Ultrastructural and histological changes induced by ivermectin in the ovary of Argas persicus after feeding

The ovarian wall of A.persicus consists of primary oocytes of three developmental stages namely , young , previtellogenic and vitellogenic in addition to interstitial cells . After feeding and mating , the three stages and interstitial cells , particularly funicle cells that carry oocytes , markedly increased in size and their cytoplasmic organelles exhibit notable changes correlated with yolk and egg shell formation . The present study examined the hitological and ultrastructural aspects during the formation of yolk and egg shell. The first seem to originate from small vesicles derived from Golgi bodies, rough endoplasmic reticulum and mitochondrial cristae. The egg shell seems to develop from vesicles derived from Golgi bodies that fuse with the cell membrane and discharge their content into the extracellular space between basement membrane and tunica propria. Glycogen aggregates and lipid droplets are commonly observed between yolk spheres. The injection of selected dose of ivermectin (400 ug/kg) prevented growth and development of oocytes. The ovary appeared studded with young and previtellogenic primary oocytes surrounding a narrow ovarian lumen or the ovarian wall, carrying oocytes, is stretched around a large fluid filled lumen. Surface microvilli of primary oocytes and coated vesicles underlying them became comparatively fewer. Mitochondria and rough endoplasmic reticulum became fewer, fragmented and finally degenerated in primary oocytes and funicle cells. Ivermectin interfered with the formation of yolk granules and egg shell. However, in the few formed vitellogenic oocytes, Golgi bodies were not affected. The egg shell appeared thinner with low electron density. The cytoplasm of funicle cells became highly vacuolated, its organelles, hardly distinguished and nuclei became swollen without definite nuclear membrane. Ivermectin completely prevented the formation of glycogen particles. Our results suggests that ivermectin causes partial blockage of the release of the vitellogenetic hormone that regulates vitellogenesis and other aspects of oogenesis as indicated by disrupted synthesis and uptake of yolk protein in the developing oocytes.