Neuropathic Pain Induced Alterations in the Opioidergic Modulation of a Descending Pain Facilitatory Area of the Brain
Neuropathic Pain Induced Alterations in the Opioidergic Modulation of a Descending Pain Facilitatory Area of the Brain
复制标题
DOI：
10.3389/fncel.2019.00287
复制
发表时间：
2019-06-28
影响因子：
5.3
通讯作者：
Tavares, Isaura
中科院分区：
文献类型：
--
作者：
Costa, Ana Rita;Carvalho, Paulina;Tavares, Isaura
阿片类药物在下行疼痛调制中起主要作用，但神经病理性疼痛对脑阿片能系统的影响仍未得到充分研究。由于神经病理性疼痛的下行促进作用增强，我们在神经病理性疼痛的备用神经损伤(SNI)模型中研究了延髓疼痛易化区--网状背核(DRT)的阿片能调制。我们首先在幼稚动物身上进行了一系列的行为学实验，以确定MU-阿片受体(MOR)在内源性和外源性阿片类药物在DRT中的作用。具体地说，我们发现慢病毒介导的在DRT的MOR-基因敲除增加了对热和机械刺激的敏感性，而MOR激动剂DAMGO则产生了相反的效果。此外，我们还发现，在DRT时，吗啡的吗啡抑制作用和CTAP对吗啡的药理阻断作用分别减弱和抑制了全身吗啡的镇痛作用。然后，我们进行体内微透析检测DRT中的脑啡肽，并分别用实时定量聚合酶链式反应和免疫组织化学方法检测DRT中MOR在mRNA、蛋白和磷酸化水平的表达。与假手术对照组相比，SNI组大鼠脑内脑啡肽水平升高，MOR标记细胞数量减少，MOR基因表达水平无变化，而MOR标记细胞的磷酸化程度较高。最后，我们在SNI动物身上进行了行为学研究，以确定全身吗啡的效力以及在DRT时对MOR的药理和遗传操作的影响。我们发现，与假动物相比，系统性吗啡在SNI动物中的抗痛觉过敏作用的效力降低。慢病毒介导的MOR过表达增加SNI动物DRT时的MOR细胞对机械性痛觉过敏没有影响。DAMGO仅在MOR过表达后才有抗痛觉作用。这些结果表明，MOR抑制DRT痛的易化作用，这一作用有助于全身阿片类药物的镇痛作用。我们进一步证明，在神经病理性疼痛过程中，MOR的抑制功能受损。这可能是由于MOR的脱敏和降解，这是由MOR磷酸化触发的受体的适应。跳过参与MOR适应的反调节通路可能会恢复疼痛易化区的阿片能抑制。
Opioids play a major role at descending pain modulation but the effects of neuropathic pain on the brain opioidergic system remain understudied. Since descending facilitation is enhanced during neuropathic pain, we studied the opioidergic modulation of the dorsal reticular nucleus (DRt), a medullary pain facilitatory area, in the spared nerve injury (SNI) model of neuropathic pain. We first performed a series of behavioral experiments in naive-animals to establish the role of mu-opioid receptor (MOR) in the effects of endogenous and exogenous opioids at the DRt. Specifically, we showed that lentiviral-mediated MOR-knockdown at the DRt increased sensitivity to thermal and mechanical stimuli while the MOR agonist DAMGO induced the opposite effects. Additionally, we showed that MOR-knockdown and the pharmacological blockade of MOR by CTAP at the DRt decreased and inhibited, respectively, the analgesic effects of systemic morphine. Then, we performed in vivo microdialysis to measure enkephalin peptides in the DRt and evaluated MOR expression in the DRt at mRNA, protein and phosphorylated form levels by quantitative real-time PCR and immunohistochemistry, respectively. SNI-animals, compared to sham control, showed higher levels of enkephalin peptides, lower MOR-labeled cells without alterations in MOR mRNA levels, and higher phosphorylated MOR-labeled cells. Finally, we performed behavioral studies in SNI animals to determine the potency of systemic morphine and the effects of the pharmacologic and genetic manipulation of MOR at the DRt. We showed a reduced potency of the antiallodynic effects of systemic morphine in SNI-animals compared to the antinociceptive effects in sham animals. Increasing MOR-cells at the DRt of SNI-animals by lentiviral-mediated MOR-overexpression produced no effects on mechanical allodynia. DAMGO induced anti-allodynia only after MOR-overexpression. These results show that MOR inhibits DRt pain facilitatory actions and that this action contributes to the analgesic effects of systemic opioids. We further show that the inhibitory function of MOR is impaired during neuropathic pain. This is likely due to desensitization and degradation of MOR which are adaptations of the receptor that can be triggered by MOR phosphorylation. Skipping counter-regulatory pathways involved in MOR adaptations might restore the opioidergic inhibition at pain facilitatory areas.