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Menzikov SA, Zaichenko DM, Moskovtsev AA, Morozov SG, Kubatiev AA. Zinc Inhibits the GABA AR/ATPase during Postnatal Rat Development: The Role of Cysteine Residue. Int J Mol Sci 2023; 24:ijms24032764. [PMID: 36769085 PMCID: PMC9917249 DOI: 10.3390/ijms24032764] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/29/2022] [Revised: 01/24/2023] [Accepted: 01/26/2023] [Indexed: 02/04/2023] Open
Abstract
Zinc ions (Zn2+) are concentrated in various brain regions and can act as a neuromodulator, targeting a wide spectrum of postsynaptic receptors and enzymes. Zn2+ inhibits the GABAARs, and its potency is profoundly affected by the subunit composition and neuronal developmental stage. Although the extracellular amino acid residues of the receptor's hetero-oligomeric structure are preferred for Zn2+ binding, there are intracellular sites that, in principle, could coordinate its potency. However, their role in modulating the receptor function during postembryonic development remains unclear. The GABAAR possesses an intracellular ATPase that enables the energy-dependent anion transport via a pore. Here, we propose a mechanistic and molecular basis for the inhibition of intracellular GABAAR/ATPase function by Zn2+ in neonatal and adult rats. The enzymes within the scope of GABAAR performance as Cl-ATPase and then as Cl-, HCO3-ATPase form during the first week of postnatal rat development. In addition, we have shown that the Cl-ATPase form belongs to the β1 subunit, whereas the β3 subunit preferably possesses the Cl-, HCO3-ATPase activity. We demonstrated that a Zn2+ with variable efficacy inhibits the GABAAR as well as the ATPase activities of immature or mature neurons. Using fluorescence recording in the cortical synaptoneurosomes (SNs), we showed a competitive association between Zn2+ and NEM in parallel changes both in the ATPase activity and the GABAAR-mediated Cl- and HCO3- fluxes. Finally, by site-directed mutagenesis, we identified in the M3 domain of β subunits the cysteine residue (C313) that is essential for the manifestation of Zn2+ potency.
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Menzikov SA, Zaichenko DM, Moskovtsev AA, Morozov SG, Kubatiev AA. Physiological Role of ATPase for GABA A Receptor Resensitization. Int J Mol Sci 2022; 23:ijms23105320. [PMID: 35628132 PMCID: PMC9141714 DOI: 10.3390/ijms23105320] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2022] [Revised: 05/03/2022] [Accepted: 05/07/2022] [Indexed: 02/01/2023] Open
Abstract
γ-Aminobutyric acid type A receptors (GABAARs) mediate primarily inhibitory synaptic transmission in the central nervous system. Following fast-paced activation, which provides the selective flow of mainly chloride (Cl−) and less bicarbonate (HCO3−) ions via the pore, these receptors undergo desensitization that is paradoxically prevented by the process of their recovery, referred to as resensitization. To clarify the mechanism of resensitization, we used the cortical synaptoneurosomes from the rat brain and HEK 293FT cells. Here, we describe the effect of γ-phosphate analogues (γPAs) that mimic various states of ATP hydrolysis on GABAAR-mediated Cl− and HCO3− fluxes in response to the first and repeated application of the agonist. We found that depending on the presence of bicarbonate, opened and desensitized states of the wild or chimeric GABAARs had different sensitivities to γPAs. This study presents the evidence that recovery of neuronal Cl− and HCO3− concentrations after desensitization is accompanied by a change in the intracellular ATP concentration via ATPase performance. The transition between the desensitization and resensitization states was linked to changes in both conformation and phosphorylation. In addition, the chimeric β3 isoform did not exhibit the desensitization of the GABAAR-mediated Cl− influx but only the resensitization. These observations lend a new physiological significance to the β3 subunit in the manifestation of GABAAR resensitization.
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Affiliation(s)
- Sergey A. Menzikov
- Institute of General Pathology and Pathophysiology, Russian Academy of Sciences, 8, Baltiyskaya St., 125315 Moscow, Russia; (D.M.Z.); (A.A.M.); (S.G.M.); (A.A.K.)
- Correspondence: ; Tel.: +7-(499)-151-1756; Fax: +7-(495)-601-2366
| | - Danila M. Zaichenko
- Institute of General Pathology and Pathophysiology, Russian Academy of Sciences, 8, Baltiyskaya St., 125315 Moscow, Russia; (D.M.Z.); (A.A.M.); (S.G.M.); (A.A.K.)
| | - Aleksey A. Moskovtsev
- Institute of General Pathology and Pathophysiology, Russian Academy of Sciences, 8, Baltiyskaya St., 125315 Moscow, Russia; (D.M.Z.); (A.A.M.); (S.G.M.); (A.A.K.)
- Russian Medical Academy of Postdoctoral Education, Federal State Budgetary Educational Institution of Further Professional Education of the Ministry of Healthcare of the Russian Federation, 2/1, Barrykadnaya St., 125993 Moscow, Russia
| | - Sergey G. Morozov
- Institute of General Pathology and Pathophysiology, Russian Academy of Sciences, 8, Baltiyskaya St., 125315 Moscow, Russia; (D.M.Z.); (A.A.M.); (S.G.M.); (A.A.K.)
| | - Aslan A. Kubatiev
- Institute of General Pathology and Pathophysiology, Russian Academy of Sciences, 8, Baltiyskaya St., 125315 Moscow, Russia; (D.M.Z.); (A.A.M.); (S.G.M.); (A.A.K.)
- Russian Medical Academy of Postdoctoral Education, Federal State Budgetary Educational Institution of Further Professional Education of the Ministry of Healthcare of the Russian Federation, 2/1, Barrykadnaya St., 125993 Moscow, Russia
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Amakhin DV, Soboleva EB, Ergina JL, Malkin SL, Chizhov AV, Zaitsev AV. Seizure-Induced Potentiation of AMPA Receptor-Mediated Synaptic Transmission in the Entorhinal Cortex. Front Cell Neurosci 2018; 12:486. [PMID: 30618633 PMCID: PMC6297849 DOI: 10.3389/fncel.2018.00486] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/06/2018] [Accepted: 11/29/2018] [Indexed: 11/22/2022] Open
Abstract
Excessive excitation is considered one of the key mechanisms underlying epileptic seizures. We investigated changes in the evoked postsynaptic responses of medial entorhinal cortex (ERC) pyramidal neurons by seizure-like events (SLEs), using the modified 4-aminopyridine (4-AP) model of epileptiform activity. Rat brain slices were perfused with pro-epileptic solution contained 4-AP and elevated potassium and reduced magnesium concentration. We demonstrated that 15-min robust epileptiform activity in slices leads to an increase in the amplitude of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR)-mediated component of the evoked response, as well as an increase in the polysynaptic γ-aminobutyric acid (GABA) and N-methyl-D-aspartate (NMDA) receptor-mediated components. The increase in AMPA-mediated postsynaptic conductance depends on NMDA receptor activation. It persists for at least 15 min after the cessation of SLEs and is partly attributed to the inclusion of calcium-permeable AMPA receptors in the postsynaptic membrane. The mathematical modeling of the evoked responses using the conductance-based refractory density (CBRD) approach indicated that such augmentation of the AMPA receptor function and depolarization by GABA receptors results in prolonged firing that explains the increase in polysynaptic components, which contribute to overall network excitability. Taken together, our data suggest that AMPA receptor enhancement could be a critical determinant of sustained status epilepticus (SE).
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Affiliation(s)
- Dmitry V Amakhin
- Laboratory of Molecular Mechanisms of Neural Interactions, Sechenov Institute of Evolutionary Physiology and Biochemistry of the Russian Academy of Sciences, Saint Petersburg, Russia
| | - Elena B Soboleva
- Laboratory of Molecular Mechanisms of Neural Interactions, Sechenov Institute of Evolutionary Physiology and Biochemistry of the Russian Academy of Sciences, Saint Petersburg, Russia
| | - Julia L Ergina
- Laboratory of Molecular Mechanisms of Neural Interactions, Sechenov Institute of Evolutionary Physiology and Biochemistry of the Russian Academy of Sciences, Saint Petersburg, Russia
| | - Sergey L Malkin
- Laboratory of Molecular Mechanisms of Neural Interactions, Sechenov Institute of Evolutionary Physiology and Biochemistry of the Russian Academy of Sciences, Saint Petersburg, Russia
| | - Anton V Chizhov
- Laboratory of Molecular Mechanisms of Neural Interactions, Sechenov Institute of Evolutionary Physiology and Biochemistry of the Russian Academy of Sciences, Saint Petersburg, Russia.,Ioffe Institute, Russian Academy of Sciences, Saint Petersburg, Russia
| | - Aleksey V Zaitsev
- Laboratory of Molecular Mechanisms of Neural Interactions, Sechenov Institute of Evolutionary Physiology and Biochemistry of the Russian Academy of Sciences, Saint Petersburg, Russia.,Institute of Experimental Medicine, Almazov National Medical Research Centre, Saint Petersburg, Russia
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Yu YH, Lee K, Sin DS, Park KH, Park DK, Kim DS. Altered functional efficacy of hippocampal interneuron during epileptogenesis following febrile seizures. Brain Res Bull 2017; 131:25-38. [DOI: 10.1016/j.brainresbull.2017.02.009] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/07/2016] [Revised: 02/17/2017] [Accepted: 02/23/2017] [Indexed: 12/22/2022]
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Soltesz I, Alger BE, Kano M, Lee SH, Lovinger DM, Ohno-Shosaku T, Watanabe M. Weeding out bad waves: towards selective cannabinoid circuit control in epilepsy. Nat Rev Neurosci 2015; 16:264-77. [PMID: 25891509 PMCID: PMC10631555 DOI: 10.1038/nrn3937] [Citation(s) in RCA: 105] [Impact Index Per Article: 11.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Endocannabinoids are lipid-derived messengers, and both their synthesis and breakdown are under tight spatiotemporal regulation. As retrograde signalling molecules, endocannabinoids are synthesized postsynaptically but activate presynaptic cannabinoid receptor 1 (CB1) receptors to inhibit neurotransmitter release. In turn, CB1-expressing inhibitory and excitatory synapses act as strategically placed control points for activity-dependent regulation of dynamically changing normal and pathological oscillatory network activity. Here, we highlight emerging principles of cannabinoid circuit control and plasticity, and discuss their relevance for epilepsy and related comorbidities. New insights into cannabinoid signalling may facilitate the translation of the recent interest in cannabis-related substances as antiseizure medications to evidence-based treatment strategies.
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Affiliation(s)
- Ivan Soltesz
- Department of Anatomy and Neurobiology, University of California, Irvine, California 92697, USA
| | - Bradley E Alger
- Department of Physiology, University of Maryland School of Medicine, Baltimore, Maryland 21201, USA
| | - Masanobu Kano
- Department of Neurophysiology, Graduate School of Medicine, The University of Tokyo, Tokyo 113-0033, Japan
| | - Sang-Hun Lee
- Department of Anatomy and Neurobiology, University of California, Irvine, California 92697, USA
| | - David M Lovinger
- Section on Synaptic Pharmacology, Laboratory for Integrative Neuroscience, National Institute on Alcohol Abuse and Alcoholism, US National Institutes of Health, Bethesda, Maryland 20892, USA
| | - Takako Ohno-Shosaku
- Department of Impairment Study, Graduate School of Medical Science, Kanazawa University, Kanazawa 920-0942, Japan
| | - Masahiko Watanabe
- Department of Anatomy, Hokkaido University Graduate School of Medicine, Sapporo 060-8638, Japan
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Abstract
Exogenous cannabinoids can limit seizures and neurodegeneration, and their actions are largely mimicked by endogenous cannabinoids (endocannabinoids). Endocannabinoids are mobilized by epileptiform activity and in turn influence this activity by inhibiting synaptic transmission; both excitatory and some inhibitory synapses can be suppressed, leading to potentially complex outcomes. Moreover, the endocannabinoid system is not a fixed entity, and its strength can be enhanced or reduced. Endocannabinoids and their receptors are altered by epileptic seizures in ways that can reduce the efficacy of both exogenous and endogenous cannabinoids in sometimes unexpected ways.
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CA1 pyramidal cell theta-burst firing triggers endocannabinoid-mediated long-term depression at both somatic and dendritic inhibitory synapses. J Neurosci 2013; 33:13743-57. [PMID: 23966696 DOI: 10.1523/jneurosci.0817-13.2013] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Endocannabinoids (eCBs) are retrograde lipid messengers that, by targeting presynaptic type 1 cannabinoid receptors (CB1Rs), mediate short- and long-term synaptic depression of neurotransmitter release throughout the brain. Short-term depression is typically triggered by postsynaptic, depolarization-induced calcium rises, whereas long-term depression is induced by synaptic activation of Gq/11 protein-coupled receptors. Here we report that a physiologically relevant pattern of postsynaptic activity, in the form of theta-burst firing (TBF) of hippocampal CA1 pyramidal neurons, can trigger long-term depression of inhibitory transmission (iLTD) in rat hippocampal slices. Paired recordings between CA1 interneurons and pyramidal cells, followed by post hoc morphological reconstructions of the interneurons' axon, revealed that somatic and dendritic inhibitory synaptic inputs equally expressed TBF-induced iLTD. Simultaneous recordings from neighboring pyramidal cells demonstrated that eCB signaling triggered by TBF was highly restricted to only a single, active cell. Furthermore, pairing submaximal endogenous activation of metabotropic glutamate or muscarinic acetylcholine receptors with submaximal TBF unmasked associative iLTD. Although CB1Rs are also expressed at Schaffer-collateral excitatory terminals, long-term plasticity under various recording conditions was spared at these synapses. Consistent with this observation, TBF also shifted the balance of excitation and inhibition in favor of excitatory throughput, thereby altering information flow through the CA1 circuit. Given the near ubiquity of burst-firing activity patterns and CB1R expression in the brain, the properties described here may be a general means by which neurons fine tune the strength of their inputs in a cell-wide and cell-specific manner.
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Neuron to astrocyte communication via cannabinoid receptors is necessary for sustained epileptiform activity in rat hippocampus. PLoS One 2012; 7:e37320. [PMID: 22615976 PMCID: PMC3352897 DOI: 10.1371/journal.pone.0037320] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/02/2012] [Accepted: 04/18/2012] [Indexed: 11/19/2022] Open
Abstract
Astrocytes are integral functional components of synapses, regulating transmission and plasticity. They have also been implicated in the pathogenesis of epilepsy, although their precise roles have not been comprehensively characterized. Astrocytes integrate activity from neighboring synapses by responding to neuronally released neurotransmitters such as glutamate and ATP. Strong activation of astrocytes mediated by these neurotransmitters can promote seizure-like activity by initiating a positive feedback loop that induces excessive neuronal discharge. Recent work has demonstrated that astrocytes express cannabinoid 1 (CB1) receptors, which are sensitive to endocannabinoids released by nearby pyramidal cells. In this study, we tested whether this mechanism also contributes to epileptiform activity. In a model of 4-aminopyridine induced epileptic-like activity in hippocampal slice cultures, we show that pharmacological blockade of astrocyte CB1 receptors did not modify the initiation, but significantly reduced the maintenance of epileptiform discharge. When communication in astrocytic networks was disrupted by chelating astrocytic calcium, this CB1 receptor-mediated modulation of epileptiform activity was no longer observed. Thus, endocannabinoid signaling from neurons to astrocytes represents an additional significant factor in the maintenance of epileptiform activity in the hippocampus.
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Messer RD, Levine ES. Epileptiform activity in the CA1 region of the hippocampus becomes refractory to attenuation by cannabinoids in part because of endogenous γ-aminobutyric acid type B receptor activity. J Neurosci Res 2012; 90:1454-63. [PMID: 22388975 DOI: 10.1002/jnr.23027] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2011] [Revised: 11/30/2011] [Accepted: 12/12/2011] [Indexed: 12/18/2022]
Abstract
The anticonvulsant properties of marijuana have been known for centuries. The recently characterized endogenous cannabinoid system thus represents a promising target for novel anticonvulsant agents; however, administration of exogenous cannabinoids has shown mixed results in both human epilepsy and animal models. The ability of cannabinoids to attenuate release of both excitatory and inhibitory neurotransmitters may explain the variable effects of cannabinoids in different models of epilepsy, but this has not been well explored. Using acute mouse brain slices, we monitored field potentials in the CA1 region of the hippocampus to characterize systematically the effects of the cannabinoid agonist WIN55212-2 (WIN) on evoked basal and epileptiform activity. WIN, acting presynaptically, significantly reduced the amplitude and slope of basal field excitatory postsynaptic potentials as well as stimulus-evoked epileptiform responses induced by omission of magnesium from the extracellular solution. In contrast, the combination of omission of magnesium plus elevation of potassium induced an epileptiform response that was refractory to attenuation by WIN. The effect of WIN in this model was partially restored by blocking γ-aminobutyric acid type B (GABA(B) ), but not GABA(A) , receptors. Subtle differences in models of epileptiform activity can profoundly alter the efficacy of cannabinoids. Endogenous GABA(B) receptor activation played a role in the decreased cannabinoid sensitivity observed for epileptiform activity induced by omission of magnesium plus elevation of potassium. These results suggest that interplay between presynaptic G protein-coupled receptors with overlapping downstream targets may underlie the variable efficacy of cannabinoids in different models of epilepsy.
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Affiliation(s)
- Ricka D Messer
- Department of Neuroscience, University of Connecticut Health Center, Farmington,CT 06030, USA
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Tominaga T, Tominaga Y. GABAA receptor-mediated modulation of neuronal activity propagation upon tetanic stimulation in rat hippocampal slices. Pflugers Arch 2010; 460:875-89. [DOI: 10.1007/s00424-010-0870-9] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/14/2010] [Revised: 07/29/2010] [Accepted: 08/09/2010] [Indexed: 11/24/2022]
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Lopantsev V, Both M, Draguhn A. Rapid plasticity at inhibitory and excitatory synapses in the hippocampus induced by ictal epileptiform discharges. Eur J Neurosci 2009; 29:1153-64. [DOI: 10.1111/j.1460-9568.2009.06663.x] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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Chen K, Neu A, Howard AL, Földy C, Echegoyen J, Hilgenberg L, Smith M, Mackie K, Soltesz I. Prevention of plasticity of endocannabinoid signaling inhibits persistent limbic hyperexcitability caused by developmental seizures. J Neurosci 2007; 27:46-58. [PMID: 17202471 PMCID: PMC6672287 DOI: 10.1523/jneurosci.3966-06.2007] [Citation(s) in RCA: 115] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023] Open
Abstract
Depolarization-induced suppression of inhibition (DSI) is an endocannabinoid-mediated short-term plasticity mechanism that couples postsynaptic Ca2+ rises to decreased presynaptic GABA release. Whether the gain of this retrograde synaptic mechanism is subject to long-term modulation by glutamatergic excitatory inputs is not known. Here, we demonstrate that activity-dependent long-term DSI potentiation takes place in hippocampal slices after tetanic stimulation of Schaffer collateral synapses. This activity-dependent, long-term plasticity of endocannabinoid signaling was specific to GABAergic synapses, as it occurred without increases in the depolarization-induced suppression of excitation. Induction of tetanus-induced DSI potentiation in vitro required a complex pathway involving AMPA/kainate and metabotropic glutamate receptor as well as CB1 receptor activation. Because DSI potentiation has been suggested to play a role in persistent limbic hyperexcitability after prolonged seizures in the developing brain, we used these mechanistic insights into activity-dependent DSI potentiation to test whether interference with the induction of DSI potentiation prevents seizure-induced long-term hyperexcitability. The results showed that the in vitro, tetanus-induced DSI potentiation was occluded by previous in vivo fever-induced (febrile) seizures, indicating a common pathway. Accordingly, application of CB1 receptor antagonists during febrile seizures in vivo blocked the seizure-induced persistent DSI potentiation, abolished the seizure-induced upregulation of CB1 receptors, and prevented the emergence of long-term limbic hyperexcitability. These results reveal a new form of activity-dependent, long-term plasticity of endocannabinoid signaling at perisomatic GABAergic synapses, and demonstrate that blocking the induction of this plasticity abolishes the long-term effects of prolonged febrile seizures in the developing brain.
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Affiliation(s)
- Kang Chen
- Department of Anatomy and Neurobiology, University of California, Irvine, California 92697, and
| | - Axel Neu
- Department of Anatomy and Neurobiology, University of California, Irvine, California 92697, and
| | - Allyson L. Howard
- Department of Anatomy and Neurobiology, University of California, Irvine, California 92697, and
| | - Csaba Földy
- Department of Anatomy and Neurobiology, University of California, Irvine, California 92697, and
| | - Julio Echegoyen
- Department of Anatomy and Neurobiology, University of California, Irvine, California 92697, and
| | - Lutz Hilgenberg
- Department of Anatomy and Neurobiology, University of California, Irvine, California 92697, and
| | - Martin Smith
- Department of Anatomy and Neurobiology, University of California, Irvine, California 92697, and
| | - Ken Mackie
- Department of Anesthesiology, University of Washington, Seattle, Washington 98195
| | - Ivan Soltesz
- Department of Anatomy and Neurobiology, University of California, Irvine, California 92697, and
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Fernández de Sevilla D, Garduño J, Galván E, Buño W. Calcium-activated afterhyperpolarizations regulate synchronization and timing of epileptiform bursts in hippocampal CA3 pyramidal neurons. J Neurophysiol 2006; 96:3028-41. [PMID: 16971683 DOI: 10.1152/jn.00434.2006] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Calcium-activated potassium conductances regulate neuronal excitability, but their role in epileptogenesis remains elusive. We investigated in rat CA3 pyramidal neurons the contribution of the Ca(2+)-activated K(+)-mediated afterhyperpolarizations (AHPs) in the genesis and regulation of epileptiform activity induced in vitro by 4-aminopyridine (4-AP) in Mg(2+)-free Ringer. Recurring spike bursts terminated by prolonged AHPs were generated. Burst synchronization between CA3 pyramidal neurons in paired recordings typified this interictal-like activity. A downregulation of the medium afterhyperpolarization (mAHP) paralleled the emergence of the interictal-like activity. When the mAHP was reduced or enhanced by apamin and EBIO bursts induced by 4-AP were increased or blocked, respectively. Inhibition of the slow afterhyperpolarization (sAHP) with carbachol, t-ACPD, or isoproterenol increased bursting frequency and disrupted burst regularity and synchronization between pyramidal neuron pairs. In contrast, enhancing the sAHP by intracellular dialysis with KMeSO(4) reduced burst frequency. Block of GABA(A-B) inhibitions did not modify the abnormal activity. We describe novel cellular mechanisms where 1) the inhibition of the mAHP plays an essential role in the genesis and regulation of the bursting activity by reducing negative feedback, 2) the sAHP sets the interburst interval by decreasing excitability, and 3) bursting was synchronized by excitatory synaptic interactions that increased in advance and during bursts and decreased throughout the subsequent sAHP. These cellular mechanisms are active in the CA3 region, where epileptiform activity is initiated, and cooperatively regulate the timing of the synchronized rhythmic interictal-like network activity.
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Abstract
The cannabinoid receptor family currently includes two types: CB1, characterized in neuronal cells and brain, and CB2, characterized in immune cells and tissues. CB1 and CB2 receptors are members of the superfamily of seven-transmembrane-spanning (7-TM) receptors, having a protein structure defined by an array of seven membrane-spanning helices with intervening intracellular loops and a C-terminal domain that can associate with G proteins. Cannabinoid receptors are associated with G proteins of the Gi/o family (Gi1, 2 and 3, and Go1 and 2). Signal transduction via Gi inhibits adenylyl cyclase in most tissues and cells, although signaling via Gs stimulates adenylyl cyclase in some experimental models. Evidence exists for cannabinoid receptor-mediated Ca2+ fluxes and stimulation of phospholipases A and C. Stimulation of CB1 and CB2 cannabinoid receptors leads to phosphorylation and activation of p42/p44 mitogen-activated protein kinase (MAPK), p38 MAPK and Jun N-terminal kinase (JNK) as signaling pathways to regulate nuclear transcription factors. The CB1 receptor regulates K+ and Ca2+ ion channels, probably via Go. Ion channel regulation serves as an important component of neurotransmission modulation by endogenous cannabinoid compounds released in response to neuronal depolarization. Cannabinoid receptor signaling via G proteins results from interactions with the second, third and fourth intracellular loops of the receptor. Desensitization of signal transduction pathways that couple through the G proteins probably entails phosphorylation of critical amino acid residues on these intracellular surfaces.
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Affiliation(s)
- A C Howlett
- Neuroscience/Drug Abuse Research Program, 208 JLC-BBRI, North Carolina Central University, 700 George Street, Durham, NC 27707, USA.
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Reich CG, Karson MA, Karnup SV, Jones LM, Alger BE. Regulation of IPSP Theta Rhythm by Muscarinic Receptors and Endocannabinoids in Hippocampus. J Neurophysiol 2005; 94:4290-9. [PMID: 16093334 DOI: 10.1152/jn.00480.2005] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Theta rhythms are behaviorally relevant electrical oscillations in the mammalian brain, particularly the hippocampus. In many cases, theta oscillations are shaped by inhibitory postsynaptic potentials (IPSPs) that are driven by glutamatergic and/or cholinergic inputs. Here we show that hippocampal theta rhythm IPSPs induced in the CA1 region by muscarinic acetylcholine receptors independent of all glutamate receptors can be briefly interrupted by action potential–induced, retrograde endocannabinoid release. Theta IPSPs can be recorded in CA1 pyramidal cell somata surgically isolated from CA3, subiculum, and even from their own apical dendrites. These results suggest that perisomatic-targeting interneurons whose output is subject to inhibition by endocannabinoids are the likely source of theta IPSPs. Interneurons having these properties include the cholecystokinin-containing cells. Simultaneous recordings from pyramidal cell pairs reveal synchronous theta-frequency IPSPs in neighboring pyramidal cells, suggesting that these IPSPs may help entrain or modulate small groups of pyramidal cells.
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Affiliation(s)
- Christian G Reich
- Department of Physiology, Program in Neuronscience, University of Maryland School of Medicine, Baltimore, 21201, USA
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Kwak SE, Kim JE, Kim DS, Jung JY, Won MH, Kwon OS, Choi SY, Kang TC. Effects of GABAergic transmissions on the immunoreactivities of calcium binding proteins in the gerbil hippocampus. J Comp Neurol 2005; 485:153-64. [PMID: 15776449 DOI: 10.1002/cne.20482] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Although reduced calcium binding protein (CBP) immunoreactivities in the epileptic hippocampus have been well established, it has been controversial that these changes may directly indicate neuronal degeneration. In the present study, therefore, we investigated CBP expressions in the gerbil hippocampus following treatment with gamma-aminobutyric acid (GABA) receptor antagonists in order to assess whether altered CBP expressions are the result of either abnormal excitation or indicative of neuronal damage/degeneration. Seizure-sensitive (SS) gerbils showed a loss/decline of CBP immunoreactivities in some hippocampal neurons as compared with seizure-resistant (SR) gerbils. In muscimol (GABA(A) receptor agonist) treated SS gerbils, expression levels of CBP were enhanced as compared with saline-treated SS gerbils. Bicuculline (a GABA(A) receptor antagonist) treatment markedly reduced CBP immunoreactivities in hippocampal neurons of the SR gerbil. Baclofen (a GABA(B) receptor agonist) treatment increased CBP immunoreactivities in the hippocampus of SS gerbils, although its effect was lower than that of muscimol treatment. Moreover, phaclofen (GABA(B) receptor antagonist) treated SR gerbil showed reduction in calbindin D-28K immunoreactivity, not parvalbumin immunoreactivity, in the hippocampus. These findings therefore suggest that reduced CBP immunoreactivities may be the consequence of abnormal discharge caused by loss of GABAergic inhibition rather than an indication of the neuronal damage/degeneration.
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Affiliation(s)
- Sung-Eun Kwak
- Department of Anatomy, College of Medicine, Hallym University, Chunchon, Kangwon-Do 200-702, South Korea
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Howlett AC, Breivogel CS, Childers SR, Deadwyler SA, Hampson RE, Porrino LJ. Cannabinoid physiology and pharmacology: 30 years of progress. Neuropharmacology 2004; 47 Suppl 1:345-58. [PMID: 15464149 DOI: 10.1016/j.neuropharm.2004.07.030] [Citation(s) in RCA: 372] [Impact Index Per Article: 18.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2004] [Revised: 07/23/2004] [Accepted: 07/23/2004] [Indexed: 10/26/2022]
Abstract
Delta9-Tetrahydrocannabinol from Cannabis sativa is mimicked by cannabimimetic analogs such as CP55940 and WIN55212-2, and antagonized by rimonabant and SR144528, through G-protein-coupled receptors, CB1 in the brain, and CB2 in the immune system. Eicosanoids anandamide and 2-arachidonoylglycerol are the "endocannabinoid" agonists for these receptors. CB1 receptors are abundant in basal ganglia, hippocampus and cerebellum, and their functional activity can be mapped during behaviors using cerebral metabolism as the neuroimaging tool. CB1 receptors couple to G(i/o) to inhibit cAMP production, decrease Ca2+ conductance, increase K+ conductance, and increase mitogen-activated protein kinase activity. Functional activation of G-proteins can be imaged by [35S]GTPgammaS autoradiography. Post-synaptically generated endocannabinoids form the basis of a retrograde signaling mechanism referred to as depolarization-induced suppression of inhibition (DSI) or excitation (DSE). Under circumstances of sufficient intracellular Ca2+ (e.g., burst activity in seizures), synthesis of endocannabinoids releases a diffusible retrograde messenger to stimulate presynaptic CB1 receptors. This results in suppression of gamma-aminobutyric acid (GABA) release, thereby relieving the post-synaptic inhibition. Tolerance develops as neurons adjust both receptor number and cellular signal transduction to the chronic administration of cannabinoid drugs. Future therapeutic drug design can progress based upon our current understanding of the physiology and pharmacology of CB1, CB2 and related receptors. One very important role for CB1 antagonists will be in the treatment of craving in the disease of substance abuse.
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Affiliation(s)
- Allyn C Howlett
- Neuroscience of Drug Abuse Research Program, Julius L. Chambers Biomedical/Biotechnology Research Institute, North Carolina Central University, Durham, NC 27707, USA.
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18
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Rivera C, Voipio J, Thomas-Crusells J, Li H, Emri Z, Sipilä S, Payne JA, Minichiello L, Saarma M, Kaila K. Mechanism of activity-dependent downregulation of the neuron-specific K-Cl cotransporter KCC2. J Neurosci 2004; 24:4683-91. [PMID: 15140939 PMCID: PMC6729393 DOI: 10.1523/jneurosci.5265-03.2004] [Citation(s) in RCA: 375] [Impact Index Per Article: 18.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/28/2003] [Revised: 04/07/2004] [Accepted: 04/07/2004] [Indexed: 11/21/2022] Open
Abstract
GABA-mediated fast-hyperpolarizing inhibition depends on extrusion of chloride by the neuron-specific K-Cl cotransporter, KCC2. Here we show that sustained interictal-like activity in hippocampal slices downregulates KCC2 mRNA and protein expression in CA1 pyramidal neurons, which leads to a reduced capacity for neuronal Cl- extrusion. This effect is mediated by endogenous BDNF acting on tyrosine receptor kinase B (TrkB), with down-stream cascades involving both Shc/FRS-2 (src homology 2 domain containing transforming protein/FGF receptor substrate 2) and PLCgamma (phospholipase Cgamma)-cAMP response element-binding protein signaling. The plasmalemmal KCC2 has a very high rate of turnover, with a time frame that suggests a novel role for changes in KCC2 expression in diverse manifestations of neuronal plasticity. A downregulation of KCC2 may be a general early response involved in various kinds of neuronal trauma.
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Affiliation(s)
- Claudio Rivera
- Department of Biosciences, University of Helsinki, Helsinki, FIN-00014 Finland.
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19
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Diana MA, Marty A. Endocannabinoid-mediated short-term synaptic plasticity: depolarization-induced suppression of inhibition (DSI) and depolarization-induced suppression of excitation (DSE). Br J Pharmacol 2004; 142:9-19. [PMID: 15100161 PMCID: PMC1574919 DOI: 10.1038/sj.bjp.0705726] [Citation(s) in RCA: 186] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Abstract
Depolarization-induced suppression of inhibition (DSI) and depolarization-induced suppression of excitation (DSE) are two related forms of short-term synaptic plasticity of GABAergic and glutamatergic transmission, respectively. They are induced by calcium concentration increases in postsynaptic cells and are mediated by the release of a retrograde messenger, which reversibly inhibits afferent synapses via presynaptic mechanisms. We review here: 1. The evidence accumulated during the 1990s that has led to the conclusion that DSI/DSE rely on retrograde signaling. 2. The more recent research that has led to the identification of endocannabinoids as the retrograde messengers responsible for DSI/DSE. 3. The possible mechanisms by which presynaptic type 1 cannabinoid receptors reduce synaptic efficacy during DSI/DSE. 4. The possible modes of induction of DSI/DSE by physiological activity patterns, and the partially conflicting evaluations of the calcium concentration increases required for cannabinoid synthesis. 5. Finally, the relation between DSI/DSE and other forms of long- and short-term synaptic inhibition, which were more recently associated with the production of endocannabinoids by postsynaptic cells. We conclude that recent studies on DSI/DSE have uncovered a specific and original mode of action for endocannabinoids in the brain, and that they have opened new avenues to understand the role of retrograde signaling in central synapses.
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Affiliation(s)
- Marco A Diana
- Laboratoire de Physiologie Cérébrale, Université Paris 5, 45, rue des Saints Pères, 75006 Paris, France.
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20
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Chen K, Ratzliff A, Hilgenberg L, Gulyás A, Freund TF, Smith M, Dinh TP, Piomelli D, Mackie K, Soltesz I. Long-term plasticity of endocannabinoid signaling induced by developmental febrile seizures. Neuron 2003; 39:599-611. [PMID: 12925275 DOI: 10.1016/s0896-6273(03)00499-9] [Citation(s) in RCA: 148] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Abstract
Febrile (fever-induced) seizures are the most common form of childhood seizures, affecting 3%-5% of infants and young children. Here we show that the activity-dependent, retrograde inhibition of GABA release by endogenous cannabinoids is persistently enhanced in the rat hippocampus following a single episode of experimental prolonged febrile seizures during early postnatal development. The potentiation of endocannabinoid signaling results from an increase in the number of presynaptic cannabinoid type 1 receptors associated with cholecystokinin-containing perisomatic inhibitory inputs, without an effect on the endocannabinoid-mediated inhibition of glutamate release. These results demonstrate a selective, long-term increase in the gain of endocannabinoid-mediated retrograde signaling at GABAergic synapses in a model of a human neurological disease.
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MESH Headings
- Action Potentials/physiology
- Animals
- Blotting, Western
- Cannabinoid Receptor Modulators
- Cells, Cultured
- Chromatography, High Pressure Liquid
- Disease Models, Animal
- Electric Stimulation
- Endocannabinoids
- Excitatory Amino Acid Antagonists/pharmacology
- Fatty Acids, Unsaturated/metabolism
- Hippocampus/drug effects
- Hippocampus/physiopathology
- Hyperthermia, Induced
- Immunohistochemistry
- Long-Term Potentiation/drug effects
- Long-Term Potentiation/physiology
- Mass Spectrometry
- Microscopy, Electron
- Neuronal Plasticity/physiology
- Neurons/physiology
- Patch-Clamp Techniques
- Presynaptic Terminals/metabolism
- Presynaptic Terminals/ultrastructure
- Rats
- Rats, Sprague-Dawley
- Receptors, Cannabinoid
- Receptors, Drug/antagonists & inhibitors
- Receptors, Drug/metabolism
- Seizures, Febrile/physiopathology
- Synaptic Transmission/physiology
- gamma-Aminobutyric Acid/metabolism
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Affiliation(s)
- Kang Chen
- Department of Anatomy and Neurobiology, University of California, Irvine, Irvine, CA 92697, USA
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21
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Hampson RE, Zhuang SY, Weiner JL, Deadwyler SA. Functional significance of cannabinoid-mediated, depolarization-induced suppression of inhibition (DSI) in the hippocampus. J Neurophysiol 2003; 90:55-64. [PMID: 12649318 DOI: 10.1152/jn.01161.2002] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
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.
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Affiliation(s)
- Robert E Hampson
- Wake Forest University Health Sciences, Department of Physiology and Pharmacology, Winston-Salem, North Carolina 27157, USA
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22
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Abstract
Research of cannabinoid actions was boosted in the 1990s by remarkable discoveries including identification of endogenous compounds with cannabimimetic activity (endocannabinoids) and the cloning of their molecular targets, the CB1 and CB2 receptors. Although the existence of an endogenous cannabinoid signaling system has been established for a decade, its physiological roles have just begun to unfold. In addition, the behavioral effects of exogenous cannabinoids such as delta-9-tetrahydrocannabinol, the major active compound of hashish and marijuana, await explanation at the cellular and network levels. Recent physiological, pharmacological, and high-resolution anatomical studies provided evidence that the major physiological effect of cannabinoids is the regulation of neurotransmitter release via activation of presynaptic CB1 receptors located on distinct types of axon terminals throughout the brain. Subsequent discoveries shed light on the functional consequences of this localization by demonstrating the involvement of endocannabinoids in retrograde signaling at GABAergic and glutamatergic synapses. In this review, we aim to synthesize recent progress in our understanding of the physiological roles of endocannabinoids in the brain. First, the synthetic pathways of endocannabinoids are discussed, along with the putative mechanisms of their release, uptake, and degradation. The fine-grain anatomical distribution of the neuronal cannabinoid receptor CB1 is described in most brain areas, emphasizing its general presynaptic localization and role in controlling neurotransmitter release. Finally, the possible functions of endocannabinoids as retrograde synaptic signal molecules are discussed in relation to synaptic plasticity and network activity patterns.
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Affiliation(s)
- Tamas F Freund
- Institute of Experimental Medicine, Hungarian Academy of Sciences, Budapest 8, Szigony u.43, H-1083 Hungary.
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23
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Yanovsky Y, Mades S, Misgeld U. Retrograde signaling changes the venue of postsynaptic inhibition in rat substantia nigra. Neuroscience 2003; 122:317-28. [PMID: 14614899 DOI: 10.1016/s0306-4522(03)00607-9] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Both endocannabinoids through cannabinoid receptor type I (CB1) receptors and dopamine through dopamine receptor type D1 receptors modulate postsynaptic inhibition in substantia nigra by changing GABA release from striatonigral terminals. By recording from visually identified pars compacta and pars reticulata neurons we searched for a possible co-release and interaction of endocannabinoids and dopamine. Depolarization of a neuron in pars reticulata or in pars compacta transiently suppressed evoked synaptic currents which were blocked by GABA(A) receptor antagonists (inhibitory postsynaptic currents [IPSCs]). This depolarization-induced suppression of inhibition (DSI) was abrogated by the cannabinoid CB1 receptor antagonist AM251 (1 microM). A correlation existed between the degree of DSI and the degree of reduction of evoked IPSCs by the CB1 receptor agonist WIN55,212-2 (1 microM). The cholinergic receptor agonist carbachol (0.5-5 microM) enhanced DSI, but suppression of spontaneous IPSCs was barely detectable pointing to the existence of GABA release sites without CB1 receptors. In dopamine, but not in GABAergic neurons DSI was enhanced by the dopamine D1 receptor antagonist SCH23390 (3-10 microM). Both the antagonist for CB1 receptors and the antagonist for dopamine D1 receptors enhanced or reduced, respectively, the amplitudes of evoked IPSCs. This tonic influence persisted if the receptor for the other ligand was blocked. We conclude that endocannabinoids and dopamine can be co-released. Retrograde signaling through endocannabinoids and dopamine changes inhibition independently from each other. Activation of dopamine D1 receptors emphasizes extrinsic inhibition and activation of CB1 receptors promotes intrinsic inhibition.
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Affiliation(s)
- Y Yanovsky
- Institut für Physiologie und Pathophysiologie, Universität Heidelberg, Im Neuenheimer Feld 326, D-69120 Heidelberg, Germany
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24
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Abstract
This review covers recent developments in the cellular neurophysiology of retrograde signaling in the mammalian central nervous system. Normally at a chemical synapse a neurotransmitter is released from the presynaptic element and diffuses to the postsynaptic element, where it binds to and activates receptors. In retrograde signaling a diffusible messenger is liberated from the postsynaptic element, and travels "backwards" across the synaptic cleft, where it activates receptors on the presynaptic cell. Receptors for retrograde messengers are usually located on or near the presynaptic nerve terminals, and their activation causes an alteration in synaptic transmitter release. Although often considered in the context of long-term synaptic plasticity, retrograde messengers have numerous roles on the short-term regulation of synaptic transmission. The focus of this review will be on a group of molecules from different chemical classes that appear to act as retrograde messengers. The evidence supporting their candidacy as retrograde messengers is considered and evaluated. Endocannabinoids have recently emerged as one of the most thoroughly investigated, and widely accepted, classes of retrograde messenger in the brain. The study of the endocannabinoids can therefore serve as a model for the investigation of other putative messengers, and most attention is devoted to a discussion of systems that use these new messenger molecules.
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Affiliation(s)
- Bradley E Alger
- Department of Physiology and Program in Neuroscience, University of Maryland School of Medicine, 655 West Baltimore Street, Baltimore, MD 21201, USA.
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25
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Carlson G, Wang Y, Alger BE. Endocannabinoids facilitate the induction of LTP in the hippocampus. Nat Neurosci 2002; 5:723-4. [PMID: 12080342 DOI: 10.1038/nn879] [Citation(s) in RCA: 252] [Impact Index Per Article: 11.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Exogenous cannabinoids disrupt behavioral learning and impede induction of long-term potentiation (LTP) in the hippocampus, yet endogenous cannabinoids (endocannabinoids) transiently suppress inhibitory post-synaptic currents (IPSCs) by activating cannabinoid CB1 receptors on GABAergic interneurons. We found that release of endocannabinoids by a rat CA1 pyramidal cell during this depolarization-induced suppression of inhibition (DSI) enabled a normally ineffective train of excitatory post-synaptic currents (EPSCs) to induce LTP in that cell, but not in neighboring cells. By showing that endocannabinoids facilitate LTP induction and help target LTP to single cells, these data shed new light on the physiological roles of endocannabinoids and may lead to a greater understanding of their effects on behavior and potential clinical use.
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Affiliation(s)
- Gregory Carlson
- Department of Physiology, University of Maryland School of Medicine, 655 West Baltimore Street, Baltimore, Maryland 21201, USA
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26
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Lasztóczi B, Kovács R, Nyikos L, Kardos J. A glutamate receptor subtype antagonist inhibits seizures in rat hippocampal slices. Neuroreport 2002; 13:351-6. [PMID: 11930136 DOI: 10.1097/00001756-200203040-00020] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
2-Methyl-4-oxo-3H-quinazoline-3-acetyl piperidine (Q5), a selective inhibitor of the fast-desensitising component of transmembrane Ca2+ ion influx to (S)-alpha-amino-3-hydroxy-5-methyliso-xazole-4-propionate ((S)-AMPA) was tested for possible anticonvulsant effects in the low-[Mg2+] model of experimental epilepsy. Evolutionary analysis of burst parameters such as half-width, decay time constant, burst multiplicity, instantaneous frequency and amplitude disclosed an approximate doubling of half-width within periods of interictal activity, being predictive for the onset of seizure-like events (SLEs). We found that SLEs observed in the CA3 region of rat hippocampal slices were suppressed by the application of 50 microM Q5. These results suggest an AMPA receptor function shaping the dynamics of spontaneous epileptiform activity.
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Affiliation(s)
- Bálint Lasztóczi
- Department of Neurochemistry, Chemical Institute, Chemical Research Center, Hungarian Academy of Sciences, Pusztaszeri út 59-67, H-1025, Budapest, Hungary
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27
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Abstract
The highly interconnected networks of the mammalian forebrain can generate a wide variety of synchronized activities, including those underlying epileptic seizures, which often appear as a transformation of otherwise normal brain rhythms. The cerebral cortex and hippocampus are particularly prone to the generation of the large, synchronized bursts of activity underlying many forms of seizures owing to strong recurrent excitatory connections, the presence of intrinsically burst-generating neurons, ephaptic interactions among closely spaced neurons, and synaptic plasticity. The simplest form of epileptiform activity in these structures is the interictal spike, a synchronized burst of action potentials generated by recurrent excitation, followed by a period of hyperpolarization, in a localized pool of pyramidal neurons. Seizures can also be generated in response to a loss of balance between excitatory and inhibitory influences and can take the form of either tonic depolarizations or repetitive, rhythmic burst discharges, either as clonic or spike-wave activity, again mediated both by intrinsic membrane properties and synaptic interactions. The interaction of the cerebral cortex and the thalamus, in conjunction with intrathalamic communication, can also generate spike waves similar to those occurring during human absence seizure discharges. Although epileptic syndromes and their causes are diverse, the cellular mechanisms of seizure generation appear to fall into only two categories: rhythmic or tonic "runaway" excitation or the synchronized and rhythmic interplay between excitatory and inhibitory neurons and membrane conductances.
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Affiliation(s)
- D A McCormick
- Section of Neurobiology, Yale University School of Medicine, New Haven, Connecticut 06510, USA.
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28
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Martin LA, Wei DS, Alger BE. Heterogeneous susceptibility of GABA(A) receptor-mediated IPSCs to depolarization-induced suppression of inhibition in rat hippocampus. J Physiol 2001; 532:685-700. [PMID: 11313439 PMCID: PMC2278572 DOI: 10.1111/j.1469-7793.2001.0685e.x] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022] Open
Abstract
Depolarization-induced suppression of inhibition (DSI) in central neurons is mediated by a transient reduction of [gamma]-aminobutyric acid (GABA) release from interneurons. DSI is induced by a retrograde signal emitted from principal cells. We used electrophysiological recordings from CA1 neurons of the rat hippocampal slice to test the hypothesis that only certain classes of interneurons are susceptible to DSI. DSI of action potential-dependent, spontaneous, inhibitory postsynaptic currents (sIPSCs) in hippocampus is facilitated by carbachol (3 microM), which increases the occurrence of large sIPSCs. Besides carbachol, noradrenaline (norepinephrine; 10 microM), or elevated extracellular potassium (8 mM), could abruptly increase the occurrence of large sIPSCs and DSI in many cases. DSI appeared and disappeared concomitantly with the onset and offset of these large sIPSCs. In contrast, application of AP-5 and CNQX often markedly increased baseline sIPSC activity without enhancing DSI. A brief train of extracellular electrical stimulation could trigger the onset of prolonged, repetitive IPSC activity that was susceptible to DSI. The magnitude of DSI of single evoked IPSCs (eIPSCs) in a given pyramidal cell could be altered by changes in stimulus strength, but there was no simple relationship between stimulus strength and DSI. Baclofen (0.5-5 microM) eliminated the increase in sIPSC activity and DSI induced by carbachol. A GABA(B)receptor antagonist, CGP 35348, reversed the effects of baclofen. Carbachol-induced sIPSCs had relatively rapid rise and decay phases. There was no marked distinction between DSI-susceptible and non-susceptible sIPSCs. Nevertheless, two kinetically distinct components of the eIPSC could be distinguished by their decay times. DSI reduced GABA(A),(fast) without affecting GABA(A),(slow). Furosemide (frusemide), which blocks only GABA(A),(fast), reduced the eIPSC and occluded DSI. The data suggest that, with respect to DSI, there are at least three functionally distinct types of IPSCs. Two types (one susceptible to DSI and one not) have relatively rapid kinetics are probably made by perisomatic synapses. A third, slow IPSC, which is insensitive to DSI, may be produced by distal dendritic synapses.
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Affiliation(s)
- L A Martin
- Department of Physiology, University of Maryland School of Medicine, 655 West Baltimore Street, Baltimore, MD 21201, USA
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29
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Semyanov A, Godukhin O. Epileptiform activity and EPSP-spike potentiation induced in rat hippocampal CA1 slices by repeated high-K(+): involvement of ionotropic glutamate receptors and Ca(2+)/calmodulin-dependent protein kinase II. Neuropharmacology 2001; 40:203-11. [PMID: 11114399 DOI: 10.1016/s0028-3908(00)00147-7] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
We have previously demonstrated that repeated brief increases in extracellular K(+) (K(+)(o)) induce a hyperexcitability in CA1 pyramidal cells that persists for a long time after the final application of K(+) [Neurosci. Lett. 223 (1997) 177; Epilepsy Research (2000) 75]. This epileptiform activity, which was associated with a lasting excitatory postsynaptic potential (EPSP)-spike potentiation, presented some of the characteristic features of traditional in vivo kindling. We have also found that Ca(2+) influx through L-type voltage-sensitive Ca(2+) channels is essential for the development of both in vitro kindling and EPSP-spike potentiation. The aims of this study were to investigate the involvement of ionotropic glutamate receptors, especially those of the NMDA subtype, and the requirement for Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) in these phenomena. Field EPSPs with presynaptic fibre volleys from the stratum radiatum, and population spikes from the stratum pyramidale, were recorded in the CA1 area of rat hippocampal slices in response to electrical stimulation of the Schaffer collateral/commissural fibres. Repeated (three episodes) brief (30 s) increases in extracellular K(+) induced a sustained decrease in the threshold for development of evoked epileptiform discharges (i.e. an in vitro kindling-like state) and a lasting potentiation of the EPSP-spike transfer in CA1 pyramidal neurons (EPSP-spike potentiation). The selective antagonist of NMDA receptors, APV (50 microM), blocked the EPSP-spike potentiation, depressed the induction phase of the in vitro kindling-like state, and blocked the maintenance phase of this state. In contrast to APV, the blockade of AMPA/kainate receptors by CNQX (10 microM) had no effect. Like APV, KN62 (3 microM), a selective membrane permeable inhibitor of CaMKII, blocked the EPSP-spike potentiation and the maintenance phase of the in vitro kindling-like state. Our previous and present results therefore demonstrate that Ca(2+) influxes through L-type voltage-dependent-and NMDA receptor-dependent-Ca(2+) channels contribute differentially to the development of an in vitro kindling-like state, and both induce EPSP-spike potentiation in CA1 hippocampal pyramidal cells in response to repeated brief increases in K(+)(o). It is suggested that these effects of intracellular Ca(2+) on the maintenance phase of the in vitro kindling-like state and EPSP-spike potentiation are mediated by CaMKII-dependent mechanisms.
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Affiliation(s)
- A Semyanov
- Institute of Theoretical and Experimental Biophysics, Russian Academy of Sciences, Pushchino, Moscow Region, 142292, Russia.
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30
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Morishita W, Alger BE. Differential effects of the group II mGluR agonist, DCG-IV, on depolarization-induced suppression of inhibition in hippocampal CA1 and CA3 neurons. Hippocampus 2001; 10:261-8. [PMID: 10902895 DOI: 10.1002/1098-1063(2000)10:3<261::aid-hipo6>3.0.co;2-1] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
We investigated the role of metabotropic glutamate receptors in the mediation of depolarization-induced suppression of inhibition (DSI), using whole-cell electrophysiological techniques in rat hippocampal slice preparation. In a previous work, we showed that a retrograde signal travels from CA1 pyramidal cells to GABA interneurons and prevents them from releasing GABA for tens of seconds at 30 degrees C. The resulting suppression of inhibition is DSI. The retrograde signal appeared to be glutamate, or a glutamate analog, which acted on group I metabotropic receptors on the interneurons. It is not known if DSI occurs in hippocampal subregions besides CA1. If DSI does occur in other regions, it will be important to know if the role of metabotropic glutamate receptors (mGluRs) in mediating DSI is the same everywhere. The distribution of mGluR subtypes varies among hippocampal subregions. In the CA3 region, unlike CA1, group II mGluRs are prevalent. It was possible, therefore, that in CA3, the group II mGluRs would mediate DSI. We have begun to investigate these issues. We now report that: 1) DSI does occur in CA3. 2) Carbachol induces IPSC activity that can be recorded in CA1 and CA3a. This carbachol-induced activity can be reduced by the selective group II mGluR agonist, DCG-IV, and by DSI. 3) Evoked IPSCs in CA3a, but not in CA1, can be reduced by DCG-IV; hence the interneurons activated by carbachol may reside in CA3a. 4) Despite the group II mGluR agonist sensitivity of CA3a interneurons, DSI in this region is not affected by a group II mGluR antagonist, CPPG, and therefore does not appear to be mediated by group II mGluRs.
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Affiliation(s)
- W Morishita
- Department of Physiology, University of Maryland School of Medicine, Baltimore 21201, USA
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31
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Bernard C, Cossart R, Hirsch JC, Esclapez M, Ben-Ari Y. What is GABAergic inhibition? How is it modified in epilepsy? Epilepsia 2000; 41 Suppl 6:S90-5. [PMID: 10999527 DOI: 10.1111/j.1528-1157.2000.tb01564.x] [Citation(s) in RCA: 94] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
A deficit of gamma-aminobutyric acid-ergic (GABAergic) inhibition is hypothesized to underlie most forms of epilepsy. Although apparently a straightforward and logical hypothesis to test, the search for a deficit of GABAergic inhibition in epileptic tissue has revealed itself to be as difficult as the quest for the Holy Grail. The investigator faces many obstacles, including the multiplicity of GABAergic inhibitory pathways and the multiplicity of variables that characterize the potency of inhibition within each inhibitory pathway. Perhaps more importantly, there seems to be no consensual definition of GABAergic inhibition. The first goal of this review is to try to clarify the notion of GABAergic inhibition. The second goal is to summarize our current knowledge of the various alterations that occur in the GABAergic pathways in temporal lobe epilepsy. Two important features will emerge: (a) according to the variable used to measure GABAergic inhibition, it may appear increased, decreased, or unchanged; and (b) these modifications are brain area- and inhibitory pathway-specific. The possible functional consequences of these alterations are discussed.
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Affiliation(s)
- C Bernard
- INSERM U29-INMED, Pare Scientifique de Luminy, Marseille, France.
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32
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Abstract
The cellular and network mechanisms of the transition of brief interictal discharges to prolonged seizures are a crucial issue in epilepsy. Here we used hippocampal slices exposed to ACSF containing 0 Mg(2+) to explore mechanisms for the transition to prolonged (3-42 sec) seizure-like ("ictal") discharges. Epileptiform activity, evoked by Shaffer collateral stimulation, triggered prolonged bursts in CA1, in 50-60% of slices, from both adult and young (postnatal day 13-21) rats. In these cases the first component of the CA1 epileptiform burst was followed by a train of population spikes at frequencies in the gamma band and above (30-120 Hz, reminiscent of tetanically evoked gamma oscillations). The gamma burst in turn could be followed by slower repetitive "tertiary" bursts. Intracellular recordings from CA1 during the gamma phase revealed long depolarizations, action potentials rising from brief apparent hyperpolarizations, and a drop of input resistance. The CA1 gamma rhythm was completely blocked by bicuculline (10-50 microm), by ethoxyzolamide (100 microm), and strongly attenuated in hyperosmolar perfusate (50 mm sucrose). Subsequent tertiary bursts were also blocked by bicuculline, ethoxyzolamide, and in hyperosmolar perfusate. In all these cases intracellular recordings from CA3 revealed only short depolarizations. We conclude that under epileptogenic conditions, gamma band oscillations arise from GABA(A)ergic depolarizations and that this activity may lead to the generation of ictal discharges.
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Telfeian AE, Federoff HJ, Leone P, During MJ, Williamson A. Overexpression of GluR6 in rat hippocampus produces seizures and spontaneous nonsynaptic bursting in vitro. Neurobiol Dis 2000; 7:362-74. [PMID: 10964607 DOI: 10.1006/nbdi.2000.0294] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
We hypothesized that overexpression of specific glutamate receptors within the hippocampus would induce seizures and the associated cellular changes seen in temporal lobe epilepsy (TLE). The GluR6 kainate receptor was overexpressed by injecting rat hippocampi with HSVGluR6, a viral vector transducing fully edited GluR6. These animals experienced limbic seizures approximately 4 h following the injection. Control animals injected with HSVlac, a vector expressing beta-galactosidase, did not have seizures. Recordings from hippocampal CA1 pyramidal cells were performed 12 to 48 h and 1 week to 1 month postinjection. We observed nonsynaptic Na(+)-mediated bursting in 77.5% of cells 12 to 48 h following injection of HSVGluR6 but not HSVlac. The synaptic responses were normal in both groups. However, the physiological properties of cells from HSVGluR6-injected hippocampi changed over time. Two weeks following HSVGluR6 injection, synaptic bursts could be evoked, but intrinsic bursting became rare. These changes persisted for at least 1 month. We postulate that this transition from intrinsic to synaptic hyperexcitability may be important in the development of TLE.
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Affiliation(s)
- A E Telfeian
- Department of Neurosurgery, Yale University School of Medicine, New Haven, Connecticut, 06520, USA
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Ohno-Shosaku T, Sawada S, Kano M. Heterosynaptic expression of depolarization-induced suppression of inhibition (DSI) in rat hippocampal cultures. Neurosci Res 2000; 36:67-71. [PMID: 10678533 DOI: 10.1016/s0168-0102(99)00110-8] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Depolarization-induced suppression of inhibition (DSI) is a transient suppression of the inhibitory synaptic transmission, observed in the hippocampus and the cerebellum, upon postsynaptic depolarization. Using rat hippocampal cultures, we examined whether DSI is confined to the inhibitory synapses on the depolarized neuron or, if DSI can spread to those on neighboring non-depolarized neurons. Whole-cell recordings were performed in 108 neuronal pairs with the following synaptic responses. Stimulation of one neuron evoked the inhibitory autaptic currents (IACs) recurrently in that neuron and also elicited the inhibitory postsynaptic currents (IPSCs) orthodromically in the other neuron. In 38 of 108 pairs, the postsynaptic depolarization caused transient suppression of IPSCs (homosynaptic DSI). In 11 of the 38 pairs exhibiting the homosynaptic DSI, the depolarization also induced suppression of IACs (heterosynaptic DSI). The heterosynaptic DSI, like the homosynaptic DSI, depended on depolarizing pulse duration and was blocked by a phorbol ester. These results suggest that DSI can spread to the synapses on a neighboring non-depolarized neuron in rat hippocampal cultures.
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Affiliation(s)
- T Ohno-Shosaku
- Department of Physiology, Kanazawa University School of Medicine, Saitama, Japan.
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35
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Lenz RA, Alger BE. Calcium dependence of depolarization-induced suppression of inhibition in rat hippocampal CA1 pyramidal neurons. J Physiol 1999; 521 Pt 1:147-57. [PMID: 10562341 PMCID: PMC2269651 DOI: 10.1111/j.1469-7793.1999.00147.x] [Citation(s) in RCA: 46] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022] Open
Abstract
1. We made whole-cell recordings from CA1 pyramidal cells in the rat hippocampal slice preparation to study the calcium (Ca2+) dependence of depolarization-induced suppression of inhibition (DSI). DSI is a retrograde signalling process in which voltage-dependent Ca2+ influx into a pyramidal cell leads to a transient decrease in the release of GABA from interneurons. 2. To investigate the Ca2+ dependence of DSI without altering extracellular divalent cations, we varied the type and amount of Ca2+ chelator (EGTA or BAPTA) in the recording pipette (keeping the chelator : Ca2+ ratio constant). Evoked inhibitory postsynaptic currents (IPSCs) were induced in the presence of antagonists of ionotropic glutamate receptors. DSI was induced by depolarizing voltage steps, lasting from 0.025 to 5 s, to 0 mV. 3. DSI was directly dependent on the duration of the voltage step used to induce it, from threshold up to a maximal value of IPSC suppression, whether EGTA or BAPTA was used, and whether their concentrations were 0.1, 0.5 or 2 mM. For instance, a voltage step lasting 1.37 s produced half-maximal DSI with 2 mM BAPTA, but with 0. 1 mM BAPTA, half-maximal DSI was achieved with a step lasting 0.186 s. Peak DSI was the same in all cases, and DSI was blocked with either 10 mM EGTA or BAPTA in the pipette. Bath application of carbachol could overcome the block of DSI by 10 mM EGTA but not by 10 mM BAPTA. 4. We calculated that a voltage step lasting approximately 100 ms would be necessary to activate half-maximal DSI in the absence of exogenous Ca2+ buffers. 5. Log-log plots of calculated total Ca2+ influx, estimated from time integrals of Ca2+ currents, versus DSI yielded a straight line with a slope of approximately 1, and increasing extracellular [Ca2+] from 2.5 to 5 mM did not change the slope. 6. The time course of decay of DSI was well described by an exponential function with a time constant of approximately 20 s and was not affected by changes in either concentration or type of Ca2+ buffer. 7. The data suggest that, in its Ca2+ dependence, DSI more closely resembles the slow release of neuropeptides and hormones than it does the process of fast release of many neurotransmitters.
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Affiliation(s)
- R A Lenz
- Department of Pharmacology and Department of Physiology, University of Maryland School of Medicine, Baltimore, MD 21201, USA
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36
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Tallent MK, Siggins GR. Somatostatin acts in CA1 and CA3 to reduce hippocampal epileptiform activity. J Neurophysiol 1999; 81:1626-35. [PMID: 10200199 DOI: 10.1152/jn.1999.81.4.1626] [Citation(s) in RCA: 79] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Although the peptide somatostatin (SST) has been speculated to function in temporal lobe epilepsy, its exact role is unclear, as in vivo studies have suggested both pro- and anticonvulsant properties. We have shown previously that SST has multiple inhibitory cellular actions in the CA1 region of the hippocampus, suggesting that in this region SST should have antiepileptic actions. To directly assess the effect of SST on epileptiform activity, we studied two in vitro models of epilepsy in the rat hippocampal slice preparation using extracellular and intracellular recording techniques. In one, GABA-mediated neurotransmission was inhibited by superfusion of the GABAA receptor antagonist bicuculline. In the second, we superfused Mg2+-free artificial cerebrospinal fluid to remove the Mg2+ block of the N-methyl-D-aspartate (NMDA) subtype of glutamate receptor. We show here that SST markedly reduces the intensity of evoked epileptiform afterdischarges and the frequency of spontaneous bursts in both CA1 and CA3. SST appears to act additively in the two regions to suppress the transmission of epileptiform events through the hippocampus. We further examined SST's actions in CA3 and found that SST dramatically reduced the frequency of paroxysmal depolarizing shifts (PDSs) recorded intracellularly in current clamp, as well as increasing the threshold for evoking "giant" excitatory postsynaptic currents (EPSCs), large polysynaptically mediated EPSCs that are the voltage-clamp correlate of PDSs. We also examined the actions of SST on pharmacologically isolated EPSCs generated at both mossy fiber (MF) and associational/commissural (A/C) synapses. SST appears to act specifically to reduce recurrent excitation between CA3 neurons because it depresses A/C- but not MF-evoked EPSCs. SST also increased paired-pulse facilitation of A/C EPSCs, suggesting a presynaptic site of action. Reciprocal activation of CA3 neurons through A/C fibers is critical for generation of epileptiform activity in hippocampus. Thus SST reduces feedforward excitation in rat hippocampus, acting to "brake" hyperexcitation. This is a function unique from that described for other hippocampal neuropeptides, which affect more standard neurotransmission. Our results suggest that SST receptors could be a unique, selective clinical target for treatment of limbic seizures.
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Affiliation(s)
- M K Tallent
- Department of Neuropharmacology, The Scripps Research Institute, La Jolla, California 92037, USA
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Lenz RA, Wagner JJ, Alger BE. N- and L-type calcium channel involvement in depolarization-induced suppression of inhibition in rat hippocampal CA1 cells. J Physiol 1998; 512 ( Pt 1):61-73. [PMID: 9729617 PMCID: PMC2231194 DOI: 10.1111/j.1469-7793.1998.061bf.x] [Citation(s) in RCA: 66] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
Abstract
1. We investigated depolarization-induced suppression of inhibition (DSI) under whole-cell voltage clamp in CA1 pyramidal neurons of rat hippocampal slices. DSI, a transient reduction in monosynaptic evoked GABAAergic IPSCs lasting for approximately 1 min, was induced by depolarizing the pyramidal cell to -10 or 0 mV for 1 or 2 s. 2. Raising extracellular Ca2+ concentration increased DSI, and varying the DSI-inducing voltage step showed that the voltage dependence of DSI was like that of high-voltage-activated Ca2+ channels. 3. The P- and Q-type Ca2+ channel blocker omega-agatoxin TK (200 nM and 1 microM) and the R- and T-type Ca2+ channel blocker Ni2+ (100 microM) reduced IPSCs without reducing DSI. 4. The specific N-type Ca2+ channel antagonist omega-conotoxin GVIA (250 nM) reduced IPSC amplitudes and almost completely abolished DSI. 5. Blocking L-type Ca2+ channels with nifedipine (10 microM) had no effect on IPSCs or DSI induced by our standard protocol, but reduced DSI induced by the unclamped Na+- and Ca2+-dependent spikes that occurred when 2(triethylamino)-N-(2,6-dimethylphenyl)acetamide (QX-314) was omitted from the recording pipette solution. 6. Although intracellular Ca2+ stores were not measured, DSI was not affected by cyclopiazonic acid (CPA, 20-40 microM), a blocker of Ca2+ uptake into intracellular stores. 7. We conclude that DSI is initiated by Ca2+ influx through N- and, under certain conditions, L-type Ca2+ channels.
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Affiliation(s)
- R A Lenz
- Department of Physiology, University of Maryland School of Medicine, Baltimore, MD 21201, USA
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