Establishment Of Chronic Pain Research Articles

Electroacupuncture prevents the development or establishment of chronic pain via IL-33/ST2 signaling in hyperalgesic priming model rats

BackgroundChronic pain is acomplexhealth issue. Compared to acute pain, which has a protective value, chronic pain is defined as persistent pain after tissue injury. Few clinical advances have been made to prevent the transition from acute to chronic pain. Electroacupuncture (EA), the most common form of acupuncture, is widely used in clinical practice to relieve pain. MethodsThe hyperalgesic priming model, established via a carrageenan injection followed by a prostaglandin E2 injection, was used to investigate the development or establishment of chronic pain. We observed the hyperalgesic effect of EA on rats and investigated the expression p38 mitogen-activated protein kinase, interleukin-33 (IL-33), and its receptor ST2 in astrocytes in the L4–L6 spinal cord dorsal horns (SDHs) after EA. The IL-33/ST2 signaling pathway in SDH is associated with the development of chronic pain. ResultsEA can reverse the pain threshold in hyperalgesic priming model rats and regulates the expression of phosphorylated p38, IL-33, and ST2 in astrocytes in the L4–L6 SDHs. We discovered that EA raises the pain threshold. This suggests that EA can prevent the development or establishment of chronic pain by inhibiting IL-33/ST2 signaling in the lower central nervous system. ConclusionsEA can alleviate the development or establishment of chronic pain by modulating IL-33/ST2 signaling in SDHs. Our findings will help clinicians understand the mechanisms of EA analgesia.

Analgesic Alkaloids Derived From Traditional Chinese Medicine in Pain Management.

Chronic pain is one of the most prevalent health problems. The establishment of chronic pain is complex. Current medication for chronic pain mainly dependent on anticonvulsants, tricyclic antidepressants and opioidergic drugs. However, they have limited therapeutic efficacy, and some even with severe side effects. We turned our interest into alkaloids separated from traditional Chinese medicine (TCM), that usually act on multiple drug targets. In this article, we introduced the best-studied analgesic alkaloids derived from TCM, including tetrahydropalmatine, aloperine, oxysophocarpine, matrine, sinomenine, ligustrazine, evodiamine, brucine, tetrandrine, Stopholidine, and lappaconitine, focusing on their mechanisms and potential clinical applications. To better describe the mechanism of these alkaloids, we adopted the concept of drug-cloud (dCloud) theory. dCloud illustrated the full therapeutic spectrum of multitarget analgesics with two dimensions, which are “direct efficacy”, including inhibition of ion channels, activating γ-Aminobutyric Acid/opioid receptors, to suppress pain signal directly; and “background efficacy”, including reducing neuronal inflammation/oxidative stress, inhibition of glial cell activation, restoring the balance between excitatory and inhibitory neurotransmission, to cure the root causes of chronic pain. Empirical evidence showed drug combination is beneficial to 30–50% chronic pain patients. To promote the discovery of effective analgesic combinations, we introduced an ancient Chinese therapeutic regimen that combines herbal drugs with “Jun”, “Chen”, “Zuo”, and “Shi” properties. In dCloud, “Jun” drug acts directly on the major symptom of the disease; “Chen” drug generates major background effects; “Zuo” drug has salutary and supportive functions; and “Shi” drug facilitates drug delivery to the targeted tissue. Subsequently, using this concept, we interpreted the therapeutic effect of established analgesic compositions containing TCM derived analgesic alkaloids, which may contribute to the establishment of an alternative drug discovery model.

Sympathetic Responses to Noxious Stimulation of Muscle and Skin.

Acute pain triggers adaptive physiological responses that serve as protective mechanisms that prevent continuing damage to tissues and cause the individual to react to remove or escape the painful stimulus. However, an extension of the pain response beyond signaling tissue damage and healing, such as in chronic pain states, serves no particular biological function; it is maladaptive. The increasing number of chronic pain sufferers is concerning, and the associated disease burden is putting healthcare systems around the world under significant pressure. The incapacitating effects of long-lasting pain are not just psychological – reflexes driven by nociceptors during the establishment of chronic pain may cause serious physiological consequences on regulation of other body systems. The sympathetic nervous system is inherently involved in a host of physiological responses evoked by noxious stimulation. Experimental animal and human models demonstrate a diverse array of heterogeneous reactions to nociception. The purpose of this review is to understand how pain affects the sympathetic nervous system by investigating the reflex cardiovascular and neural responses to acute pain and the long-lasting physiological responses to prolonged (tonic) pain. By observing the sympathetic responses to long-lasting pain, we can begin to understand the physiological consequences of long-term pain on cardiovascular regulation.

Modulation of Chronic Pain by Metabotropic Glutamate Receptors.

Metabotropic glutamate receptors (mGluRs) belong to class C G-protein-coupled receptors. They are expressed throughout the nervous system on both neurons and glial cells. In the central nervous system (CNS), mGluRs are mainly located in the proximity of the synaptic cleft where they regulate glutamatergic transmission in addition to a number of other neurotransmitters. To date, eight subtypes of mGluRs (mGluR1-mGluR8) have been cloned and classified into three groups on the basis of sequence similarities, and pharmacological and biochemical properties. Consequently, group I mGluRs includes mGluR1 and mGluR5, group II mGluRs includes mGluR2 and mGluR3, and group III mGluRs consists of mGluR4, mGluR6, mGluR7, and mGluR8. With the exception of mGluR6, whose localization is restricted within the retina, all mGluRs are ubiquitously expressed throughout the peripheral and CNS with some subtype specificity in different anatomical regions. mGluRs participate in many physiological processes and play important roles in a number of neurological conditions including anxiety, depression, schizophrenia, and neurodegenerative disorders. mGluRs also participate in the physiological transmission of pain stimuli as well as to mechanisms involved in the establishment of chronic pain. Therefore, these receptors are attractive targets for therapeutic intervention in several neurological disorders including chronic pain. Thus, understanding the physiological function and role of each mGluR subtype in the development of chronic pain will provide a better insight into the potential use of subtype-selective drugs currently being developed as orthosteric or allosteric ligands.

Alleviation of chronic neuropathic pain by environmental enrichment in mice well after the establishment of chronic pain

BackgroundIn animal models, the impact of social and environmental manipulations on chronic pain have been investigated in short term studies where enrichment was implemented prior to or concurrently with the injury. The focus of this study was to evaluate the impact of environmental enrichment or impoverishment in mice three months after induction of chronic neuropathic pain.MethodsThirty-four CD-1 seven to eight week-old male mice were used. Mice underwent surgery on the left leg under isoflurane anesthesia to induce the spared nerve injury model of neuropathic pain or sham condition. Mice were then randomly assigned to one of four groups: nerve injury with enriched environment (n = 9), nerve injury with impoverished environment (n = 8), sham surgery with enriched environment (n = 9), or sham surgery with impoverished environment (n = 8). The effects of environmental manipulations on mechanical (von Frey filaments) heat (hot plate) and cold (acetone test) cutaneous hypersensitivities, motor impairment (Rotarod), spontaneous exploratory behavior (open field test), anxiety-like behavior (elevated plus maze) and depression-like phenotype (tail suspension test) were assessed in neuropathic and control mice 1 and 2 months post-environmental change. Finally, the effect of the environment on spinal expression of the pro-nociceptive neuropeptides substance P and CGRP form the lumbar spinal cord collected at the end of the study was evaluated by tandem liquid chromatography mass spectrometry.ResultsEnvironmental enrichment attenuated nerve injury-induced hypersensitivity to mechanical and cold stimuli. In contrast, an impoverished environment exacerbated mechanical hypersensitivity. No antidepressant effects of enrichment were observed in animals with chronic neuropathic pain. Finally, environmental enrichment resulted lower SP and CGRP concentrations in neuropathic animals compared to impoverishment. These effects were all observed in animals that had been neuropathic for several months prior to intervention.ConclusionsThese results suggest that environmental factors could play an important role in the rehabilitation of chronic pain patients well after the establishment of chronic pain. Enrichment is a potentially inexpensive, safe and easily implemented non-pharmacological intervention for the treatment of chronic pain.

Increased Responsiveness of Peripheral Blood Mononuclear Cells to In Vitro TLR 2, 4 and 7 Ligand Stimulation in Chronic Pain Patients

Glial activation via Toll-like receptor (TLR) signaling has been shown in animals to play an important role in the initiation and establishment of chronic pain. However, our ability to assess this central immune reactivity in clinical pain populations is currently lacking. Peripheral blood mononuclear cells (PBMCs) are an accessible source of TLR expressing cells that may mirror similarities in TLR responsiveness of the central nervous system. The aim of this study was to characterize the IL-1β response to various TLR agonists in isolated PBMCs from chronic pain sufferers (on and not on opioids) and pain-free controls. Venous blood was collected from 11 chronic pain sufferers on opioids (≥ 20 mg of morphine / day), 8 chronic pain sufferers not on opioids and 11 pain-free controls. PBMCs were isolated and stimulated in vitro with a TLR2 (Pam3CSK4), TLR4 (LPS) or TLR7 (imiquimod) agonist. IL-1β released into the supernatant was measured with ELISA. Significantly increased IL-1β expression was found in PBMCs from chronic pain sufferers (on and not on opioids) compared with pain-free controls for TLR2 (F (6, 277) = 15, P<0.0001), TLR4 (F (8, 263) = 3, P = 0.002) and TLR7 (F (2,201) = 5, P = 0.005) agonists. These data demonstrate that PBMCs from chronic pain sufferers were more responsive to TLR agonists compared with controls, suggesting peripheral cells may have the potential to become a source of biomarkers for chronic pain.

Algorithm for diagnosis and therapy of pain

Certain basic principles are applicable to all forms of pain treatment when the aims are pain relief and the avoidance of chronicety. Such algorithms, as guidelines are even more important when pain is becoming chronic. The use of the described algorithms is necessary in the diagnosis and therapy of acute pain and also to avoid the establishment of chronic pain due to the changes of neuroplasticity in the central nervous system. The most important basic principles in the form of algorithms are first of all that therapies should be simultaneously applied and not sequentially. Secondly, the challenge should be met to create a concept where by various therapies can be preformed in a parallel fashion, without compete one another and being effective on different aspects and causes of the pain.

Neuroimaging of chronic pain: phantom limb and musculoskeletal pain.

New developments in brain imaging lead to a better understanding of cortical and subcortical processes involved in pain perception and the establishment of chronic pain. For different forms of chronic pain long-term changes in cortical structures have been described. In patients with phantom limb pain and back pain alterations in the somatotopic organization of the primary somatosensory (SI) could be observed. The amount of this reorganization is correlated with the subjective pain rating. These changes, which are based on processes of neuronal plasticity, can partially be reversed by analgesic interventions. For the investigation of cortical processes concerning reorganization, EEG and MEG methods are most suitable because of their high temporal and spatial resolution. In conclusion, these findings open a new way for therapeutic interventions to prevent the development of chronic pain.

Neuroimaging of chronic pain: phantom limb and musculoskeletal pain

New developments in brain imaging lead to a better understanding of cortical and subcortical processes involved in pain perception and the establishment of chronic pain. For different forms of chronic pain long-term changes in cortical structures have been described. In patients with phantom limb pain and back pain alterations in the somatotopic organization of the primary somatosensory (SI) could be observed. The amount of this reorganization is correlated with the subjective pain rating. These changes, which are based on processes of neuronal plasticity, can partially be reversed by analgesic interventions. For the investigation of cortical processes concerning reorganization, EEG and MEG methods are most suitable because of their high temporal and spatial resolution. In conclusion, these findings open a new way for therapeutic interventions to prevent the development of chronic pain.