The direction of growth of differentiating neurones and myoblasts from frog embryos in an applied electric field.

1. Disaggregated single neurones and myoblasts obtained from the neural tube and somites of Xenopus laevis embryos (stages 17-21) were cultured in the presence of steady small electric fields. 2. Neurites grew preferentially towards the negative pole, or cathode, in field strengths of 7-190 mV/mm. Many turned through considerable angles to do so. This effect disappeared below a threshold level of about 7 mV/mm. 3. Greater numbers of neurones sprouted neurites in cultures exposed to an electric field compared to control cultures. The difference could be as much as tenfold. The threshold level of this phenomenon was about 6-8 mV/mm. Other cell types such as pigment cells and fibroblasts were also stimulated to differentiate in culture by an electric field, although to a lesser extent than neurones. 4. Applied electric fields had no effect on the location of the origin of neurites on the cell body. 5. Spherical myoblasts cultured in applied electric fields (36-170 mV/mm) elongated with a bipolar axis of growth which was perpendicular to the electric field. The response was graded and disappeared at field strengths below 36 mV/mm. 6. It is suggested that in vivo, the direction of neural outgrowth from the neural tube and the strict spatial organization of somites might be under the control, in part, of endogenous electric fields. Possible sources of these are discussed.