Structural and functional imaging of the hippocampus in young people at familial risk of depression

Decoding Obsessive-Compulsive Disorder: The Regional Vulnerability Index and Its Association With Clinical Symptoms

BACKGROUND

Patients with obsessive-compulsive disorder (OCD) exhibit notable alterations in brain structure, which are likely to be of clinical relevance. Recently, in schizophrenia, the regional vulnerability index (RVI) was introduced to translate findings from ENIGMA (Enhancing Neuro Imaging Genetics through Meta Analysis) studies to the individual level. Building on this framework, in the current study, we sought to investigate whether the RVI might also serve as a vulnerability index for OCD.

METHODS

Toward this aim, we assessed subcortical volume and cortical thickness in a sample of 250 participants (140 patients with OCD, 110 healthy volunteers) and calculated the RVI by leveraging ENIGMA-derived deficits as the "ground truth" for expected regional brain alterations.

RESULTS

Subcortical volume and cortical thickness RVI values were significantly different in patients compared with healthy control participants. In addition, RVI values based on subcortical volume were significantly correlated with the severity of clinical symptoms. Moreover, RVI values for both subcortical volume and cortical thickness were significantly different in medicated subgroups while there was no significant difference in unmedicated patients.

CONCLUSIONS

The current results suggest that the RVI may represent an individual characteristic that reflects the degree of correspondence between individual patterns of structural alterations and disease-characteristic patterns of structural alterations. However, our findings also indicate that relatively large effect sizes in the meta-analytic ground truth are a prerequisite for obtaining a meaningful RVI parameter that can also be related to clinical severity. Therefore, the current findings require further validation through additional research to confirm the RVI's robustness and determine its predictive value.

Memory-related neurophysiological mechanisms in the hippocampus underlying stress susceptibility

Stress-induced psychiatric symptoms, such as increased anxiety, decreased sociality, and depression, differ considerably across individuals. The cognitive model of depression proposes that biased negative memory is a crucial determinant in the development of mental stress-induced disorders. Accumulating evidence from both clinical and animal studies has demonstrated that such biased memory processing could be triggered by the hippocampus, a region well known to be involved in declarative memories. This review mainly describes how memory-related neurophysiological mechanisms in the hippocampus and their interactions with other related brain regions are involved in the regulation of stress susceptibility and discusses potential interventions to prevent and treat stress-related psychiatric symptoms. Further neurophysiological insights based on memory mechanisms are expected to devise personalized prevention and therapy to confer stress resilience.

Polygenic risk for depression and anterior and posterior hippocampal volume in children and adolescents

BACKGROUND

Depression has frequently been associated with smaller hippocampal volume. The hippocampus varies in function along its anterior-posterior axis, with the anterior hippocampus more strongly associated with stress and emotion processing. The goals of this study were to examine the associations among parental history of anxiety/depression, polygenic risk scores for depression (PGS-DEP), and anterior and posterior hippocampal volumes in children and adolescents. To examine specificity to PGS-DEP, we examined associations of educational attainment polygenic scores (PGS-EA) with anterior and posterior hippocampal volume.

METHODS

Participants were 350 3- to 21-year-olds (46 % female). PGS-DEP and PGS-EA were computed based on recent, large-scale genome-wide association studies. High-resolution, T1-weighted magnetic resonance imaging (MRI) data were acquired, and a semi-automated approach was used to segment the hippocampus into anterior and posterior subregions.

RESULTS

Children and adolescents with higher polygenic risk for depression were more likely to have a parent with a history of anxiety/depression. Higher polygenic risk for depression was significantly associated with smaller anterior but not posterior hippocampal volume. PGS-EA was not associated with anterior or posterior hippocampal volumes.

LIMITATIONS

Participants in these analyses were all of European ancestry.

CONCLUSIONS

Polygenic risk for depression may lead to smaller anterior but not posterior hippocampal volume in children and adolescents, and there may be specificity of these effects to PGS-DEP rather than PGS-EA. These findings may inform the earlier identification of those in need of support and the design of more effective, personalized treatment strategies.

DECLARATIONS OF INTEREST

none.

DECLARATIONS OF INTEREST

None.

Specificity of associations between parental psychopathology and offspring brain structure

Multiple forms of parental psychopathology have been associated with differences in subcortical brain volume. However, few studies have considered the role of comorbidity. Here, we examine if alterations in child subcortical brain structure are specific to parental depression, anxiety, mania, or alcohol/substance use parental psychopathology, common across these disorders, or altered by a history of multiple disorders. We examined 6581 children aged 9 to 10 years old from the ABCD study with no history of mental disorders. We found several significant interactions such that the effects of a parental history of depression, anxiety, and substance use problems on amygdala and striatal volumes were moderated by comorbid parental history of another disorder. Interactions tended to suggest smaller volumes in the presence of a comorbid disorder. However, effect sizes were small, and no associations remained significant after correcting for multiple comparisons. Results suggest that associations between familial risk for psychopathology and offspring brain structure in 9-10-year-olds are modest, and relationships that do exist tend to implicate the amygdala and striatal regions and are moderated by a comorbid parental psychopathology history. Several methodological factors, including controlling for intracranial volume and other forms of parental psychopathology and excluding child psychopathology, likely contribute to inconsistencies in the literature.

Selective serotonin reuptake inhibitors suppress sharp wave ripples in the ventral hippocampus

Biased memory processing contributes to the development and exacerbation of depression, and thus could represent a potential therapeutic target for stress-induced mental disorders. Synchronized spikes in hippocampal neurons, corresponding to sharp wave ripples (SWRs), may play a crucial role in memory reactivation. In this study, we showed that the frequency of SWRs increased in the ventral hippocampus, but not in the dorsal hippocampus, after stress exposure. Administration of the selective serotonin reuptake inhibitors (SSRIs) fluoxetine and fluvoxamine inhibited the generation of ventral hippocampal SWRs and reduced locomotor activity and local field potential power in the gamma bands. These results suggest that the antidepressant effects of SSRIs may be mediated by the suppression of ventral hippocampal SWRs.

Hippocampal sharp wave ripples underlie stress susceptibility in male mice

The ventral hippocampus (vHC) is a core brain region for emotional memory. Here, we examined how the vHC regulates stress susceptibility from the level of gene expression to neuronal population dynamics in male mice. Transcriptome analysis of samples from stress-naïve mice revealed that intrinsic calbindin (Calb1) expression in the vHC is associated with susceptibility to social defeat stress. Mice with Calb1 gene knockdown in the vHC exhibited increased stress resilience and failed to show the increase in the poststress ventral hippocampal sharp wave ripple (SWR) rate. Poststress vHC SWRs triggered synchronous reactivation of stress memory-encoding neuronal ensembles and facilitated information transfer to the amygdala. Suppression of poststress vHC SWRs by real-time feedback stimulation or walking prevented social behavior deficits. Taken together, our results demonstrate that internal reactivation of memories of negative stressful episodes supported by ventral hippocampal SWRs serves as a crucial neurophysiological substrate for determining stress susceptibility.

Structural and Functional Brain Alterations in Populations with Familial Risk for Depression: A Narrative Review

LEARNING OBJECTIVES

After completing this activity, practitioners will be better able to:• Discuss the association between brain alterations and vulnerability or resilience to MDD in people with familial risk• Define how structural and functional brain alterations associated with vulnerability or resilience could lead to a better understanding of the pathophysiology of MDD.

AIM

Familial history is associated with an increased risk for major depressive disorder (MDD). Despite the increased risk, some members of the familial high-risk population remain healthy, that is, resilient. Defining the structural and functional brain alterations associated with vulnerability or resilience could lead to a better understanding of the pathophysiology of MDD. This study aimed to review the current literature and discuss the association between brain alterations and vulnerability or resilience to MDD in people with familial risk.

METHODS

A literature search on MRI studies investigating structural and functional alterations in populations at familial risk for MDD was performed using the PubMed and SCOPUS databases. The search was conducted through June 13, 2022.

RESULTS

We reviewed and summarized the data of 72 articles (25 structural MRI, 35 functional MRI, 10 resting-state fMRI, one structural/functional MRI combined, and one structural/functional/resting-state fMRI combined). These findings suggested that resilience in high-risk individuals is related to the amygdala structure, frontal lobe activity, and functional connectivity between the amygdala and multiple frontal regions.

CONCLUSION

Resilient and vulnerable individuals exhibit structural and functional differences in multiple frontal and limbic regions. However, further systematic longitudinal research incorporating environmental factors is required to validate the current findings.

Neural markers of familial risk for depression - A systematic review

Structural and functional brain alterations are found in adults with depression. It is not known whether these changes are a result of illness or exist prior to disorder onset. Asymptomatic offspring of parents with depression offer a unique opportunity to research neural markers of familial risk to depression and clarify the temporal sequence between brain changes and disorder onset. We conducted a systematic review to investigate whether asymptomatic offspring at high familial risk have structural and functional brain changes like those reported in adults with depression. Our literature search resulted in 44 studies on 18,645 offspring ranging from 4 weeks to 25 years old. Reduced cortical thickness and white matter integrity, and altered striatal reward processing were the most consistent findings in high-risk offspring across ages. These alterations are also present in adults with depression, suggesting the existence of neural markers of familial risk for depression. Additional studies reproducing current results, streamlining fMRI data analyses, and investigating underexplored topics (i.e intracortical myelin, gyrification, subcortical shape) may be among the next steps required to improve our understanding of neural markers indexing the vulnerability to depression.

Associations Between Parental Mood and Anxiety Psychopathology and Offspring Brain Structure: A Scoping Review

A family history of mood and anxiety disorders is one of the most well-established risk factors for these disorders in offspring. A family history of these disorders has also been linked to alterations in brain regions involved in cognitive-affective processes broadly, and mood and anxiety disorders specifically. Results from studies of brain structure of children of parents with a history of mood or anxiety disorders (high-risk offspring) have been inconsistent. We followed the PRISMA protocol to conduct a scoping review of the literature linking parental mood and anxiety disorders to offspring brain structure to examine which structures in offspring brains are linked to parental major depressive disorder (MDD), anxiety, or bipolar disorder (BD). Studies included were published in peer-reviewed journals between January 2000 and July 2021. Thirty-nine studies were included. Significant associations between parental BD and offspring caudate volume, inferior frontal gyrus thickness, and anterior cingulate cortex thickness were found. Associations were also identified between parental MDD and offspring amygdala and hippocampal volumes, fusiform thickness, and thickness in temporoparietal regions. Few studies have examined associations between parental anxiety and high-risk offspring brain structure; however, one study found associations between parental anxiety symptoms and offspring amygdala structure, and another found similar associations with the hippocampus. The direction of grey matter change across studies was inconsistent, potentially due to the large age ranges for each study and the non-linear development of the brain. Children of parents with MDD and bipolar disorders, or elevated anxiety symptoms, show alterations in a range of brain regions. Results may further efforts to identify children at high risk for affective disorders and may elucidate whether alterations in specific brain regions represent premorbid markers of risk for mood and anxiety disorders.

Immunological Disturbances and Neuroimaging Findings in Major Depressive Disorder (MDD) and Alcohol Use Disorder (AUD) Comorbid Patients

Mood disorders and Major Depressive Disorder, in particular, appear to be some of the most common psychiatric disorders with a high rate of comorbidity most frequently of anxiety or substance abuse disorders (alcohol use disorder). In both cases - MDD and AUD, a number of immunological disturbances are observed, such as chronic mild inflammation response, increased level of cytokines, hypercortisolaemia, which lead to specific changes in brain neurotransmitter functions. Some of the contemporary brain imaging techniques are functional magnetic resonance imaging (fMRI) and magnetic spectroscopy which are most commonly used to assess the brain metabolism and functional connectivity changes such as altered responses to emotional stimuli in MDD or overactivation of ventromedial prefrontal areas during delayed and underactivation of dorsolateral prefrontal regions during impulsive reward decisions in AUD and dysfunction of gamma-aminobutyric acid (GABA) and/or glutamate neurotransmitter systems, low NAA and myo-Inositol in both MDD and AUD.

Altered Dentate Gyrus Microstructure in Individuals at High Familial Risk for Depression Predicts Future Symptoms

BACKGROUND

Offspring of individuals with major depressive disorder (MDD) are at increased risk for developing MDD themselves. Altered hippocampal, and specifically dentate gyrus (DG), structure and function may be involved in depression development. However, hippocampal abnormalities could also be a consequence of the disease. For the first time, we tested whether abnormal DG micro- and macrostructure were present in offspring of individuals with MDD and whether these abnormalities predicted future symptomatology.

METHODS

We measured the mean diffusivity of gray matter, a measure of microstructure, via diffusion tensor imaging and volume of the DG via structural magnetic resonance imaging in 102 generation 2 and generation 3 offspring at high and low risk for depression, defined by the presence or absence, respectively, of moderate to severe MDD in generation 1. Prior, current, and future depressive symptoms were tested for association with hippocampal structure.

RESULTS

DG mean diffusivity was higher in individuals at high risk for depression, regardless of a lifetime history of MDD. While DG mean diffusivity was not associated with past or current depressive symptoms, higher mean diffusivity predicted higher symptom scores 8 years later. DG microstructure partially mediated the association between risk and future symptoms. DG volume was smaller in high-risk generation 2 but not in high-risk generation 3.

CONCLUSIONS

Together, these findings suggest that the DG has a role in the development of depression. Furthermore, DG microstructure, more than macrostructure, is a sensitive risk marker for depression and partially mediates future depressive symptoms.

Brain Volume Abnormalities in Youth at High Risk for Depression: Adolescent Brain and Cognitive Development Study

OBJECTIVE

Children of parents with depression are two to three times more likely to develop major depressive disorder than children without parental history; however, subcortical brain volume abnormalities characterizing major depressive disorder risk remain unclear. The Adolescent Brain and Cognitive Development (ABCD) Study provides an opportunity to identify subcortical differences associated with parental depressive history.

METHOD

Structural magnetic resonance data were acquired from 9- and 10-year-old children (N = 11,876; release 1.1, n = 4,521; release 2.0.1, n = 7,355). Approximately one-third of the children had a parental depressive history, providing sufficient power to test differences in subcortical brain volume between low- and high-risk youths. Children from release 1.1 were examined as a discovery sample, and we sought to replicate effects in release 2.0.1. Secondary analyses tested group differences in the prevalence of depressive disorders and clarified whether subcortical brain differences were present in youths with a lifetime depressive disorder history.

RESULTS

Parental depressive history was related to smaller right putamen volume in the discovery (release 1.1; d = -0.10) and replication (release 2.0.1; d = -0.10) samples. However, in release 1.1, this effect was driven by maternal depressive history (d = -0.14), whereas in release 2.0.1, paternal depressive history showed a stronger relationship with putamen volume (d = -0.09). Furthermore, high-risk children exhibited a near twofold greater occurrence of depressive disorders relative to low-risk youths (maternal history odds ratio =1.99; paternal history odds ratio = 1.45), but youths with a lifetime depressive history did not exhibit significant subcortical abnormalities.

CONCLUSION

A parental depressive history was associated with smaller putamen volume, which may affect reward learning processes that confer increased risk for major depressive disorder.

Orbitofrontal cortex grey matter volume is related to children's depressive symptoms

Adults with a history of depression show distinct patterns of grey matter volume (GMV) in frontal cortical (e.g., prefrontal cortex, orbitofrontal cortex) and limbic (e.g., anterior cingulate, amygdala, hippocampus, dorsal striatum) structures, regions relevant to the processing and regulation of reward, which is impaired in the context of depression. However, it is unclear whether these GMV associations with depression precede depressive disorder onset or whether GMV is related to early emerging symptoms or familial depression. To address these questions, we used voxel-based morphometry (VBM) to examine GMV in 85 community-dwelling children (M = 11.12 years, SD = 0.63 years) screened for current and lifetime depression. Associations between children's depressive symptoms (self- and mother-report of children's symptoms), children's maternal depression history, and GMV were examined. Although maternal depression history was unrelated to children's GMV, child GMV in the orbitofrontal cortex (OFC) was negatively related to children's self-reported depressive symptoms, using both a priori ROI and whole-brain analyses. Moderated regression analyses indicated that girls' GMV was negatively related to girls' depressive symptoms (as indexed by both self- and mother-report of girls' symptoms), whereas boys' symptoms were positively related to GMV. Our findings suggest that brain morphology in the OFC, a region with functional roles in processes relevant to depressive symptoms (i.e., reward-based learning and reward processing), is associated with early depressive symptoms prior to the development of clinically significant depression.

Chronic Stress-induced Behaviors Correlate with Exacerbated Acute Stress-induced Cingulate Cortex and Ventral Hippocampus Activation

Altered activity of corticolimbic brain regions is a hallmark of stress-related illnesses, including mood disorders, neurodegenerative diseases, and substance abuse disorders. Acute stress adaptively recruits brain region-specific functions for coping, while sustained activation under chronic stress may overwhelm feedback mechanisms and lead to pathological cellular and behavioral responses. The neural mechanisms underlying dysregulated stress responses and how they contribute to behavioral deficits are poorly characterized. Here, we tested whether prior exposure to chronic restraint stress (CRS) or unpredictable chronic mild stress (UCMS) in mice could alter functional response to acute stress and whether these changes are associated with chronic stress-induced behavioral deficits. More specifically, we assessed acute stress-induced functional activation indexed by c-Fos+ cell counts in 24 stress- and mood-related brain regions, and determined if changes in functional activation were linked to chronic stress-induced behavioral impairments, summarized across dimensions through principal component analysis (PCA). Results indicated that CRS and UCMS led to convergent physiological and anxiety-like deficits, whereas working and short-term memory were impaired only in UCMS mice. CRS and UCMS exposure exacerbated functional activation by acute stress in anterior cingulate cortex (ACC) area 24b and ventral hippocampal (vHPC) CA1, CA3, and subiculum. In dysregulated brain regions, levels of functional activation were positively correlated with principal components reflecting variance across behavioral deficits relevant to stress-related disorders. Our data supports an association between a dysregulated stress response, altered functional corticolimbic excitation/inhibition balance, and the expression of maladaptive behaviors.

Serotonergic influence on depressive symptoms and trait anxiety is mediated by negative life events and frontal activation in children and adolescents

Depression and anxiety are common in childhood and adolescence. Even though cardinal symptoms differ, there is a considerable overlap regarding the pathogenic influence of serotonergic innervation, negative life experience, disturbed emotion perception/affect regulation, and impaired neural functioning in the fronto-limbic circuit. In this study, we examined the effect of the 5-HTTLPR/rs25531 genotype on depressive symptoms and trait anxiety under the consideration of the amount of negative life events in healthy children and adolescents (N = 389). In a subsample of 49 subjects, we performed fMRI to add fronto-limbic brain activation as a second interacting factor. Across all subjects, negative life events moderated the influence of the 5-HTTLPR/rs25531 genotype on both depressive symptoms and trait anxiety. In the fMRI subsample, 5-HTTLPR/rs25531 S + S/L_G + S/L_A + L_GL_A + L_GL_G genotype-associated left middle frontal gyrus (MFG) activation mediated the influence of 5-HTTLPR/rs25531 genotype on depressive symptoms, however, only in combination with negative life events. Genetic influence on trait anxiety was predominantly mediated by negative life events; only L_AL_A genotype-specific activation in the right MFG worked as a mediator in combination with negative life events. The present findings hint towards distinct mechanisms mediating the influence of 5-HTTLPR/rs25531 genotype on depressive symptoms and anxiety, with negative life events playing a crucial role in both phenotypes. With regard to depressive symptoms, however, this influence was only visible in combination with MFG activation, whereas, in anxiety, it was independent of brain activation.

Promising Neuroimaging Biomarkers in Depression

The neuroimaging has been applied in the study of pathophysiology in major depressive disorder (MDD). In this review article, several kinds of methodologies of neuroimaging would be discussed to summarize the promising biomarkers in MDD. For the magnetic resonance imaging (MRI) and magnetoencephalography field, the literature review showed the potentially promising roles of frontal lobes, such as anterior cingulate cortex (ACC), dorsolateral prefrontal cortex (DLPFC) and orbitofrontal cortex (OFC). In addition, the limbic regions, such as hippocampus and amygdala, might be the potentially promising biomarkers for MDD. The structures and functions of ACC, DLPFC, OFC, amygdala and hippocampus might be confirmed as the biomarkers for the prediction of antidepressant treatment responses and for the pathophysiology of MDD. The functions of cognitive control and emotion regulation of these regions might be crucial for the establishment of biomarkers. The near-infrared spectroscopy studies demonstrated that blood flow in the frontal lobe, such as the DLPFC and OFC, might be the biomarkers for the field of near-infrared spectroscopy. The electroencephalography also supported the promising role of frontal regions, such as the ACC, DLPFC and OFC in the biomarker exploration, especially for the sleep electroencephalogram to detect biomarkers in MDD. The positron emission tomography (PET) and single-photon emission computed tomography (SPECT) in MDD demonstrated the promising biomarkers for the frontal and limbic regions, such as ACC, DLPFC and amygdala. However, additional findings in brainstem and midbrain were also found in PET and SPECT. The promising neuroimaging biomarkers of MDD seemed focused in the fronto-limbic regions.

Effect of stress gene-by-environment interactions on hippocampal volumes and cortisol secretion in adolescent girls

OBJECTIVE

Adolescence is a time of increased susceptibility to environmental stress and mood disorders, and girls are particularly at risk. Genes interacting with the environment (G × E) are implicated in hypothalamic-pituitary-adrenal axis dysregulation, hippocampal volume changes and risk or resilience to mood disorders. In this study, we assessed the effects of stress system G × E interactions on hippocampal volumes and cortisol secretion in adolescent girls.

METHODS

We recruited 229 girls aged 12-18 years, and scans were obtained from 202 girls. Of these, 76 had been exposed to higher emotional trauma (abuse or neglect). Hippocampal volumes were measured using Freesurfer and high-resolution structural magnetic resonance imaging scans. Saliva samples were collected for measurement of cortisol levels and genotyping of stress system genes: FKBP5, NR3C1 (both N = 194) and NR3C2 ( N = 193).

RESULTS

Among girls with the 'G' allelic variant of the NR3C1 gene, those who had been exposed to higher emotional trauma had significantly smaller left hippocampal volumes ( N = 44; mean = 4069.58 mm³, standard deviation = 376.99) than girls who had been exposed to minimal emotional trauma with the same allelic variant ( N = 69; mean = 4222.34 mm³, standard deviation = 366.74).

CONCLUSION

In healthy adolescents, interactions between emotional trauma and the 'protective' NR3C1 'GG' variant seem to induce reductions in left hippocampal volumes. These G × E interactions suggest that vulnerability to mood disorders is perhaps driven by reduced 'protection' that may be specific to emotional trauma. This novel but preliminary evidence has implications for targeted prevention of mood disorders and prospective multimodal neuroimaging and longitudinal studies are now needed to investigate this possibility.

Increased expression of a novel miRNA in peripheral blood is negatively correlated with hippocampal volume in patients with major depressive disorder

BACKGROUND

Major depressive disorder (MDD) is a serious psychiatric illness with unclear pathophysiology. As one of the post-transcriptional regulators, prior research has indicated that miRNAs are involved in the pathophysiology of MDD. The aim of this study was to screen the MDD-related miRNAs in the peripheral blood and investigate the target genes of the differentially expressed miRNAs and their potential functions in MDD pathophysiology.

METHODS

miRNA sequencing was performed using the peripheral blood of patients with MDD and matched controls (cohort A, 10 vs 10). The nominal significant results were validated in an independent sample (cohort B, 72 vs 75) by real-time quantitative polymerase chain reaction (PCR). The target genes of verified miRNAs were predicted using Miranda software. Luciferase assay was used to verify one of the predicted target genes. Furthermore, we analyzed the correlations between the expression of pmiR-chr11 and hippocampal volume.

RESULTS

Ten miRNAs were nominally significantly dysregulated in patients with MDD in cohort A. One of the 10 miRNAs, pmiR-chr11, was significantly dysregulated in cohort B. The pmiR-chr11 could regulate one of the target genes, BRPF1 (bromodomain and PHD finger containing 1), via binding its 3' untranslated region (UTR). The expression of pmiR-chr11 was negatively correlated with hippocampal volume in patients with MDD.

LIMITATIONS

The expression of the miRNAs and mRNAs detected in the peripheral blood may not reflect the expression in the brain.

CONCLUSIONS

Our findings suggested that the pmiR-chr11 may influence hippocampal volume by regulating BRPF1 in MDD.

Development of Neuroimaging-Based Biomarkers in Psychiatry

This chapter presents an overview of accumulating neuroimaging data with emphasis on translational potential. The subject will be described in the context of three disease states, i.e., schizophrenia, bipolar disorder, and major depressive disorder, and for three clinical goals, i.e., disease risk assessment, subtyping, and treatment decision.

Schisandrin rescues depressive-like behaviors induced by chronic unpredictable mild stress via GDNF/ERK1/2/ROS and PI3K/AKT/NOX signaling pathways in mice

The current study aimed to prove the antidepressant-like effects and the probable mechanisms of Schisandrin on depression, which induced by chronic unpredictable mild stress (CUMS) in mice. Four weeks of CUMS exposure resulted in depressive-like behavior, as indicated by the significant decrease in sucrose consumption and increase the immobility time in the forced swim test, but without any influence on the locomotor activity. Further, there were significant downregulations of GDNF/ERK1/2/ROS and PI3K/AKT/NOX signaling pathways in the hippocampus and prefrontal cortex in depressed mice. Treatment of mice with Schisandrin (30mg/kg) and Fluoxetine (10mg/kg) significantly ameliorated all the behavioral and biochemical changes induced by CUMS. These results suggest that Schisandrin produces an antidepressant-like effect in CUMS-induced mice, which possibly mediated, at least in part, by rectifying the signaling pathways of GDNF/ERK1/2/ROS and PI3K/AKT/NOX.

Involvement of the glutamate/glutamine cycle and glutamate transporter GLT-1 in antidepressant-like effects of Xiao Yao san on chronically stressed mice

BACKGROUND

Xiao Yao San (XYS) is an herbal prescription which is used in the treatment of depression for thousands of years from Song dynasty in China (960-1127 A.D.), and is the bestselling and most popular herb formula for treating major depression. This study aimed to assess the chronic antidepressant effects of XYS and fluoxetine in depressed mice induced by chronic unpredictable mild stress (CUMS) and its association with  alterations in glutamate/glutamine cycle and glutamate transporters.

METHODS

Mice in the control and model group were given 0.5 ml physiological saline by intragastric administration. Mice in two treatment groups were given XYS (0.25 g/kg/d) and fluoxetine (2.6 mg/kg/d), respectively. The depressive-like behaviors such as forced swim test (FST), sucrose preference test (SPT) and novelty-suppressed feeding (NSF) test were measured after mice exposed to CUMS for 21 days. Body weight, contents of glutamate and glutamine, glutamine/glutamate ratio that is usually thought to reflect glutamate/glutamine cycle, and the protein and mRNA expressions of glutamate transporters (excitatory amino acid transporter 1-2,GLAST/EAAT1 and GLT-1/EAAT2) were measured. The immunoreactivities of GLAST and GLT-1 in the hippocampus were also investigated.

RESULTS

After CUMS exposure, mice exhibited depressive-like behaviors, body weight loss, increased glutamate level, decreased glutamine level, elevated glutamine/glutamate ratio, decreased GLT-1 protein expression and mRNA level, and decreased average optical density (AOD) of GLT-1 in the CA1, CA3 and DG in the hippocampus. These abnormalities could be effectively reversed by XYS or fluoxetine treatment. In addition, the study also found that GLAST expression in the hippocampus could not be altered by 21-d CUMS.

CONCLUSION

The studies indicated that XYS may have therapeutic actions on depression -like behavior s induced by CUMS in mice possibly mediated by modulation of glutamate/glutamine cycle and glutamate transporter GLT-1 in the hippocampus.

Prospective longitudinal voxel-based morphometry study of major depressive disorder in young individuals at high familial risk

BACKGROUND

Previous neuroimaging studies indicate abnormalities in cortico-limbic circuitry in mood disorder. Here we employ prospective longitudinal voxel-based morphometry to examine the trajectory of these abnormalities during early stages of illness development.

METHOD

Unaffected individuals (16-25 years) at high and low familial risk of mood disorder underwent structural brain imaging on two occasions 2 years apart. Further clinical assessment was conducted 2 years after the second scan (time 3). Clinical outcome data at time 3 was used to categorize individuals: (i) healthy controls ('low risk', n = 48); (ii) high-risk individuals who remained well (HR well, n = 53); and (iii) high-risk individuals who developed a major depressive disorder (HR MDD, n = 30). Groups were compared using longitudinal voxel-based morphometry. We also examined whether progress to illness was associated with changes in other potential risk markers (personality traits, symptoms scores and baseline measures of childhood trauma), and whether any changes in brain structure could be indexed using these measures.

RESULTS

Significant decreases in right amygdala grey matter were found in HR MDD v. controls (p = 0.001) and v. HR well (p = 0.005). This structural change was not related to measures of childhood trauma, symptom severity or measures of sub-diagnostic anxiety, neuroticism or extraversion, although cross-sectionally these measures significantly differentiated the groups at baseline.

CONCLUSIONS

These longitudinal findings implicate structural amygdala changes in the neurobiology of mood disorder. They also provide a potential biomarker for risk stratification capturing additional information beyond clinically ascertained measures.

Subgenual anterior cingulate cortex and hippocampal volumes in depressed youth: The role of comorbidity and age

OBJECTIVES

Many studies have reported that adults with recurrent major depressive disorder (MDD) have smaller hippocampal volumes than control participants. The data are more variable in youth with MDD, where findings have been inconsistent and the effects of factors such as age and co-morbidity have not been systematically examined. This study therefore assessed hippocampus and subgenual anterior cingulate (sgACC) morphometry in 168 youth, aged 12-25, with or without MDD and comorbid anxiety.

METHODS

Structural magnetic resonance imaging (MRI) scans and clinical assessments were obtained from 80 participants with MDD (36 with comorbid anxiety disorder) and 88 age-matched control participants.

RESULTS

Participants with MDD had smaller right hippocampi than controls (p=.013). Older depressed participants (20.1-25 years) had smaller hippocampal volumes than younger ones (<20.1 years; p=.05); this age effect was not apparent in controls (p=.46). Depression scores, indexed by the HAMD17, correlated with hippocampal volumes in older depressed youth. Depressed participants with comorbid anxiety had smaller sgACC, but not hippocampal, volumes than those without anxiety (p=.042).

LIMITATIONS

Longitudinal, versus cross-sectional, studies can most optimally assess the influence of depression on neurodevelopmental profiles. Though our participants were largely treatment-naïve or in their first week of pharmacotherapy, a handful had extensive treatment histories; thus, treatment history may have influenced brain morphometry.

CONCLUSIONS

Age effects were apparent when hippocampal volumes of older and younger participants with MDD were compared; such differences were not apparent in healthy participants. Comorbid anxiety was associated with decreased sgACC volumes suggesting delayed or altered neurodevelopment in a key emotion regulation region.

Hippocampal glutamate is increased and associated with risky drinking in young adults with major depression

BACKGROUND

Risky drinking in young people is harmful, highly prevalent and often complicated by comorbid mental health problems that compound alcohol-induced impairment. The hippocampus and the glutamate system have been implicated in the pathophysiology of alcoholism and depression. This study aimed to determine whether risky drinking is associated with glutamate levels recorded within the hippocampus of young adults with major depression.

METHODS

Sixty-three young persons with major depression (22.1±3.1 years; 65% female) and 38 healthy controls were recruited. Participants completed the alcohol use disorder identification test and underwent proton magnetic resonance spectroscopy to measure in vivo glutamate levels within the hippocampus following a period of at least 48h of abstinence.

RESULTS

Young adults with depression had significantly increased hippocampal glutamate levels and a positive association between the level of alcohol use and glutamate. Regression analysis revealed that higher levels of hippocampal glutamate were predicted by having increased levels of risky drinking and depression.

LIMITATIONS

Small sample sizes for testing diagnosis by risky drinking interaction and use of creatine ratios rather than the absolute concentrations of glutamate.

DISCUSSION

The hippocampus is a critical region; given its role in learning and memory as well as mood regulation, and the neurochemical changes observed in this study may precede structural changes, which are commonly observed in both depression and alcohol misuse. These findings suggest that young adults with major depression who engage in risky drinking may be at increased risk of glutamate excitotoxicity.

Ventral hippocampal afferents to the nucleus accumbens regulate susceptibility to depression

Enhanced glutamatergic transmission in the nucleus accumbens (NAc), a region critical for reward and motivation, has been implicated in the pathophysiology of depression; however, the afferent source of this increased glutamate tone is not known. The NAc receives glutamatergic inputs from the medial prefrontal cortex (mPFC), ventral hippocampus (vHIP) and basolateral amygdala (AMY). Here, we demonstrate that glutamatergic vHIP afferents to NAc regulate susceptibility to chronic social defeat stress (CSDS). We observe reduced activity in vHIP in mice resilient to CSDS. Furthermore, attenuation of vHIP-NAc transmission by optogenetic induction of long-term depression is pro-resilient, whereas acute enhancement of this input is pro-susceptible. This effect is specific to vHIP afferents to the NAc, as optogenetic stimulation of either mPFC or AMY afferents to the NAc is pro-resilient. These data indicate that vHIP afferents to NAc uniquely regulate susceptibility to CSDS, highlighting an important, novel circuit-specific mechanism in depression.

Neurochemistry of major depression: a study using magnetic resonance spectroscopy

RATIONALE

Magnetic resonance spectroscopy (MRS) is an acceptable non-invasive means of studying brain neurochemistry in depression. Previous studies in depressed patients have focused on measurement of the amino acid neurotransmitters, γ-aminobutyric acid (GABA) and glutamate.

OBJECTIVES

The aim of this study is to use MRS in conjunction with the ultrashort echo time 'SPECIAL' technique to measure cortical levels of GABA, glutamate and glutathione (GSH) levels in unmedicated patients with major depression. We also examined the effect of 6-week treatment with the selective serotonin re-uptake inhibitor, escitalopram.

METHODS

We studied patients with DSM-IV major depression and healthy age-matched controls using proton MRS. GABA, glutamate and GSH were measured relative to creatine in a voxel placed in occipital cortex.

RESULTS

There was no difference in GABA or glutamate levels between depressed participants and controls; however, depressed patients had lower GSH levels. Six-week escitalopram treatment, which resulted in significant clinical responses in some patients, did not alter concentrations of GABA, glutamate or GSH.

CONCLUSIONS

The sources of variability of GABA and glutamate measures in different studies of depressed patients require further study. Our results suggest that concomitant treatment with selective serotonin re-uptake inhibitors (SSRIs) is unlikely to be an important confounding factor. If lowered GSH levels can be confirmed, they may represent the presence of oxidative stress in some depressed patients.