Fig. 1. Change in electromyographic (EMG) activity induced by uterine cervical distension in ovariectomized rats receiving cumulative doses of intravenous −U50,488 with (closed circles) or without (open circles) norbinaltorphimine (norBNI) pretreatment. NorBNI, 20 mg/kg, was applied intraperitoneally 48 and 24 h before testing. Each symbol represents the mean ± SEM of 6 rats. *P < 0.05 versus  control. No differences between groups.