CHANGES IN BLOOD-BRAIN-BARRIER PERMEABILITY ASSOCIATED WITH INSERTIONOF BRAIN CANNULAS AND MICRODIALYSIS PROBES

Blood-brain barrier (BBB) transcapillary transport was studied after i nsertion of cannulas and microdialysis probes into the brains of three groups of rats. Quantitative autoradiography was used to measure chan ges in BBB permeability around the insertion site. In the first group, BBB function was measured with C-14-sucrose at times from immediately , and up to 28 days, after insertion of a microdialysis probe. BBB fun ction was disrupted biphasically: a 19-fold increase in the influx con stant (K-1) of sucrose occurred immediately after insertion with a sec ond 17-fold increase at 2 days, followed by a slow decline to 5 times normal values at 28 days. In the second group, C-14-dextran (70 kDa) w as used to measure BBB transcapillary transport; K-1 was increased 90- fold after probe insertion. In the 3rd group, C-14-AIB (alpha-aminoiso butyric acid) was used to evaluate BBB transport after insertion of a 27 gauge cannula, which was used to infuse 1 mu l of saline over 5 min . The K-1 of ATE was increased 25 times control values. We conclude th at BBB transcapillary transport function is disturbed in response to i nsertion of brain cannulas and/or microdialysis probes, that BBB dysfu nction is maximal at the cannula or probe tip, varies with time after insertion, may persist for at least 28 days after insertion, and occur s over a wide molecular range of solutes. These results suggest cautio n when using microdialysis as a method to study normal BBB function, a nd suggest that microdialysis may overestimate the rate of transfer in to and out of the brain. (C) 1998 Elsevier Science B.V. All rights res erved.