Experimental models of altering the blood-brain barrier

The passage of a substance from blood to brain can be enhanced by altering the permeability of the substance itself or by altering the BBB characteristics. Example of the former is to increase lipid solubility, glycosylation and cationization, liposome entrapment and coupling to carriers. Unselective opening of the BBB can be obtained by a local or systemic increase of the intravascular pressure, by intracarotid injection of hyperosmolar solutions or by substances that alter the endothelial surface charge such as protamine sulphate. Substances that alter the fluidity of membranes can reduce or enhance the permeability of the BBB. In experimental models involving temporary opening of the BBB possible long-term hazardous effects must be considered.