Li Jianli, Cline Hollis T
Department of Cell Biology, The Scripps Research Institute, La Jolla, California 92037, USA.
J Comp Neurol. 2010 Jun 15;518(12):2365-81. doi: 10.1002/cne.22338.
Despite considerable progress in understanding the molecular components of synapses in the central nervous system, the ultrastructural rearrangements underlying synaptic development remain unclear. We used serial section transmission electron microscopy and three-dimensional reconstructions of the optic tectal neuropil of Xenopus laevis tadpoles to detect and quantify changes in synaptic ultrastructure over a 1-week period from stages 39 and 47, during which time the visual system of Xenopus tadpoles becomes functional. Synapse density, presynaptic maturation index, and number of synapses per axon bouton increase, whereas the number of DCVs per bouton decreases, between stages 39 and 47. The width of the synaptic cleft decreased and the diameter of postsynaptic profiles increased between stages 39 and 47 and then remained relatively unchanged after stage 47. We found no significant difference in synapse maturation between GABAergic and non-GABAergic synapses. To test the effect of visual experience on synaptogenesis, animals were deprived of visual experience for 3 days from stage 42 to 47. Visual deprivation decreased synapse maturation and the number of connections per bouton. Furthermore, visual deprivation increased the number of DCVs per bouton by more than twofold. The visual-deprivation-induced decrease in synaptic connections is specific to asymmetric non-GABAergic synapses; however, both symmetric GABAergic and asymmetric synapses show comparable increases in the number DCVs with visual deprivation. In both the control and the visually deprived animals, the number of DCVs per bouton is highly variable and does not correlate with either synapse maturation or the number of connected partners per bouton. These data suggest that synaptogenesis and DCV accumulation are regulated by visual experience and further suggest a complex spatial and temporal relation between DCV accumulation and synapse formation.
尽管在理解中枢神经系统突触的分子成分方面取得了相当大的进展，但突触发育背后的超微结构重排仍不清楚。我们使用连续切片透射电子显微镜和非洲爪蟾蝌蚪视顶盖神经毡的三维重建，来检测和量化从第39阶段到第47阶段的1周时间内突触超微结构的变化，在此期间非洲爪蟾蝌蚪的视觉系统开始发挥功能。在第39阶段和第47阶段之间，突触密度、突触前成熟指数以及每个轴突终扣的突触数量增加，而每个终扣的致密核心囊泡（DCV）数量减少。在第39阶段和第47阶段之间，突触间隙宽度减小，突触后轮廓直径增加，然后在第47阶段后保持相对不变。我们发现GABA能突触和非GABA能突触之间的突触成熟没有显著差异。为了测试视觉经验对突触发生的影响，从第42阶段到第47阶段剥夺动物3天的视觉经验。视觉剥夺降低了突触成熟度和每个终扣的连接数量。此外，视觉剥夺使每个终扣的DCV数量增加了两倍多。视觉剥夺引起的突触连接减少特定于不对称非GABA能突触；然而，对称GABA能突触和不对称突触在视觉剥夺时DCV数量均有类似增加。在对照动物和视觉剥夺动物中，每个终扣的DCV数量都高度可变，并且与突触成熟度或每个终扣的连接伙伴数量均无相关性。这些数据表明突触发生和DCV积累受视觉经验调节，并进一步表明DCV积累与突触形成之间存在复杂的时空关系。
