THERMOGENESIS, MYOCLONIC TWITCHING, AND ULTRASONIC VOCALIZATION IN NEONATAL RATS DURING MODERATE AND EXTREME COLD-EXPOSURE

Physiological and behavioral responses of 2- and 7-8-day-old rats were monitored during moderate and extreme cold exposure. During moderate cold exposure (30 degrees C less than or equal to air temperature less than or equal to 32.5 degrees C), pups at both ages increased heat pr oduction, maintained an elevated interscapular temperature, and mainta ined baseline levels of myoclonic twitching, a behavior commonly assoc iated with active sleep. During extreme cold exposure (21 degrees C le ss than or equal to air temperature less than or equal to 25 degrees C ), pups at both ages continued producing metabolic heat, but now exhib ited pronounced decreases in interscapular temperature and decreased r ates of myoclonic twitching. Furthermore, the 7-8-day-old pups exhibit ed significant increases in ultrasound production, and males vocalized more than females. These results suggest the presence of a narrow sub thermoneutral zone in neonates in which nonshivering thermogenesis is regulated and sleep-related behaviors are protected.