Decreased voluntary wheel running has recently been proposed as a preclinical
pain measure for inflammatory
pain, but whether this reflects
pain evoked by use of the affected limbs is unknown. To assess the role of
inflammation site as a determinant of this measure, complete
Freund's adjuvant (CFA),
formalin, or equivolume vehicle was subcutaneously injected into the plantar surface of the hind paws (bilateral) or L1 dorsum dermatome (leaving paws unaffected) of male Sprague Dawley rats. CFA-induced hind paw
mechanical allodynia (P < .001) did not correlate with reduced voluntary wheel running. Intraplantar
formalin did not attenuate voluntary running, despite eliciting robust licking/writhing/flinching behavior and hind paw
mechanical allodynia (P < .001). Subcutaneous L1 dorsum dermatome
formalin, but not CFA, induced licking/writhing/flinching behavior (P < .001), but neither induced hind paw
mechanical allodynia or attenuated voluntary running. That voluntary running is decreased by hind paw CFA, but not by L1 dorsum CFA, implies that the behavior is a measure of CFA-induced
pain evoked by use of the affected limbs rather than supraspinal
pain processing that is independent of
inflammation site. Furthermore, the results suggest that interpretation of voluntary wheel running data cannot simply be explained by correlation with
mechanical allodynia.
PERSPECTIVE: Whether decreased voluntary running is dependent on
inflammation site is unknown. We show that intraplantar, but not L1 dorsum, CFA suppressed voluntary running and
formalin-induced licking/writhing/flinching behavior but had no effect on voluntary running. These data suggest that suppressed voluntary running by CFA likely reflects
pain evoked by use of the affected limbs.