The heat is on: A device that reduces cold stress-induced tachycardia in laboratory mice

Mouse vivaria are typically maintained at an ambient temperature (T_a) of 20-26 °C which is comfortable for human researchers. However, as this T_a is well below the mouse thermoneutral zone (TNZ) of 30-32 °C, typical vivarium temperatures result in cold stress for mice. Recently, a cage has been developed that provides variable cage floor heating, allowing mice to behaviorally regulate body temperature through thermotaxis. A hand warmer provides supplemental heat, elevating cage floor surface temperature for 13 + hours up to 30 °C. This provides a heated surface for the entirety of the light phase. Here, we test the ability of these local heat sources to remove physiological signs of cold stress in mice housed at room temperature by analyzing heart rate (HR), activity, and body temperature in three experimental conditions: 23 °C, 23 °C + heated surface, or 30 °C. The location of C57Bl/6 J mice within the cage was recorded using an infrared camera. In the presence of supplemental heat at a T_a of 23 °C, mice resided atop of the area of the heated surface 85 ± 3% of the 12-h light phase, as compared to 7 ± 2% in the absence of supplemental heat. Further, addition of supplemental heat lowered light phase HR and activity to that seen at a T_a of 30 °C. These results indicate that provision of a local heat source is successful in reducing cold-induced tachycardia in mice housed at typical vivarium temperatures without increasing the ambient temperature of the entire laboratory and subjecting researchers to heat stress.