Effect of morphine and ibuprofen on nociceptive behavior, preening and motor activity following tonic chemical pain in the Japanese quail (Coturnix japonica)

Objective To establish a tonic chemical model of pain in quail and evaluate the efficacy of opioid and non-steroidal anti-inflammatory drugs. Study design A randomized, blinded, experimental Study design. Animals A total of 120 male Japanese quail, aged 7 weeks. Methods A formalin solution (0.3%, 0.6% and 0.9%; total volume of 40 mL) was injected subcutaneously (SC) into the medial aspect of the right metatarsus (shank). Foot lift and preening activities were recorded for 45 minutes following injection of formalin and scored by an investi-gator blinded to the treatment. An open field test was used to evaluate motor activity. Treatments included SC saline, SC morphine (1.25, 2.5 and 5 mg kg -1) and oral ibuprofen (5 and 10 mg kg -1). The treatment effect was analyzed by one-way ANOVA and the time course effect analyzed using repeated measures ANOVA, both followed by Dunnett's post hoc test (p < 0.05). Results All formalin concentrations induced significant foot lifting activity in the first phase (0-5 minutes), whereas only 0.6% and 0.9% formalin elicited responses in both the first and second (25-45 minutes) phases. Neither morphine nor ibuprofen affected phase 1 of the formalin test. Morphine (2.5 and 5 mg kg -1) and ibuprofen (5 and 10 mg kg -1) significantly reduced foot lift responses. Preening activity was significantly decreased following injection of 0.6% and 0.9% formalin. Preening was normalized with ibuprofen, but not with morphine. Morphine, but not ibuprofen, reduced quail activity. Conclusion and clinical relevance These results suggest that the formalin test was a reliable method for assessing tonic pain behavior in quail. The acute phase of the formalin test was not affected by morphine or ibuprofen. Although ibuprofen reduced the pain response in phase 2, the analgesic effects of morphine were not conclusive because morphine appeared to induce sedation.