Greater amygdala activity and dorsomedial prefrontal-amygdala coupling are associated with enhanced inflammatory responses to stress

The Role of Brain Structure and Function in the Association Between Inflammation and Depressive Symptoms: A Systematic Review

OBJECTIVE

Major depressive disorder and related symptoms have been shown to be associated with inflammation, and this association is likely to be mediated through changes in brain structure and function. This article provides a systematic review of studies that have used brain imaging techniques to identify neural mechanisms linking inflammation and depressive symptoms.

METHODS

A systematic search of online databases identified 26 studies that fulfilled the inclusion and exclusion criteria.

RESULTS

In general, increased peripheral inflammation was associated with differences in function in several subcortical regions, as well as medial and ventral prefrontal regions-both at rest (7 studies) and during exposure to emotional stimuli (14 studies). Also, increased activation in some of these regions was associated with depression (18 studies). Too few studies have measured neuroinflammation markers (three) or brain structure (three), so generalizations about these mechanisms cannot yet be made.

CONCLUSIONS

This review supports the view that peripheral inflammation is an etiological process that may influence depression via effects on brain function. Several methodological inconsistencies in the extant literature need to be addressed, most notably a lack of formal mediational testing in longitudinal designs and inconsistencies across imaging methods and inflammation induction and measurement techniques. Further work is also required to establish the mechanisms by which basal inflammation levels influence brain function and depressive symptoms in both healthy and clinical samples.

Persistent adaptation by chronic alcohol is facilitated by neuroimmune activation linked to stress and CRF

This review updates the conceptual basis for the association of alcohol abuse with an insidious adaptation that facilitates negative affect during withdrawal from chronic intermittent alcohol (CIA) exposure - a change that later supports sensitization of stress-induced anxiety following alcohol abstinence. The finding that a CRF1-receptor antagonist (CRF1RA) minimized CIA withdrawal-induced negative affect supported an association of alcohol withdrawal with a stress mechanism. The finding that repeated stresses or multiple CRF injections into selected brain sites prior to a single 5-day chronic alcohol (CA) exposure induced anxiety during withdrawal provided critical support for a linkage of CIA withdrawal with stress. The determination that CRF1RA injection into positive CRF-sensitive brain sites prevented CIA withdrawal-induced anxiety provided support that neural path integration maintains the persistent CIA adaptation. Based upon reports that stress increases neuroimmune function, an effort was undertaken to test whether cytokines would support the adaptation induced by stress/CA exposure. Twenty-four hours after withdrawal from CIA, cytokine mRNAs were found to be increased in cortex as well as other sites in brain. Further, repeated cytokine injections into previously identified brain sites substituted for stress and CRF induction of anxiety during CA withdrawal. Discovery that a CRF1RA prevented the brain cytokine mRNA increase induced by CA withdrawal provided critical evidence for CRF involvement in this neuroimmune induction after CA withdrawal. However, the CRF1RA did not block the stress increase in cytokine mRNA increases in controls. The latter data supported the hypothesis that distinct mechanisms linked to stress and CA withdrawal can support common neuroimmune functions within a brain site. As evidence evolves concerning neural involvement in brain neuroimmune function, a better understanding of the progressive adaptation associated with CIA exposure will advance new knowledge that could possibly lead to strategies to combat alcohol abuse.

Dorsal Anterior Cingulate Cortex Responses to Repeated Social Evaluative Feedback in Young Women with and without a History of Depression

The dorsal anterior cingulate cortex (dACC) is recruited when a person is socially rejected or negatively evaluated. However, it remains to be fully understood how this region responds to repeated exposure to personally-relevant social evaluation, in both healthy populations and those vulnerable to Major Depressive Disorder (MDD), as well as how responding in these regions is associated with subsequent clinical functioning. To address this gap in the literature, we recruited 17 young women with past history of MDD (previously depressed) and 31 healthy controls and exposed them to a social evaluative session in a neuroimaging environment. In two bouts, participants received an equal amount of positive, negative, and neutral feedback from a confederate. All participants reported increases in feelings of social evaluation in response to the evaluative task. However, compared to healthy controls, previously depressed participants tended to show greater increases in depressed mood following the task. At the neural level, in response to negative (vs. positive) feedback, no main effect of group or evaluation periods was observed. However, a significant interaction between group and evaluation periods was found. Specifically, over the two bouts of evaluation, activity in the dACC decreased among healthy participants while it increased among previously depressed individuals. Interestingly and unexpectedly, in the previously depressed group specifically, this increased activity in dACC over time was associated with lower levels of depressive symptoms at baseline and at 6-months following the evaluation session (controlling for baseline levels). Thus, the subset of previously depressed participants who showed increases in the recruitment of the dACC over time in response to the negative evaluation seemed to fair better emotionally. These findings suggest that examining how the dACC responds to repeated bouts of negative evaluation reveals a new dimension to the role of the dACC in processing exclusion and contributing to mental health outcomes in a population vulnerable to MDD. Further, investigation of the dynamics of the dACC response to negative social evaluation is warranted.

Neural mechanisms linking social status and inflammatory responses to social stress

Social stratification has important implications for health and well-being, with individuals lower in standing in a hierarchy experiencing worse outcomes than those higher up the social ladder. Separate lines of past research suggest that alterations in inflammatory processes and neural responses to threat may link lower social status with poorer outcomes. This study was designed to bridge these literatures to investigate the neurocognitive mechanisms linking subjective social status and inflammation. Thirty-one participants reported their subjective social status, and underwent a functional magnetic resonance imaging scan while they were socially evaluated. Participants also provided blood samples before and after the stressor, which were analysed for changes in inflammation. Results showed that lower subjective social status was associated with greater increases in inflammation. Neuroimaging data revealed lower subjective social status was associated with greater neural activity in the dorsomedial prefrontal cortex (DMPFC) in response to negative feedback. Finally, results indicated that activation in the DMPFC in response to negative feedback mediated the relation between social status and increases in inflammatory activity. This study provides the first evidence of a neurocognitive pathway linking subjective social status and inflammation, thus furthering our understanding of how social hierarchies shape neural and physiological responses to social interactions.

Links between inflammation, amygdala reactivity, and social support in breast cancer survivors

Psychosocial stress can affect inflammatory processes that have important consequences for cancer outcomes and the behavioral side effects of cancer treatment. To date, however, little is known about the upstream neural processes that may link psychosocial stressors and inflammation in cancer patients and survivors. To address this issue, 15 women who had been diagnosed with early-stage breast cancer and completed cancer treatment and 15 age- and ethnicity-matched women with no cancer history were recruited for a neuroimaging study. Participants provided a blood sample for levels of circulating inflammatory markers (CRP and IL-6), underwent an fMRI scan in which they completed a threat reactivity task designed to elicit activity in the amygdala, and reported their levels of perceived social attachment/support. There were no significant differences between cancer survivors and controls in levels of CRP or IL-6, in amygdala reactivity to the socially threatening images, or in levels of perceived social support. However, results showed a strong, positive correlation between CRP concentration and left amygdala reactivity in the survivor group that was not apparent in controls. Higher levels of social support in the survivor group were also associated with reduced amygdala reactivity and CRP. These data suggest the possibility of a stronger "neural-immune pipeline" among breast cancer survivors, such that peripheral inflammation is more strongly associated with neural activity in threat-related brain regions.

Divergent responses of inflammatory mediators within the amygdala and medial prefrontal cortex to acute psychological stress

There is now a growing body of literature that indicates that stress can initiate inflammatory processes, both in the periphery and brain; however, the spatiotemporal nature of this response is not well characterized. The aim of this study was to examine the effects of an acute psychological stress on changes in mRNA and protein levels of a wide range of inflammatory mediators across a broad temporal range, in key corticolimbic brain regions involved in the regulation of the stress response (amygdala, hippocampus, hypothalamus, medial prefrontal cortex). mRNA levels of inflammatory mediators were analyzed immediately following 30min or 120min of acute restraint stress and protein levels were examined 0h through 24h post-termination of 120min of acute restraint stress using both multiplex and ELISA methods. Our data demonstrate, for the first time, that exposure to acute psychological stress results in an increase in the protein level of several inflammatory mediators in the amygdala while concomitantly producing a decrease in the protein level of multiple inflammatory mediators within the medial prefrontal cortex. This pattern of changes seemed largely restricted to the amygdala and medial prefrontal cortex, with stress producing few changes in the mRNA or protein levels of inflammatory mediators within the hippocampus or hypothalamus. Consistent with previous research, stress resulted in a general elevation in multiple inflammatory mediators within the circulation. These data indicate that neuroinflammatory responses to stress do not appear to be generalized across brain structures and exhibit a high degree of spatiotemporal specificity. Given the impact of inflammatory signaling on neural excitability and emotional behavior, these data may provide a platform with which to explore the importance of inflammatory signaling within the prefrontocortical-amygdala circuit in the regulation of the neurobehavioral responses to stress.

Long-term consequences of childhood maltreatment: Altered amygdala functional connectivity

Childhood maltreatment is a serious individual, familial, and societal threat that compromises healthy development and is associated with lasting alterations to emotion perception, processing, and regulation (Cicchetti & Curtis, 2005; Pollak, Cicchetti, Hornung, & Reed, 2000; Pollak & Tolley-Schell, 2003). Individuals with a history of maltreatment show altered structural and functional brain development in both frontal and limbic structures (Hart & Rubia, 2012). In particular, previous research has identified hyperactive amygdala responsivity associated with childhood maltreatment (e.g., Dannlowski et al., 2012). However, less is known about the impact of maltreatment on the relationship between the amygdala and other brain regions. The present study employed an emotion processing functional magnetic resonance imaging task to examine task-based activation and functional connectivity in adults who experienced maltreatment as children. The sample included adults with a history of substantiated childhood maltreatment (n = 33) and comparison adults (n = 38) who were well matched on demographic variables, all of whom have been studied prospectively since childhood. The maltreated group exhibited greater activation than comparison participants in the prefrontal cortex and basal ganglia. In addition, maltreated adults showed increased amygdala connectivity with the hippocampus and prefrontal cortex. The results suggest that the intense early stress of childhood maltreatment is associated with lasting alterations to frontolimbic circuitry.

Neural pathways of embarrassment and their modulation by social anxiety

While being in the center of attention and exposed to other's evaluations humans are prone to experience embarrassment. To characterize the neural underpinnings of such aversive moments, we induced genuine experiences of embarrassment during person-group interactions in a functional neuroimaging study. Using a mock-up scenario with three confederates, we examined how the presence of an audience affected physiological and neural responses and the reported emotional experiences of failures and achievements. The results indicated that publicity induced activations in mentalizing areas and failures led to activations in arousal processing systems. Mentalizing activity as well as attention towards the audience were increased in socially anxious participants. The converging integration of information from mentalizing areas and arousal processing systems within the ventral anterior insula and amygdala forms the neural pathways of embarrassment. Targeting these neural markers of embarrassment in the (para-)limbic system provides new perspectives for developing treatment strategies for social anxiety disorders.

S100B blood levels and childhood trauma in adolescent inpatients

BACKGROUND

Serum levels of the astrocytic protein S100B have been reported to indicate disruption of the blood-brain barrier. In this study, we investigated the relationship between S100B levels and childhood trauma in a child psychiatric inpatient unit.

METHOD

Levels of S100B were measured in a group of youth with mood disorders or psychosis with and without history of childhood trauma as well as in healthy controls. Study participants were 93 inpatient adolescents admitted with a diagnosis of psychosis (N = 67), or mood disorder (N = 26) and 22 healthy adolescents with no history of trauma or psychiatric illness. Childhood trauma was documented using the Life Events Checklist (LEC) and Adverse Child Experiences (ACE).

RESULTS

In a multivariate regression model, suicidality scores and trauma were the only two variables which were independently related to serum S100B levels. Patients with greater levels of childhood trauma had significantly higher S100B levels even after controlling for intensity of suicidal ideation. Patients with psychotic diagnoses and mood disorders did not significantly differ in their levels of S100B. Patients exposed to childhood trauma were significantly more likely to have elevated levels of S100B (p < .001) than patients without trauma, and patients with trauma had significantly higher S100B levels (p < .001) when compared to the control group. LEC (p = 0.046), and BPRS-C suicidality scores (p = 0.001) significantly predicted S100B levels.

CONCLUSIONS

Childhood trauma can potentially affect the integrity of the blood-brain barrier as indicated by associated increased S100B levels.