Effects Of Different Concentration Isoflurane On Spatial Learning, Memory And Synaptophysin Expression In CA3 Area Of Hippocampus Of Aged Rats

Objective To investigate the change of hippocampal synaptophysin and spatial learning memory functions after isoflurane general anesthesia in aged rats.We want to find some morphology evidences in the research of aged rats' cognitive changes,so as to elucidate sufficiently the mechanism of cognitive dysfunction after isoflurane anesthesia.Methods Sixty-nine 24-month-old SD rats were randomly divided into three groups.The rats in group A(n=21)only inhaled mixed gas containing 40%oxygen for three hours.The rats in group B(n=24)were induced by inhalation of 3%isoflurane,after body-righting reflex disappeared,we used 1.2%isoflurane to maintain anesthesia for 3 hours. The fraction of inspired oxygen was 40%in the course of anesthesia.The rats in group C(n=24)were also induced by inhalation of 3%isoflurane, after body-righting reflex disappeared,we used 1.8%isoflurane to maintain anesthesia for 3 hours.The fraction of inspired oxygen was 40% in the course of anesthesia.Let the rats naturally wake up after anesthesia. Three rats were randomly taken from each group of group B and group C for monitoring vital sign by femoral arteriopuncture in the course of anesthesia.Twelve rats were randomly taken from each group to carry out the ethology observation for 7days with Morris water maze 24 hours after oxygen inhalation or isoflurane general anesthesia,escape latency and probe time were recorded.Three rats were randomly selected from each group at 24h(A_24h,B_24hand C_24h),72h(A_72h,B_72hand C_72h)and 7day(A_7d,B_7dand C_7d)after oxygen inhalation or isoflurane general anesthesia.The brains of the aged rats mentioned above were collected and then were fixed,embedded,sectioned and stained.The change of synaptophysin in hippocampus CA3 area was observed by means of Motic BA400/450 microscope and Motic imaged advanced 3.2 image analysis system,Results①.There is no significant difference between A_24h,B_24h and C_24hin escape latency(p＞0.05).The excape latency is 44.16±17.91s in B_48hand 47.41±20.94s in C_48h,Which is longer than 23.61±13.91s in A_48h(p＜0.01).The escape latency is 26.80±11.51s in B_72hand 27.08±11.64s in C_72h,Which is also longer than 14.87±8.37s in A_72h (p＜0.05).There is no significant difference in escape latency from the fourth day after oxygen inhalation or isoflurane general anesthesia to the sixth day.The probe time is no significant difference in the seventh day after oxygen inhalation or isoflurane general anesthesia.②.The mean gray scale value of the synaptophysin of the hippocampus CA3 area is 152.89±8.59s in B_24hand 160.67±4.59s in C_24h,Which is higher than 141.26±7.48s in A_24h(p＜0.05),the mean gray scale value of the synaptophysin of the hippocampus CA3 area is 161.46±5.94s in B_72hand 170.56±2.60s in C_72h,Which is higher than 144.0±4.90s in A_72h (p＜0.01),and the mean gray scale value of the synaptophysin of the hippocampus CA3 area is 171.40±4.19s in B_7dand 180.08±3.03s in C_7d,Which is higher than 138.60±6.28s in A_7d(p＜0.01).Conclusion The vital sign of aged rats is stable during the course of 1.2%and 1.8%isoflurane general anesthesia.The spatial learning memory of aged rats decrease after anesthesia,but it recovery at the fourth day after anesthesia.The expression of synaptophysin in hippocampus CA3 area is continuous down-regulated till seventh day after anesthesia,and the expression is more obvious in 1.8%isoflurane general anesthesia group.