title: Phase-dependent roles of reactive microglia and astrocytes in nervous system injury as delineated by imaging of peripheral benzodiazepine receptor.
abstract: Elevated levels of peripheral benzodiazepine receptor (PBR) in glia have been documented in diverse nervous system injuries, while the identity and spatiotemporal characteristics of the cells showing upregulation of PBR remain elusive. We examined the astrocytic and microglial expressions of PBR in rat brains during the duration of ethanol-induced neuronal insults in order to clarify the significance of PBR as a biomarker capable of detecting a distinctive subpopulation of these glial cells involved in the impairment and protection of neurons. The levels of PBR, as determined by autoradiographic analysis using a specific radioligand, [11C]DAA1106, began to significantly increase at 3 days after intrastriatal injection of ethanol, and peaked at 7 days. This was consistent with the results of double immunofluorescence staining and high-resolution emulsion autoradiography, which revealed upregulation of PBR in both microglia and astrocytes proliferating in nonoverlapping compartments of the injury site. Notably, increased expression of PBR in astrocytes was transiently observed in a manner parallel to the centripetal migration of these cells to the inflammatory lesion, which may be a response indispensable to the protection of intact tissue. Thereafter, astrocytic PBR was barely detectable, despite the presence of numerous glial fibrillary acidic protein-immunoreactive astrocytes forming glial scarring. By contrast, intense PBR signals were persistently present in microglia localized to the injury epicenter up to 90 days, notwithstanding a gradual reduction in the number of ionized calcium binding adapter molecule-1-positive amoeboid microglia between 7 and 90 days. The long-lasting PBR expression in microglia was finally supported by in vivo positron emission tomography imaging, and suggests that inflammatory tissue damage is potentially expandable unless it is tightly sealed by astrocytic scar. The present findings collectively support the utility of PBR in identifying a unique temporal pattern of astrocytic and microglial activation that conventional glial markers hardly pursue.
authors.affiliation: Department of Molecular Neuroimaging, National Institute of Radiological Sciences, Chiba, Japan.
authors.forename: Jun
authors.initials: J
authors.lastname: Maeda
authors.forename: Makoto
authors.initials: M
authors.lastname: Higuchi
authors.forename: Motoki
authors.initials: M
authors.lastname: Inaji
authors.forename: Bin
authors.initials: B
authors.lastname: Ji
authors.forename: Eisuke
authors.initials: E
authors.lastname: Haneda
authors.forename: Takashi
authors.initials: T
authors.lastname: Okauchi
authors.forename: Ming-Rong
authors.initials: MR
authors.lastname: Zhang
authors.forename: Kazutoshi
authors.initials: K
authors.lastname: Suzuki
authors.forename: Tetsuya
authors.initials: T
authors.lastname: Suhara
mesh_terms: D000081:Acetamides / Q000378:metabolism; D000818:Animals; D001253:Astrocytes / Q000378:metabolism*; D001667:Binding, Competitive / Q000187:drug effects / Q000502:physiology; D015415:Biomarkers / Q000032:analysis / Q000378:metabolism; D020208:Brain Injury, Chronic / Q000175:diagnosis / Q000378:metabolism* / Q000503:physiopathology; D002135:Calcium-Binding Proteins / Q000378:metabolism; D002352:Carrier Proteins / Q000032:analysis / Q000378:metabolism*; D049109:Cell Proliferation; D003342:Corpus Striatum / Q000378:metabolism / Q000473:pathology / Q000503:physiopathology; D004660:Encephalitis / Q000175:diagnosis / Q000378:metabolism* / Q000503:physiopathology; D000431:Ethanol / Q000494:pharmacology; D005455:Fluorescent Antibody Technique; D005904:Glial Fibrillary Acidic Protein / Q000378:metabolism; D005911:Gliosis / Q000175:diagnosis / Q000378:metabolism* / Q000503:physiopathology; D018836:Inflammation Mediators / Q000494:pharmacology; D008297:Male; D017628:Microglia / Q000378:metabolism*; D010647:Phenyl Ethers / Q000378:metabolism; D011869:Radioligand Assay / Q000379:methods; D051381:Rats; D017207:Rats, Sprague-Dawley; D011963:Receptors, GABA-A / Q000032:analysis / Q000378:metabolism*; D015854:Up-Regulation / Q000502:physiology
chemical_list: D000081:Acetamides; D015415:Biomarkers; D002135:Calcium-Binding Proteins; D002352:Carrier Proteins; C118942:DAA 1106; D005904:Glial Fibrillary Acidic Protein; D018836:Inflammation Mediators; D010647:Phenyl Ethers; D011963:Receptors, GABA-A; C069997:Tspo protein, rat; D000431:Ethanol