【作者】 牛磊；

【导师】 周逸峰；

【作者基本信息】 中国科学技术大学 ， 生物物理学， 2008， 博士

【摘要】 阿片滥用仍旧是当今世界的一大危害,而处在婚育年龄的女性阿片滥用问题也日益严重。此外,日益增多的药物使用也使得在出生前受到阿片暴露的婴儿数量一直在增长。因此,胚胎期阿片暴露造成的子代生理功能的损伤问题逐渐为人们所关注。阿片类,如吗啡,能通过胎盘影响子代中枢神经系统的发育,引起一系列的生理和行为损伤,特别的,会损伤其学习和记忆能力。本工作以胚胎期吗啡暴露SD大鼠为研究模型,通过在体场电位电生理记录和动物行为学方法,研究了其空间记忆损伤和海马突触可塑性的变化,以及其视觉通路的突触可塑性变化。本工作还通过形态学方法,进一步探究了这种海马突触可塑性变化的可能机制。我们用在体场电位的方法研究了胚胎期吗啡暴露对青少年期(出生后21-31天)和成年期(三个月大)子代大鼠穿通纤维(perforant path,PP)到海马角回(dentate gyrus,DG)区的突触可塑性的影响。我们发现胚胎期吗啡暴露降低了子代大鼠海马DG区神经元的兴奋性突触后电位(excitatory postsynaptic potential,EPSP)的去增强(depotentiation,DP)而不是长时程增强(long-term potentiation,LTP),而其群体峰电位(population spike,PS)的DP和LTP都被降低了。我们还发现胚胎期吗啡暴露几乎没有影响子代大鼠海马DG区基础兴奋性和短时程突触可塑性。海马DG区被认为与空间记忆密切相关,于是我们用Y-迷宫方法检测了子代大鼠的空间记忆,发现吗啡组子代大鼠的空间记忆也受到了影响。在吗啡组子代大鼠中,PS的LTP被抑制而EPSP的LTP没有被影响,说明依赖于γ-氨基丁酸(GABA,γ-aminobutyric acid)抑制性系统的EPSP-PS增强作用被胚胎期吗啡暴露削弱了,而另有报道称胚胎期吗啡暴露大鼠的GABA调控癫痫的易感性被降低了。为此,我们推测胚胎期吗啡暴露也影响了GABA能系统,并介导了突触可塑性的变化。用免疫组化方法,我们发现胚胎期吗啡暴露减少了海马DG区的GABA阳性神经元,这一证据支持了我们的推测。行为是与大脑广泛的区域联接相关的,不同感觉通路的信息整合在其中也起了非常重要的作用,但是胚胎期吗啡暴露对感觉影响的报道却很少。阿片受体在大鼠视皮层分布丰富,于是我们用在体场电位的方法研究了胚胎期吗啡暴露对青少年期(出生后23天和30天,均处在视觉发育关键期内)和成年期(三个月大)SD子代大鼠外膝体到视皮层通路的短时程突触可塑性的影响。我们发现胚胎期吗啡暴露提高了出生后23天子代大鼠的所有刺激间隔(interstimulusinterval,ISI)的双脉冲刺激反应比(paired pulse response ratio,PPRS)和串刺激诱导的频率抑制比(frequency depression ratio,FDR),也提高了出生后30天子代大鼠的大部分ISI的PPRS,而对成年大鼠的PPRS和RRA没有影响。本工作主要有两方面的结果:其一,发现胚胎期吗啡暴露会导致子代大鼠海马DG区长时程突触可塑性的改变以及其空间记忆的损伤,GABA抑制性系统可能介导了这些作用;其二,发现胚胎期吗啡暴露会导致子代大鼠视觉关键期外膝体皮层视觉通路的短时程突触可塑性的改变。这些结果将有助于解释存在于孕期阿片滥用母亲的孩子中的知觉损伤。更多还原

【Abstract】 More and more research focused on the damages to opiates abuse, especially to the abuse among pregnant women. Besides, prenatal exposure to opiates has becoming a sever problem as more and more medication were used nowadays. Hence, prenatal opiates exposure induced dysfunction in offspring is gradually becoming of major concern. Opiates, such as morphine, can cross the placenta to affect the development of the central nervous system and thereby result in a series of physical and behavioral dysfunctions, especially the deficits of learning and memory. The present study investigated the impaired spatial memory and hippocampal synaptic plasticity alteration, as well as synaptic plasticity alteration of visual pathway, induced by prenatal morphine exposure of SD rats, detected by in vivo local field potential (LFP) recording and behavioral test. Furthermore, we investigated the mechanisms of synaptic plasticity in hippocampus and visual pathway with morphological methods.We investigated the alterations of synaptic plasticity in the perforant path (PP) dentate gyrus (DG) pathway induced by prenatal morphine exposure in juvenile (postnatal day 21-31, PND 21-31) and adult offspring (three months) by LFP recording. We found that prenatal morphine exposure reduced depotentiation (DP), but not long-term potentiation (LTP), of the EPSP slope. However both LTP and DP of the EPSP slope were depressed in prenatal morphine exposed juvenile offspring. The basal synaptic transmission and the short-term synaptic plasticity in DG areas were almostly unaltered. The morphine group also showed poorer performance for the Y-maze task than the control group, suggesting a imapired spatial memory. Depressed PS LTP, but not EPSP LTP, in the morphine group suggested that prenatal morphine exposure changed GABAergic inhibition, which mediates EPSP-spike potentiation. Then a loss of GABA-containing neurons in the DG area of the morphine group was observed using immunohistochemistry.Behavior is highly controlled by different brain areas, especially the integration of signals from different sensory systems. However, the effects of prenatal morphine exposure on sensory systems remain unclear. Opiates receptors are abundant in rat visual cortex. So we investigated the short-term plasticity of geniculo-cortical visual pathway during critical period and adult offspring by LFP recording. We found that prenatal morphine exposure increased the paired pulse response ration (PPRS) of all interstimulus intervals (ISI) and the frequency depression ratio (FDR) of all frequencies. It also increased most of PPRS of PND 30 offspring, but not the PPRS and FDR of adult offspring.Taken together, our results suggest that prenatal morphine exposure impairs the juvenile offspring’s dentate synaptic plasticity and spatial memory, and that decreased GABAergic inhibition may play a role in these effects. And also prenatal morphine exposure altered the short-term synaptic plasticity of geniculo-cortical visual pathway during critical period. These findings might contribute to an explanation for the cognitive deficits in children whose mothers abuse opiates during pregnancy.更多还原