Operant thermoregulation of rats with anterior hypothalamic lesions.

The relative importance of different effector mechanisms of thermoregulation may change depending on their availability. Intact rats make only limited use of a learned response on a cold ambient temperature stimulus, and rely almost entirely on autonomic regulatory functions. After destruction of the anterior hypothalamus, rats exhibit a reduced thermoregulatory capacity; i.e. body temperature drops in the cold and rises in the heat. Under this situation a conditioned operant behavior (lever pressing for increasing or decreasing ambient temperature) becomes an important factor to keep body temperature almost constant. Receptor blockers of some putative transmitters in central thermoregulatory pathways influence thermoregulation. Phentolamine induces hypothermia in intact rats in the cold. Hypothalamic lesions are additive in effect with with the drug. Pimozide has no effect neither in the cold nor in the heat intact and lesioned rats. Biperiden in the heat reinforces hyperthermia in intact and lesioned rats as well; in the cold the drug is ineffective. Performance of lesioned rats in an operant pain titration procedure does not differ from intact rats.