Fig. 3. Using traditional scoring and our novel rat pain scale to measure morphine-induced analgesia over time in male rats.

(A) Schematic and experimental timeline: Long-Evans male rats received baseline (“b”) hind paw mechanical stimulations with VFHs or somatosensory stimuli. Rats then received a subcutaneous injection of morphine (3 mg/kg) and were returned to their home cage. At 15- and 60-min postmorphine injection, rats were returned to the testing chamber to receive hind paw stimulation using the same stimulus and procedure applied at baseline. (B) Traditional VFH thresholds after morphine treatment (3 mg/kg). (C) Proportion of withdrawal responses at 10-g VFH following morphine treatment. (D) Novel rat pain scale PCA-generated pain scores. *P < 0.05; **P < 0.01 compared to baseline measurements.