Effect of deuterium on the circadian period and metabolism in wild-type and tau mutant Syrian hamsters

Homozygous tau mutant Syrian hamsters (tau-/-) have a free-running circadian period (τ) around 20 h and a proportionally higher metabolic rate compared with wild-type hamsters (tau+/+) with a period of circa 24 h. In this study, we applied deuterium oxide (D2O) to hamsters to test whether deuteration affects the circadian period of locomotor activity and metabolic rate in both genotypes. Running wheel activity and the metabolic rate were measured in constant illumination before, during, and after administration of 25% deuterium in drinking water. Wild-type hamsters lengthened their circadian period by 1.19 h (SD = 0.29 h) due to D2O application and tau-/- hamsters by 1.20 h (SD = 0.39 h). Deuteration changed neither the amount of activity nor the duration of activity phase (α) in either genotype. The mass specific average metabolic rate (AMR, the oxygen consumption over 24 h) and the mass specific resting metabolic rate (RMR) did not differ during deuteration compared with non-deuteration conditions for either genotype. Both with and without D2O, tau-/- hamsters had higher metabolic rates than tau+/+ hamsters. There was no correlation between changes in the circadian period of locomotor activity and metabolic rates caused by D2O.

Natural entrainment of circadian systems:A study in the diurnal ground squirrel, <i>Spermophilus citellus</i>

This thesis combines studies under natural and semi-nanrtal conditions with laboratory experiments and theoretical modelling to describe the regulatory mechanisms that drive the rest-activity cycle in the European ground squirrel. The central theme is a search for the mechanism that synchronizes the endogenous rest-activity cycle to the environmental day-night cycle. Light-dark transitions are known to be important ques for this synchronisation process, but the strictly diurnal ground squirrels never see the twilights during sunrise or sunset

Photoperiodism:Shall EYA Compare Thee to a Summer's Day?

SummarySeasonal changes in day length are used by plants and animals to synchronize annual rhythms in reproduction, physiology, and behavior to the environment. Increasing day length during spring causes sudden changes in the mammalian reproductive system once the critical photoperiod is reached. The molecular mechanism behind this switch is now quickly being elucidated

Natural entrainment of circadian systems:A study in the diurnal ground squirrel, <i>Spermophilus citellus</i>

This thesis combines studies under natural and semi-nanrtal conditions with laboratory experiments and theoretical modelling to describe the regulatory mechanisms that drive the rest-activity cycle in the European ground squirrel. The central theme is a search for the mechanism that synchronizes the endogenous rest-activity cycle to the environmental day-night cycle. Light-dark transitions are known to be important ques for this synchronisation process, but the strictly diurnal ground squirrels never see the twilights during sunrise or sunset

Negative energy balance enhances ultradian rhythmicity in spring-programmed voles

Voles are small herbivorous rodents that can display both circadian activity rhythms (~24-h periodicity) and ultradian activity rhythms (~1- to 6-h periodicity). Ultradian rhythms are observed on an individual level, but also in synchronized populations. Ultradian rhythm period has been suggested to be influenced by energy balance, but the underlying mechanisms of ultradian rhythmicity are poorly understood. We manipulated energy balance by implementing the "work-for-food" paradigm, in which small rodents are exposed to increasing levels of food scarcity at different ambient temperatures in the laboratory. Photoperiodical spring-programmed voles on high workload changed their nocturnal circadian activity and body temperature rhythm to ultradian patterns, indicating that a negative energy balance induces ultradian rhythmicity. This interpretation was confirmed by the observation that ultradian patterns arose earlier at low temperatures. Interestingly, a positive relationship between ultradian period length and workload was observed in tundra voles. Spectral analysis revealed that the power of ultradian rhythmicity increased at high workload, whereas the circadian component of running wheel activity decreased. This study shows that the balance between circadian and ultradian rhythmicity is determined by energy balance, confirming flexible circadian and ultradian rhythms in females and males of 2 different vole species: the common vole (Microtus arvalis) and the tundra vole (Microtus oeconomus).</p

The neurobiology of circadian rhythms

Purpose of review There is growing awareness of the importance of circadian rhythmicity in various research fields. Exciting developments are ongoing in the field of circadian neurobiology linked to sleep, food intake, and memory. With the current knowledge of critical ‘clock genes’ (genes found to be involved in the generation of circadian rhythms) and novel techniques for imaging cyclic events in brain and peripheral tissue, this field of research is rapidly expanding. We reviewed only some of the highlights of the past year, and placed these findings into a mutual circadian perspective. Recent findings Recent findings on the organization of the circadian clock systems are addressed, ranging from the retina to the suprachiasmatic nucleus and peripheral organs. Novel developments in sleep, food intake, and memory research linked to circadian aspects are discussed. Summary The neurobiology of circadian rhythms is pivotal to the orchestration of the temporal organization of an individual’s physiology and behavior. Endogenous circadian timing systems underlie coupling and uncoupling mechanisms of many neuronal and physiological processes, the latter possibly inducing health risks to the organism. The integration of sleep, food intake and memory in a circadian setting has clear potential as a systems neurobiology line of research.

Food and temperature change photoperiodic responses in two vole species

Seasonal timing of reproduction in voles is driven by photoperiod. We hypothesized that a negative energy balance can modify spring-programmed photoperiodic responses in the hypothalamus, controlling reproductive organ development. We manipulated energy balance by the 'work-for-food' protocol, in which voles were exposed to increasing levels of food scarcity at different ambient temperatures under long photoperiod. We found that in common voles (Microtus arvalis) and tundra voles (Microtus oeconomus), photoperiod-induced pars tuberalis thyroid-stimulating hormone β-subunit (Tshβ) expression is reduced to potentially inhibit gonadal development when food is scarce. Reduction in gonadal size is more pronounced in tundra voles, in which anterior hypothalamic Kiss1 is additionally downregulated, especially in males. Low temperature additionally leads to decreased hypothalamic Rfrp expression, which potentially may facilitate further suppression of gonadal growth. Shutting off the photoperiodic axis when food is scarce in spring may be an adaptive response to save energy, leading to delayed reproductive organ development until food resources are sufficient for reproduction, lactation and offspring survival. Defining the mechanisms through which metabolic cues modify photoperiodic responses will be important for a better understanding of how environmental cues impact reproduction