GABA quantitation using MEGA-PRESS: Regional and hemispheric differences.

PURPOSE: To measure in vivo brain gamma-aminobutyric acid (GABA) concentrations, and assess regional and hemispheric differences, using MR spectroscopy (1 H-MRS). MATERIALS AND METHODS: GABA concentrations were measured bilaterally in the frontal cortex (FC), parietal cortex (PC), and occipital cortex (OC) of 21 healthy young subjects (age range 20-29 years) using 3 Tesla Philips scanner. A univariate general linear model analysis was carried out to assess the effect of region and hemisphere as well as their interaction on GABA concentrations while controlling for sex and gray matter differences. RESULTS: Results indicated a significant regional dependence of GABA levels [F(2,89) = 11.725, P < 0.001, ηp2 = .209] with lower concentrations in the FC compared with both PC (P < 0.001) and OC (P < 0.001) regions. There was no significant hemispheric differences in GABA levels [F(1,89) = .172; P = 0.679; ηp2 = .002]. CONCLUSION: This study reports the concentrations of GABA in the FC, PC, and OC brain regions of healthy young adults. GABA distribution exhibits hemispheric symmetry, but varies across regions; GABA levels in the FC are lower than those in the PC and OC. J. Magn. Reson. Imaging 2016;44:1619-1623.

Stimulus-dependent modulation of working memory for identity monitoring: A functional MRI study.

While the neural correlates of identity monitoring working memory (WM) have been well characterised in literature, the WM subsystems for different types of stimuli have not been established. The aim of our study was to examine the neural network subtending WM for identity monitoring of both verbal and visual stimuli. We used functional magnetic resonance imaging (fMRI) with words, objects, and faces as stimuli in an n-back WM task to delineate the similarities and differences in brain activation during presentation of verbal and visual stimuli. The results revealed a predominantly left lateralized core fronto-parieto-cerebellar identity WM network comprising bilateral insula, left inferior frontal gyrus, inferior parietal gyrus, and cerebellum that is common to all stimuli. In addition, our results showed stimulus-specific recruitment of brain regions, with exclusive activations in left inferior frontal gyrus and inferior temporal gyrus for identity WM for verbal stimuli, and left middle occipital gyrus and cerebellum for identity WM for visual stimuli. The present study reveals the existence of a central identity WM network for both verbal and visual information, along with activation of distinct verbal and visual representational regions that are sensitive to respective stimuli.

Anesthesia Issues in Central Nervous System Disorders.

Every year, millions of people affected by disorders of the central nervous system (CNS) undergo various diagnostic, therapeutic and surgical procedures requiring administration of anesthetic agents. Anesthetics exert their anesthetic, amnesic and analgesic effects by acting on multiple neuronal membrane proteins in the CNS. While some of the causal anesthetic targets have been identified, a large number of anesthetic targets remain unknown. The consequent longterm effect of anesthetic agents on expression of these various molecular targets has been implicated in mediating potentially long-lasting adverse effects. Recent work suggested that the effects of general anesthetics may not be entirely reversible, with animal studies demonstrating persistent changes in CNS protein expression post recovery from anesthesia. Age-associated or disease-induced alterations in the CNS can profoundly alter multiple aspects of brain structure, biochemistry, and function. Such maladaptive changes in the brain can render it increasingly vulnerable to the effects of various anesthetics. The selection of appropriate anesthesia drugs and protocol is mandatory, especially in individuals with pre-existing CNS disorders, so as to maximize anesthesia efficiency, avoid occurrence of adverse events, and ensure patient safety. This review aims to summarize and consider the effects and potential risks of commonly used anesthetic agents in patients with compromised CNS function. We provide a comprehensive review of the established as well as the implicated effects of anesthetic agents on the elderly as well as on the pathology and progression of common neurological conditions.

Brain glutathione levels--a novel biomarker for mild cognitive impairment and Alzheimer's disease.

BACKGROUND: Extant data from in vivo animal models and postmortem studies indicate that Alzheimer's disease (AD) pathology is associated with reduction of the brain antioxidant glutathione (GSH), yet direct clinical evidence has been lacking. In this study, we investigated GSH modulation in the brain with AD and assessed the diagnostic potential of GSH estimation in hippocampi (HP) and frontal cortices (FC) as a biomarker for AD and its prodromal stage, mild cognitive impairment (MCI). METHODS: Brain GSH levels were measured in HP of 21 AD, 22 MCI, and 21 healthy old controls (HC) and FC of 19 AD, 19 MCI, and 28 HC with in vivo proton magnetic resonance spectroscopy. The association between GSH levels and clinical measures of AD progression was tested. Linear regression models were used to determine the best combination of GSH estimation in these brain regions for discrimination between AD, MCI, and HC. RESULTS: AD-dependent reduction of GSH was observed in both HP and FC (p < .001). Furthermore, GSH reduction in these regions correlated with decline in cognitive functions. Receiver operator characteristics analyses evidenced that hippocampal GSH robustly discriminates between MCI and healthy controls with 87.5% sensitivity, 100% specificity, and positive and negative likelihood ratios of 8.76/.13, whereas cortical GSH differentiates MCI and AD with 91.7% sensitivity, 100% specificity, and positive and negative likelihood ratios of 9.17/.08. CONCLUSIONS: The present study provides compelling in vivo evidence that estimation of GSH levels in specific brain regions with magnetic resonance spectroscopy constitutes a clinically relevant biomarker for MCI and AD.

The emerging role of glutathione in Alzheimer's disease.

With millions of older individuals presently suffering from Alzheimer's disease (AD) worldwide, AD is an unduly common form of dementia that exacts a heavy toll on affected individuals and their families. One of the emerging causative factors associated with AD pathology is oxidative stress. This AD-related increase in oxidative stress has been attributed to decreased levels of the brain antioxidant, glutathione (GSH). In this article, we review the role of GSH in AD from a pathological as well as a diagnostic point of view. We recapitulate the literature that has assessed the role of GSH in AD onset and progression. We discuss the various methodologies through which alterations in GSH levels might be monitored, and highlight the yet uncharted potential of assaying GSH levels in vivo with magnetic resonance spectroscopy in AD therapeutics and prognostics. Finally, the present manuscript integrates findings from various studies to elucidate the possible molecular mechanisms through which disruptions in GSH homeostasis may contribute to AD pathology.

BOLDSync: a MATLAB-based toolbox for synchronized stimulus presentation in functional MRI.

BACKGROUND: Precise and synchronized presentation of paradigm stimuli in functional magnetic resonance imaging (fMRI) is central to obtaining accurate information about brain regions involved in a specific task. NEW METHOD: In this manuscript, we present a new MATLAB-based toolbox, BOLDSync, for synchronized stimulus presentation in fMRI. RESULTS: BOLDSync provides a user friendly platform for design and presentation of visual, audio, as well as multimodal audio-visual (AV) stimuli in functional imaging experiments. We present simulation experiments that demonstrate the millisecond synchronization accuracy of BOLDSync, and also illustrate the functionalities of BOLDSync through application to an AV fMRI study. COMPARISON WITH EXISTING METHODS: BOLDSync gains an advantage over other available proprietary and open-source toolboxes by offering a user friendly and accessible interface that affords both precision in stimulus presentation and versatility across various types of stimulus designs and system setups. CONCLUSIONS: BOLDSync is a reliable, efficient, and versatile solution for synchronized stimulus presentation in fMRI study.

SIRT1 regulates the neurogenic potential of neural precursors in the adult subventricular zone and hippocampus.

Within the two neurogenic niches of the adult mammalian brain, i.e., the subventricular zone lining the lateral ventricle and the subgranular zone of the hippocampus, there exist distinct populations of proliferating neural precursor cells that differentiate to generate new neurons. Numerous studies have suggested that epigenetic regulation by histone-modifying proteins is important in guiding precursor differentiation during development; however, the role of these proteins in regulating neural precursor activity in the adult neurogenic niches remains poorly understood. Here we examine the role of an NAD(+) -dependent histone deacetylase, SIRT1, in modulating the neurogenic potential of neural precursors in the neurogenic niches of the adult mouse brain. We show that SIRT1 is expressed by proliferating adult subventricular zone and hippocampal neural precursors, although its transcript and protein levels are dramatically reduced during neural precursor differentiation. Utilizing a lentiviral-mediated delivery strategy, we demonstrate that abrogation of SIRT1 signaling by RNAi does not affect neural precursor numbers or their proliferation. However, SIRT1 knock down results in a significant increase in neuronal production in both the subventricular zone and the hippocampus. In contrast, enhancing SIRT1 signaling either through lentiviral-mediated SIRT1 overexpression or through use of the SIRT1 chemical activator Resveratrol prevents adult neural precursors from differentiating into neurons. Importantly, knock down of SIRT1 in hippocampal precursors in vivo, either through RNAi or through genetic ablation, promotes their neurogenic potential. These findings highlight SIRT1 signaling as a negative regulator of neuronal differentiation of adult subventricular zone and hippocampal neural precursors. © 2013 Wiley Periodicals, Inc.

Visuospatial perception: an emerging biomarker for Alzheimer's disease.

In recent years, the focus of research on Alzheimer's disease (AD) has shifted toward finding reliable diagnostic biomarkers that enable accurate detection of mild cognitive impairment (MCI) as well as AD. Functional magnetic resonance imaging (fMRI) has the potential to identify functional changes in the preclinical stages of AD. In addition to the cardinal deficits in memory, deficits in visuospatial cognition are pervasive in AD. Recent neurophysiological and imaging studies have revealed that changes in visuospatial perception (VSP) functions can be detected in the early stages of AD. This review highlights the scope of VSP functional alterations as a biomarker for AD. We describe the neuroanatomical regions involved in the processing of various VSP tasks, and discuss the effect of AD on these regions from a pathological as well as a functional point of view. A comprehensive synopsis of the existing fMRI literature that has assessed VSP in patients with MCI and AD has been provided. The diagnostic scope of monitoring the brain activation correlates of VSP processing in AD is discussed in terms of the key advantages of utilizing VSP-related deficits in AD for early detection and longitudinal tracking of AD.

Positioning sensory terminals in the olfactory lobe of Drosophila by Robo signaling.

Olfactory receptor neurons and the interneurons of the olfactory lobe are organized in distinct units called glomeruli. We have used expression patterns and genetic analysis to demonstrate that a combinatorial code of Roundabout (Robo) receptors act to position sensory terminals within the olfactory lobe. Groups of sensory neurons possess distinct blends of Robo and Robo3 and disruption of levels by loss-of-function or ectopic expression results in aberrant targeting. In the wild type, most of the neurons send collateral branches to the contralateral lobe. Our data suggests that guidance of axons across brain hemispheres is mediated by Slit-dependent Robo2 signaling. The location of sensory arbors at distinct positions within the lobe allows short-range interactions with projection neurons leading to formation of the glomeruli.