Figure 9. COX activity in the light-adapted mouse retina is compartmentalized. A: The y-axis shows the retinal layers. There was no detectable cytochrome oxidase (COX) activity in the photoreceptor OSs. COX activity was strongest in the photoreceptor ISs, OPL, and outermost region of the INL. Moderate reactivity is localized in the proximal INL. The IPL-a is more reactive compared to the IPL-b. The GCL shows strong COX reactivity localized to the mitochondria near the somas and is more reactive in some retinal ganglion cells than others. The NFL/MGC end-feet was less reactive compared to the rest of the reactive layers. B: COX activity in different retinal layers presented as mean ± SEM of relative optical density. The COX activity in ISs is significantly greater than that in all other retinal layers as indicated by asterisk (p<0.05). GCL = ganglion cell layer, INL = inner nuclear layer, IPL-a = IPL sublamina-a, IPL-b = IPL sublamina-b, ISs = inner segments, MGC = Müller glial cell, NFL = nerve fiber layer, ONL = outer nuclear layer, OPL = outer plexiform layer, OSs = outer segments. A, scale bar = 20 μM.