CIRCADIAN-RHYTHMS OF CORNEAL MITOTIC RATE, RETINAL MELATONIN AND IMMUNOREACTIVE VISUAL PIGMENTS, AND THE EFFECTS OF MELATONIN ON THE RHYTHMS IN THE JAPANESE-QUAIL

We investigated circadian ocular rhythms in the Japanese quail, Coturn ix japonica. The birds were placed under light-dark cycles (LD 12:12), constant light (LL) and constant darkness (DD), and the retinas were dissected out at four-hour intervals throughout 24 h. Following measur ements were performed. (1) Melatonin content in the retina was measure d by radioimmunoassay. It was low in light and several folds higher in darkness under LD 12:12. The rhythm continued in DD, but disappeared in LL. (2) Mitotic figures in the corneal epithelium were counted. Sim ilar rhythms to the melatonin content were observed in the corneal mit otic rate with a slight phase delay. (3) The retinas were fixed at 4-h intervals and immunostained with anti-bovine rhodopsin serum and anti -chicken iodopsin monoclonal antibodies. The outer segments of photore ceptor cells were stained intensively throughout 24 h in LD 12: 12, LL and DD. In contrast, the stainability of the locus close to the outer limiting membrane where the Golgi apparatus exists changed diurnally. Scores showing the ratio of cells with positive staining indicated hi gh values from 4 h after the onset of light to the beginning of dark p hase under LD 12:12. The values were high throughout 24 h in LL and in termediate or low in DD. (4) To investigate the effect of melatonin on the corneal mitotic rate and visual pigments at the Golgi region, mel atonin was injected into one eye and saline into the contralateral eye . Melatonin induced a phase advance in the corneal mitotic rate under LD 12:12, but did not induce a rhythm under LL. The ratio of photorece ptor cells with positive staining to anti-visual pigment antibodies at the Golgi region was not affected by melatonin injection.