Chu-Wang I W, Oppenheim R W
J Comp Neurol. 1980 Oct 1;193(3):753-76. doi: 10.1002/cne.901930312.
Horseradish peroxidase (HRP) was injected in ovo into the ventral muscle mass of the hind limb of 5- to 7-day-old chick embryos or into the gastrocnemius muscle of 8- to 18-day embryos and localized histochemically. HRP is extensively incorporated via endocytosis into axonal growth cones or presynaptic terminals in the proximity of the injection site. Much of the tracer is taken up in vesicles and small vacuoles. Most of these are smooth-surfaced and only a few are bristle-coated. A small amount of the tracer is also incorporated into the axon terminal through the openings between the axolemma and an intricate membrane channel. The majority of the tracer-laden vesicles and vacuoles rapidly fuse with one another to become large vacuoles, some of which are transformed into multivesicular bodies (MVBs). In axon shafts, many labeled vacuoles and MVBs are transferred to tubule-like organelles, which appear to be the primary carrier for transporting the tracer back to the cell bodies in the lumbar spinal cord. HRP arrives in the sensory ganglia about 0.5-1 hour earlier than in the motoneurons of the lateral motor column. The maximal rate of the retrograde axoplasmic transport is about 3.5 mm/hour. After arriving in the cell bodies, HRP is transferred from tubule-like organelles to discrete vacuoles of various sizes and appearance. Lysosomal dense bodies and HRP-labeled vacuoles can be distinguished ultrastructurally. A fusion of HRP-labeled vacuoles with lysosomal dense bodies or Golgi vesicles was occasionally observed and the density of HRP-labeled vacuoles diminished after 2 to 3 days. Most of the HRP-labeled organelles were found to contain acid phosphatase activity. Therefore, the complete disappearance of HRP by 4 days postinjection is most likely related to lysosomal degradation. Neuronal cell bodies diffusely labeled with HRP were only observed prior to day 6. After day 6, despite various attempts to injure the peripheral axons, only granularly labeled cell bodies were found. This difference may imply that "mature" neurons have a more efficient mechanism for the sequestration of "free" HRP in the cytoplasmic matrix into membrane-bounded organelles. A mature-like retrograde transport mechanism appears to exist at the earliest stages of axonal growth in vivo.
将辣根过氧化物酶（HRP）在卵内注射到5至7日龄鸡胚后肢的腹侧肌肉团中，或注射到8至18日龄胚胎的腓肠肌中，并进行组织化学定位。HRP通过内吞作用广泛地被摄取到注射部位附近的轴突生长锥或突触前终末中。大部分示踪剂被摄取到小泡和小液泡中。其中大多数小泡表面光滑，只有少数有被毛。少量示踪剂也通过轴膜和复杂的膜通道之间的开口进入轴突终末。大多数载有示踪剂的小泡和液泡迅速相互融合形成大液泡，其中一些转变为多囊体（MVBs）。在轴突中，许多标记的液泡和MVBs被转移到管状细胞器中，这些细胞器似乎是将示踪剂运回腰脊髓细胞体的主要载体。HRP到达感觉神经节比到达外侧运动柱的运动神经元早约0.5至1小时。逆行轴浆运输的最大速率约为3.5毫米/小时。到达细胞体后，HRP从管状细胞器转移到各种大小和外观的离散液泡中。溶酶体致密体和HRP标记的液泡在超微结构上可以区分。偶尔观察到HRP标记的液泡与溶酶体致密体或高尔基体小泡融合，2至3天后HRP标记液泡的密度降低。发现大多数HRP标记的细胞器含有酸性磷酸酶活性。因此，注射后4天HRP完全消失很可能与溶酶体降解有关。仅在第6天之前观察到用HRP弥散标记的神经元细胞体。第6天之后，尽管进行了各种损伤外周轴突的尝试，只发现了颗粒状标记的细胞体。这种差异可能意味着“成熟”神经元具有更有效的机制，将细胞质基质中的“游离”HRP隔离到膜结合细胞器中。在体内轴突生长的最早阶段似乎就存在类似成熟的逆行运输机制。
