scholarly journals FAD-Linked Autofluorescence and Chemically-Evoked Zinc Changes at Hippocampal Mossy Fiber-CA3 Synapses

2021 ◽  
Author(s):  
Fatima M.C. Bastos ◽  
Carlos M. Matias ◽  
Ines O. Lopes ◽  
João P. Vieira ◽  
Rosa M. Santos ◽  
...  
Keyword(s):  
Katp Channel ◽  
Mossy Fiber ◽  
Brain Slices ◽  
Katp Channels ◽  
Synaptic Activity ◽  
Microscopy Technique ◽  
High K ◽  
Zinc Release ◽  
Presynaptic Boutons ◽  
Safeguard Mechanism

Glutamatergic vesicles in hippocampal mossy fiber presynaptic boutons release zinc, which plays a modulatory role in synaptic activity and LTP. In this work, a fluorescence microscopy technique and the fluorescent probe for cytosolic zinc, Newport Green (NG), were applied, in a combined study of autofluorescence and zinc changes at the hippocampal mossy fiber-CA3 synaptic system. In particular, the dynamics of flavoprotein (FAD) autofluorescence signals, was compared to that of postsynaptic zinc signals, elicited both by high K+ (20 mM) and by tetraethylammonium (TEA, 25 mM). The real zinc signals were obtained subtracting autofluorescence values, from corresponding total NG-fluorescence data. Both autofluorescence and zinc-related fluorescence were raised by high K+. In contrast, the same signals were reduced during TEA exposure. It is suggested that the initial outburst of TEA-evoked zinc release might activate ATP-sensitive K+ (KATP) channels, as part of a safeguard mechanism against excessive glutamatergic action. This would cause sustained inhibition of zinc signals and a more reduced mitochondrial state. In favor of the “KATP channel hypothesis”, the KATP channel blocker tolbutamide (250 μM) nearly suppressed the TEA-evoked fluorescence changes. It is concluded that recording autofluorescence from brain slices is essential for the accurate assessment of zinc signals and actions.

scholarly journals BAD and KATP channels regulate neuron excitability and epileptiform activity

eLife ◽  
2018 ◽  
Vol 7 ◽  
Author(s):  
Juan Ramón Martínez-François ◽  
María Carmen Fernández-Agüera ◽  
Nidhi Nathwani ◽  
Carolina Lahmann ◽  
Veronica L Burnham ◽  
...  
Keyword(s):  
Katp Channel ◽  
Neuronal Excitability ◽  
Epileptiform Activity ◽  
Hippocampal Slices ◽  
Brain Slices ◽  
Epileptic Seizures ◽  
Katp Channels ◽  
Brain Cell ◽  
Channel Activity

Brain metabolism can profoundly influence neuronal excitability. Mice with genetic deletion or alteration of Bad (BCL-2 agonist of cell death) exhibit altered brain-cell fuel metabolism, accompanied by resistance to acutely induced epileptic seizures; this seizure protection is mediated by ATP-sensitive potassium (KATP) channels. Here we investigated the effect of BAD manipulation on KATP channel activity and excitability in acute brain slices. We found that BAD’s influence on neuronal KATP channels was cell-autonomous and directly affected dentate granule neuron (DGN) excitability. To investigate the role of neuronal KATP channels in the anticonvulsant effects of BAD, we imaged calcium during picrotoxin-induced epileptiform activity in entorhinal-hippocampal slices. BAD knockout reduced epileptiform activity, and this effect was lost upon knockout or pharmacological inhibition of KATP channels. Targeted BAD knockout in DGNs alone was sufficient for the antiseizure effect in slices, consistent with a ‘dentate gate’ function that is reinforced by increased KATP channel activity.

Central KATP channels modulate glucose effectiveness in humans and rodents

2020 ◽  
Author(s):  
Ada Admin ◽  
Michelle Carey ◽  
Eric Lontchi-Yimagou ◽  
William Mitchell ◽  
Sarah Reda ◽  
...  
Keyword(s):  
Katp Channel ◽  
Glucose Production ◽  
Katp Channels ◽  
Endogenous Glucose Production ◽  
Elevated Plasma ◽  
Sprague Dawley ◽  
Glucose Effectiveness ◽  
Sprague Dawley Rats ◽  
The Central Nervous System

Hyperglycemia is a potent regulator of endogenous glucose production (EGP). Loss of this ‘glucose effectiveness’ is a major contributor to elevated plasma glucose concentrations in type 2 diabetes (T2D). ATP-sensitive potassium channels (K<sub>ATP</sub> channels) in the central nervous system (CNS) have been shown to regulate EGP in humans and rodents. We examined the contribution of central K<sub>ATP</sub> channels to glucose effectiveness. Under fixed hormonal conditions (‘pancreatic clamp’ studies), hyperglycemia suppressed EGP by ~50% in both non-diabetic humans and normal Sprague Dawley rats. By contrast, antagonism of K<sub>ATP</sub> channels with glyburide significantly reduced the EGP-lowering effect of hyperglycemia in both humans and rats. Furthermore, the effects of glyburide on EGP and gluconeogenic enzymes in rats were abolished by intracerebroventricular (ICV) administration of the KATP channel agonist diazoxide. These findings indicate that about half of EGP suppression by hyperglycemia is mediated by central K<sub>ATP</sub> channels. These central mechanisms may offer a novel therapeutic target for improving glycemic control in T2D.

scholarly journals GPI-1046 Increases Presenilin-1 Expression and Restores NMDA Channel Activity

2010 ◽  
Vol 37 (4) ◽  
pp. 457-467 ◽  
Author(s):  
Joseph P. Steiner ◽  
Kathryn B. Payne ◽  
Christopher Drummond Main ◽  
Sabrina D'Alfonso ◽  
Kirsten X. Jacobsen ◽  
...  
Keyword(s):  
Nmda Receptor ◽  
Synaptic Transmission ◽  
Brain Slices ◽  
Synaptic Activity ◽  
Presenilin 1 ◽  
Receptor Function ◽  
Channel Function ◽  
Nmda Channel ◽  
Nmda Receptor Function ◽  
6 Hydroxydopamine

Background:Previously we showed that 6-hydroxydopamine lesions of the substantia nigra eliminate corticostriatal LTP and that the neuroimmunolophilin ligand (NIL), GPI-1046, restores LTP.Methods:We used cDNA microarrays to determine what mRNAs may be over- or under-expressed in response to lesioning and/or GPI-1046 treatment. Patch clamp recordings were performed to investigate changes in NMDA channel function before and after treatments.Results:We found that 51 gene products were differentially expressed. Among these we found that GPI-1046 treatment up-regulated presenilin-1 (PS-1) mRNA abundance. This finding was confirmed using QPCR. PS-1 protein was also shown to be over-expressed in the striatum of lesioned/GPI-1046-treated rats. As PS-1 has been implicated in controlling NMDA-receptor function and LTP is reduced by lesioning we assayed NMDA mediated synaptic activity in striatal brain slices. The lesion-induced reduction of dopaminergic innervation was accompanied by the near complete loss of NDMA receptor-mediated synaptic transmission between the cortex and striatum. GPI-1046 treatment of the lesioned rats restored NMDA-mediated synaptic transmission but not the dopaminergic innervation. Restoration of NDMA channel function was apparently specific as the sodium channel current density was also reduced due to lesioning but GPI-1046 did not reverse this effect. We also found that restoration of NMDA receptor function was also not associated with either an increase in NMDA receptor mRNA or protein expression.Conclusion:As it has been previously shown that PS-1 is critical for normal NMDA receptor function, our data suggest that the improvement of excitatory neurotransmission occurs through the GPI-1046-induced up-regulation of PS-1.

Altered desensitization produces enhancement of EPSPs in neocortical neurons

1994 ◽  
Vol 72 (2) ◽  
pp. 1032-1036 ◽  
Author(s):  
M. R. Pelletier ◽  
J. J. Hablitz
Keyword(s):  
Nmda Receptors ◽  
Time Course ◽  
Glutamate Release ◽  
Epileptiform Activity ◽  
Brain Slices ◽  
Synaptic Activity ◽  
Membrane Properties ◽  
Repetitive Firing ◽  
Resting Membrane Potential ◽  
Bath Application

1. Neocortical brain slices were prepared from rats (35–50 days of age) and maintained in vitro. Intracellular recordings were obtained from neurons in cortical layers II/III. The effect of bath application of cyclothiazide (CYZ), a potent blocker of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA) receptor desensitization, on evoked synaptic activity and passive membrane properties was investigated. 2. Bath application of CYZ did not significantly affect resting membrane potential, input resistance, or repetitive firing. CYZ increased both the amplitude and duration of evoked excitatory postsynaptic potentials (EPSPs). Polysynaptic responses were also augumented. These effects persisted after the blockade of N-methyl-D-aspartate (NMDA) receptors with D-2-amino-5-phosphonovaleric acid (D-APV). The magnitude of these effects appeared to vary directly with stimulation intensity and presumably, amount of glutamate release. 3. Epileptiform activity was induced by bath application of bicuculline methiodide. The amplitude and duration of evoked paroxysmal discharges were increased by CYZ. Similar results were seen in presence of D-APV. 4. These results indicate that CYZ has significant effects on synaptic transmission. Desensitization of non-NMDA receptors may be an important mechanism for determining the time course of EPSPs and in curtailing epileptiform responses in the rat neocortex.

scholarly journals Spontaneous Synaptic Activity Is Primarily GABAergic in Vestibular Nucleus Neurons of the Chick Embryo

2003 ◽  
Vol 90 (2) ◽  
pp. 1182-1192 ◽  
Author(s):  
Mei Shao ◽  
June C. Hirsch ◽  
Christian Giaume ◽  
Kenna D. Peusner
Keyword(s):  
Glutamate Receptor ◽  
Vestibular Nucleus ◽  
Glycine Receptor ◽  
Brain Slices ◽  
Reversal Potential ◽  
Cell Voltage ◽  
Synaptic Activity ◽  
Pipette Solution ◽  
Principal Cells ◽  
Postsynaptic Currents

The principal cells of the chick tangential nucleus are vestibular nucleus neurons participating in the vestibular reflexes. In 16-day embryos, the application of glutamate receptor antagonists abolished the postsynaptic responses generated on vestibular-nerve stimulation, but spontaneous synaptic activity was largely unaffected. Here, spontaneous synaptic activity was characterized in principal cells from brain slices at E16 using whole cell voltage-clamp recordings. With KCl electrodes, the frequency of spontaneous inward currents was 3.1 Hz at –60 mV, and the reversal potential was +4 mV. Cs-gluconate pipette solution allowed the discrimination of glycine/GABAA versus glutamate receptor-mediated events according to their different reversal potentials. The ratio for spontaneous excitatory to inhibitory events was about 1:4. Seventy-four percent of the outward events were GABAA, whereas 26% were glycine receptor-mediated events. Both pre- and postsynaptic GABAB receptor effects were shown, with presynaptic GABAB receptors inhibiting 40% of spontaneous excitatory postsynaptic currents (sEPSCs) and 53% of spontaneous inhibitory postsynaptic currents (sIPSCs). With TTX, the frequency decreased ∼50% for EPSCs and 23% for IPSCs. These data indicate that the spontaneous synaptic activity recorded in the principal cells at E16 is primarily inhibitory, action potential-independent, and based on the activation of GABAA receptors that can be modulated by presynaptic GABAB receptors.

Regulation of ATP-sensitive K+ channels by ATP and nucleotide diphosphate in rabbit portal vein

1994 ◽  
Vol 266 (5) ◽  
pp. H1687-H1698 ◽  
Author(s):  
M. Kamouchi ◽  
K. Kitamura
Keyword(s):  
Portal Vein ◽  
Katp Channel ◽  
Single Channel ◽  
Katp Channels ◽  
K Channel ◽  
Channel Activity ◽  
Rabbit Portal Vein ◽  
Internal Side ◽  
The Right ◽  
Single Channel Currents

The modulation of ATP-sensitive K+ (KATP)-channel activity was investigated by recording single-channel currents in isolated smooth muscle cells from rabbit portal vein. K(+)-channel openers (KCOs; pinacidil, lemakalim, and nicorandil) induced burstlike openings of single KATP channels in the cell-attached configuration. After patch excision, KATP channels showed "run-down" phenomenon in the presence of KCOs, but subsequent application of Mg-ATP (1 mM) restored KATP-channel activity. Removal of Mg-ATP resulted in transient augmentation of KATP currents, which eventually decayed out. Nucleotide diphosphates (NDPs; GDP, ADP, UDP, IDP, and CDP) also induced channel reopening in the presence of KCOs, which was markedly enhanced by addition of Mg2+ in millimolar concentrations at the internal side of the membrane. The dose-response relation between ATP and the UDP-induced KATP-channel activity was shifted to the right in the presence of Mg2+ (2 mM). These results suggest that intracellular ATP, NDPs, and Mg2+ regulate the channel state of KATP channels (operative and inoperative states) and that KCOs open KATP channels only in the operative state.

Effect of tolbutamide on tetraethylammonium-induced postsynaptic zinc signals at hippocampal mossy fiber-CA3 synapses

2017 ◽  
Vol 95 (9) ◽  
pp. 1058-1063 ◽  
Author(s):  
Fatima C. Bastos ◽  
Vanessa N. Corceiro ◽  
Sandra A. Lopes ◽  
José G. de Almeida ◽  
Carlos M. Matias ◽  
...  
Keyword(s):  
Mossy Fiber ◽  
Mossy Fibers ◽  
Pyramidal Cells ◽  
Long Term Potentiation ◽  
Chemical Stimulation ◽  
Term Potentiation ◽  
Voltage Dependent ◽  
Zinc Release ◽  
Ca3 Pyramidal Cells

The application of tetraethylammonium (TEA), a blocker of voltage-dependent potassium channels, can induce long-term potentiation (LTP) in the synaptic systems CA3–CA1 and mossy fiber-CA3 pyramidal cells of the hippocampus. In the mossy fibers, the depolarization evoked by extracellular TEA induces a large amount of glutamate and also of zinc release. It is considered that zinc has a neuromodulatory role at the mossy fiber synapses, which can, at least in part, be due to the activation of presynaptic ATP-dependent potassium (KATP) channels. The aim of this work was to study properties of TEA-induced zinc signals, detected at the mossy fiber region, using the permeant form of the zinc indicator Newport Green. The application of TEA caused a depression of those signals that was partially blocked by the KATP channel inhibitor tolbutamide. After the removal of TEA, the signals usually increased to a level above baseline. These results are in agreement with the idea that intense zinc release during strong synaptic events triggers a negative feedback action. The zinc depression, caused by the LTP-evoking chemical stimulation, turns into potentiation after TEA washout, suggesting the existence of a correspondence between the observed zinc potentiation and TEA-evoked mossy fiber LTP.

Blockade of Adenosine Triphosphate–sensitive Potassium Channels by Thiamylal in Rat Ventricular Myocytes

2000 ◽  
Vol 92 (4) ◽  
pp. 1154-1159 ◽  
Author(s):  
Yasuo Tsutsumi ◽  
Shuzo Oshita ◽  
Hiroshi Kitahata ◽  
Yasuhiro Kuroda ◽  
Takashi Kawano ◽  
...  
Keyword(s):  
Adenosine Triphosphate ◽  
Katp Channel ◽  
Single Channel ◽  
Ventricular Myocytes ◽  
Katp Channels ◽  
Dependent Manner ◽  
Open Probability ◽  
Rat Ventricular Myocytes ◽  
Inside Out ◽  
Cell Attached Configuration

Background The adenosine triphosphate (ATP)-sensitive potassium (KATP) channels protect myocytes during ischemia and reperfusion. This study investigated the effects of thiamylal on the activities of KATP channels in isolated rat ventricular myocytes during simulated ischemia. Methods Male Wistar rats were anesthetized with ether. Single, quiescent ventricular myocytes were dispersed enzymatically. Membrane currents were recorded using patch-clamp techniques. In the cell-attached configuration, KATP channel currents were assessed before and during activation of these channels by 2,4-dinitrophenol and after administration of 25, 50, and 100 mg/l thiamylal. The open probability was determined from current-amplitude histograms. In the inside-out configuration, the current-voltage relation was obtained before and after the application of thiamylal (50 mg/1). Results In the cell-attached configuration, 2,4-dinitrophenol caused frequent channel opening. 2,4-Dinitrophenol-induced channel activities were reduced significantly by glibenclamide, suggesting that the channels studied were KATP channels. Open probability of KATP channels was reduced by thiamylal in a concentration-dependent manner. KATP channels could be activated in the inside-out configuration because of the absence of ATP. Thiamylal inhibited KATP channel activity without changing the single-channel conductance. Conclusions The results obtained in this study indicate that thiamylal inhibits KATP channel activities in cell-attached and inside-out patches, suggesting a direct action of this drug on these channels.

Pharmacological modulation of KATP channels

2002 ◽  
Vol 30 (2) ◽  
pp. 333-339 ◽  
Author(s):  
F. M. Gribble ◽  
F. Reimann
Keyword(s):  
Type 2 Diabetes ◽  
Cardiac Muscle ◽  
Katp Channel ◽  
Katp Channels ◽  
Β Cells ◽  
Pancreatic Β Cells ◽  
Tissue Specific ◽  
Pharmacological Modulation ◽  
Clinical Conditions

Pharmacological modulation of ATP-sensitive K+ (KATP) channels is used in the treatment of a number of clinical conditions, including type 2 diabetes and angina. The sulphonylureas and related drugs, which are used to treat type 2 diabetes, stimulate insulin secretion by closing KATP channels in pancreatic β-cells. Agents used to treat angina, by contrast, act by opening KATP channels in vascular smooth and cardiac muscle. Both the therapeutic KATP channel inhibitors and the KATP channel openers target the sulphonylurea receptor (SUR) subunit of the KATP channel, which exists in several isoforms expressed in different tissues (SUR1 in pancreatic β-cells, SUR2A in cardiac muscle and SUR2B in vascular smooth muscle). The tissue-specific action of drugs that target the KATP channel is attributed to the properties of these different SUR subtypes. In this review, we discuss the molecular basis of tissue-specific drug action, and its implications for clinical practice.

scholarly journals Human autoantibodies to amphiphysin induce defective presynaptic vesicle dynamics and composition

Brain ◽  
2015 ◽  
Vol 139 (2) ◽  
pp. 365-379 ◽  
Author(s):  
Christian Werner ◽  
Martin Pauli ◽  
Sören Doose ◽  
Andreas Weishaupt ◽  
Holger Haselmann ◽  
...  
Keyword(s):  
Central Nervous System ◽  
Nervous System ◽  
Ex Vivo ◽  
Super Resolution ◽  
Synaptic Activity ◽  
Stiff Person Syndrome ◽  
Specific Patient ◽  
Presynaptic Boutons ◽  
Presynaptic Vesicle

Abstract See Irani (doi:10.1093/awv364) for a scientific commentary on this article.  Stiff-person syndrome is the prototype of a central nervous system disorder with autoantibodies targeting presynaptic antigens. Patients with paraneoplastic stiff-person syndrome may harbour autoantibodies to the BAR (Bin/Amphiphysin/Rvs) domain protein amphiphysin, which target its SH3 domain. These patients have neurophysiological signs of compromised central inhibition and respond to symptomatic treatment with medication enhancing GABAergic transmission. High frequency neurotransmission as observed in tonic GABAergic interneurons relies on fast exocytosis of neurotransmitters based on compensatory endocytosis. As amphiphysin is involved in clathrin-mediated endocytosis, patient autoantibodies are supposed to interfere with this function, leading to disinhibition by reduction of GABAergic neurotransmission. We here investigated the effects of human anti-amphiphysin autoantibodies on structural components of presynaptic boutons ex vivo and in vitro using electron microscopy and super-resolution direct stochastic optical reconstruction microscopy. Ultrastructural analysis of spinal cord presynaptic boutons was performed after in vivo intrathecal passive transfer of affinity-purified human anti-amphiphysin autoantibodies in rats and revealed signs of markedly disabled clathrin-mediated endocytosis. This was unmasked at high synaptic activity and characterized by a reduction of the presynaptic vesicle pool, clathrin coated intermediates, and endosome-like structures. Super-resolution microscopy of inhibitory GABAergic presynaptic boutons in primary neurons revealed that specific human anti-amphiphysin immunoglobulin G induced an increase of the essential vesicular protein synaptobrevin 2 and a reduction of synaptobrevin 7. This constellation suggests depletion of resting pool vesicles and trapping of releasable pool vesicular proteins at the plasma membrane. Similar effects were found in amphiphysin-deficient neurons from knockout mice. Application of specific patient antibodies did not show additional effects. Blocking alternative pathways of clathrin-independent endocytosis with brefeldin A reversed the autoantibody induced effects on molecular vesicle composition. Endophilin as an interaction partner of amphiphysin showed reduced clustering within presynaptic terminals. Collectively, these results point towards an autoantibody-induced structural disorganization in GABAergic synapses with profound changes in presynaptic vesicle pools, activation of alternative endocytic pathways, and potentially compensatory rearrangement of proteins involved in clathrin-mediated endocytosis. Our findings provide novel insights into synaptic pathomechanisms in a prototypic antibody-mediated central nervous system disease, which may serve as a proof-of-principle example in this evolving group of autoimmune disorders associated with autoantibodies to synaptic antigens.

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