Functional role of the preoptic area and anterior hypothalamus in thermoregulation in freely moving rats

We recently reported that perfusion of tetrodotoxin (TTX) into the preoptic area and anterior hypothalamus (PO/AH), by using a microdialysis technique, induced an increase in body temperature (Tb) under normal and hot ambient temperatures (23 and 35 degreesC) in freely moving rats. However, the procedure had no effect on Tb under a cold ambient temperature (5 degreesC). The present study was designed to determine the mechanism(s) of increases in Tb after perfusion of TTX into the PO/AH, by measuring tail skin temperature (Ttail) as an index of heat loss, and heart rate (HR) and locomotor activity (Act) as indexes of heat production, under three ambient temperatures. Under normal ambient temperature (23 degreesC), perfusion of TTX induced significant hyperthermia with increased HR, Act and Ttail. In a hot environment (35 degreesC), perfusion of TTX induced a greater increase in Tb with increased HR but no change in Ttail and Act. In a cold environment (5 degreesC), perfusion of TTX had no effect on Tb with a slight increase in Act but no change in HR and Ttail. Our results suggest that the PO/AH may be involved in inhibition of heat production and excitation/inhibition of the tail vasomotor tone. (C) 2002 Elsevier Science Ireland Ltd. All rights reserved.