Von Frey hair test for mechanical allodynia

Neuropathic pain is characterized by the development of mechanical allodynia, i.e., animals exhibit pain in response to nonpainful mechanical stimuli. Accordingly, the von Frey hair test (BiosebLab, France) was conducted to assess mechanical allodynia in which response of animals to von Frey hair filaments of different bending forces (0.008 to 300g). In this test, von Frey hair filaments (of varying stiffness) were applied ten times in the ascending order of stiffness to the plantar region of the hind paw to induce paw withdrawal. The withdrawal threshold was noted in grams, which was equal to von Frey hair stiffness that evoked 50% paw withdrawal21.