30337
As will be seen , there is robust evidence that repeated exposure to drugs of abuse induces changes within the brain ' s reward regions in three major modes of epigenetic regulation - histone modifications such as acetylation and methylation , DNA methylation , and non - coding RNAs .
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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:
 None