A histological study of the gonads and the pituitary of the african lungfish, protopterus aethiopicus

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.