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Functional tests of neuronal signal processing in humans

Pathological changes in the function of nerve fibers may lead to long-term pain or itch, impairing the patients’ quality of life considerably. For a better understanding of the possible causes and mechanisms underlying such changes, we perform a range of non-invasive test procedures in healthy subjects and patients, assessing subjective, functional, structural, as well as metabolic parameters to examine the functionality and integrity of specific nerve fiber populations. Experimental models are established for studies in healthy subjects to emulate clinical symptoms of patients in the short term. These models allow us to detect changes in the receptive and axonal properties of nerve fibers as well as metabolic and modulatory influences which might indicate new therapeutic options for patients with neuropathic pain and itch.

Test procedures for specific nerve fibers include determination of local sweat gland activation (sympathetic efferents), Laser Doppler imaging to detect changes in skin blood flow and axon reflex erythema (mechano-insensitive (“silent”) C-nociceptors), microdialysis of skin mediators (interaction of nerve fibers and tissue cells), quantitative sensory testing to investigate threshold values and sensitivity to thermal and mechanical stimuli, supra-threshold mechanical impact stimuli and punctate electrical stimulation of the skin to explore axonal excitability, extraction of skin punch biopsies to analyse local protein expression patterns, and stimulus blockade models to examine the mechanisms contributing to the modulation of nociceptive afferent sensitivity.