322
G . SHELTON
important. Satchell's more recent transection experiments ( 1959) demonstrated that the mid- and forebrains could be removed without causing
marked change in the breathing pattern of the dogfish. After transection
the medulla was more susceptible to reflex inhibition, but in the absence
of reflex effects the medulla maintained rhythmic activity.
C. The Functional Organization of the Respiratory Center
It has been assumed in the foregoing account that the population
of respiratory neurons in the fish medulla is a large one. The fact that
a number of widely separate, active sites with several neurons at each
site can be found in a single fish suggests that this is so. Since the
population is a changing one, however, it is very difficult to reach an
accurate estimate of its size. Indeed, on this evidence it could be quite
small if one is prepared to accept rapid shifts from one locus to another.
Fortunately, it is possible to show that there is a little more stability
than this and some units can be held for hours, or even days, without
showing substantial change ( Shelton and Young, 1965). Furthermore,
it is possible to destroy respiratory neurons around the tip of a recording
electrode by electrocoagulation and for rhythmic breathing to go on
normally ( Shelton, 1961 ). Localized coagulation of this type was never
effective in bringing breathing to a halt, other than momentarily, even
though as many as five such sites were destroyed in a single fish. This
argues in the favor of a large rather than a small population.
1. INTRINSIC RHYTHMIC ACTIVITY IN THE RESPIRATORY CENTER
The early work of Adrian and Buytendijk (1931) is often cited as
demonstrating the autonomous nature of the fish center. They recorded
slow potential changes from the medulla of a completely isolated goldfish brain. The similarity in frequency between these potentials and
breathing movements of an intact fish was slender evidence for the
former's respiratory function. More recently, Schadk and Weiler ( 1959)
also detected slow potentials on the surface of the goldfish medulla.
In the intact animals they occurred in rhythm with the breathing movements and persisted after the fish had been paralyzed by Intocostrin
injection. Although the precise nature of these slowly changing surface
phenomena is still in doubt, their connection with some aspect of
respiratory activity seems now to be well established. Using needle
electrodes, Hukuhara and Okada ( 1956) demonstrated autonomous activity more directly within the cells of catfish and carp respiratory centers. The rhythmic bursts of action potentials, which identified the cells
G . SHELTON
important. Satchell's more recent transection experiments ( 1959) demonstrated that the mid- and forebrains could be removed without causing
marked change in the breathing pattern of the dogfish. After transection
the medulla was more susceptible to reflex inhibition, but in the absence
of reflex effects the medulla maintained rhythmic activity.
C. The Functional Organization of the Respiratory Center
It has been assumed in the foregoing account that the population
of respiratory neurons in the fish medulla is a large one. The fact that
a number of widely separate, active sites with several neurons at each
site can be found in a single fish suggests that this is so. Since the
population is a changing one, however, it is very difficult to reach an
accurate estimate of its size. Indeed, on this evidence it could be quite
small if one is prepared to accept rapid shifts from one locus to another.
Fortunately, it is possible to show that there is a little more stability
than this and some units can be held for hours, or even days, without
showing substantial change ( Shelton and Young, 1965). Furthermore,
it is possible to destroy respiratory neurons around the tip of a recording
electrode by electrocoagulation and for rhythmic breathing to go on
normally ( Shelton, 1961 ). Localized coagulation of this type was never
effective in bringing breathing to a halt, other than momentarily, even
though as many as five such sites were destroyed in a single fish. This
argues in the favor of a large rather than a small population.
1. INTRINSIC RHYTHMIC ACTIVITY IN THE RESPIRATORY CENTER
The early work of Adrian and Buytendijk (1931) is often cited as
demonstrating the autonomous nature of the fish center. They recorded
slow potential changes from the medulla of a completely isolated goldfish brain. The similarity in frequency between these potentials and
breathing movements of an intact fish was slender evidence for the
former's respiratory function. More recently, Schadk and Weiler ( 1959)
also detected slow potentials on the surface of the goldfish medulla.
In the intact animals they occurred in rhythm with the breathing movements and persisted after the fish had been paralyzed by Intocostrin
injection. Although the precise nature of these slowly changing surface
phenomena is still in doubt, their connection with some aspect of
respiratory activity seems now to be well established. Using needle
electrodes, Hukuhara and Okada ( 1956) demonstrated autonomous activity more directly within the cells of catfish and carp respiratory centers. The rhythmic bursts of action potentials, which identified the cells