74
JERALD J. BERNSTEIN
The discharge rate of caudal neurosecretory neurons was influenced
by the level of sodium ions of the blood and did not appear to depend
on other components of compounds infused into the bloodstream (Yagi
and Bern, 1965). Blood osmotic pressure per se was not the stimulus to
which the caudal neurosecretory units were responding. In addition,
caudal neurosecretory cells that were activated by sodium chloride were
generally also activated by sodium sulfate or sodium nitrate. Other
neurosecretory units were activated by sucrose and choline chloride
which are sodium ion free. In other words, the presence of sodium ions
consistently reduced responses in some neurosecretory cells and the
absence of sodium ions activated others, thus, producing the two major
classes of neurosecretory cells. This response was independent of other
ions which were present in the solutions infused (Yagi and Bern, 1965).
In an attempt to locate the center for the control of the caudal
neurosecretory system in Tilapia, Yagi and Bern (1965) transected the
spinal cord. Following spinal cord transection the neurosecretory cells
did not respond to physiological stimulation although the local blood
supply to the cclls was not interrupted. The fact that the neurosecretory
cells did not spontaneously generate action potentials after transection
of the spinal cord although they retained their excitability suggests that
the center regulating the electrical activity of the caudal neurosecretory
system is within the brain proper (Yagi and Bern, 1965).
Spinal influences on the caudal neurosecretory system and olfactory
influences on the neurohypophysial system may well be similar in
mechanism. The pattern of impulses from stimulation of the olfactory
organ affects the discharge rate and the excitability of preoptic neurons
in the neurohypophysis and partially regulates the release of neurohypophysial hormones. It may well be that a similar sensory modulation
of hormonal release is the mechanism by means of which the caudal
neurosecretory system acts in osmoregulation.
D. Regeneration of the Spinal Cord
Spinal cord regeneration in larval (Hibbard, 1963; Koppanyi, 1955;
M a r h , 1959; Niazi, 1963) and adult fish (Clemente, 1954; Healcy, 1962;
Kirsche, 1965b ) was both anatomically and physiologically successful.
The regenerative capacity of the spinal cord of fish was unparalleled
among the vertebrates. This capacity extended from the simple regrowth
of axons across the lesion to reconstitution of the parenchyma into the
former neural cytoarchitectonics and complete restitution of new nerve
cells and glia.
JERALD J. BERNSTEIN
The discharge rate of caudal neurosecretory neurons was influenced
by the level of sodium ions of the blood and did not appear to depend
on other components of compounds infused into the bloodstream (Yagi
and Bern, 1965). Blood osmotic pressure per se was not the stimulus to
which the caudal neurosecretory units were responding. In addition,
caudal neurosecretory cells that were activated by sodium chloride were
generally also activated by sodium sulfate or sodium nitrate. Other
neurosecretory units were activated by sucrose and choline chloride
which are sodium ion free. In other words, the presence of sodium ions
consistently reduced responses in some neurosecretory cells and the
absence of sodium ions activated others, thus, producing the two major
classes of neurosecretory cells. This response was independent of other
ions which were present in the solutions infused (Yagi and Bern, 1965).
In an attempt to locate the center for the control of the caudal
neurosecretory system in Tilapia, Yagi and Bern (1965) transected the
spinal cord. Following spinal cord transection the neurosecretory cells
did not respond to physiological stimulation although the local blood
supply to the cclls was not interrupted. The fact that the neurosecretory
cells did not spontaneously generate action potentials after transection
of the spinal cord although they retained their excitability suggests that
the center regulating the electrical activity of the caudal neurosecretory
system is within the brain proper (Yagi and Bern, 1965).
Spinal influences on the caudal neurosecretory system and olfactory
influences on the neurohypophysial system may well be similar in
mechanism. The pattern of impulses from stimulation of the olfactory
organ affects the discharge rate and the excitability of preoptic neurons
in the neurohypophysis and partially regulates the release of neurohypophysial hormones. It may well be that a similar sensory modulation
of hormonal release is the mechanism by means of which the caudal
neurosecretory system acts in osmoregulation.
D. Regeneration of the Spinal Cord
Spinal cord regeneration in larval (Hibbard, 1963; Koppanyi, 1955;
M a r h , 1959; Niazi, 1963) and adult fish (Clemente, 1954; Healcy, 1962;
Kirsche, 1965b ) was both anatomically and physiologically successful.
The regenerative capacity of the spinal cord of fish was unparalleled
among the vertebrates. This capacity extended from the simple regrowth
of axons across the lesion to reconstitution of the parenchyma into the
former neural cytoarchitectonics and complete restitution of new nerve
cells and glia.