(96b) In Vivo Imaging of Larval Zebrafish Neurochemistry with Near-Infrared Dopamine Nanosensors

Elucidating the relationship between the chemical activity and neuron connectivity to higher order function, such as behavior and cognition, is a fundamental goal in neuroscience. Although numerous tools exist to measure the electrical activity of neurons, the ability to directly monitor chemical communication between cells via the release and uptake of neurotransmitters and neuromodulators, such as dopamine, remains an unmet challenge. Recently, developments in the non-covalent functionalization of single-walled carbon nanotubes has produced a new class of fluorescent nanosensors for imaging dopamine. These dopamine nanosensors are water-soluble, non-toxic, and emit fluorescence in the near-infrared (NIR) window without photobleaching, making them ideally suited for long-term fluorescence imaging in high-scattering tissues like the brain. Additionally, their size and binding kinetics have been shown to capture the relevant spatial (um) and temporal (ms) dynamics of neurotransmission in the brain extracellular space.¹ Towards the goal of achieving real-time imaging of dopaminergic neuromodulation in awake and behaving animals, we present a NIR wide-field fluorescence imaging system compatible with SWNT-based dopamine nanosensors. The system leverages continuous wave epifluorescent Koehler Illumination to image live specimens. To demonstrate in vivo imaging capabilities, SWNT dopamine nanosensors injected into the brain of larval zebrafish (Danio rerio, 4-7 dpf) are shown to localize in the extracellular matrix in different subregions of the brain, where dopaminergic synapses are present. Additionally, genetically encoded calcium indicators confirm the nanosensors minimally impact general health in their presence. Our results demonstrate the utility of infrared nanosensors to visualize dopamine release in the brain of an awake animal towards a better understanding of in vivo neuromodulatory dynamics.

1 A. G. Beyene, I. R. McFarlane, R. L. Pinals and M. P. Landry, ACS Chem. Neurosci., 2017, 8, 2275–2289.