Lemes, J. B. P. | bioRxiv Science

bioRxiv2025

Measuring Joint Pain Through Tibio-Femoral Flexion: technique validation and assessment of behavior in response to different analgesics in rats

BackgroundAssessing knee joint pain in experimental OA (EOA) models remains a significant challenge. Our study demonstrates that the use of an adapted electronic von Frey (aVF) device, featuring a modified tip, surpasses the standard von Frey (sVF) in detecting knee joint pain behavior and evaluating the efficacy of analgesic treatments in OA model induced by monoiodine acetate (MIA). ResultsThe sVF was able to induce a behavior profile in naive animals characterized by a hind paw flinching and withdrawal reflex. This behavioral response was affected by intraplantar lidocaine, which prone to the increase in mechanical thresholds related to sVF and validate it as pain related behavior. On the aVF method, the animals displayed no alterations at their mechanical thresholds in presence or absence of lidocaine, suggesting minimal stimulation of hind paw by the modified methodology. In animals where an osteoarthritic phenotype was induced by MIA, the aVF was able to detect a significant reduction on joint mechanical thresholds. The behavior linked to aVF was significantly affected by systemic delivery of morphine, confirming a nociceptive-like phenotype and suggesting a pain behavior predominantly triggered by joint flexion. The aVF was also able to detect an analgesic profile in MIA-OA rats treated with dexamethasone, LPS-RS, fucoidan, and morphine, indicating effectiveness in measure different the response profile triggered by analgesic drugs that affect joint pain perception. ConclusionsOur results suggest aVF as a more appropriate method to evaluate joint pain in rats.

neuroscience↗

bioRxiv2025

Analgesic actions of Intrathecal NaV 1.7 antisense in rats: loss of antagonist channel binding, message depletion, and neuraxial distribution of oligonucleotide

BackgroundGenome targeting strategies to address NaV 1.7 mediated signaling in nociceptive afferents produce highly selective and persistent analgesic outcomes. Here, we analyze the concentration-dependent effects of the reduction of primary afferent NaV 1.7 channel expression by intrathecal delivery of an antisense oligonucleotide on pain behaviors and the covariance of Scn9a knock-down on NaV 1.7 message expression and channel binding. MethodsMale Sprague-Dawley rats were implanted with lumbar intrathecal catheters and dosed with different NaV 1.7 ASO concentrations (100 to 3000 g;10 L). Pain behavior assays were conducted 0-28 days after ASO injections. Brain, spinal cords (SC) and dorsal root ganglia (DRGs) were collected. Quantification of ASO knock-down was assessed through RT-qPCR. NaV 1.7 expression was assessed by binding of NaV 1.7 fluorescent labeled antagonist (ATTO488PTx-II). Distribution studies were performed using anti-ASO antibody staining in brain, SCs and DRGs. ResultsNaV 1.7 message was detected in nerve, DRG and SC. Intrathecal ASO induced a concentration dependent gradient of knock down in DRGs (lumbar to cervical) of Scn9a mRNA and ATTO488PTx-II binding in small DRG neurons, and in spinal parenchyma, and a suppression of pain behaviors initiated by mechanical compression, inflammation and following intraplantar NaV1.7 agonist (OD1) or formalin. At 1000 {micro}g, there was a 47% reduction in phase 2 flinching, a 60% reduction in DRG mRNA and a 36% reduction in ATTO488PTx-II DRG binding in comparison with mismatch controls. Although marked changes were seen at the sensory ganglia level and spinal dorsal horn, no changes in NaV 1.7 binding or mRNA were detected in sciatic nerves. Reduction in DRG message displayed a rostrocaudal gradient that corresponded with ASO distribution. ConclusionsThe study presents how NaV 1.7 ASOs reduce primary afferent channel binding through an effective knock-down on Scn9a mRNA, and channel binding leading to a covariate reduction in pain behavior.

neuroscience↗