Investigation of glutamine and GABA levels in patients with idiopathic generalized epilepsy using MEGAPRESS

Migraine - a borderland disease to epilepsy: near it but not of it

BACKGROUND

Migraine and epilepsy are two paroxysmal chronic neurological disorders affecting a high number of individuals and being responsible for a high individual and socioeconomic burden. The link between these disorders has been of interest for decades and innovations concerning diagnosing and treatment enable new insights into their relationship.

FINDINGS

Although appearing to be distinct at first glance, both diseases exhibit a noteworthy comorbidity, shared pathophysiological pathways, and significant overlaps in characteristics like clinical manifestation or prophylactic treatment. This review aims to explore the intricate relationship between these two conditions, shedding light on shared pathophysiological foundations, genetic interdependencies, common and distinct clinical features, clinically overlapping syndromes, and therapeutic similarities. There are several shared pathophysiological mechanisms, like CSD, the likely underlying cause of migraine aura, or neurotransmitters, mainly Glutamate and GABA, which represent important roles in triggering migraine attacks and seizures. The genetic interrelations between the two disorders can be observed by taking a closer look at the group of familial hemiplegic migraines, which are caused by mutations in genes like CACNA1A, ATP1A2, or SCN1A. The intricate relationship is further underlined by the high number of shared clinical features, which can be observed over the entire course of migraine attacks and epileptic seizures. While the variety of the clinical manifestation of an epileptic seizure is naturally higher than that of a migraine attack, a distinction can indeed be difficult in some cases, e.g. in occipital lobe epilepsy. Moreover, triggering factors like sleep deprivation or alcohol consumption play an important role in both diseases. In the period after the seizure or migraine attack, symptoms like speech difficulties, tiredness, and yawning occur. While the actual attack of the disease usually lasts for a limited time, research indicates that individuals suffering from migraine and/or epilepsy are highly affected in their daily life, especially regarding cognitive and social aspects, a burden that is even worsened using antiseizure medication. This medication allows us to reveal further connections, as certain antiepileptics are proven to have beneficial effects on the frequency and severity of migraine and have been used as a preventive drug for both diseases over many years.

CONCLUSION

Migraine and epilepsy show a high number of similarities in their mechanisms and clinical presentation. A deeper understanding of the intricate relationship will positively advance patient-oriented research and clinical work.

Prefrontal Glutathione Levels in Major Depressive Disorder Are Linked to a Lack of Positive Affect

Major depressive disorder (MDD) is one of the most common neuropsychiatric disorders, with symptoms including persistent sadness and loss of interest. MDD is associated with neurochemical alterations in GABA, glutamate, and glutamine levels but, to date, few studies have examined changes in glutathione (GSH) in MDD. This study investigated changes in GSH in an unmedicated group of young adults, including 46 participants with current (n = 12) or past MDD (n = 34) and 20 healthy controls. Glutathione levels were assessed from GSH-edited magnetic resonance (MR) spectra, acquired from a voxel in the left prefrontal cortex, and depressive symptoms were evaluated with validated questionnaires and clinical assessments. Cortisol levels were also assessed as a marker for acute stress. Participants with current MDD demonstrated elevated GSH in comparison to participants with past MDD and controls, although the results could be influenced by differences in tissue composition within the MRS voxel. In addition, participants with both current and past MDD showed elevated cortisol levels in comparison to controls. No significant association was observed between GSH and cortisol levels, but elevated GSH levels were associated with a decrease in positive affect. These results demonstrate for the first time that elevated GSH in current but not past depression may reflect a state rather than a trait neurobiological change, related to a loss of positive affect.

γ-Aminobutyric acid as a biomarker of the lateralizing and monitoring drug effect in patients with magnetic resonance imaging-negative temporal lobe epilepsy

Introduction

Despite verifying proton magnetic resonance spectroscopy (¹H-MRS) for focal localization in magnetic resonance imaging (MRI)-negative temporal lobe epilepsy (TLE), it is necessary to illustrate metabolic changes and screen for effective biomarkers for monitoring therapeutic effect. We used ¹H-MRS to investigate the role of metabolic levels in MRI-negative TLE.

Materials and methods

Thirty-seven patients (n = 37, 14 women) and 20 healthy controls (n = 20, 11 women) were investigated by ¹H-MRS. We compared the metabolite level changes in the epileptic and contralateral sides on the mesial temporal and dorsolateral prefrontal cortices and analyzed their association with clinical symptoms.

Results

γ-Aminobutyric acid (GABA) levels were significantly lower on the epileptic side (2.292 ± 0.890) than in the contralateral side (2.662 ± 0.742, p = 0.029*) in patients on the mesial temporal lobe. N-acetylaspartate (NAA) levels were significantly lower on the epileptic side (7.284 ± 1.314) than on the contralateral side (7.655 ± 1.549, p = 0.034*). NAA + N-acetylaspartylglutamate levels were significantly lower on the epileptic side (7.668 ± 1.406) than on the contralateral side (8.086 ± 1.675, p = 0.032*). Glutamate levels were significantly lower on the epileptic side (7.773 ± 1.428) than on the contralateral side (8.245 ± 1.616, p = 0.040*). Moreover, a significant negative correlation was found between GABA levels in the epileptic mesial temporal lobe and tonic-clonic seizure frequency (r = -0.338, p = 0.046*).

Conclusion

γ-Aminobutyric acid (GABA) is a potential biomarker for lateralization and monitoring seizure frequency in MRI-negative TLE.

Association of the delayed changes in glutamate levels and functional connectivity with the immediate network effects of S-ketamine

Ketamine shows rapid antidepressant effects peaking 24 h after administration. The antidepressant effects may occur through changes in glutamatergic metabolite levels and resting-state functional connectivity (rsFC) within the default mode network (DMN). A multistage drug effect of ketamine has been suggested, inducing acute effects on dysfunctional network configuration and delayed effects on homeostatic synaptic plasticity. Whether the DMN-centered delayed antidepressant-related changes are associated with the immediate changes remains unknown. Thirty-five healthy male participants (25.1 ± 4.2 years) underwent 7 T magnetic resonance spectroscopy (MRS) and resting-state functional magnetic resonance imaging (rsfMRI) before, during, and 24 h after a single S-ketamine or placebo infusion. Changes in glutamatergic measures and rsFC in the DMN node pregenual anterior cingulate cortex (pgACC) were examined. A delayed rsFC decrease of the pgACC to inferior parietal lobe (family-wise error corrected p (p_FWEc) = 0.018) and dorsolateral prefrontal cortex (PFC; p_FWEc = 0.002) was detected that was preceded by an immediate rsFC increase of the pgACC to medial PFC (p_FWEc < 0.001) and dorsomedial PFC (p_FWEc = 0.005). Additionally, the immediate rsFC reconfigurations correlated with the delayed pgACC glutamate (Glu) level increase (p = 0.024) after 24 h at trend level (p = 0.067). Baseline measures of rsFC and MRS were furthermore associated with the magnitude of the respective delayed changes (p's < 0.05). In contrast, the delayed changes were not associated with acute psychotomimetic side effects or plasma concentrations of ketamine and its metabolites. This multimodal study suggests an association between immediate S-ketamine-induced network effects and delayed brain changes at a time point relevant in its clinical context.

Altered neurovascular coupling in children with idiopathic generalized epilepsy

AIMS

Alterations in neuronal activity and cerebral hemodynamics have been reported in idiopathic generalized epilepsy (IGE) patients, possibly resulting in neurovascular decoupling; however, no neuroimaging evidence confirmed this disruption. This study aimed to investigate the possible presence of neurovascular decoupling and its clinical implications in childhood IGE using resting-state fMRI and arterial spin labeling imaging.

METHODS

IGE patients and healthy participants underwent resting-state fMRI and arterial spin labeling imaging to calculate degree centrality (DC) and cerebral blood flow (CBF), respectively. Across-voxel CBF-DC correlations were analyzed to evaluate the neurovascular coupling within the whole gray matter, and the regional coupling of brain region was assessed with the CBF/DC ratio.

RESULTS

The study included 26 children with IGE and 35 sex- and age-matched healthy controls (HCs). Compared with the HCs, the IGE group presented lower across-voxel CBF-DC correlations, higher CBF/DC ratio in the right posterior cingulate cortex/precuneus, middle frontal gyrus, and medial frontal gyrus (MFG), and lower ratio in the left inferior frontal gyrus. The increased CBF/DC ratio in the right MFG was correlated with lower performance intelligence quotient scores in the IGE group.

CONCLUSION

Children with IGE present altered neurovascular coupling, associated with lower performance intelligence quotient scores. The study shed a new insight into the pathophysiology of epilepsy and provided potential imaging biomarkers of cognitive performances in children with IGE.

Does Prefrontal Glutamate Index Cognitive Changes in Parkinson's Disease?

Introduction

Cognitive impairment is a highly prevalent non-motor feature of Parkinson's disease (PD). A better understanding of the underlying pathophysiology may help in identifying therapeutic targets to prevent or treat dementia. This study sought to identify metabolic alterations in the prefrontal cortex (PFC), a key region for cognitive functioning that has been implicated in cognitive dysfunction in PD.

Methods

Proton Magnetic Resonance Spectroscopy was used to investigate metabolic changes in the PFC of a cohort of cognitively normal individuals without PD (CTL), as well as PD participants with either normal cognition (PD-NC), mild cognitive impairment (PD-MCI), or dementia (PDD). Ratios to Creatine (Cre) resonance were obtained for glutamate (Glu), glutamine and glutamate combined (Glx), N-acetylaspartate (NAA), myoinositol (mI), and total choline (Cho), and correlated with cognitive scores across multiple domains (executive function, learning and memory, language, attention, visuospatial function, and global cognition) administered to the PD participants only.

Results

When individuals retain cognitive capabilities, the presence of Parkinson's disease does not create metabolic disturbances in the PFC. However, when cognitive symptoms are present, PFC Glu/Cre ratios decrease with significant differences between the PD-NC and PPD groups. In addition, Glu/Cre ratios and memory scores were marginally associated, but not after Bonferroni correction.

Conclusion

These preliminary findings indicate that fluctuations in prefrontal glutamate may constitute a biomarker for the progression of cognitive impairments in PD. We caution for larger MRS investigations of carefully defined PD groups.

Multiscale dynamic mean field (MDMF) model relates resting-state brain dynamics with local cortical excitatory-inhibitory neurotransmitter homeostasis

Previous computational models have related spontaneous resting-state brain activity with local excitatory–inhibitory balance in neuronal populations. However, how underlying neurotransmitter kinetics associated with E–I balance govern resting-state spontaneous brain dynamics remains unknown. Understanding the mechanisms by virtue of which fluctuations in neurotransmitter concentrations, a hallmark of a variety of clinical conditions, relate to functional brain activity is of critical importance. We propose a multiscale dynamic mean field (MDMF) model—a system of coupled differential equations for capturing the synaptic gating dynamics in excitatory and inhibitory neural populations as a function of neurotransmitter kinetics. Individual brain regions are modeled as population of MDMF and are connected by realistic connection topologies estimated from diffusion tensor imaging data. First, MDMF successfully predicts resting-state functional connectivity. Second, our results show that optimal range of glutamate and GABA neurotransmitter concentrations subserve as the dynamic working point of the brain, that is, the state of heightened metastability observed in empirical blood-oxygen-level-dependent signals. Third, for predictive validity the network measures of segregation (modularity and clustering coefficient) and integration (global efficiency and characteristic path length) from existing healthy and pathological brain network studies could be captured by simulated functional connectivity from an MDMF model.

How changes in neurotransmitter kinetics impact the organization of large-scale neurocognitive networks is an open question in neuroscience. Here, we propose a multiscale dynamic mean field (MDMF) model that incorporates biophysically realistic kinetic parameters of receptor binding in a dynamic mean field model and captures brain dynamics from the “whole brain.” MDMF could reliably reproduce the resting-state brain functional connectivity patterns. Further employing graph theoretic methods, MDMF could qualitatively explain the idiosyncrasies of network integration and segregation measures reported by previous clinical studies.

Focal corticarl dysplasia in epilepsy is associated with GABA increase

PURPOSE

Focal cortical dysplasia (FCD) is a major cause of drug-resistant epilepsy; however the underlying epileptogenic mechanisms of FCD metabolism in epilepsy patients remain unclear. The aim of this study is to detect alterations of γ-aminobutyric acid (GABA), glutathione (GSH), and the composite of glutamate and glutamine (Glx) in MRI-typical and neuropathologically confirmed FCD-associated epilepsy using Hadamard Encoding and Reconstruction of Mega-Edited Spectroscopy (HERMES).

MATERIALS AND METHODS

Fourteen epileptic patients suspected to be caused by FCD and 14 healthy controls were enrolled prospectively in this study; all subjects underwent a 3 T MRI scan, including 3D T1 weighted imaging and HERMES. The GABA signal detected by HERMES also contains signals from macromolecules and homocarnosine, so it is referred as GABA+. Signals of GABA+, GSH and Glx detected by HERMES from tumor foci, contralateral cerebral regions, and healthy controls were quantified using Gannet. Fitting errors and signal to noise ratios (SNRs) of GABA + signals were also recorded. Differences of GABA+, GSH, Glx, fitting error and SNR of GABA + among three groups were analyzed using linear mixed effects models.

RESULTS

Twelve FCD-associated epilepsy patients (7 females, aged 21.9 ± 9.3 years) and 12 matched healthy controls (7 females, aged 22.8 ± 9.8 years) were finally enrolled in this study. ANOVA results indicated that GABA levels were significantly increased in FCD foci compared with contralateral regions (p = 0.008) and with healthy controls (p = 0.003), while no difference was found in GSH and Glx levels. No difference of fitting errors or SNR of GABA + was found among FCD foci, contralateral regions and healthy controls.

CONCLUSIONS

Increased GABA levels were found in FCD foci that indicated GABA may play a central role in the pathophysiology of FCD patients with epilepsy.

Brain concentrations of glutamate and GABA in human epilepsy: A review

An imbalance between excitation and inhibition has been a longstanding proposed mechanism regarding ictogenesis and epileptogenesis. This imbalance is related to increased extracellular glutamate in the brain and/or reduction in GABA concentrations, leading to excitotoxicity, seizures, and cell death. This review aims to summarize the microdialysis and magnetic resonance spectroscopy (MRS) literature investigating glutamate and GABA concentrations in epilepsy patients, present limitations, and suggest future directions to help direct the search for novel epilepsy treatments. The majority of microdialysis studies demonstrated increased glutamate in epileptic regions either compared to control regions or to baseline levels; however, sample sizes were small, with some statistical comparisons missing. For the MRS research, two of six studies reported significant changes in glutamate levels compared to controls, though the results were mixed, with one reporting increased and the other reporting decreased glutamate levels. Eleven of 20 studies reported significant changes in Glx (glutamate + glutamine) or Glx ratios, with most reporting increased levels, except for a few epilepsy syndromes where reduced levels were reported. Few studies investigated GABA concentrations, with one microdialysis and four spectroscopy studies reporting increased GABA levels, and one study reporting decreased GABA in a different brain region. Based on this review, future research should account for medication use; include measurements of GABA, glutamate, and glutamine; use high-tesla strength MRI; and further evaluate the timing of microdialysis. Understanding the importance of brain glutamate and GABA levels in epilepsy may provide direction for future therapies and treatments.

Gamma-aminobutyric acid (GABA) changes in the hippocampus and anterior cingulate cortex in patients with temporal lobe epilepsy

PURPOSE

To explore the changes of gamma-aminobutyric acid (GABA) levels in the bilateral hippocampus and anterior cingulate cortex (ACC) of healthy control subjects and patients with temporal lobe epilepsy (TLE) and the correlation of GABA levels with the clinical symptoms by quantitative magnetic resonance spectroscopy (MRS).

METHODS

N-acetylaspartate (NAA), creatine (Cr) as well as choline (Cho) and GABA levels in the bilateral hippocampus and ACC were measured in 40 patients with TLE and 26 healthy control (NC) subjects with quantitative Meshcher-Garwood point resolved spectroscopy (MEGA-PRESS). The NAA/(Cho + Cr) and GABA/Cr ratios were compared between the NC and TLE groups. Comparisons were also made between the subgroups with lateralization (left TLE, right TLE and uncertain), short (<10 years) and longer (≥10 years) clinical seizure history (CSH), low (<1/month) and higher (≥1/month) seizure frequency (SF), with and without cognitive impairment (CI) in the patients with TLE, and by antiepileptic medications. Further analyses of the clinical information and metabolite ratios between the patients with TLE with and without CI were preformed.

RESULTS

The GABA/Cr ratio was significantly decreased in the bilateral hippocampus (left: P = 0.028, right: P = 0.035), while the NAA/(Cho + Cr) ratio was decreased only in the right hippocampus (RH) (P = 0.004) in patients with TLE compared with that of the NCs. Whereas the NAA/(Cho + Cr) ratio showed a consistent decreasing trend in bilateral hippocampus during the CSH, it only showed a significant difference in the RH. The GABA changes in the hippocampal and ACC regions were not consistent during different stages of the disease. In the bilateral hippocampus, the GABA/Cr ratio was decreased in the short seizure history (<10 years) patients with TLE compared with NCs (left: P = 0.018, right: P = 0.012), whereas the long seizure history (≥10 years) patients with TLE showed no difference with the NCs. However, in the ACC, the GABA/Cr ratio of the CI group was significantly decreased compared with that of NCs (P = 0.015). Further analysis showed that the patients with TLE with CI had obvious atrophy of the gray matter volume (GMV) and total parenchymal brain volume (PBV); GABA/Cr ratio was decreased in ACC, but increased in bilateral hippocampus compared with that of the no cognitive impairment (NOCI) group.

CONCLUSION

The GABA/Cr ratio was more valuable than the NAA/(Cho + Cr) ratio in evaluating the dynamic metabolite changes in patients with TLE. Importantly, the GABA changes in the hippocampal and ACC regions were not consistent during different stages of the disease. In the bilateral hippocampus, the GABA/Cr ratio was decreased at the early stage, but recovered to normal levels later. The decreased GABA/Cr ratio in the ACC might indicate more cerebral cortex was involved, resulting in more CI in patients with TLE.

In vivo γ-aminobutyric acid increase as a biomarker of the epileptogenic zone: An unbiased metabolomics approach

OBJECTIVE

Following surgery, focal seizures relapse in 20% to 50% of cases due to the difficulty of delimiting the epileptogenic zone (EZ) by current imaging or electrophysiological techniques. Here, we evaluate an unbiased metabolomics approach based on ex vivo and in vivo nuclear magnetic resonance spectroscopy (MRS) methods to discriminate the EZ in a mouse model of mesiotemporal lobe epilepsy (MTLE).

METHODS

Four weeks after unilateral injection of kainic acid (KA) into the dorsal hippocampus of mice (KA-MTLE model), we analyzed hippocampal and cortical samples with high-resolution magic angle spinning (HRMAS) magnetic resonance spectroscopy (MRS). Using advanced multivariate statistics, we identified the metabolites that best discriminate the injected dorsal hippocampus (EZ) and developed an in vivo MEGAPRESS MRS method to focus on the detection of these metabolites in the same mouse model.

RESULTS

Multivariate analysis of HRMAS data provided evidence that γ-aminobutyric acid (GABA) is largely increased in the EZ of KA-MTLE mice and is the metabolite that best discriminates the EZ when compared to sham and, more importantly, when compared to adjacent brain regions. These results were confirmed by capillary electrophoresis analysis and were not reversed by a chronic exposition to an antiepileptic drug (carbamazepine). Then, using in vivo noninvasive GABA-edited MRS, we confirmed that a high GABA increase is specific to the injected hippocampus of KA-MTLE mice.

SIGNIFICANCE

Our strategy using ex vivo MRS-based untargeted metabolomics to select the most discriminant metabolite(s), followed by in vivo MRS-based targeted metabolomics, is an unbiased approach to accurately define the EZ in a mouse model of focal epilepsy. Results suggest that GABA is a specific biomarker of the EZ in MTLE.

Negative association between left prefrontal GABA concentration and BDNF serum concentration in young adults

Background

The brain's major inhibitory neurotransmitter gamma-aminobutyric acid (GABA) and the brain-derived neurotrophic factor (BDNF) play important roles in several stress-related disorders. Magnetic resonance spectroscopy (MRS) allows for non-invasive quantification of GABA concentration in the brain. We investigated the relationship between GABA concentration in the left dorsolateral prefrontal cortex (DLPFC) and BDNF concentration in the serum in a community-based sample of young subjects.

Methods

For the GABA measurement a single voxel MR spectrum was assessed in the prefrontal lobe (25 × 40 × 30 mm) using the MEGA-PRESS method in 276 subjects. BDNF serum concentrations were assessed with an ELISA kit. For 147 subjects we had both MRS and BDNF serum data, and for 79 subjects we had genotype data on the BDNF rs6265 polymorphism. Depressive psychopathology was assessed using Beck's Depression Inventory (BDI), Montgomery-Asberg Depression Rating Scale (MADRS) and Structured Clinical Interviews for Diagnostic and Statistical Manual of Mental Disorders (SCID) for DSM-IV.

Results

GABA concentration in the left DLPFC was negatively associated with BDNF serum concentration (r = -.264, p = .001). This correlation remained significant if corrected for sex (r = -.264, p = .001). BDNF serum concentration was also positively associated with volumes and surface areas of the left prefrontal cortex (p = .048, p = .005). There were no significant associations or interaction with depressive psychopathology (BDI, MADRS, SCID) or rs6265.

Conclusion

The results of this study suggest that GABA, BDNF and prefrontal brain volumes are interrelated, but do not show a strong association to depressive psychopathology, possibly due to the mild forms of psychiatric conditions present in our community-based sample.

Brain proton magnetic resonance spectroscopy findings in a Beagle dog with genetically confirmed Lafora disease

Cortical atrophy has been identified using magnetic resonance imaging (MRI) in humans and dogs with Lafora disease (LD). In humans, proton magnetic resonance spectroscopy (1HMRS) of the brain indicates decreased N‐acetyl‐aspartate (NAA) relative to other brain metabolites. Brain 1HMRS findings in dogs with LD are lacking. A 6‐year‐old female Beagle was presented with a history of a single generalized tonic‐clonic seizure and episodic reflex myoclonus. Clinical, hematological, and neurological examination findings and 3‐Tesla MRI of the brain were unremarkable. Brain 1HMRS with voxel positioning in the thalamus was performed in the affected Beagle. It identified decreased amounts of NAA, glutamate‐glutamine complex, and increased total choline and phosphoethanolamine relative to water and total creatine compared with the reference range in healthy control Beagles. A subsequent genetic test confirmed LD. Abnormalities in 1HMRS despite lack of changes with conventional MRI were identified in a dog with LD.

A comparison of sLASER and MEGA-sLASER using simultaneous interleaved acquisition for measuring GABA in the human brain at 7T

γ-Aminobutyric acid (GABA), the major inhibitory neurotransmitter, is challenging to measure using proton spectroscopy due to its relatively low concentration, J-coupling and overlapping signals from other metabolites. Currently, the prevalent methods for detecting GABA at ultrahigh field strengths (≥ 7 T) are GABA-editing and model fitting of non-editing single voxel spectra. These two acquisition approaches have their own advantages: the GABA editing approach directly measures the GABA resonance at 3 ppm, whereas the fitting approach on the non-editing spectrum allows the detection of multiple metabolites, and has an SNR advantage over longer echo time (TE) acquisitions. This study aims to compare these approaches for estimating GABA at 7 T. We use an interleaved sequence of semi-LASER (sLASER: TE = 38 ms) and MEGA-sLASER (TE = 80 ms). This simultaneous interleaved acquisition minimizes the differential effect of extraneous factors, and enables an accurate comparison of the two acquisition methods. Spectra were acquired with an 8 ml isotropic voxel at six different brain regions: anterior-cingulate cortex, dorsolateral-prefrontal cortex, motor cortex, occipital cortex, posterior cingulate cortex, and precuneus. Spectral fitting with LCModel quantified the GABA to total Cr (tCr: Creatine + Phosphocreatine) concentration ratio. After correcting the T2 relaxation time variation, GABA/tCr ratios were similar between the two acquisition approaches. GABA editing showed smaller spectral fitting error according to Cramér-Rao lower bound than the sLASER approach for all regions examined. We conclude that both acquisition methods show similar accuracy but the precision of the MEGA-editing approach is higher for GABA measurement. In addition, the 2.28 ppm GABA resonance was found to be important for estimating GABA concentration without macromolecule contamination in the GABA-edited acquisition, when utilizing spectral fitting with LCModel.

Reversibility of neuroimaging markers influenced by lifetime occupational manganese exposure

Manganese (Mn) is a neurotoxicant that many workers are exposed to daily. There is limited knowledge about how changes in exposure levels impact measures in magnetic resonance imaging (MRI). We hypothesized that changes in Mn exposure would be reflected by changes in the MRI relaxation rate R1 and thalamic γ-aminobutyric acid (GABAThal). As part of a prospective cohort study, 17 welders were recruited and imaged on two separate occasions approximately two years apart. MRI relaxometry was used to assess changes of Mn accumulation in the brain. Additionally, GABA was measured using magnetic resonance spectroscopy (MRS) in the thalamic and striatal regions of the brain. Air Mn exposure ([Mn]Air) and cumulative exposure indexes of Mn (Mn-CEI) for the past three months (Mn-CEI3M), past year (Mn-CEI12M), and lifetime (Mn-CEILife) were calculated using personal air sampling and a comprehensive work history, while toenails were collected for analysis of internal Mn body burden. Finally, welders' motor function was examined using the Unified Parkinson's Disease Rating Scale (UPDRS). Median exposure decreased for all exposure measures between the first and second scan. ΔGABAThal was significantly correlated with ΔMn-CEI3M (ρ = 0.66, adjusted p = 0.02), ΔMn-CEI12M (ρ = 0.70, adjusted p = 0.006) , and Δ[Mn]Air (ρ = 0.77, adjusted p = 0.002). ΔGABAThal significantly decreased linearly with ΔMn-CEI3M (quantile regression, β = 15.22, p = 0.02) as well as Δ[Mn]Air (β = 1.27, p = 0.04). Finally, Mn-CEILife interacted with Δ[Mn]Air in the substantia nigra where higher Mn-CEILife lessened the ΔR1 per Δ[Mn]Air (F-test, p = 0.005). While R1 and GABA changed with Mn exposure, UPDRS was unaffected. In conclusion, our study shows that effects from changes in Mn exposure are reflected in thalamic GABA levels and brain Mn levels, as measured by R1, in most brain regions.

In Vivo Dentate Nucleus Gamma-aminobutyric Acid Concentration in Essential Tremor vs. Controls

Despite its high prevalence, essential tremor (ET) is among the most poorly understood neurological diseases. The presence and extent of Purkinje cell (PC) loss in ET is the subject of controversy. PCs are a major storehouse of central nervous system gamma-aminobutyric acid (GABA), releasing GABA at the level of the dentate nucleus. It is therefore conceivable that cerebellar dentate nucleus GABA concentration could be an in vivo marker of PC number. We used in vivo ¹H magnetic resonance spectroscopy (MRS) to quantify GABA concentrations in two cerebellar volumes of interest, left and right, which included the dentate nucleus, comparing 45 ET cases to 35 age-matched controls. ¹H MRS was performed using a 3.0-T Siemens Tim Trio scanner. The MEGA-PRESS J-editing sequence was used for GABA detection in two cerebellar volumes of interest (left and right) that included the dentate nucleus. The two groups did not differ with respect to our primary outcome of GABA concentration (given in institutional units). For the right dentate nucleus, [GABA] in ET cases = 2.01 ± 0.45 and [GABA] in controls = 1.86 ± 0.53, p = 0.17. For the left dentate nucleus, [GABA] in ET cases = 1.68 ± 0.49 and [GABA] controls = 1.80 ± 0.53, p = 0.33. The controls had similar dentate nucleus [GABA] in the right vs. left dentate nucleus (p = 0.52); however, in ET cases, the value on the right was considerably higher than that on the left (p = 0.001). We did not detect a reduction in dentate nucleus GABA concentration in ET cases vs.

CONTROLS

One interpretation of the finding is that it does not support the existence of PC loss in ET; however, an alternative interpretation is the observed pattern could be due to the effects of terminal sprouting in ET (i.e., collateral sprouting from surviving PCs making up for the loss of GABA-ergic terminals from PC degeneration). Further research is needed.

Association between prefrontal glutamine levels and neuroticism determined using proton magnetic resonance spectroscopy

There is growing evidence for GABA and glutamate-glutamine dysfunction in the pathogenesis of mood and anxiety disorders. It is important to study this pathology in the early phases of the illness in order to develop new approaches to secondary prevention. New magnetic resonance spectroscopy (MRS) measures allow determining glutamine, the principal metabolite of synaptic glutamate that is directly related to glutamate levels in the synaptic cleft, as well as glutamate and GABA. In contrast to previous investigations, this study used community-based recruitment methods and a combined categorical and dimensional approach to psychopathology. In the study protocol, neuroticism was defined as the primary outcome. Neuroticism shares a large proportion of its genetic variance with mood and anxiety disorders. We examined young adult participants recruited from the general population in a cross-sectional study using 3-T 1H-MRS with one voxel in the left dorsolateral prefrontal cortex (DLPFC). The total sample of N = 110 (61 females) included 18 individuals suffering from MDD and 19 individuals suffering from DSM-IV anxiety disorders. We found that glutamine and glutamine-to-glutamate ratio were correlated with neuroticism in the whole sample (r = 0.263, p = 0.005, and n = 110; respectively, r = 0.252, p = 0.008, and n = 110), even when controlling for depression and anxiety disorder diagnoses (for glutamine: beta = 0.220, p = 0.047, and n = 110). Glutamate and GABA were not significantly correlated with neuroticism (r = 0.087, p = 0.365, and n = 110; r = -0.044, p = 0.645, and n = 110). Lack of self-confidence and emotional instability were the clinical correlates of glutamate-glutamine dysfunction. In conclusion, this study suggests that prefrontal glutamine is increased in early phases of mood and anxiety disorders. Further understanding of glutamate-glutamine dysfunction in stress-related disorders may lead to new therapeutic strategies to prevent and treat these disorders.

Relationship of auditory electrophysiological responses to magnetic resonance spectroscopy metabolites in Early Phase Psychosis

Both auditory evoked responses and metabolites measured by magnetic resonance spectroscopy (MRS) are altered in schizophrenia and other psychotic disorders, but the relationship between electrophysiological and metabolic changes are not well characterized. We examined the relation of MRS metabolites to cognitive and electrophysiological measures in individuals during the early phase of psychosis (EPP) and in healthy control subjects. The mismatch negativity (MMN) of the auditory event-related potential to duration deviant tones and the auditory steady response (ASSR) to 40 Hz stimulation were assessed. MRS was used to quantify glutamate+glutamine (Glx), N-Acetylasparate (NAA), creatine (Cre), myo-inositol (Ins) and choline (Cho) at a voxel placed medially in the frontal cortex. MMN amplitude and ASSR power did not differ between groups. The MRS metabolites Glx, Cre and Cho were elevated in the psychosis group. Partial least squares analysis in the patient group indicated that elevated levels of MRS metabolites were associated with reduced MMN amplitude and increased 40 Hz ASSR power. There were no correlations between the neurobiological measures and clinical measures. These data suggest that elevated neurometabolites early in psychosis are accompanied by altered auditory neurotransmission, possibly indicative of a neuroinflammatory or excitotoxic disturbance which disrupts a wide range of metabolic processes in the cortex.

Chemical biomarkers of epileptogenesis and ictogenesis in experimental epilepsy

Epilepsy produces chronic chemical changes induced by altered cellular structures, and acute ones produced by conditions leading into individual seizures. Here, we aim to quantify 24 molecules simultaneously at baseline and during periods of lowered seizure threshold in rats. Using serial hippocampal microdialysis collections starting two weeks after the pilocarpine-induced status epilepticus, we evaluated how this chronic epilepsy model affects molecule levels and their interactions. Then, we quantified the changes occurring when the brain moves into a pro-seizure state using a novel model of physiological ictogenesis. Compared with controls, pilocarpine animals had significantly decreased baseline levels of adenosine, homovanillic acid, and serotonin, but significantly increased levels of choline, glutamate, phenylalanine, and tyrosine. Step-wise linear regression identified that choline, homovanillic acid, adenosine, and serotonin are the most important features to characterize the difference in the extracellular milieu between pilocarpine and control animals. When increasing the hippocampal seizure risk, the concentrations of normetanephrine, serine, aspartate, and 5-hydroxyindoleacetic acid were the most prominent; however, there were no specific, consistent changes prior to individual seizures.

Imaging glutamate redistribution after acute N-acetylcysteine administration: A simultaneous PET/MR study

Glutamate is the most abundant excitatory neurotransmitter in the human brain, but in vivo imaging of acute fluctuations in glutamatergic levels has not been well established. The purpose of this study was to examine acute changes in glutamate after stimulation with N-acetylcysteine (NAC) using a simultaneous positron emission tomography/magnetic resonance spectroscopy (PET/MRS) approach. Ten healthy adult males were examined in two scanning sessions, and 5g NAC was administered 1 h prior to one of the scan sessions. Simultaneous PET/MR data were acquired using an integrated 3T PET/MR scanner. Glutamate (Glu), glutamine (Gln), and glutamate + glutamine (Glx) levels were assessed from MRS data collected from the basal ganglia with PRESS and from the left prefrontal cortex with PRESS and MEGAPRESS, and mGluR5 binding (BP_ND) was assessed from PET data collected with [¹⁸F]PSS232. NAC administration was associated with a significant reduction in Glx and Gln in the basal ganglia spectra, and in Glx in the frontal MEGAPRESS spectra (p < 0.05); no differences in [¹⁸F]PSS232 BP_ND were observed with NAC, although a correlation between pre-/post-treatment Glx and baseline BPnd was found. The MRS-visible Glx signal is sensitive to acute fluctuations in glutamate. The change in Glx was mostly driven by a change in Gln, lending weight to the notion that Gln can provide a proxy marker for neurotransmitter/synaptic glutamate. [¹⁸F]PSS232 binding is not sensitive to acute glutamate shifts independently, but was associated with the extent of glutamate liberation upon NAC stimulation.

Beyond Dopamine: GABA, Glutamate, and the Axial Symptoms of Parkinson Disease

Introduction: The axial symptoms of Parkinson disease (PD) include difficulties with balance, posture, speech, swallowing, and locomotion with freezing of gait, as well as axial rigidity. These axial symptoms impact negatively on quality of life for many patients, yet remain poorly understood. Dopaminergic treatments typically have little effect on the axial symptoms of PD, suggesting that disruptions in other neurotransmitter systems beyond the dopamine system may underlie these symptoms. The purpose of the present study was to examine the relationship between the axial symptoms of PD and GABA and glutamate levels quantified with magnetic resonance spectroscopy.

Methods: The participant group included 20 patients with PD and 17 healthy control participants. Water-scaled GABA and Glx (glutamate + glutamine) concentrations were derived from GABA-edited MEGA-PRESS spectra acquired from the left basal ganglia and prefrontal cortex, and additional water-scaled Glx concentrations were acquired from standard PRESS spectra acquired from the pons. Spectra were analyzed with LCModel. The axial symptoms of PD were evaluated from subscales of the Unified Parkinson's Disease rating scale (MDS-UPDRS).

Results: PD patients demonstrated significantly higher GABA levels in the basal ganglia, which correlated with the degree of gait disturbance. Basal ganglia Glx levels and prefrontal GABA and Glx levels did not differ significantly between patient and control groups, but within the PD group prefrontal Glx levels correlated negatively with difficulties turning in bed. Results from an exploratory subgroup analysis indicate that the associations between GABA, Glx, and axial symptoms scores are typically more prominent in akinetic-rigid patients than in tremor-dominant patients.

Conclusion: Alterations in GABAergic and glutamatergic neurotransmission may contribute to some of the axial symptoms of PD.

Diurnal changes in glutamate + glutamine levels of healthy young adults assessed by proton magnetic resonance spectroscopy

The glutamatergic α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor is involved in synaptic plasticity processes, and animal studies have demonstrated altered expression across the sleep wake cycle. Accordingly, glutamate levels are reduced during non-rapid eye movement (NREM) sleep and the rate of this decrease is positively correlated with sleep EEG slow wave activity (SWA). Here, we combined proton magnetic resonance spectroscopy (¹ H-MRS) and high-density sleep EEG to assess if ¹ H-MRS is sensitive to diurnal changes of glutamate + glutamine (GLX) in healthy young adults and if potential overnight changes of GLX are correlated to SWA. ¹ H-MRS was measured in the parietal lobe in the evening and in the subsequent morning. High-density sleep EEG was recorded overnight between the evening and morning scans. Our results revealed a significant overnight reduction in GLX, but no significant changes in other metabolites. The decrease in GLX positively correlated with the decrease of SWA. Our study demonstrates that quantification of diurnal changes in GLX is possible by means of ¹ H-MRS and indicates that overnight changes in GLX are related to SWA, a marker that is closely linked to the restorative function of sleep. This relationship might be of particular interest in clinical populations in which sleep is disturbed.

Classifying dynamic transitions in high dimensional neural mass models: A random forest approach

Neural mass models (NMMs) are increasingly used to uncover the large-scale mechanisms of brain rhythms in health and disease. The dynamics of these models is dependent upon the choice of parameters, and therefore it is crucial to be able to understand how dynamics change when parameters are varied. Despite being considered low dimensional in comparison to micro-scale, neuronal network models, with regards to understanding the relationship between parameters and dynamics, NMMs are still prohibitively high dimensional for classical approaches such as numerical continuation. Therefore, we need alternative methods to characterise dynamics of NMMs in high dimensional parameter spaces. Here, we introduce a statistical framework that enables the efficient exploration of the relationship between model parameters and selected features of the simulated, emergent model dynamics of NMMs. We combine the classical machine learning approaches of trees and random forests to enable studying the effect that varying multiple parameters has on the dynamics of a model. The method proceeds by using simulations to transform the mathematical model into a database. This database is then used to partition parameter space with respect to dynamic features of interest, using random forests. This allows us to rapidly explore dynamics in high dimensional parameter space, capture the approximate location of qualitative transitions in dynamics and assess the relative importance of all parameters in the model in all dimensions simultaneously. We apply this method to a commonly used NMM in the context of transitions to seizure dynamics. We find that the inhibitory sub-system is most crucial for the generation of seizure dynamics, confirm and expand previous findings regarding the ratio of excitation and inhibition, and demonstrate that previously overlooked parameters can have a significant impact on model dynamics. We advocate the use of this method in future to constrain high dimensional parameter spaces enabling more efficient, person-specific, model calibration.

Neurotransmitter activity is linked to outcome following subthalamic deep brain stimulation in Parkinson's disease

INTRODUCTION

While the mechanisms underlying the therapeutic effects of deep brain stimulation (DBS) in Parkinson's Disease (PD) are not yet fully understood, DBS appears to exert a wide range of neurochemical effects on the network level, thought to arise from activation of inhibitory and excitatory pathways. The activity within the primary inhibitory (GABAergic) and excitatory (glutamatergic) neurotransmitter systems may therefore play an important role in the therapeutic efficacy of DBS in PD. The purpose of this study was to investigate abnormalities in GABA-ergic and glutamatergic neurotransmission in PD, and to examine the link between neurotransmitter levels and outcome following DBS.

METHODS

Magnetic resonance spectra were acquired from the pons and basal ganglia in sixteen patients with PD and sixteen matched control participants. GABA and glutamate levels were quantified with LCModel, an automated spectral fitting package. Fourteen patients subsequently underwent DBS, and PD symptoms were evaluated with the MDS-UPDRS at baseline and six months after surgery. The efficacy of DBS treatment was evaluated from the percentage improvement in MDS-UPDRS scores.

RESULTS

Basal ganglia GABA levels were significantly higher in PD patients relative to control participants (p < 0.01), while pontine glutamate + glutamine (Glx) levels were significantly lower in patients with PD (p < 0.05). While GABA levels were not significantly related to outcome post-surgery, basal ganglia glutamate levels emerged as a significant predictor of outcome, suggesting a possible role for glutamatergic neurotransmission in the therapeutic mechanism of DBS.

CONCLUSION

GABAergic and glutamatergic neurotransmission is altered in PD, and glutamatergic activity in particular may influence outcome post-surgery.

Whole brain neuronal abnormalities in focal epilepsy quantified with proton MR spectroscopy

OBJECTIVE

To test the hypothesis that localization-related epilepsy is associated with widespread neuronal dysfunction beyond the ictal focus, reflected by a decrease in patients' global concentration of their proton MR spectroscopy (1H-MRS) observed marker, N-acetyl-aspartate (NAA).

METHODS

Thirteen patients with localization-related epilepsy (7 men, 6 women) 40±13 (mean±standard-deviation)years old, 8.3±13.4years of disease duration; and 14 matched controls, were scanned at 3 T with MRI and whole-brain (WB) 1H MRS. Intracranial fractions of brain volume, gray and white matter (fBV, fGM, fWM) were segmented from the MRI, and global absolute NAA creatine (Cr) and choline (Cho) concentrations were estimated from their WB 1H MRS. These metrics were compared between patients and controls using an unequal variance t test.

RESULTS

Patients' fBV, fGM and fWM: 0.81±0.07, 0.47±0.04, 0.31±0.04 were not different from controls' 0.79±0.05, 0.48±0.04, 0.32±0.02; nor were their Cr and Cho concentrations: 7.1±1.1 and 1.3±0.2 millimolar (mM) versus 7.7±0.7 and 1.4±0.1mM (p>0.05 all). Patients' global NAA concentration: 11.5±1.5 mM, however, was 12% lower than controls' 13.0±0.8mM (p=0.004).

CONCLUSIONS

These findings indicate that neuronal dysfunction in localization-related epilepsy extends globally, beyond the ictal zone, but without atrophy or spectroscopic evidence of other pathology. This suggests a diffuse decline in the neurons' health, rather than their number, early in the disease course. WB 1H-MRS assessment, therefore, may be a useful tool for quantification of global neuronal dysfunction load in epilepsy.

Thalamic GABA levels and occupational manganese neurotoxicity: Association with exposure levels and brain MRI

Excessive occupational exposure to Manganese (Mn) has been associated with clinical symptoms resembling idiopathic Parkinson's disease (IPD), impairing cognitive and motor functions. Several studies point towards an involvement of the brain neurotransmitter system in Mn intoxication, which is hypothesized to be disturbed prior to onset of symptoms. Edited Magnetic Resonance Spectroscopy (MRS) offers the unique possibility to measure γ-amminobutyric acid (GABA) and other neurometabolites in vivo non-invasively in workers exposed to Mn. In addition, the property of Mn as Magnetic Resonance Imaging (MRI) contrast agent may be used to study Mn deposition in the human brain. In this study, using MRI, MRS, personal air sampling at the working place, work history questionnaires, and neurological assessment (UPDRS-III), the effects of chronic Mn exposure on the thalamic GABAergic system was studied in a group of welders (N=39) with exposure to Mn fumes in a typical occupational setting. Two subgroups of welders with different exposure levels (Low: N=26; mean air Mn=0.13±0.1mg/m3; High: N=13; mean air Mn=0.23±0.18mg/m3), as well as unexposed control workers (N=22, mean air Mn=0.002±0.001mg/m3) were recruited. The group of welders with higher exposure showed a significant increase of thalamic GABA levels by 45% (p<0.01, F(1,33)=9.55), as well as significantly worse performance in general motor function (p<0.01, F(1,33)=11.35). However, welders with lower exposure did not differ from the controls in GABA levels or motor performance. Further, in welders the thalamic GABA levels were best predicted by past-12-months exposure levels and were influenced by the Mn deposition in the substantia nigra and globus pallidus. Importantly, both thalamic GABA levels and motor function displayed a non-linear pattern of response to Mn exposure, suggesting a threshold effect.

Association of exposure to manganese and iron with striatal and thalamic GABA and other neurometabolites - Neuroimaging results from the WELDOX II study

OBJECTIVE

Magnetic resonance spectroscopy (MRS) is a non-invasive method to quantify neurometabolite concentrations in the brain. Within the framework of the WELDOX II study, we investigated the association of exposure to manganese (Mn) and iron (Fe) with γ-aminobutyric acid (GABA) and other neurometabolites in the striatum and thalamus of 154 men.

MATERIAL AND METHODS

GABA-edited and short echo-time MRS at 3T was used to assess brain levels of GABA, glutamate, total creatine (tCr) and other neurometabolites. Volumes of interest (VOIs) were placed into the striatum and thalamus of both hemispheres of 47 active welders, 20 former welders, 36 men with Parkinson's disease (PD), 12 men with hemochromatosis (HC), and 39 male controls. Linear mixed models were used to estimate the influence of Mn and Fe exposure on neurometabolites while simultaneously adjusting for cerebrospinal fluid (CSF) content, age and other factors. Exposure to Mn and Fe was assessed by study group, blood concentrations, relaxation rates R1 and R2* in the globus pallidus (GP), and airborne exposure (active welders only).

RESULTS

The median shift exposure to respirable Mn and Fe in active welders was 23μg/m3 and 110μg/m3, respectively. Airborne exposure was not associated with any other neurometabolite concentration. Mn in blood and serum ferritin were highest in active and former welders. GABA concentrations were not associated with any measure of exposure to Mn or Fe. In comparison to controls, tCr in these VOIs was lower in welders and patients with PD or HC. Serum concentrations of ferritin and Fe were associated with N-acetylaspartate, but in opposed directions. Higher R1 values in the GP correlated with lower neurometabolite concentrations, in particular tCr (exp(β)=0.87, p<0.01) and choline (exp(β)=0.84, p=0.04). R2* was positively associated with glutamate-glutamine and negatively with myo-inositol.

CONCLUSIONS

Our results do not provide evidence that striatal and thalamic GABA differ between Mn-exposed workers, PD or HC patients, and controls. This may be due to the low exposure levels of the Mn-exposed workers and the challenges to detect small changes in GABA. Whereas Mn in blood was not associated with any neurometabolite content in these VOIs, a higher metal accumulation in the GP assessed with R1 correlated with generally lower neurometabolite concentrations.

Temporal Dynamics of Antidepressant Ketamine Effects on Glutamine Cycling Follow Regional Fingerprints of AMPA and NMDA Receptor Densities

The anterior cingulate cortex (ACC) has shown decreased glutamate levels in patients with major depressive disorder. Subanesthetic doses of ketamine were repeatedly shown to improve depressive symptoms within 24 h after infusion and this antidepressant effect was attributed to increased α-amino-3-hydroxyl-5-methyl-4-isoxazole-propionate (AMPA) throughput. To elucidate ketamine's mechanism of action, we tested whether the clinical time course of the improvement is mirrored by the change of glutamine/glutamate ratio and if such effects show a regional and temporal specificity in two distinct subdivisions of ACC with different AMPA/N-methyl-D-aspartate receptor profiles. In a double-blind, placebo-controlled intravenous infusion study of ketamine, we measured glutamate and glutamine in the pregenual ACC (pgACC) and the anterior midcingulate cortex at 1 and 24 h post infusion with magnetic resonance spectroscopy at 7 T. A significant interaction of time, region, and treatment was found for the glutamine/glutamate ratios (placebo, n=14; ketamine, n=12). Post-hoc analyses revealed that the glutamine/glutamate ratio increased significantly in the ketamine group, compared with placebo, specifically in the pgACC after 24 h. The glutamine/glutamate increase in the pgACC caused by ketamine at 24 h post infusion was reproduced in an enlarged sample (placebo, n=24; ketamine, n=20). Our results support a significant temporal and regional response in glutamine/glutamate ratios to a single subanesthetic dose of ketamine, which mirrors the time course of the antidepressant response and reversal of the molecular deficits in patients and which may be associated with the histoarchitectonical receptor fingerprints of the ACC subregions.

Temporal brain metabolite changes in preterm infants with normal development

OBJECTIVE

Preterm infants are at high risk for developmental delay, epilepsy, and autism spectrum disorders. Some reports have described associations between these conditions and gamma-aminobutyric acid (GABA) dysfunction; however, no study has evaluated temporal changes in GABA in preterm infants. Therefore, we assessed temporal changes in brain metabolites including GABA using single-voxel 3-Tesla (T) proton magnetic resonance spectroscopy (¹H-MRS) in preterm infants with normal development.

METHODS

We performed 3T ¹H-MRS at 37-46 postmenstrual weeks (PMWs, period A) and 64-73PMWs (period B). GABA was assessed with the MEGA-PRESS method. N-acetyl aspartate (NAA), glutamate-glutamine complex (Glx), creatine (Cr), choline (Cho), and myo-inositol (Ins) were assessed with the PRESS method. Metabolite concentrations were automatically calculated using LCModel.

RESULTS

Data were collected from 20 preterm infants for periods A and B (medians [ranges], 30 [24-34] gestational weeks, 1281 [486-2030]g birth weight). GABA/Cr ratio decreased significantly in period B (p=0.03), but there was no significant difference in GABA/Cho ratios (p=0.58) between the two periods. In period B, NAA/Cr, Glx/Cr, NAA/Cho, and Glx/Cho ratios were significantly increased (p<0.01), whereas Cho/Cr, Ins/Cr, and Ins/Cho ratios were significantly decreased (p<0.01). There was no significant difference for GABA or Cho concentrations (p=0.52, p=0.22, respectively). NAA, Glx, and Cr concentrations were significantly increased (p<0.01), whereas Ins was significantly decreased (p<0.01).

CONCLUSIONS

Our results provide new information on normative values of brain metabolites in preterm infants.

Perisylvian GABA levels in schizophrenia and bipolar disorder

The aim of this study is to measure GABA levels of perisylvian cortices in schizophrenia and bipolar disorder patients, using proton magnetic resonance spectroscopy (¹H-MRS). Patients with schizophrenia (n=25), bipolar I disorder (BD-I; n=28) and bipolar II disorder (BD-II; n=20) were compared with healthy controls (n=30). ¹H-MRS data was acquired using a Siemens 3T whole body scanner to quantify right and left perisylvian structures' (including superior temporal lobes) GABA levels. Right perisylvian GABA values differed significantly between groups [χ²=9.62, df: 3, p=0.022]. GABA levels were significantly higher in the schizophrenia group compared with the healthy control group (p=0.002). Furthermore, Chlorpromazine equivalent doses of antipsychotics correlated with right hemisphere GABA levels (r²=0.68, p=0.006, n=33). GABA levels are elevated in the right hemisphere in patients with schizophrenia in comparison to bipolar disorder and healthy controls. The balance between excitatory and inhibitory controls over the cortical circuits may have direct relationship with GABAergic functions in auditory cortices. In addition, GABA levels may be altered by brain regions of interest, psychotropic medications, and clinical stage in schizophrenia and bipolar disorder.

Effect of Primidone on Dentate Nucleus γ-Aminobutyric Acid Concentration in Patients With Essential Tremor

OBJECTIVES

It is not known whether current use of the medication primidone affects brain γ-aminobutyric acid (GABA) concentrations. This is an important potential confound in studies of the pathophysiology of essential tremor (ET), one of the most common neurological diseases. We compared GABA concentrations in the dentate nucleus in 6 ET patients taking primidone versus 26 ET patients not taking primidone.

METHODS

(1)H magnetic resonance spectroscopy was performed using a 3.0-T Siemens Tim Trio scanner. The MEGA-PRESS J-editing sequence was used for GABA detection in 2 cerebellar volumes of interest (left and right) that included the dentate nucleus.

RESULTS

The right dentate GABA concentration was similar in the 2 groups (2.21 ± 0.46 [on primidone] vs 1.93 ± 0.39 [not on primidone], P = 0.15), as was the left dentate GABA concentration (1.61 ± 0.35 [on primidone] vs 1.67 ± 0.34 [not on primidone], P = 0.72). The daily primidone dose was not associated with either right or left dentate GABA concentrations (P = 0.89 and 0.76, respectively).

CONCLUSIONS

We did not find a difference in dentate GABA concentrations between 6 ET patients taking daily primidone and 26 ET patients not taking primidone. Furthermore, there was no association between daily primidone dose and dentate GABA concentration. These data suggest that it is not necessary to exclude ET patients on primidone from magnetic resonance spectroscopy studies of dentate GABA concentration, and if assessment of these concentrations was to be developed as a biomarker for ET, primidone usage would not confound interpretation of the results.

Use of quantitative brain water imaging as concentration reference for J-edited MR spectroscopy of GABA

PURPOSE

To compare two different methods of obtaining the water reference for determination of quantitative water-scaled in vivo concentration estimates of γ-aminobutyric acid (GABA).

METHODS

Water-scaled GABA estimates from localized J-difference edited MR spectroscopy experiments can be computed using standard values for tissue-specific water content and relaxation times. Water content and relaxation may, however, be altered in pathology. This work re-analyzed data from a recent study in healthy controls and patients with minimal (mHE) or grade I (HE 1) hepatic encephalopathy, a disease associated with slight elevation of brain water content. J-difference edited MR spectroscopy data were combined with quantitative brain water measures, which provided individual water density references and T1 relaxation times. Resulting GABA estimates were compared to concentration values obtained using standard tissue-specific water content and relaxation values.

RESULTS

Occipital GABA concentration values obtained from individual water and T1 maps were 1.64±0.35mM in controls, and significantly higher (P<0.01) than in mHE (1.15±0.28mM) and HE 1 patients (1.18±0.09mM). Results from the tissue-dependent approach (1.58±0.30mM (controls), 1.10±0.27mM (mHE) and 1.12±0.12mM (HE 1)) were slightly lower (P<0.05 in each group).

CONCLUSION

Water-scaled in vivo GABA estimates can be obtained with individual water density and T1 relaxation mapping. This approach may be useful for studying GABA levels in pathologies with substantial brain water content or relaxation changes.

Reproducibility and effect of tissue composition on cerebellar γ-aminobutyric acid (GABA) MRS in an elderly population

MRS provides a valuable tool for the non-invasive detection of brain γ-aminobutyric acid (GABA) in vivo. GABAergic dysfunction has been observed in the aging cerebellum. The study of cerebellar GABA changes is of considerable interest in understanding certain age-related motor disorders. However, little is known about the reproducibility of GABA MRS in an aged population. Therefore, this study aimed to explore the feasibility and reproducibility of GABA MRS in the aged cerebellum at 3.0 T and to examine the effect of differing tissue composition on GABA measurements. MRI and (1)H MRS examinations were performed on 10 healthy elderly volunteers (mean age, 75.2 ± 6.5 years) using a 3.0-T Siemens Tim Trio scanner. Among them, five subjects were scanned twice to assess the short-term reproducibility. The MEGA-PRESS (Mescher-Garwood point-resolved spectroscopy) J-editing sequence was used for GABA detection in two volumes of interest (VOIs) in the left and right cerebellar dentate. MRS data processing and quantification were performed with LCModel 6.3-0L using two separate basis sets, generated from density matrix simulations using published values for chemical shifts and J couplings. Raw metabolite levels from LCModel outputs were corrected for cerebrospinal fluid contamination and relaxation. GABA-edited spectra yielded robust and stable GABA measurements with averaged intra-individual coefficients of variation for corrected GABA+ between 4.0 ± 2.8% and 13.4 ± 6.3%, and inter-individual coefficients of variation between 12.6% and 24.2%. In addition, there was a significant correlation between GABA+ obtained with the two LCModel basis sets. Overall, our results demonstrated the feasibility and reproducibility of cerebellar GABA-edited MRS at 3.0 T in an elderly population. This information might be helpful for studies using this technique to study GABA changes in normal or diseased aging brain, e.g. for power calculations and the interpretation of longitudinal observations.

Striatal and thalamic GABA level concentrations play differential roles for the modulation of response selection processes by proprioceptive information

The selection of appropriate responses is a complex endeavor requiring the integration of many different sources of information in fronto-striatal-thalamic circuits. An often neglected but relevant piece of information is provided by proprioceptive inputs about the current position of our limbs. This study examines the importance of striatal and thalamic GABA levels in these processes using GABA-edited magnetic resonance spectroscopy (GABA-MRS) and a Simon task featuring proprioception-induced interference in healthy subjects. As a possible model of deficits in the processing of proprioceptive information, we also included Parkinson's disease (PD) patients in this study. The results show that proprioceptive information about unusual postures complicates response selection processes in controls, but not in PD patients. The well-known deficits of PD patients in processing proprioceptive information can turn into a benefit when altered proprioceptive information would normally complicate response selection processes. Striatal and thalamic GABA levels play dissociable roles in the modulation of response selection processes by proprioceptive information: Striatal GABA levels seem to be important for the general speed of responding, most likely because striatal GABA promotes response selection. In contrast, the modulation of response conflict by proprioceptive information is closely related to thalamic GABA concentrations with higher concentration being related to a smaller response conflict effect. The most likely explanation for this finding is that the thalamus is involved in the integration of sensorimotor, attentional, and cognitive information for the purpose of response formation. Yet, this effect in the thalamus vanishes when controls and PD patients were analyzed separately.

GABA and glutamate levels in occlusal splint-wearing males with possible bruxism

OBJECTIVE

The inhibitory neurotransmitter γ-aminobutyric acid (GABA) plays an important role in the pathophysiology of anxiety behavioural disorders such as panic disorder and post-traumatic stress disorder and is also implicated in the manifestation of tooth-grinding and clenching behaviours generally known as bruxism. In order to test whether the stress-related behaviours of tooth-grinding and clenching share similar underlying mechanisms involving GABA and other metabolites as do anxiety-related behavioural disorders, we performed a Magnetic Resonance Spectroscopy (MRS) study for accurate, in vivo metabolite quantification in anxiety-related brain regions.

DESIGN

MRS was performed in the right hippocampus and right thalamus involved in the hypothalamic-pituitary-adrenal axis system, together with a motor planning region (dorsal anterior cingulate cortex/pre-supplementary motor area) and right dorsolateral prefrontal cortex (DLPFC). Eight occlusal splint-wearing men (OCS) with possible tooth-grinding and clenching behaviours and nine male controls (CON) with no such behaviour were studied.

RESULTS

Repeated-measures ANOVA showed significant Group×Region interaction for GABA+ (p = 0.001) and glutamate (Glu) (p = 0.031). Between-group post hoc ANOVA showed significantly lower levels of GABA+ (p = 0.003) and higher levels of Glu (p = 0.002) in DLPFC of OCS subjects. These GABA+ and Glu group differences remained significant (GABA+, p = 0.049; Glu, p = 0.039) after the inclusion of anxiety as a covariate. Additionally, GABA and Glu levels in the DLPFC of all subjects were negatively related (Pearson's r = -0.75, p = 0.003).

CONCLUSIONS

These findings indicate that the oral behaviours of tooth-grinding and clenching, generally known as bruxism, may be associated with disturbances in brain GABAergic and glutamatergic systems.

Sleep spindles are related to schizotypal personality traits and thalamic glutamine/glutamate in healthy subjects

BACKGROUND

Schizophrenia is a severe mental disorder affecting approximately 1% of the worldwide population. Yet, schizophrenia-like experiences (schizotypy) are very common in the healthy population, indicating a continuum between normal mental functioning and the psychosis found in schizophrenic patients. A continuum between schizotypy and schizophrenia would be supported if they share the same neurobiological origin. Two such neurobiological markers of schizophrenia are: (1) a reduction of sleep spindles (12-15 Hz oscillations during nonrapid eye movement sleep), likely reflecting deficits in thalamo-cortical circuits and (2) increased glutamine and glutamate (Glx) levels in the thalamus. Thus, this study aimed to investigate whether sleep spindles and Glx levels are related to schizotypal personality traits in healthy subjects.

METHODS

Twenty young male subjects underwent 2 all-night sleep electroencephalography recordings (128 electrodes). Sleep spindles were detected automatically. After those 2 nights, thalamic Glx levels were measured by magnetic resonance spectroscopy. Subjects completed a magical ideation scale to assess schizotypy.

RESULTS

Sleep spindle density was negatively correlated with magical ideation (r = -.64, P < .01) and thalamic Glx levels (r = -.70, P < .005). No correlation was found between Glx levels in the thalamus and magical ideation (r = .12, P > .1).

CONCLUSIONS

The common relationship of sleep spindle density with schizotypy and thalamic Glx levels indicates a neurobiological overlap between nonclinical schizotypy and schizophrenia. Thus, sleep spindle density and magical ideation may reflect the anatomy and efficiency of the thalamo-cortical system that shows pronounced impairment in patients with schizophrenia.

Striatal GABA-MRS predicts response inhibition performance and its cortical electrophysiological correlates

Response inhibition processes are important for performance monitoring and are mediated via a network constituted by different cortical areas and basal ganglia nuclei. At the basal ganglia level, striatal GABAergic medium spiny neurons are known to be important for response selection, but the importance of the striatal GABAergic system for response inhibition processes remains elusive. Using a novel combination of behavior al, EEG and magnetic resonance spectroscopy (MRS) data, we examine the relevance of the striatal GABAergic system for response inhibition processes. The study shows that striatal GABA levels modulate the efficacy of response inhibition processes. Higher striatal GABA levels were related to better response inhibition performance. We show that striatal GABA modulate specific subprocesses of response inhibition related to pre-motor inhibitory processes through the modulation of neuronal synchronization processes. To our knowledge, this is the first study providing direct evidence for the relevance of the striatal GABAergic system for response inhibition functions and their cortical electrophysiological correlates in humans.