Background and aims: There is a lack of methods for studying the excitability of small cutaneous sensory nerve fibers. Our research group has therefore developed a novel perception threshold tracking (PTT) technique, which indirectly assess excitability in nerve fibers. The aim of this study was to use PTT to assess accommodation in small and large fibers. 

Methods: A multiple-pin electrode was used to preferentially activate small fibers whereas a conventional patch electrode was used for activating large fibers. We used linearly-increasing ramp currents with durations of: 1ms, 10ms, 25ms, 50ms, 100ms, and 200ms. Two detailed multi-compartment fiber models were developed to associate nerve fiber accommodation to transmembrane ion currents. The axon models included a wide range of voltage-gated ion channels: NaTTXs, NaTTXr, NaP, KDr, KM, and HCN.

Results: The large fibers displayed accommodation to ramp pulses longer than 50ms (p<0.05; rmANOVA). However, the small fibers did not accommodate; the perception thresholds decreased as the pulse duration increased (p<0.05; rmANOVA). The computational model showed that difference in accommodation could be explained by different distribution of TTX sensitive- and TTX resistant sodium channels which have different inactivation properties. 

Conclusions: The PPT technique could identify excitability changes during accommodation and may potentially become a clinical tool for evaluating excitability.
Acknowledgements: Funded by Center for Neuroplasticity and Pain (CNAP). CNAP is supported by the Danish National Research Foundation (DNRF121).

ACCOMMODATION OF CUTANEOUS NERVE FIBERS ASSESSED WITH THE PERCEPTION THRESHOLD TRACKING TECHNIQUE