Rat behavioral thermoregulation integrates with nonshivering thermogenesis during postnatal development.

Rat pups are capable of behavioral thermoregulation, both in the nest and on a thermocline, as early as the 1st week of postnatal life, and these pups can also produce heat metabolically without shivering. The rat pup's primary source of nonshivering thermogenesis is the sympathetically mediated metabolism of brown adipose tissue (BAT). BAT is well formed in newborns and functions shortly after birth. While infant behavioral thermoregulation and BAT thermogenesis have been extensively studied, little is known about the extent to which thermoregulatory behavior can be influenced by BAT thermogenesis. In the present study, 2-, 7-, and 14-day-old pups were observed on a thermal gradient following pharmacological stimulation or inhibition of BAT thermogenesis, and their thermal preferences were quantified. The authors found that 7- and 14-day-old pups treated with norepinephrine (NE), which increases BAT thermogenesis, preferred cooler portions of the gradient than saline-treated controls, whereas 2-day-olds failed to show a similar NE-induced behavioral adjustment. These findings indicate that the ability to adjust thermoregulatory behavior to compensate for enhanced metabolic thermogenesis develops during the 1st week of postnatal life.