Pain sensitivity: tail flick test

The tail flick test was performed using the D’Amour and Smith method (D'Amour and Smith, 1941; Ugo Basile apparatus). The animals were restrained manually with their tails left extended. The test consisted of focusing a beam of light on three different positions along the tail base. The light would confer radiant heat, and the latency to flitch the tail outside of the apparatus was monitored. A cutoff of 10 s was maintained; if the animal did not show painful reaction within this set time, the trial was considered invalid, and the animal would be removed from the apparatus.