BEHAVIORAL THERMOREGULATION BY HYPOXIC RATS

To address whether a shift in hypothalamic thermal setpoint might be a significant factor in induction of hypoxic hypothermia, behavioral thermoregulation was examined in 7 female Sprague-Dawley rats implanted with radiotelethermometers for deep body temperature (T(b)) measurement in a thermocline during normoxia (PO2 = 125 torr) and hypoxia (PO2 = 60 torr). Normoxic rats (T(Nox)) Selected a mean ambient temperature of 19.7 +/- 1.4 (SE)-degrees-C and maintained T(b) at 37.0 +/- 0.2-degrees-C. Hypoxic rats selected a significantly higher ambient temperature (T(Hox) = 28.6 +/- 2.2-degrees-C) but maintained T(b) significantly lower at 35.5 +/- 0.3-degrees-C. Without a thermal gradient (ambient temperature = 25-degrees-C), T(b) during hypoxia was 35.4 +/- 0.4-degrees-C. The maintenance of a lower body temperature during hypoxia through behavioral thermoregulation despite having warmer temperatures available supports the hypothesis that the thermoregulatory setpoint of hypoxic rats is shifted to promote thermoregulation at a lower T(b), effectively reducing oxygen demand when oxygen supply is limited.