Respiratory-related activity of the pharyngeal nerves in the rat

In anesthetized (n = 26) or decerebrate (n = 15) rats, vagotomized, paralyzed and artificially ventilated, we recorded efferent respiratory-related discharges of nerves supplying the pharyngeal muscles, i.e. the glossopharyngeal nerve (IX; n = 30) and the pharyngeal ramus of the vagus nerve (PH.X; n = 33). In both types of preparation, all IX nerves fired during inspiration (I); most PH.X fired either during I (n = 11), expiration (E, n = 12), or both phases (n = 4); some of them were continuously active, without any respiratory modulation (n = 6). We also examined the timing of inspiratory pharyngeal bursts in relation to the phrenic (inspiratory) bursts. We found that the burst onset occurred significantly earlier in pharyngeal nerves than in phrenic ones (pharyngeal-to-phrenic delay). In anesthetized animals, this pharyngeal-to-phrenic delay was long enough to reveal that inspiratory activity appeared first on IX, then on PH.X, and then on phrenic nerves. Since hypoxia did not significantly alter the pharyngeal-to-phrenic delay, we conclude that a reliable organization of the inspiratory drive on pharyngeal and diaphragmatic muscles should exist, in the rat.