Cerebral cortex modulation of pain

Causal relationship between rheumatoid arthritis and epilepsy in a European population: a univariate and multivariate Mendelian randomization study

Background

Several previous studies have reported an association between rheumatoid arthritis (RA) and epilepsy, but the causal relationship is unclear. The aim of this study was to assess the connection between RA and epilepsy in a European population using Mendelian randomization (MR).

Methods

Genome-wide association study summary data on RA and epilepsy from European populations were included. Univariate MR (UVMR) and multivariate MR were used to investigate the causal relationship between the two conditions. Three analysis methods were applied: inverse variance weight (IVW), MR-Egger, and weighted median, with IVW being the primary method. Cochran Q statistics, MR-PRESSO, MR-Egger intercept, leave-one-out test, and MR-Steiger test were combined for the sensitivity analysis.

Results

UVMR showed a positive association between RA and epilepsy risk (OR=1.038, 95% CI=1.007-1.038, p=0.017) that was supported by sensitivity analysis. Further MVMR after harmonizing the three covariates of hypertension, alcohol consumption, and smoking, confirmed the causal relationship between RA and epilepsy (OR=1.049, 95% CI=1.011-1.087, p=0.010).

Conclusion

This study demonstrated that RA is associated with an increased risk of epilepsy. It has emphasized that the monitoring of epilepsy risk in patients diagnosed with RA should be strengthened in clinical practice, and further studies are needed in the future to explore the potential mechanism of action connecting the two conditions.

Transcranial magnetic stimulation therapy for central post-stroke pain: systematic review and meta-analysis

Introduction

Although rare, central post-stroke pain remains one of the most refractory forms of neuropathic pain. It has been reported that repetitive transcranial magnetic stimulation (rTMS) may be effective in these cases of pain.

Aim

The aim of this study was to investigate the efficacy of rTMS in patients with central post-stroke pain (CPSP).

Methods

We included randomized controlled trials or Controlled Trials published until October 3rd, 2022, which studied the effect of rTMS compared to placebo in CPSP. We included studies of adult patients (>18 years) with a clinical diagnosis of stroke, in which the intervention consisted of the application of rTMS to treat CSP.

Results

Nine studies were included in the qualitative analysis; 6 studies (4 RCT and 2 non-RCT), with 180 participants, were included in the quantitative analysis. A significant reduction in CPSP was found in favor of rTMS compared with sham, with a large effect size (SMD: -1.45; 95% CI: -1.87; -1.03; p < 0.001; I2: 58%).

Conclusion

The findings of the present systematic review with meta-analysis suggest that there is low quality evidence for the effectiveness of rTMS in reducing CPSP.

Systematic review registration

Identifier (CRD42022365655).

Alcohol use and the pain system

The World Health Organization's epidemiological data from 2016 revealed that while 57% of the global population aged 15 years or older had abstained from drinking alcohol in the previous year, more than half of the population in the Americas, Europe, and Western Pacific consumed alcohol. The spectrum of alcohol use behavior is broad: low-risk use (sensible and in moderation), at-risk use (e.g., binge drinking), harmful use (misuse) and dependence (alcoholism; addiction; alcohol use disorder). The at-risk use and misuse of alcohol is associated with the transition to dependence, as well as many damaging health outcomes and preventable causes of premature death. Recent conceptualizations of alcohol dependence posit that the subjective experience of pain may be a significant contributing factor in the transition across the spectrum of alcohol use behavior. This narrative review summarizes the effects of alcohol at all levels of the pain system. The pain system includes nociceptors as sensory indicators of potentially dangerous stimuli and tissue damage (nociception), spinal circuits mediating defensive reflexes, and most importantly, the supraspinal circuits mediating nocifensive behaviors and the perception of pain. Although the functional importance of pain is to protect from injury and further or future damage, chronic pain may emerge despite the recovery from, and absence of, biological damage (i.e., in the absence of nociception). Like other biological perceptual systems, pain is a construction contingent on sensory information and a history of individual experiences (i.e., learning and memory). Neuroadaptations and brain plasticity underlying learning and memory and other basic physiological functions can also result in pathological conditions such as chronic pain and addiction. Moreover, the negative affective/emotional aspect of pain perception provides embodied and motivational components that may play a substantial role in the transition from alcohol use to dependence.

Dexmedetomidine relieves inflammatory pain by enhancing GABAergic synaptic activity in pyramidal neurons of the anterior cingulate cortex

Pyramidal neuron (Pyn) hyperactivity in the anterior cingulate cortex (ACC) is involved in the modulation of pain. Previous studies indicate that the activation of α2 adrenoceptors (α2-ARs) by dexmedetomidine (DEX) is a safe and effective means of alleviating multiple types of pain. Here, we showed that systemically administered DEX can ameliorate the inflammatory pain induced by hindpaw injection of formalin (FA) and further examined the molecular and synaptic mechanisms of this DEX-elicited antinociceptive effect. We found that FA caused an increase in c-Fos expression in contralateral layer 2/3 (L2/3) ACC, and that intra-ACC infusion of DEX could also relieve phase 2 inflammatory pain behavior. DEX elicited an increase in the amplitude and frequency of miniature inhibitory post-synaptic currents (mIPSCs) and evoked IPSC amplitude, as well as a reduction in the hyperexcitability and both paired-pulse and excitation/inhibition ratios in contralateral L2/3 ACC Pyns of FA mice. These electrophysiological effects were associated with the upregulation of GABA A receptor (GABAAR) subunits. The interaction of phosphorylated Akt (p-Akt) with GABAAR subunits increased in the ACC following administration of DEX. These results suggest that DEX treatment reduces hyperactivity and enhances GABAergic inhibitory synaptic transmission in ACC Pyns, which produces analgesic effects by increasing GABAAR levels and activating the Akt signaling pathway.

Longitudinal changes in human supraspinal processing after RIII-feedback training to improve descending pain inhibition

The human body has the ability to influence its sensation of pain by modifying the transfer of nociceptive information at the spinal level. This modulation, known as descending pain inhibition, is known to originate supraspinally and can be activated by a variety of ways including positive mental imagery. However, its exact mechanisms remain unknown. We investigated, using a longitudinal fMRI design, the brain activity leading up and in response to painful electrical stimulation when applying positive mental imagery before and after undergoing a previously established RIII-feedback paradigm. Time course analysis of the time preceding painful stimulation shows increased haemodynamic activity during the application of the strategy in the PFC, ACC, insula, thalamus, and hypothalamus. Time course analysis of the reaction to painful stimulation shows decreased reaction post-training in brainstem and thalamus, as well as the insula and dorsolateral PFC. Our work suggests that feedback training increases activity in areas involved in pain inhibition, while simultaneously decreasing the reaction to painful stimuli in brain areas related to pain processing, which points to an activation of decreased spinal nociception. We further suggest that the insula and the thalamus may play a more important role in pain modulation than previously assumed.

Alterations of endogenous pain-modulatory system of the cerebral cortex in the neuropathic pain

Neuropathic pain (NeP) remains a significant clinical challenge owing to insufficient awareness of its pathological mechanisms. We elucidated the aberrant metabolism of the cerebral cortex in NeP induced by the chronic constriction injury (CCI) using metabolomics and proteomics analyses. After CCI surgery, the values of MWT and TWL markedly reduced and maintained at a low level. CCI induced the significant dysregulation of 57 metabolites and 31 proteins in the cerebral cortex. Integrative analyses showed that the differentially expressed metabolites and proteins were primarily involved in alanine, aspartate and glutamate metabolism, GABAergic synapse, and retrograde endocannabinoid signaling. Targeted metabolomics and western blot analysis confirmed the alterations of some key metabolites and proteins in endogenous pain-modulatory system. In conclusion, our study revealed the alterations of endocannabinoids system and purinergic system in the CCI group, and provided a novel perspective on the roles of endogenous pain-modulatory system in the pathological mechanisms of NeP.

Insular cortex stimulation alleviates neuropathic pain via ERK phosphorylation in neurons

AIMS

The clinical use of brain stimulation is attractive for patients who have side effects or tolerance. However, studies on insular cortex (IC) stimulation are lacking in neuropathic pain. The present study aimed to investigate the effects of IC stimulation (ICS) on neuropathic pain and to determine how ICS modulates pain.

METHODS

Changes in pain behaviors were observed following ICS with various parameters in neuropathic rats. Western blotting was performed to assess molecular changes in the expression levels of phosphorylated extracellular signal-regulated kinase (pERK), neurons, astrocytes, and microglia between experimental groups. Immunohistochemistry was performed to investigate the colocalization of pERK with different cell types.

RESULTS

The most effective pain-relieving effect was induced at 50 Hz-120 μA in single trial of ICS and it maintained 4 days longer after the termination of repetitive ICS. The expression levels of pERK, astrocytes, and microglia were increased in neuropathic rats. However, after ICS, the expression levels of pERK were decreased, and colocalization of pERK and neurons was reduced in layers 2-3 of the IC.

CONCLUSION

These results indicated that ICS attenuated neuropathic pain by the regulation of pERK in neurons located in layers 2-3 of the IC. This preclinical study may enhance the potential use of ICS and identify the therapeutic mechanisms of ICS in neuropathic pain.

Comparative investigation of analgesic tolerance to taurine, sodium salicylate and morphine: Involvement of peripheral muscarinic receptors

Nowadays various analgesic medications are used for the management of acute and chronic pain. Among these opioid and non-steroidal anti-inflammatory drugs stand in the first line of therapy, however, prolonged administration of these substance is generally challenged by development of analgesic tolerance in patients. Therefore, it is highly valuable to find new pharmacological strategies for prolonged therapeutic procedures. In this respect, Taurine, a free amino acid, has been shown to induce significant analgesia at both spinal and peripheral levels through cholinergic mechanisms. In the present study, we used hot-plate analgesic test to investigate how taurine either as a single medication or in combination with sodium salicylate and morphine may affect both acute response to pain and development of analgesic tolerance. The effect of taurine was also tested on morphine withdrawal syndrome. Hyoscine butyl bromide was used to assess the role of muscarinic receptors in taurine-mediated effects. Finally, biochemical assay was done to reveal how the activity of brain acetylcholinesterase may change in relation with muscarinic receptor activity. Results indicated that acute administration of taurine-sodium salicylate combination causes more potent analgesia compared to the use of tau (but not SS alone) and this seems to be mediated via activity of muscarinic receptors in peripheral nervous system. Furthermore, the effect of this combination undergoes less analgesic tolerance during time. Combination of taurine and morphine is an effective strategy to attenuate both morphine analgesic tolerance and dependence and this also seems to depend on activity of muscarinic receptors, however through differential cellular mechanisms.

Twenty-Three Months Repetitive Transcranial Magnetic Stimulation of the Primary Motor Cortex for Refractory Trigeminal Neuralgia: A Single-Case Study

Treatment refractory or recurrent trigeminal neuralgia (TN) is a severe chronic pain illness. Single-session repetitive transcranial magnetic stimulation (rTMS) has been shown to elicit analgesic effects in several craniofacial pain syndromes, including TN. However, the safety and long-term effect of multi-session rTMS for TN have yet to be fully explored. In this study, we present a case of a patient with medical treatment-refractory TN after microvascular decompression. The patient volunteered to undergo 73 sessions of 10 Hz rTMS over 23 months. Neurovagination was used for precise localization and stimulation of the hand and face representation at the left motor cortex. The numeric pain intensity scores derived using the visual analog scale served as a daily index of treatment efficacy. The patient experienced a significant weekly reduction in pain scores, cumulating in 70.89% overall pain relief. The medication dosages were reduced and then discontinued toward the end of the intervention period. No severe adverse events were reported. From our results, we can conclude that the longitudinal multi-session application of rTMS over the hand and face area of M1 is a safe and effective method for producing long-lasting pain relief in TN. Using rTMS may thus prove helpful as an adjunct to conventional methods for treating pain in TN.

Development of a Clinical Prediction Rule for Treatment Success with Transcranial Direct Current Stimulation for Knee Osteoarthritis Pain: A Secondary Analysis of a Double-Blind Randomized Controlled Trial

The study’s objective was to develop a clinical prediction rule that predicts a clinically significant analgesic effect on chronic knee osteoarthritis pain after transcranial direct current stimulation treatment. This is a secondary analysis from a double-blind randomized controlled trial. Data from 51 individuals with chronic knee osteoarthritis pain and an impaired descending pain inhibitory system were used. The intervention comprised a 15-session protocol of anodal primary motor cortex transcranial direct current stimulation. Treatment success was defined by the Western Ontario and McMaster Universities’ Osteoarthritis Index pain subscale. Accuracy statistics were calculated for each potential predictor and for the final model. The final logistic regression model was statistically significant (p < 0.01) and comprised five physical and psychosocial predictor variables that together yielded a positive likelihood ratio of 14.40 (95% CI: 3.66−56.69) and an 85% (95%CI: 60−96%) post-test probability of success. This is the first clinical prediction rule proposed for transcranial direct current stimulation in patients with chronic pain. The model underscores the importance of both physical and psychosocial factors as predictors of the analgesic response to transcranial direct current stimulation treatment. Validation of the proposed clinical prediction rule should be performed in other datasets.

Conditioned pain modulation is associated with heightened connectivity between the periaqueductal grey and cortical regions

Introduction

Conditioned pain modulation (CPM) is a psychophysical assessment used to estimate the efficiency of an individual's endogenous modulatory mechanisms. Conditioned pain modulation has been used as a predictive assessment for the development of chronic pain and responses to pain interventions. Although much is known about the spinal cord mechanisms associated with descending pain modulation, less is known about the contribution of supraspinal and especially cortical regions.

Objectives

We aimed to explore how whole-brain connectivity of a core modulatory region, the periaqueductal grey (PAG), is associated with conditioned pain modulation, and endogenous pain modulation more broadly.

Methods

We measured CPM and resting-state connectivity of 35 healthy volunteers, absent of chronic pain diagnoses. As a region of interest, we targeted the PAG, which is directly involved in endogenous modulation of input to the spinal cord and is a key node within the descending pain modulation network.

Results

We found that CPM was associated with heightened connectivity between the PAG and key regions associated with pain processing and inhibition, such as the primary and secondary somatosensory cortices, as well as the motor, premotor, and dorsolateral prefrontal cortices. These findings are consistent with connectivity findings in other resting-state and event-related fMRI studies.

Conclusion

These findings indicate that individuals who are efficient modulators have greater functional connectivity between the PAG and regions involved in processing pain. The heightened connectivity of these regions may contribute to the beneficial outcomes in clinical pain management, as quantified by CPM. These results may function as brain-based biomarkers for vulnerability or resilience to 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.

Descending pain modulatory efficiency in healthy subjects is related to structure and resting connectivity of brain regions

The descending pain modulatory system in humans is commonly investigated using conditioned pain modulation (CPM). Whilst variability in CPM efficiency, i.e., inhibition and facilitation, is normal in healthy subjects, exploring the inter-relationship between brain structure, resting-state functional connectivity (rsFC) and CPM readouts will provide greater insight into the underlying CPM efficiency seen in healthy individuals. Thus, this study combined CPM testing, voxel-based morphometry (VBM) and rsFC to identify the neural correlates of CPM in a cohort of healthy subjects (n =40), displaying pain inhibition (n = 29), facilitation (n = 10) and no CPM effect (n = 1). Clusters identified in the VBM analysis were implemented in the rsFC analysis alongside key constituents of the endogenous pain modulatory system. Greater pain inhibition was related to higher volume of left frontal cortices and stronger rsFC between the motor cortex and periaqueductal grey. Conversely, weaker pain inhibition was related to higher volume of the right frontal cortex - coupled with stronger rsFC to the primary somatosensory cortex, and rsFC between the amygdala and posterior insula. Overall, healthy subjects showed higher volume and stronger rsFC of brain regions involved with descending modulation, while the lateral and medial pain systems were related to greater pain inhibition and facilitation during CPM, respectively. These findings reveal structural alignments and functional interactions between supraspinal areas involved in CPM efficiency. Ultimately understanding these underlying variations and how they may become affected in chronic pain conditions, will advance a more targeted subgrouping in pain patients for future cross-sectional studies investigating endogenous pain modulation.

Shedding light on pain for the clinic: a comprehensive review of using functional near-infrared spectroscopy to monitor its process in the brain

ABSTRACT

Pain is a complex experience that involves sensation, emotion, and cognition. The subjectivity of the traditional pain measurement tools has expedited the interest in developing neuroimaging techniques to monitor pain objectively. Among noninvasive neuroimaging techniques, functional near-infrared spectroscopy (fNIRS) has balanced spatial and temporal resolution; yet, it is portable, quiet, and cost-effective. These features enable fNIRS to image the cortical mechanisms of pain in a clinical environment. In this article, we evaluated pain neuroimaging studies that used the fNIRS technique in the past decade. Starting from the experimental design, we reviewed the regions of interest, probe localization, data processing, and primary findings of these existing fNIRS studies. We also discussed the fNIRS imaging's potential as a brain surveillance technique for pain, in combination with artificial intelligence and extended reality techniques. We concluded that fNIRS is a brain imaging technique with great potential for objective pain assessment in the clinical environment.

Spinal cord neural activity of patients with fibromyalgia and healthy controls during temporal summation of pain: an fMRI study

The cause for the increased sensitivity of patients with fibromyalgia (FM) to painful stimuli is unclear but sensitization of dorsal horn spinal cord neurons has been suggested. There, critical changes of sensory information occur which depend on the plasticity of second-order neurons and descending pain modulation, including facilitation and inhibition. This study used repetitive stimuli that produce temporal-summation-of-second-pain (TSSP) and central sensitization, relevant mechanisms for patients with chronic pain. We examined spinal cord neural activation during TSSP in patients with FM and healthy controls (HC) and used its functional connectivity with several brainstem nuclei to model the observed blood-oxygen-level-dependent (BOLD) time-course with pain ratings. Sixteen HC and 14 FM participants received repetitive heat stimuli to the hand at 0.4 Hz to achieve TSSP during functional imaging with a 3 T-Philips Achieva MRI scanner. Stimuli were adjusted to each individual's pain sensitivity to achieve maximal pain ratings of 50 ± 10 on a numerical pain scale (0-100). Using a 16-channel neurovascular coil, multiple image series were obtained from the cervical spinal cord to the brainstem using single-shot turbo-spin echo sequences. During repetitive, sensitivity-adjusted heat stimuli, pain ratings of all subjects increased as predicted, consistent with TSSP. HC and FM participants had similar temporal patterns of spinal activation: initial BOLD increase followed by deactivation. Structural equation modeling showed that the observed spinal activity during TSSP was associated with more BOLD activity across/within the brainstem in FM subjects than HC, suggesting differences in pain modulation.NEW & NOTEWORTHY "Windup" and its behavioral correlate "temporal-summation-of-second pain" (TSSP) represent spinal cord mechanisms of pain augmentation associated with central sensitization and chronic pain. Fibromyalgia (FM) is a chronic pain disorder, where abnormal TSSP has been demonstrated. We used fMRI to study spinal cord and brainstem activation during TSSP. We characterized the time course of spinal cord and brainstem BOLD activity during TSSP which showed abnormal brainstem activity in patients with FM, possibly due to deficient pain modulation.

Cognition and Pain: A Review

Cognition is defined as the brain's ability to acquire, process, store, and retrieve information. Pain has been described as an unpleasant sensory or emotional experience, and for experiencing pain consciously, cognitive processing becomes imperative. Moreover, evaluation of pain strongly depends on cognition as it requires learning and recall of previous experiences. There could be a possible close link between neural systems involved in cognition and pain processing, and studies have reported an association between pain and cognitive impairment. In this narrative review, we explore the available evidence that has investigated cognitive changes associated with pain. We also examine the anatomical, biochemical, and molecular association of pain and neuro-cognition. Additionally, we focus on the cognitive impairment caused by analgesic medications. There is a need to improve our understanding of pathophysiology and cognitive impairment mechanisms associated with chronic pain and its treatment. This area provides a diverse opportunity for grounding future research, aiding institution of timely interventions to prevent chronic pain and associated cognitive decline, ultimately improving patient care.

Cortical Modulation of Nociception

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

Resting-State Magnetoencephalography Reveals Neurobiological Bridges Between Pain and Cognitive Impairment

Introduction

Pain has been identified as a risk factor for cognitive dysfunction, which in turn affects pain perception. Although pain, cognitive dysfunction, and their interaction are clinically important, the neural mechanism connecting the two phenomena remains unclear.

Methods

The resting-state brain activity of 38 participants was measured using magnetoencephalography before and after the patients underwent selective nerve root block (SNRB) for the treatment of their pain. We then assessed the extent to which these data correlated with the subjective levels of pain experienced by the patients across SNRB based on the visual analogue scale and the cognitive status of the patients measured after SNRB using the Japanese versions of the Mini-Mental State Examination (MMSE-J).

Results

Slow oscillations (delta) in the right precentral gyrus, right middle temporal gyrus, and left superior frontal gyrus were negatively correlated with the subjective level of pain, and fast oscillations (gamma) in the right insular cortex and right middle temporal gyrus before SNRB were negatively correlated with the MMSE-J score afterwards. These correlations disappeared after SNRB.

Conclusion

The presently observed changes in neural activity, as indicated by oscillation changes, might represent the transient bridge between pain and cognitive dysfunction in patients with severe pain. Our findings underscore the importance of treating pain before a transient diminishment of cognitive function becomes persistent.

Up-regulation of HTR1A reverses stress-induced visceral hypersensitivity through modulating interactions among the anterior cingulate cortex, insular cortex and hippocampus

Background: This study aimed to explore the effect of 5-HT1A receptors (HTR1A) on activation of the anterior cingulate cortex and simultaneous regulation of neural activity in the insular cortex and hippocampus.

Methods: The IBS rat model was established via chronic water avoidance stress (WAS). Visceral sensitivity was measured by electromyogram, and anxiety-like behaviours were evaluated by the open field test. HTR1A-specific lentivirus expressing green fluorescent protein was used to overexpress or down-regulate HTR1A expression. Protein expression levels were detected by western blot.

Results: Up-regulation of HTR1A in ACC could inhibit ACC sensitization and reverse the visceral hypersensitivity and anxiety-like behaviours induced by chronic psychological stress. In contrast, down-regulation of HTR1A in ACC might promote these behaviors in IBS rats. Additionally, up-regulation of HTR1A in ACC could inhibit IC and hippocampus sensitization, while down-regulation might have the opposite effect.

Conclusions: In IBS rats, HTR1A could modulate ACC activation and interactions among the ACC, IC and hippocampus. These effects might in turn contribute to the development of visceral hypersensitivity and anxiety-like behaviours induced by chronic psychological stress.

A voxel-based lesion symptom mapping analysis of chronic pain in multiple sclerosis

BACKGROUND

Pain is one of the most disabling symptoms in multiple sclerosis. Chronic pain in multiple sclerosis is often neuropathic in nature, although a clear-cut distinction with nociceptive pain is not easy.

OBJECTIVE

The aim of our study was to analyze the MRIs of multiple sclerosis patients with chronic pain in order to explore possible associations with lesion sites, on a voxel-by-voxel basis.

MATERIALS AND METHODS

We enrolled patients aged > 18 years with multiple sclerosis in accordance with the 2010 McDonald criteria. Patients meeting criteria for persistent pain (frequent or constant pain lasting > 3 months) were included in the "pain group". The other patients were included in the "no pain group". We outlined lesions on FLAIR MRI scans using a semi-automated edge finding tool. To detect the association between lesion localization and persistent pain, images were analysed with the voxel-based lesion symptom mapping methods implemented in the (nonparametric mapping software included into the MRIcron.

RESULTS

We enrolled 208 MS patients (140 F, mean age 55.2 ± 9.4 years; 176 RR, 28 progressive MS; mean EDSS 2.0 + 2.0). Pain group included 96 patients and no pain group 112 patients. Lesions of the right dorsolateral prefrontal area were significantly more prevalent in patients without pain, whereas periventricular posterior lesions were significantly more prevalent in patients with persistent pain.

CONCLUSION

Our data suggest a role of the right dorsolateral prefrontal cortex in the modulation of pain perception and in the occurrence of chronic pain in MS patients. Our data also support a hemispheric asymmetry in pain perception and modulation.

Intra-cerebroventricular Administration of Crocin Attenuates Sleep Deprivation-induced Hyperalgesia in Rats

Introduction

Sleep deprivation can cause hyperalgesia and interfere with analgesic treatments. The aim of the present study was to establish an obligatory sleep-abstinence model and also evaluate the effects of Intracerebroventricular (ICV) injection of crocin on pain perception in Wistar rats.

Methods

In this experimental study, 35 adult male Wistar rats were randomly divided into 5 groups (n=7). The intra-ventricular cannulation was done for all rats before sleep deprivation. Sleep deprivation was performed by placing animals on a chamber equipped with an automatic animated conveyor (5 s with an interval of 3 min) for 72 h. Subsequently, the sleep-deprived animals received ICV injection of saline (MOD), Morphine 10 μg (MOR), Crocin 10 ug (Cr10), and Crocin40 μg (Cr40) using a microsyringe. Besides, a non-sleep-deprived group was allocated as a Control Group (NC) and only received an ICV injection of saline. Fifteen minutes after the ICV injections, pain perception was evaluated by the hot plate test (54±0.4°C).

Results

Compared with the NC group, latency significantly decreased in the MOD group (6.28±0.48 vs. 4.28± 0.48, P<0.0001). In comparison with the MOD group, both morphine (8.42±1.53) and crocin (7.60±1.45 for Cr10 and 8.14±0.89 for Cr40) could significantly increase latency in the sleep-deprived animals (P<0.0001). There was no statistically significant difference between the Cr10 and Cr40 (P=0.42), Cr10, and MOR (P=0.059) and Cr40 with MOR (P=0.86) groups.

Conclusion

Our results indicated that crocin could attenuate hyperalgesia induced by sleep deprivation in rats.

The Rostral Agranular Insular Cortex, a New Site of Oxytocin to Induce Antinociception

The rostral agranular insular cortex (RAIC) is a relevant structure in nociception. Indeed, recruitment of GABAergic activity in RAIC promotes the disinhibition of the locus ceruleus, which in turn inhibits (by noradrenergic action) the peripheral nociceptive input at the spinal cord level. In this regard, at the cortical level, oxytocin can modulate the GABAergic transmission; consequently, an interaction modulating nociception could exist between oxytocin and GABA at RAIC. Here, we tested in male Wistar rats the effect of oxytocin microinjection into RAIC during an inflammatory (by subcutaneous peripheral injection of formalin) nociceptive input. Oxytocin microinjection produces a diminution of (1) flinches induced by formalin and (2) spontaneous firing of spinal wide dynamic range cells. The above antinociceptive effect was abolished by microinjection (at RAIC) of the following: (1) L-368899 (an oxytocin receptor [OTR] antagonist) or by (2) bicuculline (a preferent GABAA receptor blocker), suggesting a GABAergic activation induced by OTR. Since intrathecal injection of an α2A-adrenoceptor antagonist (BRL 44408) partially reversed the oxytocin effect, a descending noradrenergic antinociception is suggested. Further, injection of L-368899 per se induces a pronociceptive behavioral effect, suggesting a tonic endogenous oxytocin release during inflammatory nociceptive input. Accordingly, we found bilateral projections from the paraventricular nucleus of the hypothalamus (PVN) to RAIC. Some of the PVN-projecting cells are oxytocinergic and destinate GABAergic and OTR-expressing cells inside RAIC. Aside from the direct anatomic link between PVN and RAIC, our findings provide evidence about the role of oxytocinergic mechanisms modulating the pain process at the RAIC level.SIGNIFICANCE STATEMENT Oxytocin is a neuropeptide involved in several functions ranging from lactation to social attachment. Over the years, the role of this molecule in pain processing has emerged, showing that, at the spinal level, oxytocin blocks pain transmission. The present work suggests that oxytocin also modulates pain at the cortical insular level by favoring cortical GABAergic transmission and activating descending spinal noradrenergic mechanisms. Indeed, we show that the paraventricular hypothalamicnucleus sends direct oxytocinergic projections to the rostral agranular insular cortex on GABAergic and oxytocin receptor-expressing neurons. Together, our data support the notion that the oxytocinergic system could act as an orchestrator of pain modulation.

Females are more susceptible than male mice to thermal hypernociceptive behavior induced by early-life bisphenol-A exposure: Effectiveness of diphenyl diselenide

Humans are ubiquitously exposed to bisphenol A (BPA), one of the most used synthetic monomers for manufacturing polycarbonate plastics. BPA exposure leads to abnormal nociceptive perception and neuroinflammation in rodents. This study investigated whether diphenyl diselenide (PhSe)₂, a pleiotropic selenium-containing molecule, would be effective against the hypernociceptive behavior induced by the early-life BPA exposure to mice. Three-week-old male and female Swiss mice received intragastrically BPA (5 mg/kg) from 21^st to 60^th postnatal day. After, the mice received by the intragastric route (PhSe)₂ (1 mg/kg) once a day for seven days. After the last day of treatment, the mice performed the hot plate and tail immersion tests. The cerebral cortex samples were used to determine the levels of proteins related to apoptosis and inflammation. The results demonstrated that females were more susceptible than male mice to thermal hypernociception induced by early-life exposure to BPA. (PhSe)₂ was effective against the reduction in the latency to paw and tail withdrawal induced by BPA exposure in female mice. Furthermore, (PhSe)₂ restored the impairment in the levels of inflammatory proteins (COX-2, IL-1β, and p-JNK/JNK) but not those of apoptosis in the cerebral cortex of female mice exposed to BPA. Collectively, these data showed that females were more susceptible to thermal hypernociceptive behavior induced by early-life exposure to BPA than male mice. The administration of (PhSe)₂ reduced thermal hypernociceptive behavior, a sex independent effect, in BPA-exposed mice. (PhSe)₂ modulated inflammatory protein levels in the cerebral cortex of female mice exposed to BPA.

Aristolochia trilobata: Identification of the Anti-Inflammatory and Antinociceptive Effects

Aristolochia trilobata, popularly known as “mil-homens,” is widely used for treatment of stomach aches, colic, asthma, pulmonary diseases, diabetes, and skin affection. We evaluated the antinociceptive and anti-inflammatory activities of the essential oil (EO) and the main constituent, 6-methyl-5-hepten-2-yl acetate (sulcatyl acetate, SA). EO and SA (1, 10, and 100 mg/kg, p.o.) were evaluated using chemical (formalin-induced licking) and thermal (hot-plate) models of nociception or inflammation (carrageenan-induced cell migration into the subcutaneous air pouch, SAP). The mechanism of antinociceptive activity was evaluated using opioid, cholinergic receptor antagonists (naloxone and atropine), or nitric oxide synthase inhibitor (L-NAME). EO and SA presented a central antinociceptive effect (the hot-plate model). In formalin-induced licking response, higher doses of EO and SA also reduced 1st and 2nd phases. None of the antagonists and enzyme inhibitor reversed antinociceptive effects. EO and SA reduced the leukocyte migration into the SAP, and the cytokines tumor necrosis factor and interleukin-1 (TNF-α and IL-1β, respectively) produced in the exudate. Our results are indicative that EO and SA present peripheral and central antinociceptive and anti-inflammatory effects.

Ketamine reduces remifentanil-induced postoperative hyperalgesia mediated by CaMKII-NMDAR in the primary somatosensory cerebral cortex region in mice

Remifentanil is commonly used clinically for perioperative pain relief, but it may induce postoperative hyperalgesia. Low doses of ketamine have remained a common choice in clinical practice, but the mechanisms of ketamine have not yet been fully elucidated. In this study, we examined the possible effects of ketamine on calcium/calmodulin-dependent protein kinase II α (CaMKIIα) and N-methyl-d-aspartate receptor (NMDAR) subunit NR2B in a mouse model of remifentanil-induced postoperative hyperalgesia (RIPH) in the primary somatosensory cerebral cortex (SI) region. The paw withdrawal mechanical threshold (PWMT) and paw withdrawal thermal latency (PWTL) were used to assess mechanical allodynia and thermal hyperalgesia, respectively, before and after intraoperative remifentanil administration. Before surgery, mice received intrathecal injections of the following drugs: ketamine, NMDA, BayK8644 (CaMKII activator), and KN93 (CaMKII inhibitor). Immunofluorescence was performed to determine the anatomical location and expression of activated CaMKIIα, phosphorylated CaMKIIα (p-CaMKIIα). Additionally, western blotting was performed to assess p-CaMKIIα and NMDAR expression levels in the SI region. Remifentanil decreased the PWMT and PWTL at 0.5 h, 2 h, and 5 h and increased p-CaMKIIα expression in the SI region. Ketamine increased the PWMT and PWTL and reversed the p-CaMKIIα upregulation. Both BayK8644 and NMDA reversed the effect of ketamine, decreased the PWMT and PWTL, and upregulated p-CaMKIIα expression. In contrast, KN93 enhanced the effect of ketamine by reducing hyperalgesia and downregulating p-CaMKIIα expression. These results suggested that ketamine reversed RIPH by inhibiting the phosphorylation of CaMKIIα and the NMDA receptor in the SI region in mice.

Beyond the target area: an integrative view of tDCS-induced motor cortex modulation in patients and athletes

Transcranial Direct Current Stimulation (tDCS) is a non-invasive technique used to modulate neural tissue. Neuromodulation apparently improves cognitive functions in several neurologic diseases treatment and sports performance. In this study, we present a comprehensive, integrative review of tDCS for motor rehabilitation and motor learning in healthy individuals, athletes and multiple neurologic and neuropsychiatric conditions. We also report on neuromodulation mechanisms, main applications, current knowledge including areas such as language, embodied cognition, functional and social aspects, and future directions. We present the use and perspectives of new developments in tDCS technology, namely high-definition tDCS (HD-tDCS) which promises to overcome one of the main tDCS limitation (i.e., low focality) and its application for neurological disease, pain relief, and motor learning/rehabilitation. Finally, we provided information regarding the Transcutaneous Spinal Direct Current Stimulation (tsDCS) in clinical applications, Cerebellar tDCS (ctDCS) and its influence on motor learning, and TMS combined with electroencephalography (EEG) as a tool to evaluate tDCS effects on brain function.

Preoperative anxiety induces chronic postoperative pain by activating astrocytes in the anterior cingulate cortex region

OBJECTIVE

The study aims to explore the relationship between preoperative anxiety and chronic postoperative pain.

METHODS

A total of forty rats were divided into four groups, control, single-prolonged stress alone, Hysterectomy alone, and SPS+ Hysterectomy. The paw withdrawal mechanical thresholds (PWMT) were examined. qRT-PCR and western blotting assay were performed to detect the GFAP expression in astrocytes isolated from the anterior cingulate cortex (ACC) region. In addition, the long-term potentiation (LTP) in ACC was examined.

RESULTS

Rats in the SPS group or the Hysterectomy alone group had no significant effect on chronic pain formation, but SPS can significantly induce chronic pain after surgery. Astrocytes were still active, and the LTP was significantly increased three days after modeling in the SPS+Hysterectomy group.

CONCLUSIONS

anxiety can induce chronic pain by activating astrocytes in the ACC region.

Higher Cortical Facilitation and Serum BDNF Are Associated with Increased Sensitivity to Heat Pain and Reduced Endogenous Pain Inhibition in Healthy Males

Background

Although the brain-derived neurotrophic factor (BDNF) has been intensively investigated in animal models of chronic pain, its role in human pain processing is less understood.

Objective

To study the neurophysiology of BDNF modulation on acute experimental pain, we performed a cross-sectional study.

Methods

We recruited 20 healthy male volunteers (19-40 years old) and assessed their serum BDNF levels, quantitative sensory testing, and cortical excitability parameters using transcranial magnetic stimulation.

Results

Linear regression models demonstrated that the BDNF (β = -5.245, P = 0.034) and intracortical facilitation (β = -3.311, P = 0.034) were inversely correlated with heat pain threshold (adjusted R2 = 44.26). The BDNF (β = -3.719, P ≤ 0.001) was also inversely correlated with conditioned pain modulation (adjusted R2 = 56.8).

Conclusions

Our findings indicate that higher serum BDNF and intracortical facilitation of the primary motor cortex are associated with increased sensitivity to heat pain and high serum BDNF with reduced pain inhibition during noxious heterotopic stimulation.

Altered Brain Functional Hubs and Connectivity Underlie Persistent Somatoform Pain Disorder

This study investigated the degree of brain functional impairment in persistent somatoform pain disorder (PSPD) by examining changes in the patterns of brain functional hubs. Resting-state functional magnetic resonance imaging was performed in 21 PSPD patients with headache as the main symptom and 17 sex- and age-matched healthy controls. Degree centrality (DC) analysis as well as the connectivity among these hubs by functional connectivity (FC) analysis and Granger causality analysis (GCA) were performed to characterize abnormal brain networks in PSPD (Gaussian random field corrected: P < 0.001, Z > 3.09). The relationships between DC and connectivity and clinical parameters were also examined. DC values in the bilateral inferior occipital gyrus (IOG), bilateral calcarine fissure (CAL), and left paracentral lobule (PCL) and FC values of right IOG–left CAL, right IOG–right CAL, right IOG–left IOG, left CAL–right CAL, left CAL–left IOG, left CAL–left PCL, right CAL–left PCL, and left IOG–left PCL were lower in PSPD patients as compared to controls. A negative causal effect from the left CAL to the left paracentral lobule and a positive effect from the right CAL to the right IOG were observed in PSPD patients. Abnormal DC, FC, and signed-path coefficients in PSPD patients were negatively correlated with self-rating anxiety and depression scale scores. These results indicate that altered functional hubs and connectivity patterns in the somatosensory cortex may reflect emotional disturbance in PSPD patients.

Cortical Network Response to Acupuncture and the Effect of the Hegu Point: An fNIRS Study

Acupuncture is a practice of treatment based on influencing specific points on the body by inserting needles. According to traditional Chinese medicine, the aim of acupuncture treatment for pain management is to use specific acupoints to relieve excess, activate qi (or vital energy), and improve blood circulation. In this context, the Hegu point is one of the most widely-used acupoints for this purpose, and it has been linked to having an analgesic effect. However, there exists considerable debate as to its scientific validity. In this pilot study, we aim to identify the functional connectivity related to the three main types of acupuncture manipulations and also identify an analgesic effect based on the hemodynamic response as measured by functional near-infrared spectroscopy (fNIRS). The cortical response of eleven healthy subjects was obtained using fNIRS during an acupuncture procedure. A multiscale analysis based on wavelet transform coherence was employed to assess the functional connectivity of corresponding channel pairs within the left and right somatosensory region. The wavelet analysis was focused on the very-low frequency oscillations (VLFO, 0.01–0.08 Hz) and the low frequency oscillations (LFO, 0.08–0.15 Hz). A mixed model analysis of variance was used to appraise statistical differences in the wavelet domain for the different acupuncture stimuli. The hemodynamic response after the acupuncture manipulations exhibited strong activations and distinctive cortical networks in each stimulus. The results of the statistical analysis showed significant differences (p<0.05) between the tasks in both frequency bands. These results suggest the existence of different stimuli-specific cortical networks in both frequency bands and the anaesthetic effect of the Hegu point as measured by fNIRS.

Latin American and Caribbean consensus on noninvasive central nervous system neuromodulation for chronic pain management (LAC2-NIN-CP)

Supplemental Digital Content is Available in the Text.

Introduction:

Chronic pain (CP) is highly prevalent and generally undertreated health condition. Noninvasive brain stimulation may contribute to decrease pain intensity and influence other aspects related to CP.

Objective:

To provide consensus-based recommendations for the use of noninvasive brain stimulation in clinical practice.

Methods:

Systematic review of the literature searching for randomized clinical trials followed by consensus panel. Recommendations also involved a cost-estimation study.

Results:

The systematic review wielded 24 transcranial direct current stimulation (tDCS) and 22 repetitive transcranial magnetic stimulation (rTMS) studies. The following recommendations were provided: (1) Level A for anodal tDCS over the primary motor cortex (M1) in fibromyalgia, and level B for peripheral neuropathic pain, abdominal pain, and migraine; bifrontal (F3/F4) tDCS and M1 high-definition (HD)-tDCS for fibromyalgia; Oz/Cz tDCS for migraine and for secondary benefits such as improvement in quality of life, decrease in anxiety, and increase in pressure pain threshold; (2) level A recommendation for high-frequency (HF) rTMS over M1 for fibromyalgia and neuropathic pain, and level B for myofascial or musculoskeletal pain, complex regional pain syndrome, and migraine; (3) level A recommendation against the use of anodal M1 tDCS for low back pain; and (4) level B recommendation against the use of HF rTMS over the left dorsolateral prefrontal cortex in the control of pain.

Conclusion:

Transcranial DCS and rTMS are recommended techniques to be used in the control of CP conditions, with low to moderate analgesic effects, and no severe adverse events. These recommendations are based on a systematic review of the literature and a consensus made by experts in the field. Readers should use it as part of the resources available to decision-making.

Treatment of pain post-brachial plexus injury using high-frequency spinal cord stimulation

Purpose

Brachial plexopathy can sometimes cause severe chronic pain. There are many possible treatments for such neuropathic pain, including neuromodulation. However, rigorous scientific evidence on the usefulness of spinal cord stimulation (SCS) is still scarce. Here, we report the use of high-frequency (10 kHz) SCS (HFSCS) in a patient with brachial plexus injury (root avulsion).

Objective

To assess the efficacy of HFSCS in root avulsion and to investigate the putative neurophysiological mechanisms of HFSCS.

Methods

A 32-year-old woman visited our center following an iatrogenic brachial plexus injury. She underwent traditional, paresthesia-inducing, tonic SCS with cervical lead placement. She reported that stimulation-induced paresthesia was uncomfortable, without any pain reduction. After the successful trial of HFSCS, the patient was assessed at 1 month (T1) and 6 months (T6) after HFSCS implantation with pain and quality of life (QoL) scales. Moreover, she underwent a neurophysiological assessment (somatosensory evoked potentials [SEPs], reciprocal inhibition [RI], pain-motor integration [PMI], and the habituation of intraepidermal electrical stimulation-induced evoked potentials [IEPs]) with the stimulator switched on and switched off at T6.

Results

The patient reported 100% paresthesia-free pain relief, a consistent improvement of QoL, and a complete discontinuation of her previous pain treatment at T1 and T6. Moreover, we found suppression of SEPs, restored habituation of IEPs, and strengthening of RI and PMI.

Conclusion

This is the first report to illustrate the usefulness and safety of HFSCS for treating root avulsion in a patient with failed tonic SCS. Our data indicate that HFSCS may either block large-diameter fibers or stimulate medium-/small-diameter fibers, thus inducing analgesia without paresthesia, probably by reducing the activation of the wide-dynamic-range neurons. Moreover, HFSCS seems to modulate spinal inhibitory mechanisms and the descending corticospinal inhibitory output. Thus, HFSCS can be an effective option for treating refractory pain following root avulsion.

The effect of occipital nerve field stimulation on the descending pain pathway in patients with fibromyalgia: a water PET and EEG imaging study

Background

Fibromyalgia is a chronic disorder characterized by widespread musculoskeletal pain accompanied by fatigue, sleep, memory, and mood problems. Recently, occipital nerve field stimulation (ONS) has been proposed as an effective potential treatment for fibromyalgia-related pain. The aim of this study is to unravel the neural mechanism behind occipital nerve stimulation’s ability to suppress pain in fibromyalgia patients.

Materials and methods

Seven patients implanted with subcutaneous electrodes in the C2 dermatoma were enrolled for a Positron Emission Tomography (PET) H₂¹⁵O activation study. These seven patients were selected from a cohort of 40 patients who were part of a double blind, placebo-controlled study followed by an open label follow up at six months. The H₂¹⁵O PET scans were taken during both the “ON” (active stimulation) and “OFF” (stimulating device turned off) conditions. Electroencephalogram (EEG) data were also recorded for the implanted fibromyalgia patients during both the “ON” and “OFF” conditions.

Results

Relative to the “OFF” condition, ONS stimulation resulted in activation in the dorsal lateral prefrontal cortex, comprising the medial pain pathway, the ventral medial prefrontal cortex, and the bilateral anterior cingulate cortex as well as parahippocampal area, the latter two of which comprise the descending pain pathway. Relative deactivation was observed in the left somatosensory cortex, constituting the lateral pain pathway as well as other sensory areas such as the visual and auditory cortex. The EEG results also showed increased activity in the descending pain pathway. The pregenual anterior cingulate cortex extending into the ventral medial prefrontal cortex displayed this increase in the theta, alpha1, alpha2, beta1, and beta2 frequency bands.

Conclusion

PET shows that ONS exerts its effect via activation of the descending pain inhibitory pathway and the lateral pain pathway in fibromyalgia, while EEG shows activation of those cortical areas that could be responsible for descending inhibition system recruitment.

Trial Registration

This study is registered with ClinicalTrials.gov, number NCT00917176 (June 10, 2009).

Insights About the Neuroplasticity State on the Effect of Intramuscular Electrical Stimulation in Pain and Disability Associated With Chronic Myofascial Pain Syndrome (MPS): A Double-Blind, Randomized, Sham-Controlled Trial

Background: There is limited evidence concerning the effect of intramuscular electrical stimulation (EIMS) on the neural mechanisms of pain and disability associated with chronic Myofascial Pain Syndrome (MPS). Objectives: To provide new insights into the EIMS long-term effect on pain and disability related to chronic MPS (primary outcomes). To assess if the neuroplasticity state at baseline could predict the long-term impact of EIMS on disability due to MPS we examined the relationship between the serum brain-derived-neurotrophic-factor (BDNF) and by motor evoked potential (MEP). Also, we evaluated if the EIMS could improve the descending pain modulatory system (DPMS) and the cortical excitability measured by transcranial magnetic stimulation (TMS) parameters. Methods: We included 24 right-handed female with chronic MPS, 19-65 years old. They were randomically allocated to receive ten sessions of EIMS, 2 Hz at the cervical paraspinal region or a sham intervention (n = 12). Results: A mixed model analysis of variance revealed that EIMS decreased daily pain scores by -73.02% [95% confidence interval (CI) = -95.28 to -52.30] and disability due to pain -43.19 (95%CI, -57.23 to -29.39) at 3 months of follow up. The relative risk for using analgesics was 2.95 (95% CI, 1.36 to 6.30) in the sham group. In the EIMS and sham, the change on the Numerical Pain Scale (NPS0-10) throughout CPM-task was -2.04 (0.79) vs. -0.94 (1.18), respectively, (P = 0.01). EIMS reduced the MEP -28.79 (-53.44 to -4.15), while improved DPMS and intracortical inhibition. The MEP amplitude before treatment [(Beta = -0.61, (-0.58 to -0.26)] and a more significant change from pre- to post-treatment on serum BDNF) (Beta = 0.67; CI95% = 0.07 to 1.26) were predictors to EIMS effect on pain and disability due to pain. Conclusion: These findings suggest that a bottom-up effect induced by the EIMS reduced the analgesic use, improved pain, and disability due to chronic MPS. This effect might be mediated by an enhancing of corticospinal inhibition as seen by an increase in IC and a decrease in MEP amplitude. Likewise, the MEP amplitude before treatment and the changes induced by the EIMS in the serum BDNF predicted it's long-term clinical impact on pain and disability due MPS. The trial is recorded in ClinicalTrials.gov: NCT02381171.

The increased release of amino acid neurotransmitters of the primary somatosensory cortical area in rats contributes to remifentanil-induced hyperalgesia and its inhibition by lidocaine

Background

Studies have confirmed that activation of the neurons of primary somatosensory cortex (S1) is involved in the process of remifentanil (Remi)-induced hyperalgesia (RIH), which can be suppressed by lidocaine (Lido). A total intravenous anesthesia model of rats mimicking clinical Remi-based anesthesia was set up to explore the release of amino acid neurotransmitters of S1 cortex in RIH and its inhibition by Lido in this study.

Materials and methods

Sprague Dawley rats were randomly divided into the following four groups: propofol (Pro), Remi, Remi combined Lido, and Lido groups. Mechanical hyperalgesia was evaluated by von Frey test; the amino acid neurotransmitters in the microdialysates of S1 area were detected by high-performance liquid chromatography (HPLC)-fluorescence, and conventional protein kinase C (cPKC)γ levels in the whole-cell lysates and membrane lipid rafts (MLRs) were determined by Western blotting.

Results

The von Frey test showed that co-administration of Lido significantly inhibited a Remi-induced decrease in the threshold of the paw withdrawal response in Remi group at 2 h postinfusion. Meanwhile, the Remi-induced increases in both the excitatory and inhibitory amino acid releases in S1 were suppressed by co-administrating Lido within 5 h postinfusion. Western blotting showed that the increased cPKCγ level in the membrane lipid rafts (MLR) induced by Remi was also inhibited by Lido.

Conclusion

The increased release of amino acid neurotransmitters and the translocation of cPKCγ in MLR suggest the activation of S1 neurons, which may be one of the mechanisms underlying RIH. Lido reduces the release of amino acid neurotransmitters in S1 neurons and the translocation of cPKCγ in MLRs after stopping Remi, which may be one of its antihyperalgesic mechanisms.

Altered Gene Expression in Prefrontal Cortex of a Fabry Disease Mouse Model

Fabry disease is an X-chromosome linked hereditary disease that is caused by loss of function mutations in the α-galactosidase A (α-Gal A) gene, resulting in defective glycolipid degradation and subsequent accumulation of globotriaosylceramide (Gb3) in different tissues, including vascular endothelial cells and neurons in the peripheral and central nervous system. We recently reported a differential gene expression profile of α-Gal A^(−/0) mouse dorsal root ganglia, an established animal model of Fabry disease, thereby providing new gene targets that might underlie the neuropathic pain related symptoms. To investigate the cognitive symptoms experienced by Fabry patients, we performed one-color based hybridization microarray expression profiling of prefrontal cortex samples from adult α-Gal A^(−/0) mice and age-matched wildtype controls, followed by protein-protein interaction and pathway analyses for the differentially regulated mRNAs. We found that from a total of 381 differentially expressed genes, 135 genes were significantly upregulated, whereas 246 genes were significantly downregulated between α-Gal A^(−/0) mice and wildtype controls. Enrichment analysis for downregulated genes revealed mainly immune related pathways, including immune/defense responses, regulation of cytokine production, as well as signaling and transport regulation pathways. Further analysis of the regulated genes revealed a large number of genes involved in neurodegeneration. The current analysis for the first time presents a differential gene expression profile of central nervous system tissue from α-Gal A^(−/0) mice, thereby providing novel knowledge on the deregulation and a possible contribution of gene expression to Fabry disease related brain pathologies.

Epigenetic Modifications Associated to Neuroinflammation and Neuropathic Pain After Neural Trauma

Accumulating evidence suggests that epigenetic alterations lie behind the induction and maintenance of neuropathic pain. Neuropathic pain is usually a chronic condition caused by a lesion, or pathological change, within the nervous system. Neuropathic pain appears frequently after nerve and spinal cord injuries or diseases, producing a debilitation of the patient and a decrease of the quality of life. At the cellular level, neuropathic pain is the result of neuronal plasticity shaped by an increase in the sensitivity and excitability of sensory neurons of the central and peripheral nervous system. One of the mechanisms thought to contribute to hyperexcitability and therefore to the ontogeny of neuropathic pain is the altered expression, trafficking, and functioning of receptors and ion channels expressed by primary sensory neurons. Besides, neuronal and glial cells, such as microglia and astrocytes, together with blood borne macrophages, play a critical role in the induction and maintenance of neuropathic pain by releasing powerful neuromodulators such as pro-inflammatory cytokines and chemokines, which enhance neuronal excitability. Altered gene expression of neuronal receptors, ion channels, and pro-inflammatory cytokines and chemokines, have been associated to epigenetic adaptations of the injured tissue. Within this review, we discuss the involvement of these epigenetic changes, including histone modifications, DNA methylation, non-coding RNAs, and alteration of chromatin modifiers, that have been shown to trigger modification of nociception after neural lesions. In particular, the function on these processes of EZH2, JMJD3, MeCP2, several histone deacetylases (HDACs) and histone acetyl transferases (HATs), G9a, DNMT, REST and diverse non-coding RNAs, are described. Despite the effort on developing new therapies, current treatments have only produced limited relief of this pain in a portion of patients. Thus, the present review aims to contribute to find novel targets for chronic neuropathic pain treatment.

Optogenetic exploration and modulation of pain processing

Intractable pain is the single most common cause of disability, affecting more than 20% of the population world-wide. There is accordingly a global effort to decipher how changes in nociceptive processing in the peripheral and central nervous systems contribute to the onset and maintenance of chronic pain. The past several years have brought rapid progress in the adaptation of optogenetic approaches to study and manipulate the activity of sensory afferents and spinal cord neurons in freely behaving animals, and to investigate cortical processing and modulation of pain responses. This review discusses methodological advances that underlie this recent progress, and discusses practical considerations for the optogenetic modulation of nociceptive sensory processing.

Enhanced pharmacological actions of p,p'-methoxyl-diphenyl diselenide-loaded polymeric nanocapsules in a mouse model of neuropathic pain: Behavioral and molecular insights

Neuropathic pain is a public health problem and its treatment is a global challenge. The organoselenium compound p,p'-methoxyl-diphenyl diselenide [(OMePhSe)₂] has a potential antinociceptive action and its incorporation into nanocapsules improves this action. The current study evaluated if (OMePhSe)₂ administration, free or incorporated into nanocapsules, reduces the chronic pain-like behavior induced by the partial sciatic nerve ligation (PSNL) surgery, a neuropathic pain mouse model. It was also investigated the (OMePhSe)₂ restorative effect against the increase in inflammatory and apoptotic protein contents at the central nervous system caused by PSNL to mice. Male Swiss mice were subjected to PSNL during 4 weeks and treated with (OMePhSe)₂, free or incorporated into nanocapsules, in a single (25mg/kg, i.g.) or repeated administration schedule (25mg/kg, i.g., once a day for seven days). Both treatments reduced mechanical hypernociception induced by PSNL, but the nanoencapsulation increased the (OMePhSe)₂ antinociceptive action two-fold in comparison to its free form. PSNL increased the inflammatory protein contents (iNOS, COX-2, NF-κB, IL-1β and TNF-α) and those of bax and clivated PARP, and reduced bcl-2 content, apoptotic proteins, in the mouse cerebral contral lateral cortex. Furthermore, PSNL induced an activation of MAPK pathway (ERK_1,2 and p38). The free or nanoencapsulated (OMePhSe)₂ repeated administration restored the molecular changes in the protein contents. This study demonstrates the (OMePhSe)₂ nanocapsule effectiveness in an animal model of chronic pain.

Differences in brain gray matter volume in patients with Crohn's disease with and without abdominal pain

Increasing evidence indicates that abnormal pain processing is present in the central nervous system of patients with Crohn’s disease (CD). The purposes of this study were to assess changes in gray matter (GM) volumes in CD patients in remission and to correlate structural changes in the brain with abdominal pain. We used a 3.0 T magnetic resonance scanner to examine the GM structures in 21 CD patients with abdominal pain, 26 CD patients without abdominal pain, and 30 healthy control subjects (HCs). Voxel-based morphometric analyses were used to assess the brain GM volumes. Patients with abdominal pain exhibited higher CD activity index and lower inflammatory bowel disease questionnaire scores than those of the patients without abdominal pain. Compare to HCs and to patients without abdominal pain, patients with abdominal pain exhibited lower GM volumes in the insula and anterior cingulate cortex (ACC); whereas compare to HCs and to patients with abdominal pain, the patients without abdominal pain exhibited higher GM volumes in the hippocampal and parahippocampal cortex. The GM volumes in the insula and ACC were significantly negatively correlated with daily pain scores. These results suggest that differences exist in the brain GM volume between CD patients in remission with and without abdominal pain. The negative correlation between the GM volumes in the insula and ACC and the presence and severity of abdominal pain in CD suggests these structures are closely related to visceral pain processing.

Parameter Optimization Analysis of Prolonged Analgesia Effect of tDCS on Neuropathic Pain Rats

Background: Transcranial direct current stimulation (tDCS) is widely used to treat human nerve disorders and neuropathic pain by modulating the excitability of cortex. The effectiveness of tDCS is influenced by its stimulation parameters, but there have been no systematic studies to help guide the selection of different parameters.

Objective: This study aims to assess the effects of tDCS of primary motor cortex (M1) on chronic neuropathic pain in rats and to test for the optimal parameter combinations for analgesia.

Methods: Using the chronic neuropathic pain models of chronic constriction injury (CCI), we measured pain thresholds before and after anodal-tDCS (A-tDCS) using different parameter conditions, including stimulation intensity, stimulation time, intervention time and electrode located (ipsilateral or contralateral M1 of the ligated paw on male/female CCI models).

Results: Following the application of A-tDCS over M1, we observed that the antinociceptive effects were depended on different parameters. First, we found that repetitive A-tDCS had a longer analgesic effect than single stimulus, and both ipsilateral-tDCS (ip-tDCS) and contralateral-tDCS (con-tDCS) produce a long-lasting analgesic effect on neuropathic pain. Second, the antinociceptive effects were intensity-dependent and time-dependent, high intensities worked better than low intensities and long stimulus durations worked better than short stimulus durations. Third, timing of the intervention after injury affected the stimulation outcome, early use of tDCS was an effective method to prevent the development of pain, and more frequent intervention induced more analgesia in CCI rats, finally, similar antinociceptive effects of con- and ip-tDCS were observed in both sexes of CCI rats.

Conclusion: Optimized protocols of tDCS for treating antinociceptive effects were developed. These findings should be taken into consideration when using tDCS to produce analgesic effects in clinical applications.