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The mGlu receptors are delineated into three distinct groups based on their G - protein coupling and agonist affinity and also exercise distinct roles in the way they regulate both long - term plasticity and long - term hippocampus - dependent memory .
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Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: Chemical 
Text: {0} 
Answer:
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