Fig. 1.

Spiking cells in the developing neural tube are postmitotic neurons. (A) Ca²⁺ imaging of the ventral spinal cord of a stage-24 (26-h-postfertilization) embryo for 20 min. Circles identify cells spiking during 20-min recording. Inset shows Ca²⁺ spike activity for the cell outlined in yellow. (B) (Left) After imaging, the same preparation was whole-mount immunostained for Sox2 and N-β-tubulin. (Right) Immunostaining of a transverse section of the spinal cord from a stage-24 embryo. (C) Ca²⁺ imaging of an open-book spinal cord preparation. (D) Whole-mount immunostaining of the same preparation for Sox2 and N-β-tubulin. (E) Diagram of the open-book spinal cord preparation shown in C and D. D, dorsal; V, ventral. (Scale bars, 20 μm.)