1. THE PITUITARY GLAND
55
phores are under dual control, neural and humoral, and in some species
( e.g., AnguiZZu ) humoral control predominates, so that even innervated
melanophores will respond to MSH, while in other species (e.g., FunduZus and Poecilia ) the neural component predominates and the melanophores must be denervated to demonstrate experimentally their response
to MSH (Waring, 1963; Ball and Slicher, 1962; see chapter by Fujii,
Volume I11 ) . In both Anguillu and Poecilia, the adrenocortical inhibitor
SU 4885 causes melanin dispersion, and in Anguillu (but not in Poecilia)
this is accompanied by degranulation and hypertrophy of the PbH + ve
cells, the PAS + ve cells remaining unchanged (Olivereau, 1965; Ball
and Olivereau, 1 M ) . However, in both species the ACTH cells were
activated by the drug (Section 11, B, 2), and since mammalian ACTH
possesses intrinsic MSH-like properties, the melanophore response in
Anguilla could be an effect of endogenous ACTH. Furthermore, the
darkening in Poecilia in response to SU 4885 involved innervated melanophores, which in this species are not directly responsive to exogenous
MSH or ACTH (Ball and Slicher, 1962), and it is probable that some
narcotic property of the drug was responsible for this effect in PoeciZia,
if not, indeed, in Anguillu.
In Salmo salar, the cells of the pars intermedia were inactive in the
parr during the winter months, became more active in the spring, and
were extremely active during the smolt stage (i.e., the stage of migration
to the sea), undergoing intense mitotic activity so that the whole region
enlarged. Olivereau (1954) correlated this with the rapid deposition of
melanin pigment in the smolt pectoral fins. In the adult salmon migrating
upstream from sea to spawning grounds, the pars intermedia appeared
to be degenerate, but was restored in spawning and postspawning fish,
although not as active as in the smolt (Olivereau, 1954). The blind cavefish, Cuecobarbus geertsi, is characterized by a total lack of melanin pigmentation, and Olivereau and Herlant (1954) found in correlation that
the cells of the pars intermedia were inactive and “embryonic” in
character.
Increased activity of the pars intermedia and increased melanin dispersion occur in Anguillu during a prolonged period in deionized water,
the whole pars intermedia becoming hypertrophied ( Olivereau, 196%).
The PAS + ve cells undergo a rapid and intense degranulation and hypertrophy, while the PbH + ve cells only degranulate slowly (Figs. 21 and
22) . Since melanin dispersion also develops slowly, Olivereau tentatively
suggested that the PbH cells might be the source of MSH. This conclusion would disagree with the results already cited from background adaptation of Cichlasoma and BZennius. Some role of the pars intermedia in
electrolyte regulation may be inferred from these results of Olivereau,
55
phores are under dual control, neural and humoral, and in some species
( e.g., AnguiZZu ) humoral control predominates, so that even innervated
melanophores will respond to MSH, while in other species (e.g., FunduZus and Poecilia ) the neural component predominates and the melanophores must be denervated to demonstrate experimentally their response
to MSH (Waring, 1963; Ball and Slicher, 1962; see chapter by Fujii,
Volume I11 ) . In both Anguillu and Poecilia, the adrenocortical inhibitor
SU 4885 causes melanin dispersion, and in Anguillu (but not in Poecilia)
this is accompanied by degranulation and hypertrophy of the PbH + ve
cells, the PAS + ve cells remaining unchanged (Olivereau, 1965; Ball
and Olivereau, 1 M ) . However, in both species the ACTH cells were
activated by the drug (Section 11, B, 2), and since mammalian ACTH
possesses intrinsic MSH-like properties, the melanophore response in
Anguilla could be an effect of endogenous ACTH. Furthermore, the
darkening in Poecilia in response to SU 4885 involved innervated melanophores, which in this species are not directly responsive to exogenous
MSH or ACTH (Ball and Slicher, 1962), and it is probable that some
narcotic property of the drug was responsible for this effect in PoeciZia,
if not, indeed, in Anguillu.
In Salmo salar, the cells of the pars intermedia were inactive in the
parr during the winter months, became more active in the spring, and
were extremely active during the smolt stage (i.e., the stage of migration
to the sea), undergoing intense mitotic activity so that the whole region
enlarged. Olivereau (1954) correlated this with the rapid deposition of
melanin pigment in the smolt pectoral fins. In the adult salmon migrating
upstream from sea to spawning grounds, the pars intermedia appeared
to be degenerate, but was restored in spawning and postspawning fish,
although not as active as in the smolt (Olivereau, 1954). The blind cavefish, Cuecobarbus geertsi, is characterized by a total lack of melanin pigmentation, and Olivereau and Herlant (1954) found in correlation that
the cells of the pars intermedia were inactive and “embryonic” in
character.
Increased activity of the pars intermedia and increased melanin dispersion occur in Anguillu during a prolonged period in deionized water,
the whole pars intermedia becoming hypertrophied ( Olivereau, 196%).
The PAS + ve cells undergo a rapid and intense degranulation and hypertrophy, while the PbH + ve cells only degranulate slowly (Figs. 21 and
22) . Since melanin dispersion also develops slowly, Olivereau tentatively
suggested that the PbH cells might be the source of MSH. This conclusion would disagree with the results already cited from background adaptation of Cichlasoma and BZennius. Some role of the pars intermedia in
electrolyte regulation may be inferred from these results of Olivereau,