Effect of pulmonary C-fibre afferent stimulation on cardiac vagal neurones in the nucleus ambiguus in anaesthetized cats
Article first published online: 13 AUG 2004
The Journal of Physiology
Volume 526, Issue 1, pages 157–165, July 2000
How to Cite
Wang, Y., Jones, J. F. X., Jeggo, R. D., de Burgh Daly, M., Jordan, D. and Ramage, A. G. (2000), Effect of pulmonary C-fibre afferent stimulation on cardiac vagal neurones in the nucleus ambiguus in anaesthetized cats. The Journal of Physiology, 526: 157–165. doi: 10.1111/j.1469-7793.2000.t01-1-00157.x
- Issue published online: 13 AUG 2004
- Article first published online: 13 AUG 2004
- (Received 16 February 2000; accepted after revision 7 April 2000)
- 1It has been demonstrated previously that the vagal bradycardia evoked by activation of pulmonary C-fibres is not respiratory modulated. Experiments were carried out in α-chloralose anaesthetized cats to determine if these cardiac vagal preganglionic neurones (CVPNs) in the nucleus ambiguus (NA), which have respiratory modulated activity, can be activated when pulmonary C-fibre afferents are stimulated by right atrial injections of phenylbiguanide (PBG).
- 2Eleven CVPNs with B-fibre axons in the right cardiac vagal branches were identified and found to be localized within or ventrolateral to the nucleus ambiguus. Ionophoretic application of a high current of dl-homocysteic acid (DLH) induced a vagally mediated bradycardia and hypotension in six of eight sites from which CVPNs were recorded.
- 3The activity of B-fibre CVPNs, whether spontaneous (n= 4) or induced by ionophoresis of DLH (n= 7) was respiratory modulated, firing perferentially during post-inspiration and stage 2 expiration. This activity also correlated with the rising phase of the arterial blood pressure wave consistent with these CVPNs receiving an arterial baroreceptor input.
- 4Right atrial injections of PBG excited nine of eleven CVPNs tested. In eight of these activated neurones the onset latency of the excitation was within the pulmonary circulation time, consistent with being activated only by pulmonary C-fibre afferents. In two neurones the PBG-evoked excitation still occurred when central inspiratory drive was inhibited, as indicated by the disappearance of phrenic nerve activity.
- 5In conclusion, B-fibre respiratory modulated CVPNs can be activated following stimulation of pulmonary C-fibre afferents.