Near infrared fluorescence imaging of dopamine signaling

Cells use molecules to exchange information. A very prominent example is neurotransmitter signaling between neuronal cells. The neurotransmitter dopamine is released from discrete axonal structures called varicosities. Its release is essential in behaviour and is critically implicated in prevalent neuropsychiatric diseases but existing dopamine detection methods are not able to image dopamine release events from multiple locations. Here, we develop a near infrared (NIR) fluorescent (980 nm) dopamine nanosensor 'paint' (AndromeDA) and show that action potential-evoked dopamine release is highly heterogeneous across release sites. The sensors are based on single-walled carbon nanotubes (SWCNTs) that emit fluorescence in the highly beneficial NIR tissue transparency window. We visualize dopamine release at up to 100 dopaminergic varicosities simultaneously within a single imaging field with high temporal resolution (15 images/s). We find that 'hotspots' of dopamine release are highly heterogeneous and are detected at only ~17% of all varicosities. In summary, we demonstrate NIR imaging of neurotransmitters and provide insights into the spatiotemporal organization of dopamine release.