Low Concentrations Of Serotonin Research Articles

Reproductive conditioning, spawning induction and early development of the estuarine Caribbean clam, Polymesoda arctata (Deshayes, 1854), under hatchery conditions

Polymesoda arctata is a Caribbean estuarine clam commercially important that currently is considered threatened. The reproductive conditioning, spawning and early development were evaluated under laboratory conditions using organisms collected in the lagoon system of Ciénaga Grande de Santa Marta (Colombian Caribbean) between December 2020 and May 2021. Two reproductive conditioning experiments were conducted over 7 weeks, examining the frequency of mature animals in the natural environment (controls) and in the laboratory under two water temperatures (26 and 29 °C) and different salinity regimes (constant at 5 and 15 ppt, increasing from 5 to 15 ppt, and decreasing from 15 to 5 ppt). One spawning experiment was done, comparing the spawning response of adult clams exposed to various stimuli (changes in water temperature and salinity, flow of seawater irradiated with UV light, addition of a high concentration of food and sperm to the water, as well as injections of serotonin and KCl into the foot and/or adductor muscle). Higher frequencies of mature clams were observed after 2 to 5 weeks of reproductive conditioning at a low temperature (26 °C) and under a constant salinity regime (at 5 or 15 ppt). Higher percentages of spawning and post-stimulation survival as well as spawning response speed were observed in specimens injected in the foot with a low concentration of serotonin (0.4 mL at 20 μM). The time of spawning response onset was shorter in males than in females. The fecundity increased with the live weight of the females, showing an average value of 3.4 × 106 oocytes per female. The early development of the estuarine clam from oocyte to juvenile stage was described in detail. The growth rates of larvae and spat were relatively high but their survival values were low, showing the need for additional research on the larval and post-larval rearing.

Changes in Tryptophan Hydroxylase 2 and 5HT1A Receptor Density May Contribute to Developmental Variation in Response to Serotonin in the in vitro Bullfrog Brainstem

Bullfrog, Lithobates catesbeiana, is a vertebrate animal model that can be used to study toxicology and developmental physiology. Our research is focused on better understanding vulnerability to brainstem respiratory centers in the pathology of sudden infant death syndrome (SIDS). We propose that a link between nicotine exposure during development leads to changes in the serotonergic signaling cascades of respiratory coordinating neurons. Caudal raphe neurons send serotonergic fibers that arborize and terminate directly on or near respiratory neurons in the brainstem. In bullfrogs, serotonin elicits a developmentally dependent effect on respiratory motor output. Late metamorphic tadpoles demonstrate an increase in lung burst activity with exposure to low concentrations of serotonin (≤ 0.5μM 5-hydroxytryptamine; 5-HT) mediated in part by 5-HT1a receptor (5HT1aR) activation. This developmental change in activity may be due to changes in the number of serotonergic fibers and/or 5-HT1a receptor density. Using the NIH Basic Local Alignment Search Tool (BLAST) we compared human and bullfrog 5HT1aR and tryptophan hydroxylase 2 (TH2) protein sequences and found a 34 and 65 percent identity match respectively. Quantitative western blot analysis of both proteins indicates developmental shifts in the serotonergic network during metamorphosis. These results were supported by immunohistochemical staining of 5HT1aR and TH2 in caudal raphe containing brainstem sections from pre-metamorphic tadpoles and post-metamorphic frogs. Impairments in the maturation of this serotonergic network may underlie the toxidrome associated with developmental nicotine exposure and further support the increased risk of SIDS following that exposure. This research was supported by the University of Wisconsin- La Crosse (UWL) through support from the UWL College of Science and Health, two UWL Undergraduate Research Creative Grants and a UWL FY23/24 Faculty Research Grant. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Unsubstantiated use of Selective serotonin reuptake inhibitors as an alternative for the treatment of depression

Unsubstantiated use of Selective serotonin reuptake inhibitors as an alternative for the treatment of depression

Chronic-Exposure Low-Frequency Magnetic Fields (Magnetotherapy and Magnetic Stimulation) Influence Serum Serotonin Concentrations in Patients with Low Back Pain-Clinical Observation Study.

(1) Background: The influence of serotonin on many regulatory mechanisms has not been sufficiently studied. The use of a physical method, assuming the possibility of its action on increasing the concentration of serotonin, may be the direction of therapy limiting the number of antidepressants used. The aim of the research was to study the effects of low-frequency magnetic fields of different characteristics on the circadian profile of serotonin in men with low back pain. (2) Methods: 16 men with back pain syndrome participated in the study. The patients were divided into two groups. In group 1, magnetotherapy (2.9 mT, 40 Hz, square wave, bipolar) was applied at 10.00 a.m. In group 2, the M2P2 magnetic stimulation program of the Viofor JPS device was used. Treatments in each group lasted 3 weeks, 5 days each, with breaks for Saturday and Sunday. The daily serotonin profile was determined the day before the exposure and the day after the last treatment. Blood samples (at night with red light) were collected at 8:00, 12:00, 16:00, 24:00, and 4:00. The patients did not suffer from any chronic or acute disease and were not taking any medications. (3) Results: In group 1, a significant increase in serotonin concentration was observed after 15 treatments at 4:00. In group 2, a significant increase in serotonin concentration was observed at 8:00 after the end of the treatments. In comparison between magnetotherapy and magnetic stimulation, the time points at which differences appeared after the application of serotonin occurred due to the increase in its concentrations after the application of magnetic stimulation. (4) Conclusions: Magnetotherapy and magnetic stimulation, acting in a similar way, increase the concentration of serotonin. Weak magnetic fields work similarly to the stronger ones used in TMS. It is possible to use them in the treatment of mental disorders or other diseases with low serotonin concentrations.

Neuroendocrine and Cardiovascular Activation During Aggressive Reactivity in Dogs.

Our aim was to investigate cardiovascular activation by measuring changes in facial and body surface temperature using infrared thermography, and neuroendocrine activation using salivary cortisol (CORT) and serotonin concentration (SER) in dogs exhibiting aggressive reactivity in real time. Based on two factors, owner-reported past aggressive behaviors, and detailed behavioral observations collected during a Socially Acceptable Behavior test consisting of 16 subtests and, each individual was categorized as aggressive or non-aggressive. CORT and SER showed no difference in neuroendocrine activity between dogs, but aggressive dogs with higher levels of aggression were found to have lower SER. Aggressive dogs also had an increase in facial temperature from pre-test values. The discovery of a correlation between tail wagging and left tail wagging with aggression level and aggression-related behaviors in aggressive dogs is further evidence of the right hemisphere specialization for aggression previously reported in the literature. This study provides the first evidence that both cardiovascular and neuroendocrine systems are activated during an active act of aggression in dogs.

Microglial activation and neurobiological alterations in experimental autoimmune prostatitis-induced depressive-like behavior in mice.

BackgroundPatients with chronic prostatitis/chronic pelvic pain syndrome (CP/CPPS) frequently show depressive symptoms clinically and increasing evidence indicates a correlation between CP/CPPS and depression. However, the underlying mechanisms of CP/CPPS-related depression remain poorly understood. Here, we sought to determine the role of hippocampal microglial activation and neurobiological changes in a mouse model of experimental autoimmune prostatitis (EAP)-induced depression and the treatment efficacy of Chinese herb extract baicalein.MethodsEAP was induced through intradermal injection of prostate antigen and adjuvant twice. Then, mice were assessed for affective behaviors in the open field test, elevated plus maze, forced swim test, and tail suspension test. The morphology and function of microglia and astrocytes were detected by immunofluorescence, Western blotting, and transmission electron microscopy. Proinflammatory mediators along with serotonin transporter (SLC6A4/SERT) and indoleamine 2,3-dioxygenase (IDO) were quantified with reverse transcription-polymerase chain reaction (RT‑PCR), and serum serotonin concentrations were measured by enzyme-linked immunosorbent assay (ELISA). Proton magnetic resonance spectroscopy (1H-MRS) was performed to measure hippocampal glutamate levels. In addition, baicalein was used in a subset of EAP mice to test its anti-depressant action.ResultsEAP was successfully established and induced depressive- and anxiety-like behavior in mice. Increasing levels of co-expressed ionized calcium-binding adapter molecule 1 (Iba1) and glial fibrillary acidic protein (GFAP) and ultrastructural observations suggested microglial activation and reactive astrocytosis in the hippocampus. These activated microglia resulted in increased expressions of multiple proinflammatory cytokines. Simultaneously, EAP mice showed higher gene expressions of SLC6A4 and IDO and lower concentrations of serotonin. 1H-MRS indicated a decrease in the glutamate + glutamine (Glx)/total creatine (tCr) ratio in EAP mice. Furthermore, baicalein treatment alleviated the depressive-like behavior and neuroinflammation by suppressing the nuclear factor-kappa B (NF-κB) pathway.ConclusionOur data indicate that EAP-induced depressive-like behavior is linked to microglia activation and subsequent neurotransmitter metabolism. Moreover, baicalein attenuates behavioral changes by inhibiting neuroinflammation via downregulation of the NF-κB pathway.

Mechanism of Spasmogenic Activity Stimulated by Aqueous Ethanolic Leaf Extract of Mucuna pruriens on Isolated Uterine Muscle of Albino Rats

Aims: To investigate the effect of aqueous ethanolic leaf extract of this medicinal plant on isolated uterine smooth muscle strips of the rat and to determine its mechanism of action.
 Study Design: Laboratory-experimental design was used in this study.
 Place and Duration of Study: The study was carried out in the Department of Veterinary Physiology and Biochemistry of Michael Okpara University of Agriculture, Umudike, Nigeria, Department of Pharmacology and Toxicology of the Faculty of Pharmacy, University of Nigeria, Nsukka, and the Department of Veterinary Physiology and Pharmacology, University of Nigeria, Nsukka, Nigeria between June and October 2014.
 Methodology: Fresh leaves of Mucuna pruriens were identified and collected by a taxonomist from Nsukka, Nigeria. The leaves were then air dried and pulverized into powder. This was then subjected to cold extraction using petroleum ether (70-90) and 70% aqueous ethanol, after which the extract was left to dry at room temperature. Estrogenised uterine strips (12mm) were harvested from non-pregnant, sexually matured albino rats (180 g -250 g) and suspended in a 35ml organ bath containing Krebs’ physiological salt solution. The organ bath was connected to an isometric electronic force displacement transducer and a physiograph. Drugs such as Salbutamol, Isoprenaline, Adrenaline, Propranolol, Atipamezole and Prazosin were used as either agonists or antagonists to determine the mechanism of action of the extract. Atropine sulphate and Cyproheptadine were also used as test drugs. Concentrations of these drugs presented in the body of this work represent the final nutrient bath concentrations.
 Results: M. pruriens caused a dose -dependent increase in uterine muscle contraction with an EC50 of 0.88 mg/ml, n=4. The contraction was unaffected by atropine sulphate (0.042 µmol), but abolished by salbutamol (0.012-0.4 µmol), isoprenaline (0.06-0.23 µmol), and adrenaline (16 nmol). The uterine muscle contractions were enhanced by propranolol (1 µmol) in a dose- dependent manner. Prazosin (0.069-0.14 µmol) and atipamezole (3.3-13.7 nmol) were unable to abolish contractions stimulated by the extract. However, 0.2 µmol of cyproheptadine caused 80% suppression of the extract –induced uterine contraction
 Conclusion: It is concluded that aqueous ethanolic leaf extract of M. pruriens, has ability to cause uterine smooth muscle contraction hence, justifies its reported use traditionally as a uterine stimulant. This contraction is most likely exerted via the 5-HT receptor activation (activated by low concentrations of serotonin).

IL-18 Serum Levels and Variants of the Serotonin Transporter Gene Are Related to Awareness of Emotions in Healthy Subjects: A Preliminary Study

Objective: Interaction between the nervous and immune systems may influence emotions, ultimately affecting human health. Cytokines may play a role in developing emotional dysregulation as in alexithymia, a personality construct characterized by the subclinical inability to identify and describe emotions, often associated with several psychiatric and psychosomatic disorders. The proinflammatory cytokine IL-18, with a recognized role in brain functions, may influence serotonin metabolism and appears to be associated with alexithymia. Healthy individuals carrying the long allele (L) of the serotonin transporter gene polymorphic region (5-HTTLPR), and thus having lower concentrations of serotonin in the synaptic cleft, show a greater tendency toward alexithymia, with some gender differences. To explore a potential physiological interaction between IL-18, serotonin neurotransmission, and alexithymia, we investigated whether IL-18 serum levels and 5-HTTLPR are linked to alexithymic traits in healthy subjects. Methods: We measured IL-18 serum levels in 115 Italian-Caucasian healthy subjects genotyped for 5-HTTLPR allele variants, divided by gender and assessed for alexithymia scores using the 20-item Toronto Alexithymia Scale. Results: IL-18 levels are significantly more elevated in individuals with the LL genotype (n = 25) than in carriers of the short allele (n = 90, p = 0.0073). Specifically, in LL males (n = 11), i.e., the group with the most relevant increase in IL-18, cytokine values positively correlated with difficulty identifying feelings, which is a component of alexithymia (r = 0.634, p = 0.036). Conclusions: These results indicate a possible novel interaction between IL-18 and the serotoninergic system to mediate emotional unawareness, suggesting putative biological predictors of emotional dysregulation, which in turn can act as a risk factor for a variety of medical conditions in susceptible subjects.

Vitamin D Stimulates Serotonin Production via Induction of the Tryptophan Hydroxylase 2 Isoform in B14 Rat Medullary Neurons

The active form of vitamin D3, 1,25‐dihydroxyvitamin D (1,25D), and serotonin (5‐HT) are postulated to play significant roles in abnormal social behavior associated with psychological conditions including autism spectrum disorders (ASDs) and depression. Moreover, we have observed that 1,25D regulates synthesis of two isoforms of tryptophan hydroxylase (TPH), the rate‐limiting enzyme in the 5‐HT biosynthetic pathway, including induction of the tryptophan hydroxylase 2 (TPH2) gene in the central nervous system (CNS) and suppression of tryptophan hydroxylase 1 (TPH1) expression in some peripheral tissues. Interestingly, major characteristics associated with autism may include low concentrations of serotonin in the CNS and elevated levels of serotonin in the periphery. Thus, in addition to assessing the effect of 1,25D on TPH gene expression, we also examined, for the first time, the ability of 1,25D to stimulate production of 5‐HT in neuronal cells. Rat serotonergic medullary cells (RN46A‐B14; B‐14) were cultured to confluency and plated in six‐well plates. After allowing cells to attach in the plates overnight, the cells were cultured in differentiation medium, followed by treatment of differentiated B‐14 cells with ethanol vehicle or 10−8 M 1,25D. At time zero, a 200 μL sample of media from each well was collected to serve as a baseline for 5‐HT concentration. The cells were then incubated over the next three days, and additional 200 μL samples were collected from each well at the 24‐, 48‐ and 72‐hour time points. A 5‐HT ELISA assay was then conducted using the collected samples. The results of the ELISA revealed a statistically significant increase (57%, p < 0.05) in 5‐HT production following treatment with 1,25D for 24 hours versus vehicle, with subsequently larger percent‐increases in 5‐HT synthesis observed at 48 and 72 hours (64% and 103%, respectively, p < 0.05). These results suggest that 1,25D stimulates the production of serotonin, likely through the induction of the neuronal TPH2 gene, and the time‐course of this effect appears to lag behind the induction of TPH mRNA which peaks at 24 hours. In summary, this study illuminates a novel coordinated biochemical and regulatory interaction between two neuromodulators, vitamin D and serotonin, thereby identifying a potential connection between serum vitamin D levels and the occurrence of psychiatric disorders commonly linked to an imbalance in CNS serotonin production, including autism and depression.Support or Funding InformationThis project was funded by the New College of Interdisciplinary Arts and Sciences at Arizona State University and the National Institutes of Health.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Antidepressants are selective serotonin neuronal reuptake inhibitors: 40-year history

The paper presents historical prerequisites for designing antidepressants from a group of selective serotonin neuronal reuptake inhibitors (SSRIs): to determine a lower serotonin concentration in the different tissues of depressed patients; to establish a higher serotonin concentration in the treatment of depressed patients with tricyclic antidepressants, and to formulate the serotonergic theory of depression. It also provides a consecutive account of the history of clinical introduction of individual SSRI representatives, such as fluoxetine, zimelidine, fluvoxamine, indalpine, citalopram, sertraline, paroxetine, and escitalopram. There are data from the history of studying the mechanism of SSRI action: from the theory of the importance of an increase in the concentration of serotonin in the synaptic cleft to the current understanding of complex successive intracellular rearrangements at the level of the postsynaptic neuron. The history of studying the efficacy of SSRIs in treating depression is considered in detail. Emphasis is laid on the reasons for a paradoxical difference in the evaluations of the efficiency of therapy with SSRIs versus other groups of antidepressants at different developmental stages of psychopharmacology. The role of marketing technologies in disseminating the data on the efficacy of this or that group of antidepressants is described. The practical significance of differences in individual SSRI representatives (the potency of serotonin uptake inhibition; the degree of selectivity and activity against the serotonergic system; the likelihood of an unfavorable pharmacokinetic interaction with other drugs; the half-life of elimination; the quickness of achieving a therapeutic dose) is analyzed. Whether it is possible and reasonable to differentially choose different SSRI representatives in the treatment of depressions at the present stage is discussed. The authors state their belief that researches should be continued to specify the place of SSRIs among other groups of current antidepressants for the treatment of depressions.

Serotonin activates cell survival and apoptotic death responses in cultured epithelial thyroid cells.

Anatomic and physiological interactions between central serotonergic system and thyroid gland are well established. However, the effects of locally available serotonin on the thyroid functions are poorly known. Here, we first demonstrate the expression of serotonin transporter SERT and 5-HT2A receptor subtype in rat thyroid epithelial cell line FRT both at mRNA and protein levels. In order to investigate the molecular mechanisms of serotonin action, FRT cells were exposed to increasing concentrations of the amine. Low concentrations of serotonin (up to 5μM) enhanced FRT cell growth, and ERK1/2 and SMAD2/3 phosphorylation. Cell exposure to the selective 5-HT2A receptor agonist DOI recapitulated the effects of 5-HT on ERK1/2 phosphorylation. By contrast, administration of M100907, a specific 5-HT2A receptor inhibitor, prevented 5-HT induced ERK1/2 activation. On the other hand, high doses of serotonin (50μM up to 1mM) activated a caspase-3 mediated apoptosis of cells. Overall, our findings demonstrate that low levels of serotonin, interacting with 5-HT2A receptor, are able to activate proliferative signals in the thyroid epithelial cells, while high levels of serotonin cause pro-apoptotic responses, thus suggesting an active role of the amine in the thyroid functions and disorders.

Vitamin D hormone regulates serotonin synthesis. Part 1: relevance for autism

Serotonin and vitamin D have been proposed to play a role in autism; however, no causal mechanism has been established. Here, we present evidence that vitamin D hormone (calcitriol) activates the transcription of the serotonin-synthesizing gene tryptophan hydroxylase 2 (TPH2) in the brain at a vitamin D response element (VDRE) and represses the transcription of TPH1 in tissues outside the blood-brain barrier at a distinct VDRE. The proposed mechanism explains 4 major characteristics associated with autism: the low concentrations of serotonin in the brain and its elevated concentrations in tissues outside the blood-brain barrier; the low concentrations of the vitamin D hormone precursor 25-hydroxyvitamin D [25(OH)D3]; the high male prevalence of autism; and the presence of maternal antibodies against fetal brain tissue. Two peptide hormones, oxytocin and vasopressin, are also associated with autism and genes encoding the oxytocin-neurophysin I preproprotein, the oxytocin receptor, and the arginine vasopressin receptor contain VDREs for activation. Supplementation with vitamin D and tryptophan is a practical and affordable solution to help prevent autism and possibly ameliorate some symptoms of the disorder.

Psychopathological and peripheral levels of neurobiological correlates of obsessive–compulsive symptoms in patients with epilepsy: A hospital-based study

ObjectivesObsessive–compulsive symptoms (OCSs) and disorder (OCD) are often underdiagnosed in the out-patient epilepsy clinic. This work aimed at determining the risks and comorbidities (psychopathological and neurobiological correlates) of OCSs in treated adults with idiopathic epilepsy recruited from a university hospital. MethodsPsychiatric evaluation was done using DSM-IV (The Diagnostic and Statistical Manual of Mental Health Disorders). Obsessive–compulsive disorder was identified using the Mini International Neuropsychiatric Interview (MINI). The Beck Depression Inventory (BDI-II), Hamilton Anxiety Rating Scale (HAM-A), and Yale-Brown Obsessive Compulsive Scale (Y-BOCS) were used to determine the severity of the related psychiatric symptoms. ResultsOut of 474 patients screened, included in this study were 107 with no psychiatric symptoms and 188 with OCSs [classified as those with at least OCSs=93; mild OCSs=36; moderate, severe, and extreme OCSs=59]. A hundred healthy subjects were included as controls. Blood concentrations of serotonin, adrenaline, noradrenaline, and dopamine were measured. Compared with controls, patients with OCSs had higher frequencies of depression and anxiety. Low concentrations of serotonin, adrenaline, noradrenaline, and dopamine were reported regardless of the presence or the absence of psychiatric symptoms, OCS severities, and antiepileptic drug (AED)-related variables (dose and serum drug level). Significant correlations were identified between Y-BOCS, BDI-II, and HAM-A scores, age, age at onset, and concentrations of noradrenaline. ConclusionThis study indicates that a) OCSs are common in patients with epilepsy. Male sex, age, duration of illness, seizure focus, lateralization, and intractability to AEDs are its main risks; b) depression and anxiety are comorbid psychopathologies; and c) serotonin, catecholamines, and dopamine are linked to epilepsy-related variables and its comorbid psychopathies but not to its medications.

Serotonin in blood: Assessment of its origin by concomitant determination of β-thromboglobulin (platelets) and chromogranin A (enterochromaffin cells)

Background. Serotonin is produced in enterochromaffin (EC) cells, taken up and stored in platelets and released during platelet activation. Measurement of platelet-poor plasma serotonin is difficult, mainly due to platelet activation during blood sampling. We aimed to establish a method to assess the influence of platelet release upon platelet-poor plasma serotonin measurement by concomitant determination of serotonin, β-thromboglobulin (β-TG) and chromogranin A (CgA). Methods. Blood samples from patients with thrombocytosis, thrombocytopenia and small intestinal neuroendocrine (EC-cell) tumors (SI-NETs) as well as healthy volunteers were analyzed. We also measured serotonin in venous and arterial samples from patients undergoing coronary angiography to evaluate peripheral serotonin metabolism. Results. Serotonin and CgA were significantly higher in patients with SI-NETs compared to all other groups implying EC cell origin of serotonin in patients with SI-NETs. We found that the serotonin concentration was similar in patients with thrombocytosis and thrombocytopenia, whereas plasma β-TG was higher and lower respectively. A high EDTA concentration in the sampling tubes gave significantly lower serotonin concentrations. Serotonin concentrations did not differ between arterial and venous blood. Conclusions. Our methodology to measure platelet-poor plasma serotonin was appropriate. Blood platelet numbers did not affect the level of serotonin in contrast to β-TG.

Serotonin-enhanced hyperactivation of hamster sperm

The effects of serotonin on reproductive function were examined using hamster spermatozoa. When serotonin at concentrations from 1 fmol/l to 1 μmol/l was added to modified Tyrode's albumin lactate pyruvate (mTALP) medium, hyperactivation was significantly enhanced. Agonists and antagonists of 5-hydroxytryptamine hydrochloride (5-HT) receptors (5-HT(2) and 5-HT(4) receptors) were added to the medium. Both 5-HT(2) and 5-HT(4) receptor agonists significantly enhanced hyperactivation, although the effect was greater than the former. However, both 5-HT(2) and 5-HT(4) receptor antagonists significantly suppressed serotonin-enhanced hyperactivation, with the former suppressing stimulation by a lower concentration of serotonin than the latter. These results indicate that serotonin enhances hyperactivation via 5-HT(2) and/or 5-HT(4) receptors in a dose-dependent manner.

Automated mass spectrometric analysis of urinary and plasma serotonin

Serotonin emerges as crucial neurotransmitter and hormone in a growing number of different physiologic processes. Besides extensive serotonin production previously noted in patients with metastatic carcinoid tumors, serotonin now is implicated in liver cell regeneration and bone formation. The aim was to develop a rapid, sensitive, and highly selective automated on-line solid-phase extraction method coupled to high-performance liquid chromatography–tandem mass spectrometry (XLC-MS/MS) to quantify low serotonin concentrations in matrices such as platelet-poor plasma and urine. Fifty microliters plasma or 2.5 μL urine equivalent were pre-purified by automated on-line solid-phase extraction, using weak cation exchange. Chromatography of serotonin and its deuterated internal standard was performed with hydrophilic interaction chromatography. Mass spectrometric detection was operated in multiple reaction monitoring mode using a quadrupole tandem mass spectrometer with positive electrospray ionization. Serotonin concentrations were determined in platelet-poor plasma of metastatic carcinoid patients (n = 23) and healthy controls (n = 22). Urinary reference intervals were set by analyzing 24-h urine collections of 120 healthy subjects. Total run-time was 6 min. Intra- and inter-assay analytical variation were <10%. Linearity in the 0–7300 μmol/L calibration range was excellent (R2 > 0.99). Quantification limits were 30 and 0.9 nmol/L in urine and plasma, respectively. Platelet-poor serotonin concentrations in metastatic carcinoid patients were significantly higher than in controls. The urinary reference interval was 10–78 μmol/mol creatinine. Serotonin analysis with sensitive and specific XLC-MS/MS overcomes limitations of conventional HPLC. This enables accurate quantification of serotonin for both routine diagnostic procedures and research in serotonin-related disorders.

Chronic Fluoxetine Bidirectionally Modulates Potentiating Effects of Serotonin on the Hippocampal Mossy Fiber Synaptic Transmission

Selective serotonin reuptake inhibitors (SSRIs) have been used to treat various psychiatric disorders. Although the cellular mechanisms underlying amelioration of particular symptoms are mostly unknown, recent studies have shown critical importance of the dentate gyrus of the hippocampus in behavioral effects of SSRIs in rodents. Here, we show that serotonin potentiates synaptic transmission between mossy fibers, the sole output of the dentate granule cells, and CA3 pyramidal cells in mouse hippocampal slices. This potentiation is mediated by activation of 5-HT(4) receptors and intracellular cAMP elevation. A chronic treatment of mice with fluoxetine, a widely used SSRI, bidirectionally modulates the 5-HT-induced potentiation: Fluoxetine enhances the potentiation induced by lower concentrations of serotonin, while attenuates that by the higher concentration, which represents stabilization of synaptic 5-HT action. In contrast to the chronic treatment, an acute application of fluoxetine in slices induces a leftward shift in the dose-response curve of the 5-HT-induced potentiation. Thus, acute and chronic fluoxetine treatments have distinct effects on the serotonergic modulation of the mossy fiber synaptic transmission. Exposure of mice to novel environments induces increases in locomotor activity and hippocampal extracellular 5-HT levels. In mice chronically treated with fluoxetine, the novelty-induced hyperactivity is reduced without significant alterations in home cage activity and motor skills. Our results suggest that the chronic fluoxetine treatment can stabilize the serotonergic modulation of the central synaptic transmission, which may contribute to attenuation of hyperactive behaviors.

Serotonin localization and its functional significance during mouse preimplantation embryo development

Serotonin is a neurotransmitter functioning also as a hormone and growth factor. To further investigate the biological role of serotonin during embryo development, we analysed serotonin localization as well as the expression of specific serotonin 5-HT1D receptor mRNA in mouse oocytes and preimplantation embryos. The functional significance of serotonin during the preimplantation period was examined by studying the effects of serotonin on mouse embryo development. Embryo exposure to serotonin (1 microM) highly significantly reduced the mean cell number, whereas lower concentrations of serotonin (0.1 microM and 0.01 microM) had no significant effects on embryo cell numbers. In all serotonin-treated groups a significant increase in the number of embryos with apoptotic and secondary necrotic nuclei was observed. Expression of serotonin 5-HT1D receptor mRNA in mouse oocytes and preimplantation embryos was confirmed by in situ hybridization showing a clearly distinct punctate signal. Immunocytochemistry results revealed the localization of serotonin in oocytes and embryos to the blastocyst stage as diffuse punctate cytoplasmic labelling. It appears that endogenous and/or exogenous serotonin in preimplantation embryos could be involved in complex autocrine/paracrine regulations of embryo development and embryo-maternal interactions.

Effect of Nutritional Status and Ozone Exposure on Rat Brain Serotonin

Background Ozone is an environmental pollutant that has widely documented deleterious effects on exposed organisms. In Mexico City, this pollutant frequently reaches concentrations that surpass safe health limits. In addition, it has been reported that the prevalence of malnutrition remains high in our childhood population. This experiment was carried out to determine whether malnutrition is a factor contributing to an increase in the risk of damage associated with ozone exposure. Methods Using an experimental animal model, 21-day-old rats fed normally or with induced malnutrition were subchronically exposed to 0.5 ppm of ozone or fresh air, respectively, for 30 days. At the end of this period and using HPLC, serotonin concentrations were measured in four areas of the brain: cortex, hemispheres, cerebellum, and medulla oblongata. Results Malnourished animals had a significant weight deficit beginning at 28 days with respect to well-fed animals. Among the well-fed animals, this phenomenon is seen at 35 days in exposed and non-exposed animals. In the four regions of the brain, malnourished animals show low serotonin concentrations with respect to well-nourished animals. In the cerebellum, there was an interaction between the nutritional factor and ozone exposure, while in the medulla oblongata both factors acted independently. Conclusions Our results suggest a multiplicative effect from the nutritional factor and ozone exposure in the changes observed concerning serotonergic metabolism.

VMN dopaminergic graft and feeding pattern in obese Zucker rats.

To study the role of dopamine in the ventromedial hypothalamus (VMN) in the regulation of meal size and meal number during obesity. Embryonic mesencephalic cells rich in dopaminergic neurons from lean rats were grafted into the VMN of obese Zucker rats. Since food intake is the product of meal size and number, these variables were measured using a rat 'eater meter'. Dopamine and serotonin concentrations in the VMN were assayed in grafted and control rats via in vivo microdialysis and HPLC two months after transplantation. Food intake increased in grafted rats due to an increase of both meal size and meal number 2 weeks after implantation and to an increase of meal size with insufficient compensatory decrease of meal number 2 months after transplantation. Grafted rats showed higher absolute dopamine and lower serotonin concentrations in the VMN. It would appear that an increase of dopamine and a decrease of serotonin in the VMN of grafted obese rats may correlate with increase in meal number and meal size, respectively. Since obese Zucker rats usually display an enlarged meal size, we deduce from the data that chronically elevated VMN dopamine and low serotonin are involved in producing the large meal size observed during obesity.