''Histological and ultrastructural study of the male reproductive system of non-breeding naked mole rats (heterocephalus glaber, ruppell) and in vitro interstitial (leydig) cell response to luteinizing hormone (LH)''
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.