The role of 5-HT receptors in depression

Advances in targeting neurotransmitter systems in dystonia

Dystonia is characterised as uncontrolled, often painful involuntary muscle contractions that cause abnormal postures and repetitive or twisting movements. These movements can be continuous or sporadic and affect different parts of the body and range in severity. Dystonia and its related conditions present a huge cause of neurological morbidity worldwide. Although therapies are available, achieving optimal symptom control without major unwanted effects remains a challenge. Most pharmacological treatments for dystonia aim to modulate the effects of one or more neurotransmitters in the central nervous system, but doing so effectively and with precision is far from straightforward. In this chapter we discuss the physiology of key neurotransmitters, including dopamine, noradrenaline, serotonin (5-hydroxytryptamine), acetylcholine, GABA, glutamate, adenosine and cannabinoids, and their role in dystonia. We explore the ways in which existing pharmaceuticals as well as novel agents, currently in clinical trial or preclinical development, target dystonia, and their respective advantages and disadvantages. Finally, we discuss current and emerging genetic therapies which may be used to treat genetic forms of dystonia.

Whey protein isolate attenuates depression-like behavior developed in a mouse model of breast tumor

Increasing evidence indicates that tryptophan (Trp) metabolism disturbance controls hippocampal 5-hydroxytryptamine (5-HT) and thereby affecting depression-like behavior, in which the gut microbiota (GM) might be involved. This study investigated the effect of Trp-rich whey protein isolate (WPI) on depressive-like behavior in 4T1 tumor-bearing mice. Female BALB/c mice were subcutaneously inoculated with murine 4T1 mammary carcinoma cells and received 2 g/kg of WPI by gavage daily for 21 days. The results showed that WPI exerted no significant effects on tumor weight and volume, but abrogated tumor-induced depression-like behavior, as evidenced by remarkably increased time and distance in the center of the open-field test, decreased immobility time in the tail suspension test, increased time and number of entries to the open arms in the elevated plus maze and sucrose preference. Moreover, WPI promoted the hippocampal Trp, 5-hydroxytryptophan (5-HTP), 5-HT, 5-hydroxyindoleacetic acid (5-HIAA) levels and inhibited kynurenine (Kyn) through up-regulating serotonin transporter (SERT) and down-regulating indoleamine 2, 3-dioxygenase (IDO). WPI showed an enriched microbial diversity indicated by increased Shannon index and decreased Simpson index, reduced the abundances of Proteobacteria, Rikenellaceae_RC9_gut_group, Alloprevotella and Prevotellaceae_UCG-001, and increased the abundance of unclassified_k__norank_d__Bacteria in tumor-bearing mice (P < 0.05). At level 3, WPI enhanced the function of microbial gene related to Trp metabolism in the KEGG pathways (P < 0.05). Our results suggest that WPI exhibits a potent antidepressant-like effect via the regulation of hippocampal Trp metabolism and alteration of GM composition and function, and it may be an effective prevention for cancer-related depression.

Advances in the characterization of negative affect caused by acute and protracted opioid withdrawal using animal models

Opioid use disorder (OUD) is a chronic brain disease which originates from long-term neuroadaptations that develop after repeated opioid consumption and withdrawal episodes. These neuroadaptations lead among other things to the development of a negative affect, which includes loss of motivation for natural rewards, higher anxiety, social deficits, heightened stress reactivity, an inability to identify and describe emotions, physical and/or emotional pain, malaise, dysphoria, sleep disorders and chronic irritability. The urge for relief from this negative affect is one of major causes of relapse, and thus represents a critical challenge for treatment and relapse prevention. Animal models of negative affect induced by opioid withdrawal have recapitulated the development of a negative emotional state with signs such as anhedonia, increased anxiety responses, increased despair-like behaviour and deficits in social interaction. This research has been critical to determine neurocircuitry adaptations during chronic opioid administration or upon withdrawal. In this review, we summarize the recent literature of rodent models of (i) acute withdrawal, (ii) protracted abstinence from passive administration of opioids, (iii) withdrawal or protracted abstinence from opioid self-administration. Finally, we describe neurocircuitry involved in acute withdrawal and protracted abstinence. This article is part of the Special Issue on "Opioid-induced changes in addiction and pain circuits".

Enterogenic metabolomics signatures of depression: what are the possibilities for the future

INTRODUCTION

An increasing number of studies indicate that the microbiota-gut-brain axis is an important pathway involved in the onset and progression of depression. The responses of the organism (or its microorganisms) to external cues cannot be separated from a key intermediate element: their metabolites.

AREAS COVERED

In recent years, with the rapid development of metabolomics, an increasing amount of metabolites has been detected and studied, especially the gut metabolites. Nevertheless, the increasing amount of metabolites described has not been reflected in a better understanding of their functions and metabolic pathways. Moreover, our knowledge of the biological interactions among metabolites is also incomplete, which limits further studies on the connections between the microbial-entero-brain axis and depression.

EXPERT OPINION

This paper summarizes the current knowledge on depression-related metabolites and their involvement in the onset and progression of this disease. More importantly, this paper summarized metabolites from the intestine, and defined them as enterogenic metabolites, to further clarify the function of intestinal metabolites and their biochemical cross-talk, providing theoretical support and new research directions for the prevention and treatment of depression.

Chronic unpredictable stress induces depression/anxiety-related behaviors and alterations of hippocampal monoamine receptor mRNA expression in female mice at different ages

Depression and anxiety are the most common mental health disorders. Though they affect people at any age and occur more often in females, the pathophysiological changes under these conditions are less investigated. In the present study, we examined the effects of age and stress on depression- and anxiety-related behaviors in female mice. Saccharin preference and the open field test were carried out before and after chronic unpredictable stress in 4-, 14- and 25-month-old female mice. After behavioral tests, mRNA levels of monoamine receptors in the hippocampus were measured by real-time RT-PCR. Chronic unpredictable stress decreased saccharin preference in 4-, 14- and 25-month-old mice and the time spent in the center in the open field test in 25-month-old mice. For monoamine receptors, analysis of variance revealed significant effects of age on mRNA levels of Htr1a, Htr2a, Htr6, Adra1a, Adrb2, and Adrb3, significant effects of stress on mRNA levels of Htr4, Adra2c, Adrb1, and Adrb2, and interactions of age × stress on mRNA levels of Htr1a, Htr5b, Adra1d, Adra2a, Adra2c, and Adrb1. Chronic unpredictable stress decreased mRNA levels of Htr4, Htr5b, Adra2c, and Adrb1 in 4-month-old female mice. Correlations were observed between saccharin preference and mRNA levels of Htr4, Htr5b, Htr6, Adra1d, Adra2a, and Adra2c in 4-month-old mice and between the time spent in the center in the open field test and mRNA levels of Htr1b in 4-month-old mice, Htr3a, Htr7, and Adrb2 in 14-month-old mice, and Drd2 in 4- and 14-month-old mice. Our findings support that stress induces depression- and anxiety-related behaviors and the expression of hippocampal monoamine receptors in an age-dependent manner in female mice.

Vagus nerve-dependent effects of fluoxetine on anxiety- and depression-like behaviors in mice

The vagus nerve is a major pathway in the body that is responsible for regulating the activity of the parasympathetic nervous system, which plays an important role in mood disorders including anxiety and depression. Fluoxetine, also known as Prozac, is widely used to treat depression. Nevertheless, there are few studies on the vagus nerve-mediated action of fluoxetine. In this study, we aimed to investigate the vagus nerve-dependent actions of fluoxetine in mice with restraint stress-induced or antibiotics-induced anxiety- and depression-like behaviors. Compared to sham operation, vagotomy alone did not exhibit significant effects on behavioral changes and serotonin-related biomarkers in mice not exposed to stress, antibiotics, or fluoxetine. Oral administration of fluoxetine significantly alleviated anxiety- and depression-like behaviors. However, celiac vagotomy significantly attenuated the anti-depressive effects of fluoxetine. The vagotomy also inhibited the effect of fluoxetine to attenuate restraint stress- or cefaclor-induced reduction in serotonin levels and Htr1a mRNA expression in the hippocampus. These findings suggest that the vagus nerve may regulate the efficacy of fluoxetine for depression.

Antidepressive mechanisms of rhynchophylline in mice with chronic unpredictable stress-induced depression

ETHNOPHARMACOLOGICAL RELEVANCE

Uncaria rhynchophylla ([Mi] Jack) (gouteng) exerts antidepressive effects. Rhynchophylline (RH), a major component of U. rhynchophylla, exerts similar pharmacological effects to those of gouteng. Thus, RH may have antidepressive effects.

AIM OF THE STUDY

To investigate the anti-depressive effects of RH in chronic unpredictable mild stress (CUMS)-induced depressive mice. The anti-depressive mechanism of RH determined by measuring the 5-HT levels, the expressions of cAMP-response element binding protein (CREB) and brain-derived neurotrophic factor (BDNF) in cortex and hippocampus.

MATERIALS AND METHODS

The behaviors of CUMS-induced depressive mice were measured using an open field test (OFT), forced swimming test (FST), and tail suspension test (TST). 5-HT levels were measured using an ELISA kits. The expressions of BDNF and CREB were determined using western blot test.

RESULTS

RH increased the frequency of rearing and grooming in the OFT and decreased the immobility time in the FST and TST. RH effectively increased the 5-HT level and BDNF and CREB expressions in the cortex and hippocampus.

CONCLUSION

Our findings indicate that the antidepressive mechanism of RH is related to increased levels of 5-HT from regulating CREB and BDNF expressions in cortex and hippocampus.

Serotonergic circuit dysregulation underlying autism-related phenotypes in BTBR mouse model of autism

The inbred mouse strain, BTBR T⁺Itpr3^tf/J (BTBR), possesses neuronal and circuit abnormalities that underlie atypical behavioral profiles resembling the major symptoms of human autism spectrum disorder (ASD). Forebrain serotonin (5-HT) transmission has been implicated in ASD-related behavioral alterations. In this study, we assessed 5-HT signals and the functional responsiveness in BTBR mice compared to standard C57BL/6J (B6) control mice to elucidate how 5-HT alterations contribute to behavioral abnormalities in BTBR mice. A lower number of 5-HT neurons in the median raphe, but not in the dorsal raphe, was observed in male and female BTBR mice. Acute systemic injection of buspirone, a 5-HT1A receptor agonist, induced c-Fos in several brain regions in both B6 and BTBR mice; however, blunted c-Fos induction in BTBR mice was documented in the cingulate cortex, basolateral amygdala (BLA), and ventral hippocampus (Hipp). Decreased c-Fos responses in these regions are associated with a lack of buspirone effects on anxiety-like behavior in BTBR mice. Analysis of mRNA expression following acute buspirone injection indicated that 5HTR1a gene downregulation (or upregulation) occurred in the BLA and Hipp of B6 mice, respectively, but not BTBR mice. The mRNA expression of factors associated with neurogenesis or the pro-inflammatory state was not consistently altered by acute buspirone injection. Therefore, 5-HT responsivity via 5-HT1A receptors in the BLA and Hipp are linked to anxiety-like behavior, in which circuits are disrupted in BTBR mice. Other distinct 5-HT circuits from the BLA and Hipp that regulate social behavior are restricted but preserved in BTBR mice.

Dissecting the functional organization of the C. elegans serotonergic system at whole-brain scale

Serotonin influences many aspects of animal behavior. But how serotonin acts on its diverse receptors across the brain to modulate global activity and behavior is unknown. Here, we examine how serotonin release in C. elegans alters brain-wide activity to induce foraging behaviors, like slow locomotion and increased feeding. Comprehensive genetic analyses identify three core serotonin receptors (MOD-1, SER-4, and LGC-50) that induce slow locomotion upon serotonin release and others (SER-1, SER-5, and SER-7) that interact with them to modulate this behavior. SER-4 induces behavioral responses to sudden increases in serotonin release, whereas MOD-1 induces responses to persistent release. Whole-brain imaging reveals widespread serotonin-associated brain dynamics, spanning many behavioral networks. We map all sites of serotonin receptor expression in the connectome, which, together with synaptic connectivity, helps predict which neurons show serotonin-associated activity. These results reveal how serotonin acts at defined sites across a connectome to modulate brain-wide activity and behavior.

Amygdala activity and amygdala-hippocampus connectivity: Metabolic diseases, dementia, and neuropsychiatric issues

With rapid aging of the population worldwide, the number of people with dementia is dramatically increasing. Some studies have emphasized that metabolic syndrome, which includes obesity and diabetes, leads to increased risks of dementia and cognitive decline. Factors such as insulin resistance, hyperglycemia, high blood pressure, dyslipidemia, and central obesity in metabolic syndrome are associated with synaptic failure, neuroinflammation, and imbalanced neurotransmitter levels, leading to the progression of dementia. Due to the positive correlation between diabetes and dementia, some studies have called it "type 3 diabetes". Recently, the number of patients with cognitive decline due to metabolic imbalances has considerably increased. In addition, recent studies have reported that neuropsychiatric issues such as anxiety, depressive behavior, and impaired attention are common factors in patients with metabolic disease and those with dementia. In the central nervous system (CNS), the amygdala is a central region that regulates emotional memory, mood disorders, anxiety, attention, and cognitive function. The connectivity of the amygdala with other brain regions, such as the hippocampus, and the activity of the amygdala contribute to diverse neuropathological and neuropsychiatric issues. Thus, this review summarizes the significant consequences of the critical roles of amygdala connectivity in both metabolic syndromes and dementia. Further studies on amygdala function in metabolic imbalance-related dementia are needed to treat neuropsychiatric problems in patients with this type of dementia.

Consumption of ultra-processed foods is associated with depression, mesocorticolimbic volume, and inflammation

BACKGROUND

The consumption of ultra-processed foods and drinks (UPF) has been associated with depression and inflammation and preclinical studies showed that some UPF components disrupt the amygdala-hippocampal complex. We combine diet, clinical and brain imaging data to investigate the relationship between the UPF consumption, depressive symptoms, and brain volumes in humans, considering interactions with obesity, and the mediation effect of inflammation biomarkers.

METHODS

One-hundred fifty-two adults underwent diet, depressive symptoms, anatomic magnetic resonance imaging assessments and laboratory tests. Relationships between the % of UPF consumption (in grams) of the total diet, depressive symptoms, and gray matter brain volumes were explored using several adjusted regression models, and in interaction with the presence of obesity. Whether inflammatory biomarkers (i.e., white blood cell count, lipopolysaccharide-binding protein, c-reactive protein) mediate the previous associations was investigated using R mediation package.

RESULTS

High UPF consumption was associated with higher depressive symptoms in all participants (β = 0.178, CI = 0.008-0.261) and in those with obesity (β = 0.214, CI = -0.004-0.333). Higher consumption was also associated with lower volumes in the posterior cingulate cortex and the left amygdala, which in the participants with obesity also encompassed the left ventral putamen and the dorsal frontal cortex. White blood count levels mediated the association between UPF consumption and depressive symptoms (p = 0.022).

LIMITATIONS

The present study precludes any causal conclusions.

CONCLUSIONS

UPF consumption is associated with depressive symptoms and lower volumes within the mesocorticolimbic brain network implicated in reward processes and conflict monitoring. Associations were partially dependent on obesity and white blood cell count.

The Role of Pharmacogenetics in Personalizing the Antidepressant and Anxiolytic Therapy

Pharmacotherapy for neuropsychiatric disorders, such as anxiety and depression, has been characterized by significant inter-individual variability in drug response and the development of side effects. Pharmacogenetics, as a key part of personalized medicine, aims to optimize therapy according to a patient's individual genetic signature by targeting genetic variations involved in pharmacokinetic or pharmacodynamic processes. Pharmacokinetic variability refers to variations in a drug's absorption, distribution, metabolism, and elimination, whereas pharmacodynamic variability results from variable interactions of an active drug with its target molecules. Pharmacogenetic research on depression and anxiety has focused on genetic polymorphisms affecting metabolizing cytochrome P450 (CYP) and uridine 5'-diphospho-glucuronosyltransferase (UGT) enzymes, P-glycoprotein ATP-binding cassette (ABC) transporters, and monoamine and γ-aminobutyric acid (GABA) metabolic enzymes, transporters, and receptors. Recent pharmacogenetic studies have revealed that more efficient and safer treatments with antidepressants and anxiolytics could be achieved through genotype-guided decisions. However, because pharmacogenetics cannot explain all observed heritable variations in drug response, an emerging field of pharmacoepigenetics investigates how epigenetic mechanisms, which modify gene expression without altering the genetic code, might influence individual responses to drugs. By understanding the epi(genetic) variability of a patient's response to pharmacotherapy, clinicians could select more effective drugs while minimizing the likelihood of adverse reactions and therefore improve the quality of treatment.

The efficacy and cerebral mechanism of intradermal acupuncture for major depressive disorder: a study protocol for a randomized controlled trial

Background

Major depressive disorder (MDD) has emerged as the fifth leading cause of years lived with disability, with a high prevalent, affecting nearly 4% of the global population. While available evidence suggests that intradermal acupuncture may enhance the effectiveness of antidepressants, whether its efficacy is a specific therapeutic effect or a placebo effect has not been reported. Moreover, the cerebral mechanism of intradermal acupuncture as a superficial acupuncture (usually subcutaneous needling to a depth of 1-2 mm) for MDD remains unclear.

Methods

A total of 120 participants with MDD will be enrolled and randomized to the waiting list group, sham intradermal acupuncture group and active intradermal acupuncture group. All 3 groups will receive a 6-week intervention and a 4-week follow-up. The primary outcome will be measured by the Hamilton Depression Rating Scale-17 and the secondary outcome measures will be the Self-Rating depression scale and Pittsburgh sleep quality index. Assessments will be conducted at baseline, 3 weeks, 6 weeks, and during the follow-up period. In addition, 20 eligible participants in each group will be randomly selected to undergo head magnetic resonance imaging before and after the intervention to explore the effects of intradermal acupuncture on brain activity in MDD patients.

Discussion

If the intradermal acupuncture is beneficial, it is promising to be included in the routine treatment of MDD.

Clinical Trial Registration

Clinicaltrials.gov, NCT05720637.

Antidepressant effects of p-coumaric acid isolated from Vaccinium bracteatum leaves extract on chronic restraint stress mouse model and antagonism of serotonin 6 receptor in vitro

BACKGROUND

Vaccinium bracteatum Thunb. leaves (VBL) are used in traditional herbal medicines to treat various biological diseases. p-coumaric acid (CA), the main active component of VBL, has neuroprotective effects against corticosterone-induced damage in vitro. However, the effects of CA on immobility induced by chronic restraint stress (CRS) in a mouse model and 5-HT receptor activity have not been investigated.

HYPOTHESIS/PURPOSE

We investigated the antagonistic effects of VBL, NET-D1602, and the three components of Gαs protein-coupled 5-HT receptors. Additionally, we identified the effects and mechanism of action of CA, the active component of NET-D1602, in the CRS-exposed model.

METHODS

For in vitro analyses, we used 1321N1 cells stably expressing human 5-HT₆ receptors and CHO-K1 expressing human 5-HT₄ or 5-HT₇ receptors cell lines to study the mechanism of action. For in vivo analyses, CRS-exposed mice were orally administered CA (10, 50, or 100 mg/kg) daily for 21 consecutive days. The effects of CA were analyzed by assessing behavioral changes using a forced swim test (FST), measuring levels of hypothalamic-pituitary-adrenal (HPA) axis-related hormones in ntial therapeutic effects as 5-HT6 receptor antagonists for neurodegenerative diseases and depressioserum, and acetylcholinesterase (AChE), monoamines, including 5-HT, dopamine, and norepinephrine, using enzyme-linked immunosorbent assay kits. The underlying molecular mechanisms of the serotonin transporter (SERT), monoamine oxidase A (MAO-A), and extracellular signal-regulated kinase (ERK)/protein kinase B (Akt)/mTORC1 signaling were detected using western blotting.

RESULTS

CA was confirmed to be an active component in the antagonistic effects of NET-D1602 on 5-HT₆ receptor activity through decreases in cAMP and ERK1/2 phosphorylation. Moreover, CRS-exposed mice treated with CA showed a significantly reduced immobility time in the FST. CA also significantly decreased corticosterone, corticotropin-releasing hormone (CRH), and adrenocorticotropic hormone (ACTH) levels. CA enhanced 5-HT, dopamine, and norepinephrine levels in the hippocampus (HC) and prefrontal cortex (PFC) but decreased MAO-A and SERT protein levels. Similarly, CA significantly upregulated the ERK, Ca²⁺/calmodulin-dependent protein kinase II (CaMKII), Akt/mTOR/p70S6K/S6 signaling pathways in both HC and the PFC.

CONCLUSION

CA contained in NET-D1602 may play the antidepressant effects against CRS-induced depression-like mechanism and the selective antagonist effect of 5-HT₆ receptor.

Latest updates on the serotonergic system in depression and anxiety

Psychiatric disorders are among the leading causes of global health burden, with depression and anxiety being the most disabling subtypes. The two common disorders, depression and anxiety, usually coexist and are pathologically polygenic with complicated etiologies. Current drug-based therapies include selective serotonin reuptake inhibitors, serotonin and norepinephrine reuptake inhibitors, and 5-hydroxytryptamine partial agonists. However, these modalities share common limitations, such as slow onset and low efficacy, which is why potential mechanistic insights for new drug targets are needed. In this review, we summarize recent advances in brain localization, pathology, and therapeutic mechanisms of the serotonergic system in depression and anxiety.

Exploring the molecular mechanism of Nux Vomica in treating ischemic stroke using network pharmacology and molecular docking methods

BACKGROUND

Nux Vomica (NV) has the effects of dredging collaterals, relieving pain, dispersing knots, and detumescence, and has a verified effect in treating ischemic stroke (IS), but its molecular mechanism for treating IS remains unclear. In this study, network pharmacology and molecular docking methods were adopted to explore the pharmacological mechanism of NV in treating IS.

METHODS

The Traditional Chinese Medicine Systems Pharmacology Database and Analysis Platform (TCMSP) and the HERB database were searched to screen the active components and targets of NV. IS disease targets were retrieved from the DisGeNET, DrugBank, GeneCards, and Therapeutic Target Database. Venn diagram and intersection targets were obtained from the Venny website. Subsequently, the STRING database was employed to analyze the interrelationship of the intersection targets. Metascape database was used for Gene Ontology (GO) functional enrichment analysis and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis of intersection targets. Furthermore, Cytoscape was employed to plot a drug-component-target network, and other networks, and molecular docking method was adopted to predict the effective components and targets of NV for treating IS.

RESULTS

A total of 14 active compounds and 59 targets of NV were screened, of which 35 targets were related to IS. Stigmasterol, brucine, isobrucine, isostrychnine N-oxide (I), (S)-stylopine, icaride A, and (2R)-5,7-dihydroxy-2-(4-hydroxyphenyl)chroman-4-one were the main active ingredients, and SLC6A4, NR3C1, SLC6A3, HTR3A, CHRNA7, MAOA, PTGS2, ESR1, catalase (CAT), ADRB2, and AR were the core targets. Molecular docking shows that these compounds bind well to the core targets. In addition, the treatment of IS by NV may mainly involve salivary secretion, serotonergic synapse, calcium signaling pathway, cGMP-PKG signaling pathway, and neuroactive ligand-receptor interaction.

CONCLUSIONS

This study revealed that NV exerts its therapeutic effect on IS through multi-component, multi-target, and multi-pathway, which provides a basis for clinical treatment of IS.

Sedative-Hypnotic Effects of Glycine max Merr. Extract and Its Active Ingredient Genistein on Electric-Shock-Induced Sleep Disturbances in Rats

Glycine max Merr. (GM) is a functional food that provides many beneficial phytochemicals. However, scientific evidence of its antidepressive and sedative activities is scarce. The present study was designed to investigate the antidepressive and calmative effects of GM and its biologically active compound, genistein (GE), using electroencephalography (EEG) analysis in an electric foot shock (EFS)-stressed rat. The underlying neural mechanisms of their beneficial effects were determined by assessing corticotropin-releasing factor (CRF), serotonin (5-HT), and c-Fos immunoreactivity in the brain using immunohistochemical methods. In addition, the 5-HT2C receptor binding assay was performed because it is considered a major target of antidepressants and sleep aids. In the binding assay, GM displayed binding affinity to the 5-HT2C receptor (IC50 value of 14.25 ± 11.02 µg/mL). GE exhibited concentration-dependent binding affinity, resulting in the binding of GE to the 5-HT_2C receptor (IC50, 77.28 ± 26.57 mg/mL). Administration of GM (400 mg/kg) increased non-rapid eye movement (NREM) sleep time. Administration of GE (30 mg/kg) decreased wake time and increased rapid eye movement (REM) and NREM sleep in EPS-stressed rats. In addition, treatment with GM and GE significantly decreased c-Fos and CRF expression in the paraventricular nucleus (PVN) and increased 5-HT levels in the dorsal raphe in the brain. Overall, these results suggest that GM and GE have antidepressant-like effects and are effective in sleep maintenance. These results will benefit researchers in developing alternatives to decrease depression and prevent sleep disorders.

Fifty years on: Serotonin and depression

It has been over 50 years since the original serotonin hypothesis was proposed by the British Psychiatrist Alec Coppen. Recently, some authors have questioned the validity of the hypothesis. In this narrative review, we summarise the evidence for the serotonin hypothesis of depression, focusing on psychopharmacology and molecular imaging, as well as systems-level neuroscience.

Antidepressant Potential of a Functionalized 3-Selanyl Benzo[b]Furan Compound in Mice: Focus on the Serotonergic System

The present study investigated the antidepressant-like potential of a functionalized 3-selanyl benzo[b]furan (SeBZF) in male Swiss mice. To evaluate possible antidepressant-like actions, the compounds SeBZF1-5 (50 mg/kg, intragastric, i.g., route) were acutely screened in the tail suspension tests (TSTs). The compound 3-((4-methoxyphenyl)selanyl)-2-phenylbenzofuran (SeBZF3) was then selected. Dose-response and time-response curves revealed that SeBFZ3 exerts antidepressant-like effects in the TST (5-50 mg/kg) and forced swimming test (FST; 50 mg/kg). Additional tests demonstrated that pretreatment with receptor antagonists WAY100635 (5-HT_1A; 0.1 mg/kg, subcutaneous route), ketanserin (5-HT_2A/C; 1 mg/kg, intraperitoneal, i.p.), or ondansetron (5-HT₃; 1 mg/kg, i.p.) blocked the SeBZF3 antidepressant-like effects (50 mg/kg) in the TST. In addition, the coadministration of subeffective doses of SeBZF3 (1 mg/kg, i.g.) and fluoxetine (a selective serotonin reuptake inhibitor; 5 mg/kg, i.p.) produced synergistic action. A high dose of SeBZF3 (300 mg/kg) did not produce oral acute toxicity. The present results provide evidence for the antidepressant-like action of SeBZF3 and its relative safety, as well as predict the possible interactions with the serotonergic system, aiding in the development of novel options to alleviate psychiatric disabilities.

Could peripheral 5-HT level be used as a biomarker for depression diagnosis and treatment? A narrative minireview

The serotonin hypothesis of depression is still influential, but the relationship between peripheral 5-HT levels and depression is still unknown. This review aimed to verify whether peripheral 5-HT levels could be used as a biomarker for depression diagnosis and treatment. PubMed and EMBASE were searched using terms appropriate to the area of research. Articles from 1957 to 2022 in the following terms were identified: depression, 5-HT, serotonin and peripheral (serum, plasma, blood platelets). 33 studies were included: seven clinical trials about periphery 5-HT levels in depressive patients compared to normal subjects, 15 clinical trials about changes of peripheral 5-HT levels in patients with depression after drug treatment and 11 animal experiments about peripheral 5-HT levels in animal models of depression. Peripheral 5-HT levels presented three different outcomes before and after antidepressant treatments: increased, decreased and no significant change. In conclusion, changes in peripheral 5-HT levels did not show consistent results among these studies. Peripheral 5-HT level could not be used as a biomarker both for depression diagnosis and for antidepressant efficacy evaluation.

Long-term Pu-erh tea consumption improves blue light-induced depression-like behaviors

Blue light emitted by smartphones and tablets at night increases the risk of depression. Pu-erh tea has been reported to reduce the risk of depression by regulating tryptophan metabolism, but its underlying protective mechanism on depression induced by blue light at night (BLAN) remains unclear. In this work, two groups of C57BL6/J mice were given water or 0.25% (w/v) Pu-erh tea for 120 days, followed by a 45-day BLAN treatment (400 lux blue light between 21:00 and 23:00) to simulate blue light emitted from electronic equipment. Our results indicated that BLAN induced depression-like behaviors and gut microbiota disorders in healthy mice. Pu-erh tea intake significantly reshaped the gut microbiome (especially Bifidobacterium) and regulated the metabolism of short-chain fatty acids (SCFAs) which protected the integrity of the intestinal barrier. This improvement further reduced blood-brain barrier (BBB) damage and alleviated neuroinflammation by inhibiting MyD88/NF-κB pathways which finally regulated neurotransmitters such as brain-derived neurotrophic factor (BDNF) and serotonin (5-hydroxytryptamine, 5-HT). Collectively, 0.25% (w/v) Pu-erh tea has the potential to prevent BLAN-induced depression-like behaviors by reshaping the gut microbiota and increasing the generation of SCFAs via the gut-brain axis.

Histone Methyltransferase SETDB1 Regulates the Development of Cortical Htr3a-Positive Interneurons and Mood Behaviors

BACKGROUND

GABAergic (gamma-aminobutyric acidergic) interneurons (INs) are highly heterogeneous, and Htr3a labels a subpopulation of cortical INs originating from the embryonic caudal ganglionic eminence. SETDB1 is one of the histone H3K9 methyltransferases and plays an essential role in the excitatory neurons, but its role in regulating cortical inhibitory INs remains largely unknown.

METHODS

In this study, we generated transgenic mice with conditional knockout of Setdb1 in neural progenitor cells (Setdb1-NS-cKO) and GABAergic neurons (Setdb1-Gad2-cKO). In addition, we performed RNA sequencing, ATAC-seq (assay for transposase-accessible chromatin with sequencing), chromatin immunoprecipitation sequencing, luciferase assay, chromatin conformation capture, and CRISPR (clustered regularly interspaced short palindromic repeats)/dCas9 to study the epigenetic mechanism underlying SETDB1-mediated transcriptional regulation of Htr3a. We also performed in situ hybridization and whole-cell recording to evaluate the functional properties of cortical Htr3a+ INs and behavioral tests for mood.

RESULTS

We detected significant upregulation of Htr3a expression in the embryonic ganglionic eminence of Setdb1-NS-cKO and identified the endogenous retroviral sequence RMER21B as a new target of SETDB1. RMER21B showed enhancer activity and formed distal chromatin interaction with the promoter of Htr3a. In addition, we observed an increased number and enhanced excitability of Htr3a+ INs in the knockout cortex. Moreover, Setdb1-Gad2-cKO mice exhibited anxiety- and depressive-like behaviors, which were partially reversed by a 5-HT₃ receptor antagonist.

CONCLUSIONS

These findings suggest that SETDB1 represses Htr3a transcription via RMER21B-mediated distal chromatin interaction in the embryonic ganglionic eminence and regulates the development of cortical Htr3a+ INs and mood behaviors.

In vivo serotonin 1A receptor hippocampal binding potential in depression and reported childhood adversity

BACKGROUND

Reported childhood adversity (CA) is associated with development of depression in adulthood and predicts a more severe course of illness. Although elevated serotonin 1A receptor (5-HT_1AR) binding potential, especially in the raphe nuclei, has been shown to be a trait associated with major depression, we did not replicate this finding in an independent sample using the partial agonist positron emission tomography tracer [¹¹C]CUMI-101. Evidence suggests that CA can induce long-lasting changes in expression of 5-HT_1AR, and thus, a history of CA may explain the disparate findings.

METHODS

Following up on our initial report, 28 unmedicated participants in a current depressive episode (bipolar n = 16, unipolar n = 12) and 19 non-depressed healthy volunteers (HVs) underwent [¹¹C]CUMI-101 imaging to quantify 5-HT_1AR binding potential. Participants in a depressive episode were stratified into mild/moderate and severe CA groups via the Childhood Trauma Questionnaire. We hypothesized higher hippocampal and raphe nuclei 5-HT_1AR with severe CA compared with mild/moderate CA and HVs.

RESULTS

There was a group-by-region effect (p = 0.011) when considering HV, depressive episode mild/moderate CA, and depressive episode severe CA groups, driven by significantly higher hippocampal 5-HT_1AR binding potential in participants in a depressive episode with severe CA relative to HVs (p = 0.019). Contrary to our hypothesis, no significant binding potential differences were detected in the raphe nuclei (p-values > 0.05).

CONCLUSIONS

With replication in larger samples, elevated hippocampal 5-HT_1AR binding potential may serve as a promising biomarker through which to investigate the neurobiological link between CA and depression.

S-Palmitoylation of Synaptic Proteins in Neuronal Plasticity in Normal and Pathological Brains

Protein lipidation is a common post-translational modification of proteins that plays an important role in human physiology and pathology. One form of protein lipidation, S-palmitoylation, involves the addition of a 16-carbon fatty acid (palmitate) onto proteins. This reversible modification may affect the regulation of protein trafficking and stability in membranes. From multiple recent experimental studies, a picture emerges whereby protein S-palmitoylation is a ubiquitous yet discrete molecular switch enabling the expansion of protein functions and subcellular localization in minutes to hours. Neural tissue is particularly rich in proteins that are regulated by S-palmitoylation. A surge of novel methods of detection of protein lipidation at high resolution allowed us to get better insights into the roles of protein palmitoylation in brain physiology and pathophysiology. In this review, we specifically discuss experimental work devoted to understanding the impact of protein palmitoylation on functional changes in the excitatory and inhibitory synapses associated with neuronal activity and neuronal plasticity. The accumulated evidence also implies a crucial role of S-palmitoylation in learning and memory, and brain disorders associated with impaired cognitive functions.

Dissecting the Functional Organization of the C. elegans Serotonergic System at Whole-Brain Scale

Serotonin controls many aspects of animal behavior and cognition. But how serotonin acts on its diverse receptor types in neurons across the brain to modulate global activity and behavior is unknown. Here, we examine how serotonin release from a feeding-responsive neuron in C. elegans alters brain-wide activity to induce foraging behaviors, like slow locomotion and increased feeding. A comprehensive genetic analysis identifies three core serotonin receptors that collectively induce slow locomotion upon serotonin release and three others that interact with them to further modulate this behavior. The core receptors have different functional roles: some induce behavioral responses to sudden increases in serotonin release, whereas others induce responses to persistent release. Whole-brain calcium imaging reveals widespread serotonin-associated brain dynamics, impacting different behavioral networks in different ways. We map out all sites of serotonin receptor expression in the connectome, which, together with synaptic connectivity, helps predict serotonin-associated brain-wide activity changes. These results provide a global view of how serotonin acts at defined sites across a connectome to modulate brain-wide activity and behavior.

Neuropharmacology of Alcohol Addiction with Special Emphasis on Proteomic Approaches for Identification of Novel Therapeutic Targets

Alcohol is a generic pharmacological agent with only a few recognized primary targets. Nmethyl- D-aspartate, gamma-aminobutyric acid, glycine, 5-hydroxytryptamine 3 (serotonin), nicotinic acetylcholine receptors, and L-type Ca2+ channels and G-protein-activated inwardly rectifying K channels are all involved. Following the first hit of alcohol on specific brain targets, the second wave of indirect effects on various neurotransmitter/neuropeptide systems begins, leading to the typical acute behavioral effects of alcohol, which range from disinhibition to sedation and even hypnosis as alcohol concentrations rise. Recent research has revealed that gene regulation is significantly more complex than previously thought and does not fully explain changes in protein levels. As a result, studying the proteome directly, which differs from the genome/transcriptome in terms of complexity and dynamicity, has provided unique insights into extraordinary advances in proteomic techniques that have changed the way we can analyze the composition, regulation, and function of protein complexes and pathways underlying altered neurobiological conditions. Neuroproteomics has the potential to revolutionize alcohol research by allowing researchers to gain a better knowledge of how alcohol impacts protein structure, function, connections, and networks on a global scale. The amount of information collected from these breakthroughs can aid in identifying valuable biomarkers for early detection and improved prognosis of an alcohol use disorder and future pharmaceutical targets for the treatment of alcoholism.

Therapeutic Potential of the Purinergic System in Major Depressive Disorder Associated with COVID-19

Neuroinflammation is closely related to the development of depression, since the latter is caused, among other factors, by inflammatory processes, mainly related to the activation of microglia and expression of specific genes, which occurs during the neuroinflammatory process. Thus, COVID-19 is an important risk factor for the development of depression, since in addition to generating the feeling of stress, which also increases the activity of the immune system, it is also the cause of pathological processes and physiological ones that lead to the development of neuroinflammation, microglial activation, gene expression dysfunction and decreased concentration of available serotonin. That said, drugs are being used to combat COVID-19 to reduce the oxidative stress presented in the disease. Thus, tramadol and fluoxetine are highlighted as drugs used, however, although they present some positive results, such as the reduction of pro-inflammatory cytokines, they are also associated with negative effects such as dependence, pulmonary, cardiac and brain impairment. From this, the purinergic system is highlighted in the literature as a possible therapeutic target. This is because its mechanisms are related to the regulation of microglia, astrocytes and the physiology of important neurotransmitters and hormones. Added to this, there is a modulation of inflammatory activity, especially with regard to the P2X7 receptors of this system. The latter is an important target for the treatment of depression and COVID-19, since positive results were obtained through the genetic exclusion of this receptor and the use of selective antagonists.

Are the epigenetic changes predictive of therapeutic efficacy for psychiatric disorders? A translational approach towards novel drug targets

The etiopathogenesis of mental disorders is not fully understood and accumulating evidence support that clinical symptomatology cannot be assigned to a single gene mutation, but it involves several genetic factors. More specifically, a tight association between genes and environmental risk factors, which could be mediated by epigenetic mechanisms, may play a role in the development of mental disorders. Several data suggest that epigenetic modifications such as DNA methylation, post-translational histone modification and interference of microRNA (miRNA) or long non-coding RNA (lncRNA) may modify the severity of the disease and the outcome of the therapy. Indeed, the study of these mechanisms may help to identify patients particularly vulnerable to mental disorders and may have potential utility as biomarkers to facilitate diagnosis and treatment of psychiatric disorders. This article summarizes the most relevant preclinical and human data showing how epigenetic modifications can be central to the therapeutic efficacy of antidepressant and/or antipsychotic agents, as possible predictor of drugs response.

KGML-xDTD: a knowledge graph-based machine learning framework for drug treatment prediction and mechanism description

BACKGROUND

Computational drug repurposing is a cost- and time-efficient approach that aims to identify new therapeutic targets or diseases (indications) of existing drugs/compounds. It is especially critical for emerging and/or orphan diseases due to its cheaper investment and shorter research cycle compared with traditional wet-lab drug discovery approaches. However, the underlying mechanisms of action (MOAs) between repurposed drugs and their target diseases remain largely unknown, which is still a main obstacle for computational drug repurposing methods to be widely adopted in clinical settings.

RESULTS

In this work, we propose KGML-xDTD: a Knowledge Graph-based Machine Learning framework for explainably predicting Drugs Treating Diseases. It is a 2-module framework that not only predicts the treatment probabilities between drugs/compounds and diseases but also biologically explains them via knowledge graph (KG) path-based, testable MOAs. We leverage knowledge-and-publication-based information to extract biologically meaningful "demonstration paths" as the intermediate guidance in the Graph-based Reinforcement Learning (GRL) path-finding process. Comprehensive experiments and case study analyses show that the proposed framework can achieve state-of-the-art performance in both predictions of drug repurposing and recapitulation of human-curated drug MOA paths.

CONCLUSIONS

KGML-xDTD is the first model framework that can offer KG path explanations for drug repurposing predictions by leveraging the combination of prediction outcomes and existing biological knowledge and publications. We believe it can effectively reduce "black-box" concerns and increase prediction confidence for drug repurposing based on predicted path-based explanations and further accelerate the process of drug discovery for emerging diseases.

Serotonin distinctly controls behavioral states in restrained and freely moving Drosophila

When trapped in a physical restraint, animals must select an escape strategy to increase their chances of survival. After falling into an inescapable trap, they react with stereotypical behaviors that differ from those displayed in escapable situations. Such behaviors involve either a wriggling response to unlock the trap or feigning death to fend off a predator attack. The neural mechanisms that regulate animal behaviors have been well characterized for escapable situations but not for inescapable traps. We report that restrained vinegar flies exhibit alternating flailing and immobility to free themselves from the trap. We used optogenetics and intersectional genetic approaches to show that, while broader serotonin activation promotes immobility, serotonergic cells in the ventral nerve cord (VNC) regulate immobility states majorly via 5-HT7 receptors. Restrained and freely moving locomotor states are controlled by distinct mechanisms. Taken together, our study has identified serotonergic switches of the VNC that promote environment-specific adaptive behaviors.

Insights of ligand binding in modeled h5-HT1A receptor: homology modeling, docking, MM-GBSA, screening and molecular dynamics

The pharmacologically characterized receptor subtype of the serotonin family, the 5HT1A receptor is implicated in the pathophysiology and treatment of depression and anxiety-related disorders. Being the most extensively targeted receptor for developing novel antidepressants and anxiolytics, a near-ideal theoretical model can aid in high-throughput screening of promising drug candidates. However, the design of potential drug candidates suffers owing to a lack of complete structural information. In this work, homology models of 5-HT1A receptor are generated using two distinct alignments (CW and PSTA) and model building methods (KB and EB). The developed models are validated for virtual screening using a ligand dataset of agonists and antagonists. The best-suited model was efficient in discriminating agonist/antagonist binding. Correlation plots between pKi and docking (R²_agonist≥ 0.6, R²_antagonist≥ 0.7) and MM-GBSA dG bind values (R²_agonist≥ 0.5, R²_antagonist≥ 0.7) revealed optimum corroboration between in vitro and in silico outcomes, which further suggested the usefulness of the developed model for the design of high-affinity probes for the neurological disorders.Communicated by Ramaswamy H. Sarma.

Ingestion of Lactobacillus helveticus WHH1889 improves depressive and anxiety symptoms induced by chronic unpredictable mild stress in mice

Emerging evidence indicates that the alterations in the gut microbiota-brain axis (GBA), which is the bilateral connection between the gut microbial communities and brain function, are involved in several mental illnesses, including depression. Certain probiotic strains have been revealed to improve depressive behaviours and the dysregulation of 5-hydroxytryptamine (5-HT) metabolism in depression. Here we evaluated the potential antidepressant effects of Lactobacillus helveticus strains using an in vitro enterochromaffin cell model (RIN14B). The L. helveticus strain WHH1889 was shown to significantly promote the level of 5-hydroxytryptamine (5-HTP, 5-HT precursor) and the gene expression of tryptophan hydroxylase 1 (Tph1), which is the key synthetase in the 5-HT biosynthesis in RIN14B cells. Ingestion of 0.2 ml WHH1889 (1´10⁹ cfu/ml) in a chronic unpredictable mild stress (CUMS) mouse model of depression for five weeks normalised depressive and anxiety-like behaviours in the forced swim test, tail suspension test, sucrose preference test, and open field test. Meanwhile, the CUMS-induced elevated level of serum corticosterone and declined levels of hippocampal 5-HT and 5-HTP were reversed by WHH1889. Furthermore, the disturbances of the gut microbiome composition with reduced microbial diversity were also improved by WHH1889, accompanied by the increased colonic 5-HTP level and Tph1 gene expression. In summary, these findings indicate that WHH1889 exerts antidepressant-like effects on CUMS mice, which is associated with the modulations of the 5-HT/5-HTP metabolism and gut microbiome composition. Therefore, ingestion of the L. helveticus strain WHH1889 with antidepressant potentials may become an encouraging therapeutic option in the treatment of depression.

Identification of l-Tryptophan by down-field 1 H MRS: A precursor for brain NAD+ and serotonin syntheses

PURPOSE

To explore the presence of new resonances beyond 9.4 ppm from the human brain, down-field proton MRS was performed in vivo in the human brain on 6 healthy volunteers at 7 T.

METHODS

To maximize the SNR, a large voxel was placed within the brain to cover the maximal area in such a way that sinus cavities were avoided. A spectrally selective 90° E-BURP pulse with an excitation bandwidth of 2 ppm was used to probe the spectral chemical shift range between 9.1 and 10.5 ppm. The E-BURP pulse was integrated with PRESS spatial localization to obtain non-water-suppressed proton MR spectra from the desired spectral region.

RESULTS

In the down-field proton MRS obtained from all of the volunteers scanned, we identified a new peak consistently resonating at 10.1 ppm. Protons associated with this resonance are in cross-relaxation with the bulk water, as demonstrated by the water saturation and deuterium exchange experiments.

CONCLUSION

Based on the chemical shift, this new peak was identified as the indole (-NH) proton of l-tryptophan (l-TRP) and was further confirmed from phantom experiments on l-TRP. These promising preliminary results potentially pave the way to investigate the role of cerebral metabolism of l-TRP in healthy and disease conditions.

Association between Diffusion Tensor Imaging, inflammation and immunological alterations in unipolar and bipolar depression: A review

Major Depressive Disorder (MDD) and Bipolar Disorder Depression (BDD) are common psychiatric illnesses characterized by structural and functional brain alterations and signs of neuroinflammation. In line with the neuroinflammatory pathogenesis of depressive syndromes, recent studies have demonstrated how white matter (WM) microstructural impairments detected by Diffusion Tensor Imaging, are correlated to peripheral immunomarkers in depressed patients. In this context, we performed a comprehensive systematic search on PubMed, Medline and Scopus of the original studies published till June 2022, exploring the association between immunomarkers and WM alteration patterns in patients affected by MDD or BDD. Overall, the studies included in this review showed a consistent association between blood proinflammatory and counter-regulatory immunomarkers, including regulatory T cells and natural killer cells markers, as well as measures of demyelination and dysmyelination in both MDD and BDD patients. These pathogenetic insights could outline an integrated clinical perspective to affective disorders, helping psychiatrists to develop novel biotype-to-phenotype models of depression and opening the way to tailored approaches in treatments.

Insulin modulates emotional behavior through a serotonin-dependent mechanism

Type-2 Diabetes (T2D) is characterized by insulin resistance and accompanied by psychiatric comorbidities including major depressive disorders (MDD). Patients with T2D are twice more likely to suffer from MDD and clinical studies have shown that insulin resistance is positively correlated with the severity of depressive symptoms. However, the potential contribution of central insulin signaling in MDD in patients with T2D remains elusive. Here we hypothesized that insulin modulates the serotonergic (5-HT) system to control emotional behavior and that insulin resistance in 5-HT neurons contributes to the development of mood disorders in T2D. Our results show that insulin directly modulates the activity of dorsal raphe (DR) 5-HT neurons to dampen 5-HT neurotransmission through a 5-HT1A receptor-mediated inhibitory feedback. In addition, insulin-induced 5-HT neuromodulation is necessary to promote anxiolytic-like effect in response to intranasal insulin delivery. Interestingly, such an anxiolytic effect of intranasal insulin as well as the response of DR 5-HT neurons to insulin are both blunted in high-fat diet-fed T2D animals. Altogether, these findings point to a novel mechanism by which insulin directly modulates the activity of DR 5-HT neurons to dampen 5-HT neurotransmission and control emotional behaviors, and emphasize the idea that impaired insulin-sensitivity in these neurons is critical for the development of T2D-associated mood disorders.

Schizophrenia, Bipolar and Major Depressive Disorders: Overview of Clinical Features, Neurotransmitter Alterations, Pharmacological Interventions, and Impact of Oxidative Stress in the Disease Process

Psychiatric disorders are one of the leading causes of disability worldwide and affect the quality of life of both individuals and the society. The current understanding of these disorders points toward receptor dysfunction and neurotransmitter imbalances in the brain. Treatment protocols are hence oriented toward normalizing these imbalances and ameliorating the symptoms. However, recent literature has indicated the possible role of depleted levels of antioxidants like glutathione (GSH) as well as an alteration in the levels of the pro-oxidant, iron in the pathogenesis of major psychiatric diseases, viz., schizophrenia (Sz), bipolar disorder (BD), and major depressive disorder (MDD). This review aims to highlight the involvement of oxidative stress (OS) in these psychiatric disorders. An overview of the clinical features, neurotransmitter abnormalities, and pharmacological treatments concerning these psychiatric disorders has also been presented. Furthermore, it attempts to synthesize literature from existing magnetic resonance spectroscopy (MRS) and quantitative susceptibility mapping (QSM) studies for these disorders, assessing GSH and iron, respectively. This manuscript is a sincere attempt to stimulate research discussion to advance the knowledge base for further understanding of the pathoetiology of Sz, BD, and MDD.

Multiscale neural gradients reflect transdiagnostic effects of major psychiatric conditions on cortical morphology

It is increasingly recognized that multiple psychiatric conditions are underpinned by shared neural pathways, affecting similar brain systems. Here, we carried out a multiscale neural contextualization of shared alterations of cortical morphology across six major psychiatric conditions (autism spectrum disorder, attention deficit/hyperactivity disorder, major depression disorder, obsessive-compulsive disorder, bipolar disorder, and schizophrenia). Our framework cross-referenced shared morphological anomalies with respect to cortical myeloarchitecture and cytoarchitecture, as well as connectome and neurotransmitter organization. Pooling disease-related effects on MRI-based cortical thickness measures across six ENIGMA working groups, including a total of 28,546 participants (12,876 patients and 15,670 controls), we identified a cortex-wide dimension of morphological changes that described a sensory-fugal pattern, with paralimbic regions showing the most consistent alterations across conditions. The shared disease dimension was closely related to cortical gradients of microstructure as well as neurotransmitter axes, specifically cortex-wide variations in serotonin and dopamine. Multiple sensitivity analyses confirmed robustness with respect to slight variations in analytical choices. Our findings embed shared effects of common psychiatric conditions on brain structure in multiple scales of brain organization, and may provide insights into neural mechanisms of transdiagnostic vulnerability.

Insights into the Promising Prospect of G Protein and GPCR-Mediated Signaling in Neuropathophysiology and Its Therapeutic Regulation

G protein-coupled receptors (GPCRs) are intricately involved in the conversion of extracellular feedback to intracellular responses. These specialized receptors possess a crucial role in neurological and psychiatric disorders. Most nonsensory GPCRs are active in almost 90% of complex brain functions. At the time of receptor phosphorylation, a GPCR pathway is essentially activated through a G protein signaling mechanism via a G protein-coupled receptor kinase (GRK). Dopamine, an important neurotransmitter, is primarily involved in the pathophysiology of several CNS disorders; for instance, bipolar disorder, schizophrenia, Parkinson's disease, and ADHD. Since dopamine, acetylcholine, and glutamate are potent neuropharmacological targets, dopamine itself has potential therapeutic effects in several CNS disorders. GPCRs essentially regulate brain functions by modulating downstream signaling pathways. GPR6, GPR52, and GPR8 are termed orphan GPCRs because they colocalize with dopamine D1 and D2 receptors in neurons of the basal ganglia, either alone or with both receptors. Among the orphan GPCRs, the GPR52 is recognized for being an effective psychiatric receptor. Various antipsychotics like aripiprazole and quetiapine mainly target GPCRs to exert their actions. One of the most important parts of signal transduction is the regulation of G protein signaling (RGS). These substances inhibit the activation of the G protein that initiates GPCR signaling. Developing a combination of RGS inhibitors with GPCR agonists may prove to have promising therapeutic potential. Indeed, several recent studies have suggested that GPCRs represent potentially valuable therapeutic targets for various psychiatric disorders. Molecular biology and genetically modified animal model studies recommend that these enriched GPCRs may also act as potential therapeutic psychoreceptors. Neurotransmitter and neuropeptide GPCR malfunction in the frontal cortex and limbic-related regions, including the hippocampus, hypothalamus, and brainstem, is likely responsible for the complex clinical picture that includes cognitive, perceptual, emotional, and motor symptoms. G protein and GPCR-mediated signaling play a critical role in developing new treatment options for mental health issues, and this study is aimed at offering a thorough picture of that involvement. For patients who are resistant to current therapies, the development of new drugs that target GPCR signaling cascades remains an interesting possibility. These discoveries might serve as a fresh foundation for the creation of creative methods for pharmacologically useful modulation of GPCR function.

Maternal mental health and substance use disorders in sudden unexpected death in infancy using routinely collected health data in New Zealand, 2000-2016

BACKGROUND

Mortality from sudden unexpected death in infancy (SUDI) has declined dramatically since the 'Back to Sleep' campaign. Deaths now are more prevalent in those with socioeconomic disadvantage. The investigation of SUDI frequently identifies parents that have mental health or drug, alcohol and addiction problems.

AIMS

To estimate the prevalence of maternal mental health and substance use disorders and assess the magnitude of their risk for SUDI.

METHODS

We conducted a population-based cohort study using data from the Integrated Data Infrastructure (IDI), a large research database containing linked data from a range of government agencies. The study population was all live births and their mothers in New Zealand from 2000 to 2016. The exposures of interest were maternal mental health problems and maternal substance use disorders in the year prior to the birth. The outcome was deaths from SUDI.

RESULTS

The total population was 1086 504 live births and of these 1078 811 (99.3%) were able to be linked to other data sets within the IDI. The prevalence of maternal mental health problems in the total population was 5.2% and substance use disorder was 0.7%. There were 42 deaths from SUDI (0.75/1000) that were exposed to maternal mental illness and 864 deaths (0.84/1000) that were not exposed (adjusted relative risk (aRR)=1.23, 95% CI 0.90 to 1.68). There were 21 deaths from SUDI (2.67/1000) that were exposed to maternal substance use disorders and 885 (0.83/1000) that were not exposed (aRR=1.82, 95% CI 1.17 to 2.83).

CONCLUSIONS

Maternal substance use disorders, but not maternal mental health problems, in the year prior to the child's birth was associated with an increased risk of SUDI. However, the numbers that are affected are small and the effect size moderate. This group of women should receive additional SUDI prevention services and Safe Sleep advice.

Attempting to Increase the Effectiveness of the Antidepressant Trazodone Hydrochloride Drug Using π-Acceptors

Major depressive disorder is a prevalent mood illness that is mildly heritable. Cases with the highest familial risk had recurrence and onset at a young age. Trazodone hydrochloride is an antidepressant medicine that affects the chemical messengers in the brain known as neurotransmitters, which include acetylcholine, norepinephrine, dopamine, and serotonin. In the present research, in solid and liquid phases, the 1:1 charge-transfer complexes between trazodone hydrochloride (TZD) and six different π-acceptors were synthesized and investigated using different microscopic techniques. The relation of dative ion pairs [TZD+, A-], where A is the acceptor, was inferred via intermolecular charge-transfer complexes. Additionally, a molecular docking examination was utilized to compare the interactions of protein receptors (serotonin-6BQH) with the TZD alone or in combination with the six distinct acceptor charge-transfer complexes. To refine the docking results acquired from AutoDock Vina and to better examine the molecular mechanisms of receptor-ligand interactions, a 100 ns run of molecular dynamics simulation was used. All the results obtained in this study prove that the 2,6-dichloroquinone-4-chloroimide (DCQ)/TZD complex interacts with serotonin receptors more efficiently than reactant donor TZD only and that [(TZD)(DCQ)]-serotonin has the highest binding energy value of all π-acceptor complexes.

The role and mechanism of tryptophan - kynurenine metabolic pathway in depression

Major depressive disorder (MDD) is a common mental illness characterized by persistent low mood and anhedonia, normally accompanied with cognitive impairment. Due to its rising incidence and high rate of recurrence and disability, MDD poses a substantial threat to patients' physical and mental health, as well as a significant economic cost to society. However, the etiology and pathogenesis of MDD are still unclear. Chronic inflammation may cause indoleamine-2,3-dioxygenase (IDO) to become overactive throughout the body and brain, resulting in excess quinolinic acid (QUIN) and less kynuric acid (KYNA) in the brain. QUIN's neurotoxicity damages glial cells and neurons, accelerates neuronal apoptosis, hinders neuroplasticity, and causes depression due to inflammation. Therefore, abnormal TRP-KYN metabolic pathway and its metabolites have been closely related to MDD, suggesting changes in the TRP-KYN metabolic pathway might contribute to MDD. In addition, targeting TRP-KYN with traditional Chinese medicine showed promising treatment effects for MDD. This review summarizes the recent studies on the TRP-KYN metabolic pathway and its metabolites in depression, which would provide a theoretical basis for exploring the etiology and pathogenesis of depression.

Neuroinflammation in HIV-associated depression: evidence and future perspectives

People living with HIV face a high risk of mental illness, especially depression. We do not yet know the precise neurobiological mechanisms underlying HIV-associated depression. Depression severity in the general population has been linked to acute and chronic markers of systemic inflammation. Given the associations between depression and peripheral inflammation, and since HIV infection in the brain elicits a neuroinflammatory response, it is possible that neuroinflammation contributes to the high prevalence of depression amongst people living with HIV. The purpose of this review was to synthesise existing evidence for associations between inflammation, depression, and HIV. While there is strong evidence for independent associations between these three conditions, few preclinical or clinical studies have attempted to characterise their interrelationship, representing a major gap in the literature. This review identifies key areas of debate in the field and offers perspectives for future investigations of the pathophysiology of HIV-associated depression. Reproducing findings across diverse populations will be crucial in obtaining robust and generalisable results to elucidate the precise role of neuroinflammation in this pathophysiology.

Enhanced availability of serotonin limits muscle activation during high-intensity, but not low-intensity, fatiguing contractions

Serotonin (5-HT) modulates motoneuron excitability during muscle contractions, where the release of 5-HT in the central nervous system (CNS) is linked to the intensity of physical activity. Although there is evidence that enhanced availability of 5-HT can exacerbate fatigue, these effects on the development of fatigue during different contraction intensities are largely unknown. The purpose of this study was to investigate how enhanced 5-HT availability affects voluntary muscle activation and corticospinal excitability during fatigue-inducing contractions. Two experiments were performed. In the first experiment (n = 11), twelve isometric elbow flexions at 20% maximal voluntary contractions (MVC) were performed for 2-min each with 40-s rest periods. In the second experiment (n = 14), twelve maximal isometric elbow flexions were held for 10-s each with 40-s rest periods. In both experiments, the selective serotonin reuptake inhibitor (20 mg paroxetine), or a placebo, was administered in a two-way crossover-design. Muscle responses to transcranial magnetic stimulation (TMS) of the motor cortex (both experiments 1 and 2), as well as motor point stimulation of the elbow flexors (experiment 2) were assessed. Paroxetine reduced both motor cortical (p = 0.018) and motor point voluntary activation (p = 0.036) during the maximal contraction protocol. Paroxetine also reduced exercise-induced lengthening of the TMS silent period during the submaximal (p = 0.037) and maximal (p = 0.002) contraction protocols. Activation of inhibitory 5-HT_1A receptors on motoneurons likely exacerbated exercise-induced reductions in voluntarily drive to the elbow flexors. However, 5-HT modulation of motor activity also appeared at the supraspinal level.

New investigational agents for the treatment of major depressive disorder

INTRODUCTION

Pharmacotherapy of depression is characterized by the delayed onset of action, chronic treatment requirements, and insufficient effectiveness. Ketamine, with its rapid action and long-lasting effects, represents a breakthrough in the modern pharmacotherapy of depression.

AREAS COVERED

: The current review summarizes the latest findings on the mechanism of the antidepressant action of ketamine and its enantiomers and metabolites. Furthermore, the antidepressant potential of psychedelics, non-hallucinogenic serotonergic modulators and metabotropic glutamate receptor ligands was discussed.

EXPERT OPINION

Recent data indicated that to achieve fast and long-acting antidepressant-like effects, compounds must induce durable effects on the architecture and density of dendritic spines in brain regions engaged in mood regulation. Such mechanisms underlie the actions of ketamine and psychedelics. These compounds trigger hallucinations; however, it is thought that these effects might be essential for their antidepressant action. Behavioral studies with serotonergic modulators affecting 5-HT1A (biased agonists), 5-HT4 (agonists), and 5-HT-7 (antagonists) receptors exert rapid antidepressant-like activity, but they seem to be devoid of this effects. Another way to avoid psychomimetic effects and achieve the desired rapid antidepressant-like effects is combined therapy. In this respect, ligands of metabotropic receptors show some potential.

The association between tryptophan levels and postpartum mood disorders: a systematic review and meta-analysis

Over 50% of women experience mood disturbance in the postpartum period, with significant implications for maternal and infant health but identifying those at risk is not easily possible. The essential amino acid, tryptophan (TRP) through its neuroactive metabolites, has been implicated in the pathology of mood disorders. Thus, TRP levels tested in the peripartum period have been proposed as a potential biomarker for subsequent development of postpartum mood disturbances, in particular postpartum depression (PPD). A systematic review and meta-analysis following PROSPERO guidelines [CRD42021252462] was conducted on peer-reviewed, English language studies that measured blood levels of TRP during the postpartum period in women who were also evaluated for postpartum "blues" or PPD. Thirteen studies met the inclusion criteria, of which five studies contained sufficient data to conduct a meta-analysis. Low total TRP levels in postpartum days 1 to 5 were significantly associated with PPD (SMD: -5.39, 95%CI [-7.72, -3.05]). No significant association was found between free TRP levels in the postpartum period and PPD (SMD: -3.43, 95%CI [-7.76, 0.89]). Our findings confirm the necessity for more replicable designed studies regarding TRP and its relationship to postpartum depression. If there were greater clarity regarding TRP metabolism during pregnancy, then the next step would be to consider measuring total plasma TRP levels on postpartum days 1 to 5 to identify women at greater risk of developing PPD.

Structural modelling and in silico pharmacology of β-carboline alkaloids as potent 5-HT1A receptor antagonists and reuptake inhibitors

Serotonin (5-HT) antagonists and reuptake inhibitors (SARIs) are atypical antidepressants for managing major depressive disorder. They are oftentimes applied as adjuvants for ameliorating aftereffects of SSRI antidepressants including insomnia and sexual dysfunction. The few available candidates of this class including lorpiprazole and trazodone also display some daunting side effects, making a continuous search for improved alternatives essential. Natural β-carboline alkaloids (NβCs) are interestingly renowned with broad pharmacological spectrum against several neuropsychiatric disorders including depression. However, their potentials as SARIs remain underexplored. In this study, 982 NβCs retrieved from the Ambinter-Greenpharma (Amb) database were virtually screened for potent SARI alternatives using computational and biocheminformatics approaches: homology modelling of 5-HT1A receptor, Glide HTVS, SP and XP molecular docking, molecular dynamics (MD) simulation, ADMET and mutagenicity predictions. The homology receptor was validated as a good representative of human 5HT1A receptor using the RCSB structure validation and quality protocols. From the virtual screening against the 5-HT1A receptor, Amb ligands, Amb18709727 and Amb37857532 showed higher binding affinities by XP scores of -8.725 and -7.976 kcal/mol, and MMGBSA of -87.972 and -107.585 kcal/mol respectively compared to lorpiprazole, a reference SARI with XP score and MMGBSA of -6.512 and -62.788 kcal/mol respectively. They maintained ideal contacts with pharmacologically essential amino acid residues implicated in SARI mechanisms and expressed higher stability and compactness than lorpiprazole throughout the trajectories of 100 ns MD simulation. They also displayed interesting ADME, druggability, low toxicity and mutagenicity profiles, ideal for CNS drug prospects, thus, recommended as putative SARI candidates for further study.

The serotonergic system dysfunction in diabetes mellitus

Most peripheral serotonin (5-HT) is synthesized in enterochromaffin cells, and most circulating 5-HT is stored in platelets. As a monoamine, 5-HT has several functions in various non-neuronal and neuronal systems. In the central nervous system, it functions as a neurotransmitter to modulate feeding behavior and mood. Numerous clinical trials have focused on increasing 5-HT activation in the central nervous system, including those involving anti-obesity drugs currently in the market, although severe side effects on peripheral system can lead to the withdrawal of certain drugs. Recent studies have revealed that both the peripheral and central serotonergic systems play a vital role in diabetes and its complications. This review summarizes the roles of the serotonergic system in blood glucose regulation, diabetic macroangiopathy, diabetic peripheral neuropathy, and diabetic encephalopathy, indicating its potential clinical significance as a therapeutic target for the treatment of diabetes and its complications.

Participation of Hippocampal 5-HT5A, 5-HT6 and 5-HT7 Serotonin Receptors on the Consolidation of Social Recognition Memory

Social recognition is the ability of animals to identify and recognize a conspecific. The consolidation of social stimuli in long-term memory is crucial for the establishment and maintenance of social groups, reproduction and species survival. Despite its importance, little is known about the circuitry and molecular mechanisms involved in the social recognition memory (SRM). Serotonin (5-hydroxytryptamine, 5-HT) is acknowledged as a major neuromodulator, which plays a key role in learning and memory. Focusing on the more recently described 5-HT receptors, we investigated in the CA1 region of the dorsal hippocampus the participation of 5-HT_5A, 5-HT₆ and 5-HT₇ receptors in the consolidation of SRM. Male Wistar rats cannulated in CA1 were subjected to a social discrimination task. In the sample phase the animals were exposed to a juvenile conspecific for 1 h. Immediately after, they received different pharmacological treatments. Twenty-four hours later, they were submitted to a 5 min retention test in the presence of the previously presented juvenile (familiar) and a novel juvenile. The animals that received infusions of 5-HT_5A receptor antagonist SB-699551 (10 µg/µL), 5-HT₆ receptor agonist WAY-208466 (0.63 µg/µL) or 5-HT₇ receptor agonist AS-19 (5 µg/µL) intra-CA1 were unable to recognize the familiar juvenile. This effect was blocked by the coinfusion of WAY-208466 plus 5-HT₆ receptor antagonist SB-271046 (10 µg/µL) or AS-19 plus 5-HT₇ receptor antagonist SB-269970 (5 µg/µL). The present study helps to clarify the neurobiological functions of the 5-HT receptors more recently described and extends our knowledge about mechanisms underlying the SRM.

Occlusal Disharmony-A Potential Factor Promoting Depression in a Rat Model

Objectives: Patients with occlusal disharmony (OD) may be susceptible to depression. The hypothalamus−pituitary−adrenal axis, 5-HT and 5HT2AR in the prefrontal cortex (PFC), amygdala, and hippocampus are involved in the modulation of emotion and depression. This study investigated whether OD affects the HPA axis and 5-HT system and, subsequently, produces depression-like behaviors in rats. Materials and methods: OD was produced by removing 0.5 and 0.25 mm of hard tissue from the cusps of the maxillary molars in randomly selected sides of Sprague−Dawley rats. CUS involved exposure to 2 different stressors per day for 35 days. OD-, CUS-, and OD + CUS-treated groups and an untreated control group were compared in terms of behavior, endocrine status and brain histology. Results: There were significant differences among the four groups in the behavior tests (p < 0.05), especially in the sucrose preference test, where there was a significant decrease in the OD group compared to the control group. ACTH and CORT concentrations were significantly higher in the OD + CUS group than the control group (p < 0.05). Expression of GR and 5-HT2AR in the PFC, amygdala and hippocampal CA1 was significantly higher in the OD, CUS and OD + CUS groups than the control group (p < 0.05). Conclusion: OD promotes depression-like behaviors through peripheral and central pathways via the HPA axis, GR and 5-HT system.

Persimmon leaf extract alleviates chronic social defeat stress-induced depressive-like behaviors by preventing dendritic spine loss via inhibition of serotonin reuptake in mice

Background

Fresh or dried Persimmon leaves (Diospyros kaki Thunb.) exhibit preventive effects on cardiovascular and cerebrovascular diseases. However, their antidepressant effects and underlying mechanisms are unclear. Thus, we investigated mechanisms responsible for Persimmon leaf extract (PLE) activity on chronic social defeat stress (CSDS)-induced depressive-like behaviors in mice.

Methods

CSDS was used as a mouse model of depression. We performed the sucrose preference test (SPT), forced swim test (FST), and tail suspension test (TST) to identify depressive-like behavior. Spine density and dendritic morphology were assessed using Golgi staining. Neurochemicals were quantified by microdialysis, doublecortin by immunofluorescence, and cAMP using an ELISA kit. Finally, the levels of cortical proteins of phosphorylated cAMP-response element binding protein (CREB), brain-derived neurotrophic factor (BDNF), postsynaptic density synapsin-1 and protein 95 (PSD95) were quantified by western blot. 16S rRNA gene sequencing was used to detect fecal microbiota.

Results

Treatment of CSDS-subjected mice with PLE (30.0–60.0 mg/kg, i.g.) enhanced sucrose preference, decreased immobility times in the TST and FST but did not affect locomotor activity. Furthermore, persistent social defeat stress decreased dendritic spine density and dendritic length in the brain, as well as decreased PSD95 and synapsin-1 expression. PLE, interestingly, inhibited dendritic spine loss and increased synaptic protein levels. PLE also increased brain levels of 5-HT, cAMP, phosphorylated (p)-CREB, BDNF, PSD95, and synapsin-1 in mice subjected to CSDS. Furthermore, PLE increased their doublecortin-positive cell count in the hippocampal dentate gyrus. CSDS mice represented a distinct fecal microbiota cluster which differed compared with normal C57BL/6J mice, and the phenotype was rescued by PLE.

Conclusions

PLE alleviated CSDS-induced depressive behaviors and spinal damage by suppressing serotonin reuptake and activating the cAMP/CREB/BDNF signaling pathway. Simultaneously, PLE influenced the composition of the fecal microbiota in CSDS-subjected mice.

Supplementary information

The online version contains supplementary material available at 10.1186/s13020-022-00609-4.