Inhibitory action of vagal nerve and spinal cord afferents on discharge pattern of bulbar respiratory modulated neurons.

Single vagal nerve stimuli delivered during burst discharge of respiratory modulated neurons entailed lengthening of an interspike interval in 37% of all units tested. Occasionally stimuli delivered to the spinal cord caused lengthening of interspike intervals in respiratory modulated neurons and in other bulbar units the discharge of which was not modulated with respiration. Vagal stimuli often entailed lengthening of the following interspike interval, while the interval during which stimuli were applied remained unaltered; latencies suggested that inhibitory pathways were polysynaptic. In expiratory-inspiratory (EI) and inspiratory (I) neurons, lengthenings of intervals roughly doubled those noted in inspiratory-expiratory (IE) and expiratory (E) units. Lengthening of intervals depended on stimulus incidence within the intervals and was greatest when stimuli were delivered during the late part of the intervals. In EI and I units, lengthening of intervals occurred mainly during the middle part of burst discharge, in IE and E neurons, however, towards the end of the burst. Conditioning of discharge of respiratory modulated neurons could be demonstrated.