Feature-expression heat maps - A new visual method to explore complex associations between two variable sets

Introduction: Existing methods such as correlation plots and cluster heat maps are insufficient in the visual exploration of multiple associations between genetics and phenotype, which is of importance to achieve a better understanding of the pathophysiology of psychiatric and other illnesses. The implementation of a combined presentation of effect size and statistical significance in a graphical method, added to the ordering of the variables based on the effect-ordered data display principle was deemed useful by the authors to facilitate in the process of recognizing meaningful patterns in these associations. Materials and methods: The requirements, analyses and graphical presentation of the feature-expression heat map are described. The graphs display associations of two sets of ordered variables where a one-way direction is assumed. The associations are depicted as circles representing a combination of effect size (color) and statistical significance (radius). Results: An example dataset is presented and relation to other methods, limitations, areas of application and possible future enhancements are discussed. Conclusion: The feature-expression heat map is a useful graphical instrument to explore associations in complex biological systems where one-way direction is assumed, such as genotype-phenotype pathophysiological models. (C) 2014 Elsevier Inc. All rights reserved

Diffusion tensor imaging in euthymic bipolar disorder - A tract-based spatial statistics study

Background: In the current DTI study we compared euthymic bipolar I disorder (BD-I) patients and healthy controls (HC). We subsequently divided the total patient group into lithium-users and non-lithium-users and estimated differences across the three groups. Methods: Twenty-one euthymic BD-I patients and twenty-two HC participants were included in psychiatric interviews and MRI image acquisition (diffusion-weighted (DW) and T1-weighted scans). Fractional anisotropy (FA), radial, mean and axial diffusivity (RD, MD, AD) were estimated from the DW data, using DTI. These measures were then compared between groups using FSL Tract Based Spatial Statistics (TBSS). Correlations with age at onset, number of episodes and depression score were analyzed. Results: A difference in FA, MD, RD and AD between the whole sample of euthymic BD-I patients and healthy controls could not be detected. Amongst others, lithium-using patients demonstrated a higher FA and lower RD when compared to non-lithium-using BD-I patients in the corpus callosum and left anterior corona radiata. Widespread clusters demonstrated negative FA associations and positive RD and MD associations with minor depressive symptoms. Limitations: Patients were naturalistically treated. Although the sample size is comparable to several other DTI studies, a larger sample size would have been benificial. TBSS and DTI have their own limitations. Conclusion: Our findings support the theory that previously described DTI-based microstructural differences between HC and BD patients could be less pronounced in euthymic BD patients. Differences in FA between patients using and not using lithium suggest a counteracting effect of lithium on white matter microstructural disturbances. (C) 2016 Elsevier B.V. All rights reserved

Volume, metabolites and neuroinflammation of the hippocampus in bipolar disorder - A combined magnetic resonance imaging and positron emission tomography study

Background: The hippocampus is one of the brain regions that is involved in several pathophysiological theories about bipolar disorder (BD), such as the neuroinflammation theory and the corticolimbic metabolic dysregulation theory. We compared hippocampal volume and hippocampal metabolites in bipolar I disorder (BD-I) patients versus healthy controls (HCs) with magnetic resonance imaging (MRI) and spectroscopy (MRS). We post hoc investigated whether hippocampal volume and hippocampal metabolites were associated with microglial activation and explored if potential illness modifying factors affected these hippocampal measurements and whether these were associated with experienced mood and functioning. Materials and methods: Twenty-two BD-I patients and twenty-four HCs were included in the analyses. All subjects underwent psychiatric interviews as well as an MRI scan, including a T1 scan and PRESS magnetic resonance spectroscopy (MRS). Volumetric analysis was performed with Freesurfer. MRS quantification was performed with LC Model. A subgroup of 14 patients and 11 HCs also underwent a successful [C-11]-(R)PK11195 neuroinflammation positron emission tomography scan. Results: In contrast to our hypothesis, hippocampal volumes were not decreased in patients compared to HC after correcting for individual whole-brain volume variations. We demonstrated decreased N-acetylaspartate (NAA) + N-acetyl-aspartyl-glutamate (NAAG) and creatine (Cr) + phosphocreatine (PCr) concentrations in the left hippocampus. In the explorative analyses in the left hippocampus we identified positive associations between microglial activation and the NAA + NAAG concentration, between alcohol use and NM + NAAG concentration, between microglial activation and the depression score and a negative relation between Cr + PCr concentration and experienced occupational disability. Duration of illness associated positively with volume bilaterally. Conclusion: Compared to HCs, the decreased NAA + NAAG concentration in the left hippocampus of BD-I patients suggests a decreased neuronal integrity in this region. In addition we found a positive relation between microglial activation and neuronal integrity in vivo, corresponding to a differentiated microglial function where some microglia induce apoptosis while others stimulate neurogenesis. (C) 2015 Elsevier Inc. All rights reserved

Neuroinflammation in bipolar disorder - A [C-11]-(R)-PK11195 positron emission tomography study

Background: The "monocyte-T-cell theory of mood disorders" regards neuroinflammation, i.e. marked activation of microglia, as a driving force in bipolar disorder. Microglia activation can be visualized in vivo using [C-11]-(R)-PK11195 PET. Indirect evidence suggests the hippocampus as a potential focus of neuroinflammation in bipolar disorder. We aim to determine if there is increased [C-11]-(R)-PK11195binding to activated microglia in the hippocampus of patients with bipolar I disorder when compared to healthy controls. Material and methods: Fourteen patients with bipolar I disorder and eleven healthy controls were included in the analyses. Dynamic 60-min PET scans were acquired after the injection of [C-11]-(R)-PK11195. All subjects underwent psychiatric interviews as well as an MRI scan, which was used for anatomic co-registration in the data analysis. The data from the PET scans was analyzed with a twotissue-compartment model to calculate the binding potential, using the metabolite-corrected plasma and blood curve as input. : A significantly increased [C-11]-(R)-PK11195 binding potential, which is indicative of neuroinflammation, was found in the right hippocampus of the patients when compared to the healthy controls (1.66 (CI 1.45-1.91) versus 1.33 (Cl 1.16-1.53); p = 0.033, respectively). Although the same trend was observed in the left hippocampus, this difference was not statistically significant. Conclusion: This study is the first to demonstrate the presence of focal neuroinflammation in the right hippocampus in bipolar I disorder. (C) 2014 Elsevier Inc. All rights reserved