Purpose: The goal of this research is to devise and apply new tools for tracking mobile zinc in the brain. Included are novel fluorescent sensors and fast, specific chelating agents for measuring zinc flux in the hippocampus as well as the auditory, visual, and olfactory sensory systems.
Results and Conclusions: Mobile zinc sensors are described that (i) are based on fluorescein and cyanine platforms as light-emitting units; (ii) employ fluoresceins with acetyl protecting groups to facilitate endosomal release in cells, eliminate fluorescent background, and can be deprotected with turn-on by mobile zinc; (iii) contain pH-insensitive spirobenzopyran units that convert to red-emitting cyanine dyes upon exposure to mobile zinc; and (iv) can be incorporated in peptides for cellular penetration and localization purposes as well as providing ratiometric quantitation.
Complementary tools for applying these probes include the use of ZnT3 knockout mice and fast zinc chelators for intercepting transient increases in mobile zinc. With collaborators, these probes have been applied to record (i) single synapse release of vesicular zinc in the hippocampus; (ii) modulation of extrasynaptic NMDA receptors by synaptic and tonic zinc in cartwheel cells, a class of inhibitory interneurons in the molecular layer of the dorsal cochlear nucleus that receive glutamatergic input from synaptic zinc-rich parallel fibers; (iii) release of zinc from glomeruli in the olfactory bulb upon electrophysiological stimulation in slices and as delineated in sensory maps produced in live animals following exposure to specific odorants; and (iv) mobile zinc release in the inner plexiform layer of the retina following optic nerve crush, a phenomenon used to guide the application of a fast zinc chelator as a means to promote optic nerve regeneration following crush. This work was supported by a grant from the National Institute of General Medical Sciences.