Mitochondrial nitric oxide mediates decreased vulnerability of hippocampal neurons from immature animals to NMDA

Tailoring Biomimetic Phosphorylcholine-Containing Block Copolymers as Membrane-Targeting Cellular Rescue Agents

Some synthetic polymers can block cell death when applied following an injury that would otherwise kill the cell. This cellular rescue occurs through interactions of the polymers with cell membranes. However, general principles for designing synthetic polymers to ensure strong, but nondisruptive, cell membrane targeting are not fully elucidated. Here, we tailored biomimetic phosphorylcholine-containing block copolymers to interact with cell membranes and determined their efficacy in blocking neuronal death following oxygen-glucose deprivation. By adjusting the hydrophilicity and membrane affinity of poly(2-methacryloyloxyethyl phosphorylcholine) (polyMPC)-based triblock copolymers, the surface active regime in which the copolymers function effectively as membrane-targeting cellular rescue agents was determined. We identified nonintrusive interactions between the polymer and the cell membrane that alter the collective dynamics of the membrane by inducing rigidification without disrupting lipid packing or membrane thickness. In general, our results open new avenues for biological applications of polyMPC-based polymers and provide an approach to designing membrane-targeting agents to block cell death after injury.

Complex I syndrome in striatum and frontal cortex in a rat model of Parkinson disease

Mitochondrial dysfunction named complex I syndrome was observed in striatum mitochondria of rotenone treated rats (2 mg rotenone/kg, i. p., for 30 or 60 days) in an animal model of Parkinson disease. After 60 days of rotenone treatment, the animals showed: (a) 6-fold increased bradykinesia and 60% decreased locomotor activity; (b) 35-34% decreases in striatum O₂ uptake and in state 3 mitochondrial respiration with malate-glutamate as substrate; (c) 43-57% diminished striatum complex I activity with 60-71% decreased striatum mitochondrial NOS activity, determined both as biochemical activity and as functional activity (by the NO inhibition of active respiration); (d) 34-40% increased rates of mitochondrial O₂^•- and H₂O₂ productions and 36-46% increased contents of the products of phospholipid peroxidation and of protein oxidation; and (e) 24% decreased striatum mitochondrial content, likely associated to decreased NO-dependent mitochondrial biogenesis. Intermediate values were observed after 30 days of rotenone treatment. Frontal cortex tissue and mitochondria showed similar but less marked changes. Rotenone-treated rats showed mitochondrial complex I syndrome associated with cellular oxidative stress in the dopaminergic brain areas of striatum and frontal cortex, a fact that describes the high sensitivity of mitochondrial complex I to inactivation by oxidative reactions.

α-Synuclein-Dependent Calcium Entry Underlies Differential Sensitivity of Cultured SN and VTA Dopaminergic Neurons to a Parkinsonian Neurotoxin

Parkinson's disease (PD) is a debilitating neurodegenerative disease characterized by a loss of dopaminergic neurons in the substantia nigra (SN). Although mitochondrial dysfunction and dysregulated α-synuclein (aSyn) expression are postulated to play a role in PD pathogenesis, it is still debated why neurons of the SN are targeted while neighboring dopaminergic neurons of the ventral tegmental area (VTA) are spared. Using electrochemical and imaging approaches, we investigated metabolic changes in cultured primary mouse midbrain dopaminergic neurons exposed to a parkinsonian neurotoxin, 1-methyl-4-phenylpyridinium (MPP+). We demonstrate that the higher level of neurotoxicity in SN than VTA neurons was due to SN neuron-specific toxin-induced increase in cytosolic dopamine (DA) and Ca2+, followed by an elevation of mitochondrial Ca2+, activation of nitric oxide synthase (NOS), and mitochondrial oxidation. The increase in cytosolic Ca2+ was not caused by MPP+-induced oxidative stress, but rather depended on the activity of both L-type calcium channels and aSyn expression, suggesting that these two established pathogenic factors in PD act in concert.

Redox Imbalance and Viral Infections in Neurodegenerative Diseases

Reactive oxygen species (ROS) are essential molecules for many physiological functions and act as second messengers in a large variety of tissues. An imbalance in the production and elimination of ROS is associated with human diseases including neurodegenerative disorders. In the last years the notion that neurodegenerative diseases are accompanied by chronic viral infections, which may result in an increase of neurodegenerative diseases progression, emerged. It is known in literature that enhanced viral infection risk, observed during neurodegeneration, is partly due to the increase of ROS accumulation in brain cells. However, the molecular mechanisms of viral infection, occurring during the progression of neurodegeneration, remain unclear. In this review, we discuss the recent knowledge regarding the role of influenza, herpes simplex virus type-1, and retroviruses infection in ROS/RNS-mediated Parkinson's disease (PD), Alzheimer's disease (AD), and amyotrophic lateral sclerosis (ALS).

Tumor protein Tctp regulates axon development in the embryonic visual system

The transcript encoding translationally controlled tumor protein (Tctp), a molecule associated with aggressive breast cancers, was identified among the most abundant in genome-wide screens of axons, suggesting that Tctp is important in neurons. Here, we tested the role of Tctp in retinal axon development in Xenopus laevis. We report that Tctp deficiency results in stunted and splayed retinotectal projections that fail to innervate the optic tectum at the normal developmental time owing to impaired axon extension. Tctp-deficient axons exhibit defects associated with mitochondrial dysfunction and we show that Tctp interacts in the axonal compartment with myeloid cell leukemia 1 (Mcl1), a pro-survival member of the Bcl2 family. Mcl1 knockdown gives rise to similar axon misprojection phenotypes, and we provide evidence that the anti-apoptotic activity of Tctp is necessary for the normal development of the retinotectal projection. These findings suggest that Tctp supports the development of the retinotectal projection via its regulation of pro-survival signalling and axonal mitochondrial homeostasis, and establish a novel and fundamental role for Tctp in vertebrate neural circuitry assembly.

Highlighted article: The cancer-associated protein Tctp controls neural circuitry in Xenopus via its regulation of pro-survival signalling and axonal mitochondrial homeostasis.

The Human Mitochondrial DNA Depletion Syndrome Gene MPV17 Encodes a Non-selective Channel That Modulates Membrane Potential

The human MPV17-related mitochondrial DNA depletion syndrome is an inherited autosomal recessive disease caused by mutations in the inner mitochondrial membrane protein MPV17. Although more than 30 MPV17 gene mutations were shown to be associated with mitochondrial DNA depletion syndrome, the function of MPV17 is still unknown. Mice deficient in Mpv17 show signs of premature aging. In the present study, we used electrophysiological measurements with recombinant MPV17 to reveal that this protein forms a non-selective channel with a pore diameter of 1.8 nm and located the channel's selectivity filter. The channel was weakly cation-selective and showed several subconductance states. Voltage-dependent gating of the channel was regulated by redox conditions and pH and was affected also in mutants mimicking a phosphorylated state. Likewise, the mitochondrial membrane potential (Δψm) and the cellular production of reactive oxygen species were higher in embryonic fibroblasts from Mpv17(-/-) mice. However, despite the elevated Δψm, the Mpv17-deficient mitochondria showed signs of accelerated fission. Together, these observations uncover the role of MPV17 as a Δψm-modulating channel that apparently contributes to mitochondrial homeostasis under different conditions.

Low-level laser therapy (810 nm) protects primary cortical neurons against excitotoxicity in vitro

Excitotoxicity describes a pathogenic process whereby death of neurons releases large amounts of the excitatory neurotransmitter glutamate, which then proceeds to activate a set of glutamatergic receptors on neighboring neurons (glutamate, N-methyl-D-aspartate (NMDA), and kainate), opening ion channels leading to an influx of calcium ions producing mitochondrial dysfunction and cell death. Excitotoxicity contributes to brain damage after stroke, traumatic brain injury, and neurodegenerative diseases, and is also involved in spinal cord injury. We tested whether low level laser (light) therapy (LLLT) at 810 nm could protect primary murine cultured cortical neurons against excitotoxicity in vitro produced by addition of glutamate, NMDA or kainate. Although the prevention of cell death was modest but significant, LLLT (3 J/cm(2) delivered at 25 mW/cm(2) over 2 min) gave highly significant benefits in increasing ATP, raising mitochondrial membrane potential, reducing intracellular calcium concentrations, reducing oxidative stress and reducing nitric oxide. The action of LLLT in abrogating excitotoxicity may play a role in explaining its beneficial effects in diverse central nervous system pathologies.

Low-level laser therapy (810 nm) protects primary cortical neurons against excitotoxicity in vitro

Excitotoxicity describes a pathogenic process whereby death of neurons releases large amounts of the excitatory neurotransmitter glutamate, which then proceeds to activate a set of glutamatergic receptors on neighboring neurons (glutamate, N-methyl-D-aspartate (NMDA), and kainate), opening ion channels leading to an influx of calcium ions producing mitochondrial dysfunction and cell death. Excitotoxicity contributes to brain damage after stroke, traumatic brain injury, and neurodegenerative diseases, and is also involved in spinal cord injury. We tested whether low level laser (light) therapy (LLLT) at 810 nm could protect primary murine cultured cortical neurons against excitotoxicity in vitro produced by addition of glutamate, NMDA or kainate. Although the prevention of cell death was modest but significant, LLLT (3 J/cm(2) delivered at 25 mW/cm(2) over 2 min) gave highly significant benefits in increasing ATP, raising mitochondrial membrane potential, reducing intracellular calcium concentrations, reducing oxidative stress and reducing nitric oxide. The action of LLLT in abrogating excitotoxicity may play a role in explaining its beneficial effects in diverse central nervous system pathologies.

Mitochondrial oxidant stress in locus coeruleus is regulated by activity and nitric oxide synthase

Loss of noradrenergic locus coeruleus (LC) neurons is a prominent feature of aging–related neurodegenerative diseases, like Parkinson’s disease (PD). The basis of this vulnerability is not understood. To explore possible physiological determinants, LC neurons were studied using electrophysiological and optical approaches in ex vivo mouse brain slices. These studies revealed that autonomous activity in LC neurons was accompanied by oscillations in dendritic Ca²⁺ concentration attributable to opening of L–type Ca²⁺ channels. This oscillation elevated mitochondrial oxidant stress and was attenuated by inhibition of nitric oxide synthase. The relationship between activity and stress was malleable, as arousal and carbon dioxide, each increased the spike rate, but differentially affected mitochondrial oxidant stress. Oxidant stress also was increased in an animal model of PD. Thus, our results point to activity–dependent Ca²⁺ entry and a resulting mitochondrial oxidant stress as factors contributing to the vulnerability of LC neurons.

Nitric oxide and cerebrovascular regulation

The cerebrovascular regulation involves highly complex mechanisms to assure that the brain is perfused at all times. These mechanisms depend on all components of the neurovascular units: neurons, glia, and vascular cells. All these cell types can produce nitric oxide (NO), a powerful vasodilator through different NO synthases. Many studies underlined the key role of NO in the maintenance of resting cerebral blood flow (CBF) as well as in the mechanisms that control cerebrovascular tone: autoregulation and neurovascular coupling. However, although the role of NO in the control of CBF has been largely investigated, the complexity of the NO system and the lack of specific NO synthase inhibitors led to still unresolved questions such as the origin of NO and the pathways by which it controls the vascular tone. In this chapter, the role of NO in the regulation of CBF is critically reviewed and discussed in the context of the neurovascular unit and the general principles of cerebrovascular regulation.

Recent structural and functional insights into the family of sodium calcium exchangers

Maintenance of calcium homeostasis is necessary for the development and survival of all animals. Calcium ions modulate excitability and bind effectors capable of initiating many processes such as muscular contraction and neurotransmission. However, excessive amounts of calcium in the cytosol or within intracellular calcium stores can trigger apoptotic pathways in cells that have been implicated in cardiac and neuronal pathologies. Accordingly, it is critical for cells to rapidly and effectively regulate calcium levels. The Na(+) /Ca(2+) exchangers (NCX), Na(+) /Ca(2+) /K(+) exchangers (NCKX), and Ca(2+) /Cation exchangers (CCX) are the three classes of sodium calcium antiporters found in animals. These exchanger proteins utilize an electrochemical gradient to extrude calcium. Although they have been studied for decades, much is still unknown about these proteins. In this review, we examine current knowledge about the structure, function, and physiology and also discuss their implication in various developmental disorders. Finally, we highlight recent data characterizing the family of sodium calcium exchangers in the model system, Caenorhabditis elegans, and propose that C. elegans may be an ideal model to complement other systems and help fill gaps in our knowledge of sodium calcium exchange biology.

Mitochondrial Dynamics in Retinal Ganglion Cell Axon Regeneration and Growth Cone Guidance

Failed axon regeneration and retinal ganglion cell (RGC) death after trauma or disease, including glaucomatous and mitochondrial optic neuropathies, are increasingly linked to mitochondrial dysfunction. Mitochondria are highly dynamic organelles whose size, organization, and function are regulated by a balance between mitochondrial fission and fusion. Mitochondria are ubiquitous in axonal growth cones both in vitro and in vivo and during development and regeneration. However, the roles that mitochondrial fission and fusion dynamics play in the growth cone during axon regeneration are largely unstudied. Here we discuss recent data suggesting mitochondria in the distal axon and growth cone play a central role in axon growth by integrating intrinsic axon growth states with signaling from extrinsic cues. Mitochondrial fission and fusion are intrinsically regulated in the distal axon in the growth cones of acutely purified embryonic and postnatal RGCs with differing intrinsic axon growth potentials. These differences in fission and fusion correlate with differences in mitochondrial bioenergetics; embryonic RGCs with high intrinsic axon growth potential rely more on glycolysis whereas RGCs with low intrinsic axon growth potential rely more on oxidative phosphorylation. Mitochondrial fission and fusion are also differentially modulated by KLFs that either promote or suppress intrinsic axon growth, and altering the balance between mitochondrial fission and fusion can differentially regulate axon growth rate and growth cone guidance responses to both inhibitory and permissive guidance cues.

Calcium entry and α-synuclein inclusions elevate dendritic mitochondrial oxidant stress in dopaminergic neurons

The core motor symptoms of Parkinson's disease (PD) are attributable to the degeneration of dopaminergic neurons in the substantia nigra pars compacta (SNc). Mitochondrial oxidant stress is widely viewed a major factor in PD pathogenesis. Previous work has shown that activity-dependent calcium entry through L-type channels elevates perinuclear mitochondrial oxidant stress in SNc dopaminergic neurons, providing a potential basis for their selective vulnerability. What is less clear is whether this physiological stress is present in dendrites and if Lewy bodies, the major neuropathological lesion found in PD brains, exacerbate it. To pursue these questions, mesencephalic dopaminergic neurons derived from C57BL/6 transgenic mice were studied in primary cultures, allowing for visualization of soma and dendrites simultaneously. Many of the key features of in vivo adult dopaminergic neurons were recapitulated in vitro. Activity-dependent calcium entry through L-type channels increased mitochondrial oxidant stress in dendrites. This stress progressively increased with distance from the soma. Examination of SNc dopaminergic neurons ex vivo in brain slices verified this pattern. Moreover, the formation of intracellular α-synuclein Lewy-body-like aggregates increased mitochondrial oxidant stress in perinuclear and dendritic compartments. This stress appeared to be extramitochondrial in origin, because scavengers of cytosolic reactive oxygen species or inhibition of NADPH oxidase attenuated it. These results show that physiological and proteostatic stress can be additive in the soma and dendrites of vulnerable dopaminergic neurons, providing new insight into the factors underlying PD pathogenesis.

The membrane-active tri-block copolymer pluronic F-68 profoundly rescues rat hippocampal neurons from oxygen-glucose deprivation-induced death through early inhibition of apoptosis

Pluronic F-68, an 80% hydrophilic member of the Pluronic family of polyethylene-polypropylene-polyethylene tri-block copolymers, protects non-neuronal cells from traumatic injuries and rescues hippocampal neurons from excitotoxic and oxidative insults. F-68 interacts directly with lipid membranes and restores membrane function after direct membrane damage. Here, we demonstrate the efficacy of Pluronic F-68 in rescuing rat hippocampal neurons from apoptosis after oxygen-glucose deprivation (OGD). OGD progressively decreased neuronal survival over 48 h in a severity-dependent manner, the majority of cell death occurring after 12 h after OGD. Administration of F-68 for 48 h after OGD rescued neurons from death in a dose-dependent manner. At its optimal concentration (30 μm), F-68 rescued all neurons that would have died after the first hour after OGD. This level of rescue persisted when F-68 administration was delayed 12 h after OGD. F-68 did not alter electrophysiological parameters controlling excitability, NMDA receptor-activated currents, or NMDA-induced increases in cytosolic calcium concentrations. However, F-68 treatment prevented phosphatidylserine externalization, caspase activation, loss of mitochondrial membrane potential, and BAX translocation to mitochondria, indicating that F-68 alters apoptotic mechanisms early in the intrinsic pathway of apoptosis. The profound neuronal rescue provided by F-68 after OGD and the high level of efficacy with delayed administration indicate that Pluronic copolymers may provide a novel, membrane-targeted approach to rescuing neurons after brain ischemia. The ability of membrane-active agents to block apoptosis suggests that membranes or their lipid components play prominent roles in injury-induced apoptosis.

Nitric oxide in skeletal muscle: role on mitochondrial biogenesis and function

Nitric oxide (NO) has been implicated in several cellular processes as a signaling molecule and also as a source of reactive nitrogen species (RNS). NO is produced by three isoenzymes called nitric oxide synthases (NOS), all present in skeletal muscle. While neuronal NOS (nNOS) and endothelial NOS (eNOS) are isoforms constitutively expressed, inducible NOS (iNOS) is mainly expressed during inflammatory responses. Recent studies have demonstrated that NO is also involved in the mitochondrial biogenesis pathway, having PGC-1α as the main signaling molecule. Increased NO synthesis has been demonstrated in the sarcolemma of skeletal muscle fiber and NO can also reversibly inhibit cytochrome c oxidase (Complex IV of the respiratory chain). Investigation on cultured skeletal myotubes treated with NO donors, NO precursors or NOS inhibitors have also showed a bimodal effect of NO that depends on the concentration used. The present review will discuss the new insights on NO roles on mitochondrial biogenesis and function in skeletal muscle. We will also focus on potential therapeutic strategies based on NO precursors or analogs to treat patients with myopathies and mitochondrial deficiency.

The complex contribution of NOS interneurons in the physiology of cerebrovascular regulation

Following the discovery of the vasorelaxant properties of nitric oxide (NO) by Furchgott and Ignarro, the finding by Bredt and coll. of a constitutively expressed NO synthase in neurons (nNOS) led to the presumption that neuronal NO may control cerebrovascular functions. Consequently, numerous studies have sought to determine whether neuraly-derived NO is involved in the regulation of cerebral blood flow (CBF). Anatomically, axons, dendrites, or somata of NO neurons have been found to contact the basement membrane of blood vessels or perivascular astrocytes in all segments of the cortical microcirculation. Functionally, various experimental approaches support a role of neuronal NO in the maintenance of resting CBF as well as in the vascular response to neuronal activity. Since decades, it has been assumed that neuronal NO simply diffuses to the local blood vessels and produce vasodilation through a cGMP-PKG dependent mechanism. However, NO is not the sole mediator of vasodilation in the cerebral microcirculation and is known to interact with a myriad of signaling pathways also involved in vascular control. In addition, cerebrovascular regulation is the result of a complex orchestration between all components of the neurovascular unit (i.e., neuronal, glial, and vascular cells) also known to produce NO. In this review article, the role of NO interneuron in the regulation of cortical microcirculation will be discussed in the context of the neurovascular unit.

Molecular identity and functional properties of the mitochondrial Na+/Ca2+ exchanger

The mitochondrial membrane potential that powers the generation of ATP also facilitates mitochondrial Ca(2+) shuttling. This process is fundamental to a wide range of cellular activities, as it regulates ATP production, shapes cytosolic and endoplasmic recticulum Ca(2+) signaling, and determines cell fate. Mitochondrial Ca(2+) transport is mediated primarily by two major transporters: a Ca(2+) uniporter that mediates Ca(2+) uptake and a Na(+)/Ca(2+) exchanger that subsequently extrudes mitochondrial Ca(2+). In this minireview, we focus on the specific role of the mitochondrial Na(+)/Ca(2+) exchanger and describe its ion exchange mechanism, regulation by ions, and putative partner proteins. We discuss the recent molecular identification of the mitochondrial exchanger and how its activity is linked to physiological and pathophysiological processes.

Comparative impact of voltage-gated calcium channels and NMDA receptors on mitochondria-mediated neuronal injury

Glutamate excitotoxicity, a major component of many neurodegenerative disorders, is characterized by excessive calcium influx selectively through NMDARs. However, there is a substantial uncertainty concerning why other known routes of significant calcium entry, in particular, VGCCs, are not similarly toxic. Here, we report that in the majority of neurons in rat hippocampal and cortical cultures, maximal L-type VGCC activation induces much lower calcium loading than toxic NMDAR activation. Consequently, few depolarization-activated neurons exhibit calcium deregulation and cell death. Activation of alternative routes of calcium entry induced neuronal death in proportion to the degree of calcium loading. In a small subset of neurons, depolarization evoked stronger calcium elevations, approaching those induced by toxic NMDA. These neurons were characterized by elevated expression of VGCCs and enhanced voltage-gated calcium currents, mitochondrial dysfunction and cell death. Preventing VGCC-dependent mitochondrial calcium loading resulted in stronger cytoplasmic calcium elevations, whereas inhibiting mitochondrial calcium clearance accelerated mitochondrial depolarization. Both observations further implicate mitochondrial dysfunction in VGCC-mediated cell death. Results indicate that neuronal vulnerability tracks the extent of calcium loading but does not appear to depend explicitly on the route of calcium entry.

SUMO modification of cell surface Kv2.1 potassium channels regulates the activity of rat hippocampal neurons

Voltage-gated Kv2.1 potassium channels are important in the brain for determining activity-dependent excitability. Small ubiquitin-like modifier proteins (SUMOs) regulate function through reversible, enzyme-mediated conjugation to target lysine(s). Here, sumoylation of Kv2.1 in hippocampal neurons is shown to regulate firing by shifting the half-maximal activation voltage (V_1/2) of channels up to 35 mV. Native SUMO and Kv2.1 are shown to interact within and outside channel clusters at the neuronal surface. Studies of single, heterologously expressed Kv2.1 channels show that only K470 is sumoylated. The channels have four subunits, but no more than two non-adjacent subunits carry SUMO concurrently. SUMO on one site shifts V_1/2 by 15 mV, whereas sumoylation of two sites produces a full response. Thus, the SUMO pathway regulates neuronal excitability via Kv2.1 in a direct and graded manner.

Mitochondrial membrane potential probes and the proton gradient: a practical usage guide

Fluorescent probes for monitoring mitochondrial membrane potential are frequently used for assessing mitochondrial function, particularly in the context of cell fate determination in biological and biomedical research. However, valid interpretation of results obtained with such probes requires careful consideration of numerous controls, as well as possible effects of non-protonic charges on dye behavior. In this context, we provide an overview of some of the important technical considerations, controls, and parallel complementary assays that can be employed to help ensure appropriate interpretation of results, thus providing a practical usage guide for monitoring mitochondrial membrane potentials with cationic probes. In total, this review will help illustrate both the strengths and potential pitfalls of common mitochondrial membrane potential dyes, and highlight best-usage approaches for their efficacious application in life sciences research.

SPG20 protein spartin associates with cardiolipin via its plant-related senescence domain and regulates mitochondrial Ca2+ homeostasis

Hereditary spastic paraplegias (HSPs) are a group of neurological disorders characterized clinically by spasticity of lower limbs and pathologically by degeneration of the corticospinal tract. Troyer syndrome is an autosomal recessive HSP caused by a frameshift mutation in the spartin (SPG20) gene. Previously, we established that this mutation results in a lack of expression of the truncated mutant spartin protein. Spartin is involved in many cellular processes and associates with several intracellular organelles, including mitochondria. Spartin contains a conserved plant-related senescence domain at its C-terminus. However, neither the function of this domain nor the roles of spartin in mitochondrial physiology are currently known. In this study, we determined that the plant-related senescence domain of spartin interacts with cardiolipin but not with two other major mitochondrial phospholipids, phosphatidylcholine and phosphatidylethanolamine. We also found that knockdown of spartin by small interfering RNA in a human neuroblastoma cell line resulted in depolarization of the mitochondrial membrane. In addition, depletion of spartin resulted in a significant decrease in both mitochondrial calcium uptake and mitochondrial membrane potential in cells treated with thapsigargin. Our results suggest that impairment of mitochondrial calcium uptake might contribute to the neurodegeneration of long corticospinal axons and the pathophysiology of Troyer syndrome.

Endoplasmic reticulum Ca2+ signaling and mitochondrial Cyt c release in astrocytes following oxygen and glucose deprivation

In the present study, we investigated changes of cytosolic Ca2+([Ca2+](cyt)), endoplasmic reticulum Ca2+([Ca2+](ER)) and mitochondrial Ca2+(Ca2+(m)) in astrocytes following oxygen/glucose deprivation and reoxygenation (OGD/REOX). Two hours OGD did not cause changes in [Ca2+](cyt), but led to a significant increase in [Ca2+](ER). The elevation in [Ca2+](ER) continued and reached a peak level (130 +/- 2 microM) by 90 min REOX. An abrupt release of Ca2+(ER) occurred during 1.5-2.5 h REOX, which was accompanied with a delayed and sustained rise in [Ca2+](cyt). Moreover, Ca2+(m) content was increased significantly within 15 min REOX followed by a secondary rise (approximately 4.5-fold) and a release of mitochondrial cytochrome c (Cyt c). Astrocytes exhibited translocation of Cyt c from mitochondria to endoplasmic reticulum (ER) and up regulation of ER stress protein p-eIF2alpha. Blocking Na+-K+-Cl(-) cotransporter isoform 1 activity, either by its potent inhibitor bumetanide or genetic ablation, abolished release of ER Ca2+, delayed rise in [Ca2+](cyt) and Ca2+(m). Inhibition of the reverse mode operation of the Na+/Ca2+ exchanger significantly attenuated OGD/REOX-mediated Cyt c release. In summary, this study illustrates that OGD/REOX triggers a time-dependent loss of Ca2+ homeostasis in cytosol and organelles (ER and mitochondria) in astrocytes. Collective stimulation of Na+-K+-Cl(-) cotransporter isoform 1 and reverse mode function of Na+/Ca2+ exchanger contributes to these changes.

Calcium dysregulation induces apoptosis-inducing factor release: cross-talk between PARP-1- and calpain-signaling pathways

Recent discoveries show that caspase-independent cell death pathways are a pervasive mechanism in neurodegenerative diseases, and apoptosis-inducing factor (AIF) is an important effector of this mode of neuronal death. There are currently two known mechanisms underlying AIF release following excitotoxic stress, PARP-1 and calpain. To test whether there is an interaction between PARP-1 and calpain in triggering AIF release, we used the NMDA toxicity model in rat primary cortical neurons. Exposure to NMDA resulted in AIF truncation and nuclear translocation, and shRNA-mediated knockdown of AIF resulted in neuroprotection. Both calpain and PARP-1 are involved with AIF processing as AIF truncation, nuclear translocation and neuronal death were attenuated by calpain inhibition using adeno-associated virus-mediated overexpression of the endogenous calpain inhibitor, calpastatin, or treatment with the PARP-1 inhibitor 3-ABA. Activation of PARP-1 is necessary for calpain activation as PARP-1 inhibition blocked mitochondrial calpain activation. Finally, NMDA toxicity induces mitochondrial Ca(2+) dysregulation in a PARP-1 dependent manner. Thus, PARP-1 and mitochondrial calpain activation are linked via PARP-1-induced alterations in mitochondrial Ca(2+) homeostasis. Collectively, these findings link the two seemingly independent mechanisms triggering AIF-induced neuronal death.

Sodium channel activation augments NMDA receptor function and promotes neurite outgrowth in immature cerebrocortical neurons

A range of extrinsic signals, including afferent activity, affect neuronal growth and plasticity. Neuronal activity regulates intracellular Ca(2+), and activity-dependent calcium signaling has been shown to regulate dendritic growth and branching (Konur and Ghosh, 2005). NMDA receptor (NMDAR) stimulation of Ca(2+)/calmodulin-dependent protein kinase signaling cascades has, moreover, been demonstrated to regulate neurite/axonal outgrowth (Wayman et al., 2004). We used a sodium channel activator, brevetoxin (PbTx-2), to explore the relationship between intracellular [Na(+)] and NMDAR-dependent development. PbTx-2 alone, at a concentration of 30 nM, did not affect Ca(2+) dynamics in 2 d in vitro cerebrocortical neurons; however, this treatment robustly potentiated NMDA-induced Ca(2+) influx. The 30 nM PbTx-2 treatment produced a maximum [Na(+)](i) of 16.9 +/- 1.5 mM, representing an increment of 8.8 +/- 1.8 mM over basal. The corresponding membrane potential change produced by 30 nM PbTx-2 was modest and, therefore, insufficient to relieve the voltage-dependent Mg(2+) block of NMDARs. To unambiguously demonstrate the enhancement of NMDA receptor function by PbTx-2, we recorded single-channel currents from cell-attached patches. PbTx-2 treatment was found to increase both the mean open time and open probability of NMDA receptors. These effects of PbTx-2 on NMDA receptor function were dependent on extracellular Na(+) and activation of Src kinase. The functional consequences of PbTx-2-induced enhancement of NMDAR function were evaluated in immature cerebrocortical neurons. PbTx-2 concentrations between 3 and 300 nM enhanced neurite outgrowth. Voltage-gated sodium channel activators may accordingly represent a novel pharmacologic strategy to regulate neuronal plasticity through an NMDA receptor and Src family kinase-dependent mechanism.

Nitric oxide in health and disease of the nervous system

Nitric oxide (NO) is an important messenger molecule in a variety of physiological systems. NO, a gas, is produced from L-arginine by different isoforms of nitric oxide synthase (NOS) and serves many normal physiologic purposes, such as promoting vasodilation of blood vessels and mediating communication between nervous system cells. In addition to its physiologic actions, free radical activity of NO can cause cellular damage through a phenomenon known as nitrosative stress. Here, we review the role of NO in health and disease, focusing on its role in function and dysfunction of the nervous system. Substantial evidence indicates that NO plays a key role in most common neurodegenerative diseases, and, although the mechanism of NO-mediated neurodegeneration remains uncertain, studies suggest several possibilities. NO has been shown to modify protein function by nitrosylation and nitrotyrosination, contribute to glutamate excitotoxicity, inhibit mitochondrial respiratory complexes, participate in organelle fragmentation, and mobilize zinc from internal stores. In this review, we discuss and analyze the evidence for each of these mechanisms in different neurodegenerative diseases and propose future directions for research of the role of NO in neurodegeneration.

Role of the mitochondrial sodium/calcium exchanger in neuronal physiology and in the pathogenesis of neurological diseases

In neurons, as in other excitable cells, mitochondria extrude Ca(2+) ions from their matrix in exchange with cytosolic Na(+) ions. This exchange is mediated by a specific transporter located in the inner mitochondrial membrane, the mitochondrial Na(+)/Ca(2+) exchanger (NCX(mito)). The stoichiometry of NCX(mito)-operated Na(+)/Ca(2+) exchange has been the subject of a long controversy, but evidence of an electrogenic 3 Na(+)/1 Ca(2+) exchange is increasing. Although the molecular identity of NCX(mito) is still undetermined, data obtained in our laboratory suggest that besides the long-sought and as yet unfound mitochondrial-specific NCX, the three isoforms of plasmamembrane NCX can contribute to NCX(mito) in neurons and astrocytes. NCX(mito) has a role in controlling neuronal Ca(2+) homeostasis and neuronal bioenergetics. Indeed, by cycling the Ca(2+) ions captured by mitochondria back to the cytosol, NCX(mito) determines a shoulder in neuronal [Ca(2+)](c) responses to neurotransmitters and depolarizing stimuli which may then outlast stimulus duration. This persistent NCX(mito)-dependent Ca(2+) release has a role in post-tetanic potentiation, a form of short-term synaptic plasticity. By controlling [Ca(2+)](m) NCX(mito) regulates the activity of the Ca(2+)-sensitive enzymes pyruvate-, alpha-ketoglutarate- and isocitrate-dehydrogenases and affects the activity of the respiratory chain. Convincing experimental evidence suggests that supraphysiological activation of NCX(mito) contributes to neuronal cell death in the ischemic brain and, in epileptic neurons coping with seizure-induced ion overload, reduces the ability to reestablish normal ionic homeostasis. These data suggest that NCX(mito) could represent an important target for the development of new neurological drugs.

Alternative translation initiation in rat brain yields K2P2.1 potassium channels permeable to sodium

K(2P) channels mediate potassium background currents essential to central nervous system function, controlling excitability by stabilizing membrane potential below firing threshold and expediting repolarization. Here, we show that alternative translation initiation (ATI) regulates function of K(2P)2.1 (TREK-1) via an unexpected strategy. Full-length K(2P)2.1 and an isoform lacking the first 56 residues of the intracellular N terminus (K(2P)2.1Delta1-56) are produced differentially in a regional and developmental manner in the rat central nervous system, the latter passing sodium under physiological conditions leading to membrane depolarization. Control of ion selectivity via ATI is proposed to be a natural, epigenetic mechanism for spatial and temporal regulation of neuronal excitability.

Platelet-activating factor-induced chloride channel activation is associated with intracellular acidosis and apoptosis of intestinal epithelial cells

Platelet-activating factor (PAF) is a phospholipid inter- and intracellular mediator implicated in intestinal injury primarily via induction of an inflammatory cascade. We find that PAF also has direct pathological effects on intestinal epithelial cells (IEC). PAF induces Cl(-) channel activation, which is associated with intracellular acidosis and apoptosis. Using the rat small IEC line IEC-6, electrophysiological experiments demonstrated that PAF induces Cl(-) channel activation. This PAF-activated Cl(-) current was inhibited by Ca(2+) chelation and a calcium calmodulin kinase II inhibitor, suggesting PAF activation of a Ca(2+)-activated Cl(-) channel. To determine the pathological consequences of Cl(-) channel activation, microfluorimetry experiments were performed, which revealed PAF-induced intracellular acidosis, which is also inhibited by the Cl(-) channel inhibitor 4,4'diisothiocyanostilbene-2,2'disulfonic acid and Ca(2+) chelation. PAF-induced intracellular acidosis is associated with caspase 3 activation and DNA fragmentation. PAF-induced caspase activation was abolished in cells transfected with a pH compensatory Na/H exchanger construct to enhance H(+) extruding ability and prevent intracellular acidosis. As ClC-3 is a known intestinal Cl(-) channel dependent on both Ca(2+) and calcium calmodulin kinase II phosphorylation, we generated ClC-3 knockdown cells using short hairpin RNA. PAF induced Cl(-) current; acidosis and apoptosis were all significantly decreased in ClC-3 knockdown cells. Our data suggest a novel mechanism of PAF-induced injury by which PAF induces intracellular acidosis via activation of the Ca(2+)-dependent Cl(-) channel ClC-3, resulting in apoptosis of IEC.

[Ganoderma spores may regulate the levels of mitochondria-related molecular substances in hippocampus of young rats birthed by rats with gestational hypertension]

OBJECTIVE

To investigate the effects of Ganoderma spores on mitochondria-related molecular substances in hippocampus of young rats birthed by rats with gestational hypertension.

METHODS

Nitric oxide synthase (NOS) inhibitor Nw-nitro-L-arginine methylester (L-NAME) was intraperitoneally injected into pregnant rats to induce gestational hypertension, and Ganoderma spores were administered orally. The effects of Ganoderma spores on levels of mitochondria-related molecular substances in hippocampus of young rats birthed by the rats with gestational hypertension were evaluated with immunoradiometric assay of cAMP, RT-PCR analysis of related genes, and detection of enzyme activity.

RESULTS

In hippocampus of the new-born rats birthed by rats with gestational hypertension, the cAMP level, mitochondrial DNA (mtDNA) level and adenosine triphosphatase (ATPase) activity were decreased, and the expression level of peroxisome proliferator activated receptor gamma coactivator 1 alpha (pgc1 alpha) was unchanged compared to the normal control group. The cAMP level, mtDNA level, ATPase activity and pgc1 alpha expression level in hippocampus of 30-day post-natal rats were lower than those of the rats in normal control group. After oral administration of Ganoderma spores, the cAMP and mtDNA levels in hippocampus of the new-born rats and 30-day post-natal rats recovered almost to the levels of normal control rats, and the ATPase activity and pgc1 alpha expression level were also increased significantly.

CONCLUSION

Ganoderma spores may regulate the levels of mitochondria-related molecular substances in hippocampus of young rats birthed by rats with gestational hypertension.

mAtNOS1 regulates mitochondrial functions and apoptosis of human neuroblastoma cells

mAtNOS1 is a novel gene recently reported in mammalian cells with functions that are not fully understood. The present study generated human neuroblastoma SHSY cells over- and underexpressing mAtNOS1 and shows that mAtNOS1 is involved in regulating mitochondrial nitric oxide, mitochondrial transmembrane potential, protein tyrosine nitration, cytochrome c release, and apoptosis of those cells.

Interaction of cyanide and nitric oxide with cytochrome c oxidase: implications for acute cyanide toxicity

Acute cyanide toxicity is attributed to inhibition of cytochrome c oxidase (CcOX), the oxygen-reducing component of mitochondrial electron transport; however, the mitochondrial action of cyanide is complex and not completely understood. State-3 oxygen consumption and CcOX activity were studied in rat N27 mesencephalic cells to examine the functional interaction of cyanide and nitric oxide (NO). KCN produced a concentration-dependent inhibition of cellular respiration. Cyanide's median inhibitory concentration (IC50) of oxygen consumption (13.2 +/- 1.8microM) was higher than the CcOX IC50 (7.2 +/- 0.1microM). Based on respiratory threshold analysis, 60% inhibition of CcOX was necessary before oxygen consumption was decreased. Addition of high levels of exogenous NO (100microM S-nitroso-N-acetyl-DL-penicillamine) attenuated cyanide inhibition of both respiration and CcOX. On the other hand, when endogenous NO generation was blocked by an NOS inhibitor (N(omega)-monomethyl-L-arginine ester), the cyanide IC50 for both respiration and CcOX increased to 59.6 +/- 0.9microM and 102 +/- 10microM, respectively, thus showing constitutive, low-level NO production enhanced cyanide inhibition. Laser scanning cytometry showed that cyanide elevated mitochondrial NO, which then was available to interact with CcOX to enhance the inhibition. It is concluded that the rapid, potent action of cyanide is due in part to mitochondrial generation of NO, which enhances inhibition of CcOX. At low mitochondrial oxygen tensions, the cyanide-NO interaction would be increased. Also, the antidotal action of sodium nitrite is partly explained by generation of high mitochondrial levels of NO, which antagonizes the CcOX inhibition.

NMDA and non-NMDA receptor-mediated differential Ca2+ load and greater vulnerability of motor neurons in spinal cord cultures

Glutamate receptor activated neuronal cell death has been implicated in the pathogenesis of motor neuron disease but the molecular mechanism responsible for neuronal dysfunction needs to be elucidated. In the present study, we examined the contribution of NMDA and non-NMDA sub-types of glutamate receptors in selective vulnerability of motor neurons. Glutamate receptor activated Ca2+ signaling, mitochondrial functions and neurotoxicity in motor neurons and other spinal neurons were studied in mixed spinal cord primary cultures. Exposure of cells to glutamate receptor agonists glutamate, NMDA and AMPA elevated the intracellular Ca2+, mitochondrial Ca2+ and caused mitochondrial depolarization and cytotoxicity in both motor neurons and other spinal neurons but a striking difference was observed in the magnitude and temporal patterns of the [Ca2+]i responses between the two neuronal cell types. The motor neurons elicited higher Ca2+ load than the other spinal neurons and the [Ca2+]i levels were elevated for a longer duration in motor neurons. AMPA receptor stimulation was more effective than NMDA. Both the NMDA and non-NMDA receptor antagonists APV and NBQX inhibited the Ca2+ entry and decreased the cell death significantly; however, NBQX was more potent than APV. Our results demonstrate that both NMDA and non-NMDA sub-types of glutamate receptors contribute to glutamate-mediated motor neuron damage but AMPA receptors play the major role. AMPA receptor-mediated excessive Ca2+ load and differential handling/regulation of Ca2+ buffering by mitochondria in motor neurons could be central in their selective vulnerability to excitotoxicity.

Role of Na+-K+-Cl−cotransport and Na+/Ca2+exchange in mitochondrial dysfunction in astrocytes following in vitro ischemia

Na+-K+-Cl−cotransporter isoform 1 (NKCC1) and reverse mode operation of the Na+/Ca2+exchanger (NCX) contribute to intracellular Na+and Ca2+overload in astrocytes following oxygen-glucose deprivation (OGD) and reoxygenation (REOX). Here, we further investigated whether NKCC1 and NCX play a role in mitochondrial Ca2+(Cam2+) overload and dysfunction. OGD/REOX caused a doubling of mitochondrial-releasable Ca2+( P < 0.05). When NKCC1 was inhibited with bumetanide, the mitochondrial-releasable Ca2+was reduced by ∼42% ( P < 0.05). Genetic ablation of NKCC1 also reduced Cam2+accumulation. Moreover, OGD/REOX in NKCC1+/+astrocytes caused dissipation of the mitochondrial membrane potential (Ψm) to 42 ± 3% of controls. In contrast, when NKCC1 was inhibited with bumetanide, depolarization of Ψmwas attenuated significantly (66 ± 10% of controls, P < 0.05). Cells were also subjected to severe in vitro hypoxia by superfusion with a hypoxic, acidic, ion-shifted Ringer buffer (HAIR). HAIR/REOX triggered a secondary, sustained rise in intracellular Ca2+that was attenuated by reversal NCX inhibitor KB-R7943. The hypoxia-mediated increase in Cam2+was accompanied by loss of Ψmand cytochrome c release in NKCC1+/+astrocytes. Bumetanide or genetic ablation of NKCC1 attenuated mitochondrial dysfunction and astrocyte death following ischemia. Our study suggests that NKCC1 acting in concert with NCX causes a perturbation of Cam2+homeostasis and mitochondrial dysfunction and cell death following in vitro ischemia.

The potential role of mitochondria in pediatric traumatic brain injury

Mitochondria play a central role in cerebral energy metabolism, intracellular calcium homeostasis and reactive oxygen species generation and detoxification. Following traumatic brain injury (TBI), the degree of mitochondrial injury or dysfunction can be an important determinant of cell survival or death. Literature would suggest that brain mitochondria from the developing brain are very different from those from mature animals. Therefore, aspects of developmental differences in the mitochondrial response to TBI can make the immature brain more vulnerable to traumatic injury. This review will focus on four main areas of secondary injury after pediatric TBI, including excitotoxicity, oxidative stress, alterations in energy metabolism and cell death pathways. Specifically, we will describe what is known about developmental differences in mitochondrial function in these areas, in both the normal, physiologic state and the pathologic state after pediatric TBI. The ability to identify and target aspects of mitochondrial dysfunction could lead to novel neuroprotective therapies for infants and children after severe TBI.

Mitochondrial fission is an upstream and required event for bax foci formation in response to nitric oxide in cortical neurons

Mitochondrial dysfunction is an underpinning event in many neurodegenerative disorders. Less clear, however, is how mitochondria become injured during neuronal demise. Nitric oxide (NO) evokes rapid mitochondrial fission in cortical neurons. Interestingly, proapoptotic Bax relocates from the cytoplasm into large foci on mitochondrial scission sites in response to nitrosative stress. Antiapoptotic Bcl-xL does not prevent mitochondrial fission despite its ability to block Bax puncta formation on mitochondria and to mitigate neuronal cell death. Mitofusin 1 (Mfn1) or dominant-negative dynamin-related protein 1(K38A) (Drp1(k38A)) inhibits mitochondrial fission and Bax accumulation on mitochondria induced by exposure to an NO donor. Although NO is known to cause a bioenergetic crisis, lowering ATP by glycolytic or mitochondrial inhibitors neither induces mitochondrial fission nor Bax foci formation on mitochondria. Taken together, these data indicate that the mitochondrial fission machinery acts upstream of the Bcl-2 family of proteins in neurons challenged with nitrosative stress.

CLC-3 Channels Modulate Excitatory Synaptic Transmission in Hippocampal Neurons

It is well established that ligand-gated chloride flux across the plasma membrane modulates neuronal excitability. We find that a voltage-dependent Cl(-) conductance increases neuronal excitability in immature rodents as well, enhancing the time course of NMDA receptor-mediated miniature excitatory postsynaptic potentials (mEPSPs). This Cl(-) conductance is activated by CaMKII, is electrophysiologically identical to the CaMKII-activated CLC-3 conductance in nonneuronal cells, and is absent in clc-3(-/-) mice. Systematically decreasing [Cl(-)](i) to mimic postnatal [Cl(-)](i) regulation progressively decreases the amplitude and decay time constant of spontaneous mEPSPs. This Cl(-)-dependent change in synaptic strength is absent in clc-3(-/-) mice. Using surface biotinylation, immunohistochemistry, electron microscopy, and coimmunoprecipitation studies, we find that CLC-3 channels are localized on the plasma membrane, at postsynaptic sites, and in association with NMDA receptors. This is the first demonstration that a voltage-dependent chloride conductance modulates neuronal excitability. By increasing postsynaptic potentials in a Cl(-) dependent fashion, CLC-3 channels regulate neuronal excitability postsynaptically in immature neurons.

Nitric oxide, cell bioenergetics and neurodegeneration

Following stimulation of NMDA receptors, neurons transiently synthesize nitric oxide (NO) in a calcium/calmodulin-dependent manner through the activation of neuronal NO synthase. Nitric oxide acts as a messenger, activating soluble guanylyl cyclase and participating in the transduction signalling pathways involving cyclic GMP. Nitric oxide also binds to cytochrome c oxidase, and is able to inhibit cell respiration in a process that is reversible and in competition with oxygen. This action can also lead to the release of superoxide anion from the mitochondrial respiratory chain. Here, we discuss recent evidence that this mitochondrial interaction represents a molecular switch for cell signalling pathways involved in the control of physiological functions. These include superoxide- or oxygen-dependent modulation of gene transcription, calcium-dependent cell signalling responses, changes in the mitochondrial membrane potential or AMP-activated protein kinase-dependent control of glycolysis. In pathophysiological conditions, such as brain ischaemia or neurological disorders, NO is formed excessively by NMDA receptor over-activation in neurons, or by inducible NO synthase from neighbouring glia (microglial cells and astrocytes). Elevated NO concentrations can then interact with superoxide anion, generated by the mitochondria or by other mechanisms, leading to the formation of the powerful oxidant species peroxynitrite. During pathological conditions activation of the NAD(+)-consuming enzyme poly(APD-ribose) polymerase-1 (PARP-1) is also a likely mechanism for NO-mediated energy failure and neurotoxicity. Activation of PARP-1 is, however, a repair process, which in milder forms of oxidative stress protects neurons from death. Thus, whilst NO plays a physiological role in neuronal cell signalling, its over-production may cause neuronal energy compromise leading to neurodegeneration.

Simultaneous monitoring of ionophore- and inhibitor-mediated plasma and mitochondrial membrane potential changes in cultured neurons

Although natural and synthetic ionophores are widely exploited in cell studies, for example, to influence cytoplasmic free calcium concentrations and to depolarize in situ mitochondria, their inherent lack of membrane selectivity means that they affect the ion permeability of both plasma and mitochondrial membranes. A similar ambiguity affects the interpretation of signals from fluorescent membrane-permeant cations (usually termed "mitochondrial membrane potential indicators"), because the accumulation of these probes is influenced by both plasma and mitochondrial membrane potentials. To resolve some of these problems a technique is developed to allow simultaneous monitoring of plasma and mitochondrial membrane potentials at single-cell resolution using a cationic and anionic fluorescent probe. A computer program is described that transforms the fluorescence changes into dynamic estimates of changes in plasma and mitochondrial potentials. Exploiting this technique, primary cultures of rat cerebellar granule neurons display a concentration-dependent response to ionomycin: low concentrations mimic nigericin by hyperpolarizing the mitochondria while slowly depolarizing the plasma membrane and maintaining a stable elevated cytoplasmic calcium. Higher ionomycin concentrations induce a stochastic failure of calcium homeostasis that precedes both mitochondrial depolarization and an enhanced rate of plasma membrane depolarization. In addition, the protonophore carbonyl cyanide p-trifluoromethoxyphenylhydrazone only selectively depolarizes mitochondria at submicromolar concentrations. ATP synthase reversal following respiratory chain inhibition depolarizes the mitochondria by 26 mV.

Ester Derivatives of Tournefolic Acid B Attenuate N-Methyl-d-aspartate-Mediated Excitotoxicity in Rat Cortical Neurons

The effects of tournefolic acid B (TAB) and two ester derivatives, TAB methyl ester (TABM) and TAB ethyl ester (TABE), on N-methyl-D-aspartate (NMDA)-mediated excitotoxicity and the underlying mechanisms were investigated. Treatment with 50 microM NMDA elicited neuronal death by 48.7 +/- 5.1%, coinciding with the appearance of injured morphology. TABM (50 microM) attenuated the NMDA-induced cell death by 60.9 +/- 19.7%, and to a lesser extent by TABE. The NMDA-mediated activation of calpain was not affected by TABM and TABE, as determined by the cleavage of alpha-spectrin. NMDA increased the activity of caspases 2, 3, 6, 8, and 9 and reached the maximum after 8-h treatment. TABM and TABE abrogated NMDA-induced activation of caspases 2, 3, 6, and 8 by approximately 80 to 90% and 50 to 60%, respectively, and to a higher extent for caspase 9. TABM and TABE also blocked the NMDA-mediated activation of caspase 12. Furthermore, TABM and TABE eliminated the NMDA-induced accumulation of superoxide anion (O2-*). NMDA evoked significant depolarization of mitochondria, whereas TABM elicited a mild decrease of mitochondrial membrane potential as determined by tetramethylrhodamine methyl ester perchlorate. NMDA treatment induced elevation of Ca2+ levels in cytosol, endoplasmic reticulum (ER), and mitochondria. TABM (50 microM) significantly diminished the NMDA-induced elevation of Ca2+ levels in mitochondria and ER but not cytosol. Therefore, TABM decreased mitochondrial membrane potential and attenuated the NMDA-mediated Ca2+-loading in ER and mitochondria. These events subsequently eliminated the accumulation of O2-* and blocked the activation of caspase cascade, thereby conferring their neuroprotective effects on NMDA-mediated excitotoxicity.