PHRENIC RESPONSE TO HYPERCAPNIA IN THE UNANESTHETIZED, DECEREBRATE, NEWBORN RAT

We developed a decerebrate, vagotomized, newborn rat preparation to in vestigate brainstem respiratory control mechanisms without the influen ce of anesthesia, supra-pontine structures, or vagally mediated feedba ck mechanisms. We measured the changes in phrenic nerve electrical act ivity in response to breathing 3% and 5% CO2 in unanesthetized, vagoto mized, decerebrate newborn rats from 0 to 10 days of age and compared them with the changes in anesthetized, vagotomized, newborn rats and a dult, vagotomized, decerebrate or anesthetized animals. Phrenic nerve activity was irregular in the young newborn rats and became more regul ar between 7 and 10 days of age. TI and TI/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 activit y, and inspiratory slope with no change in timing variables. These res ponses are similar to those that have been reported previously in vaga lly intact animals, suggesting that vagal feedback contributes little to the response to hypercapnia in the newborn rat. In summary, decereb rate newborn rats consistently respond to hypercapnia by increasing in spiratory drive similar to conscious animals.