AIM:To investigate the effects of minocycline on optic nerve axons and Caspase-3 expression of experimental optic neuritis in Wistar rats.METHODS:Twenty-two female experimental Wistar rats were assigned to four groups randomly:normal group and experimental autoimmue encephalomyelitis group(EAE group),minocycline group,methlprednisolone group(MP group).The pathological changes of optic nerve were observed and the expression of Caspase-3 in retinal ganglion cells(RGCs) was detected by immunohistochemistry.RESULTS:In EAE group,the optic nerve fibers showed bulb-like degeneration,the axis irregular swelling,a quantity of inflammatory cell infiltrating under light microscope.The axons showed bulb-like degeneration,myelin sheaths were loose,microtubule and microfilament disappeared under electron microscopy.The area percentage of axons:there was very significant difference(P<0.01),when EAE group,minocycline group and MP group compared with normal group.There was significant difference(P<0.05),when minocycline group and MP group compared with EAE group.In normal rats,there was little expression of Caspase-3 in retina.There was significant difference(P<0.05),when EAE group and MP group compared with minocycline group.There was significant difference(P<0.05),when MP group compared with EAE group CONCLUSION:Methlprednisolone can reduce demyelinating optic nerve axons injury,but can not reduce the expression of Caspase-3 in RGCs.Minocycline can down-regulate the expression of Caspase-3 in retina,which show that minocycline has a marked protection of RGCs in demyelinating optic neuritis by inhibiting the expression of Caspase-3.