Cognitive decline in Sprague-Dawley rats induced by neuroplasticity changes after occlusal support loss

BACKGROUND

Tooth loss is closely related to cognitive impairment, especially affecting cognitive functions involving hippocampus. The most well-known function of the hippocampus is learning and memory, and the mechanism behind is neuroplasticity, which strongly depends on the level of brain-derived neurotrophic factor (BDNF). While research has delved into the possible mechanisms behind the loss of teeth leading to cognitive dysfunction, there are few studies on the plasticity of sensory neural pathway after tooth loss, and the changes in related indicators of synaptic plasticity still need to be further explored.

METHODS

In this study, the bilateral maxillary molars were extracted in Sprague-Dawley rats of two age ranges (young and middle age) to establish occlusal support loss model; then, the spatial cognition was tested by Morris Water Maze (MWM). Quantitative real-time PCR (qPCR) and Western Blotting (WB) were used to detect BDNF, AKT, and functional proteins (viz., PSD95 and NMDAR) of hippocampal synapses. Golgi staining was used to observe changes in ascending nerve pathway. IF was used to confirm the location of BDNF and AKT expressed in hippocampus.

RESULTS

MWM showed that the spatial cognitive level of rats dropped after occlusal support loss. qPCR, WB, and IF suggested that the BDNF/AKT pathway was down-regulated in the hippocampus. Golgi staining showed the neurons of ascending sensory pathway decreased in numbers.

CONCLUSION

Occlusal support loss caused plastic changes in ascending nerve pathway and induced cognitive impairment in rats by down-regulating BDNF and synaptic plasticity.

Pain-Insomnia-Depression Syndrome: Triangular Relationships, Pathobiological Correlations, Current Treatment Modalities, and Future Direction

Pain-insomnia-depression syndrome (PIDS) is a complex triad of chronic pain, insomnia, and depression that has profound effects on an individual's quality of life and mental health. The pathobiological context of PIDS involves complex neurobiological and physiological mechanisms, including alterations in neurotransmitter systems and impaired pain processing pathways. The first-line therapeutic approaches for the treatment of chronic pain, depression, and insomnia are a combination of pharmacological and non-pharmacological therapies. In cases where patients do not respond adequately to these treatments, additional interventions such as deep brain stimulation (DBS) may be required. Despite advances in understanding and treatment, there are still gaps in knowledge that need to be addressed. To improve our understanding, future research should focus on conducting longitudinal studies to uncover temporal associations, identify biomarkers and genetic markers associated with PIDS, examine the influence of psychosocial factors on treatment responses, and develop innovative interventions that address the complex nature of PIDS. The aim of this study is to provide a comprehensive overview of these components and to discuss their underlying pathobiological relationships.

Stress, pain, anxiety, and depression in endometriosis-Targeting glial activation and inflammation

Endometriosis (EM) is a gynecological inflammatory disease often accompanied by stress, chronic pelvic pain (CPP), anxiety, and depression, leading to a diminished quality of life. This review aims to discuss the relationship between systemic and local inflammatory responses in the central nervous system (CNS), focusing on glial dysfunctions (astrocytes and microglia) as in critical brain regions involved in emotion, cognition, pain processing, anxiety, and depression. The review presents that EM is connected to increased levels of pro-inflammatory cytokines in the circulation. Additionally, chronic stress and CPP as stressors may contribute to the dysregulation of the hypothalamic-pituitary-adrenal (HPA) axis, depleting the production of inflammatory mediators in the circulatory system and the brain. The systemic cytokines cause blood-brain barrier (BBB) breakdown, activate microglia in the brain, and lead to neuroinflammation. Furthermore, CPP may induce neuronal morphological alterations in critical regions through central sensitization and the activation of glial cells. The activation of glial cells, particularly the polarization of microglia, leads to the activation of the NLRP3 inflammasome and the overproduction of inflammatory cytokines. These inflammatory cytokines interact with the signaling pathways involved in neural plasticity. Additionally, persistent inflammatory conditions in the brain lead to neuronal death, which is correlated with a reduced volume of key brain regions such as the hippocampus. This review highlights the involvement of glial cells in the pathogenesis of the mental comorbidities of EM (i.e., pain, anxiety, and depression) and to discuss potential therapeutic approaches for targeting the inflammation and activation of microglia in key brain regions.

Impact of physical therapy techniques and common interventions on sleep quality in patients with chronic pain: A systematic review

This systematic review aims to find effectful healthcare strategies, with special focus on drug-free interventions and physical therapy, as part of the treatment for sleep in patients with chronic musculoskeletal pain. Data search was conducted across seven scientific databases. This review is deposited in the Prospero International prospective register of systematic reviews (CRD42023452574). Seventeen RCTs from different healthcare fields complied with our inclusion criteria. Two RCTs investigated manual therapy, five RCTs therapeutic exercise, one RCT Fu's subcutaneous needling, two RCTs physical agents (one on balneotherapy and one on cryo-stimulation), two RCTs cognitive-behavioral therapy, and four RCTs pharmacological therapy and their effect on sleep quality and/or quantity in patients suffering from chronic pain. We included the four RCT's in this systematic review with the purpose to be able to compare natural interventions with allopathic ones. As allopathic interventions are more prone to have secondary negative effects than physical therapy, compare the two types of interventions could be in favor of choosing the most effective treatment with the least secondary negative effects. Additionally, two RCTs on neurofeedback and limbic neuromodulation were also included. The results of the included studies suggest that strategies such as manual therapy, therapeutic exercise, Fu's subcutaneous needling, balneotherapy, cryo-stimulation, neurofeedback, limbic neuromodulation, cognitive-behavioral therapy, and pharmacological therapies have positive effects on patients suffering from chronic pain and sleep disturbances, especially when they suffer musculoskeletal pain. Secondary negative effects were found for the possible overuse of certain medicines such as morphine, a huge problem in the United States. Sleep deficiency is an independent risk factor for many diseases, including chronic pain syndrome and therefore more studies are needed to find non-toxic interventions for people suffering sleep disorders associated with systemic diseases and pain.

A new perspective of frozen shoulder pathology; the interplay between the brain and the immune system

Frozen shoulder (FS), also known as adhesive capsulitis of the shoulder (FS), is a fibrotic inflammatory process of unknown etiology whose main symptoms are pain, stiffness and the loss of joint mobility. These symptoms may be associated with pathologies such as diabetes, Dupuytren's syndrome and the prevalence of today's sedentary lifestyle. This literature review provides an overview of the epidemiology and pathogenesis of this pathology, as well as the mechanisms of lowgrade chronic inflammation and infection, insulin resistance, and omics-science associated with it. We also propose a new hypothesis related to the possibility that the GABAergic system could play a decisive role in the development of frozen shoulder and that therefore diabetes type 1, endocrinological autoimmune disorders and frozen shoulder are connected by the same pathophysiological mechanisms. If that is true, the combined presence of psycho-emotional stress factors and pathogenic immune challenges could be the main causes of frozen shoulder syndrome. Finally, we propose a series of possible intervention strategies based on a multifactorial etiological and mechanistic concept.

Peripheral Pain Captured Centrally: Altered Brain Morphology on MRI in Small Fiber Neuropathy Patients With and Without an SCN9A Gene Variant

The current study aims to characterize brain morphology of pain as reported by small fiber neuropathy (SFN) patients with or without a gain-of-function variant involving the SCN9A gene and compare these with findings in healthy controls without pain. The Neuropathic Pain Scale was used in patients with idiopathic SFN (N = 20) and SCN9A-associated SFN (N = 12) to capture pain phenotype. T1-weighted, structural magnetic resonance imaging (MRI) data were collected in patients and healthy controls (N = 21) to 1) compare cortical thickness and subcortical volumes and 2) quantify the association between severity, quality, and duration of pain with morphological properties. SCN9A-associated SFN patients showed significant (P < .017, Bonferroni corrected) higher cortical thickness in sensorimotor regions, compared to idiopathic SFN patients, while lower cortical thickness was found in more functionally diverse regions (eg, posterior cingulate cortex). SFN patient groups combined demonstrated a significant (Spearman's ρ = .44-.55, P = .005-.049) correlation among itch sensations (Neuropathic Pain Scale-7) and thickness of the left precentral gyrus, and midcingulate cortices. Significant associations were found between thalamic volumes and duration of pain (left: ρ = -.37, P = .043; right: ρ = -.40, P = .025). No associations were found between morphological properties and other pain qualities. In conclusion, in SCN9A-associated SFN, profound morphological alterations anchored within the pain matrix are present. The association between itch sensations of pain and sensorimotor and midcingulate structures provides a novel basis for further examining neurobiological underpinnings of itch in SFN. PERSPECTIVE: Cortical thickness and subcortical volume alterations in SFN patients were found in pain hubs, more profound in SCN9A-associated neuropathy, and correlated with itch and durations of pain. These findings contribute to our understanding of the pathophysiological pathways underlying chronic neuropathic pain and symptoms of itch in SFN.

Beneficial Effects of Photoperiod Lengthening on Sleep Characteristics and Mechanical Hyperalgesia in Injured Rats

Sleep and muscle injury-related pain are in negative relationship, and sleep extension may be a favorable countermeasure. In response to muscle injury, an adaptive sleep response has been described in rats, characterized by an increase in total sleep time (TST) and nonrapid eye movement (NREM) sleep. This study examined the effects of photoperiod lengthening (a model of sleep prolongation in rats) on the sleep characteristics of muscle-injured rats and whether this lengthening could benefit injury-induced mechanical hyperalgesia using the Von Frey test. Switching from the conventional 12:12 light/dark (LD) photoperiod (light on: 08:00-20:00) to LD 16:8 (light extended to 24:00) gives rats an extra window of sleep. Our results show higher TST and NREM sleep times in LD 16:8 versus LD 12:12 injured rats during 4 h of light lengthening for 7 d postinjury, showing the efficiency of photoperiod lengthening to increase sleep time in injured rats. In addition, a cumulative effect with the adaptive sleep response to muscle injury occurred with higher TST and NREM sleep times in LD 16:8 injured versus noninjured rats during the dark period, reflecting the high need for sleep after the injury. Greater stability and higher relative delta power of NREM sleep during the extended light period were also observed in injured rats. Finally, the extended photoperiod limits the muscle injury-induced mechanical hyperalgesia for 13 d and allows faster recovery of the baseline mechanical threshold. This is associated with reduced pro-inflammatory cytokines levels in the hippocampus, a brain structure involved in pain processing.

5,7-Dimethoxycoumarin ameliorates vincristine induced neuropathic pain: potential role of 5HT3 receptors and monoamines

Vincristine is the drug of choice for Hodgkin's lymphoma, acute lymphoblastic leukemia, and non-Hodgkin lymphoma. Despite its significant anticancer effects, it causes dose-dependent neuropathy, leading to compulsive dose reduction. The available drugs used for vincristine-induced neuropathic pain (VINP) have a range of safety, efficacy, and tolerability issues prompting a search for new therapies. 5,7-Dimethoxycoumarin (5,7-DMC) also known as citropten, is a natural coumarin found in the essential oils of citrus plants such as lime, lemons, and bergamots, and it possesses both antidepressant and anti-inflammatory effects. This study was designed to investigate the possible analgesic and antiallodynic effects of 5,7-DMC in a murine model of VINP. Vincristine was administered to groups of BALB/c male mice (0.1 mg/kg intraperitoneally) once daily for 14 days to induce VINP. Thermal hyperalgesia and mechanical allodynia were quantified using the tail immersion test and von Frey filament application method. The levels of monoamine neurotransmitters and vitamin C in frontal cortical, striatal and hippocampal tissues, as well as the TNF-α level in plasma, were quantified using high performance liquid chromatography and ELISA respectively. On day 15 of the protocol, acute treatment with 5,7-DMC clearly reversed VINP thermal hyperalgesia, mechanical static allodynia, mechanical dynamic allodynia, and cold allodynia. The activity of 5,7-DMC against hyperalgesia and allodynia was inhibited by pretreatment with ondansetron but not naloxone, implicating a 5-HT3 receptor involvement. VINP vitamin C levels were restored by 5,7-DMC in the frontal cortex, and changes in serotonin, dopamine, adenosine, inosine and hypoxanthine levels caused by vincristine were reversed either fully or partially. Additionally, the vincristine-induced rise in hippocampal serotonin, dopamine, inosine and striatal serotonin was appreciably reversed by 5,7-DMC. 5,7-DMC also reversed the vincristine-induced increase in the plasma level of TNF-α. In negating the changes in the levels of some neurotransmitters in the brain caused by vincristine, 5,7-DMC showed stronger effects than gabapentin. It was concluded that, there is a potential role of 5-HT3 receptors and monoamines in the amelioration of VINP induced by 5,7-DMC, and the use of this compound warrants further investigation.

Potential anxiolytic and antidepressant-like effects of luteolin in a chronic constriction injury rat model of neuropathic pain: Role of oxidative stress, neurotrophins, and inflammatory factors

This study aimed to examine the effects of luteolin (LUT) on chronic neuropathic pain (NP)-induced mood disorders (i.e., anxiety and depression) by regulating oxidative stress, neurotrophic factors (NFs), and neuroinflammation. Chronic constrictive injury (CCI) was used to induce NP in the animals. Animals in the treatment groups received LUT in three doses of 10, 25, and 50 mg/kg for 21 days. The severity of pain and mood disorders were examined. Finally, animals were sacrificed, and their brain tissue was used for molecular and histopathological studies. CCI led to cold allodynia and thermal hyperalgesia. Mood alterations were proven in the CCI group, according to the behavioral tests. Levels of glial cell-derived neurotrophic factor (GDNF), brain-derived neurotrophic factor (BDNF), B-cell lymphoma-2 (Bcl2), superoxide dismutase (SOD), catalase (CAT), and nuclear factor erythroid-2-related factor 2 (Nrf2) were reduced in the hippocampus (HPC) and prefrontal cortex (PFC). Furthermore, the levels of MDA, Bcl-2-associated X protein (Bax), and inflammatory markers, including nuclear factor kappa B (NF-κB), NLR family pyrin domain containing 3 (NLRP3), interleukin-1β (IL-1β), IL-18, IL-6, and tumor necrosis factor-α (TNF-α) significantly increased in the HPC and PFC following CCI induction. LUT treatment reversed the behavioral alterations via regulation of oxidative stress, neurotrophines, and inflammatory mediators in the HPC and PFC. Findings confirmed the potency of LUT in the improvement of chronic pain-induced anxiety- and depressive-like symptoms, probably through antioxidant, anti-inflammatory, and neuroprotective properties in the HPC and PFC.

Stress circuitry: mechanisms behind nervous and immune system communication that influence behavior

Inflammatory processes are increased by stress and contribute to the pathology of mood disorders. Stress is thought to primarily induce inflammation through peripheral and central noradrenergic neurotransmission. In healthy individuals, these pro-inflammatory effects are countered by glucocorticoid signaling, which is also activated by stress. In chronically stressed individuals, the anti-inflammatory effects of glucocorticoids are impaired, allowing pro-inflammatory effects to go unchecked. Mechanisms underlying this glucocorticoid resistance are well understood, but the precise circuits and molecular mechanisms by which stress increases inflammation are not as well known. In this narrative review, we summarize the mechanisms by which chronic stress increases inflammation and contributes to the onset and development of stress-related mood disorders. We focus on the neural substrates and molecular mechanisms, especially those regulated by noradrenergic signaling, that increase inflammatory processes in stressed individuals. We also discuss key knowledge gaps in our understanding of the communication between nervous and immune systems during stress and considerations for future therapeutic strategies. Here we highlight the mechanisms by which noradrenergic signaling contributes to inflammatory processes during stress and how this inflammation can contribute to the pathology of stress-related mood disorders. Understanding the mechanisms underlying crosstalk between the nervous and immune systems may lead to novel therapeutic strategies for mood disorders and/or provide important considerations for treating immune-related diseases in individuals suffering from stress-related disorders.

The modulation effects of repeated transcutaneous auricular vagus nerve stimulation on the functional connectivity of key brainstem regions along the vagus nerve pathway in migraine patients

Background

Previous studies have shown a significant response to acute transcutaneous vagus nerve stimulation (taVNS) in regions of the vagus nerve pathway, including the nucleus tractus solitarius (NTS), raphe nucleus (RN) and locus coeruleus (LC) in both healthy human participants and migraine patients. This study aims to investigate the modulation effect of repeated taVNS on these brainstem regions by applying seed-based resting-state functional connectivity (rsFC) analysis.

Methods

70 patients with migraine were recruited and randomized to receive real or sham taVNS treatments for 4 weeks. fMRI data were collected from each participant before and after 4 weeks of treatment. The rsFC analyses were performed using NTS, RN and LC as the seeds.

Results

59 patients (real group: n = 33; sham group: n = 29) completed two fMRI scan sessions. Compared to sham taVNS, real taVNS was associated with a significant reduction in the number of migraine attack days (p = 0.024) and headache pain intensity (p = 0.008). The rsFC analysis showed repeated taVNS modulated the functional connectivity between the brain stem regions of the vagus nerve pathway and brain regions associated with the limbic system (bilateral hippocampus), pain processing and modulation (bilateral postcentral gyrus, thalamus, and mPFC), and basal ganglia (putamen/caudate). In addition, the rsFC change between the RN and putamen was significantly associated with the reduction in the number of migraine days.

Conclusion

Our findings suggest that taVNS can significantly modulate the vagus nerve central pathway, which may contribute to the potential treatment effects of taVNS for migraine.Clinical Trial Registration: http://www.chictr.org.cn/hvshowproject.aspx?id=11101, identifier ChiCTR-INR-17010559.

The effect of adverse childhood experiences on chronic pain and major depression in adulthood: a systematic review and meta-analysis

BACKGROUND

Adverse childhood experiences have been linked to increased multimorbidity, with physical and mental health consequences throughout life. Chronic pain is often associated with mood disorders, such as major depressive disorder (MDD); both have been linked to adverse childhood experiences. It is unclear how the effect of adverse childhood experiences on neural processing impacts on vulnerability to chronic pain, MDD, or both, and whether there are shared mechanisms. We aimed to assess evidence for central neural changes associated with adverse childhood experiences in subjects with chronic pain, MDD, or both using systematic review and meta-analysis.

METHODS

Electronic databases were systematically searched for neuroimaging studies of adverse childhood experiences, with chronic pain, MDD, or both. Two independent reviewers screened title, abstracts, and full text, and assessed quality. After extraction of neuroimaging data, activation likelihood estimate meta-analysis was performed to identify significant brain regions associated with these comorbidities.

RESULTS

Forty-nine of 2414 studies were eligible, of which 43 investigated adverse childhood experiences and MDD and six investigated adverse childhood experiences and chronic pain. None investigated adverse childhood experiences, chronic pain, and MDD together. Functional and structural brain abnormalities were identified in the superior frontal, lingual gyrus, hippocampus, insula, putamen, superior temporal, inferior temporal gyrus, and anterior cerebellum in patients with MDD exposed to adverse childhood experiences. In addition, brain function abnormalities were identified for patients with MDD or chronic pain and exposure to adverse childhood experiences in the cingulate gyrus, inferior parietal lobule, and precuneus in task-based functional MRI studies.

CONCLUSIONS

We found that adverse childhood experiences exposure can result in different functional and structural brain alterations in adults with MDD or chronic pain compared with those without adverse childhood experiences.

SYSTEMATIC REVIEW PROTOCOL

PROSPERO CRD42021233989.

Electrophysiology as a Tool to Decipher the Network Mechanism of Visceral Pain in Functional Gastrointestinal Disorders

Abdominal pain, including visceral pain, is prevalent in functional gastrointestinal (GI) disorders (FGIDs), affecting the overall quality of a patient's life. Neural circuits in the brain encode, store, and transfer pain information across brain regions. Ascending pain signals actively shape brain dynamics; in turn, the descending system responds to the pain through neuronal inhibition. Pain processing mechanisms in patients are currently mainly studied with neuroimaging techniques; however, these techniques have a relatively poor temporal resolution. A high temporal resolution method is warranted to decode the dynamics of the pain processing mechanisms. Here, we reviewed crucial brain regions that exhibited pain-modulatory effects in an ascending and descending manner. Moreover, we discussed a uniquely well-suited method, namely extracellular electrophysiology, that captures natural language from the brain with high spatiotemporal resolution. This approach allows parallel recording of large populations of neurons in interconnected brain areas and permits the monitoring of neuronal firing patterns and comparative characterization of the brain oscillations. In addition, we discussed the contribution of these oscillations to pain states. In summary, using innovative, state-of-the-art methods, the large-scale recordings of multiple neurons will guide us to better understanding of pain mechanisms in FGIDs.

Exogenous melatonin alleviates neuropathic pain-induced affective disorders by suppressing NF-κB/ NLRP3 pathway and apoptosis

In this study, we aimed to evaluate the anti-inflammatory and anti-apoptotic effects of melatonin (MLT) on neuropathic pain (NP)-induced anxiety and depression in a rat model. Adult male rats were separated into four groups, i.e., Sham-VEH: healthy animals received a vehicle, Sham-MLT (10 mg/kg), and chronic constrictive injury (CCI)-VEH: nerve ligation received the vehicle, and CCI-MLT. Next, we used behavioral tests to evaluate pain severity, anxiety, and depression. Finally, rats were sacrificed for molecular and histopathological studies. Behavioral tests showed that NP could induce depressive- and anxiety-like behaviors. NP activated NF-κB/NLRP3 inflammasome pathways by upregulating NF-κB, NLRP3, ASC, active Caspase-1, also enhancing the concentrations of cytokines (IL-1β and IL-18) in the prefrontal cortex (PFC) and hippocampus (HC). NP upregulated Bax, downregulated Bcl2, and increased cell apoptosis in the HC and PFC. The rats treated with MLT eliminated the effects of NP, as the reduced pain severity, improved anxiety- and depressive-like behaviors, ameliorated NF-κB/NLRP3 inflammasome pathways, and modulated levels of cytokines in the HC and PFC. MLT could promote cell survival from apoptosis by modulating Bax and Bcl2. Therefore, it might be inferred that its anti-inflammatory and anti-apoptotic properties mediate the beneficial effects of MLT in NP-induced affective disorders.

Functional magnetic resonance imaging in migraine: A systematic review

BACKGROUND

Migraine is a highly prevalent primary headache disorder. Despite a high burden of disease, key disease mechanisms are not entirely understood. Functional magnetic resonance imaging is an imaging method using the blood-oxygen-level-dependent signal, which has been increasingly used in migraine research over recent years. This systematic review summarizes recent findings employing functional magnetic resonance imaging for the investigation of migraine.

METHODS

We conducted a systematic search and selection of functional magnetic resonance imaging applications in migraine from April 2014 to December 2021 (PubMed and references of identified articles according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines). Methodological details and main findings were extracted and synthesized.

RESULTS

Out of 224 articles identified, 114 were included after selection. Repeatedly emerging structures of interest included the insula, brainstem, limbic system, hypothalamus, thalamus, and functional networks. Assessment of functional brain changes in response to treatment is emerging, and machine learning has been used to investigate potential functional magnetic resonance imaging-based markers of migraine.

CONCLUSIONS

A wide variety of functional magnetic resonance imaging-based metrics were found altered across the brain for heterogeneous migraine cohorts, partially correlating with clinical parameters and supporting the concept to conceive migraine as a brain state. However, a majority of findings from previous studies have not been replicated, and studies varied considerably regarding image acquisition and analyses techniques. Thus, while functional magnetic resonance imaging appears to have the potential to advance our understanding of migraine pathophysiology, replication of findings in large representative datasets and precise, standardized reporting of clinical data would likely benefit the field and further increase the value of observations.

Tapentadol: A Review of Experimental Pharmacology Studies, Clinical Trials, and Recent Findings

Tapentadol is an analgesic compound that acts centrally to attenuate pain. Previous studies have shown that tapentadol has dual mechanisms of action as a mu-opioid receptor agonist and noradrenaline re-uptake inhibition. Therefore, tapentadol provides a great advantage over classic opioids in pain management from nociceptive to neuropathic. Cumulative evidence from in vitro data suggests that tapentadol effect of norepinephrine re-uptake could be a new target that overcomes other classic opioids in chronic neuropathic pain. Compared to tramadol and other opioids, tapentadol is associated with fewer adverse effects than tramadol. Tapentadol is a new alternative to treat acute, chronic, and neuropathic pain. Thus, this review article was focused on understanding the studies that led to the development of tapentadol as a novel analgesic drug and its advantages over conventional opioids. Thus, tapentadol is a good alternative with fewer adverse effects and is available for human use.

Higher-order trajectories of pain and depressive symptoms link midlife financial stress to women's well-being in later life

Objectives: Consistent with biopsychosocial models, shared pathophysiological conditions underlying both physical pain and depressive symptoms can result in the clustering of pain and depressive symptoms. However, previous studies have not investigated a higher-order construct capturing both pain and depressive symptoms over time. Furthermore, research has not identified trajectory antecedents (e.g. perceived family financial stress) and their consequences for later-life health and well-being. The present study sought to address these gaps in the research.Method: Using prospective data over 23 years from 244 long-term married women, the present study estimated latent growth curves in a structural equation model (more specifically a parallel trajectory model was estimated).Results: Family financial strain in midlife was, on average, associated with a higher initial level (β = .37, p < .001) and rate of change (β = .20, p = .045) of pain-depressive symptoms trajectories, which, in turn, contributed to health and well-being challenges, including the level and rate of change in physical limitations (β = .50, p < .001 and 0.43, p < .001, respectively), memory impairment (β = .47 and .47, p < .001, respectively), and loneliness (β = .63, p = < .001 and .28, p = .022, respectively) in later years. The adverse influence of family financial strain on pain-depressive symptoms trajectories weakened under high levels of marital closeness (β = -.10, p = .032). Conclusion: These findings emphasize the necessity of policies and interventions that focus on reducing adults' stressful life circumstances and further developing protective factors that can aid in the redirection of adverse pain-depressive symptoms trajectories.Supplemental data for this article are available online at https://doi.org/10.1080/13607863.2021.1993129.

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.

Percutaneous electric nerve field stimulation alters cortical thickness in a pilot study of veterans with fibromyalgia

Objective

To evaluate changes in cortical thickness and right posterior insula (r-pIns) gamma-aminobutyric acid (GABA) concentrations in veterans with fibromyalgia treated with auricular percutaneous electric nerve field stimulation (PENFS).

Materials & methods

This was a randomized, controlled, open label investigation conducted in a government hospital. Twenty-one veterans with fibromyalgia were randomized to receive either standard therapy (ST; i.e., 4 weekly visits with a pain practitioner) or ST with auricular PENFS (ST + PENFS). Neuroimaging data was collected at baseline (i.e. before the first treatment session) and again within 2 weeks post-treatment.​ Clinical pain and physical function were also assessed at these timepoints. Single-voxel magnetic resonance spectroscopy was carried out in r-pIns to assess changes in r-pIns GABA concentrations and high-resolution T1-weighted images were collected to assess changes in regional gray matter volume using cortical thickness.

Results

Both the ST + PENFS and ST groups reported a decrease in pain with treatment. Volumetric: Cortical thickness significantly decreased in the left middle posterior cingulate (p = 0.018) and increased in the left cuneus (p = 0.014) following ST + PENFS treatment. These findings were significant following FDR correction for multiple comparisons. ST group right hemisphere insula cortical thickness increased post-treatment and was significantly (p = 0.02) inversely correlated with pain scores. ST + PENFS group right hemisphere posterior dorsal cingulate size significantly (p = 0.044) positively correlated with pain scores. GABA: There were no significant correlations with GABA, though a trend was noted towards increased GABA following treatment in both groups (p = 0.083) using a linear mixed effects model.

Conclusions

Results suggest a novel effect of PENFS reflected by differential volumetric changes compared to ST. The changes in GABA that occur in both groups are more likely related to ST. Insular GABA and cortical thickness in key regions of interest may be developed as potential biomarkers for evaluating chronic pain pathology and treatment outcomes.

The Current View on the Paradox of Pain in Autism Spectrum Disorders

Autism spectrum disorder (ASD) is a neurodevelopmental disorder, which affects 1 in 44 children and may cause severe disabilities. Besides socio-communicational difficulties and repetitive behaviors, ASD also presents as atypical sensorimotor function and pain reactivity. While chronic pain is a frequent co-morbidity in autism, pain management in this population is often insufficient because of difficulties in pain evaluation, worsening their prognosis and perhaps driving higher mortality rates. Previous observations have tended to oversimplify the experience of pain in autism as being insensitive to painful stimuli. Various findings in the past 15 years have challenged and complicated this dogma. However, a relatively small number of studies investigates the physiological correlates of pain reactivity in ASD. We explore the possibility that atypical pain perception in people with ASD is mediated by alterations in pain perception, transmission, expression and modulation, and through interactions between these processes. These complex interactions may account for the great variability and sometimes contradictory findings from the studies. A growing body of evidence is challenging the idea of alterations in pain processing in ASD due to a single factor, and calls for an integrative view. We propose a model of the pain cycle that includes the interplay between the molecular and neurophysiological pathways of pain processing and it conscious appraisal that may interfere with pain reactivity and coping in autism. The role of social factors in pain-induced response is also discussed. Pain assessment in clinical care is mostly based on subjective rather than objective measures. This review clarifies the strong need for a consistent methodology, and describes innovative tools to cope with the heterogeneity of pain expression in ASD, enabling individualized assessment. Multiple measures, including self-reporting, informant reporting, clinician-assessed, and purely physiological metrics may provide more consistent results. An integrative view on the regulation of the pain cycle offers a more robust framework to characterize the experience of pain in autism.

Lysophosphatidic acid receptor type-1 mediates brain activation in micro-Positron Emission Tomography analysis in a fibromyalgia-like mouse model

The intermittent cold stress-induced generalized pain response mimics the pathophysiological and pharmacotherapeutic features reported for fibromyalgia patients, including the presence of chronic generalized pain and female dominance. In addition, the intermittent cold stress-induced generalized pain is abolished in lysophosphatidic acid receptor type-1 knockout mice, as reported in many cases of neuropathic pain models. This study aimed to identify the brain loci involved in the intermittent cold stress generalized pain response and test their dependence on the lysophosphatidic acid receptor type-1. Positron emission tomography analyses using 2-deoxy-2-[¹⁸ F]fluoro-D-glucose in the presence of a pain stimulus showed that intermittent cold stress causes a significant increase in uptake in the ipsilateral regions, including the salience networking-related anterior cingulate cortex and insular cortex and the cognition-related hippocampus. A significant decrease was observed in the default mode network-related posterior cingulate cortex. Almost these intermittent cold stress-induced changes were abolished in lysophosphatidic acid receptor type-1 knockout mice. There results suggest that the intermittent cold stress-induced generalized pain response is mediated by the lysophosphatidic acid receptor type-1 in specific brain loci related to salience networking and cognition, which may lead to further developments in the treatment of fibromyalgia.

Individually unique dynamics of cortical connectivity reflect the ongoing intensity of chronic pain

ABSTRACT

Chronic pain diseases are characterised by an ongoing and fluctuating endogenous pain, yet it remains to be elucidated how this is reflected by the dynamics of ongoing functional cortical connections.Here, we investigated the cortical encoding of 20 chronic back pain patients and 20 chronic migraineurs in four repeated fMRI sessions. A brain parcellation approach subdivided the whole brain into 408 regions. Linear mixed effects models were fitted for each pair of brain regions to explore the relationship between the dynamic cortical connectivity and the observed trajectory of the patients' ratings of fluctuating endogenous pain.Overall, we found that periods of high and increasing pain were predominantly related to low cortical connectivity. The change of pain intensity in chronic back pain was subserved by connections in left parietal opercular regions, right insular regions, as well as large parts of the parietal, cingular and motor cortices. The change of pain intensity direction in chronic migraine was reflected by decreasing connectivity between the anterior insular cortex and orbitofrontal areas, as well as between the PCC and frontal and ACC regions.Interestingly, the group results were not mirrored by the individual patterns of pain-related connectivity, which is suggested to deny the idea of a common neuronal core problem for chronic pain diseases. The diversity of the individual cortical signatures of chronic pain encoding results adds to the understanding of chronic pain as a complex and multifaceted disease. The present findings support recent developments for more personalised medicine.

Frailty and pain, human studies and animal models

The hypothesis that pain can predispose to frailty development has been recently investigated in several clinical studies suggesting that frailty and pain may share some mechanisms. Both pain and frailty represent important clinical and social problems and both lack a successful treatment. This circumstance is mainly due to the absence of in-depth knowledge of their pathological mechanisms. Evidence of shared pathways between frailty and pain are preliminary. Indeed, many clinical studies are observational and the impact of pain treatment, and relative pain-relief, on frailty onset and progression has never been investigated. Furthermore, preclinical research on this topic has yet to be performed. Specific researches on the pain-frailty relation are needed. In this narrative review, we will attempt to point out the most relevant findings present in both clinical and preclinical literature on the topic, with particular attention to genetics, epigenetics and inflammation, in order to underline the existing gaps and the potential future interventional strategies. The use of pain and frailty animal models discussed in this review might contribute to research in this area.

Gender-Related Differences in BMP Expression and Adult Hippocampal Neurogenesis within Joint-Hippocampal Axis in a Rat Model of Rheumatoid Arthritis

BMPs regulate synovial quiescence and adult neurogenesis in the hippocampus in non-stress conditions. However, changes in BMP expression that are induced by inflammation during rheumatoid arthritis (RA) have not yet been reported. Here, we show that signalling with synovial BMPs (BMP-4 and -7) mediates the effect of systemic inflammation on adult neurogenesis in the hippocampus during pristane-induced arthritis (PIA) in Dark Agouti (DA) rats, an animal model of RA. Moreover, we show gender differences in BMP expressions and their antagonists (Noggin and Gremlin) during PIA and their correlations with the clinical course and IL-17A and TNF-α levels in serum. Our results indicate gender differences in the clinical course, where male rats showed earlier onset and earlier recovery but a worse clinical course in the first two phases of the disease (onset and peak), which correlates with the initial increase of serum IL-17A level. The clinical course of the female rats worsened in remission. Their prolonged symptoms could be a reflection of an increased TNF-α level in serum during remission. Synovial inflammation was greater in females in PIA-remission with greater synovial BMP and antagonist expressions. More significant correlations between serum cytokines (IL-17A and TNF-α), and synovial BMPs and their antagonists were found in females than in males. On the other hand, males showed an increase in hippocampal BMP-4 expression during the acute phase, but both genders showed a decrease in antagonist expressions during PIA in general. Both genders showed a decrease in the number of Ki-67⁺ and SOX-2⁺ and DCX⁺ cells and in the ratio of DCX⁺ to Ki67⁺ cells in the dentate gyrus during PIA. However, in PIA remission, females showed a faster increase in the number of Ki67⁺, SOX-2⁺, and DCX⁺ cells and a faster increase in the DCX/Ki67 ratio than males. Both genders showed an increase of hippocampal BMP-7 expression during remission, although males constantly showed greater BMP-7 expression at all time points. Our data show that gender differences exist in the BMP expressions in the periphery-hippocampus axis and in the IL-17A and TNF-α levels in serum, which could imply differences in the mechanisms for the onset and progression of the disease, the clinical course severity, and adult neurogenesis with subsequent neurological complications between genders.

Pain Modulates Responses to Emotional Stimuli

Pain and emotion are common subjective experiences that play vital roles in daily life. Pain has been clinically confirmed to increase depressive mood. However, little is known about how pain modulates cognitive emotional judgment processing. A better understanding of this may help explain the effect of pain on the development of depressive moods. We recruited 30 adult participants to test their responses to pictures of scenes (Experiment 1) and faces (Experiment 2) that represented happy, neutral, and sad emotions, while experiencing painful (induced via topical capsaicin cream) and control (hand cream) treatments. Results showed that participants in the painful condition showed lower accuracy to emotional scene stimuli and longer reaction times to both emotional scene and face stimuli, relative to the control condition. In addition, the difference values of the reaction times between the painful and control conditions were larger for sad scenes than for happy or neutral scenes. These results suggest that pain alters attentional processing of emotional stimuli, especially with regards to sad scene stimuli, which may explain how painful stimuli affect the development of depressive moods.