• Gwénaëlle Catheline, Bastien Touquet, Jean-Marie Besson, and Marie-Christine Lombard.
• Received from Ecole Pratique des Hautes Etudes, Laboratoire de Neurobiologie Intégrative et Adaptative INSERM U378, Bordeaux, France. g.catheline@imf.u-bordeaux2.fr
• Anesthesiology. 2006 Jun 1; 104 (6): 1257-65.

BackgroundPain 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.MethodsControl 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.ResultsHind 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).ConclusionsThese 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.

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