Carotid sinus baroreceptor activity in the nonhuman primate.

The carotid sinus of eight adult Macaca fascicularis monkeys was functionally isolated from the circulation and perfused with Krebs-Henseleit solution. The impulse activity in 65 carotid sinus baroreceptor fibers from the left carotid sinus nerve was studied during nonpulsatile perfusion and was compared with the impulse activity in 68 fibers from 10 adult mongrel dogs. Curves relating the discharge frequency to carotid sinus pressure were constructed. The baroreceptor fibers of the monkey had a significantly lower threshold, gain, pressure at the point of inflection, and plateau pressure than those of the dog. Hysteresis, as indicated by the separation of the stimulus-response curves obtained by increasing and then decreasing carotid sinus pressure, was observed. At any given pressure, the discharge frequency of baroreceptors was greater when carotid sinus pressure was increased than when it was decreased in both species. These results provide direct evidence that carotid sinus baroreceptors in the monkey are less sensitive to pressure changes than those in the dog.