Autonomic thermoregulation after intermittent cooling of the spinal cord and cold exposure in the rat.

1. O2 consumption, rectal and several skin temperatures were studied, at various ambient temperatures, in unanaesthetized rats that had been thermally stressed for an average of 290 h either by prolonged and intermittent cooling of the spinal cord or by prolonged and intermittent exposure to an ambient temperature which induced the same increase in O2 consumption as did the thermal stimulation of the spinal cord. 2. At all the test ambient temperatures, both groups of thermally stressed animals maintained a metabolic level higher than that of the controls. In the animals previously exposed to cold the extent by which the metabolic rate was greater than that of the control animals was independent of ambient temperature; in those previously subjected to cooling of the spinal cord, however, it increased as the ambient temperature was lowered. Rectal and average skin temperatures were essentially unaffected by the treatments. 3. It is concluded that prolonged and intermittent cooling of the spinal cord increases the gain of the temperature control system, whereas prolonged and intermittent cold exposure has no effect on it, and that these forms of thermal stimulation are therefore not equivalent.