EXCITATION OF UPPER CERVICAL INSPIRATORY NEURONS BY VAGAL-STIMULATIONIN THE CAT

THE responses of 57 upper cervical inspiratory neurones to single shoc k stimuli applied to the ipsilateral cervical vagus nerve were recorde d using peri-stimulus histograms in 19 cats. Many (47%) of the histogr ams showed a late latency (17.9 +/- 3.4 ms; mean +/- S.D.) broad peak following the stimulation preceding a similar peak in the histogram fo r 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 paucisy naptic pathway between the cervical vagus and the ipsilateral upper ce rvical inspiratory neurones. Such results suggest that the upper cervi cal inspiratory neurones are either monosynaptically excited via vagal fibres, or disynaptically excited via dorsal group inspiratory