EXCITATION OF EXPIRATORY NEURONES ADJACENT TO NUCLEUS AMBIGUUS BY CAROTID SINUS BARORECEPTOR AND TRIGEMINAL AFFERENTS

Expiratory neurones were recorded in chloralose-urethane anaesthetized cats. Both vagal nerves were cut. After raising the pressure in bilateral carotid sinus preparation the duration and the number of impulses per expiratory cycle increased, while the mean frequency decreased. Since a fall in blood pressure by intravenous acetylcholine resulted in an opposite effect, the described response of expiratory neurones is due to baroreceptor afferents. The expiratory activity was increased even more by trigeminal afferents activated by manual pressure on snout and eyeball. The location of expiratory neurones as controlled histologically, was in a caudal and lateral region of the brain stem adjacent to the nucleus ambiguus. This location and the activation of expiratory neurones by baroreceptor and trigeminal afferents known to cause a strong bradycardia give some further evidence that the nucleus ambiguus represents the origin of vagal cardiomotor efferents and that both the expiratory and vagal activity have a close functional connection. © 1969 Springer-Verlag.