Mechanisms of autonomic control of carotid chemoreceptor activity.

Single chemoreceptor fibres dissected from the cut carotid sinus nerves of cats were studied when carotid body blood flow was normal, and when it had been abruptly halted by reducing the local perfusion pressure to zero. Ten chemoreceptor fibres which, when normally supplied with blood, increased their discharge by at least 25% in response to sympathetic stimulation, and 7 fibres which, when normally supplied with blood, decreased their discharge by at least 10% in response to carotid sinus nerve stimulation, were chosen for study. The development of discharge during the period of stagnant asphyxia following stoppage of flow was reproducible in repeated control trials for each fibre investigated. Neither sympathetic nor carotid sinus nerve stimulation, commencing at the stoppage of flow and continued throughout the period of asphyxia, produced any significant alteration from the control pattern of developing chemoreceptor discharge. These experiments provide evidence that the effects of sympathetic and carotid sinus nerve stimulation on carotid chemoreceptor discharges are mediated through alterations in carotid body blood flow. When there is no flow there are no effects on discharge.