The study aims at a precise characterization of dynamic muscle activity in an extensor (vastus lateralis-VL) and a flexor (biceps femoris-BF) of healthy mice hind leg in contrast to tottering mice using a surface EMG array technique in chronic experiments. The VL and the BF of 12 female healthy adult mice (strain NMRI, body mass 36-45 g) and 6 tottering mice (gene: Cacna1a) were investigated with two supramuscular implanted 4-electrodes arrays. A 8-channel EMG (10-700 Hz, 4000 samples/s, resolution of 4.88 mV/bit) was monopolarly recorded simultaneously with high-speed videography (400 frames/s). The EMGs were rectified and smoothed by calculating a RMS-time profile, time-normalized and averaged. The EMG activity of both muscles increased during the late swing phase. While the VL activity rose steeply and peaked during mid-stance phase, the biceps activity reached a plateau during early stance phase. With increasing gait velocity, stance time decreased more than swing time. The increase in gait velocity was also associated with greater EMG amplitudes. In tottering mice the kinematographically analyzed step-characteristics as well as the simultaneous flexor and extensor activation are different in comparison to healthy animals.

Supported in part by NIH grand NS40470 (Joint Project: Dept. Neurology, Johns Hopkins University, Baltimore, USA).