Fig. 5.

Ca²⁺ spike activity is necessary for Shh-induced spinal neuron differentiation. (A) (Upper) Immunostaining of transverse sections of the spinal cord from embryos treated with agents indicated in the figure. Cyclo, cyclopamine; d, dorsal; Verat, veratridine; VGC block and VGC_bl, voltage-gated Na⁺ and Ca²⁺ channel blockers. (Lower) Graph shows mean ± SEM GABA-immunopositive cells/100 μm of spinal cord. n ≥ 5 stage-34 (45-h postfertilization) embryos per experimental group; *P < 0.05. (Scale bar, 20 μm.) (B) Model of the molecular mechanisms underlying Shh-induced Ca²⁺ spikes. α, β, γ, subunits of the heterotrimeric G protein; AC, adenylate cyclase; Cav, voltage-gated Ca²⁺ channels; ER, endoplasmic reticulum; Ptc1, Patched1. Details are given in Discussion.