2-3-dioxo-6-nitro-7-sulfamoylbenzo(f)quinoxaline and zinc-chloride

Zinc chloride (0.02 mM, 3h) did not have any influence on the survival of cerebellar granule neurons (CGNs) incubated in balanced salt solution (BSS). However, in the absence of glucose ZnCl(2) caused severe neuronal damage, decreasing cell survival to 12±2%. Either the blockade of ionotropic glutamate NMDA-receptors with MK-801 or APV or supplementation the medium with ruthenium red (mitochondrial Ca(2+) uniporter blocker) almost entirely protected CGNs from the toxic effect of ZnCl(2) during glucose deprivation (GD). However, NBQX (AMPA/kainate glutamate receptor blocker) did not show protective effect. Measurements of intracellular calcium ions concentration using fluorescent probe (Fluo-4 AM) and zinc ions (FluoZin-3AM) demonstrated that 1.5h-exposure to GD induced intensive increase of Fluo-4 fluorescence and small increase of FluoZin-3 fluorescence in neurons. The supplementation of medium with ZnCl(2) caused equal increase of FluoZin-3 fluorescence at both GD and normoglycemia, whereas the potentiation of Fluo-4 fluorescence by zinc was observed only under GD and could be prevented by MK-801. However, neither MK-801 nor NBQX could influence [Zn(2+)](i) increase caused by zinc addition under GD, while ruthenium red did cause significant increase of [Zn(2+)](i). This data implies that zinc ions during GD induce an additional overload of CGNs with calcium ions that get transported through activated NMDA-channel. Zinc and calcium ions accumulate in mitochondria and amplify individual destructive action on these organelles leading to neuronal death.

Topics: Animals; Calcium; Cell Death; Cells, Cultured; Cerebellum; Chlorides; Coloring Agents; Dizocilpine Maleate; Excitatory Amino Acid Antagonists; Glucose; Neurons; Neuroprotective Agents; Quinoxalines; Rats; Rats, Wistar; Ruthenium Red; Zinc Compounds

Approximately 10% of total zinc in the brain exists in synaptic vesicles of glutamatergic neurons; however, the function of vesicular zinc is poorly understood. The presynaptic action of zinc against excitatory and inhibitory neurotransmission was studied in rat hippocampus using in vivo microdialysis. When the hippocampal CA3 region was perfused with 10-300 microM ZnCl(2), the level of glutamate in the perfusate was decreased, whereas the level of gamma-aminobutyric acid (GABA) was increased. Chelation of endogenous zinc with CaEDTA increased the glutamate level in the perfusate but decreased the GABA level, suggesting that zinc released into the synaptic cleft acts differentially on glutamatergic and GABAergic neurons in the CA3 region. The increase of GABA level by zinc was antagonized by 2,3-dioxo-6-nitro-1,2.3,4-tetrahydrobenzo(f)quinoxaline-7-sulphonamide (NBQX), an antagonist of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA)/kainate receptors, but not affected by MK801, an antagonist of N-methyl-D-aspartate (NMDA) receptors, and verapamil, a blocker of voltage-dependent calcium channels. The present study suggests that zinc enhances GABA release via potentiation of AMPA/kainate receptors in the CA3 region, followed by a decrease in presynaptic glutamate release in the same region. Zinc seems to be an inhibitory neuromodulator of glutamate release.

Topics: Animals; Calcium Channel Blockers; Chelating Agents; Chlorides; Dizocilpine Maleate; Down-Regulation; Excitatory Amino Acid Antagonists; gamma-Aminobutyric Acid; Glutamic Acid; Hippocampus; Male; Neural Inhibition; Neural Pathways; Presynaptic Terminals; Quinoxalines; Rats; Rats, Wistar; Receptors, AMPA; Synapses; Synaptic Transmission; Up-Regulation; Zinc; Zinc Compounds