title: Topically applied capsaicin inhibits sensitivity to touch but not to warmth or heat-pain in the region of secondary mechanical hyperalgesia.
abstract: The aim of this study was to investigate tactile sensitivity near the site of primary hyperalgesia evoked by capsaicin applied topically to the dorsolateral aspect of the hand. In the first experiment (N = 15), touch thresholds increased in the fifth finger ipsilateral to the topically applied capsaicin, but remained unchanged at greater distances from the site of capsaicin treatment. In a second experiment (N = 12), the effect of the capsaicin treatment on sensations evoked not only by light touch but also by warmth, heat-pain, and pressure-pain to a 2-mm diameter steel probe was investigated in the fifth finger. Again, tactile sensitivity was inhibited at the fifth finger, even though stimulation with a cotton bud evoked no discomfort; moreover, sensitivity to warmth and heat-pain were unimpaired. However, sensitivity to pressure-pain increased in the fifth finger after the capsaicin treatment, possibly due to activation of nociceptors sandwiched between the probe tip and bone that normally responded to sharp stimuli. These findings suggest that the central mechanisms that mediate secondary mechanical hyperalgesia suppress sensitivity to innocuous tactile sensations. This effect may contribute to tactile hypoesthesia in chronic pain conditions.
authors.affiliation: School of Psychology, Murdoch University, Perth, Australia. P.Drummond@murdoch.edu.au
authors.forename: Peter D
authors.initials: PD
authors.lastname: Drummond
authors.forename: Paul
authors.initials: P
authors.lastname: Blockey
mesh_terms: D000287:Administration, Topical; D000293:Adolescent; D000328:Adult; D002211:Capsaicin / Q000009:adverse effects / Q000494:pharmacology*; D005260:Female; D007839:Functional Laterality; D006801:Humans; D006930:Hyperalgesia / Q000139:chemically induced* / Q000503:physiopathology*; D008297:Male; D008875:Middle Aged; D018689:Sensory System Agents / Q000009:adverse effects / Q000494:pharmacology*; D012684:Sensory Thresholds / Q000187:drug effects*; D014110:Touch / Q000187:drug effects*; D055815:Young Adult
chemical_list: D018689:Sensory System Agents; D002211:Capsaicin