【作者】 王绪龙；

【导师】 梁培基；

【作者基本信息】 上海交通大学 ， 生物医学工程， 2008， 博士

【摘要】 钙离子是细胞内功能最广泛的第二信使之一,在为数众多的细胞内信号通路中发挥关键作用。研究发现,鲫鱼视网膜H1型水平细胞表达对钙离子具有高通透性的NMDA受体。为揭示NMDA受体活动性对H1型水平细胞的细胞内钙离子动态过程的作用,本论文的第一部分工作结合细胞内钙成像实验和计算模型,对NMDA受体触发的H1型水平细胞的胞内钙离子动态过程进行了研究。细胞内钙成像实验显示H1细胞的胞内钙离子平均浓度在NMDA受体激活后快速升高并缓慢下降至稳态值,呈现明显的尖峰反应;进一步的实验和模型结果提示细胞内钙库的活动性对NMDA触发的H1细胞钙信号的尖峰反应具有关键作用。钙离子对神经元之间的化学突触传递具有重要作用。视网膜H1细胞从功能上对应于亮度型水平细胞(LHC)。本论文的第二部分工作对视网膜外网状层LHC与光感受器细胞之间的化学突触传递进行了研究。我们实验室在鲫鱼视网膜铺片的细胞内记录结果发现:LHC的对光反应幅度在重复性红光刺激条件下逐渐增强,细胞的绿光反应幅度同时受到削弱;另一方面,LHC对重复性绿色闪光的反应幅度没有显著变化,细胞的红光反应强度在重复性绿光刺激后同样受到削弱。这一现象提示了LHC与光感受器之间的化学突触在重复性闪光刺激条件下呈现形式多样的可塑性。本论文通过构建离子通道模型研究了以上现象的生理机制。结果提示:(1)突触后细胞内钙离子相关的对AMPA受体的调控过程对LHC的对光反应自增强具有关键作用;(2)LHC对重复性红光和绿光刺激的不对称反应以及不同颜色光之间的互压抑可能与突触前代谢型谷氨酸受体介导的对谷氨酸释放的调控过程相关。除化学突触,电突触是神经系统中另一种广泛存在的突触传递形式。在本论文的第三部分,我们通过构建神经网络模型研究了电突触与化学突触协同工作对神经系统处理毫秒尺度时间信息的可能作用。研究表明,自然刺激的时间信息在神经系统的前级环节被编码在神经元动作电位串的时序模式中;而在皮层等高级脑区则存在对特定时间信息选择性反应的神经元集合。本论文的结果提示,在电突触与化学突触协同工作的神经网络中,不同长度的时间信息可以被有效地转化为神经元集合不同的时空放电模式,从而实现神经系统利用神经元群体活动性实现对毫秒尺度时间信息的选择性编码。更多还原

【Abstract】 Calcium is one of the most versatile intracellular second messengers,playing crucial roles in many intracellular signaling pathways.It was recently reported that NMDA receptors, which are highly permeable to Ca²⁺,are expressed in carp retinal H1-type horizontal cells.To understand the functional role of NMDA receptors for intracellular free calcium concentration([Ca²⁺_i]dynamics of H1 cells,[Ca²⁺]_i changes initiated by the activation of NMDA receptors were studied in H1 cells using both experimental and computational techniques.Fura-2 fluorescence calcium imaging showed that H1 subtype horizontal cells responded to exogenously applied NMDA with a transient[Ca²⁺]_i increase which decayed to a sustained,but elevated level of[Ca²⁺]_i.Contributions of different Ca²⁺ flux pathways underlying the time course of this increment of[Ca²⁺]_i were further explored.Intracellular calcium stores were suggested to play crucial role for the initial transient dynamics of [Ca²⁺]_i.Ca²⁺ is known to play crucial roles in the chemical synapses for neuronal communica-tion.Retinal H1 cells is also called as luminosity-type horizontal cells（LHC） according to its light response properties.The second part of this thesis introduces our work on the chem-ical synapses properties between LHC and photoreceptors in the outer retina.Previous work in our laboratory indicated that repetitive red flashes progressively strengthened the synap-tic connection between red-cone and LHC,whereas weakened that between green-cone and LHC.On the other hand,repetitive green flashes remarkably depressed the LHC’s red re-sponse,but caused little changes in the cell’s green response.This phenomena indicated that the chemical synapses between LHC and photoreceptors in the outer retina are highly modi-fiable.We tried to explore the underlying mechanisms of this phenomenon by computational model.The results suggested that:（1） the auto-enhancement effect might be induced by the Ca²⁺-dependent process on the post-synaptic AMPA receptors,which could lead to changes of the ionic channel’s properties;（2） the asymmetric response to red-and green-flashes and the mutual-chromatic suppression effects might be attributed to the regulatory effects on the pre-synaptic glutamate release. Neurons in the central nervous system（CNS） communicate with each other through both chemical and electrical synapses.We tried to explore the possible roles of electrical synapses in temporal information processing by constructing neural network models.Physiological observations indicate that neurons in the sensory levels of CNS do not respond selectively to the temporal properties of external stimuli.On the other hand,neurons which show selective response to specific temporal properties,especially the duration content,have been reported in the cortex of many species.Temporal information is therefore suggested to be transformed into the spatially distributed neuronal activities in the cortex.Results in our work show that electrical synapse can substantially contribute to the temporal-to-spatial transformation of neuronal activities,and the neuronal activities in such networks can potentially represent the durations of external stimuli.更多还原