A histological study of early chondrification in Malathion-treated chick embryos, with emphasis on cell numbers, cell size, and patterns of matrix deposition

Abstract

Chick embryos were given a teratogenic dose of Malathion at the 5-day incubation stage and its effects on the early histogenesis of the tibiotarsus were studied during the 8- to 20-day incubation period. This investigation included studies of the growth rate as indicated by mitotic index and the number of cells per unit area, of cell activity as indicated by cell size and the amount of matrix per cell, and of matrix formation as indicated by rates of deposition and erosion and by histochemical staining. The Malathion caused an increased proliferation of the chondroblasts during the initial chondrification stages only. It led to an increase in the number and size of the chondrocytes, particularly in areas of reduced matrix deposition. The Malathion primarily influenced the deposition of the ground substance, causing: (1) a reduction in the amount of ground substance deposited, (2) a reduction in the degree of sulfation and polymerization of that ground substance which was deposited, and (3) a lysosomal-mediated resorption of the formed matrix along the epiphyseal–diaphyseal border. In these ways, the Malathion causes a reduction in the growth rate of the tibiotarsus and a weakening of the cartilage model which subsequently results in a bending of the tibiotarsus.