Hypoglossal long term facilitation shifts the power spectral density to higher frequencies

The frequency content of electrical activity in respiratory nerves shows distinct bands of increased content (power). Above approximately 75 Hz these bands show coherence across different respiratory nerves suggesting a pre-synaptic mechanism. Since most evidence indicates that the mechanism(s) of intermittent hypoxia-induced long-term facilitation (LTF) are post-synaptic, we hypothesized that the hypoglossal (XII) spectral content above 75 Hz would remain stable during LTF in urethane anesthetized, vagotomized and ventilated adult 129SVE mice. When arterial O2 saturation (SaO2) was held at >97% the XII power spectrum and burst amplitude were unchanged for 90 min. Three 1-min hypoxic episodes (SaO2=50±10), however, caused a persistent (>60 min) and very robust (>400%) amplitude increase. 60 min following intermittent hypoxia, spectral analyses revealed decreased power over 20-50 Hz (P<0.05) and a substantial increase at 150-200 Hz (P<0.05). Thus, the hypothesis was rejected, and we conclude that LTF in th...