Normal prefrontal gamma-aminobutyric acid levels in remitted depressed subjects determined by proton magnetic resonance spectroscopy

Proton magnetic resonance spectroscopy of N-acetyl aspartate in first depressive episode and chronic major depressive disorder: A systematic review and meta-analysis

N-acetyl aspartate (NAA) is a marker of neuronal integrity and metabolism. Deficiency in neuronal plasticity and hypometabolism are implicated in Major Depressive Disorder (MDD) pathophysiology. To test if cerebral NAA concentrations decrease progressively over the MDD course, we conducted a pre-registered meta-analysis of Proton Magnetic Resonance Spectroscopy (1H-MRS) studies comparing NAA concentrations in chronic MDD (n = 1308) and first episode of depression (n = 242) patients to healthy controls (HC, n = 1242). Sixty-two studies were meta-analyzed using a random-effect model for each brain region. NAA concentrations were significantly reduced in chronic MDD compared to HC within the frontal lobe (Hedges' g = -0.330; p = 0.018), the occipital lobe (Hedges' g = -0.677; p = 0.007), thalamus (Hedges' g = -0.673; p = 0.016), and frontal (Hedges' g = -0.471; p = 0.034) and periventricular white matter (Hedges' g = -0.478; p = 0.047). We highlighted a gap of knowledge regarding NAA levels in first episode of depression patients. Sensitivity analyses indicated that antidepressant treatment may reverse NAA alterations in the frontal lobe. We highlighted field strength and correction for voxel grey matter as moderators of NAA levels detection. Future studies should assess NAA alterations in the early stages of the illness and their longitudinal progression.

Effects of chronic lithium treatment on neuronal excitability and GABAergic transmission in an Ank3 mutant mouse model

Bipolar disorder (BD) is a common psychiatric disease that can lead to psychosocial disability, decreased quality of life, and high risk for suicide. Genome-wide association studies have shown that the ANK3 gene is a significant risk factor for BD, but the mechanisms involved in BD pathophysiology are not yet fully understood. Previous work has shown that ankyrin-G, the protein encoded by ANK3, stabilizes inhibitory synapses in vivo through its interaction with the GABAA receptor-associated protein (GABARAP). We generated a mouse model with a missense p.W1989R mutation in Ank3, that abolishes the interaction between ankyrin-G and GABARAP, which leads to reduced inhibitory signaling in the somatosensory cortex and increased pyramidal cell excitability. Humans with the same mutation exhibit BD symptoms, which can be attenuated with lithium therapy. In this study, we describe that chronic treatment of Ank3 p.W1989R mice with lithium normalizes neuronal excitability in cortical pyramidal neurons and increases inhibitory GABAergic postsynaptic currents. The same outcome in inhibitory transmission was observed when mice were treated with the GSK-3β inhibitor Tideglusib. These results suggest that lithium treatment modulates the excitability of pyramidal neurons in the cerebral cortex by increasing GABAergic neurotransmission, likely via GSK-3 inhibition. In addition to the importance of these findings regarding ANK3 variants as a risk factor for BD development, this study may have significant implications for treating other psychiatric disorders associated with alterations in inhibitory signaling, such as schizophrenia, autism spectrum disorder, and major depressive disorder.

Medial Frontal Cortex GABA Concentrations in Psychosis Spectrum and Mood Disorders: A Meta-analysis of Proton Magnetic Resonance Spectroscopy Studies

BACKGROUND

Abnormalities of GABAergic (gamma-aminobutyric acidergic) systems may play a role in schizophrenia and mood disorders. Magnetic resonance spectroscopy allows for noninvasive in vivo quantification of GABA; however, studies of GABA in schizophrenia have yielded inconsistent findings. This may stem from grouping together disparate voxels from functionally heterogeneous regions.

METHODS

We searched PubMed for magnetic resonance spectroscopy studies of GABA in the medial frontal cortex (MFC) in patients with schizophrenia, bipolar disorder, and depression and in individuals meeting criteria for ultra-high risk for psychosis. Voxel placements were classified as rostral-, rostral-mid-, mid-, or posterior MFC, and meta-analyses were conducted for each group for each subregion.

RESULTS

Of 341 screened articles, 23 studies of schizophrenia, 6 studies of bipolar disorder, 20 studies of depression, and 7 studies of ultra-high risk met the inclusion criteria. Meta-analysis revealed lower mid- (standardized mean difference [SMD] = -0.28, 95% CI, -0.48 to -0.07, p < .01) and posterior (SMD = -0.29, 95% CI, -0.49 to -0.09, p < .01) MFC GABA in schizophrenia and increased rostral MFC GABA in bipolar disorder (SMD = 0.76, 95% CI, 0.25 to -1.25, p < .01). In depression, reduced rostral MFC GABA (SMD = -0.36, 95% CI, -0.64 to -0.08, p = .01) did not survive correction for multiple comparisons. We found no evidence for GABA differences in individuals at ultra-high risk for psychosis.

CONCLUSIONS

While limited by small numbers of published studies, these results substantiate the relevance of GABA in the pathophysiology of psychosis spectrum and mood disorders and underline the importance of voxel placement.

Evaluation of Prefrontal γ-Aminobutyric Acid and Glutamate Levels in Individuals With Major Depressive Disorder Using Proton Magnetic Resonance Spectroscopy

Importance

Major depressive disorder (MDD) is one of the most prevalent illnesses worldwide. Perturbations of the major inhibitory and excitatory neurotransmitters, γ-aminobutyric acid (GABA) and glutamate (Glu), respectively, as well as Glx (Glu or glutamine [Gln]) have been extensively reported in a multitude of brain areas of individuals with depression, but few studies have examined changes in Gln, the metabolic counterpart of synaptic Glu.

Objective

To investigate changes in GABA, Glx, Glu, and Gln levels in a voxel in the left dorsolateral prefrontal cortex of participants with no, past, and current MDD using proton magnetic resonance spectroscopy (1H-MRS).

Design, Setting, and Participants

This community-based study used a cross-sectional design using 3-T 1H-MRS in participants not taking MDD medication recruited from the community. The sample consisted of 251 healthy controls, 98 participants with a history of past MDD, and 47 participants who met the diagnostic criteria for current MDD. Diagnostic groups were comparable regarding age, education, income, and diet. Data were collected from March 2014 to October 2021, and data were analyzed from October 2021 to June 2022.

Main Outcomes and Measures

GABA, Glx, Glu, and Gln concentrations in the left dorsolateral prefrontal cortex.

Results

Of 396 included participants, 258 (65.2%) were female, and the mean (SD) age was 25.0 (4.7) years. Compared with healthy controls, those with past MDD and current MDD had lower GABA concentrations (mean [SEM] concentration: healthy controls, 2.70 [0.03] mmol/L; past MDD, 2.49 [0.05] mmol/L; current MDD, 2.54 [0.07] mmol/L; 92 with past MDD vs 236 healthy controls: r = 0.18; P = .002; 44 with current MDD vs 236 healthy controls: r = 0.13; P = .04). Compared with healthy controls, those with past MDD also had lower Glu concentrations (mean [SEM] concentration: healthy controls, 7.52 [0.06] mmol/L; past MDD, 7.23 [0.11] mmol/L; 93 with past MDD vs 234 healthy controls: r = 0.16; P = .01) and higher Gln concentrations (mean [SEM] concentration: healthy controls, 1.63 [0.04] mmol/L; past MDD, 1.84 [0.07] mmol/L; 66 with past MDD 153 healthy controls: r = 0.17; P = .04).

Conclusions and Relevance

In a large, mostly medication-free community sample, reduced prefrontal GABA concentrations were associated with past MDD, consistent with histopathologic studies reporting reduced glial cell and GABA cell density in the prefrontal cortex in individuals with depression. Patients with MDD also demonstrated increased Gln levels, indicative of increased synaptic Glu release, adding to previous evidence for the Glu hypothesis of MDD.

Regional specificity and clinical correlates of cortical GABA alterations in posttraumatic stress disorder

Gamma-aminobutyric acid (GABA) metabolism is implicated in posttraumatic stress disorder (PTSD) and may be altered in prefrontal-limbic brain regions involved in arousal regulation. This study used proton magnetic resonance spectroscopy (MRS) to test the hypothesis that PTSD and trauma-exposed non-PTSD comparison (TENC) adults have significantly different GABA than healthy comparison (HC) subjects in two brain areas implicated in arousal (medial prefrontal cortex, insula) but not in a control brain area (posterior temporal cortex). We also examined whether GABA alterations correlated with hyperarousal and dissociation symptoms. One hundred and fourteen participants (39 PTSD, 34 TENC, 41 HC) underwent 3T MRS of the medial prefrontal, right insular, and right posterior temporal cortices, and the GABA plus macromolecule signal (GABA+) was normalized to creatine (Cr). The Clinician Administered PTSD Scale measured hyperarousal symptoms, including sleep disruption. The Dissociative Experiences Scale assessed dissociation symptoms. PTSD and TENC participants had significantly lower mPFC GABA+/Cr than HC participants, and this deficit was significantly correlated with greater dissociation. Compared with HC, PTSD patients but not TENC had significantly lower insula GABA+/Cr. Total hyperarousal symptoms and sleep disruption were not significantly associated with GABA+/Cr alterations in either region. Our findings point to lower GABA in cortical areas implicated in arousal regulation in PTSD and suggest that GABA alterations are associated with symptoms of trauma-related psychopathology but not always a biomarker of diagnosis. These findings also add to evidence that dissociation has distinct neural correlates within PTSD, including high excitability of medial prefrontal cortex.

Longitudinal changes in neurometabolite concentrations in the dorsal anterior cingulate cortex after concentrated exposure therapy for obsessive-compulsive disorder

BACKGROUND

The dorsal anterior cingulate cortex (dACC) plays an important role in the pathophysiology of obsessive-compulsive disorder (OCD) due to its role in error processing, cognitive control and emotion regulation. OCD patients have shown altered concentrations in neurometabolites in the dACC, particularly Glx (glutamate+glutamine) and tNAA (N-acetylaspartate+N-acetyl-aspartyl-glutamate). We investigated the immediate and prolonged effects of exposure and response prevention (ERP) on these neurometabolites.

METHODS

Glx and tNAA concentrations were measured using magnetic resonance spectroscopy (1H-MRS) in 24 OCD patients and 23 healthy controls at baseline. Patients received concentrated ERP over four days. A subset was re-scanned after one week and three months.

RESULTS

No Glx and tNAA abnormalities were observed in OCD patients compared to healthy controls before treatment or over time. Patients with childhood or adult onset differed in the change over time in tNAA (F(2,40) = 7.24, ɳ²_p= 0.27, p = 0.004): concentrations increased between one week after treatment and follow-up in the childhood onset group (t(39) = -2.43, d = -0.86, p = 0.020), whereas tNAA concentrations decreased between baseline and follow-up in patients with an adult onset (t(42) = 2.78, d = 1.07, p = 0.008). In OCD patients with versus without comorbid mood disorders, lower Glx concentrations were detected at baseline (t(38) = -2.28, d = -1.00, p = 0.028). Glx increased after one week of treatment within OCD patients with comorbid mood disorders (t(30) = -3.09, d = -1.21, p = 0.004).

LIMITATIONS

Our OCD sample size allowed the detection of moderate to large effect sizes only.

CONCLUSION

ERP induced changes in neurometabolites in OCD seem to be dependent on mood disorder comorbidity and disease stage rather than OCD itself.

GABA System in Depression: Impact on Pathophysiology and Psychopharmacology

BACKGROUND

The pathophysiology of major depressive disorder (MDD), one of the major causes of worldwide disability, is still largely unclear, despite the increasing data reporting evidence of multiple alterations of different systems. Recently, there was a renewed interest in the signalling of gamma aminobutyric acid (GABA) - the main inhibitory neurotransmitter.

OBJECTIVE

The aim of this study was to review and comment on the available literature about the involvement of GABA in MDD, as well as on novel GABAergic compounds possibly useful as antidepressants.

METHODS

We carried out a narrative review through Pubmed, Google Scholar and Scopus, by using specific keywords.

RESULTS

The results, derived from various research tools, strongly support the presence of a deficiency of the GABA system in MDD, which appears to be restored by common antidepressant treatments. More recent publications would indicate the complex interactions between GABA and all the other processes involved in MDD, such as monoamine neurotransmission, hypothalamus-pituitary adrenal axis functioning, neurotrophism, and immune response. Taken together, all these findings seem to further support the complexity of the pathophysiology of MDD, possibly reflecting the heterogeneity of the clinical pictures.

CONCLUSION

Although further data are necessary to support the specificity of GABA deficiency in MDD, the available findings would suggest that novel GABAergic compounds might constitute innovative therapeutic strategies in MDD.

Reductions in rostral anterior cingulate GABA are associated with stress circuitry in females with major depression: a multimodal imaging investigation

The interplay between cortical and limbic regions in stress circuitry calls for a neural systems approach to investigations of acute stress responses in major depressive disorder (MDD). Advances in multimodal imaging allow inferences between regional neurotransmitter function and activation in circuits linked to MDD, which could inform treatment development. The current study investigated the role of the inhibitory neurotransmitter GABA in stress circuitry in females with current and remitted MDD. Multimodal imaging data were analyzed from 49 young female adults across three groups (current MDD, remitted MDD (rMDD), and healthy controls). GABA was assessed at baseline using magnetic resonance spectroscopy, and functional MRI data were collected before, during, and after an acute stressor and analyzed using a network modeling approach. The MDD group showed an overall lower cortisol response than the rMDD group and lower rostral anterior cingulate cortex (ACC) GABA than healthy controls. Across groups, stress decreased activation in the frontoparietal network (FPN) but increased activation in the default mode network (DMN) and a network encompassing the ventromedial prefrontal cortex-striatum-anterior cingulate cortex (vmPFC-Str-ACC). Relative to controls, the MDD and rMDD groups were characterized by decreased FPN and salience network (SN) activation overall. Rostral ACC GABA was positively associated with connectivity between an overlapping limbic network (Temporal-Insula-Amygdala) and two other circuits (FPN and DMN). Collectively, these findings indicate that reduced GABA in females with MDD was associated with connectivity differences within and across key networks implicated in depression. GABAergic treatments for MDD might alleviate stress circuitry abnormalities in females.

Ventromedial prefrontal cortex/anterior cingulate cortex Glx, glutamate, and GABA levels in medication-free major depressive disorder

Glutamate (Glu) and gamma-aminobutyric acid (GABA) are implicated in the pathophysiology of major depressive disorder (MDD). GABA levels or GABAergic interneuron numbers are generally low in MDD, potentially disinhibiting Glu release. It is unclear whether Glu release or turnover is increased in depression. Conversely, a meta-analysis of prefrontal proton magnetic resonance spectroscopy (¹H MRS) studies in MDD finds low Glx (combination of glutamate and glutamine) in medicated MDD. We hypothesize that elevated Glx or Glu may be a marker of more severe, untreated MDD. We examined ventromedial prefrontal cortex/anterior cingulate cortex (vmPFC/ACC) Glx and glutamate levels using ¹H MRS in 34 medication-free, symptomatic, chronically ill MDD patients and 32 healthy volunteers, and GABA levels in a subsample. Elevated Glx and Glu were observed in MDD compared with healthy volunteers, with the highest levels seen in males with MDD. vmPFC/ACC GABA was low in MDD. Higher Glx levels correlated with more severe depression and lower GABA. MDD severity and diagnosis were both linked to higher Glx in vmPFC/ACC. Low GABA in a subset of these patients is consistent with our hypothesized model of low GABA leading to glutamate disinhibition in MDD. This finding and model are consistent with our previously reported findings that the NMDAR-antagonist antidepressant effect is proportional to the reduction of vmPFC/ACC Glx or Glu levels.

Concomitant lorazepam use and antidepressive efficacy of repetitive transcranial magnetic stimulation in a naturalistic setting

BACKGROUND/OBJECTIVES

Repetitive transcranial magnetic stimulation (rTMS) has been established as an effective therapeutic intervention for the treatment of depression. Preliminary data suggest that the efficacy of rTMS is reduced in patients taking benzodiazepines (BZD). Here, we use real-world data from a large sample to investigate the influence of lorazepam on the effectiveness of rTMS.

METHODS

From a retrospective cohort of clinically depressed patients that were treated with rTMS, we compared 176 patients not taking any BZD with 73 patients taking lorazepam with respect to changes in the Hamilton Depression Rating Scale (HRDS).

RESULTS

Both groups improved during rTMS according to HRDS scores, but the amelioration of symptoms was significantly less pronounced in patients taking lorazepam (18% vs. 38% responders in the non-lorazepam group). We could not see any association of intake regimen of lorazepam with response in rTMS.

CONCLUSION

Our observational study suggests that intake of lorazepam impedes the response to rTMS. The impact of lorazepam and other BZD on rTMS should receive more attention and be further investigated in prospective, hypothesis-based treatment studies to determine causal relationships between medication treatments and outcome. This could lead to specific recommendations for pharmacological treatment for depressed patients undergoing rTMS.

Sex differences in the transcription of glutamate transporters in major depression and suicide

BACKGROUND

Accumulating evidence indicates that the glutamate system contributes to the pathophysiology of major depressive disorder (MDD) and suicide. We previously reported higher mRNA expression of glutamate receptors in the dorsolateral prefrontal cortex (DLPFC) of females with MDD.

METHODS

In the current study, we measured the expression of mRNAs encoding glutamate transporters in the DLPFC of MDD subjects who died by suicide (MDD-S, n = 51), MDD non-suicide subjects (MDD-NS, n = 28), and individuals who did not have a history of neurological illness (CTRL, n = 32).

RESULTS

Females but not males with MDD showed higher expression of EAATs and VGLUTs relative to CTRLs. VGLUT expression was significantly higher in the female MDD-S group, relative to the other groups. EAAT expression was lower in the male violent suicides.

LIMITATIONS

This study has limitations common to most human studies, including medication history and demographic differences between the diagnostic groups. We mitigated the effects of confounders by including them as covariates in our analyses.

CONCLUSIONS

We report sex differences in the expression of glutamate transporter genes in the DLPFC in MDD. Increased neuronal glutamate transporter expression may increase synaptic glutamate, leading to neuronal and glial loss in the DLPFC in MDD. These deficits may lower DLPFC activity, impair problem solving and impair executive function in depression, perhaps increasing vulnerability to suicidal behavior. These data add to accumulating support for the hypothesis that glutamatergic transmission is dysregulated in MDD and suicide. Glutamate transporters may be novel targets for the development of rapidly acting antidepressant therapies.

Anterior cingulate gamma-aminobutyric acid concentrations and electroconvulsive therapy

OBJECTIVE

The anticonvulsant hypothesis posits that ECT's mechanism of action is related to enhancement of endogenous anticonvulsant brain mechanisms. Results of prior studies investigating the role of the inhibitory neurotransmitter gamma-aminobutyric acid ("GABA+", GABA and coedited macromolecules) in the pathophysiology and treatment of depression remain inconclusive. The aim of our study was to investigate treatment-responsive changes of GABA+ in subjects with a depressive episode receiving electroconvulsive therapy (ECT).

METHODS

In total, 41 depressed subjects (DEP) and 35 healthy controls (HC) were recruited at two independent sites in Norway and the USA. MEGA-PRESS was used for investigation of GABA+ in the anterior cingulate cortex. We assessed longitudinal and cross-sectional differences between DEP and HC, as well as the relationship between GABA+ change and change in depression severity and number of ECTs. We also assessed longitudinal differences in cognitive performance and GABA+ levels.

RESULTS

Depressive episode did not show a difference in GABA+ relative to HC (t₇₁  = -0.36, p = .72) or in longitudinal analysis (t₃₆  = 0.97, p = .34). Remitters and nonremitters did not show longitudinal (t₃₆  = 1.12, p = .27) or cross-sectional differences in GABA+. GABA+ levels were not related to changes in antidepressant response (t₃₅  = 1.12, p = .27) or treatment number (t₃₆  = 0.05, p = .96). An association between cognitive performance and GABA+ levels was found in DEP that completed cognitive effortful testing (t₁₈  = 2.4, p = .03).

CONCLUSION

Our results failed to support GABA as a marker for depression and abnormal mood state and provide no support for the anticonvulsant hypothesis of ECT. ECT-induced change in GABA concentrations may be related to change in cognitive function.

Negative association between left prefrontal GABA concentration and BDNF serum concentration in young adults

Background

The brain's major inhibitory neurotransmitter gamma-aminobutyric acid (GABA) and the brain-derived neurotrophic factor (BDNF) play important roles in several stress-related disorders. Magnetic resonance spectroscopy (MRS) allows for non-invasive quantification of GABA concentration in the brain. We investigated the relationship between GABA concentration in the left dorsolateral prefrontal cortex (DLPFC) and BDNF concentration in the serum in a community-based sample of young subjects.

Methods

For the GABA measurement a single voxel MR spectrum was assessed in the prefrontal lobe (25 × 40 × 30 mm) using the MEGA-PRESS method in 276 subjects. BDNF serum concentrations were assessed with an ELISA kit. For 147 subjects we had both MRS and BDNF serum data, and for 79 subjects we had genotype data on the BDNF rs6265 polymorphism. Depressive psychopathology was assessed using Beck's Depression Inventory (BDI), Montgomery-Asberg Depression Rating Scale (MADRS) and Structured Clinical Interviews for Diagnostic and Statistical Manual of Mental Disorders (SCID) for DSM-IV.

Results

GABA concentration in the left DLPFC was negatively associated with BDNF serum concentration (r = -.264, p = .001). This correlation remained significant if corrected for sex (r = -.264, p = .001). BDNF serum concentration was also positively associated with volumes and surface areas of the left prefrontal cortex (p = .048, p = .005). There were no significant associations or interaction with depressive psychopathology (BDI, MADRS, SCID) or rs6265.

Conclusion

The results of this study suggest that GABA, BDNF and prefrontal brain volumes are interrelated, but do not show a strong association to depressive psychopathology, possibly due to the mild forms of psychiatric conditions present in our community-based sample.

Recent Studies on Anti-Depressant Bioactive Substances in Selected Species from the Genera Hemerocallis and Gladiolus: A Systematic Review

Herbal therapy is a potential alternative applied to pharmacological alleviation of depression symptoms and treatment of this disorder, which is predicted by the World Health Organization (WHO) to be the most serious health problem worldwide over the next several years. It has been well documented that many herbs with psychotropic effects have far fewer side effects than a variety of pharmaceutical agents used by psychiatrists for the treatment of depression. This systematic review presents literature data on the antidepressant activity of representatives of the genera Hemerocallis (H. fulva and H. citrina Baroni, family Xanthorrhoeaceae) and Gladiolus (G. dalenii, family Iridaceae) and on biologically active compounds and their mechanisms of action to consider the application of herbal preparations supporting the treatment of depression.

Ketamine rapidly reverses stress-induced impairments in GABAergic transmission in the prefrontal cortex in male rodents

Dysfunction of medial prefrontal cortex (mPFC) in association with imbalance of inhibitory and excitatory neurotransmission has been implicated in depression. However, the precise cellular mechanisms underlying this imbalance, particularly for GABAergic transmission in the mPFC, and the link with the rapid acting antidepressant ketamine remains poorly understood. Here we determined the influence of chronic unpredictable stress (CUS), an ethologically validated model of depression, on synaptic markers of GABA neurotransmission, and the influence of a single dose of ketamine on CUS-induced synaptic deficits in mPFC of male rodents. The results demonstrate that CUS decreases GABAergic proteins and the frequency of inhibitory post synaptic currents (IPSCs) of layer V mPFC pyramidal neurons, concomitant with depression-like behaviors. In contrast, a single dose of ketamine can reverse CUS-induced deficits of GABA markers, in conjunction with reversal of CUS-induced depressive-like behaviors. These findings provide further evidence of impairments of GABAergic synapses as key determinants of depressive behavior and highlight ketamine-induced synaptic responses that restore GABA inhibitory, as well as glutamate neurotransmission.

Association between prefrontal glutamine levels and neuroticism determined using proton magnetic resonance spectroscopy

There is growing evidence for GABA and glutamate-glutamine dysfunction in the pathogenesis of mood and anxiety disorders. It is important to study this pathology in the early phases of the illness in order to develop new approaches to secondary prevention. New magnetic resonance spectroscopy (MRS) measures allow determining glutamine, the principal metabolite of synaptic glutamate that is directly related to glutamate levels in the synaptic cleft, as well as glutamate and GABA. In contrast to previous investigations, this study used community-based recruitment methods and a combined categorical and dimensional approach to psychopathology. In the study protocol, neuroticism was defined as the primary outcome. Neuroticism shares a large proportion of its genetic variance with mood and anxiety disorders. We examined young adult participants recruited from the general population in a cross-sectional study using 3-T 1H-MRS with one voxel in the left dorsolateral prefrontal cortex (DLPFC). The total sample of N = 110 (61 females) included 18 individuals suffering from MDD and 19 individuals suffering from DSM-IV anxiety disorders. We found that glutamine and glutamine-to-glutamate ratio were correlated with neuroticism in the whole sample (r = 0.263, p = 0.005, and n = 110; respectively, r = 0.252, p = 0.008, and n = 110), even when controlling for depression and anxiety disorder diagnoses (for glutamine: beta = 0.220, p = 0.047, and n = 110). Glutamate and GABA were not significantly correlated with neuroticism (r = 0.087, p = 0.365, and n = 110; r = -0.044, p = 0.645, and n = 110). Lack of self-confidence and emotional instability were the clinical correlates of glutamate-glutamine dysfunction. In conclusion, this study suggests that prefrontal glutamine is increased in early phases of mood and anxiety disorders. Further understanding of glutamate-glutamine dysfunction in stress-related disorders may lead to new therapeutic strategies to prevent and treat these disorders.

Altered Connectivity in Depression: GABA and Glutamate Neurotransmitter Deficits and Reversal by Novel Treatments

The mechanisms underlying the pathophysiology and treatment of depression and stress-related disorders remain unclear, but studies in depressed patients and rodent models are beginning to yield promising insights. These studies demonstrate that depression and chronic stress exposure cause atrophy of neurons in cortical and limbic brain regions implicated in depression, and brain imaging studies demonstrate altered connectivity and network function in the brains of depressed patients. Studies of the neurobiological basis of the these alterations have focused on both the principle, excitatory glutamate neurons, as well as inhibitory GABA interneurons. They demonstrate structural, functional, and neurochemical deficits in both major neuronal types that could lead to degradation of signal integrity in cortical and hippocampal regions. The molecular mechanisms underlying these changes have not been identified but are thought to be related to stress induced excitotoxic effects in combination with elevated adrenal glucocorticoids and inflammatory cytokines as well as other environmental factors. Transcriptomic studies are beginning to demonstrate important sex differences and, together with genomic studies, are starting to reveal mechanistic domains of overlap and uniqueness with regards to risk and pathophysiological mechanisms with schizophrenia and bipolar disorder. These studies also implicate GABA and glutamate dysfunction as well as immunologic mechanisms. While current antidepressants have significant time lag and efficacy limitations, new rapid-acting agents that target the glutamate and GABA systems address these issues and offer superior therapeutic interventions for this widespread and debilitating disorder.

Magnetic resonance (MR) spectroscopic measurement of γ-aminobutyric acid (GABA) in major depression before and after electroconvulsive therapy

OBJECTIVE

Prior studies suggest that a dysregulation of the inhibitory neurotransmitter γ-aminobutyric acid (GABA) is involved in the pathophysiology of major depression. We aimed to elucidate changes in cortical GABA content in relation to depression and electroconvulsive therapy (ECT) using magnetic resonance spectroscopy (MRS).

METHODS

In total, 11 patients with major depression or depressive episode of bipolar disorder (mean pre-ECT Ham-17 of 26) and 11 healthy subjects were recruited. GABA was quantified using short-TE MRS in prefrontal and occipital cortex. Other neurometabolites such as glutathione (GSH), N-acetylaspartate (NAA) and glutamate (Glu) were secondary outcome measures.

RESULTS

No significant differences in GABA/Cr levels were observed between patients at baseline and healthy subjects in prefrontal cortex, t(20)=0.089, p=0.93 or occipital cortex t(21)=0.37, p=0.72. All patients improved on Ham-17 (mean post-ECT Ham-17 of 9). No significant difference was found in GABA, Glu, glutamine, choline or GSH between pre- and post-ECT values. However, we observed a significant decrease in NAA levels following ECT t(22)=3.89, p=0.0038, and a significant correlation between the NAA decline and the number of ECT sessions p=0.035.

CONCLUSIONS

Our study does not support prior studies arguing for GABA as a key factor in the treatment effect of ECT on major depression. The reduction in NAA levels following ECT could be due to neuronal loss or a transient dysfunction in prefrontal cortex. As no long-term follow-up scan was performed, it is unknown whether NAA levels will normalise over time.

Glutamatergic neurometabolite levels in major depressive disorder: a systematic review and meta-analysis of proton magnetic resonance spectroscopy studies

Alterations in glutamatergic neurotransmission are implicated in the pathophysiology of depression, and the glutamatergic system represents a treatment target for depression. To summarize the nature of glutamatergic alterations in patients with depression, we conducted a meta-analysis of proton magnetic resonance (¹H-MRS) spectroscopy studies examining levels of glutamate. We used the search terms: depress* AND (MRS OR "magnetic resonance spectroscopy"). The search was performed with MEDLINE, Embase, and PsycINFO. The inclusion criteria were ¹H-MRS studies comparing levels of glutamate + glutamine (Glx), glutamate, or glutamine between patients with depression and healthy controls. Standardized mean differences (SMD) were calculated to assess group differences in the levels of glutamatergic neurometabolites. Forty-nine studies met the eligibility criteria, which included 1180 patients and 1066 healthy controls. There were significant decreases in Glx within the medial frontal cortex (SMD = -0.38; 95% CI, -0.69 to -0.07) in patients with depression compared with controls. Subanalyses revealed that there was a significant decrease in Glx in the medial frontal cortex in medicated patients with depression (SMD = -0.50; 95% CI, -0.80 to -0.20), but not in unmedicated patients (SMD = -0.27; 95% CI, -0.76 to 0.21) compared with controls. Overall, decreased levels of glutamatergic metabolites in the medial frontal cortex are linked with the pathophysiology of depression. These findings are in line with the hypothesis that depression may be associated with abnormal glutamatergic neurotransmission.

Choline and N-acetyl aspartate levels in the dorsolateral prefrontal cortex at the beginning of the recovery phase as markers of increased risk for depressive episode recurrence under different duration of maintenance therapy and after it: a retrospective cohort study

AIM

To evaluate the relationship between the dynamics of proton magnetic resonance spectroscopy (1H-MRS) brain metabolite levels at the beginning of the recovery phase of the index depressive episode and the time to the recurrence of depression.

METHODS

This retrospective cohort study analyzed the changes in N-acetyl aspartate (NAA), choline (Cho), and glutamate-glutamine in 48 patients with recurrent depression treated with maintenance antidepressant monotherapy at a stable dose. 1H-MRS was performed at the start of the recovery phase and 6 months later. 1H-MRS parameters, index episode descriptors, and depressive disorder course were analyzed by Cox proportional hazards model.

RESULTS

NAA and Cho decrease six months after the beginning of the recovery period were time-independent risk factors for depressive episode recurrence. Hazard ratio associated with NAA decrease was 2.02 (95% confidence interval 1.06-3.84) and that associated with Cho decrease was 2.06 (95% confidence interval 1.02-4.17). These changes were not related to symptoms severity, as Montgomery-Asberg Depression Scale score remained generally unchanged (mean -0.01; standard deviation 1.6) over the first 6 months of recovery.

CONCLUSION

Patients receiving maintenance antidepressant therapy after recovery who experience a decrease in NAA or Cho levels early in the recovery phase have a double risk of depressive episode recurrence. Sustained NAA and Cho levels at the beginning of the recovery phase may indicate increased brain resilience conferred by antidepressant therapy, while NAA and Cho decrease may indicate only the trait-related temporal effect of therapy in another stratum of patients.

Scrub typhus and depression: a nationwide cohort analysis

BACKGROUND

Studies on the relationship between depression and scrub typhus are limited. We conducted a retrospective cohort study to investigate whether scrub typhus is a risk factor for depression.

METHODS

Using Taiwan's National Health Insurance Research Database, this study investigated the incidence of depression, and its risk factors, in patients diagnosed with scrub typhus between 2000 and 2010. Scrub typhus patients who did not have a history of depression before the index date were enrolled. For each patient with scrub typhus, four controls without a history of scrub typhus and depression were randomly selected and frequency matched by sex, age, year of the index date, and comorbidities. The follow-up period was from the time of initial scrub typhus diagnosis to the date of diagnosis of depression, censoring, or December 31, 2010. Cox proportional hazards regression models were used to analyze the risk of depression according to sex, age, and comorbidities.

RESULTS

The study comprised a 5238-patient scrub typhus group and a 20,952-patient non-scrub typhus group with similar sex and age distributions. During the follow-up period, the cumulative incidence of depression was higher in the scrub typhus than the non-scrub typhus group (log-rank test P < 0.001). In the scrub typhus group, 45 patients developed depression, yielding an incidence rate of 1.67 per 1000 person-years, and in the non-scrub typhus group, 117 patients developed depression, yielding an incidence rate of 1.08 per 1000 person-years. This yielded a crude hazard ratio (HR) of 1.55 (95% confidence interval [CI] 1.41-1.70) and adjusted HR (aHR) of 1.56 (95% CI 1.42-1.71). Compared with the non-scrub typhus group, the risk of depression in the scrub typhus group was higher in patients of both sexes (men: aHR = 1.46, 95% CI 1.29-1.64; women: aHR = 1.68, 95% CI 1.45-1.96), in patients aged younger than 65 (≤ 49 years: aHR = 1.95, 50-64 years: aHR = 1.73), and in patients without comorbidities (aHR = 2.06, 95% CI 1.85-2.29).

CONCLUSIONS

The risk of depression was 1.56-fold higher in patients with scrub typhus than in the general population.

Differences in excitatory and inhibitory neurotransmitter levels between depressed patients and healthy controls: A systematic review and meta-analysis

Dysfunction of gamma-aminobutyric acid (GABA) and/or glutamate neurotransmitter systems have increasingly been implicated in the aetiology of Major Depressive Disorder (MDD). It has been proposed that alterations in GABA and/or glutamate result in an imbalance of inhibition and excitation. In a review of the current literature, we identified studies using Magnetic Resonance Spectroscopy (MRS) to examine the neurotransmitters GABA, glutamate, and the composite glutamate/glutamine measure Glx in patients diagnosed with MDD and healthy controls. Results showed patients with MDD had significantly lower GABA levels compared to controls (-0.35 [-0.61,-0.10], p = 0.007). No significant difference was found between levels of glutamate. Sub-analyses were performed, including only studies where the Anterior Cingulate Cortex (ACC) was the region of interest. GABA and Glx levels were lower in the ACC of MDD patients (-0.56 [-0.93,-0.18] p = 0.004, and 0.40 [-0.81,0.01] p = 0.05). This review indicates widespread cortical reduction of GABA in MDD, with a trend towards a localised reduction of Glx in the ACC. However, given both GABA and glutamate appear decreased a simple interpretation in terms of an imbalance of overall excitation-inhibition is not feasible.

Distinction of the GABA 2.29 ppm resonance using triple refocusing at 3 T in vivo

PURPOSE

To develop ¹ H MR spectroscopy that provides distinction of γ-aminobutyric acid (GABA) signal at 3 T in vivo.

METHODS

Triple-refocusing was tailored at 3 T, with numerical simulations and phantom validation, for distinction of the GABA 2.29-ppm resonance from the neighboring glutamate resonance. The optimization was performed on the inter-RF pulse time delays and the duration and carrier frequency of a non-slice-selective RF pulse. The optimized triple refocusing was tested in multiple regions in 6 healthy subjects, including hippocampus. The in vivo spectra were analyzed with the LCModel using in-house basis spectra. After normalization of the metabolite signal estimates to water, the metabolite concentrations were quantified with reference to medial-occipital creatine at 8 mM.

RESULTS

A triple-refocusing scheme with optimized inter-RF pulse time delays (TE = 74 ms) was obtained for GABA detection. With optimized duration (14 ms) and carrier frequency (4.5 ppm) of the non-slice-selective RF pulse, the triple refocusing gave rise to distinction between the GABA 2.29-ppm and glutamate 2.35-ppm signals. The GABA 2.29-ppm signal was clearly discernible in spectra in vivo (voxel size 4 to 12 mL; scan times 4.3 to 17 minutes). With a total of 24 spectra from 6 gray or white matter-dominant regions, the GABA concentration was measured to be 0.62 to 1.15 mM (Cramer-Rao lower bound of 8 to 14%), and the glutamate level 5.8 to 11.2 mM (Cramer-Rao lower bound of 3 to 6%).

CONCLUSION

The optimized triple refocusing provided distinction between GABA and glutamate signals and permitted direct codetection of these metabolites in the human brain at 3 T in vivo.

The dose makes the poison: from glutamate-mediated neurogenesis to neuronal atrophy and depression

Experimental evidence has demonstrated that glutamate is an essential factor for neurogenesis, whereas another line of research postulates that excessive glutamatergic neurotransmission is associated with the pathogenesis of depression. The present review shows that such paradox can be explained within the framework of hormesis, defined as biphasic dose responses. Low glutamate levels activate adaptive stress responses that include proteins that protect neurons against more severe stress. Conversely, abnormally high levels of glutamate, resulting from increased release and/or decreased removal, cause neuronal atrophy and depression. The dysregulation of the glutamatergic transmission in depression could be underlined by several factors including a decreased inhibition (γ-aminobutyric acid or serotonin) or an increased excitation (primarily within the glutamatergic system). Experimental evidence shows that the activation of N-methyl-D-aspartate receptor (NMDA) and α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors (AMPAR) can exert two opposite effects on neurogenesis and neuron survival depending on the synaptic or extrasynaptic concentration. Chronic stress, which usually underlies experimental and clinical depression, enhances glutamate release. This overactivates NMDA receptors (NMDAR) and consequently impairs AMPAR activity. Various studies show that treatment with antidepressants decreases plasma glutamate levels in depressed individuals and regulates glutamate receptors by reducing NMDAR function by decreasing the expression of its subunits and by potentiating AMPAR-mediated transmission. Additionally, it has been shown that chronic treatment with antidepressants having divergent mechanisms of action (including tricyclics, selective serotonin reuptake inhibitors, and ketamine) markedly reduced depolarization-evoked glutamate release in the hippocampus. These data, taken together, suggest that the glutamatergic system could be a final common pathway for antidepressant treatments.

Meta-analysis of central and peripheral γ-aminobutyric acid levels in patients with unipolar and bipolar depression

BACKGROUND

Many studies have measured central and peripheral γ-aminobutyric acid (GABA) levels in patients with depression. We performed a meta-analysis to provide an objective overview of GABA changes in those with unipolar or bipolar depression.

METHODS

After a systematic database search, original data were extracted with the help of seminal authors to calculate standardized mean differences. We compared GABA levels between patients with current major depressive episodes and controls, between euthymic patients and controls, and in patients before and after treatment. We performed meta-regressions to explore the influence of demographic and clinical variables on GABA significant mean differences.

RESULTS

For unipolar depression, central and peripheral GABA levels were diminished in currently depressed patients, but normal in euthymic patients, compared with the healthy controls. For bipolar disorder, GABA levels were diminished in medication-free patients, but seemed to be normalized in medicated patients, compared with the healthy controls. We found no significant association with demographic or clinical variables.

LIMITATIONS

There was a great heterogeneity across studies, probably because of the substantial variation of clinical characteristics in the included samples. Many subanalyses were performed to assess how the diagnosis, medications, or the type of measurements of peripheral or central GABA levels may affect the main results.

CONCLUSION

The GABA levels evolved differentially in patients with unipolar and bipolar disorders. Our results suggest that GABA levels could represent a biomarker of symptomatic states in patients with unipolar disorder and would be normalized by mood stabilizers in those with bipolar disorder.

Somatostatin-Positive Gamma-Aminobutyric Acid Interneuron Deficits in Depression: Cortical Microcircuit and Therapeutic Perspectives

The functional integration of external and internal signals forms the basis of information processing and is essential for higher cognitive functions. This occurs in finely tuned cortical microcircuits whose functions are balanced at the cellular level by excitatory glutamatergic pyramidal neurons and inhibitory gamma-aminobutyric acidergic (GABAergic) interneurons. The balance of excitation and inhibition, from cellular processes to neural network activity, is characteristically disrupted in multiple neuropsychiatric disorders, including major depressive disorder (MDD), bipolar disorder, anxiety disorders, and schizophrenia. Specifically, nearly 3 decades of research demonstrate a role for reduced inhibitory GABA level and function across disorders. In MDD, recent evidence from human postmortem and animal studies suggests a selective vulnerability of GABAergic interneurons that coexpress the neuropeptide somatostatin (SST). Advances in cell type-specific molecular genetics have now helped to elucidate several important roles for SST interneurons in cortical processing (regulation of pyramidal cell excitatory input) and behavioral control (mood and cognition). Here, we review evidence for altered inhibitory function arising from GABAergic deficits across disorders and specifically in MDD. We then focus on properties of the cortical microcircuit, where SST-positive GABAergic interneuron deficits may disrupt functioning in several ways. Finally, we discuss the putative origins of SST cell deficits, as informed by recent research, and implications for therapeutic approaches. We conclude that deficits in SST interneurons represent a contributing cellular pathology and therefore a promising target for normalizing altered inhibitory function in MDD and other disorders with reduced SST cell and GABA functions.

A new stress sensor and risk factor for suicide: the T allele of the functional genetic variant in the GABRA6 gene

Low GABA transmission has been reported in suicide, and GABRA6 rs3219151 T allele has been associated with greater physiological and endocrine stress response in previous studies. Although environmental stress also plays a role in suicide, the possible role of this allele has not been investigated in this respect. In our present study effect of rs3219151 of GABRA6 gene in interaction with recent negative life events on lifetime and current depression, current anxiety, as well as lifetime suicide were investigated using regression models in a white European general sample of 2283 subjects. Post hoc measures for phenotypes related to suicide risk were also tested for association with rs3219151 in interaction with environmental stress. No main effect of the GABRA6 rs3219151 was detected, but in those exposed to recent negative life events GABRA6 T allele increased current anxiety and depression as well as specific elements of suicide risk including suicidal and death-related thoughts, hopelessness, restlessness and agitation, insomnia and impulsiveness as measured by the STOP task. Our data indicate that stress-associated suicide risk is elevated in carriers of the GABRA6 rs3219151 T allele with several independent markers and predictors of suicidal behaviours converging to this increased risk.

Difference optimization: Automatic correction of relative frequency and phase for mean non-edited and edited GABA 1H MEGA-PRESS spectra

Phase and frequency corrections of magnetic resonance spectroscopic data are of major importance to obtain reliable and unambiguous metabolite estimates as validated in recent research for single-shot scans with the same spectral fingerprint. However, when using the J-difference editing technique ¹H MEGA-PRESS, misalignment between mean edited (ON‾) and non-edited (OFF‾) spectra that may remain even after correction of the corresponding individual single-shot scans results in subtraction artefacts compromising reliable GABA quantitation. We present a fully automatic routine that iteratively optimizes simultaneously relative frequencies and phases between the mean ON‾ and OFF‾¹H MEGA-PRESS spectra while minimizing the sum of the magnitude of the difference spectrum (L¹ norm). The proposed method was applied to simulated spectra at different SNR levels with deliberately preset frequency and phase errors. Difference optimization proved to be more sensitive to small signal fluctuations, as e.g. arising from subtraction artefacts, and outperformed the alternative spectral registration approach, that, in contrast to our proposed linear approach, uses a nonlinear least squares minimization (L² norm), at all investigated levels of SNR. Moreover, the proposed method was applied to 47 MEGA-PRESS datasets acquired in vivo at 3T. The results of the alignment between the mean OFF‾ and ON‾ spectra were compared by applying (a) no correction, (b) difference optimization or (c) spectral registration. Since the true frequency and phase errors are not known for in vivo data, manually corrected spectra were used as the gold standard reference (d). Automatically corrected data applying both, method (b) or method (c), showed distinct improvements of spectra quality as revealed by the mean Pearson correlation coefficient between corresponding real part mean DIFF‾ spectra of R_bd=0.997±0.003 (method (b) vs. (d)), compared to R_ad=0.764±0.220 (method (a) vs. (d)) with no alignment between OFF‾ and ON‾. Method (c) revealed a slightly lower correlation coefficient of R_cd=0.972±0.028 compared to R_bd, that can be ascribed to small remaining subtraction artefacts in the final DIFF‾ spectrum. In conclusion, difference optimization performs robustly with no restrictions regarding the input data range or user intervention and represents a complementary tool to optimize the final DIFF‾ spectrum following the mandatory frequency and phase corrections of single ON and OFF scans prior to averaging.

Disinhibition of somatostatin-positive GABAergic interneurons results in an anxiolytic and antidepressant-like brain state

Major depressive disorder (MDD) is associated with reduced concentrations of γ-aminobutyric acid (GABA) that are normalized by antidepressant therapies. Moreover, depressive-like phenotypes of GABA_A receptor mutant mice can be reversed by treatment with conventional antidepressants drugs, as well as by subanesthetic doses of ketamine. Thus GABAergic deficits may causally contribute to depressive disorders, while antidepressant therapies may enhance GABAergic synaptic transmission. Here we tested the hypothesis that sustained enhancement of GABAergic transmission alone is sufficient to elicit antidepressant-like behavior, using disinhibition of GABAergic interneurons. We focused on somatostatin-positive (SST⁺) GABAergic interneurons because of evidence that their function is compromised in MDD. To disinhibit SST⁺ interneurons, we inactivated the γ2 subunit gene of GABA_A receptors selectively in these neurons (SSTCre:γ2^f/f mice). Loss of inhibitory synaptic input resulted in increased excitability of SST⁺ interneurons. In turn, pyramidal cell targets of SST⁺ neurons showed an increased frequency of spontaneous inhibitory postsynaptic currents. The behavior of SSTCre:γ2^f/f mice mimicked the effects of anxiolytic and antidepressant drugs in a number of behavioral tests, without affecting performance in a spatial learning- and memory-dependent task. Finally, brain extracts of SSTCre:γ2^f/f mice showed decreased phosphorylation of the eukaryotic elongation factor eEF2, reminiscent of the effects of ketamine. Importantly, these effects occurred without altered activity of the mammalian target of rapamycin pathway nor did they involve altered expression of SST. However, they were associated with reduced Ca²⁺/calmodulin-dependent auto-phosphorylation of eEF2 kinase, which controls the activity of eEF2 as its single target. Thus enhancing GABAergic inhibitory synaptic inputs from SST⁺ interneurons to pyramidal cells and corresponding chronic reductions in the synaptic excitation:inhibition ratio represents a novel strategy for antidepressant therapies that reproduces behavioral and biochemical end points of rapidly acting antidepressants.

Glutamate and Gamma-Aminobutyric Acid Systems in the Pathophysiology of Major Depression and Antidepressant Response to Ketamine

In patients with major depressive disorder or bipolar disorder, abnormalities in excitatory and/or inhibitory neurotransmission and neuronal plasticity may lead to aberrant functional connectivity patterns within large brain networks. Network dysfunction in association with altered brain levels of glutamate and gamma-aminobutyric acid have been identified in both animal and human studies of depression. In addition, evidence of an antidepressant response to subanesthetic-dose ketamine has led to a collection of studies that have examined neurochemical (e.g., glutamatergic and gamma-aminobutyric acidergic) and functional imaging correlates associated with such an effect. Results from these studies suggest that an antidepressant response in association with ketamine occurs, in part, by reversing these neurochemical/physiological disturbances. Future studies in depression will require a combination of neuroimaging approaches from which more biologically homogeneous subgroups can be identified, particularly with respect to treatment response biomarkers of glutamatergic modulation.

Modelling depression in animals: at the interface of reward and stress pathways

RATIONALE

Despite substantial research efforts the aetiology of major depressive disorder (MDD) remains poorly understood, which is due in part to the heterogeneity of the disorder and the complexity of designing appropriate animal models. However, in the last few decades, a focus on the development of novel stress-based paradigms and a focus on using hedonic/anhedonic behaviour have led to renewed optimism in the use of animal models to assess aspects of MDD.

OBJECTIVES

Therefore, in this review article, dedicated to Athina Markou, we summarise the use of stress-based animal models for studying MDD in rodents and how reward-related readouts can be used to validate/assess the model and/or treatment.

RESULTS

We reveal the use and limitations of chronic stress paradigms, which we split into non-social (i.e. chronic mild stress), social (i.e. chronic social defeat) and drug-withdrawal paradigms for studying MDD and detail numerous reward-related readouts that are employed in preclinical research. Finally, we finish with a section regarding important factors to consider when using animal models.

CONCLUSIONS

One of the most consistent findings following chronic stress exposure in rodents is a disruption of the brain reward system, which can be easily assessed using sucrose, social interaction, food, drug of abuse or intracranial self-stimulation as a readout. Probing the underlying causes of such alterations is providing a greater understanding of the potential systems and processes that are disrupted in MDD.

Rapid Acting Antidepressants in Chronic Stress Models: Molecular and Cellular Mechanisms

Stress-associated disorders, including depression and anxiety, impact nearly 20% of individuals in the United States. The social, health, and economic burden imposed by stress-associated disorders requires in depth research efforts to identify suitable treatment strategies. Traditional medications (e.g., selective serotonin reuptake inhibitors, monoamine oxidase inhibitors) have significant limitations, notably a time lag for therapeutic response that is compounded by low rates of efficacy. Excitement over ketamine, a rapid acting antidepressant effective in treatment resistant patients, is tempered by transient dissociative and psychotomimetic effects, as well as abuse potential. Rodent stress models are commonly used to produce behavioral abnormalities that resemble those observed in stress-associated disorders. Stress models also produce molecular and cellular morphological changes in stress sensitive brain regions, including the prefrontal cortex and hippocampus that resemble alterations observed in depression. Rapid acting antidepressants such as ketamine can rescue stress-associated morphological and behavioral changes in rodent models. Here, we review the literature supporting a role for rapid acting antidepressants in opposing the effects of stress, and summarize research efforts seeking to elucidate the molecular, cellular, and circuit level targets of these agents.

Prefrontal Cortex GABAergic Deficits and Circuit Dysfunction in the Pathophysiology and Treatment of Chronic Stress and Depression

Psychiatric diseases, notably major depression, are associated with imbalance of excitatory and inhibitory neurotransmission within the prefrontal cortex (PFC) and related limbic brain circuitry. In many cases these illnesses are precipitated or exacerbated by chronic stress, which also alters excitatory and inhibitory neurotransmitter systems. Notably, exposure to repeated uncontrollable stress causes persistent changes in the synaptic integrity and function of the principal glutamatergic excitatory neurons in the PFC, characterized by neuronal atrophy and loss of synaptic connections. This can lead to dysfunction of the PFC circuitry that is necessary for execution of adaptive behavioral responses. In addition, an emerging literature shows that chronic stress also causes extensive alteration of GABAergic inhibitory circuits in the PFC, leading to the hypothesis that inhibitory neurotransmitter deficits contribute to changes in PFC neuronal excitability and cognitive impairments. Here we review evidence in rodents and human, which point to the mechanisms underlying stress-induced alterations of GABA transmission in the PFC, and its relevance to circuit dysfunction in mood and stress related disorders. These findings suggest that alterations of GABA interneurons and inhibitory neurotransmission play a causal role in the development of stress-related neurobiological illness, and could identify a new line of GABA related therapeutic targets.

Lower Choline-Containing Metabolites/Creatine (Cr) Rise and Failure to Sustain NAA/Cr Levels in the Dorsolateral Prefrontal Cortex Are Associated with Depressive Episode Recurrence under Maintenance Therapy: A Proton Magnetic Resonance Spectroscopy Retrospective Cohort Study

BACKGROUND

The aim of this study was to evaluate the relationship between changes in proton magnetic resonance spectroscopy (1H-MRS) parameters at the start of the index episode recovery phase and at recurrence in patients with recurrent depression who were treated with prolonged maintenance therapy.

METHODS

1H-MRS parameters were analyzed in 48 patients with recurrent depression who required maintenance therapy with antidepressant medication prescribed by a psychiatrist and who continued with the same antidepressant during the maintenance phase, either to recurrence of depression, completion of the 10-year observation period, or the start of the withdrawal phase (tapering-off antidepressant). N-acetylaspartate (NAA), choline-containing metabolites (Cho), creatine (Cr), and glutamine/glutamate were measured at the start of the recovery phase and 6 months later.

RESULTS

Recurrent depressive episodes occurred in 20 patients. These individuals had a smaller increase in Cho/Cr after the beginning of the recovery phase compared to the non-recurrent patient group and also exhibited a decreased NAA/Cr ratio.

CONCLUSION

Sustainable NAA and increased Cho levels at the onset of the recovery phase of the index episode are early markers of antidepressant effectiveness associated with a lower risk of major depressive disorder recurrence. The NAA and Cho changes in the non-recurrent group may be attributable to increased brain resilience, contrary to the transient temporal effect observed in subjects who experienced a depressive episode.

An Exploratory Study of Spectroscopic Glutamatergic Correlates of Cortical Excitability in Depressed Adolescents

Introduction: Transcranial magnetic stimulation (TMS) research has suggested dysfunction in cortical glutamatergic systems in adolescent depression, while proton magnetic resonance spectroscopy (¹H-MRS) studies have demonstrated deficits in concentrations of glutamatergic metabolites in depressed individuals in several cortical regions, including the anterior cingulate cortex (ACC). However, few studies have combined TMS and MRS methods to examine relationships between glutamatergic neurochemistry and excitatory and inhibitory neural functions, and none have utilized TMS-MRS methodology in clinical populations or in youth. This exploratory study aimed to examine relationships between TMS measures of cortical excitability and inhibition and concentrations of glutamatergic metabolites as measured by ¹H-MRS in depressed adolescents. Methods: Twenty-four adolescents (aged 11-18 years) with depressive symptoms underwent TMS testing, which included measures of the resting motor threshold (RMT), cortical silent period (CSP), short-interval intracortical inhibition (SICI), and intracortical facilitation (ICF). Fourteen participants from the same sample also completed ¹H-MRS in a 3 T MRI scanner after TMS testing. Glutamate + glutamine (Glx) concentrations were measured in medial ACC and left primary motor cortex voxels with a TE-optimized PRESS sequence. Metabolite concentrations were corrected for cerebrospinal fluid (CSF) after tissue segmentation. Pearson product-moment and Spearman rank-order correlations were calculated to assess relationships between TMS measures and [Glx]. Results: In the left primary motor cortex voxel, [Glx] had a significant positive correlation with the RMT. In the medial ACC voxel, [Glx] had significant positive correlations with ICF at the 10-ms and 20-ms interstimulus intervals (ISIs). Conclusion: These preliminary data implicate glutamate in cortical excitatory processes measured by TMS. Limitations included small sample size, lack of healthy control comparators, possible age- and sex-related effects, and observational nature of the study. Further research aimed at examining the relationship between glutamatergic metabolite concentrations measured through MRS and the excitatory and inhibitory physiology measured through TMS is warranted. Combined TMS-MRS methods show promise for future investigations of the pathophysiology of depression in adults as well as in children and adolescents.

Brain GABA levels across psychiatric disorders: A systematic literature review and meta-analysis of (1) H-MRS studies

The inhibitory gamma-aminobutyric acid (GABA) system is involved in the etiology of most psychiatric disorders, including schizophrenia, autism spectrum disorder (ASD) and major depressive disorder (MDD). It is therefore not surprising that proton magnetic resonance spectroscopy ((1) H-MRS) is increasingly used to investigate in vivo brain GABA levels. However, integration of the evidence for altered in vivo GABA levels across psychiatric disorders is lacking. We therefore systematically searched the clinical (1) H-MRS literature and performed a meta-analysis. A total of 40 studies (N = 1,591) in seven different psychiatric disorders were included in the meta-analysis: MDD (N = 437), schizophrenia (N = 517), ASD (N = 150), bipolar disorder (N = 129), panic disorder (N = 81), posttraumatic stress disorder (PTSD) (N = 104), and attention deficit/hyperactivity disorder (ADHD) (N = 173). Brain GABA levels were lower in ASD (standardized mean difference [SMD] = -0.74, P = 0.001) and in depressed MDD patients (SMD = -0.52, P = 0.005), but not in remitted MDD patients (SMD = -0.24, P = 0.310) compared with controls. In schizophrenia this finding did not reach statistical significance (SMD = -0.23, P = 0.089). No significant differences in GABA levels were found in bipolar disorder, panic disorder, PTSD, and ADHD compared with controls. In conclusion, this meta-analysis provided evidence for lower brain GABA levels in ASD and in depressed (but not remitted) MDD patients compared with healthy controls. Findings in schizophrenia were more equivocal. Even though future (1) H-MRS studies could greatly benefit from a longitudinal design and consensus on the preferred analytical approach, it is apparent that (1) H-MRS studies have great potential in advancing our understanding of the role of the GABA system in the pathogenesis of psychiatric disorders. Hum Brain Mapp 37:3337-3352, 2016. © 2016 Wiley Periodicals, Inc.

Correlation between neurochemical metabolism and memory function in adolescent patients with depression: A multi-voxel ¹H magnetic resonance spectroscopy study

AIMS

We utilized multi-voxel proton magnetic resonance spectroscopy ((1)H-MRS) to detect biochemical abnormalities in dorsolateral prefrontal white matter and anterior cingulate gray matter and to determine the correlation of biochemical changes with memory function in depressed adolescents.

METHODS

A total of 24 depressed patients and 23 healthy controls were enrolled in this study. MRS was performed to assess the N-acetylaspartate (NAA)/creatine Cr and choline (Cho)/Cr ratios in dorsolateral prefrontal white matter and anterior cingulate gray matter of participants. Memory function was measured on the basis of Wechsler Memory Scale scores, and depression was diagnosed on the basis of clinical observation, interview, and Hamilton Depression Rating Scale scores.

RESULTS

Compared with controls, depressed patients had significantly lower NAA/Cr and Cho/Cr ratios in left dorsolateral prefrontal white matter and lower NAA/Cr ratios in right dorsolateral prefrontal white matter (P < 0.05). No biochemical differences were identified in the bilateral anterior cingulate gray matter between the two groups. Nevertheless, the depressed patients showed significantly lower memory quotient than controls (P < 0.05). The NAA/Cr ratio in dorsolateral prefrontal white matter positively correlated with memory quotient (left: P < 0.01; right: P < 0.05).

CONCLUSIONS

These findings suggest that biochemical abnormalities in prefrontal white matter are involved in the pathophysiology of adolescent depression. In particular, such abnormalities are already present at the early stage of the disorder, and low NAA/Cr in bilateral anterior frontal white matter may be associated with memory impairment and related neuropathology.

Vulnerability for new episodes in recurrent major depressive disorder: protocol for the longitudinal DELTA-neuroimaging cohort study

INTRODUCTION

Major depressive disorder (MDD) is widely prevalent and severely disabling, mainly due to its recurrent nature. A better understanding of the mechanisms underlying MDD-recurrence may help to identify high-risk patients and to improve the preventive treatment they need. MDD-recurrence has been considered from various levels of perspective including symptomatology, affective neuropsychology, brain circuitry and endocrinology/metabolism. However, MDD-recurrence understanding is limited, because these perspectives have been studied mainly in isolation, cross-sectionally in depressed patients. Therefore, we aim at improving MDD-recurrence understanding by studying these four selected perspectives in combination and prospectively during remission.

METHODS AND ANALYSIS

In a cohort design, we will include 60 remitted, unipolar, unmedicated, recurrent MDD-participants (35-65 years) with ≥ 2 MDD-episodes. At baseline, we will compare the MDD-participants with 40 matched controls. Subsequently, we will follow-up the MDD-participants for 2.5 years while monitoring recurrences. We will invite participants with a recurrence to repeat baseline measurements, together with matched remitted MDD-participants. Measurements include questionnaires, sad mood-induction, lifestyle/diet, 3 T structural (T1-weighted and diffusion tensor imaging) and blood-oxygen-level-dependent functional MRI (fMRI) and MR-spectroscopy. fMRI focusses on resting state, reward/aversive-related learning and emotion regulation. With affective neuropsychological tasks we will test emotional processing. Moreover, we will assess endocrinology (salivary hypothalamic-pituitary-adrenal-axis cortisol and dehydroepiandrosterone-sulfate) and metabolism (metabolomics including polyunsaturated fatty acids), and store blood for, for example, inflammation analyses, genomics and proteomics. Finally, we will perform repeated momentary daily assessments using experience sampling methods at baseline. We will integrate measures to test: (1) differences between MDD-participants and controls; (2) associations of baseline measures with retro/prospective recurrence-rates; and (3) repeated measures changes during follow-up recurrence. This data set will allow us to study different predictors of recurrence in combination.

ETHICS AND DISSEMINATION

The local ethics committee approved this study (AMC-METC-Nr.:11/050). We will submit results for publication in peer-reviewed journals and presentation at (inter)national scientific meetings.

TRIAL REGISTRATION NUMBER

NTR3768.

A pilot in vivo proton magnetic resonance spectroscopy study of amino acid neurotransmitter response to ketamine treatment of major depressive disorder

The N-methyl-D-aspartate receptor antagonist ketamine can improve major depressive disorder (MDD) within hours. To evaluate the putative role of glutamatergic and GABAergic systems in ketamine's antidepressant action, medial prefrontal cortical (mPFC) levels of glutamate+glutamine (Glx) and γ-aminobutyric acid (GABA) were measured before, during, and after ketamine administration using proton magnetic resonance spectroscopy. Ketamine (0.5 mg kg(-1) intravenously) was administered to 11 depressed patients with MDD. Glx and GABA mPFC responses were measured as ratios relative to unsuppressed voxel tissue water (W) successfully in 8/11 patients. Ten of 11 patients remitted (50% reduction in 24-item Hamilton Depression Rating Scale and total score ⩽10) within 230 min of commencing ketamine. mPFC Glx/W and GABA/W peaked at 37.8%±7.5% and 38.0%±9.1% above baseline in ~26 min. Mean areas under the curve for Glx/W (P=0.025) and GABA/W (P=0.005) increased and correlated (r=0.796; P=0.018). Clinical improvement correlated with 90-min norketamine concentration (df=6, r=-0.78, P=0.023), but no other measures.

GABA System in Schizophrenia and Mood Disorders: A Mini Review on Third-Generation Imaging Studies

Third-generation neuroimaging research has been enriched by advances in magnetic resonance spectroscopy (MRS) measuring the concentration of important neurotrasmitters, such as the inhibitory amino acid GABA. Here, we performed a systematic mini-review on brain MRS studies measuring GABA concentration in patients affected by schizophrenia (SZ), bipolar disorder (BD), and major depressive disorder (MDD). We wondered whether multimodal investigations could overcome intrinsic technical limits of MRS giving a broader view of mental disorders pathogenesis. In SZ, unimodal studies gave mixed results, as increased, decreased, or unaltered GABA levels were reported depending on region, disease phase, and treatment. Conversely, multimodal results showed reduced level of glutamate, but not of GABA, in patients mirrored by in vitro biochemical findings revealing hippocampal reduction in glutamate signaling in SZ, and no deficits in GABA synthesis. Moreover, a mouse model confirmed the unique pathological characteristic of glutamate function in SZ. Unimodal studies in BD revealed again, inconsistent results, while no multimodal investigations including MRS on GABA exist. In MDD, unimodal studies could not differentiate patients from controls nor characterize high-risk subjects and remitted patients. However, a multimodal study combining functional magnetic resonance imaging and MRS revealed that cingulate cortex activity is related to glutamate, N-acetylaspartate levels and anhedonia in patients, and to GABA concentration in healthy subjects, improving the distinction between MDD and physiology. Overall, our results show that unimodal studies do not indicate GABA as a biomarker for the psychiatric disorders considered. Conversely, multimodal studies can widen the understanding of the link between psychopathology, genetics, neuroanatomy, and functional-biochemical brain activity in mental disorders. Although scarce, multimodal approaches seem promising for moving from GABA MRS unimodal-descriptive to causal level, and for integrating GABA results into a more comprehensive interpretation of mental disorder pathophysiology.

Indirect evidence of selective glial involvement in glutamate-based mechanisms of mood regulation in depression: meta-analysis of absolute prefrontal neuro-metabolic concentrations

Proton magnetic resonance spectroscopy ((1)H MRS) measures glutamatergic metabolites namely glutamate and glutamine located in neurons and astrocytes respectively. In this meta-analysis the contribution of glutamatergic neurotransmission to depressive symptoms was evaluated together with other putative prefrontal metabolites described in the pathogenesis of mood disorders, and in relation to treatment effects. A comprehensive literature search up to 2014 identified 17 reports which measured absolute concentrations of neurometabolites in the prefrontal cortex with (1)H MRS meeting criteria for inclusion in this meta-analysis. Excess of heterogeneity was investigated with meta-regressions. The analyses showed an exclusive reduction in absolute values of the composite measure of Glutamine and Glutamate (Glx) in the prefrontal cortex in depression, correlating in meta-regression analyses with treatment severity. Glutamate measurements in isolation did not differ vs. healthy controls or in relation to treatment and/or clinical improvement. Similarly there were no significant changes in other neurometabolites at baseline and following treatment. The analysis supports a role for glutamatergic dysfunction in the pathogeneses of mood dysregulation. The reduction in the absolute Glx values in the absence of changes in glutamate levels, suggests a possible modulatory role of astrocytes in the pathophysiology of depression.

The ups and downs of modelling mood disorders in rodents

The wide spectrum of disruptions that characterizes major depressive disorder (MDD) and bipolar disorder (BD) highlights the difficulties researchers are posed with as they try to mimic these disorders in the laboratory. Nonetheless, numerous attempts have been made to create rodent models of mood disorders or at least models of the symptoms of MDD and BD. Present antidepressants are all descendants of the serendipitous findings in the 1950s that the monoamine oxidase inhibitor iproniazid and the tricyclic antidepressant imipramine were effective antidepressants. Thus, the need for improved animal models to provide insights into the neuropathology underlying the disease is critical. Such information is in turn crucial for identifying new antidepressants and mood stabilisers. Currently, there is a shift away from traditional animal models to more focused research dealing with an endophenotype-style approach, genetic models, and incorporation of new findings from human neuroimaging and genetic studies. Such approaches are opening up more tractable avenues for understanding the neurobiological and genetic bases of these disorders. Further, such models promise to yield better translational animal models and hence more fruitful therapeutic targets. This overview focuses on such animal models and tests and how they can be used to assess MDD and BD in rodents.

Altered γ-aminobutyric acid neurotransmission in major depressive disorder: a critical review of the supporting evidence and the influence of serotonergic antidepressants

Evidence suggesting that central nervous system γ-aminobutyric acid (GABA) concentrations are reduced in patients with major depressive disorder (MDD) has been present since at least 1980, and this idea has recently gained support from more recent magnetic resonance spectroscopy data. These observations have led to the assumption that MDD’s underlying etiology is tied to an overall reduction in GABA-mediated inhibitory neurotransmission. In this paper, we review the mechanisms that govern GABA and glutamate concentrations in the brain, and provide a comprehensive and critical evaluation of the clinical data supporting reduced GABA neurotransmission in MDD. This review includes an evaluation of magnetic resonance spectroscopy data, as well as data on the expression and function of the GABA-synthesizing enzyme glutamic acid decarboxylase, GABA neuron-specific cell markers, such as parvalbumin, calretinin and calbindin, and the GABA_A and GABA_B receptors in clinical MDD populations. We explore a potential role for glial pathology in MDD-related reductions in GABA concentrations, and evidence of a connection between neurosteroids, GABA neurotransmission, and hormone-related mood disorders. Additionally, we investigate the effects of GABAergic pharmacological agents on mood, and demonstrate that these compounds have complex effects that do not universally support the idea that reduced GABA neurotransmission is at the root of MDD. Finally, we discuss the connections between serotonergic and GABAergic neurotransmission, and show that two serotonin-focused antidepressants – the selective serotonin-reuptake inhibitor fluoxetine and the multimodal antidepressant vortioxetine – modulate GABA neurotransmission in opposing ways, despite both being effective MDD treatments. Altogether, this review demonstrates that there are large gaps in our understanding of the relationship between GABA physiology and MDD, which must be remedied with more data from well-controlled empirical studies. In conclusion, this review suggests that the simplistic notion that MDD is caused by reduced GABA neurotransmission must be discarded in favor of a more nuanced and complex model of the role of inhibitory neurotransmission in MDD.

1H-MRS of the anterior cingulate cortex in childhood and adolescent obsessive-compulsive disorder: a case-control study

Abnormal glutamate concentrations in the anterior cingulate cortex (ACC) have been identified in children and adults with obsessive-compulsive disorder (OCD). The purpose of the present study was to measure in vivo (1)H-MRS neurometabolite concentrations in the ACC of children and adolescents with OCD, in order to identify metabolite abnormalities compared to healthy controls and to assess their relationship with clinical variables. 3T proton-magnetic resonance spectroscopy was used to probe ACC biochemistry in 47 paediatric and adolescent OCD patients (11-18 years old) compared to 31 healthy subjects of similar age, sex and estimated intellectual quotient. There were no significant differences in the concentration of glutamate plus glutamine (Glx) adjusted for CSF between OCD patients and healthy controls [F1,74=0.00; P=0.943], but there were significant differences in the concentration of Glx adjusted for CSF in paediatric and adolescent OCD patients according to duration of illness (less than or more than 24 months) [F2,73=3.95; P=0.024]. In addition, we found significantly lower levels of myo-inositol adjusted for CSF in the ACC [F1,74=5.686; P=0.02] in patients compared with controls. The present findings do not confirm the hypothesis of differences in Glx concentrations in the ACC between children and adolescents with OCD and healthy controls; however, the observation of differences in the Glx concentration in children and adolescent OCD patients depending on the duration of illness is of interest.

Dissociation of glutamate and cortical thickness is restricted to regions subserving trait but not state markers in major depressive disorder

BACKGROUND

The anterior cingulate cortex (ACC) plays an important role in the neuropathology of major depressive disorder (MDD). So far, the effect of local cortical alteration on metabolites in multiple subdivisions of ACC has not been studied. We aimed to investigate structural and biochemical changes and their relationship in the pregenual ACC (pgACC), dorsal ACC (dACC) in MDD.

METHODS

We obtained magnetic resonance spectroscopy (MRS) in two investigated regions for 24 depressed patients and matched controls. In each region, cortical thickness (CTh) was calculated within a template mask based on its MRS voxel. We investigated neurotransmitter concentrations of Glx, N-acetyl aspartate (NAA), and myo-inositol (m-Ins) in two investigated regions, as well as their relationships with CTh in depressed individuals and healthy controls.

RESULTS

Patients showed significantly lower cortical thickness in dACC compared to controls. Glx in dACC significantly correlated with CTh in healthy controls but not MDD patients, while NAA and CTh in dACC significantly correlated in both groups. A marginal decrease of Glx in pgACC was found in the subgroup of more severely depressive patients, compared to the mildly depressed patients.

LIMITATIONS

Modest sample size and lack of episodes of depression may limit the generalizability of our findings.

CONCLUSION

Our results indicate an abolished CTh-MRS relation in dACC-associated with structural decline-but not in pgACC, where acute MRS alterations prevailed. Our study provides the first evidence of a neurochemical basis explaining some of the inter-individual variability in CTh in MDD.

Differences in prefrontal cortex GABA/glutamate ratio after acute restraint stress in rats are associated with specific behavioral and neurobiological patterns

In patients suffering from stress-related pathologies and depression, frontal cortex GABA and glutamate contents are reported to decrease and increase, respectively. This suggests that the GABA and/or glutamate content may participate in pathological phenotype expression. Whether differences in frontal cortex GABA and glutamate contents would be associated with specific behavioral and neurobiological patterns remains unclear, especially in the event of exposure to moderate stress. We hypothesized that an increase in prefrontal cortex GABA/glutamate ratio would be associated with a blunted prefrontal cortex activation, an enhanced hypothalamo-pituitary-adrenocortical (HPA) axis activation and changes in behavior. Rats being restrained for 1-h were then tested in an open-field test in order to assess their behavior while under stress, and were sacrificed immediately afterward. The GABA/glutamate ratio was assessed by (1)H high-resolution magic angle spinning magnetic resonance spectroscopy ((1)H-HRMAS-MRS). The neurobiological response was evaluated through prefrontal cortex mRNA expression and plasma corticosterone levels. The stressed rats were distributed into two subgroups according to their high (H-G/g) or low (L-G/g) GABA/glutamate ratio. Compared to the L-G/g rats, the H-G/g rats exhibited a decrease in c-fos, Arc, Npas4, Nr4a2 mRNA expression suggesting blunted prefrontal cortex activation. They also showed a more pronounced stress with an enhanced rise in corticosterone, alanine aminotransferase (ALAT), aspartate aminotransferase (ASAT), creatine kinase (CK) and lactate dehydrogenase (LDH) levels, as well as behavioral disturbances with decreased locomotion speed. These changes were independent from prefrontal cortex energetic status as mammalian target of rapamycin (mTOR) and adenosine monophosphate-activated protein kinase (AMPK) pathway activities were similar in both subpopulations. The differences in GABA/glutamate ratio in the frontal cortex observed in the stressed animals may participate in shaping individual differences in psychophysiological reactions.

In vivo detection of acute pain-induced changes of GABA+ and Glx in the human brain by using functional 1H MEGA-PRESS MR spectroscopy

In vivo(1)H MR spectroscopic detection of pain associated metabolic changes in the human brain may allow for an objective evaluation of the perceived pain intensity and assessment of the involved neurotransmitters. Ultimately, it may lead to a deeper understanding of the mechanisms that underlie neuronal pain processing. The present study reports results of time-resolved measurements of acute heat pain induced changes of the excitatory (Glx) and inhibitory (GABA+) neurotransmitter turnover in the anterior cingulate cortex (ACC) and occipital cortex (OC) by using (1)H MEGA-PRESS spectroscopy. In ACC and OC, the ratio Glx/tCr increased by median values of 21.5% (p < 0.001) and 15.7% (p < 0.001), respectively. At the same time, GABA+/tCr decreased by median values of 15.1% (p = 0.114) in ACC and 12.7% (p < 0.001) in OC. To our knowledge, this study demonstrates for the first time the possibility of quantifying pain-induced neurotransmitter changes in the brain by using functional (1)H MEGA-PRESS. The increase of Glx/tCr may be ascribed to an elevated glutamatergic turnover, while the decrease of GABA+/tCr may reflect reduced activity of the inhibitory system in ACC and OC during pain processing.

Anxiety in major depression and cerebrospinal fluid free gamma-aminobutyric acid

BACKGROUND

Low gamma-aminobutyric acid (GABA) is implicated in both anxiety and depression pathophysiology. They are often comorbid, but most clinical studies have not examined these relationships separately. We investigated the relationship of cerebrospinal fluid (CSF) free GABA to the anxiety and depression components of a major depressive episode (MDE) and to monoamine systems.

METHODS AND MATERIALS

Patients with a DSM-IV major depressive episode (N = 167: 130 major depressive disorder; 37 bipolar disorder) and healthy volunteers (N = 38) had CSF free GABA measured by gas chromatography mass spectroscopy. Monoamine metabolites were assayed by high performance liquid chromatography. Symptomatology was assessed by Hamilton depression rating scale.

RESULTS

Psychic anxiety severity increased with age and correlated with lower CSF free GABA, controlling for age. CSF free GABA declined with age but was not related to depression severity. Other monoamine metabolites correlated positively with CSF GABA but not with psychic anxiety or depression severity. CSF free GABA was lower in MDD compared with bipolar disorder and healthy volunteers. GABA levels did not differ based on a suicide attempt history in mood disorders. Recent exposure to benzodiazepines, but not alcohol or past alcoholism, was associated with a statistical trend for more severe anxiety and lower CSF GABA.

CONCLUSIONS

Lower CSF GABA may explain increasing severity of psychic anxiety in major depression with increasing age. This relationship is not seen with monoamine metabolites, suggesting treatments targeting the GABAergic system should be evaluated in treatment-resistant anxious major depression and in older patients.

Glutamate and GABA contributions to medial prefrontal cortical activity to emotion: implications for mood disorders

The dorsomedial prefrontal cortex (MdPFC) and anterior cingulate cortices (ACC) play a critical role in implicit emotion regulation; however the understanding of the specific neurotransmitters that mediate such role is lacking. In this study, we examined relationships between MdPFC concentrations of two neurotransmitters, glutamate and γ-amino butyric acid (GABA), and BOLD activity in ACC during performance of an implicit facial emotion-processing task. Twenty healthy volunteers, aged 20-35 years, were scanned while performing an implicit facial emotion-processing task, whereby presented facial expressions changed from neutral to one of the four emotions: happy, anger, fear, or sad. Glutamate concentrations were measured before and after the emotion-processing task in right MdPFC using magnetic resonance spectroscopy (MRS). GABA concentrations were measured in bilateral MdPFC after the emotion-processing task. Multiple regression models were run to determine the relative contribution of glutamate and GABA concentration, age, and gender to BOLD signal in ACC to each of the four emotions. Multiple regression analyses revealed a significant negative correlation between MdPFC GABA concentration and BOLD signal in subgenual ACC (p<0.05, corrected) to sad versus shape contrast. For the anger versus shape contrast, there was a significant negative correlation between age and BOLD signal in pregenual ACC (p<0.05, corrected) and a positive correlation between MdPFC glutamate concentration (pre-task) and BOLD signal in pregenual ACC (p<0.05, corrected). Our findings are the first to provide insight into relationships between MdPFC neurotransmitter concentrations and ACC BOLD signal, and could further understanding of molecular mechanisms underlying emotion processing in healthy and mood-disordered individuals.