Calcium requirement for neural fold elevation in rat embryos.

To investigate the calcium requirement for the maintenance of the elevation of the neural folds in mammalian embryos 10.4-day-old-rat embryos, at a stage when the cephalic neural folds had elevated but not yet fused, were cultured in salines containing different concentrations of calcium. At 3 x 10(-3) M calcium the neural folds remained intact. As the concentration of calcium was reduced the elevated cephalic neural folds re-opened, flattened and then, at 10(-5) M calcium, collapsed. Replacement of calcium by strontium at 5 x 10(-3) M did not prevent the collapse of the cephalic neural folds, although at higher concentrations strontium partially prevented the collapse of the neural folds. In the cervical region most of the neuroepithelial cells were apically tapered. In intact cephalic neural folds nearly half of the cells were apically tapered. In cephalic neural folds which had been induced to collapse by culture in saline with low calcium there was an increase in the proportion of round cells and a decrease in the proportion of apically tapered cells.