Kaplan M S
J Hirnforsch. 1983;24(1):23-33.
New formation of stem cells in the subependymal brain layer of a normal adult primate has been documented by light and electron microscopy and through 3H-thymidine (3H-TdR) uptake studies. Serial sections (1.5 micrometer) prepared for autoradiography were examined under the light microscope and then re-embedded for electron microscopy. In individual sections subependymal cells did not appear labeled; however, serial sections revealed that many cells were slightly labeled indicating a low level of 3H-TdR incorporating during DNA synthesis. Dividing subependymal cells were also observed by light and electron microscopy. The poor incorporation of intraperitoneally injected 3H-TdR is due to the blood-brain barrier toward 3H-TdR. Rat experiments with the thymidine analogue, 125I-iododeoxyuridine (IUDR-125I) showed that after intraventricular injection of IUDR-125I about ninety times more radioactivity is incorporated into dividing stem cells of the brain than after an intraperitoneal injection of IUDR-125I. Differential corporation of 3H-TdR seems to depend on the type of stem cells, i. e., whether a stem cell may be precursor for glial or neuronal brain cells. Changes in membrane permeability, intracellular DNA activity as well as difference in locally available "cold" thymidine may be a reason for differential uptake of radioactive thymidine. Differential uptake of 3H-TdR needs consideration when autoradiography is applied on brain cells.
通过光学显微镜、电子显微镜以及³H-胸腺嘧啶核苷（³H-TdR）摄取研究，已证实在正常成年灵长类动物的脑室下层脑区会形成新的干细胞。为进行放射自显影而制备的连续切片（1.5微米）先在光学显微镜下检查，然后重新包埋用于电子显微镜观察。在单个切片中，脑室下层细胞似乎未被标记；然而，连续切片显示许多细胞有轻微标记，表明在DNA合成过程中³H-TdR掺入水平较低。通过光学显微镜和电子显微镜也观察到了正在分裂的脑室下层细胞。腹腔注射³H-TdR掺入率低是由于血脑屏障对³H-TdR的作用。用胸腺嘧啶类似物¹²⁵I-碘脱氧尿苷（IUDR-¹²⁵I）进行的大鼠实验表明，脑室内注射IUDR-¹²⁵I后，与腹腔注射IUDR-¹²⁵I相比，掺入脑内正在分裂的干细胞中的放射性约多90倍。³H-TdR的差异掺入似乎取决于干细胞的类型，即干细胞是神经胶质细胞还是神经元细胞的前体。膜通透性的变化、细胞内DNA活性以及局部可利用的“冷”胸腺嘧啶的差异可能是放射性胸腺嘧啶差异摄取的原因。对脑细胞进行放射自显影时，需要考虑³H-TdR的差异摄取。
