Circadian rhythms and performance in rhesus monkeys: Gender, gravity, and light

The circadian timing system (CTS) synchronizes virtually every physiological and behavioral variable to the light/dark (LD) cycle. Male and female rhesus (Macaca mullata) were used as subjects to examine gender differences in the CTS, as well as to explore the sensitivity of the CTS to gravity and light changes.; Rhesus were housed individually in cages at the California Regional Primate Center on a large centrifuge. Each animal was implanted with a telemetry transmitter to measure body temperature (Tb), heart rate (HR), and activity (ACT). Water was available ad libitum through a lixit system. A pelletized diet was provided through the Psychomotor Test System (PTS). Psychomotor and short-term memory performance were also monitored through PTS. Husbandry was performed one hour each day on a non-24 hour schedule. Mean, phase, and amplitude of each circadian rhythm were calculated.; The effects of menstrual cyclicity on physiological and behavioral circadian rhythms were examined. Estrogen and progesterone conjugates were assayed and quantified in female rhesus to identify phases of the menstrual cycle. There were few significant differences in circadian variables between phases of the menstrual cycle. Acrophase of HR was significantly delayed in the luteal phase. Females showed a significant delay in acrophase as compared to males in all measured circadian variables. In performance, there was a significant difference in accuracy on a short-term memory task; males scored significantly higher than females.; When exposed to a chronic hyperdynamic condition, circadian rhythms persist, but initially the amplitude of Tb is significantly decreased and HR mean significantly increased. Males and females respond similarly to 2G exposure, but the magnitude of the response in mean HR is significantly greater for females. Response time in psychomotor tasks is temporarily increased at 2G onset.; Finally, gender differences in the rate of resynchronization following an advance and delay to the lighting schedule were explored at 1G and 2G. Females resynchronized significantly faster than males in Tb, drinking and feeding rhythms. There were no significant differences in times to resynchronize between 1G and 2G. Performance was minimally affected by the changes in the LD cycle.