Intrathecal ondansetron reduces VMR evoked by noxious CRD and prevents development of visceral hyperalgesia induced by intracolonic mustard oil. (A) VMR evoked by a range of innocuous to noxious CRD pressures before and after ondansetron administration (n = 6; *P < 0.05, **P < 0.01 control vs. 60 min). (B) Collective area-under-curve data of rats given ondansetron (OND; n = 6), intracolonic mustard oil (MO; n = 8), and intracolonic mustard oil and ondansetron (MO + OND; n = 6) (*P < 0.05, **P < 0.01, ***P < 0.001).