ELECTROPHYSIOLOGICAL STUDY OF VAGAL AFFERENT AND EFFERENT UNITS IN CONSCIOUS SHEEP

Abstract

Crossed-nerve anastomoses were performed to record activity of vagal efferents and afferents during regurgitation and eructation in conscious sheep. Following anastomoses of the central end of a vagus nerve to the peripheral end of a phrenic nerve, discharges in units of the diaphragm reinnervated by vagal efferent neurones were associated with contractions of the caudal oesophagus and of the rumen. During regurgitation in the course of rumination, discharges in oesophageal efferents consisted of a characteristic pattern of two bursts in a constant association with the additional phase of the reticular contraction and the more forceful inspiratory effort. Discharges in two types of units bore a temporal relation with the motor gastric cycles. Early units are interpreted as innervating pillars of the rumen and late units its dorsal wall. Regular patterns of discharge were recorded during successive A sequences of rumen contractions. In contrast, there was a variability of pattern of activity of efferents during B sequences: a constant time relationship was not observed between discharges of both types of units. During B sequences accompanied by eructation, the most characteristic pattern in gastric and oesophageal units had the following features: the impulses in the early units increased in frequency, outlasted the discharge in the late units by 1 s and ended when a brief discharge was recorded in an oesophageal unit at the time of eructation. It is suggested from the patterns of discharge observed in both gastric and oesophageal efferents that the orderly sequence which achieves regurgitation and eructation results from the central co-ordination of efferent output. Following anastomoses of the central root of the nodose ganglion to the peripheral end of the accessory nerve, discharges in units of the mastoido-humeral muscle reinnervated by vagal afferent axons were associated with contractions of the oesophagus and movements of the larynx during swallowing and regurgitation. Discharges in oesophageal afferents coming from the caudal oesophagus were coincident with discharges observed in the vagal efferent fibres innervating this part of the oesophagus. Afferents from the pharynx and the larynx were active at the same time as the nasopharynx and the glottis were demonstrated to be closed. Thus the major characteristics of the afferents the traffic of which has been recorded in cross-sutured sheep in the course of rumination is that their discharges are occurring at the same time as motor events are developing.(ABSTRACT TRUNCATED AT 400 WORDS)