Phystology& Behavior, Vol. 28, pp. 675-679 PergamonPress and Brain Research Publ., 1982. Printed in the U.S A Homeostatic Competition Between Food Intake and Temperature Regulation in Rats K. G. JOHNSON 1 AND M. CABANAC 2 D~partement de Physiologie, Universit~ Laval, Quebec, G1K 7P4, Canada Received 23 September 1981 JOHNSON, K G. AND M CABANAC. Homeostatw competition between food intake and temperature regulanon m rats. PHYSIOL BEHAV. 28(4) 675-679, 1982.--Rats obliged to leave a thermoneurtral box to feed at air temperatures (Ta) of 25°, 5 or - 15°{2 reduced the total time spent feeding and the duration of each meal as Ta fell, but increased their food intake by eating faster. Increasing the palatability of the food offered at - 15°C Ta did not prolong feeding but further increased food intake and the speed of eating. The estimated maximum fall in rectal temperature during feeding at - 15°C was small (0.48°_+0.15°C, S.E.) but skin temperatures of ears and tail tip fell to near 0°C. These rats were able to maintmu near-normal balances of food intake and body temperature by reallocating the times spent feeding and sheltering and by altering the speed of eating; they thus resolved a conflict between hunger and cold discomfort with little evidence of a strata on homeostasis. Conflict Temperature regulation Food intake Homeostasis BEHAVIOR is the final common pathway for numerous motivations [8]. When a conflict occurs between motiva- tions, behavior is presumed to be used by an animal to satisfy its most urgent need. The situation differs somewhat for temperature-induced motivations in endotherms, for these animals can use either behavioral or autonomic means for regulating body temperature. In a natural environment for example, animals will only sometimes be in their thermal preferendum. At other times, they will be obliged to expose themselves to thermal stress because behaviors arising from non-thermal drives, such as hunger, thirst, gregariousness, migration or reproduction have pre-empted the behavioral mechanism. An endothermic animal is then free to forego behavioral thermoregulation, use its behavioral capacity for other purposes, and counter the thermal stress with greater autonomic responses. Despite the common occurrence of competition between thermoregulatory and other drives, few reports describe the behavioral modifications arising from such conflicts. When body temperature constancy was pitted against food and water balance in pigeons [10], the birds tolerated a rise in body temperatures of about 0.7°C while they satisfied their hunger. However, generalizations from operant instrumental behavior cannot necessarily be extended to complex field situations. For example [2], pigs will work for heat during cold exposure in the laboratory, but outdoors they will do so only in the daytime and not at night despite colder ambient conditions; stronger drives than thermoregulation apparently determined night-time behavior. In complex natural en- vironments, behavior presumably results from optimizing the responses not of a single homeostatic system, but of a number of interacting homeostatic systems [6]. In the present experiments, one of the simpler dilemmas that arise naturally, between temperature regulation and hunger, has been studied in rats under conditions that stimu- late field conditions while allowing measurement of variables in a way only feasible in the laboratory. The intensity of the conflict has been graded by interacting three levels of ther- mal stress with three grades of dietary attraction in the form of foods of different palatability. METHOD The experimental units were alleys, 1 m long x 200 mm wide x 230 mm high, made of black-painted wood, with wire-mesh floors allowing free ventilation (Fig. 1). The alleys were placed in a chamber in which the air temperature (Ta) was controlled in different experiments at 25 °, 5° or -15°C. In each alley, food was offered at one end (the 'restaurant') while a box at the other end (the 'home') was always kept near thermoneutrality. Each rat had its own home. When the chamber Ta was below 25°C, the 'home' box was heated by an infra-red lamp controlled so that the temperature inside a sealed bottle in the box was 20-25°C. When the infra-red lamp was on, a non-heating red bulb was also illuminated above the 'restaurant'. During experiments the rats were free to move between the home, the alley and the restaurant. Six mature, female, Wistar rats weighing 251_ 17 g (S.D.) were given access to food only between 1000 and 1200 hrs each day for 3 weeks before the experiment began. The 1On leave from Murdoch Umverslty, Perth, 6150, Australia. 2On leave from Universit6 Claude Bernard, Lyon, France. Copyright © 1982 Brain Research Publications Inc.--0031-9384/82/040675-05503.00/0