1. ANATOMY AND PHYSIOLOGY OF THE CENTRAL NERVOUS SYSTEM
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medullary neurons by stimulating the spinal cord caudal to the unit.
This stimulation produced a mixed sequence of discharges which contain
both antidromic and synaptic components. The mixed discharge and
stimulating effect demonstrated that the units were probably motor
neurons. Neurosecretory neurons in skates and teleosts were activated
synaptically by stimulation of the rostra1 spinal cord. However, the presynaptic pathway of these specialized neurons was of high threshold
and low conduction velocity (Bennett and Fox, 1962).
The unit spike responses ascribable to the motor neuron and neurosecretory cell were quantitatively different. The unit spike potentials of
neurosecretory cells were 4-10 msec in duration. Intracellular recordings
from the caudal neurosecetory cell bodies in the Japanese eel (Ishibashi,
1962; Morita et al., 1961) and in the fluke and skate (Bennett and Fox,
1962) demonstrated similar action potentials of long duration. This
response was significantly longer than other intramedullary cells and
were from 1 to 2 msec in duration. The responses from the neurosecretory
cells usually were followed by large and long-lasting undershoots of the
resting potential. A spike that was evoked in neurosecretory cells by
intracellularly applied depolarizing current was found to be of a much
shorter latency with stronger stimuli. The two types of unit spike potentials (from motor cells and neurosecretory cells) were observed in
recordings from axons in the caudal neurosecretory system in both
Tilapia (Yagi and Bern, 1965) and Cyprinus carpio (Kinosita et al.,
1962, from Yagi and Bern, 1965). These data indicated that both secretory and nonsecretory neurons of the spinal cord innervate the urophysis.
It is interesting to note that the size of the neurosecretory neurons appeared to differ but the response characteristics of these types of
neurons did not.
On the basis of response to osmotic manipulation of the blood, the
neurosecretory units of Tilapia (Yagi and Bern, 1963, 1965) were classified into two major and a third minor type. The first major type increased in discharge rate ( over spontaneous rate) following intravenous
infusion of hypotonic sodium chloride solutions ( sodium ion poor ) . The
second major type was activated by infusion of hypertonic solutions of
sodium chloride (sodium ion rich). The third or minor type of neurosecretory unit did not respond to osmotic stimuli even though other
neurosecretory units which were being recorded simultaneously were
discharging. The observed decrease in the electrical activity of some of
the units of the neurosecretory system upon the infusion of solutions of
different osmolarity indicated the presence of some inhibitory mechanism
from other centers within the nervous system that partially controls the
neurosecretory cells.
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medullary neurons by stimulating the spinal cord caudal to the unit.
This stimulation produced a mixed sequence of discharges which contain
both antidromic and synaptic components. The mixed discharge and
stimulating effect demonstrated that the units were probably motor
neurons. Neurosecretory neurons in skates and teleosts were activated
synaptically by stimulation of the rostra1 spinal cord. However, the presynaptic pathway of these specialized neurons was of high threshold
and low conduction velocity (Bennett and Fox, 1962).
The unit spike responses ascribable to the motor neuron and neurosecretory cell were quantitatively different. The unit spike potentials of
neurosecretory cells were 4-10 msec in duration. Intracellular recordings
from the caudal neurosecetory cell bodies in the Japanese eel (Ishibashi,
1962; Morita et al., 1961) and in the fluke and skate (Bennett and Fox,
1962) demonstrated similar action potentials of long duration. This
response was significantly longer than other intramedullary cells and
were from 1 to 2 msec in duration. The responses from the neurosecretory
cells usually were followed by large and long-lasting undershoots of the
resting potential. A spike that was evoked in neurosecretory cells by
intracellularly applied depolarizing current was found to be of a much
shorter latency with stronger stimuli. The two types of unit spike potentials (from motor cells and neurosecretory cells) were observed in
recordings from axons in the caudal neurosecretory system in both
Tilapia (Yagi and Bern, 1965) and Cyprinus carpio (Kinosita et al.,
1962, from Yagi and Bern, 1965). These data indicated that both secretory and nonsecretory neurons of the spinal cord innervate the urophysis.
It is interesting to note that the size of the neurosecretory neurons appeared to differ but the response characteristics of these types of
neurons did not.
On the basis of response to osmotic manipulation of the blood, the
neurosecretory units of Tilapia (Yagi and Bern, 1963, 1965) were classified into two major and a third minor type. The first major type increased in discharge rate ( over spontaneous rate) following intravenous
infusion of hypotonic sodium chloride solutions ( sodium ion poor ) . The
second major type was activated by infusion of hypertonic solutions of
sodium chloride (sodium ion rich). The third or minor type of neurosecretory unit did not respond to osmotic stimuli even though other
neurosecretory units which were being recorded simultaneously were
discharging. The observed decrease in the electrical activity of some of
the units of the neurosecretory system upon the infusion of solutions of
different osmolarity indicated the presence of some inhibitory mechanism
from other centers within the nervous system that partially controls the
neurosecretory cells.