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Juvenile circadian core temperature rhythm in Wistar and lean (Fa/-) Zucker rat pups
K Imai-Matsumura1, R Kaul, I Schmidt
1Faculty of Education, Shiga University, Otsu, Japan.
Insights
Daily rhythms of cold defense in rat pups differ from adults. Both Wistar and Zucker rat pups exhibit distinct circadian patterns in core body temperature and metabolic rate, influencing physiological responses.
Area of Science:
- Physiology
- Chronobiology
- Animal Models
Background:
- Neonatal rats exhibit distinct physiological rhythms compared to adults.
- Understanding circadian rhythms in early development is crucial for interpreting physiological data.
Purpose of the Study:
- To compare the daily rhythms of cold defense in Wistar and Zucker rat pups.
- To investigate the influence of artificial rearing on thermoregulation in neonatal rats.
Main Methods:
- Artificial rearing of Wistar and Zucker rat pups (10–13 days old) under continuous light.
- Recording of core body temperature (Tc) and metabolic rate (MR) during moderate cold exposure.
- Comparison of circadian patterns between the two rat strains.
Main Results:
- Both Wistar and Zucker rat pups displayed daily rhythms in Tc and MR, differing from adult patterns.
- A significant daily minimum Tc was observed in both strains, occurring before the typical lights-on time.
- Wistar pups had a higher average daily minimum Tc compared to Zucker pups, with similar daily maximum Tc values.
Conclusions:
- Circadian differences in cold defense are present in 10-day-old Wistar rat pups, not exclusive to Zucker rat pups.
- These findings highlight strain-specific variations in neonatal thermoregulation and circadian rhythms.
- The observed rhythms in Tc and MR suggest underlying circadian regulation of cold defense mechanisms in developing rats.
Abstract:
We compared the daily rhythms of cold defense in Wistar and lean (Fa/-) Zucker rat pups isolated from maternal care. Pups, born in a colony with lights-on from 7:00 to 19:00, were artificially reared from 10 to 13 days of age in continuous light at moderate cold loads, while we recorded core temperature (Tc) and metabolic rate (MR). Pups of both strains showed daily rhythms distinctly different from those of adult rats: on the first day of artificial rearing Tc steeply decreased shortly before the time of lights-on in the breeding colony and reached a daily minimum of 31.8 +/- 0.4 degree C at 7:17 +/- 17 min in Zucker pups (+/- SE, N = 24) and of 33.4 +/- 0.2 degree C at 8:59 +/- 9 min (N = 25) in Wistar pups. On each day, the average daily minimum Tc was significantly higher in Wistar than in Zucker rats, whereas the daily maximum Tc were close to 36 degrees C in both strains. The daily rhythms of MR resembled those of Tc. We conclude that circadian differences of cold defense, which must be expected to influence a variety of behavioral and physiological parameters, are not a peculiarity of Zucker rat pups but also occur, though with a smaller amplitude, in 10-day-old Wistar pups.