Mechanical hypersensitivity
The development of mechanical allodynia of the hind paw ipsilateral to
the MIA-injected knee (indicating referred pain) was assessed by
measuring paw withdrawal thresholds (PWT, expressed in grams) using an
electronic von Frey anesthesiometer (IITC Life Science, Woodland Hills,
CA). Animals were placed in individual plastic cages with a metal mesh
floor which allowed access to the plantar surface of each hind paw.
After the habituation period, a semi-flexible plastic von Frey filament
was applied on the plantar surface of the ipsilateral hind paw with
increasing force until a paw withdrawal response was elicited. The force
at which this reaction occurs is automatically recorded by the device.
Six to eight PWT measurements were taken at each time point and the mean
value was used for further calculations.