Synaptic Plasticity in the Pain-Related Cingulate and Insular Cortex

Inhibitory gamma-aminobutyric acidergic neurons in the anterior cingulate cortex participate in the comorbidity of pain and emotion

Pain is often comorbid with emotional disorders such as anxiety and depression. Hyperexcitability of the anterior cingulate cortex has been implicated in pain and pain-related negative emotions that arise from impairments in inhibitory gamma-aminobutyric acid neurotransmission. This review primarily aims to outline the main circuitry (including the input and output connectivity) of the anterior cingulate cortex and classification and functions of different gamma-aminobutyric acidergic neurons; it also describes the neurotransmitters/neuromodulators affecting these neurons, their intercommunication with other neurons, and their importance in mental comorbidities associated with chronic pain disorders. Improving understanding on their role in pain-related mental comorbidities may facilitate the development of more effective treatments for these conditions. However, the mechanisms that regulate gamma-aminobutyric acidergic systems remain elusive. It is also unclear as to whether the mechanisms are presynaptic or postsynaptic. Further exploration of the complexities of this system may reveal new pathways for research and drug development.

Cortical Potentiation in Chronic Neuropathic Pain and the Future Treatment

Pain, or the ability to feel pain and express the unpleasantness caused by peripheral injuries, are functions of the central nervous system. From peripheral sensory nerve terminals to certain cortical regions of the brain, activation of related neural networks underlies the sensory process. Recently, our knowledge of pain has been increasing dramatically, due to the advancement of scientific approaches. We no longer see the brain as a random matrix for pain but, rather, we are able to identify the step-by-step selective signaling proteins, neurons, and networks that preferentially contribute to the process of chronic pain and its related negative emotions, like anxiety and fear. However, there is still lacking the selective and effective drugs and methods for the treatment of chronic pain clinically. While first-line drugs for acute pain and mental diseases are also applied for the clinical management of chronic pain, their prolonged usage always causes serious side effects. In this short review, we will update and summarize the recent progress in this field and mainly focus on the roles of neural networks and synaptic mechanisms in chronic neuropathic pain. Furthermore, potential drug targets (such as plasticity-related signaling molecules, ionic channels, cytokines, and neuropeptides) and methods for the management of chronic neuropathic pain will be discussed as well. We hope this review can provide new, valuable insight into the treatment of chronic neuropathic pain.

Decoding the mechanism of proanthocyanidins in central analgesia: redox regulation and KCNK3 blockade

Neuropathic pain causes enduring physical discomfort and emotional distress. Conventional pharmacological treatments often provide restricted relief and may result in undesirable side effects, posing a substantial clinical challenge. Peripheral and spinal redox homeostasis plays an important role in pain processing and perception. However, the roles of oxidative stress and antioxidants in pain and analgesia on the cortical region during chronic pain remains obscure. Here we focus on the ventrolateral orbital cortex (VLO), a brain region associated with pain severity and involved in pain inhibition. Using a spared nerve injury mouse model, we observed the notable reactive oxygen species (ROS)-mediated suppression of the excitability of pyramidal cells (PYRVLO) in the VLO. Nasal application or microinjection of the natural antioxidants proanthocyanidins (PACs) to the VLO specifically increased the activity of PYRVLO and induced a significant analgesic effect. Mechanistically, PACs activate PYRVLO by inhibiting distinct potassium channels in different ways: (1) by scavenging ROS to reduce ROS-sensitive voltage-gated potassium currents and (2) by acting as a channel blocker through direct binding to the cap structure of KCNK3 to inhibit the leak potassium current (Ileak). These results reveal the role of cortical oxidative stress in central hyperalgesia and elucidate the mechanism and potential translational significance of PACs in central analgesia. These findings suggest that the effects of PACs extend beyond their commonly assumed antioxidant or anti-inflammatory effects.

Dualism, Materialism, and the relationship between the brain and the mind in experiencing pain

Characterizing the relationship between the brain and the mind is essential, both for understanding how we experience sensations and for attempts to create machine-based artificial intelligence. Materialists argue that the brain and the mind are both physical/material in nature whereas Cartesian dualists posit that the brain is material, the mind is non-material, and that they are separate. Recent investigations into the mechanisms responsible for pain can resolve this issue. Pain from an injury requires both the induction of a long-term potentiation (LTP) in a subset of pyramidal neurons in the anterior cingulate cortex and the creation of electromagnetic waves in the surrounding area. The LTP sensitizes synaptic transmission and, by activating enzyme cascades, changes the phenotype of the pyramidal neurons. The changes sustain the generation of the waves and the pain. The waves rapidly disseminate information about the pain to distant areas of the brain and studies using Transcranial Stimulation show that EM waves can influence the induction of LTP. According to leading contemporary theories, the waves will communicate with the mind, which is where the painfulness is experienced. The material brain and immaterial mind are therefore separate and we can no longer attribute painfulness solely to the activities of the brain. This is a radical departure from the contemporary view of brain functions and supports Cartesian Dualism. Consequently, consciousness and higher mental functions cannot be duplicated by mimicking the activities of the brain.

Pyrazolo-Pyrimidinones with Improved Solubility and Selective Inhibition of Adenylyl Cyclase Type 1 Activity for Treatment of Inflammatory Pain

Adenylyl cyclase isoform 1 (AC1) is considered a promising target for treating inflammatory pain. Our group identified the pyrazolyl-pyrimidinone scaffold as potent and selective inhibitors of Ca2+/CaM-mediated AC1 activity; however, the molecules suffered from poor aqueous solubility. The current study presents a strategy to improve aqueous solubility of the scaffold by reduction of crystal packing energy and increasing rotational degrees of freedom within the molecule. Structure-activity and property relationship studies identified the second generation lead 7-47A (AC10142A) that demonstrated and AC1 IC50 value of 0.26 μM and aqueous solubility of 74 ± 7 μM. After in vitro ADME characterization, the scaffold advanced to in vivo pharmacokinetic evaluation, demonstrating adequate levels of exposure. Finally, 7-47A exhibited antiallodynic efficacy in a rat complete Freund's adjuvant model for inflammatory pain showing improvement over previous iterations of this scaffold. These results further validate AC1 inhibition as a viable therapeutic strategy for treating chronic and inflammatory pain.

Electroacupuncture inhibited carrageenan-induced pain aversion by activating GABAergic neurons in the ACC

Pain aversion is an avoidance response to painful stimuli. Previous research has indicated that the anterior cingulate cortex (ACC) is involved in pain aversion processing. However, as interneurons, the role of GABAergic neurons in the ACC (GABAACC neurons) in pain aversion is still unclear. Electroacupuncture (EA) has been shown to ameliorate pain aversion, but the mechanism is not clarified. The present study provided evidence that inhibition of GABAACC neurons contributed to pain aversion. EA alleviated pain aversion by activating GABAACC neurons in an intensity-dependent manner. Specifically, 0.3 mA EA stimulation showed better effects on pain aversion than 0.1 mA stimulation, which could be reversed by chemical genetic inhibition of GABAACC neurons. These results provide a novel mechanism by which EA alleviates pain aversion by reversing GABAACC neurons.

Synaptic sensitization in the anterior cingulate cortex sustains the consciousness of pain via synchronized oscillating electromagnetic waves

A recent report showed that experiencing pain requires not only activities in the brain, but also the generation of electric fields in a defined area of the anterior cingulate cortex (ACC). The present manuscript presents evidence that electromagnetic (EM) waves are also necessary. Action potentials (APs) encoding information about an injury stimulate thousands synapses on pyramidal neurons within the ACC resulting in the generation of synchronized oscillating (EM) waves and the activation of NMDA receptors. The latter induces a long-term potentiation (LTP) in the pyramidal dendrites that is necessary to experience both neuropathic and visceral pain. The LTP sensitizes transmission across the synapses that sustains the duration of the waves and the pain, EM waves containing information about the injury travel throughout the brain and studies using transcranial stimulation indicate that they can induce NMDA-mediated LTP in distant neuronal circuits. What is ultimately experienced as pain depends on the almost instantaneous integration of information from numerous neuronal centers, such as the amygdala, that are widely separated in the brain. These centers also generate EM waves and I propose that the EM waves from these centers interact to rapidly adjust the intensity of the pain to accommodate past and present circumstances. Where the waves are transformed into a consciousness of pain is unknown. One possibility is the mind which, according to contemporary theories, is where conscious experiences arise. The hypothesis can be tested directly by blocking the waves from the ACC. If correct, the waves would open new avenues of research into the relationship between the brain, consciousness, and the mind.

Astrocyte Activation in the ACC Contributes to Comorbid Anxiety in Chronic Inflammatory Pain and Involves in The Excitation-Inhibition Imbalance

Neurons within the anterior cingulate cortex (ACC) orchestrate the co-occurrence of chronic pain and anxiety. The ACC hyperactivity plays a crucial role in the emotional impact of neuropathic pain. Astrocyte-mediated neuroinflammatory is responsible for regulating the balance between excitation-inhibition (E/I) in the brain. However, there is limited understanding of the possible contributions of astrocytes in the ACC to comorbidity of anxiety and chronic inflammatory pain. This paper aims to investigate the possible contribution of astrocytes in the ACC to the comorbidity between anxiety and chronic inflammatory pain, as well as their involvement in the E/I imbalance of pyramidal cells. Our results show that CFA rats displayed allodynia and anxiety-like behaviors. The E/I balance in the ACC shifts to excitement in comorbidity of chronic pain and anxiety by western blotting, and electrophysiological recording. Result of RNA-Seq also indicated that E/I imbalance and neuroinflammation of ACC were involved in pain-anxiety comorbidity. Then, positive cells of GFAP but not Iba1 in the contralateral ACC were increased; the mRNA expression of GFAP and its activation-related proinflammatory cytokines (TNF-α, IL-6, and IL-1β) in the contralateral ACC were also elevated. Furthermore, specific chemogenic inhibition of ACC astrocytes reversed comorbid pain and anxiety and suppressed high ACC excitability. Our data suggest that astrocytes participate in comorbid pain and anxiety and excitation-inhibition imbalance in ACC. Inhibition astrocyte activation can reduce anxiety related to pain and restore the imbalance in the ACC. These findings shed light on the involvement of astrocytes in comorbid conditions, offering valuable insights into a potential therapeutic approach for the co-occurrence of chronic pain and anxiety.

Involvement of the cingulate cortex and insula in patients with trigeminal neuralgia: A clinical and volumetric study

AIM

Advanced neuroimaging strategies may provide new insights into the underlying mechanisms of trigeminal neuralgia (TN). The objective of this study is to measure central pain centers in patients with long-standing trigeminal neuralgia and compare them to those of normal individuals. The findings of this study could improve the understanding of central region changes related to pain and improve the diagnosis and management of chronic trigeminal pain.

MATERIAL AND METHODS

We examined radiologic data from 20 patients with trigeminal neuralgia and 28 healthy controls who underwent 3D iso T1-weighted brain MRI at our university hospital between 2018 and 2023. Patients with a minimum pain duration of 5 years were included and compared with healthy controls. Additionally, patients were categorized into groups based on the presence of vascular compression. The pain-related subcortical structures, such as the cingulate cortex and insula, were analyzed volumetrically using volBrain software. The results were evaluated statistically.

RESULTS

Significant differences were observed in the measurement of the posterior insula (p = 0.014) when comparing patients with trigeminal neuralgia and healthy subjects. Additionally, group comparisons based on the presence of vascular compression revealed significant differences in the Middle Cingulate Cortex (0.036) and Posterior Cingulate Cortex (0.031) between groups, which may be related to the etiological factor.

CONCLUSION

Understanding changes in central regions related to pain can aid in the diagnosis and management of chronic trigeminal pain.

Investigating the brain functional abnormalities underlying pain hypervigilance in chronic neck and shoulder pain: a resting-state fMRI study

PURPOSE

To investigate pain hypervigilance in individuals suffering from chronic neck and shoulder pain (CNSP) and its underlying brain mechanism.

METHODS

The evaluation of pain vigilance was conducted through the utilization of pain vigilance and awareness questionnaires. Voxel-wise regional homogeneity (ReHo) from 60 CNSP patients and 60 healthy controls (HCs) using resting-state fMRI data. Voxel-wise two-sample T-test was conducted to reveal the ReHo variations between CNSP and HC. Correlation analyses were utilized to reveal the connection between brain abnormalities and medical measurements. Furthermore, a mediation analysis was conducted to elucidate the pathway-linking changes in brain function with medical measurements.

RESULTS

Our present study revealed three main findings. Firstly, patients with CSNP demonstrated a heightened vigilance of pain in comparison to healthy adults, a common occurrence among individuals with chronic pain conditions. Secondly, we observed brain abnormalities in various brain regions in CSNP patients, and these alterations were associated with the extent of pain vigilance. Lastly, the pain hypervigilance impact on the severity of pain was found to be controlled by regional neural activity in the anterior cingulate cortex (ACC) in subjects with CSNP.

CONCLUSION

Our findings suggested that long-term repetitive nociceptive input caused by chronic pain further aggravates the pain intensity by impairing the vigilance-related pain processing within the anterior cingulate cortex in CNSP patients.

Disrupted Resting-State Functional Connectivity and Effective Connectivity of the Nucleus Accumbens in Chronic Low Back Pain: A Cross-Sectional Study

Purpose

Chronic low back pain (cLBP) is a recurring and intractable disease that is often accompanied by emotional and cognitive disorders such as depression and anxiety. The nucleus accumbens (NAc) plays an important role in mediating emotional and cognitive processes and analgesia. This study investigated the resting-state functional connectivity (rsFC) and effective connectivity (EC) of NAc and its subregions in cLBP.

Methods

Thirty-four cLBP patients and 34 age- and sex-matched healthy controls (HC) underwent resting-state functional magnetic resonance imaging (rs-fMRI). Seed-based rsFC and Dynamic Causal Modelling (DCM) were used to examine the alteration of the rsFC and EC of the NAc.

Results

Our results showed that the cLBP group had increased rsFC of the bilateral NAc-left superior frontal cortex (SFC), orbital frontal cortex (OFC), left angular gyrus, the left NAc-bilateral middle temporal gyrus, as well as decreased rsFC of left NAc-left supramarginal gyrus, right precentral gyrus, left cerebellum, brainstem (medulla oblongata), and right insula pathways compared with the HC; the results of the subregions were largely consistent with the whole NAc. In addition, the rsFC of the left NAc-left SFC was negatively correlated with Hamilton's Depression Scale (HAMD) scores (r = -0.402, p = 0.018), and the rsFC of left NAc-OFC was positively correlated with present pain intensity scores (r = 0.406, p = 0.017) in the cLBP group. DCM showed that the cLBP group showed significantly increased EC from the left cerebellum to the right NAc (p = 0.012) as compared with HC.

Conclusion

Overall, our findings demonstrate aberrant rsFC and EC between NAc and regions that are associated with emotional regulation and cognitive processing in individuals with cLBP, underscoring the pivotal roles of emotion and cognition in cLBP.

Neural circuits regulating visceral pain

Visceral hypersensitivity, a common clinical manifestation of irritable bowel syndrome, may contribute to the development of chronic visceral pain, which is a major challenge for both patients and health providers. Neural circuits in the brain encode, store, and transfer pain information across brain regions. In this review, we focus on the anterior cingulate cortex and paraventricular nucleus of the hypothalamus to highlight the progress in identifying the neural circuits involved in visceral pain. We also discuss several neural circuit mechanisms and emphasize the importance of cross-species, multiangle approaches and the identification of specific neurons in determining the neural circuits that control visceral pain.

Astrocyte activation in hindlimb somatosensory cortex contributes to electroacupuncture analgesia in acid-induced pain

Background

Several studies have confirmed the direct relationship between extracellular acidification and the occurrence of pain. As an effective pain management approach, the mechanism of electroacupuncture (EA) treatment of acidification-induced pain is not fully understood. The purpose of this study was to assess the analgesic effect of EA in this type of pain and to explore the underlying mechanism(s).

Methods

We used plantar injection of the acidified phosphate-buffered saline (PBS; pH 6.0) to trigger thermal hyperalgesia in male Sprague-Dawley (SD) rats aged 6-8 weeks. The value of thermal withdrawal latency (TWL) was quantified after applying EA stimulation to the ST36 acupoint and/or chemogenetic control of astrocytes in the hindlimb somatosensory cortex.

Results

Both EA and chemogenetic astrocyte activation suppressed the acid-induced thermal hyperalgesia in the rat paw, whereas inhibition of astrocyte activation did not influence the hyperalgesia. At the same time, EA-induced analgesia was blocked by chemogenetic inhibition of astrocytes.

Conclusion

The present results suggest that EA-activated astrocytes in the hindlimb somatosensory cortex exert an analgesic effect on acid-induced pain, although these astrocytes might only moderately regulate acid-induced pain in the absence of EA. Our results imply a novel mode of action of astrocytes involved in EA analgesia.

Acupuncture for radicular pain: a review of analgesic mechanism

Radicular pain, a common and complex form of neuropathic pain, presents significant challenges in treatment. Acupuncture, a therapy originating from ancient traditional Chinese medicine and widely utilized for various pain types, including radicular pain, has shown promising outcomes in the management of lumbar radicular pain, cervical radicular pain, and radicular pain due to spinal stenosis. Despite its efficacy, the exact mechanisms through which acupuncture achieves analgesia are not fully elucidated and are the subject of ongoing research. This review sheds light on the current understanding of the analgesic mechanisms of acupuncture for radicular pain, offering valuable perspectives for both clinical application and basic scientific research. Acupuncture is postulated to relieve radicular pain by several mechanisms: peripherally, it reduces muscle spasms, lessens mechanical pressure on nerve roots, and improves microcirculation; at the molecular level, it inhibits the HMGB1/RAGE and TLR4/NF-κB signaling pathways, thereby decreasing the release of pro-inflammatory cytokines; within the spinal cord, it influences synaptic plasticity; and centrally, it modulates brain function, particularly affecting the medial prefrontal cortex, anterior cingulate cortex, and thalamus within the default mode network. By acting across these diverse biological domains, acupuncture presents an effective treatment modality for radicular pain, and deepening our understanding of the underlying mechanisms regarding analgesia for radicular pain is crucial for enhancing its clinical efficacy and advancement in pain management.

Motor Dysfunctions in Fibromyalgia Patients: The Importance of Breathing

The classification of fibromyalgia (FM) is not always immediate and simple, with the time from the first diagnosis, compared to the onset of symptoms, of a few years. Currently, we do not have instrumental or biochemical tests considered as gold standards; the clinician will make a diagnosis of FM based on the patient's medical history and subjective assessment. The symptoms can involve physical, cognitive and psychological disorders, with the presence of pain of different origins and classifications: nociplastic, nociceptive and neuropathic pain. Among the symptoms highlighted, postural disorders and neuromotor uncoordination emerge, whose functional dysfunctions can increase the mortality and morbidity rate. An alteration of the diaphragm muscle could generate such functional motor problems. Considering that the current literature underestimates the importance of breathing in FM, the article aims to highlight the relationship between motor and diaphragmatic difficulties in the patient, soliciting new points of view for the clinical and therapeutic framework.

Sex differences in visceral sensitivity and brain activity in a rat model of comorbid pain: a longitudinal study

ABSTRACT

Temporomandibular disorder (TMD) and irritable bowel syndrome (IBS) are 2 chronic overlapping pain conditions (COPCs) that present with significant comorbidity. Both conditions are more prevalent in women and are exacerbated by stress. While peripheral mechanisms might contribute to pain hypersensitivity for each individual condition, mechanisms underlying the comorbidity are poorly understood, complicating pain management when multiple conditions are involved. In this study, longitudinal behavioral and functional MRI-based brain changes have been identified in an animal model of TMD-like pain (masseter muscle inflammation followed by stress) that induces de novo IBS-like comorbid visceral pain hypersensitivity in rats. In particular, data indicate that increased activity in the insula and regions of the reward and limbic systems are associated with more pronounced and longer-lasting visceral pain behaviors in female rats, while the faster pain resolution in male rats may be due to increased activity in descending pain inhibitory pathways. These findings suggest the critical role of brain mechanisms in chronic pain conditions and that sex may be a risk factor of developing COPCs.

Recent advances in the understanding and management of chronic pancreatitis pain

Abdominal pain is the most common symptom of chronic pancreatitis (CP) and is often debilitating for patients and very difficult to treat. To date, there exists no cure for the disease. Treatment strategies focus on symptom management and on mitigation of disease progression by reducing toxin exposure and avoiding recurrent inflammatory events. Traditional treatment protocols start with medical management followed by consideration of procedural or surgical intervention on selected patients with severe and persistent pain. The incorporation of adjuvant therapies to treat comorbidities including psychiatric disorders, exocrine pancreatic insufficiency, mineral bone disease, frailty, and malnutrition, are in its early stages. Recent clinical studies and animal models have been designed to improve investigation into the pathophysiology of CP pain, as well as to improve pain management. Despite the array of tools available, many therapeutic options for the management of CP pain provide incomplete relief. There still remains much to discover about the neural regulation of pancreas-related pain. In this review, we will discuss research from the last 5 years that has provided new insights into novel methods of pain phenotyping and the pathophysiology of CP pain. These discoveries have led to improvements in patient selection for optimization of outcomes for both medical and procedural management, and identification of potential future therapies.

Structural and functional changes of anterior cingulate cortex subregions in migraine without aura: relationships with pain sensation and pain emotion

Migraine without aura is a multidimensional neurological disorder characterized by sensory, emotional, and cognitive symptoms linked to structural and functional abnormalities in the anterior cingulate cortex. Anterior cingulate cortex subregions play differential roles in the clinical symptoms of migraine without aura; however, the specific patterns and mechanisms remain unclear. In this study, voxel-based morphometry and seed-based functional connectivity were used to investigate structural and functional alterations in the anterior cingulate cortex subdivisions in 50 patients with migraine without aura and 50 matched healthy controls. Compared with healthy controls, patients exhibited (1) decreased gray matter volume in the subgenual anterior cingulate cortex, (2) increased functional connectivity between the bilateral subgenual anterior cingulate cortex and right middle frontal gyrus, and between the posterior part of anterior cingulate cortex and right middle frontal gyrus, orbital part, and (3) decreased functional connectivity between the anterior cingulate cortex and left anterior cingulate and paracingulate gyri. Notably, left subgenual anterior cingulate cortex was correlated with the duration of each attack, whereas the right subgenual anterior cingulate cortex was associated with migraine-specific quality-of-life questionnaire (emotion) and self-rating anxiety scale scores. Our findings provide new evidence supporting the hypothesis of abnormal anterior cingulate cortex subcircuitry, revealing structural and functional abnormalities in its subregions and emphasizing the potential involvement of the left subgenual anterior cingulate cortex-related pain sensation subcircuit and right subgenual anterior cingulate cortex -related pain emotion subcircuit in migraine.

Photic sensitization is mediated by cortico-accumbens pathway in rats with trigeminal neuropathic pain

Exposure to light stimuli may trigger or exacerbate perception of pain, also known as a common yet debilitating symptom of photophobia in patient with chronic orofacial pain. Mechanism underlying this phenomenon of photic sensitization in neuropathic condition remains elusive. Here, we found that rats developed hypersensitivity to normal light illumination after establishment of chronic constriction injury of infraorbital nerve (ION-CCI) model, which can be attenuated by blocking the exposure of photic stimulation. Additionally, this behavioral phenotype of light-sensitivity impairment was associated with overexpression of anterior cingulate cortex (ACC) c-fos positive neurons, enhancement of neural excitability in the ACC neurons and its excitatory synaptic transmission between nucleus accumbens (NAc). Optogenetic and chemogenic silencing of ACC-NAc pathway improved trigeminal sensitization in responses to light stimuli by decreasing spontaneous pain-like episodes in ION-CCI animals. In contrast, selective activation of ACC-to-NAc circuits enhanced photic hypersensitivity in dark environment. Thus, our data provided novel role of ACC and its projection to NAc in bidirectional modulation of photic sensation, which may contribute to the understanding of photic allodynia in trigeminal neuropathic pain status.

Aberrant functional and causal connectivity of the amygdala in herpes zoster and post-herpetic neuralgia patients

OBJECTIVE

Resting-state functional magnetic resonance imaging (rs-fMRI) and Granger causality analysis (GCA) were used to observe the characteristics of amygdala and whole-brain effect connections in patients with herpes zoster (HZ) and post-herpetic neuralgia (PHN) and to determine their relationship with clinical features.

METHODS

Rs-fMRI scans were performed on 50 HZ; 50 PHN; and 50 age-, sex- and education-year-matched healthy controls (HCs). Bilateral amygdala subregions were used as seeds for functional connectivity (FC). GCA was used to analyze the effective connection of brain regions that were significantly different among groups. Then, the correlation between FC, and GCA values and clinical indices was investigated.

RESULTS

PHN had impaired FC between the amygdala subregion with the putamen, cortex, anterior cingulate cortex (ACC) to HCs and reduced FC of medial amygdala (MeA) with the parieto-occipital lobe and motor cortex to HZ; HZ had reduced FC of the lateral amygdala (LA) with the insula to HCs. GCA values from the bilateral LA to the bilateral ACC, left MeA to the bilateral ACC and left putamen, and right ACC to the bilateral MeA were reduced in PHN patients compared to HCs. Compared with HCs, the GCA values from the left MeA to the left ACC and right putamen were reduced in HZ. The GCA values from the amygdala subregion to the ACC were positively correlated with HAMA or HAMD scores in PHN.

CONCLUSION

PHN showed reduced FC between the amygdala subregions and cortico-putamen and decreased effective connectivity from the amygdala subregion to the ACC and putamen.

ADVANCES IN KNOWLEDGE

HZ and PHN patients had significant changes in effective connectivity in brain regions, including diverse functional areas emanating from and projecting to the amygdala. The current findings will provide a new perspective for understanding the neuropathophysiological mechanism HZ and PHN.

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.

Massive body-brain disconnection consequent to spinal cord injuries drives profound changes in higher-order cognitive and emotional functions: A PRISMA scoping review

Spinal cord injury (SCI) leads to a massive disconnection between the brain and the body parts below the lesion level representing a unique opportunity to explore how the body influences a person's mental life. We performed a systematic scoping review of 59 studies on higher-order cognitive and emotional changes after SCI. The results suggest that fluid abilities (e.g. attention, executive functions) and emotional regulation (e.g. emotional reactivity and discrimination) are impaired in people with SCI, with progressive deterioration over time. Although not systematically explored, the factors that are directly (e.g. the severity and level of the lesion) and indirectly associated (e.g. blood pressure, sleeping disorders, medication) with the damage may play a role in these deficits. The inconsistency which was found in the results may derive from the various methods used and the heterogeneity of samples (i.e. the lesion completeness, the time interval since lesion onset). Future studies which are specifically controlled for methods, clinical and socio-cultural dimensions are needed to better understand the role of the body in cognition.

Proanthocyanidins induce analgesic and anxiolytic effects in spared nerve injured mice by decreasing in vivo firing rate of pyramidal cells in the insular cortex

Neuropathic pain is one of the most common symptoms of clinical pain that often accompanied by severe emotional changes such as anxiety. However, the treatment for comorbidity of chronic pain and anxiety is limited. Proanthocyanidins (PACs), a group of polyphenols enriched in plants and foods, have been reported to cause pain-alleviating effects. However, whether and how PACs induce analgesic and anxiolytic effects in the central nervous system remain obscure. In the present study, we observed that microinjection of PACs into the insular cortex (IC) inhibited mechanical and spontaneous pain sensitivity and anxiety-like behaviors in mice with spared nerve injury. Meanwhile, PACs application exclusively reduced the FOS expression in the pyramidal cells but not interneurons in the IC. In vivo electrophysiological recording of the IC further showed that PACS application inhibited the firing rate of spikes of pyramidal cells of IC in neuropathic pain mice. In summary, PACs induce analgesic and anxiolytic effects by inhibiting the spiking of pyramidal cells of the IC in mice with neuropathic pain, which should provide new evidence of PACs as the potential clinical treatment of chronic pain and anxiety comorbidity.

Environmental enrichment promotes resilience to neuropathic pain-induced depression and correlates with decreased excitability of the anterior cingulate cortex

Depression is a common comorbidity of chronic pain with many patients being affected. However, efficient pharmacological treatment strategies are still lacking. Therefore, it is desirable to find additional alternative approaches. Environmental enrichment has been suggested as a method to alleviate pain-induced depression. However, the neuronal mechanisms of its beneficial effects are still elusive. The anterior cingulate cortex (ACC) plays a central role in processing pain-related negative affect and chronic pain-induced plasticity in this region correlates with depressive symptoms. We studied the consequences of different durations of environmental enrichment on pain sensitivity and chronic pain-induced depression-like behaviors in a mouse model of neuropathic pain. Furthermore, we correlated the behavioral outcomes to the activity levels of pyramidal neurons in the ACC by analyzing their electrophysiological properties ex vivo. We found that early exposure to an enriched environment alone was not sufficient to cause resilience against pain-induced depression-like symptoms. However, extending the enrichment after the injury prevented the development of depression and reduced mechanical hypersensitivity. On the cellular level, increased neuronal excitability was associated with the depressive phenotype that was reversed by the enrichment. Therefore, neuronal excitability in the ACC was inversely correlated to the extended enrichment-induced resilience to depression. These results suggest that the improvement of environmental factors enhanced the resilience to developing chronic pain-related depression. Additionally, we confirmed the association between increased neuronal excitability in the ACC and depression-like states. Therefore, this non-pharmacological intervention could serve as a potential treatment strategy for comorbid symptoms of chronic pain.

Sophoridine alleviates hyperalgesia and anxiety-like behavior in an inflammatory pain mouse model induced by complete freund's adjuvant

Chronic pain, along with comorbid psychiatric disorders, is a common problem worldwide. A growing number of studies have focused on non-opioid-based medicines, and billions of funds have been put into digging new analgesic mechanisms. Peripheral inflammation is one of the critical causes of chronic pain, and drugs with anti-inflammatory effects usually alleviate pain hypersensitivity. Sophoridine (SRI), one of the most abundant alkaloids in Chinese herbs, has been proved to exert antitumor, antivirus and anti-inflammation effects. Here, we evaluated the analgesic effect of SRI in an inflammatory pain mouse model induced by complete Freund's adjuvant (CFA) injection. SRI treatment significantly decreased pro-inflammatory factors release after LPS stimuli in microglia. Three days of SRI treatment relieved CFA-induced mechanical hypersensitivity and anxiety-like behavior, and recovered abnormal neuroplasticity in the anterior cingulate cortex of mice. Therefore, SRI may be a candidate compound for the treatment of chronic inflammatory pain and may serve as a structural basis for the development of new drugs.