The uptake inhibitor L-trans-PDC enhances responses to glutamate but fails to alter the kinetics of excitatory synaptic currents in the hippocampus

1993 ◽  
Vol 70 (5) ◽  
pp. 2187-2191 ◽  
Author(s):  
J. S. Isaacson ◽  
R. A. Nicoll
Keyword(s):  
Time Course ◽  
Glutamate Uptake ◽  
Hippocampal Slices ◽  
Synaptic Cleft ◽  
Gamma Aminobutyric Acid ◽  
Patch Clamp Recording ◽  
Glutamatergic Synapses ◽  
Synaptic Currents ◽  
Ca1 Region ◽  
Transmitter Uptake

1. We have used patch-clamp recording techniques to study the physiological properties of a recently described glutamate uptake blocker, L-trans-pyrrolidine-2,4-dicarboxylic acid (L-trans-PDC), in the CA1 region of the guinea pig hippocampus. 2. L-trans-PDC markedly potentiated the action of exogenously applied glutamate and raised the ambient extracellular levels of glutamate in hippocampal slices. Despite these actions, L-trans-PDC did not affect the time course of either the N-methyl-D-aspartate (NMDA) or non-NMDA receptor-mediated synaptic currents evoked by the stimulation of a large number of neighboring synapses. 3. These findings are consistent with models of fast synaptic transmission in which transmitter is rapidly cleared from the synaptic cleft by diffusion. However, in marked contrast to fast gamma-aminobutyric acid A (GABAA) synapses in the hippocampus, uptake does not appear to play a role in regulating the "spill-over" of transmitter from neighboring, co-activated glutamatergic synapses. Therefore, either diffusion alone can effectively limit the temporal and spatial domain of synaptically released glutamate, or alternatively, L-trans-PDC like other currently available blockers is not sufficiently potent to reveal a role for transmitter uptake at glutamatergic synapses.

scholarly journals DM1 Transgenic Mice Exhibit Abnormal Neurotransmitter Homeostasis and Synaptic Plasticity in Association with RNA Foci and Mis-Splicing in the Hippocampus

2022 ◽  
Vol 23 (2) ◽  
pp. 592
Author(s):  
Brigitte Potier ◽  
Louison Lallemant ◽  
Sandrine Parrot ◽  
Aline Huguet-Lachon ◽  
Geneviève Gourdon ◽  
...  
Keyword(s):  
Time Course ◽  
Pyramidal Neurons ◽  
Granule Cells ◽  
Glutamate Uptake ◽  
Hippocampal Slices ◽  
Synaptic Cleft ◽  
Synaptic Dysfunction ◽  
Functional Changes ◽  
Rna Foci ◽  
The Impact

Myotonic dystrophy type 1 (DM1) is a severe neuromuscular disease mediated by a toxic gain of function of mutant RNAs. The neuropsychological manifestations affect multiple domains of cognition and behavior, but their etiology remains elusive. Transgenic DMSXL mice carry the DM1 mutation, show behavioral abnormalities, and express low levels of GLT1, a critical regulator of glutamate concentration in the synaptic cleft. However, the impact of glutamate homeostasis on neurotransmission in DM1 remains unknown. We confirmed reduced glutamate uptake in the DMSXL hippocampus. Patch clamp recordings in hippocampal slices revealed increased amplitude of tonic glutamate currents in DMSXL CA1 pyramidal neurons and DG granule cells, likely mediated by higher levels of ambient glutamate. Unexpectedly, extracellular GABA levels and tonic current were also elevated in DMSXL mice. Finally, we found evidence of synaptic dysfunction in DMSXL mice, suggestive of abnormal short-term plasticity, illustrated by an altered LTP time course in DG and in CA1. Synaptic dysfunction was accompanied by RNA foci accumulation in localized areas of the hippocampus and by the mis-splicing of candidate genes with relevant functions in neurotransmission. Molecular and functional changes triggered by toxic RNA may induce synaptic abnormalities in restricted brain areas that favor neuronal dysfunction.

Hippocampal inhibitory interneurons are functionally disconnected from excitatory inputs by anoxia

1993 ◽  
Vol 70 (6) ◽  
pp. 2251-2259 ◽  
Author(s):  
R. Khazipov ◽  
P. Bregestovski ◽  
Y. Ben-Ari
Keyword(s):  
Pyramidal Neurons ◽  
Hippocampal Slices ◽  
Pyramidal Cells ◽  
Gabab Receptors ◽  
Stratum Radiatum ◽  
Gamma Aminobutyric Acid ◽  
Patch Clamp Recording ◽  
Synaptic Currents ◽  
Postsynaptic Currents ◽  
Whole Cell Patch Clamp

1. The effects of anoxia on inhibitory synaptic transmission were studied in hippocampal slices of 3- to 4-wk-old rats. CA1 pyramidal cells were examined by whole-cell patch-clamp recording. Synaptic currents were evoked by “distant” (> 0.5 mm) or “close” (< 0.5 mm) electrical stimulation in the stratum radiatum. 2. The excitatory postsynaptic currents (EPSCs) and inhibitory postsynaptic currents (IPSCs) evoked by distant stimulation were completely suppressed by brief anoxia (95% N2-5% CO2 for 4-6 min) and recovered upon reoxygenation. IPSCs were more sensitive to anoxia than EPSCs. EPSCs and IPSCs evoked by distant stimulation were blocked by 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX; 20 microM) and D-2-amino-5-phosphonopentanoate (APV; 50 microM). This indicates that IPSCs were mediated via a polysynaptic pathway that involves glutamate receptors. 3. Synaptic currents evoked by close stimulation were only partly inhibited by anoxia. The bicuculline-sensitive gamma-aminobutyric acid-A (GABAA) receptor-mediated synaptic currents were particularly resistant to anoxia, suggesting that the GABAergic input to pyramidal neurons is not inhibited by anoxia. 4. At close stimulation in the stratum radiatum, monosynaptic IPSCs could be evoked in the presence of CNQX (20 microM) and APV (50 microM). The monosynaptic IPSCs had early bicuculline (15 microM) and late CGP 35348 (100 microM)-sensitive components confirming an involvement of GABAA and GABAB receptors (IPSCA and IPSCB components), respectively. 5. The monosynaptic IPSCA component evoked by close stimulation was not changed significantly during and after brief anoxia. Responses to pressure application of isoguvacine (GABAA agonist) were also not affected by anoxia.(ABSTRACT TRUNCATED AT 250 WORDS)

Agent-selective Effects of Volatile Anesthetics on GABAAReceptor–mediated Synaptic Inhibition in Hippocampal Interneurons

2001 ◽  
Vol 94 (2) ◽  
pp. 340-347 ◽  
Author(s):  
Koichi Nishikawa ◽  
M. Bruce MacIver
Keyword(s):  
Gabaa Receptor ◽  
Hippocampal Slices ◽  
Pyramidal Cells ◽  
Volatile Anesthetics ◽  
Stratum Radiatum ◽  
Synaptic Inhibition ◽  
Gamma Aminobutyric Acid ◽  
Ca1 Region ◽  
Whole Cell Patch Clamp ◽  
Cortical Regions

Background A relatively small number of inhibitory interneurons can control the excitability and synchronization of large numbers of pyramidal cells in hippocampus and other cortical regions. Thus, anesthetic modulation of interneurons could play an important role for the maintenance of anesthesia. The aim of this study was to compare effects produced by volatile anesthetics on inhibitory postsynaptic currents (IPSCs) of rat hippocampal interneurons. Methods Pharmacologically isolated gamma-aminobutyric acid type A (GABAA) receptor-mediated IPSCs were recorded with whole cell patch-clamp techniques in visually identified interneurons of rat hippocampal slices. Neurons located in the stratum radiatum-lacunosum moleculare of the CA1 region were studied. The effects of clinically relevant concentrations (1.0 rat minimum alveolar concentration) of halothane, enflurane, isoflurane, and sevoflurane were compared on kinetics of both stimulus-evoked and spontaneous GABAA receptor-mediated IPSCs in interneurons. Results Halothane (1.2 vol% approximately 0.35 mm), enflurane (2.2 vol% approximately 0.60 mm), isoflurane (1.4 vol% approximately 0.50 mm), and sevoflurane (2.7 vol% approximately 0.40 mm) preferentially depressed evoked IPSC amplitudes to 79.8 +/- 9.3% of control (n = 5), 38.2 +/- 8.6% (n = 6), 52.4 +/- 8.4% (n = 5), and 46.1 +/- 16.0% (n = 8), respectively. In addition, all anesthetics differentially prolonged the decay time constant of evoked IPSCs to 290.1 +/- 33.2% of control, 423.6 +/- 47.1, 277.0 +/- 32.2, and 529 +/- 48.5%, respectively. The frequencies of spontaneous IPSCs were increased by all anesthetics (twofold to threefold). Thus, the total negative charge transfer mediated by GABAA receptors between synaptically connected interneurons was enhanced by all anesthetics. Conclusions Volatile anesthetics differentially enhanced GABAA receptor-mediated synaptic inhibition in rat hippocampal interneurons, suggesting that hippocampal interneuron circuits are depressed by these anesthetics in an agent-specific manner.

Dual Actions of Volatile Anesthetics on GABAAIPSCs 

1999 ◽  
Vol 90 (1) ◽  
pp. 120-134 ◽  
Author(s):  
Matthew I. Banks ◽  
Robert A. Pearce
Keyword(s):  
Concentration Dependence ◽  
Time Course ◽  
Pyramidal Neurons ◽  
Hippocampal Slices ◽  
Volatile Anesthetics ◽  
Blocking Effect ◽  
Dependent Manner ◽  
Gamma Aminobutyric Acid ◽  
Baseline Noise ◽  
Volatile Agents

Background Volatile agents alter inhibitory postsynaptic currents (IPSCs) at clinically relevant concentrations, an action that is thought to make an important contribution to their behavioral effects. The authors investigated the mechanisms underlying these effects by evaluating the concentration dependence of modulation by enflurane, isoflurane, and halothane of IPSCs in rat hippocampal slices. Methods Action potential-independent gamma-aminobutyric acid(A) IPSCs (miniature IPSCs [mIPSCs]) were recorded from CA1 pyramidal neurons. The effects on mIPSC amplitude were used to distinguish between presynaptic (altered release) and postsynaptic (altered receptor response) actions of volatile agents. The concentration dependence of blocking and prolonging actions was compared among the volatile agents to determine whether a single modulatory process could account for both effects. Results The application of volatile anesthetics prolonged the decay and reduced the amplitude of mIPSCs in a dose-dependent manner. The effects on decay time for isoflurane and enflurane could not be distinguished. However, the blocking effect of enflurane was significantly greater than that of isoflurane at all concentrations. Despite the blocking effect, the net action of these agents was enhanced inhibition, because charge transfer was always significantly greater than control. Isoflurane, and to a lesser extent enflurane and halothane, caused a picrotoxin-sensitive increase in baseline noise. Moderate increases in mIPSC frequency were also observed for all agents. Conclusions These results show that enflurane, isoflurane, and halothane reduce IPSC amplitude through a direct postsynaptic action. Furthermore, the concentration dependence of the actions of the agents reveals a dissociation between the effects on the amplitude and the time course of IPSCs, suggesting that distinct mechanisms underlie the two actions.

Increase of Glutamate Uptake in Astrocytes 

1997 ◽  
Vol 86 (6) ◽  
pp. 1359-1366 ◽  
Author(s):  
Hirofumi Miyazaki ◽  
Yoichi Nakamura ◽  
Tatsuru Arai ◽  
Kiyoshi Kataoka
Keyword(s):  
Central Nervous System ◽  
Nervous System ◽  
Glutamate Uptake ◽  
Synaptic Cleft ◽  
Volatile Anesthetics ◽  
Gamma Aminobutyric Acid ◽  
Excitatory Neurotransmitter ◽  
Significant Augmentation ◽  
Uptake Activity ◽  
Entire Central Nervous System

Background Glutamate is the most ubiquitous excitatory neurotransmitter in the vertebrate central nervous system. Astrocytes play an important role in terminating glutamatergic neurotransmission by removing released glutamate from the synaptic cleft. The authors examined the effects of several anesthetics on the glutamate uptake activity of astrocytes. Methods Cultured astrocytes from hippocampi of rat embryos were incubated with solution containing [3H]glutamate, which was pre-equilibrated with 0-4% halothane at 37 degrees C. The uptake activity was evaluated as the amount of radioactivity per cell of protein. Results When the reaction solution was equilibrated with 4% halothane, glutamate uptake increased to about 165% of the control. The effect of halothane was dose-dependent, and a significant augmentation (30-50%) of glutamate uptake was observed at a range in clinical use concentrations (1-2%). On the other hand, the uptake of gamma-aminobutyric acid, an inhibitory transmitter, was hardly affected by 1-4% halothane. The effect of halothane on glutamate uptake was also examined in neuron-rich culture, and similar augmentation was observed, although the extent was less than that in astrocyte culture. Biochemical subcellular fractions (i.e., glial plasmalemmal vesicles and synaptosomes) were also examined, however, only slight (not significant) increase was detected in the glutamate uptake activity. Other volatile anesthetics, such as enflurane, isoflurane, and sevoflurane, also enhanced glutamate uptake, whereas the intravenous anesthetics ketamine and pentobarbital showed no effect on glutamate uptake. Conclusions The increase of glutamate uptake by astrocytes in the presence of volatile anesthetics potentially attenuates excitatory synaptic transmission in the entire central nervous system, a finding that may explain in part the action of volatile anesthetics.

Nitrous Oxide-induced Enhancement of γ-Aminobutyric Acid-A-mediated Chloride Currents in Acutely Dissociated Hippocampal Neurons 

1998 ◽  
Vol 88 (2) ◽  
pp. 473-480 ◽  
Author(s):  
Misa Dzoljic ◽  
Bert Van Duijn
Keyword(s):  
Nitrous Oxide ◽  
Hippocampal Neurons ◽  
Prolonged Exposure ◽  
Aminobutyric Acid ◽  
Gamma Aminobutyric Acid ◽  
General Anesthetics ◽  
Patch Clamp Recording ◽  
Gaba A ◽  
Ca1 Region ◽  
Tube Application

Background Because the synaptic inhibition in the human brain is largely mediated by gamma-aminobutyric acid (GABA), the GABA receptor is of primary interest for the study of the working mechanism of general anesthetics. This article examines the interaction between this type of ion channel and nitrous oxide (N2O). Methods Patch clamp recording techniques were applied to investigate the effects of N2O on GABA(A) receptor channels in a whole-cell configuration at room temperature. Acutely dissociated rat hippocampal cells from the CA1 region were used. Rapid application of the agonist muscimol and anesthetics (N2O, pentobarbital, and ethanol) was accomplished using a Y tube application system. Peak chloride (Cl-) currents were measured. Results Short-term application of muscimol (5-30 microM) with dissolved N2O (80%, approximately 22.5 mM) increased the Cl- current (approximately 140%) compared with muscimol alone. This effect is comparable with results the authors obtained with ethanol (800 mM) and pentobarbital (100 microM). Prolonged exposure (9 min) to N2O further increased Cl- currents by an additional 50%. Concentrations of N2O lower than 12 mM did not show an enhancement of this current, whereas application of N2O alone did not result in any Cl- conductance. Conclusions These results indicate that N2O can enhance GABA(A) channel-mediated Cl- currents by modulating the effect of the specific GABA(A) agonist; it is not active by itself.

Intracellular pH changes produced by glutamate uptake in rat hippocampal slices

1994 ◽  
Vol 72 (4) ◽  
pp. 1686-1696 ◽  
Author(s):  
A. Amato ◽  
L. Ballerini ◽  
D. Attwell
Keyword(s):  
Intracellular Ph ◽  
Chloride Channels ◽  
Glutamate Uptake ◽  
Hippocampal Slices ◽  
Disulfonic Acid ◽  
Extracellular Potassium ◽  
Gamma Aminobutyric Acid ◽  
Extracellular Potassium Concentration ◽  
Ph Changes ◽  
Glutamate Concentration

1. The mean intracellular pH in area CA1 of rat hippocampal slices was monitored fluorescently after loading the cells with the dye BCECF-AM. 2. Including L-glutamate in the solution superfusing the slice led to the intracellular pH becoming more acid. This acidification had a roughly Michaelis-Menten dependence on the superfused glutamate concentration with a half-maximal dose around 200 microM: this value must overestimate the glutamate concentration at most of the cells, which will be reduced by uptake. 3. The glutamate-evoked acidification was not significantly reduced by blockers of glutamate-gated ion channels [6-cyano-7-nitroquinoxaline-2,3- dione (CNQX) and D-aminophosphonovalerate (APV)] nor by blockers of gamma-aminobutyric acid (GABA)- and glycine-gated channels (picrotoxin and strychnine), and so was not produced by H+ entry through alpha-amino-3-hydroxy-5-methyl-4- isoxazolepropionic acid (AMPA) or N-methyl-D-aspartate (NMDA) receptor channels nor by HCO3- exit through the chloride channels controlled by GABA or glycine. 4. The glutamate-evoked acidification was not reduced by tetrodotoxin (TTX), ruling out the possibility of it being generated by action potentials. It was also unaffected by saturation of presynaptic L-amino-4-phosphonobutanoate (AP4) receptors with AP4. 5. In the presence of blockers of glutamate-, GABA-, and glycine-gated channels, the acidification showed the pharmacology of glutamate uptake and was reduced by a glutamate uptake blocker. 6. The glutamate-evoked acidification showed an ion dependence similar to that of glutamate uptake. It was abolished by removal of extracellular sodium and was reduced by raising the extracellular potassium concentration. It was unaffected by blockers of Na+/H+ exchange (amiloride) and Na+/HCO3- cotransport [4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS)] and so was not produced by the Na+ influx accompanying glutamate uptake changing the activity of these carriers. 7. These data show that the glutamate uptake carrier acidifies hippocampal cells, possibly because it transports a pH-changing anion out of the cell as in salamander glial cells. Glutamate uptake may thus contribute to activity-induced pH changes in the nervous system.

Development of Glutamatergic Synaptic Activity in Cultured Spinal Neurons

2000 ◽  
Vol 83 (2) ◽  
pp. 659-670 ◽  
Author(s):  
Antoine Robert ◽  
James R. Howe ◽  
Stephen G. Waxman
Keyword(s):  
Nmda Receptor ◽  
Ampa Receptor ◽  
Time Course ◽  
Synaptic Activity ◽  
Spinal Neurons ◽  
Glutamatergic Synapses ◽  
Synaptic Currents ◽  
Sequence Of Events ◽  
Short Times

The development of glutamatergic synapses involves a sequence of events that are still not well understood. We have studied the time course of the development of glutamatergic synapses in cultured spinal neurons by characterizing spontaneous synaptic currents recorded from cells maintained in vitro for different times. At short times in culture (2 days in vitro; DIV2), spontaneous synaptic activity consisted almost solely of N-methyl-d-aspartate (NMDA) receptor (NMDAR) openings. In contrast, older neurons (DIV5 to DIV8) displayed clear α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor (AMPAR)–mediated synaptic currents, while the NMDAR-mediated activity remained small. Between 8 and 14 days in vitro there was a large increase in the density of synaptically activated NMDARs, although there was no significant increase in the density of the NMDAR-mediated current activated by exogenous glutamate. The results indicate that there is a switch in NMDAR targeting from somatic to synaptic regions during the course of the second in vitro week. Finally, our results support the conclusion that the spontaneous synaptic activity displayed in culture depends on ongoing NMDAR-mediated activity, even when the expression of synaptic NMDARs is low.

Differences between presynaptic and postsynaptic GABAB mechanisms in rat hippocampal pyramidal cells

1994 ◽  
Vol 72 (5) ◽  
pp. 2317-2327 ◽  
Author(s):  
T. A. Pitler ◽  
B. E. Alger
Keyword(s):  
Protein Kinase C ◽  
Protein Kinase ◽  
Pertussis Toxin ◽  
Hippocampal Slices ◽  
Pyramidal Cells ◽  
Cell Voltage ◽  
Gamma Aminobutyric Acid ◽  
Ca1 Region ◽  
Kinase C ◽  
First Response

1. Whole cell voltage-clamp techniques were used in the CA1 region of rat hippocampal slices to study presynaptic and postsynaptic gamma-aminobutyric acid B (GABAB) response mechanisms. The effects of the protein kinase C activator phorbol 12,13-diacetate (PDA), barium (Ba2+), and pertussis toxin were compared on the presynaptic and postsynaptic GABAB actions of bath-applied baclofen and paired-pulse depression (PPD) of the monosynaptic GABAA inhibitory postsynaptic current (IPSC). The magnitude of PPD was dependent on the amplitude of the first response. PPD was predominantly a GABAB-mediated effect, as it was very much reduced by the GABAB antagonist CGP 35348. 2. PDA enhanced monosynaptic GABAA IPSCs through an apparently presynaptic mechanism. Iontophoretic GABAA responses were unaffected, and there was no change in EIPSC. PDA increased the frequency of spontaneous, tetrodotoxin-insensitive IPSCs without significantly affecting their amplitudes. The inactive phorbol ester, 4 alpha-PDA did not alter IPSCs. After PDA application, stimulus intensity was adjusted to produce responses of comparable amplitude to control responses. PDA had a marked and reversible depressant effect on the postsynaptic GABAB response and caused a lesser, but still significant, reduction in the baclofen-induced reduction of monosynaptic IPSCs. PDA had no effect on PPD. 3. Ba2+ dramatically reduced postsynaptic GABAB responses; it had no effect on PPD. Ba2+ tended to decrease the presynaptic baclofen reduction of IPSCs, although this was not statistically significant. 4. Pertussis toxin, injected 2–3 days earlier into the intact hippocampus, blocked all three GABAB responses equally (approximately 70% decrease). 5. We conclude that presynaptic and postsynaptic GABAB mechanisms are mediated by G proteins that couple to different mechanisms. Discrepancies with previous work are evidently due to the use of different tissue preparations and different target responses. Even though protein kinase C activation caused a partial reduction in the presynaptic effect of baclofen, its lack of effect on PPD makes a significant role for protein kinase C in modulation of PPD unlikely.

Opponent effects of potassium on GABAA-mediated postsynaptic inhibition in the rat hippocampus

1993 ◽  
Vol 69 (3) ◽  
pp. 764-771 ◽  
Author(s):  
M. S. Jensen ◽  
E. Cherubini ◽  
Y. Yaari
Keyword(s):  
Time Course ◽  
Gabab Receptor ◽  
Hippocampal Slices ◽  
Gaba Release ◽  
Extracellular Potassium ◽  
Inhibitory Interneurons ◽  
Gamma Aminobutyric Acid ◽  
Outward Rectification ◽  
High K ◽  
Input Conductance

1. The effects of raising the concentration of extracellular potassium ([K+]o) on gamma aminobutyric acid (GABA)-mediated inhibitory postsynaptic potentials (IPSPs) were investigated in adult rat hippocampal slices using intracellular recording techniques. IPSPs were evoked in CA1 pyramidal neurons by direct activation of inhibitory interneurons in slices treated with glutamatergic antagonists to block excitatory synaptic transmission. The fast (Cl(-)-dependent, GABAA receptor-mediated) IPSPs (fIPSPs) were isolated from the slow (K(+)-dependent; GABAB receptor-mediated) IPSPs (sIPSPs) by intracellular injection of QX-314, which also suppressed fast (Na(+)-dependent) action potentials. 2. In normal (3.5 mM) and in high (7.5 mM) [K+]o, the peak fIPSP amplitude changed nonlinearly with membrane potential (VM) in a way consistent with outward rectification of the underlying conductance. The input conductance of the fIPSP (GfIPSP) measured around resting VM (about -67 mV) increased 1.7-fold on changing from normal to high-K+ saline, whereas resting VM depolarized 6.8 mV. Repolarizing VM reversed the increase in GfIPSP, suggesting that it was due to outward rectification. The resting input conductance of the neurons increased 1.4-fold in high K+. 3. The time course of fIPSPs was prolonged by high K+. The half time of fIPSP decay increased 1.4-fold, and in half of the neurons the decay became conspicuously multipeaked, suggesting that neurally evoked GABA release from inhibitory interneurons was prolonged. 4. In normal K+, the reversal potentials of fIPSPs (EfIPSP; -76.5 mV) was 9.7 mV more negative than resting VM. Polarizing VM 10–20 mV for 15 min with current injection did not change EfIPSP appreciably.(ABSTRACT TRUNCATED AT 250 WORDS)

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