Fig. 3

Treatment of light-exposed mice with minocycline blocks microglia reactivity and Müller cell gliosis. Of both sexes, 10- to 14-week-old BALB/c mice were dark-adapted for 16 h. After pupil dilatation, the mice were exposed to bright white light with an intensity of 15.000 lux for 1 hour. The mice received intraperitoneal injections of minocycline at a dose of 45 mg/kg body weight twice daily for the first 2 days, starting 1 day before the light exposure and once daily for the remaining 3 days. Four days after the light exposure OCT, immunohistochemical stainings, real-time RT-PCR analysis, and RNA sequencing were performed to determine the in vivo effects of minocycline treatment (schematic drawing). Representative photomicrographs show retinal sections (a–c) and flat mounts (d–f) stained with Iba1 (green), TSPO (red) (g–i), and GFAP (red) (j–l). In control retinas, microglial cells were located in the OPL, IPL, and GCL (a, d); low levels of TSPO were only observable in the GCL (g); and signs for Müller cell gliosis were not detectable (j). b, e, h, and k Photomicrographs of light-exposed mice showed a massive thinning of the ONL and an increased number of amoeboid shaped, reactive microglia in the ONL, and the subretinal space (b, e). h A strong up-regulation of TSPO expression was detectable in microglia. k Up-regulation of GFAP indicates Müller cell gliosis. c, f, i, and l Representative photomicrographs of minocycline-treated mice 4 days after light exposure. Compared to untreated controls, the ONL of minocycline-treated mice appeared markedly preserved and less microglia were detectable in the ONL and the subretinal space (c, f). i Microglial cells were negative for TSPO expression. l GFAP expression was only detectable in astrocytes, indicating a lack of reactive Müller cells. TSPO translocator protein, GFAP glial fibrillary acid protein, ONL outer nuclear layer, OPL outer plexiform layer, INL inner nuclear layer, IPL inner plexiform layer, GCL ganglion cell layer. Scale bar 50 μm