Abstract
Effects of 5, 7-dihydroxytryptamine (5, 7-DHT) on indoleamine-accumulating (IA-) cells were investigated on the retinas (cryo-sectioned or flat-mounted) of adult carp (Cyprinus carpio), by means of a histofluorescence technique. The eyes, pretreated with a single intravitreal injection of 5, 7-DHT (15μg), were removed at various testing periods (4hr to 50d) with or without an intravitreal injection of 5, 6-dihydroxytryptamine (5, 6-DHT; one or 5μg) alone, or with the same injection of noradrenaline (NA; 5μg) plus 5, 6-DHT (5μg) 2hr prior to enucleation. In cryo-sections of the retinas loaded with 5, 6-DHT (5μg), the indoleamine was found to be taken up not only by IA-cells but also by other cells located in the amacrine cell layer. The latter class of cells was more weakly fluorescent and smaller in size than IA-cells. Two days after pretreatment with 5, 7-DHT, IA-cells already became invisible, while the accumulative ability of smaller cells for 5, 6-DHT remained. Subsequently, IA-cells were not seen again with 5, 6-DHT in flat-mounts up to 50d (the longest testing period in the present experiment) after pretreatment with 5, 7-DHT. The results obtained reveal that intravitreally given 5, 7-DHT (15μg) destroyed quasipermanently the somata of retinal IA-cells in the adult carp.
