title: Psychophysics, flare, and neurosecretory function in human pain models: capsaicin versus electrically evoked pain.
abstract: Intradermal capsaicin injection (CAP) and electrical current stimulation (ES) are analyzed in respect to patterns and test-retest reliability of pain as well as sensory and neurosecretory changes. In 10 healthy subjects, 2x CAP (50 microg) and 2x ES (5 to 30 mA) were applied to the volar forearm. The time period between 2 identical stimulations was about 4 months. Pain ratings, areas of mechanical hyperalgesia, and allodynia were assessed. The intensity of sensory changes was quantified by using quantitative sensory testing. Neurogenic flare was assessed by using laser Doppler imaging. Calcitonin gene-related peptide (CGRP) release was quantified by dermal microdialysis in combination with an enzyme immunoassay. Time course and peak pain ratings were different between CAP and ES. Test-retest correlation was high (r > or = 0.73). Both models induced primary heat hyperalgesia and primary plus secondary pin-prick hyperalgesia. Allodynia occurred in about half of the subjects. Maximum flare sizes did not differ between CAP and ES, but flare intensities were higher for ES. Test-retest correlation was higher for flare sizes than for flare intensity. A significant CGRP release could only be measured after CAP. The different time courses of pain stimulation (CAP: rapidly decaying pain versus ES: pain plateau) led to different peripheral neurosecretory effects but induced similar central plasticity and hyperalgesia.
  
  
  CONCLUSIONS
  The present study gives a detailed overview of psychophysical and neurosecretory characteristics induced by noxious stimulation with capsaicin and electrical current. We describe differences, similarities, and reproducibility of these human pain models. These data might help to interpret past and future results of human pain studies using experimental pain.
authors: Klinik und Poliklinik für Neurologie der Universität Mainz, Germany. geber@uni-mainz.de
authors: Christian
authors: C
authors: Geber
authors: Ricarda
authors: R
authors: Fondel
authors: Heidrun H
authors: HH
authors: Krämer
authors: Roman
authors: R
authors: Rolke
authors: Rolfe-Detlef
authors: RD
authors: Treede
authors: Claudia
authors: C
authors: Sommer
authors: Frank
authors: F
authors: Birklein
mesh_terms: D000328:Adult; D015740:Calcitonin Gene-Related Peptide / Q000378:metabolism*; D002211:Capsaicin / Q000009:adverse effects; D004558:Electric Stimulation / Q000009:adverse effects; D005260:Female; D006801:Humans; D006930:Hyperalgesia / Q000209:etiology / Q000503:physiopathology / Q000523:psychology; D018836:Inflammation Mediators / Q000009:adverse effects; D017078:Laser-Doppler Flowmetry; D008297:Male; D008875:Middle Aged; D008959:Models, Neurological; D036421:Nerve Fibers, Unmyelinated / Q000187:drug effects / Q000378:metabolism*; D009473:Neuronal Plasticity / Q000502:physiology; D009490:Neurosecretory Systems / Q000187:drug effects / Q000378:metabolism*; D009619:Nociceptors / Q000378:metabolism*; D010146:Pain / Q000209:etiology / Q000378:metabolism* / Q000503:physiopathology*; D010147:Pain Measurement / Q000187:drug effects / Q000379:methods; D011601:Psychophysics / Q000379:methods; D012039:Regional Blood Flow / Q000187:drug effects / Q000502:physiology; D011984:Sensory Receptor Cells / Q000378:metabolism*; D012867:Skin / Q000294:innervation / Q000378:metabolism / Q000503:physiopathology; D013997:Time Factors
chemical_list: D018836:Inflammation Mediators; D015740:Calcitonin Gene-Related Peptide; D002211:Capsaicin