Ethylenethiourea-induced hydrocephalus in vivo and in vitro with a note on the use of a constant gaseous atmosphere for rat embryo cultures.

Embryos were studied either after direct exposure to ethylenethiourea (ETU) during incubation of embryo cultures or after maternal ETU dosing and subsequent embryonic development in utero with a view to assess the similarity of these two systems to produce hydrocephalus. Ten-day-old rat embryos were incubated with nutrient media containing 0-2.0 mM of ETU in a constant gasseous environment following a newly modified method. The cultured embryos showed hydrocephalus in the form of dilated rhombencephalon and other anomalies at the 1.5 and 2.0 mM of ETU after 26 hours of incubation. No anomalies were seen in the control group. In in vivo studies, dilated rhombencephalon or hydrocephalus was not observed when dams, orally dosed with ETU on gestation day 10, were either killed daily for three postdosing days to examine embryos or killed at term to evaluate fetuses. This discrepancy in dilatation that was incidental to the rhombencephalon in the two systems pointed out that the fourth ventricle of the cranial neural tube responded by dilatation in vitro but remained unaffected in vivo following ETU exposure. ETU dosing of dams on the 12th day of pregnancy, when embryos are known to be sensitive to ETU-induced hydrocephalus, followed by serial gross examination of embryos, suggested that edema occurred in a generalized form but only after the appearance of both hydrocephalus (dilatation primarily in mesencephalon) and, the previously reported, neuroblastic necrosis.