Standard curves for quantitative RT-PCR of GluR2-flip, GluR2-flop, and G3PDH. A, Product formation as a function of the number of PCR cycles. The cDNA template for each reaction was reverse-transcribed from 15 ng of total RNA isolated from rat retina. B, Product formation as a function of total rat retinal RNA used to produce the cDNA template for PCR. In each case, 28 cycles of PCR were performed. The intensity of the bands from GluR2-flip (685 bp), GluR2-flop (685 bp), and G3PDH (452 bp) detected by ethidium bromide staining (bottom) were quantitated using a CCD image sensor.