IMMUNOCYTOCHEMICAL EVALUATION OF BLOOD-BRAIN-BARRIER TO ENDOGENOUS ALBUMIN IN ADULT, NEWBORN AND AGED MICE

The blood-brain barrier (BBB) to endogenous albumin was studied in nor mal adult, newborn and aged mice by using quantitative immunocytochemi cal procedures. For control purposes, the non-BBB-type of microvascula ture from skeletal muscle (diaphragm) was also examined. Thin sections of tissue samples embedded at low temperature in hydrophilic resin Lo wicryl K4M were exposed to anti-mouse albumin antiserum followed by pr otein A-gold. Labeling density was recorded over four compartments: Va scular lumen, endothelium, subendothelial (perivascular) space. and ad jacent neuropil. The labeling density of the vessel lumen was consider ed to represent 100% of circulating albumin. The main differences betw een the two types of microvasculature consisted in the appearance of o ne-fifth of the labeling density of circulating albumin in the perivas cular space of the non-BBB-type and only about one one-hundreth in the perivascular space of the BBB-type microvessels. The results suggest that the barrier function of brain microvasculature to endogenous albu min in newborn and aged mice is not significantly different from that in normal, adult animals. However, applied morphometrical and quantita tive analysis of the density of immunolabeling over the above-mentione d compartments makes it possible to detect even subtle deviations from normal values in both extreme-age groups.