Pharmacological validation of an automated method of pain scoring in the formalin test in rats

In 1997, we described a new automated method of scoring the pain behaviors in the formalin test, The algic behavior was automatically measured with th e help of a video-analysis system. The time during which the animal grooms, licks, or bites itself was used as the parameter of pain. In the present st udy, we tested various analgesics to realize a pharmacological validation o f the system. The effect of opiate analgesic (morphine, i.v.), nonsteroidal anti-inflammatory drugs (paracetamol, i.v., piroxicam, i.v.; indomethacin, i.v.), antidepressant drugs (clomipramine, desipramine, nortryptyline, and paroxetine, i.p.); and serotonin (i.t.) were analyzed. A dose of 1.25 mg/k g of morphine induced a decrease in the scores of phases 1 and 2. Naloxone (0.25 mg/kg) reversed the effect of morphine (2.5 mg/kg). A 20-mg/kg dose o f indomethacin induced a decrease in the second phase, and paracetamol indu ced a decrease in both phases (analgesic doses were 400 mg/kg and 200 mg/kg for first and second phases, respectively). Piroxicam had no effect on the pain scores. Clomipramine, desipramine, and paroxetine at a dose of 5 mg/k g induced a significant decrease in the second phase. Nortriptyline had no effect on the pain scores. A dose of 75 mu g of serotonin induced a decreas e in both phases 1 and 2. This study demonstrated that this system shows a good pharmacological sensitivity, although it is lower than that of manual assessment. (C) 2000 Elsevier Science Inc. All rights reserved.