Longitudinal section of adult rat optic nerve, immunostained for Thr286-phosphorylated CaMKII (pT286; green), myelin basic protein (MPB; magenta), and axonal neurofilaments (SMI-312; blue). pT286 localizes to axons and not to myelin, as SMI-312 and pT286 colocalization generates cyan within profiles circumscribed by MBP. The axon diameters range between small and large. A few large gaps between axon fascicles show some pT286 immunopositivity, but no signal for MBP or SMI-312. For more information, see the article by Partida et al. (pages 8087–8105).