Method for identifying neuronal cells suffering zinc toxicity by use of a novel fluorescent sensor

During excitotoxic brain damage, injured neurons accumulate an anomalous, pathological burden of weakly bound, rapidly exchangeable Zn²⁺ that diffusely fills the soma, nucleus and proximal dendrites. Mounting evidence indicates that this Zn²⁺ is a major contributing factor in the subsequent demise of the damaged neurons. Thus, identifying, imaging, and characterizing zinc-filled cells have become essential steps in understanding excitotoxicity. Here we demonstrate that a new fluorescent stain for zinc can rather selectively and quite vividly label zinc-filled neurons in frozen histologic sections. The method is more sensitive and selective than the existing stain TSQ, and simpler than the Timm-Danscher silver staining techniques. A previously unobserved population of apparently injured cells in the dentate gyrus has been discovered with the new reagent. Whereas cells viewed in situ in normal, healthy tissue virtually never display any perikaryal staining by histochemical methods for zinc [Histochemistry, 71 (1981) 1; Int. Rev. Neurobiol. 31 (1989) 145], injured cells stain intensely for zinc in culture [J. Neurosci. 17 (1997) 9554], acute slice preparations [J. Histochem. Cytochem. 47 (1999) 969; J. Neurosci. 22 (2002) 1273] and in tissue harvested in vivo [Science 272 (1996) 1013; Annu. Rev. Neurosci. 21 (1998) 347]. Thus, the presence of rapidly-exchangeable, "stainable" perikaryal zinc may be taken as an indicator of cell injury [J. Nutr. 130 (2000) 1471S; Biometals 14 (2001) 353].