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Tryptophan (Trp) is an essential amino acid, whose metabolism is a key gatekeeper of intestinal homeostasis. Yet, its systemic effects, particularly on atherosclerosis, remain unknown. Here we show that high-fat diet (HFD) increases the activity of intestinal indoleamine 2, 3-dioxygenase 1 (IDO), which shifts Trp metabolism from the production of microbiota-derived indole metabolites towards kynurenine production. Under HFD, the specific deletion of IDO in intestinal epithelial cells leads to intestinal inflammation, impaired intestinal barrier, augmented lesional T lymphocytes and atherosclerosis. This is associated with an increase in serotonin production and a decrease in indole metabolites, thus hijacking Trp for the serotonin pathway. Inhibition of intestinal serotonin production or supplementation with indole derivatives alleviates plaque inflammation and atherosclerosis. In summary, we uncover a pivotal role of intestinal IDO in the fine-tuning of Trp metabolism with systemic effects on atherosclerosis, paving the way for new therapeutic strategies to relieve gut-associated inflammatory diseases., (© 2024. The Author(s).)

Monoamine oxidases (MAO; MAO-A and MAO-B in mammals) are enzymes catalyzing the degradation of biogenic amines, including monoamine neurotransmitters. In humans, coding mutations in MAOs are extremely rare and deleterious. Here, we assessed the structural and biochemical consequences of a point mutation (P106L) in the single mao gene of the blind cavefish, Astyanax mexicanus. This mutation decreased mao enzymatic activity by ∼3-fold and affected the enzyme kinetics parameters, in line with potential structure-function alterations. HPLC measurements in brains of four A. mexicanus genetic lines (mutant and non-mutant cavefish, and mutant and non-mutant surface fish) showed major disturbances in serotonin, dopamine, noradrenaline and metabolite levels in mutants and demonstrated that the P106L mao mutation is responsible for monoaminergic disequilibrium in the P106L mao mutant cavefish brain. The outcomes of the mutation were different in the posterior brain (containing the raphe nucleus) and the anterior brain (containing fish-specific hypothalamic serotonergic clusters), revealing contrasting properties in neurotransmitter homeostasis in these different neuronal groups. We also discovered that the effects of the mutation were partially compensated by a decrease in activity of TPH, the serotonin biosynthesis rate-limiting enzyme. Finally, the neurochemical outcomes of the mao P106L mutation differed in many respects from a treatment with deprenyl, an irreversible MAO inhibitor, showing that genetic and pharmacological interference with MAO function are not the same. Our results shed light on our understanding of cavefish evolution, on the specificities of fish monoaminergic systems, and on MAO-dependent homeostasis of brain neurochemistry in general., Competing Interests: Competing interests The authors declare no competing or financial interests., (© 2023. Published by The Company of Biologists Ltd.)

Background:  The roles of thrombophilia and cardiovascular risk factors in sudden sensorineural hearing loss (SSNHL) remain controversial. Cochlear microthrombosis and vasospasm have been hypothesized as possible pathogenic mechanisms of SSNHL. This article investigates the circulating serotonin and homocysteine levels besides thrombophilia screening in patients with idiopathic SSNHL., Methods:  A total of 133 SSNHL patients and age- and sex-matched controls were investigated (discovery cohort). Measurement included common inherited natural coagulation inhibitors, factor VIII, von Willebrand factor (VWF), antiphospholipid antibodies, homocysteine, and serotonin (whole blood, platelet, and plasma) levels, along with frequent relevant genetic variants. A validation cohort (128 SSNHL patients) was studied for homocysteine and serotonin levels., Results and Conclusion:  In the discovery cohort, 58.6% of patients exhibited thrombophilia, of which most had a low to moderate titers of antiphospholipid antibodies and high levels of factor VIII/VWF. Twenty-seven patients (20%) had mild-to-moderate hyperhomocysteinemia or were homozygous for the methylenetetrahydrofolate reductase ( MTHFR ) C677T mutation. Regarding serotonin, SSNHL patients had elevated whole blood levels that remained within the normal range and normal platelet content. However, approximately 90% patients of both cohorts had elevated plasma serotonin. Elevated plasma serotoninemia was accompanied by serotonylation of platelet rhoA protein. This study shows that increased plasma serotonin appears as a biomarker of SSNHL (specificity: ∼96%, sensitivity: ∼90%) and could participate in the pathophysiology of SSNHL., Competing Interests: L.D. reports grants from Agence Nationale pour la Recherche (grant ANR-16-CE16–0021–03) to J.M.L. and J.C., during the conduct of the study. N.V. reports personal fees from Abbott, Roche, and Siemens, outside the submitted work., (Thieme. All rights reserved.)

Tryptophan as the precursor of several active compounds, including kynurenine and serotonin, is critical for numerous important metabolic functions. Enhanced tryptophan metabolism toward the kynurenine pathway has been associated with myelodysplastic syndromes (MDSs), which are preleukemic clonal diseases characterized by dysplastic bone marrow and cytopenias. Here, we reveal a fundamental role for tryptophan metabolized along the serotonin pathway in normal erythropoiesis and in the physiopathology of MDS-related anemia. We identify, both in human and murine erythroid progenitors, a functional cell-autonomous serotonergic network with pro-survival and proliferative functions. In vivo studies demonstrate that pharmacological increase of serotonin levels using fluoxetine, a common antidepressant, has the potential to become an important therapeutic strategy in low-risk MDS anemia refractory to erythropoietin., (Copyright © 2019 The Authors. Published by Elsevier Inc. All rights reserved.)

Rationale: The receptor protein tyrosine phosphatase PTPRG has been genetically associated with psychiatric disorders and is a ligand for members of the contactin family, which are themselves linked to autism spectrum disorders., Objective: Based on our finding of a phosphatase-null de novo mutation in PTPRG associated with a case of sporadic schizophrenia, we used PTPRG knockout (KO) mice to model the effect of a loss-of-function mutation. We compared the results with loss-of-function in its close paralogue PTPRZ, previously associated with schizophrenia. We tested PTPRG -/- , PTPRZ -/- , and wild-type male mice for effects on social behavior, forced swim test, and anxiety, as well as on regional brain neurochemistry., Results: The most notable behavioral consequences of PTPRG gene inactivation were reduced immobilization in the forced swim test, suggestive of some negative symptoms of schizophrenia. By contrast, PTPRZ -/- mice demonstrated marked social alteration with increased aggressivity, reminiscent of some positive symptoms of schizophrenia. Both knockouts showed elevated dopamine levels in prefrontal cortex, hippocampus, and most particularly amygdala, but not striatum, accompanied by reduced dopamine beta hydroxylase activity only in amygdala. In addition, PTPRG KO elicited a distinct increase in hippocampal serotonin level not observed in PTPRZ KO., Conclusion: PTPRG and PTPRZ gene loss therefore induces distinct patterns of behavioral change and region-specific alterations in neurotransmitters, highlighting their usefulness as models for neuropsychiatric disorder mechanisms and making these receptors attractive targets for therapy.

Rheumatoid arthritis is a chronic disease that results in a disabling and painful condition as it progresses to destruction of the articular cartilage and ankylosis of the joints. Although the cause of the disease is still unknown, evidence argues that autoimmunity plays an important part. There are increasing but contradictory views regarding serotonin being associated with activation of immunoinflammatory pathways and the onset of autoimmune reactions. We studied serotonin's involvement during collagen-induced arthritis in wild-type and Tph1(-/-) mice, which have markedly reduced peripheral serotonin levels. In wild-type mice, induction of arthritis triggered a robust increase in serotonin content in the paws combined with less inflammation. In Tph1(-/-) mice with arthritis, a marked increase in the clinical and pathologic arthritis scores was noticed. Specifically, in Tph1(-/-) mice with arthritis, a significant increase in osteoclast differentiation and bone resorption was observed with an increase in IL-17 levels in the paws and in Th17 lymphocytes in the draining lymph nodes, whereas T-regulatory cells were dampened. Ex vivo serotonin and agonists of the 5-HT2A and 5-HT2B receptors restored IL-17 secretion from splenocytes and Th17 cell differentiation in Tph1(-/-) mice. These findings indicate that serotonin plays a fundamental role in arthritis through the regulation of the Th17/T-regulatory cell balance and osteoclastogenesis., (Copyright © 2016 American Society for Investigative Pathology. Published by Elsevier Inc. All rights reserved.)

Diabetes is a major complication of chronic Glucocorticoids (GCs) treatment. GCs induce insulin resistance and also inhibit insulin secretion from pancreatic beta cells. Yet, a full understanding of this negative regulation remains to be deciphered. In the present study, we investigated whether GCs could inhibit serotonin synthesis in beta cell since this neurotransmitter has been shown to be involved in the regulation of insulin secretion. To this aim, serotonin synthesis was evaluated in vitro after treatment with GCs of either islets from CD1 mice or MIN6 cells, a beta-cell line. We also explored the effect of GCs on the stimulation of serotonin synthesis by several hormones such as prolactin and GLP 1. We finally studied this regulation in islet in two in vivo models: mice treated with GCs and with liraglutide, a GLP1 analog, and mice deleted for the glucocorticoid receptor in the pancreas. We showed in isolated islets and MIN6 cells that GCs decreased expression and activity of the two key enzymes of serotonin synthesis, Tryptophan Hydroxylase 1 (Tph1) and 2 (Tph2), leading to reduced serotonin contents. GCs also blocked the induction of serotonin synthesis by prolactin or by a previously unknown serotonin activator, the GLP-1 analog exendin-4. In vivo, activation of the Glucagon-like-Peptide-1 receptor with liraglutide during 4 weeks increased islet serotonin contents and GCs treatment prevented this increase. Finally, islets from mice deleted for the GR in the pancreas displayed an increased expression of Tph1 and Tph2 and a strong increased serotonin content per islet. In conclusion, our results demonstrate an original inhibition of serotonin synthesis by GCs, both in basal condition and after stimulation by prolactin or activators of the GLP-1 receptor. This regulation may contribute to the deleterious effects of GCs on beta cells.

Elevated whole-blood serotonin and decreased plasma melatonin (a circadian synchronizer hormone that derives from serotonin) have been reported independently in patients with autism spectrum disorders (ASDs). Here, we explored, in parallel, serotonin, melatonin and the intermediate N-acetylserotonin (NAS) in a large cohort of patients with ASD and their relatives. We then investigated the clinical correlates of these biochemical parameters. Whole-blood serotonin, platelet NAS and plasma melatonin were assessed in 278 patients with ASD, their 506 first-degree relatives (129 unaffected siblings, 199 mothers and 178 fathers) and 416 sex- and age-matched controls. We confirmed the previously reported hyperserotonemia in ASD (40% (35-46%) of patients), as well as the deficit in melatonin (51% (45-57%)), taking as a threshold the 95th or 5th percentile of the control group, respectively. In addition, this study reveals an increase of NAS (47% (41-54%) of patients) in platelets, pointing to a disruption of the serotonin-NAS-melatonin pathway in ASD. Biochemical impairments were also observed in the first-degree relatives of patients. A score combining impairments of serotonin, NAS and melatonin distinguished between patients and controls with a sensitivity of 80% and a specificity of 85%. In patients the melatonin deficit was only significantly associated with insomnia. Impairments of melatonin synthesis in ASD may be linked with decreased 14-3-3 proteins. Although ASDs are highly heterogeneous, disruption of the serotonin-NAS-melatonin pathway is a very frequent trait in patients and may represent a useful biomarker for a large subgroup of individuals with ASD.

Depressive, anxiety and obsessive symptoms frequently co-occur with anorexia nervosa (AN). The relationship between these clinical manifestations and the biological changes caused by starvation is not well understood. It has been hypothesised that reduced availability of tryptophan (TRP) could reduce serotonin activity and thus trigger these comorbid symptoms. The aim of this study, during re-feeding in individuals with AN, was to analyse covariations across measures of nutritional status, depressive and anxiety symptoms, and peripheral serotonin markers. Depressive and anxiety symptoms, nutritional status and serotonin markers--whole blood serotonin content, plasma TRP and the ratio between TRP and large neutral amino acids--were assessed for 42 AN participants at admission to inpatient treatment and after re-feeding. Biological measures were compared to those obtained in 42 non-eating disordered subjects. For those with AN, psychological, nutritional and biological parameters improved significantly during hospitalisation. Levels of serotonin markers were significantly lower in the AN group compared to the control group, at admission and at discharge. Increase in the TRP/LNAA ratio was correlated with a decrease in depressive symptoms. In addition, there was a positive correlation between serotonin levels and symptoms of both anxiety and depression at discharge. We speculate that enhanced TRP availability during re-feeding, as a result of the increase in the TRP/LNAA ratio, could restore serotonin neurotransmission and lead to a decrease in depressive symptoms. The association between serotonin and anxiety and depressive symptoms would be consistent with numerous observations indicating abnormal functioning of the serotoninergic system in AN., (Copyright © 2013 Elsevier Ltd. All rights reserved.)

The stability and efficacy of neuronal circuits are achieved through a detailed balance between pyramidal cell and interneuron activities. Interestingly, the neocortical excitatory-inhibitory (E-I) balance is actively maintained at the soma of Layer 5 pyramidal neurons which receive 20% of excitation and 80% of inhibition after dendritic integration, and this is not affected by changes in synaptic strength. To infer the role of serotonergic neuromodulation on the activity-dependent maintenance of the E-I balance, we performed continuous voltage clamp measurements of stimulation-locked conductance dynamics in Layer 5 pyramidal neurons before and after long-term potentiation (LTP) induction, together with chronic or acute manipulation of serotonin function. When a theta-burst stimulation was applied in Layer 2/3 of 5-HT depleted cortical slices (after in vivo treatment with the tryptophan hydroxylase inhibitor p-chlorophenylalanine (pCPA)), or after in vitro perfusion of the potent 5-HT1A receptor antagonist WAY-100,635, we observed a persistent shift of the ratio between excitation and inhibition toward more inhibition. This was due to a strong LTP of inhibition co-aligned with a weak LTP of excitation, whereas the same protocol caused a similar potentiation of excitatory and inhibitory inputs when applied in control slices. In contrast, neither excitatory nor inhibitory postsynaptic currents were potentiated when LTP protocols were delivered in the presence of either the selective serotonin reuptake inhibitor citalopram or the 5-HT1A receptor agonist 8-OH-DPAT. This is the first demonstration that serotonergic neuromodulation is crucial for the maintenance of the neocortical E-I balance during high-frequency regimes., (Copyright © 2013 IBRO. Published by Elsevier Ltd. All rights reserved.)

Background: Within the species Astyanax mexicanus, there are several interfertile populations of river-dwelling sighted fish and cave-dwelling blind fish which have evolved morphological and behavioral adaptations, the origins of which are unknown. Here, we have investigated the neural, genetic, and developmental bases for the evolution of aggressive behavior in this teleost., Results: We used an intruder-resident behavioral assay to compare aggressiveness quantitatively (attack counts) and qualitatively (pattern and nature of attacks) between the surface and cave populations of Astyanax. Using this paradigm, we characterize aggressive behavior in surface fish, bring support for the genetic component of this trait, and show that it is controlled by raphe serotonergic neurons and that it corresponds to the establishment of dominance between fish. Cavefish have completely lost such aggressive/dominance behavior. The few attacks performed by cavefish during the behavioral test instead correspond to food-seeking behavior, driven by the developmental evolution of their hypothalamic serotonergic paraventricular neurons, itself due to increased Sonic Hedgehog signaling during early forebrain embryogenesis., Conclusions: We propose that during evolution and adaptation to their cave habitat, cavefish have undergone a behavioral shift, due to modifications of their serotonergic neuronal network. They have lost the typical aggressive behavior of surface fish and evolved a food-seeking behavior that is probably more advantageous to surviving in the dark. We have therefore demonstrated a link between the development of a neuronal network and the likely adaptive behaviors it controls., (Copyright © 2013 Elsevier Ltd. All rights reserved.)

Peripheral serotonin, synthesized by tryptophan hydroxylase-1 (TPH(1)), has been shown to play a key role in several physiological functions. Recently, controversy has emerged about whether peripheral serotonin has any effect on bone density and remodeling.We therefore decided to investigate in detail bone remodeling in growing and mature TPH(1) knockout mice (TPH(1)(-/-)). Bone resorption in TPH(1)(-/-) mice, as assessed by biochemical markers and bone histomorphometry, was markedly decreased at both ages. Using bone marrow transplantation, we present evidence that the decrease in bone resorption in TPH(1)(-/-) mice is cell-autonomous. Cultures from TPH(1)(-/-) in the presence of macrophage colony-stimulating factor and receptor activator for NF-KB ligand (RANKL) displayed fewer osteoclasts, and the decreased differentiation could be rescued by adding serotonin. Our data also provide evidence that in the presence of RANKL, osteoclast precursors express TPH(1) and synthesize serotonin. Furthermore, pharmacological inhibition of serotonin receptor 1B with SB224289, and of receptor 2A with ketanserin, also reduced the number of osteoclasts. Our findings reveal that serotonin has an important local action in bone, as it can amplify the effect of RANKL on osteoclastogenesis.

Serotonin (5-HT) has long been recognized as a neurotransmitter in the central nervous system, where it modulates a variety of behavioral functions. Availability of 5-HT depends on the expression of the enzyme tryptophan hydroxylase (TPH), and the recent discovery of a dual system for 5-HT synthesis in the brain (TPH2) and periphery (TPH1) has renewed interest in studying the potential functions played by 5-HT in nonnervous tissues. Moreover, characterization of the TPH1 knockout mouse model (TPH1(-/-)) led to the identification of unsuspected roles for peripheral 5-HT, revealing the importance of this monoamine in regulating key physiological functions outside the brain. Here, we present in vivo data showing that mice deficient in peripheral 5-HT display morphological and cellular features of ineffective erythropoiesis. The central event occurs in the bone marrow where the absence of 5-HT hampers progression of erythroid precursors expressing 5-HT(2A) and 5-HT(2B) receptors toward terminal differentiation. In addition, red blood cells from 5-HT-deficient mice are more sensitive to macrophage phagocytosis and have a shortened in vivo half-life. The combination of these two defects causes TPH1(-/-) animals to develop a phenotype of macrocytic anemia. Direct evidence for a 5-HT effect on erythroid precursors is provided by supplementation of the culture medium with 5-HT that increases the proliferative capacity of both 5-HT-deficient and normal cells. Our thorough analysis of TPH1(-/-) mice provides a unique model of morphological and functional aberrations of erythropoiesis and identifies 5-HT as a key factor for red blood cell production and survival.

The amphetamine derivative 3,4-methylenedioxymethamphetamine (MDMA, ecstasy) reverses dopamine and serotonin transporters to produce efflux of dopamine and serotonin, respectively, in regions of the brain that have been implicated in reward. However, the role of serotonin/dopamine interactions in the behavioral effects of MDMA remains unclear. We previously showed that MDMA-induced locomotion, serotonin and dopamine release are 5-HT(2B) receptor-dependent. The aim of the present study was to determine the contribution of serotonin and 5-HT(2B) receptors to the reinforcing properties of MDMA.We show here that 5-HT(2B) (-/-) mice do not exhibit behavioral sensitization or conditioned place preference following MDMA (10 mg/kg) injections. In addition, MDMA-induced reinstatement of conditioned place preference after extinction and locomotor sensitization development are each abolished by a 5-HT(2B) receptor antagonist (RS127445) in wild type mice. Accordingly, MDMA-induced dopamine D1 receptor-dependent phosphorylation of extracellular regulated kinase in nucleus accumbens is abolished in mice lacking functional 5-HT(2B) receptors. Nevertheless, high doses (30 mg/kg) of MDMA induce dopamine-dependent but serotonin and 5-HT(2B) receptor-independent behavioral effects.These results underpin the importance of 5-HT(2B) receptors in the reinforcing properties of MDMA and illustrate the importance of dose-dependent effects of MDMA on serotonin/dopamine interactions.

The "club drug" 3,4-methylenedioxymethamphetamine (MDMA; also known as ecstasy) binds preferentially to and reverses the activity of the serotonin transporter, causing release of serotonin [5-hydroxytryptamine (5-HT)] stores from nerve terminals. Subsequent activation of postsynaptic 5-HT receptors by released 5-HT has been shown to be critical for the unique psychostimulatory effects of MDMA. In contrast, the effects of direct activation of presynaptic and/or postsynaptic receptors by MDMA have received far less attention, despite the agonist actions of the drug itself at 5-HT(2) receptors, in particular the 5-HT(2B) receptor. Here we show that acute pharmacological inhibition or genetic ablation of the 5-HT(2B) receptor in mice completely abolishes MDMA-induced hyperlocomotion and 5-HT release in nucleus accumbens and ventral tegmental area. Furthermore, the 5-HT(2B) receptor dependence of MDMA-stimulated release of endogenous 5-HT from superfused midbrain synaptosomes suggests that 5-HT(2B) receptors act, unlike any other 5-HT receptor, presynaptically to affect MDMA-stimulated 5-HT release. Thus, our findings reveal a novel regulatory component in the actions of MDMA and represent the first demonstration that 5-HT(2B) receptors play an important role in the brain, i.e., modulation of 5-HT release. As such, 5-HT(2B) receptor antagonists may serve as promising therapeutic drugs for MDMA abuse.

Compelling evidence suggests that serotonin (5-HT) is necessary for the refined organization of the cerebral cortex. Here we sought to analyse the short- and long-term consequences of embryonic 5-HT depletion on the development of the cerebral neocortex of the rat. We focused on the migration and differentiation of the pyramidal (projection) and nonpyramidal (interneuron) neuronal populations. Our paradigm used daily injection of DL-P-chlorophenylalanine (PCPA), a reversible inhibitor of 5-HT synthesis, during the E12-17 stage of embryonic development, when major events in corticogenesis take place. We monitored the 5-HT depletion induced by this treatment and showed that it led to subtle alterations in both the pyramidal and nonpyramidal neuronal populations. We found that E12-17 PCPA treatment altered the maturation of pyramidal neurons of layers III and V of the somatosensory cortex, with these cells displaying reduced dendritic arborization and complexity. These long-lasting alterations were not associated with modification of cortical BDNF levels at postnatal stages. We also showed that PCPA treatment transiently altered the incorporation in the cortical plate of interneurons derived from the caudal ganglionic eminence, and persistently affected the differentiation of a subpopulation expressing calretinin and/or cholecystokinin.

Serotonin 5-HT(2B) receptors are often coexpressed with 5-HT(1B) receptors, and cross-talk between the two receptors has been reported in various cell types. However, many mechanistic details underlying 5-HT(1B) and 5-HT(2B) receptor cross-talk have not been elucidated. We hypothesized that 5-HT(2B) and 5-HT(1B) receptors each affect the others' signaling by modulating the others' trafficking. We thus examined the agonist stimulated internalization kinetics of fluorescent protein-tagged 5-HT(2B) and 5-HT(1B) receptors when expressed alone and upon coexpression in LMTK(-) murine fibroblasts. Time-lapse confocal microscopy and whole-cell radioligand binding analyses revealed that, when expressed alone, 5-HT(2B) and 5-HT(1B) receptors displayed distinct half-lives. Upon coexpression, serotonin-induced internalization of 5-HT(2B) receptors was accelerated 5-fold and was insensitive to a 5-HT(2B) receptor antagonist. In this context, 5-HT(2B) receptors did internalize in response to a 5-HT(1B) receptor agonist. In contrast, co-expression did not render 5-HT(1B) receptor internalization sensitive to a 5-HT(2B) receptor agonist. The altered internalization kinetics of both receptors upon coexpression was probably not due to direct interaction because only low levels of colocalization were observed. Antibody knockdown experiments revealed that internalization of 5-HT(1B) receptors (expressed alone) was entirely clathrin-independent and Caveolin1-dependent, whereas that of 5-HT(2B) receptors (expressed alone) was Caveolin1-independent and clathrin-dependent. Upon coexpression, serotonin-induced 5-HT(2B) receptor internalization became partially Caveolin1-dependent, and serotonin-induced 5-HT(1B) receptor internalization became entirely Caveolin1-independent in a protein kinase Cepsilon-dependent fashion. In conclusion, these data demonstrate that coexpression of 5-HT(1B) and 5-HT(2B) receptors influences the internalization pathways and kinetics of both receptors.

A correlation between high plasma serotonin levels and total pulmonary resistance was reported in more than 80% of pulmonary hypertensive patients. When submitted to chronic hypoxia (10% O(2) for more than 3 weeks), wild-type mice develop lung vascular remodeling and pulmonary hypertension. We previously reported that, in contrast, the development of these hypoxia-dependent alterations is totally abolished in mice with permanent (genetic) or transient (pharmacologic) inactivation of the serotonin 5-hydroxytryptamine (5-HT)(2B) receptor. In the present study, we asked whether 5-HT(2B) receptors could be involved in the control of plasma serotonin levels. Further investigating the chronic hypoxic mouse model of pulmonary hypertension, we first show that in wild-type mice, plasma serotonin levels and 5-HT(2B) receptors expression were significantly increased after chronic exposure to hypoxia. This increase appeared before significant changes in remodeling factors could be detected and persisted when the pathology was established. Conversely, in mice with either genetically or pharmacologically inactive 5-HT(2B) receptors, plasma serotonin levels were not modified by chronic hypoxia. We then confirmed that 5-HT(2B) receptors can control plasma serotonin levels by providing in vivo evidence that an acute agonist stimulation of 5-HT(2B) receptor triggers a transient increase in plasma serotonin that is serotonin transporter dependent and blocked by 5-HT(2B) receptor-selective antagonist or genetic ablation. Our data support the notion that a 5-HT(2B) receptor-dependent regulation of serotonin uptake is implicated in the control of plasma serotonin levels.

Although compelling evidence has shown that obsessive-compulsive disorder (OCD) has a strong genetic component, its genetic basis remains to be elucidated. Identifying biological abnormalities in nonaffected relatives is one of the strategies advocated to isolate genetic vulnerability factors in complex disorders. Since peripheral serotonergic disturbances are frequently observed in OCD patients, the aim of this study was to investigate if they could represent endophenotypes, by searching for similar abnormalities in the unaffected parents of OCD patients. We assessed whole blood serotonin (5-HT) concentration, platelet 5-HT transporter (5-HTT) and 5-HT2A receptor-binding characteristics, and platelet inositol trisphosphate (IP3) content in a sample of OCD probands (n = 48) and their unaffected parents (n = 65), and compared them with sex- and age-matched controls (n = 113). Lower whole blood 5-HT concentration, fewer platelet 5-HTT-binding sites, and higher platelet IP3 content were found in OCD probands and their unaffected parents compared to controls. Whole blood 5-HT concentration showed a strong correlation within families (p < 0.001). The only parameter that appeared to discriminate affected and unaffected subjects was 5-HT2A receptor-binding characteristics, with increased receptor number and affinity in parents and no change in OCD probands. The presence of peripheral serotonergic abnormalities in OCD patients and their unaffected parents supports a familial origin of these disturbances. These alterations may serve as endophenotypic markers in OCD, and could contribute to the study of the biological mechanisms and genetic underpinnings of the disorder.

A case of pulmonary arterial hypertension in a patient with type-Ia glycogen-storage disease, a rare autosomal recessive disorder caused by a deficiency of glucose-6-phosphatase is reported in this study. It has been suggested that the occurrence of pulmonary arterial hypertension in type-Ia glycogen-storage disease could be due to an abnormal production of vasoconstrictive amines such as serotonin. To test this hypothesis, plasma serotonin concentrations were prospectively measured in 13 patients with type-Ia glycogen-storage disease, one patient with severe pulmonary hypertension and type-Ia glycogen-storage disease, 16 patients displaying severe pulmonary arterial hypertension, and 26 normal healthy controls. Elevated plasma serotonin concentrations were found in patients with either severe pulmonary arterial hypertension (38.8+/-7.3 nmol x L(-1)) or type-Ia glycogen-storage disease (36.8+/-11.5 nmol x L(-1)), as compared with controls (8.8+/-0.6 nmol x L(-1), p<0.001). Plasma serotonin was dramatically elevated in the patient with type-Ia glycogen-storage disease and pulmonary arterial hypertension (113.4 nmol x L(-1)). It is concluded that type-Ia glycogen-storage disease may be another condition in which abnormal handling of serotonin is one event in a multistep process leading to severe pulmonary arterial hypertension.

Elevated plasma serotonin is associated with primary pulmonary hypertension (PPH). To test whether this elevation could be related to platelet activation, the 2 pools of blood serotonin (platelets and plasma) and plasma 5-hydroxyindoleacetic acid (5-HIAA) as well as markers of platelet activation (alpha(IIb)beta(3), CD36, P-selectin, and CD63 membrane epitopes) were measured in 16 patients with severe PPH (group 1) before and at days 10 and 40 of treatment with a continuous infusion of epoprostenol (prostacyclin). The same biological parameters were also measured in 19 healthy subjects (group 2) and in 10 patients after cardiovascular surgery with extracorporeal circulation (group 3), a condition known to profoundly activate the platelets. Twelve PPH patients showed hemodynamic and clinical improvement, 3 remained stable, and 1 had the treatment stopped because of clinical aggravation. At day 0, mean plasma serotonin (5-hydroxytryptamine [5-HT]) concentration was much higher in PPH patients than in normal subjects (34.4+/-21.2 versus 9.1+/-6.0 nmol/L, respectively; P:<0.001) and positively correlated with total pulmonary resistance. The mean platelet 5-HT content was not significantly different in PPH compared with normal individuals. Mean plasma 5-HIAA concentrations were much higher in PPH than in normal patients (162+/-57 versus 61+/-7 nmol/L, respectively; P<0.001). These parameters did not significantly change during epoprostenol treatment. There was no correlation between the changes in plasma 5-HT during treatment and clinical or hemodynamic improvement. In PPH patients, the mean platelet volume significantly decreased (ANOVA, P<0.01) during treatment. Positive correlations were evidenced between the size of platelets and the number of alpha(IIb)beta(3) and CD36 epitopes. When compared with control platelets, the number of alpha(IIb)beta(3) epitopes detected on PPH platelets at day 0 tended to be higher, but this difference did not reach a statistical significance (41 300+/-7140 for PPH patients versus 36 010+/-3930 for control subjects, P=0.069). The number of CD36 epitopes, in the range of controls at day 0 (11 590+/-5080 for PPH patients versus 11 900+/-1790 for control subjects), decreased during treatment (ANOVA, P=0.038) and became significantly low at day 40 (8660+/-3520, P<0.001). The number of CD63 epitopes was not elevated, and P-selectin was never detected at any time point on PPH platelets. This glycoprotein profile indicates that the platelets of PPH patients were not highly activated but had an accelerated turnover and returned to normal under epoprostenol treatment without change of the elevated plasma serotonin, characteristic of PPH. In conclusion, neither platelet activation nor a significant alteration of the 5-HT endothelial metabolism explains the high level of plasma 5-HT in PPH patients. The 5-HT plasma concentration is not a predictive marker of the severity of PPH, and its evolution is independent of the clinical and hemodynamic status. Treatment by a potent antiaggregating agent, epoprostenol, does not affect the increase of plasma 5-HT, despite a therapeutic benefit.

Nerve fibres and mast cells are often described in close morphological and functional interactions in various organs such as the dura mater. The respective roles of mast cell activation and sympathetic impairment in cluster headache and migraine attacks have been repeatedly suggested. We have thus investigated the long-term effects of sympathectomy on mast cell morphology and content in the rat dura mater. Fifteen to 60 days after either sham, unilateral or bilateral superior cervical ganglionectomy, dura were removed for either histochemical or biochemical analysis. In the first case, they were fixed and mast cell heparin was stained by fluorescein isothiocyanate-conjugated avidin. Microscopic examination was followed by digital acquisitions using a tomographic process to assess mast cell density in the whole depth of the dura mater. Unilateral ganglionectomy induced a progressive and significant increase in mast cell density 15-60 days post-surgery in contralateral hemi-dura and 30 days post-surgery in ipsilateral hemi-dura. This increase was significant in both dura 60 days after bilateral ganglionectomy. Following perfusion with saline, we also examined the content of histamine and serotonin, pre-formed amines stored in mast cell granules. Biochemical analysis of dura serotonin and histamine content using high-pressure liquid chromatography and radioenzymatic assays, respectively, revealed under all conditions a serotonin tissue concentration lower than that of histamine. After sham ganglionectomy, the dura serotonin content increased from 15 to 60 days post-surgery, whereas the histamine content remained stable over the same period. After unilateral ganglionectomy, the histamine content increased progressively and significantly 30-60 days post-surgery in both hemi-dura, whereas the serotonin content became significantly different from that of sham only 60 days post-surgery in the ipsilateral dura. After bilateral ganglionectomy, the histamine level significantly increased in both hemi-dura 15-60 days post-surgery, whereas the serotonin level had significantly increased at 60 days post-surgery. These results clearly demonstrate, for the first time, a long-term trophic effect of sympathetic nerve degeneration on mast cells in the dura mater. Since mast cell activation has been described previously on the painful side of cluster headache patients during attack periods, we propose that the sympathetic impairment reported in these patients could be prominent, directly or indirectly inducing mast cell hyperplasia and changes in amine contents in the tissue concerned.

Autonomic and sensory nerves frequently contact mast cells contained in rabbit leptomeningeal arteries. We have previously shown that parasympathetic and peptidergic neurotransmitters can stimulate mast cell granule exocytosis and serotonin (5-HT) release. In the present study, we examined ex vivo the possible action of the main sympathetic neurotransmitter, norepinephrine (NE), on this exocytotic process. NE, which had no effect on mast cell 5-HT content per se, totally inhibited carbachol-induced 5-HT release and partially reduced neuropeptide-induced 5-HT release. Pretreatment with the alpha 1-adrenergic blocker did not affect the inhibitory effect of NE. Pretreatment with specific beta 1- or beta 2-adrenergic blockers antagonized this action, but the beta 2-blocker exerts a more specific dose-dependent antagonism. Together with our previous data, these results indicate that the equilibrium between autonomic and sensory nerves may determine the release of 5-HT from mast cells (parasympathetic and sensory nerves can trigger exocytosis while the sympathetics can inhibit it). Such a mechanism could be implicated in pathophysiological events in which autonomic dysfunction is likely to be involved, such as vascular headache or other phenomena involving inflammation.

The family of serotonin 5-HT2 receptors stimulates the phospholipase C second messenger pathway via the alpha subunit of the Gq GTP-binding protein. Here, we show that agonist stimulation of the 5-HT2B receptor subtype stably expressed in the mouse fibroblast LMTK- cell line causes a rapid and transient activation of the proto-oncogene product p21ras as measured by an increase in GTP-bound Ras in response to serotonin. Furthermore, 5-HT2B receptor stimulation activates p42mapk/p44mapk (ERK2/ERK1) mitogen-activated protein kinases as assayed by phosphorylation of myelin basic protein. Antibodies against p21ras, Galphaq, -beta, or -gamma2 subunits of the GTP-binding protein inhibit MAP kinase-dependent phosphorylation. The MAP kinase activation is correlated with a stimulation of cell division by serotonin. In addition to this mitogenic action, transforming activity of serotonin is mediated by the 5-HT2B receptor since its expression in LMTK- cells is absolutely required for foci formation and for these foci to form tumors in nude mice. Finally, we detected expression of the 5-HT2B receptor in spontaneous human and Mastomys natalensis carcinoid tumors and, similar to the 5-HT2B receptor transfected cells, the Mastomys tumor cells are also responsive to serotonin with similar coupling to p21ras activation.

Rabbit leptomeningeal arteries contain granular cells resembling mast cells that frequently contact autonomic and sensory nerve profiles. In the present in vitro study, we determined whether these cells could be stimulated by substance P (SP) and calcitonin gene-related peptide (CGRP), which are stored and released by sensory C fibers. Immunohistochemistry of the middle cerebral artery showed that 5-HT was stored only in mast cell-like granules. This pool of 5-HT decreased in a dose-dependent manner when exogenous SP and CGRP were added to the incubation solution or when endogenous neuropeptides were released from nerve terminals by capsaicin. The simultaneous administration of CGRP and SP induced a dramatic exocytosis and a 5-HT release significantly greater than the sum of the individual effects of the two neuropeptides. We conclude that, as in classical connective tissue mast cells, the amine content of these granular cells can be released by a degranulation process induced by neuropeptides. The effects of capsaicin suggest that this phenomenon can be triggered by axon reflex of C fibers. The data also provide the first evidence of a synergistic action of SP and CGRP on mast cell degranulation.

Serotoninergic mechanisms are thought to play a role in portal hypertension. Because this biomine is metabolized by the liver, peripheral blood and plasma levels of 5-hydroxytryptamine and 5-hydroxyindole acetic acid (the main metabolite of 5-hydroxytryptamine) were measured in 30 patients with cirrhosis. Whole-blood 5-hydroxytryptamine levels were significantly lower in patients with cirrhosis (158 +/- 28 nM) than in age-matched controls (332 +/- 19 nM), and no correlation was found between these levels and the severity of cirrhosis. Unconjugated plasma 5-hydroxytryptamine levels, an indication of the active form of 5-hydroxytryptamine, were significantly higher in patients with cirrhosis than in controls (6.8 +/- 1.7 nM and 3.4 +/- 0.5 nM, respectively), and in patients with cirrhosis these levels were higher in Pugh grade A than in Pugh grade C patients. Conjugated-plasma 5-hydroxytryptamine levels were not significantly different between patients with cirrhosis (32.2 +/- 8.1 nmol/L) and controls (16.4 +/- 1.4 nmol/L). Plasma 5-hydroxyindole acetic acid was significantly lower in patients with cirrhosis than in controls (1.5 +/- 0.1 nmol/L and 2.3 +/- 0.1 nmol/L, respectively). In conclusion, this study shows that serotoninergic mechanisms are altered in patients with cirrhosis.

Since its discovery, serotonin (5-hydroxytryptamine = 5-HT) has become a major player on the neurotransmitter "stage". Multiple receptor subtypes for 5-HT have been identified and classified, and a vast pharmacology of 5-HT has emerged. In particular, 5-HT has been shown to exert marked effects on the cardiovascular system, central nervous system (CNS) and gastrointestinal (GI) tract, and important ligands have been developed that mimic or block its action selectively. Furthermore, drugs that release 5-HT, and others that prevent its uptake, have been developed. This brief review focuses on the pharmacology of 5-HT agonists and antagonists that exhibit, at least partly, clinical relevance.

Neurochemical studies performed in vivo have suggested that serotonin-containing and -synthesizing nerves, originating in the raphe nuclei, directly innervate pial blood vessels. Nerve fibres of these vessels have been shown by immunocytochemistry to contain tryptophan hydroxylase (the rate-limiting enzyme of serotonin synthesis) but no serotonin. The present study examines this contradiction by measuring in vitro the tryptophan hydroxylase activity of rat cerebral vessels and femoral arteries (which also contain tryptophan hydroxylase-immunopositive nerves), and comparing them to the tryptophan hydroxylase activity of the rat pineal body, raphe nuclei and brain cortex under identical conditions. Oxygenated incubation solutions contained either [14C]- or "cold" L-tryptophan (2 x 10(-5) to 5 x 10(-4) M) and NSD-1015 (3-hydroxybenzylhydrazine) which inhibits the decarboxylation of 5-hydroxytryptophan, the second step of serotonin synthesis. Tissue fragments were incubated for 35-60 min. High-performance liquid chromatography (on tissue extracts and incubation solutions) as well as determination of 14C activity in the 5-hydroxytryptophan fraction of elution from tissue extracts showed that the pineal body, the raphe nuclei and cortical slices synthesize various amounts of 5-hydroxytryptophan under our experimental conditions. All these tissues contained serotonin. Femoral arteries, but not cerebral vessels, also contained small amounts of serotonin stored before incubation, probably in mast cells. In contrast to brain tissues, no measurable amounts of "cold" or [14C]5-hydroxytryptophan were found in cerebral blood vessel and femoral artery extracts or incubation solutions. Under identical experimental conditions, sympathetic nerves of both types of vessels were able to synthesize large amounts of L-DOPA when incubation solutions contained L-tyrosine instead of L-tryptophan.(ABSTRACT TRUNCATED AT 250 WORDS)

In infantile autism, the serotoninergic (5-HT) hypothesis is corroborated by biological dosages and therapeutic effects of fenfluramine which decrease blood serotonin. However other drugs, such as dopaminergic agonists or antagonists, have therapeutic effects. Therefore, we tested the hypothesis that two dopaminergic (DA) drugs have a similar 5-HT effect underlying the therapeutic efficiency. We evaluated in a randomized, double-blind and cross-over study, the effects of a DA agonist (bromocriptine) and a DA antagonist (amisulpride) on platelet 5-HT in infantile autism. The prolactinemia, reflecting the DA action, has been also measured. Nine children, aged from 4 to 13 years, according to the DSM III for infantile autism, received either drug in a random order during four weeks with an in-between placebo period of six weeks. The dosages of platelet 5-HT and serum prolactin were carried out at the beginning and at the end of every phase of treatment (active or placebo) with radioenzymology and radioimmunoassay methods respectively. The principal results on serum prolactin show neither order x treatment interaction, nor order effect but a significant treatment effect (p < 0.01): amisulpride increases serum prolactin whereas bromocriptine decreases according to the usual data. About platelet 5-HT, there is neither order x treatment interaction, nor treatment effect but a significant order effect (p < 0.01). Both drugs increase platelet 5-HT in the first phase of treatment. This order effect could be explained by a remanent effect of amisulpride after 6 wash-out weeks.(ABSTRACT TRUNCATED AT 250 WORDS)

Previously, we reported that rabbit cerebral arteries contain mast cells that frequently establish close contacts with parasympathetic-like nerve fibers. Here we have examined the possible function of this link by comparing the effects of carbachol and compound 48/80 on mast cell morphology and on the serotonin (5-HT) and histamine content of these arteries. In vivo, 2 micrograms/min of compound 48/80 or 1 micrograms/min of carbachol was infused for 30 min into one internal carotid artery of pentobarbital anesthetized rabbits, the contralateral artery being infused with vehicle. In vitro, the action of 10(-6) M carbachol was tested on isolated middle cerebral artery trees (MCAs) in the presence or absence of 10(-7) M atropine. The effects of carbachol were also tested in vitro on sympathectomized arteries. The 5-HT and histamine contents of all MCAs were measured by radioenzymatic assay, and fragments were prepared for electron microscopy. No histamine was detectable in any artery studied. The 5-HT content of arteries from control animals and those perfused with vehicle (in vivo) or incubated in the physiological solution (in vitro) was 250-300 pmol/mg protein. Both compound 48/80 and carbachol reduced this amount by approximately 50% and induced a marked degranulation of mast cells. Both secretion and degranulation were dramatically blocked in vitro by atropine. No difference in the 5-HT content was observed between intact and sympathectomized arteries under any condition. We conclude that a large proportion of rabbit cerebrovascular 5-HT is stored in mast cells and that cholinergic nerve activation could theoretically release this pool by acting on mast cell muscarinic receptors.

Significantly (p less than 0.001) decreased whole blood unconjugated serotonin levels were detected in AIDS patients as compared to patients with advanced cancers and to healthy individuals.

This preliminary study shows, for the first time to our knowledge, decreased whole blood serotonin levels in AIDS patients as compared to healthy controls and cancer patients. The lowest serotonin levels were found in AIDS patients with neuropsychiatric symptoms. Finally the present data suggest an inverse relationship between serotonin level and AIDS severity.

Primary pulmonary hypertension is a progressive and often fatal disorder in humans that results from an increase in pulmonary blood pressure associated with abnormal vascular proliferation. Dexfenfluramine increases the risk of pulmonary hypertension in humans, and its active metabolite is a selective serotonin 5-hydroxytryptamine 2B (5-HT[sub 2B]) receptor agonist. Thus, we investigated the contribution of the 5-HT[sub 2B] receptor to the pathogenesis of pulmonary hypertension. Using the chronic-hypoxic-mouse model of pulmonary hypertension, we found that the hypoxia-dependent increase in pulmonary blood pressure and lung remodeling are associated with an increase in vascular proliferation, elastase activity and transforming growth factor-β levels, and that these parameters are potentiated by dexfenfluramine treatment. In contrast, hypoxic mice with genetically or pharmacologically inactive 5-HT[sub 2B] receptors manifested no change in any of these parameters. In both humans and mice, pulmonary hypertension is associated with a substantial increase in 5-HT[sub 2B] receptor expression in pulmonary arteries. These data show that activation of 5-HT[sub 2B] receptors is a limiting step in the development of pulmonary hypertension. [ABSTRACT FROM AUTHOR]

Introduction: Notre objectif est de comprendre les mécanismes qui régulent le développement et la fonction des cellules β pour appréhender les places respectives des anomalies de masse et de fonction β dans l’étiologie du diabète de type 2. Nos travaux précédents ont montré que les glucocorticoïdes (GC) inhibent le développement des cellules β et que l’invalidation conditionnelle chez la souris du récepteur des GC (GR) dans les précurseurs pancréatiques (souris GR-Prec) aboutissait à un doublement de masse β. Le but de cette étude était de comprendre les mécanismes impliqués dans l’accroissement de cellules β. Matériels et méthodes: Nous avons étudié chez les souris GR-Prec et témoins adultes la tolérance au glucose sous régime normal ou hyperlipidique, mesuré la masse et la prolifération des cellules beta et défini le transcriptome des îlots par micropuces à ARN. Résultats: Les souris GR-Prec présentent une augmentation de la masse beta associée paradoxalement à une intolérance au glucose due à une altération de l’insulinosécrétion sous régime normal ou hyperlipidique. L’analyse du transcriptôme des îlots de souris GR-Prec a identifié les gènes Tph1 et 2 (Tryptophane hydroxylase), enzyme de synthèse de sérotonine, neurotransmetteur récemment impliqué dans la régulation de masse et fonction beta. Chez les souris GR-Prec, l’augmentation de Tph1 et 2 entraine une augmentation du contenu en sérotonine dans les îlots. L’absence de signalisation GC stimule donc le système sérotonine des cellules beta. À l’inverse, l’activation de la voie des GC dans des cellules beta in vitro diminue l’expression des gènes Tph1 et Tph2 et la synthèse de sérotonine et contre-régule la stimulation de sérotonine induite par la prolactine et l’exendine-4. Conclusion: Les GC sont des puissants inhibiteurs de la synthèse de sérotonine dans les cellules beta, suggérant que la sérotonine est un intermédiaire des effets des GC sur la masse et fonction beta. [Copyright &y& Elsevier]