Synaptically Evoked GABA Transporter Currents in Neocortical Glia

2002 ◽  
Vol 88 (6) ◽  
pp. 2899-2908 ◽  
Author(s):  
Gregory A. Kinney ◽  
William J. Spain
Keyword(s):  
Synaptic Transmission ◽  
Time Course ◽  
Glutamate Transporter ◽  
Repetitive Stimulation ◽  
Slice Preparation ◽  
Gaba Transporter ◽  
Gaba Transporters ◽  
Decay Times ◽  
Slow Rise

The presence, magnitude, and time course of GABA transporter currents were investigated in electrophysiologically characterized neocortical astrocytes in an in vitro slice preparation. On stimulation with a bipolar-tungsten stimulating electrode placed nearby, the majority of cells tested displayed long-lasting GABA transporter currents using both single and repetitive stimulation protocols. Using subtype-specific GABA transporter antagonists, long-lasting GABA transporter currents were identified in neocortical astrocytes that originated from at least two subtypes of GABA transporters: GAT-1 and GAT-2/3. These transporter currents displayed slow rise times and long decay times, contrasting the time course observed for glutamate transporter currents, and are indicative of a long extracellular time course of GABA as well as a role for glial GABA transporters during synaptic transmission.

scholarly journals Androgens Modulate NMDA Receptor–Mediated EPSCs in the Zebra Finch Song System

1999 ◽  
Vol 82 (5) ◽  
pp. 2221-2234 ◽  
Author(s):  
Stephanie A. White ◽  
Frederick S. Livingston ◽  
Richard Mooney
Keyword(s):  
Nmda Receptor ◽  
Synaptic Transmission ◽  
Time Course ◽  
Song Learning ◽  
Lateral Part ◽  
Spine Density ◽  
Song System ◽  
Decay Times ◽  
Soma Size

Androgens potently regulate the development of learned vocalizations of songbirds. We sought to determine whether one action of androgens is to functionally modulate the development of synaptic transmission in two brain nuclei, the lateral part of the magnocellular nucleus of the anterior neostriatum (LMAN) and the robust nucleus of the archistriatum (RA), that are critical for song learning and production. We focused on N-methyl-d-aspartate–excitatory postsynaptic currents (NMDA-EPSCs), because NMDA receptor activity in LMAN is crucial to song learning, and because the LMAN synapses onto RA neurons are almost entirely mediated by NMDA receptors. Whole cell recordings from in vitro brain slice preparations revealed that the time course of NMDA-EPSCs was developmentally regulated in RA, as had been shown previously for LMAN. Specifically, in both nuclei, NMDA-EPSCs become faster over development. We found that this developmental transition can be modulated by androgens, because testosterone treatment of young animals caused NMDA-EPSCs in LMAN and RA to become prematurely fast. These androgen-induced effects were limited to fledgling and juvenile periods and were spatially restricted, in that androgens did not accelerate developmental changes in NMDA-EPSCs recorded in a nonsong area, the Wulst. To determine whether androgens had additional effects on LMAN or RA neurons, we examined several other physiological and morphological parameters. In LMAN, testosterone affected α-amino-3-hydroxy-5-methyl-4-isoxazoleproprianate–EPSC (AMPA-EPSC) decay times and the ratio of peak synaptic glutamate to AMPA currents, as well as dendritic length and spine density but did not alter soma size or dendritic complexity. In contrast, testosterone did not affect any of these parameters in RA, which demonstrates that exogenous androgens can have selective actions on different song system neurons. These data are the first evidence for any effect of sex steroids on synaptic transmission within the song system. Our results support the idea that endogenous androgens limit sensitive periods for song learning by functionally altering synaptic transmission in song nuclei.

Subtype-Specific GABA Transporter Antagonists Synergistically Modulate Phasic and Tonic GABAA Conductances in Rat Neocortex

2005 ◽  
Vol 94 (3) ◽  
pp. 2073-2085 ◽  
Author(s):  
Sotirios Keros ◽  
John J. Hablitz
Keyword(s):  
Time Course ◽  
Pyramidal Cells ◽  
Gaba Uptake ◽  
Gaba Transporter ◽  
Gaba Transporters ◽  
Decay Times ◽  
Rat Neocortex ◽  
Layer I ◽  
Tonic Current

GABAergic inhibition in the brain can be classified as either phasic or tonic. γ-Aminobutyric acid (GABA) uptake by GABA transporters (GATs) can limit the time course of phasic currents arising from endogenous and exogenous GABA, as well as decrease a tonically active GABA current. GABA transporter subtypes 1 and 3 (GAT-1 and GAT-3) are the most heavily expressed of the four known GAT subtypes. The role of GATs in shaping GABA currents in the neocortex has not been explored. We obtained patch-clamp recordings from layer II/III pyramidal cells and layer I interneurons in rat sensorimotor cortex. We found that selective GAT-1 inhibition with NO711 decreased the amplitude and increased the decay time of evoked inhibitory postsynaptic currents (IPSCs) but had no effect on the tonic current or spontaneous IPSCs (sIPSCs). GAT-2/3 inhibition with SNAP-5114 had no effect on IPSCs or the tonic current. Coapplication of NO711 and SNAP-5114 substantially increased tonic currents and synergistically decreased IPSC amplitudes and increased IPSC decay times. sIPSCs were not resolvable with coapplication of NO711 and SNAP-5114. The effects of the nonselective GAT antagonist nipecotic acid were similar to those of NO711 and SNAP-5114 together. We conclude that synaptic GABA levels in neocortical neurons are controlled primarily by GAT-1, but that GAT-1 and GAT-2/3 work together extrasynaptically to limit tonic currents. Inhibition of any one GAT subtype does not increase the tonic current, presumably as a result of increased activity of the remaining transporters. Thus neocortical GAT-1 and GAT-2/3 have distinct but overlapping roles in modulating GABA conductances.

Inhibitory Transmission in Locus Coeruleus Neurons Expressing GABAA Receptor Epsilon Subunit Has a Number of Unique Properties

2009 ◽  
Vol 102 (4) ◽  
pp. 2312-2325 ◽  
Author(s):  
P. Belujon ◽  
J. Baufreton ◽  
L. Grandoso ◽  
E. Boué-Grabot ◽  
T.F.C. Batten ◽  
...  
Keyword(s):  
Synaptic Transmission ◽  
Locus Coeruleus ◽  
Differential Sensitivity ◽  
Epsilon Subunit ◽  
Recombinant Receptors ◽  
A Subunit ◽  
Slow Rise ◽  
Induced Currents

Fast inhibitory synaptic transmission in the brain relies on ionotropic GABAA receptors (GABAAR). Eighteen genes code for GABAAR subunits, but little is known about the ε subunit. Our aim was to identify the synaptic transmission properties displayed by native receptors incorporating ε. Immunogold localization detected ε at synaptic sites on locus coeruleus (LC) neurons. In situ hybridization revealed prominent signals from ε, and θ mRNAs, some low β1 and β3 signals, and no γ signal. Using in vivo extracellular and in vitro patch-clamp recordings in LC, we established that neuron firing rates, GABA-activated currents, and mIPSC charge were insensitive to the benzodiazepine flunitrazepam (FLU), in agreement with the characteristics of recombinant receptors including an ε subunit. Surprisingly, LC provided binding sites for benzodiazepines, and GABA-induced currents were potentiated by diazepam (DZP) in the micromolar range. A number of GABAAR ligands significantly potentiated GABA-induced currents, and zinc ions were only active at concentrations above 1 μM, further indicating that receptors were not composed of only α and β subunits, but included an ε subunit. In contrast to recombinant receptors including an ε subunit, GABAAR in LC showed no agonist-independent opening. Finally, we determined that mIPSCs, as well as ensemble currents induced by ultra-fast GABA application, exhibited surprisingly slow rise times. Our work thus defines the signature of native GABAAR with a subunit composition including ε: differential sensitivity to FLU and DZP and slow rise time of currents. We further propose that α3, β1/3, θ and ε subunits compose GABAAR in LC.

GABA Uptake and Heterotransport Are Impaired in the Dentate Gyrus of Epileptic Rats and Humans With Temporal Lobe Sclerosis

2001 ◽  
Vol 85 (4) ◽  
pp. 1533-1542 ◽  
Author(s):  
Peter R. Patrylo ◽  
Dennis D. Spencer ◽  
Anne Williamson
Keyword(s):  
Dentate Gyrus ◽  
Temporal Lobe ◽  
Granule Cells ◽  
Hippocampal Slices ◽  
Gaba Uptake ◽  
Mesial Temporal Sclerosis ◽  
Gaba Transporter ◽  
Gaba Transporters ◽  
Inhibitory Tone

In vivo dialysis and in vitro electrophysiological studies suggest that GABA uptake is altered in the dentate gyrus of human temporal lobe epileptics characterized with mesial temporal sclerosis (MTLE). Concordantly, anatomical studies have shown that the pattern of GABA-transporter immunoreactivity is also altered in this region. This decrease in GABA uptake, presumably due to a change in the GABA transporter system, may help preserve inhibitory tone interictally. However, transporter reversal can also occur under several conditions, including elevations in [K+]o, which occurs during seizures. Thus GABA transporters could contribute to seizure termination and propagation through heterotransport. To test whether GABA transport is compromised in both the forward (uptake) and reverse (heterotransport) direction in the sclerotic epileptic dentate gyrus, the physiological effects of microapplied GABA and nipecotic acid (NPA; a compound that induces heterotransport) were examined in granule cells in hippocampal slices from kainate (KA)-induced epileptic rats and patients with temporal lobe epilepsy (TLE). GABA- and NPA-induced responses were prolonged in granule cells from epileptic rats versus controls (51.3 and 31.3% increase, respectively) while the conductance change evoked with NPA microapplication was reduced by 40%. Furthermore the ratio of GABA/NPA conductance, but not duration, was significantly >1 in epileptic rats but not controls, suggesting a compromise in transporter function in both directions. Similar changes were observed in tissue resected from epileptic patients with medial temporal sclerosis but not in those without the anatomical changes associated with MTLE. These data suggest that the GABA transporter system is functionally compromised in both the forward and reverse directions in the dentate gyrus of chronically epileptic tissue characterized by mesial temporal sclerosis. This alteration may enhance inhibitory tone interically yet be permissive for seizure propagation due to a decreased probability for GABA heterotransport during seizures.

Patch-Clamp Investigations and Compartmental Modeling of Rod Bipolar Axon Terminals in an In Vitro Thin-Slice Preparation of the Mammalian Retina

2007 ◽  
Vol 97 (2) ◽  
pp. 1171-1187 ◽  
Author(s):  
Leif Oltedal ◽  
Svein Harald Mørkve ◽  
Margaret Lin Veruki ◽  
Espen Hartveit
Keyword(s):  
Synaptic Transmission ◽  
Computer Simulations ◽  
Bipolar Cells ◽  
Slice Preparation ◽  
Whole Cell ◽  
Axon Terminals ◽  
Postsynaptic Currents ◽  
Whole Cell Recordings ◽  
Rod Bipolar Cells

To extend the usefulness of rod bipolar cells for studies of chemical synaptic transmission, we have performed electrophysiological recordings from rod bipolar axon terminals in an in vitro slice preparation of the rat retina. Whole cell recordings from axon terminals and cell bodies were used to investigate the passive membrane properties of rod bipolar cells and analyzed with a two-compartment equivalent electrical circuit model developed by Mennerick et al. For both terminal- and soma-end recordings, capacitive current decays were well fitted by biexponential functions. Computer simulations of simplified models of rod bipolar cells demonstrated that estimates of the capacitance of the axon terminal compartment can depend critically on the recording location, with terminal-end recordings giving the best estimates. Computer simulations and whole cell recordings demonstrated that terminal-end recordings can yield more accurate estimates of the peak amplitude and kinetic properties of postsynaptic currents generated at the axon terminals due to increased electrotonic filtering of these currents when recorded at the soma. Finally, we present whole cell and outside-out patch recordings from axon terminals with responses evoked by GABA and glycine, spontaneous inhibitory postsynaptic currents, voltage-gated Ca2+ currents, and depolarization-evoked reciprocal synaptic responses, verifying that the recorded axon terminals are involved in normal pre- and postsynaptic relationships. These results demonstrate that axon terminals of rod bipolar cells are directly accessible to whole cell and outside-out patch recordings, extending the usefulness of this preparation for detailed studies of pre- and postsynaptic mechanisms of synaptic transmission in the CNS.

Differential Effects of Ethanol on GABAA and Glycine Receptor-Mediated Synaptic Currents in Brain Stem Motoneurons

2003 ◽  
Vol 90 (2) ◽  
pp. 870-875 ◽  
Author(s):  
Joy Y. Sebe ◽  
Erika D. Eggers ◽  
Albert J. Berger
Keyword(s):  
Synaptic Transmission ◽  
Brain Stem ◽  
Opposite Effect ◽  
Glycine Receptor ◽  
Slice Preparation ◽  
Hypoglossal Motoneurons ◽  
Inhibitory Synaptic Transmission ◽  
Bath Application ◽  
Gabaergic Synaptic Transmission

Ethanol potentiates glycinergic synaptic transmission to hypoglossal motoneurons (HMs). This effect on glycinergic transmission changes with postnatal development in that juvenile HMs (P9–13) are more sensitive to ethanol than neonate HMs (P1–3). We have now extended our previous study to investigate ethanol modulation of synaptic GABAA receptors (GABAARs), because both GABA and glycine mediate inhibitory synaptic transmission to brain stem motoneurons. We tested the effects of ethanol on GABAergic and glycinergic miniature inhibitory postsynaptic currents (mIPSCs) recorded from neonate and juvenile rat HMs in an in vitro slice preparation. Bath application of 30 mM ethanol had no significant effect on the GABAergic mIPSC amplitude or frequency recorded at either age. At 100 mM, ethanol significantly decreased the GABAergic mIPSC amplitude recorded from neonate (6 ± 3%, P < 0.05) and juvenile (16 ± 3%, P < 0.01) HMs. The same concentration of ethanol increased the GABAergic mIPSC frequency recorded from neonate (64 ± 17%, P < 0.05) and juvenile (40 ± 15%, n.s.) HMs. In contrast, 100 mM ethanol robustly potentiated glycinergic mIPSC amplitude in neonate (31 ± 3%, P < 0.0001) and juvenile (41 ± 7%, P < 0.001) HMs. These results suggest that glycine receptors are more sensitive to modulation by ethanol than GABAA receptors and that 100 mM ethanol has the opposite effect on GABAAR-mediated currents in juvenile HMs, that is, inhibition rather than enhancement. Further, comparing ethanol's effects on GABAergic mIPSC amplitude and frequency, ethanol modulates GABAergic synaptic transmission to HMs differentially. Presynaptically, ethanol enhances mIPSC frequency while postsynaptically it decreases mIPSC amplitude.

scholarly journals Differential regulation of synaptic transmission by pre- and postsynaptic SK channels in the spinal locomotor network

2013 ◽  
Vol 109 (12) ◽  
pp. 3051-3059 ◽  
Author(s):  
Evanthia Nanou ◽  
Michael H. Alpert ◽  
Simon Alford ◽  
Abdeljabbar El Manira
Keyword(s):  
Spinal Cord ◽  
Synaptic Transmission ◽  
Time Course ◽  
Dynamic Range ◽  
Feedback Mechanism ◽  
Sk Channels ◽  
Axon Terminals ◽  
Negative Feedback Mechanism ◽  
Tightly Coupled

The generation of activity in the central nervous system requires precise tuning of cellular properties and synaptic transmission. Neural networks in the spinal cord produce coordinated locomotor movements. Synapses in these networks need to be equipped with multiple mechanisms that regulate their operation over varying regimes to produce locomotor activity at different frequencies. Using the in vitro lamprey spinal cord, we explored whether Ca2+ influx via different routes in postsynaptic soma and dendrites and in presynaptic terminals can activate apamin-sensitive Ca2+-activated K+ (SK) channels and thereby shape synaptic transmission. We show that postsynaptic SK channels are tightly coupled to Ca2+ influx via NMDA receptors. Activation of these channels by synaptically induced NMDA-dependent Ca2+ transients restrains the time course of the synaptic current and the amplitude of the synaptic potential. In addition, presynaptic SK channels are activated by Ca2+ influx via voltage-gated channels and control the waveform of the action potential and the resulting Ca2+ dynamics in the axon terminals. The coupling of SK channels to different Ca2+ sources, pre- and postsynaptically, acts as a negative feedback mechanism to shape synaptic transmission. Thus SK channels can play a pivotal role in setting the dynamic range of synapses and enabling short-term plasticity in the spinal locomotor network.

Relative Contribution by GABA or Glycine to Cl−-Mediated Synaptic Transmission on Rat Hypoglossal Motoneurons In Vitro

2000 ◽  
Vol 84 (6) ◽  
pp. 2715-2724 ◽  
Author(s):  
Roberta Donato ◽  
Andrea Nistri
Keyword(s):  
Synaptic Transmission ◽  
Kynurenic Acid ◽  
Cell Voltage ◽  
Network Activity ◽  
Consistent Difference ◽  
Metabotropic Receptors ◽  
Relative Contribution ◽  
Decay Times ◽  
Kinetics Of

The relative contribution by GABA and glycine to synaptic transmission of motoneurons was investigated using an hypoglossus nucleus slice preparation from neonatal rats. Spontaneous, miniature, or electrically evoked postsynaptic currents (sPSCs, mPSCs, ePSCs, respectively) mediated by glycine or GABA were recorded under whole cell voltage clamp after blocking excitatory glutamatergic transmission with kynurenic acid. The overall majority of Cl−-mediated sPSCs was glycinergic, while only one-third was GABAergic; 70 ± 10% of mPSCs were glycinergic while 22 ± 8% were GABAergic. Tetrodotoxin (TTX) application dramatically reduced the frequency (and slightly the amplitude) of GABAergic events without changing frequency or amplitude of glycinergic sPSCs. These results indicate that, unlike spontaneous GABAergic transmission, glycine-mediated neurotransmission was essentially independent of network activity. There was a consistent difference in the kinetics of GABAergic and glycinergic responses as GABAergic events had significantly slower rise and decay times than glycinergic ones. Such a difference was always present whenever sPSCs, mPSCs, or ePSCs were measured. Finally, GABAergic and glycinergic mPSCs were differentially modulated by activation of glutamate metabotropic receptors (mGluRs), which are abundant in the hypoglossus nucleus. In fact, the broad-spectrum mGluR agonist (±)-1-aminocyclopentane- trans-1,3-dicarboxylic acid (50 μM), which in control solution increased the frequency of both GABAergic and glycinergic sPSCs, enhanced the frequency of glycinergic mPSCs only. These results indicate that on brain stem motoneurons, Cl−-mediated synaptic transmission is mainly due to glycine rather than GABA and that GABAergic and glycinergic events differ in terms of kinetics and pharmacological sensitivity to mGluR activation or TTX.

Rapid and Slow Swelling During Hypoxia in the CA1 Region of Rat Hippocampal Slices

1999 ◽  
Vol 82 (1) ◽  
pp. 320-329 ◽  
Author(s):  
Norman R. Kreisman ◽  
Joseph C. LaManna
Keyword(s):  
Synaptic Transmission ◽  
Cell Volume ◽  
Time Course ◽  
Hippocampal Slices ◽  
Neuronal Injury ◽  
Light Transmittance ◽  
Cell Swelling ◽  
Ca1 Region ◽  
Degree Of Recovery

The role of swelling in hypoxic/ischemic neuronal injury is incompletely understood. We investigated the extent and time course of cell swelling during hypoxia, and recovery of cell volume during reoxygenation, in the CA1 region of rat hippocampal slices in vitro. Cell swelling was measured optically and compared with simultaneous measurements of the extracellular DC potential, extracellular [K+], and synaptic transmission in the presence and absence of hypoxic depolarization. Hypoxia-induced swelling consisted of rapid and/or slow components. Rapid swelling was observed frequently and always occurred simultaneously with hypoxic depolarization. Additionally, rapid swelling was followed by a prolonged phase of swelling that was ∼15 times slower. Less frequently, slow swelling occurred independently, without either hypoxic depolarization or a preceding rapid swelling. For slices initially swelling rapidly, recovery of both cell volume and the slope of field excitatory postsynaptic potentials were best correlated with the duration of hypoxia ( r = 0.77 and 0.87, respectively). This was also the case for slices initially swelling slowly ( r = 0.70 and 0.58, respectively). In contrast, the degree of recovery of cell volume was the same at 30 or 60 min of reoxygenation, indicating that prolonging the duration of reoxygenation within these limits was ineffective in improving recovery. Spectral measurements indicated that the hypoxia-induced changes in light transmittance were related to changes in cell volume and not changes in the oxidation state of mitochondrial cytochromes. The persistent impairment of synaptic transmission in slices swelling slowly (i.e., without hypoxic depolarization) indicates that swelling may play a role in this injury and that hypoxic depolarization is not required. Additionally, the correlation between the degree of recovery of cell volume and the degree of recovery of synaptic transmission during reoxygenation supports a role for swelling in hypoxic neuronal injury.

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