脑发育期甲状腺功能低下对大鼠脑功能的影响

Effects of hypothyroidism on the development of brain functions in rat

目的:探讨脑发育期甲状腺功能低下对大鼠脑功能的影响及甲状腺激素作用的关键期。方法:大鼠饮含质量浓度为0.3 g/L甲硫咪唑的自来水诱发脑发育不同时期甲状腺功能低下大鼠模型,E1组为胚胎期甲状腺功能低下模型鼠,P1组为生后1～50 d甲状腺功能低下模型鼠,P30组为生后30～50 d甲状腺功能低下模型鼠,N组为正常对照鼠。放射免疫法测定大鼠血清游离三碘甲腺原氨酸(FT3)和血清游离甲状腺素或四碘甲腺原氨酸(FT4)。生后50 d大鼠通过冷热刺激反应、斜板和悬吊实验、旷场实验和Y迷宫实验测定大鼠的躯体感觉、运动、情感行为和学习记忆功能,TUNEL法检测脑组织细胞凋亡,并用图象分析系统计数。结果:实验组大鼠血清FT3、FT4水平明显降低;P1组大鼠冷热刺激反应时间明显延长,而E1和P30组大鼠冷热刺激反应时间与对照组无显著差异;P1组大鼠悬吊时间明显缩短,E1和P30组大鼠悬吊时间与对照组无显著差异;P1和P30组大鼠斜板转体时间明显延长,E1组大鼠转体时间与对照组无显著差异;P1和P30组大鼠旷场穿格得分明显增多,P1组大鼠穿格得分明显高于P30组,E1组大鼠穿格得分与对照组无显著差异,P1和P30组大鼠旷场后肢站立次数和粪便排出粒数明显减少,E1组大鼠后肢站立次数和粪便排出粒数与对照组无显著差异;P1和P30组大鼠Y迷宫正确反应率明显降低,P1组大鼠正确反应率明显低于P30组,P1组大鼠Y迷宫达标所需天数明显增加、记忆保持率明显降低,E1组大鼠正确反应率、达标所需天数和记忆保持率与对照组无显著差异,P30组大鼠达标所需天数和记忆保持率与对照组无显著差异;P1和P30组大鼠大脑皮层细胞凋亡数明显增加,P1组大鼠大脑皮层细胞凋亡数明显多于P30组,P1组大鼠海马和小脑细胞凋亡数明显增加。结论:脑发育期甲状腺功能低下可导致大鼠脑功能发育障碍,其发生与脑组织细胞凋亡增多有关,不同脑功能发育的甲状腺激素作用的关键期有差异。

Aim： To study the effects of hypothyroidism on the development of brain functions and the critical action period of thyroid hormone in rat. Methods： The rat pups with hypothyroidism in different periods of brain development were induced by methimazole solution of 0. 3 g · L^（-1） mass concentration added in the drinking water. The rat pups were randomly divided into 4 groups, group E1 （ hypothyroidism during embryo）, group P1 （hypothyroidism from postnatal day 1 to 50）, group P30 （hypothyroidism from postnatal day 30 to 50） and group N （control）. Serum free triiodothyronine （ FT3 ） and thyroxine or tetraiodothyronine （ FT4 ） of the rat were determined by radioimmunoassay. At postnatal day 50, the cold and hot reaction time, over hanging and inclined plane test, open field test, and Y maze test of the rat were measured to evaluate the functions of somatic sensation, body move learning and memory respectively. The apoptosis of the brain tissues at pos mined via terminal deoxynucleotidyl transferase-mediated biotin dUTP nick ment, emotion behavior, and tnatal day 50 in rat was deter- end labeling （TUNEL） staining, and the positive staining cells were counted via an image analysis system. Results： The serum concentrations of FT3 and FT4 were significantly lower in the rat of the experimental groups. The cold and hot reaction times prolonged significantly in the rat in group P1, and they were not significantly greater in the rat in group E1 and P30 than in group N. The over hanging times shortened significantly in the rat in group P1, and they were not significantly smaller in the rat in group E1 and P30 than in group N. The turning times of inclined plane prolonged significantly in the rat in group P1 and P30, and they were not significantly greater in the rat in group E1 than in group N. The crossing scores of open field test increased significantly in the rat in group P1 and P30, and they were significantly higher in the rat in group P1 than in group P30 and they were not significantly higher in the rat in group E1 than in group N. The rearing numbers and defecation numbers in open field test decreased significantly in the rat in group P1 and P30, and they were not significantly smaller in the rat in group E1 than in group N. The correct reaction rates in Y maze test decreased significantly in the rat in group P1 and P30, and they were significantly lower in the rat in group P1 than in group P30. The learning days increased and memory keeping rates decreased significantly in Y maze test in the rat in group P1. The abilities of learning and memory in the rat in group E1 were not significantly different from that in group N. The learning days and memory keeping rates in the rat in group P30 were not significantly different from that in group N. The apoptosis cells in the cerebral cortex increased significantly in the rat in group P1 and P30, and they were greater significantly in the rat in group P1 than in group P30. The apoptosis ceils in the hippocampi and cerebellum increased significantly in the rat in group P1. Conclusion：The developments of brain functions retard in the rat with hypothyroidism, which is closely related to the increased apoptosis in the brain tissues. The critical action periods of thyroid hormone for the development of different brain functions are different in rat.