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The Magnitude of Mechanical Allodynia in a Rodent Model of Lumbar Radiculopathy is Dependent on Strain and Sex

LaCroix-Fralish, Michael L., BS*; Rutkowski, Maria D., BS; Weinstein, James N., DO, MS; Mogil, Jeffrey S., PhD§; DeLeo, Joyce A., PhD*†

doi: 10.1097/01.brs.0000174122.63291.38
Basic Science
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Study Design. This study examined the differences in tactile hypersensitivity across 6 different strains of male mice, and between male and female rats of 3 different strains in a rodent model of low back pain associated with lumbar radiculopathy.

Objective. We investigated the possibility that differences in tactile allodynia following the same nerve root injury are affected by genotype and sex in rodents.

Summary of Background Data. Low back pain associated with radiculopathy affects countless people throughout the world, encompassing a wide range of individual pain susceptibility. The roles of genetics and sex on differences in nociceptive sensitivities following lumbar nerve root injury have yet to be fully characterized.

Methods. Six strains of mice (BALB/cJ, CBA/J, C57BL/6J, 129P3/J, C3H/HeJ, and C58/J; all males) and male and female Sprague Dawley, Holtzman, and Long-Evans rats underwent a lumbar nerve root injury followed by assessment of tactile allodynia.

Results. The most sensitive mouse strains following nerve root injury were: 129P3/J, C58/J, and BALB/cJ; and the less sensitive strains were: C57BL/6J, C3H/HeJ, and CBA/J. Female Sprague Dawley and Long-Evans rats displayed increased hypersensitivity following nerve root injury compared to males. No sex differences were observed in Holtzman rats.

Conclusions. Different mouse strains, and male and female rats that are exposed to identical nerve root injuries have diverse levels of tactile hypersensitivity, supporting the hypothesis that genetic factors and sex play a key role in radicular pain. Our results correlate with data compiled in identical mouse and rat strains after L5–L6 nerve ligation, suggesting that the precise nature of the injury is not relevant to the inheritance of neuropathic symptom sensitivity.

We observed varying degrees of mechanical allodynia after surgery using a rodent model of lumbar radiculopathy in 6 inbred mouse strains, and 3 strains of male and female rats. These results provide evidence that genetic factors and sex may play an important role in radicular pain in human beings.

From the Department of *Pharmacology and Toxicology, Dartmouth College, Hanover, NH, †Anesthesiology, Dartmouth-Hitchcock Medical Center, Lebanon, NH, ‡Orthopaedics, Dartmouth Medical School, Hanover, NH, and §Psychology and Centre for Research on Pain, McGill University, Montreal, QC, Canada.

Acknowledgment date: July 7, 2004. First revision date: August 12, 2004. Second revision date: September 15, 2004. Acceptance date: September 17, 2004.

Supported by grant support from the National Institute of Arthritis and Musculoskeletal and Skin Diseases AR44757 (J.A.D.) and the Bristol-Myers Squibb/Zimmer Orthopedic Foundation (J.A.D. and J.N.W.).

The manuscript submitted does not contain information about medical device(s)/drug(s).

Federal and Foundation funds were received in support of this work. No benefits in any form have been or will be received from a commercial party related directly or indirectly to the subject of this manuscript.

Address correspondence and reprint requests to Joyce A. DeLeo, PhD, Department of Anesthesiology, Dartmouth-Hitchcock Medical Center, HB 7125 One Medical Center Drive, Lebanon, NH 03756; E-mail: Joyce.A.DeLeo@Dartmouth.EDU

© 2005 Lippincott Williams & Wilkins, Inc.