Figure 5.

Maintained preservation of neuromuscular function in aged ΔNLS Wld^S transgenic mice. A, B, Recordings of FDB repetitive 1 Hz muscle twitch contractions and 20 Hz fused contractile responses, 6 d after sciatic nerve lesion from 7.5-month-old ΔNLS Wld^S transgenic (A) and age-matched native Wld^S mutant (B). Note the amplitude of isometric force generated by nerve stimulation in ΔNLS Wld^S is ∼50 times that of the native Wld^S. The fluctuating baseline discernible in B is due partly to the increased amplifier gain required to register the muscle response and partly to distributed asynchronous spontaneous contractions typically observed in axotomized Wld^S muscle. C, D, Averaged extracellular EMG recordings using nerve/muscle preparations from A and B. The initial spike is the stimulus artifact and the slower waves are produced by muscle fiber action potentials. Note the ∼10-fold greater amplitude of the evoked EMG response in ΔNLS Wld^S (C) compared with Wld^S (D). E, Representative confocal z-series projections of paraformaldehyde-fixed FDB nerve muscle preparations double labeled presynaptically with the activity-dependent nerve terminal dye AM1-43 and postsynaptically by the acetylcholine receptor marker TRITC-α-bungarotoxin. Colocalization of the green and red signals thus indicates functionally preserved NMJs.