Coherent inspiratory oscillation of cranial nerve discharges in perfused neonatal cat brainstem in vitro.

1. To understand the neural organization of respiratory movement control and its developmental transformation, we studied the temporal characteristics of inspiratory activities, especially nerve-to-nerve short-term synchronization, in an in vitro preparation of the isolated, perfused brainstem of kittens aged 0-14 days (postnatal day (P) 0-14). 2. In the inspiratory discharges of facial, vagus, glossopharyngeal and hypoglossal nerves, a stable oscillation with a period of 30-40 ms (i.e. approximately 30 Hz) was observed in all preparations examined. In addition, we demonstrated that this oscillation presents a strong short-term synchrony between distinct inspiratory nerves. This nerve-to-nerve synchronization was already apparent at approximately 12 h after birth. The degree of synchronization as evaluated by coherence spectral analysis was larger than 0.85 in all cases at any age examined. 3. This nerve-to-nerve coherence was not affected by changes in temperature (28-36 degrees C), whereas respiratory rate, oscillation frequency and oscillation amplitude as estimated by power spectral analysis were highly temperature sensitive. 4. The nerve-to-nerve synchronization, as well as the approximately 30 Hz oscillation, remained unchanged after a pontomedullary transection, indicating that the medullary network, completely isolated from other structures and afferents, is sufficient to produce both fast oscillation and nerve-to-nerve synchronization. 5. Based on these observations in vitro, we conclude that nerve-to-nerve coherent inspiratory oscillation generated in the brainstem is already functional early in life.