A Guide to the Metabolic Pathways and Function of Metabolites Observed in Human Brain 1H Magnetic Resonance Spectra

Neurometabolite differences in Autism as assessed with Magnetic Resonance Spectroscopy: A systematic review and meta-analysis

1H-Magnetic Resonance Spectroscopy (MRS) is a non-invasive technique that can be used to quantify the concentrations of metabolites in the brain in vivo. MRS findings in the context of autism are inconsistent and conflicting. We performed a systematic review and meta-analysis of MRS studies measuring glutamate and gamma-aminobutyric acid (GABA), as well as brain metabolites involved in energy metabolism (glutamine, creatine), neural and glial integrity (e.g. n-acetyl aspartate (NAA), choline, myo-inositol) and oxidative stress (glutathione) in autism cohorts. Data were extracted and grouped by metabolite, brain region and several other factors before calculation of standardised effect sizes. Overall, we find significantly lower concentrations of GABA and NAA in autism, indicative of disruptions to the balance between excitation/inhibition within brain circuits, as well as neural integrity. Further analysis found these alterations are most pronounced in autistic children and in limbic brain regions relevant to autism phenotypes. Additionally, we show how study outcome varies due to demographic and methodological factors , emphasising the importance of conforming with standardised consensus study designs and transparent reporting.

Transcranial electrical stimulation modulates emotional experience and metabolites in the prefrontal cortex in a donation task

Understanding the neural, metabolic, and psychological mechanisms underlying human altruism and decision-making is a complex and important topic both for science and society. Here, we investigated whether transcranial Direct Current Stimulation (tDCS) applied to two prefrontal cortex regions, the ventromedial prefrontal cortex (vmPFC, anode) and the right dorsolateral prefrontal cortex (DLPFC, cathode) can induce changes in self-reported emotions and to modulate local metabolite concentrations. We employed in vivo quantitative MR Spectroscopy in healthy adult participants and quantified changes in GABA and Glx (glutamate + glutamine) before and after five sessions of tDCS delivered at 2 mA for 20 min (active group) and 1 min (sham group) while participants were engaged in a charitable donation task. In the active group, we observed increased levels of GABA in vmPFC. Glx levels decreased in both prefrontal regions and self-reported happiness increased significantly over time in the active group. Self-reported guiltiness in both active and sham groups tended to decrease. The results indicate that self-reported happiness can be modulated, possibly due to changes in Glx concentrations following repeated stimulation. Therefore, local changes may induce remote changes in the reward network through interactions with other metabolites, previously thought to be unreachable with noninvasive stimulation techniques.

Alterations in metabolites in the anterior cingulate cortex and thalamus and their associations with pain and empathy in patients with chronic mild pain: a preliminary study

Proton magnetic resonance spectroscopy (1H-MRS) has shown inconsistent alterations in the brain metabolites of individuals with chronic pain. We used 3T 1H-MRS to investigate the brain metabolites in the anterior cingulate cortex and thalamus of 22 patients with chronic mild pain and no gait disturbance and 22 healthy controls. The chronic-pain group included patients with chronic low back pain and/or osteoarthritis but none suffering from hypersensitivity. There were no significant between group-differences in glutamate, glutamate plus glutamine (Glx), N-acetylaspartate, glycerophosphorylcholine (GPC), glutamine, creatine plus phosphocreatine, or myo-inositol in the anterior cingulate cortex, but the patients showed a significant decrease in GPC, but not other metabolites, in the thalamus compared to the controls. The GPC values in the patients' thalamus were significantly correlated with pain components on the Short-Form McGill Pain Questionnaire (SF-MPQ-2) and affective empathy components on the Questionnaire of Cognitive and Affective Empathy (QCAE). The GPC in the patients' anterior cingulate cortex showed significant correlations with cognitive empathy components on the QCAE. Myo-inositol in the controls' anterior cingulate cortex and Glx in the patients' thalamus each showed significant relationships with peripheral responsivity on the QCAE. These significances were not significant after Bonferroni corrections. These preliminary findings indicate important roles of GPC, myo-inositol, and Glx in the brain of patients with chronic mild pain.

Imaging neuroinflammation in individuals with substance use disorders

Increasing evidence suggests a role of neuroinflammation in substance use disorders (SUDs). This Review presents findings from neuroimaging studies assessing brain markers of inflammation in vivo in individuals with SUDs. Most studies investigated the translocator protein 18 kDa (TSPO) using PET; neuroimmune markers myo-inositol, choline-containing compounds, and N-acetyl aspartate using magnetic resonance spectroscopy; and fractional anisotropy using MRI. Study findings have contributed to a greater understanding of neuroimmune function in the pathophysiology of SUDs, including its temporal dynamics (i.e., acute versus chronic substance use) and new targets for SUD treatment.

Investigating the brain's neurochemical profile at midlife in relation to dementia risk factors

Changes in the brain's physiology in Alzheimer's disease are thought to occur early in the disease's trajectory. In this study our aim was to investigate the brain's neurochemical profile in a midlife cohort in relation to risk factors for future dementia using single voxel proton magnetic resonance spectroscopy. Participants in the multi-site PREVENT-Dementia study (age range 40-59 year old) underwent 3T magnetic resonance spectroscopy with the spectroscopy voxel placed in the posterior cingulate/precuneus region. Using LCModel, we quantified the absolute concentrations of myo-inositol, total N-acetylaspartate, total creatine, choline, glutathione and glutamate-glutamine for 406 participants (mean age 51.1; 65.3% female). Underlying partial volume effects were accounted for by applying a correction for the presence of cerebrospinal fluid in the magnetic resonance spectroscopy voxel. We investigated how metabolite concentrations related to apolipoprotein ɛ4 genotype, dementia family history, a risk score (Cardiovascular Risk Factors, Aging and Incidence of Dementia -CAIDE) for future dementia including non-modifiable and potentially-modifiable factors and dietary patterns (adherence to Mediterranean diet). Dementia family history was associated with decreased total N-acetylaspartate and no differences were found between apolipoprotein ɛ4 carriers and non-carriers. A higher Cardiovascular Risk Factors, Aging, and Incidence of Dementia score related to higher myo-inositol, choline, total creatine and glutamate-glutamine, an effect which was mainly driven by older age and a higher body mass index. Greater adherence to the Mediterranean diet was associated with lower choline, myo-inositol and total creatine; these effects did not survive correction for multiple comparisons. The observed associations suggest that at midlife the brain demonstrates subtle neurochemical changes in relation to both inherited and potentially modifiable risk factors for future dementia.

Metabolic Diaschisis in Mild Traumatic Brain Injury

Neurophysiological diaschisis presents in traumatic brain injury (TBI) as functional impairment distant to the lesion site caused by axonal neuroexcitation and deafferentation. Diaschisis studies in TBI models have evaluated acute phase functional and microstructural changes. Here, in vivo biochemical changes and cerebral blood flow (CBF) dynamics following TBI are studied with magnetic resonance. Behavioral assessments, magnetic resonance spectroscopy (MRS), and CBF measurements on rats followed cortical impact TBI. Data were acquired pre-TBI and 1-3 h, 2-days, 7-days, and 14-days post-TBI. MRS was performed on the ipsilateral and contralateral sides in the cortex, striatum, and thalamus. Metabolites measured by MRS included N-acetyl aspartate (NAA), aspartate (Asp), lactate (Lac), glutathione (GSH), and glutamate (Glu). Lesion volume expanded for 2 days post-TBI and then decreased. Ipsilateral CBF dropped acutely versus baseline on both sides (-62% ipsilateral, -48% contralateral, p < 0.05) but then recovered in cortex, with similar changes in ipsilateral striatum. Metabolic changes versus baseline included increased Asp (+640% by Day 7 post-TBI, p < 0.05) and Lac (+140% on Day 2 post-TBI, p < 0.05) in ipsilateral cortex, while GSH (-67% acutely, p < 0.05) and NAA decreased (-50% on Day 2, p < 0.05). In contralateral cortex Lac decreased (-73% acutely, p < 0.05). Analysis of variance showed significance for Side (p < 0.05), Time after TBI (p < 0.05), and interactions (p < 0.005) for Asp, GSH, Lac, and NAA. Transient decreases of GSH (-30%, p < 0.05, acutely) and NAA (-23% on Day 2, p < 0.05) occurred in ipsilateral striatum with reduced GSH (-42%, p < 0.005, acutely) in the contralateral striatum. GSH was decreased in ipsilateral thalamus (-59% ipsilateral on Day 2, p < 0.05). Delayed increases of total choline were seen in the contralateral thalamus were noted as well (+21% on Day 7 post-TBI, p < 0.05). Both CBF and neurometabolite concentration changes occurred remotely from the TBI site, both ipsilaterally and contralaterally. Decreased Lac levels on the contralateral cortex following TBI may be indicative of reduced anaerobic metabolism during the acute phase. The timing and locations of the changes suggest excitatory and inhibitory signaling processes are affecting post-TBI metabolic fluctuations.

A preliminary study of dynamic neurochemical changes in the dorsolateral prefrontal cortex during working memory

Working memory (WM) is one of the fundamental cognitive functions associated with the dorsolateral prefrontal cortex (DLPFC). However, the neurochemical mechanisms of WM, including the dynamic changes in neurometabolites such as glutamate and GABA in the DLPFC, remain unclear. Here, we investigated WM-related glutamate and GABA changes, alongside hemodynamic responses in the DLPFC, using a combination of functional magnetic resonance spectroscopy (fMRS) and functional magnetic resonance imaging (fMRI). During a WM task, we measured Glx (glutamate + glutamine) and GABA levels using GABA editing MEscher-GArwood Point REsolved Spectroscopy (MEGA-PRESS) sequence and blood-oxygen-level-dependent (BOLD) signal changes. In the DLPFC, we observed elevated Glx levels and increased BOLD signal changes during a 2-back task. Specifically, the Glx levels in the DLPFC were significantly higher during the 2-back task compared with fixation, although this difference was not significant when compared with a 0-back task. However, Glx levels during the 0-back task were higher than during fixation. Furthermore, there was a positive correlation between Glx levels in the DLPFC during the 2-back task and the corresponding BOLD signal changes. Notably, higher Glx increases were associated with increased DLPFC activation and lower WM task performance in individuals. No notable changes in DLPFC GABA levels were observed during WM processing. These findings suggest that the modulation of glutamatergic activity in the DLPFC may play a crucial role in both working memory processing and its associated performance outcomes.

1H and 31P magnetic resonance spectroscopy reveals potential pathogenic and biomarker metabolite alterations in Lafora disease

Lafora disease is a fatal teenage-onset progressive myoclonus epilepsy and neurodegenerative disease associated with polyglucosan bodies. Polyglucosans are long-branched and as a result precipitation- and aggregation-prone glycogen. In mouse models, downregulation of glycogen synthase, the enzyme that elongates glycogen branches, prevents polyglucosan formation and rescues Lafora disease. Mouse work, however, has not yet revealed the mechanisms of polyglucosan generation, and few in vivo human studies have been performed. Here, non-invasive in vivo magnetic resonance spectroscopy (1H and 31P) was applied to test scan feasibility and assess neurotransmitter balance and energy metabolism in Lafora disease towards a better understanding of pathogenesis. Macromolecule-suppressed gamma-aminobutyric acid (GABA)-edited 1H magnetic resonance spectroscopy and 31P magnetic resonance spectroscopy at 3 and 7 tesla, respectively, were performed in 4 Lafora disease patients and a total of 21 healthy controls (12 for the 1H magnetic resonance spectroscopy and 9 for the 31PMRS). Spectra were processed using in-house software and fit to extract metabolite concentrations. From the 1H spectra, we found 33% lower GABA concentrations (P = 0.013), 34% higher glutamate + glutamine concentrations (P = 0.011) and 24% lower N-acetylaspartate concentrations (P = 0.0043) in Lafora disease patients compared with controls. From the 31P spectra, we found 34% higher phosphoethanolamine concentrations (P = 0.016), 23% lower nicotinamide adenine dinucleotide concentrations (P = 0.003), 50% higher uridine diphosphate glucose concentrations (P = 0.004) and 225% higher glucose 6-phosphate concentrations in Lafora disease patients versus controls (P = 0.004). Uridine diphosphate glucose is the substrate of glycogen synthase, and glucose 6-phosphate is its extremely potent allosteric activator. The observed elevated uridine diphosphate glucose and glucose 6-phosphate levels are expected to hyperactivate glycogen synthase and may underlie the generation of polyglucosans in Lafora disease. The increased glutamate + glutamine and reduced GABA indicate altered neurotransmission and energy metabolism, which may contribute to the disease's intractable epilepsy. These results suggest a possible basis of polyglucosan formation and potential contributions to the epilepsy of Lafora disease. If confirmed in larger human and animal model studies, measurements of the dysregulated metabolites by magnetic resonance spectroscopy could be developed into non-invasive biomarkers for clinical trials.

Diffusion of brain metabolites highlights altered brain microstructure in type C hepatic encephalopathy: a 9.4 T preliminary study

Introduction

Type C hepatic encephalopathy (HE) is a decompensating event of chronic liver disease leading to severe motor and cognitive impairment. The progression of type C HE is associated with changes in brain metabolite concentrations measured by 1H magnetic resonance spectroscopy (MRS), most noticeably a strong increase in glutamine to detoxify brain ammonia. In addition, alterations of brain cellular architecture have been measured ex vivo by histology in a rat model of type C HE. The aim of this study was to assess the potential of diffusion-weighted MRS (dMRS) for probing these cellular shape alterations in vivo by monitoring the diffusion properties of the major brain metabolites.

Methods

The bile duct-ligated (BDL) rat model of type C HE was used. Five animals were scanned before surgery and 6- to 7-week post-BDL surgery, with each animal being used as its own control. 1H-MRS was performed in the hippocampus (SPECIAL, TE = 2.8 ms) and dMRS in a voxel encompassing the entire brain (DW-STEAM, TE = 15 ms, diffusion time = 120 ms, maximum b-value = 25 ms/μm2) on a 9.4 T scanner. The in vivo MRS acquisitions were further validated with histological measures (immunohistochemistry, Golgi-Cox, electron microscopy).

Results

The characteristic 1H-MRS pattern of type C HE, i.e., a gradual increase of brain glutamine and a decrease of the main organic osmolytes, was observed in the hippocampus of BDL rats. Overall increased metabolite diffusivities (apparent diffusion coefficient and intra-stick diffusivity-Callaghan's model, significant for glutamine, myo-inositol, and taurine) and decreased kurtosis coefficients were observed in BDL rats compared to control, highlighting the presence of osmotic stress and possibly of astrocytic and neuronal alterations. These results were consistent with the microstructure depicted by histology and represented by a decline in dendritic spines density in neurons, a shortening and decreased number of astrocytic processes, and extracellular edema.

Discussion

dMRS enables non-invasive and longitudinal monitoring of the diffusion behavior of brain metabolites, reflecting in the present study the globally altered brain microstructure in BDL rats, as confirmed ex vivo by histology. These findings give new insights into metabolic and microstructural abnormalities associated with high brain glutamine and its consequences in type C HE.

Assessment of sepsis-associated encephalopathy by quantitative magnetic resonance spectroscopy in a rat model of cecal ligation and puncture

Proton magnetic resonance spectroscopy (1H-MRS) is the only non-invasive technique to quantify neurometabolic compounds in the living brain. We used 1H-MRS to evaluate the brain metabolites in a rat model of Sepsis-associated encephalopathy (SAE) established by cecal ligation and puncture (CLP). 36 male Sprague-Dawley rats were randomly divided into sham and CLP groups. Each group was further divided into three subgroups: subgroup O, subgroup M, and subgroup N. Neurological function assessments were performed on the animals in the subgroup O and subgroup N at 24 h, 48 h, and 72 h. The animals in the subgroup M were examined by magnetic resonance imaging (MRI) at 12 h after CLP. Compared with the sham group, the ratio of N-acetylaspartate (NAA) to creatine (Cr) in the hippocampus was significantly lower in the CLP group. The respective ratios of lactate (Lac), myo-inositol (mIns), glutamate and glutamine (Glx), lipid (Lip), and choline (Cho) to Cr in the CLP group were clearly higher than those in the sham group. Cytochrome c, intimately related to oxidative stress, was elevated in the CLP group. Neurofilament light (NfL) chain and glial fibrillary acidic protein (GFAP) scores in the CLP group were significantly higher than those in the sham group, while zonula occludens-1 (ZO-1) was downregulated. Compared with the sham group, the CLP group displayed higher values of oxygen extraction fraction (OEF), central venous-arterial partial pressure of carbon dioxide (P (cv-a) CO2), and central venous lactate (VLac). In contrast, jugular venous oxygen saturation (SjvO2) declined. In the present study, 1H-MRS could be used to quantitatively assess brain injury in terms of microcirculation disorder, oxidative stress, blood-brain barrier disruption, and glial cell activation through changes in metabolites within brain tissue.

Inhibition of urease-mediated ammonia production by 2-octynohydroxamic acid in hepatic encephalopathy

Hepatic encephalopathy is a neuropsychiatric complication of liver disease which is partly associated with elevated ammonemia. Urea hydrolysis by urease-producing bacteria in the colon is often mentioned as one of the main routes of ammonia production in the body, yet research on treatments targeting bacterial ureases in hepatic encephalopathy is limited. Herein we report a hydroxamate-based urease inhibitor, 2-octynohydroxamic acid, exhibiting improved in vitro potency compared to hydroxamic acids that were previously investigated for hepatic encephalopathy. 2-octynohydroxamic acid shows low cytotoxic and mutagenic potential within a micromolar concentration range as well as reduces ammonemia in rodent models of liver disease. Furthermore, 2-octynohydroxamic acid treatment decreases cerebellar glutamine, a product of ammonia metabolism, in male bile duct ligated rats. A prototype colonic formulation enables reduced systemic exposure to 2-octynohydroxamic acid in male dogs. Overall, this work suggests that urease inhibitors delivered to the colon by means of colonic formulations represent a prospective approach for the treatment of hepatic encephalopathy.

Inhibition of anaerobic digestion by various ammonia sources resulted in subtle differences in metabolite dynamics

The impact of ammonia on anaerobic digestion performance and microbial dynamics has been extensively studied, but the concurrent effect of anions brought by ammonium salt should not be neglected. This paper studied this effect using metabolomics and a time-course statistical framework. Metabolomics provides novel perspectives to study microbial processes and facilitates a more profound understanding at the metabolic level. The advanced statistical framework enables deciphering the complexity of large metabolomics data sets. More specifically, a series of lab-scale batch reactors were set up with different ammonia sources added. Samples of nine time points over the degradation were analyzed with liquid chromatography-mass spectrometry. A filtering procedure was applied to select the promising metabolomic peaks from 1262 peaks, followed by modeling their intensities across time. The metabolomic peaks with similar time profiles were clustered, evidencing the correlation of different biological processes. Differential analysis was performed to seek the differences in metabolite dynamics caused by different anions. Finally, tandem mass spectrometry and metabolite annotation provided further information on the molecular structure and possible metabolic pathways. For example, the consumption of 5-aminovaleric acid, a short-chain fatty acid obtained from l-lysine degradation, was slowed down by phosphates. Overall, by investigating the effect of anions on anaerobic digestion, our study demonstrated the effectiveness of metabolomics in providing detailed information in a set of samples from different experimental conditions. With the statistical framework, the approach enables capturing subtle differences in metabolite dynamics between samples while accounting for the differences caused by time variations.

The developmental trajectory of 1H-MRS brain metabolites from childhood to adulthood

Human brain development is ongoing throughout childhood, with for example, myelination of nerve fibers and refinement of synaptic connections continuing until early adulthood. 1H-Magnetic Resonance Spectroscopy (1H-MRS) can be used to quantify the concentrations of endogenous metabolites (e.g. glutamate and γ -aminobutyric acid (GABA)) in the human brain in vivo and so can provide valuable, tractable insight into the biochemical processes that support postnatal neurodevelopment. This can feasibly provide new insight into and aid the management of neurodevelopmental disorders by providing chemical markers of atypical development. This study aims to characterize the normative developmental trajectory of various brain metabolites, as measured by 1H-MRS from a midline posterior parietal voxel. We find significant non-linear trajectories for GABA+ (GABA plus macromolecules), Glx (glutamate + glutamine), total choline (tCho) and total creatine (tCr) concentrations. Glx and GABA+ concentrations steeply decrease across childhood, with more stable trajectories across early adulthood. tCr and tCho concentrations increase from childhood to early adulthood. Total N-acetyl aspartate (tNAA) and Myo-Inositol (mI) concentrations are relatively stable across development. Trajectories likely reflect fundamental neurodevelopmental processes (including local circuit refinement) which occur from childhood to early adulthood and can be associated with cognitive development; we find GABA+ concentrations significantly positively correlate with recognition memory scores.

Early rise of glutamate-glutamine levels in mild cognitive impairment: Evidence for emerging excitotoxicity

BACKGROUND

Use proton magnetic resonance spectroscopy (1H-MRS) non invasive technique to assess the modifications of glutamate-glutamine (Glx) and gammaaminobutyric acid (GABA) brain levels in patients reporting a cognitive complain METHODS: Posterior cingular cortex 1H-MRS spectra of 46 patients (19 male, 27 female) aged 57 to 87 years (mean : 73.32 ± 7.33 years) with a cognitive complaint were examined with a MEGA PRESS sequence at 3T, and compounds Glutamateglutamine (Glx), GABA, Creatine (Cr) and NAA were measured. From this data the metabolite ratios Glx/Cr, GABA/Cr and NAA/Cr were calculated. In addition, all patient performed the Mini Mental State Evaluation (MMSE) and 2 groups were realized with the clinical threshold of 24.

RESULTS

16 patients with MMSE 〈 24 and 30 patients with MMSE 〉 24. Significant increase of Glx/Cr in PCC of patients with MMSE 〈 24 compared to patients with MMSE 〉 24. Moreover, GABA/Cr ratio exhibited a trend for a decrease in PCC between the two groups, while they showed a significant decrease NAA/Cr ratio.

CONCLUSION

Our results concerning Glx are in agreement with a physiopathological hypothesis involving a biphasic variation of glutamate levels associated with excitotoxicity, correlated with the clinical evolution of the disease. These observations suggest that MRS assessment of glutamate levels could be helpful for both diagnosis and classification of cognitive impairment in stage.

Longitudinal changes in brain metabolites following pediatric concussion

Concussion is commonly characterized by a cascade of neurometabolic changes following injury. Magnetic Resonance Spectroscopy (MRS) can be used to quantify neurometabolites non-invasively. Longitudinal changes in neurometabolites have rarely been studied in pediatric concussion, and fewer studies consider symptoms. This study examines longitudinal changes of neurometabolites in pediatric concussion and associations between neurometabolites and symptom burden. Participants who presented with concussion or orthopedic injury (OI, comparison group) were recruited. The first timepoint for MRS data collection was at a mean of 12 days post-injury (n = 545). Participants were then randomized to 3 (n = 243) or 6 (n = 215) months for MRS follow-up. Parents completed symptom questionnaires to quantify somatic and cognitive symptoms at multiple timepoints following injury. There were no significant changes in neurometabolites over time in the concussion group and neurometabolite trajectories did not differ between asymptomatic concussion, symptomatic concussion, and OI groups. Cross-sectionally, Choline was significantly lower in those with persistent somatic symptoms compared to OI controls at 3 months post-injury. Lower Choline was also significantly associated with higher somatic symptoms. Although overall neurometabolites do not change over time, choline differences that appear at 3 months and is related to somatic symptoms.

Magnetic resonance spectroscopy in the hippocampus of adult APP/PS1 mice following chronic vitamin D deficiency

Vitamin D (VitD) deficiency can exacerbate AD progression and may cause changes in brain metabolite levels that can be detected by magnetic resonance spectroscopy (MRS). The purpose of this study was to determine whether chronic VitD deficiency in an AD mouse model caused persistent metabolite levels changes in the hippocampus associated with memory performance. Six-month-old APPSwe/PS1ΔE9 (APP/PS1) mice (N = 14 mice/group) were fed either a VitD deficient (VitD-) diet or a control diet. Metabolite level changes in the hippocampus were evaluated by 1H MRS using a 9.4 T MRI. Ventricle volume was assessed by imaging and spatial memory was evaluated using the Barnes maze. All measurements were made at 6, 9, 12, and 15 months of age. At 15 months of age, amyloid plaque load and astrocyte number were evaluated histologically (N = 4 mice/group). Levels of N-acetyl aspartate and creatine were lower in VitD- mice compared to control diet mice at 12 months of age. VitD deficiency did not change ventricle volume. Lactate levels increased over time in VitD- mice and increases from 12 to 15 months were negatively correlated with changes in primary latency to the target hole in the Barns Maze. VitD- mice showed improved spatial memory performance compared to control diet mice. VitD- mice also had more astrocytes in the cortex and hippocampus at 15 months than control diet mice. This study suggests that severe VitD deficiency in APP/PS1 mice may lead to compensatory changes in metabolite and astrocyte levels that contribute to improved performance on spatial memory tasks.

Interhemispheric reactivity of the subthalamic nucleus sustains progressive dopamine neuron loss in asymmetrical parkinsonism

Parkinson's disease (PD) is characterized by the progressive and asymmetrical degeneration of the nigrostriatal dopamine neurons and the unilateral presentation of the motor symptoms at onset, contralateral to the most impaired hemisphere. We previously developed a rat PD model that mimics these typical features, based on unilateral injection of a substrate inhibitor of excitatory amino acid transporters, L-trans-pyrrolidine-2,4-dicarboxylate (PDC), in the substantia nigra (SN). Here, we used this progressive model in a multilevel study (behavioral testing, in vivo 1H-magnetic resonance spectroscopy, slice electrophysiology, immunocytochemistry and in situ hybridization) to characterize the functional changes occurring in the cortico-basal ganglia-cortical network in an evolving asymmetrical neurodegeneration context and their possible contribution to the cell death progression. We focused on the corticostriatal input and the subthalamic nucleus (STN), two glutamate components with major implications in PD pathophysiology. In the striatum, glutamate and glutamine levels increased from presymptomatic stages in the PDC-injected hemisphere only, which also showed enhanced glutamatergic transmission and loss of plasticity at corticostriatal synapses assessed at symptomatic stage. Surprisingly, the contralateral STN showed earlier and stronger reactivity than the ipsilateral side (increased intraneuronal cytochrome oxidase subunit I mRNA levels; enhanced glutamate and glutamine concentrations). Moreover, its lesion at early presymptomatic stage halted the ongoing neurodegeneration in the PDC-injected SN and prevented the expression of motor asymmetry. These findings reveal the existence of endogenous interhemispheric processes linking the primary injured SN and the contralateral STN that could sustain progressive dopamine neuron loss, opening new perspectives for disease-modifying treatment of PD.

Neurochemical differences in core regions of the autistic brain: a multivoxel 1H-MRS study in children

Autism spectrum disorder (ASD) is a neurodevelopmental condition which compromises various cognitive and behavioural domains. The understanding of the pathophysiology and molecular neurobiology of ASD is still an open critical research question. Here, we aimed to address ASD neurochemistry in the same time point at key regions that have been associated with its pathophysiology: the insula, hippocampus, putamen and thalamus. We conducted a multivoxel proton magnetic resonance spectroscopy (1H-MRS) study to non-invasively estimate the concentrations of total choline (GPC + PCh, tCho), total N-acetyl-aspartate (NAA + NAAG, tNAA) and Glx (Glu + Gln), presenting the results as ratios to total creatine while investigating replication for ratios to total choline as a secondary analysis. Twenty-two male children aged between 10 and 18 years diagnosed with ASD (none with intellectual disability, in spite of the expected lower IQ) and 22 age- and gender-matched typically developing (TD) controls were included. Aspartate ratios were significantly lower in the insula (tNAA/tCr: p = 0.010; tNAA/tCho: p = 0.012) and putamen (tNAA/tCr: p = 0.015) of ASD individuals in comparison with TD controls. The Glx ratios were significantly higher in the hippocampus of the ASD group (Glx/tCr: p = 0.027; Glx/tCho: p = 0.011). Differences in tNAA and Glx indices suggest that these metabolites might be neurochemical markers of region-specific atypical metabolism in ASD children, with a potential contribution for future advances in clinical monitoring and treatment.

Age-related fornix decline predicts conservative response strategy-based slowing in perceptual decision-making

Aging leads to response slowing but the underpinning cognitive and neural mechanisms remain elusive. We modelled older and younger adults' response times (RT) from a flanker task with a diffusion drift model (DDM) and employed diffusion-weighted magnetic resonance imaging and spectroscopy to study neurobiological predictors of DDM components (drift-rate, boundary separation, non-decision time). Microstructural indices were derived from white matter pathways involved in visuo-perceptual and attention processing [optic radiation, inferior and superior longitudinal fasciculi (ILF, SLF), fornix]. Estimates of metabolite concentrations [N-acetyl aspartate (NAA), glutamate (Glx), and γ-aminobutyric acid (GABA), creatine (Cr), choline (Cho), myoinositol (mI)] were measured from occipital (OCC), anterior cingulate (ACC) and posterior parietal cortices (PPC). Age-related increases in RT, boundary separation, and non-decision time were observed with response conservatism acounting for RT slowing. Aging was associated with reductions in white matter microstructure (lower fractional anisotropy and restricted signal fraction, larger diffusivities) and in metabolites (NAA in ACC and PPC, Glx in ACC). Regression analyses identified brain regions involved in top-down (fornix, SLF, ACC, PPC) and bottom-up (ILF, optic radiation OCC) processing as predictors for DDM parameters and RT. Fornix FA was the strongest predictor for increases in boundary separation (beta = -0.8) and mediated the effects of age on RT. These findings demonstrate that response slowing in visual discrimination is driven by the adoption of a more conservative response strategy. Age-related fornix decline may result in noisier communication of contextual information from the hippocampus to anterior decision-making regions and thus contribute to the conservative response strategy shift.

Cortical glutamate, Glx, and total N-acetylaspartate: potential biomarkers of repetitive transcranial magnetic stimulation treatment response and outcomes in major depression

Repetitive transcranial magnetic stimulation (rTMS) is an effective treatment for individuals with major depressive disorder (MDD) who have not improved with standard therapies. However, only 30-45% of patients respond to rTMS. Predicting response to rTMS will benefit both patients and providers in terms of prescribing and targeting treatment for maximum efficacy and directing resources, as individuals with lower likelihood of response could be redirected to more suitable treatment alternatives. In this exploratory study, our goal was to use proton magnetic resonance spectroscopy to examine how glutamate (Glu), Glx, and total N-acetylaspartate (tNAA) predict post-rTMS changes in overall MDD severity and symptoms, and treatment response. Metabolites were measured in a right dorsal anterior cingulate cortex voxel prior to a standard course of 10 Hz rTMS to the left DLPFC in 25 individuals with MDD. MDD severity and symptoms were evaluated via the Inventory of Depression Symptomatology Self-Report (IDS-SR). rTMS response was defined as ≥50% change in full-scale IDS-SR scores post treatment. Percent change in IDS-SR symptom domains were evaluated using principal component analysis and established subscales. Generalized linear and logistic regression models were used to evaluate the relationship between baseline Glu, Glx, and tNAA and outcomes while controlling for age and sex. Participants with baseline Glu and Glx levels in the lower range had greater percent change in full scale IDS-SR scores post-treatment (p < 0.001), as did tNAA (p = 0.007). Low glutamatergic metabolite levels also predicted greater percent change in mood/cognition symptoms (p ≤ 0.001). Low-range Glu, Glx, and tNAA were associated with greater improvement on the immuno-metabolic subscale (p ≤ 0.003). Baseline Glu predicted rTMS responder status (p = 0.025) and had an area under the receiving operating characteristic curve of 0.81 (p = 0.009), demonstrating excellent discriminative ability. Baseline Glu, Glx, and tNAA significantly predicted MDD improvement after rTMS; preliminary evidence also demonstrates metabolite association with symptom subdomain improvement post-rTMS. This work provides feasibility for a personalized medicine approach to rTMS treatment selection, with individuals with Glu levels in the lower range potentially being the best candidates.

Altered metabolites in the periaqueductal gray of COVID-19 patients experiencing headaches: a longitudinal MRS study

Background

Headache is one of the most common symptoms of acute COVID-19 infection. However, its mechanisms remain poorly understood, and there is a lack of studies investigating changes in the periaqueductal gray (PAG) in COVID-19 patients exhibiting headaches.

Purpose

The study aimed to explore the alterations in metabolites of the PAG pre- and post-COVID-19 infection in individuals who suffered from headaches during the acute phase of the disease using proton magnetic resonance spectroscopy (1H-MRS).

Methods

Fifteen participants who experienced headaches during the acute phase of COVID-19 were recruited. All subjects underwent two proton magnetic resonance spectroscopy (1H-MRS) examinations focusing on the PAG before and after they were infected. Metabolite changes were assessed between the pre- and post-infection groups.

Results

The combined glutamine and glutamate/total creatine ratio (Glx/tCr) was increased in the PAG following COVID-19 infection. The total choline/total creatine ratio (tCho/tCr) in the pre-infection group was negatively correlated with the duration of headache during the COVID-19 acute phase.

Conclusion

The present study indicates that PAG plays a pivotal role in COVID-19 headaches, thereby supporting the involvement of trigeminovascular system activation in the pathophysiology of COVID-19 headaches.

The Lack of Alterations in Metabolites in the Medial Prefrontal Cortex and Amygdala, but Their Associations with Autistic Traits, Empathy, and Personality Traits in Adults with Autism Spectrum Disorder: A Preliminary Study

Proton magnetic resonance spectroscopy (1H-MRS) has shown inconsistent alterations in brain metabolites of adults with autism spectrum disorder (ASD). We investigated brain metabolites in the medial prefrontal cortex and amygdala of 24 drug-naive adults with ASD and no intellectual disability and 24 non-ASD control subjects, using 3 T 1H-MRS. Adults with ASD showed no significant differences from control in glutamate, glutamate plus glutamine, N-acetylaspartate, glycerophosphorylcholine plus phosphorylcholine, creatine plus phosphocreatine, or myo-inositol in either region. However, ASD subjects did show significant correlations of localized brain metabolites with autistic traits, empathy deficits, and personality traits using the Autism-Spectrum Quotient, Questionnaire of Cognitive and Affective Empathy, Interpersonal Reactivity Index, and NEO Personality Inventory-Revised. These findings should be taken as preliminary or exploratory.

Brain Temperature as an Indicator of Cognitive Function in Traumatic Brain Injury Patients

Whether brain temperature noninvasively extracted by magnetic resonance imaging has a role in identifying brain changes in the later phases of mild to moderate traumatic brain injury (TBI) is not known. This prospective study aimed to evaluate if TBI patients in subacute and chronic phases had altered brain temperature measured by whole-brain magnetic resonance spectroscopic imaging (WB-MRSI) and if the measurable brain temperature had any relationship with cognitive function scores. WB-MRSI was performed on eight TBI patients and fifteen age- and sex-matched control subjects. Brain temperature (T) was extracted from the brain's major metabolites and compared between the two groups. The T of the patients was tested for correlation with cognitive function test scores. The results showed significantly lower brain temperature in the TBI patients (p < 0.05). Brain temperature derived from N-acetylaspartate (TNAA) strongly correlated with the 2 s paced auditory serial addition test (PASAT-2s) score (p < 0.05). The observation of lower brain temperature in TBI patients may be due to decreased metabolic activity resulting from glucose and oxygen depletion. The correlation of brain temperature with PASAT-2s may imply that noninvasive brain temperature may become a noninvasive index reflecting cognitive performance.

Investigating neural dysfunction with abnormal protein deposition in Alzheimer's disease through magnetic resonance spectroscopic imaging, plasma biomarkers, and positron emission tomography

In Alzheimer's disease (AD), aggregated abnormal proteins induce neuronal dysfunction. Despite the evidence supporting the association between tau proteins and brain atrophy, further studies are needed to explore their link to neuronal dysfunction in the human brain. To clarify the relationship between neuronal dysfunction and abnormal proteins in AD-affected brains, we conducted magnetic resonance spectroscopic imaging (MRSI) and assessed the neurofilament light chain plasma levels (NfL). We evaluated tau and amyloid-β depositions using standardized uptake value ratios (SUVRs) of florzolotau (18F) for tau and 11C-PiB for amyloid-β positron emission tomography in the same patients. Heatmaps were generated to visualize Z scores of glutamate to creatine (Glu/Cr) and N-acetylaspartate to creatine (NAA/Cr) ratios using data from healthy controls. In AD brains, Z score maps revealed reduced Glu/Cr and NAA/Cr ratios in the gray matter, particularly in the right dorsolateral prefrontal cortex (rDLPFC) and posterior cingulate cortex (PCC). Glu/Cr ratios were negatively correlated with florzolotau (18F) SUVRs in the PCC, and plasma NfL levels were elevated and negatively correlated with Glu/Cr (P = 0.040, r = -0.50) and NAA/Cr ratios (P = 0.003, r = -0.68) in the rDLPFC. This suggests that the abnormal tau proteins in AD-affected brains play a role in diminishing glutamate levels. Furthermore, neuronal dysfunction markers including Glu/tCr and NAA/tCr could potentially indicate favorable clinical outcomes. Using MRSI provided spatial information about neural dysfunction in AD, enabling the identification of vulnerabilities in the rDLPFC and PCC within the AD's pathological context.

A neurophysiological signature of dynamic emotion recognition associated with social communication skills and cortical gamma-aminobutyric acid levels in children

Introduction

Emotion recognition is a core feature of social perception. In particular, perception of dynamic facial emotional expressions is a major feature of the third visual pathway. However, the classical N170 visual evoked signal does not provide a pure correlate of such processing. Indeed, independent component analysis has demonstrated that the N170 component is already active at the time of the P100, and is therefore distorted by early components. Here we implemented, a dynamic face emotional paradigm to isolate a more pure face expression selective N170. We searched for a neural correlate of perception of dynamic facial emotional expressions, by starting with a face baseline from which a facial expression evolved. This allowed for a specific facial expression contrast signal which we aimed to relate with social communication abilities and cortical gamma-aminobutyric acid (GABA) levels.

Methods

We recorded event-related potentials (ERPs) and Magnetic Resonance (MRS) measures in 35 typically developing (TD) children, (10-16 years) sex-matched, during emotion recognition of an avatar morphing/unmorphing from neutral to happy/sad expressions. This task allowed for the elimination of the contribution low-level visual components, in particular the P100, by morphing baseline isoluminant neutral faces into specific expressions, isolating dynamic emotion recognition. Therefore, it was possible to isolate a dynamic face sensitive N170 devoid of interactions with earlier components.

Results

We found delayed N170 and P300, with a hysteresis type of dependence on stimulus trajectory (morphing/unmorphing), with hemispheric lateralization. The delayed N170 is generated by an extrastriate source, which can be related to the third visual pathway specialized in biological motion processing. GABA levels in visual cortex were related with N170 amplitude and latency and predictive of worse social communication performance (SCQ scores). N170 latencies reflected delayed processing speed of emotional expressions and related to worse social communication scores.

Discussion

In sum, we found a specific N170 electrophysiological signature of dynamic face processing related to social communication abilities and cortical GABA levels. These findings have potential clinical significance supporting the hypothesis of a spectrum of social communication abilities and the identification of a specific face-expression sensitive N170 which can potentially be used in the development of diagnostic and intervention tools.

Cortical GABA Levels Are Reduced in Post-Acute COVID-19 Syndrome

After recovering from the acute COVID-19 illness, a substantial proportion of people continue experiencing post-acute sequelae of COVID-19 (PASC), also termed "long COVID". Their quality of life is adversely impacted by persistent cognitive dysfunction and affective distress, but the underlying neural mechanisms are poorly understood. The present study recruited a group of mostly young, previously healthy adults (24.4 ± 5.2 years of age) who experienced PASC for almost 6 months following a mild acute COVID-19 illness. Confirming prior evidence, they reported noticeable memory and attention deficits, brain fog, depression/anxiety, fatigue, and other symptoms potentially suggestive of excitation/inhibition imbalance. Proton magnetic resonance spectroscopy (1H-MRS) was used to examine the neurochemical aspects of cell signaling with an emphasis on GABA levels in the occipital cortex. The PASC participants were compared to a control (CNT) group matched in demographics, intelligence, and an array of other variables. Controlling for tissue composition, biological sex, and alcohol intake, the PASC group had lower GABA+/water than CNT, which correlated with depression and poor sleep quality. The mediation analysis revealed that the impact of PASC on depression was partly mediated by lower GABA+/water, indicative of cortical hyperexcitability as an underlying mechanism. In addition, N-acetylaspartate (NAA) tended to be lower in the PASC group, possibly suggesting compromised neuronal integrity. Persistent neuroinflammation may contribute to the pathogenesis of PASC-related neurocognitive dysfunction.

Excitatory-inhibitory modulation of transcranial focus ultrasound stimulation on human motor cortex

AIMS

Transcranial focus ultrasound stimulation (tFUS) is a promising non-invasive neuromodulation technology. This study aimed to evaluate the modulatory effects of tFUS on human motor cortex (M1) excitability and explore the mechanism of neurotransmitter-related intracortical circuitry and plasticity.

METHODS

Single pulse transcranial magnetic stimulation (TMS)-eliciting motor-evoked potentials (MEPs) were used to assessed M1 excitability in 10 subjects. Paired-pulse TMS was used to measure the effects of tFUS on GABA- and glutamate-related intracortical excitability and 1 H-MRS was used to assess the effects of repetitive tFUS on GABA and Glx (glutamine + glutamate) neurometabolic concentrations in the targeting region in nine subjects.

RESULTS

The etFUS significantly increased M1 excitability, decreased short interval intracortical inhibition (SICI) and long interval intracortical inhibition (LICI). The itFUS significantly suppressed M1 excitability, increased SICI, LICI, and decreased intracortical facilitation (ICF). Seven times of etFUS decreased the GABA concentration (6.32%), increased the Glx concentration (12.40%), and decreased the GABA/Glx ratio measured by MRS, while itFUS increased the GABA concentration (18.59%), decreased Glx concentration (0.35%), and significantly increased GABA/Glx ratio.

CONCLUSION

The findings support that tFUS with different parameters can exert excitatory and inhibitory neuromodulatory effects on the human motor cortex. We provide novel insights that tFUS change cortical excitability and plasticity by regulating excitatory-inhibition balance related to the GABAergic and glutamatergic receptor function and neurotransmitter metabolic level.

Increased cerebral lactate levels in adults with autism spectrum disorders compared to non-autistic controls: a magnetic resonance spectroscopy study

INTRODUCTION

Autism spectrum disorder (ASD) encompasses a heterogeneous group with varied phenotypes and etiologies. Identifying pathogenic subgroups could facilitate targeted treatments. One promising avenue is investigating energy metabolism, as mitochondrial dysfunction has been implicated in a subgroup of ASD. Lactate, an indicator of energy metabolic anomalies, may serve as a potential biomarker for this subgroup. This study aimed to examine cerebral lactate (Lac+) levels in high-functioning adults with ASD, hypothesizing elevated mean Lac+ concentrations in contrast to neurotypical controls (NTCs).

MATERIALS AND METHODS

Magnetic resonance spectroscopy (MRS) was used to study cerebral Lac+ in 71 adults with ASD and NTC, focusing on the posterior cingulate cortex (PCC). After quality control, 64 ASD and 58 NTC participants remained. Lac+ levels two standard deviations above the mean of the control group were considered elevated.

RESULTS

Mean PCC Lac+ levels were significantly higher in the ASD group than in the NTC group (p = 0.028; Cohen's d = 0.404), and 9.4% of the ASD group had elevated levels as compared to 0% of the NTCs (p = 0.029). No significant correlation was found between blood serum lactate levels and MRS-derived Lac+ levels.

LIMITATIONS

A cautious interpretation of our results is warranted due to a p value of 0.028. In addition, a higher than anticipated proportion of data sets had to be excluded due to poor spectral quality.

CONCLUSION

This study confirms the presence of elevated cerebral Lac+ levels in a subgroup of adults with ASD, suggesting the potential of lactate as a biomarker for mitochondrial dysfunction in a subgroup of ASD. The lower-than-expected prevalence (20% was expected) and moderate increase require further investigation to elucidate the underlying mechanisms and relationships with mitochondrial function.

The multi-level outcome study of psychoanalysis for chronically depressed patients with early trauma (MODE): rationale and design of an international multicenter randomized controlled trial

BACKGROUND

Whether and how psychotherapies change brain structure and function is unknown. Its study is of great importance for contemporary psychotherapy, as it may lead to discovery of neurobiological mechanisms that predict and mediate lasting changes in psychotherapy, particularly in severely mentally ill patients, such as those with chronic depression. Previous studies have shown that psychoanalytic psychotherapies produce robust and enduring improvements in not only symptom severity but also personality organization in patients who have chronic depression and early life trauma, especially if therapy is delivered at a high weekly frequency.

METHODS/DESIGN

Patients with chronic major depression and a history of early life trauma will be recruited, assessed, and treated across 3 international sites: Germany, Switzerland, and the United States. They will be randomized to one of two treatment arms: either (1) once weekly psychoanalytic psychotherapies, or (2) 3-4 times weekly psychoanalytic psychotherapies. They will have full clinical characterization as well as undergo MRI scanning at study baseline prior to randomization and again one year later. A group of matched healthy controls will undergo similar assessments and MRI scanning at the same time points to help discern whether study treatments induce brain changes toward or away from normal values. Primary study outcomes will include anatomical MRI, functional MRI, and Diffusion Tensor Imaging measures. Study hypotheses will be tested using the treatment-by-time interaction assessed in multiple general linear models with repeated measures analyses in an intent-to-treat analysis.

DISCUSSION

MODE may allow the identification of brain-based biomarkers that may be more sensitive than traditional behavioral and clinical measures in discriminating, predicting, and mediating treatment response. These findings could help to personalize care for patients who have chronic depression patients and early life trauma, and they will provide new therapeutic targets for both psychological and biological treatments for major depressive illness.

Smoking, tobacco dependence, and neurometabolites in the dorsal anterior cingulate cortex

Cigarette smoking has a major impact on global health and morbidity, and positron emission tomographic research has provided evidence for reduced inflammation in the human brain associated with cigarette smoking. Given the consequences of inflammatory dysfunction for health, the question of whether cigarette smoking affects neuroinflammation warrants further investigation. The goal of this project therefore was to validate and extend evidence of hypoinflammation related to smoking, and to examine the potential contribution of inflammation to clinical features of smoking. Using magnetic resonance spectroscopy, we measured levels of neurometabolites that are putative neuroinflammatory markers. N-acetyl compounds (N-acetylaspartate + N-acetylaspartylglutamate), glutamate, creatine, choline-compounds (phosphocholine + glycerophosphocholine), and myo-inositol, have all been linked to neuroinflammation, but they have not been examined as such with respect to smoking. We tested whether people who smoke cigarettes have brain levels of these metabolites consistent with decreased neuroinflammation, and whether clinical features of smoking are associated with levels of these metabolites. The dorsal anterior cingulate cortex was chosen as the region-of-interest because of previous evidence linking it to smoking and related states. Fifty-four adults who smoked daily maintained overnight smoking abstinence before testing and were compared with 37 nonsmoking participants. Among the smoking participants, we tested for associations of metabolite levels with tobacco dependence, smoking history, craving, and withdrawal. Levels of N-acetyl compounds and glutamate were higher, whereas levels of creatine and choline compounds were lower in the smoking group as compared with the nonsmoking group. In the smoking group, glutamate and creatine levels correlated negatively with tobacco dependence, and creatine correlated negatively with lifetime smoking, but none of the metabolite levels correlated with craving or withdrawal. The findings indicate a link between smoking and a hypoinflammatory state in the brain, specifically in the dorsal anterior cingulate cortex. Smoking may thereby increase vulnerability to infection and brain injury.

Corneal immune cells as a biomarker of inflammation in multiple sclerosis: a longitudinal study

Background

Corneal immune cells (ICs) are antigen-presenting cells that are known to increase ocular and systemic inflammatory conditions.

Objective

We aimed to assess longitudinal changes in corneal IC in patients with multiple sclerosis (MS) and relation to disability and ongoing treatment.

Design

Prospective observational study conducted between September 2016 and February 2020.

Methods

Patients with relapsing-remitting MS (RRMS) (n = 45) or secondary progressive MS (SPMS) (n = 15) underwent corneal confocal microscopy (CCM) at baseline and 2-year follow-up for estimation of corneal IC density [dendritic cells with (DCF) (cells/mm2) or without nerve fiber contact (DCP); and non-dendritic cells with (NCF) or without nerve fiber contact (NCP)]. Optical coherence tomography, neuroimaging, and disability assessments were additionally performed. Healthy controls (n = 20) were assessed at baseline.

Results

In both RRMS and SPMS compared to controls, DCP (p < 0.001 and p < 0.001, respectively) and DCF (p < 0.001 and p = 0.005) were higher and NCF (p = 0.007 and p = 0.02) was lower at baseline. DCP showed excellent performance in identifying patients with MS (sensitivity/specificity = 0.88/0.90) followed by DCF (0.80/0.75) and NCF (0.80/0.85). At follow-up compared to baseline, DCP (p = 0.01) was significantly reduced, and NCP (p = 0.004) and NCF (p = 0.04) were increased. Subgroup analysis showed that baseline NCP and NCF were significantly higher (p = 0.04-0.05) in patients who switched disease-modifying treatment, and baseline NCP (p = 0.05) was higher in patients on interferon.

Conclusion

Baseline and change in corneal IC were related to axonal degeneration and treatment status. Evaluation of corneal IC using CCM may allow an assessment of ongoing inflammation, disease progression, and the effect of treatment in MS.

Neuroimaging Insights: Kava's (Piper methysticum) Effect on Dorsal Anterior Cingulate Cortex GABA in Generalized Anxiety Disorder

Generalised Anxiety Disorder (GAD) is a prevalent, chronic mental health disorder. The measurement of regional brain gamma-aminobutyric acid (GABA) offers insight into its role in anxiety and is a potential biomarker for treatment response. Research literature suggests Piper methysticum (Kava) is efficacious as an anxiety treatment, but no study has assessed its effects on central GABA levels. This study investigated dorsal anterior cingulate (dACC) GABA levels in 37 adult participants with GAD. GABA was measured using proton magnetic resonance spectroscopy (1H-MRS) at baseline and following an eight-week administration of Kava (standardised to 120 mg kavalactones twice daily) (n = 20) or placebo (n = 17). This study was part of the Kava for the Treatment of GAD (KGAD; ClinicalTrials.gov: NCT02219880), a 16-week intervention study. Compared with the placebo group, the Kava group had a significant reduction in dACC GABA (p = 0.049) at eight weeks. Baseline anxiety scores on the HAM-A were positively correlated with GABA levels but were not significantly related to treatment. Central GABA reductions following Kava treatment may signal an inhibitory effect, which, if considered efficacious, suggests that GABA levels are modulated by Kava, independent of reported anxiety symptoms. dACC GABA patterns suggest a functional role of higher levels in clinical anxiety but warrants further research for symptom benefit. Findings suggest that dACC GABA levels previously un-examined in GAD could serve as a biomarker for diagnosis and treatment response.

Effects of acute physical activity on brain metabolites as measured by magnetic resonance spectroscopy (1H-MRS) in humans: A systematic review

Physical activity (PA) promotes brain health in a variety of domains including cognition, mood, and neuroplasticity. At the neurochemical level, the mechanisms underlying these effects in the brain are not fully understood. With proton Magnetic Resonance Spectroscopy (1H-MRS), it is possible to non-invasively quantify metabolite concentrations, enabling studies to obtain measures of exercise-induced neurochemical changes. This systematic review aimed to examine the existing literature on acute effects of PA on brain metabolites as measured by 1H-MRS. Four databases (Cochrane Central Register of Controlled Trials, PubMed, Embase, and PsycINFO) were searched, identifying 2965 studies, of which 9 met the inclusion criteria. Across studies, Gamma-AminoButyric Acid (GABA) and lactate tended to increase after exercise, while no significant changes in choline were reported. For glutamine/glutamate (Glx), studies were inconclusive. Conclusions were limited by the lack of consensus on 1H-MRS data processing and exercise protocols. To reduce inter-study differences, future studies are recommended to (1): apply a standardized exercise index (2), consider the onset time of MRS scans, and (3) follow standardized MRS quantification methods.

Fecal microbial transplantation limits neural injury severity and functional deficits in a pediatric piglet traumatic brain injury model

Pediatric traumatic brain injury (TBI) is a leading cause of death and disability in children. Due to bidirectional communication between the brain and gut microbial population, introduction of key gut bacteria may mitigate critical TBI-induced secondary injury cascades, thus lessening neural damage and improving functional outcomes. The objective of this study was to determine the efficacy of a daily fecal microbial transplant (FMT) to alleviate neural injury severity, prevent gut dysbiosis, and improve functional recovery post TBI in a translational pediatric piglet model. Male piglets at 4-weeks of age were randomly assigned to Sham + saline, TBI + saline, or TBI + FMT treatment groups. A moderate/severe TBI was induced by controlled cortical impact and Sham pigs underwent craniectomy surgery only. FMT or saline were administered by oral gavage daily for 7 days. MRI was performed 1 day (1D) and 7 days (7D) post TBI. Fecal and cecal samples were collected for 16S rRNA gene sequencing. Ipsilateral brain and ileum tissue samples were collected for histological assessment. Gait and behavior testing were conducted at multiple timepoints. MRI showed that FMT treated animals demonstrated decreased lesion volume and hemorrhage volume at 7D post TBI as compared to 1D post TBI. Histological analysis revealed improved neuron and oligodendrocyte survival and restored ileum tissue morphology at 7D post TBI in FMT treated animals. Microbiome analysis indicated decreased dysbiosis in FMT treated animals with an increase in multiple probiotic Lactobacilli species, associated with anti-inflammatory therapeutic effects, in the cecum of the FMT treated animals, while non-treated TBI animals showed an increase in pathogenic bacteria, associated with inflammation and disease such in feces. FMT mediated enhanced cellular and tissue recovery resulted in improved motor function including stride and step length and voluntary motor activity in FMT treated animals. Here we report for the first time in a highly translatable pediatric piglet TBI model, the potential of FMT treatment to significantly limit cellular and tissue damage leading to improved functional outcomes following a TBI.

Protocol to conduct functional magnetic resonance spectroscopy in different age groups of human participants

We present a protocol to conduct functional magnetic resonance spectroscopy (fMRS) in human participants before, during, and after training on a visual task. We describe steps for participant setup, volume-of-interest placement, fMRS measurement, and post-scan tests. We discuss the design, analysis, and interpretation of fMRS experiments. This protocol can be adapted to investigate the dynamics of chief excitatory and inhibitory neurotransmitters (glutamate and γ-aminobutyric acid, GABA, respectively) while participants perform or learn perceptual, motor, or cognitive tasks. For complete details on the use and execution of this protocol, please refer to Frank et al. (2022).1.

Metaplasticity: Dark exposure boosts local excitability and visual plasticity in adult human cortex

An interlude of dark exposure for about 1 week is known to shift excitatory/inhibitory (E/I) balance of the mammalian visual cortex, promoting plasticity and accelerating visual recovery in animals that have experienced cortical lesions during development. However, the translational impact of our understanding of dark exposure from animal studies to humans remains elusive. Here, we used magnetic resonance spectroscopy as a probe for E/I balance in the primary visual cortex (V1) to determine the effect of 60 min of dark exposure, and measured binocular combination as a behavioural assay to assess visual plasticity in 14 normally sighted human adults. To induce neuroplastic changes in the observers, we introduced 60 min of monocular deprivation, which is known to temporarily shift sensory eye balance in favour of the previously deprived eye. We report that prior dark exposure for 60 min strengthens local excitability in V1 and boosts visual plasticity in normal adults. However, we show that it does not promote plasticity in amblyopic adults. Nevertheless, our findings are surprising, given the fact that the interlude is very brief. Interestingly, we find that the increased concentration of the excitatory neurotransmitter is not strongly correlated with the enhanced functional plasticity. Instead, the absolute degree of change in its concentration is related to the boost, suggesting that the dichotomy of cortical excitation and inhibition might not explain the physiological basis of plasticity in humans. We present the first evidence that an environmental manipulation that shifts cortical E/I balance can also act as a metaplastic facilitator for visual plasticity in humans. KEY POINTS: A brief interlude (60 min) of dark exposure increased the local concentration of glutamine/glutamate but not that of GABA in the visual cortex of adult humans. After dark exposure, the degree of the shift in sensory eye dominance in favour of the previously deprived eye from short-term monocular deprivation was larger than that from only monocular deprivation. The neurochemical and behavioural measures were associated: the magnitude of the shift in the concentration of glutamine/glutamate was correlated with the boost in perceptual plasticity after dark exposure. Surprisingly, the increase in the concentration of glutamine/glutamate was not correlated with the perceptual boost after dark exposure, suggesting that the physiological mechanism of how E/I balance regulates plasticity is not deterministic. In other words, an increased excitation did not unilaterally promote plasticity.

Event-related functional magnetic resonance spectroscopy

Proton-Magnetic Resonance Spectroscopy (MRS) is a non-invasive brain imaging technique used to measure the concentration of different neurochemicals. "Single-voxel" MRS data is typically acquired across several minutes, before individual transients are averaged through time to give a measurement of neurochemical concentrations. However, this approach is not sensitive to more rapid temporal dynamics of neurochemicals, including those that reflect functional changes in neural computation relevant to perception, cognition, motor control and ultimately behaviour. In this review we discuss recent advances in functional MRS (fMRS) that now allow us to obtain event-related measures of neurochemicals. Event-related fMRS involves presenting different experimental conditions as a series of trials that are intermixed. Critically, this approach allows spectra to be acquired at a time resolution in the order of seconds. Here we provide a comprehensive user guide for event-related task designs, choice of MRS sequence, analysis pipelines, and appropriate interpretation of event-related fMRS data. We raise various technical considerations by examining protocols used to quantify dynamic changes in GABA, the primary inhibitory neurotransmitter in the brain. Overall, we propose that although more data is needed, event-related fMRS can be used to measure dynamic changes in neurochemicals at a temporal resolution relevant to computations that support human cognition and behaviour.

Maternal prenatal immune activation associated with brain tissue microstructure and metabolite concentrations in newborn infants

Importance

Few translational human studies have assessed the association of prenatal maternal immune activation with altered brain development and psychiatric risk in newborn offspring.

Objective

To identify the effects of maternal immune activation during the 2nd and 3rd trimesters of pregnancy on newborn brain metabolite concentrations, tissue microstructure, and longitudinal motor development.

Design

Prospective longitudinal cohort study conducted from 2012 - 2017.

Setting

Columbia University Irving Medical Center and Weill Cornell Medical College.

Participants

76 nulliparous pregnant women, aged 14 to 19 years, were recruited in their 2nd trimester, and their children were followed through 14 months of age.

Exposure

Maternal immune activation indexed by maternal interleukin-6 and C-reactive protein in the 2nd and 3rd trimesters of pregnancy.

Main Outcomes and Measures

The main outcomes included (1) newborn metabolite concentrations, measured as N-acetylaspartate, creatine, and choline using Magnetic Resonance Spectroscopy; (2) newborn fractional anisotropy and mean diffusivity measured using Diffusion Tensor Imaging; and (3) indices of motor development assessed prenatally and postnatally at ages 4- and 14-months.

Results

Maternal interleukin-6 and C-reactive protein levels in the 2nd or 3rd trimester were significantly positively associated with the N-acetylaspartate, creatine, and choline concentrations in the putamen, thalamus, insula, and anterior limb of the internal capsule. Maternal interleukin-6 was associated with fractional anisotropy in the putamen, insula, thalamus, precuneus, and caudate, and with mean diffusivity in the inferior parietal and middle temporal gyrus. C-reactive protein was associated with fractional anisotropy in the thalamus, insula, and putamen. Regional commonalities were found across imaging modalities, though the direction of the associations differed by immune marker. In addition, a significant positive association was observed between offspring motor development and both maternal interleukin-6 and C-reactive protein (in both trimesters) prenatally and 4- and 14-months of age.

Conclusions and Relevance

Using a healthy sample, these findings demonstrate that levels of maternal immune activation in mid- to late pregnancy associate with tissue characteristics in newborn brain regions primarily supporting motor integration/coordination and behavioral regulation and may lead to alterations in motor development.

Progressive myoclonic epilepsy type 1 (EPM1) patients present with abnormal 1H MRS brain metabolic profiles associated with cognitive function

PURPOSE

Progressive myoclonic epilepsy, type 1A (EPM1, Unverricht-Lundborg disease), is a rare neurodegenerative autosomal recessive disorder characterized by stimulus-sensitive and action myoclonus and tonic-clonic epileptic seizures. Patients develop neurological symptoms, including ataxia, intention tremor, and dysarthria, over time, with relatively limited and nonspecific MRI atrophy findings. The effects of the disease on brain metabolism are largely unknown.

METHOD

Eighteen EPM1 patients (9 M, 9F) underwent clinical evaluation and neuropsychological testing, which included the assessment of intellectual ability, verbal memory, and psychomotor and executive functions. Magnetic resonance spectroscopy (MRS) and imaging (MRI) were performed on a 1.5 T MRI system. 2D MRS chemical shift imaging (CSI) maps (TE = 270) were obtained from the following regions of the brain: basal ganglia, thalamus, insula, splenium, and occipital white and gray matter, and N-acetyl-aspartate (NAA)-, choline (Cho)-, and lactate (Lac)-to-creatine (Cr) ratios were analyzed. Ten healthy age-and sex-matched subjects (5M, 5F) were used as controls for MRS.

RESULTS

We found significant brain metabolic changes involving lactate, NAA, and choline, which are widespread in the basal ganglia, thalamic nuclei, insula, and occipital areas of EPM1 patients. Changes, especially in the right insula, basal ganglia, and thalamus, were associated with intellectual abilities and impairment of the psychomotor and executive functions of EPM1 patients.

CONCLUSION

Multiple brain metabolic alterations suggest the presence of neurodegeneration associated with EPM1 progression. The changes in metabolite ratios are associated with the neurocognitive dysfunction caused by the disease. However, the role of MRS findings in understanding pathophysiology of EPM1 warrants further studies.

Neurometabolite levels in the brains of patients with autism spectrum disorders: A meta-analysis of proton magnetic resonance spectroscopy studies (N = 1501)

Evidence suggests that neurometabolite alterations may be involved in the pathophysiology of autism spectrum disorders (ASDs). We performed a meta-analysis of proton magnetic resonance spectroscopy (1H-MRS) studies to examine the neurometabolite levels in the brains of patients with ASD. A systematic search of PubMed and Web of Science identified 54 studies for the meta-analysis. A random-effects meta-analysis demonstrated that compared with the healthy controls, patients with ASD had lower N-acetyl-aspartate-containing compound (NAA) and choline-containing compound (Cho) levels and NAA/(creatine-containing compound) Cr ratios in the gray matter and lower NAA and glutamate + glutamine (Glx) levels in the white matter. Furthermore, NAA and gamma-aminobutyric acid (GABA) levels, NAA/Cr ratios, and GABA/Cr ratios were significantly decreased in the frontal cortex of patients with ASD, whereas glutamate (Glu) levels were increased in the prefrontal cortex. Additionally, low NAA levels and GABA/Cr ratios in the temporal cortex, low NAA levels and NAA/Cr ratios in the parietal and dorsolateral prefrontal cortices, and low NAA levels in the cerebellum and occipital cortex were observed in patients with ASD. Meta-regression analysis revealed that age was positively associated with effect size in studies analyzing the levels of gray matter NAA and white matter Glx. Taken together, these results provide strong clinical evidence that neurometabolite alterations in specific brain regions are associated with ASD and age is a confounding factor for certain neurometabolite levels in patients with ASD.

Changes in Brain GABA and Glutamate and Improvements in Physical Functioning Following Intensive Pain Rehabilitation in Youth With Chronic Pain

Intensive interdisciplinary pain treatments (IIPT) have been developed to treat youth with unmanaged chronic pain and functional disability. Dysregulation of metabolites gamma-aminobutyric acid (GABA) and glutamate are thought to play a role in the chronification of pain due to imbalances in inhibition and excitation in adults. Using magnetic resonance spectroscopy (MRS), we investigated the effect of IIPT on GABA and Glx (glutamate + glutamine) in 2 pain-related brain regions: the left posterior insula (LPI) and the anterior cingulate cortex (ACC). Data were collected in 23 youth (mean age = 16.09 ± 1.40, 19 female) at entry and discharge from a hospital-based outpatient IIPT. GABA and Glx were measured using GABA-edited MEGA-PRESS and analyzed using Gannet. Physical measures including a 6-minute walk test were recorded, and patients completed the PLAYSelf Physical Literacy Questionnaire, PROMIS Pain Interference Questionnaire, and Functional Disability Inventory. LPI GABA (P < .05) significantly decreased, but not ACC GABA (P > .05), following IIPT. There were no significant Glx changes (P > .05). The decrease in LPI GABA was associated with increased distance in the 6-minute walk test (P < .001). IIPT may decrease GABAergic inhibitory tone within the LPI, thereby promoting plasticity and contributing to improvements in physical outcomes with IIPT. PERSPECTIVE: Regional GABA changes are associated with a reduction in pain interference and improvement in physical function in youth following intensive pain rehabilitation. GABA may serve as a possible biomarker for IIPT; and may also further aid in the development of IIPT, and other treatments for chronic pain in youth.

Early metabolic alterations in the normal‑appearing grey and white matter of patients with clinically isolated syndrome suggestive of multiple sclerosis: A proton MR spectroscopic study

Proton magnetic resonance spectroscopy (¹H-MRS) is an advanced method of examining metabolic profiles. The present study aimed to assess in vivo metabolite levels in areas of normal-appearing grey (thalamus) and white matter (centrum semiovale) using ¹H-MRS in patients with clinically isolated syndrome (CIS) suggestive of multiple sclerosis and compare them to healthy controls (HCs). Data from 35 patients with CIS (CIS group), of which 23 were untreated (CIS-untreated group) and 12 were treated (CIS-treated group) with disease-modifying-therapies (DMTs) at the time of ¹H-MRS, and from 28 age- and sex-matched HCs were collected using a 3.0 T MRI and single-voxel ¹H-MRS (point resolved spectroscopy sequence; repetition time, 2,000 msec; time to echo, 35 msec). Concentrations and ratios of total N-acetyl aspartate (tNAA), total creatine (tCr), total choline (tCho), myoinositol, glutamate (Glu), glutamine (Gln), Glu + Gln (Glx) and glutathione (Glth) were estimated in the thalamic-voxel (th) and centrum semiovale-voxel (cs). For the CIS group, the median duration from the first clinical attack to ¹H-MRS was 102 days (interquartile range, 89.5.-131.5). Compared with HCs, significantly lower Glx(cs) (P=0.014) and ratios of tCho/tCr(th) (P=0.026), Glu/tCr(cs) (P=0.040), Glx/tCr(cs) (P=0.004), Glx/tNAA(th) (P=0.043) and Glx/tNAA(cs) (P=0.015) were observed in the CIS group. No differences in tNAA levels were observed between the CIS and the HC groups; however, tNAA(cs) was higher in the CIS-treated than in the CIS-untreated group (P=0.028). Compared with those in HC group, decreased Glu(cs) (P=0.019) and Glx(cs) levels (P=0.014) and lower ratios for tCho/tCr(th) (P=0.015), Gln/tCr(th) (P=0.004), Glu/tCr(cs) (P=0.021), Glx/tCr(th) (P=0.041), Glx/tCr(cs) (P=0.003), Glx/tNAA(th) (P=0.030) and Glx/tNAA(cs) (P=0.015) were found in the CIS-untreated group. The present findings showed alterations in the normal-appearing grey and white matter of patients with CIS; moreover, the present results suggested an early indirect treatment effect of DMTs on the brain metabolic profile of these patients.

Electroconvulsive therapy triggers a reversible decrease in brain N-acetylaspartate

Introduction

Based on previous research on electroconvulsive therapy (ECT) we have proposed a model where disruption, potentiation, and rewiring of brain networks occur in sequence and serve as the underlying therapeutic mechanism of ECT. This model implies that a temporary disturbance of neuronal networks (disruption) is followed by a trophic effect (potentiation), which enables the rewiring of neuronal circuits to a more euthymic functioning brain. We hypothesized that disruption of neuronal networks could trigger biochemical alterations leading to a temporary decrease in N-acetylaspartate (tNAA, considered a marker of neuronal integrity), while choline (a membrane component), myo-Inositol (mI, astroglia marker), and glutamate/glutamine (Glx, excitatory neurotransmitter) were postulated to increase. Previous magnetic resonance spectroscopy studies, reporting diverse findings, have used two different referencing methods - creatine ratios and tissue corrected values referenced to water - for the quantification of brain metabolites. Changes in creatine during ECT have also been reported, which may confound estimates adopting this as an internal reference.

Methods

Using MR spectroscopy, we investigated 31 moderately to severely depressed patients and 19 healthy controls before, during, and after ECT or at similar time points (for controls). We tested whether biochemical alterations in tNAA, choline, mI, and Glx lend support to the disrupt, potentiate, and rewire hypothesis. We used both creatine ratios and water-scaled values for the quantification of brain metabolites to validate the results across referencing methods.

Results

Levels of tNAA in the anterior cingulate cortex decreased after an ECT treatment series (average 10.6 sessions) by 6% (p = 0.007, creatine ratio) and 3% (p = 0.02, water referenced) but returned to baseline 6 months after ECT. Compared to after treatment series tNAA levels at 6-month follow-up had increased in both creatine ratio (+6%, p < 0.001) and water referenced data (+7%, p < 0.001). Findings for other brain metabolites varied and could not be validated across referencing methods.

Discussion

Our findings suggest that prior research must be interpreted with care, as several referencing and processing methods have been used in the past. Yet, the results for tNAA were robust across quantification methods and concur with relevant parts of the disrupt, potentiate, and rewire model.

Metabolic profile of complete spinal cord injury in pons and cerebellum: A 3T 1H MRS study

The aim of this exploratory study was the assessment of the metabolic profiles of persons with complete spinal cord injury (SCI) in three region-of-interests (pons, cerebellar vermis, and cerebellar hemisphere), with magnetic resonance spectroscopy, and their correlations to clinical scores. Group differences and association between metabolic and clinical scores were examined. Fifteen people with chronic SCI (cSCI), five people with subacute SCI (sSCI) and fourteen healthy controls were included. Group comparison between cSCI and HC showed lower total N-acetyl-aspartate (tNAA) in the pons (p = 0.04) and higher glutathione (GSH) in the cerebellar vermis (p = 0.02). Choline levels in the cerebellar hemisphere were different between cSCI and HC (p = 0.02) and sSCI and HC (p = 0.02). A correlation was reported for choline containing compounds (tCho) to clinical scores in the pons (rho = - 0.55, p = 0.01). tNAA to total creatine (tNAA/tCr ratio) correlated to clinical scores in the cerebellar vermis (rho = 0.61, p = 0.004) and GSH correlated to the independence score in the cerebellar hemisphere (rho = 0.56, p = 0.01). The correlation of tNAA, tCr, tCho and GSH to clinical scores might be indicators on how well the CNS copes with the post-traumatic remodeling and might be further examined as outcome markers.

Longitudinal changes in brain metabolites in healthy controls and patients with first episode psychosis: a 7-Tesla MRS study

Seven Tesla magnetic resonance spectroscopy (7T MRS) offers a precise measurement of metabolic levels in the human brain via a non-invasive approach. Studying longitudinal changes in brain metabolites could help evaluate the characteristics of disease over time. This approach may also shed light on how the age of study participants and duration of illness may influence these metabolites. This study used 7T MRS to investigate longitudinal patterns of brain metabolites in young adulthood in both healthy controls and patients. A four-year longitudinal cohort with 38 patients with first episode psychosis (onset within 2 years) and 48 healthy controls was used to examine 10 brain metabolites in 5 brain regions associated with the pathophysiology of psychosis in a comprehensive manner. Both patients and controls were found to have significant longitudinal reductions in glutamate in the anterior cingulate cortex (ACC). Only patients were found to have a significant decrease over time in γ-aminobutyric acid, N-acetyl aspartate, myo-inositol, total choline, and total creatine in the ACC. Together we highlight the ACC with dynamic changes in several metabolites in early-stage psychosis, in contrast to the other 4 brain regions that also are known to play roles in psychosis. Meanwhile, glutathione was uniquely found to have a near zero annual percentage change in both patients and controls in all 5 brain regions during a four-year follow-up in young adulthood. Given that a reduction of the glutathione in the ACC has been reported as a feature of treatment-refractory psychosis, this observation further supports the potential of glutathione as a biomarker for this subset of patients with psychosis.

Evaluating Back-to-Back and Day-to-Day Reproducibility of Cortical GABA+ Measurements Using Proton Magnetic Resonance Spectroscopy (1H MRS)

γ-aminobutyric acid (GABA) is a major inhibitory neurotransmitter implicated in neuropsychiatric disorders. The best method for quantifying GABA is proton magnetic resonance spectroscopy (¹H MRS). Considering that accurate measurements of GABA are affected by slight methodological alterations, demonstrating GABA reproducibility in healthy volunteers is essential before implementing the changes in vivo. Thus, our study aimed to evaluate the back-to-back (B2B) and day-to-day (D2D) reproducibility of GABA+ macromolecules (GABA+) using a 3 Tesla MRI scanner, the new 32-channel head coil (CHC), and Mescher-Garwood Point Resolved Spectroscopy (MEGA-PRESS) technique with the scan time (approximately 10 min), adequate for psychiatric patients. The dorsomedial pre-frontal cortex/anterior cingulate cortex (dmPFC/ACC) was scanned in 29 and the dorsolateral pre-frontal cortex (dlPFC) in 28 healthy volunteers on two separate days. Gannet 3.1 was used to quantify GABA+. The reproducibility was evaluated by Pearson's r correlation, the interclass-correlation coefficient (ICC), and the coefficient of variation (CV%) (r/ICC/CV%). For Day 1, B2B reproducibility was 0.59/0.60/5.02% in the dmPFC/ACC and 0.74/0.73/5.15% for dlPFC. For Day 2, it was 0.60/0.59/6.26% for the dmPFC/ACC and 0.54/0.54/6.89 for dlPFC. D2D reproducibility of averaged GABA+ was 0.62/0.61/4.95% for the dmPFC/ACC and 0.58/0.58/5.85% for dlPFC. Our study found excellent GABA+ repeatability and reliability in the dmPFC/ACC and dlPFC.

Multinuclear Magnetic Resonance Spectroscopy at Ultra-High-Field: Assessing Human Cerebral Metabolism in Healthy and Diseased States

The brain is a highly energetic organ. Although the brain can consume metabolic substrates, such as lactate, glycogen, and ketone bodies, the energy metabolism in a healthy adult brain mainly relies on glucose provided via blood. The cerebral metabolism of glucose produces energy and a wide variety of intermediate metabolites. Since cerebral metabolic alterations have been repeatedly implicated in several brain disorders, understanding changes in metabolite levels and corresponding cell-specific neurotransmitter fluxes through different substrate utilization may highlight the underlying mechanisms that can be exploited to diagnose or treat various brain disorders. Magnetic resonance spectroscopy (MRS) is a noninvasive tool to measure tissue metabolism in vivo. ¹H-MRS is widely applied in research at clinical field strengths (≤3T) to measure mostly high abundant metabolites. In addition, X-nuclei MRS including, ¹³C, ²H, ¹⁷O, and ³¹P, are also very promising. Exploiting the higher sensitivity at ultra-high-field (>4T; UHF) strengths enables obtaining unique insights into different aspects of the substrate metabolism towards measuring cell-specific metabolic fluxes in vivo. This review provides an overview about the potential role of multinuclear MRS (¹H, ¹³C, ²H, ¹⁷O, and ³¹P) at UHF to assess the cerebral metabolism and the metabolic insights obtained by applying these techniques in both healthy and diseased states.

Changes in brain metabolite levels across childhood

Metabolites play important roles in brain development and their levels change rapidly in the prenatal period and during infancy. Metabolite levels are thought to stabilize during childhood, but the development of neurochemistry across early-middle childhood remains understudied. We examined the developmental changes of key metabolites (total N-acetylaspartate, tNAA; total choline, tCho; total creatine, tCr; glutamate+glutamine, Glx; and myo-inositol, mI) using short echo-time magnetic resonance spectroscopy (MRS) in the anterior cingulate cortex (ACC) and the left temporo-parietal cortex (LTP) using a mixed cross-sectional/longitudinal design in children aged 2-11 years (ACC: N=101 children, 112 observations; LTP: N=95 children, 318 observations). We found age-related effects for all metabolites. tNAA increased with age in both regions, while tCho decreased with age in both regions. tCr increased with age in the LTP only, and mI decreased with age in the ACC only. Glx did not show linear age effects in either region, but a follow-up analysis in only participants with ≥3 datapoints in the LTP revealed a quadratic effect of age following an inverted U-shape. These substantial changes in neurochemistry throughout childhood likely underlie various processes of structural and functional brain development.

Brain metabolites measured with magnetic resonance spectroscopy in pediatric concussion and orthopedic injury: An Advancing Concussion Assessment in Pediatrics (A-CAP) study

Millions of children sustain a concussion annually. Concussion disrupts cellular signaling and neural pathways within the brain but the resulting metabolic disruptions are not well characterized. Magnetic resonance spectroscopy (MRS) can examine key brain metabolites (e.g., N-acetyl Aspartate (tNAA), glutamate (Glx), creatine (tCr), choline (tCho), and myo-Inositol (mI)) to better understand these disruptions. In this study, we used MRS to examine differences in brain metabolites between children and adolescents with concussion versus orthopedic injury. Children and adolescents with concussion (n = 361) or orthopedic injury (OI) (n = 184) aged 8 to 17 years were recruited from five emergency departments across Canada. MRS data were collected from the left dorsolateral prefrontal cortex (L-DLPFC) using point resolved spectroscopy (PRESS) at 3 T at a mean of 12 days post-injury (median 10 days post-injury, range 2-33 days). Univariate analyses for each metabolite found no statistically significant metabolite differences between groups. Within each analysis, several covariates were statistically significant. Follow-up analyses designed to account for possible confounding factors including age, site, scanner, vendor, time since injury, and tissue type (and interactions as appropriate) did not find any metabolite group differences. In the largest sample of pediatric concussion studied with MRS to date, we found no metabolite differences between concussion and OI groups in the L-DLPFC. We suggest that at 2 weeks post-injury in a general pediatric concussion population, brain metabolites in the L-DLPFC are not specifically affected by brain injury.

J-difference GABA-edited MRS reveals altered cerebello-thalamo-cortical metabolism in patients with hepatic encephalopathy

Hepatic encephalopathy (HE) is a common neurological manifestation of liver cirrhosis and is characterized by an increase of ammonia in the brain accompanied by a disrupted neurotransmitter balance, including the GABAergic and glutamatergic systems. The aim of this study is to investigate metabolic abnormalities in the cerebello-thalamo-cortical system of HE patients using GABA-edited MRS and links between metabolite levels, disease severity, critical flicker frequency (CFF), motor performance scores, and blood ammonia levels. GABA-edited MRS was performed in 35 participants (16 controls, 19 HE patients) on a clinical 3 T MRI system. MRS voxels were placed in the right cerebellum, left thalamus, and left motor cortex. Levels of GABA+ and of other metabolites of interest (glutamine, glutamate, myo-inositol, glutathione, total choline, total NAA, and total creatine) were assessed. Group differences in metabolite levels and associations with clinical metrics were tested. GABA+ levels were significantly increased in the cerebellum of patients with HE. GABA+ levels in the motor cortex were significantly decreased in HE patients, and correlated with the CFF (r = 0.73; p < .05) and motor performance scores (r = -0.65; p < .05). Well-established HE-typical metabolite patterns (increased glutamine, decreased myo-inositol and total choline) were confirmed in all three regions and were closely linked to clinical metrics. In summary, our findings provide further evidence for alterations in the GABAergic system in the cerebellum and motor cortex in HE. These changes were accompanied by characteristic patterns of osmolytes and oxidative stress markers in the cerebello-thalamo-cortical system. These metabolic disturbances are a likely contributor to HE motor symptoms in HE. In patients with hepatic encephalopathy, GABA+ levels in the cerebello-thalamo-cortical loop are significantly increased in the cerebellum and significantly decreased in the motor cortex. GABA+ levels in the motor cortex strongly correlate with critical flicker frequency (CFF) and motor performance score (pegboard test tPEG), but not blood ammonia levels (NH3).