Postnatal development of dopaminergic cells in the rat retina

By means of a histofluorescence technique (FGS method), a post-natal ontogeny of dopaminergic neurons (DA-cells) in the retina was studied in rats which had been born and reared under diurnal lighting (LD), reversed lighting (DL), constant lighting (LL), or continuous dark conditions (DD). The time of first appearance of DA-cells was not altered by any of the above conditions; weakly fluorescent cell bodies were visible at about the 10th postnatal day. After the eyes were open the DA fluorescence of the cell body was gradually increased in intensity in all LD, DL, and LL rats, but not for DD rats. At the 16-17th day the processes of the cell first became visible, extending laterally to the inner plexiform layer. The somata and their processes appeared to be well developed at the postnatal 4-6th week, and they resembled those of the adult rat. On the other hand, the DA-cells in the DD rats showed a weak fluorescence in both the somata and their processes. When the DD rats were transferred and reared under LD conditions for 1-3 days, the DA fluorescence was increased. These results strongly suggest that the initiation of retinal DA synthesis is independent of environmental lighting condition, but an adequate light stimulus is required for continued normal development of DA-cells. Unlike in the rat, fluorescent cells in the guinea pig and chick retinas were observed to be fairly mature at birth or hatching. The developmental pattern of DA-cells in the three species examined coincides with the maturation of visual function.