1. THE PITUITARY GLAND
59
anterior part of the neurohypophysis penetrate the pars distalis with
fingerlike processes, although in a less intricate manner than in the pars
intermedia. This ramification of the neurohypophysis into the adenohypophysis is not present in salmonids at hatching (Olivereau, 1954;
Klein, 1967), and thereafter it develops slowly and is only very slight
even at 4 months in the trout (Klein, 1967). Similarly in the elver, there
is only slight indication of the extensive penetration of the pars intermedia
by neurohypophysial processes, so characteristic of the adult eel (Knowles
and Vollrath, 1966c ) .
Two types of neurohypophysial fibers may be distinguished with the
light microscope, depending on whether or not the material contained
in the fiber will stain with the classic neurosecretory stains, AF, chrome
alum hematoxylin (CAH), aldehyde thionin (ATh), and AB. The two
fiber types appear to correspond to the Type A (“stainable”) and Type
B (“nonstainable”) fibers distinguished at the ultrastructural level by
Knowles ( see Knowles and Vollrath, 1966a,b). Neurosecretory material
in both “stainable” and “nonstainable” fibers may accumulate in the neurohypophysis in large masses termed “Herring bodies.”
The neurohypophysis and the neurosecretory cells of the hypothalamus (mainly but perhaps not all, collected into groups termed ‘%hypothalamic nuclei”) thus form a functional unit concerned in the synthesis
transport and release of neurosecretory materials (see chapter by Perks,
this volume). They also display, anatomically at least, the fundamental
feature of neurosecretory elements, in that they form “a final common
pathway linking the nervous and endocrine systems” (Bern and Knowles,
1966, to which the reader is referred for an authoritative discussion of
neurosecretion in general).
Various octapeptides with characteristic biological properties have
been isolated from the pituitary in all vertebrate groups and in many
cases have been shown to be associated with the hypothalamus and neurohypophysis (see chapter by Perks, this volume). It is these octapeptides
which are believed to be synthesized in the hypothalamic nuclei and
passed down to the neurohypophysial core, probably contained in or
associated with ultrastructural neurosecretory granules, which are generally considered equivalent to the stainable material seen with the light
microscope. In teleosts, two octapeptides have been found in the pituitary,
arginine vasotocin (AVT) and isotocin (IT), and these are thought to
be the neurohypophysial principles of these fishes ( Sawyer, 196613 ) .
1. “STAINABLE” FIBERS, PROBABLY KNOWLES’ TYPE A
The stainable fibers probably mostly originate from the nucleus preopticus (NPO) of the hypothalamus (see chapter by Bernstein, Volume
59
anterior part of the neurohypophysis penetrate the pars distalis with
fingerlike processes, although in a less intricate manner than in the pars
intermedia. This ramification of the neurohypophysis into the adenohypophysis is not present in salmonids at hatching (Olivereau, 1954;
Klein, 1967), and thereafter it develops slowly and is only very slight
even at 4 months in the trout (Klein, 1967). Similarly in the elver, there
is only slight indication of the extensive penetration of the pars intermedia
by neurohypophysial processes, so characteristic of the adult eel (Knowles
and Vollrath, 1966c ) .
Two types of neurohypophysial fibers may be distinguished with the
light microscope, depending on whether or not the material contained
in the fiber will stain with the classic neurosecretory stains, AF, chrome
alum hematoxylin (CAH), aldehyde thionin (ATh), and AB. The two
fiber types appear to correspond to the Type A (“stainable”) and Type
B (“nonstainable”) fibers distinguished at the ultrastructural level by
Knowles ( see Knowles and Vollrath, 1966a,b). Neurosecretory material
in both “stainable” and “nonstainable” fibers may accumulate in the neurohypophysis in large masses termed “Herring bodies.”
The neurohypophysis and the neurosecretory cells of the hypothalamus (mainly but perhaps not all, collected into groups termed ‘%hypothalamic nuclei”) thus form a functional unit concerned in the synthesis
transport and release of neurosecretory materials (see chapter by Perks,
this volume). They also display, anatomically at least, the fundamental
feature of neurosecretory elements, in that they form “a final common
pathway linking the nervous and endocrine systems” (Bern and Knowles,
1966, to which the reader is referred for an authoritative discussion of
neurosecretion in general).
Various octapeptides with characteristic biological properties have
been isolated from the pituitary in all vertebrate groups and in many
cases have been shown to be associated with the hypothalamus and neurohypophysis (see chapter by Perks, this volume). It is these octapeptides
which are believed to be synthesized in the hypothalamic nuclei and
passed down to the neurohypophysial core, probably contained in or
associated with ultrastructural neurosecretory granules, which are generally considered equivalent to the stainable material seen with the light
microscope. In teleosts, two octapeptides have been found in the pituitary,
arginine vasotocin (AVT) and isotocin (IT), and these are thought to
be the neurohypophysial principles of these fishes ( Sawyer, 196613 ) .
1. “STAINABLE” FIBERS, PROBABLY KNOWLES’ TYPE A
The stainable fibers probably mostly originate from the nucleus preopticus (NPO) of the hypothalamus (see chapter by Bernstein, Volume