Currents In Hippocampus Research Articles

Increased O-GlcNAcylation rapidly decreases GABAAR currents in hippocampus but depresses neuronal output

O-GlcNAcylation, a post-translational modification involving O-linkage of β-N-acetylglucosamine to Ser/Thr residues on target proteins, is increasingly recognized as a critical regulator of synaptic function. Enzymes that catalyze O-GlcNAcylation are found at both presynaptic and postsynaptic sites, and O-GlcNAcylated proteins localize to synaptosomes. An acute increase in O-GlcNAcylation can affect neuronal communication by inducing long-term depression (LTD) of excitatory transmission at hippocampal CA3-CA1 synapses, as well as suppressing hyperexcitable circuits in vitro and in vivo. Despite these findings, to date, no studies have directly examined how O-GlcNAcylation modulates the efficacy of inhibitory neurotransmission. Here we show an acute increase in O-GlcNAc dampens GABAergic currents onto principal cells in rodent hippocampus likely through a postsynaptic mechanism, and has a variable effect on the excitation/inhibition balance. The overall effect of increased O-GlcNAc is reduced synaptically-driven spike probability via synaptic depression and decreased intrinsic excitability. Our results position O-GlcNAcylation as a novel regulator of the overall excitation/inhibition balance and neuronal output.

Alpha1-Adrenoceptor Antagonists Improve Memory by Activating N-methyl-D-Aspartate-Induced Ion Currents in the Rat Hippocampus.

Purpose:Alpha1 (α1)-adrenoceptor antagonists are widely used to treat lower urinary tract symptoms. These drugs not only act on peripheral tissues, but also cross the blood-brain barrier and affect the central nervous system. Therefore, α1-adrenoceptor antagonists may enhance brain functions. In the present study, we investigated the effects of tamsulosin, an α1-adrenoceptor antagonist, on short-term memory, as well as spatial learning and memory, in rats.Methods:The step-down avoidance test was used to evaluate short-term memory, and an eight-arm radial maze test was used to evaluate spatial learning and memory. TUNEL (terminal deoxynucleotidyltransferase-mediated dUTP nick end labeling) staining was performed in order to evaluate the effect of tamsulosin on apoptosis in the hippocampal dentate gyrus. Patch clamp recordings were used to evaluate the effect of tamsulosin on ionotropic glutamate receptors, such as N-methyl-D-aspartate (NMDA), amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA), and kainate receptors, in hippocampal CA1 neurons.Results:Tamsulosin treatment improved short-term memory, as well as spatial learning and memory, without altering apoptosis. The amplitudes of NMDA-induced ion currents were dose-dependently increased by tamsulosin. However, the amplitudes of AMPA- and kainate-induced ion currents were not affected by tamsulosin.Conclusions:Tamsulosin enhanced memory function by activating NMDA receptor-mediated ion currents in the hippocampus without initiating apoptosis. The present study suggests the possibility of using tamsulosin to enhance memory under normal conditions, in addition to its use in treating overactive bladder.

The KCNQ5 potassium channel mediates a component of the afterhyperpolarization current in mouse hippocampus

Mutations in KCNQ2 and KCNQ3 voltage-gated potassium channels lead to neonatal epilepsy as a consequence of their key role in regulating neuronal excitability. Previous studies in the brain have focused primarily on these KCNQ family members, which contribute to M-currents and afterhyperpolarization conductances in multiple brain areas. In contrast, the function of KCNQ5 (Kv7.5), which also displays widespread expression in the brain, is entirely unknown. Here, we developed mice that carry a dominant negative mutation in the KCNQ5 pore to probe whether it has a similar function as other KCNQ channels. This mutation renders KCNQ5(dn)-containing homomeric and heteromeric channels nonfunctional. We find that Kcnq5(dn/dn) mice are viable and have normal brain morphology. Furthermore, expression and neuronal localization of KCNQ2 and KCNQ3 subunits are unchanged. However, in the CA3 area of hippocampus, a region that highly expresses KCNQ5 channels, the medium and slow afterhyperpolarization currents are significantly reduced. In contrast, neither current is affected in the CA1 area of the hippocampus, a region with low KCNQ5 expression. Our results demonstrate that KCNQ5 channels contribute to the afterhyperpolarization currents in hippocampus in a cell type-specific manner.

Inhibition of Action Potential Backpropagation During Postnatal Development of the Hippocampus

to the editor: In their recent article, [Fuenzalida and colleagues (2010)][1] describe the contributions not only of glutamate receptors but also postsynaptic action potential (AP) signaling, which underlie spike timing–dependent plasticity (STDP) of Schaffer collateral synapses to CA1 hippocampal

Extrasynaptic GABAergic currents in hippocampus are inhibited by adenosine A1 receptors

Event Abstract Back to Event Extrasynaptic GABAergic currents in hippocampus are inhibited by adenosine A1 receptors R. Dias1, J. Ribeiro1, D. Rombo1* and A. Sebastião1 1 Instituto de Farmacologia e Neurociências, Instituto de Medicina Molecular, Faculdade de Medicina da Universidade de Lisboa, Portugal Adenosine, through inhibitory A1 receptors is a modulator of neuronal excitability in the hippocampus by modulating the glutamatergic excitatory circuit at the pre- and postsynaptic level. The role of adenosine on GABAergic transmission in the hippocampus is much less known. We now investigated whether adenosine, through A1 receptors, modulates postsynaptic currents mediated by GABAA receptors. Muscimol (30µM, GABAA receptor agonist)-evoked postsynaptic currents (PSCs), afferent-evoked inhibitory postsynaptic currents (IPSCs) and miniature inhibitory postsynaptic currents (mIPSCs), were recorded (whole-cell configuration, Vh=-80mV) from CA1 pyramidal cells and interneurons of rat (Wistar, 3-5w) hippocampal slices. At CA1 pyramidal cells, the activation of A1 receptors with CPA (10-30nM) decreased (to 54±3.9%,p<0.0001,n=12) the peak amplitude of PSCs and this inhibition was reversed by DPCPX (50nM), an adenosine A1 receptor antagonist, to 83±2.5% of baseline (n=4,p<0.05). DPCPX per se unmasked the inhibition of PSCs by endogenous extracellular adenosine since it increased the inhibitory currents by 13±1.0% (n=5,p<0.001). Neither the amplitude nor the frequency of mIPSCs (n=12), or the amplitude of IPSCs (n=10), were affected by CPA indicating an action of A1 receptors on extrasynaptic GABAergic currents. At stratum radiatum GABAergic interneurons, the activation of A1 receptors with CPA attenuated GABAA PSCs in 4 out of 9 cells tested to 57±2.3% (p<0.001). The PSCs in the other 5 cells tested were not changed by CPA superfusion, suggesting the existence of two populations of interneurons differently sensitive to adenosine. Together, these results indicate that extrasynaptic GABAA receptor-mediated currents are modulated by adenosine A1 receptors in pyramidal hippocampal neurons and in a subset of interneurons. Support:FCT Conference: EMBO workshop: Gaba Signalling and Brain Networks , Amsterdam, Netherlands, 30 Jun - 2 Jul, 2010. Presentation Type: Poster Presentation Topic: Posters Citation: Dias R, Ribeiro J, Rombo D and Sebastião A (2010). Extrasynaptic GABAergic currents in hippocampus are inhibited by adenosine A1 receptors. Conference Abstract: EMBO workshop: Gaba Signalling and Brain Networks . doi: 10.3389/conf.fnins.2010.15.00021 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 24 Jun 2010; Published Online: 24 Jun 2010. * Correspondence: D. Rombo, Instituto de Farmacologia e Neurociências, Instituto de Medicina Molecular, Faculdade de Medicina da Universidade de Lisboa, Lisbon, Portugal, drombo@fm.ul.pt Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers R. Dias J. Ribeiro D. Rombo A. Sebastião Google R. Dias J. Ribeiro D. Rombo A. Sebastião Google Scholar R. Dias J. Ribeiro D. Rombo A. Sebastião PubMed R. Dias J. Ribeiro D. Rombo A. Sebastião Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

Chronic lentiviral expression of inwardly rectifying K + channels (Kir2.1) reduces neuronal activity and downregulates voltage-gated potassium currents in hippocampus

Strongly inwardly rectifying K + (Kir2) channels are endogenously expressed in rat brains and have recently been used as a tool to reduce the neuronal activity. But little is known about the role of Kir2 channels and the chronic effect of the reduced activity on the intrinsic excitability of neurons. Here we constructed a lentiviral vector that coexpressed Kir2.1 and GFP (LvKir2.1) and infected the vector to the hippocampal slice cultures. The LvKir2.1-infected CA1 neurons showed clear inwardly rectifying K + currents for more than 15 days. The resting membrane potential was more negative by approximately 10 mV than those uninfected or infected with the lentiviral vector expressing GFP alone. The infection of LvKir2.1 reduced the voltage change in response to current injections and the amplitude of mEPSPs with a shunting effect. The LvKir2.1 infection significantly reduced the firings evoked by depolarizing currents in the CA1 neurons. The reduction of the firing was attributed to the hyperpolarized potential rather than to the shunting effect. These reductions were limited to modest current injections, suggesting that the overexpressed Kir2.1 plays the role of a noise-filter. Moreover, the chronic overexpression of Kir2.1 downregulated the expression of the delayed rectifier potassium current in a homeostatic manner, indicating a usefulness of this viral vector to study the activity-dependent neuronal development.

Lysosomal Dysfunction Produces Distinct Alterations in Synaptic α-Amino-3-Hydroxy-5-Methylisoxazolepropionic Acid and N-Methyl-D-Aspartate Receptor Currents in Hippocampus

The early processes that lead to synaptic dysfunction during aging are not clearly understood. Dysregulation of alpha-amino-3-hydroxy-5-methylisoxazolepropionic acid (AMPA) and N-methyl-D-aspartate (NMDA) receptors may cause age-related cognitive decline. Using hippocampal slice cultures exhibiting lysosomal dysfunction, an early marker of brain aging that is linked to protein accumulation, we identified alterations to AMPA and NMDA receptor-mediated synaptic currents. The miniature and spontaneous excitatory postsynaptic currents that were examined after 3, 6, and 9 days of lysosomal disruption showed progressive changes in amplitude, frequency, and rise and decay kinetics. To investigate whether modifications in specific channel properties of single synaptic receptors contributed to changes in the amplitude and time course of synaptic currents, we examined the single channel properties of synaptic AMPA and NMDA receptors. The channel open probability and the mean open times showed decreases in both receptor populations, whereas the closed times were increased without any change in the channel conductance. The Western blot analysis revealed a progressive decline in synaptic markers including glutamate receptor subunits. These results indicate that lysosomal dysfunction leads to progressive functional perturbation of AMPA and NMDA receptors in this slice model of protein accumulation, suggesting that age-related cognitive decline could result from altered glutamate receptor function before reductions in synaptic density.

A Kinase-anchoring Protein 150 and Calcineurin Are Involved in Regulation of Acid-sensing Ion Channels ASIC1a and ASIC2a

Acid-sensing ion channel (ASIC) 1a and ASIC2a are acid-sensing ion channels in central and peripheral neurons. ASIC1a has been implicated in long-term potentiation of synaptic transmission and ischemic brain injury, whereas ASIC2a is involved in mechanosensation. Although the biological role and distribution of ASIC1a and ASIC2a subunits in brain have been well characterized, little is known about the intracellular regulation of these ion channels that modulates their function. Using pulldown assays and mass spectrometry, we have identified A kinase-anchoring protein (AKAP)150 and the protein phosphatase calcineurin as binding proteins to ASIC2a. Extended pulldown and co-immunoprecipitation assays showed that these regulatory proteins also interact with ASIC1a. Transfection of rat cortical neurons with constructs encoding green fluorescent protein- or hemagglutinin-tagged channels showed expression of ASIC1a and ASIC2a in punctate and clustering patterns in dendrites that co-localized with AKAP150. Inhibition of protein kinase A binding to AKAPs by Ht-31 peptide reduces ASIC currents in cortical neurons and Chinese hamster ovary cells, suggesting a role of AKAP150 in association with protein kinase A in ASIC function. We also demonstrated a regulatory function of calcineurin in ASIC1a and ASIC2a activity. Cyclosporin A, an inhibitor of calcineurin, increased ASIC currents in Chinese hamster ovary cells and in cortical neurons, suggesting that activity of ASICs is inhibited by calcineurin-dependent dephosphorylation. These data imply that ASIC down-regulation by calcineurin could play an important role under pathological conditions accompanying intracellular Ca(2+) overload and tissue acidosis to circumvent harmful activities mediated by these channels.

Development of GABA(A) receptor-mediated inhibitory postsynaptic currents in hippocampus.

Hippocampal CA1 pyramidal cells receive two kinetic classes of GABA(A) receptor-mediated inhibition: slow dendritic inhibitory postsynaptic currents (GABA(A,slow) IPSCs) and fast perisomatic (GABA(A,fast)) IPSCs. These two classes of IPSCs are likely generated by two distinct groups of interneurons, and we have previously shown that the kinetics of the IPSCs have important functional consequences for generating synchronous firing patterns. Here, we studied developmental changes in the properties of GABA(A,fast) and GABA(A,slow) spontaneous, miniature, and evoked IPSCs (sIPSCs, mIPSCs, and eIPSCs, respectively) using whole cell voltage-clamp recordings in brain slices from animals aged P10-P35. We found that the rate of GABA(A,slow) sIPSCs increased by over 70-fold between P11 and P35 (from 0.0017 to 0.12 s(-1)). Over this same age range, we observed a >3.5-fold increase in the maximal amplitude of GABA(A,slow) eIPSCs evoked by stratum lacunosum-moleculare (SL-M) stimuli. However, the rate and amplitude of GABA(A,slow) mIPSCs remained unchanged between P10 and P30, suggesting that the properties of GABA(A,slow) synapses remained stable over this age range, and that the increase in sIPSC rate and in eIPSC amplitude was due to increased excitability or excitation of GABA(A,slow) interneurons. This hypothesis was tested using bath application of norepinephrine (NE), which we found at low concentrations (1 microM) selectively increased the rate of GABA(A,slow) sIPSCs while leaving GABA(A,fast) sIPSCs unchanged. This effect was observed in animals as young as P13 and was blocked by coapplication of tetrodotoxin, suggesting that NE was acting to increase the spontaneous firing rate of GABA(A,slow) interneurons and consistent with our hypothesis that developmental changes in GABA(A,slow) IPSCs are due to changes in presynaptic excitability. In contrast to the changes we observed in GABA(A,slow) IPSCs, the properties of GABA(A,fast) sIPSCs remained largely constant between P11 and P35, whereas the rate, amplitude, and kinetics of GABA(A,fast) mIPSCs showed significant changes between P10 and P30, suggesting counterbalancing changes in action potential-dependent GABA(A,fast) sIPSCs. These observations suggest differential developmental regulation of the firing properties of GABA(A,fast) and GABA(A,slow) interneurons in CA1 between P10 and P35.

Central synaptic integration: linear after all?

Unitary synaptic currents in hippocampus show small variability. Experimental evidence suggests that the neuron is endowed with mechanisms to reduce location-dependent differences in amplitude and time course of synaptic events, contributing to small variability. These mechanisms may allow the neuron to count individual quanta and thereby linearize integration of unitary events.

Low Ba2+ and Ca2+ induce a sustained high probability of repolarization openings of L-type Ca2+ channels in hippocampal neurons: physiological implications.

Openings of single L-type Ca2+ channels following repolarization to negative membrane potentials from a depolarizing step (repolarization openings, ROs) have been described previously in brain cell preparations. However, these ROs have been reported to occur only infrequently. Here we report that the frequency of ROs in cell-attached patches of cultured rat hippocampal neurons can be increased dramatically by lowering the pipette Ba2+ concentration to 20 mM from the usual 90-110 mM. This increased opening probability can last for hundreds to thousands of milliseconds following repolarization. Current-voltage analyses of open probability show that the depolarization pulse threshold for inducing ROs in 20 mM Ba2+ is -10 to 0 mV but that the probability of ROs reaches maximal levels following depolarizing pulses that approach the apparent null (equilibrium) potential for Ba2+. Comparable current-voltage curves in 110 mM Ba2+ from a more positive holding potential (-50 mV) indicate that membrane surface charge screening accounts for some, but not all, of the effect of lowering the Ba2+ concentration. Consequently, current-dependent inactivation or some other ion-dependent mechanism (e.g., ion binding inside the pore) also appears to regulate this potentially major pathway of Ca2+ entry. A high probability of ROs also can be induced under relatively physiological conditions (5-ms depolarizing steps, 2-5 mM Ca2+ in the pipette). Thus, the high open probability state at negative potentials may underlie the long Ca2+ tail currents in hippocampus that were described previously and appears to have major implications for physiological functions (e.g., the slow Ca(2+)-dependent afterhyperpolarization), particularly in brain neurons.

Synchronization of pyramidal cell firing by ephaptic currents in hippocampus in situ.

Once it became clear that excitable cells generate significant electrical discharges, the idea that cell-to-cell communication is normally mediated by electrical currents came very naturally. Originally, such a mechanism was not conceived as requiring any specialized low resistance junctions, and electrical transmission was thus thought to be the predominant method of junctional transmission (Eccles, 1936).

EFFECTS EVOKED IN AN AXON BY THE ACTIVITY OF A CONTIGUOUS ONE

EFFECTS EVOKED IN AN AXON BY THE ACTIVITY OF A CONTIGUOUS ONE