| dc.description.abstract | The morphology of the male reproductive system of the
naked mole rats was studied. The testes of these animals are located
intra-abdominally and on histological examination; they reveal the
presence of a continuous mass of Leydig cells with dark staining
granules within the interstitial tissue among which are isolated
seminiferous tubules. Connective tissue, blood and lymphatic
capillaries are also few and scattered. Ultrastructurally, the Leydig
cells show a conspicuous accumulation of lipid droplets, elongated
mitochondria and abundant smooth endoplasmic reticulum that is
largely vesicular. Endocrinological investigations, however,
revealed that the Leydig cells are unresponsive to an in vitro
challenge by LH and that these animals have low plasma LH but
high plasma testosterone levels. The low levels of LH in plasma
suggests depressed release of gonadotrophin releasing hormone
(GnRH) from the hypothalamus. The seminiferous epithelium
comprises of Sertoli (sustentacular) and spermatogenic cells. The
Sertoli cells exhibit irregularly outlined nuclei with a single
nucleolus, predominant network of smooth endoplasmic reticulum,
mitochondria oriented perpendicularly and parallel to the long axis
of the cell, lipid droplets and lysosomes. These cells form recesses
into which fit the spermatogenic cells. All stages of spermatogenesis
occur although secondary spermatocytes, spermatids and
spermatozoa are few compared to spermatogonia and primary
spermatocytes. This suggests that spermatogenesis progresses to
(vii)
completion even though the rate appears to be reduced considering
the number of mature spermatogenic cells seen. This may possibly
be due to an arrest in further development occurring at primary to
secondary spermatocyte stage.
The excurrent duct system comprises of the ductuli efferenles,
ductus epididymis and ductus deferens. Ductuli efferentes occur as
small and numerous ducts whose histology and ultrastructure
reveal the presence of simple cuboidal epithelium with two main
cell types namely the principal (non-ciliated) and ciliated cells. The
ductus epididymis comprises of the initial, middle and terminal
segments. The entire duct has a pseudostratified columnar
epithelium that is high in the initial segment and a slightly reduced
height in the middle and terminal segments. The epithelial cells are
mainly the principal and basal cells although apical cells and
lymphocytes are also present in the initial segment. The cytoplasm
of principal cells in both initial and middle segments show no
conspicuous cytoplasmic modification but in the terminal segment,
apical vacuoles and basal granules are evident. In all segments,
microvilli (stereocilia) occur and the lumina of the tubules contain
some cellular debris. Ductus deferens has two segments; the
proximal and the distal segments. The proximal segment has a
markedly reduced epithelial heights with the microvilli forming the
brush border. The point of transition between the two segments is
recognised by a dramatic increase in the epithelial height and
presence of clear cells. The principal cells from the transition point
(v iii)
distally show an apocrine mode of secretion. The distal segment
has a thickened wall and the two opposite parts of the ducts are
bundled together by a fold of connective tissue. A third duct,
utriculus musculinus (remnant of Mullerian duct) is also evident at
this level. The epithelium of the ductus deferens in this segment is
thrown into folds resulting from the thick muscular coat.
Seemingly, the prostate gland is the only accessory sex gland
in these animals. The pelvic urethra has the ejaculatory ducts
(continuations of the ductus deferens) in addition to utriculus
musculinus dorsally and urethral epithelium is mainly the
transitional type. The pelvic urethra gives rise to the penile urethra
that is within the penis. The penis is of the vascular type and is
covered at its tip by a prepuce. | en |
