title: Subcutaneous Botulinum toxin type A reduces capsaicin-induced trigeminal pain and vasomotor reactions in human skin.
abstract: The present human study aimed at investigating the effect of subcutaneous administration of Botulinum toxin type A (BoNT/A) on capsaicin-induced trigeminal pain, neurogenic inflammation and experimentally induced cutaneous pain modalities. Fourteen healthy males (26.3+/-2.6 years) were included in this double-blind and placebo-controlled trial. The subjects received subcutaneous BoNT/A (22.5U) and isotonic saline in the mirror sides of their forehead. Pain and neurogenic inflammation was induced by four intradermal injections of capsaicin (100mug/muL) (before, and days 1, 3 and 7 after treatments). The capsaicin-induced pain intensity, pain area, the area of secondary hyperalgesia, the area of visible flare and vasomotor reactions were recorded together with cutaneous heat, electrical and pressure pain thresholds. BoNT/A reduced the capsaicin-induced trigeminal pain intensity compared to saline (F=37.9, P<0.001). The perceived pain area was smaller for the BoNT/A-treated side compared to saline (F=7.8, P<0.05). BoNT/A reduced the capsaicin-induced secondary hyperalgesia (F=5.3, P<0.05) and flare area (F=10.3, P<0.01) compared to saline. BoNT/A reduced blood flow (F(1,26)=109.5, P<0.001) and skin temperature (F(1,26)=63.1, P<0.001) at the capsaicin injection sites compared to saline and its suppressive effect was maximal at days 3 and 7 (P<0.05, post hoc test). BoNT/A elevated cutaneous heat pain thresholds (F=17.1, P<0.001) compared to saline; however, no alteration was recorded for electrical or pressure pain thresholds (P>0.05). Findings from the present study suggest that BoNT/A appears to preferentially target Cfibers and probably TRPV1-receptors, block neurotransmitter release and subsequently reduce pain, neurogenic inflammation and cutaneous heat pain threshold.
authors.affiliation: Center for Sensory-Motor Interactions (SMI), Department of Health Sciences and Technology, Aalborg University, Fredrik Bajers Vej 7 D-3, DK-9220 Aalborg, Denmark.
authors.forename: Parisa
authors.initials: P
authors.lastname: Gazerani
authors.forename: Natalia Spicina
authors.initials: NS
authors.lastname: Pedersen
authors.forename: Camilla
authors.initials: C
authors.lastname: Staahl
authors.forename: Asbjørn Mohr
authors.initials: AM
authors.lastname: Drewes
authors.forename: Lars
authors.initials: L
authors.lastname: Arendt-Nielsen
mesh_terms: D000328:Adult; D000704:Analysis of Variance; D019274:Botulinum Toxins, Type A / Q000627:therapeutic use*; D002211:Capsaicin; D004311:Double-Blind Method; D006801:Humans; D007271:Injections, Intradermal / Q000379:methods; D017078:Laser-Doppler Flowmetry / Q000379:methods; D008297:Male; D009465:Neuromuscular Agents / Q000627:therapeutic use*; D010147:Pain Measurement / Q000379:methods; D017288:Pain Threshold / Q000187:drug effects; D012867:Skin / Q000098:blood supply*; D012881:Skin Temperature / Q000187:drug effects; D014277:Trigeminal Neuralgia / Q000139:chemically induced / Q000188:drug therapy*; D014661:Vasoconstriction / Q000187:drug effects*; D055815:Young Adult
chemical_list: D009465:Neuromuscular Agents; D019274:Botulinum Toxins, Type A; D002211:Capsaicin