Opioid use disorder (OUD) affects over two million in the United States and is an increasing public health crisis. The abuse of fentanyl and the emergence of potent fentanyl derivatives increases the risk for the user to succumb to overdose, but also to develop OUD. While intense attention is currently focused on understanding the complexity of behaviors and neural functions that contribute to OUD, much remains to be discovered concerning the interactions of opioid intake with the immune response in the central nervous system (CNS). In the present studies, we tested the hypothesis that short-term abstinence from fentanyl self-administration associates with altered expression of innate immune markers. Male Sprague-Dawley rats were trained to self-administer fentanyl (0.0032 mg/kg/infusion) to stability followed by 24 h of abstinence. Several innate immune markers, as well as opioid receptors (ORs) and intracellular pattern recognition receptors (PRRs), were interrogated within nodes of the neurocircuitry involved in OUD processes, including the prefrontal cortex (PFC), nucleus accumbens (NAc), caudate putamen (CPu), hippocampus (HIP) and midbrain (MB). In the present study, few immune targets were impacted in the PFC and MB during short-term abstinence from fentanyl (relative to saline) self-administration. However, increased expression of cytokines [e.g., interleukin (IL)1β, IL5], chemokines [e.g., C-C motif chemokine 20 (MIP3α)], tumor necrosis factor α (TNF α) and interferon (IFN) proteins (e.g., IFN β and IFNγ)] was seen in the NAc, while decreased expression of cytokines (e.g., several ILs), chemokines [e.g., granulocyte-macrophage colony-stimulating factor (GMCSF), monocyte chemoattractant protein (MCP) MCP1, MIP3α], the chemokine ligand 5 (RANTES) and interferons (e.g., IFN β and IFNγ) in the HIP. Positive correlations were observed between cumulative fentanyl intake and expression of IL1 β and IL6 in the NAc, and significant negative correlations with fentanyl intake and IFN β, IL2, IL5, IL12p70 and IL17 in the HIP. Few changes in OR expression was observed during early abstinence from fentanyl self-administration. Excitingly, the expression of the PRR, stimulator of interferon genes (STING) negatively correlated with cumulative fentanyl intake and significantly correlated to specific cytokines, chemokines and interferon proteins in the HIP. Although the CPu appears relatively invulnerable to changes in innate immune markers, the highest correlations between cumulative fentanyl intake with MAVS and/or STING was measured in the CPu. Our findings provide the first evidence of CNS innate immune responses and implicate STING as novel mechanistic targets of immunomodulation during short-term abstinence from fentanyl self-administration.

中文翻译：

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芬太尼自我给药影响雄性 Sprague-Dawley 大鼠的脑免疫反应

阿片类药物使用障碍 (OUD) 在美国影响超过 200 万人，是日益严重的公共卫生危机。芬太尼的滥用和强效芬太尼衍生物的出现增加了使用者服药过量的风险，但也会发展为 OUD。虽然目前人们的注意力集中在理解导致 OUD 的行为和神经功能的复杂性上，但关于阿片类药物摄入与中枢神经系统 (CNS) 免疫反应的相互作用还有很多待发现。在目前的研究中，我们检验了短期戒断芬太尼自我给药与先天免疫标志物表达改变相关的假设。雄性 Sprague-Dawley 大鼠被训练自我给药芬太尼 (0.0032 mg/kg/输注) 至稳定，然后禁欲 24 小时。在 OUD 过程中涉及的神经回路节点内，包括前额叶皮层 (PFC)、伏隔核 (NAc)、尾壳核，对几种先天免疫标记物以及阿片受体 (OR) 和细胞内模式识别受体 (PRR) 进行了询问(CPu)、海马 (HIP) 和中脑 (MB)。在本研究中，在短期戒断芬太尼（相对于盐水）自我给药期间，PFC 和 MB 中几乎没有免疫靶点受到影响。然而，细胞因子 [例如白介素 (IL)1β、IL5]、趋化因子 [例如 CC 基序趋化因子 20 (MIP3α)]、肿瘤坏死因子 α (TNF α) 和干扰素 (IFN) 蛋白（例如 IFN β）的表达增加和 IFNγ)] 出现在 NAc 中，而细胞因子（例如，几种 IL）、趋化因子 [例如，粒细胞-巨噬细胞集落刺激因子 (GMCSF)、单核细胞趋化蛋白 (MCP) MCP1、MIP3α]、HIP 中的趋化因子配体 5 (RANTES) 和干扰素（例如，IFN β 和 IFNγ）。观察到累积芬太尼摄入量与 NAc 中 IL1 β 和 IL6 的表达呈正相关，与 HIP 中芬太尼摄入量和 IFN β、IL2、IL5、IL12p70 和 IL17 的表达显着负相关。在早期戒断芬太尼自我给药期间观察到 OR 表达几乎没有变化。令人兴奋的是，PRR、干扰素基因刺激物 (STING) 的表达与累积的芬太尼摄入量呈负相关，并与 HIP 中的特定细胞因子、趋化因子和干扰素蛋白显着相关。尽管 CPu 似乎对先天免疫标志物的变化相对无懈可击，在 CPu 中测量到累积芬太尼摄入量与 MAVS 和/或 STING 之间的最高相关性。我们的研究结果提供了中枢神经系统先天免疫反应的第一个证据，并暗示 STING 是短期戒断芬太尼自我给药期间免疫调节的新机制目标。