DIFFERENTIAL DISTRIBUTION OF CAM KINASES AND INDUCTION OF C-FOS EXPRESSION BY FLASHING AND SUSTAINED LIGHT IN RAT RETINAL CELLS

Purpose. To examine the expression of c-fos proto-oncogene and phospho rylation of cAMP responsive element binding (CREB) protein in the rat retina after changes in the light-dark condition. Methods. Rats were e xposed to both steady light and flashing light and were killed at the end of light exposure. The retinas were analyzed by in situ hybridizat ion using single-stranded RNA probes for c-fos transcripts and by immu nocytochemistry using phosphoSer-133 specific CREB antiserum, anti-cal cium calmodulin dependent protein (CaM) kinase II, and anti-CaM kinase IV. Results. c-fos mRNA was expressed in the outer half of the inner nuclear layer (INL) and in the ganglion cell layer (GCL) after 30 minu tes of sustained light. After 30 minutes of flashing light, c-fos expr ession also was detected in the inner border of the INL. Phosphorylate d CREB immunoreactive nuclei had similar distribution after steady and flashing light. Both CaM kinase II and CaM kinase IV, which phosphory late CREB at Ser 133 in vitro, were expressed in the GCL and in the IN L, CaM kinase II, however, was localized in the inner border of the IN L, whereas CaM kinase IV was distributed in the outer half of the INL. Conclusions. These results suggest that the differential expression o f c-fos mRNA induced by flashing and sustained light may reflect the C REB phosphorylation by CaM kinases in a different subpopulation of ret inal cells.