TRANSIENT PRESENCE OF GABA IN ASTROCYTES OF THE DEVELOPING OPTIC-NERVE

Immunostaining and high-pressure liquid chromatography (HPLC) were use d to study the developmental time course of astrocytic gamma-aminobuty ric acid (GABA) expression in rat optic nerve. GABA immunostaining was carried out on cultured astrocytes, and on whole optic nerve. Confoca l scanning laser microscopy was used to obtain optical sections in exc ised whole tissue in order to localize the cellular origins of GABA wi thin the relatively intact optic nerve. GABA immunoreactivity was loca lized in astrocytes identified by GFAP staining; GABA staining was mos t intense in early neonatal optic nerve and attenuated over 3 weeks of postnatal development. The staining was pronounced in the astrocyte c ell bodies and processes but not in the nucleus. There was a paucity o f GABA immunoreactivity by postnatal day 20, both in culture and in wh ole optic nerve. A biochemical assay for optic nerve GABA using HPLC i ndicated a relatively high concentration of GABA in the neonate, which rapidly attenuated over the first 3 postnatal weeks. Immunoreactivity for the GABA synthesis enzyme glutamic acid decarboxylase (GAD) was p ronounced in neonates but also attenuated with development. These resu lts indicate that GABA and the GABA synthesis enzyme GAD are localized in astrocytes of optic nerve, and that their expression is transient during postnatal development. (C) 1993 Wiley-Liss, Inc.