Reflex inhibition of canine inspiratory intercostals by diaphragmatic tension receptors

1. Electrical stimulation of phrenic afferent fibres in the dog elicits a r eflex inhibition of efferent activity to the inspiratory intercostal muscle s. However, electrical stimulation has a poor selectivity so the sensory re ceptors responsible for this inhibition were not identified. 2. In the present studies, cranial forces were applied during spontaneous i nspiration to the abdominal surface of the central, tendinous portion of th e canine diaphragm to activate tension mechanoreceptors in the muscle. Vaga l afferent inputs were eliminated by vagotomy. 3. The application of force to the central tendon caused a graded, reflex r eduction in inspiratory intercostal activity, especially in external interc ostal activity. This reduction was commonly associated with a decrease in i nspiratory duration and was invariably attenuated after section of the cerv ical dorsal roots. 4. In contrast, no change in inspiratory intercostal activity was seen when high frequency mechanical vibration was applied to the central tendon to s timulate diaphragmatic muscle spindles. 5. These observations provide strong evidence that tension receptors in the diaphragm, but not muscle spindles, induce reflex inhibition of inspirator y intercostal activity. The expression of this reflex probably involves sup raspinal structures.