Mood disorders are among the commonest mental disorders worldwide. Epidemiological and clinical evidence suggests that there are close links between infectious diseases and mood disorders, but the strength and direction of these association remain largely unknown. Theoretical models have attempted to explain this link based on evolutionary or immune-related factors, but these have not been empirically verified. The current study examined cross-sectional and longitudinal associations between the incidence of infectious diseases and mood disorders, while correcting for climate and economic factors, based on data from the Global Burden of Disease Studies, 1990-2019. It was found that major depressive disorder was positively associated with lower respiratory infections, while bipolar disorder was positively associated with upper respiratory infections and negatively associated with enteric and tropical infections, both cross-sectionally and over a period of thirty years. These results suggest that a complex, bidirectional relationship exists between these disorders. This relationship may be mediated through the immune system as well as through the gut-brain and lung-brain axes. Understanding the mechanisms that link these groups of disorders could lead to advances in the prevention and treatment of both.

Post-traumatic stress disorder (PTSD) is a chronic psychiatric disorder that occurs following exposure to traumatic events. The prevalence of PTSD is estimated to be 5-10% worldwide, and it is associated with significant distress and disability. Recent evidence suggests that PTSD may be a risk factor for the development of subsequent neurodegenerative disorders, including Alzheimer’s dementia and Parkinson’s disease. Identification of biomarkers known to be associated with neurodegeneration in patients with PTSD would shed light on the pathophysiological mechanisms linking these disorders, and would also help in the development of preventive approaches aimed at reducing the risk of neurodegenerative disorders in PTSD. In the current review, the PubMed and Scopus databases were searched for studies aimed at identifying genetic, biochemical, neuroimaging or behavioral markers associated with neurodegeneration in patients with PTSD. Out of a total of 342 citations retrieved, 29 relevant studies were identified for inclusion in the review. The results of these studies suggest that several potentially relevant biological markers, including cerebral cortical thinning, disrupted white matter integrity, specific genetic polymorphisms, immune-inflammatory alterations, vitamin D deficiency, metabolic syndrome and parasomnias, may be associated with an increased risk of neurodegeneration in patients with PTSD. Though many of these results need replication, they highlight a number of biological pathways that plausibly link PTSD with neurodegenerative disorders, and suggest potentially valuable avenues for prevention and early intervention in this patient population.

Depression and obesity are highly comorbid with one another, with evidence for bidirectional causal links between each disorder and a shared biological basis. The available evidence suggests that genetic factors play a major role in influencing both the occurrence of comorbid depression and obesity, their courses, and their response to existing treatments. The current paper is a scoping review of studies that have evaluated the contribution of specific genetic variants to the comorbidity between obesity and depression. Based on a search of the PubMed and EMBASE databases, 28 studies were included in this review, covering 54 candidate genes. Positive associations were identified for fourteen genetic loci (AKR1C2, APOA5, COMT, DAT1, FTO, KCNE1, MAOA, MC4R, MCHR2, NPY2R, NR3C1, Ob, PCSK9 and TAL1). Replicated findings across two or more independent samples were observed for the FTO and MC4R genes. Many of these gene products represent novel molecular targets for the pharmacological management of obesity which are not pharmacologically influenced by existing anti-obesity or antidepressant medications. The implications of these associations for future drug development are discussed, with an emphasis on recent evidence on the polygenic architecture of comorbid depression and obesity, and on a precision medicine approach to these conditions.

Several studies have identified a relationship between air pollution and depression, particularly in relation to fine particulate matter (PM2.5) exposure. However, the strength of this association appears to be moderated by variables such as age, gender, genetic vulnerability, physical activity and climatic conditions, and has not been assessed at a cross-national level to date. The current study examines the association between the prevalence of depression in each country, based on the most recent Global Burden of Disease Study data, and the average national level of PM2.5 based on the World Health Organization’s database. The observed associations were adjusted for age, gender, level of physical activity, income, education, population density, climate, and type of depression. It was observed that there was a modest but significant positive correlation between PM2.5 level and the prevalence of depression even after adjusting for the above confounders. This association was more marked above a certain threshold and applied chiefly to major depressive episodes. These findings are of significant public health importance in terms of preventive strategies aimed at reducing the population-level burden of depression.

Disruptive behaviour disorders (DBDs) in childhood, such as conduct disorder (CD) and oppositional defiant disorder (ODD) are characterized by high levels of irritability and aggression. Though psychological management is considered the first-line approach for these disorders, many children and adolescents require adjunctive pharmacotherapy for the control of specific symptoms. Several prior systematic reviews have examined the evidence for the use of antipsychotics in the symptomatic management of DBDs, but have concluded that their efficacy is marginal and limited by significant adverse effects. This paper updates existing reviews of this field by reviewing clinical trials of antipsychotics in children and adolescents with DBDs published in the period 2-1-2017 to 2-10-2022. The PubMed, Scopus and ScienceDirect databases were searched for relevant citations. Six relevant trials were identified during this period. These trials were critically evaluated in terms of outcome measures, efficacy and safety. Overall, the data from these trials suggests that certain atypical antipsychotics, such as risperidone and clozapine, are effective in the short-term management of aggression in DBDs. They have no apparent effect on cognition, but are associated with significant metabolic adverse effects. The results of these trials, and of the earlier systematic reviews, are discussed in the light of global trends towards increasing off-label prescription of antipsychotic medication in children and adolescents, and of recent literature on the neuropharmacology of aggression in this patient population. The need for rational, short-term use of these drugs is highlighted, as well as the importance of post-marketing surveillance for long-term or severe adverse events.

Anxiety disorders are among the most common mental disorders worldwide, and often respond incompletely to existing treatments. Selenium, a micronutrient that is a component of several biologically active selenoproteins, is also involved in several aspects of brain functioning, and may exert antidepressant and anxiolytic effects through multiple pathways. The current paper is a scoping review of translational, observational and interventional evidence on the potential role of selenium and its compounds in the management of anxiety and related disorders. Evidence from animal models suggests that this approach may be promising. Though evidence from observational studies in humans is inconsistent and affected by several confounding factors, the available evidence from randomized controlled trials suggests that selenium supplementation may be beneficial in the management of certain anxiety-related conditions, such as anxiety in medically ill patients, prevention of anxiety following exposure to traumatic stress, and obsessive-compulsive disorder. This paper provides a critical evaluation of the existing evidence base, including unanswered questions that could serve as the focus of further research, and outlines the potential benefits and risks associated with the use of selenium in anxiety disorders.

Parkinson’s disease and Alzheimer’s disease are the most commonly diagnosed neurodegenerative disorders. Though these disorders differ in terms of their underlying pathophysiology as well as in their clinical features and course, there is a certain degree of overlap between them. This overlap may be partly related to α-synuclein-mediated neuropathological changes. Recent evidence has found that depression is associated with an increased subsequent risk of both these neurological disorders, and that α-synuclein may also play a pathogenic role in depression. The current study examines epidemiological, population genetic and environmental exposure data in relation to the estimated prevalence of depressive disorders, Parkinson’s disease and Alzheimer’s disease using a cross-sectional, country-level analysis. The results of this study are consistent with a significant relationship between depressive disorders and neurodegenerative disorders, a possible shared genetic vulnerability related to functional polymorphisms of the α-synuclein gene SNCA, and potential gene-environment interactions involving fine particulate matter pollution. The significance of these results is discussed in the light of existing translational, clinical and epidemiological research on the links between these disorders.

The association between mental illness and violent crimes such as homicide is complex. In 1939, Lionel Penrose hypothesized that the availability of psychiatric hospital beds was inversely related to the prison population, presumably due to the hospitalization of potential offenders with a mental illness. Subsequent studies have found evidence for this association, but questions remain about the contributions of confounding factors. Moreover, there has been a move towards deinstitutionalization and community care of the mentally ill over the past six decades. In this study, the association between national homicide rates and three measures of the availability of psychiatric care – the numbers of psychiatrists, general hospital psychiatric beds, and psychiatric hospital beds per 100,000 population – was examined using a time-lagged correlation analysis. Associations between homicide rates and socioeconomic factors associated with crime were also examined. It was found that the availability of psychiatrists and of general hospital psychiatric beds were both negatively correlated with homicide rates, and that the association with general hospital psychiatric beds remained significant even after correction for confounding factors. These results suggest the need for a more nuanced interpretation of Penrose’s original formulation, involving the interplay of social, economic factors and psychological factors rather than linear causality.

Suicidal behaviour is a public health problem whose magnitude is both substantial and increasing. Since many individuals seek medical treatment following a suicide attempt, strategies aimed at reducing further attempts in this population are a valid and feasible secondary prevention approach. An evaluation of the available evidence suggests that existing treatment approaches have limited efficacy in this setting, highlighting the need for innovative approaches to suicide prevention. Existing research on the neurobiology of social pain has highlighted the importance of this phenomenon as a risk factor for suicide, and has also yielded several attractive targets for pharmacological preventive strategies. In this paper, the available evidence related to these targets is synthesized and critically evaluated. The way in which social pain is related to the “anti-suicidal” properties of recently approved treatments, such as ketamine and psilocybin, is also examined. Such strategies may be effective for the short-term reduction of suicidal ideation and behaviour in individuals who have made a suicide attempt suicide prevention, particularly in cases where social pain is identified as a contributory factor. These pharmacological approaches may be effective regardless of the presence or absence of a specific psychiatric diagnosis.

Recent research has identified the gut-brain axis as a key mechanistic pathway and potential therapeutic target in depression. In this paper, the potential role of gut hormones as potential treatments or predictors of response in depression is examined, with specific reference to the peptide hormone motilin. This possibility is explored through two methods: (a) a conceptual review of the possible links between motilin and depression, including evidence from animal and human research as well as clinical trials, and (b) an analysis of the relationship between a functional polymorphism (rs2281820) of the motilin (MLN) gene and cross-national variations in the prevalence of depression. It was observed that (a) there are several plausible mechanisms, including interactions with diet, monoamine, and neuroendocrine pathways, to suggest that motilin may be relevant to the pathophysiology and treatment of depression, and (b) there was a significant correlation between rs2281820 allele frequencies and the prevalence of depression after correcting for multiple confounding factors. These results suggest that further evaluation of the utility of motilin and related gut peptides as markers of antidepressant response is required, and that these molecular pathways represent potential future mechanisms for antidepressant drug development.

Depression is the commonest mental disorder worldwide. Both antidepressants and psychotherapy are effective in treating depression, but response to these treatments is often incomplete. Yoga-based interventions (YBIs) have emerged as a promising adjunctive treatment for depression. Recent research has attempted to identify the biological mechanisms associated with the antidepressant actions of YBIs. In this scoping review, conducted according to the PRISMA-ScR guidelines, the PubMed and Scopus databases were searched to retrieve research on biomarkers of response to YBIs in patients with depression. Eleven studies were included in the review. Based on these studies, YBIs may improve depression through beneficial effects on systemic inflammation, stress axis regulation, cardiac autonomic functioning, and possibly reductions in oxidative stress-related cellular damage. Increases in brain-derived neurotrophic factor (BDNF) may represent a final common pathway upon which these processes converge. Though these results are theoretically plausible, they should be interpreted with caution due to certain methodological limitations in the existing research. Replication of these results and improvements in study methodology, and the evaluation of other biomarkers relevant to the pathophysiology of depression, could further elucidate the mechanism of action of YBIs in this disorder, and identify which patients would benefit most from this treatment approach.