Depolarization and removal of hyperpolarization both induce distinct firing properties. A, Representative firing properties of tonic and DIB cells on diestrus and proestrus under control conditions and during treatment with Ni2+ (100 µm). B, Mean ± SEM IF of tonic (solid line) and DIB (dash line) cells on di (gray) and pro (black) plotted as a function of spike interval number. C, Rin for tonic and DIB cells on diestrus and proestrus. D, Rin for cells on diestrus and proestrus assessed using physiological (con) and Cs+-based pipette solution. E, Distribution of cells that generated rebound bursts (black bar), one rebound spike (hatched bar), or no rebound spikes (white bar) on diestrus and proestrus for tonic, DIB, and all cells combined. F, G, Initial IF (F) and overall frequency (G) of rebound bursts in tonic and DIB cells on diestrus and proestrus. *p < 0.05 calculated by two-way ANOVA with Bonferroni correction or two-way RM ANOVA and Holm–Sidak test.