Beyond day and night: The importance of ultradian rhythms in mouse physiology

Huddling substates in mice facilitate dynamic changes in body temperature and are modulated by Shank3b and Trpm8 mutation

“…Because post-QH active huddling is the lowest observable Tb in our system (i.e., ~36.4°C, Fig. 3M), these data indicate that pre-QH active huddling may be a strategy to facilitate an energy saving state (and consequently heat loss) to reach the low defended Tb set-point of rest; similarly, at the low-point of this energy-saving state, post-QH active huddling may then be used to elevate Tb in preparation for the higher defended Tb set point of the active state 4 . Shank3b mutation is associated with decreased huddling and increased Tb.…”

“…Notably, most endotherms with the ability to huddle maintain a higher and more stable Tb than their isolated counterparts 2 . However, depending on the species, developmental stage, and environmental conditions, huddling can operate in conjunction with thermoeffector pathways to increase or decrease Tb to maintain a "set point" specific to a particular behavioral state 2,4 . For example, in adult penguins 5 huddling results in lower Tb and reduced metabolic heat production, allowing individuals to maximize energy savings.…”

“…For example, mice appear to engage in huddling both when awake and when asleep. While awake and sleep states in isolation are proposed to comprise regulated defenses of upper and lower Tb set points, respectively 4 , it is unclear how awake and asleep huddling states map onto these defended set points. Moreover, it is presently unclear how adult thermal states associated with huddling are affected by ambient temperature, sex, and/or genetic factors.…”