title: Microglial Contact Prevents Excess Depolarization and Rescues Neurons from Excitotoxicity.
abstract: Microglia survey and directly contact neurons in both healthy and damaged brain, but the mechanisms and functional consequences of these contacts are not yet fully elucidated. Combining two-photon imaging and patch clamping, we have developed an acute experimental model for studying the role of microglia in CNS excitotoxicity induced by neuronal hyperactivity. Our model allows us to simultaneously examine the effects of repetitive supramaximal stimulation on axonal morphology, neuronal membrane potential, and microglial migration, using cortical brain slices from Iba-1 eGFP mice. We demonstrate that microglia exert an acute and highly localized neuroprotective action under conditions of neuronal hyperactivity. Evoking repetitive action potentials in individual layer 2/3 pyramidal neurons elicited swelling of axons, but not dendrites, which was accompanied by a large, sustained depolarization of soma membrane potential. Microglial processes migrated to these swollen axons in a mechanism involving both ATP and glutamate release via volume-activated anion channels. This migration was followed by intensive microglial wrapping of affected axons and, in some cases, the removal of axonal debris that induced a rapid soma membrane repolarization back to resting potentials. When the microglial migration was pharmacologically blocked, the activity-induced depolarization continued until cell death ensued, demonstrating that the microglia-axon contact served to prevent pathological depolarization of the soma and maintain neuronal viability. This is a novel aspect of microglia surveillance: detecting, wrapping, and rescuing neuronal soma from damage due to excessive activity.
authors.affiliation: Divison of Homeostatic Development, National Institute for Physiological Sciences, Okazaki 444-8585, Japan; Department of Physiological Sciences, The Graduate University for Advanced Studies, Okazaki 444-8585, Nishigo-naka, Myodaiji-cho, Japan.
authors.forename: Go
authors.initials: G
authors.lastname: Kato
authors.affiliation: Divison of Homeostatic Development, National Institute for Physiological Sciences, Okazaki 444-8585, Japan; Department of Physiological Sciences, The Graduate University for Advanced Studies, Okazaki 444-8585, Nishigo-naka, Myodaiji-cho, Japan.
authors.forename: Hiroyuki
authors.identifier: 0000-0003-1166-8535
authors.initials: H
authors.lastname: Inada
authors.affiliation: Divison of Homeostatic Development, National Institute for Physiological Sciences, Okazaki 444-8585, Japan; Department of Physiological Sciences, The Graduate University for Advanced Studies, Okazaki 444-8585, Nishigo-naka, Myodaiji-cho, Japan; Precursory Research for Embryonic Science and Technology, Japan Science and Technology Agency, Kawaguchi 332-0012, Saitama, Japan.
authors.forename: Hiroaki
authors.initials: H
authors.lastname: Wake
authors.affiliation: Divison of Homeostatic Development, National Institute for Physiological Sciences, Okazaki 444-8585, Japan; Department of Physiological Sciences, The Graduate University for Advanced Studies, Okazaki 444-8585, Nishigo-naka, Myodaiji-cho, Japan.
authors.forename: Ryohei
authors.initials: R
authors.lastname: Akiyoshi
authors.affiliation: Divison of Homeostatic Development, National Institute for Physiological Sciences , Okazaki 444-8585, Japan.
authors.forename: Akiko
authors.initials: A
authors.lastname: Miyamoto
authors.affiliation: Divison of Homeostatic Development, National Institute for Physiological Sciences, Okazaki 444-8585, Japan; Department of Physiological Sciences, The Graduate University for Advanced Studies, Okazaki 444-8585, Nishigo-naka, Myodaiji-cho, Japan.
authors.forename: Kei
authors.initials: K
authors.lastname: Eto
authors.affiliation: Divison of Homeostatic Development, National Institute for Physiological Sciences, Okazaki 444-8585, Japan; Department of Physiological Sciences, The Graduate University for Advanced Studies, Okazaki 444-8585, Nishigo-naka, Myodaiji-cho, Japan.
authors.forename: Tatsuya
authors.initials: T
authors.lastname: Ishikawa
authors.affiliation: Department of Physiology, School of Medical Sciences, University of New South Wales , Sydney 2052, New South Wales, Australia.
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Moorhouse
authors.affiliation: Department of Anesthesia, Critical Care and Pain Medicine, Beth Israel Deaconess Medical Center, Harvard Medical School , Boston, Massachusetts 02215.
authors.forename: Andrew M
authors.identifier: 0000-0002-0213-3048
authors.initials: AM
authors.lastname: Strassman
authors.affiliation: Divison of Homeostatic Development, National Institute for Physiological Sciences, Okazaki 444-8585, Japan; Department of Physiological Sciences, The Graduate University for Advanced Studies, Okazaki 444-8585, Nishigo-naka, Myodaiji-cho, Japan; Core Research for Evolutional Science and Technology (CREST), Japan Agency for Medical Research and Development (AMED), Tokyo, Japan.
authors.forename: Junichi
authors.initials: J
authors.lastname: Nabekura
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D001369:Axons / Q000187:drug effects / Q000473:pathology / Q000502:physiology; D002465:Cell Movement / Q000187:drug effects / Q000502:physiology; D048429:Cell Size; D003712:Dendrites / Q000187:drug effects / Q000473:pathology / Q000502:physiology; D005260:Female; D018698:Glutamic Acid / Q000378:metabolism; D007473:Ion Channels / Q000378:metabolism; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology*; D008822:Mice, Transgenic; D017628:Microglia / Q000187:drug effects / Q000473:pathology / Q000502:physiology*; D000066829:Neuroprotection / Q000187:drug effects / Q000502:physiology*; D017966:Pyramidal Cells / Q000187:drug effects / Q000473:pathology / Q000502:physiology*; D046509:Tissue Culture Techniques
chemical_list: D007473:Ion Channels; D018698:Glutamic Acid; D000255:Adenosine Triphosphate
keywords: ATP release; axonal swelling; excitotoxicty; microglia; neuronal rescue