Differential expression of GAD65 and GAD67 during the development of the rat retina

Abstract The development of synthetic enzymes in the GABAergic system (GAD 67 and GAD 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 immunohistochemistry. As previously observed for GABA, immunoreactive GAD 67 profiles are seen clearly in the inner retinal layers at birth. At the end of the 1st week of postnatal life, immunolabeling is detected in amacrine and/or ganglion cells and in horizontal cells. GAD 67 immunoreactivity is transiently expressed in horizontal cells and disappears during the 3rd postnatal week. GAD 65 however does not develop until the 5th postnatal day. Immunolabeling is detected in the processes layering the inner plexiform layer (IPL) before being detected in the amacrine and/or ganglion cell bodies. The appearance of transcripts for GAD coincided with the appearance of the proteins. A transient form of mRNA transcripts of the GAD 67 gene containing an extra exon (ES-exon) is also observed which disappears progressively from birth to the 4th postnatal week. This form synthesizes a truncated, enzymatically inactive protein, which could participate in the regulation of GABA synthesis from glutamate present at high levels during retinogenesis.