Histochem Cell Biol (2012) 138:861–879 873 and low molecular weight dextrans at early stages of development in Monodelphis domestica (Ek et al. 2003, 2006) and in rat (Johansson et al. 2006). Taken together, these data support the concept that a barrier to paracellular transfer between blood and CSF is essential early during development (Johansson et al. 2008b; Saunders et al. 1999, 2012). The sealing property of TJs results from homo- or het- erotypic interactions between Clds of adjacent cells, as well as from lateral oligomerization of Clds within each 123