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Purpose of Review The rising suicide rate in the USA will not be reversed without improved risk assessment and prevention practices. To date, the best method for clinicians to assess a patient’s risk for suicide is screening for past suicide attempts in the patient and their family. However, neuroimaging, genomic, and biochemical studies have generated a body of findings that allow description of an initial heuristic biological model for suicidal behavior that may have predictive value. Recent Findings We review studies from the past 3 years examining potential biological predictors of suicide attempt behavior. We divide findings into two major categories: (1) structural and functional brain imaging findings and (2) biochemical and genomic findings encompassing several systems, including major neurotransmitters (serotonin, catecholamines, GABA, and glutamate), the hypothalamic pituitary adrenal (HPA) axis, the inflammasome, lipids, and neuroplasticity. Summary The biomarkers that appear promising for assessing suicide risk in clinical settings include indices of serotonergic function, inflammation, neuronal plasticity, and lipids.

Major depressive disorder (MDD) was previously hypothesized to be a disease of monoamine deficiency in which low levels of monoamines in the synaptic cleft were believed to underlie depressive symptoms. More recently, however, there has been a paradigm shift toward a neuroplasticity hypothesis of depression in which downstream effects of antidepressants, such as increased neurogenesis, contribute to improvements in cognition and mood. This review takes a top-down approach to assess how changes in behavior and hippocampal-dependent circuits may be attributed to abnormalities at the molecular, structural, and synaptic level. We conclude with a discussion of how antidepressant treatments share a common effect in modulating neuroplasticity and consider outstanding questions and future perspectives.

A stress-diathesis explanatory model of suicidal behaviour has proved to be of heuristic value, and both clinical and neurobiological components can be integrated into such a model. A trait deficiency in serotonin input to the anterior cingulate and ventromedial prefrontal cortex is found in association with suicide, and more recently non-fatal suicidal behaviour, and is linked to decision-making and suicide intent by imaging and related studies in vivo. The same neural circuitry and serotonin deficiency may contribute to impulsive aggressive traits that are part of the diathesis for suicidal behaviour and are associated with early onset mood disorders and greater risk for suicidal behaviour. Other brain areas manifest deficient serotonin input, that is, a trait related to recurrent major depressive disorder and bipolar disorder. Thus the serotonin system is involved in both the diathesis for suicidal behaviour in terms of decision-making, and to a major stressor, namely episodes of major depression.

Public health and epidemiologic research have established that social connectedness promotes overall health. Yet there have been no recent reviews of findings from research examining social connectedness as a determinant of mental health. The goal of this review was to evaluate recent longitudinal research probing the effects of social connectedness on depression and anxiety symptoms and diagnoses in the general population. A scoping review was performed of PubMed and PsychInfo databases from January 2015 to December 2021 following PRISMA-ScR guidelines using a defined search strategy. The search yielded 66 unique studies. In research with other than pregnant women, 83% (19 of 23) studies reported that social support benefited symptoms of depression with the remaining 17% (5 of 23) reporting minimal or no evidence that lower levels of social support predict depression at follow-up. In research with pregnant women, 83% (24 of 29 studies) found that low social support increased postpartum depressive symptoms. Among 8 of 9 studies that focused on loneliness, feeling lonely at baseline was related to adverse outcomes at follow-up including higher risks of major depressive disorder, depressive symptom severity, generalized anxiety disorder, and lower levels of physical activity. In 5 of 8 reports, smaller social network size predicted depressive symptoms or disorder at follow-up. In summary, most recent relevant longitudinal studies have demonstrated that social connectedness protects adults in the general population from depressive symptoms and disorders. The results, which were largely consistent across settings, exposure measures, and populations, support efforts to improve clinical detection of high-risk patients, including adults with low social support and elevated loneliness.

Emerging spatial technologies, including spatial transcriptomics and spatial epigenomics, are becoming powerful tools for profiling of cellular states in the tissue context 1 , 2 , 3 , 4 – 5 . However, current methods capture only one layer of omics information at a time, precluding the possibility of examining the mechanistic relationship across the central dogma of molecular biology. Here, we present two technologies for spatially resolved, genome-wide, joint profiling of the epigenome and transcriptome by cosequencing chromatin accessibility and gene expression, or histone modifications (H3K27me3, H3K27ac or H3K4me3) and gene expression on the same tissue section at near-single-cell resolution. These were applied to embryonic and juvenile mouse brain, as well as adult human brain, to map how epigenetic mechanisms control transcriptional phenotype and cell dynamics in tissue. Although highly concordant tissue features were identified by either spatial epigenome or spatial transcriptome we also observed distinct patterns, suggesting their differential roles in defining cell states. Linking epigenome to transcriptome pixel by pixel allows the uncovering of new insights in spatial epigenetic priming, differentiation and gene regulation within the tissue architecture. These technologies are of great interest in life science and biomedical research. The authors present two technologies for spatially resolved, genome-wide, joint profiling of the epigenome and transcriptome by cosequencing chromatin accessibility and gene expression, or histone modifications and gene expression on the same tissue section at near-single-cell resolution.

Glutamate (Glu) and gamma-aminobutyric acid (GABA) are implicated in the pathophysiology of major depressive disorder (MDD). GABA levels or GABAergic interneuron numbers are generally low in MDD, potentially disinhibiting Glu release. It is unclear whether Glu release or turnover is increased in depression. Conversely, a meta-analysis of prefrontal proton magnetic resonance spectroscopy (1H MRS) studies in MDD finds low Glx (combination of glutamate and glutamine) in medicated MDD. We hypothesize that elevated Glx or Glu may be a marker of more severe, untreated MDD. We examined ventromedial prefrontal cortex/anterior cingulate cortex (vmPFC/ACC) Glx and glutamate levels using 1H MRS in 34 medication-free, symptomatic, chronically ill MDD patients and 32 healthy volunteers, and GABA levels in a subsample. Elevated Glx and Glu were observed in MDD compared with healthy volunteers, with the highest levels seen in males with MDD. vmPFC/ACC GABA was low in MDD. Higher Glx levels correlated with more severe depression and lower GABA. MDD severity and diagnosis were both linked to higher Glx in vmPFC/ACC. Low GABA in a subset of these patients is consistent with our hypothesized model of low GABA leading to glutamate disinhibition in MDD. This finding and model are consistent with our previously reported findings that the NMDAR-antagonist antidepressant effect is proportional to the reduction of vmPFC/ACC Glx or Glu levels.

Smaller hippocampal volume is reported in major depressive disorder (MDD). We hypothesize that it may be related to fewer granule neurons (GN) in the dentate gyrus (DG), a defect possibly reversible with antidepressants. We studied age-, sex-, and postmortem interval-matched groups: no major psychopathology (controls); unmedicated-MDD; and MDD treated with serotonin reuptake inhibitors (MDD*SSRI) or tricyclics (MDD*TCA). Frozen right hippocampi were fixed, sectioned (50 μm), immunostained with neuronal nuclear marker (NeuN), and counterstained with hematoxylin. GN and glial number, and DG and granule cell layer (GCL) volumes were stereologically estimated. Fewer GNs in the anterior DG were present in unmedicated-MDDs compared with controls (p=0.013). Younger age of MDD onset correlated with fewer GNs (p=0.021). Unmedicated-MDDs had fewer mid-DG GNs than MDD*SSRIs (p=0.028) and controls (p=0.032). Anterior GCL glial number did not differ between groups. Anterior/mid GCL volume was smaller in unmedicated-MDDs vs controls (p=0.008) and larger in MDD*SSRIs vs unmedicated-MDDs (p<0.001), MDD*TCAs (p<0.001), and controls (p<0.001). Anterior GCL volume and GN number (r=0.594, p=0.001), and mid DG volume and GN number (r=0.398, p=0.044) were correlated. Anterior DG capillary density correlated with GN number (p=0.027), and with GCL (p=0.024) and DG (r=0.400, p=0.047) volumes. Posterior DG volume and GN number did not differ between groups. Fewer GNs in unmedicated-MDD without fewer neuronal progenitor cells, as previously reported, suggests a cell maturation or survival defect, perhaps related to MDD duration. This may contribute to a smaller hippocampus and is potentially reversed by SSRIs. Postmortem studies are correlative and animal studies are needed to test implied causal relationships.

Disparities by sex and racial/ethnic group in suicide death rates are present in US adolescents. Whether disparities in suicide death extend to groups targeted for suicide prevention efforts, namely, those with suicidal ideation or nonfatal suicide attempts, is unknown. To examine differences in temporal trends between suicidal ideation and suicide attempts in US adolescents from 1991 through 2019 by sex and race/ethnicity subgroups. A cross-sectional analysis of the national Youth Risk Behavior Survey, weighted to represent US adolescents from 1991 to 2019, included 183 563 US high-school students in grades 9 to 12. Data were analyzed from September 16, 2020, through April 12, 2021. Calendar year, sex, race/ethnicity, and interactions of sex and race/ethnicity. Survey-weighted prevalence estimates, annual percentage changes (APCs) and average APC in the survey-weighted prevalence of suicidal ideation and nonfatal suicide attempts, constructed from self-reported suicidal ideation, plan, and attempts in each survey year, by sex, race/ethnicity (non-Hispanic White, non-Hispanic Black, Hispanic, non-Hispanic Asian or Pacific Islander and Native Hawaiian, American Indian/Alaska Native), and their interactions (sex × race/ethnicity). In 183 563 (unweighted) included adolescents (mean [SD] age, 16.07 [1.23] years; 94 282 females [weighted percentage, 49.4%; 95% CI, 48.8%-50.1%]), the prevalence of suicidal ideation decreased from 1991 to 2019 (from 19.4% to 15.8%; 95% CI, 0.7%-0.9%), whereas the prevalence of nonfatal suicide attempts increased from 1991 to 2019 (from 7.3% to 8.9%; 95% CI, 1.0%-1.4%). Joinpoint regression indicated a -3.1% (95% CI, -3.7% to -2.6%) annual decrease in suicidal ideation between 1991 and 2009, followed by a 3.4% annual increase (95% CI, 1.9% -4.8%) between 2009 and 2019. Decreasing followed by increasing trends in suicidal ideation showed modestly different turning points in female (1991-2009, 2009-2019), White (1991-2009, 2009-2019), Hispanic (1991-2007, 2007-2019), and Black (1991-2005, 2005-2019) adolescents. Although no significant trends were observed in suicide attempts from 1991 through 2019, male (68.4% increase; 95% CI, 0.2% -1.2%) and Black (79.7% increase; 95% CI, 0.1%-1.5%) adolescents had greater increases in the prevalence of suicide attempts. Interaction of sex and race/ethnicity revealed increases in suicidal ideation in White females from 2009 to 2019 (APC, 4.3%; 95% CI, 1.5%-7.1%), Black females from 2005 to 2019 (APC, 3.4%; 95% CI, 1.4%-5.4%), and Hispanic females from 2009 to 2019 (APC, 3.3%; 95% CI, 1.0%-5.6%) and suicide attempts in White females from 2009 to 2019 (APC, 3.1%; 95% CI, 0.3%-6.0%). The findings of this study show apparent sex and racial/ethnic differences in trends in suicidal ideation and suicide attempts. Increases in suicidal ideation since 2009 were observed in female individuals; changes in male and Black adolescents represented the largest increase in the prevalence of suicide attempts between 1991 and 2019. Evidence-based suicide prevention programs need to be tailored by sex and race/ethnicity, calling for greater diversification of health care system, school, and community prevention approaches.

Cellular function in tissue is dependent on the local environment, requiring new methods for spatial mapping of biomolecules and cells in the tissue context 1 . The emergence of spatial transcriptomics has enabled genome-scale gene expression mapping 2 – 5 , but the ability to capture spatial epigenetic information of tissue at the cellular level and genome scale is lacking. Here we describe a method for spatially resolved chromatin accessibility profiling of tissue sections using next-generation sequencing (spatial-ATAC-seq) by combining in situ Tn5 transposition chemistry 6 and microfluidic deterministic barcoding 5 . Profiling mouse embryos using spatial-ATAC-seq delineated tissue-region-specific epigenetic landscapes and identified gene regulators involved in the development of the central nervous system. Mapping the accessible genome in the mouse and human brain revealed the intricate arealization of brain regions. Applying spatial-ATAC-seq to tonsil tissue resolved the spatially distinct organization of immune cell types and states in lymphoid follicles and extrafollicular zones. This technology progresses spatial biology by enabling spatially resolved chromatin accessibility profiling to improve our understanding of cell identity, cell state and cell fate decision in relation to epigenetic underpinnings in development and disease. Spatial-ATAC-seq—spatially resolved chromatin accessibility profiling of tissue sections using next-generation sequencing—delineated tissue-region-specific epigenetic landscapes in mouse embryos and identified gene regulators involved in the development of the central nervous system and the lymphoid tissue.

Neuroinflammation and cyclooxygenase-2 (COX-2) upregulation are associated with the pathogenesis of degenerative brain diseases such as Alzheimer’s disease (AD), Parkinson’s disease (PD), amyotrophic lateral sclerosis (ALS), epilepsy, and a response to traumatic brain injury (TBI) or stroke. COX-2 is also induced in acute pain, depression, schizophrenia, various cancers, arthritis and in acute allograft rejection. Positron emission tomography (PET) imaging allows for the direct measurement of in vivo COX-2 upregulation and thereby enables disease staging, therapy evaluation and aid quantifying target occupancy of novel nonsteroidal anti-inflammatory drugs or NSAIDs. Thus far, no clinically useful radioligand is established for monitoring COX-2 induction in brain diseases due to the delay in identifying qualified COX-2-selective inhibitors entering the brain. This review examines radiolabeled COX-2 inhibitors reported in the past decade and identifies the most promising radioligands for development as clinically useful PET radioligands. Among the radioligands reported so far, the three tracers that show potential for clinical translation are, [11CTMI], [11C]MC1 and [18F]MTP. These radioligands demonstrated BBB permeablity and in vivo binding to constitutive COX-2 in the brain or induced COX-2 during neuroinflammation.