Short latency phrenic response to electrical vagal stimulation in rabbits

Abstract

The response of the phrenic motoneurones to single shock stimulation of- afferent vagal fibres during inspiration was studied in rabbits. The rabbits were anaesthetized with halothane, paralysed, artificially ventilated and bilaterally vagotomized. To improve the detection of the response on the non-integrated efferent phrenic activity in the presence of background discharge, 64 to 128 single responses were averaged using a sampling time of 0.1 ms. No short-latency responses were obtained to single shock at threshold strength for the coarsest afferent vagal fibres. With increased stimulus strength activating also some finer myelinated fibres, as evidenced from the effect of low-frequency stimulation on the breath duration, a short-latency inhibition followed by an enhancement was observed bilaterally. The average latency of the inhibition was 8.5 ms. The results differ from these which can be obtained in cats.