Fig. 4. Circadian rhythms of rhodopsin promoter-driven GFP expression in individual rod photoreceptor cells. (A) GFP intensity in individual rod cells during the first (top row) and second cycles (bottom row) in constant darkness (DD). Note that the times of peak expression (normalized to 1.0) varied in different cells. (B) Time-lapse images of rhodopsin promoter-driven GFP expression in two rod cells from the same slice preparation in 24 h of DD. The highest expression was detected at 13:00 h and 07:00 h, respectively, in cell 1 and cell 2. Black bars, night; gray bars, subjective day without light.