RESUMO
Opioid analgesics remain the mainstay for managing intractable chronic pain, but their use is limited by detrimental side effects such as analgesic tolerance and hyperalgesia. Calcium-dependent synaptic plasticity is a key determinant in opiates tolerance and hyperalgesia. However, the exact substrates for this calcium-dependent synaptic plasticity in mediating these maladaptive processes are largely unknown. Canonical transient receptor potential 1, 4, and 5 (TRPC1, 4, 5) proteins assemble into heteromultimeric nonselective cation channels with high Ca2+ permeability and influence various neuronal functions. However, whether and how TRPC1/4/5 channels contribute to the development of opiates tolerance and hyperalgesia remains elusive. Here, we show that TRPC1/4/5 channels contribute to the generation of morphine tolerance and hyperalgesia. Chronic morphine exposure leads to upregulation of TRPC1/4/5 channels in the spinal cord. Spinally expressed TRPC1, TPRC4, and TRPC5 are required for chronic morphine-induced synaptic long-term potentiation (LTP) as well as remodeling of synaptic spines in the dorsal horn, thereby orchestrating functional and structural plasticity during the course of morphine-induced hyperalgesia and tolerance. These effects are attributed to TRPC1/4/5-mediated Ca2+ elevation in the spinal dorsal horn induced by chronic morphine treatment. This study identifies TRPC1/4/5 channels as a promising novel target to prevent the unwanted morphine tolerance and hyperalgesia.
Assuntos
Hiperalgesia/induzido quimicamente , Hiperalgesia/metabolismo , Morfina/farmacologia , Plasticidade Neuronal/fisiologia , Medula Espinal/metabolismo , Canais de Cátion TRPC/metabolismo , Analgésicos/farmacologia , Analgésicos Opioides/farmacologia , Animais , Tolerância a Medicamentos/fisiologia , Masculino , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Knockout , Plasticidade Neuronal/efeitos dos fármacos , Neurônios/efeitos dos fármacos , Neurônios/metabolismo , Medula Espinal/efeitos dos fármacos , Corno Dorsal da Medula Espinal/efeitos dos fármacos , Corno Dorsal da Medula Espinal/metabolismoRESUMO
Chronic pathological pain is one of the most intractable clinical problems faced by clinicians and can be devastating for patients. Despite much progress we have made in understanding chronic pain in the last decades, its underlying mechanisms remain elusive. It is assumed that abnormal increase of calcium levels in the cells is a key determinant in the transition from acute to chronic pain. Exploring molecular players mediating Ca2+ entry into cells and molecular mechanisms underlying activity-dependent changes in Ca2+ signaling in the somatosensory pain pathway is therefore helpful towards understanding the development of chronic, pathological pain. Canonical transient receptor potential (TRPC) channels form a subfamily of nonselective cation channels, which permit the permeability of Ca2+ and Na+ into the cells. Initiation of Ca2+ entry pathways by these channels triggers the development of many physiological and pathological functions. In this review, we will focus on the functional implication of TRPC channels in nociception with the elucidation of their role in the detection of external stimuli and nociceptive hypersensitivity.
Assuntos
Neurônios/fisiologia , Nociceptividade/fisiologia , Dor/fisiopatologia , Canais de Potencial de Receptor Transitório/fisiologia , Animais , Encéfalo/fisiopatologia , Sinalização do Cálcio , Gânglios Espinais/fisiopatologia , Humanos , Vias Neurais/fisiopatologiaRESUMO
Previous studies have shown that the C-C motif chemokine ligand 2 (CCL2) is widely expressed in the nervous system and involved in regulating the development of chronic pain and related anxiety-like behaviors, but its precise mechanism is still unclear. This paper provides an in-depth examination of the involvement of CCL2-CCR2 signaling in the anterior cingulate cortex (ACC) in intraplantar injection of complete Freund's adjuvant (CFA) leading to inflammatory pain and its concomitant anxiety-like behaviors by modulation of glutamatergic N-methyl-D-aspartate receptor (NMDAR). Our findings suggest that local bilateral injection of CCR2 antagonist in the ACC inhibits CFA-induced inflammatory pain and anxiety-like behavior. Meanwhile, the expression of CCR2 and CCL2 was significantly increased in ACC after 14 days of intraplantar injection of CFA, and CCR2 was mainly expressed in excitatory neurons. Whole-cell patch-clamp recordings showed that the CCR2 inhibitor RS504393 reduced the frequency of miniature excitatory postsynaptic currents (mEPSC) in ACC, and CCL2 was involved in the regulation of NMDAR-induced current in ACC neurons in the pathological state. In addition, local injection of the NR2B inhibitor of NMDAR subunits, Ro 25-6981, attenuated the effects of CCL2-induced hyperalgesia and anxiety-like behavior in the ACC. In summary, CCL2 acts on CCR2 in ACC excitatory neurons and participates in the regulation of CFA-induced pain and related anxiety-like behaviors through upregulation of NR2B. CCR2 in the ACC neuron may be a potential target for the treatment of chronic inflammatory pain and pain-related anxiety.
Assuntos
Ansiedade , Quimiocina CCL2 , Giro do Cíngulo , Inflamação , N-Metilaspartato , Dor , Receptores CCR2 , Receptores de N-Metil-D-Aspartato , Transdução de Sinais , Animais , Giro do Cíngulo/metabolismo , Giro do Cíngulo/efeitos dos fármacos , Inflamação/patologia , Inflamação/metabolismo , Masculino , Ansiedade/metabolismo , Receptores de N-Metil-D-Aspartato/metabolismo , Quimiocina CCL2/metabolismo , Receptores CCR2/metabolismo , Receptores CCR2/antagonistas & inibidores , Dor/metabolismo , Dor/patologia , Transdução de Sinais/efeitos dos fármacos , Potenciais Pós-Sinápticos Excitadores/efeitos dos fármacos , Adjuvante de Freund/toxicidade , Camundongos Endogâmicos C57BL , Neurônios/metabolismo , Neurônios/efeitos dos fármacos , Comportamento Animal , Hiperalgesia/metabolismo , Hiperalgesia/patologia , Compostos de Espiro , BenzoxazinasRESUMO
Postsynaptic NMDARs at spinal synapses are required for postsynaptic long-term potentiation and chronic pain. However, how presynaptic NMDARs (PreNMDARs) in spinal nociceptor terminals control presynaptic plasticity and pain hypersensitivity has remained unclear. Here we report that PreNMDARs in spinal nociceptor terminals modulate synaptic transmission in a nociceptive tone-dependent manner. PreNMDARs depresses presynaptic transmission in basal state, while paradoxically causing presynaptic potentiation upon injury. This state-dependent modulation is dependent on Ca2+ influx via PreNMDARs. Small conductance Ca2+-activated K+ (SK) channels are responsible for PreNMDARs-mediated synaptic depression. Rather, tissue inflammation induces PreNMDARs-PKG-I-dependent BDNF secretion from spinal nociceptor terminals, leading to SK channels downregulation, which in turn converts presynaptic depression to potentiation. Our findings shed light on the state-dependent characteristics of PreNMDARs in spinal nociceptor terminals on modulating nociceptive transmission and revealed a mechanism underlying state-dependent transition. Moreover, we identify PreNMDARs in spinal nociceptor terminals as key constituents of activity-dependent pain sensitization.
Assuntos
Dor Crônica/fisiopatologia , Nociceptores/metabolismo , Terminações Pré-Sinápticas/metabolismo , Receptores de N-Metil-D-Aspartato/metabolismo , Animais , Fator Neurotrófico Derivado do Encéfalo/genética , Fator Neurotrófico Derivado do Encéfalo/metabolismo , Cálcio/metabolismo , Dor Crônica/genética , Dor Crônica/metabolismo , Proteína Quinase Dependente de GMP Cíclico Tipo I/genética , Proteína Quinase Dependente de GMP Cíclico Tipo I/metabolismo , Gânglios Espinais/citologia , Gânglios Espinais/fisiologia , Inflamação , Potenciação de Longa Duração , Depressão Sináptica de Longo Prazo , Camundongos , Camundongos Transgênicos , Substância Cinzenta Periaquedutal/citologia , Substância Cinzenta Periaquedutal/fisiologia , Canais de Potássio Cálcio-Ativados/genética , Canais de Potássio Cálcio-Ativados/metabolismo , Receptores de N-Metil-D-Aspartato/genética , Transmissão SinápticaRESUMO
Patients with neuropathic pain often experience exaggerated pain and anxiety. Central sensitization has been linked with the maintenance of neuropathic pain and may become an autonomous pain generator. Conversely, emerging evidence accumulated that central sensitization is initiated and maintained by ongoing nociceptive primary afferent inputs. However, it remains elusive what mechanisms underlie this phenomenon and which peripheral candidate contributes to central sensitization that accounts for pain hypersensitivity and pain-related anxiety. Previous studies have implicated peripherally localized cGMP-dependent protein kinase I (PKG-I) in plasticity of nociceptors and spinal synaptic transmission as well as inflammatory hyperalgesia. However, whether peripheral PKG-I contributes to cortical plasticity and hence maintains nerve injury-induced pain hypersensitivity and anxiety is unknown. Here, we demonstrated significant upregulation of PKG-I in ipsilateral L3 dorsal root ganglia (DRG), no change in L4 DRG, and downregulation in L5 DRG upon spared nerve injury. Genetic ablation of PKG-I specifically in nociceptors or post-treatment with intervertebral foramen injection of PKG-I antagonist, KT5823, attenuated the development and maintenance of spared nerve injury-induced bilateral pain hypersensitivity and anxiety. Mechanistic analysis revealed that activation of PKG-I in nociceptors is responsible for synaptic potentiation in the anterior cingulate cortex upon peripheral neuropathy through presynaptic mechanisms involving brain-derived neurotropic factor signaling. Our results revealed that PKG-I expressed in nociceptors is a key determinant for cingulate synaptic plasticity after nerve injury, which contributes to the maintenance of pain hypersensitivity and anxiety. Thereby, this study presents a strong basis for opening up a novel therapeutic target, PKG-I, in nociceptors for treatment of comorbidity of neuropathic pain and anxiety with least side effects.
Assuntos
Proteína Quinase Dependente de GMP Cíclico Tipo I , Neuralgia , Sensibilização do Sistema Nervoso Central , Gânglios Espinais , Humanos , Hiperalgesia/etiologia , Neuralgia/etiologia , NociceptoresRESUMO
Patients with neuropathic pain often experience comorbid psychiatric disorders. Cellular plasticity in the anterior cingulate cortex (ACC) is assumed to be a critical interface for pain perception and emotion. However, substantial efforts have thus far been focused on the intracellular mechanisms of plasticity rather than the extracellular alterations that might trigger and facilitate intracellular changes. Laminin, a key element of the extracellular matrix (ECM), consists of one α-, one ß-, and one γ-chain and is implicated in several pathophysiological processes. Here, we showed in mice that laminin ß1 (LAMB1) in the ACC was significantly downregulated upon peripheral neuropathy. Knockdown of LAMB1 in the ACC exacerbated pain sensitivity and induced anxiety and depression. Mechanistic analysis revealed that loss of LAMB1 caused actin dysregulation via interaction with integrin ß1 and the subsequent Src-dependent RhoA/LIMK/cofilin pathway, leading to increased presynaptic transmitter release probability and abnormal postsynaptic spine remodeling, which in turn orchestrated the structural and functional plasticity of pyramidal neurons and eventually resulted in pain hypersensitivity and anxiodepression. This study sheds new light on the functional capability of ECM LAMB1 in modulating pain plasticity and identifies a mechanism that conveys extracellular alterations to intracellular plasticity. Moreover, we identified cingulate LAMB1/integrin ß1 signaling as a promising therapeutic target for the treatment of neuropathic pain and associated anxiodepression.
Assuntos
Ansiedade/metabolismo , Comportamento Animal , Depressão/metabolismo , Laminina/metabolismo , Neuralgia/metabolismo , Doenças do Sistema Nervoso Periférico/metabolismo , Animais , Ansiedade/genética , Depressão/genética , Feminino , Técnicas de Silenciamento de Genes , Giro do Cíngulo/metabolismo , Laminina/genética , Camundongos , Neuralgia/genética , Doenças do Sistema Nervoso Periférico/genéticaRESUMO
Tweety-homolog 1 (Ttyh1) is expressed in neural tissue and has been implicated in the generation of several brain diseases. However, its functional significance in pain processing is not understood. By disrupting the gene encoding Ttyh1, we found a loss of Ttyh1 in nociceptors and their central terminals in Ttyh1-deficient mice, along with a reduction in nociceptor excitability and synaptic transmission at identified synapses between nociceptors and spinal neurons projecting to the periaqueductal grey (PAG) in the basal state. More importantly, the peripheral inflammation-evoked nociceptor hyperexcitability and spinal synaptic potentiation recorded in spinal-PAG projection neurons were compromised in Ttyh1-deficient mice. Analysis of the paired-pulse ratio and miniature excitatory postsynaptic currents indicated a role of presynaptic Ttyh1 from spinal nociceptor terminals in the regulation of neurotransmitter release. Interfering with Ttyh1 specifically in nociceptors produces a comparable pain relief. Thus, in this study we demonstrated that Ttyh1 is a critical determinant of acute nociception and pain sensitization caused by peripheral inflammation.
Assuntos
Nociceptores , Transmissão Sináptica , Animais , Proteínas de Membrana/metabolismo , Camundongos , Neurônios/metabolismo , Dor , Substância Cinzenta PeriaquedutalRESUMO
Brachial plexus avulsion (BPA) represents the most devastating nerve injury in the upper extremity and is always considered as a sophisticated problem due to its resistance to most standard pain relief medications or neurosurgical interventions. There is also a lack of understanding on the underlying mechanisms. Our study aimed to investigate whether spinal CCL2-CCR2 signaling contributed to the development of neuropathic pain following BPA via modulating glutamate N-methyl-d-aspartate receptor (NMDAR). A rat model of BPA on lower trunk (C8-T1) was established, and the sham- and BPA-operated animals were intrathecally injected with saline, C-C chemokine receptor type 2 (CCR2) inhibitor INCB3344 and NMDAR antagonist DL-AP5 one week postoperatively, the behavioral performance of the treated animals and expressions of C-C motif ligand 2 (CCL2), CCR2, and N-methyl-D-aspartic acid receptor 2B (NR2B) in spinal cord sections of each group were examined. It was shown that BPA injury significantly reduced mechanic withdrawal thresholds the next day after surgery until the end of the observation. Both CCL2 and CCR2 expressions increased in BPA rats compared to those in sham rats. CCL2 was mainly localized in astrocytes, and CCR2 was preferably expressed on astrocytes and neurons. Besides, NMDAR subunit NR2B increased in BPA-operated rats, which was reversed in response to CCR2 and NR2B inhibition. However, these inhibitors didn't change the spinal NMDAR level in sham rats. CCR2 and NMDAR inhibition efficiently alleviated mechanical allodynia caused by BPA either at early or late phase of neuropathic pain. Collectively, CCL2-CCR2 axis is associated with mechanical pain after BPA by elevating NMDAR signaling.
Assuntos
Plexo Braquial/metabolismo , Quimiocina CCL2/metabolismo , Neuralgia/metabolismo , Receptores CCR2/metabolismo , Receptores de N-Metil-D-Aspartato/metabolismo , Animais , Astrócitos/metabolismo , Plexo Braquial/lesões , Modelos Animais de Doenças , Feminino , Hiperalgesia/metabolismo , Hiperalgesia/fisiopatologia , Neuralgia/fisiopatologia , Neurônios/metabolismo , Medição da Dor/métodos , Ratos Sprague-Dawley , Medula Espinal/metabolismo , Medula Espinal/fisiopatologiaRESUMO
Previous studies have shown that CCL2 (C-C motif chemokine ligand 2) induces chronic pain, but the exact mechanisms are still unknown. Here, we established models to explore the potential mechanisms. Behavioral experiments revealed that an antagonist of extracellular signal-regulated kinase (ERK) inhibited not only CCL2-induced inflammatory pain, but also pain responses induced by complete Freund's adjuvant. We posed the question of the intracellular signaling cascade involved. Subsequent experiments showed that CCL2 up-regulated the expression of phosphorylated ERK (pERK) and N-methyl D-aspartate receptor [NMDAR] subtype 2B (GluN2B); meanwhile, antagonists of CCR2 and ERK effectively reversed these phenomena. Whole-cell patch-clamp recordings revealed that CCL2 enhanced the NMDAR-induced currents via activating the pERK pathway, which was blocked by antagonists of GluN2B and ERK. In summary, we demonstrate that CCL2 directly interacts with CCR2 to enhance NMDAR-induced currents, eventually leading to inflammatory pain mainly through the CCL2-CCR2-pERK-GluN2B pathway.
Assuntos
Quimiocina CCL2/metabolismo , MAP Quinases Reguladas por Sinal Extracelular/metabolismo , N-Metilaspartato , Dor , Receptores de N-Metil-D-Aspartato/metabolismo , Substância Gelatinosa/fisiologia , Animais , Quimiocina CCL2/antagonistas & inibidores , MAP Quinases Reguladas por Sinal Extracelular/antagonistas & inibidores , Masculino , Camundongos , Camundongos Endogâmicos C57BL , N-Metilaspartato/metabolismo , Neurônios , Transdução de SinaisRESUMO
Previous studies have shown that CCL2 may cause chronic pain, but the exact mechanism of central sensitization is unclear. In this article, we further explore the presynaptic role of CCL2. Behavioral experiments show that intervertebral foramen injection CCR2 antagonists into dorsal root ganglion (DRG) can inhibit the inflammatory pain caused by CCL2 in spinal cord. We raised the question of the role of presynaptic CCR2 in the spinal dorsal horn. Subsequent electron microscopy experiments showed that CCR2 was expressed in the presynaptic CGRP terminal in the spinal dorsal horn. CCL2 can enhance presynaptic calcium signal. Whole-cell patch-clamp recordings showed that CCL2 can enhance NMDAR-eEPSCs through presynaptic effects, and further application of glutamate sensor method proved that CCL2 can act on presynaptic CCR2 to increase the release of presynaptic glutamate. In conclusion, we suggest that CCL2 can directly act on the CCR2 on presynaptic terminals of sensory neurons in the spinal dorsal horn, leading to an increase in the release of presynaptic glutamate and participate in the formation of central sensitization.