Elevated spectroscopic glutamate/gamma-amino butyric acid in rats bred for learned helplessness

Low-dose bisphenols exposure sex-specifically induces neurodevelopmental toxicity in juvenile rats and the antagonism of EGCG

Bisphenols (BPs) can negatively affect neurobehaviors in rats, whereas the mechanism remains unclear. Here, the mechanism of BPs-induced neurodevelopmental toxicity and its effective detoxification measures were investigated in vitro and in vivo. In in vitro experiments, primary hippocampal neurons from neonatal rats of different genders were treated with bisphenol A (BPA), bisphenol S (BPS) and bisphenol B (BPB) at 1 nM-100 μM, epigallocatechin gallate (EGCG) and G15, an antagonist of G protein-coupled estrogen receptor (GPER) for 7 d. Results indicated that BPs affected neuronal morphogenesis, impaired GABA synthesis and Glu/GABA homeostasis. Neuronal morphogenetic damage induced by low-doses BPA may be mediated by GPER. Neurotoxicity of BPS is weaker than BPA and BPB. In in vivo studies, exposure to BPA (0.5 μg/kg·bw/day) on PND 10-40 caused oxidative stress and inflammation in rat hippocampus, disrupted neuronal morphogenesis and neurotransmitter homeostasis, ultimately impaired spatial memory of rats. Males are more sensitive to BPA exposure than females. Both in vivo and in vitro studies indicated that EGCG, a phytoestrogen, can alleviate BPA-induced neurotoxicity. Taken together, low-doses BPA exposure sex-specifically disrupted neurodevelopment and further impaired learning and memory ability in rats, which may be mediated by GPER. Promisingly, EGCG effectively mitigated the BPA-induced neurodevelopmental toxicity.

The priming effect of repetitive transcranial magnetic stimulation on clinical response to electroconvulsive therapy in treatment-resistant depression: a randomized, double-blind, sham-controlled study

BACKGROUND

Electroconvulsive therapy (ECT) is one of the most effective treatments for treatment-resistant depression (TRD). However, due to response delay and cognitive impairment, ECT remains an imperfect treatment. Compared to ECT, repetitive transcranial magnetic stimulation (rTMS) is less effective at treating severe depression, but has the advantage of being quick, easy to use, and producing almost no side effects. In this study, our objective was to assess the priming effect of rTMS sessions before ECT on clinical response in patients with TRD.

METHODS

In this multicenter, randomized, double-blind, sham-controlled trial, 56 patients with TRD were assigned to active or sham rTMS before ECT treatment. Five sessions of active/sham neuronavigated rTMS were administered over the left dorsolateral prefrontal cortex (20 Hz, 90% resting motor threshold, 20 2 s trains with 60-s intervals, 800 pulses/session) before ECT (which was active for all patients) started. Any relative improvements were then compared between both groups after five ECT sessions, in order to assess the early response to treatment.

RESULTS

After ECT, the active rTMS group exhibited a significantly greater relative improvement than the sham group [43.4% (28.6%) v. 25.4% (17.2%)]. The responder rate in the active group was at least three times higher. Cognitive complaints, which were assessed using the Cognitive Failures Questionnaire, were higher in the sham rTMS group compared to the active rTMS group, but this difference was not corroborated by cognitive tests.

CONCLUSIONS

rTMS could be used to enhance the efficacy of ECT in patients with TRD. ClinicalTrials.gov: NCT02830399.

Natural essential oils derived from herbal medicines: A promising therapy strategy for treating cognitive impairment

Cognitive impairment (CI), mainly Alzheimer’s disease (AD), continues to increase in prevalence and is emerging as one of the major health problems in society. However, until now, there are no first-line therapeutic agents for the allopathic treatment or reversal of the disease course. Therefore, the development of therapeutic modalities or drugs that are effective, easy to use, and suitable for long-term administration is important for the treatment of CI such as AD. Essential oils (EOs) extracted from natural herbs have a wide range of pharmacological components, low toxicity, and wide sources, In this review, we list the history of using volatile oils against cognitive disorders in several countries, summarize EOs and monomeric components with cognitive improvement effects, and find that they mainly act by attenuating the neurotoxicity of amyloid beta, anti-oxidative stress, modulating the central cholinergic system, and improving microglia-mediated neuroinflammation. And combined with aromatherapy, the unique advantages and potential of natural EOs in the treatment of AD and other disorders were discussed. This review hopes to provide scientific basis and new ideas for the development and application of natural medicine EOs in the treatment of CI.

Electroconvulsive therapy in treatment resistant depression

Electroconvulsive therapy (ECT) is a treatment modality for patients with treatment resistant depression (TRD), defined as failure of two adequate antidepressant medication trials. We provide a qualitative review of ECT's effectiveness for TRD, methods to optimize ECT parameters to improve remission rates and side effect profiles, and ECT's proposed neurobiological mechanisms. Right unilateral (RUL) electrode placement has been shown to be as effective for major depression as bilateral ECT, and RUL is associated with fewer cognitive side effects. There is mixed evidence on how to utilize ECT to sustain remission (i.e., continuation ECT, psychotropic medications alone, or a combination of ECT and psychotropic medications). Related to neurobiological mechanisms, an increase in gray matter volume in the hippocampus-amygdala complex is reported post-ECT. High connectivity between the subgenual anterior cingulate and the middle temporal gyrus before ECT is associated with better treatment response. Rodent models have implicated changes in neurotransmitters including glutamate, GABA, serotonin, and dopamine in ECT's efficacy; however, findings in humans are limited. Altogether, while ECT remains a highly effective therapy, the neurobiological underpinnings associated with improvement of depression remain uncertain.

A Systematic Review of Neuromodulation Treatment Effects on Suicidality

Introduction: Neuromodulation is an important group of therapeutic modalities for neuropsychiatric disorders. Prior studies have focused on efficacy and adverse events associated with neuromodulation. Less is known regarding the influence of neuromodulation treatments on suicidality. This systematic review sought to examine the effects of various neuromodulation techniques on suicidality. Methods: A systematic review of the literature from 1940 to 2020 following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guideline was conducted. Any reported suicide-related outcome, including suicidal ideation, suicide intent, suicide attempt, completed suicide in reports were considered as a putative measure of treatment effect on suicidality. Results: The review identified 129 relevant studies. An exploratory analysis of a randomized controlled trial comparing the effects of sertraline and transcranial direct-current stimulation (tDCS) for treating depression reported a decrease in suicidal ideation favoring tDCS vs. placebo and tDCS combined with sertraline vs. placebo. Several studies reported an association between repetitive transcranial magnetic stimulation and improvements in suicidal ideation. In 12 of the studies, suicidality was the primary outcome, ten of which showed a significant improvement in suicidal ideation. Electroconvulsive therapy (ECT) and magnetic seizure therapy was also shown to be associated with lower suicidal ideation and completed suicide rates. There were 11 studies which suicidality was the primary outcome and seven of these showed an improvement in suicidal ideation or suicide intent and fewer suicide attempts or completed suicides in patients treated with ECT. There was limited literature focused on the potential protective effect of vagal nerve stimulation with respect to suicidal ideation. Data were mixed regarding the potential effects of deep brain stimulation on suicidality. Conclusions: Future prospective studies of neuromodulation that focus on the primary outcome of suicidality are urgently needed. Systematic Review Registration: https://www.crd.york.ac.uk/prospero/display_record.php?RecordID=125599, identifier: CRD42019125599.

Xiaoyaosan Alleviates Hippocampal Glutamate-Induced Toxicity in the CUMS Rats via NR2B and PI3K/Akt Signaling Pathway

Purpose: It is revealed that Xiaoyaosan could reduce glutamate level in the hippocampus of depressed rats, whose metabolism leads to the pathophysiology of depression. However, the underlying mechanism remains unclear. This study aims to explore the effect of Xiaoyaosan on glutamate metabolism, and how to regulate the excitatory injury caused by glutamate. Methods: Rats were induced by chronic unpredictable mild stress, then divided into control, vehicle (distilled water), Xiaoyaosan, fluoxetine, vehicle (DMSO), Xiaoyaosan + Ly294002 and Ly294002 groups. Ly294002 was microinjected into the lateral ventricular catheterization at 5 mM. Xiaoyaosan (2.224 g/kg) and fluoxetine (2.0 mg/kg) were orally administered for three weeks. The open field test (OFT), forced swimming test (FST), and sucrose preference test (SPT) were used to assess depressive behavior. The glutamate and corticosterone (CORT) levels were detected by ELISA. Western blot, immunochemistry or immunofluorescence were used to detect the expressions of NR2B, MAP2, PI3K and P-AKT/Akt in the hippocampal CA1 region. The mRNA level of MAP2, NR2B and PI3K were detected by RT-qPCR. Results: Compared to the rats in control group, body weight and food intake of CUMS rats was decreased. CUMS rats also showed depression-like behavior as well as down regulate the NR2B and PI3K/Akt signaling pathway. Xiaoyaosan treatments could increase food intake and body weight as well as improved time spent in the central area, total distance traveled in the OFT. Xiaoyaosan could also decrease the immobility time as well as increase the sucrose preference in SPT. Moreover, xiaoyaosan decreased the level of glutamate in the hippocampal CA1 region and serum CORT in CUMS rats. Furthermore, xiaoyaosan improved the expression of MAP2 as well as increased the expression of NR2B, PI3K and the P-AKT/AKT ratio in the hippocampal CA1 region in the CUMS rats. Conclusion: Xiaoyaosan treatment can exert the antidepressant effect by rescuing hippocampal neurons loss induced by the glutamate-mediated excitotoxicity in CUMS rats. The underlying pathway maybe through NR2B and PI3K/Akt signaling pathways. These results may suggest the potential of Xiaoyaosan in preventing the development of depression.

Metabolomic analysis of animal models of depression

BACKGROUND

Our understanding of the molecular mechanisms of depression remains largely unclear. Previous studies have shown that the prefrontal cortex (PFC) is among most important brain regions that exhibits metabolic changes in depression. A comprehensive analysis based on candidate metabolites in the PFC of animal models of depression will provide valuable information for understanding the pathogenic mechanism underlying depression.

METHODS

Candidate metabolites that are potentially involved in the metabolic changes of the PFC in animal models of depression were retrieved from the Metabolite Network of Depression Database. The significantly altered metabolic pathways were revealed by canonical pathway analysis, and the relationships among altered pathways were explored by pathway crosstalk analysis. Additionally, drug-associated pathways were investigated using drug-associated metabolite set enrichment analysis. The interrelationships among metabolites, proteins, and other molecules were analyzed by molecular network analysis.

RESULTS

Among 88 candidate metabolites, 87 altered canonical pathways were identified, and the top five ranked pathways were tRNA charging, the endocannabinoid neuronal synapse pathway, (S)-reticuline biosynthesis II, catecholamine biosynthesis, and GABA receptor signaling. Pathway crosstalk analysis revealed that these altered pathways were grouped into three interlinked modules involved in amino acid metabolism, nervous system signaling/neurotransmitters, and nucleotide metabolism. In the drug-associated metabolite set enrichment analysis, the main enriched drug pathways were opioid-related and antibiotic-related action pathways. Furthermore, the most significantly altered molecular network was involved in amino acid metabolism, molecular transport, and small molecule biochemistry.

CONCLUSIONS

This study provides important clues for the metabolic characteristics of the PFC in depression.

Opioid system is necessary but not sufficient for antidepressive actions of ketamine in rodents

Slow response to the standard treatment for depression increases suffering and risk of suicide. Ketamine, an N-methyl-d-aspartate (NMDA) receptor antagonist, can rapidly alleviate depressive symptoms and reduce suicidality, possibly by decreasing hyperactivity in the lateral habenula (LHb) brain nucleus. Here we find that in a rat model of human depression, opioid antagonists abolish the ability of ketamine to reduce the depression-like behavioral and LHb hyperactive cellular phenotypes. However, activation of opiate receptors alone is not sufficient to produce ketamine-like effects, nor does ketamine mimic the hedonic effects of an opiate, indicating that the opioid system does not mediate the actions of ketamine but rather is permissive. Thus, ketamine does not act as an opiate but its effects require both NMDA and opiate receptor signaling, suggesting that interactions between these two neurotransmitter systems are necessary to achieve an antidepressant effect.

The influence of ketamine's repeated treatment on brain topology does not suggest an antidepressant efficacy

As ketamine is increasingly used as an effective antidepressant with rapid action, sustaining its short-lived efficacy over a longer period of time using a schedule of repeated injections appears as an option. An open question is whether repeated and single administrations would affect convergent neurocircuits. We used a combination of one of the most robust animal models of depression with high-field neuroimaging to perform a whole-brain delineation of functional mechanisms underlying ketamine's effects. Rats from two genetic strains, depressive-like and resilient, received seven treatments of 10 mg/kg S-ketamine (N = 14 depressive-like, N = 11 resilient) or placebo (N = 12 depressive-like, N = 10 resilient) and underwent resting-state functional magnetic resonance imaging. Using graph theoretical models of brain networks, we compared effects of repeated ketamine with those of single administration from a separate dataset of our previous study. Compared to single treatment, repeated ketamine evoked strain-specific brain network randomization, resembling characteristics of the depressive-like strain and patients. Several affected regions belonged to the auditory, visual, and motor circuitry, hinting at possible cumulative side effects. Finally, when compared to saline, repeated ketamine affected only a few local topological properties and had no effects on global properties. In combination with the lack of clear differences compared to placebo, our findings point toward an inefficacy of ketamine's long-term administration on brain topology, making questionable the postulated effect of repeated administration and being consistent with the recently reported absence of repeated ketamine's antidepressant efficacy in several placebo-controlled studies.

Low-dose bisphenol A exposure impairs learning and memory ability with alterations of neuromorphology and neurotransmitters in rats

To investigate the developmental neurotoxicity of environmental bisphenol A (BPA) exposure for infants and children, postnatal rats were used as the animal model and were divided into four groups. Then, they were treated with different concentrations of BPA (i.e., 0, 0.5, 50, or 5000 μg/kg·bw/day of BPA as the control, low-, medium- and high-exposed group) from postnatal days 7 to 21. Y-maze tests, Golgi-Cox assays and liquid chromatography-tandem mass spectrometry (LC/MS/MS) were performed to test the changes of learning and memory ability, hippocampal neuromorphology and neurotransmitter levels, respectively. The results showed that the BPA-exposed rats, especially the low- and high-exposed rats, needed more trials and longer times to qualify for the learned criterion than the control rats. Additionally, rats after low- or high-exposure to BPA exhibited decreased DG dendritic complexity and reduced CA1 and DG dendritic spine densities in the hippocampus. Low-dosage BPA treatment could significantly alter the neurotransmitter contents in the hippocampus. In male rats, the levels of glutamic acid (Glu) and acetylcholine increased, while the 5-hydroxytryptamine (5-HT) and γ-aminobutyric acid (GABA) levels decreased, which lead to an unbalanced Glu/GABA ratio. However, in female rats, only 5-HT levels decreased. In conclusion, postnatal exposure to BPA could sex- and dose-dependently disrupt dendritic development and neurotransmitter homeostasis in the rat hippocampus. The impaired spatial learning and memory ability of rats induced by low-dose BPA is associated with both disrupted dendritic development and neurotransmitter homeostasis in the hippocampus.

Effect of Electroconvulsive Therapy on Medial Prefrontal γ-Aminobutyric Acid Among Schizophrenia Patients: A Proton Magnetic Resonance Spectroscopy Study

OBJECTIVE

Electroconvulsive therapy (ECT) has often been applied to augment antipsychotics for schizophrenia patients. However, the underpinning mechanism is still unclear. Previous studies of major depressive disorder reported an increase in γ-aminobutyric acid (GABA) after ECT. The present study investigated the effects of ECT on medial prefrontal GABA in schizophrenia using a proton magnetic resonance spectroscopy.

METHODS

Inpatients fulfilling the diagnostic criteria for schizophrenia (Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition) were assigned to 2 groups, ECT group (n = 14) receiving ECT plus antipsychotic drugs (APD) and drug group (n = 17) only receiving antipsychotic drugs. Medial prefrontal GABA+/Cr concentrations of all patients were measured with magnetic resonance spectroscopy at baseline and after 4-week treatment. Sex- and age-matched healthy comparisons (n = 19) were scanned at baseline.

RESULTS

γ-Aminobutyric acid level did not show a significant difference among 3 groups. However, when 2 patient groups were combined, their GABA level was significantly lower than that in healthy comparisons group. For schizophrenia patients, repeated measures analysis of variance revealed that both the group effect and group × time interaction were insignificant, but the time effect of baseline versus after treatment was significant. Exploratory post hoc paired t test found a significant increase of GABA only in ECT group, but not in drug group. No correlation was found between GABA change and clinical symptom improvement in either group.

CONCLUSIONS

γ-Aminobutyric acid level in the medial prefrontal lobe was reduced in schizophrenia patients. An increase in GABA concentration in the medial prefrontal cortex is more significantly associated with ECT plus antipsychotics than antipsychotics alone, possibly supporting the hypothesis of ECT augmentation for GABA mediated neural inhibition.

International Union of Basic and Clinical Pharmacology CIV: The Neurobiology of Treatment-resistant Depression: From Antidepressant Classifications to Novel Pharmacological Targets

Major depressive disorder is one of the most prevalent and life-threatening forms of mental illnesses and a major cause of morbidity worldwide. Currently available antidepressants are effective for most patients, although around 30% are considered treatment resistant (TRD), a condition that is associated with a significant impairment of cognitive function and poor quality of life. In this respect, the identification of the molecular mechanisms contributing to TRD represents an essential step for the design of novel and more efficacious drugs able to modify the clinical course of this disorder and increase remission rates in clinical practice. New insights into the neurobiology of TRD have shed light on the role of a number of different mechanisms, including the glutamatergic system, immune/inflammatory systems, neurotrophin function, and epigenetics. Advances in drug discovery processes in TRD have also influenced the classification of antidepressant drugs and novel classifications are available, such as the neuroscience-based nomenclature that can incorporate such advances in drug development for TRD. This review aims to provide an up-to-date description of key mechanisms in TRD and describe current therapeutic strategies for TRD before examining novel approaches that may ultimately address important neurobiological mechanisms not targeted by currently available antidepressants. All in all, we suggest that drug targeting different neurobiological systems should be able to restore normal function but must also promote resilience to reduce the long-term vulnerability to recurrent depressive episodes.

The "Forgotten" Treatment of Alcohol Withdrawal Delirium With Electroconvulsive Therapy: Successful Use in a Very Prolonged and Severe Case

OBJECTIVE

Alcohol withdrawal delirium (AWD) is a notorious complication in alcohol withdrawal. Usually, the symptomatic treatment is efficacious; however, some patients show treatment resistance or a prolonged course of AWD.

METHOD

We report the case of a patient with a prolonged and severest form of AWD. Even 11 weeks after admission, he received approximately 100 mg diazepam per week to manage the symptoms of withdrawal delirium.

RESULTS

A treatment course of electroconvulsive therapy was initiated, which allowed a complete tapering off of benzodiazepines during electroconvulsive therapy without adverse effects.

CONCLUSIONS

The reported case might contribute to alternative approaches reserved for severest forms of prolonged AWD.

Lateral habenula perturbation reduces default-mode network connectivity in a rat model of depression

Hyperconnectivity of the default-mode network (DMN) is one of the most widely replicated neuroimaging findings in major depressive disorder (MDD). Further, there is growing evidence for a central role of the lateral habenula (LHb) in the pathophysiology of MDD. There is preliminary neuroimaging evidence linking LHb and the DMN, but no causal relationship has been shown to date. We combined optogenetics and functional magnetic resonance imaging (fMRI), to establish a causal relationship, using an animal model of treatment-resistant depression, namely Negative Cognitive State rats. First, an inhibitory light-sensitive ion channel was introduced into the LHb by viral transduction. Subsequently, laser stimulation was performed during fMRI acquisition on a 9.4 Tesla animal scanner. Neural activity and connectivity were assessed, before, during and after laser stimulation. We observed a connectivity decrease in the DMN following laser-induced LHb perturbation. Our data indicate a causal link between LHb downregulation and reduction in DMN connectivity. These findings may advance our mechanistic understanding of LHb inhibition, which had previously been identified as a promising therapeutic principle, especially for treatment-resistant depression.

Antidepressant-like effects of translocator protein (18 kDa) ligand ZBD-2 in mouse models of postpartum depression

The 18 kDa translocator protein (TSPO) is primarily localized in the outer mitochondrial membrane of steroid-synthesizing cells in the central and peripheral nervous systems. One of the protein’s main functions is transporting substrate cholesterol into the mitochondria in a prerequisite process for steroid synthesis. Clinical trials have indicated that TSPO ligands might be valuable in treating some neuropathies and psychopathies. However, limited information is known about the role of TSPO in postpartum depression (PPD). The TSPO ligand ZBD-2, a derivative of XBD173, was synthesized in our laboratory. Behavioral tests, enzyme linked immunosorbent assay, and Western blot were employed to evaluate ZBD-2’s efficacy against PPD and to elucidate the potential underlying molecular mechanism. The TSPO levels significantly decreased in the basolateral amygdala of PPD models. After treatment for 2 weeks, ZBD-2 alleviated depression-like behaviors and enhanced the TSPO level in a PPD animal model. The underlying mechanisms of ZBD-2 were related to regulate the hypothalamic-pituitary-adrenal axis, enhance 5-HT and BDNF secretion, and maintain the excitatory and inhibitory synaptic protein expression to normal levels. Our results directly confirm that ZBD-2 exerts a therapeutic effect on PPD, which provides a new target for anti-PPD drug development.

How Electroconvulsive Therapy Works?: Understanding the Neurobiological Mechanisms

Electroconvulsive therapy (ECT) is a time tested treatment modality for the management of various psychiatric disorders. There have been a lot of modifications in the techniques of delivering ECT over decades. Despite lots of criticisms encountered, ECT has still been used commonly in clinical practice due to its safety and efficacy. Research evidences found multiple neuro-biological mechanisms for the therapeutic effect of ECT. ECT brings about various neuro-physiological as well as neuro-chemical changes in the macro- and micro-environment of the brain. Diverse changes involving expression of genes, functional connectivity, neurochemicals, permeability of blood-brain-barrier, alteration in immune system has been suggested to be responsible for the therapeutic effects of ECT. This article reviews different neurobiological mechanisms responsible for the therapeutic efficacy of ECT.

Alcohol Use Disorder as a Possible Predictor of Electroconvulsive Therapy Response

INTRODUCTION

Two rapidly acting antidepressive treatment forms, namely, electroconvulsive therapy (ECT) and ketamine, possibly share a common mechanism of action primarily involving alterations of neurotransmission (glutamate and γ-aminobutyric acid levels). Because patients receiving ketamine and with a coexistent family history of an alcohol use disorder (AUD) seem to benefit from consistent and longer lasting antidepressive effects, we hypothesized better treatment response in ECT patients with an own history or a family history of an AUD.

METHOD

One hundred forty-one psychiatric inpatients with a major depressive episode, who were treated with ECT, were enrolled into this retrospective study. Age, sex, family or personal history of alcohol or benzodiazepine use disorder, ECT response data, and ECT treatment-related data were collected and analyzed with ordinal logistic regression and Fisher exact tests.

RESULTS

Twenty-one percent of all patients had their own history of an AUD, 11% had their own history of a benzodiazepine use disorder, and 11% reported on a positive family history of alcohol or benzodiazepine use disorder. The logistic regression analyses revealed that only patient's own history of an AUD predicts a better ECT response (P = 0.031; odds ratio, 2.1; Fisher exact test, P = 0.006).

CONCLUSIONS

Within the limitations of a retrospective study, a history of an AUD seems to be a positive predictor for an ECT response in patients experiencing a major depressive episode, which has not been found in 2 earlier studies. Findings are in line with neurobiological hypotheses of excitatory/inhibitory neurotransmitter changes with ketamine and ECT.

Brain network reorganization differs in response to stress in rats genetically predisposed to depression and stress-resilient rats

Treatment-resistant depression (TRD) remains a pressing clinical problem. Optimizing treatment requires better definition of the specificity of the involved brain circuits. The rat strain bred for negative cognitive state (NC) represents a genetic animal model of TRD with high face, construct and predictive validity. Vice versa, the positive cognitive state (PC) strain represents a stress-resilient phenotype. Although NC rats show depressive-like behavior, some symptoms such as anhedonia require an external trigger, i.e. a stressful event, which is similar to humans when stressful event induces a depressive episode in genetically predisposed individuals (gene-environment interaction). We aimed to distinguish neurobiological predisposition from the depressogenic pathology at the level of brain-network reorganization. For this purpose, resting-state functional magnetic resonance imaging time series were acquired at 9.4 Tesla scanner in NC (N=11) and PC (N=7) rats before and after stressful event. We used a graph theory analytical approach to calculate the brain-network global and local properties. There was no difference in the global characteristics between the strains. At the local level, the response in the risk strain was characterized with an increased internodal role and reduced local clustering and efficiency of the anterior cingulate cortex (ACC) and prelimbic cortex compared to the stress-resilient strain. We suggest that the increased internodal role of these prefrontal regions could be due to the enhancement of some of their long-range connections, given their connectivity with the amygdala and other default-mode-like network hubs, which could create a bias to attend to negative information characteristic for depression.

Testing different paradigms to optimize antidepressant deep brain stimulation in different rat models of depression

Deep brain stimulation (DBS) of several targets induces beneficial responses in approximately 60% of patients suffering from treatment-resistant depression (TRD). The remaining 40% indicate that these stimulation sites do not bear therapeutic relevance for all TRD patients and consequently DBS-targets should be selected according to individual symptom profiles. We here used two animal models of depression known to have different genetic backgrounds and behavioral responses: the therapy-responsive Flinders sensitive line (FSL) and the therapy-refractory congenitally learned helpless rats (cLH) to study symptom-specific DBS effects i) of different brain sites ii) at different stimulation parameters, and iii) at different expressions of the disease. Sham-stimulation/DBS was applied chronic-intermittently or chronic-continuously to either the ventromedial prefrontal cortex (vmPFC, rodent equivalent to subgenual cingulate), nucleus accumbens (Nacc) or subthalamic nucleus (STN), and effects were studied on different depression-associated behaviors, i.e. anhedonia, immobility/behavioral despair and learned helplessness. Biochemical substrates of behaviorally effective versus ineffective DBS were analyzed using in-vivo microdialysis and post-mortem high-performance liquid chromatography (HPLC). We found that i) vmPFC-DBS outperforms Nacc-DBS, ii) STN-DBS increases depressive states, iii) chronic-continuous DBS does not add benefits compared to chronic-intermittent DBS, iv) DBS-efficacy depends on the disease expression modeled and iv) antidepressant DBS is associated with an increase in serotonin turnover alongside site-specific reductions in serotonin contents. The reported limited effectiveness of vmPFC DBS suggests that future research may consider the specific disease expression, investigation of different DBS-targets and alternative parameter settings.

Oxidative Stress Implications in the Affective Disorders: Main Biomarkers, Animal Models Relevance, Genetic Perspectives, and Antioxidant Approaches

The correlation between the affective disorders and the almost ubiquitous pathological oxidative stress can be described in a multifactorial way, as an important mechanism of central nervous system impairment. Whether the obvious changes which occur in oxidative balance of the affective disorders are a part of the constitutive mechanism or a collateral effect yet remains as an interesting question. However it is now clear that oxidative stress is a component of these disorders, being characterized by different aspects in a disease-dependent manner. Still, there are a lot of controversies regarding the relevance of the oxidative stress status in most of the affective disorders and despite the fact that most of the studies are showing that the affective disorders development can be correlated to increased oxidative levels, there are various studies stating that oxidative stress is not linked with the mood changing tendencies. Thus, in this minireview we decided to describe the way in which oxidative stress is involved in the affective disorders development, by focusing on the main oxidative stress markers that could be used mechanistically and therapeutically in these deficiencies, the genetic perspectives, some antioxidant approaches, and the relevance of some animal models studies in this context.

Chronic stress, hippocampus and parvalbumin-positive interneurons: what do we know so far?

The hippocampus is a brain structure involved in the regulation of hypothalamic-pituitary-adrenal (HPA) axis and stress response. It plays an important role in the formation of declarative, spatial and contextual memory, as well as in the processing of emotional information. As a part of the limbic system, it is a very susceptible structure towards the effects of various stressors. The molecular mechanisms of structural and functional alternations that occur in the hippocampus under chronic stress imply an increased level of circulating glucocorticoids (GCs), which is an HPA axis response to stress. Certain data show that changes induced by chronic stress may be independent from the GCs levels, opening the possibility of existence of other poorly explored mechanisms and pathways through which stressors act. The hippocampal GABAergic parvalbumin-positive (PV+) interneurons represent an especially vulnerable population of neurons in chronic stress, which may be of key importance in the development of mood disorders. However, cellular and molecular hippocampal changes that arise as a consequence of chronic stress still represent a large and unexplored area. This review discusses the current knowledge about the PV+ interneurons of the hippocampus and the influence of chronic stress on this intriguing population of neurons.

Influence of regional cerebral blood volume on voxel-based morphometry

The investigation of structural brain alterations is one focus in research of brain diseases like depression. Voxel-based morphometry (VBM) based on high-resolution 3D MRI images is a widely used non-invasive tool for such investigations. However, the result of VBM might be sensitive to local physiological parameters such as regional cerebral blood volume (rCBV) changes. In order to investigate whether rCBV changes may contribute to variation in VBM, we performed analyses in a study with the congenital learned helplessness (cLH) model for long-term findings. The 3D structural and rCBV data were acquired with T2 -weighted rapid acquisition with relaxation enhancement (RARE) pulse sequences. The group effects were determined by standard statistical parametric mapping (SPM) and biological parametric mapping (BPM) and examined further using atlas-based regions. In our genetic animal model of depression, we found co-occurrence of differences in gray matter volume and rCBV, while there was no evidence of significant interaction between both. However, the multimodal analysis showed similar gray matter differences compared with the standard VBM approach. Our data corroborate the idea that two group VBM differences might not be influenced by rCBV differences in genetically different strains. Copyright © 2016 John Wiley & Sons, Ltd.

Influence of GRIK4 genetic variants on the electroconvulsive therapy response

Several lines of evidence have shown the involvement of the glutamatergic system in the function of electroconvulsive therapy (ECT). In particular, patients with treatment resistant depression (TRD) and chronic depression have lower levels of glutamate/glutamine than controls, and ECT can reverse this deficit. Genetic factors might contribute to modulating the mechanisms underlying ECT. This study aimed to evaluate the relationship between three polymorphisms (rs1954787, rs4936554 and rs11218030) of the glutamate receptor ionotropic kainate 4 (GRIK4) gene and responsiveness to ECT treatment in a sample of one hundred individuals, TRD or depressive Bipolar Disorder patients resistant to pharmacological treatments. The results revealed that GRIK4 variants were significantly associated with the response to ECT. In particular, we found that patients carrying the G allele of the GRIK4 rs11218030 had a significantly poorer response to ECT (p=2.71×10(-4)), showing five times the risk of relapse after ECT compared to the AA homozygotes. Analogously, patients carrying the GG rs1954787 genotype and rs4936554A allele carriers presented a double risk of lack of response after ECT (p=0.013 and p=0.040, respectively). In conclusion, the current study provides new evidence, indicating that some GRIK4 variants modulate the response to ECT in patients with depression resistant to treatment, suggesting a role for kainate receptor modulation.

Animal models of major depression and their clinical implications

Major depressive disorder is a common, complex, and potentially life-threatening mental disorder that imposes a severe social and economic burden worldwide. Over the years, numerous animal models have been established to elucidate pathophysiology that underlies depression and to test novel antidepressant treatment strategies. Despite these substantial efforts, the animal models available currently are of limited utility for these purposes, probably because none of the models mimics this complex disorder fully. It is presumable that psychiatric illnesses, such as affective disorders, are related to the complexity of the human brain. Here, we summarize the animal models that are used most commonly for depression, and discuss their advantages and limitations. We discuss genetic models, including the recently developed optogenetic tools and the stress models, such as the social stress, chronic mild stress, learned helplessness, and early-life stress paradigms. Moreover, we summarize briefly the olfactory bulbectomy model, as well as models that are based on pharmacological manipulations and disruption of the circadian rhythm. Finally, we highlight common misinterpretations and often-neglected important issues in this field.

Treatment-resistant depression: are animal models of depression fit for purpose?

BACKGROUND

Resistance to antidepressant drug treatment remains a major health problem. Animal models of depression are efficient in detecting effective treatments but have done little to increase the reach of antidepressant drugs. This may be because most animal models of depression target the reversal of stress-induced behavioural change, whereas treatment-resistant depression is typically associated with risk factors that predispose to the precipitation of depressive episodes by relatively low levels of stress. Therefore, the search for treatments for resistant depression may require models that incorporate predisposing factors leading to heightened stress responsiveness.

METHOD

Using a diathesis-stress framework, we review developmental, genetic and genomic models against four criteria: (i) increased sensitivity to stress precipitation of a depressive behavioural phenotype, (ii) resistance to chronic treatment with conventional antidepressants, (iii) a good response to novel modes of antidepressant treatment (e.g. ketamine; deep brain stimulation) that are reported to be effective in treatment-resistant depression and (iv) a parallel to a known clinical risk factor.

RESULTS

We identify 18 models that may have some potential. All require further validation. Currently, the most promising are the Wistar-Kyoto (WKY) and congenital learned helplessness (cLH) rat strains, the high anxiety behaviour (HAB) mouse strain and the CB1 receptor knockout and OCT2 null mutant mouse strains.

CONCLUSION

Further development is needed to validate models of antidepressant resistance that are fit for purpose. The criteria used in this review may provide a helpful framework to guide research in this area.

Correlation of maternal abuse during pregnancy with infant temperament and development

OBJECTIVE

To investigate the effects of domestic violence (DV) against pregnant women on their infant's development in China.

DESIGN

247 mothers were interviewed using the Chinese version of the Abuse Assessment Screen, and all participants underwent postnatal assessment with the Edinburgh Postpartum Depression Scale (EDPS). Plasma glutamate (Glu), γ-aminobutyric acid (GABA) and cortisol levels of the neonates were measured. After a 10-month follow-up, the infants were assessed using the Revised Infant Temperament Questionnaire (RITQ) and Bayley Scales of Infant Development (BSID).

RESULTS

86 infants of abused mothers (DV group) and 137 infants of non-abused mothers (non-DV group) completed the 10-month follow-up. Neonate levels of plasma Glu, GABA and cortisol were significantly higher in the DV group than in the non-DV group. Scores for the temperament factors, rhythmicity, approach/withdrawal, mood, distractibility and persistence, of the RITQ were rated significantly higher, and results for the Psychomotor Development Index (PDI) of the BSID were significantly lower in the DV group than in the non-DV group at 10 months. After adjustment for the EPDS as a covariate, only distractibility of the RITQ showed a statistically significant difference between the two groups. In correlation analysis, infant mood correlated significantly with levels of plasma Glu (β=0.2345) and GABA (β=0.2554), whether or not the EPDS scores were adjusted. Infant persistence and threshold of stimuli scores did not correlate significantly with DV during pregnancy after adjustment for the EPDS.

CONCLUSIONS

DV against pregnant women may be associated with impaired temperament and development in their infants.

[Ketamine as anesthetic agent in electroconvulsion therapy]

BACKGROUND

Electroconvulsive therapy (ECT) is a well-established, safe and effective treatment for severe psychiatric disorders. Ketamine is known as a core medication in anesthesiology and has recently gained interest in ECT practice as there are three potential advantages: (1) ketamine has no anticonvulsive actions, (2) according to recent studies ketamine could possess a unique intrinsic antidepressive potential and (3) ketamine may exhibit neuroprotective properties, which again might reduce the risk of cognitive side effects associated with ECT.

OBJECTIVES

The use of ketamine in psychiatric patients has been controversially discussed due to its dose-dependent psychotropic and psychotomimetic effects. This study was carried out to test if the occurrence of side effects is comparable and if seizure quality is better with ketamine when compared to thiopental.

MATERIAL AND METHODS

This retrospective study analyzed a total of 199 patients who received ketamine anesthesia for a total of 2178 ECT sessions. This cohort was compared to patients who were treated with thiopental for 1004 ECT sessions.

RESULTS AND DISCUSSION

A repeated measurement multiple logistic regression analysis revealed significant advantages in the ketamine group for seizure concordance and postictal suppression (both are surrogates for central inhibition). S-ketamin also necessitated the use of a higher dose of urapidil and a higher maximum postictal heart frequency. Clinically relevant psychiatric side effects were rare in both groups. No psychiatric side effects occurred in the subgroup of patients with schizophrenia (ketamine: n = 30). The mean dose of S-ketamine used increased in the first years but stabilized at 63 mg per patient in 2014. From these experiences it can be concluded that S-ketamine can be recommended at least as a safe alternative to barbiturates.

Ketamine reverses stress-induced depression-like behavior and increased GABA levels in the anterior cingulate: an 11.7 T 1H-MRS study in rats

Gamma-aminobutyric acid (GABA) is the major inhibitory amino acid neurotransmitter in the brain and is primarily responsible for modulating excitatory tone. Clinical neuroimaging studies show decreased GABA levels in the anterior cingulate of patients with mood disorders, including major depressive disorder. Chronic unpredictable stress (CUS) is an animal model thought to mimic the stressful events that may precipitate clinical depression in humans. In this study male Sprague-Dawley rats were subjected to a modified CUS paradigm that used a random pattern of unpredictable stressors twice daily for 10 days to explore the early developmental stages of depression-like endophenotypes. Control rats were handled daily for 10 days. Some rats from each treatment group received an injection of ketamine (40 mg/kg) after the final stressor. One day following the final stressor rats were tested for behavioral effects in the forced swim test and then euthanized to collect trunk blood and anterior cingulate brain samples. GABA levels were measured in anterior cingulate samples ex vivo using proton magnetic resonance spectroscopy ((1)H-MRS) at 11.7 T. Animals subjected to CUS had lower body weights, higher levels of blood corticosterone, and increased immobility in the forced swim test; all of which suggest that the stress paradigm induced a depression-like phenotype. GABA levels in the anterior cingulate were significantly increased in the stressed animals compared to controls. Administration of ketamine on the last day of treatment blunted the depression-like behavior and increased GABA levels in the anterior cingulate following CUS. These data indicate that stress disrupts GABAergic signaling, which may over time lead to symptoms of depression and ultimately lower basal levels of cortical (1)H-MRS GABA that are seen in humans with depression. Furthermore, the data suggests that ketamine modulates cortical GABA levels as a mechanism of its antidepressant activity.

Functionally altered neurocircuits in a rat model of treatment-resistant depression show prominent role of the habenula

Treatment-resistant depression (TRD) remains a pressing clinical problem. Optimizing treatment requires better definition of the function and specificity of the brain circuits involved. To investigate disease-related alterations of brain function we used a genetic animal model of TRD, congenital learned helplessness (cLH), and functional magnetic resonance imaging as a translational tool. High-resolution regional cerebral blood volume (rCBV) and resting-state functional connectivity measurements were acquired at 9.4T to determine regional dysfunction and interactions that could serve as vulnerability markers for TRD. Effects of cLH on rCBV were determined by statistical parametric mapping using 35 atlas-based regions of interest. Effects of cLH on functional connectivity were assessed by seed region analyses. Significant bilateral rCBV reductions were observed in the lateral habenula, dentate gyrus and subiculum of cLH rats. In contrast, focal bilateral increase in rCBV was observed in the bed nucleus of stria terminalis (BNST), a component of the habenular neurocircuitry. Functional connectivity was primarily enhanced in cLH rats, most notably with respect to serotonergic projections from the dorsal raphe nucleus to the forebrain, within the hippocampal-prefrontal network and between the BNST and lateral frontal regions. Dysregulation of neurocircuitry similar to that observed in depressed patients was detected in cLH rats, supporting the validity of the TRD model and suitability of high-field fMRI as a translational technology to detect and monitor vulnerability markers. Our findings also define neurocircuits that can be studied for TRD treatment in patients, and could be employed for translational research in rodent models.

A review of longitudinal electroconvulsive therapy: neuroimaging investigations

Electroconvulsive therapy (ECT) is the most effective treatment for a depressive episode but the mechanism of action and neural correlates of response are poorly understood. Different theories have suggested that anticonvulsant properties or neurotrophic effects are related to the unique mechanism of action of ECT. This review assessed longitudinal imaging investigations (both structural and functional) associated with ECT response published from 2002 to August 2013. We identified 26 investigations that used a variety of different imaging modalities and data analysis methods. Despite these methodological differences, we summarized the major findings of each investigation and identified common patterns that exist across multiple investigations. The ECT response is associated with decreased frontal perfusion, metabolism, and functional connectivity and increased volume and neuronal chemical metabolites. The general collective of longitudinal neuroimaging investigations support both the anticonvulsant and the neurotrophic effects of ECT. We propose a conceptual framework that integrates these seemingly contradictory hypotheses.

Differential levels of brain amino acids in rat models presenting learned helplessness or non-learned helplessness

RATIONALE

Glutamatergic and γ-aminobutyric acid (GABA)ergic abnormalities have recently been proposed to contribute to depression. The learned helplessness (LH) paradigm produces a reliable animal model of depression that expresses a deficit in escape behavior (LH model); an alternative phenotype that does not exhibit LH is a model of resilience to depression (non-LH model).

OBJECTIVES

We measured the contents of amino acids in the brain to investigate the mechanisms involved in the pathology of depression.

METHODS

LH and non-LH models were subjected to inescapable electric footshocks at random intervals following a conditioned avoidance test to determine acquirement of predicted escape deficits. Tissue amino acid contents in eight brain regions were measured via high-performance liquid chromatography.

RESULTS

The non-LH model showed increased GABA levels in the dentate gyrus and nucleus accumbens and increased glutamine levels in the dentate gyrus and the orbitofrontal cortex. The LH model had reduced glutamine levels in the medial prefrontal cortex. Changes in the ratios of GABA, glutamine, and glutamate were detected in the non-LH model, but not in the LH model. Reductions in threonine levels occurred in the medial prefrontal cortex in both models, whereas elevated alanine levels were detected in the medial prefrontal cortex in non-LH animals.

CONCLUSIONS

The present study demonstrates region-specific compensatory elevations in GABA levels in the dentate gyrus and nucleus accumbens of non-LH animals, supporting the implication of the GABAergic system in the recovery of depression.

Electroconvulsive Treatment: Hypotheses about Mechanisms of Action

No consensus has been reached on the mode of action of electroconvulsive treatment (ECT). We suggest that two features may aid in the delineation of the involved mechanisms. First, when effective, ECT would be likely to affect brain functions that are typically altered in its primary recipient group, people with severe depression. Central among these are the frontal and temporal lobes, the hypothalamus-pituitary-adrenal (HPA) stress axis, and the mesocorticolimbic dopamine system. Second, the involved mechanisms should be affected for a time period that matches the average endurance of clinical effects, which is indicated to be several days to a few weeks. To identify effects upon frontal and temporal lobe functioning we reviewed human studies using EEG, PET, SPECT, and fMRI. Effects upon the HPA axis and the dopamine system were assessed by reviewing both human and animal studies. The EEG studies indicate that ECT decelerates neural activity in the frontal and temporal lobes (increased delta and theta wave activity) for weeks to months. Comparable findings are reported from PET and SPECT studies, with reduced cerebral blood flow (functional deactivation) for weeks to months after treatment. The EEG deceleration and functional deactivation following ECT are statistically associated with reduced depression scores. FMRI studies indicate that ECT flattens the pattern of activation and deactivation that is associated with cognitive task performance and alters cortical functional connectivity in the ultra slow frequency range. A common finding from human and animal studies is that ECT acutely activates both the HPA axis and the dopamine system. In considering this evidence, we hypothesize that ECT affects the brain in a similar manner as severe stress or brain trauma which activates the HPA axis and the dopamine system and may compromise frontotemporal functions.

Synaptic abnormalities in the infralimbic cortex of a model of congenital depression

Multiple lines of evidence suggest that disturbances in excitatory transmission contribute to depression. Whether these defects involve the number, size, or composition of glutamatergic contacts is unclear. This study used recently introduced procedures for fluorescence deconvolution tomography in a well-studied rat model of congenital depression to characterize excitatory synapses in layer I of infralimbic cortex, a region involved in mood disorders, and of primary somatosensory cortex. Three groups were studied: (1) rats bred for learned helplessness (cLH); (2) rats resistant to learned helplessness (cNLH); and (3) control Sprague Dawley rats. In fields within infralimbic cortex, cLH rats had the same numerical density of synapses, immunolabeled for either the postsynaptic density (PSD) marker PSD95 or the presynaptic protein synaptophysin, as controls. However, PSD95 immunolabeling intensities were substantially lower in cLH rats, as were numerical densities of synapse-sized clusters of the AMPA receptor subunit GluA1. Similar but less pronounced differences (comparable numerical densities but reduced immunolabeling intensity for PSD95) were found in the somatosensory cortex. In contrast, non-helpless rats had 25% more PSDs than either cLH or control rats without any increase in synaptophysin-labeled terminal frequency. Compared with controls, both cLH and cNLH rats had fewer GABAergic contacts. These results indicate that congenital tendencies that increase or decrease depression-like behavior differentially affect excitatory synapses.

Progress in understanding mood disorders: optogenetic dissection of neural circuits

Major depression is characterized by a cluster of symptoms that includes hopelessness, low mood, feelings of worthlessness and inability to experience pleasure. The lifetime prevalence of major depression approaches 20%, yet current treatments are often inadequate both because of associated side effects and because they are ineffective for many people. In basic research, animal models are often used to study depression. Typically, experimental animals are exposed to acute or chronic stress to generate a variety of depression-like symptoms. Despite its clinical importance, very little is known about the cellular and neural circuits that mediate these symptoms. Recent advances in circuit-targeted approaches have provided new opportunities to study the neuropathology of mood disorders such as depression and anxiety. We review recent progress and highlight some studies that have begun tracing a functional neuronal circuit diagram that may prove essential in establishing novel treatment strategies in mood disorders. First, we shed light on the complexity of mesocorticolimbic dopamine (DA) responses to stress by discussing two recent studies reporting that optogenetic activation of midbrain DA neurons can induce or reverse depression-related behaviors. Second, we describe the role of the lateral habenula circuitry in the pathophysiology of depression. Finally, we discuss how the prefrontal cortex controls limbic and neuromodulatory circuits in mood disorders.

Behavioral and neurobiological effects of deep brain stimulation in a mouse model of high anxiety- and depression-like behavior

Increasing evidence suggests that high-frequency deep brain stimulation of the nucleus accumbens (NAcb-DBS) may represent a novel therapeutic strategy for individuals suffering from treatment-resistant depression, although the underlying mechanisms of action remain largely unknown. In this study, using a unique mouse model of enhanced depression- and anxiety-like behavior (HAB), we investigated behavioral and neurobiological effects of NAcb-DBS. HAB mice either underwent chronic treatment with one of three different selective serotonin reuptake inhibitors (SSRIs) or received NAcb-DBS for 1 h per day for 7 consecutive days. Animals were tested in established paradigms revealing depression- and anxiety-related behaviors. The enhanced depression-like behavior of HAB mice was not influenced by chronic SSRI treatment. In contrast, repeated, but not single, NAcb-DBS induced robust antidepressant and anxiolytic responses in HAB animals, while these behaviors remained unaffected in normal depression/anxiety animals (NAB), suggesting a preferential effect of NAcb-DBS on pathophysiologically deranged systems. NAcb-DBS caused a modulation of challenge-induced activity in various stress- and depression-related brain regions, including an increase in c-Fos expression in the dentate gyrus of the hippocampus and enhanced hippocampal neurogenesis in HABs. Taken together, these findings show that the normalization of the pathophysiologically enhanced, SSRI-insensitive depression-like behavior by repeated NAcb-DBS was associated with the reversal of reported aberrant brain activity and impaired adult neurogenesis in HAB mice, indicating that NAcb-DBS affects neuronal activity as well as plasticity in a defined, mood-associated network. Thus, HAB mice may represent a clinically relevant model for elucidating the neurobiological correlates of NAcb-DBS.

Where have I been? Where should I go? Spatial working memory on a radial arm maze in a rat model of depression

Disturbances in cognitive functioning are among the most debilitating problems experienced by patients with major depression. Investigations of these deficits in animals help to extend and refine our understanding of human emotional disorder, while at the same time providing valid tools to study higher executive functions in animals. We employ the "learned helplessness" genetic rat model of depression in studying working memory using an eight arm radial maze procedure with temporal delay. This so-called delayed spatial win-shift task consists of three phases, training, delay and test, requiring rats to hold information on-line across a retention interval and making choices based on this information in the test phase. According to a 2×2 factorial design, working memory performance of thirty-one congenitally helpless (cLH) and non-helpless (cNLH) rats was tested on eighteen trials, additionally imposing two different delay durations, 30 s and 15 min, respectively. While not observing a general cognitive deficit in cLH rats, the delay length greatly influenced maze performance. Notably, performance was most impaired in cLH rats tested with the shorter 30 s delay, suggesting a stress-related disruption of attentional processes in rats that are more sensitive to stress. Our study provides direct animal homologues of clinically important measures in human research, and contributes to the non-invasive assessment of cognitive deficits associated with depression.

Selective breeding for helplessness in rats alters the metabolic profile of the hippocampus and frontal cortex: a 1H-MRS study at 9.4 T

In humans metabolic changes, particularly in frontal areas of the brain, accompany depressive disorders, but few studies were conducted in animal models of depression. We used hydrogen-1 magnetic resonance spectroscopy at 9.4 T to measure the metabolic profiles of the hippocampus and frontal cortex in congenital learned helpless (cLH) and wild-type (WT) rats. The learned helplessness model of depression exposes animals to uncontrollable stress to induce changes in emotion, cognition and behaviour, but cLH rats were selectively bred to show changes in behaviour even without exposure to uncontrollable stress. Experimentally naive male 8- to 10-wk-old cLH (n = 10) and WT rats (n = 22) underwent spectroscopy and were exposed to uncontrollable stress 1 wk after the scan. We found that cLH compared to WT rats had lower levels of glutamate in the hippocampus and lower levels of choline-containing compounds in the hippocampus and frontal cortex, but higher levels of taurine and phosphocreatine in these regions, pointing to compensatory efforts of the brain to reduce excitotoxic potential and to increase neuroprotection and energy, possibly as a result of cellular stress and damage. The reduction in choline-containing phospholipids might represent a source or correlate of such stress. Overall, the results indicate that metabolic abnormalities are present in animals with a predisposition to helplessness even without exposure to explicit stress and may help identify non-invasive biomarkers in individuals who are prone to depression.

Increase of hippocampal glutamate after electroconvulsive treatment: a quantitative proton MR spectroscopy study at 9.4 T in an animal model of depression

OBJECTIVES

Recent evidence suggests that alterations in hippocampal glutamate and γ-aminobutyric acid (GABA) are associated with the pathomechanism of depression and treatment effects of electroconvulsive therapy (ECT). Thus, proton magnetic resonance spectroscopy (¹H MRS) at a 9.4 T animal system seems a promising tool to study underlying mechanisms since it allows for an accurate quantification of metabolites with distinction of glutamate, GABA and glutamine, as well as separation of taurine from choline.

METHODS

A well-validated animal model of treatment resistant depression (congenital learned helpless rats = cLH) was investigated by hippocampal in vivo ¹H MRS with and without a 1-week course of electroconvulsive shocks (ECS), an animal model of ECT, and compared to wild type (WT) animals, while saline and clomipramine injections served as additional controls.

RESULTS

Untreated cLH rats showed significantly lower glucose and higher taurine concentrations compared to WT animals. Besides alterations on these metabolites, ECS increased glutamate in WT and cLH and choline in cLH rats. Moreover, correlations between glutamate and GABA concentrations with learned helpless behaviour were revealed.

CONCLUSIONS

These findings support the idea of disordered hippocampal metabolism in an animal model of treatment resistant depression and suggest an early impact of ECS on MR-detectable hippocampal metabolites.

MRI in animal models of psychiatric disorders

Here we describe MRI and (1)H MRS protocols for the investigation of animal models (mainly mice and rats) of psychiatric disorders. The introduction provides general findings from brain imaging studies in patients with psychiatric diseases and refers to general rules regarding the use of animal models in research. The methods section includes a selection of basic 9.4 T MRI and MRS protocols applicable for the investigation of animal models of psychiatric disorders (T1W, T2W, FLAIR, (1)H MRS). The notes section discusses in detail a series of factors that can influence the outcome of the experiment: from animal handling, stress-triggering aspects, and experimental design-related factors to technical aspects that affect T (1) and T (2) measurements.

Hippocampal GABAergic dysfunction in a rat chronic mild stress model of depression

In major depression, one line of research indicates that a dysfunctional GABAergic inhibitory system is linked to the appearance of depressive symptoms. However, as the mechanistic details of such GABAergic deficit are largely unknown, we undertook a functional investigation of the GABAergic system in the rat chronic mild stress model of depression. Adult rats were exposed to an eight-week long stress protocol leading to anhedonic-like behavior. In hippocampal brain slices, phasic, and tonic GABA(A) receptor-mediated currents in dentate gyrus granule cells were examined using patch-clamp recordings. In granule cells, the frequency of spontaneous inhibitory postsynaptic currents (sIPSCs) was reduced to 41% in anhedonic-like rats, which was associated with a reduced probability of evoked GABA release. Using immunohistochemical analysis, there was no change in the number of parvalbumin-positive interneurons in the dentate gyrus. Notably, we observed a 60% increase in THIP-activated tonic GABA(A) mediated current in anhedonic-like rats, suggesting an upregulation of extrasynaptic GABA(A) receptors. Finally, five weeks treatment with the antidepressant escitalopram partially reversed the sIPSCs frequency. In summary, we have revealed a hippocampal dysfunction in the GABAergic system in the chronic mild stress model of depression in rats, caused by a reduction in action potential-dependent GABA release. Since the function of the GABAergic system was improved by antidepressant treatment, in parallel with behavioral read outs, it suggests a role of the GABAergic system in the pathophysiology of depression.

Magnetic resonance imaging and spectroscopy reveal differential hippocampal changes in anhedonic and resilient subtypes of the chronic mild stress rat model

BACKGROUND

Repeated exposure to mild stressors induces anhedonia-a core symptom of major depressive disorder-in up to 70% of the stress-exposed rats, whereas the remaining show resilience to stress. This chronic mild stress (CMS) model is well documented as an animal model of major depressive disorder. We examined the morphological, microstructural, and metabolic characteristics of the hippocampus in anhedonic and stress resilient rats that may mark the differential behavioral outcome.

METHODS

Anhedonic (n = 8), resilient (n = 8), and control (n = 8) rats were subjected to in vivo diffusion kurtosis imaging, high-resolution three-dimensional magnetic resonance imaging and proton magnetic resonance spectroscopy.

RESULTS

Diffusion kurtosis parameters were decreased in both CMS-exposed groups. A significant inward displacement in the ventral part of the right hippocampus was apparent in the resilient subjects and an increase of the glutamate:total creatine ratio and N-acetylaspartylglutamate:total creatine was observed in the anhedonic subjects.

CONCLUSIONS

Diffusion kurtosis imaging discloses subtle substructural changes in the hippocampus of CMS-exposed animals irrespective of their anhedonic or resilient nature. In contrast, proton magnetic resonance spectroscopy and magnetic resonance imaging-based shape change analysis of the hippocampus allowed discrimination of these two subtypes of stress sensitivity. Although the precise mechanism discriminating their behavior is yet to be elucidated, the present study underlines the role of the hippocampus in the etiology of depression and the induction of anhedonia. Our results reflect the potency of noninvasive magnetic resonance methods in preclinical settings with key translational benefit to and from the clinic.