Effects of different concentrations of formalin on paw edema and pain behaviors in rats.
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.
Lee
Il Ok
IO
Department of Anesthesia, College of Medicine, Korea University, Korea University Guro Hospital, 80 Guro-dong, Guro-gu, Seoul 152-703, Korea. iloklee@hotmail.com
Jeong
You Seong
YS
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
D005557:Formaldehyde