Influence Of Microglia On Spinal NMDAR₁ And GABABR₂ Expression In Rat Models Of Neuropathic Pain

Objective To investigate the influence of microglia on dorsal NMDAR1(N-methyl-D-aspartate receptor 1 subunit) and GABABR2(gama-aminobutyric acid B receptor 2 subunit) expression of spinal cord in rat models of neuropathic pain by intrathecal injection of minocycline,a selective microglial inhibitor and explore the possible downstream mechanism of microglia modulating neuropathic pain.Methods Male SD rats weighting 220～260g were used in this study. The neuropathic pain model were established by L5 spinal nerve ligation (SNL). Firstly, thirty SNL rats were randomly divided into five groups(n=6 each): control group and four minocycline groups ( intrathecal minocycline 10μg, 30μg, 50μg, 70μg were given respectively). The dose response for minocycline were evaluated by paw withdrawl threshold (PWT) at preoperative and different postoperative timepoints. Secondly, other fourty eight rats were randomly divided into four groups (n=12 each): group I, sham operation with administration of intrathecal 0.9% saline; group II, L5 spinal nerve ligation (SNL) with administration of intrathecal 0.9% saline; group III, sham operation with intrathecal minocycline 50μg; group IV, SNL with intrathecal minocycline 50μg. PWT was measured with vonfrey filagment at different timepoints (preoperation and 1, 2, 4, 6, 8, 10, 12, 14, 16, 18 day post operation) in six rats from each group. Then, NMDAR1 and GABABR2 expression in dorsal horn were detected by western blot assay at a timepoint of the lowest withdrawl thresthold in other six animals.Results Rats developed mechanical allodynia-like behavior after SNL operation ,and allodynia in the ipsilateral paw was fully expressed on 8th day after operation(P<0.01). Minocycline injected intrathecally increased PWT in a dose dependent manner significantly. Compared with that in sham-operated animals, GABABR2 level in ipsilateral dorsal horn decreased while NMDAR1 increased dramatically in SNL rats (P<0.01). Compared with saline treatment, minocycline inhibited these changes in SNL rats, but there was still a difference between sham-operated and SNL animals (P<0.05 or 0.01).Conclusion The expressions of NMDAR1 and GABABR2 in dorsal horn has plasticity which may contribute to the microglial modulation in neurophathic pain.