Inverse relationship between serotonin 5-HT(1A) receptor binding and anxiety: a [(11)C]WAY-100635 PET investigation in healthy volunteers

Imaging the effects of genetic polymorphisms on radioligand binding in the living human brain: A review on genetic neuroreceptor imaging of monoaminergic systems in psychiatry

Imaging genetics is a research field that describes the impact of genetic risk variants on brain structure and function. While magnetic resonance based imaging techniques are able to provide complex information on a system level, positron emission tomography (PET) and single photon emission computer tomography (SPECT) allow for determination of distribution and density of single receptor molecules in the human brain. Major psychiatric disorders are highly heritable, and have been associated with a dysregulation in brain dopamine and serotonin systems. Understanding the role of genetic polymorphisms within these neurotransmitter systems on brain phenotype is essential. This review tries to cover the literature on the impact of gene variants implicated in psychiatric disorders on serotonin, dopamine, and MAO-A radioligand binding in living humans. The majority of PET and SPECT studies investigated the role of polymorphisms within genes coding for the serotonin and dopamine transporters, the serotonin 1A receptor, and the dopamine D2 receptor on G protein coupled receptors or transporter proteins critically involved in serotonin or dopamine neurotransmission. Other studies investigated the impact of variants in genes for monoamine oxidase-A (MAO-A) or brain derived neurotrophic factor on monoamine transporters, receptors, or MAO-A activity. Two main findings in healthy subjects emerge from the current literature: one is an increased binding of the selective ligand [(11)C]DASB to serotonin transporters in subjects homozygous for the triallelic 5-HTTLPR LA allele. The other one is decreased binding of the radioligand [(11)C]raclopride to dopamine D2 receptors in D2 Taq1 A1 allele carriers. Other findings reported are highly interesting but require independent replication.

Personality goes a long a way: an interhemispheric connectivity study

Throughout the development of psychology the delineation of personality has played a central role. Together with the NEO-PI-R, a questionnaire derived from the Five Factor Model of Personality, and recent advances in research technology it is now possible to investigate the relationship between personality features and neurophysiological brain processes. The NEO-FFI, the short version of the NEO-PI-R, reliably measures five main personality traits: Neuroticism, Extraversion, Openness to experience, Agreeableness, and Conscientiousness. As behavior and some psychiatric disorders have been related to interhemispheric connectivity, the present study used the combination of transcranial magnetic stimulation (TMS) and electroencephalography (EEG) to measure frontal interhemispheric connectivity and its association with personality as indexed by the NEO-FFI. Results demonstrated that prefrontal interhemispheric connectivity between the left and right dorsolateral prefrontal cortex correlates with Agreeableness in healthy subjects. This is the first study to relate personality features to interhemispheric connectivity through TMS-EEG and suggests that Agreeableness relates to the effectiveness of prefrontal communication between hemispheres.

The pharmacology of anxiety

Understanding the neurochemistry of anxiety is of fundamental importance in the development and use of novel anxiolytics. Through measuring peripheral markers of brain biochemistry, direct pharmacological challenges and brain neuroimaging techniques our understanding of this field has increased substantially in the past few decades. We review the four most studied neurotransmitter systems with respect to in anxiety disorders: gamma amino-butyric acid, serotonin, noradrenaline and dopamine. We have focussed upon clinical studies to highlight the current techniques used to determine brain neurochemistry in vivo. Future research in this field will greatly benefit from recent advances in neuroimaging techniques and the discovery of novel ligands targeting specific receptors.

Personality change during depression treatment: a placebo-controlled trial

CONTEXT

High neuroticism is a personality risk factor that reflects much of the genetic vulnerability to major depressive disorder (MDD), and low extraversion may increase risk as well. Both have been linked to the serotonin system.

OBJECTIVES

To test whether patients with MDD taking selective serotonin reuptake inhibitors (SSRIs) report greater changes in neuroticism and extraversion than patients receiving inert placebo, and to examine the state effect hypothesis that self-reported personality change during SSRI treatment is merely a change of depression-related measurement bias.

DESIGN

A placebo-controlled trial.

SETTING

Research clinics. Patients Adult patients with moderate to severe MDD randomized to receive paroxetine (n = 120), placebo (n = 60), or cognitive therapy (n = 60).

OUTCOME MEASURES

NEO Five-Factor Inventory and Hamilton Rating Scale for Depression.

RESULTS

Patients who took paroxetine reported greater personality change than placebo patients, even after controlling for depression improvement (neuroticism, P < .001; extraversion, P = .002). The advantage of paroxetine over placebo in antidepressant efficacy was no longer significant after controlling for change in neuroticism (P = .46) or extraversion (P = .14). Patients taking paroxetine reported 6.8 times as much change on neuroticism and 3.5 times as much change on extraversion as placebo patients matched for depression improvement. Although placebo patients exhibited substantial depression improvement (Hamilton Rating Scale for Depression score, -1.2 SD, P < .001), they reported little change on neuroticism (-0.18 SD, P = .08) or extraversion (0.08 SD, P = .50). Cognitive therapy produced greater personality change than placebo (P </= .01); but its advantage on neuroticism was no longer significant after controlling for depression (P = .14). Neuroticism reduction during treatment predicted lower relapse rates among paroxetine responders (P = .003) but not among cognitive therapy responders (P = .86).

CONCLUSIONS

Paroxetine appears to have a specific pharmacological effect on personality that is distinct from its effect on depression. If replicated, this pattern would disconfirm the state effect hypothesis and instead support the notion that SSRIs' effects on personality go beyond and perhaps contribute to their antidepressant effects.

Influence of escitalopram treatment on 5-HT 1A receptor binding in limbic regions in patients with anxiety disorders

There is an increasing interest in the underlying mechanisms of the antidepressant and anxiolytic treatment effect associated with changes in serotonergic neurotransmission after treatment with selective serotonin (5-HT) reuptake inhibitors (SSRIs) in humans. The 5-HT(1A) receptor is known to play a crucial role in the pathophysiology of affective disorders, and altered 5-HT(1A) receptor binding has been found in anxiety patients. SSRI treatment raises the 5-HT level in the synaptic cleft and might change postsynaptic receptor densities. Therefore, our study in patients suffering from anxiety disorders investigated the effects of long-term treatment with escitalopram on the 5-HT(1A) receptor. A longitudinal positrone emission tomography (PET) study in 12 patients suffering from anxiety disorders was conducted. Two dynamic PET scans were performed applying the selective 5-HT(1A) receptor antagonist [carbonyl-(11)C]WAY-100635. Eight regions of interest were defined a priori (orbitofrontal cortex, amygdala, hippocampus, subgenual cortex, anterior and posterior cingulate cortex, dorsal raphe nucleus and cerebellum as reference). After the baseline PET scan, patients were administered escitalopram (average dose of 11.2+/-6.0 mg day(-1)) for a minimum of 12 weeks. A second PET scan was conducted after 109+/-27 days. 5-HT(1A) receptor binding potentials in 12 patients were assessed by PET applying the Simplified Reference Tissue Model.There was a significant reduction in the 5-HT(1A) receptor binding potential after a minimum of 12 weeks of escitalopram treatment in the hippocampus (P=0.006), subgenual cortex (P=0.017) and posterior cingulate cortex (P=0.034). The significance of the hippocampus region survived the Bonferroni-adjusted threshold for multiple comparisons. These PET data in humans in vivo demonstrate a reduction of the 5-HT(1A) binding potential after SSRI treatment.

The serotonin-1A receptor in anxiety disorders

The serotonin system plays an important role in the neural processing of anxiety. The involvement of the main inhibitory serotonergic receptor, the serotonin-1A (5-HT1A) subtype, in dysfunctional forms of anxiety has been supported by findings from a wide range of preclinical research and clinical trials, including treatment studies, genetic research, and neuroimaging data. The following article summarizes preclinical results with a focus on 5-HT1A receptor knockout and transgenic mice as genetic models of anxiety. Behavioral, autonomic, and endocrinological changes in these mice are reported. This article also presents genetic polymorphisms in humans associated with increased anxiety scores and pharmacological data focused on 5-HT1A receptor agonists and antagonists. Furthermore, molecular neuroimaging results are presented. Recent positron emission tomography (PET) studies have reported reduced 5-HT1A receptor binding in patients with panic disorder and social anxiety disorder, but not in posttraumatic stress disorder. In healthy subjects, increased anxiety scores might be associated with lower 5-HT1A receptor binding. This overview of preclinical and clinical data provides strong evidence for the key role of the 5-HT1A receptor in the serotonergic dysregulation of anxiety disorders.

Layer II/III of the prefrontal cortex: Inhibition by the serotonin 5-HT1A receptor in development and stress

The modulation of the prefrontal cortex by the neurotransmitter serotonin (5-HT) is thought to play a key role in determining adult anxiety levels. Layer II/III of the prefrontal cortex, which mediates communication across cortical regions, displays a high level of 5-HT(1A) receptor binding in normal individuals and a significantly lower level in patients with mood and anxiety disorders. Here, we examine how serotonin modulates pyramidal neurons in layer II/III of the rat prefrontal cortex throughout postnatal development and in adulthood. Using whole cell recordings in brain slices of the rat medial prefrontal cortex, we observed that serotonin directly inhibits layer II/III pyramidal neurons through 5-HT(1A) receptors across postnatal development (postnatal days 6-96). In adulthood, a sex difference in these currents emerges, consistent with human imaging studies of 5-HT(1A) receptor binding. We examined the effects of early life stress on the 5-HT(1A) receptor currents in layer II/III. Surprisingly, animals subjected to early life stress displayed significantly larger 5-HT(1A)-mediated outward currents throughout the third and fourth postnatal weeks after elevated 5-HT(1A) expression during the second postnatal week. Subsequent exposure to social isolation in adulthood resulted in the almost-complete elimination of 5-HT(1A) currents in layer II/III neurons suggesting an interaction between early life events and adult experiences. These data represent the first examination of functional 5-HT(1A) receptors in layer II/III of the prefrontal cortex during normal development as well as after stress.

5-HT1A receptor activation is necessary for 5-MeODMT-dependent potentiation of feeding inhibition

We propose a translational approach to the study of anorexia nervosa (AN) based on our human subject studies where there are characteristic elevations in 5-HT(1A) receptor binding, associated harm avoidance behaviors, reduced impulsivity, and comorbid anxiety disorders. Towards this goal, the hyponeophagia assay was implemented whereby food-deprived mice show increased latency to begin feeding in a novel, anxiogenic environment. The non-selective serotonin agonist, 5-MeODMT, potentiates feeding inhibition compared to the inhibition generated by the anxiogenic environment in a drug-by-environment interaction. Thus, using hyponeophagia in mice, it was possible to study the following key components of AN: anxiety; feeding inhibition; and a modulatory role of the serotonergic system. A major prediction of the proposed AN model is that 5-HT(1A) receptor activation is necessary for feeding inhibition. In support of this model, the 5-HT(1A) receptor antagonist, WAY100635, reverses the 5-MeODMT-dependent potentiation of feeding inhibition. Our findings hint at a mechanistic role for increased 5-HT(1A) receptor activation in restricting-type AN. Further implications for the interplay between anxiety and feeding inhibition in AN are discussed.

New insights into symptoms and neurocircuit function of anorexia nervosa

Individuals with anorexia nervosa have a relentless preoccupation with dieting and weight loss that results in severe emaciation and sometimes death. It is controversial whether such symptoms are secondary to psychosocial influences, are a consequence of obsessions and anxiety or reflect a primary disturbance of brain appetitive circuits. New brain imaging technology provides insights into ventral and dorsal neural circuit dysfunction - perhaps related to altered serotonin and dopamine metabolism - that contributes to the puzzling symptoms found in people with eating disorders. For example, altered insula activity could explain interoceptive dysfunction, and altered striatal activity might shed light on altered reward modulation in people with anorexia nervosa.

Research on religion, spirituality, and mental health: a review

Religious and spiritual factors are increasingly being examined in psychiatric research. Religious beliefs and practices have long been linked to hysteria, neurosis, and psychotic delusions. However, recent studies have identified another side of religion that may serve as a psychological and social resource for coping with stress. After defining the terms religion and spirituality, this paper reviews research on the relation between religion and (or) spirituality, and mental health, focusing on depression, suicide, anxiety, psychosis, and substance abuse. The results of an earlier systematic review are discussed, and more recent studies in the United States, Canada, Europe, and other countries are described. While religious beliefs and practices can represent powerful sources of comfort, hope, and meaning, they are often intricately entangled with neurotic and psychotic disorders, sometimes making it difficult to determine whether they are a resource or a liability.

5-HT1A gene variants and psychiatric disorders: a review of current literature and selection of SNPs for future studies

5-HT1A receptors are key components of the serotonin system, acting both pre- and post- synaptically in different brain areas. There is a growing amount of evidence showing the importance of 5-HT1A in different psychiatric disorders, from mood to anxiety disorders, moving through suicidal behaviour and psychotic disorders. Findings in the literature are not consistent with any definite 5-HT1A influence in psychiatric disorders. 5-HT1A gene variants have been reported to play some role in mood disorders, anxiety disorders and psychotic disorders. Again, the literature findings are not unequivocal. Concerning response to treatment, the C(-1019)G variant seems to be of primary interest in antidepressant response: C allele carriers generally show a better response to treatment, especially in Caucasian samples. Together with the C(-1019)G (rs6295) variant, the Ile28Val (rs1799921), Arg219Leu (rs1800044) and Gly22Ser (rs1799920) variants have been investigated in possible associations with psychiatric disorders, also with no definitive results. This lack of consistency can be also due to an incomplete gene investigation. To make progress on this point, a list of validated single nucleotide polymorphisms (SNPs) covering the whole gene is proposed for further investigations.

Applying neuroimaging ligands to study major depressive disorder

The recent increase in radioligands available for neuroimaging major depressive disorder has led to advancements in our understanding of the pathophysiology of this illness and improved antidepressant development. Major depressive disorder can be defined as an illness of recurrent major depressive episodes of persistently low mood, dysregulated sleep, appetite and weight, anhedonia, cognitive impairment, and suicidality. The main target sites investigated with radioligand neuroimaging include receptor sites that regulate in response to lowered monoamine levels, targets related to removal of monoamines, uptake of ligands related to regional brain function, and target sites of antidepressants.

Association study between the serotonin 1A receptor (HTR1A) gene and neuroticism, major depression, and anxiety disorders

The serotonin neurotransmitter system in general, and the serotonin 1A receptor in particular, has been broadly implicated in the pathophysiology of mood and anxiety disorders, although the results of genetic association studies have been mixed. In this study, we examined the serotonin 1A receptor gene, HTR1A, for its association with shared genetic risk across a range of anxiety and depression-related phenotypes. Using multivariate structural equation modeling, we selected twin pairs from the population-based Virginia Adult Twin Study of Psychiatric and Substance Use Disorders scoring at the extremes of a latent genetic risk factor that underlies susceptibility to neuroticism, major depression, and several anxiety disorders. One member from each selected pair was entered into a 2-stage, case-control association study for the HTR1A gene. In the resulting sample of 589 cases and 539 controls, four SNPs spanning the HTR1A locus, including the C(-1019)G functional promoter polymorphism (rs6295), were screened in stage 1, the positive results of which were tested for replication in stage 2. While one marker met threshold significance criteria in stage 1, this association was not replicated in stage 2. Post-hoc analyses did not reveal association to any of the specific psychiatric phenotypes. Our data suggests that the HTR1A gene may not play a major role in the genetic susceptibility underlying depressive and anxiety-related phenotypes.

The serotonin-1A receptor distribution in healthy men and women measured by PET and [carbonyl-11C]WAY-100635

PURPOSE

The higher prevalence rates of depression and anxiety disorders in women compared to men have been associated with sexual dimorphisms in the serotonergic system. The present positron emission tomography (PET) study investigated the influence of sex on the major inhibitory serotonergic receptor subtype, the serotonin-1A (5-HT(1A)) receptor.

METHODS

Sixteen healthy women and 16 healthy men were measured using PET and the highly specific radioligand [carbonyl-(11)C]WAY-100635. Effects of age or gonadal hormones were excluded by restricting the inclusion criteria to young adults and by controlling for menstrual cycle phase. The 5-HT(1A) receptor BP(ND) was quantified using (1) the 'gold standard' manual delineation approach with ten regions of interest (ROIs) and (2) a newly developed delineation method using a PET template normalized to the Montreal Neurologic Institute space with 45 ROIs based on automated anatomical labeling.

RESULTS

The 5-HT(1A) receptor BP(ND) was found equally distributed in men and women applying both the manual delineation method and the automated delineation approach. Women had lower mean BP(ND) values in every region investigated, with a borderline significant sex difference in the hypothalamus (p = 0.012, uncorrected). There was a high intersubject variability of the 5-HT(1A) receptor BP(ND) within both sexes compared to the small mean differences between men and women.

CONCLUSIONS

To conclude, when measured in the follicular phase, women do not differ from men in the 5-HT(1A) receptor binding. To explain the higher prevalence of affective disorders in women, further studies are needed to evaluate the relationship between hormonal status and the 5-HT(1A) receptor expression.

Neurochemical responses to antidepressants in the prefrontal cortex of mice and their efficacy in preclinical models of anxiety-like and depression-like behavior: a comparative and correlational study

RATIONALE

Marble burying and forced swimming behavior are widely used and sensitive tests for identifying clinically effective antidepressant drugs, although the underlying neurobiology of these behaviors is not fully elucidated.

OBJECTIVES

The objective of this study was to determine the relationship between the behavioral effects of antidepressant drugs and their ability to modulate extracellular neurotransmitter levels in the prefrontal cortex.

MATERIALS AND METHODS

The effects of fluoxetine, fluvoxamine, citalopram, imipramine, and desipramine (0 to 60 mg/kg by oral gavage, except fluoxetine at 0 to 40 mg/kg) were studied independently in CD-1 mice in the marble-burying task, forced swim task and on extracellular concentrations of serotonin, norepinephrine, and dopamine in the prefrontal cortex by freely moving microdialysis.

RESULTS

Fluvoxamine, fluoxetine, and citalopram all suppressed marble-burying behavior, but produced no change in immobility time in the forced swim test. In contrast, imipramine and desipramine suppressed both marble-burying behavior and increased swimming time in the forced swim test, although desipramine mildly suppressed locomotor activity at the maximal dose. Fluvoxamine, fluoxetine, and citalopram all increased extracellular levels of cortical serotonin. Desipramine and imipramine increased extracellular dopamine levels. Fluoxetine, desipramine, and imipramine increased extracellular norepinephrine levels. Correlational analysis revealed a positive correlation between efficacy of drugs in the forced swim test and cortical extracellular dopamine levels, whereas a positive correlation was found between efficacy in the marble-burying test and extracellular serotonin levels.

CONCLUSIONS

Although marble burying and forced swimming behavior have strong predictive validity in tests of antidepressant action, each assay appears to be underpinned by entirely different neurochemical systems.

Frontolimbic serotonin 2A receptor binding in healthy subjects is associated with personality risk factors for affective disorder

BACKGROUND

Serotonergic dysfunction has been associated with affective disorders. High trait neuroticism, as measured on personality inventories, is a risk factor for major depression. In this study we investigated whether neuroticism is associated with serotonin 2A receptor binding in brain regions of relevance for affective disorders.

METHODS

Eighty-three healthy volunteers completed the standardized personality questionnaire NEO-PI-R (Revised NEO Personality Inventory) and underwent [(18)F]altanserin positron emission tomography imaging for assessment of serotonin 2A receptor binding. The correlation between the neuroticism score and frontolimbic serotonin 2A receptor binding was evaluated by multiple linear regression analysis with adjustment for age and gender.

RESULTS

Neuroticism correlated positively with frontolimbic serotonin 2A receptor binding [r(79) = .24, p = .028]. Post hoc analysis of the contributions from the six constituent traits of neuroticism showed that the correlation was primarily driven by two of them: vulnerability and anxiety. Indeed, vulnerability, defined as a person's difficulties in coping with stress, displayed the strongest positive correlation, which remained significant after correction for multiple comparisons (r = .35, p = .009).

CONCLUSIONS

In healthy subjects the personality dimension neuroticism and particularly its constituent trait, vulnerability, are positively associated with frontolimbic serotonin 2A binding. Our findings point to a neurobiological link between personality risk factors for affective disorder and the serotonergic transmitter system and identify the serotonin 2A receptor as a biomarker for vulnerability to affective disorder.

Reduced serotonin-1A receptor binding in social anxiety disorder

BACKGROUND

Results from studies in serotonin-1A (5-HT1A) knockout mice and previous positron emission tomography (PET) studies in humans imply a role for 5-HT1A receptors in normal state anxiety as well as in certain anxiety disorders. The objective of this study was to investigate 5-HT1A receptor binding potential (BP) in social anxiety disorder (SAD).

METHODS

Using PET and [carbonyl-11C]WAY-100635, we compared a homogeneous group of 12 unmedicated, male SAD patients with 18 healthy control subjects (HC). A multivariate ANOVA with all regional BP values as dependent variables, age and four radiochemical variables as covariates was performed.

RESULTS

We found a significantly lower 5-HT1A BP in several limbic and paralimbic areas but not in the hippocampus (p = .234) of SAD patients. The difference in 5-HT1A binding was most significant in the amygdala (-21.4%; p = .003). There was also a more than 20% lower 5-HT(1A) BP of SAD patients in the anterior cingulate cortex (p = .004), insula (p = .003), and dorsal raphe nuclei (p = .030).

CONCLUSIONS

The lower 5-HT1A binding in the amygdala and mesiofrontal areas of SAD patients is consistent with 1) preclinical findings of elevated anxiety in 5-HT1A knockout mice, 2) a previous PET study in healthy volunteers showing an inverse correlation between 5-HT1A BP and state anxiety, and 3) another human PET study in patients with panic disorder showing reduced 5-HT1A binding, thus corroborating the potential validity of 5-HT1A receptors as targets in the treatment of human anxiety disorders.

Neuroanatomical correlates of personality in the elderly

Extraversion and neuroticism are two important and frequently studied dimensions of human personality. They describe individual differences in emotional responding that are quite stable across the adult lifespan. Neuroimaging research has begun to provide evidence that neuroticism and extraversion have specific neuroanatomical correlates within the cerebral cortex and amygdala of young adults. However, these brain areas undergo alterations in size with aging, which may influence the nature of these personality factor-brain structure associations in the elderly. One study in the elderly demonstrated associations between perisylvian cortex structure and measures of self transcendence [Kaasinen, V., Maguire, R.P., Kurki, T., Bruck, A., Rinne, J.O., 2005. Mapping brain structure and personality in late adulthood. NeuroImage 24, 315-322], but the neuroanatomical correlates of extraversion and neuroticism, or other measures of the Five Factor Model of personality have not been explored. The purpose of the present study was to investigate the structural correlates of neuroticism and extraversion in healthy elderly subjects (n=29) using neuroanatomic measures of the cerebral cortex and amygdala. We observed that the thickness of specific lateral prefrontal cortex (PFC) regions, but not amygdala volume, correlates with measures of extraversion and neuroticism. The results suggest differences in the regional neuroanatomic correlates of specific personality traits with aging. We speculate that this relates to the influences of age-related structural changes in the PFC.

Effect of fenfluramine-induced increases in serotonin release on [18F]MPPF binding: a continuous infusion PET study in conscious monkeys

[(18)F]MPPF is a selective and reversible antagonist to the serotonin-1A (5-HT(1A)) receptor. The aim of the present study was to investigate whether the binding of [(18)F]MPPF is sensitive to increases in 5-HT levels. We used the 5-HT releasing agent and reuptake inhibitor fenfluramine (FEN) to increase the concentration of 5-HT. [(18)F]MPPF binding was assessed using positron emission tomography (PET) in conscious monkeys. Possible effects of blood flow on ligand binding were excluded by using a bolus-infusion paradigm. Control scans were obtained to assess the state of ligand equilibrium. FEN (5 or 10 mg/kg, i.v.) was administered between 90 and 130 min after the start of the [(18)F]MPPF infusion. The binding potential (BP) was calculated for an early interval (30 min preceding FEN administration) and late interval (20-50 min after administration of FEN). Microdialyses results showed a 20- and 35-fold increase in extracellular 5-HT levels in the prefrontal cortex after injection of FEN at a dose of 5 mg/kg and 10 mg/kg respectively. However, despite these large increases in 5-HT levels, no differences in BP were found between the control and FEN scans. These results may imply that the majority of 5-HT(1A) receptors is in the low affinity state in the living brain.

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

In humans, 5-HT1A receptors are implicated in anxiety and depressive disorders and their treatment. However, the physiological and genetic factors controlling 5-HT1A receptor expression are undetermined in health and disease. In this study, the influence of two genetic factors on 5-HT1A receptor expression in the living human brain was assessed using the 5-HT1A-selective positron emission tomography (PET) ligand [11C]WAY 100635. After the genotyping of 140 healthy volunteers to study population frequencies of known single nucleotide polymorphisms (SNPs) in the 5-HT1A receptor gene, the influence of the common SNP [(-1018) C>G] on 5-HT1A receptor expression was examined in a group of 35 healthy individuals scanned with [11C]WAY 100635. In the PET group, we also studied the influence of a common variable number tandem repeat polymorphism [short (S) and long (L) alleles] of the 5-HT transporter (5-HTT) gene on 5-HT1A receptor density. Whereas, the 5-HT1A receptor genotype did not show any significant effects on [11C]WAY 100635 binding, 5-HT1A receptor binding potential values were lower in all brain regions in subjects with 5-HTTLPR short (SS or SL) genotypes than those with long (LL) genotypes. Although the PET groups are necessarily a small sample size for a genetic association study, our results demonstrate for the first time that a functional polymorphism in the 5-HTT gene, but not the 5-HT1A receptor gene, affects 5-HT1A receptor availability in man. The results may offer a plausible physiological mechanism underlying the association between 5-HTTLPR genotype, behavioral traits, and mood states.

Brain serotonin1A receptor binding in major depression is related to psychic and somatic anxiety

BACKGROUND

The anxious phenotype of the 5-HT1A receptor knockout mouse and the anxiolytic properties of 5-HT1A agonists suggest that the 5-HT1A receptor modulates anxiety. We investigated the relationship of anxiety expressed in major depressive disorder (MDD) to regional 5-HT1A binding.

METHODS

Positron emission tomography with [carbonyl-11C]WAY-100635 was used to estimate regional 5-HT1A binding potential (BP) in 28 medication-free MDD subjects. Stepwise linear regression assessed the predictive capacity of three anxiety components, derived from a larger MDD sample and termed psychic, somatic, and motoric anxiety, on regional 5-HT1A BP.

RESULTS

Higher psychic (beta >or= .63) and lower somatic (beta <or= -.70) anxiety predicted over 50% of the variance in 5-HT1A BP in multiple cortical regions, but not in amygdala, hippocampus, or autoreceptors of the raphe nuclei. The psychic and somatic anxiety components were not related to depression severity. Comorbid panic disorder was associated with lower cortical and subcortical 5-HT1A BP.

CONCLUSIONS

The 5-HT1A receptor in the same brain regions has different relationships to psychic anxiety versus somatic anxiety. Lower 5-HT1A BP in panic disorder may be accounted for by higher somatic and lower psychic anxiety. Further study of the pathobiology of these anxiety components may identify distinct therapeutic targets or mechanisms.

Brain 5-HT1A receptor binding in chronic fatigue syndrome measured using positron emission tomography and [11C]WAY-100635

BACKGROUND

Research from neuroendocrine challenge and other indirect studies has suggested increased central 5-HT function in chronic fatigue syndrome (CFS) and increased 5-HT1A receptor sensitivity. We assessed brain 5-HT1A receptor binding potential directly using the specific radioligand [11C]WAY-100635 and positron emission tomography (PET).

METHODS

We selected 10 patients from a tertiary referral clinic who fulfilled the CDC consensus criteria for CFS. To assemble a homogenous group and avoid confounding effects, we enrolled only subjects who were completely medication-free and did not have current comorbid psychiatric illness. We also scanned 10 healthy control subjects.

RESULTS

There was a widespread reduction in 5-HT1A receptor binding potential in CFS relative to control subjects. This was particularly marked in the hippocampus bilaterally, where a 23% reduction was observed.

CONCLUSIONS

There is evidence of decreased 5-HT1A receptor number or affinity in CFS. This may be a primary feature of CFS, related to the underlying pathophysiology, or a finding secondary to other processes, such as previous depression, other biological changes or the behavioral consequences of CFS.

The molecular neuroimaging of anxiety disorders

This paper reviews the molecular neuroimaging of anxiety disorders, and attempts to put recent advances in the context of previous findings. Knowledge of the metabolic correlates of symptom severity and treatment response in obsessive-compulsive disorder has been significantly extended, particularly response to selective serotonin reuptake inhibitor medication. However, the first neuroreceptor studies of serotonin transporter availability in obsessive-compulsive disorder have proved inconclusive, and further studies are anticipated. Reduced 5-HT1A receptor binding has been reported in panic disorder. Recent findings have extended the knowledge of hippocampal abnormalities in post-traumatic stress disorder, and have highlighted the complexity of the association between cortisol and the hippocampus in this disorder.

The serotonergic system and anxiety

The wide use of serotonin reuptake inhibitors and serotonin receptor agonists in anxiety disorders has suggested a key role for the modulatory neurotransmitter in anxiety. However, serotonin's specific role is still uncertain. This article reviews the literature concerning how and where serotonergic agents modulate anxiety. Varying and sometimes conflicting data from human and animal studies argue for both anxiolytic and anxiogenic roles for serotonin, depending on the specific disorder, structure, or behavioral task studied. However, recent data from molecular genetic studies in the mouse point toward two important roles for the serotonin 1A receptor. In development, serotonin acts through this receptor to promote development of the circuitry necessary for normal anxiety-like behaviors. In adulthood, serotonin reuptake inhibitors act through the same receptor to stimulate neurogenesis and reduce anxiety-like behaviors. These studies highlight that the complex serotonin system likely plays various roles in the regulation of anxiety both during development and in adulthood.

Adaptive and maladaptive psychobiological responses to severe psychological stress: implications for the discovery of novel pharmacotherapy

Post-traumatic stress disorder (PTSD) is one of the few DSM-IV diagnoses contingent upon a psychosocial stressor. In this context, there is an urgent need to acquire a better understanding of both the adaptive and maladaptive psychobiological responses to traumatic stress. Preclinical investigators have utilized a variety of animal models to identify the behavioral and neurobiological features of the organism's response to stress. However, given the complexity of the healthy and pathological human response to physiological and psychological stress, the extent to which the animal data is immediately transferable to human remains to be fully determined. This review draws upon preclinical and clinical literature to examine the transformation of an adaptive human stress response into a maladaptive and debilitating mental disorder. An integrative psychobiological model for PTSD is presented, linking psychological processes and behavioral patterns with current findings in neurocircuitry, neurochemistry and psychophysiology. The implications of this model for the discovery of novel pharmacological approaches to the treatment of severe psychological distress are discussed.

The role of serotonin in panic: evidence from tryptophan depletion studies

There has been growing interest in the role of serotonin (5-hydroxytryptamine, 5-HT) in anxiety, including pathological states such as panic disorder. The technique of tryptophan depletion (TD), which causes an acute, temporary and reversible reduction in brain 5-HT levels, is a useful minimally invasive paradigm to aid the research of the role of 5-HT in various disorders. This review discusses the evidence supporting the hypothesis that 5-HT function is of importance in the neurobiology of panic disorder and considers in more detail how our understanding has been influenced by work using the technique of TD. Possible avenues for future research are also discussed.

Decreased 5-HT1A receptor binding in amygdala of schizophrenia

BACKGROUND

On the basis of postmortem data and the pharmacological action of atypical antipsychotics, serotonin-1A receptors are of interest in the study of the pathophysiology of schizophrenia. To investigate serotonin-1A receptors in schizophrenia and their relation to symptoms, we measured the availability of serotonin-1A receptors in patients with schizophrenia using positron emission tomography with [carbonyl-(11)C]WAY-100635.

METHODS

Serotonin-1A receptor binding of 11 patients with schizophrenia (8 drug-naive and 3 drug-free) was compared with that of 22 age-matched and gender-matched healthy control subjects. Symptoms were assessed using the Positive and Negative Syndrome Scale. Serotonin-1A receptor binding in selected regions of interest was quantified by binding potential obtained by the reference tissue method.

RESULTS

The regional binding potential value was lower in the amygdala by about 19% in patients with schizophrenia than in normal controls. A significant negative correlation was observed between binding potential in the amygdala and the negative and depression/anxiety symptom scores on the five-symptom subscale of the Positive and Negative Syndrome Scale.

CONCLUSIONS

Decreased serotonin-1A receptor binding in the amygdala may underlie the affective components included in the symptoms of negative and depression/anxiety in schizophrenia.

The neurobiology and control of anxious states

Fear is an adaptive component of the acute "stress" response to potentially-dangerous (external and internal) stimuli which threaten to perturb homeostasis. However, when disproportional in intensity, chronic and/or irreversible, or not associated with any genuine risk, it may be symptomatic of a debilitating anxious state: for example, social phobia, panic attacks or generalized anxiety disorder. In view of the importance of guaranteeing an appropriate emotional response to aversive events, it is not surprising that a diversity of mechanisms are involved in the induction and inhibition of anxious states. Apart from conventional neurotransmitters, such as monoamines, gamma-amino-butyric acid (GABA) and glutamate, many other modulators have been implicated, including: adenosine, cannabinoids, numerous neuropeptides, hormones, neurotrophins, cytokines and several cellular mediators. Accordingly, though benzodiazepines (which reinforce transmission at GABA(A) receptors), serotonin (5-HT)(1A) receptor agonists and 5-HT reuptake inhibitors are currently the principle drugs employed in the management of anxiety disorders, there is considerable scope for the development of alternative therapies. In addition to cellular, anatomical and neurochemical strategies, behavioral models are indispensable for the characterization of anxious states and their modulation. Amongst diverse paradigms, conflict procedures--in which subjects experience opposing impulses of desire and fear--are of especial conceptual and therapeutic pertinence. For example, in the Vogel Conflict Test (VCT), the ability of drugs to release punishment-suppressed drinking behavior is evaluated. In reviewing the neurobiology of anxious states, the present article focuses in particular upon: the multifarious and complex roles of individual modulators, often as a function of the specific receptor type and neuronal substrate involved in their actions; novel targets for the management of anxiety disorders; the influence of neurotransmitters and other agents upon performance in the VCT; data acquired from complementary pharmacological and genetic strategies and, finally, several open questions likely to orientate future experimental- and clinical-research. In view of the recent proliferation of mechanisms implicated in the pathogenesis, modulation and, potentially, treatment of anxiety disorders, this is an opportune moment to survey their functional and pathophysiological significance, and to assess their influence upon performance in the VCT and other models of potential anxiolytic properties.

Clozapine, quetiapine and olanzapine among addicted schizophrenic patients: towards testable hypotheses

Although life prevalence of substance use disorders among patients with schizophrenia is close to 50%, few studies have been carried out to date to identify an integrated pharmacological treatment for this comorbidity. So far, the most promising results, that we report here, have been obtained with clozapine. To a lesser extent, quetiapine and olanzapine, both clozapine analogues, have also shown promising results. Further to these observations, the present paper critically reviews the advantages associated with clozapine, quetiapine and olanzapine, and their relevance to the treatment of addiction among schizophrenic patients. Six characteristics seem to distinguish clozapine, quetiapine and olanzapine from the first-generation antipsychotics: (1) acting preferentially on the reward system, these second-generation antipsychotics (mainly clozapine and quetiapine) induce almost no extrapyramidal symptoms; (2) quickly dissociating from D(2), theses drugs (mainly clozapine and quetiapine) seem not to induce dysphoria, unlike conventional antipsychotics like haloperidol;(3) these drugs (mainly clozapine) seem more effective in the treatment of negative symptoms than conventional antipsychotics; (4) because of a diversified activity on several serotoninergic and noradrenergic receptors, these drugs positively alter mood, which does not seem to be the case with conventional antipsychotics, except for flupenthixol; (5) these drugs have a positive impact on cognition, which is not the case with the first-generation antipsychotics; (6) unlike conventional antipsychotics, these drugs seem to have a moderate affinity for 5-HT(3), the receptor on which ondansetron, an anti-craving medication, acts.

The Vogel conflict test: procedural aspects, gamma-aminobutyric acid, glutamate and monoamines

A multitude of mechanisms are involved in the control of emotion and in the response to stress. These incorporate mediators/targets as diverse as gamma-aminobutyric acid (GABA), excitatory amino acids, monoamines, hormones, neurotrophins and various neuropeptides. Behavioural models are indispensable for characterization of the neuronal substrates underlying their implication in the etiology of anxiety, and of their potential therapeutic pertinence to its management. Of considerable significance in this regard are conflict paradigms in which the influence of drugs upon conditioned (trained) behaviours is examined. For example, the Vogel conflict test, which was introduced some 30 years ago, measures the ability of drugs to release the drinking behaviour of water-deprived rats exposed to a mild aversive stimulus ("punishment"). This model, of which numerous procedural variants are discussed herein, has been widely used in the evaluation of potential anxiolytic agents. In particular, it has been exploited in the characterization of drugs interacting with GABAergic, glutamatergic and monoaminergic networks, the actions of which in the Vogel conflict test are summarized in this article. More recently, the effects of drugs acting at neuropeptide receptors have been examined with this model. It is concluded that the Vogel conflict test is of considerable utility for rapid exploration of the actions of anxiolytic (and anxiogenic) drugs. Indeed, in view of its clinical relevance, broader exploitation of the Vogel conflict test in the identification of novel classes of anxiolytic agents, and in the determination of their mechanisms of action, would prove instructive.

Molecular targets in the treatment of anxiety

Although the cathecholamine systems have long been the focus of drug therapy in anxiety and depression, the development of novel drugs specifically aimed at new targets within these traditional neurotransmitter systems and at targets outside of these systems is now propelling the field of drug development in anxiety. A greater understanding of regional brain networks implicated in stress, anxiety, and anxious behaviors has provided localized targets for anxiolytics. Within the serotonin and norepinephrine systems, increased understanding of postsynaptic receptor regulation with chronic treatment and cross-system effects of drug therapy have been critical in furthering our understanding of effective pharmacological interventions. Receptors within the glutamate, gamma-aminobutyric acid, and neuropeptide systems provide a rich diversity of drug targets, both in localization and function. While acknowledging significant clinical and biological differences between the various anxiety disorders, an important aspect of modern neurobiological research is to look for similarities among these disorders, given that they are highly comorbid with each other and often respond to the same spectrum of treatments. Here we review current views on both traditional and new molecular targets in the treatment of anxiety, realizing that the ultimate challenge in effective anxiolytic drug development may be achieving specificity in brain regions important in generating and sustaining anxiety.

Relationship between personality trait and regional cerebral glucose metabolism assessed with positron emission tomography

There have been no studies systematically investigating relationships between biogenetic temperament dimensions and patterns of brain glucose metabolism. Nineteen healthy subjects were evaluated regarding the biogenetic temperament using Cloninger's Temperament and Character Inventory (TCI). In addition, [18F] fluorodeoxyglucose (FDG) positron emission tomography (PET) was used to measure regional brain glucose metabolism. Voxel-based correlation analysis was used to test correlations between regional brain glucose metabolism and scores on the TCI. We identified that each temperament dimension, such as Novelty Seeking, Harm Avoidance, and Reward Dependence, was significantly correlated with specific brain regions. The majority of correlations were observed in the areas of paralimbic regions and temporal lobes. The current study provides evidence linking each biogenetic temperament dimension with specific brain areas and provides a promising base for future personality research.

Crossroads of corticotropin releasing hormone, corticosteroids and monoamines. About a biological interface between stress and depression

Mental disorders are frequently preceded by stressful events or situations. Depression is a typical case in point. This raises the question, is depression - or possibly better: are certain forms of depression - caused by stress? Can stress be a true pathogenic factor? Phrased differently: can stress destabilize neuronal systems in the central nervous system to such an extent that depressive symptoms are generated? This question is discussed with the corticotrophin releasing hormone (CRH) and MA systems and hypothalamic-pituitary-adrenal (HPA) axis as major foci. The following issues are explored: the effect of antidepressants on corticosteroid receptor gene expression; the behavioral sequellae of CRH administration; CRH disturbances in depression; the impact of early life adversity on the development of the CRH system and on stress reactivity; the interrelationships of stress hormones and monoaminergic (MA ergic) transmission and finally the therapeutic potential of CRH and cortisol antagonists. The available data suggest that CRH overdrive and cortisol overproduction may play a pathogenic role in the occurrence of certain types of depression, directly and/or indirectly, i.e. by induction or exacerbation of disturbances in MA ergic transmission. Stress should, thus, become a major focus of biological depression research.

A database of [(11)C]WAY-100635 binding to 5-HT(1A) receptors in normal male volunteers: normative data and relationship to methodological, demographic, physiological, and behavioral variables

PET studies of [(11)C]WAY-100635 binding are proving to be a useful tool to evaluate 5-HT(1A) receptor function in vivo in humans. We describe the pattern of [(11)C]WAY-100635 binding in 61 healthy male brains and examine its variability. For all PET scans, binding potential (BP) values for [(11)C]WAY-100635 in different regions were calculated using a simplified reference tissue model, with the cerebellum as reference region. Specifically we describe (1) region of interest and SPM databases of PET [(11)C]WAY-100635 binding, including test-retest variability; (2) the sensitivity of [(11)C]WAY-100635 binding to manipulations of endogenous 5-HT; and (3) correlations between [(11)C]WAY-100635 binding and radiochemical, demographic, physiological, and behavioral variables. The regional distribution of [(11)C]WAY-100635 binding in healthy human brain was similar to that reported in vitro. The test-retest variability was approximately 12% (range 9-16%) and was similar for all methods of regional sampling. The binding of [(11)C]WAY-100635 was insensitive to changes in brain 5-HT induced by tryptophan infusion and depletion. Although BP values varied greatly across subjects (range 2.9-6.8), there were no significant correlations of regional and global BP with common radiochemical, demographic, physiological, and personality variables. Specifically, in contrast with two recent small studies, we found no decline of [(11)C]WAY-100635 binding with age in our large cohort over the age range of 24 to 53 years. Assessment of 5-HT(1A) receptors in vivo using PET and [(11)C]WAY-100635 gives reliable measures of 5-HT(1A) binding. The large between-subject variability observed could not be explained by common methodological, physiological, or behavioral factors and hence the biological basis of this variability remains to be clarified.