Short-Day Response in Djungarian Hamsters of Different Circadian Phenotypes

In Djungarian hamsters (Phodopus sungorus) bred at the authors' institute, a certain number of animals show activity patterns incompatible with proper entrainment of their endogenous circadian pacemaker to the environmental light-dark (LD) cycle. Even though the activity-offset in these animals is stably coupled to “light-on,” activity-onset is increasingly delayed, leading to a compression of the activity time (α). If α falls below a critical value, the circadian rhythm in these so called delayed activity-onset (DAO) hamsters starts to free-run and finally breaks down. Animals then show an arrhythmic activity pattern (AR hamsters). Previous studies revealed the mechanisms of photic entrainment have deteriorated (DAO) or the suprachiasmatic nucleus (SCN) does not generate a rhythmic signal (AR). The aim of the present study was to investigate the consequences that these deteriorations have upon photoperiodic time measurement. Animals were bred and kept under standardized housing conditions with food and water ad libitum and a 14L/10D (long day, LD) regimen. Locomotor activity was recorded continuously using passive infrared motion detectors. Body mass, testes size, and fur coloration were measured weekly or biweekly to further quantify the photoperiodic reaction. In a first experiment, adult male wild-type (WT), DAO, and AR hamsters were transferred initially to a 16L/8D cycle. After 3–4 wks, the light period was shortened symmetrically by 8?h. After 14 wks, none of the DAO and AR hamsters, and only 1 of 8 WT hamsters showed short-day (SD) traits. Therefore, in a second experiment, hamsters were transferred to SD conditions (8L/16D cycle) for 8 wks directly from standard LD conditions. In 6 of 7 WT hamsters, activity time expanded, body mass and testes size decreased, and fur coloration changed from summer to winter pelage. In contrast, none of the DAO and AR hamsters displayed an SD response. In a third experiment, DAO and AR hamsters were kept in constant darkness (DD) for 8 and 14 wks. After 8 wks, DAO hamsters showed a similar photoperiodic reaction to WT hamsters that had been kept for 8 wks under SD conditions. However, the level of adaptation was still less compared to WT hamsters, but this difference was not apparent after 14 wks. In contrast, AR animals did not display any photoperiodic reaction, even after 14 wks in DD. Type VI phase response curves (PRCs) were constructed to better understand the mechanism behind the SD response. In WT hamsters, the photosensitive phase, where light pulses induce phase shifts, was lengthened in SD condition. In DAO hamsters, in contrast, the PRCs were similar under LD and SD conditions with a compressed photosensitive phase corresponding to α. Also, “light-on” induced only weak phase advances of activity-onset, insufficient to compensate for the long endogenous period. The results show that physiological mechanisms necessary for seasonal adaptation are working in DAO hamsters and that it is the inadequate interaction of the LD cycle with the SCN that prevents the photoperiodic reaction. AR hamsters, on the other hand, are incapable of measuring photoperiodic time due to a complete disruption of circadian rhythmicity.     

The Daily Melatonin Pattern in Djungarian Hamsters Depends on the Circadian Phenotype

Djungarian hamsters (Phodopus sungorus) bred at the Institute of Halle reveal three different circadian phenotypes. The wild type (WT) shows normal locomotor activity patterns, whereas in hamsters of the DAO (delayed activity onset) type, the activity onset is continuously delayed. Since the activity offset in those hamsters remains coupled to “light-on,” the activity time becomes compressed. Hamsters of the AR (arrhythmic) type are episodically active throughout the 24?h. Previous studies showed that a disturbed interaction of the circadian system with the light-dark (LD) cycle contributes to the phenomenon observed in DAO hamsters. To gain better insight into the underlying mechanisms, the authors investigated the daily melatonin rhythm, as it is a reliable marker of the circadian clock. Hamsters were kept individually under standardized laboratory conditions (LD 14:10, T?=?22°C?±?2°C, food and water ad libitum). WT, DAO (with exactly 5?h delay of activity onset), and AR hamsters were used for pineal melatonin and urinary 6-sulfatoxymelatonin (aMT6s) measurement. Pineal melatonin content was determined at 3 time points: 4?h after “light-off” [D?+?4], 1?h before “light-on” [L???1], and 1?h after “light-on” [L?+?1]). The 24-h profile of melatonin secretion was investigated by transferring the animals to metabolic cages for 27?h to collect urine at 3-h intervals for aMT6s analysis. WT hamsters showed high pineal melatonin content during the dark time (D?+?4, L???1), which significantly decreased at the beginning of the light period (L?+?1). In contrast, DAO hamsters displayed low melatonin levels during the part of the dark period when animals were still resting (D?+?4). At the end of the dark period (L???1), melatonin content increased significantly and declined again when light was switched on (L?+?1). AR hamsters showed low melatonin levels, comparable to daytime values, at all 3 time points. The results were confirmed by aMT6s data. WT hamsters showed a marked circadian pattern of aMT6s excretion. The concentration started to increase 3?h after “light-off” and reached daytime values 5?h after “light-on.” In DAO hamsters, in contrast, aMT6s excretion started about 6?h later and reached significantly lower levels compared to WT hamsters. In AR animals, aMT6s excretion was low at all times. The results clearly indicate the rhythm of melatonin secretion in DAO hamsters is delayed in accord with their delayed activity onset, whereas AR hamsters display no melatonin rhythm at all. Since the regulatory pathways for the rhythms of locomotor activity and melatonin synthesis (which are downstream from the suprachiasmatic nucleus [SCN]) are different but obviously convey the same signal, we conclude that the origin of the phenomenon observed in DAO hamsters must be located upstream of the SCN, or in the SCN itself. (Author correspondence: weinert@zoologie.uni-halle.de)     

Daily Rhythms of Core Temperature and Locomotor Activity Indicate Different Adaptive Strategies to Cold Exposure in Adult and Aged Mouse Lemurs Acclimated to a Summer-Like Photoperiod

Daily variations in core temperature (Tc) within the normothermic range imply thermoregulatory processes that are essential for optimal function and survival. Higher susceptibility towards cold exposure in older animals suggests that these processes are disturbed with age. In the mouse lemur, a long-day breeder, we tested whether aging affected circadian rhythmicity of Tc, locomotor activity (LA), and energy balance under long-day conditions when exposed to cold. Adult (N?=?7) and aged (N?=?5) mouse lemurs acclimated to LD14/10 were exposed to 10–day periods at 25 and 12°C. Tc and LA rhythms were recorded by telemetry, and caloric intake (CI), body mass changes, and plasma IGF-1 were measured. During exposure to 25°C, both adult and aged mouse lemurs exhibited strong daily variations in Tc. Aged animals exhibited lower levels of nocturnal LA and nocturnal and diurnal Tc levels in comparison to adults. Body mass and IGF-1 levels remained unchanged with aging. Under cold exposure, torpor bout occurrence was never observed whatever the age category. Adult and aged mouse lemurs maintained their Tc in the normothermic range and a positive energy balance. All animals exhibited increase in CI and decrease in IGF-1 in response to cold. The decrease in IGF-1 was delayed in aged mouse lemurs compared to adults. Moreover, both adult and aged animals responded to cold exposure by increasing their diurnal LA compared to those under Ta?=?25°C. However, aged animals exhibited a strong decrease in nocturnal LA and Tc, whereas cold effects were only slight in adults. The temporal organization and amplitude of the daily phase of low Tc were particularly well preserved under cold exposure in both age groups. Sexually active mouse lemurs exposed to cold thus seemed to prevent torpor exhibition and temporal disorganization of daily rhythms of Tc, even during aging. However, although energy balance was not impaired with age in mouse lemurs after cold exposure, aging was associated with lower LA and Tc during the night and delayed decrease in IGF-1. This might reflect that adaptive strategies to cold exposure differ with age in mouse lemurs acclimated to a summer-like photoperiod.     

An Inbred Lineage of Djungarian Hamsters with a Strongly Attenuated Ability to Synchronize

An inbred lineage of Ph. sungorus was established at our institute showing some unusual characteristics of the circadian system that appear incompatible with an adequate adaptation to the periodic environment. We identified a hamster for which activity onset was delayed under light‐dark conditions (L:D=14∶10 h) by about 4 h in relation to the light‐dark transition. As the activity offset remained synchronized with the time of light‐on, the activity period (α) became compressed to 6 h. By means of a special breeding program, the percentage of animals showing such a phenomenon increased, indicating that it has a genetic component. Also, it is possible now to breed a larger number of hamsters to further investigate the rhythm deviations and the underlying mechanisms. Activity rhythms were investigated using passive infrared motion sensors. Whereas some of the hamsters showed a rather stable phase delay of activity onset relative to the onset of darkness, some animals progressively delayed their activity onset up to a critical, minimal length of α (3.03±0.02 h). Thereafter, the rest‐activity rhythm started to free‐run with a remarkably long period (τ=25.02 h) or became arrhythmic. Some hamsters showed several consecutive cycles alternating between a free‐running rhythm and entrainment, with increasing τ and reducing the phases of temporary entrainment. Finally, these hamsters became arrhythmic. The total amount of activity per day was similar in the wild type and delayed activity onset hamsters. The latter did increase the intensity of activity, thereby compensating for the shorter α. The period length in constant darkness was significantly longer in the delayed hamsters compared to wild type animals (24.37±0.03 h vs. 24.24±0.02 h; p<0.001). However, this difference seems too small to cause the later activity onset. The phase response following a light pulse (100 lux, 15′ at CT14 where CT12=activity onset) was similar in delayed and wild type hamsters (?1.66±0.12 h and ?1.82±0.16 h). As access to running wheels is known to influence the circadian pacemaker, particularly to strengthen oscillator coupling, a set of further experiments was conducted. The free‐running period was significantly shorter when the hamsters were provided with running wheels (24.25±0.04 h and 24.07±0.04 h in wild type and delayed hamsters, respectively; p<0.005 and p<0.05). However, the effect on the activity onset was not unequivocal. In many hamsters it was still delayed, whereas in others the unlocking of the wheels led to an expansion of α. The described inbred lineage appears to be an excellent model to further investigate the properties and the interaction of the two oscillators underlying the daily activity pattern.     

Pigment Content of Selected Planktonic Algae in Response to Simulated Natural Light Fluctuations and a Short Photoperiod

The lipophilic photosynthetic pigments in Limnothrix redekei, Planktothrix agardhii (cyanobacteria), Stephanodiscus minutulus, Synedra acus (diatoms), Scenedesmus acuminatus, and Scenedesmus armatus (chlorophycean) all isolated from an eutrophic lake were quantitatively determined by HPLC. The algae were grown semi-continuously under nutrient sufficient conditions at 20°C at a 12/12 h light/dark cycle with constant irradiance or with simulated natural light fluctuations as well as at a 6/18 h light/dark cycle with constant irradiance, all at the same daily light exposure. The zeaxanthin and the myxoxanthophyll contents of cyanobacteria were not influenced by fluctuating light, a short photoperiod or a different sampling time. The chlorophyll b/a ratio, the lutein/chlorophyll a ratio, and the neoxanthin content of chlorophycean as well as the chlorophyll c/a and the fucoxanthin/chlorophyll a ratio of diatoms were only slightly influenced by these factors. Therefore in some cases marker pigment contents and in other cases marker pigment/chlorophyll a ratios may be more useful for quantifying the relative importance of different taxonomic groups in natural phytoplankton. Simulated natural light fluctuations or the length of the photoperiod only slightly influenced the pigment content or the marker pigment/chlorophyll a ratio.     

Circadian Rhythm in Plasma Noradrenaline of Healthy Sleep-Deprived Subjects

Under normal sleep-wake conditions, noradrenaline (NA) secretions in supine subjects exhibit a weak circadian variation with a peak that occurs around noon; the sleep span is characterized by reduced NA secretion. Some investigators have reported that the circadian NA rhythm is completely obliterated during sleep deprivation. In our laboratory, plasma NA was assayed every hour for 24 h in nine healthy men 20-23 years of age. All men were deprived of sleep and were required to eat and walk around every hour to prevent sleep. However, subjects remained supine for 20 min before blood samples were collected to eliminate the effect of activity. Persistence of a slight decrease in the night concentration in several subjects, despite sleep deprivation, suggests that NA secretion may be influenced by a biological clock whose activity becomes visible when the influence of posture is removed.     

Synchronization of the Circadian Activity Rhythm in Hamsters Following Intermittent Schedule Shifts

The time course of resynchronization of the circadian activity rhythm of hamsters was observed following a 10-hr advance or delay in the light-dark cycle (LD 12:12). Twenty-six shift patterns of the lighting schedule were studied; they consisted of continuous (daily), three-step, two-step and one-step shifting. So long as the daily shift of the lighting schedule was 1 hr or less, the locomotor rhythm followed the continuous shift perfectly. As the amount of daily shift increased, the time course of activity onset deviated more from the time of lights off; the tendency was more marked in advancing than in delaying shifts. Responses of the activity rhythm to stepwise shifting were essentially the same as those to a continuous shift. They were, however, characterized by larger individual variations, and it took additional days before entrainment was achieved. By fitting the time course of entrainment to an exponential model with a constant term, estimates of time constant and shift error were derived. The time constant became shorter with increasing amounts of daily shifts up to 2 hr per day, increasing the number of shift steps, and/or reducing the amount of the initial shift of the seies. The shift error estimated was 0.51 ± 0.12 hr, indicating precise resynchronization. Accordingly, a quicker resynchronization may be expected when a multiple step shift with a moderate initial shift are employed. In the case of a 10-hr shift, for example, a shift of 3 hr followed by another 7 hr may be recommended.     

Response of Winter Wheat Seedlings Respiration to Long-Term Cold Exposure and Short-Term Daily Temperature Drops

Russian Journal of Plant Physiology - The effects of a long-term (6-day) exposure to low positive temperature (4°С, LT treatment) and short-term (3 h per a day for 6 days) daily...     

Synchronization of the Circadian Activity Rhythm in Hamsters Following Intermittent Schedule Shifts

The time course of resynchronization of the circadian activity rhythm of hamsters was observed following a 10-hr advance or delay in the light-dark cycle (LD 12:12). Twenty-six shift patterns of the lighting schedule were studied; they consisted of continuous (daily), three-step, two-step and one-step shifting. So long as the daily shift of the lighting schedule was 1 hr or less, the locomotor rhythm followed the continuous shift perfectly. As the amount of daily shift increased, the time course of activity onset deviated more from the time of lights off; the tendency was more marked in advancing than in delaying shifts. Responses of the activity rhythm to stepwise shifting were essentially the same as those to a continuous shift. They were, however, characterized by larger individual variations, and it took additional days before entrainment was achieved. By fitting the time course of entrainment to an exponential model with a constant term, estimates of time constant and shift error were derived. The time constant became shorter with increasing amounts of daily shifts up to 2 hr per day, increasing the number of shift steps, and/or reducing the amount of the initial shift of the seies. The shift error estimated was 0.51 ± 0.12 hr, indicating precise resynchronization. Accordingly, a quicker resynchronization may be expected when a multiple step shift with a moderate initial shift are employed. In the case of a 10-hr shift, for example, a shift of 3 hr followed by another 7 hr may be recommended.     

Response of Gut Microbiota to Fasting and Hibernation in Syrian Hamsters

Although hibernating mammals wake occasionally to eat during torpor, this period represents a state of fasting. Fasting is known to alter the gut microbiota in nonhibernating mammals; therefore, hibernation may also affect the gut microbiota. However, there are few reports of gut microbiota in hibernating mammals. The present study aimed to compare the gut microbiota in hibernating torpid Syrian hamsters with that in active counterparts by using culture-independent analyses. Hamsters were allocated to either torpid, fed active, or fasted active groups. Hibernation was successfully induced by maintaining darkness at 4°C. Flow cytometry analysis of cecal bacteria showed that 96-h fasting reduced the total gut bacteria. This period of fasting also reduced the concentrations of short chain fatty acids in the cecal contents. In contrast, total bacterial numbers and concentrations of short chain fatty acids were unaffected by hibernation. Denaturing gradient gel electrophoresis of PCR-amplified 16S rRNA gene fragments indicated that fasting and hibernation modulated the cecal microbiota. Analysis of 16S rRNA clone library and species-specific real-time quantitative PCR showed that the class Clostridia predominated in both active and torpid hamsters and that populations of Akkermansia muciniphila, a mucin degrader, were increased by fasting but not by hibernation. From these results, we conclude that the gut microbiota responds differently to fasting and hibernation in Syrian hamsters.Some mammalian species have evolved with the physiological phenomenon of hibernation to survive unfavorable winter environments (9). Hibernation is realized by entering torpor in order to eliminate the need to maintain a constant, high body temperature. During torpor, typical hibernating mammals, such as hamsters and ground squirrels, lower their body temperature to only a few degrees above ambient temperatures to reduce energy expenditure. Torpor is interrupted by periods of intense metabolic activity. During these interbout arousals, physiological parameters are restored rapidly to near-normal levels. Thus, hibernators alternate between hypothermic and euthermic states during hibernation.Some hibernating mammals awake to forage during torpor, while food-storing hibernators such as hamsters eat cached food during interbout arousals. However, hibernation essentially involves periods of fasting. Fasting is known to affect the gut microbiota in nonhibernating mammals such as mice (12); therefore, it is possible that hibernation also influences the gut microbiota. Given that the gut microbiota plays important roles in mammalian tissue development and homeostasis (28), it was of interest to investigate the changes in the gut microbiota that may take place during hibernation. To date, this issue has received little attention; to our knowledge, there are only two reports on the gut microbiota in hibernating mammals. Schmidt et al. showed that although the total counts of coliforms, streptococci, and psychrophilic organisms in the feces of arctic ground squirrels held in a cold room at 3°C remained constant the composition changed, with a decrease in coliform count and a 1,000-fold increase in the number of aerobic psychrophilic gram-negative bacteria (31). Barnes and Burton reported that although there was some reduction in total numbers of viable bacteria in the cecum during hibernation, composition of the microbiota remained stable (6). In terms of amphibians, Banas et al. and Gossling et al. reported a reduction and compositional changes of the gut microbiota in hibernating leopard frogs (4, 5, 18, 19).Only 20 to 40% of bacterial species from the mammalian intestinal tract can be cultured and identified using classical culture methods (22, 34, 36). In contrast, culture-independent methods based on the amplification of bacterial 16S rRNA genes by PCR have revealed a great diversity of microbiota in environmental samples (3, 37). The present study compared the gut microbiota in hibernating torpid Syrian hamsters with that in active counterparts by using culture-independent analyses.     

生理节律与日常活动对人体疲劳程度的影响

目的:研究生理节律和日常活动分别对人体疲劳程度的影响大小。方法:选取某校7名大学生志愿者,在军训期间对每日军训科目严格限制条件下进行该实验,以闪光临界融合频率、心率变异性、反应时、静态姿势图TLX-NASA量表评分作为指标,对每天分别在训练前和训练后疲劳程度的大小进行测量,以这些指标描述训练前后的疲劳程度。结果:反应时降低(0.60±0.09)、反应正确率提高(0.97±0.03);闪光临界光融合频率升高(40.84±2.14);心率变异性TP(3076.60±382.08)降低、心率变异性SDNN(55.28±16.85)降低;静态姿势图晃动减少,中低频率段(0.15±0.01)、前后方向重心变位(7.92±0.63),TLX-NASA量表评分降低(30.47±10.23)。以上差异均具有统计学意义(P<0.05)。结论:生理节律相对于日常活动对机体的疲劳状态有更大的影响。     

Circadian Rhythm of the Pupillary Response to Morphine and to Naloxone

Mice respond to morphine with characteristic mydriasis which is antagonized by naloxone. The present study presents data on the diurnal variation of these responses. The mydriatic response is at its highest level at 0800 and has a nadir at 2400. This effect is not influenced by ambient light conditions. The miotic response to naloxone in the morphine-dilated pupil is maximal between 1200 and 1600 and minimal at 0400. The curves of the responses to the two drugs, therefore, differ as do their acrophases. Pharmacokinetic factors are probably not responsible for the observed variations. It is speculated that these diurnal changes may reflect cyclic alteration in the affinity of the opiate receptors to agonists and antagonists, respectively, or in the number of available receptors.     

水稻开花期调控的分子机理研究进展

水稻准确地感知外部环境信号,通过内部复杂的基因网络做出反应,在一年中最适合的时候开花繁殖。与长日促进长日模式植物拟南芥开花相反,短日促进短日模式植物水稻开花。通过对水稻和拟南芥的开花期调控机理的对比分析,发现水稻和拟南芥有着一些相对保守的开花期控制基因,其调控机理也是相似的。另外,水稻也有一些独特的开花期控制基因和开花途径。本文着重从光周期对水稻开花期的调控途径和作用机理角度进行了阐述,并对水稻开花期的自然变异与其育种应用、生物钟关联基因、光中断现象和临界日长现象以及开花期与产量的关系进行了总结。     

Effect of Gonadectomy on the Androgen-Dependent Behavior of Ganglion Cell-Like Cells in Djungarian Hamsters (Phodopus sungorus)

Ganglion cell-like (GL) cells reside in the dermis of the ventral skin of mature male Djungarian hamsters (Phodopus sugorus) and express androgen receptor (AR). To assess whether GL cells have androgen-dependent behavior, we evaluated the histologic changes of GL cells after gonadectomy. Five male and 5 female hamsters were gonadectomized at the age of 4 wk and necropsied 14 wk later. The number, distribution, and proliferative activity of GL cells in the thoracoabdominal and dorsal skins were evaluated histologically and compared with those of corresponding intact animals. GL cells were more numerous, were distributed throughout the skin more widely, and had higher proliferative activity in the intact male hamsters than in their gonadectomized counterparts. Similar trends regarding these 3 parameters were seen in ovariectomized compared with intact female hamsters and between intact male and intact female hamsters. These results suggest that the GL cells of Djungarian hamsters demonstrate sex-associated differences in their distribution and proliferative activity and that androgen may be involved in the development of these cells.Abbreviations: AR, androgen receptor; GL cell, ganglion cell-like cellGanglion cell-like (GL) cells reside in the dermis of the abdominal and thoracic skin of mature male Djungarian hamsters (Phodopus sungorus).^1,7 GL cells have a small round nucleus with an apparent nucleolus and abundant basophilic foamy cytoplasm. These cells usually aggregate to form nests accompanied by various volumes of stromal collagen fibers. The nests increase in size and number with maturation. The nuclei of GL cells have a positive reaction for androgen receptor (AR), and the cytoplasm is positive for vimentin.^1,7 Although the morphologic characteristics and various immunophenotypes of GL cells have been documented, their behavior and role remain almost unclear. Some authors speculate that increased levels of testosterone may influence GL cell proliferation and the oncogenesis of atypical skin fibromas preferentially arising in this species.¹The current study aims to elucidate the androgen-dependent behavior of GL cells and compare the histologic changes of GL cells in gonadectomized Djungarian hamsters with those in intact control animals.     

Freezing Tolerance and Solute Changes in Contrasting Genotypes of Lolium perenne L. Acclimated to Cold and Drought

Clonal ramets of 12 contrasting genotypes of Lolium perenneL. were grown in sand or soil-based compost and maintained underwell-watered conditions at 20/15°C or acclimated to lowtemperature (2°C) or to a restricted water supply. Freezingtolerance was measured as LT₅₀ following exposure to sub-zerotemperatures in a freezing tank. Measurements were also madeof osmotic potential, water-soluble carbohydrates, free proline,free amino acids, and minerals in entire tillers. Acclimationto both drought and cold lowered LT₅₀, induced osmotic adjustment,and increased concentrations of proline and amino acids, Rootingmedium had little effect on LT₅₀, but caused large differencesin osmotic potential and in proline and amino-acid concentrations.There was considerable genetic diversity for all charactersmeasured, except for mineral contents. There was, however, norelationship between LT₅₀ and osmotic potential or solute contentthat was consistent across the three sources of variation (growingmedium, acclimation, genotype). Furthermore, the diverse genotypicvalues of cold-induced freezing tolerance were not correlatedwith those of drought-induced tolerance. It is concluded thatmore precise measurements are needed of the partitioning ofsolutes during acclimation and of the sensitivity of differentorgans and tissues to freezing.Copyright 1993, 1999 AcademicPress Perennial ryegrass, hardening, acclimation, osmotic potential, solute potential, carbohydrates, proline     

野生大豆光温反应规律的研究

野生大豆（G .Soja）是栽培大豆的近缘祖光种,利用中国野生大豆分布的广泛性,为我们了解和认识大豆在自然界中光温反应的规律提供了条件。通过对29个纬度区自然生长的野生大豆主要生育阶段光温反应特点的了解,明确了不同纬度区野生大豆在自然环境中出苗温度是13.1～14.7℃,开花期温度是20.5～26.5℃,成熟期温度是10～19℃;初花期临界光照时数是13h15min至16h40min之间。出苗越早的低纬度区野生大豆开花和成熟期越晚,而出苗越晚的高纬度区野生大豆开化和成熟期越早。     

Photoperiod and ambient temperature as environmental cues for seasonal thermogenic adaptation in the Djungarian hamster,Phodopus sungorus

For their seasonal control of thermogenesis Djungarian hamsters rely on environmental cueing by both photoperiod and ambient temperature. Their total potential for adaptive improvements of nonshivering thermogenesis is constant in summer and winter. The shortening of photoperiod in fall is used to anticipate about half of the total improvement in thermogenesis, in advance of any experience of cold, as can be concluded from the photoperiodic control of thermogenesis, cold resistance, and the protein content, cyctochrome oxidase activity and content of mitochondria in brown adipose tissue. The remainder of the seasonal thermogenic adaptation is due to stimulatory responses to chronic exposure to cold.This research was supported by the Deutsche Forschungsgemeinschaft, Schwerpunktprogramm Mechanismen der Temperaturregulation und -Adaptation.