Angiotensin II excites neurones in cat solitary tract nuclei which are involved in respiration and related reflex activities

In anaesthetized cats, effects of iontophoretic application of angiotensin II were studied in the nuclei of the tractus solitarius. Specifically, its effects were tested on single respiratory neurones, having rhythmic activity related temporally with the phrenic nerve discharge, and on presumed reflex interneurones, which lacked rhythmic activity but responded to stimulation of vagus nerve or superior laryngeal nerve. Angiotensin II (30-100 nA positive current for 30-60 s) excited 8/27 respiratory neurones; 19 were unaffected. Five of 8 reflex interneurones were excited; 3 were unaffected. Excitation consisted of a delayed, slow increase in the rate of firing which continued for about 60-120 s following the end of ejection. These results provide physiological evidence to support the possibility that angiotensin II may be a chemical mediator of synaptic transmission in the nuclei of the tractus solitarii, in pathways related to respiratory control.