AIM: To study the effect of monocular form deprivation(MD)on the synaptic density in the visual cortex of the amblyopic rats during the critical period of visual development, the visual cortical synaptophysin(SYN)expression and significance of its expression, as well as the relationship between the synaptic density and the visual function. This research will provide mechanisms underlying the pathogenesis and clinical treatment of amblyopia.

METHODS: Normal newborn Long Evans rats were randomly divided into normal control group and amblyopia model group, each with 16 rats. Both groups of rats were raised in the same environment. The normal control group did not receive any treatment. On the 13d after birth, the amblyopic model group received monocular suture to establish a classic monocular form deprived amblyopic model. Both groups of rats were received Visual evoked potential(F-VEP)detection on the 51d. Samples were taken immediately after the detection. The transmission electron microscope and Image J image analysis software were used to observe and analyse the synaptic density in the V1M of the primary visual cortex of the two groups of rats. Frozen sections of visual cortex were stained by immunofluorescence histochemical staining by bleaching method and the expression of SYN positive neurons was observed and quantitatively analyzed.

RESULTS: F-VEP examination showed that compared with the normal control group, the P2 latency of the deprived eyes in the amblyopic group was significantly long, and the amplitude of P2 wave was significantly lower than that of normal eyes(P<0.05); Transmission electron microscopy results showed that the synaptic density of the bilateral visual cortex of the amblyopic model group was significantly reduced compared with the normal control group(P<0.05), the contralateral visual cortex of the amblyopic eye decreased more significantly(P<0.05); immunofluorescence staining results showed that the brain slices in the visual cortex of the two groups were intact and the tissue structure was clear under the microscope. Compared with the normal control group, the expression intensity of SYN positive neurons in the amblyopic group was significantly reduced(P<0.01).

CONCLUSION: There is structural synaptic plasticity during the critical period of visual development. Monocular form deprivation can reduce the synaptic density, SYN expression and the visual function in the primary visual cortex of the amblyopic rats.