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We conclude that mu - opioid receptors play different roles in the mechanisms of stimulation of mesolimbic dopamine activity by ethanol and morphine .
 Chemical: dopamine; Chemical: ethanol; Chemical: morphine
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: dopamine; Chemical: ethanol; Chemical: morphine