Breathing rhythm-generation in the adult lamprey, Entosphenus japonicus

1. The breathing rhythm-generation mechanism was studied throughout the entire body of the adult lamperey, Entosphenus japonicus, with the body fixed by a specially-designed holder. 2. After brain-stem transection, the rostral part (pontine area) and the caudal part of the medulla (Fig. 2) were found not essential for the generation of respiratory rhythm: the location of the medullary respiratory rhythm-generator was in the district limited by two cross-section lines (Fig.2). 3. Complete division of the brain-stem into two halves by midline section revealed that both of the two symmetrical halves could function independently with their own frequencies for 2 hr or longer. 4. 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. 5. The reciprocal inhibition model was not necessarily considered a prerequisite for medullary respiratory rhythm-generation in the lamprey.