In vivo Techniques Quantifying Blood-Brain Barrier Permeability to Small Proteins in Mice

The blood–brain barrier (BBB) plays a crucial regulatory role in central nervous system (CNS) function and in communication between the CNS and the periphery. In addition to lipophilic molecules, many small proteins are now known to cross the BBB. Such recognition was expedited by techniques that quantify the influx and efflux of peptides and polypeptides across the BBB of the living animal. These methods are described in this review. Their use has enhanced our knowledge of the crucial link between the CNS and the rest of the body, and this has physiological and pathological implications as well as therapeutic potential.