Inflammation predicts new onset of depression in men, but not in women within a prospective, representative community cohort

Recalled parental rearing behavior shapes mental health after preterm birth: Evidence from the Gutenberg Prematurity Study

Associations of preterm birth with later-life mental distress are well-established. A research gap concerns the role of psychosocial factors such as the family context. This study investigated associations of recalled parental rearing behavior with both preterm birth characteristics and psychological symptom burden later in life. Based on birth registry data of the Mainz University Hospital in Germany (infants born between 1969 and 2002) and using a selection algorithm, a cohort study comprising four gestational age (GA) strata was conducted (≥ 37 weeks: n = 138; 33-36 weeks: n = 132; 29-32 weeks: n = 106; ≤ 28 weeks: n = 132). Participants underwent a medical examination and completed standardized questionnaires. We investigated differences in dimensions of recalled parental rearing behavior according to GA and tested pre-/perinatal stress indicators and recalled parental rearing behavior as statistical predictors of depression and anxiety symptoms later in life. Lower GA was associated with more recalled emotional warmth and overprotection. Recalled emotional warmth was associated with fewer depression and anxiety symptoms, while recalled overprotection co-occurred with more depression symptoms. The findings indicate the relevance of parental rearing behavior for the offspring's mental health. As preterm birth implicates stress for the whole family requiring adaptive parental behavior, the latter could be an important modifiable risk factor.

Pre-Surgery Inflammatory and Angiogenesis Biomarkers as Predictors of 12-Month Cancer-Related Distress: Results from the ColoCare Study

BACKGROUND

Patients with colorectal cancer commonly suffer from complex psychological distress. Elevated distress may be linked to systemic biomarkers. We investigated associations of biomarkers of inflammation and angiogenesis with cancer-related distress (CTXD) score.

METHODS

N = 315 patients (stage I-IV) from 2 centers of the ColoCare Study were included: Huntsman Cancer Institute and University of Heidelberg. Biomarkers (e.g., IL6, VEGF-A, VEGF-D) were measured in serum collected pre-surgery and 12 months thereafter. The CTXD overall score and 4 subscales were collected 12 months after surgery and dichotomized to investigate biomarkers as predictors of distress 12 months after surgery; adjusted for age, sex, body mass index, tumor stage, center, and baseline levels of biomarkers.

RESULTS

Doubling of IL6 predicted future increased risk of overall distress [odds ratio (OR), 1.20; 95% confidence interval (CI), 1.02-1.41; P = 0.03]. VEGF-A-predicted future increased risk of high family strain (VEGF-A: OR, 1.21; 95% CI, 1.01-1.44; P = 0.04) and VEGF-D was associated with medical and financial demands (OR, 1.34; 95% CI, 1.01-1.74; P = 0.03).

CONCLUSIONS

This is the first study to show that systemic biomarkers are significantly associated with future CTXD score. Distress was not measured at baseline; we cannot rule out ongoing associations of inflammation and distress throughout treatment versus a direct effect of inflammation on distress. Nonetheless, these data add to evidence that biobehavioral processes interact and that systemic biomarkers are associated with cancer-related distress one year after surgery.

IMPACT

Exercise and diet interventions that lower systemic cytokine levels may impact longer-term CTXD score and improve quality of life of patients with colorectal cancer.

Treatment-resistant depression and risk of autoimmune diseases: evidence from a population-based cohort and nested case-control study

Recent literature indicates that patients with depression had increased immune activation. We hypothesised that treatment-resistant depression (TRD), an indicator of non-responsive depression with long-term dysregulated inflammation, could be an independent risk factor for subsequent autoimmune diseases. We performed a cohort study and a nested case-control study to examine the association between TRD and risk of autoimmune diseases, and to explore potential sex-specific difference. Using electronic medical records in Hong Kong, we identified 24,576 patients with incident depression between 2014 and 2016 without autoimmune history and followed up from diagnosis to death or December 2020 to identify TRD status and autoimmune incidence. TRD was defined as having at least two antidepressant regimens and the third regimen to confirm previous treatment failures. Based on age, sex and year of depression, we matched TRD patients 1:4 to the non-TRD in the cohort analysis using nearest-neighbour matching, and matched cases and controls 1:10 using incidence density sampling in the nested case-control analysis. We conducted survival analyses and conditional logistic regression respectively for risk estimation, adjusting for medical history. Across the study period, 4349 patients without autoimmune history (17.7%) developed TRD. With 71,163 person-years of follow-up, the cumulative incidence of 22 types of autoimmune diseases among the TRD patients was generally higher than the non-TRD (21.5 vs. 14.4 per 10,000 person-years). Cox model suggested a non-significant association (HR:1.48, 95% CI: 0.99-2.24, p = 0.059), whereas conditional logistic model showed a significant association (OR: 1.67, 95% CI: 1.10-2.53, p = 0.017) between TRD status and autoimmune diseases. Subgroup analysis showed that the association was significant in organ-specific diseases but not in systemic diseases. Risk magnitudes were generally higher among men compared to women. In conclusion, our findings provide evidence for an increased risk of autoimmune diseases in patients with TRD. Controlling chronic inflammation in hard-to-treat depression might play a role in preventing subsequent autoimmunity.

Sex-specific impacts of social isolation on loneliness, depressive symptoms, cognitive impairment, and biomarkers: Results from the social environment and biomarker of aging study

OBJECTIVES

To investigate sex-specific associations between social isolation and psychological outcomes and biomarkers among community-dwelling middle-aged and older adults using a nationally representative population-based cohort study.

METHODS

Data from 757 participants from the Social Environment and Biomarkers of Aging Study (SEBAS) were retrieved for analysis, and all participants were stratified by sex. The associations between social isolation and psychological outcomes (loneliness, depressive symptoms, and cognitive impairment) at the 4-year follow-up were examined by multivariate logistic regression models, and associations between social isolation and biomarkers at the 4-year follow-up were examined by multivariate generalized linear models (GLMs).

RESULTS

For men, social isolation was not associated with the development of loneliness. However, being married (adjusted odds ratio (aOR) 0.32 [95% confidence interval (CI) 0.13-0.74], p<0.001) was associated with a lower risk of loneliness, indicating potential protective effects of marriage for men. On the other hand, social isolation was associated with a 2-fold higher risk of loneliness in women (aOR 2.26 [1.01-5.09], p<0.001). Social isolation was not associated with depressive symptoms after adjusting for other demographics. For men, being married (aOR 0.51 [0.26-0.99], p<0.05) or having good self-reported health (aOR 0.44 [0.21-0.92], p<0.05) was protective against depressive symptoms. For women, only good self-reported health (aOR 0.30 [0.13-0.70], p<0.01) provided protective effects against depressive symptoms. Similarly, other demographic factors (being married and having a higher educational level) but not social isolation were associated with lower risks of cognitive impairment. No significant associations were noted between social isolation and selected biomarkers.

CONCLUSIONS

Sex-different associations between social isolation and loneliness were noted; the effects of demographic factors, such as being married, self-reported health status, and high education levels, on subsequent loneliness, depression, and cognitive function were also sex-different. Further intervention studies are needed to explore sex-specific approaches to deal with the interplay of social isolation, loneliness, psychological outcomes and other demographic factors.

Prescription Non-Steroidal Anti-Inflammatory Drugs (NSAIDs) and Incidence of Depression Among Older Cancer Survivors With Osteoarthritis: A Machine Learning Analysis

ObjectiveS

This study examined prescription NSAIDs as one of the leading predictors of incident depression and assessed the direction of the association among older cancer survivors with osteoarthritis.

Methods

This study used a retrospective cohort (N = 14, 992) of older adults with incident cancer (breast, prostate, colorectal cancers, or non-Hodgkin's lymphoma) and osteoarthritis. We used the longitudinal data from the linked Surveillance, Epidemiology, and End Results -Medicare data for the study period from 2006 through 2016, with a 12-month baseline and 12-month follow-up period. Cumulative NSAIDs days was assessed during the baseline period and incident depression was assessed during the follow-up period. An eXtreme Gradient Boosting (XGBoost) model was built with 10-fold repeated stratified cross-validation and hyperparameter tuning using the training dataset. The final model selected from the training data demonstrated high performance (Accuracy: 0.82, Recall: 0.75, Precision: 0.75) when applied to the test data. SHapley Additive exPlanations (SHAP) was used to interpret the output from the XGBoost model.

Results

Over 50% of the study cohort had at least one prescption of NSAIDs. Nearly 13% of the cohort were diagnosed with incident depression, with the rates ranging between 7.4% for prostate cancer and 17.0% for colorectal cancer. The highest incident depression rate of 25% was observed at 90 and 120 cumulative NSAIDs days thresholds. Cumulative NSAIDs days was the sixth leading predictor of incident depression among older adults with OA and cancer. Age, education, care fragmentation, polypharmacy, and zip code level poverty were the top 5 predictors of incident depression.

Conclusion

Overall, 1 in 8 older adults with cancer and OA were diagnosed with incident depression. Cumulative NSAIDs days was the sixth leading predictor with an overall positive association with incident depression. However, the association was complex and varied by the cumulative NSAIDs days.

Screening for loneliness in representative population samples: Validation of a single-item measure

BACKGROUND

Loneliness is a highly relevant public mental health issue. This work presents the validation of a single-item measure of loneliness and its subjective experience: "I am frequently alone/have few contacts". It can be used in large-scale population surveys where an economical assessment is of key importance.

METHODS

Data was drawn from two representative German population surveys conducted in early and late 2020 (combined N = 4,984; 52.9% women; age: M = 48.39 years (SD = 17.88)). We determined the prevalence of loneliness in men and women across different age groups. In order to test concurrent validity, bivariate correlation analyses and Chi-square tests were performed. Convergent and discriminant validity were tested by investigating intercorrelations of the single-item measure of loneliness with another loneliness measure, other mental health outcomes, and associations with sociodemographic characteristics.

RESULTS

Based on the single-item measure, 23.4% of participants reported some degree of loneliness, 3.4% among them severe loneliness. Comparisons with the LS-S showed similar prevalence rates of loneliness. A moderately positive relationship between the two loneliness measures was found by bivariate correlation analysis (ρ = .57, p < .001), but results indicated only weak convergent validity. Construct validity was supported by associations with depressive symptoms, anxiety symptoms, satisfaction with life, household size, and partnership.

CONCLUSIONS

Loneliness is frequently reported in the general population. The single-item measure of loneliness is suitable as a brief screening measure in population-based assessments.

Does Mental Distress Predict Cardiac Surgical Outcome?

BACKGROUND

 Mental distress is suspected to influence the morbidity of cardiac patients. Evaluating mental distress in cardiac patients is rare and the impact on surgical outcome is still not certified.

METHODS

 In 94 cardiac surgical patients, mental distress was assessed by the Patient Health Questionnaire-4 (PHQ-4). We defined length of stay in hospital and on intensive care unit as well as time of mechanical ventilation as outcomes on surgery. Age, physical activity, diabetes, overweight, PHQ-4, and an inflammation marker were tested for their predictive value on outcomes.

RESULTS

 Reportedly prevalence of generalized anxiety was 16.0% and depression rate was 13.8%. Length of stay in hospital was 13 ± 8 days, time of mechanical ventilation was 10 (0-1,207) hours, and length of stay on intensive care unit was 3 ± 6 days. Length of stay in hospital was significantly predicted by age (p = 0.048), low physical activity (p = 0.029), and high C-reactive protein (CRP; p = 0.031). Furthermore, CRP was the only significant predictor of time of mechanical ventilation and length of stay on intensive care unit.

CONCLUSION

 Outcome was not predicted by mental distress. However, inflammation marker CRP was predictive for outcome, potentially caused by higher cardiovascular risk profile. Additionally, depression was referred to be associated with inflammation. Probably, the small sample and the timing of assessment were responsible for the missing relation between mental distress and outcome. We presume a relation with low physical activity and depression. Nevertheless, further randomized studies are needed to pay more attention on patients' distress to intervene preoperatively to improve postoperative outcome.

Self-esteem only goes so far: the moderating effect of social media screen time on self-esteem and depressive symptoms

This study assessed the independent association of self-esteem and social media screen time on depressive symptoms, as well as the moderating role of social media screen time in the relationship between self-esteem and depressive symptoms. The Mobile Screen Time Project was a cross-sectional, web-based survey conducted from March to May of 2019. 437 U.S. college students were recruited via social networks from two institutions of higher education. Multivariable logistic regression assessed the associations between self-esteem and average daily social media time with depressive symptoms; an interaction effect was explored. Self-esteem had an inverse association (AOR = 0.87, 95% CI: 0.80-0.94) and daily social media time had a significant association with depressive symptoms (AOR = 1.11, 95% CI: 1.02-1.22) after adjusting for sexual and gender status, race/ethnicity, age, social status, and insomnia. We found a significant moderating effect (p = 0.016) of daily social media time. The more time spent on social media, the less protective self-esteem was against depressive symptoms. Those suffering from depressive symptoms or low self-esteem may benefit from reducing their social media use, intentionally exposing themselves to positive content and leveraging peer-to-peer social support through social media to create a sense of belonging.

The association of smoking and smoking cessation with prevalent and incident symptoms of depression, anxiety, and sleep disturbance in the general population

BACKGROUND

Smoking is a well-established risk factor for chronic non-communicable diseases. However, the relationship between cigarette smoking and the risk of developing mental health conditions remains largely elusive. This study examined the relationship between cigarette smoking as well as smoking cessation and prevalent and incident symptoms of depression, anxiety, and sleep disturbance in the general population.

METHODS

In a cohort of 15,010 individuals from the Gutenberg Health Study (aged 35-74 years at enrollment), prevalent (at baseline from 2007 to 2012) and incident symptoms (at follow-up from 2012 to 2017) of depression, anxiety, and sleep disturbance were determined by validated questionnaires and/or medical records. Smoking status, pack-years of smoking in current and former smokers, and years since quitting smoking in former smokers were assessed by a standardized computer-assisted interview.

RESULTS

In multivariable logistic regression models with comprehensive adjustment for covariates, smoking status was independently associated with prevalent and incident symptoms of depression (Patient Health Questionnaire-9 ≥ 10), whereas this association was weaker for anxiety (Generalized Anxiety Disorder Scale-2 ≥ 3) and sleep disturbance (Patient Health Questionnaire-9 > 1). Among current and former smokers, smoking ≥30 or ≥10 pack-years, respectively, yielded in general the highest effect estimates. Smoking cessation was weakly associated with the prevalence and incidence of all outcomes, here consistent associations were observed for prevalent symptoms of depression.

LIMITATIONS

The observational nature of the study does not allow for causal inferences.

CONCLUSIONS

The results of the present study suggest that cigarette smoking is positively and that smoking cessation is negatively associated with symptoms of common mental health conditions, in particular of depression.

Rethinking minority stress: A social safety perspective on the health effects of stigma in sexually-diverse and gender-diverse populations

For over two decades, the minority stress model has guided research on the health of sexually-diverse individuals (those who are not exclusively heterosexual) and gender-diverse individuals (those whose gender identity/expression differs from their birth-assigned sex/gender). According to this model, the cumulative stress caused by stigma and social marginalization fosters stress-related health problems. Yet studies linking minority stress to physical health outcomes have yielded mixed results, suggesting that something is missing from our understanding of stigma and health. Social safety may be the missing piece. Social safety refers to reliable social connection, inclusion, and protection, which are core human needs that are imperiled by stigma. The absence of social safety is just as health-consequential for stigmatized individuals as the presence of minority stress, because the chronic threat-vigilance fostered by insufficient safety has negative long-term effects on cognitive, emotional, and immunological functioning, even when exposure to minority stress is low. We argue that insufficient social safety is a primary cause of stigma-related health disparities and a key target for intervention.

Pro-inflammatory cytokines and suicidal behavior among patients with bipolar I disorder

OBJECTIVE

Suicidal behavior and different mood states of bipolar I disorder (BD) have been shown to be associated with dysregulated proinflammatory cytokines. Only a few studies have examined the association between inflammation and SB in BD, and the association between proinflammatory cytokines, SB, and cognitive deficits in patients with BD remains unclear.

METHODS

77 patients with BD and 61 age-/sex-matched healthy controls were recruited. Patients were divided into two groups: with suicidal ideation (SI; n = 21) and no SI (n = 56). SI was defined by a score of ≥1 in item 10 of Montgomery Åsberg Depression Rating Scale. Levels of proinflammatory cytokines, including soluble interleukin-6 receptor (sIL-6R), soluble tumor necrosis factor-α receptor type 1 (sTNF-αR1), and C-reactive protein (CRP), were measured, and cognitive function was assessed using 2-back task and Go/No-Go task.

RESULTS

Patients with SI had higher levels of sTNF-αR1 than those without SI and the controls (p = .004). BD patients with or without a history of suicide attempt had higher levels of CRP than the controls. SI was associated with serum levels of sTNF-αR1 and IL-6sR, even after additionally controlling for working memory and inhibitory control (p < .05).

CONCLUSION

This study indicates that serum levels of sTNF-αR1 have distinct differences between BD patients with or without SI, and our findings strengthen the hypothesis of a link between suicidal behavior and neuro-inflammation pathophysiology in BD.

Role of Inflammation in Traumatic Brain Injury-Associated Risk for Neuropsychiatric Disorders: State of the Evidence and Where Do We Go From Here

In the past decade, there has been an increasing awareness that traumatic brain injury (TBI) and concussion substantially increase the risk for developing psychiatric disorders. Even mild TBI increases the risk for depression and anxiety disorders such as posttraumatic stress disorder by two- to threefold, predisposing patients to further functional impairment. This strong epidemiological link supports examination of potential mechanisms driving neuropsychiatric symptom development after TBI. One potential mechanism for increased neuropsychiatric symptoms after TBI is via inflammatory processes, as central nervous system inflammation can last years after initial injury. There is emerging preliminary evidence that TBI patients with posttraumatic stress disorder or depression exhibit increased central and peripheral inflammatory markers compared with TBI patients without these comorbidities. Growing evidence has demonstrated that immune signaling in animals plays an integral role in depressive- and anxiety-like behaviors after severe stress or brain injury. In this review, we will 1) discuss current evidence for chronic inflammation after TBI in the development of neuropsychiatric symptoms, 2) highlight potential microglial activation and cytokine signaling contributions, and 3) discuss potential promise and pitfalls for immune-targeted interventions and biomarker strategies to identify and treat TBI patients with immune-related neuropsychiatric symptoms.

The Antidepressant Duloxetine Inhibits Platelet Function and Protects against Thrombosis

While cardiovascular disease (CVD) is the leading cause of death, major depressive disorder (MDD) is the primary cause of disability, affecting more than 300 million people worldwide. Interestingly, there is evidence that CVD is more prevalent in people with MDD. It is well established that neurotransmitters, namely serotonin and norepinephrine, are involved in the biochemical mechanisms of MDD, and consequently, drugs targeting serotonin-norepinephrine reuptake, such as duloxetine, are commonly prescribed for MDD. In this connection, serotonin and norepinephrine are also known to play critical roles in primary hemostasis. Based on these considerations, we investigated if duloxetine can be repurposed as an antiplatelet medication. Our results-using human and/or mouse platelets show that duloxetine dose-dependently inhibited agonist-induced platelet aggregation, compared to the vehicle control. Furthermore, it also blocked agonist-induced dense and α-granule secretion, integrin αIIbβ3 activation, phosphatidylserine expression, and clot retraction. Moreover duloxetine-treated mice had a significantly prolonged occlusion time. Finally, duloxetine was also found to impair hemostasis. Collectively, our data indicate that the antidepressant duloxetine, which is a serotonin-norepinephrine antagonist, exerts antiplatelet and thromboprotective effects and inhibits hemostasis. Consequently, duloxetine, or a rationally designed derivative, presents potential benefits in the context of CVD, including that associated with MDD.

Neuroinflammation as a pathophysiological factor in the development and maintenance of functional seizures: A hypothesis

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Early-life stress may be a priming neuroinflammatory factor for later development of FS.

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Secondary trauma has emerged as an important predisposing factor for FS initiation.

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We propose an explanatory, two-hit hypothesis for FS development.

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The proposed hypothesis is based on findings from neuroimaging and biomarker studies.

The neurobiological underpinnings of functional seizure (FS) development and maintenance represent an active research area. Recent work has focused on hardware (brain structure) and software (brain function and connectivity). However, understanding whether FS are an adaptive consequence of changes in brain structure, function, and/or connectivity is important for identifying a causative mechanism and for FS treatment and prevention. Further, investigation must also uncover what causes these structural and functional phenomena. Pioneering work in the field of psychoneuroimmunology has established a strong, consistent link between psychopathology, immune dysfunction, and brain structure/function. Based on this and recent FS biomarker findings, we propose a new etiologic model of FS pathophysiology. We hypothesize that early-life stressors cause neuroinflammatory and neuroendocrine changes that prime the brain for later FS development following secondary trauma (e.g., traumatic brain injury or psychological trauma). This framework coalesces existing knowledge regarding brain aberrations underlying FS and established neurobiological theories on the pathophysiology of underlying psychiatric disorders. We also propose brain temperature mapping as a way of indirectly visualizing neuroinflammation in patients with FS, particularly in emotion regulation, fear processing, and sensory-motor integration circuits. We offer a foundation on which future research can be built, with clear recommendations for future studies.

Lärm und Luftverschmutzung: Ihr Einfluss auf psychische Erkrankungen

Immer mehr Studien belegen die Einflüsse von Lärm und Luftverschmutzung als bedeutsame Umweltrisikofaktoren für kardiovaskuläre Erkrankungen. Weniger gut geklärt ist, wie diese Faktoren die psychische Gesundheit beeinflussen. Aktuelle Studienergebnisse zeigen, dass Umgebungslärm (vor allem Verkehrslärm) und verschiedene Bestandteile von Luftverschmutzung (vor allem Feinstaub) das Risiko für psychische Erkrankungen, insbesondere Depressionen und Angststörungen, erhöhen können. Pathophysiologische Mechanismen umfassen das enge Zusammenspiel von biologischen (wie oxidativem Stress und Inflammation) und psychosozialen Faktoren (wie mentalem Stress, subjektive Lärmbelästigung und -sensitivität). Umweltrisikofaktoren wie Lärm- und Luftverschmutzung können einen signifikanten Einfluss auf die psychische Gesundheit ausüben. Aufgrund der teils heterogenen Studienergebnisse und der limitierten Verfügbarkeit von methodisch hochwertigen Längsschnittstudien sind zwingend weitere Untersuchungen notwendig, um die zugrunde liegenden Mechanismen zu verstehen und präventive Maßnahmen abzuleiten.

Characterizing Sex Differences in Depressive-Like Behavior and Glial Brain Cell Changes Following Peripheral Nerve Injury in Mice

Chronic pain and depression are intimately linked; the combination of the two leads to higher health care costs, lower quality of life, and worse treatment outcomes with both conditions exhibiting higher prevalence among women. In the current study, we examined the development of depressive-like behavior in male and female mice using the spared nerve injury (SNI) model of neuropathic pain. Males displayed increased immobility on the forced-swim test - a measure of depressive-like behavior - 2 weeks following injury, while females developed depressive-like behavior at 3-week. Since the pathogenesis of chronic pain and depression may involve overlapping mechanisms including the activation of microglial cells, we explored glial cell changes in brain regions associated with pain processing and affect. Immunohistochemical analyses revealed that microglial cells were more numerous in female SNI mice in the contralateral ventral anterior cingulate cortex (ACC), a brain region important for pain processing and affect behavior, 2-week following surgery. Microglial cell activation was not different between any of the groups for the dorsal ACC or nucleus accumbens. Analysis of astrocyte density did not reveal any significant changes in glial fibrillary acidic protein (GFAP) staining in the ACC or nucleus accumbens. Overall, the current study characterized peripheral nerve injury induced depression-like behavior in male and female mice, which may be associated with different patterns of glial cell activation in regions important for pain processing and affect.

Understanding Vulnerability to Late-Life Suicide

PURPOSE OF REVIEW

We review recent evidence on suicide among older adults, examine risk factors contributing to vulnerability to late-life suicide, and summarize possible interventions.

RECENT FINDINGS

We found a steadily increasing rate of late-life suicide in the USA in the past decade. Evidence supporting the integration of depression care managers into primary care for risk reduction is among the strongest to date. Pharmacologic and neuromodulation studies should be considered in geriatric depression complicated by suicidality. Broad societal campaigns about suicide education, as well as active outreach to psychiatric patients after discharge or a suicidal crisis, prevent suicidal behavior. Growing research supports an integrative multidisciplinary approach. Suicide is a complex and multifaceted behavior with numerous casual points for intervention. Access to deadly means, presence of depression, disease, disability, and social disconnection are factors that increase vulnerability. Quality geriatric care, regular screening in primary and emergency care settings, and a multidisciplinary approach are necessary to mitigate risk factors. The COVID-19 pandemic amplifies need for a more aggressive approach.

Knockout of NPFFR2 Prevents LPS-Induced Depressive-Like Responses in Mice

The precise neural mechanisms underlying the pathogenesis of depression are largely unknown, though stress-induced brain inflammation and serotonergic plasticity are thought to be centrally involved. Moreover, we previously demonstrated that neuropeptide FF receptor 2 (NPFFR2) overexpression provokes depressive-like behaviors in mice. Here, we assess whether NPFFR2 is involved in priming of depressive-like behaviors and downregulation of serotonergic 1A receptor (5HT1AR) after lipopolysaccharide (LPS) treatment. The forced swimming test (FST) and sucrose preference test (SPT) were used to quantify depressive-like phenotypes in wild-type (WT) and NPFFR2-knockout (KO) mice. A single dose of LPS (i.p. 1 mg/kg) readily caused increases in toll-like receptor 4 and tumor necrosis factor-α along with decreases in 5-HT1AR mRNA in the ventral hippocampus of WT mice. Furthermore, LPS treatment of WT mice increased immobility time in FST and decreased sucrose preference in SPT. In contrast, none of these effects were observed in NPFFR2-KO mice. While WT mice injected with lentiviral 5-HT1AR shRNA in the ventral hippocampus displayed an unaltered response after LPS challenge, LPS-challenged NPFFR2-KO mice displayed a profound decrease in sucrose preference when pretreated with 5-HT1AR shRNA. Taken together, these results suggest that NPFFR2 modulates LPS-induced depressive-like behavioral phenotypes by downregulating 5HT1AR in the ventral hippocampus.