Inputs from upper airway affect firing of respiratory-associated midbrain neurons.

In 16 decerebrated unanesthetized cats, we studied effects of neural inputs from upper airway on firing of 62 mesencephalic neurons that also developed respiratory-associated (RA) rhythmic firing when respiratory drive was high [Z. Chen, F. L. Eldridge, and P.G. Wagner. J. Physiol. (Lond.) 437: 305-325, 1991] and on firing of 16 neurons that did not develop the rhythmic firing (non-RA neurons). Activity in RA neurons increased after mechanical expansion of pharynx (45% of those tested) or larynx (68%) and after stimulation of glossopharyngeal (50%) or superior laryngeal nerves (77%). The increased neuronal firing occurred despite decreases or abolition of respiratory activity (expressed in phrenic nerve). Neuronal firing also increased after mechanical stimulation of nasal mucosa (66%) or by jets of air directed into the nares (48%) and after light brushing of nasal skin ( approximately 40%). Most stimuli led to decreased firing in a smaller number of neurons, and some neurons showed no response. None of the non-RA neurons developed an increase of firing after any of the stimuli, although one had decreased firing after stimulation of the superior laryngeal nerve. We conclude that inputs from the upper airway and nasal skin have independent modulatory effects on the same mesencephalic neurons that are stimulated by ascending rhythmic RA input from the medulla. These findings may have relevance to generation of the sensation of dyspnea.