title: Measurement of CFA-induced hyperalgesia and morphine-induced analgesia in rats: dorsal vs plantar mechanical stimulation of the hindpaw.
abstract: OBJECTIVE
  To compare the sensitivity of stimulating the plantar and dorsal hindpaw surfaces in the detection of mechanical allodynia and morphine analgesia.
  
  
  BACKGROUND
  Several approaches are used to assess nociceptive reactivity to mechanical stimulation in animal models of pain. Although certain techniques seem to be favored for studying specific nociceptive conditions, the differences between techniques have not been directly compared and characterized. We chose to compare methods employing stimulation applied to the dorsum of the paw with stimulation of the plantar surface to demonstrate the utility of each approach in determining baseline nociceptive thresholds, changes in those thresholds after injury, and analgesic efficacy.
  
  
  METHODS
  Withdrawal thresholds from mechanical stimulation applied to the dorsal and plantar surface of the hindpaw were measured in rats treated with morphine after receiving subcutaneous injections of complete Freund's adjuvant (CFA) using Semmes-Weinstein (S-W) monofilaments and electro von Frey (EVF) stimulation.
  
  
  RESULTS
  In contrast to stimulation of the dorsal surface, plantar hindpaw stimulation seldom elicited an aversive withdrawal response. Differences in withdrawal response from baseline were only detectable within the first 5 hours post-CFA and only with EVF stimulation. No significant differences in stimulation techniques were observed after the initial 5-hour window. Effective dose 50 (ED(50)) for analgesic efficacy was consistently lower using dorsal stimulation.
  
  
  CONCLUSIONS
  Stimulation of the plantar surface of the paw is superior for detecting small changes in paw sensitivity at very low stimulus intensities, whereas stimulation of the dorsal surface is superior for delineating baseline pain thresholds and for detecting robust analgesia.
  
  
  CONCLUSIONS
  Reliable and sensitive assessment of animal pain behaviors is critical to translational pain research. This study demonstrates the importance of using proper test protocols in animal studies and its implication in preclinical screening of potential analgesics.
authors.affiliation: Department of Psychology, University of New Orleans, New Orleans, Louisiana, USA.
authors.forename: R Denis
authors.initials: RD
authors.lastname: Soignier
authors.forename: Bradley K
authors.initials: BK
authors.lastname: Taylor
authors.forename: Brandon A
authors.initials: BA
authors.lastname: Baiamonte
authors.forename: Frank A
authors.initials: FA
authors.lastname: Lee
authors.forename: Dennis
authors.initials: D
authors.lastname: Paul
authors.forename: Harry J
authors.initials: HJ
authors.lastname: Gould
mesh_terms: D000701:Analgesics, Opioid / Q000494:pharmacology / Q000627:therapeutic use*; D000818:Animals; D001522:Behavior, Animal / Q000187:drug effects; D004195:Disease Models, Animal; D004305:Dose-Response Relationship, Drug; D005528:Foot / Q000033:anatomy & histology* / Q000502:physiology*; D005620:Freund's Adjuvant / Q000009:adverse effects*; D006930:Hyperalgesia / Q000139:chemically induced*; D008297:Male; D009020:Morphine / Q000494:pharmacology / Q000627:therapeutic use*; D010146:Pain / Q000139:chemically induced / Q000188:drug therapy; D010147:Pain Measurement / Q000379:methods; D010812:Physical Stimulation; D051381:Rats; D017207:Rats, Sprague-Dawley
chemical_list: D000701:Analgesics, Opioid; D009020:Morphine; D005620:Freund's Adjuvant