Evaluation of hyperalgesia in spared nerve injury model using mechanical, thermal, and chemical stimuli in the mouse

Neuropathic pain results from multiple etiological factors and is a debilitating condition often resulting from partial injury to a peripheral nerve. However, the mechanism underlying this syndrome remains unclear. The aim of the present study is to investigate whether a spared nerve injury model with transection of both the common peroneal nerve (CPN) and tibial nerve (TN) branches of the sciatic nerve is associated with pain or hypersensitivity in the mouse.

A skin and muscle incision was made, and we tightly ligated CPN+TN or the sural nerve (SN) alone as branches of the sciatic nerve. Mechanical and thermal allodynia were tested using von Frey filaments and radiant heat at -1, 1, 3, 5, and 7 days after surgery.

The thresholds of mechanical and thermal stimuli were increased and decreased in the CPN+TN-ligated and SN-ligated groups, respectively. Chemical hyperalgesia was estimated using two doses of intraplantar administration of formalin (0.1 and 1%) 1 week after surgery. Then behaviors were videotaped and playback was used to measure time of licking of the hind paws. The licking time induced by 0.1% formalin was significantly shortened in the CPN+TN-ligated group and significantly prolonged in the SN-ligated group. Number of c-Fos-immunoreactive cells in the spinal cord was not affected by CPN+TN ligation, but was significantly increased in the SN-ligated group.

These findings suggest that changing the combination of nerves in sciatic branch ligation produces different sensitivities to stimuli and SN ligation will be useful for inducing allodynia and hyperalgesia in the mouse.