Vagus cardioinhibitory 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 were found to consist of three major groups, A, delta-B and C. A remarkable cardioinhibition was observed on repetitive stimulation of the vagus nerve with an intensity which gave rise to the delta-B spike potential group. However, 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 conductions along A and delta-B fibers was still associated with a considerable degree of cardioinhibition. These findings indicate that activities of both C fibers and delta-B fibers contribute to vagal cardioinhibition in rats and the view that the vagal cardioinhibition is mediated by B fibers, although valid in cats, can not be held applicable to all species of mammalians.