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E S Levine

Publications and source records attributed to E S Levine.

At least 19 recordsLinked to original sources
PubMed2006

The spiral structure of the outer Milky Way in hydrogen.

We produce a detailed map of the perturbed surface density of neutral hydrogen in the outer Milky Way disk, demonstrating that the Galaxy is a non-axisymmetric multiarmed spiral. Spiral structure in the southern half of the Galaxy can be traced out to at least 25 kiloparsecs, implying a minimum radius for the gas disk. Overdensities in the surface density are coincident with regions of reduced gas thickness. The ratio of the surface density to the local median surface density is relatively constant along an arm. Logarithmic spirals can be fit to the arms with pitch angles of 20 degrees to 25 degrees .

Journal Article↗
PubMed2005

Changes in secondary glutamate release underlie the developmental regulation of excitotoxic neuronal cell death.

Vulnerability to excitotoxicity increases during development in vivo and in vitro. To determine whether the mere presence of mature N-methyl-D-aspartate (NMDA) receptors coincides with the emergence of excitotoxicity or whether post-receptor signaling processes may also contribute, we examined the temporal relationship of NMDA receptor expression, function and toxicity using cortical cell cultures. Surface expression of all NMDA receptor subunits increased with time in culture. This correlated with NMDA receptor function, assessed both biochemically and electrophysiologically, but not with the appearance of excitotoxicity. Specifically, cells at day in vitro (DIV) 10 were less susceptible to NMDA receptor-induced neurotoxicity than those cultured for 14 days, even though receptor expression/function was identical. In addition, cell-attached single channel recordings revealed that NMDA receptor conductance, open probability, and frequency of channel openings were not significantly different between the two days. Intriguingly, depolarization-induced release of glutamate from cultures grown for 10 days was significantly lower than that released from cultures grown for 14 days. Further, exogenous addition of glutamate receptor agonists immediately after removal of NMDA rendered cultures at DIV 10 susceptible to excitotoxicity, while toxicity was significantly reduced by addition of an NMDA receptor antagonist immediately after exposure to NMDA at DIV 14. These data are the first to demonstrate that the subsequent, secondary release of glutamate plays an equal, if not more important, role than NMDA receptor development per se, in mediating the enhanced vulnerability of neurons to excitotoxicity that occurs with age.

Animals↗
PubMed2000

Brain-derived neurotrophic factor increases activity of NR2B-containing N-methyl-D-aspartate receptors in excised patches from hippocampal neurons.

Growth factors, including members of the neurotrophin gene family, play a central role in the regulation of neuronal survival and differentiation during development. In addition to these relatively long-term actions of neurotrophins, recent studies have shown that these factors also rapidly modulate synaptic transmission. Brain-derived neurotrophic factor (BDNF), in particular, regulates both pre- and postsynaptic aspects of hippocampal synaptic transmission. The postsynaptic effects include an increase in glutamate responsiveness, mediated by the N-methyl-D-aspartate (NMDA) glutamate receptor subtype. It is not clear, however, where BDNF-trkB signal transduction is initiated, because trkB receptors are located in both pre- and postsynaptic membranes. In the present study, we used excised membrane patches from cultured hippocampal neurons to determine whether BDNF directly modulates postsynaptic NMDA receptor activity. The results indicate that acute exposure to BDNF increases NMDA single channel open probability via postsynaptic trkB receptors and that this effect is dependent on the presence of the NR2B subunit of the NMDA receptor.

2-Amino-5-phosphonovalerate↗
PubMed1999

Brain-derived neurotrophic factor enhances association of protein tyrosine phosphatase PTP1D with the NMDA receptor subunit NR2B in the cortical postsynaptic density.

Our recent studies revealed that brain-derived neurotrophic factor (BDNF) rapidly enhances tyrosine phosphorylation and dephosphorylation of the NMDA receptor subunit, NR2B, in the postsynaptic density (PSD), potentially regulating synaptic plasticity. To explore the molecular mechanisms underlying synaptic NR2B signaling, we examined the protein tyrosine phosphatase, PTP1D; BDNF reportedly increases association of PTP1D with tyrosine phosphorylated proteins in cortical neurons and PC 12 cells. We now report that PTP1D is an intrinsic component of the rat cerebrocortical PSD, based on Western blot analysis using specific anti-PTP1D antibodies. In addition, NR2B was co-immunoprecipitated with PTP1D using anti-NR2B antibodies or anti-PTP1D antibodies, indicating physical association of the subunit with PTP1D. Moreover, treatment of the purified PSD with BDNF for 5 min elicited a two-fold increase in the association of NR2B with PTP1D. The BDNF action appeared to be specific, since nerve growth factor, another member of the neurotrophin gene family, did not alter the association. Finally, an overlay assay revealed that BDNF caused a two-fold increase in binding of blotted PSD NR2B proteins to PTP1D-SH2 domains, revealing molecular mechanisms mediating the PTP1D-NR2B binding. Taken together, our results raise the possibility that PTP1D participates in BDNF-mediated NR2B signaling cascades at the postsynaptic site, thereby regulating synaptic plasticity.

Animals↗
PubMed1999

A simplified technique for stable transscleral suture fixation of posterior chamber intraocular lenses.

We describe a technique for implanting ciliary sulcus posterior chamber intraocular lenses (PCIOLs). This technique uses radial keratotomy (RK) markers to facilitate PCIOL centration, 2-point scleral suture fixation for each haptic to prevent PCIOL tilt, and partial thickness sclerotomies to prevent suture erosion. Postoperative results of 20 eyes with PCIOLs sutured to the ciliary sulcus were reviewed. Suture placement was determined using a Mendez degree gauge with Bores axis marker (Katena USA, Denville, NJ). Two-point scleral suture fixation without a scleral flap was used for each haptic. Average follow-up was 17.1 months. Postoperative best corrected visual acuity was 20/40 or better in 95% of eyes. Average best-corrected post-operative visual acuity was 20/29. One patient with a previous retinal disease lost 3 lines of visual acuity. This technique results in excellent postoperative visual acuity without PCIOL decentration, tilt, or suture erosion.

Aphakia, Postcataract↗
PubMed1998

NMDA receptor subunits in the postsynaptic density of rat brain: expression and phosphorylation by endogenous protein kinases.

N-methyl-D-aspartate (NMDA) receptors (NRs) play critical roles in diverse synaptic processes in the brain. However, subcellular distribution, spatiotemporal expression and regulation of NR subunits in brain synapses are unknown. We report that NR1 and NR2A-2C subunits are all enriched in the postsynaptic density (PSD), which plays critical roles in trophin-mediated synaptic plasticity. Significant expression of NRs was observed the first two weeks after birth, during synaptogenesis, and in adulthood. Functional diversity of NRs, resulting from heterogeneous composition, was supported by the finding that different NR2 subunits were associated in a region-specific manner with NR1. Phosphorylation of NR1, a key subunit of the NMDA receptor-channel complex, was significantly enhanced by activators of calmodulin (CaM) kinases (CKs) or protein kinase C (PKC), but not by those of PKA. Co-immunoprecipitation studies revealed that NR1 was physically associated with functionally active PKCgamma and the major PSD protein (mPSDp) through noncovalent interactions. Our results suggest that NMDA receptors play roles in postsynaptic mechanisms in a subunit-, composition-, brain region- and developmental-specific manner. Our findings also indicate that the PSD is a coherent functional unit containing protein kinases that potentially regulate NMDA receptor function via phosphorylation.

8-Bromo Cyclic Adenosine Monophosphate↗
PubMed1998

Brain-derived neurotrophic factor modulates hippocampal synaptic transmission by increasing N-methyl-D-aspartic acid receptor activity.

Neurotrophins (NTs) have recently been found to regulate synaptic transmission in the hippocampus. Whole-cell and single-channel recordings from cultured hippocampal neurons revealed a mechanism responsible for enhanced synaptic strength. Specifically, brain-derived neurotrophic factor augmented glutamate-evoked, but not acetylcholine-evoked, currents 3-fold and increased N-methyl-D-aspartic acid (NMDA) receptor open probability. Activation of trkB NT receptors was critical, as glutamate currents were not affected by nerve growth factor or NT-3, and increased open probability was prevented by the tyrosine kinase inhibitor K-252a. In addition, the NMDA receptor antagonist MK-801 blocked brain-derived neurotrophic factor enhancement of synaptic transmission, further suggesting that NTs modulate synaptic efficacy via changes in NMDA receptor function.

Acetylcholine↗
PubMed1998

BDNF acutely increases tyrosine phosphorylation of the NMDA receptor subunit 2B in cortical and hippocampal postsynaptic densities.

While neurotrophins are critical for neuronal survival and differentiation, recent work suggests that they acutely regulate synaptic transmission as well. Brain-derived neurotrophic factor (BDNF) enhances excitatory postsynaptic currents in cultured dissociated hippocampal neurons within 2-3 min through postsynaptic, phosphorylation-dependent mechanisms. Moreover, BDNF modulates hippocampal long-term potentiation, in which postsynaptic NMDA (N-methyl-D-aspartate) receptors (NRs) play a key role. We now report that BDNF acutely increases tyrosine phosphorylation of the specific NMDA receptor subunit NR2B, which has recently been shown to play a role in long-term potentiation. Incubation of BDNF with cortical or hippocampal postsynaptic densities for 5 min increased tyrosine phosphorylation of the NR2B subunits in a dose-dependent manner. A maximal increase to 165% of control phosphorylation occurred at a BDNF concentration of 2 ng/ml. The BDNF action appeared to be specific, since nerve growth factor, another member of the neurotrophin gene family, had no effect on NR2B phosphorylation. Further, BDNF action was selective, since it did not alter tyrosine phosphorylation of NR2A subunits. Our results suggest that tyrosine phosphorylation of NR2B subunits of the NMDA receptor may contribute to neurotrophin modulation of postsynaptic responsiveness and long-term potentiation.

Animals↗
PubMed1997

Brain-derived neurotrophic factor rapidly enhances phosphorylation of the postsynaptic N-methyl-D-aspartate receptor subunit 1.

Although neurotrophins have traditionally been regarded as neuronal survival factors, recent work has suggested a role for these factors in synaptic plasticity. In particular, brain-derived neurotrophic factor (BDNF) rapidly enhances synaptic transmission in hippocampal neurons through trkB receptor stimulation and postsynaptic phosphorylation mechanisms. Activation of trkB also modulates hippocampal long-term potentiation, in which postsynaptic N-methyl-D-aspartate glutamate receptors play a key role. However, the final common pathway through which BDNF increases postsynaptic responsiveness is unknown. We now report that BDNF, within 5 min of exposure, elicits a dose-dependent increase in phosphorylation of the N-methyl-D-aspartate receptor subunit 1. This acute effect occurred in hippocampal synaptoneurosomes, which contain pre- and postsynaptic elements, and in isolated hippocampal postsynaptic densities. Nerve growth factor, in contrast, caused no enhancement of phosphorylation. These results suggest a potential mechanism for trophin-induced potentiation of synaptic transmission.

Animals↗
PubMed1997

Depletion of mitochondrial DNA, destruction of mitochondria, and accumulation of lipid droplets result from fialuridine treatment in woodchucks (Marmota monax).

Fialuridine (FIAU, 1-(2-deoxy-2-fluoro-beta-D-arabinofuranosyl)-5-iodouracil) is toxic to liver, heart, muscle, and nerve in clinical trials for chronic viral hepatitis (CH). Mitochondrial toxicity was hypothesized. To address pathophysiologic mechanisms, we examined mitochondrial changes in FIAU-treated woodchucks (WC) with CH from woodchuck hepatitis virus infection. WC (with and without CH from woodchuck hepatitis virus infection) were treated with FIAU (1.5 mg/kg/day) for 12 weeks. WC were killed. Liver, heart, skeletal muscle, and kidney samples underwent DNA extraction and were analyzed ultrastructurally (transmission electron microscopy). Myocardium, skeletal muscles, and liver samples were analyzed histologically. Abundance of hepatic, myocardial, muscle, and kidney mtDNA decreased in FIAU-treated WC, but the magnitude varied. mtDNA decreased 55% in heart, 65% in kidney, 74% in liver, and 87% in muscle (p < 0.02 for each tissue: FIAU-treated versus FIAU-untreated). Cellular damage was characterized ultrastructurally by mitochondrial enlargement, cristae dissolution, and lipid droplets. Lipid droplets found in the heart, diaphragm, biceps, and liver were sufficient to identify FIAU-treated WC (p < 0.05 each). Widespread mitochondrial damage to many tissues resulted from chronic FIAU treatment and occurred irrespective of CH. It manifested with mtDNA depletion, intracytoplasmic lipid droplets, and destroyed mitochondrial cristae. Defective mtDNA replication with mtDNA depletion seems central to the subcellular pathophysiology of altered energy metabolism and multiorgan failure in FIAU toxicity.

Animals↗
PubMed1996

Fialuridine and its metabolites inhibit DNA polymerase gamma at sites of multiple adjacent analog incorporation, decrease mtDNA abundance, and cause mitochondrial structural defects in cultured hepatoblasts.

The thymidine analog fialuridine deoxy-2-fluoro-beta-D-arabinofuranosyl)-5-iodouracil (FIAU) was toxic in trials for chronic hepatitis B infection. One mechanism postulated that defective mtDNA replication was mediated through inhibition of DNA polymerase-gamma (DNA pol-gamma), by FIAU triphosphate (FIALTP) or by triphosphates of FIAU metabolites. Inhibition kinetics and primer-extension analyses determined biochemical mechanisms of FIAU, 1-(2-deoxy-2-fluoro-beta-D-arabinofuranosyl) -5-methyluracil (FAU), 1-(2-deoxy-2-fluoro-beta-D-arabinofuranosyl)uracil triphosphate (TP) inhibition of DNA pol-gamma. dTMP incorporation by DNA pol-gamma was inhibited competitively by FIAUTP, FMAUTP, and FAUTP (K1=0.015, 0.03, and 1.0 microM, respectively). By using oliginucleotide template-primers. DNA pol-gamma incorporated each analog into DNA opposite a single adenosine efficiently without effects on DNA chain elongation. Incorporation of multiple adjacent analogs at positions of consecutive adenosines dramatically impaired chain elongation by DNA pol-gamma. Effects of FIAU, FMAU, and FAU on HepG2 cell mmtDNA abundance and ultrastructure were determined. After 14 days, mtDNA decreased by 30% with 20 microM FIAU or 20 microM FMAU and decreased less than 10% with 100 microM FAU. FIAU and FMAU disrupted mitochondria and caused accumulation of intracytoplasmic lipid droplets. Biochemical and cell biological findings suggest that FIAU and its metabolites inhibit mtDNA replication, most likely at positions of adenosine tracts, leading to decreased mtDNA and mitochondrial ultrastructural defects.

Antiviral Agents↗
PubMed1996

Selective role for trkB neurotrophin receptors in rapid modulation of hippocampal synaptic transmission.

Neurotrophins regulate neuronal survival and phenotypic differentiation. Recent evidence also suggests a role in the modulation of synaptic activity. Using neuronal cell cultures from embryonic hippocampus, we previously found that application of brain-derived neurotrophic factor rapidly enhanced synaptic transmission. We now report that application of neurotrophin-4, another ligand for the trkB neurotrophin receptor, was equally effective in enhancing synaptic currents. In contrast, nerve growth factor, neurotrophin-3, basic fibroblast growth factor and epidermal growth factor did not share this action. Our results suggest that activation of trkB receptors plays a selective role in the regulation of synaptic efficacy in the hippocampus.

Animals↗
PubMed1995

Brain-derived neurotrophic factor rapidly enhances synaptic transmission in hippocampal neurons via postsynaptic tyrosine kinase receptors.

Although neurotrophins are primarily associated with long-term effects on neuronal survival and differentiation, recent studies have shown that acute changes in synaptic transmission can also be produced. In the hippocampus, an area critically involved in learning and memory, we have found that brain-derived neurotrophic factor (BDNF) rapidly enhanced synaptic efficacy through a previously unreported mechanism--increased postsynaptic responsiveness via a phosphorylation-dependent pathway. Within minutes of BDNF application to cultured hippocampal neurons, spontaneous firing rate was dramatically increased, as were the frequency and amplitude of excitatory postsynaptic currents. The increased frequency of postsynaptic currents resulted from the change in presynaptic firing. However, the increased amplitude was postsynaptic in origin because it was selectively blocked by intracellular injection of the tyrosine kinase receptor (Ntrk2/TrkB) inhibitor K-252a and potentiated by injection of the phosphatase inhibitor okadaic acid. These results suggest a role for BDNF in the modulation of synaptic transmission in the hippocampus.

Animals↗
PubMed1995

Differential effects of NGF and BDNF on voltage-gated calcium currents in embryonic basal forebrain neurons.

A number of studies have begun to describe the effects of nerve growth factor (NGF) and the closely related brain-derived neurotrophic factor (BDNF) on the function of basal forebrain neurons. Little is known, however, about the effects of neurotrophins on membrane calcium conductances, which may play a role in growth factor signal transduction as well as regulation of neuronal excitability. Using the whole-cell patch-clamp technique, we investigated the effects of both NGF and BDNF on voltage-gated Ca(2+)-channel currents in cultured embryonic basal forebrain neurons. Exposure for 4-6 d to NGF significantly increased both the L-type and N-type components of the whole-cell current. Conversely, similar exposure to BDNF had no effect on Ca(2+)-channel currents. Consequently, one of the important effects of NGF may be to enhance calcium entry via voltage-dependent channels.

Action Potentials↗
PubMed1993

Cardiac cell toxicity induced by 4-hydroperoxycyclophosphamide is modulated by glutathione.

OBJECTIVE: Cardiac myocytes were exposed to 4-hydroperoxycyclophosphamide (4-HC, an activated derivative of cyclophosphamide) to assess whether early ionic events are associated with the dose limiting toxicity of this chemotherapeutic agent. METHODS: Primary cultures of embryonic chick cardiac myocytes were grown to confluency and then exposed to a medium containing 4-HC. Cellular sodium, potassium, and calcium contents were measured by atomic absorption spectrophotometry and related to protein and ATP content. Pretreatment of the cultured heart cells with glutathione depleting or enhancing agents provided the basis for evaluating the involvement of glutathione in the 4-HC-induced cytotoxicity. RESULTS: Administration of 150 microM 4-HC to cardiac myocytes resulted in increases in cellular sodium and calcium contents and decreases in potassium, ATP, and protein contents. Pretreatment of cardiac myocytes with L-buthionine-SR-sulphoximine, a specific inhibitor of gamma-glutamylcysteine synthetase, depleted cellular glutathione to 12% of control and significantly reduced the minimum concentration of 4-HC causing cytotoxic changes. Conversely, elevation of cellular thiol content by the pretreatment of cardiac myocytes with glutathione monoethyl ester (but not glutathione) provided protection against 4-HC induced cytotoxicity. CONCLUSIONS: Cellular glutahione concentration can markedly influence the 4-HC induced changes in cellular ion content and ATP, which are early indicators of 4-HC induced cytotoxicity.

Adenosine Triphosphate↗
PubMed1992

Neurochemical afferents controlling the activity of serotonergic neurons in the dorsal raphe nucleus: microiontophoretic studies in the awake cat.

Serotonergic (5-HT) neurons of the brainstem dorsal raphe nucleus (DRN) have been implicated in a diversity of physiological and behavioral processes in vertebrates. However, despite extensive information about the intrinsic properties and the efferent projections of this neurochemical system, little information is available regarding the afferents that control its activity. This study investigated the neurotransmitters that regulate the activity of DRN-5-HT neurons under physiologically relevant conditions, by utilizing microiontophoresis in combination with single-unit recordings in the awake, head-restrained cat. This made it possible to examine the direct effects of neurotransmitters on DRN-5-HT neuronal activity, and, through the use of specific antagonists, to study the roles of these neurotransmitter inputs during physiological conditions that influence DRN-5-HT neuronal activity. The results indicate that (1) iontophoretic application of the GABA antagonist bicuculline reversed the typical suppression of neuronal activity seen during slow wave sleep, but had no effect on maintained activity during wakefulness. The suppression of neuronal activity during REM sleep was generally unaffected by application of bicuculline. This suggests a role for a GABAergic input to DRN-5-HT neurons in controlling some aspects of their state-dependent activity. (2) Iontophoretic application of the excitatory amino acid (EAA) antagonist kynurenic acid reduced the magnitude of the neuronal response evoked by phasic auditory stimuli, but had no effect on the spontaneous activity of these neurons, suggesting a role for an EAA input to the DRN in mediating the response to phasic sensory stimuli.(ABSTRACT TRUNCATED AT 250 WORDS)

Acoustic Stimulation↗