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ِAim: Tryptophan hydroxylase-2 mRNA (TPH, the rate limiting enzyme in 5-HT synthesis) expression levels display circadian variations in the median and dorsal raphe nuclei. This circadian pattern is under the control of the suprachiasmatic nuclei (SCN), the master clock. Photoperiodic cue is encoded by the SCN which convey the seasonal message to target sites. In the present study, we have investigated the effect of photoperiodic changes on the serotonergic neurons of the raphe nuclei. We have assessed the daily expression of TPH2 mRNA in both median and dorsal raphe nuclei of rats housed either under long photoperiod (18 h light/6 h dark cycle, LP18:6) or short photoperiod (SP6:18). ٌ Results: Our results demonstrate that under LP18:6, TPH2 mRNA levels display a progressive decrease during the dark period and a maximal expression is reported at the beginning of the light period. The expression pattern of TPH2 mRNA under SP6:18 remains unchanged during the dark period and increases significantly before the light/dark transition. This latter expression pattern is in line with the daily profiles of TPH2 mRNA reported previously under standard lighting regimen (12 h light/12 h dark cycle). Conclusion: The present results suggest that TPH2 mRNA expression pattern within DR and MR is affected by photoperiod which might in turn affect TPH content and 5‐HT release within the circadian structures, but also in all the serotonergic projection areas of the brain. [ABSTRACT FROM AUTHOR]

Premature ejaculation (PE) is one of the most common ejaculatory disorders. Recent studies have suggested a close relationship between the serotonin (5-hydroxytryptamine [5-HT]) system and brain-derived neurotrophic factor (BDNF), raising the question of whether BDNF plays a role in ejaculation regulation. To our knowledge, no previous studies have explored BDNF level of the central nervous system in ejaculatory disorders. At the same time, the interaction of central BDNF and 5-HT systems has not been undertaken in ejaculation regulation field. The aim of this study was to investigate the interaction between BDNF and 5-HT levels in raphe nuclei which contains the serotonergic neurons in a rat animal model with different ejaculatory behavior. Eighteen male rats were selected and classified as "sluggish," "normal," and "rapid" ejaculators on the basis of ejaculation frequency during copulatory behavioral testing. BDNF and 5-HT levels were determined by enzyme-linked immunosorbent assay (ELISA). Real-Time Quantitative PCR and Western blot analyses were used to measure the mRNA level of Tryptophan Hydroxylase-2 (TPH2) gene and the expression of TPH2 protein (the rate-limiting enzyme in central 5-HT synthesis) in raphe nuclei, respectively. Male rat sexual behavior, the levels of BDNF and 5-HT in raphe nuclei of rats with different ejaculatory behavior, the mRNA level of gene encoding TPH2 and the expression of TPH2 protein in raphe nuclei. The primary finding of our study was that BDNF concentration was significantly decreased in raphe nuclei of rapid ejaculators. There was a strong positive correlation between the levels of BDNF and 5-HT (r = 0.944, P <.001). Further results showed that decreased TPH2 gene expression accompanied by TPH2 protein was shown in rapid ejaculators with lower BDNF level. With refinement of current knowledge, BDNF may eventually serve as a promising biomarker in patients with PE. There are no previous studies examining the interaction of the brain BDNF and 5-HT in ejaculation regulation field. The main limitation is the limited sample size. BDNF may act via increasing the synthesis of central 5-HT in the process of ejaculation regulation. Our results suggest lack of endogenous BDNF induces the downregulation of TPH2 gene expression and the decrease of 5-HT synthesis in raphe nuclei of rapid ejaculator rats. Huang Y, Peng D, Geng H, et al. Endogenous Deficiency of Brain-Derived Neurotrophic Factor Induces the Downregulation of Tryptophan Hydroxylase-2 Expression in Raphe Nuclei of Rapid Ejaculator Rats. J Sex Med 2021;18:1491–1499. [ABSTRACT FROM AUTHOR]

A number of studies implicate biogenic amines in regulating circadian rhythms. In particular, dopamine and serotonin influence the entrainment of circadian rhythms to daily food availability. To study circadian entrainment to feeding, food availability is typically restricted to a short period within the light cycle daily. This results in a notable increase in pre-meal activity, termed “food anticipatory activity” (FAA), which typically develops within about 1 week of scheduled feeding. Several studies have implicated serotonin as a negative regulator of FAA: (1) aged rats treated with serotonin 5-HT2 and 3 receptor antagonists showed enhanced FAA, (2) mice lacking for the 2C serotonin receptor demonstrate enhanced FAA, and (3) pharmacologically increased serotonin levels suppressed FAA while decreased serotonin levels enhanced FAA in mice. We sought to confirm and extend these findings using genetic models with impairments in central serotonin production or re-uptake, but were surprised to find that both serotonin transporter (Slc6a4) and tryptophan hydroxylase-2 knockout mice demonstrated a normal behavioral response to timed, calorie restricted feeding. Our data suggest that FAA is largely independent of central serotonin and/or serotonin reuptake and that serotonin may not be a robust negative regulator of FAA.

Abstract—In order to investigate the joint influence of C1473G polymorphism in the gene encoding the key enzyme for serotonin (5-HT) biosynthesis in brain – tryptophan hydroxylase-2, and the distal fragment (103,9-112,4 Мbp) of chromosome 13, including 5-HT1A serotonin receptor gene from catalepsy-prone CBA strain, on the brain 5-HT system, new recombinant mice strain B6-1473GG.CBA-CD13Mit76С (1473GG-76C) and B6-1473GG.CBA-D13Mit76В (1473GG-76B) on the base of C57BL/6 strain were created. The 1473GG-76C and 1473GG-76B lines carry a fragment of chromosome 13 containing Htr1a gene from the CBA and the C57BL/6 strains respectively. Both lines are homozygous by 1473G-allele, reducing the activity of TPH-2. It was shown that the 1473GG-76C line is characterized by increased levels of mRNA of Htr1a, Htr2a genes and Maoa gene (monoamine oxidase type A—the main enzyme of 5-HT degradation) in the midbrain, Htr1a gene in the cortex, Htr1a and Htr2a genes in the hippocampus as compared to 1473GG-76B. In addition, the 1473GG-76C line has increased expression of genes encoding the key regulators of Htr1a gene—FREUD-1 and FREUD-2. The mRNA level of the Cc2d1a gene encoding FREUD-1 was increased in the cortex, and the expression of the Cc2d1b gene encoding FREUD-2 was enhanced in the midbrain. Also, the 1473GG-76C line has increased 5-HT levels in the midbrain, hypothalamus and hippocampus. At the same time, the level of the main 5-HT metabolite, 5-HIAA, was decreased in the midbrain and cortex of these mice. The ratio of 5-HIAA/5-HT reflecting the intensity of 5-HT metabolism was reduced in all investigated structures of 1473GG-76C mice. Thus, the combination of 1473G-allelele of Tph2 gene with Htr1a gene from the CBA strain had a significant effect on the mRNA levels of the key genes of the 5-HT system and on 5-HT metabolism in the brain of 1473GG-76C mice. [ABSTRACT FROM AUTHOR]

A number of studies implicate biogenic amines in regulating circadian rhythms. In particular, dopamine and serotonin influence the entrainment of circadian rhythms to daily food availability. To study circadian entrainment to feeding, food availability is typically restricted to a short period within the light cycle daily. This results in a notable increase in pre-meal activity, termed "food anticipatory activity" (FAA), which typically develops within about 1 week of scheduled feeding. Several studies have implicated serotonin as a negative regulator of FAA: (1) aged rats treated with serotonin 5-HT2 and 3 receptor antagonists showed enhanced FAA, (2) mice lacking for the 2C serotonin receptor demonstrate enhanced FAA, and (3) pharmacologically increased serotonin levels suppressed FAA while decreased serotonin levels enhanced FAA in mice. We sought to confirm and extend these findings using genetic models with impairments in central serotonin production or re-uptake, but were surprised to find that both serotonin transporter (Slc6a4) and tryptophan hydroxylase-2 knockout mice demonstrated a normal behavioral response to timed, calorie restricted feeding. Our data suggest that FAA is largely independent of central serotonin and/or serotonin reuptake and that serotonin may not be a robust negative regulator of FAA. [ABSTRACT FROM AUTHOR]

Serotonin and its signaling pathways are involved in the central regulation of feeding behavior and energy metabolism. The most important role in this regulation is played by dopaminergic neurons of the dorsal raphe nucleus (DRN) and ventral tegmental area (VTA) which express tryptophan hydroxylase 2 (TPH2) catalyzing the rate-limiting step in serotonin synthesis. Changes in activity of the serotonin-synthesizing system in the DRN and VTA may significantly contribute to the development of metabolic disorders, including obesity. However, data on TPH2 expression in these brain regions in obesity are unavailable. The aim of this work was to compare immunohistochemically TPH2 expression in the DRN and VTA of C57Bl/6J (a/a) female mice with a diet-induced obesity (DIO) (caused by 8- and 16-week intake of high-calorie food) and C57Bl/6J (Ay/a) agouti mice with genetically predetermined melanocortin obesity. Double immunolabeling demonstrated that in DIO mice with a 16-week high-calorie diet TPH2 expression in the DRN (the main cerebral source of serotonin) decreases while in the VTA increases. In agouti mice, TPH2 expression in the DRN did not change while in the VTA increased. In DIO mice with a 8-week high-calorie diet and in C57Bl/6J (a/a) mice resistant to this diet, TPH2 expression did not change both in the DRN and VTA. Thus, DIO mice kept on a long-term (16 weeks) diet and agouti mice with melanocortin obesity exhibit specific changes in the serotonin synthesis that are lacking in diet-resistant mice. This finding indicates a crucial role of serotonin signaling in the organismal response to excessive caloric intake. [ABSTRACT FROM AUTHOR]

Background: Sleep disturbances, such as early wakening, are frequently observed in patients with major depressive disorder (MDD). The suprachiasmatic nuclei (SCN), which controls circadian rhythm, is innervated by the raphe nucleus, a region where Tryptophan hydroxylase-2 (TPH-2) gene is primarily expressed. Although TPH-2 is often implicated in the pathophysiology of depression, few studies have applied a genetic and imaging technique to investigate the mechanism of early wakening symptom in MDD. We hypothesized that TPH-2 variants could influence the function of SCN in MDD patients with early wakening symptom.Methods: One hundred and eighty five MDD patients (62 patients without early wakening and 123 patients with early wakening) and 64 healthy controls participated in this study. Blood samples were collected and genotyping of rs4290270, rs4570625, rs11178998, rs7305115, rs41317118, and rs17110747 were performed by next-generation sequencing (NGS) technology. Logistic regression model was employed for genetic data analysis using the PLINK software. Based on the allele type, rs4290270, which was significant in the early wakening MDD group, participants were categorized into two groups (A allele and T carrier). All patients underwent whole brain resting-state functional magnetic resonance imaging (rs-fMRI) scanning and a voxel-wise functional connectivity comparison was performed between the groups.Results: rs4290270 was significantly linked to MDD patients who exhibited early wakening symptom. The functional connectivities of the right SCN with the right fusiform gyrus and right middle frontal gyrus were increased in the T carrier group compared to the A allele group. In addition, the functional connectivities of the left SCN with the right lingual gyrus and left calcarine sulcus were decreased in the T carrier group compared to the A allele group.Conclusion: These findings suggested that the TPH-2 gene variant, rs4290270, affected the circadian regulating function of SCN. The altered functional connectivities, observed between the SCN and right fusiform gyrus, right middle frontal gyrus, the right lingual gyrus and left calcarine sulcus, could highlight the neural mechanism by which SCN induces sleep-related circadian disruption in T carrier MDD patients. Hence, rs4290270 could potentially serve as a reliable biomarker to identify MDD patients with early wakening symptom.

Background: Sleep disturbances, such as early wakening, are frequently observed in patients with major depressive disorder (MDD). The suprachiasmatic nuclei (SCN), which controls circadian rhythm, is innervated by the raphe nucleus, a region where Tryptophan hydroxylase-2 (TPH-2) gene is primarily expressed. Although TPH-2 is often implicated in the pathophysiology of depression, few studies have applied a genetic and imaging technique to investigate the mechanism of early wakening symptom in MDD. We hypothesized that TPH-2 variants could influence the function of SCN in MDD patients with early wakening symptom. Methods: One hundred and eighty five MDD patients (62 patients without early wakening and 123 patients with early wakening) and 64 healthy controls participated in this study. Blood samples were collected and genotyping of rs4290270, rs4570625, rs11178998, rs7305115, rs41317118, and rs17110747 were performed by next-generation sequencing (NGS) technology. Logistic regression model was employed for genetic data analysis using the PLINK software. Based on the allele type, rs4290270, which was significant in the early wakening MDD group, participants were categorized into two groups (A allele and T carrier). All patients underwent whole brain resting-state functional magnetic resonance imaging (rs-fMRI) scanning and a voxel-wise functional connectivity comparison was performed between the groups. Results: rs4290270 was significantly linked to MDD patients who exhibited early wakening symptom. The functional connectivities of the right SCN with the right fusiform gyrus and right middle frontal gyrus were increased in the T carrier group compared to the A allele group. In addition, the functional connectivities of the left SCN with the right lingual gyrus and left calcarine sulcus were decreased in the T carrier group compared to the A allele group. Conclusion: These findings suggested that the TPH-2 gene variant, rs4290270, affected the circadian regulating function of SCN. The altered functional connectivities, observed between the SCN and right fusiform gyrus, right middle frontal gyrus, the right lingual gyrus and left calcarine sulcus, could highlight the neural mechanism by which SCN induces sleep-related circadian disruption in T carrier MDD patients. Hence, rs4290270 could potentially serve as a reliable biomarker to identify MDD patients with early wakening symptom. [ABSTRACT FROM AUTHOR]

Variants of tryptophan hydroxylase-2 (Tph2), the gene encoding enzyme responsible for the synthesis of brain serotonin (5- HT), have been associated with neuropsychiatric disorders, substance abuse and addiction. This study assessed the effect of Tph2 gene deletion on motor behavior and found that motor activity induced by 2.5 and 5 mg/kg amphetamine was enhanced in Tph2−/− mice. Using the in vivo microdialysis technique we found that the ability of amphetamine to stimulate noradrenaline ( NA) release in the striatum was reduced by about 50% in Tph2−/− mice while the release of dopamine ( DA) was not affected. Tph2 deletion did not affect the release of NA and DA in the prefrontal cortex. The role of endogenous 5- HT in enhancing the effect of amphetamine was confirmed showing that treatment with the 5- HT precursor 5-hydroxytryptophan (10 mg/kg) restored tissue and extracellular levels of brain 5- HT and the effects of amphetamine on striatal NA release and motor activity in Tph2−/− mice. Treatment with the NA precursor dihydroxyphenylserine (400 mg/kg) was sufficient to restore the effect of amphetamine on striatal NA release and motor activity in Tph2−/− mice. These findings indicate that amphetamine-induced hyperactivity is attenuated by endogenous 5- HT through the inhibition of striatal NA release. Tph2−/− mice may be a useful preclinical model to assess the role of 5- HT-dependent mechanisms in the action of psychostimulants. [ABSTRACT FROM AUTHOR]

Stressful events induce changes in the expression of numerous genes and their protein products in the brain. However, the mechanisms mediating these changes, as well as their significance for the development of stress-induced depression or for coping with stress, remain obscure. Evidence for the sensitivity of tryptophan hydroxylase-2 (TPH2), the rate-limiting enzyme of the serotonin (5-HT) pathway, to stress is concisely reviewed, as well as the neuroprotective function of the antiapoptotic protein Bcl-xL in the brain. The goal of our experiments was to investigate the gene and protein expression of TPH2 and Bcl-xL in the dorsal (DRN) and median (MRN) raphe nuclei during repeated stress events. Gene (RT PCR) and protein (immunohistochemistry) expression was assessed 24 hours after the second and fourteenth forced swim sessions. The increase in TPH2 protein expression observed after the second swim stress exposure might reflect the protective action of Bcl-xL. During the subsequent stressful events, the stress-induced increase in Bcl-xL expression decreased. This effect was associated with the weakening of serotonergic neuron function evidenced by the compensatory activation of the TPH2 gene expression without TPH2 protein increase. Thus, shortand long-term forced swimming resulted in qualitatively different alterations in brain expression of TPH2 and Bcl-xL, suggesting their specific roles during acute and chronic stages in the development of stress-induced psychopathology. These changes may constitute a component of the mechanisms underlying elevated tph2 gene expression in depressed patients. [ABSTRACT FROM AUTHOR]

Tryptophan hydroxylase-2 (TPH2) contributes to alterations in the function of neuronal serotonin (5-HT), which are associated with various psychopathologies, including major depressive disorder (MDD) or suicidal behavior. The methylation of a single CpG site in the promoter region of TPH2 affects gene expression. Suicide and MDD are strongly associated and genetic factors are at least partially responsible for the variability in suicide risk. The aim of the present study was to investigate whether variations in TPH2 methylation in peripheral blood samples may predispose patients with MDD to suicide attempts. TPH2 mRNA expression levels differed significantly between 50 patients with MDD who had attempted suicide (MDD + suicide group) and 75 control patients with MDD (MDD group); TPH2 expression levels were significantly decreased (P=0.0005) in the patients who had attempted suicide. Furthermore, the frequency of TPH2 methylation was 36.0% in the MDD + suicide group, while it was 13.0% in the MDD group. The results of the present study demonstrated that methylation in the promoter region of TPH2 significantly affected the mRNA expression levels of TPH2, thus suggesting that methylation of the TPH2 promoter may silence TPH2 mRNA expression in MDD patients with or without suicidal behavior. In addition, there was a significant correlation between the methylation status of the TPH2 promoter and depression, hopelessness and cognitive impairment in the MDD + suicide group. In conclusion, the present study demonstrated that TPH2 expression was regulated by DNA methylation of the TPH2 promoter region in patients with MDD. [ABSTRACT FROM AUTHOR]

Firing activity of serotonin (5-HT) neurons in the dorsal raphe nucleus (DRN) is controlled by inhibitory somatodendritic 5-HT1A autoreceptors. This autoinhibitory mechanism is implicated in the etiology of disorders of emotion regulation, such as anxiety disorders and depression, as well as in the mechanism of antidepressant action. Here, we investigated how persistent alterations in brain 5-HT availability affect autoinhibition in two genetically modified mouse models lacking critical mediators of serotonergic transmission: 5-HT transporter knockout (Sert -/-) and tryptophan hydroxylase-2 knockout (Tph2 -/-) mice. The degree of autoinhibition was assessed by loose-seal cell-attached recording in DRN slices. First, application of the 5-HT1A-selective agonist R(+)-8-hydroxy-2-(di-n-propylamino)tetralin showed mild sensitization and marked desensitization of 5-HT1A receptors in Tph2 -/- mice and Sert -/- mice, respectively. While 5-HT neurons from Tph2 -/- mice did not display autoinhibition in response to L-tryptophan, autoinhibition of these neurons was unaltered in Sert -/- mice despite marked desensitization of their 5-HT1A autoreceptors. When the Tph2-dependent 5-HT synthesis step was bypassed by application of 5-hydroxy-L-tryptophan (5-HTP), neurons from both Tph2 -/- and Sert -/- mice decreased their firing rates at significantly lower concentrations of 5-HTP compared to wildtype controls. Our findings demonstrate that, as opposed to the prevalent view, sensitivity of somatodendritic 5-HT1A receptors does not predict the magnitude of 5-HT neuron autoinhibition. Changes in 5-HT1A receptor sensitivity may rather be seen as an adaptive mechanism to keep autoinhibition functioning in response to extremely altered levels of extracellular 5-HT resulting from targeted inactivation of mediators of serotonergic signaling.

Abstract: Omega-3 fatty acid deficiency during development leads to enduing alterations in central monoamine neurotransmission in rat brain. Here we investigated the effects of omega-3 fatty acid deficiency on behavioral and neurochemical responses to chronic fluoxetine (FLX) treatment. Male rats were fed diets with (CON, n = 34) or without (DEF, n = 30) the omega-3 fatty acid precursor alpha-linolenic acid (ALA) during peri-adolescent development (P21–P90). A subset of CON (n = 14) and DEF (n = 12) rats were administered FLX (10 mg/kg/d) through their drinking water for 30 d beginning on P60. The forced swimming test (FST) was initiated on P90, and regional brain mRNA markers of serotonin and noradrenaline neurotransmission were determined. Dietary ALA depletion led to significant reductions in frontal cortex docosahexaenoic acid (DHA, 22:6n-3) composition in DEF (−26%, p = 0.0001) and DEF + FLX (−32%, p = 0.0001) rats. Plasma FLX and norfluoxetine concentrations did not different between FLX-treated DEF and CON rats. During the 15-min FST pretest, DEF + FLX rats exhibited significantly greater climbing behavior compared with CON + FLX rats. During the 5-min test trial, FLX treatment reduced immobility and increased swimming in CON and DEF rats, and only DEF + FLX rats exhibited significant elevations in climbing behavior. DEF + FLX rats exhibited greater midbrain, and lower frontal cortex, 5-HT1A mRNA expression compared with all groups including CON + FLX rats. DEF + FLX rats also exhibited greater midbrain alpha2A adrenergic receptor mRNA expression which was positively correlated with climbing behavior in the FST. These preclinical data demonstrate that low omega-3 fatty acid status leads to abnormal behavioral and neurochemical responses to chronic FLX treatment in male rats. [Copyright &y& Elsevier]

Summary: Women exhibit a nearly twofold increased risk of developing depression and anxiety disorders when compared to men, a fact that has been hypothesized to result in part from increased stress susceptibility. Here, we used the tryptophan hydroxylase-2 R439H knock-in mouse (Tph2KI) and the chronic unpredictable mild stress (CMS) model to examine sex differences in response to congenital 5-HT deficiency and chronic stress. Our results demonstrate that female mice, but not 5-HT-deficient animals, exhibit significantly increased susceptibility to CMS-induced despair-like behavior in the forced swim test. In addition, female 5-HT-deficient mice exhibit anhedonia-like behavior in the sucrose preference test, whereas male 5-HT-deficient animals do not, suggesting that females exhibit increased sensitivity to at least some of the effects of congenital 5-HT deficiency. Although CMS did not reduce cell proliferation in the hippocampus, low levels of brain 5-HT were associated with increased hippocampal cell proliferation, an effect that was predominantly observed in females. Overall, these results highlight the importance of interactions between psychiatric disease risk factors such as sex, chronic stress and congenital 5-HT deficiency in the development of aberrant emotional behavior. [Copyright &y& Elsevier]

Abstract: Serotonin (5-HT) has been long recognized to modulate the stress response, and dysfunction of 5-HT has been implicated in numerous stress disorders. Accordingly, the 5-HT system has been targeted for the treatment of stress disorders. Tryptophan hydroxylase (TPH) is the rate-limiting enzyme in 5-HT synthesis, and the recent identification of a second, neuron-specific TPH isoform (TPH2) opened up a new area of research. With a decade of extensive investigation, it is now recognized that: (1) TPH2 exhibits a highly flexible gene expression that is modulated by an increasing number of internal and external environmental factors including the biological clock, stressors, endogenous hormones, and antidepressant therapies; and (2) genetically determined TPH2 activity is linked to a growing body of stress-related neuronal correlates and behavioral traits. These findings reveal an active role of TPH2 in the stress response and provide new insights into the long recognized but not yet fully understood 5-HT–stress interaction. As a major modulator of 5-HT neurotransmission and the stress response, TPH2 is of both pathophysiological and pharmacological significance, and is emerging as a new therapeutic target for the treatment of stress disorders. Given that numerous antidepressant therapies influence TPH2 gene expression, TPH2 is already inadvertently targeted for the treatment of stress disorders. With increased understanding of the regulation of TPH2 activity we can now purposely utilize TPH2 as a target to develop new or optimize current therapies, which are expected to greatly improve the prevention and treatment of a wide variety of stress disorders. [Copyright &y& Elsevier]

Abstract: Tryptophan hydroxylase-2 (TPH2) is the rate limiting enzyme of serotonin synthesis in the brain. The 1473G allele of the C1473G polymorphism in mTPH2 gene is associated with reduced enzyme activity and serotonin synthesis rate in the mouse brain. Here, the influence of the 1473G allele on the antidepressant effect of selective serotonin reuptake inhibitors (SSRIs), citalopram (2.5 or 5.0mg/kg) and paroxetine (5.0 or 10.0mg/kg), in the forced swim test was studied using B6-1473G and B6-1473C congenic mouse lines with the 1473G (decreased TPH2 activity) or 1473C (normal TPH2 activity) alleles, respectively, transferred to the genome of C57BL/6 mouse strain. Paroxetine (5.0 or 10.0mg/kg) and citalopram (2.5 or 5.0mg/kg) decreased immobility time in B6-1473C mice, while both doses of paroxetine and 2.5mg/kg of citaloprame did not alter immobility time in B6-1473G mice. However, 5.0mg/kg of citalopram reduced immobility in B6-1473G mice. The results provided genetic evidence of moderate association between 1473G allele and reduced sensitivity to SSRIs in mice. [Copyright &y& Elsevier]

Abstract: 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 2.768Kb 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 50days 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. [Copyright &y& Elsevier]

ASC (Antidepressant-Sensitive Catalepsy) mice, bred for a high predisposition to catalepsy, are characterized by depression-like behavior and decreased immune responses. Chronic administration of fluoxetine, which is a selective serotonin reuptake inhibitor antidepressant widely used in clinical practice, to mice of this strain weakened catalepsy and normalized the number of rosette-forming cells in the spleen. In mice of the parental cataleptic strain CBA/Lac, fluoxetine had no effect on the level of catalepsy or the immune response. Analysis of the effects of fluoxetine on the functional activity of 5-HT1A and 5-HT2A receptors, and the expression of 5-HT1A receptor genes in the frontal cortex and midbrain and 5-HT2A receptors in the frontal cortex, as well as the tryptophan hydroxylase-2 and the serotonin transporter genes in the midbrain showed that the antidepressant had no effect on these parameters in ASC mice, but decreased the functional activity of 5-HT2A receptors in CBA/Lac mice. The possibility that the actions of fluoxetine on catalepsy and the immune response in mice with depression-like states are mediated via other serotoninergic mechanisms is discussed. [ABSTRACT FROM AUTHOR]

Tryptophan hydroxylase-2 (TPH2) synthesizes neuronal serotonin and is linked to numerous behavioral traits. We have previously characterized the functionality of polymorphisms (especially 2051A>C) in 3’-untranslated region (3’-UTR) of rhesus monkey TPH2 (rh TPH2). This study further assessed the functionality of additional polymorphisms (–1605T>C, –1491Tn, –1485(AT)n, –1454A>G, –1325In>Del and –363T>G) in rh TPH2 5’-flanking region (5’-FR), and evaluated the effects of rh TPH2 5’ and 3’ genotypes on central serotonin turnover, hypothalamic–pituitary–adrenal (HPA) axis function and self-injurious behavior (SIB) in 32 unrelated adult male monkeys of Indian origin. Haplotypes of the rh TPH2 5’-FR polymorphisms exert a significant, cell-dependent effect on reporter gene expression, primarily conferred by –1485(AT)n. The –1485(AT)n and 2051A>C polymorphisms interact to influence cerebrospinal fluid (CSF) 5-HIAA and plasma adrenocorticotropic hormone (ACTH) in the afternoon. While –1485(AT)n exerts significant main effects on the afternoon cortisol level and nocturnal HPA negative feedback, 2051A>C has significant main effects on the morning cortisol level and cortisol response to ACTH challenge, as well as marginally significant main effects on the daytime HPA negative feedback and self-biting rate. In addition, the genotype/allele frequency of the 5’-FR –1325Ins>Del differed significantly between the self-wounders and non-wounders, whereas 3’-UTR 2128S>L polymorphism differed significantly in genotype/allele frequency between the high- and low-frequency biters. This study shows the functionality of rh TPH2 5’-FR polymorphisms, and provides evidence for the differential association of rh TPH2 5’-FR and 3’-UTR polymorphisms with HPA axis function and SIB. Our findings shed light on the role of TPH2 gene variance in physiology and behavioral traits, and also contribute to the understanding of the pathophysiology and genetics of SIB [ABSTRACT FROM AUTHOR]

Abstract: Gene–environment (G×E) interactions contribute to the development of many neuropsychiatric disorders. Tryptophan hydroxylase-2 (TPH2) synthesizes neuronal serotonin and is closely related to the hypothalamic-pituitary-adrenal (HPA) axis, while early life experience is a critical environmental factor programming the HPA axis response to stress. This retrospective study investigated G×E interaction at the TPH2 locus in rhesus monkeys. Twenty-eight adult, male rhesus monkeys of Indian origin, either mother-reared or peer-reared as infants, were involved in this study. These monkeys have been previously genotyped for the functional A2051C polymorphism in rhTPH2, and had been physiologically and behaviorally characterized. rhTPH2 A2051C exerted a significant main effect (CC>AA&AC) on the cerebrospinal fluid (CSF) level of 5-hydroxyindole-3-acetic acid (5-HIAA; F (1,14) =6.42, p =0.024), plasma cortisol level in the morning (F (1,18) =14.63, p =0.002) and cortisol response to ACTH challenge (F (1,17) =6.87, p =0.018), while the rearing experience showed a significant main effect (PR>MR) on CSF CRH (F (1,20) =11.66, p =0.003) and cage shaking behavior (F (1,27) =4.45, p =0.045). The effects of rhTPH2 A2051C on the afternoon cortisol level, plasma ACTH level, dexamethasone suppression of urinary cortisol excretion, and aggression were dependent upon the rearing experience. These results were not confounded by the functional C77G polymorphism in the mu-opioid receptor (MOR). The present study supports the hypothesis that rearing experience and rhTPH2 A2051C interact to influence central 5-HT metabolism, HPA axis function, and aggressive behaviors. Our findings strengthen the involvement of G×E interactions at the loci of serotonergic genes and the utility of the nonhuman primate to model G×E interactions in the development of human neuropsychiatric diseases. [Copyright &y& Elsevier]

Abstract: Although a considerable body of literature indicates that serotoninergic neurons affect diaphragm activity both through direct inputs to phrenic motoneurons and multisynaptic connections involving the brainstem respiratory groups, the locations of the serotoninergic neurons that modulate breathing have not been well defined. The present study identified these neurons in cats by combining the transneuronal retrograde transport of rabies virus from the diaphragm with the immunohistochemical detection of the N-terminal region of tryptophan hydroxylase-2 (TPH2), the brain-specific isoform of the enzyme responsible for the initial and rate-limiting step in serotonin synthesis. TPH2-immunopositive neurons were present in the midline raphe nuclei, formed a column in the ventrolateral medulla near the lateral reticular nucleus, and were spread across the dorsal portion of the pons just below the fourth ventricle. In most animals, only a small fraction of neurons (typically <20%) labeled for TPH2 in each of the medullary raphe nuclei and the medullary ventrolateral column were infected with rabies virus. However, the percentage of medullary neurons dual-labeled for both rabies and TPH2 was much higher in animals with very advanced infections where virus had spread transneuronally through many synapses. Furthermore, in all cases, TPH2-immunopositive neurons that were infected by rabies virus were significantly less prevalent in the pons than the medulla. These findings suggest that although serotoninergic neurons with direct influences on diaphragm activity are widely scattered in the brainstem, the majority of these neurons are located in the medulla. Many non-serotoninergic neurons in the raphe nuclei were also infected with rabies virus, indicating that midline cells utilizing multiple neurotransmitters participate in the control of breathing. [Copyright &y& Elsevier]

Abstract: Tryptophan hydroxylase-2 (TPH2) catalyzes the synthesis of neuronal serotonin, a major neurotransmitter involved in many brain functions and psychiatric disorders. We have previously revealed a critical role of the human TPH2 (hTPH2) 5′-UTR in gene expression regulation. This study aimed to further characterize mechanism(s) by which the hTPH2 5′-UTR regulates gene expression. An internal ribosome entry site (IRES) activity in hTPH2 5′-UTR was suggested by the conventional bicistronic reporter assay; however, further stringent experiments, including in vitro translation, quantitative real-time PCR, Northern blot, ribonuclease protection assay, and monocistronic reporter assay, demonstrated that the hTPH2 5′-UTR harbors a bidirectional promoter, but not IRES, within its downstream segment (61–141). The antisense promoter is much stronger than the sense promoter, but the strength of both promoters are cell-line dependent, with the highest and lowest activities being observed in HEK-293T and SK-N-MC cells, respectively. In accordance with our previous findings, the upstream segment (1–60) of hTPH2 5′-UTR suppresses the neighboring promoter of both direction, independent of the cell line and its location in the 5′- or 3′-flanking regions of the gene. In summary, this study demonstrates that no IRES but an asymmetric bidirectional promoter is present in the downstream segment of hTPH2 5′-UTR, and this promoter is susceptible to a gene silencing effect caused by the upstream segment (1–60) of hTPH2 5′-UTR. Our findings point to the potential involvement of antisense transcription and non-coding RNA in the regulation of TPH2 gene expression. [Copyright &y& Elsevier]

Abstract: A dysregulation in central serotonin neurotransmission and omega-3 fatty acid deficiency have been implicated in the pathophysiology of major depression. To determine the effects of omega-3 fatty acid deficiency on indices of serotonin neurotransmission in the adult rat brain, female rats were fed diets with or without the omega-3 fatty acid precursor α-linolenic acid (ALA) during perinatal (E0-P90), post-weaning (P21-P90), and post-pubescent (P60-130) development. Ovariectomized (OVX) rats and OVX rats with cyclic estrogen treatment were also examined. Serotonin (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) content, and fatty acid composition were determined in the prefrontal cortex (PFC), and tryptophan hydroxylase-2 (TPH-2), serotonin transporter, and 5-HT1A autoreceptor mRNA expression were determined in the midbrain. ALA deficiency during perinatal (−62%, p =0.0001), post-weaning (−34%, p =0.0001), and post-pubertal (−10%, p =0.0001) development resulted in a graded reduction in adult PFC docosahexaenoic acid (DHA, 22:6n−3) composition. Relative to controls, perinatal DHA-deficient rats exhibited significantly lower PFC 5-HT content (−65%, p =0.001), significant greater 5-HIAA content (+15%, p =0.046), and a significant greater 5-HIAA/5-HT ratio (+73%, p =0.001). Conversely, post-weaning DHA-deficient rats exhibited significantly greater PFC 5-HT content (+12%, p =0.03), no change in 5-HIAA content, and a significantly smaller 5-HIAA/5-HT ratio (−9%, p =0.01). Post-pubertal DHA-deficient and OXV rats did not exhibit significant alterations in PFC 5-HT or 5-HIAA content. Only perinatal DHA-deficient rats exhibited a significant reduction in midbrain TPH-2 mRNA expression (−29%, p =0.03). These preclinical data support a causal link between perinatal omega-3 fatty acid deficiency and reduced central serotonin synthesis in adult female rats that is independent of ovarian hormones including estrogen. [Copyright &y& Elsevier]

Repeated forced swim resulted in a decrease in the concentrations of serotonin (5-HT) and its metabolite 5-hydroxyindoleacetic acid in the hypothalamus and amygdala 24 h after the second swim session. This stressor also increased the mRNA levels for tryptophan hydroxylase-2, the rate-limiting enzyme in neuronal 5-HT synthesis, and 5-HT transporter in the midbrain as well as 5-HT1A receptor in the frontal cortex. Some of these serotonergic changes may be involved in the mechanisms of a depressive-like behavior induced by a stress of repeated swim in these animals. [ABSTRACT FROM AUTHOR]

Abstract: Individual differences in brain response to emotional stimuli have previously been associated with gene variations within the serotonin transporter (5-HTT) and tryptophan hydroxylase-2 (TPH2) genes. We recently reported that these two genes exhibit an additive effect, based on recordings of event-related potentials (ERPs) from individuals viewing emotional scenes. The current study was designed to replicate and extent this initial report in an independent study sample, and use functional magnetic resonance imaging (fMRI) to identify specific neural loci that may mediate the 5-HTT–TPH2 additive effect. Furthermore, we sought to obtain convergent evidence for a gene–gene additive effect by collecting fMRI data from the same individuals engaged in two different cognitive-affective tasks, using emotional and neutral facial expressions and word stimuli. We found evidence for an additive effect of 5-HTT–TPH2 genotype, which was most robust in the putamen, a region rich in both 5-HTT and TPH2 protein, but was also observed in the amygdala at a less stringent threshold, and in other cortical regions. The additive effect was more robust effect for visuospatial than for verbal stimuli, and more robust for negatively than for positively valenced stimuli. These findings confirm and extend the additive effect of two critical genes in the serotonergic regulation of neural processing of affective stimuli, and identify the striatum as a critical site where is gene–gene regulation takes place. [Copyright &y& Elsevier]

Abstract: Tryptophan hydroxylase-2 (TPH2), the rate-limiting enzyme in 5-HT synthesis in the brain, is a candidate for participation in a mechanism mediating the antidepressant effect of selective 5-HT reuptake inhibitors such as fluoxetine. Using real-time reverse transcription-polymerase chain reaction (RT-PCR) and semi-quantitative RT-PCR techniques, we have examined the effects of fluoxetine administration with drinking water (7.5 mg/kg/day) for 2, 4 and 8 weeks on TPH2 mRNA expression in the midbrain part of the dorsal raphe nucleus (DRN) and in the brainstem containing the rest of the raphe complex. Fluoxetine treatment for 4 and 8 weeks significantly increased basal TPH2 mRNA levels in the midbrain, an effect that was correlated with the appearance of antidepressant-like effects in the forced swim test. A significant induction of TPH2 and 5-HT transporter (5-HTT) mRNAs was detected in the midbrain of untreated rats 24 h after the swim test. In these animals, the swim test also produced a marked decrease in 5-HT metabolite (5-hydroxyindoleacetic acid (5-HIAA)) content in the amygdala. Fluoxetine treatment for 4 and 8, but not for 2 weeks, abolished these swim-induced changes in TPH2 and 5-HTT mRNAs levels in the midbrain and 5-HIAA content in the amygdala. The results of the present study suggest that TPH2 gene expression in the midbrain part of the DRN is implicated in depression and stress response, as well as in the antidepressant fluoxetine action. [Copyright &y& Elsevier]

Background: Suicide and depressive disorders are strongly associated, yet not all depressed patients commit suicide. Genetic factors may partly explain this difference. We investigated whether variation at the tryptophan hydroxylase-2 (TPH2) gene and its 5’ upstream region may predispose to suicide in major depressive disorder (MDD) and whether this predisposition is mediated by impulsive-aggressive behaviors (IABs). Methods: We genotyped 14 single nucleotide polymorphisms (SNPs) in 259 depressed subjects, 114 of which committed suicide while depressed. Phenotypic assessments were carried out by means of proxy-based interviews. Single-marker and haplotype association analyses were conducted. Differences in behavioral and personality traits according to genotypic variation were investigated, as well as genetic and clinical predictors of suicide. Results: We found two upstream and two intronic SNPs associated with suicide. No direct effect of these variants was observed on IABs. However, a slight association with reward dependence scores was found. Controlling for suicide risk factors, two SNPs (rs4448731 and rs4641527) significantly predicted suicide, along with cluster B personality disorders and family history of suicide. Conclusions: The TPH2 gene and its 5’ upstream region variants may be involved in the predisposition to suicide in MDD; however, our findings do not support the role of IABs as mediators. [Copyright &y& Elsevier]

Tryptophan hydroxylase-2 (TPH2) is a newly identified second form of TPH responsible for serotonin synthesis in the brain and has been increasingly implicated as a contributor to the etiology of various psychiatric disorders. In this study, we have identified the constellation of polymorphisms in rhesus monkey TPH2 and investigated genotype/phenotype association as well as gene expression effects of specific polymorphisms. Genomic DNA was obtained from 247 rhesus monkeys, among which 24 had been previously examined for plasma cortisol level, dexamethasone suppression, and combined dexmethasone/ACTH challenge. Polymorphisms in all exons, splicing junctions and approximately 2 kb of the 5′-flanking region (5′-FR) of TPH2 were identified by sequencing. We identified 17 single nucleotide polymorphisms (SNPs) including two that are predictive of amino-acid change (25Pro>His and 75Gly>Ser, respectively), two mononucleotide repeats, one dinucleotide repeat, and one 159-bp insertion polymorphism. The 3′-UTR polymorphisms were significantly associated with hypothalamic–pituitary–adrenal (HPA) axis activity, especially 2051A>C, which was strikingly correlated with plasma cortisol level in the morning only (F=10.203, P=0.001). Luciferase reporter gene assays showed that the 3′-UTR polymorphisms and haplotypes had a profound effect on in vitro gene expression. Accordingly, these investigations revealed that polymorphisms in 3′-UTR of rhesus monkey TPH2 modulate HPA axis function, presumably by affecting levels of TPH2 expression.Molecular Psychiatry (2006) 11, 914–928. doi:10.1038/sj.mp.4001870; published online 18 July 2006 [ABSTRACT FROM AUTHOR]

Abstract: Selective serotonin (5-HT) reuptake inhibitors such as fluoxetine are widely used in the treatment of depression and anxiety; however, the mechanisms underlying their action and particularly the delay in therapeutic onset remain unclear. It is proposed that 5-HT reuptake inhibitors exert their therapeutic activity by increasing serotonergic neurotransmission; therefore, the aim of the present study was to investigate the effects of repeated treatment with fluoxetine (25 mg/kg/day p.o., 14 days) on expression of genes coding for proteins that involved in the synthesis and reuptake of 5-HT. Exposure of animals to plus-maze conditions on the first day of drug administration produced an increase in baseline anxiety on subsequent trial 2 weeks later. Fluoxetine strengthened the anxiogenic effects of maze experience. Two-week fluoxetine treatment also significantly reduced expression of tryptophan hydroxylase-2 (TPH2) and 5-HT transporter mRNAs as determined by RT-PCR in the brainstem. These changes were consistent with the decreased 5-HT levels and 5-HT turnover in the brain, and might contribute to the anxiogenic effects of the drug. The results also suggest that recently found association between treatment responses to fluoxetine and polymorphic variants of human TPH2 gene [Peters EJ, Slager SL, McGrath PJ, Knowles JA, Hamilton SP. Investigation of serotonin-related genes in antidepressant response. Mol Psychiatry 2004; 9:879–889] may be related to the drug effect on the TPH2 gene expression. [Copyright &y& Elsevier]

Abstract: We cloned the human tryptophan hydroxylase-2 (hTPH2) gene by RT-PCR, and expressed and purified its product as a maltose-binding protein (MBP)-fusion protein. We investigated the effects of essential divalent cations and l-phenylalanine (l-Phe) on the hTPH2 activity for the first time, and compared them with those on human tyrosine hydroxylase (hTH1) activity. We found that cobaltous and manganous ions inhibited the activities of both enzymes but that hTH1 was affected at lower concentrations than hTPH2. From kinetic analyses, we found that phenylalanine acted as an inhibitor more strongly against hTPH2 than against hTH1. These data are important for elucidating the molecular mechanism underlying the alterations in the contents of serotonin and catecholamines in the brain under pathological and physiological conditions, such as hyperphenylalaninemia and chronic manganese toxicity. [Copyright &y& Elsevier]

Polymorphism of tryptophan hydroxylase, the rate-limiting enzyme in the synthesis of brain serotonin (5-HT), is associated with less synthesis of brain 5-HT in DBA/2J and BALB/c than in C57BL/6J and 129/Sv mice. We selected the forced swimming test, a mouse model used to assess the antidepressant potential of drugs, and neurochemical techniques to study strain differences in the response to citalopram, a selective 5-HT reuptake inhibitor. Citalopram reduced immobility time in C57BL/6J and 129/Sv mice but had no such effect in DBA/2J and BALB/c mice. The drug reduced accumulation of 5-hydroxytryptophan (5-HTP), an indicator of 5-HT synthesis, in C57BL/6J and 129/Sv mice but much less in DBA/2J and BALB/c mice. Pretreatment with tryptophan raised 5-HTP accumulation and reinstated the antidepressant-like effect of citalopram in DBA/2J and BALB/c mice, whereas pharmacological inhibition of 5-HT synthesis prevented the effect of citalopram in C57BL/6J and 129/Sv mice. Because there were no strain differences in catecholamine synthesis, locomotor activity, and brain levels of citalopram at the end of the behavioral test, the results suggest that the failure of citalopram to reduce immobility time in DBA/2J and BALB/c mice is attributable to genotype-dependent impairment of 5-HT synthesis. Interstrain comparisons could probably be a useful strategy for understanding the mechanisms underlying the response to selective serotonin reuptake inhibitors. [ABSTRACT FROM AUTHOR]

• Corticosterone enhances the higher food intake and reduced body weight in TPH2 null mice. • TPH2 null mice exhibit an impaired corticosterone feedback regulation under chronic stress. • Chronic corticosterone accentuates the gut microbiome dysbiosis in TPH2 null mice. • Erysipelotrichaceae and Proteobacteria increased in corticosterone-treated TPH2 null mice. Dysregulation of the stress-induced activation of the hypothalamic-pituitary-adrenocortical axis can result in disease. Bidirectional communication exists between the brain and the gut, and alterations in these interactions appear to be involved in stress regulation and in the pathogenesis of neuropsychiatric diseases, such as depression. Serotonin (5HT) plays a crucial role in the functions of these two major organs but its direct influence under stress conditions remains unclear. To investigate the role of neuronal 5HT on chronic stress responses and its influence on the gut microbiome, mice lacking the gene for tryptophan hydroxylase-2 were treated with the stress hormone corticosterone (CORT) for 21 days. The intake of fluid and food, as well as body weights were recorded daily. CORT levels, expression of glucocorticoid receptors (GR) in the brain and the size of the adrenal gland were evaluated. Caecum was used for 16S rRNA gene characterization of the gut microbiota. Results show that 5HT depletion produced an increase in food intake and a paradoxical reduction in body weight that were enhanced by CORT. Neuronal 5HT depletion impaired the feedback regulation of CORT levels but had no putative effect on the CORT-induced decrease in hippocampal GR expression and the reduction of the adrenal cortex size. Finally, the composition and structure of the gut microbiota were significantly impacted by the absence of neuronal 5HT, and these alterations were enhanced by chronic CORT treatment. Therefore, we conclude that neuronal 5HT influences the stress-related responses at different levels involving CORT levels regulation and the gut microbiome. [ABSTRACT FROM AUTHOR]

Prenatal stress and overexposure to glucocorticoids (GC) during development may be associated with an increased susceptibility to a number of diseases in adulthood including neuropsychiatric disorders, such as depression and anxiety. In animal models, prenatal overexposure to GC results in hyper-responsiveness to stress in adulthood, and females appear to be more susceptible than males. Here, we tested the hypothesis that overexposure to GC during fetal development has sex-specific programming effects on the brain, resulting in altered behaviors in adulthood. We examined the effects of dexamethasone (DEX; a synthetic GC) during prenatal life on stress-related behaviors in adulthood and on the tryptophan hydroxylase-2 (TpH2) gene expression in the adult dorsal raphe nucleus (DRN). TpH2 is the rate-limiting enzyme for serotonin (5-HT) synthesis and has been implicated in the etiology of human affective disorders. Timed-pregnant rats were treated with DEX from gestational days 18-22. Male and female offspring were sacrificed on the day of birth (postnatal day 0; P0), P7, and in adulthood (P80-84) and brains were examined for changes in TpH2 mRNA expression. Adult animals were also tested for anxiety- and depressive- like behaviors. In adulthood, prenatal DEX increased anxiety- and depressive- like behaviors selectively in females, as measured by decreased time spent in the center of the open field and increased time spent immobile in the forced swim test, respectively. Prenatal DEX increased TpH2 mRNA selectively in the female caudal DRN at P7, whereas it decreased TpH2 mRNA selectively in the female caudal DRN in adulthood. In animals challenged with restraint stress in adulthood, TpH2 mRNA was significantly lower in rostral DRN of prenatal DEX-treated females compared to vehicle-treated females. These data demonstrated that prenatal overexposure to GC alters the development of TpH2 gene expression and these alterations correlated with lasting behavioral changes found in adult female offspring., (Copyright © 2016 IBRO. All rights reserved.)

Background: Disturbance of the serotonergic system contributes to the etiology of bipolar disorder (BD). Tryptophan hydroxylase-2 (TPH2) is an important rate-limiting enzyme in the synthetic pathway for brain serotonin and has been suggested to play a role in BD., Materials and Methods: We performed a systematic review and meta-analysis of all studies to date investigating the association studies between TPH2 and BD published before Aug 2014. All studies were abstracted from PubMed, Embase, HuGNet, and China National Knowledge Infrastructure (CNKI). Manuscripts and the supplementary documents of published genome-wide association studies in the field were also included. Effect sizes of independent loci that have been studied in more than three articles were synthesized using fixed and random effects models., Results: Eight eligible studies addressed association between 63 TPH2 gene single nucleotide polymorphisms (SNPs) with BD, after linkage disequilibrium analysis, 12 independent SNPs were identified. Finally, three SNPs (rs4760820, rs11178998, and rs7954758) were found associated with BD using fixed effects models, and rs4760820 and rs11178998 were still associated with BD even with the more conservative random effects models., Conclusions: rs4760820 and rs11178998 were identified to have strong genetic association with BD in present study though confirmation will require larger sample sizes and in additional populations., (© 2015 Wiley Periodicals, Inc.)

This article is part of a Special Issue "Parental Care". The effects of differential maternal care received on offspring phenotype in rodents has been extensively studied between litters, but the consequences of differential mothering within litters on offspring neurobehavioral development have been rarely examined. We here investigated how variability in maternal care received among female rat siblings (measured four times daily on postnatal days 4, 6, 8, and 10) relates to the siblings' later emotional and maternal behaviors. As previously reported, we found that some female pups received up to three times more maternal licking bouts compared to their sisters; this difference was positively correlated with the pups' body weights. The number of maternal licking bouts that females received was negatively correlated with their later neophobic behaviors in an open field during periadolescence, but positively correlated with their anxiety-related behavior in an elevated plus maze during adulthood. Licking received was also positively correlated with females' later likelihood to retrieve pups in a maternal sensitization paradigm. In addition, females' neophobia during adolescence and anxiety-related behavior during adulthood predicted some aspects of both postpartum and sensitized maternal responsiveness. Medial prefrontal cortex expression of tryptophan hydroxylase-2 (TPH2; enzyme necessary for serotonin synthesis) was negatively associated with early maternal licking received. Interestingly, cortical TPH2 was positively associated with the maternal responsiveness of sensitized virgins but negatively associated with it in postpartum females. These results indicate that within-litter differences in maternal care received is an often neglected, but important, contributor to individual differences in offspring socioemotional behaviors as well as to the cortical serotonin neurochemistry that may influence these behaviors., (Copyright © 2015 Elsevier Inc. All rights reserved.)

Huntington׳s disease (HD) is a neurodegenerative disorder caused by a mutation in the HTT gene (mHTT) encoding the protein huntingtin. An expansion in the gene׳s CAG repeat length renders a misfolded, dysfunctional protein with an abnormally long glutamine (Q) stretch at the N terminus that often incorporates into inclusion bodies and leads to neurodegeneration in many regions of the brain. HD is characterized by motor and cognitive decline as well as mood disorders, with depression being particularly common. Approximately 40% of the HD population suffers from depressive symptoms. Because these symptoms often manifest a decade or more prior to the knowledge that the person is at risk for the disease, a portion of the early depression in HD appears to be a consequence of the pathology arising from expression of the mutant gene. While the depression in HD patients is often treated with serotonin agonists, there is scant experimental evidence that the depression in HD responds well to these serotonin treatments or in a similar manner to how non-HD depression tends to respond. Additionally, at very early sub-threshold depression levels, abnormal changes in several neuronal populations are already detectable in HD patients, suggesting that a variety of brain structures may be involved. Taken together, the serotonin system is a viable candidate. However, at present there is limited evidence of the precise nuclei or circuits that play a role in HD depression. With this in mind, the current study was designed to control for the widespread brain neuropathology that occurs in HD and in transgenic mouse models of HD and focuses specifically on the influence of the midbrain dorsal raphe nucleus (DRN). The DRN provides the majority of the serotonin to the forebrain and exhibits cell loss in non-HD depression. Therefore, we employed a viral vector delivery system to investigate whether the over-expression of mHTT in the DRN׳s ventral sub-nuclei alone is sufficient to produce depressive-like behaviors. Wildtype mice were injected with an adeno-associated virus (AAV2/1) encoding HTT containing either a pathogenic (N171-82Q) or control (N171-16Q) CAG repeat length into the ventral DRN and depressive-like behaviors and motor behaviors were assessed for 12 weeks post-surgery. Quantitative PCR and immunohistochemistry (IHC) verified positive transduction in the ventral aspects of the DRN, including the ventral sub-nucleus (DRv) and interfascicular sub-nucleus (DRif). IHC demonstrated microgliosis in and around the injection site and mHTT-positive inclusions in serotonin-producing neurons and a small percentage of astrocytes in animals injected with N171-82Q compared to controls. Moreover, N171-82Q injected mice showed a 75% reduction in cells that stained positive for the serotonin synthesis enzyme, tryptophan hydroxylase-2 (TPH2) compared to controls (p<0.05). Despite mHTT-mediated pathology in the DRv and DRif, no significant changes in depressive-like behavior were detected. Consequently, we conclude that 12 weeks of N171-82Q expression in the ventral sub-nuclei of the DRN of wildtype mice causes characteristic disease-related cellular neuropathology but is not sufficient to elicit depressive-like behaviors. Ongoing studies are investigating whether a larger injection volume that transfects a larger percentage of the DRN and/or a longer time course of mHTT expression might elicit depressive-like behaviors. Moreover, mHTT expression in other regions of the brain, such as the hippocampal dentate gyrus and/or the frontal cortex might be necessary to elicit HD depression. Together, these results may prove helpful in addressing which therapeutic and/or pharmacological strategies might be most efficacious when treating depressive symptomology in patients suffering from HD., (Copyright © 2015 Elsevier B.V. All rights reserved.)

In female mammals, the postpartum period involves dramatic shifts in many socioemotional behaviors. This includes a suppression of anxiety-related behaviors that requires recent physical contact with offspring. Factors contributing to differences among females in their susceptibility to the anxiety-modulating effect of offspring contact are unknown, but could include their innate anxiety and brain monoaminergic activity. Anxiety behavior was assessed in a large group of nulliparous female rats and the least-anxious and most-anxious tertiles were mated. Anxiety was assessed again postpartum after females were permitted or prevented from contacting their offspring 4 h before testing. Levels of dopamine β-hydroxylase (DBH, norepinephrine synthesizing enzyme) and tryptophan hydroxylase-2 (TPH2, serotonin synthesizing enzyme) were measured in the brainstem and dorsal raphe, respectively. It was found that anxiety-related behavior in the two groups did not differ when dams were permitted contact with offspring before testing. Removal of the offspring before testing, however, differentially affected anxiety based on dams' innate anxiety. Specifically, dams reverted back to their pre-mating levels of anxiety such that offspring removal slightly increased anxiety in the most-anxious females but greatly lowered anxiety in the least-anxious females. This reduction in anxiety in the least-anxious females after litter removal was associated with lower brainstem DBH. There was no relationship between females' anxiety and dorsal raphe TPH2. Thus, a primary effect of recent contact with offspring on anxiety-related behavior in postpartum rats is to shift females away from their innate anxiety to a more moderate level of responding. This effect is particularly true for females with the lowest anxiety, may be mediated by central noradrenergic systems, and has implications for their ability to attend to their offspring., (Copyright © 2013 IBRO. Published by Elsevier Ltd. All rights reserved.)

The effect of glial cell line-derived neurotrophic factor (GDNF) on behavior and on the serotonin (5-HT) system of a mouse strain predisposed to depressive-like behavior, ASC/Icg (Antidepressant Sensitive Cataleptics), in comparison with the parental "nondepressive" CBA/Lac mice was studied. Within 7 days after acute administration, GDNF (800 ng, i.c.v.) decreased cataleptic immobility but increased depressive-like behavioral traits in both investigated mouse strains and produced anxiolytic effects in ASC mice. The expression of the gene encoding the key enzyme for 5-HT biosynthesis in the brain, tryptophan hydroxylase-2 (Tph-2), and 5-HT1A receptor gene in the midbrain as well as 5-HT2A receptor gene in the frontal cortex were increased in GDNF-treated ASC mice. At the same time, GDNF decreased 5-HT1A and 5-HT2A receptor gene expression in the hippocampus of ASC mice. GDNF failed to change Tph2, 5-HT1A , or 5-HT2A receptor mRNA levels in CBA mice as well as 5-HT transporter gene expression and 5-HT1A and 5-HT2A receptor functional activity in both investigated mouse strains. The results show 1) a GDNF-induced increase in the expression of key genes of the brain 5-HT system, Tph2, 5-HT1A , and 5-HT2A receptors, and 2) significant genotype-dependent differences in the 5-HT system response to GDNF treatment. The data suggest that genetically defined cross-talk between neurotrophic factors and the brain 5-HT system underlies the variability in behavioral response to GDNF., (Copyright © 2013 Wiley Periodicals, Inc.)

Serotonin is critical for shaping the development of neural circuits regulating emotion. Pet-1 (FEV-1) is an ETS-domain transcription factor essential for differentiation and forebrain targeting of serotonin neurons. Constitutive Pet-1 knockout (KO) causes major loss of serotonin neurons and forebrain serotonin availability, and behavioral abnormalities. We phenotyped Pet-1 KO mice for fear conditioning and extinction, and on a battery of assays for anxiety- and depression-related behaviors. Morphology of Golgi-stained neurons in basolateral amygdala (BLA) and prelimbic cortex was examined. Using human imaging genetics, a common variant (rs860573) in the PET-1 (FEV) gene was tested for effects on threat-related amygdala reactivity and psychopathology in 88 Asian-ancestry subjects. Pet-1 KO mice exhibited increased acquisition and expression of fear, and elevated fear recovery following extinction, relative to wild-type (WT). BLA dendrites of Pet-1 KO mice were significantly longer than in WT. Human PET-1 variation associated with differences in amygdala threat processing and psychopathology. This novel evidence for the role of Pet-1 in fear processing and dendritic organization of amygdala neurons and in human amygdala threat processing extends a growing literature demonstrating the influence of genetic variation in the serotonin system on emotional regulation via effects on structure and function of underlying corticolimbic circuitry., (© 2013.)

Extensive studies showed that monoaminergic neurotransmission that involves serotonin (5-HT), norepinephrine (NE) and dopamine (DA) exerts major influence on brain circuits concerned by the regulation of mood, reactivity to psychological stress, self-control, motivation, drive, and cognitive performance. Antidepressants targeting monoamines directly affect the functional tone of these circuits, notably in limbic and frontocortical areas, and evidence has been provided that this action plays a key role in their therapeutic efficacy. Indeed, at least some of functional changes detected by functional magnetic resonance imaging in emotion- and cognitive-related circuits such as the one involving limbic-cortical-striatal-pallidal-thalamic connections in depressed patients can be reversed by monoamine-targeted antidepressants. However, antidepressants acting selectively on only one monoamine, such as selective inhibitors of 5-HT or NE reuptake, alleviate depression symptoms in a limited percentage of patients, and are poorly effective to prevent recurrence. Thorough investigations for the last 30 years allowed the demonstration of the existence of functional interactions between 5-HT, NE and DA systems, and the identification of the specific receptors involved. In particular, 5-HT systems were shown to exert negative influence on NE and DA systems through 5-HT2A and 5-HT2C receptor- mediated mechanisms, respectively. On the other hand, complex positive and negative influences of NE system on 5-HT neurotransmission are mediated through α1- and α2-adrenergic receptors, respectively. These data provided a rationale for the design of new, multimodal, therapeutic strategies involving drugs acting not only at the "historical" targets such as the 5-HT and/or the NE transporter, but also at other molecular targets to improve their efficacy and their tolerability., (Copyright © 2013 Elsevier Inc. All rights reserved.)