The Effect Of Group?metabotropic Glutamate Receptor On The Synaptic Transmission Efficiency In The Primary Visual Cortex Of Monocular Deprivation Amblyopia Rat

Background Glutamate is the most abundant excitatory neurotransmitter in brain,acting on its receptor and modulating synaptic transmission and plasticity of visual system.The occurrence of amblyopia is closely related to glutamate receptors in the visual cortex.Studies have confirmed that mGluRs expression was decreased in visual cortex of amblyopia rats,but functional significance remains unclear.Exploring the mechanism of mGluRs synaptic modulation is essential for the understanding of pathogenesis and pathophysiological processes of amblyopia,and for the development of drugs for the treatment of amblyopia.Objectives The aims of this study are investigating the effect of group ? metabotropic glutamate receptors(group ? mGluRs)on the synaptic transmission efficiency of neurons in the primary visual cortex of monocular deprivation amblyopia rat.Methods1 Rats were divided into groups: 14 days old SD rats were randomly divided into normal control group(NC group)and monocular deprivation group(MD group),with 8 rats in each group.To produce the model of monocular deprivation amblyopia,left eyes of the rats in MD group were sutured.According to the application of different drugs,then the rats were subdivided into four groups: in NC1 and MD1 group,the drug DHPG was applied only;in NC2 and MD2 groups,we added the drugs DHPG and LY367385;in NC3 and MD3 groups,we applied the drugs DHPG and MPEP,while in the NC4 and MD4 groups,we added the drugs LY367385,MPEP and DHPG together.2 The electrophysiological experiments: 6 weeks after birth(or more than 6 weeks),all groups were recorded the field excitatory postsynaptic potential(f EPSP)of neurons in the visual cortex of V1 area used by extracellular microelectrode recording.3 Data analysis: With f EPSP slope as a parameter,we used Spike 2 software to transform f EPSP into digital signals,and then carried on the analysis.Baseline value of f EPSP-slope as 100%,we analyzed the statistical data of the changes of f EPSP-slope after drugs applied.Results1 In the NC1 and MD1 groups,the f EPSP-slopes of the visual cortical neurons were both increased than the basic values(NC1 group,136.42±17.31%,n=8,t=-5.768,p<0.001;MD1 group,120.72±12.77%,n=11,t=-4.953,p<0.001),but the increase of NC1 group was significantly higher than that of MD1 group(t=2.280,p<0.05),that is to say,group?mGluRs agonist DHPG enhanced the synaptic transmission efficiency of visual cortex in both normal rats and amblyopia rats,but the level of increase in normal rats was higher than that in amblyopia rats;2 In NC2 and MD2 groups,the increase extent of f EPSP-slope induced by DHPG was lower than that of NC1 and MD1 groups after blocked the mGluR1 by adding LY367385(NC2 group,114.92±9.29%,n=5,t=2.641,p < 0.05,versus NC1 group;MD2 group,107.27±6.02%,n=6,t=2.410,p < 0.05,versus MD1 group),and which means that LY367385 can reduce the enhancement of DHPG on synaptic transmission efficiency in the visual cortex of both normal and amblyopia rats;3 Similarly to NC2 and MD2 groups,the increase extent of f EPSP-slope induced by DHPG was lower than that of NC1 and MD1 groups after blocked the mGluR5 by adding MPEP in NC3 and MD3 groups(NC3 group,112.59±15.33%,n=8,t=2.915,p < 0.01,versus NC1group;MD3 group,110.11±4.12%,n=7,t=2.372,p<0.05,versus MD1 group),and which means that MPEP can reduce the enhancement of DHPG on synaptic transmission efficiency in the visual cortex of both normal and amblyopia rats;4 In NC4 and MD4 groups,DHPG failed to increase f EPSP-slope in the presence of both mGluR1 and 5 antagonists(NC4 group,104.51±2.15%,n=3,t=3.080,p < 0.01,versus NC1group;MD4 group,102.83±14.92%,n=4,t=2.306,p<0.01,versus MD1 group),that is the combination of both mGluR1 and 5 antagonists can block the role of DHPG on synaptic transmission efficiency in both normal and amblyopia rats completel;5 Compared with NC2 and NC3 groups,there was no statistical difference,namely mGluR1 and 5 similarly contribute to the modulation of DHPG on f EPSP slope(NC2group,114.92±9.29%,t=-0.243,p>0.05,versus NC3 group,112.59±15.33%),and so as to MD2 and MD3 groups(MD2 group,107.27±6.02%,t=-0.831,p > 0.05,versus MD3 group,110.11±4.12%).Conclusion The effect of group?mGluRs on the synaptic transmission in the visual cortex neurons of rat with monocular deprivation amblyopia was lower than that of normal rat,and the effect of mGluR1 was equivalent to mGluR5.