Search Results (96)

Sleep paralysis (SP), an REM parasomnia, can be characterized as one of the symptoms of narcolepsy. The SP phenomenon involves regaining meta-consciousness by the dreamer during REM, when the physiological atonia of skeletal muscles is accompanied by visual and auditory hallucinations that are perceived as vivid and distressing nightmares. Sensory impressions include personification of an unknown presence, strong chest pressure sensation, and intense fear resulting from subjective interaction with the unfolding nightmare. While the mechanism underlying skeletal muscle atonia is known, the physiology of hallucinations remains unclear. Their complex etiology involves interactions among various membrane receptor systems and neurotransmitters, which leads to altered neuronal functionality and disruptions in sensory perception. According to current knowledge, serotonergic activation of 5-hydroxytryptamine-receptor-2A (5-HT2A)-associated pathways plays a critical role in promoting hallucinogenesis during SP. Furthermore, they share similarities with psychedelic-substance-induced ones (i.e., LSD, psilocybin, and 2,5-dimethoxy-4-iodoamphetamine). These compounds also target the 5-HT2A receptor; however, their molecular mechanism varies from serotonin-induced ones. The current review discusses the intracellular signaling pathways responsible for promoting hallucinations in SP, highlighting the critical role of β-arrestin-2. We propose that the β-arrestin-2 signaling pathway does not directly induce hallucinations but creates a state of network susceptibility that facilitates their abrupt emergence in sensory areas. Understanding the molecular basis of serotonergic hallucinations and gaining better insight into 5-HT2A-receptor-dependent pathways may prove crucial in the treatment of multifactorial neuropsychiatric disorders associated with the dysfunctional activity of serotonin receptors. Full article

Serotoninomics is an expanding field that focuses on the comprehensive study of the serotoninergic system, including serotonin’s biosynthesis, metabolism, and regulation, as well as related scientific methodologies 5-hydroxytryptamine (5-HT). This field explores serotonin’s complex roles in various physiological and pathological contexts. The essential amino acid tryptophan (Trp) is a precursor for several metabolic and catabolic pathways, with the kynurenine (KYN) pathway being particularly significant, representing about 95% of Trp metabolism. In contrast, only a small portion (1–2%) of dietary Trp enters the serotonin pathway. Anthranilic acid (AA), a metabolite in the KYN pathway, has emerged as a potential biomarker and therapeutic target for schizophrenia. Elevated serum AA levels in patients with schizophrenia have been associated with neurotoxic effects and disruptions in neurotransmission, suggesting AA’s critical role in the disorder’s pathophysiology. Furthermore, the 5-HT_2A receptor’s involvement is particularly noteworthy, especially in relation to schizophrenia’s positive symptoms. Recent findings indicate that 5-HT_2A receptor hyperactivity is linked to positive symptoms of schizophrenia, such as hallucinations and delusions. This study investigates serotoninomics’ implications for neuropsychiatric disorders, focusing on AA in schizophrenia and analysing recent research on serotonin signalling pathways and AA’s neurochemical effects. Understanding the roles of the 5-HT_2A receptor and AA in neuropsychiatric disorders could lead to the development of more precise and less invasive diagnostic tools, specific therapeutic strategies, and improved clinical outcomes. Ongoing research is essential to uncover these pathways’ exact mechanisms and therapeutic potential, thereby advancing personalised medicine and innovative treatments in neuropsychiatry. Full article

Background: Dorsal raphe serotonin (5-hydroxytryptamine, 5-HT) neurons are spontaneously active and release 5-HT that is critical for normal brain function and regulates mood and emotion. Serotonin reuptake inhibitors (SSRIs) increase the synaptic and extracellular 5-HT level and are effective in treating depression. Treatment of two weeks or longer is often required for SSRIs to produce clinical benefits. The cellular mechanism underlying this delay is not fully understood. Methods and Results: Using whole-cell patch clamp recording in brain slices, here we show that the GABAergic inputs inhibit the spike firing of raphe 5-HT neurons. This GABAergic regulation was reduced by 5-HT; additionally, this 5-HT effect was prevented by the G-protein-activated inwardly rectifying potassium (GirK) channel inhibitor tertiapin-Q, indicating a contribution of 5-HT activation of GirK channels in GABAergic presynaptic axon terminals. Equally important, after 14 days of treatment with fluoxetine, a widely used SSRI type antidepressant, the 5-HT inhibition of GABAergic inputs was downregulated. Furthermore, chronic fluoxetine treatment downregulated the 5-HT activation of the inhibitory GirK current in 5-HT neurons. Conclusions: Taken together, our results suggest that chronic fluoxetine treatment, by blocking 5-HT reuptake and hence increasing the extracellular 5-HT level, can downregulate the function of 5-HT1B receptors on the GABAergic afferent axon terminals synapsing onto 5-HT neurons, allowing extrinsic GABAergic neurons to more effectively influence 5-HT neurons; simultaneously, chronic fluoxetine treatment also downregulated somatic 5-HT autoreceptor-activated GirK channel-mediated hyperpolarization and decrease in input resistance, rendering 5-HT neurons resistant to autoinhibition and leading to increased 5-HT neuron activity. These neuroplastic changes in raphe 5-HT neurons and their GABAergic afferents may contribute to the behavioral effect of SSRIs. Full article

The aim of the present study was to investigate the phenolic composition and the efficacy of an innovative formulation based on Mg, Vitamin B6, and water extracts from Vitex agnus-castus, Crocus sativus, Melissa officinalis, Betula pendula, and Betula pubescens developed as an effective tool to face neuroinflammation and depression symptoms occurring in premenstrual syndrome (PMS). The formulation was analyzed through colorimetric and liquid chromatography methods for determining the content in phenols and flavonoids. Additionally, scavenging/reducing properties were investigated via 2,2-diphenyl-1-picrylhydrazyl (DPPH,) 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS), and horseradish peroxidase assays. The biocompatible limits were determined via allelopathy, the brine shrimp lethality test, and Daphnia magna cardiotoxicity assay. The formulation was then assayed in an experimental model constituted by isolated mouse cortex specimens exposed to K⁺ 60 mM Krebs–Ringer buffer, a toxic depolarizing stimulus able to reproduce the burden of inflammation/oxidative stress and the increased serotonin (5-hydroxytryptamine, 5-HT) impoverishment occurring in different neurological and psychiatric conditions, including depression. The results of the phytochemical analysis showed that the formulation is rich in benzoic acids, namely gentisic acid (155.31 µg/mL) and phenylethanoid compounds, namely hydroxytyrosol (39.79 µg/mL) that support the antioxidant effects measured via DPPH (IC₅₀: 1.48 mg/mL), ABTS (IC₅₀: 0.42 mg/mL), and horseradish peroxidase (IC₅₀: 2.02 mg/mL) assays. The ecotoxicological models indicated the formulation as non-toxic, permitting the identification of a biocompatible concentration (1000 µg/mL) to be used in isolated mouse cortex exposed to K⁺ 60 mM Krebs–Ringer buffer. In this model, the gene expression of cyclooxygenase-2 (COX-2), interleukin-6 (IL-6), estrogen receptor-1 (ESR1), prolactin receptor (PRLR), brain-derived neurotrophic factor (BDNF), and serotonin transporter (SERT) was determined by real-time PCR. In the isolated mouse cortex, the formula reduced COX-2, IL-6, SERT, ESR1, and PRLR gene expression and increased BDNF and IL-10 gene expression. Overall, the study corroborated the use of the formulation as an innovative tool to contrast inflammation, oxidative stress, and neurotransmitter impairment associated with PMS. Full article

Whey proteins have anti-fatigue activity, but there are few studies that have reported the ameliorative effects of branched-chain amino acid (BCAA) oligopeptides from whey proteins on fatigue in mice. The purposes of this study were to establish a process for the preparation of BCAA oligopeptides from whey protein and to investigate the anti-fatigue activity of BCAA oligopeptides. Whey proteins were hydrolyzed by trypsin and flavourzyme and purified by ethanol precipitation and reversed-phase high performance liquid chromatography (RP-HPLC). Fraction D’ was found to contain the highest content of BCAAs and a high proportion of low-molecular-weight peptides (<1 kDa; content: 81.48%). Subsequently, mass spectrometry identified 15 BCAA oligopeptides in Fraction D’, including three dipeptides, six tripeptides, two tetrapeptides, and four pentapeptides. In addition, animal experiments showed that BCAA oligopeptides significantly prolonged the residence time on the rod and swimming time of mice. Further studies showed that BCAA oligopeptides remarkably reduced serotonin (5-hydroxytryptamine, 5-HT) synthesis in the brain by down-regulating the plasma-free tryptophan (F-Trp)/BCAA ratio, thereby alleviating fatigue. Therefore, BCAA oligopeptides can be used as an auxiliary functional dietary molecule in functional products to exert anti-fatigue activity by regulating 5-HT synthesis. Full article

Background: There is a close relationship between breast muscle glucose metabolism, peripheral 5-hydroxytryptamine (5-HT), and myopathies in animals. Here, this study aimed to investigate the effects of different photoperiods on peripheral 5-HT metabolism, white striping (WS), and wooden breast (WB) in broilers. Methods: A total of 216 healthy 5-day-old (d) Arbor Acres (AA) male broilers were randomly assigned to 12L:12D, 18L:6D, and 24L:0D photoperiods for 4 weeks. Results: Compared with the 12L:12D photoperiod, we found the WB score in broilers was significantly increased in the 18L:6D and 24L:0D photoperiod at week 4 (p < 0.05). Muscle glycogen was significantly reduced (p < 0.05) and glycolysis was promoted in the breast muscles of broilers under the 18L:6D and 24L:0D photoperiods at week 2 and 4. Peripheral 5-HT concentrations, the mRNA expression of tryptophan hydroxylase 1 (TPH1) and serotonin transporter (SERT) in the cecal mucosa, and 5-hydroxytryptamine receptor 2A (5-HTR_2A) mRNA expression in the breast muscle of broilers significantly up-regulated in the 18L:6D and 24L:0D photoperiod at week 2 and 4 (p < 0.05). Conclusions: Our findings revealed that extending the photoperiod improved the breast muscle growth rate, but up-regulated 5-HT synthesis and secretion to higher peripheral 5-HT, induced breast muscle glucose metabolism disorder, and increased WB incidence rates in broilers. Full article

Serotonin (5-hydroxytryptamine: 5-HT), a neurotransmitter that regulates mood in the brain and signaling in the gut, has receptors throughout the body that serve various functions, especially in the gut and brain. Selective serotonin reuptake inhibitors (SSRIs) are used to treat depression, but their efficacy is uncertain. Depression is often associated with early gastrointestinal symptoms. Gut disorders such as functional dyspepsia (FD), irritable bowel syndrome (IBS) and inflammatory bowel disease (IBD), including ulcerative colitis (UC) and Crohn’s disease (CD), are linked to elevated serotonin levels. In this review, we would like to discuss the approach of using serotonin as a biomarker for gut–brain, and body-wide organ communication may lead to the development of preventive and innovative treatments for gut–brain disorders, offering improved visibility and therapeutic monitoring. It could also be used to gauge stress intensity for self-care and mental health improvement. Full article

Serotonin (5-hydroxytryptamine, 5-HT) is a ubiquitous neurotransmitter in the human body. In the central nervous system, 5-HT affects sleep, pain, mood, appetite, and attention, while in the peripheral nervous system, 5-HT modulates peristalsis, mucus production, and blood vessel dilation. Fourteen membrane receptors mediate 5-HT activity. In agreement with the crucial roles played by 5-HT, many drugs target 5-HT receptors (5-HTRs). Therefore, it is unsurprising that many efforts have been devoted to discovering multitarget-directed ligands (MTDLs) capable of engaging one or more 5-HTRs plus another target phenotypically linked to a particular disease. In this review, we will describe medicinal chemistry efforts in designing MTDLs encompassing activity for one or more 5-HTRs, starting with atypical antipsychotics and moving to dual 5-HT1AR/serotonin transporter ligands, 5-HT6R antagonists/acetyl cholinesterases inhibitors, and 5-HT4R agonists/acetyl cholinesterases inhibitors. We will also provide an outlook on the most recent efforts made in the field. Full article

5-Hydroxytryptamine (5-HT) modulators are commonly prescribed medications with potentially life-threatening outcomes, particularly serotonin syndrome (SS). Early prediction of SS is critical not only to avoid lethal drug combinations but also to initiate appropriate treatment. The present work aimed to recognize the significant predictors of SS through a retrospective cross-sectional study that was conducted among patients exposed to an overdose of 5-HT modulators and admitted to a poison control center where 112 patients were enrolled. Of them, 21 patients were diagnosed with SS, and 66.7% of patients with SS were exposed to long-term co-ingestion. There was a noticeable surge in SS between April and May, and 52.4% of patients who suffered from SS were admitted after suicidal exposure (p < 0.05). Patients with SS showed severe presentation indicated by high-grade poison severity scores (PSS) and low Glasgow coma scales (GCS). PSS was a significant predictor of SS with an area under the curve of 0.879. PCO₂, pulse, GCS, HCO₃, and erythrocytic count were other significant predictors of SS. Combinations of serotonergic agents increase the likelihood of developing SS. Clinicians should be vigilant when prescribing a combination of serotonergic therapy, particularly for patients on illicit sympathomimetic and over-the-counter medications like dextromethorphan. Full article

Background: Diabetic neuropathic pain is a known complication of diabetes mellitus (DM) and results from the complex interaction of various factors affecting the nervous system. Yokuansan (YKS) is a versatile traditional Japanese herbal medicine with a wide range of applications, especially in pain management and neurological manifestations. YKS has analgesic properties for nerve damage and is a potential treatment for DM-induced neuropathic pain, especially in patients with diabetic neuropathy. Thus, we examined the anti-allodynic effect of YKS on DM-induced neuropathic pain. Methods: All experiments were performed on 6-week-old male Sprague–Dawley rats. DM and diabetic neuropathy were induced in rats with streptozotocin. Mechanical allodynia was assessed using dynamic plantar esthesiometry. Additionally, we conducted an immunological assessment of microglia cell changes in the spinal cord and an experiment to clarify the involvement of serotonin. Results: Diabetes significantly reduced withdrawal thresholds in rats during the initial two weeks of the experiment, which stabilized thereafter. However, this effect was not investigated in the control group. We assessed, using the dynamic plantar test, the anti-allodynic effects of orally administered YKS (1 g/kg). Daily YKS administration significantly increased the withdrawal threshold in DM animals. Additionally, oral YKS reduced the expression of Ibal-1-positive microglia. To elucidate the mechanism of action of YKS, we explored the involvement of serotonin (5-hydroxytryptamine [5-HT]) receptors in mediating its effects. Intrathecal administration of 5-HT receptor antagonists (WAY-100635, ketanserin, and ondansetron) inhibited the protective effects of YKS. Conclusions: YKS exhibited an anti-allodynic effect, suggesting that YKS may activate 5-HT receptors in the spinal cord, thereby alleviating diabetic neuropathic pain. Full article

Previous studies have suggested a potential role of bone morphogenetic protein 6 (BMP6) in glucose metabolism, which also seems to be regulated by serotonin (5-hydroxytryptamine, 5HT), a biogenic amine with multiple roles in the organism. In this study, we explored possible interactions between BMP6, serotonin, and glucose metabolism regulation. The effect of BMP6 or 5HT on pancreatic β-cells has been studied in vitro using the INS-1 832/13 rat insulinoma cell line. Studies in vivo have been performed on mice with the global deletion of the Bmp6 gene (BMP6−/−) and included glucose and insulin tolerance tests, gene expression studies using RT-PCR, immunohistochemistry, and ELISA analyses. We have shown that BMP6 and 5HT treatments have the opposite effect on insulin secretion from INS-1 cells. The effect of BMP6 on the 5HT system in vivo depends on the tissue studied, with no observable systemic effect on peripheral 5HT metabolism. BMP6 deficiency does not cause diabetic changes, although a mild difference in insulin tolerance test between BMP6−/− and WT mice was observed. In conclusion, BMP6 does not directly influence glucose metabolism, but there is a possibility that its deletion causes slowly developing changes in glucose and serotonin metabolism, which would become more expressed with ageing. Full article

Serotonin or 5-hydroxytryptamine (5-HT) is a monoamine that plays a critical role in insulin secretion, energy metabolism, and mitochondrial biogenesis. However, the action of serotonin in insulin production and secretion by pancreatic β cells has not yet been elucidated. Here, we investigated how exogenous nanomolar serotonin concentrations regulate insulin synthesis and secretion in rat insulinoma INS-1E cells. Nanomolar serotonin concentrations (10 and 50 nM) significantly increased insulin protein expression above the constant levels in untreated control cells and decreased insulin protein levels in the media. The reductions in insulin protein levels in the media may be associated with ubiquitin-mediated protein degradation. The levels of membrane vesicle trafficking-related proteins including Rab5, Rab3A, syntaxin6, clathrin, and EEA1 proteins were significantly decreased by serotonin treatment compared to the untreated control cells, whereas the expressions of Rab27A, GOPC, and p-caveolin-1 proteins were significantly reduced by serotonin treatment. In this condition, serotonin receptors, Gαq-coupled 5-HT2b receptor (Htr2b), and ligand-gated ion channel receptor Htr3a were significantly decreased by serotonin treatment. To confirm the serotonylation of Rab3A and Rab27A during insulin secretion, we investigated the protein levels of Rab3A and Rab27A, in which transglutaminase 2 (TGase2) serotonylated Rab3A but not Rab27A. The increases in ERK phosphorylation levels were consistent with increases in the expression of p-Akt. Also, the expression level of the Bcl-2 protein was significantly increased by 50 and 100 nM serotonin treatment compared to the untreated control cells, whereas the levels of Cu/Zn-SOD and Mn-SOD proteins decreased. These results indicate that nanomolar serotonin treatment regulates the insulin protein level but decreases this level in media through membrane vesicle trafficking-related proteins (Rab5, Rab3A, syntaxin6, clathrin, and EEA1), the Akt/ERK pathway, and Htr2b/Htr3a in INS-1E cells. Full article

Serotonin (5-hydroxytryptamine, 5-HT) is a neurotransmitter regulating numerous physiological functions, and its dysregulation is a crucial component of the pathological processes of schizophrenia, depression, migraines, and obesity. 5-HT interacts with 14 different receptors, of which 5-HT_1A-1FRs, 5-HT_2A-CRs, and 5-HT_4-7Rs are G protein-coupled receptors (GPCRs), while 5-HT₃R is a ligand-gated ion channel. Over the years, selective orthosteric ligands have been identified for almost all serotonin receptors, yielding several clinically relevant drugs. However, the high degree of homology between 5-HTRs and other GPCRs means that orthosteric ligands can have severe side effects. Thus, there has recently been increased interest in developing safer ligands of GPCRs, which bind to less conserved, more specific sites, distinct from that of the receptor’s natural ligand. The present review describes the identification of allosteric ligands of serotonin receptors, which are largely natural compounds (oleamide, cannabidiol, THC, and aporphine alkaloids), complemented by synthetic modulators developed in large part for the 5-HT_2C receptor. The latter are positive allosteric modulators sought after for their potential as drugs preferable over the orthosteric agonists as antiobesity agents for their potentially safer profile. When available, details on the interactions between the ligand and allosteric binding site will be provided. An outlook on future research in the field will also be provided. Full article

Amyloid β-peptide (Aβ) synthesis and deposition are the primary factors underlying the pathophysiology of Alzheimer’s disease (AD). Aβ oligomer (Aβo) exerts its neurotoxic effects by inducing oxidative stress and lesions by adhering to cellular membranes. Though several antidepressants have been investigated as neuroprotective agents in AD, a detailed comparison of their neuroprotection against Aβo-induced neurotoxicity is lacking. Here, we aimed to elucidate the neuroprotective effects of clinically prescribed selective serotonin reuptake inhibitors, serotonin–norepinephrine reuptake inhibitors, and noradrenergic and specific serotonergic antidepressants at the cellular level and establish the underlying mechanisms for their potential clinical applications. Therefore, we compared the neuroprotective effects of three antidepressants, fluoxetine (Flx), duloxetine (Dlx), and mirtazapine (Mir), by their ability to prevent oxidative stress-induced cell damage, using SH-SY5Y cells, by evaluating cell viability, generation of reactive oxygen species (ROS) and mitochondrial ROS, and peroxidation of cell membrane phospholipids. These antidepressants exhibited potent antioxidant activity (Dlx > Mir > Flx) and improved cell viability. Furthermore, pretreatment with a 5-hydroxytryptamine 1A (5-HT_1A) antagonist suppressed their effects, suggesting that the 5-HT_1A receptor is involved in the antioxidant mechanism of the antidepressants’ neuroprotection. These findings suggest the beneficial effects of antidepressant treatment in AD through the prevention of Aβ-induced oxidative stress. Full article

Serotonin (5-hydroxytryptamine, 5HT) homeostasis is essential for many physiological processes in the central nervous system and peripheral tissues. Hyperserotonemia, a measurable sign of 5HT homeostasis disruption, can be caused by 5HT-directed treatment of psychiatric and gastrointestinal diseases. Its impact on the long-term balance and function of 5HT in the peripheral compartment remains unresolved and requires further research due to possible effects on human health. We explored the effects of perinatal 5HT imbalance on the peripheral organs responsible for serotonin metabolism—the jejunum, a synthesis site, and the liver, a catabolism site—in adult rats. Hyperserotonemia was induced by subchronic treatment with serotonin precursor 5-hydroxytryptophan (5HTP) or serotonin degradation inhibitor tranylcypromine (TCP). The jejunum and liver were collected on postnatal day 70 and analyzed histomorphometrically. Relative mRNA levels of 5HT-regulating proteins were determined using qRT-PCR. Compared to controls, 5HTP- and TCP-treated rats had a reduced number of 5HT-producing cells and expression of the 5HT-synthesising enzyme in the jejunum, and an increased expression of 5HT-transporter accompanied by karyomegaly in hepatocytes, with these differences being more pronounced in the TCP-treated animals. Here, we report that perinatal 5HT disbalance induced long-term cellular and molecular changes in organs regulating 5HT-metabolism, which may have a negative impact on 5HT availability and function in the periphery. Our rat model demonstrates a link between the developmental abnormalities of serotonin homeostasis and 5HT-related changes in adult life and may be suitable for exploring the neurobiological substrates of vulnerability to behavioral and metabolic disorders, as well as for modeling the adverse effects of the prenatal exposure to 5HT enhancers in the human population. Full article