A pain model after gynecologic surgery: The effect of intrathecal and systemic morphine

BACKGROUND: Despite recent recognition that visceral pain differs from somatic pain in its neurophysiologic basis and treatment modalities, most laboratory studies of postoperative pain use a model of superficial somatic injury, and there is no model of postoperative pain after gynecologic surgery. We describe spontaneous behavior in rats after laparotomy with or without noxious stimulation of the uterus and cervix to more specially address pain after gynecologic surgery. METHODS: Female Sprague-Dawley rats received inhaled anesthesia only, anesthesia with laparotomy, or laparotomy plus 60 min of tonic distension of the lower uterine segment and cervix, followed by video observation of spontaneous behavior. RESULTS: Compared with anesthesia alone, laparotomy decreased some spontaneous behaviors (drinking water, grooming, and exploration). Laparotomy plus uterocervical manipulation further decreased these behaviors and increased abnormal behaviors (licking of the lower abdomen and squashing posture of the pelvis to the floor). Intrathecal and systemic morphine restored spontaneous behavior and reduced abnormal behaviors, with minor differences between routes of administration. CONCLUSIONS: These data suggest that specific behaviors may distinctly reflect somatic and visceral components of postoperative gynecologic pain, and that this model may be used to test novel therapies to relieve pain in this setting.