Hypothermia induction and recovery in free-ranging rats

1.To avoid anesthesia confounders, free-ranging rats were exposed (4 h) to cool water (CW; 10 °C; 5 cm), warm water (WW; 35 °C; 5 cm) or temperate air (TA; 25 °C) to induce hypothermia, or control for water or novel environment stress, respectively.2.While WW and TA core temperature (Tc) and the brown adipose tissue (TBAT)/subdermal skin (TSDS) temperature relationship remained similar, CW hypothermia induction was variable (34.5-26.1 °C; 9-240 min) and associated with tachycardia (517.8±4.7 bpm) greater than WW (386.5±5.5 bpm) or TA (372.2±7.7 bpm) with CW TBAT (36.5±0.03 °C) elevated above CW TSDS (35.9±0.05 °C).3.Without anesthesia to blunt thermoregulatory countermeasures to hypothermia, variable resistance to Tc depression, tachycardia rather than bradycardia and BAT thermogenic responses were demonstrated.