High dietary VitD3 increases excitability of hippocampal neurons. The I/O curves show evoked fEPSPs in response to increasing stimulus intensities in hippocampal slices from low-, medium-, and high-vitD3 groups. The steeper slope with high vitD3 demonstrates a greater response for a given stimulus [low = 0.27 ± 0.01, medium = 0.25 ± 0.01, and high = 0.34 ± 0.02; F(2,462) = 11.3, P ≤ 0.001]. Results are from 16 to 22 hippocampal slices from seven to nine animals per group.