62
J. N. BALL AND BRIDGET I. BAKER
and also from the NPO (Tuurala, 1957; Fridberg and Olsson, 1959; Arvy
et al., 1954, 1959). Eels adapted to seawater have less stainable material
in the neurohypophysial core than freshwater eels (Schiebler and Hartmann, 1963) ; on the other hand, the total amount of stainable material in
the hypothalamo-neurohypophysial tracts did not appear to alter in
response to changing salinity in the eel (Leatherland, 1967) or the goby,
Clevelandia ios (Uemura et al., 1963), nor did the material in the neurohypophysial core change appreciably in Mugil subjected to progressive
reduction in salinity ( Olivereau, 1968). Gmterosteus transferred from
one-third seawater to freshwater exhibited a rapid loss of stainable
material (Fridberg and Olsson, 1959), while in hypotonic media, or in
response to dehydration, stainable material increased in the pars magnocellularis of the NPO of Misgurnus, but decreased in the parvocellular
elements, suggesting different functions for the two components of the
NPO (Szab6 and Molnhr, 1965).
In the neurohypophysis of eels kept for long periods in deionized
water, Olivereau (1%7b) found that stainable material tended to increase
at first but then decrease, the neurohypophysis being compressed by
hypertrophy of the pars intermedia (Section 11, B, 6 ) .
Changes such as these have usually been interpreted as indicating
release or retention of neurohypophysial factors in response to osmotic
demands, there being some experimental evidence that neurohypophysial
factors, especially arginine vasotocin, may be concerned in ionic regulation and water balance in teleosts (Maetz et al., 1964; Dodd et al., 1966;
Motais and Maetz, 1967; J#rgensen and Larsen, 1967; Maetz and Rankin,
1969; see chapter by Perks, this volume). However, in some of the experiments in which fish were transferred between different salinities, the
osmotic conditions imposed must have been very severe, and it is
possible that the neurohypophysial changes could have been nonspecific
responses to stress. Olivereau and Olivereau (1968) recently reported that
surgical stress led to rarefaction of stainable material in the eel neurohypophysis, and stress has also been reported to reduce the material in
the rat neurohypophysis ( Rodeck and Braukmann, 1966). Interpretation
is all the more difficult, since ample evidence shows that many stress conditions in mammals, apart from osmotic changes, lead to discharge of the
neurohypophysial hormones (see, e.g., Tata and Buzalkov, l!366). Furthermore, it must be remembered that the amount of stainable material
in the neurohypophysis results from a balance between synthesis and
release. In order properly to interpret alterations in the amount of visible
material, one requires information about the cytological features of the
neuron cell body that would indicate low or high synthetic activity, such
as nuclear and nucleolar size and Golgi status. Failing this kind of cytological information, it is desirable to have studies on the biological activity
J. N. BALL AND BRIDGET I. BAKER
and also from the NPO (Tuurala, 1957; Fridberg and Olsson, 1959; Arvy
et al., 1954, 1959). Eels adapted to seawater have less stainable material
in the neurohypophysial core than freshwater eels (Schiebler and Hartmann, 1963) ; on the other hand, the total amount of stainable material in
the hypothalamo-neurohypophysial tracts did not appear to alter in
response to changing salinity in the eel (Leatherland, 1967) or the goby,
Clevelandia ios (Uemura et al., 1963), nor did the material in the neurohypophysial core change appreciably in Mugil subjected to progressive
reduction in salinity ( Olivereau, 1968). Gmterosteus transferred from
one-third seawater to freshwater exhibited a rapid loss of stainable
material (Fridberg and Olsson, 1959), while in hypotonic media, or in
response to dehydration, stainable material increased in the pars magnocellularis of the NPO of Misgurnus, but decreased in the parvocellular
elements, suggesting different functions for the two components of the
NPO (Szab6 and Molnhr, 1965).
In the neurohypophysis of eels kept for long periods in deionized
water, Olivereau (1%7b) found that stainable material tended to increase
at first but then decrease, the neurohypophysis being compressed by
hypertrophy of the pars intermedia (Section 11, B, 6 ) .
Changes such as these have usually been interpreted as indicating
release or retention of neurohypophysial factors in response to osmotic
demands, there being some experimental evidence that neurohypophysial
factors, especially arginine vasotocin, may be concerned in ionic regulation and water balance in teleosts (Maetz et al., 1964; Dodd et al., 1966;
Motais and Maetz, 1967; J#rgensen and Larsen, 1967; Maetz and Rankin,
1969; see chapter by Perks, this volume). However, in some of the experiments in which fish were transferred between different salinities, the
osmotic conditions imposed must have been very severe, and it is
possible that the neurohypophysial changes could have been nonspecific
responses to stress. Olivereau and Olivereau (1968) recently reported that
surgical stress led to rarefaction of stainable material in the eel neurohypophysis, and stress has also been reported to reduce the material in
the rat neurohypophysis ( Rodeck and Braukmann, 1966). Interpretation
is all the more difficult, since ample evidence shows that many stress conditions in mammals, apart from osmotic changes, lead to discharge of the
neurohypophysial hormones (see, e.g., Tata and Buzalkov, l!366). Furthermore, it must be remembered that the amount of stainable material
in the neurohypophysis results from a balance between synthesis and
release. In order properly to interpret alterations in the amount of visible
material, one requires information about the cytological features of the
neuron cell body that would indicate low or high synthetic activity, such
as nuclear and nucleolar size and Golgi status. Failing this kind of cytological information, it is desirable to have studies on the biological activity