8. THE REGULATION OF BREATHING
323
as respiratory in the intact fish, continued after medulla isolation by
nerve and brain transection.
As further evidence of the center’s independence of mechanoreceptor
feedback, a number of workers have described the effects of paralyzing
doses of neuromuscular blocking agents such as curare, succinylcholine,
and gallamine. In such preparations not only can rhythmic proprioceptive feedback be eliminated but also the ventilation can be controlled
entirely by the experimenter. There seems to be little doubt that the
respiratory neurons of mammals continue to fire rhythmically after
paralysis of the musculature (Cohen and Wang, 1959; Salmoiraghi and
von Baumgarten, 196l), although some workers have shown a change
in the pattern of activity (von Baumgarten and Kanzow, 1958). In fish
there seems to be more variation. Von Baumgarten and Salmoiraghi
(1962) sometimes recorded an unaltered discharge and sometimes a
slight increase in the frequency of rhythmic bursts from respiratory
cells of goldfish after succinylcholine paralysis. Satchel1 (1959) found a
similar increase in the frequency of bursts in efferent fibers from the
dogfish center after administration of curare. Precisely opposite results
were described by Serbenyuk (1965) working on carp. Paralysis of the
respiratory muscles produced either by curare injection or division of
the motor nerves at first caused no change in respiratory neuron activity.
After a few minutes the normal rhythmic pattern disappeared and was
replaced by activity of a different type at a much lower frequency.
Serbenyuk (1965) suggested that sensory activity from a variety of
sources could affect cells of the center by raising both their general
excitability and their frequency of oscillation. Removal of any one of
his “reflexogenic zones,” such as muscle proprioceptors, had a depressant
effect on the center more or less equivalent to the removal of any other
of the zones, such as gill or swim bladder receptors.
These results on immobilized fish are not easy to interpret for several
reasons. They depend on a pre- and postparalysis comparison of activity
from a single recording site within the medulla. It has therefore been
difficult to decide whether the changes are representative of the center
as a whole. Ballintijn (1969) has recently described three categories of
response in respiratory neurons after gallamine induced paralysis. He
found that some cells continued to fire rhythmically, some stopped firing
completely, and a third category stopped but could be started again by
appropriate, but not necessarily rhythmic, proprioceptor stimulation.
Clearly the relationships that different cells have to the central oscillator
and to the proprioceptive feedback are quite variable (Fig. 15). Moreover, immobilization of an animal affects many systems in addition to
the sensory feedback from muscles. For example, the pattern of water
323
as respiratory in the intact fish, continued after medulla isolation by
nerve and brain transection.
As further evidence of the center’s independence of mechanoreceptor
feedback, a number of workers have described the effects of paralyzing
doses of neuromuscular blocking agents such as curare, succinylcholine,
and gallamine. In such preparations not only can rhythmic proprioceptive feedback be eliminated but also the ventilation can be controlled
entirely by the experimenter. There seems to be little doubt that the
respiratory neurons of mammals continue to fire rhythmically after
paralysis of the musculature (Cohen and Wang, 1959; Salmoiraghi and
von Baumgarten, 196l), although some workers have shown a change
in the pattern of activity (von Baumgarten and Kanzow, 1958). In fish
there seems to be more variation. Von Baumgarten and Salmoiraghi
(1962) sometimes recorded an unaltered discharge and sometimes a
slight increase in the frequency of rhythmic bursts from respiratory
cells of goldfish after succinylcholine paralysis. Satchel1 (1959) found a
similar increase in the frequency of bursts in efferent fibers from the
dogfish center after administration of curare. Precisely opposite results
were described by Serbenyuk (1965) working on carp. Paralysis of the
respiratory muscles produced either by curare injection or division of
the motor nerves at first caused no change in respiratory neuron activity.
After a few minutes the normal rhythmic pattern disappeared and was
replaced by activity of a different type at a much lower frequency.
Serbenyuk (1965) suggested that sensory activity from a variety of
sources could affect cells of the center by raising both their general
excitability and their frequency of oscillation. Removal of any one of
his “reflexogenic zones,” such as muscle proprioceptors, had a depressant
effect on the center more or less equivalent to the removal of any other
of the zones, such as gill or swim bladder receptors.
These results on immobilized fish are not easy to interpret for several
reasons. They depend on a pre- and postparalysis comparison of activity
from a single recording site within the medulla. It has therefore been
difficult to decide whether the changes are representative of the center
as a whole. Ballintijn (1969) has recently described three categories of
response in respiratory neurons after gallamine induced paralysis. He
found that some cells continued to fire rhythmically, some stopped firing
completely, and a third category stopped but could be started again by
appropriate, but not necessarily rhythmic, proprioceptor stimulation.
Clearly the relationships that different cells have to the central oscillator
and to the proprioceptive feedback are quite variable (Fig. 15). Moreover, immobilization of an animal affects many systems in addition to
the sensory feedback from muscles. For example, the pattern of water