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Background: The International Conference on Applications of Neuroimaging to Alcoholism was convened at Yale University in New Haven, Connecticut. One session featured six speakers who discussed magnetic resonance spectroscopy (MRS) applications in alcoholism, with topics ranging from multimodality imaging to measurements of neurotransmitter synthesis in the human brain in vivo. MethodS: This session covered methodological topics related to 1H and 13C MRS, both theory and examples. The primary features of the 1H MR spectra were described, including resonances from creatine- and choline-choline-containing compounds, N-acetylaspartate, myo-inositol, glutamate, glutamine, GABA, and macromolecules. Methods reviewed also included MRS imaging, in which numerous MRS voxels are observed simultaneously. Other methods described J-editing of GABA and 13C MRS detection of oxidative metabolism and neurotransmitter synthesis. Results: Across studies, region-specific neurochemical changes were associated with alcohol dependence. With sobriety, many of the neurochemical alterations associated with alcohol dependence partially or fully abated, in association with partial recovery of brain structure and cognitive functions. The utility of 1H MRS to measure brain ethanol was discussed. This work highlighted the need to consider method- and analysis-dependent mechanisms that can affect the quantification of ethanol using 1H MRS. The utility of MRS as a tool to study alcohol dependence-related neurotoxicity was reviewed. In particular, the possibility that MRS may provide a noninvasive tool for studying glutamatergic activation associated with acute alcohol withdrawal may prove to be an important approach for mechanistic human studies related to neuropsychiatric complications of ethanol dependence and withdrawal, including dementia and hepatic encephalopathy. Conclusions: The International Conference on Applications of Neuroimaging to Alcoholism provided one of the first opportunities to convene a large group of investigators who used MRS techniques in the study of alcohol dependence. The range of data presented highlighted the growing range of insights related to the acute and chronic effects of ethanol on human brain chemistry. The ability to measure directly glutamate-glutamine cycling using 13C-MRS presents new and exciting opportunities to probe excitatory neurotransmission. [ABSTRACT FROM AUTHOR]

The neuronal tricarboxylic acid and glutamate/glutamine (Glu/Gln) cycles play important roles in brain function. These processes can be measured in vivo using dynamic 1 H-[ 13 C] MRS during administration of 13 C-labeled glucose. Proton-observed carbon-edited (POCE) MRS enhances the signal-to-noise ratio (SNR) compared with direct 13 C-MRS. Ultra-high field further boosts the SNR and increases spectral dispersion; however, even at 7 T, Glu and Gln 1 H-resonances may overlap. Further gain can be obtained with selective POCE (selPOCE). Our aim was to create a setup for indirect dynamic 1 H-[ 13 C] MRS in the human brain at 7 T. A home-built non-shielded transmit-receive 13 C-birdcage head coil with eight transmit-receive 1 H-dipole antennas was used together with a 32-channel 1 H-receive array. Electromagnetic simulations were carried out to ensure that acquisitions remained within local and global head SAR limits. POCE-MRS was performed using slice-selective excitation with semi-localization by adiabatic selective refocusing (sLASER) and stimulated echo acquisition mode (STEAM) localization, and selPOCE-MRS using STEAM. Sequences were tested in a phantom containing non-enriched Glu and Gln, and in three healthy volunteers during uniformly labeled 13 C-glucose infusions. In one subject the voxel position was alternated between bi-frontal and bi-occipital placement within one session. [4- 13 C]Glu-H4 and [4- 13 C]Gln-H4 signals could be separately detected using both STEAM-POCE and STEAM-selPOCE in the phantom. In vivo, [4,5- 13 C]Glx could be detected using both sLASER-POCE and STEAM-POCE, with similar sensitivities, but [4,5- 13 C]Glu and [4,5- 13 C]Gln signals could not be completely resolved. STEAM-POCE was alternately performed bi-frontal and bi-occipital within a single session without repositioning of the subject, yielding similar results. With STEAM-selPOCE, [4,5- 13 C]Glu and [4,5- 13 C]Gln could be clearly separated. We have shown that with our setup indirect dynamic 1 H-[ 13 C] MRS at 7 T is feasible in different locations in the brain within one session, and by using STEAM-selPOCE it is possible to separate Glu from Gln in vivo while obtaining high quality spectra., (© 2024 The Author(s). NMR in Biomedicine published by John Wiley & Sons Ltd.)

Objective: Obesity is associated with alterations in eating behavior and neurocognitive function. In this study, we investigate the effect of obesity on brain energy utilization, including brain glucose transport and metabolism., Methods: A total of 11 lean participants and 7 young healthy participants with obesity (mean age, 27 years) underwent magnetic resonance spectroscopy scanning coupled with a hyperglycemic clamp (target, ~180 mg/dL) using [1- 13 C] glucose to measure brain glucose uptake and metabolism, as well as peripheral markers of insulin resistance., Results: Individuals with obesity demonstrated an ~20% lower ratio of brain glucose uptake to cerebral glucose metabolic rate (T max /CMR glucose ) than lean participants (2.12 ± 0.51 vs. 2.67 ± 0.51; p = 0.04). The cerebral tricarboxylic acid cycle flux (V TCA ) was similar between the two groups (p = 0.64). There was a negative correlation between total nonesterified fatty acids and T max /CMR glucose (r = -0.477; p = 0.045)., Conclusions: We conclude that CMR glucose is unlikely to differ between groups due to similar V TCA , and, therefore, the glucose transport T max is lower in individuals with obesity. These human findings suggest that obesity is associated with reduced cerebral glucose transport capacity even at a young age and in the absence of other cardiometabolic comorbidities, which may have implications for long-term brain function and health., (© 2024 The Obesity Society.)

The olfactory bulb (OB) plays a fundamental role in the sense of smell and has been implicated in several pathologies, including Alzheimer's disease. Despite its importance, high metabolic activity and unique laminar architecture, the OB is not frequently studied using MRS methods, likely due to the small size and challenging location. Here we present a detailed metabolic characterization of OB metabolism, in terms of both static metabolite concentrations using 1 H MRS and metabolic fluxes associated with neuro-energetics and neurotransmission by tracing the dynamic 13 C flow from intravenously administered [1,6- 13 C 2 ]-glucose, [2- 13 C]-glucose and [2- 13 C]-acetate to downstream metabolites, including [4- 13 C]-glutamate, [4- 13 C]-glutamine and [2- 13 C]-GABA. The unique laminar architecture and associated metabolism of the OB, distinctly different from that of the cerebral cortex, is characterized by elevated GABA and glutamine levels, as well as increased GABAergic and astroglial energy metabolism and neurotransmission. The results show that, despite the technical challenges, high-quality 1 H and 1 H-[ 13 C] MR spectra can be obtained from the rat OB in vivo. The derived metabolite concentrations and metabolic rates demonstrate a unique metabolic profile for the OB. The metabolic model provides a solid basis for future OB studies on functional activation or pathological conditions., (© 2023 John Wiley & Sons Ltd.)

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

The mammalian succinate dehydrogenase (SDH) complex has recently been shown as capable of operating bidirectionally. Here, we develop a method (Q-Flux) capable of measuring absolute rates of both forward (V SDH(F) ) and reverse (V SDH(R) ) flux through SDH in vivo while also deconvoluting the amount of glucose derived from four discreet carbon sources in the liver. In validation studies, a mitochondrial uncoupler increased net SDH flux by >100% in awake rodents but also increased SDH cycling. During hyperglucagonemia, attenuated pyruvate cycling enhances phosphoenolpyruvate carboxykinase efficiency to drive increased gluconeogenesis, which is complemented by increased glutaminase (GLS) flux, methylmalonyl-CoA mutase (MUT) flux, and glycerol conversion to glucose. During hyperinsulinemic-euglycemic clamp, both pyruvate carboxylase and GLS are suppressed, while V SDH(R) is increased. Unstimulated MUT is a minor anaplerotic reaction but is readily induced by small amounts of propionate, which elicits glucagon-like metabolic rewiring. Taken together, Q-Flux yields a comprehensive picture of hepatic mitochondrial metabolism and should be broadly useful to researchers., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2022 Elsevier Inc. All rights reserved.)

Background: Early trauma predicts poor psychological and physical health. Glutamatergic synaptic processes offer one avenue for understanding this relationship, given glutamate's abundance and involvement in reward and stress sensitivity, emotion, and learning. Trauma-induced glutamatergic excitotoxicity may alter neuroplasticity and approach/avoidance tendencies, increasing risk for psychiatric disorders. Studies examine upstream or downstream effects instead of glutamatergic synaptic processes in vivo , limiting understanding of how trauma affects the brain. Objective: In a pilot study using a previously published data set, we examine associations between early trauma and a proposed measure of synaptic strength in vivo in one of the largest human samples to undergo Carbon-13 ( 13 C MRS) magnetic resonance spectroscopy. Participants were 18 healthy controls and 16 patients with PTSD (male and female). Method: Energy per cycle (EPC), which represents the ratio of neuronal oxidative energy production to glutamate neurotransmitter cycling, was generated as a putative measure of glutamatergic synaptic strength. Results: Results revealed that early trauma was positively correlated with EPC in individuals with PTSD, but not in healthy controls. Increased synaptic strength was associated with reduced behavioural inhibition, and EPC showed stronger associations between reward responsivity and early trauma for those with higher EPC. Conclusion: In the largest known human sample to undergo 13 C MRS, we show that early trauma is positively correlated with EPC, a direct measure of synaptic strength. Our study findings have implications for pharmacological treatments thought to impact synaptic plasticity, such as ketamine and psilocybin.

Anaplerosis occurs predominately in astroglia through the action of pyruvate carboxylase (PC). The rate of PC (Vpc) has been reported for cerebral cortex (or whole brain) of awake humans and anesthetized rodents, but regional brain rates remain largely unknown and, hence, were subjected to investigation in the current study. Awake male rats were infused with either [2- 13 C]glucose or [1- 13 C]glucose (n = 27/30) for 8, 15, 30, 60 or 120 min, followed by rapid euthanasia with focused-beam microwave irradiation to the brain. Blood plasma and extracts of cerebellum, hippocampus, striatum, and cerebral cortex were analyzed by 1 H-[ 13 C]-NMR to establish 13 C-enrichment time courses for glutamate-C4,C3,C2, glutamine-C4,C3, GABA-C2,C3,C4 and aspartate-C2,C3. Metabolic rates were determined by fitting a three-compartment metabolic model (glutamatergic and GABAergic neurons and astroglia) to the eighteen time courses. Vpc varied by 44% across brain regions, being lowest in the cerebellum (0.087 ± 0.004 µmol/g/min) and highest in striatum (0.125 ± 0.009) with intermediate values in cerebral cortex (0.106 ± 0.005) and hippocampus (0.114 ± 0.005). Vpc constituted 13-19% of the oxidative glucose consumption rate. Combination of cerebral cortical data with literature values revealed a positive correlation between Vpc and the rates of glutamate/glutamine-cycling and oxidative glucose consumption, respectively, consistent with earlier observations.

Gradient modulated RF pulses, especially gradient offset independent adiabaticity (GOIA) pulses, are increasingly gaining attention for high field clinical magnetic resonance spectroscopy and spectroscopic imaging (MRS/MRSI) due to the lower peak B 1 amplitude and associated power demands achievable relative to its non-modulated adiabatic full passage counterparts. In this work we describe the development of two GOIA RF pulses: 1) A power efficient, 3.0 ms wideband uniform rate with smooth truncation (WURST) modulated RF pulse with 15 kHz bandwidth compatible with a clinically feasible peak B 1 amplitude of 0.87 kHz (or 20 µT), and 2) A highly selective asymmetric 6.66 ms RF pulse with 20 kHz bandwidth designed to achieve a single-sided, fractional transition width of only 1.7%. Effects of potential asynchrony between RF and gradient-modulated (GM) waveforms for 3 ms GOIA-WURST RF pulses was evaluated by simulation and experimentally. Results demonstrate that a 20+ µs asynchrony between RF and GM functions substantially degrades inversion performance when using large RF offsets to achieve translation. A projection-based method is presented that allows a quick calibration of RF and GM asynchrony on pre-clinical/clinical MR systems. The asymmetric GOIA pulse was implemented within a multi-pulse OVS sequence to achieve power efficient, highly-selective, and B 1 and T 1 -independent signal suppression for extracranial lipid suppression. The developed GOIA pulses were utilized with linear gradient modulation (X, Y, Z gradient fields), and with second-order-field modulations (Z2, X2Y2 gradient fields) to provide elliptically-shaped regions-of-interest for MRS and MRSI acquisitions. Both described GOIA-RF pulses have substantial clinical value; specifically, the 3.0 ms GOIA-WURST pulse is beneficial to realize short TE sLASER localized proton MRS/MRSI sequences, and the asymmetric GOIA RF pulse has applications in highly selective outer volume signal suppression to allow interrogation of tissue proximal to extracranial lipids with full-intensity., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier Inc. All rights reserved.)

Background: The development of treatments for cognitive deficits associated with central nervous system disorders is currently a significant medical need. Despite the great need for such therapeutics, a significant challenge in the drug development process is the paucity of robust biomarkers to assess target modulation and guide clinical decisions. We developed a novel, translatable biomarker of neuronal glutamate metabolism, the 13 C-glutamate+glutamine (Glx) H3:H4 labeling ratio, in nonhuman primates using localized 1 H-magnetic resonance spectroscopy combined with 13 C-glucose infusions., Methods: We began with numerical simulations in an established model of brain glutamate metabolism, showing that the 13 C-Glx H3:H4 ratio should be a sensitive biomarker of neuronal tricarboxylic acid cycle activity, a key measure of overall neuronal metabolism. We showed that this biomarker can be measured reliably using a standard 1 H-magnetic resonance spectroscopy method (point-resolved spectroscopy sequence/echo time = 20 ms), obviating the need for specialized hardware and pulse sequences typically used with 13 C-magnetic resonance spectroscopy, thus improving overall clinical translatability. Finally, we used this biomarker in 8 male rhesus macaques before and after administration of the compound BNC375, a positive allosteric modulator of the α7 nicotinic acetylcholine receptor that enhances glutamate signaling ex vivo and elicits procognitive effects in preclinical species., Results: The 13 C-Glx H3:H4 ratios in the monkeys showed that BNC375 increases neuronal metabolism in nonhuman primates in vivo, detectable on an individual basis., Conclusions: This study demonstrates that the ratio of 13 C-Glx H3:H4 labeling is a biomarker that may provide an objective readout of compounds affecting glutamatergic neurotransmission and could improve decision making for the development of therapeutic agents., (Copyright © 2020 Society of Biological Psychiatry. Published by Elsevier Inc. All rights reserved.)

Aims/hypothesis: We have previously shown that individuals with uncontrolled type 2 diabetes have a blunted rise in brain glucose levels measured by 1 H magnetic resonance spectroscopy. Here, we investigate whether reductions in HbA 1c normalise intracerebral glucose levels., Methods: Eight individuals (two men, six women) with poorly controlled type 2 diabetes and mean ± SD age 44.8 ± 8.3 years, BMI 31.4 ± 6.1 kg/m 2 and HbA 1c 84.1 ± 16.2 mmol/mol (9.8 ± 1.4%) underwent 1 H MRS scanning at 4 Tesla during a hyperglycaemic clamp (~12.21 mmol/l) to measure changes in cerebral glucose at baseline and after a 12 week intervention that improved glycaemic control through the use of continuous glucose monitoring, diabetes regimen intensification and frequent visits to an endocrinologist and nutritionist., Results: Following the intervention, mean ± SD HbA 1c decreased by 24.3 ± 15.3 mmol/mol (2.1 ± 1.5%) (p=0.006), with minimal weight changes (p=0.242). Using a linear mixed-effects regression model to compare glucose time courses during the clamp pre and post intervention, the pre-intervention brain glucose level during the hyperglycaemic clamp was significantly lower than the post-intervention brain glucose (p<0.001) despite plasma glucose levels during the hyperglycaemic clamp being similar (p=0.266). Furthermore, the increases in brain glucose were correlated with the magnitude of improvement in HbA 1c (r = 0.71, p=0.048)., Conclusion/interpretation: These findings highlight the potential reversibility of cerebral glucose transport capacity and metabolism that can occur in individuals with type 2 diabetes following improvement of glycaemic control. Trial registration ClinicalTrials.gov NCT03469492., (© 2022. This is a U.S. government work and not under copyright protection in the U.S.; foreign copyright protection may apply.)

Background: Trauma and chronic stress are believed to induce and exacerbate psychopathology by disrupting glutamate synaptic strength. However, in vivo in human methods to estimate synaptic strength are limited. In this study, we established a novel putative biomarker of glutamatergic synaptic strength, termed energy-per-cycle (EPC). Then, we used EPC to investigate the role of prefrontal neurotransmission in trauma-related psychopathology., Methods: Healthy controls (n = 18) and patients with posttraumatic stress (PTSD; n = 16) completed 13 C-acetate magnetic resonance spectroscopy (MRS) scans to estimate prefrontal EPC, which is the ratio of neuronal energetic needs per glutamate neurotransmission cycle (V TCA /V Cycle )., Results: Patients with PTSD were found to have 28% reduction in prefrontal EPC ( t  = 3.0; df  = 32, P  = .005). There was no effect of sex on EPC, but age was negatively associated with prefrontal EPC across groups ( r  = -0.46, n = 34, P  = .006). Controlling for age did not affect the study results., Conclusion: The feasibility and utility of estimating prefrontal EPC using 13 C-acetate MRS were established. Patients with PTSD were found to have reduced prefrontal glutamatergic synaptic strength. These findings suggest that reduced glutamatergic synaptic strength may contribute to the pathophysiology of PTSD and could be targeted by new treatments., Competing Interests: Declaration of Conflicting Interests: The author(s) declared the following potential conflicts of interest with respect to the research, authorship, and/or publication of this article: Dr. Averill has served as a consultant, speaker and/or on advisory boards for Guidepoint, Transcend Therapeutics, and Ampelis. Dr. Abdallah has served as a consultant, speaker and/or on advisory boards for Aptinyx, Genentech, Janssen, Psilocybin Labs, Lundbeck, Guidepoint, and FSV7, and as editor of Chronic Stress for Sage Publications, Inc. He also filed a patent for using mTORC1 inhibitors to augment the effects of antidepressants (Aug 20, 2018). Dr. Krystal is a consultant for Aptinyx, Inc., Atai Life Sciences, AstraZeneca Pharmaceuticals, Biogen, Idec, MA, Biomedisyn Corporation, Bionomics, Limited (Australia), Boehringer Ingelheim International, Cadent Therapeutics, Inc., Clexio Bioscience, Ltd., COMPASS Pathways, Limited, United Kingdom, Concert Pharmaceuticals, Inc., Epiodyne, Inc., EpiVario, Inc., Greenwich Biosciences, Inc., Heptares Therapeutics, Limited (UK), Janssen Research & Development, Jazz Pharmaceuticals, Inc., Otsuka America Pharmaceutical, Inc., Perception Neuroscience Holdings, Inc., Spring Care, Inc., Sunovion Pharmaceuticals, Inc., Takeda Industries, Taisho Pharmaceutical Co., Ltd. Dr. Krystal also reports the following disclosures: Scientific Advisory Board: Biohaven Pharmaceuticals, BioXcel Therapeutics, Inc. (Clinical Advisory Board), Cadent Therapeutics, Inc. (Clinical Advisory Board), Cerevel Therapeutics, LLC, EpiVario, Inc., Eisai, Inc., Lohocla Research Corporation, Novartis Pharmaceuticals Corporation, PsychoGenics, Inc., RBNC Therapeutics, Inc., Tempero Bio, Inc., Terran Biosciences, Inc. Stock: Biohaven Pharmaceuticals, Sage Pharmaceuticals, Spring Care, Inc. Stock Options: Biohaven Pharmaceuticals Medical Sciences, EpiVario, Inc., RBNC Therapeutics, Inc., Terran Biosciences, Inc. Tempero Bio, Inc. Income Greater than $10,000: Editorial Board: Editor - Biological Psychiatry. Patents and Inventions: (1) Seibyl JP, Krystal JH, Charney DS. Dopamine and noradrenergic reuptake inhibitors in treatment of schizophrenia. US Patent #:5,447,948.September 5, 1995. (2) Vladimir, Coric, Krystal, John H, Sanacora, Gerard – Glutamate Modulating Agents in the Treatment of Mental Disorders. US Patent No. 8,778,979 B2 Patent Issue Date: July 15, 2014. US Patent Application No. 15/695,164: Filing Date: 09/05/2017. (3) Charney D, Krystal JH, Manji H, Matthew S, Zarate C., - Intranasal Administration of Ketamine to Treat Depression United States Patent Number: 9592207, Issue date: 3/14/2017. &#9;Licensed to Janssen Research & Development. (4) Zarate, C, Charney, DS, Manji, HK, Mathew, Sanjay J, Krystal, JH, Yale University “Methods for Treating Suicidal Ideation”, Patent Application No. 15/379,013 filed on December 14, 2016 by Yale University Office of Cooperative Research. (5) Arias A, Petrakis I, Krystal JH. – Composition and methods to treat addiction. Provisional Use Patent Application no.61/973/961. April 2, 2014. Filed by Yale University Office of Cooperative Research. (6) Chekroud, A., Gueorguieva, R., & Krystal, JH. “Treatment Selection for Major Depressive Disorder” [filing date 3rd June 2016, USPTO docket number Y0087.70116US00]. Provisional patent submission by Yale University. (7) Gihyun, Yoon, Petrakis I, Krystal JH – Compounds, Compositions and Methods for Treating or Preventing Depression and Other Diseases. U. S. Provisional Patent Application No. 62/444,552, filed on January10, 2017 by Yale University Office of Cooperative Research OCR 7088 US01. (8) Abdallah, C, Krystal, JH, Duman, R, Sanacora, G. Combination Therapy for Treating or Preventing Depression or Other Mood Diseases. U.S. Provisional Patent Application No. 62/719,935 filed on August 20, 2018 by Yale University Office of Cooperative Research OCR 7451 US01. On Non-Federal Research Support: AstraZeneca Pharmaceuticals provides the drug, Saracatinib, for research related to NIAAA grant “Center for Translational Neuroscience of Alcoholism [CTNA-4] Novartis provides the drug, Mavoglurant, for research related to NIAAA grant “Center for Translational Neuroscience of Alcoholism [CTNA-4] Dr. Gueorguieva discloses royalties from book “Statistical Methods in Psychiatry and Related Fields” published by CRC Press, honorarium as a member of the Working Group for PTSD Adaptive Platform Trial of Cohen Veterans Bioscience and a United States patent application 20200143922 by Yale University: Chekroud, A., Krystal, J., Gueorguieva, R. and Chandra, A. “Methods and Apparatus for Predicting Depression Treatment Outcomes”. Dr. Sanacora has received consulting fees from Alkermes, Allergan, AstraZeneca, Avanier Pharmaceuticals, Axsome Therapeutics, Biohaven Pharmaceuticals, Boehringer Ingelheim, Bristol-Myers Squibb, Clexio Biosciences, Denovo Biopharma, EMA Wellness, Engrail, Gilgamesh, Hoffmann–La Roche, Intra-Cellular Therapies, Janssen, Lundbeck, Merck, Minerva Neurosciences, Navitor Pharmaceuticals, Neurocrine, Novartis, Noven Pharmaceuticals, Otsuka, Perception Neuroscience, Praxis Therapeutics, Sage Pharmaceuticals, Seelos Pharmaceuticals, Taisho Pharmaceuticals, Teva, Valeant, Vistagen Therapeutics, and XW labs. Scientific Advisory Board: Biohaven Pharmaceuticals, Gilgamesh Pharmaceuticals. VistaGen Therapetutics Stock: Biohaven Pharmaceuticals, Gilead Sciences. Stock Options: Biohaven Pharmaceuticals Medical Sciences, Income Greater than $10,000: Biohaven pharmaceteuticals. Patents and Inventions: (1) Vladimir, Coric, Krystal, John H, Sanacora, Gerard – Glutamate Modulating Agents in the Treatment of Mental Disorders. US Patent No. 8,778,979 B2 Patent Issue Date: July 15, 2014. US Patent Application No. 15/695,164: Filing Date: 09/05/2017. (2) Abdallah, C, Krystal, JH, Duman, R, Sanacora, G. Combination Therapy for Treating or Preventing Depression or Other Mood Diseases. U.S. Provisional Patent Application No. 62/719,935 filed on August 20, 2018 by Yale University Office of Cooperative Research OCR 7451 US01. On Non-Federal Research Support: Dr. Sanacora has received research contracts from AstraZeneca, Bristol-Myers Squibb, Eli Lilly, Johnson & Johnson, Hoffmann–La Roche, Merck, Naurex, Servier Pharmaceuticals, and Usona. No-cost medication was provided to Dr. Sanacora for an NIH-sponsored study by Sanofi-Aventis. All other authors declared no conflict of interests., (© The Author(s) 2022.)

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 ( 1 H-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 1 H-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., (Copyright © 2022 The Authors. Published by Elsevier Inc. All rights reserved.)

Several coronavirus disease 2019 (COVID-19) studies have focused on neuropathology. In this issue of the JCI, Qin, Wu, and Chen et al. focused specifically on people whose acute infection lacked obvious neurological involvement. Severely infected patients showed abnormal gray matter volumes, white matter diffusion, and cerebral blood flow compared with healthy controls and those with mild infection. The data remain associative rather than mechanistic, but correlations with systemic immune markers suggest effects of inflammation, hypercoagulation, or other aspects of disease severity. Mechanistic research is warranted. Given the lack of obvious neurological symptoms, neurocognitive assessments were not performed, but the findings suggest that such assessments may be warranted in severely affected patients, even without obvious symptoms. Further, studying CNS involvement of other disorders with overlapping pathophysiologies such as inflammation, coagulation, hypoxia, or direct viral infection may reveal the causes for COVID-19-related neuropathology.

Rationale: After alcohol ingestion, the brain partly switches from consumption of glucose to consumption of the alcohol metabolite acetate. In heavy drinkers, the switch persists after abrupt abstinence, leading to the hypothesis that the resting brain may be "starved" when acetate levels suddenly drop during abstinence, despite normal blood glucose, contributing to withdrawal symptoms. We hypothesized that ketone bodies, like acetate, could act as alternative fuels in the brain and alleviate withdrawal symptoms., Objectives: We previously reported that a ketogenic diet during alcohol exposure reduced acute withdrawal symptoms in rats. Here, our goals were to test whether (1) we could reproduce our findings, in mice and with longer alcohol exposure; (2) ketone bodies alone are sufficient to reduce withdrawal symptoms (clarifying mechanism); (3) introduction of ketogenic diets at abstinence (a clinically more practical implementation) would also be effective., Methods: Male C57BL/6NTac mice had intermittent alcohol exposure for 3 weeks using liquid diet. Somatic alcohol withdrawal symptoms were measured as handling-induced convulsions; anxiety-like behavior was measured using the light-dark transition test. We tested a ketogenic diet, and a ketone monoester supplement with a regular carbohydrate-containing diet., Results: The regular diet with ketone monoester was sufficient to reduce handling-induced convulsions and anxiety-like behaviors in early withdrawal. Only the ketone monoester reduced handling-induced convulsions when given during abstinence, consistent with faster elevation of blood ketones, relative to ketogenic diet., Conclusions: These findings support the potential utility of therapeutic ketosis as an adjunctive treatment in early detoxification in alcohol-dependent patients seeking to become abstinent., Trial Registration: clinicaltrials.gov NCT03878225, NCT03255031.

Alterations in muscle mitochondrial substrate preference have been postulated to play a major role in the pathogenesis of muscle insulin resistance. In order to examine this hypothesis, we assessed the ratio of mitochondrial pyruvate oxidation (V PDH ) to rates of mitochondrial citrate synthase flux (V CS ) in muscle. Contrary to this hypothesis, we found that high-fat-diet (HFD)-fed insulin-resistant rats did not manifest altered muscle substrate preference (V PDH /V CS ) in soleus or quadriceps muscles in the fasting state. Furthermore, hyperinsulinemic-euglycemic (HE) clamps increased V PDH /V CS in both muscles in normal and insulin-resistant rats. We then examined the muscle V PDH /V CS flux in insulin-sensitive and insulin-resistant humans and found similar relative rates of V PDH /V CS , following an overnight fast (∼20%), and similar increases in V PDH /V CS fluxes during a HE clamp. Altogether, these findings demonstrate that alterations in mitochondrial substrate preference are not an essential step in the pathogenesis of muscle insulin resistance., Competing Interests: Declaration of Interests The authors declare no competing interests., (Copyright © 2020 Elsevier Inc. All rights reserved.)

The mitochondrial GTP (mtGTP)-dependent phosphoenolpyruvate (PEP) cycle couples mitochondrial PEPCK (PCK2) to pyruvate kinase (PK) in the liver and pancreatic islets to regulate glucose homeostasis. Here, small molecule PK activators accelerated the PEP cycle to improve islet function, as well as metabolic homeostasis, in preclinical rodent models of diabetes. In contrast, treatment with a PK activator did not improve insulin secretion in pck2 -/- mice. Unlike other clinical secretagogues, PK activation enhanced insulin secretion but also had higher insulin content and markers of differentiation. In addition to improving insulin secretion, acute PK activation short-circuited gluconeogenesis to reduce endogenous glucose production while accelerating red blood cell glucose turnover. Four-week delivery of a PK activator in vivo remodeled PK phosphorylation, reduced liver fat, and improved hepatic and peripheral insulin sensitivity in HFD-fed rats. These data provide a preclinical rationale for PK activation to accelerate the PEP cycle to improve metabolic homeostasis and insulin sensitivity., Competing Interests: Declaration of Interests C.K. is an employee of and stockholder in Agios Pharmaceuticals. R.G.K. has been a paid consultant for Agios Pharmaceuticals. The remaining authors declare no competing interests., (Copyright © 2020 Elsevier Inc. All rights reserved.)

Major depressive disorder is the leading cause of disability and suicidality worldwide. Here, we evaluated neural metabolic activity in prefrontal cortex (PFC) in C57BL6 mice undergoing a chronic unpredictable mild stress (CUMS) for three weeks to induce depression. Further, the efficacy of Lanicemine, a low trapping NMDA receptor antagonist, on behavioral and neurometabolic measures in CUMS mice was evaluated. The PFC neuronal and astroglial metabolic activity was evaluated by Proton Observed Carbon Edited (POCE) MR spectroscopy together with an infusion of [1,6- 13 C 2 ]glucose and [2- 13 C]acetate, respectively. The rates of glutamatergic, GABAergic and astrocytic TCA cycles and neurotransmitter cycling were obtained by fitting a three-compartment metabolic model to 13 C turnover of amino acids. Mice subjected to CUMS exhibited significantly reduced sucrose preference (CUMS 58.0 ± 12.5%, n = 29; Control 86.3 ± 6.4%, n = 30; p < 0.0001), and increased immobility (CUMS 146.1 ± 60.8s, n = 29; Control 29.9 ± 19.3s, n = 30; p < 0.0001) in the forced swim test. The concentrations of 13 C labeled amino acids from [2- 13 C]acetate were decreased suggesting reduced astroglial metabolic activity in CUMS mice. The glutamatergic and GABAergic TCA cycle rates were decreased in CUMS mice when compared with controls. In addition, GABA-glutamine and glutamate-glutamine neurotransmitter cycling were reduced in mice subjected to CUMS regimen. Most interestingly, a short time intervention of lanicemine restored behavioral measures (sucrose preference and immobility), and rates of glucose oxidation in glutamatergic and GABAergic neurons in CUMS mice. In summary, our findings suggest that depression leads to a reduction in excitatory and inhibitory neurotransmission in PFC, and targeting glutamatergic pathway may have potential therapeutic role in chronic depression., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

Early life stress (ELS) and glutamate neurotransmission have been implicated in the pathophysiology of major depressive disorder (MDD). In non-human primates, ELS was positively correlated with cortical Glx (i.e., glutamate + glutamine). However, the relationship between ELS and cortical glutamate in adult patients with MDD is not fully known. Using 1 H Magnetic Resonance Spectroscopy (MRS), we conducted exploratory analyses measuring occipital cortical glutamate and glutamine levels in 36 medication-free patients with MDD. In a subsample (n=11), we measured dynamic glutamate/glutamine cycling (V cycle ) using advanced 13 C MRS methods. ELS history was assessed using Early-life Trauma Inventory (ETI). Exploratory analyses suggest a relationship between ETI and glutamine as reflected by a significant positive correlation between ETI scores and occipital glutamine (r s =0.39, p=0.017) but not glutamate. Post-hoc analyses showed that the association with glutamine was driven by the ETI emotional abuse (ETI-EA) subscale (r s =0.39, p=0.02). V cycle correlation with ETI was at trend level (r s =0.55, p=0.087) and significantly correlated with ETI-EA (r s =0.67, p=0.03). In this small sample of patients with MDD, those with childhood emotional abuse appear to have increased occipital glutamate neurotransmission as reflected by increased glutamate/glutamine cycling and glutamine level. Future studies would be needed to confirm this pilot evidence and to examine whether ELS effects on glutamate neurotransmission underlie the relationship between ELS and psychopathology., (Published by Elsevier B.V.)

Multiple insulin-regulated enzymes participate in hepatic glycogen synthesis, and the rate-controlling step responsible for insulin stimulation of glycogen synthesis is unknown. We demonstrate that glucokinase (GCK)-mediated glucose phosphorylation is the rate-controlling step in insulin-stimulated hepatic glycogen synthesis in vivo, by use of the somatostatin pancreatic clamp technique using [ 13 C 6 ]glucose with metabolic control analysis (MCA) in three rat models: 1) regular chow (RC)-fed male rats (control), 2) high fat diet (HFD)-fed rats, and 3) RC-fed rats with portal vein glucose delivery at a glucose infusion rate matched to the control. During hyperinsulinemia, hyperglycemia dose-dependently increased hepatic glycogen synthesis. At similar levels of hyperinsulinemia and hyperglycemia, HFD-fed rats exhibited a decrease and portal delivery rats exhibited an increase in hepatic glycogen synthesis via the direct pathway compared with controls. However, the strong correlation between liver glucose-6-phosphate concentration and net hepatic glycogen synthetic rate was nearly identical in these three groups, suggesting that the main difference between models is the activation of GCK. MCA yielded a high control coefficient for GCK in all three groups. We confirmed these findings in studies of hepatic GCK knockdown using an antisense oligonucleotide. Reduced liver glycogen synthesis in lipid-induced hepatic insulin resistance and increased glycogen synthesis during portal glucose infusion were explained by concordant changes in translocation of GCK. Taken together, these data indicate that the rate of insulin-stimulated hepatic glycogen synthesis is controlled chiefly through GCK translocation., Competing Interests: Competing interest statement: A.V. serves on an advisory board for vTv Therapeutics., (Copyright © 2020 the Author(s). Published by PNAS.)

In the last 25 years 13 C MRS has been established as the only noninvasive method for measuring glutamate neurotransmission and cell specific neuroenergetics. Although technically and experimentally challenging 13 C MRS has already provided important new information on the relationship between neuroenergetics and neuronal function, the high energy cost of brain function in the resting state and the role of altered neuroenergetics and neurotransmitter cycling in disease. In this paper we review the metabolic and neurotransmitter pathways that can be measured by 13 C MRS and key findings on the linkage between neuroenergetics, neurotransmitter cycling, and brain function. Applications of 13 C MRS to neurological and psychiatric disease as well as brain cancer are reviewed. Recent technological developments that may help to overcome spatial resolution and brain coverage limitations of 13 C MRS are discussed., (© 2019 John Wiley & Sons, Ltd.)

There is tremendous interest in the role of the neuroimmune system and inflammatory processes in substance use disorders (SUDs). Imaging biomarkers of the neuroimmune system in vivo provide a vital translational bridge between preclinical and clinical research. Herein, we examine two imaging techniques that measure putative indices of the neuroimmune system and review their application among SUDs. Positron emission tomography (PET) imaging of 18 kDa translocator protein availability is a marker associated with microglia. Proton magnetic resonance spectroscopy quantification of myo- inositol levels is a putative glial marker found in astrocytes. Neuroinflammatory responses are initiated and maintained by microglia and astrocytes, and thus represent important imaging markers. The goal of this review is to summarize neuroimaging findings from the substance use literature that report data using these markers and discuss possible mechanisms of action. The extant literature indicates abused substances exert diverse and complex neuroimmune effects. Moreover, drug effects may change across addiction stages, i.e. the neuroimmune effects of acute drug administration may differ from chronic use. This burgeoning field has considerable potential to improve our understanding and treatment of SUDs. Future research is needed to determine how targeting the neuroimmune system may improve treatment outcomes., Competing Interests: The authors have no conflicts of interests to declare.

The impact of glycemic variability on brain glucose transport kinetics among individuals with type 1 diabetes mellitus (T1DM) remains unclear. Fourteen individuals with T1DM (age 35 ± 4 years; BMI 26.0 ± 1.4 kg/m 2 ; HbA 1c 7.6 ± 0.3) and nine healthy control participants (age 32 ± 4; BMI 23.1 ± 0.8; HbA 1c 5.0 ± 0.1) wore a continuous glucose monitor (Dexcom) to measure hypoglycemia, hyperglycemia, and glycemic variability for 5 days followed by 1 H MRS scanning in the occipital lobe to measure the change in intracerebral glucose levels during a 2-h glucose clamp (target glucose concentration 220 mg/dL). Hyperglycemic clamps were also performed in a rat model of T1DM to assess regional differences in brain glucose transport and metabolism. Despite a similar change in plasma glucose levels during the hyperglycemic clamp, individuals with T1DM had significantly smaller increments in intracerebral glucose levels ( P = 0.0002). Moreover, among individuals with T1DM, the change in brain glucose correlated positively with the lability index ( r = 0.67, P = 0.006). Consistent with findings in humans, streptozotocin-treated rats had lower brain glucose levels in the cortex, hippocampus, and striatum compared with control rats. These findings that glycemic variability is associated with brain glucose levels highlight the need for future studies to investigate the impact of glycemic variability on brain glucose kinetics., (© 2018 by the American Diabetes Association.)

The ability of ketamine administration to activate prefrontal glutamate neurotransmission is thought to be a key mechanism contributing to its transient psychotomimetic effects and its delayed and sustained antidepressant effects. Rodent studies employing carbon-13 magnetic resonance spectroscopy ( 13 C MRS) methods have shown ketamine and other N-methyl-D-aspartate (NMDA) receptor antagonists to transiently increase measures reflecting glutamate-glutamine cycling and glutamate neurotransmission in the frontal cortex. However, there are not yet direct measures of glutamate neurotransmission in vivo in humans to support these hypotheses. The current first-level pilot study employed a novel prefrontal 13 C MRS approach similar to that used in the rodent studies for direct measurement of ketamine effects on glutamate-glutamine cycling. Twenty-one participants (14 healthy and 7 depressed) completed two 13 C MRS scans during infusion of normal saline or subanesthetic doses of ketamine. Compared to placebo, ketamine increased prefrontal glutamate-glutamine cycling, as indicated by a 13% increase in 13 C glutamine enrichment (t = 2.4, p = 0.02). We found no evidence of ketamine effects on oxidative energy production, as reflected by 13 C glutamate enrichment. During ketamine infusion, the ratio of 13 C glutamate/glutamine enrichments, a putative measure of neurotransmission strength, was correlated with the Clinician-Administered Dissociative States Scale (r = -0.54, p = 0.048). These findings provide the most direct evidence in humans to date that ketamine increases glutamate release in the prefrontal cortex, a mechanism previously linked to schizophrenia pathophysiology and implicated in the induction of rapid antidepressant effects.

Purpose: 13 C magnetic resonance spectroscopy (MRS) in combination with infusion of 13 C-labeled substrates has led to unique insights into human brain metabolism and neurotransmitter cycling. However, the low sensitivity of direct 13 C MRS and high radiofrequency power requirements has limited 13 C MRS studies to predominantly data acquisition in large volumes of the occipital cortex. The purpose of this study is to develop an MRS technique for localized detection of 13 C-labeling of glutamate and glutamine in the human frontal lobe., Methods: We used an indirect ( 1 H-[ 13 C]), proton-observed, carbon-edited MRS sequence (selPOCE) for detection of 13 C-labeled metabolites in relatively small volumes located in the frontal lobe at 4 T. The SelPOCE method allows for selective and separate detection of glutamate and glutamine resonances, which significantly overlap at magnetic field strengths used for clinical MRI., Results: Phantom data illustrate how selPOCE can be tuned to selectively detect 13 C labeling in different metabolites. Three-dimensional specific absorption rate simulations of radiofrequency power deposition show that the selPOCE method operates comfortably within the global and local Food and Drug Administration specific absorption rate guidelines. In vivo selPOCE data are presented, which were acquired from a 45-mL volume in the frontal lobe of healthy subjects. The in vivo data show the time-dependent 13 C-labeling of glutamate and glutamine during intravenous infusion of [1- 13 C]-glucose. Metrics describing spectral fitting quality of the glutamate and glutamine resonances are reported., Conclusions: The SelPOCE sequence allows the detection of 13 C-labeling in glutamate and glutamine from a relatively small volume in the human frontal lobe at low radiofrequency power requirements. Magn Reson Med 80:11-20, 2018. © 2017 International Society for Magnetic Resonance in Medicine., (© 2017 International Society for Magnetic Resonance in Medicine.)

Background: Preclinical and postmortem studies have implicated the metabotropic glutamate receptor 5 (mGluR5) in the pathophysiology of major depressive disorder (MDD). The goal of the present study was to determine the role of mGluR5 in a large group of individuals with MDD compared to healthy controls (HC) in vivo with [ 18 F]FPEB and positron emission tomography (PET). Furthermore, we sought to determine the role glutamate plays on mGluR5 availability in MDD., Methods: Sixty-five participants (30 MDD and 35 HC) completed [ 18 F]FPEB PET to estimate the primary outcome measure - mGluR5 volume of distribution ( V T ), and the secondary outcome measure - mGluR5 distribution volume ratio ( DVR ). A subgroup of 39 participants (16 MDD and 23 HC) completed proton magnetic resonance spectroscopy ( 1 H MRS) to estimate anterior cingulate (ACC) glutamate, glutamine, and Glx (glutamate + glutamine) levels relative to creatine (Cr)., Results: No significant between-group differences were observed in mGluR5 V T or DVR . Compared to HC, individuals with MDD had higher ACC glutamate, glutamine, and Glx levels. Importantly, the ACC mGluR5 DVR negatively correlated with glutamate/Cr and Glx/Cr levels., Conclusions: In this novel in vivo examination, we show an inverse relationship between mGluR5 availability and glutamate levels. These data highlight the need to further investigate the role of glutamatergic system in depression.

Purpose: To determine the reproducibility of a comprehensive single-session measurement of glutathione (GSH), γ-aminobutyric acid (GABA), glutamate, and other biochemicals implicated in the pathophysiology of multiple sclerosis (MS) in the human brain with 1 H magnetic resonance spectroscopy (MRS)., Materials and Methods: Five healthy subjects were studied twice in separate 1-hour sessions at 7T. One MS patient was also scanned once. GSH and GABA were measured with J-difference editing using a semilocalized by adiabatic selective refocusing sequence (semi-LASER, TE = 72 msec). A stimulated echo acquisition mode sequence (STEAM, TE = 10 msec) was used to detect glutamate along with the overall biochemical profile. Spectra were quantified with LCModel. Quantification accuracy was assessed through Cramer-Rao lower bounds (CRLB). Reproducibility of the metabolite quantification was tested using coefficients of variation (CoV)., Results: CRLB were ≤7% for GSH, GABA, and glutamate and average CoV of 7.8 ± 3.2%, 9.5 ± 7.0%, and 3.2 ± 1.7% were achieved, respectively. The average test/retest concentration differences at this measurement reproducibility and quantification accuracy were smaller for GABA and glutamate than intersubject variations in metabolite content with CoV ratios of 0.6 and 0.8, respectively. As proof of principle, GSH, GABA, and glutamate were also detected in an MS patient., Conclusion: GSH, GABA, glutamate, and other metabolites relevant in MS can be quantified at 7T with high accuracy and reproducibility in a single 1-hour session. This methodology might serve as a clinical research tool to investigate biochemical markers associated with MS., Level of Evidence: 2 J. Magn. Reson. Imaging 2017;45:187-198., (© 2016 International Society for Magnetic Resonance in Medicine.)

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., (Copyright © 2015 by the Research Society on Alcoholism.)

Research on novel treatments for major depressive disorder focuses quite deeply on glutamate function, and this research would benefit from a brain-imaging technique that precisely quantified glutamate function. Signs of a specific form of glutamate-related dysfunction that could be targeted by novel therapies were found using novel, state-of-the-art techniques to address this issue.

(13)C Nuclear Magnetic Resonance (NMR) studies of rodent and human brain using [1-(13)C]/[1,6-(13)C2]glucose as labeled substrate have consistently found a lower enrichment (∼25% to 30%) of glutamine-C4 compared with glutamate-C4 at isotopic steady state. The source of this isotope dilution has not been established experimentally but may potentially arise either from blood/brain exchange of glutamine or from metabolism of unlabeled substrates in astrocytes, where glutamine synthesis occurs. In this study, the contribution of the former was evaluated ex vivo using (1)H-[(13)C]-NMR spectroscopy together with intravenous infusion of [U-(13)C5]glutamine for 3, 15, 30, and 60 minutes in mice. (13)C labeling of brain glutamine was found to be saturated at plasma glutamine levels >1.0 mmol/L. Fitting a blood-astrocyte-neuron metabolic model to the (13)C enrichment time courses of glutamate and glutamine yielded the value of glutamine influx, VGln(in), 0.036±0.002 μmol/g per minute for plasma glutamine of 1.8 mmol/L. For physiologic plasma glutamine level (∼0.6 mmol/L), VGln(in) would be ∼0.010 μmol/g per minute, which corresponds to ∼6% of the glutamine synthesis rate and rises to ∼11% for saturating blood glutamine concentrations. Thus, glutamine influx from blood contributes at most ∼20% to the dilution of astroglial glutamine-C4 consistently seen in metabolic studies using [1-(13)C]glucose.

Reading disability is a brain-based difficulty in acquiring fluent reading skills that affects significant numbers of children. Although neuroanatomical and neurofunctional networks involved in typical and atypical reading are increasingly well characterized, the underlying neurochemical bases of individual differences in reading development are virtually unknown. The current study is the first to examine neurochemistry in children during the critical period in which the neurocircuits that support skilled reading are still developing. In a longitudinal pediatric sample of emergent readers whose reading indicators range on a continuum from impaired to superior, we examined the relationship between individual differences in reading and reading-related skills and concentrations of neurometabolites measured using magnetic resonance spectroscopy. Both continuous and group analyses revealed that choline and glutamate concentrations were negatively correlated with reading and related linguistic measures in phonology and vocabulary (such that higher concentrations were associated with poorer performance). Correlations with behavioral scores obtained 24 months later reveal stability for the relationship between glutamate and reading performance. Implications for neurodevelopmental models of reading and reading disability are discussed, including possible links of choline and glutamate to white matter anomalies and hyperexcitability. These findings point to new directions for research on gene-brain-behavior pathways in human studies of reading disability.

Neuroimaging, including PET, MRI, and MRS, is a powerful approach to the study of brain function. This article reviews neuroimaging findings related to alcohol and other drugs of abuse that have been published since 2011. Uses of neuroimaging are to characterize patients to determine who will fare better in treatment and to investigate the reasons underlying the effect on outcomes. Neuroimaging is also used to characterize the acute and chronic effects of substances on the brain and how those effects are related to dependence, relapse, and other drug effects. The data can be used to provide encouraging information for patients, as several studies have shown that long-term abstinence is associated with at least partial normalization of neurological abnormalities.

Background: Previous studies have demonstrated that antidepressant medication and electroconvulsive therapy increase occipital cortical γ-aminobutyric acid (GABA) in major depressive disorder (MDD), but a small pilot study failed to show a similar effect of cognitive-behavioral therapy (CBT) on occipital GABA. In light of these findings we sought to determine if baseline GABA levels predict treatment response and to broaden the analysis to other metabolites and neurotransmitters in this larger study., Methods: A total of 40 MDD outpatients received baseline proton magnetic resonance spectroscopy (1H-MRS), and 30 subjects completed both pre- and post-CBT 1H-MRS; 9 CBT nonresponders completed an open-label medication phase followed by an additional/3rd 1H-MRS. The magnitude of treatment response was correlated with occipital amino acid neurotransmitter levels., Results: Baseline GABA did not predict treatment outcome. Furthermore, there was no significant effect of CBT on GABA levels. However, we found a significant group × time interaction (F1, 28 = 6.30, p = 0.02), demonstrating reduced glutamate in CBT responders, with no significant glutamate change in CBT nonresponders., Conclusions: These findings corroborate the lack of effect of successful CBT on occipital cortical GABA levels in a larger sample. A reduction in glutamate levels following treatment, on the other hand, correlated with successful CBT and antidepressant medication response. Based on this finding and other reports, decreased occipital glutamate may be an antidepressant response biomarker. Healthy control comparator and nonintervention groups may shed light on the sensitivity and specificity of these results.

Exposure to drug-associated cues evokes drug-seeking behavior and is regarded as a major cause of relapse. Cues evoke burst firing of ventral tegmental area (VTA) dopamine (DA) neurons and phasic DA release in the nucleus accumbens (NAc). Cholinergic and glutamatergic input to the VTA is suggested to gate phasic DA activity. However, the role of VTA cholinergic and glutamatergic receptors in regulating phasic dopamine release and cue-induced drug-seeking in cocaine experienced subjects is not known. In male Sprague-Dawley rats, we found that VTA inactivation strongly inhibited, while VTA stimulation promoted, cocaine-seeking behavior during early withdrawal. Blockade of phasic activated D1 receptors in the NAc core also strongly inhibited cue-induced cocaine-seeking--suggesting an important role of phasic DA activity in the VTA to NAc core circuit. Next, we examined the role of VTA acetylcholine receptors (AChRs) and N-methyl-D-aspartate receptors (NMDARs) in regulating both NAc core phasic DA release and cue-induced cocaine-seeking. In cocaine naïve subjects, VTA infusion of the nicotinic acetylcholine receptor (AChR) antagonist mecamylamine, the muscarinic AChR antagonist scopolamine, or the NMDAR antagonist AP-5, led to robust attenuation of phasic DA release in the NAc core. During early cocaine withdrawal, VTA infusion of AP-5 had limited effects on NAc phasic DA release and cue-induced cocaine-seeking while VTA infusion of mecamylamine or scopolamine robustly inhibited both phasic DA release and cocaine-seeking. The results demonstrate that VTA AChRs, but not NMDARs, strongly regulate cue-induced cocaine-seeking and phasic DA release during early cocaine withdrawal., (Copyright © 2013 Elsevier Ltd. All rights reserved.)

Most ingested ethanol is metabolized in the liver to acetaldehyde and then to acetate, which can be oxidized by the brain. This project assessed whether chronic exposure to alcohol can increase cerebral oxidation of acetate. Through metabolism, acetate may contribute to long-term adaptation to drinking. Two groups of adult male Sprague-Dawley rats were studied, one treated with ethanol vapor and the other given room air. After 3 weeks the rats received an intravenous infusion of [2-(13) C]ethanol via a lateral tail vein for 2 h. As the liver converts ethanol to [2-(13) C]acetate, some of the acetate enters the brain. Through oxidation the (13) C is incorporated into the metabolic intermediate α-ketoglutarate, which is converted to glutamate (Glu), glutamine (Gln), and GABA. These were observed by magnetic resonance spectroscopy and found to be (13) C-labeled primarily through the consumption of ethanol-derived acetate. Brain Gln, Glu, and, GABA (13) C enrichments, normalized to (13) C-acetate enrichments in the plasma, were higher in the chronically treated rats than in the ethanol-naïve rats, suggesting increased cerebral uptake and oxidation of circulating acetate. Chronic ethanol exposure increased incorporation of systemically derived acetate into brain Gln, Glu, and GABA, key neurochemicals linked to brain energy metabolism and neurotransmission. The liver converts ethanol to acetate, which may contribute to long-term adaptation to drinking. Astroglia oxidize acetate and generate neurochemicals, while neurons and glia may also oxidize ethanol. When (13) C-ethanol is administered intravenously, (13) C-glutamine, glutamate, and GABA, normalized to (13) C-acetate, were higher in chronic ethanol-exposed rats than in control rats, suggesting that ethanol exposure increases cerebral oxidation of circulating acetate., (© 2013 International Society for Neurochemistry.)

Previous studies have reported that brain metabolism of acetate is increased more than twofold during hypoglycemia in type 1 diabetic (T1D) subjects with hypoglycemia unawareness. These data support the hypothesis that upregulation of blood-brain barrier monocarboxylic acid (MCA) transport may contribute to the maintenance of brain energetics during hypoglycemia in subjects with hypoglycemia unawareness. Plasma lactate concentrations are ∼10-fold higher than acetate concentrations, making lactate the most likely alternative MCA as brain fuel. We therefore examined transport of [3-(13)C]lactate across the blood-brain barrier and its metabolism in the brains of T1D patients and nondiabetic control subjects during a hypoglycemic clamp using (13)C magnetic resonance spectroscopy. Brain lactate concentrations were more than fivefold higher (P < 0.05) during hypoglycemia in the T1D subjects compared with the control subjects. Surprisingly, we observed no increase in the oxidation of blood-borne lactate in the T1D subjects, as reflected by similar (13)C fractional enrichments in brain glutamate and glutamine. Taken together, these data suggest that in addition to increased MCA transport at the blood-brain barrier, there may be additional metabolic adaptations that contribute to hypoglycemia unawareness in patients with T1D.

Context: Intensive insulin therapy reduces the risk for long-term complications in patients with type 1 diabetes mellitus (T1DM) but increases the risk for hypoglycemia-associated autonomic failure (HAAF), a syndrome that includes hypoglycemia unawareness and defective glucose counterregulation (reduced epinephrine and glucagon responses to hypoglycemia)., Objective: The objective of the study was to address mechanisms underlying HAAF, we investigated whether nonglucose fuels such as acetate, a monocarboxylic acid (MCA), can support cerebral energetics during hypoglycemia in T1DM individuals with hypoglycemia unawareness., Design: Magnetic resonance spectroscopy was used to measure brain transport and metabolism of [2-(13)C]acetate under hypoglycemic conditions., Setting: The study was conducted at the Yale Center for Clinical Investigation Hospital Research Unit, Yale Magnetic Resonance Research Center., Patients and Other Participants: T1DM participants with moderate to severe hypoglycemia unawareness (n = 7), T1DM controls without hypoglycemia unawareness (n = 5), and healthy nondiabetic controls (n = 10) participated in the study., Main Outcome Measure(s): Brain acetate concentrations, (13)C percent enrichment of glutamine and glutamate, and absolute rates of acetate metabolism were measured., Results: Absolute rates of acetate metabolism in the cerebral cortex were 1.5-fold higher among T1DM/unaware participants compared with both control groups during hypoglycemia (P = .001). Epinephrine levels of T1DM/unaware subjects were significantly lower than both control groups (P < .05). Epinephrine levels were inversely correlated with levels of cerebral acetate use across the entire study population (P < .01), suggesting a relationship between up-regulated brain MCA use and HAAF., Conclusion: Increased MCA transport and metabolism among T1DM individuals with hypoglycemia unawareness may be a mechanism to supply the brain with nonglucose fuels during episodes of acute hypoglycemia and may contribute to the syndrome of hypoglycemia unawareness, independent of diabetes.

It has been reported that chronic and acute alcohol exposure decreases cerebral glucose metabolism and increases acetate oxidation. However, it remains unknown how much ethanol the living brain can oxidize directly and whether such a process would be affected by alcohol exposure. The questions have implications for reward, oxidative damage, and long-term adaptation to drinking. One group of adult male Sprague-Dawley rats was treated with ethanol vapor and the other given room air. After 3 wk the rats received i.v. [2-(13)C]ethanol and [1, 2-(13)C2]acetate for 2 h, and then the brain was fixed, removed, and divided into neocortex and subcortical tissues for measurement of (13)C isotopic labeling of glutamate and glutamine by magnetic resonance spectroscopy. Ethanol oxidation was seen to occur both in the cortex and the subcortex. In ethanol-naïve rats, cortical oxidation of ethanol occurred at rates of 0.017 ± 0.002 µmol/min/g in astroglia and 0.014 ± 0.003 µmol/min/g in neurons, and chronic alcohol exposure increased the astroglial ethanol oxidation to 0.028 ± 0.002 µmol/min/g (P = 0.001) with an insignificant effect on neuronal ethanol oxidation. Compared with published rates of overall oxidative metabolism in astroglia and neurons, ethanol provided 12.3 ± 1.4% of cortical astroglial oxidation in ethanol-naïve rats and 20.2 ± 1.5% in ethanol-treated rats. For cortical astroglia and neurons combined, the ethanol oxidation for naïve and treated rats was 3.2 ± 0.3% and 3.8 ± 0.2% of total oxidation, respectively. (13)C labeling from subcortical oxidation of ethanol was similar to that seen in cortex but was not affected by chronic ethanol exposure.

Hypoglycemia occurs frequently during intensive insulin therapy in patients with both type 1 and type 2 diabetes and remains the single most important obstacle in achieving tight glycemic control. Using a rodent model of hypoglycemia, we demonstrated that exposure to antecedent recurrent hypoglycemia leads to adaptations of brain metabolism so that modest increments in circulating lactate allow the brain to function normally under acute hypoglycemic conditions. We characterized 3 major factors underlying this effect. First, we measured enhanced transport of lactate both into as well as out of the brain that resulted in only a small increase of its contribution to total brain oxidative capacity, suggesting that it was not the major fuel. Second, we observed a doubling of the glucose contribution to brain metabolism under hypoglycemic conditions that restored metabolic activity to levels otherwise only observed at euglycemia. Third, we determined that elevated lactate is critical for maintaining glucose metabolism under hypoglycemia, which preserves neuronal function. These unexpected findings suggest that while lactate uptake was enhanced, it is insufficient to support metabolism as an alternate substrate to replace glucose. Lactate is, however, able to modulate metabolic and neuronal activity, serving as a "metabolic regulator" instead.

When a person consumes ethanol, the body quickly begins to convert it to acetic acid, which circulates in the blood and can serve as a source of energy for the brain and other organs. This study used 13C magnetic resonance spectroscopy to test whether chronic heavy drinking is associated with greater brain uptake and oxidation of acetic acid, providing a potential metabolic reward or adenosinergic effect as a consequence of drinking. Seven heavy drinkers, who regularly consumed at least 8 drinks per week and at least 4 drinks per day at least once per week, and 7 light drinkers, who consumed fewer than 2 drinks per week were recruited. The subjects were administered [2-13C]acetate for 2 hours and scanned throughout that time with magnetic resonance spectroscopy of the brain to observe natural 13C abundance of N-acetylaspartate (NAA) and the appearance of 13C-labeled glutamate, glutamine, and acetate. Heavy drinkers had approximately 2-fold more brain acetate relative to blood and twice as much labeled glutamate and glutamine. The results show that acetate transport and oxidation are faster in heavy drinkers compared with that in light drinkers. Our finding suggests that a new therapeutic approach to supply acetate during alcohol detoxification may be beneficial.

Ethanol vapor chambers have been utilized widely in alcohol research since their introduction in 1971, and implementations of these systems are now available commercially. Here, we present a modification of the chamber that can be built at lower cost and greater simplicity of operation. The six-chamber system for rats has multiple air pumps. Ethanol vapor levels are adjusted with the air flow rate, ethanol drip rate, and dilution with room air, without a heater or fans. Ethanol vapor concentrations are measured with a breathalyzer, using room air to dilute the vapor chamber output into the range of the breathalyzer. Multiple pumps provide backup to ensure animal survival in the case of failure of the primary air pump. Tests in animals demonstrated comfortable and stable elevation of blood ethanol, with tight control of the ethanol vapor concentrations and the ability to select from a broad range of levels. The ethanol vapor measurement was rapid and efficient. The parts cost was a few thousand U.S. dollars. This vapor chamber system features low cost, ease of use, and convenient and inexpensive measurement of ethanol vapor concentrations. The lack of a heater and electrical components that could come into contact with ethanol in our case facilitated institutional approval., (Copyright © 2012 Elsevier B.V. All rights reserved.)

Study Objectives: GABA is increasingly recognized as an important neurotransmitter for the initiation and maintenance of sleep. We sought to measure cortical GABA content through proton magnetic resonance spectroscopy (MRS) in persons with and without primary insomnia, and relate brain GABA levels to polysomnographic sleep measures., Design: Two-group comparison study., Setting: Outpatient study at a university research clinic., Participants: Non-medicated persons with primary insomnia (N = 16) and no sleep complaints (N = 17)., Interventions: Participants kept sleep diaries and a regular time-in-bed schedule for 9 days, culminating in 2 consecutive nights of ambulatory polysomnography and a single proton MRS session. The main outcome measure was occipital GABA/creatine ratios; secondary measures included sleep measurements and relationship between polysomnographically measured time awake after sleep onset and occipital GABA content., Measurements and Results: The primary insomnia group was distinguished from persons with no sleep complaints on self-reported and polysomnographically measured sleep. The two groups did not differ in age, sex, body mass index, habitual bed- and wake-times, napping, use of caffeine, or use of cigarettes. Mean occipital GABA level was 12% higher in persons with insomnia than in persons without sleep complaints (P < 0.05). In both groups, GABA levels correlated negatively with polysomnographically measured time awake after sleep onset (P < 0.05)., Conclusions: Increased GABA levels in persons with insomnia may reflect an allostatic response to chronic hyperarousal. The preserved, negative relationship between GABA and time awake after sleep onset supports this notion, indicating that the possible allostatic response is adaptive.

Background: Ethanol modulates glutamate and γ-aminobutyric (GABA) function. However, little is known about the acute pharmacologic effects of ethanol on levels of GABA, glutamate, and other metabolites measurable in the human cortex in vivo with proton magnetic resonance spectroscopy ((1)H-MRS)., Methods: Eleven healthy social drinkers received two intravenous ethanol infusions that raised breath alcohol levels to a clamped plateau of 60 mg/dL over 60-70 min. The first infusion established tolerability of the procedure, and the second procedure, conducted 15 ± 12 days later, was performed during (1)H-MRS of occipital GABA, glutamate, and other metabolites., Results: The time course of brain ethanol approximated that of breath ethanol, but venous ethanol lagged by approximately 7 min. The GABA fell 13 ± 8% after 5 min of the ethanol infusion and remained reduced (p = .003) throughout the measurement. The combination of N-acetylaspartate and N-acetylaspartyl glutamate (summed as NAA) fell steadily during the infusion by 8 ± 3% (p = .0036)., Conclusions: Ethanol reduced cortical GABA and NAA levels in humans. Reductions in GABA levels are consistent with facilitation of GABA(A) receptor function by ethanol. The gradual decline in NAA levels suggests inhibition of neural or metabolic activity in the brain., (Copyright © 2012 Society of Biological Psychiatry. Published by Elsevier Inc. All rights reserved.)

Ketone bodies are important alternate brain fuels, but their capacity to replace glucose and support neural function is unclear. In this study, the contributions of ketone bodies and glucose to cerebral cortical metabolism were measured in vivo in halothane-anesthetized rats fasted for 36 hours (n=6) and receiving intravenous [2,4-(13)C(2)]-D-β-hydroxybutyrate (BHB). Time courses of (13)C-enriched brain amino acids (glutamate-C4, glutamine-C4, and glutamate and glutamine-C3) were measured at 9.4 Tesla using spatially localized (1)H-[(13)C]-nuclear magnetic resonance spectroscopy. Metabolic rates were estimated by fitting a constrained, two-compartment (neuron-astrocyte) metabolic model to the (13)C time-course data. We found that ketone body oxidation was substantial, accounting for 40% of total substrate oxidation (glucose plus ketone bodies) by neurons and astrocytes. D-β-Hydroxybutyrate was oxidized to a greater extent in neurons than in astrocytes (≈ 70:30), and followed a pattern closely similar to the metabolism of [1-(13)C]glucose reported in previous studies. Total neuronal tricarboxylic acid cycle (TCA) flux in hyperketonemic rats was similar to values reported for normal (nonketotic) anesthetized rats infused with [1-(13)C]glucose, but neuronal glucose oxidation was 40% to 50% lower, indicating that ketone bodies had compensated for the reduction in glucose use.