No abstract

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.The respiratory pumping mechanism in adult lampreys is basically different from that in gnathostomata. According to ROBERTS (1950), adult lampreys possess only a synergistic respiratory muscular system; their breathing is produced by a

To examine the breathing rhythm-generating mechanism, effects of brain sectioning, immobilization, and electric stimulation on medullary respiratory activities were investigated in adult lampreys. 1) The rostra! part of the medulla (rostrally to the level of the caudal border of "internal acoustic pore") is not indispensable for breathing rhythm -generation. The rostra! part itself, however, was also capable of driving periodic movement of only the first branchial baskets. 2) After immobilization, respiratory discharges continued without changing their pattern, indicating that respiratory afferents do not modulate the centrally generating rhythm. 3) Respiratory discharges recorded simultaneously from the right and left side of the medulla showed bilateral synchronization. After sectioning the midline of the brain, each of the symmetric halves of the medulla behaved as an independent respiratory pacemaker. 4) Respiratory discharges were driven in one-to-one fashion by electric stimulus applied to the medulla, almost independently of timing of stimulus delivery. Stimulus pulses applied during respiratory discharges did not inhibit these discharges : electrically driven discharge summated or fused with the spontaneous firing. 5) Slow and smoothly depolarizing potential preceding respiratory spike discharges was recorded intracellularly from the half of the brain-stem divided by midline sagittal sectioning in the immobilized animal. 6) These results were discussed in light of the hypothesis that respiratory burst generator mechanism in the lamprey may be similar to cardiac pacemakers.

Feeding behavior was initiated in juvenile and adult lampreys, Ichthyomyzon unicuspis, by attachment to goldfish or by injection of saline extracts of goldfish skin and muscle into the sucker cavity. Feeding was confirmed by the apparent swallowing of fish extract plus food dye by lampreys. Distinctive characteristics of feeding behavior included low frequency cycles, long duration (hours), variable biphasic pressure changes in the sucker cavity, and protraction of the tongue-like apicalis. In contrast, pumping behavior was used to move excess fluid from the sucker through the pharynx and out the gill pores; it was characterized by transient, high-frequency, monophasic suctions, simple retraction of the apicalis, and lack of swallowing.

Vascular perfusion of the isolated head of the carp was carried out with physiological saline.Respiratory movement of the gill covers and respiratory discharges of cranial motor nerves were recorded in the preparation. 2) Blood vascular vessels supplying 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.