Effect of chronic cold exposure on noradrenergic modulation in the preoptic area of thermoregulation in freely moving rats

Abstract

For this study, we compared the thermoregulatory involvement of noradrenaline (NA) in the medial preoptic area (mPOA) of non-cold acclimated rats to that of cold-acclimated rats. We quantified the release of NA in the mPOA during 3 h cold (5 °C) exposure in room-temperature-acclimated rats (RA group, kept at 23 °C for 2 weeks) and cold-acclimated rats (CA group, kept at 5 °C for 2 weeks). We concurrently monitored the core body temperature ( T c), heart rate (HR), and tail skin temperature ( T t). Cold exposure significantly increased T c and HR, and decreased T t in both groups. However, the cold-induced increase of the extracellular NA levels in mPOA was observed only in the RA group: not in the CA group. To elucidate these different results in NA levels further, and to evaluate participation of the mPOA in thermoregulation in the cold, we measured T c, HR, and T t during perfusion of α-adrenoceptor antagonist phenoxybenzamine during cold exposure (5 °C). This pharmacological procedure induced marked hypothermia, with decreases in HR only in the RA group; no changes were observed in T c or any thermoregulatory parameter in the CA group. These results suggest that NA in the mPOA modulates heat production in response to acute cold stress in the RA group. However, this thermoregulatory action of NA in the mPOA was attenuated in the CA group.