Fig. 2. Mean day (lower) and night time (upper) body temperature changes, recorded through an implantable sensor and transmitter system (Mini Mitter, Co. Inc., Bend, OR, USA), in a single rat exposed to hypobaric hypoxia initiated at Day 0. For each daily cycle, the higher temperature is recorded during the dark, behavioral active phase (night). After an initial drop and loss of diurnal rhythm, there is a recovery within 1 week and then a secondary minor down trend of about 0.015°C day^–1 (LaManna et al., unpublished observations).