Dysfunction of Nucleus Accumbens Is Associated With Psychiatric Problems in Patients With Chronic Low Back Pain: A Functional Magnetic Resonance Imaging Study

Gray Matter Abnormalities in Patients with Chronic Low Back Pain: A Systematic Review and Meta-Analysis of Voxel-Based Morphometry Studies

BACKGROUND

Numerous studies utilizing voxel-based morphometry (VBM) have documented gray matter (GM) alterations in patients with chronic low back pain (CLBP) compared to healthy controls. However, the inconsistency in GM abnormalities observed across different studies has hindered their potential application as objective neuroimaging biomarkers or therapeutic targets. To address this issue, we conducted a comprehensive meta-analysis of VBM studies to identify robust GM differences between CLBP patients and healthy controls.

METHODS

The databases including PubMed, Embase, and Web of Science were systematically searched from January 2000 to September 2022 to identify eligible neuroimaging studies. In this coordinate-based meta-analysis of VBM studies, the Seed-based d Mapping with Permutation of Subject Images method was used to quantitatively assess regional differences in GM between CLBP patients and healthy controls.

RESULTS

Thirteen VBM studies, involving a total of 574 CLBP patients and 1239 healthy controls, were included in the meta-analysis. The findings revealed that CLBP patients exhibited increased GM in the left striatum and left postcentral gyrus and decreased GM in the left superior frontal gyrus, left cerebellum, right striatum, left insula, and right middle occipital gyrus compared to healthy controls. The jackknife sensitivity analysis confirmed the robustness of these neuroimaging findings.

CONCLUSIONS

This study provides new insights into potential treatment strategies for CLBP and identifies neuroimaging biomarkers for pain chronification. These findings highlight the importance of considering regional GM abnormalities in the development of clinical interventions for CLBP.

The Alterations in the Brain Corresponding to Low Back Pain: Recent Insights and Advances

Low back pain (LBP) is a leading cause of global disabilities. Numerous molecular, cellular, and anatomical factors are implicated in LBP. Current issues regarding neurologic alterations in LBP have focused on the reorganization of peripheral nerve and spinal cord, but neural mechanisms of exactly what LBP impacts on the brain required further researches. Based on existing clinical studies that chronic pain problems were accompanying alterations in brain structures and functions, researchers proposed logical conjectures that similar alterations occur in LBP patients as well. With recent extensive studies carried out using noninvasive neuroimaging technique, increasing number of abnormalities and alterations has been identified. Here, we reviewed brain alterations including white matters, grey matters, and neural circuits between brain areas, which are involved in chronic LBP. Moreover, brain structural and functional connectivity abnormalities are correlated to the happening and transition of LBP. The negative emotions related to back pain indicate possible alterations in emotional brain regions. Thus, the aim of this review is to summarize current findings on the alterations corresponding to LBP in the brain. It will not only further our understanding of etiology of LBP and understanding of negative emotions accompanying with back pain but also provide ideas and basis for new accesses to the diagnosis, treatment, and rehabilitation afterward based on integral medicine.

Assessing the impact of preferred web app-based music-listening on pain processing at the central nervous level in older black adults with low back pain: An fNIRS study

BACKGROUND

Low back pain (LBP) disproportionately affects older black adults, often leading to inadequate treatment due to clinician biases. Objective pain measures are imperative, and Functional Near-Infrared Spectroscopy (fNIRS) shows promise for pain detection.

AIM

To determine the impact of listening to home-based preferred web app-based music on underlying pain processing mechanisms at the central nervous level in older black adults aged ≥65 with LBP.

METHODS

Twenty older black adults with LBP listened to preferred music twice daily for four days using the MUSIC CARE® app. Neuroimaging data were collected using fNIRS. Data were transformed to changes in oxy-hemoglobin and deoxy-hemoglobin concentrations and analyzed.

RESULTS

Significant cortical activation pattern differences were observed between pre-and post-intervention scans, particularly in somatosensory regions. Post-intervention scans showed significantly reduced hemodynamic activities.

CONCLUSION

Preferred music listening has the potential to alleviate pain, and fNIRS emerges as a promising tool for exploring cortical-level pain-related neural circuits.

Chronic pain precedes disrupted eating behavior in low-back pain patients

Chronic pain is associated with anhedonia and decreased motivation. These behavioral alterations have been linked to alterations in the limbic brain and could explain the increased risk for obesity in pain patients. The mechanism of these behavioral changes and how they set in in relation to the development of chronic pain remain however poorly understood. Here we asked how eating behavior was affected in low-back pain patients before and after they transitioned to chronic pain, compared to patients whose pain subsided. Additionally, we assessed how the hedonic perception of fat-rich food, which is altered in chronic pain patients, related to the properties of the nucleus accumbens in this patients' population. We hypothesized that the accumbens would be directly implicated in the hedonic processing of fat-rich food in pain patients because of its well-established role in hedonic feeding and fat ingestion, and its emerging role in chronic pain. Accordingly, we used behavioral assays and structural brain imaging to test sub-acute back pain patients (SBP) and healthy control subjects at baseline and at approximately one-year follow-up. We also studied a sample of chronic low-back pain patients (CLBP) at one time point only. We found that SBP patients who recovered at follow-up (SBPr) and CLBP patients showed disrupted eating behaviors. In contrast, SBP patients who persisted in having pain at follow-up (SBPp) showed intact eating behavior. From a neurological standpoint, only SBPp and CLBP patients showed a strong and direct relationship between hedonic perception of fat-rich food and nucleus accumbens volume. This suggests that accumbens alterations observed in SBPp patients in previous works might protect them from hedonic eating disruptions during the early course of the illness. We conclude that disrupted eating behavior specifically sets in after pain chronification and is accompanied by structural changes in the nucleus accumbens.

Involvement between social defeat stress and pain-related behavior in a rat lumbar disk herniation model

INTRODUCTION

Psychological and social factors are involved in the disability and chronicity of pain. Our study aim was to investigate whether social defeat stress (SDS) as a psychophysical stress affected mechanical withdrawal thresholds in the lumbar disk herniation (LDH) rat model. Changes in microglia and astrocytes, which play important roles in neuropathic pain states, were also investigated.

MATERIALS AND METHODS

For the LDH model, nucleus pulposus (NP) was applied to the L5 dorsal root ganglion (DRG) in adult female Sprague-Dawley rats. SDS was performed 15 min daily for 8 days. Mechanical withdrawal thresholds were measured, and immunoreactive cells of glial fibrillary acidic protein (GFAP) and ionized calcium-binding adaptor molecule-1 (Iba-1), which were used as markers of microglia, satellite glial cells, and astrocytes, were assessed in the DRG, spinal cord (SC), and ventrolateral periaqueductal gray matter (VLPAG).

RESULTS

Mechanical withdrawal thresholds decreased in the NP group for 21 days and for 35 days in the NP + SDS group. Expression of GFAP and Iba-1 in the DRG and SC increased up to day 21 in the NP and NP + SDS groups. In the sham + SDS and NP + SDS groups, expression of GFAP in the VLPAG decreased until day 35.

CONCLUSION

SDS prolongs mechanical allodynia induced by NP. Changes of GFAP expression in the VLPAG were associated with mechanical allodynia of the NP + SDS group during the late phase. These results suggest that psychological chronic stress might delay recovery from mechanical allodynia induced by the LDH model.

Functional MRI Signature of Chronic Pain Relief From Deep Brain Stimulation in Parkinson Disease Patients

BACKGROUND

Chronic pain occurs in 83% of Parkinson disease (PD) patients and deep brain stimulation (DBS) has shown to result in pain relief in a subset of patients, though the mechanism is unclear.

OBJECTIVE

To compare functional magnetic resonance imaging (MRI) data in PD patients with chronic pain without DBS, those whose pain was relieved (PR) with DBS and those whose pain was not relieved (PNR) with DBS.

METHODS

Functional MRI (fMRI) with blood oxygen level-dependent activation data was obtained in 15 patients in control, PR, and PNR patients. fMRI was obtained in the presence and absence of a mechanical stimuli with DBS ON and DBS OFF. Voxel-wise analysis using pain OFF data was used to determine which regions were altered during pain ON periods.

RESULTS

At the time of MRI, pain was scored a 5.4 ± 1.2 out of 10 in the control, 4.25 ± 1.18 in PNR, and 0.8 ± 0.67 in PR cohorts. Group analysis of control and PNR groups showed primary somatosensory (SI) deactivation, whereas PR patients showed thalamic deactivation and SI activation. DBS resulted in more decreased activity in PR than PNR (P < .05) and more activity in anterior cingulate cortex (ACC) in PNR patients (P < .05).

CONCLUSION

Patients in the control and PNR groups showed SI deactivation at baseline in contrast to the PR patients who showed SI activation. With DBS ON, the PR cohort had less activity in SI, whereas the PNR had more anterior cingulate cortex activity. We provide pilot data that patients whose pain responds to DBS may have a different fMRI signature than those who do not, and PR and PNR cohorts produced different brain responses when DBS is employed.

Brain Activation in a Cynomolgus Macaque Model of Chymopapain-Induced Discogenic Low Back Pain: A Preliminary Study

Introduction

There is currently a lack of translatable, preclinical models of low back pain (LBP). Chymopapain, a proteolytic enzyme used to treat lumbar intervertebral disc (IVD) herniation, could induce discogenic LBP. The current study developed a behavioral model of discogenic LBP in nonhuman primates. Significant brain activation is observed in clinical LBP. Thus, the current study also sought to define brain activation over time in a macaque with discogenic LBP.

Methods

Responses to pressure applied to the back at L4/L5 were measured in eight adult male Macaca fasciculata using a pressure algometer. The nucleus pulpous of the IVD between L4 and L5 was aspirated and chymopapain (1 mg/mL) was injected under fluoroscopic guidance (n = 2). In two macaques, the nucleus pulpous was only aspirated. Brain activation in response to pressure applied to the lower back was assessed using a 3.0T magnetic resonance imaging scanner in four macaques before and 1, 3, 9, and 14 days after treatment.

Results

The mean (±SD) response pressure before treatment was 1.4 ± 0.1 kg. One day after chymopapain treatment, the response pressure decreased to 0.6 ± 0.05 kg (P < 0.01), suggestive of pressure hypersensitivity. Over time, the pressure thresholds following chymopapain treatment gradually returned to normal. Following aspiration only, the response pressure was 1.4 ± 0.05 kg, which was not significantly different from the uninjured controls. There was activation of the secondary somatosensory cortex and insular cortex one and three days after chymopapain treatment; there was no activation following aspiration only.

Conclusions

Enzymatic treatment of the nucleus pulpous leads to acute LBP and pressure-evoked activation in pain-related brain areas. The current model of discogenic LBP parallels clinical LBP and could be used to further elaborate the mechanism of acute LBP.

Effect and neurophysiological mechanism of acupuncture in patients with chronic sciatica: protocol for a randomized, patient-assessor blind, sham-controlled clinical trial

Background

Sciatica is a relatively frequent illness that easily becomes a chronic and relapsing condition. Although numerous systematic reviews have analyzed various therapies for sciatica, the validity of their included studies is limited. Considering the limitations of conventional treatment options for sciatica, acupuncture is a possible option; however, evidence supporting its efficacy and mechanism in patients with sciatica is lacking. The aim of this proposed protocol is to investigate the effect and neurophysiological mechanism of acupuncture in patients with chronic sciatica.

Methods/design

This study is a randomized, patient-assessor blind, two-arm, parallel, non-penetrating, sham-controlled clinical trial. Eligible participants will include adults (aged 19–70 years old) with a clinical diagnosis of chronic sciatica (40 mm or more of a 100-mm visual analog scale (VAS) for bothersomeness) blinded to the treatment received. Patients will be randomly allocated into the acupuncture treatment group (manual acupuncture plus electroacupuncture (EA), n = 34) or the sham acupuncture control group (sham acupuncture plus placebo EA without electrical stimulation, n = 34). Groups will receive treatment twice a week for a total of eight sessions over 4 weeks. Functional magnetic resonance imaging will be implemented at baseline and endpoint to investigate the mechanism of acupuncture. The primary outcome measure is the VAS for bothersomeness and secondary outcomes include the VAS for pain intensity, Oswestry Disability Index, EuroQol 5-Dimension, Coping Strategy Questionnaire, Beck’s Depression Inventory, and State-Trait Anxiety Inventory. Adverse events will be assessed at every visit.

Discussion

The results of this trial (which will be available in 2020) should provide important clinical evidence for the effect of acupuncture and demonstrate how acupuncture can be helpful for the treatment of chronic sciatica.

Trial registration

ClinicalTrials.gov, ID: NCT03350789. Registered on 15 November 2017.

Electronic supplementary material

The online version of this article (10.1186/s13063-018-3164-8) contains supplementary material, which is available to authorized users.

Suppressed descending pain modulatory and enhanced sensorimotor networks in patients with chronic low back pain

PURPOSE

Although cerebral structural and functional changes were uncovered by neuroimaging in patients with chronic low back pain (CLBP), their associations remain to be clarified. We co-analyzed anatomical and functional magnetic resonance imaging data in those patients and tested whether cortical gray matter volume changes are associated with altered pain modulatory networks underlying chronification of pain.

METHODS

In 16 patients with CLBP and 16 heathy controls, we performed functional magnetic resonance imaging during mechanical pain stimulation on the lower back followed by anatomical imaging. We performed voxel-based morphometry and functional connectivity analysis from the seeds with altered gray matter volume, and examined correlations between imaging and psychophysical parameters.

RESULTS

Patients showed decreases in gray matter volume at the right dorsolateral prefrontal cortex, middle occipital gyrus, and cerebellum, and showed increases at the bilateral primary sensorimotor cortices, left fusiform gyrus, and right cerebellum compared with controls (P < 0.001). Dorsolateral prefrontal and fusiform volumes showed negative associations with affective comorbidity, whereas motor cortex volume with impaired daily activity (P < 0.05). Connectivity was decreased between the cerebellar and limbic, and increased between the bilateral sensorimotor regions (P_FDR < 0.05). Higher pain intensity and unpleasantness correlated with enhanced bilateral sensorimotor and dorsolateral-medial prefrontal networks, respectively (P < 0.05).

CONCLUSION

Patients showed a decreased volume of cortical center for descending pain modulation and an increased volume of sensorimotor network, in association with suppressed descending pain modulatory and cerebellum-limbic networks and enhanced sensorimotor network during pain. Such structural and functional alterations might be part of cerebral pathophysiology of CLBP.

Hypersensitivity of Prelimbic Cortex Neurons Contributes to Aggravated Nociceptive Responses in Rats With Experience of Chronic Inflammatory Pain

Previous experience of chronic pain causes enhanced responses to upcoming noxious events in both humans and animals, but the underlying mechanisms remain unclear. In the present study, we found that rats with complete Freund's adjuvant (CFA)-induced chronic inflammatory pain experience exhibited aggravated pain responses to later formalin test. Enhanced neuronal activation upon formalin assaults and increased phosphorylated cAMP-response element binding protein (CREB) were observed in the prelimbic cortex (PL) of rats with chronic inflammatory pain experience, and inhibiting PL neuronal activities reversed the aggravated pain. Inflammatory pain experience induced persistent p38 mitogen-activated protein kinase (MAPK; p38) but not extracellular regulated protein kinase (ERK) or c-Jun N-terminal kinase (JNK) hyperphosphorylation in the PL. Inhibiting the p38 phosphorylation in PL reversed the aggravated nociceptive responses to formalin test and down-regulated enhanced phosphorylated CREB in the PL. Chemogenetics identified PL-periaqueductal gray (PAG) but not PL-nucleus accumbens (NAc) as a key pathway in inducing the aggravated formalin pain. Our results demonstrate that persistent hyperphosphorylation of p38 in the PL underlies aggravated nociceptive responses in rats with chronic inflammatory pain experience.

Anterior insular volume decrease is associated with dysfunction of the reward system in patients with chronic pain

BACKGROUND

Chronification of pain is associated with both anatomical and functional alterations of the brain. Alteration in regional grey matter volume might potentially be associated with modified activity of specific brain networks. In this cross-sectional, observational study, we sought to identify brain regions with grey matter volume changes in patients with chronic pain and to reveal its significance by analysing alteration in functional connectivity from those regions. We further explored relevance of such alterations with psychometrics of chronic pain.

METHODS

We recruited 23 patients with chronic pain and 17 age-, gender-matched healthy control subjects. After completing multiple psychophysical questionnaires, each subject underwent resting-state functional magnetic resonance imaging and three-dimensional anatomical imaging on a 3 Tesla magnetic resonance imaging scanner.

RESULTS

Patients with chronic pain showed significant volume decrease at the right anterior insular cortex (p < 0.001) and the left middle cingulate cortex (p < 0.001) compared with healthy controls. They also showed decreased connectivity between the right anterior insular cortex and the left nucleus accumbens in negative association with the Pain Catastrophizing Scale (R²  = 0.20, p = 0.046) and the Beck's Depression Inventory scores (R²  = 0.24, p = 0.017).

CONCLUSIONS

Decreased grey matter volumes of those core regions for affective processing of pain might be a common cerebral feature shared by, at least some of, different aetiologies of chronic pain. Dysfunctional network between the anterior insular cortex and the nucleus accumbens might reflect affective and motivational disability involved in chronic pain. Such anatomical and functional profiles could potentially be part of a cerebral signature for chronification of pain.

SIGNIFICANCE

This article illustrates decreased network activity of the reward system in association with insular cortical volume decrease in patients with chronic pain, and its close relationships with affective and cognitive morbidity of pain. Attenuation of brain's reward system involving cortical plastic changes might have a key role in chronification of pain.

Association between brain and low back pain

Most chronic low back pain includes elements of nociceptive pain, neuropathic pain, and nonorganic pain. We conducted screening for nonorganic pain with use of the Brief Scale for Psychiatric Problems in Orthopaedic Patients (BS-POP), which is simple and can be used for multidimensional assessment. Research on pain areas using functional magnetic resonance imaging (fMRI) and positron emission tomography has shown that the dopamine system contributes to the pathology of chronic low back pain. Chronic low back pain patients show decreased activation of the anterior cingulate cortex, prefrontal cortex, and nucleus accumbens. Given that both the anterior cingulate cortex and prefrontal cortex belong to the descending inhibitory system, and that the nucleus accumbens, which is involved in the dopamine system, releases μ-opioids that act to relieve pain, decreased activation in these three brain regions may be related to decreased function of the descending inhibitory system. A pathological condition that can be explained at the molecular biological level clearly exists between chronic low back pain and psychosocial factors, and investigations of a pathological condition of chronic low back pain including brain function are needed.

Reward Circuitry Plasticity in Pain Perception and Modulation

Although pain is a widely known phenomenon and an important clinical symptom that occurs in numerous diseases, its mechanisms are still barely understood. Owing to the scarce information concerning its pathophysiology, particularly what is involved in the transition from an acute state to a chronic condition, pain treatment is frequently unsatisfactory, therefore contributing to the amplification of the chronic pain burden. In fact, pain is an extremely complex experience that demands the recruitment of an intricate set of central nervous system components. This includes cortical and subcortical areas involved in interpretation of the general characteristics of noxious stimuli. It also comprises neural circuits that process the motivational-affective dimension of pain. Hence, the reward circuitry represents a vital element for pain experience and modulation. This review article focuses on the interpretation of the extensive data available connecting the major components of the reward circuitry to pain suffering, including the nucleus accumbens, ventral tegmental area, and the medial prefrontal cortex; with especial attention dedicated to the evaluation of neuroplastic changes affecting these structures found in chronic pain syndromes, such as migraine, trigeminal neuropathic pain, chronic back pain, and fibromyalgia.

Upregulation of prefrontal metabotropic glutamate receptor 5 mediates neuropathic pain and negative mood symptoms after spinal nerve injury in rats

Patients with chronic pain easily accompany the negative mood symptoms such as depression and anxiety, and these disturbances in turn affect the aversive perception of pain. However, the underlying mechanisms are largely unknown. We hypothesized that the alteration of metabotropic glutamate receptor 5 (mGluR5) in the brain region underlies such a comorbidity of aversive states. We scanned the brain of chronic neuropathic pain model rats using positron emission tomography (PET) technique with an mGluR5-selective radiotracer [11C] ABP688 and found various brain regions with higher or lower level of mGluR5 compared to control rats. Among the brain areas, a prominent upregulation of mGluR5 was shown in the prelimbic region (PrL) of the medial prefrontal cortex (mPFC) of chronic neuropathic pain animals. A pharmacological blockade of upregulated mGluR5 in the PrL ameliorated the negative symptoms including tactile hypersensitivity and depressive-like behavior, which relieved the subjects from the unpleasant state of chronic neuropathic pain condition. Conversely, lentiviral overexpression of the mGluR5 in the PrL of naïve rats successfully induced comorbid pain and negative moods. Our data provide deeper insight into the shared mechanism of pain perception and negative emotions, identifying a therapeutic target for the treatment of chronic pain and mood disorders.