Article

Central 5-HT4 receptor binding as biomarker of serotonergic tonus in humans: A [11C]SB207145 PET study

November 2013
Molecular Psychiatry 19(4)

DOI:10.1038/mp.2013.147

Source
PubMed

Authors:

Mette Haahr

Region Hovedstadens Psykiatri

Patrick MacDonald Fisher

Center for Integrated Molecular Brain Imaging

Christian Gaden Jensen

University of Copenhagen

Vibe G. Frokjaer

Rigshospitalet

Show all 11 authorsHide

Identification of a biomarker that can inform on extracellular serotonin (5-HT) levels in the brains of living humans would enable greater understanding of the way brain circuits are modulated by serotonergic neurotransmission. Substantial evidence from studies in animals and humans indicates an inverse relationship between central 5-HT tonus and 5-HT type 4 receptor (5-HT4R) density, suggesting that 5-HT4R receptor density may be a biomarker marker for 5-HT tonus. Here, we investigated whether a 3-week administration of a selective serotonin reuptake inhibitor, expected to increase brain 5-HT levels, is associated with a decline in brain 5-HT4R binding. A total of 35 healthy men were studied in a placebo-controlled, randomized, double-blind study. Participants were assigned to receive 3 weeks of oral dosing with placebo or fluoxetine, 40 mg per day. Brain 5-HT4R binding was quantified at baseline and at follow-up with [(11)C]SB207145 positron emission tomography (PET). Three weeks of intervention with fluoxetine was associated with a 5.2% reduction in brain 5-HT4R binding (P=0.017), whereas placebo intervention did not change 5-HT4R binding (P=0.52). Our findings are consistent with a model, wherein the 5-HT4R density adjusts to changes in the extracellular 5-HT tonus. Our data demonstrate for the first time in humans that the imaging of central 5-HT4R binding may be used as an in vivo biomarker of the central 5-HT tonus.Molecular Psychiatry advance online publication, 5 November 2013; doi:10.1038/mp.2013.147.

Concurrent anxiety in patients with major depression and cerebral serotonin 4 receptor binding. A NeuroPharm-1 study

Article

Full-text available

Jul 2022

Concurrent anxiety is frequent in major depressive disorder and a shared pathophysiological mechanism between anxiety and other depressive symptoms is plausible. The serotonin 4 receptor (5-HT4R) has been implicated in both depression and anxiety. This is the first study to investigate the association between the cerebral 5-HT4R binding and anxiety in patients with depression before and after antidepressant treatment and the association to treatment response. Ninety-one drug-free patients with depression were positron emission tomography scanned with the 5-HT4R ligand [¹¹C]-SB207145. Depression severity and concurrent anxiety was measured at baseline and throughout 8 weeks of antidepressant treatment. Anxiety measures included four domains: anxiety/somatization factor score; Generalized Anxiety Disorder 10-items (GAD-10) score; anxiety/somatization factor score ≥7 (anxious depression) and syndromal anxious depression. Forty patients were rescanned at week 8. At baseline, we found a negative association between global 5-HT4R binding and both GAD-10 score (p < 0.01) and anxiety/somatization factor score (p = 0.06). Further, remitters had a higher baseline anxiety/somatization factor score compared with non-responders (p = 0.04). At rescan, patients with syndromal anxious depression had a greater change in binding relative to patients with non-syndromal depression (p = 0.04). Concurrent anxiety in patients with depression measured by GAD-10 score and anxiety/somatization factor score is negatively associated with cerebral 5-HT4R binding. A lower binding may represent a subtype with reduced natural resilience against anxiety in a depressed state, and concurrent anxiety may influence the effect on the 5-HT4R from serotonergic antidepressants. The 5-HT4R is a promising neuroreceptor for further understanding the underpinnings of concurrent anxiety in patients with depression.

Predicting Treatment Outcome in Major Depressive Disorder Using Serotonin 4 Receptor PET Brain Imaging, Functional MRI, Cognitive-, EEG-Based, and Peripheral Biomarkers: A NeuroPharm Open Label Clinical Trial Protocol

Article

Full-text available

Jul 2020

Background Between 30 and 50% of patients with major depressive disorder (MDD) do not respond sufficiently to antidepressant regimens. The conventional pharmacological treatments predominantly target serotonergic brain signaling but better tools to predict treatment response and identify relevant subgroups of MDD are needed to support individualized and mechanistically targeted treatment strategies. The aim of this study is to investigate antidepressant-free patients with MDD using neuroimaging, electrophysiological, molecular, cognitive, and clinical examinations and evaluate their ability to predict clinical response to SSRI treatment as individual or combined predictors.Methods We will include 100 untreated patients with moderate to severe depression (>17 on the Hamilton Depression Rating Scale 17) in a non-randomized open clinical trial. We will collect data from serotonin 4 receptor positron emission tomography (PET) brain scans, functional magnetic resonance imaging (fMRI), electroencephalogram (EEG), cognitive tests, psychometry, and peripheral biomarkers, before (at baseline), during, and after 12 weeks of standard antidepressant treatment. Patients will be treated with escitalopram, and in case of non-response at week 4 or intolerable side effects, offered to switch to a second line treatment with duloxetine. Our primary outcome (treatment response) is assessed using the Hamilton depression rating subscale 6-item scores at week 8, compared to baseline. In a subset of the patients (n = ~40), we will re-assess the neurobiological response (using PET, fMRI, and EEG) 8 weeks after initiated pharmacological antidepressant treatment, to map neurobiological signatures of treatment responses. Data from matched controls will either be collected or is already available from other cohorts.DiscussionThe extensive investigational program with follow-up in this large cohort of participants provides a unique possibility to (a) uncover potential biomarkers for antidepressant treatment response, (b) apply the findings for future stratification of MDD, (c) advance the understanding of pathophysiological underpinnings of MDD, and (d) uncover how putative biomarkers change in response to 8 weeks of pharmacological antidepressant treatment. Our data can pave the way for a precision medicine approach for optimized treatment of MDD and also provides a resource for future research and data sharing.Clinical Trial RegistrationThe study was registered at clinicaltrials.gov prior to initiation (NCT02869035; 08.16.2016, URL: https://clinicaltrials.gov/ct2/results?cond=&term=NCT02869035&cntry=&state=&city=&dist=)

Oral contraceptives and the serotonin 4 receptor: A molecular brain imaging study in healthy women

Article

Full-text available

Jul 2020

Objective Sex steroid hormones potently shape brain functions, including those critical to maintain mental health such as serotonin signalling. Use of oral contraceptives (OCs) profoundly changes endogenous sex steroid hormone levels and dynamics. Recent register‐based studies show that starting an OC is associated with increased risk of developing depression. Here, we investigate if use of OCs in healthy women is associated with a marker of the serotonin system in terms of serotonin 4 receptor (5‐HT4R) brain imaging. Methods [¹¹C]SB207145‐PET imaging data on 53 healthy women, of whom 16 used OCs, were available from the Cimbi database. We evaluated global effects of OC use on 5‐HT4R binding in a latent variable model based on 5‐HT4R binding across cortical and subcortical regions. Results We demonstrate that OC users have 9‐12% lower global brain 5‐HT4R binding potential compared to non‐users. Univariate region‐based analyses (pallidostriatum, caudate, hippocampus, amygdala, anterior cingulate cortex, and neocortex) supported the global effect of OC use with the largest difference present in the hippocampus (‐12.8% (95% CI [‐21.0;‐3.9], pcorrected=0.03). Conclusion We show that women who use OCs have markedly lower brain 5‐HT4R binding relative to non‐users, which constitutes a plausible molecular link between OC use and increased risk of depressive episodes. We propose that this reflects a reduced 5‐HT4R gene expression, possibly related to a blunted ovarian hormone state among OC users.

Three weeks of SSRI administration enhances the visual perceptual threshold - a randomized placebo-controlled study

Article

Full-text available

Jun 2019
PSYCHOPHARMACOLOGY

Rationale The serotonergic system has been repeatedly linked to visual attention in general, but the effects of selective serotonin reuptake inhibitor (SSRI) on specific components of visual attention remain unknown. Changes in distinct perceptual and cognitive processes are not readily evident in most attention paradigms. Objective In this study, we isolate basic components of visual attention to investigate potential effects of longer-term SSRI administration on non-emotional aspects of visual attention in healthy males. Methods In a randomized double-blind placebo-controlled design, 32 young healthy males were tested on multiple attentional parameters, before and after a 3-week SSRI intervention with fluoxetine (40 mg daily) or placebo. Data were modeled with a computational theory of visual attention to derive independent estimates of five distinct components of visual attention. Results The SSRI intervention selectively and significantly lowered the threshold for conscious visual perception. Specifically, we demonstrate that this improvement does not stem from a general increase in the speed of visual processing, as previously suggested, but specifically from a change in the perceptual threshold. Conclusions The study provides a novel description of the attentional dynamics affected by SSRI, while supporting previous findings on attentional effects of SSRI. Furthermore, it accentuates the utility of employing accuracy-based measures of attentional performance when conducting psychopharmacological research.

High brain serotonin levels in migraine between attacks: A 5-HT 4 receptor binding PET study

Article

Full-text available

Jan 2018

Migraine has been hypothesized to be a syndrome of chronic low serotonin (5-HT) levels, but investigations of brain 5-HT levels have given equivocal results. Here, we used positron emission tomography (PET) imaging of the 5-HT4 receptor as a proxy for brain 5-HT levels. Given that the 5-HT4 receptor is inversely related to brain 5-HT levels, we hypothesized that between attacks migraine patients would have higher 5-HT4 receptor binding compared to controls. Eighteen migraine patients without aura (migraine free >48 h), and 16 age- and sex-matched controls underwent PET scans after injection of [¹¹C]SB207145, a specific 5-HT4 receptor radioligand. An investigator blinded to group calculated a neocortical mean [¹¹C]SB207145 binding potential (BPND). Three migraine patients reported a migraine attack within 48 h after the scan and were excluded from the primary analysis. Comparing 15 migraine patients and 16 controls, we found that migraine patients have significantly lower neocortical 5-HT4 receptor binding than controls (0.60 ± 0.09 vs. 0.67 ± 0.05, p = .024), corrected for 5-HTTLPR genotype, sex and age. We found no association between 5-HT4 receptor binding and attack frequency, years with migraine or time since last migraine attack. Our finding of lower 5-HT4 receptor binding in migraine patients is suggestive of higher brain 5-HT levels. This is in contrast with the current belief that migraine is associated with low brain 5-HT levels. High brain 5-HT levels may represent a trait of the migraine brain or it could be a consequence of migraine attacks.

Sexual health and serotonin 4 receptor brain binding in unmedicated patients with depression—a NeuroPharm study

Article

Full-text available

Jul 2023

Sexual dysfunction is prominent in Major Depressive Disorder (MDD) and affects women with depression more than men. Patients with MDD relative to healthy controls have lower brain levels of the serotonin 4 receptor (5-HT4R), which is expressed with high density in the striatum, i.e. a key hub of the reward system. Reduced sexual desire is putatively related to disturbed reward processing and may index anhedonia in MDD. Here, we aim to illuminate plausible underlying neurobiology of sexual dysfunction in unmedicated patients with MDD. We map associations between 5-HT4R binding, as imaged with [¹¹C]SB207145 PET, in the striatum, and self-reported sexual function. We also evaluate if pre-treatment sexual desire score predicts 8-week treatment outcome in women. From the NeuroPharm study, we include 85 untreated MDD patients (71% women) who underwent eight weeks of antidepressant drug treatment. In the mixed sex group, we find no difference in 5-HT4R binding between patients with sexual dysfunction vs normal sexual function. However, in women we find lower 5-HT4R binding in the sexual dysfunctional group compared to women with normal sexual function (β = −0.36, 95%CI[−0.62:−0.09], p = 0.009) as well as a positive association between sexual desire and 5-HT4R binding (β = 0.07, 95%CI [0.02:0.13], p = 0.012). Sexual desire at baseline do not predict treatment outcome (ROC curve AUC = 52%[36%:67%]) in women. Taken together, we find evidence for a positive association between sexual desire and striatal 5-HT4R availability in women with depression. Interestingly, this raises the question if direct 5-HT4R agonism can target reduced sexual desire or anhedonia in MDD.

Association between brain serotonin 4 receptor binding and reactivity to emotional faces in depressed and healthy individuals

Article

Full-text available

May 2023

Brain serotonergic (5-HT) signaling is posited to modulate neural responses to emotional stimuli. Dysfunction in 5-HT signaling is implicated in major depressive disorder (MDD), a disorder associated with significant disturbances in emotion processing. In MDD, recent evidence points to altered 5-HT4 receptor (5-HT4R) levels, a promising target for antidepressant treatment. However, how these alterations influence neural processing of emotions in MDD remains poorly understood. This is the first study to examine the association between 5-HT4R binding and neural responses to emotions in patients with MDD and healthy controls. The study included one hundred and thirty-eight participants, comprising 88 outpatients with MDD from the NeuroPharm clinical trial (ClinicalTrials.gov identifier: NCT02869035) and 50 healthy controls. Participants underwent an [¹¹C]SB207145 positron emission tomography (PET) scan to quantify 5-HT4R binding (BPND) and a functional magnetic resonance imaging (fMRI) scan during which they performed an emotional face matching task. We examined the association between regional 5-HT4R binding and corticolimbic responses to emotional faces using a linear latent variable model, including whether this association was moderated by depression status. We observed a positive correlation between 5-HT4R BPND and the corticolimbic response to emotional faces across participants (r = 0.20, p = 0.03). This association did not differ between groups (parameter estimate difference = 0.002, 95% CI = −0.008: 0.013, p = 0.72). Thus, in the largest PET/fMRI study of associations between serotonergic signaling and brain function, we found a positive association between 5-HT4R binding and neural responses to emotions that appear unaltered in MDD. Future clinical trials with novel pharmacological agents targeting 5-HT4R are needed to confirm whether they ameliorate emotion processing biases in MDD.

Estimating Risk of Antidepressant Withdrawal from a Review of Published Data

Article

Full-text available

Dec 2022

Adaptation of the brain to the presence of a drug predicts withdrawal on cessation. The outcome of adaptation is often referred to as ‘physical dependence’ in pharmacology, as distinct from addiction, although these terms have unfortunately become conflated in some diagnostic guides. Physical dependence to antidepressants may occur in some patients, consistent with the fact that some patients experience withdrawal effects from these medications. It is thought that longer duration of use, higher dose and specific antidepressants affect the risk of antidepressant withdrawal effects as they might cause greater adaptation of the brain. We searched PubMed for relevant systematic reviews and other relevant analyses to summarise existing data on determinants of antidepressant withdrawal incidence, severity and duration. Overall, data were limited. From survey data, increased duration of use was associated with an increased incidence and severity of withdrawal effects, consistent with some evidence from data provided by drug manufacturers. Duration of use may be related to duration of withdrawal effects but data are heterogenous and sparse. Serotonin and noradrenaline reuptake inhibitors and paroxetine are associated with higher risks than other antidepressants, though data for some antidepressants are lacking. Higher doses of antidepressant has some weak association with an increased risk of withdrawal, with some ceiling effects, perhaps reflecting receptor occupancy relationships. Past experience of withdrawal effects is known to predict future risk. Based on these data, we outline a preliminary rubric for determining the risk of withdrawal symptoms for a particular patient, which may have relevance for determining tapering rates. Given the limited scope of the current research, future research should aim to clarify prediction of antidepressant withdrawal risk, especially by examining the risk of withdrawal in long-term users of medication, as well as the severity and duration of effects, to improve the preliminary tool for predictive purposes. Further research into the precise adaptations in long-term antidepressant use may improve the ability to predict withdrawal effects for a particular patient.

The Impact of Hormonal Contraceptive Use on Serotonergic Neurotransmission and Antidepressant Treatment Response: Results From the NeuroPharm 1 Study

Article

Full-text available

Mar 2022

Background Hormonal contraceptive (HC) use has been associated with an increased risk of developing a depressive episode. This might be related to HC’s effect on the serotonergic brain system as suggested by recent cross-sectional data from our group, which show that healthy oral contraceptive (OC) users relative to non-users have lower cerebral serotonin 4 receptor (5-HT4R) levels. Here, we determine if cerebral 5-HT4R binding differs between HC non-users, OC users, and hormonal intrauterine device (HIUD) users among women with an untreated depressive episode. Also, we test if antidepressant drug treatment response and its association with pre-treatment 5-HT4R binding depends on HC status.Methods[11C]-SB207145 Positron Emission Tomography imaging data from the NeuroPharm-NP1 Study (NCT02869035) were available from 59 depressed premenopausal women, of which 26 used OCs and 10 used HIUDs. The participants were treated with escitalopram. Treatment response was measured as the relative change in the Hamilton Depression Rating Scale 6 items (rΔHAMD6) from baseline to week eight. Latent variable models were used to evaluate the association between global 5-HT4R binding and OC and HIUD use as well as rΔHAMD6.ResultsWe found no evidence of a difference in global 5-HT4R binding between depressed HC users and non-users (p≥0.51). A significant crossover interaction (p=0.02) was observed between non-users and OC users in the association between baseline global 5-HT4R binding and week eight rΔHAMD6; OC users had 3-4% lower binding compared to non-users for every 10% percent less improvement in HAMD6. Within the groups, we observed a trend towards a positive association in non-users (padj=0.10) and a negative association in OC users (padj=0.07). We found no strong evidence of a difference in treatment response between the groups (p=0.13).Conclusions We found no difference in 5-HT4R binding between HC users vs. non-users in depressed women, however, it seemed that 5-HT4R settings differed qualitatively in their relation to antidepressant drug treatment response between OC users and non-users. From this we speculate that depressed OC users constitutes a special serotonin subtype of depression, which might have implications for antidepressant drug treatment response.

May antidepressant drugs worsen the conditions they are supposed to treat? The clinical foundations of the oppositional model of tolerance

Article

Full-text available

Nov 2020

Giovanni A. Fava

In recent years there has been a considerable debate on antidepressant drugs. Continued drug treatment with antidepressant medications may stimulate processes that run counter to the initial acute effects of a drug. The oppositional model of tolerance may explain loss of treatment efficacy during maintenance treatment and the fact that some side effects tend to occur only after a certain time. These processes may also direct the illness into a treatment-unresponsive course, including manifestations of bipolar disorder or paradoxical reactions. When drug treatment ends, oppositional processes no longer encounter resistance, resulting in potential onset of new withdrawal symptoms, persistent post-withdrawal disorders, hypomania, and resistance to treatment if it is reinstituted. In all these cases, antidepressant medications may constitute a form of iatrogenic comorbidity, which increases chronicity and vulnerability to depressive episodes. Antidepressant medications are essential drugs for the treatment of major depressive episodes. They are less likely, however, to provide protection for relapse prevention. Current prescription practices need to be reformulated in light of consideration of vulnerabilities and adverse effects of treatment. The oppositional model of tolerance provides a conceptual framework for weighing all these elements in the individual case. The model does not appear to apply to all patients who undergo treatment with AD, but only to a part of them. Studying the variables that are associated with such occurrence in certain patients and not in others would be one of the most important tasks of current therapeutic research. Current diagnostic systems in psychiatry do not consider the iatrogenic components of psychopathology, and can be applied to only patients who are drug free. They are suited for a patient who no longer exists: most of the cases that are seen in psychiatric clinical practice receive psychotropic drugs and such treatment is likely to affect prognosis and treatment choices.

Alterations of Expression of the Serotonin 5-HT4 Receptor in Brain Disorders

Article

Full-text available

Nov 2018
INT J MOL SCI

The serotonin 4 receptor, 5-HT4R, represents one of seven different serotonin receptor families and is implicated in a variety of physiological functions and their pathophysiological variants, such as mood and depression or anxiety, food intake and obesity or anorexia, or memory and memory loss in Alzheimer’s disease. Its central nervous system expression pattern in the forebrain, in particular in caudate putamen, the hippocampus and to lesser extent in the cortex, predispose it for a role in executive function and reward-related actions. In rodents, regional overexpression or knockdown in the prefrontal cortex or the nucleus accumbens of 5-HT4R was shown to impact mood and depression-like phenotypes, food intake and hypophagia; however, whether expression changes are causally involved in the etiology of such disorders is not clear. In this context, more data are emerging, especially based on PET technology and the use of ligand tracers that demonstrate altered 5-HT4R expression in brain disorders in humans, confirming data stemming from post-mortem tissue and preclinical animal models. In this review, we would like to present the current knowledge of 5-HT4R expression in brain regions relevant to mood/depression, reward and executive function with a focus on 5-HT4R expression changes in brain disorders or caused by drug treatment, at both the transcript and protein levels.

Is serotonin transporter brain binding associated with the cortisol awakening response? An independent non-replication

Article

Full-text available

Aug 2023
PLOS ONE

Background: Serotonergic brain signaling is considered critical for an appropriate and dynamic adaptation to stress, seemingly through modulating limbic system functions, such as the hypothalamic-pituitary-adrenal (HPA)-axis. This interplay is of great interest since it holds promise as a target for preventing stress-related brain disorders, e.g., major depression. Our group has previously observed that prefrontal serotonin transporter (5-HTT) binding, imaged with positron emission tomography (PET), is positively associated with the cortisol awakening response (CAR), an index of HPA axis stress hormone dynamics. The aim of this cross-sectional study was to replicate the previous finding in a larger independent group of healthy individuals. Methods: Molecular imaging and cortisol data were available for 90 healthy individuals. Prefrontal 5-HTT binding was imaged with [11C]DASB brain PET. Non-displaceable 5-HTT binding potential (BPND) was quantified using the Multilinear Reference Tissue Model 2 (MRTM2) with cerebellum as the reference region. CAR was based on five serial salivary cortisol samples within the first hour upon awakening. The association between CAR and prefrontal 5-HTT BPND was evaluated using a multiple linear regression model adjusted for age and sex. Further, we tested for sex differences in the association. Finally, an exploratory analysis of the association, was performed in 8 additional brain regions. Results: We observed no statistically significant association between 5-HTT binding and CAR corrected for age and sex in the prefrontal cortex (β = -0.28, p = 0.26). We saw no interaction with sex on the association (p = 0.99). Conclusion: We could not confirm a positive association between CAR and prefrontal 5-HTT BPND in this independent dataset. Also, sex differences in the association were not apparent. Our data do not exclude that the serotonin transporter system is involved in the regulation of stress responses in at-risk or manifest depressed states.

Stress Hormone Dynamics Are Coupled to Brain Serotonin 4 Receptor Availability in Unmedicated Patients With Major Depressive Disorder: A NeuroPharm Study

Article

Full-text available

Aug 2023
INT J NEUROPSYCHOPH

Background: A prominent finding in Major Depressive Disorder (MDD) is distorted stress hormone dynamics, which is regulated by serotonergic brain signaling. An interesting feature of the cerebral serotonin system is the serotonin 4 receptor (5-HT4R), which is lower in depressed relative to healthy individuals, and also has been highlighted as a promising novel antidepressant target. Here, we test the novel hypothesis that brain 5-HT4R availability in untreated patients with MDD is correlated with cortisol dynamics, indexed by the cortisol awakening response (CAR). Further, we evaluate if CAR changes with antidepressant treatment including selective serotonin reuptake inhibitor, and if pretreatment CAR can predict treatment outcome. Methods: Sixty-six patients (76% women) with a moderate to severe depressive episode underwent positron emission tomography (PET) imaging with [ 11C]SB207145 for quantification of brain 5-HT4R binding using BPND as outcome. Serial home sampling of saliva in the first hour from awakening was performed to assess CAR before and after 8 weeks of antidepressant treatment. Treatment outcome was measured by change in Hamilton Depression Rating Scale 6 items. Results: In the unmedicated depressed state, prefrontal and anterior cingulate cortices 5-HT4R binding was positively associated with CAR. CAR remained unaltered after 8 weeks of antidepressant treatment, and pretreatment CAR did not significantly predict treatment outcome. Conclusions: Our findings highlight a link between serotonergic disturbances in MDD and cortisol dynamics which likely is involved in disease- and treatment mechanisms. Further, our data support 5-HT4R agonism as a promising precision target in patients with MDD and disturbed stress hormone dynamics.

Radiotracers for the Central Serotoninergic System

Article

Full-text available

May 2022

This review lists the most important radiotracers described so far for imaging the central serotoninergic system. Single-photon emission computed tomography and positron emission tomography radiotracers are reviewed and critically discussed for each receptor.

Distinguishing relapse from antidepressant withdrawal: clinical practice and antidepressant discontinuation studies

Article

Full-text available

Apr 2022

We now recognise that withdrawal symptoms from antidepressants are common, and can be severe and long-lasting in some people. Many withdrawal symptoms overlap with symptoms of anxiety or depression, making it difficult to distinguish withdrawal from relapse. We describe how their onset soon after dose reduction, the association of psychological with physical symptoms, their prompt response to reinstatement, and their typical ‘wave’ pattern of onset, peak and resolution can help distinguish withdrawal symptoms from relapse. We also examine evidence that suggests that antidepressant withdrawal symptoms are misdiagnosed as relapse in discontinuation studies aimed at demonstrating the ability of antidepressants to prevent future relapse (relapse prevention properties). In these discontinuation studies people have their antidepressants stopped abruptly, or rapidly, making withdrawal symptoms very likely, and little effort is made to measure withdrawal symptoms or distinguish them from relapse. We conclude that there is currently no robust evidence for the relapse prevention properties of antidepressants, and current guidance might need to be re-evaluated.

Protracted withdrawal syndrome after stopping antidepressants: A descriptive quantitative analysis of consumer narratives from a large internet forum https://doi.org/10.1177/2045125320980573

Article

Full-text available

Dec 2020

Background: Protracted withdrawal syndrome (PWS) after stopping antidepressants (frequently also referred to as post-acute withdrawal syndrome or PAWS) has been described in a few case reports. However, a detailed quantitative analysis of specific symptom manifestations in antidepressant PWS is still lacking. Methods: We extracted patient narratives from a large English-language internet forum SurvivingAntidepressants.org, a peer support site concerned about withdrawal from antidepressants. PWS was ascertained based on diagnostic criteria proposed by Chouinard and Chouinard, specifically ⩾6 months of continuous antidepressant use, with emergence of new and/or more intense symptoms after discontinuation that last beyond the initial 6 weeks of acute withdrawal. We assessed medication history, outcome of PWS, and the prevalence of specific symptoms. Results: In total, n = 69 individual reports of protracted withdrawal were selected for analysis. At time of the subjects’ most recent reports, duration of PWS ranged from 5 to 166 months, mean = 37 months, median = 26 months. Length of time on the antidepressant causing protracted withdrawal ranged from 6 to 278 months, mean = 96 months, and median = 79 months. Throughout the withdrawal experience, affective symptoms, mostly anxiety, depression, emerging suicidality and agitation, were reported by 81%. Somatic symptoms, mostly headache, fatigue, dizziness, brain zaps, visual changes, muscle aches, tremor, diarrhea, and nausea were reported by 75%. Sleep problems (44%) and cognitive impairments (32%) were mentioned less frequently. These broad symptom domains were largely uncorrelated. Conclusion: PWS or PAWS from antidepressants can be severe and long-lasting, and its manifestations clinically heterogeneous. Long-term antidepressant exposure may cause multiple body system impairments. Although both somatic and affective symptoms are frequent, they are mostly unrelated in terms of occurrence. Proper recognition and detection of PWS thus requires a comprehensive assessment of medication history, duration of the withdrawal syndrome, and its various somatic, affective, sleep, and cognitive symptoms. Keywords antidepressant, discontinuation, PAWS, persistent post-withdrawal disorder, protracted

Constitutive Serotonin Tone Modulates Molecular and Behavioral Response to Chronic Fluoxetine Treatment: A Study on Genetic Rat Model

Article

Full-text available

Oct 2021

Selective serotonin reuptake inhibitors (SSRIs) are the most commonly prescribed medications for the treatment of mood disorders. Yet, individual response to SSRIs is highly variable, with only a portion of patients showing the desired therapeutic effect. To better understand the molecular basis underlying individual variability in response to SSRIs, here we comparatively studied behavioral and molecular consequences of chronic treatment with fluoxetine, a widely used SSRI, in two sublines of rats with constitutionally different serotonin (5HT) homeostasis: the high-5HT and low-5HT sublines. Platelet 5HT levels, a recognized indicator of SSRI efficacy, were decreased by fluoxetine treatment in both 5HT-sublines. On the other hand, biologically active plasma 5HT levels were reduced only in high-5HT rats. The anxiolytic effect of fluoxetine was also evident only in high-5HT rats, as supported by spatio-temporal and ethological behavioral measures in the elevated plus maze (EPM) test and exploratory behavior measures in the open field (OF) test. None of the behavioral EPM or OF measures were significantly altered by fluoxetine treatment in low-5HT rats. Unexpectedly, 5HT levels in cerebral cortices tended to be reduced only in low-5HT rats. Moreover, the effects of fluoxetine on cortical expression levels of 5HT-related proteins were also present only in low-5HT rats, with serotonin transporter ( 5HTT ) and serotonin receptor type 1a ( Htr1a ) being down-regulated, while serotonin receptor type 4 ( Htr4 ) was up-regulated by fluoxetine treatment. The obtained results support a role of individual 5HT tone as an important influencing factor on the biological actions of SSRI antidepressants.

Evidence for a serotonergic subtype of major depressive disorder: A NeuroPharm-1 study

Preprint

Full-text available

Jun 2021

Selective serotonin reuptake inhibitors (SSRIs) are the first line pharmacological treatment of Major Depressive Disorder (MDD), but only about half of patients benefit from it. Cerebral serotonin 4 receptor (5-HT4R) binding measured with positron emission tomography (PET) is inversely related to serotonin levels and can serve as a proxy for brain serotonin levels. We here determine if 5-HT4R differs between healthy and MDD individuals and if it is associated with successful outcomes of serotonergic treatment of MDD. We [11C]-SB207145 PET-scanned 100 (71 F) untreated patients with moderate to severe MDD and 91 (55 F) healthy controls; 40 patients were re-scanned after 8 weeks treatment. All patients started treatment with the SSRI escitalopram and were followed clinically after 1, 2, 4, 8 and 12 weeks. Treatment response was measured as change from baseline. Before treatment, patients with MDD had 8% lower global 5-HT4R binding than controls (95%CI[-13.1%;-2.5%], p<0.001). Non-responders did not differ from controls, whereas remitters had 9% lower binding than controls ([-16.1%;-2.7%], p=0.004). Independent of treatment outcomes, patients reduced their neostriatal 5-HT4R binding (-9%, [-12.8%;-5.0%], p<0.001) after serotonergic intervention. Overall, patients with MDD have lower cerebral 5-HT4R binding than controls, suggesting that 5-HT4R is a biomarker for MDD. The observation that SSRI treatment leads to reduced neostriatal 5-HT4R binding supports that the treatment does indeed increase brain 5-HT levels. Patients who remit to SSRIs have lower cerebral 5-HT4R prior to treatment than controls whereas non-responders do not differ. We propose that non-responders to SSRI's constitute a subgroup with non-serotonergic depression.

Synthèse de ligands iodés et fluorés en série indazole : application en imagerie des récepteurs 5-HT4 centraux

Thesis

Dec 2020

Reynald Mangeant

Depuis leur découverte en 1988, les récepteurs sérotoninergiques de type 4 (5-HT4R) sont devenus une cible de choix dans le développement de nouveaux outils diagnostiques et thérapeutiques. En effet, leur implication dans certains désordres neuropsychiatriques comme la dépression ou l’anorexie et dans certaines pathologies neurodégénératives comme la maladie d’Alzheimer (MA) ont poussé de nombreuses équipes de recherche à les caractériser via le développement de radiotraceurs affins et spécifiques de cette cible. Actuellement, aucun d’entre eux n’est utilisable chez l’homme limitant les perspectives d’un diagnostic précoce de ces pathologies.Ainsi, nous avons décidé de développer une nouvelle série de ligands affins des 5-HT4R en série fluoroindazole avec pour objectif final de mettre au point un radiotraceur utilisable en imagerie TEP (Tomodensitométrie par Emission de Positrons). Nous avons établi une nouvelle voie convergente et efficiente de synthèse nous permettant d’accéder, en un minimum d’étape, à plus d’une vingtaine de nouveaux ligands affins pour les 5-HT4R. Parmi eux, nous avons sélectionné trois composés d’intérêt « lead » en vue d’un radiomarquage au fluor-18. Cette sélection est issue d’une approche multiparamétrique mettant en évidence les propriétés remarquables des composés les plus prometteurs.Actuellement, le MR35806 est en cours de radiomarquage au CEA, nous offrant un espoir d’obtenir le premier radiotraceur affin et sélectif vis-à-vis des 5-HT4R utilisable en imagerie TEP.

Serotonin, food intake, and obesity

Article

Full-text available

Feb 2021
OBES REV

The role of serotonin in food intake has been studied for decades. Food intake is mainly regulated by two brain circuitries: (i) the homeostatic circuitry, which matches energy intake to energy expenditure, and (ii) the hedonic circuitry, which is involved in rewarding and motivational aspects of energy consumption. In the homeostatic circuitry, serotonergic signaling contributes to the integration of metabolic signals that convey the body's energy status and facilitates the ability to suppress food intake when homeostatic needs have been met. In the hedonic circuitry, serotonergic signaling may reduce reward-related, motivational food consumption. In contrast, peripherally acting serotonin promotes energy absorption and storage. Disturbed serotonergic signaling is associated with obesity, emphasizing the importance to understand the role of serotonergic signaling in food intake. However, unraveling the serotonin-mediated regulation of food intake is complex, as the effects of serotonergic signaling in different brain regions depend on the regional expression of serotonin receptor subtypes and downstream effects via connections to other brain regions. We therefore provide an overview of the effects of serotonergic signaling in brain regions of the homeostatic and hedonic regulatory systems on food intake. Furthermore, we discuss the disturbances in serotonergic signaling in obesity and its potential therapeutic implications.

The darkness and the light: diurnal rodent models for seasonal affective disorder

Article

Full-text available

Jan 2021

The development of animal models is a critical step for exploring the underlying pathophysiological mechanisms of major affective disorders and for evaluating potential therapeutic approaches. Although most neuropsychiatric research is performed on nocturnal rodents, differences in how diurnal and nocturnal animals respond to changing photoperiods, combined with a possible link between circadian rhythm disruption and affective disorders, has led to a call for the development of diurnal animal models. The need for diurnal models is most clear for seasonal affective disorder (SAD), a widespread recurrent depressive disorder that is linked to exposure to short photoperiods. Here, we briefly review what is known regarding the etiology of SAD and then examine progress in developing appropriate diurnal rodent models. Although circadian disruption is often invoked as a key contributor to SAD, a mechanistic understanding of how misalignment between endogenous circadian physiology and daily environmental rhythms affects mood is lacking. Diurnal rodents show promise as models of SAD, as changes in affective-like behaviors are induced in response to short photoperiods or dim-light conditions, and symptoms can be ameliorated by brief exposure to intervals of bright light coincident with activity onset. One exciting avenue of research involves the orexinergic system, which regulates functions that are disturbed in SAD, including sleep cycles, the reward system, feeding behavior, monoaminergic neurotransmission and hippocampal neurogenesis. However, although diurnal models make intuitive sense for the study of SAD and are more likely to mimic circadian disruption, their utility is currently hampered by a lack of genomic resources needed for the molecular interrogation of potential mechanisms.

Protracted withdrawal syndrome after stopping antidepressants: a descriptive quantitative analysis of consumer narratives from a large internet forum

Article

Full-text available

Dec 2020

Background Protracted withdrawal syndrome (PWS) after stopping antidepressants (frequently also referred to as post-acute withdrawal syndrome or PAWS) has been described in a few case reports. However, a detailed quantitative analysis of specific symptom manifestations in antidepressant PWS is still lacking. Methods We extracted patient narratives from a large English-language internet forum SurvivingAntidepressants.org , a peer support site concerned about withdrawal from antidepressants. PWS was ascertained based on diagnostic criteria proposed by Chouinard and Chouinard, specifically ⩾6 months of continuous antidepressant use, with emergence of new and/or more intense symptoms after discontinuation that last beyond the initial 6 weeks of acute withdrawal. We assessed medication history, outcome of PWS, and the prevalence of specific symptoms. Results In total, n = 69 individual reports of protracted withdrawal were selected for analysis. At time of the subjects’ most recent reports, duration of PWS ranged from 5 to 166 months, mean = 37 months, median = 26 months. Length of time on the antidepressant causing protracted withdrawal ranged from 6 to 278 months, mean = 96 months, and median = 79 months. Throughout the withdrawal experience, affective symptoms, mostly anxiety, depression, emerging suicidality and agitation, were reported by 81%. Somatic symptoms, mostly headache, fatigue, dizziness, brain zaps, visual changes, muscle aches, tremor, diarrhea, and nausea were reported by 75%. Sleep problems (44%) and cognitive impairments (32%) were mentioned less frequently. These broad symptom domains were largely uncorrelated. Conclusion PWS or PAWS from antidepressants can be severe and long-lasting, and its manifestations clinically heterogeneous. Long-term antidepressant exposure may cause multiple body system impairments. Although both somatic and affective symptoms are frequent, they are mostly unrelated in terms of occurrence. Proper recognition and detection of PWS thus requires a comprehensive assessment of medication history, duration of the withdrawal syndrome, and its various somatic, affective, sleep, and cognitive symptoms.

Discontinuation of medications classified as reuptake inhibitors affects treatment response of MDMA-assisted psychotherapy

Article

Full-text available

Feb 2021
PSYCHOPHARMACOLOGY

Rationale MDMA-assisted psychotherapy is under investigation as a novel treatment for posttraumatic stress disorder (PTSD). The primary mechanism of action of MDMA involves the same reuptake transporters targeted by antidepressant medications commonly prescribed for PTSD. Objectives Data were pooled from four phase 2 trials of MDMA-assisted psychotherapy. To explore the effect of tapering antidepressant medications, participants who had been randomized to receive active doses of MDMA (75–125 mg) were divided into two groups (taper group (n = 16) or non-taper group (n = 34)). Methods Between-group comparisons were made for PTSD and depression symptom severity at the baseline and the primary endpoint, and for peak vital signs across two MDMA sessions. Results Demographics, baseline PTSD, and depression severity were similar between the taper and non-taper groups. At the primary endpoint, the non-taper group (mean = 45.7, SD = 27.17) had a significantly (p = 0.009) lower CAPS-IV total scores compared to the taper group (mean = 70.3, SD = 33.60). More participants in the non-taper group (63.6%) no longer met PTSD criteria at the primary endpoint than those in the taper group (25.0%). The non-taper group (mean = 12.7, SD = 10.17) had lower depression symptom severity scores (p = 0.010) compared to the taper group (mean = 22.6, SD = 16.69). There were significant differences between groups in peak systolic blood pressure (p = 0.043) and diastolic blood pressure (p = 0.032). Conclusions Recent exposure to antidepressant drugs that target reuptake transporters may reduce treatment response to MDMA-assisted psychotherapy.

Slow-release delivery enhances the pharmacological properties of oral 5-hydroxytryptophan: mouse proof-of-concept

Article

Full-text available

Apr 2019

5-hydroxytryptophan (5-HTP) has shown therapeutic promise in a range of human CNS disorders. But native 5-HTP immediate release (IR) is poorly druggable, as rapid absorption causes onset of adverse events, and rapid elimination causes fluctuating exposure. Recently, we reported that 5-HTP delivered as slow-release (SR) in mice augmented the brain pro-serotonergic effect of selective serotonin reuptake inhibitors (SSRIs), without the usual adverse events associated with 5-HTP IR. However, our previous study entailed translational limitations, in terms of route, dose, and duration. Here we modeled oral 5-HTP SR in mice by administering 5-HTP via the food. We modeled oral SSRI treatment via fluoxetine in the water, in a regimen recapitulating clinical pharmacokinetics and pharmacodynamics. 5-HTP SR produced plasma 5-HTP levels well within the range enhancing brain 5-HT function in humans. 5-HTP SR robustly increased brain 5-HT synthesis and levels. When administered with an SSRI, 5-HTP SR enhanced 5-HT-sensitive behaviors and neurotrophic mRNA expression. 5-HTP SR’s pro-serotonergic effects were stronger in mice with endogenous brain 5-HT deficiency. In a comprehensive screen, 5-HTP SR was devoid of overt toxicological effects. The present preclinical data, appreciated in the context of published 5-HTP clinical data, suggest that 5-HTP SR could represent a new therapeutic approach to the plethora of CNS disorders potentially treatable with a pro-serotonergic drug. 5-HTP SR might in particular be therapeutically relevant when brain 5-HT deficiency is pathogenic and as an adjunctive augmentation therapy to SSRI therapy.

Tapering of SSRI treatment to mitigate withdrawal symptoms

Article

Mar 2019

Serotonin in eating behavior

Chapter

Jan 2020

Valérie Compan

The association between brain serotonin transporter binding and impulsivity and aggression in healthy individuals

Article

Jul 2023
J PSYCHIATR RES

The serotonin system plays a critical role in the modulation of impulsive aggression. Although serotonin transporters (SERT) are key in modulating synaptic serotonin levels, few studies have investigated the role of SERT levels in human impulsive aggression. The aim of this study was to investigate whether brain SERT levels are associated with trait impulsive aggression. We included 148 healthy individuals (mean age 29.3 ± 13.0, range 18-80 years, 91 females) who had undergone positron emission positron (PET) examinations with the SERT tracer [11C]DASB and filled in self-report questionnaires of trait aggression, trait impulsivity and state aggression. We evaluated the association between cerebral SERT binding (BPND) and trait impulsive aggression in a latent variable model, with one latent variable (LVSERT) modelled from SERT BPND in frontostriatal and frontolimbic networks implicated in impulsive aggression, and another latent variable (LVIA) modelled from various trait measures of impulsivity and aggression. The LVSERT was not significantly associated with the LVIA (p = 0.8). Post-hoc univariate analyses did not reveal any significant associations between regional SERT levels and trait aggression, trait impulsivity or state aggression, but we found that state aggression at the day of PET scan was significantly lower in LA/LA homozygotes vs S-carriers of the 5-HTTLPR gene (p = 0.008). We conclude that brain SERT binding was not related to variations in trait impulsive aggression or state aggression. Our findings do not support that SERT is involved in mediating the serotonergic effects on aggression and impulsivity, at least not in individuals with non-pathological levels of impulsive aggression.

Association between the loudness dependence of auditory evoked potential, serotonergic neurotransmission and treatment outcome in patients with depression

Article

Feb 2023

Previous studies have suggested that the loudness dependence of auditory evoked potential (LDAEP) is associated with the effectiveness of antidepressant treatment in patients with major depressive disorders (MDD). Furthermore, both LDAEP and the cerebral serotonin 4 receptor (5-HT4R) density is inversely related to brain serotonin levels. We included 84 patients with MDD and 22 healthy controls to examined the association between LDAEP and treatment response and its association with cerebral 5-HT4R density. Participants underwent both EEG and 5-HT4R neuroimaging with [11C]SB207145 PET. Thirty-nine patients with MDD were re-examined after 8 weeks of treatment with selective serotonin reuptake inhibitors/serotonin noradrenaline reuptake inhibitor (SSRI/SNRI). We found that the cortical source of LDAEP was higher in untreated patients with MDD compared to healthy controls (p=0.03). Prior to SSRI/SNRI treatment, subsequent treatment responders had a negative association between LDAEP and depressive symptoms and a positive association between scalp LDAEP and symptom improvement at week 8. This was not found in source LDAEP. In healthy controls, we found a positive correlation between both scalp and source LDAEP and cerebral 5-HT4R binding but that was not observed in patients with MDD. We did not see any changes in scalp and source LDAEP in response to SSRI/SNRI treatment. These results support a theoretical framework where both LDAEP and cerebral 5-HT4R are indices of cerebral 5-HT levels in healthy individuals while this association seems to be disrupted in MDD. The combination of the two biomarkers may be useful for stratifying patients with MDD. Clinical Trials Registration:https://clinicaltrials.gov/ct2/show/NCT02869035?draw=1Registration number: NCT0286903.

Serotonin 4 Receptor Brain Binding in Major Depressive Disorder and Association With Memory Dysfunction

Article

Feb 2023

Importance: The cerebral serotonin 4 (5-HT4) receptor is a promising novel target for treatment of major depressive disorder (MDD), and pharmacological stimulation of the 5-HT4 receptor has been associated with improved learning and memory in healthy individuals. Objective: To map the neurobiological signatures of patients with untreated MDD compared with healthy controls and to examine the association between cerebral 5-HT4 receptor binding and cognitive functions in the depressed state. Design, setting, and participants: This case-control study used baseline data from the NeuroPharm clinical depression trial in Denmark. Adult participants included antidepressant-free outpatients with a current moderate to severe depressive episode and healthy controls. All participants completed positron emission tomography (PET) scanning with [11C]SB207145 for quantification of brain 5-HT4 receptor binding, but only the patients underwent cognitive testing. Data analyses were performed from January 21, 2020, to April 22, 2022. Main outcomes and measures: The main study outcome was the group difference in cerebral 5-HT4 receptor binding between patients with MDD and healthy controls. In addition, the association between 5-HT4 receptor binding and verbal memory performance in the patient group was tested. Other cognitive domains (working memory, reaction time, emotion recognition bias, and negative social emotions) were assessed as secondary outcomes. Results: A total of 90 patients with untreated MDD (mean [SD] age, 27.1 [8.2] years; 64 women [71.1%]) and 91 healthy controls (mean [SD] age, 27.1 [8.0] years; 55 women [60.4%]) were included in the analysis. Patients with current MDD had significantly lower cerebral 5-HT4 receptor binding than healthy controls (-7.0%; 95% CI, -11.2 to -2.7; P = .002). In patients with MDD, there was a correlation between cerebral 5-HT4 receptor binding and verbal memory (r = 0.29; P = .02). Conclusions and relevance: Results of this study show that cerebral 5-HT4 receptor binding was lower in patients with MDD than in healthy controls and that the memory dysfunction in patients with MDD was associated with lower cerebral 5-HT4 receptor binding. The cerebral 5-HT4 receptor is a promising treatment target for memory dysfunction in patients with MDD.

P.302 Healthy women who use oral contraceptives show lower brain serotonin 4 receptor binding relative to nonusers

Article

Dec 2019
EUR NEUROPSYCHOPHARM

P.352 Patients with major depressive disorder have lower cerebral serotonin 4 receptor binding than healthy controls

Article

Dec 2019
EUR NEUROPSYCHOPHARM

P.849 Serotonin 4 receptor binding is positively associated with brain response to reward

Article

Dec 2019
EUR NEUROPSYCHOPHARM

P.553 5-HT4R binding is positively correlated with obsessive-compulsive features: a preliminary analysis in healthy volunteers

Article

Dec 2019
EUR NEUROPSYCHOPHARM

Positron Emission Tomography (PET) Imaging Tracers for Serotonin Receptors

Article

Full-text available

Aug 2022

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.

Serotonin regulation of behaviour via large-scale neuromodulation of serotonin receptor networks

Preprint

Full-text available

Oct 2021

Although we understand how serotonin receptors function at the single-cell level, what role different serotonin receptors play in regulating brain-wide activity and, in turn, human behaviour, remains unknown. Here, we developed transcriptomic-neuroimaging mapping to characterise brain-wide functional signatures associated with specific serotonin receptors: serotonin receptor networks (SRNs). Probing SRNs with optogenetics-fMRI and pharmacology in mice, we show that activation of dorsal raphe serotonin neurons differentially modulates the amplitude and functional connectivity of different SRNs, showing that receptors’ spatial distributions can confer specificity not only at the local, but also at the brain-wide, network-level. In humans, using resting state fMRI, different sets of SRNs are linked to different behavioural phenotypes. These results provide compelling evidence that heterogeneous brain-wide distributions of different serotonin receptor types may underpin behaviourally-distinct modes of serotonin regulation. This suggests that dorsal raphe serotonin neurons may regulate multiple aspects of human behaviour via modulation of large-scale receptor networks.

Applications, Advances, and Limitations of Molecular Imaging of Brain Receptors

Chapter

Jan 2021

The molecular imaging of brain receptors by positron emission tomography (PET) and single photon emission computed tomography (SPECT) has evolved into a mature technology through parallel developments in radiopharmaceutical chemistry, instrumentation, image reconstruction, and kinetic modeling. PET researchers had early success in studies of dopamine D2-like receptors using spiperone derivates labeled with carbon-11 or fluorine-18. However, quantitation of these ligands is difficult due to their slow approach to equilibrium binding, and due to offtarget binding at serotonin receptors. These problems were resolved with the discovery of [¹¹C]raclopride, a benzamide antagonist ligand with rapid kinetics, near absence of brain-penetrating metabolites, and admirable selectivity for dopamine D2/3 receptors. The displaceability of its specific binding by endogenous dopamine enabled a new field of research aiming to measure indirectly the competition from dopamine in the living brain. Furthermore, higher affinity benzamide ligands can detect the less abundant ex-striatal D2/3 receptors, albeit with the requirement of hours-long PET recordings for the striatum. Meanwhile, there emerged a series of PET ligands with selectivity for serotonin receptor subtypes, notably the 5HT2A receptors of the cerebral cortex, the 5HT1A receptors found in the hippocampus and serotonin neurons. Opioid receptors are the next best documented pharmacological class, with the preponderance of PET studies focusing on the μ-subtype. The opioid receptor literature is matched in scope by studies of acetylcholine receptors, notably the muscarinic receptors and the nicotinic receptors, now extending to the α7-subtype. Overall, the literature is heavily weighted to this short list of receptor types, and important receptor types such as the NMDA-type glutamate receptors remain elusive targets for molecular imaging. PET technology is now widely used for measuring target engagement in the living human brain. However, there are few instances where molecular imaging of brain receptors is pathognomonic of brain disease.

The Modulatory Role of Serotonin on Human Impulsive Aggression

Article

Full-text available

May 2021
BIOL PSYCHIAT

The hypothesis of chronically low brain serotonin levels as pathophysiologically linked to impulsive aggression has been around for several decades. Whereas the theory was initially based on indirect methods to probe serotonin function, our understanding of the neural mechanisms involved in impulsive aggression has progressed with recent advances in neuroimaging. The review integrates evidence based on data from several neuroimaging domains in humans. In vivo molecular neuroimaging findings demonstrate associations between impulsive aggression and high serotonin 1B and serotonin 4 receptor binding, high serotonin transporter levels and low monoamine oxidase A levels, suggesting that low interstitial serotonin levels is a neurobiological risk factor for impulsive aggressive behavior. Imaging genetics suggest that serotonergic-related genetic polymorphisms associate with antisocial behavior, and some evidence indicate that the low-expressing monoamine oxidase A genotype specifically predisposes for impulsive aggression, which may be mediated by effects on corticolimbic function. Interventions that (presumably) alter serotonin levels have effects on brain activity within brain regions involved in impulsive aggression, notably the amygdala, dorsal striatum, anterior cingulate, insula and prefrontal cortex. Based on these findings, we propose a model for the modulatory role of serotonin in impulsive aggression. Future studies should ensure that clinical features unique for impulsive aggression are appropriately assessed and we propose investigations of knowledge-gaps that can help confirm, refute or modify our proposed model of impulsive aggression.

Molecular Imaging of Depressive Disorders

Chapter

Jan 2021

This chapter summarizes findings of a large number of molecular imaging studies in the field of unipolar and bipolar depression (BD). Brain metabolism in depressed unipolar and bipolar patients is generally hypoactive in the middle frontal gyri, the pregenual and posterior anterior cingulate, the superior temporal gyrus, the insula, and the cerebellum, while hyperactivity exists in subcortical (caudate nucleus, thalamus), limbic (amygdala, anterior hippocampus), and medial and inferior frontal regions. Interestingly, after depletion of serotonin or noradrenalin/dopamine in vulnerable (recovered) major depressive disorder (MDD) patients, a similar response pattern in metabolism occurs. Findings on the pre- and postsynaptic dopaminergic system show indications that, at least in subgroups of retarded MDD patients, presynaptic dopaminergic markers may be decreased, while postsynaptic markers may be increased. The findings regarding serotonin synthesis, pre- and postsynaptic imaging can be integrated to a presumable loss of serotonin in MDD, while this remains unclear in BD. This reduction of serotonin and dopamine in MDD was recently summarized in a revised version of the monoamine hypothesis, which focuses more on a dysfunction at the level of the MAO enzyme. This should be addressed further in future studies. Nevertheless, it should be acknowledged that the serotonergic and dopaminergic systems appear adaptive; therefore, it remains difficult to distinguish state and trait abnormalities. Therefore, future longitudinal molecular imaging studies in the same subjects at different clinical mood states (preferably with different tracers and imaging modalities) are needed to clarify whether the observed changes in transporters and receptors are compensatory reactions or reflect different, potentially causal mechanisms. Several suggestions for future developments are also provided at the end of this chapter.

Imaging of the Serotonin System: Radiotracers and Applications in Memory Disorders

Chapter

Sep 2020

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 serotonin (5-HT) receptors. This chapter provides the current status of radioligands used for positron emission tomography (PET) and single-photon emission computerised tomography (SPECT) imaging of the human brain 5-HT receptors and the 5-HT transporter (SERT) with particular emphasis on the applications in Alzheimer’s disease (AD). Currently available radioligands for in vivo brain imaging of the 5-HT system in humans include radiolabelled compounds for the 5-HT1A, 5-HT1B, 5-HT2A, 5-HT4 and to some extent 5-HT6 receptors and for SERT. Imaging of serotonergic targets in humans has given invaluable insight into the normal brain function and into brain disorders where the serotonergic system is perturbed. Imaging studies show that the 5-HT1A receptor binding is increased, and 5-HT2A receptor binding is decreased in mild cognitive impairment (MCI). In early AD, 5-HT4 receptor binding is increased, whereas in early and more advanced AD, SERT and the 5-HT1A and 5-HT2A receptor binding are reduced in a region-specific manner. Future studies should focus on the association between serotonergic dysfunction and symptomatology in order to increase our understanding of the neurobiological background for neuropsychiatric symptoms in neurodegenerative and neuropsychiatric disorders.

Activation and Blockade of Serotonin-4 Receptors in the Lateral Habenula Produce Antidepressant Effects in the Hemiparkinsonian Rat

Article

Jul 2020

Background: The 5-hydroxytryptamine (5-HT) neurotransmitter system and lateral habenula (LHb) are involved in the regulation of depression, while the mechanisms remain to be clarified. Objectives: The effects and possible mecha-nism underlying activation or blockade of 5-HT4 receptors (5-HT4Rs) in the LHb in depression were investigated by behavioral and neurochemical methods based on a Parkinson's disease (PD) rat model. Method: 6-Hydroxydopamine (6-OHDA) was injected unilaterally into the substantia nigra pars compacta to establish the PD rat model. The depressive-like behaviors were measured by the forced swimming test (FST) and sucrose preference test (SPT). The concentrations of dopamine (DA), noradrenaline (NA) and 5-HT in the related brain regions were measured by a neurochemical method. Results: The 6-OHDA lesions increased the immobility time in the FST and decreased the sucrose consumption in the SPT, suggesting the induction of depressive-like behaviors. Intra-LHb injection of BIMU-8 (5-HT4R agonist) or GR113808 (5-HT4R antagonist) produced antidepressant effects in the lesioned rats. Intra-LHb injection of BIMU-8 significantly increased the DA levels in the medial prefrontal cortex (mPFC) and ventral hippocampus (vHip), increased the 5-HT level in the mPFC and decreased the NA level in the vHip only in the lesioned rats, while intra-LHb injection of GR113808 changed DA, NA and 5-HT levels in the mPFC, LHb and vHip in both sham and the lesioned rats. Conclusions: All these results suggest that activation or blockade of the LHb 5-HT4Rs produce antidepressant effects in the 6-OHDA-lesioned rats, which are related to the changes of monoamines in the limbic and limbic-related regions.

Translating the promise of 5HT 4 receptor agonists for the treatment of depression

Article

Full-text available

Apr 2020

Animal experimental studies suggest that 5-HT 4 receptor activation holds promise as a novel target for the treatment of depression and cognitive impairment. 5-HT 4 receptors are post-synaptic receptors that are located in striatal and limbic areas known to be involved in cognition and mood. Consistent with this, 5-HT 4 receptor agonists produce rapid antidepressant effects in a number of animal models of depression, and pro-cognitive effects in tasks of learning and memory. These effects are accompanied by molecular changes, such as the increased expression of neuroplasticity-related proteins that are typical of clinically useful antidepressant drugs. Intriguingly, these antidepressant-like effects have a fast onset of their action, raising the possibility that 5-HT 4 receptor agonists may be a particularly useful augmentation strategy in the early stages of SSRI treatment. Until recently, the translation of these effects to humans has been challenging. Here, we review the evidence from animal studies that the 5-HT 4 receptor is a promising target for the treatment of depression and cognitive disorders, and outline a potential pathway for the efficient and cost-effective translation of these effects into humans and, ultimately, to the clinic.

A single psilocybin dose is associated with long-term increased mindfulness, preceded by a proportional change in neocortical 5-HT2A receptor binding

Article

Mar 2020
EUR NEUROPSYCHOPHARM

A single dose of the serotonin 2A receptor (5-HT2AR) agonist psilocybin can have long-lasting beneficial effects on mood, personality, and potentially on mindfulness, but underlying mechanisms are unknown. Here, we for the first time conduct a study that assesses psilocybin effects on cerebral 5-HT2AR binding with [¹¹C]Cimbi-36 positron emission tomography (PET) imaging and on personality and mindfulness. Ten healthy and psychedelic-naïve volunteers underwent PET neuroimaging of 5-HT2AR at baseline (BL) and one week (1W) after a single oral dose of psilocybin (0.2–0.3 mg/kg). Personality (NEO PI-R) and mindfulness (MAAS) questionnaires were completed at BL and at three-months follow-up (3M). Paired t-tests revealed statistically significant increases in personality Openness (puncorrected = 0.04, mean change [95%CI]: 4.2[0.4;∞]), which was hypothesized a priori to increase, and mindfulness (pFWER = 0.02, mean change [95%CI]: 0.5 [0.2;0.7]). Although 5-HT2AR binding at 1W versus BL was similar across individuals (puncorrected = 0.8, mean change [95%CI]: 0.007 [−0.04;0.06]), a post hoc linear regression analysis showed that change in mindfulness and 5-HT2AR correlated negatively (β [95%CI] = −5.0 [−9.0; −0.9], pFWER= 0.046). In conclusion, we confirm that psilocybin intake is associated with long-term increases in Openness and – as a novel finding – mindfulness, which may be a key element of psilocybin therapy. Cerebral 5-HT2AR binding did not change across individuals but the negative association between changes in 5-HT2AR binding and mindfulness suggests that individual change in 5-HT2AR levels after psilocybin is variable and represents a potential mechanism influencing long-term effects of psilocybin on mindfulness.

EVALUATION OF MITOCHONDRIAL AND SYNAPTIC FUNCTION IN ALZHEIMER'S DISEASE (AD): A [18F]BCPP-EF, [11C]SA4503 AND [11C]UCB-J PET STUDY

Article

Jan 2019

Objectives: Mitochondrial deficits leading to synaptic dysfunction have been hypothesised in the pathophysiology of neurodegenerative disease, with Ab/tau impairing mito-chondrial function in AD. To date a combined evaluation of human mitochondrial and synaptic function has not been performed directlyin vivo. We describe the pilot results of MINDMAPS-AD, a study within the MINDMAPS1 pro-gramme aiming to evaluate mitochondrial and synaptic function in the brain of patients with MCI/AD. MINDMAPS-AD uses the novel radioligands [18F]BCPP-EF, [11C]SA4503 and [11C]UCB-J, to compare the regional density of mitochondrial complex I (MC1), the sigma 1 receptor (s1R) and synaptic vesicular protein 2A (SV2A) respectively. Methods: Six participants with a range of AD related pathologies, EMCI (n=2), LMCI (n=2), and AD (n=2), were enrolled into the study. Participants fulfilled NIA-AA criteria and were amyloid-beta þve confirmed by [18F]Florbetaben PET. All participants underwent three PET scans with [18F]BCPP-EF, [11C]SA4503 and [11C]UCB-J. Arterial blood samples were collected and ametabolite corrected arterial plasma input function was estimated to derive regional volumes of distribution (VT). These data were compared to six age/sex matched cognitively normal (CN) healthy subjects recruited for ongoing studies within the MINDMAPS programme. Regions of interest (ROIs) were defined on individual subject MR images using an anatomical atlas and included: frontal cortex, hippocampus, amygdala, anterior cingulate, posterior cingulate, thalamus, temporal cortex, parietal cortex, caudate, putamen, and occipital lobe. Regional target density was evaluated using the VT, as well as VT corrected fo rthe plasma free fraction of the radioligand (fP; VT/fp), and the regional VT ratio versus the VT in the centrum semi-ovale, a white matter region expected to have low levels of the targets evaluated (DVR). Comparison of regional target density and fP between AD and CN was performed using a two tailed, unpaired student’s t-test. Results:The fP values in the AD participants were higher for [18F]BCPP-EF and [11C]UCB-J (27%, p<0.02; and 14%,p<0.08 respectively) and hence VT/fP and DVR were chosen as the parameters of interest. VT/fP and DVR analyses provided consistent results, with lower mean density of MC1 (–10%) and SV2A (–16%) across the brain regions, and higher density of s1R (þ16%) in participants with AD (Figure 1). Although statistical significance was reached in only some of the ROI, the overall pattern was consistent across ROI in this small pilot group. Conclusions: Differences in molecular markers of mitochondrial and synaptic function were seen in a pilot group of AD subjects recruited for the MINDMAPS-AD study. The differences are consistent with thea priori hypothesis (reductions in SV2A and MC1 with increases in s1R density). Evaluation of the full MINDMAPS-AD group, will clarify the magnitude of changes with AD pathology, and whether these molecular markers demonstrate significant change in a longitudinal assessment over 12 months.

P.310 Patients with major depressive disorder have lower cerebral serotonin 4 receptor binding than healthy controls

Article

Feb 2020
EUR NEUROPSYCHOPHARM

P.333 Obstetric outcomes in women with bipolar disorder treated with lithium in the perinatal period: a case-control study

Article

Feb 2020
EUR NEUROPSYCHOPHARM

Visualising the pulsing brain; a feasibility study combining MRI with transcranial tissue doppler (TCTD) ultrasound measurements

Conference Paper

Full-text available

Jul 2019

Objectives Previous studies of brain tissue motion have used either MRI,1,2 or a phased-array ultrasound probe3,4 to describe and quantify motion of the brain over the cardiac cycle. The brain is found to exhibit an initial sudden rostral movement after cardiac ejection followed by a longer period of caudal motion towards the brain centre. In 2018, Terem et al. introduced a new amplified MRI (aMRI) brain motion visualisation method, based on amplifying cardiac-gated MR images using a phase-based algorithm.2 This healthy subject feasibility study is the first to present complementary qualitative and quantitative information about brain tissue pulsation by combining T1-weighted imaging and aMRI with transcranial Tissue Doppler (TCTD) ultrasound measurements. Method MRI scans included a 3-plane localiser, 3-D T1-weighted imaging, aMRI cine acquisitions,2 and time-of-flight MR angiography. Pairs of fluid-filled markers were attached to the surface of the scalp to aid positioning of the ultrasound probe and visualisation of the path of the ultrasound beam using a 3D multi-planar reconstruction tool (Xinapse Systems, UK). Brain pulsation measurements were obtained using a prototype TCTD system developed in collaboration with Nihon Kohden (Japan). By combining anatomical information from MRI with pulsation waveforms measured using TCTD we were able to confidently visualise brain tissue motion over the cardiac cycle in relation to anatomy. Results MRI and TCTD measurements were successfully obtained from 5 subjects. Measured brain tissue pulsations confirmed similar displacement amplitudes as reported in previous ultrasound and MR studies [1, 4]. Comparison of brain tissue pulsations with anatomy revealed brain tissue regions with high levels of correlation separated by discontinuities between anatomical structures. Propagation of pulses from the centre of the brain to peripheral tissue was observed with peak displacement of tissue reached sooner at the ventricles (213 ± 33 ms) than at the frontal lobe (347 ± 60 ms). Conclusion This feasibility study is the first to combine anatomical and motion imaging from MRI with real-time quantitative assessment of brain tissue pulsations from TCTD. This revealed pronounced regional variations in pulsation waveforms associated with different anatomical structures within the brain and provides qualitative insights into the motion of healthy brains over the cardiac cycle. This information may be useful for guiding future studies comparing healthy brain motion with pathological brain motion in neurological disease states, such as traumatic brain injury, stroke, Chiari I malformation, hydrocephalus, and dementia.

The Effect of Selective Serotonin Reuptake Inhibitors in Healthy Subjects Revisited: A Systematic Review of the Literature

Article

Full-text available

Mar 2019

Selective serotonin reuptake inhibitors (SSRIs) are the first-line drugs in the treatment of depression. Investigations of the effects of SSRIs in healthy individuals is a useful model to understand the mechanisms of SSRI action and potentially the underlying pathophysiology of depression. We conducted an updated systematic review of all randomized multiple-dose, placebo-controlled trials on the effect of intervention with SSRI for ≥ 7 days in healthy nonpsychiatric subjects. Tables were drawn for characteristics of the trial, quality assessment, outcome measures, and the effect of intervention with SSRI. The search strategy identified a total of 51 placebo-controlled randomized trials investigating seven different SSRIs and 249 different outcome measures. Among trials, using the same outcome measure, most associations were either contradictory or statistically nonsignificant. Replication of statistically significant findings in two or more trials showed that SSRIs compared with placebo decreased divided attention, sustained attention network, negative affects, hostility, sleep quality, and platelet 5-HT content and further increased activity in the amygdala in relation to happy faces. Factors such as age, gender, family history of psychiatric disorder, and drug level influenced the findings but were rarely systematically investigated. The newly published retrieved trials fulfilled more criteria according to the CONSORT statement. This systematic review points to effects of SSRIs increasing positive emotional processing and decreasing divided and sustained attention besides physiological effects decreasing sleep quality and platelet 5-HT content in healthy subjects. Larger studies with a translational medicines approach with improved methodology are needed on the effects of SSRIs in healthy subjects. (PsycINFO Database Record (c) 2019 APA, all rights reserved).

Migraine is associated with high brain 5-HT levels as indexed by 5-HT 4 receptor binding

Article

Aug 2018

Introduction: Serotonin (5-HT) plays a role in migraine pathophysiology, but whether brain 5-HT is involved in the conversion from episodic to chronic migraine is unknown. Here, we investigated brain 5-HT levels, as indexed by 5-HT4 receptor binding, in chronic migraine patients and evaluated whether these were associated with migraine frequency. Methods: Sixteen chronic migraine patients underwent a dynamic PET scan after injection of [11C]SB207145, a specific 5-HT4 receptor radioligand. Data from 15 episodic migraine patients and 16 controls were included for comparison. Quantification of 5-HT4 receptor binding was used as a proxy for brain 5-HT levels, since 5-HT4 receptor binding is inversely related to brain 5-HT levels. Results: Chronic migraine patients had 9.1% (95% CI: [-17%; -1.0%]) lower 5-HT4 receptor binding compared to controls ( p = 0.039). There was no difference in 5-HT4 receptor binding between chronic and episodic migraine patients ( p = 0.48) and no association between number of monthly migraine days and 5-HT4 receptor binding (slope estimate 0.003, 95% CI: [-0.004; 0.715], p = 0.39). Conclusion: The finding of low 5-HT4 receptor binding suggests that cerebral levels of 5-HT are elevated in chronic migraine patients. This is in line with observations made in patients with episodic migraine. Elevated brain 5-HT levels may thus be an inherent trait of the migraine brain rather than a risk factor for conversion from episodic to chronic migraine.

Seasonality-resilient individuals downregulate their cerebral 5-HT transporter binding in winter – A longitudinal combined 11 C-DASB and 11 C-SB207145 PET study

Article

Aug 2018
EUR NEUROPSYCHOPHARM

We have recently shown that the emergence and severity of seasonal affective disorder (SAD) symptoms in the winter is associated with an increase in cerebral serotonin (5-HT) transporter (SERT) binding. Intriguingly, we also found that individuals resilient to SAD downregulate their cerebral SERT binding in the winter. In the present paper, we provide an analysis of the SERT- and 5-HT dynamics as indexed by 5-HT4 receptor (5-HT4R) binding related to successful stress coping. We included 46 11C-DASB positron emission tomography (PET) scans (N = 23, 13 women, age: 26 ± 6 years) and 14 11C-SB207145 PET scans (7 participants, 3 women, age: 25 ± 3 years) from 23 SAD-resilient Danes. Data was collected longitudinally in summer and winter. We found that compared to the summer, raphe nuclei and global brain SERT binding decreased significantly in the winter (praphe = 0.003 and pglobal = 0.003) and the two measures were positively correlated across seasons (summer: R2 = 0.33, p = .004, winter: R2 = 0.24, p = .018). A voxel-based analysis revealed prominent changes in SERT in clusters covering both angular gyri (0.0005 < pcorrected < 0.0016), prefrontal cortices (0.00087 < pcorrected < 0.0039) and the posterior temporal and adjacent occipital cortices (0.0001 < pcorrected < 0.0066). We did not observe changes in 5-HT4R binding, suggesting that 5-HT levels remained stable across seasons. We conclude that resilience to SAD is associated with a global downregulation of SERT levels in winter which serves to keep 5-HT levels across seasons.

Low Serum Testosterone in Outpatient Psychiatry Clinics: Addressing Challenges to the Screening and Treatment of Hypogonadism

Article

Nov 2017

Introduction: The symptoms of low testosterone frequently overlap with psychiatric complaints including depression and fatigue. Testosterone repletion has been shown to improve mood symptoms in men with low testosterone, although this finding has not been consistent across all studies. Despite the potential importance of low testosterone for psychiatry, the prevalence of low testosterone in men who present to psychiatric clinics with mental health complaints is unknown. Aim: To provide an overview of the current state of knowledge of the psychiatric complications of male hypogonadism, the challenges of screening for hypogonadism in a psychiatric population, and the potential mental health treatment implications of hypogonadism. Methods: A literature review was conducted using PubMed. Main outcome measures: Publications pertaining to the epidemiology, psychiatric symptomatology, and impact of treatment of male hypogonadism on psychiatric outcomes. Results: A review of the literature suggests a lack of information on the prevalence of low testosterone in patients presenting with psychiatric complaints despite an overlap in clinical symptoms. The identification of low testosterone could have a significant impact on treatment through urologic referral for testosterone repletion or the use of treatments that spare the gonadal axis. Conclusion: We hope our results will help those who care for patients in psychiatric settings to better assess for the presence of hypogonadism and its potential contribution to depressive illness. Smith JB, Rosen J, Colbert A. Low Serum Testosterone in Outpatient Psychiatry Clinics: Addressing Challenges to the Screening and Treatment of Hypogonadism. Sex Med Rev 2017;X:XXX-XXX.

Measuring endogenous changes in serotonergic neurotransmission in humans: A [11C] CUMI-101 PET challenge study

Article

Full-text available

Jun 2012

Serotonin (5-HT) neurotransmission is implicated in cognitive and emotional processes and a number of neuropsychiatric disorders. The use of positron emission tomography (PET) to measure ligand displacement has allowed estimation of endogenous dopamine release in the human brain; however, applying this methodology to assess central 5-HT release has proved more challenging. The aim of this study was to assess the sensitivity of a highly selective 5-HT 1A partial agonist radioligand [11C] CUMI-101 to changes in endogenous 5-HT levels induced by an intravenous challenge with the selective 5-HT re-uptake inhibitor (SSRI), citalopram, in healthy human participants. We studied 15 healthy participants who underwent PET scanning in conjunction with [11C] CUMI-101 after receiving an intravenous infusion of citalopram 10 mg or placebo in a double-blind, crossover, randomized design. Regional estimates of binding potential (BPND) were obtained by calculating total volumes of distribution (V T) for presynaptic dorsal raphe nucleus (DRN) and postsynaptic cortical regions. Relative to placebo, citalopram infusion significantly increased [11C] CUMI-101 BP ND at postsynaptic 5-HT1A receptors in several cortical regions, but there was no change in binding at 5-HT1A autoreceptors in the DRN. Across the postsynaptic brain regions, citalopram treatment induced a mean 7% in [ 11C] CUMI-101 BPND (placebo 1.3 (0.2); citalopram 1.4 (0.2); paired t-test P0.003). The observed increase in postsynaptic [ 11C] CUMI-101 availability identified following acute citalopram administration could be attributable to a decrease in endogenous 5-HT availability in cortical terminal regions, consistent with preclinical animal studies, in which acute administration of SSRIs decreases DRN cell firing through activation of 5-HT1A autoreceptors to reduce 5-HT levels in postsynaptic regions. We conclude that [11C] CUMI-101 may be sensitive to changes in endogenous 5-HT release in humans.

Spatial resolution of the HRRT PET scanner using 3D-OSEM PSF reconstruction

Conference Paper

Full-text available

Dec 2009

In this paper, the resolution of the Siemens high resolution research tomograph (HRRT) was centrally (r < 60 mm) homogenous with a FWHM of 1.4 mm for <sup>18</sup>F-FDG in air. This was where the main part of the brain is located if the patient has been positioned correctly. The 1.4 mm resolution was obtained using the newly develop 3D-OSEM PSF reconstruction algorithm, which was a significant improvement over 3D-OSEM reconstruction without PSF. The algorithm uses a simple PSF model that was the same for all the pixels in the FOV and does not regulate for the circular/octagonal scanner geometry. This supports that the FWHM of the radial axis is increasing with the distance from the center for r > 60mm.

Genetic variation in 5-hydroxytryptamine transporter expression causes adaptive changes in 5-HT4 receptor levels

Article

Full-text available

Aug 2011
INT J NEUROPSYCHOPH

Genetic variation in 5-HT transporter (5-HTT) expression is a key risk factor for psychiatric disorder and has been linked to changes in the expression of certain 5-HT receptor subtypes. This study investigated the effect of variation in 5-HTT expression on 5-HT₄ receptor levels in both 5-HTT knockout (KO) and overexpressing (OE) mice using autoradiography with the selective 5-HT₄ receptor radioligand, [³H]SB207145. Compared to wild-type (5-HTT⁺/⁺) controls, homozygous 5-HTT KO mice (5-HTT⁻/⁻) had reduced 5-HT₄ receptor binding site density in all brain regions examined (35-65% of 5-HTT⁺/⁺). In contrast, the density of 5-HT₄ receptor binding sites was not significantly different between heterozygous 5-HTT KO mice (5-HTT⁻/⁺) and 5-HTT⁺/⁺ mice. The 5-HT synthesis inhibitor p-chlorophenylalanine (250 mg/kg twice daily for 3 d) abolished the difference in 5-HT₄ binding between 5-HTT⁻/⁻ and 5-HTT⁺/⁺ mice in all brain regions. Compared to wild-type (WT) littermate controls, 5-HTT OE mice had increased 5-HT₄ binding density across all brain regions, except amygdala (118-164% of WT) and this difference between genotypes was reduced by the 5-HTT inhibitor, fluoxetine (20 mg/kg twice daily, 3 d). Together, these findings suggest that variation in 5-HTT expression causes adaptive changes in 5-HT₄ receptor levels which are directly linked to alterations in 5-HT availability.

Paterson LM, Tyacke RJ, Nutt DJ, Knudsen GMMeasuring endogenous 5-HT release by emission tomography: promises and pitfalls. J Cereb Blood Flow Metab 30:1682-1706

Article

Full-text available

Oct 2010
J CEREBR BLOOD F MET

Molecular in vivo neuroimaging techniques can be used to measure regional changes in endogenous neurotransmitters, evoked by challenges that alter synaptic neurotransmitter concentration. This technique has most successfully been applied to the study of endogenous dopamine release using positron emission tomography, but has not yet been adequately extended to other neurotransmitter systems. This review focuses on how the technique has been applied to the study of the 5-hydroxytryptamine (5-HT) system. The principles behind visualising fluctuations in neurotransmitters are introduced, with reference to the dopaminergic system. Studies that aim to image acute, endogenous 5-HT release or depletion at 5-HT receptor targets are summarised, with particular attention to studies in humans. Radiotracers targeting the 5-HT(1A), 5-HT(2A), and 5-HT(4) receptors and the serotonin reuptake transporter have been explored for their sensitivity to 5-HT fluctuations, but with mixed outcomes; tracers for these targets cannot reliably image endogenous 5-HT in humans. Shortcomings in our basic knowledge of the mechanisms underlying changes in binding potential are addressed, and suggestions are made as to how the selection of targets, radiotracers, challenge paradigms, and experimental design might be optimised to improve our chances of successfully imaging endogenous neurotransmitters in the future.

Kinetic Modeling of C-11-SB207145 Binding to 5-HT4 Receptors in the Human Brain In Vivo

Article

Full-text available

Jul 2009

The serotonin 4 receptor (5-HT(4) receptor) is known to be involved in learning and memory. We evaluated for the first time the quantification of a novel 5-HT(4) receptor radioligand, (11)C-SB207145, for in vivo brain imaging with PET in humans. For evaluation of reproducibility, 6 subjects were scanned twice with (11)C-SB207145 on the same day. A further 2 subjects were scanned before and after blocking with the selective 5-HT(4) receptor inverse agonist piboserod (SB207266). Arterial blood samples were drawn for the calculation of metabolite-corrected arterial input functions. Regions of interest were delineated automatically on the individual's MR images coregistered to the PET images, and regional time-activity curves were extracted. Quantitative tracer kinetic modeling was investigated with 1- and 2-tissue-compartment models using plasma input functions and the simplified reference tissue model (SRTM). (11)C-SB207145 readily entered the brain and showed a distribution consistent with the known localization of the 5-HT(4) receptor. Using plasma input models, the time-activity data were well described by the 2-tissue-compartment model in all regions and allowed for the estimate of binding potentials relative to the reference region (BP(ND): striatum, 3.38 +/- 0.72; hippocampus, 0.82 +/- 0.19; parietal cortex, 0.30 +/- 0.08). Quantification with the 1-tissue-compartment model, 2-tissue-compartment model, and SRTM were associated with good test-retest reproducibility and time stability. However, the SRTM-generated BP(ND) values in the striatum were underestimated by 20%-43% in comparison to the 2-tissue-compartment model. The blocking study with piboserod confirmed that the radioligand was selective for the 5-HT(4) receptor, that the cerebellum was a suitable reference region devoid of specific binding, and that nonspecific binding was constant across brain regions. In vivo imaging of cerebral 5-HT(4) receptors can be determined reliably using (11)C-207145 PET with arterial input in humans. SRTM showed high reproducibility and reliability but bias in the striatum, and therefore, the use of SRTM should be considered carefully for individual applications.

Association of Anxiety-Related Traits with a Polymorphism in the Serotonin Transporter Gene Regulatory Region

Article

Full-text available

Dec 1996

Transporter-facilitated uptake of serotonin (5-hydroxytryptamine or 5-HT) has been implicated in anxiety in humans and animal models and is the site of action of widely used uptake-inhibiting antidepressant and antianxiety drugs. Human 5-HT transporter (5-HTT) gene transcription is modulated by a common polymorphism in its upstream regulatory region. The short variant of the polymorphism reduces the transcriptional efficiency of the 5-HTT gene promoter, resulting in decreased 5-HTT expression and 5-HT uptake in lymphoblasts. Association studies in two independent samples totaling 505 individuals revealed that the 5-HTT polymorphism accounts for 3 to 4 percent of total variation and 7 to 9 percent of inherited variance in anxiety-related personality traits in individuals as well as sibships.

Dose escalation for insufficient response to standard-dose selective serotonin reuptake inhibitors in major depressive disorder - Systematic review

Article

Full-text available

Nov 2006

Although selective serotonin reuptake inhibitors (SSRIs) are frequently used for major depressive disorder, only 50-60% of patients respond to a standard dose. For non-responders, dose escalation is often applied. To systematically review the evidence for dose escalation of SSRIs. A systematic literature search in MEDLINE, EMBASE, CINAHL and PsycInfo was performed. Randomised controlled trials and meta-analyses investigating dose escalation of SSRIs were identified. Relevant articles were retrieved and critically appraised. Results were summarised in an evidence table. Pooling was not justified because of heterogeneity of the identified studies. Eight true dose-escalation studies and three meta-analyses were identified. The available data provided no unequivocal base for dose escalation. Dose escalation before 4 weeks of treatment at a standard dose appeared to be ineffective. Dose escalation of SSRIs is equivocally supported by evidence of randomised controlled trials; methodological difficulties in the studies may account for this lack of evidence.

Impact of Image-Space Resolution Modeling for Studies with the High-Resolution Research Tomograph

Article

Full-text available

Jul 2008

Brain PET in small structures is challenged by low resolution inducing bias in the activity measurements. Improved spatial resolution may be obtained by using dedicated tomographs and more comprehensive modeling of the acquisition system during reconstruction. In this study, we assess the impact of resolution modeling (RM) during reconstruction on image quality and on the estimates of biologic parameters in a clinical study performed on a high-resolution research tomograph. An accelerated list-mode ordinary Poisson ordered-subset expectation maximization (OP-OSEM) algorithm, including sinogram-based corrections and an experimental stationary model of resolution, has been designed. Experimental phantom studies are used to assess contrast and noise characteristics of the reconstructed images. The binding potential of a selective tracer of the dopamine transporter is also assessed in anatomic volumes of interest in a 5-patient study. In the phantom experiment, a slower convergence and a higher contrast recovery are observed for RM-OP-OSEM than for OP-OSEM for the same level of statistical noise. RM-OP-OSEM yields contrast recovery levels that could not be reached without RM as well as better visual recovery of the smallest spheres and better delineation of the structures in the reconstructed images. Statistical noise has lower variance at the voxel level with RM than without at matched resolution. In a uniform activity region, RM induces higher positive and lower negative correlations with neighboring voxels, leading to lower spatial variance. Clinical images reconstructed with RM demonstrate better delineation of cortical and subcortical structures in both time-averaged and parametric images. The binding potential in the striatum is also increased, a result similar to the one observed in the phantom study. In high-resolution PET, RM during reconstruction improves quantitative accuracy by reducing the partial-volume effects.

Effect of a single dose of escitalopram on serotonin concentration in the non-human and human primate brain

Article

Jan 2013
INT J NEUROPSYCHOPH

The UKU side effect rating scale for psychotropic drugs and a cross-sectional study of side effects in neuroleptic-treated patients

Article

Jan 1987
ACTA PSYCHIAT SCAND

Quantitative analysis of multiple psychotherapeutic drugs in human serum using UPLC-MS/MS

Conference Paper

Jun 2008
THER DRUG MONIT

The 5-HT4 Receptor Levels in Hippocampus Correlates Inversely With Memory Test Performance in Humans

Article

Nov 2013
HUM BRAIN MAPP

The cerebral serotonin (5-HT) system is involved in cognitive functions such as memory and learning and animal studies have repeatedly shown that stimulation of the 5-HT type 4 receptor (5-HT(4) R) facilitates memory and learning and further that the 5-HT(4) R modulates cellular memory processes in hippocampus. However, any associations between memory functions and the expression of the 5-HT(4) R in the human hippocampus have not been investigated. Using positron emission tomography with the tracer [(11) C]SB207145 and Reys Auditory Verbal Learning Test we aimed to examine the individual variation of the 5-HT4R binding in hippocampus in relation to memory acquisition and consolidation in healthy young volunteers. We found significant, negative associations between the immediate recall scores and left and right hippocampal BP(ND) , (p = 0.009 and p = 0.010 respectively) and between the right hippocampal BP(ND) and delayed recall (p = 0.014). These findings provide evidence that the 5-HT(4) R is associated with memory functions in the human hippocampus and potentially pharmacological stimulation of the receptor may improve episodic memory. Hum Brain Mapp, 2012. © 2012 Wiley Periodicals, Inc.

No change in [11C]CUMI-101 binding to 5-HT1A receptors after intravenous citalopram in human

Article

Oct 2012
SYNAPSE

The main objective of this study was to determine the sensitivity of [¹¹C]CUMI-101 to citalopram challenge aiming at increasing extracellular 5-HT. CUMI-101 has agonistic properties in human embryonic kidney 293 cells transfected with human recombinant 5-HT(1A) receptors (Hendry et al. [2011] Nucl Med Biol 38:273-277; Kumar et al. [2006] J Med Chem 49:125-134) and has previously been demonstrated to be sensitive to bolus citalopram in monkeys (Milak et al. [2011] J Cereb Blood Flow Metab 31:243-249). We studied six healthy individuals. Two PET-scans were performed on the same day in each individual before and after constant infusion of citalopram (0.15 mg/kg). The imaging data were analyzed using two tissue compartment kinetic modeling with metabolite corrected arterial input and Simplified Reference Tissue Modeling using cerebellum as a reference region. There was no significant difference in regional distribution volume or non-displaceable binding potential values before and after citalopram infusion. The mean receptor occupancy was 0.03 (range -0.14 to 0.17). Our data imply that [¹¹C]CUMI-101 binding is not sensitive to citalopram infusion in humans.

Obesity is associated with high serotonin 4 receptor availability in the brain reward circuitry

Article

Mar 2012
NEUROIMAGE

The neurobiology underlying obesity is not fully understood. The neurotransmitter serotonin (5-HT) is established as a satiety-generating signal, but its rewarding role in feeding is less well elucidated. From animal experiments there is now evidence that the 5-HT(4) receptor (5-HT(4)R) is involved in food intake, and that pharmacological or genetic manipulation of the receptor in reward-related brain areas alters food intake. Here, we used positron emission tomography in humans to examine the association between cerebral 5-HT(4)Rs and common obesity. We found in humans a strong positive association between body mass index and the 5-HT(4)R density bilaterally in the two reward ‘hot spots’ nucleus accumbens and ventral pallidum, and additionally in the left hippocampal region and orbitofrontal cortex. These findings suggest that the 5-HT(4)R is critically involved in reward circuits that regulate people's food intake. They also suggest that pharmacological stimulation of the cerebral 5-HT(4)R may reduce reward-related overeating in humans.

5-HTTLPR status predictive of neocortical 5-HT4 binding assessed with [11C]SB207145 PET in humans

Article

May 2012
NEUROIMAGE

Serotonin (5-HT) is a neuromodulator affecting myriad aspects of personality and behavior and has been implicated in the pathophysiology of affective disorders including depression and anxiety. The 5-HTTLPR is a common genetic polymorphism within the promoter region of the gene coding for the serotonin transporter such that the S allele is associated with reduced transcriptional efficacy compared to the L allele, potentially contributing to increased serotonin levels. In humans, this genetic variant has been linked to inter-individual variability in risk for affective disorders, related aspects of personality and brain function including response to threat. However, its effects on aspects of serotonin signaling in humans are not fully understood. Studies in animals suggest that the 5-HT 4 receptor (5-HT(4)) shows a monotonic inverse association with long-term changes in serotonin levels indicating that it may be a useful measure for identifying differences in serotonergic neurotransmission. In 47 healthy adults we evaluated the association between 5-HTTLPR status and in vivo 5-HT(4) receptor binding assessed with [(11)C]SB207145 positron emission tomography (PET). We observed a significant association within the neocortex where [(11)C]SB207145 binding was 9% lower in S carriers compared to LL homozygotes. We did not find evidence for an effect of season or a season-by-5-HTTLPR interaction effect on regional [(11)C]SB207145 binding. Our findings are consistent with a model wherein the 5-HTTLPR S allele is associated with relatively increased serotonin levels. These findings provide novel evidence supporting an effect of 5-HTTLPR status on serotonergic neurotransmission in adult humans. There were no indications of seasonal effects on serotonergic neurotransmission.

Non-adherence and non-response in the treatment of anxiety disorders

Article

Feb 2012

Mass dose effects and in vivo affinity in brain PET receptor studies — a study of cerebral 5-HT4 receptor binding with [11C]SB207145

Article

Aug 2011

Attention to tracer dose principles is crucial in positron emission tomography (PET), and deviations can induce serious errors. In this study, we devise a method for determining receptor occupancy of the mass dose of the radioligand itself and the in vivo affinity. The approach was used for [(11)C]SB207145, a new PET radioligand for imaging the cerebral 5-HT(4) receptors in humans. Test-retest PET studies with varying specific activities of [(11)C]SB207145 were conducted in seven healthy subjects, and the output parameter regional BP(ND) was modeled. Individual occupancy plots were first computed to estimate the mass dose that saturates 50% of receptors (ID(50)), and subsequently, the maximal mass dose that can be injected (arbitrarily set at an occupancy <5%) was calculated. Scatchard plots were computed to estimate the in vivo K(D). Increasing the mass dose resulted in a decrease in BP(ND), whilst the relative cerebellar uptake was unchanged. The ID(50) was 85.4±30.2 μg, and the upper mass dose limit was 4.5±1.6 μg, which does not require ultrahigh specific activity. The estimated in vivo K(D) was 2.8 nM (range 1.0-4.8), without any regional differences. The presented method for estimating the upper mass dose limit is suggested as part of validation of PET radioligands.

Reduced signal transduction by 5-HT4 receptors after long-term venlafaxine treatment in rats

Article

Oct 2010
BRIT J PHARMACOL

The 5-HT(4) receptor may be a target for antidepressant drugs. Here we have examined the effects of the dual antidepressant, venlafaxine, on 5-HT(4) receptor-mediated signalling events. The effects of 21 days treatment (p.o.) with high (40 mg·kg(-1)) and low (10 mg·kg(-1)) doses of venlafaxine, were evaluated at different levels of 5-HT(4) receptor-mediated neurotransmission by using in situ hybridization, receptor autoradiography, adenylate cyclase assays and electrophysiological recordings in rat brain. The selective noradrenaline reuptake inhibitor, reboxetine (10 mg·kg(-1), 21 days) was also evaluated on 5-HT(4) receptor density. Treatment with a high dose (40 mg·kg(-1)) of venlafaxine did not alter 5-HT(4) mRNA expression, but decreased the density of 5-HT(4) receptors in caudate-putamen (% reduction = 26 ± 6), hippocampus (% reduction = 39 ± 7 and 39 ± 8 for CA1 and CA3 respectively) and substantia nigra (% reduction = 49 ± 5). Zacopride-stimulated adenylate cyclase activation was unaltered following low-dose treatment (10 mg·kg(-1)) while it was attenuated in rats treated with 40 mg·kg(-1) of venlafaxine (% reduction = 51 ± 2). Furthermore, the amplitude of population spike in pyramidal cells of CA1 of hippocampus induced by zacopride was significantly attenuated in rats receiving either dose of venlafaxine. Chronic reboxetine did not modify 5-HT(4) receptor density. Our data indicate a functional desensitization of 5-HT(4) receptors after chronic venlafaxine, similar to that observed after treatment with the classical selective inhibitors of 5-HT reuptake.

Seasonal Changes in Brain Serotonin Transporter Binding in Short Serotonin Transporter Linked Polymorphic Region-Allele Carriers but Not in Long-Allele Homozygotes

Article

Jun 2010

A polymorphism in the promoter region of the serotonin transporter gene (5-HTTLPR) has been associated with seasonality both in patients with seasonal affective disorder and in the general population. We used in vivo molecular imaging to measure cerebral serotonin transporter (5-HTT) binding in 57 healthy Scandinavians and related the outcome to season of the year and to the 5-HTTLPR carrier status. We found that the number of daylight minutes at the time of scanning correlated negatively with 5-HTT binding in the putamen and the caudate, with a similar tendency in the thalamus, whereas this association was not observed for the midbrain. Furthermore, in the putamen, an anatomic region with relatively dense serotonin innervation, we found a significant gene x daylight effect, such that there was a negative correlation between 5-HTT binding and daylight minutes in carriers of the short 5-HTTLPR allele but not in homozygote carriers of the long allele. Our findings are in line with S-carriers having an increased response in neural circuits involved in emotional processing to stressful environmental stimuli but here demonstrated as a endophenotype with dynamic changes in serotonin reuptake.

Brain imaging of serotonin 4 receptors in humans with [11C]SB207145-PET

Article

Apr 2010
NEUROIMAGE

Pharmacological stimulation of the serotonin 4 (5-HT(4)) receptor has shown promise for treatment of Alzheimer's disease and major depression. A new selective radioligand, [(11)C]SB207145, for positron emission tomography (PET) was used to quantify brain 5-HT(4) receptors in sixteen healthy subjects (20-45 years, 8 males) using the simplified reference tissue model. We tested within our population the effect of age and other demographic factors on the endpoint. In seven subjects, we tested the vulnerability of radioligand binding to a pharmacolological challenge with citalopram, which is expected to increase competition from endogenous serotonin. Given radiotracer administration at a range of specific activities, we were able to use the individual BP(ND) measurements for population-based estimation of the saturation binding parameters; B(max) ranged from 0.3 to 1.6 nM. B(max) was in accordance with post-mortem brain studies (Spearman's r=0.83, p=0.04), and the regional binding potentials, BP(ND), were on average 2.6 in striatum, 0.42 in prefrontal cortex, and 0.91 in hippocampus. We found no effect of sex but a decreased binding with age (p=0.046). A power analysis showed that, given the low inter-and intrasubject variation, use of the present method will enable detection of a 15% difference in striatum with only 7-13 subjects in a 2-sample test and with only 4-5 subjects in a paired test. The citalopram challenge did not discernibly alter [(11)C]SB207145 binding. In conclusion, the 5-HT(4) receptor binding in human brain can be reliably assessed with [(11)C]SB207145, which is encouraging for future PET studies of drug occupancy or patients with neuropsychiatric disorders.

A longitudinal study of 5-HT outflow during chronic fluoxetine treatment using a new technique of chronic microdialysis in a highly emotional mouse strain

Article

Nov 2009

The onset of a therapeutic response to antidepressant treatment exhibits a delay of several weeks. The present study was designed to know whether extracellular serotonin (5-HT) levels need to be increased in territories of 5-HT innervation in order to obtain beneficial effects from a chronic treatment with a serotonin-selective reuptake inhibitor (SSRI). Thus, we performed a longitudinal study of a chronic fluoxetine treatment in a model of highly emotional mice (BALB/cJ). The function of the 5-HT system in the raphe nuclei and hippocampus, was assessed by using repeated in vivo microdialysis sessions in awake freely moving mice, then studying its relation with behavior, analyzed mainly with open field paradigm. One of the neural mechanisms underlying such delay has been proposed to be the functional status of 5-HT1A autoreceptors in raphe nuclei. Thus, we also assessed the degree of 5-HT1A autoreceptor desensitization by using a local infusion in the raphe of the antagonist, WAY 100635 via reverse microdialysis. We report that the anxiolytic-like effects of fluoxetine correlate in time and amplitude with 5-HT1A autoreceptor desensitization, but neither with the extracellular levels of 5-HT in the raphe nuclei, nor in the hippocampus. Our study suggests that the beneficial anxiolytic/antidepressant-like effects of chronic SSRI treatment indeed depend on 5-HT1A autoreceptor internalization, but do not require a sustained increase in extracellular 5-HT levels in a territory of 5-HT projection such as hippocampus.

Long-term treatment with fluoxetine induces desensitization of 5-HT4 receptor-dependent signalling and functionality in rat brain

Article

Jul 2009
J NEUROCHEM

The mode of action of antidepressant drugs may be related to mechanisms of monoamines receptor adaptation, including serotonin 5-HT(4) receptor subtypes. Here we investigated the effects of repeated treatment with the selective serotonin reuptake inhibitor fluoxetine for 21 days (5 and 10 mg/kg, p.o., once daily) on the sensitivity of 5-HT(4) receptors by using receptor autoradiography, adenylate cyclase assays and extracellular recording techniques in rat brain. Fluoxetine treatment decreased the density of 5-HT(4) receptor binding in the CA1 field of hippocampus as well as in several areas of the striatum over the doses of 5-10 mg/kg. In a similar way, we found a significant lower response to zacopride-stimulated adenylate cyclase activity in the fluoxetine 10 mg/kg/day treated group. Furthermore, post-synaptic 5-HT(4) receptor activity in hippocampus-measured as the excitatory action of zacopride in the pyramidal cells of CA1 evoked by Schaffer collateral stimulation was attenuated in rats treated with both doses of fluoxetine. Taken together, these results support the concept that a net decrease in the signalization pathway of 5-HT(4) receptors occurs after chronic selective serotonin reuptake inhibitor treatment: this effect may underlie the therapeutic efficacy of these drugs.

Licht CL, Marcussen AB, Wegener G, Overstreet DH, Aznar S, Knudsen GM. The brain 5-HT4 receptor binding is down-regulated in the Flinders Sensitive Line depression model and in response to paroxetine administration. J Neurochem 109: 1363-1374

Article

Jul 2009
J NEUROCHEM

The 5-hydroxytryptamine (5-HT(4)) receptor may be implicated in depression and is a new potential target for antidepressant treatment. We have investigated the brain 5-HT(4) receptor [(3)H]SB207145 binding in the Flinders Sensitive Line rat depression model by quantitative receptor autoradiography, and related this to 5-HT transporter (S)-[N-methyl-(3)H]citalopram binding. We also determined the regulation of 5-HT(4) receptor binding by 1, 14, and 21 days of paroxetine administration and subchronic 5-HT depletion, and compared this with changes in 5-HT(2A) receptor [(3)H]MDL100907 binding. In the Flinders Sensitive Line, the 5-HT(4) receptor and 5-HT transporter binding were decreased in the dorsal and ventral hippocampus, and the changes in binding were directly correlated within the dorsal hippocampus. Chronic but not acute paroxetine administration caused a 16-47% down-regulation of 5-HT(4) receptor binding in all regions evaluated including the basal ganglia and hippocampus, while 5-HT depletion increased the 5-HT(4) receptor binding in the dorsal hippocampus, hypothalamus, and lateral globus pallidus. In comparison, the 5-HT(2A) receptor binding was decreased in the frontal and cingulate cortices after chronic paroxetine administration, and markedly reduced in several regions after 5-HT depletion. Thus, the 5-HT(4) receptor binding was decreased in the Flinders Sensitive Line depression model and in response to chronic paroxetine administration.

Fluvoxamine Preferentially Increases Extracellular 5-Hydroxytryptamine in the Raphe Nuclei – an Invivo Microdialysis Study

Article

Jan 1993
EUR J PHARMACOL

The effects of systemic administration of fluvoxamine on extracellular serotonin (5-hydroxytryptamine, 5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) concentrations in the frontal cortex and raphe nuclei of freely moving rats were examined. Fluvoxamine significantly increased extracellular 5-HT concentrations in both regions at the two doses used (1 and 10 mg/kg i.p.). However, the increase in the raphe nuclei was several-fold that in the frontal cortex. Dialysate 5-HIAA concentrations decreased after treatment with fluvoxamine. These results confirm that 5-HT uptake inhibitors preferentially increase extracellular concentrations of 5-HT in the vicinity of cell bodies and dendrites of serotonergic neurones.

Citalopram's ability to increase the extracellular concentrations of serotonin in the dorsal raphe prevents the drug's effect in the frontal cortex

Article

Aug 1992
BRAIN RES

Administered intraperitoneally to rats at 1 mg/kg, citalopram, a potent and selective inhibitor of serotonin uptake, significantly increased dialysate serotonin in the dorsal raphe, but not in the frontal cortex. At 10 mg/kg citalopram had a greater effect on raphe serotonin and a moderate and short-lasting increase in the dialysate serotonin in the frontal cortex. Citalopram 1 mg/kg i.p. significantly increased the extracellular concentration of serotonin in the frontal cortex of rats which had received a continuous infusion of 1 microM methiothepine in the dorsal raphe, a condition which by itself did not change cortical serotonin concentrations. The results suggest that the ability of serotonin uptake inhibitors to enhance the extracellular concentrations of serotonin in the dorsal raphe attenuates the drug's effect in the frontal cortex.

Rapid Automated Algorithm for Aligning and Reslicing PET Images

Article

Jul 1992

A computer algorithm for the three-dimensional (3D) alignment of PET images is described. To align two images, the algorithm calculates the ratio of one image to the other on a voxel-by-voxel basis and then iteratively moves the images relative to one another to minimize the variance of this ratio across voxels. Since the method relies on anatomic information in the images rather than on external fiducial markers, it can be applied retrospectively. Validation studies using a 3D brain phantom show that the algorithm aligns images acquired at a wide variety of positions with maximum positional errors that are usually less than the width of a voxel (1.745 mm). Simulated cortical activation sites do not interfere with alignment. Global errors in quantitation from realignment are less than 2%. Regional errors due to partial volume effects are largest when the gantry is rotated by large angles or when the bed is translated axially by one-half the interplane distance. To minimize such partial volume effects, the algorithm can be used prospectively, during acquisition, to reposition the scanner gantry and bed to match an earlier study. Computation requires 3-6 min on a Sun SPARCstation 2.

The UKU side effect rating scale: A new comprehensive rating scale for psychotropic drugs and a cross-sectional study of side effects in neuroleptic-treated patients

Article

Feb 1987
Acta Psychiatr Scand Suppl

The monoaminergic innervation of primate cortex

Article

Feb 1986
Hum Neurobiol

In brain, the monoamines, dopamine, norepinephrine, and serotonin, are confined to anatomically distinct neuronal systems, each of which furnishes widespread projections to neocortex. In primate, but not in rat, the terminal patterns of each of these systems have a high degree of regional and laminar specificity. These findings suggest that there are different sites of action and possibly different functional roles for each of the monoamines. This type of precise anatomic information is essential to our understanding of the possible involvement of monoamines in human disease states.

The pharmacologic profile of fluoxetine

Article

Apr 1985

Fluoxetine is a selective inhibitor of serotonin uptake in vitro. Unlike many antidepressant drugs, fluoxetine has little affinity for muscarinic, histaminic H1, serotonergic 5-HT1 or 5-HT2, or noradrenergic alpha 1 or alpha 2 receptors on rat brain membranes in vitro. Fluoxetine inhibits serotonin uptake in vivo without affecting norepinephrine uptake. Neuroendocrine and behavioral consequences of enhanced serotonergic function resulting from fluoxetine's inhibition of serotonin uptake in vivo are described. Fluoxetine is relatively nontoxic in several animal species. The specificity of action of fluoxetine makes it a good candidate as an antidepressant drug.

A Global Measure of Perceived Stress

Article

Jan 1984

This paper presents evidence from three samples, two of college students and one of participants in a community smoking-cessation program, for the reliability and validity of a 14-item instrument, the Perceived Stress Scale (PSS), designed to measure the degree to which situations in one's life are appraised as stressful. The PSS showed adequate reliability and, as predicted, was correlated with life-event scores, depressive and physical symptomatology, utilization of health services, social anxiety, and smoking-reduction maintenance. In all comparisons, the PSS was a better predictor of the outcome in question than were life-event scores. When compared to a depressive symptomatology scale, the PSS was found to measure a different and independently predictive construct. Additional data indicate adequate reliability and validity of a four-item version of the PSS for telephone interviews. The PSS is suggested for examining the role of nonspecific appraised stress in the etiology of disease and behavioral disorders and as an outcome measure of experienced levels of stress.

Comparison of Direct Interview and Family History Diagnoses of Alcohol Dependence

Article

Sep 1995

Central 5-HT4 receptor binding as biomarker of serotonergic tonus in humans: A [11C]SB207145 PET study

Abstract

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