Correlation between astrogliogenesis and blood-brain barrier formation: immunocytochemical demonstration by using astroglia-specific enzyme glutathione S-transferase.

The formation of the capillary-glial complex of developing rat brain ranging in age from embryonic day 16 (E16) rats to birth, which occurs at E20, and in the postnatal rats to day 56 (P56) was determined by measuring the horseradish peroxidase (HRP) activity, which was exogenously injected and penetrated within the brain. The activity of glutathione S-transferases (GSTs) which are located exclusively in astroglial cells was also determined. HRP penetrated into and resided within the central nervous system until birth, although after this age the tracers were rarely observed to be included. On the other hand, GST activity was first detected at E18, and after P5 it increased remarkably. The functional significance of astroglial cells located at the blood-brain or blood-ventricle interface is considered, and we suggest that the ontogenetic development of a blood-brain barrier is compatible with the corresponding appearance of GST.