Imaging Striatal Dopamine Release Using a Non-Genetically Encoded Near-Infrared Fluorescent Catecholamine Nanosensor

Abraham G. Beyene; Kristen Delevich; Jackson Travis Del Bonis-O’Donnell; David J. Piekarski; Wan Chen Lin; A. Wren Thomas; Sarah J. Yang; Polina Kosillo; Darwin Yang; Linda Wilbrecht; Markita P. Landry

Ideally, to understand how neuromodulation sculpts brain activity, we need to develop tools that can optically report modulatory neurotransmitter concentrations in the brain extracellular space (ECS) in a manner that is compatible with pharmacology and other available tools to image neural structure and activity, and minimally interferes with the underlying biology. This goal motivates our effort to design an optical probe that can report extracellular catecholamine dynamics with high spatial and temporal fidelity within a unique near-infrared spectral profile. In this work, we describe the design, characterization, and implementation of a nanoscale near-infrared (nIR) non-genetically encoded fluorescent reporter that allows precise measurement of catecholamine dynamics in brain tissue. This technology makes use of a single wall carbon nanotube (SWNT) noncovalently functionalized with single strand (GT)6 oligonucleotides to form the nearinfrared catecholamine nanosensor (nIRCat). nIRCats respond to dopamine with ΔF/F of up to 24-fold in the fluorescence emission window of 1000-1300 nm 48 , a wavelength range that has shown utility for non-invasive through-skull imaging in mice. 21 First, we show in vitro characterization of the nanosensor's specificity for the catecholamines dopamine and norepinephrine, and demonstrate its insensitivity to GABA, glutamate, and acetylcholine. Second, we use ex vivo brain slices containing the dorsal striatum to demonstrate that nIRCats exhibit a fractional change in fluorescence that has the dynamic range and signalto-noise ratio to report dopamine efflux in response to brief electrical or optogenetic stimulation of dopaminergic terminals. Next, optogenetic stimulation of this preparation is also used to demonstrate the selectivity of the nIRCat nanosensor response to dopaminergic over glutamatergic terminal stimulation. In both stimulation contexts, we show that bath application of dopamine receptor antagonist sulpiride and agonist quinpirole modulates nIRCat signals in a manner consistent with predicted effects of presynaptic D2 autoreceptor manipulation. Finally, we show that the presence of a dopamine reuptake inhibitor yields a prolonged nIRCat fluorescent signal indicating that the sensors report a change in the time course of dopamine diffusion and reuptake in striatal brain tissue. These data indicate that nIRCats provide a unique synthetic tool compatible with pharmacology to interrogate the release, diffusion, and reuptake of neuromodulators in neural tissue.