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Offspring born from non - stressed mothers ( control mice ) showed high levels of DNMT1 and 3a mRNA expression in the frontal cortex at birth , but these levels progressively decreased at post - natal days ( PND ) 7 , 14 , and 60 .
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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