ABSTRACT
Immobilization, used in clinical practice to treat traumatologic problems, causes changes in muscle, but it is not known whether changes also occur in nerves. We investigated the effects of immobilization on excitability and compound action potential (CAP) and the ultrastructure of the rat sciatic nerve. Fourteen days after immobilization of the right leg of adult male Wistar rats (n=34), animals were killed and the right sciatic nerve was dissected and mounted in a moist chamber. Nerves were stimulated at a baseline frequency of 0.2 Hz and tested for 2 min at 20, 50, and 100 Hz. Immobilization altered nerve excitability. Rheobase and chronaxy changed from 3.13±0.05 V and 52.31±1.95 µs (control group, n=13) to 2.84±0.06 V and 59.71±2.79 µs (immobilized group, n=15), respectively. Immobilization altered the amplitude of CAP waves and decreased the conduction velocity of the first CAP wave (from 93.63±7.49 to 79.14±5.59 m/s) but not of the second wave. Transmission electron microscopy showed fragmentation of the myelin sheath of the sciatic nerve of immobilized limbs and degeneration of the axon. In conclusion, we demonstrated that long-lasting leg immobilization can induce alterations in nerve function.
Subject(s)
Animals , Male , Action Potentials/physiology , Hindlimb/innervation , Immobilization/adverse effects , Nerve Degeneration/physiopathology , Sciatic Nerve/physiopathology , Chronaxy/physiology , Microscopy, Electron, Transmission , Myelin Sheath/physiology , Rats, Wistar , Time FactorsABSTRACT
Standard electrical quantity (a), chronaxie (?), rheobase (Rh), "b" in Weiss' formula and intensity threshold of duration being 40 ?s and 300 ?s (T_(?) and T_(200)) were measured on peroneus nerves in rabbits. The results show that "a" is an actual index for measuring the excitability of various groups of fibers. The larger fibers, the higher excitability and the smaller "a" values. "b" does not indicate excitability. "?" , "Rh" , "T_(40)" and "T_(200)" are not actual indexes for measuring excitability because they are influenced by "b" in Weiss' formula.
ABSTRACT
The changes of rheobase(Rh), chronaxie(Chr), standard electrical quantity(a) and mtensity-duration curve(i. t. c) were studied for understanding the effect of aging on the excitability of sciatic and caudal nerves in Wistar rats of different age. The results show that before grown-up excitability of the peripheral nerves increases progressively with age, after that it tends to decrease. Chronaxie as an index can not reflect the change of excitability of the peripheral nerves correctly.
ABSTRACT
Effects of temperature and anesthesia on various excitability indexes of sciatic—peronael nerve were observed in toads. The results show that standard electrical quantity(a) changes regularly with the change of excitability. The higher excitability, the less the "a" value. But "b" in Weiss's fomula, chronaxie (Chr), rheobase (Rh), and intensity-duration curve do not indicate excitability. The time constant (RC)of the cell membrane is not related to the changes of excitability. Thus, "a" is an actual index of measuring excitability.