| Objective: Mild cognitive impairment(MCI),as a transitional state that was insufficient to diagnose Alzheimer's disease(AD)but more serious than normal aging,is associated with an increased risk of developing dementia and instability.Studies found that selection of inappropriate anesthetics during surgery is associated with high incidence of MCI and patients develop into AD rapidly.To avoid aggravating preexisting cerebral impairment in these patients,it is important to carefully select the combination of anesthetics for anesthetists.Previous studies of our research group have demonstrated that neurotoxicity of isoflurane correlated positively with the doses,whereas sub-doses of propofol(20mg·kg-1·h-1)post-conditioning had protective effects on cerebral ischemia with a mechanism that activate the pathway of KCC2-GABA_A receptors.Hence,the present study screen the proper combination of isoflurane and propofol for MCI rats by way of imitating open reduction and internal fixation surgery(ORIF)under different combination of isoflurane and propofol,and discuss the regulatory mechanism of combination of isoflurane and propofol for GABA_A receptor ?1 subunit of cell surface and endoplasmic reticulum stress in MCI rats.Methods: Two parts in our experiment.Part1,To observe the effect of different doses of isoflurane and propofol on cognition of MCI rats at 14 d after ORIF.Establishment of the MCI model: Male Wistar rats were divided into control group and model group randomly,and rats of control group were only exposed bilateral common carotid artery(CCA)without bilateral narrowing,while CCA of model group were narrowed.30 d later,Morris Water Maze were used to sreen MCI rats.At 36 d,MCI rats were divided into 5 groups(n=12)randomly and then performed ORIF surgery.Sham group(group S);Group IP1,isoflurane(1%)+ propofol(20 mg·kg-1·h-1)for 3 h;Group IP2,isoflurane(1.4%)+ propofol(10 mg·kg-1·h-1)for 3 h;Group I,isoflurane(1.9 %)3 h;and Group P,propofol(40 mg·kg-1·h-1)for 3 h.Only skin incision and suture was performed on rats in group S.Y-maze reference task was used to assess the spatial learning and memory formation in MCI rats at day 14 afer ORIF surgery.Then,GABA_A receptor ?1 subunits surface protein levels were detected in the hippocampus by western blotting at 14 day after ORIF surgery and combined with results of cognitive function to determine an ideal combination of isoflurane and propofol for MCI rats.Part2,To investigate the role of GABA_A receptor ?1 subunit surface protein and endoplasmic reticulum stress play in it.MCI rats were divided into 6 groups(n=84)randomly and then performed ORIF surgery,Sham group(group S)for 3 h;Group IP1,isoflurane(1%)+ propofol(20 mg·kg-1·h-1)for 3 h;Group IP2,isoflurane(1.4%)+ propofol(10 mg·kg-1·h-1)for 3 h;Group ?-S,?-cct(30 mg· kg-1 i.p.)+ Sham 3 h;Group ?-IP1,?-cct(30 mg kg-1 i.p.)+ isoflurane(1%)+ propofol(20 mg·kg-1·h-1)3 h;and Group ?-IP2,?-cct(30 mg· kg-1 i.p.)+isoflurane(1.4%)+propofol(10mg·kg-1·h-1)3h.?-cct(t-butyl-b-carboline-3-carbox ylate)was administered to the MCI rats i.p.10 min before ORIF.The fear conditioning test were performed,and the remaining rats were sacrificed,their hippocampus isolated to study the expression of GABA_A receptor ?1 subunits surface protein levels,CHOP and caspase-12 by western blotting and Nissl's staining at 1,7 and14 days after ORIF.Results: Part1,Y maze showed that the percentage of time spent in the novel arm in group IP1 were lower than group S,but no statistically difference were found;however,compared with IP1 and S group,the percentage of time spent in the novel arm of IP2 group was impaired significantly(P<0.05).compared with group IP2,the percentage of time spent in the novel arm of group I and P were both declined markedly(P<0.05),western blotting showed that the GABA_A-?1 surface protein levels in group S presented no difference with group IP1(P>0.05),the GABA_A-?1 surface protein levels in group IP2 were higher than group I and P but lower than group IP1.Part 2,The results showed no differences in the GABA_A-?1 surface protein levels,the number of surviving neurons and the cognition between groups S and IP1(P>0.05),whereas the GABA_A-?1 surface protein levels,the number of surviving neurons on 1,7 and 14 days and the percentage of freezing time on 7 and 14 days decreased in the IP2 group compared with the IP1 group(P<0.05).Furthermore,treatment with ?cct antagonist led to the GABA_A-?1 surface protein levels,the number of surviving neurons on 1,7 and 14 days and the percentage of freezing time on 7 and 14 days significant decreased,as evidenced in groups ?S,?IP1 and ?IP2,compared with groups S,IP1 and IP2,respectively(p < 0.05).Specifically,the GABA_A-?1 surface protein levels,the number of surviving neurons on 1,7 and 14 days and the percentage of freezing time on 7 and 14 days were higher in group ?IP2 than group ?S(p < 0.05),but lower than that of group ?IP1 in the two sessions.On day 1 and day 7,the western blotting showed no differences in the expression of CHOP and caspase-12 between groups IP1 and S(P>0.05).Also,CHOP and caspase-12 protein levels in group IP1 was found to be markedly lower than group IP2(p < 0.05).Compared with group ?IP2,CHOP and caspase-12 levels in both ?S and ?IP1 decreased significantly(p < 0.05).Furthermore,the the expression of in group ?IP1 was compareable with ?S(P>0.05).On day 14,no differences were found between the six groups about levels of CHOP and caspase-12(p > 0.05).Conclusion: Isoflurane combined with propofol for general anaesthesia was better than isoflurane or propofol alone for MCI rats who underwent ORIF,and treatment with 1% isoflurane and 20 mg·kg-1·h-1 propofol was the most suitable combination.We also found that maintaining GABA_A-?1 surface protein was important in protecting the cognitive function of MCI rats.Isoflurane combined with propofol reduced ER stress and regulated GABA_A-?1 surface protein. |
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