2. THE NEUROHYPOPHYSIS
163
the central end of the severed axons, and a similar accumulation has been
seen after hypophysectomy in Anguilla anguilla and in Lophius pkcatorius (Stutinsky, 1953; Matty, 1966).
The connection of the preoptico-hypophysial tract to the pituitary is
notably different in Anguilla anguillu and in Lophius piscatorius (de
Beer, 1926; Charipper, 1937). The pituitary of Anguillu, and of other
relatively primitive teleost fish, is closely applied to the infundibulum, in
a way which is reminiscent of the preteleost groups. On the other hand,
the pituitary of Lophius, and of many other more advanced teleosts, is
suspended from the brain by a long stalk, which contains the distal
preoptico-hypophysial tract. Lophius represents an extreme case, since
its pituitary is not merely suspended and rotated, as in Esox lzlcius and
Cyprinus carpio, but it is drawn out to lie rostra1 to the brain (de Beer,
1926; Charipper, 1937). This unusual stalk has been used in an attempt to
determine whether neurosecretory cells are capable of conducting nervous
impulses. Potter and Loewenstein (1955) detected impulses which were
similar in conduction velocity (0.5 meter/sec) and in refractory period
(3-10 msec) to those of unmyelinated, Type C fibers from the frog. When
these investigators stimulated the hypothalamus close to the base of the
peduncle, the electrical responses of the stalk were variable and delayed,
which suggested the presence of synapses between neurosecretory cells
and other nerve cells. These results are interesting, but they are open to
slight doubt since a few nonneurosecretory fibers are known to be present
in the stalk. In some cases, the stalk appears to be a hollow structure;
Sathyanesan (196513) has noted that the cavity of the third ventricle extends into the remarkably long peduncle ( 4 3 mm) of Porichtfys notatus.
In the case of Platypoecilus maculutus, the stalk is funnel-shaped, and it
shows a decussation of nerve fibers at its narrowest point; after this the
axons continue into the pars nervosa, in association with blood vessels
( Oztan, 1963).
The preoptico-hypophysial tract of the more primitive teleosts, such
as Anguillu, enters the pituitary gland medially, and toward its caudal
region (Fig. 9 ) . It forms a dorsal area of neural tissue, which constitutes
the most discrete part of the pars nervosa. This pars nervosa is essentially
a thickening of the infundibular wall from which processes project ventrally; in structure, it is reminiscent of that of the preteleost bony fish
(Charipper, 1937; Dodd and Kerr, 1963; Leatherland et al., 1966; Klein,
1967). In more advanced teleosts such as Lophius piscatorius or Cyprinus
carpio, the relationships may appear to be altered by variations in the
direction of the incoming stalk, and by the tendency of the adenohypophysis to envelop the neural component, so that the pars nervosa
becomes the central core of the gland (Fig. 6; Dodd and Kerr, 1963).
163
the central end of the severed axons, and a similar accumulation has been
seen after hypophysectomy in Anguilla anguilla and in Lophius pkcatorius (Stutinsky, 1953; Matty, 1966).
The connection of the preoptico-hypophysial tract to the pituitary is
notably different in Anguilla anguillu and in Lophius piscatorius (de
Beer, 1926; Charipper, 1937). The pituitary of Anguillu, and of other
relatively primitive teleost fish, is closely applied to the infundibulum, in
a way which is reminiscent of the preteleost groups. On the other hand,
the pituitary of Lophius, and of many other more advanced teleosts, is
suspended from the brain by a long stalk, which contains the distal
preoptico-hypophysial tract. Lophius represents an extreme case, since
its pituitary is not merely suspended and rotated, as in Esox lzlcius and
Cyprinus carpio, but it is drawn out to lie rostra1 to the brain (de Beer,
1926; Charipper, 1937). This unusual stalk has been used in an attempt to
determine whether neurosecretory cells are capable of conducting nervous
impulses. Potter and Loewenstein (1955) detected impulses which were
similar in conduction velocity (0.5 meter/sec) and in refractory period
(3-10 msec) to those of unmyelinated, Type C fibers from the frog. When
these investigators stimulated the hypothalamus close to the base of the
peduncle, the electrical responses of the stalk were variable and delayed,
which suggested the presence of synapses between neurosecretory cells
and other nerve cells. These results are interesting, but they are open to
slight doubt since a few nonneurosecretory fibers are known to be present
in the stalk. In some cases, the stalk appears to be a hollow structure;
Sathyanesan (196513) has noted that the cavity of the third ventricle extends into the remarkably long peduncle ( 4 3 mm) of Porichtfys notatus.
In the case of Platypoecilus maculutus, the stalk is funnel-shaped, and it
shows a decussation of nerve fibers at its narrowest point; after this the
axons continue into the pars nervosa, in association with blood vessels
( Oztan, 1963).
The preoptico-hypophysial tract of the more primitive teleosts, such
as Anguillu, enters the pituitary gland medially, and toward its caudal
region (Fig. 9 ) . It forms a dorsal area of neural tissue, which constitutes
the most discrete part of the pars nervosa. This pars nervosa is essentially
a thickening of the infundibular wall from which processes project ventrally; in structure, it is reminiscent of that of the preteleost bony fish
(Charipper, 1937; Dodd and Kerr, 1963; Leatherland et al., 1966; Klein,
1967). In more advanced teleosts such as Lophius piscatorius or Cyprinus
carpio, the relationships may appear to be altered by variations in the
direction of the incoming stalk, and by the tendency of the adenohypophysis to envelop the neural component, so that the pars nervosa
becomes the central core of the gland (Fig. 6; Dodd and Kerr, 1963).