Circadian Potency Spectrum in Light-Adapted Humans.

Light exposure at night can disrupt the circadian timing of cellular processes and is associated with a broad range of health disorders. To spectrally engineer lighting which minimizes circadian disruption at night it is necessary to define the precise spectral sensitivity of the human circadian system. Prior attempts have used short monochromatic light exposures in dark-adapted human subjects, or dark-adapted isolated retina or melanopsin.

Circadian Potency Spectrum with Extended Exposure to Polychromatic White LED Light under Workplace Conditions.

Electric light has enabled humans to conquer the night, but light exposure at night can disrupt the circadian timing system and is associated with a diverse range of health disorders. To provide adequate lighting for visual tasks without disrupting the human circadian timing system, a precise definition of circadian spectral sensitivity is required. Prior attempts to define the circadian spectral sensitivity curve have used short (≤90-min) monochromatic light exposures in dark-adapted human subjects or in vitro dark-adapted isolated retina or melanopsin.

Circadian alertness simulator for fatigue risk assessment in transportation: application to reduce frequency and severity of truck accidents.

The Circadian Alertness Simulator (CAS) was developed as a practical tool for assessing the risk of diminished alertness at work. Applications of CAS include assessment of operational fatigue risk, work schedule optimization, and fatigue-related accident investigation. Based on the documented work schedules of employees, sleep and alertness patterns are estimated and a cumulative fatigue score is calculated.

EEG delta activity during undisturbed sleep in the squirrel monkey.

The squirrel monkey (Saimiri sciureus) exhibits a robust daily rhythm of sleep-wakefulness that is under circadian control, but the nature of homeostatic sleep regulation in this diurnal primate is poorly understood. Since delta frequency (0.5-2.

Circadian and homeostatic influences on sleep in the squirrel monkey: sleep after sleep deprivation.

A series of sleep deprivation (SD) experiments were performed to examine the relative influence of circadian and homeostatic factors on the timing of sleep in squirrel monkeys free-running in constant illumination. All SDs started at the beginning of subjective night and lasted 0, 1/4, 1/2, 1, 1 1/4, or 1 1/2 circadian cycles. These six lengths represented three pairs: (0.

MidnightSun: software for determining light exposure and phase-shifting schedules during global travel.

The application of circadian principles has the potential to alleviate jet-lag in global travelers, but their application is hampered by the difficulty of determining light exposure along international flight routes. Computerized tools can solve this problem algorithmically. We have developed a program for Macintosh computers, called MidnightSun, which allows researchers to display ambient lighting conditions at any geographical location at any time of the year.

Thermoregulatory responses of rhesus monkeys during spaceflight.

This study examines the activity, axillary temperature (T(ax)), and ankle skin temperature (Tsk) of two male Rhesus monkeys exposed to microgravity in space. The animals were flown on a Soviet biosatellite mission (COSMOS 1514). Measurements on the flight animals, as well as synchronous flight controls, were performed in the Soviet Union.

Renal response to 7 days of lower body positive pressure in squirrel monkeys.

The purpose of this study was to characterize the renal response to central volume expansion using lower body positive pressure (LBPP) in the adult male squirrel monkey (Saimiri sciureus). Urinary excretion of sodium, potassium, and water and plasma aldosterone concentrations were measured during a control day, 7 days of LBPP, and a recovery day. Time control experiments in the same animals included chair sitting without exposure to LBPP.

The benzodiazepine triazolam phase-shifts circadian activity rhythms in a diurnal primate, the squirrel monkey (Saimiri sciureus).

Triazolam can shift the phase of circadian rhythms in hamsters recorded in constant light or dark. This effect is apparently mediated by physical activity stimulated by the drug. We examined whether triazolam can shift the phase of circadian rhythms in a diurnal primate, the squirrel monkey, that is sedated by triazolam.

Effects of aging on food-entrained circadian rhythms in the rat.

Twenty-four hour schedules of restricted food availability entrain a component of the circadian activity rhythm in rats via a food-entrainable pacemaker separate from the light-entrainable pacemaker. The effect of aging on food-entrained circadian rhythms was examined in 6 rats maintained on a restricted diurnal feeding schedule from age 3-21 months and again from 24-25 months. Food-entrainment, measured as behavioral anticipation of a 1-hr daily mealtime during the middle of the light period and persistence of this anticipation rhythm during food deprivation, was apparent in the aged rats when recorded in wheel-running cages from 20-21 months of age.

Lithium lengthens circadian period in a diurnal primate, Saimiri sciureus.

Lithium lengthens the period of free-running circadian rhythms in a variety of species, but this effect has not been demonstrated unequivocally in primates. Because of the possible link between lithium's action on the circadian clock and its therapeutic action in human mood disorders, we tested the ability of lithium to lengthen circadian period in a diurnal primate with circadian properties similar to those of humans. Lithium carbonate was administered in food pellets to 8 adult male squirrel monkeys (Saimiri sciureus) for at least 27 consecutive days.

Food-anticipatory rhythms under 24-hour schedules of limited access to single macronutrients.

Food-restricted rats anticipate a fixed daily mealtime by entrainment of a circadian timekeeping mechanism separate from that which generates daily light-entrainable activity rhythms. The entrainment pathways and rhythm-generating substrates for food-anticipatory rhythms are unknown. In this study, we attempted to define minimal food-related stimuli necessary or sufficient for food anticipation by employing schedules of restricted macronutrient availability, with or without free access to a complementary diet.

Characteristics of food-entrained circadian rhythms in rats during long-term exposure to constant light.

Rats possess a system of circadian oscillators that permit entrainment of circadian activity rhythms independently to 24 hr cycles of light-dark and food access. The nature of interactions between food- and light-entrainable oscillators was examined by observing the generation and persistence of food-entrained circadian rhythms in rats whose light-entrainable rhythms were eliminated by long-term exposure to constant light. Most of these rats showed a delayed generation of food-entrained rhythms and only one of eight animals showed persistence of food associated rhythms during a 4-day food deprivation test.

Effects of restricted feeding schedules on circadian organization in squirrel monkeys.

Free running circadian rhythms of motor activity, food-motivated lever-pressing, and either drinking (N = 7) or body temperature (N = 3) were recorded from 10 squirrel monkeys maintained in constant illumination with unlimited access to food. Food availability was then restricted to a single unsignaled 3-hour interval each day. The feeding schedule failed to entrain the activity rhythms of 8 monkeys, which continued to free-run.

In vivo metabolic activity of the suprachiasmatic nuclei: non-uniform intranuclear distribution of 14C-labeled deoxyglucose uptake.

Anatomical techniques have shown that the suprachiasmatic nuclei (SCN) are organized into distinct dorsomedial and ventrolateral subdivisions. As a functional correlate to this morphological organization, the intranuclear distribution of SCN glucose utilization was mapped using the autoradiographic 14C-labeled deoxyglucose method. In nocturnal rats and diurnal squirrel monkeys injected with the tracer during the light portion of the light-dark cycle, the middle of the SCN was metabolically more active than its rostral or caudal ends.

[Circadian rhythms and temperature homeostasis in monkeys during a flight on the Kosmos 1514 biosatellite].

In the course of a 5-day space flight of two rhesus-monkeys the following parameters were recorded at an interval of 16 min: core body temperature (Tc), skin temperature (Ts), and motor activity (MA). The telemetric Tc sensor was implanted subcutaneously in the right axilla, Ts thermistor was attached to the right ankle, and the MA piezotape was fixed to the inner side of the vest. Circadian rhythms of Tc varied with a period of 24 hours in one monkey and 25 hours in the other.

Resynchronization of circadian sleep-wake and temperature cycles in the squirrel monkey following phase shifts of the environmental light-dark cycle.

Circadian rhythms in physiological and behavioral functions gradually resynchronize after phase shifts in environmental time cues. In order to characterize the rate of circadian resynchronization in a diurnal primate model, the temperature, locomotor activity, and polygraphically determined sleep-wake states were monitored in squirrel monkeys before and after 8-h phase shifts of an environmental light-dark cycle of 12 h light and 12 h dark (LD 12:12). For the temperature rhythm, resynchronization took 4 d after phase delay shift and 5 d after phase advance shift; for the rest-activity cycle, resynchronization times were 3 d and 6 d, respectively.

Estrogen modifies the circadian timing and amplitude of the luteinizing hormone surge in female hamsters exposed to short photoperiods.

LH surges occur 3 h later in intact anovulatory hamsters exposed to nonstimulatory photoperiods (6L:18D) for 8 wk than the proestrous LH surges from the same hamsters housed in 6L:18D for 3 weeks. In ovariectomized hamsters housed in 6L:18D for 3 wk, the LH surge was observed at the same time of day as in intact anovulatory hamsters at 8 wk. Implanting Silastic capsules containing estradiol benzoate (EB) advanced the timing of the daily surge of LH in ovariectomized hamsters housed in 6L:18D for 8 wk.

Physiology of the circadian timing system: predictive versus reactive homeostasis.

Since Cannon first formulated the concept of homeostasis 60 years ago, attention has been focused on the corrective responses initiated after the steady state of the organism is perturbed. In this lecture it is argued that the concept of homeostasis should be extended to include the precisely timed mechanisms of the circadian (and circannual) timing system which enables organisms to predict when environmental challenges are most likely to occur. A mature understanding of homeostasis should encompass both "reactive" responses to changes in physiological variables which have already occurred and the "predictive" responses initiated in anticipation of predictably timed challenges.

GABA and circadian timekeeping: implications for manic-depression and sleep disorders.

Circadian rhythms, evident in a wide variety of physiological and behavioural parameters, are under the control of central neural pacemakers, the best characterized of which is the suprachiasmatic nucleus of the hypothalamus. The neurophysiological mechanisms involved in central pacemaker function are unknown. Recent biochemical, pharmacological and behavioural evidence suggests that the inhibitory transmitter gamma-aminobutyric acid (GABA), present in the small interneurones of the suprachiasmatic nucleus, plays an important role in circadian timekeeping.

Sleep-wake stages during the subjective night of the squirrel monkey.

The study of the circadian sleep-wake cycle is beset by unique technical challenges. Continuous polygraphic recordings are necessary to characterize circadian phenomena; however, the traditional method of recording sleep at high (15 mm/sec) chart speed is impractical for continuous animal studies that may last several weeks at a stretch. A system to determine four sleep-wake stages (awake, transitional, non-REM, REM) from low chart speed (1.

Daily rhythms of benzodiazepine receptor numbers in frontal lobe and cerebellum of the rat.

Behavioural, biochemical and neurophysiological evidence suggests that gamma-aminobutyric acid (GABA) may play an important role in the neural control of circadian rhythms. Central receptors for benzodiazepines are functionally coupled to GABA receptors and appear to mediate behavioural effects of exogenous benzodiazepines. The binding of 3H-flunitrazepam to synaptic plasma membranes prepared from various regions of rat brain was examined at 6-hour intervals over a 36-hour period.

Forced internal desynchronization between circadian temperature and activity rhythms in squirrel monkeys.

In an attempt to force internal desynchronization between the rest-activity rhythm and the body temperature rhythm of the squirrel monkey (Saimiri sciureus), five animals were studied in a 14:14 light-dark cycle. In four animals a 28-h spectral component was found to predominate in the rest-activity rhythm, whereas an unentrained circadian component (tau = 25.9 +/- 0.

Role of heat loss and heat production in generation of the circadian temperature rhythm of the squirrel monkey.

To study heat production and heat loss in determination of the daily body temperature rhythm, we examined colonic temperature, skin (tail, foot and abdomen) temperatures and oxygen consumption in chair-restrained squirrel monkeys maintained in isolation in an environmental chamber with a 24-hr light-dark cycle (LD 12:12), maintained at a constant thermoneutral temperature (26 degrees C). In all experiments repeated high amplitude (2 degrees C) diurnal rhythms in colonic temperature were observed. Heat loss, estimated from changes in skin temperature, also displayed a circadian rhythm, although there was considerable variation in waveform.