Efferent control of arterial chemoreceptors mediated by glossopharyngeal fibres and artifacts introduced by stimulation techniques.

1. In anaesthetized cats, stimulation of the cut carotid sinus nerve generally caused a reduction in discharge in afferent fibres peeled from the nerve distal to the stimulating electrodes, though this was somewhat variable. In four out of five fibres the inhibition was reduced or abolished by close intra-arterial injection of atropine. Only single fibres were used.2. There was a risk of adventitious excitation of the afferent fibre by stimulus escape. Some of the features of this excitation and the ease with which it occurred were investigated using an isolated length of vagus, baroreceptor fibres and chemoreceptor fibres. Low concentrations of local anaesthetic could raise the threshold for adventitious excitation whilst not affecting the normal passage of impulses.3. During stimulation of the efferent components of the sinus nerve, a continuous check for adventitious excitation was kept, utilizing the fact that chemoreceptor fibres show a minimum inter-spike interval of about 10 msec.4. The true inhibition of discharge would seem to be vasomotor in origin.