Genetic selection of rats with high and low body temperatures

Body (core) temperature (T,) directly affects all biological processes, inc luding sensitivity to toxic chemicals, development, aging, and drug metabol ism. To understand how T-c affects these processes it is necessary to alter T-c independently of other physiological processes. The purpose of this st udy was to determine whether selective breeding techniques can be used to d evelop lines of rats with hyperthermic and hypothermic T-c's. T-c and motor activity of 24 female and 23 male rats (parental line) of the NIH heteroge nous stock were monitored by telemetry for 96 h at a T-a of 22 degreesC. Th e mean 24 h T-c of the male and female rats was 37.3 degreesC with a range of 37-38.2 degreesC. T-c was not correlated with motor activity or body wei ght. Pairs with the lowest and highest Tc's were selected for breeding. The Fl generation consisted of 10 offspring from the hyperthermic group and 20 from the hypothermic group. They were implanted with transmitters at 60 d of age. T-c of rats derived from the hyperthermic parental line had a signi ficantly warmer T-c than the rats derived from the hypothermic parental lin e. Motor activity was significantly higher in the hyperthermic Fl males and hypothermic Fl females. Breeding of hyperthermic and hypothermic rats has shown that adult offspring of the fourth generation maintain significantly different core temperatures but have similar patterns of motor activity. Th e results demonstrate that T-c is heritable and that it should be feasible to develop lines of rats that regulate T-c above or below normal. Published by Elsevier Science Ltd.