Effects Of Hypothermia During Anesthesia On Learning And Memory Ability And Hippocampal Apoptosis In Neonatal Rats

Objective:To investigate the effects of hypothermia on learning and memory ability and hippocampal apoptosis in neonatal rats and the role of p-ERK and p-CREB in anesthesia.Methods:80 of SD Newborn rats born 7d were divided into four groups（n=20）:control group（Group C）,anesthesia Group（Group A）,anesthesia hypothermia group（Group AH）and physical hypothermia group（Group H）.Group C was Intraperitoneal injected of 0.1 ml saline and a heating pad to maintain rectal temperature in 38³9℃;Group A was intraperitoneal injected with 25mg/kg of propofol 0.1 ml,each 20min additional initial dose of 1/2,anesthesia to maintain 2 H,the same method to maintain rectal temperature in 38³9℃.The anesthesia mode and time of Group AH are the same as Group A,rats do not keep warm during anesthesia,control room temperature is 23℃,make body temperature drop naturally;Group H was intraperitoneal injected 0.1 ml saline,control room temperature is 23℃,make body temperature drop naturally.The four groups of rats sustained oxygen inhalation during anesthesia,from the beginning of anesthesia to the end of anesthesia,every20min record of oxygen saturation and temperature changes,marking time points for T₀^T₆.Immediately after the anesthesia recovered,each group randomly took 10 rats,5 using Western blot to detect hippocampal phosphorylation-extracellular signal-regulated kinase（p-ERK）,phosphorylation-cyclic adenosine triphosphate response element binding protein（p-CREB）expression.The remaining 10 rats in each group were kept up to 30d for the test of their spatial learning and memory ability,and5 rats were detected respectively in hippocampus p-ERK,p-CREB expression and hippocampal apoptosis rate in each group.Results:There was no statistically significant difference between the SpO₂ of four groups of rats（P>0.05）.Compared with Group C and A,the rectal temperature of Group AH and H decreased significantly（P<0.05）,at T₃ point,the body temperature was reduced to about 25℃,followed by the end of the anesthesia and the two groups of rats’body temperature remained at this level;At 7 days age:（1）Compared with Group C and A,Group AH and H hippocampal tissue apoptosis rate increased（P<0.05）,there were no significantly different between Group C and Group A,Group AH and Group H（P>0.05）,there was no obvious interaction between anesthesia and hypothermia on the apoptosis rate of hippocampal tissue（P>0.05）.（2）Compared with Group C and A,Group AH and H p-ERK and p-CREB protein expression significantly reduced（P<0.05）,there were no significantly different between Group C and Group A,Group AH and Group H（P>0.05）,there was no significant interaction between anesthesia and hypothermia on the expression of p-ERK and p-CREB（P>0.05）.At 36 days age,（1）There was no statistically significant difference between the number of the crossing platform and the duration of the original platform quadrant in four groups of rats escaping latency（P>0.05）.（2）There was no statistically significant difference in the expression of p-ERK and p-CREB protein in four groups of rats（P>0.05）.（3）And there was no statistically significant difference in the apoptosis rate of hippocampal tissue in four groups of rats（P>0.05）.Conclusion:In The rate of apoptosis in hippocampal tissue of neonatal rats can be increased when the temperature drops to25℃during anesthesia,and the mechanism might be related to the decrease of p-ERK and p-CREB expression,but there was no significant effect on the long-term learning and memory ability.