Ultrasonic vocalization, laryngeal braking, and thermogenesis in rat pups: a reappraisal

In these experiments we tested the hypothesis that the respiratory events underlying rat pup ultrasonic vocalization (USV) facilitate brown adipose tissue (BAT) thermogenesis, as proposed by Blumberg and Alberts (1990). Laryngeal denervation or tracheostomy were used to reduce or eliminate laryngeal braking and prevent USV in 9- to 10-day-old pups during recovery from deep hypothermia and during cooling induced by isolation for 1 hr at room temperature. Both forms of devocalization slowed rewarming of hypothermic pups, but neither had any effects on cooling rate or BAT thermogenesis in normothermic pups that were allowed to cool from 35 degrees C to 29 degrees C. Physiological effects of laryngeal braking on thermogenesis appear to be limited to conditions, such as severe hypothermia, in which ventilatory and oxygen transport functions are compromised. The results have implications for understanding the regulation and evolution of USV.