Figure 3: Outline of Research Results (IMAGE) Kanazawa University Caption Lower frame: We observed the expression of melatonin receptor (Mel-R), melatonin synthesizing enzyme (ASMT), and CALCITONIN (an osteoclast-inhibiting hormone) in osteoblasts in regenerating goldfish scales. Melatonin stimulated CALCITONIN production in the scales, which has also been detected in mammalian bones. The autocrine and paracrine effects of melatonin could stimulate CALCITONIN production in scales, in turn suppressing osteoclast activity. Upper frame: Microgravity during space flight accelerated the multinucleation and resorption activity in scale osteoclasts, which was associated with the stimulated gene expression of Rankl (a major factor for osteoclastogenesis) and the suppressed gene expression of Calcitonin. Melatonin administration maintained the normal gene expression levels of the factors during space flight and suppressed microgravity-stimulated osteoclast activity. The results suggest that melatonin could be used as a prophylactic drug to prevent bone loss in astronauts during space flight. OB, osteoblasts; OC, osteoclasts; POC, preosteoclasts; RANKL, receptor activator of nuclear factor κB ligand; Mel, melatonin; Mel-R, melatonin receptor; CALCITONIN-R, CALCITONIN receptor; ASMT: N-acetylserotonin O-methyltransferase; ISS, the International Space Station. Credit Kanazawa University Usage Restrictions The image may only be used with appropriate caption and credit. License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.