HISTOGENESIS AND TOPOGRAPHICAL DISTRIBUTION OF TYROSINE-HYDROXYLASE IMMUNOREACTIVE AMACRINE CELLS IN THE DEVELOPING CHICK RETINA

There is a delay from the time when amacrine cells are generated to the time when the dopaminergic phenotype is first expressed, in the chick retina. In order to determine the birthdate of amacrine cells expressing the tyrosine hydroxylase (TH) phenotype, we combined autoradiography of [H-3]thymidine incorporated into dividing cells with the immunocytochemical method for TH in mature retinas. We also investigated the morphogenesis and the topographical distribution of dopaminergic amacrine cells using radial and horizontal sections of the chick retina. Although TH immunoreactivity was first detected at E12, the morphological pattern of TH-immunoreactive (TH-IR) amacrine cells started to be defined at E16, with an increasing arborization complexity until hatching. The topographical distribution of dopaminergic cells revealed that TH-IR neurons were predominantly concentrated in the dorsal retina of E13 and E14 embryos. At E18 and PH2 the distribution of dopaminergic cells was uniform throughout the retina. Autoradiography of [H-3]thymidine incorporated association with TH immunocytochemistry showed that dopaminergic amacrine cells are generated during a discrete period (E3 through E7) of amacrinogenesis that occurs from E3 to E9. Therefore, a delay of days between histogenesis of dopaminergic amacrine cells and their differentiation is observed.