21568
Research efforts have mainly focused on alterations in monoaminergic neurotransmission , especially in relation to the serotonergic system , due to its key role in the regulation of mood and related biological functions .
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Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: Chemical 
Text: {0} 
Answer:
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