不同程度和时程低温对犬创伤性脑损伤的影响

Effects of different degrees and duration of hypothermia on traumatic brain injury in dogs

目的 探讨不同程度和时程低温对犬创伤性脑损伤的影响.方法 健康犬36只,体重13～15 kg,犬龄1年.采用改进的Feeney法制备创伤性脑损伤模型.采用正交设计,根据实验因素[温度（因素A）、控温时程（因素B）]和水平[A1：正常体温（38 ℃）,A2：31℃,A3：35 ℃,B1：6 h,B2：12 h]采用L12（3×24）正交表,分为6组（n=6）：A1B1组、A1B2组、A2B1组、A2B2组、A3B1组和A3 B2组.各组均于创伤性脑损伤模型制备后20 min时开始维持目标体温.维持目标温度结束时行动脉血气分析.模型制备后24、48、72 h时进行神经功能缺陷评分（NDS）,并取静脉血样,测定血清神经特异性烯醇化酶（NSE）、髓鞘碱性蛋白（MBP）和血浆S-100β蛋白的浓度.最后一次采集静脉血样后取脑组织,测定Bcl-2、Bax的表达水平和细胞凋亡情况,计算细胞凋亡率.结果 与A1B1组或A1B2组比较,其余4组模型制备后血清NSE、MBP及血浆S-100β浓度和NDS评分降低,脑组织Bcl-2表达上调,Bax表达下调,细胞凋亡率降低（P＜0.05或0.01）;A3B1组、A3B2组、A2B1组和A2B2组血清NSE、MBP及血浆S-100β浓度依次升高,脑组织Bcl-2表达依次下调,细胞凋亡率依次升高（P＜0.01）,A2B1组、A3B2组、A2B2组和A2B1组,脑组织Bax表达依次上调（P＜0.01）,4组NDS评分差异无统计学意义（P＞0.05）.结论 低温减轻犬创伤性脑损伤的效应无程度和时程依赖性.

Objective To investigate the effects of different degrees and duration of hypothermia on severe traumatic brain injury in dogs. Methods Thirty-six one-year-old healthy dogs weighing 13-15 kg were used in this study. Traumatic brain injury model was estabhshed according to the method described by Feeney. Orthogonal design was used in this experiment. Two empirical factors： temperature （factor A） and duration （factor B） were used. Body temperature was maintained at 38 ℃ （A1）, 31 ℃ （A2） or35 ℃ （A3） for 6 h （B1） or 12 h （B2）.The dogs were divided into 6 groups： group A1B1 , A1B2, A2B1, A2B2, A3B1 and A3B2. Blood gas analysis was performed after the target temperature was maintained for the target duration. Neurological deficit was assessed and scored （0 = no deficit, 500 = severe neurological deficit） and blood samples were obtained at 24, 48 and 72 h after brain injury for determination of serum concentrations of neuron-specific enolase （NSE） and myelin basic protein （MBP） and plasma S-100β protein concentration. Brains were removed at the 72 h after brain injury for determination of Bcl-2 and Bax expression and detection of apoptosis in the brain. Results Hypothermia significantly decreased serum NSE, MBP and plasma S-100β concentrations, neuronal apoptosis and NDS scores;up-regulated Bcl-2 expression and down-regulated Bax expression in brain tissue in the 4 hypothermia groups （group A2B1, A2B2, A3B1 and A3B2） as compared with the control groups （group A1 B1, A1 B2）. Best neuroprotective effects were observed in group A3 B1 （35 ℃ for 6 h） in terms of serum NSE, NBP and plasma S-100β concentrations, neuronal apoptosis and cerebral Bax and Bcl-2 expression, but there was no significant difference in the NDS scores among the 4 hypothermia groups. Conclusion Hypothermia can provide neuroprotection in a dog model of traumatic brain injury but the neuroprotective effect is independent of the degree and duration of hypothermia.