scholarly journals Factors Underlying Bursting Behavior in a Network of Cultured Hippocampal Neurons Exposed to Zero Magnesium

2004 ◽  
Vol 91 (2) ◽  
pp. 946-957 ◽  
Author(s):  
Patrick S. Mangan ◽  
Jaideep Kapur
Keyword(s):  
Nmda Receptor ◽  
Action Potential ◽  
Receptor Antagonist ◽  
Hippocampal Neurons ◽  
Pyramidal Neurons ◽  
Membrane Surface ◽  
Nmda Receptor Antagonist ◽  
Low Density ◽  
Hippocampal Cell Culture ◽  
Low Culture

Factors contributing to reduced magnesium-induced neuronal action potential bursting were investigated in primary hippocampal cell culture at high and low culture density. In nominally zero external magnesium medium, pyramidal neurons from high-density cultures produced recurrent spontaneous action potential bursts superimposed on prolonged depolarizations. These bursts were partially attenuated by the NMDA receptor antagonist d-APV. Pharmacological analysis of miniature excitatory postsynaptic currents (EPSCs) revealed 2 components: one sensitive to d-APV and another to the AMPA receptor antagonist DNQX. The components were kinetically distinct. Participation of NMDA receptors in reduced magnesium-induced synaptic events was supported by the localization of the NR1 subunit of the NMDA receptor with the presynaptic vesicular protein synaptophysin. Presynaptically, zero magnesium induced a significant increase in EPSC frequency likely attributable to increased neuronal hyperexcitability induced by reduced membrane surface charge screening. Mean quantal content was significantly increased in zero magnesium. Cells from low-density cultures did not exhibit action potential bursting in zero magnesium but did show increased EPSC frequency. Low-density neurons had less synaptophysin immunofluorescence and fewer active synapses as determined by FM1-43 analysis. These results demonstrate that multiple factors are involved in network bursting. Increased probability of transmitter release presynaptically, enhanced NMDA receptor-mediated excitability postsynaptically, and extent of neuronal interconnectivity contribute to initiation and maintenance of elevated network excitability.

scholarly journals Nicotinic and Muscarinic Reduction of Unitary Excitatory Postsynaptic Potentials in Sensory Cortex; Dual Intracellular Recording In Vitro

2006 ◽  
Vol 95 (4) ◽  
pp. 2155-2166 ◽  
Author(s):  
Robert B. Levy ◽  
Alex D. Reyes ◽  
Chiye Aoki
Keyword(s):  
Nmda Receptor ◽  
Receptor Antagonist ◽  
Pyramidal Neurons ◽  
Glutamate Release ◽  
Receptor Activation ◽  
Nmda Receptor Antagonist ◽  
Excitatory Postsynaptic Potentials ◽  
Postsynaptic Potentials ◽  
Sensory Activity

We studied the cholinergic modulation of glutamatergic transmission between neighboring layer 5 regular-spiking pyramidal neurons in somatosensory cortical slices from young rats (P10-P26). Brief bath application of 5–10 μM carbachol, a nonspecific cholinergic agonist, decreased the amplitude of evoked unitary excitatory postsynaptic potentials (EPSPs). This effect was blocked by 1 μM atropine, a muscarinic receptor antagonist. Nicotine (10 μM), in contrast to carbachol, reduced EPSPs in nominally magnesium-free solution but not in the presence of 1 mM Mg+2, indicating the involvement of NMDA receptors. Likewise, when the postsynaptic cell was depolarized under voltage clamp to allow NMDA receptor activation in the presence of 1 mM Mg+2, synaptic currents were reduced by nicotine. Nicotinic EPSP reduction was prevented by the NMDA receptor antagonist d-AP5 (50 μM) and by the nicotinic receptor antagonist mecamylamine (10 μM). Both carbachol and nicotine reduced short-term depression of EPSPs evoked by 10 Hz stimulation, indicating that EPSP reduction happens via reduction of presynaptic glutamate release. In the case of nicotine, several possible mechanisms for NMDAR-dependent EPSP reduction are discussed. As a result of NMDA receptor dependence, nicotinic EPSP reduction may serve to reduce the local spread of cortical excitation during heightened sensory activity.

Neurotoxicity Mediated by Aberrant Patterns of Synaptic Activity Between Rat Hippocampal Neurons in Culture

1998 ◽  
Vol 80 (5) ◽  
pp. 2688-2698 ◽  
Author(s):  
John R. McLeod ◽  
Maoxing Shen ◽  
Daniel J. Kim ◽  
Stanley A. Thayer
Keyword(s):  
Cell Death ◽  
Nmda Receptor ◽  
Receptor Antagonist ◽  
Hippocampal Neurons ◽  
Cell Voltage ◽  
Nmda Receptor Antagonist ◽  
Synaptic Activity ◽  
Slow Inward Current ◽  
Inward Current

McLeod, John R., Jr., Maoxing Shen, Daniel J. Kim, and Stanley A. Thayer. Neurotoxicity mediated by aberrant patterns of synaptic activity between rat hippocampal neurons in culture. J. Neurophysiol. 80: 2688–2698, 1998. Reducing the extracellular Mg2+ concentration ([Mg2+]o) to 0.1 mM evoked an aberrant pattern of glutamatergic activity in the synaptic network formed by rat hippocampal neurons grown in primary culture. This treatment resulted in a significant increase in neuronal death when maintained for 20–24 h; 0.1 mM [Mg2+]o elicited a stable and repetitive series of intracellular Ca2+ concentration ([Ca2+]i) spikes as indicated by indo-1-based microfluorimetry. Fura-2-based digital imaging experiments found that the [Ca2+]i spikes were synchronized for all the neurons in a given field. Thus electrophysiological recordings from individual cells were reasonable representations of the field as a whole, enabling correlation of electrical activity to viability. Underlying each [Ca2+]i spike was an intense burst of action potentials. Whole cell voltage-clamp experiments showed that a burst was composed of fast action currents superimposed on a slow inward current. The N-methyl-d-aspartate (NMDA) receptor antagonist CGS19755 (10 μM) blocked [Ca2+]i spiking, the slow inward current, and the cell death induced by low [Mg2+]o. The L-type Ca2+ channel antagonist nimodipine (10 μM) blocked [Ca2+]i spiking, all synaptic activity, and the cell death induced by low [Mg2+]o. The non-NMDA receptor antagonist 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX, 10 μM) exerted variable effects on [Ca2+]i spiking and blocked the slow inward current only when the cells were held at a relatively negative holding potential. CNQX did not afford any protection from 0.1 mM [Mg2+]o-induced neurotoxicity. [Ca2+]i imaging experiments showed that CNQX inhibited [Ca2+]i spiking in a subset of neurons within an active network. Thus, the neurons that were insensitive to CNQX appear to be those that were destined to die. We characterized an in vitro model that allowed us to correlate specific electrophysiological components of glutamatergic synaptic activity to the subsequent viability of the network. A slow NMDA receptor-mediated inward current was required to elicit [Ca2+]i spiking and neurotoxicity. Non-NMDA receptors did not contribute to synaptically mediated cell death in this model. An L-type Ca2+ channel antagonist was neuroprotective when used at concentrations that blocked synaptic activity, suggesting that dendritic L-type Ca2+ channels present a useful target for neuroprotective drugs.

scholarly journals Effect of memantine on calcium signaling in hippocampal neurons cultured with β-amyloid

2021 ◽  
Vol 67 (2) ◽  
pp. 3-10
Author(s):  
V.M. Shkryl ◽  
◽  
V.V. Ganzha ◽  
E.A. Lukyanetz ◽  
◽  
...  
Keyword(s):  
Nmda Receptor ◽  
Calcium Signaling ◽  
Receptor Antagonist ◽  
Calcium Ions ◽  
Hippocampal Neurons ◽  
Neurological Diseases ◽  
Neuroprotective Effect ◽  
Nmda Receptor Antagonist ◽  
Voltage Dependent ◽  
Ca2 Channels

Alzheimer’s disease (AD) is the most common type of dementia and is characterized by accumulating amyloid (Aβ) plaques and neurofibrillary tangles in the brain. Excessive stimulation of glutamate receptors, mainly NMDA-type, causes intense entry of calcium ions into cells and is a key early step in glutamateinduced excitotoxicity, resulting in many neurological diseases, including AD. Memantine, an NMDA receptor antagonist, blocks NMDA receptors and reduce the influx of calcium ions into neuron. In our experiments, we have modeled AD on cultured rat hippocampal neurons to test the effects of memantine on calcium signaling in neurons. Our results show that the neuroprotective effect of memantine could be provided not only through the inhibition of NMDA receptor current but also through the suppression of voltage-dependent Ca2+ channels, most likely L-type. This study suggests that NMDA receptor antagonist memantine can protect hippocampal neurons from calcium overloading induced by Aβ1–42 amyloid exposure via blocking Ca2+ channels

Na+ Dependence and the Role of Glutamate Receptors and Na+ Channels in Ion Fluxes During Hypoxia of Rat Hippocampal Slices

2000 ◽  
Vol 84 (4) ◽  
pp. 1869-1880 ◽  
Author(s):  
Michael Müller ◽  
George G. Somjen
Keyword(s):  
Nmda Receptor ◽  
Receptor Antagonist ◽  
Glutamate Receptors ◽  
Pyramidal Neurons ◽  
Hippocampal Slices ◽  
Nmda Receptor Antagonist ◽  
Tissue Slices ◽  
Glutamate Antagonists ◽  
Voltage Gated ◽  
Current Flows

Spreading depression (SD) as well as hypoxia-induced SD-like depolarization in forebrain gray matter are characterized by near complete depolarization of neurons. The biophysical mechanism of the depolarization is not known. Earlier we reported that simultaneous pharmacological blockade of all known major Na+ and Ca2+ channels prevents hypoxic SD. We now recorded extracellular voltage, Na+, and K+concentrations and the intracellular potential of individual CA1 pyramidal neurons during hypoxia of rat hippocampal tissue slices after substituting Na+ in the bath by an impermeant cation, or in the presence of channel blocking drugs applied individually and in combination. Reducing extracellular Na+ concentration [Na+]o to 90 mM postponed the hypoxia-induced extracellular DC-potential deflection (Δ V o) and reduced its amplitude, and it also postponed the SD-like depolarization of neurons. After lowering [Na+]o to 25 mM, SD-like Δ V o became very small, indicating that an influx of Na+ is required for SD; influx of Ca2+ ions alone is not sufficient. We then asked whether the SD-related Na+ current flows through glutamate-controlled and/or through voltage-gated Na+channels. Administration of either the non- N-methyl-d-aspartate (NMDA) receptor antagonist 6,7-dinitroquinoxaline-2,3-dione (DNQX), or the NMDA receptor antagonist (±)-3-(2-carboxypiperazin-4-yl)-propyl-1-phosphonic acid (CPP) postponed the hypoxic Δ V o and depressed its amplitude but the effect of the combined administration of these two drugs was not greater than that of either alone. During the early phase of hypoxia, before SD onset, [K+]oincreased faster and reached a much higher level in the presence of glutamate antagonists than in their absence. The [K+]o level reached at the height of hypoxic SD was, however, not affected. When TTX was added to DNQX and CPP, SD was prevented in half the trials. When SD did occur, it was greatly delayed, yet eventually neurons depolarized to the same extent as in normal solution. The SD-related sudden drop in [Na+]o was depressed by only 19% in the presence of the three drugs, indicating that Na+ can flow into cells through pathways other than ionotropic glutamate receptors and TTX-sensitive Na+ channels. We conclude that, when they are functional, glutamate-receptor-mediated and voltage-gated Na+ currents are the major generators of the self-regenerative rapid depolarization, but in their absence other pathways can sometimes take their place. The final level of SD-like depolarization is determined by positive feedback and not by the number of channels available. A schematic flow chart of the events generating hypoxic SD is discussed.

Imaging NMDA- and kainate-induced intrinsic optical signals from the hippocampal slice

1996 ◽  
Vol 76 (4) ◽  
pp. 2707-2717 ◽  
Author(s):  
R. D. Andrew ◽  
J. R. Adams ◽  
T. M. Polischuk
Keyword(s):  
Nmda Receptor ◽  
Receptor Antagonist ◽  
Ampa Receptors ◽  
Hippocampal Slice ◽  
Field Potential ◽  
Nmda Receptor Antagonist ◽  
Light Transmittance ◽  
Stratum Radiatum ◽  
Cell Swelling ◽  
Tissue Resistance

1. Brain ischemia causes excess release and accumulation of glutamate that binds to postsynaptic receptors. This opens ionotropic channels that mediate neuronal depolarization and ionic fluxes that can lead to neuronal death. 2. The CA1 pyramidal cell region of the hippocampus is particularly susceptible to this neurotoxic process. Brain cell swelling is considered an early excitotoxic event, but remains poorly under stood and documented. As cells swell, light transmittance (LT) increases through brain tissue, so we hypothesized that brief exposure to glutamate agonists would elicit cell swelling that could be imaged in real time in the hippocampal slice. 3. A 1-min bath application of 100 microM N-methyl-D-aspartate (NMDA) or 100 microM kainate at 22 degrees C greatly increased LT, particularly in the dendritic regions of CA1. The response peaked by 2-3 min and slowly reversed over the subsequent 20 min following exposure. Peak LT increases were > 50% in CA1 stratum radiatum and > 20% in both CA1 stratum oriens and the dendritic region of the dentate gyrus, all areas with a high concentration of NMDA and alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA) receptors. The CA3 stratum radiatum, which contains fewer of these receptors, showed a comparatively small LT increase. 4. The NMDA receptor antagonist 2-amino-5-phosphonovalerate (AP-5) [but not 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX)] blocked the CA1 response to NMDA, whereas the non-NMDA receptor antagonist CNQX (but not AP-5) blocked the response to kainate. The relative tissue resistance measured across CA1 stratum radiatum increased after NMDA or kainate exposure with a time course similar to the LT change described above. The increase in relative tissue resistance was blocked by kynurenate, a nonspecific glutamate antagonist. Increases in both LT and tissue resistance provide two independent lines of evidence that cell swelling rapidly developed in CA1 dendritic areas after activation of NMDA or AMPA receptors. 5. This swelling at 22 degrees C was accompanied by a temporary loss of the evoked CA1 field potential. However, at 37 degrees C the dendritic swelling rapidly progressed to an irreversible LT increase (swelling) of the CA1 cell bodies accompanied by a permanent loss of the evoked field. 6. We propose that dendritic swelling mediated by NMDA and AMPA receptors is an early excitotoxic event that can herald permanent damage to CA1 neurons, those cells most vulnerable to ischemic insult.

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