Electrical stimulation of an epibranchial vagal ganglion, which innervates the gill region, had a marked influence on the respiratory rhythm of the carp Cyprinus carpio. Vagal input could initiate ventilation in fish displaying intermittent respiration. In fish breathing steadily, vagal stimuli could reset the respiratory rhythm by modifying the existing breathing cycle. An increase of stimulus intensity evoked a cough-like movement, thus delaying the onset of following cycles. Rhythmic stimulation, at intervals not more than 10° longer or shorter than the breathing cycle period, could entrain the respiratory rhythm in a one-toone ratio. Larger differences between the stimulation interval and the period of the breathing cycle resulted in either a cyclic modification of the respiratory cycle period or entrainment patterns with coupling ratios of 2:1 or 2:3. Coughing decreased in frequency or even stopped during rhythmic vagal stimulation.

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