Autonomic and behavioral thermoregulation in guinea pigs during postnatal maturation.

Serial experiments were carried out on seven chronically instrumented Hartley-strain guinea pigs at 1, 3, and 5 wk of age to define their autonomic and behavioral thermoregulatory profiles and to test the hypothesis that they have the mechanisms in place shortly after birth that allow them to optimize their energy expenditure for thermoregulation by selecting a thermal environment that requires the lowest metabolic oxygen requirements. Each animal was studied in both a thermocline to determine selected ambient temperature and in a metabolic chamber to determine the thermoregulatory response to forced changes in ambient temperature. In the thermocline, the guinea pigs at all postnatal ages selected an ambient temperature that placed core temperature, oxygen consumption, thermal conductance, heart rate, and respiratory rate at levels comparable to those observed at ambient temperatures in which minimal oxygen consumption occurred in the metabolic chamber. Thus our experiments provide evidence that guinea pigs have the neurophysiological mechanisms in place shortly after birth that allow them to optimize their energy expenditure for thermoregulation by selecting a thermal environment that corresponds to the lowest metabolic oxygen requirements.