Comparison of the CO₂ ventilatory response through development in three rodent species: Effect of fossoriality

Burrowing rodents have a blunted ventilatory response to CO₂ in comparison to non-burrowing rodents. Non-burrowing rats display a period during development where ventilatory responses to hypercarbia become transiently blunted. This study examined the ventilatory responses to CO₂ of rats, hamsters and ground squirrels through neonatal development to determine whether the blunted adult response of burrowing species is a retention of the blunting period seen in rats or present from birth. All three species increased ventilation in response to hypercarbia on the day of birth (70-170% in response to 5% CO₂; 100-250% in response to 7% CO₂). Rats in our study exhibited the triphasic ventilatory response (when expressed as %Δ) to CO₂ previously described. In golden-Syrian hamsters, the ventilatory response slowly and progressively waned to a blunted adult response while in the 13-lined ground squirrels, the early ventilatory response to CO₂ decreased within days and remained attenuated through development. Our study shows three distinct developmental patterns in the hypercarbic ventilatory response.