Feng, J. et al. Neuron https://doi.org/10.1016/j.neuron.2019.02.037 (2019).

Genetically encoded fluorescent sensors for several neurotransmitters have recently been reported. Feng et al. have added to this toolbox by developing norepinephrine sensors with high and medium sensitivity. Norepinephrine has crucial roles in vertebrates, allowing organisms to cope with the environment and internal states. Malfunction of the noradrenergic system has been implicated in stress, anxiety, depression, and attention deficit hyperactivity disorder. The norepinephrine sensors are based on the α2-adrenergic receptor and include a circularly permuted EGFP that fluoresces when the receptor undergoes a conformational change after norepinephrine binding. The sensor variants are specific to norepinephrine (and epinephrine) and do not detect other neurotransmitters at relevant concentrations. The researchers imaged norepinephrine signaling in zebrafish that were exposed to looming stimuli. Furthermore, the researchers monitored norepinephrine in behaving mice via fiber photometry.