Circadian rhythm in the subcommissural organ of the frog,Rana arvalis Nilsson,under natural conditions

Summary A circadian activity of SCO ependymal cells, judged by changes in the nuclear volume, has been found in juvenile frogs (Rana arvalis) under natural summer conditions. The nuclear volume reaches its maximum at 12.00 h and a minimum at 24.00 h. A significant increase in activity occurs between 06.00 and 09.00 h and a gradual decrease is observed from 12.00 to 24.00 h.