Study On The Development Of Visual System Of MS And MD Rats Within And The End Of Crucial Perioeds

ObjectiveThe VEP,specific Nissle's staining techniques,DTI,immuno-histochemical and methods were used to study the change of visual system in MS and MD amblyopia rats,and to investigate the persistence of neuronal plasticity in the Lateral geniculate nucleus and visual cortex of MS and MD amblyopia rats within and the end of the critical period of visual development.Methods60 normal SD rats aged 13 postnatal days were randomly divided into 3 groups:20 normal (N1),20monocular strabismus(MS)and 20 monocular deprivation(MD) amblyopia group.Each group take out at early(P25),middle(P35),end(P45) of critical period of visual development and overgrown(P120).Surgery to produce iatrogenic convergent strabismus were enforced to the MS group amblyopia rats to set up the monocular strabismus amblyopia animal model; Monocular tarsorrhaphy were enforced to the MD group amblyopia rats to set up the monocular deprivation amblyopia animal model.Rats of MS,MD and N groups were reared together in the dark box 24 hours.After flash visual evoked poteitial(F-VEP) test of MS group.After half an hour exposure to ambient light,the illumination amblyopia rats were perfuse transaortically;.Sections of the 17 areas of visual cortex and ateral geniculate nucleus were cut and then processed for c-fos immuno-histochemistry and stained for Nissl substances.The impact of photostimulation(visual input) on the expression of c-fos protein in the visual cortex were compared;differentiation of morphological parameter of neurons in visual cortex and Lateral geniculate nucleus together with results of c-fos immunohistochemistry between MS,MD amblyopia groups and normal groups were analysed statistically. The fractional anisotropy(FA),neural fiber tracts of corpus callosum and optic radiations between N4,MS4,MD4 groups were compared by diffusion tensor imaging(DTI)with tractography(DTT).ResultsBy light microscope and under Nissl staining,the LGN and visual cortical cells in amblyopia rats showed smaller size compared with normal rats;light exposure for 0.5 hour dramatically increased the number of c-fos positive neurons in the LGN and visual cortex in rats;the density ofc-fos immunoreactive cells in visual cortex of monocular deprivation amblyopia rats and monocular strabismus amblyopia rats was much higher than in normal rats(P＜0.05).By DTI,FA values of amblyopic groups in bilateral optic radiations were lower compared with the normal group,FA values of amblyopic eye in relevant optic radiations were lower compared with the normal eye(P＜0.05).ConclusionsAs one of the functional identification mark,the expression of c-fos protein in the neurons of LGN and visual cortex of amblyopia rats exceed that in the normal group,suggesting there are determinate persistence of neuronal plasticity in the LGN and visual cortex of amblyopia rats which has overgrown the critical period of visual development.The disruption in the development of bilateral optic radiations and thereduced activity of the neurons of MS and MD amblyopic groups is more than normal group.The damage of optic radiations of MS group were higherer compared with the MS group.