Phrenic response to hypercapnia in the unanesthetized, decerbrate, newborn rat.

We developed a decerebrate, vagotomized, newborn rat preparation to investigate brainstem respiratory control mechanisms without the influence of anesthesia, supra-pontine structures, or vagally mediated feedback mechanisms. We measured the changes in phrenic nerve electrical activity in response to breathing 3% and 5% CO2 in unanesthetized, vagotomized, decerebrate newborn rats from 0 to 10 days of age and compared them with the changes in anesthetized, vagotomized, newborn rats and adult, vagotomized, decerebrate or anesthetized, animals. Phrenic nerve activity was irregular in the young newborn rats and became more regular between 7 and 10 days of age. T1 and T1/Ttot increased with age but increasing age had no influence on the response to CO2. The response to CO2 was dominated by increases in phrenic amplitude, minute activity, and inspiratory slope with no change in timing variables. These responses are similar to those that have been reported previously in vagally intact animals, suggesting that vagal feedback contributes little to the response to hypercapnia in the newborn rat. In summary, decerebrate newborn rats consistently respond to hypercapnia by increasing inspiratory drive similar to conscious animals.