title: Effects of different concentrations of formalin on paw edema and pain behaviors in rats.
abstract: The aim of this study was to determine whether formalin reliably provokes a paw edema and pain behavior. The paw of male Sprague-Dawley rats were injected with 100 microliter of formalin with 2.5% (F2.5), 5% (F5), and 10% (F10) concentrations. Following the formalin (n=8) or saline (control, n=6) injection, the flinching or licking of the paw was recorded for the phase 1 response (0-5 min after injection) and phase 2 response (20-60 min). The formalin-induced paw edema was assessed by measuring the diameters of the injected paws at 4 hr after injection. As for flinching, phase 1 and 2 of all three groups showed higher frequency than those of the control group (p<0.05). As for licking, phase 1 cumulative time of the F2.5 and F10 groups, and phase 2 cumulative time of the F2.5 and F5 groups showed a longer duration than those in the control group (p<0.05). The diameters of the paw in the F10 group were significantly larger than those in the control group (p<0.05). Flinching behavior was more reliably expressed the biphasic response than licking response at all formalin concentrations. Peak of the licking was reached at 2.5% and that of flinching was reached at 5%, whereas the paw edema peaked at 10% concentration. This suggests that there may be some dissociation of nociception from the edema formation.
authors.affiliation: Department of Anesthesia, College of Medicine, Korea University, Korea University Guro Hospital, 80 Guro-dong, Guro-gu, Seoul 152-703, Korea. iloklee@hotmail.com
authors.forename: Il Ok
authors.initials: IO
authors.lastname: Lee
authors.forename: You Seong
authors.initials: YS
authors.lastname: Jeong
mesh_terms: D000818:Animals; D001522:Behavior, Animal; D004487:Edema / Q000139:chemically induced*; D005121:Extremities; D005557:Formaldehyde / Q000009:adverse effects*; D008297:Male; D010146:Pain / Q000139:chemically induced*; D051381:Rats; D017207:Rats, Sprague-Dawley
chemical_list: D005557:Formaldehyde