Figure 3. Neuronal activity of LMO4-deficient Sim1 neurons is reduced. A, GFP-positive neurons of the PVH (dashed oval, area recorded). Scale bar, 100 μm. B, Representative traces showing spontaneous firing. C, Lmo4 KO neurons have a lower spontaneous firing frequency than their littermate controls (WT). D, Representative traces show low-threshold spiking (LTS) in Lmo4 KO and littermate control (WT) neurons of the caudal PVH. LTS, containing 2–4 action potentials at ∼60 Hz, were elicited by injecting negative current (1 s) to hyperpolarize the membrane from −50 mV (holding potential) to −90 mV. Enlarged (200 ms) traces (inset) are shown. E, Percentage of the Sim1 neurons (WT, n = 19 from 7 mice; KO, n = 26 from 9 mice) showing LTS. F, Representative traces showing neuronal activity in response to depolarizing currents (20, 40, and 60 pA) from −50 mV of holding potential. G, Tonic spike frequency in response to various depolarizing currents presented as mean ± SEM, F(1,9) = 64.90; two-way ANOVA: *p < 0.05; **p < 0.01; ***p < 0.001.