Autonomic thermoregulation after separation of the preoptic area from the hypothalamus in rats

To clarify the role of the hypothalamic preoptic area in autonomic thermoregulation, the preoptic area (POA) of rats was disconnected from the rest of the brain-stem by bilateral microknife cuts which spared or included the medial forebrain bundle. The animals' metabolic responses to exogenous norepinephrine (0.5 mg/kg, im) were then measured at ambient temperatures of 25 degrees and 15 degrees C. Oxygen uptake and colonic and tail skin temperatures were also measured at ambient temperatures of 34 degrees, 25 degrees, and 15 degrees C. Finally, the febrile response to a challenge with live Salmonella enteritidis was studied. Except for a slightly higher oxygen uptake at all ambient temperatures in the rats in which the medial forebrain bundle was cut, no differences were found in any of the variables studied between the POA-disconnected and the sham-operated animals. We conclude, therefore, that the POA is not essential for the integration of autonomic thermoregulatory responses in the rat.