ERR2/3 are required for the acquisition of a gamma motor neuron biophysical signature.

(A) Example traces of whole-cell patch-clamp recordings upon 240, 380, or 680 pA, 1 second square current pulses from small soma motor neurons exhibiting high levels of FG incorporation (FG^high) from control mice or ERR2/3^cko mice. Control FG^high motor neurons (A’) exhibit higher firing rates compared to FG^high ERR2/3^cko motor neurons (A”) and gear up their firing rates more rapidly in response to current pulses. (B) Scatter plot: lack of segregation of ERR2/3^cko FG^high gamma motor neuron and ERR2/3^cko FG^low alpha motor neuron electrophysiological signatures. (C) ERR2/3^cko FG^high motor neurons show higher rheobase (419.72 ± 84.11), lower firing frequency (27.61 ± 3.15), and lower gain (84.01 ± 12.34) compared control FG^high motor neuron rheobase (221.87 ± 31.34), firing frequency (50.65 ± 3.23), gain (161.01 ± 9.77), respectively. (D) Example traces of whole-cell patch-clamp recordings upon 900, 1,040, or 1,340 pA, 1 second square current pulses from large soma motor neurons with lower levels of FG incorporation (FG^low) from control mice or ERR2/3^cko mice. ERR2/3^cko FG^high motor neurons exhibit comparable firing rates and properties to control FG^low motor neurons. (E) Scatter plot: segregation of electrophysiological signatures between control FG^high gamma motor neurons versus control FG^low alpha motor neurons. (Note: Data are from Fig 1D). (F) No significant differences seen in ERR2/3^cko FG^low alpha motor neuron subtype rheobase (855.55 ± 124.85), firing frequency (25.03 ± 3.76), and gain (43.04 ± 9.81) when compared to control FG^low alpha motor neuron subtype rheobase (909.09 ± 82.11), firing frequency (20.41 ± 1.70), gain (32.64 ± 4.02), respectively (see S1 Table for details). Data are presented as mean ± SEM. n = # of neurons and N = # of mice. Statistically significant differences between FG^high and FG^low neurons are indicated as *p < 0.05, **p < 0.01, ***p < 0.001, n.s. = not significant, Student t test). Data for Fig 3B, 3C, 3E, and 3F can be found in S1 Data.