| The brain is particularly vulnerable to ischemia. Complete interruption of blood flow tothe brain for only 5 minutes triggers the death of vulnerable neurons in several brainregions leading to ischemic stroke [Jin-Moo Lee et. al (2000)]. This is one of the leadingcauses of death and serious long-term disability in adults. Initially, this disease wasthought to be caused by energy failure when brain stores of glucose or glycogen arelimited. However, over the last 15 years, evidence has emerged indicating that energeticsconsiderations and energy substrate limitations are not solely responsible for the brain'sheightened vulnerability to ischemia. Rather, it appears that the brain's intrinsic cell-celland intracellular signaling mechanisms, normally responsible for information processing,become harmful under ischemic conditions, hastening energy failure and enhancing thefinal pathways underlying ischemic cell death in all tissues, including free radicalproduction (such as nitric oxide) , activation of catabolic enzymes( mediated mostly byglutamate), membrane failure, apoptosis, and inflammation. This had suggested that themechanism of neuronal death is more complicated than general energy failure and leadsto the present concept of excitotoxicity hypothesis which is a term coined to label theprocess by which glutamate and related excitatory amino acids could kill neurons.Modern medicine has had very little power over the disease caused by ischemiacommonly called Stroke, though the world of stroke is changing and new and bettertherapies are being developed every day, there is no "Penicillin" for stroke till date.Researchers are studying the mechanisms of this disease and ways to prevent this injuryto the brain. Scientists hope to develop surgical techniques and neuroprotective agents toprevent this damage and restore important functions to stroke patients This paper studiedthe mechanisms underlying calcium influx through NMDA-receptor and L-type channelsleading to an increase in intracellular calcium and other diseases caused by neuronaldamage from the excitotoxicity perspective. Neuroprotectve effects by antagonist likeMK-801 and nimodipine in animal model in vitro were assessed. In the first part of thestudy the effect of oxygen-glucose deprivation (OGD) on the intracellular Ca2 wasinvestigated in cultured hippocampal neurons.The increase in intracellular Ca2+ was evaluated using confocal laser scanning microscopy with Fluo-3 as the Ca2+ probe Digital imaging processing techniques were used in assessing the concentration changes. Results showed that OGD induced an increase in intracellular Ca2+ concentration.In the second part of the study, the mechanisms of Ca2+ influx from extracellular fluid (ACSF) into the neurons were investigated following stimulation of neurons by NMDA and glycine. When a non-competitive NMDA antagonist MK-801 was applied, the Ca2+ level was significantly reduced, suggesting that the main path of Ca2+ entry into the neuron during stimulation by NMDA with glycine as co-agonist is through the NMDA receptor channel.This evidence suggests that antagonists of the NMDA receptor can provide significant protection against neuronal death caused by glutamate in tissue cultures and in animal models of stroke. Unfortunately, data from clinical trials with MK-801 has revealed unwanted side effects, and therefore a failure in humans. This had called for further researching into the other Ca2+ channels. Other sources of Ca2+ include accumulation from voltage-gated calcium channels (VGCC) and release from intracellular storages. Voltage dependent calcium channels are reported to be involved in many neuronal functions including synaptic transmission between neurons.. Furthermore, other NMDA-independent forms of plasticity have been shown to depend on L-type VGCC. Therefore we tested whether blocking L-type VGCC with nimodipine affected Ca2+ influx. The High concentration of K.C1 (150mM) was used to activate the ne...
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