Pre- and Postsynaptic Activation of M-Channels By a Novel Opener Dampens Neuronal Firing and Transmitter Release

The M-type K+ current (M-current), encoded by Kv7.2/3 (KCNQ2/3) K+ channels, plays a critical role in regulating neuronal excitability because it counteracts subthreshold depolarizations. Here we have characterized the functions of pre- and postsynaptic M-channels using a novel Kv7.2/3 channel opener, NH6, which we synthesized as a new derivative of N-phenylanthranilic acid. NH6 exhibits a good selectivity as it does not affect Kv7.1 and IKS K+ currents as well as NR1/NR2B, AMPA, and GABAA receptor-mediated currents. Superfusion of NH6 increased recombinant Kv7.2/3 current amplitude (EC50 = 18 μM) by causing a hyperpolarizing shift of the voltage activation curve and by markedly slowing the deactivation kinetics. Activation of native M-currents by NH6 robustly reduced the number of evoked and spontaneous action potentials in cultured cortical, hippocampal and dorsal root ganglion neurons. In hippocampal slices, NH6 decreased somatically evoked spike afterdepolarization of CA1 pyramidal neurons and induced regular firing in bursting neurons. Activation of M-channels by NH6, potently reduced the frequency of spontaneous excitatory and inhibitory postsynaptic currents. Activation of M-channels also decreased the frequency of miniature excitatory (mEPSC) and inhibitory (mIPSC) postsynaptic currents without affecting their amplitude and waveform, thus suggesting that M-channels presynaptically inhibit glutamate and GABA release. Our results suggest a role of presynaptic M-channels in the release of glutamate and GABA. They also indicate that M-channels act pre- and postsynaptically to dampen neuronal excitability.

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Benzolamide inhibits low-threshold calcium currents in hippocampal pyramidal neurons

Journal of Neurophysiology ◽

10.1152/jn.1995.74.6.2774 ◽

1995 ◽

Vol 74 (6) ◽

pp. 2774-2777 ◽

Cited By ~ 9

Author(s):

J. A. Gottfried ◽

M. Chesler

Keyword(s):

Carbonic Anhydrase ◽

Pyramidal Neurons ◽

Hippocampal Slices ◽

Pyramidal Cells ◽

Calcium Currents ◽

Dorsal Root Ganglion Neurons ◽

High Threshold ◽

Low Threshold ◽

Ganglion Neurons ◽

Ca Currents

1. Benzolamide is a poorly permeant sulfonamide inhibitor of the enzyme carbonic anhydrase. We studied the effect of benzolamide on low-threshold (LT) Ca currents in neonatal hippocampal CAl neurons. 2. In hippocampal slices, benzolamide (2-10 microM) inhibited the LT current 30-75% in voltage-clamped CAl pyramidal cells (n = 6). In slices bathed in N-2-hydroxypiperazine-N'-2-ethane-sulfonic acid (HEPES)-buffered Ringer, benzolamide also reduced the LT current, indicating that the action of the drug was not bicarbonate dependent. 3. Benzolamide inhibited LT Ca currents 20-75% in acutely dissociated CAl neurons in HEPES (n = 18): inhibition was 36 +/- 8% (mean +/- SE; n = 7) and 50 +/- 8% (n = 7) at 10 and 50 microM benzolamide, respectively. By contrast, high-threshold calcium currents recorded in CAl pyramidal cells (n = 18) and dorsal root ganglion neurons (n = 4) were virtually unaffected by benzolamide. 4. These results indicate that benzolamide inhibits LT Ca channels in central neurons and suggest caution in the use of this agent to inhibit extracellular carbonic anhydrase in excitable tissues.

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Metformin Enhances Excitatory Synaptic Transmission onto Hippocampal CA1 Pyramidal Neurons

Brain Sciences ◽

10.3390/brainsci10100706 ◽

2020 ◽

Vol 10 (10) ◽

pp. 706

Author(s):

Wen-Bing Chen ◽

Jiang Chen ◽

Zi-Yang Liu ◽

Bin Luo ◽

Tian Zhou ◽

...

Keyword(s):

Synaptic Transmission ◽

Neuronal Excitability ◽

Pyramidal Neurons ◽

Glutamate Release ◽

Hippocampal Slices ◽

Hippocampal Pyramidal Neurons ◽

Beneficial Effects ◽

Ca1 Pyramidal Neurons ◽

Postsynaptic Currents ◽

Hippocampal Ca1

Metformin (Met) is a first-line drug for type 2 diabetes mellitus (T2DM). Numerous studies have shown that Met exerts beneficial effects on a variety of neurological disorders, including Alzheimer’s disease (AD), Parkinson’s disease (PD) and Huntington’s disease (HD). However, it is still largely unclear how Met acts on neurons. Here, by treating acute hippocampal slices with Met (1 μM and 10 μM) and recording synaptic transmission as well as neuronal excitability of CA1 pyramidal neurons, we found that Met treatments significantly increased the frequency of miniature excitatory postsynaptic currents (mEPSCs), but not amplitude. Neither frequency nor amplitude of miniature inhibitory postsynaptic currents (mIPSCs) were changed with Met treatments. Analysis of paired-pulse ratios (PPR) demonstrates that enhanced presynaptic glutamate release from terminals innervating CA1 hippocampal pyramidal neurons, while excitability of CA1 pyramidal neurons was not altered. Our results suggest that Met preferentially increases glutamatergic rather than GABAergic transmission in hippocampal CA1, providing a new insight on how Met acts on neurons.

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Synaptic Regulation of the Slow Ca2+-Activated K+ Current in Hippocampal CA1 Pyramidal Neurons: Implication in Epileptogenesis

Journal of Neurophysiology ◽

10.1152/jn.2001.86.6.2878 ◽

2001 ◽

Vol 86 (6) ◽

pp. 2878-2886 ◽

Cited By ~ 47

Author(s):

Eduardo D. Martín ◽

Alfonso Araque ◽

Washington Buño

Keyword(s):

Neuronal Excitability ◽

Pyramidal Neurons ◽

Metabotropic Glutamate Receptor ◽

Epileptiform Activity ◽

Critical Role ◽

Hippocampal Slices ◽

Synaptic Activity ◽

Cooperative Action ◽

Epileptiform Discharges ◽

Group I

The slow Ca2+-activated K+ current (sIAHP) plays a critical role in regulating neuronal excitability, but its modulation during abnormal bursting activity, as in epilepsy, is unknown. Because synaptic transmission is enhanced during epilepsy, we investigated the synaptically mediated regulation of the sIAHP and its control of neuronal excitability during epileptiform activity induced by 4-aminopyridine (4AP) or 4AP+Mg2+-free treatment in rat hippocampal slices. We used electrophysiological and photometric Ca2+ techniques to analyze the sIAHP modifications that parallel epileptiform activity. Epileptiform activity was characterized by slow, repetitive, spontaneous depolarizations and action potential bursts and was associated with increased frequency and amplitude of spontaneous excitatory postsynaptic currents and a reduced sIAHP. The metabotropic glutamate receptor (mGluR) antagonist (S)-α-methyl-4-carboxyphenylglycine did not modify synaptic activity enhancement but did prevent sIAHP inhibition and epileptiform discharges. The mGluR-dependent regulation of the sIAHP was not caused by modulated intracellular Ca2+ signaling. Histamine, isoproterenol, and (±)-1-aminocyclopentane- trans-1,3-dicarboxylic acid reduced the sIAHP but did not increase synaptic activity and failed to evoke epileptiform activity. We conclude that 4AP or 4AP+Mg-free–induced enhancement of synaptic activity reduced the sIAHP via activation of postsynaptic group I/II mGluRs. The increased excitability caused by the lack of negative feedback provided by the sIAHP contributes to epileptiform activity, which requires the cooperative action of increased synaptic activity.

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S-Palmitoylation of the sodium channel Nav1.6 regulates its activity and neuronal excitability

Journal of Biological Chemistry ◽

10.1074/jbc.ra119.012423 ◽

2020 ◽

Vol 295 (18) ◽

pp. 6151-6164 ◽

Cited By ~ 1

Author(s):

Yanling Pan ◽

Yucheng Xiao ◽

Zifan Pei ◽

Theodore R. Cummins

Keyword(s):

Neuronal Excitability ◽

Cell Voltage ◽

Dorsal Root Ganglion Neurons ◽

Hek 293 ◽

Voltage Gated Sodium Channels ◽

Protein Functions ◽

Steady State Inactivation ◽

And Shifts ◽

Ganglion Neurons ◽

Hek 293 Cell Line

S-Palmitoylation is a reversible post-translational lipid modification that dynamically regulates protein functions. Voltage-gated sodium channels are subjected to S-palmitoylation and exhibit altered functions in different S-palmitoylation states. Our aim was to investigate whether and how S-palmitoylation regulates Nav1.6 channel function and to identify S-palmitoylation sites that can potentially be pharmacologically targeted. Acyl-biotin exchange assay showed that Nav1.6 is modified by S-palmitoylation in the mouse brain and in a Nav1.6 stable HEK 293 cell line. Using whole-cell voltage clamp, we discovered that enhancing S-palmitoylation with palmitic acid increases Nav1.6 current, whereas blocking S-palmitoylation with 2-bromopalmitate reduces Nav1.6 current and shifts the steady-state inactivation in the hyperpolarizing direction. Three S-palmitoylation sites (Cys1169, Cys1170, and Cys1978) were identified. These sites differentially modulate distinct Nav1.6 properties. Interestingly, Cys1978 is exclusive to Nav1.6 among all Nav isoforms and is evolutionally conserved in Nav1.6 among most species. Cys1978S-palmitoylation regulates current amplitude uniquely in Nav1.6. Furthermore, we showed that eliminating S-palmitoylation at specific sites alters Nav1.6-mediated excitability in dorsal root ganglion neurons. Therefore, our study reveals S-palmitoylation as a potential isoform-specific mechanism to modulate Nav activity and neuronal excitability in physiological and diseased conditions.

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Of mice and intrinsic excitability: genetic background affects the size of the postburst afterhyperpolarization in CA1 pyramidal neurons

Journal of Neurophysiology ◽

10.1152/jn.00257.2011 ◽

2011 ◽

Vol 106 (3) ◽

pp. 1570-1580 ◽

Cited By ~ 10

Author(s):

Shannon J. Moore ◽

Benjamin T. Throesch ◽

Geoffrey G. Murphy

Keyword(s):

Genetic Background ◽

Neuronal Excitability ◽

Pyramidal Neurons ◽

Critical Role ◽

Genetically Engineered ◽

Gradual Transition ◽

Cellular Mechanisms ◽

Ca1 Pyramidal Neurons ◽

Genetically Engineered Mice ◽

Cell Current

As the use of genetically engineered mice has become increasingly prevalent in neurobiological research, evidence has steadily accumulated that substantial differences exist between strains. Although a number of studies have reported effects of genetic background on behavior, few have focused on differences in neurophysiology. The postburst afterhyperpolarization (AHP) is an important determinant of intrinsic neuronal excitability and has been suggested to play a critical role in the cellular mechanisms underlying learning and memory. Using whole cell current-clamp recordings of CA1 pyramidal neurons, we examined the magnitude of different phases of the AHP (peak, medium, and slow) in two commonly used genetic backgrounds, C57BL/6 (B6) and 129SvEv (129), as well as in an F2 hybrid B6:129 background (F2). We found that neurons from B6 and F2 animals exhibited a significantly larger AHP compared with 129 animals and that this difference was consistent across all phases. Furthermore, our recordings revealed a marked dichotomy in the shape of the AHP waveform, which was independent of genetic background. Approximately 60% of cells exhibited an AHP with a sharp transition between the peak AHP and medium AHP, whereas the remaining 40% exhibited a more gradual transition. Our data add to the growing body of work suggesting that genetic background can affect neuronal function as well as behavior. In addition, these results highlight the innate heterogeneity of CA1 pyramidal neurons, even within a single genetic background. These differences should be taken into consideration during the analysis and comparison of experimental results.

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Streptozotocin Inhibits Electrophysiological Determinants of Excitatory and Inhibitory Synaptic Transmission in CA1 Pyramidal Neurons of Rat Hippocampal Slices: Reduction of These Effects by Edaravone

Cellular Physiology and Biochemistry ◽

10.1159/000453181 ◽

2016 ◽

Vol 40 (6) ◽

pp. 1274-1288 ◽

Cited By ~ 4

Author(s):

Ting Ju ◽

Yuru Li ◽

Xiaoran Wang ◽

Lifeng Xiao ◽

Li Jiang ◽

...

Keyword(s):

Pyramidal Neurons ◽

Hippocampal Slices ◽

Free Radical Scavenger ◽

Radical Scavenger ◽

Paired Pulse ◽

Ca1 Pyramidal Neurons ◽

Postsynaptic Currents ◽

Pulse Ratio ◽

Synaptic Mechanisms

Background: Streptozotocin (STZ) has served as an agent to generate an Alzheimer's disease (AD) model in rats, while edaravone (EDA), a novel free radical scavenger, has recently emerged as an effective treatment for use in vivo and vitro AD models. However, to date, these beneficial effects of EDA have only been clearly demonstrated within STZ-induced animal models of AD and in cell models of AD. A better understanding of the mechanisms of EDA may provide the opportunity for their clinical application in the treatment of AD. Therefore, the purpose of this study was to investigate the underlying mechanisms of STZ and EDA as assessed upon electrophysiological alterations in CA1 pyramidal neurons of rat hippocampal slices. Methods: Through measures of evoked excitatory postsynaptic currents (eEPSCs), AMPAR-mediated eEPSCs (eEPSCsAMPA), evoked inhibitory postsynaptic currents (eIPSCs), evoked excitatory postsynaptic current paired pulse ratio (eEPSC PPR) and evoked inhibitory postsynaptic current paired pulse ratio (eIPSC PPR), it was possible to investigate mechanisms as related to the neurotoxicity of STZ and reductions in these effects by EDA. Results: Our results showed that STZ (1000 µM) significantly inhibited peak amplitudes of eEPSCs, eEPSCsAMPA and eIPSCs, while EDA (1000 µM) attenuated these STZ-induced changes at holding potentials ranging from -60mV to +40 mV for EPSCs and -60mV to +20 mV for IPSCs. Our work also indicated that mean eEPSC PPR were substantially altered by STZ, effects which were partially restored by EDA. In contrast, no significant effects upon eIPSC PPR were obtained in response to STZ and EDA. Conclusion: Our data suggest that STZ inhibits glutamatergic transmission involving pre-synaptic mechanisms and AMPAR, and that STZ inhibits GABAergic transmission by post-synaptic mechanisms within CA1 pyramidal neurons. These effects are attenuated by EDA.

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Defective function of GABA-containing synaptic vesicles in mice lacking the AP-3B clathrin adaptor

The Journal of Cell Biology ◽

10.1083/jcb.200405032 ◽

2004 ◽

Vol 167 (2) ◽

pp. 293-302 ◽

Cited By ~ 75

Author(s):

Fubito Nakatsu ◽

Motohiro Okada ◽

Fumiaki Mori ◽

Noriko Kumazawa ◽

Hiroto Iwasa ◽

...

Keyword(s):

Synaptic Vesicles ◽

Neuronal Excitability ◽

Critical Role ◽

Physiological Role ◽

Adaptor Protein ◽

Epileptic Seizures ◽

Gaba Release ◽

Long Term Potentiation ◽

Clathrin Adaptor ◽

And Function

AP-3 is a member of the adaptor protein (AP) complex family that regulates the vesicular transport of cargo proteins in the secretory and endocytic pathways. There are two isoforms of AP-3: the ubiquitously expressed AP-3A and the neuron-specific AP-3B. Although the physiological role of AP-3A has recently been elucidated, that of AP-3B remains unsolved. To address this question, we generated mice lacking μ3B, a subunit of AP-3B. μ3B−/− mice suffered from spontaneous epileptic seizures. Morphological abnormalities were observed at synapses in these mice. Biochemical studies demonstrated the impairment of γ-aminobutyric acid (GABA) release because of, at least in part, the reduction of vesicular GABA transporter in μ3B−/− mice. This facilitated the induction of long-term potentiation in the hippocampus and the abnormal propagation of neuronal excitability via the temporoammonic pathway. Thus, AP-3B plays a critical role in the normal formation and function of a subset of synaptic vesicles. This work adds a new aspect to the pathogenesis of epilepsy.

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Somatostatin Depresses Excitatory but not Inhibitory Neurotransmission in Rat CA1 Hippocampus

Journal of Neurophysiology ◽

10.1152/jn.1997.78.6.3008 ◽

1997 ◽

Vol 78 (6) ◽

pp. 3008-3018 ◽

Cited By ~ 76

Author(s):

Melanie K. Tallent ◽

George R. Siggins

Keyword(s):

Pyramidal Neurons ◽

Hippocampal Slices ◽

Maximal Effect ◽

Direct Effects ◽

Inhibitory Effects ◽

Hippocampal Pyramidal Neurons ◽

M Current ◽

Postsynaptic Currents ◽

Inhibitory Neurotransmission ◽

Presynaptic Mechanisms

Tallent, Melanie K. and George R. Siggins. Somatostatin depresses excitatory but not inhibitory neurotransmission in rat CA1 hippocampus. J. Neurophysiol. 78: 3008–3018, 1997. In rat CA1 hippocampal pyramidal neurons (HPNs), somatostatin (SST) has inhibitory postsynaptic actions, including hyperpolarization of the membrane at rest and augmentation of the K+ M-current. However, the effects of SST on synaptic transmission in this brain region have not been well-characterized. Therefore we used intracellular voltage-clamp recordings in rat hippocampal slices to assess the effects of SST on pharmacologically isolated synaptic currents in HPNs. SST depressed both (R,S)-α-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA)/kainate and N-methyl-d-aspartate (NMDA) receptor-mediated excitatory postsynaptic currents (EPSCs) in a reversible manner, with an apparent IC50 of 22 nM and a maximal effect at 100 nM. In contrast, SST at concentrations up to 5 μM had no direct effects on either γ-aminobutyric acid-A (GABAA) or GABAB receptor–mediated inhibitory postsynaptic currents (IPSCs). The depression of EPSCs by SST was especially robust during hyperexcited states when polysynaptic EPSCs were present, suggesting that this peptide could play a compensatory role during seizurelike activity. SST effects were greatly attenuated by the alkylating agent N-ethylmaleimide, thus implicating a transduction mechanism involving the Gi/Go family of G-proteins. Use of 2 M Cs+ in the recording electrode blocked the postsynaptic modulation of K+ currents by SST, but did not alter the effects of SST on EPSCs, indicating that postsynaptic K+ currents are not involved in this action of SST. However, 2 mM external Ba2+ blocked the effect of SST on EPSCs, suggesting that presynaptic K+ channels or other presynaptic mechanisms may be involved. These findings and previous results from our laboratory show that SST has multiple inhibitory effects in hippocampus.

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Presynaptic Inactivation of Action Potentials and Postsynaptic Inhibition of GABAA Currents Contribute to KA-Induced Disinhibition in CA1 Pyramidal Neurons

Journal of Neurophysiology ◽

10.1152/jn.01231.2003 ◽

2004 ◽

Vol 92 (2) ◽

pp. 873-882 ◽

Cited By ~ 10

Author(s):

Ning Kang ◽

Li Jiang ◽

Wei He ◽

Jun Xu ◽

Maiken Nedergaard ◽

...

Keyword(s):

Action Potentials ◽

Pyramidal Neurons ◽

Hippocampal Slices ◽

Mean Amplitude ◽

Stratum Radiatum ◽

Depressant Effect ◽

Patch Clamp Recording ◽

Postsynaptic Inhibition ◽

Inhibitory Postsynaptic Currents ◽

Postsynaptic Currents

Kainate-type glutamate ionotropic receptors (KAR) mediate either depression or potentiation of inhibitory transmission. The mechanisms underlying the depressant effect of KAR agonists have been controversial. Under dual patch-clamp recording techniques in synaptically coupled pairs of CA1 interneurons and pyramidal neurons in hippocampal slices, micromolar concentrations of KAR agonists, kainic acid (KA, 10 μM) and ATPA (10 μM), induced inactivation of action potentials (APs) in 58 and 50% of presynaptic interneurons, respectively. Inactivation of interneuronal APs might have significantly contributed to KA-induced decreases in evoked inhibitory postsynaptic currents (eIPSCs) that are obtained by stimulating the stratum radiatum. With controlled interneuronal APs, KAR agonists induced a decrease in the potency (mean amplitude of successful events) and mean amplitude (including failures) of unitary inhibitory postsynaptic currents (uIPSCs) without significantly changing the success rate (Ps) at perisomatic high-Ps synapses. In contrast, KAR agonists induced a decrease in both the Ps and potency of uIPSCs at dendritic high-Ps synapses. KAR agonists induced an inhibition of GABAA currents by activating postsynaptic KARs in pyramidal neurons; this was more prominent at dendrites than at soma. Both the exogenous GABA-induced current and the amplitude of miniature IPSCs (mIPSCs) were attenuated by KAR agonists. Thus the postsynaptic KAR-mediated inhibition of GABAA currents may contribute to the KAR agonist-induced decrease in the potency of uIPSCs and KA-induced disinhibition.

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