Growth fac-tors such as PDGF and VEGF can increase BBB permeability by disrupting tight junctions and stimulating angiogenesis (Dobrogowska et al., 1998, Harhaj et al., 2002, Wang et al., 1996 and Wang et al., 2001). To induce better barrier properties, some plasma-derived sera are treated with charcoal to reduce the concentrations of these growth factors. However the charcoal-stripping click here of serum can lead to removal/reduction of other biologically important factors such as hormones, vitamins, enzymes

and electrolytes (Cao et al., 2009). In the present model, we chose to use BPDS, which being derived from adult bovine plasma, is collected with generally less stress to the donor, and contains lower concentrations of growth factors (e.g. PDGF, VEGF) and other vasoactive/proliferative

factors than foetal or neonatal calf serum (Abbott et al., 1992). BPDS increased the TEER of the brain endothelial cells compared with serum-free medium, consistent with observations that serum proteins stabilise capillary endothelial permeability, by cross-linking the glycocalyx and possibly also the exposed proteins of the outer zones of the junctional complexes (Curry and Michel, 1980). Where experiments need to be done under serum-free conditions, the monolayers withstand serum removal for 24 h before experiments. Both mono-culture (Patabendige et al., this issue) and co-culture (Skinner et al., 2009) of the PBEC model variants are capable of giving monolayers of TEER >400 Ω cm2. Selleck Bortezomib For many applications examining the BBB flux of drug-like molecules and other small solutes, this is sufficient to give good resolution between transcellular and paracellular flux (Gaillard and de Boer, 2000). The relationship between Acesulfame Potassium Papp mannitol and TEER observed in our model ( Fig. 10) is similar to that reported by Gaillard and de Boer (2000) using two other paracellular permeability markers, sodium fluorescein and 4 kDa FITC-dextran; in our model, Papp was relatively independent of TEER when TEER was >200 Ω cm2. As TEER is inversely related to the small ion conductance (and hence permeability) of the monolayer, TEER recorded at the start

of an experiment is a good measure of the ‘basal’ paracellular permeability of the cells, as reference for studies e.g. with drugs which may themselves alter permeability. For leakier monolayers, the TEER can be used to derive a corrected permeability coefficient for a drug from the measured Papp ( Gaillard and de Boer, 2000); however, when TEER is high enough for Papp to be relatively independent of TEER, the measured Papp is sufficient without correction, and suitable for comparisons between laboratories. There is an extensive literature showing that exposure to astrocytes or astrocyte-conditioned medium increases the expression of several BBB features in brain endothelial monolayers (Dehouck et al., 1990 and Pottiez et al.