New method to discriminate sedative and analgesic effects of drugs in the automated formalin test in rats.

We developed an automated technique based on the detection of pain-related behaviours (like licking or biting) and small activities (mostly grooming) in the formalin pain test. By comparing automated and manual scoring, we determined that the interphase score was mostly independent of pain-related behaviours and it was used as an index of sedative events. The non-pain-related behaviours, still present during the second phase, were eliminated in order to visualize only pain-related behaviours. This new method, validated using classical analgesic (morphine) and sedative drugs (diazepam) could be used to discriminate sedative from analgesic effects of pharmacological treatments in the formalin test.