The distance between the two electrode tips can greatly influence the parameters used for recording compound nerve action potentials.
To investigate the optimal parameters for these recordings in the rat median nerve, Prof. Jie Lao and colleagues from HuaShan Hospital, Fudan University in China dissociated the nerve using different methods and compound nerve action potentials were orthodromically or antidromically recorded with different electrode spacings.
Compound nerve action potentials could be consistently recorded using a method in which the middle part of the median nerve was intact, with both ends dissociated from the surrounding fascia and a ground wire inserted into the muscle close to the intact part.
A distance of 5 mm between recording and stimulating electrodes and a distance of 10 mm between recording and stimulating sites were found to be optimal for compound nerve action potential recording in the rat median nerve.
In addition, the orthodromic compound action potential, with a biphasic waveform that was more stable and displayed less interference (however also required a higher threshold and higher supramaximal stimulus), was found to be superior to the antidromic compound action potential.
This shows the different approaches to compound nerve action potential recording. Both ends of the median nerve had electrodes placed, leaving the middle part of approximately 4-5 mm intact. The two electrodes were placed under both ends of the nerve trunk, distal and proximal to the middle. The ground wire was inserted into the muscle close to the intact part (Method A; n = 10). In Method B (n = 10), the median nerve was completely dissociated, then otherwise treated as in Method A. In the third approach, the ground wire was placed beneath the middle part of the completely dissociated median nerve trunk (Method C; n = 10). Sti: Stimulating electrodes; Rec: recording electrodes; Gnd: ground wire.
Credit: Neural Regeneration Research