Characteristics of brachiocephalic and carotid sinus baroreceptors with non‐medullated afferents in rabbit

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Abstract
The characteristics of brachiocephalic and carotid sinus baroreceptors with non‐medullated afferents have been studied in rabbits. The conduction velocities of 18 non‐medullated fibers arising from the brachiocephalic baroreceptors were 0.4–0.8 m/s (0.59±0.03 m/s, mean ± SE) and their thresholds were 74–104 mmHg (84±2 mmHg). 29 non‐medullated carotid sinus baroreceptor afferents had thresholds ranging from 60 to 125 mmHg (92±3 mmHg). Their conduction velocities were 0.5–1.1 m/s (0.65±0.05 m/s). Blood pressure‐baroreceptor response curves of both the brachiocephalic and the carotid sinus baroreceptors were constructed. As the aortic arch non‐medullated baroreceptor afferents, the brachiocephalic and the carotid sinus baroreceptors with non‐medullated afferents exhibited thresholds about 30 mmHg higher than the medullated ones, considerably lower firing rates, comparatively rapid adaptation and remarkable irregular discharge pattern. It is suggested that the non‐medullated baroreceptor afferents are of little importance for the cardiovascular regulation under normal conditions but are likely to play an important role during a sudden rise in arterial pressure.