Anodal Block in Evaluation of Nerve Conduction Changes in Anesthetized Rats: Preclinical Non-Randomized Experimental Study

Background. There is currently no gold standard for functional assessment of nerve regeneration. Different researchers use various methods to assess the functionality of the regenerated nerve directly and indirectly. Indirect methods have the advantage of being minimally invasive, and the benefit of direct methods is recording the signal directly in the nerve.

Objectives. To identify significant parameters of neurogram changes in the sciatic nerve in an anaesthetized rat when the anode block is applied and to evaluate neurography as a method for functional assessment of nerve regeneration.

Methods. A series of experiments was performed on 10 anaesthetized rats. A DC anode was placed on the exposed sciatic nerve, more proximal and more distal to the recording electrodes, and a common cathode in the form of a needle was introduced into one of the forelimbs. Needle nichrome electrodes were introduced into the nerve using a manipulator. An original neurogram and a neurogram against anode activation were recorded by closing the DC circuit of different voltages to block the afferent signal, efferent signal and afferent and efferent signals simultaneously.

Results. When the anodal block of different voltages was applied to the afferent signal, efferent signal, and afferent and efferent signals simultaneously in all 10 experiments, the frequency-amplitude characteristics of the neurogram changed significantly as compared to the original neurogram. The amplitude of the neurogram increased considerably, while the frequency decreased, though not so dramatically. The changes in amplitude and frequency parameters were revealed to depend on the voltage value. In most cases, this relationship was directly proportional to the amplitude and inversely proportional to the frequency.

Conclusion. Considering the nature of the dynamics of the neurogram when exposed to the anodal block, the most significant parameter of its change is the amplitude. Changes in nerve fibre composition during its regeneration after damage cause changes in afferent and efferent signals, which is likely to be displayed in the neurogram as compared to the initial state. Thus, the anodal block can be used as a model of nerve damage, and the analysis of the dynamics of neurogram parameters — as a method for functional assessment of nerve regeneration.