Department of Anesthesiology and Perioperative Medicine, Center for Neuroscience, Pittsburgh Center for Pain Research, Pittsburgh Project to end Opioid Misuse, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania.
Anesthesiology. 2023 Dec 1;139(6):840-857. doi: 10.1097/ALN.0000000000004735.
Intersectional genetics have yielded tremendous advances in our understanding of molecularly identified subpopulations and circuits within the dorsal horn in neuropathic pain. The authors tested the hypothesis that spinal µ opioid receptor-expressing neurons (Oprm1-expressing neurons) contribute to behavioral hypersensitivity and neuronal sensitization in the spared nerve injury model in mice.
The authors coupled the use of Oprm1Cre transgenic reporter mice with whole cell patch clamp electrophysiology in lumbar spinal cord slices to evaluate the neuronal activity of Oprm1-expressing neurons in the spared nerve injury model of neuropathic pain. The authors used a chemogenetic approach to activate or inhibit Oprm1-expressing neurons, followed by the assessment of behavioral signs of neuropathic pain.
The authors reveal that spared nerve injury yielded a robust neuroplasticity of Oprm1-expressing neurons. Spared nerve injury reduced Oprm1 gene expression in the dorsal horn as well as the responsiveness of Oprm1-expressing neurons to the selective µ agonist (D-Ala2, N-MePhe4, Gly-ol)-enkephalin (DAMGO). Spared nerve injury sensitized Oprm1-expressing neurons, as reflected by an increase in their intrinsic excitability (rheobase, sham 38.62 ± 25.87 pA [n = 29]; spared nerve injury, 18.33 ± 10.29 pA [n = 29], P = 0.0026) and spontaneous synaptic activity (spontaneous excitatory postsynaptic current frequency in delayed firing neurons: sham, 0.81 ± 0.67 Hz [n = 14]; spared nerve injury, 1.74 ± 1.68 Hz [n = 10], P = 0.0466), and light brush-induced coexpression of the immediate early gene product, Fos in laminae I to II (%Fos/tdTomato+: sham, 0.42 ± 0.57% [n = 3]; spared nerve injury, 28.26 ± 1.92% [n = 3], P = 0.0001). Chemogenetic activation of Oprm1-expressing neurons produced mechanical hypersensitivity in uninjured mice (saline, 2.91 ± 1.08 g [n = 6]; clozapine N-oxide, 0.65 ± 0.34 g [n = 6], P = 0.0006), while chemogenetic inhibition reduced behavioral signs of mechanical hypersensitivity (saline, 0.38 ± 0.37 g [n = 6]; clozapine N-oxide, 1.05 ± 0.42 g [n = 6], P = 0.0052) and cold hypersensitivity (saline, 6.89 ± 0.88 s [n = 5] vs. clozapine N-oxide, 2.31 ± 0.52 s [n = 5], P = 0.0017).
The authors conclude that nerve injury sensitizes pronociceptive µ opioid receptor-expressing neurons in mouse dorsal horn. Nonopioid strategies to inhibit these interneurons might yield new treatments for neuropathic pain.
交叉遗传学在理解神经病理性疼痛背角中分子鉴定的亚群和回路方面取得了巨大进展。作者测试了这样一个假设，即在 spared nerve injury 模型中，脊髓 μ 阿片受体表达神经元（Oprm1 表达神经元）有助于行为过敏和神经元致敏。
作者将 Oprm1Cre 转基因报告小鼠与腰椎脊髓切片全细胞膜片钳电生理学相结合，以评估神经病理性疼痛 spared nerve injury 模型中 Oprm1 表达神经元的神经元活动。作者使用化学遗传方法激活或抑制 Oprm1 表达神经元，然后评估神经病理性疼痛的行为迹象。
作者揭示了 spared nerve injury 导致 Oprm1 表达神经元的强大神经可塑性。spared nerve injury 降低了背角中的 Oprm1 基因表达以及 Oprm1 表达神经元对选择性 μ 激动剂（D-Ala2，N-MePhe4，Gly-ol）-脑啡肽（DAMGO）的反应性。spared nerve injury 使 Oprm1 表达神经元致敏，这反映在其固有兴奋性增加（rheobase，假手术 38.62±25.87 pA[n=29]；spared nerve injury，18.33±10.29 pA[n=29]，P=0.0026）和自发性突触活动增加（延迟放电神经元的自发性兴奋性突触后电流频率：假手术 0.81±0.67 Hz[n=14]；spared nerve injury，1.74±1.68 Hz[n=10]，P=0.0466），以及光刷诱导的即刻早期基因产物 Fos 在 laminae I 到 II 的共表达（%Fos/tdTomato+：假手术 0.42±0.57%[n=3]；spared nerve injury，28.26±1.92%[n=3]，P=0.0001）。化学遗传激活 Oprm1 表达神经元在未受伤的小鼠中产生机械性过敏（生理盐水，2.91±1.08 g[n=6]；氯氮平 N-氧化物，0.65±0.34 g[n=6]，P=0.0006），而化学遗传抑制减少了机械性过敏的行为迹象（生理盐水，0.38±0.37 g[n=6]；氯氮平 N-氧化物，1.05±0.42 g[n=6]，P=0.0052）和冷过敏（生理盐水，6.89±0.88 s[n=5]与氯氮平 N-氧化物，2.31±0.52 s[n=5]，P=0.0017）。
作者得出结论，神经损伤使小鼠背角中的促伤害性 μ 阿片受体表达神经元致敏。非阿片类抑制这些中间神经元的策略可能为神经病理性疼痛提供新的治疗方法。
