KAINATE-STIMULATED ZN2-NEURONS WITH CA2+-PERMEABLE AMPA( UPTAKE LABELS CORTICAL)KAINATE CHANNELS/

The endogenous cation, Zn2+, is synaptically released and may trigger neurodegeneration after permeating through NMDA channels, voltage sens itive Ca2+ channels (VSCC), or Ca2+ permeable AMPA/kainate channels (C a-A/K). Neurons expressing Ca-A/K can be identified by a histochemical stain based upon kainate-stimulated Co2+ uptake (Co2+(+) neurons). Th e primary objective of this study was to determine whether a similar a pproach could be employed to visualize agonist-stimulated intracellula r Zn2+ accumulation, and, thus, to test the hypothesis that Ca-A/K per mit particularly rapid Zn2+ flux. Substituting Zn2+ for Co2+ during ag onist-stimulated uptake, followed by Timm's sulfide-silver staining to visualize intracellular Zn2+, resulted in distinct labeling of a subp opulation of cortical neurons (Zn2+(+) neurons) closely resembling Co2 +(+) neurons, suggesting that, like Co2+, Zn2+ may permeate Ca-A/K wit h particular rapidity. Neither NMDA nor high K+ triggered comparable Z n2+ accumulation, indicating substantially greater permeation through Ca-A/K than through NMDA channels or VSCC. Both fluorescence studies o f intracellular Zn2+ accumulation and double staining studies (using S MI-32 and anti-glutamate decarboxylase antibodies, both markers of cor tical neuronal subsets), support the contention that Zn2+ and Co2+ lab eling identify a common set of neurons characterized by expression of AMPA/kainate channels directly permeable to Zn2+ and Co2+ as well as C a2+. Furthermore, the preferential destruction of Zn2+(+) neurons (Lik e Co2+(+) neurons) after brief kainate exposures in the presence of lo wer, more physiologic concentrations of Zn2+ suggests that Zn2+ permea tion through Ca-A/K could contribute to selective neurodegeneration in disease. Finally, the study provides a novel and potentially advantag eous histochemical approach for kainate-stimulated Co2+ or Zn2+ uptake labeling, using a room temperature technique (Timm's staining) rather than the usual hot AgNO3 development of the Co2+ stain. (C) 1998 Else vier Science B.V.