The Effects of 5-HTR1A Polymorphism on Cingulum Connectivity in Patients with Panic Disorder

Effects of BDNF Val66Met Polymorphism on White Matter Microalterations of the Corpus Callosum in Patients with Panic Disorder in Korean Populations

OBJECTIVE

The brain-derived neurotrophic factor (BDNF) Val66Met (rs6265) polymorphism is suggested to be associated with the pathophysiology of anxiety disorders, including panic disorder (PD). Although the fronto-limbic white matter (WM) microstructures have been investigated, the corpus callosum (CC) has not yet been studied regarding its relationship with BDNF Val66Met polymorphism in PD.

METHODS

Ninety-five PD patients were enrolled. The Neuroticism, the Anxiety Sensitivity Inventory-Revised, Panic Disorder Severity Scale, and Beck Depression Inventory-II (BDI-II) were administered. Voxel-wise statistical analysis of diffusion tensor imaging data was performed within the CC regions using Tract-Based Spatial Statistics.

RESULTS

The GG genotype in BDNF Val66Met polymorphism has significantly higher fractional anisotropy (FA) values of the body and splenium of the CC, neuroticism and depressive symptom scale scores than the non-GG genotype in PD. The FA values of the body of the CC in the two groups were significantly different independent of age, sex, neuroticism, and BDI-II.

CONCLUSION

Our findings demonstrate that the BDNF Val66Met polymorphism is associated with WM connectivity of the body and splenium of the CC, and may be related to neuroticism and depressive symptoms in PD. Additionally, the CC connectivity according to BDNF polymorphism may play a role in the pathophysiology of PD.

White Matter-Based Structural Brain Network of Anxiety

Anxiety disorders are characterized by excessive fear and anxiety and related behavioral disturbances. Because diffusion tensor imaging is sensitive to detect subtle pathology of the brain, it has been used to characterize differences in white matter microstructure for a broad spectrum of psychiatric disorders. The neurobiological underpinnings of a trait anxiety seem to be associated with the uncinate fasciculus, a major pathway between the amygdala and orbitofrontal cortex. Apparent WM micro-alterations in patients with panic disorder are present in diverse and widespread regions, although alterations vary in terms of clinical symptom severity and comorbidities. Social anxiety disorder is associated with structural dysconnectivity in a fronto-limbic network consistent with reduced fractional anisotropy values in uncinate fasciculus and inferior longitudinal fasciculus. The pathogenesis of obsessive-compulsive disorder may include abnormal findings in not only the fronto-striato-thalamic circuit but also the posterior and temporal regions of forceps major and cingulum bundle. Studies of white matter status in anxiety revealed overlapping patterns of front-cortical and fronto-limbic changes with uncinate fasciculus and cingulum alterations a frequent component.

Genetic, epigenetic and posttranscriptional mechanisms for treatment of major depression: the 5-HT1A receptor gene as a paradigm

Major depression and anxiety are highly prevalent and involve chronic dysregulation of serotonin, but they remain poorly understood. Here, we review novel transcriptional (genetic, epigenetic) and posttranscriptional (microRNA, alternative splicing) mechanisms implicated in mental illness, focusing on a key serotonin-related regulator, the serotonin 1A (5-HT1A) receptor. Functional single-nucleotide polymorphisms and stress-induced DNA methylation of the 5-HT1A promoter converge to differentially alter pre- and postsynaptic 5-HT1A receptor expression associated with major depression and reduced therapeutic response to serotonergic antidepressants. Major depression is also associated with altered levels of splice factors and microRNA, posttranscriptional mechanisms that regulate RNA stability. The human 5-HT1A 3′-untranslated region is alternatively spliced, removing microRNA sites and increasing 5-HT1A expression, which is reduced in major depression and may be genotype-dependent. Thus, the 5-HT1A receptor gene illustrates the convergence of genetic, epigenetic and posttranscriptional mechanisms in gene expression, neurodevelopment and neuroplasticity, and major depression. Understanding gene regulatory mechanisms could enhance the detection, categorization and personalized treatment of major depression.

Functional neuroanatomy in panic disorder: Status quo of the research

AIM

To provide an overview of the current research in the functional neuroanatomy of panic disorder.

METHODS

Panic disorder (PD) is a frequent psychiatric disease. Gorman et al (1989; 2000) proposed a comprehensive neuroanatomical model of PD, which suggested that fear- and anxiety-related responses are mediated by a so-called “fear network” which is centered in the amygdala and includes the hippocampus, thalamus, hypothalamus, periaqueductal gray region, locus coeruleus and other brainstem sites. We performed a systematic search by the electronic database PubMed. Thereby, the main focus was laid on recent neurofunctional, neurostructural, and neurochemical studies (from the period between January 2012 and April 2016). Within this frame, special attention was given to the emerging field of imaging genetics.

RESULTS

We noted that many neuroimaging studies have reinforced the role of the “fear network” regions in the pathophysiology of panic disorder. However, recent functional studies suggest abnormal activation mainly in an extended fear network comprising brainstem, anterior and midcingulate cortex (ACC and MCC), insula, and lateral as well as medial parts of the prefrontal cortex. Interestingly, differences in the amygdala activation were not as consistently reported as one would predict from the hypothesis of Gorman et al (2000). Indeed, amygdala hyperactivation seems to strongly depend on stimuli and experimental paradigms, sample heterogeneity and size, as well as on limitations of neuroimaging techniques. Advanced neurochemical studies have substantiated the major role of serotonergic, noradrenergic and glutamatergic neurotransmission in the pathophysiology of PD. However, alterations of GABAergic function in PD are still a matter of debate and also their specificity remains questionable. A promising new research approach is “imaging genetics”. Imaging genetic studies are designed to evaluate the impact of genetic variations (polymorphisms) on cerebral function in regions critical for PD. Most recently, imaging genetic studies have not only confirmed the importance of serotonergic and noradrenergic transmission in the etiology of PD but also indicated the significance of neuropeptide S receptor, CRH receptor, human TransMEMbrane protein (TMEM123D), and amiloride-sensitive cation channel 2 (ACCN2) genes.

CONCLUSION

In light of these findings it is conceivable that in the near future this research will lead to the development of clinically useful tools like predictive biomarkers or novel treatment options.

White matter correlates of anxiety sensitivity in panic disorder

BACKGROUND

Anxiety sensitivity (AS) refers to a fear of anxiety-related sensations and is a dispositional variable especially elevated in patients with panic disorder (PD). Although several functional imaging studies of AS in patients with PD have suggested the presence of altered neural activity in paralimbic areas such as the insula, no study has investigated white matter (WM) alterations in patients with PD in relation to AS. The objective of this study was to investigate the WM correlates of AS in patients with PD.

METHODS

One-hundred and twelve right-handed patients with PD and 48 healthy control (HC) subjects were enrolled in this study. The Anxiety Sensitivity Inventory-Revised (ASI-R), the Panic Disorder Severity Scale (PDSS), the Albany Panic and Phobia Questionnaire (APPQ), the Beck Anxiety Inventory (BAI), and the Beck Depression Inventory (BDI) were administered. Tract-based spatial statistics were used for diffusion tensor magnetic resonance imaging analysis.

RESULTS

Among the patients with PD, the ASI-R total scores were significantly correlated with the fractional anisotropy values of the WM regions near the insula, the splenium of the corpus callosum, the tapetum, the fornix/stria terminalis, the posterior limb of the internal capsule, the retrolenticular part of the internal capsule, the posterior thalamic radiation, the sagittal striatum, and the posterior corona radiata located in temporo-parieto-limbic regions and are involved in interoceptive processing (p<0.01; threshold-free cluster enhancement [TFCE]-corrected). These WM regions were also significantly correlated with the APPQ interoceptive avoidance subscale and BDI scores in patients with PD (p<0.01, TFCE-corrected). Correlation analysis among the HC subjects revealed no significant findings.

LIMITATIONS

There has been no comparative study on the structural neural correlates of AS in PD.

CONCLUSIONS

The current study suggests that the WM correlates of AS in patients with PD may be associated with the insula and the adjacent temporo-parieto-limbic WM regions, which may play important roles in interoceptive processing in the brain and in depression in PD.