Metabolite concentration ratios in thalami of patients with migraine and trigeminal neuralgia measured with1H-MRS

Thalamic neurometabolite alterations in chronic low back pain: a common phenomenon across musculoskeletal pain conditions?

ABSTRACT

Recently, we showed that patients with knee osteoarthritis (KOA) demonstrate alterations in the thalamic concentrations of several metabolites compared with healthy controls: higher myo-inositol (mIns), lower N-acetylaspartate (NAA), and lower choline (Cho). Here, we evaluated whether these metabolite alterations are specific to KOA or could also be observed in patients with a different musculoskeletal condition, such as chronic low back pain (cLBP). Thirty-six patients with cLBP and 20 healthy controls were scanned using 1 H-magnetic resonance spectroscopy (MRS) and a PRESS (Point RESolved Spectroscopy) sequence with voxel placement in the left thalamus. Compared with healthy controls, patients with cLBP demonstrated lower absolute concentrations of NAA ( P = 0.0005) and Cho ( P < 0.05) and higher absolute concentrations of mIns ( P = 0.01) when controlling for age, as predicted by our previous work in KOA. In contrast to our KOA study, mIns levels in this population did not significantly correlate with pain measures (eg, pain severity or duration). However, exploratory analyses revealed that NAA levels in patients were negatively correlated with the severity of sleep disturbance ( P < 0.01), which was higher in patients compared with healthy controls ( P < 0.001). Additionally, also in patients, both Cho and mIns levels were positively correlated with age ( P < 0.01 and P < 0.05, respectively). Altogether, these results suggest that thalamic metabolite changes may be common across etiologically different musculoskeletal chronic pain conditions, including cLBP and KOA, and may relate to symptoms often comorbid with chronic pain, such as sleep disturbance. The functional and clinical significance of these brain changes remains to be fully understood.

Development status of novel spectral imaging techniques and application to traditional Chinese medicine

Traditional Chinese medicine (TCM) is a treasure of the Chinese nation, providing effective solutions to current medical requisites. Various spectral techniques are undergoing continuous development and provide new and reliable means for evaluating the efficacy and quality of TCM. Because spectral techniques are noninvasive, convenient, and sensitive, they have been widely applied to in vitro and in vivo TCM evaluation systems. In this paper, previous achievements and current progress in the research on spectral technologies (including fluorescence spectroscopy, photoacoustic imaging, infrared thermal imaging, laser-induced breakdown spectroscopy, hyperspectral imaging, and surface enhanced Raman spectroscopy) are discussed. The advantages and disadvantages of each technology are also presented. Moreover, the future applications of spectral imaging to identify the origins, components, and pesticide residues of TCM in vitro are elucidated. Subsequently, the evaluation of the efficacy of TCM in vivo is presented. Identifying future applications of spectral imaging is anticipated to promote medical research as well as scientific and technological explorations.

Proteomics profiling reveals mitochondrial damage in the thalamus in a mouse model of chronic migraine

BACKGROUND

Migraine, a complex brain disorder, is regarded as a possible clinical manifestation of brain energy dysfunction. The trigeminovascular system is considered the basis for the pathogenesis of migraine, hence we depicted the proteomics profiling of key regions in this system, then focusing on protein alterations related to mitochondrial function. The aim of this study is to illustrate the role of mitochondria in migraine.

METHODS

A mouse model of chronic migraine (CM) was established by repeated nitroglycerin (NTG) stimulation and evaluated by von-Frey filaments, a hot plate and a light-dark box. Differentially expressed proteins (DEPs) in some subcortical brain regions of the trigeminovascular system were screened through liquid chromatography-tandem mass spectrometry (LC‒MS/MS) to analyse the specificity of key signaling pathways in different brain regions. And then mitochondrial function, structure and dynamics were determined by qPCR, ELISA, and transmission electron microscope (TEM). Finally, the effect of mitochondrial intervention-Urolithin A (UA) on CM was investigated.

RESULTS

Repeated NTG injection triggered photophobia, periorbital and hind paw allodynia in mice. The proteomics profiling of CM model showed that 529, 109, 163, 152 and 419 DEPs were identified in the thalamus, hypothalamus, periaqueductal grey (PAG), trigeminal ganglion (TG) and trigeminocervical complex (TCC), respectively. The most significant changes in the brain region-specific pathways pointed to thalamic mitochondrial impairment. NTG induced mitochondrial structural disruption, dysfunction and homeostatic dysregulation, which could be partially attenuated by UA intervention.

CONCLUSION

Our findings highlight the involvement of mitochondrial damage in the thalamus in central sensitization of CM, which provides evidence of possible metabolic mechanisms in migraine pathophysiology.

Energy Metabolic Disorder of Astrocytes May Be an Inducer of Migraine Attack

Migraine is a chronic headache disease, which ranks second in years lost due to disability. However, the mechanism of migraines is still not clear. In migraine patients, fasting can trigger headache attacks. We explored the probable mechanism of why fasting can induce headaches. Nitroglycerin (NTG) was used to induce acute migraine attacks in mice. Primary astrocytes were used to study the pathophysiological mechanism and a Seahorse analyzer was used to detect mitochondrial function. NTG induced more serious headaches in the fasting group. Both the head-scratching times and climbing-cage times in the fasting group were higher than those in normal-diet group. More ROS and inflammatory factors, such as IL-6 and IL-1β, were induced in low-glucose conditions. Seahorse showed that the basal oxygen consumption rate (OCR) and OCR for ATP production were lower in mice who had received NTG with low glucose levels than in other groups. The activity of AMPK was inhibited in this group, which may explain the Seahorse results. We concluded that in the low-glucose state, astrocytes produce more inflammatory factors, ROS, which may be a result of mitochondrial metabolism dysfunction. Improving mitochondrial function and supplying enough substrates may be an option for relieving migraine attacks.

The thalamus in trigeminal neuralgia: structural and metabolic abnormalities, and influence on surgical response

BACKGROUND

Medically-refractory trigeminal neuralgia (TN) can be treated successfully with operative intervention, but a significant proportion of patients are non-responders despite undergoing technically successful surgery. The thalamus is a key component of the trigeminal sensory pathway involved in transmitting facial pain, but the role of the thalamus in TN, and its influence on durability of pain relief after TN surgery, are relatively understudied. We aimed to test the hypothesis that variations in thalamic structure and metabolism are related to surgical non-response in TN.

METHODS

We performed a longitudinal, peri-operative neuroimaging study of the thalamus in medically-refractory TN patients undergoing microvascular decompression or percutaneous balloon compression rhizotomy. Patients underwent structural MRI and MR spectroscopy scans pre-operatively and at 1-week following surgery, and were classified as responders or non-responders based on 1-year post-operative pain outcome. Thalamus volume, shape, and metabolite concentration (choline/creatine [Cho/Cr] and N-acetylaspartate/creatine [NAA/Cr]) were evaluated at baseline and 1-week, and compared between responders, non-responders, and healthy controls.

RESULTS

Twenty healthy controls and 23 patients with medically-refractory TN treated surgically (17 responders, 6 non-responders) were included. Pre-operatively, TN patients as a group showed significantly larger thalamus volume contralateral to the side of facial pain. However, vertex-wise shape analysis showed significant contralateral thalamus volume reduction in non-responders compared to responders in an axially-oriented band spanning the outer thalamic circumference (peak p = 0.019). Further, while pre-operative thalamic metabolite concentrations did not differ between responders and non-responders, as early as 1-week after surgery, long-term non-responders showed a distinct decrease in contralateral thalamic Cho/Cr and NAA/Cr, irrespective of surgery type, which was not observed in responders.

CONCLUSIONS

Atrophy of the contralateral thalamus is a consistent feature across patients with medically-refractory TN. Regional alterations in preoperative thalamic structure, and very early post-operative metabolic changes in the thalamus, both appear to influence the durability of pain relief after TN surgery.

Altered Metabolites in the Occipital Lobe in Migraine Without Aura During the Attack and the Interictal Period

Background: Although there have been many magnetic resonance spectroscopy (MRS) studies of migraine, few have focused on migraines during an attack. Here, we aimed to assess metabolite changes in the brain of patients with migraine, both during an attack and in the interictal phase.

Methods: Six patients (one man and five women, mean age: 39 ± 10 years) with migraine without aura during the attack (MWoA-DA), 13 patients (three men and 10 women, mean age: 31 ± 9 years) with migraine without aura during the interictal period (MWoA-DI), and 13 healthy controls (HC) (four men and nine women, mean age: 31 ± 9 years) were studied. All subjects underwent an MRS examination focusing on the occipital lobe. Metabolite changes were investigated among three groups.

Results: The MWoA-DA patients had lower glutathione/total creatine ratio (GSH/tCr) than the MWoA-DI patients and HC. Furthermore, MWoA-DI patients showed lower total choline/total creatine ratio (tCho/tCr) than those in the other two groups. The GSH/tCr ratio was positively correlated with attack frequency in the MWoA-DI group. The tCho/tCr ratio was positively correlated with attack frequency and Migraine Disability Assessment Scale (MIDAS) scores in the MWoA-DA group.

Conclusion: The present study suggests the existence of distinct pathophysiological states between the MWoA-DA and MWoA-DI groups. Neuronal dysfunction is a possible predisposing factor for migraine attack onset, along with oxidative stress and inflammation.

Structural and Functional Brain Changes in Migraine

Migraine is a prevalent primary headache disorder and is usually considered as benign. However, structural and functional changes in the brain of individuals with migraine have been reported. High frequency of white matter abnormalities, silent infarct-like lesions, and volumetric changes in both gray and white matter in individuals with migraine compared to controls have been demonstrated. Functional magnetic resonance imaging (MRI) studies found altered connectivity in both the interictal and ictal phase of migraine. MR spectroscopy and positron emission tomography studies suggest abnormal energy metabolism and mitochondrial dysfunction, as well as other metabolic changes in individuals with migraine. In this review, we provide a brief overview of neuroimaging studies that have helped us to characterize some of these changes and discuss their limitations, including small sample sizes and poorly defined control groups. A better understanding of alterations in the brains of patients with migraine could help not only in the diagnosis but may potentially lead to the optimization of a targeted anti-migraine therapy.

Neurochemical metabolite alterations of the occipital lobe in migraine without aura by proton magnetic resonance spectroscopy

BACKGROUND

Migraine without aura is the most common type of migraine headache, accounting for about 80% of all migraines. The aim of the present investigation was to determine the neurochemical metabolite alterations in the occipital lobe of patients suffering from migraine without aura using proton magnetic resonance spectroscopy (1H-MRS).

METHODS

Fifteen patients suffering from migraine without aura with an occipital plaque and 16 healthy controls were included in this study. Changes in the neurochemical metabolites in the occipital lobe were assessed using 1H-MRS. The ratios of N-acetylaspartate (NAA) to creatine (Cr), choline (Cho) to Cr and myo-inositol (MI) to NAA were measured by voxel volume at 8 cm3.

RESULTS

The mean NAA/Cr ratio decreased significantly in patients compared to controls. Cho/Cr and MI/NAA ratios increased significantly in patients. In addition, the duration of the disease and the frequency of headache attacks were significantly associated with a decrease in the NAA/Cr ratio and an increase in the Cho/Cr ratio.

CONCLUSIONS

Migraine without aura shows a significant association with changes in neurochemical metabolites detectable by 1H-MRS in the occipital lobe of patients. In addition, changes in metabolic ratios showed a significant relationship with the duration of the disease and the frequency of headache attacks.

Magnetic Resonance Imaging in Pediatric Migraine

This literature review provides an overview of the research using magnetic resonance imaging (MRI) in pediatric migraine and compares findings with the adult migraine literature. A literature search using PubMed was conducted using all relevant sources up to February 2019. Using MRI methods to categorize and explain pediatric migraine in comparison with adult migraine is important, in order to recognize and appreciate the differences between the two entities, both clinically and physiologically. We aim to demonstrate the differences and similarities between pediatric and adult migraine using data from white matter and gray matter structural studies, cerebral perfusion, metabolites, and functional MRI (fMRI) studies, including task-based and resting-state blood oxygen level-dependent studies. By doing this we identify areas that need further research, as well as possible areas where intervention could alter outcomes.

Advanced Imaging in the Evaluation of Migraine Headaches

The use of advanced imaging in routine diagnostic practice appears to provide only limited value in patients with migraine who have not experienced recent changes in headache characteristics or symptoms. However, advanced imaging may have potential for studying the biological manifestations and pathophysiology of migraine headaches. Migraine with aura appears to have characteristic spatiotemporal changes in structural anatomy, function, hemodynamics, metabolism, and biochemistry, whereas migraine without aura produces more subtle and complex changes. Large, controlled, multicenter imaging-based observational trials are needed to confirm the anecdotal evidence in the literature and test the scientific hypotheses thought to underscore migraine pathophysiology.

Chronic Dysregulation of Cortical and Subcortical Metabolism After Experimental Traumatic Brain Injury

Traumatic brain injury (TBI) is a leading cause of death and long-term disability worldwide. Although chronic disability is common after TBI, effective treatments remain elusive and chronic TBI pathophysiology is not well understood. Early after TBI, brain metabolism is disrupted due to unregulated ion release, mitochondrial damage, and interruption of molecular trafficking. This metabolic disruption causes at least part of the TBI pathology. However, it is not clear how persistent or pervasive metabolic injury is at later stages of injury. Using untargeted 1H-NMR metabolomics, we examined ex vivo hippocampus, striatum, thalamus, frontal cortex, and brainstem tissue in a rat lateral fluid percussion model of chronic brain injury. We found altered tissue concentrations of metabolites in the hippocampus and thalamus consistent with dysregulation of energy metabolism and excitatory neurotransmission. Furthermore, differential correlation analysis provided additional evidence of metabolic dysregulation, most notably in brainstem and frontal cortex, suggesting that metabolic consequences of injury are persistent and widespread. Interestingly, the patterns of network changes were region-specific. The individual metabolic signatures after injury in different structures of the brain at rest may reflect different compensatory mechanisms engaged to meet variable metabolic demands across brain regions.

Current understanding of thalamic structure and function in migraine

OBJECTIVE

To review and discuss the literature on the role of thalamic structure and function in migraine.

DISCUSSION

The thalamus holds an important position in our understanding of allodynia, central sensitization and photophobia in migraine. Structural and functional findings suggest abnormal functional connectivity between the thalamus and various cortical regions pointing towards an altered pain processing in migraine. Pharmacological nociceptive modulation suggests that the thalamus is a potential drug target.

CONCLUSION

A critical role for the thalamus in migraine-related allodynia and photophobia is well established. Additionally, the thalamus is most likely involved in the dysfunctional pain modulation and processing in migraine, but further research is needed to clarify the exact clinical implications of these findings.

Acupuncture therapy in treating migraine: results of a magnetic resonance spectroscopy imaging study

Background

Acupuncture has been proven to be effective as an alternative therapy in treating migraine, but the pathophysiological mechanisms of the treatment remain unclear. This study investigated possible neurochemical responses to acupuncture treatment.

Patients and methods

Proton magnetic resonance spectroscopy imaging was used to investigate biochemical levels pre- and post-acupuncture treatment. Participants (N=45) included subjects diagnosed with: 1) migraine without aura; 2) cervicogenic headache; and 3) healthy controls. Participants in the two patient groups received verum acupuncture using acupoints that target migraine without aura but not cervicogenic headache, while the healthy controls received a sham treatment. All participants had magnetic resonance spectroscopy scans before and after the acupuncture therapy. Levels of brain metabolites were examined in relation to clinical headache assessment scores.

Results

A significant increase in N-acetylaspartate/creatine was observed in bilateral thalamus in migraine without aura after the acupuncture treatment, which was significantly correlated with the headache intensity score.

Conclusion

The data demonstrate brain biochemical changes underlying the effect of acupuncture treatment of migraine.

Subacute Pain after Traumatic Brain Injury Is Associated with Lower Insular N-Acetylaspartate Concentrations

Persistent pain is experienced by more than 50% of persons who sustain a traumatic brain injury (TBI), and more than 30% experience significant pain as early as 6 weeks after injury. Although neuropathic pain is a common consequence after CNS injuries, little attention has been given to neuropathic pain symptoms after TBI. Magnetic resonance spectroscopy (MRS) studies in subjects with TBI show decreased brain concentrations of N-acetylaspartate (NAA), a marker of neuronal density and viability. Although decreased brain NAA has been associated with neuropathic pain associated with spinal cord injury (SCI) and diabetes, this relationship has not been examined after TBI. The primary purpose of this study was to test the hypothesis that lower NAA concentrations in brain areas involved in pain perception and modulation would be associated with greater severity of neuropathic pain symptoms. Participants with TBI underwent volumetric MRS, pain and psychosocial interviews. Cluster analysis of the Neuropathic Pain Symptom Inventory subscores resulted in two TBI subgroups: The Moderate Neuropathic Pain (n = 17; 37.8%), with significantly (p = 0.038) lower insular NAA than the Low or no Neuropathic Pain group (n = 28; 62.2%), or age- and sex-matched controls (n = 45; p < 0.001). A hierarchical linear regression analysis controlling for age, sex, and time post-TBI showed that pain severity was significantly (F = 11.0; p < 0.001) predicted by a combination of lower insular NAA/Creatine (p < 0.001), lower right insular gray matter fractional volume (p < 0.001), female sex (p = 0.005), and older age (p = 0.039). These findings suggest that neuronal dysfunction in brain areas involved in pain processing is associated with pain after TBI.

What has functional connectivity and chemical neuroimaging in fibromyalgia taught us about the mechanisms and management of 'centralized' pain?

Research suggests that fibromyalgia is a central, widespread pain syndrome supported by a generalized disturbance in central nervous system pain processing. Over the past decades, multiple lines of research have identified the locus for many functional, chronic pain disorders to the central nervous system, and the brain. In recent years, brain neuroimaging techniques have heralded a revolution in our understanding of chronic pain, as they have allowed researchers to non-invasively (or minimally invasively) evaluate human patients suffering from various pain disorders. While many neuroimaging techniques have been developed, growing interest in two specific imaging modalities has led to significant contributions to chronic pain research. For instance, resting functional connectivity magnetic resonance imaging (fcMRI) is a recent adaptation of fMRI that examines intrinsic brain connectivity - defined as synchronous oscillations of the fMRI signal that occurs in the resting basal state. Proton magnetic resonance spectroscopy (1H-MRS) is a non-invasive magnetic resonance imaging technique that can quantify the concentration of multiple metabolites within the human brain. This review will outline recent applications of the complementary imaging techniques - fcMRI and 1H-MRS - to improve our understanding of fibromyalgia pathophysiology and how pharmacological and non-pharmacological therapies contribute to analgesia in these patients. A better understanding of the brain in chronic pain, with specific linkage as to which neural processes relate to spontaneous pain perception and hyperalgesia, will greatly improve our ability to develop novel therapeutics. Neuroimaging will play a growing role in the translational research approaches needed to make this a reality.

Altered regional homogeneity of spontaneous brain activity in idiopathic trigeminal neuralgia

The pathophysiology of idiopathic trigeminal neuralgia (ITN) has conventionally been thought to be induced by neurovascular compression theory. Recent structural brain imaging evidence has suggested an additional central component for ITN pathophysiology. However, far less attention has been given to investigations of the basis of abnormal resting-state brain activity in these patients. The objective of this study was to investigate local brain activity in patients with ITN and its correlation with clinical variables of pain. Resting-state functional magnetic resonance imaging data from 17 patients with ITN and 19 age- and sex-matched healthy controls were analyzed using regional homogeneity (ReHo) analysis, which is a data-driven approach used to measure the regional synchronization of spontaneous brain activity. Patients with ITN had decreased ReHo in the left amygdala, right parahippocampal gyrus, and left cerebellum and increased ReHo in the right inferior temporal gyrus, right thalamus, right inferior parietal lobule, and left postcentral gyrus (corrected). Furthermore, the increase in ReHo in the left precentral gyrus was positively correlated with visual analog scale (r=0.54; P=0.002). Our study found abnormal functional homogeneity of intrinsic brain activity in several regions in ITN, suggesting the maladaptivity of the process of daily pain attacks and a central role for the pathophysiology of ITN.

Thalamic metabolic alterations with cognitive dysfunction in idiopathic trigeminal neuralgia: a multivoxel spectroscopy study

INTRODUCTION

Although abnormalities in metabolite compositions in the thalamus are well described in patients with idiopathic trigeminal neuralgia (ITN), differences in distinct thalamic subregions have not been measured with proton magnetic resonance spectroscopy ((1)H-MRS), and whether there are correlations between thalamic metabolites and cognitive function still remain unknown.

METHODS

Multivoxel MRS was recorded to investigate the metabolic alterations in the thalamic subregions of patients with ITN. The regions of interest were localized in the anterior thalamus (A-Th), intralaminar portion of the thalamus (IL-Th), posterior lateral thalamus (PL-Th), posterior medial thalamus (PM-Th), and medial and lateral pulvinar of the thalamus (PuM-Th and PuL-Th). The N-acetylaspartate to creatine (NAA/Cr) and choline to creatine (Cho/Cr) ratios were measured in the ITN and control groups. Scores of the visual analogue scale (VAS) and the Montreal Cognitive Assessment (MoCA) were analyzed to correlate with the neuroradiological findings.

RESULTS

The NAA/Cr ratio in the affected side of PM-Th and PL-Th in ITN patients was statistically lower than that in the corresponding regions of the thalamus in controls. The NAA/Cr ratio in the affected PM-Th was negatively associated with VAS and disease duration. Furthermore, decreases of NAA/Cr and Cho/Cr were detected in the affected side of IL-Th, and lower Cho/Cr was positively correlated with MoCA values in the ITN group.

CONCLUSIONS

Our result of low level of NAA/Cr in the affected PM-Th probably serves as a marker of the pain-rating index, and decreased Cho/Cr in IL-Th may be an indicator of cognitive disorder in patients with ITN.

Alterations in regional homogeneity assessed by fMRI in patients with migraine without aura stratified by disease duration

Background

Advanced neuroimaging approaches have been employed to prove that migraine was a central nervous system disorder. This study aims to examine resting-state abnormalities in migraine without aura (MWoA) patients stratified by disease duration, and to explore the neuroimaging markers for reflecting the disease duration.

Methods

40 eligible MWoA patients and 20 matched healthy volunteers were included in the study. Regional homogeneity (ReHo) analysis was used to identify the local features of spontaneous brain activity in MWoA patients stratified by disease duration, and analysis was performed to investigate the correlation of overlapped brain dysfunction in MWoA patients with different disease duration (long-term and short-term) and course of disease.

Results

Compared with healthy controls, MWoA patients with long-term disease duration showed comprehensive neuronal dysfunction than patients with short-term disease duration. In addition, increased average ReHo values in the thalamus, brain stem, and temporal pole showed significantly positive correlations with the disease duration. On the contrary, ReHo values were negatively correlated with the duration of disease in the anterior cingulate cortex, insula, posterior cingulate cortex and superior occipital gyrus.

Conclusions

Our findings of progressive brain damage in relation to increasing disease duration suggest that migraine without aura is a progressive central nervous disease, and the length of the disease duration was one of the key reasons to cause brain dysfunction in MwoA patients. The repeated migraine attacks over time result in resting-state abnormalities of selective brain regions belonging to the pain processing and cognition. We predict that these brain regions are sensitive neuroimaging markers for reflecting the disease duration of migraine patients without aura.

Capturing brain metrics of neuropathic pain using nuclear magnetic resonance

SUMMARY Neuropathic pain is typically caused by a lesion or dysfunction in the nervous system that results in both negative (i.e., reduced sensitivity) and positive symptoms (i.e., paraesthesia, spontaneous ongoing pain with shooting, electric shock-like sensations and abnormal responses to evoked pain). Intriguingly, chronic pain disorders manifest profound alterations in brain structure and function, and thus, modern nuclear magnetic resonance (NMR) techniques have allowed us to begin to dissect the complexities of how neuropathic pain affects the brain. NMR approaches can be used as an independent measure to improve our understanding of key changes in brain structure, function and chemistry in chronic neuropathic pain. Accordingly, NMR techniques provide neurobiological metrics that allow us to understand the neurobiological basis of chronic neuropathic pain. Additionally, although at an early stage, NMR methods can also be useful to define clinical metrics to predict chronification of neuropathic pain and responses to drugs. This article provides a review of NMR techniques and their capacity to study spontaneous pain and evoked pain, as well as structural, functional and neurochemical alterations that have repeatedly been associated with chronic neuropathic pain. Finally, the importance for quantifying disease state and treatment efficacy in neuropathic pain using NMR techniques is discussed.

Mitochondrial dysfunction in migraine

Migraine is the most frequent type of headache in children. In the 1980s, scientists first hypothesized a connection between migraine and mitochondrial (mt) disorders. More recent studies have suggested that at least some subtypes of migraine may be related to a mt defect. Different types of evidence support a relationship between mitochondria (mt) and migraine: (1) Biochemical evidence: Abnormal mt function translates into high intracellular penetration of Ca(2+), excessive production of free radicals, and deficient oxidative phosphorylation, which ultimately causes energy failure in neurons and astrocytes, thus triggering migraine mechanisms, including spreading depression. The mt markers of these events are low activity of superoxide dismutase, activation of cytochrome-c oxidase and nitric oxide, high levels of lactate and pyruvate, and low ratios of phosphocreatine-inorganic phosphate and N-acetylaspartate-choline. (2) Morphologic evidence: mt abnormalities have been shown in migraine sufferers, the most characteristic ones being direct observation in muscle biopsy of ragged red and cytochrome-c oxidase-negative fibers, accumulation of subsarcolemmal mt, and demonstration of giant mt with paracrystalline inclusions. (3) Genetic evidence: Recent studies have identified specific mutations responsible for migraine susceptibility. However, the investigation of the mtDNA mutations found in classic mt disorders (mt encephalomyopathy with lactic acidosis and stroke-like episodes, myoclonus epilepsy with ragged red fibers, Kearns-Sayre syndrome, and Leber hereditary optic neuropathy) has not demonstrated any association. Recently, 2 common mtDNA polymorphisms (16519C→T and 3010G→A) have been associated with pediatric cyclic vomiting syndrome and migraine. Also, POLG mutations (eg, p.T851 A, p.N468D, p.Y831C, p.G517V, and p.P163S) can cause disease through impaired replication of mtDNA, including migraine. Further studies to investigate the relationship between mtDNA and migraine will require very large sample sizes to obtain statistically significant results. (4) Therapeutic evidence: Several agents that have a positive effect on mt metabolism have shown to be effective in the treatment of migraines. The agents include riboflavin (B2), coenzyme Q10, magnesium, niacin, carnitine, topiramate, and lipoic acid. Further study is warranted to learn how mt interact with other factors to cause migraines. This will facilitate the development of new and more specific treatments that will reduce the frequency or severity or both of this disease.

Magnetic resonance spectroscopy to assess neuroinflammation and neuropathic pain

Proton magnetic resonance spectroscopy ((1)H MRS) has been applied to numerous clinical studies, especially for neurological disorders. This technique can non-invasively evaluate brain metabolites and neurochemicals in selected brain regions and is particularly useful for assessing neuroinflammatory disorders. Neurometabolites assessed with MRS include the neuronal markers N-acetylaspartate (NAA) and glutamate (Glu), as well as the glial marker myo-inositol (MI). Therefore, the concentrations of these metabolites typically correspond to disease severity and often correlate well with clinical variables in the various brain disorders. Neuroinflammation with activated astrocytes and microglia in brain disorders are often associated with elevated MI, and to a lesser extent elevated total creatine (tCr) and choline containing compounds (Cho), which are found in higher concentrations in glia than neurons, while neuronal injury is indicated by lower than normal levels of NAA and Glu. This review summarizes the neurometabolite abnormalities found in MRS studies performed in patients with neuroinflammatory disorders or neuropathic pain, which also may be associated with neuroinflammation. These brain disorders include multiple sclerosis, neuroviral infections (including Human Immunodeficiency virus and Hepatitis C), degenerative brain disorders (including Alzheimer's disease and Parkinson's disease), stimulant abuse (including methamphetamine and cocaine) as well as several chronic pain syndromes.

Magnetic resonance spectroscopy in migraine: what have we learned so far?

OBJECTIVE

To summarize and evaluate proton ((1)H) and phosphorus ((31)P) magnetic resonance spectroscopy (MRS) findings in migraine.

METHODS

A thorough review of (1)H and/or (31)P-MRS studies in any form of migraine published up to September 2011.

RESULTS

Some findings were consistent in all studies, such as a lack of ictal/interictal brain pH change and a disturbed energy metabolism, the latter of which is reflected in a drop in phosphocreatine content, both in the resting brain and in muscle following exercise. In a recent interictal study ATP was found to be significantly decreased in the occipital lobe of migraine with aura patients, reinforcing the concept of a mitochondrial component to the migraine threshold, at least in a subgroup of patients. In several studies a correlation between the extent of the energy disturbance and the clinical phenotype severity was apparent. Less consistent but still congruent with a disturbed energy metabolism is an observed lactate increase in the occipital cortex of several migraine subtypes (MwA, migraine with prolonged aura). No increases in brain glutamate levels were found.

CONCLUSION

The combined abnormalities found in MRS studies imply a mitochondrial component in migraine neurobiology. This could be due to a primary mitochondrial dysfunction or be secondary to, for example, alterations in brain excitability. The extent of variation in the data can be attributed to both the variable clinical inclusion criteria used and the variation in applied methodology. Therefore it is necessary to continue to optimize MRS methodology to gain further insights, especially concerning lactate and glutamate.

Serum levels of N-acetyl-aspartate in migraine and tension-type headache

Serum levels of N-acetyl-aspartate (NAA) may be considered a useful marker of neuronal functioning. We aimed to measure serum NAA in cohorts of migraine and tension-type headache patients versus controls, performing correlations with main clinical features. A total of 147 migraine patients (including migraine without aura, with aura and chronic migraine), 65 tension-type headache (including chronic and frequent episodic tension-type headache) and 34 sex- and age-matched controls were selected. Serum was stored at -80 °C. Quantification of NAA was achieved by the standard addition approach and analysis was performed with liquid-chromatography-mass-spectrometry (LC/MS) technique. The NAA levels were significantly decreased in migraine group (0.065 ± 0.019 mol/L), compared with both tension-type headache patients (0.078 ± 0.016 mol/L) and controls (0.085 ± 0.013 mol/L). Control subjects were significantly different from migraine with and without aura and chronic migraine, who differed significantly from episodic and chronic tension-type headache. Migraine with aura patients showed lower NAA levels when compared to all the other headache subtypes, including migraine without aura and chronic migraine. In the migraine group, no significant correlation was found between NAA serum levels, and headache frequency, allodynia and interval from the last and the next attack. The low NAA in the serum may be a sign of neuronal dysfunction predisposing to migraine, probably based on reduced mitochondria function.

Imaging central neurochemical alterations in chronic pain with proton magnetic resonance spectroscopy

Proton magnetic resonance spectroscopy has been used extensively in the study of various neurobiological disorders: depression, schizophrenia, autism, etc. But its application to chronic pain is relatively new. Not many studies in chronic pain have used (1)H-MRS. The unique ability of (1)H-MRS to assess both static and dynamic levels of glutamate and γ-aminobutyric acid (GABA) gives this method a unique position in neuroscience. Emerging evidence in chronic pain suggests an elevated excitatory/inhibitory neurotransmitter ratio is present within brain regions involved in pain processing. The combination of (1)H-MRS imaging with pharmacologic interventions holds significant promise as a direct one-to-one matching of disease pathology with drug mechanism of action can be made. As such (1)H-MRS may be useful in discovery of novel compounds for chronic pain. Research in these areas may lead to improved diagnosis and treatment of these complex patients.

Reduced hippocampal glutamate-glutamine levels in irritable bowel syndrome: preliminary findings using magnetic resonance spectroscopy

OBJECTIVES

Enhanced stress responsiveness is an important pathophysiological factor in irritable bowel syndrome (IBS), suggesting the presence of a dysregulated hypothalamic-pituitary-adrenal (HPA) axis. A possible mechanism involves maladaption of the feedback mechanism of the HPA axis. We hypothesized that hippocampus, a key brain region providing inhibitory feedback to the HPA axis, would exhibit reduced excitatory glutamatergic neurotransmission and reduced N-acetyl-aspartate (NAA; a marker of neuronal integrity) levels in IBS patients.

METHODS

In this preliminary study, proton magnetic resonance spectroscopy was used to quantify absolute concentrations of metabolites in bilateral hippocampi of 15 IBS patients without significant psychiatric comorbidity and 15 age-matched controls.

RESULTS

The main finding was a reduction in hippocampal glutamate-glutamine (Glx) in IBS patients. Furthermore, Glx concentrations were inversely related to emotional stress indicators in patients only. No difference was found between subject groups for other metabolite concentrations, including NAA. However, an elevated myo-inositol (mI)/NAA ratio was found in IBS patients.

CONCLUSIONS

Our results provide preliminary evidence for the presence of abnormal hypofunction of hippocampal glutamatergic neurotransmission in IBS patients without psychiatric comorbidity, possibly as a result of the chronic pain. This supports the notion of an imbalance in regulatory brain regions in this subgroup of IBS patients. The inverse relationship between Glx and emotional stress indicators is in agreement with the inhibitory role of hippocampus on the stress system and suggests a sensitization of the mechanism to emotional arousal. The elevated mI/NAA ratio in IBS patients further suggests the presence of hippocampal glial proliferation and remodeling.

(1)H-MRS of brain metabolites in migraine without aura: absolute quantification using the phantom replacement technique

OBJECTIVE

Several studies have demonstrated differences in migraine patients when performing (1)H-MRS; however, no studies have performed (1)H-MRS in migraine without aura (MwoA), the most common migraine subtype. The aim of this (1)H-MRS study was to elucidate whether any differences could be found between MwoA patients and controls by performing absolute quantification.

MATERIALS AND METHODS

(1)H-MRS was performed in 22 MwoA patients and 25 control subjects. Absolute quantification was based on the phantom replacement technique. Corrections were made for T (1) and T (2) relaxation effects, CSF content, coil loading and temperature. The method was validated by phantom measurements and in vivo measurements in the occipital visual cortex.

RESULTS

After calibration of the quantification procedure and the implementation of the required correction factors, measured absolute concentrations in the visual cortex of MwoA patients showed no significant differences compared to controls, in contrast to relative results obtained in earlier studies.

CONCLUSION

In this study, we demonstrate the implementation of quantitative in vivo (1)H-MRS spectroscopy in migraine patients. Despite rigorous quantification, no spectroscopic abnormalities could be found in patients with migraine without aura.

Excitatory neurotransmitters in brain regions in interictal migraine patients

OBJECTIVE

To examine biochemical differences in the anterior cingulate cortex (ACC) and insula during the interictal phase of migraine patients. We hypothesized that there may be differences in levels of excitatory amino acid neurotransmitters and/or their derivatives in migraine group based on their increased sensitivity to pain.

METHODS

2D J-resolved proton magnetic resonance spectroscopy (1H-MRS) data were acquired at 4.0 Tesla (T) from the ACC and insula in 10 migraine patients (7 women, 3 men, age 43 +/- 11 years) and 8 age gender matched controls (7 women, 3 men, age 41 +/- 9 years).

RESULTS

Standard statistical analyses including analysis of variance (ANOVA) showed no significant metabolite differences between the two subject cohorts in the ACC nor the insula. However, linear discriminant analysis (LDA) introduced a clear separation between subject cohorts based on N-acetyl aspartylglutamate (NAAG) and glutamine (Gln) in the ACC and insula.

CONCLUSION

These results are consistent with glutamatergic abnormalities in the ACC and insula in migraine patients during their interictal period compared to healthy controls. An alteration in excitatory amino acid neurotransmitters and their derivatives may be a contributing factor for migraineurs for a decrease in sensitivity for migraine or a consequence of the chronic migraine state. Such findings, if extrapolated to other regions of the brain would offer new opportunities to modulate central system as interictal or preemptive medications in these patients.