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

EEG oscillations reveal neuroplastic changes in pain processing associated with long-term meditation

The experience of pain is a combined product of bottom-up and top-down influences mediated by attentional and emotional factors. Meditation states and traits are characterized by enhanced attention/emotion regulation and expanded self-awareness that can be expected to modify pain processing. The main objective of the present study was to explore the effects of long-term meditation on neural mechanisms of pain processing. EEG pain-related oscillations (PROs) were analysed in highly experienced practitioners and novices during a non-meditative resting state with respect to (a) local frequency-specific and temporal synchronizing characteristics to reflect mainly bottom-up mechanisms, (b) spatial synchronizing patterns to reflect the neural communication of noxious information, (c) pre-stimulus oscillations to reflect top-down mechanisms during pain expectancy, and (d) the P3b component of the pain-related potential to compare the emotional/cognitive reappraisal of pain events by expert and novice meditators. Main results demonstrated that in experienced (long-term) meditators as compared to non-experienced (short-term) meditators (1) the temporal and spatial synchronizations of multispectral (from theta-alpha to gamma) PROs were substantially suppressed at primary and secondary somatosensory regions contra-lateral to pain stimulation within 200 ms after noxious stimulus; (2) pre-stimulus alpha activity was significantly increased at the same regions, which predicted the suppressed synchronization of PROs in long-term meditators; (3) the decrease of the P3b component was non-significant. These novel observations provide evidence that even when subjected to pain outside of meditation, experienced meditators exhibit a pro-active top-down inhibition of somatosensory areas resulting in suppressed processing and communication of sensory information at early stages of painful input. The emotional/cognitive appraisal of pain is reduced but remains preserved revealing a capacity of experienced meditators to dissociate pro-active and reactive top-down processes during pain control.

Anatomical characterisation of somatostatin-expressing neurons belonging to the anterolateral system

Anterolateral system (ALS) spinal projection neurons are essential for pain perception. However, these cells are heterogeneous, and there has been extensive debate about the roles of ALS populations in the different pain dimensions. We recently performed single-nucleus RNA sequencing on a developmentally-defined subset of ALS neurons, and identified 5 transcriptomic populations. One of these, ALS4, consists of cells that express Sst, the gene coding for somatostatin, and we reported that these were located in the lateral part of lamina V. Here we use a SstCre mouse line to characterise these cells and define their axonal projections. We find that their axons ascend mainly on the ipsilateral side, giving off collaterals throughout their course in the spinal cord. They target various brainstem nuclei, including the parabrachial internal lateral nucleus, and the posterior triangular and medial dorsal thalamic nuclei. We also show that in the L4 segment Sst is expressed by ~ 75% of ALS neurons in lateral lamina V and that there are around 120 Sst-positive lateral lamina V cells on each side. Our findings indicate that this is a relatively large population, and based on projection targets we conclude that they are likely to contribute to the affective-motivational dimension of pain.

Exploratory study on the ascending pain pathway in patients with chronic neck and shoulder pain based on combined brain and spinal cord diffusion tensor imaging

Objective

To explore the changes in the white matter microstructure of the ascending pain conduction pathways in patients with chronic neck and shoulder pain (CNSP) using combined brain and spinal cord diffusion tensor imaging techniques, and to assess its correlation with clinical indicators and cognitive functions.

Materials and methods

A 3.0T MRI scanner was used to perform combined brain and spinal cord diffusion tensor imaging scans on 31 CNSP patients and 24 healthy controls (HCs), extracting the spinothalamic tract (STT) and quantitatively analyzing the fractional anisotropy (FA) and mean diffusivity (MD) which reflect the microstructural integrity of nerve fibers. Additionally, these differences were subjected to partial correlation analysis in relation to Visual Analog Scale (VAS) scores, duration of pain, Self-Rating Anxiety Scale (SAS), and Self-Rating Depression Scale (SDS).

Results

Compared to HCs, CNSP patients showed decreased mean FA values and increased mean MD values in bilateral intracranial STT compared to the HC group, but two-sample t-test results indicated no statistically significant differences (p > 0.05). FA values of the left STT (C2 segment, C5 segment) and right STT (C1 segment, C2 segment) were significantly decreased in bilateral cervical STTs of CNSP patients; MD values of the left STT (C1 segment, C2 segment, C5 segment) and right STT (C1 segment, C5 segment) were significantly increased (p < 0.05). Partial correlation analysis results showed that FA values of STT in CNSP patients were negatively correlated with VAS scores, duration of pain, SAS scores, and SDS scores, while MD values were positively correlated with VAS scores and duration of pain (Bonferroni p < 0.05).

Conclusion

This research identified that patients with CNSP exhibited reduced mean FA and increased mean MD in the bilateral intracranial STT, although these differences were not statistically significant (p > 0.05). Conversely, significant abnormalities were observed in specific segments of the bilateral cervical STT (p < 0.05), which were also correlated with variations in pain intensity, illness duration, and levels of anxiety and depression. These findings contribute a novel neuroimaging perspective to the evaluation and elucidation of the pathophysiological mechanisms underlying chronic pain in the ascending conduction pathways.

Modulating nociception networks: the impact of low-intensity focused ultrasound on thalamocortical connectivity

Pain engages multiple brain networks, with the thalamus serving as a critical subcortical hub. This study aims to explore the effects of low-intensity transcranial focused ultrasound-induced suppression on the organization of thalamocortical nociceptive networks. We employed MR-guided focused ultrasound, a potential non-invasive therapy, with real-time ultrasound beam localization feedback and fMRI monitoring. We first functionally identified the focused ultrasound target at the thalamic ventroposterior lateral nucleus by mapping the whole-brain blood oxygenation level-dependent responses to nociceptive heat stimulation of the hand using fMRI in each individual macaque monkey under light anaesthesia. The blood oxygenation level-dependent fMRI signals from the heat-responsive thalamic ventroposterior lateral nucleus were analysed to derive thalamocortical effective functional connectivity network using the psychophysical interaction method. Nineteen cortical regions across sensorimotor, cognitive, associative and limbic networks exhibited strong effective functional connectivity to the thalamic ventroposterior lateral during heat nociceptive processing. Focused ultrasound-induced suppression of heat activity in the thalamic ventroposterior lateral nucleus altered nociceptive responses in most of the 19 regions. Data-driven hierarchical clustering analyses of blood oxygenation level-dependent time courses across all thalamocortical region-of-interest pairs identified two effective functional connectivity subnetworks. The concurrent suppression of thalamic heat response with focused ultrasound reorganized these subnetworks and modified thalamocortical connection strength. Our findings suggest that the thalamic ventroposterior lateral nucleus has extensive and causal connections to a wide array of cortical areas during nociceptive processing. The combination of MR-guided focused ultrasound with fMRI enables precise dissection and modulation of nociceptive networks in the brain, a capability that no other device-based neuromodulation methods have achieved. This presents a promising non-invasive tool for modulating pain networks with profound clinical relevance. The robust modulation of nociceptive effective functional connectivity networks by focused ultrasound strongly supports the thalamic ventroposterior lateral as a viable target for pain management strategies.

Discovery of Novel Pain Regulators Through Integration of Cross-Species High-Throughput Data

AIMS

Chronic pain is an impeding condition that affects day-to-day life and poses a substantial economic burden, surpassing many other health conditions. This study employs a cross-species integrated approach to uncover novel pain mediators/regulators.

METHODS

We used weighted gene coexpression network analysis to identify pain-enriched gene module. Functional analysis and protein-protein interaction (PPI) network analysis of the module genes were conducted. RNA sequencing compared pain model and control mice. PheWAS was performed to link genes to pain-related GWAS traits. Finally, candidates were prioritized based on node degree, differential expression, GWAS associations, and phenotype correlations.

RESULTS

A gene module significantly over-enriched with the pain reference set was identified (referred to as "pain module"). Analysis revealed 141 pain module genes interacting with 46 pain reference genes in the PPI network, which included 88 differentially expressed genes. PheWAS analysis linked 53 of these genes to pain-related GWAS traits. Expression correlation analysis identified Vdac1, Add2, Syt2, and Syt4 as significantly correlated with pain phenotypes across eight brain regions. NCAM1, VAMP2, SYT2, ADD2, and KCND3 were identified as top pain response/regulator genes.

CONCLUSION

The identified genes and molecular mechanisms may enhance understanding of pain pathways and contribute to better drug target identification.

Electrical stimulation of the sciatic nerve restores inspiratory diaphragm function in mice after spinal cord injury

Introduction

Spinal cord injury in the high cervical cord can impair breathing due to disruption of pathways between brainstem respiratory centers and respiratory motor neurons in the spinal cord. Electrical stimulation of limb afferents can increase ventilation in healthy humans and animals, but it is not known if limb afferent stimulation can improve breathing following a cervical injury.

Methods

We stimulated the sciatic nerve while using electromyography to measure diaphragm function in anesthetized mice following a cervical (C2) hemisection spinal cord injury, as well as in uninjured controls. The amplitude and frequency of inspiratory bursts was analyzed over a range of stimulation thresholds.

Results

We show that electrical stimulation (at sufficient current thresholds) of either the left or right sciatic nerve could restore inspiratory activity to the previously paralyzed diaphragm ipsilateral to a C2 hemisection injury at either acute (1 day) or chronic (2 months) stages after injury. We also show that sciatic nerve stimulation can increase the frequency and amplitude of diaphragm inspiratory bursts in uninjured mice.

Discussion

Our findings indicate that therapies targeting limb afferents could potentially be used to improve breathing in patients with cervical spinal cord injury and provide an experimental model to further investigate the neural pathways by which limb afferents can increase respiratory muscle activity.

Local abnormal white matter microstructure in the spinothalamic tract in people with chronic neck and shoulder pain

Objective

To investigate differences in the microstructure of the spinothalamic tract (STT) white matter in people with chronic neck and shoulder pain (CNSP) using diffusion tensor imaging, and to assess its correlation with pain intensity and duration of the pain.

Materials and methods

A 3.0T MRI scanner was used to perform diffusion tensor imaging scans on 31 people with CNSP and 24 healthy controls (HCs), employing the Automatic Fiber Segmentation and Quantification (AFQ) method to extract the STT and quantitatively analyze the fractional anisotropy (FA) and mean diffusivity (MD), reflecting the microstructural integrity of nerve fibers. Correlations of these differences with duration of pain and visual analog scale (VAS) scores were analyzed.

Results

No significant differences in the mean FA or MD values of the bilateral STT were observed between people with CNSP and HCs (p > 0.05), as indicated by the two-sample t test. Further point-by-point comparison along 100 equidistant nodes within the STT pathway revealed significant reductions in FA values in the left (segments 12-18, 81-89) and right (segments 9-19, 76-80) STT in the CNSP group compared to HCs; significant increases in MD values were observed in the left (segments 1-13, 26-30, 71-91) and right (segments 8-17, 76-91) STT (p < 0.05, FWE corrected). Partial correlation analysis indicates that in people with CNSP, the FA values of the STT in regions with damaged white matter structure show a negative correlation with VAS scores and duration of pain, whereas MD values show a positive correlation with VAS scores and duration of pain.

Conclusion

This study found that people with CNSP exhibit white matter microstructural abnormalities in the specific segments of STT. These abnormalities are associated with the patient's pain intensity and disease duration. The findings offer a new neuroimaging perspective on the pathophysiological basis of chronic pain in the ascending conduction process and its potential role in developing targeted intervention strategies. However, due to the limited sample size and the lack of statistical significance when analyzing the entire spinothalamic tract, these conclusions should be interpreted with caution. Further research with larger cohorts is necessary to validate these results.

The Neurophysiological Impact of Touch-Based Therapy: Insights and Clinical Benefits

The evidence on how touch-based therapy acts on the brain activity opens novel cues for the treatment of chronic pain conditions for which no definitive treatment exists. Touch-based therapies, particularly those involving C-tactile (CT)-optimal touch, have gained increasing attention for their potential in modulating pain perception and improving psychological well-being. While previous studies have focused on the biomechanical effects of manual therapy, recent research has shifted towards understanding the neurophysiological mechanisms underlying these interventions. CT-optimal touch, characterized by gentle stroking that activates CT afferents, may be used to reduce pain perception in chronic pain conditions and to enhance psychological well-being. Further research is needed to fully elucidate the neurophysiological mechanisms involved and to establish the therapeutic efficacy of CT-optimal touch in various clinical populations.

Pathophysiology of Pain and Mechanisms of Neuromodulation: A Narrative Review (A Neuron Project)

Pain serves as a vital innate defense mechanism that can significantly impact an individual's quality of life. Understanding the physiological effects of pain well plays an important role in developing novel pain treatments. Nociceptor neurons play a key role in pain and inflammation. Interactions between nociceptors and the immune system occur both at the site of injury and within the central nervous system. Modulating chemical mediators and nociceptor activity offers promising new approaches to pain management. Essentially, the sensory nervous system is essential for modulating the body's protective response, making it critical to understand these interactions to discover new pain treatment strategies. New innovations in neuromodulation have led to alternatives to opioids individuals with chronic pain with consequent improvement in disease-based treatment and nerve targeting. New neural targets from cellular and structural perspectives have revolutionized the field of neuromodulation. This narrative review aims to elucidate the mechanisms of pain transmission and processing, examine the characteristics and properties of nociceptors, and explore how the immune system influences pain perception. It further provides an updated overview of the physiology of pain and neuromodulatory mechanisms essential for managing acute and chronic pain. We assess the current understanding of different pain types, focusing on key molecules involved in each type and their physiological effects. Additionally, we compare painful and painless neuropathies and discuss the neuroimmune interactions involved in pain manifestation.

Subcortical Alterations in Newly Diagnosed Epilepsy and Associated Changes in Brain Connectivity and Cognition

Patients with chronic focal epilepsy commonly exhibit subcortical atrophy, particularly of the thalamus. The timing of these alterations remains uncertain, though preliminary evidence suggests that observable changes may already be present at diagnosis. It is also not yet known how these morphological changes are linked to the coherence of white matter pathways throughout the brain, or to neuropsychological function often compromised before antiseizure medication treatment. This study investigates localized atrophy in subcortical regions using surface shape analysis in individuals with newly diagnosed focal epilepsy (NDfE) and assesses their implications on brain connectivity and cognitive function. We collected structural (T1w) and diffusion-weighted MRI and neuropsychological data from 104 patients with NDfE and 45 healthy controls (HCs) matched for age, sex, and education. A vertex-based shape analysis was performed on subcortical structures to compare patients with NDfE and HC, adjusting for age, sex, and intracranial volume. The mean deformation of significance areas (pcor < 0.05) was used to identify white matter pathways associated with overall shape alterations in patients relative to controls using correlational tractography. Additionally, the relationship between significant subcortical shape values and neuropsychological outcomes was evaluated using a generalized canonical correlation approach. Shape analysis revealed bilateral focal inward deformation (a proxy for localized atrophy) in anterior areas of the right and left thalamus and right pallidum in patients with NDfE compared to HC (FWE corrected). No structures showed areas of outward deformation in patients. The connectometry analysis revealed that fractional anisotropy (FA) was positively correlated with thalamic and pallidal shape deformation, that is, reduced FA was associated with inward deformation in tracts proximal to and or connecting with the thalamus including the fornix, frontal, parahippocampal, and corticothalamic pathways. Thalamic and pallidal shape changes were also related to increased depression and anxiety and reduced memory and cognitive function. These findings suggest that atrophy of the thalamus, which has previously been associated with the generation and maintenance of focal seizures, may present at epilepsy diagnosis and relate to alterations in both white matter connectivity and cognitive performance. We suggest that at least some alterations in brain structure and consequent impact on cognitive and affective processes are the result of early epileptogenic processes rather than exclusively due to the chronicity of longstanding epilepsy, recurrent seizures, and treatment with antiseizure medication.

Lateral lamina V projection neuron axon collaterals connect sensory processing across the dorsal horn of the mouse spinal cord

Spinal projection neurons (PNs) are defined by long axons that travel from their origin in the spinal cord to the brain where they relay sensory information from the body. The existence and function of a substantial axon collateral network, also arising from PNs and remaining within the spinal cord, is less well appreciated. Here we use a retrograde viral transduction strategy to characterise a novel subpopulation of deep dorsal horn spinoparabrachial neurons. Brainbow assisted analysis confirmed that virally labelled PN cell bodies formed a discrete cell column in the lateral part of Lamina V (LVlat) and the adjoining white matter. These PNs exhibited large dendritic territories biased to regions lateral and ventral to the cell body column and extending considerable rostrocaudal distances. Optogenetic activation of LVLat PNs confirmed this population mediates widespread signalling within spinal cord circuits, including activation in the superficial dorsal horn. This signalling was also demonstrated with patch clamp recordings during LVLat PN photostimulation, with a range of direct and indirect connections identified and evidence of a postsynaptic population of inhibitory interneurons. Together, these findings confirm a substantial role for PNs in local spinal sensory processing, as well as relay of sensory signals to the brain.

Spatiotemporal integration of contextual and sensory information within the cortical hierarchy in human pain experience

Pain is not a mere reflection of noxious input. Rather, it is constructed through the dynamic integration of current predictions with incoming sensory input. However, the temporal dynamics of the behavioral and neural processes underpinning this integration remain elusive. In the current study involving 59 human participants, we identified a series of brain mediators that integrated cue-induced expectations with noxious inputs into ongoing pain predictions using a semicircular scale designed to capture rating trajectories. Temporal mediation analysis revealed that during the early-to-mid stages of integration, the frontoparietal and dorsal attention network regions, such as the lateral prefrontal, premotor, and parietal cortex, mediated the cue effects. Conversely, during the mid-to-late stages of integration, the somatomotor network regions mediated the effects of stimulus intensity, suggesting that the integration occurs along the cortical hierarchy from the association to sensorimotor brain systems. Our findings advance the understanding of how the brain integrates contextual and sensory information into pain experience over time.

Characteristics of pain empathic networks in healthy and primary dysmenorrhea women: an fMRI study

Pain empathy enables us to understand and share how others feel pain. Few studies have investigated pain empathy-related functional interactions at the whole-brain level across all networks. Additionally, women with primary dysmenorrhea (PDM) have abnormal pain empathy, and the association among the whole-brain functional network, pain, and pain empathy remain unclear. Using resting-state functional magnetic resonance imaging (fMRI) and machine learning analysis, we identified the brain functional network connectivity (FNC)-based features that are associated with pain empathy in two studies. Specifically, Study 1 examined 41 healthy controls (HCs), while Study 2 investigated 45 women with PDM. Additionally, in Study 3, a classification analysis was performed to examine the differences in FNC between HCs and women with PDM. Pain empathy was evaluated using a visual stimuli experiment, and trait and state of menstrual pain were recorded. In Study 1, the results showed that pain empathy in HCs relied on dynamic interactions across whole-brain networks and was not concentrated in a single or two brain networks, suggesting the dynamic cooperation of networks for pain empathy in HCs. In Study 2, PDM exhibited a distinctive network for pain empathy. The features associated with pain empathy were concentrated in the sensorimotor network (SMN). In Study 3, the SMN-related dynamic FNC could accurately distinguish women with PDM from HCs and exhibited a significant association with trait menstrual pain. This study may deepen our understanding of the neural mechanisms underpinning pain empathy and suggest that menstrual pain may affect pain empathy through maladaptive dynamic interaction between brain networks.

Differential activation of lateral parabrachial nuclei and their limbic projections during head compared with body pain: A 7-Tesla functional magnetic resonance imaging study

Pain is a complex experience that involves sensory, emotional, and motivational components. It has been suggested that pain arising from the head and orofacial regions evokes stronger emotional responses than pain from the body. Indeed, recent work in rodents reports different patterns of activation in ascending pain pathways during noxious stimulation of the skin of the face when compared to noxious stimulation of the body. Such differences may dictate different activation patterns in higher brain regions, specifically in those areas processing the affective component of pain. We aimed to use ultra-high field functional magnetic resonance imaging (fMRI at 7-Tesla) to determine whether noxious thermal stimuli applied to the surface of the face and body evoke differential activation patterns within the ascending pain pathway in awake humans (n=16). Compared to the body, noxious heat stimulation to the face evoked more widespread signal changes in prefrontal cortical regions and numerous brainstem and subcortical limbic areas. Moreover, facial pain evoked significantly different signal changes in the lateral parabrachial nucleus, substantia nigra, paraventricular hypothalamus, and paraventricular thalamus, to those evoked by body pain. These results are consistent with recent preclinical findings of differential activation in the brainstem and subcortical limbic nuclei and associated cortices during cutaneous pain of the face when compared with the body. The findings suggest one potential mechanism by which facial pain could evoke a greater emotional impact than that evoked by body pain.

Mechanical pain sensitivity is associated with hippocampal structural integrity

ABSTRACT

Rodents and human studies indicate that the hippocampus, a brain region necessary for memory processing, responds to noxious stimuli. However, the hippocampus has yet to be considered a key brain region directly involved in the human pain experience. One approach to answer this question is to perform quantitative sensory testing on patients with hippocampal damage-ie, medial temporal lobe epilepsy. Some case studies and case series have performed such tests in a handful of patients with various types of epilepsy and have reported mixed results. Here, we aimed to determine whether mechanical pain sensitivity was altered in patients diagnosed with temporal lobe epilepsy. We first investigated whether mechanical pain sensitivity in patients with temporal lobe epilepsy differs from that of healthy individuals. Next, in patients with temporal lobe epilepsy, we evaluated whether the degree of pain sensitivity is associated with the degree of hippocampal integrity. Structural integrity was based on hippocampal volume, and functional integrity was based on verbal and visuospatial memory scores. Our findings show that patients with temporal lobe epilepsy have lower mechanical pain sensitivity than healthy individuals. Only left hippocampal volume was positively associated with mechanical pain sensitivity-the greater the hippocampal damage, the lower the sensitivity to mechanical pain. Hippocampal measures of functional integrity were not significantly associated with mechanical pain sensitivity, suggesting that the mechanisms of hippocampal pain processing may be different than its memory functions. Future studies are necessary to determine the mechanisms of pain processing in the hippocampus.

Circadian functional changes of pain-processing brainstem nuclei and implications for cluster headache: A 7 Tesla imaging study

BACKGROUND

Pain thresholds and primary headaches, including cluster headache attacks, have circadian rhythmicity. Thus, they might share a common neuronal mechanism.

OBJECTIVE

This study aimed to elucidate how the modulation of nociceptive input in the brainstem changes from noon to midnight. Insights into the mechanism of these fluctuations could allow for new hypotheses about the pathophysiology of cluster headache.

METHODS

This repeated measure observational study was conducted at the University Hospital Zurich from December 2019 to November 2022. Healthy adults between 18 and 85 years of age were eligible. All participants were examined at noon and midnight. We tested the pain threshold on both sides of the foreheads with quantitative sensory testing, assessed tiredness levels, and obtained high-field (7 Tesla) and high-resolution functional magnetic resonance imaging (MRI) at each visit. Functional connectivity was assessed at the two visits by performing a region-of-interest analysis. We defined nuclei in the brainstem implicated in processing nociceptive input as well as the thalamus and suprachiasmatic nucleus as the region-of-interest.

RESULTS

Ten people were enrolled, and seven participants were included. First, we did not find statistically significant differences between noon and midnight of A-delta-mediated pain thresholds (median mechanical pain threshold at noon: left 9.2, right 9.2; at night: left 6.5, right 6.1). Second, after correction for a false discovery rate, we found changes in the mechanical pain sensitivity to have a statistically significant effect on changes in the functional connectivity between the left parabrachial nucleus and the suprachiasmatic nucleus (T = -40.79).

CONCLUSION

The MRI data analysis suggested that brain stem nuclei and the hypothalamus modulate A-delta-mediated pain perception; however, these changes in pain perception did not lead to statistically significantly differing pain thresholds between noon and midnight. Hence, our findings shed doubt on our hypothesis that the physiologic circadian rhythmicity of pain thresholds could drive the circadian rhythmicity of cluster headache attacks.

Cerebellar Non-Invasive Brain Stimulation: A Frontier in Chronic Pain Therapy

Chronic pain poses a widespread and distressing challenge; it can be resistant to conventional therapies, often having significant side effects. Non-invasive brain stimulation (NIBS) techniques offer promising avenues for the safe and swift modulation of brain excitability. NIBS approaches for chronic pain management targeting the primary motor area have yielded variable outcomes. Recently, the cerebellum has emerged as a pivotal hub in human pain processing; however, the clinical application of cerebellar NIBS in chronic pain treatment remains limited. This review delineates the cerebellum's role in pain modulation, recent advancements in NIBS for cerebellar activity modulation, and novel biomarkers for assessing cerebellar function in humans. Despite notable progress in NIBS techniques and cerebellar activity assessment, studies targeting cerebellar NIBS for chronic pain treatment are limited in number. Nevertheless, positive outcomes in pain alleviation have been reported with cerebellar anodal transcranial direct current stimulation. Our review underscores the potential for further integration between cerebellar NIBS and non-invasive assessments of cerebellar function to advance chronic pain treatment strategies.

Exercise Training Alleviates Symptoms and Cognitive Decline in a Reserpine-induced Fibromyalgia Model by Activating Hippocampal PGC-1α/FNDC5/BDNF Pathway

The purpose of this study was to assess, from a behavioral, biochemical, and molecular standpoint, how exercise training affected fibromyalgia (FM) symptoms in a reserpine-induced FM model and to look into the potential involvement of the hippocampal PGC-1α/FNDC5/BDNF pathway in this process. Reserpine (1 mg kg-1) was subcutaneously injected once daily for three consecutive days and then the rats were exercised for 21 days. Mechanical allodynia was evaluated 1, 11, and 21 days after the last injection. At the end of the exercise training protocol forced swim, open field and Morris water maze tests were performed to assess depression, locomotion and cognition, respectively. Additionally, biochemical and molecular markers related to the pathogenesis of the FM and cognitive functions were measured. Reserpine exposure was associated with a decrease in locomotion, an increase in depression, an increase in mechanical allodynia, and a decrease in spatial learning and memory (p < 0.05). These behavioral abnormalities were found to be correlated with elevated blood cytokine levels, reduced serotonin levels in the prefrontal cortex, and altered PGC-1α/FNDC5/BDNF pathway in the hippocampus (p < 0.05). Interestingly, exercise training attenuated all the neuropathological changes mentioned above (p < 0.05). These results imply that exercise training restored behavioral, biochemical, and molecular changes against reserpine-induced FM-like symptoms in rats, hence mitigating the behavioral abnormalities linked to pain, depression, and cognitive functioning.

Substance P's Impact on Chronic Pain and Psychiatric Conditions-A Narrative Review

Substance P (SP) plays a crucial role in pain modulation, with significant implications for major depressive disorder (MDD), anxiety disorders, and post-traumatic stress disorder (PTSD). Elevated SP levels are linked to heightened pain sensitivity and various psychiatric conditions, spurring interest in potential therapeutic interventions. In chronic pain, commonly associated with MDD and anxiety disorders, SP emerges as a key mediator in pain and emotional regulation. This review examines SP's impact on pain perception and its contributions to MDD, anxiety disorders, and PTSD. The association of SP with increased pain sensitivity and chronic pain conditions underscores its importance in pain modulation. Additionally, SP influences the pathophysiology of MDD, anxiety disorders, and PTSD, highlighting its potential as a therapeutic target. Understanding SP's diverse effects provides valuable insights into the mechanisms underlying these psychiatric disorders and their treatment. Further research is essential to explore SP modulation in psychiatric disorders and develop more effective treatment strategies.

Neuropathic pain in cats: Mechanisms and multimodal management

PRACTICAL RELEVANCE

Chronic pain is a significant welfare concern in cats, and neuropathic pain, which arises from aberrant processing of sensory signals within the nervous system, is a subcategory of this type of pain. To comprehend this condition and how multimodal pharmacotherapy plays a central role in alleviating discomfort, it is crucial to delve into the anatomy of nociception and pain perception. In addition, there is an intricate interplay between emotional health and chronic pain in cats, and understanding and addressing the emotional factors that contribute to pain perception, and vice versa, is essential for comprehensive care.Clinical approach:Neuropathic pain is suspected if there is abnormal sensation in the area of the distribution of pain, together with a positive response to trial treatment with drugs effective for neuropathic pain. Ideally, this clinical suspicion would be supported by confirmation of a lesion at this neurolocalisation using diagnostic modalities such as MRI and neuroelectrophysiology. Alternatively, there may be a history of known trauma at that site. A variety of therapies, including analgesic, anti-inflammatory and adjuvant drugs, and neuromodulation (eg, TENS or acupuncture), can be employed to address different facets of pain pathways.Aim:This review article, aimed at primary care/ general practitioners, focuses on the identification and management of neuropathic pain in cats. Three case vignettes are included and a structured treatment algorithm is presented to guide veterinarians in tailoring interventions.Evidence base:The review draws on current literature, where available, along with the author's extensive experience and research.

Re-examining the Mysterious Role of the Cerebellum in Pain

Pain is considered a multidimensional experience that embodies not merely sensation, but also emotion and perception. As is appropriate for this complexity, pain is represented and processed by an extensive matrix of cortical and subcortical structures. Of these structures, the cerebellum is gaining increasing attention. Although association between the cerebellum and both acute and chronic pain have been extensively detailed in electrophysiological and neuroimaging studies, a deep understanding of what functions are mediated by these associations is lacking. Nevertheless, the available evidence implies that lobules IV-VI and Crus I are especially pertinent to pain processing, and anatomical studies reveal that these regions connect with higher-order structures of sensorimotor, emotional, and cognitive function. Therefore, we speculate that the cerebellum exerts a modulatory role in pain via its communication with sites of sensorimotor, executive, reward, and limbic function. On this basis, in this review, we propose numerous ways in which the cerebellum might contribute to both acute and chronic pain, drawing particular attention to emotional and cognitive elements of pain. In addition, we emphasise the importance of advancing our knowledge about the relationship between the cerebellum and pain by discussing novel therapeutic opportunities that capitalize on this association.

Effectiveness of Duloxetine on Oxaliplatin-induced Allodynia and Hyperalgesia in Rats

Development of painful oxaliplatin-induced peripheral neuropathy (OIPN) is a major problem in people who receive oxaliplatin as part of cancer treatment. The pain experienced by those with OIPN can be seriously debilitating and lead to discontinuation of an otherwise successful treatment. Duloxetine is currently the only recommended treatment for established painful OIPN recommended by the American Society of Clinical Oncology, but its preventative ability is still not clear. This study examined the ability of duloxetine to prevent signs of chronic OIPN in female (n = 12) and male (n = 21) rats treated with the chemotherapeutic agent oxaliplatin. Using an established model of OIPN, rats were started on duloxetine (15 mg) one week prior to oxaliplatin administration and continued duloxetine for 32 days. Behavioral testing for mechanical allodynia and mechanical hyperalgesia was done with selected von Frey filaments. Significant posttreatment differences were found for allodynia in female (p = .004), but not male rats. Duloxetine was associated with significant differences for hyperalgesia in both female (p < .001) and male (p < .001) rats. These findings provide preliminary evidence of the preventative effects of duloxetine on both oxaliplatin-induced allodynia and hyperalgesia in male and female rats, with a difference noted in response between the sexes.

Functional Stimulation and Imaging to Predict Neuromodulation of Chronic Low Back Pain

Back pain is one of the most common aversive sensations in human experience. Pain is not limited to the sensory transduction of tissue damage; rather, it encompasses a range of nervous system activities including lateral modulation, long-distance transmission, encoding, and decoding. Although spine surgery may address peripheral pain generators directly, aberrant signals along canonical aversive pathways and maladaptive influence of affective and cognitive states can result in persistent subjective pain refractory to classical surgical intervention. The clinical identification of who will benefit from surgery-and who will not-is increasingly grounded in neurophysiology.

The functional and anatomical characterization of three spinal output pathways of the anterolateral tract

The nature of spinal output pathways that convey nociceptive information to the brain has been the subject of controversy. Here, we provide anatomical, molecular, and functional characterizations of two distinct anterolateral pathways: one, ascending in the lateral spinal cord, triggers nociceptive behaviors, and the other one, ascending in the ventral spinal cord, when inhibited, leads to sensorimotor deficits. Moreover, the lateral pathway consists of at least two subtypes. The first is a contralateral pathway that extends to the periaqueductal gray (PAG) and thalamus; the second is a bilateral pathway that projects to the bilateral parabrachial nucleus (PBN). Finally, we present evidence showing that activation of the contralateral pathway is sufficient for defensive behaviors such as running and freezing, whereas the bilateral pathway is sufficient for attending behaviors such as licking and guarding. This work offers insight into the complex organizational logic of the anterolateral system in the mouse.

Copaifera langsdorffii Desf. tree oleoresin-induced antinociception recruits µ1- and κ -opioid receptors in the ventrolateral columns of the periaqueductal gray matter

Popular medicine has been using oleoresin from several species of copaíba tree for the treatment of various diseases and its clinical administration potentially causes antinociception. Electrical stimulation of ventrolateral (vlPAG) and dorsolateral (dlPAG) columns of the periaqueductal gray matter also causes antinociception. The aim this study was to verify the antinociceptive effect of oleoresin extracted from Copaifera langsdorffii tree and to test the hypothesis that oleoresin-induced antinociception is mediated by µ1- and κ-opioid receptors in the vlPAG and dlPAG. Nociceptive thresholds were determined by the tail-flick test in Wistar rats. The copaíba tree oleoresin was administered at different doses (50, 100 and 200 mg/kg) through the gavage technique. After the specification of the most effective dose of copaíba tree oleoresin (200 mg/kg), rats were pretreated with either the µ1-opioid receptor selective antagonist naloxonazine (at 0.05, 0.5 and 5 µg/ 0.2 µl in vlPAG, and 5 µg/ 0.2 µl in dlPAG) or the κ-opioid receptor selective antagonist nor-binaltorphimine (at 1, 3 and 9 nmol/ 0.2 µl in vlPAG, and 9 nmol/ 0.2 µl in dlPAG). The blockade of µ1 and κ opioid receptors of vlPAG decreased the antinociception produced by copaíba tree oleoresin. However, the blockade of these receptors in dlPAG did not alter copaíba tree oleoresin-induced antinociception. These data suggest that vlPAG µ1 and κ opioid receptors are critically recruited in the antinociceptive effect produced by oleoresin extracted from Copaifera langsdorffii.

Functional Anatomy of the Spinal Cord

Localization of lesions in the spinal cord requires knowledge of the functional anatomy of gray and white matter tracts. Using decussation points for white matter tracts can help determine lesion level. Pathologies can affect gray and white matter tracts in distinct ways and pattern recognition can help narrow down the differential diagnosis.

Mechanisms of pain in aging and age-related conditions: Focus on caregivers

Pain is a complex, subjective experience that can significantly impact quality of life, particularly in aging individuals, by adversely affecting physical and emotional well-being. Whereas acute pain usually serves a protective function, chronic pain is a persistent pathological condition that contributes to functional deficits, cognitive decline, and emotional disturbances in the elderly. Despite substantial progress that has been made in characterizing age-related changes in pain, complete mechanistic details of pain processing mechanisms in the aging patient remain unknown. Pain is particularly under-recognized and under-managed in the elderly, especially among patients with Alzheimer's disease (AD), Alzheimer's disease-related dementias (ADRD), and other age-related conditions. Furthermore, difficulties in assessing pain in patients with AD/ADRD and other age-related conditions may contribute to the familial caregiver burden. The purpose of this article is to discuss the mechanisms and risk factors for chronic pain development and persistence, with a particular focus on age-related changes. Our article also highlights the importance of caregivers working with aging chronic pain patients, and emphasizes the urgent need for increased legislative awareness and improved pain management in these populations to substantially alleviate caregiver burden.

Thermal stimulus task fMRI in the cervical spinal cord at 7 Tesla

Although functional magnetic resonance imaging (fMRI) is widely applied in the brain, fMRI of the spinal cord is more technically demanding. Proximity to the vertebral column and lungs results in strong spatial inhomogeneity and temporal fluctuations in B0 . Increasing field strength enables higher spatial resolution and improved sensitivity to blood oxygenation level-dependent (BOLD) signal, but amplifies the effects of B0 inhomogeneity. In this work, we present the first task fMRI in the spinal cord at 7 T. Further, we compare the performance of single-shot and multi-shot 2D echo-planar imaging (EPI) protocols, which differ in sensitivity to spatial and temporal B0 inhomogeneity. The cervical spinal cords of 11 healthy volunteers were scanned at 7 T using single-shot 2D EPI at 0.75 mm in-plane resolution and multi-shot 2D EPI at 0.75 and 0.6 mm in-plane resolutions. All protocols used 3 mm slice thickness. For each protocol, the BOLD response to 13 10-s noxious thermal stimuli applied to the right thumb was acquired in a 10-min fMRI run. Image quality, temporal signal to noise ratio (SNR), and BOLD activation (percent signal change and z-stat) at both individual- and group-level were evaluated between the protocols. Temporal SNR was highest in single-shot and multi-shot 0.75 mm protocols. In group-level analyses, activation clusters appeared in all protocols in the ipsilateral dorsal quadrant at the expected C6 neurological level. In individual-level analyses, activation clusters at the expected level were detected in some, but not all subjects and protocols. Single-shot 0.75 mm generally produced the highest mean z-statistic, while multi-shot 0.60 mm produced the best-localized activation clusters and the least geometric distortion. Larger than expected within-subject segmental variation of BOLD activation along the cord was observed. Group-level sensory task fMRI of the cervical spinal cord is feasible at 7 T with single-shot or multi-shot EPI. The best choice of protocol will likely depend on the relative importance of sensitivity to activation versus spatial localization of activation for a given experiment. PRACTITIONER POINTS: First stimulus task fMRI results in the spinal cord at 7 T. Single-shot 0.75 mm 2D EPI produced the highest mean z-statistic. Multi-shot 0.60 mm 2D EPI provided the best-localized activation and least distortion.

Psycho-Neuroendocrinology in the Rehabilitation Field: Focus on the Complex Interplay between Stress and Pain

Chronic stress and chronic pain share neuro-anatomical, endocrinological, and biological features. However, stress prepares the body for challenging situations or mitigates tissue damage, while pain is an unpleasant sensation due to nociceptive receptor stimulation. When pain is chronic, it might lead to an allostatic overload in the body and brain due to the chronic dysregulation of the physiological systems that are normally involved in adapting to environmental challenges. Managing stress and chronic pain (CP) in neurorehabilitation presents a significant challenge for healthcare professionals and researchers, as there is no definitive and effective solution for these issues. Patients suffering from neurological disorders often complain of CP, which significantly reduces their quality of life. The aim of this narrative review is to examine the correlation between stress and pain and their potential negative impact on the rehabilitation process. Moreover, we described the most relevant interventions used to manage stress and pain in the neurological population. In conclusion, this review sheds light on the connection between chronic stress and chronic pain and their impact on the neurorehabilitation pathway. Our results emphasize the need for tailored rehabilitation protocols to effectively manage pain, improve treatment adherence, and ensure comprehensive patient care.

Insight gained from using animal models to study pain in Parkinson's disease

Pain is one of the key non-motor symptoms experienced by a large proportion of people living with Parkinson's disease (PD), yet the mechanisms behind this pain remain elusive and as such its treatment remains suboptimal. It is hoped that through the study of animal models of PD, we can start to unravel some of the contributory mechanisms, and perhaps identify models that prove useful as test beds for assessing the efficacy of potential new analgesics. However, just how far along this journey are we right now? Is it even possible to model pain in PD in animal models of the disease? And have we gathered any insight into pain mechanisms from the use of animal models of PD so far? In this chapter we intend to address these questions and in particular highlight the findings generated by others, and our own group, following studies in a range of rodent models of PD.

Exploring CNS Involvement in Pain Insensitivity in Hereditary Sensory and Autonomic Neuropathy Type 4: Insights from Tc-99m ECD SPECT Imaging

Hereditary sensory and autonomic neuropathy type 4 (HSAN4), also known as congenital insensitivity to pain with anhidrosis (CIPA), is a rare genetic disorder caused by NTRK1 gene mutations, affecting nerve growth factor signaling. This study investigates the central nervous system's (CNS) involvement and its relation to pain insensitivity in HSAN4. We present a 15-year-old girl with HSAN4, displaying clinical signs suggestive of CNS impact, including spasticity and a positive Babinski's sign. Using Technetium-99m ethyl cysteinate dimer single-photon emission computed tomography (Tc-99m ECD SPECT) imaging, we discovered perfusion deficits in key brain regions, notably the cerebellum, thalamus, and postcentral gyrus. These regions process pain signals, providing insights into HSAN4's pain insensitivity. This study represents the first visualization of CNS perfusion abnormality in an HSAN4 patient. It highlights the intricate relationship between the peripheral and central nervous systems in HSAN4. The complexity of HSAN4 diagnosis, involving potential unidentified genes, underscores the need for continued research to refine diagnostic approaches and develop comprehensive treatments.

The role of pain modulation pathway and related brain regions in pain

Pain is a multifaceted process that encompasses unpleasant sensory and emotional experiences. The essence of the pain process is aversion, or perceived negative emotion. Central sensitization plays a significant role in initiating and perpetuating of chronic pain. Melzack proposed the concept of the "pain matrix", in which brain regions associated with pain form an interconnected network, rather than being controlled by a singular brain region. This review aims to investigate distinct brain regions involved in pain and their interconnections. In addition, it also sheds light on the reciprocal connectivity between the ascending and descending pathways that participate in pain modulation. We review the involvement of various brain areas during pain and focus on understanding the connections among them, which can contribute to a better understanding of pain mechanisms and provide opportunities for further research on therapies for improved pain management.

The effect of methylphenidate on pain perception thresholds in children with attention deficit hyperactivity disorder

BACKGROUND

Pain perception is important in children with attention deficit hyperactivity disorder (ADHD) since they are more likely to experience painful events due to increased accident rates. The aim of this study is to contribute to the literature concerning the relationship between ADHD diagnosis, methylphenidate (MPH) therapy, and pain thresholds, since findings regarding the change in pain perception in children with ADHD are scarce and inconsistent.

METHODS

Children aged 8-13 years constituted both the ADHD group (n = 82) and the healthy controls (n = 41). The ADHD group was divided into two subgroups, ADHD without MPH (not treated pharmacologically) and ADHD with MPH (treated pharmacologically for at least three-months). The Conners' Parent Rating Scale-Revised: Short Form was employed to assess ADHD, a visual analog scale was applied to evaluate chronic pain severity, and a manual pressure algometer was used to assess pain thresholds.

RESULT

Children with ADHD had lower pain thresholds than the healthy controls (P < 0.05). However, lower regional pain thresholds were observed in the ADHD group without MPH compared to both the healthy control and ADHD with MPH groups. Although pain thresholds in the ADHD with MPH group were regionally lower than in the healthy controls, low pain thresholds were found in fewer regions compared to the ADHD without MPH group.

CONCLUSIONS

Children with ADHD are more sensitive to pain sensation, and MPH may help normalize these individuals' pain experiences by raising pain thresholds. Families and clinicians must be aware of situations that may cause pain in children with ADHD. In addition, these children's low threshold for pain may lead them to experience it more intensely.

Converging circuits between pain and depression: the ventral tegmental area as a therapeutic hub

Chronic pain and depression are highly prevalent pathologies and cause a major socioeconomic burden to society. Chronic pain affects the emotional state of the individuals suffering from it, while depression worsens the prognosis of chronic pain patients and may diminish the effectiveness of pain treatments. There is a high comorbidity rate between both pathologies, which might share overlapping mechanisms. This review explores the evidence pinpointing a role for the ventral tegmental area (VTA) as a hub where both pain and emotional processing might converge. In addition, the feasibility of using the VTA as a possible therapeutic target is discussed. The role of the VTA, and the dopaminergic system in general, is highly studied in mood disorders, especially in deficits in reward-processing and motivation. Conversely, the VTA is less regarded where it concerns the study of central mechanisms of pain and its mood-associated consequences. Here, we first outline the brain circuits involving central processing of pain and mood disorders, focusing on the often-understudied role of the dopaminergic system and the VTA. Next, we highlight the state-of-the-art findings supporting the emergence of the VTA as a link where both pathways converge. Thus, we envision a promising part for the VTA as a putative target for innovative therapeutic approaches to treat chronic pain and its effects on mood. Finally, we emphasize the urge to develop and use animal models where both pain and depression-like symptoms are considered in conjunction.

A direct spino-cortical circuit bypassing the thalamus modulates nociception

Nociceptive signals are usually transmitted to layer 4 neurons in somatosensory cortex via the spinothalamic-thalamocortical pathway. The layer 5 corticospinal neurons in sensorimotor cortex are reported to receive the output of neurons in superficial layers; and their descending axons innervate the spinal cord to regulate basic sensorimotor functions. Here, we show that a subset of layer 5 neurons receives spinal inputs through a direct spino-cortical circuit bypassing the thalamus, and thus define these neurons as spino-cortical recipient neurons (SCRNs). Morphological studies revealed that the branches from spinal ascending axons formed a kind of disciform structure with the descending axons from SCRNs in the basilar pontine nucleus (BPN). Electron microscopy and calcium imaging further confirmed that the axon terminals from spinal ascending neurons and SCRNs made functional synaptic contacts in the BPN, linking the ascending sensory pathway to the descending motor control pathway. Furthermore, behavioral tests indicated that the spino-cortical connection in the BPN was involved in nociceptive responses. In vivo calcium imaging showed that SCRNs responded to peripheral noxious stimuli faster than neighboring layer 4 cortical neurons in awake mice. Manipulating activities of SCRNs could modulate nociceptive behaviors. Therefore, this direct spino-cortical circuit represents a noncanonical pathway, allowing a fast sensory-motor transition of the brain in response to noxious stimuli.

Chronic pain is a risk factor for incident Alzheimer's disease: a nationwide propensity-matched cohort using administrative data

Introduction

Chronic pain (CP) is one of the most disabling conditions in the elderly and seems to be a risk factor for the development of Alzheimer's disease and related dementias (ADRD). Only one study, using national administrative health databases, assessed and demonstrated that chronic pain (all types of pain) was a risk factor for dementia, but without assessing the impact of pain medications.

Method

To assess the impact of all types of chronic pain and the long-term use of pain medications on the person-years incidence of ADRD, a retrospective nationwide healthcare administrative data study was performed using the national inter-regime health insurance information system (SNIIRAM) to the French national health data system (SNDS). Incident people >50 years old with chronic pain, defined by at least 6-months duration analgesics treatment or by a diagnosis/long-term illness of chronic pain between 2006 and 2010, were included. Chronic pain individuals were matched with non-CP individuals by a propensity score. Individuals were followed up from 9 to 13 years to identify occurrences of ADRD from 2006.

Results

Among 64,496 French individuals, the incidence of ADRD was higher in the chronic pain population than control (1.13% vs. 0.95%, p <0.001). Chronic pain increases the risk of ADRD (HR = 1.23) and the incidence of ADRD was higher for women and increased significantly with age.

Discussion

Our study highlights the importance of prevention, diagnosis, and management of chronic pain in elderly to reduce the risk of development and/or worsening of dementia.

Nociception in Chicken Embryos, Part III: Analysis of Movements before and after Application of a Noxious Stimulus

Many potentially noxious interventions are performed on chicken embryos in research and in the poultry industry. It is therefore essential and in the interest of animal welfare to be able to precisely define the point at which a chicken embryo is capable of nociception in ovo. The present part III of a comprehensive study examined the movements of developing chicken embryos with the aim of identifying behavioral responses to a noxious stimulus. For this purpose, a noxious mechanical stimulus and a control stimulus were applied in a randomized order. The recorded movements of the embryos were evaluated using the markerless pose estimation software DeepLabCut and manual observations. After the application of the mechanical stimulus, a significant increase in beak movement was identified in 15- to 18-day-old embryos. In younger embryos, no behavioral changes related to the noxious stimulus were observed. The presented results indicate that noxious mechanical stimuli at the beak base evoke a nocifensive reaction in chicken embryos starting at embryonic day 15.

Disrupting nociceptive information processing flow through transcranial focused ultrasound neuromodulation of thalamic nuclei

BACKGROUND

MRI-guided transcranial focused ultrasound (MRgFUS) as a next-generation neuromodulation tool can precisely target and stimulate deep brain regions with high spatial selectivity. Combined with MR-ARFI (acoustic radiation force imaging) and using fMRI BOLD signal as functional readouts, our previous studies have shown that low-intensity FUS can excite or suppress neural activity in the somatosensory cortex.

OBJECTIVE

To investigate whether low-intensity FUS can suppress nociceptive heat stimulation-induced responses in thalamic nuclei during hand stimulation, and to determine how this suppression influences the information processing flow within nociception networks.

FINDINGS

BOLD fMRI activations evoked by 47.5 °C heat stimulation of hand were detected in 24 cortical regions, which belong to sensory, affective, and cognitive nociceptive networks. Concurrent delivery of low-intensity FUS pulses (650 kHz, 550 kPa) to the predefined heat nociceptive stimulus-responsive thalamic centromedial_parafascicular (CM_para), mediodorsal (MD), ventral_lateral (VL_ and ventral_lateral_posteroventral (VLpv) nuclei suppressed their heat responses. Off-target cortical areas exhibited reduced, enhanced, or no significant fMRI signal changes, depending on the specific areas. Differentiable thalamocortical information flow during the processing of nociceptive heat input was observed, as indicated by the time to reach 10% or 30% of the heat-evoked BOLD signal peak. Suppression of thalamic heat responses significantly altered nociceptive processing flow and direction between the thalamus and cortical areas. Modulation of contralateral versus ipsilateral areas by unilateral thalamic activity differed. Signals detected in high-order cortical areas, such as dorsal frontal (DFC) and ventrolateral prefrontal (vlPFC) cortices, exhibited faster response latencies than sensory areas.

CONCLUSIONS

The concurrent delivery of FUS suppressed nociceptive heat response in thalamic nuclei and disrupted the nociceptive network. This study offers new insights into the causal functional connections within the thalamocortical networks and demonstrates the modulatory effects of low-intensity FUS on nociceptive information processing.

Duloxetine for the Prevention of Oxaliplatin Induced Peripheral Neuropathy: A Randomized, Placebo-Controlled, Double-blind Clinical Trial

PURPOSE

Peripheral neuropathy is a dose-limiting adverse effect of oxaliplatin. The aim of this study was to evaluate the efficacy and safety of duloxetine in the prevention of oxaliplatin-induced peripheral neuropathy (OIPN).

METHOD

Cancer patients receiving oxaliplatin based chemotherapy were randomized into two arms. Duloxetine 60 mg capsule was given in the first 14 days of each chemotherapy cycle to one arm and placebo was similarly given to another. We compared the two arms based on the incidence of neuropathy and the results of the nerve conduction study (NCS). Grade of complained neuropathy was recorded according to Common Terminology Criteria for Adverse Events (CTCAE).

RESULTS

Thirty-two patients mostly rectal cancer (90.6%) were randomized to duloxetine and placebo arms. Highest grade of neuropathy in each cycle was not significantly different between the two groups. Six weeks after treatment incidence of neuropathy of any grade was 52.9 in duloxetine arm compared to 76.9% in placebo arm (P: 0.26). Patients in the duloxetine arm had a lower percentage of chemotherapy cycles (mean) in which they reported distal paresthesia (51% vs. 84%, P = 0.01) and throat discomfort (37% vs. 69%, P = 0.01). Results of NCS were mostly comparable between the two arms except for the velocity in two of the examined nerve which was significantly higher in duloxetine group. Duloxetine was safe and well-tolerated.

CONCLUSION

Although a definite conclusion might be difficult to draw but administering duloxetine for 14 days in each chemotherapy cycle could not decrease the incidence of acute OIPN based on CTCAE grading system.

Resting state functional connectivity differentiation of neuropathic and nociceptive pain in individuals with chronic spinal cord injury

Many individuals with spinal cord injury live with debilitating chronic pain that may be neuropathic, nociceptive, or a combination of both in nature. Identification of brain regions demonstrating altered connectivity associated with the type and severity of pain experience may elucidate underlying mechanisms, as well as treatment targets. Resting state and sensorimotor task-based magnetic resonance imaging data were collected in 37 individuals with chronic spinal cord injury. Seed-based correlations were utilized to identify resting state functional connectivity of regions with established roles in pain processing: the primary motor and somatosensory cortices, cingulate, insula, hippocampus, parahippocampal gyri, thalamus, amygdala, caudate, putamen, and periaqueductal gray matter. Resting state functional connectivity alterations and task-based activation associated with individuals' pain type and intensity ratings on the International Spinal Cord Injury Basic Pain Dataset (0-10 scale) were evaluated. We found that intralimbic and limbostriatal resting state connectivity alterations are uniquely associated with neuropathic pain severity, whereas thalamocortical and thalamolimbic connectivity alterations are associated specifically with nociceptive pain severity. The joint effect and contrast of both pain types were associated with altered limbocortical connectivity. No significant differences in task-based activation were identified. These findings suggest that the experience of pain in individuals with spinal cord injury may be associated with unique alterations in resting state functional connectivity dependent upon pain type.

Understanding the physiological role of NaV1.9: Challenges and opportunities for pain modulation

Voltage-activated Na⁺ (Na_V) channels are crucial contributors to rapid electrical signaling in the human body. As such, they are among the most targeted membrane proteins by clinical therapeutics and natural toxins. Several of the nine mammalian Na_V channel subtypes play a documented role in pain or other sensory processes such as itch, touch, and smell. While causal relationships between these subtypes and biological function have been extensively described, the physiological role of Na_V1.9 is less understood. Yet, mutations in Na_V1.9 can cause striking disease phenotypes related to sensory perception such as loss or gain of pain and chronic itch. Here, we explore our current knowledge of the mechanisms by which Na_V1.9 may contribute to pain and elaborate on the challenges associated with establishing links between experimental conditions and human disease. This review also discusses the lack of comprehensive insights into Na_V1.9-specific pharmacology, an unfortunate situation since modulatory compounds may have tremendous potential in the clinic to treat pain or as precision tools to examine the extent of Na_V1.9 participation in sensory perception processes.

Inhibition of spinal ferroptosis-like cell death alleviates hyperalgesia and spontaneous pain in a mouse model of bone cancer pain

Bone cancer pain (BCP) impairs patients' quality of life. However, the underlying mechanisms are still unclear. This study investigated the role of spinal interneuron death using a pharmacological inhibitor of ferroptosis in a mouse model of BCP. Lewis lung carcinoma cells were inoculated into the femur, resulting in hyperalgesia and spontaneous pain. Biochemical analysis revealed that spinal levels of reactive oxygen species and malondialdehyde were increased, while those of superoxide dismutase were decreased. Histological analysis showed the loss of spinal GAD65+ interneurons and provided ultrastructural evidence of mitochondrial shrinkage. Pharmacologic inhibition of ferroptosis using ferrostatin-1 (FER-1, 10 mg/kg, intraperitoneal for 20 consecutive days) attenuated ferroptosis-associated iron accumulation and lipid peroxidation and alleviated BCP. Furthermore, FER-1 inhibited the pain-associated activation of ERK1/2 and COX-2 expression and prevented the loss of GABAergic interneurons. Moreover, FER-1 improved analgesia by the COX-2 inhibitor Parecoxib. Taken together, this study shows that pharmacological inhibition of ferroptosis-like cell death of spinal interneurons alleviates BCP in mice. The results suggest that ferroptosis is a potential therapeutic target in patients suffering on BCP and possibly other types of pain.

Parabrachial tachykinin1-expressing neurons involved in state-dependent breathing control

Breathing is regulated automatically by neural circuits in the medulla to maintain homeostasis, but breathing is also modified by behavior and emotion. Mice have rapid breathing patterns that are unique to the awake state and distinct from those driven by automatic reflexes. Activation of medullary neurons that control automatic breathing does not reproduce these rapid breathing patterns. By manipulating transcriptionally defined neurons in the parabrachial nucleus, we identify a subset of neurons that express the Tac1, but not Calca, gene that exerts potent and precise conditional control of breathing in the awake, but not anesthetized, state via projections to the ventral intermediate reticular zone of the medulla. Activating these neurons drives breathing to frequencies that match the physiological maximum through mechanisms that differ from those that underlie the automatic control of breathing. We postulate that this circuit is important for the integration of breathing with state-dependent behaviors and emotions.

Evaluating the effects of duloxetine on prophylaxis of oxaliplatin-induced peripheral neuropathy in patients with gastrointestinal cancer: A randomized double-blind placebo controlled clinical trial

BACKGROUND

Oxaliplatin is a key drug in treatment of gastrointestinal (GI) cancer. Peripheral neuropathy (PN) is a troublesome and dose-dependent adverse effect of oxaliplatin. It can occur in two distinct forms: acute and chronic. Its incidence is estimated about 65-98%, of which 22% of cases need to stop chemotherapy. In some cases, PN has a long-lasting effect on patient's quality of life (QOL). Therefore, this study was done to evaluate efficacy of duloxetine on prevention of oxaliplatin- induced peripheral neuropathy (OIPN) in patients with GI cancer.

METHODOLOGY

In this randomized and double -blind clinical trial study conducted in a tertiary teaching hospital, eligible patients were divided into two groups. Treatment group received duloxetine the day before initiation of chemotherapy regimen at a dose of 30 mg/day for one week and then, the dose was titrated up to 60 mg/day until 12 weeks. For placebo group, one placebo capsule was prescribed daily for one week followed by 2 capsules daily until 12 weeks. In each of chemotherapy courses, PN was assessed using national cancer institute-common terminology criteria for adverse effects (NCI-CTCAE v4.03). Also, chemotherapy -related QOL at the baseline and 12 weeks was assessed by functional assessment of cancer treatment gynecologic oncology group - neurotoxicity (FACT/GOG-NTX).

RESULTS

Forty patients were randomly assigned to treatment and placebo groups which were similar to each other in terms of chemotherapy regimen, type, and stage of cancer. Analysis of results obtained from the NCI-CTCAE (v4.03) showed that duloxetine could prevent worsening of paresthesia more than placebo (P = 0.025) and patients in duloxetine group experienced less peripheral sensory neuropathy (P = 0.001) than placebo group. Analysis of results obtained from the FACT/GOG-NTX demonstrated a significant worsening of tingling and discomfort in hands (P = 0.002, 0.001, respectively) and feet (P = 0.017, 0.019, respectively) in placebo group compared to duloxetine group. Also, patients experienced more cold temperature -induced pain in extremities (P = 0.001) in placebo group compared to duloxetine group. On the other hand, duloxetine could not improve QOL (P = 0.06) and had not significant effects on trouble feeling the shape of small objects in hand (P = 0.420) or trouble buttoning buttons (P = 0.086). The P-value < 0.05 was considered to be statistically significant.

Role of Sensory Pathway Injury in Central Post-Stroke Pain: A Narrative Review of Its Pathogenetic Mechanism

Central post-stroke pain (CPSP) is a severe chronic neuropathic pain syndrome that is a direct result of cerebrovascular lesions affecting the central somatosensory system. The pathogenesis of this condition remains unclear owing to its extensive clinical manifestations. Nevertheless, clinical and animal experiments have allowed a comprehensive understanding of the mechanisms underlying CPSP occurrence, based on which different theoretical hypotheses have been proposed. We reviewed and collected the literature and on the mechanisms of CPSP by searching the English literature in PubMed and EMBASE databases for the period 2002-2022. Recent studies have reported that CPSP occurrence is mainly due to post-stroke nerve injury and microglial activation, with an inflammatory response leading to central sensitization and de-inhibition. In addition to the primary injury at the stroke site, peripheral nerves, spinal cord, and brain regions outside the stroke site are involved in the occurrence and development of CPSP. In the present study, we reviewed the mechanism of action of CPSP from both clinical studies and basic research based on its sensory pathway. Through this review, we hope to increase the understanding of the mechanism of CPSP.

Selective and replicable neuroimaging-based indicators of pain discriminability

Neural indicators of pain discriminability have far-reaching theoretical and clinical implications but have been largely overlooked previously. Here, to directly identify the neural basis of pain discriminability, we apply signal detection theory to three EEG (Datasets 1-3, total N = 366) and two fMRI (Datasets 4-5, total N = 399) datasets where participants receive transient stimuli of four sensory modalities (pain, touch, audition, and vision) and two intensities (high and low) and report perceptual ratings. Datasets 1 and 4 are used for exploration and others for validation. We find that most pain-evoked EEG and fMRI brain responses robustly encode pain discriminability, which is well replicated in validation datasets. The neural indicators are also pain selective since they cannot track tactile, auditory, or visual discriminability, even though perceptual ratings and sensory discriminability are well matched between modalities. Overall, we provide compelling evidence that pain-evoked brain responses can serve as replicable and selective neural indicators of pain discriminability.

An Analysis of Theoretical Perspectives in Research on Nature-Based Interventions and Pain

Chronic pain results from a complex series of biomechanical, inflammatory, neurological, psychological, social, and environmental mechanisms. Pain and pain-related diseases are the leading causes of disability and disease burden globally. Employing nature-based interventions for the treatment of pain is an emerging field. Current theory driving the suggested mechanism(s) linking the pain reducing effects of nature-based interventions is lacking. A two-step approach was taken to complete a theoretical review and analysis. First, a literature review was completed to gather a substantive amount of research related to theoretical frameworks on the topic of nature-based interventions and pain. Secondly, a theoretical analysis as proposed by Walker and Avant was completed to explore current theoretical frameworks accepted in the literature on nature-based interventions and pain. Stress reduction theory and attention restoration theory were the most common theoretical frameworks identified. Neither theoretical framework explicitly identifies, describes, or intends to adequately measure the concept of pain, revealing a limitation for their application in research with nature-based interventions and pain. Theoretical development is needed, as it pertains to nature-based interventions and pain. Without this development, research on nature-based interventions and pain will continue to use proxy concepts for measurement and may result in misrepresented findings.

Emerging Approaches for the Management of Chemotherapy-Induced Peripheral Neuropathy (CIPN): Therapeutic Potential of the C5a/C5aR Axis

Chemotherapy-induced peripheral neuropathy (CIPN) is the most common neurologic complication of chemotherapy, resulting in symptoms like pain, sensory loss, and numbness in the hands and feet that cause lots of uneasiness in patients with cancer. They often suffer from pain so severe that it interrupts the treatment, thus invalidating the entire chemotherapy-based healing process, and significantly reducing their quality of life. In this paper, we underline the role of the complement system in CIPN, highlighting the relevance of the C5a fragment and its receptor C5aR1, whose activation is thought to be involved in triggering a cascade of events that can lead to CIPN onset. Recent experimental data showed the ability of docetaxel and paclitaxel to specifically bind and activate C5aR1, thus shining light on one of the molecular mechanisms by which taxanes may activate a cascade of events leading to neuropathy. According to these new evidence, it was possible to suggest new mechanisms underlying the pathophysiology of CIPN. Hence, the C5a/C5aR1 axis may represent a new target for CIPN treatment, and the use of C5aR1 inhibitors can be proposed as a potential new therapeutic option to manage this high unmet medical need.