Neuroanatomy of the pain system and of the pathways that modulate pain

From nociception to pain perception, possible implications of astrocytes

Astrocytes are determinants for the functioning of the CNS. They respond to neuronal activity with calcium increases and can in turn modulate synaptic transmission, brain plasticity as well as cognitive processes. Astrocytes display sensory-evoked calcium responses in different brain structures related to the discriminative system of most sensory modalities. In particular, noxious stimulation evoked calcium responses in astrocytes in the spinal cord, the hippocampus, and the somatosensory cortex. However, it is not clear if astrocytes are involved in pain. Pain is a private, personal, and complex experience that warns us about potential tissue damage. It is a perception that is not linearly associated with the amount of tissue damage or nociception; instead, it is constructed with sensory, cognitive, and affective components and depends on our previous experiences. However, it is not fully understood how pain is created from nociception. In this perspective article, we provide an overview of the mechanisms and neuronal networks that underlie the perception of pain. Then we proposed that coherent activity of astrocytes in the spinal cord and pain-related brain areas could be important in binding sensory, affective, and cognitive information on a slower time scale.

Cellular and circuit diversity determines the impact of endogenous opioids in the descending pain modulatory pathway

The descending pain modulatory pathway exerts important bidirectional control of nociceptive inputs to dampen and/or facilitate the perception of pain. The ventrolateral periaqueductal gray (vlPAG) integrates inputs from many regions associated with the processing of nociceptive, cognitive, and affective components of pain perception, and is a key brain area for opioid action. Opioid receptors are expressed on a subset of vlPAG neurons, as well as on both GABAergic and glutamatergic presynaptic terminals that impinge on vlPAG neurons. Microinjection of opioids into the vlPAG produces analgesia and microinjection of the opioid receptor antagonist naloxone blocks stimulation-mediated analgesia, highlighting the role of endogenous opioid release within this region in the modulation of nociception. Endogenous opioid effects within the vlPAG are complex and likely dependent on specific neuronal circuits activated by acute and chronic pain stimuli. This review is focused on the cellular heterogeneity within vlPAG circuits and highlights gaps in our understanding of endogenous opioid regulation of the descending pain modulatory circuits.

Thalamocortical bistable switch as a theoretical model of fibromyalgia pathogenesis inferred from a literature survey

Fibromyalgia (FM) is an unsolved central pain processing disturbance. We aim to provide a unifying model for FM pathogenesis based on a loop network involving thalamocortical regions, i.e., the ventroposterior lateral thalamus (VPL), the somatosensory cortex (SC), and the thalamic reticular nucleus (TRN). The dynamics of the loop have been described by three differential equations having neuron mean firing rates as variables and containing Hill functions to model mutual interactions among the loop elements. A computational analysis conducted with MATLAB has shown a transition from monostability to bistability of the loop behavior for a weakening of GABAergic transmission between TRN and VPL. This involves the appearance of a high-firing-rate steady state, which becomes dominant and is assumed to represent pathogenic pain processing giving rise to chronic pain. Our model is consistent with a bulk of literature evidence, such as neuroimaging and pharmacological data collected on FM patients, and with correlations between FM and immunoendocrine conditions, such as stress, perimenopause, chronic inflammation, obesity, and chronic dizziness. The model suggests that critical targets for FM treatment are to be found among immunoendocrine pathways leading to GABA/glutamate imbalance having an impact on the thalamocortical system.

Sex Differences in the Amygdaloid Projections to the Ventrolateral Periaqueductal Gray and Their Activation During Inflammatory Pain in the Rat

Preclinical and clinical studies have reported sex differences in pain and analgesia. These differences may be linked to anatomical structures of the central nervous system pain modulatory circuitry, and/or hormonal milieu. The midbrain periaqueductal gray is a critical brain region for descending inhibition of pain. The PAG projects to the rostral ventromedial medulla (RVM), which projects bilaterally to the spinal cord to inhibit pain. In addition to pain, this descending circuit (or pathway) can be engaged by endogenous opioids (i.e., endorphins) or exogenous opioids (i.e., morphine), and we have previously reported sex differences in the activation of this circuit during pain and analgesia. Forebrain structures, including the amygdala, project to and engage the PAG-RVM circuit during persistent inflammatory pain. However, there are limited studies in females detailing this amygdalar-PAG pathway and its involvement during persistent inflammatory pain. The objective of the present study was to delineate the neural projections from the amygdala to the PAG in male and female rats to determine if they are sexually distinct in their anatomical organization. We also examined the activation of this pathway by inflammatory pain and the co-localization of receptors for estrogen. Injection of the retrograde tracer fluorogold (FG) into the ventrolateral PAG (vlPAG) resulted in dense retrograde labeling in both the central amygdala (CeA) and medial amygdala (MeA). While the number of CeA-vlPAG neurons were comparable between the sexes, there were more MeA-vlPAG neurons in females. Inflammatory pain resulted in greater activation of the amygdala in males; however, females displayed higher Fos expression within CeA-vlPAG projection neurons. Females expressed higher ERα in the MeA and CeA and the same was true of the projection neurons. Together, these data indicate that although the MeA-vlPAG projections are denser in females, inflammatory pain does not significantly activate these projections. In contrast, inflammatory pain resulted in a greater activation of the CeA-vlPAG pathway in females. As females experience a greater number of chronic pain syndromes, the CeA-vlPAG pathway may play a facilitatory (and not inhibitory) role in pain modulation.

Pain modalities in the body and brain: Current knowledge and future perspectives

Development and validation of pain biomarkers has become a major issue in pain research. Recent advances in multimodal data acquisition have allowed researchers to gather multivariate and multilevel whole-body measurements in patients with pain conditions, and data analysis techniques such as machine learning have led to novel findings in neural biomarkers for pain. Most studies have focused on the development of a biomarker to predict the severity of pain with high precision and high specificity, however, a similar approach to discriminate different modalities of pain is lacking. Identification of more accurate and specific pain biomarkers will require an in-depth understanding of the modality specificity of pain. In this review, we summarize early and recent findings on the modality specificity of pain in the brain, with a focus on distinct neural activity patterns between chronic clinical and acute experimental pain, direct, social, and vicarious pain, and somatic and visceral pain. We also suggest future directions to improve our current strategy of pain management using our knowledge of modality-specific aspects of pain.

Central and peripheral contributions of T-type calcium channels in pain

Chronic pain is a severely debilitating condition that reflects a long-term sensitization of signal transduction in the afferent pain pathway. Among the key players in this pathway are T-type calcium channels, in particular the Cav3.2 isoform. Because of their biophysical characteristics, these channels are ideally suited towards regulating neuronal excitability. Recent evidence suggests that T-type channels contribute to excitability of neurons all along the ascending and descending pain pathways, within primary afferent neurons, spinal dorsal horn neurons, and within pain-processing neurons in the midbrain and cortex. Here we review the contribution of T-type channels to neuronal excitability and function in each of these neuronal populations and how they are dysregulated in chronic pain conditions. Finally, we discuss their molecular pharmacology and the potential role of these channels as therapeutic targets for chronic pain.

Dry Eye Symptoms and Signs in US Veterans With Gulf War Illness

PURPOSE

To examine dry eye (DE) symptoms and signs in individuals with vs without Gulf War illness (GWI).

DESIGN

Prospective cross-sectional study.

METHODS

We performed a prospective, cross-sectional study of South Florida veterans who were active duty during the Gulf War era (GWE; 1990-1991) and seen at an eye clinic between October 1, 2020, and March 13, 2021. Veterans were split into 2 groups: those who met Kansas criteria for GWI (cases, n = 30) and those who did not (controls, n = 41). DE symptoms were assessed via standardized questionnaires whereas DE signs were assessed using a series of ocular surface parameters. Differences between groups were assessed via Mann-Whitney U test. Linear regression analyses were used to examine which GWI symptoms most closely aligned with DE symptoms.

RESULTS

Veterans with GWI had higher DE symptoms scores compared to controls (Ocular Surface Disease Index [OSDI] scores: mean 41.20±22.92 vs 27.99±24.03, P = .01). In addition, veterans with GWI had higher eye pain scores compared with controls (average eye pain over past week: 2.63±2.72 vs 1.22±1.50, P = .03), including on neuropathic ocular pain questionnaires (Neuropathic Pain Symptom Inventory modified for the Eye [NPSI-E]: 17.33±17.20 vs 9.63±12.64, P = .03). DE signs were mostly similar between the groups. GWI symptoms "nausea or upset stomach" (β=14.58, SE = 3.02, P < .001) and "headache" (β=7.90, SE = 2.91, P = .011) correlated with higher OSDI scores.

CONCLUSION

Individuals with GWI have more severe DE symptoms and ocular pain scores but similar tear and ocular surface parameters compared to controls without GWI. This finding suggests that mechanisms beyond tear dysfunction drive eye symptoms in GWI.

Drug treatment for chemotherapy-induced peripheral neuropathy in patients with pancreatic cancer

Pancreatic cancer (PC) is a lethal disease where most tumors are too advanced at diagnosis for resection, leaving chemotherapy as the mainstay of treatment. Although the prognosis of unresectable PC is poor, it has been dramatically improved by new chemotherapy treatments, such as the combination of 5-fluorouracil, oxaliplatin, irinotecan, and leucovorin (FOLFIRINOX) or gemcitabine plus nab-paclitaxel. However, as oxaliplatin and paclitaxel are common neurotoxic drugs, chemotherapy-induced peripheral neuropathy (CIPN) is a common and severe adverse effect of both treatments. As there are no agents recommended in the ASCO guidelines, we review the methods used to treat CIPN caused by PC treatment. The efficacy of duloxetine was observed in a large randomized controlled trial (RCT). In addition, pregabalin was more effective than duloxetine for CIPN in two RCTs. Although duloxetine and pregabalin can be effective for CIPN, they have several side effects. Therefore, the choice between the two drugs should be determined according to effect and tolerability. Mirogabalin is also used in patients with PC and there is hope it will yield positive outcomes when treating CIPN in the future.

The State-of-the-art Pharmacotherapeutic Options for the Treatment of Chronic Non-Cancer Pain

INTRODUCTION

Pharmacotherapeutic options continue to expand for the treatment of chronic non-cancer pain. There has been an increasing emphasis on multimodal analgesia. This strategy employs use of multiple analgesic medications each with a distinct mechanism of action, which when administered concomitantly may provide profound analgesia.

AREAS COVERED

The authors describe evidence from randomized controlled trials and systematic reviews on a variety of established medications including anti-inflammatory agents, opioids, anti-convulsants, anti-depressants, N-methyl-D-aspartate receptor antagonists, sodium channel blockers, cannabinoids, and alpha-2-receptor blockers. Furthermore, they provide developing evidence on more novel pharmacotherapeutics including alpha lipoic acid, acetyl-L-carnitine, low dose naltrexone, calcitonin gene-related peptide antagonists, targeted toxin therapy, Nav1.7 inhibitors, neurotensin agonists, purinoceptor antagonists, and sigma-1 receptor antagonists. Furthermore, the authors review the safety and adverse effect profile for these agents.

EXPERT OPINION

In this era of the opioid epidemic, clinicians should first offer non-opioid analgesics and employ a multimodal analgesic strategy. Current guidelines recommend a personalized approach to the chronic pain treatment, in each case accounting for type, location, severity, and chronicity of pain. Clinicians should also carefully consider the risk-to-benefit ratio to the patient based on the drug side effect profile, patient age, and comorbidities.

Brainstem Diffusion Tensor Tractography and Clinical Applications in Pain

The brainstem is one of the most vulnerable brain structures in many neurological conditions, such as pain, sleep problems, autonomic dysfunctions, and neurodegenerative disorders. Diffusion tensor imaging and tractography provide structural details and quantitative measures of brainstem fiber pathways. Until recently, diffusion tensor tractographic studies have mainly focused on whole-brain MRI acquisition. Due to the brainstem's spatial localization, size, and tissue characteristics, and limits of imaging techniques, brainstem diffusion MRI poses particular challenges in tractography. We provide a brief overview on recent advances in diffusion tensor tractography in revealing human pathways connecting the brainstem to the subcortical regions (e.g., basal ganglia, mesolimbic, basal forebrain), and cortical regions. Each of these pathways contains different distributions of fiber tracts from known neurotransmitter-specific nuclei in the brainstem. We compare the brainstem tractographic approaches in literature and our in-lab developed automated brainstem tractography in terms of atlas building, technical advantages, and neuroanatomical implications on neurotransmitter systems. Lastly, we summarize recent investigations of using brainstem tractography as a promising tool in association with pain.

Unique features of central neuropathic pain in multiple sclerosis: Results of a cluster analysis

Background

Central neuropathic pain (CNP) is an excruciating condition, prevalent in up to a third of patients with multiple sclerosis (MS). Identifying CNP among MS patients is particularly challenging considering the ample comorbid chronic pain conditions and sensory disturbances entailed by the disease. The aim was to identify sensory features unique to CNP beyond those of chronic pain and MS.

Methods

Participants were 112 MS patients: 44 with a diagnosis of CNP, 28 with a diagnosis of chronic musculoskeletal pain (MSP), and 40 pain free. Participants underwent testing of thermal and mechanical thresholds, thermal grill illusion (TGI), pain adaptation (PA), and offset analgesia (OA), and chronic pain was characterized. A two‐step cluster analysis was performed, and the association between the cluster membership and the clinical group membership (CNP, MSP, pain free) was evaluated.

Results

The CNP and MSP groups were similar in most of the chronic pain variables (e.g., severity, location and quality) and MS‐related variables (e.g., type, severity and medication intake). The three created clusters had unique sensory features: (1) ‘Hyposensitivity’ (increased thermal and touch thresholds) characterized the CNP group; (2) ‘Poor inhibition and hyperalgesia’ (worst PA and OA and decreased TGI threshold) characterized the MSP group; and (3) ‘Efficient inhibition’ (best PA and OA, smallest sensory loss) characterized the pain‐free group.

Conclusions

The unique sensory features of CNP and MSP provide insight into their pathophysiology, and evaluating them may increase the ability to provide individually based interventions. Efficient inhibition may protect MS patients from chronic pain.

Significance

Cluster analysis among patients with multiple sclerosis (MS) revealed that while central neuropathic pain is associated with thermal and mechanical hypoesthesia, musculoskeletal pain is involved with reduced pain inhibition and hyperalgesia; sensory profiles that provide insights into the mechanisms of these conditions and may promote an individually based pain management.

Kinds of Harm: Animal Law Language from a Scientific Perspective

Simple Summary

Clarity and consistency of legal language are essential qualities of the law. Without a sufficient level of those, legal acts are often hardly capable of determining legal duties appropriately. The review of rules governing the protection of animals reveals that the current language remains far from satisfactory. Therefore, the paper discusses the most sensitive notions relevant for defining animal harm and argues for action to make the legal language of respective legal regulations more scientifically accurate and adequate to the actual needs of animal protection.

Abstract

The current language of animal welfare laws is inconsistent and unclear in the basic terms pertaining to animal sensations and potential harms. In the case of law, the exact language often plays an essential role in determining legal duties and establishing their scope. Thus, for further progress in animal law, a coherent and unified basic conceptual framework is needed. To establish such a framework, the relevant legal terminology should be discussed in a prescriptive rather than interpretive manner while drawing on the medical sciences. Here, we propose a way to clarify the relevant terms to prevent misconceptions and improve the consistency of animal law.

Patterns of pain complaints and insomnia symptoms are associated with abusive supervision in the Norwegian working population: a latent class analysis

OBJECTIVES

Previous findings suggest that abusive supervision, i.e., subordinates' perceptions of their supervisor's behaviours as hostile (excluding physical aggression), may increase the risk of health complaints. In addition, recent data suggest that the FKBP5 genotype rs9470080 important in the regulation of cortisol release, influences the same outcome. Adding to this complexity, different health complaints often co-occur. The present study aimed to (1) uncover patterns of pain complaints and insomnia symptoms by using latent class analysis, (2) determine whether abusive supervision or FKBP5 rs9470080 was associated with these patterns, and (3) examine the interaction between abusive supervision and FKBP5 genotype regarding pain and insomnia symptoms.

METHODS

The data was collected through a national probability survey of 5,000 employees drawn from the National Central Employee Register by Statistics Norway. Abusive supervision was measured by a 5-item version of the Tepper's 2000 scale. Pain and insomnia symptoms were measured by 5 items reflecting pain and 3 items reflecting insomnia. The FKBP5 rs9470080 genotyping was carried out using TaqMan assay.

RESULTS

A total of 1,226 participants returned the questionnaire and the saliva kit sample. Based on these the latent class analyses revealed four classes based on response patterns of pain and insomnia symptoms. In the regression analysis, abusive supervision was a significant predictor for the response patterns. However, neither the FKBP5 nor the interaction between abusive supervision and FKBP5 showed significant contributions.

CONCLUSIONS

In conclusion, awareness of the association between abusive supervision and the revealed four pain- and insomnia subgroups, and what separates them, may be important for prognosis and an optimal follow-up for those affected.

Mating-induced analgesia is dependent of copulatory male pattern in high- and low- yawning male rats

Mating behavior in rodents can modulate pain sensations in both sexes. In males, the execution of mounts, intromissions, and ejaculations induced a progressive increase in their vocalization thresholds induced by tail shocks and other types of noxious stimuli. We selectively inbred two sublines from Sprague-Dawley (SD) rats that differed in their spontaneous yawning frequency. The high-yawning (HY) subline had a mean of 20 yawns/h and a different pattern of sexual behavior characterized by longer interintromission intervals and more sexual bouts that delayed ejaculation. The low-yawning (LY) subline and SD rats yawned as a mean 2 and 1 yawns/h, respectively. So, we determine mating-induced analgesia in HY, LY, and SD male rats by measuring vocalization thresholds in response to noxious electric tail shocks. Our results showed that the magnitude of mating-induced analgesia was lower in HY and LY rats with respect to SD rats. When the rats performed different components of male sexual pattern, both sublines exhibited a significantly lower increase in their vocalization thresholds with respect to SD rats-being sublines less responsive regarding mating-induced analgesia. Pain modulation mechanisms depend on responses to stress, so the low levels of analgesia obtained in the yawning sublines may be due either to differences in their response to stress in other paradigms, or to atypical performance of male sexual behavior during mating, an event which as a stressful event in rats. Therefore, the yawning sublines are a suitable model for analyzing how a different temporal pattern in the display of male sexual behavior affects analgesia mechanisms. Our results concur with Wistar rats with different endophenotypes that could apply to humans as well.

Dorsal root entry zone procedure and other surgeries for pain

Pain is a very common symptom that often serves a protective function. It is typically treated medically. When pain becomes chronic and intractable, it no longer serves a protective function and often requires more aggressive forms of treatment. Many types of surgeries can be performed for the management of pain. These surgeries can involve ablation (destruction) or augmentation (stimulation or facilitation) of some part of the nervous system. In many of these surgeries, neurophysiologic intraoperative monitoring (NIOM) is not needed, however, in others neuromonitoring serves a mapping and monitoring purpose. The prototype of pain surgery for this chapter is the dorsal root entry zone (DREZ) procedure. Both mapping and monitoring can help improve lesioning precision and outcomes in this surgery. In this chapter, the DREZ procedures and other surgeries for primarily pain relief in which NIOM is used are discussed. Surgeries, such as spinal stenosis, in which pain relief is important but not the sole purpose, are not discussed here and are covered elsewhere.

Regular Aerobic Exercise Attenuates Pain and Anxiety in Mice by Restoring Serotonin-modulated Synaptic Plasticity in the ACC

PURPOSE

Clinical studies found that regular aerobic exercise has analgesic and anti-anxiety effects; however, the underlying neural mechanisms remain unclear. Multiple studies have suggested that regular aerobic exercise may exert brain-protective effects by promoting the release of serotonin, which may be a pain modulator. The anterior cingulate cortex (ACC) is a key brain area for pain information processing, receiving dense serotonergic innervation. As a result, we hypothesized that exercise may increase the release of serotonin in the ACC, thus improving pain and anxiety behaviours.

METHODS

Integrative methods were used, including behavioural, electrophysiological, pharmacological, biochemical, and genetic approaches, to explore the effects of regular aerobic exercise and the underlying neural mechanisms.

RESULTS

Regular aerobic exercise in the form of voluntary wheel running for 30 minutes daily for 15 days showed significant effectiveness in relieving pain and concomitant anxiety in complete Freund's adjuvant (CFA)-induced chronic inflammation pain models. c-Fos staining and multielectrode array recordings revealed alterations in neuronal activities and synaptic plasticity in the ACC. Moreover, systemic pharmacological treatment with 4-chloro-DL-phenylalanine (PCPA) to deplete endogenous serotonin and local delivery of serotonin to the ACC revealed that exercise-related serotonin release in the ACC bidirectionally modulates pain sensitization and anxiety behaviours by modulating synaptic plasticity in the ACC. Furthermore, we found that 5-HT1A and 5-HT7 receptors mediated the serotonin modulation effects under conditions of regular aerobic exercise through local infusion of a selective antagonist and shRNA in the ACC.

CONCLUSIONS

Our results reveal that regular aerobic exercise can increase serotonin release and modulate synaptic plasticity in the ACC, ultimately improving pain and concomitant anxiety behaviours through the functions of the 5-HT1A and 5-HT7 receptors.

Neuromodulation using ultra low frequency current waveform reversibly blocks axonal conduction and chronic pain

Chronic pain remains a leading cause of disability worldwide, and there is still a clinical reliance on opioids despite the medical side effects associated with their use and societal impacts associated with their abuse. An alternative approach is the use of electrical neuromodulation to produce analgesia. Direct current can block action potential propagation but leads to tissue damage if maintained. We have developed a form of ultra low frequency (ULF) biphasic current and studied its effects. In anesthetized rats, this waveform produced a rapidly developing and completely reversible conduction block in >85% of spinal sensory nerve fibers excited by peripheral stimulation. Sustained ULF currents at lower amplitudes led to a slower onset but reversible conduction block. Similar changes were seen in an animal model of neuropathic pain, where ULF waveforms blocked sensory neuron ectopic activity, known to be an important driver of clinical neuropathic pain. Using a computational model, we showed that prolonged ULF currents could induce accumulation of extracellular potassium, accounting for the slowly developing block observed in rats. Last, we tested the analgesic effects of epidural ULF currents in 20 subjects with chronic leg and back pain. Pain ratings improved by 90% after 2 weeks. One week after explanting the electrodes, pain ratings reverted to 72% of pretreatment screening value. We conclude that epidural spinal ULF neuromodulation represents a promising therapy for treating chronic pain.

Sex differences in neuroimmune and glial mechanisms of pain

ABSTRACT

Pain is the primary motivation for seeking medical care. Although pain may subside as inflammation resolves or an injury heals, it is increasingly evident that persistency of the pain state can occur with significant regularity. Chronic pain requires aggressive management to minimize its physiological consequences and diminish its impact on quality of life. Although opioids commonly are prescribed for intractable pain, concerns regarding reduced efficacy, as well as risks of tolerance and dependence, misuse, diversion, and overdose mortality rates limit their utility. Advances in development of nonopioid interventions hinge on our appreciation of underlying mechanisms of pain hypersensitivity. For instance, the contributory role of immunity and the associated presence of autoimmune syndromes has become of particular interest. Males and females exhibit fundamental differences in innate and adaptive immune responses, some of which are present throughout life, whereas others manifest with reproductive maturation. In general, the incidence of chronic pain conditions, particularly those with likely autoimmune covariates, is significantly higher in women. Accordingly, evidence is now accruing in support of neuroimmune interactions driving sex differences in the development and maintenance of pain hypersensitivity and chronicity. This review highlights known sexual dimorphisms of neuroimmune signaling in pain states modeled in rodents, which may yield potential high-value sex-specific targets to inform future analgesic drug discovery efforts.

Punctate Midline Myelotomy: A Historical Overview and Case Series with Detailed Efficacy and Side Effect Profiles

OBJECTIVE

To review our experience with punctate midline myelotomy (PMM) for malignant and benign visceral pain with an emphasis on detailed side-effect profiles and efficacy.

METHODS

Thirteen adults (5 men) underwent microsurgical transverse-crush PMM.

RESULTS

Median follow-up for the benign pain group (n = 6) was 17.5 months (10-72) and for the malignant group (n = 7) was 8 months (0.5-31). Five of seven patients in the malignant pain group obtained excellent, lasting relief. Two had initial relief followed by worsening pain with disease progression. In the benign pain group, two patients with endodermal-origin pain (gastrointestinal tract, bladder) had complete, long-lasting relief. Three patients with mesodermal-origin pain (ureter) had excellent relief for 2-3 months, followed by recurrence in two and partial (40%) recurrence in the third. One man with pre-existing cervical myelopathy underwent PMM for benign testicular-region pain from which he had long-term relief but only transient relief of coexisting low-back and leg pain. There were no motor deficits in either group, and all patients remained ambulatory and continent. The most common side effect was transient numbness of the medial leg and foot. Two patients (both with pre-existing spinal pathology) reported persistent moderate reduction of bowel, bladder, and sexual sensation.

CONCLUSIONS

PMM offers substantial pain relief for carefully selected patients with intractable visceral pain. Relief from primarily endoderm-derived structures was most complete and long-lasting. Relief from mesoderm-derived structures was typically transient or incomplete. There was essentially no relief from pain of ectoderm-derived structures. Detailed preoperative counseling is important, especially for those with pre-existing neurologic deficits.

Brainstem damage is associated with poorer sleep quality and increased pain in gulf war illness veterans

AIMS

Gulf War Illness (GWI) is manifested as multiple chronic symptoms, including chronic pain, chronic fatigue, sleep problems, neuropsychiatric disorders, respiratory, gastrointestinal, and skin problems. No single target tissue or unifying pathogenic process has been identified that accounts for this variety of symptoms. The brainstem has been suspected to contribute to this multiple symptomatology. The aim of this study was to assess the role of the brainstem in chronic sleep problems and pain in GWI veterans.

MATERIALS AND METHODS

We enrolled 90 veterans (Age = 50 ± 5, 87% Male) who were deployed to the 1990-91 Gulf War and presented with GWI symptoms. Sleep quality was evaluated using the global Pittsburgh Sleep Quality Index. Pain intensities were obtained with the Brief Pain Inventory sum score. Volumes in cortical, subcortical, brainstem, and brainstem subregions and diffusion tensor metrics in 10 bilateral brainstem tracts were tested for correlations with symptom measures.

KEY FINDINGS

Poorer sleep quality was significantly correlated with atrophy of the whole brainstem and brainstem subregions (including midbrain, pons, medulla). Poorer sleep quality also significantly correlated with lower fractional anisotropy in the nigrostriatal tract, medial forebrain tract, and the dorsal longitudinal fasciculus. There was a significant correlation between increased pain intensity and decreased fractional anisotropy in the dorsal longitudinal fasciculus. These correlations were not altered after controlling for age, sex, total intracranial volumes, or additional factors, e.g., depression and neurological conditions.

SIGNIFICANCE

These findings suggest that the brainstem plays an important role in the aberrant neuromodulation of sleep and pain symptoms in GWI.

Current Status of Pain Management in Parkinson's Disease

BACKGROUND

Pain is a non-motor symptom in Parkinson's disease (PD) which commonly goes underreported. Adequate treatment for pain in PD remains challenging, and to date, no clear guidelines for management are available.

METHODS

With the goal of understanding and organizing the current status of pain management in PD, we conducted a review of pharmacological and non-pharmacological treatments for pain in patients with PD. Suitable studies cataloged in PubMed and the Cochrane database up to October 31, 2019, were included prioritizing randomized controlled trials. Post-hoc analyses and open-label studies were also included.

RESULTS

Treatment with levodopa increases pain thresholds in patients with PD. Apomorphine did not have similar efficacy. Duloxetine provided benefit in an open-label trial. Oxycodone-naloxone PR did not have a significant improvement in pain, but per-protocol analysis showed a reduction in pain when adherence was strong. Rotigotine patch had numerical improvement on pain scales with no statistical significance. Safinamide significantly improved the "bodily discomfort" domain in the PDQ-39 questionnaire. Botulinum toxin A had a non-significant signal toward improving dystonic limb pain in PD. DBS to the subthalamic nucleus may modulate central pain thresholds, and a pilot study of cranioelectric therapy warrants future research in the area.

CONCLUSION

After optimizing dopaminergic therapy, understanding the type of pain a patient is experiencing is essential to optimizing pain control in PD. While recommendations can be made regarding the treatment options in each domain, evidence remains weak and future randomized controlled studies are needed.

Nonlinear increase of pain in distance-based and area-based spatial summation

ABSTRACT

When nociceptive stimulation affects a larger body area, pain increases. This effect is called spatial summation of pain (SSp). The aim of this study was to describe SSp as a function of the size or distance of a stimulated area(s) and to test how this function is shaped by the intensity and SSp test paradigm. Thirty-one healthy volunteers participated in a within-subject experiment. Participants were exposed to area-based and distanced-based SSp. For area-based SSp, electrocutaneous noxious stimuli were applied by up to 5 electrodes (5 areas) forming a line-like pattern; for distance-based SSp, the same position and lengths of stimuli were used but only 2 electrodes were stimulated. Each paradigm was repeated using pain of low, moderate, and high intensity. It was found that the pattern of pain intensity followed a logarithmic (power) rather than a linear function. The dynamics of the pain increase were significantly different across pain intensities, with more summation occurring when pain was perceived as low. Results indicated that area-based SSp is more painful than distance-based SSp when low and moderate but not when high pain intensity is induced. Presented findings have important implications for all studies in which the spatial dimension of pain is measured. When the area or separation between nociceptive stimulation increases, pain does not increase linearly and the pattern of the pain increase is a result of the interaction between intensity and the number of nociceptive sites. A power function should be considered when predicting the size of a nociceptive source.

The role of the anterior pretectal nucleus in pain modulation: A comprehensive review

Descending pain modulation involves multiple encephalic sites and pathways that range from the cerebral cortex to the spinal cord. Behavioral studies conducted in the 1980s revealed that electrical stimulation of the pretectal area causes antinociception dissociation from aversive responses. Anatomical and physiological studies identified the anterior pretectal nucleus and its descending projections to several midbrain, pontine, and medullary structures. The anterior pretectal nucleus is morphologically divided into a dorsal part that contains a dense neuron population (pars compacta) and a ventral part that contains a dense fiber band network (pars reticulata). Connections of the two anterior pretectal nucleus parts are broad and include prominent projections to and from major encephalic systems associated with somatosensory processes. Since the first observation that acute or chronic noxious stimuli activate the anterior pretectal nucleus, it has been established that numerous mediators participate in this response through distinct pathways. Recent studies have confirmed that at least two pain inhibitory pathways are activated from the anterior pretectal nucleus. This review focuses on rodent anatomical, behavioral, molecular, and neurochemical data that have helped to identify mediators of the anterior pretectal nucleus and pathways related to its role in pain modulation.

Ascorbic Acid in the Acute Care Setting

Ascorbic acid (AA) is an essential nutrient with many physiologic roles not limited to the prevention of scurvy. Beyond its role as a supplement, it has gained popularity in the acute care setting as an inexpensive medication for a variety of conditions. Because of limitations with absorption of oral formulations and reduced serum concentrations observed in acute illness, intravenous (IV) administration, and higher doses, may be needed to produce the desired serum concentrations for a particular indication. Following a PubMed search, we reviewed published studies relevant to AA in the acute care setting and summarized the results in a narrative review. In the acute care setting, AA may be used for improved wound healing, improved organ function in sepsis and acute respiratory distress syndrome, faster resolution of vasoplegic shock after cardiac surgery, reduction of resuscitative fluids in severe burn injury, and as an adjunctive analgesic, among other uses. Each indication differs in its level of evidence supporting exogenous administration of AA, but overall, AA was not commonly associated with adverse effects in the identified studies. Use of AA remains an active area of clinical investigation for various indications in the acute care patient population.

Central neuropathic pain in multiple sclerosis is associated with impaired innocuous thermal pathways and neuronal hyperexcitability

OBJECTIVE

About a third of patients with multiple sclerosis (MS) suffer from chronic and excruciating central neuropathic pain (CNP). The mechanism underlying CNP in MS is not clear, since previous studies are scarce and their results are inconsistent. Our aim was to determine whether CNP in MS is associated with impairment of the spinothalamic-thalamocortical pathways (STTCs) and/or increased excitability of the pain system.

DESIGN

Cross sectional study.

SETTING

General hospital.

SUBJECTS

47 MS patients with CNP, 42 MS patients without CNP, and 32 healthy controls.

METHODS

Sensory testing included the measurement of temperature, pain, and touch thresholds and the thermal grill illusion (TGI) for evaluating STTCs function, and hyperpathia and allodynia as indicators of hyperexcitability. CNP was characterized using interviews and questionnaires.

RESULTS

The CNP group had higher cold and warm thresholds (p < 0.01), as well as higher TGI perception thresholds (p < 0.05), especially in painful body regions compared to controls, whereas touch and pain thresholds values were normal. The CNP group also had a significantly greater prevalence of hyperpathia and allodynia. Regression analysis revealed that whereas presence of CNP was associated with a higher cold threshold, CNP intensity, and the number of painful body regions were associated with allodynia and hyperpathia, respectively.

CONCLUSIONS

CNP in MS is characterized by a specific impairment of STTC function; the innocuous thermal pathways, and by pain hyperexcitability. Whereas CNP presence is associated with STTC impairment, its severity and extent are associated with pain hyperexcitability. Interventions that reduce excitability level may therefore mitigate CNP severity.

Cortical Modulation of Nociception

Nociception is the neuronal process of encoding noxious stimuli and could be modulated at peripheral, spinal, brainstem, and cortical levels. At cortical levels, several areas including the anterior cingulate cortex (ACC), prefrontal cortex (PFC), ventrolateral orbital cortex (VLO), insular cortex (IC), motor cortex (MC), and somatosensory cortices are involved in nociception modulation through two main mechanisms: (i) a descending modulatory effect at spinal level by direct corticospinal projections or mostly by activation of brainstem structures (i.e. periaqueductal grey matter (PAG), locus coeruleus (LC), the nucleus of raphe (RM) and rostroventral medulla (RVM)); and by (ii) cortico-cortical or cortico-subcortical interactions. This review summarizes evidence related to the participation of the aforementioned cortical areas in nociception modulation and different neurotransmitters or neuromodulators that have been studied in each area. Besides, we point out the importance of considering intracortical neuronal populations and receptors expression, as well as, nociception-induced cortical changes, both functional and connectional, to better understand this modulatory effect. Finally, we discuss the possible mechanisms that could potentiate the use of cortical stimulation as a promising procedure in pain alleviation.

Complementary and alternative medicine therapies for uremic pruritus - A systematic review of randomized controlled trials

INTRODUCTION

Uremic pruritus (UP) is one of the most bothersome symptoms among chronic kidney disease (CKD) patients. The pathophysiology of UP remains elusive, resulting in limited treatment options. The inability of standard medical treatments to provide effective relief has piqued interest in complementary and alternative medicine (CAM).

METHODOLOGY

A systematic review of randomized controlled trials (RCTs) summarizing the efficacy and safety profile of CAM used for UP in CKD patients was performed. CAM interventions were classified using categories proposed by the National Center for Complementary and Integrative Health. The efficacy of each CAM was determined from changes in UP severity and all reported adverse effects were extracted.

RESULTS

Of 5242 articles screened, 34 RCTs were included, with 15 (44.1 %) studies having a sample size greater than 50. The studies considered 21 treatments including omega-3 fatty acid supplementation (n=5), acupuncture (n=5), topical capsaicin (n=4) and acupressure (n=3). Acupuncture, acupressure and topical capsaicin were shown to be effective in improving uremic pruritus. Interventions which include oral omega-3 fatty acid and zinc supplementation demonstrated mixed efficacy. Other therapies such as evening primrose oil, turmeric, vitamin B3, vitamin D and thermal therapy were not effective for treatment of UP. Common adverse effects reported with topical capsaicin included mild burning sensations (50.0-88.2 %) or erythema (6.7-22.7%) while that of acupuncture included soreness (7.5 %), bleeding (6.0-7.5%) and hematoma (1.9 %).

CONCLUSIONS

Acupuncture, acupressure and topical capsaicin have the largest body of evidence for efficacy in the treatment of UP. Larger and higher quality RCTs are required to examine the efficacy and safety of promising CAM.

The Effect of Perioperative Vitamin C on Postoperative Analgesic Consumption: A Meta-Analysis of Randomized Controlled Trials

Because the analgesic effect of vitamin C against acute pain remains poorly addressed, this meta-analysis aimed at investigating its effectiveness against acute postoperative pain. A total of seven randomized controlled trials with placebo/normal controls were identified from PubMed, Cochrane Library, Medline, Google Scholar, and Embase databases. Pooled analysis showed a lower pain score (standardized mean difference (SMD) = -0.68, 95% CI: -1.01 to -0.36, p < 0.0001; I2 = 57%) and a lower morphine consumption (weighted mean difference (WMD) = -2.44 mg, 95% CI: -4.03 to -0.86, p = 0.003; I2 = 52%) in the vitamin group than that in the placebo group within postoperative 1-2 h. At postoperative 24 h, a lower pain score (SMD = -0.65, 95% CI: -1.11 to -0.19, p = 0.005; I2 = 81%) and lower morphine consumption (WMD = -6.74 mg, 95% CI: -9.63 to -3.84, p < 0.00001; I2 = 85%) were also noted in the vitamin group. Subgroup analyses demonstrated significant reductions in pain severity and morphine requirement immediately (1-2 h) and 24 h after surgery for patients receiving intravenous vitamin C but not in the oral subgroup. These findings showed significant reductions in pain score and opioid requirement up to postoperative 24 h, respectively, suggesting the effectiveness of perioperative vitamin C use. Further large-scale trials are warranted to elucidate its optimal intravenous dosage and effectiveness against chronic pain in the postoperative pain control setting.

Abnormal white matter microstructure along the thalamus fiber pathways in women with primary dysmenorrhea

Primary dysmenorrhea (PDM) is a cyclic menstrual pain in the absence of pelvic anomalies, and women with PDM have an increased sensitivity to pain than the internal and external areas associated with menstrual pain. However, the brain abnormality in the ascending pain pathways in dysmenorrhea remains largely unclear. As the thalamus plays a significant role in transmission of nociceptive input, we examined whether white matter microstructure of the thalamus-related fiber tracts obtained by DTI in women with PDM (n = 47) differs from healthy controls. A novel tractography atlas-based analysis method that detects tract integrity and altered microstructural properties along selected fibers was employed. The fiber bundles of interest contained the thalamus- primary somatosensory cortex (SI), thalamus- dorsal anterior cingulate cortex (dACC)/supplementary motor area (SMA), thalamus-insula, and thalamus-ACC. As compared with controls, abnormal white matter microstructures were found along the thalamus-related white matter fiber tracts. Additionally, the intensity of menstrual pain was significantly associated with diffusion measures of thalamus-SI fiber connections. Our study suggested that the thalamus-related pain processing pathways had altered white matter integrity that persisted beyond the time of menstruation, and the white matter microstructure of the thalamus-SI pathways was closely related to menstrual pain in the intensity by women with PDM.

Neural Oscillations: Understanding a Neural Code of Pain

Neural oscillations play an important role in the integration and segregation of brain regions that are important for brain functions, including pain. Disturbances in oscillatory activity are associated with several disease states, including chronic pain. Studies of neural oscillations related to pain have identified several functional bands, especially alpha, beta, and gamma bands, implicated in nociceptive processing. In this review, we introduce several properties of neural oscillations that are important to understand the role of brain oscillations in nociceptive processing. We also discuss the role of neural oscillations in the maintenance of efficient communication in the brain. Finally, we discuss the role of neural oscillations in healthy and chronic pain nociceptive processing. These data and concepts illustrate the key role of regional and interregional neural oscillations in nociceptive processing underlying acute and chronic pains.

Regional Hyperexcitability and Chronic Neuropathic Pain Following Spinal Cord Injury

Spinal cord injury (SCI) causes maladaptive changes to nociceptive synaptic circuits within the injured spinal cord. Changes also occur at remote regions including the brain stem, limbic system, cortex, and dorsal root ganglia. These maladaptive nociceptive synaptic circuits frequently cause neuronal hyperexcitability in the entire nervous system and enhance nociceptive transmission, resulting in chronic central neuropathic pain following SCI. The underlying mechanism of chronic neuropathic pain depends on the neuroanatomical structures and electrochemical communication between pre- and postsynaptic neuronal membranes, and propagation of synaptic transmission in the ascending pain pathways. In the nervous system, neurons are the only cell type that transmits nociceptive signals from peripheral receptors to supraspinal systems due to their neuroanatomical and electrophysiological properties. However, the entire range of nociceptive signaling is not mediated by any single neuron. Current literature describes regional studies of electrophysiological or neurochemical mechanisms for enhanced nociceptive transmission post-SCI, but few studies report the electrophysiological, neurochemical, and neuroanatomical changes across the entire nervous system following a regional SCI. We, along with others, have continuously described the enhanced nociceptive transmission in the spinal dorsal horn, brain stem, thalamus, and cortex in SCI-induced chronic central neuropathic pain condition, respectively. Thus, this review summarizes the current understanding of SCI-induced neuronal hyperexcitability and maladaptive nociceptive transmission in the entire nervous system that contributes to chronic central neuropathic pain.

The role of the locus coeruleus in the generation of pathological anxiety

This review aims to synthesise a large pre-clinical and clinical literature related to a hypothesised role of the locus coeruleus norepinephrine system in responses to acute and chronic threat, as well as the emergence of pathological anxiety. The locus coeruleus has widespread norepinephrine projections throughout the central nervous system, which act to globally modulate arousal states and adaptive behavior, crucially positioned to play a significant role in modulating both ascending visceral and descending cortical neurocognitive information. In response to threat or a stressor, the locus coeruleus–norepinephrine system globally modulates arousal, alerting and orienting functions and can have a powerful effect on the regulation of multiple memory systems. Chronic stress leads to amplification of locus coeruleus reactivity to subsequent stressors, which is coupled with the emergence of pathological anxiety-like behaviors in rodents. While direct in vivo evidence for locus coeruleus dysfunction in humans with pathological anxiety remains limited, recent advances in high-resolution 7-T magnetic resonance imaging and computational modeling approaches are starting to provide new insights into locus coeruleus characteristics.

A meta-analysis of the potential antidepressant effects of buprenorphine versus placebo as an adjunctive pharmacotherapy for treatment-resistant depression

BACKGROUND

Numerous reports have suggested that buprenorphine may have antidepressant effects. Many individuals with depressive disorders don't respond to first-line treatment and are classified with treatment-resistant depression (TRD). Novel therapies for depression are required to better treat this population. This meta-analysis of randomized placebo-controlled trials sought to evaluate the potential antidepressant effects of buprenorphine as an adjunctive pharmacological treatment for individuals with TRD.

METHODS

PubMed, Embase, CINAHL, Web of Science, and ClinicalTrials.gov databases were searched until June 2019 for original peer-reviewed reports of buprenorphine used for the treatment of depression. Standardized mean differences (SMD) were generated from random effects models. Risk of publication bias was assessed using a funnel plot. Potential sources of heterogeneity were explored in subgroup analyses.

RESULTS

In six studies that met inclusion criteria, depression symptom severity in individuals with TRD was not significantly decreased after an adjunctive intervention with buprenorphine when compared to placebo (SMD = -0.07, 95% CI: -0.21-0.06, p = 0.30). Five of the six studies utilized a combination of buprenorphine/samidorphan. In these studies, depression symptom severity was also not significantly reduced after intervention compared to placebo (SMD = -0.08, 95% CI: -0.21 - 0.05, p = 0.23).

LIMITATIONS

Five included studies were performed by the same research group with significant conflicts of interest.

CONCLUSIONS

This meta-analysis did not reveal a significant reduction in depression symptom severity in individuals with TRD after an adjunctive intervention with buprenorphine when compared to placebo. However, more optimal doses of buprenorphine (2 mg/day) and longer treatment lengths should be explored.

The Pathways and Processes Underlying Spinal Transmission of Low Back Pain: Observations From Dorsal Root Ganglion Stimulation Treatment

BACKGROUND

Dorsal root ganglion stimulation (DRG-S) is a novel approach to treat chronic pain. Lead placement at L2 has been reported to be an effective treatment for axial low back pain (LBP) primarily of discogenic etiology. We have recently shown, in a diverse cohort including cases of multilevel instrumentation following extensive prior back surgeries, that DRG-S lead placement at T12 is another promising target. Local effects at the T12 DRG, alone, are insufficient to explain these results.

MATERIALS AND METHODS

We performed a literature review to explore the mechanisms of LBP relief with T12 DRG-S.

FINDINGS

Branches of individual spinal nerve roots innervate facet joints and posterior spinal structures, while the discs and anterior vertebrae are carried via L2, and converge in the dorsal horn (DH) of the spinal cord at T8-T9. The T12 nerve root contains cutaneous afferents from the low back and enters the DH of the spinal cord at T10. Low back Aδ and C-fibers then ascend via Lissauer's tract (LT) to T8-T9, converging with other low back afferents. DRG-S at T12, then, results in inhibition of the converged low back fibers via endorphin-mediated and GABAergic frequency-dependent mechanisms. Therefore, T12 lead placement may be the optimal location for DRG-S to treat LBP.

Development and persistence of neuropathic pain through microglial activation and KCC2 decreasing after mouse tibial nerve injury

Gamma-amino butyric acid (GABA) is an inhibitory neurotransmitter in the mature brain, but is excitatory during development and after motor nerve injury. This difference in GABAergic action depends on the intracellular chloride ion concentration ([Cl-]i), primarily regulated by potassium chloride co-transporter 2 (KCC2). To reveal precise processes of the neuropathic pain through changes in GABAergic action, we prepared tibial nerve ligation and severance models using male mice, and examined temporal relationships amongst changes in (1) the mechanical withdrawal threshold in the sural nerve area, (2) localization of the molecules involved in GABAergic transmission and its upstream signaling in the dorsal horn, and (3) histology of the tibial nerve. In the ligation model, tibial nerve degeneration disappeared by day 56, but mechanical allodynia, reduced KCC2 localization, and increased microglia density remained until day 90. Microglia density was higher in the tibial zone than the sural zone before day 21, but this result was inverted after day 28. In contrast, in the severance model, all above changes were detected until day 28, but were simultaneously and significantly recovered by day 90. These results suggested that in male mice, allodynia may be caused by reduced GABAergic synaptic inhibition, resulting from elevated [Cl-]i after the reduction of KCC2 by activated microglia. Furthermore, our results suggested that factors from degenerating nerve terminals may diffuse into the sural zone, whereby they induced the development of allodynia in the sural nerve area, while other factors in the sural zone may mediate persistent allodynia through the same pathway.

Multiple Brain Networks Mediating Stimulus-Pain Relationships in Humans

The brain transforms nociceptive input into a complex pain experience comprised of sensory, affective, motivational, and cognitive components. However, it is still unclear how pain arises from nociceptive input and which brain networks coordinate to generate pain experiences. We introduce a new high-dimensional mediation analysis technique to estimate distributed, network-level patterns that formally mediate the relationship between stimulus intensity and pain. We applied the model to a large-scale analysis of functional magnetic resonance imaging data (N = 284), focusing on brain mediators of the relationship between noxious stimulus intensity and trial-to-trial variation in pain reports. We identify mediators in both traditional nociceptive pathways and in prefrontal, midbrain, striatal, and default-mode regions unrelated to nociception in standard analyses. The whole-brain mediators are specific for pain versus aversive sounds and are organized into five functional networks. Brain mediators predicted pain ratings better than previous brain measures, including the neurologic pain signature (Wager et al. 2013). Our results provide a broader view of the networks underlying pain experience, as well as novel brain targets for interventions.

Gastrointestinal pain

Gastrointestinal (GI) pain - a form of visceral pain - is common in some disorders, such as irritable bowel syndrome, Crohn's disease and pancreatitis. However, identifying the cause of GI pain frequently represents a diagnostic challenge as the clinical presentation is often blurred by concomitant autonomic and somatic symptoms. In addition, GI pain can be nociceptive, neuropathic and associated with cancer, but in many cases multiple aetiologies coexist in an individual patient. Mechanisms of GI pain are complex and include both peripheral and central sensitization and the involvement of the autonomic nervous system, which has a role in generating the symptoms that frequently accompany pain. Treatment of GI pain depends on the precise type of pain and the primary disorder in the patient but can include, for example, pharmacological therapy, cognitive behavioural therapies, invasive surgical procedures, endoscopic procedures and lifestyle alterations. Owing to the major differences between organ involvement, disease mechanisms and individual factors, treatment always needs to be personalized and some data suggest that phenotyping and subsequent individual management of GI pain might be options in the future.

Attenuation of reserpine-induced fibromyalgia via ROS and serotonergic pathway modulation by fisetin, a plant flavonoid polyphenol

Fibromyalgia (FM) is a chronic complex musculoskeletal disorder characterized by widespread musculoskeletal pain accompanied by fatigue, sleep disturbance, memory defects and mood changes. Fisetin, a plant flavonoid polyphenol, has been reported to possess potent antioxidant, antinociceptive and neuroprotective activities. The present study aimed to evaluate the efficacy of fisetin against reserpine-induced FM (RIF) in rats. RIF was induced in male Wistar rats (180–220 gm) using reserpine (1 mg/kg; subcutaneous; once daily for 3 consecutive days) and the rats were treated with fisetin (5, 10 and 25 mg/kg) for 21 days. Various behavioral, biochemical and molecular parameters were evaluated. Administration of reserpine induced allodynia, hyperalgesia and depression, which were significantly ameliorated (P<0.05) by fisetin (10 and 25 mg/kg), as reflected by an increase in paw and tail withdrawal latency, increased paw withdrawal threshold, and decreased immobility time. Reserpine led to decreased biogenic amine levels [5-hydroxytryptamine (5-HT), noradrenaline (NA) and dopamine (DA)] and increased the ratio to their metabolite 3,4-dihydroxyphenylacetic acid. 5-hydroxyindoleacetic acid in the spinal cord, thalamus and prefrontal cortex was significantly decreased (P<0.05) by fisetin. Immunohistological analysis of brain tissue revealed that fisetin significantly inhibited (P<0.05) reserpine-induced depletion of 5-HT. It also significantly inhibited (P<0.05) elevated oxido-nitrosative stress and reactive oxygen species (ROS) levels, as analyzed by flow cytometry in RIF rats. Fisetin exerts its antinociceptive and anti-depressive potential via modulation of decreased levels of biogenic amines (5-HT, NA and DA), elevated oxido-nitrosative stress and ROS to ameliorate allodynia, hyperalgesia, and depression in experimental RIF.

Neuropharmacological Properties of the Essential Oil of Bergamot for the Clinical Management of Pain-Related BPSDs

BACKGROUND

Alzheimer's Disease (AD) accounts for approximately 50% of all cases of dementia and, in spite of the great effort for the development of disease-modifying drugs, a definitive treatment of cognitive impairment is not available yet. A perfect adherence to the current therapy of cognitive decline is needed for a better control of the disease and this is proven to reduce, though not completely abolish, the associated Behavioural and Psychological Symptoms of Dementia (BPSDs) from occurring. This cluster of symptoms, remarkably affecting patients' health-related quality of life (HRQL), is tightly associated with pain states. Antipsychotics are the only treatment for BPSDs. However, these drugs are more effective and safer in the short-term (6-12 weeks), they are able to manage aggression but not agitation and they cannot control pain. Aromatherapy with Melissa officinalis and Lavandula officinalis has been employed to handle BPSDs, but it has not provided strong evidence to offer relief from pain.

OBJECTIVE

Bergamot Essential Oil (BEO) exerts antinociceptive activity through several pharmacological mechanisms: in particular, it is able to enhance autophagy, a process undergoing derangement in chronic pain. Thus, the sound pharmacological basis for clinical translation of aromatherapy with BEO in the treatment of BPSDs has been pointed out.

CONCLUSION

The antinociceptive effects elicited by BEO in experimental pain models make it a possible candidate for the pharmacological management of pain-related BPSDs.

The sensory and affective components of pain: are they differentially modifiable dimensions or inseparable aspects of a unitary experience? A systematic review

BACKGROUND

Pain is recognised to have both a sensory dimension (intensity) and an affective dimension (unpleasantness). Pain feels like a single unpleasant bodily experience, but investigations of human pain have long considered these two dimensions of pain to be separable and differentially modifiable. The evidence underpinning this separability and differential modifiability is seldom presented. We aimed to fill this gap by evaluating the current evidence base for whether or not the sensory and affective dimensions of pain can be selectively modulated using cognitive manipulations.

METHODS

A rigorous systematic search, based on a priori search terms and consultation with field experts, yielded 4270 articles. A detailed screening process was based on the following recommendations: (i) evaluation of effectiveness; (ii) examination of methodological rigour, including each study having an a priori intention to cognitively modulate one of the two dimensions of pain; and (iii) sound theoretical reasoning. These were used to ensure that included studies definitively answered the research question.

RESULTS

After in-depth critique of all 12 articles that met the inclusion criteria, we found that there is no compelling evidence that the sensory and affective dimensions of pain can be selectively and intentionally modulated using cognitive manipulations in humans.

CONCLUSIONS

We offer potential explanations for this discrepancy between assumptions and evidence and contend that this finding highlights several important questions for the field, from both the research and clinical perspectives.

Collateral Projections from the Medullary Dorsal Horn to the Ventral Posteromedial Thalamic Nucleus and the Parafascicular Thalamic Nucleus in the Rat

Medullary dorsal horn (MDH), the homolog of spinal dorsal horn, plays essential roles in processing of nociceptive signals from orofacial region toward higher centers, such as the ventral posteromedial thalamic nucleus (VPM) and parafascicular thalamic nucleus (Pf), which belong to the sensory-discriminative and affective aspects of pain transmission systems at the thalamic level, respectively. In the present study, in order to provide morphological evidence for whether neurons in the MDH send collateral projections to the VPM and Pf, a retrograde double tracing method combined with immunofluorescence staining for substance P (SP), SP receptor (SPR) and Fos protein was used. Fluoro-gold (FG) was injected into the VPM and the tetramethylrhodamine-dextran (TMR) was injected into the Pf. The result revealed that both FG- and TMR-labeled projection neurons were observed throughout the entire extent of the MDH, while the FG/TMR double-labeled neurons were mainly located in laminae I and III. It was also found that some of the FG/TMR double-labeled neurons within lamina I expressed SPR and were in close contact with SP-immunoreactive (SP-ir) terminals. After formalin injection into the orofacial region, 41.4% and 34.3% of the FG/TMR double-labeled neurons expressed Fos protein in laminae I and III, respectively. The present results provided morphological evidence for that some SPR-expressing neurons within the MDH send collateral projections to both VPM and Pf and might be involved in sensory-discriminative and affective aspects of acute orofacial nociceptive information transmission.

Somatotopic organization of the human spinothalamic tract: in vivo computed tomography-guided mapping in awake patients undergoing cordotomy

OBJECTIVE

The location of the human spinothalamic tract (STT) in the anterolateral spinal cord has been known for more than a century. The exact nature of the neuronal fiber lamination within the STT, however, remains controversial. After correlating in vivo macrostimulation-induced pain/temperature sensation during percutaneous cervical cordotomy with simultaneous CT imaging of the electrode tip location, the authors present a modern description of the somatotopy of the human cervical STT.

METHODS

Twenty patients underwent CT-guided percutaneous cervical cordotomy to alleviate contralateral medication-refractory cancer pain. Patient responses to electrical stimulation (0.01-0.1 V, 50 Hz, 1 msec) were recorded and the electrode location for each response was documented with a contemporaneous CT scan. In a post hoc analysis of the data, the location for each patient's response(s) was measured and drawn on a diagram of their cord. Positive responses were represented only when the lowest possible voltage (≤ 0.02 V) elicited a response. Negative responses were recorded if there was no clinical response at 0.1 V.

RESULTS

Clinically, patients did well with an average reduction in opiates of 75% at 1 week, and 67% were able to leave the palliative care unit. The size of the cervical cord varied between patients, with an average lateral extent (width) of 11 mm and a height of 9 mm. Responses from the lower limb were represented superficially (lateral) and posteriorly within the anterolateral cord. The area with responses from the upper limb was larger and surrounded those with responses from the lower limb primarily anteriorly and medially, but also posteriorly.

CONCLUSIONS

In this study, the somatotopic organization of the human STT was elucidated for the first time using in vivo macrostimulation and contemporaneous CT imaging during cordotomy. In this cohort of patients, the STT from the lower-limb region was located superficially and posteriorly in the anterolateral quadrant of the cervical cord, with the STT from the upper-limb region surrounding it primarily anteriorly and medially (deep) but also posteriorly. The authors discuss how the previous methods of cordotomy may have biased the earlier versions of STT lamination. They suggest that an ideal spinal cord entry site for cordotomy of either the upper- or lower-limb pain fibers is halfway between the equator and anterior pole of the cord.

Interplay of spinal and vagal pathways on esophageal acid-related anterior cingulate cortex functional networks in rats

Esophageal acid sensory signals are transmitted by both vagal and spinal pathways to the cerebral cortex. The influence and interplay of these pathways on esophageal acid-related functional connectivity has been elusive. Our aim was to evaluate the esophageal acid exposure-related effect on the anterior cingulate cortex (ACC) functional connectivity networks using functional MRI-guided functional connectivity MRI (fcMRI) analysis. We studied six Sprague-Dawley rats for fcMRI experiments under dexmedetomidine hydrochloride anesthesia. Each rat was scanned for 6 min before and after esophageal hydrochloric acid infusion (0.1 N, 0.2 ml/min). The protocol was repeated before and after bilateral cervical vagotomy on the same rat. Seed-based fcMRI analysis was used to examine ACC networks and acid-induced network alterations. Three-factor repeated-measures ANOVA analysis among all four subgroups revealed that the interaction of acid infusion and bilateral vagotomy was mainly detected in the hypothalamus, insula, left secondary somatosensory cortex, left parietal cortex, and right thalamus in the left ACC network. In the right ACC network, this interaction effect was detected in the caudate putamen, insula, motor, primary somatosensory cortex, secondary somatosensory cortex, and thalamic regions. These regions in the ACC networks showed decreased intranetwork connectivity due to acid infusion. However, after bilateral vagotomy, intranetwork connectivity strength inversed and became stronger following postvagotomy acid infusion. Signals transmitted through both the vagal nerve and spinal nerves play a role in esophageal acid-related functional connectivity of the ACC. The vagal signals appear to dampen the acid sensation-related functional connectivity of the ACC networks. NEW & NOTEWORTHY These studies show that esophageal acid-induced brain functional connectivity changes are vagally mediated and suggest that signals transmitted through both the vagal nerve and spinal nerves play a role in esophageal acid-related functional connectivity of the anterior cingulate cortex. This paper focuses on the development of a novel rat functional MRI model fostering improved understanding of acid-related esophageal disorders.

Mechanisms, Predictors, and Challenges in Assessing and Managing Painful Chemotherapy-Induced Peripheral Neuropathy

OBJECTIVE

To describe the known predictors and pathophysiological mechanisms of chronic painful chemotherapy-induced peripheral neuropathy (CIPN) in cancer survivors and the challenges in assessing and managing it.

DATA SOURCES

PubMed/Medline, CINAHL, Scopus, and PsycINFO.

CONCLUSION

The research on chronic painful CIPN is limited. Additional research is needed to identify the predictors and pathophysiological mechanisms of chronic painful CIPN to inform the development of assessment tools and management options for this painful and possibly debilitating condition.

IMPLICATIONS FOR NURSING PRACTICE

Recognition of the predictors of chronic painful CIPN and proactive CIPN assessment and palliative management are important steps in reducing its impact on physical function and quality of life.

Pain and consciousness

The aversive experience we call "pain" results from the coordinated activation of multiple brain areas, commonly described as a "pain matrix". This is not a fixed arrangement of structures but rather a fluid system composed of several interacting networks: A 'nociceptive matrix' includes regions receiving input from ascending nociceptive systems, and ensures the bodily characteristics of physical pain. A further set of structures receiving secondary input supports the 'salience' attributes of noxious stimuli, triggers top-down cognitive controls, and -most importantly- ensures the passage from pre-conscious nociception to conscious pain. Expectations and beliefs can still modulate the conscious experience via activity in supramodal regions with widespread cortical projections such as the ventral tegmental area. Intracortical EEG responses in humans show that nociceptive cortical processing is initiated in parallel in sensory, motor and limbic areas; it progresses rapidly to the recruitment of anterior insular and fronto-parietal networks, and finally to the activation of perigenual, posterior cingulate and hippocampal structures. Functional connectivity between sensory and high-level networks increases during the first second post-stimulus, which may be determinant for access to consciousness. A model is described, progressing from unconscious sensori-motor and limbic processing of spinothalamic and spino-parabrachial input, to an immediate sense of awareness supported by coordinated activity in sensorimotor and fronto-parieto-insular networks, and leading to full declarative consciousness through integration with autobiographical memories and self-awareness, involving posterior cingulate and medial temporal areas. This complete sequence is only present during full vigilance states. We contend, however, that even in unconscious subjects, repeated limbic and vegetative activation by painful stimuli via spino-amygdalar pathways can generate implicit memory traces and stimulus-response abnormal sequences, possibly contributing to long-standing anxiety or hyperalgesic syndromes in patients surviving coma.

Aspects of Pain, Its Assessment and Evaluation from An Acupuncture Perspective

Pain is a major clinical problem that causes great suffering for the individual and incurs costs for society. Accurate assessment and evaluation of perceived pain is necessary for diagnosis, for choice of treatment, and for the evaluation of treatment efficacy. The assessment of an individual's pain is a challenge since pain is a subjective, multidimensional experience, and assessment is based on the person's own self-report. The results are often varied, possibly due to inter-individual variation, but also in relation to gender and aetiology.

A gold standard for pain assessment is still lacking, but rating scales, questionnaires, and methods derived from psychophysical concepts, such as threshold assessments and perceptual matching, are used. In the evaluation of pain and associated variables, both systematic and individual variation should be taken into account, as should pain-associated symptoms.

Recommendations for pain treatment should be based on the patient's specific needs. Therefore, it is important to assess the level of perceived pain taking individual variation into account. The methods used should preferably have proved to be useful in randomised controlled trials, and analysis of pain assessment should consider its non-metric properties. In the future, the use of studies with a naturalistic protocol together with individual assessment of individual pain responses could increase the internal and external validity.