Development of retinopetal projections in the cichlid fish, Herotilapia multispinosa

This paper reports a study of the development of cells that project to the retina from the telencephalic nucleus olfactoretinalis and the diencephalon. Stell et al. (Proc. Natl. Acad. Sci. USA 81:940-944, '84) have shown that the FMRFamide-immunoreactive (FMRFamide-ir) cells in the nucleus olfactoretinalis project to the retina. Therefore, we used immunocytochemistry to study the development of these cells in the nucleus olfactoretinalis. Twenty hours after fry hatched, FMRFamide-ir cells were unambiguously seen in the nucleus olfactoretinalis. At this time the axons of these cells could be traced into the optic nerve. A few hours later the axons were visible in the retina and soon attained their adult position in the inner plexiform layer near the amacrine cells. In older frey, tracers were used to fill retinopetal cells in both the nucleus olfactoretinalis and the diencephalon. Counts of these cells demonstrated that over one-third of the adult number of retinopetal cells in the nucleus olfactoretinalis are present and have axons in the retina when the fry is 9 days old, and the percentage grows to one-half by the time the fry is 1 month old. Development of the retinopetal cells in the diencephalon lags behind that of the cells in the nucleus olfactoretinalis. However, about one-third of the adult number extend their axons into the optic nerve by 1 month of age. These results support our suggestion that the retinopetal cells have axons in the old part of the optic nerve because these cells were born and extended axons early in the life of the fish.