@phdthesis{ForeroEcheverry2020,
  author    = {Forero Echeverry, Andrea Marcela},
  title     = {Impact of Cadherin-13 deficiency on the brain serotonin system using mouse models and human iPSC-derived neurons},
  doi       = {10.25972/OPUS-21659},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-216592},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2020},
  abstract  = {Serotonin (5-hydroxytryptamine, 5-HT) is a neurotransmitter involved in early developmental processes such as cell proliferation, migration, and differentiation. Recent research in humans showed that the brain 5-HT system and CDH13 are interlinked in the genetics of neurodevelopmental disorders including attention- deficit/hyperactivity disorder and autism spectrum disorder (Lesch et al., 2008; Neale et al., 2008; Neale, Medland, Ripke, Anney, et al., 2010; Neale, Medland, Ripke, Asherson, et al., 2010; Sanders et al., 2011; Sanders et al., 2015; Zhou et al., 2008). This study introduces Cadherin-13 (CDH13), a cell adhesion protein, as a contributor to the development and function of the 5-HT system. Our experiments show that the absence of CDH13 increases the density of 5-HT neurons in the developing dorsal raphe (DR) and increases the 5-HT innervation of the prefrontal cortex in mouse embryonic stages. CDH13 is also observed in radial glial cells, an important progenitor cell type linked to neuronal migration. A three-dimensional reconstruction carried out with super-resolution microscopy, identifies 5-HT neurons intertwined with radial glial cells, and CDH13 clusters at contact points between these cells. This indicates a potential contribution of CDH13 to the migration of DR 5-HT neurons. As CDH13 is strongly expressed in 5-HT neurons, we asked whether the selective deletion of CDH13 from these cells is sufficient to generate the alterations observed in the Cdh13 constitutive knockout mouse line. In 5-HT conditional Cdh13 knockout mice (Cdh13 cKO) an increase in DR 5-HT neurons in the embryonic and adult brains is observed, as well as 5-HT hyperinnervation of cortical regions. Therefore, illustrating that the lack of CDH13 from 5-HT neurons alone impacts DR formation and serotonergic innervation. Behavioral testing conducted on Cdh13 cKO mice showed delayed learning in visuospatial learning and memory processing, as well as, changes in sociability parameters. To find out how CDH13 localizes in human 5-HT neurons, CDH13 was visualized in neurons that derived from human induced pluripotent stem cells (iPSC). Super-resolution microscopy confirmed CDH13 expression in a subgroup of induced human neurons positive for typical hallmarks of 5-HT neurons, such as expression of Tph2, the neuron-specific tryptophan hydroxylase, and synaptic structures. In summary, the work included in this thesis presents a detailed analysis of CDH13 expression and localization in the 5-HT system and shows that deletion of CDH13 from 5-HT neurons affects specific higher-order functions of the brain.},
  language  = {en}
}
@phdthesis{Kriegebaum2009,
  author    = {Kriegebaum, Claudia},
  title     = {Spatio-temporal Expression Patterns of the Serotonin Synthesis Enzymes TPH1 and TPH2 and Effects of Acute Stress},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-40839},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2009},
  abstract  = {Several lines of evidence implicate a dysregulation of tryptophan hydroxylase (TPH)-dependent serotonin (5-HT) synthesis in emotions and stress and point to their potential relevance to the etiology and pathogenesis of various neuropsychiatric disorders. However, the differential expression pattern of the two isoforms TPH1 and TPH2 which encode two forms of the rate-limiting enzyme of 5-HT synthesis is controversial. Here, a comprehensive spatio-temporal analysis clarifies TPH1 and TPH2 expression during pre- and postnatal development of the mouse brain and in adult human brain as well as in peripheral organs including the pineal gland. Four different methods (real time PCR, in situ hybridization, immunohistochemistry and Western blot analysis) were performed to systematically control for tissue-, species- and isoform-specific expression on both the pre- and posttranslational level. TPH2 expression was consistently detected in the raphe nuclei, as well as in fibres in the deep pineal gland and in the gastrointestinal tract. Although TPH1 expression was found in these peripheral tissues, no significant TPH1 expression was detected in the brain, neither during murine development, nor in mouse and human adult brain. Also under conditions like stress and clearing the tissue from blood cells, no changes in expression levels were detectable. Furthermore, the reuptake of 5-HT into the presynaptic neuron by the serotonin transporter (SERT) is the major mechanism terminating the neurotransmitter signal. Thus, mice with a deletion in the Sert gene (Sert KO mice) provide an adequate model for human affective disorders to study lifelong modified 5-HT homeostasis in interaction with stressful life events. To further explore the role of TPH isoforms, Tph1 and Tph2 expression was studied in the raphe nuclei of Sert deficient mice under normal conditions as well as following exposure to acute immobilization stress. Interestingly, no statistically significant changes in expression were detected. Moreover, in comparison to Tph2, no relevant Tph1 expression was detected in the brain independent from genotype, gender and treatment confirming expression in data from native animals. Raphe neurons of a brain-specific Tph2 conditional knockout (cKO) model were completely devoid of Tph2-positive neurons and consequently 5-HT in the brain, with no compensatory activation of Tph1 expression. In addition, a time-specific Tph2 inducible (i) KO mouse provides a brain-specific knockdown model during adult life, resulting in a highly reduced number of Tph2-positive cells and 5-HT in the brain. Intriguingly, expression studies detected no obvious alteration in expression of 5-HT system-associated genes in these brain-specific Tph2 knockout and knockdown models. The findings on the one hand confirm the specificity of Tph2 in brain 5-HT synthesis across the lifespan and on the other hand indicate that neither developmental nor adult Tph2-dependent 5-HT synthesis is required for normal formation of the serotonergic system, although Tph1 does not compensate for the lack of 5-HT in the brain of Tph2 KO models. A further aim of this thesis was to investigate the expression of the neuropeptide oxytocin, which is primarily produced in the hypothalamus and released for instance in response to stimulation of 5-HT and selective serotonin reuptake inhibitors (SSRIs). Oxytocin acts as a neuromodulator within the central nervous system (CNS) and is critically involved in mediating pain modulation, anxiolytic-like effects and decrease of stress response, thereby reducing the risk for emotional disorders. In this study, the expression levels of oxytocin in different brain regions of interest (cortex, hippocampus, amygdala, hypothalamus and raphe nuclei) from female and male wildtype (WT) and Sert KO mice with or without exposure to acute immobilization stress were investigated. Results showed significantly higher expression levels of oxytocin in brain regions which are involved in the regulation of emotional stimuli (amygdala and hippocampus) of stressed male WT mice, whereas male Sert KO as well as female WT and Sert KO mice lack these stress-induced changes. These findings are in accordance with the hypothesis of oxytocin being necessary for protection against stress, depressive mood and anxiety but suggest gender-dependent differences. The lack of altered oxytocin expression in Sert KO mice also indicates a modulation of the oxytocin response by the serotonergic system and provides novel research perspectives with respect to altered response of Sert KO mice to stress and anxiety inducing stimuli.},
  subject      = {Serotonin},
  language  = {en}
}