The glutamate receptor types determining concentrational dependence of its neurotoxic effect on rat cerebral cortex neurons

Abstract

Mechanisms mediating neurotoxic glutamate effect on the rat brain cortex neurons developing in the primary tissue culture for 7 days have been studied. The neuron death identification was performed using the vital stain trypane blue and a fluorescent kit. Both dynamics and the neurodegeneration degree, produced by Glu and achieved by the experiment end depended on its concentration. For example, in the presence of 1 mmole/l and 10 mmole/l Glu the number of dead neurons by the 6th hour of recording was about 30 and 60%, respectively. The effect of 1 mmole/l Glu has the pharmacological sensitivity coinciding with the NMDA effect: it was potentiated by Gly, inhibited by AP5, and decreased essentially in the presence of 2 mmole/l Mg2+ in saline. The neurotoxic effect of 3 mmole/l Glu was resistant to effects of substances specific to towards NMDA-R, i.e., it seemed to be mediated by activation of other Glu-R. To confirm this suggestion there was studied the neurotoxic effect of AMPA and KA—agonists of the AMPA-R and KA-R. In the presence of both KA concentrations (30 and 300 μmole/l) its effect was similar and the number of dead neurons amounted to about 55% by the experiment end. Neurotoxicity of 10 μmole/l AMPA was expressed to the lesser degree: the number of dead neurons did not exceed 20% by 5 h of recording. However, addition of 100 μmole/l of cyclothiazide that eliminated AMPA-R desensitization was accompanied by a significant increase of the AMPA effect, it became as pronounced as the KA effect. It is essential that CNQX protected the neurons from death caused by AMPA and by KA actions. The data identify two components of the Glu neurotoxic effect. Effect of low concentrations is mediated by activation of NMDA-R, while effect of high concentration is determined by predominant activation of AMPA-R and KA-R.