Mean thermal antinociceptive responses to chronic administration of morphine with or without ULD naloxone.

Control (C3H/HeOuJ) and TLR4 mutant (C3H/HeJ) mice were treated with vehicle (saline, SAL), morphine (10 mg/kg, MS), MS and (−)naloxone (1 ng/kg, NLX), or MS and (+)naloxone (1 ng/kg) once daily (i.p) for 5 days. Antinociception was measured 30 minutes post-injection by the hot-water tail flick test and are expressed as means ± s.e.m.*significantly different compared to morphine-treated group of same genotype. Responses were not different between genotypes for any treatment at any time point.