L6 spinal nerve ligation produces prolonged development of mechanical allodynia and gradual increase of GFAP on ipsilateral dorsal horn

Abstract

L5/6 spinal nerve ligation (SNL), one of the most widely used approaches rat models for neuropathic pain, results in the rapid development of mechanical allodynia within 24-72 h. However, the result of a single L6 SNL remains unclear. The first series of experiments were performed to examine the pain behavior of rats with different nerve ligations. Thirty-six rats were randomly assigned to four groups as follows: group I, controls (n = 6); group II, L5/6 nerve ligation (n = 6); group III, single L6 nerve ligation (n = 18); and group IV, the sham operation group (n = 6). The mechanical allodynia of rats was assessed using a 50 % paw withdrawal threshold (PWT), and tail antinociception was determined using the percentage of the maximal possible antinociceptive effect (% MPE). The second series of experiments were performed using Western blots to evaluate dorsal horn GFAP expression in different groups at different time points (D1, D7, D14, and D28). For this series of experiments, fifty-four rats were randomly divided into three groups: group I, controls (n = 6); group II, L5/6 nerve ligation (n = 24); and group III, L6 nerve ligation (n = 24). In this study, a single L6 SNL induced prolonged development (1-14 days) of mechanical allodynia and gradually increased expression of glial fibrillary acidic protein (GFAP) in the ipsilateral dorsal horn. Notably, once mechanical allodynia developed, both the severity of mechanical allodynia and the alteration of GFAP expression were similar regardless of the identity of the ligated nerve (L5/6 or L6 only). Single L6 SNL might be used as an effective model for researching the development period of neuropathic pain and is thus worth further investigation.