Alterations in the circadian system in advanced age

In addition to light, a variety of non-photic stimuli can induce phase shifts in the circadian clock of rodents. We have examined the effects of advanced age on the response of the circadian clock to both photic and non-photic stimuli in old hamsters (i.e., over 16 months of age). Among the age-related changes in the circadian rhythm of locomotor activity are: (1) alterations in the phase angle of entrainment to the light-dark cycle; (2) an altered response to the phase-shifting effects of light pulses; (3) changes in the time it takes to re-entrain to a new light-dark cycle; and (4) a loss of responsiveness to the phase-shifting or entraining effects of stimuli which induce an acute increase of activity. Many of the effects of ageing on the circadian clock system can be simulated in young animals by depleting brain monoamine levels, suggesting that ageing alters monoaminergic inputs to the clock. Some of the age-related changes in the response of the clock to an activity-inducing stimulus can be reversed by implanting old animals with fetal suprachiasmatic nuclear tissue. Determining the physiological basis of age-related changes in the responsiveness of the clock to both internal and external stimuli, and the mechanisms by which normal circadian functioning can be restored, should lead to new insight into the functioning of the circadian clock and may suggest new approaches to the normalization of disturbed circadian rhythms.

Prenatal stress in rats predicts immobility behavior in the forced swim test

Prenatally-stressed (PS) rats are characterized by a general impairment of the hypothalamo-pituitary-adrenal (HPA) axis and sleep disturbances indicating that this model has face validity with some clinical features observed in a subpopulation of depressed patients. The prolonged corticosterone secretion shown by PS rats in response to stress was positively correlated with an increased immobility behavior in the forced swim test. To investigate the predictive validity of this model, a separate group of animals was chronically treated with the antidepressant tianeptine (10 mg/kg i.p. for 21 days). Such chronic treatment reduced in PS rats immobility time in the forced swim test. These findings suggest that the PS rat is an interesting animal model for the evaluation of antidepressant treatment.

Prenatal stress and long-term consequences: implications of glucocorticoid hormones

We have shown that prenatal restraint stress (PNRS) induces higher levels of anxiety, greater vulnerability to drugs, a phase advance in the circadian rhythm of locomotor activity and an increase in the paradoxical sleep in adult rats. These behavioral effects result from permanent modifications to the functioning of the brain, particularly in the feedback mechanisms of the hypothalamic-pituitary-adrenal (HPA) axis: the secretion of corticosterone is prolonged after stress and the number of the central glucocorticoid receptors is reduced. These abnormalities are associated with modifications in the synthesis and/or release of certain neurotransmitters. Dysfunction of the HPA axis is due, in part, to stress-induced maternal increase of glucocorticoids, which influences fetal brain development. Some biological abnormalities in depression can be related to those found in PNRS rats reinforcing the idea of the usefulness of PNRS rats as an appropriate animal model to study new pharmacological approaches.

Circadian clock functioning is linked to acute stress reactivity in rats

At least two major physiological systems are involved in the adaptation of the organism to environmental challenges: the circadian system and the stress reaction. This study addressed the possibility that interindividual differences in stress sensitivity and in the functioning of the circadian system are related. At 2 months of age, corticosterone secretion in response to a 20-min restraint stress was assessed in 9 Sprague-Dawley rats for which running wheel activity was recorded as a rhythmic behavioral marker of the circadian clock. Two weeks later, the adaptive response of the circadian system to an abrupt shift in the light:dark (LD) cycle was assessed in those rats using a jet-lag paradigm. Finally, after resynchronization to the new LD cycle, rats were transferred to constant darkness to assess the free-running period of their circadian rhythm of running-wheel activity. Results indicate that stress-induced corticosterone secretion was (1) positively correlated with the number of days to resynchronize the circadian activity rhythm to the new LD cycle, and with the value of its free-running period, and (2) negatively correlated with the intensity of daily locomotor activity. Those data, emphasizing the interactions between the stress response of an organism and the functioning of its circadian system, could explain interindividual differences in humans' susceptibility to shift work or other circadian-related disorders.

[Fatigue and sleep: the point of view of the chronobiologist]

Chrono-fatigue is often present in patients engaged in shift or night work, as well as in passengers travelling across many time zones (jet lag syndrome). Some disturbances of the circadian system are responsible for clinical syndromes characterized by chrono-fatigue, one of them being the sleep delayed phase insomnia. Circadian sleep disorders, either functional or structural, are characterized not only by disturbances in sleep architecture and/or sleep quality, but also by the inability to fall asleep and stay awake at desired times. Similarly, sleep and fatigue present in those circadian disorders typically exhibit a daily cyclic pattern. Night workers and shift workers do have chronic sleep deprivation and desynchronisation of their circadian system with the entraining environment. Those phenomena are responsible for severe vigilance problems, a decrease in work productivity and deleterious health side effects. Fatigue and sleep problems in circadian disorders can now benefit from treatments based on the programed use of synchronizers of the circadian clock, like chronotherapy, bright light and melatonin, combined with adequate sleep hygiene recommendations.

Hormonal and behavioural abnormalities induced by stress in utero: an animal model for depression

Prenatal stress in rats can exert profound influence on the off spring's development, inducing abnormalities such as increased "anxiety", "emotionality" or "depression-like" behaviours.Prenatal stress has long-term effects on the development of the hypothalamo-pituitary-adrenal(HPA) axis and forebrain cholinergic systems. These long-term neuroendocrinological effects are mediated, at least in part, by stress-induced maternal corticosterone increase during pregnancy and stress-induced maternal anxiety during the postnatal period. We have shown a significant phase advance in the circadian rhythms of corticosterone secretion and locomotor activity in prenatally-stressed (PNS) rats. When subjected to an abrupt shift in the light-dark(LD) cycle, PNS rats resynchronized their activity rhythm more slowly than control rats. In view of the data suggesting abnormalities in the circadian timing system in these animals, we have investigated the effects of prenatal stress on the sleep-wake cycle in adult male rats. PNS rats exhibited various changes in sleep-wake parameters, including a dramatic increase in the amount of paradoxical sleep. Taken together, our results indicate that prenatal stress can induce increased responses to stress and abnormal circadian rhythms and sleep in adult rats.Various clinical observations in humans suggest a possible pathophysiological link between depression and disturbances in circadian rhythmicity. Circadian abnormalities in depression can be related to those found in PNS rats. Interestingly, we have recently shown that the increased immobility in the forced swimming test observed in PNS rats can be corrected by chronic treatment with the antidepressant tianeptine, or with melatonin or S23478, a melatonin agonist. Those results reinforce the idea of the usefulness of PNS rats as an appropriate animal model to study human depression and support a new antidepressant-like effect of melatonin and the melatonin agonist S23478.

Sleep deprivation decreases phase-shift responses of circadian rhythms to light in the mouse: role of serotonergic and metabolic signals

The circadian pacemaker in the suprachiasmatic nuclei is primarily synchronized to the daily light-dark cycle. The phase-shifting and synchronizing effects of light can be modulated by non-photic factors, such as behavioral, metabolic or serotonergic cues. The present experiments examine the effects of sleep deprivation on the response of the circadian pacemaker to light and test the possible involvement of serotonergic and/or metabolic cues in mediating the effects of sleep deprivation. Photic phase-shifting of the locomotor activity rhythm was analyzed in mice transferred from a light-dark cycle to constant darkness, and sleep-deprived for 8 h from Zeitgeber Time 6 to Zeitgeber Time 14. Phase-delays in response to a 10-min light pulse at Zeitgeber Time 14 were reduced by 30% in sleep-deprived mice compared to control mice, while sleep deprivation without light exposure induced no significant phase-shifts. Stimulation of serotonin neurotransmission by fluoxetine (10 mg/kg), a serotonin reuptake inhibitor that decreases light-induced phase-delays in non-deprived mice, did not further reduce light-induced phase-delays in sleep-deprived mice. Impairment of serotonin neurotransmission with p-chloroamphetamine (three injections of 10 mg/kg), which did not increase light-induced phase-delays in non-deprived mice significantly, partially normalized light-induced phase-delays in sleep-deprived mice. Injections of glucose increased light-induced phase-delays in control and sleep-deprived mice. Chemical damage of the ventromedial hypothalamus by gold-thioglucose (600 mg/kg) prevented the reduction of light-induced phase-delays in sleep-deprived mice, without altering phase-delays in control mice. Taken together, the present results indicate that sleep deprivation can reduce the light-induced phase-shifts of the mouse suprachiasmatic pacemaker, due to serotonergic and metabolic changes associated with the loss of sleep.

Melatonin or a melatonin agonist corrects age-related changes in circadian response to environmental stimulus

The effects of a melatonin agonist, S-20098, included in the diet were tested on a specific effect of aging in hamsters: the marked decline in the phase shifting effects of a 6-h pulse of darkness on a background of constant light. In contrast to young hamsters, old hamsters fed with the control diet showed little or no phase shifts in response to a dark pulse presented in the middle of their inactive or active period. Old hamsters fed with S-20098 showed phase shifts that were ~70% of the ones in young animals and significantly greater than those in old controls. The phase advancing response to a dark pulse presented during the inactive period was dose dependent and reversed after S-20098 discontinuation. Melatonin included in the diet showed comparable restorative effects on the phase shifting response to a dark pulse in old hamsters. Replacement therapy with melatonin or melatonin-related compounds could prove useful in treating, preventing, or delaying disturbances of circadian rhythmicity and/or sleep in older people.

A melatonin agonist facilitates circadian resynchronization in old hamsters after abrupt shifts in the light-dark cycle

Age-related changes in the mammalian circadian system may be associated with a decline in circulating melatonin levels. Using 'jet lag' paradigms involving abrupt shifts in the light-dark cycle, we showed that a melatonin agonist, S-20098, accelerated by approximately 25% resynchronization of the circadian activity rhythm in old hamsters to the new light-dark cycle. It suggests the usefulness of melatonin-related compounds to treat circadian disorders associated with aging.

Sleep and circadian disturbances in shift work: strategies for their management

More and more businesses are providing their full range of services 24 h a day, 7 days a week, thus forcing their employees to work either rotating shifts or fixed night shifts. Dictates of our endogenous circadian clock prevent our brains and bodies to be indefinitely adaptable to those work schedules. Shift work operations are thus associated with serious healthy and social problems for the workers. Various interventions can counteract circadian desynchronization, sleep disturbances, and social disruption associated with shift work: changes in work schedules, sleeping and napping strategies, use of appropriately timed exposure to bright light, experimental drug treatments, or exercise.

[Melatonin. II. Physiological and therapeutic effects]

Melatonin is a hormone mainly secreted by the pineal gland during the dark phase of the light-dark cycle. The most known function of melatonin in mammals is to transmit information concerning light-dark cycles playing the role of an active neuroendocrine transducer of environmental information. Given this chronobiologic role of pineal melatonin, it seems to be useful in the management of shift work, jet lag and some sleep disorders. In vitro like in vivo melatonin seems to be effective as an antioxidant and oncostatic agent. Melatonin may provide protection against aging process, degenerative diseases, cancer and play a role also in sexual maturation, reproduction, immune function and psychiatric illness. The administration of melatonin in the jet-lag syndrome is well codified. Further clinical research is needed for a better understanding and definition of other indications, treatment regimens and safety of the hormone. The aim of this paper is to review the current knowledge on its clinical implications.

Sleep in the Wistar-Kyoto rat, a putative genetic animal model for depression

The Wistar-Kyoto (WKY) rat exhibits several behavioral and hormonal abnormalities often associated with depression. One of the hallmarks of depression consists of alterations in the sleep-wake cycle, particularly in rapid eye movement (REM) sleep. If the WKY rat is indeed an animal model for depression, we hypothesized that it should also show sleep abnormalities relative to the control strain, the Wistar (WIS) rat Under baseline conditions, WKY rats showed a 50% increase in total REM sleep time during the 12 h light phase and an increase in sleep fragmentation during both the light and dark phase. The WKY rats also exhibited lower EEG power densities over the entire frequency range (0.2-25.0 Hz) during REM sleep. After a 6 h sleep deprivation, the REM sleep rebound was more pronounced during the dark but not the light phase in the WKY rats. Since the WKY rat represents a genetic model for depression with altered EEG sleep patterns, this strain may be particularly useful for investigating the relationship between depression and sleep abnormalities.

High corticosterone levels in prenatally stressed rats predict persistent paradoxical sleep alterations

Prenatal stress predisposes rats to long-lasting disturbances that persist throughout adulthood (e.g., high anxiety, dysfunction of the hypothalamo-pituitary-adrenal axis, and abnormal circadian timing). These disturbances parallel to a large extent those found in depressed patients, in which hypercortisolemia and sleep alterations may be related to stress-inducing events. We studied sleep-wake parameters in control and prenatally stressed adult rats (3-4 months old) and examined possible relationships with their corticosterone levels (determined at 2 months of age). Under baseline conditions, prenatally stressed rats showed increased amounts of paradoxical sleep, positively correlated to plasma corticosterone levels. Other changes include increased sleep fragmentation, total light slow-wave sleep time, and a slight decrease in the percentage of deep slow-wave sleep relative to total sleep time. During recovery sleep from acute restraint stress, all sleep changes persisted and were correlated with stress-induced corticosterone secretion. High corticosterone levels under baseline conditions as well as an acute stress challenge may thus predict long-term sleep-wake alterations in rats. Taken together with other behavioral and hormonal abnormalities in prenatally stressed animals, the pronounced changes in sleep-wake parameters that are similar to those found in depressed patients suggest that prenatal stress may be a useful animal model of depression.

Prenatal stress alters circadian activity of hypothalamo-pituitary-adrenal axis and hippocampal corticosteroid receptors in adult rats of both gender

Prenatal stress impairs activity of the hypothalamo-pituitary-adrenal (HPA) axis in response to stress in adult offspring. So far, very few data are available on the effects of prenatal stress on circadian functioning of the HPA axis. Here, we studied the effects of prenatal stress on the circadian rhythm of corticosterone secretion in male and female adult rats. To evaluate the effects of prenatal stress on various regulatory components of corticosterone secretion, we also assessed the diurnal fluctuation of adrenocorticotropin, total and free corticosterone levels, and hippocampal corticosteroid receptors. Finally, in the search of possible maternal factors, we studied the effects of repeated restraint stress on the pattern of corticosterone secretion in pregnant female rats. Results demonstrate that prenatal stress induced higher levels of total and free corticosterone secretion at the end of the light period in both males and females, and hypercorticism over the entire diurnal cycle in females. No diurnal fluctuation of adrenocorticotropin was observed in any group studied. The effects of prenatal stress on corticosterone secretion could be mediated, at least in part, by a reduction in corticosteroid receptors at specific times of day. Results also show that prepartal stress alters the pattern of corticosterone secretion in pregnant females. Those data indicate that prenatally stressed rats exhibit an altered temporal functioning of the HPA axis, which, taken together with their abnormal response to stress, reinforces the idea of a general homeostatic dysfunction in those animals.

A single oral dose of S 22153, a melatonin antagonist, blocks the phase advancing effects of melatonin in C3H mice

Disorders of the circadian system have been associated with adverse mental and physical conditions, raising the possibility that pharmacological agents acting on the circadian system could have therapeutic benefit. Compounds acting as agonists or antagonists of melatonin, an endogenous hormone able to feed back on the circadian clock, are currently under development for possible use in modulating circadian rhythmicity. In the present study, we examined the ability of an oral dose of S 22153, a synthetic melatonin antagonist, to block the phase advancing effect of a melatonin injection at circadian time 10 in free running C3H mice. Our results show that S 22153 had no effect per se on the phase or the period of the locomotor activity rhythm but was able to block the phase advancing effect of melatonin, suggesting potent antagonist effects at melatonin receptors. Availability of a melatonin antagonist may yield new insight into the role of melatonin in physiological processes and such compounds may find widespread clinical applications.

[Biologic rhythms. Nyctemeral variation in man]

CORTICOTROPIC AXIS: The nycthemeral pattern of cortisol is a good marker of the circadian clock. Cortisol levels fluctuate between a peak level, observed in the early hours of the morning, and a minimal level around midnight. This variability is considerably reduced or even abolished in Cushing s syndrome. THYREOTROPIC AXIS: The nycthemeral pattern of TSH secretion is dependent on both the circadian clock and sleep (which inhibits hormone secretion). The moment of the evening rise is a reliable marker of the circadian rhythmicity. SOMATOTROPIC AXIS: Growth hormone is essentially pulsatile. GH levels are often undetectable between pulses. The circadian rhythmicity plays only a minor role in the regulation of growth hormone secretion. LACTOTROPIC AXIS: Nycthemeral variations in prolactin secretion are mainly regulated by wake-sleep cycles; peak levels occur in the middle of the night. Prolactin secretion is also modulated by the circadian rhythmicity. GONADOTROPIC AXIS: Gonadotropins are secreted in pulses, following the pulses of GnRH secretion. In adult women, nycthemeral variations in LH are strongly modulated by the menstrual cycle. MELATONIN: The nychtemeral pattern of melatonin is an excellent marker of the circadian clock. Diurnal concentrations are low and vary little whereas peak levels are observed in the middle of the night. Melatonin rhythmicity is not influenced by sleep, but is dependent on exposure to light and darkness.

[Biologic rhythms. Circadian, ultradian and seasonal rhythms]

CIRCADIAN RHYTHMS: Our knowledge of the genetic and molecular mechanisms regulating the principal circadian clock located in the suprachiasmatic nuclei is progressing. The clock's intrinsic period varies from one species to another and to a lesser degree from one individual to another. In humans, the intrinsic period is slightly over 24 hours. The clock is capable of synchronizing itself to the surrounding environment by reacting to outside factors or zeitgebers (time-givers). Light-dark cycles are the main zeitgebers; meals, the social environment, and locomotor activity also affect the circadian clock. In addition, the circadian clock acts as an internal timer, providing the organism with a means of synchronizing the function of multiple biochemical and physiological systems. ULTRADIAN RHYTHMS: The frequency of ultradian rhythms varies considerably form one species to another and from one parameter to another. In humans, several functions oscillate at 60-120 minute intervals, rhythms which are sometimes superimposed on other functions oscillating at 3 to 5 minute intervals. SEASONAL RHYTHMS: Several mechanisms allow living organisms to adapt to seasonal variations in the environment. In certain species, reproduction functions are stimulated at appropriate moments in the yearly cycle, optimizing the newborn's chances of survival. Such seasonal variations are much less marked in humans.

[Biologic rhythms. Effect of aging on the desynchronization of endogenous rhythmicity and environmental conditions]

CIRCADIAN AND PULSATILE RHYTHMICITY IN THE AGING PROCESS: The aging process produces morphological and neurochemical alterations in the suprachiasmatic nuclei as well as major alterations in the quality of sleep. In addition, aging is frequently accompanied by changes in life style due to different, often less demanding, social and occupational activities, leading to an attenuation of the synchronizing effects of the light-dark and activity-rest cycles. Together, these different elements contribute to a decline in temporal organization in the elderly, a phenomenon which starts in the third decade for some variables. There is a characteristic phase shift with age: in an 80-year-old individual, the circadian cortisol peak occurs about 3 hours earlier than in a 20 year-old-individual. JET LAG AND NIGHT SHIFT WORK: The circadian rhythm and environmental conditions can become desynchronized after transmeridian flights, a phenomenon commonly called jet lag. In night shift workers, such desynchronization creates an important public health problem. The impact may be underestimated since 15 to 20% of the work force in industrialized countries work permanently or occasionally on night shifts. The resulting dissociation between environmental signals and the wake-sleep cycle leads to various health problems. No truly effective therapeutic strategy has been developed although ongoing research, particularly on the use of light and/or melatonin, provides some promising perspectives.

Chronobiotic effects of gepirone, a potential antidepressant with 5HT1A receptor partial agonist properties

Abnormal timing in the circadian system is reported in endogenous depression. Gepirone, a 5HT1A receptor partial agonist, has anxiolytic and antidepressant properties. We determined whether gepirone was able to modify the functioning of the circadian system. Single i.p. injections of gepirone in hamsters induced phase-advances in the circadian activity rhythm when administered during the subjective day, but had no effect when given during the subjective night. Single i.p. gepirone injections also blocked the phase-shifting effects of a light pulse, at a time when gepirone by itself had no effect on the activity rhythm. Chronic gepirone treatment in hamsters kept under a 14/10 light-dark cycle induced a phase-advance in the activity rhythm, modifying the phase-relationship between this rhythm and the light-dark cycle. After transfer to constant darkness, gepirone-treated hamsters showed a shortened free-running period of activity, compared to controls. Both acute and chronic gepirone treatment thus have major effects on the circadian rhythm of locomotor activity in rodents. In view of the hypothesized role for disturbed circadian rhythms in the pathophysiology of depression, and the use of 5HT-related drugs for its treatment, the results provide further support for the possibility that some of the therapeutic effects of these compounds may be due to their effects on temporal organization.

Pharmacologic and therapeutic features of sulbutiamine

Asthenia is the most frequent medical reason for people seeking help from their physician. In 75% of cases, the cause is functional (either reactive or psychiatric) and in 25% it is organic. In order to provide patients with rapid relief of symptoms, appropriate antiasthenic treatment should be initiated immediately, while at the same time, adequate clinical and laboratory assessments should be performed to detect the underlying cause of asthenia. Sulbutiamine, a highly lipophilic thiamine derivative, is the only antiasthenic compound known to cross the blood-brain barrier and to be selectively active on specific brain structures directly involved in asthenia. This article reviews the current knowledge on the effects of sulbutiamine in animal models and in various forms of human asthenia.

Resynchronisation of a diurnal rodent circadian clock accelerated by a melatonin agonist

Using 'jet lag' paradigms involving phase shifts in the light-dark (LD) cycle, we studied the effects of S-20098 on the circadian clock of a diurnal rodent. Arvicanthis mordax, entrained to a regular LD cycle, were subjected to advance shifts (i.e. 4, 6 or 8 h) in the LD cycle and injected with vehicle or the melatonin agonist S-20098 (20 mg/kg) the day of the shift (and also on subsequent days in the 6 h or 8 h shift paradigms). In each condition, S-20098 accelerated by about 30% resynchronization to the new LD cycle. These data, which are the first to demonstrate the chronobiotic effects of a melatonin agonist in a diurnal rodent, provide new insights for the design of human chronopharmacological protocols.

Effects of exercise on neuroendocrine secretions and glucose regulation at different times of day

To study the effects of time of day on neuroendocrine and metabolic responses to exercise, body temperature, plasma glucose, insulin secretion rates (ISR), and plasma cortisol, growth hormone (GH) and thyrotropin (TSH) were measured in young men, both at bed rest and during a 3-h exercise period (40-60% maximal O2 uptake). Exercise was performed at three times of day characterized by marked differences in cortisol levels, i.e., early morning (n = 5), afternoon (n = 8), and around midnight (n = 9). The subjects were kept awake and fasted, but they received a constant glucose infusion to avoid hypoglycemia. Exercise-induced elevations of temperature were higher in the early morning than at other times of day. The exercise-induced glucose decrease was approximately 50% greater around midnight, when cortisol was minimal and not stimulated by exercise, than in the afternoon or early morning (P < 0.05). This effect of time of day appeared unrelated to decreases in ISR or increases in temperature and GH. Robust TSH increases occurred in all exercise periods and were maximal at night. The results demonstrate the existence of circadian variations in neuroendocrine and metabolic responses to exercise.

Comparative effects of a melatonin agonist on the circadian system in mice and Syrian hamsters

S-20098 has potent and specific agonist properties on melatonin receptors both in vitro and in vivo. Behavioral studies on rodents already showed that repeated intraperitoneal administration of S-20098 could dose-dependently alter the functioning of the circadian clock. To determine whether single administration of S-20098 could alter the circadian rhythms of rodents, we first used the phase-response curve (PRC) approach in two different species: Syrian hamsters and mice (C3H/HeJ). Our results show that the shape, circadian times and extent of the PRC to S-20098 look very similar in mice and hamsters. In both species, the phase advance portion of the PRC to S-20098 is limited to a 3 h window preceding the onset of locomotor activity, but the magnitude of phase shifts is larger in mice. We also tested the phase shifting effects of increasing doses of S-20098 during the interval of maximal sensitivity to this compound. Treatment with S-20098 induces dose-dependent phase shifts, with maximal shifts observed after injections of 20 and 25 mg/kg S-20098 i.p., respectively, in mice and hamsters. Those results are in agreement with the limited distribution of melatonin-binding sites within the circadian clock of adult Syrian hamsters, as compared to other rodents.

Sleepiness, performance, and neuroendocrine function during sleep deprivation: effects of exposure to bright light or exercise

The temporal profiles of subjective fatigue (as assessed by the Stanford Sleepiness Scale), of cognitive performance (on a digit symbol substitution test and a symbol copying task), of body temperature, and of the peripheral concentrations of melatonin, thyroid-stimulating hormone (TSH), and cortisol were obtained simultaneously at frequent intervals in 17 normal young subjects submitted to a 43-h period of constant routine conditions involving continuous wakefulness at bed rest in dim indoor light. The subjects had knowledge of time of day. Caloric intake was exclusively in the form of an intravenous glucose infusion, and plasma glucose levels were monitored continuously in 8 of the 17 subjects. Under these conditions, fluctuations in plasma glucose reflect primarily changes in glucose use because endogenous glucose production is suppressed by the exogenous infusion. Following the completion of a baseline constant routine study, the volunteers participated in two subsequent studies using the same protocol to determine the immediate psychophysiological effects of exposure to a 3-h pulse of bright light or to a 3-h pulse of physical exercise. Sleepiness and performance varied in a mirror image, with significant negative correlations. Sleepiness scores were minimal around noon and then increased at a modest rate throughout the rest of the normal waking period. Staying awake during usual bedtime hours was associated with an acceleration in the rate of increase in sleepiness, which coincided with decreasing body temperature, rapidly rising cortisol concentrations, and maximal levels of melatonin and TSH. When body temperature reached its nadir, a further major increase in sleepiness occurred in parallel with a pronounced decrease in plasma glucose (reflecting increased glucose use). Recovery from maximal sleepiness started when blood glucose levels stopped falling and when significant decreases in cortisol and melatonin concentrations were initiated. Lower levels of subjective sleepiness resumed when glucose concentrations and body temperature had returned to levels similar to those observed prior to sleep deprivation and when melatonin and TSH concentrations had returned to daytime levels. The synchrony of behavioral, neuroendocrine, and metabolic changes suggests that circulating hormonal levels could exert modulatory influences on sleepiness and that metabolic alterations may underlie the sudden increase in fatigue consistently occurring at the end of a night of sleep deprivation. Effects of bright light or exercise exposure on subjective sleepiness appeared to be critically dependent on the timing of exposure.

Demonstration of rapid light-induced advances and delays of the human circadian clock using hormonal phase markers

To determine the magnitude and direction of phase shifts of human circadian rhythms occurring within 1 day after a single exposure to bright light, plasma thyrotropin, melatonin, and cortisol levels and body temperature were monitored for 38 h in 17 men who were each studied two times, once during continuous dim light conditions and once with light exposure. After a period of entrainment to a fixed sleep-wake cycle, a 3-h light pulse (5,000 lux) was presented under constant routine conditions, and the resultant phase shifts were measured, also under constant routine conditions, on the 1st day after pulse presentation. The phase shifts in response to light occurred within 24 h and were in the delaying direction for most of the nocturnal period, with the crossover to phase advances occurring approximately 1 h after the temperature minimum. Phase shifts averaged 1 h, with delays being larger than advances, and were achieved without significant changes in rhythm amplitude. The immediate response of the human circadian clock to a single 3-h light pulse is thus characteristic of "type 1" resetting.

Nocturnal exercise phase delays circadian rhythms of melatonin and thyrotropin secretion in normal men

To determine whether a single episode of physical activity is capable of inducing rapid phase shifts in human circadian rhythms, 17 subjects were studied two times under constant routine conditions, once in the absence of stimulus and once with a 3-h nighttime pulse of exercise interrupting the constant routine conditions. The profiles of plasma cortisol, thyrotropin (TSH), and melatonin and of body temperature were monitored continuously to derive estimations of circadian phase position. The phase shifts were measured on the 1st day after exercise exposure. The timing of the exercise period ranged from -5 h to +4 h around the time of the minimum body temperature rhythm. Nighttime exercise was associated with 1- to 2-h phase delays of both the melatonin and TSH rhythms, with the size of the delays tending to be smaller when the exercise was presented in the latter part of the nighttime period and in the early morning. These data demonstrate that nonphotic stimuli may exert phase-shifting effects on the human circadian pacemaker.

Daily exposure to a nonphotic stimulus can alter photoperiodic response to short days in hamsters

The ability of mammals to measure seasonal changes in daylength depends upon a circadian clock and the phase-relationship between this clock and the light: dark cycle. Recently, a number of pharmacological and nonpharmacological stimuli have been shown to have pronounced effects on the phase of the circadian clock of rodents. The objective of the present study was to determine if a drug-induced change in the phase-relationship between a measurable circadian rhythm (i.e., wheel running behavior) and the light:dark cycle would alter the effects of the light cycle on the neuroendocrine-gonadal axis. Adult male hamsters with regressed testes due to exposure to an inhibitory 10:14-hr light:dark cycle were daily injected with vehicle or the short-acting benzodiazepine, triazolam, while remaining on short days, while a control group of hamsters was transferred to a photostimulatory 14:10-hr light:dark cycle. Two other groups of hamsters with regressed testes were blinded and daily injected with vehicle or triazolam. The injections were timed to occur about 4 hr before activity onset because previous studies had demonstrated that injections of triazolam at this time can lead to a phase advance in the activity rhythm. The circadian rhythm of wheel running behavior was measured in all the animals maintained on the 10:14-hr light:dark cycle in order to monitor circadian phase. While no testicular growth was observed after 25 days of vehicle injections, growth was observed in the triazolam-treated animals that was comparable to that observed in control animals transferred to long days. Testicular growth in triazolam-treated animals was associated with an earlier onset of locomotor activity, when compared with the vehicle-treated animals. Importantly, triazolam had no effect on the testicular size of blind animals. These results indicate that daily injections of triazolam can stimulate neuroendocrine-gonadal activity by altering the phase-relationship between the cycle and the circadian clock involved in photoperiodic time measurement, and that agents which can affect the clock may be useful in altering seasonal cycles.

Grafting fetal suprachiasmatic nuclei in the hypothalamus of old hamsters restores responsiveness of the circadian clock to a phase shifting stimulus

In the present study, 18-25-month-old hamsters free-running in constant dim light were injected, both before and after receiving fetal grafts containing either cerebellar tissue or the suprachiasmatic nuclei (SCN), with a dose of triazolam given at a time known to reliably phase shift the rhythm of locomotor activity in young hamsters. SCN-grafted animals, but not control animals implanted with fetal cerebellar tissue, showed a significantly greater response to the phase shifting effects of triazolam, demonstrating that at least some age-related changes in the circadian system can be reversed by neuronal transplantation. These results raise the possibility that neuropharmacological interventions that can simulate the effects of fetal SCN grafts might be useful in the treatment of age-related disorders in circadian function.

Fos protein expression in the circadian clock is not associated with phase shifts induced by a nonphotic stimulus, triazolam

Recent studies have shown that light-induced phase shifts of the circadian rhythm of locomotor activity are associated with c-fos expression in the suprachiasmatic nucleus (SCN) and intergeniculate leaflet (IGL) of the lateral geniculate nucleus of rodents. In order to determine whether c-fos expression is necessary for the phase shifting effects of a non-photic stimulus, we assessed Fos-like immunoreactivity (Fos-lir) in the SCN and IGL at various times after an injection of the short-acting benzodiazepine, triazolam, at circadian time (CT) 6; i.e. at a time when triazolam induces an acute increase in locomotor activity and maximal phase advances in the circadian rhythm of locomotor activity. Specific Fos-lir staining was not observed in the SCN or IGL regions of any animals treated with triazolam or vehicle at any time point examined. These results indicate that exposure to an activity-inducing stimulus at circadian times when this stimulus induces phase shifts does not induce Fos protein synthesis in the SCN or IGL regions.

Aging alters the entraining effects of an activity-inducing stimulus on the circadian clock

In young hamsters, a single injection of the short-acting benzodiazepine, triazolam, can induce permanent phase shifts in the circadian clock, while repeated injections of triazolam entrain the circadian clock to the period of the injections. Triazolam appears to act on the circadian clock by inducing an acute increase in the activity of the animals, which in turn phase-shifts the circadian clock. Surprisingly, single injections of benzodiazepines do not phase-shift the activity rhythm of old hamsters, despite the fact that such treatment induces similar acute changes in the activity state of young and old animals. We compared the entraining effects of repeated injections of triazolam on the circadian clock of young and old hamsters; while six out of seven young hamsters were entrained to the triazolam injections, only one out of seven old animals was entrained by this treatment. Three of the remaining six old hamsters showed a lengthening of the activity rhythm, while no consistent effect on the period of the activity rhythm was observed in the remaining three old animals. These results indicate that the circadian system of old hamsters becomes selectively unresponsive to synchronizing signals mediated by the activity-rest state, and suggest that aging is associated with a weakened coupling between the activity-rest cycle and the circadian clock.

Aging alters feedback effects of the activity-rest cycle on the circadian clock

Two different stimuli (i.e., benzodiazepines and dark pulses) inducing phase shifts in the circadian clock of young hamsters through changes in the level of activity do not induce phase shifts in old hamsters, despite the fact that these stimuli induce a similar acute change in locomotor activity in young and old animals. In contrast, old hamsters remain sensitive to the phase-shifting effects of stimuli clearly not associated with any change in locomotor activity (i.e., protein synthesis inhibitors or light). Thus the circadian system of old animals becomes selectively unresponsive to synchronizing signals mediated by the activity-rest state of the animals. Previous age-related changes in circadian rhythmicity that have been observed in mammals, including humans, may be related to a weakened coupling between the activity-rest cycle and the circadian clock.

Changes in the phase response curve of the circadian clock to a phase-shifting stimulus

Experiments were conducted in hamsters to determine whether the phase response curve (PRC) to injections of the short-acting benzodiazepine triazolam is a fixed or a labile property of the circadian clock. The results indicated that (1) both the shape and the amplitude of the PRC to triazolam generated on the first day of transfer from a light-dark cycle (LD 14:10) to constant darkness (DD) (i.e., PRCLD) were different from those of the PRC generated after many days in DD (PRCDD); and (2) the phase-shifting effects of triazolam on the activity rhythms of hamsters transferred from LD 14:10 or 12:12 to DD changed dramatically within the first 8-9 days spent in DD. In an attempt to accelerate the resynchronization of the circadian clock of hamsters subjected to an 8-hr advance in the LD cycle, triazolam was given to the animals at a time selected on the basis of the characteristics of PRCLD. The activity rhythms of five of eight triazolam-treated animals were resynchronized to the new LD cycle within 2-4 days after the shift, whereas those of most of the control animals were resynchronized 21-29 days after the shift. These findings suggest that attempts to use pharmacological or nonpharmacological tools to phase-shift circadian clocks under entrained conditions should take into account information derived from PRCs generated at the time of transition from entrained to free-running conditions.

The effects of short periods of immobilization on the hamster circadian clock

Recent findings indicate that stimuli which induce an acute increase in locomotor activity can induce phase shifts in the circadian clock of hamsters. Support for the actual role of the acute increase in activity in the mediation of these phase shifts is provided by the observation that immobilization can totally block phase shifts in the activity rhythm that are normally induced in response to exposure to two of these stimuli, either a pulse of darkness or an injection of a benzodiazepine. In order to further examine the effects of immobilization on the circadian system of hamsters, 3 studies were carried out. In a first study, the effects of a 3-h period of immobilization procedure on the phase of the free running circadian rhythm of locomotor activity were tested at 8 different circadian times. Immobilization during the highly active part of the animal's activity cycle resulted in phase delays in the activity rhythm, while immobilization at other circadian times had little or no effect on the circadian time-keeping system. In two other studies, we reported that immobilization had no effect on phase shifts normally induced by 3-h pulses of light or injections of the protein synthesis inhibitor, cycloheximide, two stimuli that are clearly not associated with an increase in locomotor activity in hamsters. Thus, the ability of immobilization to block stimulus-induced phase shifts in the circadian clock appears to be specific to those stimuli that induce an acute increase in locomotor activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of amiodarone on serum T3 and T4 concentrations in hyperthyroid patients treated with propylthiouracil

Amiodarone (Cordarone) has been proven to be useful in the management of atrial fibrillation. However, because of a large iodine content, this drug is not used in this complication of thyrotoxicosis. We previously have observed a greater fall in serum T3 and T4 concentrations in hyperthyroid patients treated with amiodarone and methimazole than with methimazole alone. In the present study, we determined whether the addition of amiodarone to propylthiouracil (PTU) could improve the levels of circulating thyroid hormones in hyperthyroid patients, and we assessed the release of iodide from amiodarone by measuring the 24 h urinary iodine excretion. Twelve hyperthyroid patients were treated either with PTU, 600 mg daily for 10 days (group PTU), or with amiodarone (A), 1200 mg daily for 3 days in addition to PTU (group A-PTU). Basal serum T4, T3, and rT3 concentrations (mean +/- SEM) were respectively 206 +/- 13 nmol/L, 5.13 +/- 0.8 nmol/L, and 81 +/- 7 ng/dL for group PTU and 238 +/- 39 nmol/L, 4.73 +/- 1.06 nmol/L, and 84 +/- 12 ng/dL for group A-PTU (NS). In group A-PTU, plasma amiodarone peaked on day 3 (mean +/- SEM: 0.48 +/- 0.11 mg/L), and urinary iodine reached 5.27 +/- 1.28 mg/day on day 5. The fall in serum T3 and the increase in serum rT3 concentrations were significantly greater in group A-PTU than in group PTU (ANOVA, p less than 0.05). In group A-PTU, the minimal serum T3 concentration was observed on day 5 of treatment (28 +/- 6% of the pretreatment values).(ABSTRACT TRUNCATED AT 250 WORDS)

Daily injections of triazolam induce long-term changes in hamster circadian period

Previous experiments in hamsters indicate that daily injections of the short-acting benzodiazepine, triazolam, can entrain the free-running circadian activity rhythm to the period of the injections and that, after discontinuation of triazolam injections, the period of the free-running activity rhythm remains close to that of the previous injection schedule for 20-50 cycles. In this paper, we extend these findings and demonstrate that 1) long-term treatment with triazolam can induce aftereffects on the period of the circadian clock underlying the activity rhythm that can last for up to 100 days, 2) triazolam-induced changes in period can lead to a loss of effect of daily injections of triazolam which can be restored if the time of injection is altered, and 3) chronic treatment with triazolam also alters the period of the circadian clock in animals entrained to a light-dark cycle, and such changes in period alter the phase relationship between the circadian clock and the entraining light-dark cycle.

Rapid correction of hyponatraemia with urea may protect against brain damage in rats

1. Rapid correction of hyponatraemia in humans has been reported to be associated with central pontine myelinolysis (CPM). In patients with hyponatraemia related to the syndrome of inappropriate antidiuretic hormone secretion (SIADH) we have rapidly corrected hyponatraemia by using urea, without observing clinical CPM. This led us to analyse the brain damage induced by hypertonic saline and by urea when used for the correction of hyponatraemia in a rat model of SIADH. 2. Severe hyponatraemia (serum Na+ less than 115 mmol/l) was produced in 28 rats. Seven rats were excluded from statistical analysis because they died during the correction of hyponatraemia, or because they were under- or over-corrected. Normalization of serum Na+ (135-146 mmol/l) was obtained in 48 h by hypertonic saline (group I, n = 7) or urea (group II, n = 8). 3. Despite similar correction of serum Na+ at 24 h and 48 h, all the rats treated with hypertonic saline presented severe brain damage, whereas those treated with urea were free of any brain damage. A third group of rats (n = 6) who spontaneously corrected their serum sodium level and presented mild hyponatraemia at 48 h (129 +/- 5.2 mmol/l) were also free of any brain damage.

Stimulated activity mediates phase shifts in the hamster circadian clock induced by dark pulses or benzodiazepines

A number of environmental and pharmacological stimuli capable of inducing phase shifts and/or period changes in the circadian clock of mammals have now been identified. Agents that can alter circadian clocks provide a means for investigating the cellular and neural mechanisms responsible for their generation, regulation and entrainment. Two stimuli that have been used to probe the basis of circadian rhythmicity are pulses of darkness on a background of constant light and injections of short-acting benzodiazepines, such as triazolam. Surprisingly, these two very different stimuli have remarkably similar phase-shifting effects on the circadian clock of hamsters. The observation that a short-term increase in locomotor activity occurs when the circadian activity rhythm of hamsters is shifted by dark pulses or triazolam injections, coupled with the finding that activity bouts themselves are capable of shifting this rhythm, raises the possibility that dark pulses or triazolam alter the circadian clock by inducing acute hyperactivity. Here we demonstrate that the phase-advancing and phase-delaying effects of dark pulses or triazolam on the circadian activity rhythm can be totally suppressed by immobilization of the animals during treatment. These results indicate that behavioural events mediate the phase-shifting effects of both dark pulses and triazolam on the circadian activity rhythm and question present hypotheses regarding the pathways by which light-dark information and pharmacological agents influence circadian pacemakers.

Administering triazolam on a circadian basis entrains the activity rhythm of hamsters

A single injection of the short-acting benzodiazepine, triazolam, can induce permanent phase shifts in the circadian rhythm of locomotor activity in free-running hamsters, with the direction and magnitude of the phase shifts being dependent on the circadian time of treatment. The shape of the "phase-response curve" to triazolam injections is totally different from that for light pulses. These findings raise the possibility that repeated injections of triazolam on a circadian basis might be capable of entraining the circadian pacemaker underlying the activity rhythm of hamsters and that the entrainment pattern might differ from that observed in animals entrained to light pulses. To test this hypothesis, blind hamsters received intraperitoneal injections of triazolam (or vehicle) every 23.34, 23.72, 24.00 or 24.66 h for 19-20 days, and the effect of these injections on the period of the rhythm of wheel-running behavior was determined during and after treatment. Repeated injections of 0.1 mg triazolam at these time intervals resulted in the entrainment of the activity rhythm in 36 of 40 animals, whereas 0 of 40 animals entrained to vehicle injections. Importantly, the phase relationship between triazolam injections and the circadian activity rhythm was dependent on the period of drug treatment and could be predicted from the phase-response curve to single injections of triazolam. These phase relationships are dramatically different from those observed between the activity rhythm and 1-h light pulses presented at similar circadian intervals.(ABSTRACT TRUNCATED AT 250 WORDS)

Use of benzodiazepines to manipulate the circadian clock regulating behavioral and endocrine rhythms

Extensive studies have now been carried out demonstrating that the systemic administration of the short-acting benzodiazepine, triazolam, can have pronounced effects on both behavioral and endocrine circadian rhythms. For example, three daily injections of triazolam can phase-advance the circadian rhythm of pituitary luteinizing hormone release and locomotor activity by about 2-3 h in female hamsters maintained in constant light. Triazolam has also been found to facilitate the rate of reentrainment of the activity rhythm following an 8-hour advance or delay in the light-dark cycle. Limited studies with other short-acting benzodiazepines indicate that the effects of triazolam on the circadian system of hamsters can be generalized to this class of drugs. Recent studies in humans indicate that treatment with triazolam can alter the time it takes for human endocrine rhythms to become reentrained following an 8-hour delay in the sleep-wake and light-dark cycle. Such findings raise the possibility that short-acting benzodiazepines may prove useful in reducing the symptoms associated with 'jet-lag' and rotating shift-work schedules as well as in the treatment of various physical and mental illnesses that have been associated with a disorder of biological timekeeping.

A benzodiazepine antagonist, Ro 15-1788, can block the phase-shifting effects of triazolam on the mammalian circadian clock

A single injection of the short acting benzodiazepine, triazolam, can induce permanent phase advances as well as phase delays in the onset of the circadian rhythm of wheel running behavior in hamsters free-running under constant environmental conditions. If the phase shifting effects of triazolam on the circadian system are mediated through the benzodiazepine-GABA receptor complex, then it should be possible to block these effects with RO 15-1788, a selective benzodiazepine antagonist, which acts at the benzodiazepine-GABA receptor level. To test this hypothesis, hamsters free running in constant light received an intraperitoneal injection of various doses of Ro 15-1788 15 min before a single i.p. injection of 0.5 mg of triazolam. This dose of triazolam is known to induce maximal phase shifts in the circadian rhythm of wheel running behavior in hamster. Treatment with Ro 15-1788 totally blocked both the phase advancing and phase delaying effects of triazolam, while the administration of Ro 15-1788 alone did not phase shift the activity rhythm. These results support the hypothesis that the phase shifting effects of triazolam are mediated through the benzodiazepine-GABA receptor complex. The absence of any phase shifting effects of Ro 15-1788 when delivered alone suggests that Ro 15-1788 has no partial agonist properties in this experimental paradigm.

Manipulation of the circadian clock with benzodiazepines: implications for altering the sleep-wake cycle

Abnormal circadian rhythms have been linked to at least some forms of depression and to disturbances in the sleep-wake cycle. In addition, mental and physical disorders associated with rapid travel across time zones (i.e. the jet-lag syndrome) and with rotating shift-work schedules, are thought to involve a disruption of normal circadian rhythmicity. It might be possible to alleviate some of the adverse effects associated with abnormal circadian rhythms if pharmacological agents could be used to manipulate the central circadian pacemaker(s) that regulates these rhythms. Recent findings indicate that treatment with a short-acting benzodiazepine, triazolam, can induce major shifts in the circadian clock of golden hamsters. In the absence of a synchronizing light-dark cycle (i.e. during exposure to constant light or constant dark), a single injection of triazolam can induce a permanent phase shift in the circadian rhythm in locomotor activity. In addition, following a shift in the light-dark cycle, a single injection of triazolam can facilitate the time it takes for the activity rhythm to be resynchronized to the new lighting schedule. Triazolam, or drugs with similar phase-shifting effects on the mammalian circadian system, might be useful in the treatment of various sleep and mental disorders that have been associated with a disorder in circadian time-keeping in humans.

Distribution of neuropeptide Y immunoreactivity in human visual cortex and underlying white matter

Immunocytochemical techniques have been used to study neuropeptide Y (NPY) distribution in the human visual cortex (Brodman's areas 17, 18 and 19) NPY cell bodies belong mostly to inhibitory (multipolar and bitufted) but also to excitatory (bipolar and some pyramidal) neuronal types. Their distribution is similar in the three cortical areas studied: 20 to 40% of the NPY perikarya are located in the cortical gray matter, mostly in the deep layers, while the remaining 60 to 80% are located in the underlying white matter. Immunoreactive NPY processes form a rich network of intersecting fibers throughout the entire visual cortex. A superficial plexus (layers I and II) and a deep plexus (deep layer V and layer VI) of NPY fibers are present in areas 17, 18 and 19. In area 17, an additional well developed plexus is present in layers IVb and IVc. These plexuses receive branches from long parallel fibers arising from deep cortical layers or underlying white matter and terminating in superficial layers. Local or extrinsic NPY terminals wind around vessels in the cortex as well as in the white matter, and either penetrate them or form clusters of club endings on their walls. Our results suggest a role for NPY in human visual circuitry and in cortical blood flow regulation.

Effect of amiodarone on serum T4 and T3 levels in hyperthyroid patients treated with methimazole

We investigated the course of thyroid hormones levels in the serum of hyperthyroid patients acutely treated with amiodarone. Ten patients were treated either with amiodarone, 3 X 400 mg daily for 3 days in addition to methimazole, 3 X 20 mg daily for 10 days (Group I; n = 5) or with a placebo plus methimazole at the same doses (Group II; n = 5). Basal T3, T4 and rT3 serum concentrations were: 297 ng/dl, 16.6 micrograms/dl and 507 pg/dl, respectively in Group I and 377 ng/dl, 17.6 micrograms/dl and 362 pg/dl in Group II (NS). Compared with basal values, the drop in serum T3 concentration became significant on Day 1 in Group I, but not until day 5 in Group II. The decrease in serum T3 concentration was significantly higher in Group I than in Group II from Day 1 to Day 7. In Group I, T4 concentration was significantly lower on Days 2, 4 and 6; the percentage drop in T4 calculated from the areas under the curves was higher and the T3/T4 ratio lower on Days 3-5, 7 and 9; rT3 was higher on Days 4 and 5 and its rise was significant on Days 1, 3 and 4. During the follow-up period a transient rise in T4 and T3 concentrations was observed in two patients in Group I when the methimazole dosage was tapered or stopped because of agranulocytosis. In conclusion, in our hyperthyroid patients, amiodarone in conjunction with methimazole induced a greater fall in T3 and T4 than did methimazole alone.