ONTOGENY OF 4 BLOOD-BRAIN-BARRIER MARKERS - AN IMMUNOCYTOCHEMICAL COMPARISON OF PIAL AND CEREBRAL CORTICAL MICROVESSELS

Pial and cortical microvessels possess many blood-brain barrier (BBB) properties in common, including impermeability to electron dense trace rs, high transendothelial electrical resistance and specialised endoth elial cell ultrastructural features. To compare pial and cortical micr ovessels further, a developmental, immunocytochemical study was undert aken of 4 BBB markers in the rat: OX-47, EBA, GLUT-1 and s-laminin. Th e appearance oi. the markers was monitored from embryonic d 16, to pos tnatal and adult stages. Each of the 4 markers appeared simultaneously in both pial and cortical vessels. GLUT-I and OX-47 were present in e ndothelial cells of the BBB from E 16 to the adult, EBA and s-laminin appeared from postnatal d 7 through to the adult. Pial microvessels la ck the ensheathment of astrocytes which may be involved in the inducti on and/or maintenance of BBB markers in the cortex. It is possible tha t astrocyte-derived factors diffusing from the brain surface are respo nsible for induction of BBB properties in the pial microvessels.