A trial Receptors with Nonmedullated Vagal Afferents in the Cat Discharge Frequency and Pattern in Relation to Atrial Pressure

SUMMARY The response of 14 atrial receptors with nonmedul-lated vagal afferents to changes in atrial pressure was determined in anesthetized thoracotomized cats. Recordings were made from 11 single fibers and three two-fiber filaments. Mean conduction velocity was 0.9 m/sec (range, 0.35 to 2.2 m/sec). During the control period, either no activity was detected or there was a sparse discharge (mean, 1.4 impulses/sec), which occasionally was related to the a or v waves. As atrial pressure was increased by transfusion or by occlusion of the aortic, pulmonary arterial, mitral, and tricuspid orifices, an increased rate of firing occurred, often related to the atrial v wave. The threshold for individual receptors was between 2 and 3 mm Hg (mean pressure) in the right atrium, and 5 and 12 mm Hg in the left atrium. The maximal firing rate was 5-11 impulses/sec for right atrial and 10-20 impulses/sec for left atrial receptors. The receptors w»re localized by probing the opened heart, and were identified in bot