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 in amacrine cells, and to a lesser extent in other cell types. During development, GABA is expressed transiently in additional cells, including retinal ganglion cells and horizontal cells. Elements of the GABA system, 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 component of the GABA system in the mature retina, and is most likely responsible for GABA release early in development, prior to the establishment of vesicular synaptic transmission. GABA, produced by amacrine cells and retinal ganglion cells, may serve a developmental role in the establishment of circuitry in the retinal inner plexiform layer and may also be involved in the formation of appropriate central connections by retinal ganglion cell axons.