Figure 6. Microglial activity during light damage.
Dark-adapted albino zebrafish were placed in constant intense light for various lengths of time, sacrificed, and retinal sections were colabeled with the 4C4 monoclonal antibody, which detects microglia (red), and anti-PCNA monoclonal antibody (green). Undamaged retinas possessed a limited number of microglia in the plexiform layers and associated with the rod outer segment region (A, arrowheads). After 16 ours of constant-intense light, larger, activated microglia (arrowhead) were found in the ONL (B). At 31 hours of constant light, activated microglia were restricted to the apical regions of the INL and the ONL (C, arrowhead), whereas PCNA-positive Müller glia were present in the basal INL (C, arrow). At 96 hours of constant light, activated microglia filled much of the ONL and the space formerly occupied by the rod outer segments, as well as some infiltration in the INL (D, arrowheads). (E–M) Immunohistochemistry of microglia in albino Tg(XlRho:EGFP)fl1 transgenic retinas. Dark-adapted albino Tg(XlRho:EGFP)fl1 zebrafish were treated with either 0.65% NaCl (E–G), 20 mM MSOP (H–J), or 20 mM L-SOP (K–M), subjected to 24 hours of constant intense light, sectioned, and labeled with 4C4 monoclonal antibody (E, G, H, J, K, and M, red). EGFP was detected throughout the rods (F, G, I, J, L, and M, green). Despite abundant numbers in the outer segments, an average of fewer than 5 4C4-positive microglia were observed in 400 μm of the ONL and INL of the L-SOP, MSOP, and saline-injected retinas. GCL ganglion cell layer; INL, inner nuclear layer; ONL, outer nuclear layer. Scale bar represents 50 μm and is the same for panels A–D and E–M.