Functional Correlation between the Reflexogenic Afferent Pathways from the Upper and Lower Airways

Abstract

In order to elucidate the relationship of respiratory neurons in the lateral part of the bulbar reticular formation to reflexogenic afferent inputs, responses of respiratory neurons to afferent stimulation of the vagus and internal branches of the superior laryngeal nerves were investigated under controlling evoked potentials of both nerves. Besides the respiratory neurons (type 1, 101 neurons in cats, 130 in rabbits), the unitary discharge pattern of which was changed by afferent stimulation, the other neurons (type 2=input respiratory neuron, 55 neurons in cats, 32 in rabbits) responded to afferent nerve stimulation with single orthodromic spike with latency ranging from 1.9 to 19 msec in cats, and 1.4 to 7.0 msec in rabbits. Three subtypes of input respiratory neurons could be differentiated with respect to their relation to the afferent pathways: neuron driven by vagal stimulation: one activated by stimulation given to another nerve; and cell which receives synaptic inputs mediated mainly by the Aα-γ fiber groups of both nerves. A striking difference in the proportion of the 3 subtypes between the two species was noted. The input respiratory neurons responded also to the adequate stimulus respectively, e. g., to lung inflation and/or to mechanical stimulation to the laryngeal mucosa. The specific neuronal organization found in the input respiratory neuron population may play an important role in the central integrative process in the brain stem for the reflexogenic afferent inputs of various modalities originating in the upper and lower airways.