2. THE NEUROHYPOPHYSIS
167
Legait and Legait, 1957; see also Fridberg and Olsson, 1959, and Lederis,
1965). In general, neurosecretory material may occur throughout the
processes, or it may be densely packed toward the boundary with the
pars intermedia (Dodd and Kerr, 1963). It occurs as irregular granules,
or as beadlike droplets ( Platypoecilus maculutus; Oztan, 1963), but
Herring bodies, which are present in adult fish, appear to be absent in
juvenile specimens ( Lebistes reticulatus, Follenius and Porte, 1962;
Porichthys notatus, Sathyanesan, 1965b). Electron microscopy has shown
that the neurosecretory material consists of elementary vesicles similar in
size and form to those of the preoptic nucleus ( Gadus morrhua; Lederis,
1962; AnguiUa anguilla; Knowles and Vollrath, 1966a; Leatherland, 1967).
If the results of different workers are compared, there are apparent discrepancies between the sizes of these vesicles in different parts of the
neurohypophysial system, even within one species. However, these differences probably result from variations in fixation procedures, since
Leatherland (1967) has noted that the sizes of elementary vesicles in the
preoptic nucleus and in the pars nervosa are identical, if they are compared in the same preparation. Knowles and Vollrath (1966a), working
in Anguillu anguillu, have suggested that the two size ranges found in
these elementary vesicles indicate that the caudal pars nervosa contains
two types of nerve fibers; one possesses elementary vesicles of 16001800 A in diameter (Type A, ) , while the second contains elementary vesicles 1200 A across (Type A, ) , It is tempting to speculate that these may
correspond to the two hormonal peptides found in the teleost neurohypophysis. Lederis (1962) has noted that in Gadus mrrhuu the pressor
activity typical of arginine vasotocin is associated with the relatively small
elementary vesicles, 800-200OA in diameter, but the source of the 4 Ser,
8 Ile oxytocin has not yet been determined. Knowles and Vollrath
(1966a) have recognized the presence of a few scattered fibers with
small irregular vesicles, 700 A in diameter, in the caudal neural processes;
these are similar to the Type B fibers of the rostra1 region of the pars
nervosa, so that it is probable that the fibers typical of each region are not
strictly segregated from one another.
In general, the nerve fibers terminate in swellings, which appear under
the light microscope either as varicose expansions of fine fibers or as
greatly hypertrophied structures often termed “Herring bodies” (carp,
sazan; Polenov, 1960). Electron microscopy shows that the swellings contain mitochondria and large numbers of small, relatively electron-lucent
vesicles, 500A in diameter, which are generally regarded as synaptic
vesicles (Salmo irideus; Legait and Legait, 1957; Gadus morrhua; Lederis,
1962; Lebistes reticulutus; Follenius and Porte, 1962; Anguilla anguilla;
Knowles and Vollrath, 1965a, 1966a). In Anguilla anguillu, these synaptic
167
Legait and Legait, 1957; see also Fridberg and Olsson, 1959, and Lederis,
1965). In general, neurosecretory material may occur throughout the
processes, or it may be densely packed toward the boundary with the
pars intermedia (Dodd and Kerr, 1963). It occurs as irregular granules,
or as beadlike droplets ( Platypoecilus maculutus; Oztan, 1963), but
Herring bodies, which are present in adult fish, appear to be absent in
juvenile specimens ( Lebistes reticulatus, Follenius and Porte, 1962;
Porichthys notatus, Sathyanesan, 1965b). Electron microscopy has shown
that the neurosecretory material consists of elementary vesicles similar in
size and form to those of the preoptic nucleus ( Gadus morrhua; Lederis,
1962; AnguiUa anguilla; Knowles and Vollrath, 1966a; Leatherland, 1967).
If the results of different workers are compared, there are apparent discrepancies between the sizes of these vesicles in different parts of the
neurohypophysial system, even within one species. However, these differences probably result from variations in fixation procedures, since
Leatherland (1967) has noted that the sizes of elementary vesicles in the
preoptic nucleus and in the pars nervosa are identical, if they are compared in the same preparation. Knowles and Vollrath (1966a), working
in Anguillu anguillu, have suggested that the two size ranges found in
these elementary vesicles indicate that the caudal pars nervosa contains
two types of nerve fibers; one possesses elementary vesicles of 16001800 A in diameter (Type A, ) , while the second contains elementary vesicles 1200 A across (Type A, ) , It is tempting to speculate that these may
correspond to the two hormonal peptides found in the teleost neurohypophysis. Lederis (1962) has noted that in Gadus mrrhuu the pressor
activity typical of arginine vasotocin is associated with the relatively small
elementary vesicles, 800-200OA in diameter, but the source of the 4 Ser,
8 Ile oxytocin has not yet been determined. Knowles and Vollrath
(1966a) have recognized the presence of a few scattered fibers with
small irregular vesicles, 700 A in diameter, in the caudal neural processes;
these are similar to the Type B fibers of the rostra1 region of the pars
nervosa, so that it is probable that the fibers typical of each region are not
strictly segregated from one another.
In general, the nerve fibers terminate in swellings, which appear under
the light microscope either as varicose expansions of fine fibers or as
greatly hypertrophied structures often termed “Herring bodies” (carp,
sazan; Polenov, 1960). Electron microscopy shows that the swellings contain mitochondria and large numbers of small, relatively electron-lucent
vesicles, 500A in diameter, which are generally regarded as synaptic
vesicles (Salmo irideus; Legait and Legait, 1957; Gadus morrhua; Lederis,
1962; Lebistes reticulutus; Follenius and Porte, 1962; Anguilla anguilla;
Knowles and Vollrath, 1965a, 1966a). In Anguilla anguillu, these synaptic