2. THE NEUROHYPOPHYSIS
125
freshwater and those immersed for a short period in more concentrated
saline (4 hr in 45% seawater; Bentley and Follett, 1963).
A completely different action of neurohypophysial peptides has been
suggested by the fact that arginine vasotocin, in doses similar to those
which affect sodium metabolism, will cause a rapid rise in blood sugar
and in muscle glycogen (Bentley and Follett, 1965). An injection of
arginine vasotocin amounting to 1.2 mpmoles, or 150 mU oxytocic activity (as calculated from W. H. Sawyer, 1965b), resulted in at least 40%
rise in the blood glucose level, possibly by a fat mobilizing action. The
dose used was high, and the same considerations which were dealt with
under sodium metabolism apply here. Again, the physiological significance of the response is uncertain.
The lamprey neurohypophysis may be of local as well as of systemic
importance, but the only evidence available, at present, is from histology.
W. H. Sawyer et al. (1960) have pointed out that the close relationship
between the neurohypophysis, the intervening blood capillaries, and the
pars intermedia suggest that neurohypophysial peptides could pass to
the adenohypophysis and modulate its function. It is possible that this
action could be of special importance at metamorphosis and spawning.
Van der Kamer and Schreurs (1959) have shown the presence of a considerable accumulation of neurosecretion in the ammocoete larva of
Lampetra planeri; however, there is a dramatic loss of this material at
metamorphosis. During metamorphosis, neurosecretion is found mainly
in the nerve terminals which border capillaries that enter the adenohypophysis. It is also found in the fibers which reach the ependyma.
Metamorphosis is accompanied by activity of the pars intermedia, and
the lamprey takes on an adult color pattern (Dodd et al., 1960). After
spawning, the neurohypophysis is almost empty of granules (van der
Kamer and Schreurs, 1959). These observations are highly suggestive of
involvement of the neurohypophysis in metamorphosis and spawning, but
they do not prove that there is a direct relationship. There is a small possibility that the changes in neurosecretion are linked to the emergence of
the larva from the dark mud. Oztan and Gorbman (1960a,b) have seen
that the distribution of neurosecretion in Lampetra lamottei and Petromyzon marinus is influenced by light. When these species are placed in
continuous darkness there is a dense accumulation of neurosecretion in
the preoptic nucleus and its axons. When the lampreys are returned to
continuous light, the material is depleted. However, unlike the changes
seen in metamorphosis, the nerve terminals of the pars nervosa are not
affected. It is possible that these various observations indicate a neurohypophysial control of the pars intermedia, but more direct information
is needed before any conclusions can be drawn.
125
freshwater and those immersed for a short period in more concentrated
saline (4 hr in 45% seawater; Bentley and Follett, 1963).
A completely different action of neurohypophysial peptides has been
suggested by the fact that arginine vasotocin, in doses similar to those
which affect sodium metabolism, will cause a rapid rise in blood sugar
and in muscle glycogen (Bentley and Follett, 1965). An injection of
arginine vasotocin amounting to 1.2 mpmoles, or 150 mU oxytocic activity (as calculated from W. H. Sawyer, 1965b), resulted in at least 40%
rise in the blood glucose level, possibly by a fat mobilizing action. The
dose used was high, and the same considerations which were dealt with
under sodium metabolism apply here. Again, the physiological significance of the response is uncertain.
The lamprey neurohypophysis may be of local as well as of systemic
importance, but the only evidence available, at present, is from histology.
W. H. Sawyer et al. (1960) have pointed out that the close relationship
between the neurohypophysis, the intervening blood capillaries, and the
pars intermedia suggest that neurohypophysial peptides could pass to
the adenohypophysis and modulate its function. It is possible that this
action could be of special importance at metamorphosis and spawning.
Van der Kamer and Schreurs (1959) have shown the presence of a considerable accumulation of neurosecretion in the ammocoete larva of
Lampetra planeri; however, there is a dramatic loss of this material at
metamorphosis. During metamorphosis, neurosecretion is found mainly
in the nerve terminals which border capillaries that enter the adenohypophysis. It is also found in the fibers which reach the ependyma.
Metamorphosis is accompanied by activity of the pars intermedia, and
the lamprey takes on an adult color pattern (Dodd et al., 1960). After
spawning, the neurohypophysis is almost empty of granules (van der
Kamer and Schreurs, 1959). These observations are highly suggestive of
involvement of the neurohypophysis in metamorphosis and spawning, but
they do not prove that there is a direct relationship. There is a small possibility that the changes in neurosecretion are linked to the emergence of
the larva from the dark mud. Oztan and Gorbman (1960a,b) have seen
that the distribution of neurosecretion in Lampetra lamottei and Petromyzon marinus is influenced by light. When these species are placed in
continuous darkness there is a dense accumulation of neurosecretion in
the preoptic nucleus and its axons. When the lampreys are returned to
continuous light, the material is depleted. However, unlike the changes
seen in metamorphosis, the nerve terminals of the pars nervosa are not
affected. It is possible that these various observations indicate a neurohypophysial control of the pars intermedia, but more direct information
is needed before any conclusions can be drawn.