GnRH neuron excitability is increased on proestrus versus diestrus. A, Representative traces from a neuron in each group during 500-ms current injections of 12 and 24 pA (current injection protocol below). B, Mean ± SEM spikes elicited for each current injection step (two-way repeated-measures ANOVA cycle stage: F(2,22) = 10.2, current: F(15,330) = 93.03, interaction: F(30,330) = 9.503, *p < 0.05 diestrous PM vs proestrous PM and p < 0.05 proestrous AM vs proestrous PM; *p < 0.05 among all three groups, Fisher’s LSD). C–H, Individual values and mean ± SEM for: (C) rheobase current (ANOVA F(2,22) = 12.8, *p < 0.05, **p < 0.0001), (D) latency to first spike (ANOVA F(2,22) = 2.85, p = 0.0792), (E) action potential threshold (ANOVA F(2,22) = 6.18, *p < 0.01 Tukey), (F) action potential amplitude (ANOVA, F(2,22) = 0.676), (G) FWHM (ANOVA F(2,22) = 26.2, **p < 0.0001 Tukey), (H) action potential rate of rise (Kruskal–Wallis, KW = 6.69, *p < 0.05 Dunn’s), (I) AHP amplitude (ANOVA F(2,22) = 0.252), and (J) AHP time (Kruskal–Wallis, KW = 7.03, *p < 0.05 Dunn’s).