Lateral distribution of hypothalamic signals controlling thermoregulatory vasomotor activity and shivering in rats

The present study explored the laterality of central nervous thermoregulatory control in anesthetized rats by measuring paw skin vasomotor activity and cold-induced shivering in hind leg muscles during unilateral preoptic area and anterior hypothalamus (POAH) warming and electrical stimulation or during unilateral thermal stimulation of abdominal skin. Unilateral POAH warming produced vasodilation on both sides of the body, but vasodilation on the ipsilateral side always either occurred at a lower threshold hypothalamic temperature or was stronger than on the contralateral side. In a cold environment (5°C), shivering was suppressed simultaneously in both hind legs when one side of the POAH was warmed, and shivering reappeared simultaneously on both sides when POAH warming stopped. These results suggest that different thermoregulatory effectors are regulated in a different way by each side of the POAH. Unilateral thermal stimulation of the abdominal skin, on the other hand, affected vasomotor activity and shivering equally on both sides of the body, as previously reported for its influence on salivary secretion. Skin thermal signals from both sides of the body therefore seem to converge before they act on different thermoregulatory effector systems.