To study the conduction characteristics of regenerating peripheral nerves under pulsed magnetic fields.
The sciatic nerve of rats was crushed with a surgical forceps. After the wound was closed, the animals were allowed to recover for 15-38 days (and exposed). After nerve crush injury and damage to the myelin sheath 4-aminopyridine sensitive potassium ion channels are reorganized (following injury the incomplete regeneration of the myelin sheath causes an increase in potassium currents through these ion channels).
The sciatic nerves were resected, placed in a sucrose gap apparatus and stimulated with short (0.05 ms) depolarizing pulses. The nerves were stimulated with a single stimulus every minute for 30 min at the lowest stimulation rate. To examine the stimulation frequency, three consecutive frequencies (10, 40, and 100 Hz) were used.
The following groups were investigated: two sham crush surgery (same surgical conditions, but no crush) groups (each n=6; sham exposed for 15 or 38 days) and four crush injury groups (each n=8; two exposure groups (exposed for 15 or 38 days) and two sham exposure groups (sham exposed for 15 or 38 days). Additionally, there were two groups of intact (unoperated) rats (each n=14; sham exposed for 15 or 38 days) and two groups of intact rats (each n=8, exposed for 15 or 38 days). Furthermore, two crush groups (no exposure) were investigated after 15 or 38 days and used as controls (each n=8).
| Exposure | Parameters |
|---|---|
|
Exposure 1:
1–100 Hz
Modulation type:
pulsed
Exposure duration:
1 h/day for 15 days or 38 days (see add. information)
|
|
for further information on the setup see also: Mert T, Gunay I, Gocmen C, Kaya M, Polat S. 2006. Regenerative effects of pulsed magnetic field on injured peripheral nerves. Altern Ther Health Med 12(5):42-49.
| Exposure source | |
|---|---|
| Setup | pair of Helmholtz coils with a diameter of 60 cm, placed 30 cm apart in a Faraday cage; rats placed in a 30 cm x 20 cm x 15 cm all-plastic restrainer in the center of the coil system; field homogeneous within 5 % |
| Sham exposure | A sham exposure was conducted. |
| Additional info | for pulse trains of (1 Hz, 10 Hz, 40 Hz, 100 Hz) with an interval of 1 min between them; each pulse train lasted 4 min |
| Measurand | Value | Type | Method | Mass | Remarks |
|---|---|---|---|---|---|
| magnetic flux density | 1.51 mT | peak value | measured | - | 1.49 mT - 1.51 mT |
| electric field strength | 0.61 V/m | peak value | calculated | - | 0.59 V/m - 0.61 V/m |
The data showed that pulsed magnetic field application for 15 or 38 days to injured animals did not cause any significant changes in the electrophysiological properties of the nerves. However, in the presence of 4-aminopyridine, significant electrophysiological differences were noted in the pulsed magnetic field-treated 38 days post-crush group (e.g. increase of compound action potential amplitude and decrease of amplitude and prolonged duration of delayed depolarisation).
At the stimulation frequency of 100 Hz, the pulsed magnetic field reduced the influence of 4-aminopyridine on the compound action potential amplitude (but only the highest stimulation frequency of 100 Hz, not at 40 or 10 Hz).
Taken together, these data suggest that application of pulsed magnetic field for 38 days may provoke the process of myelin compaction, or may decrease the breaks in the myelin sheath and prevent the appearance of abnormal impulse patterns.
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