Thermoregulatory responses to preoptic-anterior hypothalamic heating and cooling in the bat,Eptesicus fuscus

Summary The central nervous control of temperature regulation in the bat, Eptesicus fuscus, was evaluated by heating the preoptic-anterior hypothalamus (PO/AH) of active, unanaesthetized bats. Because bats are metabolically very variable, change in body temperature was used as the criterion of change in heat balance in response to change in brain temperature and change in wing temperature as an indicator of vasomotor changes.Heating the preoptic-anterior hypothalamic area (PO/AH) of the bat Eptesicus fuscus caused an average increase in wing temperature due to vasodilation of 1.0° C and an average increase in body temperature of 0.4° C. Conversely, cooling the PO/AH led to an average decline in wing temperature due to vasoconstriction of 0.9° C and an average decline in body temperature of 0.4° C.Bats were heat-stressed to augment the responsiveness of the PO/AH. Heat-stress alone causes a rise in body temperature and wing temperature. Release from heat stress causes a fall in body temperature and a fall in wing temperature. When the PO/AH is heated following a period of high heat-stress, the body temperature continues to fall but wing temperature reverses its direction of change and rises. When bats are given a low heat-stress and simultaneous heating of the PO/AH, wing temperature rises in response to PO/AH temperature and the body temperature stabilizes. When the PO/AH is cooled in bats under high heat-stress, body temperature stabilizes and wing temperature falls. When bats are cold-stressed, body temperature and wing temperature fall regardless of heating of the PO/AH.These responses are related to the life habits of the bat.It is concluded that the PO/AH of the bat Eptesicus fuscus may be less thermally sensitive than the PO/AH in other vertebrates studied, and that other central nervous structures have acquired an increased thermoregulatory function.We thank Mrs. Ruth Chalmers for her excellent histological preparstions.This work was supported, in part, by National science Foundation grant GB 6303 and GB 13797.