ONTOGENIC EXPRESSION OF THE ERYTHROID-TYPE GLUCOSE-TRANSPORTER (GLUT-1) IN THE TELENCEPHALON OF THE MOUSE - CORRELATION TO THE TIGHTENING OF THE BLOOD-BRAIN-BARRIER

Since Glut 1 was shown to be highly abundant in brain microvessels, it s distribution during early developmental stages seems of importance i n respect to the timing of blood-brain barrier (bbb) formation in the developing CNS. Here we have followed the temporal expression of the e rythroid-type glucose transporter Glut 1 in the telencephalon of the e mbryonic and newborn mouse, beginning at the 9th intrauterine day. Glu t 1 immunofluorescence staining was done on cryosections using a rabbi t polyclonal antiserum to purified human erythrocyte glucose transport er. Endothelial cells resp. capillaries were detected by staining with a rhodamin-coupled Bandeiraea simplicifolia lectin (BSL). In parallel , the developmental tightening of the embryonic bbb was assessed by pe rfusion of mouse embryos with Trypan blue and horse radish-peroxidase. At E9, prior to the onset of intraneural neovascularization, strong G lut 1 immunoreactivity was found in the whole neuroectoderm but only m inor staining was seen in the perineural domain. Glut 1 expression rem ained uniformly distributed in the intraneural tissue at E10, the begi nning of intraneural neovascularization in the mouse. From Ell onwards , Glut 1 immunoreactivity was invisible in neuroepithelial cells, but appeared tightly associated with intraneural capillaries. Perfusion of E12 embryos using trypan blue solution and HRP revealed that most par ts of the CNS and spinal cord were impermeable to the tracer substance s at that stage. Thus, we suggest that the bbb is established very ear ly in CNS development, probably in the course of intraneural neovascul arization. In addition, our data indicate that the restriction of Glut 1 expression to the intraneual capillaries reflects the onset of bbb function in the mouse embryo.