Chronaxie - Significance

Significance

The main value of chronaxie is comparing excitability across different experiments and measurements using the same standard, thus making data comparisons easier. Electrical stimulation based on chronaxie could regulate myoD gene expression in denervated muscle fibers. 20 muscle contractions, induced by electrical stimulation using surface electrodes and applied on alternate days based on muscle excitability, similar to protocols used in human clinical rehabilitation, were able to reduce the accumulation of mRNA in the myoD and atrogin-1 of denervated muscles, these expressions being related to muscle growth and atrophy, respectively. The increase in myoD levels after denervation is possibly related not only to activation and proliferation of the satellite cells but also to regulation of the cell cycle. Several studies have suggested that the function of denervation-induced myoD may be to prevent the muscle atrophy induced by denervation. To assess contractility of denervated leg muscles, rheobase and chronaxie were determined in anaesthetized rat by surface electrical stimulation and palpation of the leg muscles. The values of chronaxie of TA muscle measured up to 9-month after sciatectomy. Muscle excitability decreased early after denervation. Chronaxie from 0.1-0.2 msec in innervated muscle changed to 0.5-1 ms within one to two days after denervation (i.e., after Wallerian degeneration of the nerve) and progressively increased to about 20 msec during the following month. Chronaxie remained at this level up to 6 months postsciatectomy (Mid-term denervation stage in the rat model: from 2 to 6 months sciatectomy). Afterwards, the twitch contraction became questionably palpable and thus chronaxie increased to much longer values (from 50 msec to infinitum, i.e., the muscle twitch was not palpable). This third stage is defined as the “long-term denervation stage” of the rat model, i.e., denervation time longer than six months). In 3 out of 36 leg muscles, reinnervation occurred spontaneously and chronaxie shortened to 0.1 msec, which is the value of normal innervated muscle.