Activation of extracellular signal-regulated kinase in the anterior cingulate cortex contributes to the induction and expression of affective pain

Targeting the insular cortex for neuropathic pain modulation: Insights into synaptic and neuronal mechanisms

Neuropathic pain, caused by nerve damage, greatly affects quality of life. Recent research proposes modulating brain activity, particularly through electrical stimulation of the insular cortex (IC), as a treatment option. This study aimed to understand how IC stimulation (ICS) affects pain modulation. In a rat neuropathy model, researchers used optogenetic and ICS techniques to evaluate changes in mechanical allodynia and synaptic changes, focusing on glutamate receptors (AMPAR, NR2A, NR2B). Optogenetic inhibition of IC neurons relieved pain without altering synaptic plasticity. However, repetitive ICS combined with optogenetic activation diminished the pain-relieving effects of ICS and increased AMPAR and NR2B receptor levels. Additionally, activating inhibitory neurons also reduced pain, while repetitive activation of excitatory neurons lessened the effectiveness of ICS and was associated with heightened receptor expression. These findings suggest that inhibiting excitatory neurons or activating inhibitory neurons in the IC could help modulate pain in neuropathic conditions, shedding light on how ICS can influence pain management through changes in synaptic plasticity.

Glutamate transporter activator LDN-212320 prevents chronic pain-induced cognitive impairment and anxiety-like behaviors in a mouse model

The astroglial glutamate transporter in the hippocampus and anterior cingulate cortex (ACC) is critically involved in chronic pain-induced cognitive and psychiatric abnormalities. We have previously reported that LDN-212320, a glutamate transporter-1 (GLT-1) activator, attenuates complete Freund's adjuvant (CFA)-induced acute and chronic nociceptive pain. However, the cellular and molecular mechanisms underlying GLT-1 modulation in the hippocampus and ACC during chronic pain-induced cognitive deficit-like and anxiety-like behaviors remain unknown. Here, we have investigated the effects of LDN-212320 on CFA-induced chronic pain associated with cognitive deficit-like and anxiety-like behaviors in mice. We have evaluated the effects of LDN-212320 on CFA-induced impaired spatial, working, and recognition memory using Y-maze and object-place recognition tests. In addition, we have determined the effects of LDN-21230 on chronic pain-induced anxiety-like behaviors using elevated plus maze and marble burying test. We have also examined the effects of LDN-212320 on cAMP response element-binding protein (pCREB), brain-derived neurotrophic factor (BDNF), protein kinase A (PKA), and Ca2 +/calmodulin-dependent protein kinase II (CaMKII) expression in the hippocampus and ACC during CFA-induced cognitive deficit-like and anxiety-like behaviors using the Western blot analysis and immunofluorescence assay. Pretreatment with LDN-212320 (20 mg/kg) significantly attenuated CFA-induced impaired spatial, working, and recognition memory. Furthermore, LDN-212320 (20 mg/kg) significantly reduced CFA-induced anxiety-like behaviors. Additionally, LDN-212320 (20 mg/kg) significantly reversed CFA-induced decreased pCREB, BDNF, PKA and CaMKII expression in the hippocampus and ACC. Overall, these results suggest that the LDN-212320 prevents CFA-induced cognitive deficit-like and anxiety-like behaviors by activating CaMKII/CREB/BDNF signaling pathway in the hippocampus and ACC. Therefore, LDN-212320 could be a potential treatment for chronic pain associated with cognitive impairment and anxiety-like behaviors.

Berberine alleviates chronic pain-induced anxiety-like behaviors by inhibiting the activation of VLT-projecting cACC (Cg2) neurons

Chronic pain is often accompanied by anxiety, and gradually increasing anxiety makes the pain itself more protracted. Berberine has been found to be able to cross the blood-brain barrier to treat psychiatric disorders, but its neurocirculatory mechanisms remain unclear. Here, we found that neurons in cingulate area 2 (Cg2) of the caudal anterior cingulate cortex (cACC), but not in Cg1 of the cACC, projected to the ventral lateral thalamus (VLT). Next, we induced chronic inflammatory pain by plantar injection of complete Freund's adjuvant (CFA) and observed stable anxiety-like behaviors until two weeks postinjection. We specifically activated VLT-projecting cACC (Cg2) neurons in one-week-old CFA-induced mice without anxiety-like behaviors and in normal control mice to induce anxiety-like behaviors. We inhibited the activation of VLT-projecting cACC (Cg2) neurons in two-week-old CFA-treated mice with anxiety-like behaviors and observed that their anxiety-like behaviors were alleviated. On this basis, we further screened the effective dose of berberine for anxiolysis in two-week-old CFA-treated mice. We observed that the effective dose of berberine obtained above decreased the activity of VLT-projecting cACC (Cg2) neurons. The activation of VLT-projecting cACC (Cg2) neurons abrogated the anxiolytic effect of berberine in two-week-old CFA-treated mice.

Overactive PKA signaling underlies the hyperalgesia in an ADHD mouse model

There is an intimate relationship between pain hypersensitivity and attention deficit hyperactivity disorder (ADHD); however, the underlying mechanisms are still elusive. Individuals carrying the mutation in CRY1 (c. 1657 + 3A > C), which leads to deletion of exon 11 expression in the CRY1 protein (CRY1Δ11), exhibit ADHD symptoms. Here, we demonstrate that the responses to thermal and mechanical stimuli were amplified in the Cry1Δ11 mice. RNA-sequencing analysis identified protein kinase A (PKA) signaling as being overactive in the spinal cords of Cry1Δ11 mice. The neuronal excitability was significantly enhanced in the spinal cords of Cry1Δ11 mice as determined by in vitro electrophysiology. The PKA inhibitor H89 normalized hyperalgesia in Cry1Δ11 mice, underscoring the causative effect of overactive PKA signaling. Our results thus point to the PKA signaling pathway as the underlying mechanism and a potential therapeutic target for pain hypersensitivity in a validated ADHD mouse model.

S. Sanches P, P. Silva D, Torres ILS, Fregni F, Caumo W. Modulation of neural networks and symptom correlated in fibromyalgia: A randomized double-blind multi-group explanatory clinical trial of home-based transcranial direct current stimulation

BACKGROUND

Transcranial direct current stimulation (tDCS) might modulate neural activity and promote neural plasticity in patients with fibromyalgia (FM). This multi-group randomized clinical trial compared home-based active tDCS (HB-a-tDCS) on the left dorsolateral prefrontal cortex (l-DLPFC) or home-based sham tDCS (HB-s-tDCS), and HB-a-tDCS or HB-s-tDCS on the primary motor cortex (M1) in the connectivity analyses in eight regions of interest (ROIs) across eight resting-state electroencephalography (EEG) frequencies.

METHODS

We included 48 women with FM, aged 30 to 65, randomly assigned to 2:1:2:1 to receive 20 sessions during 20 minutes of HB-a-tDCS 2mA or HB-s-tDCS, over l-DLPFC or M1, respectively. EEG recordings were obtained before and after treatment with eyes open (EO) and eyes closed (EC).

RESULTS

In the EC condition, comparing pre to post-treatment, the HB-a-tDCS on l-DLPFC decreased the lagged coherence connectivity in the delta frequency band between the right insula and left anterior cingulate cortex (ACC) (t = -3.542, p = .048). The l-DLPFC HB-a-tDCS compared to HB-s-tDCS decreased the lagged coherence connectivity in the delta frequency band between the right insula and left ACC (t = -4.000, p = .017). In the EO condition, the l-DLPFC HB-a-tDCS compared to M1 HB-s-tDCS increased the lagged coherence connectivity between the l-DLPFC and left ACC in the theta band (t = -4.059, p = .048). Regression analysis demonstrated that the HB-a-tDCS effect on the l-DLPFC was positively correlated with sleep quality. On the other hand, the HB-a-tDCS on l-DLPFC and HB-s-tDCS on M1 were positively correlated with pain catastrophizing.

CONCLUSIONS

These results show that HB-a-tDCS affects the neural connectivity between parts of the brain that control pain's emotional and attentional aspects, which are most noticeable at lower EEG frequencies in a rest state. This effect on neural oscillations could serve as a neural marker associated with its efficacy in alleviating fibromyalgia symptoms.

CLINICAL TRIAL REGISTRATION

identifier [NCT03843203].

Transient Receptor Potential Ankyrin 1-dependent Activation of Extracellular Signal-regulated Kinase 2 in the Cerebral Cortices Contributes to Cortical Spreading Depolarization

Extracellular signal-regulated kinase (ERK) are serine/threonine-selective proteins and ERK1/2 can be phosphorylated in peripheral and central brain regions after cortical spreading depolarization (CSD) and calcitonin gene-related peptide; However, it remains unclear about whether and how ERK activity modulates CSD that correlates to migraine aura. Here, we determined the role of ERK in regulating CSD and explored the underlying mechanism involving transient receptor potential ankyrin 1 (TRPA1), a stress-sensing cation channel. CSD was recorded using intrinsic optical imaging in mouse brain slices, and electrophysiology in rats. Phosphorylated ERK (pERK1/2) and interleukin-1β (IL-1β) protein levels were detected using Western blot or enzyme-linked immunosorbent assay, respectively. IL-1β mRNA level was detected using qPCR. The results showed that an ERK inhibitor, SCH77298, markedly prolonged CSD latency and reduced propagation rate in mouse brain slices. Corresponding to this, CSD induction increased levels of cytosolic pERK1/2 in ipsilateral cerebral cortices of rats, the elevation of which correlated to the level of IL-1β mRNA. Mechanistic analysis showed that pre-treatment of an anti-TRPA1 antibody reduced the cytosolic pERK2 level but not pERK1 following CSD in cerebral cortices of rats and this level of pERK2 correlated with that of cerebral cortical IL-1β protein. Furthermore, an ERK activator, AES16-2M, but not its scrambled control, reversed the prolonged CSD latency by a TRPA1 inhibitor, HC-030031, in mouse brain slices. These data revealed a crucial role of ERK activity in regulating CSD, and elevation of pERK and IL-1β production induced by CSD is predominantly TRPA1 channel-dependent, thereby contributing to migraine pathogenesis.

Exploring altered oscillatory activity in the anterior cingulate cortex after nerve injury: Insights into mechanisms of neuropathic allodynia

While neural oscillations play a critical role in sensory perception, it remains unclear how these rhythms function under conditions of neuropathic allodynia. Recent studies demonstrated that the anterior cingulate cortex (ACC) is associated with the affective-aversive component of pain, and plasticity changes in this region are closely linked to abnormal allodynic sensations. Here, to study the mechanisms of allodynia, we recorded local field potentials (LFPs) in the bilateral ACC of awake-behaving rats and compared the spectral power and center frequency of brain oscillations between healthy and CCI (chronic constriction injury) induced neuropathic pain conditions. Our results indicated that activation of the ACC occurs bilaterally in the presence of neuropathic pain, similar to the healthy condition. Furthermore, CCI affects both spontaneous and stimulus-induced activity of ACC neurons. Specifically, we observed an increase in spontaneous beta activity after nerve injury compared to the healthy condition. By stimulating operated or unoperated paws, we found more intense event-related desynchronization (ERD) responses in the theta, alpha, and beta frequency bands and faster alpha center frequency after CCI compared to before CCI. Although the behavioral manifestation of allodynia was more pronounced in the operated paw than the unoperated paw following CCI, there was no significant difference in the center frequency and ERD responses observed in the ACC between stimulation of the operated and unoperated limbs. Our findings offer evidence supporting the notion that aberrancies in ACC oscillations may contribute to the maintenance and development of neuropathic allodynia.

Cingulate cGMP-dependent protein kinase I facilitates chronic pain and pain-related anxiety and depression

ABSTRACT

Patients with chronic pain often experience exaggerated pain response and aversive emotion, such as anxiety and depression. Central plasticity in the anterior cingulate cortex (ACC) is assumed to be a critical interface for pain perception and emotion, which has been reported to involve activation of NMDA receptors. Numerous studies have documented the key significance of cGMP-dependent protein kinase I (PKG-I) as a crucial downstream target for the NMDA receptor-NO-cGMP signaling cascade in regulating neuronal plasticity and pain hypersensitivity in specific regions of pain pathway, ie, dorsal root ganglion or spinal dorsal horn. Despite this, whether and how PKG-I in the ACC contributes to cingulate plasticity and comorbidity of chronic pain and aversive emotion has remained elusive. Here, we uncovered a crucial role of cingulate PKG-I in chronic pain and comorbid anxiety and depression. Chronic pain caused by tissue inflammation or nerve injury led to upregulation of PKG-I expression at both mRNA and protein levels in the ACC. Knockdown of ACC-PKG-I relieved pain hypersensitivity as well as pain-associated anxiety and depression. Further mechanistic analysis revealed that PKG-I might act to phosphorylate TRPC3 and TRPC6, leading to enhancement of calcium influx and neuronal hyperexcitability as well as synaptic potentiation, which results in the exaggerated pain response and comorbid anxiety and depression. We believe this study sheds new light on the functional capability of ACC-PKG-I in modulating chronic pain as well as pain-associated anxiety and depression. Hence, cingulate PKG-I may represent a new therapeutic target against chronic pain and pain-related anxiety and depression.

The potent analgesia of intrathecal 2R, 6R-HNK via TRPA1 inhibition in LF-PENS-induced chronic primary pain model

BACKGROUND

Chronic primary pain (CPP) is an intractable pain of unknown cause with significant emotional distress and/or dysfunction that is a leading factor of disability globally. The lack of a suitable animal model that mimic CPP in humans has frustrated efforts to curb disease progression. 2R, 6R-hydroxynorketamine (2R, 6R-HNK) is the major antidepressant metabolite of ketamine and also exerts antinociceptive action. However, the analgesic mechanism and whether it is effective for CPP are still unknown.

METHODS

Based on nociplastic pain is evoked by long-term potentiation (LTP)-inducible high- or low-frequency electrical stimulation (HFS/LFS), we wanted to develop a novel CPP mouse model with mood and cognitive comorbidities by noninvasive low-frequency percutaneous electrical nerve stimulation (LF-PENS). Single/repeated 2R, 6R-HNK or other drug was intraperitoneally (i.p.) or intrathecally (i.t.) injected into naïve or CPP mice to investigate their analgesic effect in CPP model. A variety of behavioral tests were used to detect the changes in pain, mood and memory. Immunofluorescent staining, western blot, reverse transcription-quantitative real-time polymerase chain reaction (RT-qPCR) and calcium imaging of in cultured dorsal root ganglia (DRG) neurons by Fluo-8-AM were used to elucidate the role and mechanisms of 2R, 6R-HNK in vivo or in vitro.

RESULTS

Intrathecal 2R, 6R-HNK, rather than intraperitoneal 2R, 6R-HNK or intrathecal S-Ketamine, successfully mitigated HFS-induced pain. Importantly, intrathecal 2R, 6R-HNK displayed effective relief of bilateral pain hypersensitivity and depressive and cognitive comorbidities in a dose-dependent manner in LF-PENS-induced CPP model. Mechanically, 2R, 6R-HNK markedly attenuated neuronal hyperexcitability and the upregulation of calcitonin gene-related peptide (CGRP), transient receptor potential ankyrin 1 (TRPA1) or vanilloid-1 (TRPV1), and vesicular glutamate transporter-2 (VGLUT2) in peripheral nociceptive pathway. In addition, 2R, 6R-HNK suppressed calcium responses and CGRP overexpression in cultured DRG neurons elicited by the agonists of TRPA1 or/and TRPV1. Strikingly, the inhibitory effects of 2R, 6R-HNK on these pain-related molecules and mechanical allodynia were substantially occluded by TRPA1 antagonist menthol.

CONCLUSIONS

In the newly designed CPP model, our findings highlighted the potential utility of intrathecal 2R, 6R-HNK for preventing and therapeutic modality of CPP. TRPA1-mediated uprgulation of CGRP and neuronal hyperexcitability in nociceptive pathways may undertake both unique characteristics and solving process of CPP.

Janus effect of the anterior cingulate cortex: Pain and emotion

Over the past 20 years, clinical and preclinical studies point to the anterior cingulate cortex (ACC) as a site of interest for several neurological and psychiatric conditions. The ACC plays a critical role in emotion, autonomic regulation, pain processing, attention, memory and decision making. An increasing number of studies have demonstrated the involvement of the ACC in the emotional component of pain and its comorbidity with emotional disorders such as anxiety and depression. Thanks to the development of animal models combined with state-of-the-art technologies, we now have a better mechanistic understanding of the functions of the ACC. Hence, the primary aim of this review is to compile the most recent preclinical studies on the role of ACC in the emotional component and consequences of chronic pain. Herein, we thus thoroughly describe the pain-induced electrophysiological, molecular and anatomical alterations in the ACC and in its related circuits. Finally, we discuss the next steps that are needed to strengthen our understanding of the involvement of the ACC in emotional and pain processing.

Glial Glutamate Transporter Modulation Prevents Development of Complete Freund's Adjuvant-Induced Hyperalgesia and Allodynia in Mice

Glial glutamate transporter (GLT-1) modulation in the hippocampus and anterior cingulate cortex (ACC) is critically involved in nociceptive pain. The objective of the study was to investigate the effects of 3-[[(2-methylphenyl) methyl] thio]-6-(2-pyridinyl)-pyridazine (LDN-212320), a GLT-1 activator, against microglial activation induced by complete Freund's adjuvant (CFA) in a mouse model of inflammatory pain. Furthermore, the effects of LDN-212320 on the protein expression of glial markers, such as ionized calcium-binding adaptor molecule 1 (Iba1), cluster of differentiation molecule 11b (CD11b), mitogen-activated protein kinases (p38), astroglial GLT-1, and connexin 43 (CX43), were measured in the hippocampus and ACC following CFA injection using the Western blot analysis and immunofluorescence assay. The effects of LDN-212320 on the pro-inflammatory cytokine interleukin-1β (IL-1β) in the hippocampus and ACC were also assessed using an enzyme-linked immunosorbent assay. Pretreatment with LDN-212320 (20 mg/kg) significantly reduced the CFA-induced tactile allodynia and thermal hyperalgesia. The anti-hyperalgesic and anti-allodynic effects of LDN-212320 were reversed by the GLT-1 antagonist DHK (10 mg/kg). Pretreatment with LDN-212320 significantly reduced CFA-induced microglial Iba1, CD11b, and p38 expression in the hippocampus and ACC. LDN-212320 markedly modulated astroglial GLT-1, CX43, and, IL-1β expression in the hippocampus and ACC. Overall, these results suggest that LDN-212320 prevents CFA-induced allodynia and hyperalgesia by upregulating astroglial GLT-1 and CX43 expression and decreasing microglial activation in the hippocampus and ACC. Therefore, LDN-212320 could be developed as a novel therapeutic drug candidate for chronic inflammatory pain.

Insular cortex stimulation alleviates neuropathic pain via ERK phosphorylation in neurons

AIMS

The clinical use of brain stimulation is attractive for patients who have side effects or tolerance. However, studies on insular cortex (IC) stimulation are lacking in neuropathic pain. The present study aimed to investigate the effects of IC stimulation (ICS) on neuropathic pain and to determine how ICS modulates pain.

METHODS

Changes in pain behaviors were observed following ICS with various parameters in neuropathic rats. Western blotting was performed to assess molecular changes in the expression levels of phosphorylated extracellular signal-regulated kinase (pERK), neurons, astrocytes, and microglia between experimental groups. Immunohistochemistry was performed to investigate the colocalization of pERK with different cell types.

RESULTS

The most effective pain-relieving effect was induced at 50 Hz-120 μA in single trial of ICS and it maintained 4 days longer after the termination of repetitive ICS. The expression levels of pERK, astrocytes, and microglia were increased in neuropathic rats. However, after ICS, the expression levels of pERK were decreased, and colocalization of pERK and neurons was reduced in layers 2-3 of the IC.

CONCLUSION

These results indicated that ICS attenuated neuropathic pain by the regulation of pERK in neurons located in layers 2-3 of the IC. This preclinical study may enhance the potential use of ICS and identify the therapeutic mechanisms of ICS in neuropathic pain.

Segmental Upregulation of ASIC1 Channels in the Formalin Acute Pain Mouse Model

BACKGROUND

Hindpaw injection of formalin in rodents is used to assess acute persistent pain. The response to formalin is biphasic. The initial response (first minutes) is thought to be linked to inflammatory, peripheral mechanisms, while the latter (around 30 min after the injection), is linked to central mechanisms. This model is useful to analyze the effect of drugs at one or both phases, and the involvement of ion channels in the response. Acid-sensing ion channels (ASICs) regulate synaptic activities and play important roles in pain conditions. Recently, psalmotoxin-1 (Pctx-1), a toxin that inhibits ASIC1a-constituted channels, and antisense ASIC1a-RNA, intrathecal administered in mice were shown to affect both phases of the test.

METHODS

The mouse formalin test was performed on C57/BL6 7- to 9-week-old mice. Behavioral tests were conducted and tissue was extracted to detect proteins (ASIC1 and pERK) and ASIC1-mRNA and mir485-5p levels.

RESULTS

The injection of formalin was accompanied by an increase in ASIC1 levels. This was detected at the contralateral anterior cingulate cortex (ACC) compared to the ipsilateral side, and both sides of the ACC of vehicle-injected animals. At the spinal cord and dorsal root ganglia, ASIC1 levels followed a gradient stronger at lumbar (L) 3 and decreased towards L5. Gender differences were detected at the ACC; with female mice showing higher ASIC1a levels at the ACC. No significant changes in ASIC1-mRNA levels were detected. Evidence suggests ASIC1 upregulation depends on regulatory microRNAs.

CONCLUSION

This work highlights the important role of ASIC1 in pain and the potential role of pharmacological therapies aimed at this channel.

Multidimensional Pain Modulation by Acupuncture Analgesia: The Reward Effect of Acupuncture on Pain Relief

Pain is an intrinsically unpleasant experience with features that protect an organism by promoting motivation and learning. Pain relief, a negative reinforcement of pain, is considered a reward and activates the brain's reward system. The reward circuit in the brain involves reward and pain. Acupuncture has a multidimensional and comprehensive regulating effect on chronic pain. However, the reward effect of acupuncture in relieving chronic pain and the mechanism of the brain reward circuit involved in acupuncture analgesia are not thoroughly studied. In this article, we have reviewed the definition of pain abnormalities and negative emotions in patients with chronic pain, the conceptual characteristics of analgesic reward, and the new progress in studying brain reward circuits and functions. Moreover, we have expounded on the critical clinical and scientific significance of studying the reward effect of acupuncture analgesia and related brain reward circuits, the pain mechanism obtained from human neuroimaging studies, and the survey results on the effects of acupuncture on reward/motivation circuits. Some viewpoints and suggestions on the reward effect of acupuncture analgesia and related reward circuits have been put forward to clarify the multidimensional characteristics and benign regulation of acupuncture analgesia. Studies on the reward effect of acupuncture in relieving chronic pain and the regulating effect of the brain reward loop on acupuncture analgesia help to deepen the clinical understanding of acupuncture analgesia, innovate the research concept of acupuncture analgesia, and provide help for further studies on the central mechanism of acupuncture in improving chronic pain in the future.

Astrocytic ERK/STAT1 signaling contributes to maintenance of stress-related visceral hypersensitivity in rats

The rostral anterior cingulate cortex (rACC) has been found to be an important brain region in mediating visceral hypersensitivity. However, the underlying mechanisms remain unclear. This study aimed to explore the role of astrocytes in the maintenance of visceral hypersensitivity induced by chronic water avoidance stress (WAS) as well as the potential signaling pathway that activates astrocytes in the rACC. We found that ACC-reactive astrogliosis resulted in the overexpression of c-fos, TSP-1, and BDNF in stress-related visceral hypersensitivity rats. Visceral hypersensitivity was reversed by pharmacological inhibition of astrocytic activation after WAS, as were the overexpression of c-fos, TSP-1 and BDNF. Activation of the astrocytic Gi-pathway increased the visceral sensitivity and expression of c-fos, TSP-1, and BDNF. Visceral hypersensitivity was also ameliorated by the pharmacological inhibition of ERK and STAT1 phosphorylation after WAS. Furthermore, inhibition of the ERK-STAT1 cascade reduced astrocytic activation. These findings suggest that astrocytic ERK/STAT1 signaling in the rACC contributes to the maintenance of stress-related visceral hypersensitivity. PERSPECTIVE: Visceral hypersensitivity is a key factor in the pathophysiology of irritable bowel syndrome. This study highlights the important role of astrocytic ERK/STAT1 signaling in activating astrocytes in the rostral anterior cingulate cortex, which contributes to visceral hypersensitivity.

Inflammatory Pain Alters Dopaminergic Modulation of Excitatory Synapses in the Anterior Cingulate Cortex of Mice

Pain modulation of dopamine-producing nuclei is known to contribute to the affective component of chronic pain. However, pain modulation of pain-related cortical regions receiving dopaminergic inputs is understudied. The present study demonstrates that mice with chronic inflammatory injury of the hind paws develop persistent mechanical hypersensitivity and transient anxiety. Peripheral inflammation induced by injection of complete Freund's Adjuvant (CFA) induced potentiation of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic receptor (AMPAR) currents with a presynaptic component in layer II/III of the ACC. After four days of inflammatory pain, the dopamine-mediated inhibition of AMPAR currents was significantly reduced in the ACC. Furthermore, dopamine enhanced presynaptic modulation of excitatory transmission, but only in mice with inflammatory pain. High-performance liquid chromatography (HPLC) analysis of dopamine tissue concentration revealed that dopamine neurotransmitter concentration in the ACC was reduced three days following CFA. Our results demonstrate that inflammatory pain induces activity-dependent changes in excitatory synaptic transmission and alters dopaminergic homeostasis in the ACC.

Are TRPA1 and TRPV1 channel-mediated signalling cascades involved in UVB radiation-induced sunburn?

Burn injuries are underappreciated injuries associated with substantial morbidity and mortality. Overexposure to ultraviolet (UV) radiation has dramatic clinical effects in humans and is a significant public health concern. Although the mechanisms underlying UVB exposure are not fully understood, many studies have made substantial progress in the pathophysiology of sunburn in terms of its molecular aspects in the last few years. It is well established that the transient receptor potential ankyrin 1 (TRPA1), and vanilloid 1 (TRPV1) channels modulate the inflammatory, oxidative, and proliferative processes underlying UVB radiation exposure. However, it is still unknown which mechanisms underlying TRPV1/A1 channel activation are elicited in sunburn induced by UVB radiation. Therefore, in this review, we give an overview of the TRPV1/A1 channel-mediated signalling cascades that may be involved in the pathophysiology of sunburn induced by UVB radiation. These data will undoubtedly help to explain the various features of sunburn and contribute to the development of novel therapeutic approaches to better treat it.

Rostral Anterior Cingulate Cortex–Ventrolateral Periaqueductal Gray Circuit Underlies Electroacupuncture to Alleviate Hyperalgesia but Not Anxiety-Like Behaviors in Mice With Spared Nerve Injury

Neuropathic pain is a common cause of chronic pain and is often accompanied by negative emotions, making it complex and difficult to treat. However, the neural circuit mechanisms underlying these symptoms remain unclear. Herein, we present a novel pathway associated with comorbid chronic pain and anxiety. Using chemogenetic methods, we found that activation of glutamatergic projections from the rostral anterior cingulate cortex (rACC^Glu) to the ventrolateral periaqueductal gray (vlPAG) induced both hyperalgesia and anxiety-like behaviors in sham mice. Inhibition of the rACC^Glu-vlPAG pathway reduced anxiety-like behaviors and hyperalgesia in the spared nerve injury (SNI) mice model; moreover, electroacupuncture (EA) effectively alleviated these symptoms. Investigation of the related mechanisms revealed that the chemogenetic activation of the rACC^Glu-vlPAG circuit effectively blocked the analgesic effect of EA in the SNI mice model but did not affect the chronic pain-induced negative emotions. This study revealed a novel pathway, the rACC^Glu-vlPAG pathway, that mediates neuropathic pain and pain-induced anxiety.

Nociceptor-localized cGMP-dependent protein kinase I is a critical generator for central sensitization and neuropathic pain

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.

Gene Transcript Alterations in the Spinal Cord, Anterior Cingulate Cortex, and Amygdala in Mice Following Peripheral Nerve Injury

Chronic neuropathic pain caused by nerve damage is a most common clinical symptom, often accompanied by anxiety- and depression-like symptoms. Current treatments are very limited at least in part due to incompletely understanding mechanisms underlying this disorder. Changes in gene expression in the dorsal root ganglion (DRG) have been acknowledged to implicate in neuropathic pain genesis, but how peripheral nerve injury alters the gene expression in other pain-associated regions remains elusive. The present study carried out strand-specific next-generation RNA sequencing with a higher sequencing depth and observed the changes in whole transcriptomes in the spinal cord (SC), anterior cingulate cortex (ACC), and amygdala (AMY) following unilateral fourth lumbar spinal nerve ligation (SNL). In addition to providing novel transcriptome profiles of long non-coding RNAs (lncRNAs) and mRNAs, we identified pain- and emotion-related differentially expressed genes (DEGs) and revealed that numbers of these DEGs displayed a high correlation to neuroinflammation and apoptosis. Consistently, functional analyses showed that the most significant enriched biological processes of the upregulated mRNAs were involved in the immune system process, apoptotic process, defense response, inflammation response, and sensory perception of pain across three regions. Moreover, the comparisons of pain-, anxiety-, and depression-related DEGs among three regions present a particular molecular map among the spinal cord and supraspinal structures and indicate the region-dependent and region-independent alterations of gene expression after nerve injury. Our study provides a resource for gene transcript expression patterns in three distinct pain-related regions after peripheral nerve injury. Our findings suggest that neuroinflammation and apoptosis are important pathogenic mechanisms underlying neuropathic pain and that some DEGs might be promising therapeutic targets.

Extracellular signal-regulated kinases 2 (Erk2) and Erk5 in the central nervous system differentially contribute to central sensitization in male mice

Nervous systems are designed to become extra sensitive to afferent nociceptive stimuli under certain circumstances such as inflammation and nerve injury. How pain hypersensitivity comes about is key issue in the field since it ultimately results in chronic pain. Central sensitization represents enhanced pain sensitivity due to increased neural signaling within the central nervous system (CNS). Particularly, much evidence indicates that underlying mechanism of central sensitization is associated with the change of spinal neurons. Extracellular signal-regulated kinases have received attention as key molecules in central sensitization. Previously, we revealed the isoform-specific function of extracellular signal-regulated kinase 2 (Erk2) in spinal neurons for central sensitization using mice with Cre-loxP-mediated deletion of Erk2 in the CNS. Still, how extracellular signal-regulated kinase 5 (Erk5) in spinal neurons contributes to central sensitization has not been directly tested, nor is the functional relevance of Erk5 and Erk2 known. Here, we show that Erk5 and Erk2 in the CNS play redundant and/or distinct roles in central sensitization, depending on the plasticity context (cell types, pain types, time, etc.). We used male mice with Erk5 deletion specifically in the CNS and found that Erk5 plays important roles in central sensitization in a formalin-induced inflammatory pain model. Deletion of both Erk2 and Erk5 leads to greater attenuation of central sensitization in this model, compared to deletion of either isoform alone. Conversely, Erk2 but not Erk5 plays important roles in central sensitization in neuropathic pain, a type of chronic pain caused by nerve damage. Our results suggest the elaborate mechanisms of Erk signaling in central sensitization.

Role of the Anterior Cingulate Cortex in Translational Pain Research

As the most common symptomatic reason to seek medical consultation, pain is a complex experience that has been classified into different categories and stages. In pain processing, noxious stimuli may activate the anterior cingulate cortex (ACC). But the function of ACC in the different pain conditions is not well discussed. In this review, we elaborate the commonalities and differences from accumulated evidence by a variety of pain assays for physiological pain and pathological pain including inflammatory pain, neuropathic pain, and cancer pain in the ACC, and discuss the cellular receptors and signaling molecules from animal studies. We further summarize the ACC as a new central neuromodulation target for invasive and non-invasive stimulation techniques in clinical pain management. The comprehensive understanding of pain processing in the ACC may lead to bridging the gap in translational research between basic and clinical studies and to develop new therapies.

Astrocytic Regulation of Neural Circuits Underlying Behaviors

Astrocytes, characterized by a satellite-like morphology, are the most abundant type of glia in the central nervous system. Their main functions have been thought to be limited to providing homeostatic support for neurons, but recent studies have revealed that astrocytes actually actively interact with local neural circuits and play a crucial role in information processing and generating physiological and behavioral responses. Here, we review the emerging roles of astrocytes in many brain regions, particularly by focusing on intracellular changes in astrocytes and their interactions with neurons at the molecular and neural circuit levels.

Differential Role of Anterior Cingulate Cortical Glutamatergic Neurons in Pain-Related Aversion Learning and Nociceptive Behaviors in Male and Female Rats

Pain is comprised of both sensory and affective components. The anterior cingulate cortex (ACC) is a key brain region involved in the emotional processing of pain. Specifically, glutamatergic transmission within the ACC has been shown to modulate pain-related aversion. In the present study, we use in vivo optogenetics to activate or silence, using channelrhodopsin (ChR2) and archaerhodopsin (ArchT) respectively, calmodulin-kinase IIα (CaMKIIα)-expressing excitatory glutamatergic neurons of the ACC during a formalin-induced conditioned place aversion (F-CPA) behavioral paradigm in both female and male adult Sprague-Dawley rats. Expression of c-Fos, a marker of neuronal activity, was assessed within the ACC using immunohistochemistry. Optogenetic inhibition of glutamatergic neurons of the ACC abolished F-CPA without affecting formalin-induced nociceptive behavior during conditioning. In male rats, optogenetic activation of ACC glutamatergic neurons decreased formalin-induced nociceptive behavior during conditioning without affecting F-CPA. Interestingly, the opposite effect was seen in females, where optogenetic activation of glutamatergic neurons of the ACC increased formalin-induced nociceptive behavior during conditioning. The abolition of F-CPA following optogenetic inhibition of glutamatergic neurons of the ACC was associated with a reduction in c-Fos immunoreactivity in the ACC in male rats, but not female rats. These results suggest that excitatory glutamatergic neurons of the ACC play differential and sex-dependent roles in the aversion learning and acute sensory components of pain.

Antinociceptive Effects of the GPR55 Antagonist CID16020046 Injected into the Rat Anterior Cingulate Cortex

The G-protein coupled receptor, GPR55, modulates nociceptive processing. Given the expression of GPR55 in the anterior cingulate cortex (ACC), a key brain region involved in the cognitive and affective dimensions of pain, the present study tested the hypothesis that GPR55 signalling in the ACC facilitates inflammatory pain behaviour in rats. The expression of GPR55 in the ACC was confirmed by both western blotting and immunostaining, with evidence for neuronal localisation. Microinjection of the selective GPR55 antagonist CID16020046 into the ACC of adult male Sprague-Dawley rats significantly reduced second phase formalin-evoked nociceptive behaviour compared with vehicle-treated controls. CID16020046 administration was associated with a reduction in phosphorylation of extracellular signal-regulated kinase (ERK), a downstream target of GPR55 activation, in the ACC. Intra-ACC administration of CID16020046 prevented the formalin-induced increases in expression of mRNA coding for the immediate early gene and marker of neuronal activity, c-Fos, in the ipsilateral dorsal horn of the spinal cord. Intra-plantar injection of formalin reduced tissue levels of the endogenous GPR55 ligand 2-arachidonoyl-sn-glycero-3-phosphoinositol (2-AGPI) in the ACC, likely reflecting its increased release/utilisation. These data suggest that endogenous activation of GPR55 signalling and increased ERK phosphorylation in the ACC facilitates inflammatory pain via top-down modulation of descending pain control.

Objective functional impairment in lumbar degenerative disease: concurrent validity of the baseline severity stratification for the five-repetition sit-to-stand test

OBJECTIVE

The five-repetition sit-to-stand (5R-STS) test provides a new dimension of clinical assessment by capturing objective functional impairment (OFI). Through the utilization of data from two prospective studies, the authors sought to evaluate the concurrent validity of the proposed 5R-STS baseline severity stratification (BSS) for OFI with the following levels based on time to completion in seconds: none, ≤ 10.4; mild, 10.5-15.2; moderate, 15.3-22.0; and severe, > 22.0 seconds.

METHODS

Patients with degenerative diseases of the spine performed the 5R-STS test and completed visual analog scales (VASs) for back and leg pain, the Oswestry Disability Index (ODI), the Roland-Morris Disability Questionnaire (RMDQ), and EQ-5D questionnaires. The degree of OFI severity was assessed based on the previously proposed BSS, and its association with patient-reported scales was evaluated using ANOVA as well as crude and adjusted linear regression models.

RESULTS

Our sample included 240 patients, of whom 101 exhibited no OFI, whereas 80, 34, and 25 were judged to have mild, moderate, and severe OFI, respectively. A higher baseline severity was strongly associated with loss of working ability (p < 0.001), as well as results of all patient-reported scales (p ≤ 0.001), with the exception of the VAS for leg pain (p = 0.556). Crude and adjusted regression analyses corroborated these findings, although only patients with moderate and severe OFI as judged by using the 5R-STS BSS demonstrated clinically relevant differences compared with patients without OFI.

CONCLUSIONS

The degree of OFI-based on the 5R-STS BSS-is strongly associated with measures of back pain, subjective functional impairment, and health-related quality of life. However, leg pain severity is not reflected within the dimension of OFI measured by the 5R-STS. The proposed BSS appears to be a concurrently valid and clinically relevant measure of OFI in patients with degenerative spinal pathologies.

Distinct Function of Estrogen Receptors in the Rodent Anterior Cingulate Cortex in Pain-related Aversion

BACKGROUND

Brain-derived estrogen is implicated in pain-related aversion; however, which estrogen receptors mediate this effect remains unclear. This study hypothesized that the different estrogen receptors in the rostral anterior cingulate cortex play distinct roles in pain-related aversion.

METHODS

Formalin-induced conditioned place avoidance and place escape/avoidance paradigms were used to evaluate pain-related aversion in rodents. Immunohistochemistry and Western blotting were used to detect estrogen receptor expression. Patch-clamp recordings were used to examine N-methyl-D-aspartate-mediated excitatory postsynaptic currents in rostral anterior cingulate cortex slices.

RESULTS

The administration of the estrogen receptor-β antagonist 4-(2-phenyl-5,7-bis [trifluoromethyl] pyrazolo [1,5-a] pyrimidin-3-yl) phenol (PHTPP) or the G protein-coupled estrogen receptor-1 antagonist (3aS*,4R*,9bR*)-4-(6-bromo-1,3-benzodioxol-5-yl)-3a,4,5,9b-3H-cyclopenta [c] quinolone (G15) but not the estrogen receptor-α antagonist 1,3-bis (4-hydroxyphenyl)-4-methyl-5-[4-(2-piperidinylethoxy) phenol]-1H-pyrazole dihydrochloride (MPP) into the rostral anterior cingulate cortex blocked pain-related aversion in rats (avoidance score, mean ± SD: 1,3-bis [4-hydroxyphenyl]-4-methyl-5-(4-[2-piperidinylethoxy] phenol)-1H-pyrazole dihydrochloride (MPP): 47.0 ± 18.9%, 4-(2-phenyl-5,7-bis [trifluoromethyl] pyrazolo [1,5-a] pyrimidin-3-yl) phenol (PHTPP): -7.4 ± 20.6%, and [3aS*,4R*,9bR*]-4-[6-bromo-1,3-benzodioxol-5-yl]-3a,4,5,9b-3H-cyclopenta [c] quinolone (G15): -4.6 ± 17.0% vs. vehicle: 46.5 ± 12.2%; n = 7 to 9; P < 0.0001). Consistently, estrogen receptor-β knockdown but not estrogen receptor-α knockdown by short-hairpin RNA also inhibited pain-related aversion in mice (avoidance score, mean ± SD: estrogen receptor-α-short-hairpin RNA: 26.0 ± 7.1% and estrogen receptor-β-short-hairpin RNA: 6.3 ± 13.4% vs. control short-hairpin RNA: 29.1 ± 9.1%; n = 7 to 10; P < 0.0001). Furthermore, the direct administration of the estrogen receptor-β agonist 2,3-bis (4-hydroxyphenyl)-propionitrile (DPN) or the G protein-coupled estrogen receptor-1 agonist (±)-1-([3aR*,4S*,9bS*]-4-(6-bromo-1,3-benzodioxol-5-yl)-3a,4,5,9b-tetrahydro-3H-cyclopenta [c]quinolin-8-yl)-ethanone (G1) into the rostral anterior cingulate cortex resulted in conditioned place avoidance (avoidance score, mean ± SD: 2,3-bis (4-hydroxyphenyl)-propionitrile (DPN): 35.3 ± 9.5% and (±)-1-([3aR*,4S*,9bS*]-4-(6-bromo-1,3-benzodioxol-5-yl)-3a,4,5,9b-tetrahydro-3H-cyclopenta [c]quinolin-8-yl)-ethanone (G1): 43.5 ± 22.8% vs. vehicle: 0.3 ± 14.9%; n = 8; P < 0.0001) but did not affect mechanical or thermal sensitivity. The activation of the estrogen receptor-β/protein kinase A or G protein-coupled estrogen receptor-1/protein kinase B pathway elicited the long-term potentiation of N-methyl-D-aspartate-mediated excitatory postsynaptic currents.

CONCLUSIONS

These findings indicate that estrogen receptor-β and G protein-coupled estrogen receptor-1 but not estrogen receptor-α in the rostral anterior cingulate cortex contribute to pain-related aversion by modulating N-methyl-D-aspartate receptor-mediated excitatory synaptic transmission.

Ketamine induces rapid and sustained antidepressant-like effects in chronic pain induced depression: Role of MAPK signaling pathway

Chronic pain produces psychologic distress, which often leads to mood disorders such as depression. Co-existing chronic pain and depression pose a serious socio-economic burden and result in disability affecting millions of individuals, which urges the development of treatment strategies targeting this comorbidity. Ketamine, a noncompetitive antagonist of the N-methyl-d-aspartate (NMDA) receptor, is shown to be efficient in treating both pain and depression-related symptoms. However, the molecular characteristics of its role in chronic pain-induced depression remain largely unexplored. Hence, we studied the behavioral and molecular effects of a single systemic administration of ketamine (15 mg/kg, i.p.) on mechanical hypersensitivity and depressive-like consequences of chronic neuropathic pain. We showed that ketamine transiently alleviated mechanical hypersensitivity (lasting <24 h), while its antidepressant effect was observed even 72 h after administration. In addition, ketamine normalized the upregulated expression of the mitogen activated protein kinase (MAPK) phosphatase 1 (MKP-1) and the downregulated phosphorylation of extracellular signal-regulated kinase (pERK) in the anterior cingulate cortex (ACC) of mice displaying neuropathic pain-induced depressive-like behaviors. This effect of ketamine on the MKP-1 was first detected 30 min after the ketamine administration and persisted until up to 72 h. Altogether, these findings provide insight into the behavioral and molecular changes associated with single ketamine administration in the comorbidity of chronic pain and depression.

The Medial Prefrontal Cortex as a Central Hub for Mental Comorbidities Associated with Chronic Pain

Chronic pain patients frequently develop and suffer from mental comorbidities such as depressive mood, impaired cognition, and other significant constraints of daily life, which can only insufficiently be overcome by medication. The emotional and cognitive components of pain are processed by the medial prefrontal cortex, which comprises the anterior cingulate cortex, the prelimbic, and the infralimbic cortex. All three subregions are significantly affected by chronic pain: magnetic resonance imaging has revealed gray matter loss in all these areas in chronic pain conditions. While the anterior cingulate cortex appears hyperactive, prelimbic, and infralimbic regions show reduced activity. The medial prefrontal cortex receives ascending, nociceptive input, but also exerts important top-down control of pain sensation: its projections are the main cortical input of the periaqueductal gray, which is part of the descending inhibitory pain control system at the spinal level. A multitude of neurotransmitter systems contributes to the fine-tuning of the local circuitry, of which cholinergic and GABAergic signaling are particularly emerging as relevant components of affective pain processing within the prefrontal cortex. Accordingly, factors such as distraction, positive mood, and anticipation of pain relief such as placebo can ameliorate pain by affecting mPFC function, making this cortical area a promising target region for medical as well as psychosocial interventions for pain therapy.

Electroacupuncture Alleviates Pain-Related Emotion by Upregulating the Expression of NPS and Its Receptor NPSR in the Anterior Cingulate Cortex and Hypothalamus

Objective

Electroacupuncture (EA) is reported effective in alleviating pain-related emotion; however, the underlying mechanism of its effects still needs to be elucidated. The NPS-NPSR system has been validated for the involvement in the modulation of analgesia and emotional behavior. Here, we aimed to investigate the role of the NPS-NPSR system in the anterior cingulate cortex (ACC), hypothalamus, and central amygdala (CeA) in the use of EA to relieve affective pain modeled by complete Freund's adjuvant- (CFA-) evoked conditioned place aversion (C-CPA). Materials and Methods. CFA injection combined with a CPA paradigm was introduced to establish the C-CPA model, and the elevated O-maze (EOM) was used to test the behavioral changes after model establishment. We further explored the expression of NPS and NPSR at the protein and gene levels in the brain regions of interest by immunofluorescence staining and quantitative real-time PCR.

Results

We observed that EA stimulation delivered to the bilateral Zusanli (ST36) and Kunlun (BL60) acupoints remarkably inhibited sensory pain, pain-evoked place aversion, and anxiety-like behavior. The current study showed that EA significantly enhanced the protein expression of this peptide system in the ACC and hypothalamus, while the elevated expression of NPSR protein alone was just confined to the affected side in the CeA. Moreover, EA remarkably upregulated the mRNA expression of NPS in CeA, ACC, and hypothalamus and NPSR mRNA in the hypothalamus and CeA.

Conclusions

These data suggest the effectiveness of EA in alleviating affective pain, and these benefits may at least partially be attributable to the upregulation of the NPS-NPSR system in the ACC and hypothalamus.

Effect of Low Back Pain Chronicity on Patient Outcomes Treated in Outpatient Physical Therapy: A Retrospective Observational Study

OBJECTIVE

To examine the potential relationship between physical therapy (PT) treatment outcomes and chronicity of low back pain (LBP) in the outpatient setting.

DESIGN

Retrospective observational study.

SETTING

Outpatient PT clinics across 11 states.

PARTICIPANTS

A total of 11,941 patients with LBP provided with PT services and discharged from care between January 1, 2017, and December 31, 2018.

MAIN OUTCOME MEASURES

Focus on Therapeutic Outcome Low Back Functional Status (FS) Patient-Reported Outcome Measure (PROM) was the primary outcomes measure used. It assesses the patients' perceived physical abilities for patients experiencing LBP impairments. It determined a functional score on a linear metric ranging from 0 (low functioning) to 100 (high functioning). The difference in score between the intake FS and final FS score produced the FS change, which represented the overall improvement of the episode of care.

RESULTS

The mean FS change was 16.997 (n=11,945). Patients with chronic symptoms (>90-d duration) had an FS change of 15.920 (n=7264) across 14.63 visits. Patients with subacute symptoms (15-90d) had an FS change of 21.66 (n=3631) across 14.05. Patients with acute symptoms (0-14d) had an FS change of 29.32 (n=1050) across 13.66 visits. Stepwise regression analysis revealed a significant â for chronicity (-4.155) with all models.

CONCLUSIONS

Overall, this study shows patients experiencing shorter duration of LBP symptoms before starting a PT episode of care experience significantly better outcomes than patients who waited. Furthermore, the number of treatment session and duration of care was similar between groups, indicating potential ineffective or insufficient care was provided for patients with chronic pain.

Emotional intelligence impairments in women with fibromyalgia: Associations with widespread pain

This study aimed at testing the differences in emotional intelligence ability between women with fibromyalgia (cases) and their age-matched counterparts not with fibromyalgia from the general population (controls) and analysing the association between emotional intelligence ability and widespread pain in women with fibromyalgia. A total of 133 cases and 77 controls participated in this cross-sectional study. Controls performed better than cases on emotion understanding. Higher emotion perception and management were significantly associated with lower widespread pain. Therefore, women with fibromyalgia may experience difficulties in understanding emotional information. In fibromyalgia, higher emotion perception and management abilities are independently related to lower widespread pain.

Regional Differences Within the Anterior Cingulate Cortex in the Generation Versus Suppression of Pain Affect in Rats

The anterior cingulate cortex (ACC) modulates emotional responses to pain. Whereas, the caudal ACC (cACC) promotes expression of pain affect, the rostral ACC (rACC) contributes to its suppression. Both subdivisions receive glutamatergic innervation, and the present study evaluated the contribution of N-methyl-d-aspartic acid (NMDA) receptors within these subdivisions to rats' expression of pain affect. Vocalizations that follow a brief noxious tail shock (vocalization afterdischarges, VAD) are a validated rodent model of pain affect. The threshold current for eliciting VAD was increased in a dose-dependent manner by injecting NMDA into the rACC, but performance (latency, amplitude, and duration) at threshold was not altered. Alternately, the threshold current for eliciting VAD was not altered following injection of NMDA into the cACC, but its amplitude and duration at threshold were increased in a dose-dependent manner. These effects were limited to Cg1 of the rACC and cACC, and blocked by pretreatment of the ACC with the NMDA receptor antagonist d-2-amino-5-phosphonovalerate. These findings demonstrate that NMDA receptor agonism within the cACC and rACC either increases or decreases emotional responses to noxious stimulation, respectively. PERSPECTIVE: NMDA receptor activation of the rostral and caudal ACC respectively inhibited or enhanced rats' emotional response to pain. These findings mirror those obtained from human neuroimaging studies; thereby, supporting the use of this model system in evaluating the contribution of ACC to pain affect.

Increased CXCL13 and CXCR5 in Anterior Cingulate Cortex Contributes to Neuropathic Pain-Related Conditioned Place Aversion

Pain consists of sensory-discriminative and emotional-affective components. The anterior cingulate cortex (ACC) is a critical brain area in mediating the affective pain. However, the molecular mechanisms involved remain largely unknown. Our recent study indicated that C-X-C motif chemokine 13 (CXCL13) and its sole receptor CXCR5 are involved in sensory sensitization in the spinal cord after spinal nerve ligation (SNL). Whether CXCL13/CXCR5 signaling in the ACC contributes to the pathogenesis of pain-related aversion remains unknown. Here, we showed that SNL increased the CXCL13 level and CXCR5 expression in the ACC after SNL. Knockdown of CXCR5 by microinjection of Cxcr5 shRNA into the ACC did not affect SNL-induced mechanical allodynia but effectively alleviated neuropathic pain-related place avoidance behavior. Furthermore, electrophysiological recording from layer II-III neurons in the ACC showed that SNL increased the frequency and amplitude of spontaneous excitatory postsynaptic currents (sEPSCs), decreased the EPSC paired-pulse ratio, and increased the α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor/N-methyl-D-aspartate receptor ratio, indicating enhanced glutamatergic synaptic transmission. Finally, superfusion of CXCL13 onto ACC slices increased the frequency and amplitude of spontaneous EPSCs. Pre-injection of Cxcr5 shRNA into the ACC reduced the increase in glutamatergic synaptic transmission induced by SNL. Collectively, these results suggest that CXCL13/CXCR5 signaling in the ACC is involved in neuropathic pain-related aversion via synaptic potentiation.

Silencing of spinal Trpv1 attenuates neuropathic pain in rats by inhibiting CAMKII expression and ERK2 phosphorylation

Accumulating evidence suggests a potential role of transient receptor potential vanilloid 1 (TRPV1) channels in inflammatory and cancer-related pain. However, the role of TRPV1 in the maintenance of neuropathic pain remains elusive. The current study investigated the effects of transient Trpv1 gene silencing using a small interference RNA (siRNA) on neuropathic pain induced by chronic constriction injury (CCI) of the sciatic nerve in rats. Seven days after CCI, the TRPV1 siRNA was intrathecally administered (5 µg/15 µl, once daily for 2 days). TRPV1 and Ca²⁺/calmodulin-dependent protein kinase II (CAMKII) expression and extracellular signal-regulated kinase (ERK) phosphorylation in the spinal cord were detected using western blotting. The thresholds to mechanical and thermal stimuli were determined before and after intrathecal TRPV1 siRNA administration. TRPV1 and CAMKII expression and ERK2 phosphorylation in the spinal cord were upregulated after CCI. Intrathecal administration of the TRPV1 siRNA not only attenuated behavioural hyperalgesia but also reduced the expression of TRPV1 and CAMKII, as well as ERK2 phosphorylation. Based on these results, silencing of the TRPV1 gene in the spinal cord attenuates the maintenance of neuropathic pain by inhibiting CAMKII/ERK2 activation and suggests that TRPV1 represents a potential target in pain therapy.

Effects of glial glutamate transporter activator in formalin-induced pain behaviour in mice

BACKGROUND

Nociceptive pain remains a prevalent clinical problem and often poorly responsive to the currently available analgesics. Previous studies have shown that astroglial glutamate transporter-1 (GLT-1) in the hippocampus and anterior cingulate cortex (ACC) is critically involved in pain processing and modulation. However, the role of astroglial GLT-1 in nociceptive pain involving the hippocampus and ACC remains unknown. We investigated the role of 3-[[(2-Methylphenyl) methyl]thio]-6-(2-pyridinyl)-pyridazine (LDN-212320), a GLT-1 activator, in nociceptive pain model and hippocampal-dependent behavioural tasks in mice.

METHODS

We evaluated the effects of LDN-212320 in formalin-induced nociceptive pain model. In addition, formalin-induced impaired hippocampal-dependent behaviours were measured using Y-maze and object recognition test. Furthermore, GLT-1 expression and extracellular signal-regulated kinase phosphorylation (pERK1/2) were measured in the hippocampus and ACC using Western blot analysis and immunohistochemistry.

RESULTS

The LDN-212320 (10 or 20 mg/kg, i.p) significantly attenuated formalin-evoked nociceptive behaviour. The antinociceptive effects of LDN-212320 were reversed by systemic administration of DHK (10 mg/kg, i.p), a GLT-1 antagonist. Moreover, LDN-212320 (10 or 20 mg/kg, i.p) significantly reversed formalin-induced impaired hippocampal-dependent behaviour. In addition, LDN-212320 (10 or 20 mg/kg, i.p) increased GLT-1 expressions in the hippocampus and ACC. On the other hand, LDN-212320 (20 mg/kg, i.p) significantly reduced formalin induced-ERK phosphorylation, a marker of nociception, in the hippocampus and ACC.

CONCLUSION

These results suggest that the GLT-1 activator LDN-212320 prevents nociceptive pain by upregulating astroglial GLT-1 expression in the hippocampus and ACC. Therefore, GLT-1 activator could be a novel drug candidate for nociceptive pain.

SIGNIFICANCE

The present study provides new insights and evaluates the role of GLT-1 activator in the modulation of nociceptive pain involving hippocampus and ACC. Here, we provide evidence that GLT-1 activator could be a potential therapeutic utility for the treatment of nociceptive pain.

Dexmedetomidine Attenuates Neuropathic Pain by Inhibiting P2X7R Expression and ERK Phosphorylation in Rats

α2-Adrenoceptor agonists attenuate hypersensitivity under neuropathic conditions. However, the mechanisms underlying this attenuation remain largely unknown. In the present study, we explored the potential roles of purinergic receptor 7 (P2X7R)/extracellular signal-regulated kinase (ERK) signaling in the anti-nociceptive effect of dexmedetomidine in a rat model of neuropathic pain induced by chronic constriction injury (CCI) of the sciatic nerve. An animal model of CCI was adopted to mimic the clinical neuropathic pain state. Behavioral hypersensitivity to mechanical and thermal stimuli was determined by von Frey filament and Hargreaves' tests, and the spinal P2X7R expression level and ERK phosphorylation were analyzed using western blot analysis and immunohistochemistry. In parallel with the development of mechanical and thermal hyperalgesia, a significant increase in P2X7R expression was noted in the ipsilateral spinal cord on day 7 after CCI. Intrathecal administration of dexmedetomidine (2.5 µg) for 3 days not only attenuated neuropathic pain but also inhibited the CCI-induced P2X7R upregulation and ERK phosphorylation. Intrathecal dexmedetomidine administration did not produce obvious effects on locomotor function. The present study demonstrated that dexmedetomidine attenuates the neuropathic pain induced by CCI of the sciatic nerve in rats by inhibiting spinal P2X7R expression and ERK phosphorylation, indicating the potential therapeutic implications of dexmedetomidine administration for the treatment of neuropathic pain.

Alkali Burn Induced Corneal Spontaneous Pain and Activated Neuropathic Pain Matrix in the Central Nervous System in Mice

PURPOSE

To explore whether alkali burn causes corneal neuropathic pain and activates the neuropathic pain matrix in the central nervous system in mice.

METHODS

A corneal alkali burn mouse model (grade II) was used. The mechanical threshold in the cauterized area was tested using Von Frey hairs. Spontaneous pain behavior was investigated with conditioned place preference. Phosphor extracellular signal-regulated kinase (ERK), which is a marker for neuronal activation in chronic pain processing, was investigated in several representative areas of the neuropathic pain matrix: the 2 regions of the spinal trigeminal nucleus (subnucleus interpolaris/caudalis, Vi/Vc; subnucleus caudalis/upper cervical cord, Vc/C1), insular cortex, anterior cingulated cortex (ACC), and the rostroventral medulla (RVM). Furthermore, pharmacologically blocking pERK activation in the ACC of alkali burn mice was performed in a separate study.

RESULTS

Corneal alkali burn caused long-lasting damage to the corneal subbasal nerve fibers, and mice exhibited spontaneous pain behavior. By testing in several representative areas of the neuropathic pain matrix in the higher nervous system, phosphor ERK was significantly activated in Vc/C1, but not in Vi/Vc. Also, ERK was activated in the insular cortex, ACC, and RVM. Furthermore, pharmacologically blocking ERK activation in the ACC abolished alkali burn induced corneal spontaneous pain.

CONCLUSIONS

Alkali burn could cause corneal spontaneous pain and activate the neuropathic pain matrix in the central nervous system. Furthermore, activation of ERK in the ACC is required for alkali burn induced corneal spontaneous pain.

Antinociceptive effects of novel epibatidine analogs through activation of α4β2 nicotinic receptors

The study of α4β2 nicotinic receptors has provided new indications in the treatment of pain. Efforts have been made to explore new α4β2 nicotinic receptor agonists, including TC-2559, as antinociceptive drugs. In this study, we discovered a set of novel epibatidine analogs with strong binding affinities to the α4β2 nicotinic receptors. Among these compounds, C-159, C-163, and C-9515 attenuated formalin-induced nociceptive responses in mice; C-9515 caused the most potent analgesic effect, which was blocked by mecamylamine, a non-selective nicotinic receptor antagonist. Furthermore, C-9515 potently inhibited chronic constriction injury (CCI)-induced neuropathic pain in rats, which was sensitive to DHβE, a selective α4β2 subtype antagonist, indicating that its analgesic effect was mediated by the activation of the α4β2 nicotinic receptors. In conclusion, the epibatidine analog C-9515 was found to be a potent α4β2 nicotinic receptor agonist with potent analgesic function, which demonstrated potential for the further exploration of its druggability.

Neurobiological Correlates of Pain Avoidance-Like Behavior in Morphine-Dependent and Non-Dependent Rats

Repeated use of opioids can lead to the development of analgesic tolerance and dependence. Additionally, chronic opioid exposure can cause a paradoxical emergence of heightened pain sensitivity to noxious stimuli, termed hyperalgesia, which may drive continued or escalated use of opioids to manage worsening pain symptoms. Opioid-induced hyperalgesia has traditionally been measured in rodents via reflex-based assays, including the von Frey method. To better model the cognitive/motivational dimension of pain in a state of opioid dependence and withdrawal, we employed a recently developed non-reflex-based method for measuring pain avoidance-like behavior in animals (mechanical conflict avoidance test). Adult male Wistar rats were administered an escalating dose regimen of morphine (opioid-dependent group) or repeated saline (control group). Morphine-dependent rats exhibited significantly greater avoidance of noxious stimuli during withdrawal. We next investigated individual relationships between pain avoidance-like behavior and alterations in protein phosphorylation in central motivation-related brain areas. We discovered that pain avoidance-like behavior was significantly correlated with alterations in phosphorylation status of protein kinases (ERK, CaMKII), transcription factors (CREB), presynaptic markers of neurotransmitter release (Synapsin), and the rate-limiting enzyme for dopamine synthesis (TH) across specific brain regions. Our findings suggest that alterations in phosphorylation events in specific brain centers may support cognitive/motivational responses to avoid pain.

MEK/ERK- and calcineurin/NFAT-mediated mechanism of cerebral hyperemia and brain injury following NMDA receptor activation

N-methyl-d-aspartate (NMDA) receptor activation increases regional cerebral blood flow (rCBF) and induces neuronal injury, but similarities between these processes are poorly understood. In this study, by measuring rCBF in vivo, we identified a clear correlation between cerebral hyperemia and brain injury. NMDA receptor activation induced brain injury as a result of rCBF increase, which was attenuated by an inhibitor of mitogen-activated protein kinase or calcineurin. Moreover, NMDA induced phosphorylation of extracellular signal-regulated kinase (ERK) and nuclear translocation of nuclear factor of activated T-cell (NFAT) in neurons. Therefore, a MEK/ERK- and calcineurin/NFAT-mediated mechanism of neurovascular coupling underlies the pathophysiology of neurovascular disorders.

Sinomenine attenuates chronic inflammatory pain in mice

Sinomenine, an alkaloid originally isolated from the roots of Sinomeniumacutum, is used as a traditional Chinese medicine for rheumatic arthritis. However, little is known about the neuronal mechanisms underlying the analgesic effects of sinomenine in animals with chronic inflammatory pain. In this study, we investigated the persistent inflammatory pain induced by hind paw injection of complete Freund's adjuvant (CFA) in mice, which was reversed by sinomenine administration. In the anterior cingulate cortex (ACC), a region highly associated with chronic pain processing, the upregulation of GluN2B-containing N-methyl-D-aspartate (NMDA) receptors and Ca²⁺/calmodulin-dependent protein kinase II, total levels of GluA1, and phosphorylation of GluA1 at Ser831 (p-GluA1-Ser831) were reversed by systemically administrating sinomenine. Furthermore, sinomenine treatment downregulated the mammalian target of rapamycin (mTOR) pathway. Increases in p-mTOR, p-p70S6k, p-S6, and p-4EBP, which were induced by chronic inflammation, were all changed. However, sinomenine did not affect the levels of GluN2A-containing NMDA receptors and p-GluA1-Ser845, as well as the total levels of mTOR, p70S6k, S6, and 4EBP. In conclusion, results indicated that sinomenine reduced the chronic inflammatory pain induced by CFA, at least partially by regulating the GluN2B receptors and mTOR signals in the ACC.