Control of respiratory motor pattern by sensory neurons in spinal cord of lamprey.

Extracellular stimulation over the dorsal funiculus in the spinal cord of lampreys was found to selectively activate prolonged episodes of fictive arousal respiration. The induced episodes showed comparable increases in cycle frequency and motoneuron burst duration to the spontaneous arousal pattern observed in isolated brain preparations. Intracellular stimulation of primary sensory neurons with axons in the dorsal funiculus, called 'dorsal cells', also elicited the arousal pattern. Mechanoreceptive dorsal cells respond to cutaneous stimulation. When mechanical stimuli were applied to the skin of intact lampreys or to lampreys with ipsilateral vagotomy, arousal respiration was induced. Bilateral, but not unilateral, trigeminal lesion blocked dorsal cell induction of the arousal response. Spontaneous arousal respiration was recorded from intact, unrestrained lampreys. These results suggest that fictive arousal respiration is the in vitro correlate of natural arousal respiration in lampreys, and that one mechanism leading to arousal respiration may be the activity of sensory dorsal cells. A model for respiratory motor pattern switching in lamprey is proposed. The model suggests that the normal and arousal patterns are produced by separately engaging rostral or caudal pattern generators in the medulla, rather than by modifying one pattern generator.