318
G . SHELTON
in others they are thought to interact with further neuron groups such
as apneustic and pneumotaxic centers before normal activity is produced (Wang and Ngai, 1963; Kahn and Wang, 1967). The differences
and problems result from studying a system of dispersed yet interacting
neurons with methods which to some extent are all inadequate.
The extent of damage caused by transection or electrical coagulation
is seldom easy to determine. In addition, it is not clear whether the
changes in breathing always result from the destruction of regions or
neurons exclusively associated with this particular function. Thus Wang
and Ngai (1964), following a number of earlier workers, found that
pontine transection provided evidence for both a pneumotaxic center
and apneustic center in the pontine region of cat brains. However, Hoff
and Breckenridge (1949), using similar techniques on the dog, were led
to conclude that apneusis was the result of a generalized activity in the
facilitator system of the reticular formation. They thought that pontine
transection produced the necessary facilitator-suppressor imbalance
to give inspiratory cramps. Nor are stimulation experiments free from
these limitations. Stimulus spread, using either chemical or electrical
methods, can be controlled with care but not, so far, to the point where
drugs can be administered into the immediate environment of a neuron
or a single unit can be stimulated electrically (Salmoiraghi, 1962;
Liljestrand, 1953). Furthermore, the precise status of the region stimulated, whether exclusively respiratory or more general in function,
whether neuron or interconnecting nerve tract, is often in doubt. In the
medulla of mammals, for example, electrical stimulation has always led
to a wider and, to some extent, a different area being implicated in
respiratory control than determinations made by recording electrodes.
The recording technique, on the other hand, can only be used to identify
neurons as respiratory when they are rhythmically active and synchronized precisely with the breathing movements. Cells, discharging in ways
different from this may be involved in respiratory coordination but cannot be recognized. Moreover, the technique has provided little information about neuron interaction because single neurons or, with less
selective electrodes, single groups of neurons only have been studied.
Some workers have tried to combine the stimulation and recording
techniques. For example, Gill and Kuno (1963) studied the effect of
medulla stimulation on activity in phrenic motor neurons, Keder-Stepanova and Ponomarev (1965) stimulated the medial region of the medulla
and examined the effect this had on respiratory activity in more laterally
situated neurons, and Hori (1966) recorded the changes produced in
respiratory center cells by mesencephalic stimulation. Multielectrode
preparations recording from several respiratory neurons, or stimulating
G . SHELTON
in others they are thought to interact with further neuron groups such
as apneustic and pneumotaxic centers before normal activity is produced (Wang and Ngai, 1963; Kahn and Wang, 1967). The differences
and problems result from studying a system of dispersed yet interacting
neurons with methods which to some extent are all inadequate.
The extent of damage caused by transection or electrical coagulation
is seldom easy to determine. In addition, it is not clear whether the
changes in breathing always result from the destruction of regions or
neurons exclusively associated with this particular function. Thus Wang
and Ngai (1964), following a number of earlier workers, found that
pontine transection provided evidence for both a pneumotaxic center
and apneustic center in the pontine region of cat brains. However, Hoff
and Breckenridge (1949), using similar techniques on the dog, were led
to conclude that apneusis was the result of a generalized activity in the
facilitator system of the reticular formation. They thought that pontine
transection produced the necessary facilitator-suppressor imbalance
to give inspiratory cramps. Nor are stimulation experiments free from
these limitations. Stimulus spread, using either chemical or electrical
methods, can be controlled with care but not, so far, to the point where
drugs can be administered into the immediate environment of a neuron
or a single unit can be stimulated electrically (Salmoiraghi, 1962;
Liljestrand, 1953). Furthermore, the precise status of the region stimulated, whether exclusively respiratory or more general in function,
whether neuron or interconnecting nerve tract, is often in doubt. In the
medulla of mammals, for example, electrical stimulation has always led
to a wider and, to some extent, a different area being implicated in
respiratory control than determinations made by recording electrodes.
The recording technique, on the other hand, can only be used to identify
neurons as respiratory when they are rhythmically active and synchronized precisely with the breathing movements. Cells, discharging in ways
different from this may be involved in respiratory coordination but cannot be recognized. Moreover, the technique has provided little information about neuron interaction because single neurons or, with less
selective electrodes, single groups of neurons only have been studied.
Some workers have tried to combine the stimulation and recording
techniques. For example, Gill and Kuno (1963) studied the effect of
medulla stimulation on activity in phrenic motor neurons, Keder-Stepanova and Ponomarev (1965) stimulated the medial region of the medulla
and examined the effect this had on respiratory activity in more laterally
situated neurons, and Hori (1966) recorded the changes produced in
respiratory center cells by mesencephalic stimulation. Multielectrode
preparations recording from several respiratory neurons, or stimulating