AN OPEN CEPHALIC NEURAL-TUBE REPRODUCIBLY INDUCED BY CYTOCHALASIN-D IN RAT EMBRYOS IN-VITRO

Rat embryos at the head-fold stage (Slc:SD strain; 9.5 days of gestati on) were cultured in rat serum in the presence of a relatively low con centration of cytochalasin D (2 X 10(-8) M). Embryos developed into C- shaped structures (with the open part of the C directed ventrally) wit h an open cephalic neural tube. Elevation and apposition of the neural folds and eversion of the neural plates at the procencephalon, mesenc ephalon and some parts of rhombencephalon were observed during the cou rse of development of the treated embryos. In control embryos, stainin g with rhodamine-conjugated phalloidin was observed at the basal regio n of the lateral margin of the fusing neural folds and at the luminal surface of the roof plates of the procencephalic neural tube. The latt er diminished as embryos developed. However, the staining was confined to the edges of the apposed neural folds in the treated embryos and b ecame intense at the luminal surface of the everted neural plates. By contrast, some parts of the rhombencephalon of the treated embryos sho wed fusion of the neural folds. The staining was observed in roof plat es of the rhombencephalon in these embryos as like as control embryos. The area of the staining at the luminal surface of the roof plates sp read as the fourth ventricle expanded. These results suggest that micr ofilaments do not play an essential role in the elevation of the neura l plates but do play an important role in fusion of the neural folds a nd the moulding of the cephalic neural tube. Delicate changes in the d istribution of microfilaments may result in changes in cell shape that cause the fusion of the neural folds and the moulding of the cephalic neural tube.