1. THE PITUITrARY GLAND
63
present in the neurohypophysis parallel to the changes in the stainable
material. Such studies are almost nonexistent in fishes, but one is outstanding. Lederis (1962) showed that a high vasopressor activity is
associated with those fractions of Gadus pituitary that contain particles
resembling neurosecretory granules. In Salmo gairdneri, Lederis ( 1963,
1964) further found that on transfer to seawater there was a transitory
decrease in the number of granules in some of the neurohypophysial
fibers, which was correlated with a 50% reduction in the pituitary content
of AVT. This suggests perhaps that this particular neurohypophysial
principle is associated with the granules, although as Lederis emphasized
the parallelism between AVT content and disappearance of these granules
was very imperfect, only relatively few fibers displaying loss of granules,
and this author emphasized that lack of stainability or of electron density
are not necessarily related to absence of neurohypophysial principles.
Apart from alterations in neurosecretory material in relation to osmotic
changes, the number of synaptic contacts between Type A1 fibers and
pituicytes ( in neurohypophysial projections into the pars intermedia ) was
observed to increase when Anguillu was transferred to seawater (Knowles
and Vollrath, 1966a).
There are other observations which relate fluctuations in the amount
of stainable material to the reproductive cycle. Sawyer and Pickford
(1963) reported a depletion of pituitary content of isotocin, but not AVT,
during the reproductive season of female Fundulus heteroclitus, although
not in the male. Neurohypophysial factors play a role in spawning behavior in this fish (Wilhelmi et al., 1955), and in studying the pituitary
Sokol (1961) found a decrease in the stainable material associated with
the spawning period in both sexes. Similar observations were made in
both sexes of Tor (Barbus) tor (Rai, 1966a,b). A reduction in the amount
of stainable material in the neurohypophysis occurs during oviposition
in Oryzias, which may be correlated with the demonstration that injections of neurohypophysial preparations will stimulate oviposition in this
fish (Egami and Ishii, 1962). Olivereau ( 1967a) found a rarefaction of
stainable material in the neurohypophysis of female eels brought to
sexual maturity by treatment with a partially pursed carp gonadotropin
extract, and a similar change occurred in male eels brought to maturity
by injections of human chorionic gonadotropin (Olivereau and Herlant,
1960). The significance of this change is obscure, since the mechanism
whereby exogenous gonadotropins activate the eel gonadotrops is unknown (see Section 11, B, 4). Oztan ( 1966b) observed depletion of A F +
ve material and of the ultrastructural granules from the NPO cells of
Zoarces viviparus during the process of gonad maturation and the
accumulation of these materials in the cells during early pregnancy.
Several workers have been interested in the functional relationship
63
present in the neurohypophysis parallel to the changes in the stainable
material. Such studies are almost nonexistent in fishes, but one is outstanding. Lederis (1962) showed that a high vasopressor activity is
associated with those fractions of Gadus pituitary that contain particles
resembling neurosecretory granules. In Salmo gairdneri, Lederis ( 1963,
1964) further found that on transfer to seawater there was a transitory
decrease in the number of granules in some of the neurohypophysial
fibers, which was correlated with a 50% reduction in the pituitary content
of AVT. This suggests perhaps that this particular neurohypophysial
principle is associated with the granules, although as Lederis emphasized
the parallelism between AVT content and disappearance of these granules
was very imperfect, only relatively few fibers displaying loss of granules,
and this author emphasized that lack of stainability or of electron density
are not necessarily related to absence of neurohypophysial principles.
Apart from alterations in neurosecretory material in relation to osmotic
changes, the number of synaptic contacts between Type A1 fibers and
pituicytes ( in neurohypophysial projections into the pars intermedia ) was
observed to increase when Anguillu was transferred to seawater (Knowles
and Vollrath, 1966a).
There are other observations which relate fluctuations in the amount
of stainable material to the reproductive cycle. Sawyer and Pickford
(1963) reported a depletion of pituitary content of isotocin, but not AVT,
during the reproductive season of female Fundulus heteroclitus, although
not in the male. Neurohypophysial factors play a role in spawning behavior in this fish (Wilhelmi et al., 1955), and in studying the pituitary
Sokol (1961) found a decrease in the stainable material associated with
the spawning period in both sexes. Similar observations were made in
both sexes of Tor (Barbus) tor (Rai, 1966a,b). A reduction in the amount
of stainable material in the neurohypophysis occurs during oviposition
in Oryzias, which may be correlated with the demonstration that injections of neurohypophysial preparations will stimulate oviposition in this
fish (Egami and Ishii, 1962). Olivereau ( 1967a) found a rarefaction of
stainable material in the neurohypophysis of female eels brought to
sexual maturity by treatment with a partially pursed carp gonadotropin
extract, and a similar change occurred in male eels brought to maturity
by injections of human chorionic gonadotropin (Olivereau and Herlant,
1960). The significance of this change is obscure, since the mechanism
whereby exogenous gonadotropins activate the eel gonadotrops is unknown (see Section 11, B, 4). Oztan ( 1966b) observed depletion of A F +
ve material and of the ultrastructural granules from the NPO cells of
Zoarces viviparus during the process of gonad maturation and the
accumulation of these materials in the cells during early pregnancy.
Several workers have been interested in the functional relationship