Corticotropin-releasing factor (CRF) orchestrates our body's response to stressful stimuli. Pain is often stressful and counterbalanced by activation of CRF receptors along the nociceptive pathway, although the involvement of the CRF receptor subtypes 1 and/or 2 (CRF-R1 and CRF-R2, respectively) in CRF-induced analgesia remains controversial. Thus, the aim of the present study was to examine CRF-R1 and CRF-R2 expression within the spinal cord of rats with Freund's complete adjuvant-induced unilateral inflammation of the hind paw using reverse transcriptase polymerase chain reaction, Western blot, radioligand binding, and immunofluorescence confocal analysis. Moreover, the antinociceptive effects of intrathecal (i.t.) CRF were measured by paw pressure algesiometer and their possible antagonism by selective antagonists for CRF-R1 and/or CRF-R2 as well as for opioid receptors. Our results demonstrated a preference for the expression of CRF-R2 over CRF-R1 mRNA, protein, binding sites and immunoreactivity in the dorsal horn of the rat spinal cord. Consistently, CRF as well as CRF-R2 agonists elicited potent dose-dependent antinociceptive effects which were antagonized by the i.t. CRF-R2 selective antagonist K41498, but not by the CRF-R1 selective antagonist NBI35965. In addition, i.t. applied opioid antagonist naloxone dose-dependently abolished the i.t. CRF- as well as CRF-R2 agonist-elicited inhibition of somatic pain. Importantly, double immunofluorescence confocal microscopy of the spinal dorsal horn showed CRF-R2 on enkephalin (ENK)-containing inhibitory interneurons in close opposition of incoming mu-opioid receptor-immunoreactive nociceptive neurons. CRF-R2 was, however, not seen on pre- or on postsynaptic sensory neurons of the spinal cord. Taken together, these findings suggest that i.t. CRF or CRF-R2 agonists inhibit somatic inflammatory pain predominantly through CRF-R2 receptors located on spinal enkephalinergic inhibitory interneurons which finally results in endogenous opioid-mediated pain inhibition.

中文翻译：

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参与躯体疼痛缓解的大鼠脊髓促肾上腺皮质激素释放因子受体亚型的功能和解剖学特征。

促肾上腺皮质激素释放因子 (CRF) 协调我们的身体对压力刺激的反应。尽管 CRF 受体亚型 1 和/或 2（分别为 CRF-R1 和 CRF-R2）在 CRF 诱导的镇痛中的参与仍然存在争议，但疼痛通常是压力性的，并且通过沿着伤害感受途径激活 CRF 受体来抵消。因此，本研究的目的是使用逆转录酶聚合酶链反应、蛋白质印迹、放射性配体结合来检查弗氏完全佐剂诱导的后爪单侧炎症大鼠脊髓内 CRF-R1 和 CRF-R2 的表达。和免疫荧光共聚焦分析。此外，鞘内注射的镇痛作用（它 ) CRF 是通过爪压痛计测量的，并且它们可能通过 CRF-R1 和/或 CRF-R2 以及阿片受体的选择性拮抗剂拮抗。我们的结果表明，大鼠脊髓背角中 CRF-R2 的表达优于 CRF-R1 mRNA、蛋白质、结合位点和免疫反应性。一致地，CRF 和 CRF-R2 激动剂引发了有效的剂量依赖性镇痛作用，这些作用被 it CRF-R2 选择性拮抗剂 K41498 拮抗，但不被 CRF-R1 选择性拮抗剂 NBI35965 拮抗。此外，它应用阿片拮抗剂纳洛酮剂量依赖性地消除了it CRF-以及CRF-R2激动剂引起的躯体疼痛抑制。重要的，脊髓背角的双免疫荧光共聚焦显微镜显示 CRF-R2 位于含有脑啡肽 (ENK) 的抑制性中间神经元上，与传入的 mu-阿片受体免疫反应性伤害性神经元密切相关。然而，在脊髓的突触前或突触后感觉神经元上没有看到 CRF-R2。总之，这些发现表明，CRF 或 CRF-R2 激动剂主要通过位于脊髓脑啡肽能抑制性中间神经元上的 CRF-R2 受体抑制躯体炎症性疼痛，最终导致内源性阿片类药物介导的疼痛抑制。