Introduction

For many applications, in situ brain perfusion offers a number of advantages over other methods when studying the penetration of solutes into brain. The technique is particularly suited to solutes that penetrate into brain slowly as it allows for an extended exposure of the solute of interest to the cerebral vascular endothelium that forms the blood–brain barrier. In addition, the composition of the perfusing medium can be precisely manipulated, thus allowing the inclusion of competitive and noncompetitive inhibitors of transport in the perfusate and so allowing kinetic studies to be performed. When investigating kinetics and rates of uptake with brain perfusion methods the technique is essentially revealing events at the luminal plasma membrane of the cerebral vasculature, which for most solutes will be the rate-limiting step.

If a saline-based perfusate is used, the exclusion of plasma enzymes allows the brain-uptake of solutes that are unstable in the general circulation to be determined in an intact form. A saline-based perfusion fluid also allows the role of specific ectoenzymes to be studied where these are relevant, for example peptidases embedded in the luminal plasma membrane of the endothelial cells forming the blood–brain barrier, (Zlokovic et al., 1988a; Begley, 1996).

Usually radiolabelled tracers are included in the perfusate and are subsequently quantified in brain tissue by scintillation counting or autoradiography.