Methylmercury (MeHg) induced an increase in inhibitory postsynaptic current (IPSC) frequency in lumbar spinal motor neurons (MNs). A: representative current recordings in lumbar spinal MNs before and after MeHg exposure (20 μM, 15 min) illustrate increased IPSC frequency. B and C: comparison of control and MeHg-exposed conditions (solid and dashed lines, respectively) across the population of sampled lumbar spinal MNs (n = 11). MeHg induced a significant (P = 2.41e-41, Kolmogorov–Smirnov test) leftward shift in the cumulative intersynaptic interval (ISI) distribution compared with control, indicating an increase in IPSC frequency. D and E: despite the increased number of events, there was no significant change in IPSC amplitude. F–H: across the population, the IPSC mean ISI (430.5 ± 52 and 273.2 ± 43 ms, control and MeHg-treated, respectively) decreased significantly (P = 0.03, Wilcoxon rank sum test) compared with control. The corresponding frequencies were 2.3 ± 0.4 Hz for control and 3.7 ± 0.5 Hz after MeHg exposure. The IPSC amplitudes for control and MeHg-treated neurons (47 ± 7 and 51 ± 8 pA, respectively) were not significantly different. con, Control. Black arrows indicate the geometric mean of the distribution.