160
A. M. PERKS
tory materials, once formed, concentrate around the nucleus of the cell,
and then spread out into its processes (carp, sazan, Polenov, 1960; Platypoecilus muculatus, Oztan, 1963). In some species, the secretion may
leave the cell in greater quantities at particular seasons, perhaps in correlation with the breeding cycles; such seasonal variations in stainable
neurosecretion, and in the cytology of the preoptic cells, have been reported in the carp, the sazan, in Salvelinus leucomaenis pluuius, and in
Anguilla anguilla (Polenov, 1960; Honma and Tamura, 1965; Leatherland
et al., 1966). Oztan (1966) has noted reduced numbers of elementary
vesicles and smooth-surfaced vesicles in the preoptic cells of Zoarces
viviparus during summer, and also in response to continuous light.
Neurosecretory products may leave the preoptic nucleus by a number
of possible routes. Since the preoptic cells are intimately associated with a
rich capillary plexus (Carmsius auratus, Palay, 1960), the possibility of
a direct passage into the blood of the hypothalamus cannot be discounted
at present. Indeed, there are observations which suggest that it could
occur. Oztan (1963) has observed that dendrites from the preoptic cells
connect to nearby capillaries in Platypoecilus maculatus, and Sathyanesan
( 1965b) has noted that section of the preoptico-hypophysial tract, followed by “activation” of the system by continuous light, will produce
dilation of blood vessels around the preoptic nucleus of Porichthys
notatus. However, in general, this direct route into the hypothalamic blood
vessels is not considered to be important.
In some species, neurosecretory materials may pass to the cerebrospinal fluid. In a number of species of Anguilla, it is clear that thick
dendrites or even whole preoptic cells may protrude into the third
ventricle, where they are sometimes associated with a coagulum (Stutinsky, 1953; Enami, 1954; Leatherland et al., 1966, 1969a). Enami
(1954) has suggested that the dendrites continue as Reissner’s fiber
and carry neurosecretory granules to the subcommisural organ for
storage; however, these interesting possibilities have not yet been confirmed, and Leatherland and Dodd ( 1968) have demonstrated staining
differences between the Gomori-positive materials of the preoptic nucleus
and those of the subcommisural organ. Dendrites-sometimes with granules-have been seen to reach the ependyma and ventricle of the carp,
the sazan, and the goldfish, Carmsius auratus (Polenov, 1960; Palay,
1960). However, this may not be a universal situation in the teleosts, for
Oztan (1963) has remarked on the absence of such connections in Platypoecilus muculatus. This observation would prevent the general acceptance of Knowles and Vollrath‘s suggestions (1965b) that the ventricular dendrites are concerned in feedback mechanisms which control the
preoptic nucleus. Nevertheless, such connections are well marked in a
A. M. PERKS
tory materials, once formed, concentrate around the nucleus of the cell,
and then spread out into its processes (carp, sazan, Polenov, 1960; Platypoecilus muculatus, Oztan, 1963). In some species, the secretion may
leave the cell in greater quantities at particular seasons, perhaps in correlation with the breeding cycles; such seasonal variations in stainable
neurosecretion, and in the cytology of the preoptic cells, have been reported in the carp, the sazan, in Salvelinus leucomaenis pluuius, and in
Anguilla anguilla (Polenov, 1960; Honma and Tamura, 1965; Leatherland
et al., 1966). Oztan (1966) has noted reduced numbers of elementary
vesicles and smooth-surfaced vesicles in the preoptic cells of Zoarces
viviparus during summer, and also in response to continuous light.
Neurosecretory products may leave the preoptic nucleus by a number
of possible routes. Since the preoptic cells are intimately associated with a
rich capillary plexus (Carmsius auratus, Palay, 1960), the possibility of
a direct passage into the blood of the hypothalamus cannot be discounted
at present. Indeed, there are observations which suggest that it could
occur. Oztan (1963) has observed that dendrites from the preoptic cells
connect to nearby capillaries in Platypoecilus maculatus, and Sathyanesan
( 1965b) has noted that section of the preoptico-hypophysial tract, followed by “activation” of the system by continuous light, will produce
dilation of blood vessels around the preoptic nucleus of Porichthys
notatus. However, in general, this direct route into the hypothalamic blood
vessels is not considered to be important.
In some species, neurosecretory materials may pass to the cerebrospinal fluid. In a number of species of Anguilla, it is clear that thick
dendrites or even whole preoptic cells may protrude into the third
ventricle, where they are sometimes associated with a coagulum (Stutinsky, 1953; Enami, 1954; Leatherland et al., 1966, 1969a). Enami
(1954) has suggested that the dendrites continue as Reissner’s fiber
and carry neurosecretory granules to the subcommisural organ for
storage; however, these interesting possibilities have not yet been confirmed, and Leatherland and Dodd ( 1968) have demonstrated staining
differences between the Gomori-positive materials of the preoptic nucleus
and those of the subcommisural organ. Dendrites-sometimes with granules-have been seen to reach the ependyma and ventricle of the carp,
the sazan, and the goldfish, Carmsius auratus (Polenov, 1960; Palay,
1960). However, this may not be a universal situation in the teleosts, for
Oztan (1963) has remarked on the absence of such connections in Platypoecilus muculatus. This observation would prevent the general acceptance of Knowles and Vollrath‘s suggestions (1965b) that the ventricular dendrites are concerned in feedback mechanisms which control the
preoptic nucleus. Nevertheless, such connections are well marked in a