The embryogenesis of trypan-blue induced spina bifida aperta and short tail in the rat.

The study of litters from 140 Wistar-derived rats injected with trypan blue during gestation leads to conclusion that a myelocele can result from faulty closure of the neural plate and that this is accompanied in many cases by blebs in the paraxial mesoderm. Haematomata usually underlie the open neural plate at an early stage and they form by extravasation of blood from the dorsal aortae into the blebs. Local ventral deflection of the notochord beneath a myelocele probably results from delayed separation of the notochord from the hindgut. Complete failure of separation and abnormality induced in the tail-bud could result in sacral agenesis and/or a short tail. All these malformations may result from varying severity of the action of the trypan blue at different developmental stages.