Indirect and direct cannabinoid agonists differentially affect mesolimbic dopamine release and related behaviors.

The cannabinoid system is being researched as a potential pharmaceutical target for a multitude of disorders. The present study examined the effect of indirect and direct cannabinoid agonists on mesolimbic dopamine release and related behaviors in C57BL/6J (B6) mice. The indirect cannabinoid agonist N-arachidonoyl serotonin (AA-5-HT) indirectly agonizes the cannabinoid system by preventing the metabolism of endocannabinoids through fatty acid amide hydrolase inhibition while also inhibiting transient receptor potential vanilloid Type 1 channels. Effects of AA-5-HT were compared with the direct cannabinoid receptor Type 1 agonist arachidonoyl-2'-chloroethylamide (ACEA). In Experiment 1, mice were pretreated with seven daily injections of AA-5-HT, ACEA, or vehicle prior to assessments of locomotor activity using open field (OF) testing and phasic dopamine release using in vivo fixed potential amperometry. Chronic exposure to AA-5-HT did not alter locomotor activity or mesolimbic dopamine functioning. Chronic exposure to ACEA decreased rearing and decreased phasic dopamine release while increasing the dopaminergic response to cocaine. In Experiment 2, mice underwent AA-5-HT, ACEA, or vehicle conditioned place preference, then saccharin preference testing, a measure commonly associated with anhedonia. Mice did not develop a conditioned place preference or aversion for AA-5-HT or ACEA, and repeated exposure to AA-5-HT or ACEA did not alter saccharin preference. Altogether, the findings suggest that neither of these drugs induce behaviors that are classically associated with abuse liability in mice; however, direct cannabinoid receptor Type 1 agonism may play more of a role in mediating mesolimbic dopamine functioning than indirect cannabinoid agonism. (PsycInfo Database Record (c) 2024 APA, all rights reserved).

Activator of KAT3 histone acetyltransferase family ameliorates a neurodevelopmental disorder phenotype in the syntaxin 1A ablated mouse model.

Syntaxin-1A (stx1a) repression causes a neurodevelopmental disorder phenotype, low latent inhibition (LI) behavior, by disrupting 5-hydroxytryptaminergic (5-HTergic) systems. Herein, we discovered that lysine acetyltransferase (KAT) 3B increases stx1a neuronal transcription and TTK21, a KAT3 activator, induces stx1a transcription and 5-HT release in vitro. Furthermore, glucose-derived CSP-TTK21 could restore decreased stx1a expression, 5-HTergic systems in the brain, and low LI in stx1a (+/-) mice by crossing the blood-brain barrier, whereas the KAT3 inhibitor suppresses stx1a expression, 5-HTergic systems, and LI behaviors in wild-type mice. Finally, in wild-type and stx1a (-/-) mice treated with IKK inhibitors and CSP-TTK21, respectively, we show that KAT3 activator-induced LI improvement is a direct consequence of KAT3B-stx1a pathway, not a side effect. In conclusion, KAT3B can positively regulate stx1a transcription in neurons, and increasing neuronal stx1a expression and 5-HTergic systems by a KAT3 activator consequently improves the low LI behavior in the stx1a ablation mouse model.

The 'PSILAUT' protocol: an experimental medicine study of autistic differences in the function of brain serotonin targets of psilocybin.

BACKGROUND: The underlying neurobiology of the complex autism phenotype remains obscure, although accumulating evidence implicates the serotonin system and especially the 5HT2A receptor. However, previous research has largely relied upon association or correlation studies to link differences in serotonin targets to autism. To directly establish that serotonergic signalling is involved in a candidate brain function our approach is to change it and observe a shift in that function. We will use psilocybin as a pharmacological probe of the serotonin system in vivo. We will directly test the hypothesis that serotonergic targets of psilocybin - principally, but not exclusively, 5HT2A receptor pathways-function differently in autistic and non-autistic adults. METHODS: The 'PSILAUT' "shiftability" study is a case-control study autistic and non-autistic adults. How neural responses 'shift' in response to low doses (2 mg and 5 mg) of psilocybin compared to placebo will be examined using multimodal techniques including functional MRI and EEG. Each participant will attend on up to three separate visits with drug or placebo administration in a double-blind and randomized order. RESULTS: This study will provide the first direct evidence that the serotonin targets of psilocybin function differently in the autistic and non-autistic brain. We will also examine individual differences in serotonin system function. CONCLUSIONS: This work will inform our understanding of the neurobiology of autism as well as decisions about future clinical trials of psilocybin and/or related compounds including stratification approaches. TRIAL REGISTRATION: NCT05651126.

Serotonin Receptors in Myocardial Infarction: Friend or Foe?

Acute myocardial infarction (AMI) is one of the leading causes of death worldwide and treatment costs pose a major burden on the global health care system. Despite the variety of treatment options, individual recovery can be still poor and the mortality rate, especially in the first few years after the event, remains high. Therefore, intense research is currently focused on identifying novel target molecules to improve the outcome following AMI. One of the potentially interesting targets is the serotonergic system (5-HT system), not at least because of its connection to mental disorders. It is known that patients suffering from AMI have an increased risk of developing depression and vice versa. This implicates that the 5-HT system can be affected in response to AMI and might thus represent a target structure for patients' treatment. This review aims to highlight the importance of the 5-HT system after AMI by describing the role of individual serotonin receptors (5-HTR) in the regulation of physiological and pathophysiological responses. It particularly focuses on the signaling pathways of the serotonin receptors 1, 2, 4, and 7, which are expressed in the cardiovascular system, during disease onset, and the following remodeling process. This overview also emphasizes the importance of the 5-HT system in AMI etiology and highlights 5-HTRs as potential treatment targets.

MDMA enhances empathy-like behaviors in mice via 5-HT release in the nucleus accumbens.

MDMA (3,4-methylenedioxymethamphetamine) is a psychoactive drug with powerful prosocial effects. While MDMA is sometimes termed an "empathogen," empirical studies have struggled to clearly demonstrate these effects or pinpoint underlying mechanisms. Here, we paired the social transfer of pain and analgesia-behavioral tests modeling empathy in mice-with region-specific neuropharmacology, optogenetics, and transgenic manipulations to explore MDMA's action as an empathogen. We report that MDMA, given intraperitoneally or infused directly into the nucleus accumbens (NAc), robustly enhances the social transfer of pain and analgesia. Optogenetic stimulation of 5-HT release in the NAc recapitulates the effects of MDMA, implicating 5-HT signaling as a core mechanism. Last, we demonstrate that systemic MDMA or optogenetic stimulation of NAc 5-HT inputs restores deficits in empathy-like behaviors in the Shank3-deficient mouse model of autism. These findings demonstrate enhancement of empathy-related behaviors by MDMA and implicate 5-HT signaling in the NAc as a core mechanism mediating MDMA's empathogenic effects.

Identification of the potassium-binding site in serotonin transporter.

Clearance of serotonin (5-hydroxytryptamine, 5-HT) from the synaptic cleft after neuronal signaling is mediated by serotonin transporter (SERT), which couples this process to the movement of a Na+ ion down its chemical gradient. After release of 5-HT and Na+ into the cytoplasm, the transporter faces a rate-limiting challenge of resetting its conformation to be primed again for 5-HT and Na+ binding. Early studies of vesicles containing native SERT revealed that K+ gradients can provide an additional driving force, via K+ antiport. Moreover, under appropriate conditions, a H+ ion can replace K+. Intracellular K+ accelerates the resetting step. Structural studies of SERT have identified two binding sites for Na+ ions, but the K+ site remains enigmatic. Here, we show that K+ antiport can drive substrate accumulation into vesicles containing SERT extracted from a heterologous expression system, allowing us to study the residues responsible for K+ binding. To identify candidate binding residues, we examine many cation binding configurations using molecular dynamics simulations, predicting that K+ binds to the so-called Na2 site. Site-directed mutagenesis of residues in this site can eliminate the ability of both K+ and H+ to drive 5-HT accumulation into vesicles and, in patch clamp recordings, prevent the acceleration of turnover rates and the formation of a channel-like state by K+ or H+. In conclusion, the Na2 site plays a pivotal role in orchestrating the sequential binding of Na+ and then K+ (or H+) ions to facilitate 5-HT uptake in SERT.

Biosensors for psychiatric biomarkers in mental health monitoring.

Psychiatric disorders are associated with serve disturbances in cognition, emotional control, and/or behavior regulation, yet few routine clinical tools are available for the real-time evaluation and early-stage diagnosis of mental health. Abnormal levels of relevant biomarkers may imply biological, neurological, and developmental dysfunctions of psychiatric patients. Exploring biosensors that can provide rapid, in-situ, and real-time monitoring of psychiatric biomarkers is therefore vital for prevention, diagnosis, treatment, and prognosis of mental disorders. Recently, psychiatric biosensors with high sensitivity, selectivity, and reproducibility have been widely developed, which are mainly based on electrochemical and optical sensing technologies. This review presented psychiatric disorders with high morbidity, disability, and mortality, followed by describing pathophysiology in a biomarker-implying manner. The latest biosensors developed for the detection of representative psychiatric biomarkers (e.g., cortisol, dopamine, and serotonin) were comprehensively summarized and compared in their sensitivities, sensing technologies, applicable biological platforms, and integrative readouts. These well-developed biosensors are promising for facilitating the clinical utility and commercialization of point-of-care diagnostics. It is anticipated that mental healthcare could be gradually improved in multiple perspectives, ranging from innovations in psychiatric biosensors in terms of biometric elements, transducing principles, and flexible readouts, to the construction of 'Big-Data' networks utilized for sharing intractable psychiatric indicators and cases.

Serotonin receptor 2B induces visceral hyperalgesia in rat model and patients with diarrhea-predominant irritable bowel syndrome.

BACKGROUND: Serotonin receptor 2B (5-HT2B receptor) plays a critical role in many chronic pain conditions. The possible involvement of the 5-HT2B receptor in the altered gut sensation of irritable bowel syndrome with diarrhea (IBS-D) was investigated in the present study. AIM: To investigate the possible involvement of 5-HT2B receptor in the altered gut sensation in rat model and patients with IBS-D. METHODS: Rectosigmoid biopsies were collected from 18 patients with IBS-D and 10 patients with irritable bowel syndrome with constipation who fulfilled the Rome IV criteria and 15 healthy controls. The expression level of the 5-HT2B receptor in colon tissue was measured using an enzyme-linked immunosorbent assay and correlated with abdominal pain scores. The IBS-D rat model was induced by intracolonic instillation of acetic acid and wrap restraint. Alterations in visceral sensitivity and 5-HT2B receptor and transient receptor potential vanilloid type 1 (TRPV1) expression were examined following 5-HT2B receptor antagonist administration. Changes in visceral sensitivity after administration of the TRPV1 antagonist were recorded. RESULTS: Here, we observed greater expression of the 5-HT2B receptor in the colonic mucosa of patients with IBS-D than in that of controls, which was correlated with abdominal pain scores. Intracolonic instillation of acetic acid and wrap restraint induced obvious chronic visceral hypersensitivity and increased fecal weight and fecal water content. Exogenous 5-HT2B receptor agonist administration increased visceral hypersensitivity, which was alleviated by successive administration of a TRPV1 antagonist. IBS-D rats receiving the 5-HT2B receptor antagonist exhibited inhibited visceral hyperalgesia.Moreover, the percentage of 5-HT2B receptor-immunoreactive (IR) cells surrounded by TRPV1-positive cells (5-HT2B receptor I+) and total 5-HT2B receptor IR cells (5-HT2B receptor IT) in IBS-D rats was significantly reduced by the administration of a 5-HT2B receptor antagonist. CONCLUSION: Our finding that increased expression of the 5-HT2B receptor contributes to visceral hyperalgesia by inducing TRPV1 expression in IBS-D patients provides important insights into the potential mechanisms underlying IBS-D-associated visceral hyperalgesia.

Molecular Design of SERTlight: A Fluorescent Serotonin Probe for Neuronal Labeling in the Brain.

The serotonergic transmitter system plays fundamental roles in the nervous system in neurotransmission, synaptic plasticity, pathological processes, and therapeutic effects of antidepressants and psychedelics, as well as in the gastrointestinal and circulatory systems. We introduce a novel small molecule fluorescent agent, termed SERTlight, that specifically labels serotonergic neuronal cell bodies, dendrites, and axonal projections as a serotonin transporter (SERT) fluorescent substrate. SERTlight was developed by an iterative molecular design process, based on an aminoethyl-quinolone system, to integrate structural elements that impart SERT substrate activity, sufficient fluorescent brightness, and a broad absence of pharmacological activity, including at serotonin (5-hydroxytryptamine, 5HT) receptors, other G protein-coupled receptors (GPCRs), ion channels, and monoamine transporters. The high labeling selectivity is not achieved by high affinity binding to SERT itself but rather by a sufficient rate of SERT-mediated transport of SERTlight, resulting in accumulation of these molecules in 5HT neurons and yielding a robust and selective optical signal in the mammalian brain. SERTlight provides a stable signal, as it is not released via exocytosis nor by reverse SERT transport induced by 5HT releasers such as MDMA. SERTlight is optically, pharmacologically, and operationally orthogonal to a wide range of genetically encoded sensors, enabling multiplexed imaging. SERTlight enables labeling of distal 5HT axonal projections and simultaneous imaging of the release of endogenous 5HT using the GRAB5HT sensor, providing a new versatile molecular tool for the study of the serotonergic system.

Role of Serotonergic System in Regulating Brain Tumor-Associated Neuroinflammatory Responses.

Serotonin signaling regulates wide arrays of both neural and extra-neural functions. Serotonin is also found to affect cancer progression directly as well as indirectly by modulating the immune cells. In the brain, serotonin plays a key role in regulating various functions; disturbance of the normal activities of serotonin leads to various mental illnesses, including the neuroinflammatory response in the central nervous system (CNS). The neuroinflammatory response can be initiated in various psychological illnesses and brain cancer. Serotonergic signaling can impact the functions of both glial as well as the immune cells. It can also affect the tumor immune microenvironment and the inflammatory response associated with brain cancers. Apart from this, many drugs used for treatment of psychological illness are known to modulate serotonergic system and can cross the blood-brain barrier. Understanding the role of serotonergic pathways in regulating neuroinflammatory response and brain cancer will provide a new paradigm in modulating the serotonergic components in treating brain cancer and associated inflammation-induced brain damages.

Glioma induces atypical depression-like behaviors in mice through the 5-HT and glutamatergic synapse pathways.

Glioma patients often undertake psychiatric disorders such as depression and anxiety. There are several clinical epidemiological studies on glioma-associated depression, but basic research and corresponding animal experiments are still lacking. Here, we observed that glioma-bearing mice exhibited atypical depression-like behaviors in orthotopic glioma mouse models. The concentrations of monoamine neurotransmitters were detected by enzyme-linked immunosorbent assay (ELISA), revealing a decrease in 5-hydroxytryptamine (5-HT) levels in para-glioma tissues. The related gene expression levels also altered, detected by quantitative RT-PCR. Then, we developed a glioma-depression comorbidity mouse model. Through sucrose preference test (SPT), forced swimming test (FST), tail suspension test (TST) and other tests, we found that the occurrence of glioma could lead to changes in depression-like behaviors in a chronic unpredictable mild stress (CUMS) mouse model. The results of RNA sequencing (RNA-seq) indicated that the altered expression of glutamatergic synapse related genes in the paratumor tissues might be one of the main molecular features of the comorbidity model. Our findings suggested that the presence of glioma caused and altered depression-like behaviors, which was potentially related to the 5-HT and glutamatergic synapse pathways.

Shen Yuan extract exerts a hypnotic effect via the tryptophan/5-hydroxytryptamine/melatonin pathway in mice.

ETHNOPHARMACOLOGICAL RELEVANCE: Sleep plays a critical role in several physiologic processes, and sleep disorders increase the risk of depression, dementia, stroke, cancer, and other diseases. Stress is one of the main causes of sleep disorders. Ginseng Radix et Rhizoma and Polygalae Radix have been reported to have effects of calming the mind and intensifying intelligence in Chinese Pharmacopoeia. Traditional Chinese medicine prescriptions composed of Ginseng Radix et Rhizoma and Polygalae Radix (Shen Yuan, SY) are commonly used to treat insomnia, depression, and other psychiatric disorders in clinical practice. Unfortunately, the underlying mechanisms of the SY extract's effect on sleep are still unknown. AIM OF THE STUDY: This study aimed to investigate the hypnotic effect of the SY extract in normal mice and mice with chronic restraint stress (CRS)-induced sleep disorders and elucidate the underlying mechanisms. MATERIALS AND METHODS: The SY extract (0.5 and 1.0 g/kg) was intragastrically administered to normal mice for 1, 14, and 28 days and to CRS-treated mice for 28 days. The open field test (OFT) and pentobarbital sodium-induced sleep test (PST) were used to evaluate the hypnotic effect of the SY extract. Liquid chromatography-tandem mass spectrometry and enzyme-linked immunosorbent assay were utilized to detect the levels of neurotransmitters and hormones. Molecular changes at the mRNA and protein levels were determined using real-time quantitative polymerase chain reaction and Western blot analysis to identify the mechanisms by which SY improves sleep disorders. RESULTS: The SY extract decreased sleep latency and increased sleep duration in normal mice. Similarly, the sleep duration of mice subjected to CRS was increased by administering SY. The SY extract increased the levels of tryptophan (Trp) and 5-hydroxytryptamine (5-HT) and the expression of tryptophan hydroxylase 2 (TPH2) in the cortex of normal mice. The SY extract increased the Trp level, transcription and expression of estrogen receptor beta and TPH2 in the cortex in mice with sleep disorders by decreasing the serum corticosterone level, which promoted the synthesis of 5-HT. Additionally, the SY extract enhanced the expression of arylalkylamine N-acetyltransferase, which increased the melatonin level and upregulated the expressions of melatonin receptor-2 (MT2) and Cryptochrome 1 (Cry1) in the hypothalamus of mice with sleep disorders. CONCLUSIONS: The SY extract exerted a hypnotic effect via the Trp/5-HT/melatonin pathway, which augmented the synthesis of 5-HT and melatonin and further increased the expressions of MT2 and Cry1.

Serotonin Signaling in Hippocampus during Initial Cocaine Abstinence Drives Persistent Drug Seeking.

The initiation of abstinence after chronic drug self-administration is stressful. Cocaine-seeking behavior on the first day of the absence of the expected drug (Extinction Day 1, ED1) is reduced by blocking 5-HT signaling in dorsal hippocampal cornu ammonis 1 (CA1) in both male and female rats. We hypothesized that the experience of ED1 can substantially influence later relapse behavior and that dorsal raphe (DR) serotonin (5-HT) input to CA1 may be involved. We inhibited 5-HT1A/1B receptors (WAY-100635 plus GR-127935), or DR input (chemogenetics), in CA1 on ED1 to test the role of this pathway on cocaine-seeking persistence 2 weeks later. We also inhibited 5-HT1A or 5-HT1B receptors in CA1 during conditioned place preference (CPP) for cocaine, to examine mechanisms involved in the persistent effects of ED1 manipulations. Inhibition of DR inputs, or 5-HT1A/1B signaling, in CA1 decreased drug seeking on ED1 and decreased cocaine seeking 2 weeks later revealing that 5-HT signaling in CA1 during ED1 contributes to persistent drug seeking during abstinence. In addition, 5-HT1B antagonism alone transiently decreased drug-associated memory performance when given prior to a CPP test, whereas similar antagonism of 5-HT1A alone had no such effect but blocked CPP retrieval on a test 24 h later. These CPP findings are consistent with prior work showing that DR inputs to CA1 augment recall of the drug-associated context and drug seeking via 5-HT1B receptors and prevent consolidation of the updated nondrug context via 5-HT1A receptors. Thus, treatments that modulate 5-HT-dependent memory mechanisms in CA1 during initial abstinence may facilitate later maintenance of abstinence.

Peripheral peroxisomal ß-oxidation engages neuronal serotonin signaling to drive stress-induced aversive memory in C. elegans.

Physiological dysfunction confers negative valence to coincidental sensory cues to induce the formation of aversive associative memory. How peripheral tissue stress engages neuromodulatory mechanisms to form aversive memory is poorly understood. Here, we show that in the nematode C. elegans, mitochondrial disruption induces aversive memory through peroxisomal ß-oxidation genes in non-neural tissues, including pmp-4/very-long-chain fatty acid transporter, dhs-28/3-hydroxylacyl-CoA dehydrogenase, and daf-22/3-ketoacyl-CoA thiolase. Upregulation of peroxisomal ß-oxidation genes under mitochondrial stress requires the nuclear hormone receptor NHR-49. Importantly, the memory-promoting function of peroxisomal ß-oxidation is independent of its canonical role in pheromone production. Peripheral signals derived from the peroxisomes target NSM, a critical neuron for memory formation under stress, to upregulate serotonin synthesis and remodel evoked responses to sensory cues. Our genetic, transcriptomic, and metabolomic approaches establish peroxisomal lipid signaling as a crucial mechanism that connects peripheral mitochondrial stress to central serotonin neuromodulation in aversive memory formation.

Design, synthesis, and biological evaluation of aralkyl piperazine and piperidine derivatives targeting SSRI/5-HT1A/5-HT7.

Serotonin reuptake inhibition combined with the action targeting 5-hydroxytryptamine receptor subtypes can serve as a potential target for the development of antidepressant drugs. Herein a series of new aralkyl piperazines and piperidines were designed and synthesized by the structural modifications of the previously discovered aralkyl piperidine compound 1, targeting SSRI/5-HT1A/5-HT7. The results exhibited that compound 5a showed strong binding to 5-HT1A and 5-HT7 (Ki of 0.46 nM, 2.7 nM, respectively) and a high level of serotonin reuptake inhibition (IC50 of 1.9 nM), all of which were significantly elevated compared to 1. In particular, compound 5a showed weaker inhibitory activity against hERG than 1, and demonstrated good stability in liver microsomes in vitro. The preliminary screening using FST indicated that orally administered 5a, at a high dose, could reduce immobility time in mice markedly, indicating potential antidepressant activity.

Sumatriptan attenuates fear-learning despair induced by social isolation stress in mice: Mediating role of hypothalamic-pituitary-adrenal axis.

OBJECTIVES: Research has demonstrated that chronic stress experienced early in life can lead to impairments in memory and learning. These deficits are attributed to an imbalance in the interaction between glucocorticoids, the end product of the hypothalamic-pituitary-adrenal (HPA) axis, and glucocorticoid receptors in brain regions responsible for mediating memory, such as the hippocampus. This imbalance can result in detrimental conditions like neuroinflammation. The aim of this study was to assess the impact of sumatriptan, a selective agonist for 5-HT 1B/1D receptors, on fear learning capabilities in a chronic social isolation stress model in mice, with a particular focus on the role of the HPA axis. METHODS: Mice were assigned to two opposing conditions, including social condition (SC) and isolated condition (IC) for a duration of five weeks. All mice underwent passive avoidance test, with their subsequent freezing behavior serving as an indicator of fear retrieval. Mice in the IC group were administered either a vehicle, sumatriptan, GR-127935 (a selective antagonist for 5-HT 1B/1D receptors), or a combination of sumatriptan and GR-127935 during the testing sessions. At the end, all mice were sacrificed and samples of their serum and hippocampus were collected for further analysis. RESULTS: Isolation was found to significantly reduce freezing behavior (p<0.001). An increase in the freezing response among IC mice was observed following the administration of varying doses of sumatriptan, as indicated by a one-way ANOVA analysis (p<0.001). However, the mitigating effects of sumatriptan were reversed upon the administration of GR-127935. An ELISA assay conducted before and after the passive avoidance test revealed no significant change in serum corticosterone levels among SC mice. In contrast, a significant increase was observed among IC mice, suggesting hyper-responsiveness of the HPA axis in isolated animals. This hyper-responsiveness was ameliorated following the administration of sumatriptan. Furthermore, both the sumatriptan and SC groups exhibited a similar trend, showing a significant increase in the expression of hippocampal glucocorticoid receptors following the stress of the passive avoidance test. Lastly, the elevated production of inflammatory cytokines (TNF-α, IL-1ß) observed following social isolation was attenuated in the sumatriptan group. CONCLUSION: Sumatriptan improved fear learning probably through modulation of HPA axis and hippocampus neuroinflammation.

Improved green and red GRAB sensors for monitoring spatiotemporal serotonin release in vivo.

The serotonergic system plays important roles in both physiological and pathological processes, and is a therapeutic target for many psychiatric disorders. Although several genetically encoded GFP-based serotonin (5-HT) sensors were recently developed, their sensitivities and spectral profiles are relatively limited. To overcome these limitations, we optimized green fluorescent G-protein-coupled receptor (GPCR)-activation-based 5-HT (GRAB5-HT) sensors and developed a red fluorescent GRAB5-HT sensor. These sensors exhibit excellent cell surface trafficking and high specificity, sensitivity and spatiotemporal resolution, making them suitable for monitoring 5-HT dynamics in vivo. Besides recording subcortical 5-HT release in freely moving mice, we observed both uniform and gradient 5-HT release in the mouse dorsal cortex with mesoscopic imaging. Finally, we performed dual-color imaging and observed seizure-induced waves of 5-HT release throughout the cortex following calcium and endocannabinoid waves. In summary, these 5-HT sensors can offer valuable insights regarding the serotonergic system in both health and disease.

Deciphering the antidepressant effects of Rosa damascena essential oil mediated through the serotonergic synapse signaling pathway.

ETHNOPHARMACOLOGICAL RELEVANCE: Rosa damascena is an ancient plant with significance in both medicine and perfumery that have a variety of therapeutic properties, including antidepressant, anti-anxiety, and anti-stress effects. Rose damascena essential oil (REO) has been used to treat depression, anxiety and other neurological related disorders in Iranian traditional medicine. However, its precise mechanism of action remains elusive. AIM OF THE STUDY: The aim of this study was to investigate the impact and mechanism underlying the influence of REO on chronic unpredictable mild stress (CUMS) rats. MATERIALS AND METHODS: Gas chromatography-mass spectrometry (GC-MS) technique coupling was used to analyze of the components of REO. A CUMS rat model was replicated to assess the antidepressant effects of varying doses of REO. This assessment encompassed behavioral evaluations, biochemical index measurements, and hematoxylin-eosin staining. For a comprehensive analysis of hippocampal tissues, we employed transcriptomics and incorporated weighting coefficients by means of network pharmacology. These measures allowed us to explore differentially expressed genes and biofunctional pathways affected by REO in the context of depression treatment. Furthermore, GC-MS metabolomics was employed to assess metabolic profiles, while a joint analysis in Metscape facilitated the construction of a network elucidating the links between differentially expressed genes and metabolites, thereby elucidating potential relationships and clarifying key pathways regulated by REO. Finally, the expression of relevant proteins in the key pathways was determined through immunohistochemistry and Western blot analysis. Molecular docking was utilized to investigate the interactions between active components and key targets, thereby validating the experimental results. RESULTS: REO alleviated depressive-like behavior, significantly elevated levels of the neurotransmitter 5-hydroxytryptamine (5-HT), and reduced hippocampal neuronal damage in CUMS rats. This therapeutic effect may be associated with the modulation of the serotonergic synapse signaling pathway. Furthermore, REO rectified metabolic disturbances, primarily through the regulation of amino acid metabolic pathways. Joint analysis revealed five differentially expressed genes (EEF1A1, LOC729197, ATP8A2, NDST4, and GAD2), suggesting their potential in alleviating depressive symptoms by modulating the serotonergic synapse signaling pathway and tryptophan metabolism. REO also modulated the 5-HT2A-mediated extracellular regulated protein kinases-cAMP-response element binding protein-brain-derived neurotrophic factor (ERK-CREB-BDNF) pathway. In addition, molecular docking results indicated that citronellol, geraniol and (E,E)-farnesol in REO may serve as key active ingredients responsible for its antidepressant effects. CONCLUSIONS: This study is the first to report that REO can effectively alleviate CUMS-induced depression-like effects in rats. Additionally, the study offers a comprehensive understanding of its intricate antidepressant mechanism from a multi-omics and multi-level perspective. Our findings hold promise for the clinical application and further development of this essential oil.

Maturation of cortical input to dorsal raphe nucleus increases behavioral persistence in mice.

The ability to persist toward a desired objective is a fundamental aspect of behavioral control whose impairment is implicated in several behavioral disorders. One of the prominent features of behavioral persistence is that its maturation occurs relatively late in development. This is presumed to echo the developmental time course of a corresponding circuit within late-maturing parts of the brain, such as the prefrontal cortex, but the specific identity of the responsible circuits is unknown. Here, we used a genetic approach to describe the maturation of the projection from layer 5 neurons of the neocortex to the dorsal raphe nucleus in mice. Using optogenetic-assisted circuit mapping, we show that this projection undergoes a dramatic increase in synaptic potency between postnatal weeks 3 and 8, corresponding to the transition from juvenile to adult. We then show that this period corresponds to an increase in the behavioral persistence that mice exhibit in a foraging task. Finally, we used a genetic targeting strategy that primarily affected neurons in the medial prefrontal cortex, to selectively ablate this pathway in adulthood and show that mice revert to a behavioral phenotype similar to juveniles. These results suggest that frontal cortical to dorsal raphe input is a critical anatomical and functional substrate of the development and manifestation of behavioral persistence.

Enhancing thermostability of tryptophan hydroxylase via protein engineering and its application in 5-hydroxytryptophan production.

5-Hydroxytryptophan (5-HTP), as the precursor of serotonin and melatonin in animals, can regulate mood, sleep, and behavior, which is widely used in pharmaceutical and health products industry. The enzymatic production of 5-hydroxytryptophan (5-HTP) from L-tryptophan (L-Trp) using tryptophan hydroxylase (TPH) show huge potential in application due to its advantages, such as mild reaction conditions, avoidance of protection/deprotection processes, excellent regioselectivity and considerable catalytic efficiency, compared with chemical synthesis and natural extraction. However, the low thermostability of TPH restricted its hydroxylation efficiency toward L-Trp. In this study, we aimed to improve the thermostability of TPH via semi-rational design guided by (folding free energy) ΔΔG fold calculation. After two rounds of evolution, two beneficial mutants M1 (S422V) and M30 (V275L/I412K) were obtained. Thermostability evaluation showed that M1 and M30 possessed 5.66-fold and 6.32-fold half-lives (t1/2) at 37 °C, and 4.2 °C and 6.0 °C higher melting temperature (Tm) than the WT, respectively. The mechanism behind thermostability improvement was elucidated with molecular dynamics simulation. Furthermore, biotransformation of 5-HTP from L-Trp was performed, M1 and M30 displayed 1.80-fold and 2.30-fold than that of WT, respectively. This work provides important insights into the thermostability enhancement of TPH and generate key mutants that could be robust candidates for practical production of 5-HTP.