Fasciolo hepatica: Development of excretory and parenchymal systems during migration in the mouse

Abstract

Concretions, which fill the major descending ducts and excretory bladder of the newly excysted juvenile (nej) Fasciola hepatica occur only rarely in juveniles recovered from the peritoneal cavity of mice 12 hr postinfection (pi) and are absent 24 hr pi. The syncytium lining the major descending ducts and excretory bladder commences adult-like lipid excretion in the nej and contains large numbers of lipid droplets 12 hr pi. At 12 hr pi the apical plasma membrane of the syncytium has more lamellae and the basal plasma membrane has more basal invaginations than the nej. The juvenile, thus, has an adult-like excretory system at 12 hr pi. Pinocytosis occurs on the luminal surfaces of flame cells, efferent ducts, and primary ducts of juveniles throughout migration in the host. Ascending ducts, which connect the primary ducts to the major descending ducts, have lamellae on their luminal surfaces and contain groups of cilia. The ascending ducts, major features of the excretory system of the nej, do not change during maturation of the fluke. In the nej the parenchymal cells are filled with high concentrations of glycogen. They have junctional complexes with neighboring parts of the tegumental and excretory system but not with the ceca. At 12 hr pi the parenchymal cells are depleted of glycogen and increased in volume compared with the nej. This increase in volume together with replenishment of the glycogen stores 1 and 2 days pi and the appearance of junctional complexes with the ceca at 1 day pi, bring the parenchymal cells to the adult condition.