Morphological and Morphometric Study of the Development of Leydig Cell population of Donkey (Equus asinus) Testis from Birth to Maturity
In this investigation, the postnatal morphologic and morphometric characteristics of Leydig cells and testicular interstitial tissue in 20 healthy donkey testes were studied. The volume percentage of the interstitial tissue was about 87.24% in neonates and decreased gradually with postnatal age reaching about 21.56% in mature animals. The Leydig cell population underwent evident morphologic and morphometric changes during the postnatal life. Morphologically, there were two discrete types of Leydig cells, which recognized side by side in the testis of neonatal and suckling animals. The first type (steroidogenic fetal Leydig cells), was large, contained partially shrunken nucleus together with vacuolated granular cytoplasm. This cellular type, were predominant in neonates, underwent degeneration and decreased gradually until being very few at two months of age. The second type (non-steroidogenic) was small, few at birth and contained large central nucleus. This type develops from undifferentiated fibroblastic elements and underwent gradual increase in number with age, where it dominated in the late suckling period. Some of these cells were degenerated and the remaining became transformed into the adult type of Leydig cells. The volume percentage and absolute number of Leydig cells displayed the same pattern of undulation during postnatal development, which being very high in late suckling animals. The volume percentage of the vascular components of the interstitial tissue displayed a slight decrease between neonatal and early suckling periods (from about 8% to about 7% of the interstitium); however, they increased steadily through premature and mature animals (about 12% and 20% respectively). The present study provides baseline information for further experimental or quantitative studies exploring the normal development of the Leydig cells in donkey testis and other related species.