Maintenance of respiratory rhythm-generation by vascular perfusion with physiological saline in the isolated head of the carp.

1) Vascular perfusion of the isolated head of the carp was carried out with physiological saline. Respiratory movement of the grill covers and respiratory discharges of cranial motor nerves were recorded in the preparation. 2) Blood vascular vessels supply the brain were anatomically investigated. Concentrations (electrolytes, O2, CO2, and glucose) and perfusing pressure of the saline were determined by reference to the useful information already available in fish physiology. 3) The movement of the operculum could be maintained in regular respiratory rhythm for more than 34 hr. Efferent discharges of cranial motor nerves also indicated that the respiratory rhythm generator functioned normally. Interruption of perfusate flow always immediately disturbed the opercular rhythm and resulted in respiratory arrest. 4) In conclusion, vascular perfusion is indispensable for the maintenance of breathing rhythm-generation in the isolated head of the carp; as the perfusate, the colloid-free physiological saline was found tenable for the long-term preservation of brain function in the carp.