title: Carbon monoxide treatment reduces microglial activation in the ischemic rat retina.
abstract: OBJECTIVE
  Ischemia and reperfusion (I/R) injury damages retinal neurons. Retinal injury is accompanied by activation of microglia, which scavenge the dead or dying neurons, but increasing evidence now indicates that amoeboid-shaped microglia cells activated in the brain after ischemia have neurotoxic and damaging properties in their own right. A previous study showed that postconditioning with carbon monoxide (CO) protects retinal ganglion cells (RGCs) after I/R through anti-apoptotic and anti-inflammatory mechanisms. The present study was designed to investigate and quantify the activation of retinal microglia after I/R with and without CO postconditioning.
  
  
  METHODS
  Adult Sprague-Dawley rats underwent retinal ischemia by increasing the ocular pressure to 120 mmHg for 1 h through a needle inserted into the anterior chamber. Reperfusion was induced by removing the needle. After I/R, one group of animals was kept in a CO (250 ppm) atmosphere for 1 h; the other group was kept in room air (Air). At 1, 2, 3, and 7 days after I/R, the eyes were enucleated and fixed. Intracardiac blood was analyzed for systemic effects of CO or I/R. Retinal cross sections were taken from the middle third of the eye and were stained with anti-Iba-1. Microglia cells were graded as amoeboid or ramified phenotypes according to morphologic criteria. Retinal thicknesses were determined.
  
  
  RESULTS
  Evaluation of retinal tissue revealed a significant reduction of amoeboid microglia cells after I/R + CO when compared to the I/R + Air group. The peak number of amoeboid microglia was observed at day 2 post-I/R + Air. This rise was attenuated by CO postconditioning (815 versus 572 cells/mm2for I/R + Air versus I/R + CO, respectively; p = 0.005). CO reduced and further postponed the peak in the numbers of amoeboid and ramified microglia cells in ischemic eyes and prevented microglial activation in the contralateral eyes. I/R-induced leucocytosis was inhibited by CO inhalation. The reduction of retinal thickness after I/R was more serious after Air inhalation when compared to the CO group.
  
  
  CONCLUSIONS
  Numerous activated microglia cells appear in the inner retina after I/R, and CO-treatment significantly attenuates this glial response. Antagonism of microglial activation may be a further neuroprotective effect of CO, apart from its direct anti-apoptotic capacity.
authors.affiliation: Department of Anesthesiology and Intensive Care, Medical Center, University of Freiburg, Hugstetter Strasse 55, Freiburg im Breisgau, 79106, Germany.|Faculty of Medicine, University of Freiburg, Freiburg im Breisgau, Germany.
authors.forename: Felix
authors.initials: F
authors.lastname: Ulbrich
authors.affiliation: Department of Anesthesiology and Intensive Care, Medical Center, University of Freiburg, Hugstetter Strasse 55, Freiburg im Breisgau, 79106, Germany.|Faculty of Medicine, University of Freiburg, Freiburg im Breisgau, Germany.
authors.forename: Ulrich
authors.initials: U
authors.lastname: Goebel
authors.affiliation: Eye Center, Medical Center, University of Freiburg, Killianstrasse 5, Freiburg im Breisgau, 79106, Germany.|Faculty of Medicine, University of Freiburg, Freiburg im Breisgau, Germany.
authors.forename: Daniel
authors.initials: D
authors.lastname: Böhringer
authors.affiliation: Eye Center, Medical Center, University of Freiburg, Killianstrasse 5, Freiburg im Breisgau, 79106, Germany.|Faculty of Medicine, University of Freiburg, Freiburg im Breisgau, Germany.
authors.forename: Petar
authors.initials: P
authors.lastname: Charalambous
authors.affiliation: Eye Center, Medical Center, University of Freiburg, Killianstrasse 5, Freiburg im Breisgau, 79106, Germany.|Faculty of Medicine, University of Freiburg, Freiburg im Breisgau, Germany.
authors.forename: Wolf Alexander
authors.initials: WA
authors.lastname: Lagrèze
authors.affiliation: Eye Center, Medical Center, University of Freiburg, Killianstrasse 5, Freiburg im Breisgau, 79106, Germany. julia.biermann@uniklinik-freiburg.de.|Faculty of Medicine, University of Freiburg, Freiburg im Breisgau, Germany. julia.biermann@uniklinik-freiburg.de.
authors.forename: Julia
authors.identifier: http://orcid.org/0000-0001-5510-3857
authors.initials: J
authors.lastname: Biermann
mesh_terms: D000818:Animals; D001773:Blood Cells; D002135:Calcium-Binding Proteins / Q000378:metabolism; D002248:Carbon Monoxide / Q000008:administration & dosage*; D004195:Disease Models, Animal; D005260:Female; D019084:Fluorescent Antibody Technique, Indirect; D008297:Male; D008840:Microfilament Proteins / Q000378:metabolism; D017628:Microglia / Q000378:metabolism* / Q000473:pathology; D018696:Neuroprotective Agents; D051381:Rats; D017207:Rats, Sprague-Dawley; D015427:Reperfusion Injury / Q000378:metabolism / Q000473:pathology / Q000517:prevention & control*; D012162:Retinal Degeneration / Q000378:metabolism / Q000473:pathology / Q000517:prevention & control*; D012165:Retinal Ganglion Cells / Q000378:metabolism* / Q000473:pathology; D012171:Retinal Vessels / Q000473:pathology
chemical_list: C100745:Aif1 protein, rat; D002135:Calcium-Binding Proteins; D008840:Microfilament Proteins; D018696:Neuroprotective Agents; D002248:Carbon Monoxide
keywords: Ischemia; Microglia; Neuroinflammation; Neuroprotection; Retina; Retinal ganglion cell