| dc.description.abstract | A histological study on the gonads and the
pituitary of the African lungfish Protopterus
aethiopicus was undertaken, aimed at determining
the pattern of gonadal changes and changes in the
st~te of the pars distalis that could be correlated
with gonadal variation.
Testis: The germ cell generations in the testis
of P. aethiopicus i.e. spermatogonia, primary and
secondary spermatocytes, spermatids and spermatozoa,
are described histomorphologically. Characteristics
of the five maturational'stages (I-V) are also
described. In summary, the interstitial cells consisted
of some amorphous cells and fibroblasts and exhibited
no observable or evident variation in morphology
or distribution (amount) with the different
maturational stages. A clear cystic arrangement of
the late secondary spermatocytes only, was evident in
the post-spawning testis of Stage V. Ultrastructurally,
the Sertoli cells appeared to be modified fibroblasts
and revealed the presence of cisternal, rough endoplasmic
reticulum, numerous large mitochondria with
well-developed tubular cristae, Golgi complexes and a
few lipid droplets within their cytoplasm. The interstitial
cells however, appeared to be undifferentiated
or undeveloped fibroblasts and their cytoplasm lacked
developed or recognizable organelles such as those
present in the Sertoli cells. The possible steroidogenic
and nutritive functions of the Sertoli cell and
the steroidogenic capacity of the interstitial cells
arediscussed in the light of previous and recent
research on the piscine and amphibian groups.
Ovary: Oocyte maturational stages from the preprotoplasmic
stages, through the protoplasmic stages
and to the various vitellogenic stages, are described.
Cytoplasmic and nuclear characteristics or features
including their dimensions are also noted. Furthermore,
the pattern of yolk granule accumulation during the
vitellogenic stages and the changes in the surrounding
follicle cells with these maturational stages, are
included in the definition of the different vitellogenic
oocyte stages. The probable physiological
significance of organelles such as nucleoli, yolk
nucleus and "larnpbrush" chromosomes, is discussed.
In the ultrastructural study, the formation of the
zona pellucida, its characteristics and those of the
follicular layer with different stages of oocyte
maturation, are further described. The follicle cells
of vitellogenic oocytes revealed cisternal, rough
endoplasmic reticulum, several mitochondria with
developed tubular cristae, areas of Golgi vesicles,
and other large vesicles, some of which contained
only coarse, electron-dense granules while others
contained a non-granular material together with the
coarse granules. The possible steroidogenic function
of the follicle cells is discussed. The thecal cells
or fibroblasts are undifferentiated as compared with
the follicle cells, and contain undeveloped mitochondria
and small Golgi complexes within their cytoplasm.
Endoplasmic reticulum, either of a granular or
agranularvariety, is lacking.
Pituitary: In the pars distalis of all the lungfish
ranging from 18.5crnto 66.5crnin body length,
the type 2 basophils (as described by Kerr and van
Oordt, 1966) are absent. Only basophils type 1 and 3
occur in the pars distalis, of which the former cell
type exhibited obvious variation in distribution,
granulation, extent and staining intensity of their
chromophilic substance, with the different stages of
gonadal maturation. From previous research by other
workers, the type 3 basophils in the South American
lungfish Lepidosiren paradoxa and in the amphibians,
which are phylogenetically related to the lungfishes,
were demonstrated by immunohistochemistry to be the
ACTH-producing cells, while the types 1 and 2 basophils
in the anurans were demonstrated to be the TSHand
FSH-producing cells respectively. The•possibility
whether the type 1 basophils are gonadotropin or
thyroptopin-producing cells in P. aethiopicus, is
discussed. | en |
