Dopaminergic cell differentiation in the developing chick retina.

The distribution and morphology of dopaminergic (DA) neurons in the chick retina was studied in the course of development. Fluorescent DA cells were first detected on the 13th day of incubation. They were always found in positions two or three cell rows externally from the junction between the inner plexiform layer (IPL) and inner nuclear layer (INL). On the 14th day, DA cells were found in the innermost row of the INL. Subsequently their processes extended not only bilaterally along the IPL-INL junction but also vertically into the IPL. As a result, three fiber layers were formed as laminae 1, 3 and 5 in the IPL. In the newly-hatched chick retina, a number of growth cone-like fluorescent structures with fine spikes were seen at the IPL-INL junction, indicating that DA fibers were still growing and elongating at least at hatching. On the 4th postnatal day, the ramification of dendritic processes was very prominent and they often showed a spiral configuration.