Redecker P, Veh R W
Abteilung Anatomie 1, Medizinische Hochschule Hannover, Germany.
Cell Tissue Res. 1994 Dec;278(3):579-88. doi: 10.1007/BF00331377.
Mammalian pinealocytes have been shown to contain synaptic-like microvesicles with putative secretory functions. As a first step to elucidate the possibility that pinealocyte microvesicles store messenger molecules, such as neuroactive amino acids, we have studied the distributional pattern of glutamate immunoreactivity in the pineal gland of the Mongolian gerbil (Meriones unguiculatus) at both light- and electron-microscopic levels. In semithin sections of plastic-embedded pineals, strong glutamate immunoreactivity could be detected in pinealocytes throughout the pineal gland. The density of glutamate immunolabeling in pinealocytes varied among individual cells and was mostly paralleled by the density of immunostaining for synaptophysin, a major integral membrane protein of synaptic and synaptic-like vesicles. Postembedding immunogold staining of ultrathin pineal sections revealed that gold particles were enriched over pinealocytes. In particular, a high degree of immunoreactivity was associated with accumulations of microvesicles that filled dilated process terminals of pinealocytes. A positive correlation between the number of gold particles and the packing density of microvesicles was found in three out of four process terminals analyzed. However, the level of glutamate immunoreactivity in pinealocyte process endings was lower than in presumed glutamatergic nerve terminals of the cerebellum and posterior pituitary. The present results provide some evidence for a microvesicular compartmentation of glutamate in pinealocytes. Our findings thus lend support to the hypothesis that glutamate serves as an intrapineal signal molecule of physiological relevance to the neuroendocrine functions of the gland.
哺乳动物的松果体细胞已被证明含有具有假定分泌功能的突触样微泡。作为阐明松果体细胞微泡是否储存信使分子（如神经活性氨基酸）可能性的第一步，我们在光镜和电镜水平上研究了蒙古沙鼠（Meriones unguiculatus）松果体中谷氨酸免疫反应性的分布模式。在塑料包埋松果体的半薄切片中，整个松果体的松果体细胞中均可检测到强烈的谷氨酸免疫反应性。松果体细胞中谷氨酸免疫标记的密度在不同细胞间有所变化，且大多与突触素（一种突触和突触样小泡的主要整合膜蛋白）的免疫染色密度平行。超薄松果体切片的包埋后免疫金染色显示，金颗粒在松果体细胞上富集。特别是，高度的免疫反应性与充满松果体细胞扩张的突起末端的微泡聚集有关。在分析的四个突起末端中的三个中，发现金颗粒数量与微泡堆积密度之间呈正相关。然而，松果体细胞突起末端的谷氨酸免疫反应性水平低于小脑和垂体后叶假定的谷氨酸能神经末梢。目前的结果为松果体细胞中谷氨酸的微泡分隔提供了一些证据。因此，我们的发现支持了这样一种假说，即谷氨酸作为一种与该腺体神经内分泌功能具有生理相关性的松果体内信号分子。
