The Impact Of Age And Visual Experience On The Expression NR_2A,NR_2B Subunits Of The NMDA Receptor In Rats Visual Cortex

Objective:To study the impact of age and visual experience on the expression NR_2A,NR_2Bsubunits of the NMDA receptor in rats visual cortex.Contents:Part 1:To observe the changes of expression in quantity of NMDA receptor subunits NR_2Aand NR_2Bfrom neonatal to 90-day wistar rats in visual cortex. Part 2:①To study the effect of visual deprivation on the expression of NR_2Aand NR_2Bin the visual cortex of critical period rats;②To observe the effect of the late-onset visual deprivation on the expression of NR_2Aand NR_2Bin the visual cortex of adult rats,to provide the molecular mechanism of the visual plasticity.Methods:Part 1:Forty neonatal healthy pureblooded wistar rats was divided into eight groups randomly,five in each group and then were killed at eight time-point 0,14,21,28,35,45,60,90d respectively,0.5μm thick sections were cut from paraffin imbedded tissue of visual cortex in coronary side then the expressions of NR_2Aand NR_2Bin the visual cortex of rats were examined by immunohistochemial methods with monoclonal anti-NR_2Aantibody and anti-NR_2Bantibody respectively.After streptomycin avidin biotin peroxidase complex(SABC)staining,microscope and computer-assisted image analyses were used to explore the developing changes of NMDA receptor subunits protein.Pictures were collected with Olympus micro-image system,integrated optical density(IOD)were determined with image analysis system. Analyzed and compared the IOD,experiment data was indicated with mean±standard deviation.Analyzed data with SPSS 11.5.Part 2:①Five neonatal wistar rats with their mother were raised in complete darkness to P21,the Control group was five rats borne in the alike environment,which were raised on a 12 h light/dark cycle to P21.②Ten 80-day-old healthy Wistar rats were randomly divided into 2 groups: Five in every group,the Late-onset visual deprivation was achieved by placing animals into a completely dark room for 10 d,the Control group were raised on a 12 h light/dark cycle for 10 days.The collection of IOD and the method of analysis were same as above.Analyzed data with SPSS11.5,adopted t-test in normal and visual deprivation groups.Results:Part 1:①The neurons in every layer lined in order.NR_2A,NR_2Breaction products were brown,mainly located in cell body,dendrites and axons of neuron. Most of the positive cells were pyramidal cells and granular cells.NR_2A,NR_2Bwere produced in neonatal rats;②The quantity of the expression of NR_2Aof neonatal rats is very low,the IOD is 9.00±3.55,then increased gradually.The climax value was reached in 35-day rats,the IOD is 203.75±9.93.Then decreased slightly and maintained stably in adults,.③The Expression of NR_2Bin neonatal rats is higher,the IOD is 56.59±7.36,and reached its climax value in 14-day,the IOD is 223.94±63.34.Then decreased gradually and reached stable by the postnatal 60-day. significant deviation existed among different ages with one-factor analysis of variance(P＜0.05).④The ratios between NR_2Aand NR_2Bincreased from the 0.07±0.02 at the P14 to the 1.33±0.13 at the P35,then decreased gradually and reached stable in adults,significant deviation existed among different ages with one-factor analysis of variance(P＜0.05).Part 2:(1)For the rats of critical period:①The IOD of NR_2Ain visual cortex of visual deprivation rats was 114.03±12.21, obviously lower than the normal group 124.63±11.76(t=3.567,P＜0.05);②The IOD of NR_2Bin visual cortex of visual deprivation rats was 235.96±32.05,obviously higher than the normal group 200.18±39.91(t=-6.739,P＜0.05).③The visual deprivation decreased the ratio between NR_2Aand NR_2B(t=4.45,P＜0.05).(2)For the adult rats:There were no discrimination of the expression of NR_2Aand NR_2Bbetween the normal group and the visual deprived group in adult rats' visual cortex.Conclusion:Part 1:The quantity of the expression of NR2A,NR2B correlated with the onset and decline of the critical period.It proposed that one of the mechanisms for experience-dependent modulation of synoptic plasticity in the visual cortex may be the regulation of NMDAR subunits.Part 2:①In critical period,visual deprivation can stop the increasing of NR_2Abut contribute to the increasing of NR_2B. As a result the ratio between NR_2Aand NR_2Bdecreased.The result indicated the construction of NMDA receptor depended on the visual experience in critical period.②This study,the construction of NMDA receptor didn't changed with the visual experience.It supposed that the visual system of adult animal changed more stable, visual experience had little influence on the visual cortex's plasticity.