Project description:Neuropathic pain is an apparently spontaneous experience triggered by abnormal physiology of the peripheral or central nervous system, which evolves with time. Neuropathic pain arising from peripheral nerve injury is characterized by a combination of spontaneous pain, hyperalgesia and allodynia. There is no evidence of this type of pain in human infants or rat pups; brachial plexus avulsion, which causes intense neuropathic pain in adults, is not painful when the injury is sustained at birth. Since infants are capable of nociception from before birth and display both acute and chronic inflammatory pain behaviour from an early neonatal age, it appears that the mechanisms underlying neuropathic pain are differentially regulated over a prolonged postnatal period. We used microarrays to detail the global programme of gene expression underlying the differences in nerve injury between along the postnatal development and identified distinct classes of regulated genes during the injury Experiment Overall Design: We have performed a microarray analysis of the rat L4/L5 dorsal root ganglia, 7 days post spared nerve injury, a model of neuropathic pain. Genes that are regulated in adult rats displaying neuropathic behaviour were compared to those regulated in young rats (10 days old) that did not show the same neuropathic behaviour.
Project description:Chronic neuropathic pain is a major morbidity of neural injury, yet its mechanisms are incompletely understood. Hypersensitivity to previously non-noxious stimuli (allodynia) is a common symptom. Here, we demonstrate that the onset of cold hypersensitivity precedes tactile allodynia and this temporal divergence was associated with major differences in global gene expression in dorsal root ganglia. Transcripts whose expression correlate with the onset of cold allodynia were nociceptor-related whereas those correlating with tactile hypersensitivity were enriched for immune cell activity. Selective ablation of TrpV1 lineage nociceptors resulted in mice that did not acquire cold allodynia but developed normal tactile hypersensitivity. Whereas depletion of macrophages or T cells reduced neuropathic tactile allodynia but not cold hypersensitivity. We conclude that neuropathic pain is contributed to by reactive processes of sensory neurons and immune cells, each leading to distinct forms of pain hypersensitivity, potentially allowing effective drug development targeted to each pain modality.
Project description:Chronic neuropathic pain is a major morbidity of neural injury, yet its mechanisms are incompletely understood. Hypersensitivity to previously non-noxious stimuli (allodynia) is a common symptom. Here, we demonstrate that the onset of cold hypersensitivity precedes tactile allodynia and this temporal divergence was associated with major differences in global gene expression in dorsal root ganglia (DRG). Transcripts whose expression correlate with the onset of cold allodynia were nociceptor-related, whereas those correlating with tactile hypersensitivity were enriched for immune cell activity. Selective ablation of TrpV1 lineage nociceptors resulted in mice that did not acquire cold allodynia but developed normal tactile hypersensitivity. Whereas, depletion of macrophages or T cells reduced neuropathic tactile allodynia but not cold hypersensitivity. We conclude that neuropathic pain is contributed to by reactive processes of sensory neurons and immune cells, each leading to distinct forms of pain hypersensitivity, potentially allowing effective drug development targeted to each pain modality.
Project description:Neuropathic pain is a prevalent and debilitating chronic disease that is characterized by activation in glial cells in various pain-related regions within the central nervous system. Recent studies have suggested a sexually dimorphic role of microglia in the maintenance of neuropathic pain in rodents. Here, we utilized RNA sequencing analysis of microglia to identify whether there is a common neuropathic microglial signature and characterize the sex differences in microglia in pain-related regions in nerve injury and chemotherapy-induced peripheral neuropathy mouse models. Whilst mechanical allodynia and behavioral changes were observed in all models, transcriptomic analysis of microglia revealed no common transcriptional changes in spinal and supraspinal regions and in different neuropathic models. However, there was a substantial change in microglial gene expression within the ipsilateral lumbar spinal cord 7-days after chronic constriction injury (CCI) of the sciatic nerve. Both sexes upregulated genes associated with inflammation, phagosome, and lysosome activation, though males revealed a prominent global transcriptional shift not observed in female mice. This study demonstrates a lack of a common neuropathic microglial signature and indicates distinct sex differences in spinal microglia, suggesting they contribute to the sex-specific pain processing following nerve injury.
Project description:Neuropathic pain is an apparently spontaneous experience triggered by abnormal physiology of the peripheral or central nervous system, which evolves with time. Neuropathic pain arising from peripheral nerve injury is characterized by a combination of spontaneous pain, hyperalgesia and allodynia. There is no evidence of this type of pain in human infants or rat pups; brachial plexus avulsion, which causes intense neuropathic pain in adults, is not painful when the injury is sustained at birth. Since infants are capable of nociception from before birth and display both acute and chronic inflammatory pain behaviour from an early neonatal age, it appears that the mechanisms underlying neuropathic pain are differentially regulated over a prolonged postnatal period. We used microarrays to detail the global programme of gene expression underlying the differences in nerve injury between along the postnatal development and identified distinct classes of regulated genes during the injury
Project description:Neuropathic pain is a refractory condition that involves de novo protein synthesis in the nociceptive pathway. The mechanistic target of rapamycin (mTOR) is a master regulator of protein synthesis; however, mechanisms underlying its role in neuropathic pain remain elusive. Using spared nerve injury-induced neuropathic pain model, we found mTOR activation in large-diameter dorsal root ganglion (DRG) neurons and spinal microglia. However, selective ablation of mTOR in DRG neurons, rather than microglia, alleviated neuropathic pain. Combining transcriptomic profiling, electrophysiological recording and pharmacologic manipulations, we demonstrated that activated mTOR promoted neuropeptide Y (NPY) induction in mechanoreceptors and that NPY acted on Y2 receptors (Y2R) but not Y1R to enhance nociceptor excitability. Peripheral replenishment of NPY reversed pain alleviation upon mTOR removal, whereas Y2R antagonists prevented its function. Our findings reveal an unexpected link between mTOR and NPY in promoting nociceptor sensitization and neuropathic pain, through NPY/Y2R signaling-mediated intra-ganglionic transmission.
Project description:We produced single-cell transcriptomes from the mouse spinal cord using Drop-seq in animals modeling neuropathic pain and superficial injury (SI) controls. We used the spared nerve injury (SNI) model of neuropathic pain. ~10,000 cells from sham surgery controls and ~9,000 cells from SNI animals were sequenced. Unbiased cell clustering yielded 66 spinal cell subtypes sequenced at relatively low depth (~1200 transcripts/cell). Comparisons between SI and SNI cells were performed to investigate cell-specific differences during a neuropathic pain state.
Project description:Six different mouse pain models were studied: (1) tumour-injection model for bone cancer pain; (2) partial sciatic nerve ligation (PSL) for neuropathic pain; (3) mechanical joint loading for osteoarthritis pain; (4) oxaliplatin-induced painful neuropathy for chemotherapy-induced pain; (5) hyperalgesic priming model for chronic muscle pain; and (6) complete Freund’s adjuvant (CFA)-injection for inflammatory pain. Transcriptomic microarray analyses were performed using RNA isolated from dorsal root ganglia.