Central mechanisms for thermoregulation in a hot environment.

Homeothermic animals regulate body temperature by autonomic and behavioral thermoeffector responses. The regulation is conducted mainly in the brain. Especially, the preoptic area (PO) in the hypothalamus plays a key role. The PO has abundant warm-sensitive neurons, sending excitatory signals to the brain regions involved in heat loss mechanisms, and inhibitory signals to those involved in heat production mechanisms. The sympathetic fibers determine tail blood flow in rats, which is an effective heat loss process. Some areas in the midbrain and medulla are involved in the control of tail blood flow. Recent study also showed that the hypothalamus is involved in heat escape behavior in rats. However, our knowledge about behavioral regulation is limited. The central mechanism for thermal comfort and discomfort, which induce various behavioral responses, should be clarified. In the heat, dehydration affects both autonomic and behavioral thermoregulation by non-thermoregulatory factors such as high Na+ concentration. The PO seems to be closely involved in these responses. The knowledge about the central mechanisms involved in thermoregulation is important to improve industrial health, e.g. preventing accidents associated with the heat or organizing more comfortable working environment.