Showing papers on "Serotonin published in 2020"
TL;DR: The potential role of tryptophan metabolism in the modulation of brain function by the gut microbiota, including serotonin synthesis and degradation pathways of the host, is focused on.
231 citations
TL;DR: The psychoneuroimmunological consequences of tryptophan metabolism and the susceptibility of this pathway to modulation by a variety of nutritional and lifestyle-related factors have important implications for the development of both diagnostic and treatment options.
Abstract: In the past, accelerated tryptophan breakdown was considered to be a feature of clinical conditions, such as infection, inflammation, and malignant disease. More recently, however, the focus has changed to include the additional modulation of tryptophan metabolism by changes in nutrition and microbiota composition. The regulation of tryptophan concentration is critical for the maintenance of systemic homeostasis because it integrates essential pathways involved in nutrient sensing, metabolic stress response, and immunity. In addition to tryptophan being important as a precursor for the synthesis of the neurotransmitter serotonin, several catabolites along the kynurenine axis are neuroactive. This emphasizes the importance of the immunometabolic fate of this amino acid for processes relevant to neuropsychiatric symptoms. In humans, besides hepatic catabolism, there is usually a strong relationship between immune activation-associated tryptophan breakdown and increased levels of biomarkers, such as neopterin, which has particular relevance for both acute and chronic diseases. A shift towards neopterin synthesis during oxidative stress may indicate a corresponding decrease in tetrahydrobiopterin, a cofactor of several mono-oxygenases, providing a further link between tryptophan metabolism and serotonergic and catecholaminergic neurotransmission. The psychoneuroimmunological consequences of tryptophan metabolism and the susceptibility of this pathway to modulation by a variety of nutritional and lifestyle-related factors have important implications for the development of both diagnostic and treatment options.
90 citations
TL;DR: The traditional and modern functions of 5-HT are discussed, with particular focus on the interaction of gut-derived serotonin with the gut microbiota, and emerging evidence linking this relationship with host homeostasis is addressed.
73 citations
TL;DR: The presence of A. muciniphila and its EVs in the gut promotes serotonin concentration, they also affect serotonin signaling/metabolism through the gut-brain axis and may be considered in new therapeutic strategies to ameliorate serotonin-related disorders.
Abstract: Several studies have reported that the host-microbe interactions in the gut modulate the host serotonin or 5-hydroxytryptamine (5-HT) system. Here, we evaluated the effects of Akkermansia muciniphila and its extracellular vesicles (EVs) on genes pertaining to the serotonergic system in the colon and hippocampus of mice. Male C57BL/6J mice were administered viable A. muciniphila and its EVs for 4 weeks. The serotonin levels in the colon, hippocampus, and serum of mice, as well as the human colon carcinoma cells (Caco-2), were measured by ELISA assays. Also, the effects of A. muciniphila and its EVs on the expression of serotonin system genes in the colon and hippocampus were examined. A. muciniphila and its EVs may have a biological effect on the induction of serotonin levels in the colon and hippocampus of mice. Also, EVs increased the serotonin level in the Caco-2 cell line. In contrast, both treatments decreased the serotonin level in the serum. Both the bacterium and its EVs had significant effects on the mRNA expression of genes, involved in serotonin signaling/metabolism in the colon and hippocampus of mice. Moreover, A. muciniphila and its EVs affected the mRNA expression of inflammatory cytokines (Il-10 and Tnf-α) in the colon, however, there is no significant difference in inflammatory cell infiltrate in the histopathology of the colon. The presence of A. muciniphila and its EVs in the gut promotes serotonin concentration, they also affect serotonin signaling/metabolism through the gut-brain axis and may be considered in new therapeutic strategies to ameliorate serotonin-related disorders.
62 citations
TL;DR: Serotonin decreases virulence gene expression by enterohemorrhagic E. coli and Citrobacter rodentium and is repurposing serotonin agonists to inhibit CpxA, which may represent a potential therapeutic intervention for enteric bacteria.
61 citations
TL;DR: Serotonergic toxicity can mimic other serious syndromes, such as malignant hyperthermia, sepsis, thyroid storm, and neuroleptic malignant syndrome, and Anaesthetists must maintain a heightened awareness of its possible occurrence and a readiness to engage in early treatment to avoid poor outcomes.
Abstract: Summary Most cases of serotonin toxicity are provoked by therapeutic doses of a combination of two or more serotonergic drugs, defined as drugs affecting the serotonin neurotransmitter system. Common serotonergic drugs include many antidepressants, antipsychotics, and opioid analgesics, particularly fentanyl, tramadol, meperidine (pethidine), and methadone, but rarely morphine and other related phenanthrenes. Symptoms of serotonin toxicity are attributable to an effect on monoaminergic transmission caused by an increased synaptic concentration of serotonin. The serotonin transporter (SERT) maintains low serotonin concentrations and is important for the reuptake of the neurotransmitter into the presynaptic nerve terminals. Some opioids inhibit the reuptake of serotonin by inhibiting SERT, thus increasing the plasma and synaptic cleft serotonin concentrations that activate the serotonin receptors. Opioids that are good inhibitors of SERT (tramadol, dextromethorphan, methadone, and meperidine) are most frequently associated with serotonin toxicity. Tramadol also has a direct serotonin-releasing action. Fentanyl produces an efflux of serotonin, and binds to 5-hydroxytryptamine (5-HT)1A and 5-HT2A receptors, whilst methadone, meperidine, and more weakly tapentadol, bind to 5-HT2A but not 5-HT1A receptors. The perioperative period is a time where opioids and other serotonergic drugs are frequently administered in rapid succession, sometimes to patients with other serotonergic drugs in their system. This makes the perioperative period a relatively risky time for serotonin toxicity to occur. The intraoperative recognition of serotonin toxicity is challenging as it can mimic other serious syndromes, such as malignant hyperthermia, sepsis, thyroid storm, and neuroleptic malignant syndrome. Anaesthetists must maintain a heightened awareness of its possible occurrence and a readiness to engage in early treatment to avoid poor outcomes.
58 citations
TL;DR: These first-of-their-kind observations in the human brain reveal a role for sub-second striatal dopamine and serotonin signaling in non-reward-based aspects of cognition and action.
51 citations
TL;DR: In this article, a review of the main natural sources of 5-HTP, chemical analysis and synthesis, biosynthesis and microbial production of 5HTP by molecular engineering is described.
Abstract: L-5-hydroxytryptophan (5-HTP) is both a drug and a natural component of some dietary supplements. 5-HTP is produced from tryptophan by tryptophan hydroxylase (TPH), which is present in two isoforms (TPH1 and TPH2). Decarboxylation of 5-HTP yields serotonin (5-hydroxytryptamine, 5-HT) that is further transformed to melatonin (N-acetyl-5-methoxytryptamine). 5-HTP plays a major role both in neurologic and metabolic diseases and its synthesis from tryptophan represents the limiting step in serotonin and melatonin biosynthesis. In this review, after an look at the main natural sources of 5-HTP, the chemical analysis and synthesis, biosynthesis and microbial production of 5-HTP by molecular engineering will be described. The physiological effects of 5-HTP are discussed in both animal studies and human clinical trials. The physiological role of 5-HTP in the treatment of depression, anxiety, panic, sleep disorders, obesity, myoclonus and serotonin syndrome are also discussed. 5-HTP toxicity and the occurrence of toxic impurities present in tryptophan and 5-HTP preparations are also discussed.
44 citations
TL;DR: In this article, tryptophan and metabolites of serotonin and kynurenine were investigated extensively in 173 patients suffering from a current major depressive episode (MDE) and compared to 214 healthy controls (HC).
Abstract: Aim Tryptophan is the sole precursor of both peripherally and centrally produced serotonin and kynurenine. In depressed patients, tryptophan, serotonin, kynurenine, and their metabolite levels remain unclear. Therefore, peripheral tryptophan and metabolites of serotonin and kynurenine were investigated extensively in 173 patients suffering from a current major depressive episode (MDE) and compared to 214 healthy controls (HC). Methods Fasting plasma levels of 11 peripheral metabolites were quantified: tryptophan, serotonin pathway (serotonin, its precursor 5-hydroxytryptophan and its metabolite 5-hydroxyindoleacetic acid), and kynurenine pathway (kynurenine and six of its metabolites: anthranilic acid, kynurenic acid, nicotinamide, picolinic acid, xanthurenic acid, and 3-hydroxyanthranilic acid). Results Sixty (34.7%) patients were antidepressant-drug free. Tryptophan levels did not differ between MDE patients and HC. Serotonin and its precursor (5-hydroxytryptophan) levels were lower in MDE patients than in HC, whereas, its metabolite (5-hydroxyindoleacetic acid) levels were within the standard range. Kynurenine and four of its metabolites (kynurenic acid, nicotinamide, picolinic acid, and xanthurenic acid) were lower in MDE patients. Conclusion Whilst the results of this study demonstrate an association between the metabolites studied and depression, conclusions about causality cannot be made. This study uses the largest ever sample of MDE patients, with an extensive assessment of peripheral tryptophan metabolism in plasma. These findings provide new insights into the peripheral signature of MDE. The reasons for these changes should be further investigated. These results might suggest new antidepressant therapeutic strategies.
43 citations
TL;DR: The known roles of 5-HT7 receptors in the immune system, as well as their potential therapeutic implication in inflammatory and immune-mediated disorders are reviewed.
Abstract: In mammalians, serotonin (5-HT) has critical roles in the central nervous system (CNS), including mood stability, pain tolerance, or sleep patterns. However, the vast majority of serotonin is produced by intestinal enterochromaffin cells of the gastrointestinal tract and circulating blood platelets, also acting outside of the CNS. Serotonin effects are mediated through its interaction with 5-HT receptors (5-HTRs), a superfamily with a repertoire of at least fourteen well-characterized members. 5-HT7 receptors are the last 5-HTR member to be identified, with well-defined functions in the nervous, gastrointestinal, and vascular systems. The effects of serotonin on the immune response are less well understood. Mast cells are known to produce serotonin, while T cells, dendritic cells, monocytes, macrophages and microglia express 5-HT7 receptor. Here, we review the known roles of 5-HT7 receptors in the immune system, as well as their potential therapeutic implication in inflammatory and immune-mediated disorders.
41 citations
TL;DR: KYNA reversed immobility, climbing, and swimming times, suggesting the antidepressant-like effects of KYNA, for the first time, in a modified mouse FST.
03 Jan 2020
TL;DR: The results indicate that kynurenine functions as an oncometabolite, at least in part, by activating the transcription factor AHR, which then regulates growth promoting genes in cancer cells, and proposes that blocking kynuranine production or activity can be an efficient approach to specifically limit the growth of colon cancer cells.
Abstract: Tryptophan is one of the eight essential amino acids that must be obtained from the diet. Interestingly, tryptophan is the least abundant amino acid in most proteins, a large portion of cellular tryptophan is converted into metabolites of the serotonin and kynurenine pathways. In a recent study, (Venkateswaran, Lafita-Navarro et al., 2019, Genes Dev), we discovered that colon cancer cells display greater uptake and processing of tryptophan than normal colonic cells and tissues. This process is mediated by the oncogenic transcription factor MYC that promotes the expression of the tryptophan importers SLC1A5 and SLC7A5 and the tryptophan metabolizing enzyme AFMID. The metabolism of tryptophan in colon cancer cells generates kynurenine, a biologically active metabolite necessary to maintain continuous cell proliferation. Our results indicate that kynurenine functions as an oncometabolite, at least in part, by activating the transcription factor AHR, which then regulates growth promoting genes in cancer cells. We propose that blocking kynurenine production or activity can be an efficient approach to specifically limit the growth of colon cancer cells. Here, we describe our findings and new questions for future studies targeted at understanding AHR-independent function of kynurenine, as well as interfering with the enzyme AFMID as a new strategy to target the kynurenine pathway.
TL;DR: In MDD patients the antidepressant response to escitalopram was positively associated with baseline serotonin levels and inversely associated with activation of the kynurenine pathway, consistent with previous literature showing that biomarker evidence of inflammation is associated with lower response to antidepressants from the selective serotonin reuptake inhibitor class.
Abstract: Introduction The response of patients with major depressive disorders (MDD) to antidepressant treatments have been shown to be affected by multiple factors, including disease severity and inflammation. Increasing evidence indicates that the kynurenine metabolic pathway is activated by inflammation in MDD patients and plays a role in the pathophysiology of depression. Antidepressant treatments have been reported to affect kynurenine pathway metabolite levels as well. This study investigates differential associations between the antidepressant treatment outcome to escitalopram versus desvenlafaxine with the pre-treatment and post-treatment-changes in serotonin and kynurenine pathway metabolite levels. Methods The levels of serotonin and of kynurenine pathway metabolites were measured in plasma using liquid chromatography-mass spectrometry (LC-MS) in 161 currently depressed patients with MDD at baseline and after 8 weeks of treatment with either escitalopram or desvenlafaxine. Treatment response was defined conventionally by a reduction of at least 50% in the Hamilton Depression Rating Scale 21 item (HAMD-21) total score from baseline; remission was defined by reaching a post-treatment HAMD-21 score ≤7. Results Response to escitalopram treatment was associated with higher baseline serotonin levels (p = 0.022), lower baseline kynurenine (Kyn)/tryptophan (Trp) ratio (p = 0.008) and lower baseline quinolinic acid (QuinA)/tryptophan (Trp) ratio (p = 0.047), suggesting a lower inflammation state. Greater improvement in depression symptoms as measured by percent change of HAMD-21 score from baseline was also associated with higher baseline serotonin levels (p = 0.033) in escitalopram treatment arm. Furthermore, remitters to escitalopram treatment showed significant increases in the kynurenic acid (KynA)/3-hydroxykynurenine (3HK) ratio after treatment (p = 0.015). In contrast, response to desvenlafaxine treatment was not associated with any metabolite analyzed. We also confirmed a previous report that plasma serotonin levels are lower in MDD patients compared to healthy controls (p = 0.004) and that the kynurenine plasma level is negatively associated with depression symptom severity (p = 0.047). Conclusions In MDD patients the antidepressant response to escitalopram was positively associated with baseline serotonin levels and inversely associated with activation of the kynurenine pathway. These results appear consistent with previous literature showing that biomarker evidence of inflammation is associated with lower response to antidepressants from the selective serotonin reuptake inhibitor class. Moreover, increases in the kynurenic acid (KynA)/3-hydroxykynurenine (3HK) ratio, which previously has been characterized as a neuroprotective index, were associated with full remission under escitalopram treatment.
University of Alabama at Birmingham1, Veterans Health Administration2, University of Münster3, Belarusian State University4, University of Tennessee Health Science Center5, Nicolaus Copernicus University in Toruń6, University of Texas Health Science Center at San Antonio7, University College Dublin8
TL;DR: A serotonin‐NAS system in human skin that is a part of local neuroendocrine system regulating skin homeostasis is characterized and produced endogenously in the epidermal, dermal, and adnexal compartments of human skin and in cultured skin cells.
Abstract: Tryptophan hydroxylase (TPH) activity was detected in cultured epidermal melanocytes and dermal fibroblasts with respective Km of 5.08 and 2.83 mM and Vmax of 80.5 and 108.0 µmol/min. Low but detectable TPH activity was also seen in cultured epidermal keratinocytes. Serotonin and/or its metabolite and precursor to melatonin, N-acetylserotonin (NAS), were identified by LC/MS in human epidermis and serum. Endogenous epidermal levels were 113.18 ± 13.34 and 43.41 ± 12.45 ng/mg protein for serotonin (n = 8/8) and NAS (n = 10/13), respectively. Their production was independent of race, gender, and age. NAS was also detected in human serum (n = 13/13) at a concentration 2.44 ± 0.45 ng/mL, while corresponding serotonin levels were 295.33 ± 17.17 ng/mL (n = 13/13). While there were no differences in serum serotonin levels, serum NAS levels were slightly higher in females. Immunocytochemistry studies showed localization of serotonin to epidermal and follicular keratinocytes, eccrine glands, mast cells, and dermal fibrocytes. Endogenous production of serotonin in cultured melanocytes, keratinocytes, and dermal fibroblasts was modulated by UVB. In conclusion, serotonin and NAS are produced endogenously in the epidermal, dermal, and adnexal compartments of human skin and in cultured skin cells. NAS is also detectable in human serum. Both serotonin and NAS inhibited melanogenesis in human melanotic melanoma at concentrations of 10-4 -10-3 M. They also inhibited growth of melanocytes. Melanoma cells were resistant to NAS inhibition, while serotonin inhibited cell growth only at 10-3 M. In summary, we characterized a serotonin-NAS system in human skin that is a part of local neuroendocrine system regulating skin homeostasis.
TL;DR: Results show that activation of 5-HT efferents from the MRN rapidly induces expression of anxiety-like behaviour, in part via projections to the dHC, revealing an important neural circuit implicated in the expression ofxiety in female mice.
TL;DR: A novel model of serotonin homeostasis in the term placenta is proposed with special focus on the protective role of organic cation transporter 3 (OCT3/SLC22A3).
Abstract: Aim Serotonin is crucial for proper foetal development, and the placenta has been described as a 'donor' of serotonin for the embryo/foetus. However, in later stages of gestation the foetus produces its own serotonin from maternally-derived tryptophan and placental supply is no longer needed. We propose a novel model of serotonin homeostasis in the term placenta with special focus on the protective role of organic cation transporter 3 (OCT3/SLC22A3). Methods Dually perfused rat term placenta was employed to quantify serotonin/tryptophan transport and metabolism. Placental membrane vesicles isolated from human term placenta were used to characterize serotonin transporters on both sides of the syncytiotrophoblast. Results We obtained the first evidence that serotonin is massively taken up from the foetal circulation by OCT3. This uptake is concentration-dependent and inhibitable by OCT3 blockers of endogenous (glucocorticoids) or exogenous (pharmaceuticals) origin. Population analyses in rat placenta revealed that foetal sex influences placental extraction of serotonin from foetal circulation. Negligible foetal serotonin levels were detected in maternal-to-foetal serotonin/tryptophan transport and metabolic studies. Conclusion We demonstrate that OCT3, localized on the foetus-facing membrane of syncytiotrophoblast, is an essential component of foeto-placental homeostasis of serotonin. Together with serotonin degrading enzyme, monoamine oxidase-A, this offers a protective mechanism against local vasoconstriction effects of serotonin in the placenta. However, this system may be compromised by OCT3 inhibitory molecules, such as glucocorticoids or antidepressants. Our findings open new avenues to explore previously unsuspected/unexplained complications during pregnancy including prenatal glucocorticoid excess and pharmacotherapeutic risks of treating pregnant women with OCT3 inhibitors.
TL;DR: TPH1 deficient mice were shown to be protected from diverse diseases including hemostatic, inflammatory, fibrotic, gastrointestinal, and metabolic disorders and therefore serotonin synthesis inhibition emerged as a reasonable therapeutic paradigm.
TL;DR: It is shown that hippocampal parvalbumin interneurons express functionally silent serotonin 5A receptors, which translocate to the cell membrane and become active upon chronic, but not acute, treatment with a selective serotonin reuptake inhibitor (SSRI).
Abstract: The behavioral response to antidepressants is closely associated with physiological changes in the function of neurons in the hippocampal dentate gyrus (DG). Parvalbumin interneurons are a major class of GABAergic neurons, essential for DG function, and are involved in the pathophysiology of several neuropsychiatric disorders. However, little is known about the role(s) of these neurons in major depressive disorder or in mediating the delayed behavioral response to antidepressants. Here we show, in mice, that hippocampal parvalbumin interneurons express functionally silent serotonin 5A receptors, which translocate to the cell membrane and become active upon chronic, but not acute, treatment with a selective serotonin reuptake inhibitor (SSRI). Activation of these serotonergic receptors in these neurons initiates a signaling cascade through which Gi-protein reduces cAMP levels and attenuates protein kinase A and protein phosphatase 2A activities. This results in increased phosphorylation and inhibition of Kv3.1β channels, and thereby reduces the firing of the parvalbumin neurons. Through the loss of this signaling pathway in these neurons, conditional deletion of the serotonin 5A receptor leads to the loss of the physiological and behavioral responses to chronic antidepressants.
TL;DR: The results indicate that the serotonergic input from the DR to the P Bel via 5HT 2a receptors is critical for modulating the sensitivity of the PBel CGRP neurons that cause arousal to rising levels of blood CO 2.
Abstract: During obstructive sleep apnea, elevation of CO2 during apneas contributes to awakening and restoring airway patency. We previously found that glutamatergic neurons in the external lateral parabrachial nucleus (PBel) containing calcitonin gene related peptide (PBelCGRP neurons) are critical for causing arousal during hypercapnia. However, others found that genetic deletion of serotonin (5HT) neurons in the brainstem also prevented arousal from hypercapnia. To examine interactions between the two systems, we showed that dorsal raphe (DR) 5HT neurons selectively targeted the PBel. Either genetically directed deletion or acute optogenetic silencing of DRSert neurons dramatically increased the latency of mice to arouse during hypercapnia, as did silencing DRSert terminals in the PBel. This effect was mediated by 5HT2a receptors which are expressed by PBelCGRP neurons. Our results indicate that the serotonergic input from the DR to the PBel via 5HT2a receptors is critical for modulating the sensitivity of the PBelCGRP neurons that cause arousal to rising levels of blood CO2. Dorsal raphe 5HT(DRSert) neurons regulate arousal from hypercapnia by their projections to the neurons in the external lateral parabrachial nucleus (PBel) that are glutamatergic and also express calcitonin gene related peptide (PBelCGRP). The DRSert input to the PBel modulates the arousal system to rising levels of blood CO2, and may be mediated by 5HT2a receptors on the PBelCGRP neurons.
TL;DR: It is shown that MC4R signaling in the dorsal raphe nucleus (DRN) affects feeding, anxiety, and depression, and that PRCP-ablatedMC4R mice show metabolic and behavioral phenotypes comparable to those of PrcpDRNKD mice.
TL;DR: Chronic indole production by the gut microbiota increased the vulnerability of male mice to the adverse effects of chronic mild stress on emotional behaviors and targeted catecholamine biosynthetic pathway of the adrenal medulla, which plays a pivotal role in body's physiological adaptation to stressful events.
TL;DR: It is shown in mice that SSRIs impair motor function by acting on 5-HT2C receptors in the substantia nigra pars reticulata (SNr), which in turn inhibits Nigra pars compacta (SNc) DAergic neurons, and that 5- HT2C receptor antagonism potentiates the antidepressant and anxiolytic effects of SSRI.
Abstract: Serotonin (5-HT) selective reuptake inhibitors (SSRIs) are widely used in the treatment of depression and anxiety disorders, but responsiveness is uncertain and side effects often lead to discontinuation. Side effect profiles suggest that SSRIs reduce dopaminergic (DAergic) activity, but specific mechanistic insight is missing. Here we show in mice that SSRIs impair motor function by acting on 5-HT2C receptors in the substantia nigra pars reticulata (SNr), which in turn inhibits nigra pars compacta (SNc) DAergic neurons. SSRI-induced motor deficits can be reversed by systemic or SNr-localized 5-HT2C receptor antagonism. SSRIs induce SNr hyperactivity and SNc hypoactivity that can also be reversed by systemic 5-HT2C receptor antagonism. Optogenetic inhibition of SNc DAergic neurons mimics the motor deficits due to chronic SSRI treatment, whereas local SNr 5-HT2C receptor antagonism or optogenetic activation of SNc DAergic neurons reverse SSRI-induced motor deficits. Lastly, we find that 5-HT2C receptor antagonism potentiates the antidepressant and anxiolytic effects of SSRIs. Together our findings demonstrate opposing roles for 5-HT2C receptors in the effects of SSRIs on motor function and affective behavior, highlighting the potential benefits of 5-HT2C receptor antagonists for both reduction of motor side effects of SSRIs and augmentation of therapeutic antidepressant and anxiolytic effects.
TL;DR: The data indicate that the urinary excretion pattern of neurotransmitters after consumption of their precursor is far more complex than previously appreciated and might be relevant to understanding the effects of the precursors in other organs.
Abstract: Amino acid precursors of dopamine and serotonin have been administered for decades to treat a variety of clinical conditions including depression, anxiety, insomnia, obesity, and a host of other illnesses. Dietary administration of these amino acids is designed to increase dopamine and serotonin levels within the body, particularly the brain. Convincing evidence exists that these precursors normally elevate dopamine and serotonin levels within critical brain tissues and other organs. However, their effects on urinary excretion of neurotransmitters are described in few studies and the results appear equivocal. The purpose of this study was to define, as precisely as possible, the influence of both 5-hydroxytryptophan (5-HTP) and tyrosine on urinary excretion of serotonin and dopamine in a large human population consuming both 5-HTP and tyrosine. Curiously, only 5-HTP exhibited a marginal stimulatory influence on urinary serotonin excretion when 5-HTP doses were compared to urinary serotonin excretion; however, a robust relationship was observed when alterations in 5-HTP dose were compared to alterations in urinary serotonin excretion in individual patients. The data indicate three statistically discernible components to 5-HTP responses, including inverse, direct, and no relationships between urinary serotonin excretion and 5-HTP doses. The response to tyrosine was more consistent but primarily yielded an unexpected reduction in urinary dopamine excretion. These data indicate that the urinary excretion pattern of neurotransmitters after consumption of their precursors is far more complex than previously appreciated. These data on urinary neurotransmitter excretion might be relevant to understanding the effects of the precursors in other organs.
TL;DR: The findings suggest that activating 5-HT4R acutely in the mPFC or targetingmPFC pyramidal cell terminals in the DRN might constitute a strategy to produce a fast anxiolytic response.
TL;DR: A molecular and neuroanatomical map of the 5-HT system within the insular cortex is defined, providing ground knowledge to identify the potential role of serotonergic modulation of selective insular populations in anxiety.
Abstract: The serotonin (5-HT) system is the target of multiple anxiolytics, including Buspirone, which is a partial agonist of the serotonin 1A receptor (5-HT1A) Similarly, ligands of the serotonin 2A receptor (5-HT2A) were shown to alter anxiety level The 5-HT1A and 2A receptors are widely expressed across the brain, but the target region(s) underlying the influence of those receptors on anxiety remain unknown Interestingly, recent studies in human and non-human primates have shown that the 5-HT1A and 5-HT2A binding potentials within the insular cortex (insula) are correlated to anxiety As an initial step to define the function of 5-HT transmission in the insula, we quantified the proportion of specific neuronal populations of the insula expressing 5-HT1A or 5-HT2A We analyzed seven neural populations, including three defined by a molecular marker (putative glutamate, GABA or parvalbumin), and four defined by their projections to different downstream targets First, we found that more than 70% of putative glutamatergic neurons, and only 30% of GABAergic neurons express the 5-HT1A Second, within insular projection neurons, 5-HT1A is highly expressed (75–80%) in the populations targeting one sub-nuclei of the amygdala (central or basolateral), or targeting the rostral or caudal sections of the lateral hypothalamus (LH) Similarly, 70% of putative glutamatergic neurons and only 30% of insular GABAergic neurons contain 5-HT2A Finally, the 5-HT2A is present in a majority of insula-amygdala and insula-LH projection neurons (73–82%) These observations suggest that most glutamatergic neurons can respond to 5-HT through 5-HT1A or 5-HT2A in the insula, and that 5-HT directly affects a limited number of GABAergic neurons This study defines a molecular and neuroanatomical map of the 5-HT system within the insular cortex, providing ground knowledge to identify the potential role of serotonergic modulation of selective insular populations in anxiety
TL;DR: The utility of the novel 5-HT2A receptor agonist radioligand, [11C]CIMBI-36, and a d-amphetamine challenge are demonstrated and the evaluation of the human brain serotonin system in neuropsychiatric disorders, such as major depression and Parkinson’s disease is enabled.
TL;DR: The quantum mechanics/molecular mechanics simulation of the rate-limiting step for the serotonin decomposition, which consists of hydride transfer from the serotonin methylene group to the N5 atom of the flavin moiety, provides strong evidence for the validity of the proposedhydride-transfer mechanism.
Abstract: The enzyme-catalyzed degradation of the biogenic amine serotonin is an essential regulatory mechanism of its level in the human organism. In particular, monoamine oxidase A (MAO A) is an important ...
TL;DR: The data provide the first comprehensive evidence of changes in placental homeostasis of tryptophan and its metabolites as a function of gestational age, which is critical for proper placental function and fetal development.
Abstract: L-Tryptophan is an essential amino acid and a precursor of several physiologically active metabolites. In the placenta, the serotonin and kynurenine metabolic pathways of tryptophan metabolism have been identified, giving rise to various molecules of neuroactive or immunoprotective properties, such as serotonin, melatonin, kynurenine, kynurenic acid, or quinolinic acid. Current literature suggests that optimal levels of these molecules in the fetoplacental unit are crucial for proper placenta functions, fetal development and programming. Placenta is a unique endocrine organ that, being equipped with a battery of biotransformation enzymes and transporters, precisely orchestrates homeostasis of tryptophan metabolic pathways. However, because pregnancy is a dynamic process and placental/fetal needs are continuously changing throughout gestation, placenta must adapt to these changes and ensure proper communication in the feto-placental unit. Therefore, in this study we investigated alterations of placental tryptophan metabolic pathways throughout gestation. Quantitative polymerase chain reaction (PCR) analysis of 21 selected genes was carried out in first trimester (n = 13) and term (n = 32) placentas. Heatmap analysis with hierarchical clustering revealed differential gene expression of serotonin and kynurenine pathways across gestation. Subsequently, digital droplet PCR, Western blot, and functional analyses of the rate-limiting enzymes suggest preferential serotonin synthesis early in pregnancy with a switch to kynurenine production toward term. Correspondingly, increased function and/or protein expression of serotonin degrading enzyme and transporters at term indicates efficient placental uptake and metabolic degradation of serotonin. Lastly, gene expression analysis in choriocarcinoma-derived cell lines (BeWo, BeWo b30, JEG-3) revealed dissimilar expression patterns and divergent effect of syncytialization compared to primary trophoblast cells isolated from human term placentas; these findings show that the commonly used in vitro placental models are not suitable to study placental handling of tryptophan. Altogether, our data provide the first comprehensive evidence of changes in placental homeostasis of tryptophan and its metabolites as a function of gestational age, which is critical for proper placental function and fetal development.
TL;DR: It is shown that α1-AR-mediated excitatory synaptic transmission is mediated by the ionotropic glutamate receptor homolog cation channel, delta glutamate receptor 1 (GluD1), which is proposed to be widespread in the nervous system.
Abstract: The dorsal raphe nucleus is the predominant source of central serotonin, where neuronal activity regulates complex emotional behaviors. Action potential firing of serotonin dorsal raphe neurons is driven via α1-adrenergic receptors (α1-AR) activation. Despite this crucial role, the ion channels responsible for α1-AR-mediated depolarization are unknown. Here, we show in mouse brain slices that α1-AR-mediated excitatory synaptic transmission is mediated by the ionotropic glutamate receptor homolog cation channel, delta glutamate receptor 1 (GluD1). GluD1R-channels are constitutively active under basal conditions carrying tonic inward current and synaptic activation of α1-ARs augments tonic GluD1R-channel current. Further, loss of dorsal raphe GluD1R-channels produces an anxiogenic phenotype. Thus, GluD1R-channels are responsible for α1-AR-dependent induction of persistent pacemaker-type firing of dorsal raphe neurons and regulate dorsal raphe-related behavior. Given the widespread distribution of these channels, ion channel function of GluD1R as a regulator of neuronal excitability is proposed to be widespread in the nervous system.
TL;DR: In mice treated with DSS, Trp supplementation before DSS administration improved colonic immune responses partly by reducing colonic serotonin and subsequent interactions with HTR1A and HTR4, which are known to be present on neutrophils and macrophages.
Abstract: BACKGROUND L-tryptophan (Trp) has been reported to regulate gut immune responses during inflammation. However, the underlying mechanisms are largely unknown. OBJECTIVE We investigated the role of Trp supplementation on the serotonin receptor (HTR)-mediated immune response in the colon of mice with dextran sodium sulfate (DSS)-induced colitis. METHODS In Experiment 1, male C57BL/6 mice were randomly assigned to 1 of 4 groups: Control (Con) or L-Trp supplementation [0.1 mg/(g body weight·d) in drinking water] (Trp) with (+DSS) or without 2% DSS in drinking water from days 8 to 14 of the 17-d study. In Experiments 2 and 3, Trp + DSS (Expt. 2) or DSS (Expt. 3) mice were treated as described above and subcutaneously administered with HTR1A or HTR4 antagonists (or their combination) or an HTR2 agonist from days 8 to 14 of the 15-d study. Changes in immune cell phenotypes, inflammatory mediators, and related cell signaling molecules were assessed by flow cytometry, real-time PCR, or Western blot. The mRNA abundances of Trp hydroxylase (Tph1), serotonin reuptake transporter (Slc6a4), and Htr in the colon were also assessed. RESULTS Trp supplementation before DSS treatment upregulated the expression of colonic Slc6a4 (0.49 compared with 0.30), Htr1a (1.14 compared with 0.65), and Htr4 (1.08 compared with 0.70), downregulated the expression of Htr2a (1.54 compared with 1.89), and decreased the colonic serotonin concentration (11.5 compared with 14.8 nmol/g tissue) (P < 0.01). Trp regulated the DSS-induced immune response partly through attenuating the activation of toll-like receptor 4 (TLR4)-STAT3 signaling and nucleus p-65. Either an HTR2 agonist or HTR1A and HTR4 antagonists reversed the effects of Trp. CONCLUSIONS In mice treated with DSS, Trp supplementation before DSS administration improved colonic immune responses partly by reducing colonic serotonin and subsequent interactions with HTR1A and HTR4, which are known to be present on neutrophils and macrophages.