A Comparative Study of the Chronological Appearance of Adenohypophysial Cells in Vertebrates with Emphasis on the Japanese Soft-Shelled Turtle (Pelodiscus sinensis japonicus)

We previously reported the chronological appearance of adenohypophysial cells in several vertebrates using an immunocytochemical technique. The present study investigated the chronological appearance of adenohypophysial cells in the freshwater Japanese soft-shelled turtle (Pelodiscus sinensis japonicus). The results were compared with those of the sea turtle, as well as other vertebrates which were studied by us and other researchers. In adult Japanese soft-shelled turtle adenohypophysis, six or seven types of secretory cells were distinguished; prolactin (PRL), growth hormone (GH), thyroid stimulating hormone (TSH), gonadotropic hormones (LH and FSH), adrenocorticotropic hormone (ACTH), and melanophore stimulating hormone (MSH). Chronologically, on five days after spawning, the first cells to appear were TSH, LH, ACTH and MSH cells. Subsequently, 13 days after spawning, a few FSH cells were observed; 22 days after spawning, GH and PRL cells appeared. These results, relating to the localization patterns and chronological order of appearance of the adenohypophysial cells, were similar to the sea turtle. Moreover, we demonstrate the chronological appearance of six other animal species (rainbow trout, Nile tilapia, Ayu, Japanese whiting, clouded salamander and golden hamster). A comparative study of other animals investigated by different researchers showed that each animal had a species-specific order of the appearance of the adenohypophysial cells and suggested the order was closely related to developmental style, spawning and environment of each animal. Hormones appearing during the early developmental stage may be required to survive in each species-specific environment.