Alterations of body temperature, feeding, drinking, and sleep-wake circadian rhythms in Rhesus monkey during a 19 day Spacelab flight simulation.

Previous experiments performed with mammals during spaceflight suggest that microgravity may affect the circadian timekeeping system. However, this system could also be influenced by other factors related to the spaceflight environment, such as the animal compartment. The Rhesus project is a joint program of C.N.E.S. and N.A.S.A in which investigators in various disciplines of physiology will take advantage of flights of the Spacelab to study problems that interest them, using the Rhesus monkey as animal model. The technical characteristics of the Rhesus Research Facility in the Spacelab have been described elsewhere. In order to clarify the influence of the spaceflight environment, other than microgravity itself, on the circadian timekeeping system, we evaluated the characteristics of the circadian rhythms of body temperature, food and water intake, and sleep-wake cycles in Rhesus monkeys during the first 19-day flight simulation of this project.