2-3-dioxo-6-nitro-7-sulfamoylbenzo(f)quinoxaline and thiazolyl-blue

Zinc distributes widely in the central nervous system, especially in the hippocampus, amygdala and cortex. The dynamic balance of zinc is critical for neuronal functions. Zinc modulates the activity of N-methyl-D-aspartate receptors (NMDARs) through the direct inhibition and various intracellular signaling pathways. Abnormal NMDAR activities have been implicated in the aetiology of many brain diseases. Sustained zinc accumulation in the extracellular fluid is known to link to pathological conditions. However, the mechanism linking this chronic zinc exposure and NMDAR dysfunction is poorly understood.. We reported that chronic zinc exposure reduced the numbers of NR1 and NR2A clusters in cultured hippocampal pyramidal neurons. Whole-cell and synaptic NR2A-mediated currents also decreased. By contrast, zinc did not affect NR2B, suggesting that chronic zinc exposure specifically influences NR2A-containg NMDARs. Surface biotinylation indicated that zinc exposure attenuated the membrane expression of NR1 and NR2A, which might arise from to the dissociation of the NR2A-PSD-95-Src complex.. Chronic zinc exposure perturbs the interaction of NR2A to PSD-95 and causes the disorder of NMDARs in hippocampal neurons, suggesting a novel action of zinc distinct from its acute effects on NMDAR activity.

Topics: Amygdala; Animals; Biotinylation; Brain; Cell Death; Cell Survival; Cerebral Cortex; Disks Large Homolog 4 Protein; Dose-Response Relationship, Drug; Electrophysiology; Hippocampus; Intracellular Signaling Peptides and Proteins; Membrane Potentials; Membrane Proteins; Mitochondria; Models, Biological; Neurons; Nimodipine; Quinoxalines; Rats; Rats, Sprague-Dawley; Receptors, N-Methyl-D-Aspartate; Surface Properties; Tetrazolium Salts; Thiazoles; Zinc

We investigated the effect of agmatine on cell viability of rat cerebellar granule neurons in a high-K+ (27.5 mM) medium. Exposure of cultured rat cerebellar granule neurons to agmatine (200-800 microM) resulted in a significant decrease in cell viability. Agmatine-induced neuronal death began to occur 6-12 h after addition, and gradually progressed. The agmatine neurotoxicity was attenuated by N-methyl-D-aspartate (NMDA) receptor antagonists and by enzymatic degradation of L-glutamate with glutamic pyruvic transaminase. Furthermore, a significant increase in extracellular L-glutamate concentration was detected before cell death occurred. In addition, agmatine-induced glutamate release and cell death were both blocked by pretreatment with botulinum toxin C, which is known to specifically inhibit the exocytosis. The agmatine neurotoxicity was not observed when extracellular K+ concentration was lower (10 mM). These results suggest that agmatine induces glutamate release through the exocytosis and thereby causes NMDA receptor-mediated neuronal death in conditions in which extracellular K+ concentrations are elevated.

Topics: Agmatine; Animals; Botulinum Toxins; Cell Death; Cell Survival; Cells, Cultured; Cerebellum; Dizocilpine Maleate; Excitatory Amino Acid Antagonists; Glutamic Acid; L-Lactate Dehydrogenase; Neurons; Potassium; Quinoxalines; Rats; Tetrazolium Salts; Thiazoles