Chronic pain and pain processing in Parkinson's disease

Oxycodone or Higher Dose of Levodopa for the Treatment of Parkinsonian Central Pain: OXYDOPA Trial

BACKGROUND

Among the different types of pain related to Parkinson's disease (PD), parkinsonian central pain (PCP) is the most disabling.

OBJECTIVES

We investigated the analgesic efficacy of two therapeutic strategies (opioid with oxycodone- prolonged-release (PR) and higher dose of levodopa/benserazide) compared with placebo in patients with PCP.

METHODS

OXYDOPA was a randomized, double-blind, double-dummy, placebo-controlled, multicenter parallel-group trial run at 15 centers within the French NS-Park network. PD patients with PCP (≥30 on the Visual Analogue Scale [VAS]) were randomly assigned to receive oxycodone-PR (up to 40 mg/day), levodopa/benserazide (up to 200 mg/day) or matching placebo three times a day (tid) for 8 weeks at a stable dose, in add-on to their current dopaminergic therapy. The primary endpoint was the change in average pain intensity over the previous week rated on VAS from baseline to week-10 based on modified intention-to-treat analyses.

RESULTS

Between May 2016 and August 2020, 66 patients were randomized to oxycodone-PR (n = 23), levodopa/benserazide (n = 20) or placebo (n = 23). The mean change in pain intensity was -17 ± 18.5 on oxycodone-PR, -8.3 ± 11.1 on levodopa/benserazide, and -14.3 ± 18.9 in the placebo groups. The absolute difference versus placebo was -1.54 (97.5% confidence interval [CI], -17.0 to 13.90; P = 0.8) on oxycodone-PR and +7.79 (97.5% CI, -4.99 to 20.58; P = 0.2) on levodopa/benserazide. Similar proportions of patients in each group experienced all-cause adverse events. Those leading to study discontinuation were most frequently observed with oxycodone-PR (39%) than levodopa/benserazide (5%) or placebo (15%).

CONCLUSIONS

The present trial failed to demonstrate the superiority of oxycodone-PR or a higher dose of levodopa in patients with PCP, while oxycodone-PR was poorly tolerated. © 2024 The Author(s). Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Posterior insula repetitive transcranial magnetic stimulation for chronic pain in patients with Parkinson disease - pain type matters: A double-blinded randomized sham-controlled trial

OBJECTIVES

Altered somatosensory processing in the posterior insula may play a role in chronic pain development and contribute to Parkinson disease (PD)-related pain. Posterior-superior insula (PSI) repetitive transcranial magnetic stimulation (rTMS) has been demonstrated to have analgesic effects among patients with some chronic pain conditions. This study aimed at assessing the efficacy of PSI-rTMS for treating PD-related pain.

METHODS

This was a double-blinded, randomized, sham-controlled, parallel-arm trial (NCT03504748). People with PD (PwP)-related chronic pain underwent five daily PSI-rTMS sessions for a week, followed by once weekly maintenance stimulations for seven weeks. rTMS was delivered at 10 Hz and 80% of the resting motor threshold. The primary outcome was a ≥ 30% pain intensity reduction at 8 weeks compared to baseline. Functionality, mood, cognitive, motor status, and somatosensory thresholds were also assessed.

RESULTS

Twenty-five patients were enrolled. Mean age was 55.2 ± 9.5 years-old, and 56% were female. Nociceptive pain accounted for 60%, and neuropathic and nociplastic for 20% each. No significant difference was found for 30% pain reduction response rates between active (42.7%) and sham groups (14.6%, p = 0.26). Secondary clinical outcomes and sensory thresholds also did not differ significantly. In a post hoc analysis, PwP with nociceptive pain sub-type experienced more pain relief after active (85.7%) compared to sham PSI-rTMS (25%, p = 0.032).

CONCLUSION

Our preliminary results suggest that different types of PD-related pain may respond differently to treatment, and therefore people with PD may benefit from having PD-related pain well characterized in research trials and in clinical practice.

Activation and polarization of striatal microglia and astrocytes are involved in bradykinesia and allodynia in early-stage parkinsonian mice

In addition to the cardinal motor symptoms, pain is a major non-motor symptom of Parkinson's disease (PD). Neuroinflammation in the substantia nigra pars compacta and dorsal striatum is involved in neurodegeneration in PD. But the polarization of microglia and astrocytes in the dorsal striatum and their contribution to motor deficits and hyperalgesia in PD have not been characterized. In the present study, we observed that hemiparkinsonian mice established by unilateral 6-OHDA injection in the medial forebrain bundle exhibited motor deficits and mechanical allodynia. In these mice, both microglia and astrocytes in the dorsal striatum were activated and polarized to M1/M2 microglia and A1/A2 astrocytes as genes specific to these cells were upregulated. These effects peaked 7 days after 6-OHDA injection. Meanwhile, striatal astrocytes in parkinsonian mice also displayed hyperpolarized membrane potentials, enhanced voltage-gated potassium currents, and dysfunction in inwardly rectifying potassium channels and glutamate transporters. Systemic administration of minocycline, a microglia inhibitor, attenuated the expression of genes specific to M1 microglia and A1 astrocytes in the dorsal striatum (but not those specific to M2 microglia and A2 astrocytes), attenuated the damage in the nigrostriatal dopaminergic system, and alleviated the motor deficits and mechanical allodynia in parkinsonian mice. By contrast, local administration of minocycline into the dorsal striatum of parkinsonian mice mitigated only hyperalgesia. This study suggests that M1 microglia and A1 astrocytes in the dorsal striatum may play important roles in the development of pathophysiology underlying hyperalgesia in the early stages of PD.

Frozen Shoulder and the Risk of Parkinson's Disease: A Danish Registry-Based Cohort Study

Background

Frozen shoulder may be an early preclinical symptom of Parkinson's disease (PD).

Objective

To examine PD risk after frozen shoulder diagnosis and to evaluate this disorder as a possible manifestation of parkinsonism preceding the clinical recognition of PD and possible target for screening.

Methods

Danish population-based medical registries were used to identify patients aged ≥40 years with a first-time frozen shoulder diagnosis (1995-2016). A comparison cohort was randomly selected from the general population matched on age and sex. To address detection bias and the specificity of frozen shoulder diagnosis, we performed a sensitivity analysis, using similar matching criteria to select a cohort of patients with back pain diagnosis. The outcome was incident PD. Cumulative incidences and adjusted hazard ratios (HRs) were estimated with 95% confidence intervals (CIs).

Results

We identified 37,041 individuals with frozen shoulder, 370,410 general population comparators, and 111,101 back pain comparators. The cumulative incidence of PD at 0-22 years follow-up was 1.51% in the frozen shoulder cohort, 1.03% in the general population cohort, and 1.32% in the back pain cohort. For frozen shoulder versus general population, adjusted HRs were 1.94 (CI: 1.20-3.13) at 0-1 years and 1.45 (CI: 1.24-1.70) at 0-22 years follow-up. For frozen shoulder versus back pain, adjusted HRs were 0.89 (CI: 0.54-1.46) and 1.01 (CI: 0.84-1.21), respectively.

Conclusion

Patients with frozen shoulder had an increased PD risk compared with the general population, although the absolute risks were low. Frozen shoulder might sometimes represent early manifestations of PD. Detection bias probably cannot account for the increased PD risk during the long-term follow-up.

Pain in Parkinson's disease: a neuroanatomy-based approach

Parkinson's disease is a progressive neurodegenerative disorder characterized by the deposition of misfolded alpha-synuclein in different regions of the central and peripheral nervous system. Motor impairment represents the signature clinical expression of Parkinson's disease. Nevertheless, non-motor symptoms are invariably present at different stages of the disease and constitute an important therapeutic challenge with a high impact for the patients' quality of life. Among non-motor symptoms, pain is frequently experienced by patients, being present in a range of 24-85% of Parkinson's disease population. Moreover, in more than 5% of patients, pain represents the first clinical manifestation, preceding by decades the exordium of motor symptoms. Pain implies a complex biopsychosocial experience with a downstream complex anatomical network involved in pain perception, modulation, and processing. Interestingly, all the anatomical areas involved in pain network can be affected by a-synuclein pathology, suggesting that pathophysiology of pain in Parkinson's disease encompasses a 'pain spectrum', involving different anatomical and neurochemical substrates. Here the various anatomical sites recruited in pain perception, modulation and processing are discussed, highlighting the consequences of their possible degeneration in course of Parkinson's disease. Starting from peripheral small fibres neuropathy and pathological alterations at the level of the posterior laminae of the spinal cord, we then describe the multifaceted role of noradrenaline and dopamine loss in driving dysregulated pain perception. Finally, we focus on the possible role of the intertwined circuits between amygdala, nucleus accumbens and habenula in determining the psycho-emotional, autonomic and cognitive experience of pain in Parkinson's disease. This narrative review provides the first anatomically driven comprehension of pain in Parkinson's disease, aiming at fostering new insights for personalized clinical diagnosis and therapeutic interventions.

Pathological pain: Non-motor manifestations in Parkinson disease and its treatment

In addition to motor symptoms, non-motor manifestations of Parkinson's disease (PD), i.e. pain, depression, sleep disturbance, and autonomic disorders, have received increasing attention. As one of the non-motor symptoms, pain has a high prevalence and is considered an early pre-motor symptom in the development of PD. In relation to pathological pain and its management in PD, particularly in the early stages, it is hypothesized that the loss of dopaminergic neurons causes a functional deficit in supraspinal structures, leading to an imbalance in endogenous descending modulation. Deficits in dopaminergic-dependent pathways also affect non-dopaminergic neurotransmitter systems that contribute to the pathological processing of nociceptive input, the integration, and modulation of pain in PD. This review examines the onset and progression of pain in PD, with a particular focus on alterations in the central modulation of nociception. The discussion highlights the importance of abnormal endogenous descending facilitation and inhibition in PD pain, which may provide potential clues to a better understanding of the nature of pathological pain and its effective clinical management.

Activation of Pedunculopontine Tegmental Nucleus Alleviates the Pain Induced by the Lesion of Midbrain Dopaminergic Neurons

The loss of midbrain dopaminergic (DA) neurons is the fundamental pathological feature of Parkinson's disease (PD). PD causes chronic pain in two-thirds of patients. Recent studies showed that the activation of the pedunculopontine tegmental nucleus (PPTg) can effectively relieve inflammatory pain and neuropathic pain. The PPTg is located in the pontomesencephalic tegmentum, a target of deep brain stimulation (DBS) treatment in PD, and is involved in motor control and sensory integration. To test whether the lesion of midbrain DA neurons induced pain hypersensitivity, and whether the chemogenetic activation of the PPTg could modulate the pain, the AAV-hM3Dq receptor was transfected and expressed into the PPTg neurons of 6-hydroxydopamine-lesioned mice. In this study, von Frey, open field, and adhesive tape removal tests were used to assess animals' pain sensitivity, locomotor activity, and sensorimotor function and somatosensory perception, respectively. Here, we found that the lesion of midbrain DA neurons induced a minor deficit in voluntary movement but did not affect sensorimotor function and somatosensory perception in the tape removal test. The results showed that lesion led to pain hypersensitivity, which could be alleviated both by levodopa and by the chemogenetic activation of the PPTg. Activating the PPTg may be a potential therapeutic strategy to relieve pain phenotypes in PD.

TDCS for parkinson's disease disease-related pain: A randomized trial

OBJECTIVE

To evaluate the effects of transcranial direct current stimulation (tDCS) on Parkinson's disease (PD)-related pain.

METHODS

This triple-blind randomized controlled trial included twenty-two patients (age range 38-85, 10 male) with PD-related pain. Eleven subjects received ten sessions of 20 minutes tDCS over the primary motor cortex contralateral to pain at 2 mA intensity. Eleven subjects received sham stimulation. Outcome measures included changes in the Kinǵs Parkinsońs Pain Scale (KPPS), Brief Pain Inventory (BPI), widespread mechanical hyperalgesia (WMH), temporal summation of pain (TS), and conditioned pain modulation (CPM).

RESULTS

Significant differences were found in KPPS between groups favoring the active-tDCS group compared to the sham-tDCS group at 15-days follow-up (p = 0.014) but not at 2 days post-intervention (p = 0.059). The active-group showed significant improvements over the sham-group after 15 days (p = 0.017). Significant changes were found in CPM between groups in favor of active-tDCS group at 2 days post-intervention (p = 0.002) and at 15 days (p = 0.017). No meaningful differences were observed in BPI or TS.

CONCLUSIONS

tDCS of the primary motor cortex alleviates perceived PD-related pain, reduces pain sensitization, and enhances descending pain inhibition.

SIGNIFICANCE

This is the first study to test and demonstrate the use of tDCS for improving PD-related pain.

High mobility group box-1: A therapeutic target for analgesia and associated symptoms in chronic pain

The number of patients with chronic pain continues to increase against the background of an ageing society and a high incidence of various epidemics and disasters. One factor contributing to this situation is the absence of truly effective analgesics. Chronic pain is a persistent stress for the organism and can trigger a variety of neuropsychiatric symptoms. Hence, the search for useful analgesic targets is currently being intensified worldwide, and it is anticipated that the key to success may be molecules involved in emotional as well as sensory systems. High mobility group box-1 (HMGB1) has attracted attention as a therapeutic target for a variety of diseases. It is a very unique molecule having a dual role as a nuclear protein while also functioning as an inflammatory agent outside the cell. In recent years, numerous studies have shown that HMGB1 acts as a pain inducer in primary sensory nerves and the spinal dorsal horn. In addition, HMGB1 can function in the brain, and is involved in the symptoms of depression, anxiety and cognitive dysfunction that accompany chronic pain. In this review, we will summarize recent research and discuss the potential of HMGB1 as a useful drug target for chronic pain.

CT-optimal touch and chronic pain experience in Parkinson's Disease; An intervention study

One of the most underdiagnosed and undertreated non-motor symptoms of Parkinson's Disease is chronic pain. This is generally treated with analgesics which is not always effective and can cause several side-effects. Therefore, new ways to reduce chronic pain are needed. Several experimental studies show that CT-optimal touch can reduce acute pain. However, little is known about the effect of CT-optimal touch on chronic pain. The aim of the current study is to investigate whether CT-optimal touch can reduce the chronic pain experience in Parkinson patients. In this intervention study, 17 Parkinson patients underwent three conditions; no touch, CT-optimal touch and CT non-optimal touch with a duration of one week each. During each touch week, participants received touch from their partners twice a day for 15 minutes. Results show that both types of touch ameliorate the chronic pain experience. Furthermore, it appears that it is slightly more beneficial to apply CT-optimal touch also because it is perceived as more pleasant. Therefore, we argue that CT-optimal touch might be used when immediate pain relief is needed. Importantly, this study shows that CT-optimal touch can reduce chronic pain in Parkinson's Disease and can be administered by a partner which makes it feasible to implement CT-optimal touch as daily routine.

Constipation and pain in Parkinson's disease: a clinical analysis

Parkinson's Disease (PD) is a neurodegenerative disorder characterized by both motor and non-motor symptoms (NMS). Among NMS, constipation and pain are both highly prevalent and debilitating affecting up to 80% of PD patients and impairing their quality of life. Here, we investigated the relationship between constipation and pain in PD patients. This is a retrospective study assessing the relationship between pain and constipation in a PD patient population from a clinical database of patients attending the outpatient clinic of the movement disorders division, Neurology Unit of Policlinico Tor Vergata, in Rome. Subjects were assessed with the Unified Parkinson's Disease Rating Scale (UPDRS) part III, Hoehn and Yahr (H&Y) stage, King's Parkinson's Disease Pain Scale (KPPS), Brief Pain Inventory (BPI), Non-Motor Symptoms Scale (NMSS) and Beck Depression Inventory (BDI). Patients were further divided in two groups (Group 1, 32 patients with constipation and Group 2, 35 PD patients without constipation) ANOVA and ANCOVA analysis were used to compare the two groups. PD patients with constipation had significantly higher pain severity and pain interference, as measured by the BPI scale and higher total KPPS score, fluctuation-related pain, nocturnal pain, and radicular pain when compared to PD patients without constipation. This study highlights for the first time a possible interplay between constipation and pain in PD that deserves further investigations.

Musculoskeletal pain in Parkinson's disease: Association with dopaminergic deficiency in the caudate nucleus

BACKGROUND

Musculoskeletal (MSK) pain affects over 80% of People with Parkinson's (PD, PwP) and may, in part, be dopaminergic in origin, as dopaminergic medication often leads to its relief.

METHODS

PwP who underwent striatal dopamine transporter visualization with a radiopharmaceutical DaTscan™ (123 I-Ioflupane Injection) using a single-photon emission computed tomography (SPECT) as a part of their clinical-diagnostic work up were enrolled in the "Non-motor International Longitudinal Study" (NILS; UK National Institute for Health Research Clinical Research Network Number 10084) and included in this cross-sectional analysis. The association between specific DaTscan binding ratios for each striatum, the caudate nucleus and putamen and clinical ratings for MSK pain (assessed using the King's Parkinson's Disease Pain Scale (KPPS)) were analysed.

RESULTS

53 PwP (30.2% female; age: 63.79 ± 11.31 years; disease duration (DD): 3.32 (0.31-14.41) years; Hoehn & Yahr stage (H&Y): 2 (1-4); Levodopa Equivalent Daily Dose (LEDD): 543.08 ± 308.94 mg) were assessed and included in this analysis. MSK pain was highly prevalent (71.7% of all participants, mean KPPS Item 1 score 5.34 ± 4.76) and did not correlate with the motor symptoms burden (SCOPA-Motor total score; p = 0.783) but showed a significant correlation with quality of life (PDQ-8, rs  = 0.290, p = 0.035). z-scores for the caudate nucleus (Exp (B) = 0.367, 95% CI for Exp (B) 0.148-0.910, p = 0.031) and striatum (Exp (B) = 0.338, 95% CI for Exp (B) 0.123-0.931, p = 0.036), adjusted for DD, H&Y and LEDD, were significant determinants of MSK pain.

CONCLUSIONS

Our findings suggest an association between MSK pain in PwP and the severity of dopaminergic deficiency in the caudate nucleus.

SIGNIFICANCE

In People with Parkinson's, musculoskeletal pain does not arise simply as a direct sequel to motor symptoms-instead, it is linked to the severity of dopaminergic depletion in the caudate nucleus.

Risk factors of neuropathic pain in multiple sclerosis: a retrospective case-cohort study

Background

Pain is a common symptom in multiple sclerosis (MS), especially neuropathic pain, which has a significant impact on patients' mental and physical health and quality of life. However, risk factors that related to neuropathic pain, still remain unclear.

Objective

The study aimed to explore the risk factors of neuropathic pain among MS patients.

Materials and methods

This retrospective study examined the consecutive patients diagnosed with MS in the Department of Neurology of Guangdong Provincial Hospital of Chinese Medicine between August 2011 and October 2022. Neuropathic pain was defined as "pain arising as a direct consequence of a lesion or disease affecting the somatosensory system". Demographic and clinical features were obtained from the electronic system of the hospital.

Results

Our cohort revealed that the prevalence of patients with neuropathic pain in MS was 34.1%. The results indicated that the longer the spinal lesions, the greater the neuropathic pain risks (2-4: OR, 13.3(2.1-82), >5: OR, 15.2(2.7-86.8), p for tread: 0.037). Meanwhile, multivariate regression analysis showed that cervical and thoracic lesions (OR 4.276, 95% CI 1.366-13.382, P = 0.013), upper thoracic lesions (T1-T6) (OR 3.047, 95% CI 1.018-9.124, P = 0.046) were positively correlated with neuropathic pain, while basal ganglia lesions (OR 0.188, 95% CI 0.044-0.809, P = 0.025) were negatively correlated with neuropathic pain among MS patients.

Conclusion

Extended spinal lesions (≥3 spinal lesions), cervical and thoracic lesions, upper thoracic lesions were independent risk factors of neuropathic pain among MS patients. Furthermore, our study found that the longer the spinal lesions, the greater the neuropathic pain risks.

Inhibition of calcium-stimulated adenylyl cyclase subtype 1 (AC1) for the treatment of pain and anxiety symptoms in Parkinson's disease mice model

Pain and anxiety are two common and undertreated non-motor symptoms in Parkinson's disease (PD), which affect the life quality of PD patients, and the underlying mechanisms remain unclear. As an important subtype of adenylyl cyclases (ACs), adenylyl cyclase subtype 1 (AC1) is critical for the induction of cortical long-term potentiation (LTP) and injury induced synaptic potentiation in the cortical areas including anterior cingulate cortex (ACC) and insular cortex (IC). Genetic deletion of AC1 or pharmacological inhibition of AC1 improved chronic pain and anxiety in different animal models. In this study, we proved the motor deficit, pain and anxiety symptoms of PD in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated mice model. As a lead candidate AC1 inhibitor, oral administration (1 dose and seven doses) of NB001 (20 and 40 mg/kg) showed significant analgesic effect in MPTP-treated mice, and the anxiety behavior was also reduced (40 mg/kg). By using genetic knockout mice, we found that AC1 knockout mice showed reduced pain and anxiety symptoms after MPTP administration, but not AC8 knockout mice. In summary, genetic deletion of AC1 or pharmacological inhibition of AC1 improved pain and anxiety symptoms in PD model mice, but didn't affect motor function. These results suggest that NB001 is a potential drug for the treatment of pain and anxiety symptoms in PD patients by inhibiting AC1 target.

Graph-Based Fusion of Imaging, Genetic and Clinical Data for Degenerative Disease Diagnosis

Graph learning methods have achieved noteworthy performance in disease diagnosis due to their ability to represent unstructured information such as inter-subject relationships. While it has been shown that imaging, genetic and clinical data are crucial for degenerative disease diagnosis, existing methods rarely consider how best to use their relationships. How best to utilize information from imaging, genetic and clinical data remains a challenging problem. This study proposes a novel graph-based fusion (GBF) approach to meet this challenge. To extract effective imaging-genetic features, we propose an imaging-genetic fusion module which uses an attention mechanism to obtain modality-specific and joint representations within and between imaging and genetic data. Then, considering the effectiveness of clinical information for diagnosing degenerative diseases, we propose a multi-graph fusion module to further fuse imaging-genetic and clinical features, which adopts a learnable graph construction strategy and a graph ensemble method. Experimental results on two benchmarks for degenerative disease diagnosis (Alzheimers Disease Neuroimaging Initiative and Parkinson's Progression Markers Initiative) demonstrate its effectiveness compared to state-of-the-art graph-based methods. Our findings should help guide further development of graph-based models for dealing with imaging, genetic and clinical data.

What is available to support pain management in Parkinson's: a scoping review protocol

OBJECTIVE

A scoping review will be undertaken to examine and map the available evidence that has been produced in relation to pain management in Parkinson's, with a focus on behavioural interventions, resources and/or how professionals support people with Parkinson's self-management of pain.

METHODS

This review will be based on the methodological framework given by Arksey and O'Malley's (2005), including enhancements by Levac et al., Peters et al. and the Joanna Briggs Institute. We will include studies from PubMed, SCOPUS, CINAHL, MEDLINE Web of Science, APA PsycINFO and ASSIA from January, 2010 onwards. Both quantitative and qualitative data will be analysed separately to identify the characteristics of support for pain management available, orientation of the approach and any identifiable behaviour change components and their outcomes. The COM-B behaviour change model and Theoretical Domains Framework will provide a theoretical framework for synthesising evidence in this review.

CONCLUSION

This scoping review will help to explore studies focusing on the evidence supporting a range of interventions relating to the management of pain experienced by people living with Parkinson's. The focus will be on describing what is available to support self-management, identify what behaviour change components have been used and their effectiveness, identify barriers and enablers to pain management and explore gaps in current provision of pain management. This review will identify implications and priorities for the follow-up phases to the larger 'Pain in Parkinson's' Project which is designed to support clinicians and individuals living with Parkinson's.

Dysregulated neuromodulation in the anterior cingulate cortex in chronic pain

Chronic pain is a significant global socioeconomic burden with limited long-term treatment options. The intractable nature of chronic pain stems from two primary factors: the multifaceted nature of pain itself and an insufficient understanding of the diverse physiological mechanisms that underlie its initiation and maintenance, in both the peripheral and central nervous systems. The development of novel non-opioidergic analgesic approaches is contingent on our ability to normalize the dysregulated nociceptive pathways involved in pathological pain processing. The anterior cingulate cortex (ACC) stands out due to its involvement in top-down modulation of pain perception, its abnormal activity in chronic pain conditions, and its contribution to cognitive functions frequently impaired in chronic pain states. Here, we review the roles of the monoamines dopamine (DA), norepinephrine (NE), serotonin (5-HT), and other neuromodulators in controlling the activity of the ACC and how chronic pain alters their signaling in ACC circuits to promote pathological hyperexcitability. Additionally, we discuss the potential of targeting these monoaminergic pathways as a therapeutic strategy for treating the cognitive and affective symptoms associated with chronic pain.

Ultrasonographic imaging findings of the shoulder in patients with Parkinson disease

BACKGROUND

Shoulder disorders, including frozen shoulder, bursitis, and rotator cuff lesions, are common musculoskeletal problems in patients with Parkinson disease (PD). Because musculoskeletal ultrasound (US) can clearly image shoulder joints, we aimed to evaluate shoulder joints using US in patients with PD and healthy participants and correlation between US and PD severity.

METHODS

This is a prospective case-control study. 50 patients with PD and 50 healthy subjects from the outpatient department were administered US for bilateral shoulders. For data analysis, we chose the more severely affected side in the PD group for matching with the corresponding shoulder in the control group according to age, sex, and body mass index. Pain and disability were measured using the Visual Analogue Scale (VAS) for pain, Shoulder Pain and Disability Index (SPADI), and the Shoulder Disability Questionnaire (SDQ).

RESULTS

The PD group had higher VAS pain scores during activity (p = 0.003) and rest (p < 0.001), as well as the SPADI and SDQ scores (p < 0.001). In US findings, biceps long head tendon sheath effusion (p = 0.001), humeral head cortical irregularity (p = 0.012), and abnormality in the supraspinatus tendon (p = 0.003) were significantly greater in the PD group. Intra-group analysis in the PD group demonstrated a significant difference in passive flexion (p = 0.019) and supraspinatus tendinopathy (p = 0.033) on US examination during different disease stages.

CONCLUSIONS

Patients with PD had more supraspinatus tendinopathy on US findings than control subjects. The lesion was significantly associated with disease severity.

CLINICAL TRIAL NUMBER

NCT02702232.

Research trends and hotspots of neuropathic pain in neurodegenerative diseases: a bibliometric analysis

Background

Neuropathic pain is caused by a neurological injury or disease and can have a significant impact on people's daily lives. Studies have shown that neuropathic pain is commonly associated with neurodegenerative diseases. In recent years, there has been a lot of literature on the relationship between neuropathic pain and neurodegenerative diseases. However, bibliometrics is rarely used in analyzing the general aspects of studies on neuropathic pain in neurodegenerative diseases.

Methods

The bibliometric analysis software CiteSpace and VOSviewer were used to analyze the knowledge graph of 387 studies in the Science Citation Index Expanded of the Web of Science Core Collection Database.

Results

We obtained 2,036 documents through the search, leaving 387 documents after culling. 387 documents were used for the data analysis. The data analysis showed that 330 papers related to neuropathic pain in neurodegenerative diseases were published from 2007-2022, accounting for 85.27% of all published literature. In terms of contributions to the scientific study of neuropathic pain, the United States is in the top tier, with the highest number of publications, citations, and H-indexes.

Conclusion

The findings in our study may provide researchers with useful information about research trends, frontiers, and cooperative institutions. Multiple sclerosis, Parkinson's disease, and Alzheimer's disease are the three most studied neurodegenerative diseases. Among the pathological basis of neurodegenerative diseases, microglia-regulated neuroinflammation is a hot research topic. Deep brain stimulation and gamma knife radiosurgery are two popular treatments.

Serotonin and Dopamine Show Different Response Profiles to Acute Stress in the Nucleus Accumbens and Medial Prefrontal Cortex of Rats with Neuropathic Pain

The ability to adaptively guide behaviour requires the integration of external information with internal motivational factors. Decision-making capabilities can be impaired by acute stress and is often exacerbated by chronic pain. Chronic neuropathic pain patients often present with cognitive dysfunction, including impaired decision-making. The mechanisms underlying these changes are not well understood but may include altered monoaminergic transmission in the brain. In this study we investigated the relationships between dopamine, serotonin, and their metabolites in key brain regions that regulate motivated behaviour and decision-making. The neurochemical profiles of the medial prefrontal cortex, orbital prefrontal cortex, and nucleus accumbens were analysed using HPLC in rats that received a chronic constriction injury (CCI) of the right sciatic nerve and an acute stress (15-min restraint), prior to an outcome devaluation task. CCI alone significantly decreased dopamine but not serotonin concentrations in the medial prefrontal cortex. By contrast, restraint stress acutely increased dopamine in the medial prefrontal cortex, and the nucleus accumbens; and increased serotonin in the medial prefrontal cortex 2 h later. The sustained dopaminergic and serotonergic responses to acute stress highlight the importance of an animal's ability to mount an effective coping response. In addition, these data suggest that the impact of nerve injury and acute stress on outcome-devaluation occurs independently of dopaminergic and serotonergic transmission in the medial prefrontal cortex, orbital prefrontal cortex and nucleus accumbens of rats.

Effectiveness and Therapeutic Mechanism of Pharmacopuncture for Pain in Parkinson's Disease: A Study Protocol for a Pilot Pragmatic Randomized, Assessor-Blinded, Usual Care-Controlled, Three-Arm Parallel Trial

Pain in Parkinson's disease (PD) represents a complex phenotype known to decrease quality of life. This pragmatic randomized, controlled clinical trial evaluated the efficacy of pharmacopuncture (PA) for improving pain symptoms and investigated the corresponding therapeutic mechanisms in patients with PD. Ninety patients with PD-related pain were randomly allocated to receive either PA, manual acupuncture, or usual care in a 1:1:1 ratio; sixty healthy controls were included for comparative analysis of brain imaging data. Over 12 weeks, study treatment provided 2 days per week for 8 weeks with a follow-up period of 4 weeks. The primary outcome measure was the King's Parkinson's Disease Pain Scale score for assessing improvement in PD-related pain, including a sub-analysis to investigate the pattern of changes in pain according to a PD-related pain mechanism-based classification. Secondary outcome measures included a numerical rating scale-based assessment of the intensity and location of pain and changes in pain-associated symptoms, such as depression, anxiety, and sleep disorders. Exploratory outcome measures included structural and functional brain patterns on magnetic resonance imaging, blood molecular signature changes, gait analysis, facial expression and movement assessment in response to emotional stimuli, and a traditional Korean medicine syndrome differentiation questionnaire. The trial findings provided important clinical evidence for the effectiveness of PA in the management of PD-related pain and its associated symptoms, and helped elucidate the mechanism of its therapeutic effect on PD-related pain.

PAQR8 and PAQR9 expression is altered in the ventral tegmental area of aged rats infected with varicella zoster virus

Infection with varicella zoster virus (VZV) results in chicken pox and reactivation of VZV results in herpes zoster (HZ) or what is often referred to as shingles. Patients with HZ experience decreased motivation and increased emotional distress consistent with functions of the ventral tegmental area (VTA) of the brain. In addition, activity within the ventral tegmental area is altered in patients with HZ. HZ primarily affects individuals that are older and the VTA changes with age. To begin to determine if the VTA has a role in HZ symptoms, a screen of 10,000 genes within the VTA in young and old male rats was completed after injecting the whisker pad with VZV. The two genes that had maximal change were membrane progesterone receptors PAQR8 (mPRβ) and PAQR9 (mPRε). Neurons and non-neuronal cells expressed both PAQR8 and PAQR9. PAQR8 and PAQR9 protein expression was significantly reduced after VZV injection of young males. In old rats PAQR9 protein expression was significantly increased after VZV injection and PAQR9 protein expression was reduced in aged male rats versus young rats. Consistent with previous results, pain significantly increased after VZV injection of the whisker pad and aged animals showed significantly more pain than young animals. Our data suggests that PAQR8 and PAQR9 expression is altered by VZV injection and that these changes are affected by age.

Recent hospitalization and risk of antidepressant initiation in people with Parkinson's disease

BACKGROUND

People with Parkinson's disease (PD) are more likely to be hospitalized and initiate antidepressant use compared to people without PD. It is not known if hospitalization increases the risk of antidepressant initiation. We studied whether a recent hospitalization associates with antidepressant initiation in people with PD.

METHODS

A nested case-control study within the nationwide register-based FINPARK cohort which includes community-dwelling Finnish residents diagnosed with PD between years 1996 and 2015 (N = 22,189) was conducted. Initiation of antidepressant use after PD diagnosis was identified from Prescription Register with 1-year washout period (cases). One matched non-initiator control for each case was identified (N = 5492 age, sex, and time since PD diagnosis-matched case-control pairs). Hospitalizations within the 14 day-period preceding the antidepressant initiation were identified from the Care Register for Health Care.

RESULTS

The mean age at antidepressant initiation was 73.5 years with median time since PD diagnosis 2.9 years. Selective serotonin reuptake inhibitors (48.1%) and mirtazapine (35.7%) were the most commonly initiated antidepressants. Recent hospitalization was more common among antidepressant initiators than non-initiators (48.3 and 14.3%, respectively) and was associated with antidepressant initiation also after adjusting for comorbidities and use of medications during the washout (adjusted OR, 95% CI 5.85, 5.20-6.59). The initiators also had longer hospitalizations than non-initiators. PD was the most common main discharge diagnosis among both initiators (54.6%) and non-initiators (28.8%). Discharge diagnoses of mental and behavioral disorders and dementia were more common among initiators.

CONCLUSIONS

Hospitalisation is an opportunity to identify and assess depressive symptoms, sleep disorders and pain, which may partially explain the association. Alternatively, the indication for antidepressant initiation may have led to hospitalisation, or hospitalisation to aggravation of, e.g., neuropsychiatric symptoms leading to antidepressant initiation.

A nigro-subthalamo-parabrachial pathway modulates pain-like behaviors

The basal ganglia including the subthalamic nucleus (STN) and substantia nigra pars reticulata (SNr) are involved in pain-related responses, but how they regulate pain processing remains unknown. Here, we identify a pathway, consisting of GABAergic neurons in the SNr (SNr^GABA) and glutamatergic neurons in the STN (STN^Glu) and the lateral parabrachial nucleus (LPB^Glu), that modulates acute and persistent pain states in both male and female mice. The activity of STN neurons was enhanced in acute and persistent pain states. This enhancement was accompanied by hypoactivity in SNr^GABA neurons and strengthening of the STN-LPB glutamatergic projection. Reversing the dysfunction in the SNr^GABA-STN^Glu-LPB^Glu pathway attenuated activity of LPB^Glu neurons and mitigated pain-like behaviors. Therefore, the SNr^GABA-STN^Glu-LPB^Glu pathway regulates pathological pain and is a potential target for pain management.

Cannabinoids in movement disorders

INTRODUCTION

On the basis of both scientific progress and popular lore, there is growing optimism in the therapeutic potential of cannabis (marijuana) and cannabinoid-based chemicals for movement disorders. There is also notable skepticism regarding the scientific basis for this therapeutic optimism and significant concerns regarding the safety and regulation of cannabinoid products, particularly those available without prescription.

METHODS

In recognition of the high interest and controversial nature of this subject, the meeting committee of the International Parkinson and Movement Disorders Society arranged for a talk on cannabis at the 2019 annual meeting's Controversies in Movement Disorders plenary session. This paper summarizes the highlights of this session.

RESULTS

The endocannabinoid system is strongly tied to motor function and dysfunction, with basic research suggesting several promising therapeutic targets related to cannabinoids for movement disorders. Clinical research on cannabinoids for motor and nonmotor symptoms in Parkinson's disease, Huntington's disease, Tourette's syndrome, dystonia, and other movement disorders to date are promising at best and inconclusive or negative at worst. Research in other populations suggest efficacy for common symptoms like pain. While social campaigns against recreational cannabinoid use focus on cognitive changes in adolescents, the long-term sequelae of regulated medical use in older adults with movement disorders is unknown. The overall risks of cannabinoids may be similar to other commonly used medications and include falls and apathy.

CONCLUSION

Further research is greatly needed to better understand the actual clinical benefits and long-term side effects of medical cannabis products for movement disorders indications and populations.

Cellular and Molecular Machinery of Neuropathic Pain: an Emerging Insight

Purpose of Review

Neuropathic pain (NP) has been ubiquitously characterized by lesion and its linked somatosensory system either the central nervous system (CNS) or peripheral nervous system (PNS) This PNS episode is the most prevalent site of NP origin and is found to be associated with afferent nerve fibers carrying pain signals from injured/trauma site to the CNS including the brain. Several kinds of pharmacotherapeutic drugs shuch as analgesics, anti-convulsants, and anti-depressants are being employed for the its possible interventions. The NP has been a great interest to follow different pathophysiological mechanisms which are often considered to correlate with the metabolic pathways and its mediated disease. There is paucity of knowledge to make such mechanism via NP.

Recent Finding

Most notably, recent pandemic outbreak of COVID-19 has also been reported in chronic pain mediated diabetes, inflammatory disorders, and cancers. There is an increasing incidence of NP and its complex mechanism has now led to identify the possible investigations of responsible genes and proteins via bioinformatics tools. The analysis might be more instrumental as collecting the genes from pain genetic database, analyzing the variants through differential gene expression (DEG) and constructing the protein–protein interaction (PPI) networks and thereby determining their upregulating and downregulating pathways.

Summary

This review sheds a bright light towards several mechanisms at both cellular and molecular level, correlation of NP-mediated disease mechanism and possible cell surface biomarkers (receptors), and identified genes could be more promising for their pharmacological targets.

The pain conductor: brainstem modulation in acute and chronic pain

PURPOSE OF REVIEW

It is well established in experimental settings that brainstem circuits powerfully modulate the multidimensional experience of pain. This review summarizes current understanding of the roles of brainstem nuclei in modulating the intensity of pain, and how these circuits might be recruited therapeutically for pain relief in chronic and palliative settings.

RECENT FINDINGS

The development of ultra-high field magnetic resonance imaging and more robust statistical analyses has led to a more integrated understanding of brainstem function during pain. It is clear that a number of brainstem nuclei and their overlapping pathways are recruited to either enhance or inhibit incoming nociceptive signals. This review reflects on early preclinical research, which identified in detail brainstem analgesic function, putting into context contemporary investigations in humans that have identified the role of specific brainstem circuits in modulating pain, their contribution to pain chronicity, and even the alleviation of palliative comorbidities.

SUMMARY

The brainstem is an integral component of the circuitry underpinning pain perception. Enhanced understanding of its circuitry in experimental studies in humans has, in recent years, increased the possibility for better optimized pain-relief strategies and the identification of vulnerabilities to postsurgical pain problems. When integrated into the clinical landscape, these experimental findings of brainstem modulation of pain signalling have the potential to contribute to the optimization of pain management and patient care from acute, to chronic, to palliative states.

Adherence rate, barriers to attend, safety and overall experience of a physical exercise program via telemonitoring during COVID-19 pandemic for individuals with Parkinson's disease: A feasibility study

Background

Telemonitoring can maintain daily exercise routine during the COVID‐19 pandemic of individuals with Parkinson's disease (PD). However, there are barriers to adherence and attendance with remote physical rehabilitation. The main objective of this study was to evaluate adherence rate, barriers to attendance, and safety of a telemonitoring program for individuals with PD; and secondarily to evaluate the individual and their family members perceived overall experience when performing the telemonitoring physical exercise program.

Methods

This was a phase 1 of a clinical trial, engaging 19 individuals with idiopathic PD of an in‐person community rehabilitation program. For 24 weeks an asynchronous telemonitoring physical exercise program delivered two sessions per week by video including warm‐up, balance, aerobic and resistance exercises, and cool‐down. During the remote program were verified: adherence rate at entrance, attendance rate, barriers to attend, safety, and overall experience of the program.

Results and conclusion

Only one participant did not perform any session and 18 participants completed between 2 and 34 sessions. Participants with a caregiver showed higher attendance rates. The most frequently cited barriers to attend the program were: pain; lack of motor skills; and reduced physical fitness. In relation to safety of the program, the most frequently reported was fear of falling. Although participants reported the telemonitoring program induced health benefits and they had positive experiences for themselves and for their families, most of participants prefer an in‐person program. In this sense, the asynchronous telemonitoring physical exercise program was safe, showed moderate adherence, with attendance rate depending on the presence of a companion.

Altered Pain Processing Associated with Administration of Dopamine Agonist and Antagonist in Healthy Volunteers

Striatal dopamine dysfunction is associated with the altered top-down modulation of pain processing. The dopamine D2-like receptor family is a potential substrate for such effects due to its primary expression in the striatum, but evidence for this is currently lacking. Here, we investigated the effect of pharmacologically manipulating striatal dopamine D2 receptor activity on the anticipation and perception of acute pain stimuli in humans. Participants received visual cues that induced either certain or uncertain anticipation of two pain intensity levels delivered via a CO₂ laser. Rating of the pain intensity and unpleasantness was recorded. Brain activity was recorded with EEG and analysed via source localisation to investigate neural activity during the anticipation and receipt of pain. Participants completed the experiment under three conditions, control (Sodium Chloride), D2 receptor agonist (Cabergoline), and D2 receptor antagonist (Amisulpride), in a repeated-measures, triple-crossover, double-blind study. The antagonist reduced an individuals’ ability to distinguish between low and high pain following uncertain anticipation. The EEG source localisation showed that the agonist and antagonist reduced neural activations in specific brain regions associated with the sensory integration of salient stimuli during the anticipation and receipt of pain. During anticipation, the agonist reduced activity in the right mid-temporal region and the right angular gyrus, whilst the antagonist reduced activity within the right postcentral, right mid-temporal, and right inferior parietal regions. In comparison to control, the antagonist reduced activity within the insula during the receipt of pain, a key structure involved in the integration of the sensory and affective aspects of pain. Pain sensitivity and unpleasantness were not changed by D2R modulation. Our results support the notion that D2 receptor neurotransmission has a role in the top-down modulation of pain.

Musculoskeletal Pain in Parkinson's Disease

BACKGROUND

Musculoskeletal pain is commonly experienced in patients with Parkinson's disease (PD). Few studies have investigated the clinical characteristics and risk factors associated with musculoskeletal pain.

OBJECTIVES

To investigate the distribution, clinical characteristics, and factors associated with musculoskeletal pain in a large sample of patients with PD.

METHODS

We enrolled 452 patients from two clinics and used a standardized questionnaire to collect demographic and clinical information. Musculoskeletal pain was diagnosed based on the Ford Classification System, and pain severity was assessed with the numeric rating scale (NRS). Multivariate regression models explored the association between clinical features of PD and quality of life and pain.

RESULTS

Two hundred and six patients (45.58%) reported musculoskeletal pain, typically in their lower limbs and backs. Levodopa resulted in a ≥30% reduction in pain intensity scores in 170 subjects. Female sex (odds ratio [OR], 1.57; 95% CI, 1.07-2.29) and Levodopa-equivalent daily doses (LEDDs; OR, 3.35; 95% CI, 1.63-6.59) were associated with an increased risk for musculoskeletal pain. Pain duration (p = 0.017), motor symptoms (p < 0.001), and depression (p < 0.001) were significantly associated with quality of life.

CONCLUSIONS

The lower limbs and back are common sites of musculoskeletal pain in patients with PD, and up to 82.52% of patients were responsive to Levodopa. Female sex and LEDDs are associated with musculoskeletal pain, suggesting that dopamine deficiencies, and not the motor and non-motor impairment, might be the most critical baseline risk factor of musculoskeletal pain.

Central high mobility group box-1 induces mechanical hypersensitivity with spinal microglial activation in a mouse model of hemi-Parkinson's disease

Parkinson's disease (PD) patients often complain of pain, but this problem has been neglected and is poorly understood. High mobility group box-1 (HMGB1), an alarmin/damage-associated molecular patterns protein, is increased in the cerebrospinal fluid in PD patients. However, little is known of the relationship between HMGB1 and pain associated with PD. Here, we investigated the role of central HMGB1 in the regulation of nociceptive hypersensitivity in a mouse model of PD. Male ddY mice were microinjected unilaterally with 6-hydroxydopamine (6OHDA) into the striatum. These hemi-PD mice were treated with anti-HMGB1 neutralizing antibody (nAb; 10 µg in 10 µL) by intranasal (i.n.) administration. The mechanical hypersensitivity of the hind paws was evaluated with the von Frey test. Spinal microglial activity was analyzed by immunostaining for ionized calcium-binding adapter molecule 1. The 6OHDA-administered mice displayed unilateral loss of dopamine neurons in the substantia nigra and mechanical hypersensitivity in both hind paws. Moreover, spinal microglia were activated in these hemi-PD mice. Twenty-eight days after the 6OHDA injections, repeated i.n., but not systemic, treatment with anti-HMGB1 nAb inhibited the bilateral mechanical hypersensitivity and spinal microglial activation. However, the anti-HMGB1 nAb did not ameliorate the dopamine neuron loss. Moreover, intracerebroventricular injection with recombinant HMGB1 induced mechanical hypersensitivity. These findings indicate that HMGB1 is involved in the maintenance of nociceptive symptoms in hemi-PD mice via spinal microglial activation. Therefore, central HMGB1 may have potential as a therapeutic target for pain associated with PD.

Behavioral, Cellular and Molecular Responses to Cold and Mechanical Stimuli in Rats with Bilateral Dopamine Depletion in the Mesencephalic Dopaminergic Neurons

Pain is the major non-motor symptom in Parkinson's disease (PD). Preclinical studies have mostly investigated mechanical pain by considering the decrease in a nociceptive threshold. Only a few studies have focused on thermal pain in animal models of PD. Therefore, the goal of this study was to assess the thermal nociceptive behavior of rats subjected to 6-hydroxydopamine (6-OHDA) administration, which constitutes an animal model of PD. Thermal plate investigation demonstrated significant thermal sensitivity to cold temperatures of 10 °C and 15 °C, and not to higher temperatures, in 6-OHDA-lesioned rats when compared with sham. 6-OHDA-lesioned rats also showed cold allodynia as demonstrated by a significant difference in the number of flinches, latency and reaction time to acetone stimulus. Ropinirole administration, a dopamine receptor 2 (D2R) agonist, blocked the acetone-induced cold allodynia in 6-OHDA-lesioned rats. In addition, mechanical hypersensitivity and static allodynia, as demonstrated by a significant difference in the vocalization threshold and pain score respectively, were noticed in 6-OHDA-lesioned rats. Acetone stimulus induced a significant increase in extracellular signal-regulated protein kinases 1 and 2 (ERK1/2) phosphorylation, a pain process molecular marker, in the spinal dorsal horn (SDH), the insular and cingulate cortices in 6-OHDA-lesioned rats when compared to sham. In 6-OHDA-lesioned rats, there was a significant augmentation in the expression of both protein kinase C gamma (PKCγ) and glutamate decarboxylase 67 (GAD67) in the SDH. This highlighted an increase in excitation and a decrease in inhibition in the SDH. Overall, the present study demonstrated a clear cold thermal hypersensitivity, in addition to a mechanical one, in 6-OHDA-lesioned rats.

Neuro-Immunity and Gut Dysbiosis Drive Parkinson's Disease-Induced Pain

Parkinson's disease (PD) is the second most common neurodegenerative disorder, affecting 1-2% of the population aged 65 and over. Additionally, non-motor symptoms such as pain and gastrointestinal dysregulation are also common in PD. These impairments might stem from a dysregulation within the gut-brain axis that alters immunity and the inflammatory state and subsequently drives neurodegeneration. There is increasing evidence linking gut dysbiosis to the severity of PD's motor symptoms as well as to somatosensory hypersensitivities. Altogether, these interdependent features highlight the urgency of reviewing the links between the onset of PD's non-motor symptoms and gut immunity and whether such interplays drive the progression of PD. This review will shed light on maladaptive neuro-immune crosstalk in the context of gut dysbiosis and will posit that such deleterious interplays lead to PD-induced pain hypersensitivity.

Dopamine-neurotransmission and nociception in zebrafish: An anti-nociceptive role of dopamine receptor drd2a

Dopamine (DA) is an important modulator in nociception and analgesia. Spinal DA receptors are involved in descending modulation of the nociceptive transmission. Genetic variations within DA neurotransmission have been associated with altered pain sensitivity and development of chronic pain syndromes. The variant rs6277 in dopamine receptor 2 a (drd2a) has been associated with a decreased D₂ receptor availability and increased nociception. The aim of this study is to further characterize the role of DA neurotransmission in nociception and the anti-nociceptive function of drd2a. The phenotype caused by rs6277 was modelled in zebrafish larvae using morpholino's and the effect on nociception was tested using a validated behavioural assay. The anti-nociceptive role of drd2a was tested using pharmacological intervention of D₂ agonist Quinpirole. The experiments demonstrate that a decrease in drd2a expression results in a pro-nociceptive behavioural phenotype (P = 0.016) after a heat stimulus. Furthermore, agonism of drd2a with agonist Quinpirole (0.2 μM) results in dose-dependent anti-nociception (P = 0.035) after a heat stimulus. From these results it is concluded that the dopamine receptor drd2a is involved in anti-nociceptive behaviour in zebrafish. The model allows further screening and testing of genetic variation and treatment involved in nociception.

Decreased dopaminergic inhibition of pyramidal neurons in anterior cingulate cortex maintains chronic neuropathic pain

Pyramidal neurons in the anterior cingulate cortex (ACC), a prefrontal region involved in processing the affective components of pain, display hyperexcitability in chronic neuropathic pain conditions, and their silencing abolishes hyperalgesia. We show that dopamine, through D1 receptor (D1R) signaling, inhibits pyramidal neurons of mouse ACC by modulation of hyperpolarization-activated cyclic nucleotide-gated (HCN) channels. Activation of Gs-coupled D1R by dopamine induces the opening of HCN channels at physiological membrane potentials, driving a significant decrease in input resistance and excitability. Systemic L-DOPA in chronic neuropathic mice rescues HCN channel activity, normalizes pyramidal excitability in ACC, and blocks mechanical and thermal allodynia. Moreover, microinjection of a selective D1R agonist in the ACC relieves the aversiveness of ongoing neuropathic pain, while an ACC D1R antagonist blocks gabapentin- and lidocaine-evoked antinociception. We conclude that dopaminergic inhibition via D1R in ACC plays an analgesic role in physiological conditions and is decreased in chronic pain.

Synaptic potentiation of anterior cingulate cortex contributes to chronic pain of Parkinson's disease

Parkinson’s disease (PD) is a multi-system neurodegenerative disorder. Patients with PD often suffer chronic pain. In the present study, we investigated motor, sensory and emotional changes in three different PD mice models. We found that 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treatment caused significant changes in all measurements. Mechanical hypersensitivity of PD model induced by MPTP peaked at 3 days and persisted for at least 14 days. Using Fos transgenic mice, we found that neurons in the anterior cingulate cortex (ACC) were activated after MPTP treatment. Inhibiting ACC by bilateral microinjection of muscimol significantly reduced mechanical hypersensitivity and anxiety-like responses. By contrast, MPTP induced motor deficit was not affected, indicating ACC activity is mostly responsible for sensory and emotional changes. We also investigated excitatory synaptic transmission and plasticity using brain slices of MPTP treated animals. While L-LTP was blocked or significantly reduced. E-LTP was not significantly affected in slices of MPTP treated animals. LTD induced by repetitive stimulation was not affected. Furthermore, we found that paired-pulse facilitation and spontaneous release of glutamate were also altered in MPTP treated animals, suggesting presynaptic enhancement of excitatory transmission in PD. Our results suggest that ACC synaptic transmission is enhanced in the animal model of PD, and cortical excitation may play important roles in PD related pain and anxiety.

Effects of safinamide adjunct therapy on pain in patients with Parkinson's disease: Post hoc analysis of a Japanese phase 2/3 study

INTRODUCTION

The non-dopaminergic and dopaminergic actions of safinamide may alleviate pain in patients with Parkinson's disease (PD). We investigated the efficacy of safinamide for pain when administered as an adjunct to levodopa in Japanese patients with PD.

METHODS

This was a post hoc analysis of a phase 2/3 clinical study of safinamide in Japanese patients with PD who were experiencing wearing-off. Pain was assessed using the Unified Parkinson's Disease Rating Scale (UPDRS) Part II 'sensory symptoms' item 17, on a scale of 0-4, and the 39-item Parkinson's Disease Questionnaire (PDQ-39) 'bodily discomfort' domain score. Subgroup analyses, according to baseline symptoms and concomitant medications, were also performed.

RESULTS

Least square (LS) mean changes in the UPDRS item 17 score from baseline to Week 24 in the placebo, safinamide 50-mg and safinamide 100-mg groups during the OFF phase were 0.08, -0.15 (p = 0.0133 vs placebo) and -0.18 (p = 0.0054), respectively, and during the ON phase were 0.04, -0.08 (p = 0.0529) and -0.08 (p = 0.0505), respectively. Changes from baseline to Week 24 in PDQ-39 'bodily discomfort' scores were not significantly different in safinamide groups vs placebo. The presence of moderate-to-severe bradykinesia or early-morning dystonia at baseline resulted in numerically greater effect sizes in UPDRS item 17 scores during the OFF phase.

CONCLUSIONS

Safinamide 50 mg and 100 mg reduced the UPDRS item 17 score in patients with PD, especially during the OFF phase. Patients with moderate-to-severe bradykinesia and early-morning dystonia may benefit from safinamide treatment.

A Meta-Analysis of the Effect of Subthalamic Nucleus-Deep Brain Stimulation in Parkinson's Disease-Related Pain

Pain from Parkinson's disease (PD) is a non-motor symptom affecting the quality of life and has prevalence of 20–80%. However, it is unclear whether subthalamic nucleus deep brain stimulation (STN–DBS), a well-established treatment for PD, is effective forPD-related pain. Thus, the objective of this meta-analysis was to investigate the efficacy of STN-DBS on PD-related pain and explore how its duration affects the efficacy of STN-DBS. A systematic search was performed using PubMed, Embase, and the Cochrane Library. Nine studies included numerical rating scale (NRS), visual analog scale (VAS), or non-motor symptom scale (NMSS) scores at baseline and at the last follow-up visit and therefore met the inclusion criteria of the authors. These studies exhibited moderate- to high-quality evidence. Two reviewers conducted assessments for study eligibility, risk of bias, data extraction, and quality of evidence rating. Random effect meta-analysis revealed a significant change in PD-related pain as assessed by NMSS, NRS, and VAS (P <0.01). Analysis of the short and long follow-up subgroups indicated delayed improvement in PD-related pain. These findings (a) show the efficacy of STN-DBS on PD-related pain and provide higher-level evidence, and (b) implicate delayed improvement in PD-related pain, which may help programming doctors with supplement selecting target and programming.

Systematic Review Registration: This study is registered in Open Science Framework (DOI: 10.17605/OSF.IO/DNM6K).

Glutamic Acid Transporters: Targets for Neuroprotective Therapies in Parkinson's Disease

Parkinson's disease (PD) is a common neurodegenerative disease in middle-aged and elderly individuals. At present, no effective drug has been developed to treat PD. Although a variety of drugs exist for the symptomatic treatment of PD, they all have strong side effects. Most studies on PD mainly focus on dopaminergic neurons. This review highlights the function of glutamic acid transporters (GLTs), including excitatory amino acid transporters (EAATs) and vesicular glutamate transporters (VGLUTs), during the development of PD. In addition, using bioinformatics, we compared the expression of different types of glutamate transporter genes in the cingulate gyrus of PD patients and healthy controls. More importantly, we suggest that the functional roles of glutamate transporters may prove beneficial in the treatment of PD. In summary, VGLUTs and EAATs may be potential targets in the treatment of PD. VGLUTs and EAATs can be used as clinical drug targets to achieve better efficacy. Through this review article, we hope to enable future researchers to improve the condition of PD patients.

The role of glutamatergic neurotransmission in the motor and non-motor symptoms in Parkinson's disease: Clinical cases and a review of the literature

Glutamate is the major excitatory neurotransmitter in the central nervous system and, as such, many brain regions, including the basal ganglia, are rich in glutamatergic neurons. The importance of the basal ganglia in the control of voluntary movement has long been recognised, with the effect of dysfunction of the region exemplified by the motor symptoms seen in Parkinson's disease (PD). However, the basal ganglia and the associated glutamatergic system also play a role in the modulation of emotion, nociception and cognition, dysregulation of which result in some of the non-motor symptoms of PD (depression/anxiety, pain and cognitive deficits). Thus, while the treatment of PD has traditionally been approached from the perspective of dopaminergic replacement, using agents such as levodopa and dopamine receptor agonists, the glutamatergic system offers a novel treatment target for the disease. Safinamide has been approved in over 20 countries globally for fluctuating PD as add-on therapy to levodopa regimens for the management of 'off' episodes. The drug has both dopaminergic and non-dopaminergic pharmacological effects, the latter including inhibition of abnormal glutamate release. The effect of safinamide on the glutamatergic system might present some advantages over dopamine-based therapies for PD by providing efficacy for motor (levodopa-induced dyskinesia) as well as non-motor (anxiety, mood disorders, pain) symptoms. In this article, we discuss the potential role of glutamatergic inhibition on these symptoms, using illustrative real-world examples of patients we have treated with safinamide.

Covid-19 Infection and Parkinsonism: Is There a Link?

Severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2) is an opportunistic pathogen that infects the upper respiratory tract in humans and causes serious illness, including fatal pneumonia and neurological disorders. Several studies have reported that SARS‐CoV‐2 may worsen the symptoms of Parkinson's disease (PD), with the potential to increase mortality rates in patients with advanced disease. The potential risk of SARS‐CoV‐2 to induce PD has also been suggested because the virus can enter the brain, where it can trigger cellular processes involved in neurodegeneration. In this review, we will discuss the potential of SARS‐CoV‐2 to exacerbate and cause certain neurological disorders, including PD. We will then elucidate its impact on the brain while examining its pathways and mechanisms of action. © 2021 International Parkinson and Movement Disorder Society

Pain in Parkinson's disease: Mechanism-based treatment strategies

PURPOSE OF REVIEW

Chronic pain, highly prevalent throughout the course of Parkinson's disease (PD), has been ranked as one of the top ten most bothersome symptoms people with Parkinson's (PwP) are experiencing. Yet, robust evidence-based treatment strategies are lacking. This unmet need is partly attributable to the multifaceted nature of PD-related pain, which results in part from a complex and poorly understood interplay involving a range of neurotransmitter pathways. Degeneration of nigrostriatal dopaminergic pathways and alterations of central nervous system extra-striatal dopaminergic, noradrenergic, serotoninergic, glutamatergic, opioidergic and endocannabinoid circuits may all promote a heightened experience of pain in PwP. Thus, the potential targets for mechanism-based pain-relieving strategies in PwP are several. These targets are discussed herein.

RECENT FINDINGS

An increasing number of clinical trials and experimental studies in animal models of PD are being designed with the aim of addressing the pathophysiological mechanism(s) underlying PD-related pain. Overall, recent research findings highlight the analgesic effects of dopaminergic and opioidergic medication for certain subtypes of pain in PwP, whereas proposing novel strategies that involve targeting other neurotransmitter pathways.

SUMMARY

The origin of pain in PwP remains under investigation. Although our understanding of the mechanisms underpinning persistent pain in PD has improved in recent years, this has not yet translated to clinical alleviation of this most troublesome nonmotor symptom. Patient stratification linked with evidence-based personalized pain-treatment plans for optimal analgesic relief will rely on advances in our understanding of the dopaminergic and nondopaminergic targets outlined in this review.

Neural Plasticity in the Brain during Neuropathic Pain

Neuropathic pain is an intractable chronic pain, caused by damage to the somatosensory nervous system. To date, treatment for neuropathic pain has limited effects. For the development of efficient therapeutic methods, it is essential to fully understand the pathological mechanisms of neuropathic pain. Besides abnormal sensitization in the periphery and spinal cord, accumulating evidence suggests that neural plasticity in the brain is also critical for the development and maintenance of this pain. Recent technological advances in the measurement and manipulation of neuronal activity allow us to understand maladaptive plastic changes in the brain during neuropathic pain more precisely and modulate brain activity to reverse pain states at the preclinical and clinical levels. In this review paper, we discuss the current understanding of pathological neural plasticity in the four pain-related brain areas: the primary somatosensory cortex, the anterior cingulate cortex, the periaqueductal gray, and the basal ganglia. We also discuss potential treatments for neuropathic pain based on the modulation of neural plasticity in these brain areas.

Neural basis of affective touch and pain: A novel model suggests possible targets for pain amelioration

Pain is one of the most common health problems and has a severe impact on quality of life. Yet, a suitable and efficient treatment is still not available for all patient populations suffering from pain. Interestingly, recent research shows that low threshold mechanosensory C‐tactile (CT) fibres have a modulatory influence on pain. CT‐fibres are activated by slow gentle stroking of the hairy skin, providing a pleasant sensation. Consequently, slow gentle stroking is known as affective touch. Currently, a clear overview of the way affective touch modulates pain, at a neural level, is missing. This review aims to present such an overview. To explain the interaction between affective touch and pain, first the neural basis of the affective touch system and the neural processing of pain will be described. To clarify these systems, a schematic illustration will be provided in every section. Hereafter, a novel model of interactions between affective touch and pain systems will be introduced. Finally, since affective touch might be suitable as a new treatment for chronic pain, possible clinical implications will be discussed.

Dopamine Inputs from the Ventral Tegmental Area into the Medial Prefrontal Cortex Modulate Neuropathic Pain-Associated Behaviors in Mice

The medial prefrontal cortex (mPFC) is a brain region involved in the affective components of pain and undergoes plasticity during the development of chronic pain. Dopamine (DA) is a key neuromodulator in the mesocortical circuit and modulates working memory and aversion. Although DA inputs into the mPFC are known to modulate plasticity, whether and how these inputs affect pain remains incompletely understood. By using optogenetics, we find that phasic activation of DA inputs from the ventral tegmental area (VTA) into the mPFC reduce mechanical hypersensitivity during neuropathic pain states. Mice with neuropathic pain exhibit a preference for contexts paired with photostimulation of DA terminals in the mPFC. Fiber photometry-based calcium imaging reveals that DA increases the activity of mPFC neurons projecting to the ventrolateral periaqueductal gray (vlPAG). Together, our findings indicate an important role of mPFC DA signaling in pain modulation.

Methylation quantitative trait locus analysis of chronic postsurgical pain uncovers epigenetic mediators of genetic risk

Background: Overlap of pathways enriched by single nucleotide polymorphisms and DNA-methylation underlying chronic postsurgical pain (CPSP), prompted pilot study of CPSP-associated methylation quantitative trait loci (meQTL). Materials & methods: Children undergoing spine-fusion were recruited prospectively. Logistic-regression for genome- and epigenome-wide CPSP association and DNA-methylation-single nucleotide polymorphism association/mediation analyses to identify meQTLs were followed by functional genomics analyses. Results: CPSP (n = 20/58) and non-CPSP groups differed in pain-measures. Of 2753 meQTLs, DNA-methylation at 127 cytosine-guanine dinucleotides mediated association of 470 meQTLs with CPSP (p < 0.05). At PARK16 locus, CPSP risk meQTLs were associated with decreased DNA-methylation at RAB7L1 and increased DNA-methylation at PM20D1. Corresponding RAB7L1/PM20D1 blood eQTLs (GTEx) and cytosine-guanine dinucleotide-loci enrichment for histone marks, transcription factor binding sites and ATAC-seq peaks suggest altered transcription factor-binding. Conclusion: CPSP-associated meQTLs indicate epigenetic mechanisms mediate genetic risk. Clinical trial registration: NCT01839461, NCT01731873 (ClinicalTrials.gov).