Nitric oxide-mediated mechanism of neuronal nitric oxide synthase and inducible nitric oxide synthase expression during hypoxia in the cerebral cortex of newborn piglets

α acid fraction from Hop extract exerts an endothelium-derived hyperpolarization vasorelaxant effect through TRPV4 employing the feedforward mechanism of PKCα

Until now, the beneficial vascular properties of Hop reported in the literature have been mainly attributed to specific compound classes, such as tannins and phenolic acids. However, the potential vascular action of a Hop subfraction containing a high amount of α or β acids remains completely understood. Therefore, this study aims to investigate the vascular effects of the entire Hop extract and to fraction the Hop extract to identify the main bioactive vascular compounds. A pressure myograph was used to perform vascular reactivity studies on mouse resistance arteries. Phytocomplex fractionation was performed on a semi-prep HPLC system and characterized by UHPLC-PDA-MS/MS coupled to mass spectrometry. Western blot analysis was performed to characterize the phosphorylation site enrolled. The entire Hop extract exerts a direct dose-dependent endothelial vascular action. The B1 subfraction, containing a high concentration of α acids, recapitulates the vascular effect of the crude extract. Its vasorelaxant action is mediated by the opening of Transient Receptor Potential Vanilloid type 4 (TRPV4), potentiated by PKCα, and subsequent involvement of endothelial small-conductance calcium-activated potassium channels (SKCa) and intermediate-conductance calcium-activated potassium channels (IKCa) that drives endothelium-dependent hyperpolarization (EDH) through heterocellular myoendothelial gap junctions (MEGJs). This is the first comprehensive investigation of the vascular function of Hop-derived α acids in resistance arteries. Overall, our data suggest that the B1 subfraction from Hop extracts, containing only α acids, has great potential to be translated into the useful armamentarium of natural bioactive compounds with cardiovascular benefits.

Molecular Characterization and Expression of Cytochrome P450 Aromatase in Atlantic Croaker Brain: Regulation by Antioxidant Status and Nitric Oxide Synthase During Hypoxia Stress

We have previously shown that nitric oxide synthase (NOS, an enzyme) is significantly increased during hypoxic stress in Atlantic croaker brains and modulated by an antioxidant (AOX). However, the influence of NOS and AOX on cytochrome P450 aromatase (AROM, CYP19a1, an enzyme) activity on vertebrate brains during hypoxic stress is largely unknown. In this study, we characterized brain AROM (bAROM, CYP19a1b) cDNA in croaker and examined the interactive effects of hypoxia and a NOS-inhibitor or AOX on AROM activity. The amino acid sequence of croaker bAROM cDNA is highly homologous (76–80%) to other marine teleost bAROM cDNAs. Both real-time PCR and Northern blot analyses showed that bAROM transcript (size: ∼2.8 kb) is highly expressed in the preoptic-anterior hypothalamus (POAH). Hypoxia exposure (dissolved oxygen, DO: 1.7 mg/L for 4 weeks) caused significant decreases in hypothalamic AROM activity, bAROM mRNA and protein expressions. Hypothalamic AROM activity and mRNA levels were also decreased by pharmacological treatment with N-ethylmaleimide (NEM, an alkylating drug that modifies sulfhydryl groups) of fish exposed to normoxic (DO: ∼6.5 mg/L) conditions. On the other hand, treatments with Nω-nitro-L-arginine methyl ester (NAME, a competitive NOS-inhibitor) or vitamin-E (Vit-E, a powerful AOX) prevented the downregulation of hypothalamic AROM activity and mRNA levels in hypoxic fish. Moreover, NAME and Vit-E treatments also restored gonadal growth in hypoxic fish. Double-labeled immunohistochemistry results showed that AROM and NOS proteins are co-expressed with NADPH oxidase (generates superoxide anion) in the POAH. Collectively, these results suggest that the hypoxia-induced downregulation of AROM activity in teleost brains is influenced by neuronal NOS activity and AOX status. The present study provides, to the best of our knowledge, the first evidence of restoration of AROM levels in vertebrate brains by a competitive NOS-inhibitor and potent AOX during hypoxic stress.

The Roles of Nitric Oxide Synthase/Nitric Oxide Pathway in the Pathology of Vascular Dementia and Related Therapeutic Approaches

Vascular dementia (VaD) is the second most common form of dementia worldwide. It is caused by cerebrovascular disease, and patients often show severe impairments of advanced cognitive abilities. Nitric oxide synthase (NOS) and nitric oxide (NO) play vital roles in the pathogenesis of VaD. The functions of NO are determined by its concentration and bioavailability, which are regulated by NOS activity. The activities of different NOS subtypes in the brain are partitioned. Pathologically, endothelial NOS is inactivated, which causes insufficient NO production and aggravates oxidative stress before inducing cerebrovascular endothelial dysfunction, while neuronal NOS is overactive and can produce excessive NO to cause neurotoxicity. Meanwhile, inflammation stimulates the massive expression of inducible NOS, which also produces excessive NO and then induces neuroinflammation. The vicious circle of these kinds of damage having impacts on each other finally leads to VaD. This review summarizes the roles of the NOS/NO pathway in the pathology of VaD and also proposes some potential therapeutic methods that target this pathway in the hope of inspiring novel ideas for VaD therapeutic approaches.

Prenatal Systemic Hypoxia-Ischemia and Oligodendroglia Loss in Cerebellum

Hypoxic-ischemic (HI) injury is an important cause of death and disabilities. Despite all improvements in neonatal care, the number of children who suffer some kind of injury during birth has remained stable in the last decade. A great number of studies have shown alterations in neural cells and many animal models have been proposed in the last 5 decades. Robinson et al. (2005) proposed an HI model in which the uterine arteries are temporarily clamped on the 18th gestation day. The findings were quite similar to the ones observed in postmortem studies. The white matter is clearly damaged, and a great amount of astrogliosis takes place both in the gray and white matters. Motor changes were also found but no data regarding the cerebellum, an important structure related to motor performance, was presented. Using this model, we have shown an increased level of iNOS at P0 and microgliosis and astrogliosis at P9, and astrogliosis at P23 (up to 4 weeks from the insult). NO is important in migration, maturation, and synaptic plasticity, but in exacerbated levels it may also contribute to cellular and tissue damage. We have also evaluated oligodendroglia development in the cerebellum. At P9 in HI animals, we found a decrease in the number of PDGFRα+ cells and an apparent delay in myelination, suggesting a failure in oligodendroglial progenitors migration/maturation and/or in the myelination process. These results point to an injury in cerebellar development that might help to explain the motor problems in HI.

Restoration of tryptophan hydroxylase functions and serotonin content in the Atlantic croaker hypothalamus by antioxidant treatment during hypoxic stress

Antioxidants are prototypical scavengers of oxygen-free radicals and have been shown to prevent neuroendocrine dysfunction in vertebrates during oxidative stress. In the present study, we investigated whether antioxidant treatment can reverse hypoxia-induced down-regulation of hypothalamic tryptophan hydroxylase (TPH) and serotonergic functions in Atlantic croaker. Hypothalamic neuronal contents of TPH-1 and TPH-2 proteins, serotonin (5-hydroxytryptamine, 5-HT) and its precursor, 5-hydroxytryptophan (5-HTP) as well as hypothalamic TPH-1 and TPH-2 mRNA expression and TPH activity were measured in croaker after exposure to hypoxia and treatment with pharmacological agents. Multiple injections of N-ethylmaleimide, a sulfhydryl alkylating agent, caused comparable decreases in hypothalamic TPHs functions and 5-HT contents to that induced by hypoxia exposure (dissolved oxygen: 1.7 mg/L for 4 weeks) which were partially restored by repeated injections with a nitric oxide synthase (NOS)-inhibitor and/or vitamin E. Double-labeled immunohistochemical results showed that TPHs and 5-HT neurons were co-expressed with neuronal NOS (nNOS, a neuroenzyme) that catalyzes the production of nitric oxide, a free radical, in hypothalamic neurons. These results suggest that hypoxia-induced impairment of TPH and serotonergic functions are mediated by nNOS and involve the generation of free radicals and a decrease in the antioxidant status. This study provides, to our knowledge, the first evidence of a protective role for an antioxidant in maintaining neural TPHs functions and 5-HT regulation in an aquatic vertebrate during hypoxic stress.

Ca²⁺/calmodulin-dependent protein kinase II contributes to hypoxic ischemic cell death in neonatal hippocampal slice cultures

We have recently shown that p38MAP kinase (p38MAPK) stimulates ROS generation via the activation of NADPH oxidase during neonatal hypoxia-ischemia (HI) brain injury. However, how p38MAPK is activated during HI remains unresolved and was the focus of this study. Ca²⁺/calmodulin-dependent protein kinase II (CaMKII) plays a key role in brain synapse development, neural transduction and synaptic plasticity. Here we show that CaMKII activity is stimulated in rat hippocampal slice culture exposed to oxygen glucose deprivation (OGD) to mimic the condition of HI. Further, the elevation of CaMKII activity, correlated with enhanced p38MAPK activity, increased superoxide generation from NADPH oxidase as well as necrotic and apoptotic cell death. All of these events were prevented when CaMKII activity was inhibited with KN93. In a neonatal rat model of HI, KN93 also reduced brain injury. Our results suggest that CaMKII activation contributes to the oxidative stress associated with neural cell death after HI.

Ultrasound-induced release of GDNF from lipid coated microbubbles injected into striatum reduces hypoxic-ischemic injury in neonatal rats

Previous studies showed that inflammation and apoptosis were involved in the pathogenesis of hypoxic-ischemic brain injury. The immature brain is particularly vulnerable to damage. Intracerebral injection of glial cell line-derived neurotrophic factor (GDNF) has been shown to reduce the injury induced by hypoxia-ischemia (HI). In this study, the neuroprotective effect of intracerebral ultrasound-induced dissolution of lipid-coated GDNF microbubbles was investigated in a neonatal rat model of hypoxic-ischemic brain injury. Hypoxic-ischemic injury was induced in 7-day-old rats in the present study. The rats with hypoxia-ischemia received intracerebral injections of GDNF-containing microbubbles (0.5 mg/kg). They then received low frequency ultrasound stimulation (20 kHz, 2 h intervals for a total of 24 h and each time lasted for 1 min) to induce release of GDNF into the right striatum. We found that low frequency ultrasound stimulation can induce lipid-coated GDNF microbubbles to release GDNF. Ultrasound-induced dissolution of lipid-coated GDNF microbubbles treatment reduced infarction volume and improved neurological outcomes in neonatal rats. In the meanwhile, the microbubbles attenuated the production of inducible nitric oxide synthase, nitric oxide and tumor necrosis factor-alpha, as well as the activation of caspase-3 in insulted side of brain in neonatal rats. These data demonstrated that ultrasound-induced dissolution of lipid-coated GDNF microbubbles treatment can provide a neuroprotective effect against hypoxia-ischemia in neonatal rats.

Hypoxia-induced cellular and vascular changes in the nucleus tractus solitarius and ventrolateral medulla

Major changes in arterial pressure, autonomic, and respiratory activity occur in response to hypoxia. We analyzed structural damage and increased vascular permeability in the ventrolateral medulla and nucleus tractus solitarius, which control autonomic, respiratory, and cardiovascular functions in adult Wistar rats subjected to 2 hours of hypoxia (7% oxygen + 93% nitrogen) for up to 14 days after hypoxicexposure. Brainstem tissue levels of vascular endothelial growth factor (VEGF), nitric oxide (NO), and glutamate were significantly increased over control levels after hypoxic injury. By electron microscopy, swollen neurons and dendrites, degenerating axons, disrupted myelin sheaths, and swollen astrocyte processes were observed in the nucleus tractus solitarius and ventrolateral medulla. Leakage of intravenously administered horseradish peroxidase was observed through vascular walls in hypoxic rats. These results suggest that increased VEGF and NO production in hypoxia resulted in increased vascular permeability, which, along with increased levels of glutamate, may have induced structural alterations of the neurons, dendrites, and axons. Administration of the antioxidant neurohormone melatonin (10mg/kg) before and after the hypoxia reduced VEGF, NO, and glutamate levels and improved ultrastructural abnormalities induced by hypoxia exposure, suggesting that it may have a therapeutic potential in reducing hypoxia-associated brainstem damage.

Inducible nitric oxide synthase expression correlates with angiogenesis, lymphangiogenesis, and poor prognosis in gastric cancer patients

Increased nitric oxide synthase expression plays a key role in tumor progression. To examine inducible nitric oxide synthase expression and its correlation with clinical variables, such as tumor progression, angiogenesis, lymphangiogenesis, and prognosis in gastric cancer, we studied inducible nitric oxide synthase expression in gastric cancer samples from 211 patients with 5-year follow-up. CD105 and D2-40 were adopted as biomarkers for tumor angiogenesis and lymphangiogenesis, respectively. Inducible nitric oxide synthase staining was mainly found in the cytoplasm of gastric cancer tumor cells. Positive inducible nitric oxide synthase immunoreactivity was seen in 54.03% of gastric cancer specimens, which was correlated with lymph node metastasis, vascular invasion, distant metastasis, and TNM stage. Compared with inducible nitric oxide synthase negative patients, inducible nitric oxide synthase-positive patients had significantly shorter survival times and higher microvessel density and lymphatic vessel density. Intratumor and peritumor blood microvessel density and lymphatic vessel density correlated with inducible nitric oxide synthase expression (Spearman ρ test, P < .05). We conclude that inducible nitric oxide synthase expression correlates with lymph node metastasis, vascular invasion, distant metastasis, TNM stage, and poor survival rate in gastric cancer. We propose that synthesized inducible nitric oxide synthase increases angiogenesis, and lymphangiogenesis thus promotes tumor progression. Inducible nitric oxide synthase expression may be a good biomarker for poor prognosis in gastric cancer.

Curcumin attenuates the effects of transport stress on serum cortisol concentration, hippocampal NO production, and BDNF expression in the pig

Curcumin, the active component of curcuma longa, has been reported to be effective in alleviating chronic stress-induced disorders in rodents by modulating neuroprotection and neuroendocrine functions of the central nervous system, especially hippocampus. However, it is unclear whether curcumin can attenuate the subacute stress response induced by 2 h of road transport in the pig. Therefore, the present study was designed to identify the changes of serum cortisol concentration, hippocampal nitric oxide (NO) production, and related gene expression in response to 2 h of transport and to explore whether curcumin treatment (8 mg/kg, p.o.) for 21 d before transport may alleviate the stress-induced responses in the hippocampus of pigs. We found that 2 h of transport elevated serum cortisol concentration (P < 0.01), increased hippocampal NO content, and reduced brain-derived neurotrophic factor (BDNF) mRNA expression in pigs not treated with curcumin, whereas these stress responses were all reversed or attenuated in curcumin-treated pigs. In addition, the stress-induced increase in the expression of constitutive nitric oxide synthase (cNOS) and enzyme activities of total NOS, cNOS, and inducible NOS (iNOS) was also reversed or attenuated in curcumin-treated pigs. However, neither transport nor curcumin caused significant alterations in hippocampal expression of 11β-hydroxysteroid dehydrogenase type 1 and type 2 (11β-HSD1 and 2), glucocorticoid and mineralocorticoid receptors (GR and MR), or pro-/anti-apoptotic molecules (Bax-α and Bcl-xL). These results suggest that curcumin can alleviate subacute stress response in pigs through its neuroprotective effects on modulating hippocampal NO production and BDNF expression.

Hypoxia-induced activation of epidermal growth factor receptor (EGFR) kinase in the cerebral cortex of newborn piglets: the role of nitric oxide

The present study aims to investigate the mechanism of EGFR kinase activation during hypoxia and tests the hypothesis that hypoxia-induced increased activation of EGFR kinase in the cerebral cortical membrane fraction of newborn piglets is mediated by nitric oxide (NO) derived from neuronal nitric oxide synthase (nNOS). Fifteen newborn piglets were divided into normoxic (Nx, n = 5), hypoxic (Hx, n = 5) and hypoxic-treated with nNOS inhibitor (Hx-nNOSi, n = 5). Hypoxia was induced by an FiO2 of 0.07 for 60 min. nNOS inhibitor I (selectivity >2,500 vs. endothelial NOS, eNOS, and >500 vs. inducible NOS, iNOS) was administered (0.4 mg/kg, i. v.) 30 min prior to hypoxia. EGFR kinase tyrosine phosphorylation at Tyr1173, an index of activation of EGFR kinase, was determined by Western blot analysis using an anti-phospho (pTyr(1173))-EGFR kinase antibody. Protein bands were analyzed by imaging densitometry and expressed as absorbance (OD x mm(2)). EGFR kinase activity was determined radiochemically using immunopurified enzyme. EGFR kinase activity was expressed as pmols/mg protein/hr. Density of phosphor (pTyr(1173))-EGFR kinase (OD x mm(2)) was 60.2 +/- 9.8 in Nx, 177.0 +/- 26.9 in Hx (P < 0.05 vs. Nx) and 79.9 +/- 15.7 in Hx-nNOSi (P < 0.05 vs. Hx, P = NS vs. Nx). Activity of EGFR kinase (pmoles/mg protein/hr) was 4,603 +/- 155 in Nx, 8,493 +/- 427 in Hx (P < 0.05 vs. Nx) and 4,516 +/- 104 in Hx-nNOSi (P < 0.05 vs. Hx, P = NS vs. Nx). Pretreatment with nNOS inhibitor prevented the hypoxia-induced increased phosphorylation and increased activity of EGFR kinase. We conclude that the mechanism of hypoxia-induced increased activation of EGFR kinase is mediated by nNOS-derived NO.

Minocycline attenuates cognitive impairment and restrains oxidative stress in the hippocampus of rats with chronic cerebral hypoperfusion

OBJECTIVE

Nitric oxide (NO) was speculated to play an important role in the pathophysiology of cerebral ischemia. Minocycline, a tetracycline derivative, reduced inflammation and protected against cerebral ischemia. To study the neuroprotection mechanism of minocycline for vascular dementia, the influences of minocycline on expressions of inducible nitric oxide synthase (iNOS) and endothelial nitric oxide synthase (eNOS) were observed in the brains of Wistar rats.

METHODS

The vascular dementia rat model was established by permanent bilateral common carotid arteries occlusion (BCCAO). Wistar rats were divideded into 3 groups randomly: sham-operation group (S group), vascular dementia model group (M group), and minocycline treatment group (MT group). The behaviour was tested with Morris water maze and open-field task. Expressions of iNOS and eNOS were measured by immunohistochemistry and reverse transcriptase-polymerase chain reaction (RT-PCR). The optical density value was measured by imaging analysis. Percentage of positive cells with iNOS and eNOS expression was analyzed with optical microscope.

RESULTS

Minocycline attenuated cognitive impairment. Inducible NOS was significantly down-regulated in MT group, compared with that in M group (P < 0.01), while eNOS was significantly up-regulated, compared with that in M group (P < 0.01). The expressions of iNOS and eNOS in M and MT groups were higher than those in S group (P < 0.01).

CONCLUSION

Minocycline can down-regulate the expression of iNOS and up-regulate the expression of eNOS in vascular dementia, which restrains apoptosis and oxidative stress to protect neural function.

Antioxidant therapy and neuroprotection in the newborn

Injury to the perinatal brain is a leading cause of childhood mortality and lifelong disability. Despite recent improvements in neonatal care, no effective treatment for perinatal brain lesions is available. The newborn, especially if preterm, is highly prone to oxidative stress (OS) and to the toxic effect of free radicals (FRs). At birth, the newborn is exposed to a relatively hyperoxic environment caused by an increased oxygen bioavailability with greatly enhanced generation of FRs. Additional sources (e.g., inflammation, hypoxia, ischemia, glutamate and free iron release) occur, magnifying OS. In the preterm baby, the perinatal transition is accompanied by the immaturity of the antioxidant systems and the reduced ability to induce efficient homeostatic mechanisms designed to control overproduction of cell-damaging FRs. Improved understanding of the pathophysiological mechanism involved in perinatal brain lesions helps to identify potential targets for neuroprotective interventions, and the knowledge of these mechanisms has enabled scientists to develop new therapeutic strategies that have confirmed their neuroprotective effects in animal studies. Considering the growing role of OS in preterm newborn morbidity in respect to the higher risk of FR damage in these babies, erythropoietin, allopurinol, melatonin and hypothermia demonstrate great promise as potential neuroprotectans. This article provides an overview of the pathogenesis of FR-mediated diseases of the newborn and the antioxidant strategies now tested in order to reduce OS and its damaging effects.

Melatonin attenuates hypoxia-induced ultrastructural changes and increased vascular permeability in the developing hippocampus

Hypoxic injury in the perinatal period may be involved in damaging the developing hippocampus. The damage may be mediated by excess production of vascular endothelial growth factor (VEGF) and nitric oxide (NO). We examined the hippocampus of neonatal Wistar rats subjected to hypoxia for VEGF and NO production. The mRNA and protein expression of hypoxia inducible factor-1alpha, endothelial, neuronal, inducible nitric oxide synthase and VEGF was found to be up-regulated significantly after the hypoxic exposure. Tissue VEGF concentration and NO production were also increased. By electron microscopy, swollen dendrites, vacuolated axons and hypertrophic astrocyte end feet associated with blood vessels were observed in hypoxic animals. In hypoxic rats, the passage of rhodamine isothiocyanate (RhIC) and horseradish peroxidase, administered intraperitoneally or intravenously, was observed through vascular walls. Furthermore, immunoglobulin G was localized in the neuropil and neurons. We suggest that increased VEGF and NO production in hypoxia had resulted in increased vascular permeability, leading to structural alteration of the dendrites and axons. Melatonin administration reduced VEGF and NO levels as well as leakage of RhIC, suggesting that it has a therapeutic potential in reducing hypoxia-associated damage in the developing hippocampus.

Transient hypoxia stimulates mitochondrial biogenesis in brain subcortex by a neuronal nitric oxide synthase-dependent mechanism

The adaptive mechanisms that protect brain metabolism during and after hypoxia, for instance, during hypoxic preconditioning, are coordinated in part by nitric oxide (NO). We tested the hypothesis that acute transient hypoxia stimulates NO synthase (NOS)-activated mechanisms of mitochondrial biogenesis in the hypoxia-sensitive subcortex of wild-type (Wt) and neuronal NOS (nNOS) and endothelial NOS (eNOS)-deficient mice. Mice were exposed to hypobaric hypoxia for 6 h, and changes in immediate hypoxic transcriptional regulation of mitochondrial biogenesis was assessed in relation to mitochondrial DNA (mtDNA) content and mitochondrial density. There were no differences in cerebral blood flow or hippocampal PO2 responses to acute hypoxia among these strains of mice. In Wt mice, hypoxia increased mRNA levels for peroxisome proliferator-activated receptor-gamma coactivator-1alpha (PGC-1 alpha), nuclear respiratory factor-1, and mitochondrial transcription factor A. After 24 h, new mitochondria, localized in reporter mice expressing mitochondrial green fluorescence protein, were seen primarily in hippocampal neurons. eNOS-/- mice displayed lower basal levels but maintained hypoxic induction of these transcripts. In contrast, nuclear transcriptional regulation of mitochondrial biogenesis in nNOS-/- mice was normal at baseline but did not respond to hypoxia. After hypoxia, subcortical mtDNA content increased in Wt and eNOS-/- mice but not in nNOS-/- mice. Hypoxia stimulated PGC-1alpha protein expression and phosphorylation of protein kinase A and cAMP response element binding (CREB) protein in Wt mice, but CREB only was activated in eNOS-/- mice and not in nNOS-/- mice. These findings demonstrate that hypoxic preconditioning elicits subcortical mitochondrial biogenesis by a novel mechanism that requires nNOS regulation of PGC-1alpha and CREB.

Increased vascular permeability and nitric oxide production in response to hypoxia in the pineal gland

This study examined the factors that may be involved in altering the function of pineal gland in hypoxic conditions. Adult Wistar rats were subjected to hypoxia and the pineal gland was examined for the mRNA and protein expression of hypoxia-inducible factor-1alpha (HIF-1alpha), vascular endothelial growth factor (VEGF), endothelial, neuronal and inducible nitric oxide synthase (eNOS, nNOS, iNOS) at 3 hr-14 days after hypoxic exposure by real time reverse transcription-polymerase chain reaction, Western blotting and immunohistochemistry. Upregulated mRNA and protein expression of HIF-1alpha, VEGF, eNOS, nNOS and iNOS was observed in response to hypoxia. VEGF concentrations as determined by enzyme immunoassay and nitric oxide (NO) production measured by colorimetric assay were significantly higher after hypoxic exposure when compared with the controls. Melatonin content of the pineal gland, as determined by ELISA, was significantly reduced after the hypoxic exposure. Dilated blood vessels expressing eNOS were observed in hypoxic rats. Cells immunoreactive for VEGF were identified as the astrocytes whereas those immunoreactive for iNOS were pinealocytes and macrophages. Our findings indicate that excess production of VEGF and NO in pineal gland in response to hypoxia may be involved in increased vascular permeability as evidenced by an enhanced leakage of rhodamine isothiocyanate (RhIC). The increased vascular permeability may allow free access of serum-derived substances in the pineal gland that may affect the secretory function of the pinealocytes. Administration of exogenous melatonin may be beneficial as it reduced VEGF concentration and NO production significantly in hypoxic rats, and leakage of RhIC was concomitantly reduced.

Effect of 7-nitroindazole sodium on the cellular distribution of neuronal nitric oxide synthase in the cerebral cortex of hypoxic newborn piglets

Cerebral hypoxia results in generation of nitric oxide (NO) free radicals by Ca(++)-dependent activation of neuronal nitric oxide synthase (nNOS). The present study tests the hypothesis that the hypoxia-induced increased expression of nNOS in cortical neurons is mediated by NO. To test this hypothesis the cellular distribution of nNOS was determined immunohistochemically in the cerebral cortex of hypoxic newborn piglets with and without prior exposure to the selective nNOS inhibitor 7-nitroindazole sodium (7-NINA). Studies were conducted in newborn piglets, divided into normoxic (n = 6), normoxic treated with 7-NINA (n = 6), hypoxic (n = 6) and hypoxic pretreated with 7-NINA (n = 6). Hypoxia was induced by lowering the FiO(2) to 0.05-0.07 for 1 h. Cerebral tissue hypoxia was documented by decrease of ATP and phosphocreatine levels in both the hypoxic and 7-NINA pretreated hypoxic groups (P < 0.01). An increase in the number of nNOS immunoreactive neurons was observed in the frontal and parietal cortex of the hypoxic as compared to the normoxic groups (P < 0.05) which was attenuated by pretreatment with 7-NINA (P < 0.05 versus hypoxic). 7-NINA affected neither the cerebral energy metabolism nor the cellular distribution of nNOS in the cerebral cortex of normoxic animals. We conclude that nNOS expression in cortical neurons of hypoxic newborn piglets is NO-mediated. We speculate that nNOS inhibition by 7-NINA will protect against hypoxia-induced NO-mediated neuronal death.