【作者】 李英霞；

【导师】 雷皓；

【作者基本信息】 中国科学院研究生院（武汉物理与数学研究所） ， 无线电物理， 2006， 博士

【摘要】 钙离子(Ca²⁺)是重要的神经传导介质,在神经元的功能活动中起着极为重要的作用。生物学上,锰离子(Mn²⁺)是Ca²⁺的类似物,可通过电压门控Ca²⁺通道进入神经元,并可通过微管系统在神经细胞内传输。同时,Mn²⁺具有顺磁性,可用作磁共振成像造影剂。基于Mn²⁺的这两个特性,Lin和Koretsky在1997年提出了锰离子增强磁共振成像（MEMRI）技术,他们利用Mn²⁺作为Ca²⁺的示踪剂,显示功能或病理状态下Ca²⁺在神经细胞内外以及神经突触间的传递过程,并以此来记录和反映神经元的功能活动。经过几年的发展,该项技术已被广泛用来研究大脑功能活动,追踪神经传导路径和显示脑组织精细结构等方面。本论文首先研究了在进行MEMRI时所涉及的一些基础问题,包括锰化合物的选择、脑内注射锰化合物对神经元的影响以及不同引入锰离子方式对磁共振成像结果的影响等。综合考虑其易得性、水溶性、氧化还原性以及对水质子弛豫时间影响大小等多种因素,我们决定采用MnCl2作为锰离子增强磁共振成像的对比剂。鉴于Mn²⁺具有生物毒性,我们观察了脑内注射不同浓度MnCl2溶液对注射点附近神经元数目的影响。发现注射100 nL浓度为200mM的MnCl2溶液不会导致注射点附近神经元数量的显著减少,而相同体积的浓度为400mM的溶液会导致神经元数目明显减少。在生物体内引入外源性Mn²⁺的不同方式（如自由口腔摄入、腹腔注射和侧脑室注射等）会对MEMRI的结果产生影响。自由口腔摄入是一种较为安全的方式,但通过此种方式进入脑组织的Mn²⁺量比较少,不易产生高对比度的T1加权磁共振像。腹腔注射条件下,Mn²⁺可较快进入脑室,但是由于血脑屏障的存在使之不能快速进入脑组织,即使在使用α-氯代丙三醇部分破坏血脑屏障后也不能快速进入,说明了Mn²⁺通过血脑屏障的能力有限。侧脑室注射可使Mn²⁺更快进入脑实质,并在海马锥体细胞区及腹侧苍白球处产生明显沉积。这些研究结果说明,锰化合物的种类,Mn²⁺的浓度以更多还原

【Abstract】 Calcium ion (Ca²⁺) is an important substrate for neurotransmission, which plays an essential role in neural function. Biologically divalent manganese ion (Mn²⁺) is an analog to Ca²⁺, which can enter neurons via voltage-gated Ca²⁺ channels and be transported through neuronal microtubule system. In addition, Mn²⁺ is paramagnetic and can be used as contrast agent in magnetic resonance imaging （MRI）. Taking advantage of these properties of Mn²⁺, Lin and Koretsky developed manganese-enhanced magnetic resonance imaging （MEMRI） in 1997. Using Mn²⁺ as the tracer for Ca²⁺, they showed that, serving as the surrogate for neuronal activities, the intracellular and trans-synaptic transport of Mn²⁺ in the central nervous system could be monitored and recorded by MRI. Nowadays, this method has found wide applications in studying brain and heart activities, neuronal tracts tracing and delineation of fine cerebral neuroarchitecture etc.In this dissertation, three basic questions in MEMRI were addressed. First, which manganese compound is the most suitable for MEMRI? Based on experimental evidence and taking into account the availability, water solubility, redox properties, toxicity and relaxitivity of the manganese compounds, MnCl2 were selected for use in MEMRI. Secondly, at which concentration and dosage, intracerebrally injected MnCl2 will not cause significant toxicity to neurons near the injection site? The experiments showed that injecting 100 nL of 400mM MnCl2 solution into brain result in significant neuronal loss, but injection of the same amount of 200mM MnCl2 solution is safe. Thirdly, how should exogenous Mn²⁺ be administered into the subjects? The results showed that oral administration, though safe and less stressful, results in only minimal manganese deposition in the brain. Intraperitonially injected Mn²⁺ rapidly enters cerebral ventricles via choroid plexus in mice, but the transportation to brain parenchyma is slow due to the limited ability of Mn²⁺ to cross blood brain barrier （BBB） even when it is partly damaged by （S）-3-chloro-1,2-propanediol. In comparison, intraventricularlly injected Mn²⁺ can enter brain parenchyma more rapidly, and deposit selectively in the hippocampus and ventral globus pallidus. These studies suggest that in MEMRI one should choose the更多还原