GABA AS A DEVELOPMENTAL SIGNAL IN THE INNER RETINA AND OPTIC-NERVE

Gamma-aminobutyric acid (GABA) acts as an inhibitory neurotransmitter in the mature vertebrate retina, where it is localized predominantly i n amacrine cells, and to a lesser extent in other cell types. During d evelopment, GABA is expressed transiently in additional cells, includi ng retinal ganglion cells and horizontal cells. Elements of the GABA s ystem, including GABA uptake and release mechanisms and GABA receptors , are also expressed early in retinal development, well in advance of the onset of visual function. The GABA transporter is a major componen t of the GABA system in the mature retina, and is most likely responsi ble for GABA release early in development, prior to the establishment of vesicular synaptic transmission. GABA, produced by amacrine cells a nd retinal ganglion cells, may serve a developmental role in the estab lishment of circuitry in the retinal inner plexiform layer and may als o be involved in the formation of appropriate central connections by r etinal ganglion cell axons.