Single-fiber recordings of unmyelinated afferents in pig.

Microneurography has provided valuable data on single-fiber characteristics in healthy volunteers and patients, featuring a unique setting that allows linking discharge of single fibers to percept. This advantage is of particular value, when pain patients are examined. Latest results on specific changes of axonal excitability differentially expressed in various C-fiber classes have incited studies linking axonal excitability changes to the mechanism of chronic pain. These studies are mainly based on investigating patients rather than establishing animal models and have led to specific questions on the molecular mechanisms underlying axonal excitability changes. However, pharmacological interventions are limited in human microneurography and therefore an animal model is required. Ideally, the distribution of fiber classes and their sensory and axonal characteristics should be comparable to human. Here we report on corresponding C-fiber classes between human and pig. Nociceptive and non-nociceptive fiber classes found in pig correlate with human fiber classes, in both distribution and axonal excitability changes. It is suggested that the pig is an attractive model for studying modulation of excitability in nociceptive and non-nociceptive C-fiber classes that correspond to those in man.