BLOOD-NERVE AND BLOOD-BRAIN-BARRIER PERMEABILITIES AND NERVE VASCULAR SPACE IN FISCHER-344 RATS OF DIFFERENT AGES

The permeability-surface area product (PA) of [H-3]- or [C-14]sucrose at the blood-nerve barrier (BNB) of the sciatic nerve; and at the blood-brain barrier (BBB), were determined in Fischer-344 rats at 3, 11 and 31 months of age. PA was determined by using an in vivo i.v. bolus injection of radiotracer with two-time point graphic and quantitative autoradiographic methods. Vascular space and water content of the tibial nerve of these rats also were determined using quantitative morphometry and dry and wet weight ratios, respectively. There was no significant difference between mean PA(BNB) in any age group [(PA(BNB) at 3 months = 1.2 +/- 0.1 (mean +/- S.E.), at 11 months = 1.8 +/- 0.3; and at 31 months = 1.4 +/- 0.2 x 10(-50 ml/s . g wet wt; n = 5- 8 rats], nor any difference in PA(BBB). The mean ratio (%) of surface area of endoneurial blood vessels/nerve cross-section of the tibial nerve also did not differ between any group [3 months: 16 +/- 2 vessels; mean surface area ratios = 2.20 +/- 0.10%, n = 5; 11 months: 22 +/- 3 vessels and 2.48 +/- 0.21%, n = 5; and at 31 months: 26 +/- 1 vessels and 2.40 +/- 0.23%, n = 4). The mean nerve water in rats at 31 months was 64.8 +/- 1.1% wet wt and did not differ from that at 11 months (66.0 +/- 0.6% wet wt) or at 3 months (65.1 +/- 1.0% wet wt) (n = 5-8 nerves). Our results indicate that BBB and BNB integrities are not altered in senescent Fischer-344 rats.