Neurogenesis of Photoreceptor Cells in the Pineal Organ and Retina of the Adult Fish

点击翻译按钮获取中文摘要

Cell proliferation in the pineal organ of the immature and matured rainbow trout Oncorhynchus mykiss was investigated by immunocytochemical demonstration of proliferating cell nuclear antigen (PCNA) and BrdU (thymidine analogue) -labeling together with photoreceptor-specific opsin. Numerous PCNA-immunoreactive cells were found throughout the pineal end-vesicle and stalk. Two types of PCNA-immunoreactive cells were distinguished : intensely stained, large ovoid and round cells, and mildly stained, slender fusiform cells. Occasionally, close approaches were found between the opsin-immunoreactive photoreceptor outer segments and the PCNA-immunoreactive cells, which expressed mildly stained, nuclear and cytoplasmic signals. In addition, close connections or overlaps of the opsin-immunoreactive outer segments with the BrdU-labeled cells were found here and there within the pineal epithelium of the rainbow trout. Compared with these findings of the rainbow trout, PCNA-immunoreactive cells or BrdU-labeled cells were found scarcely in the pineal organs of the other fish, such as tilapia Oreochromis niloticus, zebrafish Danio rerio and goldfish Carassius auratus. Consequently, these results suggest that the proliferation and neurogenesis of the pineal photoreceptor cells persist through the life of the rainbow trout, thus maintaining highly sensitive, photo-signal transduction mechanisms for melatonin synthesis and reproduction