gamma-Aminobutyric acid system in developing and degenerating mouse retina

Freeze-dried sections (14 microns thick) of retinal layers were prepared from mice with retinal degeneration (C3H strain) and control mice (C57BL strain). The weighed sections (2-30 ng dry weight) were analyzed using our microassay methods. In the control retina, gamma-aminobutyric acid (GABA) concentration and glutamate decarboxylase (GAD) activity, on a dry weight basis, increased from birth to 9 weeks of age and decreased slightly at 20 weeks. In the degenerated retina, the levels of GABA and GAD activity were higher at birth than in the control retina, and continued to increase until 20 weeks of age, at which time the GAD activity reached a markedly high level. This increase was found when the total GABA and GAD levels per retina were determined. In the normal retinal layers, GABA and GAD were confined primarily to the inner plexiform layer. In the degenerated retina, GAD activity gradually increased in the inner layers during postnatal development, but by 20 weeks the increase was most prominent in the inner part of inner nuclear layer and in the outer part of inner plexiform layer. GABA transaminase activity and its distribution were not much different in both normal and degenerated retinas during development.