A noninvasive analysis of urinary musculoskeletal collagen metabolism markers from rhesus monkeys subject to chronic hypergravity.

A decrease in load-bearing activity, as experienced during spaceflight or immobilization, affects the musculoskeletal system in animals and humans, resulting in the loss of bone and connective tissue. It has been suggested that hypergravity (HG) can counteract the deleterious effects of microgravity-induced musculoskeletal resorption. However, little consensus information has been collected on the noninvasive measurement of collagen degradation products associated with enhanced load-bearing stress on the skeleton. The purpose of this study is to assess the urinary collagen metabolic profiles of rhesus monkeys (Macaca mulatta) during 1) 2 wk of basal 1 G (pre-HG), 2) 2 wk of HG (2 G), and 3) two periods of post-HG recovery (1 G). Urine was collected over a 24-h period from six individual rhesus monkeys. Hydroxyproline (Hyp) and collagen cross-links (hydroxylysylpyridinoline and lysylpyridinoline) were measured by reverse-phase HPLC. Urinary calcium, measured by atomic absorption, and creatinine were also assayed. The results indicate no changes in nonreducible cross-links and Hyp during HG. Collagen cross-link biomarker levels were significantly elevated during the 2nd wk of HG. Urinary calcium content was significantly lower during HG than during the 1-G control period, suggesting calcium retention by the body. We conclude that there is an adaptation of the nonhuman primate musculoskeletal system during hyperloading and that noninvasive measurements of musculoskeletal biomarkers can be used as indicators of collagen and mineral metabolism during HG and recovery in nonhuman primates.

Gravity and light effects on the circadian clock of a desert beetle, Trigonoscelis gigas.

Circadian function is affected by exposure to altered ambient force environments. Under non-earth gravitational fields, both basic features of circadian rhythms and the expression of the clock responsible for these rhythms are altered. We examined the activity rhythm of the tenebrionid beetle, Trigonoscelis gigas, in conditions of microgravity (microG; spaceflight), earth's gravity (1 G) and 2 G (centrifugation). Data were recorded under a light-dark cycle (LD), constant light (LL), and constant darkness (DD). Free-running period (tau) was significantly affected by both the gravitational field and ambient light intensity. In DD, tau was longer under 2 G than under either 1 G or microG. In addition, tauLL was significantly different from tauDD under microG and 1 G, but not under 2 G.

Effects of 2G exposure on lean and genetically obese Zucker rats.

Changes in the ambient force environment alter the regulation of adiposity, food intake and energy expenditure (i.e., energy balance). Lean (Fa/Fa) and obese (fa/fa) male Zucker rats were exposed to 2G (twice Earth's normal gravity) for eight weeks via centrifugation to test the hypothesis that the Fa/Fa rats recover to a greater degree from the effects of an increased ambient force environment on body mass and food intake, than do the fa/fa rats which have a dysfunctional leptin regulatory system. The rats (lean and obese exposed to either 1G or 2G) were individually housed in standard vivarium cages with food and water provided ad libitum. The acute response to 2G included a transient hypophagia accompanied by decreased body mass, followed by recovery of feeding to new steady-states. In the lean rats, body mass-independent food intake had returned to 1G control levels six weeks after the onset of centrifugation, and body mass increased towards that of the 1G rats. In contrast, food intake and body mass of the 2G obese rats plateaued at a level lower than that of the 1G controls. Although percent carcass fat was reduced more in the 2G leans vs. 2G obese rats, the latter lost significantly more grams of fat than did the leans. Our data suggest that with respect to food intake and body mass, the lean rats recover from the initial effects of 2G exposure to a greater degree than do the fatty rats, a difference that likely reflects the functionality of the leptin regulatory system in the leans.

Circadian rhythms in Macaca mulatta monkeys during Bion 11 flight.

Circadian rhythms of primate brain temperature, head and ankle skin temperature, motor activity, and heart rate were studied during spaceflight and on the ground. In space, the circadian rhythms of all the parameters were synchronized with diurnal Zeitgebers. However, in space the brain temperature rhythm showed a significantly more delayed phase angle, which may be ascribed to an increase of the endogenous circadian period.

Thermal regulation in Macaca mulatta during space flight.

The results of studies of body temperature and thermal regulation in Macaca mulatta flown on biosatellites Bion 6-11 are presented. The effect of microgravity on deep body temperature as compared to skin temperature was investigated. In most animals, deep body temperature declined moderately and then tended to return to normal. Brain temperature/ankle temperature correlation changed. The system of thermal regulation was found to function adequately in space.

Energy metabolism of Macaca mulatta during spaceflight.

The mean daily energy expenditure rates of two rhesus monkeys (Macaca mulatta) were determined during spaceflight on the joint U.S./Russian Bion 11 mission by the doubly labeled water (DLW, 2H218O) method. Control values were obtained from two studies performed under flight-like conditions (n = 4). The mean inflight energy expenditure for the two Bion 11 monkeys was 81.3 kcal/kg/day, which was higher than that seen previously. The average energy expenditure (77.6 +/- 4.4 kcal/kg/day) for the four ground control monkeys was slightly lower than had been measured previously.

Alterations in endogenous circadian rhythm of core temperature in senescent Fischer 344 rats.

We assessed whether alterations in endogenous circadian rhythm of core temperature (CRT) in aging rats are associated with chronological time or with a biological marker of senescence, i.e., spontaneous rapid body weight loss. CRT was measured in male Fischer 344 (F344) rats beginning at age 689 days and then continuously until death. Young rats were also monitored. The rats were housed under constant dim red light at 24-26 degrees C, and core temperature was recorded every 10 min via biotelemetry. The CRT amplitude of the body weight-stable (presenescent) old rats was significantly less than that of young rats at all analysis periods. At the onset of spontaneous rapid weight loss (senescence), all measures of endogenous CRT differed significantly from those in the presenescent period. The suprachiasmatic nucleus (a circadian pacemaker) of the senescent rats maintained its light responsiveness as determined by an increase in c-fos expression after a brief light exposure. These data demonstrate that some characteristics of the CRT are altered slowly with chronological aging, whereas others occur rapidly with the onset of senescence.

Development of circadian rhythms in rat pups exposed to microgravity during gestation.

Ten pregnant Sprague Dawley rat dams were exposed to spaceflight aboard the Space Shuttle (STS-70) for gestational days 11-20 (G 11-20; FLT group). Control dams were maintained in either a flight-like (FDS group) or vivarium cage environment (VIV group) on earth. All dams had ad lib access to food and water and were exposed to a light-dark cycle consisting of 12 hours of light (approximately 30 lux) followed by 12 hours of darkness. The dams were closely monitored from G 22 until parturition. All pups were cross-fostered at birth; each foster dam had a litter of 10 pups. Pups remained with their foster dam until post natal day 21 (PN 21). Pup body mass was measured twice weekly. At PN 14 FLT pups had a smaller body mass than did the VIV pups (p < 0.01). Circadian rhythms of body temperature and activity of pups from two FLT dams (n = 8), two FDS dams (n = 9) and two VIV dams (n = 7) were studied starting from age PN 21. All pups had circadian rhythms of temperature and activity at this age. There were no significant differences in rhythms between groups that could be attributed to microgravity exposure. These results indicate that exposure to the microgravity environment of spaceflight during this embryonic development period does not affect the development of the circadian rhythms of body temperature and activity.

Effects of microgravity on circadian rhythms in insects.

NASA: The desert beetle Trigonoscelis gigas Reitt. was used as a biological model in studies that examined the effects of space flight on the circadian timing system. Results from studies aboard the Bion-10, Bion-11, and Photon-11 missions are reported. The control study is an ongoing Mir experiment. The studies indicate that the free-running period in beetles may be longer during space flight.^ieng

Gravitational biology on Mir.

The focus of this paper is to describe the experiences of a first time Space Life Sciences Principal Investigator. The Mir Beetle experiment was developed as a result of the joint US-Russian Mir Program. Dr. Alexei Alpatov collaborated as the Russian Co-Investigator. This experiment examined the long term effects of microgravity on the biological clock of a desert-dwelling beetle, Trigonoscelis gigas. The performance of this Space Life Sciences investigation involved: developing the proposal, design and testing of the hardware and execution of the spaceflight experiment.

The effect of spaceflight on retino-hypothalamic tract development.

NASA: Researchers examined the effect of late prenatal exposure to microgravity on the development of the retina, retinohypothalamic tract, geniculo-hypothalamic tract, and suprachiasmatic nucleus. Results indicate an effect on c-fos activity in the intergeniculate leaflet between gestational day 20 and postnatal day 8, suggesting a delay in development of the circadian timing system.^ieng

Response of insect activity rhythms to altered gravitational environments.

NASA: Researchers describe the development of the Beetle Activity Monitor (BAM), constructed to support an experiment with the desert beetle, Trigonoscelis gigas, proposed for the NASA-Mir program. The BAM tracks beetle movement via a wheel which turns as the animal moves in the cage. In addition to design features that conform to shuttle specifications and animal housing standards, it holds a maximum number of animals, allows for continuous recording of activity, and provides a controlled lighting environment. An experiment with 32 beetles collected data in 5-minute increments for animals exposed to constant darkness and 12-hour light-dark periods. Results of this experiment indicate that the light-dark cycle entrained the beetle circadian rhythm.^ieng

Primate circadian rhythms during spaceflight: results from Cosmos 2044 and 2229.

The circadian timing system (CTS) coordinates an animal's physiology and behavior both internally and with the 24-h day. Previous studies have suggested that the CTS is sensitive to changes in gravity. To examine this question, the expression of the CTS in four juvenile male rhesus macaques (Macaca mulatta) were studied in space. These animals were flown on the Cosmos 2044 and 2229 missions. Activity, heart rate, and axillary and brain (Cosmos 2229) temperatures were recorded. In both flights, the subjects exhibited delays in the phasing of their temperature rhythms and a decrease in mean heart rate compared with ground control studies. These data are in support of other studies that demonstrate that the CTS is sensitive to changes in the gravitational environment. Furthermore, the data also support the concept of a multioscillator organization of the primate CTS due to the differential responses of the rhythms measured.

Acute exposure to 2G phase shifts the rat circadian timing system.

The circadian timing system (CTS) provides internal and external temporal coordination of an animal's physiology and behavior. In mammals, the generation and coordination of these circadian rhythms is controlled by a neural pacemaker, the suprachiasmatic nucleus (SCN), located within the hypothalamus. The pacemaker is synchronized to the 24 hour day by time cues (zeitgebers) such as the light/dark cycle. When an animal is exposed to an environment without time cues, the circadian rhythms maintain internal temporal coordination but exhibit a "free-running" condition in which the period length is determined by the internal pacemaker. Maintenance of internal and external temporal coordination are critical for normal physiological and psychological function in human and non-human primates. Exposure to altered gravitational environments has been shown to affect the amplitude, mean, and timing of circadian rhythms in species ranging from unicellular organisms to man. However, it has not been determined whether altered gravitational fields have a direct effect on the neural pacemaker, or affect peripheral physiological systems that express these circadian parameters. In previous studies, the ability of a stimulus to phase shift circadian rhythms was used to determine whether a stimulus has a direct effect on the neural pacemaker. The present experiment was performed in order to determine whether acute exposure to a hyperdynamic field could phase shift circadian rhythms.

Changes in hypothalamic [correction of hypothalmic] staining for c-Fos following 2G exposure in rats.

The static gravitational field of the earth has been an important selective pressure that has shaped the evolution of biological organisms. This is illustrated by the evolution of tetrapods from a water environment where gravitational force was partially negated to a terrestrial environment where gravity is of greater consequence. Terrestrial invasion resulted in a series of new structural, physiological, and behavioral features. Therefore, it is not surprising that alterations in the gravitational field can cause widespread effects in many physiological systems and behaviors. Our previous studies have demonstrated that both exposure to hyperdynamic fields and the microgravity condition of space flight have significant effects on body temperature, heartrate, activity, feeding, drinking, and circadian rhythms. However, it has not been determined whether these physiological adaptations are associated with changes in neural activity within the hypothalamic nuclei that regulate these functions. This study examined the changes in body temperature, activity, body weight and food and water intake in rats caused by exposure to a hyperdynamic field. In addition, the immediate early gene activation marker, c-Fos, was used to examine potential protein synthesis changes in the hypothalamic nuclei that regulate these functions.

Influence of gravity on the circadian timing system.

The circadian timing system (CTS) is responsible for daily temporal coordination of physiological and behavioral functions both internally and with the external environment. Experiments in altered gravitational environments have revealed changes in circadian rhythms of species ranging from fungi to primates. The altered gravitational environments examined included both the microgravity environment of spaceflight and hyperdynamic environments produced by centrifugation. Acute exposure to altered gravitational environments changed homeostatic parameters such as body temperature. These changes were time of day dependent. Exposure to gravitational alterations of relatively short duration produced changes in both the homeostatic level and the amplitude of circadian rhythms. Chronic exposure to a non-earth level of gravity resulted in changes in the period of the expressed rhythms as well as in the phase relationships between the rhythms and between the rhythms and the external environment. In addition, alterations in gravity appeared to act as a time cue for the CTS. Altered gravity also affected the sensitivity of the pacemaker to other aspects of the environment (i.e., light) and to shifts of time cues. Taken together, these studies lead to the conclusion that the CTS is indeed sensitive to gravity and its alterations. This finding has implications for both basic biology and space medicine.