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These findings suggest that prolonged ketamine exposure produces an increase in NMDA receptor expression ( compensatory upregulation ) , which allows for a higher / toxic influx of calcium into neurons once ketamine is removed from the system , leading to elevated ROS generation and neuronal cell death .
 Chemical: ketamine; Chemical: NMDA; Chemical: calcium; Chemical: ketamine
Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: Chemical 
Text: {0} 
Answer:
 Chemical: ketamine; Chemical: NMDA; Chemical: calcium; Chemical: ketamine