Renken, Kim LauraKim LauraRenken2025-11-142025-11-142025-10-17https://media.suub.uni-bremen.de/handle/elib/23209https://doi.org/10.26092/elib/4889Despite significant advances in neuroscience, our understanding of the brain, its functions, and the underlying molecular signaling pathways that influence behavior and health remains incomplete. The immense complexity of neural networks and their dynamic interactions poses major challenges in deciphering the mechanisms that govern both normal brain function and neurological disorders. To address these challenges, the development and application of advanced tools and models to investigate brain function and its underlying mechanisms are of central importance. One approach involves the use of transgenic mouse models, which provide valuable insights into biological processes, behavior, and their relevance to neurological and psychiatric disorders. Among these, the NEX-Cre mouse line is widely used to study cortical development and neuronal function. In the first project of this thesis, the behavior and neuronal architecture across all NEX-Cre genotypes were comprehensively characterized and compared to the commonly used wild-type C57BL/6J line. While transgenic models are powerful tools, understanding synaptic signaling at the cellular and molecular levels requires their combination with advanced techniques. The second project introduces PinkyCaMP, a novel red fluorescent calcium indicator based on mScarlet, which enables real-time visualization of neural activity with high brightness, photostability, and compatibility with optogenetics. The third project examines the role of serotonin in major depressive disorder through a comprehensive review, highlighting how modern biosensor approaches help uncover the molecular and neural foundations of psychiatric disorders. Together, the projects in this thesis contribute to the development and refinement of tools and models for neuroscience research, offering insights into brain function and their potential applications in the study of neurological and psychiatric disorders.enhttps://creativecommons.org/licenses/by-nc-nd/4.0/MEDICINE::Morphology, cell biology, pathology::Cell biology::Neurosciencetransgenic mouse modelsNEX-CrePinkyCaMPserotonin5-HTdepressionMDD500 Naturwissenschaften und Mathematik::570 Biowissenschaften; BiologieDissertation10.26092/elib/4889urn:nbn:de:gbv:46-elib232092