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John H Weiss

Publications and source records attributed to John H Weiss.

13 recordsLinked to original sources
PubMed2006

BMAA selectively injures motor neurons via AMPA/kainate receptor activation.

The toxin beta-methylamino-l-alanine (BMAA) has been proposed to contribute to amyotrophic lateral sclerosis-Parkinsonism Dementia Complex of Guam (ALS/PDC) based on its ability to induce a similar disease phenotype in primates and its presence in cycad seeds, which constituted a dietary item in afflicted populations. Concerns about the apparent low potency of this toxin in relation to estimated levels of human ingestion led to a slowing of BMAA research. However, recent reports identifying potential new routes of exposure compel a re-examination of the BMAA/cycad hypothesis. BMAA was found to induce selective motor neuron (MN) loss in dissociated mixed spinal cord cultures at concentrations ( approximately 30 muM) significantly lower than those previously found to induce widespread neuronal degeneration. The glutamate receptor antagonist NBQX prevented BMAA-induced death, implicating excitotoxic activation of AMPA/kainate receptors. Using microfluorimetric techniques, we further found that BMAA induced preferential [Ca(2+)](i) rises and selective reactive oxygen species (ROS) generation in MNs with minimal effect on other spinal neurons. Cycad seed extracts also triggered preferential AMPA/kainate-receptor-dependent MN injury, consistent with the idea that BMAA is a crucial toxic component in this plant. Present findings support the hypothesis that BMAA may contribute to the selective MN loss in ALS/PDC.

Amino Acids, Diamino↗
PubMed2006

Calcium-permeable AMPA channels in neurodegenerative disease and ischemia.

Compelling evidence supports contributions of glutamate receptor overactivation ('excitotoxicity') to neurodegeneration in both acute conditions, such as stroke, and chronic neurodegenerative conditions, such as amyotrophic lateral sclerosis. However, anti-excitotoxic therapeutic trials, which have generally targeted highly Ca2+ permeable NMDA-type glutamate channels, have to date failed to demonstrate impressive efficacy. Whereas most AMPA type glutamate channels are Ca2+ impermeable, an evolving body of evidence supports the contention that relatively unusual Ca2+ permeable AMPA channels might be crucial contributors to injury in these conditions. These channels are preferentially expressed in discrete neuronal subpopulations, and their numbers appear to be upregulated in amyotrophic lateral sclerosis and stroke. In addition, unlike NMDA channels, Ca2+ permeable AMPA channels are not blocked by Mg2+, but are highly permeable to another potentially harmful endogenous cation, Zn2+. The targeting of these channels might provide efficacious new avenues in the therapy of certain neurological diseases.

Amyotrophic Lateral Sclerosis↗
PubMed2005

Tumor necrosis-factor-alpha (TNF-alpha) induces rapid insertion of Ca2+-permeable alpha-amino-3-hydroxyl-5-methyl-4-isoxazole-propionate (AMPA)/kainate (Ca-A/K) channels in a subset of hippocampal pyramidal neurons.

The presence of cell surface Ca2+ permeable alpha-amino-3-hydroxyl-5-methyl-4-isoxazole-propionate (AMPA)/kainate (Ca-A/K) channels on subsets of central neurons influences both normal physiological function and vulnerability to excitotoxicity. Factors that regulate the formation and membrane insertion of Ca-A/K channels, however, are poorly understood. Recently, the cytokine tumor necrosis factor-alpha (TNF-alpha) was shown to increase the cell surface expression of an AMPA receptor (AMPAR) subunit (GluR1) and to potentiate vulnerability to AMPAR-mediated injury. In this study, we examined the possibility that TNF-alpha might also increase numbers of functional Ca-A/K channels. In acute hippocampal slice preparations, TNF-alpha appeared to increase Ca-A/K channel numbers in pyramidal neurons (HPNs), as assessed using a histochemical stain based on kainate-induced uptake of Co2+ ions (Co2+ labeling). In dissociated hippocampal neuronal cultures, TNF-alpha exposure (6 nM, 15 min) induced a rapid increase in cell surface levels not only of GluR1, but also of the AMPAR subunit GluR2, on most neurons, without evident new protein synthesis. Furthermore, consistent with the slice studies, fluorescence Ca2+ imaging techniques revealed an increase in numbers of Ca-A/K channels on what appeared to be a subset of HPNs. These observations are the first to provide evidence for the rapid upregulation of neuronal Ca-A/K channels in response to a cytokine or any other soluble factor, and provide a novel mechanism through which TNF-alpha may modulate both synaptic function and neuronal vulnerability.

Aniline Compounds↗
PubMed2004

Method for identifying neuronal cells suffering zinc toxicity by use of a novel fluorescent sensor.

During excitotoxic brain damage, injured neurons accumulate an anomalous, pathological burden of weakly bound, rapidly exchangeable Zn(2+) that diffusely fills the soma, nucleus and proximal dendrites. Mounting evidence indicates that this Zn(2+) is a major contributing factor in the subsequent demise of the damaged neurons. Thus, identifying, imaging, and characterizing zinc-filled cells have become essential steps in understanding excitotoxicity. Here we demonstrate that a new fluorescent stain for zinc can rather selectively and quite vividly label zinc-filled neurons in frozen histologic sections. The method is more sensitive and selective than the existing stain TSQ, and simpler than the Timm-Danscher silver staining techniques. A previously unobserved population of apparently injured cells in the dentate gyrus has been discovered with the new reagent. Whereas cells viewed in situ in normal, healthy tissue virtually never display any perikaryal staining by histochemical methods for zinc, injured cells stain intensely for zinc in culture, acute slice preparations and in tissue harvested in vivo. Thus, the presence of rapidly-exchangeable, "stainable" perikaryal zinc may be taken as an indicator of cell injury.

Animals↗
PubMed2003

Heterogeneity of Ca2+-permeable AMPA/kainate channel expression in hippocampal pyramidal neurons: fluorescence imaging and immunocytochemical assessment.

The presence of Ca2+-permeable AMPA/kainate (Ca-A/K) channels on hippocampal pyramidal neurons (HPNs) has been controversial, although they are present on many forebrain GABAergic neurons. We combined high-resolution fluorescence Ca2+ imaging with surface AMPA receptor (AMPAR) subunit immunocytochemistry to examine the expression of functional Ca-A/K channels in dissociated hippocampal neurons at the subcellular level. In GABAergic neurons [identified by glutamate decarboxylase (GAD) immunocytochemistry], focal application of AMPA induced large dendrosomatic intracellular [Ca2+] ([Ca2+]i) rises, consistent with their known strong Ca-A/K channel expression. Surface immunostaining for the AMPAR subunits GluR1 and GluR2 revealed abundant dendritic GluR1 puncta containing little or no GluR2, which, when present, was limited to diffuse staining in the soma and proximal dendrites. In contrast, the majority of HPNs (putatively identified by morphological criteria and lack of GAD labeling) showed little or no AMPA-induced [Ca2+]i rise. Correspondingly, most HPNs showed strong dendritic labeling for both GluR1 and GluR2 that colocalized extensively. A subpopulation of HPNs, however, displayed noticeable [Ca2+]i rises that began and often reached their highest levels in discrete dendritic regions. In these HPNs, levels of GluR1 relative to GluR2 were higher, and GluR1 was often present without overlying GluR2. The present studies, which are the first to directly examine the relationship between the local complement of cell surface AMPAR and the presence of dendritic Ca-A/K channels, clearly indicate that considerable cell surface GluR2 does not preclude the presence of Ca-A/K channels and further show that HPNs display considerable heterogeneity in terms of apparent Ca-A/K channel expression.

Animals↗
PubMed2003

A sodium zinc exchange mechanism is mediating extrusion of zinc in mammalian cells.

Zinc influx, driven by a steep inward electrochemical gradient, plays a fundamental role in zinc signaling and in pathophysiologies linked to intracellular accumulation of toxic zinc. Yet, the cellular transport mechanisms that actively generate or maintain the transmembrane gradients are not well understood. We monitored Na+-dependent Zn2+ transport in HEK293 cells and cortical neurons, using fluorescent imaging. Treatment of the HEK293 cells with CaPO4 precipitates induced Na+-dependent Zn2+ extrusion, against a 500-fold transmembrane zinc gradient, or zinc influx upon reversal of Na+ gradient, thus indicating that Na+/Zn2+ exchange is catalyzing active Zn2+ transport. Depletion of intracellular ATP did not inhibit the Na+-dependent Zn2+ extrusion, consistent with a mechanism involving a secondary active transporter. Inhibitors of the Na+/Ca2+ exchanger failed to inhibit Na+-dependent Zn2+ efflux. In addition, zinc transport was unchanged in HEK293 cells heterologously expressing functional cardiac or neuronal Na+/Ca2+ exchangers, thus indicating that the Na+/Zn2+ exchange activity is not mediated by the Na+/Ca2+ exchanger. Sodium-dependent zinc exchange, facilitating the removal of intracellular zinc, was also monitored in neurons. To our knowledge, the Na+/Zn2+ exchanger described here is the first example of a mammalian transport mechanism capable of Na+-dependent active extrusion of zinc. Such mechanism is likely to play an important role, not only in generating the transmembrane zinc gradients, but also in protecting cells from the potentially toxic effects of permeation of this ion.

Animals↗
PubMed2003

Modulation of mitochondrial function by endogenous Zn2+ pools.

Recent evidence suggests that intracellular Zn(2+) accumulation contributes to the neuronal injury that occurs in epilepsy or ischemia in certain brain regions, including hippocampus, amygdala, and cortex. Although most attention has been given to the vesicular Zn(2+) that is released into the synaptic space and may gain entry to postsynaptic neurons, recent studies have highlighted pools of intracellular Zn(2+) that are mobilized in response to stimulation. One such Zn(2+) pool is likely bound to cytosolic proteins, like metallothioneins. Applying imaging techniques to cultured cortical neurons, this study provides novel evidence for the presence of a mitochondrial pool distinct from the cytosolic protein or ligand-bound pool. These pools can be pharmacologically mobilized largely independently of each other, with Zn(2+) release from one resulting in apparent net Zn(2+) transfer to the other. Further studies found evidence for complex and potent effects of Zn(2+) on isolated brain mitochondria. Submicromolar levels, comparable to those that might occur on strong mobilization of intracellular compartments, induced membrane depolarization (loss of Deltapsi(m)), increases in currents across the mitochondrial inner membrane as detected by direct patch clamp recording of mitoplasts, increased O(2) consumption and decreased reactive oxygen species (ROS) generation, whereas higher levels decreased O(2) consumption and increased ROS generation. Finally, strong mobilization of protein-bound Zn(2+) appeared to induce partial loss of Deltapsi(m), suggesting that movement of Zn(2+) between cytosolic and mitochondrial pools might be of functional significance in intact neurons.

Animals↗
PubMed2003

Disruption of glial glutamate transport by reactive oxygen species produced in motor neurons.

Observations of elevated CSF glutamate in amyotrophic lateral sclerosis (ALS), together with findings that motor neurons are selectively vulnerable to glutamate receptor-mediated ("excitotoxic") injury, support an excitotoxic contribution to the motor neuron loss in the disease. However, the basis of the apparent loss of astrocytic glutamate transport capacity in affected areas of motor cortex and spinal cord, which probably underlies the extracellular glutamate elevations, is unexplained. Here, we find that glutamate induces far greater reactive oxygen species (ROS) generation in cultured motor neurons than in other spinal neurons. In addition, we found that the ROS seem to be able to leave the motor neurons and induce oxidation and disruption of glutamate uptake in neighboring astrocytes. Correspondingly, in a transgenic mouse model of ALS, protein oxidation was increased in regions immediately surrounding motor neurons. These results provide a mechanism that can account for the localized loss of glial glutamate transport seen in the disease. Furthermore, the observations lend support for a feedforward model involving reciprocal interactions between motor neurons and glia, which may prove useful in understanding ALS pathogenesis.

Amyotrophic Lateral Sclerosis↗
PubMed2003

A new mitochondrial fluorescent zinc sensor.

A novel cationic fluorescent zinc (Zn2+) indicator (RhodZin-3) with nanomolar affinity for Zn2+ has been synthesized. RhodZin-3 exhibits large pH-independent fluorescence increases in the orange region of the visible wavelength spectrum with increasing zinc concentrations, and no sensitivity to physiologically relevant Ca2+ concentrations. Experiments in neuronal cell cultures show that RhodZin-3 effectively localizes into mitochondria and detects changes of intramitochondrial free Zn2+ ([Zn2+]m).

Animals↗
PubMed2002

Zn2+ currents are mediated by calcium-permeable AMPA/kainate channels in cultured murine hippocampal neurones.

Permeation of the endogenous cation Zn2+ through calcium-permeable AMPA/kainate receptor-gated (Ca-A/K) channels might subserve pathological and/or physiological signalling roles. Voltage-clamp recording was used to directly assess Zn2+ flux through these channels on cultured murine hippocampal neurones. Ca-A/K channels were present in large numbers only on a minority of neurones (Ca-A/K+ neurones), many of which were GABAergic. The presence of these channels was assessed in whole-cell or outside-out patch recording as the degree of inward rectification of kainate-activated currents, quantified via a rectification index (RI = G+40/G-60), which ranged from <0.4 (strongly inwardly rectifying) to >2 (outwardly rectifying). The specificity of a low RI as an indication of robust Ca-A/K channel expression was verified by two other techniques, kainate-stimulated cobalt-uptake labelling, and fluorescence imaging of kainate-induced increases in intracellular Ca2+. In addition, the degree of inward rectification of kainate-activated currents correlated strongly with the positive shift of the reversal potential (V(rev)) upon switching to a sodium-free, 10 mM Ca2+ buffer. With Zn2+ (3 mM) as the only permeant extracellular cation, kainate-induced inward currents were only observed in neurones that had previously been identified as Ca-A/K+. A comparison between the V(rev) observed with 3 mM Zn2+ and that observed with Ca2+ as the permeant cation revealed a P(Ca)/P(Zn) of approximately 1.8. Inward currents recorded in 3 mM Ca2+ were unaffected by the addition of 0.3 mM Zn2+, while microfluorimetrically detected increases in the intracellular concentration of Zn2+ in Ca-A/K+ neurones upon kainate exposure in the presence of 0.3 mM Zn2+ were only mildly attenuated by the addition of 1.8 mM Ca2+. These results provide direct evidence that Zn2+ can carry currents through Ca-A/K channels, and that there is little interference between Ca2+ and Zn2+ in permeating these channels.

Animals↗
PubMed2002

Blockade of Ca2+-permeable AMPA/kainate channels decreases oxygen-glucose deprivation-induced Zn2+ accumulation and neuronal loss in hippocampal pyramidal neurons.

Synaptic release of Zn2+ and its translocation into postsynaptic neurons probably contribute to neuronal injury after ischemia or epilepsy. Studies in cultured neurons have revealed that of the three major routes of divalent cation entry, NMDA channels, voltage-sensitive Ca2+ channels (VSCCs), and Ca2+-permeable AMPA/kainate (Ca-A/K) channels, Ca-A/K channels exhibit the highest permeability to exogenously applied Zn2+. However, routes through which synaptically released Zn2+ gains entry to postsynaptic neurons have not been characterized in vivo. To model ischemia-induced Zn2+ movement in a system approximating the in vivo situation, we subjected mouse hippocampal slice preparations to controlled periods of oxygen and glucose deprivation (OGD). Timm's staining revealed little reactive Zn2+ in CA1 and CA3 pyramidal neurons of slices exposed in the presence of O2 and glucose. However, 15 min of OGD resulted in marked labeling in both regions. Whereas strong Zn2+ labeling persisted if both the NMDA antagonist MK-801 and the VSCC blocker Gd3+ were present during OGD, the presence of either the Ca-A/K channel blocker 1-naphthyl acetyl spermine (NAS) or the extracellular Zn2+ chelator Ca2+ EDTA substantially decreased Zn2+ accumulation in pyramidal neurons of both subregions. In parallel experiments, slices were subjected to 5 min OGD exposures as described above, followed 4 hr later by staining with the cell-death marker propidium iodide. As in the Timm's staining experiments, substantial CA1 or CA3 pyramidal neuronal damage occurred despite the presence of MK-801 and Gd3+, whereas injury was decreased by NAS or by Ca2+ EDTA (in CA1).

Animals↗
PubMed2002

Mitochondrial sequestration and Ca(2+)-dependent release of cytosolic Zn(2+) loads in cortical neurons.

The endogenous divalent cations, Ca(2+) and Zn(2+), are both highly toxic upon excessive glutamate triggered intracellular accumulation. Given apparent parallels in their neurotoxic mechanisms, the present study aimed to explore interactions between these cations, by examining effects of moderate intracellular Zn(2+) loading on responses to subsequent Ca(2+) influx. Cortical cultures were briefly exposed to high-K(+) buffer in the presence or absence of Zn(2+) (50-100 microM), to activate and permit a modestly toxic amount of Zn(2+) to enter through VSCC. After 1 h, the cultures were loaded with fluorescent probes, and 2 h after the Zn(2+) exposure, imaged before and after induction of Ca(2+) entry or addition of other drugs. In Zn(2+) preexposed cultures loaded with the Zn(2+) probe, Newport Green, induction of Ca(2+) entry through either VSCC or NMDA channels induced cytoplasmic release of sequestered Zn(2+). The source of this Ca(2+) dependent intracellular Zn(2+) release appears largely to be mitochondria, as indicated by the ability of the mitochondrial protonophore, FCCP, the mitochondrial uncoupler, dinitrophenol with the K(+) ionophore, valinomycin, or the inducer of mitochondrial permeability transition (mPT), phenylarsine oxide (PAO), to substitute for NMDA in triggering Zn(2+) release. Suggesting functional consequences of mitochondrial Zn(2+) uptake, Zn(2+) preexposures resulted in long-lasting mitochondrial depolarization (assessed with rhodamine 123), and reduced mitochondrial reactive oxygen species generation (assessed with hydroethidine) in response to subsequent NMDA triggered Ca(2+) influx.

Animals↗