Exaggerated amygdala response to threat and association with immune hyperactivity in depression

Oral Oxytocin Blurs Sex Differences in Amygdala Responses to Emotional Scenes

BACKGROUND

Sex differences are shaped both by innate biological differences and the social environment and are frequently observed in human emotional neural responses. Oral administration of oxytocin (OXT), as an alternative and noninvasive intake method, has been shown to produce sex-dependent effects on emotional face processing. However, it is unclear whether oral OXT produces similar sex-dependent effects on processing continuous emotional scenes.

METHODS

The current randomized, double-blind, placebo-controlled neuropsychopharmacological functional magnetic resonance imaging experiment was conducted in 147 healthy participants (OXT = 74, men/women = 37/37; placebo = 73, men/women = 36/37) to examine the oral OXT effect on plasma OXT concentrations and neural response to emotional scenes in both sexes.

RESULTS

At the neuroendocrine level, women showed lower endogenous OXT concentrations than men, but oral OXT increased OXT concentrations equally in both sexes. Regarding neural activity, emotional scenes evoked opposite valence-independent effects on right amygdala activation (women > men) and its functional connectivity with the insula (men > women) in men and women in the placebo group. This sex difference was either attenuated (amygdala response) or even completely eliminated (amygdala-insula functional connectivity) in the OXT group. Multivariate pattern analysis confirmed these findings by developing an accurate sex-predictive neural pattern that included the amygdala and the insula under the placebo but not the OXT condition.

CONCLUSIONS

The results of the current study suggest a pronounced sex difference in neural responses to emotional scenes that was eliminated by oral OXT, with OXT having opposite modulatory effects in men and women. This may reflect oral OXT enhancing emotional regulation to continuous emotional stimuli in both sexes by facilitating appropriate changes in sex-specific amygdala-insula circuitry.

A theory of the neural mechanisms underlying negative cognitive bias in major depression

The widely acknowledged cognitive theory of depression, developed by Aaron Beck, focused on biased information processing that emphasizes the negative aspects of affective and conceptual information. Current attempts to discover the neurological mechanism underlying such cognitive and affective bias have successfully identified various brain regions associated with severally biased functions such as emotion, attention, rumination, and inhibition control. However, the neurobiological mechanisms of how individuals in depression develop this selective processing toward negative is still under question. This paper introduces a neurological framework centered around the frontal-limbic circuit, specifically analyzing and synthesizing the activity and functional connectivity within the amygdala, hippocampus, and medial prefrontal cortex. Firstly, a possible explanation of how the positive feedback loop contributes to the persistent hyperactivity of the amygdala in depression at an automatic level is established. Building upon this, two hypotheses are presented: hypothesis 1 revolves around the bidirectional amygdalohippocampal projection facilitating the amplification of negative emotions and memories while concurrently contributing to the impediment of the retrieval of opposing information in the hippocampus attractor network. Hypothesis 2 highlights the involvement of the ventromedial prefrontal cortex in the establishment of a negative cognitive framework through the generalization of conceptual and emotional information in conjunction with the amygdala and hippocampus. The primary objective of this study is to improve and complement existing pathological models of depression, pushing the frontiers of current understanding in neuroscience of affective disorders, and eventually contributing to successful recovery from the debilitating affective disorders.

Childhood Maltreatment and Amygdala Response to Interpersonal Threat in a Transdiagnostic Adult Sample: The Role of Trait Dissociation

BACKGROUND

Childhood maltreatment (CM) confers risk for different mental disorders as well as transdiagnostic symptoms such as dissociation. Aberrant amygdala response to interpersonal threat may link CM to transdiagnostic psychopathology and has recently been shown to depend on type and developmental timing of CM experiences. Still, most studies on CM and threat-related amygdala response employ categorical disorder-specific perspectives and fail to consider type and timing of CM exposure. We aimed to investigate associations between CM, amygdala response to interpersonal threat, and dimensional psychopathological symptoms including trait dissociation in a transdiagnostic adult sample, specifically considering type, timing, and duration of CM.

METHODS

We conducted a cross-sectional neuroimaging study in 141 participants with varying levels of CM, including mostly female participants with major depressive disorder (n = 36), posttraumatic stress disorder (n = 34), and somatic symptom disorder (n = 35) and healthy volunteers (n = 36). Participants underwent functional magnetic resonance imaging during an emotional face-matching task, completed the brief German interview version of the Maltreatment and Abuse Chronology of Exposure scale, and answered self-report measures of transdiagnostic CM-related symptoms including trait dissociation. Data were analyzed using a machine learning-based model comparison procedure.

RESULTS

In our transdiagnostic sample, neither type nor timing or duration of CM predicted amygdala response to interpersonal threat. Instead, trait dissociation predicted blunted bilateral amygdala response and emerged as a possible mediator between CM and amygdala function.

CONCLUSIONS

Trait dissociation may be an important confounder in the widely documented association between CM and threat-related amygdala response, which should be considered in future longitudinal studies.

The association of positive emotions with absenteeism and presenteeism in Japanese workers

BACKGROUND

Negative emotions such as depression have been associated with increased absenteeism and presenteeism, contributing to substantial economic loss. However, no study has investigated if positive emotions such as happiness influence absenteeism and presenteeism.

METHODS

Using data from the Japan COVID-19 and Society Internet Survey (JACSIS), a nationwide survey conducted in September-October 2022 (n = 19,214), we investigated if two major, representative positive emotions (happiness and gratitude) are associated with absenteeism and presenteeism. Absenteeism was defined as reporting more than one day of sick leave in the past one month. Presenteeism was measured with the Work Functioning Impairment Scale. Logistic regression was used to estimate odds ratios.

RESULTS

12.4 % and 21.8 % of subjects reported absenteeism and presenteeism, respectively. Logistic regression estimated that after adjusting covariates, happiness was associated with lower odds of absenteeism (OR = 0.792, 95 % CI [0.706, 0.888]) and presenteeism (OR = 0.531, 95 % CI [0.479, 0.588]) while gratitude was associated with lower odds of presenteeism only (OR = 0.705, 95 % CI [0.643, 0.774]). Furthermore, simultaneous presence of both happiness and gratitude was associated with further lower odds of presenteeism (OR = 0.385, 95%CI [0.338, 0.439]), indicating a synergetic relation.

DISCUSSION

This study is the first to investigate the association between positive emotions and absenteeism and presenteeism. Given the substantial economic loss due to absenteeism and presenteeism, strategies to enhance positive emotions are necessary.

Cell-liposome delivery system based on neuroinflammation to target the amygdala for ameliorating depressive-like behaviors

Depression is a serious psychiatric disorder with unsatisfactory outcomes due to difficulties in delivering therapeutic molecules from the periphery to the brain. Neuroinflammation plays a key role in neurobiology and the treatment of depression. Neutrophils can cross the blood-brain barrier (BBB) and infiltrate key brain regions related to the pathophysiology of depression during neuroinflammation. N-Acetyl Pro-Gly-Pro (PGP) peptides efficiently bind to CXCR2 receptors on the surface of neutrophils. The neuropeptide oxytocin demonstrated antidepressant properties in preclinical and clinical studies, but its inability to penetrate the BBB hampers its therapeutic applications. In this study, we established a novel drug delivery system based on neutrophil infiltration in key brain regions during neuroinflammation. PGP was used to modify oxytocin-loaded liposomes (PGP-OTL) as the target ligand. Systematic administration of PGP-OTL exhibited enhanced antidepressant properties resulting from elevated oxytocin concentrations, especially in the amygdala, a crucial depression-implicated brain region. Enhanced antidepressant effects of PGP-OTL, similar to the ones caused by central oxytocin infusion, were observed in behavioral measurement including forced swim and tail suspension tests. Our study demonstrated that PGP-OTL can "hitchhike" neutrophils and enhance delivery of therapeutics into the brain, thus providing the means for developing novel cell-liposome-based drug delivery strategies for depression therapy.

Ketamine and serotonergic psychedelics: An update on the mechanisms and biosignatures underlying rapid-acting antidepressant treatment

The discovery of ketamine as a rapid-acting antidepressant spurred significant research to understand its underlying mechanisms of action and to identify other novel compounds that may act similarly. Serotonergic psychedelics (SPs) have shown initial promise in treating depression, though the challenge of conducting randomized controlled trials with SPs and the necessity of long-term clinical observation are important limitations. This review summarizes the similarities and differences between the psychoactive effects associated with both ketamine and SPs and the mechanisms of action of these compounds, with a focus on the monoaminergic, glutamatergic, gamma-aminobutyric acid (GABA)-ergic, opioid, and inflammatory systems. Both molecular and neuroimaging aspects are considered. While their main mechanisms of action differ-SPs increase serotonergic signaling while ketamine is a glutamatergic modulator-evidence suggests that the downstream mechanisms of action of both ketamine and SPs include mechanistic target of rapamycin complex 1 (mTORC1) signaling and downstream GABAA receptor activity. The similarities in downstream mechanisms may explain why ketamine, and potentially SPs, exert rapid-acting antidepressant effects. However, research on SPs is still in its infancy compared to the ongoing research that has been conducted with ketamine. For both therapeutics, issues with regulation and proper controls should be addressed before more widespread implementation. This article is part of the Special Issue on "Ketamine and its Metabolites".

Inflammation-Related Functional and Structural Dysconnectivity as a Pathway to Psychopathology

Findings from numerous laboratories and across neuroimaging modalities have consistently shown that exogenous administration of cytokines or inflammatory stimuli that induce cytokines disrupts circuits and networks involved in motivation and motor activity, threat detection, anxiety, and interoceptive and emotional processing. While inflammatory effects on neural circuits and relevant behaviors may represent adaptive responses promoting conservation of energy and heightened vigilance during immune activation, chronically elevated inflammation may contribute to symptoms of psychiatric illnesses. Indeed, biomarkers of inflammation such as cytokines and acute phase reactants are reliably elevated in a subset of patients with unipolar or bipolar depression, anxiety-related disorders, and schizophrenia and have been associated with differential treatment responses and poor clinical outcomes. A growing body of literature also describes higher levels of endogenous inflammatory markers and altered, typically lower functional or structural connectivity within these circuits in association with transdiagnostic symptoms such as anhedonia and anxiety in psychiatric and at-risk populations. This review presents recent evidence that inflammation and its effects on the brain may serve as one molecular and cellular mechanism of dysconnectivity within anatomically and/or functionally connected cortical and subcortical regions in association with transdiagnostic symptoms. We also discuss the need to establish reproducible methods to assess inflammation-associated dysconnectivity in relation to behavior for use in translational studies or biomarker-driven clinical trials for novel pharmacological or behavioral interventions targeting inflammation or its effects on the brain.