Ma Dan, Morris John F
Department of Human Anatomy and Genetics, South Parks Road, Oxford OX1 3QX, UK.
J Chem Neuroanat. 2002 Mar;23(3):171-86. doi: 10.1016/s0891-0618(01)00158-2.
There is growing evidence of local protein synthesis in neuronal dendrites, especially in relation to synaptic activity. The hypothalamic magnocellular system is a robust model for peptidergic neurons, especially for the study of dendrites. Quantitative electron microscopy, immunocytochemistry and non-radioactive in situ hybridization (with tyramide signal amplification) were used to compare dendrites of magnocellular neurons in the supraoptic nucleus of wild-type rats and of homozygous Brattleboro (BB) rats which are subject to long-term hyper-osmotic stimulation because they cannot secrete vasopressin. The dendrites contained free polyribosomes, cisterns of rough endoplasmic reticulum (ER) and small Golgi-like elements. These were clustered in the dendrites, mostly near the plasma membrane. All were increased in amount in the enlarged dendrites of the BB rats. The presence of polyribosomes and cisterns of rER implies that both cytosolic and membrane-inserting proteins are synthesized in the dendrites. The ER marker protein disulfide isomerase extended far into dendrites, but Golgi element markers (mid-Golgi and trans-Golgi network) were distributed mainly in their proximal parts. In BB rats, all the labeling was stronger. 28S rRNA, initiator tRNA(Met), and poly(A) mRNA were revealed extending into proximal and middle parts of dendrites where intensely reactive punctate structures were common. 28S rRNA could be detected in the distal parts of the dendrites. The length of positively stained dendrites was increased significantly for all these RNAs in BB rats. The results provide morphological evidence that magnocellular dendrites have the capacity for local protein syntheses and that this is increased in chronic hyperosmotic stress.
越来越多的证据表明，神经元树突中存在局部蛋白质合成，尤其是与突触活动相关的局部蛋白质合成。下丘脑大细胞系统是肽能神经元的一个强大模型，尤其适用于树突的研究。我们使用定量电子显微镜、免疫细胞化学和非放射性原位杂交（酪胺信号放大）来比较野生型大鼠视上核大细胞神经元的树突与纯合布拉德福德（BB）大鼠的树突，BB大鼠由于不能分泌血管加压素而受到长期高渗刺激。树突中含有游离多核糖体、粗面内质网（ER）池和小的类高尔基体元件。这些元件聚集在树突中，大多靠近质膜。在BB大鼠增大的树突中，所有这些元件的数量都增加了。多核糖体和粗面内质网池的存在意味着树突中既合成胞质蛋白也合成插入膜的蛋白。内质网标记蛋白二硫键异构酶深入树突，但高尔基体元件标记物（高尔基中间膜囊和反式高尔基网络）主要分布在其近端部分。在BB大鼠中，所有标记都更强。28S rRNA、起始tRNA(Met)和聚腺苷酸mRNA延伸至树突的近端和中部，那里常见强反应性点状结构。在树突的远端部分也能检测到28S rRNA。在BB大鼠中，所有这些RNA阳性染色的树突长度均显著增加。这些结果提供了形态学证据，表明大细胞树突具有局部蛋白质合成能力，并且在慢性高渗应激下这种能力会增强。
