during different time periods of reperfusion in rats exposed to global cerebral ischemia. Ischemic animals were either sacrificed or exposed to the first HBO treatment 2, 24, 48 or 168 h after ischemic insult (for SOD activities measurement) or immediately, 0.5, 1, 2, 6, 24, 48, 72 or 168 h after ischemic procedure (for Na(+),K(+)-ATPase activities measurement). Hyperbaric oxygenation procedure was repeated for seven consecutive days. The results of presented experiments demonstrated the statistically significant increase in the hippocampal SOD activity 24 and 48 h after global cerebral ischemia followed by a decrease in the enzymatic activity 168 h after ischemic insult. In the ischemic rats treated with HBO the level of hippocampal SOD activity was significantly higher after 168 h of reperfusion in comparison to the ischemic, non HBO-treated animals. In addition, it was found that global cerebral ischemia induced a statistically significant decrease of the hippocampal Na(+),K(+)-ATPase activity starting from 1 to 168 h of reperfusion. Maximal enzymatic inhibition was obtained 24 h after the ischemic damage. Decline in Na(+),K(+)-ATPase activity was prevented in the animals exposed to HBO treatment within the first 24 h of reperfusion. Our results suggest that global cerebral ischemia induces significant alterations in the hippocampal SOD and Na(+),K(+)-ATPase activities during different periods of reperfusion. Enhanced SOD activity and preserved Na(+),K(+)-ATPase activity within particular periods of reperfusion, could be indicators of a possible beneficial role of HBO treatment in severe brain ischemia.

The influence of MK-801 on the hippocampal free arachidonic acid level and Na+,K+-ATPase activity in global cerebral ischemia-exposed rats

The influence of 20 min global cerebral ischemia on the free arachidonic acid (FAA) level and Na+,K+-ATPase activity in the rat hippocampus at different time points after ischemia was examined. In addition, the effect of MK-801 on mentioned parameters was studied. Animals were exposed to 20 min global cerebral ischemia and were sacrificed immediately, 0.5, 1, 2, 6, 24, 48, 72, and 168 h after ischemic procedure. The level of the FAA and the Na+,K+-ATPase activity was measured during all reperfusion periods examined. Various doses of MK-801 (0.3, 1.0, 3.0, and 5.0 mg/kg) had been injected 30 min before ischemic procedure started. It was found that 20 min global cerebral ischemia induces a statistically significant increase of the FAA level immediately after ischemia and during the first 0.5 h of reperfusion. After a transient decrease, the level of FAA level increased again after 24 and 168 h of recirculation. Treatment with 3.0 mg/kg of MK-801 significantly prevented the FAA accumulation immediately and 0.5 h after ischemic insult while application of 5.0 mg/kg of MK-801 exerted a protective effect during the first 24 h. Global cerebral ischemia induces the significant decline in the Na+,K+-ATPase activity in the hippocampus starting from 1 to 168 h of reperfusion. Maximal inhibition was obtained 24 h after the ischemic damage. Application of 3.0 mg/kg of MK-801 exerted statistically significant protection during the first 24 h while the treatment with 5.0 mg/kg of MK-801 prevented fall in enzymatic activity during all reperfusion periods examined. Our results suggest that, in spite of different and complex pathophysiological mechanisms involved in the increase of FAA level and the decrease of the Na+,K+-ATPase activity, blockade of NMDA receptor subtype provides a very important strategy for the treatment of the postischemic excitotoxicity.

Ischemic cell death in brain neurons

This review is directed at understanding how neuronal death occurs in two distinct insults, global ischemia and focal ischemia. These are the two principal rodent models for human disease. Cell death occurs by a necrotic pathway characterized by either ischemic/homogenizing cell change or edematous cell change. Death also occurs via an apoptotic-like pathway that is characterized, minimally, by DNA laddering and a dependence on caspase activity and, optimally, by those properties, additional characteristic protein and phospholipid changes, and morphological attributes of apoptosis. Death may also occur by autophagocytosis. The cell death process has four major stages. The first, the induction stage, includes several changes initiated by ischemia and reperfusion that are very likely to play major roles in cell death. These include inhibition (and subsequent reactivation) of electron transport, decreased ATP, decreased pH, increased cell Ca(2+), release of glutamate, increased arachidonic acid, and also gene activation leading to cytokine synthesis, synthesis of enzymes involved in free radical production, and accumulation of leukocytes. These changes lead to the activation of five damaging events, termed perpetrators. These are the damaging actions of free radicals and their product peroxynitrite, the actions of the Ca(2+)-dependent protease calpain, the activity of phospholipases, the activity of poly-ADPribose polymerase (PARP), and the activation of the apoptotic pathway. The second stage of cell death involves the long-term changes in macromolecules or key metabolites that are caused by the perpetrators. The third stage of cell death involves long-term damaging effects of these macromolecular and metabolite changes, and of some of the induction processes, on critical cell functions and structures that lead to the defined end stages of cell damage. These targeted functions and structures include the plasmalemma, the mitochondria, the cytoskeleton, protein synthesis, and kinase activities. The fourth stage is the progression to the morphological and biochemical end stages of cell death. Of these four stages, the last two are the least well understood. Quite little is known of how the perpetrators affect the structures and functions and whether and how each of these changes contribute to cell death. According to this description, the key step in ischemic cell death is adequate activation of the perpetrators, and thus a major unifying thread of the review is a consideration of how the changes occurring during and after ischemia, including gene activation and synthesis of new proteins, conspire to produce damaging levels of free radicals and peroxynitrite, to activate calpain and other Ca(2+)-driven processes that are damaging, and to initiate the apoptotic process. Although it is not fully established for all cases, the major driving force for the necrotic cell death process, and very possibly the other processes, appears to be the generation of free radicals and peroxynitrite. Effects of a large number of damaging changes can be explained on the basis of their ability to generate free radicals in early or late stages of damage. Several important issues are defined for future study. These include determining the triggers for apoptosis and autophagocytosis and establishing greater confidence in most of the cellular changes that are hypothesized to be involved in cell death. A very important outstanding issue is identifying the critical functional and structural changes caused by the perpetrators of cell death. These changes are responsible for cell death, and their identity and mechanisms of action are almost completely unknown.

Changes in erythrocyte membrane ATPases and plasma lipid peroxides in upper abdominal surgery under intravenous procaine-balanced anesthesia

AIM: To observe the changes in erythrocyte membrane ATPases and plasma lipid peroxides (LPO) patients with in abdominal surgery under intravenous procaine balanced anesthesia.

METHODS: By determining the ATPase activities of erythrocyte membrane, effects of upper abdominal surgery under intravenous procaine-balanced anesthesia on the function of erythrocytes were observed in 15 patients undergoing cholecystectomy and gastrectomy (5 males and 10 females, aged 45.9 ± 10.20 years and weighed 60.60 kg ± 11.93 kg). All patients were free from severe renal,hepatic, pulmonary, cardiac, metabolic and endocrinological diseases and acute infection for at least 2 weeks before surgery. Patients receiving any drug known to affect carbohydrate metabolism prior to anesthesia were excluded from the study.

RESULTS: Erythrocyte membrane Na⁺, K⁺-ATPase, Mg²⁺-ATPase, Ca²⁺, Mg²⁺-ATPase activities were not significantly changed 60 min-90 min after incision as compared with 30min before anesthesia, but were decreased markedly 10min and 24 h after completion of operation (P ＜ 0.01). Plasma lipid peroxides (LPO) were increased significantly 24 h after surgery (P ＜ 0.01) following an initially marked but transient reduction. Plasma LPO changes were not correlated with erythrocyte membrane ATPase activities, r = -0.0396, -0.0097 and 0.4383, respectively (P ＞ 0.05).

CONCLUSION: Abdominal surgical trauma under intravenous procaine-balanced anesthesia may be associated with the decreased ATPase activities of erythrocyte membrane and increased LPO in plasma.

Relationships between ATP depletion, membrane potential, and the release of neurotransmitters in rat nerve terminals. An in vitro study under conditions that mimic anoxia, hypoglycemia, and ischemia

BACKGROUND AND PURPOSE

It is known that the extracellular accumulation of glutamate during anoxia/ischemia is responsible for initiating neuronal injury. However, little information is available on the release of monoamines and whether the mechanism of its release resembles that of glutamate, which may itself influence the release of monoamines by activating presynaptic receptors. This study was designed to characterize the release of both amino acids and monoamines under chemical conditions that mimic anoxia, hypoglycemia, and ischemia.

METHODS

The contents of synaptosomes in adenine nucleotides (ATP, ADP, and AMP), amino acids (aspartate, glutamate, taurine, and gamma-aminobutyric acid), and monoamines (dopamine, noradrenaline, and 5-hydroxytryptamine) were measured by high-performance liquid chromatography, after the synaptosomes were subjected to anoxia (KCN + oligomycin), hypoglycemia (2 mmol/L 2-deoxyglucose in glucose-free medium), and ischemia (anoxia plus hypoglycemia).

RESULTS

The anoxia- and ischemia-induced release or noradrenaline, dopamine, 5-hydroxytryptamine, and glutamate correlated well with ATP depletion. The correlation observed between glutamate levels and the release of dopamine and 5-hydroxytryptamine in ischemic conditions suggests a functional linkage between the two transmitter systems. However, the antagonists of presynaptic glutamate receptors failed to alter the amount of monoamines released. The inhibition of Na+,K+-ATPase by ouabain had an effect similar to that produced by ischemia.

CONCLUSIONS

The decrease in Na+ and K+ gradients resulting from the energy depletion of the synaptosomes under ischemic conditions or resulting from the inhibition of Na+, K+-ATPase by ouabain promotes the reversal of the neurotransmitter transporters. The decrease in uptake of neurotransmitters may also contribute to the rise in the extracellular concentration of different transmitters observed during brain ischemia.

Age-related changes by hypoxia and TRH analogue on synaptic ATPase activities

Some synaptosomal energy-requiring ATPases were evaluated in the cerebral cortex from 3- and 24-month-old normoxic rats and rats submitted to either mild or severe chronic (4 weeks) intermittent normobaric hypoxia. Furthermore, 4-week treatment with saline or TRH analogue posatireline was performed. The activities of Na+,K(+)-ATPase, low- and high-affinity Ca(2+)-ATPase, and Ca2+,Mg(2+)-ATPase were assayed in synaptosomes and synaptosomal subfractions, namely synaptosomal plasma membranes and synaptic vesicles. With the exception of the high-affinity Ca(2+)-ATPase, aging induced a decrease in the ATPase activities from normoxic rats. The adaptation to chronic intermittent mild hypoxia was characterized by an increase in the activity of Mg(2+)-ATPase in 3-month-old rats, concomitant with a decrease in the activities of: a) Na+,K(+)-ATPase and high-affinity Ca(2+)-ATPase in both 3- and 24-month-old rats, and b) Ca2+,Mg(2+)-ATPase in 3-month-old ones. The TRH analogue posatireline increased the high-affinity Ca(2+)-ATPase in both 3- and 24-month-old hypoxic rats, concomitant with an increase in Mg(2+)-ATPase activity in 24-month-old ones. The adaptation to chronic intermittent severe hypoxia was characterized by a decrease in the activities of: a) Na+,K(+)-ATPase, Ca2+,Mg(2+)-ATPase and high-affinity Ca(2+)-ATPase in both 3- and 24-month-old rats, and b) low-affinity Ca(2+)-ATPase only in 24-month-old ones. The effect on Mg(2+)-ATPase activity was characterized by a decrease in the enzymatic form located in the synaptic plasma membranes, concomitant with an increase in the form located in the synaptic vesicles.(ABSTRACT TRUNCATED AT 250 WORDS)

Synaptosomal non-mitochondrial ATPase activities: age-related alterations by chronic normobaric intermittent hypoxia

In synaptosomes and synaptosomal subfractions (namely, synaptosomal plasma membranes and synaptic vesicles) the age-related alteration in the plasticity of synaptic energy-requiring ATPases (Na+, K(+)-ATPase, low- and high-affinity Ca(2+)-ATPase, Mg(2+)-ATPase and Ca2+, Mg(2+)-ATPase) were assayed in the cerebral cortex from 3- and 24-month-old normoxic rats and rats subjected to either mild or severe chronic (4 weeks) intermittent normobaric hypoxia. With the exception of the high-affinity Ca(2+)-ATPase, aging induced a decrease in the ATPase activities from normoxic rats. The adaptation to mild hypoxia was characterized by an increase in the activity of Mg(2+)-ATPase in 3-month-old rats, concomitant with a decrease in the activities of: (i) Na+,K(+)-ATPase and high-affinity Ca(2+)-ATPase in both 3- and 24-month-old rats; and (ii) Ca2+,Mg(2+)-ATPase in 3-month-old ones. The adaptation to chronic intermittent severe hypoxia was characterized by a decrease in the activities of: (i) Na+,K(+)-ATPase, Ca2+,Mg(2+)-ATPase and high-affinity Ca(2+)-ATPase in both 3- and 24-month-old rats and (ii) low-affinity Ca(2+)-ATPase only in 24-month-old ones. The effect on Mg(2+)-ATPase activity was characterized by a decrease in the activity of the enzymatic form located in the synaptic plasma membranes (involved in ATP hydrolysis to adenosine production), concomitant with an increase in the activity of the form located in the synaptic vesicles (involved in the turnover of transmitters, e.g., glutamate).

Modifications by hypoxia and drug treatment of cerebral ATPase plasticity

The plasticity of synaptosomal non-mitochondrial ATPases was evaluated in cerebral cortex from 3-month-old normoxic rats and rats subjected to either mild or severe intermittent normobaric hypoxia [12 hr daily exposure to N2:O2 (90:10 or 91.5:8.5) for four weeks]. The activities of Na+, K(+)-ATPase, low- and high-affinity Ca(2+)-ATPase, Mg(2+)-ATPase, and Ca2+,Mg(2+)-ATPase were assayed in synaptosomes and synaptosomal subfractions, namely synaptosomal plasma membranes and synaptic vesicles. The evaluations were performed after a 4-week treatment with saline (controls) or alpha-adrenergic agents (delta-yohimbine, clonidine), a vasodilator compound (papaverine), and an oxygen-partial pressure increasing agent (almitrine). These treatments differently changed the adaptation to chronic intermittent hypoxia characterized by a decrease in the activity of Na+,K(+)-ATPase, Ca2+,Mg(2+)-ATPase, and high-affinity Ca(2+)-ATPase, concomitant with a modification in the activity of Mg(2+)-ATPase supported in a different way by the enzymatic forms located into the synaptosomal plasma membranes and synaptic vesicles.

Age-related alterations by chronic intermittent hypoxia on cerebral synaptosomal ATPase activities

The age-related alterations in the plasticity of synaptic energy-requiring ATPases [Na+,K(+)-ATPase, low- and high-affinity Ca(2+)-ATPase, Mg(2+)-ATPase, and Ca2+,Mg(2+)-ATPase] were assayed in synaptosomes and synaptosomal subfractions [namely, synaptosomal plasma membranes and synaptic vesicles] in the cerebral cortex from 3- and 24-month-old normoxic rats and rats subjected to either mild or severe chronic (four weeks) intermittent normobaric hypoxia. With the exception of the high-affinity Ca(2+)-ATPase, aging induced a decrease in the ATPase activities from normoxic rats. The adaptation to mild hypoxia was characterized by an increase in the activity of Mg(2+)-ATPase in 3-month-old rats, concomitant with a decrease in the activities of: (i) Na+,K(+)-ATPase and high-affinity Ca(2+)-ATPase in both 3- and 24-month-old rats, and (ii) Ca2+,Mg(2+)-ATPase in 3-month-old ones. The adaptation to chronic intermittent severe hypoxia was characterized by a decrease in the activities of: (i) Na+,K(+)-ATPase, Ca2+,Mg(2+)-ATPase and high-affinity Ca(2+)-ATPase in both 3- and 24-month-old rats, and (ii) low-affinity Ca(2+)-ATPase only in 24-month-old ones. The effect on Mg(2+)-ATPase activity was characterized by a decrease in the activity of the enzymatic form located in the synaptic plasma membranes [involved in ATP hydrolysis to adenosine production], concomitant with an increase in the activity of the form located in the synaptic vesicles [involved in the turnover of transmitters, e.g., glutamate].

Protein kinase C as an early and sensitive marker of ischemia-induced progressive neuronal damage in gerbil hippocampus

In the model of transient brain ischemia of 6-min duration in gerbils we have estimated: 1. The concentration of brain gangliosides: A significant decrease to about 70% of control was observed selectively in the hippocampus at 3 and 7 d after ischemia. 2. The activity of Na+,K(+)-ATPase: The enzyme activity was not affected in either hippocampus nor in cerebral cortex. 3. The malonaldehyde (MDA) concentration: The levels of MDA had increased at 30 min after ischemia up to 123 and 129% of control in hippocampus and cerebral cortex, respectively. 4. Immunoreactivity of protein kinase C detected by Western blotting: In hippocampus the early translocation toward membranes was followed by a decrease in total enzyme content at 6, 24, 72, and 96 h of postischemic recovery. Also, a sharp increase of 50 kDa isoform (PKM) was noticed immediately and at the early recovery times. The behavior of these biochemical markers of ischemic brain injury in the hippocampus after the short (6 min) insult was contrasted with their reaction in the cerebral cortex as well as after prolongation of the ischemia to 15 min. These results taken together indicate that an early increase in PKC translocation followed by a decrease is the most symptomatic for selective, delayed, postischemic hippocampal injury, resulting from short duration (6 min) ischemia of the gerbil brain.

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.

Effect of intermittent mild hypoxia and drug treatment on synaptosomal nonmitochondrial ATPase activities

Synaptosomal nonmitochondrial ATPases linked to the energy-utilizing systems were evaluated in cerebral cortex from normoxic rats and rats submitted to mild intermittent normobaric hypoxia [12 hr daily exposure to N2:O2 (90:10) mixture for 4 weeks]. The activities of Na+,K(+)-ATPase; high- and low-affinity Ca(2+)-ATPase; basal Mg(2+)-ATPase; and Ca2+, Mg(2+)-ATPase were assayed in synaptosomes and synaptosomal subfractions, namely, synaptosomal plasma membranes and synaptic vesicles. The evaluations were performed either in normoxic rats or in hypoxic rats submitted to 4-week treatment with saline (controls) or a vasodilator agent (papaverine), an energy-metabolism interfering agent (theniloxazine), a calcium blocker (nicardipine), and a lipid-metabolism interfering agent (phosphatidylcholine) in order to define the plasticity and the selective changes in individual ATPases. In synaptosomes from rat cerebral cortex, the enzyme adaptation to the daily mild intermittent hypoxia for 4 weeks was characterized by an increase in the activity of Mg(2+)-ATPase, concomitant with a decrease in the activities of Na+,K(+)-ATPase, high-affinity Ca(2+)-ATPase, and Ca2+, Mg(2+)-ATPase. In hypoxic rats the enzyme adaptation to the 4-week treatment with phosphatidylcholine was characterized by an increase in Ca2+, Mg(2+)-ATPase activity and a decrease in Mg(2+)-ATPase activity. The action involves the enzymatic form located in the synaptic plasma membranes. In hypoxic rats the adaptation to the 4 week treatment with nicardipine was characterized by an increase in high-affinity Ca(2+)-ATPase activity, while the 4-week-treatment with theniloxazine induced an increase in Na+,K(+)-ATPase activity. The actions of both nicardipine and theniloxazine were related to the enzymatic forms located in the synaptic plasma membranes. The effects on the biophase induced by the sequential cycles of hypoxia/normoxia and the treatment with the various agents tested should also be related to the changes induced in the activity of some synaptosomal ATPases.

Glucose and oxygen deprivation induces a Ca(2+)-mediated decrease in (Na(+)+K+)-ATPase activity in rat brain slices

Exposure of rat brain cortical slices to a medium lacking in glucose, oxygen or both glucose and oxygen, resulted in a decrease of the tissue ATP content and a reduction of (Na(+)+K+)-ATPase activity in membranes prepared from the slices. These treatments also inhibited partial reactions of (Na(+)+K+)-ATPase such as Na(+)-dependent phosphorylation and K(+)-stimulated phosphatase, as well as specific binding of [3H]ouabain in membranes prepared from the slices. Glucose deprivation and hypoxia decreased (Na(+)+K+)-ATPase activity in the absence of extracellular Ca2+, but the effects were blocked by 1,2-bis(2-amino-phenoxy)ethane-N,N,N',N'-tetraacetic acid tetra-acetomethyl ester (BAPTA-AM), a chelator of intracellular Ca2+. Metabolic inhibitors mimicked the effects of glucose deprivation and hypoxia. The effect of glucose-free hypoxia was dependent on extracellular Ca2+. It was blocked by Mg2+ at high concentration, bepridil or amiloride, but not by voltage-sensitive Ca2+ channel antagonists and glutamate receptor antagonists. None of the drugs tested here, except for dithiothreitol, affected the inhibitory effect of glucose-free hypoxia on the enzyme activity. In contrast to brain (Na(+)+K+)-ATPase, the kidney enzyme was insensitive to glucose and oxygen deprivation and metabolic inhibitors which depleted the tissue ATP.

Post-ischemic regional changes in acetylcholine synthesis following transient forebrain ischemia in gerbils

The synthesis rate of brain acetylcholine (ACh) was estimated 30 min and 5 days following transient forebrain ischemia performed by 10 min bilateral carotid occlusion in gerbils. ACh synthesis was evaluated from the conversion of radiolabeled choline (Ch) into ACh after an i.v. administration of [methyl-3H]Ch. Endogenous and labeled Ch and ACh were quantified by HPLC. The synthesis rate of Ach was significantly decreased following 30 min of recirculation. The reductions reached 55.4% in the hippocampus, 51.2% in the cerebral cortex and 44.4% in the striatum. Five days after ischemia, the values returned to normal in the cerebral cortex and in the striatum, while ACh synthesis remained selectively lowered (-30.4%, p less than 0.01) in the hippocampus. These cholinergic alterations may account for both early and delayed post-ischemic behavioral and mnesic deficits.

Neurochemical correlates of selective neuronal loss following cerebral ischemia: role of decreased Na+,K(+)-ATPase activity

In order to investigate the role of Na+,K(+)-ATPase in the development of neuronal necrosis following cerebral ischemia, ischemia was induced in gerbils by occluding the common carotid artery unilaterally for 10 min. A time-course analysis revealed that significant reductions of the Na+,K(+)-ATPase activity in the cerebral cortex and hippocampus were manifested at 15 min, 30 min, and 1 h, and returned to the control level one day following recirculation. No apparent alterations of the Mg(2+)-ATPase activity, on the other hand, were obtained throughout the experimental period. Furthermore, Scatchard analyses of [3H]ouabain binding to the cerebral cortex membranes disclosed that the Bmax values invariably decreased without any change of Kd values following ischemia. It has also been shown that treatment of the animals with an agent known to mitigate ischemic neuronal necrosis, i.e. BY-1949, significantly reversed such derangements. These results suggest that the recovery of decreased Na+,K(+)-ATPase activity shortly after ischemia exerts a protective effect against ischemic brain damage.

The neuroprotective pharmacology of methylprednisolone

A 24-hour intensive intravenous dosing regimen with the glucocorticoid steroid methylprednisolone has recently been shown to be effective in enhancing neurological recovery in spinal cord-injured patients when initiated within 8 hours after injury. The state of knowledge concerning the neuroprotective pharmacology of methylprednisolone, including mechanism(s) of action, dosing requirements, and time-action considerations is reviewed, as are the results of studies with high doses in experimental and clinical head injury, subarachnoid hemorrhage, and cerebral ischemia. A primary neuroprotective mechanism of action in each of these cases is hypothesized to involve the ability of high doses of methylprednisolone to inhibit oxygen free radical-induced lipid peroxidation, although additional mechanisms may contribute. Unresolved issues are also addressed, including the therapeutic window, optimum duration of treatment, and rational combination with other neuroprotective agents. A newer methylprednisolone pro-drug with improved solution stability is discussed, together with a brief consideration of novel nonglucocorticoid steroids that surpass methylprednisolone's lipid antioxidant effects without unwanted glucocorticoid properties.

Inhibition of sodium-potassium-ATPase: a potentially ubiquitous mechanism contributing to central nervous system neuropathology

Direct and indirect evidence suggests that Na+/K(+)-ATPase activity is reduced or insufficient to maintain ionic balances during and immediately after episodes of ischemia, hypoglycemia, epilepsy, and after administration of excitotoxins (glutamate agonists). Recent results show that inhibition of this enzyme results in neuronal death, and thus a hypothesis is proposed that a reduction and/or inhibition of this enzyme contributes to producing the central neuropathy found in the above disorders, and identifies potential mechanisms involved. While the extent of inhibition of Na+/K(+)-ATPase during ischemia, hypoglycemia and epilepsy may be insufficient to cause neuronal death by itself, unless the inhibition is severe and prolonged, there are a number of interactions which can lead to a potentiation of the neurotoxic actions of glutamate, a prime candidate for causing part of the damage following trauma. Presynaptically, inhibition of the Na+/K(+)-ATPase destroys the sodium gradient which drives the uptake of acidic amino acids and a number of other neurotransmitters. This results in both a block of reuptake and a stimulation of the release not only of glutamate but also of other neurotransmitters which modulate the neurotoxicity of glutamate. An exocytotic release of glutamate can also occur as inhibition of the enzyme causes depolarization of the membrane, but exocytosis is only possible when ATP levels are sufficiently high. Postsynaptically, the depolarization could alleviate the magnesium block of NMDA receptors, a major mechanism for glutamate-induced neurotoxicity, while massive depolarization results in seizure activity. With less severe inhibition, the retention of sodium results in osmotic swelling and possible cellular lysis. A build-up of intracellular calcium also occurs via voltage-gated calcium channels following depolarization and as a consequence of a failure of the sodium-calcium exchange system, maintained by the sodium gradient.

The neurotoxicity of ouabain, a sodium-potassium ATPase inhibitor, in the rat hippocampus

Intrahippocampal injection of 1 nmol ouabain, a sodium/potassium (Na+,K(+)-)ATPase inhibitor, produced a necrotic lesion within 4 days, characterised by a massive invasion by foaming macrophages. A lower dose of ouabain (0.1 nmol) produced a more discrete lesion of all groups of neuronal perikarya in the hippocampus, with only a minimal degree of glial infiltration. The neuronal perikaryal death produced in the subicular, CA1 and CA2 regions was only partially decreased by intraperitoneal injections of the anticonvulsants diazepam and MK-801; these drugs were without effect in the CA3 or hilar interneuronal regions. At neither dose of ouabain was there any indication of neuronal loss in brain regions outside the hippocampus, typically produced by prolonged seizure activity. It is suggested that ouabain has a two-fold action, a release of toxic acidic amino acids and a prolonged depolarization of neurons leading to osmolysis or calcium necrosis.

Rapid decrease of high affinity ouabain binding sites in hippocampal CA1 region following short-term global cerebral ischemia in rat

High affinity [3H]ouabain binding was examined in the hippocampal CA1 region and frontal cortex of rats subjected to 5 min complete cerebral ischemia in a clinical death model, and to subsequent resuscitation. A decrease of Bmax directly after ischemia and its further gradual decrease during 120 min of reperfusion were noted in the ischemia-vulnerable CA1 region, whereas no change of Bmax was observed in frontal cortex. The apparent Kd constant showed insignificant fluctuations in either of the two brain regions. Since ouabain binds with high affinity to the neuronal (alpha +)-form of Na+/K+-ATPase, the results indicate a rapid enzyme loss in CA1 neurons. The high affinity ouabain binding test proved to be a sensitive detector of premorphological changes in nerve cell membranes in ischemia.

The role of free radicals and eicosanoids in the pathogenetic mechanism underlying ischemic brain edema

Results of our consecutive study on the pathogenic mechanism underlying ischemic brain edema are summarized in this paper. Pertinent findings are as follows: (1) there is a close correlation between the influxes of water and sodium following ischemia; (2) the edema fluid can be regarded as the ultrafiltrate of serum; (3) there is a significant increase in the brain content of HETEs following ischemia; (4) the lipoxygenase activity of brain microvessels is increased following ischemia; (5) the lipoxygenase activity as well as the Na+, K+-ATPase activity of brain microvessels are enhanced by a hydroperoxide, 15-HPETE; (6) inhibition of Na+, K+-ATPase of brain microvessels by intraarterial infusion of ouabain resulted in a significant decrease in edema formation; and (7) not the cyclooxygenase, but the lipoxygenase pathway seems to be involved in the enhancement of microvessel Na+, K+-ATPase. Lipoxygenase(s) and Na+-K+-ATPase of brain microvessels, the activities of which are enhanced by an increased level of free radicals and/or hydroperoxides, may play a significant role in the occurrence of ischemic brain edema.

Regional profiles of steady-state levels of cyclic nucleotides, cyclic AMP phosphodiesterase, and guanylate cyclase activities during late stages of unilateral ischemia in gerbil forebrain

The present study was an extension of earlier work regarding the role of cyclic nucleotides and related enzymes during cerebral ischemia in the gerbil. Following unilateral carotid occlusion, levels of cyclic AMP and cyclic GMP were measured in four rapidly inactivated brain regions at 3, 6, and 24 hr after permanent occlusion and at 2 hr of occlusion plus 1 hr of reflow. An analysis of variance indicated significant minor fluctuations in the steady-state levels of the two cyclic nucleotides within the frontal cortex, the hippocampus, the striatum, and especially the olfactory tubercle with respect to occlusion time (3 and 24 hr) but not when comparing control vs ischemic hemispheres (except at 3 hr). Changes occurred only in animals developing neurological symptoms of ischemia. At 24 hr postocclusion the specific activity of the low-Km form of cyclic AMP phosphodiesterase was elevated especially on the ischemic side when determined in homogenates of the four brain regions. Alternatively, the high-Km form of the enzyme in the presence or absence of Ca2+-calmodulin was unchanged. Guanylate cyclase activity in tissue homogenates was not influenced by the conditions of ischemia until 24 hr had elapsed, an event likewise unique to symptomatic gerbils. The sensitivity of the enzyme to hematin-catalase was decreased in the ischemic hemispheres of the hippocampus, striatum, and olfactory tubercle. In addition, further activation of the hematin-catalase response by NaN3 was depressed in the ischemic side of the hippocampus and striatum. Taken together these and previous studies indicate that fluctuations in the steady-state levels of cyclic nucleotides that occur rather prominently during acute and to a lesser degree during prolonged ischemia are not correlated with associated changes in enzymes responsible for their synthesis and/or degradation.

Protective action of calcium channel blockers on Na+,K+-ATPase in gerbil cerebral cortex following ischemia

The present study was initiated to determine whether pretreatment of gerbils with calcium channel blockers, flunarizine and verapamil would prevent injury to cerebral ATPases following secondary ischemia consisting of 60-min bilateral clamping of the carotids followed by 40 min of reperfusion. The sequence of ischemia produced a deficit in Na+,K+-ATPase activity without influencing Ca++,Mg++- or Mn++-sensitive ATPases. Pretreatment with flunarizine significantly prevented the damage to Na+,K+-ATPase while the effect of verapamil was marginal. Verapamil, along with dimethylsulfoxide (DMSO), reduced the mortality rate of gerbils subjected to the paradigm of ischemia. When added directly to the cerebral fractions in vitro the two calcium channel blockers inhibited Na+,K+-ATPase alone. Flunarizine was more potent in vitro than verapamil.

Inhibitors of cation pump enzyme equally present in normal and ischemic gerbil brain

This was a search for endogenous inhibitors of the cation pump enzyme in normal and ischemic gerbil brain. The first model of ischemia was bilateral common carotid clamping for 30 minutes followed by reperfusion periods of 0, 1, 2.5, and 4 hours. After bilateral clamping, K-paranitrophenylphosphatase (K-pNPPase) activity fell significantly after 0, 1, and 2.5 hours of reflow but only slightly by 4 hours. The second model was decapitation with timed delays of 0, 15, 60 and 240 minutes. There was no decline in K-pNPPase activity after total ischemia produced by decapitation. Thus, the model of partial ischemia was more deleterious to the cation pump enzyme than was the model of total ischemia. All brains contained endogenous K-pNPPase inhibitors. Boiled supernatant fractions inhibited K-pNPPase activity by about 50-60% while Amicon filtrates of brain homogenate inhibited about 12%. Factors in normal and ischemic brain may modify the activity of the cation pump enzyme, but no differences in inhibitory effects were found between normal and ischemic brain extracts.

Free radicals generated by xanthine oxidase-hypoxanthine damage adenylate cyclase and ATPase in gerbil cerebral cortex

The generation of superoxide radicals from xanthine oxidase-hypoxanthine in a particulate fraction of gerbil cerebral cortex influenced the activity of the synaptic enzyme adenylate cyclase, as well as Mn2+- and Na+,K+-sensitive forms of ATPase. Low concentrations of xanthine oxidase actually elevated the sensitivity of adenylate cyclase to GTP, GTP + norepinephrine (NE), and forskolin but not significantly to Mn2+. Higher levels of xanthine oxidase elicited a marked inhibition of these responses. The stimulation of adenylate cyclase mechanisms requiring GTP (GTP, forskolin, and NE) was more susceptible than was Mn2+, suggesting that the guanine nucleotide stimulatory protein was more vulnerable to free radical attack than the catalytic site of adenylate cyclase. Superoxide dismutase (SOD), but not catalase, partially protected the forskolin-sensitive enzyme from the action of xanthine oxidase-hypoxanthine. A combination of SOD plus catalase preserved enzyme responses to forskolin. In comparison, additions of SOD plus mannitol or catalase plus flunarizine were less effective. The sensitivity of the particulate ATPase to Mn2+ was more labile to the consequence of superoxide formation than Na+, K+ -ATPase. In this regard the Ca2+,Mg2+ sensitivity of the enzyme was reduced only to a marginal extent. The findings might be analogous to in vivo data in which cerebral adenylate cyclase and Na+, K+-ATPase are damaged following postischemic reperfusion in gerbils, a process thought to be mediated by free radicals.

Further probes into the molecular sites of damage to cerebral adenylate cyclase following postischemic reperfusion

A variety of pharmacological agents were used as experimental probes to determine with greater precision the site(s) of damage to cerebral adenylate cyclase as a consequence of postischemic reperfusion in the gerbil. A paradigm of 60-min bilateral ischemia followed by 40-min reperfusion results in a decreased sensitivity of the catalytic site of adenylate cyclase to Mn2+. Likewise, the GTP-transducer site (guanine nucleotide regulatory or G protein) revealed depressed responses to GTP in the absence or presence of norepinephrine, dopamine agonists, substance P, yohimbine, and cholera and pertussis toxins. Moreover, a crude preparation of GTPase disclosed that damage elicited by postischemic reperfusion was directed to the higher-affinity form of this enzyme, which is associated with the overall function of the guanine nucleotide regulatory protein. Injury to adenylate cyclase was unrelated either to the ability of adrenergic ligands to bind to associated receptor sites or to the capacity of the brain to generate visual evoked potentials in response to visual stimuli.

Effects of naloxone and morphine on cerebral ischemia in gerbils

A therapeutic role for naloxone during stroke has been suggested, but a neurochemical site of action remains to be determined. Previous work with the gerbil cerebral cortex has shown that either bilateral secondary ischemia (60-min occlusion of the carotid arteries followed by 40-min reflow) or unilateral primary ischemia (permanent ligation of one carotid artery for 6 hr in symptomatic animals) produced deficits in both Na+, K+-ATPase (EC 3.6.1.3) activity and various parameters of activation of adenylate cyclase (EC 4.6.1.1). Pretreatment of gerbils with either naloxone or morphine failed to ameliorate or exacerbate, respectively, the neurological signs of ischemia; however, morphine did reduce mortality. Infusion of naloxone prior to ischemia afforded varying degrees of protection to forskolin, GTP analogs, and NE (norepinephrine) activation of adenylate cyclase, as well as to Na+, K+-ATPase (bilateral ischemia only). Similarly, morphine inhibited damage to basal activity of adenylate cyclase and to stimulation by NE, forskolin, and Gpp (NH)p (5'-guanylyl imidodiphosphate). Under in vitro conditions morphine increased the basal activity of adenylate cyclase but reduced responses to NE and forskolin. Furthermore, morphine injected into control gerbils elevated basal- and forskolin-elicited activities but reduced the activation of adenylate cyclase by NE.