延髓腹内侧部G蛋白偶联型雌激素受体反向调控痛痒觉的环路与分子机制解析

Pain and itch are distinct sensory experiences, yet they are also closely related and impact each other. With the advancement of new technologies such as optogenetics, there has been major breakthroughs in the study of the neurocircuitry and molecular mechanisms of pain and itch at the peripheral and the spinal cord dorsal horn levels. However, little is known about the role of the supraspinal descending system in the interaction between pain and itch. The mu-type opioid receptor (MOR) in the rostral ventromedial medulla, an essential part of the descending pain modulation system, mediates both analgesia and itch. Two subtypes (splice variants) of MOR, namely, MOR-1 and MOR-1C, are present in RVM and likely mediates analgesia and itch, respectively. We have recently revealed the presence of a population of neurons which specifically express the G protein-coupled estrogen receptor (GPER) in RVM. Activation of GPER promotes phosphorylation of MOR, leading to enhancement of pain. GPER-deficient rats and mice are protected from inflammatory pain and morphine tolerance, but paradoxically exhibit hypersensitivity to mechanical and chemical itch. These results indicate that GPER in the RVM facilitates pain and inhibits itch via promoting MOR phosphorylation. In the current proposal, we intend to delineate the neural circuitry that underlie the differential control of pain and itch by GPER in the RVM, and to reveal the significance of GPER-mediated modulation of MOR-1 and MOR-1C in the interaction between pain and itch.

疼痛和瘙痒是不同的感觉体验，但两者又密切联系和相互影响。应用光遗传等新技术，有关外周和脊髓水平痛痒觉互作的环路和分子机制研究已获重要进展。然而，对脑的下行调控系统在痛痒觉互作中的作用尚缺乏深入研究。下行调控系统的核心结构—头端延髓腹内侧部(RVM)的μ型阿片受体(MOR)既介导镇痛也引起瘙痒，该部位分布有两种MOR剪接变异体—MOR-1和MOR-1C，可能分别介导镇痛和瘙痒。我们的研究发现，RVM的ON细胞特异表达G蛋白偶联型雌激素受体(GPER)；激活GPER可导致MOR磷酸化和痛觉增强；GPER缺陷大鼠和小鼠痛觉减轻，对吗啡耐受抵抗，却呈现可被纳曲酮逆转的痒觉敏化，提示GPER通过介导MOR磷酸化而增强痛觉和抑制痒觉。本项目拟应用行为学、电生理和光/化学遗传等方法，探究RVM部位GPER反向调节痛痒觉的环路机制，揭示GPER对MOR-1和MOR-1C的调控在痛痒觉互作中的意义。

疼痛和瘙痒是不同的感觉体验，但两者又密切联系和相互影响。应用光遗传等新技术，有关外周和脊髓水平痛痒觉互作的环路和分子机制研究已获重要进展。然而，对脑的下行调控系统在痛痒觉互作中的作用尚缺乏深入研究。下行调控系统的核心结构—头端延髓腹内侧部(RVM）的μ型阿片受体(MOR)既介导镇痛也引起瘙痒，本项目揭示了该部位G蛋白偶联型雌激素受体（GPER）通过介导μ型阿片受体(MOR)磷酸化而易化痛觉和抑制痒觉的机制。我们发现：1）RVM内微量注射雌激素可增强痛觉并减弱吗啡镇痛效应；2）在体电生理记录表明雌激素通过GPER选择性兴奋ON神经元；3）GPER阳性神经元具有ON细胞的典型功能特征；4）GPER阳性神经元是长投射GABA能神经元，其接受丰富的脑啡肽能突触输入，表达u型阿片受体（MOR）；5）光遗传/化学遗传激活GPER阳性神经元增强痛觉相关行为而抑制痒觉相关行为，选择性损毁或抑制GPER+神经元则抑制痛觉而增强痒觉感觉；6）GPER缺失大鼠或小鼠疼痛相关行为降低，吗啡镇痛效应增强，而出现痒觉高敏状态；7）GPER的激活通过PLC/IP3依赖的途径引起胞内钙释放，激活蛋白激酶C，继而引起MOR磷酸化，使之与钾通道脱偶联，从而提高ON细胞的兴奋性；8）RVM内GPER阳性神经元与5-HT能神经元之间存在交互性局部投射联系。以上结果证明GPER是RVM的ON神经元的特异性分子标记，同时GPER介导的阿片受体磷酸化参与痛痒觉调节和阿片耐受，是潜在的镇痛干预靶点。