Central patterning of inspiratory activity in the neonatal period

We hypothesized that synchronization of neonatal inspiratory motoneurons is achieved by common inputs from one or more central pattern generators. Such inputs are manifested in neural discharges as medium-frequency (less than 50 Hz) and/or high-frequency (greater than or equal to 50 Hz) oscillations. Furthermore, if both oscillations appeared, one or both might be gated, i.e. present only in the first or second half of inspiration. The spontaneous discharges of phrenic (C5 and C6) roots and hypoglossal nerves were recorded in anesthetized or decerebrated, vagotomized, paralyzed and artificially ventilated neonatal swine. Autopower spectral analyses showed that phrenic discharges had peaks in the medium- and/or the high-frequency band. Phrenic spectra, derived from either half of inspiration, demonstrated that, while both types of oscillation were present throughout inspiration, their amplitudes were larger during the second half of inspiration. However, comparisons of the relative distributions of power in each half of inspiration showed that the increase of high-frequency power was much larger than that of medium-frequency power during the second half of inspiration. In contrast to phrenic spectra, hypoglossal spectra had peaks only at medium-frequencies; consequently, correlated frequencies (indicative of common inputs) in phrenic-hypoglossal coherence spectra were present at those frequencies. The presence of highly correlated frequencies provided strong evidence of a medium-frequency pattern generator which may remain operative beyond the neonatal period.