Embryonic development of monoaminergic neurons in the chick retina

By means of a histofluorescence technique, embryonic and postnatal development of monoaminergic neurons was followed in the chicken retina with or without intravitreal injection of monoamines 30-60 minutes before eye removal. Fluorescent cells were tentatively classified into five subsets with respect to the soma shape, localization, migration of somata during retinal development, uptake capacity (color and intensity in fluorescence), and sensitivity to neurotoxins. The five subsets of cells were endogenous dopaminergic (DA), catecholamine-accumulating (CA), indoleamine-accumulating (IA), CA-bipolarlike, and IA-bipolarlike cells. Greenish endogenous DA-cells first appeared at the 14-15th embryonic day. The cell body of DA-cells was initially fusiform and located slightly distal to the innermost level of the inner nuclear layer (INL). They became round or oval and migrated to the innermost level of the INL by day 20. Both large and small bottle-shaped CA-cells were visualized at an intermediate portion of INL by intravitreal injection of exogenously applied dopamine or noradrenaline (1-2 micrograms/eye) at day 10. Large bottle-shaped cells, like the DA cells, changed to round or oval and migrated to the innermost level of the INL by day 20. On the other hand, small bottle-shaped CA-cells retained their cell shape and location in the INL as retinal development progressed. Therefore, the large bottle-shaped CA-cells seen in an early developmental stage correspond to the DA-cells. IA-cells were visualized one or two cell rows outward in the INL first at day 13-14 by intravitreal injection of 5,6-dihydroxytryptamine or 5-hydroxytryptamine (1-5 micrograms).(ABSTRACT TRUNCATED AT 250 WORDS)