invading vessels are in direct contact with pericytes, but
not with astrocytes. With the progression of development, foot processes of astrocytes are gathered around
retinal vessels and the maturation of tight junction ZO-
1 in endothelial cells is more clearly defined [64]. Tight
junctions can be formed with contact from pericytes
without the ensheathment of the astrocytic foot processes. From in vitro studies it is clear that pericytes
induce synthesis of both occludin and claudin through
the release of angiopoetin-1 [65]. Thus tight junction
formation in the BBB could be developed, in part, by
cellular interactions between EC and pericytes followed
by astrocytes (as reviewed in [66]). The expression of
ZO-1 is augmented by astrocytes [67]. Moreover, ZO-1
as well as occludin or claudin together may be biological
indicators of barrier maturation [67]. The role of the
pericyte in BBB function will be discussed below