Field Studies on Circadian Rhythms of Core Temperature in Tropical Inhabitants Compared with Those in European Inhabitants

In order to know the characteristics of circadian rhythms in core temperature in tropical inhabitants, we measured rectal temperatures every 10 min for 50 h in 6 Vietnamese, 20-22 years old (5 males and 1 female) under natural conditions. Ambient temperatures ranged from 33 to 36°C. These data obtained in tropical inhabitants were compared with those in Polish inhabitants. The participants in both groups were usually sitting during wakefulness and lying in bed during sleep. The results obtained are summarized as follows: (1) The average maximum value was 37.7°C, which was significantly higher than in the Europeans; (2) The average minimum value was 36.2°C, which was lower; (3) A range of oscillation was 1.5°C, which was clearly greater than in the Europeans. The higher maximum value of core temperature, which was actively regulated under warm temperature, seemed of adaptive significance in order to reduce water consumption. A greater rage of oscillation in tropical Vietnamese people might have ecological significance for efficient acclimatization in the warm environment, suggesting that the setpoint of core temperature could show a greater range of oscillation.     

温度对红尾沙蜥代谢昼夜节律的影响

爬行动物很多生理、生化和行为指标都表现出昼夜节律。代谢昼夜节律不仅涉及内在因子的固有控制,而且受到多种外部因素的影响。为了探究温度对代谢昼夜节律的影响,在恒定的温度下(18℃和28℃)测定了红尾沙蜥Phrynocephalus erythrurus体温、心率、标准代谢率(SMR)和血糖浓度的昼夜变化。结果表明:(1)在2个温度下红尾沙蜥体温没有明显的昼夜变化;(2)昼间SMR明显高于夜间,18℃下SMR水平以及SMR昼夜变化的范围都低于28℃下的结果;(3)心率的变化也与代谢率的变化一致,但最低点提前了2 h;(4)28℃下的血糖浓度整体水平显著高于18℃下的,而波动规律却不同:28℃条件下白天平均值高于晚上,血糖浓度在16∶00显著高于20∶00、00∶00和12∶00;18℃条件下,血糖浓度在20∶00和08∶00明显低于00∶00和12∶00(P0.05),而在04∶00和16∶00处于中间水平。该研究证实了红尾沙蜥SMR、心率和血糖浓度等生理生化指标也存在明显的昼夜节律,虽然这种现象受环境温度的影响,但主要还是由内在因子决定,这可能与某些激素的分泌活动有关。     

Plasticity of Circadian Activity and Body Temperature Rhythms in Golden Spiny Mice

Most animals can be categorized as nocturnal, diurnal, or crepuscular. However, rhythms can be quite plastic in some species and vary from one individual to another within a species. In the golden spiny mouse (Acomys russatus), a variety of rhythm patterns have been seen, and these patterns can change considerably as animals are transferred from the field into the laboratory. We previously suggested that these animals may have a circadian time‐keeping system that is fundamentally nocturnal and that diurnal patterns seen in their natural habitat reflect mechanisms operating outside of the basic circadian time‐keeping system (i.e., masking). In the current study, we further characterized plasticity evident in the daily rhythms of golden spiny mice by measuring effects of lighting conditions and access to a running wheel on rhythms in general activity (GA) and body temperature (Tb). Before the wheel was introduced, most animals were active mainly during the night, though there was considerable inter‐individual variability and patterns were quite plastic. The introduction of the wheel caused an increase in the level of nighttime activity and Tb in most individuals. The periods of the rhythms in constant darkness (DD) were very similar, and even slightly longer in this study (24.1±0.2 h) than in an earlier one in which animals had not been provided with running wheels. We found no correlation between the distance animals ran in their wheels and the period of their rhythms in DD. Re‐entrainment after phase delays of the LD cycle occurred more rapidly in the presence than absence of the running wheel. The characteristics of the rhythms of golden spiny mice seen in this study may be the product of natural selection favoring plasticity of the circadian system, perhaps reflecting what can happen during an evolutionary transition as animals move from a nocturnal to a diurnal niche.     

Chronic Administration of Imipramine and Lithium Changes the Phase-Angle Relationship Between the Activity and Core Body Temperature Circadian Rhythms in Rats

Evidence suggests that there is an association between the pathophysiology of depression and a disturbance of circadian rhythms. Accordingly, attention has focused on the possible effects of antidepressants on circadian rhythms. In the present study, we examined the effects of chronic administration of two clinically effective antidepressant agents, imipramine and lithium, on several circadian rhythms in the rat. Activity, core body temperature, and drinking rhythms were assessed in constant darkness (DD) and light-dark (LD) conditions. In DD, lithium significantly lengthened the circadian period of the activity, temperature, and drinking rhythms, while imipramine had no effect. In LD, both drugs significantly delayed the phase of the activity rhythm, but did not change that of the other two rhythms. As a result, the phase-angle differences between the activity and temperature rhythms significantly increased. Neither lithium nor imipramine produced any effect on the resynchronization of these rhythms after an 8-h delay in the LD cycle. These results indicate that although both drugs produced different effects on the circadian period of individual rhythms, both caused a relative phase advance of the temperature rhythm as compared to the activity rhythm, and this effect may be related to the similarity in their antidepressant effects. (Chronobiology International, 13(4), 251-259, 1996)     

Quantification of Circadian Rhythms in Single Cells

Bioluminescence techniques allow accurate monitoring of the circadian clock in single cells. We have analyzed bioluminescence data of Per gene expression in mouse SCN neurons and fibroblasts. From these data, we extracted parameters such as damping rate and noise intensity using two simple mathematical models, one describing a damped oscillator driven by noise, and one describing a self-sustained noisy oscillator. Both models describe the data well and enabled us to quantitatively characterize both wild-type cells and several mutants. It has been suggested that the circadian clock is self-sustained at the single cell level, but we conclude that present data are not sufficient to determine whether the circadian clock of single SCN neurons and fibroblasts is a damped or a self-sustained oscillator. We show how to settle this question, however, by testing the models'' predictions of different phases and amplitudes in response to a periodic entrainment signal (zeitgeber).     

Effects of Histamine on Circadian Rhythms and Hibernation

Histamine appears to play a role in regulation of sleep and arousal as well as in synchronizing endogenous circadian rhythms with exogenous photic cues. Direct application of histamine to the suprachiasmatic nucleus (SCN), the site of the mammalian circadian pacemaker, phase shifts the circadian rhythm in neural activity. Intraventricular injections of histamine also phase shift circadian rhythms as do micro-injections directed towards the SCN. The magnitude and direction of the phase shifting effects of histamine depend on circadian phase in a manner similar to light. Depletion of brain histamine levels by inhibition of histamine synthesis reduces phase shifts to light. Histamine appears to influence phase shifts to light via a direct modulation of NMDA receptors in the SCN. Increased histamine levels and turnover observed in hibernating animals render it possible that histamine is a key regulator of hibernation. Thus histamine participates in an important link between sleep, circadian rhythms, and hibernation.     

Effects of Histamine on Circadian Rhythms and Hibernation

Histamine appears to play a role in regulation of sleep and arousal as well as in synchronizing endogenous circadian rhythms with exogenous photic cues. Direct application of histamine to the suprachiasmatic nucleus (SCN), the site of the mammalian circadian pacemaker, phase shifts the circadian rhythm in neural activity. Intraventricular injections of histamine also phase shift circadian rhythms as do micro-injections directed towards the SCN. The magnitude and direction of the phase shifting effects of histamine depend on circadian phase in a manner similar to light. Depletion of brain histamine levels by inhibition of histamine synthesis reduces phase shifts to light. Histamine appears to influence phase shifts to light via a direct modulation of NMDA receptors in the SCN. Increased histamine levels and turnover observed in hibernating animals render it possible that histamine is a key regulator of hibernation. Thus histamine participates in an important link between sleep, circadian rhythms, and hibernation.     

Effect of Sex,Menstrual Cycle Phase,and Oral Contraceptive Use on Circadian Temperature Rhythms

The circadian rhythm of rectal temperature was continuously recorded over several consecutive days in young men and women on regular nocturnal sleep schedules. There were 50 men, 21 women with natural menstrual cycles [i.e., not taking oral contraceptives (OCs) (10 in the follicular phase and 11 in the luteal phase)], and 14 women using OCs (6 in the pseudofollicular phase and 8 in the pseudoluteal phase). Circadian phase and amplitude were estimated using a curve-fitting procedure, and temperature levels were determined from the raw data. A two-way analysis of variance (ANOVA) on the data from the four groups of women, with factors menstrual cycle phase (follicular, luteal) and OC use (yes, no), showed that temperature during sleep was lower during the follicular phase than during the luteal phase. Since waking temperatures were similar in the two phases, the circadian amplitude was also larger during the follicular phase. The lower follicular phase sleep temperature also resulted in a lower 24-h temperature during the follicular phase. The two-way ANOVA showed that temperature during sleep and 24-h temperature were lower in naturally cycling women than in women taking OCs. A one-way ANOVA on the temperature rhythm parameters from the five groups of subjects showed that the temperature rhythms of the men and of the naturally cycling women in the follicular phase were not significantly different. Both of these groups had lower temperatures during sleep, lower 24-h temperatures, and larger circadian amplitudes than the other groups. There were no significant differences in circadian phase among the five groups studied. In conclusion, menstrual cycle phase, OC use, and sex affect the amplitude and level, but not the phase, of the overt circadian temperature rhythm.     

Effect of Sex, Menstrual Cycle Phase, and Oral Contraceptive Use on Circadian Temperature Rhythms

The circadian rhythm of rectal temperature was continuously recorded over several consecutive days in young men and women on regular nocturnal sleep schedules. There were 50 men, 21 women with natural menstrual cycles [i.e., not taking oral contraceptives (OCs) (10 in the follicular phase and 11 in the luteal phase)], and 14 women using OCs (6 in the pseudofollicular phase and 8 in the pseudoluteal phase). Circadian phase and amplitude were estimated using a curve-fitting procedure, and temperature levels were determined from the raw data. A two-way analysis of variance (ANOVA) on the data from the four groups of women, with factors menstrual cycle phase (follicular, luteal) and OC use (yes, no), showed that temperature during sleep was lower during the follicular phase than during the luteal phase. Since waking temperatures were similar in the two phases, the circadian amplitude was also larger during the follicular phase. The lower follicular phase sleep temperature also resulted in a lower 24-h temperature during the follicular phase. The two-way ANOVA showed that temperature during sleep and 24-h temperature were lower in naturally cycling women than in women taking OCs. A one-way ANOVA on the temperature rhythm parameters from the five groups of subjects showed that the temperature rhythms of the men and of the naturally cycling women in the follicular phase were not significantly different. Both of these groups had lower temperatures during sleep, lower 24-h temperatures, and larger circadian amplitudes than the other groups. There were no significant differences in circadian phase among the five groups studied. In conclusion, menstrual cycle phase, OC use, and sex affect the amplitude and level, but not the phase, of the overt circadian temperature rhythm.     

Circadian Rhythms of Core Body Temperature and Urinary Noradrenaline Secretion under the Influence of Skin Pressure due to Foundation Garments Worn during Wakefulness

The present experiment investigated the effects of skin pressure by foundation garments (brassiere plus girdle) worn during wakefulness on the circadian rhythms of core temperature and endocrine secretion. Eight healthy females (18–23 yrs) maintaining regular sleep-wake cycles for a week prior to participation in the experiment served as participants. The experiments were performed from June to August, 1999, using a bioclimatic chamber controlled at 26.5 ± 0.2°C and 62 ± 3% RH. Ambient light intensity was controlled at 500 lx from 07:30 h to 17:30 h, 100 lx from 17:30 h to 19:30 h, 20 lx from 19:30 h to 23:30 h and there was total darkness from 23:30 h to 07:30 h. The experiment lasted for 58?h over 3 nights. The participant rose at 07:30?h in the morning of the first day and retired at 23:30 h, adhering to a set schedule for 24 h but without wearing foundation garments. From 07:30 h to 23:30 h of the second day the participant wore foundation garments but did not wear foundation garments during the sleep. Rectal and leg skin temperatures were continuously measured throughout the experiment. Urine was collected every 4 h for the analysis of catecholamines. Skin pressure applied by the foundation garments was in the range 11–17 gf/cm² at the regions of abdomen, hip, chest and back. The main results were as follows: Rectal temperature was significantly higher (p < 0.01) during wakefulness, but significantly lower (p < 0.01) during sleep with than without foundation garments. Furthermore, the amplitude of rectal temperature was larger with than without foundation garments (p < 0.033). Urinary noradrenaline was mostly lower with foundation garments throughout the day and night. The results suggest that skin pressure by foundation garments worn during wakefulness could influence the level of core body temperature and noradrenaline secretion not only during wakefulness, but also during sleep.     

Rhythms of Enzyme Activity Associated with Circadian Conidiation in Neurospora crassa

The mycelial growth front of the band strain of Neurospora grown on a solid surface exhibits a circadian rhythm of conidiation. Enzyme assays on extracts from that mycelium have shown that the activities of 6 of 13 enzymes (nicotinamide adenine dinucleotide nucleosidase, isocitrate lyase, citrate synthase, glyceraldehydephosphate dehydrogenase, phosphogluconate dehydrogenase, and glucose-6-phosphate dehydrogenase) and soluble-protein content oscillate with the visible morphological change. The rhythmic enzymes associated with the Krebs and glyoxylate cycles are more active during conidiogenesis, whereas the activities of the rhythmic enzymes of glycolysis and the hexose monophosphate shunt are reduced during that phase. The absence of enzyme oscillations in wild-type and fluffy strains which do not form conidia under the conditions employed suggests that the enzyme fluctuations are associated with conidiogenesis itself. Oscillations of enzyme activity as a function of time are restricted to the growth front. A permanent record of rhythmicity associated with conidial and nonconidial regions does, however, exist in the mycelial mat behind the growth front. The activities of three enzymes (nicotinamide adenine dinucleotide nucleosidase, glucose-6-phosphate dehydrogenase, and phosphogluconate dehydrogenase) are not directly influenced by CO(2) concentration, but are correlated with the prescence or absence of conidiation which is controlled by CO(2) concentration. In contrast, citrate synthase and malate dehydrogenase activities are correlated with changes in CO(2) concentration.     

The Circadian Activity and Body Temperature Rhythms of Mice During Their Last Days of Life

Motor activity and body temperature rhythms have been investigated telemetrically in old mice until their death. The present paper is based mainly on the data of two animals which could be monitored over a sufficient length of time (more than three weeks), though the other three animals showed similar results. The daily body temperature rhythm of old mice was more stable as compared to the activity rhythm and was detectable until the last day of life. Its magnitude, defined as the difference between maximum and minimum, was similar to that obtained in middle-aged mice. By contrast, the activity rhythm disappeared or started to become erratic earlier. Unlike the position in younger animals, the body temperature rhythm was phase delayed with respect to the activity rhythm. In one mouse, the increased instability of the phase position two weeks before its death led to a free run with a period length of about 23.7 h. Both activity and temperature rhythms were fragmented in old mice. In the case of the body temperature this was obviously caused by masking. After purifying the raw temperatures, the fragmentation disappeared. On the other hand, the free-run condition was not caused by masking. The sensitivity of body temperature to motor activity was different from younger mice, and this probably reflects changes/deteriorations in the physiology of thermoregulation during the last days of life. In one mouse, during the last 4 days of life, a sharp, torpor-like decrease of body temperature corresponding with the time of the daily minimum was observed. This phenomenon was not found in other mice, though all of them died during the falling period of the temperature rhythm. The results confirm our hypothesis that the endogenous clock may work even during the very last days of life. The ability to synchronize with the periodic environment deteriorates earlier. Also they suggest that these phenomena are not only typical for the activity rhythm but apply also to the body temperature rhythm.     

The Circadian Activity and Body Temperature Rhythms of Mice During Their Last Days of Life

Motor activity and body temperature rhythms have been investigated telemetrically in old mice until their death. The present paper is based mainly on the data of two animals which could be monitored over a sufficient length of time (more than three weeks), though the other three animals showed similar results. The daily body temperature rhythm of old mice was more stable as compared to the activity rhythm and was detectable until the last day of life. Its magnitude, defined as the difference between maximum and minimum, was similar to that obtained in middle-aged mice. By contrast, the activity rhythm disappeared or started to become erratic earlier. Unlike the position in younger animals, the body temperature rhythm was phase delayed with respect to the activity rhythm. In one mouse, the increased instability of the phase position two weeks before its death led to a free run with a period length of about 23.7 h. Both activity and temperature rhythms were fragmented in old mice. In the case of the body temperature this was obviously caused by masking. After purifying the raw temperatures, the fragmentation disappeared. On the other hand, the free-run condition was not caused by masking. The sensitivity of body temperature to motor activity was different from younger mice, and this probably reflects changes/deteriorations in the physiology of thermoregulation during the last days of life. In one mouse, during the last 4 days of life, a sharp, torpor-like decrease of body temperature corresponding with the time of the daily minimum was observed. This phenomenon was not found in other mice, though all of them died during the falling period of the temperature rhythm. The results confirm our hypothesis that the endogenous clock may work even during the very last days of life. The ability to synchronize with the periodic environment deteriorates earlier. Also they suggest that these phenomena are not only typical for the activity rhythm but apply also to the body temperature rhythm.     

Circadian Temperature and Activity Rhythms in Mice under Free-Running and Entrained Conditions; Assessment after Purification of the Temperature Rhythm

Six female mice were studied separately for six weeks, first in constant light (300 lx), and then on a 12 : 12 L : D schedule (light on 07:00–19:00–h). Food and water were available ad libitum. Abdominal temperature and spontaneous locomotor activity were measured every 10 min. In constant light, the animals free-ran with both temperature and activity records showing circadian rhythms that were significantly greater than 24 h; by contrast, in the LD schedule, the circadian rhythms had become entrained and showed a stable phase relation to this schedule. The direct masking effects upon raw temperatures caused by bursts of activity were clearly seen, and could be removed by a process of ‘purification’. A comparison of the activity profiles during the entrained and free-running phases showed that the imposed light-dark cycle resulted in decreased activity in the light, increased activity in the dark, and bursts of activity at the light-dark and dark-light transitions. Masking effects due to the activity profile were present in the raw temperature profile, and many could be removed by purification using the activity profile; however, there was evidence that other masking effects, independent of activity, were present also. The efficacy of thermoregulatory compensation, as assessed from the rise of core temperature produced by spontaneous locomotor activity, was, in comparison with the free-running condition, increased in the dark phase and decreased in the light phase; this would appear to be one way to limit the temperature rise that occurs in the active phase of the rest-activity cycle.     

Circadian Temperature and Activity Rhythms in Mice under Free-Running and Entrained Conditions; Assessment after Purification of the Temperature Rhythm

Six female mice were studied separately for six weeks, first in constant light (300 lx), and then on a 12 : 12 L : D schedule (light on 07:00-19:00-h). Food and water were available ad libitum. Abdominal temperature and spontaneous locomotor activity were measured every 10 min. In constant light, the animals free-ran with both temperature and activity records showing circadian rhythms that were significantly greater than 24 h; by contrast, in the LD schedule, the circadian rhythms had become entrained and showed a stable phase relation to this schedule. The direct masking effects upon raw temperatures caused by bursts of activity were clearly seen, and could be removed by a process of 'purification'. A comparison of the activity profiles during the entrained and free-running phases showed that the imposed light-dark cycle resulted in decreased activity in the light, increased activity in the dark, and bursts of activity at the light-dark and dark-light transitions. Masking effects due to the activity profile were present in the raw temperature profile, and many could be removed by purification using the activity profile; however, there was evidence that other masking effects, independent of activity, were present also. The efficacy of thermoregulatory compensation, as assessed from the rise of core temperature produced by spontaneous locomotor activity, was, in comparison with the free-running condition, increased in the dark phase and decreased in the light phase; this would appear to be one way to limit the temperature rise that occurs in the active phase of the rest-activity cycle.     

Effects of Acute Clomipramine Administration on Syrian Hamster Circadian Rhythms

Drugs linked to the serotonergic system, like antidepressants, are able to modify the circadian system. The present experiments were designed to test whether clomipramine, a 5-HT reuptake inhibitor, was able to modify: a) the phase of free running activity rhythms; b) the light-induced phase shifts in Syrian hamsters. Clomipramine had a phase-dependent effect on the free running activity rhythm, with phase advances at CT 0-8 being significantly higher than at CT 8-16. Pretreatment with clomipramine inhibited phase advances in response to light pulses when applied at CT 19 while delays remained unaffected. The results suggest that acute clomipramine treatment can affect the expression of the circadian rhythmicity in Syrian hamsters.     

Effects of Acute Clomipramine Administration on Syrian Hamster Circadian Rhythms

Drugs linked to the serotonergic system, like antidepressants, are able to modify the circadian system. The present experiments were designed to test whether clomipramine, a 5-HT reuptake inhibitor, was able to modify: a) the phase of free running activity rhythms; b) the light-induced phase shifts in Syrian hamsters. Clomipramine had a phase-dependent effect on the free running activity rhythm, with phase advances at CT 0-8 being significantly higher than at CT 8-16. Pretreatment with clomipramine inhibited phase advances in response to light pulses when applied at CT 19 while delays remained unaffected. The results suggest that acute clomipramine treatment can affect the expression of the circadian rhythmicity in Syrian hamsters.     

Circadian Variations in the Number of Actively Secreting Sebaceous Follicles and Androgen Circadian Rhythms

Sebum excretion has been shown to demonstrate a circadian rhythm using a gravimetric method (cigarette paper). With the newly introduced method of Sebutape, we confirmed this periodicity and showed that the elevation in sebum excretion is correlated with an increase in the number of secreting follicles. We found, furthermore, that the number of secreting follicles on the forehead showed a distinct and statistically significant circadian rhythmicity, in contrast to those of the chest, which remained almost constant. The quantification in plasma levels of cortisol, melatonin, δ-4-androstenedione, dehydroepiandrosterone sulphate, and free testosterone showed no correlation with sebum excretion at either site. These observations suggest that local factors are involved in control of sebum secretion.     

Circadian Variations in the Number of Actively Secreting Sebaceous Follicles and Androgen Circadian Rhythms

Sebum excretion has been shown to demonstrate a circadian rhythm using a gravimetric method (cigarette paper). With the newly introduced method of Sebutape, we confirmed this periodicity and showed that the elevation in sebum excretion is correlated with an increase in the number of secreting follicles. We found, furthermore, that the number of secreting follicles on the forehead showed a distinct and statistically significant circadian rhythmicity, in contrast to those of the chest, which remained almost constant. The quantification in plasma levels of cortisol, melatonin, δ-4-androstenedione, dehydroepiandrosterone sulphate, and free testosterone showed no correlation with sebum excretion at either site. These observations suggest that local factors are involved in control of sebum secretion.