Waerhaug O, Ottersen O P
Department of Anatomy, University of Oslo, Norway.
Anat Embryol (Berl). 1993 Nov;188(5):501-13. doi: 10.1007/BF00190144.
Motor nerve terminals and adjacent structures in the extensor digitorum longus and soleus muscles of young adult rats were examined for their content of glutamate by means of quantitative, electron microscopic immunocytochemistry employing colloidal gold particles as markers. The level of glutamate immunoreactivity was stronger in the extensor digitorum longus terminals than in the soleus terminals. In both muscles the glutamate immunolabelling was stronger in the nerve terminals than in the synaptic clefts and the postsynaptic tissue separating the secondary clefts, but the differences were larger in the extensor digitorum longus than in the soleus muscle. The myofibrils of the soleus muscle were more densely labelled than those in the extensor digitorum longus muscle. The level of immunoreactivity was high in the Schwann cells of both muscles. By comparing the labelling intensity of motor nerve terminals with that of muscle fibres and hippocampal mossy fibres (compartments that have been analysed previously with respect to their glutamate content), the mean concentration of fixed glutamate in the extensor digitorum terminals was estimated to be in the range of 10-20 mmol/l. An association of glutamate immunoreactivity with synaptic vesicles was demonstrated in the most strongly labelled terminals. Whether these epitopes were localized in the interior of the vesicles or at their external surface could not be resolved with the present technique. These data indicate that motor nerve terminals contain glutamate, and that the enrichment of this amino acid is more pronounced in the terminals of the extensor digitorum longus muscle (a fast muscle) than in those of the soleus muscle (a slow muscle). A possible modulatory or trophic role of glutamate in the mammalian neuromuscular junction should be considered.
采用以胶体金颗粒作为标记物的定量电子显微镜免疫细胞化学方法，对年轻成年大鼠趾长伸肌和比目鱼肌中的运动神经末梢及相邻结构进行了谷氨酸含量检测。趾长伸肌末梢的谷氨酸免疫反应性水平比目鱼肌末梢更强。在这两块肌肉中，神经末梢的谷氨酸免疫标记都比突触间隙和分隔次级间隙的突触后组织更强，但趾长伸肌中的差异比目鱼肌更大。比目鱼肌的肌原纤维比趾长伸肌的肌原纤维标记更密集。两块肌肉的施万细胞中免疫反应性水平都很高。通过比较运动神经末梢与肌肉纤维和海马苔藓纤维（先前已对其谷氨酸含量进行过分析的区域）的标记强度，估计趾长伸肌末梢中固定谷氨酸的平均浓度在10 - 20 mmol/l范围内。在标记最强的末梢中，谷氨酸免疫反应性与突触小泡存在关联。利用现有技术无法确定这些表位是位于小泡内部还是其外表面。这些数据表明运动神经末梢含有谷氨酸，并且这种氨基酸在趾长伸肌（快肌）末梢中的富集比目鱼肌（慢肌）末梢更为明显。应考虑谷氨酸在哺乳动物神经肌肉接头中可能的调节或营养作用。
