Developmental role of tryptophan hydroxylase in the nervous system

Dorsal raphe nucleus to basolateral amygdala 5-HTergic neural circuit modulates restoration of consciousness during sevoflurane anesthesia

The advent of general anesthesia (GA) has significant implications for clinical practice. However, the exact mechanisms underlying GA-induced transitions in consciousness remain elusive. Given some similarities between GA and sleep, the sleep-arousal neural nuclei and circuits involved in sleep-arousal, including the 5-HTergic system, could be implicated in GA. Herein, we utilized pharmacology, optogenetics, chemogenetics, fiber photometry, and retrograde tracing to demonstrate that both endogenous and exogenous activation of the 5-HTergic neural circuit between the dorsal raphe nucleus (DR) and basolateral amygdala (BLA) promotes arousal and facilitates recovery of consciousness from sevoflurane anesthesia. Notably, the 5-HT1A receptor within this pathway holds a pivotal role. Our findings will be conducive to substantially expanding our comprehension of the neural circuit mechanisms underlying sevoflurane anesthesia and provide a potential target for modulating consciousness, ultimately leading to a reduction in anesthetic dose requirements and side effects.

BH4 as a Therapeutic Target for ADHD: Relevance to Neurotransmitters and Stress-Driven Symptoms

Tetrahydrobiopterin (BH4) is a critical cofactor in a variety of metabolic pathways that have been linked to ADHD. There have been no previous studies utilizing BH4 as a supplement for ADHD. BH4 has been approved as a treatment for phenylketonuria (PKU). Individuals with PKU and ADHD appear to have low DA levels in common, suggesting that the hypodopaminergic state seen in both illnesses could be a relationship between the two. Clinical research involving supplementation of BH4 has shown low occurrence of adverse. In experiments, BH4 has also been found to have good blood-brain barrier permeability. BH4 also has the ability in scavenging ROS activity, which is an implication of stress and is seen in ADHD. BH4's significance in ADHD is reviewed in this paper because of its involvement in numerous neurodevelopmental metabolic pathways, and we anticipate that exogenous BH4 can be used to treat ADHD.

A mouse model of the 3-hit effects of stress: Genotype controls the effects of life adversities in females

Helplessness is a dysfunctional coping response to stressors associated with different psychiatric conditions. The present study tested the hypothesis that early and adult adversities cumulate to produce helplessness depending on the genotype (3-hit hypothesis of psychopathology). To this aim, we evaluated whether Chronic Unpredictable Stress (CUS) differently affected coping and mesoaccumbens dopamine (DA) responses to stress challenge by adult mice of the C57BL/6J (B6) and DBA/2J (D2) inbred strains depending on early life experience (Repeated Cross Fostering, RCF). Three weeks of CUS increased the helplessness expressed in the Forced Swimming Test (FST) and the Tail Suspension Test by RCF-exposed female mice of the D2 strain. Moreover, female D2 mice with both RCF and CUS experiences showed inhibition of the stress-induced extracellular DA outflow in the Nucleus Accumbens, as measured by in vivo microdialysis, during and after FST. RCF-exposed B6 mice, instead, showed reduced helplessness and increased mesoaccumbens DA release. The present results support genotype-dependent additive effects of early experiences and adult adversities on behavioral and neural responses to stress by female mice. To our knowledge, this is the first report of a 3-hit effect in an animal model. Finally, the comparative analyses of behavioral and neural phenotypes expressed by B6 and D2 mice suggest some translationally relevant hypotheses of genetic risk factors for psychiatric disorders.

Metabolic changes during larval-pupal metamorphosis of Helicoverpa armigera

Energy metabolism is essential for insect metamorphosis. The accumulation and utilization of energy is still not completely clear during larval-pupal metamorphosis of holometabolous insects. We used metabolome and transcriptome analysis to reveal key metabolic changes in the fat body and plasma and the underlying metabolic regulation mechanism of Helicoverpa armigera, an important global agricultural insect pest, during larval-pupal metamorphosis. During the feeding stage, activation of aerobic glycolysis provided intermediate metabolites and energy for cell proliferation and lipid synthesis. During the non-feeding stages (the initiation of the wandering stage and the prepupal stage), aerobic glycolysis was suppressed, while, triglyceride degradation was activated in the fat body. The blocking of metabolic pathways in the fat body was probably caused by 20-hydroxyecdysone-induced cell apoptosis. 20-hydroxyecdysone cooperated with carnitine to promote the degradation of triglycerides and the accumulation of acylcarnitines in the hemolymph, allowing rapid transportation and supply of lipids from the fat body to other organs, which provided a valuable reference for revealing the metabolic regulation mechanism of lepidopteran larvae during the last instar. Carnitine and acylcarnitines are first reported to be key factors that mediate the degradation and utilization of lipids during larval-pupal metamorphosis of lepidopteran insects.

The Role of Pharmacogenetics in Personalizing the Antidepressant and Anxiolytic Therapy

Pharmacotherapy for neuropsychiatric disorders, such as anxiety and depression, has been characterized by significant inter-individual variability in drug response and the development of side effects. Pharmacogenetics, as a key part of personalized medicine, aims to optimize therapy according to a patient's individual genetic signature by targeting genetic variations involved in pharmacokinetic or pharmacodynamic processes. Pharmacokinetic variability refers to variations in a drug's absorption, distribution, metabolism, and elimination, whereas pharmacodynamic variability results from variable interactions of an active drug with its target molecules. Pharmacogenetic research on depression and anxiety has focused on genetic polymorphisms affecting metabolizing cytochrome P450 (CYP) and uridine 5'-diphospho-glucuronosyltransferase (UGT) enzymes, P-glycoprotein ATP-binding cassette (ABC) transporters, and monoamine and γ-aminobutyric acid (GABA) metabolic enzymes, transporters, and receptors. Recent pharmacogenetic studies have revealed that more efficient and safer treatments with antidepressants and anxiolytics could be achieved through genotype-guided decisions. However, because pharmacogenetics cannot explain all observed heritable variations in drug response, an emerging field of pharmacoepigenetics investigates how epigenetic mechanisms, which modify gene expression without altering the genetic code, might influence individual responses to drugs. By understanding the epi(genetic) variability of a patient's response to pharmacotherapy, clinicians could select more effective drugs while minimizing the likelihood of adverse reactions and therefore improve the quality of treatment.

Development of the Placenta and Brain Are Affected by Selective Serotonin Reuptake Inhibitor Exposure During Critical Periods

Selective serotonin reuptake inhibitors (SSRIs) are usually prescribed to treat major depression and anxiety disorders. Fetal brain development exhibits dependency on serotonin (5-hydroxytryptamine, 5-HT) from maternal, placental, and fetal brain sources. At very early fetal stages, fetal serotonin is provided by maternal and placental sources. However, in later fetal stages, brain sources are indispensable for the appropriate development of neural circuitry and the rise of emergent functions implied in behavior acquisition. Thus, susceptible serotonin-related critical periods are recognized, involving the early maternal and placental 5-HT synthesis and the later endogenous 5-HT synthesis in the fetal brain. Acute and chronic exposure to SSRIs during these critical periods may result in short- and long-term placental and brain dysfunctions affecting intrauterine and postnatal life. Maternal and fetal cells express serotonin receptors which make them susceptible to changes in serotonin levels influenced by SSRIs. SSRIs block the serotonin transporter (SERT), which is required for 5-HT reuptake from the synaptic cleft into the presynaptic neuron. Chronic SSRI administration leads to pre- and postsynaptic 5-HT receptor rearrangement. In this review, we focus on the effects of SSRIs administered during critical periods upon placentation and brain development to be considered in evaluating the risk-safety balance in the clinical use of SSRIs.

The Role of Nerve Fibers in the Tumor Immune Microenvironment of Solid Tumors

The importance of neurons and nerve fibers in the tumor microenvironment (TME) of solid tumors is now acknowledged after being unexplored for a long time; this is possible due to the development of new technologies that allow in situ characterization of the TME. Recent studies have shown that the density and types of nerves that innervate tumors can predict a patient's clinical outcome and drive several processes of tumor biology. Nowadays, several efforts in cancer research and neuroscience are taking place to elucidate the mechanisms that drive tumor-associated innervation and nerve-tumor and nerve-immune interaction. Assessment of neurons and nerves within the context of the TME can be performed in situ, in tumor tissue, using several pathology-based strategies that utilize histochemical and immunohistochemistry principles, hi-plex technologies, and computational pathology approaches to identify measurable histopathological characteristics of nerves. These features include the number and type of tumor associated nerves, topographical location and microenvironment of neural invasion of malignant cells, and investigation of neuro-related biomarker expression in nerves, tumor cells, and cells of the TME. A deeper understanding of these complex interactions and the impact of nerves in tumor biology will guide the design of better strategies for targeted therapy in clinical trials.

Peptide OM-LV20 protects astrocytes against oxidative stress via the 'PAC1R/JNK/TPH1' axis

Stroke can lead to severe nerve injury and debilitation, resulting in considerable social and economic burdens. Due to the high complexity of post-injury repair mechanisms, drugs approved for use in stroke are extremely scarce, and thus, the discovery of new antistroke drugs and targets is critical. Tryptophan hydroxylase 1 (TPH1) is involved in a variety of mental and neurobehavioral processes, but its effects on stroke have not yet been reported. Here, we used primary astrocyte culture, quantitative real-time PCR, double immunofluorescence assay, lentiviral infection, cell viability analysis, Western blotting, and other biochemical experiments to explore the protective mechanism of peptide OM-LV20, which previously exhibited neuroprotective effects in rats after ischemic stroke via a mechanism that may involve TPH1. First, we showed that TPH1 was expressed in rat astrocytes. Next, we determined that OM-LV20 impacted expression changes of TPH1 in CTX-TNA2 cells and exhibited a protective effect on the decrease in cell viability and catalase (CAT) levels induced by hydrogen peroxide. Importantly, we also found that TPH1 expression induced by OM-LV20 may be related to the level of change in the pituitary adenylate cyclase-activating peptide type 1 receptor (PAC1R) and to the JNK signaling pathways, thereby exerting a protective effect on astrocytes against oxidative stress. The protective effects of OM-LV20 likely occur via the ‘PAC1R/JNK/TPH1’ axis, thus highlighting TPH1 as a novel antistroke drug target.

Melatonin biosynthesis pathways in nature and its production in engineered microorganisms

Melatonin is a biogenic amine that can be found in plants, animals and microorganism. The metabolic pathway of melatonin is different in various organisms, and biosynthetic endogenous melatonin acts as a molecular signal and antioxidant protection against external stress. Microbial synthesis pathways of melatonin are similar to those of animals but different from those of plants. At present, the method of using microorganism fermentation to produce melatonin is gradually prevailing, and exploring the biosynthetic pathway of melatonin to modify microorganism is becoming the mainstream, which has more advantages than traditional chemical synthesis. Here, we review recent advances in the synthesis, optimization of melatonin pathway. l-tryptophan is one of the two crucial precursors for the synthesis of melatonin, which can be produced through a four-step reaction. Enzymes involved in melatonin synthesis have low specificity and catalytic efficiency. Site-directed mutation, directed evolution or promotion of cofactor synthesis can enhance enzyme activity and increase the metabolic flow to promote microbial melatonin production. On the whole, the status and bottleneck of melatonin biosynthesis can be improved to a higher level, providing an effective reference for future microbial modification.

Association between TPH1 polymorphisms and the risk of suicide behavior: An updated meta-analysis of 18,398 individuals

OBJECTIVES

We aimed to examine the association of TPH1 polymorphisms with the risk of suicide behavior (SB).

DESIGN

Systematic review and meta-analysis.

METHOD

All relevant studies that evaluated the association between the A218C (rs1800532), A779C (rs1799913) and A6526G (rs4537731) polymorphisms and the susceptibility to SB published up to September 2021 were identified through a comprehensive systematic search in PubMed, Scopus, EBSCO and Science Direct electronic databases. The association between TPH1 gene polymorphisms and SB was evaluated using inherence models by odds ratio (OR) and 95% confidence interval (CI). Subgroup analyses, heterogeneity analyses, and publication bias were also tested in this meta-analysis.

RESULTS

The meta-analysis for TPH1 A218C revealed an increased risk of SB in the dominant model (OR = 1.11, 95%CI 1.01-1.22). We also observed a positive association in the allelic (OR = 1.13, 95%CI 1.05-1.21), homozygous (OR = 1.22, 95%CI 1.06-1.40), heterozygous (OR = 1.21, 95%CI 1.08-1.37) and dominant (OR = 1.21, 95%CI 1.09-1.34) inherence models with the suicide attempt. Additionally, in the heterozygous (OR = 0.84, 95%CI 0.73-0.97) and dominant (OR = 0.79, 95%CI 0.68-0.91) inherence models we detected an association with completed suicide. Based on ethnicity, an association of SB in the European population also was observed (OR = 1.29, 95%CI 1.12-1.51). However, for both A779C and A6526G polymorphisms we did not find evidence of an association with SB.

CONCLUSION

This meta-analysis suggests that the A218C polymorphism of TPH1 gene could be a possible risk factor of SB. Future large-scale studies are required to analyze the molecular mechanisms by which affect the susceptibility of developing suicide behavior.

Serotonergic Regulation of Hepatic Energy Metabolism

The liver is a vital organ that regulates systemic energy metabolism and many physiological functions. Nonalcoholic fatty liver disease (NAFLD) is the commonest cause of chronic liver disease and end-stage liver failure. NAFLD is primarily caused by metabolic disruption of lipid and glucose homeostasis. Serotonin (5-hydroxytryptamine [5-HT]) is a biogenic amine with several functions in both the central and peripheral systems. 5-HT functions as a neurotransmitter in the brain and a hormone in peripheral tissues to regulate systemic energy homeostasis. Several recent studies have proposed various roles of 5-HT in hepatic metabolism and inflammation using tissue-specific knockout mice and 5-HT-receptor agonists/antagonists. This review compiles the most recent research on the relationship between 5-HT and hepatic metabolism, and the role of 5-HT signaling as a potential therapeutic target in NAFLD.

The Effect of Chronic Mild Stress and Escitalopram on the Expression and Methylation Levels of Genes Involved in the Oxidative and Nitrosative Stresses as Well as Tryptophan Catabolites Pathway in the Blood and Brain Structures

Previous studies suggest that depression may be associated with reactive oxygen species overproduction and disorders of the tryptophan catabolites pathway. Moreover, one-third of patients do not respond to conventional pharmacotherapy. Therefore, the study investigates the molecular effect of escitalopram on the expression of Cat, Gpx1/4, Nos1/2, Tph1/2, Ido1, Kmo, and Kynu and promoter methylation in the hippocampus, amygdala, cerebral cortex, and blood of rats exposed to CMS (chronic mild stress). The animals were exposed to CMS for two or seven weeks followed by escitalopram treatment for five weeks. The mRNA and protein expression of the genes were analysed using the TaqMan Gene Expression Assay and Western blotting, while the methylation was determined using methylation-sensitive high-resolution melting. The CMS caused an increase of Gpx1 and Nos1 mRNA expression in the hippocampus, which was normalised by escitalopram administration. Moreover, Tph1 and Tph2 mRNA expression in the cerebral cortex was increased in stressed rats after escitalopram therapy. The methylation status of the Cat promoter was decreased in the hippocampus and cerebral cortex of the rats after escitalopram therapy. The Gpx4 protein levels were decreased following escitalopram compared to the stressed/saline group. It appears that CMS and escitalopram influence the expression and methylation of the studied genes.

Lactobacillus plantarum DR7 improved brain health in aging rats via the serotonin, inflammatory and apoptosis pathways

Aging processes affect the brain in many ways, ranging from cellular to functional levels which lead to cognitive decline and increased oxidative stress. The aim of this study was to investigate the potentials of Lactobacillus plantarum DR7 on brain health including cognitive and memory functions during aging and the impacts of high fat diet during a 12-week period. Male Sprague-Dawley rats were separated into six groups: (1) young animals on normal diet (ND, (2) young animals on a high fat diet (HFD), (3) aged animals on ND, (4) aged animals on HFD, (5) aged animals on HFD and L. plantarum DR7 (10⁹ cfu/day) and (6) aged animals receiving HFD and lovastatin. To induce ageing, all rats in group 3 to 6 were injected sub-cutaneously at 600 mg/kg/day of D-galactose daily. The administration of DR7 has reduced anxiety accompanied by enhanced memory during behavioural assessments in aged-HFD rats (P<0.05). Hippocampal concentration of all three pro-inflammatory cytokines were increased during aging but reduced upon administration of both statin and DR7. Expressions of hippocampal neurotransmitters and apoptosis genes showed reduced expressions of indoleamine dioxygenase and P53 accompanied by increased expression of TPH1 in aged- HFD rats administered with DR7, indicating potential effects of DR7 along the pathways of serotonin and oxidative senescence. This study provided an insight into potentials of L. plantarum DR7 as a prospective dietary strategy to improve cognitive functions during aging. This study provided an insight into potentials of L. plantarum DR7 as a prospective dietary strategy to improve cognitive functions during aging.

Albumin is a secret factor involved in multidirectional interactions among the serotoninergic, immune and endocrine systems that supervises the mechanism of CYP1A and CYP3A regulation in the liver

This review focuses on albumin, which is involved in multidirectional interactions among the immune, endocrine and serotoninergic systems and supervises the regulation of cytochrome P450 (CYP) isoforms under conditions of both normal liver function and liver insufficiency. Special attention is paid to albumin, thyroid hormones, testosterone and tryptophan hydroxylase in these interactions as well as their potential roles in liver regeneration. The association of these factors with inflammation and the modification of the mechanism of hepatic drug-metabolizing CYP isoform regulation are also presented because changes in the expression of CYP isoforms in the liver may result in subsequent changes to a marker substance used for testing CYP activity, thus providing a simple way to control the liver regeneration process or the dangerous stimulation of hepatocarcinogenesis.

The Role of Sex in the Pathophysiology of Pulmonary Hypertension

Pulmonary arterial hypertension (PAH) is a progressive disease characterised by increased pulmonary vascular resistance and pulmonary artery remodelling as result of increased vascular tone and vascular cell proliferation, respectively. Eventually, this leads to right heart failure. Heritable PAH is caused by a mutation in the bone morphogenetic protein receptor-II (BMPR-II). Female susceptibility to PAH has been known for some time, and most recent figures show a female-to-male ratio of 4:1. Variations in the female sex hormone estrogen and estrogen metabolism modify FPAH risk, and penetrance of the disease in BMPR-II mutation carriers is increased in females. Several lines of evidence point towards estrogen being pathogenic in the pulmonary circulation, and thus increasing the risk of females developing PAH. Recent studies have also suggested that estrogen metabolism may be crucial in the development and progression of PAH with studies indicating that downstream metabolites such as 16α-hydroxyestrone are upregulated in several forms of experimental pulmonary hypertension (PH) and can cause pulmonary artery smooth muscle cell proliferation and subsequent vascular remodelling. Conversely, other estrogen metabolites such as 2-methoxyestradiol have been shown to be protective in the context of PAH. Estrogen may also upregulate the signalling pathways of other key mediators of PAH such as serotonin.

Blood-based biomarkers predicting response to antidepressants

Major depressive disorder is a common, serious and in some cases, life-threatening condition and affects approximately 350 million people globally. Although there is effective treatment available for it, more than 50% of the patients fail to respond to the first antidepressant they receive. The selection of a distinct treatment is still exclusively based on clinical judgment without incorporating lab-derived objective measures. However, there is growing evidence of biomarkers that it helps to improve diagnostic processes and treatment algorithms. Here genetic markers and blood-based biomarkers of the monoamine pathways, inflammatory pathways and the hypothalamic-pituitary-adrenal (HPA) axis are reviewed. Promising findings arise from studies investigating inflammatory pathways and immune markers that may identify patients suitable for anti-inflammatory based treatment regimes. Next, an early normalization of a disturbed HPA axis or depleted neurotrophic factors may predict stable treatment response. Genetic markers within the serotonergic system may identify patients who are vulnerable because of stressful life events, but evidence for guiding treatment regimes still is inconsistent. Therefore, there is still a great need for studies investigating and validating biomarkers for the prediction of treatment response to facilitate the treatment selection and shorten the time to remission and thus provide personalized medicine in psychiatry.

Role for Egr1 in the Transcriptional Program Associated with Neuronal Differentiation of PC12 Cells

PC12 cells are a well-established model to study how differences in signal transduction duration can elicit distinct cell behaviors. Epidermal growth factor (EGF) activates transient ERK signaling in PC12 cells that lasts 30–60 min, which in turn promotes proliferation; nerve growth factor (NGF) activates more sustained ERK signaling that lasts 4–6 h, which in turns induces neuronal differentiation. Data presented here extend a previous study by Mullenbrock et al. (2011) that demonstrated that sustained ERK signaling in response to NGF induces preferential expression of a 69-member gene set compared to transient ERK signaling in response to EGF and that the transcription factors AP-1 and CREB play a major role in the preferential expression of several genes within the set. Here, we examined whether the Egr family of transcription factors also contributes to the preferential expression of the gene set in response to NGF. Our data demonstrate that NGF causes transient induction of all Egr family member transcripts, but a corresponding induction of protein was detected for only Egr1 and 2. Chromatin immunoprecipitation experiments provided clearest evidence that, after induction, Egr1 binds 12 of the 69 genes that are preferentially expressed during sustained ERK signaling. In addition, Egr1 expression and binding upstream of its target genes were both sustained in response to NGF versus EGF within the same timeframe that its targets are preferentially expressed. These data thus provide evidence that Egr1 contributes to the transcriptional program activated by sustained ERK signaling in response to NGF, specifically by contributing to the preferential expression of its target genes identified here.

A comparison of biomarker responses in juvenile diploid and triploid African catfish, Clarias gariepinus, exposed to the pesticide butachlor

Influence of waterborne butachlor (BUC), a commonly used pesticide, on morphometric, biochemical, and molecular biomarkers was evaluated in juvenile, full sibling, diploid and triploid African catfish (Clarias gariepinus). Fish were exposed for 21 days to one of three concentrations of BUC [mean measured µg/L: 22, 44 or 60]. Unexposed (control) triploids were heavier and longer and had higher visceral-somatic index (VSI) than diploids. Also, they had lighter liver weight (HSI) and showed lower transcript levels of brain gonadotropin-releasing hormone (GnRH), aromatase (cyp191b) and fushi tarazu-factor (ftz-f1), and plasma testosterone levels than diploids. Butachlor treatments had no effects, in either diploid or triploid fish, on VSI, HSI, weight or length changes, condition factor (CF), levels of plasma testosterone, 17-β estradiol (E2), cortisol, cholesterol, or mRNA levels of brain tryptophan hydroxylase (tph2), forkhead box L2 (foxl2), and 11 β-hydroxysteroid dehydrogenase type 2 (11β-hsd2). Expressions of cyp191b and ftz-f1 in triploids were upregulated by the two highest concentrations of BUC. In diploid fish, however, exposures to all BUC concentrations decreased GnRH transcription and the medium BUC concentration decreased ftz-f1 transcription. Substantial differences between ploidies in basal biomarker responses are consistent with the reported impaired reproductive axis in triploid C. gariepinus. Furthermore, the present study showed the low impact of short term exposure to BUC on reproductive axis in C. gariepinus.

Enteric co-innervation of striated muscle in the esophagus: still enigmatic?

The existence of a distinct ganglionated myenteric plexus between the two layers of the striated tunica muscularis of the mammalian esophagus has represented an enigma for quite a while. Although an enteric co-innervation of vagally innervated motor endplates in the esophagus has been suggested repeatedly, it was not possible until recently to demonstrate this dual innervation. Twenty-two years ago, we were able to demonstrate that motor endplates in the rat esophagus receive dual innervation from both vagal nerve fibers originating in the brain stem and from varicose enteric nerve fibers originating in the myenteric plexus. Meanwhile, a considerable amount of data has been gathered on enteric co-innervation and its occurrence in the esophagus of a variety of species including humans, its neurochemistry, spatial relationships on motor endplates, ontogeny and possible functional roles. These data underline the significance of this newly discovered innervation component, although its function in vivo is still largely unknown. The aim of this review, which is an update of our previous paper (Wörl and Neuhuber in Histochem Cell Biol 123(2):117-130. doi: 10.1007/s00418-005-0764-7 , 2005a), is to summarize the current knowledge about enteric co-innervation of esophageal striated muscle and to provide some hints as to its functional significance.

Enhancing tyrosine hydroxylase and tryptophan hydroxylase expression and improving oxidative stress involved in the antidepressant effect of sodium valproate on rats undergoing chronic unpredicted stress

Depression is a common worldwide mental disorder whose etiology remains unclear; there is also a lack of effective therapeutic agents. Sodium valproate (VPA) is a traditional antiepileptic drug with mood-stabilization effect and is increasingly being used to treat bipolar disorders and depression, but its antidepressant mechanism remains unknown. The aim of the present study was to investigate the possible mechanisms of antidepressant action by studying malondialdehyde level, catalase, and superoxide dismutase activities in the serum and the mRNA and protein expression of tyrosine hydroxylase (TH) and tryptophan hydroxylase (TPH) in the prefrontal cortex of rats exposed to chronic unpredicted stress (CUS). Male Sprague-Dawley rats were used to establish a depression model by CUS. VPA (300 mg/kg once daily) and an equivalent volume of vehicle were administered to rats by an intragastric gavage. Rat behaviors, serum malondialdehyde level, serum catalase and superoxide dismutase activities, and the mRNA and protein expressions of TH and TPH in the prefrontal cortex were determined. The results showed that VPA treatment led to a significant decrease in depression-like behaviors, improvement in oxidative stress imbalance, and enhancement of TH, TPH mRNA, and protein expression in stressed rats, but failed to show any significant changes in control rats. This could indicate that the antidepressant mechanism of VPA is perhaps linked to upregulation of TH and TPH expression and inhibition of oxidative damage in CUS rats.

Diploid and triploid African catfish (Clarias gariepinus) differ in biomarker responses to the pesticide chlorpyrifos

The impacts of environmental stressors on polyploid organisms are largely unknown. This study investigated changes in morphometric, molecular, and biochemical parameters in full-sibling diploid and triploid African catfish (Clarias gariepinus) in response to chlorpyrifos (CPF) exposures. Juvenile fish were exposed to three concentrations of CPF (mean measured μg/L (SD): 9.71 (2.27), 15.7 (3.69), 31.21 (5.04)) under a static-renewal condition for 21days. Diploid control groups had higher hepatosomatic index (HSI), plasma testosterone (T), and brain GnRH and cyp19a2 expression levels than triploids. In CPF-exposed groups, changes in HSI, total weight and length were different between the diploid and triploid fish. In contrast, condition factor did not alter in any of the treatments, while visceral-somatic index (VSI) changed only in diploids. In diploid fish, exposure to CPF did not change brain 11β-hsd2, ftz-f1, foxl2, GnRH or cyp19a2 mRNA levels, while reduced tph2 transcript levels compared to the control group. In contrast, 11β-hsd2 and foxl2 expression levels were changed in triploids following CPF exposures. In diploids, plasma T levels showed a linear dose-response reduction across CPF treatments correlating with liver weight and plasma total cholesterol concentrations. In contrast, no changes in plasma cholesterol and T concentrations were observed in triploids. Plasma cortisol and 17-β estradiol (E2) showed no response to CPF exposure in either ploidy. Results of this first comparison of biomarker responses to pesticide exposure in diploid and polyploid animals showed substantial differences between diploid and triploid C. gariepinus.

A functional genomics screen identifies an Importin-α homolog as a regulator of stem cell function and tissue patterning during planarian regeneration

Background

Planarians are renowned for their regenerative capacity and are an attractive model for the study of adult stem cells and tissue regeneration. In an effort to better understand the molecular mechanisms underlying planarian regeneration, we performed a functional genomics screen aimed at identifying genes involved in this process in Schmidtea mediterranea.

Methods

We used microarrays to detect changes in gene expression in regenerating and non-regenerating tissues in planarians regenerating one side of the head and followed this with high-throughput screening by in situ hybridization and RNAi to characterize the expression patterns and function of the differentially expressed genes.

Results

Along with five previously characterized genes (Smed-cycD, Smed-morf41/mrg-1, Smed-pdss2/dlp1, Smed-slbp, and Smed-tph), we identified 20 additional genes necessary for stem cell maintenance (Smed-sart3, Smed-smarcc-1, Smed-espl1, Smed-rrm2b-1, Smed-rrm2b-2, Smed-dkc1, Smed-emg1, Smed-lig1, Smed-prim2, Smed-mcm7, and a novel sequence) or general regenerative capability (Smed-rbap46/48-2, Smed-mcm2, Smed-ptbp1, and Smed-fen-1) or that caused tissue-specific defects upon knockdown (Smed-ddc, Smed-gas8, Smed-pgbd4, and Smed-b9d2). We also found that a homolog of the nuclear transport factor Importin-α plays a role in stem cell function and tissue patterning, suggesting that controlled nuclear import of proteins is important for regeneration.

Conclusions

Through this work, we described the roles of several previously uncharacterized genes in planarian regeneration and implicated nuclear import in this process. We have additionally created an online database to house our in situ and RNAi data to make it accessible to the planarian research community.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-015-1979-1) contains supplementary material, which is available to authorized users.

Serotonin receptor 6 mediates defective brain development in monoamine oxidase A-deficient mouse embryos

Monoamine oxidases A and B (MAO-A and MAO-B) are enzymes of the outer mitochondrial membrane that metabolize biogenic amines. In the adult central nervous system, MAOs have important functions for neurotransmitter homeostasis. Expression of MAO isoforms has been detected in the developing embryo. However, suppression of MAO-B does not induce developmental alterations. In contrast, targeted inhibition and knockdown of MAO-A expression (E7.5-E10.5) caused structural abnormalities in the brain. Here we explored the molecular mechanisms underlying defective brain development induced by MAO-A knockdown during in vitro embryogenesis. The developmental alterations were paralleled by diminished apoptotic activity in the affected neuronal structures. Moreover, dysfunctional MAO-A expression led to elevated levels of embryonic serotonin (5-hydroxytryptamine (5-HT)), and we found that knockdown of serotonin receptor-6 (5-Htr6) expression or pharmacologic inhibition of 5-Htr6 activity rescued the MAO-A knockdown phenotype and restored apoptotic activity in the developing brain. Our data suggest that excessive 5-Htr6 activation reduces activation of caspase-3 and -9 of the intrinsic apoptotic pathway and enhances expression of antiapoptotic proteins Bcl-2 and Bcl-XL. Moreover, we found that elevated 5-HT levels in MAO-A knockdown embryos coincided with an enhanced activation of extracellular signal-regulated kinase 1/2 (ERK1/2) and a reduction of proliferating cell numbers. In summary, our findings suggest that excessive 5-HT in MAO-A-deficient mouse embryos triggers cellular signaling cascades via 5-Htr6, which suppresses developmental apoptosis in the brain and thus induces developmental retardations.

A Pitx transcription factor controls the establishment and maintenance of the serotonergic lineage in planarians

In contrast to adult vertebrates, which have limited capacities for neurogenesis, adult planarians undergo constitutive cellular turnover during homeostasis and are even able to regenerate a whole brain after decapitation. This enormous plasticity derives from pluripotent stem cells residing in the planarian body in large numbers. It is still obscure how these stem cells are programmed for differentiation into specific cell lineages and how lineage identity is maintained. Here we identify a Pitx transcription factor of crucial importance for planarian regeneration. In addition to patterning defects that are co-dependent on the LIM homeobox transcription factor gene islet1, which is expressed with pitx at anterior and posterior regeneration poles, RNAi against pitx results in islet1-independent specific loss of serotonergic (SN) neurons during regeneration. Besides its expression in terminally differentiated SN neurons we found pitx in stem cell progeny committed to the SN fate. Also, intact pitx RNAi animals gradually lose SN markers, a phenotype that depends neither on increased apoptosis nor on stem cell-based turnover or transdifferentiation into other neurons. We propose that pitx is a terminal selector gene for SN neurons in planarians that controls not only their maturation but also their identity by regulating the expression of the Serotonin production and transport machinery. Finally, we made use of this function of pitx and compared the transcriptomes of regenerating planarians with and without functional SN neurons, identifying at least three new neuronal targets of Pitx.

Medullary serotonin neurons are CO2 sensitive in situ

Brainstem central chemoreceptors are critical to the hypercapnic ventilatory response, but their location and identity are poorly understood. When studied in vitro, serotonin-synthesizing (5-HT) neurons within the rat medullary raphé are intrinsically stimulated by CO2/acidosis. The contributions of these neurons to central chemosensitivity in vivo, however, are controversial. Lacking is documentation of CO2-sensitive 5-HT neurons in intact experimental preparations and understanding of their spatial and proportional distribution. Here we test the hypothesis that 5-HT neurons in the rat medullary raphé are sensitive to arterial hypercapnia. We use extracellular recording and hypercapnic challenge of spontaneously active medullary raphé neurons in the unanesthetized in situ perfused decerebrate brainstem preparation to assess chemosensitivity of individual cells. Juxtacellular labeling of a subset of recorded neurons and subsequent immunohistochemistry for the 5-HT-synthesizing enzyme tryptophan hydroxylase (TPH) identify or exclude this neurotransmitter phenotype in electrophysiologically characterized chemosensitive and insensitive cells. We show that the medullary raphé houses a heterogeneous population, including chemosensitive and insensitive 5-HT neurons. Of 124 recorded cells, 16 cells were juxtacellularly filled, visualized, and immunohistochemically identified as 5-HT synthesizing, based on TPH-immunoreactivity. Forty-four percent of 5-HT cells were CO2 stimulated (increased firing rate with hypercapnia), while 56% were unstimulated. Our results demonstrate that medullary raphé neurons are heterogeneous and clearly include a subset of 5-HT neurons that are excited by arterial hypercapnia. Together with data identifying intrinsically CO2-sensitive 5-HT neurons in vitro, these results support a role for such cells as central chemoreceptors in the intact system.

The microbiome-gut-brain axis during early life regulates the hippocampal serotonergic system in a sex-dependent manner

Bacterial colonisation of the intestine has a major role in the post-natal development and maturation of the immune and endocrine systems. These processes are key factors underpinning central nervous system (CNS) signalling. Regulation of the microbiome-gut-brain axis is essential for maintaining homeostasis, including that of the CNS. However, there is a paucity of data pertaining to the influence of microbiome on the serotonergic system. Germ-free (GF) animals represent an effective preclinical tool to investigate such phenomena. Here we show that male GF animals have a significant elevation in the hippocampal concentration of 5-hydroxytryptamine and 5-hydroxyindoleacetic acid, its main metabolite, compared with conventionally colonised control animals. Moreover, this alteration is sex specific in contrast with the immunological and neuroendocrine effects which are evident in both sexes. Concentrations of tryptophan, the precursor of serotonin, are increased in the plasma of male GF animals, suggesting a humoral route through which the microbiota can influence CNS serotonergic neurotransmission. Interestingly, colonisation of the GF animals post weaning is insufficient to reverse the CNS neurochemical consequences in adulthood of an absent microbiota in early life despite the peripheral availability of tryptophan being restored to baseline values. In addition, reduced anxiety in GF animals is also normalised following restoration of the intestinal microbiota. These results demonstrate that CNS neurotransmission can be profoundly disturbed by the absence of a normal gut microbiota and that this aberrant neurochemical, but not behavioural, profile is resistant to restoration of a normal gut flora in later life.

TPH gene polymorphisms are associated with disease perception and quality of life in women with irritable bowel syndrome

The aims of this exploratory study were to examine whether tryptophan hydroxylase (TPH) gene polymorphisms are associated with psychosocial factors in women with irritable bowel syndrome (IBS). TPH is the rate-limiting enzyme in the biosynthesis of serotonin and has two isoforms, TPH1 and TPH2. Four single nucleotide polymorphisms (SNPs) in the TPH1 gene and one SNP in the TPH2 gene were selected based on previous studies investigating associations between these SNPs and psychiatric or behavioral disorders. One hundred ninety-nine Caucasian women with IBS were included. Results of univariate analysis showed no association between TPH1and TPH2 gene SNPs and current level of psychological distress or psychiatric illness. However, TPH1 gene SNPs were associated with IBS-related cognitions (rs4537731 and rs21105) and quality of life (rs684302 and rs1800532), in particular the mental health and energy subscales. These associations were independent of the subjects' levels of gastrointestinal symptoms. These results suggest that patients' perception of their illness, and of the impact it has on their lives, may be subject to genetic influences, in this case sequence variants in TPH1. However, caution should be used in interpreting these results given the large number of hypothesis tests performed in this exploratory hypothesis-generating study, and the results should be considered tentative until confirmed in an independent sample.

Tryptophan hydroxylase 2 (TPH2) in a neuronal cell line: modulation by cell differentiation and NRSF/rest activity

Serotonin (5-HT) is a neurotransmitter involved in many aspects of the neuronal function. The synthesis of 5-HT is initiated by the hydroxylation of tryptophan, catalyzed by tryptophan hydroxylase (TPH). Two isoforms of TPH (TPH1 and TPH2) have been identified, with TPH2 almost exclusively expressed in the brain. Following TPH2 discovery, it was reported that polymorphisms of both gene and non-coding regions are associated with a spectrum of psychiatric disorders. Thus, insights into the mechanisms that specifically regulate TPH2 expression and its modulation by exogenous stimuli may represent a new therapeutic approach to modify serotonergic neurotransmission. To this aim, a CNS-originated cell line expressing TPH2 endogenously represents a valid model system. In this study, we report that TPH2 transcript and protein are modulated by neuronal differentiation in the cell line A1 mes-c-myc (A1). Moreover, we show luciferase activity driven by the human TPH2 promoter region and demonstrate that upon mutation of the NRSF/REST responsive element, the promoter activity strongly increases with cell differentiation. Our data suggest that A1 cells could represent a model system, allowing an insight into the mechanisms of regulation of TPH2 and to identify novel therapeutic targets in the development of drugs for the management of psychiatric disorders.

Neurotrophic actions of dopamine on the development of a serotonergic feeding circuit in Drosophila melanogaster

BACKGROUND

In the fruit fly, Drosophila melanogaster, serotonin functions both as a neurotransmitter to regulate larval feeding, and in the development of the stomatogastric feeding circuit. There is an inverse relationship between neuronal serotonin levels during late embryogenesis and the complexity of the serotonergic fibers projecting from the larval brain to the foregut, which correlate with perturbations in feeding, the functional output of the circuit. Dopamine does not modulate larval feeding, and dopaminergic fibers do not innervate the larval foregut. Since dopamine can function in central nervous system development, separate from its role as a neurotransmitter, the role of neuronal dopamine was assessed on the development, and mature function, of the 5-HT larval feeding circuit.

RESULTS

Both decreased and increased neuronal dopamine levels in late embryogenesis during development of this circuit result in depressed levels of larval feeding. Perturbations in neuronal dopamine during this developmental period also result in greater branch complexity of the serotonergic fibers innervating the gut, as well as increased size and number of the serotonin-containing vesicles along the neurite length. This neurotrophic action for dopamine is modulated by the D2 dopamine receptor expressed during late embryogenesis in central 5-HT neurons. Animals carrying transgenic RNAi constructs to knock down both dopamine and serotonin synthesis in the central nervous system display normal feeding and fiber architecture. However, disparate levels of neuronal dopamine and serotonin during development of the circuit result in abnormal gut fiber architecture and feeding behavior.

CONCLUSIONS

These results suggest that dopamine can exert a direct trophic influence on the development of a specific neural circuit, and that dopamine and serotonin may interact with each other to generate the neural architecture necessary for normal function of the circuit.

Global expression analysis identified a preferentially nerve growth factor-induced transcriptional program regulated by sustained mitogen-activated protein kinase/extracellular signal-regulated kinase (ERK) and AP-1 protein activation during PC12 cell differentiation

Neuronal differentiation of PC12 cells in response to NGF is a prototypical model in which signal duration determines a biological response. Sustained ERK activity induced by NGF, as compared with transient activity induced by EGF, is critical to the differentiation of these cells. To characterize the transcriptional program activated preferentially by NGF, we compared global gene expression profiles between cells treated with NGF and EGF for 2-4 h, when sustained ERK signaling in response to NGF is most distinct from the transient signal elicited by EGF. This analysis identified 69 genes that were preferentially up-regulated in response to NGF. As expected, up-regulation of these genes was mediated by sustained ERK signaling. In addition, they were up-regulated in response to other neuritogenic treatments (pituitary adenylate cyclase-activating polypeptide and 12-O-tetradecanoylphorbol-13-acetate plus dbcAMP) and were enriched for genes related to neuronal differentiation/function. Computational analysis and chromatin immunoprecipitation identified binding of CREB and AP-1 family members (Fos, FosB, Fra1, JunB, JunD) upstream of >30 and 50%, respectively, of the preferentially NGF-induced genes. Expression of several AP-1 family members was induced by both EGF and NGF, but their induction was more robust and sustained in response to NGF. The binding of Fos family members to their target genes was similarly sustained in response to NGF and was reduced upon MEK inhibition, suggesting that AP-1 contributes significantly to the NGF transcriptional program. Interestingly, Fra1 as well as two other NGF-induced AP-1 targets (HB-EGF and miR-21) function in positive feedback loops that may contribute to sustained AP-1 activity.

Selective p38α MAPK deletion in serotonergic neurons produces stress resilience in models of depression and addiction

Maladaptive responses to stress adversely affect human behavior, yet the signaling mechanisms underlying stress-responsive behaviors remain poorly understood. Using a conditional gene knockout approach, the α isoform of p38 mitogen-activated protein kinase (MAPK) was selectively inactivated by AAV1-Cre-recombinase infection in specific brain regions or by promoter-driven excision of p38α MAPK in serotonergic neurons (by Slc6a4-Cre or ePet1-Cre) or astrocytes (by Gfap-CreERT2). Social defeat stress produced social avoidance (a model of depression-like behaviors) and reinstatement of cocaine preference (a measure of addiction risk) in wild-type mice, but not in mice having p38α MAPK selectively deleted in serotonin-producing neurons of the dorsal raphe nucleus. Stress-induced activation of p38α MAPK translocated the serotonin transporter to the plasma membrane and increased the rate of transmitter uptake at serotonergic nerve terminals. These findings suggest that stress initiates a cascade of molecular and cellular events in which p38α MAPK induces a hyposerotonergic state underlying depression-like and drug-seeking behaviors.

Gender differences in tryptophan hydroxylase-2 mRNA, serotonin, and 5-hydroxytryptophan levels in the brain of catfish, Clarias gariepinus, during sex differentiation

Tryptophan hydroxylase (tph) is the key regulator in serotonin (5-HT) biosynthesis that stimulates the release of GnRH and gonadotropins by acting at the level of hypothalamo-hypophyseal axis. In brain, 5-HT is expressed predominantly in preoptic area-hypothalamus (POA-HYP) region in teleosts. Therefore, in the present study we isolated tph2 from catfish brain to evaluate its expression pattern in male and female brains during early development. Tph2 cloned from catfish brain is 2.768 Kb in length which encodes predicted protein of 488 amino acid residues. The characterization of recombinant tph2 was done by transient transfection in CHO cells. Tissue distribution of tph2 revealed ubiquitous expression except ovary. Real time PCR analysis in discrete regions of adult male brain revealed that tph2 mRNA was abundant in the POA-HYP and optic tectum+cerebellum+thalamus (OCT) regions. Differential expression of tph2 was observed at mRNA and protein levels in the POA-HYP and OCT regions of male and female brains during development that further correlate with the 5-hydroxytryptophan (5-HTP) and 5-HT levels measured using HPLC method in these regions of male and female brains. Tph2 immunoreactive neurons were observed in different regions of brain at 50 days post hatch using catfish specific tph2 antibody. Changes in tph2 mRNA expression, 5-HTP, and 5-HT levels in the POA-HYP+OCT region of brains of methyltestosterone and para-chlorophenylalanine treated fishes during development further endorse our results. Based on our results, we propose that the serotonergic system is involved in brain sex differentiation in teleosts.

Genetics of depression: an overview of the current science

Most psychiatric disorders, including major depressive disorder (MDD), are known to involve complex interactions between genetic and environmental influences that impact the development and severity of symptomatology. Health care practitioner competencies have been expanded to include application of genetic knowledge in mental health. Yet this information is difficult to decipher and apply. To assist with these challenges, this article synthesizes recent literature related to the genetics of MDD and illustrates the genetic pathways for major depression.

The role of serotonin in respiratory function and dysfunction

Serotonin (5-HT) is a neuromodulator-transmitter influencing global brain function. Past and present findings illustrate a prominent role for 5-HT in the modulation of ponto-medullary autonomic circuits. 5-HT is also involved in the control of neurotrophic processes during pre- and postnatal development of neural circuits. The functional implications of 5-HT are particularly illustrated in the alterations to the serotonergic system, as seen in a wide range of neurological disorders. This article reviews the role of 5-HT in the development and control of respiratory networks in the ponto-medullary brainstem. The review further examines the role of 5-HT in breathing disorders occurring at different stages of life, in particular, the neonatal neurodevelopmental diseases such as Rett, sudden infant death and Prader-Willi syndromes, adult diseases such as sleep apnoea and mental illness linked to neurodegeneration.

Dimorphic expression of tryptophan hydroxylase in the brain of XX and XY Nile tilapia during early development

Serotonin (5-HT) is well known for modulating the release of GnRH and gonadotropin in teleosts. Reports on increased female:male ratio after the blockade of 5-HT biosynthesis proposed a role for 5-HT in brain sex differentiation. Two types of tryptophan hydroxylase (Tph), rate-limiting enzyme in the biosynthesis of 5-HT were cloned from vertebrates. In the present study, we cloned Tph from brain and evaluated its importance during early development of XX and XY Nile tilapia. Tph cloned from tilapia brain is 1888 bp in length and it encodes predicted protein of 462 amino acid residues. Tph activity of tilapia was confirmed by demonstrating the conversion of L-tryptophan to 5-hydroxy tryptophan by the recombinant protein after transient transfection of this cDNA clone in COS-7 cells. Northern blot identified single transcript around 2kb in male brain. Tissue distribution of Tph revealed high abundance in brain, kidney, liver and testis. Semi-quantitative RT-PCR revealed exclusive expression of Tph in the male brain from 5 to 20 days post hatch (dph) while in the female brain, it was from 25 dph. These results were authenticated by localization of Tph transcripts in olfactory bulb-telencephalon region of 11 dph male brain using in situ hybridization. Tph immunoreactivity (-ir) was also evident in the nucleus preopticus-periventricularis area of male brain as early as 12 dph. However, Tph-ir was observed in several regions of both male and female brain without any distinction from 30 dph. Dimorphic expression pattern of Tph during early brain development around the critical period (7-21 dph) of gonadal sex determination and differentiation may implicate a role for Tph in brain sex differentiation of tilapia.

Is tryptophan 'more' essential than other essential aminoacids in development? A morphologic study

An ontogenetic study was designed on developing rats in uterus of mothers tryptophan deprived at day 1 (exp. 1) and day 14.5 (exp. 2) of conception to verify the supposed determining role of the serotoninergic system (SS) in sexual differentiation in mammals. Tryptophan-free feeding was pursued uninterruptedly in the litter after birth, during lactation and post-natal development. Tryptophan-free pregnant rats were obtained by exclusion of tryptophan sources from chow. In both exp. 1 and exp. 2, the litter showed at birth a significant physical under evolution that worsened, during post-natal development, to a much more marked dwarfism in exp. 1 pups. Growth hormone concentrations in both sexes of dwarf rats were lower than that in the control rats. At 30 days post-natal age, whereas exp. 1 female rats showed a right-timed onset of puberty, no descensus of testes could be observed in male rats of same experiment. Dwarf male rats showed an evident hypotrophy of the whole reproductive apparatus. In histological examination of testes, neither spermatogenesis nor Leydig cells have been observed. Moreover, dwarf female rats showed a pronounced hypotrophy of reproductive organs, but a normal puberal status pattern was evident. In exp. 2, litters showed a less pronounced dwarfism, but a normal right-timed onset of puberty in both male and female rats. Data indicate that role of tryptophan in physical and sexual maturation in both male and female rats is essential.

TPH1 218A/C polymorphism is associated with major depressive disorder and its treatment response

The association between the tryptophan hydroxylase 1 (TPH1) 218A/C polymorphism and (1) severity of major depressive disorder (MDD) and (2) response to treatment was studied. There were three study populations, the first consisting of 119 treatment-resistant MDD inpatients treated with electro-convulsive therapy (ECT), and the second of 98 MDD open care patients treated with selective serotonin reuptake inhibitors (SSRI). In addition, there was a control population of 395 healthy blood donors. The first aim of the study was to compare the genotypes of the patient with those of the healthy controls and between patient populations. The second aim was to compare the genotypes of MDD patients achieving remission with basic SSRI treatment (MADRS<8) with the genotypes of non-responders to ECT (defined as MADRS>15). TPH1 218A/C polymorphism was associated with the risk of MDD. CC genotype was significantly more common in patients (including both ECT and SSRI treated patients) than in controls (38.2% and 26.8% respectively; p=0.008), and its frequency was significantly higher in more severe forms of depression, i.e. in ECT treated patients compared with SSRI treated patients (42.0% and 33.7%, p=0.026). CC genotype was also associated with lower probability of achieving remission. It was significantly more frequent among ECT non-responders than among SSRI remitters (53.1% and 23.3%, p=0.049). In this Finnish population TPH1 218A/C polymorphism was associated with the risk of MDD and treatment response; CC genotype was associated with the increased risk of MDD and lower probability of responding treatment. Further studies with larger samples will be required to confirm the results.

Medullary serotonin defects and respiratory dysfunction in sudden infant death syndrome

Sudden infant death syndrome (SIDS) is defined as the sudden and unexpected death of an infant less than 12 months of age that occurs during sleep and remains unexplained after a complete autopsy, death scene investigation, and review of the clinical history. It is the leading cause of postneonatal mortality in the developed world. The cause of SIDS is unknown, but is postulated to involve impairment of brainstem-mediated homeostatic control. Extensive evidence from animal studies indicates that serotonin (5-HT) neurons in the medulla oblongata play a role in the regulation of multiple aspects of respiratory and autonomic function. A subset of SIDS infants have several abnormalities in medullary markers of 5-HT function and genetic polymorphisms impacting the 5-HT system, informing the hypothesis that SIDS results from a defect in 5-HT brainstem-mediated control of respiratory (and autonomic) regulation. Here we review the evidence from postmortem human studies and animal studies to support this hypothesis and discuss how the pathogenesis of SIDS is likely to originate in utero during fetal development.

Production and Peripheral Roles of 5-HTP, a Precursor of Serotonin

Serotonin (5-hydroxytryptamine [5-HT]) has been implicated in a variety of physiological and pathological functions. Multiple steps of enzyme reactions enable biosynthesis of 5-HT. The first and rate-limiting step of the reaction is the synthesis of 5-hydroxy-L-tryptophan (5-HTP) from L-tryptophan. This step is dictated by an enzyme, tryptophan hydroxylase (TPH). TPH requires 6R-L-erythro-5,6,7,8-tetrahydrobiopterin (BH4) as a co-substrate of TPH. 5-HTP has been simply regarded as a precursor of 5-HT and it is believed that the biological significance of 5-HTP is essentially ascribed to the production of 5-HT. However, recent works shed light on the specific functions of 5-HTP in the periphery. In this review article, we focus on the specific roles of exogenous 5-HTP as well as the endogenous 5-HTP in the gut epithelial cells. Since systemic treatment with 5-HTP is applied to patients with lower 5-HT levels, the studies on the specific role of 5-HTP might create an opportunity to explore the effects of exogenously-applied 5-HTP in the gut in man.

Predominant expression of tryptophan hydroxylase 1 mRNA in the pituitary: a postmortem study in human brain

Although the predominant role of tryptophan hydroxylase 2 (TPH2) in the CNS and its influence on the vulnerability to psychiatric disorders have clearly been demonstrated in several studies, the role of TPH1 on neuronal mechanisms, respectively on behavioral traits is still poorly understood. In a previous study of tryptophan hydroxylase 1 (TPH1) and TPH2 mRNA expression in different human brain regions we observed significantly higher TPH1 than TPH2 mRNA concentrations in the pituitary (unpublished observations). Considering the importance of the pituitary in the functional circuits between brain and body, we investigated the TPH1 and TPH2 mRNA expression in more detail, using human postmortem samples of the posterior and anterior pituitary compared to cortex, hippocampus and raphe nuclei. Specimens were available from different psychiatric patients (drug abusers, n=12; suicide victims, n=11; schizophrenics, n=9) and controls (n=15). Additionally we performed immunohistochemical analysis applying monospecific antibodies for both TPH isoforms to verify that the mRNA is of cellular and not just vascular or other origin. Highest TPH2 mRNA levels were observed in the raphe nuclei in patients and controls. By contrast, in the anterior and posterior pituitary TPH1 was found to be the predominantly expressed isoform in all subgroups. TPH1 and TPH2 mRNA expression in the further brain regions was only marginal and nearly identical except in the hypothalamus where higher TPH1 than TPH2 mRNA levels could be measured. Interindividual differences between the subgroups were not detectable. The results of the present study extended our previous findings by the additional immunohistochemical determination of the neuronal TPH1 and TPH2 protein expression in the anterior pituitary and provide evidence against a strictly separated duality of the serotonergic system. It seems that TPH1 might also have an impact on neuronal mechanisms via hypothalamic-pituitary-adrenal axis regulation by its predominant localization in the pituitary. These observations may open up new research strategies not only for several psychiatric disorders, but also for the relationship between psychiatric and somatic diseases.

Comparative analysis of serotonin receptor (HTR1A/HTR1B families) and transporter (slc6a4a/b) gene expression in the zebrafish brain

In this study we analyze 5-hydroxytryptamine [5-HT]; serotonin) signaling in zebrafish, an increasingly popular vertebrate disease model. We compare and contrast expression of the 5-HT transporter genes slc6a4a and slc6a4b, which identify 5-HT-producing neurons and three novel 5-HT receptors, htr1aa, htr1ab, and htr1bd. slc6a4a and slc6a4b are expressed in the raphe nuclei, retina, medulla oblongata, paraventricular organ, pretectal diencephalic complex, and caudal zone of the periventricular hypothalamus, in line with the expression profiles of homologues from other vertebrates. Our analysis of serotonin transporter (SERT)-encoding genes also identifies parallel genetic pathways used to build the 5-HT system in zebrafish. In cells in which 5-HT is synthesized by tph1, slc6a4b is used for re-uptake, whereas tph2-positive cells utilize slc6a4a. The receptors htr1aa, htr1ab, and htr1bd also show widespread expression in both the larval and adult brain. Receptor expression is seen in the superior raphe nucleus, retina, ventral telencephalon, optic tectum, thalamus, posterior tuberculum, cerebellum, hypothalamus, and reticular formation, thus implicating 5-HT signaling in several neural circuits. We also examine larval brains double-labeled with 5-HTergic and dopaminergic pathway-specific antibodies, to uncover the identity of some 5-HTergic target neurons. Furthermore, comparison of the expression of transporter and receptor genes also allows us to map sites of autoreceptor activity within the brain. We detect autoreceptor activity in the pretectal diencephalic cluster (htr1aa-, htr1ab-, htr1bd-, and slc6a4a-positive), superior raphe nucleus (htr1aa-, htr1ab-, and slc6a4a-positive), paraventricular organ (htr1aa-, htr1ab-, htr1bd-, and slc6a4b-positive), and the caudal zone of the periventricular hypothalamus (htr1ab- and slc6a4b-positive).