Gitler Daniel, Takagishi Yoshiko, Feng Jian, Ren Yong, Rodriguiz Ramona M, Wetsel William C, Greengard Paul, Augustine George J
Department of Neurobiology, Duke University Medical Center, Durham, North Carolina 27710, USA.
J Neurosci. 2004 Dec 15;24(50):11368-80. doi: 10.1523/JNEUROSCI.3795-04.2004.
The functions of synapsins were examined by characterizing the phenotype of mice in which all three synapsin genes were knocked out. Although these triple knock-out mice were viable and had normal brain anatomy, they exhibited a number of behavioral defects. Synaptic transmission was altered in cultured neurons from the hippocampus of knock-out mice. At excitatory synapses, loss of synapsins did not affect basal transmission evoked by single stimuli but caused a threefold increase in the rate of synaptic depression during trains of stimuli. This suggests that synapsins regulate the reserve pool of synaptic vesicles. This possibility was examined further by measuring synaptic vesicle density in living neurons transfected with green fluorescent protein-tagged synaptobrevin 2, a marker of synaptic vesicles. The relative amount of fluorescent synaptobrevin was substantially lower at synapses of knock-out neurons than of wild-type neurons. Electron microscopy also revealed a parallel reduction in the number of vesicles in the reserve pool of vesicles >150 nm away from the active zone at excitatory synapses. Thus, synapsins are required for maintaining vesicles in the reserve pool at excitatory synapses. In contrast, basal transmission at inhibitory synapses was reduced by loss of synapsins, but the kinetics of synaptic depression were unaffected. In these terminals, there was a mild reduction in the total number of synaptic vesicles, but this was not restricted to the reserve pool of vesicles. Thus, synapsins maintain the reserve pool of glutamatergic vesicles but regulate the size of the readily releasable pool of GABAergic vesicles.
通过对所有三个突触结合蛋白基因均被敲除的小鼠的表型进行特征分析，研究了突触结合蛋白的功能。尽管这些三基因敲除小鼠能够存活且脑解剖结构正常，但它们表现出一些行为缺陷。敲除小鼠海马体培养神经元中的突触传递发生了改变。在兴奋性突触处，突触结合蛋白的缺失并不影响单个刺激诱发的基础传递，但在一串刺激期间导致突触抑制率增加了三倍。这表明突触结合蛋白调节突触小泡的储备池。通过测量用绿色荧光蛋白标记的突触囊泡蛋白2（一种突触小泡标记物）转染的活神经元中的突触小泡密度，进一步研究了这种可能性。在敲除神经元的突触处，荧光突触囊泡蛋白的相对量明显低于野生型神经元。电子显微镜还显示，在兴奋性突触处，距离活性区>150 nm的突触小泡储备池中，小泡数量也相应减少。因此，突触结合蛋白是维持兴奋性突触储备池中突触小泡所必需的。相比之下，抑制性突触处的基础传递因突触结合蛋白的缺失而降低，但突触抑制的动力学不受影响。在这些终末，突触小泡的总数略有减少，但这并不局限于突触小泡储备池。因此，突触结合蛋白维持谷氨酸能突触小泡的储备池，但调节γ-氨基丁酸能突触小泡的易释放池的大小。
