Hippocampal GABAergic Synapses Research Articles

A modulatory role of ASICs on GABAergic synapses in rat hippocampal cell cultures.

Rapid acidification occurring during synaptic vesicle release can activate acid-sensing ion channels (ASICs) both on pre- and postsynaptic neurons. In the latter case, a fraction of postsynaptic current would be mediated by cation-selective acid-sensing ion channels. Additionally, in both cases, activation of acid-sensing ion channels could modulate synaptic strength by affecting transmitter release and/or sensitivity of postsynaptic receptors. To address potential involvement of acid-sensing ion channels in mediation/modulation of synaptic transmission at hippocampal GABAergic synapses, we studied effects of three structurally different blockers of acid-sensing ion channels on evoked postsynaptic currents using the patch-clamp technique. We found that GABAergic postsynaptic currents, recorded below their reversal potential as inward currents, are suppressed by all the employed blockers of acid-sensing ion channels. These currents were suppressed by ~ 20 % in the presence of a novel blocker 5b (1 μM) and by ~30 % in the presence of either amiloride (25 μM) or diminazene (20 μM). In the same cells the suppression of postsynaptic currents, recorded above their reversal potential as outward currents was statistically insignificant. These results imply that the effects of blockers in our experiments are at least partially postsynaptic. On the other hand, in the case of mediation of a fraction of postsynaptic current by acid-sensing ion channels, an increase of outward currents would be expected under our experimental conditions. Our analysis of a bicuculline-resistant fraction of postsynaptic currents also suggests that effects of the blockers are predominantly modulatory. In this work we present evidence for the first time that acid-sensing ion channels play a functional role at hippocampal GABAergic synapses. The suppressing effect of the blockers of acid-sensing ion channels on GABAergic transmission is due, at least partially, to a postsynaptic but (predominantly) modulatory mechanism. We hypothesize that the modulatory effect is due to functional crosstalk between ASICs and GABAA-receptors recently reported in isolated neurons, however, verification of this hypothesis is necessary.Electronic supplementary materialThe online version of this article (doi:10.1186/s13041-016-0269-4) contains supplementary material, which is available to authorized users.

A kinetic model for the frequency dependence of cholinergic modulation at hippocampal GABAergic synapses

In this paper we use a simple model of presynaptic neuromodulation of GABA signaling to decipher paired whole-cell recordings of frequency dependent cholinergic neuromodulation at CA1 parvalbumin-containing basket cell (PV BC)-pyramidal cell synapses. Variance-mean analysis is employed to normalize the data, which is then used to estimate parameters in the mathematical model. Various parameterizations and hidden parameter dependencies are investigated using Markov Chain Monte Carlo (MCMC) parameter estimation techniques. This analysis reveals that frequency dependence of cholinergic modulation requires both calcium-dependent recovery from depression and mAChR-induced inhibition of presynaptic calcium entry. A reduction in calcium entry into the presynaptic terminal in the kinetic model accounted for the frequency-dependent effects of mAChR activation.

Different pools of postsynaptic GABAA receptors mediate inhibition evoked by low‐ and high‐frequency presynaptic stimulation at hippocampal synapses

Patterns of short-term synaptic plasticity could considerably differ between synapses of the same axon. This may lead to separation of synaptic receptors transmitting either low- or high-frequency signals and, therefore, may have functional consequences for the information transfer in the brain. Here, we estimated a degree of such separation at hippocampal GABAergic synapses using a use-dependent GABAA receptor antagonist, picrotoxin, to selectively suppress a pool of GABAA receptors monosynaptically activated during the low-frequency stimulation. The relative changes in postsynaptic responses evoked by the high-frequency stimulation before and after such block were used to estimate the contribution of this GABAA receptor pool to synaptic transmission at high frequencies. Using this approach, we have shown that IPSCs evoked by low-frequency (0.2 Hz) stimulation and asynchronous currents evoked by high-frequency (20-40 Hz) stimulation are mediated by different pools of postsynaptic GABAA receptors. Thus, our findings suggest that inhibition produced by a single hippocampal interneuron may be selectively routed to different postsynaptic targets depending on the presynaptic discharge frequency.

Endocannabinoids Gate State-Dependent Plasticity of Synaptic Inhibition in Feeding Circuits

Changes in food availability alter the output of hypothalamic nuclei that underlie energy homeostasis. Here, we asked whether food deprivation impacts the ability of GABA synapses in the dorsomedial hypothalamus (DMH), an important integrator of satiety signals, to undergo activity-dependent changes. GABA synapses in DMH slices from satiated rats exhibit endocannabinoid-mediated long-term depression (LTD(GABA)) in response to high-frequency stimulation of afferents. When CB1Rs are blocked, however, the same stimulation elicits long-term potentiation (LTP(GABA)), which manifests presynaptically and requires heterosynaptic recruitment of NMDARs and nitric oxide (NO). Interestingly, NO signaling is required for eCB-mediated LTD(GABA). Twenty-four hour food deprivation results in a CORT-mediated loss of CB1R signaling and, consequently, GABA synapses only exhibit LTP(GABA). These observations indicate that CB1R signaling promotes LTD(GABA) and gates LTP(GABA). Furthermore, the satiety state of an animal, through regulation of eCB signaling, determines the polarity of activity-dependent plasticity at GABA synapses in the DMH.

NMDA Receptors in Hippocampal GABAergic Synapses and Their Role in Nitric Oxide Signaling

GABAergic inhibition plays a central role in the control of pyramidal cell ensemble activities; thus, any signaling mechanism that regulates inhibition is able to fine-tune network patterns. Here, we provide evidence that the retrograde nitric oxide (NO)-cGMP cascade triggered by NMDA receptor (NMDAR) activation plays a role in the control of hippocampal GABAergic transmission in mice. GABAergic synapses express neuronal nitric oxide synthase (nNOS) postsynaptically and NO receptors (NO-sensitive guanylyl cyclase) in the presynaptic terminals. We hypothesized that--similar to glutamatergic synapses--the Ca(2+) transients required to activate nNOS were provided by NMDA receptor activation. Indeed, administration of 5 μm NMDA induced a robust nNOS-dependent cGMP production in GABAergic terminals, selectively in the CA1 and CA3c areas. Furthermore, using preembedding, postembedding, and SDS-digested freeze-fracture replica immunogold labeling, we provided quantitative immunocytochemical evidence that NMDAR subunits GluN1, GluN2A, and GluN2B were present in most somatic GABAergic synapses postsynaptically. These data indicate that NMDARs can modulate hippocampal GABAergic inhibition via NO-cGMP signaling in an activity-dependent manner and that this effect is subregion specific in the mouse hippocampus.

NMDA receptors in hippocampal GABAergic synapses and their possible role in nitric oxide signaling

Event Abstract Back to Event NMDA receptors in hippocampal GABAergic synapses and their possible role in nitric oxide signaling Eszter Szabadits1*, András Szonyi1, Csaba Cserép1, Yugo Fukazawa2, Masahiko Watanabe3, Jan D. Vente4, Ryuichi Shigemoto2, Tamás Freund1 and Gábor Nyiri1 1 Hungarian Academy of Sciences, Laboratory of Cerebral Cortex Research in the Institute of Experimental Medicine, Hungary 2 National Institute for Physiological Sciences, Japan 3 Hokkaido University School of Medicine, Department of Anatomy, Japan 4 Maastricht University, Department of Psychiatry and Neuropsychology, Division of Cellular Neuroscience, Netherlands Nitric oxide (NO) plays an important role in the plasticity of hippocampal excitatory synapses, and its production requires NMDA receptor-dependent calcium influx. Accordingly, the NO synthesizing enzyme, neuronal nitric oxide synthase (nNOS) and NMDA receptors (NMDA-R) were found to colocalize in excitatory postsynaptic active zones. In our previous study we showed that nNOS is also present in a large number of GABAergic synapses postsynaptically. Here we investigated whether NMDA-R could be a source of calcium entry at GABAergic basket cell synapses, and whether its activation can lead to NO production and subsequent cGMP syntheses. Using freeze fracture replica immunolabeling we showed that at least two-thirds of the GABAergic synapses contain both major types of NMDA-R subunits (NR1 and NR2) on the somata in the postsynaptic active zones. To identify the type of interneuron synapses that could be modulated by NMDA-Rs, we carried out preembedding double-immunolabeling and found that most cholecystokinin/vesicular glutamate transporter 3 containing terminals were positive for NMDA-R, while many of the parvalbumin-positive synapses also contained NMDA-Rs. Using fluorescent immunolabeling in acute hippocampal slices, we tested whether NMDA-R activation was able to induce NO-dependent cGMP production in these basket cell terminals. We found that administration of 5-10 uM NMDA induced a high level of cGMP production selectively in GABAergic terminals. This effect could be blocked postsynaptically by both NMDA-R and nNOS blockers, as well as presynaptically by an NO receptor blocker. Furthermore, NMDA-R activation had no influence on cGMP levels in nNOS knock-out mice. We conclude that NMDA receptors and nNOS coexist at hippocampal GABAergic basket cell synapses, and activation of these NMDA receptors results in an NO-mediated production of cGMP in GABAergic terminals. Conference: IBRO International Workshop 2010, Pécs, Hungary, 21 Jan - 23 Jan, 2010. Presentation Type: Poster Presentation Topic: Cellular neuroscience Citation: Szabadits E, Szonyi A, Cserép C, Fukazawa Y, Watanabe M, Vente JD, Shigemoto R, Freund T and Nyiri G (2010). NMDA receptors in hippocampal GABAergic synapses and their possible role in nitric oxide signaling. Front. Neurosci. Conference Abstract: IBRO International Workshop 2010. doi: 10.3389/conf.fnins.2010.10.00126 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: 28 Apr 2010; Published Online: 28 Apr 2010. * Correspondence: Eszter Szabadits, Hungarian Academy of Sciences, Laboratory of Cerebral Cortex Research in the Institute of Experimental Medicine, Budapest, Hungary, szabadits@koki.hu 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 Eszter Szabadits András Szonyi Csaba Cserép Yugo Fukazawa Masahiko Watanabe Jan D Vente Ryuichi Shigemoto Tamás Freund Gábor Nyiri Google Eszter Szabadits András Szonyi Csaba Cserép Yugo Fukazawa Masahiko Watanabe Jan D Vente Ryuichi Shigemoto Tamás Freund Gábor Nyiri Google Scholar Eszter Szabadits András Szonyi Csaba Cserép Yugo Fukazawa Masahiko Watanabe Jan D Vente Ryuichi Shigemoto Tamás Freund Gábor Nyiri PubMed Eszter Szabadits András Szonyi Csaba Cserép Yugo Fukazawa Masahiko Watanabe Jan D Vente Ryuichi Shigemoto Tamás Freund Gábor Nyiri 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.

Reactive Oxygen Species Mediate the Potentiating Effects of ATP on GABAergic Synaptic Transmission in the Immature Hippocampus

Reactive oxygen species (ROS) constitute important signaling molecules in the central nervous system. They regulate a number of different functions both under physiological conditions and under pathological conditions. Here we tested the hypothesis that in the immature hippocampus ATP, the most diffuse neurotransmitter in the brain, modulates synaptic transmission via ROS. We show that ATP, acting on metabotropic P2Y1 receptors, increased the frequency of GABA(A)-mediated spontaneous postsynaptic currents (SPSCs) in CA3 principal cells, an effect that was prevented by the antioxidant N-acetyl-cysteine or by catalase, an enzyme that breaks down H2O2. The effect of ATP on SPSCs was mimicked by H2O2 or by the pro-oxidant, Fe2+, which, through the Fentol reaction, catalyzes the conversion of H2O2 into highly reactive hydroxyl radicals. MRS-2179, a P2Y1 receptor antagonist, removed the facilitatory action of Fe2+ on SPSCs, suggesting that endogenous ATP acting on P2Y1 receptors is involved in Fe2+-induced modulation of synaptic transmission. Imaging ROS with the H2O2-sensitive dye DCF revealed that ATP induces generation of peroxide in astrocytes via activation of P2Y1 receptors coupled to intracellular calcium rise. Neither N-acetyl-cysteine nor catalase prevented Ca2+ transients induced by ATP in astrocytes. Since a single hippocampal astrocyte can contact many neurons, ATP-induced ROS signaling may control thousands of synapses. This may be crucial for information processing in the immature brain when GABAergic activity is essential for the proper wiring of the hippocampal network.

SNAP-25 Modulation of Calcium Dynamics Underlies Differences in GABAergic and Glutamatergic Responsiveness to Depolarization

SNAP-25 is a component of the SNARE complex implicated in synaptic vesicle exocytosis. In this study, we demonstrate that hippocampal GABAergic synapses, both in culture and in brain, lack SNAP-25 and are resistant to the action of botulinum toxins type A and E, which cleave this SNARE protein. Relative to glutamatergic neurons, which express SNAP-25, GABAergic cells were characterized by a higher calcium responsiveness to depolarization. Exogenous expression of SNAP-25 in GABAergic interneurons lowered calcium responsiveness, and SNAP-25 silencing in glutamatergic neurons increased calcium elevations evoked by depolarization. Expression of SNAP-25 1-197 but not of SNAP-25 1-180 inhibited calcium responsiveness, pointing to the involvement of the 180–197 residues in the observed function. These data indicate that SNAP-25 is crucial for the regulation of intracellular calcium dynamics and, possibly, of network excitability. SNAP-25 is therefore a multifunctional protein that participates in exocytotic function both at the mechanistic and at the regulatory level .

Endocannabinoids: Inhibiting Inhibitory Input

Cannabinoids are active components in marijuana, and endocannabinoids, which are derived from lipids through the actions of such enzymes as phospholipase D, phospholipase A, and diacylglycerol (DAG) lipase, are the body's own version of these signaling molecules. Endocannabinoids were known to mediate a retrograde signal that can transiently regulate inhibitory neurons in the brain. Chevaleyre and Castillo show that endocannabinoids, specifically 2-arachidonyl glycerol (2-AG), mediate a long-term depression (LTD) of inhibitory input (I-LTD) in the hippocampus. I-LTD was produced in response to two types of high-frequency stimulation under conditions where ionotropic glutamate receptors ( N -methyl-D-aspartate and the kainate and AMPA receptors) were blocked. This I-LTD only occurred upon stimulation of neurons that synapsed on the dendritic regions of the hippocampal CA1 neurons and not the somatic regions. Pharmacological manipulation indicated that I-LTD required metabotropic glutamate type I receptors (mGluR1), but not γ-aminobutyric acid B (GABA B ) receptors. Because electrophysiological data suggested that the I-LTD was due to decreased inhibitory input in response to postsynaptic activity, the authors tested for the involvement of a retrograde signal. Pharmacological inhibition of the endocannabinoid receptor CB 1 blocked I-LTD produced through high-frequency stimulation or in response to pharmacological activation of mGluR1. Experiments designed to compare I-LTD with the transient form of inhibition mediated by endocannabinoids suggested that these two events were mediated by different endocannabinoids produced in response to different signaling cascades. The transient form of inhibition requires a calcium-dependent production of endocannabinoids, whereas I-LTD required phospholipase C activation, production of DAG, and the activity of DAG lipase, which produces 2-AG. Further discussion of these two endocannabinoid-mediated inhibitory processes and their roles in long-term potentiation and learning and memory is provided by Freund and Hájos. V. Chevaleyre, P. E. Castillo, Heterosynaptic LTD of hippocampal GABAergic synapses: A novel role of endocannabinoids in regulating excitability. Neuron 38 , 461-472 (2003). [Online Journal] T. F. Freund, N. Hájos, Excitement reduces inhibition via endocannabinoids. Neuron 38 , 362-365 (2003). [Online Journal]

Functional significance of cannabinoid-mediated, depolarization-induced suppression of inhibition (DSI) in the hippocampus.

A number of recent studies have demonstrated that a well-known form of short-term plasticity at hippocampal GABAergic synapses, called depolarization-induced suppression of inhibition (DSI), is in fact mediated by the retrograde actions of endocannabinoids released in response to depolarization of the postsynaptic cells. These studies suggest that endogenous cannabinoids may play an important role in regulating inhibitory tone in the mammalian CNS. Despite the widespread interest and potential physiological importance of DSI, many questions regarding the physiological relevance of DSI remain. To that end, this study set out to define the specific limiting conditions that could elicit DSI at GABAergic synapses in CA1 hippocampal pyramidal neurons and to determine if DSI could be elicited with pulse trains that mimic hippocampal cell-firing patterns that occur in vivo. Whole cell recordings from hippocampal neurons under voltage-clamp configuration were made in rat hippocampal slices. Spontaneous and evoked gamma-aminobutyric acid-A (GABAA) receptor-mediated inhibitory postsynaptic currents (sIPSCs and eIPSCs, respectively) were recorded prior to and following depolarization of CA1 hippocampal pyramidal cells. Depolarizing voltage pulses were shaped to evoke currents in QX-314-treated cells similar to those accompanying single spontaneous voltage-clamped action potentials recorded from the soma. Attempts were made to elicit DSI with trains of these pulses that mimicked hippocampal cell firing patterns in vivo, for instance, when animals traverse place fields or are performing a short-term memory task. DSI could not be elicited by such pulse trains or by a number of other combinations of behaviorally specific firing parameters. The minimum duration of depolarization necessary to elicit DSI in hippocampal neurons determined by paired-pulse manipulation was 50 -75 ms at a critical interval of 20 -30 ms between pulse pairs. Under the conditions tested, the normal firing patterns of hippocampal neurons that occur in vivo do not appear to elicit DSI.