Retina isolated from the formalin-fixed eyes was rinsed overnight in running water and incubated at 37 °C with 3% crude trypsin (Invitrogen-Gibco, Grand Island, NY, USA) containing 200 mM sodium fluoride for 45 to 70 min. After cleaning the retinal vasculature under a dissecting microscope, it was stained with periodic acid-Schiff-hematoxylin to count acellular capillaries [24 (link), 31 (link)].
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