Geinisman Y, Morrell F, de Toledo-Morrell L
Department of Cell Biology and Anatomy, Northwestern University Medical School, Chicago, IL 60611.
Brain Res. 1987 Oct 13;423(1-2):179-88. doi: 10.1016/0006-8993(87)90838-9.
Axospinous synapses were examined in the molecular layer of the rat dentate gyrus. Serial section analysis of synapses, which exhibited a discontinuity of the postsynaptic density (PSD) in at least one consecutive section, was performed. Reconstruction of each discontinuous PSD was made in a plane perpendicular to that of serial sections. The results obtained confirm earlier observations that profiles of 'perforated' synapses visualized in random sections of osmicated material are produced by sectioning of synapses with perforated and horseshoe-shaped PSDs. Additionally, it has been found that two other synaptic subtypes, namely synapses with notched and segmented PSD, contribute to the number of profiles of 'perforated' synapses. Synaptic contacts with notched PSD are characterized by an indentation of an otherwise continuous PSD, relatively small dimensions and simple shape. They appear to be unrelated to the category of synapses with discontinuous PSD. Synaptic contacts with segmented PSD are distinguished by the presence of 2-5 discrete PSD segments at the interface between a presynaptic axon terminal and a postsynaptic dendritic spine. Some PSD segments exhibit 1-3 perforations, while others are horseshoe-shaped. It is postulated that the segmented PSD may evolve through the stages of perforated and horseshoe-shaped PSD to form a specialized synaptic contact of an unusually high efficacy. Every PSD segment is a component of a separate synaptic complex, each one comparable to that of a small, simple-shaped synapse. A concerted activation of several synaptic complexes belonging to a single synaptic junction may provide a mechanism for an amplification of synaptic transmission.
对大鼠齿状回分子层中的轴棘突触进行了检查。对突触进行了连续切片分析，这些突触在至少一个连续切片中表现出突触后致密部（PSD）的不连续性。在与连续切片平面垂直的平面上对每个不连续的PSD进行重建。所得结果证实了早期的观察结果，即在经锇酸处理材料的随机切片中可视化的“穿孔”突触轮廓是由具有穿孔和马蹄形PSD的突触切片产生的。此外，还发现另外两种突触亚型，即具有切口状和分段状PSD的突触，也构成了“穿孔”突触轮廓的数量。具有切口状PSD的突触接触的特征是原本连续的PSD有一个凹陷，尺寸相对较小且形状简单。它们似乎与具有不连续PSD的突触类别无关。具有分段状PSD的突触接触的特征是在突触前轴突终末和突触后树突棘之间的界面处存在2至5个离散的PSD片段。一些PSD片段有1至3个穿孔，而其他的是马蹄形。据推测，分段状PSD可能通过穿孔状和马蹄形PSD阶段演变而来，以形成一种效能异常高的特殊突触接触。每个PSD片段都是一个单独突触复合体的组成部分，每个复合体都与一个小的、形状简单的突触相当。属于单个突触连接的几个突触复合体的协同激活可能为突触传递的放大提供一种机制。
