72
J. N. BALL AND BRIDGET I. BAKER
Lepidogobius (Kobayashi et al., 1959), and Honma and Tamura ( 1967)
found that both NPO and NLT fibers terminated on neurohypophysial
blood vessels in Salvelinus. Nucleus preopticus fibers terminate on neurohypophysial capillaries and also among proximal pars distalis cells in
Porichthys (Sathyanesan, 1965a).
3. A POSSIBLE THIRD ROUTE VIA THE THIRD VENTRICLE
Cellular processes from cells of both the NPO and the NLT have
been observed to penetrate the ependyma and project into the third
ventricle, with evidence of secretion into the ventricle ( Stahl and Leray,
1962; Samuelsson and Fridberg, 1964; Sathyanesan, 1966; Oztan, 1967,
and references therein). Similar appearances have been described in
other vertebrate groups (Bern and Knowles, 1966; Oztan, 1967). Stahl
and Leray (1962) suggested that cells of the NLT might release their
secretion into the third ventricle, to be transported thence by capillaries
to the pituitary, or by being absorbed by the specialized ependymal cells
lining the infundibular recess which appear to send fibers containing
PAS + ve or AF + ve material toward the pituitary (Stahl and Leray,
1962; Honma and Tamura, 1967). In view of the evidence that NPO and
NLT fibers penetrate the pituitary directly, it is difficult to assess the
meaning of these appearances in terms of hypothalamic control. We
should note, also, that some workers consider the specialized ependymal
cells as secretory (into the third ventricle) rather than absorptive
( Nishioka et al., 1964).
Thus, anatomically, the neurosecretory fibers of the neurohypophysis
display features that strongly suggest they are concerned with regulation
of adenohypophysial function. In addition (Section 11, C), the neurohypophysis contains the biologically active octapeptides, AVT and IT.
These or similar principles have well-documented systemic hormonal
functions in tetrapods, and there is some evidence, perhaps not conclusive, that AVT and IT have peripheral actions in teleosts (Section 11, C
and the chapter by Perks, this volume). How these neurohypophysial
principles relate to the fiber types of the neurohypophysis is not certain, although the work of Lederis (1962, 1964) suggests that in Gadus
and Salmo AVT is associated with Type A granules; this agrees with
the suggestion of Knowles (1965) that Type A fibers may be concerned with elaboration of peptide molecules, whereas Type B fibers may
secrete some nonpeptide material, possibly aromatic amines in line with
indications from other vertebrates (rat, Kobayashi et al., 1966; toad,
Iturriza, 1964, 1966; and frog, Ito, 1968). The problem is to reconcile the
histological and ultrastructural evidence that Type A fibers are involved
J. N. BALL AND BRIDGET I. BAKER
Lepidogobius (Kobayashi et al., 1959), and Honma and Tamura ( 1967)
found that both NPO and NLT fibers terminated on neurohypophysial
blood vessels in Salvelinus. Nucleus preopticus fibers terminate on neurohypophysial capillaries and also among proximal pars distalis cells in
Porichthys (Sathyanesan, 1965a).
3. A POSSIBLE THIRD ROUTE VIA THE THIRD VENTRICLE
Cellular processes from cells of both the NPO and the NLT have
been observed to penetrate the ependyma and project into the third
ventricle, with evidence of secretion into the ventricle ( Stahl and Leray,
1962; Samuelsson and Fridberg, 1964; Sathyanesan, 1966; Oztan, 1967,
and references therein). Similar appearances have been described in
other vertebrate groups (Bern and Knowles, 1966; Oztan, 1967). Stahl
and Leray (1962) suggested that cells of the NLT might release their
secretion into the third ventricle, to be transported thence by capillaries
to the pituitary, or by being absorbed by the specialized ependymal cells
lining the infundibular recess which appear to send fibers containing
PAS + ve or AF + ve material toward the pituitary (Stahl and Leray,
1962; Honma and Tamura, 1967). In view of the evidence that NPO and
NLT fibers penetrate the pituitary directly, it is difficult to assess the
meaning of these appearances in terms of hypothalamic control. We
should note, also, that some workers consider the specialized ependymal
cells as secretory (into the third ventricle) rather than absorptive
( Nishioka et al., 1964).
Thus, anatomically, the neurosecretory fibers of the neurohypophysis
display features that strongly suggest they are concerned with regulation
of adenohypophysial function. In addition (Section 11, C), the neurohypophysis contains the biologically active octapeptides, AVT and IT.
These or similar principles have well-documented systemic hormonal
functions in tetrapods, and there is some evidence, perhaps not conclusive, that AVT and IT have peripheral actions in teleosts (Section 11, C
and the chapter by Perks, this volume). How these neurohypophysial
principles relate to the fiber types of the neurohypophysis is not certain, although the work of Lederis (1962, 1964) suggests that in Gadus
and Salmo AVT is associated with Type A granules; this agrees with
the suggestion of Knowles (1965) that Type A fibers may be concerned with elaboration of peptide molecules, whereas Type B fibers may
secrete some nonpeptide material, possibly aromatic amines in line with
indications from other vertebrates (rat, Kobayashi et al., 1966; toad,
Iturriza, 1964, 1966; and frog, Ito, 1968). The problem is to reconcile the
histological and ultrastructural evidence that Type A fibers are involved