Magnetic resonance spectroscopy studies of substance use disorders: Current landscape and potential future directions

Excitatory and inhibitory neurometabolites in anorexia nervosa: A systematic review of proton magnetic resonance spectroscopy studies

The dysregulation of excitatory and inhibitory neurotransmission is considered a pathological marker of Anorexia Nervosa (AN), however, no systematic evaluation of the proton Magnetic Resonance Spectroscopy (1H-MRS) literature has been conducted to date. Accordingly, we conducted a systematic review of neurometabolite differences between individuals with AN and healthy controls (HC). A comprehensive database search (until June 2023) identified seven studies meeting inclusion criteria. Samples included adolescents and adults with similar mean age (AN: 22.20 HC: 22.60), and female percentages (AN: 98%; HC: 94%). The review found a considerable need for improving study design and the reporting of MRS sequence parameters and analysis. Reduced glutamate concentrations in the ACC and OCC, and reduced Glx concentrations in the ACC were reported by one and two studies, respectively. Lastly, only one study to date has quantified GABA concentrations, with no significant differences found. In conclusion, there is currently insufficient evidence of excitatory and inhibitory neurometabolites changes in AN. As the 1H-MRS literature in AN increases, the key questions herein proposed must be revisited.

Updated Perspectives on the Neurobiology of Substance Use Disorders Using Neuroimaging

Substance use problems impair social functioning, academic achievement, and employability. Psychological, biological, social, and environmental factors can contribute to substance use disorders. In recent years, neuroimaging breakthroughs have helped elucidate the mechanisms of substance misuse and its effects on the brain. Functional magnetic resonance imaging (MRI), positron emission tomography (PET), single-photon emission computed tomography (SPECT), and magnetic resonance spectroscopy (MRS) are all examples. Neuroimaging studies suggest substance misuse affects executive function, reward, memory, and stress systems. Recent neuroimaging research attempts have provided clinicians with improved tools to diagnose patients who misuse substances, comprehend the complicated neuroanatomy and neurobiology involved, and devise individually tailored and monitorable treatment regimens for individuals with substance use disorders. This review describes the most recent developments in drug misuse neuroimaging, including the neurobiology of substance use disorders, neuroimaging, and substance use disorders, established neuroimaging techniques, recent developments with established neuroimaging techniques and substance use disorders, and emerging clinical neuroimaging technology.

N-acetylcysteine does not alter neurometabolite levels in non-treatment seeking adolescents who use alcohol heavily: A preliminary randomized clinical trial

Current treatments for adolescent alcohol use disorder (AUD) are mainly psychosocial and limited in their efficacy. As such, pharmacotherapies are being investigated as potential adjunctive treatments to bolster treatment outcomes. N-acetylcysteine is a promising candidate pharmacotherapy for adolescent AUD because of its tolerability and demonstrated ability to modulate glutamatergic, GABAergic, and glutathione systems. The primary objective of this double-blind, placebo-controlled, within-subjects crossover preliminary investigation was to measure potential changes within glutamate + glutamine (Glx), GABA, and glutathione levels in the dorsal anterior cingulate cortex (dACC) using proton magnetic resonance spectroscopy during 10-days of N-acetylcysteine (1200 mg twice daily) compared to 10-days of placebo in non-treatment seeking adolescents who use alcohol heavily (N = 31; 55% female). Medication adherence was confirmed via video. Effects on alcohol use were measured using Timeline Follow-Back as an exploratory aim. Linear mixed effects models controlling for baseline metabolite levels, brain tissue composition, alcohol use, cannabis use, and medication adherence found no significant differences in Glx, GABA, or glutathione levels in the dACC after N-acetylcysteine compared to placebo. There were also no measurable effects on alcohol use; however, this finding was underpowered. Findings were consistent in the subsample of participants who met criteria for AUD (n = 19). The preliminary null findings in brain metabolite levels may be due to the young age of participants, relatively low severity of alcohol use, and non-treatment seeking status of the population investigated. Future studies can use these findings to conduct larger, well-powered studies within adolescents with AUD.

Improving the reproducibility of proton magnetic resonance spectroscopy brain thermometry: Theoretical and empirical approaches

In proton magnetic resonance spectroscopy (¹ H MRS)-based thermometry of brain, averaging temperatures measured from more than one reference peak offers several advantages, including improving the reproducibility (i.e., precision) of the measurement. This paper proposes theoretically and empirically optimal weighting factors to improve the weighted average of temperatures measured from three references. We first proposed concepts of equivalent noise and equivalent signal-to-noise ratio in terms of frequency measurement and a concept of relative frequency that allows the combination of different peaks in a spectrum for improving the precision of frequency measurement. Based on these, we then derived a theoretically optimal weighting factor and proposed an empirical weighting factor, both involving equivalent noise levels, for a weighted average of temperatures measured from three references (i.e., the singlets of NAA, Cr, and Ch in the ¹ H MR spectrum). We assessed these two weighting factors by comparing their errors in measurement of temperatures with the errors of temperatures measured from individual references; we also compared these two new weighting factors with two previously proposed weighting factors. These errors were defined as the standard deviations in repeated measurements or in Monte Carlo studies. Both the proposed theoretical and empirical weighting factors outperformed the two previously proposed weighting factors as well as the three individual references in all phantom and in vivo experiments. In phantom experiments with 4- or 10-Hz line broadening, the theoretical weighting factor outperformed the empirical one, but the latter was superior in all other repeated and Monte Carlo tests performed on phantom and in vivo data. The proposed weighting factors are superior to the two previously proposed weighting factors and can improve the reproducibility of temperature measurement using ¹ H MRS-based thermometry.

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.

Structure-guided design enables development of a hyperpolarized molecular probe for the detection of aminopeptidase N activity in vivo

Dynamic nuclear polarization (DNP) is a cutting-edge technique that markedly enhances the detection sensitivity of molecules using nuclear magnetic resonance (NMR)/magnetic resonance imaging (MRI). This methodology enables real-time imaging of dynamic metabolic status in vivo using MRI. To expand the targetable metabolic reactions, there is a demand for developing exogenous, i.e., artificially designed, DNP-NMR molecular probes; however, complying with the requirements of practical DNP-NMR molecular probes is challenging because of the lack of established design guidelines. Here, we report Ala-[1-¹³C]Gly-d₂-NMe₂ as a DNP-NMR molecular probe for in vivo detection of aminopeptidase N activity. We developed this probe rationally through precise structural investigation, calculation, biochemical assessment, and advanced molecular design to achieve rapid and detectable responses to enzyme activity in vivo. With the fabricated probe, we successfully detected enzymatic activity in vivo. This report presents a comprehensive approach for the development of artificially derived, practical DNP-NMR molecular probes through structure-guided molecular design.

Effects of cannabinoid exposure on short-term memory and medial orbitofrontal cortex function and chemistry in adolescent female rhesus macaques

Aim

There is increasing concern that cannabinoid exposure during adolescence may disturb brain maturation and produce long-term cognitive deficits. However, studies in human subjects have provided limited evidence for such causality. The present study utilized behavioral and neuroimaging endpoints in female non-human primates to examine the effects of acute and chronic exposure during adolescence to the cannabinoid receptor full agonist, AM2389, on cognitive processing and brain function and chemistry.

Materials and methods

Adolescent female rhesus macaques were trained on a titrating-delay matching-to-sample (TDMTS) touchscreen task that assays working memory. TDMTS performance was assessed before and during chronic exposure to AM2389, following antagonist (rimonabant) administration, and after discontinuation of the chronic regimen. Resting-state fMRI connectivity and magnetic resonance spectroscopy data were acquired prior to drug treatment, during chronic exposure, and following its discontinuation. Voxels were placed in the medial orbitofrontal cortex (mOFC), a region involved in memory processing that undergoes maturation during adolescence.

Results

TDMTS performance was dose-dependently disrupted by acute AM2389; however, chronic treatment resulted in tolerance to these effects. TDMTS performance also was disrupted by discontinuation of the chronic regimen but surprisingly, not by rimonabant administration during chronic AM2389 treatment. mOFC N-acetylaspartate/creatine ratio decreased after acute and chronic administration but returned to baseline values following discontinuation of chronic treatment. Finally, intra-network functional connectivity (mOFC) increased during the chronic regimen and returned to baseline values following its discontinuation.

Conclusion

Neural effects of a cannabinergic drug may persist during chronic exposure, notwithstanding the development of tolerance to behavioral effects. However, such effects dissipate upon discontinuation, reflecting the restorative capacity of affected brain processes.

MR spectroscopy and diffusion imaging in people with human immunodeficiency virus: Relationships to clinical and immunologic findings

BACKGROUND AND PURPOSE

People with human immunodeficiency virus (HIV; PWH) present a complex array of immunologic and medical disorders that impact brain structure and metabolism, complicating the interpretation of neuroimaging. This pilot study of well-characterized multi-morbid PWH examined how medical and immunologic factors predicted brain characteristics on proton MR spectroscopy (1H-MRS) and diffusion-weighted imaging (DWI).

METHODS

Eighteen individuals on combination antiretroviral therapy (cART), with mean age of 56 years, underwent medical history review, neuroimaging, and on the day of imaging, blood draw for assay of 20 plasma cytokines and flow cytometric characterization of peripheral blood mononuclear cell subsets. Predictors of n-acetyl aspartate, choline, myoinositol, glutamate/glutamine, fractional anisotropy and mean diffusivity were identified through bivariate correlation; those significant at p < .1000 were advanced to multivariate analysis, with models created for each neuroimaging outcome.

RESULTS

Monocyte subsets and diverse cytokines accounted for 16 of 25 (64%) variables predicting 1H-MRS spectra in frontal gray and white matter and basal ganglia; monocyte subsets did not predict any DWI characteristic. In contrast, age, presence of hypertension, and duration of HIV infection accounted for 13 of 25 (52%) variables predicting diffusion characteristics in the corpus callosum, thalamic radiations, and basal ganglia but only 3 of 25 (12%) predictors of 1H-MRS features.

CONCLUSIONS

1H-MRS neurometabolites were most often predicted by immunologic factors sensitive to temporal variation, whereas DWI metrics were more often related to longer-term disease state. In multi-morbid cART-era populations, selection and interpretation of neuroimaging modalities should account for complex temporal and pathogenetic influences of immunologic abnormality, disease state, and aging.