Excitation of upper cervical inspiratory neurones by vagal stimulation in the cat.

The responses of 57 upper cervical inspiratory neurones to single shock stimuli applied to the ipsilateral cervical vagus nerve were recorded using peri-stimulus histograms in 19 cats. Many (47%) of the histograms showed a late latency (17.9 +/- 3.4 ms; mean +/- S.D.) broad peak following the stimulation preceding a similar peak in the histogram for the phrenic activity. Nine (16%) showed a short latency (5.2 +/- 1.2 ms) peak preceding that for the phrenic activity. These peaks were of narrow half-amplitude width (1.0 +/- 0.4 ms), indicative of a paucisynaptic pathway between the cervical vagus and the ipsilateral upper cervical inspiratory neurones. Such results suggest that the upper cervical inspiratory neurones are either monosynaptically excited via vagal fibres, or disynaptically excited via dorsal group inspiratory neurones.