RESUMO
BACKGROUND: Peripheral nerve injury induces up-regulation of the calcium channel alpha2delta (alpha2delta) subunit and TRPM8 in the dorsal root ganglion (DRG) which might contribute to allodynia development. We investigated the expression of the alpha2delta subunit and TRPM8 in the DRG of sympathetically maintained pain (SMP) and sympathetic independent pain (SIP) rat model. METHODS: For the SMP model, the L5 and L6 spinal nerves were ligated tightly distal to the DRG. For the SIP model, the tibial and sural nerves were transected, while the common peroneal nerve was spared. After a 7 day postoperative period, tactile and cold allodynia were assessed using von Frey filaments and acetone drops, respectively. Expression of the alpha2delta subunit and TRPM8 in the L5 and L6 DRG were subsequently examined by a Western blot. RESULTS: There were no significant differences between the two models for the thresholds of tactile and cold allodynia. Expression of the alpha2delta subunit in the ipsilateral DRG to the injury was increased as determined on a Western blot as compared to that in the contralateral or sham-operated DRG of the SMP model, but there was no difference in expression seen with the use of the SIP model. There was no difference in the expression of TRPM8 in the ipsilateral DRG to the injury and the contralateral or sham-operated DRG of either model. CONCLUSIONS: Up-regulation of the alpha2delta subunit in injured DRG may play a role that contributes to tactile allodynia development in SMP, but not TRPM8 to cold allodynia after peripheral nerve injury.