Lateralization of the serotonin-1A receptor distribution in language areas revealed by PET

Effects of the suppression of 5-HT1A receptors in the left, right, or bilateral basolateral amygdala on memory consolidation in chronic stress in male rats

The serotonin-1A receptors (5-HT1A) in the two cerebral hemispheres are differentially involved in memory. The distribution of 5-HT1A receptors in the left and right amygdala is different. Furthermore, evidence shows that the 5-HT1A receptors in the left and right amygdala work differently in memory function. The basolateral amygdala (BLA) also regulates hippocampal long-term potentiation (LTP) during stress. However, which BLA structure in each hemisphere underlies such lateralized function is unclear. The present research investigated the possible involvement of 5-HT1A lateralization in the BLA on stress-induced memory impairment. 5-HT1A receptor antagonist (Way-100-635) was injected into the left, right, or bilateral BLA twenty minutes before chronic restraint stress (CRS) for 14 consecutive days. Results indicated that suppression of 5HT1A-receptors in the BLA plays an essential role in reducing the acquisition of passive avoidance in the shuttle box test and spatial memory in the Barnes maze test in the stress animals. This decrease was significant in the CRS animals with left and bilateral suppressed 5HT1A-receptors in the BLA. Field potential recording results showed that the left, right, and bilateral injection of Way-100-635 into the BLA significantly reduced the slope and amplitude of fEPSP in the CA1 area of the hippocampus in stressed rats. No significant difference was observed in neuronal arborization in the CA1 area of the hippocampus. In conclusion, the 5-HT1A receptor in the left and right sides of BLA nuclei play a different role in memory consolidation in the hippocampus under stress.

Lateralization of the 5-HT1A receptors in the basolateral amygdala in metabolic and anxiety responses to chronic restraint stress

Behavioral and functional studies describe hemispheric asymmetry in anxiety and metabolic behaviors in responses to stress. However, no study has reported serotonergic receptor (the 5-HT1A receptor) lateralization in the basolateral amygdala (BLA) in vivo on anxiety and metabolic behaviors under stress. In the present study, the effect of unilateral and bilateral suppression of the 5-HT1A receptor in the BLA on anxiety, and metabolic responses to chronic restraint stress was assessed. Male Wistar rats 7 days after cannulation into the BLA received chronic restraint stress for 14 consecutive days. 20 minutes before induction of stress, WAY-100-635 (selective 5-HT1A antagonist) or sterile saline (vehicle) was administered either uni- or bi-laterally into the BLA. Behavioral (elevated plus maze; EPM, and open field test), and metabolic parameter studies were performed. Results showed that stress causes a significant increase in weight gain compared to control. In the non-stress condition, the left and bilaterally, and in the stress condition the right, left, and both sides, inhibition of 5-HT1A in the BLA reduced weight gain. In the restraint stress condition, only inhibition of the 5-HT1A receptor in the left BLA led to decreased food intake compared to the control group. In stress conditions, inhibition of the 5-HT1A receptor on the right, left, and bilateral BLA increased water intake compared to the stress group. Inhibition of the 5-HT1A receptor on the left side of the BLA by WAY-100-635 induced anxiety-like behaviors in stressed rats. Similarly, WAY-100-635 on the left BLA effectively caused anxiety-like behaviors in both EPM and open field tests in the control animals. In conclusion, it seems that 5-HT1A receptors in the left BLA are more responsible for anxiety-like behaviors and metabolic changes in responses to stress.

Effects of bilateral sequential theta-burst stimulation on 5-HT1A receptors in the dorsolateral prefrontal cortex in treatment-resistant depression: a proof-of-concept trial

Theta-burst stimulation (TBS) represents a brain stimulation technique effective for treatment-resistant depression (TRD) as underlined by meta-analyses. While the methodology undergoes constant refinement, bilateral stimulation of the dorsolateral prefrontal cortex (DLPFC) appears promising to restore left DLPFC hypoactivity and right hyperactivity found in depression. The post-synaptic inhibitory serotonin-1A (5-HT1A) receptor, also occurring in the DLPFC, might be involved in this mechanism of action. To test this hypothesis, we performed PET-imaging using the tracer [carbonyl-11C]WAY-100635 including arterial blood sampling before and after a three-week treatment with TBS in 11 TRD patients compared to sham stimulation (n = 8 and n = 3, respectively). Treatment groups were randomly assigned, and TBS protocol consisted of excitatory intermittent TBS to the left and inhibitory continuous TBS to the right DLPFC. A linear mixed model including group, hemisphere, time, and Hamilton Rating Scale for Depression (HAMD) score revealed a 3-way interaction effect of group, time, and HAMD on specific distribution volume (VS) of 5-HT1A receptor. While post-hoc comparisons showed no significant changes of 5-HT1A receptor VS in either group, higher 5-HT1A receptor VS after treatment correlated with greater difference in HAMD (r = -0.62). The results of this proof-of-concept trial hint towards potential effects of TBS on the distribution of the 5-HT1A receptor. Due to the small sample size, all results must, however, be regarded with caution.

Data-driven analysis of kappa opioid receptor binding in major depressive disorder measured by positron emission tomography

Preclinical studies have implicated kappa opioid receptors (KORs) in stress responses and depression-related behaviors, but evidence from human studies is limited. Here we present results of a secondary analysis of data acquired using positron emission tomography (PET) with the KOR radiotracer [¹¹C]GR103545 in 10 unmedicated, currently depressed individuals with major depressive disorder (MDD; 32.6 ± 6.5 years, 5 women) and 13 healthy volunteers (34.8 ± 10 years, 6 women). Independent component analysis was performed to identify spatial patterns of coherent variance in KOR binding (tracer volume of distribution, V_T) across all subjects. Expression of each component was compared between groups and relationships to symptoms were explored using the 17-item Hamilton Depression Rating Scale (HDRS). Three components of variation in KOR availability across ROIs were identified, spatially characterized by [¹¹C]GR103545 V_T in (1) bilateral frontal lobe; (2) occipital and parietal cortices, right hippocampus, and putamen; and (3) right anterior cingulate, right superior frontal gyrus and insula, coupled to negative loading in left middle cingulate. In MDD patients, component 3 was negatively associated with symptom severity on the HDRS (r = -0.85, p = 0.0021). There were no group-wise differences in expression of any component between patients and controls. These preliminary findings suggest that KOR signaling in cortical regions relevant to depression, particularly right anterior cingulate, could reflect MDD pathophysiology.

Pretreatment qEEG biomarkers for predicting pharmacological treatment outcome in major depressive disorder: Independent validation from the NeuroPharm study

Several electroencephalogram (EEG) biomarkers for prediction of drug response in major depressive disorder (MDD) have been proposed, but validations in larger independent datasets are missing. In the current study, we investigated the prognostic value of previously suggested EEG biomarkers. We gathered data that matched prior studies in terms of EEG methodology, clinical criteria for MDD, and statistical approach as closely as possible. The NeuroPharm study is a non-randomized and open label prospective clinical trial. One hundred antidepressant free patients with MDD were enrolled in the study and 79 (57 female) were included in the per-protocol analysis. The biomarkers candidates for cross-validation were derived from prior studies such as iSPOT-D and EMBARC and include frontal and occipital alpha power and asymmetry and delta and theta activity at anterior cingulate cortex (ACC). The alpha asymmetry, reported in two out of six prior studies, could be partially validated. We found that in female patients, larger right than left frontal alpha power prior to drug treatment was associated with better clinical outcome 8 weeks later. Moreover, female non-responder had higher central left alpha power relative to the right. In contrast to prior reports, we found that lower theta activity at ACC was present in remitters and was associated with greater improvement at week 8. We provide evidence that in women with MDD, alpha asymmetry seems to be the most promising EEG biomarker for prediction of treatment response. Registration number: NCT02869035.

Citalopram reduces glutamatergic synaptic transmission in the auditory cortex via activation of 5-HT1A receptors

Serotonin modulates cognitive processes and is related to various psychiatric disorders, including major depression. Administration of citalopram reduces the amplitude of auditory evoked potentials in depressed people and animal models, suggesting that 5-HT has an inhibitory role. Here, we characterize the modulation of excitatory post-synaptic currents by application of either 5-HT or agonists of 5-HT1A and 5-HT2 receptors, or by endogenous 5-HT evoked by citalopram on pyramidal neurons from layer II/III of rat auditory cortex. We found that application of 5-HT concentration-dependently reduces excitatory post-synaptic currents amplitude without changing the paired-pulse ratio, suggesting a post-synaptic modulation. We observed that selective agonists of 5-HT1A and 5-HT2 receptors [8-OH-DPAT (10 µM) and DOI (10 µM), respectively] mimic the effect of 5-HT on the excitatory post-synaptic currents. Effect of 5-HT was entirely blocked by co-application of the antagonists NAN-190 (1 µM) and ritanserin (200 nM). Similarly, citalopram application (1 μM) reduced the amplitude of the evoked excitatory post-synaptic currents. Reduction in the magnitude of the excitatory post-synaptic currents by endogenous 5-HT was interpolated in the dose-response curve elicited by exogenous 5-HT, yielding that citalopram raised the extracellular 5-HT concentration to 823 nM. Effect of citalopram was blocked by the previous application of NAN-190 but not ritanserin, indicating that citalopram reduces glutamatergic synaptic transmission via 5-HT1A receptors in layer II/III of the auditory cortex. These results suggest that the local activity of 5-HT contributes to decrease in the basal excitability of the auditory cortex for enhancing the detection of external relevant acoustic signals.

Effects of Serotonin Transporter Gene Variation on Impulsivity Mediated by Default Mode Network: A Family Study of Depression

Serotonergic neurotransmission, potentially through effects on the brain's default mode network (DMN), may regulate aspects of attention including impulse control. Indeed, genetic variants of the serotonin transporter (5-HTT) have been implicated in impulsivity and related psychopathology. Yet it remains unclear the mechanism by which the 5-HTT genetic variants contribute to individual variability in impulse control. Here, we tested whether DMN connectivity mediates an association between the 5-HTT genetic variants and impulsivity. Participants (N = 92) were from a family cohort study of depression in which we have previously shown a broad distribution of 5-HTT variants. We genotyped for 5-HTTLPR and rs25531 (stratified by transcriptional efficiency: 8 low/low, 53 low/high, and 31 high/high), estimated DMN structural connectivity using diffusion probabilistic tractography, and assessed behavioral measures of impulsivity (from 12 low/low, 48 low/high, and 31 high/high) using the Continuous Performance Task. We found that low transcriptional efficiency genotypes were associated with decreased connection strength between the posterior DMN and the superior frontal gyrus (SFG). Path modeling demonstrated that decreased DMN-SFG connectivity mediated the association between low-efficiency genotypes and increased impulsivity. Taken together, this study suggests a gene-brain-behavior pathway that perhaps underlies the role of the serotonergic neuromodulation in impulse control.

Epistasis of HTR1A and BDNF risk genes alters cortical 5-HT1A receptor binding: PET results link genotype to molecular phenotype in depression

Alterations of the 5-HT_1A receptor and BDNF have consistently been associated with affective disorders. Two functional single nucleotide polymorphisms (SNPs), rs6295 of the serotonin 1A receptor gene (HTR1A) and rs6265 of brain-derived neurotrophic factor gene (BDNF), may impact transcriptional regulation and expression of the 5-HT_1A receptor. Here we investigated interaction effects of rs6295 and rs6265 on 5-HT_1A receptor binding. Forty-six healthy subjects were scanned with PET using the radioligand [carbonyl-¹¹C]WAY-100635. Genotyping was performed for rs6265 and rs6295. Subjects showing a genotype with at least three risk alleles (G of rs6295 or A of rs6265) were compared to control genotypes. Cortical surface binding potential (BP_ND) was computed for 32 cortical regions of interest (ROI). Mixed model was applied to study main and interaction effects of ROI and genotype. ANOVA was used for post hoc analyses. Individuals with the risk genotypes exhibited an increase in 5-HT_1A receptor binding by an average of 17% (mean BP_ND 3.56 ± 0.74 vs. 2.96 ± 0.88). Mixed model produced an interaction effect of ROI and genotype on BP_ND and differences could be demonstrated in 10 ROI post hoc. The combination of disadvantageous allelic expression of rs6295 and rs6265 may result in a 5-HT_1A receptor profile comparable to affective disorders as increased 5-HT_1A receptor binding is a well published phenotype of depression. Thus, epistasis between BDNF and HTR1A may contribute to the multifactorial risk for affective disorders and our results strongly advocate further research on this genetic signature in affective disorders.

Toward the Language Oscillogenome

Language has been argued to arise, both ontogenetically and phylogenetically, from specific patterns of brain wiring. We argue that it can further be shown that core features of language processing emerge from particular phasal and cross-frequency coupling properties of neural oscillations; what has been referred to as the language ‘oscillome.’ It is expected that basic aspects of the language oscillome result from genetic guidance, what we will here call the language ‘oscillogenome,’ for which we will put forward a list of candidate genes. We have considered genes for altered brain rhythmicity in conditions involving language deficits: autism spectrum disorders, schizophrenia, specific language impairment and dyslexia. These selected genes map on to aspects of brain function, particularly on to neurotransmitter function. We stress that caution should be adopted in the construction of any oscillogenome, given the range of potential roles particular localized frequency bands have in cognition. Our aim is to propose a set of genome-to-language linking hypotheses that, given testing, would grant explanatory power to brain rhythms with respect to language processing and evolution.

Associations Between Brain Structure and Connectivity in Infants and Exposure to Selective Serotonin Reuptake Inhibitors During Pregnancy

IMPORTANCE

Selective serotonin reuptake inhibitor (SSRI) use among pregnant women is increasing, yet the association between prenatal SSRI exposure and fetal neurodevelopment is poorly understood. Animal studies show that perinatal SSRI exposure alters limbic circuitry and produces anxiety and depressive-like behaviors after adolescence, but literature on prenatal SSRI exposure in humans is limited and mixed.

OBJECTIVE

To examine associations between prenatal SSRI exposure and brain development using structural and diffusion magnetic resonance imaging (MRI).

DESIGN, SETTING, AND PARTICIPANTS

A cohort study conducted at Columbia University Medical Center and New York State Psychiatric Institute included 98 infants: 16 with in utero SSRI exposure, 21 with in utero untreated maternal depression exposure, and 61 healthy controls. Data were collected between January 6, 2011, and October 25, 2016.

EXPOSURES

Selective serotonin reuptake inhibitors and untreated maternal depression.

MAIN OUTCOMES AND MEASURES

Gray matter volume estimates using structural MRI with voxel-based morphometry and white matter structural connectivity (connectome) using diffusion MRI with probabilistic tractography.

RESULTS

The sample included 98 mother (31 [32%] white, 26 [27%] Hispanic/Latina, 26 [27%] black/African American, 15 [15%] other) and infant (46 [47%] boys, 52 [53%] girls) dyads. Mean (SD) age of the infants at the time of the scan was 3.43 (1.50) weeks. Voxel-based morphometry showed significant gray matter volume expansion in the right amygdala (Cohen d = 0.65; 95% CI, 0.06-1.23) and right insula (Cohen d = 0.86; 95% CI, 0.26-1.14) in SSRI-exposed infants compared with both healthy controls and infants exposed to untreated maternal depression (P < .05; whole-brain correction). In connectome-level analysis of white matter structural connectivity, the SSRI group showed a significant increase in connectivity between the right amygdala and the right insula with a large effect size (Cohen d = 0.99; 95% CI, 0.40-1.57) compared with healthy controls and untreated depression (P < .05; whole connectome correction).

CONCLUSIONS AND RELEVANCE

Our findings suggest that prenatal SSRI exposure has an association with fetal brain development, particularly in brain regions critical to emotional processing. The study highlights the need for further research on the potential long-term behavioral and psychological outcomes of these neurodevelopmental changes.

Sex steroid hormones and brain function: PET imaging as a tool for research

Sex steroid hormones are major regulators of sexual characteristic among species. These hormones, however, are also produced in the brain. Steroidal hormone-mediated signalling via the corresponding hormone receptors can influence brain function at the cellular level and thus affect behaviour and higher brain functions. Altered steroid hormone signalling has been associated with psychiatric disorders, such as anxiety and depression. Neurosteroids are also considered to have a neuroprotective effect in neurodegenerative diseases. So far, the role of steroid hormone receptors in physiological and pathological conditions has mainly been investigated post mortem on animal or human brain tissues. To study the dynamic interplay between sex steroids, their receptors, brain function and behaviour in psychiatric and neurological disorders in a longitudinal manner, however, non-invasive techniques are needed. Positron emission tomography (PET) is a non-invasive imaging tool that is used to quantitatively investigate a variety of physiological and biochemical parameters in vivo. PET uses radiotracers aimed at a specific target (eg, receptor, enzyme, transporter) to visualise the processes of interest. In this review, we discuss the current status of the use of PET imaging for studying sex steroid hormones in the brain. So far, PET has mainly been investigated as a tool to measure (changes in) sex hormone receptor expression in the brain, to measure a key enzyme in the steroid synthesis pathway (aromatase) and to evaluate the effects of hormonal treatment by imaging specific downstream processes in the brain. Although validated radiotracers for a number of targets are still warranted, PET can already be a useful technique for steroid hormone research and facilitate the translation of interesting findings in animal studies to clinical trials in patients.

Association of Protein Distribution and Gene Expression Revealed by PET and Post-Mortem Quantification in the Serotonergic System of the Human Brain

Regional differences in posttranscriptional mechanisms may influence in vivo protein densities. The association of positron emission tomography (PET) imaging data from 112 healthy controls and gene expression values from the Allen Human Brain Atlas, based on post-mortem brains, was investigated for key serotonergic proteins. PET binding values and gene expression intensities were correlated for the main inhibitory (5-HT1A) and excitatory (5-HT2A) serotonin receptor, the serotonin transporter (SERT) as well as monoamine oxidase-A (MAO-A), using Spearman's correlation coefficients (rs) in a voxel-wise and region-wise analysis. Correlations indicated a strong linear relationship between gene and protein expression for both the 5-HT1A (voxel-wise rs = 0.71; region-wise rs = 0.93) and the 5-HT2A receptor (rs = 0.66; 0.75), but only a weak association for MAO-A (rs = 0.26; 0.66) and no clear correlation for SERT (rs = 0.17; 0.29). Additionally, region-wise correlations were performed using mRNA expression from the HBT, yielding comparable results (5-HT1Ars = 0.82; 5-HT2Ars = 0.88; MAO-A rs = 0.50; SERT rs = -0.01). The SERT and MAO-A appear to be regulated in a region-specific manner across the whole brain. In contrast, the serotonin-1A and -2A receptors are presumably targeted by common posttranscriptional processes similar in all brain areas suggesting the applicability of mRNA expression as surrogate parameter for density of these proteins.

Relations between cortical thickness, serotonin 1A receptor binding, and structural connectivity: A multimodal imaging study

Serotonin 1A (5-HT_1A ) receptors play a direct role in neuronal development, cell proliferation, and dendritic branching. We hypothesized that variability in 5-HT_1A binding can affect cortical thickness, and may account for a subtype of major depressive disorder (MDD) in which both are altered. To evaluate this, we measured cortical thickness from structural magnetic resonance imaging (MRI) and 5-HT_1A binding by positron emission tomography (PET) in an exploratory study. To examine a range of 5-HT_1A binding and cortical thickness values, we recruited 25 healthy controls and 19 patients with MDD. We hypothesized increased 5-HT_1A binding in the raphe nucleus (RN) would be negatively associated with cortical thickness due to reduced serotonergic transmission. Contrary to our hypothesis, raphe 5-HT_1A binding was positively correlated with cortical thickness in right posterior cingulate cortex (PCC), a region implicated in the default mode network. Cortical thickness was also positively correlated with 5-HT_1A in each cortical region. We further hypothesized that the strength of 5-HT_1A -cortical thickness correlation depends on the number of axons between the raphe nucleus and each region. To explore this we related 5-HT_1A -cortical thickness correlation coefficients to the number of tracts connecting that region and the raphe, as measured by diffusion tensor imaging (DTI) in an independent sample. The 5-HT_1A -cortical thickness association correlated significantly with the number of tracts to each region, supporting our hypothesis. We posit a defect in the raphe may affect the PCC within the default mode network in MDD through serotonergic fibers, resulting in increased ruminative processing.

Interaction effect between 5-HTTLPR and HTR1A rs6295 polymorphisms on the frontoparietal network

Previous studies have shown a close relationship between the serotonin system and working memory (WM), but the neural mechanism for the role of the serotonin system on the WM is unclear. The frontoparietal network is involved in WM and is associated with the serotonin system. Therefore, this study investigated the interaction effect of the serotonin transporter-linked polymorphic region (5-HTTLPR) and the polymorphism in the serotonin 1A receptor gene (rs6295) on the frontoparietal network obtained from the independent component analysis in a large, young Chinese sample population. The current study found a significant interaction effect of 5-HTTLPR and rs6295 on the connectivity within the right frontoparietal network, specifically in the middle frontal gyrus and inferior parietal lobule. Moreover, the mean connectivity in the right inferior parietal lobule was positively correlated with WM performance. These brain network analysis findings could provide a new perspective on the neural mechanisms of gene-gene interactions and on individual differences in cognitive functions.

The influence of the rs6295 gene polymorphism on serotonin-1A receptor distribution investigated with PET in patients with major depression applying machine learning

Major depressive disorder (MDD) is the most common neuropsychiatric disease and despite extensive research, its genetic substrate is still not sufficiently understood. The common polymorphism rs6295 of the serotonin-1A receptor gene (HTR1A) is affecting the transcriptional regulation of the 5-HT_1A receptor and has been closely linked to MDD. Here, we used positron emission tomography (PET) exploiting advances in data mining and statistics by using machine learning in 62 healthy subjects and 19 patients with MDD, which were scanned with PET using the radioligand [carbonyl-¹¹C]WAY-100635. All the subjects were genotyped for rs6295 and genotype was grouped in GG vs C allele carriers. Mixed model was applied in a ROI-based (region of interest) approach. ROI binding potential (BP_ND) was divided by dorsal raphe BP_ND as a specific measure to highlight rs6295 effects (BP_Div). Mixed model produced an interaction effect of ROI and genotype in the patients' group but no effects in healthy controls. Differences of BP_Div was demonstrated in seven ROIs; parahippocampus, hippocampus, fusiform gyrus, gyrus rectus, supplementary motor area, inferior frontal occipital gyrus and lingual gyrus. For classification of genotype, 'RandomForest' and Support Vector Machines were used, however, no model with sufficient predictive capability could be computed. Our results are in line with preclinical data, mouse model knockout studies as well as previous clinical analyses, demonstrating the two-pronged effect of the G allele on 5-HT_1A BP_ND for, we believe, the first time. Future endeavors should address epigenetic effects and allosteric heteroreceptor complexes. Replication in larger samples of MDD patients is necessary to substantiate our findings.

Interhemispheric gene expression differences in the cerebral cortex of humans and macaque monkeys

Handedness and language are two well-studied examples of asymmetrical brain function in humans. Approximately 90% of humans exhibit a right-hand preference, and the vast majority shows left-hemisphere dominance for language function. Although genetic models of human handedness and language have been proposed, the actual gene expression differences between cerebral hemispheres in humans remain to be fully defined. In the present study, gene expression profiles were examined in both hemispheres of three cortical regions involved in handedness and language in humans and their homologues in rhesus macaques: ventrolateral prefrontal cortex, posterior superior temporal cortex (STC), and primary motor cortex. Although the overall pattern of gene expression was very similar between hemispheres in both humans and macaques, weighted gene correlation network analysis revealed gene co-expression modules associated with hemisphere, which are different among the three cortical regions examined. Notably, a receptor-enriched gene module in STC was particularly associated with hemisphere and showed different expression levels between hemispheres only in humans.

Laterality of Brain Activation for Risk Factors of Addiction

Background:

Laterality of brain activation is reported for tests of risk factors of addiction - impulsivity and craving - but authors rarely address the potential significance of those asymmetries.

Objective:

The purpose of this study is to demonstrate this laterality and discuss its relevance to cognitive and neurophysiological asymmetries associated with drug abuse vulnerability in order to provide new insights for future research in drug abuse.

Method:

From published reports, brain areas of activation for two tests of response inhibition or craving for drugs of abuse were compiled from fMRI activation peaks and were tabulated for eight sections (octants) in each hemisphere. Percent asymmetries were calculated (R-L/R+L) across studies for each area.

Results:

For impulsivity, most activation peaks favored the right hemisphere. Overall, the percent difference was 32% (Χ² = 16.026; p < 0.0001) with the greater asymmetry for anterior peaks (46.8%; Χ² = 17.329; p < 0.0001). The asymmetries for cue-induced craving were opposite, favoring the left hemisphere by 6.7% (Χ² = 4.028; p < 0.05). The consistency of left asymmetry was found for almost all drugs. For nicotine, studies where subjects were not allowed to smoke (deprived) prior to measurement had the same left hemisphere activation but those who smoked (satiated) before the fMRI measure showed right asymmetry.

Conclusion:

Brain activation studies demonstrate different left/right hemispheric contributions for impulsivity versus craving - factors related to addiction. Failure to take laterality into consideration is a missed opportunity in designing studies and gaining insight into the etiology of drug abuse and pathways for treatment.

Symmetric Bihemispheric Postmortem Brain Cutting to Study Healthy and Pathological Brain Conditions in Humans

Neuropathologists, at times, feel intimidated by the amount of knowledge needed to generate definitive diagnoses for complex neuropsychiatric phenomena described in those patients for whom a brain autopsy has been requested. Although the advancements of biomedical sciences and neuroimaging have revolutionized the neuropsychiatric field, they have also generated the misleading idea that brain autopsies have only a confirmatory value. This false idea created a drastic reduction of autopsy rates and, consequently, a reduced possibility to perform more detailed and extensive neuropathological investigations, which are necessary to comprehend numerous normal and pathological aspects yet unknown of the human brain. The traditional inferential method of correlation between observed neuropsychiatric phenomena and corresponding localization/characterization of their possible neurohistological correlates continues to have an undeniable value. In the context of neuropsychiatric diseases, the traditional clinicopathological method is still the best possible methodology (and often the only available) to link unique neuropsychiatric features to their corresponding neuropathological substrates, since it relies specifically upon the direct physical assessment of brain tissues. The assessment of postmortem brains is based on brain cutting procedures that vary across different neuropathology centers. Brain cuttings are performed in a relatively extensive and systematic way based on the various clinical and academic contingencies present in each institution. A more anatomically inclusive and symmetric bi-hemispheric brain cutting methodology should at least be used for research purposes in human neuropathology to coherently investigate, in depth, normal and pathological conditions with the peculiarities of the human brain (i.e., hemispheric specialization and lateralization for specific functions). Such a method would provide a more comprehensive collection of neuropathologically well-characterized brains available for current and future biotechnological and neuroimaging techniques. We describe a symmetric bi-hemispheric brain cutting procedure for the investigation of hemispheric differences in human brain pathologies and for use with current as well as future biomolecular/neuroimaging techniques.

Spreading activation in nonverbal memory networks

Theories of spreading activation primarily involve semantic memory networks. However, the existence of separate verbal and visuospatial memory networks suggests that spreading activation may also occur in visuospatial memory networks. The purpose of the present investigation was to explore this possibility. Specifically, this study sought to create and describe the design frequency corpus and to determine whether this measure of visuospatial spreading activation was related to right hemisphere functioning and spreading activation in verbal memory networks. We used word frequencies taken from the Controlled Oral Word Association Test and design frequencies taken from the Ruff Figural Fluency Test as measures of verbal and visuospatial spreading activation, respectively. Average word and design frequencies were then correlated with measures of left and right cerebral functioning. The results indicated that a significant relationship exists between performance on a test of right posterior functioning (Block Design) and design frequency. A significant negative relationship also exists between spreading activation in semantic memory networks and design frequency. Based on our findings, the hypotheses were supported. Further research will need to be conducted to examine whether spreading activation exists in visuospatial memory networks as well as the parameters that might modulate this spreading activation, such as the influence of neurotransmitters.

Serotonin 1A Receptors on Astrocytes as a Potential Target for the Treatment of Parkinson's Disease

Astrocytes are the most abundant neuron-supporting glial cells in the central nervous system. The neuroprotective role of astrocytes has been demonstrated in various neurological disorders such as amyotrophic lateral sclerosis, spinal cord injury, stroke and Parkinson’s disease (PD). Astrocyte dysfunction or loss-of-astrocytes increases the susceptibility of neurons to cell death, while astrocyte transplantation in animal studies has therapeutic advantage. We reported recently that stimulation of serotonin 1A (5-HT_1A) receptors on astrocytes promoted astrocyte proliferation and upregulated antioxidative molecules to act as a neuroprotectant in parkinsonian mice. PD is a progressive neurodegenerative disease with motor symptoms such as tremor, bradykinesia, rigidity and postural instability, that are based on selective loss of nigrostriatal dopaminergic neurons, and with non-motor symptoms such as orthostatic hypotension and constipation based on peripheral neurodegeneration. Although dopaminergic therapy for managing the motor disability associated with PD is being assessed at present, the main challenge remains the development of neuroprotective or disease-modifying treatments. Therefore, it is desirable to find treatments that can reduce the progression of dopaminergic cell death. In this article, we summarize first the neuroprotective properties of astrocytes targeting certain molecules related to PD. Next, we review neuroprotective effects induced by stimulation of 5-HT_1A receptors on astrocytes. The review discusses new promising therapeutic strategies based on neuroprotection against oxidative stress and prevention of dopaminergic neurodegeneration.

Mesocorticolimbic dopamine functioning in primary psychopathy: A source of within-group heterogeneity

Despite similar emotional deficiencies, primary psychopathic individuals can be situated on a continuum that spans from controlled to disinhibited. The constructs on which primary psychopaths are found to diverge, such as self-control, cognitive flexibility, and executive functioning, are crucially regulated by dopamine (DA). As such, the goal of this review is to examine which specific alterations in the meso-cortico-limbic DA system and corresponding genes (e.g., TH, DAT, COMT, DRD2, DRD4) might bias development towards a more controlled or disinhibited expression of primary psychopathy. Based on empirical data, it is argued that primary psychopathy is generally related to a higher tonic and population activity of striatal DA neurons and lower levels of D2-type DA receptors in meso-cortico-limbic projections, which may boost motivational drive towards incentive-laden goals, dampen punishment sensitivity, and increase future reward-expectancy. However, increasingly higher levels of DA activity in the striatum (moderate versus pathological elevations), lower levels of DA functionality in the prefrontal cortex, and higher D1-to-D2-type receptor ratios in meso-cortico-limbic projections may lead to increasingly disinhibited and impetuous phenotypes of primary psychopathy. Finally, in order to provide a more coherent view on etiological mechanisms, we discuss interactions between DA and serotonin that are relevant for primary psychopathy.

Asymmetry of the Brain: Development and Implications

Although the left and right hemispheres of our brains develop with a high degree of symmetry at both the anatomical and functional levels, it has become clear that subtle structural differences exist between the two sides and that each is dominant in processing specific cognitive tasks. As the result of evolutionary conservation or convergence, lateralization of the brain is found in both vertebrates and invertebrates, suggesting that it provides significant fitness for animal life. This widespread feature of hemispheric specialization has allowed the emergence of model systems to study its development and, in some cases, to link anatomical asymmetries to brain function and behavior. Here, we present some of what is known about brain asymmetry in humans and model organisms as well as what is known about the impact of environmental and genetic factors on brain asymmetry development. We specifically highlight the progress made in understanding the development of epithalamic asymmetries in zebrafish and how this model provides an exciting opportunity to address brain asymmetry at different levels of complexity.

The role of early posttraumatic neuropsychological outcomes in the appearance of latter psychiatric disorders in adults with brain trauma

BACKGROUND

The objective was to determine the predictors of posttraumatic psychiatric disorders (PTPD) during the first 6 months following traumatic brain injury (TBI) focusing on neuroimaging, clinical and neuropsychological appraisements during acute and discharge phase of TBI.

MATERIALS AND METHODS

We designed a prospective, longitudinal study in which 150 eligible TBI patients were entered. Postresuscitation brain injury severity and discharged functional outcome were evaluated by standard clinical scales. First neuroimaging was done at a maximum of 24 h after head trauma. Early posttraumatic (PT) neuropsychological outcomes were assessed using Persian neuropsychological tasks at discharge. The standardized psychiatric assessments were carefully implemented 6 months postinjury. A total of 133 patients returned for follow-up assessment at 6 months. They were divided into two groups according to the presence of PTPD.

RESULTS

Apparently, aggression was the most prevalent type of PTPD (31.48%). There was no significant difference between groups regarding functional outcome at discharge. Diffuse axonal injury (12.96%) and hemorrhages (40.74%) within the cortex (42.59%) and sub-cortex (33.33) significantly occurred more prevalent in PTPD group than non-PTPD ones. Primary postresuscitation TBI severity, early PT lingual deficit and subcortical lesion on first scan were able to predict PTPD at 6 months follow-up.

CONCLUSION

Almost certainly, the expansive dissociation risk of cortical and subcortical pathways related to linguistic deficits due to severe intracranial lesions over a period of time can augment possibility of subsequent conscious cognitive-emotional processing deficit, which probably contributes to latter PTPD. Hence, early combined therapeutic supplies including neuroprotective pharmacotherapy and neurofeedback for neural function reorganization can dampen the lesion expansion and latter PTPD.

Interaction between MAOA and FOXP2 in association with autism and verbal communication in a Korean population

Expression levels of monoamine oxidase A (MAOA), the enzyme that related to monoamine neurotransmitters metabolism such as serotonin, are related to schizophrenia and autism spectrum disorder. Forkhead box protein P2 (FOXP2), a transcription factor, is associated with abnormal language development and is expressed in several areas of the central nervous system in response to serotonin. For this reason, we undertook interaction analysis between MAOA and FOXP2 in autism spectrum disorder, including testing the verbal communication score of the childhood autism rating scale. In interaction analysis, the FOXP2-TCGC (rs12531289-rs1350135-rs10230087-rs2061183) diplotype and MAOA-TCG (rs6323-rs1801291-rs3027407) haplotype were significantly associated with autism spectrum disorder in males. However, when the interaction term was omitted, neither MAOA nor FOXP2 was associated with autism spectrum disorder or verbal communication. These results indicate that language and speech ability is affected by an interaction between FOXP2 and MAOA, but not by either gene separately.

Increased binding of 5-HT1A receptors in a dissociative amnesic patient after the recovery process

Dissociative amnesia is characterized by an inability to retrieve information already saved in memories. 5-HT has some role in neural regulatory control and may be related to the recovery from dissociative amnesia. To examine the role of 5-HT1A receptors in the recovery from dissociative amnesia, we performed two positron emission tomography (PET) scans on a 30-year-old patient of dissociative amnesia using [(11)C]WAY-100635, the first at amnesic state, and the second at the time he had recovered. Exploratory voxel-based analysis (VBA) was performed using SPM software. 5-HT1A BPND images were compared between the patient at amnesic and recovery states and healthy subjects (14 males, mean age 29.8 ± 6.45) with Jack-knife analysis. 5-HT1A receptor bindings of the patient at the recovery state were significantly higher than those of healthy subjects in the right superior and middle frontal cortex, left inferior frontal and orbitofrontal cortex and bilateral inferior temporal cortex. The increase in BPND values of recovery state was beyond 10% of those of amnesia state in these regions except in the right superior frontal cortex. We considered that neural regulatory control by the increase of 5-HT1A receptors in cortical regions played a role in the recovery from dissociative amnesia.

Gender differences in association between serotonin transporter gene polymorphism and resting-state EEG activity

Human brain oscillations represent important features of information processing and are highly heritable. Gender has been observed to affect association between the 5-HTTLPR (serotonin-transporter-linked polymorphic region) polymorphism and various endophenotypes. This study aimed to investigate the effects of 5-HTTLPR on the spontaneous electroencephalography (EEG) activity in healthy male and female subjects. DNA samples extracted from buccal swabs and resting EEG recorded at 60 standard leads were collected from 210 (101 men and 109 women) volunteers. Spectral EEG power estimates and cortical sources of EEG activity were investigated. It was shown that effects of 5-HTTLPR polymorphism on electrical activity of the brain vary as a function of gender. Women with the S/L genotype had greater global EEG power compared to men with the same genotype. In men, current source density was markedly different among genotype groups in only alpha 2 and alpha 3 frequency ranges: S/S allele carriers had higher current source density estimates in the left inferior parietal lobule in comparison with the L/L group. In women, genotype difference in global power asymmetry was found in the central-temporal region. Contrasting L/L and S/L genotype carriers also yielded significant effects in the right hemisphere inferior parietal lobule and the right postcentral gyrus with L/L genotype carriers showing lower current source density estimates than S/L genotype carriers in all but gamma bands. So, in women, the effects of 5-HTTLPR polymorphism were associated with modulation of the EEG activity in a wide range of EEG frequencies. The significance of the results lies in the demonstration of gene by sex interaction with resting EEG that has implications for understanding sex-related differences in affective states, emotion and cognition.

Relation of progesterone and DHEAS serum levels to 5-HT1A receptor binding potential in pre- and postmenopausal women

Preclinical research and clinical experience point to a modulation of 5-HT1A receptor expression by gonadal steroid hormones. We examined the effect of estradiol, progesterone and DHEAS on serotonin neurotransmission in 16 premenopausal and 28 postmenopausal women, differentiating by reproductive status. By means of positron emission tomography and the radiotracer [carbonyl-(11)C]WAY-100635, the 5-HT1A receptor binding potential (BP) was quantified in 45 brain regions of interest. Median BP was used as a surrogate marker to estimate the whole brain effect of the steroid hormones on receptor binding. We found a strong negative effect of serum progesterone and DHEAS levels on 5-HT1A receptor binding in postmenopausal women both in the Median BP and on a regional level. Furthermore, there was a non-linear, U-shaped relationship between DHEAS levels and 5-HT1A receptor binding in the pooled sample. Presynaptic 5-HT1A receptor BP in the raphe nuclei was significantly explained in a non-linear way by both progesterone and DHEAS in the pooled sample. Our study confirms in humans a preclinically suggested relation of the steroid hormones progesterone and DHEAS to 5-HT1A receptor binding. We show differential effects of the hormones with regard to reproductive hormonal status. Non-linear, U-shaped relationships between hormone serum concentrations and serotonin neurotransmission might explain paradoxical effects of these hormones on mood.

Monoamine metabolites in ventricular CSF of children with posterior fossa tumors: correlation with tumor histology and cognitive functioning

OBJECT

The biogenic amines (dopamine, epinephrine, norepinephrine, and serotonin) are involved in the regulation of multiple neuronal functions, and changes in monoamine concentrations in the CSF have been detected in several disorders. The aim of the present study was to investigate the role of biogenic amines in the ventricular CSF of children suffering from posterior fossa tumors and their possible correlation with tumor histology and cognitive functioning.

METHODS

Twenty-two children with posterior fossa tumors who were treated surgically at Children's Hospital "Agia Sofia" were studied. Patients ranged in age from 5.5 to 15 years. The study population included patients who suffered from hydrocephalus and were treated by ventriculoperitoneal shunt placement. During the operation for shunt placement, a CSF sample was obtained for the assessment of 3-methoxy-4-hydroxyphenylglycol (MHPG), homovanillic acid (HVA), and 5-hydroxyindoleacetic acid (5-HIAA). Simultaneously, a blood sample was also obtained for assessment of the same metabolites in the serum. The concentration of vanillylmandelic acid (VMA) was evaluated in 24-hour urine samples in 11 patients. Cerebrospinal fluid from a control group of children was also studied. Executive functions were assessed using the short form of the Wechsler Intelligence Scale for Children (WISC).

RESULTS

Twelve patients suffered from astrocytomas, 9 from medulloblastomas, and 1 from an ependymoma. The MHPG concentration in CSF was significantly higher in patients with astrocytomas compared with patients with medulloblastomas. Twenty-four-hour urine samples of VMA were significantly higher in patients with astrocytomas compared with patients with medulloblastomas. The MHPG concentration in CSF was negatively correlated with the verbal scale of the WISC and there was a trend toward a significant negative correlation with the total WISC score. Homovanillic acid in CSF was positively correlated with the performance scale of the WISC. There was a significant correlation between HVA and MHPG levels in CSF. The CSF concentration of 5-HIAA was significantly correlated with the HVA concentration in serum. Twenty-four-hour urine VMA samples were statistically significantly correlated with HVA concentration in both CSF and serum, with MHPG in CSF, and with 5-HIAA in serum.

CONCLUSIONS

This study showed that children with posterior fossa tumors have differences in the levels of monoamine metabolites in CSF. Further studies with a larger number of patients are obviously needed to verify these observations as well as studies to correlate the monoamine metabolite levels with the neuropsychological and behavioral findings in children with posterior fossa tumors.

Regional differences in SERT occupancy after acute and prolonged SSRI intake investigated by brain PET

Blocking of the serotonin transporter (SERT) represents the initial mechanism of action of selective serotonin reuptake inhibitors (SSRIs) which can be visualized due to the technical proceedings of SERT occupancy studies. When compared to the striatum, higher SERT occupancy in the midbrain and lower values in the thalamus were reported. This indicates that occupancy might be differently distributed throughout the brain, which is supported by preclinical findings indicating a regionally varying SERT activity and antidepressant drug concentration. The present study therefore aimed to investigate regional SERT occupancies with positron emission tomography and the radioligand [(11)C]DASB in 19 depressed patients after acute and prolonged intake of oral doses of either 10mg/day escitalopram or 20mg/day citalopram. Compared to the mean occupancy across cortical and subcortical regions, we detected increased SERT occupancies in regions commonly associated with antidepressant response, such as the subgenual cingulate, amygdala and raphe nuclei. When acute and prolonged drug intake was compared, SERT occupancies increased in subcortical areas that are known to be rich in SERT. Moreover, SERT occupancy in subcortical brain areas after prolonged intake of antidepressants was predicted by plasma drug levels. Similarly, baseline SERT binding potential seems to impact SERT occupancy, as regions rich in SERT showed greater binding reduction as well as higher residual binding. These findings suggest a region-specific distribution of SERT blockage by SSRIs and relate the postulated link between treatment response and SERT occupancy to certain brain regions such as the subgenual cingulate cortex.

Differential responses to anticipation of reward after an acute dose of the designer drugs benzylpiperazine (BZP) and trifluoromethylphenylpiperazine (TFMPP) alone and in combination using functional magnetic resonance imaging (fMRI)

RATIONALE

Functional magnetic resonance imaging (fMRI) studies have reported increased activation of the mesolimbic system in response to anticipation of rewarding stimuli. The anticipation of uncertain outcomes evokes activation in the amygdala, orbitofrontal cortex, inferior frontal gyrus and insula. Drugs known to effect dopaminergic and serotonergic neurons also alter regional activation.

OBJECTIVES

Benzylpiperazine (BZP) and/or trifluoromethylphenylpiperazine (TFMPP) have been recreationally used worldwide for more than a decade. BZP affects mainly dopaminergic neurons, while TFMPP has serotonergic effects.

METHODS

We investigated the effects of an acute dose of BZP, TFMPP or a combination of BZP and TFMPP on the anticipation of reward in a double-blind, placebo-controlled, crossover study using fMRI. An event-related gambling paradigm was completed by healthy controls 90 min after taking an oral dose of either BZP (200 mg), TFMPP (either 50 or 60 mg), BZP + TFMPP (100 + 30 mg) or placebo.

RESULTS

After giving BZP, the anticipation of a $4 reward decreased the activation of the inferior frontal gyrus, insula and occipital regions in comparison to placebo. TFMPP increased the activation of the putamen but decreased the activity in the insula relative to placebo. When BZP and TFMPP were given in combination, activation of the rolandic operculum occurred. The magnitude of reward also affected neural correlates.

CONCLUSION

We propose that the effects of BZP and TFMPP on dopaminergic and serotonergic circuitry, respectively, reflect regional changes. The dopaminergic effects of BZP appear to increase positive arousal and subsequently reduce the response to uncertainty, while TFMPP appears to alter the response to uncertainty by increasing emotional responses.

Cerebrovascular reactivity across the menstrual cycle in young healthy women

This study evaluated the relationship of cerebrovascular reactivity in young healthy women with changes in concentrations of circulating ovarian hormones throughout the menstrual cycle. Nineteen healthy nulliparous, right-handed, regularly menstruating women (age 23-25 years) underwent color-coded duplex sonography of the common (CCA), internal (ICA) and external (ECA) carotid arteries on both sides. Mean blood flow velocity values measured before and ten minutes after intravenous administration of 1000 mg acetazolamide (ACE) were assessed in relation to the serum concentration of estrogen and progesterone on days 5, 13 and 26 of the cycle. After ACE administration flow velocity in the right CCA and ICA increased by 23% and 35% on day 5, 12% and 31% on day 13 and 30% and 47% on day 26 respectively, and the changes were significantly larger on the right side (F=6.793 and F=4.098 respectively; both p<0.05). Changes in blood flow velocity in the right CCA and ICA after ACE injection were significantly associated with ovarian hormone concentrations (F=3.828, P=0.028 and F=3.671, P=0.032 respectively). We conclude that cerebrovascular reactivity changes across the menstrual cycle are associated with ovarian steroid hormone changes, and are asymmetric. The results imply that vasculature of the right hemisphere may undergo cyclic vasodilation across the menstrual cycle and this effect should be considered in studies of cerebrovascular reactivity in women with migraine and mood disorders.

Asymmetry of the endogenous opioid system in the human anterior cingulate: a putative molecular basis for lateralization of emotions and pain

Lateralization of the processing of positive and negative emotions and pain suggests an asymmetric distribution of the neurotransmitter systems regulating these functions between the left and right brain hemispheres. By virtue of their ability to selectively mediate euphoria, dysphoria, and pain, the μ-, δ-, and κ-opioid receptors and their endogenous ligands may subserve these lateralized functions. We addressed this hypothesis by comparing the levels of the opioid receptors and peptides in the left and right anterior cingulate cortex (ACC), a key area for emotion and pain processing. Opioid mRNAs and peptides and 5 "classical" neurotransmitters were analyzed in postmortem tissues from 20 human subjects. Leu-enkephalin-Arg (LER) and Met-enkephalin-Arg-Phe, preferential δ-/μ- and κ-/μ-opioid agonists, demonstrated marked lateralization to the left and right ACC, respectively. Dynorphin B (Dyn B) strongly correlated with LER in the left, but not in the right ACC suggesting different mechanisms of the conversion of this κ-opioid agonist to δ-/μ-opioid ligand in the 2 hemispheres; in the right ACC, Dyn B may be cleaved by PACE4, a proprotein convertase regulating left-right asymmetry formation. These findings suggest that region-specific lateralization of neuronal networks expressing opioid peptides underlies in part lateralization of higher functions, including positive and negative emotions and pain in the human brain.

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

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

Testosterone in the brain: neuroimaging findings and the potential role for neuropsychopharmacology

Testosterone plays a substantial role in a number of physiological processes in the brain. It is able to modulate the expression of certain genes by binding to androgen receptors. Acting via neurotransmitter receptors, testosterone shows the potential to mediate a non-genomic so-called "neuroactive effect". Various neurotransmitter systems are also influenced by the aromatized form of testosterone, estradiol. The following article summarizes the findings of preclinical and clinical neuroimaging studies including structural and functional magnetic resonance imaging (MRI/fMRI), voxel based morphometry (VBM), as well as pharmacological fMRI (phfMRI) and positron emission tomography (PET) regarding the effects of testosterone on the human brain. The impact of testosterone on the pathogenesis of psychiatric disorders and on sex-related prevalence differences have been supported by a wide range of clinical studies. An antidepressant effect of testosterone can be implicitly explained by its effects on the limbic system--especially amygdala, a major target in the treatment of depression--solidly demonstrated by a large body of neuroimaging findings.

Global decrease of serotonin-1A receptor binding after electroconvulsive therapy in major depression measured by PET

Electroconvulsive therapy (ECT) is a potent therapy in severe treatment-refractory depression. Although commonly applied in psychiatric clinical routine since decades, the exact neurobiological mechanism regarding its efficacy remains unclear. Results from preclinical and clinical studies emphasize a crucial involvement of the serotonin-1A receptor (5-HT(1A)) in the mode of action of antidepressant treatment. This includes associations between treatment response and changes in 5-HT(1A) function and density by antidepressants. Further, alterations of the 5-HT(1A) receptor are consistently reported in depression. To elucidate the effect of ECT on 5-HT(1A) receptor binding, 12 subjects with severe treatment-resistant major depression underwent three positron emission tomography (PET) measurements using the highly selective radioligand [carbonyl-(11)C]WAY100635, twice before (test-retest variability) and once after 10.08±2.35 ECT sessions. Ten patients (~83%) were responders to ECT. The voxel-wise comparison of the 5-HT(1A) receptor binding (BP(ND)) before and after ECT revealed a widespread reduction in cortical and subcortical regions (P<0.05 corrected), except for the occipital cortex and the cerebellum. Strongest reductions were found in regions consistently reported to be altered in major depression and involved in emotion regulation, such as the subgenual part of the anterior cingulate cortex (-27.5%), the orbitofrontal cortex (-30.1%), the amygdala (-31.8%), the hippocampus (-30.6%) and the insula (-28.9%). No significant change was found in the raphe nuclei. There was no significant difference in receptor binding in any region comparing the first two PET scans conducted before ECT. This PET study proposes a global involvement of the postsynaptic 5-HT(1A) receptor binding in the effect of ECT.

Cerebral serotonin transporter asymmetry in females, males and male-to-female transsexuals measured by PET in vivo

The serotonergic system modulates brain functions that are considered to underlie affective states, emotion and cognition. Several lines of evidence point towards a strong lateralization of these mental processes, which indicates similar asymmetries in associated neurotransmitter systems. Here, our aim was to investigate a potential asymmetry of the serotonin transporter distribution using positron emission tomography and the radioligand [(11)C]DASB in vivo. As brain asymmetries may differ between sexes, we further aimed to compare serotonin transporter asymmetry between females, males and male-to-female (MtF) transsexuals whose brains are considered to be partly feminized. Voxel-wise analysis of serotonin transporter binding in all groups showed both strong left and rightward asymmetries in several cortical and subcortical structures including temporal and frontal cortices, anterior cingulate, hippocampus, caudate and thalamus. Further, male controls showed a rightward asymmetry in the midcingulate cortex, which was absent in females and MtF transsexuals. The present data support the notion of a lateralized serotonergic system, which is in line with previous findings of asymmetric serotonin-1A receptor distributions, extracellular serotonin concentrations, serotonin turnover and uptake. The absence of serotonin transporter asymmetry in the midcingulate in MtF transsexuals may be attributed to an absence of brain masculinization in this region.

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.

Extended Broca's area in the functional connectome of language in adults: combined cortical and subcortical single-subject analysis using fMRI and DTI tractography

Traditional models of the human language circuitry encompass three cortical areas, Broca's, Geschwind's and Wernicke's, and their connectivity through white matter fascicles. The neural connectivity deep to these cortical areas remains poorly understood, as does the macroscopic functional organization of the cortico-subcortical language circuitry. In an effort to expand current knowledge, we combined functional MRI (fMRI) and diffusion tensor imaging to explore subject-specific structural and functional macroscopic connectivity, focusing on Broca's area. Fascicles were studied using diffusion tensor imaging fiber tracking seeded from volumes placed manually within the white matter. White matter fascicles and fMRI-derived clusters (antonym-generation task) of positive and negative blood-oxygen-level-dependent (BOLD) signal were co-registered with 3-D renderings of the brain in 12 healthy subjects. Fascicles connecting BOLD-derived clusters were analyzed within specific cortical areas: Broca's, with the pars triangularis, the pars opercularis, and the pars orbitaris; Geschwind's and Wernicke's; the premotor cortex, the dorsal supplementary motor area, the middle temporal gyrus, the dorsal prefrontal cortex and the frontopolar region. We found a functional connectome divisible into three systems-anterior, superior and inferior-around the insula, more complex than previously thought, particularly with respect to a new extended Broca's area. The extended Broca's area involves two new fascicles: the operculo-premotor fascicle comprised of well-organized U-shaped fibers that connect the pars opercularis with the premotor region; and (2) the triangulo-orbitaris system comprised of intermingled U-shaped fibers that connect the pars triangularis with the pars orbitaris. The findings enhance our understanding of language function.

A review on the relationship between testosterone and the interpersonal/affective facet of psychopathy

Testosterone (T) has received increasing interest in the recent years as a probable biological determinant in the etiology of male-biased clinical conditions such as psychopathy (i.e. psychopathy is more prevalent in men and leads to an earlier onset and more severe expression of antisocial and aggressive behavior in men compared to women). In this review, the authors evaluated the potential relationship between T and different constructs closely related to the core characteristics of psychopathy (affective empathy, fear-reactivity, and instrumental aggression). After a thorough examination of the literature, it is concluded that high T exposure in utero and high circulating T levels throughout important life phases (most notably adolescence) or in response to social challenges (e.g. social stress, competition) could be an important etiological risk factor in the emergence of psychopathic behavior. Nevertheless, studies consistently indicate that high T is not related to a significantly reduced fear-reactivity and is only indirectly associated with the increased levels of instrumental aggression observed in psychopathic individuals. Therefore, psychopathy is likely to arise from an interaction between high T levels and other biological and socio-psychological risk factors, such as a constitutionally based dampened fear-reactivity, insecure/disordered attachment processes in childhood, and social discrimination/rejection in adolescence and/or adulthood.

Whose side are you on: does serotonin preferentially activate the right hemisphere and norepinephrine the left?

Serotonin (5-HT) and norepinephrine (NE) innervate both the left and right hemispheres of the brain, but whether they affect lateralization of function is unknown. This paper concisely examines evidence that these two neurotransmitters differentially affect the two hemispheres, and puts forth the novel hypothesis 5-HT preferentially activates the right hemisphere (RH) and NE the left hemisphere (LH). The principal lines of evidence comprise studies of: (1) 5-HT and NE level measurement, (2) receptor binding, (3) functional brain imaging, (4) dichotic listening, and (5) electroencephalography and evoked potentials. In assessing these 5 lines, emphasis is placed on studies of pharmaceutical drugs that affect the 5-HT and NE systems. While all of the data do not support the hypothesis, they are generally consistent with it, or a variant of the hypothesis that there is a bias toward 5-HT preferentially activating a majority of brain areas or functions in the RH, and NE a majority of LH areas or functions. If this hypothesis, or a variant of it, is correct, it may be relevant to understanding the physiological basis of neuropsychiatric disorders that could involve dysfunction in brain monoaminergic systems, as well as understanding potential lateralization of the effects of drugs that act on these systems.

Combining image-derived and venous input functions enables quantification of serotonin-1A receptors with [carbonyl-11C]WAY-100635 independent of arterial sampling

image- derived input functions (IDIFs) represent a promising technique for a simpler and less invasive quantification of PET studies as compared to arterial cannulation. However, a number of limitations complicate the routine use of IDIFs in clinical research protocols and the full substitution of manual arterial samples by venous ones has hardly been evaluated. This study aims for a direct validation of IDIFs and venous data for the quantification of serotonin-1A receptor binding (5-HT(1A)) with [carbonyl-(11)C]WAY-100635 before and after hormone treatment.

METHODS

Fifteen PET measurements with arterial and venous blood sampling were obtained from 10 healthy women, 8 scans before and 7 after eight weeks of hormone replacement therapy. Image-derived input functions were derived automatically from cerebral blood vessels, corrected for partial volume effects and combined with venous manual samples from 10 min onward (IDIF+VIF). Corrections for plasma/whole-blood ratio and metabolites were done separately with arterial and venous samples. 5-HT(1A) receptor quantification was achieved with arterial input functions (AIF) and IDIF+VIF using a two-tissue compartment model.

RESULTS

Comparison between arterial and venous manual blood samples yielded excellent reproducibility. Variability (VAR) was less than 10% for whole-blood activity (p>0.4) and below 2% for plasma to whole-blood ratios (p>0.4). Variability was slightly higher for parent fractions (VARmax=24% at 5 min, p<0.05 and VAR<13% after 20 min, p>0.1) but still within previously reported values. IDIFs after partial volume correction had peak values comparable to AIFs (mean difference Δ=-7.6 ± 16.9 kBq/ml, p>0.1), whereas AIFs exhibited a delay (Δ=4 ± 6.4s, p<0.05) and higher peak width (Δ=15.9 ± 5.2s, p<0.001). Linear regression analysis showed strong agreement for 5-HT(1A) binding as obtained with AIF and IDIF+VIF at baseline (R(2)=0.95), after treatment (R(2)=0.93) and when pooling all scans (R(2)=0.93), with slopes and intercepts in the range of 0.97 to 1.07 and -0.05 to 0.16, respectively. In addition to the region of interest analysis, the approach yielded virtually identical results for voxel-wise quantification as compared to the AIF.

CONCLUSIONS

Despite the fast metabolism of the radioligand, manual arterial blood samples can be substituted by venous ones for parent fractions and plasma to whole-blood ratios. Moreover, the combination of image-derived and venous input functions provides a reliable quantification of 5-HT(1A) receptors. This holds true for 5-HT(1A) binding estimates before and after treatment for both regions of interest-based and voxel-wise modeling. Taken together, the approach provides less invasive receptor quantification by full independence of arterial cannulation. This offers great potential for the routine use in clinical research protocols and encourages further investigation for other radioligands with different kinetic characteristics.

Unilateral hemispherectomy at adulthood asymmetrically affects motor performance of male Swiss mice

Evidence exists indicating that cerebral lateralization is a fundamental feature of all vertebrates. In humans, a series of studies demonstrated that the left hemisphere plays a major role in controlling movement. No such asymmetries have been identified in rodents, in spite of the fact that these animals have been frequently used in studies assessing motor behavior. In this regard, here, we used unilateral hemispherectomy to study the relative importance of each hemisphere in controlling movement. Adult Swiss mice were submitted to right unilateral hemispherectomy (RH), left unilateral hemispherectomy (LH) or sham surgery. Fifteen days after surgery, motor performance was assessed in the accelerating rotarod test and in the foot-fault test (in which performance depends on skilled limb use) and in the elevated body swing test (in which performance depends on trunk movements). The surgical removal of the right hemisphere caused a more pronounced impairment in performance than the removal of the left hemisphere both in the rotarod and in the foot-fault tests. In the rotarod, the RH group presented smaller latencies to fall than both LH and sham groups. In the foot-fault test, while both the sham and the LH groups showed no differences between left and right hind limbs, the RH group showed significantly worse performance with the left hind limb than with the right one. The elevated body swing test revealed a similar impairment in the two hemispherectomized groups. Our data suggest a major role of the right hemisphere in controlling skilled limb movements in mice.

Differential modulation of the default mode network via serotonin-1A receptors

Reflecting one's mental self is a fundamental process for evaluating the personal relevance of life events and for moral decision making and future envisioning. Although the corresponding network has been receiving growing attention, the driving neurochemical mechanisms of the default mode network (DMN) remain unknown. Here we combined positron emission tomography and functional magnetic resonance imaging to investigate modulations of the DMN via serotonin-1A receptors (5-HT(1A)), separated for 5-HT autoinhibition (dorsal raphe nucleus) and local inhibition (heteroreceptors in projection areas). Using two independent approaches, regional 5-HT(1A) binding consistently predicted DMN activity in the retrosplenial cortex for resting-state functional magnetic resonance imaging and the Tower of London task. On the other hand, both local and autoinhibitory 5-HT(1A) binding inversely modulated the posterior cingulate cortex, the strongest hub in the resting human brain. In the frontal part of the DMN, a negative association was found between the dorsal medial prefrontal cortex and local 5-HT(1A) inhibition. Our results indicate a modulation of key areas involved in self-referential processing by serotonergic neurotransmission, whereas variations in 5-HT(1A) binding explained a considerable amount of the individual variability in the DMN. Moreover, the brain regions associated with distinct introspective functions seem to be specifically regulated by the different 5-HT(1A) binding sites. Together with previously reported modulations of dopamine and GABA, this regional specialization suggests complex interactions of several neurotransmitters driving the default mode network.

Event related potential (ERP) evidence for selective impairment of verbal recollection in abstinent recreational methylenedioxymethamphetamine ("Ecstasy")/polydrug users

OBJECTIVES

Ecstasy is a recreational drug whose active ingredient, 3,4-methylenedioxymethamphetamine (MDMA), acts predominantly on the serotonergic system. Although MDMA is known to be neurotoxic in animals, the long-term effects of recreational Ecstasy use in humans remain controversial but one commonly reported consequence is mild cognitive impairment particularly affecting verbal episodic memory. Although event-related potentials (ERPs) have made significant contributions to our understanding of human memory processes, until now they have not been applied to study the long-term effects of Ecstasy. The aim of this study was to examine the effects of past Ecstasy use on recognition memory for both verbal and non-verbal stimuli using ERPs.

METHODS

We compared the ERPs of 15 Ecstasy/polydrug users with those of 14 cannabis users and 13 non-illicit drug users as controls.

RESULTS

Despite equivalent memory performance, Ecstasy/polydrug users showed an attenuated late positivity over left parietal scalp sites, a component associated with the specific memory process of recollection.

CONCLUSIONS

[corrected] This effect was only found in the word recognition task which is consistent with evidence that left hemisphere cognitive functions are disproportionately affected by Ecstasy, probably because the serotonergic system is laterally asymmetrical. Experimentally, decreasing central serotonergic activity through acute tryptophan depletion also selectively impairs recollection, and this too suggests the importance of the serotonergic system. Overall, our results suggest that Ecstasy users, who also use a wide range of other drugs, show a durable abnormality in a specific ERP component thought to be associated with recollection.

Reduced language lateralization in first-episode medication-naive schizophrenia

Diminished functional lateralization in language-related areas is found in chronic schizophrenia. It is not clear at what stage of illness these abnormalities in lateralization arise, or whether they are affected by medication. In addition, it is hypothesized that reduced language lateralization is related to positive symptoms of schizophrenia, but studies addressing this issue have yielded contradictory results. In this study we used functional MRI to measure language lateralization in 35 first-episode medication-naive schizophrenia patients and 43 matched healthy controls. Subjects performed three language tasks: a paced verb generation task, an antonym generation task, and a semantic decision task. Lateralization Index (LI) was calculated, using a relative threshold technique, in seven Regions of Interest (ROIs), including the main language-related areas and their contralateral homologues. In addition, we investigated whether language lateralization was correlated with psychotic symptoms. Across all ROIs, LI was significantly reduced in patients (p<0.001) compared to controls. Post-hoc tests revealed that this reduction was most prominent in the inferior frontal gyrus (part of Broca's area) (p=0.003) and the superior temporal gyrus (part of Wernicke's area) (p<0.001). LI was not correlated with the positive subscale of the PANSS, nor with hallucinations or disorganization. This is the first study to report reduced LI at the onset of schizophrenia, before medical treatment is initiated.