A functional genetic variation of the serotonin (5-HT) transporter affects 5-HT1A receptor binding in humans

Determining the association of the 5HTTLPR polymorphism with delusions and hallucinations in Lewy body dementias

OBJECTIVES

To determine whether the 5HTTLPR serotonin transporter polymorphism is associated with delusions and hallucinations in people with dementia with Lewy bodies (DLB) and Parkinson disease dementia (PDD).

DESIGN

Prospective cohort study.

PARTICIPANTS

A total of 187 individuals, recruited from centres in Norway, Sweden, and the United Kingdom were included in this study; 97 with clinically or neuropathologically diagnosed DLB/PDD and 90 cognitively normal individuals as a comparison group.

MEASUREMENTS

All participants with dementia underwent serial evaluation of neuropsychiatric symptoms to assess the presence of persistent delusions and hallucinations using the Columbia University Scale for Psychopathology in Alzheimer disease, the Neuropsychiatric Inventory, or the Present Behavioural Examination. Severity of cognitive impairment was measured using the Mini Mental State Examination (MMSE). Individuals were genotyped for the 5HTTLPR polymorphism.

RESULTS

Logistic regression demonstrated that homozygosity for the L/L genotype and lower MMSE were associated with an increased risk for delusions (odds ratio: 11.5 and 1.16, respectively). Neither was significantly associated with hallucinations.

CONCLUSIONS

This study is the first to demonstrate the 5HTTLPR polymorphism is associated with delusions in Lewy body dementias, with important implications regarding the mechanisms underlying this symptom across the AD/DLB/PDD spectrum. Further studies are warranted to investigate this relationship further and examine treatment opportunities.

The influence of 5-HTTLPR genotype on the association between the plasma concentration and therapeutic effect of paroxetine in patients with major depressive disorder

INTRODUCTION

The efficacy of treatment with selective serotonin reuptake inhibitors in patients with major depressive disorder (MDD) can differ depending on the patient's serotonin transporter-linked polymorphic region (5-HTTLPR) genotype, and the effects of varying plasma concentrations of drugs can also vary. We investigated the association between the paroxetine plasma concentration and clinical response in patients with different 5-HTTLPR genotypes.

METHODS

Fifty-one patients were enrolled in this study. The Montgomery-Asberg Depression Rating Scale (MADRS) was used to evaluate patients at 0, 1, 2, 4, and 6 weeks. The patients' paroxetine plasma concentrations at week 6 were measured using high-performance liquid chromatography. Additionally, their 5-HTTLPR polymorphisms (alleles S and L) were analyzed using a polymerase chain reaction with specific primers. We divided the participants into two groups based on their L haplotype: the SS group and the SL and LL group. We performed single and multiple regression analyses to investigate the associations between MADRS improvement and paroxetine plasma concentrations or other covariates for each group.

RESULTS

There were no significant differences between the two groups with regard to demographic or clinical data. In the SS group, the paroxetine plasma concentration was significantly negatively correlated with improvement in MADRS at week 6. In the SL and LL group, the paroxetine plasma concentration was significantly positively correlated with improvement in MADRS at week 6 according to the results of the single regression analysis; however, it was not significantly correlated with improvement in MADRS at week 6 according to the results of the multiple regression analysis.

CONCLUSION

Among patients with MDD who do not respond to paroxetine, a lower plasma concentration or a lower oral dose of paroxetine might be more effective in those with the SS genotype, and a higher plasma concentration might be more effective in those with the SL or LL genotype.

[Polymorphism in the Serotonin Transporter Gene (SLC6A4) and Emotional Bipolar Disorder in Two Regional Mental Health Centers from the Eje Cafetero (Colombia)]

INTRODUCTION

The indel polymorphisms in the promoting region and the 2(nd) intron polymorphisms in the serotonin transporter gene (SLC6A4) have been associated to bipolar disorder 1 (BD1) in several population studies. The objective was to analyze the genotypic and allelic frequencies in both gene regions in a study of cases and controls with individuals from Risaralda and Quindío (Colombia) so as to establish possible associations to BD1, and compare results with previous and similar studies.

METHODS

133 patients and 120 controls were studied. L and S indel polymorphisms in the promoting region were analyzed by PCR, together with VNTR STin2.10 and STin 2.12 VNTRs polymorphisms in the 2(nd) intron of the SL-C6A4 gene

RESULTS

Genotypic and allelic frequencies for the S and L polymorphisms were similar both in cases and controls. However, the LL genotype was significantly increased both in BD1 population (OR=1.89; CI95%=1.1-3.68), and when discriminated by gender. This particular genotype in general population is OR=2.22; IC95%=1.04-5.66 for women, and OR=1.62; IC 95%=0.71-4.39 for men. No significant genotypic and allelic differences were found for VNTR STin2.10 and STin 2.12. polymorphisms.

CONCLUSIONS

No association was found between polymorphisms of 5-HTTLPR polymorphisms and the 2(nd) intron of the serotonin transporting gene in general patients with BD1, nor when compared by gender. Our results are similar to those reported for Caucasian populations and differ from those of Asian and Brazilian populations.

Serotonin transporter-linked polymorphic region (5-HTTLPR) genotype and stressful life events interact to predict preschool-onset depression: a replication and developmental extension

BACKGROUND

Scientific enthusiasm about gene × environment interactions, spurred by the 5-HTTLPR (serotonin transporter-linked polymorphic region) × SLEs (stressful life events) interaction predicting depression, have recently been tempered by sober realizations of small effects and meta-analyses reaching opposing conclusions. These mixed findings highlight the need for further research. Converging evidence suggests that the effects of 5-HTTLPR genotype may be neurodevelopmental in origin, but we are not aware of empirical studies that have investigated whether the 5-HTTLPR genotype × SLE interaction predicts preschool-onset depression (PO-MDD), the earliest validated form of depression.

METHODS

Children (n = 234) aged 3-5 were recruited for a longitudinal study designed to examine PO-MDD. In a comprehensive baseline assessment, the child's primary caregivers completed questionnaires and were interviewed about their child's behaviors, psychiatric symptoms, and exposure to SLEs.

RESULTS

A 5-HTTLPR × SLEs interaction emerged, such that children homozygous for the short allele were more susceptible to depression in the context of elevated SLE than long allele carriers. In contrast, at low SLE exposure, short allele homozygotes had fewer depressive symptoms. The data were best fit by a plasticity model with a substantial reduction in fit by diathesis-stress models.

CONCLUSIONS

Extending studies in adult and adolescent populations, these data suggest that 5-HTTLPR genotype may provide plasticity to environmental influence, for better or worse. Specifically, children homozygous for the short allele were more susceptible to the depressogenic effects of SLEs but benefitted, in the form of reduced depressive symptoms, in the context of relatively benign environmental conditions (i.e. relatively low SLE exposure). These data highlight the importance of examining gene × environment interactions across development, environment, and outcome but should be interpreted cautiously given the small sample size.

Serotonin transporter polymorphism is associated with increased apnea-hypopnea index in older adults

RATIONALE

A functional polymorphism of the serotonin transporter gene (5-HTTLPR) has previously been related to upper airway pathology, but its contribution to obstructive sleep apnea (OSA), a highly prevalent sleep disorder in older adults, remains unclear.

OBJECTIVES

We aimed to investigate the relationship between apnea-hypopnea index (AHI) and genetic variations in the promoter region of the 5-HTTLPR in older adults.

METHODS

DNA samples from 94 community-dwelling older adults (57% female, mean age 72 ± 8) were genotyped for the 5-HTTLPR polymorphism. All participants were assessed in their homes with full ambulatory polysomnography in order to determine AHI and related parameters such as hypoxia, sleep fragmentation, and self-reported daytime sleepiness.

RESULTS

The 5-HTT l allele was significantly associated with AHI (p = 0.019), with l allele carriers displaying a higher AHI than s allele homozygotes. A single allele change in 5-HTTLPR genotype from s to l resulted in an increase of AHI by 4.46 per hour of sleep (95% CI, 0.75-8.17). The l allele was also associated with increased time during sleep spent at oxygen saturation levels below 90% (p = 0.014).

CONCLUSIONS

The observed significant association between the 5-HTTLPR l allele and severity of OSA in older adults suggests that the l allele may be important to consider when assessing for OSA in this age group. This association may also explain some of the observed variability among serotonergic pharmacological treatment studies for OSA, and 5-HTT genotype status may have to be taken into account in future therapeutic trials involving serotonergic agents.

Oestradiol alters central 5-HT1A receptor binding potential differences related to psychosocial stress but not differences related to 5-HTTLPR genotype in female rhesus monkeys

Social subordination in female macaques represents a well-described model of chronic psychosocial stress. Additionally, a length polymorphism (5-HTTLPR) in the regulatory region of the serotonin (5-HT) transporter (5-HTT) gene (SLC6A4) is present in rhesus macaques, which has been linked to adverse outcomes similar to that described in humans with an analogous 5-HTTLPR polymorphism. The present study determined the effects of social status and the 5-HTTLPR genotype on 5-HT1A receptor binding potential (5-HT1A BP(ND)) in brain regions implicated in emotional regulation and stress reactivity in ovariectomised female monkeys, and then assessed how these effects were altered by 17β-oestradiol (E(2)) treatment. Areas analysed included the prefrontal cortex [anterior cingulate (ACC); medial prefrontal cortex (mPFC); dorsolateral prefrontal cortex; orbitofrontal prefrontal cortex], amygdala, hippocampus, hypothalamus and raphe nucleui. Positron emission tomography using p-[(18) F]MPPF was performed to determine the levels of 5-HT1A BP(ND) under a non-E(2) and a 3-week E(2) treatment condition. The short variant (s-variant) 5-HTTLPR genotype produced a significant reduction in 5-HT1A BP(ND) in the mPFC regardless of social status, and subordinate s-variant females showed a reduction in 5-HT1A BP(ND) within the ACC. Both these effects of 5-HTTLPR were unaffected by E(2). Additionally, E(2) reduced 5-HT1A BP(ND) in the dorsal raphe of all females irrespective of psychosocial stress or 5-HTTLPR genotype. Hippocampal 5-HT1A BP(ND) was attenuated in subordinate females regardless of 5-HTTLPR genotype during the non-E(2) condition, an effect that was normalised with E(2). Similarly, 5-HT1A BP(ND) in the hypothalamus was significantly lower in subordinate females regardless of 5-HTTLPR genotype, an effect reversed with E(2). Taken together, the data indicate that the effect of E(2) on modulation of central 5HT1A BP(ND) may only occur in brain regions that show no 5-HTTLPR genotype-linked control of 5-HT1A binding.

Panic disorder and serotonin reuptake inhibitors predict coupling of cortical and cardiac activity

Panic attacks, the cardinal symptom of panic disorder (PD), are characterized by intense physiological reactions including accelerated heart activity. Although cortical processes are thought to trigger and potentiate panic attacks, it is unknown whether individuals with PD have a general tendency to show elevated cortico-cardiac interactions, which could predispose them for brain-driven modulations of heart activity during panic. Consistent with this hypothesis, serotonin, a highly relevant neurotransmitter for panic and PD presumably affects the cortical control of the heart. The current study thus aimed to test whether PD and serotonin reuptake inhibitor (SRI) intake are related to cortico-cardiac interactions in the absence of acute panic. Human participants with PD (N=22), major depression (MD, clinical control group, N=21) or no psychiatric diagnosis (healthy control group, N=23) performed a gambling task. To measure cortico-cardiac coupling, the within-subject covariation of single-trial EEG after feedback presentation and subsequent changes in heart period was determined. As in prior studies, there was a significant time-lagged covariation of EEG and heart activity indicating that trial-by-trial fluctuations of feedback-evoked EEG amplitude determined how much heart activity accelerated seconds later. Importantly, this covariation pattern was significantly potentiated in PD vs control participants. Moreover, concurrent SRI intake further augmented brain-heart covariation in individuals with PD and MD. The present findings demonstrate that PD and serotonin are associated with altered brain-heart interactions in a non-panic situation. Future work should clarify whether brain-heart coupling has a causal role in PD, for example by facilitating panic attacks.

Cognitive impairment in studies of 5HTTLPR and psychosis in Alzheimer's disease: a systematic review

BACKGROUND/AIMS

Cognitive impairment is a well-established correlate of psychotic symptoms in Alzheimer's disease (AD-P). We review whether this relationship has confounded previous genetic association studies of 5HTTLPR and AD-P.

METHODS

We reviewed all studies on 5HTTLPR and conducted a semi-quantitative analysis.

RESULTS

Three out of 4 studies with low MMSE reported a significant association, while 1 out of 4 with high MMSE reported a significant association.

CONCLUSIONS

Variation in cognitive impairment in past studies has contributed to the inconsistency in findings. The findings presented here bring a greater clarity to our understanding of the role of 5HTTLPR in AD-P.

Lack of serotonin reuptake during brain development alters rostral raphe-prefrontal network formation

Besides its "classical" neurotransmitter function, serotonin (5-HT) has been found to also act as a neurodevelopmental signal. During development, the 5-HT projection system, besides an external placental source, represents one of the earliest neurotransmitter systems to innervate the brain. One of the targets of the 5-HT projection system, originating in the brainstem raphe nuclei, is the medial prefrontal cortex (mPFC), an area involved in higher cognitive functions and important in the etiology of many neurodevelopmental disorders. Little is known, however, about the exact role of 5-HT and its signaling molecules in the formation of the raphe-prefrontal network. Using explant essays, we here studied the role of the 5-HT transporter (5-HTT), an important modulator of the 5-HT signal, in rostral raphe-prefrontal network formation. We found that the chemotrophic nature of the interaction between the origin (rostral raphe cluster) and a target (mPFC) of the 5-HT projection system was affected in rats lacking the 5-HTT (5-HTT(-/-)). While 5-HTT deficiency did not affect the dorsal raphe 5-HT-positive outgrowing neurites, the median raphe 5-HT neurites switched from a strong repulsive to an attractive interaction when co-cultured with the mPFC. Furthermore, the fasciculation of the mPFC outgrowing neurites was dependent on the amount of 5-HTT. In the mPFC of 5-HTT(-/-) pups, we observed clear differences in 5-HT innervation and the identity of a class of projection neurons of the mPFC. In the absence of the 5-HTT, the 5-HT innervation in all subareas of the early postnatal mPFC increased dramatically and the number of Satb2-positive callosal projection neurons was decreased. Together, these results suggest a 5-HTT dependency during early development of these brain areas and in the formation of the raphe-prefrontal network. The tremendous complexity of the 5-HT projection system and its role in several neurodevelopmental disorders highlights the need for further research in this largely unexplored area.

Impact of COMT genotype on serotonin-1A receptor binding investigated with PET

Alterations of the inhibitory serotonin-1A receptor (5-HT1A) constitute a solid finding in neuropsychiatric research, particularly in the field of mood and anxiety disorders. Manifold factors influencing the density of this receptor have been identified, e.g., steroid hormones, sunlight exposure and genetic variants of serotonin-related genes. Given the close interactions between serotonergic and dopaminergic neurotransmission, we investigated whether a common single-nucleotide-polymorphism of the catechol-O-methyltransferase (COMT) gene (VAL158MET or rs4680) coding for a key enzyme of the dopamine network that is associated with the pathogenesis of mood disorders and antidepressant treatment response, directly affects 5-HT1A receptor binding potential. Fifty-two healthy individuals (38 female, mean age ± standard deviation = 40.48 ± 14.87) were measured via positron emission tomography using the radioligand [carbonyl-(11)C]WAY-100635. Genotyping for rs4680 was performed using DNA isolated from whole blood with the MassARRAY platform of the software SEQUENOM(®). Whole brain voxel-wise ANOVA resulted in a main effect of genotype on 5-HT1A binding. Compared to A carriers (AA + AG) of rs4680, homozygote G subjects showed higher 5-HT1A binding potential in the posterior cingulate cortex (F (2,49) = 17.7, p = 0.05, FWE corrected), the orbitofrontal cortex, the anterior cingulate cortex, the insula, the amygdala and the hippocampus (voxel-level: p < 0.01 uncorrected, t > 2.4; cluster-level: p < 0.05 FWE corrected). In light of the frequently reported alterations of 5-HT1A binding in anxiety and mood disorders, this study proposes a potential implication of the COMT genotype, more specifically the VAL158MET polymorphism, via modulation of the serotonergic neurotransmission.

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-HT_1A 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-HT_1A-selective agonist R(+)-8-hydroxy-2-(di-n-propylamino)tetralin showed mild sensitization and marked desensitization of 5-HT_1A 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-HT_1A 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-HT_1A receptors does not predict the magnitude of 5-HT neuron autoinhibition. Changes in 5-HT_1A 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.

Neuroimaging methods for adolescent substance use disorder prevention science

Magnetic resonance imaging (MRI) methods safely provide in vivo indicators of cerebral macrostructure, microstructure, and activation that can be examined in relation to substance use disorder (SUD) risks and effects. This article will provide an overview of MRI approaches, including volumetric measures, diffusion tensor imaging, and functional MRI, that have been applied to studies of adolescent neuromaturation in relationship to risk phenotypes and adolescent SUD. To illustrate these applications, examples of research findings will be presented. MRI indicators have demonstrated that neurobiological maturation continues throughout adolescence. MRI research has suggested that variations in neurobiological maturation may contribute to SUD risk, and that substance use adversely influences adolescent brain development. Directly measured neurobiological variables may be viable preventive intervention targets and outcome indicators. Further research is needed to provide definitive findings on neurodevelopmental immaturity as an SUD risk and to determine the directions such observations suggest for advancing prevention science.

Modulatory effects of the piccolo genotype on emotional memory in health and depression

Major depressive disorder (MDD) has been associated with biased memory formation for mood-congruent information, which may be related to altered monoamine levels. The piccolo (PCLO) gene, involved in monoaminergic neurotransmission, has previously been linked to depression in a genome-wide association study. Here, we investigated the role of the PCLO risk allele on functional magnetic resonance imaging (MRI) correlates of emotional memory in a sample of 89 MDD patients (64 PCLO risk allele carriers) and 29 healthy controls (18 PCLO risk allele carriers). During negative word encoding, risk allele carriers showed significant lower activity relative to non-risk allele carriers in the insula, and trend-wise in the anterior cingulate cortex and inferior frontal gyrus. Moreover, depressed risk allele carriers showed significant lower activity relative to non-risk allele carriers in the striatum, an effect which was absent in healthy controls. Finally, amygdalar response during processing new positive words vs. known words was blunted in healthy PCLO+ carriers and in MDD patients irrespective of genotype, which may indicate that signalling of salient novel information does not occur to the same extent in PCLO+ carriers and MDD patients. The PCLO risk allele may increase vulnerability for MDD by modulating local brain function with regard to responsiveness to salient stimuli (i.e. insula) and processing novel negative information. Also, depression-specific effects of PCLO on dorsal striatal activation during negative word encoding and the absence of amygdalar salience signalling for novel positive information further suggest a role of PCLO in symptom maintenance in MDD.

Serotonin transporter genotype affects serotonin 5-HT1A binding in primates

Disruption of the serotonin system has been implicated in anxiety and depression and a related genetic variation has been identified that may predispose individuals for these illnesses. The relationship of a functional variation of the serotonin transporter promoter gene (5-HTTLPR) on serotonin transporter binding using in vivo imaging techniques have yielded inconsistent findings when comparing variants for short (s) and long (l) alleles. However, a significant 5-HTTLPR effect on receptor binding at the 5-HT(1A) receptor site has been reported in humans, suggesting the 5-HTTLPR polymorphism may play a role in serotonin (5-HT) function. Rhesus monkeys possess a 5-HTTLPR length polymorphism similar to humans and serve as an excellent model for studying the effects of this orthologous genetic variation on behaviors and neurochemical functions related to the 5-HT system. In this study, PET imaging of [(18)F]mefway was performed on 58 rhesus monkeys (33 l/l, 25 s-carriers) to examine the relation between 5-HT(1A) receptor-specific binding and 5-HTTLPR genotypes. Significantly lower 5-HT(1A) binding was found in s-carrier subjects throughout both cortical brain regions and the raphe nuclei. These results demonstrate that the underlying 5-HT neurochemical system is influenced by this functional polymorphism and illustrate the strong potential for extending the nonhuman primate model into investigating the role of this genetic variant on behavior and gene-environment interactions.

A neurogenetics approach to understanding individual differences in brain, behavior, and risk for psychopathology

Neurogenetics research has begun to advance our understanding of how genetic variation gives rise to individual differences in brain function, which, in turn, shapes behavior and risk for psychopathology. Despite these advancements, neurogenetics research is currently confronted by three major challenges: (1) conducting research on individual variables with small effects, (2) absence of detailed mechanisms, and (3) a need to translate findings toward greater clinical relevance. In this review, we showcase techniques and developments that address these challenges and highlight the benefits of a neurogenetics approach to understanding brain, behavior and psychopathology. To address the challenge of small effects, we explore approaches including incorporating the environment, modeling epistatic relationships and using multilocus profiles. To address the challenge of mechanism, we explore how non-human animal research, epigenetics research and genome-wide association studies can inform our mechanistic understanding of behaviorally relevant brain function. Finally, to address the challenge of clinical relevance, we examine how neurogenetics research can identify novel therapeutic targets and for whom treatments work best. By addressing these challenges, neurogenetics research is poised to exponentially increase our understanding of how genetic variation interacts with the environment to shape the brain, behavior and risk for psychopathology.

The serotonin 1A receptor gene confer susceptibility to mood disorders: results from an extended meta-analysis of patients with major depression and bipolar disorder

The serotonin 1A receptor gene (HTR1A) has been associated with mood disorders (MDs), including major depressive disorder (MDD) and bipolar disorder (BP). Therefore, we conducted a systematic review and meta-analysis between rs6295 (C-1019G) as well as rs878567 in HTR1A and MDs. Searching PubMed through May 2012, 15 studies, including our own, previously unpublished association study (135 MDD patients and 107 healthy controls), met inclusion criteria for the meta-analysis of rs6295 (4,297 MDs patients and 5,435 controls). Five association studies met criteria for the meta-analysis of rs878567 (2041MDs patients and 2,734 controls). rs6295 was associated with combined MDs (P allele model = 0.007 and P recessive model = 0.01). When divided by diagnostic subgroup (MDD = 3,119 patients and 4,380 controls or BP = 1,170 patients and 2,252 controls), rs6295 was associated with each MDs separately (MDD: P allele model = 0.006, P recessive model = 0.01; BP: P dominant model = 0.003). Likewise, rs878567 was associated with combined MDs (2,041 patients and 2,734 controls (P allele model = 0.0002, P dominant model = 0.0008, and P recessive model = 0.01). When divided by diagnostic subgroup (MDD = 1,013 patients and 1,728 controls or BP = 1,051 patients and 2,099 controls), rs878567 was associated with MDD (P allele model = 0.0007 and P dominant model = 0.01), while only one BP study had such data, precluding a meta-analysis. All of these significances survived correction for multiple comparisons. Results from this expanded meta-analysis, which included our own new study, suggest that rs6295 (C-1019G) and rs878567 in HTR1A are related to the pathophysiology of MDs, with overlap between MDD and BP. Findings provide additional clues to the underlying biology and treatment targets in MDs.

5-HTTLPR and anxiety modulate brain-heart covariation

To date, little is known about genes affecting the interplay of brain and heart activity. Because serotonin (5-HT) is involved in corticovagal neurotransmission, we tested whether the 5-HT transporter polymorphism 5-HTTLPR affects brain-heart covariation. Further, associations with neuroticism/anxiety (NANX) were tested, as anxiety is related to 5-HT and neurogenic changes of heart period (HP). N = 168 participants performed a time-estimation task while EEG and HP were recorded. Brain-heart covariation was measured using time-lagged within-subject correlations of centromedial feedback-evoked single-trial EEG at 300 ms and subsequent changes of HP. EEG-HP correlations were higher in 5-HTTLPR long allele carriers. Moreover, after negative feedback, EEG-HP correlations and feedback-related negativity amplitudes independently correlated with NANX. The results indicate that individual differences in brain-heart covariation relate to 5-HT and NANX.

Identifying serotonergic mechanisms underlying the corticolimbic response to threat in humans

A corticolimbic circuit including the amygdala and medial prefrontal cortex (mPFC) plays an important role in regulating sensitivity to threat, which is heightened in mood and anxiety disorders. Serotonin is a potent neuromodulator of this circuit; however, specific serotonergic mechanisms mediating these effects are not fully understood. Recent studies have evaluated molecular mechanisms mediating the effects of serotonin signalling on corticolimbic circuit function using a multi-modal neuroimaging strategy incorporating positron emission tomography and blood oxygen level-dependent functional magnetic resonance imaging. This multi-modal neuroimaging strategy can be integrated with additional techniques including imaging genetics and pharmacological challenge paradigms to more clearly understand how serotonin signalling modulates neural pathways underlying sensitivity to threat. Integrating these methodological approaches offers novel opportunities to identify mechanisms through which serotonin signalling contributes to differences in brain function and behaviour, which in turn can illuminate factors that confer risk for illness and inform the development of more effective treatment strategies.

The role of the serotonergic system at the interface of aggression and suicide

Alterations in serotonin (5-HT) neurochemistry have been implicated in the aetiology of all major neuropsychiatric disorders, ranging from schizophrenia to mood and anxiety-spectrum disorders. This review will focus on the multifaceted implications of 5-HT-ergic dysfunctions in the pathophysiology of aggressive and suicidal behaviours. After a brief overview of the anatomical distribution of the 5-HT-ergic system in the key brain areas that govern aggression and suicidal behaviours, the implication of 5-HT markers (5-HT receptors, transporter as well as synthetic and metabolic enzymes) in these conditions is discussed. In this regard, particular emphasis is placed on the integration of pharmacological and genetic evidence from animal studies with the findings of human experimental and genetic association studies. Traditional views postulated an inverse relationship between 5-HT and aggression and suicidal behaviours; however, ample evidence has shown that this perspective may be overly simplistic, and that such pathological manifestations may reflect alterations in 5-HT homoeostasis due to the interaction of genetic, environmental and gender-related factors, particularly during early critical developmental stages. The development of animal models that may capture the complexity of such interactions promises to afford a powerful tool to elucidate the pathophysiology of impulsive aggression and suicidability, and identify new effective therapies for these conditions.

The role of the serotonergic system in suicidal behavior

Serotonin is a widely investigated neurotransmitter in several psychopathologies, including suicidal behavior (SB); however, its role extends to several physiological functions involving the nervous system, as well as the gastrointestinal and cardiovascular systems. This review summarizes recent research into ten serotonergic genes related to SB. These genes - TPH1, TPH2, SLC6A4, SLC18A2, HTR1A, HTR1B, HTR2A, DDC, MAOA, and MAOB - encode proteins that are vital to serotonergic function: tryptophan hydroxylase; the serotonin transporter 5-HTT; the vesicular transporter VMAT2; the HTR1A, HTR1B, and HTR2A receptors; the L-amino acid decarboxylase; and the monoamine oxidases. This review employed a systematic search strategy and a narrative research methodology to disseminate the current literature investigating the link between SB and serotonin.

Transcriptional regulation of the 5-HT1A receptor: implications for mental illness

The serotonin-1A (5-HT(1A)) receptor is an abundant post-synaptic 5-HT receptor (heteroreceptor) implicated in regulation of mood, emotion and stress responses and is the major somatodendritic autoreceptor that negatively regulates 5-HT neuronal activity. Based on animal models, an integrated model for opposing roles of pre- and post-synaptic 5-HT(1A) receptors in anxiety and depression phenotypes and response to antidepressants is proposed. Understanding differential transcriptional regulation of pre- versus post-synaptic 5-HT(1A) receptors could provide better tools for their selective regulation. This review examines the transcription factors that regulate brain region-specific basal and stress-induced expression of the 5-HT(1A) receptor gene (Htr1a). A functional polymorphism, rs6295 in the Htr1a promoter region, blocks the function of specific repressors Hes1, Hes5 and Deaf1, resulting in increased 5-HT(1A) autoreceptor expression in animal models and humans. Its association with altered 5-HT(1A) expression, depression, anxiety and antidepressant response are related to genotype frequency in different populations, sample homogeneity, disease outcome measures and severity. Preliminary evidence from gene × environment studies suggests the potential for synergistic interaction of stress-mediated repression of 5-HT(1A) heteroreceptors, and rs6295-induced upregulation of 5-HT(1A) autoreceptors. Targeted therapeutics to inhibit 5-HT(1A) autoreceptor expression and induce 5-HT(1A) heteroreceptor expression may ameliorate treatment of anxiety and major depression.

Contemporary Genetics for Gender Researchers

Over the past century, much of genetics was deterministic, and feminist researchers framed justified criticisms of genetics research. However, over the past two decades, genetics research has evolved remarkably and has moved far from earlier deterministic approaches. Our article provides a brief primer on modern genetics, emphasizing contemporary evidence for the complex interplay between genes and environment. We focus particularly on the role of gene–environment interactions for gender-imbalanced disorders such as depression. We review research on epigenetics, which is one mechanism by which environment influences gene expression. Modern genetics is not based on a model of genetic determinism; instead, it recognizes the complexity of genetic influences and the nuanced interplay between genes and environment across life span development. Even with the modern genetics approaches, of course, there is still room for criticism and input from gender researchers. We outline methodological and conceptual issues more generally and from a gender researcher’s perspective. We argue that, with interdisciplinary collaborations, modern genetics can be integrated into gender research and vice versa in ways that will create progress in both fields.

Serotonin-1A receptor polymorphism (rs6295) associated with thermal pain perception

Background

Serotonin (5-HT) is highly involved in pain regulation and serotonin-1A (5-HT1A) receptors are important in determining central 5-HT tone. Accordingly, variation in the 5-HT1A receptor gene (HTR1A) may contribute to inter-individual differences in human pain sensitivity. The minor G-allele of the HTR1A single nucleotide polymorphism (SNP) rs6295 attenuates firing of serotonergic neurons and reduces postsynaptic expression of the receptor. Experiments in rodents suggest that 5-HT1A-agonism modulates pain in opposite directions at mild compared to high noxious intensities. Based upon this and several other similar observations, we hypothesized that G-carriers would exhibit a relative hypoalgesia at mild thermal stimuli but tend towards hyperalgesia at higher noxious intensities.

Methods

Fourty-nine healthy individuals were selectively genotyped for rs6295. Heat- and cold-pain thresholds were assessed along with VAS-ratings of a range of suprathreshold noxious heat intensities (45°C–49°C). Nociceptive-flexion reflex (NFR) thresholds were also assessed.

Results

Volunteers did not deviate significantly from Hardy-Weinberg equilibrium. G-carriers were less sensitive to threshold-level thermal pain. This relative hypoalgesia was abolished at suprathreshold noxious intensities where G-carriers instead increased their ratings of heat-pain significantly more than C-homozygotes. No differences with regard to NFR-thresholds emerged.

Conclusion/Significance

To the best of our knowledge this is the first study of human pain perception on the basis of variation in HTR1A. The results illustrate the importance of including a range of stimulus intensities in assessments of pain sensitivity. In speculation, we propose that an attenuated serotonergic tone may be related to a ‘hypo- to hyperalgesic’ response-pattern. The involved mechanisms could be of clinical interest as variation in pain regulation is known to influence the risk of developing pain pathologies. Further investigations are therefore warranted.

Raphe-Hippocampal Serotonin Neurotransmission In The Sex Related Differences of Adaptation to Stress: Focus on Serotonin-1A Receptor

Stress is the major predisposing and precipitating factor in the onset of depression which is the most significant mental health risk for women. Behavioral studies in animal models show that female sex though less affected by an acute stressor; exposure to repeated stressors induces coping deficits to impair adaptation in them. A decrease in the function of 5-hydroxytryptamine (5-HT; serotonin) in the hippocampus and an increased function of the 5-HT-1A receptor in the raphe nucleus coexist in depression. Pharmacological and neurochemical data are relevant that facilitation of serotonin neurotransmission via hippocampus due to desensitization of somatodendritic 5-HT1A receptors may lead to adaptation to stress. The present article reviews research on sex related differences of raphe-hippocampal serotonin neurotransmission to find a possible answer that may account for the sex differences of adaptation to stress reported in preclinical research and greater incidence of depression in women than men.

Interaction of serotonin transporter linked polymorphic region and childhood neglect on criminal behavior and substance use for males and females

Childhood neglect has been cited as a risk factor for later substance abuse and criminal behavior. However, a large body of literature shows that a substantial percentage of neglected and abused individuals do not go on to abuse substances or engage in criminal behavior. The current study investigates whether a genetic variant (serotonin transporter linked polymorphic region [5-HTTLPR]) in the 5-hydroxytryptamine (5-HTT) gene moderates the effect of childhood neglect on alcohol use problems, marijuana use, and criminal behavior. Data from the National Longitudinal Study of Adolescent Health shows that 5-HTTLPR conditions the effect of neglect on marijuana use for females, but not for males. Findings also reveal a significant gene-environment correlation between 5-HTTLPR and neglect for females only. These results suggest that 5-HTTLPR is associated with an increased risk of neglect for females, and it also increases neglected females' risk of abusing marijuana.

Short sleep as an environmental exposure: a preliminary study associating 5-HTTLPR genotype to self-reported sleep duration and depressed mood in first-year university students

OBJECTIVES

This study examined whether the 5-HTTLPR polymorphism in the SLC6A4 gene is associated with self-reported symptoms of depressed mood in first-year university students with a persistent pattern of short sleep.

DESIGN

Students provided DNA samples and completed on-line sleep diaries and a mood scale during the first semester. A priori phenotypes for nocturnal sleep and mood scores were compared for the distribution of genotypes.

SETTING

Brown University, Providence, Rhode Island.

PARTICIPANTS

A sample of 135 first-year students, 54 male, 71 Caucasian, mean age 18.1 (± 0.5) yr.

INTERVENTIONS

None.

MEASUREMENTS

Students completed on-line sleep diaries daily across the first term (21-64 days; mean = 51 days ± 11) and Center for Epidemiologic Studies-Depression (CES-D) mood scale after 8 wk. DNA was genotyped for the triallelic 5-HTTLPR polymorphism. Low-expressing S and L(G)polymorphisms were designated S', and high-expressing L(A) was designated L'. Phenotype groups were identified from a combination of CES-D (median split: high > 12; low < 13) and mean nocturnal total sleep time (TST) from diaries: (shorter ≤ 7 hr; longer ≥ 7.5 hr). Three genotypes were identified (S'S', S'L', L'L'); the S'S' genotype was present in a higher proportion of Asian than non-Asian students.

RESULTS

FOUR PHENOTYPE GROUPS WERE COMPARED: 40 students with shorter TST/high CES-D; 34 with shorter TST/low CES-D; 29 with longer TST/high CES-D; 32 with longer TST/low CES-D. Female:male distribution did not vary across phenotype groups (chi-square = 1.39; df = 3; P = 0.71). S'S' participants (n = 23) were overrepresented in the shorter TST/high CES-D group (chi- square = 15.04; df = 6; P < 0.02). This association was sustained after removing participants with preexisting evidence of depressed mood (chi-square = 12.90; df = 6; P = 0.045).

CONCLUSION

These data indicate that young adults who reported shorter nocturnal sleep and higher depressed mood are more likely than others to carry a variant of the SLC6A4 gene associated with low expression of the serotonin transporter.

Depression and epilepsy: epidemiologic and neurobiologic perspectives that may explain their high comorbid occurrence

Depression is the most frequent psychiatric comorbidity in people with epilepsy (PWE) with lifetime prevalence rates ranging between 30 and 35%. Multifactorial variables play a pathogenic role in the high comorbid occurrence of these two disorders. These variables were critically examined during an international symposium held in Chicago in September 2010, the results of which are presented in two companion manuscripts. The first manuscript summarizes new epidemiologic data highlighting the bidirectional relation between depression and epilepsy and related methodological issues in studying this relationship. An examination of the neurobiologic aspects of primary mood disorders, mood disorders in PWE and pathogenic mechanisms of epilepsy derived from studies in animal models and humans is allowing a better understanding of the complex relation between the two conditions. In the first manuscript, we review data from animal models of epilepsy in which equivalent symptoms of depression and anxiety disorders develop and, conversely, animal models of depression in which the kindling process is facilitated. Data from structural and functional neuroimaging studies in humans provide a further understanding of potential common pathogenic mechanisms operant in depression and epilepsy that may explain their high comorbidity. The negative impact of depression on the control of seizure disorders has been documented in various studies. In this manuscript, these data are reviewed and potential mechanisms explaining this phenomenon are proposed.

Linking variability in brain chemistry and circuit function through multimodal human neuroimaging

Identifying neurobiological mechanisms mediating the emergence of individual differences in behavior is critical for advancing our understanding of relative risk for psychopathology. Neuroreceptor positron emission tomography (PET) and functional magnetic resonance imaging (fMRI) can be used to assay in vivo regional brain chemistry and function, respectively. Typically, these neuroimaging modalities are implemented independently despite the capacity for integrated data sets to offer unique insight into molecular mechanisms associated with brain function. Through examples from the serotonin and dopamine system and its effects on threat- and reward-related brain function, we review evidence for how such a multimodal neuroimaging strategy can be successfully implemented. Furthermore, we discuss how multimodal PET-fMRI can be integrated with techniques such as imaging genetics, pharmacological challenge paradigms and gene-environment interaction models to more completely map biological pathways mediating individual differences in behavior and related risk for psychopathology and inform the development of novel therapeutic targets.

Altered response to the selective serotonin reuptake inhibitor escitalopram in mice heterozygous for the serotonin transporter: an electrophysiological and neurochemical study

A serotonin (5-HT) transporter (5-HTT; SERT) polymorphism has been associated with depressive states and poor responses to selective serotonin reuptake inhibitors (SSRIs). Given the similar attenuation of SERT activity in SERT+/- mice and in humans with short allele(s) of SERT in its promoter region, it is conceivable that SERT+/- mice offer an adequate model to mimic the human subpopulation with respect to their altered response to SSRIs. This study investigated the effects of the most selective SSRI escitalopram, in heterozygous SERT+/- mice using a combined electrophysiological and neurochemical approach. Results indicated that administration of escitalopram for 2 d resulted in a 72% and 63% decrease in dorsal raphe 5-HT neuronal firing rate in SERT+/+ and SERT+/- mice, respectively. In contrast, administration of escitalopram for 21 d produced a gradual recovery of 5-HT neuronal firing rate to basal level in SERT+/+, but not in SERT+/- mice. In the hippocampus, microdialysis revealed that sustained administration of escitalopram produced a greater increase in extracellular 5-HT ([5-HT]ext) outflow in SERT+/- than in the wild-types with or without a washout of the SSRI. Nevertheless, the ability of microiontophoretically applied 5-HT to inhibit the firing rate of CA3 pyramidal neurons was not different between SERT+/+ and SERT+/- mice given escitalopram for 21 d. The data indicate that the poor response to SSRIs of depressive patients with short allele(s) of SERT is not attributable to a lesser increase in 5-HT transmission in the hippocampus.

Increased serotonin-1A (5-HT1A) autoreceptor expression and reduced raphe serotonin levels in deformed epidermal autoregulatory factor-1 (Deaf-1) gene knock-out mice

Altered regulation of the serotonin-1A (5-HT1A) receptor gene is implicated in major depression and mood disorders. The functional human 5-HT1A C(-1019)G promoter polymorphism (rs6295), which prevents the binding of Deaf-1/NUDR leading to dysregulation of the receptor, has been associated with major depression. In cell models Deaf-1 displays dual activity, repressing 5-HT1A autoreceptor expression in serotonergic raphe cells while enhancing postsynaptic 5-HT1A heteroreceptor expression in nonserotonergic neurons. A functional Deaf-1 binding site on the mouse 5-HT1A promoter was recognized by Deaf-1 in vitro and in vivo and mediated dual activity of Deaf-1 on 5-HT1A gene transcription. To address regulation by Deaf-1 in vivo, Deaf-1 knock-out mice bred to a C57BL/6 background were compared with wild-type siblings for changes in 5-HT1A RNA and protein by quantitative RT-PCR, in situ hybridization, and immunofluorescence. In the dorsal raphe, Deaf-1 knock-out mice displayed increased 5-HT1A mRNA, protein, and 5-HT1A-positive cell counts but reduced 5-HT levels, whereas other serotonergic markers, such as tryptophan hydroxylase (TPH)- or 5-HT-positive cells and TPH2 RNA levels, were unchanged. By contrast, 5-HT1A mRNA and 5-HT1A-positive cells were reduced in the frontal cortex of Deaf-1-null mice, with no significant change in hippocampal 5-HT1A RNA, protein, or cell counts. The region-specific alterations of brain 5-HT1A gene expression and reduced raphe 5-HT content in Deaf-1(-/-) mice indicate the importance of Deaf-1 in regulation of 5-HT1A gene expression and provide insight into the role of the 5-HT1A G(-1019) allele in reducing serotonergic neurotransmission by derepression of 5-HT1A autoreceptors.

Polymorphisms in the 5-HTTLPR gene mediate storage capacity of visual working memory

Working memory (WM) is a limited capacity system that permeates nearly all levels of cognition, ranging from perceptual awareness to intelligence. Through behavioral, electrophysiological, and neuroimaging work, substantial gains have been made in understanding this capacity-limited system. In the current work, we examined genetic contributions to the storage capacity of WM. Multiple studies have demonstrated a link between the serotonin transporter-linked polymorphic region (5-HTTLPR) and cognition, where better performance is observed in individuals possessing a copy of the short (s) variant of the polymorphism compared with individuals homozygous for the long (l) variant. We predicted the same profile in WM performance, such that estimated capacities of l/l carriers should be smaller than s/s and s/l carriers. To measure WM capacity, we implemented a change detection task, which requires observers to actively maintain the color and spatial location of briefly presented squares over a short retention interval. In line with our prediction, we observed similar WM performance between s/s and s/l groups, and these individuals performed better than the l/l group. We then discuss the distribution of the serotonin transporter system and parallels between WM and attention to provide insight into how variation in the 5-HTT polymorphism could lead to individual differences in the storage capacity of WM.

17β-estradiol-induced regulation of the novel 5-HT1A-related transcription factors NUDR and Freud-1 in SH SY5Y cells

Nuclear deformed epidermal autoregulatory factor-1 (NUDR/Deaf-1) and five prime repressor element under dual repression (Freud-1) are novel transcriptional regulators of the 5-HT(1A) receptor, a receptor that has been implicated in the pathophysiology of various psychiatric illnesses. The antidepressant effect of 17β-Estradiol (17βE(2)) is purported to involve the downregulation of this receptor. We investigated the possible role of NUDR and Freud-1 in 17βE(2)-induced downregulation of the 5-HT(1A) receptor in the neuroblastoma cell line SH SY5Y. Cells were treated with 10 nM of 17βE(2) for 3 or 48 h, followed by a 24-h withdrawal period. Proteins were isolated and analyzed by western blotting. 17βE(2) treatment increased NUDR immunoreactivity while Freud-1 and the 5-HT(1A) receptor showed significant decreases. Upon withdrawal of 17βE(2), protein expression returned to control levels, except for NUDR, which remained significantly elevated in the 3-h treatment. Taken together, these data support a non-genomic downregulation of 5-HT(1A) receptor protein by 17βE(2), which does not involve NUDR and Freud-1. Rather, changes in both transcription factors seem to be compensatory/homeostatic responses to changes in 5-HT(1A) receptor induced by 17βE(2). These observations further highlight the importance of NUDR and Freud-1 in regulating 5-HT(1A) receptor expression.

Toward a mechanistic understanding of how variability in neurobiology shapes individual differences in behavior

Research has begun to identify how variability in brain function contributes to individual differences in complex behavioral traits. Examining variability in molecular signaling pathways with emerging and established methodologies such as pharmacologic fMRI, multimodal PET/fMRI, and hormonal assays are beginning to provide a mechanistic understanding of how individual differences in brain function arise. Against this background, functional genetic polymorphisms are being utilized to understand the origins of variability in signaling pathways as well as to efficiently model how such emergent variability impacts behaviorally relevant brain function and health outcomes. This chapter provides an overview of a research strategy that integrates these complimentary levels of analysis; existing empirical data is used to illustrate the effectiveness of this approach in illuminating the mechanistic neurobiology of individual differences in complex behavioral traits. This chapter also discusses how such efforts can contribute to the identification of predictive risk markers that interact with unique environmental factors to precipitate psychopathology.

Age, sex, and reproductive hormone effects on brain serotonin-1A and serotonin-2A receptor binding in a healthy population

There is a need for rigorous positron emission tomography (PET) and endocrine methods to address inconsistencies in the literature regarding age, sex, and reproductive hormone effects on central serotonin (5HT) 1A and 2A receptor binding potential (BP). Healthy subjects (n=71), aged 20-80 years, underwent 5HT1A and 2A receptor imaging using consecutive 90-min PET acquisitions with [(11)C]WAY100635 and [(18)F]altanserin. Logan graphical analysis was used to derive BP using atrophy-corrected distribution volume (V(T)) in prefrontal, mesiotemporal, occipital cortices, and raphe nucleus (5HT1A only). We used multivariate linear regression modeling to examine BP relationships with age, age(2), sex, and hormone concentrations, with post hoc regional significance set at p<0.008. There were small postsynaptic 5HT1A receptor BP increases with age and estradiol concentration in women (p=0.004-0.005) and a tendency for small 5HT1A receptor BP declines with age and free androgen index in men (p=0.05-0.06). Raphe 5HT1A receptor BP decreased 4.5% per decade of age (p=0.05), primarily in men. There was a trend for 15% receptor reductions in prefrontal cortical regions in women relative to men (post hoc p=0.03-0.10). The significant decline in 5HT2A receptor BP relative to age (8% per decade; p<0.001) was not related to sex or hormone concentrations. In conclusion, endocrine standardization minimized confounding introduced by endogenous hormonal fluctuations and reproductive stage and permitted us to detect small effects of sex, age, and endogenous sex steroid exposures upon 5HT1A binding. Reduced prefrontal cortical 5HT1A receptor BP in women vs men, but increased 5HT1A receptor BP with aging in women, may partially explain the increased susceptibility to affective disorders in women during their reproductive years that is mitigated in later life. 5HT1A receptor decreases with age in men might contribute to the known increased risk for suicide in men over age 75 years. Low hormone concentrations in adults <50 years of age may be associated with more extreme 5HT1A receptor BP values, but remains to be studied further. The 5HT2A receptor declines with age were not related to sex or hormone concentrations in this sample. Additional study in clinical populations is needed to further examine the affective role of sex-hormone-serotonin receptor relationships.

The genetic blueprint of major depressive disorder: contributions of imaging genetics studies

OBJECTIVES

To review neuroimaging intermediate phenotypes of MDD and their relation to genetic risk variants.

METHODS

A systematic literature search of peer-reviewed English language articels using PubMed ( www.pubmed.org ) was performed.

RESULTS

Comprehensive evidence on the influence of serotonergic genes (SLC6A4, HTR1A, MAOA, TPH2) and BDNF on the following neural intermediate phenotypes is displayed: amygdala reactivity, coupling of amygdala-anterior cingulate cortex (ACC) activity, ACC volume, hippocampal volume and serotonin receptor 1A (5-HT1A) binding potential (BP).

CONCLUSIONS

Intermediate phenotypes may bridge the gap between genotype and phenotype by reducing the impreciseness of psychiatric phenotypes and yield more insights into the underlying biology.

Presynaptic 5-HT1A is related to 5-HTT receptor density in the human brain

5-Hydroxytryptamine (5-HT or serotonin) is an important neurotransmitter for a number of brain functions and widely distributed throughout the brain. Physiological and pharmacological relationship between 5-HT1A receptors and serotonin transporter (5-HTT) in the regulation of 5-HT neurotransmission has now been documented. A relationship between 5-HT1A receptors and 5-HTT is also suggested by the pathophysiology of depression and the mechanism of action of antidepressants. We have scanned 42 healthy adults with both [11C] WAY-100635 and [11C] DASB to investigate the anatomical co-distribution of multiple serotonergic markers. We hypothesized that lower 5-HTT densities in the dorsal raphe nucleus (DRN) and limbic regions will be accompanied by lower 5-HT1A receptor density in the same regions, contributing to the 5-HT1A receptor desensitization. In addition, variations in DRN 5-HT1A receptor density can theoretically influence the density and/or function of other serotonin receptor subtypes and the 5-HTT consequent to changes in serotonergic tone. In a comparatively large sample of volunteers, we have shown that the relationship between 5-HT1A and 5-HTT PET indices was complex. We were unable to demonstrate robust, intra-regional relationships between 5-HT1A and 5-HTT densities. Inter-regionally, DRN 5-HT1A receptors were related to cortical (temporal and frontal regions) and paralimbic (insula), but not limbic 5-HTT. This latter finding may reflect differences in 5-HT tone between individuals, and highlights probable substrates sensitive to variations in DRN 5-HT function.

Implication of serotonin-transporter (5-HTT) gene polymorphism in subjective memory complaints and mild cognitive impairment (MCI)

Serotonin-transporter-linked polymorphism (5-HTTLPR) is involved in neuropsychiatric diseases and recently the S-isoform has been correlated with a higher risk of developing emotion-induced retrograde amnesia. In order to better clarify the possible role of the 5-HTT S/L polymorphism and its effects on cognitive ability, especially on memory skills, we report here the distributions of the 5-HTT genetic variant and the Apolipoprotein E (ApoE) ɛ-4 allele and their association with neuropsychological measures in older adults reporting problems with everyday memory. Moreover, we verified the presence of a possible association between the S-allele with depression and the personal trait of neuroticism. Our results indicate an association between the 5-HTTLPR S-allele and the risk of developing MCI. No association was found in the other three groups. We found a positive dose-dependent association between the S-allele and the Rey-Osterrieth complex figure test (recall) score. Finally, our data did not find an association between the same allele and depression or neuroticism. This data, in our opinion shows a slight, non-established influence of 5-HTTLPR on memory skills exhibited in challenging memory tests but no influence on other extra-mnesic cognitive abilities.

Association of the C(-1019)G 5-HT1A promoter polymorphism with exposure to stressors preceding hospitalization for bipolar depression

RATIONALE

In animals, a higher density of 5-HT1A receptors has been associated with increased behavioral despair after stress. In humans, the G variant of the C(-1019)G 5-HT1A receptor promoter gene polymorphism (rs6295) has been associated with higher expression of 5-HT1A receptors, increased depression, and lower stress preceding completed suicide.

OBJECTIVES

We studied the association of rs6295 with the amount of stress in early life and preceding hospitalization for a major depressive episode in course of bipolar disorder.

MATERIALS AND METHODS

In 74 consecutively admitted inpatients, early life and recent stressors were rated on the Social Readjustment Rating Scale and on the Risky Family Questionnaire.

RESULTS

Homozygote carriers of the rs6295 G variant reported less stressful events before current hospitalization for bipolar depression, but not in early life. The G variant was also associated with a higher overall medication load in naturalistic settings before hospitalization.

CONCLUSIONS

This is the first study that associated 5-HT1A receptor promoter gene variants with stressors preceding the need of hospitalization for bipolar depression. Our findings support the hypothesis that genetic factors affecting serotonergic neurotransmission might contribute to shape the individual resilience to the depressogenic effects of stress in clinical settings.

The importance of serotonin for orbitofrontal function

The orbitofrontal cortex (OFC) receives a dense serotonin (5-hydroxytryptamine, or 5-HT) innervation from the dorsal raphe nucleus, with a smaller contribution from the median raphe nucleus. The reciprocal innervation from the OFC enables the OFC to regulate not only its own 5-HT input but the 5-HT input to the rest of the forebrain. This article reviews the evidence from studies in rodents and primates that implicate 5-HT in the OFC in the ability of animals to adapt their responding to changes in reward contingencies in the environment. A consensus is emerging that reductions in orbitofrontal 5-HT, whether the result of localized infusions of 5,7-dihydroxytryptamine (5,7-DHT), peripheral treatment with parachloroamphetamine (PCA) or para-chlorophenylalanine (PCPA), or chronic cold stress impairs this ability. Genetic variation in the 5-HT transporter can also affect this ability. An explanation regarding insensitivity to reward loss is ruled out by the finding that marmosets with 5-HT reductions in the OFC display a decline of responding as rapid as that of control animals when reward is withheld during extinction of a two-pattern discrimination task. The failure of these same animals to explore alternative stimuli during extinction, along with the recent electrophysiological evidence that dorsal raphe nucleus neurons encode future motivational outcomes, implicates orbitofrontal 5-HT in the process by which animals either exploit current resources or explore alternative resources based on current reward expectations.