2.14. Assessment of mechanical hyperalgesia–Randall Selitto test (paw pressure test)

The assessment of mechanical hyperalgesia consisted of measuring the withdrawal threshold of the paw both ipsilateral and contralateral to the site of nerve injury or inflammation in response to continuously-increased pressure (noxious stimuli) using Randall Selitto method.⁵³ Animals were exposed to the testing apparatus and the experimenter for 1 day prior to testing for 3 times. Paw withdrawal threshold was assessed using the Randall–Selitto nociceptive paw withdrawal flexion reflex test with an Ugo-Basile algesymeter (Stoelting, Chicago, IL), which applies a linearly increasing mechanical force to the plantar surface of the rat’s hind paw. A sharp withdrawal of the paw or vocalization is the end point. Testing was performed in alternating fashion on left and right hind paws for 3 times. Reported paw withdrawal thresholds are the mean of 3 tests. Paw withdrawal thresholds (in grams) are calculated according to the weight applied: 0 weight = 10× of the reading; 1 weight = 20× of the reading; 2 weights = 30× of the reading. Cutoff at 500 g. Compared to the baseline, an increase/decrease of the paw withdrawal threshold indicates the analgesic/hyperalgesic effects of the treatments.