Biology subjects

Bulmer, D. C.

Publications and source records attributed to Bulmer, D. C..

13 recordsLinked to original sources

bioRxiv2026

Cromolyn inhibits PGE2-mediated sensitisation of TRPV1 in a GPR35-dependent manner in sensory neurons

There is a pressing need for effective alternatives to opioid analgesics, the development of which requires the identification of novel anti-nociceptive drug targets. Here, we have further investigated the anti-nociceptive properties of a GPR35 agonist, cromolyn, in an in vitro model of inflammatory sensitisation. We used ratiometric Ca2+ imaging of cultured sensory neurons to examine the effect of cromolyn on prostaglandin E2 (PGE2)-mediated sensitisation of the pro-nociceptive ion channel, transient receptor potential cation channel, subfamily V, member 1 (TRPV1). The sensitisation of TRPV1 by PGE2 was inhibited by cromolyn in a GPR35-dependent manner. These observations provide further evidence in support of an anti-nociceptive role for GPR35, highlighting the potential use of GPR35 agonists as analgesics.

neuroscience↗

bioRxiv2025

Protease-activated receptor 1-mediated matrix metalloprotease signalling in sensory neurons

Visceral pain is a prevalent and debilitating symptom of inflammatory bowel disease (IBD). However, current pain therapies are often ineffective, raising the possibility that novel disease mediators might be contributing to pain during inflammation. Our study provides new insights into how matrix metalloproteinases (MMPs), which are elevated in IBD, stimulate sensory neurons. We demonstrate that MMP3, MMP8, and MMP9 induce intracellular Ca2+ release in dorsal root ganglion (DRG) neurons through activation of protease-activated receptor 1 (PAR1) and subsequent activation of phospholipase C (PLC). Characterisation of the neuronal populations stimulated by these MMPs suggests that a subset is likely nociceptive. In contrast, MMP2 and MMP13, although capable of cleaving PAR1 in other cell types, do not induce Ca2+ mobilisation in DRG neurons. Interestingly, pre-treatment with MMP2 or MMP13 reduces the neuronal response to MMP3 or PAR1 agonist, suggesting that MMP2 and MMP13 act on PAR1 in a manner which prevents further activation. Additionally, MMP10 induces Ca2+ mobilisation in DRG neurons but through a PAR1-independent mechanism. These findings uncover a previously unrecognised role for MMP signalling in sensory neurons, highlighting a potential mechanism by which MMPs could contribute to the pro-nociceptive environment in the inflamed bowel.

neuroscience↗

bioRxiv2024

Pro-inflammatory mediators sensitise Transient Receptor Potential Melastatin 3 cation channel (TRPM3) signalling in mouse sensory neurons

Pro-inflammatory mediators can directly activate pain-sensing neurons, known as nociceptors. Additionally, these mediators can potentiate or sensitise ion channels and receptors expressed by these cells through transcriptional and post-translational modulation, leading to nociceptor hypersensitivity. A well-characterised group of ion channels that subserve nociceptor sensitisation is the transient receptor potential (TRP) superfamily of cation channels. For example, the roles of TRP channels vanilloid 1 (TRPV1) and ankyrin 1 (TRPA1) in nociceptor sensitisation and inflammatory pain have been extensively documented. In the case of TRP melastatin 3 (TRPM3), however, despite the increasing recognition of this channels role in inflammatory pain, the mechanisms driving its sensitisation during inflammation remain poorly understood. Here, we found that an inflammatory soup of bradykinin, interleukin 1{beta} (IL-1{beta}) and tumour necrosis factor (TNF) sensitised TRPM3 function in isolated mouse sensory neurons; IL-1{beta} and TNF, but not bradykinin, independently potentiated TRPM3 function. TRPM3 expression and translocation to the membrane remained unchanged upon individual or combined exposure to these inflammatory mediators, which suggests post-translational modification occurs. Finally, using the model of complete Freunds adjuvant-induced knee inflammation, we found that pharmacological blockade of TRPM3 does not alleviate inflammatory pain, which contrasts with previous reports using different pain models. We propose that the nuances of the immune response may determine the relative contribution of TRPM3 to nociceptive signalling in different neuro-immune contexts. Collectively, our findings improve insight into the role of TRPM3 sensitisation in inflammatory pain. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=164 SRC="FIGDIR/small/612393v1_ufig1.gif" ALT="Figure 1"> View larger version (34K): org.highwire.dtl.DTLVardef@11e90acorg.highwire.dtl.DTLVardef@1ac1c2aorg.highwire.dtl.DTLVardef@6d116forg.highwire.dtl.DTLVardef@93c605_HPS_FORMAT_FIGEXP M_FIG O_FLOATNOGraphical abstractC_FLOATNO C_FIG

neuroscience↗

bioRxiv2024

TRPV4 stimulates colonic afferents through mucosal release of ATP and glutamate

Background and PurposeAbdominal pain is a leading cause of morbidity for people living with gastrointestinal disease. While the vanilloid transient receptor potential 4 (TRPV4) ion channel has been implicated in the pathogenesis of abdominal pain, the relative paucity of TRPV4 expression in colon-projecting sensory neurons suggests that non-neuronal cells may also contribute to TRPV4-mediated nociceptor stimulation. Experimental ApproachChanges in murine colonic afferent activity were examined using ex vivo electrophysiology in tissues with the gut mucosa present or removed. ATP and glutamate release were measured by bioluminescence assay from human colon organoid cultures and mouse colon. Dorsal root ganglion sensory neuron activity was evaluated by Ca2+ imaging when cultured alone or co-cultured with colonic mucosal cells. Key ResultsThe TRPV4 agonist GSK1016790A elicited a robust increase in murine colonic afferent activity, which was abolished by removal of the gut mucosa. GSK1016790A promoted ATP and glutamate release from human colon organoid cultures and mouse colon. Inhibition of ATP degradation in mouse colon enhanced the afferent response to GSK1016790A. Pre-treatment with purinoreceptor or glutamate receptor antagonists attenuated and abolished the response to GSK1016790A when given alone or in combination, respectively. Sensory neurons co-cultured with colonic mucosal cells produced a marked increase in intracellular Ca2+ to GSK1016790A compared to neurons cultured alone. Conclusions and ImplicationsOur data indicate that mucosal release of ATP and glutamate is responsible for the stimulation of colonic afferents following TRPV4 activation. These findings highlight an opportunity to target the gut mucosa for the development of new visceral analgesics. Bullet Point SummaryWhat is already known? O_LIActivation of TRPV4 causes visceral hypersensitivity via the stimulation of colonic afferents. C_LI What does this study add? O_LITRPV4-mediated colonic afferent activation is dependent on mucosal release of ATP and glutamate. C_LI What is the clinical significance? O_LIMucosal TRPV4-mediated colonic afferent activation provides a gut restricted target for treating abdominal pain. C_LI

pharmacology and toxicology↗

bioRxiv2024

Implantable Bioelectronics for Real-time in vivo Recordings of Enteric Neural Activity

The gastrointestinal tract is regulated by a complex network of electrically-active cell types that communicate to drive gut function. One of these systems, the enteric nervous system, represents a primary point of contact for a host of factors that influence bodily health and behavior. This division of the autonomic nervous system is unique in both its extensivity, with neurons distributed throughout the gastrointestinal tract from the esophagus to the rectum, and its capability for local information processing. However, the constant intrinsic and extrinsic motion of the gut as well as the sparse distribution of the neurons that constitute the enteric nervous system has made, access and analysis for study of this important component of the gastrointestinal tract exceedingly challenging. Here, we present the construction and validation of a bioelectronic implant for accessing neural information from the distal colon. The implant, constructed for compatibility with a novel surgical approach applicable across multiple species, is designed to be positioned within the colonic wall in close proximity to the enteric nervous plexi. We captured complex multi-frequency electrophysiological responses to neural chemical stimulants and showed that we can record distension activity mimicking gut motility. We also show the feasibility of utilizing this device for recording from putative single neurons in freely-moving rats and examining colonic activity in the context of food intake and stress. This work marks a significant advancement in understanding the complex pathways of the gut-brain axis. Our bioelectronic monitoring system demonstrates the power of real-time electrophysiological monitoring for the distal areas of the autonomic nervous system. Furthermore, direct access to the communication pathways of the enteric nervous system paves the way for novel neuromodulation strategies targeting the gut-brain axis.

neuroscience↗

bioRxiv2023

GPR35 inhibits TRPA1-mediated colonic afferent hypersensitivity through suppression of Substance P release

The development of non-opioid analgesics for the treatment of chronic abdominal pain is a pressing area of unmet clinical need. To address this, we examined the expression of Gi/o-coupled receptors in colonic sensory neurons, which, like opioid receptors, have the potential to inhibit nociceptor activation due to their inhibitory G protein coupling. This led to the identification of the orphan receptor GPR35 as a visceral analgesic drug target due to its marked co-expression with TRPA1, a mediator of noxious mechanotransduction in the bowel. Consistent with in silico docking studies which identified binding sites for the mast cell stabiliser cromolyn and phosphodiesterase inhibitor zaprinast at GPR35, we demonstrated, using GPR35 knockout mice, that the antinociceptive effects of these drugs on TRPA1-mediated colonic nociceptor activation and mechanosensitisation were GPR35-dependent. Further work showed these antinociceptive effects occurred through the inhibition of substance P (SP) release. This confirmed both the pronociceptive effect of SP on colonic afferents, and the contribution of SP to TRPA1-mediated colonic nociceptor activation and sensitisation. We also found that TRPA1-induced contraction of the colon was mediated by SP signalling and could be inhibited by cromolyn in a GPR35-dependent manner. Our data identify GPR35, through its inhibition of SP-mediated colonic contractility and nociceptor activation and sensitisation, as a putative mechanism for the reported clinical efficacy of cromolyn in the treatment of irritable bowel syndrome. These findings highlight the potential utility of GPR35 agonists to deliver non-opioid analgesia for the treatment of abdominal pain associated with gastrointestinal diseases such as irritable bowel syndrome and inflammatory bowel disease.

physiology↗

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↗

bioRxiv2023

Transcriptomic profiling reveals a pro-nociceptive role for Angiotensin II in inflammatory bowel disease

ObjectiveVisceral pain is a leading cause of morbidity in inflammatory bowel disease (IBD), contributing significantly to reduced quality of life. Currently available analgesics often lack efficacy or have intolerable side-effects, driving the need for a more complete understanding of the mechanisms causing pain. MethodsWhole transcriptome gene expression analysis was performed by bulk RNA sequencing of colonic biopsies from patients with ulcerative colitis (UC) and Crohns disease (CD) reporting abdominal pain and compared with non-inflamed control biopsies. Putative pro-nociceptive mediators were identified based on pathway analysis of differentially expressed genes in IBD tissue and single cell gene expression in colonic neurons. Pro-nociceptive activity of identified mediators was assessed in assays of sensory neuron and colonic afferent activity. ResultsRNA sequencing analysis highlighted a 7.6-fold increase in the expression of angiotensinogen transcripts, Agt, the precursor to angiotensin II (Ang II), in samples from UC patients (p = 3.2x10-8). Consistent with the marked expression of the angiotensin AT1 receptor in colonic neurons, Ang II elicited an increase in intracellular Ca2+ in capsaicin-sensitive, voltage gated sodium channel subtype NaV1.8-positive sensory neurons. Ang II also evoked action potential discharge in high-threshold colonic nociceptors. These effects were inhibited by the AT1 receptor antagonist valsartan. ConclusionFindings from our study identify AT1 receptor-mediated colonic nociceptor activation as a novel pathway of visceral nociception in IBD patients with UC. This work highlights the potential utility of angiotensin receptor blockers, such as valsartan, as treatments for pain in IBD.

neuroscience↗

bioRxiv2023

KV7 but not dual SK/IK channel openers inhibit the activation of colonic afferents by noxious stimuli

In numerous subtypes of central and peripheral neurons, small and intermediate conductance Ca2+-activated K+ (SK and IK, respectively) channels are important regulators of neuronal excitability. Transcripts encoding SK channel subunits, as well as the closely related IK subunit, are co-expressed in the soma of colonic afferent neurons with receptors for the algogenic mediators adenosine triphosphate (ATP) and bradykinin, P2X3 and B2, highlighting the potential utility of these channels as drug targets for the treatment of abdominal pain in gastrointestinal diseases such as irritable bowel syndrome. Despite this, pre-treatment with the dual SK/IK channel opener SKA-31 had no effect on the colonic afferent response to ATP, bradykinin or noxious ramp distention of the colon. Inhibition of SK or IK channels with apamin or TRAM-34, respectively, yielded no change in spontaneous baseline afferent activity, indicating these channels are not tonically active. In contrast to its lack of effect in electrophysiological experiments, comparable concentrations of SKA-31 abolished ongoing peristaltic activity in the colon ex vivo. Treatment with the KV7 channel opener retigabine blunted the colonic afferent response to all applied stimuli. Our data therefore highlight the potential utility of KV7, but not SK/IK, channel openers as analgesic agents for the treatment of abdominal pain.

neuroscience↗

bioRxiv2022

Sensitisation of colonic nociceptors by IL-13 is dependent on JAK and p38 MAPK activity

The effective management of visceral pain is a significant unmet clinical need for those affected by gastrointestinal diseases, such as inflammatory bowel disease (IBD). The rational design of novel analgesics requires a greater understanding of the mediators and mechanisms underpinning visceral pain. Interleukin-13 (IL-13) production by immune cells residing in the gut is elevated in IBD, and IL-13 appears to be important in the development of experimental colitis. Whats more, receptors for IL-13 are expressed by neurons innervating the colon, though it is not known whether IL-13 plays any role in visceral nociception per se. To resolve this, we employed Ca2+ imaging of cultured sensory neurons and ex vivo electrophysiological recording from the lumbar splanchnic nerve innervating the distal colon. Ca2+ imaging revealed the stimulation of small-diameter, capsaicin-sensitive sensory neurons by IL-13, indicating that IL-13 likely stimulates nociceptors. IL-13-evoked Ca2+ signals were attenuated by inhibition of Janus (JAK) and p38 kinases. In the lumbar splanchnic nerve, IL-13 did not elevate baseline firing, nor sensitise the response to capsaicin application, but did enhance the response to distention of the colon. In line with Ca2+ imaging experiments, IL-13-mediated sensitisation of the afferent response to colon distention was blocked by inhibition of either JAK or p38 kinase signalling. Together, these data highlight a potential role for IL-13 in visceral nociception and implicate JAK and p38 kinases in pro-nociceptive signalling downstream of IL-13. Key Points SummaryThe pro-inflammatory cytokine IL-13 is elevated in gastrointestinal (GI) diseases and known to sensitise sensory neurons. This study confirms a role for IL-13 in colonic afferent sensitisation and defines a role for downstream JAK and p38 MAPK signalling in colonic mechanosensitisation. IL-13-mediated increase in [Ca2+]i in capsaicin-sensitive sensory neurons is dependent on p38 MAPK and JAK signalling. IL-13-induced sensitisation of colonic afferents to noxious mechanical distension is abolished by inhibition of p38 MAPK and JAK. We have built on the current understanding of IL-13 and its neuronal interactions, highlighting the therapeutic potential of targeting p38 MAPK and JAK signalling pathways to treat visceral pain in GI disease.

physiology↗

bioRxiv2022

Sensitisation of colonic nociceptors by TNFα is dependent on TNFR1 expression and p38 MAPK activity

Visceral pain is a leading cause of morbidity in gastrointestinal diseases, which is exacerbated by the gut related side-effects of many analgesics. New treatments are needed and further understanding of the mediators and mechanisms underpinning visceral nociception in disease states is required to facilitate this. The pro-inflammatory cytokine TNF is linked to pain in both patients with inflammatory bowel disease and irritable bowel syndrome, and has been shown to sensitise colonic sensory neurons. Somatic, TNF- triggered thermal and mechanical hypersensitivity is mediated by TRPV1 signalling and p38 MAPK activity respectively, downstream of TNFR1 receptor activation. We therefore hypothesised that TNFR1-evoked p38 MAPK activity may also be responsible for TNF sensitisation of colonic afferent responses to the TRPV1 agonist capsaicin, and noxious distension of the bowel. Using Ca2+ imaging of dorsal root ganglion sensory neurons, we observed TNF-mediated increases in intracellular [Ca2+] and sensitisation of capsaicin responses. The sensitising effects of TNF were dependent on TNFR1 expression and attenuated by p38 MAPK inhibition. Consistent with these findings, ex vivo colonic afferent fibre recordings demonstrated enhanced response to noxious ramp distention of the bowel and bath application of capsaicin following TNF pre-treatment. Responses were reversed by p38 MAPK inhibition and absent in tissue from TNFR1 knockout mice. Our findings demonstrate a contribution of TNFR1, p38 MAPK and TRPV1 to TNF-induced sensitisation of colonic afferents, highlighting the potential utility of these drug targets for the treatment of visceral pain in GI disease. Abstract figure legendTNF sensitised Ca2+ responses to the TRPV1 agonist capsaicin in dorsal root ganglion sensory neurons. Sensitisation was TNFR1-dependent and attenuated by inhibition of p38 MAPK. Direct Ca2+ responses to TNF were TRPV1-and TRPA1-dependent. In ex vivo colonic afferent recordings, TNF increased sensitivity to noxious ramp distension and capsaicin, both of which were absent in TNFR1-/- tissue or blocked by inhibition of p38 MAPK. These findings establish a role for TNFR1, p38 MAPK and TRPV1 in TNF-mediated sensitisation of colonic afferents. Key Points SummaryO_LITNF sensitises sensory neurons and colonic afferents to the TRPV1 agonist capsaicin. C_LIO_LITNF-mediated sensitisation of sensory neurons and colonic nociceptors is dependent on TNFR1 expression. C_LIO_LITNF sensitisation of sensory neurons and colonic afferents to capsaicin and noxious ramp distension is abolished by inhibition of p38 MAPK. C_LI

neuroscience↗

bioRxiv2019

Sensitization of knee-innervating sensory neurons by tumor necrosis factor-α activated fibroblast-like synoviocytes: an in vitro, co-culture model of inflammatory pain

Pain is a principal contributor to the global burden of arthritis with peripheral sensitization being a major cause of arthritis-related pain. Within the knee joint, distal endings of dorsal root ganglion neurons (knee neurons) interact with fibroblast-like synoviocytes (FLS) and the inflammatory mediators they secrete, which are thought to promote peripheral sensitization. Correspondingly, RNA-sequencing has demonstrated detectable levels of pro-inflammatory genes in FLS derived from arthritic patients. This study confirms that stimulation with tumor necrosis factor (TNF-), results in expression of pro-inflammatory genes in mouse and human FLS (derived from OA and RA patients), as well as increased secretion of cytokines from mouse TNF- stimulated FLS (TNF-FLS). Electrophysiological recordings from retrograde labelled knee neurons co-cultured with TNF-FLS, or supernatant derived from TNF-FLS, revealed a depolarized resting membrane potential, increased spontaneous action potential firing and enhanced TRPV1 function, all consistent with a role for FLS in mediating the sensitization of pain-sensing nerves in arthritis. Therefore, data from this study demonstrate the ability of FLS activated by TNF- to promote neuronal sensitization, results that highlight the importance of both non-neuronal and neuronal cells to the development of pain in arthritis.

neuroscience↗

bioRxiv2019

Galanin inhibits visceral afferent responses to noxious mechanical and inflammatory stimuli

Galanin is a neuropeptide expressed by sensory neurones innervating the gastrointestinal (GI) tract. Galanin displays inhibitory effects on vagal afferent signalling within the upper GI tract, and the goal of this study was to determine the actions of galanin on colonic spinal afferent function. Specifically, we sought to evaluate the effect of galanin on lumbar splanchnic nerve (LSN) mechanosensitivity to noxious distending pressures and the development of hypersensitivity in the presence of inflammatory stimuli and colitis. Using ex vivo electrophysiological recordings we show that galanin produces a dose-dependent inhibition of colonic LSN responses to mechanical stimuli and prevents the development of hypersensitivity to acutely administered inflammatory mediators. Using galanin receptor (GalR) agonists, we show that GalR1 activation, but not GalR2/3 activation, inhibits mechanosensitivity. The inhibitory effect of galanin on colonic afferent activity was not observed in tissue from mice with dextran sodium sulphate-induced colitis. We conclude that galanin has a marked inhibitory effect on colonic mechanosensitivity at noxious distending pressures and prevents the acute development of mechanical hypersensitivity to inflammatory mediator, an effect not seen in the inflamed colon. These actions highlight a potential role for galanin in the regulation of mechanical nociception from the bowel and the therapeutic potential of targeting galaninergic signalling to treat visceral hypersensitivity.\n\nKey point summaryO_LIGalanin inhibits visceral afferent mechanosensitivity to noxious phasic distension of the colon via GalR1.\nC_LIO_LIGalanin attenuates afferent mechanical hypersensitivity induced by the application of inflammatory mediators.\nC_LIO_LIInhibition of afferent mechanosensitivity by galanin is not observed in tissues isolated from mice undergoing DSS-induced colitis\nC_LIO_LIGalanin inhibits the transmission of noxious mechanical stimuli by colonic afferents and its sensitisation by inflammatory mediators highlighting an antinociceptive role for galanin in the colon.\nC_LI

neuroscience↗