Non – shivering thermogenesis in neonates: the hidden mechanism of thermal adaptation

Thermoregulation is an important physiological challenge for neonates because they have a high surface-area-to-body-mass ratio, limited energy reserves, and an immature ability to regulate body temperature. Unlike adults, newborns have a limited capacity for effective shivering and therefore depend on non-shivering thermogenesis (NST) to maintain body temperature. Brown adipose tissue (BAT) is the major site of NST and produces heat primarily through mitochondrial uncoupling protein 1 (UCP1). In addition, skeletal muscle can contribute to NST through mechanisms involving sarcolipin (SLN)-mediated regulation of the sarcoplasmic reticulum Ca²⁺ pump SERCA. Other proposed mechanisms include creatine cycling, lipid cycling, and mitochondrial proton leak. Cold exposure activates the sympathetic nervous system, particularly norepinephrine-mediated pathways, which stimulate thermogenic tissues and increase metabolic heat production. Understanding these mechanisms is important for explaining neonatal adaptation to the extrauterine environment and for preventing cold stress and hypothermia in newborn animals and humans.