Glial cells, including astrocytes and microglia, interact closely with neurons and modulate pain transmission, particularly under pathological conditions. In this study, we examined the excitability of substantia gelatinosa (SG) neurons of the spinal dorsal horn using a patch clamp recording to investigate the roles of microglial activation in the nociceptive processes of rats. We used xanthine/xanthine oxidase (X/XO), a generator of superoxide anion (O2∙–), to induce a pathological pain condition. X/XO treatment induced an inward current and membrane depolarization. The inward current was significantly inhibited by minocycline, a microglial inhibitor, and fluorocitrate, an astrocyte inhibitor. To examine whether toll-like receptor 4 (TLR4) in microglia was involved in the inward current, we used lipopolysaccharide (LPS), a highly specific TLR4 agonist. The LPS induced inward current, which was decreased by pretreatment with Tak-242, a TLR4-specific inhibitor, and phenyl N-t-butylnitrone, a reactive oxygen species scavenger. The X/XO-induced inward current was also inhibited by pretreatment with Tak-242. These results indicate that the X/XO-induced inward current of SG neurons occurs through activation of TLR4 in microglial cells, suggesting that neuroglial cells modulate the nociceptive process through central sensitization.

Introduction
Materials and Methods
    1. 척수절편 제작
    2. 실험용액
    3. 전기생리학적 기록방법
    4. 실험자료의 분석
Results
    1. 척수아교질 뉴론의 흥분성에 대한 X/XO의 효과
    2. 척수아교질 세포에서 X/XO의 효과에 대한 신경교세포의역할
    3. X/XO의 효과에 대한 TLR4의 역할
Discussion
Acknowledgements
Conflicts of Interest
References

• Areum Park(Department of Dental Hygiene, Gangdong University)
• Sang Woo Chun(Department of Oral Physiology, College of Dentistry, Wonkwang Dental Research Institute) Correspondence to