Hippocampus In Depression Research Articles

Pentraxin 3 promotes microglial M2 polarization and excitatory synapse formation in the hippocampus in depression.

Depression is a prevalent mental illness that significantly impairs individuals' overall quality of life and physical well-being. However, the pathological mechanisms of depression remain unclear, and effective treatment strategies are urgently needed. Pentraxin 3 (PTX3), a long pentraxin protein, plays a significant role in various pathological conditions, including infections, immune responses, and tissue repair. In this study, we collected serum from patients with depression and established both animal and cell models of depression. We found that PTX3 expression was significantly reduced in both the serum of patients with depression and the hippocampus of chronic unpredictable mild stress (CUMS) mice. PTX3 supplementation markedly improved depressive-like behavior in CUMS mice and promoted microglial M2 polarization. In the LPS-induced BV2 cell model, PTX3 overexpression facilitated microglial M2 polarization via activation of the CREB/CEBPb axis. Additionally, PTX3 enhanced fibroblast growth factor 22 (FGF22) expression and excitatory synapse formation in the CA3 region of the hippocampus in CUMS mice. In the dexamethasone (DXM)-treated SH-SY5Y cell model, PTX3 overexpression increased SPI1 expression, elevated FGF22 transcriptional activity, and promoted the expression of excitatory synapse-related proteins PSD95 and VGLUT1. In summary, our study demonstrates that PTX3 promotes microglial M2 polarization and excitatory synapse formation in the hippocampus, suggesting potential antidepressant effects and providing theoretical support for considering PTX3 as a therapeutic target for depression.

HDAC6 Modulates Signaling Pathways Relevant to Synaptic Biology and Neuronal Differentiation in Human Stem-Cell-Derived Neurons.

Recent studies show that histone deacetylase 6 (HDAC6) has important roles in the human brain, especially in the context of a number of nervous system disorders. Animal models of neurodevelopmental, neurodegenerative, and neuropsychiatric disorders show that HDAC6 modulates important biological processes relevant to disease biology. Pan-selective histone deacetylase (HDAC) inhibitors had been studied in animal behavioral assays and shown to induce synaptogenesis in rodent neuronal cultures. While most studies of HDACs in the nervous system have focused on class I HDACs located in the nucleus (e.g., HDACs 1,2,3), recent findings in rodent models suggest that the cytoplasmic class IIb HDAC, HDAC6, plays an important role in regulating mood-related behaviors. Human studies suggest a significant role for synaptic dysfunction in the prefrontal cortex (PFC) and hippocampus in depression. Studies of HDAC inhibitors (HDACi) in human neuronal cells show that HDAC6 inhibitors (HDAC6i) increase the acetylation of specific lysine residues in proteins involved in synaptogenesis. This has led to the hypothesis that HDAC6i may modulate synaptic biology not through effects on the acetylation of histones, but by regulating acetylation of non-histone proteins.

Parsing the Hippocampus in Depression: Chronic Stress, Hippocampal Volume, and Major Depressive Disorder

Parsing the Hippocampus in Depression: Chronic Stress, Hippocampal Volume, and Major Depressive Disorder

The Hippocampus in Depression: More Than the Sum of Its Parts? Advanced Hippocampal Substructure Segmentation in Depression

Hippocampal volume reduction is the most replicated finding in neuroimaging studies of major depressive disorder (MDD). Varying hippocampal volume definition is a well-established problem in this field. Given that hippocampal function can be mapped onto anatomically defined substructures and that detailed examination of substructure volumes is now possible, we examined different hippocampal composite measures in MDD to look for hippocampal markers of MDD. Magnetic resonance imaging brain scans were compared between 80 patients with a range of MDD duration and 83 healthy control subjects. High-resolution T1-weighted and T2-weighted-fluid-attenuated inversion recovery magnetic resonance images were examined using the automated hippocampal substructure module in FreeSurfer 6.0. Between-group volumetric assessments were performed at substructure and composite substructures levels. Patients with MDD showed a bilateral pattern of volume reduction in principal hippocampal substructures: the cornu ammonis (CA1-CA4), dentate gyrus, and subiculum. Changes were more pronounced on the left of these structures and in recurrent depression. CA2 to CA4 were the only substructures reduced in first-presentation depression. Overall changes were most marked in the left CA1, and CA1 volume was a predictor of illness duration. Hippocampal involvement in MDD is confined to principal substructures only. Differences between patients with MDD and healthy control subjects increased with progressively restricted hippocampal definitions, with the left CA1 emerging as a potential marker of MDD. Changes were more extensive in patients with recurrent, as opposed to first-presentation, MDD, suggesting a hippocampal disease process. These findings identify core hippocampal regions in the pathology of MDD, suggesting a potential marker of disease progression in MDD.

Altered hippocampal function in major depression despite intact structure and resting perfusion.

Hippocampal volume reductions in major depression have been frequently reported. However, evidence for functional abnormalities in the same region in depression has been less clear. We investigated hippocampal function in depression using functional magnetic resonance imaging (fMRI) and neuropsychological tasks tapping spatial memory function, with complementing measures of hippocampal volume and resting blood flow to aid interpretation. A total of 20 patients with major depressive disorder (MDD) and a matched group of 20 healthy individuals participated. Participants underwent multimodal magnetic resonance imaging (MRI): fMRI during a spatial memory task, and structural MRI and resting blood flow measurements of the hippocampal region using arterial spin labelling. An offline battery of neuropsychological tests, including several measures of spatial memory, was also completed. The fMRI analysis showed significant group differences in bilateral anterior regions of the hippocampus. While control participants showed task-dependent differences in blood oxygen level-dependent (BOLD) signal, depressed patients did not. No group differences were detected with regard to hippocampal volume or resting blood flow. Patients showed reduced performance in several offline neuropsychological measures. All group differences were independent of differences in hippocampal volume and hippocampal blood flow. Functional abnormalities of the hippocampus can be observed in patients with MDD even when the volume and resting perfusion in the same region appear normal. This suggests that changes in hippocampal function can be observed independently of structural abnormalities of the hippocampus in depression.

The Relationship between Cortisol and the Hippocampal Volume in Depressed Patients – A MRI Pilot Study

Abstract Stress is responsible for increased cortisol levels in depression, affecting different areas of the brain, especially the prefrontal cortex and the hippocampus. Our paper is analysing the interrelation between cortisol – as a marker of neuroendocrine response to stress and the hippocampal volume subfields – as markers of neurogenesis and neuroplasticity theory. The main goal of the research was focused to investigate and to prove the relation between the increased level of cortisol and the reduced volume of hippocampus in depression. We measured the morning serum cortisol level in a fasting state. For the volume of the hippocampus all patients underwent a MRI of the brain examination. The investigations have shown that both the right and the left hippocampal volumes are reduced in MDD patients. Higher levels of cortisol are associated with lower hippocampal subfield volumes, especially on the right.

Decreased quinolinic acid in the hippocampus of depressive patients: evidence for local anti-inflammatory and neuroprotective responses?

Disturbances of glutamatergic neurotransmission and mononuclear phagocyte system activation have been described uni- and bipolar depression (UD/BD). Linking the glutamate and immune hypotheses of depression, quinolinic acid (QUIN) is synthesized by activated microglia and acts as an endogenous N-methyl-D-aspartate glutamate receptor (NMDA-R) agonist with neurotoxic properties. Recently, we observed an increased microglial QUIN expression in the subgenual and supracallosal, but not in the pregenual part of the anterior cingulate cortex in postmortem brains of suicide cases with severe depression. Since several hints point to a role of the hippocampus in depression, we extended our study and addressed the question whether microglial QUIN is also changed in subregions of the hippocampus (CA1 and CA2/3 areas) in these patients. Postmortem brains of 12 acutely depressed patients (UD, n=6; BD, n=6) and 10 neuropsychiatric healthy age- and gender-matched control subjects were analyzed using QUIN-immunohistochemistry. Hippocampal volumes were determined in order to assess possible neurotoxic or neurodegenerative aspects. Microglial QUIN expression in the whole group of depressed patients was either comparable (left CA1, right CA2/3) or decreased (right CA1: p=0.004, left CA2/3: p=0.044) relative to controls. Post hoc tests showed that QUIN was reduced both in UD and BD in the right CA1 field (UD, p=0.048; BD, p=0.031). No loss of hippocampal volume was detected. Our data indicate that UD and BD are associated with a local reduction in QUIN-immunoreactive microglia in the hippocampus and underline the importance of the NMDA-R signaling in depressive disorders.

State-dependent changes in hippocampal grey matter in depression

Reduced hippocampal volume has been reported in depression and may be involved in the aetiology of depressive symptoms and vulnerability to depressive relapse. Neuroplasticity following antidepressant drug treatment in the hippocampus has been demonstrated in animal models but adaptive changes after such treatment have not been shown in humans. In this study, we determined whether grey matter loss in the hippocampus in depression (1) is present in medication-free depressed (2) changes in response to antidepressant treatment and (3) is present as a stable trait in medication-free remitted patients. Sixty-four medication-free unipolar depressed patients: 39 currently depressed and 25 in remission, and 66 healthy controls (HC) underwent structural magnetic resonance imaging in a cross-sectional and longitudinal design. Thirty-two currently depressed participants were then treated with the antidepressant citalopram for 8 weeks. Adherence to treatment was evaluated by measuring plasma citalopram concentration. We measured regional variation in grey matter concentration by using voxel-based morphometry-Diffeomorphic Anatomical Registration Through Exponentiated Lie algebra. Patients with current depression had bilaterally reduced grey matter in the hippocampus compared with HC and untreated patients in stable remission with the latter groups not differing. An increase in grey matter was observed in the hippocampus following treatment with citalopram in currently depressed patients. Grey matter reduction in the hippocampus appears specific to the depressed state and is a potential biomarker for a depressive episode.

A New, Blue Gene Highlights Glutamate and Hippocampus in Depression

Depression is a common and debilitating psychiatric syndrome with a complex risk architecture marked by interacting genetic and environmental factors. In this issue of Neuron, the study by Kohli etal. (2011) reports a novel genome-wide supported risk variant for depression that affects hippocampal gene expression, anatomy, and biochemistry.

Amygdala responsivity related to memory of emotionally neutral stimuli constitutes a trait factor for depression

Episodic memory impairment is considered to be a core cognitive deficit of Major Depressive Disorder (MDD) and has motivated a line of research investigating the role of the amygdala and the hippocampus in depression. While functional neuroimaging studies have focused on memory for emotional but not for neutral stimuli, in order to probe amygdala function, structural imaging studies have tied episodic memory to hippocampal function. We therefore investigated the neural correlates of episodic memory formation for neutral stimuli in 20 patients with a first depressive episode, 20 patients recovered from a first episode and 20 healthy controls. Because there is evidence that the amygdala exhibits hyperactive responses even to neutral stimuli in depressed subjects, we specifically explored the potential role of the amygdala in forming episodic memories with neutral content. Both patient groups showed stronger subsequent memory effects in the amygdala when compared to controls, in the absence of any differences in hippocampal activity between groups. Patients with a first episode of MDD showed increased activity related to episodic memory formation in a fronto-limbic network. These state-related activations may be related to a compensatory mechanism, which is supported by the absence of any differences in memory performance between groups. These findings represent initial evidence for a neurocognitive trait or vulnerability marker of depression-amygdala involvement in episodic memory formation of neutral stimuli.

High-dimensional mapping of the hippocampus in depression.

Abnormalities of the hippocampus may play a role in the pathophysiology of depression, but efforts to identify a structural abnormality in this brain structure among depressed patients have produced mixed results. Previous research may have been limited by exclusive reliance on measures of hippocampal volume. High-dimensional brain mapping is a new analytic method that quantitatively characterizes the shape as well as volume of a brain structure. In this study, high-dimensional brain mapping was used to evaluate hippocampal shape and volume in patients with major depressive disorder and healthy comparison subjects. By using magnetic resonance imaging, brain scans were obtained from 27 patients with major depressive disorder and 42 healthy comparison subjects. High-dimensional brain mapping generated a series of 10 variables (components) that represented hippocampal shape, and hippocampal volumes were also computed. Analysis of variance techniques were used to compare depressed patients and comparison subjects on hippocampal shape and volume. While the depressed patients and comparison subjects did not differ in hippocampal volume, there were highly significant group differences in hippocampal shape. The two groups did not overlap on a discriminant function computed from a model comprising the 10 components. The pattern of hippocampal surface deformation in the depressed patients suggested specific involvement of the subiculum. Patients with major depression may have structural abnormalities of the hippocampus that can be detected by analysis of hippocampal shape but not volume. A specific defect in the subiculum could have widespread effects throughout neurocircuits that appear to be abnormal in depression.