Electrical neuromodulation is an established non-pharmacological treatment for chronic pain. Howe... more Electrical neuromodulation is an established non-pharmacological treatment for chronic pain. However, existing devices using pulsatile stimulation are not suitable for all types of chronic pain. Direct current stimulation is a recently developed technology which shows better selectivity for small-diameter fibres. We investigated if this selectivity could be applied to preferentially suppress nociceptive signalling. We applied direct current to the sciatic nerve of rats and compared its effects on spinal activity produced by physiological (non-electrical) stimuli delivered to the foot. Tests were performed across models of neuropathic and inflammatory pain to further clarify potential clinical applications. We found that direct current could effectively suppress activity relating to painful stimuli in both pain models tested. These findings strongly support the use of direct current neuromodulation for chronic pain relief, and suggest that it may be effective at treating a broader ra...
Recent years have yielded significant advances in our understanding of microglia, the immune cell... more Recent years have yielded significant advances in our understanding of microglia, the immune cells of the central nervous system (CNS). Microglia are key players in CNS development, immune surveillance, and the maintenance of proper neuronal function throughout life. In the healthy brain, homeostatic microglia have a unique molecular signature. In neurological diseases, microglia become activated and adopt distinct transcriptomic signatures, including disease-associated microglia (DAM) implicated in neurodegenerative disorders. Homeostatic microglia synthesise the endogenous cannabinoids 2-arachidonoylglycerol and anandamide and express the cannabinoid receptors CB1 and CB2 at constitutively low levels. Upon activation, microglia significantly increase their synthesis of endocannabinoids and upregulate their expression of CB2 receptors, which promote a protective microglial phenotype by enhancing their production of neuroprotective factors and reducing their production of pro-inflammatory factors. Here, we summarise the effects of the microglial cannabinoid system in the CNS demyelinating disease multiple sclerosis, the neurodegenerative diseases Alzheimer's disease, Parkinson's disease and amyotrophic lateral sclerosis, chronic inflammatory and neuropathic pain, and psychiatric disorders including depression, anxiety and schizophrenia. We discuss the therapeutic potential of cannabinoids in regulating microglial activity and highlight the need to further investigate their specific microglia-dependent immunomodulatory effects.
Regulatory T (Treg) cells are a special subpopulation of immunosuppressive T cells that are essen... more Regulatory T (Treg) cells are a special subpopulation of immunosuppressive T cells that are essential for sustaining immune homeostasis. They maintain self-tolerance, inhibit autoimmunity, and act as critical negative regulators of inflammation in various pathological states including autoimmunity, injury, and degeneration of the nervous system. Treg cells are known to convey both beneficial and detrimental influences in certain disease contexts, and accumulating research suggests that their action may be altered in a range of peripheral and central nervous system pathologies. In this review, we discuss emerging evidence for the dichotomous role of Treg cells in various neurological pathologies including multiple sclerosis, Guillain-Barré syndrome, neuropathic pain, traumatic central nervous system injury, stroke, and neurodegenerative diseases such as amyotrophic lateral sclerosis, Alzheimer's disease, and Parkinson's disease. We are in the early stages of uncovering the ro...
Sensory problems such as neuropathic pain are common and debilitating symptoms in multiple sclero... more Sensory problems such as neuropathic pain are common and debilitating symptoms in multiple sclerosis (MS), an autoimmune inflammatory disorder of the CNS. Regulatory T (Treg) cells are critical for maintaining immune homeostasis, but their role in MS-associated pain remains unknown. Here, we demonstrate that Treg cell ablation is sufficient to trigger experimental autoimmune encephalomyelitis (EAE) and facial allodynia in immunized female mice. In EAE-induced female mice, adoptive transfer of Treg cells and spinal delivery of the Treg cell cytokine interleukin-35 (IL-35) significantly reduced facial stimulus-evoked pain and spontaneous pain independent of disease severity and increased myelination of the facial nociceptive pathway. The effects of intrathecal IL-35 therapy were Treg-cell dependent and associated with upregulated IL-10 expression in CNS-infiltrating lymphocytes and reduced monocyte infiltration in the trigeminal afferent pathway. We present evidence for a beneficial r...
Background Genetic risk factors for chemotherapy-induced peripheral neuropathy (CIPN), a major do... more Background Genetic risk factors for chemotherapy-induced peripheral neuropathy (CIPN), a major dose-limiting side-effect of paclitaxel, are not well understood. Methods We performed a genome-wide association study (GWAS) in 183 paclitaxel-treated patients to identify genetic loci associated with CIPN assessed via comprehensive neuropathy phenotyping tools (patient-reported, clinical and neurological grading scales). Bioinformatic analyses including pathway enrichment and polygenic risk score analysis were used to identify mechanistic pathways of interest. Results In total, 77% of the cohort were classified with CIPN (n = 139), with moderate/severe neuropathy in 36%. GWAS was undertaken separately for the three measures of CIPN. GWAS of patient-reported CIPN identified 4 chromosomal regions that exceeded genome-wide significance (rs9846958, chromosome 3; rs117158921, chromosome 18; rs4560447, chromosome 4; rs200091415, chromosome 10). rs4560447 is located within a protein-coding gene...
Introduction/AimsClinically, the chemotherapeutic agent oxaliplatin can cause peripheral neuropat... more Introduction/AimsClinically, the chemotherapeutic agent oxaliplatin can cause peripheral neuropathy, impaired balance, and muscle wastage. Using a preclinical model, we investigated whether exercise intervention could improve these adverse conditions.MethodsMice were chronically treated with oxaliplatin alone or in conjunction with exercise. Behavioral studies, including mechanical allodynia, rotarod, open‐field, and grip‐strength tests, were performed. After euthanasia, multiple organs and four different muscle types were dissected and weighed. The cross‐sectional area (CSA) of muscle fibers in the gastrocnemius muscle was assessed and gene expression analysis performed on the forelimb triceps muscle.ResultsOxaliplatin‐treated mice displayed reduced weight gain, mechanical allodynia, and exploratory behavior deficits that were not significantly improved by exercise. Oxaliplatin‐treated exercised mice showed modest evidence of reduced muscle wastage compared with mice treated with o...
Peripheral nerve injuries caused by focal constriction are characterised by local nerve ischaemia... more Peripheral nerve injuries caused by focal constriction are characterised by local nerve ischaemia, axonal degeneration, demyelination, and neuroinflammation. The aim of this study was to understand temporal changes in the excitability properties of injured motor axons in a mouse model of nerve constriction injury (NCI). The excitability of motor axons following unilateral sciatic NCI was studied in male C57BL/6J mice distal to the site of injury at the acute (6 hours‐1 week) and chronic (up to 20 weeks) phases of injury, using threshold tracking. Multiple measures of nerve excitability, including strength‐duration properties, threshold electrotonus, current‐threshold relationship, and recovery cycle were examined using the automated nerve excitability protocol (TRONDNF). Acutely, injured motor axons developed a pattern of excitability characteristic of ischemic depolarisation. In most cases, the sciatic nerve became transiently inexcitable. When a liminal compound muscle action pote...
This chapter summarizes a standard approach to identifying neuropathic pain for the clinician. Fo... more This chapter summarizes a standard approach to identifying neuropathic pain for the clinician. For neuropathic pain, and for the condition of complex regional pain syndrome (CRPS) especially, the six Ss should be queried when obtaining details regarding the affected region. A useful tool to rapidly and accurately localize sources of chronic pain and assist in the diagnosis of causes of neuropathic pain is a pain diagram. The examination of a chronic pain patient should start with an appropriate and directed general examination including a neurological examination. Quantitative sensory testing (QST) provides indirect information used to evaluate underlying sensory function abnormalities using only small, portable tools and with less time requirement than protocols developed by the German Neuropathic Research Network. In the future, bedside QST is expected to continue to play a role in determining potential pain mechanisms to help direct further evaluation and treatment.
Tissue damage, inflammation or injury of the nervous system may result in chronic neuropathic pai... more Tissue damage, inflammation or injury of the nervous system may result in chronic neuropathic pain characterised by increased sensitivity to painful stimuli (hyperalgesia), the perception of innocuous stimuli as painful (allodynia) and spontaneous pain. Neuropathic pain has been described in about 1% of the US population, is often severely debilitating and largely resistant to treatment. Animal models of peripheral neuropathic pain are now available in which the mechanisms underlying hyperalgesia and allodynia due to nerve injury or nerve inflammation can be analysed. Recently, it has become clear that inflammatory and immune mechanisms both in the periphery and the central nervous system play an important role in neuropathic pain. Infiltration of inflammatory cells, as well as activation of resident immune cells in response to nervous system damage, leads to subsequent production and secretion of various inflammatory mediators. These mediators promote neuroimmune activation and can sensitise primary afferent neurones and contribute to pain hypersensitivity. Inflammatory cells such as mast cells, neutrophils, macrophages and T lymphocytes have all been implicated, as have immune-like glial cells such as microglia and astrocytes. In addition, the immune response plays an important role in demyelinating neuropathies such as multiple sclerosis (MS), in which pain is a common symptom, and an animal model of MS-related pain has recently been demonstrated. Here, we will briefly review some of the milestones in research that have led to an increased awareness of the contribution of immune and inflammatory systems to neuropathic pain and then review in more detail the role of immune cells and inflammatory mediators.
Chronic neuropathic pain, resulting from damage to the central or peripheral nervous system, is a... more Chronic neuropathic pain, resulting from damage to the central or peripheral nervous system, is a prevalent and debilitating condition, affecting 7-18% of the population(1,2). Symptoms include spontaneous (tingling, burning, electric-shock like) pain, dysaesthesia, paraesthesia, allodynia (pain resulting from normally non-painful stimuli) and hyperalgesia (an increased response to painful stimuli). The sensory symptoms are co-morbid with behavioural disabilities, such as insomnia and depression. To study chronic neuropathic pain several animal models mimicking peripheral nerve injury have been developed, one of the most widely used is Bennett and Xie's (1988) unilateral sciatic nerve chronic constriction injury (CCI)(3) (Figure 1). Here we present a method for performing CCI and testing pain hypersensitivity. CCI is performed under anaesthesia, with the sciatic nerve on one side exposed by making a skin incision, and cutting through the connective tissue between the gluteus superficialis and biceps femoris muscles. Four chromic gut ligatures are tied loosely around the sciatic nerve at 1 mm intervals, to just occlude but not arrest epineural blood flow. The wound is closed with sutures in the muscle and staples in the skin. The animal is then allowed to recover from surgery for 24 hrs before pain hypersensitivity testing begins. For behavioural testing, rats are placed into the testing apparatus and are allowed to habituate to the testing procedure. The area tested is the mid-plantar surface of the hindpaw (Figure 2), which falls within the sciatic nerve distribution. Mechanical withdrawal threshold is assessed by mechanically stimulating both injured and uninjured hindpaws using an electronic dynamic plantar von Frey aesthesiometer or manual von Frey hairs(4). The mechanical withdrawal threshold is the maximum pressure exerted (in grams) that triggers paw withdrawal. For measurement of thermal withdrawal latency, first described by Hargreaves et al (1988), the hindpaw is exposed to a beam of radiant heat through a transparent glass surface using a plantar analgesia meter(5,6). The withdrawal latency to the heat stimulus is recorded as the time for paw withdrawal in both injured and uninjured hindpaws. Following CCI, mechanical withdrawal threshold, as well as thermal withdrawal latency in the injured paw are both significantly reduced, compared to baseline measurements and the uninjured paw (Figure 3). The CCI model of peripheral nerve injury combined with pain hypersensitivity testing provides a model system to investigate the effectiveness of potential therapeutic agents to modify chronic neuropathic pain. In our laboratory, we utilise CCI alongside thermal and mechanical sensitivity of the hindpaws to investigate the role of neuro-immune interactions in the pathogenesis and treatment of neuropathic pain.
Electrical neuromodulation is an established non-pharmacological treatment for chronic pain. Howe... more Electrical neuromodulation is an established non-pharmacological treatment for chronic pain. However, existing devices using pulsatile stimulation are not suitable for all types of chronic pain. Direct current stimulation is a recently developed technology which shows better selectivity for small-diameter fibres. We investigated if this selectivity could be applied to preferentially suppress nociceptive signalling. We applied direct current to the sciatic nerve of rats and compared its effects on spinal activity produced by physiological (non-electrical) stimuli delivered to the foot. Tests were performed across models of neuropathic and inflammatory pain to further clarify potential clinical applications. We found that direct current could effectively suppress activity relating to painful stimuli in both pain models tested. These findings strongly support the use of direct current neuromodulation for chronic pain relief, and suggest that it may be effective at treating a broader ra...
Recent years have yielded significant advances in our understanding of microglia, the immune cell... more Recent years have yielded significant advances in our understanding of microglia, the immune cells of the central nervous system (CNS). Microglia are key players in CNS development, immune surveillance, and the maintenance of proper neuronal function throughout life. In the healthy brain, homeostatic microglia have a unique molecular signature. In neurological diseases, microglia become activated and adopt distinct transcriptomic signatures, including disease-associated microglia (DAM) implicated in neurodegenerative disorders. Homeostatic microglia synthesise the endogenous cannabinoids 2-arachidonoylglycerol and anandamide and express the cannabinoid receptors CB1 and CB2 at constitutively low levels. Upon activation, microglia significantly increase their synthesis of endocannabinoids and upregulate their expression of CB2 receptors, which promote a protective microglial phenotype by enhancing their production of neuroprotective factors and reducing their production of pro-inflammatory factors. Here, we summarise the effects of the microglial cannabinoid system in the CNS demyelinating disease multiple sclerosis, the neurodegenerative diseases Alzheimer's disease, Parkinson's disease and amyotrophic lateral sclerosis, chronic inflammatory and neuropathic pain, and psychiatric disorders including depression, anxiety and schizophrenia. We discuss the therapeutic potential of cannabinoids in regulating microglial activity and highlight the need to further investigate their specific microglia-dependent immunomodulatory effects.
Regulatory T (Treg) cells are a special subpopulation of immunosuppressive T cells that are essen... more Regulatory T (Treg) cells are a special subpopulation of immunosuppressive T cells that are essential for sustaining immune homeostasis. They maintain self-tolerance, inhibit autoimmunity, and act as critical negative regulators of inflammation in various pathological states including autoimmunity, injury, and degeneration of the nervous system. Treg cells are known to convey both beneficial and detrimental influences in certain disease contexts, and accumulating research suggests that their action may be altered in a range of peripheral and central nervous system pathologies. In this review, we discuss emerging evidence for the dichotomous role of Treg cells in various neurological pathologies including multiple sclerosis, Guillain-Barré syndrome, neuropathic pain, traumatic central nervous system injury, stroke, and neurodegenerative diseases such as amyotrophic lateral sclerosis, Alzheimer's disease, and Parkinson's disease. We are in the early stages of uncovering the ro...
Sensory problems such as neuropathic pain are common and debilitating symptoms in multiple sclero... more Sensory problems such as neuropathic pain are common and debilitating symptoms in multiple sclerosis (MS), an autoimmune inflammatory disorder of the CNS. Regulatory T (Treg) cells are critical for maintaining immune homeostasis, but their role in MS-associated pain remains unknown. Here, we demonstrate that Treg cell ablation is sufficient to trigger experimental autoimmune encephalomyelitis (EAE) and facial allodynia in immunized female mice. In EAE-induced female mice, adoptive transfer of Treg cells and spinal delivery of the Treg cell cytokine interleukin-35 (IL-35) significantly reduced facial stimulus-evoked pain and spontaneous pain independent of disease severity and increased myelination of the facial nociceptive pathway. The effects of intrathecal IL-35 therapy were Treg-cell dependent and associated with upregulated IL-10 expression in CNS-infiltrating lymphocytes and reduced monocyte infiltration in the trigeminal afferent pathway. We present evidence for a beneficial r...
Background Genetic risk factors for chemotherapy-induced peripheral neuropathy (CIPN), a major do... more Background Genetic risk factors for chemotherapy-induced peripheral neuropathy (CIPN), a major dose-limiting side-effect of paclitaxel, are not well understood. Methods We performed a genome-wide association study (GWAS) in 183 paclitaxel-treated patients to identify genetic loci associated with CIPN assessed via comprehensive neuropathy phenotyping tools (patient-reported, clinical and neurological grading scales). Bioinformatic analyses including pathway enrichment and polygenic risk score analysis were used to identify mechanistic pathways of interest. Results In total, 77% of the cohort were classified with CIPN (n = 139), with moderate/severe neuropathy in 36%. GWAS was undertaken separately for the three measures of CIPN. GWAS of patient-reported CIPN identified 4 chromosomal regions that exceeded genome-wide significance (rs9846958, chromosome 3; rs117158921, chromosome 18; rs4560447, chromosome 4; rs200091415, chromosome 10). rs4560447 is located within a protein-coding gene...
Introduction/AimsClinically, the chemotherapeutic agent oxaliplatin can cause peripheral neuropat... more Introduction/AimsClinically, the chemotherapeutic agent oxaliplatin can cause peripheral neuropathy, impaired balance, and muscle wastage. Using a preclinical model, we investigated whether exercise intervention could improve these adverse conditions.MethodsMice were chronically treated with oxaliplatin alone or in conjunction with exercise. Behavioral studies, including mechanical allodynia, rotarod, open‐field, and grip‐strength tests, were performed. After euthanasia, multiple organs and four different muscle types were dissected and weighed. The cross‐sectional area (CSA) of muscle fibers in the gastrocnemius muscle was assessed and gene expression analysis performed on the forelimb triceps muscle.ResultsOxaliplatin‐treated mice displayed reduced weight gain, mechanical allodynia, and exploratory behavior deficits that were not significantly improved by exercise. Oxaliplatin‐treated exercised mice showed modest evidence of reduced muscle wastage compared with mice treated with o...
Peripheral nerve injuries caused by focal constriction are characterised by local nerve ischaemia... more Peripheral nerve injuries caused by focal constriction are characterised by local nerve ischaemia, axonal degeneration, demyelination, and neuroinflammation. The aim of this study was to understand temporal changes in the excitability properties of injured motor axons in a mouse model of nerve constriction injury (NCI). The excitability of motor axons following unilateral sciatic NCI was studied in male C57BL/6J mice distal to the site of injury at the acute (6 hours‐1 week) and chronic (up to 20 weeks) phases of injury, using threshold tracking. Multiple measures of nerve excitability, including strength‐duration properties, threshold electrotonus, current‐threshold relationship, and recovery cycle were examined using the automated nerve excitability protocol (TRONDNF). Acutely, injured motor axons developed a pattern of excitability characteristic of ischemic depolarisation. In most cases, the sciatic nerve became transiently inexcitable. When a liminal compound muscle action pote...
This chapter summarizes a standard approach to identifying neuropathic pain for the clinician. Fo... more This chapter summarizes a standard approach to identifying neuropathic pain for the clinician. For neuropathic pain, and for the condition of complex regional pain syndrome (CRPS) especially, the six Ss should be queried when obtaining details regarding the affected region. A useful tool to rapidly and accurately localize sources of chronic pain and assist in the diagnosis of causes of neuropathic pain is a pain diagram. The examination of a chronic pain patient should start with an appropriate and directed general examination including a neurological examination. Quantitative sensory testing (QST) provides indirect information used to evaluate underlying sensory function abnormalities using only small, portable tools and with less time requirement than protocols developed by the German Neuropathic Research Network. In the future, bedside QST is expected to continue to play a role in determining potential pain mechanisms to help direct further evaluation and treatment.
Tissue damage, inflammation or injury of the nervous system may result in chronic neuropathic pai... more Tissue damage, inflammation or injury of the nervous system may result in chronic neuropathic pain characterised by increased sensitivity to painful stimuli (hyperalgesia), the perception of innocuous stimuli as painful (allodynia) and spontaneous pain. Neuropathic pain has been described in about 1% of the US population, is often severely debilitating and largely resistant to treatment. Animal models of peripheral neuropathic pain are now available in which the mechanisms underlying hyperalgesia and allodynia due to nerve injury or nerve inflammation can be analysed. Recently, it has become clear that inflammatory and immune mechanisms both in the periphery and the central nervous system play an important role in neuropathic pain. Infiltration of inflammatory cells, as well as activation of resident immune cells in response to nervous system damage, leads to subsequent production and secretion of various inflammatory mediators. These mediators promote neuroimmune activation and can sensitise primary afferent neurones and contribute to pain hypersensitivity. Inflammatory cells such as mast cells, neutrophils, macrophages and T lymphocytes have all been implicated, as have immune-like glial cells such as microglia and astrocytes. In addition, the immune response plays an important role in demyelinating neuropathies such as multiple sclerosis (MS), in which pain is a common symptom, and an animal model of MS-related pain has recently been demonstrated. Here, we will briefly review some of the milestones in research that have led to an increased awareness of the contribution of immune and inflammatory systems to neuropathic pain and then review in more detail the role of immune cells and inflammatory mediators.
Chronic neuropathic pain, resulting from damage to the central or peripheral nervous system, is a... more Chronic neuropathic pain, resulting from damage to the central or peripheral nervous system, is a prevalent and debilitating condition, affecting 7-18% of the population(1,2). Symptoms include spontaneous (tingling, burning, electric-shock like) pain, dysaesthesia, paraesthesia, allodynia (pain resulting from normally non-painful stimuli) and hyperalgesia (an increased response to painful stimuli). The sensory symptoms are co-morbid with behavioural disabilities, such as insomnia and depression. To study chronic neuropathic pain several animal models mimicking peripheral nerve injury have been developed, one of the most widely used is Bennett and Xie's (1988) unilateral sciatic nerve chronic constriction injury (CCI)(3) (Figure 1). Here we present a method for performing CCI and testing pain hypersensitivity. CCI is performed under anaesthesia, with the sciatic nerve on one side exposed by making a skin incision, and cutting through the connective tissue between the gluteus superficialis and biceps femoris muscles. Four chromic gut ligatures are tied loosely around the sciatic nerve at 1 mm intervals, to just occlude but not arrest epineural blood flow. The wound is closed with sutures in the muscle and staples in the skin. The animal is then allowed to recover from surgery for 24 hrs before pain hypersensitivity testing begins. For behavioural testing, rats are placed into the testing apparatus and are allowed to habituate to the testing procedure. The area tested is the mid-plantar surface of the hindpaw (Figure 2), which falls within the sciatic nerve distribution. Mechanical withdrawal threshold is assessed by mechanically stimulating both injured and uninjured hindpaws using an electronic dynamic plantar von Frey aesthesiometer or manual von Frey hairs(4). The mechanical withdrawal threshold is the maximum pressure exerted (in grams) that triggers paw withdrawal. For measurement of thermal withdrawal latency, first described by Hargreaves et al (1988), the hindpaw is exposed to a beam of radiant heat through a transparent glass surface using a plantar analgesia meter(5,6). The withdrawal latency to the heat stimulus is recorded as the time for paw withdrawal in both injured and uninjured hindpaws. Following CCI, mechanical withdrawal threshold, as well as thermal withdrawal latency in the injured paw are both significantly reduced, compared to baseline measurements and the uninjured paw (Figure 3). The CCI model of peripheral nerve injury combined with pain hypersensitivity testing provides a model system to investigate the effectiveness of potential therapeutic agents to modify chronic neuropathic pain. In our laboratory, we utilise CCI alongside thermal and mechanical sensitivity of the hindpaws to investigate the role of neuro-immune interactions in the pathogenesis and treatment of neuropathic pain.
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Papers by Gila Moalem-Taylor