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An Excitatory Loop with Astrocytes Contributes to Drive Neurons to Seizure Threshold

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  • Marta Gómez-Gonzalo
  • Gabriele Losi
  • Angela Chiavegato
  • Micaela Zonta
  • Mario Cammarota
  • Marco Brondi
  • Francesco Vetri
  • Laura Uva
  • Tullio Pozzan
  • Marco de Curtis
  • Gian Michele Ratto
  • Giorgio Carmignoto

Abstract

Studies in rodent brain slices suggest that seizures in focal epilepsies are sustained and propagated by the reciprocal interaction between neurons and astroglial cellsSeizures in focal epilepsies are sustained by a highly synchronous neuronal discharge that arises at restricted brain sites and subsequently spreads to large portions of the brain. Despite intense experimental research in this field, the earlier cellular events that initiate and sustain a focal seizure are still not well defined. Their identification is central to understand the pathophysiology of focal epilepsies and to develop new pharmacological therapies for drug-resistant forms of epilepsy. The prominent involvement of astrocytes in ictogenesis was recently proposed. We test here whether a cooperation between astrocytes and neurons is a prerequisite to support ictal (seizure-like) and interictal epileptiform events. Simultaneous patch-clamp recording and Ca2+ imaging techniques were performed in a new in vitro model of focal seizures induced by local applications of N-methyl-D-aspartic acid (NMDA) in rat entorhinal cortex slices. We found that a Ca2+ elevation in astrocytes correlates with both the initial development and the maintenance of a focal, seizure-like discharge. A delayed astrocyte activation during ictal discharges was also observed in other models (including the whole in vitro isolated guinea pig brain) in which the site of generation of seizure activity cannot be precisely monitored. In contrast, interictal discharges were not associated with Ca2+ changes in astrocytes. Selective inhibition or stimulation of astrocyte Ca2+ signalling blocked or enhanced, respectively, ictal discharges, but did not affect interictal discharge generation. Our data reveal that neurons engage astrocytes in a recurrent excitatory loop (possibly involving gliotransmission) that promotes seizure ignition and sustains the ictal discharge. This neuron–astrocyte interaction may represent a novel target to develop effective therapeutic strategies to control seizures.Author Summary: In focal epilepsy, seizures are generated by a localized, synchronous neuronal electrical discharge that may spread to large portions of the brain. Despite intense experimental research in this field, a key question relevant to the human epilepsy condition remains completely unanswered: what are the cellular events that lead to the onset of a seizure in the first place? In various in vitro models of seizures using rodent brain slices, we simultaneously recorded neuronal firing and Ca2+ signals both from neurons and from astrocytes, the principal population of glial cells in the brain. We found that activation of astrocytes by neuronal activity and signalling from astrocytes back to neurons contribute to the initiation of a focal seizure. This reciprocal excitatory loop between neurons and astrocytes represents a new mechanism in the pathophysiology of epilepsy that should be considered by those aiming to develop more effective therapies for epilepsies that are not controlled by currently available treatments.

Suggested Citation

  • Marta Gómez-Gonzalo & Gabriele Losi & Angela Chiavegato & Micaela Zonta & Mario Cammarota & Marco Brondi & Francesco Vetri & Laura Uva & Tullio Pozzan & Marco de Curtis & Gian Michele Ratto & Giorgio , 2010. "An Excitatory Loop with Astrocytes Contributes to Drive Neurons to Seizure Threshold," PLOS Biology, Public Library of Science, vol. 8(4), pages 1-19, April.
  • Handle: RePEc:plo:pbio00:1000352
    DOI: 10.1371/journal.pbio.1000352
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    References listed on IDEAS

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    1. Paola Bezzi & Giorgio Carmignoto & Lucia Pasti & Sabino Vesce & Daniela Rossi & Barbara Lodi Rizzini & Tullio Pozzan & Andrea Volterra, 1998. "Prostaglandins stimulate calcium-dependent glutamate release in astrocytes," Nature, Nature, vol. 391(6664), pages 281-285, January.
    2. Christian Henneberger & Thomas Papouin & Stéphane H. R. Oliet & Dmitri A. Rusakov, 2010. "Long-term potentiation depends on release of d-serine from astrocytes," Nature, Nature, vol. 463(7278), pages 232-236, January.
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    1. Junli Zhao & Jinyi Sun & Yang Zheng & Yanrong Zheng & Yuying Shao & Yulan Li & Fan Fei & Cenglin Xu & Xiuxiu Liu & Shuang Wang & Yeping Ruan & Jinggen Liu & Shumin Duan & Zhong Chen & Yi Wang, 2022. "Activated astrocytes attenuate neocortical seizures in rodent models through driving Na+-K+-ATPase," Nature Communications, Nature, vol. 13(1), pages 1-15, December.
    2. Zhao, Jinyi & Yu, Ying & Wang, Qingyun, 2022. "Dynamical regulation of epileptiform discharges caused by abnormal astrocyte function with optogenetic stimulation," Chaos, Solitons & Fractals, Elsevier, vol. 164(C).
    3. Liza J. Severs & Nicholas E. Bush & Lely A. Quina & Skyler Hidalgo-Andrade & Nicholas J. Burgraff & Tatiana Dashevskiy & Andy Y. Shih & Nathan A. Baertsch & Jan-Marino Ramirez, 2023. "Purinergic signaling mediates neuroglial interactions to modulate sighs," Nature Communications, Nature, vol. 14(1), pages 1-14, December.

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