Short talk:
A fluorescent nanosensor paint detects dopamine release at axonal varicosities with high spatiotemporal resolution

Sofia Elizarova1,2,3, Abed Alrahman Chouaib4, Ali Shaib3,5, Björn Hill6, Florian Mann7, Nils Brose3, Sebastian Kruss6,7,8, James Daniel3

1Leibniz-Forschungsinstitut für Molekulare Pharmakologie, Department of Molecular Physiology and Cell Biology, Berlin, Germany,
2University of Göttingen, Göttingen Graduate School for Neurosciences, Biophysics, and Molecular Biosciences, Göttingen, Germany,
3Max Planck Institute for Multidisciplinary Sciences (City-Campus), Department of Molecular Neurobiology, Göttingen, Germany,
4Center for Integrative Physiology and Molecular Medicine, Department of Cellular Neurophysiology, Saarland University, Homburg, Germany,
5University Medical Center, Institute for Neuro- and Sensory Physiology, Göttingen, Germany,
6Ruhr University, Physical Chemistry II, Faculty of Science, Bochum, Germany,
7University of Göttingen, Institute of Physical Chemistry, Göttingen,,
8Biomedical Nanosensors, Fraunhofer Institute of Microelectronic Circuits and Systems, Duisburg, Germany

The neurotransmitter dopamine (DA) controls vital brain functions and is involved in several prevalent brain diseases. Despite this importance, our understanding of the molecular mechanisms that control DA release has been limited by the low spatial resolution of DA detection methods. Dopaminergic secretion sites (varicosities) are functionally and structurally highly diverse, and a detection method with high spatial resolution is required to dissect the molecular basis underlying this diversity. We developed and present a technique that uses small (0.7 nm x 200 nm) near-infrared fluorescent DA nanosensors for the optical detection of DA secretion from cultured murine dopaminergic neurons: AndromeDA (adsorbed nanosensors detecting release of dopamine). Through imaging of millions of nanosensors in parallel, AndromeDA detects local DA secretion events (hotspots) from up to 100 varicosities simultaneously. Using AndromeDA, we describe discrete hotspots, and find that they occur at only ∼17% of all varicosities, indicating that many varicosities are functionally silent. In addition, using a mouse KO model, we find that Munc13 priming proteins are required for DA release. Imaging with AndromeDA is versatile and readily applicable to other in vitro systems, with an unprecedented ability to spatially correlate DA secretion events to subcellular structures. This method will enable a detailed dissection of the molecular mechanisms that give rise to the heterogeneity of the DA system

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