D-半乳糖致衰老大鼠脑海马外周型苯二氮受体改变及其与认知行为的相关研究

Correlation of changes of peripheral benzodiazepine receptors in hippocampus synaptosomes with cognitive impairment: experiment with D-galactose-induced senescent rats

目的观察海马突触体外周型苯二氮受体(PBR)水平对大鼠空间学习和记忆能力的影响。方法SD大鼠随机分为对照组和D-半乳糖组。D-半乳糖组动物连续皮下注射D-半乳糖(100mg/kg,每日1次)56次,对照组注射生理盐水。利用Morris水迷宫测试动物学习记忆能力后制备海马突触体,测定PBR最大结合容量(Bmax)和平衡解离常数(KD)。结果与对照组比较,D-半乳糖组动物学习记忆能力降低(P<0.001),KD无显著变化。D-半乳糖组Bmax(177.2fmol/mg±26·7fmol/mg)低于对照组(296.7fmol/mg±33.5fmol/mg)(P<0.001),海马突触体[3H]PK11195特异性结合活性与迷宫试验动物逃避潜伏期(r=-0.854)、平台象限游泳时间(r=0.845)及距离(r=0·851)显著相关(P<0.001)。结论海马突触体PBR表达量可能与大鼠空间学习和记忆有关。

Objective To investigate the effects of peripheral benzodiazepine receptor （PBR） in hippocampus synaptosomes on spatial learning and memory. Methods Twenty-four Sprague-Dawley rats of both sexes were randomly divided into 2 equal groups： D-galactose-treated group, receiving subcutaneous injection of D-galactose 100 mg/kg once a day for 56 days, and normal saline （NS） control group, receiving comparable injections of NS. Spatial learning and memory were assessed by Morris water maze test for 5 days. After the behavioral testing all rats were decapitated and the hippocampus was removed immediately. Then, the synaptosomes in hippocampus were purified by density gradient centrifugation. The PBR binding parameters, maximal binding site density （Bin.） and equilibrium dissociation constant （KD）, were estimated by radioligand [^3H ] PK11195 binding assays. Results Two weeks after the beginning of experiment the D-galactose-treated rats began to show symptoms of aging. On the 5th day of behavioral testing the D-galactose-induced aging rots presented significant impairment in water maze performance comparecl with the NS controls （P 〈0. 001）. The decrease in specific [^3H] PK11195 binding in the hippocampus synaptosomes of the D-galactose-treated group was 67.3 ± 18.6 fmol/mg, significantly lower than that of the saline control group （127.9 ± 20.1 fmol/mg, P 〈0.01 ）. The Scatchard analysis revealed that the Bin. of the D-galactose-treated group was 177.2 ±26.7 fmol/mg, significantly lower than that of the saline group （ 296.7 ±33.5 fmol/mg, P 〈 0.01 ）, and the KD of the D-galactose-treated group was 0. 503 ± 0.06 nmol/L, not significantly different from that of the saline control group （0. 502 ±0.05 nmol/L）. Correlation analysis showed that the specific [^3H] PK11195 binding in hippocampus synaptosomes was closely related to the escaping latency （ r = - 0. 854）, swimming time （ r = 0. 845 ）, and distance （ r = 0.851） in platform quadrant in Morris water maze in all rats （all P〈0.001）. Conclusion The decreased expression of PBR in hippocampus synaptosomes is possibly associated with the spatial learning-memory impairments induced by D-galactose.