Fig. 7. MOR antagonists decrease fentanyl-induced anti-nociception in the hot plate assay. C57Bl/6 J mice were treated with either 10 mg kg⁻¹ of naloxone hydrochloride, 6-CF₂-NLX (5) and 6-CF₂-NTX (6), or vehicle (10% DMSO, 90% PBS). At (A) 1 h, (B) 8 h, and (C) 24 h post treatment, mice received 0.4 mg kg⁻¹ of fentanyl and latency on the hot plate was tested 15 minutes post fentanyl injection. Open symbols are female mice; closed symbols are male mice. * p < 0.05, ** p < 0.01 one-way ANOVA with Tukey post-hoc analysis.