Hillman D E, Chen S
J Neurocytol. 1985 Aug;14(4):673-87. doi: 10.1007/BF01200804.
Our previous investigations demonstrated an increase in the size of remaining synaptic sites as an intermediate or possible alternative to sprouting plasticity. The total amount of postsynaptic contact area remained relatively constant for each target neuron even though there was a marked decrease in the number of sites on these neurons. In addition, enlarged boutons containing numerous synaptic vesicles were positioned adjacent to enlarged postsynaptic sites. The question posed by this study was to determine whether dense projections, parts of the presynaptic grids of the remaining parallel fibres, spread to cover the enlarged postsynaptic sites, or if the number of these densities increased on each site to maintain the structural organization of the presynaptic grid. In addition, the number of synaptic vesicles per bouton was quantitated to determine whether they compensated by increasing their number in relationship to the increased area of the presynaptic grid. The number of parallel fibre synapses on Purkinje cells was reduced by transection of a narrow bundle of parallel fibres accompanied by a small lesion undercutting the molecular layer to destroy granule cells contributing to this bundle. The number of presynaptic dense projections was quantitated in control and lesioned preparations (using ethanolic acid staining) in order to determine their correlation to the area of each site. In addition, the average number of synaptic vesicles in boutons was compared to the average size of boutons and the average contact area of the synaptic sites. At 3 to 7 days following partial deafferentation of Purkinje cells in adult rats, the density of dense projections of parallel fibre synapses on Purkinje cell spines remained uniform. This occurred throughout a range of reduction in the number of synapses in conjunction with a reciprocal increase in the size of sites. The finding of a uniform density of these projections and an increase in the size implies that each granule cell axon must gain dense projections. In addition, the remaining presynaptic boutons had a uniform density of synaptic vesicles even though the volume of the boutons and the area of the synaptic contact doubled. Thus, the number of synaptic vesicles gained in proportion to the total enlargement of the contact site and the bouton size. These results strongly suggest that deficits or losses in synaptic connections of parallel fibre on Purkinje cell spines produces a compensation in the total number of synaptic vesicles and presynaptic dense projections of the remaining boutons.(ABSTRACT TRUNCATED AT 400 WORDS)
我们之前的研究表明，作为发芽可塑性的一种中间或可能的替代方式，剩余突触位点的大小会增加。尽管这些神经元上的突触位点数量显著减少，但每个靶神经元的突触后接触面积总量仍保持相对恒定。此外，含有大量突触小泡的增大的终扣位于增大的突触后位点附近。本研究提出的问题是，确定剩余平行纤维的突触前网格的致密突起部分是否会扩展以覆盖增大的突触后位点，或者这些致密突起在每个位点上的数量是否会增加以维持突触前网格的结构组织。此外，对每个终扣中的突触小泡数量进行定量，以确定它们是否通过相对于突触前网格增加的面积增加数量来进行补偿。通过横断一束狭窄的平行纤维并在分子层下方进行小损伤以破坏构成该束的颗粒细胞，减少了浦肯野细胞上平行纤维突触的数量。在对照和损伤的标本中（使用乙醇酸染色）对突触前致密突起的数量进行定量，以确定它们与每个位点面积的相关性。此外，将终扣中突触小泡的平均数量与终扣的平均大小以及突触位点的平均接触面积进行比较。在成年大鼠浦肯野细胞部分去传入神经后的3至7天，浦肯野细胞棘突上平行纤维突触的致密突起密度保持均匀。这发生在突触数量减少的整个范围内，同时位点大小相应增加。这些突起密度均匀且大小增加的发现意味着每个颗粒细胞轴突必须获得致密突起。此外，尽管终扣的体积和突触接触面积增加了一倍，但剩余的突触前终扣的突触小泡密度保持均匀。因此，突触小泡的数量与接触位点和终扣大小的总增大成比例增加。这些结果强烈表明，浦肯野细胞棘突上平行纤维突触连接的缺陷或丧失会导致剩余终扣的突触小泡总数和突触前致密突起产生补偿。（摘要截断于400字）
