The individual development of circadian temperature rhythm in infants

Abstract

The aim of this study was to explore the individual development of the circadian rhythm of human body temperature. Dailyperiodicchanges of body temperature were examined longitudinally in four infants from 3 to 18 months of age. At the 3rd month of life, the day‐night rhythm of the body temperature was obscure but at the 6th month it became moreevident. From the 12th month on, the circadian temperature rhythm with phase similar to that of the adult was discerned. However, the amplitude in circadian rhythm was significantly larger in children between 6 and 18 months of age than in the adult. These findings suggest that the adult type of circadian rhythm of human body temperature is established during the first year of life with regard to phase but not to amplitude.     

Diurnal patterns in brain biogenic amines of rats exposed to 60-Hz electric fields

Levels of brain neurotransmitters and their metabolites, as well as concentrations of enzymes associated with their synthesis and metabolism, fluctuate during the day in patterns defined as circadian. The present study examined these rhythms in albino rats exposed to 60-Hz electric fields. Thirty-six animals were exposed to a 39 kV/m field for 4 weeks, 20 h/day, in a parallel-plate electrode system. A group of 36 sham animals was similarly handled and housed in a nonenergized exposure system. On the sampling day, animals were sacrificed at 4-h intervals throughout the 24-h day. Brains were removed, dissected, and kept frozen until chemically analyzed. The levels of biogenic amines and their acidic metabolites in the striatum, hypothalamus, and hippocampus were determined by high-performance liquid chromatography with electrochemical detection (HPLC-ECD) methods. Repeated exposure to 60-Hz electric fields produced significant alterations in the diurnal rhythms of several biogenic amines: dihydroxyphenylacetic acid (DOPAC, the primary metabolite of dopamine in the rat) in the striatum, and norepinephrine, dopamine, and 5-hydroxyindoleacetic acid (5-HIAA; serotonin metabolite) in the hypothalamus. Levels of serotonin in the striatum and hypothalamus showed clear circadian patterns that was not affected by the field. No diurnal or field-related changes were observed in the hippocampal amines.     

Serotonergic innervation of the hypothalamic suprachiasmatic nucleus and photic regulation of circadian rhythms

Converging lines of evidence have firmly established that the hypothalamic suprachiasmatic nucleus (SCN) is a light-entrainable circadian oscillator in mammals, critically important for the expression of behavioral and physiological circadian rhythms. Photic information essential for the daily phase resetting of the SCN circadian clock is conveyed directly to the SCN from retinal ganglion cells via the retinohypothalamic tract. The SCN also receives a dense serotonergic innervation arising from the mesencephalic raphe. The terminal fields of retinal and serotonergic afferents within the SCN are co-extensive, and serotonergic agonists can modify the response of the SCN circadian oscillator to light. However, the functional organization and subcellular localization of 5HT receptor subtypes in the SCN are just beginning to be clarified. This information is necessary to understand the role 5HT afferents play in modulating photic input to the SCN. In this paper, we review evidence suggesting that the serotonergic modulation of retinohypothalamic neurotransmission may be achieved via at least two different cellular mechanisms: 1) a postsynaptic mechanism mediated via 5HT_1A or 5ht₇ receptors located on SCN neurons; and 2) a presynaptic mechanism mediated via 5HT_1B receptors located on retinal axon terminals in the SCN. Activation of either of these 5HT receptor mechanisms in the SCN by specific 5HT agonists inhibits the effects of light on circadian function. We hypothesize that 5HT modulation of photic input to the SCN may serve to set the gain of the SCN circadian system to light.     

Seasonal changes in entrainment cues for the circadian rhythm of the supratidal amphipod Talorchestia longicornis

The supratidal amphipod Talorchestia longicornis Say has a circadian rhythm in activity, in which it is active on the substrate surface at night and inactive in burrows during the day. The present study determined: (1) the circadian rhythms in individual versus groups of amphipods; (2) the range of temperature cycles that entrain the circadian rhythm; (3) entrainment by high-temperature cycles versus light?:?dark cycles, and (4) seasonal substrate temperature cycles. The circadian rhythm was determined by monitoring temporal changes in surface activity using a video system. Individual and groups of amphipods have similar circadian rhythms. Entrainment occurred only to temperature cycles that included temperatures below 20°C (10–20, 15–20, 17–19, 15–25°C) but not to temperatures above 20°C (20–25, 20–30°C), and required only a 2°C temperature cycle (17–19°C). Diel substrate temperatures were above 20°C in the summer and below 20°C during the winter. Upon simultaneous exposure to a diel high-temperature cycle (20–30°C) and a light?:?dark cycle phased differently, amphipods entrained to the light?:?dark cycle. Past studies found that a temperature cycle below 20°C overrode the light?:?dark cycle for entrainment. The functional significance of this change in entrainment cues may be that while buried during the winter, the activity rhythm remains in phase with the day?:?night cycle by the substrate temperature cycles. During the summer, T. longicornis switches to the light?:?dark cycle for entrainment, perhaps as a mechanism to phase activity precisely to the short summer nights.     

Reproductive phase dependent circadian variation in hypothalamic concentration of serotonin, dopamine and peripheral thyroxine levels in Japanese Quail following 5-HTP and L-DOPA administration at specific time intervals

Temporal phase relations of circadian hypothalamic neurotransmitters are reported to regulate seasonal reproduction in some avian species. Present experiments were designed to study circadian variation in the hypothalamic concentration of neurotransmitters (serotonin and dopamine) and the plasma thyroxine level in sexually active (long day) and inactive (short day) Japanese Quail. A significant circadian cycle was noted in the hypothalamic content of both serotonin and dopamine, but with different patterns. In breeding Quail, peak activity of serotonin and dopamine was noted at 10.00 A.M. and 10.00 P.M. respectively i.e. at the interval of 12 hours. However, during sexually quiescent condition, peaks of both neurotransmitters occurred at 2.00 P.M. i.e. having a 0-hour temporal relationship. During the breeding phase, the plasma thyroxine level showed a biphasic pattern with two circadian peaks at 10.00 A.M. and 10.00 P.M. whereas in the non-breeding condition a single peak was observed at 10.00 A.M. In the second experiment, to study the effect of temporal synergism of neurotransmitter precursor drugs on circadian cycles, two groups of Quail were administered daily with serotonin precursor 5-HTP (5-hydroxytryptophan) and dopamine precursor L-DOPA (L-dihydroxyphenylalanine) (5 mg/100 g body weight) 12 hour (12-hr) and 8 hour (8-hr) apart over a period of 11 days under continuous conditions of light and then transferred to long day length for 15 days when the experiment was terminated. When compared to controls, the 12-hr condition induced breeding while the 8-hr condition led to a non-breeding condition. The circadian pattern of serotonin levels of control and 12-hr Quail was similar to that of a normal sexually active bird, while that of the 8-hr Quail showed the pattern of a sexually inactive bird. The plasma thyroxine level exhibited a biphasic pattern in 12-hr Quail, which was similar to a normally breeding bird, whereas unlike sexually inactive birds, the thyroxine concentration in 8-hr Quail was relatively low and did not show significant cyclicity. Interestingly, the plasma testosterone level of 12-hr Quail followed a more or less similar pattern with peak activities coinciding with that of thyroxine i.e. biphasic in the sexually active condition (12-hr and control) but a single peak in the quiescent (8-hr) condition. These findings suggest that the temporal phase relation of circadian serotonergic and dopaminergic oscillator varies as a function of reproductive status of the bird, and breeding/non-breeding conditions may be induced experimentally by changing the phase relation of these oscillations.     

Acute dim light at night increases body mass,alters metabolism,and shifts core body temperature circadian rhythms

The circadian system is primarily entrained by the ambient light environment and is fundamentally linked to metabolism. Mounting evidence suggests a causal relationship among aberrant light exposure, shift work, and metabolic disease. Previous research has demonstrated deleterious metabolic phenotypes elicited by chronic (>4 weeks) exposure to dim light at night (DLAN) (～5?lux). However, the metabolic effects of short-term (<2 weeks) exposure to DLAN are unspecified. We hypothesized that metabolic alterations would arise in response to just 2 weeks of DLAN. Specifically, we predicted that mice exposed to dim light would gain more body mass, alter whole body metabolism, and display altered body temperature (T_b) and activity rhythms compared to mice maintained in dark nights. Our data largely support these predictions; DLAN mice gained significantly more mass, reduced whole body energy expenditure, increased carbohydrate over fat oxidation, and altered temperature circadian rhythms. Importantly, these alterations occurred despite similar activity locomotor levels (and rhythms) and total food intake between groups. Peripheral clocks are potently entrained by body temperature rhythms, and the deregulation of body temperature we observed may contribute to metabolic problems due to “internal desynchrony” between the central circadian oscillator and temperature sensitive peripheral clocks. We conclude that even relatively short-term exposure to low levels of nighttime light can influence metabolism to increase mass gain.     

Relationship of CSF neurotransmitter metabolite levels to disease severity and disability in multiple sclerosis

Axonal degeneration and brain tissue loss occur during disease progression in multiple sclerosis (MS) and are expected to influence neurotransmitter activities, with consequences on neurologic and psychiatric symptomatology. We searched for relationships of disease duration, disability, and severity of MS patients to CSF levels of the major metabolites of noradrenaline, dopamine, and serotonin, MHPG, methoxyhydroxyphenylglycol (MHPG), homovanillic acid, and 5-hydroxyindoleacetic acid (5-HIAA), respectively, in 39 patients with relapsing–remitting (RR) MS in remission, and 26 patients with progressive (PR) MS. Disability and Disease Severity were assessed by the Expanded Disability Status Scale (EDSS) and the Multiple Sclerosis Severity Score (MSSS). Compared with the levels of 50 control subjects, MHPG levels were not different in either MS group, correlated negatively to duration of illness and number of relapses in the RRMS group, but not to EDSS score or to MSSS. Homovanillic acid levels were significantly lower only in the PRMS group, with a negative correlation to duration of illness, and a strong negative correlation to EDSS score, but not to MSSS. 5-HIAA was significantly lower in both RRMS and PRMS groups. In the RRMS group, 5-HIAA levels were negatively related to EDSS and to MSSS. Multiple regression analyses revealed a significant association of MHPG to duration of illness, and a strong negative association of 5-HIAA to MSSS rather than to EDSS. The strong negative correlation of MSSS to CSF 5-HIAA levels in RRMS group of patients indicates that deficits in central serotonergic activity are related to the rate of disability accumulation in RRMS, and could be linked to the reported reduction of disease activity by serotonergic drugs.     

Effects of weight, temperature and behaviour on the circadian rhythm of salivary cortisol in growing pigs

In farm animals, salivary cortisol has become a widely used parameter for measuring stress responses. However, only few studies have dealt with basal levels of concentration of cortisol in pigs and its circadian rhythm. The aim of this study was to examine the effects of ambient temperature and thermoregulatory behaviour on the circadian rhythm of salivary cortisol levels in fattening pigs. Subjects were 30 fattening pigs of different weight (60 to 100 kg), kept in six groups in an uninsulated building in pens with partly slatted floors. Saliva samples were taken every 2 h over periods of 24 h at different ambient temperatures at two times in winter and four times in summer. Thermoregulatory behaviour was recorded in the same 24-h time periods. The effect of time of day, body weight, ambient temperature and behaviour on the cortisol level was analysed using a mixed-effects model. Two peaks of cortisol levels per day were found. This circadian pattern became more pronounced with increasing weight and on days where thermoregulatory behaviour was shown. Mean cortisol levels per day were affected by weight but not by thermoregulatory behaviour. From our data, we conclude that long-term variations in cortisol concentration may be influenced by increasing age and weight more than by the respective experimental situation. In assessing animal welfare, it seems more reliable to consider the circadian pattern of cortisol concentration instead of only one value per day.     

Responsiveness to light of the circadian clock controlling eclosion in the blowfly, Lucilia cuprina

ABSTRACT. Eclosion in Lucilia cuprina (Wiedemann) occurs near dawn. The rhythm of eclosion persists in both darkness and constant light of high intensity (490μW cm^-2) with a period close to 24h. The sensitivity to light of the circadian clock controlling eclosion varies greatly according to the stage of the life cycle. During larval life the free running rhythm in darkness can be phase shifted by light pulses of 100μW cm^-2 intensity, with the transition from a Type 1 phase response curve to a Type 0, occurring with pulses of between 1 and 8h. Extending the last light period of LD to 24 h followed by constant darkness resets the phase of the rhythm by 12h, a transition from constant light to constant darkness initiates rhythmicity in flies made arrhythmic by being reared from eggs collected from adults maintained in constant light. After pupariation, the rhythm is relatively insensitive to light. Rhythmicity is sometimes induced by a transition from constant light to constant darkness, but the phase of the rhythm is not shifted by extending the last light period of LD before entering constant darkness. Repeated LD cycles applied after pupariation initiate and entrain the rhythm.     

Effects of altered photoperiod on circadian clock and lipid metabolism in rats

Disruption of circadian clock timekeeping due to changes in the photoperiod enhances the risk of lipid metabolism disorders and metabolic syndrome. However, the effects of altered photoperiods on the circadian clock and lipid metabolism are not well understood. To explore the effects of altered photoperiods, we developed a rat model where rats were exposed to either short-day or long-day conditions. Our findings demonstrated that altered photoperiods mediated circadian clocks by partly disrupting rhythmicity and shifting phase values of clock genes. We also showed that compared to long-day conditions, rats under short-day conditions exhibited more photoperiodic changes in a variety of physiological outputs related to lipid metabolism, such as significant increases in serum triglyceride (TG), high-density lipoprotein, and leptin levels, as well as increased body weight, fat:weight ratio, and hepatic TG levels. These increments were gained possibly through upregulated expression of forkhead box O1 (FoxO1), which partly mediates the expression of peroxisome proliferator-activated receptorα (PPARα) to increase the expression of phosphoenolpyruvate carboxykinase (PEPCK), peroxisome proliferator-activated receptor-g coactivator-1β (PGC1β), and fatty acid synthase (Fasn). In addition, the oscillation rhythms of FoxO1, PEPCK, PGC1β, and Fasn expression levels in the livers of rats exposed to a short-day photoperiod were more robust than those exposed to a long-day photoperiod. These findings suggest that a change in photoperiod can partly disrupt the circadian rhythmcity of clock genes, impair lipid metabolism, and promote obesity.     

Twofold effect of blue light on a circadian rhythm in Acetabularia

Abstract

The circadian chloroplast migration in Acetabularia mediterranea was monitored by continuously measuring the transmission of the cells near the apex. Under continuous red light the amplitude of the rhythm decreased rapidly within a few days. However, circadian changes of chloroplast density were still detectable even after 28 days of red light, indicating the persistence of the rhythm. When blue light was added after red light preirradiation of several days phase shifts were observed which were expressed as advances as well as delays. The period of the rhythm proved to be strongly dependent on the intensity of the continuous blue light which was given in addition to red light. Different red light intensities did not change the period. The occurrence of both effects indicates that the sensory transduction of blue light photoreception in Acetabularia works in two different ways: quanta counting processes and processes of light intensity measurement.     

Suppression of circadian rhythms of pineal and testicular hormones following lithium treatment in normal and reversed light-dark cycles, constant light and constant dark in rats

The aim of the current investigation was to study the effect of lithium on circadian rhythms of pineal - testicular hormones by quantitations of pineal and serum serotonin, N-acetylserotonin and melatonin, and serum testosterone at four time points (06.00, 12.00, 18.00 and 24.00) of a 24-hr period under normal photoperiod (L:D), reversed photoperiod (D:L), constant light (L:L) and constant dark phase (D:D) in rats. Circadian rhythms were observed in pineal hormones in all the combinations of photoperiodic regimens, except in constant light, and in testosterone levels in all the photoperiodic combinations. Pineal and serum N-acetylserotonin and melatonin levels were higher than serotonin at night (24.00 hr), in natural L:D cycle, in reversed L:D cycle or similar to normal L:D cycle in constant dark phase, without any change in constant light. In contrast, testosterone level was higher in light phase (12.00 hr through 18.00 hr) than in the dark phase (24.00 hr through 06.00 hr) in normal L:D cycle, in reversed L:D cycle, similar to normal L:D cycle in constant dark (D:D), and reversed to that of the normal L:D cycle in constant light (L:L). Lithium treatment (2 mEq/kg body weight daily for 15 days) suppressed the magnitude of circadian rhythms of pineal and serum serotonin, N-acetylserotonin and melatonin, and testosterone levels by decreasing their levels at four time points of a 24-hr period in natural L:D or reversed D:L cycle and in constant dark (D:D). Pineal indoleamine levels were reduced after lithium treatment even in constant light (L:L). Moreover, lithium abolished the melatonin rhythms in rats exposed to normal (L:D) and reversed L:D (D:L) cycles, and sustained the rhythms in constant dark. But testosterone rhythm was abolished after lithium treatment in normal (L:D)/reversed L:D (D:L) cycle or even in constant light/dark. The findings indicate that the circadian rhythm exists in pineal hormones in alternate light - dark cycle (L:D/D:L) and in constant dark (D:D), but was absent in constant light phase (L:L) in rats. Lithium not only suppresses the circadian rhythms of pineal hormones, but abolishes the pineal melatonin rhythm only in alternate light - dark cycles, but sustains it in constant dark. The testosterone rhythm is abolished after lithium treatment in alternate light - dark cycle and constant light/dark. It is suggested that (a) normal circadian rhythms of pineal hormones are regulated by pulse dark phase in normal rats, (b) lithium abolishes pineal hormonal rhythm only in pulse light but sustains it in constant dark phase, and (c) circadian testosterone rhythm occurs in both pulse light or pulse dark phase in normal rats, and lithium abolishes the rhythm in all the combinations of the photoperiod. The differential responses of circadian rhythms of pineal and testicular hormones to pulse light or pulse dark in normal and lithium recipients are discussed.     

Effect of LED light spectra on exogenous prolactin-regulated circadian rhythm in goldfish,Carassius auratus

We investigated the effect of light spectra on circadian rhythm by exogenous prolactin (PRL) using light-emitting diodes (LEDs): red, green and purple. We injected PRL into live fish or treated cultured brain cells with PRL. We measured changes in the expressions of period 2 (Per2), cryptochrome 1 (Cry1), melatonin receptor 1 (MT1) mRNAs, and MT1 proteins, and in the plasma PRL, serotonin and melatonin levels. After PRL injection and exposure to green light, MT1 expression and plasma melatonin levels were significantly lower, but the expressions of Per2 and Cry1 were significantly higher than the others. Plasma serotonin after PRL injection and exposure to red light was significantly lower than others. These results indicate that injection of high concentration PRL inhibits melatonin, and inhibited melatonin regulates circadian rhythm via clock genes and serotonin. Thus, exogenous PRL regulates the circadian rhythm and light spectra influence the effect of PRL in goldfish.     

Late circadian phase in adults and children is correlated with use of high color temperature light at home at night

Light is the strongest synchronizer of human circadian rhythms, and exposure to residential light at night reportedly causes a delay of circadian rhythms. The present study was conducted to investigate the association between color temperature of light at home and circadian phase of salivary melatonin in adults and children. Twenty healthy children (mean age: 9.7 year) and 17 of their parents (mean age: 41.9 years) participated in the experiment. Circadian phase assessments were made with dim light melatonin onset (DLMO). There were large individual variations in DLMO both in adults and children. The average DLMO in adults and in children were 21:50 ± 1:12 and 20:55 ± 0:44, respectively. The average illuminance and color temperature of light at eye level were 139.6 ± 82.7 lx and 3862.0 ± 965.6 K, respectively. There were significant correlations between color temperature of light and DLMO in adults (r = 0.735, p < 0.01) and children (r = 0.479, p < 0.05), although no significant correlations were found between illuminance level and DLMO. The results suggest that high color temperature light at home might be a cause of the delay of circadian phase in adults and children.     

Blooming rhythms of cactus Cereus peruvianus with nocturnal peak at full moon during seasons of prolonged daytime photoperiod

Cereus peruvianus (Peruvian apple cactus) is a large erect and thorny succulent cactus characterized by column-like (cereus [L]: column), that is, candle-shaped, appendages. For three successive years (1100 days), between early April and late November, we studied the flowering patterns of eight cacti growing in public gardens and rural areas of north and central Tunisia, far from nighttime artificial illumination, in relation to natural environmental light, temperature, relative humidity and precipitation parameters. Flower blooming was assessed nightly between 23:00 h and until at least 02:00 h, and additionally around-the-clock at ~1 h intervals for 30 consecutive days during the late summer of each year of study to quantify both nyctohemeral (day–night) and lunar patterns. During the summer months of prolonged daytime photoperiod, flower blooming of C. peruvianus exhibited predictable-in-time variation as “waves” with average period of 29.5 days synchronized by the light of the full moon. The large-sized flower (~16 cm diameter) opens almost exclusively at night, between sunset and sunrise, as a 24 h rhythm during a specific 3–4-day span of the lunar cycle (full moon), with a strong correlation between moon phase and number and proportion of flowers in bloom (ranging from r = +0.59 to +0.91). Black, blue and red cotton sheets were used to filter specific spectral bands of nighttime moonlight from illuminating randomly selected plant appendages as a means to test the hypothesis of a “gating” 24 h rhythm phenomenon of photoreceptors at the bud level. Relative to control conditions (no light filtering), black sheet covering inhibited flower bud induction by 87.5%, red sheet covering by 46.6% and blue sheet covering by 34%, and the respective inhibiting effects on number of flowers in bloom were essentially 100%, ~81% and ~44%. C. peruvianus is a unique example of a terrestrial plant that exhibits a circadian flowering rhythm (peak ~00:00 h) “gated” by 24 h, lunar 29.5-day (bright light of full moon) and annual 365.25-day (prolonged summertime day length) environmental photoperiod cycles.     

The role of circadian rhythm on the pharmacokinetic of methotrexate in streptozotocin-induced diabetes mellitus rats

Chronopharmacokinetic studies have been conducted both in animals and humans. Anticancer agents are of great interest due to their narrow therapeutic range and large pharmacokinetic variability. It was reported that the pharmacokinetics of MTX showed a circadian rhythm in rats and humans. Since diabetes-induced physiological changes can affect pharmacokinetics of drugs, it was reported that MTX blood concentration in diabetic rats was higher than that of the control groups. The present study was designed to elucidate whether these diabetes-induced changes in pharmacokinetics occurred during the day and thus administered MTX at four different times in streptozotocin-induced diabetes mellitus (SIDM) rats. Blood samples were drawn at 5, 15, 30, and 60 min after IV infusion of MTX in both the SIDM and control groups. Control and SIDM Area under the concentration - time curve (AUC) values showed a significant circadian rhythm with a peak located in mid-dark phase at 14:00. Clearance values were significantly low at 14:00 in the diabetic group when compared to other periods and the control group. The MTX AUC was increased when treatment with dexamethasone was given to suppress the endogenous production of corticosterone in both control and SIDM rats. These results suggest that the extent of MTX pharmacokinetics varies with the time of day in the SIDM rats and these variations might be related to changes in corticosterone concentrations.     

Anatomical and physiological characteristics of the petiole of Abutilon theophrasti in relation to circadian leaf movements

Leaf movements in Abutilon theophrasti Medic, were monitored manually and by a continuous electronic recording device. Plants entrained to a daily regime of a 15 h light span followed by 9 h of darkness showed rhythmic movements that persisted under conditions of continuous illumination and constant temperature with a circadian period. The rhythmic change in orientation of the leaf from a near horizontal (day) to a near vertical (night) position was attributed to movement of the blade and not the petiole. The end of the petiole next to the blade functions as a joint or pulvinus. Anatomical confirmation of the existence of a pulvinus in the Abutilon leaf was provided by light microscopy. Vascular tissue in this region forms a solid cylinder with no pith, and the cortex is parenchymatous. In the main part of the petiole, the vascular tissue is arranged in four to six bundles, a pith is present, and the cortex contains a sub-epidermal ring of collenchyma. Both the functional and anatomical evidence indicate the presence of a pulvinus that functions in circadian leaf movements of Abutilon.     

Diel rhythms of adipokinetic hormone, fat body response, and haemolymph lipid and sugar levels in the house cricket

Abstract. The adipokinetic hormone (Grb-AKH) content in the corpora car-diaca of the house cricket, Acheta domesticus , varied during a day with two peaks in the scotophase and one peak in the photophase. There were two distinct peaks of total lipid concentration in the blood, one early in the photophase and the other early in the scotophase. Fat body sensitivity to adipokinetic hormone also varied in close synchrony with the lipid rhythm. It was not possible to attribute the rhythm of blood lipid titre unequivocally to either the rhythm of adipokinetic hormone content in the corpora cardiaca or to the rhythm of sensitivity of the fat body to the hormone. In adult crickets the blood carbohydrate titre had two peaks in adult females, one towards the end of scotophase and another in the late photophase (c. 12h apart), but a single peak at the end of scotophase was apparent in last instar larvae. The blood carbohydrate rhythm persists in DD and is therefore endogenous. Carbohydrates were not mobilized by the Grb-AKH, therefore could not be involved in the blood carbohydrate rhythm. Exposure to various day lengths caused shifts in the patterns of the carbohydrate rhythms, but imposition of a cyclic temperature regime had no effect on the rhythm.     

Activity,sleep and ambient light have a different impact on circadian blood pressure,heart rate and body temperature rhythms

The aim of the present study was to investigate the impact of endogenous and exogenous factors for the expression of the daily rhythms of body temperature (BT), blood pressure (BP) and heart rate (HR). One hundred and seventy-three young adults (YA), 17–24 years old (y.o.), of both genders were studied under a modified constant-routine (CR) protocol for 26 h. Participants were assigned randomly to groups with different lighting regimens: CR-LD, n = 77, lights (>400 l×) on from 09:00 to 17:00 h and off (<10 l×) from 17:00 to 09:00 next morning; CR-LL, n = 81, lights on (>400 l×) during the whole experimental session; CR-DD, n = 15, constant dim light (<10 l×) during the whole experiment. Systolic (SBP) and diastolic (DBP) BP, HR and BT were measured every 2 h. For comparison, the results of the former studies performed under conditions of regular life with an activity period from 07:00 to 23:00 h and sleep from 23:00 till 07:00 h (Control) were reanalyzed. Seven-day Ambulatory Blood Pressure Monitoring (ABPM) records from 27 YA (16–38 y.o.) and BT self-measurement data from 70 YA (17–30 y.o.) taken on ≥ 3 successive days at 08:00, 11:00, 14:00, 17:00, 20:00, 23:00 and 03:00 were available.

The obtained daily patterns were different between Control and CR-DD groups, due to effects of activity, sleep and light. The comparison of Control and CR-LD groups allowed the effects of sleep and activity to be estimated since the lighting conditions were similar. The activity level substantially elevated SBP, but not DBP. Sleep, on the other hand, lowered the nighttime DBP, but has no effect on SBP. HR was affected both by activity and sleep. In accordance with previous studies, these results confirm that the steep BP increase in the morning is not driven by the circadian clock, but rather by sympathoadrenal factors related to awakening and corresponding anticipatory mechanisms. The effect on BT was not significant.

To investigate the impact of light during the former dark time and darkness during the former light time, the CR-LL and CR-DD groups were each compared with the CR-LD group. Light delayed the evening decrease of BT, most likely via a suppression of the melatonin rise. Besides, it had a prominent arousal effect on SBP both in the former light and dark phases, a moderate effect on DBP and no effect on HR. Darkness induced decline in BT. BP values were decreased during the former light time. No effects on HR were found. Altogether, the results of the present paper show that BT, BP and HR are affected by exogenous factors differently. Moreover, the effect was gender-specific. Especially, the response of BT and BP to ambient light was evident only in females.

We suppose that the distinct, gender-specific responses of SBP, DBP and HR to activity, sleep and ambient light do reflect fundamental differences in the circadian control of various cardiovascular functions. Furthermore, the presented data are important for the elaboration of updated reference standards, the interpretation of rhythm disorders and for personalized chronotherapeutic approaches to prevent adverse cardiovascular events more effectively.     

Rhythmic changes in metabolism of dopamine in the chick retina: the importance of light versus biological clock

Rhythmic changes in dopamine (DA) content and metabolism were studied in retinas of chicks that were adapted to three different lighting conditions: 12-h light : 12-h dark (LD), constant darkness (DD) and continuous light (LL). Retinas of chicks kept under LD conditions exhibited light-dark-dependent variations in the steady-state level of DA and the two metabolites of DA, i.e. 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanilic acid (HVA). Concentrations of DA, DOPAC and HVA were high in light hours and low in dark hours of the LD illumination cycle. In retinas of chicks kept under DD, the content of DA, DOPAC and HVA oscillated in a rhythmic manner for 2 days, with higher values during the subjective light phase than during the subjective dark phase. The amplitudes of the observed oscillations markedly and progressively declined compared with the amplitudes recorded under the LD cycle. In retinas of chicks kept under LL conditions, levels of DA, DOPAC and HVA were similar to those found during the light phase of the LD cycle. Changes in the retinal contents of DA and HVA did not exhibit pronounced daily oscillations, while on the first day of LL the retinal concentrations of DOPAC were significantly higher during the subjective light phase than during the subjective dark phase. Acute exposure of chicks to light during the dark phase of the LD cycle markedly increased DA and DOPAC content in the retina. In contrast, light deprivation during the day decreased the retinal concentrations of DA and DOPAC. It is suggested that of the two regulatory factors controlling the level and metabolism of DA in the retina of chick, i.e. light and biological clock, environmental lighting conditions seem to be of major importance, with light conveying a stimulatory signal for the retinal dopaminergic cells.