Uptake of tracer proteins in the developing cerebellum, particularly by the growth cones and blood vessels
Uptake of tracer proteins in the developing cerebellum, particularly by the growth cones and blood vessels
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发育中的小脑对示踪蛋白的摄取，特别是生长锥和血管的摄取
DOI：
10.1002/cne.901570302
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发表时间：
1974
期刊：
影响因子：
--
通讯作者：
M. Cerro
中科院分区：
文献类型：
--
作者：
M. Cerro
将示踪蛋白铁蛋白(分子量50万道尔顿)和辣根过氧化物酶(分子量40000道尔顿)注射到乳鼠小脑内，以研究发育中的神经组织中生长锥和其他结构对大分子的摄取。在注射后30分钟至6小时内处死动物，并对邻近但不包括注射部位的区域进行电子显微镜和光学显微镜对照研究。
在所有的时间间隔中，这两种蛋白质都存在于细胞外和细胞内的隔室中，尽管后者的浓度明显随着时间的推移而增加。这两种示踪剂都流经细胞间隙，渗透到突触间隙，并大量聚集在软脑膜和血管的基底层。当穿过椎板时，标记物被软膜细胞和内皮细胞结合。后者显示吞噬小泡在管腔表面接受标记，类似标记的小泡在管腔表面下或实际上开口进入血管管腔。浸泡固定的小脑血管显示相似的摄取模式，毛细血管腔内可见游离示踪剂。这些数据表明，在这些实验条件下，囊泡介导的蛋白质从实质到血液的跨内皮通道发生了。
神经元和神经胶质细胞的体细胞高度融合，蛋白质被胞吞作用摄取并储存在溶酶体中。充满生长锥体的小泡(“生长小泡”)有规律地含有标记，尽管比例不同。在任何时候，神经胶质锥体中的小泡大部分被标记，而在轴突和树突锥体中只有部分被标记。由于胞饮活性在生长锥体中很低，“生长小泡”的标记可以用假设它们在开放并与锥体膜结合时成为被动标记的假设来解释(如Bray‘s’73模型)。如果是这样的话，神经锥和神经胶质锥之间的差异标记可能是膜增加的不同速率的指示，因此也是不同的生长速率的标志。
Tracer proteins ferritin (M. W. 500,000 daltons) and horseradish peroxidase (M. W. 40,000 daltons) were injected into the cerebella of suckling rats to study the uptake of macromolecules by growth cones and other structures in the developing nervous tissue. The animals were killed between 30 minutes and 6 hours after injection, and areas adjacent to, but excluding the injection site were studied by electron microscopy with optical microscopical controls.
At all time intervals both proteins were present in the extra- and intracellular compartments, although there was a clear time-related increase of the concentration in the latter. Both tracers flowed through the intercellular gaps, permeated synaptic clefts, and concentrated in large amounts within the basal laminae of the pia mater and blood vessels. Upon crossing the laminae the markers were incorporated by pial and endothelial cells. The latter showed pinocytotic vesicles taking the marker at the abluminal surface and similarly labeled vesicles underneath the luminal surface or actually opening into the vascular lumina. Vessels of cerebella fixed by immersion showed similar uptake pattern and free tracer was found in the capillary lumina. These data indicate that a vesicle-mediated transendothelial passage of proteins, from the parenchyma to the blood takes place under these experimental conditions.
The somata of neurons and glial cells showed a high degree of incorproation, the protein being taken by pinocytosis and stored in lysosomes. The vesicles populating growth cones (“growth vesicles”) regularly contained marker although in variable proportions. At any given time most of the vesicles in the glial cones were labeled, while only some were labeled in the axonal and dendritic cones. Since pinocytotic activity was low in growth cones, labeling of the “growth vesicles” could be tentatively explained by postulating that they become passively labeled when they open into and coalesce with the membrane of the cone (as in Bray's, '73, model). If that were the case differential labeling between neural and glial cones could be an indication of a differential rate of membrane increment and therefore a differential rate of growth. Alternative possiblities are considered.