Interaction of brain 5-HT synthesis deficiency, chronic stress and sex differentially impact emotional behavior in Tph2 knockout mice.

RATIONALE: While brain serotonin (5-HT) function is implicated in gene-by-environment interaction (GxE) impacting the vulnerability-resilience continuum in neuropsychiatric disorders, it remains elusive how the interplay of altered 5-HT synthesis and environmental stressors is linked to failure in emotion regulation. OBJECTIVE: Here, we investigated the effect of constitutively impaired 5-HT synthesis on behavioral and neuroendocrine responses to unpredictable chronic mild stress (CMS) using a mouse model of brain 5-HT deficiency resulting from targeted inactivation of the tryptophan hydroxylase-2 (Tph2) gene. RESULTS: Locomotor activity and anxiety- and depression-like behavior as well as conditioned fear responses were differentially affected by Tph2 genotype, sex, and CMS. Tph2 null mutants (Tph2(-/-)) displayed increased general metabolism, marginally reduced anxiety- and depression-like behavior but strikingly increased conditioned fear responses. Behavioral modifications were associated with sex-specific hypothalamic-pituitary-adrenocortical (HPA) system alterations as indicated by plasma corticosterone and fecal corticosterone metabolite concentrations. Tph2(-/-) males displayed increased impulsivity and high aggressiveness. Tph2(-/-) females displayed greater emotional reactivity to aversive conditions as reflected by changes in behaviors at baseline including increased freezing and decreased locomotion in novel environments. However, both Tph2(-/-) male and female mice were resilient to CMS-induced hyperlocomotion, while CMS intensified conditioned fear responses in a GxE-dependent manner. CONCLUSIONS: Our results indicate that 5-HT mediates behavioral responses to environmental adversity by facilitating the encoding of stress effects leading to increased vulnerability for negative emotionality.

Conservation of 5-HT1A receptor-mediated autoinhibition of serotonin (5-HT) neurons in mice with altered 5-HT homeostasis.

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.

GABA concentration and GABAergic neuron populations in limbic areas are differentially altered by brain serotonin deficiency in Tph2 knockout mice.

While tryptophan hydroxylase-2 (Tph2) null mutant (Tph2(-/-)) mice are completely deficient in brain serotonin (5-HT) synthesis, the formation of serotonergic neurons and pathfinding of their projections are not impaired. However, 5-HT deficiency, during development and in the adult, might affect morphological and functional parameters of other neural systems. To assess the influence of 5-HT deficiency on γ-amino butyric acid (GABA) systems, we carried out measurements of GABA concentrations in limbic brain regions of adult male wildtype (wt), heterozygous (Tph2(+/-)) and Tph2(-/-) mice. In addition, unbiased stereological estimation of GABAergic interneuron numbers and density was performed in subregions of amygdala and hippocampus. Amygdala and prefrontal cortex displayed significantly increased and decreased GABA concentrations, respectively, exclusively in Tph2(+/-) mice while no changes were detected between Tph2(-/-) and wt mice. In contrast, in the hippocampus, increased GABA concentrations were found in Tph2(-/-) mice. While total cell density in the anterior basolateral amygdala did not differ between genotypes, the number and density of the GABAergic interneurons were significantly decreased in Tph2(-/-) mice, with the group of parvalbumin (PV)-immunoreactive (ir) interneurons contributing somewhat less to the decrease than that of non-PV-ir GABAergic interneurons. Major morphological changes were also absent in the dorsal hippocampus, and only a trend toward reduced density of PV-ir cells was observed in the CA3 region of Tph2(-/-) mice. Our findings are the first to document that life-long reduction or complete lack of brain 5-HT transmission causes differential changes of GABA systems in limbic regions which are key players in emotional learning and memory processes. The changes likely reflect a combination of developmental alterations and functional adaptations of emotion circuits to balance the lack of 5-HT, and may underlie altered emotional behavior in 5-HT-deficient mice. Taken together, our findings provide further insight into the mechanisms how life-long 5-HT deficiency impacts the pathogenesis of anxiety- and fear-related disorders.

Degeneration of serotonergic neurons in amyotrophic lateral sclerosis: a link to spasticity.

Spasticity is a common and disabling symptom observed in patients with central nervous system diseases, including amyotrophic lateral sclerosis, a disease affecting both upper and lower motor neurons. In amyotrophic lateral sclerosis, spasticity is traditionally thought to be the result of degeneration of the upper motor neurons in the cerebral cortex, although degeneration of other neuronal types, in particular serotonergic neurons, might also represent a cause of spasticity. We performed a pathology study in seven patients with amyotrophic lateral sclerosis and six control subjects and observed that central serotonergic neurons suffer from a degenerative process with prominent neuritic degeneration, and sometimes loss of cell bodies in patients with amyotrophic lateral sclerosis. Moreover, distal serotonergic projections to spinal cord motor neurons and hippocampus systematically degenerated in patients with amyotrophic lateral sclerosis. In SOD1 (G86R) mice, a transgenic model of amyotrophic lateral sclerosis, serotonin levels were decreased in brainstem and spinal cord before onset of motor symptoms. Furthermore, there was noticeable atrophy of serotonin neuronal cell bodies along with neuritic degeneration at disease onset. We hypothesized that degeneration of serotonergic neurons could underlie spasticity in amyotrophic lateral sclerosis and investigated this hypothesis in vivo using tail muscle spastic-like contractions in response to mechanical stimulation as a measure of spasticity. In SOD1 (G86R) mice, tail muscle spastic-like contractions were observed at end-stage. Importantly, they were abolished by 5-hydroxytryptamine-2b/c receptors inverse agonists. In line with this, 5-hydroxytryptamine-2b receptor expression was strongly increased at disease onset. In all, we show that serotonergic neurons degenerate during amyotrophic lateral sclerosis, and that this might underlie spasticity in mice. Further research is needed to determine whether inverse agonists of 5-hydroxytryptamine-2b/c receptors could be of interest in treating spasticity in patients with amyotrophic lateral sclerosis.

Impacts of brain serotonin deficiency following Tph2 inactivation on development and raphe neuron serotonergic specification.

Brain serotonin (5-HT) is implicated in a wide range of functions from basic physiological mechanisms to complex behaviors, including neuropsychiatric conditions, as well as in developmental processes. Increasing evidence links 5-HT signaling alterations during development to emotional dysregulation and psychopathology in adult age. To further analyze the importance of brain 5-HT in somatic and brain development and function, and more specifically differentiation and specification of the serotonergic system itself, we generated a mouse model with brain-specific 5-HT deficiency resulting from a genetically driven constitutive inactivation of neuronal tryptophan hydroxylase-2 (Tph2). Tph2 inactivation (Tph2-/-) resulted in brain 5-HT deficiency leading to growth retardation and persistent leanness, whereas a sex- and age-dependent increase in body weight was observed in Tph2+/- mice. The conserved expression pattern of the 5-HT neuron-specific markers (except Tph2 and 5-HT) demonstrates that brain 5-HT synthesis is not a prerequisite for the proliferation, differentiation and survival of raphe neurons subjected to the developmental program of serotonergic specification. Furthermore, although these neurons are unable to synthesize 5-HT from the precursor tryptophan, they still display electrophysiological properties characteristic of 5-HT neurons. Moreover, 5-HT deficiency induces an up-regulation of 5-HT(1A) and 5-HT(1B) receptors across brain regions as well as a reduction of norepinephrine concentrations accompanied by a reduced number of noradrenergic neurons. Together, our results characterize developmental, neurochemical, neurobiological and electrophysiological consequences of brain-specific 5-HT deficiency, reveal a dual dose-dependent role of 5-HT in body weight regulation and show that differentiation of serotonergic neuron phenotype is independent from endogenous 5-HT synthesis.

Targeting brain serotonin synthesis: insights into neurodevelopmental disorders with long-term outcomes related to negative emotionality, aggression and antisocial behaviour.

Aggression, which comprises multi-faceted traits ranging from negative emotionality to antisocial behaviour, is influenced by an interaction of biological, psychological and social variables. Failure in social adjustment, aggressiveness and violence represent the most detrimental long-term outcome of neurodevelopmental disorders. With the exception of brain-specific tryptophan hydroxylase-2 (Tph2), which generates serotonin (5-HT) in raphe neurons, the contribution of gene variation to aggression-related behaviour in genetically modified mouse models has been previously appraised (Lesch 2005 Novartis Found Symp. 268, 111-140; Lesch & Merschdorf 2000 Behav. Sci. Law 18, 581-604). Genetic inactivation of Tph2 function in mice led to the identification of phenotypic changes, ranging from growth retardation and late-onset obesity, to enhanced conditioned fear response, increased aggression and depression-like behaviour. This spectrum of consequences, which are amplified by stress-related epigenetic interactions, are attributable to deficient brain 5-HT synthesis during development and adulthood. Human data relating altered TPH2 function to personality traits of negative emotionality and neurodevelopmental disorders characterized by deficits in cognitive control and emotion regulation are based on genetic association and are therefore not as robust as the experimental mouse results. Mouse models in conjunction with approaches focusing on TPH2 variants in humans provide unexpected views of 5-HT's role in brain development and in disorders related to negative emotionality, aggression and antisocial behaviour.

Recovery and aging of serotonergic fibers after single and intermittent MDMA treatment in Dark Agouti rat.

3,4-Methylenedioxymethamphetamine (MDMA; ecstasy) is a popular party drug known to cause selective serotonergic damage. Here we examined the long-term recovery and aging of serotonergic fibers and levels of brain-derived neurotrophic factor (BDNF) after intermittent MDMA administration (15 mg kg(-1) i.p. every 7th day for 4 weeks, MDMA ×4) and a single-dose treatment (15 mg kg(-1) i.p., MDMA ×1) in adolescent/young adult male Dark Agouti rats. After MDMA treatment, tryptophan hydroxylase-immunoreactive fiber density decreased and then recovered in all brain regions. Recovery was more pronounced in the MDMA ×4 group compared with the MDMA ×1 group, but similar long-term BDNF responses were found after both treatments. Twenty-two months after treatment, there were fewer clusters of aberrant serotonergic fibers in the parietal cortex in the MDMA ×4 group compared with the MDMA ×1 group. There was no difference in the density of microglial cells or astrocytes in treated groups versus the control 22 months after the treatments. These results indicate that recovery of serotonergic fibers is faster after intermittent MDMA treatment than after single-dose administration, and differences in BDNF levels per se are unlikely to account for this difference. Moreover, it seems that intermittent MDMA treatment attenuates the morphological signs of aging in serotonergic fibers. In addition, neither intermittent nor single-dose MDMA exposition of young animals induces accelerated aging processes or neurodegeneration in senescence, as indicated by the unaltered densities of microglial cells and astrocytes in the treated groups compared with the control.

Adult raphe-specific deletion of Lmx1b leads to central serotonin deficiency.

The transcription factor Lmx1b is essential for the differentiation and survival of central serotonergic (5-HTergic) neurons during embryonic development. However, the role of Lmx1b in adult 5-HTergic neurons is unknown. We used an inducible Cre-LoxP system to selectively inactivate Lmx1b expression in the raphe nuclei of adult mice. Pet1-CreER(T2) mice were generated and crossed with Lmx1b(flox/flox) mice to obtain Pet1-CreER(T2); Lmx1b(flox/flox) mice (which termed as Lmx1b iCKO). After administration of tamoxifen, the level of 5-HT in the brain of Lmx1b iCKO mice was reduced to 60% of that in control mice, and the expression of tryptophan hydroxylase 2 (Tph2), serotonin transporter (Sert) and vesicular monoamine transporter 2 (Vmat2) was greatly down-regulated. On the other hand, the expression of dopamine and norepinephrine as well as aromatic L-amino acid decarboxylase (Aadc) and Pet1 was unchanged. Our results reveal that Lmx1b is required for the biosynthesis of 5-HT in adult mouse brain, and it may be involved in maintaining normal functions of central 5-HTergic neurons by regulating the expression of Tph2, Sert and Vmat2.

Tryptophan hydroxylase-2 (TPH2) in disorders of cognitive control and emotion regulation: a perspective.

Based on genetic variation, there is accumulating evidence that altered function of tryptophan hydroxylase-2 (TPH2), the enzyme critical for synthesis of serotonin (5-HT) in the brain, plays a role in anxiety-, aggression- and depression-related personality traits and in the pathogenesis of disorders featuring deficits in cognitive control and emotion regulation. Here, we appraise the genetic and neurobiological evidence to illustrate the critical role of TPH2 in central 5-HT system function and in the pathophysiology of a wide spectrum of disorders of cognitive control and emotion regulation, ranging from depression to attention-deficit/hyperactivity disorder (ADHD), a phenotype commonly associated with difficulties in the control of emotion and with a high co-morbidity of depression. Findings from psychophysiological and functional imaging studies are indicative of various TPH2 polymorphisms directly influencing serotonergic function and thus impacting on mood disorders and on the response to antidepressant treatment. Especially a combination with uncontrollable stress seems to potentiate these effects linking gene-environment interaction directly with behavioral dysfunction in human and animal models. TPH2-deficient mice display alterations in anxiety-like behavior which is accompanied by adaptational changes of 5-HT(1A) receptors and its associated signaling pathway. Mouse models in conjunction with cognitive neuroscience approaches in humans are providing unexpected results and it may well be that future research on TPH2 will provide an entirely new view of 5-HT in brain development and function related to neuropsychiatric disorders.

Ultrastructural characterization of tryptophan hydroxylase 2-specific cortical serotonergic fibers and dorsal raphe neuronal cell bodies after MDMA treatment in rat.

RATIONALE: 3,4-Methylenedioxymethamphetamine (MDMA, "ecstasy") is a widely used recreational drug known to cause selective long-term serotonergic damage. OBJECTIVES: The aim of this study was to characterize the ultrastructure of serotonergic pericarya and proximal neurites in the dorsal raphe nucleus as well as the ultrastructure of serotonergic axons in the frontal cortex of adolescent Dark Agouti rats 3 days after treatment with 15 mg/kg i.p. MDMA. METHODS: Light microscopic immunohistochemistry and pre-embedding immunoelectron microscopy with a novel tryptophan hydroxylase-2 (Tph2) specific antibody, as a marker of serotonergic structures. RESULTS: Light microscopic analysis showed reduced serotonergic axon density and aberrant swollen varicosities in the frontal cortex of MDMA-treated animals. According to the electron microscopic analysis, Tph2 exhibited diffuse cytoplasmic immunolocalization in dorsal raphe neuronal cell bodies. The ultrastructural-morphometric analysis of these cell bodies did not indicate pathological changes or significant alteration in the cross-sectional areal density of any examined organelles. Proximal serotonergic neurites in the dorsal raphe exhibited no ultrastructural alteration. However, in the frontal cortex among intact fibers, numerous serotonergic axons with destructed microtubules were found. Most of their mitochondria were intact, albeit some injured axons also contained degenerating mitochondria; moreover, a few of them comprised confluent membrane whorls only. CONCLUSIONS: Our treatment protocol does not lead to ultrastructural alteration in the serotonergic dorsal raphe cell bodies and in their proximal neurites but causes impairment in cortical serotonergic axons. In these, the main ultrastructural alteration is the destruction of microtubules although a smaller portion of these axons probably undergo an irreversible damage.

Brain-specific conditional and time-specific inducible Tph2 knockout mice possess normal serotonergic gene expression in the absence of serotonin during adult life.

Several lines of evidence implicate a dysregulation of tryptophan hydroxylase (TPH)-dependent serotonin (5-HT) synthesis in emotional behaviour and stress, and point to its relevance for the etiology and pathogenesis of various neuropsychiatric disorders. We therefore studied different animal models featuring reduced Tph2 expression to investigate the consequences of impaired brain 5-HT synthesis on neuronal development. Specifically, brain-specific conditional and time-specific inducible Tph2 knockout (KO) models were generated and investigated for altered serotonergic neuron-specific gene expression. Raphe neurons of a brain-specific constitutive Tph2 KO were completely devoid of Tph2-positive neurons and, consequently, 5-HT in the brain, and also displayed no compensatory up-regulation of Tph1 expression. In contrast, an inducible Tph2 KO mouse facilitates the generation of a brain-specific 5-HT-reduction model selectively during adult life. This resulted in a highly reduced number of Tph2-positive cells and thus 5-HT in the brain. Intriguingly, expression studies detected no alteration in the expression of genes relevant to the 5-HT system in the brain-specific Tph2 KO and the 5-HT-reduction models. These findings confirm the specificity of Tph2 in brain 5-HT synthesis across the lifespan, yet also suggest that neither developmental nor adult 5-HT synthesis is required for the expression of genes specific for serotonergic signalling. The formation of the serotonergic system thus seems to be a preserved expressional pattern due to intrinsic cellular programs which occurs also in the absence of its key molecule, namely 5-HT.

The expression of the transcription factor FEV in adult human brain and its association with affective disorders.

A wide range of physiological processes and neuronal functioning is modulated by the serotonergic system. Serotonin (5-HT) plays an important role during early brain development. Moreover, dysfunction of the 5-HT system is implicated in psychiatric disorders, especially in affective disorders. Little is known, however, about the transcriptional mechanisms leading to a functional 5-HT system in humans. The Fifth Ewing Variant (FEV), an E-twenty-six (ETS) transcription factor, is assumed to be involved in the transcription of gene(s) in the serotonergic pathway and to play a role in early brain development. To investigate its specificity, we performed an expression analysis of FEV in different human brain regions utilizing quantitative real-time polymerase chain reaction. Our results demonstrate that FEV is not exclusively expressed in serotonergic neurons, but, on the contrary, also in several non-serotonergic brain regions such as locus coeruleus, caudate nucleus and putamen. In the latter two regions, FEV expression levels actually were higher when compared with the pons and the medulla oblongata, which contain the raphe nuclei. Additionally, we examined whether genetic variance in the FEV gene contributes to the susceptibility towards affective disorders. Direct re-sequencing, however, did not provide evidence for FEV mutations in patients, and neither were non-coding single nucleotide polymorphisms associated with disease. FEV therefore might not account for the genetic risk towards depression or bipolar disorder. Furthermore, the specificity of FEV for the serotonergic system should be reconsidered.

Spatio-temporal expression of tryptophan hydroxylase isoforms in murine and human brain: convergent data from Tph2 knockout mice.

Dysregulation of tryptophan hydroxylase (TPH)-dependent serotonin (5-HT) synthesis, has been implicated in various neuropsychiatric disorders, although the differential expression pattern of the two isoforms is controversial. Here, we report a comprehensive spatio-temporal isoform-specific analysis of TPH1 and TPH2 expression during pre- and postnatal development of mouse brain and in adult human brain. TPH2 expression was consistently detected in the raphe nuclei, as well as in fibers in the deep pineal gland and in small intestine. Although TPH1 expression was found in these peripheral tissues, no significant TPH1 expression was detected in the brain, neither during murine development, nor in mouse and human adult brain. In support of TPH2 specificity in brain 5-HT synthesis, raphe neurons of Tph2 knockout mice were completely devoid of 5-HT, with no compensatory activation of Tph1 expression. In conclusion, our findings indicate that brain 5-HT synthesis across the lifespan is exclusively maintained by TPH2.

Influence of functional variant of neuronal nitric oxide synthase on impulsive behaviors in humans.

CONTEXT: Human personality is characterized by substantial heritability but few functional gene variants have been identified. Although rodent data suggest that the neuronal isoform of nitric oxide synthase (NOS-I) modifies diverse behaviors including aggression, this has not been translated to human studies. OBJECTIVES: To investigate the functionality of an NOS1 promoter repeat length variation (NOS1 Ex1f variable number tandem repeat [VNTR]) and to test whether it is associated with phenotypes relevant to impulsivity. DESIGN: Molecular biological studies assessed the cellular consequences of NOS1 Ex1f VNTR; association studies were conducted to investigate the impact of this genetic variant on impulsivity; imaging genetics was applied to determine whether the polymorphism is functional on a neurobiological level. SETTING: Three psychiatric university clinics in Germany. PARTICIPANTS: More than 3200 subjects were included in the association study: 1954 controls, 403 patients with personality disorder, 383 patients with adult attention-deficit/hyperactivity disorder (ADHD), 151 with familial ADHD, 189 suicide attempters, and 182 criminal offenders. MAIN OUTCOME MEASURES: For the association studies, the major outcome criteria were phenotypes relevant to impulsivity, namely, the dimensional phenotype conscientiousness and the categorical phenotypes adult ADHD, aggression, and cluster B personality disorder. RESULTS: A novel functional promoter polymorphism in NOS1 was associated with traits related to impulsivity, including hyperactive and aggressive behaviors. Specifically, the short repeat variant was more frequent in adult ADHD, cluster B personality disorder, and autoaggressive and heteroaggressive behavior. This short variant came along with decreased transcriptional activity of the NOS1 exon 1f promoter and alterations in the neuronal transcriptome including RGS4 and GRIN1. On a systems level, it was associated with hypoactivation of the anterior cingulate cortex, which is involved in the processing of emotion and reward in behavioral control. CONCLUSION: These findings implicate deficits in neuronal signaling via nitric oxide in moderation of prefrontal circuits underlying impulsivity-related behavior in humans.

Deficiency of brain 5-HT synthesis but serotonergic neuron formation in Tph2 knockout mice.

The relative contribution of the two tryptophan hydroxylase (TPH) isoforms, TPH1 and TPH2, to brain serotonergic system function is controversial. To investigate the respective role of TPH2 in neuron serotonin (5-HT) synthesis and the role of 5-HT in brain development, mice with a targeted disruption of Tph2 were generated. The preliminary results indicate that in Tph2 knockout mice raphe neurons are completely devoid of 5-HT, whereas no obvious alteration in morphology and fiber distribution are observed. The findings confirm the exclusive specificity of Tph2 in brain 5-HT synthesis and suggest that Tph2-synthesized 5-HT is not required for serotonergic neuron formation.

Interaction between BDNF Val66Met and dopamine transporter gene variation influences anxiety-related traits.

The involvement in neural plasticity and the mediation of effects of repeated stress exposure and long-term antidepressant treatment on hippocampal neurogenesis supports a critical role of brain-derived neurotrophic factor (BDNF) in the pathophysiology of affective and other stress-related disorders. A previously reported valine to methionine substitution at amino-acid position 66 (BDNF Val66Met) seems to account for memory disturbance and hippocampal dysfunction. In the present study, we evaluated the impact of the BDNF Val66Met polymorphism on individual differences in personality traits in a sample of healthy volunteers in relation to other common gene variants thought to be involved in the pathophysiology of affective disorders, such as the serotonin transporter promoter polymorphism (5-HTTLPR) and a variable number of tandem repeat polymorphism of the dopamine transporter gene (DAT VNTR). Personality traits were assessed using the NEO personality inventory (NEO-PI-R) and Tridimensional Personality Questionnaire (TPQ). There was a significant DAT VNTR-dependent association between NEO-PI-R Neuroticism and the BDNF Val66Met polymorphism. Among individuals with at least one copy of the DAT 9-repeat allele, carriers of the BDNF Met allele exhibited significantly lower Neuroticism scores than noncarriers. This interaction was also observed for TPQ Harm Avoidance, a personality dimension related to Neuroticism. Our results support the notion that allelic variation at the BDNF locus--in interaction with other gene variants--influences anxiety- and depression-related personality traits.

Tryptophan hydroxylase-2 gene variation influences personality traits and disorders related to emotional dysregulation.

Variation in the tryptophan hydroxylase-2 gene (TPH2) coding for the rate-limiting enzyme of serotonin (5-HT) synthesis in the brain modulates responses of limbic circuits to emotional stimuli and has been linked to a spectrum of clinical populations characterized by emotional dysregulation. Here, we tested a set of common single nucleotide polymorphisms (SNPs) in and downstream of the transcriptional control region of TPH2 for association with personality traits and with risk for personality disorders in two cohorts comprising of 336 healthy individuals and 420 patients with personality disorders. Personality dimensions were assessed by the Tridimensional Personality Questionnaire (TPQ) and the revised NEO Personality Inventory (NEO-PI-R). Personality disorders were diagnosed with the Structured Clinical Interview of DSM-IV and were allocated to clusters A, B, and C. Individual SNP and haplotype analyses revealed significant differences in genotype frequencies between controls and cluster B as well as cluster C patients, respectively. In both patient groups, we observed overrepresentation of T allele carriers of a functional polymorphism in the upstream regulatory region of TPH2 (SNP G-703T, rs4570625) which was previously shown to bias responsiveness of the amygdala, a structure critically involved in emotionality. Furthermore, significant effects of TPH2 variants on anxiety-related traits defined primarily by the TPQ Harm Avoidance were found in healthy individuals. The results link potentially functional TPH2 variants to personality traits related to emotional instability as well as to cluster B and cluster C personality disorders. These findings implicate alterations of 5-HT synthesis in emotion regulation and confirm TPH2 as a susceptibility and/or modifier gene of affective spectrum disorders.

Interaction of serotonergic and noradrenergic gene variants in panic disorder.

OBJECTIVE: Panic disorder is an anxiety disorder with an estimated heritability of 48%. Associations findings have been obtained with candidate genes from both serotonergic and noradrenergic pathways including regulatory and coding variants of the serotonin receptor 1A gene, the monoamine oxidase A gene, the catechol-O-methyltransferase gene and the norepinephrine transporter gene. METHODS: In the present study, an analysis of interactions between the functional serotonin receptor 1A polymorphism, the norepinephrine transporter variants and the other respective polymorphisms of the above-mentioned genes is reported. The analysis is based on genotype results from 115 cases and 115 age and sex-matched controls. RESULTS: A nominally significant (P=0.04) interaction between the serotonin receptor 1A and the catechol-O-methyltransferase polymorphisms was observed. Stratified analysis revealed that the odds ratio of each polymorphism was highest in the presence of the low-risk genotype(s) of the other polymorphism and low in the presence of the high-risk genotype(s) of the other polymorphism. CONCLUSIONS: This is the first possible interaction of genetic variations in panic disorder that has been observed. As the sample size was small and no adjustment for multiple testing was made, the assessment of the interacting risk alleles needs replication in a larger sample with higher power.

The novel brain-specific tryptophan hydroxylase-2 gene in panic disorder.

Panic disorder is a common psychiatric disorder characterized by recurrent anxiety attacks and anticipatory anxiety. Due to the severity of the symptoms of the panic attacks and the frequent additional occurrence of agoraphobia, panic disorder is an often debilitating disease. Elevation of central serotonin levels by drugs such as clomipramine represents one of the most effective treatment options for panic disorder. This points to an important role of dysregulation of the serotonergic system in the genetic etiology of panic disorder. The novel brain-specific 5-HT synthesizing enzyme, tryptophan hydroxylase-2 (TPH2), which represents the rate-limiting enzyme of 5-HT production in the brain, may therefore be of particular importance in panic disorder. We focused on the putative transcriptional control region of TPH2 and identified two novel common single nucleotide polymorphisms (SNPs) of TPH2 in and close to this region. Moreover, a recently described loss-of-function mutation of TPH2 which results in an 80% reduction of serotonin production, was assessed. In an analysis of the putative transcriptional control region SNPs in a sample of panic disorder patients and controls no association of the disorder with the TPH2 SNPs or haplotypes was found. Moreover, the loss-of-function R441H mutation of TPH2 was not present in the panic disorder patients. The results of this first study of TPH2 in panic disorder argue against an importance of allelic variation of TPH2 in the pathogenesis of panic disorder with or without agoraphobia.

Transmission disequilibrium of polymorphic variants in the tryptophan hydroxylase-2 gene in children and adolescents with obsessive-compulsive disorder.

Dysfunction of the central serotonergic system has been implicated in the pathophysiology of obsessive-compulsive disorder (OCD). The genetic contribution to the development of OCD is particularly high in early-onset OCD. The aim of this study was to investigate the effect of polymorphic variants in the gene of the novel brain-specific tryptophan hydroxylase-2 (TPH2), the rate-limiting enzyme of serotonin (5-HT) synthesis in the brain, in OCD with disease onset in childhood and adolescence. We analysed two common single nucleotide polymorphisms (SNPs) of TPH2 in the putative transcriptional control region and in intron 2 of the TPH2 gene in a unique family-based sample of OCD patients with onset of the disease in childhood and adolescence comprising 71 complete, independent trios. The transmission disequilibrium test was used to determine transmission of alleles and haplotypes from parents to offspring. In this first study of TPH2 in OCD, analysis of the SNPs, rs4570625 and rs4565946, revealed a significant preferential transmission of haplotype G-C to children and adolescents with OCD. Moreover, a trend towards preferential transmission of the C allele of SNP rs4565946 to the patients was found. The genotype relative-risk estimate for homozygous C allele carriers of SNP rs4565946 was 2.58 (95% CI 0.98-6.82). In conclusion, the results link TPH2 variations to the pathogenesis of early-onset OCD and further support the aetiological relevance of 5-HT signalling in OCD.