Body Temperature Cycles Research Articles

Circadian Rhythms: Per2bations in the Liver Clock

A master circadian clock resides in the brain and is required to synchronize the clocks in peripheral tissues such as the liver. Until now, it has been unclear how the central clock synchronizes the peripheral ones. New work points to one of the core clock genes, mPer2, as an essential link in this chain.

Relationship Between Body Temperature and Ovarian Cycle in Asian and African Elephants

The aim of the present study was to investigate whether changes in body temperature are related to the ovarian cycle in elephants. Rectal, tongue or fecal temperature was measured for 2 Asian and 5 African elephants using an electric thermometer. Evaluation of ovarian cycles was based on the changes in serum or fecal progestin. The mean +/- SD values of the rectal, tongue, and fecal temperatures were 36.3 +/- 0.3 (2 Asian), 36.2 +/- 0.5 (1 African) and 36.5 +/- 0.3 C (4 African), respectively; the fecal temperature was the highest of the 3 temperatures (P<0.01). The longitudinal changes in body temperatures correlated with the ovarian cycle, with higher temperatures occurring during the luteal phase. The fecal temperatures of one acyclic African elephant did not change cyclically. These results suggest that measurement of body temperature can be used to easily evaluate the ovarian cyclicity of an individual animal, although it might not be able to determine the ovarian cycle length.

Agonistes et antagonistes des récepteurs mélatoninergiques : perspectives thérapeutiques

The chronobiotic neurohormone melatonin, synthetized in the pineal gland during darkness periods governs the circadian and seasonal biological rhythms. Physiologically, melatonin regulates the sleep/activity alternance, together with the circadian cycle of body temperature and cortisol secretion, and influences various immune, endocrine and metabolic functions. Dysfunction of the endogenous melatonin secretion is associated with mood and behavioral disorders including body weight. Patients with severe depression exhibit desynchronized and reduced melatonin secretion, in parallel with marked sleep disturbances whereas exogenous melatonin administration and antidepressive drugs restore melatonin secretion. A dysregulated melatonin secretion is also observed in obese subjects. Implication of melatonin in these disorders stimulated the search for melatonin analogues with enhanced antidepressive and body weight control effects. The melatoninergic agonist S 20098, or agomelatin, disclosed a potent antidepressive and anxiolytic activity in preclinical studies, which was confirmed in clinical trials in patients with major depression. The antagonist S 20928 was shown to limit seasonal weight gain in an hibernating rodent model. Thus, development of melatoninergic agonists and antagonists appear as an innovative approach in the treatment of depression and obesity, two major public health problems.

A noninvasive technique to determine peripheral blood flow and heat generation in a human limb

The temperature at the surface of a human body is strongly related to heat generation in underlying tissue, and its perfusion by blood. The phenomena of heat generation and dissipation unfold the thermo-regulatory control of a human body. Excursions of body temperatures from “normal” have long been considered as evidence of ill health or abnormal physiological states. In this paper, a noninvasive technique is presented to determine the peripheral rates of heat generation and blood flow in a human limb from its recorded skin surface temperature. The technique involves an analysis based on calculus-of-variation, and features the well-known circadian cycle of mammalian body temperature. The method can readily be adapted to different body parts given appropriate heat transfer models. Further, the method may confirm or contribute to greater reliability of medical diagnosis of individuals for whom recorded skin surface temperatures are available. The technique is demonstrated for a set of skin surface temperature data.

Circadian adaptation to night-shift work by judicious light and darkness exposure.

In this combined field and laboratory investigation, the authors tested the efficacy of an intervention designed to promote circadian adaptation to night-shift work. Fifteen nurses working permanent night schedules (> or = 8 shifts/ 15 days) were recruited from area hospitals. Following avacation period of > or = 10 days on a regular daytime schedule, workers were admitted to the laboratory for the assessment of circadian phase via a 36-h constant routine. They returned to work approximately 12 night shifts on their regular schedules under one of two conditions. Treatment group workers (n = 10, mean age +/- SD = 41.7 +/- 8.8 years) received an intervention including 6 h of intermittent bright-light exposure in the workplace (approximately 3,243 lux) and shielding from bright morning outdoor light with tinted goggles (15% visual light transmission). Control group workers (n = 9, mean age +/- SD = 42.0 +/- 7.2 years) were observed in their habitual work environments. On work days, participants maintained regular sleep/wake schedules including a single 8-h sleep/darkness episode beginning 2 h after the end of the night shift. A second 36-h constant routine was performed following the series of night shifts. In the presence of the intervention, circadian rhythms of core body temperature and salivary melatonin cycles were delayed by an average (+/- SEM) of -9.32 +/- 1.06 h and -11.31 +/- 1.13 h, respectively. These were significantly greater than the phase delays of -4.09 +/- 1.94 h and -5.08 +/- 2.32 h displayed by the control group (p = 0.03 and p = 0.02, respectively). The phase angle between circadian markers and the shifted schedule was reestablished to its baseline position only in the treatment group of workers. These results support the efficacy of a practical intervention for promoting circadian adaptation to night-shift work under field conditions. They also underline the importance of controlling the overall pattern of exposure to light and darkness in circadian adaptation to shifted sleep/wake schedules.

Rhythms of Mammalian Body Temperature Can Sustain Peripheral Circadian Clocks

Background: Low-amplitude temperature oscillations can entrain the phase of circadian rhythms in several unicellular and multicellular organisms, including Neurospora and Drosophila. Because mammalian body temperature is subject to circadian variations of 1°C–4°C, we wished to determine whether these temperature cycles could serve as a Zeitgeber for circadian gene expression in peripheral cell types.Results: In RAT1 fibroblasts cultured in vitro, circadian gene expression could be established by a square wave temperature rhythm with a ΔT of 4°C (12 hr 37°C/12 hr 33°C). To examine whether natural body temperature rhythms can also affect circadian gene expression, we first measured core body temperature cycles in the peritoneal cavities of mice by radiotelemetry. We then reproduced these rhythms with high precision in the liquid medium of cultured fibroblasts for several days by means of a homemade computer-driven incubator. While these “in vivo” temperature rhythms were incapable of establishing circadian gene expression de novo, they could maintain previously induced rhythms for multiple days; by contrast, the rhythms of control cells kept at constant temperature rapidly dampened. Moreover, circadian oscillations of environmental temperature could reentrain circadian clocks in the livers of mice, probably via the changes they imposed upon both body temperature and feeding behavior. Interestingly, these changes in ambient temperature did not affect the phase of the central circadian pacemaker in the suprachiasmatic nucleus (SCN) of the hypothalamus.Conclusions: We postulate that both endogenous and environmental temperature cycles can participate in the synchronization of peripheral clocks in mammals.

Cycle characteristics after discontinuation of oral contraceptives

Nearly 60% of the women between 20 and 40 years of age who do not want to conceive choose oral contraceptives (OCs) for contraception in Germany. In an ongoing prospective study on the use of natural familyplanning in Germany, 175 women have been observed for 3048 cycles immediately after having discontinued OCs (post-pill group). They were compared to a control group of 284 women observed for 6251 cycles,who had never taken OCs. Both groups were comparable in age and sociodemographic characteristics. After discontinuing OCs, 57.9% of all first cycles were ovulatory with sufficient luteal phases. However,for the total post-pill group the cycle length was significantly prolonged up to the ninth cycle. A significantly higher number of luteal phases were insufficient in the post-pill group. Major cycle disturbances(cycle length > 35 days or luteal phase of < 10 days of elevated basal body temperature or anovulatory cycles) were significantly more frequent in the post-pill group up to the seventh cycle.Cycledisturbances after discontinuing OCs were reversible but the time of regeneration took up to 9 months (significant) or even longer (not significant). These results will help to counsel couples who wishto conceive after discontinuing OCs or who want to continue contraception with alternative methods.

Changes in egg and body temperature indicate triggering of egg desertion at a body mass threshold in fasting incubating blue petrels ( Halobaena caerulea )

The triggering of transitory egg desertion in fasting and incubating blue petrels (Halobaena caerulea, nocturnal burrowing seabirds living in the subantarctic region) was investigated by continuously monitoring both body temperature (T sto) and egg temperature (T egg) with a telemetry system, and by measuring body mass (BM) loss. The birds were kept captive in their burrow and incubated day and night without any interruption; there was no day-night cycle in T sto and T egg, which averaged 39.9 °C and 32.0 °C, respectively. There was no evidence of hypothermia as a way to save energy in this fasting situation. Egg desertion occurred at night and was an abrupt and definitive phenomenon reflected by a simultaneous fall in T egg and a peak in T sto. After egg desertion, a distinct day-night cycle of body temperature was observed, T sto being 0.6 °C higher during night-time (P < 0.05), probably reflecting increased nocturnal activity. BM at egg desertion averaged 166.7 ± 3.8 g in telemetered birds and 164.4 ± 1.6 g in␣a group of free-living birds. Throughout fasting, the␣specific daily BM loss remained at 46 ± 1 g · kg−1 · day−1, but increased sharply below a critical BM of 160.0 ± 2.5 g. Thus, fasting incubating blue petrels spontaneously desert their egg when reaching a BM threshold. This BM is very close to a critical value in fasting birds and mammals that corresponds to a critical depletion of fat stores and to a shift from lipid to protein utilization. This strongly suggests that such a metabolic shift triggers behavioural changes leading to egg desertion and refeeding, which is of great relevance to the understanding of the long-term control of food intake and BM.

Relationship of Circadian Temperature and Activity Rhythms in Two Rodent Species

Despite the large number of publications concerning circadian body temperature in rodents, relatively little is known about phase relationships of the body temperature cycle relative to daily locomotor rhythms. Phase angle differences between core body temperature and locomotor activity were determined by a group of overlapping methods for 14 hamsters and 11 chipmunks under constant light (LL) and entrained (LD) photo schedules. The study compared the onset of the body temperature cycle with three separate components of daily locomotor activity: the onset of wheel running, the onset of total activity in a standard wheel cage, and the onset of total activity in a restricted cage, respectively. The temperature cycle showed a pronounced phase lead over onset of wheel-running activity in all hamsters and in the majority of chipmunks, but the phase lead was reduced when total activity was considered. With activity restriction, the onset of temperature rise and activity onset concurred. The body temperature onset in some species may serve as a valid phase point for indirect measurement of circadian timing, but the potential artifact of masking by heat generated from muscular activity should be kept clearly in mind.

Body temperature changes in wild‐living badgers Meles meles through the winter

In central Norway, the body temperatures of two wild‐living badgers Meles meles, one male and one female, were recorded in the morning and evening from early November to late March using an implanted temperature‐sensitive radio transmitter. The external ambient and internal sett temperatures were also recorded. Both badgers showed a general decrease in their mean daily body temperature from early November until the second half of December, followed by a general increase until the beginning of March. The reduction in body temperature for both animals was around 2–3 °C. The female spent most of the winter under a building, in a crawl space where the internal temperature varied from +4°C to ‐11°C, being strongly influenced by the external ambient temperature. The male spent the winter in a natural sett where the temperature was rather constant (+2–5°C), and where the external ambient temperature had little influence on the internal sett temperature. However, the external ambient temperature only accounted for 11 and 12% of the observed body temperature variations in the male and female, respectively. When the length of daylight was compared with the body temperatures, it was found to account for 60 and 30% of the variations in the male and female temperatures, respectively. Thus, the data indicate that the photoperiod, at its minimum at the winter solstice, acted as the primary synchroniser of the body temperature cycle in the badgers during their winter lethargy.

Sleep fragmentation, and changes in locomotor activity and body temperature in trypanosome-infected rats

The rest-activity and body temperature 24 h cycles, as well as the structure of spontaneous sleep, were studied in rats 3 weeks after infection with monomorphic Trypanosoma brucei brucei. This parasite belongs to the species of trypanosomes that causes in humans African sleeping sickness, a neuropsychiatric syndrome that involves alterations of endogenous biological rhythms. In the infected rats, entrained to a 12 h:12 h photoperiod, a considerable hypokinesia was detected during the hours of darkness. A significant oscillation of the body temperature during 24 h was lost in some infected animals. In the other infected animals, the body temperature cycle displayed a lower amplitude and a phase advance. The mean temperature was slightly higher in the infected than in control rats during the period of light A detailed analysis of the structure of spontaneous sleep, based on daytime electroencephalographic recordings, revealed during trypanosome infection an increased relative proportion of wake, and a decreased percent value of synchronized sleep. A marked reduction of the mean REM latency and a fragmented pattern of synchronized sleep, resulting in a considerable alteration of the REM-non-REM sleep sequences, were also observed In the infected animals. These findings indicate that trypanosomiasis in the rat results in a striking sleep fragmentation, as well as in changes of locomotor activity and body temperature rhythm. Thus, trypanosome infection in the rat provides an experimental model of sleep dysregulation in a structurally intact brain, and may provide an animal model of endogenous rhythm changes documented in African sleeping sickness.

Adaptation of Human Sleep‐Wake and Body Temperature Cycles to a New Sleep‐Wake Schedule: A Study with a Short‐Acting Benzodiazepine

Abstract: Twelve healthy male subjects were divided into 2 groups–the triazolam and placebo groups. The first three days were designated the baseline days. On the last three days, the bedtime and rising time were advanced 3 hours compared with the baseline days, and 0.5 mg of triazolam or a placebo was orally administered at bedtime. Their sleep was monitored polygraphically. Rectal temperature was measured for 6 days. There were no marked changes in the sleep pattern except that the sleep onset time was advanced by 3 hours. On the other hand, the nadir and acrophase of the body temperature were significantly advanced in the triazolam group. These findings suggest triazolam changes the phase of the human body temperature rhythm.

Timing of sleep and wakefulness in Alzheimer's disease patients residing at home

Dysfunction of the circadian timing system has long been suspected in Alzheimer's d i ~ (AD) because such patients frequently, though not inevitably, have sleep disturbance (Bliwise 1989). Despite such sleep disruption, some studies of various physiological phenomena typically showing diurnal variation (e.g., body temperature, cortisol, prolactin, melatonin) have had difficulty showing differences between AD patients and controls (Prinz et al 1984; Touitou 1982; Christie et al 1983), perhaps owing to selection bias in patients studied (Witting et al 1990). More recently, Campbell et al (1988) reported the existence of an earlier acrophase in the body temperature cycle in male AD patients relative to age-matched, nondemented controls. This finding contrasts with the data of Satlin et al (1991) who reported a delayed acrophase in the rest/activity cycle in AD patients. Here we present data on the timing of sleep/wakefulness in AD patients in their home as recorded by caregivers in a l-week sleep log. To the best of our knowledge, no data currently exist on the timing of sleep and wakefulness in a group of well-characterized AD patients in their natural environments. Methods

Short‐term memory, alertness and performance: a reappraisal of their relationship to body temperature

Previous studies have led to the beliefs: (1) that short-term memory is best during the night when the body temperature is at its nadir, and (2) that the circadian rhythms of short-term memory and subjective alertness are driven by oscillators independent from each other and from the body temperature cycle. Unfortunately, these conclusions, which would have major implications for understanding the organization of the human circadian timing system, are largely based on field and laboratory studies, which in many cases sampled data infrequently and/or limited data collection to normal waking hours. In order to investigate these points further, we have monitored behavioural variables in two different protocols under controlled laboratory conditions: (1) during a period of 36-60 h of sustained wakefulness; and (2) during forced desynchrony between the body temperature and sleep/wake cycles, allowing testing of non-sleep-deprived subjects at all circadian phases. Contrary to earlier findings, we report here that the circadian rhythm of short-term memory varies in parallel with the circadian rhythms of subjective alertness, calculation performance, and core body temperature under both these experimental conditions. These results challenge the notion that short-term memory is inversely linked to the body temperature cycle and suggest that the human circadian pacemaker, which drives the body temperature cycle, is the primary determinant of endogenous circadian variations in subjective alertness and calculation performance as well as in the immediate recall of meaningful material.

Circadian rhythms in early human development

The body temperature, heart rate and rest-activity cycles of 12 low-risk preterm infants (29–35 weeks) were continuously recorded in the neonatal intensive care unit over a period of 1–2 weeks. Throughout the recordings the light was on continuously, the feeding was done intra-gastrically every 2 h and the incubator temperature was constant. Under such conditions a significant circadian rhythm was found in the body temperature and heart rate of more than 50% of the infants. These findings indicate the possible existence of an endogenous circadian rhythm in early human infancy. Since lights are continuously on in the neonatal intensive care unit, this might impair the time of emergence of day-night entrainment of the biological clock in preterm infants.

Daily and seasonal cycles of body temperature and aspects of heterothermy in the hedgehog Eriuaceus europaeus.

Summary. Intra-abdominal temperature-sensitive radio transmitters were used to collect more than 350 sets of body temperature (Tb) data from 23 captive adult hedgehogs over a 3-year period. Each data set comprised measurements made every 1/2 h for 24-h periods. Between 20 and 60 such data sets were recorded every calendar month, and a total of 17400 measurements of Tb were collected. The hedgehogs were exposed to natural environmental conditions at 57 ⁰N in NE Scotlad. Hedgehogs showed seasonal changes in mean daily euthermic Tb, with a July maximum of 35.9±0.2 ⁰C a September minimum of 34.7± 0.9 ⁰C and a marked circadian Tb cycle that correlates closely with photoperiod Maximal Tb occurred within 2 h of midnight and this pattern of nocturnal maximum and diurnal minimum Tb was most marked between April and September. The circadian Tbcycle was least correlated with photoperiod during winter. Hibernal Tb during winter correlated with ambient temperature (Ta), it was maximal in September(17.7± 1.0 ⁰C and minimal in December (5.2±0.9 ⁰C Apart from the tracking of Ta and Tb during hibernalb outs, with a time-lag of 4-6 h, circadian rhythmicity of hibernal Tb was not evident. However, the Tb of hibernating hedgehogs rose significantly when Ta fell below-5 ⁰C although the animals did not neccessarily arouse.Although hibernal bouts occurred between September and April, 89.5% of such bouts were recorded between November and February. The mean time of entry into hibernation was 01:45 ±5./h GMT while the mean time of the start of spontaneous arousal from hibernation was 11 : 53 ± 4.8 h GMT. Therefore, during hibernation hedgehogs were either fully aroused at night,when euthermic hedgehogs have maximal Tb, or in deep hibernation around midday, when euthermic hedgehogs have minimal Tb. Since wild hedgehogs will feed during spontaneous arousal from hibernation, these timings are probably adaptive, and suggest that entry into, and arousal from, hibernation may be extensions of circadian cyclicity. Spontaneous bouts of transient shallow torpor (TST) were recorded throughout the year, with nearly 80% of observations occurring during August and September, at the start of the hibernal period. TST bouts lasted for 4.9±2.9 h, with T b falling to 25.8±3.1 ⁰C Only 20% of TST bouts immediately preceded hibernation and their duration did not correlate with Ta or body mass. TST bouts started at O6:51± 4.7 h GMT, significantly later than entry into hibernation, and ended at 13:04±5.4 h GMT. The function of TST bouts is unclear,but they may be preparation for the hibernation season or a further energy conservation strategy. When arousing from hibernation hedgehogs warmed at a rate of 1.9±0.4⁰C -1, and when entering hibernation cooled at 7.9±1.9 ⁰C h- 1. Warming rates were slightly higher during mid-winter when Tb and body mass were minimal, but cooling rates were 44% higher at the end of the hibernal period compared to the start. Cooling and warming rates were strikingly similar to those measured in hedgehogs at 31 ⁰N These results demonstrate that thermoregulation in the hedgehog is closely regulated and changes on a seasonal basis, in meeting with requirements of surviving food shortages and low temperature during winter.

Regulated nocturnal hypothermia induced in pigeons by food deprivation.

The daily body temperature (Tb) cycle of pigeons is altered by food deprivation in that Tb falls to lower and lower levels on consecutive nights after the onset of deprivation, whereas the Tb levels during corresponding days remain nearly unchanged. Manipulations of spinal cord temperature, a major feedback parameter in the avian thermoregulatory system, reveal that episodes of nocturnal hypothermia are regulated. The spinal cord threshold temperature for inducing increases in metabolic heat production falls to progressively lower levels each night and returns to normal euthermic levels during the day.

Energy metabolism and body temperature in 13 sunbird species (Nectariniidae)

1. 1. Diurnal cycles of body temperature, T b, and energy metabolism, M, at different ambient temperatures ( T a: +5 −+ 32°C) were tested in 13 sunbird species from various habitats and of different body masses (5.2–14.2 g) including one of the smallest passerines, Aethopyga christinae. 2. 2. Resting M-level (night) reaches T a- dependent mean values of 54% (+5°C) and 49% (+25°C) of activity M-levels (day). Expected level is ca 75%. 3. 3. Resting metabolic rate of sunbirds lies within the range of theoretically expected values for birds. 4. 4. Mean linear metabolism-weight regression of the night values follows: M = 0.102 × W 0.712 ( M = energy metabolism in kJ/hr and W = body mass in g). 5. 5. Thermal conductances, T c, are lower (−24%) than the predicted values. This is caused by a decrease of T b at low T a. Mean nocturnal T c is 3.2 J/g × hr × °C, mean day-time value is 4.3 J/g × hr × °C. 6. 6. The zone of thermoneutrality is, in most species, within a T a- range of 24–28°C. 7. 7. Normal day and night levels of T b are in the same range as reported for other birds of the same weight class. T b decreases slightly with falling T a (partial heterothermia). Lowest recorded T b was 34.2°C. 8. 8. No species tested showed any sign of torpor at night, independent of T a, body mass or habitat origin.

Diagnosis of the child with fever in the emergency department (continuing education credit).

Fever in young children is one of the more common complaints precipitating a visit to the emergency room. Yet in spite of a wealth of medical literature in this field, few people can even define at what temperature fever begins. It is helpful, however, to have a specific numerical point of reference. An arbitrary but useful point where fever can be said to begin is 37.5O C (99.5O F) orally or 38.1 o C (100.5“ F) rectally. The most notable exception to this rule is the patient with the possibility of appendicitis. In this case, 37.2’ C (99O F) orally or 37.8’ C (100’ F) rectally is an appropriate demarcation for the clinical sign of fever. Lowering the expectation of where fever begins in patients with appendicitis is done out of respect for the subtle signs with which children who have that disease may be seen initially. Some 100 years ago, Wunderlich reintroduced the concept that body temperature as measured by a thermometer may be indicative of disease in human subjects. At that time, only axillary temperatures were taken. Although some studies suggest that axillary temperatures taken by electronic thermometers are useful,’ in 1984 Kresch determined that axillary temperature taken using a glass thermometer is quite insensitive for the detection of fever. In this study, using 37.3’ C (99.1’ F) axillary temperature as the definition of fever, axillary measurement detected only 33.3% of febrile patients. And when a fever was found by axillary measurement, it was confirmed by rectal temperature only 78% of the time.2 The argument is often made that rectal temperatures are dangerous to perform because of the possibility of bowel perforation.3 This risk can be lowered by taking rectal temperatures more carefully.4 A new concern about rectal thermometry relates to anxieties about the transmission of human immunodeficiency virus (HIV, the agent of acquired immunodeficiency syndrome [AIDS]). It has been demonstrated repeatedly that HIV is easily inactivated using standard reagents (including 40% ethyl alcohol, 1% lysol, 5% phenol, 200 ppm sodium hypochlorite, NP-40, hydrogen peroxide, phenolics, and paraformaldehyde). As long as fecal debris, which a reagent might not be able to penetrate, is removed from the thermometer, chemical disinfection will be more than adequate to eradicate the virus.5 The diurnal cycle of human body temperature should not alter the previously mentioned guidelines of what temperature constitutes fever. The daily minimum body temperature occurs between 2 and 4 AM, and the daily maximum temperature occurs some 12 to 16 hours later. The range between the minimum and maximum values is about one half a degree centigrade. The child with a high fever is commonly seen in the emergency department with a concerned parent and offers both a problem and an opportunity to the ED nurse to calm the parent and to comfort the child. The parents should be asked what they’ve already done for the child. Specifically, it is important to find out what medications have been given, in what dose, and when. (Depending on the gravity of the situation, it may sometimes be appropriate to send someone home to retrieve a medicine if its name can’t be recalled.) No matter how little the parents have done,

Overwintering strategies of the badger, Meles meles, at 57 °N

Over two eight‐month periods (October/November‐May) during successive winters (1983/4 and 1984/5), the body temperatures and activity patterns of captive badgers, Meles meles, living under semi‐natural conditions, were studied at 57 d̀N in Scotland. Temperature‐sensitive radio transmitters and automated telemetry systems provided long‐term records of body temperatures and times badgers were absent from an artificial sett.Badger body temperatures of 28–34 d̀C, significantly below euthermic levels, were recorded between October/November and March each winter, with differences between mean daily maxima and minima varying from 1.6 to 8.9 d̀C. This was associated with a reduction, by up to 90%, in the time that the badgers spent outside their sett in mid‐winter. Body temperatures did not show circadian cyclicity, but from February onwards most locomotor activity occurred between 22:00 and 02:00 GMT. The extent to which activity was concentrated around midnight increased with decreasing night length in spring.The body temperatures of one female badger fell to a nadir of 28 d̀C immediately prior to ovo‐implantation. During post‐implantation gestation, the body temperature of this female rose steadily, but had reached only 34.6 d̀C at parturition.Photoperiod correlated closely with seasonal changes in body temperatures and activity levels, and is suggested as the primary synchronizer of seasonal activity and body temperature cycles. Other environmental variables, particularly ambient temperature and snow‐cover, appeared to act as modulating influences on these cycles.It is postulated that during the winter, when climatic conditions are responsible for a shortage of food and an increase in heat loss, winter lethargy is an adaptation which enables the European badger to maintain energy balance. Reduced activity and confinement within sheltered setts, together with reduced body temperatures, enable the badgers to rely heavily on energy stored in adipose tissue during the autumn.