Breathing Rhythm-generation in the Adult Lamprey, Entosphenus japonicus

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Abstract
The breathing rhythm-generation mechanism was studied throughout the entire body of the adult lamprey, E. japonicus, with the body fixed by a specially-designed holder. After brain-stem transection, the rostral part (pontine area) and the caudal part of the medulla were found not essential for the generation of respiratory rhythm: the location of the medullary respiratory rhythm-generator was in the district limited by 2 cross-section lines. Complete division of the brain-stem into 2 halves by midline section revealed that both of the 2 symmetrical halves could function independently with their own frequencies for 2 h or longer. Respiratory burst discharges were recorded from the isolated medial part of the medulla, preceded by a so called diastolic slow depolarization. The forms of these neural activities resemble those reported in pacemaker cells in some crustacean heart ganglion. No periodic discharges correlating exclusively to the relaxation and/or resting period of branchial muscle were observed. The reciprocal inhibition model was not necessarily considered a prerequisite for medullary respiratory rhythm-generation in the lamprey.