Phase and fluorescence micrographs of neonatal OLGs, either untreated (Ctrl) or treated with cer, sph, or SPP. Concentration of cer, sph, or SPP: 10 μm. Duration of treatment: 4.5 hr. PI was added to cultures for 5 min before fixation. Failure to exclude PI was observed only in sph-treated OLGs, although both cer- and sph-treated OLGs exhibited decreased number of processes. Scale bar, 30 μm.