Mechanisms of central transmission of respiratory reflexes

Several types of respiratory reflex actions can be discerned according to the reactions of typical respiratory neurons in the efferent part of the central rhythmogenic structure. Whereas respiration runs closely parallel with inspiratory neuron activity the behaviour of expiratory neurons cannot be derived from the resulting reflex changes of respiration. So expiratory apnoea can be combined with continuous activity or with inactivation of expiratory neurons. Extracellular records from a closed uniformly reacting population of expiratory neurons and from neighbouring reticular neurons allowed experimental differentiation between different types of central respiratory reflex actions. In experiments on anaesthetized dogs the responses to chemoreceptor and baroreceptor excitation and to pulmonary inflation were investigated. Chemoreceptor excitation leads to activation of inspiratory, expiratory, and reticular neurons, whereas the baroreceptor afferents act in the opposite direction. In contrast moderate lung inflation causes more specific effects: activation of expiratory neurons, inactivation of inspiratory neurons. But if a certain degree of lung inflations is exceeded a more general inhibition of both inspiratory and expiratory neurons takes place. These results only apply to the "typical" respiratory neurons. The principles used to distinguish between the different types of reflexes are proposed for a basis of classification also of other neural, chemical or pharmacological influences on breathing.