MR spectroscopy: its potential role for drug development for the treatment of psychiatric diseases

Alcohol Craving and Severity are Associated with Dorsal Anterior Cingulate Choline Levels in Individuals with an Alcohol Use Disorder

AIMS

Magnetic resonance spectroscopy (MRS) has been used to probe inflammation in the brain. While altered MRS metabolite levels have previously been found in individuals with alcohol use disorder (AUD), the relationship between potential metabolite markers of inflammation and the clinical correlates of AUD remains understudied. Therefore, this exploratory study sought to elucidate the clinical significance of inflammation in AUD by examining relationships between metabolites, AUD severity, alcohol consumption, and craving in individuals with AUD.

METHODS

Data for this secondary analysis are derived from a two-week clinical trial of ibudilast to treat AUD. Forty-three non-treatment-seeking individuals with an AUD (26M/17F) completed an MRS scan and alcohol-related questionnaires. MRS was performed using a multi-voxel array placed above the corpus callosum, extending from the pregnenual anterior cingulate to premotor cortex. The dorsal anterior cingulate was selected as the volume of interest. Metabolite levels of choline-compounds (Cho), myo-inositol (mI), and creatine+phosphocreatine (Cr) were quantified. Separate hierarchical regression models were used to evaluate the independent effects of metabolite levels on alcohol craving, alcohol problem severity, and alcohol consumption.

RESULTS

Dorsal anterior cingulate Cho predicted alcohol craving and alcohol problem severity over and above demographics, medication, and alcohol consumption measures. mI and Cr did not predict alcohol craving or alcohol problem severity. Metabolite markers were not predictive of alcohol consumption.

CONCLUSIONS

This preliminary study indicates that dACC Cho is sensitive to clinical characteristics of AUD. This is a further step in advancing neurometabolites, particularly Cho, as potential biomarkers and treatment targets for AUD.

Distinguishing glutamate and glutamine in in vivo 1 H MRS based on nuclear spin singlet order filtering

PURPOSE

The signals of glutamate (Glu) and glutamine (Gln) are often significantly overlapped in routine ¹ H-MR spectra of human brain in vivo. Selectively probing the signals of Glu and Gln in vivo is very important for the study of the metabolisms in which Glu and Gln are involved.

METHODS

The Glu-/Gln- targeted pulse sequences are developed to selectively probe the signals of Glu and Gln. The core part of the Glu-/Gln- targeted pulse sequences lies on the preparation of the nuclear spin singlet orders (SSOs) of the five-spin systems of Glu and Gln. The optimal control method is used to prepare the SSOs of Glu and Gln with high efficiency.

RESULTS

The Glu-/Gln- targeted pulse sequences have been applied on phantoms to selectively probe the signals of Glu and Gln. Moreover, in the in vivo experiments, the signals of Glu and Gln in human brains of healthy subjects have been successfully probed separately.

CONCLUSION

The developed Glu-/Gln- targeted pulse sequences can be used to distinguish the ¹ H-MR signals of Glu and Gln in human brains in vivo. The optimal control method provides an effective way to prepare the SSO of a specific spin system with high efficiency and in turn selectively probe the signals of a targeted molecule.

Fronto-Cerebellar Neurometabolite Alterations After Methylphenidate in Children and Adolescents With ADHD: A Proton Magnetic Resonance Spectroscopy Study

OBJECTIVE

The fronto-cerebellar circuit is involved in ADHD pathophysiology. Methylphenidate, as a first-line medication for ADHD, affects different brain regions, however, its effect on the fronto-cerebellar circuit is not investigated sufficiently. We aimed to investigate the effect of 8-week treatment with methylphenidate on neurometabolite ratios in the fronto-cerebellar circuit in ADHD participants using magnetic resonance spectroscopy (MRS).

METHODS

Fifteen drug-naïve ADHD children and adolescents were enrolled in the present study. Two single-voxel MR spectra were acquired from the right dorsolateral prefrontal cortex (DLPFC) and left Crus 1, before and after the medication. Also, neuropsychological and behavioral assessments were administered.

RESULTS

After medication, the glutamate/creatine in the DLPFC and the choline/creatine in the Crus 1 decreased in the ADHD participants.

CONCLUSION

These findings propose that methylphenidate-induced metabolite changes in the fronto-cerebellar circuit could be associated with improvement in cognitive/behavioral characteristics in ADHD. Also, results highlighted cerebellar engagement in ADHD pathophysiology.

Quantifying GABA in Addiction: A Review of Proton Magnetic Resonance Spectroscopy Studies

Gamma-aminobutyric acid (GABA) signaling plays a crucial role in drug reward and the development of addiction. Historically, GABA neurochemistry in humans has been difficult to study due to methodological limitations. In recent years, proton magnetic resonance spectroscopy (¹H-MRS, MRS) has emerged as a non-invasive imaging technique that can detect and quantify human brain metabolites in vivo. Novel sequencing and spectral editing methods have since been developed to allow for quantification of GABA. This review outlines the clinical research utilization of ¹H-MRS in understanding GABA neurochemistry in addiction and summarizes current literature that reports GABA measurements by MRS in addiction. Research on alcohol, nicotine, cocaine, and cannabis addiction all suggest medications that modulate GABA signaling may be effective in reducing withdrawal, craving, and other addictive behaviors. Thus, we discuss how improvements in current MRS techniques and design can optimize GABA quantification in future studies and explore how monitoring changes to brain GABA could help identify risk factors, improve treatment efficacy, further characterize the nature of addiction, and provide crucial insights for future pharmacological development.

Cortical GABA levels are reduced in young adult binge drinkers: Association with recent alcohol consumption and sex

Binge drinking refers to a pattern of alcohol intake that raises blood alcohol concentration to or above legal intoxication levels. It is common among young adults and is associated with health risks that scale up with alcohol intake. Acute intoxication depresses neural activity via complex signaling mechanisms by enhancing inhibition mediated by gamma-amino butyric acid (GABA), and by decreasing excitatory glutamatergic effects. Evidence primarily rooted in animal research indicates that the brain compensates for the acute depressant effects under the conditions of habitual heavy use. These neuroadaptive changes are reflected in neural hyperexcitability via downregulated inhibitory signaling, which becomes apparent as withdrawal symptoms. However, human evidence on the compensatory reduction in GABA signaling is scant. The neurochemical aspect of this mechanistic model was evaluated in the present study with proton magnetic resonance spectroscopy (¹H-MRS) which is sensitive to GABA plus macromolecule signal (GABA + ). Furthermore, we examined sex differences in GABA + levels as a function of a recent history of binge drinking, given interactions between endogenous neurosteroids, GABA signaling, and alcohol. The study recruited young adult women and men (22.2 ± 2.8 years of age) who were classified as binge drinkers (BDs, N = 52) if they reported ≥ 5 binge episodes in the previous six months. Light drinkers (LDs, N = 49) reported drinking regularly, but not exceeding ≤ 2 binge episodes in the past six months. GABA-edited ¹H-MR spectra were acquired from the occipital cortex at 3 T with the MEGA-PRESS sequence. GABA + signal was analyzed relative to water and total creatine (Cr) levels as a function of binge drinking history and sex. Controlling for within-voxel tissue composition, both GABA + indices showed decreased GABA + levels in BDs relative to LDs. The reduced GABA + concentration was associated with occasional high-intensity drinking in the BD group. This evidence is consistent with compensatory GABA downregulation that accompanies alcohol misuse, tipping the excitation/inhibition balance towards hyperexcitability. Analysis of the time course of GABA + neuroplasticity indicated that GABA + was lowest when measured one day after the last drinking occasion in BDs. While the BD vs LD differences were primarily driven by LD women, there was no interaction between Sex and a history of binge drinking. GABA + was higher in LD women compared to LD men. Aligned with the allostasis model, the mechanistic compensatory GABA downregulation observed in young emerging adults engaging in occasional binge drinking complements direct neural measures of hyperexcitability in BDs. Notably, these results suggest that neuroadaptation to alcohol is detectable at the levels of consumption that are within a normative range, and may contribute to adverse health outcomes.

Neurochemical Alterations in Social Anxiety Disorder (SAD): A Systematic Review of Proton Magnetic Resonance Spectroscopic Studies

(1) Objective: Considering that current knowledge of mechanisms involved in the molecular pathogenesis of Social Anxiety Disorder (SAD) is limited, we conducted a systematic review to evaluate cumulative data obtained by Proton Magnetic Resonance Spectroscopic (¹H MRS) studies. (2) Methods: A computer-based literature search of Medline, EMBASE, PsycInfo, and ProQuest was performed. Only cross-sectional studies using ¹H MRS techniques in participants with SAD and healthy controls (HCs) were selected. (3) Results: The search generated eight studies. The results indicated regional abnormalities in the ‘fear neurocircuitry’ in patients with SAD. The implicated regions included the anterior cingulate cortex (ACC), dorsomedial prefrontal cortex (dmPFC), dorsolateral prefrontal cortex (dlPFC), insula, occipital cortex (OC), as well as the subcortical regions, including the thalamus, caudate, and the putamen. (4) Conclusions: The evidence derived from eight studies suggests that possible pathophysiological mechanisms of SAD include impairments in the integrity and function of neurons and glial cells, including disturbances in energy metabolism, maintenance of phospholipid membranes, dysregulations of second messenger systems, and excitatory/inhibitory neurocircuitry. Conducting more cross-sectional studies with larger sample sizes is warranted given the limited evidence in this area of research.

Motion correction in magnetic resonance spectroscopy

In vivo proton magnetic resonance spectroscopy and spectroscopic imaging (MRS/MRSI) are valuable tools to study normal and abnormal human brain physiology. However, they are sensitive to motion, due to strong crusher gradients, long acquisition times, reliance on high magnetic field homogeneity, and particular acquisition methods such as spectral editing. The effects of motion include incorrect spatial localization, phase fluctuations, incoherent averaging, line broadening, and ultimately quantitation errors. Several retrospective methods have been proposed to correct motion-related artifacts. Recent advances in hardware also allow prospective (real-time) correction of the effects of motion, including adjusting voxel location, center frequency, and magnetic field homogeneity. This article reviews prospective and retrospective methods available in the literature and their implications for clinical MRS/MRSI. In combination, these methods can attenuate or eliminate most motion-related artifacts and facilitate the acquisition of high-quality data in the clinical research setting.

Increased inflammation and brain glutamate define a subtype of depression with decreased regional homogeneity, impaired network integrity, and anhedonia

Combined increases in peripheral inflammation and brain glutamate may identify a subtype of depression with distinct neuroimaging signatures. Two contrasting subgroups of depressed subjects-with and without combined elevations in plasma C-reactive protein (CRP) and basal ganglia glutamate (high and low CRP-Glu, respectively) were identified by hierarchical clustering using plasma CRP (indexing peripheral inflammation) and magnetic resonance spectroscopy (MRS)-based measurement of left basal ganglia glutamate. High CRP-Glu group status was associated with greater severity of anhedonia and cognitive and motor slowing. Local- and network-level measures of functional integrity were determined using brain oxygen level-dependent (BOLD)-oscillatory activity and graph theory. Greater decreases in concordance of oscillatory activity between neighboring voxels (Regional Homogeneity 'ReHo', p < 0.01) within the MRS volume-of-interest was associated with the High CRP-Glu subgroup. Using brain-wide, CRP-Glu ReHo contrast maps, a covariance network of 41 regions-of-interest (ROIs) with similar ReHo decreases was identified in the High CRP-Glu group and was located to brain structures previously implicated in depression. The 41-ROI network was further decomposed into four subnetworks. ReHo decreases within Subnetwork4-comprised of reward processing regions -was associated with anhedonia. Subnetwork4 ReHo also predicted decreased network integrity, which mediated the link between local ReHo and anhedonia in the Low but not High CRP-Glu group. These findings suggest that decreased ReHo and related disruptions in network integrity may reflect toxic effects of inflammation-induced increases in extrasynaptic glutamate signaling. Moreover, local BOLD oscillatory activity as reflected in ReHo might be a useful measure of target-engagement in the brain for treatment of inflammation-induced behaviors.

Two-Dimensional Proton Magnetic Resonance Spectroscopy versus J-Editing for GABA Quantification in Human Brain: Insights from a GABA-Aminotransferase Inhibitor Study

Metabolite-specific, scalar spin-spin coupling constant (J)-editing ¹H MRS methods have become gold-standard for measuring brain γ-amino butyric acid (GABA) levels in human brain. Localized, two-dimensional (2D) ¹H MRS technology offers an attractive alternative as it significantly alleviates the problem of severe metabolite signal overlap associated with standard 1D MRS and retains spectroscopic information for all MRS-detectable species. However, for metabolites found at low concentration, a direct, in vivo, comprehensive methods comparison is challenging and has not been reported to date. Here, we document an assessment of comparability between 2D ¹H MRS and J-editing methods for measuring GABA in human brain. This clinical study is unique in that it involved chronic administration a GABA-amino transferase (AT) inhibitor (CPP-115), which induces substantial increases in brain GABA concentration, with normalization after washout. We report a qualitative and quantitative comparison between these two measurement techniques. In general, GABA concentration changes detected using J-editing were closely mirrored by the 2D ¹H MRS time courses. The data presented are particularly encouraging considering recent 2D ¹H MRS methodological advances are continuing to improve temporal resolution and spatial coverage for achieving whole-brain, multi-metabolite mapping.

Metabolic effects of light deprivation in the prefrontal cortex of rats with depression-like behavior: In vivo proton magnetic resonance spectroscopy at 7T

Recent evidence suggests that the glutamate system plays an important role in the pathogenesis of major depressive disorder (MDD). The aim of this study was to investigate the effects of light deprivation (LD) in the prefrontal cortex (PFC) of animals with depression-like behavior, targeting the glutamate system, using in vivo proton magnetic resonance spectroscopy (¹H MRS). Male Sprague-Dawley rats were housed in constant darkness for six weeks (n = 12; LD group), while controls (n = 8) were housed under normal light cycles. The animals were assessed with forced swim tests. Point-resolved spectroscopy was used to quantify metabolite levels in the PFC. To substantiate the validity of the use of in vivo¹H MRS in this study, the spectra obtained in the in vivo¹H MRS, parametrically matched spectral simulation, and in vitro experiments were analyzed. The results of the spectral analyses showed that the quantification of glutamate and glutamine was not significantly affected by spectral overlaps. Thus, these results suggested that in vivo¹H MRS can be used to reliably investigate the glutamate system. The results of the forced swim test showed LD-induced behavioral despairs in the animals. The levels of glutamate, myo-inositol, phosphocreatine, and total creatine were found significantly (p < 0.010) increased in the PFC of the LD animals compared with the controls. These results suggested that the LD-induced metabolic changes were consistent with the previous findings in patients with MDD and that short-echo-time in vivo¹H MRS can be used to effectively measure depression-induced alterations in glutamate systems.

In Vivo Detection of CPP-115 Target Engagement in Human Brain

CPP-115, a next-generation γ-amino butyric acid (GABA)-aminotransferase (AT) inhibitor, shows comparable pharmacokinetics, improved safety and tolerability, and a more favorable toxicity profile when compared with vigabatrin. The pharmacodynamic characteristics of CPP-115 remain to be evaluated. The present study employed state-of-the-art proton magnetic resonance spectroscopy techniques to measure changes in brain GABA+ (the composite resonance of GABA, homocarnosine, and macromolecules) concentrations in healthy subjects receiving oral daily doses of CPP-115 or placebo. Six healthy adult males were randomized to receive either single daily 80 mg doses of CPP-115 (n=4) or placebo (n=2) for 6, 10, or 14 days. Metabolite-edited spectra and two-dimensional J-resolved spectroscopy data were acquired from the parietal-occipital cortex and supplementary motor area in all subjects. Four scans were performed in each subject that included a predrug baseline measure, two scans during the dosing timeframe, and a final scan that occurred 1 week after drug cessation. CPP-115 induced robust and significant increases in brain GABA+ concentrations that ranged between 52 and 141% higher than baseline values. Elevated GABA+ concentrations returned to baseline values following drug clearance. Subjects receiving placebo showed no significant changes in GABA+ concentration. CPP-115-induced changes were exclusive to GABA and homocarnosine, and CPP-115 afforded brain GABA+ concentration changes comparable to or greater than previous vigabatrin spectroscopy studies in healthy epilepsy-naive subjects. The return to baseline GABA+ concentration indicates the reversible GABA-AT resynthesis following drug washout. These preliminary data warrant further spectroscopy studies that characterize the acute pharmacodynamic effects of CPP-115 with additional dose-descending measures.

9.4 T small animal MRI using clinical components for direct translational studies

BACKGROUND

Magnetic resonance is a major preclinical and clinical imaging modality ideally suited for longitudinal studies, e.g. in pharmacological developments. The lack of a proven platform that maintains an identical imaging protocol between preclinical and clinical platforms is solved with the construction of an animal scanner based on clinical hard- and software.

METHODS

A small animal magnet and gradient system were connected to a clinical MR system. Several hardware components were either modified or built in-house to achieve compatibility. The clinical software was modified to account for the different field-of-view of a preclinical MR system. The established scanner was evaluated using clinical QA protocols, and platform compatibility for translational research was verified against clinical scanners of different field strength.

RESULTS

The constructed animal scanner operates with the majority of clinical imaging sequences. Translational research is greatly facilitated as protocols can be shared between preclinical and clinical platforms. Hence, when maintaining sequences parameters, maximum similarity between pulses played out on a human or an animal system is maintained.

CONCLUSION

Coupling of a small animal magnet with a clinical MR system is a flexible, easy to use way to establish and advance translational imaging capability. It provides cost and labor efficient translational capability as no tedious sequence reprogramming between moieties is required and cross-platform compatibility of sequences facilitates multi-center studies.

Hippocampus Glutamate and N-Acetyl Aspartate Markers of Excitotoxic Neuronal Compromise in Posttraumatic Stress Disorder

Hippocampus atrophy is implicated in posttraumatic stress disorder (PTSD), and may partly reflect stress-induced glutamate excitotoxicity that culminates in neuron injury and manifests as re-experiencing symptoms and other memory abnormalities. This study used high-field proton magnetic resonance spectroscopy (MRS) to determine whether PTSD is associated with lower hippocampus levels of the neuron marker N-acetyl aspartate (NAA), along with higher levels of glutamate (Glu) and Glu/NAA. We also predicted that metabolite levels would correlate with re-experiencing symptoms and lifetime trauma load. Twenty-four adult PTSD patients and 23 trauma-exposed normal controls (TENC) underwent 4T MRS of the left and right hippocampus. Participants received psychiatric interviews, and completed the Traumatic Life Events Questionnaire to define lifetime trauma load. Relative to TENC participants, PTSD patients exhibited significantly lower NAA in right and left hippocampi, and significantly higher Glu and Glu/NAA in the right hippocampus. Re-experiencing symptoms were negatively correlated with left and right NAA, and positively correlated with right Glu and right Glu/NAA. Trauma load was positively correlated with right Glu/NAA in PTSD patients. When re-experiencing symptoms and trauma load were examined together in relation to right Glu/NAA, only re-experiencing symptoms remained a significant correlate. This represents the first report that PTSD is associated with MRS markers of hippocampus Glu excess, together with indices of compromised neuron integrity. Their robust associations with re-experiencing symptoms affirm that MRS indices of hippocampus neuron integrity and glutamate metabolism may reflect biomarkers of clinically significant disease variation in PTSD.

Searching for Cross-Diagnostic Convergence: Neural Mechanisms Governing Excitation and Inhibition Balance in Schizophrenia and Autism Spectrum Disorders

Recent theoretical accounts have proposed excitation and inhibition (E/I) imbalance as a possible mechanistic, network-level hypothesis underlying neural and behavioral dysfunction across neurodevelopmental disorders, particularly autism spectrum disorder (ASD) and schizophrenia (SCZ). These two disorders share some overlap in their clinical presentation as well as convergence in their underlying genes and neurobiology. However, there are also clear points of dissociation in terms of phenotypes and putatively affected neural circuitry. We highlight emerging work from the clinical neuroscience literature examining neural correlates of E/I imbalance across children and adults with ASD and adults with both chronic and early-course SCZ. We discuss findings from diverse neuroimaging studies across distinct modalities, conducted with electroencephalography, magnetoencephalography, proton magnetic resonance spectroscopy, and functional magnetic resonance imaging, including effects observed both during task and at rest. Throughout this review, we discuss points of convergence and divergence in the ASD and SCZ literature, with a focus on disruptions in neural E/I balance. We also consider these findings in relation to predictions generated by theoretical neuroscience, particularly computational models predicting E/I imbalance across disorders. Finally, we discuss how human noninvasive neuroimaging can benefit from pharmacological challenge studies to reveal mechanisms in ASD and SCZ. Collectively, we attempt to shed light on shared and divergent neuroimaging effects across disorders with the goal of informing future research examining the mechanisms underlying the E/I imbalance hypothesis across neurodevelopmental disorders. We posit that such translational efforts are vital to facilitate development of neurobiologically informed treatment strategies across neuropsychiatric conditions.

Inflammation Effects on Brain Glutamate in Depression: Mechanistic Considerations and Treatment Implications

There has been increasing interest in the role of glutamate in mood disorders, especially given the profound effect of the glutamate receptor antagonist ketamine in improving depressive symptoms in patients with treatment-resistant depression. One pathway by which glutamate alterations may occur in mood disorders involves inflammation. Increased inflammation has been observed in a significant subgroup of patients with mood disorders, and inflammatory cytokines have been shown to influence glutamate metabolism through effects on astrocytes and microglia. In addition, the administration of the inflammatory cytokine interferon-alpha has been shown to increase brain glutamate in the basal ganglia and dorsal anterior cingulate cortex as measured by magnetic resonance spectroscopy (MRS). Moreover, MRS studies in patients with major depressive disorder have revealed that increased markers of inflammation including C-reactive protein correlate with increased basal ganglia glutamate, which in turn was associated with anhedonia and psychomotor retardation. Finally, human and laboratory animal studies have shown that the response to glutamate antagonists such as ketamine is predicted by increased inflammatory cytokines. Taken together, these data make a strong case that inflammation may influence glutamate metabolism to alter behavior, leading to depressive symptoms including anhedonia and psychomotor slowing.

The impact of synapsin III gene on the neurometabolite level alterations after single-dose methylphenidate in attention-deficit hyperactivity disorder patients

OBJECTIVE

To investigate the neurometabolite level changes according to synapsin III gene rs133945G>A and rs133946C>G polymorphisms by using magnetic resonance spectroscopy (MRS) in patients with attention-deficit hyperactivity disorder (ADHD).

METHODS

Fifty-seven adults diagnosed with ADHD were recruited for the study. The participants were examined by single-voxel (1)H MRS when medication naïve and 30 minutes after oral administration of 10 mg methylphenidate (Mph). Those who had been on a stimulant discontinued the medication 48 hours before MRS imaging. Spectra were taken from the anterior cingulate cortex, dorsolateral prefrontal cortex, striatum, and cerebellum, and N-acetylaspartate (NAA), choline, and creatine levels were examined. For genotyping of the synapsin III gene polymorphisms, DNA was isolated from peripheral blood leukocytes. The effects of age, sex, and ADHD subtypes were controlled in the analyses.

RESULTS

After a single dose of Mph, choline levels increased significantly in the striatum of rs133945G>A polymorphism-GG genotypes (P=0.020) and NAA levels rose in the anterior cingulate cortex of rs133946C>G polymorphism-CG genotypes (P=0.014). Both rs133945G>A and rs133946C>G polymorphisms were found to statistically significantly affect the alteration of NAA levels in response to Mph in dorsolateral prefrontal cortex with two-way repeated measure of analysis of variance. Post hoc comparisons revealed a significant difference between CG and GG genotypes of rs133946C>G polymorphisms after Bonferroni adjustment (P=0.016).

CONCLUSION

Synapsin III gene polymorphisms may be affecting the changes in neurometabolite levels in response to Mph in adult ADHD patients. Future studies are needed to confirm our findings.

How Imaging Glutamate, γ-Aminobutyric Acid, and Dopamine Can Inform the Clinical Treatment of Alcohol Dependence and Withdrawal

Neuroimaging studies have dramatically advanced our understanding of the neurochemical basis of alcohol dependence, a major public health issue. In this paper, we review the research generated from neurochemical specific imaging modalities including magnetic resonance spectroscopy, positron emission tomography, and single-photon emission computed tomography in studies of alcohol dependence and withdrawal. We focus on studies interrogating γ-aminobutyric acid (GABA), glutamate, and dopamine, as these are prominent neurotransmitter systems implicated in alcohol dependence. Highlighted findings include diminished dopaminergic functioning and modulation of the GABA system by tobacco smoking during alcohol withdrawal. Then, we consider how these findings impact the clinical treatment of alcohol dependence and discuss directions for future experiments to address existing gaps in the literature, for example, sex differences and smoking comorbidity. These and other considerations provide opportunities to build upon the current neurochemistry imaging literature of alcohol dependence and withdrawal, which may usher in improved therapeutic and relapse prevention strategies.

The Utility of Magnetic Resonance Spectroscopy for Understanding Substance Use Disorders: A Systematic Review of the Literature

The aim of this article is to present a systematic review of magnetic resonance spectroscopy (MRS) studies of substance use disorders. As a noninvasive and nonionizing imaging technique, MRS is being widely used in substance abuse research to evaluate the effects substances of abuse have on brain chemistry. Nearly 40 peer-reviewed research articles that focused on the utility of MRS in alcohol, methamphetamine, 3,4-methylenedioxymethamphetamine, cocaine, opiates, opioids, marijuana, and nicotine use disorders were reviewed. Findings indicate inconsistencies with respect to alterations in brain chemistry within each substance of abuse, and the most consistent finding across substances was decreased N-acetylaspartate and choline levels with chronic alcohol, methamphetamine, and nicotine use. Variation in the brain regions studied, imaging technique, as well as small sample sizes might explain the discrepancies in findings within each substance. Future well-designed MRS studies offer promise in examining novel treatment approaches in substance use disorders.

(1)H NMR-Based Metabolomics and Neurotoxicity Study of Cerebrum and Cerebellum in Rats Treated with Cinnabar, a Traditional Chinese Medicine

Cinnabar, an important traditional Chinese mineral medicine, has been widely used as a Chinese patent medicine ingredient for sedative therapy. Nevertheless, the neurotoxic effects of cinnabar have also been noted. In this study, (1)H NMR-based metabolomics, combined with multivariate pattern recognition, were applied to investigate the neurotoxic effects of cinnabar after intragastrical administration (dosed at 2 and 5 g/kg body weight) on male Wistar rats. The metabolite variations induced by cinnabar were characterized by increased levels of glutamate, glutamine, myo-inositol, and choline, as well as decreased levels of GABA, taurine, NAA, and NAAG in tissue extracts of the cerebellum and cerebrum. These findings suggested that cinnabar induced glutamate excitotoxicity, neuronal cell loss, osmotic state changes, membrane fluidity disruption, and oxidative injury in the brain. We also show here that there is a dose- and time-dependent neurotoxicity of cinnabar, and that cerebellum was more sensitive to cinnabar induction than cerebrum. This work illustrates the utility and reliability of (1)H NMR-based metabolomics approach for examining the potential neurotoxic effects of cinnabar and other traditional Chinese medicines.

N-acetylaspartate normalization in bipolar depression after lamotrigine treatment

OBJECTIVES

The aim of the present study was to examine N-acetylaspartate (NAA), a general marker of neuronal viability, and total NAA (tNAA), the combined signal of NAA and N-acetylaspartylglutamate, in bipolar depression before and after lamotrigine treatment. Given that NAA is synthesized through direct acetylation of aspartate by acetyl-coenzyme A-l-aspartate-N-acetyltransferase, we hypothesized that treatment with lamotrigine would be associated with an increase in NAA level.

METHODS

Patients with bipolar depression underwent two-dimensional proton magnetic resonance spectroscopy of the anterior cingulate at baseline (n = 15) and after 12 weeks of lamotrigine treatment (n = 10). A group of age-matched healthy controls (n = 9) underwent scanning at baseline for comparison.

RESULTS

At baseline, patients with bipolar depression had significantly lower NAA [mean standard deviation (SD) = 1.13 (0.21); p = 0.02] than controls [mean (SD) = 1.37 (0.27)]. Significant increases in NAA [mean (SD) = 1.39 (0.21); p = 0.01] and tNAA [mean (SD) = 1.61 (0.25); p = 0.02] levels were found after 12 weeks of lamotrigine treatment.

CONCLUSIONS

These data suggest an NAA deficit in bipolar depression that is normalized after lamotrigine treatment. Future research is warranted to evaluate whether baseline NAA level is a potential biomarker for identifying lamotrigine response patterns and whether this functional brain change has an associated clinical response.

A review of MR spectroscopy studies of pediatric bipolar disorder

Pediatric bipolar disorder is a severe mental illness whose pathophysiology is poorly understood and for which there is an urgent need for improved diagnosis and treatment. MR spectroscopy is a neuroimaging method capable of in vivo measurement of neurochemicals relevant to bipolar disorder neurobiology. MR spectroscopy studies of adult bipolar disorder provide consistent evidence for alterations in the glutamate system and mitochondrial function. In bipolar disorder, these 2 phenomena may be linked because 85% of glucose in the brain is consumed by glutamatergic neurotransmission and the conversion of glutamate to glutamine. The purpose of this article is to review the MR spectroscopic imaging literature in pediatric bipolar disorder, at-risk samples, and severe mood dysregulation, with a focus on the published findings that are relevant to glutamatergic and mitochondrial functioning. Potential directions for future MR spectroscopy studies of the glutamate system and mitochondrial dysfunction in pediatric bipolar disorder are discussed.

Prefrontal grey and white matter neurometabolite changes after atomoxetine and methylphenidate in children with attention deficit/hyperactivity disorder: a (1)H magnetic resonance spectroscopy study

Attention deficit/hyperactivity disorder (ADHD) is the most common neurobehavioral childhood disorder. Dysfunction of prefrontal neural circuits which are responsible for executive and attentional functions has been previously shown in ADHD. We investigated the neurometablite changes in areas included in dorsolateral prefrontal neural circuits after 2 months of long-acting methylphenidate or atomoxetine medication in children with ADHD who were responders to treatment. Twenty-one ADHD children were examined by single voxel (1)H-magnetic resonance spectroscopy (MRS) before and after 2 months of medication with OROS methylphenidate (n=10) or atomoxetine (n=11). The spectra were taken from the dorsolateral prefrontal cortex (DLPFC, 8ml) and white matter behind the DLPFC (anterior semioval center, 7.5ml), bilaterally. NAA and NAA/Cr (N-acetylaspartate/creatine) decreased in the left DLPFC and Cho/Cr (choline/creatine) increased in the right DLPFC after atomoxetine medication. Glu+Gln and Glu+Gln/Cr (glutamate/glutamine) increased in the left white matter after methylphenidate medication. We hypothesize that atomoxetine could decrease hyperactivation of DLPFC neurons and methylphenidate could lead to increased activation of cortical glutamatergic projections with the consequences of increased tonic dopamine release in the mesocortical system.

Glutamate and glutamine: a review of in vivo MRS in the human brain

Our understanding of the roles that the amino acids glutamate (Glu) and glutamine (Gln) play in the mammalian central nervous system has increased rapidly in recent times. Many conditions are known to exhibit a disturbance in Glu-Gln equilibrium, and the exact relationships between these changed conditions and these amino acids are not fully understood. This has led to increased interest in Glu/Gln quantitation in the human brain in an array of conditions (e.g. mental illness, tumor, neuro-degeneration) as well as in normal brain function. Accordingly, this review has been undertaken to describe the increasing number of in vivo techniques available to study Glu and Gln separately, or pooled as 'Glx'. The present MRS methods used to assess Glu and Gln vary in approach, complexity, and outcome, thus the focus of this review is on a description of MRS acquisition approaches, and an indication of relative utility of each technique rather than brain pathologies associated with Glu and/or Gln perturbation. Consequently, this review focuses particularly on (1) one-dimensional (1)H MRS, (2) two-dimensional (1)H MRS, and (3) one-dimensional (13)C MRS techniques.

γ-Amino butyric acid and glutamate abnormalities in adolescent chronic marijuana smokers

BACKGROUND

An increasing body of evidence from neuropsychological and neuroimaging studies suggests that exposure to marijuana throughout adolescence disrupts key cortical maturation processes occurring during this developmental phase. GABA-modulating pharmacologic treatments that elevate brain GABA concentration recently have been shown to decrease withdrawal symptoms and improve executive functioning in marijuana-dependent adult subjects. The goal of this study was to investigate whether the lower ACC glutamate previously reported in adolescent chronic marijuana smokers is associated with lower ACC GABA levels.

METHODS

Standard and metabolite-edited proton MRS data were acquired from adolescent marijuana users (N=13) and similarly aged non-using controls (N=16) using a clinical 3T MRI system.

RESULTS

The adolescent marijuana-using cohort showed significantly lower ACC GABA levels (-22%, p=0.03), which paralleled significantly lower ACC glutamate levels (-14%, p=0.01). Importantly, the lower ACC GABA and glutamate levels detected in the adolescent cohort remained significant after controlling for age and sex.

CONCLUSIONS

The present spectroscopic findings support functional neuroimaging data documenting cingulate dysfunction in marijuana-dependent adolescents. Glutamatergic and GABAergic abnormalities potentially underlie cingulate dysfunction in adolescent chronic marijuana users, and the opportunity for testing suitable pharmacologic treatments with a non-invasive pharmacodynamic evaluation exists.

Developmental risk I: depression and the developing brain

This article discusses recent findings on the neurobiology of pediatric depression as well as the interplay between genetic and environmental factors in determining the risk for the disorder. Utilizing data from both animal and human studies, the authors focus on the evolving understanding of the developmental neurobiology of emotional regulation, cognitive function and social behavior as it applies to the risk and clinical course of depression. Treatment implications and directions for future research are also discussed.

Hippocampal neurometabolite changes in depression treatment: a (1)H magnetic resonance spectroscopy study

Previous studies using magnetic resonance spectroscopy have related abnormalities in hippocampal metabolism to depression. Current evidence is consistent with the conclusion that the hippocampal formation plays an important role in the presentation of depressive symptoms. Eighteen adult patients with major depressive disorder, aged 20 to 60 years, underwent magnetic resonance spectroscopy of the hippocampus during a period of depressive symptomatology and after 7-11 weeks of antidepressant medication with at least 50% reduction in the Montgomery-Åsberg Depression Rating Scale ()MADRS score. During therapy, we found a significantly decreased Lac/Cr ratio in the left hippocampus. The Ins/Cr ratio showed a significant negative correlation with the severity of depression as assessed by the MADRS at baseline. Moreover, we found a negative association of NAA/Cho with age and a positive association of Cho/Cr with age, both on the left and right sides at baseline. In light of our findings and previous studies results we hypothesize that mitochondrial dysfunction leading to predominantly anaerobic glycolysis in connection with the intracellular signaling pathways disturbances and decreased astrocytic function/number might subsequently lead to decreased brain neuroplasticity in depression. These mechanisms could be positively influenced by antidepressant treatment with selective serotonin or norepineprine reuptake inhibitors, with potential effects on untimely neuronal aging in depression.

Alternate strategies to obtain mass balance without the use of radiolabeled compounds: application of quantitative fluorine (19F) nuclear magnetic resonance (NMR) spectroscopy in metabolism studies

Nuclear magnetic resonance (NMR) spectroscopy is playing an increasingly important role in the quantitation of small and large molecules. Recently, we demonstrated that (1)H NMR could be used to quantitate drug metabolites isolated in submilligram quantities from biological sources. It was shown that these metabolites, once quantitated by NMR, were suitable to be used as reference standards in quantitative LC/MS-based assays, hence circumventing the need for radiolabeled material or synthetic standards to obtain plasma exposure estimates in humans and preclinical species. The quantitative capabilities of high-field NMR is further demonstrated in the current study by obtaining the mass balance of fluorinated compounds using (19)F-NMR. Two fluorinated compounds which were radio-labeled with carbon-14 on metabolically stable positions were dosed in rats and urine and feces collected. The mass balance of the compounds was obtained initially by counting the radioactivity present in each sample. Subsequently, the same sets of samples were analyzed by (19)F-NMR, and the concentrations determined by this method were compared with data obtained using radioactivity counting. It was shown that the two methods produced comparable values. To demonstrate the value of this analytical technique in drug discovery, a fluorinated compound was dosed intravenously in dogs and feces and urine collected. Initial profiling of samples showed that this compound was excreted mainly unchanged in feces, and hence, an estimate of mass balance was obtained using (19)F-NMR. The data obtained by this method was confirmed by additional quantitative studies using mass spectrometry. Hence cross-validations of the quantitative (19)F-NMR method by radioactivity counting and mass spectrometric analysis were demonstrated in this study. A strategy outlining the use of fluorinated compounds in conjunction with (19)F-NMR to understand their routes of excretion or mass balance in animals is proposed. These studies demonstrate that quantitative (19)F-NMR could be used as an alternate technique to obtain an estimate of the mass balance of fluorinated compounds, especially in early drug development where attrition of the compounds is high, and cost savings could be realized through the use of such a technique rather than employing radioactive compounds. The potential application of qNMR in conducting early human ADME studies with fluorinated compounds is also discussed.

Ex vivo detection for chronic ethanol consumption-induced neurochemical changes in rats

The aim of this study was to quantitatively investigate the chronic ethanol-induced cerebral metabolic changes in various regions of the rat brain, using the proton high resolution magic angle spinning spectroscopy technique. The rats were divided into two groups (control group: N=11, ethanol-treated group: N=11) and fed with the liquid diets for 10 weeks. In each week, the mean intake volumes of liquid diet were measured. The brain tissues, including cerebellum (Cere), frontal cortex (FC), hippocampus (Hip), occipital cortex (OC) and thalamus (Thal), were harvested immediately after the end of experiments. The ex vivo proton spectra for the five brain regions were acquired with the Carr-Purcell-Meiboom-Gill (CPMG) pulse sequence at 500-MHz NMR spectrometer. All of the spectra were processed using the LCModel software, with simulated basis-set file, and the metabolite levels were referenced to total creatine. In the ethanol liquid diet group, there were significant increases in the metabolites ratio levels, as compared to control (Cere: alanine, glutathione, and N-acetlyaspartate; FC: phosphocholine and taurine; Hip: alanine, glutamine, and N-acetylaspartate; OC: glutamine; Thal: alanine, γ-aminobutyric acid, glutamate, glycerophosphocholine, phosphocholine, taurine, and free choline). However, in the ethanol liquid diet group, the myo-inositol levels of the OC were significantly lower. The present study demonstrates how chronic ethanol consumption affects cerebral metabolites in the chronic ethanol-treated rat. Therefore, this result could be useful to pursue clinical applications for quantitative diagnosis in human alcoholism.

Tissue-specific toxicological effects of cadmium in green mussels (Perna viridis): nuclear magnetic resonance-based metabolomics study

Toxicity tests for metals have traditionally focused on selected biomarkers to characterize the biological stress induced by metals in marine organisms. Here nuclear magnetic resonance (NMR)-based metabolomics, a system biology tool, was applied to the marine green mussel, Perna viridis, to investigate the toxicological effects of Cd in both digestive gland and adductor muscle tissues. After Cd exposure for either two or four weeks, there was no significant metabolic change in the mussels exposed to Cd at 2 µg/L. At 20 µg/L, there were major metabolite changes related to amino acids, osmolytes, and energy metabolites. Digestive gland tissue was more sensitive to Cd than adductor muscle tissue. The adductor muscle tissue showed elevated levels of glutamine, glutamate, and lactate, and reduced levels of branched chain amino acids, aspartate, phenylalanine, and tyrosine. Overall, four weeks of Cd exposure produced neurotoxicity and metabolic disturbances and disturbed osmoregulation. These results suggest that the adductor muscle tissue of mussels may be a suitable supplemental biomarker for exposure to toxicants. In addition, the results demonstrate that (1) H-NMR-based metabolomic analysis can provide a systematic view of the toxicological effects of metals on mussels, suggesting that it might be employed to investigate the toxicological effects of other marine pollutants.

Interindividual, repositioning, and time-of-day effects on single voxel proton MR spectroscopy of the anterior cingulate cortex

PURPOSE

To measure interindividual, repositioning, and time-of-day effects of single voxel PRESS (Point RESolved Spectroscopy) proton magnetic resonance spectroscopy ((1)H-MRS) acquisition of the anterior cingulate cortex (AC) in healthy human subjects.

MATERIALS AND METHODS

AC (1)H-MRS measurements were performed in 15 healthy adult volunteers using a short echo PRESS sequence (GE Healthcare 3 Tesla, TE/TR = 30/2500 ms, 192 acquisitions, 6 cm(3) voxels). For each individual, a total of eight spectra were obtained during two identical scanning sessions separated by 3.5 h. In each, two consecutive AC spectra were acquired. After the first two scans, the subject left the scanner, then immediately returned for repositioning and acquisition of two more consecutive spectra. The subject then left the imaging centre to return 3.5 h later for a repeated procedure. Spectroscopic postprocessing was done using LCmodel. Interindividual, repositioning and time-of-day effects were measured using restricted maximum likelihood (REML) models of variance components analysis, where response variables were levels of creatine/phosphocreatine (Cr), N-acetyl-aspartate (NAA), myo-inositol (mI), choline (Cho), and the glutamate-glutamine complex (Glx).

RESULTS

Interindividual effects were markedly higher than time-of-day and repositioning effects for all metabolites.

CONCLUSION

Our findings show that (1)H-MRS measurements of the AC are sensitive to interindividual differences, while time of day and repositioning are markedly less important.

Review: magnetic resonance spectroscopy studies of pediatric major depressive disorder

Introduction. This paper focuses on the application of Magnetic Resonance Spectroscopy (MRS) to the study of Major Depressive Disorder (MDD) in children and adolescents. Method. A literature search using the National Institutes of Health's PubMed database was conducted to identify indexed peer-reviewed MRS studies in pediatric patients with MDD. Results. The literature search yielded 18 articles reporting original MRS data in pediatric MDD. Neurochemical alterations in Choline, Glutamate, and N-Acetyl Aspartate are associated with pediatric MDD, suggesting pathophysiologic continuity with adult MDD. Conclusions. The MRS literature in pediatric MDD is modest but growing. In studies that are methodologically comparable, the results have been consistent. Because it offers a noninvasive and repeatable measurement of relevant in vivo brain chemistry, MRS has the potential to provide insights into the pathophysiology of MDD as well as the mediators and moderators of treatment response.

Hypothalamic glutamate levels following serotonergic stimulation: a pilot study using 7-Tesla magnetic resonance spectroscopy in healthy volunteers

INTRODUCTION AND PURPOSE

Functional proton magnetic resonance spectroscopy (MRS) can be applied to measure pharmacodynamic effects of central nervous system (CNS)-active drugs. The serotonin precursor 5-hydroxytryptophan (5-HTP), administered together with carbidopa and granisetron to improve kinetics and reduce adverse effects, acutely enhances central serotonergic neurotransmission and induces hypothalamus-pituitary-adrenal-(HPA) axis activation. We studied the hypothalamic levels of glutamate/glutamine (Glx), choline (Chol), N-acetyl-aspartate (NAA) and creatine using 7-Tesla (7T) MRS, and adrenocorticotropic hormone (ACTH) and cortisol in peripheral blood, after the administration of the 5-HTP function test in healthy volunteers.

METHODS

A randomized, double blind, placebo-controlled, two-way cross-over study was performed in 12 healthy males with a 7day wash-out period. After administration of the oral 5-HTP function test, ACTH and cortisol were measured over 4h and MRS scans at 7T were performed every 30min over 3h measuring Glx:Creatine, Chol:Creatine and NAA:Creatine ratios.

RESULTS

In the hypothalamus, the administration of 5-HTP had no effect on the average Glx, Chol or NAA levels over 180min but induced a significant decrease of Glx at 60min on post-hoc analysis. 5-HTP-induced significant ACTH release reaching an E(max) of 60.2ng/L at 80min followed by cortisol with an E(max) of 246.4ng/mL at 110min.

CONCLUSIONS

The reduction in hypothalamic Glx levels after serotonergic stimulation is compatible with activation of excitatory neurons in this region, which is expected to cause depletion of local glutamate stores. The hypothalamic MRS-response reached its maximum prior to subsequent increases of ACTH and cortisol, which support the functional relevance of hypothalamic Glx-depletion for activation of the HPA-axis. This exploratory study shows that MRS is capable of detecting neuronal activation following functional stimulation of a targeted brain area.

Neurochemistry of drug action: insights from proton magnetic resonance spectroscopic imaging and their relevance to addiction

Proton magnetic resonance spectroscopy ((1)H MRS) is a noninvasive imaging technique that permits measurement of particular compounds or metabolites within the tissue of interest. In the brain, (1)H MRS provides a snapshot of the neurochemical environment within a defined volume of interest. A search of the literature demonstrates the widespread utility of this technique for characterizing tumors, tracking the progress of neurodegenerative disease, and for understanding the neurobiological basis of psychiatric disorders. As of relatively recently, (1)H MRS has found its way into substance abuse research, and it is beginning to become recognized as a valuable complement in the brain imaging toolbox that also contains positron emission tomography, single-photon-emission computed tomography, and functional magnetic resonance imaging. Drug abuse studies using (1)H MRS have identified several biochemical changes in the brain. The most consistent alterations across drug class were reductions in N-acetylaspartate and elevations in myo-inositol, whereas changes in choline, creatine, and amino acid transmitters also were abundant. Together, the studies discussed herein provide evidence that drugs of abuse may have a profound effect on neuronal health, energy metabolism and maintenance, inflammatory processes, cell membrane turnover, and neurotransmission, and these biochemical changes may underlie the neuropathology within brain tissue that subsequently gives rise to the cognitive and behavioral impairments associated with drug addiction.

High-resolution, in vivo magnetic resonance imaging of Drosophila at 18.8 Tesla

High resolution MRI of live Drosophila was performed at 18.8 Tesla, with a field of view less than 5 mm, and administration of manganese or gadolinium-based contrast agents. This study demonstrates the feasibility of MR methods for imaging the fruit fly Drosophila with an NMR spectrometer, at a resolution relevant for undertaking future studies of the Drosophila brain and other organs. The fruit fly has long been a principal model organism for elucidating biology and disease, but without capabilities like those of MRI. This feasibility marks progress toward the development of new in vivo research approaches in Drosophila without the requirement for light transparency or destructive assays.

Applications of magnetic resonance spectroscopy to tinnitus research: initial data, current issues, and future perspectives

Conducting tinnitus research on humans poses challenges for investigators because of its subjective nature, the complexities involved in establishing underlying generator sites, the diversity of potential causes, and the inherent difficulties in dissociating reactive changes in the central nervous system (CNS), secondary to peripheral hearing loss, from those effects that may be due to tinnitus. One area of considerable interest concerns biomarker development, particularly in the areas of metabolism and biochemistry. Establishing a biomarker or a profile of metabolic and neurobiochemical constituents of tinnitus-related activity within the CNS could be of considerable importance for understanding the fundamental properties of this disorder. Therefore, in an effort to gain greater insight into mechanisms of tinnitus, magnetic resonance spectroscopy (MRS) is being proposed as one of the several tools that can address pertinent issues. Apart from its long-standing use in analytical chemistry and physics, MRS is also being applied with greater frequency in the neurosciences to gain insight into human brain function under normal and pathological states. By considering the history of this method and advances made to date, MRS has the potential to: (1) identify unique in vivo metabolic and neurobiochemical biomarkers associated with tinnitus in specific regions of the CNS, (2) clarify and track disease pathogenesis, (3) monitor short and long-term treatment effects, and (4) serve as a tool in testing of drugs that may be used in treatment of tinnitus.

Variation of the choline signal intensity in the dorsolateral prefrontal cortex of rats exposed to the forced swimming test as detected by in vivo 1H MR spectroscopy

BACKGROUND

(1)H magnetic resonance spectroscopy (MRS) has documented an increased Cho/Cr ratio in the dorsolateral prefrontal cortex (DLPFC) in major depressive disorder (MDD). The aim of this study was to investigate neurochemical alterations in the left DLPFC, considered a main area of pathogenesis in depression, using rats exposed to the forced swimming test (FST).

MATERIALS AND METHODS

Twenty-four male rats were used for the MRI and in vivo(1)H MRS studies. Rats exposed to the FST to induce a depressed mental status. Using in vivo(1)H MRS, the metabolite ratios of the rats with a depressed mental status and the controls, were measured and the values of the two groups were compared.

RESULTS

The Cho/Cr and Cho/NAA ratios in the DLPFC of the rats with a depressed mental status were significantly higher than that in the controls.

CONCLUSIONS

The present study demonstrates a significantly increased Cho/Cr ratio in the DLPFC of rats with depression compared with controls. This result may suggest an accelerated turnover of membrane without neuronal loss is occurring in the DLPFC of the rats with depression.