2.3.1 von Frey test

At baseline (before surgery) and either 21 or 28 dpo (see below), a subset of mice was transferred to acrylic chambers in a behavioral testing room for the von Frey test of mechanical sensitivity. This assay was not performed 1 day after surgery since SCI mice had BMS scores of 0 or 1, indicating very little hindpaw placement. All mice were acclimated to the behavioral suite and testing apparatuses for at least 3 days prior to surgery. On testing days, following a 30-min acclimation period, individual animals were assayed for mechanical sensitivity (paw withdrawal responses) according to the established up-down method (Chaplan et al., 1994). Calibrated von Frey hairs (NC12775-99, North Coast Medical, Inc., Morgan Hill, CA, USA) starting with filament evaluator size 3.22 (target force 0.16 g) were administered from below a metal mesh platform to test each animal’s sensitivity to mechanical stimulation of the hindpaw. Right and left paw withdrawal thresholds were averaged to determine overall mechanical sensitivity. A reduction in von Frey withdrawal threshold values from their baseline levels corresponded to increased mechanical sensitivity.