Familial risk for mood disorder and the personality risk factor, neuroticism, interact in their association with frontolimbic serotonin 2A receptor binding

Locus coeruleus catecholamines link neuroticism and vulnerability to tau pathology in aging

Higher neuroticism is a risk factor for Alzheimer's disease (AD), and is implicated in disordered stress responses. The locus coeruleus (LC)-catecholamine system is activated during perceived threat and is a centerpiece of developing models of the pathophysiology of AD, as it is the first brain region to develop abnormal tau. We examined relationships among the "Big 5" personality traits, LC catecholamine synthesis capacity measured with [18F]Fluoro-m-tyrosine PET, and tau burden measured with [18F]Flortaucipir PET in cognitively normal older adults (n = 47). β-amyloid (Aβ) status was determined using [11C]Pittsburgh compound B PET (n = 14 Aβ positive). Lower LC catecholamine synthesis capacity was associated with higher neuroticism, more depressive symptoms as measured by the Geriatric Depression Scale, and higher amygdala tau-PET binding. Exploratory analyses with other personality traits revealed that low trait conscientiousness was also related to both lower LC catecholamine synthesis capacity, and more depressive symptoms. A significant indirect path linked both high neuroticism and low conscientiousness to greater amygdala tau burden via their mutual association with low LC catecholamine synthesis capacity. Together, these findings reveal LC catecholamine synthesis capacity to be a promising marker of affective health and pathology burden in aging, and identifies candidate neurobiological mechanisms for the effect of personality on increased vulnerability to dementia.

Brain Serotonin Release Is Reduced in Patients With Depression: A [11C]Cimbi-36 Positron Emission Tomography Study With a d-Amphetamine Challenge

BACKGROUND

The serotonin hypothesis of depression proposes that diminished serotonergic (5-HT) neurotransmission is causal in the pathophysiology of the disorder. Although the hypothesis is over 50 years old, there is no firm in vivo evidence for diminished 5-HT neurotransmission. We recently demonstrated that the 5-HT_2A receptor agonist positron emission tomography (PET) radioligand [¹¹C]Cimbi-36 is sensitive to increases in extracellular 5-HT induced by an acute d-amphetamine challenge. Here we applied [¹¹C]Cimbi-36 PET to compare brain 5-HT release capacity in patients experiencing a major depressive episode (MDE) to that of healthy control subjects (HCs) without depression.

METHODS

Seventeen antidepressant-free patients with MDE (3 female/14 male, mean age 44 ± 13 years, Hamilton Depression Rating Scale score 21 ± 4 [range 16-30]) and 20 HCs (3 female/17 male, mean age 32 ± 9 years) underwent 90-minute dynamic [¹¹C]Cimbi-36 PET before and 3 hours after a 0.5-mg/kg oral dose of d-amphetamine. Frontal cortex (main region of interest) 5-HT_2A receptor nondisplaceable binding was calculated from kinetic analysis using the multilinear analysis-1 approach with the cerebellum as the reference region.

RESULTS

Following d-amphetamine administration, frontal nondisplaceable binding potential (BP_ND) was significantly reduced in the HC group (1.04 ± 0.31 vs. 0.87 ± 0.24, p < .001) but not in the MDE group (0.97 ± 0.25 vs. 0.92 ± 0.22, not significant). ΔBP_ND of the MDE group was significantly lower than that of the HC group (HC: 15% ± 14% vs. MDE: 6.5% ± 20%, p = .041).

CONCLUSIONS

This first direct assessment of 5-HT release capacity in people with depression provides clear evidence for dysfunctional serotonergic neurotransmission in depression by demonstrating reduced 5-HT release capacity in patients experiencing an MDE.

Positron Emission Tomography (PET) Imaging Tracers for Serotonin Receptors

Serotonin (5-hydroxytryptamine, 5-HT) and 5-HT receptors (5-HTRs) have crucial roles in various neuropsychiatric disorders and neurodegenerative diseases, making them attractive diagnostic and therapeutic targets. Positron emission tomography (PET) is a noninvasive nuclear molecular imaging technique and is an essential tool in clinical diagnosis and drug discovery. In this context, numerous PET ligands have been developed for "visualizing" 5-HTRs in the brain and translated into human use to study disease mechanisms and/or support drug development. Herein, we present a comprehensive repertoire of 5-HTR PET ligands by focusing on their chemotypes and performance in PET imaging studies. Furthermore, this Perspective summarizes recent 5-HTR-focused drug discovery, including biased agonists and allosteric modulators, which would stimulate the development of more potent and subtype-selective 5-HTR PET ligands and thus further our understanding of 5-HTR biology.

Decreases in State and Trait Anxiety Post-psilocybin: A Naturalistic, Observational Study Among Retreat Attendees

Anxiety disorders are the most common type of psychiatric disorders among Western countries. Evidence-based treatment modalities including pharmacological and cognitive-behavioral therapy result in deficient treatment responses. Historical and recent research suggests psychedelic drugs may be efficacious in alleviating anxiety-related symptoms among healthy and clinical populations. The main aim of the present study was investigation of the effects of psilocybin-containing truffles, when taken in a supportive group setting, on ratings of state and trait anxiety across self-reported healthy volunteers. Attendees of psilocybin ceremonies were asked to complete a test battery at three separate occasions: before the ceremony (baseline), the morning after, and 1 week after the ceremony. The test battery included questionnaires assessing state and trait anxiety (State-Trait Anxiety Inventory), mindfulness capacities (Five Facet Mindfulness Questionnaire), and personality (Big Five Inventory). Additionally, the psychedelic experience was quantified with the Persisting Effects Questionnaire and the Ego Dissolution Inventory. The total amount of psilocybin-containing truffles consumed by each participant was recorded, and a sample of the truffles was analyzed to determine psilocin concentrations. Fifty-two attendees (males = 25; females = 25; others = 2) completed parts of the baseline assessment, 46 (males = 21; females = 24; others = 1) completed assessments the morning after the ceremony, and 23 (males = 10; females = 13) completed assessments at the 1-week follow-up. Average psilocin consumption across individuals was 27.1 mg. The morning after the ceremony, we observed medium reductions in anxiety measures (both state and trait) compared to baseline ( d ¯ = 6.4; p < 0.001 and d ¯ = 6; p = 0.014, respectively), which persisted over a 1-week period post-ceremony ( d ¯ = 6.7; p = 0.001 and d ¯ = 8.6; p = 0.004, respectively). At 1 week post-ceremony, the non-judging facet of the mindfulness scale was increased ( d ¯ = 1.5; p = 0.03), while the personality trait neuroticism decreased ( d ¯ = 5.2; p = 0.005), when compared to baseline. Additionally, we found ratings of ego dissolution (mean: 59.7, SD: 28.3) and changes in neuroticism to be the strongest predictors of reductions in state and trait anxiety, respectively. In sum, results suggest rapid and persisting (up to 1 week) anxiolytic effects in individuals with sub-clinical anxiety symptoms, which are related to the acute experience of ego dissolution, as well as lasting changes in trait neuroticism. Results also add support to the feasibility and potential efficacy of group sessions with psychedelics. To understand whether these effects extend to wider populations suffering from heightened anxiety, and the mechanisms involved, further experimental research is needed.

Therapeutic effects of classic serotonergic psychedelics: A systematic review of modern-era clinical studies

OBJECTIVE

To conduct a systematic review of modern-era (post-millennium) clinical studies assessing the therapeutic effects of serotonergic psychedelics drugs for mental health conditions. Although the main focus was on efficacy and safety, study characteristics, duration of antidepressants effects across studies, and the role of the subjective drug experiences were also reviewed and presented.

METHOD

A systematic literature search (1 Jan 2000 to 1 May 2020) was conducted in PubMed and PsychINFO for studies of patients undergoing treatment with a serotonergic psychedelic.

RESULTS

Data from 16 papers, representing 10 independent psychedelic-assisted therapy trials (psilocybin = 7, ayahuasca = 2, LSD = 1), were extracted, presented in figures and tables, and narratively synthesized and discussed. Across these studies, a total of 188 patients suffering either cancer- or illness-related anxiety and depression disorders (C/I-RADD), major depressive disorder (MDD), obsessive-compulsive disorder (OCD) or substance use disorder (SUD) were included. The reviewed studies established feasibility and evidence of safety, alongside promising early data of efficacy in the treatment of depression, anxiety, OCD, and tobacco and alcohol use disorders. For a majority of patients, the therapeutic effects appeared to be long-lasting (weeks-months) after only 1 to 3 treatment session(s). All studies were conducted in line with guidelines for the safe conduct of psychedelic therapy, and no severe adverse events were reported.

CONCLUSION

The resurrection of clinical psychedelic research provides early evidence for treatment efficacy and safety for a range of psychiatric conditions, and constitutes an exciting new treatment avenue in a health area with major unmet needs.

Common HTR2A variants and 5-HTTLPR are not associated with human in vivo serotonin 2A receptor levels

The serotonin 2A receptor (5‐HT2AR) is implicated in the pathophysiology and treatment of various psychiatric disorders. [¹⁸F]altanserin and [¹¹C]Cimbi‐36 positron emission tomography (PET) allow for high‐resolution imaging of 5‐HT2AR in the living human brain. Cerebral 5‐HT2AR binding is strongly genetically determined, though the impact of specific variants is poorly understood. Candidate gene studies suggest that HTR2A single nucleotide polymorphisms including rs6311/rs6313, rs6314, and rs7997012 may influence risk for psychiatric disorders and mediate treatment response. Although known to impact in vitro expression of 5‐HT2AR or other serotonin (5‐HT) proteins, their effect on human in vivo brain 5‐HT2AR binding has as of yet been insufficiently studied. We thus assessed the extent to which these variants and the commonly studied 5‐HTTLPR predict neocortex in vivo 5‐HT2AR binding in healthy adult humans. We used linear regression analyses and likelihood ratio tests in 197 subjects scanned with [¹⁸F]altanserin or [¹¹C]Cimbi‐36 PET. Although we observed genotype group differences in 5‐HT2AR binding of up to ~10%, no genetic variants were statistically significantly predictive of 5‐HT2AR binding in what is the largest human in vivo 5‐HT2AR imaging genetics study to date. Thus, in vitro and post mortem results suggesting effects on 5‐HT2AR expression did not carry over to the in vivo setting. To any extent these variants might affect clinical risk, our findings do not support that 5‐HT2AR binding mediates such effects. Our observations indicate that these individual variants do not significantly contribute to genetic load on human in vivo 5‐HT2AR binding.

Pharmacological sex hormone manipulation as a risk model for depression

Sex hormone transition may trigger severe depressive episodes in some women. In order to map mechanisms related to such phenomena we developed a pharmacological preclinical human model using sex hormone manipulation with gonadotropin releasing hormone agonist (GnRHa) in a placebo‐controlled design. Here the findings from this model is synthesized and discussed in the context of related literature on hormonal contributions to reproductive mental health disorders. The GnRha model work points to an estradiol‐dependent depressive response in healthy women undergoing short‐term sex hormone manipulation with GnRHa, which is linked to serotonin transporter changes (a key regulator of synaptic serotonin), a disengagement of hippocampus, and overengagement of brain networks recruited when processing emotional salient information. Further, the GnRHa model suggest that key brain regions in the reward circuit are less engaged in positive stimuli when undergoing sex hormone manipulation, which may underlie anhedonia. Also, the work supports that enhanced sensitivity to estrogen signaling at the level of gene expression may drive increased risk for depressive symptoms when exposed to sex steroid hormone fluctuations. In conclusion, the GnRHa model work highlights the brain signatures of rapid and profound changes in sex steroid hormone milieu, which reflect plausible mechanisms by which risk for mood disorders works. This model points to the role of estrogen dynamics and sensitivity, and offers a rationale for personalized prevention in hormonal transition phases, for example pregnancy to postpartum transition, perimenopause, and hormone treatments, which now can move into clinical translation and ideally pave the way for protecting mental and cognitive health.

Trait Openness and serotonin 2A receptors in healthy volunteers: A positron emission tomography study

Recent research found lasting increases in personality trait Openness in healthy individuals and patients after administration of the serotonin 2A receptor (5-HT_2A R) agonist psilocybin. However, no studies have investigated whether 5-HT_2A R availability as imaged using positron emission tomography (PET) is associated with this trait. In 159 healthy individuals (53 females), the association between 5-HT_2A R binding in neocortex imaged with [¹⁸ F]altanserin or [¹¹ C]Cimbi-36 PET and personality trait Openness was investigated using linear regression models. In these models the influence of sex on the association was also investigated. Trait Openness was assessed with the NEO Personality Inventory-Revised. No significant associations between neocortical 5-HT_2A R binding and trait Openness were found for [¹⁸ F]altanserin (p = 0.5) or [¹¹ C]Cimbi-36 (p = 0.8). Pooling the data in a combined model did not substantially change our results (p = 0.4). No significant interactions with sex were found (p > 0.35). Our results indicate that differences in 5-HT_2A R availability are not related to variations in trait Openness in healthy individuals. Although stimulation of the 5-HT_2A R with compounds such as psilocybin may contribute to long-term changes in trait Openness, there is no evidence in favor of an association between 5-HT_2A R and trait Openness.

Neuroticism predicts the impact of serotonin challenges on fear processing in subgenual anterior cingulate cortex

The personality trait neuroticism is associated with increased vulnerability to anxiety and mood disorders, conditions linked with abnormal serotonin neurotransmission and emotional processing. The interaction between neuroticism and serotonin during emotional processing is however not understood. Here we investigate how individual neuroticism scores influence the neural response to negative emotional faces and their sensitivity to serotonergic tone. Twenty healthy participants performed an emotional face task under functional MRI on three occasions: increased serotonin tone following infusion of a selective serotonin reuptake inhibitor (SSRI), decreased serotonin tone following acute tryptophan depletion (ATD) protocol, and no serotonin challenge (control). During the task, participants performed a gender-discrimination task of neutral, fearful or angry facial expressions. Individual variations in neuroticism scores were associated with neural response of subgenual anterior cingulate cortex to fearful facial expressions. The association was however opposite under the two serotoninergic challenges. The fear-related response in this region and individual neuroticism scores correlated negatively during citalopram challenge and positively during ATD. Thus, neuroticism scores were associated with the relative impact of serotonin challenges on fear processing in subgenual anterior cingulate cortex. This finding may link to a neural mechanism for the variable therapeutic effect of SSRI treatment observed in clinical populations.

More Realistic Forecasting of Future Life Events After Psilocybin for Treatment-Resistant Depression

Background: Evidence suggests that classical psychedelics can promote enduring changes in personality, attitudes and optimism, as well as improvements in mental health outcomes. Aim: To investigate the effects of a composite intervention, involving psilocybin, on pessimism biases in patients with treatment-resistant depression (TRD). Methods: Patients with TRD (n = 15) and matched, untreated non-depressed controls (n = 15) performed the Prediction Of Future Life Events (POFLE) task. The POFLE task requires participants to predict the likelihood of certain life events occurring within a 30-day period, after which the actual rate of event occurrence is reported; this gives an index of potential pessimism versus optimism bias. Psilocybin was administered in two oral dosing sessions (10 and 25 mg) one week apart. Main outcome measures were collected at baseline and one week after the second dosing session. Results: Patients showed a significant pessimism bias at baseline [t(14) = -3.260, p = 0.006; 95% CI (-0.16, -0.03), g = 1.1] which was related to the severity of their depressive symptoms (r_s = -0.55, p = 0.017). One week after psilocybin treatment, this bias was significantly decreased [t(14) = -2.714, p = 0.017; 95% CI (-0.21, -0.02), g = 0.7] and depressive symptoms were greatly improved [t(14) = 7.900, p < 0.001; 95% CI (16.17, 28.23), g = 1.9]; moreover, the magnitude of change in both variables was significantly correlated (r = -0.57, p = 0.014). Importantly, post treatment, patients became significantly more accurate at predicting the occurrence of future life events [t(14) = 1.857, p = 0.042; 95% CI (-0.01, 0.12), g = 0.6] whereas no such change was observed in the control subjects. Conclusion: These findings suggest that psilocybin with psychological support might correct pessimism biases in TRD, enabling a more positive and accurate outlook.

New Trends and Current Status of Positron-Emission Tomography and Single-Photon-Emission Computerized Tomography Radioligands for Neuronal Serotonin Receptors and Serotonin Transporter

The critical role of serotonin (5-hydroxytryptamine; 5-HT) and its receptors (5-HTRs) in the pathophysiology of diverse neuropsychiatric and neurodegenerative disorders render them attractive diagnostic and therapeutic targets for brain disorders. Therefore, the in vivo assessment of binding of 5-HT receptor ligands under a multitude of physiologic and pathologic scenarios may support more-accurate identification of disease and its progression and the patient's response to therapy as well as the screening of novel therapeutic strategies. The present Review aims to focus on the current status of radioligands used for positron-emission tomography (PET) and single-photon-emission computerized tomography (SPECT) imaging of human brain serotonin receptors. We further elaborate upon and emphasize the attributes that qualify a radioligand for theranostics on the basis of its frequency of use in clinics, its benefit to risk assessment in humans, and its continuous evolution, along with the major limitations.

No evidence for a role of the serotonin 4 receptor in five-factor personality traits: A positron emission tomography brain study

Serotonin (5-HT) brain architecture appears to be implicated in normal personality traits as supported by genetic associations and studies using molecular brain imaging. However, so far, no studies have addressed potential contributions to variation in normal personality traits from in vivo serotonin 4 receptor (5-HT₄R) brain availability, which has recently become possible to image with Positron Emission Tomography (PET). This is particularly relevant since availability of 5-HT₄R has been shown to adapt to synaptic levels of 5-HT and thus offers information about serotonergic tone in the healthy brain. In 69 healthy participants (18 females), the associations between personality traits assessed with the five-factor NEO Personality Inventory-Revised (NEO PI-R) and regional cerebral 5-HT₄R binding in neocortex, amygdala, hippocampus, and anterior cingulate cortex (ACC) were investigated using linear regression models. The associations between each of the five personality traits and a latent variable construct of global 5-HT₄R levels were also evaluated using latent variable structural equation models. We found no significant associations between the five NEO personality traits and regional 5-HT₄R binding (all p-values > .17) or the latent construct of global 5-HT₄R levels (all p-values > .37). Our findings indicate that NEO personality traits and 5-HT₄R are not related in healthy participants. Under the assumption that global 5-HT₄R levels index 5-HT tone, our data also suggest that 5-HT tone per se is not directly implicated in normal personality traits.

LSD-induced entropic brain activity predicts subsequent personality change

Personality is known to be relatively stable throughout adulthood. Nevertheless, it has been shown that major life events with high personal significance, including experiences engendered by psychedelic drugs, can have an enduring impact on some core facets of personality. In the present, balanced-order, placebo-controlled study, we investigated biological predictors of post-lysergic acid diethylamide (LSD) changes in personality. Nineteen healthy adults underwent resting state functional MRI scans under LSD (75µg, I.V.) and placebo (saline I.V.). The Revised NEO Personality Inventory (NEO-PI-R) was completed at screening and 2 weeks after LSD/placebo. Scanning sessions consisted of three 7.5-min eyes-closed resting-state scans, one of which involved music listening. A standardized preprocessing pipeline was used to extract measures of sample entropy, which characterizes the predictability of an fMRI time-series. Mixed-effects models were used to evaluate drug-induced shifts in brain entropy and their relationship with the observed increases in the personality trait openness at the 2-week follow-up. Overall, LSD had a pronounced global effect on brain entropy, increasing it in both sensory and hierarchically higher networks across multiple time scales. These shifts predicted enduring increases in trait openness. Moreover, the predictive power of the entropy increases was greatest for the music-listening scans and when "ego-dissolution" was reported during the acute experience. These results shed new light on how LSD-induced shifts in brain dynamics and concomitant subjective experience can be predictive of lasting changes in personality. Hum Brain Mapp 37:3203-3213, 2016. © 2016 Wiley Periodicals, Inc.

Neuroticism and serotonin 5-HT1A receptors in healthy subjects

Neuroticism is a personality trait associated with vulnerability for mood and anxiety disorders. Serotonergic mechanisms likely contribute to neuroticism. Serotonin 5-HT1A receptors are altered in mood and anxiety disorders, but whether 5-HT1A receptors are associated with neuroticism in healthy subjects is unclear. We measured brain serotonin 5-HT1A receptor in 34 healthy subjects in vivo using positron emission tomography (PET) and [carbonyl-(11)C]WAY-100635. Binding potential (BPP) was determined using the golden standard of kinetic compartmental modeling using arterial blood samples and radiometabolite determination. Personality traits were assessed using the Karolinska Scales of Personality. We found a strong negative association between serotonin 5-HT1A receptor BPP and neuroticism. That is, individuals with high neuroticism tended to have lower 5-HT1A receptor binding than individuals with low neuroticism. This finding was confirmed with an independent voxel-based whole-brain analysis. Other personality traits did not correlate with 5-HT1A receptor BPP. Previous observations have reported lower serotonin 5-HT1A receptor density in major depression. This neurobiological finding may be a trait-like phenomenon and partly explained by higher neuroticism in patients with affective disorders. The link between personality traits and 5-HT1A receptors should be studied in patients with major depression.

Role of Serotonin Transporter Changes in Depressive Responses to Sex-Steroid Hormone Manipulation: A Positron Emission Tomography Study

BACKGROUND

An adverse response to acute and pronounced changes in sex-hormone levels during, for example, the perimenopausal or postpartum period appears to heighten risk for major depression in women. The underlying risk mechanisms remain elusive but may include transiently compromised serotonergic brain signaling. Here, we modeled a biphasic ovarian sex hormone fluctuation using a gonadotropin-releasing hormone agonist (GnRHa) and evaluated if emergence of depressive symptoms was associated with change in cerebral serotonin transporter (SERT) binding following intervention.

METHODS

A double-blind, randomized, placebo-controlled study included 63 healthy female volunteers (mean age 24.3 ± 4.9 years) with regular menstrual cycles between 23 and 35 days. Participants were randomized to active (goserelin [GnRHa] 3.6 mg implant) or placebo intervention. Sixty women completed follow-up and entered the analyses. Primary outcome measures were changes from baseline in depressive symptoms assessed on the 17-item Hamilton Depression Rating Scale and SERT binding as imaged by [(11)C]DASB positron emission tomography. Outcome measures were acquired at baseline in the follicular phase (cycle day 6.6 ± 2.2) and at follow-up (16.2 ± 2.6 days after intervention start).

RESULTS

Sex hormone manipulation with GnRHa significantly triggered subclinical depressive symptoms within-group (p = .003) and relative to placebo (p = .02), which were positively associated with net decreases in estradiol levels (p = .02) from baseline within the GnRHa group. Depressive symptoms were associated with increases in neocortical SERT binding in the GnRHa group relative to placebo (p = .003).

CONCLUSIONS

Our data imply both serotonergic signaling and estradiol in the mechanisms by which sex-steroid hormone fluctuations provoke depressive symptoms and thus provide a rationale for future preventive strategies in high-risk groups.

Self-transcendence trait and its relationship with in vivo serotonin transporter availability in brainstem raphe nuclei: An ultra-high resolution PET-MRI study

Self-transcendence is an inherent human personality trait relating to the experience of spiritual aspects of the self. We examined the relationship between self-transcendence and serotonin transporter (SERT) availability in brainstem raphe nuclei, which are collections of five different serotonergic nuclei with rostro-caudal extension, using ultra-high resolution magnetic resonance imaging (MRI) and positron emission tomography (PET) with (11)C-3-amino-4-(2-dimethylaminomethylphenylthio)benzonitrile ([(11)C]DASB) to elucidate potential roles of serotonergic neuronal activities in this personality trait. Sixteen healthy subjects completed 7.0T MRI and High Resolution Research Tomograph (HRRT) PET. The regions of interest (ROIs) included the dorsal raphe nucleus (R1), median raphe nucleus (R2), raphe pontis (R3), and the caudal raphe nuclei (R4 and R5). For the estimation of SERT availability, the binding potential (BPND) was derived using the simplified reference tissue model (SRTM2). The Temperament and Character Inventory was used to measure self-transcendence. The analysis revealed that the self-transcendence total score had a significant negative correlation with the [(11)C]DASB BPND in the caudal raphe (R5). The subscale score for spiritual acceptance was significantly negatively correlated with the [(11)C]DASB BPND in the median raphe nucleus (R2). The results indicate that the self-transcendence trait is associated with SERT availability in specific raphe subnuclei, suggesting that the serotonin system may serve as an important biological basis for human self-transcendence. Based on the connections of these nuclei with cortico-limbic and visceral autonomic structures, the functional activity of these nuclei and their related neural circuitry may play a crucial role in the manifestation of self-transcendence.

The Center for Integrated Molecular Brain Imaging (Cimbi) database

We here describe a multimodality neuroimaging containing data from healthy volunteers and patients, acquired within the Lundbeck Foundation Center for Integrated Molecular Brain Imaging (Cimbi) in Copenhagen, Denmark. The data is of particular relevance for neurobiological research questions related to the serotonergic transmitter system with its normative data on the serotonergic subtype receptors 5-HT1A, 5-HT1B, 5-HT2A, and 5-HT4 and the 5-HT transporter (5-HTT), but can easily serve other purposes. The Cimbi database and Cimbi biobank were formally established in 2008 with the purpose to store the wealth of Cimbi-acquired data in a highly structured and standardized manner in accordance with the regulations issued by the Danish Data Protection Agency as well as to provide a quality-controlled resource for future hypothesis-generating and hypothesis-driven studies. The Cimbi database currently comprises a total of 1100 PET and 1000 structural and functional MRI scans and it holds a multitude of additional data, such as genetic and biochemical data, and scores from 17 self-reported questionnaires and from 11 neuropsychological paper/computer tests. The database associated Cimbi biobank currently contains blood and in some instances saliva samples from about 500 healthy volunteers and 300 patients with e.g., major depression, dementia, substance abuse, obesity, and impulsive aggression. Data continue to be added to the Cimbi database and biobank.

Serotonin and mental disorders: a concise review on molecular neuroimaging evidence

Serotonin is one of the most important neurotransmitters influencing mental health and, thus, is a potential target for pharmaco-logical treatments. Functional neuroimaging techniques, such as positron-emission tomography (PET) and single photon emission computed tomography (SPECT), could provide persuasive evidence for the association between mental disorders and serotonin. In this concise review, we focus on evidence of the links between serotonin and major depressive disorders, as well as other mood disorders, anxiety disorders, schizophrenia, addiction, attention deficit hyperactivity disorder (ADHD), and autism.

Familial risk for major depression is associated with lower striatal 5-HT₄ receptor binding

BACKGROUND

The 5-HT4 receptor provides a novel potential target for antidepressant treatment. No studies exist to elucidate the 5-HT4 receptor's in vivo distribution in the depressed state or in populations that may display trait markers for major depression disorder (MDD). The aim of this study was to determine whether familial risk for MDD is associated with cerebral 5-HT4 receptor binding as measured with [(11)C]SB207145 brain PET imaging. Familial risk is the most potent risk factor of MDD.

METHODS

We studied 57 healthy individuals (mean age 36 yrs, range 20-86; 21 women), 26 of which had first-degree relatives treated for MDD.

RESULTS

We found that having a family history of MDD was associated with lower striatal 5-HT4 receptor binding (p = 0.038; in individuals below 40 years, p = 0.013). Further, we found evidence for a "risk-dose effect" on 5-HT4 receptor binding, since the number of first-degree relatives with a history of MDD binding correlated negatively with 5-HT4 receptor binding in both the striatum (p = 0.001) and limbic regions (p = 0.012).

CONCLUSIONS

Our data suggest that the 5-HT4 receptor is involved in the neurobiological mechanism underlying familial risk for depression, and that lower striatal 5-HT4 receptor binding is associated with increased risk for developing MDD. The finding is intriguing considering that the 5-HT4 receptor has been suggested to be an effective target for antidepressant treatment.

Effects of serotonin-2A receptor binding and gender on personality traits and suicidal behavior in borderline personality disorder

Impulsivity and aggressiveness are personality traits associated with a vulnerability to suicidal behavior. Behavioral expression of these traits differs by gender and has been related to central serotonergic function. We assessed the relationships between serotonin-2A receptor function, gender, and personality traits in borderline personality disorder (BPD), a disorder characterized by impulsive-aggression and recurrent suicidal behavior. Participants, who included 33 BPD patients and 27 healthy controls (HC), were assessed for Axis I and II disorders with the Structured Clinical Interview for DSM-IV and the International Personality Disorders Examination, and with the Diagnostic Interview for Borderline Patients-Revised for BPD. Depressed mood, impulsivity, aggression, and temperament were assessed with standardized measures. Positron emission tomography with [(18)F]altanserin as ligand and arterial blood sampling was used to determine the binding potentials (BPND) of serotonin-2A receptors in 11 regions of interest. Data were analyzed using Logan graphical analysis, controlling for age and non-specific binding. Among BPD subjects, aggression, Cluster B co-morbidity, antisocial PD, and childhood abuse were each related to altanserin binding. BPND values predicted impulsivity and aggression in BPD females (but not BPD males), and in HC males (but not HC females.) Altanserin binding was greater in BPD females than males in every contrast, but it did not discriminate suicide attempters from non-attempters. Region-specific differences in serotonin-2A receptor binding related to diagnosis and gender predicted clinical expression of aggression and impulsivity. Vulnerability to suicidal behavior in BPD may be related to serotonin-2A binding through expression of personality risk factors.

Dorsal prefrontal cortical serotonin 2A receptor binding indices are differentially related to individual scores on harm avoidance

Although the serotonergic system has been implicated in healthy as well as in pathological emotional states, knowledge about its involvement in personality is limited. Earlier research on this topic suggests that post-synaptic 5-HT2A receptors could be involved in particular in frontal cortical areas. In drug-naïve healthy individuals, we examined the relationship between these 5-HT2A receptors and the temperament dimension harm avoidance (HA) using 123I-5-I-R91150 single photon emission computed tomography (SPECT). HA is a personality feature closely related to stress, anxiety and depression proneness, and it is thought to be mediated by the serotonergic system. We focused on the prefrontal cortices as these regions are frequently implicated in cognitive processes related to a variety of affective disorders. We found a positive relationship between dorsal prefrontal cortical (DPFC) 5-HT2A receptor binding indices (BI) and individual HA scores. Further, our results suggest that those individuals with a tendency to worry or to ruminate are particularly prone to display significantly higher 5-HT2A receptor BI in the left DPFC. Although we only examined psychologically healthy individuals, this relationship suggests a possible vulnerability for affective disorders.

The association between negative affect and prescription opioid misuse in patients with chronic pain: the mediating role of opioid craving

Over the past decade, considerable research has accumulated showing that chronic pain patients experiencing high levels of negative affect (NA) are at increased risk for prescription opioid misuse. The primary objective of the present study was to examine the factors that underlie the association between NA and prescription opioid misuse among patients with chronic pain. In this study, 82 patients with chronic musculoskeletal pain being prescribed opioid medication completed the Current Opioid Misuse Measure, a well-validated self-report questionnaire designed to assess prescription opioid misuse. Patients were also asked to complete self-report measures of pain intensity, NA, and opioid craving. A bootstrapped multiple mediation analysis was used to examine the mediating role of patients' pain intensity and opioid craving in the association between NA and prescription opioid misuse. Consistent with previous research, we found a significant association between NA and prescription opioid misuse. Interestingly, results revealed that opioid craving, but not pain intensity, mediated the association between NA and opioid misuse. The Discussion addresses the potential psychological and neurobiological factors that might contribute to the interrelationships among NA, opioid craving, and prescription opioid misuse in patients with pain. The clinical implications of our findings are also discussed.

PERSPECTIVE

Our study provides new insights into the factors that underlie the association between negative affect and prescription opioid misuse in patients with chronic pain. Our findings could have important clinical implications, particularly for patients being prescribed opioid medication, and for reducing rates of opioid misuse in patients with pain.

Trait aggression and trait impulsivity are not related to frontal cortex 5-HT2A receptor binding in healthy individuals

Numerous studies indicate that the serotonergic (5-HT) transmitter system is involved in the regulation of impulsive aggression and there is from post-mortem, in vivo imaging and genetic studies evidence that the 5-HT2A receptor may be involved. We investigated 94 healthy individuals (60 men, mean age 47.0±18.7, range 23-86) to determine if trait aggression and trait impulsivity were related to frontal cortex 5-HT2A receptor binding (5-HT2AR) as measured with [18F]-altanserin PET imaging. Trait aggression and trait impulsivity were assessed with the Buss-Perry Aggression Questionnaire (AQ) and the Barratt Impulsiveness Scale 11 (BIS-11). Statistical analyses were conducted using a multiple linear regression model and internal consistency reliability of the AQ and BIS-11 was evaluated by Cronbach's alpha. Contrary to our hypothesis, results revealed no significant associations between 5-HT2AR and the AQ or BIS-11 total scores. Also, there was no significant interaction between gender and frontal cortex 5-HT2AR in predicting trait aggression and trait impulsivity. This is the first study to examine how 5-HT2AR relates to trait aggression and trait impulsivity in a large sample of healthy individuals. Our findings are not supportive of a selective role for 5-HT2AR in mediating the 5-HT related effects on aggression and impulsivity in psychiatrically healthy individuals.

Prefrontal serotonin transporter availability is positively associated with the cortisol awakening response

Stress sensitivity and serotonergic neurotransmission interact, e.g. individuals carrying the low-expressing variants (S and LG) of the 5-HTTLPR promoter polymorphism of the serotonin transporter (SERT) gene are at higher risk for developing mood disorders when exposed to severe stress and display higher cortisol responses when exposed to psychosocial stressors relative to high expressing 5-HTTLPR variants. However, it is not clear how the relation between SERT and cortisol output is reflected in the adult brain. We investigated the relation between cortisol response to awakening (CAR) and SERT binding in brain regions considered relevant to modify the cortisol awakening response.

METHODS

thirty-two healthy volunteers underwent in vivo SERT imaging with [(11)C]DASB-Positron Emission Tomography (PET), genotyping, and performed home-sampling of saliva to assess CAR.

RESULTS

CAR, defined as the area under curve with respect to increase from baseline, was positively coupled to prefrontal SERT binding (p=0.02), independent of adjustment for 5-HTTLPR genotype. Although S- and LG-allele carriers tended to show a larger CAR (p=0.07) than LA homozygous, 5-HTTLPR genotype did not modify the coupling between CAR and prefrontal SERT binding as tested by an interaction analysis (genotype×CAR).

CONCLUSION

prefrontal SERT binding is positively associated with cortisol response to awakening. We speculate that in mentally healthy individuals prefrontal serotonergic neurotransmission may exert an inhibitory control on the cortisol awakening response.

The neurobiology of depression and antidepressant action

We present a comprehensive overview of the neurobiology of unipolar major depression and antidepressant drug action, integrating data from affective neuroscience, neuro- and psychopharmacology, neuroendocrinology, neuroanatomy, and molecular biology. We suggest that the problem of depression comprises three sub-problems: first episodes in people with low vulnerability ('simple' depressions), which are strongly stress-dependent; an increase in vulnerability and autonomy from stress that develops over episodes of depression (kindling); and factors that confer vulnerability to a first episode (a depressive diathesis). We describe key processes in the onset of a 'simple' depression and show that kindling and depressive diatheses reproduce many of the neurobiological features of depression. We also review the neurobiological mechanisms of antidepressant drug action, and show that resistance to antidepressant treatment is associated with genetic and other factors that are largely similar to those implicated in vulnerability to depression. We discuss the implications of these conclusions for the understanding and treatment of depression, and make some strategic recommendations for future research.

The 5-HT deficiency theory of depression: perspectives from a naturalistic 5-HT deficiency model, the tryptophan hydroxylase 2Arg439His knockin mouse

A decreased level of brain 5-hydroxytryptamine (5-HT) has been theorized to be a core pathogenic factor in depression for half a century. The theory arose from clinical observations that drugs enhancing extracellular levels of 5-HT (5-HT(Ext)) have antidepressant effects in many patients. However, whether such drugs indeed correct a primary deficit remains unresolved. Still, a number of anomalies in putative biomarkers of central 5-HT function have been repeatedly reported in depression patients over the past 40 years, collectively indicating that 5-HT deficiency could be present in depression, particularly in severely ill and/or suicidal patients. This body of literature on putative 5-HT biomarker anomalies and depression has recently been corroborated by data demonstrating that such anomalies indeed occur consequent to severely reduced 5-HT(Ext) levels in a mouse model of naturalistic 5-HT deficiency, the tryptophan hydroxylase 2 His(439) knockin (Tph2KI) mouse. In this review, we will critically assess the evidence for 5-HT deficiency in depression and the possible role of polymorphisms in the Tph2 gene as a causal factor in 5-HT deficiency, the latter investigated from a clinical as well as preclinical angle.

The development, past achievements, and future directions of brain PET

The early developments of brain positron emission tomography (PET), including the methodological advances that have driven progress, are outlined. The considerable past achievements of brain PET have been summarized in collaboration with contributing experts in specific clinical applications including cerebrovascular disease, movement disorders, dementia, epilepsy, schizophrenia, addiction, depression and anxiety, brain tumors, drug development, and the normal healthy brain. Despite a history of improving methodology and considerable achievements, brain PET research activity is not growing and appears to have diminished. Assessments of the reasons for decline are presented and strategies proposed for reinvigorating brain PET research. Central to this is widening the access to advanced PET procedures through the introduction of lower cost cyclotron and radiochemistry technologies. The support and expertize of the existing major PET centers, and the recruitment of new biologists, bio-mathematicians and chemists to the field would be important for such a revival. New future applications need to be identified, the scope of targets imaged broadened, and the developed expertize exploited in other areas of medical research. Such reinvigoration of the field would enable PET to continue making significant contributions to advance the understanding of the normal and diseased brain and support the development of advanced treatments.

Neural and personality correlates of individual differences related to the effects of acute tryptophan depletion on future reward evaluation

BACKGROUND/AIMS

In general, humans tend to discount the value of delayed reward. An increase in the rate of discounting leads to an inability to select a delayed reward over a smaller immediate reward (reward-delay impulsivity). Although deficits in the serotonergic system are implicated in this reward-delay impulsivity, there is individual variation in response to serotonin depletion. The aim of the present study was to investigate whether the effects of serotonin depletion on the ability to evaluate future reward are affected by individual personality traits or brain activation.

METHODS

Personality traits were assessed using the NEO-Five Factor Inventory and Temperament and Character Inventory. The central serotonergic levels of 16 healthy volunteers were manipulated by dietary tryptophan depletion. Subjects performed a delayed reward choice task that required the continuous estimation of reward value during functional magnetic resonance imaging scanning.

RESULTS

Discounting rates were increased in 9 participants, but were unchanged or decreased in 7 participants in response to tryptophan depletion. Participants whose discounting rate was increased by tryptophan depletion had significantly higher neuroticism and lower self-directedness. Furthermore, tryptophan depletion differentially affected the groups in terms of hemodynamic responses to the value of predicted future reward in the right insula.

CONCLUSIONS

These results suggest that individuals who have high neuroticism and low self-directedness as personality traits are particularly vulnerable to the effect of low serotonin on future reward evaluation accompanied by altered brain activation patterns.

Genetic co-morbidity between neuroticism, anxiety/depression and somatic distress in a population sample of adolescent and young adult twins

BACKGROUND

Genetic studies in adults indicate that genes influencing the personality trait of neuroticism account for substantial genetic variance in anxiety and depression and in somatic health. Here, we examine for the first time the factors underlying the relationship between neuroticism and anxiety/depressive and somatic symptoms during adolescence.

METHOD

The Somatic and Psychological Health Report (SPHERE) assessed symptoms of anxiety/depression (PSYCH-14) and somatic distress (SOMA-10) in 2459 adolescent and young adult twins [1168 complete pairs (35.4% monozygotic, 53% female)] aged 12-25 years (mean=15.5 ± 2.9). Differences between boys and girls across adolescence were explored for neuroticism, SPHERE-34, and the subscales PSYCH-14 and SOMA-10. Trivariate analyses partitioned sources of covariance in neuroticism, PSYCH-14 and SOMA-10.

RESULTS

Girls scored higher than boys on both neuroticism and SPHERE, with SPHERE scores for girls increasing slightly over time, whereas scores for boys decreased or were unchanged. Neuroticism and SPHERE scores were strongly influenced by genetic factors [heritability (h(2)) = 40-52%]. A common genetic source influenced neuroticism, PSYCH-14 and SOMA-10 (impacting PSYCH-14 more than SOMA-10). A further genetic source, independent of neuroticism, accounted for covariation specific to PSYCH-14 and SOMA-10. Environmental influences were largely specific to each measure.

CONCLUSIONS

In adolescence, genetic risk factors indexed by neuroticism contribute substantially to anxiety/depression and, to a lesser extent, perceived somatic health. Additional genetic covariation between anxiety/depressive and somatic symptoms, independent of neuroticism, had greatest influence on somatic distress, where it was equal in influence to the factor shared with neuroticism.

Is treatment-resistance in unipolar melancholic depression characterized by decreased serotonin₂A receptors in the dorsal prefrontal - anterior cingulate cortex?

OBJECTIVES

Quite a number of patients diagnosed with major depression are resistant to several well carried-out psychopharmacological interventions. It remains unclear as to how the serotonergic system is implicated in the phenomenon of treatment-resistance.

METHODS

We examined the involvement of post-synaptic 5-HT(2A) receptors in the pathophysiology of treatment-resistance in unipolar melancholic major depression with (123)I-5-I-R91150 SPECT. 15 antidepressant-naïve (ADN) first-episode depressed patients, 15 antidepressant-free treatment-resistant depressed (TRD) patients and 15 never-depressed individuals, matched for age and gender were studied.

RESULTS

Compared to ADN patients and healthy controls, TRD patients displayed significantly lower 5-HT(2A) receptor binding index (BI) in the dorsal regions of the prefrontal and the anterior cingulate cortex. No significant 5-HT(2A) receptor BI differences between ADN patients and controls were observed.

CONCLUSIONS

At the cortical level, 5-HT(2A) receptor BI does not significantly differ in first-episode melancholic depressed patients compared to healthy controls. This observation might imply a limited short-term impact on the serotonergic system in first episode depression. Our results also suggest that when encountered with treatment-resistance, the 5-HT(2A) receptors in the DPFC-ACC axis are significantly down-regulated. However, whether this assumed underlying pathophysiological mechanism is due solely to abnormalities in the serotonergic system remains to be answered. This article is part of a Special Issue entitled 'Anxiety and Depression'.

Serotonin receptor expression in human prefrontal cortex: balancing excitation and inhibition across postnatal development

Serotonin and its receptors (HTRs) play critical roles in brain development and in the regulation of cognition, mood, and anxiety. HTRs are highly expressed in human prefrontal cortex and exert control over prefrontal excitability. The serotonin system is a key treatment target for several psychiatric disorders; however, the effectiveness of these drugs varies according to age. Despite strong evidence for developmental changes in prefrontal Htrs of rodents, the developmental regulation of HTR expression in human prefrontal cortex has not been examined. Using postmortem human prefrontal brain tissue from across postnatal life, we investigated the expression of key serotonin receptors with distinct inhibitory (HTR1A, HTR5A) and excitatory (HTR2A, HTR2C, HTR4, HTR6) effects on cortical neurons, including two receptors which appear to be expressed to a greater degree in inhibitory interneurons of cerebral cortex (HTR2C, HTR6). We found distinct developmental patterns of expression for each of these six HTRs, with profound changes in expression occurring early in postnatal development and also into adulthood. However, a collective look at these HTRs in terms of their likely neurophysiological effects and major cellular localization leads to a model that suggests developmental changes in expression of these individual HTRs may not perturb an overall balance between inhibitory and excitatory effects. Examining and understanding the healthy balance is critical to appreciate how abnormal expression of an individual HTR may create a window of vulnerability for the emergence of psychiatric illness.

5-HT radioligands for human brain imaging with PET and SPECT

The serotonergic system plays a key modulatory role in the brain and is the target for many drug treatments for brain disorders either through reuptake blockade or via interactions at the 14 subtypes of 5-HT receptors. This review provides the history and current status of radioligands used for positron emission tomography (PET) and single photon emission computerized tomography (SPECT) imaging of human brain serotonin (5-HT) receptors, the 5-HT transporter (SERT), and 5-HT synthesis rate. Currently available radioligands for in vivo brain imaging of the 5-HT system in humans include antagonists for the 5-HT(1A), 5-HT(1B), 5-HT(2A), and 5-HT(4) receptors, and for SERT. Here we describe the evolution of these radioligands, along with the attempts made to develop radioligands for additional serotonergic targets. We describe the properties needed for a radioligand to become successful and the main caveats. The success of a PET or SPECT radioligand can ultimately be assessed by its frequency of use, its utility in humans, and the number of research sites using it relative to its invention date, and so these aspects are also covered. In conclusion, the development of PET and SPECT radioligands to image serotonergic targets is of high interest, and successful evaluation in humans is leading to invaluable insight into normal and abnormal brain function, emphasizing the need for continued development of both SPECT and PET radioligands for human brain imaging.

Cerebral 5-HT2A receptor and serotonin transporter binding in humans are not affected by the val66met BDNF polymorphism status or blood BDNF levels

Recent studies have proposed an interrelation between the brain-derived neurotrophic factor (BDNF) val66met polymorphism and the serotonin system. In this study, we investigated whether the BDNF val66met polymorphism or blood BDNF levels are associated with cerebral 5-hydroxytryptamine 2A (5-HT(2A)) receptor or serotonin transporter (SERT) binding in healthy subjects. No statistically significant differences in 5-HT(2A) receptor or SERT binding were found between the val/val and met carriers, nor were blood BDNF values associated with SERT binding or 5-HT(2A) receptor binding. In conclusion, val66met BDNF polymorphism status is not associated with changes in the serotonergic system. Moreover, BDNF levels in blood do not correlate with either 5-HT(2A) or SERT binding.