Developmental effects of ketamine on inspiratory hypoglossal nerve activity studied in vivo and in vitro

The effects of the anesthetic ketamine on properties of inspiratory bursts (I-bursts) in mouse hypoglossal nerve activity were studied in vivo and in vitro. In urethane anesthetized mice we observed rhythmic I-phase activity in only one of eight pups at P9 days. In contrast in older mice rhythmic I-phase hypoglossal activity was almost always observed. Ketamine caused a reduction in I-burst frequency and an increase in peak integrated hypoglossal nerve activity in all three age groups studied (P10-P13, P15-P20 and adult mice). In these mice I-phase oscillations, due to hypoglossal motoneurons firing clusters of action potentials at a particular frequency, were observed in control and after ketamine. Ketamine did not change the frequency of the dominant spectral peak determined from power spectra examined from 0 to 200 Hz. The effects of ketamine were also studied in vitro in the mouse rhythmic medullary slice preparation. Ketamine reduced hypoglossal I-burst frequency and I-burst peak integrated amplitude. Oscillations were observed in I-phase activity, and as in the in vivo studies ketamine did not shift the dominant spectral peak frequency. These results demonstrate that in vivo and in vitro ketamine results in significant changes in I-burst frequency and peak integrated hypoglossal nerve activity, but changes in the oscillation frequency are minimal.