OBJECTIVES Many rheumatoid arthritis (RA) patients continue to experience persistent pain even after successful management of joint inflammation. Clinical data indicate that RA patients treated with the JAK inhibitor baricitinib consistently achieve pain relief that cannot be entirely attributed to its anti-inflammatory effects. In this study, we investigated the antinociceptive properties of baricitinib using the collagen antibody-induced arthritis (CAIA) model in which mechanical hypersensitivity persists long after resolution of joint inflammation. METHODS The effects of baricitinib, etanercept (tumour necrosis factor inhibitor), and LP-922761 (adaptor protein-2 (AP2) associated kinase 1 (AAK1) inhibitor) on pain-like behaviour in CAIA mice were examined. Tissue samples from the late, low-grade inflammatory phase were examined for the effect of the treatments. Additionally, in vitro experiments using dorsal root ganglion (DRG) cells were conducted to assess baricitinib's influence on neuronal excitability and cell morphology. RESULTS Baricitinib reduced CAIA-induced joint inflammation, but its antinociceptive effects were most pronounced during the late phase when etanercept was ineffective. Administering baricitinib both early and late significantly decreased CAIA-induced bone loss, synovial innervation, and baseline STAT3 phosphorylation in ankle joints and DRGs. Unlike etanercept, baricitinib effectively reduced pain-like behaviour and synovial hyperinnervation when administered exclusively in the late phase. Additionally, baricitinib modulated glial cell morphology and neuronal excitability in vitro. Notably, it inhibited AAK1 signalling in DRGs, with AAK1 kinase activity blockade providing an antinociceptive effect in the CAIA model. CONCLUSIONS Our data suggests that baricitinib has antinociceptive effects by targeting not only immune cells but also neurons and glia cells via inhibition of 2 signalling pathways linked to chronic pain.

The blood–DRG barrier is composed of endothelial cells with high permeability and is monitored by a subset of CD163+ perivascular macrophages, a process that is arteriovenously zonated. Vascular monitoring is abrogated by interfering with caveolar transcytosis in endothelial cells or by depleting CD163+ macrophages.

Highlights • Microarray analysis of dorsal root ganglia from mice subjected to collagen antibody-induced arthritis (CAIA) and controls revealed that arthritis leads to differential expression of 120 circular RNA genes.• Bioinformatical analysis indicates that altered levels of circRNAs in DRG is associated with sensitization-related processes.• Microarray or RT-qPCR analysis showed increased levels of circVps13 and circMicall1 in the inflammatory phase and circNufip1 the late “post-inflammatory” phase in DRG from mice subjected to CAIA.

In a recent study published in Nature Serger connected intermittent fasting (IF) to gut microbiome alterations and enhanced peripheral nerve regeneration following injury. 1 Fasting has been purported to have neuroregenerative effects, but the underlying mechanisms remained unclear. The authors found that IF-induced elevation of IPA (a microbiome-derived metabolite) promotes neutrophil in fi ltration into the dorsal root ganglia (DRG), which enhances the regeneration of sciatic nerve fi bers 1). 2 for

Background: The dorsal root ganglion (DRG) is structurally complex and pivotal to systems processing nociception. Whole mount analysis allows examination of intricate microarchitectural and cellular relationships of the DRG in three-dimensional (3D) space. New method: We present DRGquant a set of tools and techniques optimized as a pipeline for automated image analysis and reconstruction of cells/structures within the DRG. We have developed an open source software pipeline that utilizes machine learning to identify substructures within the DRG and reliably classify and quantify them. Results: Our methods were sufficiently sensitive to isolate, analyze, and classify individual DRG substructures including macrophages. The activation of macrophages was visualized and quantified in the DRG following intrathecal injection of lipopolysaccharide, and in a model of chemotherapy induced peripheral neuropathy. The percent volume of infiltrating macrophages was similar to a commercial source in quantification. Circulating fluorescent dextran was visualized within DRG macrophages using whole mount preparations, which enabled 3D reconstruction of the DRG and DRGquant demonstrated subcellular spatial resolution within individual macrophages. Comparison with existing method(s): Here we describe a reliable and efficient methodologic pipeline to prepare cleared and whole mount DRG tissue. DRGquant allows automated image analysis without tedious manual gating to reduce bias. The quantitation of DRG macrophages was superior to commercial solutions. Conclusions: Using machine learning to separate signal from noise and identify individual cells, DRGquant enabled us to isolate individual structures or areas of interest within the DRG for a more granular and fine-tuned analysis. Using these 3D techniques, we are better able to appreciate the biology of the DRG under experimental inflammatory conditions.