VAGUS CARDIO-INHIBITORY FIBERS IN RATS

In chloralose-urethane anesthetized rats, compound spike potentials provoked in the cervical vagus nerve with electrical stimulation of the central cut end consisted of 3 major groups, A, .delta.-B and C. Cardioinhibition was observed on repetitive stimulation of the vagus nerve with an intensity which gave rise to the .delta.-B spike potential group. When the stimulus intensity was increased further beyond the level where the .delta.-B potential group had reached the maximum, the potency of cardioinhibition continued to be reinforced with the development of the C potential group. Selective activation of C fibers by anodal block of conduction along A and .delta.-B fibers was still associated with a considerable degree of cardioinhibition. Activities of both C fibers and .delta.-B fibers contribute to vagal cardioinhibition in rats and although vagal cardioinhibition is apparently mediated by B fibers in cats; this mechanism does not apply in a species of mammals.