A positive effect of Gas6 on dying cell clearance in vitro has been reported for multiple cell types, and the ability of rhGas6 to affect phagocytosis in murine microglia by acting on Axl/Mer has been shown previously in vitro. The clearance of cellular and WZ4002 msds myelin debris might be an initial and important early step for recovery in the corpus callosum. Efficient clearance of damaged cells and myelin debris likely impacts upon remyelination and cell survival. In this study, a significantly greater number of SMI32-positive axonal spheroids were observed in PBS- versus rhGas6-treated mice. After treatment with different doses of rhGas6, all doses noticeably reduced the number of SMI32 positive axonal swellings relative to PBS treatment. SMI32-positive immunoreactivity in axons as well as the presence of axonal swellings or spheroids is considered pathologic and was previously shown to occur during cuprizone treatment and during MOG-induced experimental autoimmune encephalomyelitis. Increased SMI32-positive immunoreactivity correlates with axonal injury due to dephosphorylation of neurofilament H. Further, SMI32 immunoreactivity is found in chronic lesions from patients with MS. Similarly, increased APP immunoreactivity within axons represents a defect in axonal transport and serves as a marker of axonal injury resulting from cytoskeletal breakdown and calcium influx that interrupts axoplasmic flow and subsequent accumulation of organelles. By EM, we showed that the percentage of small dystrophic axons was greater in mice treated with rhGas6 whereas the percentage of large axonal spheroids was higher in PBS-treated mice relative to rhGas6. Thus, data from EM support our conclusion that mice treated with rhGas6 have a reduction in axonal spheroids. The results obtained demonstrate a beneficial effect of rhGas6 on axonal survival and the maintenance of axon integrity following cuprizone toxicity. In this context, we previously showed in vitro that 400 ng/ml rhGas6 had a maximal positive effect on human oligodendrocyte survival using oligodendrocytes isolated from human fetal spinal cord. This suggests that rhGas6 serves as a survival factor for oligodendrocytes during development. In the present study, we evaluated how rhGas6 affected remyelination following cuprizone withdrawal by MBP immunostaining. We used gray value analysis to distinguish the intensity of MBP expression between PBS- and rhGas6-treated mice. Extensive demyelination in the corpus callosum, was observed after 4 weeks of cuprizone treatment. The extensive myelin loss had the lowest gray value which correlated with weak MBP immunoreactivity. Our data are consistent with other studies demonstrating demyelination in the corpus callosum 3–4 weeks after cuprizone treatment. Quantification of MBP staining revealed that gray values gradually increased after cuprizone removal in both PBS- and rhGas6-treated mice. The increase in gray values likely reflected progressive remyelination consistent with the MBP expression.