Prior Exposure to Immunosuppressors Sensitizes Retinal Microglia and Accelerates Optic Nerve Regeneration in Zebrafish

Figure 7

Multiple intravitreal injections with dex cause an inflammatory response in the retina. (a) Schematic representation of the experimental setup. Intravitreal injection (IVT) of dex (or saline) is performed three times, at days 0, 2, and 4. Retinas are harvested just before and at 6 hours after each injection (days 0, 2, and 4), at days 1 and 7, to assess their number and morphology in the inner retina. (b-i) Intravitreal injection of saline does not alter the number of retinal microglia, or their morphology, at any of the time points under study. (j-q) As a result of the first dex injection (at day 0), the retina is almost completely devoid of microglia at days 1 and 2. Yet, surprisingly, the second dex injection (at day 2) induces an increase in the number of retinal microglia/macrophages and the infiltration of neutrophils (yellow). Subsequent application of dex (at day 4) has a similar effect: it increases rather than decreases the number of microglia/macrophages in the retina. At day 7, the inflammatory status seems to have normalized again. Scale bars: 50 μm.