Yeow M B, Peterson E H
Department of Zoological and Biomedical Sciences, College of Osteopathic Medicine, Ohio University, Athens 45701.
J Comp Neurol. 1991 May 15;307(3):475-86. doi: 10.1002/cne.903070310.
A common observation in studies of neuronal structure is that axons differ in the size of their synaptic boutons. The significance of this size variation is unclear, in part because we do not know how the size of synaptic boutons is related to their internal organization. The present study has addressed this issue by using three-dimensional reconstruction of serial thin sections to examine the ultrastructure of synaptic boutons that vary in size. Our observations are based on complete or near-complete reconstructions of 53 synaptic boutons contacting large neurons in the ventromedial gray matter of the upper cervical spinal cord (probable neck motor neurons). We characterized bouton size in terms of volume and total area of membrane apposed to the motor neuron surface (apposition area). Boutons vary in apposition area by a factor of 40, and there is a significant positive correlation between our two measures of bouton size. In addition, bouton size is systematically related to four ultrastructural variables: 1) total active zone area, 2) number of active zones, 3) individual active zone area, and 4) number of synaptic vesicles. The correlations between these variables and both of our measures of bouton size are positive and significant. These data suggest that bouton size may be an index of ultrastructural features that are thought to influence transmitter storage and release.
在对神经元结构的研究中，一个常见的观察结果是轴突的突触小体大小存在差异。这种大小变化的意义尚不清楚，部分原因是我们不知道突触小体的大小与其内部组织是如何相关的。本研究通过对连续薄切片进行三维重建来检查大小不同的突触小体的超微结构，从而解决了这个问题。我们的观察基于对上颈段脊髓腹内侧灰质中与大型神经元（可能是颈部运动神经元）接触的53个突触小体的完整或近乎完整的重建。我们根据与运动神经元表面相对的膜的体积和总面积（相对面积）来表征突触小体的大小。突触小体的相对面积相差40倍，并且我们对突触小体大小的两种测量之间存在显著的正相关。此外，突触小体大小与四个超微结构变量系统相关：1）总活性区面积，2）活性区数量，3）单个活性区面积，4）突触小泡数量。这些变量与我们对突触小体大小的两种测量之间的相关性均为正且显著。这些数据表明，突触小体大小可能是被认为会影响神经递质储存和释放的超微结构特征的一个指标。
