Earle K L, Mitrofanis J
Institute for Biomedical Research, Department of Anatomy & Histology, University of Sydney, Australia.
J Neurocytol. 1998 Feb;27(2):127-39. doi: 10.1023/a:1006951423251.
We have explored two aspects of internal capsule development that have not been described previously, namely, the development of glia and of blood vessels. To these ends, we used antibodies to glial fibrillary acidic protein (GFAP) and to vimentin (to identify astrocytes and to radial glia) and Griffonia simplicifolia (lectin; to identify microglia and blood vessels). Further, we made intracardiac injections of Evans Blue to examine the permeability of this dye in the vessels of the internal capsule during neonatal development. Our results show that large numbers of radial glia, astrocytes and microglia are not labelled with these markers in the white matter of the internal capsule until about birth; very few are labelled earlier, during the critical stages of corticofugal and corticopetal axonal ingrowth (E15-E20). The large glial labelling in the internal capsule at birth is accompanied by a dense vascular innervation of the capsule; as with the glia, very few labelled patent vessels are seen earlier. After intracardiac injections of Evans Blue, we find that the blood vessels of the internal capsule are not particularly permeable to Evans Blue. At each age examined (P0, P5, P15), blood vessels are outlined very clearly and there is no diffuse haze of fluorescence within the extracellular space, which is indicative of a leaky vessel. There are three striking differences between the glial environment of the internal capsule and that of the adjacent thalamus. First, the internal capsule is never rich with radial glial fibres (vimentin- and GFAP-immunoreactive) during development (except at P0), whereas the thalamus has many radial fibres from very early development (E15-E17). Second, astrocytes (vimentin- and GFAP-immunoreactive) first become apparent in the internal capsule (E20-P0) well before they do in the thalamus (P15). Third, the internal capsule houses a large transient population of amoeboid microglia (P0-P22), whereas the thalamus does not; only ramified microglia are seen in the thalamus. In summary, our results indicate that all three types of glia in the internal capsule are associated closely with the vasculature, suggesting they may play a role in the development of the blood-brain barrier among the vessels in this white matter region of the forebrain.
我们探究了内囊发育中两个此前未被描述的方面，即神经胶质和血管的发育。为此，我们使用了针对胶质纤维酸性蛋白（GFAP）和波形蛋白的抗体（用于识别星形胶质细胞和放射状胶质细胞）以及非洲相思子凝集素（用于识别小胶质细胞和血管）。此外，我们进行了心内注射伊文思蓝，以检查这种染料在新生儿发育期间在内囊血管中的渗透性。我们的结果表明，在内囊白质中，大量的放射状胶质细胞、星形胶质细胞和小胶质细胞直到出生左右才被这些标记物标记；在皮质离心和皮质向心轴突长入的关键阶段（E15 - E20），早期被标记的细胞极少。出生时内囊中大量的胶质细胞标记伴随着密集的血管神经支配；与胶质细胞一样，早期可见的标记有活性的血管极少。在心内注射伊文思蓝后，我们发现内囊血管对伊文思蓝的渗透性并不特别高。在每个检查的年龄（P0、P5、P15），血管轮廓都非常清晰，细胞外空间没有弥漫性的荧光 haze，这表明血管没有渗漏。内囊的胶质环境与相邻丘脑的胶质环境有三个显著差异。第一，在内囊发育过程中（P0 除外），内囊从未富含放射状胶质纤维（波形蛋白和 GFAP 免疫反应阳性），而丘脑从发育早期（E15 - E17）就有许多放射状纤维。第二，星形胶质细胞（波形蛋白和 GFAP 免疫反应阳性）在内囊中最早在 E20 - P0 出现，远早于在丘脑中出现的时间（P15）。第三，内囊中有大量短暂存在的阿米巴样小胶质细胞（P0 - P22），而丘脑中没有；丘脑中仅可见分支状小胶质细胞。总之，我们的结果表明，内囊中所有三种类型的胶质细胞都与脉管系统密切相关，这表明它们可能在前脑这个白质区域的血管之间血脑屏障的发育中发挥作用。
