Postnatal changes in O2 and CO2 sensitivity in rodents. 
In rodents, the ventilatory responses to hypoxia (low O2) and hypercarbia (high CO2) change significantly over postnatal development.  In hypoxia, most adult rodents increase ventilation and decrease metabolism to some degree.  Hypercarbia, however, leads to an increase in ventilation with little, to no change in metabolism.  Neonates, on the other hand, respond to hypoxia with a profound metabolic depression, and a severely attenuated ventilatory response.  In hypercarbia, they exhibit a strong ventilatory response early in development that blunts, reaches a nadir, and then rises back to the adult-like response, thus, stabilizing postnatally.  In this review we discuss how the O2 and CO2 ventilatory responses develop in rodents, the possible mechanisms that drive these postnatal changes, and how being raised in a burrow, an environment putatively low in O2 and high in CO2, may affect the development of O2 and CO2 sensitivity in rodents.