title: Burrowing as a non-reflex behavioural readout for analgesic action in a rat model of sub-chronic knee joint inflammation.
abstract: BACKGROUND
  Innate responses against spontaneous pain are proposed to improve the predictive validity of preclinical analgesia models. Therefore, development and validation of novel readouts is necessary. To investigate whether innate rodent burrowing is a useful alternative behavioural readout for assessment of analgesic efficacy, a complete Freund's adjuvant (CFA)-induced model of sub-chronic inflammation was used to compare the effects of naproxen, ibuprofen and pregabalin in weight-bearing (WB), open-field (OF) and burrowing assays.
  
  
  METHODS
  Male Sprague Dawley rats were injected with 150 μL of CFA (2 mg/mL) into the knee (hind leg) 3 days before testing. Naproxen, ibuprofen and pregabalin were administered at different doses 30, 90 and 60 min, respectively, before testing. WB was determined using a rat incapacitance tester; horizontal distance moved and vertical rearings were recorded in an OF; and burrowing was measured by the weight of gravel remaining in a hollow tube after 60 min.
  
  
  RESULTS
  CFA-induced arthritis reduced WB, OF activity and burrowing. Naproxen, pregabalin and ibuprofen treatment normalized WB; however, horizontal OF activity was not improved by any treatment; rearing behaviour was moderately reinstated by ibuprofen (100 mg/kg). In burrowing, naproxen (100 mg/kg), ibuprofen (31.6 and 100 mg/kg) and pregabalin (10 mg/kg) reversed CFA-induced deficits.
  
  
  CONCLUSIONS
  Burrowing performance is an alternative non-reflex readout relying on innate rodent behaviour that is affected by nociceptive behaviour and can be pharmacologically manipulated. The burrowing assay appears to be more sensitive than OF assays and is as sensitive as WB assays at distinguishing between analgesic doses and doses that impair locomotion.
authors.affiliation: Department of Pharmacology Pain, Global Biomedical Sciences, Grünenthal GmbH, Aachen, Germany.
authors.forename: K
authors.initials: K
authors.lastname: Rutten
authors.forename: K
authors.initials: K
authors.lastname: Schiene
authors.forename: A
authors.initials: A
authors.lastname: Robens
authors.forename: A
authors.initials: A
authors.lastname: Leipelt
authors.forename: T
authors.initials: T
authors.lastname: Pasqualon
authors.forename: S J
authors.initials: SJ
authors.lastname: Read
authors.forename: T
authors.initials: T
authors.lastname: Christoph
mesh_terms: D000698:Analgesia / Q000379:methods; D000700:Analgesics / Q000008:administration & dosage / Q000627:therapeutic use*; D000818:Animals; D000894:Anti-Inflammatory Agents, Non-Steroidal / Q000627:therapeutic use*; D001522:Behavior, Animal; D002908:Chronic Disease; D004195:Disease Models, Animal; D007052:Ibuprofen / Q000008:administration & dosage / Q000627:therapeutic use*; D007249:Inflammation / Q000188:drug therapy; D007719:Knee Joint / Q000187:drug effects*; D008297:Male; D009288:Naproxen / Q000627:therapeutic use*; D010146:Pain / Q000188:drug therapy; D010147:Pain Measurement; D051381:Rats; D017207:Rats, Sprague-Dawley; D012018:Reflex / Q000502:physiology
chemical_list: D000700:Analgesics; D000894:Anti-Inflammatory Agents, Non-Steroidal; D009288:Naproxen; D007052:Ibuprofen