Low-Pressure-Sensitive Baroreceptor Fibers Recorded From Rabbit Carotid Sinus Nerves

Activity was recorded from physiologically identified baroreceptor or chemoreceptor fibers in carotid sinus nerves of urethane-anesthetized spontaneously breathing rabbits. A carotid sinus area was vascularly isolated so that carotid sinus pressure and perfusion medium (Lockeʼs solution or rabbit blood) could be controlled. The cervical sympathetic, vagus, and aortic depressor nerves were bilaterally cut to eliminate vagal and cardiopulmonary reflexes. Baroreceptor fibers could be divided into two groupsfibers with a mean firing threshold of 47.6±1.9 mm Hg and no activity below this threshold (37 fibers) and fibers that were active at low intrasinus pressures (18.1±2.2 impulses/sec at an intrasinus pressure of 0 mm Hg). The baroreceptor fibers that were spontaneously active at low pressures were also chemically sensitivedischarge rate was increased by 5-hydroxytryptamine (10 fibers, p