Medium-frequency oscillations dominate the inspiratory nerve discharge of anesthetized newborn rats

In this study we examined the synchronization of the discharge of phrenic a nd recurrent laryngeal motoneurons in anesthetized rat pups 14 to 36 days o f age and kittens, 14-15 days old. We found that the inspiratory nerve acti vity consisted of synchronized bursts separated by 20-35 ms, corresponding to medium-frequency oscillations (MFO). Accordingly, the autospectra of the neurograms had two peaks. one at the respiratory rare and the other betwee n 22.8-43.0 Hz. No significant coherence was found between MFOs in the disc harges of different nerves. High-frequency oscillations (HFO) characteristi c for the adult inspiratory nerve activity were not present in the newborn rats. These findings demonstrate that phrenic nerve discharge of rat pups, like that of kittens and piglets, is in the MFO range, and suggest that MFO activity is an index of an early developmental stage of the respiratory sy stem, (C) 1999 Elsevier Science B.V. All rights reserved.