as cell bodies in the myentenc plexus showed faint staining. This was consistent with the staining pattern observed in the distal colon in which staining was also detected in submucosal plexus cell bodies. In fundus circular muscle, rat NmU-23 (0.1 nM0.1 g,M) had no effect on elecmcafiy-evoked, nerve-mediated contractile responses but concentration-dependently increased nerve-mediated contractile responses in distal colon preparations, ECso ~ 15 riM; n=6-8 (stomach) and n=3-4 (colon), each concentration. Rat NmU-23 (0.1 nM0.1 g-M) concentration-dependently contracted both mouse gastric fundns (ECs0 ~0.08 g.M) and distal colon smooth muscle, EC~0 ~ 1 p,M; n = 12 (stomach) and n = 4 (colon), each concentration. CONCLUSIONS: NmU potently contracts mouse gastric fundns but not colon smooth muscle and has an ability to exert prokinetic-like activity in colon but not gastric fundus preparations. Based on localisation studies, these effects may be mediated via NmU-R2, although NmURl-mediated effects cannot be excluded.