title: Parturition in the rat: a physiological pain model.
abstract: BACKGROUND
  Pain during labor is a common and severe phenomenon, but its clinical management remains haphazard because its neurophysiology is poorly understood. In the current study, the authors evaluate the parturient rat as a relevant model to study the pharmacology of labor pain.
  
  
  METHODS
  Control of birth timing in term pregnant rats was achieved by gavage with RU 486 (5 mg/kg) the day before the expected day of parturition. The behavioral events preceding the expulsion of the first pup were analyzed, and immunodetection of the c-Fos protein was used to evaluate the spinal neuronal activity at the lumbosacral level where genital and perineal inputs terminate.
  
  
  RESULTS
  Hind limb and abdominal stretches occurred during labor (mean number, 57 +/- 10), arbitrarily defined as the time elapsed between the first stretch and the expulsion of the first pup (mean duration, 62 +/- 5 min). Subcutaneous oxytocin increased the frequency of stretches, accounting for the fact that these manifestations are linked to uterine contractions. Finally, epidural morphine (30 microg/10 microl) in oxytocin-treated rats, although resulting in no change of labor duration, significantly decreased the number of stretches (8 +/- 2 vs. 57 +/- 12 for epidural saline) and the number of c-Fos-positive neurons in the lumbosacral spinal segments (80 +/- 25 vs. 165 +/- 17 for epidural saline).
  
  
  CONCLUSIONS
  These results indicate that stretches during labor in the rat correspond to a behavioral response to nociception associated with uterine contractions and suggest that parturition in the rat could be a relevant model to investigate nociceptive mechanisms associated with parturition in women.
authors.affiliation: Received from Ecole Pratique des Hautes Etudes, Laboratoire de Neurobiologie Intégrative et Adaptative INSERM U378, Bordeaux, France. g.catheline@imf.u-bordeaux2.fr
authors.forename: Gwénaëlle
authors.initials: G
authors.lastname: Catheline
authors.forename: Bastien
authors.initials: B
authors.lastname: Touquet
authors.forename: Jean-Marie
authors.initials: JM
authors.lastname: Besson
authors.forename: Marie-Christine
authors.initials: MC
authors.lastname: Lombard
mesh_terms: D000818:Animals; D004195:Disease Models, Animal; D005260:Female; D009020:Morphine / Q000494:pharmacology; D010121:Oxytocin / Q000494:pharmacology; D010146:Pain / Q000503:physiopathology*; D036801:Parturition / Q000502:physiology* / Q000523:psychology; D011247:Pregnancy; D016760:Proto-Oncogene Proteins c-fos / Q000032:analysis; D051381:Rats; D017207:Rats, Sprague-Dawley; D014590:Uterine Contraction
chemical_list: D016760:Proto-Oncogene Proteins c-fos; D010121:Oxytocin; D009020:Morphine