TY - JOUR T1 - Topical Capsaicin-Induced Allodynia in Unanesthetized Primates: Pharmacological Modulation JF - Journal of Pharmacology and Experimental Therapeutics JO - J Pharmacol Exp Ther SP - 1106 LP - 1114 DO - 10.1124/jpet.103.052381 VL - 306 IS - 3 AU - Eduardo R. Butelman AU - Jonathan W. Ball AU - Todd J. Harris AU - Mary Jeanne Kreek Y1 - 2003/09/01 UR - http://jpet.aspetjournals.org/content/306/3/1106.abstract N2 - Topically administered capsaicin produces thermal allodynia, and this effect has been used to investigate pain transduction and its pharmacological modulation. This study investigated the parameters of topical capsaicin-induced thermal allodynia in unanesthetized rhesus monkeys and its pharmacological modulation by centrally acting compounds [a κ-opioid agonist: (5α,7α,8β)-(+)-N-methyl-N-(7-[1-pyrrolidinyl]-1-oxaspiro [4.5]dec-8-yl)-benzeneacetamide (U69,593); and noncompetitive N-methyl-d-aspartate (NMDA) antagonists: ketamine and MK-801 (dizocilpine)]. Rhesus monkeys (n = 4) were studied within the warm water tail withdrawal assay (20-s maximum latency), using thermal stimuli that are normally not noxious (38 and 42°C). Capsaicin was applied topically on the tail (0.0013 and 0.004 M capsaicin solution on a 1-cm2 patch; 15-min contact). Topical capsaicin produced concentration-dependent thermal allodynia in both temperatures, robustly detected 15 to 90 min after topical capsaicin removal. A similar allodynic profile was observed with topical administration of the “endovanilloid” N-arachidonoyl-dopamine. The κ-agonist U69,593 (0.01-0.1 mg/kg, s.c.) dose dependently prevented capsaicin (0.004 M)-induced allodynia in 38 and 42°C, and the largest U69,593 dose also reversed ongoing allodynia within this model. Two NMDA antagonists, ketamine and MK-801 (0.32-1.8 and 0.032-0.056 mg/kg, respectively), also prevented capsaicin-induced allodynia in 38°C, but only variably in 42°C, at doses that did not cause robust thermal antinociceptive effects. At the largest doses studied, ketamine but not MK-801 also briefly reversed ongoing capsaicin-induced allodynia. The present model of topical capsaicin administration may be used to study antiallodynic effects of opioid and nonopioid compounds, as well as their ability to prevent and reverse allodynia, in unanesthetized nonhuman primates in the absence of tissue disruption. The American Society for Pharmacology and Experimental Therapeutics ER -