Artificial pacemaking of breathing movements by medullary stimulation in adult lampreys

1. The effect of medullary stimulation on breathing movement was studied in the adult lamprey, Entosphenus japonicus. 2. A single, as well as low frequency (less than 5 Hz) pulses applied extracellularly to the medial part of the medulla (as shown in Fig. 1) produced one-to-one movement (contraction followed by relaxation) of branchial baskets, which are similar in shape, as well as in bilateral synchronization, to spontaneously occurring movement. 3. medullary stimulation never produced active immediate relaxation of branchial baskets. Intravenous application of d-tubocurarine resulted in sustained relaxation of branchial baskets. EMG recorded from branchial muscles always correlated with the phase of contraction of branchial baskets. 4. The rhythm of respiratory movement was reset by driving stimuli at low frequencies. Alteration of driving frequency did not markedly affect the duration of branchial movement. 5. With high frequency stimulation (more than 5 Hz), individual responses fused into one continuous contraction (sustained compression) of branchial baskets; it may be called a systolic arrest or expiratory arrest of breathing movement. 6. After the repetitive stimulation had been turned off, there was a pause in the respiratory movement. This sustained relaxation of branchial baskets may be called a diastolic arrest or inspiratory arrest. During this arrest, applied pulse shocks induced one-to-one movement of branchial baskets. 7. These results were discussed whilst considering an analogy between respiratory rhythmogenesis in the lamprey and cardiac pacemaking in crustacean heart ganglion.