Mol Pain
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Cancer-induced bone pain (CIBP) is one of the most common and feared symptoms in patients with advanced tumors. The X-C motif chemokine ligand 12 (CXCL12) and the CXCR4 receptor have been associated with glial cell activation in bone cancer pain. Moreover, mitogen-activated protein kinases (MAPKs), as downstream CXCL12/CXCR4 signals, and c-Jun, as activator protein AP-1 components, contribute to the development of various types of pain. ⋯ Immunofluorescence images showed activated microglia in the spinal cord on day 14 after TCI and co-expression of CXCL12/CXCR4, p-MAPKs (p-JNK, p-ERK, p-p38 MAPK), and p-c-Jun in microglia. Intrathecal injection of the CXCR4 inhibitor AMD3100 reduced JNK and c-Jun phosphorylations, and intrathecal injection of the JNK inhibitor SP600125 and esketamine also alleviated TCI-induced pain and reduced the expression of p-JNK and p-c-Jun in microglia. Overall, our data suggest that the CXCL12/CXCR4-JNK-c-Jun signaling pathway of microglia in the spinal cord mediates neuronal sensitization and pain hypersensitivity in cancer-induced bone pain and that esketamine exerts its analgesic effect by inhibiting the JNK-c-Jun pathway.
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Ca2+ imaging is frequently used in the investigation of sensory neuronal function and nociception. In vitro imaging of acutely dissociated sensory neurons using membrane-permeant fluorescent Ca2+ indicators remains the most common approach to study Ca2+ signalling in sensory neurons. Fluo4 is a popular choice of single-wavelength indicator due to its brightness, high affinity for Ca2+ and ease of use. ⋯ Here, we show that a method scarcely used in sensory neurophysiology - first proposed by Maravall and colleagues (2000) - can provide reliable estimates of absolute cytosolic Ca2+ concentration ([Ca2+]cyt) in acutely dissociated sensory neurons using Fluo4. This method is straightforward to implement; is applicable to any high-affinity single-wavelength Ca2+ indicator with a large dynamic range; and provides estimates of [Ca2+]cyt in line with other methods, including ratiometric imaging. Use of this method will improve the granularity of sensory neuron Ca2+ imaging data obtained with Fluo4.
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While opioids remain amongst the most effective treatments for moderate-to-severe pain, their substantial side effect profile remains a major limitation to broader clinical use. One such side effect is opioid-induced hyperalgesia (OIH), which includes a transition from opioid-induced analgesia to pain enhancement. Evidence in rodents supports the suggestion that OIH may be produced by the action of opioids at Toll-like Receptor 4 (TLR4) either on immune cells that, in turn, produce pronociceptive mediators to act on nociceptors, or by a direct action at nociceptor TLR4. ⋯ In the present in vitro patch-clamp electrophysiology experiments, we demonstrate that low dose morphine directly sensitizes human as well as rodent dorsal root ganglion (DRG) neurons, an effect of this opioid analgesic that is antagonized by LPS-RS Ultrapure, a selective TLR4 antagonist. We found that low concentration (100 nM) of morphine reduced rheobase in human (by 36%) and rat (by 26%) putative C-type nociceptors, an effect of morphine that was markedly attenuated by preincubation with LPS-RS Ultrapure. Our findings support the suggestion that in humans, as in rodents, OIH is mediated by the direct action of opioids at TLR4 on nociceptors.
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Methylglyoxal (MGO), a highly reactive dicarbonyl metabolite of glucose primarily formed during the glycolytic pathway, is a precursor of advanced glycation end-products (AGEs). Recently, numerous studies have shown that MGO accumulation can cause pain and hyperalgesia. However, the mechanism through which MGO induces pain in the spinal dorsal horn remains unclear. ⋯ ROS also potentially induce pain via TRPA1 and TRPV1 in the spinal dorsal horn. Furthermore, we examined the effect of MGO in the presence of N-tert-butyl-α-phenylnitrone (PBN), a non-selective ROS scavenger, and found that the effect of MGO was completely inhibited. These results suggest that MGO increases spontaneous glutamate release from the presynaptic terminal to spinal dorsal horn neurons through TRPA1, TRPV1, and ROS and could enhance excitatory synaptic transmission.
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Chondromalacia, characterized by the softening of cartilage, is a prevalent condition affecting joint health with complex etiology. The immune system's role in its pathogenesis has been implicated but remains to be fully elucidated. To address a critical knowledge gap, we conducted a two-sample Mendelian randomization analysis of 731 immune cell phenotypes, assessing parameters like fluorescence, cell count, and morphology. ⋯ This breakthrough sheds light on the pathophysiological mechanisms of the condition. The identification of protective and risk-associated immune cell phenotypes provides a foundation for further exploration of immunological mechanisms in chondromalacia and may pave the way for targeted interventions. Future research is warranted to validate these findings and explore their clinical implications.