Confocal microscope image of a labeled vertical section of 13-lined ground squirrel outer retina collected during midwinter torpor. Red, PNA labels the extracellular matrix surrounding cone outer segments (OS). Green, anti-cytochrome oxidase-1 label indicates mitochondrial function. Blue, Anti-rhodopsin labels ROS. Amongst lightly-labeled cone inner segment (IS) ellipsoids, a rod IS ellipsoid retains the robust anti-COX 1 label (arrow) found uniformly in all ellipsoids of retinas collected during summer arousal (data not shown). Magnification bar equal to 20 micrometers. (Adapted from Gruber et al., Assn Res Vis Ophthalmol., 2006).