The goal of this chapter is to highlight methods used to demonstrate in vivo changes in astrocyte expression at the blood–brain
barrier (BBB). Loss of BBB integrity is seen in many acute and chronic disease conditions. However, despite the importance
of the BBB to homeostasis and correct functioning of the CNS, the nature of factors responsible for the induction and maintenance
of BBB properties in development and the adult remains unclear. We have studied the role of astrocytes in modulating BBB integrity
in two in vivo models using a gliotoxin (3-chloropropanediol), and under hypoxic stress. 3-chloropropanediol-induced astrocytic
loss within the inferior colliculus leads to loss of endothelial tight junction protein expression and loss of BBB integrity.
As glial fibrillary acidic protein (GFAP)-immunopositive astrocytes repopulated the lesion, tight junction protein expression
returned to paracellular domains and BBB integrity was restored. Under hypoxic conditions, increased GFAP expression was seen
with changes in tight junction protein expression and loss of BBB integrity. These studies suggest a critical role for glial/endothelial
interactions in regulating BBB integrity in health and disease.