Repeated prenatal corticosteroids reduce glial fibrillary acidic protein in the ovine central nervous system

INTRODUCTION: A single course of corticosteroid reduces intracranial hemorrhage in preterm infants. The mechanism of protection is unclear. Glial fibrillary acidic protein (GFAP), expressed by astrocytes, is regulated by glucosteroids and is an important component of the cells forming the blood brain barrier. We have evaluated the effect of prenatal corticosteroid upon ovine GFAP. METHODS: Date-mated ewes were studied in two protocols and lambs delivered on day 125 or 145 (term = 150). In the maternal injection protocol (n = 36) ewes were administered saline, single or repeated injections of corticosteroid. In the fetal injection protocol (n = 48) direct ultrasound-guided fetal injections of saline, single or repeated corticosteroid were administered, and an additional control group did not receive fetal injections. Optic nerve GFAP immunohistochemistry was performed and quantified. RESULTS: At 125 days, repeated, but not single, administration of corticosteroid, by either maternal or fetal route, was associated with a significant reduction in GFAP (both p < 0.002); by 145 days, the deficit had recovered (both p > 0.05). The process of performing repeated fetal injections had an independent effect upon GFAP at 145 days (p = 0.002). CONCLUSION: Repeated administration of corticosteroid results in a reduction in GFAP in the developing ovine optic nerve, with recovery demonstrated by 145 days.