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Pronounced juvenile circadian core temperature rhythms exist in several strains of rats but not in rabbits
B Nuesslein-Hildesheim1, K Imai-Matsumura, H Döring
1Max-Planck-Institut für Physiologische und Klinische Forschung, W. G. Kerckhoff-Institut, Bad Nauheim, Germany.
Insights
Juvenile rats exhibit torpor-like circadian rhythms in core body temperature and metabolic rate, a trait shared across multiple rat strains. Rabbit pups, however, do not display this pronounced daily temperature variation.
Area of Science:
- Physiology
- Chronobiology
- Comparative Biology
Background:
- Suckling-age Zucker rat pups display torpor-like circadian variations in core body temperature.
- This juvenile circadian rhythm's prevalence in other rat strains and species is not well understood.
Purpose of the Study:
- To investigate the expression of juvenile circadian rhythms in core temperature and metabolic rate across different rat strains.
- To determine if a similar circadian rhythm is present in rabbit pups at a comparable developmental stage.
Main Methods:
- Artificially reared rat pups (Wistar, Brown Norway, Long Evans) and rabbit pups (Chinchilla bastard) were studied.
- Core body temperature and metabolic rate were recorded for 30 hours under moderate cold conditions (28°C ambient temperature).
- Data were collected at ages relevant to established rhythms in Zucker rats and early detection in rats.
Main Results:
- All studied rat strains exhibited clear circadian rhythms, with significant decreases in core temperature and metabolic rate during the subjective morning.
- The amplitude of core temperature rhythms varied among rat strains: Wistar < Brown Norway < Zucker < Long Evans.
- Rabbit pups maintained stable, high levels of core temperature and metabolic rate throughout the study period, lacking a discernible circadian rhythm.
Conclusions:
- The torpor-like decrease in core body temperature during the morning is not exclusive to Zucker rats but is also observed in other pigmented rat strains.
- Rabbit pups at a similar developmental stage do not exhibit a circadian core temperature rhythm, indicating species-specific differences in thermoregulation.
- This study highlights the diverse expression of juvenile circadian thermoregulation across mammalian species.
Abstract:
Torpor-like circadian variations of core temperature are well documented for suckling-age Zucker rat pups. To determine (1) whether this juvenile circadian rhythm is as strongly expressed in other rat strains, and (2) whether a similar rhythm is expressed in rabbit pups, we recorded core temperature and metabolic rate of artificially reared pups. Wistar, Brown Norway, and Long Evans pups were studied for 30 h under moderate cold loads (ambient temperature = 28 degrees C) when 9-11 days old, i.e. at the age and ambient temperature for which the rhythm has been most thoroughly characterized in Zucker rats. Chinchilla bastard rabbit pups were studied under similar conditions when they were 3-8 days old, the youngest age at which the rhythm can be easily detected in rats. Rat pups of each strain showed clear circadian rhythms with sharp decreases of core temperature and metabolic rate in subjective morning. Core temperature amplitudes were in the order Wistar < Brown Norway < Zucker < Long Evans strain. In contrast, the rabbit pups maintained stable high levels of core temperature and metabolic rate throughout the day. A torpor-like decrease of core temperature in the morning is thus not a peculiarity of the Zucker rat strain but also occurs in other pigmented rat strains, whereas rabbit pups at a similar developmental stage do not show a circadian core temperature rhythm.