Excitotoxicity calcium influx

During ischaemia, NOS is activated by calcium influx or by cytokines like tumour necrosis factor (TNF) or by lipopolysaccharide (LPS) and NO is produced in excess. It has been proposed that the excitotoxic effect of glutamate, which contributes to ischaemia-induced neuronal damage, is mediated by increased production of NO via a chain of events that includes increases in intracellular calcium (via glutamate activation of NMDA receptors), calcium activation of NOS, production of NO and peroxynitrite, and induction of lipid peroxidation. In fact, N-nitro-L-atginine, a selective inhibitor of NOS, has been shown to prevent glutamate-induced neurotoxicity in cortical cell cultures (Dawson rf /., 1991). 

Nonaka S, Chuang DM. Chronic lithium treatment robustly protects neurons in the central nervous system against excitotoxicity by inhibiting N -methyl-D-aspartate receptor-mediated calcium influx. Proc Natl Acad Sci USA 1998 95 2642-2647. 

It is well known that prolonged NMDA glutamate receptor activation results in degeneration of neurons (excitotoxicity). This has been attributed to a large increase in calcium influx, which activates the calmodulin-dependent NOS-1 and leads to sustained elevation of nitric oxide concentrations. The increase in neurodegeneration caused by excitatory amino acids may be due to enhanced oxygen radical formation since superoxide dismutase has a beneficial effect in... 

The mechanism of cell loss involves excitotoxicity provoked by intense neuronal firing (Grisar, 1986). There is excessive excitatory neurotransmitter release by activation of N-methyl-D-aspartate (NMDA) receptors and voltage-activated calcium channels which enables intracellular calcium influx in the neurons and glia. This calcium influx leads to a cascade of biochemical processes that ultimately lead to cell death mitochondrial dysfunction with uncoupling of oxidative phosphorylation, generation of reactive oxygen species, and activation of many proteolytic and catabolic enzymes that adversely affect cell function. 

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