Calverley R K, Jones D G
Department of Anatomy, University of Otago, Dunedin, New Zealand.
Brain Res Brain Res Rev. 1990 Sep-Dec;15(3):215-49. doi: 10.1016/0165-0173(90)90002-6.
The dynamic nature of synaptic connections has presented morphologists with considerable problems which, from a structural perspective, have frustrated the development of ideas on synaptic plasticity. Gradually, however, progress has been made on concepts such as the structural remodelling and turnover of synapses. This has been considerably helped by the recent elaboration of unbiased stereological procedures. The major emphasis of this review is on naturally occurring synaptic plasticity, which is regarded as an ongoing process in the postdevelopmental CNS. The focus of attention are PSs, with their characteristically discontinuous synaptic active zone, since there is mounting evidence that this synaptic type is indicative of synaptic remodelling and turnover in the mature CNS. Since the majority of CNS synapses can only be considered in terms of their relationship to dendritic spines, the contribution of these spines to synaptic plasticity is discussed initially. Changes in the configuration of these spines appears to be crucial for the plasticity, and these can be viewed in terms of the significance of the cytoskeleton, of various dendritic organelles, and also of the biophysical properties of spines. Of the synaptic characteristics that may play a role in synaptic plasticity, the PSD, synaptic curvature, the spinule, coated vesicles, polyribosomes, and the spine apparatus have all been implicated. Each of these is assessed. Special emphasis is placed on PSs because of their ever-increasing significance in discussions of synaptic plasticity. The possibility of their being artefacts is dismissed on a number of grounds, including consideration of the results of serial section studies. Various roles, other than one in synaptic plasticity have been put forward in discussing PSs. Although relevant to synaptic plasticity, these include a role in increasing synaptic efficacy, as a more permanent type of synaptic connection, or as a route for the intercellular exchange of metabolites or membrane components. The consideration of many estimates of synaptic density, and of PS frequency, have proved misleading, since studies have reported diverse and sometimes low figures. A recent reassessment of PS frequency, using unbiased stereological procedures, has provided evidence that in some brain regions PSs may account for up to 40% of all synapses. All ideas that have been put forward to date regarding the role of PSs are examined, with particular attention being devoted to the major models of Nieto-Sampedro and co-workers.(ABSTRACT TRUNCATED AT 400 WORDS)
突触连接的动态特性给形态学家带来了相当大的问题，从结构角度来看，这些问题阻碍了关于突触可塑性的观点的发展。然而，逐渐地，在突触的结构重塑和更新等概念上取得了进展。最近详细阐述的无偏倚立体学程序对此有很大帮助。本综述的主要重点是自然发生的突触可塑性，它被视为发育后中枢神经系统中一个持续的过程。关注的焦点是具有特征性间断突触活性区的PSs，因为越来越多的证据表明这种突触类型指示了成熟中枢神经系统中的突触重塑和更新。由于大多数中枢神经系统突触只能根据它们与树突棘的关系来考虑，因此首先讨论这些树突棘对突触可塑性的贡献。这些树突棘构型的变化似乎对可塑性至关重要，并且可以从细胞骨架、各种树突细胞器以及树突棘的生物物理特性的重要性方面来审视。在可能参与突触可塑性的突触特征中，PSD、突触曲率、小棘、被膜小泡、多核糖体和树突棘装置都有涉及。对每一项进行了评估。由于PSs在突触可塑性讨论中的重要性不断增加，因此对其给予了特别强调。基于包括对连续切片研究结果的考虑等多个理由，排除了它们是人为产物的可能性。在讨论PSs时，除了在突触可塑性方面的作用外，还提出了它们的各种其他作用。尽管与突触可塑性相关，但这些作用包括在提高突触效能方面的作用、作为一种更持久的突触连接类型，或者作为代谢物或膜成分细胞间交换的途径。对许多突触密度估计值和PS频率的考虑已被证明具有误导性，因为研究报告的数据各不相同，有时还很低。最近使用无偏倚立体学程序对PS频率进行的重新评估提供了证据，表明在某些脑区，PSs可能占所有突触的40%。研究了迄今为止提出的关于PSs作用的所有观点，特别关注了Nieto - Sampedro及其同事的主要模型。（摘要截选至400字）
