Zebrafish model of the blood-brain barrier: morphological and permeability studies

The blood-brain barrier (BBB) is a monolayer of endothelial cells that is regulated by the proximity of a unique basement membrane and a tightly controlled molecular interaction between specialized subsets of cells including pericytes, astrocytes, and neurons. Working together, these cells form a neurovascular unit (NVU) that is dedicated to the local regulation of vascular function in the brain and BBB integrity. Accordingly, the intrinsic complexity of the cell-matrix-cell interactions of the NVU has made analyzing gene function in cell culture, tissue explants, and even animal models difficult and the inability to study gene function in the BBB in vivo has been a critical hurdle to advancing BBB research.Zebrafish has emerged as a premier vertebrate organism to model and analyze complex cellular interactions in vivo and genetic mechanisms of embryonic development. To this end, we provide a technical overview of the procedures that can be used in Zebrafish to analyze BBB integrity with a focus on the cerebrovasculature of adult fish where the BBB is now defined. The techniques that are used to measure the functional integrity, the cell biology, and the ultrastructure of the BBB include permeability assays, fluorescent imaging of reporter genes, and electron microscopy, respectively. Each can be applied to the functional analysis of mutant fish in ways that characterize the molecular sequelae to pathological insults that compromise BBB integrity. Due to the highly conserved nature of both the genetics and cell biology of zebrafish when compared with higher vertebrates, drug discovery techniques can be used in zebrafish models to complement drug development studies in other model systems.