Specific Fluorescent Probe Based on “Protect–Deprotect” To Visualize the Norepinephrine Signaling Pathway and Drug Intervention Tracers

In recent years, increased social pressure and other factors have led to a surge in the number of people suffering from depression: studies show that quite a few people will experience major depression in their lifetime. Currently, it is widely believed that the internal cause of major depression is reduced levels of norepinephrine (NE) in brain tissue. Norepinephrine is very similar in structure and chemical properties to the other two catecholamine neurotransmitters, epinephrine (EP) and dopamine (DA). These three neurotransmitters are synthesized sequentially through enzymatic reactions in the biological system. Therefore, design of a norepinephrine-specific fluorescent probe is very challenging. In this work, we utilized a "protect–deprotect" strategy: longer emission wavelength cyanine containing water-soluble sulfonate was protected by a carbonic ester linking departing group thiophenol; the β-hydroxy ethyl amine moiety of norepinephrine may react with the carbonic ester via nucleophilic substitution and intramolecular nucleophilic cyclization to release the fluorophore. The process realized the specific red fluorescence detection of norepinephrine. Imaging of the norepinephrine nerve signal transduction stimulated by potassium ion was studied. More importantly, real-time fluorescence imaging of norepinephrine levels in the brain of rats stimulated by antidepressant drugs was studied for the first time.