Interactions between baroreceptor and sympathetic pathways.

Abstract

The interactions between baroreceptor and sympathetic pathways were determined in anesthetized cats using computer summation techniques. Electrical stimuli applied to baroreceptor afferent nerves produced an early and late period of inhibition of sympathetic nervous discharge (SND) recorded from the external carotid or inferior cardiac nerves. The late period of baroreceptor-induced inhibition summated algebraically with the cardiac-locked slow wave of SND during all phases of the cardiac cycle. Increases in the intensity of baroreceptor stimulation resulted in an increase in the amplitude and duration of the late inhibition. Alterations in the periodicity of SND failed to effect the late phase of inhibition. Picrotoxin blocked the late period of baroreceptor-induced inhibition but enhanced the cardiac locking of SND. These data indicate that the late period of inhibition reflects the ability of afferent nerves to modulate the amplitude of central sympathetic outflow, regardless of its periodicity. In addition, the central baroreceptor pathways involved in amplitude modulation and temporal locking of SND to the cardiac cycle are distinct and are located at the level of the brain stem. A spinal component of baroreceptor-induced sympathoinhibition is also described.