THERMOGENIC, RESPIRATORY, AND ULTRASONIC RESPONSES OF WEEK-OLD RATS ACROSS THE TRANSITION FROM MODERATE TO EXTREME COLD-EXPOSURE

Previously, it was reported that week-old rats exposed to air temperat ures that elicited submaximal levels of heat production (designated mo derate cold exposure) remained asleep and did not vocalize (Blumberg & Stolba, 1996). In contrast, pups exposed to air temperatures that eli cited maximal levels of heat production (designated extreme cold expos ure) woke rip and emitted ultrasonic vocalizations. We now report on t he physiological and behavioral responses of pups in the transitional region between moderate and extreme air temperatures. Small decreases in air temperature across the transition resulted in pronounced decrea ses in physiological temperature and concomitant increases in ultrasou nd production. In a second experiment, it was shown that during modera te cold exposure respiratory frequency increased as air temperature de creased but, as extreme air temperatures were reached respiratory freq uency was maximized as ultrasound production began. The results from t hese two experiments illustrate how air temperatures that differ by as little as 2 degrees C can differentially modify the physiological and behavioral responses of neonates. (C) 1997 John Wiley & Sons, Inc.