We examined the relationship between body temperature, tail vasomotor response, and work intensity at different ambient temperatures in rats, using a treadmill and continuously measuring oxygen uptake during exercise. At an ambient temperature (Ta) of 24°C, rectal temperature (Tre) at the beginning of tail vasodilation during exercise increased in proportion to work intensity. After tail vasodilation Tre remained steady, and at the end of 30 min exercise Tre level was proportional to work intensity. At Ta of 14°C, Tre at the end of exercise was slightly higher than at 24°C, and was higher at higher work intensities. At Ta of 4°C, Tre rose slower during exercise than at higher Tas and even dropped at relatively low work intensities. Tail vasodilation did not occur in most cases. At Ta of 34°C, TCe rose continuously during exercise. These data indicate that body temperature of rats during exercise rises in proportion to work intensity, but the extent of body temperature rises differs according to Ta. Key words ; rectal temperature, tail vasomotor response, work intensity, ambient temperature, rat.Deep body temperature in man rises during exercise in proportion to work intensity, irrespective of ambient temperature (Ta) of 5 to 25°C (NIELSEN,1938). The physiological mechanism of this exercise-induced hyperthermia is not clear. Although man has been given detailed attention in many studies, methodological limitations have necessitated animal studies as well.The rat, extensively used as an experimental animal in acute and chronic studies, has made a great contribution to elucidate central nervous mechanism for thermoregulation. Since the rat, however, does not sweat or pant (ADOLF, 1947), and moreover cannot spread saliva effectively during exercise, how is body temperature of the rats during exercise influenced by work intensity and Ta? Although some reports have investigated the relationship between work intensity

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 degrees 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.

SUMMARY1. In urethane or ketamine-anaesthetized rats, salivary secretion was observed when local brain sites or trunk skin were stimulated thermally or electrically.2. Salivary secretion was facilitated by bilateral local brain warming. Sensitive sites were restricted to the preoptic area and anterior hypothalamus, but in a region distinct from a previously reported sensitive site for producing saliva-spreading behaviour.3. Unilateral warming of the preoptic area produced greater salivary secretion from the ipsilateral submandibular/sublingual salivary glands than from the contralateral glands. Electrical stimulation of the same sites elicited salivation only from the ipsilateral glands.4. Trunk skin, not including the scrotum, was unilaterally cooled when spontaneous salivary secretion was observed in a hot environment. Salivary secretion from both sides was equally suppressed in response to the unilateral skin cooling.5. We conclude that efferent signals from the anterior part of the hypothalamus project dominantly to the ipsilateral salivary gland for thermally induced salivary secretion. Thermal signals from the skin of either side of the trunk, on the other hand, appear to be integrated and to affect salivary secretion bilaterally.

SUMMARY1. At neutral (24°C) and at hot (40°C) ambient temperatures (TR) salivary secretion from the submandibular gland of freely moving rats was recorded, together with simultaneous observation of saliva-spreading behaviour (grooming).2. At a Ta of 24°C, basal salivary flow was less than 2 /tl/min. When rats were first placed in the experimental chamber, brief grooming bouts often occurred. Transient secretion at more than 10 ,l/min was associated with this grooming, and the rate of salivary flow was positively correlated with the duration of grooming activity.3. At a Ta of 40°C, grooming appeared frequently and salivary secretion at more than 20 u1/min continued even between grooming bouts. Threshold rectal temperatures (Tre) for thermally induced grooming (38-2 + 0-2°C) and for salivary secretion (38-2 + 01°C) were similar, and for eleven of sixteen rats the two thresholds coincided.4. At the threshold Tle both the rate of salivary secretion and the duration of grooming increased in a stepwise fashion. Above the threshold, there was no correlation between the duration of grooming and the rate of salivary flow.5. Thermally induced salivary secretion and grooming behaviour appear to be controlled by independent mechanisms.

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