Interaction of baroreceptor afferents from carotid sinus and aorta at the nucleus tractus solitarii

Summary In chloralose-urethane anaesthetized cats, low-threshold baroreceptor afferents of the carotid sinus and aortic nerves were stimulated electrically. Evoked responses were recorded within the nucleus tractus solitarii near the obex. At a certain electrode position in this area an evoked potential (E. P.) was elicited by stimulation of the homolateral carotid sinus or aortic nerve as well as the contralateral sinus or aortic nerve.At this site an interaction of these four baroreceptor nerves was demonstrated by testing the E. P. of one nerve after a conditioning stimulation of another nerve. Simultaneous E. P.'s did not show arithmetical summation. A strong reduction of the test-E.P. (mean value of reduction: 50%) occurred with a conditioning-testing interval of 10–20 msec. The test-E. P. came back to the control amplitude at an interval of 100–150 msec.Neither picrotoxin nor strychnine changed the time course or extent of these interactions.It was further observed that the most effective conditioning-testing interval for inhibition of test response corresponded closely to the difference between the arrival times of arotic and sinus nerve activities evoked by the cardiovascular pulse (aortic 16±5 msec before sinus nerve).A summary of these studies was presented at the 35th Meeting of the Deutsche Physiologische Gesellschaft [5].