Afferent sympathetic nerve fibres with aortic endings.

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Abstract
The electrical impulse activity of 35 single afferent fibers with aortic endings isolated from the 3rd to the 6th left thoracic sympathetic rami communicantes of anesthetized cats was recorded. The endings of each fiber were localized by mechanical probing of the opened aorta at the end of each experiment. Some (24) fibers had a single aortic receptive field: 11 fibers had several and distinct receptive fields (from 2 to 4). They were usually located in nearby aortic areas or in other proximal portions of the arterial tree or in the adjacent pleura and connective tissue. Twenty-nine fibers had conduction velocites ranging between 5-27 m/s (group A.delta.), while 6 fibers had conduction velocities between 0.2 and 1.2 m/s (Group C). The spontaneous impulse activity was in phase with the aortic pressure pulse and consisted of not more than 1 impulse/pressure pulse. It was increased during increases in aortic pressure and decreased during decreases in aortic pressure. In vivo and postmortem studies showed that these mechanoreceptors had an impulse activity which rapidly adapted during sustained stimuli. They seem to signal pulsatile aortic stretch. These aortic sympathetic afferents are likely to be part of a nervous pathway through which pressor reflexes, exhibiting positive feed-back characteristics, can be elicited.