Differential expression of GAD(65) and GAD(67) during the development of the rat retina

The development of synthetic enzymes in the GABAergic system (GAD(67) and G AD(65)) of the rat retina was analyzed from birth to the 4th postnatal week by the reverse transcriptase polymerase chain reaction (RT-PCR) and by imm unohistochemistry. As previously observed for GABA, immunoreactive GAD(65) profiles are seen clearly in the inner retinal layers at birth. At the end of the Ist week of postnatal life, immunolabeling is detected in amacrine a nd/or ganglion cells and in horizontal cells. GAD(67) immunoreactivity is t ransiently expressed in horizontal cells and disappears during the 3rd post natal week. GAD,, however does not develop until the 5th postnatal day. Imm unolabeling is detected in the processes layering the inner plexiform layer (IPL) before being detected in die amacrine and/or ganglion cell bodies. T he appearance of transcripts for GAD coincided with the appearance of the p roteins. A transient form of mRNA transcripts of the GAD(67) gene containin g an extra exon (ES-exon) is also observed which disappears progressively f rom birth to the 4th postnatal week. This form synthesizes a truncated, enz ymatically inactive protein, which could participate in the regulation of G ABA synthesis from glutamate present at high levels during retinogenesis. ( C) 2001 Elsevier Science B.V. All rights reserved.