Bax and caspases are inhibited by endogenous nitric oxide in dorsal root ganglion neurons in vitro

Identifying the Long-Term Role of Inducible Nitric Oxide Synthase after Contusive Spinal Cord Injury Using a Transgenic Mouse Model

Inducible nitric oxide synthase (iNOS) is a potent mediator of oxidative stress during neuroinflammation triggered by neurotrauma or neurodegeneration. We previously demonstrated that acute iNOS inhibition attenuated iNOS levels and promoted neuroprotection and functional recovery after spinal cord injury (SCI). The present study investigated the effects of chronic iNOS ablation after SCI using inos-null mice. iNOS^-/- knockout and wild-type (WT) control mice underwent a moderate thoracic (T8) contusive SCI. Locomotor function was assessed weekly, using the Basso Mouse Scale (BMS), and at the endpoint (six weeks), by footprint analysis. At the endpoint, the volume of preserved white and gray matter, as well as the number of dorsal column axons and perilesional blood vessels rostral to the injury, were quantified. At weeks two and three after SCI, iNOS^-/- mice exhibited a significant locomotor improvement compared to WT controls, although a sustained improvement was not observed during later weeks. At the endpoint, iNOS^-/- mice showed significantly less preserved white and gray matter, as well as fewer dorsal column axons and perilesional blood vessels, compared to WT controls. While short-term antagonism of iNOS provides histological and functional benefits, its long-term ablation after SCI may be deleterious, blocking protective or reparative processes important for angiogenesis and tissue preservation.

Paroxetine ameliorates changes in hippocampal energy metabolism in chronic mild stress-exposed rats

The molecular mechanisms underlying stress-induced depression have not been fully outlined. Hence, the current study aimed at testing the link between behavioral changes in chronic mild stress (CMS) model and changes in hippocampal energy metabolism and the role of paroxetine (PAROX) in ameliorating these changes. Male Wistar rats were divided into three groups: vehicle control, CMS-exposed rats, and CMS-exposed rats receiving PAROX (10 mg/kg/day intraperitoneally). Sucrose preference, open-field, and forced swimming tests were carried out. Corticosterone (CORT) was measured in serum, while adenosine triphosphate and its metabolites, cytosolic cytochrome-c (Cyt-c), caspase-3 (Casp-3), as well as nitric oxide metabolites (NOx) were measured in hippocampal tissue homogenates. CMS-exposed rats showed a decrease in sucrose preference as well as body weight compared to control, which was reversed by PAROX. The latter further ameliorated the CMS-induced elevation of CORT in serum (91.71±1.77 ng/mL vs 124.5±4.44 ng/mL, P<0.001) as well as the changes in adenos-ine triphosphate/adenosine diphosphate (3.76±0.02 nmol/mg protein vs 1.07±0.01 nmol/mg protein, P<0.001). Furthermore, PAROX reduced the expression of Cyt-c and Casp-3, as well as restoring NOx levels. This study highlights the role of PAROX in reversing depressive behavior associated with stress-induced apoptosis and changes in hippocampal energy metabolism in the CMS model of depression.

Nitric oxide in neurodegeneration: potential benefits of non-steroidal anti-inflammatories

The cellular messenger nitric oxide (NO) has been linked to neurodegenerative disorders due to the increased expression of the enzymes that catalyze its synthesis in postmortem tissues derived from sufferers of these diseases. Nitrated proteins have also been detected in these samples, revealing that NO is biologically active in regions damaged during neurodegeneration. Modulation of NO levels has been reported not only in the neurons of the central nervous system, but also in the glial cells (microglia and astroglia) activated during the neuroinflammatory response. Neuroinflammation has been found in some neurodegenerative conditions, and inhibition of these neuroinflammatory signals has been shown to delay the progress of such disorders. Thus NO and the pathways triggering its release are emerging as an important research focus in the search for strategies to prevent, halt or cure neurodegenerative diseases.

Nitric oxide averts hypoxia-induced damage during reoxygenation in rat heart

Nitric oxide (NO), synthesized by the hemoproteins NO synthases (NOS), is known to play important roles in physiological and pathological conditions in the heart, including hypoxia/reoxygenation (H/R). This work investigates the role that endogenous NO plays in the cardiac H/R-induced injury. A follow-up study was conducted in Wistar rats subjected to 30 min of hypoxia, with or without prior treatment using the nonselective NOS inhibitor L-NAME (1.5 mM). The rats were studied at 0 h, 12 h, and 5 days of reoxygenation, analysing parameters of cell, and tissue damage (lipid peroxidation, apoptosis, and protein nitration), as well as in situ NOS activity and NO production (NOx). The results showed that after L-NAME administration, in situ NOS activity was almost completely eliminated in all the experimental groups, and consequently, NOx levels fell. Contrarily, the lipid peroxidation level and the percentage of apoptotic cells rose throughout the reoxygenation period. These results reveal that NOS inhibition exacerbates the peroxidative and apoptotic damage observed before the treatment with L-NAME in the hypoxic heart, pointing to a cardioprotective role of NOS-derived NO against H/R-induced injury. These findings could open the possibility of future studies to design new therapies for H/R-dysfunctions based on NO-pharmacology.

[Effects of Chinese herbal medicine Yiqi Huayu Recipe on apoptosis of dorsal root ganglion neurons and expression of caspase-3 in rats with lumbar nerve root compression]

OBJECTIVE

To observe the effects of Yiqi Huayu Recipe, a Chinese compound herbal medicine, on apoptosis of dorsal root ganglion (DRG) neurons and expression of caspase-3 in rats after lumbar nerve root compression injury.

METHODS

A total of 40 male Sprague-Dawley rats were randomly allocated into 4 groups: control group, untreated group, Methylcobal group and Yiqi Huayu Recipe group. Surgery was performed on rats of untreated group, Methylcobal group and Yiqi Huayu Recipe group to place a micro-silica gel on right L₄ DRG, while control group received skin and paravertebral muscle incision only. Rats in Methylcobal group and Yiqi Huayu Recipe group were given Methylcobal by intramuscular injection and Yiqi Huayu Recipe intragastrically respectively. Rats in control group and untreated group received saline intragastrically as equal amount as Yiqi Huayu Recipe group. The compressed nerve roots were harvested at the 10th day after treatment. Apoptosis of DRG neurons was detected by terminal deoxynucleotidyl transferase-mediated nick-end labeling. Caspase-3 activity and mRNA expression in compressed nerve roots were detected with spectrophotography and real-time polymerase chain reaction respectively.

RESULTS

Apoptosis of DRG neurons was significantly increased in the rat model. The apoptosis index of untreated group was higher than that of control group (P<0.01). Yiqi Huayu Recipe and Methylcobal could reduce the apoptosis of DRG neurons, and both groups showed a lower apoptosis index than untreated group (P<0.01). Caspase-3 activity and its gene expression were significantly increased in untreated group. The levels of caspase-3 activity and its gene expression in untreated group were higher than those in control group (P<0.05 or P<0.01). Yiqi Huayu Recipe and Methylcobal could reduce the overexpression of caspase-3 mRNA, and statistically significant differences were found between the untreated group and Yiqi Huayu Recipe group or Methylcobal group (P<0.01).

CONCLUSION

Lumbar nerve root compression results in overexpression of caspase-3 in nerve root tissue and increase of DRG neuron apoptosis. Yiqi Huayu Recipe can inhibit the overexpression of caspase-3 and alleviate the apoptosis of DRG neurons after nerve injury.

Spinal motoneuron synaptic plasticity after axotomy in the absence of inducible nitric oxide synthase

Background

Astrocytes play a major role in preserving and restoring structural and physiological integrity following injury to the nervous system. After peripheral axotomy, reactive gliosis propagates within adjacent spinal segments, influenced by the local synthesis of nitric oxide (NO). The present work investigated the importance of inducible nitric oxide synthase (iNOS) activity in acute and late glial responses after injury and in major histocompatibility complex class I (MHC I) expression and synaptic plasticity of inputs to lesioned alpha motoneurons.

Methods

In vivo analyses were carried out using C57BL/6J-iNOS knockout (iNOS^-/-) and C57BL/6J mice. Glial response after axotomy, glial MHC I expression, and the effects of axotomy on synaptic contacts were measured using immunohistochemistry and transmission electron microscopy. For this purpose, 2-month-old animals were sacrificed and fixed one or two weeks after unilateral sciatic nerve transection, and spinal cord sections were incubated with antibodies against classical MHC I, GFAP (glial fibrillary acidic protein - an astroglial marker), Iba-1 (an ionized calcium binding adaptor protein and a microglial marker) or synaptophysin (a presynaptic terminal marker). Western blotting analysis of MHC I and nNOS expression one week after lesion were also performed. The data were analyzed using a two-tailed Student's t test for parametric data or a two-tailed Mann-Whitney U test for nonparametric data.

Results

A statistical difference was shown with respect to astrogliosis between strains at the different time points studied. Also, MHC I expression by iNOS^-/- microglial cells did not increase at one or two weeks after unilateral axotomy. There was a difference in synaptophysin expression reflecting synaptic elimination, in which iNOS^-/- mice displayed a decreased number of the inputs to alpha motoneurons, in comparison to that of C57BL/6J.

Conclusion

The findings herein indicate that iNOS isoform activity influences MHC I expression by microglial cells one and two weeks after axotomy. This finding was associated with differences in astrogliosis, number of presynaptic terminals and synaptic covering of alpha motoneurons after lesioning in the mutant mice.

Oxidative stress, nitric oxide, endothelial dysfunction and tinnitus

To assess whether pathogenic endothelial dysfunction is involved in acute idiopathic tinnitus we enrolled 44 patients and 25 healthy volunteers. In blood from the internal jugular vein and brachial vein we determined malonaldehyde, 4-hydroxynonenal, myeloperoxidase, glutathione peroxidase, nitric oxide, L-arginine and L-ornitine, thrombomodulin (TM) and von Willebrand factor (vWF) activity during tinnitus and asymptomatic period. Higher plasma concentrations of oxidative markers and L-arginine, and lower nitric oxide and L-ornitine levels were observed in jugular blood of patients with tinnitus, there being a significant difference between brachial and jugular veins. TM and vWF activity were significantly higher in patients' jugular blood than in brachial blood. Our results suggest oxidant, TM, vWF activity production are increased and nitric oxide production reduced in brain circulation reflux blood of patients with acute tinnitus. These conditions are able to cause a general cerebro-vascular endothelial dysfunction, which in turn induce a dysfunction of microcirculation in the inner ear.

Changes in mRNA for CAPON and Dexras1 in adult rat following sciatic nerve transection

Peripheral nerve transection has been implicated to cause a production of neuronal nitric oxide synthase (nNOS), which may influence a range of post-axotomy processes necessary for neuronal survival and nerve regeneration. Carboxy-terminal post synaptic density protein/Drosophila disc large tumor suppressor/zonula occuldens-1 protein (PDZ) ligand of neuronal nitric oxide synthase (CAPON), as an adaptor, interacts with nNOS via the PDZ domain helping regulate nNOS activity at postsynaptic sites in neurons. And Dexras1, a small G protein mediating multiple signal transductions, has been reported to form a complex with CAPON and nNOS. A role for the physiologic linkage by CAPON of nNOS to Dexras1 has suggested that NO-mediated activation of Dexras1 is markedly enhanced by CAPON. We investigated the changes in mRNA for CAPON, Dexras1 and nNOS in the sciatic nerve, dorsal root ganglia and lumbar spinal cord of adult rat following sciatic axotomy by TaqMan quantitative real-time PCR and in situ hybridization combined with immunofluorescence. Signals of mRNA for CAPON and Dexras1 were initially expressed in these neural tissues mentioned, transiently increased at certain time periods after sciatic axotomy and finally recovered to the basal level. It was also found that nNOS mRNA underwent a similar change pattern during this process. These results suggest that CAPON as well as Dexras1 may be involved in the different pathological conditions including nerve regeneration, neuron loss or survival and even pain process, possibly via regulating the nNOS activity or through the downstream targets of Dexras1.

Effect of peripheral axotomy on gene expression of NIDD in rat neural tissues

Peripheral nerve lesion-induced production of neuronal nitric oxide synthase (nNOS) was implicated to influence a range of postaxotomy processes necessary for neuronal survival and nerve regeneration (Zochodne et al., Neuroscience, 91:1515-1527, 1999; Keilhoff et al., Journal of Chemical Neuroanatomy, 24:181-187, 2002, Nitric Oxide, 10:101-111, 2004). Protein-protein interactions represent an important mechanism in the control of NOS spatial distribution or activity (Alderton et al., Biochemical Journal, 357:593-615, 2001; Dedio et al., FASEB Journal, 15:79-89, 2001; Zimmermann et al., Proceedings of the National Academy of Sciences, 99:17167-17172, 2002). As one of the nNOS-binding proteins, nNOS-interacting DHHC domain-containing protein with dendritic mRNA (NIDD) has recently been identified to increase nNOS enzyme activity by targeting nNOS to the synaptic plasma membrane in a postsynaptic density protein 95/discs-large/zona occlusens-1 domain dependent manner (Saitoh et al., Journal of Biological Chemistry, 279:29461-29468, 2004). In this paper, we established a rat model with peripheral axotomy to investigate the gene expression patterns of NIDD in neural tissues using TaqMan quantitative real-time polymerase chain reaction and in situ hybridization combined with immunofluorescence. It revealed that NIDD mRNA was upregulated after sciatic nerve transection with the similar expressing styles as that of the nNOS in the injured nerves, corresponding dorsal root ganglia, and lumbar spinal cord. These findings imply that NIDD may be involved in the different pathological conditions including nerve regeneration, neuron loss or survival, and even pain process, possibly via regulating the enzyme nNOS activity.

Nitric oxide-NGF mediated PPTA/SP, ADNP, and VIP expression in the peripheral nervous system

Nerve growth factor (NGF)-deprivation or axotomy of dorsal root ganglion (DRG) neurons causes stress, which they cope by triggering various mechanisms. Among several molecular changes, in the present study, we demonstrate preprotachykinin-A-substance P (PPTA-SP) and activity-dependent neuroprotective protein-vasoactive intestinal peptide (ADNP-VIP) expression pattern using DRG neurons-Schwann cells coculture and axotomy model. In the presence of NGF, DRG cultures showed high levels of PPTA and ADNP mRNA expression, which were significantly suppressed in the absence of NGF and/or nitric oxide synthase (NOS) inhibition by NG-nitro-L-arginine methyl ester (L-NAME), suggesting that both NGF and nitric oxide (NO) can regulate PPTA and ADNP expression. However, treating coculture with NO donor, diethylenetriamine nitric oxide (DETA-NO) did not increase PPTA and ADNP expression in the presence or absence of NGF, although there was a marginal increase in ADNP expression in the absence of NGF. NGF-deprivation increases endogenous NO; thus, DETA-NO had no further effect on PPTA and ADNP expression. Alternatively, NGF produced from NO-stimulated Schwann cells influence gene expression. In addition, interestingly, DETA-NO treatment of Schwann cells alone suppresses both PPTA and ADNP, suggesting differential response of DRG neurons-Schwann cells coculture to DETA-NO. SP and ADNP immunostaining of axotomized DRGs revealed significant reduction in SP and ADNP compared to intact DRG, which was partially recovered in neuronal NOS blocker, 7-nitroindazole (7-NI)-treated DRGs, particularly intense ADNP staining in satellite glia. As ADNP is VIP-responsive gene, we further explored VIP expression in DRGs. Axotomy increased VIP in DRG neurons, but 7-NI treatment caused intense VIP staining in satellite glia. These observations suggest a complex interaction of NO-NGF with PPTA/SP and ADNP-VIP in neuron-glial communication when neurons are stressed.

Evidence of Postnatal Neurogenesis in Dorsal Root Ganglion: Role of Nitric Oxide and Neuronal Restrictive Silencer Transcription Factor

The various mechanisms underlying postnatal neurogenesis from discrete CNS regions have emerged recently. However, little is known about postnatal neurogenesis in dorsal root ganglion (DRG). BrdU incorporation and subsequent immunostaining for BrdU, neural stem cell marker, nestin and neuronal marker, PGP 9.5 have provided evidence for postnatal neurogenesis in DRG. We further demonstrate, in vivo and in vitro, that nitric oxide (NO) regulates neural stem cells (nestin+) proliferation and, possibly, differentiation into neurons. Surprisingly, nerve growth factor (NGF) had no effect on nestin+ cells proliferation. Axotomy or NGF-deprivation of DRG neurons-satellite glia co-culture increases NO production by neurons and treating with a NO synthase (NOS) inhibitor, N G-nitro-L-arginine methylester (L-NAME) in vitro or 7-nitroindazole (7NI) in vivo, causes a significant increase in nestin+ cell numbers. However, a soluble guanylyl cyclase (sGC) blocker, 1H-[1, 2, 4] oxadiazolo [4, 3-a] quinoxalin-1-one (ODQ) treatment of NGF-deprived DRG neurons-satellite glia co-culture had no significant effect on nestin+ cell numbers. This implies NO regulates nestin+ cell proliferation independent of cGMP. We hypothesised that the neuronal-restrictive silencer transcription factor (NRSF, also termed REST), a master regulator of neuronal genes in non-neuronal cells, may be modulated by NO in satellite glia cultures. A NO donor, dimethyl-triamino-benzidine (DETA)-NO treatment of satellite glia cell cultures results in a significant increase in the NRSF/REST mRNA expression. The majority of cultured satellite glia cells express nestin, and also show increased levels of NOS, thus L-NAME treatment of these cultures causes a dramatic reduction in NRSF/REST mRNA. Overall these results suggest that NO inhibits neurogenesis in DRG and this is correlated with modulation of NRSF, a known modulator of differentiation.

NO-cGMP mediated galanin expression in NGF-deprived or axotomized sensory neurons

Leukaemia inhibitory factor (LIF) and nerve growth factor (NGF) are well characterized regulators of galanin expression. However, LIF knockout mice containing the rat galanin 5' proximal promoter fragment (- 2546 to + 15 bp) driving luciferase responded to axotomy in the same way as control mice. Also, LIF had no effect on reporter gene expression in vitro, neither in the presence or absence of NGF, suggesting that other factors mediate an axotomy response from the galanin promoter. We then addressed the role of nitric oxide (NO) using NGF-deprived rat dorsal root ganglion (DRG) neuron cultures infected with viral vectors containing the above-mentioned construct, and also studied endogenous galanin expression in axotomized DRG in vivo. Blocking endogenous NO in NGF-deprived DRG cultures suppressed galanin promoter activity. Consistent with this, axotomized/NGF-deprived DRG neurons expressed high levels of neuronal NO synthase (nNOS) and galanin. Further, using pharmacological NOS blockers, or adenoviral vectors expressing dominant-negative either for nNOS or soluble guanylate cyclase in vivo and in vitro, we show that the NO-cGMP pathway induces endogenous galanin in DRG neurons. We propose that both LIF and NO, acting at different promoter regions, are important for the up-regulation of galanin, and for DRG neuron survival and regeneration after axotomy.

Heat Shock Protein 60 or 70 Activates Nitric-oxide Synthase (NOS) I- and Inhibits NOS II-associated Signaling and Depresses the Mitochondrial Apoptotic Cascade during Brain Stem Death

The cellular and molecular basis of brain stem death remains an enigma. As the origin of a "life-and-death" signal that reflects the progression toward brain stem death, the rostral ventrolateral medulla (RVLM) is a suitable neural substrate for mechanistic delineation of this phenomenon. Here, we evaluated the hypothesis that heat shock proteins (HSPs) play a neuroprotective role in the RVLM during brain stem death and delineated the underlying mechanisms, using a clinically relevant animal model that employed the organophosphate pesticide mevinphos (Mev) as the experimental insult. In Sprague-Dawley rats, proteomic, Western blot, and real-time PCR analyses demonstrated that Mev induced de novo synthesis of HSP60 or HSP70 in the RVLM without affecting HSP90 level. Loss-of-function manipulations of HSP60 or HSP70 in the RVLM using anti-serum or antisense oligonucleotide potentiated Mev-elicited cardiovascular depression alongside reduced nitric-oxide synthase (NOS) I/protein kinase G signaling, enhanced NOS II/peroxynitrite cascade, intensified nucleosomal DNA fragmentation, elevated cytoplasmic histone-associated DNA fragments or activated caspase-3, and augmented the cytochrome c/caspase-3 cascade of apoptotic signaling in the RVLM. Co-immunoprecipitation experiments further revealed a progressive increase in the complex formed between HSP60 and mitochondrial or cytosolic Bax or mitochondrial Bcl-2 during Mev intoxication, alongside a dissociation of the cytosolic HSP60-Bcl-2 complex. We conclude that HSP60 and HSP70 confer neuroprotection against Mev intoxication by ameliorating cardiovascular depression via an anti-apoptotic action in the RVLM. The possible underlying intracellular processes include enhancing NOS I/protein kinase G signaling and inhibiting the NOS II/peroxynitrite cascade. In addition, HSP60 exerts its effects against apoptosis by blunting Mev-induced activation of the Bax/cytochrome c/caspase-3 cascade.

Stimulation of the cAMP pathway protects cultured cerebellar granule neurons against alcohol-induced cell death by activating the neuronal nitric oxide synthase (nNOS) gene

Neuronal loss is a key component of fetal alcohol syndrome pathophysiology. Therefore, identification of molecules and signaling pathways that ameliorate alcohol-induced neuronal death is important. We have previously reported that neuronal nitric oxide synthase (nNOS) can protect developing cerebellar granule neurons (CGN) against alcohol-induced death both in vitro and in vivo. However, the upstream signal controlling nNOS expression in CGN is unknown. Activated cAMP response element binding protein (CREB) has been strongly linked to the survival of multiple cell types, including CGN. Furthermore, the promoter of the nNOS gene contains two cAMP response elements (CRE). Using cultures of CGN, we tested the hypothesis that cAMP mediates nNOS activation and the protective effect of nNOS against alcohol-induced cell death. Forskolin, an activator of the cAMP pathway, stimulated expression of a reporter gene under the control of the nNOS promoter, and this stimulation was substantially reduced when the two CREs were mutated. Forskolin increased nNOS mRNA levels several fold, increased production of nitric oxide, and abolished alcohol's toxic effect in wild type CGN. Furthermore, forskolin's protective effect was substantially reduced in CGN cultures genetically deficient for nNOS (from nNOS-/- mice). Delivery of nNOS cDNA using a replication-deficient adenoviral vector into nNOS-/- CGN abolished alcohol-induced neuronal death. In addition, overexpression of nNOS in wild type CGN ameliorated alcohol-induced cell death. These results indicate that the neuroprotective effect of the cAMP pathway is mediated, in part, by the pathway's downstream target, the nNOS gene.

Nitric oxide synthase regulation and diversity: Implications in Parkinson’s disease

Nitric oxide (NO) is a janus faced chemical messenger, which, in the recent years, has been the focus of neurobiologists for its involvement in neurodegenerative disorders in particular, Parkinson's disease (PD). Nitric oxide synthase, the key enzyme involved in NO production exists in three known isoforms. The neuronal and inducible isoforms have been implicated in the pathogenesis of PD. These enzymes are subject to complex expressional and functional regulation involving mRNA diversity, phosphorylation and protein interaction. In the recent years, mRNA diversity and polymorphisms have been identified in the NOS isoforms. Some of these genetic variations have been associated with PD, indicating an etiological role for the NOS genes. This review mainly focuses on the NOS genes - their differential regulation and genetic heterogeneity, highlighting their significance in the pathobiology of PD.

Severe alcohol-induced neuronal deficits in the hippocampus and neocortex of neonatal mice genetically deficient for neuronal nitric oxide synthase (nNOS)

Alcohol can severely damage the developing brain, and neuronal loss is a critical component of this injury. Thus, identification of molecular factors that ameliorate alcohol-induced neuronal loss is of great importance. Previous in vitro work has demonstrated that nitric oxide (NO) protects neurons against alcohol toxicity. We tested the hypothesis that neonatal mice carrying a null mutation for neuronal nitric oxide synthase (nNOS), the enzyme that synthesizes NO in neurons, have an increased vulnerability to alcohol-induced neuronal loss in the neocortex and hippocampus. Wildtype mice and nNOS-/- mice received ethanol (0.0, 2.2, 3.3, or 4.4 g/kg) daily over postnatal days (P) 4-9 and were sacrificed on P10. The number of hippocampal CA1 and CA3 pyramidal cells, dentate gyrus granule cells, and neocortical neurons were determined using stereological methods. Alcohol pharmacokinetics did not differ between wildtype and nNOS-/- strains. Alcohol induced dose-dependent reductions in all four neuronal populations, and the losses were substantially more severe in the nNOS-/- mice than in wildtype. Furthermore, the threshold dose of alcohol to induce cell death was lower in the nNOS-/- mice than in the wildtype mice for all neuronal populations. While nNOS deficiency worsened alcohol-induced neuronal losses, the magnitude of this exacerbation varied among brain regions and depended on alcohol dose. These results demonstrate that nNOS deficiency decreases the ability of developing neurons in vivo to survive the toxic effects of alcohol and strengthen the hypothesis that NO exerts a neuroprotective effect against alcohol toxicity in the developing brain.

cAMP-responsive element binding protein mediates a cGMP/protein kinase G-dependent anti-apoptotic signal induced by nitric oxide in retinal neuro-glial progenitor cells

Nitric oxide (NO) is cytoprotective to certain types of neuronal cells. The neuroprotective ability of NO in the retina was reportedly mediated by the cyclic GMP (cGMP) to protein kinase G (PKG) pathway. Cyclic AMP-responsive element binding protein (CREB) plays an essential role in the NO/cGMP/PKG-mediated survival of rat cerebellar granule cells. We tested whether CREB transduces the NO/cGMP/PKG anti-apoptotic cascade in R28 neuro-glial progenitor cells. Apoptosis was induced in R28 cells by serum deprivation for 24 h. Varying concentrations of two NO donors, sodium nitroprusside (SNP) and nipradilol, were added to medium with or without an NO scavenger, a soluble guanylyl cyclase inhibitor, or a PKG inhibitor. The cells were immunostained against activated caspase-3 and counterstained with Hoechst 33258. Apoptosis was quantified by counting activated caspase-3 positive or pyknotic cells. SNP and nipradilol rescued R28 cells from apoptosis in a dose-dependent manner, at an optimal concentration of 1.0 microM and 10 microM, respectively. Higher concentrations were cytotoxic. The NO scavenger and the inhibitors decreased the anti-apoptotic effect of the NO donors. Intracellular cGMP levels were increased after exposure to SNP and nipradilol. Western blotting showed that both NO donors increased CREB phosphorylation, which was blocked when pre-exposed to the inhibitors. Transfection with a dominant negative CREB construct defective of phosphorylation at Ser-133 interfered with the anti-apoptotic activity of SNP. These results indicate that CREB at least in part mediates the cGMP/PKG-dependent anti-apoptotic signal induced by NO in R28 cells.

ATF3 expression in L4 dorsal root ganglion neurons after L5 spinal nerve transection

Activating transcription factor 3 (ATF3) is a widely used marker of damaged primary sensory neurons that is induced in essentially all dorsal root ganglion (DRG) neurons by spinal nerve axotomy. Whether such injuries induce its expression in neurons of adjacent DRGs remains unknown. Following L5 spinal nerve ligation, experimental but not sham-operated rats develop thermal and mechanical hypersensitivity. In the L4 DRG, 11-12% of neurons were ATF3 positive by 1 day post-surgery, and numbers remain unchanged at 2 weeks. Importantly, sham exposure of the L5 spinal nerve produced a nearly identical number of ATF3-positive neurons in the L4 DRG and also a substantial increase in the L5 DRG, with a similar time-course to experimental animals. There was no correlation between behaviour and magnitude of ATF3 expression. Co-localization studies with the DRG injury markers galanin, neuropeptide Y and nitric oxide synthase (NOS) showed that approximately 75, 50 and 25%, respectively, of L4 ATF3-positive neurons co-expressed these markers after L5 transection or sham surgery. Additionally, increases in galanin and NOS were seen in ATF3-negative neurons in L4. Our results strongly suggest that the surgical exposure of spinal nerves induces ATF3 in the L4-5 DRG, irrespective of whether the L5 nerve is subsequently cut. This probably reflects minor damage to the neurons or their axons but nevertheless is sufficient to induce phenotypic plasticity. Caution is therefore warranted when interpreting the phenotypic plasticity of DRG neurons in adjacent ganglia in the absence of positive evidence that they are not damaged.

Programmed cell death in the apical ganglion during larval metamorphosis of the marine mollusc Ilyanassa obsoleta

The apical ganglion (AG) of larval caenogastropods, such as Ilyanassa obsoleta, houses a sensory organ, contains five serotonergic neurons, innervates the muscular and ciliary components of the velum, and sends neurites into a neuropil that lies atop the cerebral commissure. During metamorphosis, the AG is lost. This loss had been postulated to occur through some form of programmed cell death (PCD), but it is possible for cells within the AG to be respecified or to migrate into adjacent ganglia. Evidence from histological sections is supported by results from a terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay, which indicate that cells of the AG degenerate by PCD. PCD occurs after metamorphic induction by serotonin or by inhibition of nitric oxide synthase (NOS) activity. Cellular degeneration and nuclear condensation and loss were observed within 12 h of metamorphic induction by NOS inhibition and occur before loss of the velar lobes, the ciliated tissue used for larval swimming and feeding. Velar disintegration happens more rapidly after metamorphic induction by serotonin than by 7-nitroindazole, a NOS inhibitor. Loss of the AG was complete by 72 h after induction. Spontaneous loss of the AG in older competent larvae may arise from a natural decrease in endogenous NOS activity, giving rise to the tendency of aging larvae to display spontaneous metamorphosis in culture.

Fundamental role of nitric oxide in neuritogenesis of PC12h cells

1 We investigated the neuritogenic action of nitric oxide (NO)-generating agents and their mechanisms of action in a subclone of rat pheochromocytoma, PC12h cells. 2 NO donors such as sodium nitroprusside (SNP, 0.05-1 microM), NOR1 (5-100 microM), NOR2 (5-20 microM), NOR3 (5-20 microM), NOR4 (5-100 microM), or S-nitroso-N-acetyl-DL-penicillamine (SNAP, 10-100 microM) significantly induced neurite outgrowth. 3 NOR4-induced neurite outgrowth was accompanied by expression of neurofilament 200 kDa subunit (NF200) protein, an axonal marker, and was significantly inhibited by an NO scavenger, a soluble GC inhibitor, and a PKG inhibitor: 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazole-1-oxyl-3-oxide (carboxy-PTIO, 20-100 microM), 1H-[1,2,4]oxadiazolo[4,3-a] quinoxalin-1-one (ODQ, 100 microM) and KT5823 (0.2-1 microM), respectively. 4 The intracellular cGMP concentration of cells was markedly increased by treatment with NOR4 (100 microM). 5 A mitogen-activated protein kinase (MAPK) kinase inhibitor, PD98059 (10-50 microM), abolished the NOR4-induced neurite outgrowth. In agreement with this observation, NOR4 did phosphorylate extracellular signal-regulated kinase (ERK) 1 and 2, substrates of MAPK kinase. 6 A membrane-permeable cGMP analog, 8-Br-cGMP (1 mM) also induced significant neurite outgrowth. The 8-Br-cGMP-induced neurite outgrowth was almost completely inhibited by both KT5823 (0.5 microM) and PD98059 (50 microM). Moreover, sustained ERK phosphorylation was observed in the 8-Br-cGMP-treated PC12h cells. 7 These results suggest that NO itself has the ability to induce neurite outgrowth and that NO-induced ERK activation involves the NO-cGMP-PKG signaling pathway in PC12h cells.

The physiology and pathophysiology of nitric oxide in the brain

Nitric oxide (NO) is a molecule with pleiotropic effects in different tissues. NO is synthesized by NO synthases (NOS), a family with four major types: endothelial, neuronal, inducible and mitochondrial. They can be found in almost all the tissues and they can even co-exist in the same tissue. NO is a well-known vasorelaxant agent, but it works as a neurotransmitter when produced by neurons and is also involved in defense functions when it is produced by immune and glial cells. NO is thermodynamically unstable and tends to react with other molecules, resulting in the oxidation, nitrosylation or nitration of proteins, with the concomitant effects on many cellular mechanisms. NO intracellular signaling involves the activation of guanylate cyclase but it also interacts with MAPKs, apoptosis-related proteins, and mitochondrial respiratory chain or anti-proliferative molecules. It also plays a role in post-translational modification of proteins and protein degradation by the proteasome. However, under pathophysiological conditions NO has damaging effects. In disorders involving oxidative stress, such as Alzheimer's disease, stroke and Parkinson's disease, NO increases cell damage through the formation of highly reactive peroxynitrite. The paradox of beneficial and damaging effects of NO will be discussed in this review.

Nerve Growth Factor-Independent Neuronal Survival: A Role for NO Donors: Fig. 1

Because of the limited therapeutic applications of nerve growth factor (NGF), there has been increasing focus on the development of pharmacological tools to bypass the requirement of NGF for the activation of the TrkA tyrosine kinase receptor neuronal survival pathway. In this issue of Molecular Pharmacology, the work by Culmsee et al. (p. 1006) shows that NGF-independent activation of TrkA by protein tyrosine phosphatase (PTP) inhibitors is only achieved when accompanied by release of nitric oxide (NO). This work identifies the integration of the NO/cGMP/protein kinase G (PKG) and NGF/TrkA pathways to induce activation of Akt and ERK1/2 and mediate neuronal survival in the absence of NGF. In addition, it underscores the potential therapeutic effects of ethyl-3,4-dephostatin (DPN), a stable analog of the naturally occurring PTP inhibitor dephostatin, which serves as a NO donor and protects neurons from apoptosis. This Perspective comparatively reviews two major signal transduction pathways that mediate NGF-independent neuronal survival by activating the TrkA pathway: the NO/cGMP/PKG and adenosine/G-protein-coupled receptor (GPCR) pathways.

Overexpression of manganese superoxide dismutase protects against ATP depletion-mediated cell death of proximal tubule cells

We have previously shown that in vivo renal ischemia/reperfusion results in ATP depletion, oxidant production, and manganese superoxide dismutase (MnSOD) inactivation. Current studies were designed to compare the effect of ATP depletion (Antimycin A treatment) on cell death pathways using renal proximal tubular cells and identical cells that overexpress MnSOD. ATP depletion in wild-type cells induced an apoptotic cascade that involved caspase 9 activation; MnSOD overexpressing cells afforded protection against apoptosis. This protection did not appear to involve a cytochrome c-related mechanism, but may be related to altered levels of nitric oxide within the cell. Further studies suggested that nitric oxide was required to protect the renal cells from caspase-mediated cell death. Interestingly, treatment of renal cell extracts with reductants (DTT and ascorbate) enhanced caspase activation. Taken together, these results suggest that cysteine nitrosylation may be playing a role in caspase dysfunction in cells overexpressing MnSOD following ATP depletion.

Satellite glial cells in sensory ganglia: from form to function

Current information indicates that glial cells participate in all the normal and pathological processes of the central nervous system. Although much less is known about satellite glial cells (SGCs) in sensory ganglia, it appears that these cells share many characteristics with their central counterparts. This review presents information that has been accumulated recently on the physiology and pharmacology of SGCs. It appears that SGCs carry receptors for numerous neuroactive agents (e.g., ATP, bradykinin) and can therefore receive signals from other cells and respond to changes in their environment. Activation of SGCs might in turn influence neighboring neurons. Thus SGCs are likely to participate in signal processing and transmission in sensory ganglia. Damage to the axons of sensory ganglia is known to contribute to neuropathic pain. Such damage also affects SGCs, and it can be proposed that these cells have a role in pathological changes in the ganglia.

Survival and phenotypic characteristics of axotomized neurons in spinal ganglia

Trauma to the peripheral processes of sensory neurons of different subpopulations was followed by indirect immunohistochemical analysis of the expression of Bcl-X(L) and Bax, which are, respectively, antiapoptotic and proapoptotic proteins of the Bcl-2 family, and also of the cytokine interleukin-1beta, with the aim of identifying the roles of these substances in controlling apoptosis. The survival abilities of these neurons after central and peripheral axotomy were compared by studying the expression of the high molecular weight component of the neurofilament triplet NF200 and isolectin B4 (IB4). By day 30 after central axotomy, there were no changes in the total numbers of neurons in ganglia L(IV)-L(V) in rats, though there were significant reductions in the numbers of NF200+ neurons. In spinal ganglion L(V) of mice, the proapoptotic protein was detected in the nuclei of 46% of small neurons, which account for 20% of all neurons in the ganglion. By day 30 after nerve compression, Bax was expressed in the nuclei of 30% of neurons and the cytoplasm of 20% of neurons. In intact animals, the antiapoptotic protein Bcl-X(L) was seen in the cytoplasm of 30% of small neurons, as well as in satellite cells surrounding large and intermediate neurons. By day 30 after nerve trauma, Bcl-X(L) was not expressed in spinal ganglion L(V). Interleukin-1beta was present in the cytoplasm of 17% of neurons belonging to the subpopulations of large and intermediate neurons. By day 30 after nerve compression, interleukin-1 beta+ neurons were not identified.

Cytoprotection by nipradilol, an anti-glaucomatous agent, via down-regulation of apoptosis related gene expression and activation of NF-κB

It has been reported that nipradilol, a nonselective beta- and selective alpha1-receptor antagonist, has cytoprotective effects. We attempted to clarify the effects of nipradilol on the expression of apoptosis associated genes and the activity of nuclear factor-kappaB, a transcription factor, in PC12 cells during serum deprivation induced apoptosis. PC12 cells were cultured in serum free RPMI1640 medium with or without 0.01, 0.1, 1, or 10 microM of nipradilol, or in serum-added medium as a control. The gene expressions of Bax, Bcl-2, Fas, FasL, Caspase-1, 2, 3, and 9, p53, and Smac/DIABLO were examined using a quantitative real time polymerase chain reaction method, while nuclear factor-kappaB activity was examined using an electrophoresis mobility shift assay with a nuclear factor-kappaB consensus sequenced DNA probe. The effects of denitronipradilol were also examined to clarify the effect of nitric oxide donative action. Nipradilol down-regulated Bax gene expression 12 hr after serum deprivation, and that of the capase-9 and Smac/DIABLO genes at 24 hr, compared to the serum-free sample, while it also increased cell viability and decreased DNA ladder formation at 48 hr. However, the expressions of other examined genes were not affected by the agent. In addition, nuclear factor-kappaB activity was increased 2 hr after the addition of 0.1 or 1 microM of nipradilol. In contrast, denitronipradilol did not show any effects toward PC12 cells. Our results suggest that nipradilol may have an effect on apoptosis associated gene expression and nuclear factor-kappaB activity during the prevention of apoptosis via nitric oxide donative action.

Glial-mediated neuroprotection: evidence for the protective role of the NO-cGMP pathway via neuron-glial communication in the peripheral nervous system

The NO-cGMP pathway has emerged as a neuroprotective signaling system involved in communication between neurons and glia. We have previously shown that axotomy or nerve growth factor (NGF)-deprivation of dorsal root ganglion (DRG) neurons leads to increased production of NO and at the same time an increase in cGMP production in their satellite glia cells. Blockade of NO or its receptor, the cGMP synthesizing enzyme soluble guanylate cyclase (sGC), results in apoptosis of neurons and glia. We now show that co-culture of neonatal DRG neurons with either Schwann cells pre-treated with an NO donor or a membrane-permeant cGMP analogue; or neurons maintained in the medium from Schwann cell cultures treated in the same way, prevents neuronal apoptosis. Both NO donor and cGMP treatment of Schwann cells results in synthesis of NGF and NT3. Furthermore, if the Schwann cells are previously infected with adenoviral vectors expressing a dominant negative sGC mutant transgene, treatment of these Schwann cells with an NO donor now fails to prevent neuronal apoptosis. Schwann cells treated in this way also fail to express neither cGMP nor neurotrophins. These findings suggest NO-sGC-cGMP-mediated NGF and NT3 synthesis by Schwann cells protect neurons.

The intimate relation between nitric oxide and superoxide in apoptosis and cell survival

Intra- and intercellular communication in or between cells allows adaptation to changes in the environment. Formation of reactive oxygen (ROS) and nitrogen (RNS) species in response to external insults gained considerable attention in provoking cell demise along an apoptotic subroute of cell death, thus attributing radical formation to pathologies. In close association, stabilization of the tumor suppressor p53 and activation of caspases convey proapoptotic signaling. Complexity was added with the notion that ROS and RNS signals overlap and/or produce synergistic as well as antagonistic effects. With respect to nitric oxide (NO) signaling, it became clear that the molecule is endowed with pro- or antiapoptotic signaling capabilities, depending to some extend on the concentration and cellular context, i.e., ROS generation. Here, some established concepts are summarized that allow an explanation of p53 accumulation under the impact of NO and an understanding of NO-evoked cell protection at the level of caspase inhibition, cyclic GMP formation, or expression of antiapoptotic proteins. In addition, the overlapping sphere of ROS and RNS signaling is recapitulated to appreciate cell physiology/pathology with the notion that marginal changes in the flux rates of either NO or superoxide may shift vital signals used for communication and cell survival into areas of pathology in close association with apoptosis/necrosis.

Imbalance of the mitochondrial pro- and anti-apoptotic mediators in neuroblastoma tumours with unfavourable biology

It has been proposed that a lack of apoptosis plays an important role in neuroblastoma (NB) progression. We therefore screened cDNA array filters, including 198 apoptotic genes, in order to identify mRNA transcripts that are differentially expressed in tumours with unfavourable versus favourable biology. Twenty-one genes were analysed further using real-time reverse-transcriptase-polymerase chain reaction (RT-PCR). Significantly lower levels of DNCL1 (PIN; P(c)(corrected) = 0.0054) and NTRK1 (TrkA; P(c) = 0.039) were found in NB tumours with unfavourable biology. In addition, BID, BCL2, APAF1, CASP2, CASP3 and CASP9 were found to be preferentially expressed in tumours with favourable biology, whereas CDKN1A (p21), IL2RA, and MCL1, were found to be preferentially expressed in NB tumours with unfavourable biology. In conclusion, mRNA levels of transcripts encoding pro-apoptotic mediators of the mitochondrial apoptotic pathway were found to be expressed to a lower extent in tumours with unfavourable biology. Our data also suggest that the mitochondrial pathway is suppressed in advanced stages of NB tumours, due to an imbalance between anti-apoptotic and pro-apoptotic mediators which is a finding that may have therapeutic significance.

Either nitric oxide or nerve growth factor is required for dorsal root ganglion neurons to survive during embryonic and neonatal development

During early embryonic (E12) development almost all dorsal root ganglion (DRG) neurons express the neuronal isoform of nitric oxide synthase (nNOS). At this stage, the axons of these neurons are rudimentary and have not made contact with peripheral tissue targets. As their axons establish contact with peripheral targets such as the skin, the number of neurons expressing nNOS decrease that correspond to increased immunoreactivity for nerve growth factor (NGF) in the skin, and its high affinity receptor, tyrosine kinase A (trkA) in both skin and DRG neurons. During late postnatal development, very few DRG neurons express nNOS; however, axotomy or NGF deprivation of cultured DRG neurons induce nNOS and NOS blockade causes neuronal death. In contrast, NGF-deprived embryonic and neonatal DRG neurons die by apoptosis, while NOS blockade has no effect. Overall, these observations suggest that NGF and nitric oxide (NO) interact during embryonic and postnatal development to facilitate neuronal selection and survival. The roles of NO, NGF and its receptor trkA in DRG neurons during different stages of development are discussed.

Role of nitric oxide in the regulation of neuronal proliferation, survival and differentiation

Nitric oxide (NO), an important cellular messenger, has been linked to both neurodegenerative and neuroprotective actions. In the present review, we focus on recent data establishing a survival and differentiation role for NO in several neural in vitro and in vivo models. Nitric oxide has been found to be essential for survival of neuronal cell lines and primary neurons in culture under various death challenges. Furthermore, its lack may aggravate some neuropathological conditions in experimental animals. Several cellular pathways and signaling systems subserving this neuroprotective role of NO are considered in the review. Survey of recent data related to the developmental role of NO mainly focus on its action as a negative regulator of neuronal precursor cells proliferation and on its role of promotion of neuronal differentiation. Discussion on discrepancies arising from the literature is focused on the Janus-faced properties of the molecule and it is proposed that most controversial results are related to the intrinsic property of NO to compensate among functionally opposed effects. As an example, the increased proliferation of neural cell precursors under conditions of NO shortage may be, later on in the development, compensated by increased elimination through programmed cell death as a consequence of the lack of the survival-promoting action of the molecule. To elucidate these complex, and possibly contrasting, effects of NO is indicated as an important task for future researches.

Helicobacter pylori infection activates NF-kappaB signaling pathway to induce iNOS and protect human gastric epithelial cells from apoptosis

Helicobacter pylori infection induces apoptosis and inducible nitric oxide synthase (iNOS) expression in gastric epithelial cells. In this study, we investigated the effects of NF-kappaB activation and iNOS expression on apoptosis in H. pylori-infected gastric epithelial cells. The suppression of NF-kappaB significantly increased caspase-3 activity and apoptosis in H. pylori-infected MKN-45 and Hs746T gastric epithelial cell lines as well as primary gastric epithelial cells. An NF-kappaB signaling pathway via NF-kappaB-inducing kinase and IkappaB kinase-beta activation was found to be involved in the inhibition of apoptosis in H. pylori-infected gastric epithelial cells. In gastric epithelial cells transfected with retrovirus containing IkappaBalpha superrepressor, iNOS mRNA and protein levels were reduced, indicating that H. pylori infection induced the expression of iNOS by activating NF-kappaB. Moreover, a NO donor, S-nitroso-N-acetylpenicillamine (100 microM), decreased caspase-3 activity and apoptosis in NF-kappaB-suppressed cells infected with H. pylori. These results suggest that NF-kappaB activation may play a role in protecting gastric epithelial cells from H. pylori-induced apoptosis by upregulating endogenous iNOS.

Neuronal Nitric Oxide Synthase Modulation of Dorsal Horn Neuronal Responses in the Rat: A Developmental Study

Nitric oxide (NO) is a diffusible chemical messenger functionally linked to N-methyl-D-aspartate (NMDA) receptor activity and has been shown to be involved in modulating numerous pathways in the central nervous system. In order to investigate the role of the neuronal NO synthase type I (nNOS)/NO system in the postnatal development of dorsal horn nociceptive pathways in rats, the specific nNOS inhibitor 7-nitroindazole sodium salt (7-NI) and the non-specific NOS inhibitor nitro-L-arginine methyl ester (L-NAME) were applied spinally at postnatal days (P) 14, 21, 28 and >56 (adult) and their effects on neuronal responses were compared. In response to a train of 16 noxious electrical stimuli, the wide dynamic range neurones in the deep dorsal horn showed a dose-dependent inhibition of C-fibre-evoked response, post-discharge and windup to both 7-NI and L-NAME. No difference between any age group was observed with either agent on these responses. However, the effect of both 7-NI and L-NAME on the primary evoked response, a measure of the events occurring pre-synaptic and intrinsic to the neurone recorded, was significantly different between the P14 and older age groups. nNOS is known to be expressed later in postnatal development than the NMDA receptor and from the results presented here, it is fully mature and functional from P14 onwards. The subtle differences in attenuation of the primary evoked response at P14 compared with older ages may reflect the immaturity of the dorsal horn and in particular the incomplete development of intrinsic and descending inhibitory controls.

Inflammatory neurodegeneration mediated by nitric oxide, glutamate, and mitochondria

In inflammatory, infectious, ischemic, and neurodegenerative pathologies of the central nervous system (CNS) glia become "activated" by inflammatory mediators, and express new proteins such as the inducible isoform of nitric oxide synthase (iNOS). Although these activated glia have benefi- cial roles, in vitro they potently kill cocultured neurons, and there is increasing evidence that they contribute to pathology in vivo. Nitric oxide (NO) from iNOS appears to be a key mediator of such glial-induced neuronal death. The high sensitivity of neurons to NO is partly due to NO causing inhibition of respiration, rapid glutamate release from both astrocytes and neurons, and subsequent excitotoxic death of the neurons. NO is a potent inhibitor of mitochondrial respiration, due to reversible binding of NO to cytochrome oxidase in competition with oxygen, resulting in inhibition of energy production and sensitization to hypoxia. Activated astrocytes or microglia cause a potent inhibition of respiration in cocultured neurons due to glial NO inhibiting cytochrome oxidase within the neurons, resulting in ATP depletion and glutamate release. In some conditions, glutamate- induced neuronal death can itself be mediated by N-methyl-D-aspartate (NMDA)-receptor activation of the neuronal isoform of NO synthase (nNOS) causing mitochondrial damage. In addition NO can be converted to a number of reactive derivatives such as peroxynitrite, NO2, N2O3, and S-nitrosothiols that can kill cells in part by inhibiting mitochondrial respiration or activation of mitochondrial permeability transition, triggering neuronal apoptosis or necrosis.

Deficiency of neuronal nitric oxide synthase (nNOS) worsens alcohol-induced microencephaly and neuronal loss in developing mice

Previous work conducted in vitro suggests that nitric oxide (NO) protects developing neurons against the toxic effects of alcohol. We tested the hypothesis that neonatal mice carrying a null mutation for neuronal nitric oxide synthase (nNOS), the enzyme which synthesizes NO in neurons, have increased vulnerability to alcohol-induced microencephaly and neuronal loss. Wild-type mice and mutant (nNOS(-/-)) mice received a single intraperitoneal injection of ethanol (0.0, 2.2, 3.3, or 4.4 g/kg) daily over postnatal days (PD) 4-9 and were sacrificed on PD 10. Peak blood alcohol concentrations were approximately 170, 280, and 385 mg/dl for the 2.2, 3.3 and 4.4 g/kg/day treatment groups, respectively, and did not differ significantly between wild-type and nNOS(-/-) strains. Exposure to alcohol induced dose-dependent reductions in total brain weight, forebrain weight and cerebellum weight in both strains of mice. However, the reductions in brain weight were significantly more severe in the nNOS(-/-) mice than in wild type. Quantification of cerebellar neurons revealed that alcohol-induced losses of Purkinje cells and granule cells were both significantly greater in the nNOS(-/-) mice than in wild type. The increased vulnerability of nNOS-deficient neurons to alcohol-induced cell death was confirmed in vitro. Cerebellar granule cell cultures derived from nNOS(-/-) and wild-type mice were exposed for 24 h to 0, 100, 200 or 400 mg/dl ethanol. At each alcohol concentration, the nNOS(-/-) neurons had a significantly greater cell loss than did the wild-type neurons. The results demonstrate that deficiency of nNOS decreases the ability of developing neurons to survive the toxic effects of alcohol. Because NO upregulates intracellular cGMP, which can activate cGMP-dependent protein kinase (PKG), we hypothesize that the NO-cGMP-PKG pathway has a neuroprotective role against alcohol toxicity within the developing brain.

Neuronal nitric oxide synthase is the dominant nitric oxide supplier for the survival of dorsal root ganglia after peripheral nerve axotomy

This study was designed to determine whether nitric oxide supply may be a major factor in the survival of dorsal root ganglia in a sciatic nerve injury model. Wild-type (WT) mice were compared with knockout (KO) mice lacking neuronal nitric oxide synthase (nNOS) or endothelial (eNOS). The NO-generating capacities were analysed by NOS immunohistochemistry and NADPH-diaphorase staining 1, 2, 6, and 12 weeks after nerve transection. The occurrence and morphological type of neuronal death were determined by TUNEL reaction and ultrastructural examination. Cell loss following nerve section, whist dependent on the availability of NO, as shown by its marked elevation in nNOS KO mice, did not correlate well with nNOS expression in WT animals. Whereas a lack of eNOS was tolerated, deficiency of nNOS led to an enhanced cell loss. The results suggest a crucial role of NO supply after transection of peripheral nerves with a particular significance of the nNOS isoform.

The roles of nitric oxide in dorsal root ganglion neurons

The functions of nitric oxide (NO) in primary somatosensory neurons are reviewed. During the early development of these neurons the neuronal isoform of nitric oxide synthase (nNOS) is expressed during neurite extension. As their axons extend peripherally and start to take up nerve growth factor (NGF), nNOS starts to disappear from the majority of these neurons. A small number (less than 5%) continue to express nNOS, and for this small population NO may have a role in synaptic transmission. Following peripheral nerve section in adult rats, nNOS is reexpressed in many small peptidergic DRG neurons that have been axotomized. At the same time cGMP synthesis is increased in satellite glia cells. From culture studies, it was established that NGF negatively regulates nNOS synthesis in DRG neurons and that block of NO production leads to neuronal death. Further recent data is reviewed that supports the view that NO has a neuroprotective action preventing loss of DRG neurons and facilitates regeneration.