TY - JOUR
T1 - Methodological refinements to the mouse paw formalin test. An animal model of tonic pain
AU - Murray, Christopher W.
AU - Porreca, Frank
AU - Cowan, Alan
N1 - Funding Information:
This researchw as supportedb y Grant DA03945f romthe NationalI nstituteo n Drug Abuse, U.S.A. The authorsg ratefullya cknowledgeth e excellentte chnicala ssistanceo f Sheila Mulvaney.
PY - 1988/9
Y1 - 1988/9
N2 - The formalin tonic pain test has recently been adapted for use in mice. We have observed two problems with this procedure. First, compared to a vehicle control group, the majority of mice injected in a hind paw with dilute formalin exhibited a significant nociceptive response (paw licking), including peaks of activity, well beyond the end of the recommended observation period; and, second, an unacceptably wide variation in response occurred. We report two modifications that eliminate these difficulties: a) extending the observation period to 20-45 min postformalin injection, and b) lightly anesthetizing the mice with ether before injection of formalin into the paw. The modified protocol was tested by evaluating morphine, pentazocine and zomepirac (analgesic A50 values were 2.1, 23.8, and > 100 mg/kg, s.c., respectively). An intrathecal or intracerebroventricular injection of saline, given to the lightly anesthetized mouse, did not interfere with the nociceptive behavior; this finding widens the applicability and usefulness of the test. Collectively, these refinements significantly improve the mouse formalin model of tonic pain.
AB - The formalin tonic pain test has recently been adapted for use in mice. We have observed two problems with this procedure. First, compared to a vehicle control group, the majority of mice injected in a hind paw with dilute formalin exhibited a significant nociceptive response (paw licking), including peaks of activity, well beyond the end of the recommended observation period; and, second, an unacceptably wide variation in response occurred. We report two modifications that eliminate these difficulties: a) extending the observation period to 20-45 min postformalin injection, and b) lightly anesthetizing the mice with ether before injection of formalin into the paw. The modified protocol was tested by evaluating morphine, pentazocine and zomepirac (analgesic A50 values were 2.1, 23.8, and > 100 mg/kg, s.c., respectively). An intrathecal or intracerebroventricular injection of saline, given to the lightly anesthetized mouse, did not interfere with the nociceptive behavior; this finding widens the applicability and usefulness of the test. Collectively, these refinements significantly improve the mouse formalin model of tonic pain.
KW - Analgesia
KW - Analgesic testing
KW - Chronic pain
KW - Formalin test
KW - Nociception
KW - Tonic pain
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U2 - 10.1016/0160-5402(88)90078-2
DO - 10.1016/0160-5402(88)90078-2
M3 - Article
C2 - 3221681
AN - SCOPUS:0023715818
SN - 0160-5402
VL - 20
SP - 175
EP - 186
JO - Journal of Pharmacological Methods
JF - Journal of Pharmacological Methods
IS - 2
ER -