Serotonin transporter binding in bipolar disorder assessed using [11C]DASB and positron emission tomography

Positron emission tomography quantification of serotonin transporter in suicide attempters with major depressive disorder

BACKGROUND

Several lines of evidence implicate abnormal serotonergic function in suicidal behavior and completed suicide, including low serotonin transporter binding in postmortem studies of completed suicide. We have also reported low in vivo serotonin transporter binding in major depressive disorder (MDD) during a major depressive episode using positron emission tomography (PET) with [(11)C]McN5652. We quantified regional brain serotonin transporter binding in vivo in depressed suicide attempters, depressed nonattempters, and healthy controls using PET and a superior radiotracer, [(11)C]DASB.

METHODS

Fifty-one subjects with DSM-IV current MDD, 15 of whom were past suicide attempters, and 32 healthy control subjects underwent PET scanning with [(11)C]DASB to quantify in vivo regional brain serotonin transporter binding. Metabolite-corrected arterial input functions and plasma free-fraction were acquired to improve quantification.

RESULTS

Depressed suicide attempters had lower serotonin transporter binding in midbrain compared with depressed nonattempters (p = .031) and control subjects (p = .0093). There was no difference in serotonin transporter binding comparing all depressed subjects with healthy control subjects considering six a priori regions of interest simultaneously (p = .41).

CONCLUSIONS

Low midbrain serotonin transporter binding appears to be related to the pathophysiology of suicidal behavior rather than of major depressive disorder. This is consistent with postmortem work showing low midbrain serotonin transporter binding capacity in depressed suicides and may partially explain discrepant in vivo findings quantifying serotonin transporter in depression. Future studies should investigate midbrain serotonin transporter binding as a predictor of suicidal behavior in MDD and determine the cause of low binding.

Clinical application of brain imaging for the diagnosis of mood disorders: the current state of play

In response to queries about whether brain imaging technology has reached the point where it is useful for making a clinical diagnosis and for helping to guide treatment selection, the American Psychiatric Association (APA) has recently written a position paper on the Clinical Application of Brain Imaging in Psychiatry. The following perspective piece is based on our contribution to this APA position paper, which specifically emphasized the application of neuroimaging in mood disorders. We present an introductory overview of the challenges faced by researchers in developing valid and reliable biomarkers for psychiatric disorders, followed by a synopsis of the extant neuroimaging findings in mood disorders, and an evidence-based review of the current research on brain imaging biomarkers in adult mood disorders. Although there are a number of promising results, by the standards proposed below, we argue that there are currently no brain imaging biomarkers that are clinically useful for establishing diagnosis or predicting treatment outcome in mood disorders.

Gender-specific abnormalities in the serotonin transporter system in panic disorder

The central serotonergic system has been implicated in the pathophysiology of panic disorder (PD) by evidence of abnormally elevated serotonin-turnover, reduced pre- and post-synaptic 5-HT(1A)-receptor sensitivity and binding and clinical improvement during administration of agents that enhance serotonergic transmission. Polymorphisms in genes that putatively influence serotonergic neurotransmission increase the vulnerability for developing PD specifically in males. We tested the hypotheses that serotonin transporter (5-HTT) binding is elevated in PD subjects vs. healthy controls in regions where in vivo evidence exists for both elevated 5-HTT and 5-HT(1A) receptor levels in PD and investigated whether the extent of this difference depends upon gender. Volunteers were out-patients with current PD (n=24) and healthy controls (n=24). The non-displaceable component of 5-HTT binding-potential (BP(ND)) was measured using positron emission tomography and the 5-HTT selective radioligand, [(11)C]DASB. PD severity was assessed using the PD Severity Scale. The 5-HTT-BP(ND) was increased in males with PD relative to male controls in the anterior cingulate cortex (F=8.96, p(FDR)=0.01) and midbrain (F=5.09, p(FDR)=0.03). In contrast, BP(ND) did not differ between females with PD and female controls in any region examined. The finding that 5-HTT-binding is elevated in males but not in females with PD converges with other evidence suggesting that dysfunction within the central serotonergic system exists in PD, and also indicates that such abnormalities are influenced by gender. These findings conceivably may reflect a sexual dimorphism that underlies the greater efficacy of serotonin reuptake inhibitor treatment in females vs. males with PD.

Temperament, character and serotonin activity in the human brain: a positron emission tomography study based on a general population cohort

BACKGROUND

The psychobiological model of personality by Cloninger and colleagues originally hypothesized that interindividual variability in the temperament dimension 'harm avoidance' (HA) is explained by differences in the activity of the brain serotonin system. We assessed brain serotonin transporter (5-HTT) density in vivo with positron emission tomography (PET) in healthy individuals with high or low HA scores using an 'oversampling' study design. Method Subjects consistently in either upper or lower quartiles for the HA trait were selected from a population-based cohort in Finland (n = 2075) with pre-existing Temperament and Character Inventory (TCI) scores. A total of 22 subjects free of psychiatric and somatic disorders were included in the matched high- and low-HA groups. The main outcome measure was regional 5-HTT binding potential (BPND) in high- and low-HA groups estimated with PET and [11C]N,N-dimethyl-2-(2-amino-4-methylphenylthio)benzylamine ([11C]MADAM). In secondary analyses, 5-HTT BPND was correlated with other TCI dimensions.

RESULTS

5-HTT BPND did not differ between high- and low-HA groups in the midbrain or any other brain region. This result remained the same even after adjusting for other relevant TCI dimensions. Higher 5-HTT BPND in the raphe nucleus predicted higher scores in 'self-directedness'.

CONCLUSIONS

This study does not support an association between the temperament dimension HA and serotonin transporter density in healthy subjects. However, we found a link between high serotonin transporter density and high 'self-directedness' (ability to adapt and control one's behaviour to fit situations in accord with chosen goals and values). We suggest that biological factors are more important in explaining variability in character than previously thought.

The 5-HT1A receptor and 5-HT transporter in temporal lobe epilepsy

OBJECTIVE

To study 5-HT transport and 5-HT1A receptors in temporal lobe epilepsy (TLE) and depression.

METHODS

Thirteen patients had PET with [(11)C]DASB for 5-HTT and [(18)F]FCWAY for 5-HT1A receptor binding, MRI, and psychiatric assessment. Sixteen healthy volunteers had [(11)C]DASB, 19 had [(18)F]FCWAY, and 6 had both PET studies. We used a reference tissue model to estimate [(11)C]DASB binding. [(18)F]FCWAY volume of distribution was corrected for plasma-free fraction. Images were normalized to common space. The main outcome was the regional asymmetry index. Positive asymmetry indicates relative reduced binding (reflecting transporter activity) ipsilateral to epileptic foci.

RESULTS

Mean regional [(11)C]DASB binding and asymmetry did not differ between patients and controls. [(18)F]FCWAY asymmetry was significantly greater for patients than controls in hippocampus, amygdala, and fusiform gyrus. On analysis of variance with region as a repeated measure, depression diagnosis had a significant effect on [(11)C]DASB asymmetry, with significantly higher [(11)C]DASB asymmetry in insular cortex (trend for fusiform gyrus). In insular cortex, patients had a significant correlation between [(18)F]FCWAY asymmetry and [(11)C]DASB asymmetry.

CONCLUSIONS

Our study showed increased [(11)C]DASB asymmetry in insula and fusiform gyrus, and relatively reduced transporter activity, in subjects with both TLE and depression, as compared to subjects with TLE alone, implying reduced reuptake and thus increased synaptic 5-HT availability. This finding may represent a compensatory mechanism for 5-HT1A receptor loss. Altered serotonergic mechanisms have an important role in TLE and concomitant depression.

Impaired cognition in bipolar I disorder: the roles of the serotonin transporter and brain-derived neurotrophic factor

BACKGROUND

Studies have proposed that cognitive deficits are present in a variety of mood states in bipolar disorder (BD). The goal of this study was to find the cognitive deficits in euthymic BD patients and to further explore possible underlying mechanisms of the deficits.

METHODS

Thirty-three healthy controls (HCs) and twenty-three euthymic BD type I patients were recruited. Single photon emission computed tomography (SPECT) with (123)I-ADAM was used to image the serotonin transporter (SERT). Ten milliliters of venous blood was drawn for the measurement of brain derived neurotrophic factor (BDNF). Cognitive functions were tested included attention, memory, and executive function.

RESULTS

We found that the SERT availability in both the midbrain and striatal regions was decreased in the BD patients compared with the HCs; however, the BDNF were not different between the two groups. There was no correlation between the SERT availability and the BDNF. Interestingly, there were statistically significant differences in sub-items of the facial memory test and the Wisconsin Card Sorting Test between the BD patients and the HCs, which showed that there was a cognitive deficit in the BD patients. However, the overall deficits in cognition were not significantly correlated with the SERT availability or the BDNF.

LIMITATION

The effect of medications on cognitive function and BDNF should be considered.

CONCLUSIONS

We replicated previous findings that showed cognitive deficits in euthymic BD patients. However, the underlying mechanism of cognitive deficits in euthymic BD patients cannot be entirely explained by SERT and BDNF.

The association of bipolar spectrum disorders and borderline personality disorder

Bipolar disorder (BD) and borderline personality disorder (BPD) are two different entities sharing a variety of common features in a number of fields and, thus, presenting difficulties in their differential diagnosis. The aim of the review is to identify similarities and differences between BD and BPD concerning the symptomatology, causes, course and treatment of the two disorders. A systematic electronic search of Pubmed (Medline) was conducted in order to identify all relevant scientific articles published between 1990 and 2010. The main common clinical features of BD and BPD are affective instability and impulsivity, which, however, present with quality differences in each disorder. In the field of neuroanatomy, BD and BPD demonstrate similarities such as alterations in the limbic system, as well as specific differences, such as the increase in size of the amygdala in BD and the decrease in BPD. Both disorders appear to have a significant percentage of heritability, but environmental factors seem to hold an important role in BPD, in particular. Both BD and BPD are affected by alterations in the dopaminergic and serotonergic system. Fuctionability and prognosis are slightly worse for BPD. Concerning medication treatment, antidepressants are considered effective in BPD, whereas mood stabilizers are the main treatment of choice in BD. The effectiveness of a variety of psychotherapeutic methods is still under research for both disorders. Despite the similarities and differences already being traced in clinical and biological fields, the relationship of the two disorders has not yet been thoroughly defined.

The relation of developmental changes in brain serotonin transporter (5HTT) and 5HT1A receptor binding to emotional behavior in female rhesus monkeys: effects of social status and 5HTT genotype

The goal of the present study was to examine how social subordination stress and 5HTT polymorphisms affect the development of brain serotonin (5HT) systems during the pubertal transition in female rhesus monkeys. We also examined associations with developmental changes in emotional reactivity in response to a standardized behavioral test, the Human Intruder (HI). Our findings provide the first longitudinal evidence of developmental increases in 5HT1A receptor and 5HTT binding in the brain of female primates from pre- to peripuberty. The increase in 5HT1A BP(ND) in these socially housed female rhesus monkeys is a robust finding, occurring across all groups, regardless of social status or 5HTT genotype, and occurring in the left and right hemispheres of all prefrontal regions studied, as well as the amygdala, hippocampus, hypothalamus, and raphe nuclei. 5HTT BP(ND) also showed an increase with age in raphe, anterior cingulate cortex, and dorsolateral prefrontal cortex. These changes in brain 5HT systems take place as females establish more adult-like patterns of social behavior, as well as during the HI paradigm. Indeed, the main developmental changes in behavior during the HI (increase in freezing and decrease in submission/appeasement) were related to neurodevelopmental increases in 5HT1A receptors and 5HTT, because the associations between these behaviors and 5HT endpoints emerge at peripuberty. We detected an effect of social status on 5HT1A BP(ND) in the hypothalamus and on 5HTT BP(ND) in the orbitofrontal cortex, with subordinates showing higher BP(ND) than dominants in both cases during the pubertal transition. No main effects of 5HTT genotype were observed for 5HT1A or 5HTT BP(ND). Our findings indicate that adolescence in female rhesus monkeys is a period of central 5HT reorganization, partly influenced by exposure to the social stress of subordination, that likely functions to integrate adrenal and gonadal systems and shape the behavioral response to emotionally challenging social situations.

Normative database of the serotonergic system in healthy subjects using multi-tracer PET

The highly diverse serotonergic system with at least 16 different receptor subtypes is implicated in the pathophysiology of most neuropsychiatric disorders including affective and anxiety disorders, obsessive compulsive disorder, post-traumatic stress disorder, eating disorders, sleep disturbance, attention deficit/hyperactivity disorder, drug addiction, suicidal behavior, schizophrenia, Alzheimer, etc. Alterations of the interplay between various pre- and postsynaptic receptor subtypes might be involved in the pathogenesis of these disorders. However, there is a lack of comprehensive in vivo values using standardized procedures. In the current PET study we quantified 3 receptor subtypes, including the major inhibitory (5-HT(1A) and 5-HT(1B)) and excitatory (5-HT(2A)) receptors, and the transporter (5-HTT) in the brain of healthy human subjects to provide a database of standard values. PET scans were performed on 95 healthy subjects (age=28.0 ± 6.9 years; 59% males) using the selective radioligands [carbonyl-(11)C]WAY-100635, [(11)C]P943, [(18)F]altanserin and [(11)C]DASB, respectively. A standard template in MNI stereotactic space served for region of interest delineation. This template follows two anatomical parcellation schemes: 1) Brodmann areas including 41 regions and 2) AAL (automated anatomical labeling) including 52 regions. Standard values (mean, SD, and range) for each receptor and region are presented. Mean cortical and subcortical binding potential (BP) values were in good agreement with previously published human in vivo and post-mortem data. By means of linear equations, PET binding potentials were translated to post-mortem binding (provided in pmol/g), yielding 5.89 pmol/g (5-HT(1A)), 23.5 pmol/g (5-HT(1B)), 31.44 pmol/g (5-HT(2A)), and 11.33 pmol/g (5-HTT) being equivalent to the BP of 1, respectively. Furthermore, we computed individual voxel-wise maps with BP values and generated average tracer-specific whole-brain binding maps. This knowledge might improve our interpretation of the alterations taking place in the serotonergic system during neuropsychiatric disorders.

Striatal and cortical midline circuits in major depression: implications for suicide and symptom expression

BACKGROUND

In major depression, the neural mechanisms underlying suicide related thoughts and behaviors as well as the expression of other depressive symptoms are incompletely characterized. Evidence indicates that both the striatum and cortical midline structures (CMS) may be involved with both suicide and emotional dysregulation in unipolar illness. The aim of this study was to identify striatal-CMS circuits associated with current depression severity and suicidal ideation (SI) as well as a history of self-harm.

METHODS

Twenty-two male subjects with recurrent unipolar depression were studied using functional MRI. All subjects were unmedicated and without current psychiatric comorbidity. Correlational analyses were used to determine whether striatal-CMS functional connectivity was associated with any of the three clinical variables.

RESULTS

A network involving the bilateral striatum and anterior CMS was found to be associated with depressive symptom severity. Current SI was associated with a similar but less extensive circuit in the left hemisphere. A distinct striatal motor/sensory network was associated with self-harm behaviors, but not current SI or depression severity.

CONCLUSIONS

The striatal-anterior CMS circuit likely plays a significant role in the expression of depressive symptoms and SI. In contrast, a striatum-motor/sensory cortex network may be a trait marker of suicide-related behaviors. If replicated, this result might eventually lead to the development of a biomarker that would be useful for studies of pharmacologic and/or psychotherapeutic suicide prevention interventions.

Key players in major and bipolar depression--a retrospective analysis of in vivo imaging studies

In the present study, we evaluated the contribution of the individual synaptic constituents of all assessed neurotransmitter systems by subjecting all available in vivo imaging studies on patients with unipolar major depressive disorder (MDD) and bipolar depression (BD) to a retrospective analysis. In acute MDD, findings revealed significant increases of prefrontal and frontal DA synthesis, decreases of thalamic and midbrain SERT, increases of insular SERT, decreases of midbrain 5-HT(1A) receptors and decreases of prefrontal, frontal, occipital and cingulate 5-HT(2A) receptors, whereas, in remission, decreases of striatal D₂ receptors, midbrain SERT, frontal, parietal, temporal, occipital and cingulate 5-HT(1A) receptors and parietal 5-HT(2A) receptors were observed. In BD, findings indicated a trend towards increased striatal D₂ receptors in depression and mania, decreased striatal DA synthesis in remission and decreased frontal D₁ receptors in all three conditions. Additionally, there is some evidence that ventrostriatal and hippocampal SERT may be decreased in depression, whereas in remission and mania elevations of thalamic and midbrain SERT, respectively, were observed. Moreover, in depression, limbic 5-HT(1A) receptors were elevated, whereas in mania a decrease of both cortical and limbic 5-HT(2A) receptor binding was observed. Furthermore, in depression, prefrontal, frontal, occipital and cingulate M2 receptor binding was found to be reduced. From this, a complex pattern of dysregulations within and between neurotransmitter systems may be derived, which is likely to be causally linked not only with the subtype and duration of disease but also with the predominance of individual symptoms and with the kind and duration of pharmacological treatment(s).

Self-referential thinking, suicide, and function of the cortical midline structures and striatum in mood disorders: possible implications for treatment studies of mindfulness-based interventions for bipolar depression

Bipolar depression is often refractory to treatment and is frequently associated with anxiety symptoms and elevated suicide risk. There is a great need for adjunctive psychotherapeutic interventions. Treatments with effectiveness for depressive and anxiety symptoms as well as suicide-related thoughts and behaviors would be particularly beneficial. Mindfulness-based interventions hold promise, and studies of these approaches for bipolar disorder are warranted. The aim of this paper is to provide a conceptual background for such studies by reviewing key findings from diverse lines of investigation. Results of that review indicate that cortical midline structures (CMS) appear to link abnormal self-referential thinking to emotional dysregulation in mood disorders. Furthermore, CMS and striatal dysfunction may play a role in the neuropathology underlying suicide-related thoughts and behaviors. Thus, combining studies of mindfulness interventions targeting abnormal self-referential thinking with functional imaging of CMS and striatal function may help delineate the neurobiological mechanisms of action of these treatments.

The suicidal mind and brain: a review of neuropsychological and neuroimaging studies

OBJECTIVES. We aimed at reviewing studies exploring dysfunctional cognitive processes, and their neuroanatomical basis, in suicidal behaviour, and to develop a neurocognitive working model. Methods. A literature search was conducted. RESULTS. Several limitations were found. The main reported neuropsychological findings are a higher attention to specific negative emotional stimuli, impaired decision-making, lower problem-solving abilities, reduced verbal fluency, and possible reduced non-specific attention and reversal learning in suicide attempters. Neuroimaging studies mainly showed the involvement of ventrolateral orbital, dorsomedial and dorsolateral prefrontal cortices, the anterior cingulate gyrus, and, to a lesser extent, the amygdala. In addition, alterations in white matter connections are suggested. CONCLUSIONS. These studies support the concept of alterations in suicidal behaviour distinct from those of comorbid disorders. We propose that a series of neurocognitive dysfunctions, some with trait-like characteristics, may facilitate the development of a suicidal crisis during stressful circumstances: (1) an altered modulation of value attribution, (2) an inadequate regulation of emotional and cognitive responses, and (3) a facilitation of acts in an emotional context. This preliminary model may represent a framework for the design of future studies on the pathophysiology, prediction and prevention of these complex human behaviours.

Hypermethylation of serotonin transporter gene in bipolar disorder detected by epigenome analysis of discordant monozygotic twins

Bipolar disorder (BD) is a severe mental disorder characterized by recurrent episodes of mania and depression. Serotonin transporter (HTT) is a target of antidepressants and is one of the strongest candidate molecules of mood disorder, however, genetic study showed equivocal results. Here, we performed promoter-wide DNA methylation analysis of lymphoblastoid cell lines (LCLs) derived from two pairs of monozygotic twins discordant for BD. To rule out the possible discordance of copy number variation (CNV) between twins, we performed CNV analysis and found the copy number profiles were nearly identical between the twin pairs except for immunoglobulin-related regions. Among the three genes we obtained as candidate regions showing distinct difference of DNA methylation between one of the two pairs, hypermethylation of SLC6A4, encoding HTT, in the bipolar twin was only confirmed by bisulfite sequencing. Then, promoter hypermethylation of SLC6A4 in LCLs of BD patients was confirmed in a case-control analysis. DNA methylation of SLC6A4 was significantly correlated with its mRNA expression level in individuals with the S/S genotype of HTTLPR, and mRNA expression level was lower in BD patients carrying the S/S genotype. Finally, DNA methylation of the same site was also higher in the postmortem brains of BD patients. This is the first study to report the role of epigenetic modification of SLC6A4 in BD using an unbiased approach, which provides an insight for its pathophysiology.

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

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

Functional neuroimaging in geriatric depression

Abnormalities in specific cerebral networks likely confer vulnerability that increases the susceptibility for development of geriatric depression and affect the course of symptoms. Functional neuroimaging enables the in vivo identification of alterations in cerebral function that characterize disease vulnerability and contribute to variability in depressive symptoms and antidepressant response. Judicious use of functional neuroimaging tools can advance pathophysiologic models of geriatric depression. Furthermore, geriatric depression provides a logical context within which to study the role of specific functional abnormalities in both antidepressant response and key behavioral and cognitive abnormalities of mood disorders.

Neural mechanisms of antidepressant efficacy of the dopamine receptor agonist pramipexole in treatment of bipolar depression

The D₂/D₃ receptor agonist pramipexole has clinical efficacy as an antidepressant, but its neural mechanisms are unknown. We used ¹⁸FDG-PET to investigate the cerebral metabolic effects of pramipexole augmentation of mood stabilizers in bipolar II depression. Fifteen bipolar II depressed patients on mood stabilizers were imaged at baseline and following 6 wk of pramipexole (n=7) or placebo (n=8) augmentation. Relative to placebo, pramipexole treatment was associated with reductions in normalized metabolism in bilateral orbitofrontal cortex, left ventrolateral prefrontal cortex (PFC), and right anteromedial PFC. Voxel-wise analyses additionally showed decreased normalized metabolism in the left inferior parietal cortex and medial frontopolar cortical (BA 10P) area of the anteromedial PFC following pramipexole treatment. These pramipexole-induced effects on regional metabolism suggest a mechanism of antidepressant action distinct from that previously reported under serotonin reuptake inhibitor treatment and appear compatible with evidence that the central dopaminergic system plays a role in the pathophysiology of bipolar depression.

The neuroscience of suicidal behaviors: what can we expect from endophenotype strategies?

Vulnerability to suicidal behavior (SB) is likely mediated by an underlying genetic predisposition interacting with environmental and probable epigenetic factors throughout the lifespan to modify the function of neuronal circuits, thus rendering an individual more likely to engage in a suicidal act. Improving our understanding of the neuroscience underlying SBs, both attempts and completions, at all developmental stages is crucial for more effective preventive treatments and for better identification of vulnerable individuals. Recent studies have characterized SB using an endophenotype strategy, which aims to identify quantitative measures that reflect genetically influenced stable changes in brain function. In addition to aiding in the functional characterization of susceptibility genes, endophenotypic research strategies may have a wider impact in determining vulnerability to SB, as well as the translation of human findings to animal models, and vice versa. Endophenotypes associated with vulnerability to SB include impulsive/aggressive personality traits and disadvantageous decision making. Deficits in realistic risk evaluation represent key processes in vulnerability to SB. Serotonin dysfunction, indicated by neuroendocrine responses and neuroimaging, is also strongly implicated as a potential endophenotype and is linked with impulsive aggression and disadvantageous decision making. Specific endophenotypes may represent heritable markers for the identification of vulnerable patients and may be relevant targets for successful suicide prevention and treatments.

Central serotonin transporter levels are associated with stress hormone response and anxiety

RATIONALE

Negative mood states are characterized by both stress hormone dysregulation and serotonergic dysfunction, reflected by altered thalamic serotonin transporter (5-HTT) levels. However, so far, no study examined the individual association between cortisol response and cerebral in vivo 5-HTT levels in patients suffering from negative mood states.

OBJECTIVE

The objective of this cross-sectional study was to assess the interrelation of cortisol response, thalamic 5-HTT levels, and anxiety in healthy subjects and two previously published samples of patients with unipolar major depression (UMD) and obsessive-compulsive disorder (OCD), controlling for age, gender, 5-HTT genotype, smoking, and seasonality.

METHODS

Regional 5-HTT levels and cortisol response to dexamethasone-corticotropin (Dex-CRH) challenge were assessed in consecutive samples of medication-free patients suffering from UMD (N = 10) and OCD (N = 10), and 20 healthy volunteers. The intervention used was combined Dex-CRH test and [(11)C]DASB positron emission tomography. The main outcome measures were: 5-HTT binding potential (BP(ND)) in a predefined thalamic ROI, cortisol response defined as the maximum cortisol increase in the combined Dex-CRH-test, and state of anxiety from the state-trait-anxiety inventory.

RESULTS

Reduced thalamic 5-HTT BP(ND) was associated with increased cortisol response (r = -0.35, p < 0.05; in patients: r = -0.53, p < 0.01) and with increased state anxiety (r = -0.46, p < 0.01), surviving correction for age, gender, 5-HTT genotype, smoking, and seasonality (p < 0.05). The 5-HTT genotype, on the contrary, was not significantly associated with cortisol response (p = 0.19) or negative mood (p = 0.23).

CONCLUSION

The association between stress hormone response, thalamic 5-HTT levels, and anxiety in patients suffering from negative mood states suggests an interaction between two major mechanisms implicated in negative mood states in humans.

Diminished brain 5-HT transporter binding in major depression: a positron emission tomography study with [11C]DASB

BACKGROUND

The serotonin transporter (5-HTT) plays a critical role in the regulation of serotonin neurotransmission and has been implicated in the pathophysiology of major depression. In a previous positron emission tomography study, we found no difference in brain 5-HTT binding between unmedicated recovered depressed patients and healthy controls.

AIM

This study aims to assess brain 5-HTT binding in a group of unmedicated acutely depressed patients in comparison to healthy controls.

METHODS

We studied 5-HTT binding using [(11)C]DASB in conjunction with positron emission tomography in 12 medication-free depressed patients with a mean duration of illness of about 1 year and 24 healthy controls.

RESULTS

The depressed patients had lowered 5-HTT binding in several brain regions including brain stem, thalamus, caudate, putamen, anterior cingulate cortex and frontal cortex.

CONCLUSIONS

These results suggest that diminished availability of the 5-HTT in the brain may be a state marker of acute depression. Alternatively, low 5-HTT binding may delineate a group of depressed patients with a poor long-term prognosis.

The role of the aminergic systems in the pathophysiology of bipolar disorder

Bipolar disorder (BPD) is a major medical and social burden, but little is known about the specific pathophysiology of BPD. The key biogenic amines in the aminergic system include serotonin (5-HT), norepinephrine (NE), dopamine (DA), and acetylcholine (ACh). By analyzing these neurotransmitters, this chapter highlights three hypotheses in the pathophysiology of BPD: the biogenic amine hypothesis, the cholinergic-aminergic balance hypothesis, and the permissive hypothesis. Evidence from select studies of cerebrospinal fluid, postmortem subjects, neuroimaging, genetic factors, and pharmacological agents will be used to reconcile these hypotheses. Possible explanations for discrepancies in these hypotheses are given, and directions for future studies are suggested.

Gender differences in alpha-[(11)C]MTrp brain trapping, an index of serotonin synthesis, in medication-free individuals with major depressive disorder: a positron emission tomography study

Women are at higher risk than men for developing major depressive disorder (MDD), but the mechanisms underlying this higher risk are unknown. Here, we report proportionally normalized alpha-[(11)C]methyl-L-tryptophan brain trapping constant (alpha-[(11)C]MTrp K*(N)), an index of serotonin synthesis, in 25 medication-free individuals with MDD and in 25 gender- and age-matched healthy subjects who were studied using positron emission tomography (PET). Comparisons of alpha-[(11)C]MTrp K*(N) values between the men and women were conducted at the voxel and cluster levels using Statistical Parametric Mapping 2 (SPM2) analysis. In addition, the alpha-[(11)C]MTrp K*(N) values on both sides of the brain were extracted and compared to identify the left to right differences, as well as the gender differences. Women with MDD displayed higher alpha-[(11)C]MTrp K*(N) than men in the inferior frontal gyrus, anterior cingulate cortex (ACC), parahippocampal gyrus, precuneus, superior parietal lobule, and occipital lingual gyrus. In a matched group of normal subjects the gender differences were opposite from those found in MDD patients. Significant hemispheric differences in fronto-limbic structures between men and women with MDD were also observed. The K*(N) extracted from the volumes identified in MDD patients and in male and female normal subjects suggested no significant differences between males and females. In conclusion, depressed women have higher serotonin synthesis in multiple regions of the prefrontal cortex and limbic system involved with mood regulation, as compared with depressed men. Gender differences in brain serotonin synthesis may be related to higher risk for MDD in women.

Cortical GABA, striatal dopamine and midbrain serotonin as the key players in compulsive and anxiety disorders--results from in vivo imaging studies

Various factors are discussed in the pathophysiology of anxiety disorders, including dysfunctions of the (DA)ergic, serotonin (5-HT)ergic and GABAergic system. We assessed the contribution of the individual synaptic constituents by subjecting all available in vivo imaging studies on patients with anxiety disorders to a retrospective analysis. On a total of 504 patients with obsessive-compulsive disorder (OCD), generalized anxiety disorder (GAD), panic disorder (PD), phobia, or posttraumatic stress-disorder (PTSD) and 593 controls, investigations of VMAT2, DAT, SERT, D1, D2, 5-HTIA, 5-HT2A, GABA(A), and NK1 receptor binding in neostriatum, ventral striatum, thalamus, neocortex, limbic system, cingulate, midbrain/ pons or cerebellum were performed using either PET or SPECT. Separate analyses of the individual disorders showed significant decreases of striatal D2 receptors in OCD (-18%), mesencephalic SERT in OCD (-13%), frontocortical GABAA receptors in PD (-13%) and temporocortical GABAA receptors in GAD (-16%). Pooling of all disorders yielded a significant reduction of mesencephalic SERT (-13%), mesencephalic (-27%) as well as cingulate 5-HT1A receptors (-18%), striatal D2 receptors (-21%) and frontal (-14%), temporal (-14%), occipital (-13%) and cingulate GABAA receptors (-15%). The results show that DA, 5-HT, and GABA play a major role in all subtypes of anxiety disorders. In particular, the findings imply that the regulation state of DA as modulated by GABA and 5-HT may be crucial for the development of anxiety- and compulsion-related disorders. As GABA and 5-HT inhibit DAergic neurotransmission, the reductions of GABAA, 5-HT1A and SERT can be assumed to result in an enhanced activity of the mesolimbic DAergic system. This notion is also reflected by the decrease of striatal D2 receptor binding, which is indicative of an increased availability of synaptic DA.

Cerebral blood flow, metabolic, receptor, and transporter changes in bipolar disorder: the role of PET and SPECT studies

The basic concepts of positron emission tomography (PET) and single photon emission computed tomography (SPECT) scanning are introduced, and the two modalities are compared. Applications to bipolar disorder (BD) are reviewed. Regional cerebral metabolic rate and blood flow, often used as surrogate measures of neuronal synaptic activity, are increased in the frontal lobes in both unipolar and bipolar depression. In mania, metabolism increases in the dorsal cingulate cortex, striatal regions, and the nucleus accumbens, as well as in limbic structures of the temporal lobes, but decreases in dorsolateral prefrontal cortex, possibly reflecting its loss of modulatory control over limbic structures. Specifically targeted PET radioligands are used to investigate neurotransmitter systems. D1 receptor binding potentials are reduced in frontal cortex, but striatal D2 receptor density is normal in all phases of non-psychotic BD. Psychotic BD patients show higher D2 receptor densities in the caudate, which correlate with the degree of psychosis but not mood symptoms. The serotonin transporter shows increased density in the thalamus, dorsal cingulate cortex, medial preftontal cortex, and insula of depressed BD patients. In the dorsal cingulate cortex and insula, it correlates with anxiety (and in the cingulate, with suicide attempts).

Genetic variation in HTR2A influences serotonin transporter binding potential as measured using PET and [11C]DASB

In a previous study we showed that genetic variation in HTR2A, which encodes the serotonin 2A receptor, influenced outcome of citalopram treatment in patients with major depressive disorder. Since chronic administration of citalopram, which selectively and potently inhibits the serotonin transporter (5-HTT), putatively enhances serotonergic transmission, it is conceivable that genetic variation within HTR2A also influences pretreatment 5-HTT function or serotonergic transmission. The present study used positron emission tomography (PET) and the selective 5-HTT ligand, [11C]DASB, to investigate whether the HTR2A marker alleles that predict treatment outcome also predict differences in 5-HTT binding. Brain levels of 5-HTT were assessed in vivo using PET measures of the non-displaceable component of the [11C]DASB binding potential (BPND). DNA from 43 patients and healthy volunteers, all unmedicated, was genotyped with 14 single nucleotide polymorphisms located within or around HTR2A. Allelic association with BPND was assessed in eight brain regions, with covariates to control for race and ethnicity. We detected allelic association between [11C]DASB BPND in thalamus and three markers in a region spanning the 3' untranslated region and second intron of HTR2A (rs7333412, p=0.000045; rs7997012, p=0.000086; rs977003, p=0.000069). The association signal at rs7333412 remained significant (p<0.05) after applying corrections for multiple testing via permutation. Genetic variation in HTR2A that was previously associated with citalopram treatment outcome was also associated with thalamic 5-HTT binding. While further work is needed to identify the actual functional genetic variants involved, these results suggest that a relationship exists between genetic variation in HTR2A and either 5-HTT expression or central serotonergic transmission that influences the therapeutic response to 5-HTT inhibition in major depression.

Assessing the neuronal serotonergic target-based antidepressant stratagem: impact of in vivo interaction studies and knockout models

Depression remains a challenge in the field of affective neuroscience, despite a steady research progress. Six out of nine basic antidepressant mechanisms rely on serotonin neurotransmitter system. Preclinical studies have demonstrated the significance of serotonin receptors (5-HT_1-3,6,7), its signal transduction pathways and classical down stream targets (including neurotrophins, neurokinins, other peptides and their receptors) in antidepressant drug action. Serotonergic control of depression embraces the recent molecular requirements such as influence on proliferation, neurogenesis, plasticity, synaptic (re)modeling and transmission in the central nervous system. The present progress report analyses the credibility of each protein as therapeutically relevant target of depression. In vivo interaction studies and knockout models which identified these targets are foreseen to unearth new ligands and help them transform to drug candidates. The importance of the antidepressant assay selection at the preclinical level using salient animal models/assay systems is discussed. Such test batteries would definitely provide antidepressants with faster onset, efficacy in resistant (and co-morbid) types and with least adverse effects. Apart from the selective ligands, only those molecules which bring an overall harmony, by virtue of their affinities to various receptor subtypes, could qualify as effective antidepressants. Synchronised modulation of various serotonergic sub-pathways is the basis for a unique and balanced antidepressant profile, as that of fluoxetine (most exploited antidepressant) and such a profile may be considered as a template for the upcoming antidepressants. In conclusion, 5-HT based multi-targeted antidepressant drug discovery supported by in vivo interaction studies and knockout models is advocated as a strategy to provide classic molecules for clinical trials.

Real-time, spatially resolved analysis of serotonin transporter activity and regulation using the fluorescent substrate, ASP+

The serotonin transporter (SERT) mediates clearance of serotonin from the synapse, thereby, regulating extracellular serotonin concentrations. Radioligand uptake techniques are typically used to assess SERT function in tissue and heterologous expression systems. The need for sufficient protein in samples, however, requires use of homogenate preparations, potentially masking effects limited to specific cell populations. 4-(4-(dimethylamino)-styryl)-N-methylpyridinium (ASP(+)) is a fluorescent monoamine transporter substrate that has been used for real-time monitoring of dopamine and norepinephrine transporter function in single cells. The present live cell imaging studies examine the utility of ASP(+) for quantifying human SERT function in HEK293 and neuroblastoma cells. We show rapid membrane binding and intracellular ASP(+) accumulation in human SERT-expressing cells. Accumulation is saturable; dependent on temperature and the presence of sodium and chloride in the media, and attenuated by serotonin. Acute or prolonged exposure of cells to serotonin re-uptake inhibitors produces a concentration-dependent decrease in accumulation. Similar effects are produced by protein kinase C activation whereas p38 MAPK activation increases ASP(+) accumulation. These data demonstrate the validity of ASP(+) as a probe for monitoring SERT function in living cells. Alterations in SERT binding and uptake can be quantified in the same cell and use of a within-cell design permits analysis of time-related alterations in SERT function.

Decreased brain serotonin transporter binding in the euthymic state of bipolar I but not bipolar II disorder: a SPECT study

OBJECTIVES

Previous positron emission tomography studies have demonstrated that serotonin transporter (SERT) binding in the midbrain is decreased in the depressive state of bipolar disorder (BD). The aim of this study was to assess SERT binding in the midbrain of patients in a euthymic state of BD.

METHODS

Twenty-eight healthy controls and 24 patients in a euthymic state of medicated BD were recruited. Euthymic state was defined as Montgomery-Asberg Depression Rating Scale scores < 10 and Young Mania Rating Scale scores < 7 within a consecutive eight-week period. Single photon emission computed tomography with the radiotracer (123)I-ADAM was used to measure SERT binding in the midbrain. An equilibrium ratio model was used for data analysis. Specific uptake ratio (SUR), which represents availability of SERT binding in the midbrain, was the primary measurement outcome.

RESULTS

The averaged SURs were not different between healthy controls and BD patients in euthymic state (p = 0.27). However, a three-way ANCOVA analysis comparing SURs in healthy controls, bipolar I disorder (BD I) patients, and bipolar II disorder (BD II) patients, covarying education duration and sex, showed that the averaged SURs were significantly lower in BD I than BD II patients and healthy controls (p = 0.042). The decreased SURs in BD I patients were well correlated with duration of illness (R = -0.742, p = 0.014) only.

CONCLUSIONS

Our findings demonstrate that there is differential biological regulation in BD I and BD II patients after stable treatment, which may support the existence of a dichotomy in BD.

Imaging serotonergic transmission with [11C]DASB-PET in depressed and non-depressed patients infected with HIV

INTRODUCTION

Site-selective imaging can provide significant insight into the mechanism of HIV-associated neurological disease. The goal of this study was to evaluate the involvement of serotonergic transmission in HIV-associated depression using [(11)C]DASB, a serotonin transporter (5-HTT)-specific radiopharmaceutical for positron emission tomography (PET).

METHODS

Nine depressed HIV+ subjects (HIV-D), 9 non-depressed HIV+ subjects (HIV-ND) and 7 healthy controls (HC) underwent an MRI scan and a [(11)C]DASB-PET scan. The outcome measure was 5-HTT binding potential normalized to non-displaceable tissue radioligand (BP(ND)).

RESULTS

HIV-ND subjects had lower mean regional 5-HTT BP(ND) estimates across regions compared to HC, while HIV-D subjects demonstrated higher mean regional binding values than HIV-ND subjects in most regions. Prior to correction for the false discovery rate, HIV-ND had significantly lower BP(ND) values compared to HC subjects in two regions (insula and anterior cingulate) and all HIV+ patients had significantly lower binding than HC in all regions except for the midbrain, thalamus and pons. After correction for the false discovery rate, only the insula showed significantly lower binding in HIV+ subjects compared to HC (P<0.0045). Despite a significant difference in the duration of illness between the HIV-D and HIV-ND groups, there was no definite correlation between the duration of illness and BP(ND).

CONCLUSION

Lower [(11)C]DASB binding in HIV+ patients compared to HC may reflect serotonergic neuronal loss as a component of generalized HIV-associated neurodegeneration. Higher mean regional BP(ND) values in HIV-D compared to HIV-ND subjects could reflect increased density of 5-HTT, leading to increased clearance of serotonin from the synapse, which could account, in part, for symptoms of depression. The lack of correlation between duration of illness and binding argues against these findings being the result of differential neurodegeneration only. Our findings suggest a possible role for dysregulated serotonergic transmission in HIV-associated depression.

Focus on HTR2C: A possible suggestion for genetic studies of complex disorders

HTR2C is one of the most relevant and investigated serotonin receptors. Its role in important brain structures such as the midbrain, the lateral septal complex, the hypothalamus, the olfactory bulb, the pons, the choroid plexus, the nucleus pallidus, the striatum and the amygdala, the nucleus accumbens and the anterior cingulated gyrus candidate it as a promising target for genetic association studies. The biological relevance of these brain structures is reviewed by way of the focus on HTR2C activity, with a special attention paid to psychiatric disorders. Evidence from the genetic association studies that dealt with HTR2C is reviewed and discussed alongside the findings derived from the neuronatmic investigations. The reasons for the discrepancies between these two sets of reports are discussed. As a result, HTR2C is shown to play a pivotal role in many different psychiatric behaviors or psychiatric related disrupted molecular balances, nevertheless, genetic association studies brought inconsistent results so far. The most replicated association involve the feeding behavior and antipsychotic induced side effects, both weight gain and motor related: Cys23Ser (rs6318) and -759C/T (rs3813929) report the most consistent results. The lack of association found in other independent studies dampens the clinical impact of these reports. Here, we report a possible explanation for discrepant findings that is poorly or not at all usually considered, that is that HTR2C may exert different or even opposite activities in the brain depending on the structure analyzed and that mRNA editing activity may compensate possible genetically controlled functional effects. The incomplete coverage of the HTR2C variants is proposed as the best cost-benefit ratio bias to fix. The evidence of brain area specific HTR2C mRNA editing opens a debate about how the brain can differently modulate stress events, and process antidepressant treatments, in different brain areas. The mRNA editing activity on HTR2C may play a major role for the negative association results.

A voxel-based diffusion tensor imaging study of white matter in bipolar disorder

There is evidence from post-mortem and magnetic resonance imaging studies that hyperintensities, oligodendroglial abnormalities, and gross white matter volumetric alterations are involved in the pathophysiology of bipolar disorder. There is also functional imaging evidence for a defect in frontal cortico-subcortical pathways in bipolar disorder, but the white matter comprising these pathways has not been well investigated. Few studies have investigated white matter integrity in patients with bipolar disorder compared to healthy volunteers and the majority of studies have used manual region-of-interest approaches. In this study, we compared fractional anisotropy (FA) values between 30 patients with bipolar disorder and 38 healthy volunteers in the brain white matter using a voxelwise analysis following intersubject registration to Talairach space. Compared to healthy volunteers, patients demonstrated significantly (p<0.001; cluster size > or =50) higher FA within the right and left frontal white matter and lower FA within the left cerebellar white matter. Examination of individual eigenvalues indicated that group differences in both axial diffusivity and radial diffusivity contributed to abnormal FA within these regions. Tractography was performed in template space on averaged diffusion tensor imaging data from all individuals. Extraction of bundles passing through the clusters that differed significantly between groups suggested that white matter abnormalities along the pontine crossing tract, corticospinal/corticopontine tracts, and thalamic radiation fibers may be involved in the pathogenesis of bipolar disorder. Our findings are consistent with models of bipolar disorder that implicate dysregulation of cortico-subcortical and cerebellar regions in the disorder and may have relevance for phenomenology.

Role of variation in the serotonin transporter protein gene (SLC6A4) in trait disturbances in the ventral anterior cingulate in bipolar disorder

Bipolar disorder (BD) is associated with abnormalities of the ventral anterior cingulate cortex (vACC) and its connection sites, including the amygdala, which are key components of a corticolimbic neural system that subserves emotional regulation. Decreased functional connectivity from the vACC to the amygdala in healthy individuals is associated with the short 's' allele--as opposed to the long 'l' allele--of a well-known serotonin transporter promoter polymorphism (5-HTTLPR, locus SLC6A4), as are features of BD. This study tests the hypothesis that the s allele influences dysfunction in the vACC-amygdala neural system in BD. A total of 30 euthymic individuals with BD (20 s carriers, 10 ll) and 48 healthy comparison (HC) participants (34 s, 14 ll) participated in an event-related functional magnetic resonance imaging scan while processing fearful, happy, or neutral faces. During fear and happy face processing, vACC activation was significantly lower in the BD compared to the HC group, and in s carriers compared to ll individuals within both the HC and BD groups, such that BD s carriers exhibited the greatest magnitude of vACC dysfunction. No significant differences were detected in amygdala activation. The findings suggest that the 5-HTTLPR s allele may contribute to a trait-related, genetically derived, neurobiological subgroup within BD characterized by prominent vACC dysfunction. Future treatment may be optimized for this BD subgroup by targeting the serotonergic system and the vACC.

The supra-additive hyperactivity caused by an amphetamine-chlordiazepoxide mixture exhibits an inverted-U dose response: negative implications for the use of a model in screening for mood stabilizers

One of the few preclinical models used to identify mood stabilizers is an assay in which amphetamine-induced hyperactivity (AMPH) is potentiated by the benzodiazepine chlordiazepoxide (CDP), an effect purportedly blocked by mood stabilizers. Our data here challenge this standard interpretation of the AMPH-CDP model. We show that the potentiating effects of AMPH-CDP are not explained by a pharmacokinetic interaction as both drugs have similar brain and plasma exposures whether administered alone or in combination. Of concern, however, we find that combining CDP (1-12 mg/kg) with AMPH (3 mg/kg) results in an inverted-U dose response in outbred CD-1 as well as inbred C57Bl/6N and 129S6 mice (peak hyperactivity at 3 mg/kg CDP+3 mg/kg AMPH). Such an inverted-U dose response complicates interpreting whether a reduction in hyperactivity produced by a mood stabilizer reflects a "blockade" or a "potentiation" of the mixture. In fact, we show that the prototypical mood stabilizer valproic acid augments the effects of CDP on hypolocomotion and anxiolytic-like behavior (increases punished crossings by Swiss-Webster mice in the four-plate test). We argue that these data, in addition to other practical and theoretical concerns surrounding the model, limit the utility of the AMPH-CDP mixture model in drug discovery.

Substance use disorders and suicide attempts in bipolar subtypes

Bipolar disorder (BD) is associated with high rates of suicide attempt and completion. Substance use disorders (SUD) have been identified as potent risk factors for suicidal behavior in BD. However, little is known concerning differences between BD subtypes with regard to SUD as a risk factor for suicidal behavior. We studied previous suicidal behavior in adults with a major depressive episode in context of BD type I (BD-I; N=96) or BD type II (BD-II; N=42), with and without history of SUD. Logistic regressions assessed the association between SUD and suicide attempt history by BD type, and exploratory analyses examined the effects of other clinical characteristics on these relationships. SUD were associated with suicide attempt in BD-I but not BD-II, an effect not attributable to sample size differences. The higher suicide attempt rate associated with alcoholism in BD-I was mostly explained by higher aggression scores, and earlier age of BD onset increased the likelihood that alcohol use disorder would be associated with suicide attempt(s). The higher suicide attempt rate associated with other drug use disorders in BD-I was collectively explained by higher impulsivity, hostility, and aggression scores. The presence of both alcohol and drug use disorders increased odds of a history of suicide attempt in a multiplicative fashion: 97% of BD-I who had both co-morbid drug and alcohol use disorders had made a suicide attempt. A critical next question is how to target SUD and aggressive traits for prevention of suicidal behavior in BD-I.

2-(2'-((Dimethylamino)methyl)-4'-(3-[(18)F]fluoropropoxy)-phenylthio)benzenamine for positron emission tomography imaging of serotonin transporters

INTRODUCTION

A new (18)F ligand, 2-(2'-((dimethylamino)methyl)-4'-(3-[(18)F]fluoropropoxy)-phenylthio)benzenamine ([(18)F]1), for positron emission tomography (PET) imaging of serotonin transporters (SERT) was evaluated.

METHODS

Binding affinity was determined through in vitro binding assays with LLC-PK1 cells overexpressing SERT, NET or DAT (LLC-SERT, LLC-NET and LLC-DAT) and with rat cortical homogenates. Localization and selectivity of [(18)F]1 binding in vivo were evaluated by biodistribution, autoradiography and A-PET imaging studies in rats.

RESULTS

This compound displayed excellent binding affinity for SERT in vitro with K(i)=0.33 and 0.24 nM in LLC-SERT and rat cortical homogenates, respectively. Biodistribution studies with [(18)F]1 showed good brain uptake (1.61% dose/g at 2 min postinjection), high uptake into the hypothalamus (1.22% dose/g at 30 min) and a high target-to-nontarget (hypothalamus to cerebellum) ratio of 9.66 at 180 min postinjection. Pretreatment with a SERT selective inhibitor considerably inhibited [(18)F]1 binding in biodistribution studies. Ex vivo autoradiography reveals [(18)F]1 localization to brain regions with high SERT density, and this binding was blocked by pretreatment with SERT selective inhibitors. Small animal PET (A-PET) imaging in rats provided clear images of tracer localization in the thalamus, midbrain and striatum. In A-PET chasing experiments, injecting a SERT selective inhibitor 75 min post-tracer injection causes a dramatic reduction in regional radioactivity and the target-to-nontarget ratio.

CONCLUSION

The results of the biological studies and the ease of radiosynthesis with moderately good radiochemical yield (RCY=10-35%) make [(18)F]1 an excellent candidate for SERT PET imaging.

Brain structural and functional abnormalities in mood disorders: implications for neurocircuitry models of depression

The neural networks that putatively modulate aspects of normal emotional behavior have been implicated in the pathophysiology of mood disorders by converging evidence from neuroimaging, neuropathological and lesion analysis studies. These networks involve the medial prefrontal cortex (MPFC) and closely related areas in the medial and caudolateral orbital cortex (medial prefrontal network), amygdala, hippocampus, and ventromedial parts of the basal ganglia, where alterations in grey matter volume and neurophysiological activity are found in cases with recurrent depressive episodes. Such findings hold major implications for models of the neurocircuits that underlie depression. In particular evidence from lesion analysis studies suggests that the MPFC and related limbic and striato-pallido-thalamic structures organize emotional expression. The MPFC is part of a larger "default system" of cortical areas that include the dorsal PFC, mid- and posterior cingulate cortex, anterior temporal cortex, and entorhinal and parahippocampal cortex, which has been implicated in self-referential functions. Dysfunction within and between structures in this circuit may induce disturbances in emotional behavior and other cognitive aspects of depressive syndromes in humans. Further, because the MPFC and related limbic structures provide forebrain modulation over visceral control structures in the hypothalamus and brainstem, their dysfunction can account for the disturbances in autonomic regulation and neuroendocrine responses that are associated with mood disorders. This paper discusses these systems together with the neurochemical systems that impinge on them and form the basis for most pharmacological therapies.

Brain structural and functional abnormalities in mood disorders: implications for neurocircuitry models of depression

The neural networks that putatively modulate aspects of normal emotional behavior have been implicated in the pathophysiology of mood disorders by converging evidence from neuroimaging, neuropathological and lesion analysis studies. These networks involve the medial prefrontal cortex (MPFC) and closely related areas in the medial and caudolateral orbital cortex (medial prefrontal network), amygdala, hippocampus, and ventromedial parts of the basal ganglia, where alterations in grey matter volume and neurophysiological activity are found in cases with recurrent depressive episodes. Such findings hold major implications for models of the neurocircuits that underlie depression. In particular evidence from lesion analysis studies suggests that the MPFC and related limbic and striato-pallido-thalamic structures organize emotional expression. The MPFC is part of a larger "default system" of cortical areas that include the dorsal PFC, mid- and posterior cingulate cortex, anterior temporal cortex, and entorhinal and parahippocampal cortex, which has been implicated in self-referential functions. Dysfunction within and between structures in this circuit may induce disturbances in emotional behavior and other cognitive aspects of depressive syndromes in humans. Further, because the MPFC and related limbic structures provide forebrain modulation over visceral control structures in the hypothalamus and brainstem, their dysfunction can account for the disturbances in autonomic regulation and neuroendocrine responses that are associated with mood disorders. This paper discusses these systems together with the neurochemical systems that impinge on them and form the basis for most pharmacological therapies.

Serotonin transporter genotype and depressive phenotype determination by discriminant analysis of glucose metabolism under acute tryptophan depletion

Acute tryptophan depletion (ATD) putatively results in a transient reduction in central serotonin transmission, and induces depressed mood in some un-medicated subjects with remitted major depressive disorder (MDD). The 5-HT transporter promoter region length polymorphism (5-HTTLPR) has been shown to influence behavioral and metabolic responses to ATD, as well as the risk for developing MDD within the context of stress. The current study investigates the relationships between 5-HTTLPR genotype, neurophysiologic response to ATD, and diagnostic phenotype (healthy control subjects versus MDD subjects differentiated by their depressive response to ATD) using (18)FDG-PET. Un-medicated subjects with remitted MDD and healthy controls were genotyped for the long (l) and short (s) alleles of the 5-HTTLPR polymorphism and categorized into one of three genotypes. On two separate occasions, subjects received either a placebo or an amino acid mixture designed to deplete plasma tryptophan, followed by (18)FDG-PET scanning. Depressive symptoms were rated to determine the diagnostic phenotype. Descriptive and predictive discriminant analyses were performed using brain regional metabolic data to classify according to phenotype and genotype. Overall, 79% of the cases were classified correctly by genotype, and 85% were classified correctly by phenotype. In a leave-one-out cross-validation, 72% of the subjects were classified correctly as carrying an s-allele, and 79% of the subjects were classified correctly by primary diagnosis. The robust nature of the classification results indicates that much of the variance in metabolic response to ATD is accounted for by genotypic and phenotypic category.

Neurophysiological endophenotypes across bipolar and schizophrenia psychosis

The search for liability genes of the world's 2 major psychotic disorders, schizophrenia and bipolar disorder I (BP-I), has been extremely difficult even though evidence suggests that both are highly heritable. This difficulty is due to the complex and multifactorial nature of these disorders. They encompass several intermediate phenotypes, some overlapping across the 2 psychotic disorders that jointly and/or interactively produce the clinical manifestations. Research of the past few decades has identified several neurophysiological deficits in schizophrenia that frequently occur before the onset of psychosis. These include abnormalities in smooth pursuit eye movements, P50 sensory gating, prepulse inhibition, P300, mismatch negativity, and neural synchrony. Evidence suggests that many of these physiological deficits are distinct from each other. They are stable, mostly independent of symptom state and medications (with some exceptions) and are also observed in non-ill relatives. This suggests a familial and perhaps genetic nature. Some deficits are also observed in the BP-I probands and to a lesser extent their relatives. These deficits in physiological measures may represent the intermediate phenotypes that index small effects of genes (and/or environmental factors). The use of these measures in genetic studies may help the hunt for psychosis liability genes and clarify the extent to which the 2 major psychotic disorders share etio-pathophysiology. In spite of the rich body of work describing these neurophysiological measures in psychotic disorders, challenges remain: Many of the neurophysiological phenotypes are still relatively complex and are associated with low heritability estimates. Further refinement of these physiological phenotypes is needed that could identify specific underlying physiological deficits and thereby improve their heritability estimates. The extent to which these neurophysiological deficits are unique or overlap across BP-I and schizophrenia is unclear. And finally, the clinical and functional consequences of the neurophysiological deficits both in the probands and their relatives are not well described.

Cytology and receptor architecture of human anterior cingulate cortex

Anterior cingulate cortex (ACC) is involved in emotion, mood, and autonomic regulation. Although a subgenual part of ACC (sACC) may be vulnerable in depression and area 25 is cytologically unique, there are no assessments that contrast this region with pregenual ACC (pACC). Thus, we undertook independent multimodal verifications of architectural differences among subregions and areas. Areas 24a and 24b have pregenual and subgenual components. The latter have a thin layer III. Area 24c has dorsal (pd24c) and ventral (pv24c) parts. Area pd24c has larger neurofilament-expressing neurons in layer Va, and neurons in Vb form aggregates in area pv24c. Area pd24c occupies both banks of the cingulate sulcus, with pv24c on the ventral bank. Layer III of pd24cd has many larger neurofilament-expressing neurons and a richer dendritic plexus. Area 32 has pregenual (p32) and subgenual (s32) components. Layer II in s32 is of particular note because it has a neuron-dense IIa and sparse IIb. Area 25 has anterior (25a) and posterior (25p) parts; 25p has the thinnest layer III in the cingulate gyrus. Area 25a contains significantly higher AMPA, kainate, NMDA, GABA(A), GABA(B), and alpha(1) densities than 25p. Area 33 continues around the genu and ventrally to encompass the full caudal extent of area 25. Subgenual ACC has significantly higher GABA(A), GABA(B), benzodiazepine (BZ), alpha(1), and 5-HT(1A) densities than pACC. GABA(B), BZ, and alpha(1) binding confirms the subdivision of area pd24c. In conclusion, ACC comprises two parts that are unique in terms of their cytoarchitecture and neurotransmitter receptor organization.

Assessing the role of cingulate cortex in bipolar disorder: neuropathological, structural and functional imaging data

OBJECTIVES

Most of the neuroanatomical models of bipolar disorder (BD) propose a key role for the anterior cingulate cortex (ACC). We provide here a review of currently available data regarding the CC neuroimaging and neuropathological alterations in BD.

MATERIALS AND METHODS

After an exploratory search of the MEDLINE, we first identified all English-written articles that provide separate data for BD patients and report original experimental data on cingulate gyrus. Subsequently, we selected those including neuroimaging or neuropathological data. Among the 161 articles updated through June 2007, 81 articles were retained using this procedure.

RESULTS

The review of in vivo volumetric imaging data, as well as ex vivo morphometric and histological studies indicates that BD patients show volume changes of the subgenual ACC (sgACC-BA 25 and part of 24) during the early stages of the disease. Whether this phenomenon is due to neuronal and glial depletion or damage of corticocortical connections is still a matter of debate. The resting state activity in the left BA 25 appears to be state dependent showing significant increase during mania and decrease during depressive phases. The presence of a deficient GABAergic activity in ACC is also documented. Pharmacological treatment partly restores BD-related functional imaging changes.

CONCLUSION

The present review reveals the striking discrepancies of the experimental results present both for functional and structural imaging studies but also for neuropathological analyses. Methodological and conceptual limitations are addressed with particular reference to the heterogeneity of BD clinical patterns. We also critically discuss the validity of CC changes as possible trait- or state-markers of the disease.

The changes of AgNOR parameters of anterior cingulate pyramidal neurons are region-specific in suicidal and non-suicidal depressive patients

The anterior cingulate cortex (AC) is consistently implicated in the pathophysiology of depression. While suicide has been shown in previous reports to be closely related to depression, it is still a distinct phenomenon. The aim to differentiate between depression and suicide was approached by the karyometric analysis of AC pyramidal neurons. The study was performed on paraffin-embedded brains from 20 depressive patients (10 of whom had committed suicide) and 24 matched controls. The karyometric parameters of the layer III and V pyramidal neurons of the dorsal and ventral AC were evaluated bilaterally by Argyrophilic Nucleolar Organiser (AgNOR) silver staining method. Control-specific was the increased nuclear area in ontogenetically younger pyramidal neurons layer III in the left dorsal compared with ventral AC (Wilcoxon test, P<0.01). The decreased AgNOR number per nucleus in these cells in the right ventral AC was depression-specific compared with controls (t-test, P=0.047). On the other hand, the diffuse decrease in AgNOR ratio throughout pyramidal neurons on the left side was specific for suicidal depressive patients compared with non-suicidal patients and controls (ANOVA, P=0.028). The results suggest that regionally differentiated depression- and suicide-specific disturbed function of the most important AC output cells exists in depressive patients.