Role of endogenous hydrogen sulfide of the spinal cord in the maintenance of diabetic neuropathic pain in rats

Abstract

Objective To evaluate the role of endogenous hydrogen sulfide in the maintenance of diabetic neuropathic pain (DNP) in rats.Methods The DNP models were established by intraperitoneal injection of stretopzin (STZ) in 24 male SD rats aged 4 weeks (150-170 g),and other 24 rats were intraperitoneally injected with the same volume of normal saline as normal group.All the rats were implanted intrathecal catheter.The rats with DNP were randomly divided into 2 subgroups (n =12 each):saline group (group D) and methemoglobin group (group DM).The rats in normal group were randomly divided into 2 subgroups (n =12 each):saline group (group C) and methemoglobin group (group CM).Three weeks after intraperitoneal injection,the rats were separately intrathecally administered methemoglobin 10 μ mol/L (10 μ1) (group DM),saline 10 μl (group D),methemoglobin 10 μmol/L (10 μl) (group CM) and saline 10 μl (group C),respectively,once a day for 4 days.The paw withdrawal mechanical threshold (PWT) of the rats were measured before and after injection at 1 (T1),2 (T2),3 (T3),4 (T4) days,then the rats were sacrificed at T4 point after the measurement and the lumbar segments of the spinal cord were removed for determination of N-methyl-D-aspartate receptor subunit 2B (NR2B) protein expression (by Western blotting) and NR2B mRNA expression [by reverse transcriptase-polymerase chain reaction (RT-PCR)].Results As compared with group C and group CM,the PWT in group D and group DM was significantly reduced (P ＜ 0.05),while the expression of NR2B protein and mRNA was significantly increased (P ＜ 0.05).As Compared with group D [NR2B mRNA (0.89 ± 0.09),NR2B protein (1.28 ± 0.17)],the PWT in group DM was significantly increased at T2-T4 point before the injection and T1-T4 point after the injection,while the expression of NR2B mRNA (0.69 ±0.11) and NR2B protein (0.98 ± 0.14) in group DM was significantly decreased (P ＜ 0.05).As compared with the point before the injection (3.8 ± 0.9 and 6.1 ± 1.4),the PWT in group DM were significantly increased at T1-T2 point after the injection (7.5 ± 1.8 and 8.7 ± 1.6) (P ＜ 0.05).Conclusion Endogenous hydrogen sulfide in the spinal cord is involved in the maintenance of DNP in rats and the possible mechanisms were related with up-regulation of NR2B in the spinal dorsal horn. Key words: Hydrogen sulfide; N-methyl-D-aspartate receptor subunit 2B; Spinal dorsal horn; Diabete ; Pain