Differential susceptibility to neurotoxicity mediated by neurotrophins and neuronal nitric oxide synthase

Strong Binding of Phytochemicals to the Catalytic Domain of Tyrosine Hydroxylase as a Trojan Horse Decreases Dopamine in Dopaminergic Cells: Pharmaceutical Considerations in Schizophrenia and Parkinson's Disease

BACKGROUND

Imbalances in dopamine levels result in neurological and psychological disorders such as elevated dopamine in Parkinson's disease.

OBJECTIVE

Despite a considerable number of advertisements claiming Aloe-vera's effectiveness in PD treatment, it has hidden long-term disadvantages for healthy people and PD patients.

METHODS

In the present investigation, the impacts of Aloe-vera on dopaminergic cells were evaluated.

RESULTS

The results indicated that the focal adhesion kinase (FAK) enhancement was in line with the Bax/Bcl2 ratio decrement, reactive oxygen specious (ROS) production, and nonsignificant alteration in the sub-G1phase of the cell cycle. It led to glial cell-derived neurotrophic factor (GDNF) upregulation but did not significantly change the BDNF level involved in depression and motor impairment recovery. These events apparently resulted in the enhancement in dopaminergic cell viability and neurite length and attenuated PI+ cells. However, it also induced neuronal nitric oxide synthase (nNOS) overexpression and nitric oxide (NO) and lactate dehydrogenase (LDH) production. Notably, docking results of the catalytic domain in tyrosine hydroxylase (TH) with the Aloe-vera constituents showed strong binding of most Aloe-vera constituents with the catalytic domain of TH, even stronger than L-tyrosine as an original substrate. Following the docking results, Aloe-vera downregulated TH protein and attenuated dopamine.

CONCLUSION

It can be hypothesized that Aloe-vera improves PD symptoms through enhancement in antiapoptotic markers and neurotrophic factors, while it suppresses TH and dopamine in the form of a Trojan horse, later resulting in the future deterioration of the disease symptoms. The results provide cues to pharmaceutical companies to use the active components of Aloe-vera as putative agents in neurological and psychiatric disorders and diseases to decrease dopamine in patients with enhanced dopamine levels.

Opposite Roles of NT-3 and BDNF in Synaptic Remodeling of the Inner Ear Induced by Electrical Stimulation

With the development of neural prostheses, neural plasticity including synaptic remodeling under electrical stimulation is drawing more and more attention. Indeed, intracochlear electrical stimulation used to restore hearing in deaf can induce the loss of residual hearing and synapses of the inner hair cells (IHCs). However, the mechanism under this process is largely unknown. Considering that the guinea pig is always a suitable and convenient choice for the animal model of cochlea implant (CI), in the present study, normal-hearing guinea pigs were implanted with CIs. Four-hour electrical stimulation with the intensity of 6 dB above electrically evoked compound action potential (ECAP) threshold (which can decrease the quantity of IHC synapses and the excitability of the auditory nerve) resulted in the upregulation of Bdnf (p < 0.0001) and downregulation of Nt-3 (p < 0.05). Intracochlear perfusion of exogenous NT-3 or TrkC/Fc (which blocks NT-3) can, respectively, resist or aggravate the synaptic loss induced by electrical stimulation. In contrast, local delivery of exogenous BDNF or TrkB/Fc (which blocks BDNF) to the cochlea, respectively, exacerbated or protected against the synaptic loss caused by electrical stimulation. Notably, the synaptic changes were only observed in the basal and middle halves of the cochlea. All the findings above suggested that NT-3 and BDNF may play opposite roles in the remodeling of IHC synapses induced by intracochlear electrical stimulation, i.e. NT-3 and BDNF promoted the regeneration and degeneration of IHC synapses, respectively.

The AAA + ATPase Thorase is neuroprotective against ischemic injury

Neuronal preconditioning in vitro or in vivo with a stressful but non-lethal stimulus leads to new protein expression that mediates a profound neuroprotection against glutamate excitotoxicity and experimental stroke. The proteins that mediate neuroprotection are relatively unknown and under discovery. Here we find that the expression of the AAA + ATPase Thorase is induced by preconditioning stimulation both in vitro and in vivo. Thorase provides neuroprotection in an ATP-dependent manner against oxygen-glucose deprivation (OGD) neurotoxicity or glutamate N-Methyl-D-aspartate (NMDA) receptor-mediated excitotoxicity in vitro. Knock-down of Thorase prevents the establishment of preconditioning induced neuroprotection against OGD or NMDA neurotoxicity. Transgenic overexpression of Thorase provides neuroprotection in vivo against middle cerebral artery occlusion (MCAO)-induced stroke in mice, while genetic deletion of Thorase results in increased injury in vivo following stroke. These results define Thorase as a neuroprotective protein and understanding Thorase signaling could offer a new therapeutic strategy for the treatment of neurologic disorders.

Calcium Release Mediated by Redox-Sensitive RyR2 Channels Has a Central Role in Hippocampal Structural Plasticity and Spatial Memory

AIMS

Previous studies indicate that hippocampal synaptic plasticity and spatial memory processes entail calcium release from intracellular stores mediated by ryanodine receptor (RyR) channels. In particular, RyR-mediated Ca²⁺ release is central for the dendritic spine remodeling induced by brain-derived neurotrophic factor (BDNF), a neurotrophin that stimulates complex signaling pathways leading to memory-associated protein synthesis and structural plasticity. To examine if upregulation of ryanodine receptor type-2 (RyR2) channels and the spine remodeling induced by BDNF entail reactive oxygen species (ROS) generation, and to test if RyR2 downregulation affects BDNF-induced spine remodeling and spatial memory.

RESULTS

Downregulation of RyR2 expression (short hairpin RNA [shRNA]) in primary hippocampal neurons, or inhibition of nitric oxide synthase (NOS) or NADPH oxidase, prevented agonist-mediated RyR-mediated Ca²⁺ release, whereas BDNF promoted cytoplasmic ROS generation. RyR2 downregulation or inhibitors of N-methyl-d-aspartate (NMDA) receptors, or NOS or of NADPH oxidase type-2 (NOX2) prevented RyR2 upregulation and the spine remodeling induced by BDNF, as did incubation with the antioxidant agent N-acetyl l-cysteine. In addition, intrahippocampal injection of RyR2-directed antisense oligodeoxynucleotides, which caused significant RyR2 downregulation, caused conspicuous defects in a memorized spatial memory task.

INNOVATION

The present novel results emphasize the key role of redox-sensitive Ca²⁺ release mediated by RyR2 channels for hippocampal structural plasticity and spatial memory.

CONCLUSION

Based on these combined results, we propose (i) that BDNF-induced RyR2-mediated Ca²⁺ release and ROS generation via NOS/NOX2 are strictly required for the dendritic spine remodeling and the RyR2 upregulation induced by BDNF, and (ii) that RyR2 channel expression is crucial for spatial memory processes. Antioxid. Redox Signal. 29, 1125-1146.

The signaling pathways underlying BDNF-induced Nrf2 hippocampal nuclear translocation involve ROS, RyR-Mediated Ca2+ signals, ERK and PI3K

The neurotrophin Brain-Derived Neurotrophic Factor (BDNF) induces complex neuronal signaling cascades that are critical for the cellular changes underlying synaptic plasticity. These pathways include activation of Ca²⁺ entry via N-methyl-D-aspartate receptors and sequential activation of nitric oxide synthase and NADPH oxidase, which via generation of reactive nitrogen/oxygen species stimulate Ca²⁺-induced Ca²⁺ release mediated by Ryanodine Receptor (RyR) channels. These sequential events underlie BDNF-induced spine remodeling and type-2 RyR up-regulation. In addition, BDNF induces the nuclear translocation of the transcription factor Nrf2, a master regulator of antioxidant protein expression that protects cells against the oxidative damage caused by injury and inflammation. To investigate the possible BDNF-induced signaling cascades that mediate Nrf2 nuclear translocation in primary hippocampal cultures, we tested here whether reactive oxygen species, RyR-mediated Ca²⁺ release, ERK or PI3K contribute to this response. We found that pre-incubation of cultures with inhibitory ryanodine to suppress RyR-mediated Ca²⁺ release, with the reducing agent N-acetylcysteine or with inhibitors of ERK or PI3K activity, prevented the nuclear translocation of Nrf2 induced by incubation for 6 h with BFNF. Based on these combined results, we propose that the key role played by BDNF as an inducer of neuronal antioxidant responses, characterized by BDNF-induced Nfr2 nuclear translocation, entails crosstalk between reactive oxygen species and RyR-mediated Ca²⁺ release, and the participation of ERK and PI3K activities.

Nitric Oxide Signaling in Neurodegeneration and Cell Death

In this tribute to Solomon H. Snyder (Sol) we discuss the mechanisms by which nitric oxide (NO) kills neurons. We provide a historical perspective regarding the discovery that glutamate excitotoxicity is mediated by NO. It also contains a discussion of the discovery that neuronal nitric oxide synthase (nNOS) catalytic activity accounts for NADPH diaphorase activity and its localization in the central nervous system. NADPH diaphorase/nNOS neurons are unique in that they are resistant to toxic effects of excess glutamate and that they are resistant to neurodegeneration in a variety of neurodegenerative diseases. NADPH diaphorase/nNOS neurons are resistant to neurotoxicity and neurodegeneration through the overexpression of manganese superoxide dismutase. The review also delves into the mechanisms by which NO kills neurons including NO's activation of the glyceraldehyde-3-phosphate dehydrogenase-dependent cell pathway. In addition, there is a review of parthanatos in which NO combines with the superoxide anion ( [Formula: see text] ) to form peroxynitrite (ONOO^-) that damages DNA and activates poly (ADP-ribose) (PAR) polymerase (PARP). This ultimately leads to activation of the PARP-dependent apoptosis-inducing factor-associated nuclease, the final executioner in NO-dependent cell death. Finally, there is a discussion of potential targets that are under development that target the mechanisms by which NO kills neurons.

Cultured networks of excitatory projection neurons and inhibitory interneurons for studying human cortical neurotoxicity

Translating neuroprotective treatments from discovery in cell and animal models to the clinic has proven challenging. To reduce the gap between basic studies of neurotoxicity and neuroprotection and clinically relevant therapies, we developed a human cortical neuron culture system from human embryonic stem cells or human inducible pluripotent stem cells that generated both excitatory and inhibitory neuronal networks resembling the composition of the human cortex. This methodology used timed administration of retinoic acid to FOXG1(+) neural precursor cells leading to differentiation of neuronal populations representative of the six cortical layers with both excitatory and inhibitory neuronal networks that were functional and homeostatically stable. In human cortical neuronal cultures, excitotoxicity or ischemia due to oxygen and glucose deprivation led to cell death that was dependent on N-methyl-D-aspartate (NMDA) receptors, nitric oxide (NO), and poly(ADP-ribose) polymerase (PARP) (a cell death pathway called parthanatos that is distinct from apoptosis, necroptosis, and other forms of cell death). Neuronal cell death was attenuated by PARP inhibitors that are currently in clinical trials for cancer treatment. This culture system provides a new platform for the study of human cortical neurotoxicity and suggests that PARP inhibitors may be useful for ameliorating excitotoxic and ischemic cell death in human neurons.

Brain BDNF levels are dependent on cerebrovascular endothelium-derived nitric oxide

Scientific evidence continues to demonstrate a link between endothelial function and cognition. Besides, several studies have identified a complex interplay between nitric oxide (NO) and brain-derived neurotrophic factor (BDNF), a neurotrophin largely involved in cognition. Therefore, this study investigated the link between cerebral endothelium-derived NO and BDNF signaling. For this purpose, levels of BDNF and the phosphorylated form of endothelial NO synthase at serine 1177 (p-eNOS) were simultaneously measured in the cortex and hippocampus of rats subjected to either bilateral common carotid occlusion (n = 6), physical exercise (n = 6) or a combination of both (n = 6) as experimental approaches to modulate flow-induced NO production by the cerebrovasculature. Tropomyosin-related kinase type B (TrkB) receptors and its phosphorylated form at tyrosine 816 (p-TrkB) were also measured. Moreover, we investigated BDNF synthesis in brain slices exposed to the NO donor glyceryl trinitrate. Our results showed increased p-eNOS and BDNF levels after exercise and decreased levels after vascular occlusion as compared to corresponding controls, with a positive correlation between changes in p-eNOS and BDNF (r = 0.679). Exercise after vascular occlusion did not change levels of these proteins. Gyceryl trinitrate increased proBDNF and BDNF levels in brain slices, thus suggesting a possible causal relationship between NO and BDNF. Moreover, vascular occlusion, like exercise, resulted in increased TrkB and p-TrkB levels, whereas no change was observed with the combination of both. These results suggest that brain BDNF signaling may be dependent on cerebral endothelium-derived NO production.

BDNF-induced nitric oxide signals in cultured rat hippocampal neurons: time course, mechanism of generation, and effect on neurotrophin secretion

BDNF and nitric oxide signaling both contribute to plasticity at glutamatergic synapses. However, the role of combined signaling of both pathways at the same synapse is largely unknown. Using NO imaging with diaminofluoresceine in cultured hippocampal neurons we analyzed the time course of neurotrophin-induced NO signals. Application of exogenous BDNF, NT-4, and NT-3 (but not NGF) induced NO signals in the soma and in proximal dendrites of hippocampal neurons that were sensitive to NO synthase activity, TrkB signaling, and intracellular calcium elevation. The effect of NO signaling on neurotrophin secretion was analyzed in BDNF-GFP, and NT-3-GFP transfected hippocampal neurons. Exogenous application of the NO donor sodium-nitroprusside markedly inhibited neurotrophin secretion. However, endogenously generated NO in response to depolarization and neurotrophin stimulation, both did not result in a negative feedback on neurotrophin secretion. These results suggest that a negative feedback of NO signaling on synaptic secretion of neurotrophins operates only at high intracellular levels of nitric oxide that are under physiological conditions not reached by depolarization or BDNF signaling.

Brain Tissues Oxidative Damage as A Possible Mechanism of Deleterious Effects of Propylthiouracil- Induced Hypothyroidism on Learning and Memory in Neonatal and Juvenile Growth in Rats

INTRODUCTION

The role of brain tissues oxidative damage in learning and memory impairments has been well documented. It is also well known that thyroid hormones have a critical role for the brain functions. The purpose of this study was to investigate the role of brain tissues oxidative damage as a possible mechanism of deleterious effects of propylthiouracil (PTU) - induced hypothyroidism on learning and memory in neonatal and juvenile growth in rats.

METHODS

Fourteen pregnant female Wistar rats were kept in separate cages. After delivery, they were randomly divided into two groups including control and PTU. Rats in the control group received normal drinking water, whereas the second group received drinking water supplemented with 0.02% PTU from the first day after delivery through the first two months of the life of offspring (the pups of rats). After 60 days, nine male offspring of each group were randomly selected and tested in the Morris water maze (MWM). Then, samples of blood were collected to measure thyroxine. Finally, the brains were removed and total thiol groups and molondialdehyde (MDA) concentrations were determined.

RESULTS

Compared to the control group's offspring, serum thyroxine levels in the PTU group's off spring were significantly low (P<0.001). In MWM, the escape latency and traveled path in the PTU group were significantly higher than that in the control group (P<0.01- P<0.001). In PTU group, the total thiol concentrations in both cortical and hippocampal tissues were significantly lower and MDA concentrations were higher than control group (P<0.001).

DISCUSSION

It seems that deleterious effect of hypothyroidism during neonatal and juvenile growth on learning and memory is at least in part due to brain tissues oxidative damage.

Homeostatic NMDA receptor down-regulation via brain derived neurotrophic factor and nitric oxide-dependent signalling in cortical but not in hippocampal neurons

Nitric oxide (NO) has been proposed to down-regulate NMDA receptors (NMDA-Rs) in a homeostatic manner. However, NMDA-R-dependent NO synthesis also can cause excitotoxic cell death. Using bicuculline-stimulated hippocampal and cortical cell cultures, we have addressed the role of the brain-derived neurotrophic factor-NO pathway in NMDA-R down-regulation. This pathway protected cortical cells from NMDA-induced death and led to NMDA-R inhibition. In contrast, no evidence was gained for the presence of this protective pathway in hippocampal neurons, in which NMDA-induced NO synthesis was confirmed to be toxic. Therefore, opposing effects of NO depended on the activation of different signalling pathways. The pathophysiological relevance of this observation was investigated in synaptosomes and post-synaptic densities isolated from rat hippocampi and cerebral cortices following kainic acid-induced status epilepticus. In cortical, but not in hippocampal synaptosomes, brain-derived neurotrophic factor induced NO synthesis and inhibited NMDA-R currents present in isolated post-synaptic densities. In conclusion, we identified a NO-dependent homeostatic response in the rat cerebral cortex induced by elevated activity. A low performance of this pathway in brain areas including the hippocampus may be related to their selective vulnerability in pathologies such as temporal lobe epilepsy.

The expression mechanism of the residual LTP in the CA1 region of BDNF k.o. mice is insensitive to NO synthase inhibition

BDNF and nitric oxide signaling both contribute to long-term potentiation (LTP) at glutamatergic synapses, but to date, few studies analyzed the interaction of both signaling cascades in the same synaptic pathway. Here we addressed the question whether the residual LTP in the CA1 region of hippocampal slices from heterozygous BDNF knockout mice (BDNF⁺/⁻) is dependent on nitric oxide (NO) signaling. Extracellular recording of synaptic field potentials elicited by presynaptic Schaffer collateral stimulation was performed in the CA1 region of hippocampal slices of 4- to 6-week-old mice, and LTP was induced by a theta burst stimulation protocol. Application of the nitric oxide inhibitor L-NAME (200 μM) strongly inhibited LTP by 70% in wildtype animals. This inhibition of LTP was not a consequence of altered basal synaptic properties. In CA1 of BDNF⁺/⁻ mice, stimulated with the same theta burst protocol, LTP was reduced by 50% as compared to wildtype animals. This impairment in the expression of LTP in BDNF⁺/⁻ mice did not result from an increased synaptic fatigue. The residual LTP in BDNF⁺/⁻ was not further reduced by preincubation of slices with L-NAME. These results suggest that BDNF and NO share overlapping intracellular signaling cascades to mediate LTP in CA1, and part of their signaling cascades are most likely arranged consecutively in the signaling pathway mediating LTP.

Inhibition of nitric oxide-induced nuclear localization of CAPON by NMDA receptor antagonist in cultured rat primary astrocytes

Astrocytes play a key role in regulating aspects of inflammation in the central nervous system. It was observed that nNOS had located in the nucleus of cultured cerebral cortical astrocytes of 7 days. In the present study, we found that carboxy-terminal PDZ ligand of nNOS (CAPON) mainly located in the nucleus of astrocytes stimulated with NO donor sodium nitroprusside (SNP) or GSNO or N-methyl-d-aspartate (NMDA) receptor agonist-NMDA. However, originally, it was localized mostly in the cytoplasm of normal astrocytes. Immunocytochemistry showed that nNOS was co-localized with CAPON in the nucleus of astrocytes stimulated with SNP. In addition to the nuclear localization, treatment with SNP increased the mRNA and protein expression of CAPON. When SNP was removed from media, CAPON accumulated in nucleus transported back to cytoplasm. MK801, an inhibitor of NMDA receptor, was able to reverse the nuclear localization of CAPON resulted from SNP, suggesting that there is a functional relationship of NO with NMDA receptor in the regulation of the nuclear localization of CAPON. These findings provide a new insight in the understanding of the physical and pathological significances of CAPON/nNOS/NMDA receptor.

Norepinephrine and nitric oxide promote cell survival signaling in hippocampal neurons

Nitric oxide (NO), physical exercise and/or antidepressant drugs, through the increased release of norepinephrine and brain-derived neurotrophic factor (BDNF), have been shown to exert profound protective, pro-survival effects on neurons otherwise compromised by injury, disease, prolonged stress, and subsequent depression in vivo. We sought, therefore, to evaluate such survival and neuroprotection in hippocampal neurons in culture, which, in an analogous model of in vivo cellular stress, was deprived of several vital nutrients. We assessed pro-survival outcomes following the application of norepinephrine or the noradrenergic partial agonist, clonidine, a general nitric oxide synthase inhibitor and NO donor, using a cell survival assay and quantitative Western blotting of the survival signaling molecules, BDNF, P-CREB, P-Akt, and P-MAPK in hippocampal neuronal lysates. We demonstrate that norepinephrine, clonidine, the NO donor and various combinations of these drugs increased cell survival and the immunoreactivity of the four survival signaling molecules in the face of nutrient deprivation stress, whereas the NO synthase inhibitor, and each of several survival signaling pathway inhibitors all decreased cell survival even below that of controls without nutrient supplementation. These results demonstrate that conditions that make cells vulnerable to environmental/toxic insult can be offset by norepinephrine and its related drugs or by NO donors and exacerbated by drugs that specifically inhibit a key survival signaling pathway. These results indicate that pharmacological intervention can promote neuroprotection and survival signaling in the face of nutrient withdrawal, but that this may require that several pathways remain intact.

Nitric oxide contributes to learning and memory deficits observed in hypothyroid rats during neonatal and juvenile growth

INTRODUCTION

Severe cognitive impairment follows thyroid hormone deficiency during the neonatal period. The role of nitric oxide (NO) in learning and memory has been widely investigated.

METHODS

This study aimed to investigate the effect of hypothyroidism during neonatal and juvenile periods on NO metabolites in the hippocampi of rats and on learning and memory. Animals were divided into two groups and treated for 60 days from the first day of lactation. The control group received regular water, whereas animals in a separate group were given water supplemented with 0.03% methimazole to induce hypothyroidism. Male offspring were selected and tested in the Morris water maze. Samples of blood were collected to measure the metabolites of NO, NO2, NO3 and thyroxine. The animals were then sacrificed, and their hippocampi were removed to measure the tissue concentrations of NO2 and NO3.

DISCUSSION

Compared to the control group's offspring, serum thyroxine levels in the methimazole group's offspring were significantly lower (P<0.01). In addition, the swim distance and time latency were significantly higher in the methimazole group (P<0.001), and the time spent by this group in the target quadrant (Q1) during the probe trial was significantly lower (P<0.001). There was no significant difference in the plasma levels of NO metabolites between the two groups; however, significantly higher NO metabolite levels in the hippocampi of the methimazole group were observed compared to controls (P<0.05).

CONCLUSION

These results suggest that the increased NO level in the hippocampus may play a role in the learning and memory deficits observed in childhood hypothyroidism; however, the precise underlying mechanism(s) remains to be elucidated.

The intranigral injection of tissue plasminogen activator induced blood-brain barrier disruption, inflammatory process and degeneration of the dopaminergic system of the rat

Tissue-type plasminogen activator (tPA) is the only drug approved for the treatment of thromboembolic stroke, but it might lead to some neurotoxic side effects. tPA is a highly specific serine proteinase, one of the two principal plasminogen activators and one of the three trypsin-like serine proteinases of the tissue kallikrein family. We have observed that tPA injection in the SN leads to the degeneration of the dopaminergic neurons in a dose-dependent manner, without affecting the GABAergic neurons. We also found that tPA injected in the substantia nigra of rats produced the disruption of the blood-brain barrier (BBB) integrity, the induction of microglial activation, the loss of astroglia and the expression of aquaporin 4 (AQP4), as well as an increase in the expression of NMDA receptors and the brain derived neurothrophic factor (BDNF). All these effects, along with the changes produced in the phosphorylated forms of several MAP kinases and the transcription factor CREB, and the increase in the expression of nNOS and iNOS observed under our experimental conditions, could be involved in the loss of dopaminergic neurons.

Effects of Gingko Extract (EGb761) on oxidative damage under different conditions of serum supply

Standardized Ginkgo biloba extract EGb761 is known to have multivalent properties such as anti-oxidation and anti-apoptosis. In this study, we determined in rat pheochromocytoma (PC12) cells effects of EGb761 treatment on oxidative damage under three different conditions of serum supply: normal growth medium (NGM), serum deprivation (SE) and serum deprivation followed by re-supply (SERS). It was found that, under the condition of serum deprivation, oxidative damage induced less cell death than the condition of serum supply. This appears to be related to inhibition of mitochondrial metabolism. Moreover, after serum deprivation, serum re-supply exacerbated cell necrosis, possibly through enhancement of oxidative damage. EGb761 could attenuate oxidative damage under the condition of serum supply whereas no protective effect on serum-depleted cells was observed. These results suggest that, there is a synergistic effect between trophic factors and EGb761. EGb761 treatment may protect cells from possible oxidative damage induced by the trophic factors. On the other hand, trophic factors appear to strengthen the protective effect of EGb761. To fully understand the synergistic interaction between antioxidants and trophic factors will help to sort out rational use of drugs in clinic practice.

Neuroprotective Effect of Chuk-Me-Sun-Dan on NMDA- and AMPA-Evoked Nitric Oxide Synthase Activity in Mouse Brain

Chukmesundan (CMSD) is composed of 8 medicinal herbs including Panex ginseng C.A. MEYER, Atractylodes macrocephala KOID, Poria cocos WOLF, Pinellia ternata BREIT, Brassica alba BOISS, Aconitum carmichaeli DEBX, Cynanchum atratum BGE, and Cuscuta chinensis LAM and used for the treatment of various symptoms accompanying hypertension and cerebrovascular disorders. This study was carried out to examine the effects of CMSD on N-methyl-D-aspartate (NMDA)-evoked, and alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)-evoked nitric oxide synthase (NOS) activity in mouse brain. In adult forebrain, CMSD influences neuronal maintenance and is neuroprotective in several injury models through mechanisms that are incompletely understood. Interaction is observed between CMSD and nitric oxide (NO). Because NO affects both neural plasticity and degeneration, we hypothesized that CMSD might rapidly modulate NO production. Using in vivo microdialysis we measured conversion of L-[14C] arginine to L-[14C] citrulline as an accurate reflection of NOS activity in adult mouse hippocampus. CMSD significantly reduced NOS activities to 62% of basal levels within 2 days of onset of delivery and maintained NOS activity at less than 45% of baseline throughout 3 days of delivery. These effects did not occur with control (distilled water) and were not mediated by effect of CMSD on glutamate levels. In addition, simultaneous delivery of CMSD treatment prevented significant increases in NOS activity triggered by the glutamate receptor agonists NMDA and AMPA. Rapid suppression by CMSD of basal and glutamate-stimulated NOS activity may regulate neuromodulatory functions of NO or protect neurons from NO toxicity and suggests a novel mechanism for rapidly mediating functions of CMSD. It is shown that NMDA receptor stimulation leads to activation of p21ras (Ras) through generation of NO via neuronal NOS. The competitive NOS inhibitor, L-nitroarginine methyl ester, and CMSD prevents Ras activation elicited by NMDA, thus supporting the physiologic relevance of endogenous NO regulation of Ras. These results suggest that Ras is a physiologic target of endogenously produced NO and indicates a signaling pathway for NMDA receptor activation that may be important for long-lasting neuronal responses.

Maternal thyroid hormone: a strong repressor of neuronal nitric oxide synthase in rat embryonic neocortex

Understanding of how maternal thyroid inadequacy during early gestation poses a risk for developmental outcomes is still a challenge for the neuroendocrine community. Early neocortical neurogenesis is accompanied by maternal thyroid hormone (TH) transfer to fetal brain, appearance of TH receptors, and absence of antineurogenesis signals, followed by optimization of neuronal numbers through apoptosis. However, the effects of TH deprivation on neurogenesis and neuronal cell death before the onset of fetal thyroid are still not clear. We show that maternal TH deficiency during early gestational period causes massive premature elevation in the expression of neuronal nitric oxide synthase (nNOS) with an associated neuronal death in embryonic rat neocortex. Maternal hypothyroidism was induced by feeding methimazole (0.025% wt/vol) in the drinking water to pregnant Sprague Dawley rats from embryonic d 6. Cerebral cortices from fetuses were harvested at different embryonic stages (embryonic d 14, 16, and 18) of hypothyroid and euthyroid groups. Immunoblotting and real-time PCR results showed that both protein and RNA levels of nNOS were prematurely increased under maternal hypothyroidism, and showed reversibility upon T4 administration. Immunohistochemistry revealed an increased nNOS immunoreactivity in both the cortical plate and proliferative zone of neocortex along with a corroborative decrease in the microtubule associated protein-2 positive neurons under maternal TH insufficiency. Results combined, put forth nNOS as a novel target of maternal TH action in embryonic neocortex, and underscore the importance of prenatal screening and timely rectification of maternal TH insufficiency, even of a moderate degree.

Simvastatin prevents the inflammatory process and the dopaminergic degeneration induced by the intranigral injection of lipopolysaccharide

Anti-inflammatory strategies have attracted much interest for their potential to prevent further deterioration of Parkinson's disease. Recent experimental and clinical evidence indicate that statins - extensively used in medical practice as effective lipid-lowering agents - have also anti-inflammatory effects. In this study, we investigated the influence of simvastatin on the degenerative process of the dopaminergic neurons of the rat following intranigral injection of lipopolysaccharide (LPS), a potent inductor of inflammation that we have previously used as an animal model of Parkinson's disease. We evaluated TH positive neurons, astroglial, and microglial populations and found that simvastatin prevented the inflammatory processes, as the induction of interleukin-1beta, tumor necrosis factor-alpha, and iNOS and the consequent dopaminergic degeneration induced by LPS. Moreover, simvastatin produced the activation of the neurotrophic factor BDNF, along with the prevention of the oxidative damage to proteins. Moreover, it also prevents the main changes produced by LPS on different mitogen-activated protein kinases, featured as increases of P-c-Jun N-terminal protein kinase, P-extracellular signal-regulated kinase, p-38, and P-glycogen synthase kinase and the decrease of the promotion of cell survival signals such as cAMP response element-binding protein and Akt. Our results suggest that statins could delay the progression of dopaminergic degeneration in disorders involving inflammatory processes.

Nitric oxide signaling participates in norepinephrine-induced activity of neuronal intracellular survival pathways

Much evidence has gathered that nitric oxide (NO) signaling, via cGMP-dependent mechanisms, may activate pro-survival pathways in hippocampal neurons and inhibit apoptosis. Past research has revealed that the enhancement of monoaminergic neurotransmission via exercise or treatment with antidepressant medications leads to an enhanced expression of brain-derived neurotrophic factor (BDNF). In isolated hippocampal neurons, norepinephrine (NE) application also increases the immunoreactivity of BDNF and several pro-survival signaling molecules. The data herein support the possibility that NO signaling plays an important role in enhancing neurotrophin expression and activation of the pro-survival phosphatidylinositol 3' kinase (PI-3K) pathway stimulated by NE. In isolated hippocampal neurons, the NO donor, sodium nitroprusside, increases BDNF, PI-3K, and phospho-ERK1 immunoreactivity. Specific inhibitors of the NO system suggest that NE-induced increases in hippocampal BDNF and the PI-3K pathway, but not stimulation of the MAPK pathway, depend upon NO signaling. In addition, inhibiting cGMP suggest that the effects of NE on BDNF immunoreactivity and Akt phosphorylation are also cGMP-dependent. Finally, the application of l-NAME to hippocampal neurons increases cell death. This is the first study of its kind demonstrating the involvement of NE-induced pro-survival signaling in three distinct signaling pathways: PI-3K, MAPK, and NO/cGMP. Possible mechanisms are discussed in light of the results.

Nitric oxide from neuronal nitric oxide synthase sensitises neurons to hypoxia-induced death via competitive inhibition of cytochrome oxidase

Hypoxia/ischaemia is known to trigger neuronal death, but the role of neuronal nitric oxide synthase (nNOS) in this process is controversial. Nitric oxide (NO) inhibits cytochrome oxidase in competition with oxygen. We tested whether NO derived from nNOS synergises with hypoxia to induce neuronal death by inhibiting mitochondrial cytochrome oxidase. Sixteen hours of hypoxia (2% oxygen) plus deoxyglucose (an inhibitor of glycolysis) caused extensive, excitotoxic death of neurons in rat cerebellar granule cell cultures. Three different nNOS inhibitors (including the selective inhibitor N-4S-4-amino-5-2-aminoethyl-aminopentyl-N'-nitroguanidine) decreased this neuronal death by half, indicating a contribution of nNOS to hypoxic death. The selective nNOS inhibitor did not, however, block neuronal death induced either by added glutamate or by added azide (an uncompetitive inhibitor of cytochrome oxidase), indicating that nNOS does not act downstream of glutamate or cytochrome oxidase. Hypoxia plus deoxyglucose-induced glutamate release and neuronal depolarisation, and the nNOS inhibitor decreased this. Hypoxia inhibited cytochrome oxidase activity in the cultures, but a selective nNOS inhibitor prevented this inhibition, indicating NO from nNOS was inhibiting cytochrome oxidase in competition with oxygen. These data indicate that hypoxia synergises with NO from nNOS to induce neuronal death via cytochrome oxidase inhibition causing neuronal depolarisation. This mechanism might contribute to ischaemia/stroke-induced neuronal death in vivo.

Involvement of the nitric oxide/protein kinase G pathway in polychlorinated biphenyl-induced cell death in SH-SY 5Y neuroblastoma cells

Polychlorinated biphenyls (PCB) are persistent environmental contaminants whose chronic exposure can affect nervous system development and function. The cellular and molecular mechanisms underlying neuronal damage are not yet clear. In the present study, we investigated whether nitric oxide (NO) could be involved in aroclor 1254 (A1254; a PCB mixture)-induced cytotoxicity in SH-SY5Y human neuroblastoma cells. Prolonged exposure (24 hr) to A1254 (10-100 microg/ml) caused a dose-dependent reduction of cell viability that was attenuated in the presence of a calcium entry blocker, gadolinum (Gd(3+)) at 10 microM, a concentration able to block voltage-sensitive calcium channels. In addition, A1254 caused an increase of cytosolic calcium that was dependent on extracellular calcium, as measured by fura-2 videomicroscopy. A1254-induced calcium rise may stimulate NO production through an activation of neuronal NOS (nNOS). Indeed, the concomitant addition of the selective nNOS inhibitor N(omega)-propyl-L-arginine (NPLA) and A1254 prevented cell injury, suggesting that NO production plays a major role in A1254-evoked cell injury. Furthermore, the exposure (14 hr) to A1254 (30 microg/ml) produced an up-regulation of the expression of beta isoform of nNOS. This up-regulation was calcium dependent and was accompanied by an enhancement of NO production as demonstrated by an increase of nitrite formation. Moreover, A1254-induced cell injury was prevented when KT 5823, a selective cGMP/PKG inhibitor, was added concomitantly to 30 microg/ml A1254. These results suggest that PCB-induced cell death in neuroblastoma cells is mediated by an activation of the cGMP/PKG pathway triggered by NO production.

Post-traumatic application of brain-derived neurotrophic factor and glia-derived neurotrophic factor on the rat spinal cord enhances neuroprotection and improves motor function

We examined the potential efficacy of brain-derived neurotrophic factor (BDNF) and glial-derived neurotrophic factor (GDNF) applied over traumatized spinal cord, alone or in combination, for attenuating motor dysfunction, blood-spinal cord barrier (BSCB) breakdown, edema formation, and cell injury in a rat model. Under Equithesin anesthesia, spinal cord injury (SCI) was performed by making a unilateral incision into the right dorsal horn of the T10-11 segment. The rats were allowed to survive 5 hours after trauma. The BDNF or GDNF was applied (0.1 to 1 microg/10 microl in phosphate buffer saline) 30, 60, or 90 minutes after SCI. Topical application of BDNF or GDNF 30 minutes after SCI in high concentration (0.5 microg and 1 microg) significantly improved motor function and reduced BSCB breakdown, edema formation, and cell injury at 5 hours. These beneficial effects of neurotrophins were markedly absent when administered separately either 60 or 90 minutes after injury. However, combined application of BDNF and GDNF at 60 or 90 minutes after SCI resulted in a significant reduction in motor dysfunction and spinal cord pathology. These novel observations suggest that neurotrophins in combination have potential therapeutic value for the treatment of SCI in clinical situations.

Post-ischaemic mild hypothermia inhibits apoptosis in the penumbral region by reducing neuronal nitric oxide synthase activity and thereby preventing endothelin-1-induced hydroxyl radical formation

Previously, we showed that treatment with resuscitative, post-ischaemic mild hypothermia (34 degrees C for 2 h) reduced apoptosis in the penumbra (cortex), but not in the core (striatum) of an endothelin-1 (Et-1)-induced focal cerebral infarct in the anaesthetized rat. Therefore, the purpose of this study was to investigate by which pathways resuscitative mild hypothermia exerts its neuroprotective effect in this model. The amino acids glutamate, serine, glutamine, alanine, taurine, arginine and the NO-related compound citrulline were sampled from the striatum and cortex of the ischaemic hemisphere using in vivo microdialysis. The in vivo salicylate trapping method was applied for monitoring hydroxyl radical formation via 2,3 dihydroxybenzoic acid (2,3 DHBA) detection. Caspase-3, neuronal nitric oxide synthase (nNOS) immunoreactivity and the volume of ischaemic damage were determined 24 h after the insult. In both the striatum and the cortex, Et-1-induced increases in glutamate, taurine and alanine were refractory to mild hypothermia. However, mild hypothermia significantly attenuated the ischaemia-induced 2,3 DHBA levels and the nNOS immunoreactivity in the cortex, but not in the striatum. These observations were associated with a decreased caspase-3 immunoreactivity. These results suggest that mild hypothermia exerts its neuroprotective effect in the penumbra partially by reducing nNOS activity and thereby preventing oxidative stress. Furthermore, we confirm our previous findings that the neuroprotective effect of resuscitative hypothermia is not mediated by changes in ischaemia-induced amino acid release as they could not be associated with the ischaemia-induced damage in the Et-1 rat model.

Nitric oxide synthesis is required for exercise-induced increases in hippocampal BDNF and phosphatidylinositol 3' kinase expression

Previous studies have shown that running exercise, either alone or in combination with antidepressant treatment, results in increased hippocampal BDNF levels. Nitric oxide (NO) is an important signaling molecule that has neuronal survival-promoting properties and has been shown to play an important role in plasticity associated with activating interventions. Herein, we administered the NO synthase (NOS) inhibitor, N-nitro-L-arginine methyl ester (L-NAME), in conjunction with the monoamine oxidase inhibitor (MAOI) antidepressant, tranylcypromine, and voluntary wheel-running exercise to determine whether the enhancement in full-length BDNF mRNA occurring with these interventions is dependent upon NO synthesis. Our results demonstrate that both chronic exercise and chronic exercise-plus-tranylcypromine lead to enhanced hippocampal BDNF mRNA and protein expression. NOS inhibition prevents this effect of chronic exercise, but only partly prevents the effects of the exercise/antidepressant combination. Thus, the robust enhancement in BDNF mRNA occurring with exercise appears to be NO synthesis-dependent, but the intervention including antidepressant may enhance BDNF expression through alternative intracellular mechanisms. In addition, because exercise and antidepressants have both been shown to activate survival-promoting genes, we evaluated the levels of hippocampal phosphatidylinositol 3' kinase (PI-3K), an important signaling molecule within a principal neuronal survival-promoting intracellular pathway. Like BDNF mRNA and protein, exercise increases the expression of PI-3K, whereas concomitant NOS inhibition prevents this increase in PI-3K immunoreactivity above control levels. Our results are discussed in light of possible overlapping, but distinct intracellular pathways activated by exercise and antidepressant treatment to bring about enhancements in BDNF expression and other survival-promoting effects. These findings further demonstrate the potential therapeutic potential of chronic exercise to supplement pharmacotherapeutic treatment of mood disorders.

Role of MAPK/ERK in Neurotrophin-4 Potentiation of Necrotic Neuronal Death

Neurotrophic factors have been proposed for the treatment of a variety of neurological diseases. However, to this point they have failed in clinical trials. One potential problem is that while neurotrophic factors attenuate apoptosis, they have the potential to enhance necrosis. In this study we show that neurotrophin-4 (NT-4) attenuated apoptotic neuronal death while potentiating necrotic neuronal death in cortical cultures. The protective effects of NT-4 were not blocked by the mitogen-activated protein kinase kinase (MEK) inhibitors PD098059 or U0126, while the injury potentiation by NT-4 was blocked by these inhibitors. NT-4 stimulated the phosphorylation of ERK1/2 and this phosphorylation was attenuated by U0126 and PD098059. The results indicate a disassociation between the pathway by which NT-4 potentiates necrosis, and that by which it attenuates apoptosis, and suggest that addition of a MEK inhibitor may enhance the beneficial effects of NT-4 in treating complex injuries such as occur in vivo.

Effects of nerve graft on nitric oxide synthase, NAD(P)H oxidase, and antioxidant enzymes in chronic spinal cord injury

Oxidative stress and nitrosative stress play important roles in the pathogenesis of secondary spinal cord injury. Recently, we demonstrated that peripheral nerve grafts (PNG) with acidic fibroblast growth factor (aFGF) partially restore hind limb locomotion in adult rats with completely transected spinal cords. This study investigated the protein abundances of the superoxide (O2*)-generating enzyme nicotinamide adenine dinucleotide (phosphate) oxidase (NAD(P)H oxidase; gp91phox subunit), nitric oxide synthases (NOS), antioxidant enzymes, superoxide dismutases (Cu Zn SOD, Mn SOD), catalase, and glutathione peroxidase (GPX) as well as nitrotyrosine in the spinal cord tissue 4 months after spinal cord transection in rats with and without PNG and aFGF. The protein abundances of the gp91phox subunit of NAD(P)H oxidase, Mn SOD, catalase, GPX, eNOS, and nitrotyrosine were significantly upregulated, whereas Cu Zn SOD and nNOS were unchanged in the injury group compared to the sham controls. The nerve graft with aFGF treated group showed significantly better hind limb locomotion recovery than the injury group. Although the protein abundances of gp91phox, nitrotyrosine, and Cu Zn SOD were similar in the treated group (nerve graft with aFGF) compared to the injury group, Mn SOD, GPX, catalase, and eNOS protein abundances were significantly higher, whereas nNOS was markedly lower in the treated group. We conclude that the combination of nerve graft and aFGF enhances the local antioxidant defense system after spinal cord transection in rats.

Effects of estrone on N-METHYL-d-aspartic acid- and staurosporine-induced changes in caspase-3-like protease activity and lactate dehydrogenase-release: time- and tissue-dependent effects in neuronal primary cultures

A growing body of evidence indicates that estrogens affect apoptotic processes in neuronal cells. However, their effects seem to depend on type of neuronal tissue, stage of development and apoptosis inducing factors. In the present study we compared effects of estrone (100 and 500 nM) on N-methyl-D-aspartic acid (NMDA) (1 mM)- and staurosporine (1 microM)-induced caspase-3-like activity and lactate dehydrogenase (LDH)-release in primary cultures of rat hippocampal and neocortical neurons. Fluorometric and colorimetric determination of enzyme activity was performed 6 h, 14 h, and 24 h after exposure to apoptotic agents. In the hippocampal cell cultures on 7 days in vitro (DIV), a time-dependent NMDA-induced activation of caspase-3-like proteases was accompanied by increased LDH-release. In neocortical cell cultures on 7 DIV NMDA did not affect caspase activity and decreased LDH-release. In neocortical cell cultures on 12 DIV NMDA inhibited spontaneous caspase activity, but was toxic to neurons after 24 h exposure suggesting that these cells underwent necrotic rather than apoptotic death. Estrone has attenuated both pro- and anti-apoptotic NMDA-induced changes in rat primary neuronal cultures acting independently of estrogen receptors, as detected with ICI 182, 780. In hippocampal neurons estrone antagonized not only the NMDA-induced caspase-3-like activity, but also NMDA-mediated LDH-release. However, in neocortical neurons estrone either attenuated NMDA-induced inhibition of caspase-3-like activity (12 DIV) or partly blocked NMDA-mediated decrease in LDH-release (7 DIV). In contrast to NMDA, staurosporine elevated caspase-3-like activity and LDH-release in a time-dependent manner in all used culture systems. Estrone inhibited pro-apoptotic effects of staurosporine in neocortical neurons, but only at later stage of development in vitro, which points to the protective role of estrogens during the brain tissue maturation. Since estrone triggered its effects via non-genomic mechanisms, it suggests that the other estradiol metabolites exhibiting low affinity to hormone receptors may be potent neuroprotective agents, which could retain the favorable and minimize the adverse side effects of estrogens.

Preconditioning of cortical neurons by oxygen-glucose deprivation: tolerance induction through abbreviated neurotoxic signaling

Transient exposure of rat cortical cultures to nonlethal oxygen-glucose deprivation (OGD preconditioning) induces tolerance to otherwise lethal oxygen-glucose deprivation (OGD) or N-methyl-D-aspartate 24 h later. This study evaluates the role of cytosolic and mitochondrial Ca2+-dependent cellular signaling. Mechanistic findings are placed in context with other models of ischemic preconditioning or known neurotoxic pathways within cortical neurons. Tolerance to otherwise lethal OGD is suppressed by performing OGD preconditioning in the presence of the broad-scope catalytic antioxidants Mn(III)tetra(4-carboxyphenyl)porphyrin (MnTBAP) or Zn(II)tetra(4-carboxyphenyl)porphyrin [Zn(II)TBAP], but not by a less active analog, Mn(III)tetra(4-sulfonatophenyl)porphyrin, or a potent superoxide scavenger, Mn(III)tetra(N-ethyl-2-pyridyl)porphyrin chloride. Inhibitors of adenosine A1 receptors, nitric oxide synthase, mitogen-activated protein kinase, and poly(ADP-ribose) polymerase fail to suppress OGD preconditioning despite possible links with reactive oxygen species in other models of ischemic preconditioning. Preconditioning is suppressed by 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS), which has been ascribed elsewhere to inhibition of superoxide transport to the cytosol through mitochondrial anion channels. However, although it induces mitochondrial Ca2+ uptake, neuronal preconditioning is largely insensitive to mitochondrial uncoupling with carbonyl cyanide p-(trifluoromethoxy)phenylhydrazone or 2,4-dinitrophenol. Un-couplers will prevent production of mitochondrial reactive oxygen species, implying nonmitochondrial targets by MnTBAP, Zn(II)TBAP, and DIDS. Emphasizing the importance of an increase in cytosolic Ca2+ during preconditioning, a Ca2+/calmodulin-dependent protein kinase II inhibitor, KN-62, suppresses development of subsequent tolerance. Summarizing, only those cellular transduction pathways that have the potential to be neurotoxic may be activated by preconditioning in cortical neurons. Finally, a marked decrease in extracellular glutamate is observed during otherwise lethal OGD in preconditioned cultures, suggesting that this end effector may represent a point of convergence across different preconditioning models.

Alzheimer's disease-affected brain: presence of oligomeric A beta ligands (ADDLs) suggests a molecular basis for reversible memory loss

A molecular basis for memory failure in Alzheimer's disease (AD) has been recently hypothesized, in which a significant role is attributed to small, soluble oligomers of amyloid beta-peptide (A beta). A beta oligomeric ligands (also known as ADDLs) are known to be potent inhibitors of hippocampal long-term potentiation, which is a paradigm for synaptic plasticity, and have been linked to synapse loss and reversible memory failure in transgenic mouse AD models. If such oligomers were to build up in human brain, their neurological impact could provide the missing link that accounts for the poor correlation between AD dementia and amyloid plaques. This article, using antibodies raised against synthetic A beta oligomers, verifies the predicted accumulation of soluble oligomers in AD frontal cortex. Oligomers in AD reach levels up to 70-fold over control brains. Brain-derived and synthetic oligomers show structural equivalence with respect to mass, isoelectric point, and recognition by conformation-sensitive antibodies. Both oligomers, moreover, exhibit the same striking patterns of attachment to cultured hippocampal neurons, binding on dendrite surfaces in small clusters with ligand-like specificity. Binding assays using solubilized membranes show oligomers to be high-affinity ligands for a small number of nonabundant proteins. Current results confirm the prediction that soluble oligomeric A beta ligands are intrinsic to AD pathology, and validate their use in new approaches to therapeutic AD drugs and vaccines.

Exercise increases the vulnerability of rat hippocampal neurons to kainate lesion

Available evidence suggests that regular, moderate-intensity exercise has beneficial effects on neural health, perhaps including neuroprotection. To evaluate this idea further, we compared the severity of kainate-induced neuronal loss in exercised versus sedentary female rats. Stereological estimations of neuron number revealed that rats in the exercise condition exhibited significantly greater neuron loss in hippocampal region CA2/3, suggesting that high levels of physical activity may increase neuronal vulnerability to excitotoxicity.

Neurotrophin potentiation of iron-induced spinal cord injury

Previous studies have shown that pretreatment with neurotrophins can potentiate the vulnerability of cultured neurons to excitotoxic and free radical-induced necrosis, in contrast to their well known neuroprotective effects against apoptosis. Here we tested the hypothesis that this unexpected injury-potentiating effect of neurotrophins would also take place in the adult rat spinal cord. Fe(3+)-citrate was injected stereotaxically into spinal cord gray matter in adult rats in amounts sufficient to produce minimal tissue injury 24 h later. Twenty-four-hour pretreatment with brain-derived neurotrophic factor, neurotrophin-3, or neurotrophin-4/5, but not nerve growth factor, markedly enhanced tissue injury in the gray matter as evidenced by an increase in the damaged area, as well as the loss of neurons and oligodendrocytes. Consistent with maintained free radical mediation, the neurotrophin-potentiated iron-induced spinal cord damage was blocked by co-application of the antioxidant N-tert-butyl-(2-sulfophenyl)-nitrone. These data support the hypothesis that the overall neuroprotective properties of neurotrophins in models of acute injury to the spinal cord may be limited by an underlying potentiation of free radical-mediated necrosis.

BDNF-induced survival of auditory neurons in vivo: Cessation of treatment leads to accelerated loss of survival effects

Neurotrophic factors are important for the development and maintenance of the auditory system. They have also been shown to act as survival factors for auditory neurons in animal deafness models. Studies have demonstrated recently that these neurotrophic factors not only maintain survival of auditory neurons, but that these surviving neurons retain functionality. It remains to be determined, however, if a single administration of a neurotrophic factor is sufficient to maintain auditory neuron survival after loss of hair cells, or if sustained delivery is required. This study investigated the longevity of the survival effects of BDNF on auditory neurons in deafened guinea pigs. Briefly, the left cochleae of deafened guinea pigs were infused with BDNF for 28 days via a mini-osmotic pump, and neuronal survival was analyzed at various stages after the completion of treatment. BDNF treatment prevented the degeneration of auditory neurons that normally is seen after a loss of hair cells, supporting previous studies. Our results indicate, however, that cessation of BDNF treatment leads to an accelerated decline in auditory neuron survival as compared to that observed in deafened, untreated cochleae. These findings indicate that much work remains to be done to establish a technique for the long-term survival of auditory neurons in the deaf ear.

BDNF heightens the sensitivity of motor neurons to excitotoxic insults through activation of TrkB

The survival promoting and neuroprotective actions of brain-derived neurotrophic factor (BDNF) are well known but under certain circumstances this growth factor can also exacerbate excitotoxic insults to neurons. Prior exploration of the receptor through which BDNF exerts this action on motor neurons deflects attention away from p75. Here we investigated the possibility that BDNF acts through the receptor tyrosine kinase, TrkB, to confer on motor neurons sensitivity to excitotoxic challenge. We blocked BDNF activation of TrkB using a dominant negative TrkB mutant or a TrkB function blocking antibody, and found that this protected motor neurons against excitotoxic insult in cultures of mixed spinal cord neurons. Addition of a function blocking antibody to BDNF to mixed spinal cord neuron cultures is also neuroprotective indicating that endogenously produced BDNF participates in vulnerability to excitotoxicity. We next examined the intracellular signaling cascades that are engaged upon TrkB activation. Previously we found that inhibition of the phosphatidylinositide-3'-kinase (PI3'K) pathway blocks BDNF-induced excitotoxic sensitivity. Here we show that expression of a constitutively active catalytic subunit of PI3'K, p110, confers excitotoxic sensitivity (ES) upon motor neurons not incubated with BDNF. Parallel studies with purified motor neurons confirm that these events are likely to be occuring specifically within motor neurons. The abrogation of BDNF's capacity to accentuate excitotoxic insults may make it a more attractive neuroprotective agent.

Global loss of Na,K-ATPase and its nitric oxide-mediated regulation in a transgenic mouse model of amyotrophic lateral sclerosis

Na,K-ATPase plays a critical role in energy metabolism and ion fluxes. Its loss was investigated in the G93A mouse model of amyotrophic lateral sclerosis (ALS) in which the mutation of Cu/Zn superoxide dismutase (SOD1) is thought to lead to aberrant oxidative damage. Observed losses in spinal cord Na,K-ATPase activity exceeded all expectations. All three catalytic subunit isoforms (alpha1, alpha2, alpha3) were reduced, and the global alpha subunit loss affected not just neurons, glia, and myelinated axon tracts but even ependymal and pial membranes. Decreases in Na,K-ATPase activity were greater than losses of protein, and there were losses of Na,K-ATPase alpha, but not beta, subunits. Together, these observations are consistent with selective degradation of the alpha subunit after damage. Overexpression of normal SOD1 does not cause ALS-like symptoms, but it has other known pathological effects. In transgenic mice overexpressed normal human SOD1 had a smaller but still considerable effect on Na,K-ATPase. Furthermore, the nitric oxide-mediated regulatory pathway for Na,K-ATPase inhibition was undetectable in spinal cord tissue slices from mice overexpressing either mutant or normal human SOD1. Na,K-ATPase activity did not respond to nitric oxide donors, and the free radical-dependent step of the pathway could not be bypassed by the addition of the downstream protein kinase G activator, 8-Br-cGMP. The data demonstrate that Na,K-ATPase is vulnerable to aberrant SOD1 activity, making it a potential contributing factor in disease pathology. Moreover, the global cellular distribution of Na,K-ATPase loss indicates that SOD1 overexpression is far-reaching in its pathological effects.

Brain-derived neurotrophic factor can act as a pronecrotic factor through transcriptional and translational activation of NADPH oxidase

Several lines of evidence suggest that neurotrophins (NTs) potentiate or cause neuronal injury under various pathological conditions. Since NTs enhance survival and differentiation of cultured neurons in serum or defined media containing antioxidants, we set out experiments to delineate the patterns and underlying mechanisms of brain-derived neurotrophic factor (BDNF)-induced neuronal injury in mixed cortical cell cultures containing glia and neurons in serum-free media without antioxidants, where the three major routes of neuronal cell death, oxidative stress, excitotoxicity, and apoptosis, have been extensively studied. Rat cortical cell cultures, after prolonged exposure to NTs, underwent widespread neuronal necrosis. BDNF-induced neuronal necrosis was accompanied by reactive oxygen species (ROS) production and was dependent on the macromolecular synthesis. cDNA microarray analysis revealed that BDNF increased the expression of cytochrome b558, the plasma membrane-spanning subunit of NADPH oxidase. The expression and activation of NADPH oxidase were increased after exposure to BDNF. The selective inhibitors of NADPH oxidase prevented BDNF-induced ROS production and neuronal death without blocking antiapoptosis action of BDNF. The present study suggests that BDNF-induced expression and activation of NADPH oxidase cause oxidative neuronal necrosis and that the neurotrophic effects of NTs can be maximized under blockade of the pronecrotic action.

Mechanisms of bFGF and NT-4 potentiation of necrotic neuronal death

The effects of neurotrophic factors on necrotic neuronal death are controversial. In this study we found that both neurotrophin-4 (NT-4) and basic fibroblast growth factor (bFGF) potentiated necrotic neuronal death caused by exposure to oxygen-glucose deprivation or iron-citrate (Fe) in cortical cultures. However, there were significant differences in the actions of the two neurotrophic factors. Neurotrophin-4 protected against apoptotic neuronal death, while bFGF had no effect on apoptotic death in these cultures. Furthermore, potentiation of oxygen-glucose deprivation induced necrotic death by NT-4 required pretreatment (24 h), while pretreatment with bFGF had no effect. However, acute treatment with bFGF during oxygen-glucose deprivation did potentiate neuronal death. Both neurotrophic factors potentiated free radical mediated necrotic neuronal death induced by exposure to Fe. However, the RNA synthesis inhibitor, actinomycin-D, blocked the injury potentiation by NT-4, but not that caused by bFGF. Also, NT-4, but not bFGF, potentiated Fe induced necrotic death in pure neuronal cultures. Expression of mRNA for FGF receptors FGFR1 and FGFR2 was observed at high levels in astrocytes. The results indicate that the injury enhancing effects of bFGF are acute, while those of NT-4 require prolonged exposure and new protein synthesis. Furthermore, the effects of bFGF appear to be mediated through actions on astrocytes, while NT-4 appears to act directly on neurons. The fact that neurotrophic factors from two distinct families can potentiate neuronal death by two different mechanisms suggests that such injury potentiation may be a common concern regarding the use of neurotrophic factors.

The role of NADPH oxidase and neuronal nitric oxide synthase in zinc-induced poly(ADP-ribose) polymerase activation and cell death in cortical culture

In the present study, we examined the role and the mechanism of poly(ADP-ribose) polymerase (PARP) and poly(ADP-ribose) glycohydrolase (PARG) activation in zinc-induced cell death in cortical culture. After brief exposure to 400 microM zinc, cortical cells exhibited DNA fragmentation, increased poly(ADP-ribosyl)ation, and decreased levels of nicotinamide adenine dinucleotide (NAD) and ATP and subsequently underwent cell death. Inhibitors of PARP/PARG attenuated both zinc-induced NAD/ATP depletion and cell death, thereby implicating the PARP/PARG cascade in these processes. The zinc-inducible enzymes NADPH oxidase and neuronal nitric oxide synthase (nNOS) contributed to PARP activation as their inhibitors attenuated zinc-induced poly(ADP-ribosyl)ation. Levels of nitric oxide and nitrites increased following zinc exposure, consistent with NOS activation. In addition, Western blots and RT-PCR analysis revealed that protein and mRNA levels of nNOS specifically increased following zinc exposure in a manner similar to that of NADPH oxidase. The present study demonstrates that induction of NADPH oxidase and nNOS actively contributes to PARP/PARG-mediated NAD/ATP depletion and cell death induced by zinc in cortical culture.

The role of NADPH oxidase, neuronal nitric oxide synthase and poly(ADP ribose) polymerase in oxidative neuronal death induced in cortical cultures by brain-derived neurotrophic factor and neurotrophin-4/5

Certain neurotrophins promote or induce oxidative neuronal death in cortical cultures. However, the effector mechanisms mediating this phenomenon have not been delineated. In this study, we investigated the possibility that NADPH oxidase and nitric oxide synthase (NOS) function as such effectors. Western blot analysis showed that treatment with brain-derived neurotrophic factor (BDNF) and neurotrophin (NT)-4/5 increased the levels of NADPH oxidase subunits. Moreover, neurotrophin treatment resulted in membrane translocation of p67phox, a characteristic feature of NADPH oxidase activation. Administration of the specific NADPH oxidase inhibitor, 4-(2-aminoethyl)benzenesulfonylfluoride (AEBSF), attenuated increases in oxygen free radicals thereby suggesting that NADPH oxidase contributes to the oxidative stress induced by neurotrophins. Furthermore, neuronal death induced by BDNF or NT-4/5 was significantly attenuated by AEBSF. Treatment with BDNF has previously been shown to induce neuronal NOS (nNOS). Our data indicated that inhibitors of nNOS attenuated neuronal death induced by BDNF or NT-4/5, consistent with an active role of nNOS in the mediation of neurotrophin neurotoxicity. As in other models of oxidative cell death, BDNF-induced neuronal death was accompanied by poly(ADP ribose) polymerase (PARP) activation. AEBSF or N-nitro-l-arginine (NNA) reduced BDNF-mediated PARP activation. PARP and poly(ADP ribose) glycohydrolase (PARG) are actively involved in mediating neurotrophin neurotoxicity since inhibitors of PARP and PARG significantly reduced levels of cell death. These results suggest that NADPH oxidase and nNOS contribute to increased oxidative stress, subsequent activation of PARP/PARG, and neuronal death induced by prolonged neurotrophin exposure.

Neurotrophin-3 promotes cell death induced in cerebral ischemia, oxygen-glucose deprivation, and oxidative stress: possible involvement of oxygen free radicals

To explore the role of neurotrophin-3 (NT-3) during cerebral ischemia, NT-3-deficient brains were subjected to transient focal ischemia. Conditional mutant brains produced undetectable amounts of NT-3 mRNA, whereas the expression of the neurotrophin, BDNF, the NT-3 receptor, TrkC, and the nonselective, low-affinity neurotrophin receptor p75NTR, were comparable to wild-type. Baseline absolute blood flow, vascular and neuroanatomical features, as well as physiological measurements were also indistinguishable from wild-type. Interestingly, the absence of NT-3 led to a significantly decreased infarct volume 23 h after middle cerebral artery occlusion. Consistent with this, the addition of NT-3 to primary cortical cell cultures exacerbated neuronal death caused by oxygen-glucose deprivation. Coincubation with the oxygen free radical chelator, trolox, diminished potentiation of neuronal death. NT-3 also enhanced neuronal cell death and the production of reactive oxygen species caused by oxidative damage inducing agents. We conclude that endogenous NT-3 enhanced neuronal injury during acute stroke, possible by increasing oxygen-radical mediated cell death.

Glial-derived arginine, the nitric oxide precursor, protects neurons from NMDA-induced excitotoxicity

Excitotoxic neuronal cell death is characterized by an overactivation of glutamate receptors, in particular of the NMDA subtype, and the stimulation of the neuronal nitric oxide synthase (nNOS), which catalyses the formation of nitric oxide (NO) from l-arginine (L-Arg). At low L-Arg concentrations, nNOS generates NO and superoxide (O2(.)(-)), favouring the production of the toxin peroxynitrite (ONOO-). Here we report that NMDA application for five minutes in the absence of added L-Arg induces neuronal cell death, and that the presence of L-Arg during NMDA application prevents cell loss by blocking O2(.)(-) and ONOO- formation and by inhibiting mitochondrial depolarization. Because L-Arg is transferred from glial cells to neurons upon activation of glial glutamate receptors, we hypothesized that glial cells play an important modulator role in excitotoxicity by releasing L-Arg. Indeed, as we further show, glial-derived L-Arg inhibits NMDA-induced toxic radical formation, mitochondrial dysfunction and cell death. Glial cells thus may protect neurons from excitotoxicity by supplying L-Arg. This potential neuroprotective mechanism may lead to an alternative approach for the treatment of neurodegenerative diseases involving excitotoxic processes, such as ischemia.

Brain-derived neurotrophic factor in the control human brain, and in Alzheimer's disease and Parkinson's disease

Brain-derived neurotrophic factor (BDNF) is a small dimeric protein, structurally related to nerve growth factor, which is abundantly and widely expressed in the adult mammalian brain. BDNF has been found to promote survival of all major neuronal types affected in Alzheimer's disease and Parkinson's disease, like hippocampal and neocortical neurons, cholinergic septal and basal forebrain neurons, and nigral dopaminergic neurons. In this article, we summarize recent work on the molecular and cellular biology of BDNF, including current ideas about its intracellular trafficking, regulated synthesis and release, and actions at the synaptic level, which have considerably expanded our conception of BDNF actions in the central nervous system. But our primary aim is to review the literature regarding BDNF distribution in the human brain, and the modifications of BDNF expression which occur in the brain of individuals with Alzheimer's disease and Parkinson's disease. Our knowledge concerning BDNF actions on the neuronal populations affected in these pathological states is also reviewed, with an aim at understanding its pathogenic and pathophysiological relevance.

Nitric oxide-stimulated increase in extracellular adenosine accumulation in rat forebrain neurons in culture is associated with ATP hydrolysis and inhibition of adenosine kinase activity

Adenosine is a putative endogenous sleep-inducing substance, and nitric oxide has been implicated in arousal and sleep mechanisms. We found that various nitric oxide donors, including diethylamine NONOate (DEA/NO), stimulated large increases in extracellular adenosine in nearly pure cultures of forebrain neurons. The effect of DEA/NO could be blocked by 2-phenyl-4,4,5, 5-tetramethyl-imidazoline-1-oxyl-oxide and could not be mimicked by degraded solutions of DEA/NO or by DEA itself; therefore, it was caused by nitric oxide release on hydrolysis of the parent compound. The accumulation of adenosine was not blocked by probenecid or GMP, suggesting that neither extracellular cAMP nor extracellular AMP was the source, and that adenosine was therefore the most likely species transported across the plasma membrane. To pursue this further, we tested the effect of DEA/NO on cellular ATP and found a significant fall in ATP associated with exposure to nitric oxide. In addition, exposure to DEA/NO nearly completely inhibited adenosine kinase activity. It has been found previously that adenosine kinase is inhibited by its substrate, adenosine. We found that exposure to nitric oxide increased intracellular adenosine to 125 +/- 18% of control values (p < 0.01), consistent with the possibility that in our system the inhibition of adenosine kinase is related to an increase in intracellular adenosine, and that the effect of nitric oxide on extracellular adenosine is significantly potentiated by substrate inhibition of adenosine kinase. Furthermore, nitric oxide-stimulated adenosine accumulation may be important in the regulation of behavioral state.

NT-4/5 exacerbates free radical-induced neuronal necrosis in vitro and in vivo

Neurotrophins render neurons highly vulnerable to certain injuries. We examined the possibility that NT-4/5 would enhance free radical neurotoxicity in vivo as well as in vitro. Striatal neurons exposed to 10 microM Fe(2+) or 1 mM l-buthionine-[S, R]-sulfoximine (BSO) underwent mild degeneration within 24 h. With concurrent addition of 10-100 ng/ml NT-4/5, neuronal death following exposure to Fe(2+) or BSO was significantly increased and suppressed by addition of 100 microM trolox, an antioxidant. In the adult brain, the intrastriatal injections of 20 nmol Fe(2+) revealed features of neuronal necrosis such as swelling cell body and mitochondria, fenestration of plasma membrane prior to nuclear membrane, and scattering condensation of nuclear chromatin. Cotreatment with 1.8 microg NT-4/5 augmented the striatal damage 24 h following the injections of Fe(2+). This study implies that free radicals produce necrotic degeneration in vivo as well as in vitro that becomes more sensitive in the presence of neurotrophins.

Nitric oxide (NO.) stabilizes whereas nitrosonium (NO+) enhances filopodial outgrowth by rat retinal ganglion cells in vitro

Recent observations suggest that nitric oxide (NO(.)) can increase or decrease growth cone motility. Here, these apparently paradoxical results are explained by distinct actions of different NO-related species. Filopodial morphology of 223 rat retinal ganglion cells was monitored under computer-enhanced video microscopy in the presence of NO synthase (NOS) substrates or inhibitors, donors of specific NO-related species, and membrane-permeant cyclic nucleotide analogs. Physiological NOS activity induced filopodial outgrowth, whereas inhibition of NOS stabilized filopodia. Similar to NOS, nitrosonium (NO(+) transfer) and peroxynitrite (ONOO(-)), which can regulate the activity of growth-associated proteins by S-nitrosylation and oxidation, respectively, induced filopodial outgrowth. In contrast, NO(.), which stimulates guanylate cyclase to increase cGMP, stabilized filopodial activity. Thus disparate NO-related species may offer a dynamic process of filopodial growth regulation.