Progressive motor unit loss in the G93A mouse model of amyotrophic lateral sclerosis is unaffected by gender

We examined whether there are gender differences in the progressive loss of functional motor units in SOD1(G93A) transgenic mice. Isometric muscle and motor unit twitch contractions were recorded in fast- and slow-twitch muscles in response to stimulation of the sciatic nerve. Using a modified motor unit number estimation technique (ITS-MUNE), we found that motor unit numbers declined rapidly from 40 to 90 days of age during the asymptomatic phase of ALS in fast- but not slow-twitch hindlimb muscles of both male and female mice. There was a corresponding decline in twitch and tetanic contractile forces of the fast-twitch muscles. Gender did not affect the progressive loss of motor units and associated decline in force production. We conclude that gender does not alter progressive, muscle-specific motor unit loss in ALS, even though gender does influence disease onset.