Integrity of blood-brain barrier to peroxidase in senescent mice.

The brain distribution of systemically-administered horseradish peroxidase was studied in senescent mice and compared with the distribution in a group of young mice. The distribution of HRP was surveyed in both the experimental and control groups by light and electron microscopy by an observer unaware of the source of the material. No qualitative differences were observed in the brain distribution of systemically-administered HRP in old mice compared to young mice. The results of this study suggest that the blood-brain barrier to HRP is preserved in senescent mice.