Nitric oxide synthase in cerebral ischemia. Possible contribution of nitric oxide synthase activation in brain microvessels to cerebral ischemic injury

Effects of prenatal hypoxia-ischemia on male rat periaqueductal gray matter: Hyperalgesia, astrogliosis and nitrergic system impairment

Prenatal hypoxic-ischemic insult (HI) may lead to a variety of neurological consequences that may persist throughout adulthood. In the most severe cases, HI is known to increase pain sensitivity which profoundly impacts quality of life. Periaqueductal gray matter (PAG) is a relevant region of the descending pain pathway and its function may be modulated by a complex network that includes nitrergic neurons and glial response, among other factors. Astrocytes, central players in pain modulation, are known to respond to HI by inducing hyperplasia, hypertrophy and increasing the number of their processes and the staining of glial fibrillary acidic protein (GFAP). In this work we investigated the effects of prenatal HI on touch and pain sensitivity, besides the distribution of the neuronal isoform of Nitric Oxide Synthase (nNOS) and GFAP in the PAG of young and adult male rats. At 18 days of gestation, rats had their uterine arteries clamped for 45 min (HI group). SHAM-operated animals were also generated (SHAM group). At post-natal day 30 (P30) or 90 (P90), the offspring was submitted to the behavioral tests of Von Frey and formalin or histological processing to perform immunohistochemistry for nNOS and GFAP. Although there was no significant difference between the groups concerning touch sensitivity, we observed an increase in pain sensitivity in HI P30 and HI P90. The number of nNOS + cells was reduced in HI adult animals in dlPAG and vlPAG. GFAP immunostaining was increased in HI P90 in dlPAG and dmPAG. Our results demonstrated for the first time an increase in pain sensitivity as a consequence of prenatal HI in an animal model. It reinforces the relevance of this model to mimic the effects of prenatal HI, as hyperalgesia.

4-Hydroxy-2-nonenal antimicrobial toxicity is neutralized by an intracellular pathogen

Pathogens encounter numerous antimicrobial responses during infection, including the reactive oxygen species (ROS) burst. ROS-mediated oxidation of host membrane poly-unsaturated fatty acids (PUFAs) generates the toxic alpha-beta carbonyl 4-hydroxy-2-nonenal (4-HNE). Although studied extensively in the context of sterile inflammation, research into 4-HNE’s role during infection remains limited. Here, we found that 4-HNE is generated during bacterial infection, that it impacts growth and survival in a range of bacteria, and that the intracellular pathogen Listeria monocytogenes induces many genes in response to 4-HNE exposure. A component of the L. monocytogenes 4-HNE response is the expression of the genes lmo0103 and lmo0613, deemed rha1 and rha2 (reductase of host alkenals), respectively, which code for two NADPH-dependent oxidoreductases that convert 4-HNE to the product 4-hydroxynonanal (4-HNA). Loss of these genes had no impact on L. monocytogenes bacterial burdens during murine or tissue culture infection. However, heterologous expression of rha1/2 in Bacillus subtilis significantly increased bacterial resistance to 4-HNE in vitro and promoted bacterial survival following phagocytosis by murine macrophages in an ROS-dependent manner. Thus, Rha1 and Rha2 are not necessary for 4-HNE resistance in L. monocytogenes but are sufficient to confer resistance to an otherwise sensitive organism in vitro and in host cells. Our work demonstrates that 4-HNE is a previously unappreciated component of ROS-mediated toxicity encountered by bacteria within eukaryotic hosts.

Synergistic oxidative impact of aluminum chloride and sodium fluoride exposure during early stages of brain development in the rat

Aluminum is widely used in industry and in cooking utensils, especially in countries with low economic and social standards. Fluoride is also used in industry, a major component of toothpaste and is added to the drinking water in many countries to fight teeth decay and cavities. Consequently, the coexistence of aluminum and fluoride is highly probable. Growing evidence indicates that environmental pollutants during the early stages of embryonic development may reprogram the offspring's brain capabilities to encounter oxidative stress during the rest of their postnatal life. This study investigated the impact of sodium fluoride (NaF, 0.15 g/L) and aluminum chloride (AlCl₃, 500 mg/L) added, individually or in combination, to the deionized drinking water starting from day 6 of gestation until just after weaning, or until the age of 70 days postnatal life. A significant decline was observed in tissue contents of vitamin C, reduced glutathione, GSH/GSSH ratio, and the total protein, as well as in the activities of Na⁺/K⁺-ATPase and superoxide dismutase (SOD) in almost all cases. On the contrary, lipid peroxidation and NO, as total nitrate, exhibited a significant increase in comparison with the corresponding control. Based on the present results, administration of Al and NaF, alone or in combination abated the quenching effects of the antioxidant system and induced oxidative stress in most brain regions under investigation. In conclusion, aluminum and fluoride are very noxious environmental pollutants that interfere with the proper functions of the brain neurons and their combination together aggravates their hazard.

Guanosine prevents nitroxidative stress and recovers mitochondrial membrane potential disruption in hippocampal slices subjected to oxygen/glucose deprivation

Guanosine, the endogenous guanine nucleoside, prevents cellular death induced by ischemic events and is a promising neuroprotective agent. During an ischemic event, nitric oxide has been reported to either cause or prevent cell death. Our aim was to evaluate the neuroprotective effects of guanosine against oxidative damage in hippocampal slices subjected to an in vitro ischemia model, the oxygen/glucose deprivation (OGD) protocol. We also assessed the participation of nitric oxide synthase (NOS) enzymes activity on the neuroprotection promoted by guanosine. Here, we showed that guanosine prevented the increase in ROS, nitric oxide, and peroxynitrite production induced by OGD. Moreover, guanosine prevented the loss of mitochondrial membrane potential in hippocampal slices subjected to OGD. Guanosine did not present an antioxidant effect per se. The protective effects of guanosine were mimicked by inhibition of neuronal NOS, but not of inducible NOS. The neuroprotective effect of guanosine may involve activation of cellular mechanisms that prevent the increase in nitric oxide production, possibly via neuronal NOS.

Accessible Method for the Development of Novel Sterol Analogues with Dipeptide-like Side Chains That Act as Neuroinflammation Inhibitors

A number of novel sterol derivatives with dipeptide-like side chains were synthesized using an Ugi four-component condensation method and assayed to test their anti-inflammatory effects in activated microglial cells. Compound 18b ((3S,10R,13S)-N-((R)-1-(tert-butylamino)-1-oxo-3-phenylpropan-2-yl)-3-hydroxy-N,10,13-trimethyl-2,3,4,7,8,9,10,11,12,13,14,15-dodecahydro-1H-cyclopenta[a]phenanthrene-17-carboxamide) was identified as the most potent anti-inflammatory agent in the series of compounds analyzed. Compound 18b markedly inhibited the expression of proinflammatory factors, including inducible nitric oxide synthase, interleukin (IL)-6, IL-1β, tumor necrosis factor-α, and cyclooxygenase-2 in lipopolysaccharide-stimulated microglial cells. Further studies showed that compound 18b significantly suppressed the transcriptional activity of AP-1 and NF-κB in activated microglial cells, which was likely mediated by the inhibition of the p38 MAPK and JNK signal transduction pathways. In addition, compound 18b displayed neuroprotective effects in a microglial-conditioned medium/neuron coculture and an experimental focal ischemic mouse model.

Microsphere embolism-induced endothelial nitric oxide synthase expression mediates disruption of the blood-brain barrier in rat brain

Microsphere embolism (ME)-induced up-regulation of endothelial nitric oxide synthase (eNOS) in endothelial cells of brain microvessels was observed 2-48 h after ischemia. eNOS induction preceded disruption of the blood-brain barrier (BBB) observed 6-72 h after ischemia. In vascular endothelial cells, ME-induced eNOS expression was closely associated with protein tyrosine nitration, which is a marker of generation of peroxynitrite. Leakage of rabbit IgG from microvessels was also evident around protein tyrosine nitration-immunoreactive microvessels. To determine whether eNOS expression and protein tyrosine nitration in vascular endothelial cells mediates BBB disruption in the ME brain, we tested the effect of a novel calmodulin-dependent NOS inhibitor, 3-[2-[4-(3-chloro-2-methylphenyl)-1-piperazinyl]ethyl]-5,6-dimethoxy-1-(4-imidazolylmethyl)-1H-indazole dihydrochloride 3.5 hydrate (DY-9760e), which inhibits eNOS activity and, in turn, protein tyrosine nitration. Concomitant with inhibition of protein tyrosine nitration in vascular endothelial cells, DY-9760e significantly inhibited BBB disruption as assessed by Evans blue (EB) excretion. DY-9760e also inhibited cleavage of poly (ADP-ribose) polymerase as a marker of the apoptotic pathway in vascular endothelial cells. Taken together with previous evidence in which DY-9760e inhibited brain edema, ME-induced eNOS expression in vascular endothelial cells likely mediates BBB disruption and, in turn, brain edema.

A dose-response study of graded reoxygenation on the carotid haemodynamics, matrix metalloproteinase-2 activities and amino acid concentrations in the brain of asphyxiated newborn piglets

PURPOSE

It is controversial to choose an appropriate oxygen concentration to resuscitate asphyxiated newborns regarding the clinical and biochemical oxidative effects. We examined the vasomotor response to reoxygenation with graded reoxygenation and the effects on matrix metalloproteinases and amino acids of the immature brain.

METHODS

Thirty-two piglets (1-3 days, 1.5-2.1 kg) were instrumented for continuous monitoring of left common carotid and pulmonary arterial flows (Transonic). Piglets were randomized to a sham-operated control group (without hypoxia/reoxygenation) or 2 h hypoxia induced by decreasing the inspired oxygen concentration to 10-15%, followed by reoxygenation with 21, 50 or 100% oxygen for 1 h and then 21% oxygen for 3 h (n=8 each). The brains were then flash frozen and analyzed for matrix metalloproteinases and amino acid levels by zymography and HPLC, respectively.

RESULTS

After 2 h oxygen deprivation, the absolute carotid flow remained similar but accounted for 38% of cardiac output (increased from 17% at baseline, p=0.001). During early reoxygenation, the flow rose in the piglets resuscitated with air (p<0.05), but not in those with supplemental oxygen. Carotid vascular resistance correlated significantly with the arterial partial pressure of oxygen (r=0.7). There was an oxygen-dependent increase in global cerebral activity of matrix metalloproteinase-2 with specific increases in the basal ganglia of all hypoxic-reoxygenated brains. There were no significant differences in glutamate and other amino acids in any brain regions.

CONCLUSIONS

Although using high oxygen concentration to resuscitate asphyxiated newborn piglets increased carotid vascular resistance and cerebral matrix metalloproteinase-2 activity, there is no detrimental effect observed in this acute model of hypoxia-reoxygenation.

Nitric oxide synthase inhibitors in experimental ischemic stroke and their effects on infarct size and cerebral blood flow: a systematic review

Nitric oxide produced by the neuronal or inducible isoform of nitric oxide synthase (nNOS, iNOS) is detrimental in acute ischemic stroke (IS), whereas that derived from the endothelial isoform is beneficial. However, experimental studies with nitric oxide synthase inhibitors have given conflicting results. Relevant studies were found from searches of EMBASE, PubMed, and reference lists; of 456 references found, 73 studies involving 2321 animals were included. Data on the effects of NOS inhibition on lesion volume (mm3, %) and cerebral blood flow (CBF; %, ml * min(-1) * g(-1)) were analyzed using the Cochrane Review Manager software. NOS inhibitors reduced total infarct volume in models of permanent (standardized mean difference (SMD) -0.56, 95% confidence interval (95% CI) -0.86, -0.26) and transient (SMD -0.99, 95% CI -1.25, -0.72) ischemia. Cortical CBF was reduced in models of permanent but not transient ischemia. When assessed by type of inhibitor, total lesion volume was reduced in permanent models by nNOS and iNOS inhibitors, but not by nonselective inhibitors. All types of NOS inhibitors reduced infarct volume in transient models. NOS inhibition may have negative effects on CBF but further studies are required. Selective nNOS and iNOS inhibitors are candidate treatments for acute IS.

Role of nitric oxide after brain ischaemia

Ischaemic stroke is the second or third leading cause of death in developed countries. In the last two decades substantial research and efforts have been made to understand the biochemical mechanisms involved in brain damage and to develop new treatments. The evidence suggests that nitric oxide (NO) can exert both protective and deleterious effects depending on factors such as the NOS isoform and the cell type by which NO is produced or the temporal stage after the onset of the ischaemic brain injury. Immediately after brain ischaemia, NO release from eNOS is protective mainly by promoting vasodilation; however, after ischaemia develops, NO produced by overactivation of nNOS and, later, NO release by de novo expression of iNOS contribute to the brain damage. This review article summarizes experimental and clinical data supporting the dual role of NO in brain ischaemia and the mechanisms by which NO is regulated after brain ischaemia. We also review NO-based therapeutic strategies for stroke treatment, not only those directly linked with the NO pathway such as NO donors and NOS inhibitors but also those partially related like statins, aspirin or lubeluzole.

The neuronal nitric oxide synthase inhibitor, TRIM, as a neuroprotective agent: effects in models of cerebral ischaemia using histological and magnetic resonance imaging techniques

Most neuroprotective compounds that appear promising in the pre-clinical phase of testing are subsequently dismissed as relatively ineffective when entered into large-scale clinical trials. Many pre-clinical studies of potential neuroprotective candidates evaluate efficacy in only one or possibly two different models of ischaemia. In this study we examined the effects of 1,2-trifluoromethylphenyl imidazole (TRIM), a novel neuronal nitric oxide synthase (nNOS) inhibitor, in three models of cerebral ischaemia (global gerbil, global rat and focal rat). In addition, to follow the progression of the pathology, we also compared traditional histology methods with more advanced magnetic resonance imaging (MRI) as endpoint measures for neurological damage and neuroprotection. TRIM (50 mg/kg i.p.) prevented ischaemia-induced hippocampal damage following global ischaemia in gerbils when administered before or immediately post-occlusion, but failed to protect when administration was delayed until 30 min post-occlusion. Further studies indicated that the compound (administered at 50 mg/kg, i.p., immediately after occlusion) also protected in a rat four-vessel occlusion (4-VO) model using both histological and diffusion-weighted (DW) imaging techniques. In a final study, TRIM (50 mg/kg i.p. 30 min after occlusion) provided a significant reduction in infarct volume at 4 and 24 h as measured using diffusion-weighted (DW) and proton density (PD)-weighted magnetic resonance imaging (MRI). This was confirmed using histological techniques. These studies confirm that nNOS inhibitors may have utility in stroke and provide evidence that combined magnetic resonance and histological methods can provide a powerful method of assessing neuronal damage in rodent models of cerebral ischaemia.

Neurogenic neuroprotection

1. Stimulation of the rostral-ventromedial pole of the cerebellar fastigial nucleus exerts powerful effects on systemic and cerebral circulation. 2. Excitation of fibers passing through the fastigial nucleus evokes sympathoactivation and increases in arterial pressure. 3. Increase in cerebral blood flow evoked by excitation of fibers passing through the FN is mediated by intrinsic brain mechanisms independently of metabolism. 4. Excitation of the fastigial nucleus neurons in contrast decreases arterial pressure and cerebral blood flow. The latter probably is secondary to the suppression of brain metabolism. 5. Excitation of the fastigial nucleus neurons significantly decreases damaging effects of focal and global ischemia on the brain. 6. The fastigial nucleus-evoked neuroprotection can be conditioned: 1-h stimulation protects the brain for up to 3 weeks. 7. Other brain structures such as subthalamic cerebrovasodilator area and dorsal periaqueductal gray matter also produce long-lasting brain salvage when stimulated. 8. More than one mechanism may account for neurogenic neuroprotection. 9. Early neuroprotection, which develops immediately after the stimulation, involves opening of potassium channels. 10. Delayed long-lasting neuroprotection may involve changes in genes expression resulting in suppression of inflammatory reaction and apoptotic cascade. 11. It is conceivable that intrinsic neuroprotective system exists within the brain, which renders the brain more tolerant to adverse stimuli when activated. 12. Knowledge of the mechanisms of neurogenic neuroprotection will allow developing new neuroprotective approaches.

Hypobaric hypoxia modifies constitutive nitric oxide synthase activity and protein nitration in the rat cerebellum

Ischemic hypoxia provokes alterations in the production system of nitric oxide in the cerebellum. We hypothesize that the nitric oxide system may undergo modifications due to hypobaric hypoxia and that may play a role in high altitude pathophysiology. Therefore, changes in the nitric oxide system of the cerebellum of rats submitted to acute hypobaric hypoxia were investigated. Adult rats were exposed for 7 h to a simulated altitude of 8235 m (27000 ft.) and then killed after 0 h or 1, 3, 5 and 10 days of reoxygenation. Nitric oxide synthase calcium-dependent and -independent activity, immunoblotting and immunohistochemistry of neuronal, endothelial, and inducible nitric oxide synthase, and nitrotyrosine were evaluated. Immunoreactivity for neuronal nitric oxide synthase slightly increased in the baskets of the Purkinje cell layer and in the granule cells, after 0 h of reoxygenation, although no changes in neuronal nitric oxide synthase immunoblotting densitometry were detected. Calcium-dependent activity significantly rose after 0 h of reoxygenation, reaching control levels in the following points, and being coincident with a peak of eNOS expression. Nitrotyrosine formation showed significant increments after 0 h and 1 day of reoxygenation. Nitrotyrosine immunoreactivity showed an intracellular location change in the neurons of the cerebellar nuclei and in addition, an appearance of nitration in the soma of the Purkinje cells was detected. No changes in inducible nitric oxide synthase activity, immunoblotting or immunohistochemistry were detected. We conclude that at least part of the nitric oxide system is involved in cerebellum responses to hypobaric hypoxia.

Attenuation of nitric oxide synthase isoform expression by mild hypothermia after focal cerebral ischemia: variations depending on timing of cooling

OBJECT

In this study the authors examined the influence of mild hypothermia on early expression of nitric oxide synthase (NOS) isoforms and peroxynitrite generation after experimental stroke.

METHODS

In 82 male Sprague-Dawley rats, middle cerebral artery occlusion was performed for 2 hours by using the intraluminal suture model. The rats were maintained at their normal body temperature or exposed to 2 hours of intraischemic or postischemic (2-hour delay) mild hypothermia. Brains were collected 2, 6, and 24 hours after onset of ischemia for immunohistochemical and Western blot analysis of neuronal (n)NOS and inducible (i)NOS expression and peroxynitrite generation.

CONCLUSIONS

Western blots showed significantly increased nNOS and iNOS expression in the ischemic cortex at 2, 6, and 24 hours compared with sham-operated animals. The NOS expression was highest at 24 hours. Postischemic hypothermia attenuated nNOS expression at 6 and 24 hours to a greater extent than intraischemic hypothermia. Intraischemic hypothermia reduced iNOS expression at both 2 and 24 hours, whereas postischemic hypothermia decreased iNOS expression at 24 hours. Results of immunohistochemical studies showed that nNOS colocalized with the neuronal marker MAP-2 at all time points, whereas iNOS was initially localized to vessels, and then localized to activated microglia by 24 hours. Intraischemic but not postischemic hypothermia decreased the number of nitrotyrosine-positive cells in the ischemic cortex at 24 hours. Mild hypothermia significantly but differentially attenuates increases in NOS isoforms, with more robust nNOS suppression when cooling is delayed. This may have important implications for understanding the mechanism of hypothermic neuroprotection and for stroke therapy.

L-NAME reduces infarction, neurological deficit and blood-brain barrier disruption following cerebral ischemia in mice

The role of nitric oxide (NO) in the development of post-ischemic cerebral infarction has been extensively examined, but fewer studies have investigated its role in other outcomes. In the present study, we first determined the temporal evolution of infarct volume, NO production, neurological deficit and blood-brain barrier disruption in a model of transient focal cerebral ischemia in mice. We then examined the effect of the nonselective NO-synthase inhibitor N(omega)-nitro-L-arginine-methylester (L-NAME). L-NAME given at 3 mg/kg 3 h after ischemia reduced by 20% the infarct volume and abolished the increase in brain NO production evaluated by its metabolites (nitrites/nitrates) 48 h after ischemia. L-NAME with this protocol also reduced the neurological deficit evaluated by the grip test and decreased by 65% the extravasation of Evans blue, an index of blood-brain barrier breakdown. These protective activities of L-NAME suggest that NO has multiple deleterious effects in cerebral ischemia.

Transient focal ischemia increases endothelial nitric oxide synthase in cerebral blood vessels

BACKGROUND AND PURPOSE

Production of NO by endothelial NO synthase (eNOS) plays a protective role in cerebral ischemia. We studied the effects of transient focal ischemia on eNOS expression.

METHODS

Wistar rats (n=72) underwent reversible filament occlusion of the right middle cerebral artery for 75 minutes. After 6, 24, 72, or 168 hours of reperfusion, brains were removed and coronal sections cut for eNOS immunohistochemistry, eNOS-alkaline phosphatase costaining, and hematoxylin-eosin staining. Samples for eNOS immunoblots were taken from corresponding striatum and overlying parietal cortex bilaterally.

RESULTS

eNOS protein occurred in virtually all blood vessels and was consistently increased in microvessels in the ischemic striatum after 24 to 168 hours of reperfusion but not at 6 hours. eNOS upregulation in the parietal cortex was only present in animals with evidence of cortical infarcts documented on adjacent HE-stained sections. Costaining of endogenous alkaline phosphatase and eNOS demonstrated eNOS expression in all segments of cerebral microvessels. Quantitative analysis of eNOS immunostaining and immunoblots showed no attenuated increase in animals that were treated with indomethacin (5 mg/kg IP), NS398 (20 mg/kg IP), or L-arginine-methyl ester (10 mg/kg IP). In contrast to eNOS, levels of brain NOS did not increase after ischemia.

CONCLUSION

eNOS protein is upregulated in pre- and postcapillary microvessels and upregulation appears slower after transient compared with permanent ischemia. Cyclooxygenase and NOS products do not play a major role in postischemic eNOS induction.

Effects of dexamethasone on apoptosis-related cell death after spinal cord injury

OBJECT

The purpose of this study was to analyze the expression of F7-26 (Apostain) in injured spinal cord tissue, and the modifying effects of dexamethasone administration.

METHODS

A total of 56 adult female Wistar rats were subjected to traumatic spinal cord injury (SCI) to induce complete paraplegia. These rats were divided into two groups according to whether they received dexamethasone (doses of 1 mg/kg daily) post-SCI. Injured spinal cord tissue was studied by means of conventional histological techniques, and Apostain expression was determined by immunohistochemical analysis at 1, 4, 8, 24, and 72 hours, and at 1 and 2 weeks after SCI in all the animals. Apostain-positive cells, mainly neurons and glial cells, were detected 1 hour after injury, peaking at 8 hours, after which the number decreased. One week after injury, apoptosis was limited to a few glial cells, mainly oligodendrocytes, and 2 weeks after injury there was no evidence of Apostain-positive cells. In the group of paraplegic rats receiving post-SCI intraperitoneal dexamethasone, there was a significant decrease in the number of Apostain-positive cells.

CONCLUSIONS

Analysis of the results indicated that apoptosis plays a role in the early period after SCI and that administration of dexamethasone decreases apoptosis-related cell death in the injured spinal cord tissue.

Role of nitric oxide in focal microcirculation disorder of guinea pig cochlea

This study was designed to evaluate the role of endogenous nitric oxide (NO) in focal microcirculation disorder of the guinea pig cochlea. Focal microcirculation disorder was induced by a photochemical reaction at the lateral wall of the second cochlear turn. Saline or N omega-nitro-L-arginine methyl ester (L-NAME) was administered before the onset of photochemical reaction. Cochlear blood flow (CBF) was measured at the focal lesion (ischemic core), 1 mm from the lesion in the apical and basal direction (ischemic border zone) by using a novel non-contact laser blood flowmeter. NO synthase activities were measured by radioenzymeassay. In the saline pretreatment group, CBF was significantly decreased to 58.8+/-4.4% of the baseline at the ischemic core 30 min after the onset of photochemical reaction (P<0.01), while CBF showed no significant change at the ischemic border zone. In the L-NAME pretreatment group, CBF was significantly decreased not only at the focal lesion (48.3+/-6.5%, P<0.01), but also at the ischemic border zone (apical, 49.3+/-2.3%, P<0.05; basal, 58.7+/-7.1%, P<0.05, respectively). NO synthase III activity of cochlea was increased significantly (P<0.01) 15 min after microcirculation disorder. These findings suggest that formation of endogenous NO plays a key role in the maintenance of CBF in acute focal cochlear microcirculation disorder.

ARL 17477, a selective nitric oxide synthase inhibitor, with neuroprotective effects in animal models of global and focal cerebral ischaemia

In the present studies, we have evaluated the effects of N-[4-(2-¿[(3-Chlorophenyl)methyl]amino¿ethyl)phenyl]-2-thiophenecarbo ximidamide dihydrochloride (ARL 17477) on recombinant human neuronal NOS (nNOS) and endothelial NOS (eNOS). We then carried out pharmacokinetic studies and measured cortical nitric oxide synthase (NOS) inhibition to determine that the compound crossed the blood brain barrier. Finally, the compound was evaluated in a model of global ischaemia in the gerbil and two models of transient focal ischaemia in the rat. The IC(50) values for ARL 17477 on human recombinant human nNOS and eNOS were 1 and 17 microM, respectively. ARL 17477 (50 mg/kg i.p.) produced a significant reduction in the ischaemia-induced hippocampal damage following global ischaemia when administered immediately post-occlusion, but failed to protect when administration was delayed until 30 min post-occlusion. In the endothelin-1 model of focal ischaemia, ARL 17477 (1 mg/kg i.v.) significantly attenuated the infarct volume when administered at either 0, 1 or 2 h post-endothelin-1 (P<0.05). In the intraluminal suture model, ARL 17477 at both 1 and 3 mg/kg i.v. failed to reduce the infarct volume measured at 1, 3 or 7 days post-occlusion. These results demonstrate that ARL 17477 protects against global ischaemia in gerbils and provides some reduction in infarct volume following transient middle cerebral artery occlusion in rats, indicating that nNOS inhibition may be a useful treatment of ischaemic conditions.

Reduced nitric oxide is involved in prenatal ischemia-induced tolerance to neonatal hypoxic-ischemic brain injury in rats

To explore the role of nitric oxide (NO) in the hypoxic-ischemic (HI) tolerance phenomenon, NO production and brain injury following neonatal hypoxia-ischemia (induced by unilateral common carotid artery ligation followed by hypoxic exposure) were assessed in rat pups with or without HI preconditioning. A previously demonstrated prenatal HI rat model of preconditioning was used in this study. On G17, rat fetuses were subjected to either HI in utero (PreHI) for 30 min or a sham operation (SH). The PreHI treatment provided significant protection against neonatal HI-induced brain injury, as indicated by decreased ipsilateral brain weight reduction, less severe tissue damage, and decreased activation of caspase-3. Concomitant with the protective effect of prenatal HI preconditioning, elevation of nitrite/nitrate content in the ipsilateral cortex of the brain, as an indirect measure of NO production, was significantly lower in the PreHI group than in the SH group following neonatal HI. The protective effect of prenatal HI preconditioning could be reversed by sodium nitroprusside (SNP), a spontaneous NO donor, while SNP had no effect on neonatal HI-induced brain injury in the SH group. Intraperitoneal administration of SNP to pups from the PreHI group (2 mg/kg, 24 and 1.5 h before neonatal HI) increased neonatal HI-induced brain injury similar to that observed in the SH group. On the other hand, L-N(G)-nitro-arginine (2 mg/kg, i.p., 1.5 h before the hypoxic exposure), an NO synthase inhibitor, significantly attenuated neonatal HI-induced brain injury in the SH group. The overall results indicate that reduced NO production in the preconditioned rat brain contributes to prenatal HI-induced tolerance to neonatal HI brain injury.

Prenatal hypoxia-ischemia alters expression and activity of nitric oxide synthase in the young rat brain and causes learning deficits

Inhibition of nitric oxide synthase (NOS) is known to possibly impair learning and memory. Our previous studies have demonstrated that prenatal hypoxia-ischemia (HI) decreases NOS expression and NOS activity in the neonatal rat brain. To investigate whether effects of prenatal HI on NOS expression continue and whether prenatal HI affects learning and memory in young rats, NOS expression and NOS activity were determined in the hippocampus of rat brains at 28 days of age following a prenatal HI insult on G17. Performances in the passive avoidance test and the Morris water maze test were also studied in these young rats prior to sampling. Rat fetuses were subjected to either a 30-min prenatal HI insult or a sham operation (SH) on gestation day 17 and rat pups were delivered naturally. Increased locomotor activity was observed in the prenatal HI rats as compared to the SH rats on postnatal days 13 and 15, but not on postnatal days 20 and 30. Prenatal HI affected learning ability in these young rats at 28 days of age, as indicated by a delayed acquisition of passive avoidance and by longer escape latency in the Morris water maze test as compared to the SH group. Prenatal HI did not affect retention of passive avoidance and spatial memory. Concomitant with these learning deficits, expression of neuronal NOS and endothelial NOS mRNAs as well as Ca2(+)-dependent NOS activity in the hippocampus of the prenatal HI rat brain were significantly decreased as compared to the SH group. These results suggest that a 30-min prenatal HI insult on gestation day 17 in rats has long-lasting effects on NOS expression and NOS activity in the offspring brain and on learning ability of these young rats. The learning deficit in offspring is possibly associated with the reduction in expression of NOS mRNA and NOS activity in the hippocampus of these animals.

Effects of L-NAME and 7-NI on NOS catalytic activity and behavioral outcome after traumatic brain injury in the rat

Traumatic brain injury (TBI) produces transient increases in constitutive nitric oxide synthase (cNOS) activity and prolonged behavioral abnormalities. This study investigated the effects of nitro-L-arginine-methyl ester (L-NAME) and 3-bromo-7-nitroindazole (7-NI) treatment on cNOS catalytic activity and sensorimotor behavioral outcome after TBI. Rats underwent moderate (1.8-2.2 atm) parasagittal fluid percussion brain injury (FPI). At 5 min after FPI, cNOS activity was significantly increased within the damaged cerebral cortex of vehicle-treated rats compared to the noninjured contralateral cortex (206.7 +/- 150.5 % of contralateral, p < 0.01). Pretreatment with L-NAME and 7-NI significantly reduced injury-induced cNOS activation (47.7 +/- 42.6 %, p < 0.05, and 96.16 +/- 12.76, p < 0.05, respectively). Pretreatment with L-NAME and 7-NI also inhibited cNOS activity within the contralateral noninjured cerebral cortex compared to vehicle-treated rats (L-NAME 43.7 +/- 12.47%, p < 0.05; 7-NI 36.8 +/- 7.47%, p < 0.05). Furthermore, pretreatment with 7-NI, but not L-NAME, significantly reduced forelimb placing sensorimotor deficits (3.14 +/- 1.07, p < 0.05) at 1 day after TBI compared to vehicle-treated rats (5.38 +/- 0.42). These data indicate that inhibition of injury-induced elevations in neuronal NOS activity has a beneficial effect on neurological outcome after parasagittal FPI brain injury.

Nitric oxide mediates cerebral ischemic tolerance in a neonatal rat model of hypoxic preconditioning

Neuroprotection against cerebral ischemia can be realized if the brain is preconditioned by previous exposure to a brief period of sublethal ischemia. The present study was undertaken to test the hypothesis that nitric oxide (NO) produced from the neuronal isoform of NO synthase (NOS) serves as a necessary signal for establishing an ischemia-tolerant state in brain. A newborn rat model of hypoxic preconditioning was used, wherein exposure to sublethal hypoxia (8% oxygen) for 3 hours renders postnatal day (PND) 6 animals completely resistant to a cerebral hypoxic-ischemic insult imposed 24 hours later. Postnatal day 6 animals were treated 0.5 hour before preconditioning hypoxia with the nonselective NOS inhibitor L-nitroarginine (2 mg/kg intraperitoneally). This treatment, which resulted in a 67 to 81% inhibition of calcium-dependent constitutive NOS activity 0.5 to 3.5 hours after its administration, completely blocked preconditioning-induced protection. However, administration of the neuronal NOS inhibitor 7-nitroindazole (40 mg/kg intraperitoneally) before preconditioning hypoxia, which decreased constitutive brain NOS activity by 58 to 81%, was without effect on preconditioning-induced cerebroprotection, as was pretreatment with the inducible NOS inhibitor aminoguanidine (400 mg/kg intraperitoneally). The protective effects of preconditioning were also not blocked by treating animals with competitive [3-(2-carboxypiperazin-4-yl)propyl-1-phosphonate; 5 mg/kg intraperitoneally] or noncompetitive (MK-801; 1 mg/kg intraperitoneally) N-methyl-D-aspartate receptor antagonists prior to preconditioning hypoxia. These findings indicate that NO production and activity are critical to the induction of ischemic tolerance in this model. However, the results argue against the involvement of the neuronal NOS isoform, activated secondary to a hypoxia-induced stimulation of N-methyl-D-aspartate receptors, and against the involvement of the inducible NOS isoform, but rather suggest that NO produced by the endothelial NOS isoform is required to mediate this profound protective effect.

Chronic administration of adenosine A3 receptor agonist and cerebral ischemia: neuronal and glial effects

We have previously shown that chronic administration of the selective A3 receptor agonist N6-(3-iodobenzyl)-5'-N-methylcarboxoamidoadenosine (IB-MECA) leads to a significant improvement of postocclusive cerebral blood flow, and protects against neuronal damage and mortality induced by severe forebrain ischemia in gerbils. Using immunocytochemical methods we now show that chronic with IB-MECA results in a significant preservation of ischemia-sensitive microtubule associated protein 2 (MAP-2), enhancement of the expression of glial fibrillary acidic protein (GFAP), and a very intense depression of nitric oxide synthase in the brain of postischemic gerbils. These changes demonstrate that the cerebroprotective actions of chronically administered IB-MECA involve both neurons and glial cells, and indicate the possibility of distinct mechanisms that are affected in the course of chronic administration of the drug.

Stimulation of cerebellar fastigial nucleus inhibits interleukin-1beta-induced cerebrovascular inflammation

Electrical stimulation of the cerebellar fastigial nucleus (FN) in rat protects the brain against ischemia. We studied whether FN could reduce the cerebrovascular inflammation as a mechanism of protection. FN or dentate nucleus (sham controls) was electrically stimulated for 1 h, and 72 h later rats were either injected with interleukin (IL)-1beta into the striata or processed to analyze inflammatory responses in isolated brain microvessels. In striata, IL-1beta induced a recruitment of leukocytes that was reduced by 50% by FN stimulation. In isolated microvessels, IL-1beta induced the transient and dose-dependent upregulation of the mRNAs encoding for the inducible nitric oxide synthase (NOS-2), intercellular adhesion molecule 1 (ICAM-1), and inhibitory kappaB-alpha (IkappaB-alpha), an inhibitor of nuclear factor-kappaB. FN stimulation decreased the upregulation of NOS-2 and ICAM-1 mRNAs, whereas it increased IkappaB-alpha mRNA expression. Dentate nucleus stimulation did not mimic the FN actions. These findings suggest that FN stimulation may render brain microvessels refractory to IL-1beta by overproduction of IkappaB-alpha and support the hypothesis that alteration of microvascular inflammation may contribute to the central neurogenic neuroprotection elicited from the FN.

Inhibition of nitric oxide synthase blocks osteoclastic bone resorption in adaptive bone modeling

In this study, the auditory bulla of the gerbil was pressurized, leading to active modeling of the bone of the bulla wall with a significant increase in osteoclast surface and mineral apposition rate. Systemic infusion of L-N(G)-nitro-arginine-methyl ester (L-NAME), an inhibitor of nitric oxide synthase (NOS), inhibited this modeling process. The percentage osteoclast surface (Oc.S/BS) on the inner surface bulla wall was significantly reduced in the L-NAME-treated animals when compared with pressurized saline-treated bullae. Fluorescent bone surface (BSf) mineral apposition rates (MAR) and bone formation rate (BFR) were not significantly different in the pressurized bullae when the L-NAME group was compared with the control (vehicle only) group. However, L-NAME significantly suppressed BSf in the unpressurized bullae. Therefore, it is likely that nitric oxide is a mediator of osteoclastic resorption due to adaptive bone modeling through one or more of the isoforms of NOS.

Intrauterine hypoxia-ischemia alters nitric oxide synthase expression and activity in fetal and neonatal rat brains

The effects of intrauterine hypoxia-ischemia (HI) on nitric oxide synthase (NOS) activity and on expression of NOS isoforms were investigated in fetal and neonatal rat brains. Rat fetuses were subjected to either a 30-min intrauterine HI insult or a sham operation (SH) on gestational day 17 (G17). NOS activity in the homogenate of the rat brain was detectable on G17 and increased with age. NOS activity in the HI group was 20-30% higher than in the SH group from 6 to 48 h after the HI, but was 30% lower than in the SH group from postnatal day 8 to 14. Expression of the inducible NOS (iNOS) mRNA, as examined by RT-PCR, was increased as compared to the SH group from 6 to 24 h after the HI surgery. Expression of the constitutive neuronal NOS (nNOS) mRNA was reduced in the HI group from 24 h after the HI surgery up to postnatal day 14. Immunoblotting data have shown that alterations in NOS isoform protein expression caused by the intrauterine HI were consistent with the mRNA expression data. The overall results indicate that prenatal HI has long-lasting effects on function and expression of NOS in fetal and neonatal rat brains and that the altered NOS activity may be associated with prenatal HI-induced neurological abnormalities.

Aluminum treatment induces nitric oxide synthase in the rat brain

In an attempt to delineate the capacity of aluminum to promote pro-oxidant events in the central nervous system, levels of nitric oxide synthase (NOS) have been determined in the cerebellum of rats exposed to an aluminum salt, either alone or in combination with an iron compound. Relatively acute treatment with aluminum over a three-day period, increased cerebellar levels of NOS. Parallel results were obtained when animals were dosed over a more extended three-week period. Dosing with an iron compound resulted in no changes in levels of this enzyme. Concurrent treatment with aluminum and iron did not potentiate the NOS-inducing effects of aluminum. By use of selective inhibitors, the specific induction of iNOS by aluminum treatment was found. The results suggest that the presence of aluminum can induce cerebellar NOS and that these changes are independent of any interaction between aluminum and erogenous iron.

Cerebellar stimulation reduces inducible nitric oxide synthase expression and protects brain from ischemia

A focal infarction produced by occlusion of the middle cerebral artery (MCAO) in spontaneously hypertensive rats induced expression of inducible nitric oxide synthase (iNOS) mRNA, measured by competitive reverse transcription-polymerase chain reaction. The mRNA appeared simultaneously in the ischemic core and penumbra at 8 h, peaked between 14 and 24 h, and disappeared by 48 h. At 24 h, inducible nitric oxide synthase (iNOS)-like immunoreactivity was present in the endothelium of cerebral microvessels and in scattered cells, probably representing leukocytes or activated microglia. Electrical stimulation of the cerebellar fastigial nucleus (FN) for 1 h, 48 h before MCAO, reduced infarct volumes by 45% by decreasing cellular death in the ischemic penumbra. It also reduced by >90% the expression of iNOS mRNA and protein in the penumbra, but not core, and decreased by 44% the iNOS enzyme activity. We conclude that excitation of neuronal networks represented in the cerebellum elicits a conditioned central neurogenic neuroprotection associated with the downregulation of iNOS mRNA and protein. This neuroimmune interaction may, by blocking the expression of iNOS, contribute to neuroprotection.

Core and Penumbral Nitric Oxide Synthase Activity During Cerebral Ischemia and Reperfusion

Background and Purpose —The present studies examined the hypothesis that the distribution of cerebral injury after a focal ischemic insult is associated with the regional distribution of nitric oxide synthase (NOS) activity.

Methods —Based on previous studies that certain anatomically well-defined areas are prone to become either core or penumbra after middle cerebral artery occlusion (MCAO), we measured NOS activity in these areas from the right and left hemispheres in a spontaneously hypertensive rat filament model. Four groups were studied: (1) controls (immediate decapitation); (2) 1.5 hours of MCAO with no reperfusion (R0); (3) 1.5 hours of MCAO with 0.5 hour of reperfusion (R0.5); and (4) 1.5 hours of MCAO with 24 hours of reperfusion (R24). Three groups of corresponding isoflurane sham controls were also included: 1.5 (S1.5) or 2 (S2.0) hours of anesthesia and 1.5 hours of anesthesia+24 hours of observation (S24).

Results —Control core NOS activity for combined right and left hemispheres was 129% greater than penumbral NOS activity ( P <0.05). Combined core NOS activity was also greater ( P <0.05) in the three sham groups: 208%, 122%, and 161%, respectively. In the three MCAO groups, ischemic and nonischemic core NOS remained higher than penumbral regions ( P <0.05). However, NOS activity was lower in the ischemic than in the nonischemic core in all three groups: R0 (29% lower), R0.5 (48%), and R24 (86%) ( P <0.05). Addition of cofactors (10 μmol/L tetrahydrobiopterin, 3 μmol/L flavin adenine dinucleotide, and 3 μmol/L flavin mononucleotide) increased NOS activity in all groups and lessened the decrease in ischemic core and penumbral NOS.

Conclusions —Greater NOS activity in core regions could explain in part the increased vulnerability of that region to ischemia and could theoretically contribute to the progression of the infarct over time. The data also suggest that NOS activity during ischemia and reperfusion could be influenced by the availability of cofactors.

The effect of nitric oxide inhibition on ischemic brain edema

The involvement of nitric oxide (NO) in the development of ischemic cytotoxic edema was investigated by inhibiting nitric oxide synthase (NOS) activity with N omega-nitro-L-arginine (NLA). Bilateral carotid artery occlusion (15 min) alone or with release (15 and 60 min) served as a model for edema induction. NLA, N omega-nitro-D-arginine methyl ester (D-NAME) or Ringer's solution were administered 4 hr prior to ischemia or sham operation. Treatment with a stable nitroxide radical, 4-hydroxy-2,2, 6,6-tetramethylpiperidine-L-oxyl (TPL), was used to assess free radical involvement in edema. Accumulation of tissue water was evaluated by measuring specific gravity (SG) of brain cortex and histological examination. There was a greater reduction of cortical SG in early reperfusion (15 min) and a lesser decrease in SG (60 min later) in NLA-than in D-NAME- or Ringer's-treated gerbils. The NLA effect was confirmed by histological examination of the brain tissue. TPL treatment (pre- and postischemic) ameliorated the formation of edema to the same degree as NLA. The findings indicate a biphasic NLA modulation of cytotoxic edema most likely mediated through absence or presence of NO-derived free radicals.

Regulation of the cerebral circulation: role of endothelium and potassium channels

Several new concepts have emerged in relation to mechanisms that contribute to regulation of the cerebral circulation. This review focuses on some physiological mechanisms of cerebral vasodilatation and alteration of these mechanisms by disease states. One mechanism involves release of vasoactive factors by the endothelium that affect underlying vascular muscle. These factors include endothelium-derived relaxing factor (nitric oxide), prostacyclin, and endothelium-derived hyperpolarizing factor(s). The normal vasodilator influence of endothelium is impaired by some disease states. Under pathophysiological conditions, endothelium may produce potent contracting factors such as endothelin. Another major mechanism of regulation of cerebral vascular tone relates to potassium channels. Activation of potassium channels appears to mediate relaxation of cerebral vessels to diverse stimuli including receptor-mediated agonists, intracellular second messenger, and hypoxia. Endothelial- and potassium channel-based mechanisms are related because several endothelium-derived factors produce relaxation by activation of potassium channels. The influence of potassium channels may be altered by disease states including chronic hypertension, subarachnoid hemorrhage, and diabetes.

Transient changes in the presence of nitric oxide synthases and nitrotyrosine immunoreactivity after focal cortical lesions

Since ischemic insults lead to a deregulation of nitric oxide production which contributes to delayed neuronal death, we investigated changes in the distribution and amount of nitric oxide synthases I and II and in the appearance of nitrotyrosine caused by small, well-defined photothrombic lesions (2 mm in diameter) in the somatosensory cortex of rats. Four hours after lesioning, cell loss was evident in the core of the lesion and no nitric oxide synthase was present within this area, indicating that neurons expressing nitric oxide synthase I were lost or that nitric oxide synthase I was degraded. No increase in the number of neurons expressing nitric oxide synthase I was visible in the area surrounding the lesion, nor in other parts of the brain. One day after lesioning, NADPH-diaphorase- and nitric oxide synthase II-positive leucocytes had invaded the perilesional cortex and were accumulated in injured blood vessels. By two to three days post-lesion, layer V and VI pyramidal neurons, microglia, astrocytes and invading leucocytes had become strongly immunoreactive for nitric oxide synthase II within a perilesional rim. The number of cells expressing nitric oxide synthase I remained stable. Nitric oxide synthase II immunoreactivity and related NADPH-diaphorase had decreased by seven days post-lesion in most animals. However, the number of activated microglia or macrophages and astrocytes, as revealed by other markers, remained elevated. In addition, nitrotyrosine immunoreactivity was evident in the blood vessels close to the lesion, as well as in the ipsilateral hippocampus and thalamus. These findings indicate that no perilesional changes in the number of neurons expressing nitric oxide synthase I occur, but that a transient increase in nitric oxide synthase II does take place in the aftermath of small cortical lesions. The results suggest that increased nitric oxide production is limited to certain post-lesional intervals in this experimental model. It is also obvious that the vast majority of nitric oxide synthase-positive cells are nitric oxide synthase II-containing astrocytes three days after lesioning, suggesting that astrocyte-derived nitric oxide plays a significant role in delayed neuronal death. Such a condition points to an important aspect of post-lesional astrocytosis.

Neuroprotective effects of the antioxidant LY231617 and NO synthase inhibitors in global cerebral ischaemia

Recent studies have shown that the novel antioxidant LY231617 protects against ischaemia-induced neuronal damage in rat models of global cerebral ischaemia. In the present studies we have examined the effects of LY231617 in the gerbil model of global cerebral ischaemia. We also examined the effects of four nitric oxide synthase inhibitors (3-bromo-7-nitroindazole, N(G)-nitro-L-arginine methyl ester, aminoguanidine and S-methylisothiourea sulphate) in this model. LY231617 (50 mg/kg p.o. or 30 mg/kg i.p.) was administered either 30 min prior to occlusion or immediately post-occlusion followed by three further doses at 4, 24 and 48 h after the initial dose. 3-Bromo-7-nitroindazole was administered at 40 mg/kg i.p. immediately after occlusion followed by 20 mg/kg i.p. at 3, 6, 24 and 48 h, N(G)-nitro-L-arginine methyl ester was administered at 10 mg/kg i.p. immediately after occlusion followed by 5 mg/kg i.p. at 3, 6, 24 and 48 h. Aminoguanidine was administered at 80 mg/kg i.p. immediately after occlusion followed by 40 mg/kg i.p. at 3, 6, 24 and 48 h and S-methylisothiourea sulphate was administered at 10 mg/kg i.p. immediately, 3, 6, 24 and 48 h after occlusion. We also examined the effects of aminoguanidine administered at 80 mg/kg i.p. immediately after occlusion followed by 40 mg/kg i.p. at 3, 6, 24, 48, 72 and 96 h and S-methylisothiourea sulphate administered at 10 mg/kg i.p. immediately, 3, 6, 24, 48, 72 and 96 h after occlusion. Control animals were either sham operated or subjected to 5 min bilateral carotid occlusion. Extensive neuronal death was observed in the CA1 layer of the hippocampus in 5-min bilateral carotid artery occluded animals 5 days after surgery. LY231617 provided significant neuroprotection against the ischaemia-induced brain damage when administration was initiated before or after occlusion (P < 0.05). The neuronal NO synthase inhibitors, 3-bromo-7-nitroindazole and a general NO synthase inhibitor, N(G)-nitro-L-arginine methyl ester also provided significant neuroprotection (P < 0.05). In contrast aminoguanidine and S-methylisothiourea sulphate (two inducible NO synthase inhibitors) failed to protect against the ischaemia-induced brain damage. These results indicate that free radicals and nitric oxide are involved in ischaemia-induced brain damage following global cerebral ischaemia. Antioxidants such as LY231617 or neuronal NO synthase inhibitors can prevent the ischaemia-induced neurodegeneration and may be useful as anti-ischaemic agents.

Reduction of CuZn-superoxide dismutase activity exacerbates neuronal cell injury and edema formation after transient focal cerebral ischemia

Apoptotic neuronal cell death has recently been associated with the development of infarction after cerebral ischemia. In a variety of studies, CuZn-superoxide dismutase (CuZn-SOD) has been shown to protect the brain from ischemic injury. A possible role for CuZn-SOD-related modulation of neuronal viability is suggested by the finding that CuZn-SOD inhibits apoptotic neuronal cell death in response to some forms of cellular damage. We evaluated this possibility in the model of transient focal cerebral ischemia in mice bearing a disruption of the CuZn-SOD gene (Sod1). Homozygous mutant (Sod1 -/-) mice had no detectable CuZn-SOD activity, and heterozygous mutants (Sod1 +/-) showed a 50% decrease compared with wild-type mice. Sod1 -/- mice showed a high level of blood-brain barrier disruption soon after 1 hr of middle cerebral artery occlusion and 100% mortality at 24 hr after ischemia. Sod1 +/- mice showed 30% mortality at 24 hr after ischemia, and neurological deficits were exacerbated compared with wild-type controls. The Sod1 +/- animals also had increased infarct volume and brain swelling, accompanied by increased apoptotic neuronal cell death as indicated by the in situ nick-end labeling technique to detect DNA fragmentation and morphological criteria. These results suggest that oxygen-free radicals, especially superoxide anions, are an important factor for the development of infarction by brain edema formation and apoptotic neuronal cell death after focal cerebral ischemia and reperfusion.

Neuroprotective effects of 7-nitroindazole in the gerbil model of global cerebral ischaemia

To evaluate the role played by nitric oxide in global cerebral ischaemia we examined the effects of 7-nitroindazole and a sodium salt of 7-nitroindazole (inhibitors of neuronal nitric oxide (NO) synthase) and NG-nitro-L-arginine methyl ester (a more general inhibitor of NO synthase) in the gerbil model of cerebral ischaemia. Four experiments were carried out. In the first experiment, animals were either sham-operated, subjected to 5 min bilateral carotid occlusion (BCAO) or administered 7-nitroindazole or NG-nitro-L-arginine methyl ester immediately after occlusion followed by three further doses at 3, 6 and 24 h post-occlusion. In the second experiment, we examined the effects of a sodium salt of 7-nitroindazole, which is more soluble than 7-nitroindazole, using the same protocol. In the third experiment, the effects of the sodium salt of 7-nitroindazole administered at 10 mg/kg at 0, 3, 6, 24, 27, 30, 33, 52, 55, 72, 75 and 78 h post-occlusion or at 0.05 mg/h for 72 h via mini-pumps were evaluated. In separate experiments, we examined the effects of three reference compounds dizocilpine (MK-801), 2, 3-dihydroxy-6-nitro-7-sulphamoyl-benz(F)-quinoxaline (NBQX) and eliprodil using the same model. Extensive neuronal death was observed in the CA1 layer of the hippocampus in 5 min bilateral carotid occluded animals 5 days after surgery. Both 7-nitroindazole and NG-nitro-L-arginine methyl ester provided significant neuroprotection (P < 0.01) against this neuronal death. The sodium salt of 7-nitroindazole showed no protection when administered up to 12 times post-occlusion, but did provide significant (P < 0.01) neuroprotection when administered via mini-pump. The neuroprotection was similar to that provided by MK-801 and eliprodil, but not as good as that observed with NBQX. These results indicate that nitric oxide plays a role in ischaemic cell death and that selective neuronal nitric oxide synthase inhibitors can protect against ischaemic brain damage.

Nitric oxide and antioxidant status in glucose and oxygen deprived neonatal and adult rat brain synaptosomes

Nitric oxide (NO.) has been implicated in the process of cerebral ischemia/reperfusion injury. We have examined the production of NO., as reflected by nitrite (NO2-) + nitrate (NO3-) accumulation, from synaptosomes isolated from neonatal or adult rat brain and subjected to a period of glucose and oxygen deprivation. There was a significant increase in the amount of NO2- + NO3- production from adult synaptosomes under these conditions, whereas there was no difference compared to control in the production of NO2- + NO3- from the neonatal synaptosomes. The total antioxidant status of the synaptosomes at these different stages of brain development was found to be the same. These data suggest that the vulnerability of the adult brain to ischemia/reperfusion injury may be associated with the production of NO. from nerve terminals. The ratios of antioxidant capacity to NO. production under such conditions have been shown here to be different between the neonatal and adult nerve terminals. Thus the well documented resistance of neonatal brain to ischemia/reperfusion injury may involve the neonatal nerve terminal being under less oxidative stress than the adult.