Oka Y, Ichikawa M
Zoological Institute, Faculty of Science, University of Tokyo.
J Comp Neurol. 1991 Feb 8;304(2):161-71. doi: 10.1002/cne.903040202.
In our previous light microscopic studies (Oka et al., Brain Res. 367: 341-345, '86; Oka and Ichikawa, J. Comp. Neurol. 300: 511-522, '90), we reported that there are at least two types of terminal nerve (TN) cells based on cell size and immunoreactivity: type I cells had large cell bodies, while type II cells had smaller cell bodies. Type I TN cells were immunoreactive to gonadotropin-releasing hormone (GnRH) and may be the major source of GnRH-immunoreactive fibers that are widely distributed throughout the brain. Type II TN cells, on the other hand, were not immunoreactive to GnRH. In the present paper, we examined the cytology and synaptology of these two types of TN cells with electron microscopy. Type I TN cell bodies were found to have morphological characteristics similar to those of other peptide-synthesizing neurons and are likely to be actively synthesizing GnRH. The frequent occurrence of coated vesicles close to the plasma membrane of the cell body was suggestive of membrane retrieval following exocytosis of the vesicular contents from the cell surface. Neighboring TN cells were either in direct juxtaposition with one another or made specialized "glomeruloid" cell-to-cell contacts; these specializations may be relevant for nonsynaptic intercellular communications among the TN cells. Within these glomeruloid complexes, the somatic processes of TN cells received inputs from two types of synaptic terminals: one containing only spherical synaptic vesicles and another containing a small number of dense-cored vesicles in addition to the spherical synaptic vesicles. Axosomatic synapses were rare on type I TN cell bodies. In contrast, type II TN cell bodies had morphological characteristics similar to those of neurons in other brain regions. These receive axosomatic inputs from synaptic terminals containing only spherical synaptic vesicles and those with a small number of dense-cored vesicles in addition to the spherical synaptic vesicles. Thus, each type of TN cell has unique fine structural characteristics which may correlate to their different functional roles.
在我们之前的光学显微镜研究中（冈田等人，《脑研究》367: 341 - 345, '86；冈田和市川，《比较神经学杂志》300: 511 - 522, '90），我们报道基于细胞大小和免疫反应性至少存在两种类型的终末神经（TN）细胞：I型细胞具有大的细胞体，而II型细胞具有较小的细胞体。I型TN细胞对促性腺激素释放激素（GnRH）具有免疫反应性，可能是广泛分布于整个大脑的GnRH免疫反应性纤维的主要来源。另一方面，II型TN细胞对GnRH没有免疫反应性。在本文中，我们用电子显微镜检查了这两种类型TN细胞的细胞学和突触学。发现I型TN细胞体具有与其他肽合成神经元相似的形态特征，并且可能在活跃地合成GnRH。靠近细胞体质膜处频繁出现的有被小泡提示小泡内容物从细胞表面胞吐后进行膜回收。相邻的TN细胞要么彼此直接并列，要么形成特殊的“球状”细胞间接触；这些特化可能与TN细胞之间的非突触性细胞间通讯有关。在这些球状复合体中，TN细胞的体细胞突起接受来自两种类型突触终末的输入：一种仅含有球形突触小泡，另一种除了球形突触小泡外还含有少量致密核心小泡。I型TN细胞体上轴体突触很少见。相比之下，II型TN细胞体具有与其他脑区神经元相似的形态特征。它们接受来自仅含有球形突触小泡以及除球形突触小泡外还含有少量致密核心小泡的突触终末的轴体输入。因此，每种类型的TN细胞都具有独特的精细结构特征，这可能与其不同的功能作用相关。
