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Introduced in 1992 by Kim and Chung(1), spinal nerve L5/L6 ligation (SNL) in rats has become well recognized and accepted as an animal model for mechanistic studies of peripheral neuropathy and for screening of novel analgesics. However, the spinal nerve L5/6 ligation model has not been widely utilized in mice, in part because surgery, particularly ligation of mouse L6, and behavioral testing in such small and active animals are challenging. Based on a recent report that mouse L3 and L4 neural segments are anatomically and functionally homologous with rat L4 and L5 segments(2), we investigated individually ligating L4 or L5, and L4/L5 ligation in albino C57 mice using the von Frey test to evaluate the resultant allodynia and histological dissection to confirm the ligations. Aside from a single exception, none of the L4 or L4/L5-ligated animals (n=78) lost the use of their ipsilateral leg which indicates that, in contrast to rats, L4 does not significantly innervate major proximal leg muscles in mice. The data from von Frey testing on postoperative weeks 1 – 6 revealed statistically significant reductions of the 50% withdrawal threshold in all three ligation groups, with the order of significance being L4/L5 > L4 > L5. In addition, the von Frey-sensitive area on the mouse plantar surface is wider for L4-ligated mice than it is for L5-ligated mice. With its greater ease of surgery and robust allodynia, the ligation of spinal nerves L4/L5 optimizes the SNL model in mice.

(1) Kim SH and Chung JM, 1992, Pain 50: 355-363

(2) Rigaud M, Gemes G, Barabas ME, et al, 2008, Pain 136: 188-201