First-breath response of medullary inspiratory neurones to the mechanical loading of inspiration

Abstract

Experiments have been conducted to investigate whether electrical activity of medullary inspiratory neurones is altered on the first breath following mechanical loading of inspiration. The predominant effect of resistive loading was an increase in both rate and duration of neurone activity. This facilitation was completely eliminated by vagotomy suggesting that the vagi are the only source of sensory information impinging on the inspiratory neurones conveying information about the loaded breath. In the intact animal, elastic loading and tracheal occlusion elicited the following responses : 1) an extended firing time of all neurones, 2) increased rate of unit activity in one population of neurones, 3) a decreased rate of unit activity in another population of neurones. Following vagotomy the only response noted with these types of loading was a decrease in the firing rate of some neurones. A probable source of the observed inhibition are the tendon organs of the diaphragm and /or external intercostal muscles via dorsal root pathways.