Dai-Youl Kim

Effects of exercise and steroid on skeletal muscle apoptosis in the mdx mouse.

Reports concerning the influence of exercise loading and steroid administration on dystrophinopathy are inconsistent. To investigate the effect of muscle exercise in Duchenne muscular dystrophy (DMD), 15 control and 15 mdx mice, an animal model of DMD, were divided into free‐living (n = 6), exercise (n = 6), and immobilization (n = 3) groups. Free‐living and exercise groups were further divided into steroid‐treated and sham‐treated groups to evaluate the effect of steroid administration. We measured apoptotic changes by in situ DNA nick‐end labeling (TUNEL), DNA fragmentation assay, and Western blotting for Bcl‐2 and BAX. Apoptosis was most prominent in the sham‐treated exercise group, and it was significantly reduced in the steroid‐treated exercise group. The steroid‐treated free‐living group showed a higher rate of apoptotic change than the sham‐treated free‐living group. Apoptosis was minimized in the free‐living condition, whereas exercise loading and immobilization caused apoptotic change in this muscular dystrophy animal model. Steroid administration induced apoptosis in muscle of free‐living mice, but alleviated the apoptotic damage caused by exercise loading in mdx mice. These findings suggest that steroid administration may be effective in preventing a postexercise deterioration of skeletal muscle in animal models of DMD. Muscle Nerve 30: 456–462 2004

The control of parameters within the therapeutic range in neuromuscular electrical stimulation.

The purpose of this article was to investigate the pattern of differences among three parameters according to the increased level of the muscle force obtained in response to neuromuscular electrical stimulation (NMES). Ten healthy subjects were enrolled in this study, which involved applying NMES to the wrist extensor of the nondominant side. The threshold intensity that induced target motion was determined at first and NMES was then applied while changing three parameters. The muscle force was measured by means of a dynamometer for each parameter. Thus, the increased pattern of the muscle force was compared for each parameter. Compared with the duration or the frequency, the increase of the muscle force that accompanied the increase of intensity was more prominent. When the duration was doubled, the increase of muscle force was more evident at threshold intensity than at high intensity (p < .01). When the intensity was doubled, the increase of muscle force was more prominent at 0.2 than at 0.4 milliseconds duration (p < .01). However, there was no such interaction between the increase of the frequency and either the duration or the intensity. The data suggest that stimulus intensity may be the most effective parameter that can be used to enhance the strengthening of the muscle.

Excitability profile of motor evoked potentials and silent periods.

The aim of this study was to confirm the excitability profile of human cortical circuits on the motor evoked potential (MEP) and the silent period (SP) after paired transcranial magnetic stimulation (TMS) with variable interstimulus intervals (ISI), and to compare the time courses of MEP and SP after paired TMS at variable ISIs. MEPs were elicited at the hypothenar muscles at rest, and during tonic muscle contraction by applying paired TMS to the motor cortex. The authors measured the MEP amplitude during rest and the duration of SP during tonic muscle contraction at various ISIs. The response to paired stimuli was inhibited by an ISI of 1–5 ms and facilitated by an ISI of 10–20 ms. The SP at an ISI of 1–5 ms was shorter than that at the single suprathreshold stimulus, but the SP at an ISI of 15–25 ms was longer than this. A significant correlation was observed between the MEP amplitude and the duration of SP at ISIs of 1–20 ms and for a CS of 80% of threshold. These results may provide useful data for the study of the function of cortical excitability in disease states and suggest that the neural circuits underlying MEP and SP differ partly.