Morphine

8-12 weeks old female C57BL/6 or Nrf2^−/− (B6.129X1-Nfe2l2tm1Ywk/J, The Jackson Laboratory, Maine, USA) mice weighing 18-22g were used for all experiments. All experiments that utilized Nrf2^−/− mice were genotyped as previously described^{23 (link)}. Animals were anesthetized by i/p injection of 0.024 ml/per g of Avertin and had their dorsal and flank hair clipped. A subcutaneous injection of morphine (3 mg/kg; Baxter Healthcare) was given prior to burn injury for pain control. To create a full-thickness thermal burn of approximately 20% Total Body Surface Area (TBSA), a 65 g copper rod (1.9 cm in diameter), heated to 100°C was applied to four separate areas, each for 10 seconds, to the animal’s dorsum and flank at a standard pressure that we have demonstrated produces a full-thickness burn²⁴ . 2 mL of warmed lactated Ringer’s solution (Hospira) was administered intraperitoneally immediately after burn injury for fluid resuscitation. Animals were recovered on a heating pad, returned to individual cages, provided food and morphinated water, and continuously monitored until euthanasia per protocol or 24 hours post-burn injury. Temperature measurements were determined by rectal probe thermometer. Sham controls underwent all described interventions except for the burn injury.