【作者】 曹秀菁；

【导师】 阮迪云；

【作者基本信息】 中国科学技术大学 ， 生物物理学， 2008， 博士

【摘要】 慢性铅暴露可以引起学习记忆和认知功能的损伤,长时程增强(long-termpotentiation,LTP)被认为是与学习记忆相关的一种突触可塑性模型,被广泛应用于研究学习记忆的细胞机制。已有研究结果表明,在发育早期(孕期和哺乳期),慢性铅暴露损伤了大鼠空间学习记忆,同时损伤了海马CA1区和DG区的LTP的诱导。目前临床上治疗铅中毒的主要药物为鳌合剂,由于其并不能修复因铅引起的学习记忆损伤及其本身的副作用等弊端,鳌合剂不适合长期低铅暴露的儿章。因此,积极探索治疗效果明显且能有效修复其学习记忆损伤的药物和有关心理行为干预方法显得意义重大。有文献报道腺苷蛋氨酸(S -adenosyl-L-methionine,SAM)能降低铅中毒大鼠及病人血铅浓度及升高血δ-氨基乙酰丙酸脱水酶(δ-Aminolevulinic Acid Dehydratase,ALAD)活力,但其对铅暴露导致的学习记忆功能损伤有无作用国内外未见报道,由于该药对儿童尚未发现明显的毒副作用,因此对该药进行进一步的研究非常有实际意义。丰富的环境刺激这一低成本低风险的心理行为干预方法已被广泛用于如低出生体重、缺血缺氧性脑病等脑发育异常的干预,对于发育早期铅中毒的神经毒性方面的干预研究较少。本文运用Morris水迷宫作为大鼠空间学习记忆的测试工具,并用在位场电位记录的方法在发育早期(孕期和哺乳期)慢性铅暴露大鼠模型上分别研究了药物腺苷蛋氨酸和心理行为干预——丰富的环境刺激对发育早期慢性铅暴露造成的空间学习记忆和突触可塑性损伤的修复和保护作用,主要的研究方法和结果如下:1.自母鼠受孕第1天至仔鼠断奶为止给予母鼠1.5g/L的醋酸铅饮用水染铅,对照组则饮用自来水,仔鼠断奶后选取雄性仔鼠每天腹腔注射20mg/kg的SAM或10ml/kg的生理盐水,为期22天,在44—54天时进行Morris水迷宫试验及在海马DG区记录兴奋性突触后电位(excitatory postsynaptic potential,EPSP)和群峰电位(population spike,PS),并检测血铅和血、脑、海马的氧化指标。结果表明:发育早期慢性铅暴露可以明显延长大鼠在水迷宫的逃避潜伏期、缩短在原平台象限的游泳时间,并且明显降低DG区诱导的EPSP和PS LTP幅度,而在铅+SAM组发现其对铅暴露引起的空间学习记忆损伤和海马LTP损伤有明显的改善作用。同时还发现给予SAM能降低铅组大鼠的血铅浓度,提高了肝脏、脑及海马组织中GSH含量,降低了肝脏、脑组织中MDA含量。结果提示SAM对临床上慢性铅中毒儿童,尤其对学习记忆功能损伤的修复可能具有一定意义。2。自母鼠受孕第1天至仔鼠断奶为止给予母鼠1.5g/L的醋酸铅饮用水染铅,对照组则饮用自来水,21天断奶后停止喂铅,将两组仔鼠中的雄鼠用以接下来的实验:两组中各随机挑选一半为普通环境饲养,另一半在丰富的环境条件下饲养,直至实验结束,这样就将动物最终分成了四组:正常对照组(Con)、对照+丰富环境组(Con/EE)、铅组(Pb)、铅+丰富环境组(Pb/EE)。在大鼠出生后56天时对四组大鼠实施Morris水迷宫试验及在海马DG区记录兴奋性突触后电位(excitatory postsynaptic potential,BPSP)和群峰电位(population spike,PS),结果发现丰富的环境刺激能修复发育期铅暴露所致的空间学习记忆损伤和因铅暴露而受损的大鼠海马DG区的EPSP和PSLTP,与对照组相比差异无显著性。更多还原

【Abstract】 Chronic developmental lead exposure is known to be associated with learningand memory and cognitive dysfunction in children. Synaptic plasticity such aslong-term potentiation (LTP) is believed to be the mechanism underling certain typeof learning and memory. The hippocampus-dependent spatial learning and memoryare correlated closely with hippocampal LTP, impairment of which often leads tomemory deficits. Previous studies have demonstrated that Pb impairs LTP of CA1 invitro and LTP of dentate gyrus in vivo. At present, chelation therapy is popular fortreating lead-induced neurotoxicity. But the common chelation agents have manyadverse effects and are incapable of alleviating lead-induceed neurotoxicity. It is veryimportant to explore medicine and intervention to rescue the impairment of learningand memory induced by lead. S-adenosyl-L-methionine (SAM) has beendemonstrated effective in reducing blood lead concentation and improving ALADactivity in humans and rats. But it is not clear if SAM is helpful to rescue theimpairment of learning and memory induced by lead. Enriched environment(EE) hasbeen adopted to interfere some brain damage such as very low birth weight andhypoxic-ischemic encephalopathy(HIE).Epidemiological studies showed that thechildren exposed to low lead from fortunate socioeconomic environments werecognitively intact while those in poor socioeconomic environments were cognitivelyimpaired. It is not very clear about the change of synaptic plasticity by EE treatmenton lead-exposed rats. In this thesis, the studies were carried out to investigate SAMand EE on the impairment of spatial learning and memory and LTP induced bydevelopmental lead exposure respectively. The results as follows:1.Rats drank 1500ppm lead acetate (PbAc) solution or distilled water throughout gestation and lactation. After weaning at postnatal day 22, one half of the control and lead-exposed male offspring were intraperitoneally injected 20 mg SAM/kg daily over a period of 20-22 days. Electrophysiological and Morris Water maze (MWM) test were performed at 44-54 days of age. The blood lead concentration and oxidative stress in liver, brain and hippocampus were also detected in the four groups as well. The result showed that the impaired learning ability induced by lead could be improved significantly by SAM. Furthermore, our results revealed that EPSP LTP and PS LTP impairments induced by lead were also ameliorated by SAM treatment. A significant recovery of blood lead, liver, brain glutathion (GSH) and malondialdehyde (MDA) level was clearly produced in lead-exposed rats after SAM treatment as well. This study showed that SAM is beneficial in the treatment of lead intoxication especially in the rescue of learning and memory impairment induced by lead and deserves more detailed research.2. Rats drank 1500ppm PbAc solution or distilled water throughout gestation and lactation. After weaning at postnatal day 21, one half of the control and lead-exposed male offspring were given the environmental enrichment treatment through all experiments until tested. Electrophysiological and Morris Water maze test were performed at 8 weeks of age. The result showed that the impaired learning ability induced by lead could be reversed by EE. Furthermore, our results revealed that EPSP LTP and PS LTP impairments induced by lead were also reversible by EE experience.更多还原