Effects Of Isoflurane On Cognition And Synaptic Interface Structure In Hippocampal CA3 Area In Aged Rats

Objective To investigate the effects of isoflurane on aged rats'cognition with Y-maze training, then observe the change ofultramicrostructure in hippocampal CA3 area after general isofluraneanesthesia by mean of electron microscope. We want to find somemorphology evidences in the research of aged rats' cognitive changes, soas to elucidate sufficiently the mechanism of cognitive dysfunction afterisoflurane anesthesia.Methods To use one-trial passive avoidance response to select 71good-remembrance 22-month-old SD rats, and then randomly dividedthem into group contrast(group C, n=33)and group isoflurane(groupâ… ,n=38). The rats in group C only inhaled mixed gas containing 40ï¼…oxygen for two hours. The rats in groupâ… were induced by inhalation of3ï¼…isoflurane, after body-righting reflex disappeared (about 10±2min),we use 1.2ï¼…isoflurane to maintain anesthesia for 2 hours. The fraction ofinspired oxygen is 40ï¼…in the course of anesthesia. We randomly took 5rats for monitoring vital sign by femoral arteriopuncture in the course ofanesthesia. Let the rats naturally wake up after anesthesia. We use Y-mazetraining to carry out the ethology observation from 24 hours after wakingup (Groupâ… ) or inhalation of 40ï¼…oxygen (group C). The training time is3 days and 20 times per day. The number of correct reaction, totalreactive time, the number of initiative avoidance and the rate of acquirethe task in 3 days are recorded.Three rats were randomly selected from each group at 24h (group C_24hand group I_24h) and 72h (group C_72h and group I_72h) after stopping oxygenor isoflurane inhalation. The right hippocampus of the aged ratsmentioned above was cut down, and then was fixed, embedded, sectionedand stained. By means of Hitachi-7500 transmission electron microscopewe observed the change of ultramicrostructure in hippocampal CA3 area,such as curvature of synaptic interface, postsynaptic density(PSD),breadth of synaptic cleft, length of synaptic active area.Resultsâ‘ The number of correct reaction in I₂₄ is 10.97±3.48, which is less than 13.57±2.62 in C₂₄ (P＜0.01); the number of initiativeavoidance in I₂₄ is 1.11±1.07, which is less than 3.20±2.59 in C₂₄ (P＜0.01). The number of correct reaction in I₄₈ is 13.53±3.42, which is lessthan 16.07±2.79 in C₄₈(P＜0.01); the number of initiative avoidance in I₄₈is 1.27±1.55, which is less than 6.45±4.97 in C4s (P＜0.01); the totalreactive time in I₄₈ is 81.93±45.01 sec, which is more than 59.27±26.37sec in C₄₈ (P＜0.05). There is no significant difference between I₇₂ andC₇₂ in every index. The rate of acquire the task in 3 days in group C is73ï¼…, which is more than 53ï¼…in groupâ… (P＜0.05).â‘¡.The elementarystructure of aged rats' hippocampal neural cell is integrated with electronmicroscope observation. The thickness of PSD in group I_24h is50.16±9.59nm, which is less than 55.83±7.80nm in group C_24h (P＜0.01);The breadth of synaptic cleft in group I_24h is 20.92±4.37nm, which ismore than 18.30±3.57nm in group C_24h (P＜0.05), and these changesrecoveried 72h after the anesthesia.Conclusion Isoflurane anesthesia may result in cognitiveimpairment in the aged rats, but the change almost recovery 72 hoursafter the anesthesia. And this phenomenon may be related to the changesof synaptic interface in CA₃ area of hippocampus. The changes of PSDand synaptic cleft were concordant with cognitive change.