Daily Anesthesiology Research Analysis

Objectively measuring pain in laboratory animals is essential for pain research and analgesic development. Despite the development of various behavioral tests to measure evoked pain in animal models, measuring spontaneous pain remains challenging. To address this unmet need, we developed a novel imaging approach to detect spontaneous nociception in animal pain models. To do this, we generated a Bacterial Artificial Chromosomes transgenic mouse that expresses Redquorin under the murine synapsin 1 promoter. Redquorin is a fusion protein consisting of chimera and a 2x tandem dimer Tomato Aequorin (tdTA), which emits long wavelength bioluminescence from activated neurons in the presence of coelenterazine. This luminescence can penetrate tissues and form a projected image on the body surface that can be detected with a spectrum In Vivo Imaging System, thus creating a Nociceptive Neuronal Activity Imaging mouse. We used the tdTA mice to image bioluminescence in the spinal regions as a surrogate of spontaneous pain induced by capsaicin, the HIV-1 envelope glycoprotein gp120, and spinal nerve ligation. Results show that Redquorin-emitted bioluminescence is a sensitive optical surrogate to measure spontaneous pain. This approach offers a new method to measure spontaneous pain in animal models for basic and translational research. PERSPECTIVE: This article presents a novel noninvasive imaging to visualize pain in mice, based on calcium dependent bioluminescence. Potentially, this approach can be used in high throughput screening of analgesics as it relies on non-reflexive pain measurement.

BACKGROUND: Neuraxial analgesia is the gold standard for labor pain relief, yet procedure-related neurological symptoms may occur. Guided by the theory of neuraxial homeostasis, this study compared a sequential spinal-epidural analgesia (SSEA) technique with conventional combined spinal-epidural analgesia (CSEA) to determine whether preserving neuraxial stability was associated with a reduction in neurological symptoms and enhanced maternal satisfaction. METHODS: In this randomized trial, 740 parturients requesting labor analgesia were assigned to receive either SSEA (subarachnoid injection followed by epidural catheterization, n = 368) or conventional CSEA (needle-through-needle technique, n = 372). The primary outcome was analyzed in the intention-to-treat (ITT) population of all 740 randomized participants. For secondary outcomes assessed after delivery, 116 women who underwent cesarean section were not applicable for analyses requiring vaginal delivery, leaving 624 parturients who completed vaginal delivery (312 per group) for those specific analyses. The primary outcome was the incidence of intraprocedural neurological symptoms (radiating pain or involuntary muscle twitching during puncture). Secondary outcomes included post-procedural neurological symptoms, adverse effects, analgesic efficacy (Visual Analogue Scale [VAS] scores), analgesic quality, maternal/fetal outcomes, and maternal satisfaction (5-point Likert scale). An exploratory structural equation model (SEM) examined factors influencing satisfaction. RESULTS: Baseline characteristics were balanced. In the ITT analysis (n = 740), SSEA was associated with a significantly lower incidence of intraprocedural neurological symptoms (1.36% vs. 23.12%; risk difference [RD] - 0.218, 95% CI - 0.267 to - 0.169; P < 0.001). Among the 624 vaginal deliveries, SSEA also showed lower rates of neurological symptoms at 48 h (0.32% vs. 2.56%; RD - 0.022, - 0.041 to - 0.004; P = 0.019), lower back pain (1.28% vs. 6.41%; RD - 0.051, - 0.081 to - 0.021; P = 0.001), and persistent paresthesia at 1 week (0% vs. 5.13%; RD - 0.051, - 0.076 to - 0.026; P < 0.001). Overall maternal satisfaction was higher with SSEA (12.81 ± 1.46 vs. 11.26 ± 1.23; Cohen's d = 1.15; P < 0.001), driven by greater satisfaction with the overall experience (d = 2.08) and willingness to recommend (d = 0.98), whereas satisfaction with pain relief did not differ (P = 0.139). VAS scores, adverse effects, and maternal/fetal outcomes were comparable between groups. In an exploratory SEM, intraprocedural neurological symptoms showed the strongest negative association with satisfaction (standardized β=-0.140, P < 0.001), followed by poor analgesic quality (β=-0.101, P = 0.011) and higher mean VAS (β=-0.092, P = 0.023). CONCLUSION: In this study, preserving neuraxial homeostasis by performing spinal puncture before epidural catheterization was associated with a lower incidence of observed neurological symptoms and higher maternal satisfaction scores compared with conventional CSEA, without compromising analgesic efficacy. While these findings suggest potential benefits of the SSEA technique, confirmation in blinded, multi-center trials is needed, and the assessment of satisfaction was limited by the use of a non-validated instrument. TRIAL REGISTRATION: ChiCTR, ChiCTR2500111828. Registered 30 November 2023 (prospectively registered); first participant enrolled 10 February 2024.

BACKGROUND: Chemotherapy-induced peripheral neuropathy (CIPN) causes debilitating pain that limits anticancer treatment, yet effective therapies remain limited. Mast cells (MCs) regulate neuroimmune signaling implicated in CIPN, but their receptor-specific contributions remain poorly understood. In mice, oxaliplatin and paclitaxel produce robust mechanical and cold hypersensitivities that mirror CIPN pain. Mas-related G-protein-coupled receptor B2 (MrgprB2) and its human orthologue MrgprX2 are MC-restricted receptors that mediate non-IgE-mediated activation. However, whether MrgprB2 signaling differently contributes to oxaliplatin- versus paclitaxel-induced CIPN pain remains unclear. METHODS: We employed a comparative mechanistic approach using wild-type (WT) and MrgprB2 knockout (KO) mice to define receptor-specific contributions to oxaliplatin- versus paclitaxel-induced CIPN pain. Behavioral assessments of mechanical and cold hypersensitivity were integrated with histological profiling of MC recruitment and mediator profiles. Genetic findings were validated pharmacologically with osthole, a natural MrgprB2/X2 antagonist. RESULTS: Both oxaliplatin and paclitaxel induced cutaneous MC accumulation in the hindpaw of WT mice, but they triggered distinct MC mediator-release profiles in vivo: oxaliplatin preferentially elevated tryptase, while paclitaxel was associated with greater histamine enrichment. Yet, neither drug directly activate MCs in vitro, as indicated by unchanged β-hexosaminidase release and calcium signaling. Importantly, MrgprB2 KO selectively attenuated oxaliplatin-induced tryptase upregulation and mechanical and cold hypersensitivity in vivo, without affecting paclitaxel-induced histamine changes or pain behavior. Consistently, with these genetic results, osthole selectively attenuated oxaliplatin-induced pain, but not paclitaxel-induced pain in WT mice. CONCLUSIONS: These findings support a mechanistic dichotomy in CIPN pain, indicating that MrgprB2 contributes selectively to oxaliplatin-induced, but not paclitaxel-induced, CIPN in mice. More broadly, they suggest that CIPN involves mechanistically distinct neuroimmune states depending on the chemotherapeutic class and highlight MrgprB2/X2 as a drug class-selective target for platinum-induced CIPN pain treatment.