[Ultrastructural studies of the evolution of the notochord and dorsal embryonic constituents derived from the mesoderm in the chicken and Japanese quail during teratogenic exposures to parathion].

After experimental expositions to parathion--an organophosphorous insecticide which, in birds, gives rise to elective axial abnormalities--the evolution of the notochord and the different dorsal embryonic tissues issued from the mesoderm was analysed with the chicken and the japanese quail embryos. The abnormalities being settled, the notochord, which has normally developed, exhibited no ultrastructural change. Sclerotomic cells had normally migrated and, at the time when the provertebrae were formed, it was not possible to detect any histological and cytological alterations at their level. At later stages (8-9 days of incubation), the cartilaginous cells of the vertebral body did not show particular sign of an organophosphorous cytotoxicity but their secretory function was weakened, fact that may explain growth retardation. On these observations, it is evident that the tardive cartilaginous injuries cannot determine the axial abnormalities occurring earlier. The main results of this study deal with the cytological alterations of the myotomic elements which appeared to be the earliest and the more important ones. At the beginning (5th day), the myopathic changes were relatively located but they extended to the all cervical area. At 8-9 days, the cervical muscular cells are especially characterised by a lack of myofibrills. In showing only muscular lesions at the first step of teratogenesis, the present investigation set aside a chordal or sclerotomic cells intervention in the teratism induced by parathion. On the other hand, fromthe involvement of the contractile tissue in the formation and in the maintenance of the articulations, it appears that the muscular lesions can offer an embryologic interpretation to the parathion axial abnormalities. The possible effect of parathion in the myopathic evolution by the way of its anticholinesterasic properties is proposed.