72
JERALD J. BERNSTEIN
that urophysial extracts acted like certain neurohypophysial factors, in
particular a prolactinlike hormone (see section on diencephalon) . Urophysial extracts affected sodium ion influx across the gills, renal diaresis,
and sodium ion excretion. It is also interesting to note that although a
prolactinlike hormone was present, urophysial extract was not sufficient
to sustain hypophysectomized Fundulus heteroclitus in freshwater.
Therefore, the prolactinlike influence of the extract was not of sufficient
quantity to maintain the animal without supplementation by neurohypophysial function (Pickford et al., 1965).
The urophysis has been implicated in the regulation of buoyancy in
the fish (Enami, 1959). However, further attempts to demonstrate this
function have been unsuccessful (Fridberg and Bern, 1968; Kawamoto,
1962). It appears then that the caudal neurosecretory system is a neural
center within the spinal cord whose discharge to its endorgan (urophysis) results in the release of substances that regulate the osmotic
balance in fish.
C. Electrophysiological Properties of the Neurosecretory Cells
and Intramedullary Neurons
The discharge patterns of the caudal neurosecretory cells (Dahlgren
cells) have been recorded. In general, the response of the cells was
different from that of the other spinal neurons in the area. Many species
of fish have been utilized such as skates, Raja (Bennett and Fox, 1962),
the Japanese eel, Anguillu japonica (Ishibashi, 1962; Morita et al., 1961),
the fluke, Paralichthys dentatus (Bennett and Fox, 1962) and Tilapia
mossambica (Yagi and Bern, 1963, 1965). The results of the former
experiments demonstrate an interesting parallel between the function of
the caudal neurosecretory and the neurohypophysial system. Comparisons
can be made between the influence of osmotic changes owing to
sodium ion flux on the discharge rate of neurosecretory cells as well
as the influence of higher nervous system centers on the activity of cells
within the secretory systems.
Caudal neurosecretory neurons were distinguished from other intramedullary neurons by several characteristics (Bennett and Fox, 1962).
Orthodromic subthreshold stimulation of intramedullary neurons were
obtained by stimulation of the spinal cord rostra1 to the unit (stimulation of descending pathways). This stimulation produced graded subthreshold postsynaptic potentials in the neuron. Increased stimulus intensity increased the amplitude of the postsynaptic potential until adequate
to produce a spike. Antidromic spikes also can be evoked within intra-
JERALD J. BERNSTEIN
that urophysial extracts acted like certain neurohypophysial factors, in
particular a prolactinlike hormone (see section on diencephalon) . Urophysial extracts affected sodium ion influx across the gills, renal diaresis,
and sodium ion excretion. It is also interesting to note that although a
prolactinlike hormone was present, urophysial extract was not sufficient
to sustain hypophysectomized Fundulus heteroclitus in freshwater.
Therefore, the prolactinlike influence of the extract was not of sufficient
quantity to maintain the animal without supplementation by neurohypophysial function (Pickford et al., 1965).
The urophysis has been implicated in the regulation of buoyancy in
the fish (Enami, 1959). However, further attempts to demonstrate this
function have been unsuccessful (Fridberg and Bern, 1968; Kawamoto,
1962). It appears then that the caudal neurosecretory system is a neural
center within the spinal cord whose discharge to its endorgan (urophysis) results in the release of substances that regulate the osmotic
balance in fish.
C. Electrophysiological Properties of the Neurosecretory Cells
and Intramedullary Neurons
The discharge patterns of the caudal neurosecretory cells (Dahlgren
cells) have been recorded. In general, the response of the cells was
different from that of the other spinal neurons in the area. Many species
of fish have been utilized such as skates, Raja (Bennett and Fox, 1962),
the Japanese eel, Anguillu japonica (Ishibashi, 1962; Morita et al., 1961),
the fluke, Paralichthys dentatus (Bennett and Fox, 1962) and Tilapia
mossambica (Yagi and Bern, 1963, 1965). The results of the former
experiments demonstrate an interesting parallel between the function of
the caudal neurosecretory and the neurohypophysial system. Comparisons
can be made between the influence of osmotic changes owing to
sodium ion flux on the discharge rate of neurosecretory cells as well
as the influence of higher nervous system centers on the activity of cells
within the secretory systems.
Caudal neurosecretory neurons were distinguished from other intramedullary neurons by several characteristics (Bennett and Fox, 1962).
Orthodromic subthreshold stimulation of intramedullary neurons were
obtained by stimulation of the spinal cord rostra1 to the unit (stimulation of descending pathways). This stimulation produced graded subthreshold postsynaptic potentials in the neuron. Increased stimulus intensity increased the amplitude of the postsynaptic potential until adequate
to produce a spike. Antidromic spikes also can be evoked within intra-