Electron paramagnetic resonance study on nitric oxide production during brain focal ischemia and reperfusion in the rat

Investigation of NO Role in Neural Tissue in Brain and Spinal Cord Injury

Nitric oxide (NO) production in injured and intact brain regions was compared by EPR spectroscopy in a model of brain and spinal cord injury in Wistar rats. The precentral gyrus of the brain was injured, followed by the spinal cord at the level of the first lumbar vertebra. Seven days after brain injury, a reduction in NO content of 84% in injured brain regions and 66% in intact brain regions was found. The difference in NO production in injured and uninjured brain regions persisted 7 days after injury. The copper content in the brain remained unchanged one week after modeling of brain and spinal cord injury. The data obtained in the experiments help to explain the problems in the therapy of patients with combined brain injury.

A Review of Low-Frequency EPR Technology for the Measurement of Brain pO2 and Oxidative Stress

EPR can uniquely measure paramagnetic species. Although commercial EPR was introduced in 1950s, the early studies were mostly restricted to chemicals in solution or cellular experiments using X-band EPR equipment. Due to its limited penetration (<1 mm), experiments with living animals were almost impossible. To overcome these difficulties, Swartz group, along with several other leaders in field, pioneered the technology of low frequency EPR (e.g., L-band, 1-2 GHz). The development of low frequency EPR and the associated probes have dramatically expanded the application of EPR technology into the biomedical research field, providing answers to important scientific questions by measuring specific parameters that are impossible or very difficult to obtain by other approaches. In this review, which is aimed at highlighting the seminal contribution from Swartz group over the last several decades, we will focus on the development of EPR technology that was designed to deal with the potential challenges arising from conducting EPR spectroscopy in living animals. The second half of the review will be concentrated on the application of low frequency EPR in measuring cerebral tissue pO₂ changes and oxidative stress in various physiological and pathophysiological conditions in the brain of animal disease models.

Nitric oxide and the brain. Part 2: Effects following neonatal brain injury-friend or foe?

Nitric oxide (NO) has critical roles in a wide variety of key biologic functions and has intricate transport mechanisms for delivery to key distal tissues under normal conditions. However, NO also plays important roles during disease processes, such as hypoxia-ischemia, asphyxia, neuro-inflammation, and retinopathy of prematurity. The effects of exogenous NO on the developing neonatal brain remain controversial. Inhaled NO (iNO) can be neuroprotective or toxic depending on a variety of factors, including cellular redox state, underlying disease processes, duration of treatment, and dose. This review identifies key gaps in knowledge that should prompt further investigation into the possible role of iNO as a therapeutic agent after injury to the brain. IMPACT: NO is a key signal mediator in the neonatal brain with neuroprotective and neurotoxic properties. iNO, a commonly used medication, has significant effects on the neonatal brain. Dosing, duration, and timing of administration of iNO can affect the developing brain. This review article summarizes the roles of NO in association with various disease processes that impact neonates, such as brain hypoxia-ischemia, asphyxia, retinopathy of prematurity, and neuroinflammation. The impact of this review is that it clearly describes gaps in knowledge, and makes the case for further, targeted studies in each of the identified areas.

Nitric oxide homeostasis is maintained during acute in vitro hypoxia and following reoxygenation in naked mole-rat but not mouse cortical neurons

Reactive nitrogen species (RNS), including nitric oxide (NO), are important cellular messengers when tightly regulated, but unregulated production of RNS during hypoxia or ischemia and reoxygenation is deleterious to hypoxia-intolerant brain. Therefore, maintaining NO homeostasis during hypoxia/ischemia and reoxygenation may be a hallmark of hypoxia-tolerant brain. Unlike most mammals, naked mole-rats (NMRs; Heterocephalus glaber) are tolerant of repeated bouts of hypoxia in vivo. Although there is some evidence that NMR brain is tolerant of hypoxia/ischemia, little is known about the underlying neuroprotective mechanism(s), and their tolerance to reoxygenation injury has not been examined. We hypothesized that NMR brain would maintain NO homeostasis better than hypoxia-intolerant mouse brain during hypoxic/ischemic stresses and following reoxygenation. To test this, we exposed adult NMR and mouse cortical slices to transitions from normoxia (21% O₂) to hypoxia (< 1% O₂) or ischemia (oxygen glucose deprivation, OGD), followed by reoxygenation, while measuring neuronal NO production. We report that NMR cortical neurons maintain NO homeostasis during hypoxia/OGD and avoid bursts of NO upon reoxygenation. Conversely, mouse cortical neurons maintain NO homeostasis in OGD but not hypoxia and exhibit a burst of NO upon reperfusion. This suggests that maintenance of NO homeostasis during fluctuating O₂ availability may be a contributing neuroprotective mechanism against hypoxia/ischemia and reoxygenation injury in hypoxia-tolerant NMR brain.

Protective effect of oxysophoridine on cerebral ischemia/reperfusion injury in mice

Oxysophoridine, a new alkaloid extracted from Sophora alopecuroides L., has been shown to have a protective effect against ischemic brain damage. In this study, a focal cerebral ischemia/reperfusion injury model was established using middle cerebral artery occlusion in mice. Both 62.5, 125, and 250 mg/kg oxysophoridine, via intraperitoneal injection, and 6 mg/kg nimodipine, via intragastric administration, were administered daily for 7 days before modeling. After 24 hours of reperfusion, mice were tested for neurological deficit, cerebral infarct size was assessed and brain tissue was collected. Results showed that oxysophoridine at 125, 250 mg/kg and 6 mg/kg nimodipine could reduce neurological deficit scores, cerebral infarct size and brain water content in mice. These results provided evidence that oxysophoridine plays a protective role in cerebral ischemia/reperfusion injury. In addition, oxysophoridine at 62.5, 125, and 250 mg/kg and 6 mg/kg nimodipine increased adenosine-triphosphate content, and decreased malondialdehyde and nitric oxide content. These compounds enhanced the activities of glutathione-peroxidase, superoxide dismutase, catalase, and lactate dehydrogenase, and decreased the activity of nitric oxide synthase. Protein and mRNA expression levels of N-methyl-D-aspartate receptor subunit NR1 were markedly inhibited in the presence of 250 mg/kg oxysophoridine and 6 mg/kg nimodipine. Our experimental findings indicated that oxysophoridine has a neuroprotective effect against cerebral ischemia/reperfusion injury in mice, and that the effect may be due to its ability to inhibit oxidative stress and expression of the N-methyl-D-aspartate receptor subunit NR1.

Continuous monitoring of changes in plasma nitrite following cerebral ischemia in a rabbit embolic stroke model

In this proof-of-concept study, we investigated direct, continuous monitoring of plasma nitrite as an indicator of cerebral ischemia following clot embolization of rabbits via an indwelling carotid catheter. Two groups of rabbits were studied to compare the effects of embolization on nitrite levels. In the control group, blood was continuously obtained from a jugular venous catheter. The blood was immediately passed through an ultrafiltration filter; the filtrate was chemically reduced to convert free nitrite to nitric oxide (NO) and then measured using a NO-specific electrode. In the embolized group, after a baseline nitrite level was achieved, blood clots were injected into the brain via the carotid artery catheter, and then nitrite levels were continuously measured from jugular venous blood. The stroke group showed a significantly greater increase in nitrite as compared to controls (p=0.017). Using the area-under-the-curve (AUC) method, results reached statistical significance (p<0.05) within 3 min of embolization. In embolized rabbits, NO(2) levels increased 424±256% compared to baseline. This study shows that nitrite can be measured immediately following a stroke and that our system measures nitrite independent of the extent of the stroke. This study provides evidence for the feasibility of using nitrite as a marker of ischemic stroke.

Exogenous nitric oxide negatively regulates the S-nitrosylation p38 mitogen-activated protein kinase activation during cerebral ischaemia and reperfusion

AIMS

A number of studies have suggested that nitric oxide (NO) plays an important role in the reactive phosphorylation of p38MAPKα (p38). However, whether S-nitrosylation of p38 is activated by NO and the details remain unclear. The aim of the present work was to assess the activation of p38, the S-nitrosylation site and the p38 signalling pathway in rat hippocampus and in HEK293 cell induced by exogenous NO.

METHODS

Primary hippocampal cultures, HEK293 cells and rat model of cerebral ischaemia/reperfusion (brain ischaemia was induced by four-vessel occlusion procedure) were used in this study. Biotin-switch method and immunoblotting were performed to study the S-nitrosylation and phosphorylation of p38, and neuronal loss was observed by histology.

RESULTS

Endogenous NO increased p38 phosphorylation and S-nitrosylation, and the activation of p38 was dependent on the S-nitrosylation of Cys-211, which was critical for the NO-mediated activation of p38. The exogenous NO donor sodium nitroprusside, S-nitrosoglutathione, 7-nitroindazole, the inhibitor of the neuronal nitric oxide synthase, inhibited the activation of p38 signal pathway induced by cerebral ischaemia/reperfusion and attenuated the damage in rat hippocampal neurones. Moreover, the N-methyl-D-aspartate receptor (NMDAR) is probably involved in the p38 activation process of S-nitrosylation and phosphorylation.

CONCLUSION

Endogenous NO induces the S-nitrosylation and phosphorylation of p38 and mediates p38 signalling pathway by NMDAR, and as exogenous NO inhibits this process and is neuroprotective in rat cerebral ischaemia/reperfusion, it may make a contribution to stroke therapy.

Insulin inhibits lipopolysaccharide-induced nitric oxide synthase expression in rat primary astrocytes

Excessive production of nitric oxide (NO) by inducible nitric oxide synthase (iNOS) from reactive astrocytes and microglia may contribute to the development of many types of neurological diseases. Insulin has been shown to inhibit the expression of iNOS, in several organs and cell types. Although insulin and its receptors are present in the central nervous system, the effects of insulin on the iNOS pathway in the brain have not been determined. In this study, using lipopolysaccharide (LPS)-stimulated astrocytes as a model of reactive astrocytes, we investigated the effects of insulin on iNOS expression in activated astrocytes and the mechanism involved. The expression of iNOS was significantly upregulated by LPS in astrocytes. Insulin applied prior to LPS, dose-dependently inhibited LPS-induced iNOS gene expression and iNOS protein levels. In agreement with the suppressive effects of insulin on iNOS expression, insulin also inhibited LPS-induced iNOS activity and NO production. Moreover, insulin was found to significantly inhibit LPS-induced IκB-α phosphorylation and degradation, which led to a decrease in levels of the p65 subunit of NF-κB in the nuclear fraction. Therefore, insulin inhibited LPS-induced iNOS expression via suppressing NF-κB pathway in astrocytes. In addition, treatment with insulin had no effect on LPS-induced PKB phosphorylation. Based on our results, it is plausible to speculate that insulin in the brain may play a neuroprotective role in neurological disorders by controlling the release of NO via the regulation of iNOS expression in astrocytes.

Free cholesterol accumulation impairs antioxidant activities and aggravates apoptotic cell death in menadione-induced oxidative injury

Although the relationship between hypercholesterolemia and oxidative stress has been extensively investigated, direct evidence regarding to the roles of cholesterol accumulation in the generations of reactive oxygen species (ROS) and apoptotic cell death under oxidative stress is lack. In this study, we investigated productions of superoxide anions (O(2)(-)) and nitric oxide (NO), and apoptotic cell death in wild type Chinese hamster ovary (CHO) cells and cholesterol accumulated CHO cells genetically and chemically. Oxidative stress was induced by menadione challenge. The results revealed that abundance of free cholesterol (FC) promoted menadione-induced O(2)(-) and NO productions. FC accumulation down-regulated eNOS expression but up-regulated NADPH oxidases, and inhibited the activities of superoxide dismutase (SOD) and catalase. Treatment of menadione increased the expressions of iNOS and qp91 phox, enhanced the activities of SOD and catalase in the wild-type CHO cells but inhibited the activity of glutathione peroxidase in the cholesterol accumulated CHO cells. Moreover, FC abundance promoted apoptotic cell death in these cells. Taken together, those results suggest that free cholesterol accumulation aggravates menadione-induced oxidative stress and exacerbates apoptotic cell death.

Determination of in vivo nitric oxide levels in animal tissues using a novel spin trapping technology

It has been established that microdialysis ensured by the passage of aqueous solutions of Fe(3+) complexes with N-methyl-D: -glucamine dithiocarbamate (MGDMGD ) through fine dialysis fibers permeable for compounds with molecular weights below 5 kDa. These fibers can be implanted into heart, liver, and kidney tissues, enabling effective binding of Fe(3+)-MGD complexes to nitric oxide generated in interstitial fluids of narcotized rats in vivo. Subsequent treatment of dialyzate samples (60 μL) with sodium dithionite favors conversion of newly formed diamagnetic NO-Fe(3+)-MGD complexes into electron paramagnetic resonance-detectable NO-Fe(2+)-MGD complexes. The basal levels of NO determined from the concentrations of the complexes in the respective tissues are similar (1 μМ). The microdialysis data suggest that treatment of rats with a water-soluble analogue of nitroglycerine or a dinitrosyl iron complex with thiosulfate induces a long-lasting (>1 h) increase in the steady-state level of NO in animal tissues. This novel technology can be used for comparative analyses of production rates of NO and reactive oxygen species when using iron-dithiocarbamate complexes and spin traps for reactive oxygen species, respectively.

Nitrotyrosine in brain tissue of neonates after perinatal asphyxia

HYPOTHESIS

Nitrotyrosine, a reaction product of peroxynitrite and proteins, could be demonstrated in the postmortem examination of brain tissue of full-term neonates who had severe perinatal asphyxia.

METHODS

The brain tissue of 22 full-term neonates who died after severe perinatal asphyxia was examined, including cerebral cortex, basal ganglia, thalamus, hippocampus, brain stem, olives and cerebellum. Median age at death was 52 h. Routine histopathological examination and additional immunohistological staining were carried out with anti-cysteine protease protein 32 antibodies to detect activated caspase 3, anti-nitrotyrosine antibodies to detect nitrotyrosine and anti-CD68 antibodies to detect activated microglia and macrophages, which might be associated with the production of nitric oxide. Staining was scored as none, weak (1-25% positive cells), moderate (26-75% positive cells) or severe (>75% positive cells).

RESULTS

14 patients showed global injury, 4 showed injury of the basal ganglia and thalamus, and 4 showed predominantly parasagittal brain injury. One neonate without perinatal asphyxia served as a control. Nitrotyrosine staining of neurones was shown in all neonates with asphyxia, mostly in the thalamus (70%) and inferior olives (68%). Total nitrotyrosine staining tended to be less in the base of the pons and inferior olives of neonates with parasagittal brain injury. Activated caspase 3 was found mostly in the thalamus (60%) and hippocampus (53%). Positive CD68 staining was mainly present in the thalamus (70% positive).

CONCLUSION

Nitrotyrosine was found in brain tissue of full-term neonates, suggesting that nitric oxide toxicity might have a role in hypoxic-ischaemic brain injury at term. This may be relevant for neuroprotective strategies in full-term neonates with perinatal asphyxia.

Detection of angiotensin II mediated nitric oxide release within the nucleus of the solitary tract using electron-paramagnetic resonance (EPR) spectroscopy

We previously identified an action of nitric oxide (NO) within the nucleus tractus solitarii (NTS) that attenuates the cardiac component of the baroreceptor reflex. In the present study we have tested the hypothesis that angiotensin II (AngII), acting on angiotensin type 1 receptors (AT1R), can release NO within the NTS and that its actions are mediated by soluble guanylate cyclase (sGC). Utilising cryogenic electron paramagnetic resonance (EPR), we have detected NO release in brainstem samples following AngII, but not saline, microinjections into the NTS. In these experiments, we confirmed that both AngII and a NO donor (diethylamine NONOate) in the NTS both depressed the baroreflex bradycardia. In additional studies, we showed that the latter effects were both sensitive to blockade of sGC using 1H-[1,2,4]oxadiazolo-[4,3-a]quinoxalin-1-one (ODQ). To initiate studies to resolve the cellular source of NO released by angiotensin II in the NTS, we performed immunohistochemical/electron microscopy studies on the distribution of AT1R. We found AT1R located on NTS neurones and blood vessels. Since a rise in intracellular calcium [Ca]i levels is prerequisite for nNOS activation, we imaged responses in [Ca]i in NTS neurones during exposure to AngII in vitro using confocal microscopy. Our data indicate a paucity of neurones showing changes in [Ca]i when exposed to AngII (200 nM). We suggest that AngII-induced release of NO is from non-neuronal sites. With the presence of AT1R on blood vessel endothelial cells we propose that AngII released NO in the NTS is due to activation of endothelial nitric oxide synthase located within the endothelium. The present study supports the novel concept that AngII can trigger NO release in the NTS by a mechanism of vascular-neuronal signalling that affects central neuronal networks regulating cardiovascular function.

Nitric oxide down-regulates caveolin-1 expression in rat brains during focal cerebral ischemia and reperfusion injury

As a signalling molecule of the integral membrane protein family, caveolin participates in cellular signal transduction via interaction with other signalling molecules. The nature of interaction between nitric oxide (NO) and caveolin in the brain, however, remains largely unknown. In this study we investigated the role(s) of NO in regulating caveolin-1 expression in rat ischemic brains with middle cerebral artery occlusion (MCAO). Exposure to 1 h ischemia induced the increases in neuronal nitric oxide synthase (nNOS) and NO concentration with concurrent down-regulation of caveolin-1 expression in the ischemic core of rat brains. Subsequent 24 h or more reperfusion time led to an increase in inducible NOS (iNOS) expression and NO production, as well as a decline of caveolin-1 protein at the core and penumbra of the ischemic brain. Afterwards, NOS inhibitors and an NO donor were utilized to clarify the link between NO production and caveolin-1 expression in the rats with 1 h ischemia plus 24 h reperfusion. N(G)-nitro-l-arginine methyl ester (L-NAME, a non-selective NOS inhibitor), N(6)-(1-iminoethyl)-lysine (NIL, an iNOS inhibitor), and 7-nitroindazole (7-NI, a nNOS inhibitor) prevented the loss of caveolin-1 in the core and penumbra of the ischemic brain, whereas l-N(5)-(1-iminoethyl)-ornithine (L-NIO, an endothelial NOS inhibitor) showed less effect than the other NOS inhibitors. S-Nitroso-N-acetylpenicillamine (SNAP, a NO donor) down-regulated the expression of caveolin-1 protein in normal and ischemic brains. These results, when taken together, suggest that NO modulates the expression of caveolin-1 in the brain and that the loss of caveolin-1 is associated with NO production in the ischemic brain.

Upregulated expression of neuronal nitric oxide synthase by insulin in both neurons and astrocytes

Both insulin and nitric oxide (NO) play important roles in the brain. However, there are no unequivocal evidences pointing to a direct effect of insulin on nitric oxide pathway in the brain. In the present study, the effects of insulin on the expression and activity of neuronal nitric oxide synthase (nNOS) were investigated in the cultured cerebellum cell line R2, cerebral cortical astrocytes, and neurons of rats by using flow cytometry, in situ hybridization, RT-PCR, and electron spin resonance (ESR) techniques. In astrocytes, the expression of nNOS was significantly stimulated by insulin in a concentration-dependent manner, with a maximal increase of about 47.6% compared with the control values (p<0.05, t test, n=5). Furthermore, in situ hybridization analysis showed that the expression of nNOS was also significantly increased by insulin (0.64 ng/ml, 6 h), reaching 134.2+/-9.6% of the control values (p<0.05, t test, n=3). In addition, by using nNOS specific primers, RT-PCR analysis also demonstrated the same effect of insulin (0.64 ng/ml, 6 h) on nNOS mRNA expression. Similarly, significant increase of the expression of nNOS protein and mRNA were also observed in both R2 cells and neurons of rats after incubation with insulin. In addition, significant increase of the activity of nNOS in R2 cells and astrocytes were also detected after incubation with insulin (0.64 ng/ml, 9 h) by using ESR technique. Overall, our results suggested that exogenous insulin could upregulate the expression and activity of nNOS in R2 cells, cerebral cortical astrocytes, and neurons of rats. The phenomena opened new insights for further investigation of the physical and pathological significances of insulin in the brain.

Evidence of nuclear localization of neuronal nitric oxide synthase in cultured astrocytes of rats

With immunocytochemistry, we have observed the nuclear localization of neuronal nitric oxide synthase (nNOS) in cultured cerebral cortical astrocytes of rats. During the early six days in the subcultures of these cells, nNOS-immunoreactivity was mainly distributed in the cytoplasm. However, nNOS-immunoreactivity was mainly distributed in the nucleus at day 7, and this nuclear localization lasted about ten hours. Meanwhile, inducible nitric oxide synthase expression was significantly inhibited in these cells. Thereafter, nNOS-immunoreactivity was mainly distributed in the cytoplasm again. By confocal microscopy and western blot analysis, the phenomenon of nNOS nuclear localization was further confirmed; and the activity of nNOS in nuclear protein extracts from astrocytes of day 7-subculture could be detected using electron spin resonance (ESR) technique. These results may represent a new pathway of nitric oxide/nNOS participating in inducible nitric oxide synthase gene transcription regulation.

Characterization of suppression of nitric oxide production by carbon monoxide poisoning in the striatum of free-moving rats, as determined by in vivo brain microdialysis

We examined the effect of carbon monoxide (CO) poisoning on the nitric oxide (NO) system in the striatum of free-moving rats by means of in vivo brain microdialysis. The extracellular levels of the oxidative NO products, nitrite (NO(2)(-)) and nitrate (NO(3)(-)), decreased during exposure to CO at 3000 ppm for 40 min, a condition which causes CO poisoning. The extracellular levels of citrulline (Cit; a by-product of NO production) and arginine (Arg; an NO precursor) also decreased during CO exposure. Following reoxygenation by withdrawal of CO, the NO(2)(-) and NO(3)(-) levels gradually recovered to the control values, though Arg and Cit remained at lower levels, except for a rapid, but transient, recovery shortly before and after reoxygenation, respectively. Simultaneous application of exogenous L-Arg (50 and 100 mM) with CO exposure attenuated the decreases in NO(2)(-) and NO(3)(-) during the CO exposure and accelerated their recovery following reoxygenation. However, D-Arg (100 mM) had no effect on the decrease in NO(2)(-) and NO(3)(-), except for slight and transient attenuation shortly after reoxygenation. Exogenous L-Cit (10 and 100 mM) failed to attenuate the CO-induced decrease in NO(2)(-) and NO(3)(-) levels. The decrease in the NO(2)(-) and NO(3)(-) levels during 8% O(2) exposure for 40 min, which was comparable with that in response to 3000 ppm CO, was resistant to exogenous 100 mM L-Arg, but the recovery of the NO(2)(-) and NO(3)(-) levels following reoxygenation was strongly accelerated. These findings suggest that CO poisoning suppresses NO production in rat striatum in vivo though a mechanism which may not be common with that in hypoxic hypoxia.

Melatonin reduces nitric oxide level during ischemia but not blood-brain barrier breakdown during reperfusion in a rat middle cerebral artery occlusion stroke model

Melatonin is a potent antioxidant and free radical scavenger. Previously, we showed that a single injection of melatonin before ischemia significantly reduced the infarct volume in both permanent and 3-hr middle cerebral artery occlusion (MCAO) rat stroke models. Nitric oxide (NO) and other free radicals play an important role in the pathogenesis of cerebral ischemia, and they have been postulated to mediate the breakdown of the blood-brain barrier (BBB) during ischemia. In this study, we evaluated the influence of melatonin, given at 30 min before MCAO, on brain NO concentration and BBB breakdown. Brain NO concentration was measured at 15 min of MCAO using electron paramagnetic resonance spectroscopy. BBB breakdown at 3 hr of reperfusion following 3 hr of MCAO was assessed using Evans blue extravasation. The relative brain NO concentration was increased to 141.69 +/- 9.71% (mean +/- S.E.M.; n = 9) at 15 min of MCAO. Treatment with melatonin at 1.5, 5, or 50 mg/kg significantly reduced the brain NO concentration to 104.20 +/- 11.20% (n = 8), 55.67 +/- 5.58% (n = 11), and 104.86 +/- 12.56% (n = 9), respectively. Melatonin at 5 mg/kg did not affect Evans blue extravasation. Our results suggest that a single injection of melatonin protects against focal cerebral ischemia partly via inhibition of ischemia-induced NO production and that this regimen does not prevent BBB breakdown following ischemia-reperfusion.

S-nitrosylation of matrix metalloproteinases: signaling pathway to neuronal cell death

Matrix metalloproteinases (MMPs) are implicated in the pathogenesis of neurodegenerative diseases and stroke. However, the mechanism of MMP activation remains unclear. We report that MMP activation involves S-nitrosylation. During cerebral ischemia in vivo, MMP-9 colocalized with neuronal nitric oxide synthase. S-Nitrosylation activated MMP-9 in vitro and induced neuronal apoptosis. Mass spectrometry identified the active derivative of MMP-9, both in vitro and in vivo, as a stable sulfinic or sulfonic acid, whose formation was triggered by S-nitrosylation. These findings suggest a potential extracellular proteolysis pathway to neuronal cell death in which S-nitrosylation activates MMPs, and further oxidation results in a stable posttranslational modification with pathological activity.

Developmental expression and activity variation of nitric oxide synthase in the brain of golden hamster

Nitric oxide (NO) is the downstream effector after the activation of N-methyl-D-aspartate (NMDA) receptors. It is involved in various physiological processes, such as synapse reconstruction and plasticity, neurotoxity and neuronal death. It also participates in the development and maturation of cortical neurons. The expression of nitric oxide synthase (NOS) during the postnatal development of the visual cortex was investigated by both electron spin resonance (ESR) and Western blot methods. A typical spectrum of (DETC)(2)-Fe(II)-NO complex was found in the visual cortex of different age golden hamsters by ESR method. The signal intensity increased after birth, peaked at postnatal day 14 (PD14) and then gradually decreased. An analysis of variance (ANOVA) implied that the NO synthase expression significantly correlated with the developmental processes (p < 0.05). Results of Western blot further confirmed (one-way ANOVA, p < 0.05) the developmental relating expression pattern of NO synthase shown by ESR technique.

Neuropeptide Y-Y1 receptor modulates nitric oxide level during stroke in the rat

In a rat endovascular middle cerebral artery occlusion (MCAO) stroke model, we previously showed that intracerebroventricular (ICV) injection of neuropeptide Y (NPY) or an Y1 receptor agonist, [Leu(31),Pro(34)]-NPY, increased the infarct volume, that an Y1 receptor antagonist, BIBP3226, reduced the infarct volume, and that an Y2 receptor agonist, NPY3-36, had no effect. In this study, we used electron paramagnetic resonance (EPR) spectroscopy to measure nitric oxide (NO) and examined how ICV administration of NPY or its receptor analogs would modulate the brain NO level between the bregma levels +2 and -4 mm during MCAO, since excessive NO mediates ischemic damage. The relative brain NO concentration was increased to 131.94 +/- 7.99% (mean +/- SEM; n = 8) at 15 min of MCAO. NPY treatment further increased the relative brain NO concentration to 250.94 +/- 50.48% (n = 8), whereas BIBP3226 significantly reduced the brain NO concentration to 69.63 +/- 8.84% (n = 8). [Leu(31),Pro(34)]-NPY (137.61 +/- 14.54%; n = 7) or NPY3-36 (129.23 +/- 21.77%; n = 8) did not affect the brain NO concentration at 15 min of MCAO. Our results suggest that the NPY-Y1 receptor activation mediates ischemic injury via NO overproduction and that inhibition of the Y1 receptor may confer protection via suppression of excessive NO production during ischemia.

Increased synthesis of nitric oxide in rat brain cortex due to halogenated volatile anesthetics confirmed by EPR spectroscopy

BACKGROUND

Halogenated volatile anesthetics (HVAs) are considered to be inhibitors of nitric oxide synthase (NOS). On other hand, NO mediates the vasodilation produced by HVAs. Thus, both increase and decrease of NO concentration in brain tissues are possible during anesthesia. Previously, we have observed an increase of NO content in rat brain cortex under halothane anesthesia. The goal of this study was to determine whether the observed phenomenon was general for this anesthetic group, if it was specific for brain cortex, and if the NO increase was due changes in NOS activity.

METHODS

NO scavengers were injected to adult rats 30 min prior to anesthesia. Rats were anesthetized by inhalation of an O2 mixture with volatile anesthetics (1.5% for halothane; 1% for isoflurane, 2% for sevoflurane). After 30 min of anesthesia, rats were decapitated and brain cortex, cerebellum, liver, heart, kidneys and testes were dissected, frozen in liquid nitrogen and subjected to EPR spectroscopy. Nitric oxide content was determined quantitatively based on the intensity of the NO-Fe-DETC complex spectrum and its comparison with the calibration curve.

RESULTS

In rats anesthetized with HVAs, we observed a greater than twofold increase of NO content in brain cortex as compared to the nonanesthetized animals. No significant changes were detected in other organs. The NOS inhibitor N(omega)-nitro-L-arginine abolished the increase of NO content in brain produced by volatile anesthetics.

CONCLUSION

The action of volatile anesthetics is coupled with an increase of NO content in the cortex dependent on NOS activity.

Molecular Mechanisms of Neurologic Injury Following Cardiopulmonary Bypass

Neurologic injury is a potentially devastating consequence of heart surgery. Between 1% and 5% of patients undergoing cardiopulmonary bypass have postoperative strokes and 30% to 80% of patients demonstrate some neurologic dysfunction postoperatively. This review focuses on anatomic, molecular and clinical markers of neurologic injury following cardiopulmonary bypass. Attention is directed to the molecular mechanisms underlying neurologic injury and clinical biochemical markers of injury during heart surgery. Novel strategies to modulate injury are also discussed.

Inhibition of nitric oxide synthesis following severe hypoxia-ischemia restores autoregulation of cerebral blood flow in newborn lambs

Birth asphyxia impairs the autoregulatory ability of the cerebral blood flow. Inappropriate synthesis of vasodilatory nitric oxide may be important in this respect. We investigated if nitric oxide synthesis inhibition by N(omega)-nitro-L-arginine (NLA) could restore cerebral autoregulation after severe hypoxia-ischemia (HI). HI was induced in 15 newborn lambs. Cerebral blood flow (carotid artery blood flow [ml/min]: Qcar) and mean aortic blood pressure [mmHg]: MABP) were measured over a 30 min period before HI (pre-HI), 0-30 min after completion of HI (0-30 post-HI) and from 60 to 120 min post-HI (60-120 post-HI). Immediately after completion of HI, 5 lambs received a placebo (PLAC), 5 low dose NLA (10 mg/kg/iv: NLA-10) and 5 high dose NLA (40 mg/kg/iv: NLA-40). Pre-HI, all groups showed cerebral autoregulation with an upper limit of regulatory ability between 75 and 90 mm Hg. At 0-30 post-HI, all groups lacked autoregulatory ability of the cerebral vascular bed and showed an aortic blood pressure-passive Q(car). At 60-120 post-HI autoregulation was restored in NLA-10 and NLA-40-treated lambs (upper limit of autoregulation was shifted to higher MABP in NLA40-treated lambs), but not in placebo-treated lambs. At 60-120 post-HI MABP was higher in both NLA-groups than in PLAC group (83+/-15 [NLA-10] and 78+/-14 [NLA-40] vs. 65+/-9 mmHg [PLAC], P<0.05). We conclude that severe HI in newborn lambs induces impairment of the autoregulatory ability of the cerebral vascular bed. Even low-dose nitric oxide-synthesis inhibition started upon reperfusion restored autoregulation, suggesting a role for nitric oxide-induced vasodilation in the impairment of autoregulation of the cerebral blood flow after birth asphyxia.

Nitric oxide-forming reaction between the iron-N-methyl-D-glucamine dithiocarbamate complex and nitrite

The objective of this study was to elucidate the origin of the nitric oxide-forming reactions from nitrite in the presence of the iron-N-methyl-D-glucamine dithiocarbamate complex ((MGD)(2)Fe(2+)). The (MGD)(2)Fe(2+) complex is commonly used in electron paramagnetic resonance (EPR) spectroscopic detection of NO both in vivo and in vitro. Although it is widely believed that only NO can react with (MGD)(2)Fe(2+) complex to form the (MGD)(2)Fe(2+).NO complex, a recent article reported that the (MGD)(2)Fe(2+) complex can react not only with NO, but also with nitrite to produce the characteristic triplet EPR signal of (MGD)(2)Fe(2+).NO (Hiramoto, K., Tomiyama, S., and Kikugawa, K. (1997) Free Radical Res. 27, 505-509). However, no detailed reaction mechanisms were given. Alternatively, nitrite is considered to be a spontaneous NO donor, especially at acidic pH values (Samouilov, A., Kuppusamy, P., and Zweier, J. L. (1998) Arch Biochem. Biophys. 357, 1-7). However, its production of nitric oxide at physiological pH is unclear. In this report, we demonstrate that the (MGD)(2)Fe(2+) complex and nitrite reacted to form NO as follows: 1) (MGD)(2)Fe(2).NO complex was produced at pH 7.4; 2) concomitantly, the (MGD)(3)Fe(3+) complex, which is the oxidized form of (MGD)(2)Fe(2+), was formed; 3) the rate of formation of the (MGD)(2)Fe(2+).NO complex was a function of the concentration of [Fe(2+)](2), [MGD], [H(+)] and [nitrite].

Detection and imaging of endogenously produced nitric oxide with electron paramagnetic resonance spectroscopy

Nitric oxide (NO) represents a new paradigm for second messengers in regulation. Despite the numerous physiological and pathophysiological functions of NO, its importance as an endogenous second messenger and a cytostatic and/or cytotoxic agent was unknown until 1987. Recent developments in detection methods for endogenous NO produced directly or indirectly from NO synthases (NOSs) have enabled major advances in our understanding of the role of NO in biological systems. The spin-trapping technique combined with electron paramagnetic resonance (EPR) spectroscopy is a method for analyzing NO production directly both in vivo and in vitro. Iron complexes with dithiocarbamate derivatives are noteworthy among the spin-trapping reagents for NO because NO has a high affinity for iron complexes. The resultant stable nitrosyl iron complexes exhibit an intense three-line signal at room temperature and an axial signal at low temperature. Besides the facility and wide applicability of this method, its outstanding feature is that noninvasive in vivo measurements are available by using a low-frequency EPR spectrometer. In this article, we review on previous and recent developments of in vitro, in vivo, and ex vivo EPR detection and imaging of endogenously produced NO.

Drastic increase in nitric oxide content in rat brain under halothane anesthesia revealed by EPR method

A drastic increase in nitric oxide (NO) content was revealed by the EPR method in rat brain cortex and cerebellum under halothane anesthesia. The NO scavenger diethyldithiocarbamate sodium salt (DETC) and ferrous citrate were injected into adult rats 30-60 min before anesthesia. Rats were anesthetized by inhalation of a halothane-oxygen mixture (1%, 1.5%, 2%, or 4%). After different times of anesthesia, rats were decapitated, and brain cortex and cerebellum were dissected, frozen in liquid nitrogen, and subjected to EPR spectroscopy. The concentration of NO was determined from the NO-Fe-DETC radical spectrum. In control animals, NO content in the cerebellum was only 68% of that in the cortex. We observed a time-dependent increase in NO content in the cortex and cerebellum of rats anesthetized with 1.5% halothane. In brain cortex, the NO level increased to six times that of waking animals after 30 min and remained at this level up to 60 min of anesthesia. In cerebellum the changes were less drastic, the NO level showing only a 2-fold increase. The same effect was produced by 1% and 2% halothane. Ketamine, chloral hydrate, and pentobarbital were used as reference drugs. None of these anesthetics produced effects similar to those of halothane. In ketamine-anesthetized rat brain, the NO content slightly decreased. Pentobarbital and chloral hydrate produced an insignificant increase in NO. Data are discussed in the context of possible interference of halothane in the regulation of nitric oxide synthase activity.

Role of nitric oxide in intestinal ischaemia-reperfusion injury studied using electron paramagnetic resonance

BACKGROUND

The role of nitric oxide in intestinal ischaemia-reperfusion (I/R) remains poorly defined, partly because of difficulty in detecting the nitric oxide free radical. In this study nitric oxide production was assessed during intestinal I/R by direct measurement using electron paramagnetic resonance (EPR), and the production of nitric oxide in jejunum and ileum was correlated with their different abilities to resist I/R injury.

METHODS

Rats were given an electron spin trapper (diethyldithiocarbamate/ferrous citrate) by intraperitoneal injection. Thirty-six segments each of jejunum and ileum were subjected to 15-90 min of ischaemia and 25 min of reperfusion. Tissue samples were analysed for EPR signals using a spectrometer.

RESULTS

Mean(s.d.) basal nitric oxide level was significantly higher in ileum (3.39(1.42) units) than jejunum (0. 65(0.05) units) (P = 0.0005). Increasing ischaemic times in the ileum resulted in decreasing nitric oxide levels (85, 32 and 13 per cent of basal level at 30, 60 and 90 min respectively); reperfusion resulted in further nitric oxide reduction (mean decrease 26 per cent). Severe (grade 3) histological damage was observed in low nitric oxide states (after 15 min of I/R in jejunum, 60 min of I/R in ileum).

CONCLUSION

Nitric oxide can be measured in intestinal tissues directly by EPR. The findings support a protective role for nitric oxide in I/R, and offer an explanation for the greater resistance to I/R of ileum.

Nitric oxide and nitric oxide synthase in the early phase of perinatal asphyxia of the rat

The role of nitric oxide, a compound involved in neurotransmission and regulation of cerebral blood flow, in cerebral ischemia is still not fully elucidated yet. Although well studied in adult systems of cerebral ischemia/hypoxia, information on nitric oxide in perinatal asphyxia is limited and, in particular, no direct evidence for its generation has been provided. We therefore decided to study nitric oxide generation in brain of asphyctic rat pups by biophysical and biochemical methods. We used a simple, non-invasive rat model resembling the clinical situation in perinatal asphyxia: rat pups delivered by Caesarean section were placed into a water bath at 37 degrees C still in patent membranes for various asphyctic periods (up to 20 min). Brain pH, cerebral blood flow, neuronal nitrix oxide synthase messenger RNA (by northern and dot blot analysis), immunoreactive protein (by western blot analysis) and nitric oxide synthase activity were determined; generation of nitric oxide was evaluated directly by electron paramagnetic resonance spectroscopy. Neuronal nitric oxide synthase messenger RNA activity and nitric oxide generation were unaffected, whereas neuronal nitric oxide synthase-immunoreactive protein of 150,000 mol. wt was decreased and of 136,000 mol. wt was increased with the length of the asphyctic period. This is the first report on direct evidence for the generation of nitric oxide in perinatal asphyxia and we demonstrate that nitric oxide production remains unaffected even by 20 min of asphyxia, at a time-point when cerebral blood flow was increased four-fold and severe acidosis was present. However, it was found that levels of immunoreactive neuronal nitric oxide synthase of 136,000 mol. wt were increased paralleling the length of asphyxia. Levels of the 150,000 mol. wt immunoreactive neuronal nitric oxide synthase protein decreased, suggesting a different regulation pattern. Thus, the present biochemical and biophysical results form the basis for further investigations on nitric oxide in perinatal asphyxia.

Continuous monitoring of in vivo nitric oxide formation using EPR analysis in biliary flow

A method to continuously monitor the nitric oxide (NO) level in anesthetized rats, using an in vivo trapping reaction of NO by iron-dithiocarbamate complex, is reported. Previously, we developed a method of monitoring NO in bile samples containing an NO complex excreted from the liver (Anal. Biochem. 243, 8-14, 1996). In the present study, we modified the method so that the bile flows directly through the EPR sample cell. Rats were injected with low doses of lipopolysaccharide (LPS) to induce NO formation and were later anesthetized. After cannulation, the bile duct was connected to the inlet of the EPR sample cell and the trapping agent iron complex of D-N-methylglucamine dithiocarbamate (MGD-Fe) was administered. The EPR signal level from NO complex of MGD-Fe in the flowing bile was continuously monitored. Using this method, immediate changes in in vivo NO level in rats were observed following administration of drugs that can affect NO formation. In addition, a continuous intravenous saline containing MGD-Fe made the EPR signal level stable and improved animal condition as well as survival time. Therefore, this method has two merits; (1) one can continuously monitor NO formation until it reaches the maximum level; (2) a rapid change in NO level after intervention can be followed. Using this method, we tested the effect of the substrate L-arginine and inhibitors for NO synthase activity and NO synthase induction. The sensitivity of the present method was tested by monitoring NO formation in rats after exposure to ionizing radiation.

Effects of hypoxia-ischemia and inhibition of nitric oxide synthase on cerebral energy metabolism in newborn piglets

The present study was designed to examine the effects of inhibition of nitric oxide synthase on cerebral energy metabolism after hypoxia-ischemia in newborn piglets. Ten 1- to 3-d-old piglets received N(omega)-nitro-L-arginine (NNLA), an inhibitor of nitric oxide synthase (NNLA-hypoxia, n = 5), or normal saline (hypoxia, n = 5) 1 h before cerebral hypoxia-ischemia. After the infusion, hypoxia-ischemia was induced by bilateral occlusion of the carotid arteries and decreasing FiO2 to 0.07 and maintained for 60 min. Thereafter, animals were resuscitated and ventilated for another 3 h. Using 1H- and 31P-magnetic resonance spectroscopy, cerebral energy metabolism was measured in vivo at 15-min intervals throughout the experiment. Phosphocreatine to inorganic phosphate ratios decreased from 2.74 +/- 0.14 to 0.74 +/- 0.36 (hypoxia group) and 2.32 +/- 0.17 to 0.18 +/- 0.10 (NNLA-hypoxia group) during hypoxia-ischemia. Thereafter, phosphocreatine to inorganic phosphate ratios returned rapidly to baseline values in the hypoxia group, but remained below baseline values in the NNLA-hypoxia group. Intracellular pH decreased during hypoxia-ischemia and returned to baseline values on reperfusion in both groups. Intracellular pH values were lower in the NNLA-hypoxia group (p < 0.001, ANOVA). Lactate was not present during the baseline period. After hypoxia-ischemia, lactate to N-acetylaspartate ratios increased to 1.34 +/- 0.28 (hypoxia group) and 2.22 +/- 0.46 (NNLA-hypoxia group). Lactate had disappeared after 3 h of reperfusion in the hypoxia group, whereas lactate to N-acetylaspartate ratios were 1.37 +/- 1.37 in the NNLA-hypoxia group. ANOVA demonstrated a significant effect of NNLA on lactate to N-acetylaspartate ratios (p < 0.001). Inhibition of nitric oxide synthase by NNLA tended to compromise cerebral energy status during and after cerebral hypoxia-ischemia in newborn piglets.

Roles of nitric oxide in brain hypoxia-ischemia

A large body of evidence has appeared over the last 6 years suggesting that nitric oxide biosynthesis is a key factor in the pathophysiological response of the brain to hypoxia-ischemia. Whilst studies on the influence of nitric oxide in this phenomenon initially offered conflicting conclusions, the use of better biochemical tools, such as selective inhibition of nitric oxide synthase (NOS) isoforms or transgenic animals, is progressively clarifying the precise role of nitric oxide in brain ischemia. Brain ischemia triggers a cascade of events, possibly mediated by excitatory amino acids, yielding the activation of the Ca2+-dependent NOS isoforms, i.e. neuronal NOS (nNOS) and endothelial NOS (eNOS). However, whereas the selective inhibition of nNOS is neuroprotective, selective inhibition of eNOS is neurotoxic. Furthermore, mainly in glial cells, delayed ischemia or reperfusion after an ischemic episode induces the expression of Ca2+-independent inducible NOS (iNOS), and its selective inhibition is neuroprotective. In conclusion, it appears that activation of nNOS or induction of iNOS mediates ischemic brain damage, possibly by mitochondrial dysfunction and energy depletion. However, there is a simultaneous compensatory response through eNOS activation within the endothelium of blood vessels, which mediates vasodilation and hence increases blood flow to the damaged brain area.

Nitric oxide production in the CA1 field of the gerbil hippocampus after transient forebrain ischemia : effects of 7-nitroindazole and NG-nitro-L-arginine methyl ester

BACKGROUND AND PURPOSE

The present study was designed to examine the time course of nitric oxide (NO) production and the source of NO in the CA1 field of the gerbil hippocampus after transient forebrain ischemia.

METHODS

The production of NO in the CA1 field of the hippocampus after transient ischemia was monitored consecutively by measuring total NO metabolites (NOx-, NO2- plus NO3-) with the use of brain microdialysis. 7-Nitroindazole (7-NI) and NG-nitro-L-arginine methyl ester were used to dissect the relative contributions of neuronal NO synthase and endothelial NO synthase to the NO production. The histological outcomes of 7-NI in 5- and 10-minute global ischemia were also evaluated.

RESULTS

The production of NO in the CA1 field of the hippocampus after ischemia was dependent on the severity of ischemia. Ischemia for 2 or 5 minutes did not induce a significant increase in NOx- levels in the CA1 field of the hippocampus after reperfusion, whereas the 10- and 15-minute ischemias produced significant and persistent increases in NOx- levels. 7-NI did not inhibit the basal NOx- levels and showed no effects on NOx- levels after 5 minutes of ischemia. However, it completely inhibited the increased NOx- levels after 10 or 15 minutes of ischemia. 7-NI provided minor neuroprotection in 5 minutes but not in 10 minutes of global ischemia.

CONCLUSIONS

The increased NO level in the CA1 field of the hippocampus after ischemia is produced mostly by neuronal NO synthase, whereas the basal NO level mainly originates from endothelial NO synthase. The observed neuroprotective effect of 7-NI in 5-minute global ischemia in gerbils may not be due to neuronal NO synthase inhibition by this drug.

Influence of the antioxidant quercetin in vivo on the level of nitric oxide determined by electron paramagnetic resonance in rat brain during global ischemia and reperfusion

We characterized the changes in nitric oxide (NO) levels in the brain during global forebrain ischemia and reperfusion and tested the ability of the natural flavonoid, quercetin, and a synthetic flavonoid, FB277, to increase the amount of available NO by elimination of the superoxide radicals produced during reperfusion. In Sprague-Dawley rats, we used a four-vessel occlusion model of forebrain ischemia (15 min) and reperfusion (30 min). Brain NO was measured on samples of cerebral cortex and cerebellum ex vivo by electron paramagnetic resonance (EPR) spectroscopy. The spin trap used was diethyldithiocarbamate sodium salt (DETC) associated with ferrous citrate. The complex Fe(DETC)2NO was detected at 77 K as a triplet signal at g = 2.035. Groups of animals were treated with quercetin or FB277 (3-morpholinomethyl-3',4',5,7tetramethoxyflavone) or polyethylene glycol-conjugated superoxide dismutase (PEG-SOD). In control (intact anesthetized animals), the signal was about 3 times greater in the cortex than in the cerebellum. During ischemia, the signal rose to 110% in cortex (NS) and 283% in cerebellum (P < 0.05). In reperfusion, it fell again to 91% of control in cerebellum (NS) and 35% in cortex (P < 0.05). Treatment by quercetin (5 mg/kg i.v.) of intact and ischemia-reperfusion groups did not significantly change the signal amplitude in the cerebellum, but did double it in the cortex (to 76% of control) for the ischemia-reperfusion group (P < 0.05). In contrast, FB277 (3.75 mg/kg i.v.) did not increase the signal in the cortex during ischemia-reperfusion, but did do so in the cerebellum (to 152% of control, P < 0.05). The results obtained for PEG-SOD (10,000 U/kg i.v.) were similar to those for FB277. In separate in vitro measurements, we found that quercetin but not FB277 efficiently scavenged superoxide. We hypothesize that quercetin but not FB277 scavenged superoxide anions released in the cortex during reperfusion, thus diminishing the amount of NO removed by the formation of peroxynitrite. The lack of effect of PEG-SOD may be related to the need for chronic treatment to obtain protection.

Dual role for nitric oxide in dynorphin spinal neurotoxicity

The pharmacological effects of nitric oxide synthase (NOS) inhibitors, NO donor, and NOS substrate on dynorphin(Dyn) A(1-17) spinal neurotoxicity were studied. Intrathecal (i.t.) pretreatment with both 7-nitroindazole 1 micromol, a selective neuronal constitutive NOS (ncNOS) inhibitor, and aminoguanidine 1 micromol, a selective inducible NOS (iNOS) inhibitor, 10 min prior to i.t. Dyn A(1-17) 20 nmol significantly ameliorated Dyn-induced neurological outcome. Both 7-nitroindazole and aminoguanidine significantly antagonized the increases of cNOS and iNOS activities measured by conversion of 3H-L-arginine to 3H-L-citrulline in the ventral spinal cord, and blocked the Dyn-induced increases of ncNOS-immunoreactivity in the ventral horn cells 4 h after i.t. Dyn A(1-17) 20 nmol. Pretreatment with Nomega-nitro-L-arginine methyl ester (L-NAME) 1 micromol, a cNOS inhibitor nonselective to both ncNOS and endothelial NOS (ecNOS), did not antagonize Dyn A(1-17) 20 nmol-induced permanent paraplegia but aggravated Dyn A(1-17) 10 nmol-induced transient paralysis and caused permanent paraplegia. Pretreatment with L-NAME 1 micromol 10 min before i.t. Dyn A(1-17) 1.25 and 2.5 nmol, which produced no significant motor dysfunction alone, induced transient paralysis in seven out of 12 and five out of seven rats, respectively. L-NAME 1 micromol plus Dyn A(1-17) 10 nmol induced ncNOS-immunoreactivity expression in ventral horn cells. Both low and high doses of aminoguanidine (0.2-30 micromol) did not affect spinal motor function, but high doses of L-NAME (5-20 micromol) induced dose-dependent hindlimb and tail paralysis associated with spinal cord injury in normal rats. Pretreatment with low-dose Spermine NONOate, a controlled NO releaser, 0.1 and 0.5 micromol 10 min before i.t. Dyn A(1-17) 20 nmol, significantly prevented Dyn spinal neurotoxicity, and high-dose Spermine NONOate 2 micromol i.t. per se induced transient and incomplete paraplegia. But pretreatment with L-Arg 10 micromol 10 min before Dyn A(1-17) 20 nmol produced only partial blockade of Dyn-induced paraplegia. These results demonstrated that relatively specific inhibition of ncNOS and iNOS block Dyn-induced increases in cNOS and iNOS activities and ncNOS-immunoreactivity in ventral spinal cord, but nonspecific inhibition of ncNOS and ecNOS aggravated Dyn spinal neurotoxicity. It suggested that both ncNOS and iNOS play an important role, but ecNOS might be beneficial in Dyn spinal neurotoxicity. Moderate production of NO (at vascular level) has an apparently neuroprotective effect, and overproduction of NO (at cellular level) induces neurotoxicity.

Amelioration of ischaemia-induced neuronal death in the rat striatum by NGF-secreting neural stem cells

The objective of the present study was to explore whether grafted immortalized neural stem cells, genetically modified to secrete nerve growth factor (NGF), can ameliorate neuronal death in the adult rat striatum following transient middle cerebral artery occlusion (MCAO). One week after cell implantation in the striatum, animals were subjected to 30 min of MCAO. Striatal damage was evaluated at the cellular level after 48 h of recirculation using immunocytochemical and stereological techniques. The ischaemic insult caused an extensive degeneration of projection neurons, immunoreactive for dopamine- and adenosine 3': 5'-monophosphate-regulated phosphoprotein with a molecular weight of 32 kilodaltons (DARPP-32). 3H-Thymidine autoradiography demonstrated surviving grafted cells in the lesioned striatum in all transplanted rats. The loss of striatal projection neurons was significantly reduced (by an average of 45%) in animals with NGF-secreting grafts, whereas control cells, not producing NGF, had no effect. The neuroprotective action of NGF-secreting grafts was also observed when the total number of striatal neurons immunopositive for the neuronal marker NeuN was quantified, as well as in cresyl violet-stained sections. The present findings indicate that administration of NGF by ex vivo gene transfer and grafting of neural stem cells can ameliorate death of striatal projection neurons caused by transient focal ischaemia.

Effects of EGb 761 on nitric oxide and oxygen free radicals, myocardial damage and arrhythmia in ischemia-reperfusion injury in vivo

The cardioprotective effects of EGb 761 on the release of nitric oxide (NO), the concentration of serum thiobarbituric acid reaction substance (TBARS), the activity of creatine kinase (CK) and the incidence of ventricular arrhythmias were investigated in myocardial ischemia-reperfusion injury in vivo. Using sodium nitrite (NaNO2) as standard source of nitric oxide (NO), we compared the correlation coefficients of the three measuring methods used currently in the determination of NOFe2+(DETC)2 complex with that of the measuring method suggested in this study. The result showed that measuring the whole height of three splitting signals is the best linear correlation to the concentration of NO comparing with other methods in this system. Using this method, we observed the effects of EGb 761 on NOFe2+(DETC)2 complex in myocardial ischemia-reperfusion injury in vivo. The hearts of the Wistar rats were subjected to 30 min of ischemia and 10 min of reperfusion in vivo. Different doses of EGb 761 (25, 50, 100, 200 mg/kg i.p.), superoxide dismutase (SOD, 10(4) U/kg), l-arginine (50 mg/kg i.p.) and nitric oxide synthase (NOS) inhibitor NG-nitro-l-arginine (NNA, 50 mg/kg i.p.) were administered to the ischemia-reperfusion rats. EGb 761 under the dose of 100 mg/kg increased the signal intensity of NOFe2+(DETC)2 complex, while EGb 761 at 200 mg/kg showed an effect of decreasing the signal intensity of NOFe2+(DETC)2 complex. EGb 761 inhibited the formation of TBARS, the release of CK, and mitigated the incidence of ventricular arrhythmias in a dose dependent way. Both l-arginine and SOD increased the signal intensity of NOFe2+(DETC)2 complex and inhibited the formation of TBARS, the leakage of CK and the incidence of ventricular arrhythmia. NNA not only had no protective effects on myocardial injury, but also increased the incidence of reperfusion-induced arrhythmia. In conclusion, EGb 761 has cardiovascular protective effects by means of adjusting the level of NO and inhibiting oxygen free radicals induced lipid peroxidation in myocardial ischemia-reperfusion injury in vivo.

In vivo nitric oxide detection in the septic rat brain by electron paramagnetic resonance

To detect nitric oxide (NO) in the rat brain during lipopolysaccharide (LPS)-induced sepsis, electron paramagnetic resonance (EPR) was employed with the NO trapping technique, using an iron and N,N-diethyldithiocarbamate (DETC) complex. An X-band (about 9.5 GHz) EPR system detected a triplet signal (g = 2.038) derived from an NO-Fe-DETC complex being superimposed on the g(perpendicular) signal of Cu-DETC complex at liquid nitrogen temperature. The height of the triplet signal peaked seven hours after injection of 40 mg/kg of LPS, and over 25 x 10(4) U/kg of IFN-gamma enhanced the LPS-induced NO formation. Pretreatment with N(G)-monomethyl-L-arginine (NMMA), an NO synthase inhibitor, deleted only the triplet signal. A triplet signal (g(iso) = 2.040, aN = 1.28 mT) derived from the NO-Fe-DETC complex was also observed at ambient temperature. Then, a home-built 700 MHz EPR system was used to detect an NO signal in the septic rat brain in vivo. We successfully monitored the NO-Fe-DETC signal in the head region of a living rat under the condition that provided maximum height of the NO-Fe-DETC signal in the X-band EPR study. Pretreatment with NMMA again deleted the NO-Fe-DETC signal. This is the first EPR observation of endogenous NO in the brain of living rats.

Profiles of cortical tissue depolarization in cat focal cerebral ischemia in relation to calcium ion homeostasis and nitric oxide production

Cortical depolarization was investigated in a topographic gradient of ischemic density after 1-hour transient middle cerebral artery occlusion in halothane-anesthetized cats. A laser Doppler flow probe, an ion-selective microelectrode, and a nitric oxide (NO) electrode measured regional CBF (rCBF), direct current (DC) potential, extracellular Ca2+ concentration ([Ca2+]o), and NO concentration in ectosylvian and suprasylvian gyri of nine animals. Recordings revealed 12 of 18 sites with persistent negative shifts of the DC potential, severe rCBF reduction, and a drop of [Ca2+]o characteristic for core regions of focal ischemia. Among these sites, two types were distinguished by further analysis. In Type 1 (n = 5), rapid, negative DC shifts resembled anoxic depolarization as described for complete global ischemia. In this type, ischemia was most severe (8.9 +/- 2.5% of control rCBF), [Ca2+]o dropped fast and deepest (0.48 +/- 0.20 mmol/L), and NO concentration increased transiently (36.1 +/- 24.0 nmol/L at 2.5 minutes), and decreased thereafter. In Type 2 (n = 7), the DC potential fell gradually over the first half of the ischemic episode, rCBF and [Ca2+]o reductions were smaller than in Type 1 (16.2 +/- 8.2%; 0.77 +/- 0.41 mmol/L), and NO increased continuously during ischemia (53.1 +/- 60.4 nmol/L at 60 minutes) suggesting that in this type NO most likely exerts its diverse actions on ischemia-threatened tissue. In the remaining six recording sites, a third type (Type 3) attributable to the ischemic periphery was characterized by minimal DC shifts, mild ischemia (37.2 +/- 13.3%), nonsignificant alterations of [Ca2+]o, but decreased NO concentrations during middle cerebral artery occlusion. Reperfusion returned the various parameters to baseline levels within 1 hour, the recovery of [Ca2+]o and NO concentration being delayed in Type 1. An NO synthase inhibitor (N(G)-nitro-L-arginine, 50 mg/kg intravenously; four animals) abolished NO elevation during ischemia. In conclusion, even in the core of focal cerebral ischemia and reperfusion, different ischemic densities produce different types of cortical tissue manifesting distinctive chronological profiles of depolarization, Ca2+ influx, and NO synthesis.

Cerebrovascular reactivity in hypertensive patients: a transcranial Doppler study

PURPOSE

We studied the usefulness of transcranial Doppler sonography for assessing changes in vasoreactivity in patients with hypertension and the hemodynamic consequences of hypertension.

METHODS

The study group comprised 25 patients with chronic severe hypertension and 25 age- and sex-matched healthy subjects. Cerebrovascular reserve capacity was assessed by transcranial Doppler recording of the blood flow velocity in both middle cerebral arteries before and 5, 10, 15, and 20 minutes after intravenous injection of 1 g of acetazolamide (Diamox). Blood pressure, blood gases, and other blood parameters were also measured before and after acetazolamide injection. The sizes of the left atrium, left ventricle, and aortic root were measured by echocardiography and correlated with the vasoreactivity after acetazolamide injection.

RESULTS

After acetazolamide injection, no significant changes in blood pressure were observed in either group. The mean blood flow velocity in the middle cerebral arteries of hypertensive patients (60.8 +/- 2.6 cm/sec) was not significantly different from that of controls (58.8 +/- 1.9 cm/sec) before acetazolamide injection. Ten minutes after acetazolamide injection, the percentage change in blood flow velocity was significantly lower in the hypertensive group (36.2 +/- 4.5%) than in the controls (52.6 +/- 3.7%). A significant negative correlation (p < 0.05) between decreased vasoreactivity and increased size of the left atrium and aortic root was observed.

CONCLUSIONS

Vasoreactivity decreases in hypertensive patients without neurologic deficits or computed tomography abnormalities. Enlargement of the left atrium correlates well with the severity of the impairment in vasoreactivity. Transcranial Doppler sonography can be a sensitive tool in the investigation of vascular impairment caused by hypertension and in the follow-up of hypertensive patients.

Function of cell membranes in cerebral cortical tissue of newborn piglets after hypoxia and inhibition of nitric oxide synthase

Hypoxia-induced brain cell membrane lipid peroxidation can be caused by free radicals that are produced during hypoxia. Recently, the production of nitric oxide (NO), a free radical, has been shown to be increased during cerebral hypoxia-ischemia. The present study tested the hypothesis that inhibition of NO synthase (NOS) reduced hypoxia-induced modifications of Na+,K+-ATPase activity, lipid peroxidation, and [3H]MK-801 binding to the N-methyl-D-aspartate (NMDA) receptor in cerebral cortical tissue of newborn piglets. Studies were performed in 26 newborn piglets. Cerebral NOS was inhibited by the i.v. administration of 25 or 50 mg/kg N(omega)-nitro-L-arginine (NNLA) over 30 min. Control animals received normal saline. Six groups of piglets were thus created (normoxia, no NNLA; normoxia + NNLA 25 mg/kg; normoxia + NNLA 50 mg/kg; hypoxia, no NNLA; hypoxia + NNLA 25 mg/kg; hypoxia + NNLA 50 mg/kg). One hour after the start of NNLA or saline infusion, hypoxia was induced by lowering the FiO2 to 0.07 in the three hypoxia groups, whereas in the three other groups normoxia was maintained. After 60 min of hypoxia, the brain was taken out and frozen. NOS activity, Na+,K+-ATPase activity, conjugated dienes, and [3H]MK-801 binding to the NMDA receptor of cerebral cortical tissue were determined. NOS activity was reduced to 34% of its baseline value with NNLA 25 mg/kg, and to 19-27% of its baseline value with NNLA 50 mg/kg, respectively. Administration of NNLA did neither significantly alter the hypoxia-induced production of conjugated dienes, indicating lipid peroxidation nor the decrease of Na+,K+-ATPase activity after hypoxia. [3H]MK-801 binding studies of the NMDA receptor, however, showed that NNLA preserved Bmax and Kd after hypoxia. We conclude that inhibition of NOS does not change the hypoxia-induced decrease of Na+,K+-ATPase activity and production of conjugated dienes in brain cell membranes. Inhibition of NOS preserved the binding of [3H]MK-801 to the NMDA receptor after hypoxia.

Glial cell line-derived neurotrophic factor protects against ischemia-induced injury in the cerebral cortex

Glial cell line-derived neurotrophic factor (GDNF), a recently described and cloned member of the transforming growth factor (TGF)-beta superfamily, has been shown to have marked trophic activity on several populations of central neurons. Survival-promoting and injury protectant activity in vitro and in vivo, using several paradigms, has been demonstrated for ventral mesencephalic dopaminergic neurons and spinal cord motoneurons. In view of a proposed commonality of mechanisms, involving intracellular free radical generation, depolarization-induced Ca2+ influx, and mitochondrial respiratory enzyme injury, between such GDNF-responsive paradigms and those of ischemia-induced injury, we tested the effects of GDNF on the extent of neural degeneration induced by transient middle cerebral artery (MCA) occlusion. We now report that intracerebroventricular and intraparenchymal administration of GDNF potently protects the cerebral hemispheres from damage induced by MCA occlusion. In addition, the increase in nitric oxide that accompanies MCA occlusion and subsequent reperfusion is blocked almost completely by GDNF. Thus, this protein may play an important role in the treatment of cerebrovascular occlusive disease.

Stimulation and inhibition of nitric oxide production in macrophages and neural cells as observed by spin trapping

We have combined electron paramagnetic resonance (EPR) and spin trapping techniques to measure nitric oxide (NO) production by activated macrophages and neural cells in vitro. Macrophages stimulated by bacterial lipopolysaccharide (LPS), gamma interferon (IFN gamma), or both, produced NO. Differentiated and undifferentiated neural cells activated by KCl and CaCl2, N-methyl-D-aspartate (NMDA), and IFN gamma were shown to produce NO as well. The mechanism of activation in neural cells could be either by channels or receptors. Maximum NO production in macrophages was achieved when stimulated by a combination of LPS and IFN gamma administered sequentially or concurrently. IFN gamma was the most effective stimulant for neural cells. The in vitro production of NO by all these cells was inhibited by NG-monomethyl L-arginine (L-NMMA) in a dose-dependent manner. Complete inhibition of NO production occurred when cells were grown in L-arginine free medium, indicating that L-arginine was essential for NO production. We also concluded from our study that NO production in macrophages was in greater amounts and more long lasting in duration than that observed in the neural cells.