The effects of electrical stimulation of the distal end of the cut sinus and aortic nerves on peripheral arterial chemoreceptor activity in the cat.

1. In anaesthetized cats, stimulation of efferent components of the carotid sinus or aortic nerves depressed chemoreceptor discharge from the relevant chemoreceptor afferents. The local application of 2% procaine hydrochloride to the sinus nerve trunk, peripheral to the site of the stimulating electrodes and proximal to that of the afferent nerve twig, abolished the depression of afferent chemoreceptor discharge caused by electrical stimulation; on washing the procaine away electrical stimulation once more induced depression of chemoreceptor discharge.2. The depressant effect of efferent stimulation on carotid chemoreceptor activity was still seen during complete carotid glomeral ischaemia. Atropine given by close intra-arterial injection to the carotid body did not affect the depressant influence of efferent sinus nerve stimulation on carotid body chemoreceptor discharge.3. Stimulation of the sinus nerve efferents usually increased carotid body blood flow. Close arterial injection of atropine abolished this effect.4. The responses of glomeral blood flow and carotid chemoreceptor activity to efferent stimulation of the cut sinus nerve were not temporally related. It seems improbable that the depressant effect of such stimulation on chemoreceptor discharge was due to alterations of glomeral blood flow.5. Stimulation of the peripheral end of the cervical vagus in atropinized cats reduced chemoreceptor activity recorded in the ipsilateral aortic nerve.