Schematic drawing of PEMF exposure system and PEMF pulse protocol.

(A) Modified Helmholtz coils consisted of three identical coils with diameters of 800 mm which were in series connection and mounted coaxially at a distance of 304 mm apart. Two cubic plastic rat cages whose length was along O–Y direction (Origin is the center of the middle coil, O–X direction is the axial direction of the coil and the coordinate system meets right-hand rule) were put in the center of every two neighboring coils and cages were supported by stands to let the activities of rats restrict on the XY plane. The modified Helmholtz coils were wired to the GHY-III pulse generator. (B) The pulse stimulator (GHY-III) generated an open-circuit voltage waveform of PEMF with a repetitive burst frequency at 15 Hz (burst width, 5 ms; burst wait, 60 ms; pulse width, 0.2 ms; pulse wait, 0.02 ms; pulse rise and fall time: 0.3 µs, 2.0 µs).