Neuroprotective effects of N-acetylaspartylglutamate in a neonatal rat model of hypoxia-ischemia

Parallel Metabolomics and Lipidomics of a PSMA/GCPII Deficient Mouse Model Reveal Alteration of NAAG Levels and Brain Lipid Composition

Glutamate carboxypeptidase II (GCPII, also known as PSMA or FOLH1) is responsible for the cleavage of N-acetyl-aspartyl-glutamate (NAAG) to N-acetyl-aspartate and glutamate in the central nervous system and facilitates the intestinal absorption of folate by processing dietary folyl-poly-γ-glutamate in the small intestine. The physiological function of GCPII in other organs like kidneys is still not known. GCPII inhibitors are neuroprotective in various conditions (e.g., ischemic brain injury) in vivo; however, their utilization as potential drug candidates has not been investigated in regard to not yet known GCPII activities. To explore the GCPII role and possible side effects of GCPII inhibitors, we performed parallel metabolomic and lipidomic analysis of the cerebrospinal fluid (CSF), urine, plasma, and brain tissue of mice with varying degrees of GCPII deficiency (fully deficient in Folh1, -/-; one allele deficient in Folh1, +/-; and wild type, +/+). Multivariate analysis of metabolites showed no significant differences between wild-type and GCPII-deficient mice (except for NAAG), although changes were observed between the sex and age. NAAG levels were statistically significantly increased in the CSF, urine, and plasma of GCPII-deficient mice. However, no difference in NAAG concentrations was found in the whole brain lysate likely because GCPII, as an extracellular enzyme, can affect only extracellular and not intracellular NAAG concentrations. Regarding the lipidome, the most pronounced genotype-linked changes were found in the brain tissue. In brains of GCPII-deficient mice, we observed statistically significant enrichment in phosphatidylcholine-based lipids and reduction of sphingolipids and phosphatidylethanolamine plasmalogens. We hypothesize that the alteration of the NAA-NAAG axis by absent GCPII activity affected myelin composition. In summary, the absence of GCPII and thus similarly its inhibition do not have detrimental effects on metabolism, with just minor changes in the brain lipidome.

Dendrimer-enabled targeted delivery attenuates glutamate excitotoxicity and improves motor function in a rabbit model of cerebral palsy

Glutamate carboxypeptidase II (GCPII), localized on the surface of astrocytes and activated microglia, regulates extracellular glutamate concentration in the central nervous system (CNS). We have previously shown that GCPII is upregulated in activated microglia in the presence of inflammation. Inhibition of GCPII activity could reduce glutamate excitotoxicity, which may decrease inflammation and promote a 'normal' microglial phenotype. 2-(3-Mercaptopropyl) pentanedioic acid (2-MPPA) is the first GCPII inhibitor that underwent clinical trials. Unfortunately, immunological toxicities have hindered 2-MPPA clinical translation. Targeted delivery of 2-MPPA specifically to activated microglia and astrocytes that over-express GCPII has the potential to mitigate glutamate excitotoxicity and attenuate neuroinflammation. In this study, we demonstrate that 2-MPPA when conjugated to generation-4, hydroxyl-terminated polyamidoamine (PAMAM) dendrimers (D-2MPPA) localize specifically in activated microglia and astrocytes only in newborn rabbits with cerebral palsy (CP), not in controls. D-2MPPA treatment led to higher 2-MPPA levels in the injured brain regions compared to 2-MPPA treatment, and the extent of D-2MPPA uptake correlated with the injury severity. D-2MPPA was more efficacious than 2-MPPA in decreasing extracellular glutamate level in ex vivo brain slices of CP kits, and in increasing transforming growth factor beta 1 (TGF-β1) level in primary mixed glial cell cultures. A single systemic intravenous dose of D-2MPPA on postnatal day 1 (PND1) decreased microglial activation and resulted in a change in microglial morphology to a more ramified form along with amelioration of motor deficits by PND5. These results indicate that targeted dendrimer-based delivery specifically to activated microglia and astrocytes can improve the efficacy of 2-MPPA by attenuating glutamate excitotoxicity and microglial activation.

Dendrimer-Conjugated Glutamate Carboxypeptidase II Inhibitor Restores Microglial Changes in a Rabbit Model of Cerebral Palsy

We have previously shown that maternal endotoxin exposure leads to a phenotype of cerebral palsy and pro-inflammatory microglia in the brain in neonatal rabbits. "Activated" microglia overexpress the enzyme glutamate carboxypeptidase II (GCPII) that hydrolyzes N-acetylaspartylglutamate to N-acetylaspartate and glutamate, and we have shown previously that inhibiting microglial GCPII is neuroprotective. Glutamate-induced injury and associated immune signaling can alter microglial responses including microglial process movements for surveillance and phagocytosis. We hypothesize that inhibition of GCPII activity could alter microglial phenotype and normalize microglial process movement/dynamics. Newborn rabbit kits exposed to endotoxin in utero, when treated with dendrimer-conjugated 2-(phosphonomethyl)-pentanedioic acid (D-2PMPA), a potent and selective inhibitor of microglial GCPII, showed profound changes in microglial phenotype within 48 h of treatment. Live imaging of hippocampal microglia in ex vivo brain slice preparations revealed larger cell body and phagocytic cup sizes with less stable microglia processes in CP kits compared to healthy controls. D-2PMPA treatment led to significant reversal of microglial process stability to healthy control levels. Our results emphasize the importance of microglial process dynamics in determining the state of microglial function in the developing brain and demonstrate how GCPII inhibition specifically in microglia can effectively change the microglial process motility to healthy control levels, potentially impacting migration, phagocytosis, and inflammatory functions.

Hippocampal region-specific endogenous neuroprotection as an approach in the search for new neuroprotective strategies in ischemic stroke. Fiction or fact?

Ischemic stroke is the leading cause of death and long-term disability worldwide, and, while considerable progress has been made in understanding its pathophysiology, the lack of effective treatments remains a major concern. In that context, receiving more and more consideration as a promising therapeutic method is the activation of natural adaptive mechanisms (endogenous neuroprotection) - an approach that seeks to enhance and/or stimulate the endogenous processes of plasticity and protection of the neuronal system that trigger the brain's intrinsic capacity for self-defence. Ischemic preconditioning is a classic example of endogenous neuroprotection, being the process by which one or more brief, non-damaging episodes of ischemia-reperfusion (I/R) induce tissue resistance to subsequent prolonged, damaging ischemia. Another less-known example is resistance to an I/R episode mounted by the hippocampal region consisting of CA2, CA3, CA4 and the dentate gyrus (here abbreviated to CA2-4, DG). This can be contrasted with the ischemia-vulnerable CA1 region. There is not yet a good understanding of these different sensitivities of the hippocampal regions, and hence of the endogenous neuroprotection characteristic of CA2-4, DG. However, this region is widely reported to have properties distinct from CA1, and capable of generating resistance to an I/R episode. These include activation of neurotrophic and neuroprotective factors, greater activation of anti-excitotoxic and anti-oxidant mechanisms, increased plasticity potential, a greater energy reserve and improved mitochondrial function. This review seeks to summarize properties of CA2-4, DG in the context of endogenous neuroprotection, and then to assess the potential utility of these properties to therapeutic approaches. In so doing, it appears to represent the first such addressing of the issue of ischemia resistance attributable to CA2-4, DG.

Transcriptional regulation of NRF1 on metabotropic glutamate receptors in a neonatal hypoxic‑ischemic encephalopathy rat model

BACKGROUND

Neonatal hypoxic-ischemic encephalopathy (HIE) is a kind of brain injury that causes severe neurological disorders in newborns. Metabotropic glutamate receptors (mGluRs) and ionotropic glutamate receptors (iGluRs) are significantly associated with HIE and are involved in ischemia-induced excitotoxicity. This study aimed to investigate the upstream mechanisms of mGluRs and the transcriptional regulation by nuclear respiratory factor 1 (NRF1).

METHODS

The rat model of neonatal HIE was created using unilateral carotid artery ligation and in vitro oxygen-glucose deprivation paradigm. We used western blot, immunofluorescence, Nissl staining, and Morris water maze to investigate the impact of NRF1 on brain damage and learning memory deficit by HIE. We performed ChIP and luciferase activities to identify the transcriptional regulation of NRF1 on mGluRs.

RESULTS

The neuronal NRF1 and some glutamatergic genes expression synchronously declined in infarcted tissues. The NRF1 overexpression effectively restored the expression of some glutamatergic genes and improved cognitive performance. NRF1 regulated some members of mGluRs and iGluRs in hypoxic-ischemic neurons. Finally, NRF1 is bound to the promoter regions of Grm1, Grm2, and Grm8 to activate their transcription.

CONCLUSIONS

NRF1 is involved in the pathology of the neonatal HIE rat model, suggesting a novel therapeutic approach to neonatal HIE.

IMPACT

NRF1 and some glutamatergic genes were synchronously downregulated in the infarcted brain of the neonatal HIE rat model. NRF1 overexpression could rescue cognitive impairment caused by the neonatal HIE rat model. NRF1 regulated the expressions of Grm1, Grm2, and Grm8, which activated their transcription by binding to the promoter regions.

Group II Metabotropic Glutamate Receptors Reduce Apoptosis and Regulate BDNF and GDNF Levels in Hypoxic-Ischemic Injury in Neonatal Rats

Birth asphyxia causes brain injury in neonates, but a fully successful treatment has yet to be developed. This study aimed to investigate the effect of group II mGlu receptors activation after experimental birth asphyxia (hypoxia-ischemia) on the expression of factors involved in apoptosis and neuroprotective neurotrophins. Hypoxia-ischemia (HI) on 7-day-old rats was used as an experimental model. The effects of intraperitoneal application of mGluR2 agonist LY379268 (5 mg/kg) and the specific mGluR3 agonist NAAG (5 mg/kg) (1 h or 6 h after HI) on apoptotic processes and initiation of the neuroprotective mechanism were investigated. LY379268 and NAAG applied shortly after HI prevented brain damage and significantly decreased pro-apoptotic Bax and HtrA2/Omi expression, increasing expression of anti-apoptotic Bcl-2. NAAG or LY379268 applied at both times also decreased HIF-1α formation. HI caused a significant decrease in BDNF concentration, which was restored after LY379268 or NAAG administration. HI-induced increase in GDNF concentration was decreased after administration of LY379268 or NAAG. Our results show that activation of mGluR2/3 receptors shortly after HI prevents brain damage by the inhibition of excessive glutamate release and apoptotic damage decrease. mGluR2 and mGluR3 agonists produced comparable results, indicating that both receptors may be a potential target for early treatment in neonatal HI.

G-Protein-Coupled Receptors and Ischemic Stroke: a Focus on Molecular Function and Therapeutic Potential

In ischemic stroke, there is only one approved drug, tissue plasminogen activator, to be used in clinical conditions for thrombolysis. New neuroprotective therapies for ischemic stroke are desperately needed. Several targets and pathways have been shown to confer neuroprotective effects in ischemic stroke. G-protein-coupled receptors (GPCRs) are one of the most frequently targeted receptors for developing novel therapeutics for central nervous system disorders. GPCRs are a large family of cell surface receptors that response to a wide variety of extracellular stimuli. GPCRs are involved in a wide range of physiological and pathological processes. More than 90% of the identified non-sensory GPCRs are expressed in the brain, where they play important roles in regulating mood, pain, vision, immune responses, cognition, and synaptic transmission. There is also good evidence that GPCRs are implicated in the pathogenesis of stroke. This review narrates the pathophysiological role and possible targeted therapy of GPCRs in ischemic stroke.

Pretreatment with mGluR2 or mGluR3 Agonists Reduces Apoptosis Induced by Hypoxia-Ischemia in Neonatal Rat Brains

Hypoxia-ischemia (HI) in an immature brain results in energy depletion and excessive glutamate release resulting in excitotoxicity and oxidative stress. An increase in reactive oxygen species (ROS) production induces apoptotic processes resulting in neuronal death. Activation of group II mGluR was shown to prevent neuronal damage after HI. The application of agonists of mGluR3 (N-acetylaspartylglutamate; NAAG) or mGluR2 (LY379268) inhibits the release of glutamate and reduces neurodegeneration in a neonatal rat model of HI, although the exact mechanism is not fully recognized. In the present study, the effects of NAAG (5 mg/kg) and LY379268 (5 mg/kg) application (24 h or 1 h before experimental birth asphyxia) on apoptotic processes as the potential mechanism of neuroprotection in 7-day-old rats were investigated. Intraperitoneal application of NAAG or LY379268 at either time point before HI significantly reduced the number of TUNEL-positive cells in the CA1 region of the ischemic brain hemisphere. Both agonists reduced expression of the proapoptotic Bax protein and increased expression of Bcl-2. Decreases in HI-induced caspase-9 and caspase-3 activity were also observed. Application of NAAG or LY379268 24 h or 1 h before HI reduced HIF-1α formation likely by reducing ROS levels. It was shown that LY379268 concentration remains at a level that is required for activation of mGluR2 for up to 24 h; however, NAAG is quickly metabolized by glutamate carboxypeptidase II (GCPII) into glutamate and N-acetyl-aspartate. The observed effect of LY379268 application 24 h or 1 h before HI is connected with direct activation of mGluR2 and inhibition of glutamate release. Based on the data presented in this study and on our previous findings, we conclude that the neuroprotective effect of NAAG applied 1 h before HI is most likely the result of a combination of mGluR3 and NMDA receptor activation, whereas the beneficial effects of NAAG pretreatment 24 h before HI can be explained by the activation of NMDA receptors and induction of the antioxidative/antiapoptotic defense system triggered by mild excitotoxicity in neurons. This response to NAAG pretreatment is consistent with the commonly accepted mechanism of preconditioning.

Neuroprotective effects of a dendrimer-based glutamate carboxypeptidase inhibitor on superoxide dismutase transgenic mice after neonatal hypoxic-ischemic brain injury

The result of a deprivation of oxygen and glucose to the brain, hypoxic-ischemic encephalopathy (HIE), remains the most common cause of death and disability in human neonates globally and is mediated by glutamate toxicity and inflammation. We have previously shown that the enzyme glutamate carboxypeptidase (GCPII) is overexpressed in activated microglia in the presence of inflammation in fetal/newborn rabbit brain. We assessed the therapeutic utility of a GCPII enzyme inhibitor called 2-(3-Mercaptopropyl) pentanedioic acid (2MPPA) attached to a dendrimer (D-2MPPA), in order to target activated microglia in an experimental neonatal hypoxia-ischemia (HI) model using superoxide dismutase transgenic (SOD) mice that are often more injured after hypoxia-ischemia than wildtype animals. SOD overexpressing and wild type (WT) mice underwent permanent ligation of the left common carotid artery followed by 50 min of asphyxiation (10% O₂) to induce HI injury on postnatal day 9 (P9). Cy5-labeled dendrimers were administered to the mice at 6 h, 24 h or 72 h after HI and brains were evaluated by immunofluorescence analysis 24 h after the injection to visualize microglial localization and uptake over time. Expression of GCPII enzyme was analyzed in microglia 24 h after the HI injury. The expression of pro- and anti-inflammatory cytokines were analyzed 24 h and 72 h post-HI. Brain damage was analyzed histologically 7 days post-HI in the three randomly assigned groups: control (C); hypoxic-ischemic (HI); and HI mice who received a single dose of D-2MPPA 6 h post-HI (HI+D-2MPPA). First, we found that GCPII was overexpressed in activated microglia 24 h after HI in the SOD overexpressing mice. Also, there was an increase in microglial activation 24 h after HI in the ipsilateral hippocampus which was most visible in the SOD+HI group. Dendrimers were mostly taken up by microglia by 24 h post-HI; uptake was more prominent in the SOD+HI mice than in the WT+HI. The inflammatory profile showed significant increase in expression of KC/GRO following injury in SOD mice compared to WT at 24 and 72 h. A greater and significant decrease in KC/GRO was seen in the SOD mice following treatment with D-2MPPA. Seven days after HI, D-2MPPA treatment decreased brain injury in the SOD+HI group, but not in WT+HI. This reduced damage was mainly seen in hippocampus and cortex. Our data indicate that the best time point to administer D-2MPPA is 6 h post-HI in order to suppress the expression of GCPII by 24 h after the damage since dendrimer localization in microglia is seen as early as 6 h with the peak of GCPII upregulation in activated microglia seen at 24 h post-HI. Ultimately, treatment with D-2MPPA at 6 h post-HI leads to a decrease in inflammatory profiles by 24 h and reduction in brain injury in the SOD overexpressing mice.

Hippocampal Sector-Specific Metabolic Profiles Reflect Endogenous Strategy for Ischemia-Reperfusion Insult Resistance

The gerbil is a well-known model for studying cerebral ischemia. The CA1 of the hippocampus is vulnerable to 5 min of ischemia, while the CA2–4 and dentate gyrus (DG) are resistant to it. Short-lasting ischemia, a model of transient ischemic attacks in men, results in CA1 neuron death within 2–4 days of reperfusion. Untargeted metabolomics, using LC-QTOF-MS, was used to enrich the knowledge about intrinsic vulnerability and resistance of hippocampal regions and their early post-ischemic response (IR). In total, 30 significant metabolites were detected. In controls, taurine was significantly lower and guanosine monophosphate was higher in CA1, as compared to that in CA2–4,DG. LysoPG and LysoPE were more abundant in CA1, while LysoPI 18:0 was detected only in CA2–4,DG. After IR, a substantial decrease in the citric acid level in CA1, an accumulation of pipecolic acid in both regions, and opposite changes in the amount of PE and LysoPE were observed. The following metabolic pathways were identified as being differentially active in control CA1 vs. CA2–4,DG: metabolism of taurine and hypotaurine, glycerophospholipid, and purine. These results may indicate that a regulation of cell volume, altered structure of cell membranes, and energy metabolism differentiate hippocampal regions. Early post-ischemia, spatial differences in the metabolism of aminoacyl-tRNA biosynthesis, and amino acids and their metabolites with a predominance of those which upkeep their well-being in CA2–4,DG are shown. Presented results are consistent with genetic, morphological, and functional data, which may be useful in further study on endogenous mechanisms of neuroprotection and search for new targets for therapeutic interventions.

N-Acetylaspartylglutamate (NAAG) Pretreatment Reduces Hypoxic-Ischemic Brain Damage and Oxidative Stress in Neonatal Rats

N-acetylaspartylglutamate (NAAG), the most abundant peptide transmitter in the mammalian nervous system, activates mGluR3 at presynaptic sites, inhibiting the release of glutamate, and acts on mGluR3 on astrocytes, stimulating the release of neuroprotective growth factors (TGF-β). NAAG can also affect N-methyl-d-aspartate (NMDA) receptors in both synaptic and extrasynaptic regions. NAAG reduces neurodegeneration in a neonatal rat model of hypoxia-ischemia (HI), although the exact mechanism is not fully recognized. In the present study, the effect of NAAG application 24 or 1 h before experimental birth asphyxia on oxidative stress markers and the potential mechanisms of neuroprotection on 7-day old rats was investigated. The intraperitoneal application of NAAG at either time point before HI significantly reduced the weight deficit of the ischemic brain hemisphere, radical oxygen species (ROS) content and activity of antioxidant enzymes, and increased the concentration of reduced glutathione (GSH). No additional increase in the TGF-β concentration was observed after NAAG application. The fast metabolism of NAAG and the decrease in TGF-β concentration that resulted from NAAG pretreatment, performed up to 24 h before HI, excluded the involvement mGluR3 in neuroprotection. The observed effect may be explained by the activation of NMDA receptors induced by NAAG pretreatment 24 h before HI. Inhibition of the NAAG effect by memantine supports this conclusion. NAAG preconditioning 1 h before HI results in a mixture of mGluR3 and NMDA receptor activation. Preconditioning with NAAG induces the antioxidative defense system triggered by mild excitotoxicity in neurons. Moreover, this response to NAAG pretreatment is consistent with the commonly accepted mechanism of preconditioning. However, this theory requires further investigation.

The activation of group II metabotropic glutamate receptors protects neonatal rat brains from oxidative stress injury after hypoxia-ischemia

Birth asphyxia resulting in brain hypoxia-ischemia (H-I) can cause neonatal death or lead to persistent brain damage. Recent investigations have shown that group II metabotropic glutamate receptor (mGluR2/3) activation can provide neuroprotection against H-I but the mechanism of this effect is not clear. The aim of this study was to investigate whether mGluR2/3 agonists applied a short time after H-I reduce brain damage in an experimental model of birth asphyxia, and whether a decrease in oxidative stress plays a role in neuroprotection. Neonatal H-I in 7-day-old rats was used as an experimental model of birth asphyxia. Rats were injected intra peritoneally with mGluR2 (LY 379268) or mGluR3 (NAAG) agonists 1 h or 6 h after H-I (5 mg/kg). The weight deficit of the ischemic brain hemisphere, radical oxygen species (ROS) content levels, antioxidant enzymes activity and the concentrations of reduced glutathione (GSH) were measured. Both agonists reduced weight loss in the ischemic hemisphere and mitigated neuronal degeneration in the CA1 hippocampal region and cerebral cortex. Both agonists reduced the elevated levels of ROS in the ipsilateral hemisphere observed after H-I and prevented an increase in antioxidant enzymes activity in the injured hemisphere restoring them to control levels. A decrease in GSH level was also restored after agonists application. The results show that the activation of mGluR2 and mGluR3 a short time after H-I triggers neuroprotective mechanisms that act through the inhibition of oxidative stress and ROS production. The prevention of ROS production by the inhibition of glutamate release and decrease in its extracellular concentration is likely the main mechanism involved in the observed neuroprotection.

Maternal inflammation leads to impaired glutamate homeostasis and up-regulation of glutamate carboxypeptidase II in activated microglia in the fetal/newborn rabbit brain

Astrocyte dysfunction and excessive activation of glutamatergic systems have been implicated in a number of neurologic disorders, including periventricular leukomalacia (PVL) and cerebral palsy (CP). However, the role of chorioamnionitis on glutamate homeostasis in the fetal and neonatal brains is not clearly understood. We have previously shown that intrauterine endotoxin administration results in intense microglial 'activation' and increased pro-inflammatory cytokines in the periventricular region (PVR) of the neonatal rabbit brain. In this study, we assessed the effect of maternal inflammation on key components of the glutamate pathway and its relationship to astrocyte and microglial activation in the fetal and neonatal New Zealand white rabbit brain. We found that intrauterine endotoxin exposure at gestational day 28 (G28) induced acute and prolonged glutamate elevation in the PVR of fetal (G29, 1day post-injury) and postnatal day 1 (PND1, 3days post-injury) brains along with prominent morphological changes in the astrocytes (soma hypertrophy and retracted processes) in the white matter tracts. There was a significant increase in glutaminase and N-Methyl-d-Aspartate receptor (NMDAR) NR2 subunit expression along with decreased glial L-glutamate transporter 1 (GLT-1) in the PVR at G29, that would promote acute dysregulation of glutamate homeostasis. This was accompanied with significantly decreased TGF-β1 at PND1 in CP kits indicating ongoing neuroinflammation. We also show for the first time that glutamate carboxypeptidase II (GCPII) was significantly increased in the activated microglia at the periventricular white matter area in both G29 and PND1 CP kits. This was confirmed by in vitro studies demonstrating that LPS activated primary microglia markedly upregulate GCPII enzymatic activity. These results suggest that maternal intrauterine endotoxin exposure results in early onset and long-lasting dysregulation of glutamate homeostasis, which may be mediated by impaired astrocyte function and GCPII upregulation in activated microglia.

A high fat diet alters metabolic and bioenergetic function in the brain: A magnetic resonance spectroscopy study

Diet-induced obesity and associated metabolic effects can lead to neurological dysfunction and increase the risk of developing Alzheimer's disease (AD) and Parkinson's disease (PD). Despite these risks, the effects of a high-fat diet on the central nervous system are not well understood. To better understand the mechanisms underlying the effects of high fat consumption on brain regions affected by AD and PD, we used proton magnetic resonance spectroscopy ((1)H-MRS) to measure neurochemicals in the hippocampus and striatum of rats fed a high fat diet vs. normal low fat chow. We detected lower concentrations of total creatine (tCr) and a lower glutamate-to-glutamine ratio in the hippocampus of high fat rats. Additional effects observed in the hippocampus of high fat rats included higher N-acetylaspartylglutamic acid (NAAG), and lower myo-inositol (mIns) and serine (Ser) concentrations. Post-mortem tissue analyses revealed lower phosphorylated AMP-activated protein kinase (pAMPK) in the striatum but not in the hippocampus of high fat rats. Hippocampal pAMPK levels correlated significantly with tCr, aspartate (Asp), phosphoethanolamine (PE), and taurine (Tau), indicating beneficial effects of AMPK activation on brain metabolic and energetic function, membrane turnover, and edema. A negative correlation between pAMPK and glucose (Glc) indicates a detrimental effect of brain Glc on cellular energy response. Overall, these changes indicate alterations in neurotransmission and in metabolic and bioenergetic function in the hippocampus and in the striatum of rats fed a high fat diet.

The Good and Bad Sides of NAAG

Why has such a small peptide been the source of controversy in neuroscience over the last 5 decades? Is N-acetyl-aspartyl-glutamate (NAAG) a neurotransmitter? Is NAAG located in neuronal tissue or in astrocytes? Is NAAG involved in neuropsychiatric and neurodegenerative disorders? Is NAAG therapeutically beneficial in the treatment of stroke or in initiating cascades of events leading to psychosis? After many years of intense research there is no clear consensus within the scientific community on how NAAG behaves in the brain. One of the major controversies about NAAG is its physiological action at N-methyl-d-aspartate (NMDA) receptors. While some researchers strongly argue that NAAG acts as a weak agonist at NMDA receptors, others have suggested that NAAG could behave as a potent antagonist. Published data from our laboratory demonstrate that the effect of NAAG on NMDA receptors could be influenced by a number of factors including the subcellular localization and subunit composition of NMDA receptors, as well as protons. In this chapter, we will summarize the knowledge of the literature on NAAG, however, we will place emphasis on our recently published data. More specifically, we have reported interesting findings on the effects of NAAG on NMDA receptors at synaptic and extrasynaptic sites using a pharmacological paradigm to distinguish the two populations of NMDA receptors. Additionally, we have evaluated the role of NAAG on GluN2A- and GluN2B-containing NMDA receptors using a HEK293 cell recombinant system. Finally, we have studied the effects of NAAG on GluN2A- and GluN2B-containing NMDA receptors in different extracellular pH conditions. We believe that our findings could potentially resolve some aspects of the debate regarding the role of NAAG at NMDA receptors.

Erythropoietin Ameliorates Neonatal Hypoxia-Ischemia-Induced Neurobehavioral Deficits, Neuroinflammation, and Hippocampal Injury in the Juvenile Rat

The hematopoietic growth factor erythropoietin (EPO) has been shown to be neuroprotective against hypoxia-ischemia (HI) in Postnatal Day 7 (P7)–P10 or adult animal models. The current study was aimed to determine whether EPO also provides long-lasting neuroprotection against HI in P5 rats, which is relevant to immature human infants. Sprague-Dawley rats at P5 were subjected to right common carotid artery ligation followed by an exposure to 6% oxygen with balanced nitrogen for 1.5 h. Human recombinant EPO (rEPO, at a dose of 5 units/g) was administered intraperitoneally one hour before or immediately after insult, followed by additional injections at 24 and 48 h post-insult. The control rats were injected with normal saline following HI. Neurobehavioral tests were performed on P8 and P20, and brain injury was examined on P21. HI insult significantly impaired neurobehavioral performance including sensorimotor, locomotor activity and cognitive ability on the P8 and P20 rats. HI insult also resulted in brain inflammation (as indicated by microglia activation) and neuronal death (as indicated by Jade B positive staining) in the white matter, striatum, cortex, and hippocampal areas of the P21 rat. Both pre- and post-treatment with rEPO significantly improved neurobehavioral performance and protected against the HI-induced neuronal death, microglia activation (OX42+) as well as loss of mature oligodendrocytes (APC-CC1+) and hippocampal neurons (Nissl+). The long-lasting protective effects of rEPO in the neonatal rat HI model suggest that to exert neurotrophic activity in the brain might be an effective approach for therapeutic treatment of neonatal brain injury induced by hypoxia-ischemia.

Differential effects of N-acetyl-aspartyl-glutamate on synaptic and extrasynaptic NMDA receptors are subunit- and pH-dependent in the CA1 region of the mouse hippocampus

Ischemic strokes cause excessive release of glutamate, leading to overactivation of N-methyl-d-aspartate receptors (NMDARs) and excitotoxicity-induced neuronal death. For this reason, inhibition of NMDARs has been a central focus in identifying mechanisms to avert this extensive neuronal damage. N-acetyl-aspartyl-glutamate (NAAG), the most abundant neuropeptide in the brain, is neuroprotective in ischemic conditions in vivo. Despite this evidence, the exact mechanism underlying its neuroprotection, and more specifically its effect on NMDARs, is currently unknown due to conflicting results in the literature. Here, we uncover a pH-dependent subunit-specific action of NAAG on NMDARs. Using whole-cell electrophysiological recordings on acute hippocampal slices from adult mice and on HEK293 cells, we found that NAAG increases synaptic GluN2A-containing NMDAR EPSCs, while effectively decreasing extrasynaptic GluN2B-containing NMDAR EPSCs in physiological pH. Intriguingly, the results of our study further show that in low pH, which is a physiological occurrence during ischemia, NAAG depresses GluN2A-containing NMDAR EPSCs and amplifies its inhibitory effect on GluN2B-containing NMDAR EPSCs, as well as upregulates the surface expression of the GluN2A subunit. Altogether, our data demonstrate that NAAG has differential effects on NMDAR function based on subunit composition and pH. These findings suggest that the role of NAAG as a neuroprotective agent during an ischemic stroke is likely mediated by its ability to reduce NMDAR excitation. The inhibitory effect of NAAG on NMDARs and its enhanced function in acidic conditions make NAAG a prime therapeutic agent for the treatment of ischemic events.

Combination of therapeutic hypothermia and other neuroprotective strategies after an ischemic cerebral insult

Abrupt deprivation of substrates to neuronal tissue triggers a number of pathological events (the “ischemic cascade”) that lead to cell death. As this is a process of delayed neuronal cell death and not an instantaneous event, several pharmacological and non-pharmacological strategies have been developed to attenuate or block this cascade. The most promising neuroprotectant so far is therapeutic hypothermia and its beneficial effects have inspired researchers to further improve its protective benefit by combining it with other neuroprotective agents. This review provides an overview of all neuroprotective strategies that have been combined with therapeutic hypothermia in rodent models of focal cerebral ischemia. A distinction is made between drugs interrupting only one event of the ischemic cascade from those mitigating different pathways and having multimodal effects. Also the combination of therapeutic hypothermia with hemicraniectomy, gene therapy and protein therapy is briefly discussed. Furthermore, those combinations that have been studied in a clinical setting are also reviewed.

Glutamate carboxypeptidase II in diagnosis and treatment of neurologic disorders and prostate cancer

Glutamate carboxypeptidase II (GCPII) is a membrane-bound binuclear zinc metallopeptidase with the highest expression levels found in the nervous and prostatic tissue. Throughout the nervous system, glia-bound GCPII is intimately involved in the neuron-neuron and neuron-glia signaling via the hydrolysis of N-acetylaspartylglutamate (NAAG), the most abundant mammalian peptidic neurotransmitter. The inhibition of the GCPII-controlled NAAG catabolism has been shown to attenuate neurotoxicity associated with enhanced glutamate transmission and GCPII-specific inhibitors demonstrate efficacy in multiple preclinical models including traumatic brain injury, stroke, neuropathic and inflammatory pain, amyotrophic lateral sclerosis, and schizophrenia. The second major area of pharmacological interventions targeting GCPII focuses on prostate carcinoma; GCPII expression levels are highly increased in androgen-independent and metastatic disease. Consequently, the enzyme serves as a potential target for imaging and therapy. This review offers a summary of GCPII structure, physiological functions in healthy tissues, and its association with various pathologies. The review also outlines the development of GCPII-specific small-molecule compounds and their use in preclinical and clinical settings.

Neuroprotective effect of oligodendrocyte precursor cell transplantation in a long-term model of periventricular leukomalacia

Perinatal white matter injury, or periventricular leukomalacia (PVL), is the most common cause of brain injury in premature infants and is the leading cause of cerebral palsy. Despite increasing numbers of surviving extreme premature infants and associated long-term neurological morbidity, our understanding and treatment of PVL remains incomplete. Inflammation- or ischemia/hypoxia-based rodent models, although immensely valuable, are largely restricted to reproducing short-term features of up to 3 weeks after injury. Given the long-term sequelae of PVL, there is a need for subchronic models that will enable testing of putative neuroprotective therapies. Here, we report long term characterization of a neonatal inflammation-induced rat model of PVL. We show bilateral ventriculomegaly, inflammation, reactive astrogliosis, injury to pre-oligodendrocytes, and neuronal loss 8 weeks after injury. We demonstrate neuroprotective effects of oligodendrocyte precursor cell transplantation. Our findings present a subchronic model of PVL and highlight the tissue protective effects of oligodendrocyte precursor cell transplants that demonstrate the potential of cell-based therapy for PVL.

Progress in the discovery and development of glutamate carboxypeptidase II inhibitors

During the past 10 years, substantial progress has been made in the discovery and development of small molecule glutamate carboxypeptidase II (GCP II) inhibitors. These inhibitors have provided the necessary tools to investigate the physiological role of GCP II as well as the potential therapeutic benefits of its inhibition in neurological disorders of glutamatergic dysregulation. This review article details key GCP II inhibitors discovered in the last decade and important findings from preclinical and clinical studies.

Neuropeptidases

Neuropeptides are neurotransmitters and modulators distributed in the central nervous system (CNS) and peripheral nervous system. Their abnormalities cause neurological and mental diseases. Neuropeptidases are enzymes crucial for the biosynthesis and biodegradation of neuropeptides. We here focus on the peptidases involved in the metabolism of the well-studied opioid peptides. Bioactive enkephalins are formed from propeptides by processing enzymes—prohormone thiol protease, prohormone convertase 1 and 2 (PC 1 and 2), carboxypeptidase H/E, and Arg/Lys aminopeptidase. After they exert their biological effects, enkephalins are likely to be inactivated by degrading enzymes—angiotensin-converting enzyme (ACE), aminopeptidase N (APN), puromycin-sensitive aminopeptidase (PSA), and endopeptidase 24.11. Recently, a neuron-specific aminopeptidase (NAP), which was a putative enkephalin-inactivating enzyme at the synapses, was found. Neuropeptidases are useful drug targets and their inhibitors can be therapeutic. Synthetic anti-enkephalinases and anti-aminopeptidases are being developed. They are potent analgesics but have fewer side effects than the opiates.

Effects of NAAG peptidase inhibitor 2-PMPA in model chronic pain - relation to brain concentration

N-acetylated-alpha-linked-acidic peptidase (NAAG peptidase) converts N-acetyl-aspartyl-glutamate (NAAG, mGluR3 agonist) into N-acetyl-aspartate and glutamate. The NAAG peptidase inhibitor 2-PMPA (2-(phosphonomethyl)pentanedioic acid) had neuroprotective activity in an animal model of stroke and anti-allodynic activity in CCI model despite its uncertain ability to penetrate the blood-brain barrier. The NAAG concentration in brain ECF under basal conditions and its alteration in relation to the brain ECF concentration of 2-PMPA is unclear. We therefore assessed those brain concentrations after i.p. administration of 2-PMPA, using in vivo microdialysis combined with LC/MS/MS analysis. Administration of 2-PMPA (50mg/kg) produced a mean peak concentration of 2-PMPA of 29.66+/-8.1microM. This concentration is about 100,000 fold more than is needed for inhibition of NAAG peptidase, and indicates very good penetration to the brain. Application of 2-PMPA was followed by a linear increase of NAAG-concentration reaching a maximum of 2.89+/-0.42microM at the end of microdialysis. However, during the time the anti-allodynic effects of 2-PMPA were observed, the NAAG concentration in the ECF did not reach levels which are likely to have an impact on any known target. It appears therefore that the observed behavioural effects of 2-PMPA may not be mediated by NAAG nor, in turn, by mGluR3 receptors.

Differential negative coupling of type 3 metabotropic glutamate receptor to cyclic GMP levels in neurons and astrocytes

Metabotropic receptors may couple to different G proteins in different cells or perhaps even in different regions of the same cell. To date, direct studies of group II and group III metabotropic glutamate receptors' (mGluRs) relationships to second messenger cascades have reported negative coupling of these receptors to cyclic AMP (cAMP) levels in neurons, astrocytes and transfected cells. In the present study, we found that the peptide neurotransmitter N-acetylaspartylglutamate (NAAG), an mGluR3-selective agonist, decreased sodium nitroprusside (SNP)-stimulated cyclic GMP (cGMP) levels in cerebellar granule cells and cerebellar astrocytes. The mGluR3 and group II agonists FN6 and LY354740 had similar effects on cGMP levels. The mGluR3 and group II antagonists beta-NAAG and LY341495 blocked these actions. Treatment with pertussis toxin inhibited the effects of NAAG on SNP-stimulated cGMP levels in rat cerebellar astrocytes but not in cerebellar neurons. These data support the conclusion that mGluR3 is also coupled to cGMP levels and that this mGluR3-induced reduction of cGMP levels is mediated by different G proteins in cerebellar astrocytes and neurons. We previously reported that this receptor is coupled to a cAMP cascade via a pertussis toxin-sensitive G protein in cerebellar neurons, astrocytes and transfected cells. Taken together with the present data, we propose that mGluR3 is coupled to two different G proteins in granule cell neurons. These data greatly expand knowledge of the range of second messenger cascades induced by mGluR3, and have implications for clinical conditions affected by NAAG and other group II mGluR agonists.

Neuroprotective effects of the agonist of metabotropic glutamate receptors ABHxD-I in two animal models of cerebral ischaemia

The neuroprotective efficacy of 2-aminobicyclo[2.1.1]hexane-2,5-dicarboxylic acid-I (ABHxD-I), a rigid agonist of metabotropic glutamate receptors, was studied using a 3-min global cerebral ischaemia model in Mongolian gerbils and the hypoxia/ischaemia model in 7-day-old rats. The effects on brain damage of ABHxD-I (30 mg/kg, intraperitoneally or 7.5 microg intracerebroventricularly) administered 30 min before global ischaemia or 30 min after hypoxia/ischaemia was evaluated 14 days after the insults. Treatment of adult gerbils with ABHxD-I injected i.c.v. but not systemically, prevented post-ischaemic hyperthermia and substantially reduced brain damage. These effects may reflect low permeability of the adult blood-brain barrier to ABHxD-I, and the role of reduced body and brain temperature in neuroprotection after its i.c.v. administration. ABHxD-I given either i.p. or i.c.v. to developing rats reduced brain damage by 55 and 37%, respectively, without affecting the body temperature. Due to immaturity and increased post-ischaemic permeability of the blood-brain barrier in developing rats, ABHxD-I may induce neuroprotection by direct interference with brain metabotropic glutamate receptors.

NAAG peptidase inhibitors and their potential for diagnosis and therapy

Modulation of N-acetyl-L-aspartyl-L-glutamate peptidase activity with small-molecule inhibitors holds promise for a wide variety of diseases that involve glutamatergic transmission, and has implications for the diagnosis and therapy of cancer. This new class of compounds, of which at least one has entered clinical trials and proven to be well tolerated, has demonstrated efficacy in experimental models of pain, schizophrenia, amyotrophic lateral sclerosis, traumatic brain injury and, when appropriately functionalized, can image prostate cancer. Further investigation of these promising drug candidates will be needed to bring them to the marketplace. The recent publication of the X-ray crystal structure for the enzymatic target of these compounds should facilitate the development of other new agents with enhanced activity that could improve both the diagnosis and treatment of neurological disorders.

Neuroprotective effect of N-acetyl-aspartyl-glutamate in combination with mild hypothermia in the endothelin-1 rat model of focal cerebral ischaemia

Previously we showed that treatment with mild hypothermia (34 degrees C for 2 h) after a focal cerebral infarct was neuroprotective by reducing apoptosis in the penumbra (cortex), but not in the core (striatum) of the infarct. In this study we examined whether administration of N-acetyl-aspartyl-glutamate (NAAG) in combination with mild hypothermia could improve striatal neuroprotection in the endothelin-1 rat model. NAAG (10 mg/kg i.p.) was injected under normothermic (37 degrees C) or mild hypothermic conditions, either 40 min before or 20 min after the insult. NAAG reduced caspase 3 immunoreactivity in the striatum, irrespective of the time of administration and brain temperature. This neuroprotective effect could be explained, at least partially, by decreased nitric oxide synthase activity in the striatum and was blocked by the group II metabotropic glutamate receptor antagonist, LY341495. Hypothermia applied together with NAAG reduced both cortical and striatal caspase 3 immunoreactivity, as well as the overall ischaemic damage in these areas. However, no pronounced improvement was seen in total damaged brain volume. Extracellular glutamate levels did not correlate with the observed protection, whatever treatment protocol was applied. We conclude that treatment with NAAG causes the same degree of neuroprotection as treatment with hypothermia. Combination of the two treatments, although reducing apoptosis, does not considerably improve ischaemic damage.

Protection against glucose-induced neuronal death by NAAG and GCP II inhibition is regulated by mGluR3

Glutamate carboxypeptidase II (GCP II) inhibition has previously been shown to be protective against long-term neuropathy in diabetic animals. In the current study, we have determined that the GCP II inhibitor 2-(phosphonomethyl) pentanedioic acid (2-PMPA) is protective against glucose-induced programmed cell death (PCD) and neurite degeneration in dorsal root ganglion (DRG) neurons in a cell culture model of diabetic neuropathy. In this model, inhibition of caspase activation is mediated through the group II metabotropic glutamate receptor, mGluR3. 2-PMPA neuroprotection is completely reversed by the mGluR3 antagonist (S)-alpha-ethylglutamic acid (EGLU). In contrast, group I and III mGluR inhibitors have no effect on 2-PMPA neuroprotection. Furthermore, we show that two mGluR3 agonists, the direct agonist (2R,4R)-4-aminopyrrolidine-2, 4-dicarboxylate (APDC) and N-acetyl-aspartyl-glutamate (NAAG) provide protection to neurons exposed to high glucose conditions, consistent with the concept that 2-PMPA neuroprotection is mediated by increased NAAG activity. Inhibition of GCP II or mGluR3 may represent a novel mechanism to treat neuronal degeneration under high-glucose conditions.

GCP II (NAALADase) inhibition suppresses mossy fiber-CA3 synaptic neurotransmission by a presynaptic mechanism

We tested the hypothesis that endogenous N-acetylaspartylglutamate (NAAG) presynaptically inhibits glutamate release at mossy fiber-CA3 synapses. For this purpose, we made use of 2-(3-mercaptopropyl)pentanedioic acid (2-MPPA), an inhibitor of glutamate carboxypeptidase II [GCP II; also known as N-acetylated alpha-linked acidic dipeptidase (NAALADase)], the enzyme that hydrolyzes NAAG into N-acetylaspartate and glutamate. Application of 2-MPPA (1-20 microM) had no effect on intrinsic membrane properties of CA3 pyramidal neurons recorded in vitro in whole cell current- or voltage-clamp mode. Bath application of 10 microM 2-MPPA suppressed evoked excitatory postsynaptic current (EPSC) amplitudes. Attenuation of EPSC amplitudes was accompanied by a significant increase in paired-pulse facilitation (50-ms interpulse intervals), suggesting that a presynaptic mechanism is involved. The group II metabotropic glutamate receptor (mGluR) antagonist 2S-2-amino-2-(1S,2S-2-carboxycyclopropyl-1-yl)-3-(xanth-9-y l) propanoic acid (LY341495) prevented the 2-MPPA-dependent suppression of EPSC amplitudes. 2-MPPA reduced the frequencies of TTX-insensitive miniature EPSCs (mEPSC), without affecting their amplitudes, further supporting a presynaptic action for GCP II inhibition. 2-MPPA-induced reduction of mEPSC frequencies was prevented by LY341495, reinforcing the role of presynaptic group II mGluR. Because GCP II inhibition is thought to increase NAAG levels, these results suggest that NAAG suppresses synaptic transmission at mossy fiber-CA3 synapses through presynaptic activation of group II mGluRs.

Treatment with tamoxifen reduces hypoxic–ischemic brain injury in neonatal rats

Tamoxifen, an estrogen receptor modulator, is neuroprotective in adult rats. Does tamoxifen reduce brain injury in the rat pup? Seven-day-old rat pups had the right carotid artery permanently ligated followed by 2.5 h of hypoxia (8% oxygen). Tamoxifen (10 mg/kg) or vehicle was given i.p. 5 min prior to hypoxia, or 5 min after reoxygenation, with a second dose given 6 h after the first. Brain damage was evaluated by weight deficit of the right hemisphere 22 days following hypoxia and gross and microscopic morphology. Tamoxifen pre-treatment reduced brain weight loss from 21.5+/-4.0% in vehicle pups (n=27) to 2.6+/-2.5% in the treated pups (n=22, P<0.05). Treatment 5 min after reoxygenation reduced brain weight loss from 27.5+/-4.0% in vehicle pups (n=42) to 12.0+/-3.9% in the treated pups (n=30, P<0.05). Tamoxifen reduces brain injury in the neonatal rat.

Effects of GCP-II inhibition on responses of dorsal horn neurones after inflammation and neuropathy: an electrophysiological study in the rat

N-Acetylaspartylglutamate (NAAG) is a peptide neurotransmitter present in the brain and spinal cord. It is hydrolysed by glutamate carboxypeptidase II (GCPII); thus, the GCP-II inhibitor 2-[phosphono-methyl]-pentanedioic acid (2-PMPA) protects endogenous NAAG from degradation, allowing its effects to be studied in vivo. We recorded the effect of spinal 2-PMPA (50-1000 microg) on the electrical-evoked activity of dorsal horn neurones in normal and carrageenan-inflamed animals, and in the spinal nerve ligation (SNL) model of neuropathy and sham-operated animals. In normal animals, 1000 microg 2-PMPA selectively inhibited noxious-evoked activity (input, post-discharge and C- and Adelta-fibre-evoked responses), and not low threshold Abeta-fibre-evoked responses. After carrageenan inflammation, the lower dose of 100 microg 2-PMPA inhibited input, post-discharge, C- and Adelta-fibre-evoked responses by a significantly greater amount than the same dose in normal animals. 2-PMPA inhibited neuronal responses less consistently in sham-operated and SNL animals, and effects were not significantly different from those seen in normal animals. NAAG is an agonist at the inhibitory metabotropic glutamate receptor mGluR3, and 2-PMPA may inhibit nociceptive transmission in normal animals by elevating synaptic NAAG levels, allowing it to activate mGluR3 and thus reducing transmitter release from afferent nerve terminals. mGluR3 expression in the superficial dorsal horn is upregulated after peripheral inflammation, perhaps explaining the greater inhibition of neuronal responses we observed after carrageenan inflammation. These results support an important role of endogenous NAAG in the spinal processing of noxious information.

Brain-derived neurotrophic factor protection of cortical neurons from serum withdrawal-induced apoptosis is inhibited by cAMP

Programmed cell death plays an important role both during the development of the CNS and in its homeostasis throughout adulthood. A complex balance between cell death- and survival-inducing signals determines the fate of individual neurons. Intracellular cAMP is thought to regulate neuronal survival, and previous studies have shown that the survival of retinal ganglion cells by brain-derived neurotrophic factor (BDNF) is dependent on cAMP. Here we report the surprising observation that cAMP attenuates the ability of BDNF to rescue cortical neurons from apoptosis after serum deprivation, a process mediated via the phosphatidylinositol 3 (PI3)-kinase signal transduction cascade. Depolarization by KCl, which increases cAMP in cortical neurons, also attenuates BDNF protection against serum withdrawal. Our data indicate that cAMP antagonizes neurotrophin protection from serum withdrawal by inhibiting the PI3-kinase signal transduction cascade. This study indicates that cAMP may inhibit some forms of neurotrophin-mediated neuronal survival and suggests that a number of PI3-kinase-regulated processes in neurons may be inhibited by cAMP.

Cardiovascular responses and nitric oxide production in cerebral ischemic rats

We investigated that the role of nitric oxide (NO) on ischemic rats in brain and heart. Ischemia was induced by both common carotid arteries (CCA) occlusion for 24h following reperfusion. Then tissue samples were removed and measured NOx. In brain, NOx was increased by about 40% vs. normal and it was significantly inhibited by aminoguanidine, selective iNOS inhibitor. This result showed that NOx concentration was increased by iNOS. We investigated the role of Ca2+ during ischemia. Nimodipine, L-type calcium channel blocker, didn't inhibit the increases of NOx concentration during ischemia. It suggested that increased NOx was due to calcium-independent NOS. MK-801, which N-methyl-D-aspartate (NMDA) receptor antagonist, didn't significantly prevent the increases of NOx. In heart, ischemia caused NOx decrease and it is inconsistent with NOx increase in brain. Aminoguanidine and nimodipine didnt affect on NOx decrease. But MK-801 more lowered NOx concentration than those of ischemia control group. It seemed that Ca2+ influx in heart partially occurred via NMDA receptor and inhibited by NMDA receptor antagonist. The mean arterial pressure (MAP) in ischemic rats after 24h of CCA occlusion was decreased when compared to normal value, whereas the heart rates (HR) was not different between two groups. Aminoguanidine or MK801 had no effect on MAP or HR, but nimodipine reduced MAP. There was no difference the effects of aminoguanidine, nimodipine, or MK-801, on MAP and HR between normal rats and ischemic rats. In summary, ischemic model caused an increase of NOx concentration, suggesting that this may be produced via iNOS, which is calcium independent in brain. However in heart, ischemia decreased NOx concentration and NMDA receptor was partially involved. The basal MAP was decreased in ischemic rats but HR was not different from normal control, suggesting that increased NOx in brain of ischemic rat may result in the hypotension.