2.4 Mechanical allodynia test
Mechanical allodynia in the diabetic rats was assessed as previously described (Lu et al., 2021). Briefly, rats were individually placed in plexiglass enclosures (28×22×18 cm) with a wire mesh bottom and allowed to acclimate for at least 30 minutes. Using a commercial electronic von Frey apparatus (model 2390, IITC Life Science Inc., Woodland Hills, CA, USA), pressure was applied to the median plantar surface of the right hind paw by a von Frey fiber with a maximum pressure of 55 g. A positive response was defined as an induced pain response (sudden withdrawal, shaking or licking of the hind paw) from the pressure of a filament, and the number on the liquid crystal display was then recorded. The test was performed at intervals of at least 5 minutes to eliminate interference from a previous stimulation. The test continued until three MWT readings were collected after the first change in response. The MWT for each subject was considered the mean of the 3 collected values. To minimize animal discomfort, mechanical nociceptive thresholds were tested in only one hind paw.