Behavioral thermoregulation in the study of drugs affecting body temperature.

A method of measuring thermoregulatory behavior in the rat has been developed, which allows analysis of the mechanism of action of drugs which modify body temperature. The test measures the amount of time a rat will remain exposed to an infrared heat source before making an escape and this evidence has been used to divide drugs into those which act on the central thermostats and those which act on effector systems. A peripherally acting hypothermic drug (N-methyldiphenhydramine) increased the time of exposure to the heat lamp. Tri-iodothyronine increased body temperature and decreased exposure to the heat lamp. Intraventricular oxotremorine caused hypothermia but a decreased exposure to heat suggesting it acts to lower the set-point of the central thermostats. Both effects were blocked by atropine. The possibility that central cholinergic mechanisms in the hypothalamus have a function in determining the setting of the central thermostats is discussed.