scholarly journals Rapid regulation of tonic GABA currents in cultured rat hippocampal neurons

2013 ◽  
Vol 109 (3) ◽  
pp. 803-812 ◽  
Author(s):  
Christopher B. Ransom ◽  
Wucheng Tao ◽  
Yuanming Wu ◽  
William J. Spain ◽  
George B. Richerson
Keyword(s):  
Hippocampal Neurons ◽  
Brain Slices ◽  
Reversal Potential ◽  
Gaba Release ◽  
Tonic Inhibition ◽  
Concanamycin A ◽  
Voltage Dependent ◽  
Tonic Current ◽  
Induced Changes ◽  
Time Frames

Subacute and chronic changes in tonic GABAergic inhibition occur in human and experimental epilepsy. Less is known about how tonic inhibition is modulated over shorter time frames (seconds). We measured endogenous tonic GABA currents from cultured rat hippocampal neurons to evaluate how they are affected by 1) transient increases in extracellular GABA concentration ([GABA]), 2) transient postsynaptic depolarization, and 3) depolarization of presynaptic cells. Transient increases in [GABA] (1 μM) reduced tonic currents; this reduction resulted from GABA-induced shifts in the reversal potential for GABA currents ( EGABA). Transient depolarization of postsynaptic neurons reversed the effects of exogenous GABA and potentiated tonic currents. The voltage-dependent potentiation of tonic GABA currents was independent of EGABA shifts and represented postdepolarization potentiation (PDP), an intrinsic GABAA receptor property (Ransom CB, Wu Y, Richerson GB. J Neurosci 30: 7672–7684, 2010). Inhibition of vesicular GABA release with concanamycin A (ConA) did not affect tonic currents. In ConA-treated cells, transient application of 12 mM K+ to depolarize presynaptic neurons and glia produced a persistent increase in tonic current amplitude. The K+-induced increase in tonic current was reversibly inhibited by SKF89976a (40 μM), indicating that this was caused by nonvesicular GABA release from GABA transporter type 1 (GAT1). Nonvesicular GABA release due to GAT1 reversal also occurred in acute hippocampal brain slices. Our results indicate that tonic GABA currents are rapidly regulated by GABA-induced changes in intracellular Cl− concentration, PDP of extrasynaptic GABAA receptors, and nonvesicular GABA release. These mechanisms may influence tonic inhibition during seizures when neurons are robustly depolarized and extracellular GABA and K+ concentrations are elevated.

Vigabatrin Induces Tonic Inhibition Via GABA Transporter Reversal Without Increasing Vesicular GABA Release

2003 ◽  
Vol 89 (4) ◽  
pp. 2021-2034 ◽  
Author(s):  
Yuanming Wu ◽  
Wengang Wang ◽  
George B. Richerson
Keyword(s):  
Patch Clamp ◽  
Gaba Receptors ◽  
Hippocampal Neurons ◽  
Gaba Release ◽  
Tonic Inhibition ◽  
Gabaergic Inhibition ◽  
Gaba Transporter ◽  
Whole Cell ◽  
Ambient Gaba

Two forms of GABAergic inhibition coexist: fast synaptic neurotransmission and tonic activation of GABA receptors due to ambient GABA. The mechanisms regulating ambient GABA have not been well defined. Here we examined the role of the GABA transporter in the increase in ambient [GABA] induced by the anticonvulsant vigabatrin. Pretreatment of cultured rat hippocampal neurons with vigabatrin (100 μM) for 2–5 days led to a large increase in ambient [GABA] that was measured as the change in holding current induced by bicuculline during patch-clamp recordings. In contrast, there was a decrease in the frequency of spontaneous miniature inhibitory postsynaptic currents mIPSCs with no change in their amplitude distribution, and a decrease in the magnitude of IPSCs evoked by presynaptic stimulation during paired recordings. The increase in ambient [GABA] was not prevented by blockade of vesicular GABA release with tetanus toxin or removal of extracellular calcium. During perforated patch recordings, the increase in ambient [GABA] was prevented by blocking the GABA transporter, indicating that the GABA transporter was continuously operating in reverse and releasing GABA. In contrast, blocking the GABA transporter increased ambient [GABA] during whole cell patch-clamp recordings unless GABA and Na+ were added to the recording electrode solution, indicating that whole cell recordings can lead to erroneous conclusions about the role of the GABA transporter in control of ambient GABA. We conclude that the equilibrium for the GABA transporter is a major determinant of ambient [GABA] and tonic GABAergic inhibition. We propose that fast GABAergic neurotransmission and tonic inhibition can be independently modified and play complementary roles in control of neuronal excitability.

N-Type Voltage-Dependent Calcium Channels Mediate the Nicotinic Enhancement of GABA Release in Chick Brain

1999 ◽  
Vol 81 (2) ◽  
pp. 447-454 ◽  
Author(s):  
Trevor L. Tredway ◽  
Jian-Zhong Guo ◽  
Vincent A. Chiappinelli
Keyword(s):  
Calcium Channels ◽  
Channel Blocker ◽  
Brain Slices ◽  
Gaba Release ◽  
Channel Blockers ◽  
Chick Brain ◽  
Voltage Dependent ◽  
Voltage Dependent Calcium Channels ◽  
Whole Cell Recordings

N-type voltage-dependent calcium channels mediate the nicotinic enhancement of GABA release in chick brain. The role of voltage-dependent calcium channels (VDCCs) in the nicotinic acetylcholine receptor (nAChR)-mediated enhancement of spontaneous GABAergic inhibitory postsynaptic currents (IPSCs) was investigated in chick brain slices. Whole cell recordings of neurons in the lateral spiriform (SpL) and ventral lateral geniculate (LGNv) nuclei showed that cadmium chloride (CdCl2) blocked the carbachol-induced increase of spontaneous GABAergic IPSCs, indicating that VDCCs might be involved. To conclusively show a role for VDCCs, the presynaptic effect of carbachol on SpL and LGNv neurons was examined in the presence of selective blockers of VDCC subtypes. ω-Conotoxin GVIA, a selective antagonist of N-type channels, significantly reduced the nAChR-mediated enhancement of γ-aminobutyric acid (GABA) release in the SpL by 78% compared with control responses. Nifedipine, an L-type channel blocker, and ω-Agatoxin-TK, a P/Q-type channel blocker, did not inhibit the enhancement of GABAergic IPSCs. In the LGNv, ω-Conotoxin GVIA also significantly reduced the nAChR-mediated enhancement of GABA release by 71% from control values. Although ω-Agatoxin-TK did not block the nicotinic enhancement, L-type channel blockers showed complex effects on the nAChR-mediated enhancement. These results indicate that the nAChR-mediated enhancement of spontaneous GABAergic IPSCs requires activation of N-type channels in both the SpL and LGNv.

The Transmembrane Sodium Gradient Influences Ambient GABA Concentration by Altering the Equilibrium of GABA Transporters

2006 ◽  
Vol 96 (5) ◽  
pp. 2425-2436 ◽  
Author(s):  
Yuanming Wu ◽  
Wengang Wang ◽  
George B. Richerson
Keyword(s):  
Hippocampal Slices ◽  
Gaba Release ◽  
Synaptic Cleft ◽  
Tonic Inhibition ◽  
Multiple Sources ◽  
Sodium Removal ◽  
Gaba Transporters ◽  
Sodium Gradient ◽  
Ambient Gaba ◽  
Tonic Current

Tonic inhibition is widely believed to be caused solely by “spillover” of GABA that escapes the synaptic cleft and activates extrasynaptic GABAA receptors. However, an exclusively vesicular source is not consistent with the observation that tonic inhibition can still occur after blocking vesicular release. Here, we made patch-clamp recordings from neurons in rat hippocampal cultures and measured the tonic current that was blocked by bicuculline or gabazine. During perforated patch recordings, the tonic GABA current was decreased by the GAT1 antagonist SKF-89976a. Zero calcium solution did not change the amount of tonic current, despite a large reduction in vesicular GABA release. Perturbations that would be expected to alter the transmembrane sodium gradient influenced the tonic current. For example, in zero calcium Ringer, TTX (which can decrease cytosolic [Na+]) reduced tonic current, whereas veratridine (which can increase cytosolic [Na+]) increased tonic current. Likewise, removal of extracellular sodium led to a large increase in tonic current. The increases in tonic current induced by veratridine and sodium removal were completely blocked by SKF89976a. When these experiments were repeated in hippocampal slices, similar results were obtained except that a GAT1- and GAT3-independent nonvesicular source(s) of GABA was found to contribute to the tonic current. We conclude that multiple sources can contribute to ambient GABA, including spillover and GAT1 reversal. The source of GABA release may be conceptually less important in determining the amount of tonic inhibition than the factors that control the equilibrium of GABA transporters.

Carrier-Mediated GABA Release Activates GABA Receptors on Hippocampal Neurons

1998 ◽  
Vol 80 (1) ◽  
pp. 270-281 ◽  
Author(s):  
Heidi L. Gaspary ◽  
Wengang Wang ◽  
George B. Richerson
Keyword(s):  
Gaba Receptors ◽  
Hippocampal Neurons ◽  
Reversal Potential ◽  
Gaba Release ◽  
Receptor Activation ◽  
Neuronal Firing ◽  
Gaba Transporter ◽  
Gaba Transporters ◽  
Acid Hydrochloride

Gaspary, Heidi L., Wengang Wang, and George B. Richerson. Carrier-mediated GABA release activates GABA receptors on hippocampal neurons. J. Neurophysiol. 80: 270–281, 1998. γ-Aminobutyric acid (GABA) transporters are electrogenic and sodium-dependent and can operate in reverse when cells are depolarized or when there is reversal of the inward sodium gradient. However, the functional relevance of this phenomenon is unclear. We have examined whether depolarization induced by a physiologically relevant increase in extracellular [K+] leads to sufficient amounts of carrier-mediated GABA release to activate GABAA receptors on neurons. Patch-clamp recordings were made from rat hippocampal neurons in culture with solutions designed to isolate chloride currents in the recorded neuron. Pressure microejection was used to increase extracellular [K+] from 3 to 12 mM. After blockade of vesicular GABA release by removal of extracellular calcium, this stimulus induced a large conductance increase in hippocampal neurons [18.9 ± 6.8 (SD) nS; n = 16]. This was blocked by the GABAA receptor antagonists picrotoxin and bicuculline and had a reversal potential that followed the Nernst potential for chloride, indicating that it was mediated by GABAA receptor activation. Similar responses occurred after block of vesicular neurotransmitter release by tetanus toxin. GABAA receptors also were activated when an increase in extracellular [K+] (from 3 to 13 mM) was combined with a reduction in extracellular [Na+] or when cells were exposed to a decrease in extracellular [Na+] alone. These results indicate that depolarization and/or reversal of the Na+ gradient activated GABA receptors via release of GABA from neighboring cells. We found that the GABA transporter antagonists 1-(4,4-diphenyl-3-butenyl)-3-piperidinecarboxylic acid hydrochloride (SKF89976A; 20–100 μM) and 1-(2-{[(diphenylmethylene)amino]oxy}ethyl) -1, 2, 5, 6 - tetrahydro - 3 - pyridine - carboxylic acid hydrochloride (NO-711; 10 μM) both decreased the responses, indicating that the release of GABA resulted from reversal of the GABA transporter. We propose that carrier-mediated GABA release occurs in vivo during high-frequency neuronal firing and seizures, and dynamically modulates inhibitory tone.

scholarly journals Activation of the Tonic GABAC Receptor Current in Retinal Bipolar Cell Terminals by Nonvesicular GABA Release

2009 ◽  
Vol 102 (2) ◽  
pp. 691-699 ◽  
Author(s):  
S. M. Jones ◽  
M. J. Palmer
Keyword(s):  
Bipolar Cell ◽  
Ganglion Cells ◽  
Gaba Release ◽  
Visual Signal ◽  
Inhibitory Input ◽  
Axon Terminals ◽  
Gaba Transporters ◽  
Concanamycin A ◽  
Vesicular Release ◽  
Tonic Current

Within the second synaptic layer of the retina, bipolar cell (BC) output to ganglion cells is regulated by inhibitory input to BC axon terminals. GABAA receptors (GABAARs) mediate rapid synaptic currents in BC terminals, whereas GABAC receptors (GABACRs) mediate slow evoked currents and a tonic current, which is strongly regulated by GAT-1 GABA transporters. We have used voltage-clamp recordings from BC terminals in goldfish retinal slices to determine the source of GABA for activation of these currents. Inhibition of vesicular release with concanamycin A or tetanus toxin significantly inhibited GABAAR inhibitory postsynaptic currents and glutamate-evoked GABAAR and GABACR currents but did not reduce the tonic GABACR current, which was also not dependent on extracellular Ca2+. The tonic current was strongly potentiated by inhibition of GABA transaminase, under both normal and Ca2+-free conditions, and was activated by exogenous taurine; however inhibition of taurine transport had little effect. The tonic current was unaffected by GAT-2/3 inhibition and was potentiated by GAT-1 inhibition even in the absence of vesicular release, indicating that it is unlikely to be evoked by reversal of GABA transporters or by ambient GABA. In addition, GABA release does not appear to occur via hemichannels or P2X7 receptors. BC terminals therefore exhibit two forms of GABACR-mediated inhibition, activated by vesicular and by nonvesicular GABA release, which are likely to have distinct functions in visual signal processing. The tonic GABACR current in BC terminals exhibits similar properties to tonic GABAAR and glutamate receptor currents in the brain.

scholarly journals GABA-mediated tonic inhibition differentially modulates gain in functional subtypes of cortical interneurons

2019 ◽  
Author(s):  
Alexander Bryson ◽  
Robert Hatch ◽  
Bas-Jan Zandt ◽  
Christian Rossert ◽  
Samuel Berkovic ◽  
...  
Keyword(s):  
Action Potential ◽  
Computational Models ◽  
Potassium Currents ◽  
Tonic Inhibition ◽  
Network Activity ◽  
Neuron Models ◽  
Electrophysiological Properties ◽  
Cortical Interneurons ◽  
Voltage Dependent ◽  
Tonic Current

ABSTRACTThe binding of GABA to extra-synaptic GABAAreceptors generates tonic inhibition that acts as a powerful modulator of cortical network activity. Despite GABA being present at low levels throughout the extracellular space of the brain, previous work has shown that GABA may differentially modulate the excitability of neuron subtypes through variation in chloride gradient. Here, we introduce a distinct mechanism through which extracellular GABA can differentially modulate the excitability of neuron subtypes through variation in neuronal electrophysiological properties. Using biophysically-detailed computational models, we found that tonic inhibition enhanced the responsiveness (or gain) of models with electrophysiological features typically observed in somatostatin (Sst) interneurons and reduced gain in models with features typical for parvalbumin (Pv) interneurons. These predictions were experimentally verified using patch-clamp recordings. Further analysis revealed that differential gain modulation is also dependent upon the extent of outward rectification of the GABAAreceptor-mediated tonic current. Our detailed neuron models demonstrate two subcellular consequences of tonic inhibition. First, tonic inhibition enhances somatic action potential repolarisation by increasing current flow into the dendritic compartment. This enhanced repolarisation then reduces voltage-dependent potassium currents at the soma during the afterhyperpolarisation. Finally, we show that reductions of potassium current selectively increase gain within neurons exhibiting action potential dynamics typical for Sst interneurons. Potassium currents in Pv-type interneurons are not sensitive to this mechanism as they deactivate rapidly and are unavailable for further modulation. These findings introduce a neuromodulatory paradigm in which GABA can induce a state of differential interneuron excitability through differences in intrinsic electrophysiological properties.

Single voltage-dependent potassium channels in cultured rat hippocampal neurons

1986 ◽  
Vol 56 (2) ◽  
pp. 481-493 ◽  
Author(s):  
M. A. Rogawski
Keyword(s):  
Hippocampal Neurons ◽  
Single Channel ◽  
Reversal Potential ◽  
Resting Potential ◽  
Moderate Degree ◽  
Patch Clamp Technique ◽  
Membrane Pore ◽  
Channel Opening ◽  
Voltage Dependent ◽  
Single Channel Currents

Single-channel recordings using the gigohm seal patch-clamp technique were carried out on the somatic membranes of dissociated embryonic rat hippocampal neurons grown in cell culture. The recording medium contained tetrodotoxin to block the voltage-dependent Na+ conductance and Cd2+ to block Ca2+ and Ca2+-activated conductances. In the cell-attached configuration, depolarizing voltage steps activated outward directed single-channel currents with conductance 15-20 pS. The channel openings exhibited a moderate degree of flickering. The mean burst lifetimes ranged from 5 to 13 ms with a tendency to increase slightly at more depolarized potentials (T = 21-25 degrees C). Reversal potential measurements using excised membrane patches indicated that the channels behaved as expected of a K+-selective membrane pore. Channel opening occurred in Ca2+-free EGTA-containing solutions but was never observed in the presence of tetraethylammonium (TEA; 20 mM). The frequency of channel opening increased as the membrane was depolarized by up to 50 mV from resting potential; the fraction of time spent in the open state during the first 300 ms following a step depolarization increased e-fold for a 8-25 mV change in potential. First-latency histograms and simulations of the macroscopic current based on channel data obtained during repeated depolarizing voltage steps indicated that the probability of the channel being in the open state increases gradually with time after a step depolarization. During repeated depolarizing steps the channels appeared to randomly enter and exit a long-lived inactive state. It is concluded that these channels may underly the slowly activating, very slowly inactivating, TEA-sensitive voltage-dependent K+ current (IK) in cultured hippocampal neurons.

Voltage dependence of conductance changes evoked by glycine release in the zebrafish brain

1995 ◽  
Vol 73 (6) ◽  
pp. 2404-2412 ◽  
Author(s):  
P. Legendre ◽  
H. Korn
Keyword(s):  
Voltage Dependence ◽  
Reversal Potential ◽  
Voltage Sensitivity ◽  
M Cell ◽  
Open Probability ◽  
Similar Time ◽  
Whole Cell ◽  
Glycine Release ◽  
Cell Recording ◽  
Voltage Dependent

1. The kinetics and mechanisms underlying the voltage dependence of inhibitory postsynaptic currents (IPSCs) recorded in the Mauthner cell (M cell) were investigated in the isolated medulla of 52-h-old zebrafish larvae, with the use of whole cell and outside-out patch-clamp recordings. 2. Spontaneous miniature IPSCs (mIPSCs) were recorded in the presence of 10(-6) M tetrodotoxin (TTX), 10 mM MgCl2, and 0.1 mM [CaCl2]o. Depolarizing the cell from -50 to +50 mV did not evoke any significant change in the distribution of mIPSC amplitudes, whereas synaptic currents were prolonged at positive voltages. The average decay time constant was increased twofold at +50 mV. 3. The voltage dependence of the kinetics of glycine-activated channels was first investigated during whole cell recording experiments. Currents evoked by voltage steps in the presence of glycine (50 microM) were compared with those obtained without glycine. The increase in chloride conductance (gCl-) evoked by glycine was time and voltage dependent. Inactivation and reactivation of the chloride current were observed during voltage pulses from 0 to -50 mV and from -50 to 0 mV, respectively, and they occurred with similar time constants (2-3 s). During glycine application, voltage-ramp analysis revealed a shift in the reversal potential (ECl-) occurring at all [Cl-]i tested. 4. The basis of the voltage sensitivity of glycine-evoked gCl- was first analyzed by measuring the relative changes in the total open probability (NPo) of glycine-activated channels with voltage.(ABSTRACT TRUNCATED AT 250 WORDS)

Altered Regulation of Potassium and Calcium Channels by GABAB and Adenosine Receptors in Hippocampal Neurons From Mice Lacking Gαo

2000 ◽  
Vol 83 (2) ◽  
pp. 1010-1018 ◽  
Author(s):  
Gabriela J. Greif ◽  
Deborah L. Sodickson ◽  
Bruce P. Bean ◽  
Eva J. Neer ◽  
Ulrike Mende
Keyword(s):  
Time Constant ◽  
Hippocampal Neurons ◽  
Ionic Currents ◽  
Absolute Requirement ◽  
Voltage Dependent ◽  
Hippocampal Ca3 ◽  
Ca3 Neurons ◽  
Inwardly Rectifying ◽  
G Protein Coupled

To examine the role of Go in modulation of ion channels by neurotransmitter receptors, we characterized modulation of ionic currents in hippocampal CA3 neurons from mice lacking both isoforms of Gαo. In CA3 neurons from Gαo −/− mice, 2-chloro-adenosine and the GABAB-receptor agonist baclofen activated inwardly rectifying K+ currents and inhibited voltage-dependent Ca2+ currents just as effectively as in Gαo +/+ littermates. However, the kinetics of transmitter action were dramatically altered in Gαo −/− mice in that recovery on washout of agonist was much slower. For example, recovery from 2-chloro-adenosine inhibition of calcium current was more than fourfold slower in neurons from Gαo −/− mice [time constant of 12.0 ± 0.8 (SE) s] than in neurons from Gαo +/+ mice (time constant of 2.6 ± 0.2 s). Recovery from baclofen effects was affected similarly. In neurons from control mice, effects of both baclofen and 2-chloro-adenosine on Ca2+ currents and K+currents were abolished by brief exposure to external N-ethyl-maleimide (NEM). In neurons lacking Gαo, some inhibition of Ca2+ currents by baclofen remained after NEM treatment, whereas baclofen activation of K+ currents and both effects of 2-chloro-adenosine were abolished. These results show that modulation of Ca2+ and K+ currents by G protein-coupled receptors in hippocampal neurons does not have an absolute requirement for Gαo. However, modulation is changed in the absence of Gαo in having much slower recovery kinetics. A likely possibility is that the very abundant Gαo is normally used but, when absent, can readily be replaced by G proteins with different properties.

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