Effects of laparotomy on spontaneous exploratory activity and conditioned operant responding in the rat: a model for postoperative pain.
                             
                            
                            
                                
                            
                            
                                
                            
                            
                            
                                
                                    
                                            
    Martin TJ, Buechler NL, Kahn W, Crews JC, Eisenach JC. Effects of laparotomy on spontaneous exploratory activity and conditioned operant responding in the rat: a model for postoperative pain. Anesthesiology. 2004 Jul; 101(1):191-203.