58
J. N. BALL AND BRIDGET I. BAKER
numerous during gonadal maturation (Scruggs, 1951) while the PAS + ve
cells increase after the reproductive period. In the herring, Clupea, intense secretory activity has been seen in the pars intermedia during the
spawning period (Buchmann, 1940). It is not yet possible to offer functional interpretation of such observations, but the variety of conditions
affecting the activity of the pars intermedia cells underlines the possibility
that the hormone(s) produced by this region might be concerned in
functions other than control of pigmentation.
Both trout and eel pituitaries will synthesize and release MSH in uitro
after separation from the hypothalamus (Baker, 196713). In the case of
the eel, a cytological study of the cultured glands has failed to determine
the source of MSH, since both the PAS + ve and the PbH + ve cells
underwent gradual degranulation but retained an active appearance. In
the trout gland in uitro, the rapid decline in the stored MSH content of
the pituitary is associated with degranulation of the single PbH + ve
cell type, in the presence of active-looking nuclei and nucleoli (Baker,
1964b). In contrast, both cell types in the pars intermedia of ectopic
pituitary transplants in Poecilia fomosa presented a histological picture
of involution (Olivereau and Ball, 1966).
C. The Neurohypophysis in Teleosts
The neurohypophysis is composed of axonal nerve fibers, mostly nonmyelinated, originating from neuronal cell bodies in the hypothalamus.
These nerve fibers extend down the pituitary stalk (neurohypophysial
tract) into the pituitary gland to form the main bulk of the neurohypophysis (neurohypophysial core) which forms the center of the whole
gland. Many fibers terminate in the neurohypophysial core in close
relationship to blood vessels, and many other fibers extend beyond the
core and invade all regions of the adenohypophysis, an arrangement
peculiar to teleosts. Scattered ependymal cells and glial cells, collectively
termed "pituicytes," occur throughout the neuohypophysis but are
especially abundant in the posterior part of the core close to the pars
intermedia ( see chapter by Perks, this volume). Tubelike extensions of
the third ventricle bordered by pituicytes may penetrate into the posterior
neurohypophysial core, forming a hollow center in the fingerlike projections of the neurohypophysis into the pars intermedia (eel, Knowles and
Vollrath, 1965c, l W a , cf. primitive bony fishes, Section 111).
A special feature of the fish pituitary is the extensive penetration of
the pars intermedia by the neurohypophysis, the two regions mixing in
complex interdigitation. Teleosts have specialized further in having the
J. N. BALL AND BRIDGET I. BAKER
numerous during gonadal maturation (Scruggs, 1951) while the PAS + ve
cells increase after the reproductive period. In the herring, Clupea, intense secretory activity has been seen in the pars intermedia during the
spawning period (Buchmann, 1940). It is not yet possible to offer functional interpretation of such observations, but the variety of conditions
affecting the activity of the pars intermedia cells underlines the possibility
that the hormone(s) produced by this region might be concerned in
functions other than control of pigmentation.
Both trout and eel pituitaries will synthesize and release MSH in uitro
after separation from the hypothalamus (Baker, 196713). In the case of
the eel, a cytological study of the cultured glands has failed to determine
the source of MSH, since both the PAS + ve and the PbH + ve cells
underwent gradual degranulation but retained an active appearance. In
the trout gland in uitro, the rapid decline in the stored MSH content of
the pituitary is associated with degranulation of the single PbH + ve
cell type, in the presence of active-looking nuclei and nucleoli (Baker,
1964b). In contrast, both cell types in the pars intermedia of ectopic
pituitary transplants in Poecilia fomosa presented a histological picture
of involution (Olivereau and Ball, 1966).
C. The Neurohypophysis in Teleosts
The neurohypophysis is composed of axonal nerve fibers, mostly nonmyelinated, originating from neuronal cell bodies in the hypothalamus.
These nerve fibers extend down the pituitary stalk (neurohypophysial
tract) into the pituitary gland to form the main bulk of the neurohypophysis (neurohypophysial core) which forms the center of the whole
gland. Many fibers terminate in the neurohypophysial core in close
relationship to blood vessels, and many other fibers extend beyond the
core and invade all regions of the adenohypophysis, an arrangement
peculiar to teleosts. Scattered ependymal cells and glial cells, collectively
termed "pituicytes," occur throughout the neuohypophysis but are
especially abundant in the posterior part of the core close to the pars
intermedia ( see chapter by Perks, this volume). Tubelike extensions of
the third ventricle bordered by pituicytes may penetrate into the posterior
neurohypophysial core, forming a hollow center in the fingerlike projections of the neurohypophysis into the pars intermedia (eel, Knowles and
Vollrath, 1965c, l W a , cf. primitive bony fishes, Section 111).
A special feature of the fish pituitary is the extensive penetration of
the pars intermedia by the neurohypophysis, the two regions mixing in
complex interdigitation. Teleosts have specialized further in having the