Nitric oxide induces cultured cortical neuron apoptosis

Disrupting nNOS-PSD95 Interaction Improves Neurological and Cognitive Recoveries after Traumatic Brain Injury

Excessive activation of N-methyl-D-aspartate receptors (NMDARs) and the resulting neuronal nitric oxide synthase (nNOS) activation plays a crucial role in the pathogenesis of traumatic brain injury (TBI). However, directly inhibiting NMDARs or nNOS produces adverse side effects because they play key physiological roles in the normal brain. Since interaction of nNOS-PSD95 is a key step in NMDAR-mediated excitotoxicity, we investigated whether disrupting nNOS-PSD95 interaction with ZL006, an inhibitor of nNOS-PSD95 interaction, attenuates NMDAR-mediated excitotoxicity. In cortical neuronal cultures, ZL006 treatment significantly reduced glutamate-induced neuronal death. In a mouse model of controlled cortical impact (CCI), administration of ZL006 (10 mg/kg, i.p.) at 30 min postinjury significantly inhibited nNOS-PSD95 interaction, reduced TUNEL- and phospho-p38-positive neurons in the motor cortex. ZL006 treatment also significantly reduced CCI-induced cortical expression of apoptotic markers active caspase-3, PARP-1, ratio of Bcl-2/Bax, and phosphorylated p38 MAPK (p-p38). Functionally, ZL006 treatment significantly improved neuroscores and sensorimotor performance, reduced somatosensory and motor deficits, reversed CCI-induced memory deficits, and attenuated cognitive impairment. Histologically, ZL006 treatment significantly reduced the brain lesion volume. These findings collectively suggest that blocking nNOS-PSD95 interaction represents an attractive strategy for ameliorating consequences of TBI and that its action is mediated via inhibiting neuronal apoptosis and p38 MAPK signaling.

Fipronil sulfone induced higher cytotoxicity than fipronil in SH-SY5Y cells: Protection by antioxidants

Fipronil is a broad spectrum insecticide from the phenyl pyrazole family, which targets GABA receptor. Limited information is available about the metabolite fipronil sulfone cytotoxic actions. This study examined in vitro neurotoxicity of fipronil and fipronil sulfone and evaluated Trolox (vitamin E analog) (0.3, 1μM), N-acetyl-cysteine (0.5, 1mM), melatonin (0.1, 1μM) and Tempol (superoxide dismutase analog) (0.3, 0.5mM) protective role in SH-SY5Y cells. MTT and LDH assays were carried out to assess the cytotoxicity of fipronil and fipronil sulfone at 3-100μM concentrations. Fipronil sulfone was more toxic than fipronil. Tempol showed the best neuroprotectant profile against fipronil (50 and 150μM) and fipronil sulfone (3 and 10μM) reaching control levels. Fipronil (100μM) and fipronil sulfone (3μM) treatments induced a 4.7- and 5-fold increases in lipid peroxides measured as malondialdehyde (MDA) and a 2.2- and 2.0-fold increases in the levels of nitric oxide (NO). These results suggest that oxidative stress observed may be one of the major mechanisms of fipronil-induced neurotoxicity and it may be attributed in part to fipronil disposition and metabolism. Our results led us postulate that metabolite fipronil sulfone might be responsible for the fipronil-induced toxicity rather than fipronil itself.

Allopurinol reduces severity of delayed neurologic sequelae in experimental carbon monoxide toxicity in rats

Approximately half of those who survive severe carbon monoxide (CO) poisoning develop delayed neurologic sequelae. Growing evidence supports the crucial role of free radicals in delayed brain injury associated with CO toxicity. Xanthine oxidase (XO) has been reported to play a pivotal role in the generation of reactive oxygen species (ROS) in CO poisoning. A recent report indicates that allopurinol both attenuated oxidative stress and possessed anti-inflammatory properties in an animal model of acute liver failure. In this study, we aimed to explore the potential of allopurinol to reduce the severity of delayed neurologic sequelae. The rats were first exposed to 1000 ppm CO for 40 min and then to 3000 ppm CO for another 20 min. Following CO poisoning, the rats were injected with allopurinol (50 mg/kg, i.p.) six times. Results showed that allopurinol significantly reduced neuronal death and suppressed expression of pro-inflammatory factors, including tumor necrosis factor-α, intercellular adhesion molecule-1, ionized calcium-binding adapter molecule 1, and degraded myelin basic protein. Furthermore, behavioral studies revealed an improved performance in the Morris water maze test. Our findings indicated that allopurinol may have protective effects against delayed neurologic sequelae caused by CO toxicity.

6-Hydroxydopamine and lipopolysaccharides induced DNA damage in astrocytes: involvement of nitric oxide and mitochondria

The present study was conducted to investigate the effect of the neurotoxins 6-hydroxydopamine and lipopolysaccharide on astrocytes. Rat astrocyte C6 cells were treated with different concentration of 6-hydroxydopamine (6-OHDA)/lipopolysaccharides (LPS) for 24 h. Both neurotoxins significantly decreased the viability of astrocytes, augmented the expression of inducible nitric oxide synthase (iNOS) and the astrocyte marker--glial fibrillar acidic protein. A significantly decreased mitochondrial dehydrogenase activity, mitochondrial membrane potential, augmented reactive oxygen species (ROS) level, caspase-3 mRNA level, chromatin condensation and DNA damage was observed in 6-OHDA/LPS treated astroglial cells. 6-OHDA/LPS treatment also caused the significantly increased expression of iNOS and nitrite level. Findings showed that 6-OHDA/LPS treatment caused mitochondrial dysfunction mediated death of astrocytes, which significantly involve the nitric oxide. Since we have observed significantly increased level of iNOS along with mitochondrial impairment and apoptotic cell death in astrocytes, therefore to validate the role of iNOS, the cells were co-treated with iNOS inhibitor aminoguanidine (AG, 100 μM). Co-treatment of AG significantly attenuated the 6-OHDA/LPS induced cell death, mitochondrial activity, augmented ROS level, chromatin condensation and DNA damage. GFAP and caspase-3 expression were also inhibited with co-treatment of AG, although the extent of inhibition was different in both experimental sets. In conclusion, the findings showed that iNOS mediated increased level of nitric oxide acts as a key regulatory molecule in 6-OHDA/LPS induced mitochondrial dysfunction, DNA damage and apoptotic death of astrocytes.

Neuroinflammation in schizophrenia especially focused on the role of microglia

An accumulating body of evidence point to the significance of neuroinflammation and immunogenetics also in schizophrenia. Recent genome-wide studies in schizophrenia suggest immune involvement in schizophrenia. Microglia are the resident macrophage of the brain and major players in innate immunity in the CNS. They respond rapidly to even minor pathological changes in the brain and may contribute directly to the neuronal degeneration by producing various pro-inflammatory cytokines and free radicals. In many aspects, the neuropathology of schizophrenia is closely associated with microglial activation. We and other researchers have shown the inhibitory effects of some typical or atypical antipsychotics on the release of inflammatory cytokines and free radicals from activated microglia, both of which are not only directly toxic to neurons but also cause a decrease in neurogenesis as well as white matter abnormalities in the brains of the patients with schizophrenia. The treatment through the inhibition of microglial activation may shed new light on the therapeutic strategy of schizophrenia.

Neuroprotective properties of Loranthus parasiticus aqueous fraction against oxidative stress-induced damage in NG108-15 cells

Loranthus parasiticus, a Chinese folk medicine, has been widely used for the treatment of brain diseases, particularly in southwest China. Hence, the present neuroprotection model was designed to investigate its neuroprotective properties against H(2)O(2)-induced oxidative stress in NG108-15 cells. L. parasiticus aqueous fraction (LPAF), which was selected in the present study, had proved to be the most active fraction among the other tested extracts and fractions in our previous screening. The restoration of depleted intracellular glutathione (GSH), a major endogenous antioxidant, by LPAF was observed after H(2)O(2) insult. Pretreatment with LPAF substantially reduced the production of intracellular reactive oxygen species generated from H(2)O(2). Apoptotic features such as externalization of phosphatidylserine and disruption of mitochondrial membrane potential were significantly attenuated by LPAF. In addition, cell cycle analysis revealed a prominent decrease in the H(2)O(2)-induced sub-G(1) population by LPAF. Moreover, apoptotic morphological analysis by DAPI nuclear staining demonstrated that NG108-15 cells treated with H(2)O(2) exhibited apoptotic features, while such changes were greatly reduced in cells pretreated with LPAF. Taken together, these findings confirmed that LPAF exerts marked neuroprotective activity, which raises the possibility of potential therapeutic application of LPAF for managing oxidative stress-related neurological disorders and supports the traditional use of L. parasiticus in treating brain-related diseases.

Exploration of beneficial and deleterious effects of inflammation in stroke: dynamics of inflammation cells

The inflammatory process during stroke consists of activation of resident brain microglia and recruitment of leucocytes, namely neutrophils and monocytes/macrophages. During inflammation, microglial cells, neutrophils and macrophages secrete inflammatory cytokines and chemokines, and phagocytize dead cells. The recruitment of blood cells (neutrophils and macrophages) is mediated by the leucocyte-endothelium interactions and more specifically by cell adhesion molecules. A mathematical model is proposed to represent the dynamics of various brain cells and of immune cells (neutrophils and macrophages). This model is based on a set of six ordinary differential equations and explores the beneficial and deleterious effects of inflammation, respectively phagocytosis by immune cells and the release of pro-inflammatory mediators and nitric oxide (NO). The results of our simulations are qualitatively consistent with those observed in experiments in vivo and would suggest that the increase of phagocytosis could contribute to the increase of the percentage of living cells. The inhibition of the production of cytokines and NO and the blocking of neutrophil and macrophage infiltration into the brain parenchyma led also to the improvement of brain cell survival. This approach may help to explore the respective contributions of the beneficial and deleterious roles of the inflammatory process in stroke, and to study various therapeutic strategies in order to reduce stroke damage.

Cytokines and schizophrenia: Microglia hypothesis of schizophrenia

The etiology of schizophrenia remains unclear, while there has been a growing amount of evidence for the neuroinflammation and immunogenetics, which are characterized by an increased serum concentration of several pro-inflammatory cytokines. Despite the fact that microglia comprise only <10% of the total brain cells, microglia respond rapidly to even minor pathological changes in the brain and may contribute directly to the neuronal degeneration by producing various pro-inflammatory cytokines and free radicals. In many aspects, the neuropathology of schizophrenia has recently been reported to be closely associatedwith microglial activation. Previous studies have shown the inhibitory effects of some typical/atypical antipsychotics on the release of inflammatory cytokines and free radicals from activated microglia, both of which have recently been known to cause a decrease in neurogenesis as well as white matter abnormalities in the brains of patients with schizophrenia. The microglia hypothesis of schizophrenia may shed new light on the therapeutic strategy for schizophrenia.

Platycodin D and 2''-O-acetyl-polygalacin D2 isolated from Platycodon grandiflorum protect ischemia/reperfusion injury in the gerbil hippocampus

Platycodi radix is used as a folk remedy for several conditions. In this study, we investigated the neuroprotective effects of five major extracts; deapioplatycoside E (DPE), platycoside E (PE), platyconic acid A (PA), platycodin D (PD) and 2''-o-acetyl-polygalacin D2 (PD2) isolated from the P.radix in the hippocampal CA1 region (CA1) 4 or 10 days after ischemia/reperfusion (I/R). Each extract was administered into gerbils with intraperitoneal injection (5 mg/kg/day) 10 days before ischemic surgery and the gerbils were sacrificed 4 or 10 days after I/R. Fluoro-Jade B (F-J B, a marker for neurodegeneration) positive ((+)) neurons increased significantly in the stratum pyramidale of the CA1 region in the vehicle-treated group after I/R. A similar pattern was observed in the DPE-, PE- and PA-treated groups; however, in the PD- and PD2-treated groups, F-J B(+) neurons were small in number. We also observed that activations of astrocytes and microglia in the CA1 region after I/R were blocked by the PD- and PD2 treatments. In addition, we found that Cu,Zn-superoxide dismutase (SOD1) immunoreactivity in the pyramidal layer of the PD- and PD2-treated groups was similar to that of the sham group and COX-2(+) and NF-kappaB(+) cells were significantly lower in the PD- and PD2-treated group than those in the vehicle-treated group after I/R. These results suggest that PD and PD2 rescue neurons in the CA1 region from an ischemic damage.

Vasoactive intestinal peptide inhibits toll-like receptor 3-induced nitric oxide production in Schwann cells and subsequent sensory neuronal cell death in vitro

We have previously reported that polyinosinic-polycytidylic acids [poly(I:C)], a synthetic toll-like receptor 3 (TLR3) agonist, induce Schwann cell activation, which exerts neurotoxic effects on sensory neurons. In this study, we investigated the effects of vasoactive intestinal peptide (VIP), a neuropeptide implicated in nerve regeneration, on TLR3-induced Schwann cell activation. VIP receptors VPAC1 and VPAC2 were constitutively expressed in rat Schwann cells. VIP pretreatment inhibited TLR3-induced inducible nitric oxide synthase (iNOS) gene expression and NO production in Schwann cells. Studies on the intracellular signal transduction pathways indicate that the VIP effect is mediated by protein kinase A activation. VIP also inhibited the poly(I:C)-induced p38 activation that is responsible for the iNOS gene expression in Schwann cells. Finally, VIP inhibited dorsal rooyt ganglion neuronal cell death caused by NO produced in activated Schwann cells. Taken together, our data suggest that VIP exerts a neuroprotective effect by inhibiting neurotoxic Schwann cell activation.

Serum inflammatory adhesion molecules and high-sensitivity C-reactive protein correlates with delayed ischemic neurologic deficits after subarachnoid hemorrhage

BACKGROUND

The purpose of the present study was to investigate the relationship between serum concentrations of the immunoglobulin-like superfamily, selectins, hsCRP, and the development of DIND in patients with aneurysmal SAH.

METHODS

Serum ICAM-1, VCAM-1, E-selectin, P-selectin, L-selectin, and hsCRP were measured in 33 patients with SAH who underwent aneurysmal clipping within 48 hours of the onset of symptoms. Serum samples were obtained during the early period (day 0) and the late period (day 7).

RESULTS

The serum concentrations of ICAM-1 (P = .009), VCAM-1 (P = .0383) and hsCRP (P = .0014) during the early period were significantly higher in patients with SAH than in control patients. Further, serum hsCRP concentration during the late period was significantly higher in patients with SAH than in control patients (P = 0033). Finally, serum concentrations of ICAM-1, VCAM-1, and hsCRP during the early (P = .0055, P = .0266, and P = .0266) and late (P = .0423, P = .0041, and P = .0004) period were significantly higher in patients with DIND than in patients without DIND.

CONCLUSIONS

Serum levels of ICAM-1, VCAM-1 and hsCRP during the early and late period following SAH correlate with DIND.

The effect of atypical antipsychotics, perospirone, ziprasidone and quetiapine on microglial activation induced by interferon-gamma

An accumulating body of evidences point to the significance of neuroinflammation and immunogenetics in schizophrenia, characterized by increased serum concentration of several pro-inflammatory cytokines. In the central nervous system (CNS), the microglial cells are the major immunocompetent cells which release pro-inflammatory cytokines, nitric oxide (NO) and reactive oxygen species to mediate the inflammatory process. In the present study, we investigated whether or not atypical antipsychotics, namely perospirone, quetiapine and ziprasidone, would have anti-inflammatory effects on the activated microglia which may potentiate neuroprotection. All three atypical antipsychotics significantly inhibited NO generation from activated microglia while perospirone and quetiapine significantly inhibited the TNF-alpha release from activated microglia. Antipsychotics, especially perospirone and quetiapine may have an anti-inflammatory effect via the inhibition of microglial activation, which is not only directly toxic to neurons but also has an inhibitory effect on neurogenesis and oligodendrogenesis, both of which have been reported to play a crucial role in the pathology of schizophrenia.

Differential ex vivo nitric oxide production by acutely isolated neonatal and adult microglia

Microglia are the macrophage population residing in the parenchyma of the central nervous system (CNS), and are thought to play critical roles in CNS development, homeostasis and defense against pathogens. Microglia are capable of rapidly responding to microbial pathogens through engagement of their Toll-like receptors (TLRs). We first compared the efficiency of these responses in primary microglia acutely isolated from adult and neonatal mice. While the cytokine and chemokine responses of adult microglia were generally higher than those of neonatal cells stimulated ex vivo through TLRs, the nitric oxide response of neonatal microglia was markedly enhanced relative to the adult cells. We then went on to identify culture conditions such as exposure to M-SCF or GM-CSF that markedly enhanced the nitric oxide response of microglia, particularly those from the adult CNS. Finally, we demonstrate that the differential nitric oxide response of neonatal and adult microglia is not only limited to the mouse, but also extends to rat microglia.

Hypoxia-mediated induction of heme oxygenase type I and carbon monoxide release from astrocytes protects nearby cerebral neurons from hypoxia-mediated apoptosis

To study a putative paracellular protective mechanism of astrocytes for neurons, immunohistochemical analysis was performed in ischemic rat brain, which colocalized with the expression of heme oxygase-1 (HO- 1) in astroglias surrounding dying TUNEL-positive neurons. As an in vitro paradigm for ischemia, cultured astrocytes were exposed to normobaric hypoxia (pO(2) asymptotically equal to 10 torr), which triggered marked increase in the expression of a 33 kDa stress protein, identified as HO-1. Induction of HO-1 message was observed within 4 h of hypoxia and peaked at 12 h, accompanied by an accelerated transcription of HO-1 message. Consistent with the induction of HO-1, a platelet bioassay revealed production of carbon monoxide by reoxygenated astrocytes. The presence of CO in the medium decelerated the hypoxia-mediated apoptotic type of cell death in cultured cerebral neurons via lowering the activity of caspase-3, a key enzyme regulating apoptotic cell death. This protection against apoptosis was likely mediated by CO-mediated increases in intracellular cGMP, because exposure of hypoxic neurons to CO increased intracellular cGMP levels, and addition of cGMP analogue to hypoxic neuronal cultures suppressed caspase-3 activity and promoted neuronal survival. These data describe a potentially important paracellular pathway through which astrocytes may rescue nearby neurons from ischemic death.

Mechanisms of nitric oxide-induced apoptosis in bovine chromaffin cells: Role of mitochondria and apoptotic proteins

The aim of this work was to establish the possible involvement of mitochondria in the apoptotic event triggered by nitric oxide (NO) in chromaffin cells. Using bovine chromaffin cells in primary culture and several NO donors (SNP, SNAP, and GSNO) at apoptotic concentrations (50 microM-1 mM), we have shown that NO induces a time-dependent decrease in the mitochondrial transmembrane potential (DeltaPsi(m)), which correlates with the appearance of hypodiploid cells. Disruption in DeltaPsi(m) is followed by cytochrome c release to the cytosol, which in turn precedes caspase 3 activation. In this mechanism participates the Bcl-2 protein family, because NO donors downregulate the expression of anti-apoptotic members of the family such as Bcl-2 and Bcl-XL, and increase the expression of pro-apoptotic members, Bax and Bcl-Xs, inductors of cytochrome c release to cytosol. Different cell signaling pathways seem to regulate Bax induction and Bcl-2 inhibition because decreased Bcl-2 levels are detected later than enhanced Bax expression. The tumour suppressor protein p53 is also upregulated in a very early phase (30 min) of the NO-induced apoptosis and may be responsible for the further induction of Bax expression. Finally, the translocation of NF-kappaB to the nucleus seems to be another early event in NO-induced apoptosis and it may be involved in the regulation of p53 expression. These results support strongly the participation of mitochondrial mechanisms in NO-induced apoptosis in chromaffin cells and suggest that these cells may be good models for the investigation of molecular basis of neurodegeneration and neuroprotection.

Detrimental effects of nitric oxide inhibition on hepatic encephalopathy in rats with thioacetamide-induced fulminant hepatic failure: role of nitric oxide synthase isoforms

BACKGROUND

Hepatic encephalopathy is a complex neuropsychiatric syndrome. A previous study showed that chronic nitric oxide (NO) inhibition aggravated the severity of encephalopathy in thioacetamide (TAA)-treated rats. The present study investigated the relative contribution of NO synthase (NOS) isoforms on the severity of hepatic encephalopathy in TAA-treated rats.

METHOD

Fulminant hepatic failure was induced in male Sprague-Dawley rats by intraperitoneal injection of TAA (350 mg/kg/day) for 3 days. Rats were divided into three groups to receive N(omega)-nitro-L-arginine methyl ester (L-NAME, a non-selective NOS inhibitor, 25 mg/kg/day in tap water), L-canavanine (an inducible NOS inhibitor, 100 mg/kg/day via intraperitoneal injection) or normal saline (N/S) from 2 days prior to TAA administration and lasting for 5 days. Severity of encephalopathy was assessed by the counts of motor activity. Plasma levels of tumor necrosis factor-alpha (TNF- alpha) were determined by enzyme-linked immunosorbent assay (ELISA), and total bilirubin, alanine aminotransferase (ALT) and creatinine were determined by colorimetric assay.

RESULTS

Compared with L-canavanine or N/S-treated rats (0% and 4%, respectively), the mortality rate was significantly higher in rats receiving L-NAME administration (29%, P < 0.005). Inhibition of NO created detrimental effects on the counts of motor activities (P < 0.05). Rats treated with L-NAME had significantly higher plasma levels of total bilirubin, ALT, creatinine and TNF- alpha as compared with rats treated with L-canavanine or N/S (P < 0.01).

CONCLUSION

Chronic L-NAME administration, but not L-canavanine, had detrimental effects on the severity of hepatic damage and motor activities in TAA-treated rats. These results suggest that constitutive NOS activities play a major protective role in rats with fulminant hepatic failure.

Systemic administration of argatroban reduces secondary brain damage in a rat model of intracerebral hemorrhage: histopathological assessment

This study investigated the effects of argatroban, a thrombin inhibitor, on brain edema and inflammation in a rat intracerebral hemorrhage (ICH) model. ICH was induced by injecting collagenase IV into the right caudate nucleus. Argatroban was administered intraperitoneally. Argatroban reduced brain edema from 44.6 to 14.3 microl at 72 h. Infiltration of polymorphonuclear leukocytes at 24 h and monocyte/macrophage at 24 and 72 h was significantly suppressed by argatroban. Argatroban did not increase the volume of hematoma. Systemic administration of argatroban reduced secondary brain damage including edema and inflammation in a rat ICH model.

Nitric-oxide-induced depolarization of neuronal mitochondria: implications for neuronal cell death

Nitric oxide (NO(*)) has known toxic effects on central nervous system neurons. This study characterized the effect of NO(*) on mitochondrial membrane changes by exploring the relationship among NO(*), excitatory receptor activation, and the induction of peroxynitrite, a highly toxic NO(*) reactant, to neuronal injury. Cultured rat cortical neurons were exposed to the NO(*) generator, diethylenetriamine/nitric oxide adduct, and were examined for signs of cell death, mitochondrial membrane potential changes (Deltapsi(m)), and the induction of a mitochondrial permeability transition (MPT). Neurons were also examined for nitrotyrosine (NT) immunoreactivity, a marker of reactive nitrogen species (RNS) formation. Neurons exposed to NO(*) or to N-methyl-D-aspartate (NMDA) exhibited similar rapid depolarization of mitochondria, which was prevented by an NMDA receptor antagonist. Electrophysiological studies demonstrated NO(*) potentiation of NMDA-induced NMDA receptor currents. NO(*) and NMDA-treated neurons had evidence of mitochondrial-specific NT immunoreactivity that was prevented by a SOD/catalase mimetic (EUK-134). EUK-134 treatment reduced both NO(*) and NMDA-induced NT formation and neuronal cell death. EUK-134 did not prevent NO-induced Deltapsi(m) but partially prevented NMDA-induced Deltapsi(m) loss. Although NO(*) and NMDA both induced MPT and MPT inhibitors prevented NO-induced Deltapsi(m), they did not result in significant neuroprotection, in contrast to treatment designed to decrease peroxynitrite formation. These data suggest that NO-induced NMDA receptor activation is closely linked to intramitochondrial NO-peroxynitrite/RNS formation and thereby acts as a major mediator of neuronal cell death.

Postnatal changes in the nitric oxide system of the rat cerebral cortex after hypoxia during delivery

The impact of hypoxia in utero during delivery was correlated with the immunocytochemistry, expression and activity of the neuronal (nNOS) and inducible (iNOS) isoforms of the nitric oxide synthase enzyme as well as with the reactivity and expression of nitrotyrosine as a marker of protein nitration during early postnatal development of the cortex. The expression of nNOS in both normal and hypoxic animals increased during the first few postnatal days, reaching a peak at day P5, but a higher expression was consistently found in hypoxic brain. This expression decreased progressively from P7 to P20, but was more prominent in the hypoxic group. Immunoreactivity for iNOS was also higher in the cortex of the hypoxic rats and was more evident between days P0 and P5, decreasing dramatically between P10 and P20 in both groups of rats. Two nitrated proteins of 52 and 38 kDa, were also identified. Nitration of the 52-kDa protein was more intense in the hypoxic animals than in the controls, increasing from P0 to P7 and then decreasing progressively to P20. The 38-kDa nitrated protein was seen only from P10 to P20, and its expression was more intense in control than in the hypoxic group. These results suggest that the NO system may be involved in neuronal maturation and cortical plasticity over postnatal development. Overproduction of NO in the brain of hypoxic animals may constitute an effort to re-establish normal blood flow and may also trigger a cascade of free-radical reactions, leading to modifications in the cortical plasticity.

Deltamethrin induces apoptotic cell death in cultured cerebral cortical neurons

In this study we investigated the induction of apoptotic cell death and its potential mechanisms in cultured cortical neurons in response to deltamethrin exposure. The cultured cortical neurons were treated at 7 days with deltamethrin at concentrations of 10, 100, and 1000 nM, respectively. MTT assay showed that higher concentrations of deltamethrin (100 and 1000 nM) decreased neuronal viability in a time- and dose-dependent way. TUNEL staining revealed that numerous apoptotic cells appeared in the treated cultures compared to controls at 24, 48, and 72 h after treatment of 100 nM deltamethrin. Western blot analysis demonstrated that p53 and Bax expression were dramatically increased at the same time points, whereas Bcl-2 expression was significantly reduced at all time points after deltamethrin treatment. Further, we found that nitric oxide synthase inhibitor N(G)-nitro-L-arginine prevented deltamethrin-induced neuronal apoptosis and altered expression of p53, Bax, and Bcl-2. These results suggest that nitric oxide synthase might mediate deltamethrin-elicited neuronal apoptosis through modulating the expression of apoptosis-related genes.

Enhanced neuronal damage by co-administration of quinolinic acid and free radicals, and protection by adenosine A2A receptor antagonists

1. Quinolinic acid may be an important endogenous excitotoxin, but its concentrations in brain are low. We have therefore attempted to determine whether its neurotoxicity can be increased by the simultaneous presence of free radicals. 2. Quinolinic acid was injected into the hippocampus of anaesthetized rats at doses of 40 and 80 nmols which produced little neuronal loss, and 120 nmols which produced over 90% neuronal loss. 3. A mixture of xanthine and xanthine oxidase, a known source of free radical reactive oxygen species, also generated little damage alone, but killed over 80% of CA1 neurons when combined with 80 nmols of quinolinic acid. Similarly, the nitric oxide donor S-nitroso-N-acetylpenicillamine (SNAP) potentiated the damage produced by quinolinic acid. 4. The glutamate antagonist 5,7-dichlorokynurenic acid prevented the damage produced by 120 nmols of quinolinic acid, but not that produced by quinolinic acid plus xanthine/xanthine oxidase, indicating that damage was not simply the result of free radical enhancement of NMDA receptor activation. 5. Three chemically dissimilar antagonists at adenosine A(2A) receptors prevented the damage caused by quinolinic acid and xanthine/xanthine oxidase or by quinolinic acid plus SNAP. 6. It is concluded that reactive oxygen species can potentiate the neurotoxicity of quinolinic acid. The site of interaction is probably distal to the NMDA receptor. Blockade of adenosine A(2A) receptors can protect against this combined damage, suggesting potential value in the prevention of brain damage.

Galectin-3 protects human breast carcinoma cells against nitric oxide-induced apoptosis: implication of galectin-3 function during metastasis

Galectin-3 is a beta-galactoside-binding protein which regulates many biological processes including cell adhesion, migration, cell growth, tumor progression, metastasis, and apoptosis. Although the exact function of galectin-3 in cancer development is unclear, galectin-3 expression is associated with neoplastic progression and metastatic potential. Since studies have suggested that tumor cell survival in microcirculation determines the metastatic outcome, we examined the effect of galectin-3 overexpression in human breast carcinoma cell survival using the liver ischemia/reperfusion metastasis model. While the majority of control cells died by hepatic ischemia/reoxygenation, nearly all of galectin-3 overexpressing cells survived. We showed that galectin-3 inhibits nitrogen free radical-mediated apoptosis, one of the major death pathways induced during hepatic ischemia/reperfusion. Galectin-3 inhibition of apoptosis involved protection of mitochondrial integrity, inhibition of cytochrome c release and caspase activation. Taking these results together with the previous observation that galectin-3 inhibits apoptosis induced by loss of cell adhesion, we propose that galectin-3 is a critical determinant for anchorage-independent and free radical-resistant cell survival during metastasis.

Prooxidant and antioxidant functions of nitric oxide in liver toxicity

In response to tissue damage and inflammation induced by a variety of xenobiotics including acetaminophen, carbon tetrachloride, ethanol, galactosamine, and endotoxin, as well as disease states such as viral hepatitis, and postischemic and regenerative injury, the liver produces large quantities of nitric oxide. Indeed, nearly all cell types in the liver including hepatocytes, Kupffer cells, stellate cells, and endothelial cells have the capacity to generate nitric oxide. Thus, these cells, as well as infiltrating leukocytes, may indirectly augment tissue injury. In many models of liver damage, nitric oxide and its oxidation products such as peroxynitrite contribute to the injury process by directly damaging the tissue or by initiating additional immunologic reactions that result in damage. In some models, nitric oxide donors or peroxynitrite can mimic the cytotoxic actions of liver toxins. Moreover, agents that prevent the generation of nitric oxide or antioxidants that bind reactive nitrogen intermediates, or knockout mice with reduced capacity to produce nitric oxide, are protected from xenobiotic-induced tissue injury. In contrast, there have been reports that blocking nitric oxide production enhances xenobiotic-induced tissue injury. This has led to the concept that nitric oxide either inactivates proteins critical for xenobiotic-induced tissue injury or acts as an antioxidant, reducing cellular levels of cytotoxic reactive oxygen intermediates. Whether or not nitric oxide or secondary oxidants generated from nitric oxide act as mediators of tissue injury or protect against toxicity is likely to depend on the precise targets of these reactive nitrogen intermediates, as well as levels of superoxide anion present and the extent to which tissue injury is mediated by reactive oxygen intermediates. In addition, as toxicity is a complex process involving a variety of cell types and many soluble mediators, the contribution of each of these factors must be taken into account when considering the role of nitric oxide as a determinant of tissue injury.

Retinoic acid-mediated enhancement of the cholinergic/neuronal nitric oxide synthase phenotype of the medial septal SN56 clone: establishment of a nitric oxide-sensitive proapoptotic state

It is unclear what mechanisms lead to the degeneration of basal forebrain cholinergic neurons in Alzheimer's or other human brain diseases. Some brain cholinergic neurons express neuronal nitric oxide (NO) synthase (nNOS), which produces a free radical that has been implicated in some forms of neurodegeneration. We investigated nNOS expression and NO toxicity in SN56 cells, a clonal cholinergic model derived from the medial septum of the mouse basal forebrain. We show here that, in addition to expressing choline acetyltransferase (ChAT), SN56 cells express nNOS. Treatment of SN56 cells with retinoic acid (RA; 1 microM) for 48 h increased ChAT mRNA (+126%), protein (+88%), and activity (+215%) and increased nNOS mRNA (+98%), protein (+400%), and activity (+15%). After RA treatment, SN56 cells became vulnerable to NO excess generated with S-nitro-N-acetyl-DL-penicillamine (SNAP) and exhibited increased nuclear DNA fragmentation that was blocked with a caspase-3 inhibitor. Treatment with dexamethasone, which largely blocked the RA-mediated increase in nNOS expression, or inhibition of nNOS activity with methylthiocitrulline strongly potentiated the apoptotic response to SNAP in RA-treated SN56 cells. Caspase-3 activity was reduced when SNAP was incubated with cells or cell lysates, suggesting that NO can directly inhibit the protease. Thus, whereas RA treatment converts SN56 cells to a proapoptotic state sensitive to NO excess, endogenously produced NO appears to be anti-apoptotic, possibly by tonically inhibiting caspase-3.

The role of volume transmission of adaptogenic signals in forming the adaptive reactions of the brain

This review presents published data and results from our own studies providing evidence for the important role of volume, non-synaptic transmission of adaptogenic signals in the mechanisms forming the long-term adaptive reactions of the brain. The importance of chemical factors involved in volume transmission and secreted by cells in this process is discussed. Special attention is paid to peptides-possible mediators of volume transmission of adaptive-type signals. Evidence has been obtained for the presence of peptides and their role in the mechanism of development of adaptive brain reactions of different origins, especially those arising in response to tetanic stimulation of neurons and transient hypoxic stress. An original method for testing for the effects of neuromodulator factors released by cells in donor slices subjected to these treatments on recipient slices was used to show that these factors had pronounced effects on synaptic transmission and could induce long-term potentiation of synaptic transmission, protecting against functional derangements due to prolonged anoxia. Blockade of protein synthesis in donor slices subjected to adaptogenic treatments suppressed the appearance of these effects. The review concludes with a discussion of the mechanisms of interaction of the synaptic and volume transmission of signals involved in forming long-term adaptive brain reactions.

The anti-death league: associative control of apoptosis in developing retinal tissue

Apoptosis, the major form of programmed cell death (PCD), is executed through a proteolytic cascade that can be differentially engaged by various extracellular signals. Modulation of both the sensitivity to PCD and of the actual sequence of apoptotic events is, therefore, strongly dependent on cell interactions. This paper reviews the use of a retinal explant preparation as a model of the organized nervous tissue, to study the effects of neural messengers in the control of sensitivity to apoptosis. Studies of retinal explants showed that dopamine, glutamate and nitric oxide may have anti-apoptotic effects upon developing retinal cells. At least the effects of nitric oxide are clearly paracrine. In addition, preliminary evidence has been gathered of a role for gap junctional communication in the control of sensitivity of retinal cells to the induction of apoptosis. These findings underscore the importance of selective cell interactions in the control of PCD in the developing nervous system.

Hydrogen peroxide-induced oxidative damage and apoptosis in cerebellar granule cells: protection by Ginkgo biloba extract

The ability of oxidative stress to induce apoptosis and the protective effects of Ginkgo biloba extract (EGb761) against this induction were studied in cultures of rat cerebellar granule cells. Cells were exposed to oxidative stress by treatment with 50 microm hydrogen peroxide+100 microm ferrous sulphate which generates hydroxyl radicals by Fenton reaction. Both morphological observation and biochemical analysis revealed that H(2)O(2)/FeSO(4)treatment induced apoptotic cell death in cerebellar granule cells, which was characterized by chromatin condensation and DNA fragmentation. During this process, the fluidity of the cell membrane decreased markedly, and the conformation of membrane proteins altered significantly. Pretreating cerebellar granule cells with the antioxidant EGb761 (Ginkgo biloba extract) effectively attenuated oxidative damage induced by H(2)O(2)/FeSO(4), and prevented cells from apoptotic cell death. The results suggested that EGb761 might be used as a potential drug for neuronal diseases associated with the excessive production of reactive oxygen species.

Deltamethrin induces delayed apoptosis and altered expression of p53 and bax in rat brain

Our previous work indicates that deltamethrin induces degeneration and apoptosis in rat brain at 24 and 48 h after treatment. To determine whether molecular characteristics of apoptosis is involved in neurodegeneration in rat brain after deltamethrin treatment, we investigated the effects of deltamethrin on the mRNA expression of p53 and bax and their correlation with deltamethrin-induced apoptotic cell death in rat brain. Hematoxylin-eosin and cresyl violet staining revealed numerous degenerative cells in cortex and hippocampus at 5 and 24 h after deltamethrin treatment. Apoptotic cells were detected in cortex and hippocampus of treated rats at 24 h by in situ end labeling, whereas no apoptotic cells were observed in the same brain regions at 5 h after treatment. By using in situ hybridization, it was demonstrated that the increase of p53 and bax mRNA levels appeared at 5 and also at 24 h after treatment. The alterations in mRNA expression of p53 and bax preceded the occurrence of delayed apoptotic cell death in the same brain regions after deltamethrin treatment. These results indicate that (1) deltamethrin induces delayed apoptotic cell death, which may play an important role in deltamethrin-elicited neurodegeneration; (2) deltamethrin leads to the persistent increase of p53 and bax mRNA levels, which may contribute to delayed apoptosis in rat brain following deltamethrin treatment.

Membrane asymmetry and DNA degradation: functionally distinct determinants of neuronal programmed cell death

The ability to elucidate the molecular mechanisms that modulate programmed cell death (PCD) may provide the crucial clues to unravel the cellular basis of neurodegenerative disorders. Employing both a novel assay to follow serially PCD in individual living neurons and the neuroprotective agent lubeluzole as an investigative tool, we examined the development of nitric oxide (NO)-induced PCD over time through the reversible annexin V labelling of membrane phosphatidylserine (PS) exposure and the electron microscopy of genomic DNA in primary rat hippocampal neurons. Exposure to the NO generators SNP (300 microM) or NOC-9 (300 microM) alone increased annexin V-positive neurons in the population from 7% +/- 4% in untreated cultures to 13% +/- 4% at 1 hr and to 61% +/- 5% at 24 hr. Administration of a neuroprotective concentration of lubeluzole (750 nM) at the time of NO exposure initially prevented the exposure of PS residues, but consistently maintained DNA integrity over a 24 hr period. During posttreatment paradigms of lubeluzole (750 nM) at 2, 4, and 6 hr following NO exposure, progression of membrane PS inversion was reversed and subsequently suppressed over a 24 hr course. Our work illustrates that neuronal PCD is composed of at least two physiologically distinct and separate pathways that consist of the externalization of membrane PS residues and the independent maintenance of genomic DNA integrity. In addition, neuronal injury is fluid and reversible in nature, suggesting a "window of opportunity" for the repair and reversal of neurons yet to be committed to PCD.

Effects of deltamethrin on nitric oxide synthase and poly(ADP-ribose) polymerase in rat brain

The effects of deltamethrin on the activities of nitric oxide synthase (NOS) and poly(ADP-ribose) polymerase (PARP) and the protein expression of neuronal NOS (nNOS) and PARP in rat brain were investigated in the present study. The activity of NOS was significantly increased in cortex and hippocampus at 5 h after deltamethrin treatment, and maintained at an increased level at 24 h. The activity of PARP was also elevated at the same time points in the same brain regions of treated rats. By immunohistochemical analysis, it was demonstrated that the nNOS-immunoreactive cells were markedly increased at 24 h after treatment in the cortex and hippocampus, whereas few nNOS-immunoreactive cells were observed in the same brain regions of control and treated rats at 5 h after treatment. The immunoreactivity for PARP was also increased in the same brain regions, showing the similar time course of the induction of nNOS by deltamethrin. These results indicate that deltamethrin increases the activities of NOS and PARP and initiates the protein expression of nNOS and PARP, suggesting that NOS and PARP might play important roles in neurotoxicity of deltamethrin.

Astrocytes prevent neuronal death induced by reactive oxygen and nitrogen species

Reactive oxygen and nitrogen species (RO/NS) such as nitric oxide (NO), hydroxyl radical (OH.), and superoxide anion (O(2)(-)) are generated in a variety of neuropathological processes and damage neurons. In the present study, we investigated the neuroprotective effects of rat astrocytes against RO/NS-induced damage using neuron-glia cocultures, and the effects were compared to those of microglial cells. Sodium nitroprusside (SNP), 3-morpholinosydnonimine (SIN-1), and FeSO(4) were used to generate NO, O(2)(-) and NO, and OH., respectively. Solely cultured neurons, which were transiently exposed to these agents, degenerated, possibly through apoptotic mechanisms as revealed by in situ detection of DNA fragmentation, whereas neurons cocultured with either astrocytes or microglial cells were viable even after exposure to RO/NS. In contrast, most neurons cocultured with meningeal fibroblasts degenerated. Astrocyte-conditioned medium partially attenuated RO/NS-induced neuronal damage. When neurons were cultured on astrocyte-derived extracellular matrix (AsECM), neuronal death induced by SNP and FeSO(4) was almost completely inhibited. AsECM contained significant amounts of laminin and fibronectin, and pure fibronectin and laminin also protected neurons against RO/NS-induced damage in the same manner as AsECM. These results suggest that astrocytes can protect neurons against RO/NS-induced damage by secreting soluble and insoluble factors.

Nitrinergic neurons in the developing and adult human telencephalon: transient and permanent patterns of expression in comparison to other mammals

A subpopulation of cerebral cortical neurons constitutively express nitric oxide synthase (NOS) and, upon demand, produce a novel messenger molecule nitric oxide (NO) with a variety of proposed roles in the developing, adult, and diseased brain. With respect to the intensity of their histochemical (NADPH-diaphorase histochemistry) and immunocytochemical (nNOS and eNOS immunocytochemistry) staining, these nitrinergic neurons are generally divided in type I and type II cells. Type I cells are usually large, intensely stained interneurons, scattered throughout all cortical layers; they frequently co-express GABA, neuropeptide Y, and somatostatin, but rarely contain calcium-binding proteins. Type II cells are small and lightly to moderately stained, about 20-fold more numerous than type I cells, located exclusively in supragranular layers, and found almost exclusively in the primate and human brain. In the developing cerebral cortex, nitrinergic neurons are among the earliest differentiating neurons, mostly because the dominant population of prenatal nitrinergic neurons are specific fetal subplate and Cajal-Retzius cells, which are the earliest generated neurons of the cortical anlage. However, at least in the human brain, a subpopulation of principal (pyramidal) cortical neurons transiently express NOS proteins in a regionally specific manner. In fact, transient overexpression of NOS-activity is a well-documented phenomenon in the developing mammalian cerebral cortex, suggesting that nitric oxide plays a significant role in the establishment and refinement of the cortical synaptic circuitry. Nitrinergic neurons are also present in human fetal basal forebrain and basal ganglia from 15 weeks of gestation onwards, thus being among the first chemically differentiated neurons within these brain regions. Finally, a subpopulation of human dorsal pallidal neurons transiently express NADPH-diaphorase activity during midgestation.

The antioxidant EPC-K1 attenuates NO-induced mitochondrial dysfunction, lipid peroxidation and apoptosis in cerebellar granule cells

In this study we investigated the effects of nitric oxide (NO) on cultured cerebellar granule cells. Exposure to NO donors, S-nitrosoglutathione (GSNO; 250 microM) or sodium nitroprusside (SNP; 500 microM), triggered apoptosis in immature cultures of cerebellar granule cells, which was characterized by chromatin condensation, nuclei fragmentation, and DNA laddering. Exposure of cerebellar granule cells to NO donors led to a decrease in the mitochondrial transmembrane potential and intracellular ATP content, which suggested that NO treatment caused mitochondrial dysfunction. NO treatment also induced oxidative stress in cerebellar granule cells as measured by thiobarbituric acid (TBA) assay. Pretreating cells with L-ascorbic acid 2-[3,4-dihydro-2,5,7,8-tetramethyl-2-(4,8,12-trimethyltridecyl)-2H -1-benzopyran-6-yl-hydrogen phosphate] potassium salt (EPC-K1), a novel antioxidant, attenuated NO-induced mitochondrial dysfunction and oxidative stress to some extent, and prevented the cells from apoptosis. The results of the present investigation suggest that a superoxide/peroxynitrite-mediated oxidative stress may be an important pathway leading to NO-associated neuronal damage. Pretreating cells with the antioxidant EPC-K1 attenuated NO-induced neurotoxicity by scavenging superoxide/peroxynitrite and/or its breakdown products.

Direct temporal analysis of apoptosis induction in living adherent neurons

Destruction of neurons through the genetically directed process of programmed cell death (PCD) is an area of intense interest because this is the underlying mechanism in a variety of developmental and neurodegenerative diseases. The ability to identify and track viable neurons subjected to PCD could be invaluable in development of strategies to prevent or reverse the downstream mechanisms of neuronal PCD. We have developed a novel assay for PCD in viable, adherent cells using annexin V labeling. Annexin V binds to the highly negatively charged plasma membrane phosphatidylserine residues that undergo membrane translocation during PCD. Current annexin V techniques are almost exclusively restricted to flow cytometric analysis. Our unique technique permits repeated examination of individual viable neurons without altering their survival. Correlation with electron microscopy and dye exclusion assays demonstrate both sensitivity and specificity for our method to detect PCD. To our knowledge, this is the first account of a technique that positively identifies PCD in viable, adherent cells.

Group I metabotropic receptors down-regulate nitric oxide induced caspase-3 activity in rat hippocampal neurons

Invoking the modulation of parallel cellular pathways, the G-protein metabotropic glutamate receptors (mGluRs) and nitric oxide (NO) have been shown to require a host of signal transduction pathways to modulate neuronal programmed cell death (PCD). Since the cysteine protease caspase-3 (CPP32) is one of the principal mediators of PCD in several nonneuronal cell systems, we investigated whether CPP32 activity was linked to both NO induced PCD and mGluR neuroprotection. We demonstrate that NO directly increases the activity of CPP32 by approximately 400% over a 6 h period that is necessary, at least in part, for the generation of neuronal PCD. Activation of only Group I mGluRs completely ameliorates the induction of CPP32 activity by NO and prevents the induction of PCD.

Nitric oxide-enhanced excitotoxicity-independent apoptosis of glucose-deprived neurons

Glucose deprivation has been shown to elicit neuronal death via extracellular glutamate accumulation. Here we report that immunostimulated glial expression of inducible nitric oxide synthase enhances the apoptotic death of glucose-deprived cerebellar granule cells (CGC) via the excitotoxicity-independent pathway. CGC cultures were immunostimulated by interferon-gamma (100 U/ml) and lipopolysaccharides (1 microg/ml) and 2 days later were challenged by glucose deprivation. Neither a 2-h Glucose deprivation nor a 2-day immunostimulation altered the viability of CGC. A 2-day immunostimulation, however, markedly enhanced the apoptotic death of CGC glucose-deprived for 1 h. The increased apoptotic death of glucose-deprived CGC after immunostimulation was mimicked by the nitric oxide (NO) releasing reagent 3-morpholinosydnonimine (200 microM, 30 min) and was partially prevented by the NO synthase (NOS) inhibitor N(G)-nitroarginine. The enhanced apoptotic death was not blocked by the N-methyl-D-aspartate (NMDA) receptor antagonists D-2-amino-5-phosphovalerate (APV) and dizocilpine (MK-801) or the non-NMDA receptor antagonist 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX). Moreover, the NO-induced enhanced apoptotic death occurred without a significant increase of the concentration of glutamate in the bathing medium. Our data indicate that immunostimulated glial cells potentiate the apoptotic death of glucose-deprived CGC in part through the expression of inducible NOS but not through NMDA receptor activation. Potentiation of glucose-deprived CGC death by immunostimulated glial cells may be clinically implicated in the tendency of recurrent ischemic insults to be more severe and fatal than an initial ischemic insult.

Nitric oxide synthase expression and apoptotic cell death in brains of AIDS and AIDS dementia patients

OBJECTIVES

To determine the occurrence and cellular localization of inducible nitric oxide synthase (iNOS), NOS activity and its association with cell death in brains of AIDS and AIDS dementia complex (ADC) patients.

DESIGN AND METHODS

Post-mortem cerebral cortex tissue of eight AIDS patients, eight ADC patients and eight control subjects was processed for iNOS immunocytochemistry, NADPH-diaphorase activity staining as an index of NOS activity, and in situ end-labelling to detect cell death.

RESULTS

iNOS-positive cells were present in the white matter of 14 out of 16 AIDS and ADC patients, whereas two out of eight control subjects showed iNOS-positive cells. iNOS immunoreactivity was exclusively localized in activated macrophages and microglial cells that both showed NADPH-diaphorase activity. In addition, NADPH-diaphorase activity, not related to iNOS immunoreactivity, was observed in astrocytes in both white and grey matter of AIDS and ADC patients. All AIDS and ADC patients, and only one control subject showed characteristic features of apoptotic cell death.

CONCLUSIONS

Different forms of NOS are present in microglial cells and astrocytes of AIDS and ADC patients but are largely absent in control subjects. Although more NOS-expressing cells occur in ADC than in AIDS patients, apoptotic cell death was found in both patient groups to the same extent. We postulate that NO production in brains of AIDS patients results in cumulative cortical cell loss, which becomes neurologically evident at later stages of disease and is expressed as ADC.

Nitric oxide induction of neuronal endonuclease activity in programmed cell death

Neuronal survival is intricately linked to the maintenance of intact DNA. In contrast, neuronal degeneration following nitric oxide (NO) exposure is dependent, in part, on the degradation of DNA through programmed cell death (PCD). We therefore investigated in primary rat hippocampal neurons the role of endogenous deoxyribonucleases, enzymes responsible for metabolically derived DNA cleavage, during NO-induced neurodegeneration. Twenty-four hours following exposure to the NO generators sodium nitroprusside (300 microM) and SIN-1 (300 microM), neuronal survival was reduced from approximately 88 to 23%. Treatment with aurintricarboxylic acid (1-100 microM), an endonuclease inhibitor, during NO exposure increased neuronal survival from 23 to 80% and decreased DNA fragmentation from 70 to 30% over a 24-h period. Enhancement of endonuclease activity alone with zinc chelation actively decreased neuronal survival from approximately 80% to approximately 34%. DNA digestion assays identified not only two constitutively active endonucleases, an acidic endonuclease (pH 4.0-7.0) and a calcium/magnesium-dependent endonuclease (pH 7.2-8.0), but also a NO-inducible magnesium-dependent endonuclease (pH 8.0). In the absence of endonuclease activity, DNA degradation did not occur during NO application, suggesting that endonuclease activity was a requisite pathway for NO-induced PCD. In addition, NO independently altered intracellular pH in ranges that were physiologically relevant for the activity of the endonucleases responsible for DNA degradation. Our identification and characterization of specific neuronal endonucleases suggest that the constitutive endonucleases may play a role in the initial stages of NO-induced PCD, but the subsequent "downstream" degradation of DNA may ultimately be dependent upon the NO-inducible endonuclease.

Metabotropic glutamate receptors prevent programmed cell death through the modulation of neuronal endonuclease activity and intracellular pH

Metabotropic glutamate receptor (mGluR) activation prevents neurodegeneration against nitric oxide (NO)-induced programmed cell death (PCD). We therefore investigated whether specific neuronal endogenous deoxyribonucleases, enzymes recently identified to be responsible for the maintenance of DNA integrity, mediated mGluR protection against NO. In rat primary hippocampal neurons, injury was assessed by using a 0.4% trypan blue dye exclusion method and TUNEL assay 24 h following treatment with the NO generators sodium nitroprusside (300 microM) or SIN-1 (300 microM). DNA digestion studies using neuronal cell extracts were employed to assess specific endonuclease activity. Individual application of aurintricarboxylic acid (ATA) (10 microM), an endonuclease inhibitor, or the mGluR agonists 1S,3R-ACPD (750 microM), DHPG (750 microM), L-CCG-I (750 microM), or L-AP4 (750 microM) prior to NO exposure significantly increased neuronal survival. Yet, combination therapy with ATA (10 microM) and the mGluR agonists did not synergistically improve neuronal survival, suggesting a common pathway of protection for ATA and the mGluRs that is dependent upon the modulation of neuronal endonuclease activity. In further support of this premise, protection by the mGluR agonists 1S,3R-ACPD, DHPG, L-CCG-I, and L-AP4 was significantly decreased during enhancement of endonuclease activity with the zinc chelator, N,N,N',N',-tetrakis (2-pyridylmethyl) ethylenediamine. Antagonism of the mGluR system was ineffective against endonuclease induced DNA destruction. Further assessment with DNA digestion assays identified two distinct mechanisms to maintain DNA integrity, a Ca2+/Mg2+-dependent endonuclease inhibited by L-AP4 and a magnesium dependent endonuclease inhibited by 1S,3R-ACPD. These neuroprotective mechanisms during activation of the mGluR system were also intricately linked to the active reversal of the biphasic intracellular pH changes induced by NO. Further investigation into the molecular pathways modulated by mGluRs may identify specific mechanisms that can maintain DNA integrity during adverse cellular environments.

Expression of neuronal nitric oxide synthase during embryonic development of the rat cerebral cortex

The expression of neuronal nitric oxide synthase (nNOS) during the development of the rat cerebral cortex from embryonic day (E) 13 to postnatal day (P) 0 was analyzed by immunocytochemical procedures using a specific antibody against rat brain nNOS. Expression of nNOS was first seen on E14 in cells of Cajal-Retzius morphology located in the marginal zone. Neuronal NOS immunoreactivity persisted in this layer throughout the embryonic period and only began to decrease on E20, when neuronal migration is coming to an end. From E17 onwards, migrating neurons expressing nNOS were observed in the intermediate zone with their leading processes directed towards the cortical plate. At the same time, efferent nNOS-immunoreactive axons originating from cortical plate cells entered the intermediate zone. From E19 onwards, cells expressing nNOS and with the morphological characteristics of migrating cells were observed in and near the subventricular zone. Confocal analysis of double immunostaining for nNOS and glial fibrillary acidic protein or nestin showed no coexpression of nNOS and glial markers in these cells, suggesting that nNOS-positive cells leaving the subventricular zone were not glial cells. Commissural, callosal and fimbrial fibers were seen to express nNOS on E18 and E19. This expression decreased from E20 and was very weak on E21 and P0. The observations suggest that nitric oxide is synthesized during embryonic life in relation to maturational processes such as the organization of cerebral lamination, and is involved in controlling migrational processes and fiber ingrowth.

Potentiation of N-methyl-D-aspartate-mediated neurotoxicity by immunostimulated murine microglia

Microglia have been shown to be immunostimulated by inflammatory cytokines and produce a number of toxic mediators. Here we report that immunostimulated microglia can synergistically enhance the N-methyl-D-aspartate (NMDA) receptor-mediated excitotoxicity in rat cerebellar granule cells (CGC) in culture. Neurotoxicity was assessed by morphological examination and by measuring the release of lactate dehydrogenase and DNA fragmentation. Cultured microglia were immunostimulated by interferon-gamma (200 U/ml) and lipopolysaccharides (10 microg/ml) and one or two days later they were used for co-culture with CGC. Co-culture of CGC with immunostimulated microglia resulted in a remarkable enhancement of the NMDA receptor-mediated death of CGC. This enhanced neurotoxicity was mimicked by the nitric oxide releaser 3-morpholinosydnonimine (SIN-1) or S-nitroso-N-acetylpenicillamine (SNAP). Superoxide dismutase and catalase, which stabilise NO by removing superoxide anion, ameliorated the potentiation of the NMDA-mediated death of CGC in co-culture with immunostimulated microglia, implying that reactions of NO with superoxide to form peroxynitrite can be implicated in the potentiated neurotoxicity. Our data indicate that immunostimulated microglia, which may involve in various neuropathologies, potentiate the NMDA receptor-mediated excitotoxicity in part through the expression of inducible nitric oxide synthase.