ArticleThe formalin test in the mouse: a parametric analysis of scoring propertiesSaddi, Ghada-Mariaa; Abbott, Frances V.b,* Author Information aDepartment of Family Medicine, McGill University, 515–517 Pine Avenue West, Montreal, QC, H2W 1S4, Canada bDepartment of Psychiatry, McGill University, 1033 Pine Avenue West, Montreal, QC, H3A 1A1, Canada *Corresponding author. Tel.: +1-514-398-7320; fax: +1-514-398-4370 E-mail: [email protected] Received 22 December 1999; received in revised form 15 May 2000; accepted 24 May 2000. Pain: December 2000 - Volume 89 - Issue 1 - p 53-63 doi: 10.1016/S0304-3959(00)00348-1 Buy Metrics Abstract We investigated the scoring properties of the mouse formalin test using the time-sampling method recently developed for infant and adult rats. Formalin was injected under the plantar surface of one rear paw (10 μl, 1–8%), and pain behaviours (paw favouring, lifting and licking) and behavioural state were recorded. Correlational and regression analyses indicated that scores composed of combinations of all three pain behaviours, either summed or weighted, provided less variable indices of pain than licking alone. The maximum percent effect (MPE50; i.e. pain behaviour 50% of the time) for the log formalin concentration–effect curves was 3–4% in both phases. Habituation to the test environment prior to testing did not alter the MPE50s, but slopes were lower in unhabituated mice, dramatically increasing the size of the confidence interval. Formalin dose-dependently reduced locomotion, rearing and sniffing in both the first phase and the early part of the second phase. The combination measures were sensitive to morphine (2–8 mg/kg), amphetamine (1–4 mg/kg), dipyrone (50–200 mg/kg), xylazine (0.25–1 mg/kg), and acepromazine (0.25–1 mg/kg), and resistant to diazepam (0.5–2 mg/kg), pimozide (0.05–0.25 mg/kg), pentobarbital (10 and 15 mg/kg) and indomethacin (2–8 mg/kg). Decreased pain was correlated with increased motor activity for morphine and amphetamine, and with decreased activity for xylazine and acepromazine; dipyrone and indomethacin did not alter activity levels. © 2000 Lippincott Williams & Wilkins, Inc.