Electrophysiological analysis was performed as previously described [48]. Briefly, intracellular recordings from identified quadriceps motor neurons were made using sharp electrodes (75–120 MΩ, 3M KCl). Average responses (10–20 trials) from suprathreshold nerve stimulation (1.5 times the strength that evokes maximal monosynaptic response) of the quadriceps nerve were acquired with LTP software [49]. Only cells with stable resting potentials more negative than −50 mV were considered for analysis. Monosynaptic amplitudes were determined offline using custom routines in the Matlab environment (The Mathworks, Natick, Massachusetts, United States) as previously described [48].