External awareness and GABA--a multimodal imaging study combining fMRI and [18F]flumazenil-PET

GABA, glutamatergic dynamics and BOLD contrast assessed concurrently using functional MRS during a cognitive task

A recurring issue in functional neuroimaging is how to link task-driven haemodynamic blood oxygen level dependent functional MRI (BOLD-fMRI) responses to underlying neurochemistry at the synaptic level. Glutamate and γ-aminobutyric acid (GABA), the major excitatory and inhibitory neurotransmitters respectively, are typically measured with MRS sequences separately from fMRI, in the absence of a task. The present study aims to resolve this disconnect, developing acquisition and processing techniques to simultaneously assess GABA, glutamate and glutamine (Glx) and BOLD in relation to a cognitive task, at 3 T. Healthy subjects (N = 81) performed a cognitive task (Eriksen flanker), which was presented visually in a task-OFF, task-ON block design, with individual event onset timing jittered with respect to the MRS readout. fMRS data were acquired from the medial anterior cingulate cortex during task performance, using an adapted MEGA-PRESS implementation incorporating unsuppressed water-reference signals at a regular interval. These allowed for continuous assessment of BOLD activation, through T2 *-related changes in water linewidth. BOLD-fMRI data were additionally acquired. A novel linear model was used to extract modelled metabolite spectra associated with discrete functional stimuli, building on well established processing and quantification tools. Behavioural outcomes from the flanker task, and activation patterns from the BOLD-fMRI sequence, were as expected from the literature. BOLD response assessed through fMRS showed a significant correlation with fMRI, specific to the fMRS-targeted region of interest; fMRS-assessed BOLD additionally correlated with lengthening of response time in the incongruent flanker condition. While no significant task-related changes were observed for GABA+, a significant increase in measured Glx levels (~8.8%) was found between task-OFF and task-ON periods. These findings verify the efficacy of our protocol and analysis pipelines for the simultaneous assessment of metabolite dynamics and BOLD. As well as establishing a robust basis for further work using these techniques, we also identify a number of clear directions for further refinement in future studies.

GABAA receptor availability relates to emotion-induced BOLD responses in the medial prefrontal cortex: simultaneous fMRI/PET with [11C]flumazenil

Introduction

The fMRI BOLD response to emotional stimuli highlighting the role of the medial prefrontal cortex (MPFC) has been thoroughly investigated. Recently, the relationship between emotion processing and GABA levels has been studied using MPFC proton magnetic resonance spectroscopy (1H-MRS). However, the role of GABAA receptors in the MPFC during emotion processing remains unexplored.

Methods

Using [11C]flumazenil PET, we investigated the relationship between the binding potential of GABAA receptors and emotion processing as measured using simultaneous fMRI BOLD. We hypothesized a correlation between the percent signal change in the BOLD signal and the binding potential of GABAA receptors in the MPFC. In a combined simultaneous fMRI and [11C]flumazenil-PET study, we analyzed the data from 15 healthy subjects using visual emotional stimuli. Our task comprised two types of emotional processing: passive viewing and appraisal. Following the administration of a bolus plus infusion protocol, PET and fMRI data were simultaneously acquired in a hybrid 3 T MR-BrainPET.

Results

We found a differential correlation of BOLD percent signal change with [11C]flumazenil binding potential in the MPFC. Specifically, [11C]flumazenil binding potential in the ventromedial prefrontal cortex (vMPFC) correlated with passive viewing of emotionally valenced pictures. In contrast, the [11C]flumazenil binding potential and the BOLD signal induced by picture appraisal did show a correlation in the paracingulate gyrus.

Conclusion

Our data deliver first evidence for a relationship between MPFC GABAA receptors and emotion processing in the same region. Moreover, we observed that GABAA receptors appear to play different roles in emotion processing in the vMPFC (passive viewing) and paracingulate gyrus (appraisal).

Suprachiasmatic nucleus functional connectivity related to insomnia symptoms in adolescents with major depressive disorder

Background

Insomnia is a commonly seen symptom in adolescents with major depressive disorder (MDD). The suprachiasmatic nucleus (SCN), which is the circadian rhythm regulation center, plays a crucial role in the regulation of sleep-wake circulation. Nevertheless, how SCN function contributes to the exact neural mechanisms underlying the associations between insomnia and depressive symptoms has not been explored in adolescents. In the current study, we aimed to explore the relationship between SCN functional connectivity (FC) and insomnia symptoms in adolescents with MDD using a seed-based FC method.

Methods

In the current study, we recruited sixty-eight first-episode drug-naïve adolescents with MDD and classified them into high insomnia (MDD-HI) and low insomnia (MDD-LI) groups according to the sleep disturbance subscale of the Hamilton Depression Rating Scale (HAMD-S). Forty-three age/gender-matched healthy controls (HCs) were also recruited. SCN FC maps were generally for all subjects and compared among three groups using one-way ANOVA with age, gender and adjusted HAMD score as covariates. We used partial correlations to explore associations between altered FC and clinical symptoms, including sleep quality scores.

Results

Adolescents with MDD showed worse sleep quality, which positively correlated with the severity of depression. Compared to MDD-LI and HCs, MDD-HI adolescents demonstrated significantly decreased FC between the right SCN and bilateral precuneus, and there was no significant difference between the MDD-LI and HC groups. The HAMD-S scores were negatively correlated with bilateral SCN-precuneus connectivity, and the retardation factor score of HAMD was negatively correlated with right SCN-precuneus connectivity.

Conclusion

The altered FC between the SCN and precuneus may underline the neural mechanism of sleep-related symptoms in depressive adolescents and provide potential targets for personalized treatment strategies.

A Molecular Toolbox of Positron Emission Tomography Tracers for General Anesthesia Mechanism Research

With appropriate radiotracers, positron emission tomography (PET) allows direct or indirect monitoring of the spatial and temporal distribution of anesthetics, neurotransmitters, and biomarkers, making it an indispensable tool for studying the general anesthesia mechanism. In this Perspective, PET tracers that have been recruited in general anesthesia research are introduced in the following order: 1) ¹¹C/¹⁸F-labeled anesthetics, i.e., PET tracers made from inhaled and intravenous anesthetics; 2) PET tracers targeting anesthesia-related receptors, e.g., neurotransmitters and voltage-gated ion channels; and 3) PET tracers for studying anesthesia-related neurophysiological effects and neurotoxicity. The radiosynthesis, pharmacodynamics, and pharmacokinetics of the above PET tracers are mainly discussed to provide a practical molecular toolbox for radiochemists, anesthesiologists, and those who are interested in general anesthesia.

Human brain functional MRS reveals interplay of metabolites implicated in neurotransmission and neuroenergetics

While functional MRI (fMRI) localizes brain activation and deactivation, functional MRS (fMRS) provides insights into the underlying metabolic conditions. There is much interest in measuring task-induced and resting levels of metabolites implicated in neuroenergetics (e.g., lactate, glucose, or β-hydroxybutyrate (BHB)) and neurotransmission (e.g., γ-aminobutyric acid (GABA) or pooled glutamate and glutamine (Glx)). Ultra-high magnetic field (e.g., 7T) has boosted the fMRS quantification precision, reliability, and stability of spectroscopic observations using short echo-time (TE) 1H-MRS techniques. While short TE 1H-MRS lacks sensitivity and specificity for fMRS at lower magnetic fields (e.g., 3T or 4T), most of these metabolites can also be detected by J-difference editing (JDE) 1H-MRS with longer TE to filter overlapping resonances. The 1H-MRS studies show that JDE can detect GABA, Glx, lactate, and BHB at 3T, 4T and 7T. Most recently, it has also been demonstrated that JDE 1H-MRS is capable of reliable detection of metabolic changes in different brain areas at various magnetic fields. Combining fMRS measurements with fMRI is important for understanding normal brain function, but also clinically relevant for mechanisms and/or biomarkers of neurological and neuropsychiatric disorders. We provide an up-to-date overview of fMRS research in the last three decades, both in terms of applications and technological advances. Overall the emerging fMRS techniques can be expected to contribute substantially to our understanding of metabolism for brain function and dysfunction.

Out-of-step: brain-heart desynchronization in anxiety disorders

Imaging studies in anxiety disorders (AD) show abnormal functional connectivity primarily in the salience network (SN), somatomotor network (SMN), and default mode network (DMN). However, it is not clear how precisely these network changes occur including their relation to psychopathological symptoms. Here, we show that the functional networks affected in AD overlap with cortical regions that receive visceral inputs (the so-called central/visceral autonomic network). Focusing on cardiac afferents, we suggest that network changes in AD may be due to reduced phase synchronization between ongoing neural and cardiac activity. This neuro-cardiac desynchronization occurs due to the abnormal phase resetting of neural activity at the onset of each heartbeat, as measured by a lower intertrial coherence and heartbeat-evoked potential. Biochemically, cardiac afferents reach subcortical serotonergic raphe nuclei and noradrenergic locus coeruleus (among others) which, in turn, are known to reciprocally modulate the DMN and SMN/SN on the cortical level. Consistent with the network changes in AD, decreases in serotonergic and noradrenergic activity are known to increase connectivity in both SMN and SN while, at the same time, they decrease DMN connectivity. SMN and SN increases, in turn, lead to increased emotional arousal/anxiety and bodily awareness whereas decreased DMN connectivity leads to an unstable sense-of-self in AD. Finally, we integrate our proposal with interoceptive predictive processing models suggesting neuro-cardiac desynchronization as a mechanism for "noisy" bottom-up information leading to a persistently uncertain bodily state in top-down models. In sum, integrating theories on active interference and hyperarousal, we propose a precise neuro-cardiac and biochemically -driven mechanisms for key psychopathological symptoms of AD.

Upregulation of cortical GABAA receptor concentration in fibromyalgia

An imbalance between excitatory and inhibitory neurotransmission has been linked to fibromyalgia (FM). Magnetic resonance spectroscopy has shown increased levels of glutamate in the insula and posterior cingulate cortex in FM as well as reduced insular levels of gamma-aminobutyric acid (GABA). Both of these changes have been associated with increased pain sensitivity. However, it is not clear whether excitatory and/or inhibitory neurotransmission is altered across the brain. Therefore, the aim of this study was to quantify GABAA receptor concentration on the whole brain level in FM to investigate a potential dysregulation of the GABAergic system. Fifty-one postmenopausal women (26 FM, 25 matched controls) underwent assessments of pain sensitivity, attention and memory, psychological status and function, as well as positron emission tomography imaging using a tracer for GABAA receptors, [F]flumazenil. Patients showed increased pain sensitivity, impaired immediate memory, and increased cortical GABAA receptor concentration in the attention and default-mode networks. No decrease of GABAA receptor concentration was observed. Across the 2 groups, GABAA receptor concentration correlated positively with functional scores and current pain in areas overlapping with regions of increased GABAA receptor concentration. This study shows increased GABAA receptor concentration in FM, associated with pain symptoms and impaired function. The changes were widespread and not restricted to pain-processing regions. These findings suggest that the GABAergic system is altered, possibly indicating an imbalance between excitatory and inhibitory neurotransmission. Future studies should try to understand the nature of the dysregulation of the GABAergic system in FM and in other pain syndromes.

Insula shows abnormal task-evoked and resting-state activity in first-episode drug-naïve generalized anxiety disorder

BACKGROUND

Interoception is associated with neural activity in the insula of healthy humans. On the basis of the somatic symptoms in generalized anxiety disorder (GAD), especially abnormal heartbeat perception, we hypothesized that abnormal activity in the insula was associated with interoceptive awareness in patients with GAD.

METHODS

We investigated the psychological correlates of interoceptive awareness in a sample of 34 patients with first-onset, drug-naïve GAD and 30 healthy controls (HCs). Furthermore, we compared blood oxygenation level-dependent responses between the two groups during a heartbeat perception task to assess task-evoked activity and its relationship with psychological measures. We also examined between-group differences in insular subregions resting-state functional connectivity (rsFC), and its relationship with anxiety severity.

RESULTS

Patients with GAD had significantly higher body perception scores than HCs. They also exhibited greater task-evoked activity in the left anterior insula, left posterior insula, and right anterior insula during interoceptive awareness than HCs. Left anterior insula activity was positively correlated with body awareness in patients with GAD, and rsFC between the left anterior insula and left medial prefrontal gyrus was negatively correlated with somatic anxiety severity.

CONCLUSIONS

Investigating a sample of first-episode, drug-naïve patients, our study demonstrated abnormal interoceptive awareness in patients with GAD and that this was related to abnormal anterior insular activity during both rest and task. These results shed new light on the psychological and neural substrates of somatic symptoms in GAD, and they may serve to establish abnormal interoceptive awareness as a neural and psychological marker of GAD.

Impaired cognitive self-awareness mediates the association between alexithymia and excitation/inhibition balance in the pgACC

BACKGROUND

Previous research showed that automatic emotion regulation is associated with activation of subcortical areas and subsequent feedforward processes to cortical areas. In contrast, cognitive awareness of emotions is mediated by negative feedback from cortical to subcortical areas. Pregenual anterior cingulate cortex (pgACC) is essential in the modulation of both affect and alexithymia. We considered the interplay between these two mechanisms in the pgACC and their relationship with alexithymia.

METHOD

In 68 healthy participants (30 women, age = 26.15 ± 4.22) we tested associations of emotion processing and alexithymia with excitation/inhibition (E/I) balance represented as glutamate (Glu)/GABA in the pgACC measured via magnetic resonance spectroscopy in 7 T.

RESULTS

Alexithymia was positively correlated with the Glu/GABA ratio (N = 41, p = 0.0393). Further, cognitive self-awareness showed an association with Glu/GABA (N = 52, p = 0.003), which was driven by a correlation with GABA. In contrast, emotion regulation was only correlated with glutamate levels in the pgACC (N = 49, p = 0.008).

CONCLUSION

Our results corroborate the importance of the pgACC as a mediating region of alexithymia, reflected in an altered E/I balance. Furthermore, we could specify that this altered balance is linked to a GABA-related modulation of cognitive self-awareness of emotions.

Regional GABA Concentrations Modulate Inter-network Resting-state Functional Connectivity

Coordinated activity within and differential activity between large-scale neuronal networks such as the default mode network (DMN) and the control network (CN) is a critical feature of brain organization. The CN usually exhibits activations in response to cognitive tasks while the DMN shows deactivations; in addition, activity between the two networks is anti-correlated at rest. To address this issue, we used functional MRI to measure whole-brain BOLD signal during resting-state and task-evoked conditions, and MR spectroscopy (MRS) to quantify GABA and glutamate concentrations, in nodes within the DMN and CN (MPFC and DLPFC, respectively) in 19 healthy individuals at 3 Tesla. We found that GABA concentrations in the MPFC were significantly associated with DMN deactivation during a working memory task and with anti-correlation between DMN and CN at rest and during task performance, while GABA concentrations in the DLPFC weakly modulated DMN-CN anti-correlation in the opposite direction. Highlighting specificity, glutamate played a less significant role related to brain activity. These findings indicate that GABA in the MPFC is potentially involved in orchestrating between-network brain activity at rest and during task performance.

Anxiety Disorders and the Brain's Resting State Networks: From Altered Spatiotemporal Synchronization to Psychopathological Symptoms

Anxiety disorders include a variety of different disorders including panic disorder (PD), social anxiety disorder (SAD), generalized anxiety disorder (GAD), and phobias. We here focus our review on GAD, SAD, and PD and put a specific emphasis on resting state networks and the coupling between the brain and the heart as all anxiety disorders exhibit abnormal perception of their own heartbeat in some way or the other. Resting state functional connectivity (rsFC) studies demonstrate abnormalities in default-mode network (DMN) in all anxiety disorders, e.g., mostly decreases in rsFC of DMN. In contrast, resting state fMRI shows increased rsFC in salience network (SN) (SAD, GAD) and/or somato-motor/sensory network (SMN) (PD). Since rsFC is coherence- or phase-based operating in the infraslow frequency domain (0.01-0.1 Hz), these data suggest spatiotemporal hypo- or hyper-synchronization in DMN and SMN/SN, respectively. These abnormalities in the neural network's spatiotemporal synchronization may, in turn, impact phase-based temporal synchronization of neural and cardiac activities resulting in decreased (DMN) or increased (SMN/SN) neuro-cardiac coupling in anxiety disorders. That, in turn, may be related to the various psychopathological symptoms like unstable sense of self (as based on unstable DMN showing spatiotemporal hypo-synchronization), increased emotions and specifically anxiety (as related to increased SN showing spatiotemporal hyper-synchronization), and increased bodily awareness (mediated by increased SMN with spatiotemporal hyper-synchronization) in anxiety disorders. Taken together, we here suggest altered spatiotemporal synchronization of neural and cardiac activity within the brain's resting state to underlie various psychopathological symptoms in anxiety disorders. Such spatiotemporal basis of psychopathological symptoms is well compatible with the recently suggested "Spatiotemporal Psychopathology."

GABAA receptor availability is not altered in adults with autism spectrum disorder or in mouse models

Preliminary studies have suggested that γ-aminobutyric acid type A (GABA_A) receptors, and potentially the GABA_A α5 subtype, are deficient in autism spectrum disorder (ASD). However, prior studies have been confounded by the effects of medications, and these studies did not compare findings across different species. We measured both total GABA_A and GABA_A α5 receptor availability in two positron emission tomography imaging studies. We used the tracer [¹¹C]flumazenil in 15 adults with ASD and in 15 control individuals without ASD and the tracer [¹¹C]Ro15-4513 in 12 adults with ASD and in 16 control individuals without ASD. All participants were free of medications. We also performed autoradiography, using the same tracers, in three mouse models of ASD: the Cntnap2 knockout mouse, the Shank3 knockout mouse, and mice carrying a 16p11.2 deletion. We found no differences in GABA_A receptor or GABA_A α5 subunit availability in any brain region of adults with ASD compared to those without ASD. There were no differences in GABA_A receptor or GABA_A α5 subunit availability in any of the three mouse models. However, adults with ASD did display altered performance on a GABA-sensitive perceptual task. Our data suggest that GABA_A receptor availability may be normal in adults with ASD, although GABA signaling may be functionally impaired.

Altered cerebral benzodiazepine receptor binding in post-traumatic stress disorder

Agonists of the γ-aminobutyric acid (GABA) type A benzodiazepine (BZD) receptor exert anxiolytic effects in anxiety disorders, raising the possibility that altered GABA-ergic function may play a role in the pathophysiology of anxiety disorders, such as post-traumatic stress disorder (PTSD). However, few neuroimaging studies have assessed the function or binding potential of the central GABA_A BZD receptor system in PTSD. Therefore, our aim was to compare the BZD receptor binding potential between PTSD patients and healthy controls. Twelve medication-free participants with a current diagnosis of PTSD and 15 matched healthy controls underwent positron emission tomography (PET) imaging using [¹¹C] flumazenil. Structural magnetic resonance imaging (MRI) scans were obtained and co-registered to the PET images to permit co-location of neuroanatomical structures in the lower resolution PET image data. Compared to healthy controls, PTSD patients exhibited increased BZD binding in the caudal anterior cingulate cortex and precuneus (p's < 0.05). Severity of PTSD symptoms positively correlated with BZD binding in the left mid- and anterior insular cortices. This study extends previous findings by suggesting that central BZD receptor system involvement in PTSD includes portions of the default mode and salience networks, along with insular regions that support interoception and autonomic arousal.

Flumazenil reduces respiratory complications during anesthesia emergence in children with preoperative upper respiratory tract infections

Despite its benignity, upper respiratory infections (URIs) 1 increase the risk of postoperative respiratory complications during the perioperative and postoperative periods. Flumazenil could improve the symptoms of respiratory obstruction.To evaluate the effect of flumazenil on the occurrence of respiratory complications during anesthesia emergence of children with preoperative URI.This was a prospective study of 164 consecutive pediatric patients who underwent strabismus surgery under general anesthesia at the Tianjin Eye Hospital between August 2016 and April 2017. The patients were grouped as: normal airway (N), recent mild URI (I), normal airway and flumazenil (NF), and recent mild URI and flumazenil (group IF) (n = 41/group). An initial dose of flumazenil (0.1 mg) was administrated intravenously to groups IF and NF. The intraoperative and postoperative respiratory complications were recorded by one anesthesiologist unaware of the grouping.All patients underwent surgery uneventfully. The incidence of postoperative respiratory complications in post-anesthesia care unit (PACU) was higher in group I compared with the other 3 groups (IF: 17%; I: 41%; NF: 5%; N: 10%; P = .0147). During the PACU period, significant differences among groups were seen for cough (IF: 15%; I: 20%; NF: 2%; N: 0%; P = .004), secretion (IF: 17%; I: 29%; NF: 5%; N: 7%; P = .007), low oxygen saturation (IF: 12%; I: 32%; NF: 2%; N: 7%; P = .001), and glossocoma (IF: 15%; I: 34%; NF: 10%; N: 32%; P = .015).Respiratory complications during anesthesia emergence were higher in patients with recent preoperative URI compared to patients with healthy airways. Postoperative flumazenil could reduce the incidence of glossocoma.

Selected PET Radioligands for Ion Channel Linked Neuroreceptor Imaging: Focus on GABA, NMDA and nACh Receptors

Positron emission tomography (PET) neuroimaging of ion channel linked receptors is a developing area of preclinical and clinical research. The present review focuses on recent advances with radiochemistry, preclinical and clinical PET imaging studies of three receptors that are actively pursued in neuropsychiatric drug discovery: namely the γ-aminobutyric acid-benzodiazapine (GABA) receptor, nicotinic acetylcholine receptor (nAChR), and N-methyl-D-aspartate (NMDA) receptor. Recent efforts to develop new PET radioligands for these targets with improved brain uptake, selectivity, stability and pharmacokinetics are highlighted.

Role of Hybrid Brain Imaging in Neuropsychiatric Disorders

This is a focused review of imaging literature to scope the utility of hybrid brain imaging in neuropsychiatric disorders. The review focuses on brain imaging modalities that utilize hybrid (fusion) techniques to characterize abnormal brain molecular signals in combination with structural and functional changes that have been observed in neuropsychiatric disorders. An overview of clinical hybrid brain imaging technologies for human use is followed by a selective review of the literature that conceptualizes the use of these technologies in understanding basic mechanisms of major neuropsychiatric disorders and their therapeutics. Neuronal network abnormalities are highlighted throughout this review to scope the utility of hybrid imaging as a potential biomarker for each disorder.

Interoception in insula subregions as a possible state marker for depression-an exploratory fMRI study investigating healthy, depressed and remitted participants

Background: Interoceptive awareness (iA), the awareness of stimuli originating inside the body, plays an important role in human emotions and psychopathology. The insula is particularly involved in neural processes underlying iA. However, iA-related neural activity in the insula during the acute state of major depressive disorder (MDD) and in remission from depression has not been explored.

Methods: A well-established fMRI paradigm for studying (iA; heartbeat counting) and exteroceptive awareness (eA; tone counting) was used. Study participants formed three independent groups: patients suffering from MDD, patients in remission from MDD or healthy controls. Task-induced neural activity in three functional subdivisions of the insula was compared between these groups.

Results: Depressed participants showed neural hypo-responses during iA in anterior insula regions, as compared to both healthy and remitted participants. The right dorsal anterior insula showed the strongest response to iA across all participant groups. In depressed participants there was no differentiation between different stimuli types in this region (i.e., between iA, eA and noTask). Healthy and remitted participants in contrast showed clear activity differences.

Conclusions: This is the first study comparing iA and eA-related activity in the insula in depressed participants to that in healthy and remitted individuals. The preliminary results suggest that these groups differ in there being hypo-responses across insula regions in the depressed participants, whilst non-psychiatric participants and patients in remission from MDD show the same neural activity during iA in insula subregions implying a possible state marker for MDD. The lack of activity differences between different stimulus types in the depressed group may account for their symptoms of altered external and internal focus.

Antibodies to GABAA receptor α1 and γ2 subunits: clinical and serologic characterization

Objective:

To search for antibodies against neuronal cell surface proteins.

Methods:

Using immunoprecipitation from neuronal cultures and tandem mass spectrometry, we identified antibodies against the α1 subunit of the γ-aminobutyric acid A receptor (GABA_AR) in a patient whose immunoglobulin G (IgG) antibodies bound to hippocampal neurons. We searched 2,548 sera for antibodies binding to GABA_AR α, β, and γ subunits on live HEK293 cells and identified the class, subclass, and GABA_AR subunit specificities of the positive samples.

Results:

GABA_AR-Abs were identified in 40 of 2,046 (2%) referred sera previously found negative for neuronal antibodies, in 5/502 (1%) previously positive for other neuronal surface antibodies, but not in 92 healthy individuals. The antibodies in 40% bound to either the α1 (9/45, 20%) or the γ2 subunits (9/45, 20%) and were of IgG1 (94%) or IgG3 (6%) subclass. The remaining 60% had lower antibody titers (p = 0.0005), which were mainly immunoglobulin M (IgM) (p = 0.0025), and showed no defined subunit specificity. Incubation of primary hippocampal neurons with GABA_AR IgG1 sera reduced surface GABA_AR membrane expression. The clinical features of 15 patients (GABA_AR α1 n = 6, γ2 n = 5, undefined n = 4) included seizures (47%), memory impairment (47%), hallucinations (33%), or anxiety (20%). Most patients had not been given immunotherapies, but one with new-onset treatment-resistant catatonia made substantial improvement after plasma exchange.

Conclusions:

The GABA_AR α1 and γ2 are new targets for antibodies in autoimmune neurologic disease. The full spectrum of clinical features, treatment responses, correlation with antibody specificity, and in particular the role of the IgM antibodies will need to be assessed in future studies.

Altered brain long-range functional interactions underlying the link between aberrant self-experience and self-other relationship in first-episode schizophrenia

Self-experience anomalies are elementary features of schizophrenic pathology. Such deficits can have a profound impact on self-other relationship, but how they are related through aberrant brain function remains poorly understood. In this functional magnetic resonance imaging (fMRI) study, we provide new evidence for a cortical link between aberrant self-experience and social cognition in first-episode schizophrenia (FES). As identified in previous studies, ventral premotor cortex (vPMC) and posterior insula (pIC) are candidate brain regions underlying disturbances in both self-experience and self-other relationship due to their processing of predominantly externally guided (vPMC; goal-oriented behavior) and internally guided (pIC; interoception) stimuli. Results from functional interaction analysis in a sample of 24 FES patients and 22 healthy controls show aberrant functional interactions (background/intrinsic connectivity) of right vPMC and bilateral pIC with posterior cingulate cortex (PCC), a midline region that has been shown central in mediating self-experience. More specifically, our results show increased functional coupling between vPMC and PCC, which positively correlated with basic symptoms (subjective self-experience disturbances). pIC showed reduced functional coupling with PCC and postcentral gyrus and increased functional interactions with anterior insula. Taken together, our results suggest an imbalance in the processing between internally and externally guided information and its abnormal integration with self-referential processing as mediated by PCC. Due to our correlation findings, we suggest this imbalance to be closely related to basic symptoms in FES and thus anomalous self-experience. The findings further disentangle the cortical basis of how self-experience anomalies may pervade the social domain.

Associations of regional GABA and glutamate with intrinsic and extrinsic neural activity in humans—a review of multimodal imaging studies

The integration of multiple imaging modalities is becoming an increasingly well used research strategy for studying the human brain. The neurotransmitters glutamate and GABA particularly lend themselves towards such studies. This is because these transmitters are ubiquitous throughout the cortex, where they are the key constituents of the inhibition/excitation balance, and because they can be easily measured in vivo through magnetic resonance spectroscopy, as well as with select positron emission tomography approaches. How these transmitters underly functional responses measured with techniques such as fMRI and EEG remains unclear though, and was the target of this review. Consistently shown in the literature was a negative correlation between GABA concentrations and stimulus-induced activity within the measured region. Also consistently found was a positive correlation between glutamate concentrations and inter-regional activity relationships, both during tasks and rest. These findings are outlined along with results from populations with mental disorders to give an overview of what brain imaging has suggested to date about the biochemical underpinnings of functional activity in health and disease. We conclude that the combination of functional and biochemical imaging in humans is an increasingly informative approach that does however require a number of key methodological and interpretive issues be addressed before can meet its potential.

GABAA receptors predict aversion-related brain responses: an fMRI-PET investigation in healthy humans

The perception of aversive stimuli is essential for human survival and depends largely on environmental context. Although aversive brain processing has been shown to involve the sensorimotor cortex, the neural and biochemical mechanisms underlying the interaction between two independent aversive cues are unclear. Based on previous work indicating ventromedial prefrontal cortex (vmPFC) involvement in the mediation of context-dependent emotional effects, we hypothesized a central role for the vmPFC in modulating sensorimotor cortex activity using a GABAergic mechanism during an aversive-aversive stimulus interaction. This approach revealed differential activations within the aversion-related network (eg, sensorimotor cortex, midcingulate, and insula) for the aversive-aversive, when compared with the aversive-neutral, interaction. Individual differences in sensorimotor cortex signal changes during the aversive-aversive interaction were predicted by GABAA receptors in both vmPFC and sensorimotor cortex. Together, these results demonstrate the central role of GABA in mediating context-dependent effects in aversion-related processing.

GABA in the insula - a predictor of the neural response to interoceptive awareness

The insula has been identified as a key region involved in interoceptive awareness. Whilst imaging studies have investigated the neural activation patterns in this region involved in intero- and exteroceptive awareness, the underlying biochemical mechanisms still remain unclear. In order to investigate these, a well-established fMRI task targeting interoceptive awareness (heartbeat counting) and exteroceptive awareness (tone counting) was combined with magnetic resonance spectroscopy (MRS). Controlling for physiological noise, neural activity in the insula during intero- and exteroceptive awareness was confirmed in an independent data sample using the same fMRI design. Focussing on MRS values from the left insula and combining them with neural activity during intero- and exteroceptive awareness in the same healthy individuals, we demonstrated that GABA concentration in a region highly involved in interoceptive processing is correlated with neural responses to interoceptive stimuli, as opposed to exteroceptive stimuli. In addition, both GABA and interoceptive signal changes in the insula predicted the degree of depressed affect, as measured by the Beck Hopelessness Scale. On the one hand, the association between GABA concentration and neural activity during interoceptive awareness provides novel insight into the biochemical underpinnings of insula function and interoception. On the other, through the additional association of both GABA and neural activity during interoception with depressed affect, these data also bear potentially important implications for psychiatric disorders like depression and anxiety, where GABAergic deficits, altered insula function and abnormal affect coincide.

Chronic opioid therapy and opioid tolerance: a new hypothesis

Opioids are efficacious and cost-effective analgesics, but tolerance limits their effectiveness. This paper does not present any new clinical or experimental data but demonstrates that there exist ascending sensory pathways that contain few opioid receptors. These pathways are located by brain PET scans and spinal cord autoradiography. These nonopioid ascending pathways include portions of the ventral spinal thalamic tract originating in Rexed layers VI-VIII, thalamocortical fibers that project to the primary somatosensory cortex (S1), and possibly a midline dorsal column visceral pathway. One hypothesis is that opioid tolerance and opioid-induced hyperalgesia may be caused by homeostatic upregulation during opioid exposure of nonopioid-dependent ascending pain pathways. Upregulation of sensory pathways is not a new concept and has been demonstrated in individuals impaired with deafness or blindness. A second hypothesis is that adjuvant nonopioid therapies may inhibit ascending nonopioid-dependent pathways and support the clinical observations that monotherapy with opioids usually fails. The uniqueness of opioid tolerance compared to tolerance associated with other central nervous system medications and lack of tolerance from excess hormone production is discussed. Experimental work that could prove or disprove the concepts as well as flaws in the concepts is discussed.

GABA(A) receptors in visual and auditory cortex and neural activity changes during basic visual stimulation

Recent imaging studies have demonstrated that levels of resting γ-aminobutyric acid (GABA) in the visual cortex predict the degree of stimulus-induced activity in the same region. These studies have used the presentation of discrete visual stimulus; the change from closed eyes to open also represents a simple visual stimulus, however, and has been shown to induce changes in local brain activity and in functional connectivity between regions. We thus aimed to investigate the role of the GABA system, specifically GABA(A) receptors, in the changes in brain activity between the eyes closed (EC) and eyes open (EO) state in order to provide detail at the receptor level to complement previous studies of GABA concentrations. We conducted an fMRI study involving two different modes of the change from EC to EO: an EO and EC block design, allowing the modeling of the haemodynamic response, followed by longer periods of EC and EO to allow the measuring of functional connectivity. The same subjects also underwent [(18)F]Flumazenil PET to measure GABA(A) receptor binding potentials. It was demonstrated that the local-to-global ratio of GABA(A) receptor binding potential in the visual cortex predicted the degree of changes in neural activity from EC to EO. This same relationship was also shown in the auditory cortex. Furthermore, the local-to-global ratio of GABA(A) receptor binding potential in the visual cortex also predicted the change in functional connectivity between the visual and auditory cortex from EC to EO. These findings contribute to our understanding of the role of GABA(A) receptors in stimulus-induced neural activity in local regions and in inter-regional functional connectivity.