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Development of circadian cycle of core temperature in juvenile rats
1W.G. Kerckhoff-Institut, Max-Planck-Institut fur Physiologische, Bad Nauheim, Federal Republic of Germany.
Insights
Juvenile rats can maintain circadian rhythms of core body temperature (Tc) even without daily light cues. This demonstrates a functional internal biological clock in young rats, even when isolated.
Area of Science:
- Chronobiology
- Animal Physiology
- Developmental Biology
Background:
- Circadian rhythms are crucial for physiological regulation.
- Understanding the development of these rhythms in early life is essential.
- Diurnal cues are typically important for entraining circadian clocks.
Purpose of the Study:
- To investigate if juvenile rats can sustain circadian rhythms of core body temperature (Tc) without external diurnal cues.
- To determine the age at which endogenous circadian rhythms become functional in rats.
- To differentiate between age-dependent changes and effects of isolation on circadian rhythms.
Main Methods:
- Continuous core body temperature (Tc) recording in isolated juvenile rats for 12 days.
- Artificial rearing in constant dim light to exclude environmental cues.
- Comparison between early-isolated (from 4 days) and late-isolated (from 10 days) pups.
- Control for maternal entrainment by using mothers with opposing light-dark cycles.
Main Results:
- Isolated juvenile rats exhibited Tc cycles synchronized with their colony's previous light cycle.
- Rhythm amplitude was highest between 10 and 13 days of age.
- Early-isolated pups maintained Tc cycles for up to 12 days, while late-isolated pups showed fading after 6 days.
- Rhythms gradually diminished in the third postnatal week.
Conclusions:
- Juvenile rats possess a functional endogenous clock capable of sustaining circadian rhythms of core body temperature in the absence of diurnal cues.
- The ability to sustain these rhythms is age-dependent and robust in early development.
- This study confirms the presence of a self-sustained circadian clock in juvenile rats.
Abstract:
To find out whether or not juvenile rats can sustain circadian rhythms of core temperature (Tc) in the absence of diurnal cues, we continuously recorded Tc for 12 days in isolated pups artificially reared in continuous dim light. Possible effects of uncontrolled environmental 24-h cycles were excluded by simultaneously studying pups born on the same day to two mothers entrained to 12:12 h light-dark cycles 180 degrees out of phase. Age-dependent changes were discriminated from the effects of sustained isolation by comparing Tc records between pups isolated from 10 or from 4 days of age (late- or early-isolated pups). Both groups of pups showed Tc cycles in phase with the light cycle in the colony of origin and with highest amplitudes from 10 to 13 days of age. Tc cycles with a period length close to 24 h could be seen through the 12th day of artificial rearing for early-isolated pups but only until the 6th day for late-isolated pups. In the third postnatal week the rhythm faded gradually. Self-sustained circadian Tc rhythms observed in isolated 1- to 2-wk-old pups demonstrate a functional endogenous clock in the juvenile rat.