Astrocytes enhance the tolerance of rat cortical neurons to glutamate excitotoxicity

Glutamate excitotoxicity is responsible for neuronal death in acute neurological disorders, including stroke, trauma and neurodegenerative diseases. Astrocytes are the main cells for the removal of glutamate in the synaptic cleft and may affect the tolerance of neurons to the glutamate excitotoxicity. Therefore, the present study aimed to investigate the tolerance of rat cortical neurons to glutamate excitotoxicity in the presence and absence of astrocytes. Rat cortical neurons in the presence or absence of astrocytes were exposed to different concentrations of glutamate (10-2,000 mu M) and 10 mu M glycine for different incubation periods. After 24 h, the Cell Counting kit-8 (CCK-8) assay was used to measure the cytotoxicity to neurons in the presence or absence of astrocytes. According to the results, in the absence of astrocytes, glutamate induced a concentration-dependent decrease of neuronal survival rate compared with the control rat cortical neurons, and the neurotoxic half-maximal inhibitory concentration (IC50) at 15, 30 and 60 min was 364.5, 258.5 and 138.3 mu M, respectively. Furthermore, in the presence of astrocytes, glutamate induced a concentration-dependent decrease of neuronal survival rate compared with the control rat cortical neurons, and the neurotoxic IC50 at 15, 30 and 60 min was 1,935, 932.8 and 789.3 mu M, respectively. However, astrocytic toxicity was not observed when the rat cortical astrocytes alone were exposed to different concentrations of glutamate (500, 1,000 and 2,000 mu M) for 6, 12 and 24 h. In conclusion, the glutamate-induced neurotoxic IC50 values at 15, 30 and 60 min were respectively higher in the presence of astrocytes as compared with those in the absence of astrocytes, suggesting that astrocytes can protect against rat cortical neuronal acute damage induced by glutamate.