Nerve excitability in the rat forelimb: a technique to improve translational utility

Abstract Background Nerve excitability testing by threshold-tracking is the only available method to study axonal ion channel function and membrane potential in the clinical setting. The measures are, however, indirect and the interpretation of neuropathic changes remains challenging. The same multiple measures of axonal excitability were adapted to further explore the pathophysiological changes in rodent disease models under pharmacologic and genetic manipulations. These studies are typically limited to the investigation of the “long nerves” such as the tail or the tibial nerves. New method We introduce a novel setup to explore the ulnar nerve excitability in rodents. We provide normative ulnar data in 11 adult female Long Evans rats under anaesthesia by comparison with tibial and caudal nerves. Additionally, these measures were repeated weekly on 3 occasions to determine the repeatability of these tests. Results Nerve excitability assessment of ulnar nerve proved to be a longitudinally repeatable measure of axonal function mature in rats, as were measures in tibial and caudal nerves. Comparison with existing method: Ulnar nerve motor excitability measures were different from the caudal and tibial excitability measures. Most notably, ulnar nerve showed the largest threshold changes during both depolarizing and hyperpolarizing threshold electrotonus. Conclusions Ulnar nerves demonstrate a distinct nerve excitability profile than the caudal and tibial nerves which could have functional and pathological implications.