Introduction: Shift workers are frequently exposed to the harsh combination of night work in a low-temperature environment. In this project, we aimed to determine if acute induction of thermoregulatory markers UCP1 and FGF21 by cold exposure depend on the timing of the exposure, and to investigate if the neural processing of thermal information has a potential role. Methods: Six groups of C57BI/J6 mice (N=8) were habituated for 2 months to a 12 h light/ 12 h dark regiment at thermoneutral temperature 27 °C (TN). After this period, groups were acutely exposed to an ambient temperature of 15 °C (COLD) or a continuation of TN temperature. Temperature exposures of groups were applied at three different time-points of the day lasting for 8 hours before tissues were harvested at ZT4, ZT12 or ZT20 (i.e. 4, 12 or 20 hours after the light is on, respectively). Thermoregulatory markers were measured in plasma, brown adipose tissue (BAT), liver and the peripheral somatosensory neurons in dorsal root ganglion (DRG) using RTPCR and immunodetection. Furthermore, behaviour testing was used to evaluate thermal preference. Results: UCP1 expression increased in BAT from COLD mice, as compared to TN mice. A higher induction of UCP1 was observed at ZT12 than the other time points. Plasma levels of FGF21 were induced acutely in COLD mice at ZT4 and ZT12, compared to the time-matched TN controls, but COLD mice at ZT20 did not display increase of FGF21 plasma levels. Cold exposure affected mRNA expression patterns of core circadian clock components in BAT (Bmal1, Clock, Per1/2/3, Cry1/2, Nr1d1/2), but in liver these transcripts were not affected. Behavior testing showed that COLD mice developed cold tolerance behaviors at ZT4 but less at ZT12. Analyses of gene expression in the somatosensory DRG neurons revealed circadian oscillations of core components and gene regulation due to cold exposure. Summary: In a nutshell, data suggest that the timing of cold exposure might impact physiological and behavioural adaptations to cold environments. This was associated with diurnal variations of gene expression in DRG neurons. Supported with an internal grant at STAMI. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.
Haugen et al. (Wed,) studied this question.