The Effect Of Hydrogen Sulfide On Nociception In Rats

Objective: Hydrogen sulfide（H₂S）, with the odor of rotten eggs, istraditionally used as chemical reagent. Nevertheless, H₂S is generatedendogenously from L-cysteine by pyridoxal-5′-phosphate （PLP）-dependentenzymes, namely cystathionine-β-synthase （CBS） and cystathionine-γ-lyase（CSE） and PLP-independent enzyme3-mercaptopyruvate sulfurtransferase（3-MST）. Many studies have showed the physiological and pathologicalrelevance of H₂S in vivo, such as blood pression regulation, pain modulation,inflammatory reponse and so on. H₂S might function as a neurotrasmitter incentral nervous system, H₂S can facilitate the induction of hippocampallong-term potention（LTP）, which mediated by N-methyl-D-asparticacid（NMDA） receptors.NMDA receptors are excitatory glutamate receptors. NMDA receptorslocated in spinal cord play important role in the induction and development ofpain. Recently increasing evidences have showed that H₂S is associated withnociception. Both endogenous and exogenous H₂S can play an important rolein pain modulation. But little is known whether the role of spinal NMDAreceptors involves in pain modulation of H₂S. Therefore, the purpose of thisstudy is to observe the effects of H₂S on behavior and expression of NMDAreceptors in spinal cord in rats, further to explore the mechanism of H₂Sinvolved in nociception and provide a new strategy for treatment of clinicalpain.Methods:1Using intrathecal catheter technology, thirty-two normalSprague-Dawley （SD） rats were intrathecal administration of sodiumhydrosulfide（NaHS）, a H₂S donor, and（or） memantine, a NMDA receptorsantagonist, the changes in the paw withdrawal threshold （PWT） in rats wereobserved,and after administration of NaHS, the expressions of NR1and NR2B protein in spinal dorsal horn in rats were determined using western blotmethod.2Rats were intraplantar injection of NaHS for five days, the changes ofPWT in rats were observed and then spinal dorsal horn and dorsal rootganglion （DRG） were removed for determination of the expression of NR2Bsubunit by RT-PCR and western blot analysis, at the same time compared withthose injected formalin. In addition, rats were also intrathecalpreadministration of H₂S scavenger methemoglobin or CBS inhibitorhydroxylamine（HA） after injection of NaHS, the PWT and the expression ofNR2B protein in spinal dorsal horn in rats were measured.Results:1The effects of intrathecal injection of NaHS on PWT and NMDArecepors located in spinal cord in ratsThe PWT at15minute after intrathecal administration of NaHS in ratswas significantly lower（P<0.05）, which can be reduced from（14.40±1.83）gto（5.76±1.82）g. Preadministration of memantine would reverse the effectcompletely（P<0.05）.After intrathecal injection of NaHS, the expression of NR1protein, butnot NR2B protein, in spinal dorsal horn in rats was upregulated （P<0.05）.2The effects of intraplantar administration of NaHS or formalin on PWTand NR2B subunit located in spinal cord and DRG in ratsThe PWT in the contralateral hindpaw in rats sujected to NaHSintraplantar injection was significantly decreased （P<0.05）, which reducedfrom （13.50±2.30）g to （4.20±1.86）g, but the PWT in formalin-treated rats wasnot decreased.NR2B mRNA and protein levels in spinal dorsal horn, but not in DRG,were increased after NaHS injection（P<0.05）, and NR2B mRNA and proteinlevels in spinal dorsal horn and DRG were both upregulated informalin-treated rats（P<0.05）.3The inhibitory effects of intrathecal injection of methemiglobin or HAon PWT and NR2B subunit located in spinal cord in rats. Intrathecal preadministration of methemoglobin blocked reduction ofPWT and increased expression of NR2B protein induced by intraplantarinjection of NaHS（P<0.05）.In addition, NaHS-induced alteration of PWT and NR2B expression waspartly attenuated by intrathecal injection of HA（P<0.05）, but the two effectsdid not return to nomal level（P<0.05）.Conclusion:1Intrathecal administration of NaHS can induce hyperalgesia in rats,which may associate with upregulation of NMDA receptors, especially NR1subunit in spinal dorsal horn.2Continuous intraplantar injection of NaHS also causes persistenthyperalgesia in rats, the upregulation of NR2B in spinal dorsal horn andincreased production of endogenous H₂S may contribute hyperalgesia.