苯并[a]芘亚慢性染毒对大鼠海马胆碱能系统的影响

Effects of subchronic benzo[a]pyrene exposure on hippocampal cholinergic system in rats

目的通过观察亚慢性染毒苯并[a]芘（B[a]P）对大鼠神经行为及海马组织中乙酰胆碱（Ach）含量、胆碱酯酶（AChE）活力和乙酰胆碱受体d7亚型（nAChRα7）mRNA和蛋白表达的影响，探讨B[a]P的神经毒性机制。方法选择60只健康雄性SD大鼠，随机分为空白对照组，溶剂对照组，1．0、2．5、6．25mg／kgB[a]P染毒组，隔日腹腔注射连续染毒90d。Morris水迷宫和跳台试验检测大鼠学习记忆能力。碱性羟胺法检测海马组织Ach含量，DNTB法检测AChE活力。荧光定量PCR和Western-blot法分别检测海马组织nAChRα7mRNA和蛋白表达水平。结果Morris水迷宫、跳台试验结果显示，2．5、6．25mg／kgB[a]P组大鼠学习记忆能力比空白和溶剂对照组大鼠明显下降，差异有统计学意义（P〈0．05）。2．5、6．25mg／kgB[a]P组大鼠海马组织Ach含量明显低于空白、溶剂对照和1．0mg／kgB[a]P组，差异有统计学意义（P〈0．05），6．25mg／kgB[a]P组AChE活力明显低于空白对照、溶剂对照和1．0mg／kgB[a]P组，差异有统计学意义（P〈0．05）。各组之间nAChRα7mRNA和蛋白表达水平的差异无统计学意义（P〉0．05）。大鼠海马组织Ach含量与大鼠平均逃避潜伏期和总路程呈负相关（相关系数r分别为-0．567和-0．503，P〈0．01），与平台象限滞留时间呈正相关（r=0．800，P〈0．01）。结论亚慢性染毒B[a]P可损伤大鼠学习记忆功能，其机制与大鼠海马组织Ach含量下降有关。

Objective To observe the effects of subchronic benzo[a]pyrene （B[a]P） exposure on the neurobehavior and hippocampal acetylcholine （Ach） level, acetylcholinesterase （ACHE） activity, and mRNA and protein expression of nicotinic acetylcholine receptor α7 subtype （nAChR α7） in rats, and to investigate the neurotoxic mechanism of B[a]P. Methods Sixty healthy male SD rats were randomly divided into blank control group, solvent control group, and B [a]P exposure groups. Each rat in the exposure groups was intraperi- toneally injected with B[a]P at 1.0, 2.5, or 6.25 mg/kg once every other day for 90 days. The learning and memo- ry ability of the rats was examined by Morris water maze test and step-down test; the hippocampal Ach level was measured by alkaline hydroxylamine method; the AChE activity was measured by DNTB method; the mRNA and protein expression levels of hippocampal nAChR α7 were measured by quantitative PCR and Western blot. Results The 2.5 and 6.25 mg/kg B[a]P exposure groups showed significantly lower learning and memory abili- ties than the blank control group and solvent control group （P〈0.05）; also, the two groups had significantly low- er hippocampal Ach levels than the blank control group, solvent control group, and 1.0 mg/kg B[a]P exposure group （P〈0.05）. The 6.25 mg/kg B[a]P exposure group showed significantly lower hippocampal AChE activity than the blank control group, solvent control group, and 1.0 mg/kg B[a]P exposure group （P〈0.05）. There were no significant differences in the mRNA and protein expression levels of nAChR a7 among all groups （P〉0.05）. The hippocampal Ach level was negatively correlated with the mean escape latency period and total distance travelled （r=-0.567, P〈0.01; r=-0.503, P〈0.01） but positively correlated with the time in platform quadrant （r=0.800, P〈0.01 ）. Conclusion Subchronic B[a]P exposure may impair the learning and memory ability inrats, which is related to the downregulation of hippocampal Ach level.