Biology subjects

Rickman, R. H.

Publications and source records attributed to Rickman, R. H..

3 recordsLinked to original sources

bioRxiv2024

The osteoarthritis associated sphingolipid sphingomyelin 34:1 causes inflammatory pain in mice

ObjectiveOsteoarthritis (OA) has a multifactorial pathogenesis, pain being the main symptom driving clinical decision making. Dysregulation of multiple mediators occurs in OA, the roles of many remaining to be identified. In dogs and humans with OA, synovial fluid lipidome dysregulation occurs, some findings being replicated in the plasma lipidome in a mouse OA model. One upregulated lipid is the sphingomyelin N-palmitoyl-D-erythro-sphingosylphosphorylcholine (d18:1/16:0), referred to here as SM. This study aimed to determine if SM causes joint pain and neuronal hyperexcitability in mice. DesignThe effects of SM or a structurally related ceramide (CM) on mouse sensory neuron excitability were measured using patch-clamp electrophysiology, as well as the ability of intraarticular SM and CM to induce inflammatory pain in mice. ResultsIncubation of sensory neurons with 1 {micro}M SM decreased rheobase, compared to incubation with vehicle (p-adj = 0.0000146, 95% confidence interval (CI): 50.20, 76.73) or CM (p-adj = 0.138, CI: 103.45, 171.55). Similarly, SM induced mechanical hypersensitivity in mice compared to mice receiving vehicle (p-adj = 0.000003, 95% confidence interval (CI): 166.82, 251.63) or CM (p-adj = 0.055, 95% CI: 218.28, 268.12), which was coupled with a significant decrease in rheobase of knee-innervating neurons isolated from SM-injected mice compared to those receiving vehicle (p-adj = 0.0138, CI: 50.19, 76.73) or CM (p-adj = 1.0, CI: 103.45, 171.55). ConclusionsThe results generated demonstrate that a dysregulated lipidome can contribute to inflammatory OA pain, further work being necessary to determine the mechanism by which SM exerts its activity.

neuroscience↗

bioRxiv2024

Activation of the proton-sensing GPCR, GPR65 on fibroblast-like synoviocytes contributes to inflammatory joint pain.

Inflammation is associated with localised acidosis, however, attributing physiological and pathological roles to proton-sensitive receptors is challenging due to their diversity and widespread expression. Here, agonists of the proton-sensing GPCR, GPR65, were systematically characterised. The synthetic agonist BTB09089 (BTB) recapitulated many proton-induced signalling events and demonstrated selectivity for GPR65. BTB was used to show that GPR65 activation on fibroblast-like synoviocytes (FLS), cells that line synovial joints, results in the secretion of pro-inflammatory mediators capable of recruiting immune cells and sensitising sensory neurons. Intra-articular injection of BTB resulted in GPR65-dependent sensitisation of knee-innervating neurons and nocifensive behaviours in mice. Stimulation of GPR65 on human FLS also triggered the release of inflammatory mediators and synovial fluid samples from human osteoarthritis patients were shown to activate GPR65. These results suggest a role of GPR65 in mediating cell-cell interactions that drive inflammatory joint pain in both mice and humans.

neuroscience↗

bioRxiv2023

Digging deeper into pain - an ethological behavior assay correlating well-being in mice with human pain experience.

The pressing need for safer, more efficacious analgesics is felt worldwide. Pre-clinical tests in animal models of painful conditions represent one of the earliest checkpoints novel therapeutics must negotiate before consideration for human use. Traditionally, the pain status of laboratory animals has been inferred from evoked nociceptive assays which measure their responses to noxious stimuli. The disconnect between how pain is tested in laboratory animals and how it is experienced by humans may in part explain the shortcomings of current pain medications and highlights a need for refinement. Here, we survey human chronic pain patients who assert that everyday aspects of life, such as cleaning and leaving the house, are affected by their on-going level of pain. Accordingly, we test the impact of painful conditions on an ethological behavior of mice, digging. Stable digging behavior was observed over time in naive mice of both sexes. By contrast, deficits in digging were seen following acute knee inflammation. The analgesia conferred by meloxicam and gabapentin was compared in the monosodium iodoacetate knee osteoarthritis model, meloxicam more effectively ameliorating digging deficits, in line with human patients finding meloxicam more effective. Lastly, in a visceral pain model, the decrease in digging behavior correlated with the extent of disease. Ultimately, we make a case for adopting ethological assays, such as digging, in studies of pain in laboratory animals, which we believe to be more representative of the human experience of pain and thus valuable in assessing clinical potential of novel analgesics in animals.

neuroscience↗