Is serotonin an upper or a downer? The evolution of the serotonergic system and its role in depression and the antidepressant response

What we got wrong about depression and its treatment

The paradigm is shifting with respect to how we think about depression and its treatment. Some of that shift can be attributed to new findings with respect to its epidemiology and genetics and the rest can be attributed to the incorporation of a new perspective derived from evolutionary theory. In brief, depression is far more prevalent than previously recognized with the bulk of additional cases involving individuals who do not go on to become recurrent. Nonpsychotic unipolar depression (but not bipolar mania which likely is a "true" disease) appears to be an adaptation that evolved to facilitate rumination in the service of resolving complex social problems in our ancestral past. Cognitive behavior therapy appears to structure that rumination so that patients at elevated risk for recurrence do not get "stuck" blaming themselves for their misfortunes, whereas antidepressant medications may suppress symptoms at the expense of prolonging the underlying episode such that patients remain at elevated risk for relapse whenever they try to discontinue. This means that patients not otherwise at risk for recurrence may be put on medications that they do not need and kept on them indefinitely whether they need to be or not.

Association between exposure to organophosphorus pesticide and suicidal ideation among U.S. adults: A population-based study

OBJECTIVE

This study aims to investigate the potential link between exposure to organophosphorus pesticides (OPPs) and suicidal ideation (SI) among adults.

METHODS

This study encompassed four cycles of the National Health and Nutrition Examination Survey (NHANES), involving 5244 participants aged 20 and above. SI was assessed using the Patient Health Questionnaire-9. The levels of exposure to OPPs were estimated by analyzing concentrations of OPP metabolites in urine samples. Multivariate logistic regression models were used to explore the association between exposure to each OPP and SI. Stratified analyses and interaction tests were conducted across various groups, including pairwise combinations of gender and age, as well as body mass index, smoking status, hypertension, and diabetes. Weighted Quantile Sum (WQS) regression and Bayesian Kernel Machine Regression (BKMR) models were applied to assess the cumulative impact of exposure to the four OPPs on SI, along with their respective contributions. Additionally, the potential interactions among these four OPPs were evaluated.

RESULTS

Multivariate logistic regression revealed that only dimethylthiophosphate (DMTP) among OPPs demonstrated a statistically significant positive association with SI [OR: 1.18; 95 % CI: 1.02-1.37]. Stratified analyses indicated that the influence of OPPs on SI was particularly pronounced in young and older men. The WQS regression analysis revealed a statistically significant association between the mixed metabolites of OPPs and SI [OR = 1.10, 95 % CI: 1.04-1.16], with DMTP (weighted 0.63) contributing the most. Furthermore, the BKMR model supported a positive trend in the overall impact of these OPP metabolites on SI, displaying notable individual exposure-response relationships for DMTP (PIP: 0.77).

CONCLUSIONS

Our study suggests an association between exposure to DMTP and an increased risk of SI. Specifically, young adult males and older males appear particularly susceptible to the effects of OPP exposure.

Serotonin transporter knockdown relieves depression-like behavior and ethanol-induced CPP in mice after chronic social defeat stress

Patients with stress-triggered major depression disorders (MDD) can often seek comfort or temporary relief through alcohol consumption, as they may turn to it as a means of self-medication or coping with overwhelming emotions. The use of alcohol as a coping mechanism for stressful events can escalate, fostering a cycle where the temporary relief it provides from depression can deepen into alcohol dependence, exacerbating both conditions. Although, the specific mechanisms involved in stress-triggered alcohol dependence and MDD comorbidities are not well understood, a large body of literature suggests that the serotonin transporter (SERT) plays a critical role in these abnormalities. To further investigate this hypothesis, we used a lentiviral-mediated knockdown approach to examine the role of hippocampal SERT knockdown in social defeat stress-elicited depression like behavior and ethanol-induced place preference (CPP). The results showed that social defeat stress-pro depressant effects were reversed following SERT knockdown demonstrated by increased sucrose preference, shorter latency to feed in the novelty suppressed feeding test, and decreased immobility time in the tail suspension and forced swim tests. Moreover, and most importantly, social stress-induced ethanol-CPP acquisition and reinstatement were significantly reduced following hippocampal SERT knockdown using short hairpin RNA shRNA-expressing lentiviral vectors. Finally, we confirmed that SERT hippocampal mRNA expression correlated with measures of depression- and ethanol-related behaviors by Pearson's correlation analysis. Taken together, our data suggest that hippocampal serotoninergic system is involved in social stress-triggered mood disorders as well as in the acquisition and retrieval of ethanol contextual memory and that blockade of this transporter can decrease ethanol rewarding properties.

Effect of icariin on depressive behaviour in rat pups. Evidences for its mechanism of action by integrating network pharmacology, metabolomics and gut microbiota composition

BACKGROUND

Prenatal stress (PS) can cause cognitive disorder and a range of psychological illnesses, including anxiety and depression. Icariin (ICA) has shown promising effects in improving PS-induced depressive behaviour. However, its mechanism of action remains unclear.

PURPOSE

This study was performed to reveal the key targets, metabolites and gut microbiota for ICA in improving depressive behaviour in PS rat pups.

METHODS

A prenatal restraint stress animal model was established for Sprague-Dawley (SD) rats in late pregnancy. Male pups were randomly divided into six groups: no stress group (NS), PS group, PS + saline group (PS_S), PS + high-dose ICA group (ICAH, 80 mg/kg*day), PS + low-dose ICA group (ICAL, 40 mg/kg*day) and PS + fluoxetine group (FLU, 10 mg/kg*day). The depressive behaviour of each group of rat pups was evaluated using open field test, forced swimming test and sucrose preference test. Different metabolites were identified using untargeted metabolomics of serum and faeces, and metabolic pathways were analyzed through MetaboAnalyst. Targets for ICA acting on depression were determined after network pharmacology was applied. An integrated network of network pharmacology and metabolomics were constructed using Cytoscape software, and molecular docking were performed to verify the interactions between ICA and key targets. Finally, gut microbiota of rat pups in each group were analyzed after 16S rDNA sequencing.

RESULTS

PS could cause rat pups to exhibit depressive behaviour, and ICA could significantly improve this depressive behaviour. A total of 49 differential metabolites were found in serum and 23 differential metabolites were found in faeces, and 24 metabolites in serum and 6 metabolites in faeces could be reversed following ICA administration. Integrated analysis focused on five key targets (i.e. adenosyl homocysteinase; medium-chain specific acyl-CoA dehydrogenase, mitochondrial; thymidine phosphorylase; cGMP-specific 3',5'-cyclic phosphodiesterase and xanthine dehydrogenase/oxidase) and three metabolites (i.e. palmitoylcarnitine, methionine and hypoxanthine). Molecular docking indicated that ICA combined well with key targets. Gut microbiota analysis showed that g_Bacteroides, f_Bacteroidaceae and s_Lactobacillus reuteri were required for ICA to improve depressive behaviour.

CONCLUSION

In this study, the antidepressant mechanism of ICA was clarified with a strategy of integrating metabolomics, network pharmacology and gut microbiota. ICA has a good effect on improving metabolism and increasing the abundance of probiotics in the intestine. The present research provided new insights into the anti-depressant mechanism of ICA.

Doxycycline reversal of amphetamine-induced mania-like behavior is related to adjusting brain monoamine abnormalities and antioxidant effects in primary hippocampal neurons

Mania is associated with disturbed dopaminergic transmission in frontotemporal regions. D-amphetamine (AMPH) causes increased extracellular DA levels, considered an acknowledged mania model in rodents. Doxycycline (DOXY) is a second-generation tetracycline with promising neuroprotective properties. Here, we tested the hypothesis that DOXY alone or combined with Lithium (Li) could reverse AMPH-induced mania-like behavioral alterations in mice by the modulation of monoamine levels in brain areas related to mood regulation, as well as cytoprotective and antioxidant effects in hippocampal neurons. Male Swiss mice received AMPH or saline intraperitoneal (IP) injections for 14 days. Between days 8-14, mice receive further IP doses of DOXY, Li, or their combination. For in vitro studies, we exposed hippocampal neurons to DOXY in the presence or absence of AMPH. DOXY alone or combined with Li reversed AMPH-induced risk-taking behavior and hyperlocomotion. DOXY also reversed AMPH-induced hippocampal and striatal hyperdopaminergia. In AMPH-exposed hippocampal neurons, DOXY alone and combined with Li presented cytoprotective and antioxidant effects, while DOXY+Li also increased the expression of phospho-Ser133-CREB. Our results add novel evidence for DOXY's ability to reverse mania-like features while revealing that antidopaminergic activity in some brain areas, such as the hippocampus and striatum, as well as hippocampal cytoprotective effects may account for this drug's antimanic action. This study provides additional rationale for designing clinical trials investigating its potential as a mood stabilizer agent.

Behavioral and neurophysiological effects of buspirone in healthy and depression-like state juvenile salmon

A proportion of farmed salmon in seawater show a behaviorally inhibited, growth stunted profile known as a depression-like state (DLS). These DLS fish are characterized by chronically elevated serotonergic signaling and blood plasma cortisol levels and the inability to react further to acute stress, which is suggestive of chronic stress. In this study, we characterize the neuroendocrine profile of growth stunted freshwater parr and confirm that they show a DLS-like neuroendocrine profile with a blunted cortisol response and no serotonergic increase in response to acute stress. Furthermore, we attempted to reverse this DLS-like profile through pharmacological manipulation of the serotonin (5-HT) system with buspirone, an anxiolytic medication that acts as a serotonin receptor agonist (i.e., decreases serotonergic signaling). We found that while buspirone decreases anxiolytic-type behavior in healthy fish, no quantifiable behavioral change was found in DLS-like fish. However, there was a physiological effect of diminished basal serotonergic signaling. This suggests that at the physiological level, buspirone appears to reverse the neuroendocrine DLS profile. With a deeper understanding of what causes DLS profiles and growth stunting in juvenile fish, steps can be taken in terms of husbandry to prevent repeated stressors and the formation of the DLS profile, potentially reducing losses in aquaculture due to chronic stress.

Associations of antidepressant medication consumption with changes in personality pathology and quality of life among community-dwelling adults

BACKGROUND

Although antidepressant medication (ADM) has produced small advantages over pill placebo in randomized controlled trials, consuming ADM has predicted prospectively increasing depressive symptom severity in samples of community-dwelling adults.

OBJECTIVE

We extended the community literature by testing ADM's relations to changes in personality and quality of life that may underpin depression.

METHOD

In this longitudinal, observational study, community-dwelling adults (N = 601) were assessed twice, 8 months apart on average. Assessments included depressive symptoms, personality, life satisfaction and quality, and prescription medication consumption.

RESULTS

Consuming ADM at time 1 predicted relative increases in depressive symptoms (dysphoria), maladaptive traits (negative affect, negative temperament, disinhibition, low conscientiousness), personality dysfunction (non-coping, self-pathology), and decreases in life satisfaction and quality from time 1 to 2, before and after adjustment for age, gender, race, income, education, physical health problems, and use of other psychotropics. In no analysis did ADM use predict better outcomes.

CONCLUSION

Among community-dwelling adults, ADM use is a risk factor for psychosocial deterioration in domains including depressive symptoms, personality pathology, and quality of life. Until mechanisms connecting ADM to poor outcomes in community samples are understood, additional caution in use of ADM and consideration of empirically supported non-pharmacologic treatments is prudent.

Perinatal Depression and the Role of Synaptic Plasticity in Its Pathogenesis and Treatment

Emerging evidence indicates that synaptic plasticity is significantly involved in the pathophysiology and treatment of perinatal depression. Animal models have demonstrated the effects of overstimulated or weakened synapses in various circuits of the brain in causing affective disturbances. GABAergic theory of depression, stress, and the neuroplasticity model of depression indicate the role of synaptic plasticity in the pathogenesis of depression. Multiple factors related to perinatal depression like hormonal shifts, newer antidepressants, mood stabilizers, monoamine systems, biomarkers, neurotrophins, cytokines, psychotherapy and electroconvulsive therapy have demonstrated direct and indirect effects on synaptic plasticity. In this review, we discuss and summarize the various patho-physiology-related effects of synaptic plasticity in depression. We also discuss the association of treatment-related aspects related to psychotropics, electroconvulsive therapy, neuromodulation, psychotherapy, physical exercise and yoga with synaptic plasticity in perinatal depression. Future insights into newer methods of treatment directed towards the modulation of neuroplasticity for perinatal depression will be discussed.

Serotonergic multilocus genetic variation moderates the association between interpersonal relationship and adolescent depressive symptoms

BACKGROUND

Research suggests that genetic variants linked to serotonin functioning moderate the association between environmental stressors and depressive symptoms, but examining gene-environment interactions with single polymorphisms limits power.

METHODS

A multilocus genetic profile score (MGPS) approach to measuring serotonergic multilocus genetic variation and examined interactions with interpersonal relationship, insomnia with depressive symptoms as outcomes in an adolescent sample (average age = 14.15 ± 0.63 years since first measurement; range: 13 to 15).

RESULTS

(1) interpersonal relationship predicted adolescent depressive symptoms; (2) insomnia mediated the effect of interpersonal relationships on adolescent depressive symptoms; (3) the THP2 gene rs4570625 polymorphism G allele was a key risk factor for depressive symptom, and the MGPS moderated the effects of teacher-student relationship and insomnia on adolescent depressive symptom. Specifically, as the MGPS increased, the effects of insomnia on adolescent depressive symptom were enhanced; further, when the MGPS score increased, the effect of teacher-student relationship on depression showed a similar phenomenon with an increased slope and enhanced prediction; and (4) the results of sensitivity analysis showed that multilocus genetic interaction with the environment had a better explanatory power and stability for depression than single polymorphism studies.

CONCLUSION

MGPS provides substantial power to examine gene-environmental interactions linked to affective outcomes among adolescents.

Lactobacillus reuteri ATG-F4 Alleviates Chronic Stress-induced Anhedonia by Modulating the Prefrontal Serotonergic System

Mental health is influenced by the gut-brain axis; for example, gut dysbiosis has been observed in patients with major depressive disorder (MDD). Gut microbial changes by fecal microbiota transplantation or probiotics treatment reportedly modulates depressive symptoms. However, it remains unclear how gut dysbiosis contributes to mental dysfunction, and how correction of the gut microbiota alleviates neuropsychiatric disorders. Our previous study showed that chronic consumption of Lactobacillus reuteri ATG-F4 (F4) induced neurometabolic alterations in healthy mice. Here, we investigated whether F4 exerted therapeutic effects on depressive-like behavior by influencing the central nervous system. Using chronic unpredictable stress (CUS) to induce anhedonia, a key symptom of MDD, we found that chronic F4 consumption alleviated CUS-induced anhedonic behaviors, accompanied by biochemical changes in the gut, serum, and brain. Serum and brain metabolite concentrations involved in tryptophan metabolism were regulated by CUS and F4. F4 consumption reduced the elevated levels of serotonin (5-HT) in the brain observed in the CUS group. Additionally, the increased expression of Htr1a, a subtype of the 5-HT receptor, in the medial prefrontal cortex (mPFC) of stressed mice was restored to levels observed in stress-naïve mice following F4 supplementation. We further demonstrated the role of Htr1a using AAV-shRNA to downregulate Htr1a in the mPFC of CUS mice, effectively reversing CUS-induced anhedonic behavior. Together, our findings suggest F4 as a potential therapeutic approach for relieving some depressive symptoms and highlight the involvement of the tryptophan metabolism in mitigating CUS-induced depressive-like behaviors through the action of this bacterium.

Disruptive mutations in the serotonin transporter associate serotonin dysfunction with treatment-resistant affective disorder

Affective or mood disorders are a leading cause of disability worldwide. The serotonergic system has been heavily implicated in the complex etiology and serves as a therapeutic target. The serotonin transporter (SERT) is a major regulator of serotonin neurotransmission, yet the disease-relevance of impaired SERT function remains unknown. Here, we present the first identification and functional characterization of disruptive coding SERT variants found in patients with psychiatric diseases. In a unique cohort of 144 patients characterized by treatment-resistant chronic affective disorders with a lifetime history of electroconvulsive therapy, we identified two previously uncharacterized coding SERT variants: SERT-N217S and SERT-A500T. Both variants were significantly enriched in the patient cohort compared to GnomAD (SERT-N217S: OR = 151, P = 0.0001 and SERT-A500T: OR = 1348, P = 0.0022) and ethnicity-matched healthy controls (SERT-N217S: OR ≥ 17.7, P ≤ 0.013 and SERT-A500T: OR = ∞, P = 0.029). Functional investigations revealed that the mutations exert distinct perturbations to SERT function, but their overall effects converge on a partial loss-of-function molecular phenotype. Thus, the SERT-A500T variant compromises the catalytic activity, while SERT-N217S disrupts proper glycosylation of SERT with a resulting dominant-negative trafficking deficiency. Moreover, we demonstrate that the trafficking deficiency of SERT-N217S is amenable to pharmacochaperoning by noribogaine. Collectively, our findings describe the first disease-associated loss-of-function SERT variants and implicate serotonergic disturbances arising from SERT dysfunction as a risk factor for chronic affective disorders.

Associations of the serotonin transporter gene polymorphism, 5-HTTLPR, and adverse life events with late life depression in the elderly Lithuanian population

Late-life depression (LLD) is a multifactorial disorder, with susceptibility and vulnerability potentially influenced by gene-environment interaction. The aim of this study was to investigate whether the 5-HTTLPR polymorphism is associated with LLD. The sample of 353 participants aged 65 years and over was randomly selected from the list of Kaunas city inhabitants by Residents' Register Service of Lithuania. Depressive symptoms were ascertained using the EURO-D scale. The List of Threatening Events Questionnaire was used to identify stressful life events that happened over the last 6 months and during lifetime. A 5-HTTLPR and lifetime stressful events interaction was indicated by higher odds of depression in those with s/s genotype who experienced high stress compared to l/l carriers with low or medium stress, while 5-HTTLPR and current stressful events interaction analysis revealed that carriers of either one or two copies of the s allele had increased odds of depressive symptoms associated with stress compared to participants with the l/l genotype not exposed to stressful situations. Although no significant direct association was found between the 5-HTTLPR short allele and depression, our findings demonstrated that lifetime or current stressful life events and their modification by 5-HTTLPR genotype are risk factors for late-life depression.

A review of new insights into existing major depressive disorder biomarkers

As major depressive disorder (MDD) is such a diverse condition, there are currently no clear ways for determining its severity, endophenotype, or therapy response. The distinctive nature of depression, the variability of analysis in literature and the large number of conceptually complicated biomarkers are some of the many reasons for the lack of progress. Markers are involved in the process of neurotrophic, metabolic, and inflammation as well as neuroendocrine and neurotransmitter systems' components. Some clinical indicators are strong enough so that can be measured using assessments of proteomic, genetic, metabolomics, neuroimaging, epigenetic and transcriptomic. Markers of oxidative stress, endocrine, inflammatory, proteomic, and growth indicators are currently among the promising biologic systems/markers identified in this analysis. This narrative review examines succinct studies which investigated cytokines of inflammatory factors, peripheral factors of development, metabolic and endocrine markers as pathophysiological biomarkers of MDD, and treatment responses. Endocrine and metabolic alterations have also been linked to MDD in various studies. So, this study summarizes all of the numerous biomarkers that are significant in the detection or treatment of MDD patients. The paper also provides an overview of various biomarkers which are important for the regulation and its effects on MDD.

Long-term exposure to a pharmaceutical pollutant affects geotaxic behaviour in the adult but not juvenile life stage of killifish

Ecosystems around the world are increasingly polluted with pharmaceutical compounds that may perturb wildlife behaviour. Because many pharmaceuticals are continuously present in the aquatic environment, animals are often exposed to them across several life stages or even their entire life. Despite a large body of literature showing various impacts of exposure to pharmaceuticals on fish, hardly any long-term studies across different life stages have been conducted which makes it hard to accurately estimate the ecological outcomes of pharmaceutical pollution. Here, we performed a laboratory experiment in which we exposed hatchlings of the fish model Nothobranchius furzeri to an environmentally relevant concentration (0.5 μg/L) of the antidepressant fluoxetine until well into adulthood. We monitored total body length and geotaxic behaviour (i.e. gravity-mediated activity) of each fish as two traits that are ecologically relevant and naturally differ between juvenile and adult killifish. Fish exposed to fluoxetine were smaller compared to control fish, an effect that became more apparent as fish aged. Even though fluoxetine did not affect average swimming depth of either juveniles or adults, nor the time spent at the surface or bottom of the water column, exposed fish changed their position in the water column (depth) more frequently in the adult but not juvenile phase. These results suggest that important morphological and behavioural responses to pharmaceutical exposure-and their potential ecological consequences-may only emerge later in time and/or during specific life stages. Therefore, our results highlight the importance of considering ecologically relevant timescales across developmental stages when studying the ecotoxicology of pharmaceuticals.

Early antidepressant treatment response prediction in major depression using clinical and TPH2 DNA methylation features based on machine learning approaches

OBJECTIVE

To identify DNA methylation and clinical features, and to construct machine learning classifiers to assign the patients with major depressive disorder (MDD) into responders and non-responders after a 2-week treatment into responders and non-responders.

METHOD

Han Chinese patients (291 in total) with MDD comprised the study population. Datasets contained demographic information, environment stress factors, and the methylation levels of 38 methylated sites of tryptophan hydroxylase 2 (TPH2) genes in peripheral blood samples. Recursive Feature Elimination (RFE) was employed to select features. Five classification algorithms (logistic regression, classification and regression trees, support vector machine, logitboost and random forests) were used to establish the models. Performance metrics (AUC, F-Measure, G-Mean, accuracy, sensitivity, specificity, positive predictive value and negative predictive value) were computed with 5-fold-cross-validation. Variable importance was evaluated by random forest algorithm.

RESULT

RF with RFE outperformed the other models in our samples based on the demographic information and clinical features (AUC = 61.2%, 95%CI: 60.1-62.4%) / TPH2 CpGs features (AUC = 66.6%, 95%CI: 65.4-67.8%) / both clinical and TPH2 CpGs features (AUC = 72.9%, 95%CI: 71.8-74.0%).

CONCLUSION

The effects of TPH2 on the early-stage antidepressant response were explored by machine learning algorithms. On the basis of the baseline depression severity and TPH2 CpG sites, machine learning approaches can enhance our ability to predict the early-stage antidepressant response. Some potentially important predictors (e.g., TPH2-10-60 (rs2129575), TPH2-2-163 (rs11178998), age of first onset, age) in early-stage treatment response could be utilized in future fundamental research, drug development and clinical practice.

High-cholesterol diet promotes depression- and anxiety-like behaviors in mice by impact gut microbe and neuroinflammation

Neuropsychiatric disorders, including anxiety and depression, are one of the most common mental illnesses worldwide. A growing body of evidence shows that there is a complex relationship between dietary patterns and mental health. In our study, C57BL/6J mice were divided into three groups: control diet group (CON, 10 % kcal fat), high-cholesterol diet model group (HCD, 42.0 % kcal fat + 1.25 % kcal Cholesterol), and chronic restraint stress group (CRS, 10 % kcal fat) which as a positive control group for the depression model. Six weeks later, depressive- and anxiety-like behavior were evaluated for using the OFT, SPT and TST. Glucose intolerance and liver fat were detected by IGTT and liver lipid kit. The expression of peripheral and central inflammation was detected by LEGEND plex kits. 5-HT (also named 5-hydroxytryptamine, 5-HT) and related receptors expression were monitored by ELISA, RT-PCR and Western blot. Meantime, gut microbe of stool samples was performed by 16S rRNA gene sequencing. Similar to CRS model, short-term HCD intervention induced anxiety and depression-like behavior behavioral abnormalities in mice. HCD consumption resulted in significantly increased body weight, liver fat (LDL-C, TC, TG), peripheral inflammation (IL-1β, MCP-1, IL-17A) and neuroinflammation (MCP-1). The concentration of 5-HT increased in the hippocampus, meanwhile, the expression of 5-HT receptor HTR2A was distinct in different regions of the brain tissue. More importantly, we found that compared with the CON diet, HCD induced the decrease of intestinal flora diversity, especially the decrease the relative abundance of Akkermansia_muciniphila, which was statistically significant. Further, Pearson correlation analysis showed that Akkermansia_muciniphila was significantly negatively correlated with the concentration of MCP-1, IL-17A in serum and 5-HT in hippocampus. Therefore, we speculated that the disorder of neuroinflammation induced by HCD consumption promotes depression- and anxiety-like behaviors in mice through the gut microbe.

Serotonin acts through YAP to promote cell proliferation: mechanism and implication in colorectal cancer progression

Serotonin, also known as 5-hydroxytryptamine (5-HT), is a key messenger that mediates several central and peripheral functions in the human body. Emerging evidence indicates that serotonin is critical in tumorigenesis, but its role in colorectal cancer remains elusive. Herein, we report that serotonin transporter (SERT) transports serotonin into colorectal cancer cells, enhancing Yes-associated protein (YAP) expression and promoting in vitro and in vivo colon cancer cell growth. Once within the cells, transglutaminase 2 (TG2) mediates RhoA serotonylated and activates RhoA-ROCK1/2 signalling to upregulate YAP expression in SW480 and SW1116 cells. Blocking SERT with citalopram reversed the serotonin-induced YAP expression and cell proliferation, inhibiting serotonin's effects on tumour formation in mice. Moreover, SERT expression was correlated with YAP in pathological human colorectal cancer samples and the levels of 5-HT were highly significant in the serum of patients with colorectal cancer. Together, our findings suggested that serotonin enters cells via SERT to activate RhoA/ROCK/YAP signalling to promote colon cancer carcinogenesis. Consequently, targeting serotonin-SERT-YAP axis may be a potential therapeutic strategy for colorectal cancer. Video abstract.

Imbalance of Essential Metals in Traumatic Brain Injury and Its Possible Link with Disorders of Consciousness

Dysfunction of the complex cerebral networks underlying wakefulness and awareness is responsible for Disorders of Consciousness (DoC). Traumatic Brain Injury (TBI) is a common cause of DoC, and it is responsible for a multi-dimensional pathological cascade that affects the proper functioning of the brainstem and brain consciousness pathways. Iron (Fe), Zinc (Zn), and Copper (Cu) have a role in the neurophysiology of both the ascending reticular activating system, a multi-neurotransmitter network located in the brainstem that is crucial for consciousness, and several brain regions. We aimed to summarize the role of these essential metals in TBI and its possible link with consciousness alterations. We found that TBI alters many neuronal molecular mechanisms involving essential metals, causing neurodegeneration, neural apoptosis, synaptic dysfunction, oxidative stress, and inflammation. This final pattern resembles that described for Alzheimer's disease (AD) and other neurological and psychiatric diseases. Furthermore, we found that amantadine, zolpidem, and transcranial direct current stimulation (tDCS)-the most used treatments for DoC recovery-seem to have an effect on essential metals-related pathways and that Zn might be a promising new therapeutic approach. This review summarizes the neurophysiology of essential metals in the brain structures of consciousness and focuses on the mechanisms underlying their imbalance following TBI, suggesting their possible role in DoC. The scenario supports further studies aimed at getting a deeper insight into metals' role in DoC, in order to evaluate metal-based drugs, such as metal complexes and metal chelating agents, as potential therapeutic options.

Increased depressive-like behaviour of postpartum Flinders sensitive and resistant line rats is reversed by a predictable postpartum stressor

During the peripartum period, women are at an increased risk to develop perinatal distress, presenting as symptoms of depression and/or anxiety. Yet, due to practical and ethical restrictions, our understanding of this condition remains limited. Animal studies that focus on the neuropsychiatric mechanisms associated with the postpartum period, often ignore the genetical predisposition factor. We therefore investigated whether pregnancy could alter the bio-behavioural profile of the Flinders sensitive and resistant line rats, and whether these effects are exacerbated by a postpartum stressor. Postpartum dams were compared to nulliparous controls in behavioural tests, analysing depressive- and anxiety-like behaviours. Next, postpartum dams were subjected to a maternal separation and early weaning (MSEW) regimen, with their behaviour and serotonergic and noradrenergic concentrations compared to rats not separated from their pups. Regardless of strain, pregnancy decreased time spent in the open arms of the elevated plus maze and hippocampal serotonin concentrations. Time spent immobile in the forced swim test was also increased, with a significant effect in the FRL and a strong trend in the FSL rats. MSEW reversed these behaviours in both strains and increased social interaction with a male counterpart in the FSL rats, without influencing hippocampal or cortical serotonin or norepinephrine. Taken together, these results suggest that pregnancy influences postpartum behaviour, in a strain-dependent manner. Contrary to what we expected, MSEW overall decreased depressive- and anxiety-like behaviours, with strain specific differences, indicating that a chronic, predictable stressor may not necessarily adversely affect postpartum behaviour.

Plausible Role of Stem Cell Types for Treating and Understanding the Pathophysiology of Depression

Major Depressive Disorder (MDD), colloquially known as depression, is a debilitating condition affecting an estimated 3.8% of the population globally, of which 5.0% are adults and 5.7% are above the age of 60. MDD is differentiated from common mood changes and short-lived emotional responses due to subtle alterations in gray and white matter, including the frontal lobe, hippocampus, temporal lobe, thalamus, striatum, and amygdala. It can be detrimental to a person’s overall health if it occurs with moderate or severe intensity. It can render a person suffering terribly to perform inadequately in their personal, professional, and social lives. Depression, at its peak, can lead to suicidal thoughts and ideation. Antidepressants manage clinical depression and function by modulating the serotonin, norepinephrine, and dopamine neurotransmitter levels in the brain. Patients with MDD positively respond to antidepressants, but 10–30% do not recuperate or have a partial response accompanied by poor life quality, suicidal ideation, self-injurious behavior, and an increased relapse rate. Recent research shows that mesenchymal stem cells and iPSCs may be responsible for lowering depression by producing more neurons with increased cortical connections. This narrative review discusses the plausible functions of various stem cell types in treating and understanding depression pathophysiology.

Effects of a variable light intensity lighting program on the welfare and performance of commercial broiler chickens

Our previous variable-light intensity lighting program studies indicate the light intensity preference behavior of broilers for their daily activity including eating and resting. To evaluate the effects of variable-light intensity lighting program on performance and welfare of broilers, four commercial trials were conducted for looking at behaviors, mortality, leg-health, performance, and brain welfare indicator genes including tryptophan hydroxylase 2 and tyrosine hydroxylase (TH), glucocorticoid receptor (GR), brain-derived neurotropic factor (BDNF), and melanopsin (Opn4) gene expression. One-day-old broilers were housed in four commercial broiler houses. Each quadrant (section) of the house was placed with 4,800 chicks. A total of four lighting programs began on day 7 with 5 lux (lx), 20 lx, natural light (NL, 480 lx), and variable light (2-5/40 lx) using LED lights on a 16L:8D photoperiod. In the variable-light house, the number of dustbathing holes was significantly higher than that in natural-light houses and 5-lx and 20-lx houses. Daily physical activities, footpad condition, fear response to novel objects, body weight, feed conversion ratio, and the number of leg-problem induced culled birds were affected by the variable-light intensity lighting program. Expression of tryptophan hydroxylase 2 in the DRN and VTA of variable-light treated birds was lower than that of 5-lx- and 20-lx-treated birds on day 42 (p < 0.05). Higher expression of VTA-TH in 5-lx-treated birds than that in 20-lx-, NL-, and variable-light-treated birds suggests the high stress-susceptibility of 5-lx treated birds. Lower VTA-GR expression in 20-lx- and variable-light-treated birds indicates lower stress than that in NL- and 5-lx-treated birds (p < 0.05). The VTA-BDNF expression of NL-treated birds was 2.5 fold higher than that of 5-lx-, 20-lx-, and variable-light-treated birds (p < 0.05), and variable-light-treated birds showed the lowest level of BDNF expression (p < 0.05), suggesting the chronic social defeat stress in NL-treated birds. The result of VTA-Opn4 expression on day 42 suggests the possible role of VTA-Opn4 in broiler welfare through central light perception. Taken together, the variable-light intensity lighting program increased volunteer natural behaviors and physical activity, which may improve footpad condition and leg health of birds, consequently. Performance data including the increased daily weight gain and the lowered feed conversion ratio and results of brain welfare indicator gene expression showed the beneficial effect of the variable-light intensity lighting program on the performance and welfare of commercial broilers.

Advances in the Functions of Thioredoxin System in Central Nervous System Diseases

Significance: The thioredoxin system comprises thioredoxin (Trx), thioredoxin reductase (TrxR), and nicotinamide adenine dinucleotide phosphate, besides an endogenous Trx inhibitor, the thioredoxin-interacting protein (TXNIP). The Trx system plays critical roles in maintaining the redox homeostasis in the central nervous system (CNS), in which oxidative stress damage is prone to occurrence due to its high-energy demand. Recent Advances: Increasing studies have demonstrated that the expression or activity of Trx/TrxR is usually decreased and that TXNIP expression is increased in patients with CNS diseases, including neurodegenerative diseases, cerebral ischemia, traumatic brain injury, and depression, as well as in their cellular and animal models. The compromise of Trx/TrxR enhances the susceptibility of neurons to related pathological state. Increased TXNIP not only enhances the inhibition of Trx activity, but also activates the NOD-like receptor protein 3 inflammasome, resulting in neuroinflammation in the brain. Critical Issues: In this review, we highlight the sources of oxidative stress in the CNS. The expression and function of the Trx system are summarized in different CNS diseases. This review also mentions that some inducers of Trx show neuroprotection in CNS diseases. Future Directions: Accumulating evidence has demonstrated the important roles of the Trx system in CNS diseases, suggesting that the Trx system may be a promising therapeutic target for CNS diseases. Further study should aim to develop the most effective inducers of Trx and specific inhibitors of TXNIP and to apply them in the clinical trials for the treatment of CNS diseases. Antioxid. Redox Signal. 38, 425-441.

Effects of a variable light intensity lighting program on the welfare and performance of commercial broiler chickens

Our previous variable-light intensity lighting program studies indicate the light intensity preference behavior of broilers for their daily activity including eating and resting. To evaluate the effects of variable-light intensity lighting program on performance and welfare of broilers, four commercial trials were conducted for looking at behaviors, mortality, leg-health, performance, and brain welfare indicator genes including tryptophan hydroxylase 2 and tyrosine hydroxylase (TH), glucocorticoid receptor (GR), brain-derived neurotropic factor (BDNF), and melanopsin (Opn4) gene expression. One-day-old broilers were housed in four commercial broiler houses. Each quadrant (section) of the house was placed with 4,800 chicks. A total of four lighting programs began on day 7 with 5 lux (lx), 20 lx, natural light (NL, 480 lx), and variable light (2-5/40 lx) using LED lights on a 16L:8D photoperiod. In the variable-light house, the number of dustbathing holes was significantly higher than that in natural-light houses and 5-lx and 20-lx houses. Daily physical activities, footpad condition, fear response to novel objects, body weight, feed conversion ratio, and the number of leg-problem induced culled birds were affected by the variable-light intensity lighting program. Expression of tryptophan hydroxylase 2 in the DRN and VTA of variable-light treated birds was lower than that of 5-lx- and 20-lx-treated birds on day 42 (p < 0.05). Higher expression of VTA-TH in 5-lx-treated birds than that in 20-lx-, NL-, and variable-light-treated birds suggests the high stress-susceptibility of 5-lx treated birds. Lower VTA-GR expression in 20-lx- and variable-light-treated birds indicates lower stress than that in NL- and 5-lx-treated birds (p < 0.05). The VTA-BDNF expression of NL-treated birds was 2.5 fold higher than that of 5-lx-, 20-lx-, and variable-light-treated birds (p < 0.05), and variable-light-treated birds showed the lowest level of BDNF expression (p < 0.05), suggesting the chronic social defeat stress in NL-treated birds. The result of VTA-Opn4 expression on day 42 suggests the possible role of VTA-Opn4 in broiler welfare through central light perception. Taken together, the variable-light intensity lighting program increased volunteer natural behaviors and physical activity, which may improve footpad condition and leg health of birds, consequently. Performance data including the increased daily weight gain and the lowered feed conversion ratio and results of brain welfare indicator gene expression showed the beneficial effect of the variable-light intensity lighting program on the performance and welfare of commercial broilers.

Is depression the missing link between inflammatory mediators and cancer?

Patients with cancer are at greater risk of developing depression in comparison to the general population and this is associated with serious adverse effects, such as poorer quality of life, worse prognosis and higher mortality. Although the relationship between depression and cancer is now well established, a common underlying pathophysiological mechanism between the two conditions is yet to be elucidated. Existing theories of depression, based on monoamine neurotransmitter system dysfunction, are insufficient as explanations of the disorder. Recent advances have implicated neuroinflammatory mechanisms in the etiology of depression and it has been demonstrated that inflammation at a peripheral level may be mirrored centrally in astrocytes and microglia serving to promote chronic levels of inflammation in the brain. Three major routes to depression in cancer in which proinflammatory mediators are implicated, seem likely. Activation of the kynurenine pathway involving cytokines, increases tryptophan catabolism, resulting in diminished levels of serotonin which is widely acknowledged as being the hallmark of depression. It also results in neurotoxic effects on brain regions thought to be involved in the evolution of major depression. Proinflammatory mediators also play a crucial role in impairing regulatory glucocorticoid mediated feedback of the hypothalamic-pituitary-adrenal axis, which is activated by stress and considered to be involved in both depression and cancer. The third route is via the glutamatergic pathway, whereby glutamate excitotoxicity may lead to depression associated with cancer. A better understanding of the mechanisms underlying these dysregulated and other newly emerging pathways may provide a rationale for therapeutic targeting, serving to improve the care of cancer patients.

All the brain's a stage for serotonin: the forgotten story of serotonin diffusion across cell membranes

In the conventional model of serotonin neurotransmission, serotonin released by neurons in the midbrain raphe nuclei exerts its actions on forebrain neurons by interacting with a large family of post-synaptic receptors. The actions of serotonin are terminated by active transport of serotonin back into the releasing neuron, which is mediated by the serotonin reuptake transporter (SERT). Because SERT is expressed pre-synaptically and is widely thought to be the only serotonin transporter in the forebrain, the conventional model does not include serotonin transport into post-synaptic neurons. However, a large body of evidence accumulating since the 1970s has shown that serotonin, despite having a positive charge, can cross cell membranes through a diffusion-like process. Multiple low-affinity, high-capacity, sodium-independent transporters, widely expressed in the brain, allow the carrier-mediated diffusion of serotonin into forebrain neurons. The amount of serotonin crossing cell membranes through this mechanism under physiological conditions is considerable. Most prominent textbooks fail to include this alternative method of serotonin uptake in the brain, and even most neuroscientists are unaware of it. This failure has limited our understanding of a key regulator of serotonergic neurotransmission, impeded research on the potential intracellular actions of serotonin in post-synaptic neurons and glial cells, and may have impeded our understanding of the mechanism by which antidepressant medications reduce depressive symptoms.

Carbon Dots Derived from Os Draconis and Their Anxiolytic Effect

BACKGROUND

At present, people are susceptible to developing depression and anxiety disorders in response to stress. However, there is no specific medicine for anxiety. Os Draconis (OD, named "Long gu" in Chinese) are fossilized bones that have been used in traditional Chinese medicine to treat neurological diseases for thousands of years. Thus, we conducted this study to determine the biological basis for the anxiolytic effect of OD.

METHODS

In this study, novel carbon dots (OD-CDs) from OD decoctions were discovered and separated. OD-CDs were anatomized using nanomaterials characterization methods to characterize the morphological structure, optical properties, and functional group properties. Four behavioural tests were conducted to observe the behavioural activities of mice, including the open field test (OFT), light/dark box test (LDT), elevated plus maze test (EPMT), and novelty-suppressed feeding test (NSFT), to determine its anxiolytic effects. Moreover, we assessed the possible mechanisms of the OD-CDs by detecting hormones associated with the hypothalamic-pituitary-adrenal (HPA) axis.

RESULTS

OD-CDs were spherical and monodispersed with a narrow size distribution between 1 and 5 nm and had a yield of 3.67%. OD-CDs increased the activity time of mice in the central zone in the OFT. The mice in the experimental group showed more frequent activity in the light compartment and the open arms, in LDT and EPMT, respectively. In addition, OD-CDs shortened the feeding latency in the NSFT. Furthermore, the results after OD-CDs intervention showed a significant increase in serum serotonin (5-HT) and norepinephrine (NE). In addition, the concentrations of corticotropin-releasing hormone (CRH), adrenocorticotropic hormone (ATCH), and corticosterone (CORT) were decreased.

CONCLUSION

These results demonstrate a definite anxiolytic effect of OD-CDs and reveal the possible mechanism of action of OD-CDs' anxiolytic effect, which supports the research of OD for neurological disorders and a promising new trend of therapeutic approach and drug development.

SUMOylation and Major Depressive Disorder

Since the discovery of the small ubiquitin-like modifier (SUMO) protein in 1995, SUMOylation has been considered a crucial post-translational modification in diverse cellular functions. In neurons, SUMOylation has various roles ranging from managing synaptic transmitter release to maintaining mitochondrial integrity and determining neuronal health. It has been discovered that neuronal dysfunction is a key factor in the development of major depressive disorder (MDD). PubMed and Google Scholar databases were searched with keywords such as ‘SUMO’, ‘neuronal plasticity’, and ‘depression’ to obtain relevant scientific literature. Here, we provide an overview of recent studies demonstrating the role of SUMOylation in maintaining neuronal function in participants suffering from MDD.

What Can Reinforcement Learning Models of Dopamine and Serotonin Tell Us about the Action of Antidepressants?

Although evidence suggests that antidepressants are effective at treating depression, the mechanisms behind antidepressant action remain unclear, especially at the cognitive/computational level. In recent years, reinforcement learning (RL) models have increasingly been used to characterise the roles of neurotransmitters and to probe the computations that might be altered in psychiatric disorders like depression. Hence, RL models might present an opportunity for us to better understand the computational mechanisms underlying antidepressant effects. Moreover, RL models may also help us shed light on how these computations may be implemented in the brain (e.g., in midbrain, striatal, and prefrontal regions) and how these neural mechanisms may be altered in depression and remediated by antidepressant treatments. In this paper, we evaluate the ability of RL models to help us understand the processes underlying antidepressant action. To do this, we review the preclinical literature on the roles of dopamine and serotonin in RL, draw links between these findings and clinical work investigating computations altered in depression, and appraise the evidence linking modification of RL processes to antidepressant function. Overall, while there is no shortage of promising ideas about the computational mechanisms underlying antidepressant effects, there is insufficient evidence directly implicating these mechanisms in the response of depressed patients to antidepressant treatment. Consequently, future studies should investigate these mechanisms in samples of depressed patients and assess whether modifications in RL processes mediate the clinical effect of antidepressant treatments.

Improved Serotonin Measurement with Fast-Scan Cyclic Voltammetry: Mitigating Fouling by SSRIs

Selective serotonin reuptake inhibitors (SSRIs) have been used for decades to treat disorders linked to serotonin dysregulation in the brain. Moreover, SSRIs are often used in studies aimed at measuring serotonin with fast-scan cyclic voltammetry (FSCV) in living tissues. Here, we show that three different SSRIs - fluoxetine, escitalopram, and sertraline - significantly diminish the faradaic oxidation current of serotonin when employing the commonly used Jackson waveform. Coating carbon-fiber microelectrodes (CFMs) with Nafion resulted in further degradation of peak current, increased response times, and decreased background charging currents compared to bare CFMs. To decrease fouling, we employed a recently published extended serotonin waveform, which scans to a maximum positive potential of +1.3 V, rather than +1.0 V used in the Jackson waveform. Use of this waveform with bare CFMs alleviated the decrease in faradaic current, indicating decreased electrode fouling. Collectively, our results suggest that fouling considerations are important when designing FSCV experiments that employ SSRIs and that they can be overcome by using the appropriate waveform.

Oral administration of Lactococcus lactis WHH2078 alleviates depressive and anxiety symptoms in mice with induced chronic stress

Depression is a mood disorder with a high prevalence rate globally, which is associated with abnormalities in 5-hydroxytryptamine (5-HT) metabolism. Emerging evidence suggests that certain probiotics that modulate 5-HT metabolism confer beneficial effects on depression. In this study, in vitro enterochromaffin RIN14B cells were used for screening potential antidepressant probiotic Lactococcus lactis strains. The L. lactis strain WHH2078 increased to high levels the 5-HT precursor 5-hydroxytryptophan (5-HTP) and the expression of tryptophan hydroxylase 1 (Tph1), which converts tryptophan to 5-HTP in RIN14B cells. The oral administration of WHH2078 (1 × 10⁹ CFU mL^-1) in mice with induced chronic unpredictable mild stress (CUMS) for 5 weeks significantly ameliorated depressive and anxiety-like behaviors in the tail suspension test, forced swim test, sucrose preference test, and open field test. Besides, WHH2078 significantly reduced the serum corticosterone level and restored the central levels of 5-HT, 5-HTP, and brain-derived neurotrophic factor in CUMS-induced mice. Moreover, WHH2078 also reversed the 5-HTP levels in the serum and colon, accompanied by an upregulation in colonic Tph1 gene expression. Using 16S rRNA high-throughput sequencing of feces, WHH2078 was shown to improve the CUMS-induced gut microbial dysbiosis, through restoring alpha diversity and the abundances of Firmicutes and Bacteroidetes. In summary, these results indicate that WHH2078 can alleviate rodent depressive and anxiety-like behaviors in response to CUMS, which is associated with the improvement of 5-HT metabolism and modulation of the gut microbiome composition. Therefore, supplementation of the L. lactis strain WHH2078 with antidepressant properties may serve as a promising therapeutic strategy for chronic stress-induced depression.

Neuroinflammation as an etiological trigger for depression comorbid with inflammatory bowel disease

Patients with inflammatory bowel disease (IBD) suffer from depression at higher rates than the general population. An etiological trigger of depressive symptoms is theorised to be inflammation within the central nervous system. It is believed that heightened intestinal inflammation and dysfunction of the enteric nervous system (ENS) contribute to impaired intestinal permeability, which facilitates the translocation of intestinal enterotoxins into the blood circulation. Consequently, these may compromise the immunological and physiological functioning of distant non-intestinal tissues such as the brain. In vivo models of colitis provide evidence of increased blood–brain barrier permeability and enhanced central nervous system (CNS) immune activity triggered by intestinal enterotoxins and blood-borne inflammatory mediators. Understanding the immunological, physiological, and structural changes associated with IBD and neuroinflammation may aid in the development of more tailored and suitable pharmaceutical treatment for IBD-associated depression.

Tryptophan Metabolism in Central Nervous System Diseases: Pathophysiology and Potential Therapeutic Strategies

The metabolism of L-tryptophan (TRP) regulates homeostasis, immunity, and neuronal function. Altered TRP metabolism has been implicated in the pathophysiology of various diseases of the central nervous system. TRP is metabolized through two main pathways, the kynurenine pathway and the methoxyindole pathway. First, TRP is metabolized to kynurenine, then kynurenic acid, quinolinic acid, anthranilic acid, 3-hydroxykynurenine, and finally 3-hydroxyanthranilic acid along the kynurenine pathway. Second, TRP is metabolized to serotonin and melatonin along the methoxyindole pathway. In this review, we summarize the biological properties of key metabolites and their pathogenic functions in 12 disorders of the central nervous system: schizophrenia, bipolar disorder, major depressive disorder, spinal cord injury, traumatic brain injury, ischemic stroke, intracerebral hemorrhage, multiple sclerosis, Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis, and Huntington's disease. Furthermore, we summarize preclinical and clinical studies, mainly since 2015, that investigated the metabolic pathway of TRP, focusing on changes in biomarkers of these neurologic disorders, their pathogenic implications, and potential therapeutic strategies targeting this metabolic pathway. This critical, comprehensive, and up-to-date review helps identify promising directions for future preclinical, clinical, and translational research on neuropsychiatric disorders.

Meta-analysis of association between TPH2 single nucleotide poiymorphism and depression

Tryptophan hydroxylase 2 (TPH2) plays a crucial role in the human brain. Although the association between the TPH2 gene and depression has been suggested in previous meta-analyses, studies based on Chinese subjects are often neglected. Therefore, we included some previous studies based on Chinese subjects to explore the relationship between TPH2 polymorphisms and depression via conducting an extensive meta-analysis. We reviewed 40 research papers that included data on TPH2 gene single nucleotide polymorphisms (SNPs) from 5766 patients with depression and 5988 healthy subjects. The analysis showed an association between polymorphisms in the TPH2 gene and depression, and some results were significant in 24 studies that included Chinese Han study participants. The results of our meta-analysis showed that rs4570625, rs17110747, rs120074175, rs4290270, rs120074175, and rs4290270 may be significantly associated with depression, and that rs11178997 (A/A genotype) may be a significant risk factor for depression in the Chinese subjects. Based on the results of this study, biological experiments should be performed in the future to explore how different SNPs affect depression.

Imaging of cerebral tryptophan metabolism using 7-[18F]FTrp-PET in a unilateral Parkinsonian rat model

Degradation products of the essential amino acid tryptophan (Trp) are important signaling molecules in the mammalian brain. Trp is metabolized either through the kynurenine pathway or enters serotonin and melatonin syntheses. The aim of the present work was to examine the potential of the novel PET tracer 7-[¹⁸F]fluorotryptophan ([¹⁸F]FTrp) to visualize all three pathways in a unilateral 6-OHDA rat model. [¹⁸F]FDOPA-PET scans were performed in nine 6-OHDA-injected and six sham-operated rats to assess unilateral dopamine depletion severity four weeks after lesion placement. Afterwards, 7-[¹⁸F]FTrp-PET scans were conducted at different timepoints up to seven months after 6-OHDA injection. In addition, two 6-OHDA-injected rats were examined for neuroinflammation using [¹⁸F]DAA1106-PET. 7-[¹⁸F]FTrp-PET showed significantly increased tracer uptake at the 6-OHDA injection site which was negatively correlated to time after lesion placement. Accumulation of [¹⁸F]DAA1106 at the injection site was increased as well, suggesting that 7-[¹⁸F]FTrp uptake in this region may reflect kynurenine pathway activity associated with inflammation. Bilaterally in the dorsal hippocampus, 7-[¹⁸F]FTrp uptake was significantly decreased and was inversely correlated to dopamine depletion severity, indicating that it reflects reduced serotonin synthesis. Finally, 7-[¹⁸F]FTrp uptake in the pineal gland was significantly increased in relation with dopamine depletion severity, providing evidence that melatonin synthesis is increased in the 6-OHDA rat model. We conclude that 7-[¹⁸F]FTrp is able to detect alterations in both serotonin/melatonin and kynurenine metabolic pathways, and can be applied to visualize pathologic changes related to neurodegenerative processes.

Identifying patients with major depressive disorder based on tryptophan hydroxylase-2 methylation using machine learning algorithms

OBJECTIVES

This study aimed to identify patients with major depressive disorder (MDD) by developing different machine learning (ML) models based on tryptophan hydroxylase-2 (TPH2) methylation and environmental stress.

METHODS

The data were collected from 291 patients with MDD and 100 healthy control participants: individual basic information, the Negative Life Events Scale (NLES) scores, the Childhood Trauma Questionnaire (CTQ) scores and the methylation level at 38 CpG sites in TPH2. Information gain was used to select critical input variables. Support vector machine (SVM), back propagation neural network (BPNN) and random forest (RF) algorithms were used to build recognition models, which were evaluated by the 10-fold cross-validation. SHapley Additive exPlanations (SHAP) method was used to evaluate features importance.

RESULTS

Gender, NLES scores, CTQ scores and 13 CpG sites in TPH2 gene were considered as predictors in the models. Three ML algorithms showed satisfactory performance in predicting MDD and the BPNN model indicated best prediction effects.

CONCLUSION

ML models with TPH2 methylation and environmental stress were identified to possess great performance in identifying patients with MDD, which provided precious experience for artificial intelligence to assist traditional diagnostic methods in the future.

Identifying the effectual-combination ingredients of Zhi-zi-Hou-po decoction based on metabolic difference-oriented network regulation strategy

Zhi-zi-Hou-po decoction (ZZHPD) has been used to treat depression in the clinic for thousand years in China. However, the pharmacodynamic substance of ZZHPD is still not totally clear due to its complex components. The objective of this study was to identify the effectual combination ingredients (ECIs) of ZZHPD, which could represent the antidepressant effect of the original formula. Firstly, differential plasma absorbed components with different variable importance in projection (VIP) value in chronic unpredictable mild stress (CUMS)-induced depression and control rat were revealed by untargeted metabolomics-driven strategy based on HPLC-ESI-TOF/MS, XCMS online and SIMCA-p software. Secondly, network topology scores (NTS) of plasma absorbed components were exposed by protein-protein interaction (PPI) network analysis based on components-related genes and depression-related genes, which were performed by network pharmacology tools. Finally, the ECIs were screened by considered of VIP value and NTS. Then the bioactivity was evaluated by cell viability and expression of glial fibrillary acid protein (GFAP), tumor necrosis factor α (TNFα) and interleukin 1β (IL-1β) of a lipopolysaccharide-induced astrocyte depression model. An effective combination composed with 12 components was filtrated as ECIs of ZZHPD, exposed to which the cell viability effect, the expression of GFAP and IL-1β in astrocytes were essentially equivalent with original ZZHPD (p > 0.05), and that both characteristic constituents and trace compounds of ZZHPD might exert synergistic actions through multi-targets. The result of this study provided useful information for the clinical application and modern development of ZZHPD, and the proposed strategy could be regard as an alternative solution for effective combination screening of herbal medicines.

Acute Corticotropin-Releasing Factor Receptor Type 2 Agonism Results in Sustained Symptom Improvement in Myalgic Encephalomyelitis/Chronic Fatigue Syndrome

Background

Myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) is a complex multi-symptom disease with widespread evidence of disrupted systems. The authors hypothesize that it is caused by the upregulation of the corticotropin-releasing factor receptor type 2 (CRFR2) in the raphé nuclei and limbic system, which impairs the ability to maintain homeostasis. The authors propose utilizing agonist-mediated receptor endocytosis to downregulate CRFR2.

Materials and Methods

This open-label trial tested the safety, tolerability and efficacy of an acute dose of CT38s (a short-lived, CRFR2-selective agonist, with no known off-target activity) in 14 ME/CFS patients. CT38s was subcutaneously-infused at one of four dose-levels (i.e., infusion rates of 0.01, 0.03, 0.06, and 0.20 μg/kg/h), for a maximum of 10.5 h. Effect was measured as the pre-/post-treatment change in the mean 28-day total daily symptom score (TDSS), which aggregated 13 individual patient-reported symptoms.

Results

ME/CFS patients were significantly more sensitive to the transient hemodynamic effects of CRFR2 stimulation than healthy subjects in a prior trial, supporting the hypothesized CRFR2 upregulation. Adverse events were generally mild, resolved without intervention, and difficult to distinguish from ME/CFS symptoms, supporting a CRFR2 role in the disease. The acute dose of CT38s was associated with an improvement in mean TDSS that was sustained (over at least 28 days post-treatment) and correlated with both total exposure and pre-treatment symptom severity. At an infusion rate of 0.03 μg/kg/h, mean TDSS improved by -7.5 ± 1.9 (or -25.7%, p = 0.009), with all monitored symptoms improving.

Conclusion

The trial supports the hypothesis that CRFR2 is upregulated in ME/CFS, and that acute CRFR2 agonism may be a viable treatment approach warranting further study.

Clinical Trial Registration

ClinicalTrials.gov, identifier NCT03613129.

Antidepressants in Alzheimer's Disease: A Focus on the Role of Mirtazapine

Mirtazapine belongs to the category of antidepressants clinically used mainly in major depressive disorder but also used in obsessive-compulsive disorders, generalized anxiety, and sleep disturbances. This drug acts mainly by antagonizing the adrenergic α2, and the serotonergic 5-HT2 and 5-HT3 receptors. Neuropsychiatric symptoms, such as depression and agitation, are strongly associated with Alzheimer’s disease, reducing the life quality of these patients. Thus, it is crucial to control depression in Alzheimer’s patients. For this purpose, drugs such as mirtazapine are important in the control of anxiety, agitation, and other depressive symptoms in these patients. Indeed, despite some contradictory studies, evidence supports the role of mirtazapine in this regard. In this review, we will focus on depression in Alzheimer’s disease, highlighting the role of mirtazapine in this context.

Biomarkers of Post-COVID Depression

The COVID-19 pandemic is spreading around the world and 187 million people have already been affected. One of its after-effects is post-COVID depression, which, according to the latest data, affects up to 40% of people who have had SARS-CoV-2 infection. A very important issue for the mental health of the general population is to look for the causes of this complication and its biomarkers. This will help in faster diagnosis and effective treatment of the affected patients. In our work, we focused on the search for major depressive disorder (MDD) biomarkers, which are also present in COVID-19 patients and may influence the development of post-COVID depression. For this purpose, we searched PubMed, Scopus and Google Scholar scientific literature databases using keywords such as 'COVID-19', 'SARS-CoV-2', 'depression', 'post-COVID', 'biomarkers' and others. Among the biomarkers found, the most important that were frequently described are increased levels of interleukin 6 (IL-6), soluble interleukin 6 receptor (sIL-6R), interleukin 1 β (IL-1β), tumor necrosis factor α (TNF-α), interferon gamma (IFN-γ), interleukin 10 (IL-10), interleukin 2 (IL-2), soluble interleukin 2 receptor (sIL-2R), C-reactive protein (CRP), Monocyte Chemoattractant Protein-1 (MCP-1), serum amyloid a (SAA1) and metabolites of the kynurenine pathway, as well as decreased brain derived neurotrophic factor (BDNF) and tryptophan (TRP). The biomarkers identified by us indicate the etiopathogenesis of post-COVID depression analogous to the leading inflammatory hypothesis of MDD.

Mechanisms of Neurotoxicity Associated with Exposure to the Herbicide Atrazine

Atrazine is an herbicide commonly used on crops to prevent broadleaf weeds. Atrazine is an endocrine-disrupting chemical mainly targeting the neuroendocrine system and associated axes, especially as a reproductive toxicant through attenuation of the luteinizing hormone (LH). Current regulatory levels for chronic exposure are based on no observed adverse effect levels (NOAELs) of these LH alterations in rodent studies. Atrazine has also been studied for its effects on the central nervous system and neurotransmission. The European Union (EU) recognized the health risks of atrazine exposure as a public health concern with no way to contain contamination of drinking water. As such, the EU banned atrazine use in 2003. The United States recently reapproved atrazine's use in the fall of 2020. Research has shown that there is a wide array of adverse health effects that are seen across multiple models, exposure times, and exposure periods leading to dysfunction in many different systems in the body with most pointing to a neuroendocrine target of toxicity. There is evidence of crosstalk between systems that can be affected by atrazine exposure, causing widespread dysfunction and leading to changes in behavior even with no direct link to the hypothalamus. The hypothetical mechanism of toxicity of atrazine endocrine disruption and neurotoxicity can therefore be described as a web of pathways that are influenced through changes occurring in each and their multiple feedback loops with further research needed to refine NOAELs for neurotoxic outcomes.

Antidepressant-like effects of albiflorin involved the NO signaling pathway in rats model of chronic restraint stress

The depressant-like effects of albiflorin (AF) were studied on stressed chronic restraint stress (CRS) rats. Experimental rats were subjected to immobilization stress for a daily 6 h-restraining in a plastic restrainer for continuous 21 d and were treated with 30 or 15 mg·kg^-1 of AF for 21 d. Control rats were maintained in completely non stressed conditions. Behavioral tests and biochemical analysis were applied to investigating a regulatory mechanism of anti-stress of AF. Treatment with AF significantly restored the depressant-like behaviors. Besides, AF increased the levels of 5-hydroxytryptophan (5-HT), 5-hydroxyindoleacetic acid (5-HIAA), noradrenaline (NE) and dopamine (DA) in the hippocampus and increased the level of brain-derived neurotrophic factor (BDNF) in serum and protein expression in hippocampus. In addition, AF decreased the levels of hypothalamo-pituitary-adrenal (HPA) cascade, reduced the level of NO and cGMP in serum and inhibited the overexpression of 5-HT_2AR mRNA and protein expression. Taken together, AF can modulate the NO-mediated network pathway in the hippocampus against stress-induced depressive-like behaviors. These physiological and behavioral changes allow rats to avoid potential deleterious effects of stress that may result from chronically elevated levels of glucocorticosteroids over days.

Effect of chronic handling and social isolation on emotion and cognition in adolescent rats

Adolescence is a critical period of establishing social relations through social interactions that affect the emotional development associated with stress responses, anxiety, depression, and cognitive development. We investigated the behavioral and neurobiological changes induced by handling and social isolation in adolescent rats to determine social interaction effects. Rats were randomly divided into groups and used as a control, a handling, and a social isolation group. After 12 weeks, the handling group showed a significant increase in mobility in the open field test and in tryptophan hydroxylase expression in the dorsal raphe nucleus, as well as significantly reduced immobility times in the forced swim test, compared to the control group (p < 0.05). The social isolation group, in contrast, showed a significant increase in immobility times in the forced swim test and in glucocorticoid and SIRT1 expression in the hippocampus, as well as a significant reduction in mobility in the open field test and in escape latency times in the passive avoidance test, compared to the control group (p < 0.05). The present results show that while handling did not improve cognitive function, it reduced anxiety and lowered depression levels; social isolation, in contrast, significantly impaired the animals' stress response, anxiety and depression levels, and cognitive function. Our findings indicate that handling and social isolation have a strong effect on adolescents' emotional and cognitive development into healthy adults.

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.

Integrating the monoamine and cytokine hypotheses of depression: Is histamine the missing link?

Psychiatric diseases, like depression, largely affect the central nervous system (CNS). While the underlying neuropathology of depressive illness remains to be elucidated, several hypotheses have been proposed as molecular underpinnings for major depressive disorder, including the monoamine hypothesis and the cytokine hypothesis. The monoamine hypothesis has been largely supported by the pharmaceuticals that target monoamine neurotransmitters as a treatment for depression. However, these antidepressants have come under scrutiny due to their limited clinical efficacy, side effects, and delayed onset of action. The more recent, cytokine hypothesis of depression is supported by the ability of immune-active agents to induce "sickness behaviour" akin to that seen with depression. However, treatments that more selectively target inflammation have yielded inconsistent antidepressive results. As such, neither of these hypotheses can fully explain depressive illness pathology, implying that the underlying neuropathological mechanisms may encompass aspects of both theories. The goal of the current review is to integrate these two well-studied hypotheses and to propose a role for histamine as a potential unifying factor that links monoamines to cytokines. Additionally, we will focus on stress-induced depression, to provide an updated perspective of depressive illness research and thereby identify new potential targets for the treatment of major depressive disorder.

Stress-Related Dysfunction of Adult Hippocampal Neurogenesis-An Attempt for Understanding Resilience?

Newborn neurons in the adult hippocampus are regulated by many intrinsic and extrinsic cues. It is well accepted that elevated glucocorticoid levels lead to downregulation of adult neurogenesis, which this review discusses as one reason why psychiatric diseases, such as major depression, develop after long-term stress exposure. In reverse, adult neurogenesis has been suggested to protect against stress-induced major depression, and hence, could serve as a resilience mechanism. In this review, we will summarize current knowledge about the functional relation of adult neurogenesis and stress in health and disease. A special focus will lie on the mechanisms underlying the cascades of events from prolonged high glucocorticoid concentrations to reduced numbers of newborn neurons. In addition to neurotransmitter and neurotrophic factor dysregulation, these mechanisms include immunomodulatory pathways, as well as microbiota changes influencing the gut-brain axis. Finally, we discuss recent findings delineating the role of adult neurogenesis in stress resilience.

Cognitive Behavior Therapy for Depression From an Evolutionary Perspective

Evolutionary medicine attempts to solve a problem with which traditional medicine has struggled historically; how do we distinguish between diseased states and "healthy" responses to disease states? Fever and diarrhea represent classic examples of evolved adaptations that increase the likelihood of survival in response to the presence of pathogens in the body. Whereas, the severe mental disorders like psychotic mania or the schizophrenias may involve true "disease" states best treated pharmacologically, most non-psychotic "disorders" that revolve around negative affects like depression or anxiety are likely adaptations that evolved to serve a function that increased inclusive fitness in our ancestral past. What this likely means is that the proximal mechanisms underlying the non-psychotic "disorders" are "species typical" and neither diseases nor disorders. Rather, they are coordinated "whole body" responses that prepare the individual to respond in a maximally functional fashion to the variety of different challenges that our ancestors faced. A case can be made that depression evolved to facilitate a deliberate cognitive style (rumination) in response to complex (often social) problems. What this further suggests is that those interventions that best facilitate the functions that those adaptations evolved to serve (such as rumination) are likely to be preferred over those like medications that simply anesthetize the distress. We consider the mechanisms that evolved to generate depression and the processes utilized in cognitive behavior therapy to facilitate those functions from an adaptationist evolutionary perspective.