Harris K M, Stevens J K
Department of Neurology, Children's Hospital, Boston, Massachusetts 02115.
J Neurosci. 1989 Aug;9(8):2982-97. doi: 10.1523/JNEUROSCI.09-08-02982.1989.
Serial electron microscopy and 3-D reconstructions of dendritic spines from hippocampal area CA 1 dendrites were obtained to evaluate 2 questions about relationships between spine geometry and synaptic efficacy. First, under what biophysical conditions are the spine necks likely to reduce the magnitude of charge transferred from the synapses on the spine heads to the recipient dendrite? Simulation software provided by Charles Wilson (1984) was used to determine that if synaptic conductance is 1 nS or less, only 1% of the hippocampal spine necks are sufficiently thin and long to reduce charge transfer by more than 10%. If synaptic conductance approaches 5 nS, however, 33% of the hippocampal spine necks are sufficiently thin and long to reduce charge transfer by more than 10%. Second, is spine geometry associated with other anatomical indicators of synaptic efficacy, including the area of the postsynaptic density and the number of vesicles in the presynaptic axon? Reconstructed spines were graphically edited into head and neck compartments, and their dimensions were measured, the areas of the postsynaptic densities (PSD) were measured, and all of the vesicles in the presynaptic axonal varicosities were counted. The dimensions of the spine head were well correlated with the area of PSD and the number of vesicles in the presynaptic axonal varicosity. Spine neck diameter and length were not correlated with PSD area, head volume, or the number of vesicles. These results suggest that the dimensions of the spine head, but not the spine neck, reflect differences in synaptic efficacy. We suggest that the constricted necks of hippocampal dendritic spines might reduce diffusion of activated molecules to neighboring synapses, thereby attributing specificity to activated or potentiated synapses.
通过对海马体CA1区树突棘进行连续电子显微镜观察和三维重建，以评估关于棘突几何形状与突触效能之间关系的两个问题。首先，在何种生物物理条件下，棘突颈部可能会降低从棘突头部的突触传递到接收树突的电荷量？使用查尔斯·威尔逊（1984年）提供的模拟软件来确定，如果突触电导为1纳西门子或更低，只有1%的海马体棘突颈部足够细且长，能使电荷转移减少超过10%。然而，如果突触电导接近5纳西门子，33%的海马体棘突颈部足够细且长，能使电荷转移减少超过10%。其次，棘突几何形状是否与突触效能的其他解剖学指标相关，包括突触后致密区的面积和突触前轴突中的囊泡数量？将重建的棘突图形编辑为头部和颈部区域，并测量其尺寸，测量突触后致密区（PSD）的面积，并对突触前轴突膨体中的所有囊泡进行计数。棘突头部的尺寸与PSD面积以及突触前轴突膨体中的囊泡数量密切相关。棘突颈部直径和长度与PSD面积、头部体积或囊泡数量无关。这些结果表明，棘突头部而非棘突颈部的尺寸反映了突触效能的差异。我们认为，海马体树突棘的狭窄颈部可能会减少激活分子向相邻突触的扩散，从而赋予激活或增强的突触特异性。
