Development of retinal monoamine neurons in larval goldfish: a histofluorescence study

The emergence of retinal monoamine neurons was explored in embryonic and larval goldfish (Carassius auratus) by means of a histofluorescence technique. The high-affinity uptake capacity of dopamine (DA) and indoleamine-accumulating (IA) neurons for exogenously applied DA and 5,6-dihydroxytryptamine began to occur simultaneously on the hatching day (stage 25/26). Endogenous DA neurons were first detected on the third postnatal day (stage 26/27). The appearance of DA and IA neurons was found to begin in the central part and to extend to the peripheral part of individual retinas. The first DA and IA neurons to be detected were situated in the inner nuclear layer and migrated proximally to the innermost level of the inner nuclear layer 5-7 days after hatching. The developmental process of monoamine neurons observed represents an aspect of cellular differentiation and maturation in the goldfish retina.