Measurement of Nociceptive Behavior in the Formalin Test

Paw flinching is one of the behaviors related to nociception in the formalin model and is characterized by spontaneous, rapid, brief flinching, or lifting of the leg. Therefore, each episode of shaking, vibrating, or raising the leg was counted as one flinch. The antinociceptive response was measured by evaluating the time course. Subsequently, the area under the curve was calculated by the trapezoid method [48] of the number of flinches in relation to time. From these results, the percentage of antinociception was calculated, using the formula presented below:

where:

AUC Vehicle: Area under the curve of the vehicle group

AUC post-treatment: Area under the curve of the treated groups

Two types of pain are measured in this test: 0 to 10 min (phase 1) represents nociceptive pain, and 15 to 60 min (phase 2) corresponds to inflammatory pain.