Bower J M, Haberly L B
Proc Natl Acad Sci U S A. 1986 Feb;83(4):1115-9. doi: 10.1073/pnas.83.4.1115.
Pyramidal cells in piriform cortex receive excitatory inputs from two different sources that are segregated onto adjacent segments of their apical dendrites. The present studies show that excitatory postsynaptic potentials (EPSPs) evoked by primary olfactory tract afferents that terminate on distal apical segments display paired shock facilitation whereas ESPSs evoked by intrinsic association fibers that terminate on proximal apical segments do not. An ultrastructural comparison of the presynaptic elements of these two fiber systems has revealed that the facilitating olfactory tract afferent synapses have a much lower packing density of synaptic vesicles than do the nonfacilitating association fiber synapses. Further, a search of the literature has revealed that where both morphological and physiological data are available for the same synapses, this same correlation appears to apply. We propose a hypothesis to account for this correlation based on synaptic vesicles to buffer internal calcium and the biochemical characteristics of preterminal calcium-dependent mechanisms affecting the number of vesicles available for release.
梨状皮质中的锥体细胞从两个不同来源接收兴奋性输入，这些输入分隔在其顶端树突的相邻节段上。目前的研究表明，终止于顶端远端节段的初级嗅束传入纤维诱发的兴奋性突触后电位（EPSP）表现出双脉冲易化，而终止于顶端近端节段的内在联合纤维诱发的EPSP则没有。对这两种纤维系统突触前成分的超微结构比较显示，具有易化作用的嗅束传入突触的突触小泡堆积密度比不具有易化作用的联合纤维突触低得多。此外，对文献的检索表明，在同一突触既有形态学数据又有生理学数据的情况下，这种相同的相关性似乎也适用。我们提出一个假说，基于突触小泡缓冲细胞内钙以及影响可用于释放的小泡数量的终末前钙依赖性机制的生化特性来解释这种相关性。
