Trommald M, Hulleberg G
Department of Neurophysiology, University of Oslo, Blindern, Norway.
J Comp Neurol. 1997 Jan 6;377(1):15-28. doi: 10.1002/(sici)1096-9861(19970106)377:1<15::aid-cne3>3.0.co;2-m.
In the hippocampus, most excitatory synapses are located on dendritic spines. It has been postulated that the geometry of spines and/or postsynaptic density (PSD) influences synaptic efficiency and may contribute to the expression of plastic processes such as learning or long-term potentiation (LTP). Based on three-dimensional reconstructions of dentate granule cell dendrites from serial electron micrographs, we have measured head dimensions, neck cross-sectional areas, neck length, and PSD area and form of 115 spines of dentate granule cells in the medial perforant path termination zone. All dimensions showed a large variability, with up to 100-fold differences in values. A calculated diffusion index for transport of molecules through the reconstructed neck varied over a 100-fold range. The neck and head dimensions were moderately positively correlated, whereas the PSD area was strongly correlated with head volume. Distribution histograms and scatter plots of various spine dimensions did not reveal any systematic clustering, suggesting that there is a continuum of spine geometries rather than distinct classes for granule cell dendritic spines in the middle molecular layer. Transversely (n = 13) and longitudinally (n = 27) sectioned dendrites had mean spine densities of 2.66 and 1.01 spines/microns, respectively, uncorrected for so-called hidden spines. Bifurcating spines made up 2.1% of the total spine number in transversely and 2.3% in longitudinally sectioned dendrites. The twin spine heads never shared the same presynaptic bouton. Fenestrated or split PSDs shared the same presynaptic element in all but two cases, arguing against PSD division as an intermediate step in synapse formation.
在海马体中，大多数兴奋性突触位于树突棘上。据推测，树突棘的几何形状和/或突触后致密区（PSD）会影响突触效率，并可能有助于诸如学习或长时程增强（LTP）等可塑性过程的表达。基于对连续电子显微镜图像中齿状颗粒细胞树突的三维重建，我们测量了内侧穿通通路终末区内115个齿状颗粒细胞树突棘的头部尺寸、颈部横截面积、颈部长度以及PSD的面积和形态。所有尺寸都显示出很大的变异性，数值差异高达100倍。计算得出的分子通过重建颈部运输的扩散指数在100倍的范围内变化。颈部和头部尺寸呈中度正相关，而PSD面积与头部体积呈强相关。各种树突棘尺寸的分布直方图和散点图未显示出任何系统性聚类，这表明在中间分子层中，颗粒细胞树突棘的几何形状是连续的，而非存在明显的类别。横向（n = 13）和纵向（n = 27）切片的树突的平均树突棘密度分别为2.66和1.01个树突棘/微米，未对所谓的隐藏树突棘进行校正。分叉树突棘在横向切片树突中占总树突棘数的2.1%，在纵向切片树突中占2.3%。双树突棘头从不共享同一个突触前终扣。除两例情况外，有孔或分裂的PSD共享同一个突触前元件，这表明PSD分裂并非突触形成的中间步骤。
