Effect of NAX 409-9 in an acute assay of antinociceptive activity, the tail flick assay. Following compound administration, mice were placed under restraint for assessment of latency to tail flick following thermal stimulation (focused light). Mice were treated with either vehicle (1% Tween 20/saline), NAX 505-5 (8 mg/kg), NAX 409-9 (24 mg/kg), or morphine (6 mg/kg). Neither the GalR1-preferring, centrally active analog NAX 505-5 nor NAX 409-9 was effective in increasing tail flick latency, in comparison with morphine. N = 4–8 per group. **P < 0.01 compared with vehicle.