大鼠严重烧伤后早期下丘脑NMDA受体NR1和NR2B亚基的表达

Expressions of NMDA receptor subunits NR1 and NR2B in the hypothalamus of severe burn rats

目的观察大鼠严重烧伤后早期下丘脑N-甲基-D-天冬氨酸（N-methyl-D-asparticacid，NMDA）受体NRl及NR2B亚基表达的变化，探讨严重烧伤后下丘脑-垂体-肾上腺皮质（hypothalamus-pituitary—adrenal，HPA）轴活化状态发生变化的机制。方法按随机数字表法将40只SD大鼠分为对照组和烧伤组（包括伤后6，24，48h组），并建立30％体表面积背部皮肤Ⅲ度烧伤模型，采用免疫组织化学染色、Westernblot蛋白印迹法观察大鼠下丘脑组织中NMDA受体NRl、NR2B亚基表达的变化。结果大鼠在严重烧伤后HPA轴活性显著增强，血清皮质醇浓度及血流动力学相关指标在伤后均发生了明显变化，血清皮质醇在伤后6h达到高峰，伤后48h仍显著高于对照组（P〈0．05），收缩压（SP）、舒张压（DP）、左心室收缩压（LVSP）均在伤后6h显著下降，其中SP、DP在伤后48h时仍低于对照组（P〈0．05）。Westernblot检测结果显示，烧伤各组NRl亚基表达增加，伤后24h达到高峰（1．12±0．27），与对照组（0．45±0．15）比较，差异有统计学意义（P〈0．05）；而NR2B亚基的表达明显减少，6h最为明显（0．65±0．21），与对照组（1．38±0．51）比较，差异有统计学意义（P〈0．05），48h恢复到伤前水平（1．25±0．30），与对照组比较，差异无统计学意义（P〉0．05）。下丘脑室旁核（hypothalamus paraventricular nucleus，PVN）免疫组织化学染色中获得与Westernblot相一致的结果。结论下丘脑NRl及NR2B亚基长时间的可塑性变化可能是严重烧伤后早期HPA轴活化状态发生变化的机制之一。

Objective To observe the early changes of N-methyl-D-aspartic acid （NMDA） re- ceptor subunit NR1 and NR2B expressions in the hypothalamus so as to discuss the underlying mechanism of the excitability alternation of hypothalamus-pituitary-adrenal （HPA） axis following severe burn in rats. Methods A total of 40 Sprague-Dawley rats were randomized into the control group and the experimental groups （including 6, 24 and 48 hours after burn） and a 30% total body surface area full-thickness burn was induced by immersing the shaved dorsum into boiling water for 40 s. Then, the expression changes of the NMDA receptor subunits NR1 and NR2B in the hypothalamus tissue were examined by using immuno- histochemistry and Western blot. Results There was an obvious enhancement of the excitability of HPA axis and obvious changes of serum concentration of cortisol and hemodynamics. The serum concen- trations of cortisol of the experimental groups reached the peak at 6 hour after burn and were significantly higher than the control group even 48 hours later （P 〈 0.05 ）. Systolic pressure （SP） , diastolic pressure （DP） and left ventricular systolic pressure （LVSP） of the experimental groups were all decreased at 6 hours after burn, of which SP and DP were still lower than the control group at 48 hours after burn （P 〈 0.05）. Based on the Western blot assay, the NR1 level was increased and reached the peak （ 1.12 ±0. 27） in the experimental groups and 0.45 ± 0. 15 in the control group at 24 hours after burn （P 〈 0.05 ）. In the meantime, the NR2B level was decreased significantly and reached the lowest for 0.65±0. 21 at 6 hours after burn, with statistical difference in comparison with 1.38 ±0.51 in the control group （P 〈0.05. The NR2B level recovered to pre-burn level for 1.25 ±0.30 at 48 hours in the experimental groups, with no statistical difference compared with 1.38 ± 0.51 in the control group （ P 〉 0.05 ）. The immunohistochemistry results on hypothaiamus paraventrieular nucleus （PVN） was consistent with the Western blot results. Conclusion The persistent plasticity changes of hypothalamus subunits NR1 and NR2B may be on of important mechanisms for early excitability alteration of HPA axis after severe burn.