Artificially induced torpor during pregnancy impairs fetal growth in mice

Fetal development in endothermic mammals relies on a tightly regulated maternal body temperature. In animal models, deviations from normothermia during gestation cause fetal developmental abnormalities. However, the direct and physiological manipulation of the maternal core temperature has been technologically challenging, as traditional methods involve the imposition of external thermal stress. Recent advances in the identification of thermoregulatory neurons in the mouse preoptic area have allowed precise control of maternal body temperature without altering environmental conditions. Here we show that the activation of excitatory neurons in the medial preoptic area (MPO) induces a torpor-like hypothermic state in pregnant mice. When induced during early gestation, this state resulted in pregnancy loss, likely due to implantation failure. Hypothermia in mid- and late-gestation reduced fetal liver and kidney size and caused severe growth retardation. Similar outcomes were observed following pyroglutamylated RFamide peptide (Qrfp)-expressing neuron activation in the MPO, whereas inhibitory neuron activation had minimal effect. Furthermore, activating MPO excitatory neurons projecting to the dorsomedial hypothalamic nucleus reproduced both the torpor-like state and fetal growth retardation. These results underscore the importance of a stable maternal body temperature in fetal development and establish a new model for studying the effects of altered maternal temperature on embryogenesis.