Developmental regulation of tryptophan hydroxylase messenger RNA expression and enzyme activity in the raphe and its target fields

Neonatal treatment with para-chlorophenylalanine (pCPA) induces adolescent hyperactivity associated with changes in the paraventricular nucleus Crh and Trh expressions

Disruption of the brain serotoninergic (5-HT) system during development induces long-lasting changes in molecular profile, cytoarchitecture, and function of neurons, impacting behavioral regulation throughout life. In male and female rats, we investigate the effect of neonatal tryptophan hydroxylase (TPH) inhibition by using para-chlorophenylalanine (pCPA) on the expression of 5-HTergic system components and neuropeptides related to adolescent social play behavior regulation. We observed sex-dependent 5-HT levels decrease after pCPA-treatment in the dorsal raphe nucleus (DRN) at 17 and 35 days. Neonatal pCPA-treatment increased playing, social and locomotory behaviors assessed in adolescent rats of both sexes. The pCPA-treated rats demonstrated decreased Crh (17 days) and increased Trh (35 days) expression in the hypothalamic paraventricular nucleus (PVN). There was sex dimorphism in Htr2c (17 days) and VGF (35 days) in the prefrontal cortex, with the females expressing higher levels of it than males. Our results indicate that neonatal pCPA-treatment results in a long-lasting and sex-dependent DRN 5-HT synthesis changes, decreased Crh, and increased Trh expression in the PVN, resulting in a hyperactivity-like phenotype during adolescence. The present work demonstrates that the impairment of TPH function leads to neurobehavioral disorders related to hyperactivity and impulsivity, such as attention deficit hyperactivity disorder (ADHD).

Maternal Inflammation with Elevated Kynurenine Metabolites Is Related to the Risk of Abnormal Brain Development and Behavioral Changes in Autism Spectrum Disorder

Several studies show that genetic and environmental factors contribute to the onset and progression of neurodevelopmental disorders. Maternal immune activation (MIA) during gestation is considered one of the major environmental factors driving this process. The kynurenine pathway (KP) is a major route of the essential amino acid L-tryptophan (Trp) catabolism in mammalian cells. Activation of the KP following neuro-inflammation can generate various endogenous neuroactive metabolites that may impact brain functions and behaviors. Additionally, neurotoxic metabolites and excitotoxicity cause long-term changes in the trophic support, glutamatergic system, and synaptic function following KP activation. Therefore, investigating the role of KP metabolites during neurodevelopment will likely promote further understanding of additional pathophysiology of neurodevelopmental disorders, including autism spectrum disorder (ASD). In this review, we describe the changes in KP metabolism in the brain during pregnancy and represent how maternal inflammation and genetic factors influence the KP during development. We overview the patients with ASD clinical data and animal models designed to verify the role of perinatal KP elevation in long-lasting biochemical, neuropathological, and behavioral deficits later in life. Our review will help shed light on new therapeutic strategies and interventions targeting the KP for neurodevelopmental disorders.

Neonatal Serotonin Depletion Induces Hyperactivity and Anxiolytic-like Sex-Dependent Effects in Adult Rats

The serotoninergic system plays an important role in the ontogeny of the mammalian central nervous system, and changes in serotonin production during development may lead to permanent changes in brain cytoarchitecture and function. The present study investigated the programming effects of neonatal serotonin depletion on behavior and molecular components of the serotoninergic system in adult male and female rats. Subcutaneous para-chlorophenylalanine (pCPA) administration (100 mg kg^-1) was performed daily on postnatal days 8-16 to deplete brain serotonin content. During adulthood, elevated plus-maze, open field, social interaction, forced swimming, and food, saline, and sucrose intake tests were performed. Relative expression of serotonin neurotransmission components in several brain areas was determined by qPCR. Additionally, serotonin immunofluorescence and neuropeptide mRNA expression were assessed in dorsal raphe (DRN) and paraventricular (PVN) nuclei, respectively. Rat performance in behavioral tests demonstrated a general increase in locomotor activity and active escape behavior as well as decreased anxiety-like behavior after neonatal brain serotonin depletion. The behavioral programming effects due to neonatal serotonin depletion were more pronounced in females than males. At the gene expression level, the mRNA of Tph1 and Tph2 were lower in DRN while Htr2c was higher in the amygdala of pCPA-treated males, while Htr1a, Htr2c, Oxt, Avp, Crh, and Trh were not different in any treatments or sex in PVN. The results indicate that neonatal serotonin depletion has long-term consequences on locomotion and anxiety-like behavior associated with long-lasting molecular changes in the brain serotoninergic system in adult rats.

Analyzing the Potential Biological Determinants of Autism Spectrum Disorder: From Neuroinflammation to the Kynurenine Pathway

Autism Spectrum Disorder (ASD) etiopathogenesis is still unclear and no effective preventive and treatment measures have been identified. Research has focused on the potential role of neuroinflammation and the Kynurenine pathway; here we review the nature of these interactions. Pre-natal or neonatal infections would induce microglial activation, with secondary consequences on behavior, cognition and neurotransmitter networks. Peripherally, higher levels of pro-inflammatory cytokines and anti-brain antibodies have been identified. Increased frequency of autoimmune diseases, allergies, and recurring infections have been demonstrated both in autistic patients and in their relatives. Genetic studies have also identified some important polymorphisms in chromosome loci related to the human leukocyte antigen (HLA) system. The persistence of immune-inflammatory deregulation would lead to mitochondrial dysfunction and oxidative stress, creating a self-sustaining cytotoxic loop. Chronic inflammation activates the Kynurenine pathway with an increase in neurotoxic metabolites and excitotoxicity, causing long-term changes in the glutamatergic system, trophic support and synaptic function. Furthermore, overactivation of the Kynurenine branch induces depletion of melatonin and serotonin, worsening ASD symptoms. Thus, in genetically predisposed subjects, aberrant neurodevelopment may derive from a complex interplay between inflammatory processes, mitochondrial dysfunction, oxidative stress and Kynurenine pathway overexpression. To validate this hypothesis a new translational research approach is necessary.

Effect of sildenafil citrate on brain central fatigue after exhaustive swimming exercise in rats

Sildenafil citrate, a potent and selective inhibitor of phosphodiesterase type-5, is used clinically to treat erectile dysfunction and pulmonary arterial hypertension. We investigated the effect of sildenafil citrate on brain central fatigue through serotonin (5-hydroxytryptamine, 5-HT) synthesis after exhaustive swimming exercise in rats. The rats in the sildenafil citrate-treated groups received sildenafil citrate orally once a day for 14 consecutive days at respective dosage. On the 14 days after starting experiment, each animal was submitted to swimming test with intensity equivalent to overload. The exhaustion was defined as a state in which coordinated movements did not return to the water surface for breathing within 10 sec. Immunohistochemistry for 5-HT, tryptophan hydroxylase (TPH), and western blot for serotonergic type 1A (5-HT1_A) receptor and 5-HT transporter (5-HTT) were performed. Exhaustive swimming exercise increased 5-HT and TPH expressions in the dorsal raphe and sildenafil citrate suppressed 5-HT and TPH expressions in the exhaustive swimming exercise rats. Exhaustive swimming exercise increased 5-HT1_A receptor and 5-HTT expressions in the dorsal raphe and sildenafil citrate suppressed 5-HT1_A receptor and 5-HTT expressions in the exhaustive swimming exercise rats. The significant suppressing effect appeared in the 20-mg/kg sildenafil citrate. Sildenafil citrate might be proposed as a potential ergogenic aid through anticentral fatigue.

Treadmill exercise improves depression-like symptoms by enhancing serotonergic function through upregulation of 5-HT1A expression in the olfactory bulbectomized rats

The olfactory bulbectomy (OBX) is a well-known method inducing animal model of depression. Depression is associated with dysfunction of serotonin (5-hydroxytryptamine, 5-HT) system. In the present study, antidepressive effect of treadmill exercise was investigated using olfactory bulbectomized rats. After bilateral bulbectomy, the rats in the treadmill exercise groups were subjected to run on a treadmill for 30 min once a day during 28 days. Increased immobility time and decreased fast time in the forced swim test were observed in the olfactory bulbectomized rats. Sucrose preference in the sucrose preference test was decreased and activity in the open field test was also increased in the olfactory bulbectomized rats. Treadmill exercise decreased immobility time and activity and increased fast time and sucrose preference in the olfactory bulbectomized rats. Expressions of 5-HT and tryptophan hydroxylase (TPH) in the dorsal raphe of rats were suppressed by OBX and treadmill exercise increased the expressions of 5-HT and TPH in the olfactory bulbectomized rats. Serotonin receptor type 1A (5-HT1A) expression in the dorsal raphe was reduced by OBX and treadmill exercise increased 5-HT1A expression in the olfactory bulbectomized rats. In the present study, treadmill exercise ameliorated OBX-induced depressive symptoms. The antidepressive effect of treadmill exercise might be ascribed to the enhancement of serotonergic function through upregulation of 5-HT1A expression in the dorsal raphe.

Cellular architecture and transmitter phenotypes of neurons of the mouse median raphe region

The median raphe region (MRR, which consist of MR and paramedian raphe regions) plays a crucial role in regulating cortical as well as subcortical network activity and behavior, while its malfunctioning may lead to disorders, such as schizophrenia, major depression, or anxiety. Mouse MRR neurons are classically identified on the basis of their serotonin (5-HT), vesicular glutamate transporter type 3 (VGLUT3), and gamma-aminobutyric acid (GABA) contents; however, the exact cellular composition of MRR regarding transmitter phenotypes is still unknown. Using an unbiased stereological method, we found that in the MR, 8.5 % of the neurons were 5-HT, 26 % were VGLUT3, and 12.8 % were 5-HT and VGLUT3 positive; whereas 37.2 % of the neurons were GABAergic, and 14.4 % were triple negative. In the whole MRR, 2.1 % of the neurons were 5-HT, 7 % were VGLUT3, and 3.6 % were 5-HT and VGLUT3 positive; whereas 61 % of the neurons were GABAergic. Surprisingly, 25.4 % of the neurons were triple negative and were only positive for the neuronal marker NeuN. PET-1/ePET-Cre transgenic mouse lines are widely used to specifically manipulate only 5-HT containing neurons. Interestingly, however, using the ePET-Cre transgenic mice, we found that far more VGLUT3 positive cells expressed ePET than 5-HT positive cells, and about 38 % of the ePET cells contained only VGLUT3, while more than 30 % of 5-HT cells were ePET negative. These data should facilitate the reinterpretation of PET-1/ePET related data in the literature and the identification of the functional role of a putatively new type of triple-negative neuron in the MRR.

Vortioxetine promotes maturation of dendritic spines in vitro: A comparative study in hippocampal cultures

Cognitive dysfunction is prevalent in patients with major depressive disorder (MDD), and cognitive impairments can persist after relief of depressive symptoms. The multimodal-acting antidepressant vortioxetine is an antagonist at 5-HT3, 5-HT7, and 5-HT1D receptors, a partial agonist at 5-HT1B receptors, an agonist at 5-HT1A receptors, and an inhibitor of the serotonin (5-HT) transporter (SERT) and has pro-cognitive properties. In preclinical studies, vortioxetine enhances long-term potentiation (LTP), a cellular correlate of neuroplasticity, and enhances memory in various cognitive tasks. However, the molecular mechanisms by which vortioxetine augments LTP and memory remain unknown. Dendritic spines are specialized, actin-rich microdomains on dendritic shafts and are major sites of most excitatory synapses. Since dendritic spine remodeling is implicated in synaptic plasticity and spine size dictates the strength of synaptic transmission, we assessed if vortioxetine, relative to other antidepressants including ketamine, duloxetine, and fluoxetine, plays a role in the maintenance of dendritic spine architecture in vitro. We show that vortioxetine, ketamine, and duloxetine induce spine enlargement. However, only vortioxetine treatment increased the number of spines in contact with presynaptic terminals. In contrast, fluoxetine had no effect on spine remodeling. These findings imply that the various 5-HT receptor mechanisms of vortioxetine may play a role in its effect on spine dynamics and in increasing the proportion of potentially functional synaptic contacts.

Effects of chronic fluoxetine treatment on neurogenesis and tryptophan hydroxylase expression in adolescent and adult rats

The antidepressant drug fluoxetine (Prozac) has been increasingly prescribed to children and adolescents with depressive disorders despite a lack of thorough understanding of its therapeutic effects in the paediatric population and of its putative neurodevelopmental effects. Within the framework of PRIOMEDCHILD ERA-NET, we investigated; a) effects of chronic fluoxetine treatment on adult hippocampal neurogenesis, a structural readout relevant for antidepressant action and hippocampal development; b) effects on tryptophan hydroxylase (TPH) expression, a measure of serotonin synthesis; c) whether treatment effects during adolescence differed from treatment at an adult age, and d) whether they were subregion-specific. Stereological quantification of the number of proliferating (Ki-67+) cells and of the number of young migratory neurons (doublecortin+), revealed a significant age-by-treatment interaction effect, indicating that fluoxetine affects both proliferation and neurogenesis in adolescent-treated rats differently than it does in adult-treated rats. In terms of subregional differences, fluoxetine enhanced proliferation mainly in the dorsal parts of the hippocampus, and neurogenesis in both the suprapyramidal and infrapyramidal blades of the dentate gyrus in adolescent-treated rats, while no such differences were seen in adult-treated rats. Fluoxetine exerted similar age-by-treatment interaction effects on TPH cells mainly in the ventral portion of the dorsal raphe nucleus. We conclude that fluoxetine exerts divergent effects on structural plasticity and serotonin synthesis in adolescent versus adult-treated rats. These preliminary data indicate a differential sensitivity of the adolescent brain to this drug and thus warrant further research into their behavioural and translational aspects. Together with recent related findings, they further call for caution in prescribing these drugs to the adolescent population.

Modeling of the hypothalamic-pituitary-adrenal axis-mediated interaction between the serotonin regulation pathway and the stress response using a Boolean approximation: a novel study of depression

Major depressive disorder (MDD) is a multifactorial disorder known to be influenced by both genetic and environmental factors. MDD presents a heritability of 37%, and a genetic contribution has also been observed in studies of family members of individuals with MDD that imply that the probability of suffering the disorder is approximately three times higher if a first-degree family member is affected. Childhood maltreatment and stressful life events (SLEs) have been established as critical environmental factors that profoundly influence the onset of MDD. The serotonin pathway has been a strong candidate for genetic studies, but it only explains a small proportion of the heritability of the disorder, which implies the involvement of other pathways. The serotonin (5-HT) pathway interacts with the stress response pathway in a manner mediated by the hypothalamic-pituitary-adrenal (HPA) axis. To analyze the interaction between the pathways, we propose the use of a synchronous Boolean network (SBN) approximation. The principal aim of this work was to model the interaction between these pathways, taking into consideration the presence of selective serotonin reuptake inhibitors (SSRIs), in order to observe how the pathways interact and to examine if the system is stable. Additionally, we wanted to study which genes or metabolites have the greatest impact on model stability when knocked out in silico. We observed that the biological model generated predicts steady states (attractors) for each of the different runs performed, thereby proving that the system is stable. These attractors changed in shape, especially when anti-depressive drugs were also included in the simulation. This work also predicted that the genes with the greatest impact on model stability were those involved in the neurotrophin pathway, such as CREB, BDNF (which has been associated with major depressive disorder in a variety of studies) and TRkB, followed by genes and metabolites related to 5-HT synthesis.

Role of NAD(+), Oxidative Stress, and Tryptophan Metabolism in Autism Spectrum Disorders

Autism spectrum disorder (ASD) is a pervasive neuro-developmental disorder characterized by impaired social interaction, reduced/absent verbal and non-verbal communication, and repetitive behavior during early childhood. The etiology of this developmental disorder is poorly understood, and no biomarkers have been identified. Identification of novel biochemical markers related to autism would be advantageous for earlier clinical diagnosis and intervention. Studies suggest that oxidative stress-induced mechanisms and reduced antioxidant defense, mitochondrial dysfunction, and impaired energy metabolism (NAD(+), NADH, ATP, pyruvate, and lactate), are major causes of ASD. This review provides renewed insight regarding current autism research related to oxidative stress, mitochondrial dysfunction, and altered tryptophan metabolism in ASD.

Perinatal exposure to bisphenol A enhances contextual fear memory and affects the serotoninergic system in juvenile female mice

Perinatal exposure to bisphenol A (BPA), an endocrine-disrupting chemical, affects the central nervous system, including effects on emotional responses and neurotransmitter release. In this study, we investigated the effects of BPA (250 ng/kg/day, from gestational day 10 to postnatal day 20) on fear memory and serotonin (5-HT) metabolites in the brain using contextual fear conditioning (FC) and high-performance liquid chromatography (HPLC), respectively, in adult and juvenile mice of both sexes. Furthermore, we studied the effects of BPA on the gene expression of 5-HT metabolite-related enzymes and 5-HT receptors using quantitative real-time RT PCR in the brains of juvenile females. BPA enhanced fear memory and increased serotonin metabolite (5-HIAA) levels and 5-HIAA/5-HT in the hippocampus, the striatum, the midbrain, the pons, and the medulla oblongata of juvenile female mice. In contrast, alterations in those areas were much smaller in adult females and in both juvenile and adult males. Furthermore, BPA induced increases in the expression levels of Tph2, Slc6a4, and Maoa mRNA in the hippocampus of juvenile females, indicating that BPA induces hyper 5-HT turnover in the hippocampus. Our results suggest that perinatal exposure to a low dose of BPA enhances fear memory and the 5-HTergic system in juvenile mice.

Interaction between tryptophan hydroxylase I polymorphisms and childhood abuse is associated with increased risk for borderline personality disorder in adulthood

INTRODUCTION

Borderline personality disorder (BPD) is a severe disorder with high morbidity and mortality, but unknown etiology. Childhood abuse has been proposed as an etiological factor, but the mechanism by which an abuse history could influence the risk for BPD has not been determined. The aim of this study was to determine whether the tryptophan hydroxylase 1 (TPH1) gene is related to BPD in a clinical sample, and whether TPH1 genotypes or haplotypes moderate the relationship between abuse history and BPD.

METHODS

Three hundred and ninety-eight patients diagnosed with mood disorders were genotyped for TPH1 G-6526A promoter polymorphism (rs4537731) and the A218C intron 7 polymorphism (rs1800532) and a set of ancestry informative markers, assessed for Diagnostic and Statistical Manual of Mental Disorders, 4th edition diagnoses, and assessed for a history of physical and sexual abuse.

RESULTS

Patients with a diagnosis of BPD were more likely to be risk allele carriers (A alleles at both loci) than the non-BPD group. Logistic regression analysis predicting BPD diagnosis with both single-nucleotide polymorphisms and haplotypes showed significant interaction effects between genotype and abuse history. Poisson regression predicting the number of BPD diagnostic criteria met with the same predictor set also included a significant interaction term. Risk allele carriers with a history of abuse had an increased likelihood of a BPD diagnosis.

CONCLUSION

Variation in TPH1 may increase risk for developing BPD as a result of childhood abuse. Elements of BPD pathology may be due in part to a genetically influenced serotonergic dysfunction, which in turn may lead to a differential response to environmental stressors.

Postnatal changes in tryptophan hydroxylase and serotonin transporter immunoreactivity in multiple brainstem nuclei of the rat: implications for a sensitive period

Previously, we found that the brainstem neuronal network in normal rats undergoes abrupt neurochemical, metabolic, and physiological changes around postnatal days (P) 12-13, a critical period when the animal's response to hypoxia is also the weakest. This has special implications for sudden infant death syndrome (SIDS), insofar as seemingly normal infants succumb to SIDS when exposed to respiratory stressors (e.g., hypoxia) during a narrow postnatal window. Because an abnormal serotonergic system has recently been implicated in SIDS, we conducted a large-scale investigation of the 5-HT-synthesizing enzyme tryptophan hydroxylase (TPH) and serotonin transporter (SERT) with semiquantitative immunohistochemistry in multiple brainstem nuclei of normal rats aged P2-21. We found that 1) TPH and SERT immunoreactivity in neurons of raphé magnus, obscurus, and pallidus and SERT in the neuropil of the pre-Bötzinger complex, nucleus ambiguus, and retrotrapezoid nucleus were high at P2-11 but decreased markedly at P12 and plateaued thereafter until P21; 2) SERT labeling in neurons of the lateral paragigantocellular nucleus (LPGi) and parapyramidal region (pPy) was high at P2-9 but fell significantly at P10, followed by a gradual decline until P21; 3) TPH labeling in neurons of the ventrolateral medullary surface was stable except for a significant fall at P12; and 4) TPH and SERT immunoreactivity in a number of other nuclei was relatively stable from P2 to P21. Thus, multiple brainstem nuclei exhibited a significant decline in TPH and SERT immunoreactivity during the critical period, suggesting that such normal development can contribute to a narrow window of vulnerability in postnatal animals.

The tryptophan hydroxylase 1 (TPH1) gene, schizophrenia susceptibility, and suicidal behavior: a multi-centre case-control study and meta-analysis

Serotonin (5-hydroxytryptamin; 5-HT) alternations has since long been suspected in the pathophysiology of schizophrenia. Tryptophan hydroxylase (tryptophan 5-monooxygenase; TPH) is the rate-limiting enzyme in the biosynthesis of 5-HT, and sequence variation in intron 6 of the TPH1 gene has been associated with schizophrenia. The minor allele (A) of this polymorphism (A218C) is also more frequent in patients who have attempted suicide and individuals who died by suicide, than in healthy control individuals. In an attempt to replicate previous findings, five single nucleotide polymorphisms (SNPs) were genotyped in 837 Scandinavian schizophrenia patients and 1,473 controls. Three SNPs spanning intron 6 and 7, including the A218C and A779C polymorphisms, were associated with schizophrenia susceptibility (P = 0.019). However there were no differences in allele frequencies of these loci between affected individuals having attempted suicide at least once and patients with no history of suicide attempts (P = 0.84). A systematic literature review and meta-analysis support the A218C polymorphism as a susceptibility locus for schizophrenia (odds ratio 1.17, 95% confidence interval 1.07-1.29). Association studies on suicide attempts are however conflicting (heterogeneity index I(2) = 0.54) and do not support the A218C/A779C polymorphisms being a susceptibility locus for suicidal behavior among individuals diagnosed with a psychiatric disorder (OR = 0.96 [0.80-1.16]). We conclude that the TPH1 A218/A779 locus increases the susceptibility of schizophrenia in Caucasian and Asian populations. In addition, the data at hand suggest that the locus contributes to the liability of psychiatric disorders characterized by elevated suicidal rates, rather than affecting suicidal behavior of individuals suffering from a psychiatric disorder.

Vardenafil increases cell proliferation in the dentate gyrus through enhancement of serotonin expression in the rat dorsal raphe

This study was conducted to evaluate the effects of vardenafil (Levitra), a phosphodiesterase-5 (PDE-5) inhibitor, on cell proliferation in the hippocampal dentate gyrus and on 5-hyroxytryptamine (5-HT, serotonin) synthesis and tryptophan hydroxylase (TPH) expression in the rat dorsal raphe nucleus. Male Sprague-Dawley rats were divided into 6 groups (n=5 in each group): a control group, a 0.5 mg/kg-1 day vardenafil-treated group, a 1 mg/kg-1 day vardenafil-treated group, a 2 mg/kg-1 day vardenafil-treated group, a 1 mg/kg-3 day vardenafil-treated group, and a 1 mg/kg-7 day vardenafil-treated group. 5-bromo-2'-deoxyuridine (BrdU) immunohistochemistry was then performed to evaluate cell proliferation in the dentate gyrus. In addition, 5-HT and TPH immunohistochemistry was conducted to evaluate serotonin expression in the dorsal raphe. The results revealed that treatment with vardenafil increased cell proliferation in the dentate gyrus and enhanced 5-HT synthesis and TPH expression in the dorsal raphe in a dose- and duration-dependent manner. The findings demonstrate that the increasing effect of vardenafil on cell proliferation is closely associated with the enhancing effect of vardenafil on serotonin expression under normal conditions.

The tryptophan hydroxylase-1 A218C polymorphism is associated with diagnosis, but not suicidal behavior, in borderline personality disorder

While there is some preliminary evidence that the tryptophan hydroxylase I (TPH1) polymorphisms are related to Borderline Personality Disorder (BPD), it is not clear if this association is due to the high rates of suicidal behavior in this patient group. Because of the reported association between TPH1 polymorphisms and suicidal behavior, determining whether TPH1 is related to BPD independent of suicidal behavior is of particular importance. One hundred patients diagnosed with BPD and 101 healthy controls were genotyped for TPH1 intron 7 A218C polymorphism and assessed for impulsiveness and hostility. The BPD patient group had a higher frequency of A allele carriers (AA/AC genotypes) than the control group (chi(2) = 6.12, df = 1, P = 0.01), and differed by genotype frequencies (P = 0.03). Suicide attempter status in the patient group was not related to genotype. Logistic regression analysis controlling for age and gender predicted BPD diagnosis from TPH1 allele group (AA/AC vs. CC, P = 0.03), and TPH1 heterozygotes (AC) appeared to have the highest risk for BPD (P = 0.03). In the full sample, participants with the AC genotype had higher impulsiveness and hostility scores. However, TPH1 did not predict these traits in either of the groups independently, suggesting the association may be an artifact of the association between TPH1 and BPD. Results suggest that the A allele of the tryptophan hydroxylase-1 A218 polymorphism may be associated with BPD, and that it does not appear to be related to suicidal behavior in this population. An aspect of BPD pathology may be due to serotonergic dysfunction.

Early life stress and novelty seeking behavior in adolescent monkeys

Recent evidence suggests that early exposure to mild stress promotes the development of novelty seeking behavior. Here we test this hypothesis in squirrel monkeys and investigate whether novelty seeking behavior is associated with differences in cerebrospinal fluid (CSF) levels of the serotonin metabolite 5-hydroxyindoleacetic acid (5HIAA), the dopamine metabolite homovanillic acid (HVA), the norepinephrine metabolite 3-methoxy-4-hydroxyphenylethylene glycol (MHPG), and the neuropeptide corticotrophin-releasing factor (CRF). Monkeys were randomized early in life to either mild intermittent stress (IS) or no stress (NS) conditions, and subsequently presented with opportunities to interact with a familiar or novel object in a test box that was connected to each monkey's home cage. To further minimize the potentially stressful nature of the test situation, monkeys were acclimated to the test procedures prior to study initiation. Post-test plasma levels of cortisol in IS and NS monkeys did not differ significantly from baseline levels measured in undisturbed conditions. During testing, more IS than NS monkeys voluntarily left the home cage, and IS monkeys spent more time in the test box compared to NS monkeys. More IS than NS monkeys engaged in object exploration in the test box, and IS monkeys preferred to interact with the novel vs. familiar object. Novelty seeking was not associated with differences in 5HIAA, HVA, MHPG, or CRF, but correlated with differences in object exploration observed in a different test situation at an earlier age. These trait-like differences in novelty seeking appear to reflect mild early stress-induced adaptations that enhance curiosity and resilience.

Late developmental stage-specific role of tryptophan hydroxylase 1 in brain serotonin levels

Serotonin [5-hydroxytryptamine (5-HT)] is a major therapeutic target of psychiatric disorders. Tryptophan hydroxylase (TPH) catalyzes the rate-limiting reaction in the biosynthesis of 5-HT. Two isoforms (TPH1 and TPH2) having tryptophan hydroxylating activity were identified. Association studies have revealed possible TPH1 involvement in psychiatric conditions and behavioral traits. However, TPH1 mRNA was reported to be mainly expressed in the pineal gland and the periphery and to be barely detected in the brain. Therefore, contribution of TPH1 to brain 5-HT levels is not known, and the mechanisms how TPH1 possibly contributes to the pathogenesis of psychiatric disorders are not understood. Here, we show an unexpected role of TPH1 in the developing brain. We found that TPH1 is expressed preferentially during the late developmental stage in the mouse brain. TPH1 showed higher affinity to tryptophan and stronger enzyme activity than TPH2 in a condition reflecting that of the developing brainstem. Low 5-HT contents in the raphe nucleus were seen during development in New Zealand white (NZW) and SWR mice having common functional polymorphisms in the TPH1 gene. However, the 5-HT contents in these mice were not reduced in adulthood. In adult NZW and SWR mice, depression-related behavior was observed. Considering an involvement of developmental brain disturbance in psychiatric disorders, TPH1 may act specifically on development of 5-HT neurons, and thereby influence behavior later in life.

Neonatal antidepressant exposure has lasting effects on behavior and serotonin circuitry

A significant fraction of infants born to mothers taking selective serotonin reuptake inhibitors (SSRIs) during late pregnancy display clear signs of antidepressant withdrawal indicating that these drugs can penetrate fetal brain in utero at biologically significant levels. Previous studies in rodents have demonstrated that early exposure to some antidepressants can result in persistent abnormalities in adult behavior and indices of monoaminergic activity. Here, we show that chronic neonatal (postnatal days 8-21) exposure to citalopram (5 mg/kg, twice daily, s.c.), a potent and highly selective SSRI, results in profound reductions in both the rate-limiting serotonin synthetic enzyme (tryptophan hydroxylase) in dorsal raphe and in serotonin transporter expression in cortex that persist into adulthood. Furthermore, neonatal exposure to citalopram produces selective changes in behavior in adult rats including increased locomotor activity and decreased sexual behavior similar to that previously reported for antidepressants that are nonselective monoamine transport inhibitors. These data indicate that the previously reported neurobehavioral effects of antidepressants are a consequence of their effects on the serotonin transporter. Moreover, these data argue that exposure to SSRIs at an early age can disrupt the normal maturation of the serotonin system and alter serotonin-dependent neuronal processes. It is not known whether this effect of SSRIs is paralleled in humans; however, these data suggest that in utero, exposure to SSRIs may have unforeseen long-term neurobehavioral consequences.

Postnatal development of cholinergic neurons in the mesopontine tegmentum revealed by histochemistry

Cholinergic neurons in the laterodorsal tegmental nucleus (LDT) and pedunculopontine tegmental nucleus (PPT) play a role in the regulation of several kinds of behavior. Some of them, such as locomotion, motor inhibition or sleep, show dramatic changes at a certain period of postnatal development. To understand the neural substrate for the development of these physiological functions, we studied the development of cholinergic neurons in the LDT and PPT of postnatal and adult rats using histochemical staining of NADPH-diaphorase (NADPH-d) and immunohistochemical staining of choline acetyltransferase (ChAT) and the vesicular acetylcholine transporter (VAChT). At postnatal day 1 (P1), ChAT- and VAChT-stained cells localized more dorsally than those of NADPH-d-stained cells, and at P7 their distributions became similar to those of NADPH-d-stained cells. The number of NADPH-d-stained cells increased rapidly after birth, reaching the adult level by P7. In contrast, the number of ChAT- and VAChT-stained cells and the intensity of their staining decreased from P1 to P3 and then increased through P21. The volume of the LDT increased during the second postnatal week. These findings indicate that cholinergic neurons in the LDT develop their cholinergic properties during the second postnatal week and mature functionally thereafter. We discuss these results in light of the several physiological functions regulated by the cholinergic neurons in the mesopontine tegmentum.

Maternal ethanol administration inhibits 5-hydroxytryptamine synthesis and tryptophan hydroxylase expression in the dorsal raphe of rat offspring

Maternal ethanol consumption during pregnancy has a detrimental effect on the central nervous system (CNS) development of fetus. 5-Hydroxytryptamine (5-HT) is an important neurotransmitter and/or neuromodulator in the mammalian CNS. Tryptophan hydroxylase (TPH) is the rate limiting enzyme of 5-HT synthesis. Ethanol is known to induce neuropsychiatric disorders by alteration of the central serotonergic system. In the present study, the effects of maternal ethanol intake on the 5-HT synthesis and the TPH expression in the dorsal raphe of rat offspring were investigated. The present results show that the synthesis of 5-HT and the expression of TPH in the dorsal raphe of rat offspring were suppressed by maternal ethanol intake and that the suppressive effect of alcohol was more potent in the 5 weeks old rat pups compared to the 3 weeks old rat pups. Based on the present study, it can be suggested that the pathogenesis of ethanol-induced neuropsychological disorders involves ethanol-induced suppression on the 5-HT synthesis and the TPH expression in the dorsal raphe of offspring.

Cerebrospinal fluid and serum markers of inflammation in autism

Systemic immune abnormalities have no known relevance to brain dysfunction in autism. In order to find evidence for neuroinflammation, we compared levels of sensitive indicators of immune activation: quinolinic acid, neopterin, and biopterin, as well as multiple cytokines and cytokine receptors, in cerebrospinal fluid and serum from children with autism, to control subjects with other neurologic disorders. In cerebrospinal fluid from 12 children with autism, quinolinic acid (P = 0.037) and neopterin (P = 0.003) were decreased, and biopterin (P = 0.040) was elevated, compared with control subjects. In sera from 35 persons with autism, among cytokines, only tumor necrosis factor receptor II was elevated compared with controls (P < 0.02). Decreased quinolinic acid and neopterin in cerebrospinal fluid are paradoxical and suggest dysmaturation of metabolic pathways and absence of concurrent infection, respectively, in autism. Alternatively, they may be produced by microglia but remain localized and not expressed in cerebrospinal fluid.

The Ets transcription factor Fev is specifically expressed in the human central serotonergic neurons

In the mouse and the rat brain, the Ets transcription factor pet-1 is exclusively expressed in the central serotonin (5-hydroxytryptaminergic: 5-HT) system. In pet-1 null mice, the defect of this factor induces early disruption of the 5-HT function, resulting in an increase in anxiety and aggression; thus indicating its pivotal role in this system. Here, we studied the expression of fev, the homologue of pet-1, in the human brain. We showed that this transcription factor is exclusively expressed in the midline part of the human brainstem containing raphe nuclei, which also specifically expressed 5-HT transporter (sert) and tryptophan hydroxylase (tph), two markers of the 5-HT neurotransmitter system. This clearly suggests that fev is expressed in human serotonergic neurons. While the deficiency of the central serotonergic signaling is a major factor involved in the development of some psychiatric disorders, Fev could be a good diagnosis marker as well as a good target for pharmacological treatments of these patients.

Median and dorsal raphe neurons are not electrophysiologically identical

The dorsal (DR) and median raphe (MR) nuclei contain 5-hydroxytryptamine (serotonin, 5-HT) cell bodies that give rise to the majority of the ascending 5-HT projections to the forebrain limbic areas that control emotional behavior. In the past, the electrophysiological identification of neurochemically identified 5-HT neurons has been limited. Recent technical developments have made it possible to re-examine the electrophysiological characteristics of identified 5-HT- and non-5-HT-containing neurons. Visualized whole cell electrophysiological techniques in combination with fluorescence immunohistochemistry for 5-HT were used. In the DR, both 5-HT- and non-5-HT-containing neurons exhibited similar characteristics that have historically been attributed to putative 5-HT neurons. In contrast, in the MR, the 5-HT-and non-5-HT-containing neurons had very different characteristics. Interestingly, the MR 5-HT-containing neurons had a shorter time constant and larger afterhyperpolarization (AHP) amplitude than DR 5-HT-containing neurons. The 5-HT(1A) receptor-mediated response was also measured. The efficacy of the response elicited by 5-HT(1A) receptor activation was greater in 5-HT-containing neurons in the DR than the MR, whereas the potency was similar, implicating greater autoinhibition in the DR. Non-5-HT-containing neurons in the DR were responsive to 5-HT(1A) receptor activation, whereas the non-5-HT-containing neurons in the MR were not. These differences in the cellular characteristics and 5-HT(1A) receptor-mediated responses between the MR and DR neurons may be extremely important in understanding the role of these two 5-HT circuits in normal physiological processes and in the etiology and treatment of pathophysiological states.

Characterization of reproductive steroid receptors and response to estrogen in a rat serotonergic cell line

Study of the cellular and molecular consequences of steroid hormone action in the serotonin neural system will provide new avenues for pharmacotherapeutic intervention in mental illness related to reproductive function. However, it is difficult to probe intracellular mechanisms with whole animal models. We sought the steroid receptor compliment and estrogen response of two rat serotonin cell lines in order to determine if they could be of future assistance in this matter. Immunohistochemistry with a panel of antibodies, RT-PCR and a serotonin ELISA were utilized to characterize the RN46A-V1 cells (herein called RN46A), and the subclone RN46A-B14 (herein called B14) that is stably transfected with brain derived neurotrophic factor (BDNF). RN46A and B14 cells express estrogen receptor beta (ERbeta), androgen receptors (AR) and nuclear factor kappa B (NFkappaB) but not estrogen receptor alpha (ERalpha) or progestin receptors (PR). RT-PCR confirmed the presence of ERbeta and the absence of ERalpha and PR in both cell lines. B14 cells contain more immunodetectable BDNF and serotonin than the RN46A parent line. In addition, immunofluorescence for the serotonin reuptake transporter (SERT) was observed in the cell body region of undifferentiated B14 cells. After differentiation at a nonpermissive temperature, SERT immunostaining was observed in both the cell body region and along the extent of the axons. Serotonin content as determined by ELISA was higher in B14 than RN46A cells. Estrogen (0.1 and 1.0 nM) stimulated serotonin in the B14 cells in serum free medium. In summary, the RN46A cells and the B14 subclone contain the same compliment of nuclear steroid receptors as rat raphe serotonin neurons and thus may provide a convenient in vitro model for study of intracellular mechanisms of action of steroid hormones in the context of a serotonin neuron.

Corn feeding during development induces changes in the number of serotonergic neurons in the raphe nuclei

Serotonin (5-HT) plays a trophic role during brain development; chronic changes in cerebral concentration of this neurotransmitter during the critical stage of development can produce severe damage in the formation of the neural circuits. For the present work a hypoproteic (HYP) diet based on corn (CORN) meal which is deficient in tryptophan (TRY) was given to rats before and during pregnancy, which continued to the offspring until they reached 60 days of age. An isocaloric but hypoproteic diet containing normal amount of TRY, and normal chow (Ch) Purina were given with the same scheme to two groups of rats considered as controls. 5-HT immunohistochemistry was revealed by avidin-biotin complex (ABC) method to quantify serotonergic nerve cells in the nine raphe nuclei. The number of cells immunoreactive to 5-HT immunoreactive (5-HTir) were quantified by means of stereological analysis. Results demonstrated a significant variation in 5-HT expression in the raphe nuclei. Thus, a significant reduction in the number of 5-HTir cells in the rostral raphe nuclei was seen at all ages studied in the animals fed the corn diet, compared to data obtained from the control groups. This decrease was more evident between the postnatal ages of 30 and 60 days. It is concluded that the variations in the available TRY affect the brain cells producing 5-HT and the innervation of their target areas.

Pet-1 ETS gene plays a critical role in 5-HT neuron development and is required for normal anxiety-like and aggressive behavior

The central serotonin (5-HT) neurotransmitter system is an important modulator of diverse physiological processes and behaviors; however, the transcriptional mechanisms controlling its development are largely unknown. The Pet-1 ETS factor is a precise marker of developing and adult 5-HT neurons and is expressed shortly before 5-HT appears in the hindbrain. Here we show that in mice lacking Pet-1, the majority of 5-HT neurons fail to differentiate. Remaining ones show deficient expression of genes required for 5-HT synthesis, uptake, and storage. Significantly, defective development of the 5-HT system is followed by heightened anxiety-like and aggressive behavior in adults. These findings indicate that Pet-1 is a critical determinant of 5-HT neuron identity and implicate a Pet-1-dependent program in serotonergic modulation of behavior.

Alcohol and nicotine administration inhibits serotonin synthesis and tryptophan hydroxylase expression in dorsal and median raphe of young rats

Serotonin (5-hydroxytryptamine, 5-HT) has been implicated in the pathophysiology of various neuropsychiatric disorders. In the present study, the effects of alcohol and nicotine on the synthesis of 5-HT and the expression of tryptophan hydroxylase (TPH), the rate-limiting enzyme of 5-HT synthesis, in the dorsal and median raphe of young rats were investigated via immunohistochemistry. The numbers of the 5-HT-positive and TPH-positive cells were reduced by alcohol and nicotine treatment in a dose-dependent manner. Based on the results, it can be suggested that the pathogenesis of alcohol- and nicotine-induced neuropsychological disorders involves alcohol- and nicotine-induced suppression of 5-HT synthesis and TPH expression in raphe, and that this may be of particular relevance in the consumption of alcohol and nicotine during adolescence.

Autoregulation of cell-specific MAP kinase control of the tryptophan hydroxylase promoter

The neurotransmitter serotonin controls a wide range of biological systems, including its own synthesis and release. As the rate-limiting enzyme in serotonin biosynthesis, tryptophan hydroxylase (TPH) is a potential target for this autoregulation. Using the serotonergic neuron-like CA77 cell line, we have demonstrated that treatment with a 5-hydroxytryptamine autoreceptor agonist, CGS 12066A, can lower TPH mRNA levels and promoter activity. We reasoned that this repression might involve inhibition of MAP kinases, since 5-HT1 receptors can increase mitogen-activated protein (MAP) kinase phosphatase levels. To test this hypothesis, we first showed that the TPH promoter can be activated 20-fold by mitogen-activated extracellular-signal regulated kinase kinase kinase (MEKK), an activator of MAP kinases. This activation was then blocked by CGS 12066A. The maximal MAP kinase and CGS repression regulatory region was mapped to between -149 and -45 base pairs upstream of the transcription start site. The activation by MEKK appears to be cell-specific, because MEKK did not activate the TPH promoter in nonneuronal cell lines. At least part, but not all, of the MAP kinase responsiveness was mapped to an inverted CCAAT box that binds the transcription factor NF-Y. These data suggest a model for the autoregulation of serotonin biosynthesis by repression of MAP kinase stimulation of the TPH promoter.