Effects of enriched environment on the subunits N-mehyl-D-aspartate receptors at the 17th area of the visual cortex in adult amblyopia rats

Abstract

Objective To explore the effect of enriched environment on the level of NR2A and NR2B subunits of N-mehyl-D-aspartate (NMDA) receptors which belong to glutamate receptors with excitability at the 17th area of the visual cortex in amblyopia rats after the critical period, and to understand the possible mechanism of synaptic plasticity of the visual cortex in adult amblyopia rats. Methods Eighty Wistar rats were divided into normal group and experimental group by random number table.Right eyelids of all rats were sutured through the whole critical period in order to establish monocular deprivation (MD) amblyopia model.The rats in experimental group were divided into the amblyopia group, standard environment (SE) group and environmental enrichment (EE) group on P45 in random.The sutured right eyelids were opened on P46 in the SE group and EE group.All rats were sacrificed to get the 17th area of the left visual cortex on P60, P75 and P105.Three rats were used at different time points from each group.The Ⅰ-Ⅵ layers of the visual cortex area 17 were observed by using hematoxylin-eosin staining.The expression of NMDA-NR2A and NMDA-NR2B was detected by immunohistochemistry.Integrated optical density of NMDA-NR2A and NMDA-NR2B was detected by using special image analysis software (Image-Pro Plus 6.0). The use of animals complied with Regulation on the Managenment Experimental Ainimals from Shandong Eye Institute and Association for Research in Vision and Ophthalmology (ARVO). Results The positive expression of NMDA-NR2A and NMDA-NR2B were observed in the visual cortex.The positive cells were mostly round or elliptical and mainly expressed in cell membrane.The expression of NMDA-NR2A in P60, P75 and P105 from four groups had statistical differences (all at P 0.05). Conclusions The plasticity of visual cortex exists not only in the critical period but also after the critical period of visual development.EE, as a non-invasion method, can improve and recover the synaptic plasticity in visual cortex of adult rats by the expression of NMDA-NR2A and NMDA-NR2B. Key words: Amblyopia; Visual cortex; Synapse; Enriched environment; N-mehyl-D-aspartate receptors